text stringlengths 559 401k | source stringlengths 13 121 |
|---|---|
In wired computer networking a hop occurs when a packet is passed from one network segment to the next. Data packets pass through routers as they travel between source and destination. The hop count refers to the number of network devices through which data passes from source to destination (depending on routing protocol, this may include the source/destination, that is, the first hop is counted as hop 0 or hop 1).
Since store and forward and other latencies are incurred through each hop, a large number of hops between source and destination implies lower real-time performance.
== Hop count ==
In wired networks, the hop count refers to the number of networks or network devices through which data passes between source and destination (depending on routing protocol, this may include the source/destination, that is, the first hop is counted as hop 0 or hop 1). Thus, hop count is a rough measure of distance between two hosts. For a routing protocol using 1-origin hop counts (such as RIP), a hop count of n means that n networks separate the source host from the destination host. Other protocols such as DHCP use the term "hop" to refer to the number of times a message has been forwarded.
On a layer 3 network such as Internet Protocol (IP), each router along the data path constitutes a hop. By itself, this metric is, however, not useful for determining the optimum network path, as it does not take into consideration the speed, load, reliability, or latency of any particular hop, but merely the total count. Nevertheless, some routing protocols, such as Routing Information Protocol (RIP), use hop count as their sole metric.
Each time a router receives a packet, it modifies the packet, decrementing the time to live (TTL). The router discards any packets received with a zero TTL value. This prevents packets from endlessly bouncing around the network in the event of routing errors. Routers are capable of managing hop counts, but other types of network devices (e.g. Ethernet hubs and bridges) are not.
== Hop limit ==
Known as time to live (TTL) in IPv4, and hop limit in IPv6, this field specifies a limit on the number of hops a packet is allowed before being discarded. Routers modify IP packets as they are forwarded, decrementing the respective TTL or hop limit fields. Routers do not forward packets with a resultant field of 0 or less. This prevents packets from following a loop forever.
== Next hop ==
When configuring network devices the hop may refer to next hop. When a hop forwards network traffic the next hop is what the local hop considers to be the next element towards the final destination. A routing table usually consists of a list of possible destination networks or IP addresses for which the next hop is known. By only storing next-hop information, next-hop routing or next-hop forwarding reduces the size of routing tables. A given gateway only knows one step along the path, not the complete path to a destination. If no next hop is known a hop may silently discard a packet or return an error depending on the type of network. Devices in consumer networks are often only provided with routes for the local network as well as a default gateway as the traffic can only ever reach the local network or be forwarded to the internet service provider. Routers require multiple routes to be able to forward traffic between different networks. In practice routes are configured either implicitly with address assignment by means of a netmask, by manual assignment using tools such as route, or dynamically using configuration protocols like DHCP or routing protocols.
In TCP/IP networks using Ethernet as the link layer the destination is always an IP address, however the next hop is not technically required to be of the same address family. As the packet needs to be forwarded on the link layer the next hop needs only to resolve to a link layer address such as a MAC address. On Linux for instance the next hop is required to be either an IP address or an interface. The address families of the destination address and the next hop need not match, therefore it is possible to forward IPv4 traffic on an IPv6 network and vice versa. If no address is provided the destination is assumed to be present on the local link, otherwise the next hop is used. Either address is then passed to NDP or ARP for IPv6 and IPv4 respectively to be resolved to the link layer address required to pass the packet along on the network stack. In other scenarios link layer resolution may require different methods such as a virtual private network which needs to determine the peer to send the packet to. What is common to forwarding is that the next hop needs to be logically connected to the current hop, thereby building an uninterrupted chain between source and destination. A logical connection does not necessitate a physical connection as the packet may be passed on to a virtual tunnel.
Source routing describes networks in which data is encoded in the packet that allows a hop (such as the source of the packet) to influence routing decisions on intermediary hops. This allows for advanced teletraffic engineering used to improve network delay, decrease network congestion, or meet other requirements.
== Diagnostics ==
The traceroute command can be used to measure the number of router hops from one host to another. Hop counts are often useful to find faults in a network or to discover if routing is indeed correct.
== Wireless ad hoc networking ==
In a wireless ad hoc network, commonly, every participating node is also acting as a router. This means that the terms "hop" and "hop count" are often the subject of confusion. Often, the sending node is simply counted as the first hop, thus yielding the same number for "hops" for both interpretations of "hop" as "traversed routers" and "jumps from node to node". For example, RFC 6130 defines a "1-hop neighbor" as any other node that is directly reachable via the wireless interface.
== See also ==
Internet Control Message Protocol
Ping (networking utility)
== References == | Wikipedia/Hop_(networking) |
Peer-to-peer (P2P) computing or networking is a distributed application architecture that partitions tasks or workloads between peers. Peers are equally privileged, equipotent participants in the network, forming a peer-to-peer network of nodes. In addition, a personal area network (PAN) is also in nature a type of decentralized peer-to-peer network typically between two devices.
Peers make a portion of their resources, such as processing power, disk storage, or network bandwidth, directly available to other network participants, without the need for central coordination by servers or stable hosts. Peers are both suppliers and consumers of resources, in contrast to the traditional client–server model in which the consumption and supply of resources are divided.
While P2P systems had previously been used in many application domains, the architecture was popularized by the Internet file sharing system Napster, originally released in 1999. P2P is used in many protocols such as BitTorrent file sharing over the Internet and in personal networks like Miracast displaying and Bluetooth radio. The concept has inspired new structures and philosophies in many areas of human interaction. In such social contexts, peer-to-peer as a meme refers to the egalitarian social networking that has emerged throughout society, enabled by Internet technologies in general.
== Development ==
While P2P systems had previously been used in many application domains, the concept was popularized by file sharing systems such as the music-sharing application Napster. The peer-to-peer movement allowed millions of Internet users to connect "directly, forming groups and collaborating to become user-created search engines, virtual supercomputers, and filesystems". The basic concept of peer-to-peer computing was envisioned in earlier software systems and networking discussions, reaching back to principles stated in the first Request for Comments, RFC 1.
Tim Berners-Lee's vision for the World Wide Web was close to a P2P network in that it assumed each user of the web would be an active editor and contributor, creating and linking content to form an interlinked "web" of links. The early Internet was more open than the present day, where two machines connected to the Internet could send packets to each other without firewalls and other security measures. This contrasts with the broadcasting-like structure of the web as it has developed over the years. As a precursor to the Internet, ARPANET was a successful peer-to-peer network where "every participating node could request and serve content". However, ARPANET was not self-organized, and it could not "provide any means for context or content-based routing beyond 'simple' address-based routing."
Therefore, Usenet, a distributed messaging system that is often described as an early peer-to-peer architecture, was established. It was developed in 1979 as a system that enforces a decentralized model of control. The basic model is a client–server model from the user or client perspective that offers a self-organizing approach to newsgroup servers. However, news servers communicate with one another as peers to propagate Usenet news articles over the entire group of network servers. The same consideration applies to SMTP email in the sense that the core email-relaying network of mail transfer agents has a peer-to-peer character, while the periphery of Email clients and their direct connections is strictly a client-server relationship.
In May 1999, with millions more people on the Internet, Shawn Fanning introduced the music and file-sharing application called Napster. Napster was the beginning of peer-to-peer networks, as we know them today, where "participating users establish a virtual network, entirely independent from the physical network, without having to obey any administrative authorities or restrictions".
== Architecture ==
A peer-to-peer network is designed around the notion of equal peer nodes simultaneously functioning as both "clients" and "servers" to the other nodes on the network. This model of network arrangement differs from the client–server model where communication is usually to and from a central server. A typical example of a file transfer that uses the client-server model is the File Transfer Protocol (FTP) service in which the client and server programs are distinct: the clients initiate the transfer, and the servers satisfy these requests.
=== Routing and resource discovery ===
Peer-to-peer networks generally implement some form of virtual overlay network on top of the physical network topology, where the nodes in the overlay form a subset of the nodes in the physical network. Data is still exchanged directly over the underlying TCP/IP network, but at the application layer peers can communicate with each other directly, via the logical overlay links (each of which corresponds to a path through the underlying physical network). Overlays are used for indexing and peer discovery, and make the P2P system independent from the physical network topology. Based on how the nodes are linked to each other within the overlay network, and how resources are indexed and located, we can classify networks as unstructured or structured (or as a hybrid between the two).
==== Unstructured networks ====
Unstructured peer-to-peer networks do not impose a particular structure on the overlay network by design, but rather are formed by nodes that randomly form connections to each other. (Gnutella, Gossip, and Kazaa are examples of unstructured P2P protocols).
Because there is no structure globally imposed upon them, unstructured networks are easy to build and allow for localized optimizations to different regions of the overlay. Also, because the role of all peers in the network is the same, unstructured networks are highly robust in the face of high rates of "churn"—that is, when large numbers of peers are frequently joining and leaving the network.
However, the primary limitations of unstructured networks also arise from this lack of structure. In particular, when a peer wants to find a desired piece of data in the network, the search query must be flooded through the network to find as many peers as possible that share the data. Flooding causes a very high amount of signaling traffic in the network, uses more CPU/memory (by requiring every peer to process all search queries), and does not ensure that search queries will always be resolved. Furthermore, since there is no correlation between a peer and the content managed by it, there is no guarantee that flooding will find a peer that has the desired data. Popular content is likely to be available at several peers and any peer searching for it is likely to find the same thing. But if a peer is looking for rare data shared by only a few other peers, then it is highly unlikely that the search will be successful.
==== Structured networks ====
In structured peer-to-peer networks the overlay is organized into a specific topology, and the protocol ensures that any node can efficiently search the network for a file/resource, even if the resource is extremely rare.
The most common type of structured P2P networks implement a distributed hash table (DHT), in which a variant of consistent hashing is used to assign ownership of each file to a particular peer. This enables peers to search for resources on the network using a hash table: that is, (key, value) pairs are stored in the DHT, and any participating node can efficiently retrieve the value associated with a given key.
However, in order to route traffic efficiently through the network, nodes in a structured overlay must maintain lists of neighbors that satisfy specific criteria. This makes them less robust in networks with a high rate of churn (i.e. with large numbers of nodes frequently joining and leaving the network). More recent evaluation of P2P resource discovery solutions under real workloads have pointed out several issues in DHT-based solutions such as high cost of advertising/discovering resources and static and dynamic load imbalance.
Notable distributed networks that use DHTs include Tixati, an alternative to BitTorrent's distributed tracker, the Kad network, the Storm botnet, and the YaCy. Some prominent research projects include the Chord project, Kademlia, PAST storage utility, P-Grid, a self-organized and emerging overlay network, and CoopNet content distribution system. DHT-based networks have also been widely utilized for accomplishing efficient resource discovery for grid computing systems, as it aids in resource management and scheduling of applications.
==== Hybrid models ====
Hybrid models are a combination of peer-to-peer and client–server models. A common hybrid model is to have a central server that helps peers find each other. Spotify was an example of a hybrid model [until 2014]. There are a variety of hybrid models, all of which make trade-offs between the centralized functionality provided by a structured server/client network and the node equality afforded by the pure peer-to-peer unstructured networks. Currently, hybrid models have better performance than either pure unstructured networks or pure structured networks because certain functions, such as searching, do require a centralized functionality but benefit from the decentralized aggregation of nodes provided by unstructured networks.
==== CoopNet content distribution system ====
CoopNet (Cooperative Networking) was a proposed system for off-loading serving to peers who have recently downloaded content, proposed by computer scientists Venkata N. Padmanabhan and Kunwadee Sripanidkulchai, working at Microsoft Research and Carnegie Mellon University. When a server experiences an increase in load it redirects incoming peers to other peers who have agreed to mirror the content, thus off-loading balance from the server. All of the information is retained at the server. This system makes use of the fact that the bottleneck is most likely in the outgoing bandwidth than the CPU, hence its server-centric design. It assigns peers to other peers who are 'close in IP' to its neighbors [same prefix range] in an attempt to use locality. If multiple peers are found with the same file it designates that the node choose the fastest of its neighbors. Streaming media is transmitted by having clients cache the previous stream, and then transmit it piece-wise to new nodes.
=== Security and trust ===
Peer-to-peer systems pose unique challenges from a computer security perspective. Like any other form of software, P2P applications can contain vulnerabilities. What makes this particularly dangerous for P2P software, however, is that peer-to-peer applications act as servers as well as clients, meaning that they can be more vulnerable to remote exploits.
==== Routing attacks ====
Since each node plays a role in routing traffic through the network, malicious users can perform a variety of "routing attacks", or denial of service attacks. Examples of common routing attacks include "incorrect lookup routing" whereby malicious nodes deliberately forward requests incorrectly or return false results, "incorrect routing updates" where malicious nodes corrupt the routing tables of neighboring nodes by sending them false information, and "incorrect routing network partition" where when new nodes are joining they bootstrap via a malicious node, which places the new node in a partition of the network that is populated by other malicious nodes.
==== Corrupted data and malware ====
The prevalence of malware varies between different peer-to-peer protocols. Studies analyzing the spread of malware on P2P networks found, for example, that 63% of the answered download requests on the gnutella network contained some form of malware, whereas only 3% of the content on OpenFT contained malware. In both cases, the top three most common types of malware accounted for the large majority of cases (99% in gnutella, and 65% in OpenFT). Another study analyzing traffic on the Kazaa network found that 15% of the 500,000 file sample taken were infected by one or more of the 365 different computer viruses that were tested for.
Corrupted data can also be distributed on P2P networks by modifying files that are already being shared on the network. For example, on the FastTrack network, the RIAA managed to introduce faked chunks into downloads and downloaded files (mostly MP3 files). Files infected with the RIAA virus were unusable afterwards and contained malicious code. The RIAA is also known to have uploaded fake music and movies to P2P networks in order to deter illegal file sharing. Consequently, the P2P networks of today have seen an enormous increase of their security and file verification mechanisms. Modern hashing, chunk verification and different encryption methods have made most networks resistant to almost any type of attack, even when major parts of the respective network have been replaced by faked or nonfunctional hosts.
=== Resilient and scalable computer networks ===
The decentralized nature of P2P networks increases robustness because it removes the single point of failure that can be inherent in a client–server based system. As nodes arrive and demand on the system increases, the total capacity of the system also increases, and the likelihood of failure decreases. If one peer on the network fails to function properly, the whole network is not compromised or damaged. In contrast, in a typical client–server architecture, clients share only their demands with the system, but not their resources. In this case, as more clients join the system, fewer resources are available to serve each client, and if the central server fails, the entire network is taken down.
=== Distributed storage and search ===
There are both advantages and disadvantages in P2P networks related to the topic of data backup, recovery, and availability. In a centralized network, the system administrators are the only forces controlling the availability of files being shared. If the administrators decide to no longer distribute a file, they simply have to remove it from their servers, and it will no longer be available to users. Along with leaving the users powerless in deciding what is distributed throughout the community, this makes the entire system vulnerable to threats and requests from the government and other large forces.
For example, YouTube has been pressured by the RIAA, MPAA, and entertainment industry to filter out copyrighted content. Although server-client networks are able to monitor and manage content availability, they can have more stability in the availability of the content they choose to host. A client should not have trouble accessing obscure content that is being shared on a stable centralized network. P2P networks, however, are more unreliable in sharing unpopular files because sharing files in a P2P network requires that at least one node in the network has the requested data, and that node must be able to connect to the node requesting the data. This requirement is occasionally hard to meet because users may delete or stop sharing data at any point.
In a P2P network, the community of users is entirely responsible for deciding which content is available. Unpopular files eventually disappear and become unavailable as fewer people share them. Popular files, however, are highly and easily distributed. Popular files on a P2P network are more stable and available than files on central networks. In a centralized network, a simple loss of connection between the server and clients can cause a failure, but in P2P networks, the connections between every node must be lost to cause a data-sharing failure. In a centralized system, the administrators are responsible for all data recovery and backups, while in P2P systems, each node requires its backup system. Because of the lack of central authority in P2P networks, forces such as the recording industry, RIAA, MPAA, and the government are unable to delete or stop the sharing of content on P2P systems.
== Applications ==
=== Content delivery ===
In P2P networks, clients both provide and use resources. This means that unlike client–server systems, the content-serving capacity of peer-to-peer networks can actually increase as more users begin to access the content (especially with protocols such as BitTorrent that require users to share, refer a performance measurement study). This property is one of the major advantages of using P2P networks because it makes the setup and running costs very small for the original content distributor.
=== File-sharing networks ===
Peer-to-peer file sharing networks such as Gnutella, G2, and the eDonkey network have been useful in popularizing peer-to-peer technologies. These advancements have paved the way for Peer-to-peer content delivery networks and services, including distributed caching systems like Correli Caches to enhance performance. Furthermore, peer-to-peer networks have made possible the software publication and distribution, enabling efficient sharing of Linux distribution and various games through file sharing networks.
==== Copyright infringements ====
Peer-to-peer networking involves data transfer from one user to another without using an intermediate server. Companies developing P2P applications have been involved in numerous legal cases, primarily in the United States, over conflicts with copyright law. Two major cases are Grokster vs RIAA and MGM Studios, Inc. v. Grokster, Ltd.. In the last case, the Court unanimously held that defendant peer-to-peer file sharing companies Grokster and Streamcast could be sued for inducing copyright infringement.
=== Multimedia ===
The P2PTV and PDTP protocols are used in various peer-to-peer applications. Some proprietary multimedia applications leverage a peer-to-peer network in conjunction with streaming servers to stream audio and video to their clients. Peercasting is employed for multicasting streams. Additionally, a project called LionShare, undertaken by Pennsylvania State University, MIT, and Simon Fraser University, aims to facilitate file sharing among educational institutions globally. Another notable program, Osiris, enables users to create anonymous and autonomous web portals that are distributed via a peer-to-peer network.
=== Other P2P applications ===
Dat is a distributed version-controlled publishing platform. I2P, is an overlay network used to browse the Internet anonymously. Unlike the related I2P, the Tor network is not itself peer-to-peer; however, it can enable peer-to-peer applications to be built on top of it via onion services. The InterPlanetary File System (IPFS) is a protocol and network designed to create a content-addressable, peer-to-peer method of storing and sharing hypermedia distribution protocol, with nodes in the IPFS network forming a distributed file system. Jami is a peer-to-peer chat and SIP app. JXTA is a peer-to-peer protocol designed for the Java platform. Netsukuku is a Wireless community network designed to be independent from the Internet. Open Garden is a connection-sharing application that shares Internet access with other devices using Wi-Fi or Bluetooth.
Resilio Sync is a directory-syncing app. Research includes projects such as the Chord project, the PAST storage utility, the P-Grid, and the CoopNet content distribution system. Secure Scuttlebutt is a peer-to-peer gossip protocol capable of supporting many different types of applications, primarily social networking. Syncthing is also a directory-syncing app. Tradepal l and M-commerce applications are designed to power real-time marketplaces. The U.S. Department of Defense is conducting research on P2P networks as part of its modern network warfare strategy. In May 2003, Anthony Tether, then director of DARPA, testified that the United States military uses P2P networks. WebTorrent is a P2P streaming torrent client in JavaScript for use in web browsers, as well as in the WebTorrent Desktop standalone version that bridges WebTorrent and BitTorrent serverless networks. Microsoft, in Windows 10, uses a proprietary peer-to-peer technology called "Delivery Optimization" to deploy operating system updates using end-users' PCs either on the local network or other PCs. According to Microsoft's Channel 9, this led to a 30%-50% reduction in Internet bandwidth usage. Artisoft's LANtastic was built as a peer-to-peer operating system where machines can function as both servers and workstations simultaneously. Hotline Communications Hotline Client was built with decentralized servers and tracker software dedicated to any type of files and continues to operate today. Cryptocurrencies are peer-to-peer-based digital currencies that use blockchains
List of cryptocurrencies
List of blockchains
== Social implications ==
=== Incentivizing resource sharing and cooperation ===
Cooperation among a community of participants is key to the continued success of P2P systems aimed at casual human users; these reach their full potential only when large numbers of nodes contribute resources. But in current practice, P2P networks often contain large numbers of users who utilize resources shared by other nodes, but who do not share anything themselves (often referred to as the "freeloader problem").
Freeloading can have a profound impact on the network and in some cases can cause the community to collapse. In these types of networks "users have natural disincentives to cooperate because cooperation consumes their own resources and may degrade their own performance". Studying the social attributes of P2P networks is challenging due to large populations of turnover, asymmetry of interest and zero-cost identity. A variety of incentive mechanisms have been implemented to encourage or even force nodes to contribute resources.
Some researchers have explored the benefits of enabling virtual communities to self-organize and introduce incentives for resource sharing and cooperation, arguing that the social aspect missing from today's P2P systems should be seen both as a goal and a means for self-organized virtual communities to be built and fostered. Ongoing research efforts for designing effective incentive mechanisms in P2P systems, based on principles from game theory, are beginning to take on a more psychological and information-processing direction.
==== Privacy and anonymity ====
Some peer-to-peer networks (e.g. Freenet) place a heavy emphasis on privacy and anonymity—that is, ensuring that the contents of communications are hidden from eavesdroppers, and that the identities/locations of the participants are concealed. Public key cryptography can be used to provide encryption, data validation, authorization, and authentication for data/messages. Onion routing and other mix network protocols (e.g. Tarzan) can be used to provide anonymity.
Perpetrators of live streaming sexual abuse and other cybercrimes have used peer-to-peer platforms to carry out activities with anonymity.
== Political implications ==
=== Intellectual property law and illegal sharing ===
Although peer-to-peer networks can be used for legitimate purposes, rights holders have targeted peer-to-peer over the involvement with sharing copyrighted material. Peer-to-peer networking involves data transfer from one user to another without using an intermediate server. Companies developing P2P applications have been involved in numerous legal cases, primarily in the United States, primarily over issues surrounding copyright law. Two major cases are Grokster vs RIAA and MGM Studios, Inc. v. Grokster, Ltd. In both of the cases the file sharing technology was ruled to be legal as long as the developers had no ability to prevent the sharing of the copyrighted material.
To establish criminal liability for the copyright infringement on peer-to-peer systems, the government must prove that the defendant infringed a copyright willingly for the purpose of personal financial gain or commercial advantage. Fair use exceptions allow limited use of copyrighted material to be downloaded without acquiring permission from the rights holders. These documents are usually news reporting or under the lines of research and scholarly work. Controversies have developed over the concern of illegitimate use of peer-to-peer networks regarding public safety and national security. When a file is downloaded through a peer-to-peer network, it is impossible to know who created the file or what users are connected to the network at a given time. Trustworthiness of sources is a potential security threat that can be seen with peer-to-peer systems.
A study ordered by the European Union found that illegal downloading may lead to an increase in overall video game sales because newer games charge for extra features or levels. The paper concluded that piracy had a negative financial impact on movies, music, and literature. The study relied on self-reported data about game purchases and use of illegal download sites. Pains were taken to remove effects of false and misremembered responses.
=== Network neutrality ===
Peer-to-peer applications present one of the core issues in the network neutrality controversy. Internet service providers (ISPs) have been known to throttle P2P file-sharing traffic due to its high-bandwidth usage. Compared to Web browsing, e-mail or many other uses of the internet, where data is only transferred in short intervals and relative small quantities, P2P file-sharing often consists of relatively heavy bandwidth usage due to ongoing file transfers and swarm/network coordination packets. In October 2007, Comcast, one of the largest broadband Internet providers in the United States, started blocking P2P applications such as BitTorrent. Their rationale was that P2P is mostly used to share illegal content, and their infrastructure is not designed for continuous, high-bandwidth traffic.
Critics point out that P2P networking has legitimate legal uses, and that this is another way that large providers are trying to control use and content on the Internet, and direct people towards a client–server-based application architecture. The client–server model provides financial barriers-to-entry to small publishers and individuals, and can be less efficient for sharing large files. As a reaction to this bandwidth throttling, several P2P applications started implementing protocol obfuscation, such as the BitTorrent protocol encryption. Techniques for achieving "protocol obfuscation" involves removing otherwise easily identifiable properties of protocols, such as deterministic byte sequences and packet sizes, by making the data look as if it were random. The ISP's solution to the high bandwidth is P2P caching, where an ISP stores the part of files most accessed by P2P clients in order to save access to the Internet.
== Current research ==
Researchers have used computer simulations to aid in understanding and evaluating the complex behaviors of individuals within the network. "Networking research often relies on simulation in order to test and evaluate new ideas. An important requirement of this process is that results must be reproducible so that other researchers can replicate, validate, and extend existing work." If the research cannot be reproduced, then the opportunity for further research is hindered. "Even though new simulators continue to be released, the research community tends towards only a handful of open-source simulators. The demand for features in simulators, as shown by our criteria and survey, is high. Therefore, the community should work together to get these features in open-source software. This would reduce the need for custom simulators, and hence increase repeatability and reputability of experiments."
Popular simulators that were widely used in the past are NS2, OMNeT++, SimPy, NetLogo, PlanetLab, ProtoPeer, QTM, PeerSim, ONE, P2PStrmSim, PlanetSim, GNUSim, and Bharambe.
Besides all the above stated facts, there has also been work done on ns-2 open source network simulators. One research issue related to free rider detection and punishment has been explored using ns-2 simulator here.
== See also ==
== References ==
== External links == | Wikipedia/Peer-to-peer_network |
Global Wrestling Network (GWN) was a digital streaming service and mobile app owned by Impact Wrestling (now Total Nonstop Action Wrestling), a subsidiary of Anthem Sports & Entertainment. It primarily featured content from the Impact video library, along with original programming and content from independent and international promotions. The service ceased operating on May 1, 2019, when it was replaced by Impact Plus (now TNA+).
== History ==
The first service to stream Total Nonstop Action Wrestling (TNA) content on-demand happened in 2009, when the company launched its own 'TNA Video Vault'. The service changed its name to 'TNA On Demand' in 2010 and ran up until around early 2013. The company also launched the 'TNA Wrestling Plus' YouTube channel - where users could rent pay-per-views and documentaries previously released on DVD. In early 2017, Anthem launched the 'Total Access TNA' (later renamed 'Total Access Impact') originally for UK users after Challenge TV's TNA broadcasting contract had expired.
In June 2017, Executive Vice President of Anthem Sports and Entertainment Ed Nordholm told The Tennessean that the company once known as TNA had rebranded. As part of expanding the brand, Nordholm said he had been planning an on demand service that would tap into TNA's video library. The Tennessean noted that the library was valuable as TNA had previously signed many legendary wrestlers and several wrestlers who appeared in TNA later signed with WWE.
At the time of the rebranding, the company had been named Impact Wrestling after its flagship program, and had assumed the name of Global Force Wrestling (GFW). In October 2017, Jeff Jarrett left the company and it reverted to the Impact Wrestling name as Jarrett owned the rights to GFW. The Global Wrestling Network (GWN) name had been influenced by its connection to GFW.
The launch of GWN was hinted on Impact!, until an announcement on the August 31, 2017 episode revealed a planned release in September. Nordholm appeared on Wrestling Observer Radio on September 9 and stated that the goal of the network was to be an alternative brand to the WWE Network. The network temporarily went live on September 12, 2017 while the infrastructure was being tweaked, but was taken down by the next day.
Global Wrestling Network officially launched on October 10, 2017. A 30-day free trial period was offered at launch. The service features free content for subscribers along with a premium content service for $7.99 USD in all available territories. Over 1,000 hours of content from the Impact Wrestling libraries are available to subscribers but the network also includes tape libraries from the Fight Network, Border City Wrestling, Wrestling at the Chase and other sources.
In November 2017, content from several independent promotions such as WrestleCade, Rocky Mountain Pro, DEFY Wrestling and Future Stars of Wrestling were added to GWN.
On August 14, 2018 Jeff Jarrett and his company Global Force Entertainment announced that it had filed a lawsuit against Impact Wrestling's parent company Anthem Sports & Entertainment in the District Court of Tennessee for copyright infringement over the GFW rights, as Jarrett owned all Global Force Wrestling properties since its creation in 2014. Impact would have needed to suspend the operations of GWN had the lawsuit been successful.
Impact announced the launch of its new premium streaming service, Impact Plus, on April 28, 2019, during its Rebellion pay-per-view. Impact Plus subsequently replaced Global Wrestling Network. Three months later, Anthem counter-sued Jarrett and claimed that the looks and trademarks of GFW and GWN were not similar.
== Programming ==
At the time the service was shut down, the following programming was included:
=== TNA/Impact ===
==== Repeat/archival programming ====
All pay-per-view events (except most recent pay-per-view event)
Select One Night Only events (All 2013–2015, 2017–present; 7 of 10 2016)
All TNA weekly pay-per-views (aka the Asylum Years)
All episodes of TNA British Boot Camp
Select episodes of Impact! (All 2004-2005, 2017–present (except those which aired within 10 days); select 2006-2007, 2015–2016)
Select episodes of Impact! Xplosion (All 2017-2018, select 2016)
Select episodes of TNA Legends
Select episodes of TNA Unfinished Business
Select episodes of TNA's Greatest Matches
Select episodes of TNA Epics
All episodes of Inside Impact
All episodes of Twitch Specials
Impact in 60
Classic Compilations (TNA's home video releases)
Hidden Gems
=== Other ===
==== Classic wrestling ====
All 12 volumes of Wrestling at the Chase
Pro Wrestling Superstars
==== Indy wrestling ====
AML wrestling
Border City Wrestling
Capitol Wrestling
Championship Wrestling from Arizona
Championship Wrestling from Hollywood
Destiny World Wrestling
Future Stars of Wrestling
Great White North Wrestling
International Pro Wrestling
PCW UK
Prestige Wrestling
Smash Wrestling
Superkick'd
Rocky Mountain Pro
RISE Wrestling
World Series Wrestling
WrestleCade
WrestlePro
==== Original Specials ====
Conversations
My Best 5
Retrospectives
Documentaries
Bret Hart: Survival of the Hitman
== References ==
== External links ==
Official website | Wikipedia/Global_Wrestling_Network |
The open music model is an economic and technological framework for the recording industry based on research conducted at the Massachusetts Institute of Technology. It predicts that the playback of prerecorded music will be regarded as a service rather than as individually sold products, and that the only system for the digital distribution of music that will be viable against piracy is a subscription-based system supporting file sharing and free of digital rights management. The research also indicated that US$9 per month for unlimited use would be the market clearing price at that time, but recommended $5 per month as the long-term optimal price.
Since its creation in 2002, a number of its principles have been adopted throughout the recording industry, and it has been cited as the basis for the business model of many music subscription services.
== Overview ==
The model asserts that there are five necessary requirements for a viable commercial music digital distribution network:
The model was proposed by Shuman Ghosemajumder in his 2002 research paper Advanced Peer-Based Technology Business Models at the MIT Sloan School of Management. It was the first of several studies that found significant demand for online, open music sharing systems. The following year, it was publicly referred to as the Open Music Model.
The model suggests changing the way consumers interact with the digital property market: rather than being seen as a good to be purchased from online vendors, music would be treated as a service being provided by the industry, with firms based on the model serving as intermediaries between the music industry and its consumers. The model proposed giving consumers unlimited access to music for the price of $5 per month ($9 in 2024), based on research showing that this could be a long-term optimal price, expected to bring in a total revenue of over US$3 billion per year.
The research demonstrated the demand for third-party file sharing programs. Insofar as the interest for a particular piece of digital property is high, and the risk of acquiring the good via illegitimate means is low, people will naturally flock towards third-party services such as Napster and Morpheus (more recently, Bittorrent and The Pirate Bay).
The research showed that consumers would use file sharing services not primarily due to cost but because of convenience, indicating that services which provided access to the most music would be the most successful.
== Industry adoption ==
The model predicted the failure of online music distribution systems based on digital rights management.
Criticisms of the model included that it would not eliminate the issue of piracy. Others countered that it was in fact the most viable solution to piracy, since piracy was "inevitable". Supporters argued that it offered a superior alternative to the current law-enforcement based methods used by the recording industry. One startup in Germany, Playment, announced plans to adapt the entire model to a commercial setting as the basis for its business model.
Several aspects of the model have been adopted by the recording industry and its partners over time:
The abolition of digital rights management represented a major shift for the industry. In 2007, Steve Jobs, CEO of Apple, published a letter calling for an end to DRM in music. A few months later, Amazon.com launched a store single individual DRM-free mp3's. One year later, iTunes Store abolished DRM on most of its individual tracks.
Open payment was relatively straightforward to implement, and the iTunes Store offered gift cards, which could be purchased with cash, from its launch in 2003.
In 2010, Rhapsody announced a download ability for their subscribers using iPhones.
In 2011, Apple launched its iTunes Match service with a subscription model, supporting file-sharing between a user's own devices. However, the subscription price did not include the cost of acquiring content, which would still have to be purchased on a per track basis from the iTunes Store.
Pricing close to the model's suggested $5 per month price, or its $9 per month market clearing price, has been adopted by many platforms:
In 2005, Yahoo! Music was launched at $5 per month with digital rights management.
In 2011, Spotify introduced a $5 per month premium subscription in the United States with digital rights management, recognized as adhering closely to the model.
In 2011, Microsoft Zune offered a subscription service for music downloads with digital rights management known as a Zune Pass, at $10 a month.
in 2012, Google Play Music launched unlimited music streaming for a subscription price of $9.99 per month. Users can upload their own MP3s to the service and download them, but cannot download songs they have not uploaded themselves.
In 2014, Amazon added DRM music streaming to their Amazon Prime service.
In 2015, Apple announced Apple Music, which would offer unlimited streaming of songs encrypted with FairPlay DRM for a subscription price of $9.99 per month, and compensate artists on the basis of song popularity. Apple reportedly wanted to enter the market with a lower price but was pressured by record labels to adopt a higher subscription fee.
According to inflation calculated through the United States Consumer Price Index calculator, the $9 per month estimated market-clearing price in 2002 would become US$13.72 per month in 2021, closer to Apple Music's family plan price of $14.99.
== See also ==
Comparison of online music stores
Comparison of on-demand streaming music services
Disk sharing
Fan-funded music
File sharing
File sharing timeline
File-sharing program
Peer-to-peer
Record industry
Subscription business model
Threshold pledge system
== References == | Wikipedia/Open_Music_Model |
Sony Entertainment Network (SEN) was a digital media delivery service operated by Sony Network Entertainment International (SNEI). SEN provided access to services, including PlayStation Network for games, Video Unlimited for film and television, Music Unlimited for music, and PlayMemories for photographs and videos. On 28 January 2015, the Sony Entertainment Network was superseded by the PlayStation Network.
== History ==
Sony Entertainment Network was first introduced on 31 August 2011 by Kaz Hirai, the president of Sony Computer Entertainment Inc., at the IFA tradeshow in Berlin. Sony decided to create the Sony Entertainment Network platform as a way for the community to access digital entertainment. The platform was operated by Sony Network Entertainment International, a subsidiary of Sony Corporation America. With the new name, also came new logos for the different services on the Sony Entertainment Network. Qriocity services was used by Sony as the video and music downloading platform; it was renamed Video Unlimited and Music Unlimited in 2011. This allowed Sony to expand the Music Unlimited service into Norway, Sweden, Finland, Denmark, the Netherlands and Belgium by the end of 2011.
During 2012, the Sony Entertainment Network was released to the community and was available on Sony's different devices. Instead of using a web-serviced browser in their Bravia Televisions, it was decided by Sony to integrate the Music and Video Unlimited into the TV's home menu. The interface was purposely created for the Sony Entertainment Network and make is more accessible for users to access the services that Sony Entertainment Network offered.
On 28 January 2015, the Sony Entertainment Network, along with its Music Unlimited and Video Unlimited services, were fully absorbed into the PlayStation Network, succeeding SEN as Sony's leading entertainment service brand. Following this, Music Unlimited and Video Unlimited were rebranded as PlayStation Music and PlayStation Video, respectively.
== Services ==
=== Video Unlimited ===
Video Unlimited allowed users to purchase or rent videos. Purchases and rentals could be made online through the Sony Entertainment Network store, through the PlayStation Store on PlayStation 3, PlayStation 4, and PlayStation Vita, through the Video Unlimited store on many Sony Blu-ray disc players and Bravia TVs or via an Xperia smartphone and tablet app. The services provided customers with an easy and accessible way to watch and discover new movies and TV. Through the wide range of options that Video Unlimited has, a user could choose from new movies, classic movies or to keep up with a TV series. The use of logging in enabled the customer to easily choose and watch videos from anywhere, on devices that are compatible with Video Unlimited. Video Unlimited was later replaced by PlayStation Video.
=== Music Unlimited ===
Music Unlimited was a cloud-based music service. According to Sony, the music catalog contained 25 million songs and was available in 19 countries. There were two subscription levels: Access, which allowed for listening to all available music on Mac, PC, PlayStation 4 or PlayStation 3; and Premium, which added availability for mobile devices and Walkman players as well as Blu-ray players and Bravia TVs. Like any normal music service, Music Unlimited allowed users to create playlists, find new songs and songs that are recommended to them through their own taste of music. A special feature that made the Music Unlimited stand out was the ability to listen to music on a PlayStation 4 whilst playing a game. The service was replaced in 2015 by PlayStation Music with Spotify.
== Sony Entertainment Network Store ==
The interface through the Sony Entertainment Network Store was grouped into sections where users were able to see Top Rated Games, Latest Released Movies, DLC, Coming Soon, Deals and Offers, and PlayStation Plus. The top of the interface displayed the games, movies and TV. The store was the main home to where users could search for different movies, games and other media.
=== Games ===
The games section kept track of all of the games that were stored in the Sony Entertainment Network store. Games were used for users who wished to buy games for the PlayStation consoles, the main location for purchasing games on the Sony Entertainment Network.
== References == | Wikipedia/Sony_Entertainment_Network |
Founded in 2000, CDNetworks is a full-service content delivery network (CDN) which provides technology, network infrastructure, and customer services for the delivery of Internet content and applications. The company is positioning itself as a multinational provider of content delivery services, with a particular emphasis on emerging Internet markets, including South America, India and China. The company's content delivery network consists of 1,500 Point of Presence (PoPs) on five continents. Services include CDN, video acceleration, DDoS protection, cloud storage, cloud access security broker (CASB), web application firewall (WAF) and managed DNS with cloud load balancing. Key differentiators include a large number of global PoPs, good network presence in China and Russia, and high-profile clients such as Forbes, Samsung and Hyundai. CDNetworks has offices in the U.S., South Korea, China, Japan, UK and Singapore.
CDNetworks has changed their logo colours in 2018 from blue green to a multi-coloured one, adding a tagline "Accelerate, Secure, Control".
The headquarters have been relocated to Singapore at the end of 2018 from Hong Kong.
== History ==
On December 20, 2007, CDNetworks raised $96.5 million from Oak Investment Partners, Shinhan Private Equity and Goldman Sachs International.
On February 25, 2009, CDNetworks acquired Panther Express.
On October 21, 2011, Japanese Telco KDDI bought Content Delivery Network CDNetworks for $167 million.
On 26 March, 2017, Wangsu Science & Technology bought 100% of shares from KDDI for $185.72 million.
== See also ==
Software as a service
List of managed DNS providers
== References ==
== External links ==
Akamai & The CDN Price Wars Archived 2010-07-25 at the Wayback Machine | Wikipedia/CDNetworks |
Content delivery network interconnection (CDNI) is a set of interfaces and mechanisms required for interconnecting two independent content delivery networks (CDNs) that enables one to deliver content on behalf of the other. Interconnected CDNs offer many benefits, such as footprint extension, reduced infrastructure costs, higher availability, etc., for content service providers (CSPs), CDNs, and end users. Among its many use cases, it allows small CDNs to interconnect and provides services for CSPs that allows them to compete against the CDNs of global CSPs.
== Rationale ==
Thanks to the many benefits of CDNs, e.g. reduced delivery cost, improved quality of experience (QoE), and increased robustness of delivery, CDNs have become popular for large-scale content delivery of cacheable content. For this reason, CDN providers are scaling up their infrastructure and many Internet service providers (ISPs)/network service providers (NSPs) have deployed or are deploying their own CDNs for their own use or for lease, if a business and technical arrangement between them and a CDN provider were made. Those stand-alone CDNs with well-defined request routing, delivery, acquisition, accounting systems and protocols may sooner or later face either footprint, resource or capability limits. The CDNI targets at leveraging separate CDNs to provide end-to-end delivery of content from CSPs to end users, regardless of their location or attachment network.
== Example of operation ==
Let's consider an interconnection of two CDNs as presented in the below figure. The ISP-A deploys an authoritative upstream CDN (uCDN), and he has established a technical and business arrangement with the CSP. Because the CDN-A is authorised to serve on behalf of the CSP, a user in the network of ISP-B requests content from CDN-A (1). The uCDN can either serve the request itself or redirect it to a downstream CDN (dCDN) if, for example, dCDN is closer to the user equipment (UE). If the request is redirected, the interconnected CDNs must provide the requested content to the dCDN. If the content is not available in the uCDN, it can be acquired first from CSP (2) and then submitted to a surrogate in the dCDN (3). The UE following the redirection will request the content from the dCDN (4), and finally, the requested content will be distributed from the surrogate.
In this example, all four parties can benefit from the interconnection: the end users can benefit from better quality of service (QoS); the CSP benefits because it has to make only one business and technical arrangement with uCDN; the uCDN benefits because it does not have to deploy such an extensive CDN; and the dCDN will receive some compensation for the delivery. The procedures and algorithms responsible for choosing the right dCDN, choosing a surrogate and the procedure for acquiring the content to be submitted to the surrogate can differ, but the dCDN serves the content on behalf of the uCDN.
== Use cases ==
Below is an incomplete list of use cases for which CDNI was presented. The use cases seem to be convergent among the standardisation approaches (see Standardisation status section).
=== Footprint extension ===
Footprint is defined as a region for which a CDN is able to deliver content. With a deployed CDNI, non-global CDN providers may offer CSPs an extended geographical footprint without
compromising the quality of delivery;
additional transit costs, if the content is to be served from geographically or topologically remote surrogates; and
deploying and operating surrogates not justified in the corresponding region, e.g. high investments costs and low delivery volume.
An interconnection may be attractive to a large CDN provider who possesses many CDNs in various locations and who may want to make them interoperable.
A CDNI footprint extension is also beneficial for cases in which CDN providers deliver a lot of popular content to networks of a few ISPs. If so, interconnection of such CDNs would offer improved QoS and QoE to end users, reduce and allow control of ingress traffic in the ISP's network, reduce hardware capacity and footprint of uCDN and allow the ISP to derive some revenue.
Additionally, interconnected networks may allow nomadic end users to access content with a consistent QoE across a range of devices and/or geographic regions.
=== Offload ===
A CDNI can be very useful in overload handling because it allows the unexpected spikes in traffic, e.g. a flash crowd that exceeds the peaks for which a CDN was dimensioned, to be spread between the uCDN and the dCDN. If the CDNs share their resources, they may benefit from dimensioning savings. For such a mechanism to work properly, the uCDN requires information in real time from a dCDN on the amount of traffic it can offload. Whereas for planned events, such as maintenance or special event distribution, a static resource reservation can be sufficient.
Additionally, a CDNI provides means for resiliency against content delivery and acquisition failure. Deploying it, for cases in which the CSPs' surrogates and origin servers are unavailable, allows delivery requests to be redirected towards another CDN. Similarly, with a deployed CDNI, if a default acquisition source fails, other sources within the interconnection, e.g. an alternate uCDN, can be used. This, in turn, provides load balancing between content acquisition sources.
=== Capability ===
A CDNI can be a means of extending a supported range of devices and network technologies if a CDN is not able to support them or if its provider is not willing to provide them. For example, a CDN provider may want to extend its portfolio of services to HTTP Adaptive streaming and/or IPv6 while supporting HTTP streaming and/or IPv4 only. This extension can be realized by interconnecting to a CDN that can provide the requested protocols. Similarly, an interconnection may enable a fixed-line CDN provider to extend its services to mobile devices.
When a CDN provider runs many networks in different technologies, has a multi-vendor strategy or deploys separate networks for many CSPs an interconnection can ease its establishing technology and vendor interoperability by simplification or automatisation of some inter-CDN operations.
Another use case would be an improvement of QoS and QoE for a CDN provider if an interconnection option with a network of surrogates closer to end users existed.
== Interfaces in CDNI ==
The Internet Engineering Task Force (IETF) (see Standardisation status section) defines five interfaces required to interconnect a pair of CDNs from a technical perspective, as depicted in Figure 2. The interfaces are control plane interfaces operating at the application layer that aim to reuse or leverage existing protocols, e.g. HTTP, rather than to define a new one. This model of the CDNI does not define content acquisition, delivery, request interfaces and mechanisms because today CDNs already use standardised protocols for them, e.g. HTTP, FTP, rsync, etc. are used for content acquisition. The interconnection allows a number of CDNs to be connected in various topologies, such as line, mesh or start topology. It is important to note that in order to deploy a CDNI, additional business arrangements have to be established between the CSP and the uCDN and between the uCDN and the dCDN. At the time of this writing detailed operations of interfaces and the structure of exchanged objects are under standardisation process. The defined interfaces are briefly described as follows.
=== Control interface (CI) ===
The CI is designed to initiate an interconnection across two CDNs and bootstrap the other CDNI interfaces. For example, the control interface can be used to provide the address of the logging server in order to bootstrap the logging interface, or it can be used to establish security associations for other interfaces. It can also allow an uCDN to preposition, revalidate or purge metadata and content on a dCDN.
=== Request routing redirection interface (RI) ===
Redirects and selects a delivery dCDN for a given user request. This interface provides loop prevention and detection mechanism for the served requests.
=== Footprint and capabilities advertisement interface (FCI) ===
Enables asynchronous exchange of routing information on capabilities and footprint to support dCDN selection for subsequent user requests. The union of the RI and FCI interfaces denotes the request interface.
=== Metadata interface (MI) ===
Allows a dCDN to provide content metadata from an uCDN. The metadata may include information on required authorization, geo-blocking, availability windows and delegation white- and blacklists. This information can, for example, limit the distribution to a given country or make content intended for adults available only in late-night hours. The collected metadata is used later for CDNI redirection and user content request responses.
=== Logging interface (LI) ===
Enables content distribution and delivery activity details to be exchanged via interconnection. Real-time exchange can be used for traffic monitoring and offline exchange can be used for billing of end user or billing between interconnected CDNs.
== Downstream CDN selection criteria ==
For selection of a dCDN, the information on its footprint and capabilities is mainly used. The footprint can be specified with the use of IP subnets, autonomous systems (AS) numbers or country, state and code combinations. The capabilities describe features, services and states a CDN can or cannot meet and includes network and administrative capabilities, information about caches and the resources. The network information may disclose details on QoS or the supported streaming bandwidth. The administrative capabilities may inform on established limits and policies. The data about the caches may inform about the load and the available resources. The resource information may specify supported delivery technologies and content types, such as the ability to stream video to a particular device type.
Given the information on footprint and capabilities, the uCDN may proceed to the initial selection of a dCDN—first on the basis of footprint and then on the basis of capabilities. However, such procedures may lead to suboptimal or incorrect decisions; for example when the dCDN is selected on the basis of footprint, it cannot provide the requested delivery technology. Therefore, a more approved procedure involves making the footprint information part of the capabilities requirements.
Various protocols are considered for exchange of information on either footprint, such as BGP, on capabilities, such as HTTP, or on both footprint and capabilities, such as Application Layer Traffic Optimization (ALTO).
== Redirection of content request in CDN ==
For user request redirection, two mechanisms, among others, are used in CDNs: mainly HTTP and DNS redirection.
The HTTP method uses the HTTP redirection response, e.g. 302, containing a new URL to visit. Besides the option of changing the name of the server in the new URL, the URL can contain the name of the original server, which provides a means for an in-band communication. Moreover, the redirection mechanism can use the information on the IP address of a client, the requested content type or user agent for target surrogate selection. Unfortunately, change of a URL's domain will cause web browsers to not send cookies.
The DNS redirection is completely transparent to the end user in comparison to the HTTP method. In the simple DNS redirection, the authoritative DNS server for the name returns an IP address based on the characteristic of a client. Which IP address is returned as a result depends, among other factors, on either the localisation of the end user or the surrogate server's load. There is another DNS redirection method in which the authoritative server returns a CNAME response. This forces the peer to restart the name lookup using a new name. To preserve the freshness of the redirection in case of cached DNS responses, an appropriate value of the time-to-live parameter is set. A drawback of this method is that DNS caches hide the end user's IP address.
Both redirection methods, HTTP and DNS based, can be performed in the CDNI, either iteratively or recursively. The recursive redirection is more transparent for the end user because it involves only one UE redirection, but it has other dependencies on the interconnection realisation. A single UE redirection may be preferable if the number of interconnected CDNs exceeds two.
== Exemplary operation of CDNI interfaces in content delivery ==
The sequence diagram presented in the figure below provides some details on CDNI and the iterative DNS redirection operation. In the depicted example, a UE downloads content from the address cdn.csp.com/foo, which is primarily delivered by the CDN-A on behalf of a CSP with the address csp.com.
Before any request redirection, the CDN-B (dCDN) announces information on supported footprint and capabilities.
The UE performs a DNS lookup for a server cdn.csp.com in the domain of the CSP from which it is going to download the content.
A request router in CDN-A (uCDN) servicing the domain cdn.csp.com processes the request and recognises, based on the source IP address of the request, that the end user could be better served by the dCDN. Therefore, it performs an inquiry in dCDN to determine if it is willing and able to serve this request.
If the dCDN is able to handle the request, the request router in uCDN returns a DNS CNAME response. This response contains a new domain, e.g. b.cdn.csp.com, indicating dCDN and the original domain and an NS record that maps this new domain to a request router in dCDN.
The UE does a DNS lookup using the new domain (b.cdn.csp.com). A request router in dCDN responds to this request with the IP address of a suitable delivery node.
The UE requests the content /foo from the delivery node in dCDN. At this point, the delivery node receives the real IP address of the UE and the information on the requested content. If the redirections in previous steps were incorrect, the delivery node could perform a HTTP redirection.
If the metadata for content /foo is not available in dCDN, the metadata interface is used to request it from the uCDN.
If the request is going to be served, i.e. metadata restrictions were met and a cache miss occurs, the delivery node in dCDN must start the acquisition process. The delivery node does a DNS lookup for an internal domain address op-b-acq.op-a.net. The uCDN recognises that the request is from a dCDN, rather than from a UE, and returns an IP address of a delivery node in the uCDN.
The content /foo is delivered to the delivery node in dCDN from the delivery node in uCDN.
The content /foo is delivered to the UE from the delivery node in dCDN.
After some time, the uCDN may instruct the dCDN to purge the content /foo to ensure that it is not delivered again.
After the content is delivered a log of delivery actions is provided to the uCDN.
== HTTP adaptive streaming ==
If addressed in CDNI specifications, support of HTTP adaptive streaming (HAS) is particularly realised. Large objects are broken into a sequence of small, independent chunks, e.g. videos, that are perceived as if there were no relationship between the chunks. As a result, content acquisition and chunk purging are performed on a per-chunk basis. In order to reduce the CDNI load, specifications either allow relative Uniform Resource Locators (URLs) or modify absolute URLs in the manifest file of a resource distributed via HAS.
== Security ==
The security of the CDNI is optional, and its support is introduced as a capability of a CDN. Security of the CDNI involves content confidentiality protection, authenticated peers communication and data origin authentication. The data origin authentication is of high importance if the trust of the link between CDN is questioned. The security is enforced by switching to secure versions of protocols deployed in the CDNI, e.g. HTTPS. Usually, if a CDNI is established via secure protocols, secure protocols are also used for content acquisition and distribution.
Further issues related to security could be various end user privacy requirements in relation to the exchanged logs across different countries or authenticity of logs for delivery charging across CDNs. What consequences a security breakage would have depends on the interface and its function; for example, a corruption of the control interface could corrupt other interfaces, while a corrupted logging interface could enable a fraud in charging.
== Standardisation status ==
A number of organisations and projects, i.e. IETF, European Telecommunications Standards Institute (ETSI), Alliance for Telecommunications Industry Solutions (ATIS) and Open ContEnt Aware Networks (OCEAN), have been working or are working on the standardisation of CDNI interfaces and methods. There exist some mismatches and differences between the specifications in the defined interfaces as well as in terminology.
The ETSI specifications
describe three CDNI interfaces. The first one, the interconnection control, seems to map on the union of ETSI's control and logging interfaces. The next one, the request and content control, seems to map in turn on the union of ETSI's request routing and metadata interfaces. The third one is the distribution of content interface.
The OCEAN framework exhaustively specifies the open interfaces and processes of the proposed CDNI. The documents define additional business, acquisition and inner metadata interfaces. Further, the metadata interface as defined by the ETSI is split into two more specialised interfaces that, together, result in the reference model with nine interfaces.
The paid ATIS standards and technical reports define specification of use cases and high-level requirements for a CDNI. According to the freely available abstracts these specifications cover, among other aspects, the interconnection of two CDN providers as a foundation for using multicast as a means for distributing content across two CDN providers and for joining together a multiple of CDN providers to form a CDN federation.
== See also ==
Content delivery network
Interconnection
Federation (information technology)
Load balancing (computing)
Country code
URL redirection
CNAME record
Dynamic Adaptive Streaming over HTTP
== Further reading ==
S. Puopolo, M. Latouche, F. Le Faucheur, and J. Defour. Content Delivery Network (CDN) Federations How SPs Can Win the Battle for Content-Hungry Consumers, 2011.
A. Pathan and R. Buyya. A Taxonomy and Survey of Content Delivery Networks. Technical Report, GRIDS-TR-2007-4, Grid Computing and Distributed Systems Laboratory, The University of Melbourne, Australia., Feb. 2007.
== References ==
== External links ==
Content Delivery Networks Interconnection (cdni)
OpenCDN | CDN Federation | EdgeCast
SwiftServe - Transparent Caching and Content Delivery Network (CDN) Technology
Multi-CDN Federation | Cedexis - Real time data for real time decisions Archived 2017-09-22 at the Wayback Machine
CDN strategy blog, CDN news, CDN industry news, content delivery network strategies Archived 2013-10-28 at the Wayback Machine
What is Multi-CDN and how does it work? | Wikipedia/Content_delivery_network_interconnection |
Starlight Networks was founded in 1991 by Charlie Bass, Jim Long and Mark Gang with backing from investors Accel Partners and Interwest Partners. The company created some of the first commercial video-on-demand and video streaming products. The first Starlight Networks product was named StarWorks and enabled on-demand MPEG1 full motion videos to be randomly accessed on corporate IP networks. Later a version was released for Novell named Starware.
Originally, the press to networked video as "store & forward video" but that changed after Starlight Networks began describing it as "streaming video". In late 1996 as Starlight added support for live presentations integrating live streaming video with slides and chat, they referred to such solutions as "InterMedia Networking". The 'live' streaming product was named StarLive.
In 1995, Starlight introduced streaming video over satellites with Hughes Network Systems. In February 1998 Starlight introduced one of the first full motion video Web conferencing products, StarLive! (the exclamation point was part of the product name). Technology analyst Om Malik wrote in May 1998 how Starlight software helped power Bloomberg Television and Starlight partnered with RealNetworks to enable Web conferencing at Smith Barney. General Electric also tapped Starlight Products for corporate communications and training. Starlight streaming VOD products were also used for media applications such as powering all the video kiosks in the brand new at the time Cleveland Rock N' Roll Hall of Fame or Universal Studios using a networked Starlight video server to serve up 'dailies' to employees rather than using video-tapes copied for all and distributed manually.
Other investors included: Sequoia Capital, and Merrill, Pickard, Anderson, and Eyre Ventures. Starlight was acquired by PictureTel Corp. in 1998.
== References == | Wikipedia/Starlight_Networks |
Responsive web design (RWD) or responsive design is an approach to web design that aims to make web pages render well on a variety of devices and window or screen sizes from minimum to maximum display size to ensure usability and satisfaction.
A responsive design adapts the web-page layout to the viewing environment by using techniques such as fluid proportion-based grids, flexible images, and CSS3 media queries, an extension of the @media rule, in the following ways:
The fluid grid concept calls for page element sizing to be in relative units like percentages, rather than absolute units like pixels or points.
Flexible images are also sized in relative units, so as to prevent them from displaying outside their containing element.
Media queries allow the page to use different CSS style rules based on characteristics of the device the site is being displayed on, e.g. width of the rendering surface (browser window width or physical display size).
Responsive layouts automatically adjust and adapt to any device screen size, whether it is a desktop, a laptop, a tablet, or a mobile phone.
Responsive web design became more important as users of mobile devices came to account for the majority of website visitors. In 2015, for instance, Google announced Mobilegeddon and started to boost the page ranking of mobile-friendly sites when searching from a mobile device.
Responsive web design is an example of user interface plasticity.
== Challenges, and other approaches ==
Luke Wroblewski has summarized some of the RWD and mobile design challenges and created a catalog of multi-device layout patterns. He suggested that, compared with a simple RWD approach, device experience or RESS (responsive web design with server-side components) approaches can provide a user experience that is better optimized for mobile devices. Server-side CSS generator implementation of stylesheet languages like Sass can be part of such an approach. Google has recommended responsive design for smartphone websites over other approaches.
Although many publishers have implemented responsive designs, one challenge for RWD adoption was that some banner advertisements and videos were not fluid. However, search advertising and (banner) display advertising came to support specific device platform targeting and different advertisement size formats for desktop, smartphone, and basic mobile devices. Different landing page URLs have been used for different platforms, or Ajax has been used to display different advertisement variants on a page. CSS tables permitted hybrid fixed and fluid layouts.
There have been many ways of validating and testing RWD designs, ranging from mobile site validators and mobile emulators to simultaneous testing tools like Adobe Edge Inspect. The Chrome, Firefox and Safari browsers and developer tools have offered responsive design viewport resizing tools, as do third parties.
== History ==
The W3C specification of HTML+ stated that websites have to be rendered according to the user preferences. The customization of web page layout was lacking however. Many web developers resorted to ordinary HTML tables as a way to customize the layout and bring some basic responsiveness to their websites at the same time.
First major site to feature a layout that adapts in a non-trivial manner to browser viewport width was Audi.com launched in late 2001, created by a team at razorfish consisting of Jürgen Spangl and Jim Kalbach (information architecture), Ken Olling (design), and Jan Hoffmann (interface development). Limited browser capabilities meant that for Internet Explorer, the layout could adapt dynamically in the browser whereas, for Netscape, the page had to be reloaded from the server when resized.
Cameron Adams created a demonstration in 2004. By 2008, a number of related terms such as "flexible", "liquid", "fluid", and "elastic" were being used to describe layouts. CSS3 media queries were almost ready for prime time in late 2008/early 2009. Ethan Marcotte coined the term responsive web design—and defined it to mean fluid grid / flexible images / media queries—in a May 2010 article in A List Apart. He described the theory and practice of responsive web design in his brief 2011 book titled Responsive Web Design. Responsive design was listed as #2 in Top Web Design Trends for 2012 by .net magazine after progressive enhancement at #1.
Mashable called 2013 the Year of Responsive Web Design.
== Related concepts ==
Mobile-first design and progressive enhancement are related concepts that predate RWD. Browsers of basic mobile phones do not understand JavaScript or media queries, so a recommended practice was to create a basic web site and enhance it for smartphones and personal computers, rather than rely on graceful degradation to make a complex, image-heavy site work on mobile phones.
== See also ==
== References == | Wikipedia/Responsive_Web_Design |
Wangsu Science & Technology Co., Ltd. (Chinese: 网宿科技股份有限公司) is a China-based company that provides content delivery network (CDN) and Internet data center (IDC) services. It was founded in 2000 and listed on the Shenzhen Stock Exchange in 2009.
It operates businesses in China as ChinaNetCenter Co., and overseas markets as Quantil, Inc. for CDN services and Quantil Networks, Inc. for IDC services.
== Corporate affairs ==
The largest shareholder is Chen Baozhen, who co-founded one of the predecessor companies of Wangsu, holding 21% of the shares of the company.
Its Chinese domestic markets are divided into East China, South China, North China, Central China, the western region and the northeast region.
== Acquisitions ==
In February 2017, the company announced its acquisition of South Korean competitor CDNetworks for 21.1 billion yen ($185 million) to continue expanding its network and business operations outside of China. The deal involved purchasing 85% percent of CDNetworks’ shares from KDDI.
== References ==
== External links ==
Official website | Wikipedia/Wangsu_Science_&_Technology |
This is a comparison of streaming media systems. A more complete list of streaming media systems is also available.
== General ==
The following tables compare general and technical information for a number of streaming media systems both audio and video. Please see the individual systems' linked articles for further information.
== Operating system support ==
== Container format support ==
Information about what digital container formats are supported.
== Protocol support ==
Information about which internet protocols are supported for broadcasting streaming media content.
== Features ==
== See also ==
== References ==
== External links ==
See the container and protocol of VLC Media Player from here: [1] | Wikipedia/Comparison_of_streaming_media_systems |
Vecima Networks is a Canadian company that develops hardware and software for broadband access, content delivery, and telematics. It was founded in Saskatoon, Saskatchewan, and currently has offices in Saskatoon, Burnaby, Atlanta, London, Amsterdam, Tokyo, and is headquartered in Victoria. Vecima sells its products to original equipment manufacturers (OEMs), system integrators, MSOs and other service providers.
Sumit Kumar is the CEO and president. Surinder Kumar is the founder of the company and is the chairman of the board.
== History ==
In 1988 Wavecom Electronics was founded and incorporated by Surinder Kumar. In 1990, the first commercial products included a line of modulators for the cable television industry. In 1998, Wavecom relocated its corporate headquarters to Victoria.
In 2003, Wavecom changed the company name to VCom.
In 2005, VCom transitioned to a public company – VCM on the TSX. In the same year, VCom wins the Advancing Technology award at BC Export Awards.
In 2006 VCom changed its name to Vecima Networks. In December 2008, Vecima signed a supply agreement with Cisco Systems.
In 2013, Vecima announced the appointment of Sumit Kumar to position of CEO.
In 2017, Vecima sold YourLink to Xplornet.
== Acquisitions ==
In 2003, VCom acquired YourLink, a wireless service provider.
In 2007, Vecima acquired Spectrum Signal Processing (Burnaby), a signal processing hardware company.
In 2016, Vecima acquired Contigo Systems, a telematics company.
In 2017, Vecima acquired Concurrent Computer Corporation, a video content delivery and storage company.
== References == | Wikipedia/Vecima_Networks |
Mixcrate was an online audio distribution platform based in California, United States that enabled its users to upload, promote and share their DJ mixes to a worldwide audience and to help DJs promote and grow their careers as professional DJs. It was a community-based platform designed for DJs mainly aimed at promoting their mixes and for fans to follow the work of their favorite DJs. It also catered to music listeners, club promoters, radio stations and event organizers looking to discover new talent.
The service has been described as "the premier platform to enable DJs to share their talent with a worldwide audience while connecting with their peers and fans" and "one of the best known DJ mix hosting sites in the world" by Digital DJ Tips.
On October 20, 2016, Mixcrate shut down. A message posted to the site and to its Facebook Page read: "Unfortunately, Mixcrate received a letter from a respected entity in the record industry. While Mixcrate does not believe the site violates any laws, we do not have the means to operate under current conditions. It's with deep regret that we must shut down the website."
== History ==
Mixcrate was founded and launched by Chris Yee in November 2009. The idea for Mixcrate came about after Yee mentioned the idea to Genghis Mendoza while at their Silicon Valley tech job. Both Yee and Mendoza are from San Francisco and grew up within the mobile DJ scene of the Bay Area. They realized their passion for DJing and web development could create a user-focused destination that would build on the idea of a community. After the development of the site, it was launched to twenty DJ friends and family members to help test. The site gained international viewership from many countries around the world even during the testing period.
Mixcrate was the most trafficked social network for DJ artists in the United States, according to Comscore.
Though now defunct, Mixcrate's official Facebook and Twitter accounts are still active.
== Features ==
Mixcrate allowed users to browse and listen to DJ mixes on the site. Registered users could "like", download (if enabled and logged in), save a mix to their playlist, and comment on a mix. Users could also "follow" other users, both DJs and listeners, to be notified of their recent activities on the site such as newly uploaded mixes (by DJs), recent likes and comments etc., which is displayed on the activity feed on the homepage. Registered DJs could upload an unlimited number of mixes, with a file size limit of 190MB for each mix.
Users also had the option of directly sharing mixes via Facebook, Twitter and Google+.
== Impact and recognition ==
In a Vice magazine interview with culture writer, record collector, music journalist, author, podcast host, DJ and Professor of Sociology Oliver Wang about the history of the San Francisco Bay Area's Filipino American mobile DJ scene, when asked if there was "Anything cool you can point our readers to online?", he responded: "Mixcrate.com, for example, is one platform where quite a few mobile DJs from this scene have posted up old mixes." Notable Filipino American DJs such as Qbert, Mix Master Mike, Shortkut and Apollo had posted their mixes to the site.
Mixcrate has been included in many lists of top/best alternatives to SoundCloud by publications and websites such as in the following:
"SoundCloud Alternatives: The Best Websites for Mixtapes and New Music If SoundCloud Shuts Down" – The Independent
"4 Alternatives to SoundCloud for Hosting DJ Mixes" – Digital DJ Tips
"Best SoundCloud Alternatives - Top 5 Apps Like SoundCloud to Try" – PhoneWorld
"Six Alternatives to SoundCloud for Hosting DJ Mixes" – Fact Magazine
"Every Good Alternative to SoundCloud for DJs" – DJTechTools
"Best SoundCloud Alternatives" – Techboomers
"Top SoundCloud Alternatives" – APowerSoft
"5 SoundCloud Alternatives" – TechShout
"Four Soundcloud Alternatives to Discover and Share Great Music" – Lifehacker
"SoundCloud Is Now, But What's Next? Five Great Alternatives" – Trax Magazine
"6 Alternatives to SoundCloud" – TuExperto
"Top SoundCloud Alternatives to Get Your Music Heard" – GuidingTech
"Six SoundCloud Alternatives" – 5Mag
"SoundCloud Alternatives for DJ Mixes" – OnTheRiseAcademy
"Best SoundCloud Alternatives" – CompsMag
"Best SoundCloud Alternatives - Top 5 Music Apps like SoundCloud" – iTubeGo
"Best SoundCloud Alternatives" – BestReviews
Bobby Owsinski, writing for Forbes magazine, included Mixcrate in his article "Why SoundCloud's Demise Would Hurt Indie Artists" as a "competitive service similar to SoundCloud." Mixcrate was also included in "best sites" lists such as in "The Best Places to Host Your DJ Mixes Online" by Trackhunter and "Best Sites to Share Your DJ Mix Online" by Digital DJ Hub.
TopSitesLike.com produced a list of 13 sites similar to Mixcrate.
== Similar services ==
Mixcloud
SoundCloud
Play.fm
Pandora
== References ==
== External links ==
Mixcrate on Facebook | Wikipedia/Mixcrate |
Measurable Accurate Digital Solutions (doing business as M.A.D Solutions) is a Nigerian music distribution company founded in 2017 by Bugwu Aneto-Okeke.
== History ==
M.A.D Solutions was established by Bugwu Aneto-Okeke in May 2017 in Lagos and started off by securing licensing agreements with Apple Music and YouTube. Aneto-Okeke then partnered with Merlin to explore more licensing rights. In 2021, the headquarters were moved to Houston, Texas.
M.A.D Solutions distributes contents using digital service providers (DSPs) such as Spotify, Boomplay, Ayoba, Audiomack, Triller, and TikTok.
As of 2023 M.A.D
Solutions has amassed over 3 billion streams across its DSPs.
== Services ==
M.A.D Solutions distributes audio and video contents in over 45 distributions services across different genres.
Through ENGAGE, a record label and subsidiary of MAD Solutions, through a partnership with Chordcash and Artsplit, MAD Solutions allows fans to support their artist. Engage as a record label and talent incubator offer a 360 label service to artist.
M.A.D Solutions distributes music for Afrobeats artists such as Runtown, Phyno, Flavour, Ric Hassani, Simi and Nigerian gospel artists such as Mercy Chinwo and Moses Bliss.
== References == | Wikipedia/MAD_Solutions |
Edgio, Inc., formerly Limelight Networks, was an American company that provides a content delivery network (CDN) service, used for delivery of digital media content and software.
Following a 2022 acquisition of Edgecast, the company re-branded as Edgio, and now includes edge computing and cybersecurity services, such as DDoS mitigation.
As of January 2023, the company's network has more than 300 points-of-presence and delivers with 250+ terabits per second of egress capacity across the globe.
The company went bankrupt in 2024 and ceased operation on 15 January 2025.
== Company history ==
Edgio was founded in 2001 in Tempe, Arizona as Limelight Networks, a provider of content delivery network services. The company's Limelight Orchestrate Platform delivers Live and On-Demand video and online content to any connected device anywhere in the world.
In July 2006, the company closed a $130 million equity financing round led by Goldman Sachs Capital Partners. Limelight Networks later raised $240 million in an initial public offering, during June 2007, selling 16 million shares at $15. In April 2008, company founder Michael Gordon was recognized as a "Streaming Media All-Star" by StreamingMedia Magazine, for his contributions to the industry.
In January 2021, Limelight Networks and its board of directors announced that Bob Lyons has been named as the new president and CEO of Limelight Networks, Inc. and will join the company and the board of directors effective February 1, 2021. Mr. Lyons was formerly CEO of Alert Logic.
In September 2021, Limelight Networks acquired Moov Corporation, which did business as Layer0. The acquisition of Layer0 added website orchestration and workflow products, now part of Edgio's Applications suite.
On June 16, 2022, Limelight Networks completed the acquisition of Edgecast from Yahoo! Inc. and rebranded itself to Edgio. The acquisition of Edgecast expanded the reach of Edgio's global delivery network, and also added enterprise-class security solutions to the product portfolio. Additionally, Edgecast brought the Uplynk product - a video workflow and orchestration tool for the streaming of live and on-demand events. Following this acquisition, Edgio developed two distinct offerings - its Applications suite, consisting of website orchestration and cybersecurity solutions; and its Media suite, consisting of media delivery on its global edge network and video streaming solutions.
Edgio had received several industry accolades. In November 2022, an Industry Analyst firm, Quadrant Knowledge Solutions, conducted research into the commercial content delivery network services marketplace and named Edgio as a Leader in the 2022 SPARK Matrix Report.
In March 2023, another leading Industry analyst firm, IDC, categorized Edgio as a Major Cloud Platform for Cloud-Native PaaS Solutions.
In early June 2023, Frost & Sullivan assessed the holistic web protection platform industry and based on its findings, recognized Edgio with the 2023 Global Customer Value Leadership Award.
In late June 2023, GigaOm, a technology focused analyst firm and media company, awarded Edgio the Leadership and Outperformer position in its latest GigaOm Radar for Edge Platforms v3 Report. Edgio was recognized as the leader in the graphic and several tables, and defined as a platform player with maturity within the market.
In July 2023, Edgio was recognized as a Leader in the Frost Radar: Global Content Delivery Network, 2023, by research and consulting firm Frost & Sullivan.
On 9 September 2024, Edgio filed for Chapter 11 bankruptcy protection. The company plans to sell its assets to Lynrock Lake LP, a private equity firm, for around $110 million. Akamai Technologies purchased Edgio's customer contracts and patents among assets.
== Technologies ==
Edgio operates its own private network with more than 250+ terabits per second of global egress capacity. The network consists of dense clusters of specially configured servers in more than 300 delivery locations (points-of-presence) which are interconnected through the company's global network and connected to more than 1000 Internet service provider (ISP) networks. Edgio caches web content for its customers in multiple delivery locations around the world, serving it to users from the fastest location. A private fiber network backbone between its delivery locations allows cache-fill traffic and dynamic content to bypass the public internet and improve the delivery speed of content. This architecture is managed by intelligent proprietary software that increases the speed of delivery with fewer cache misses and can scale to handle surges in end-user demand. Edgio networks mainly uses FreeBSD as operating system on their infrastructures.
=== The Edgio Platform ===
The Edgio Platform is composed of services including content delivery, video packaging and content management, web acceleration, cloud security (including DDoS and WAF protection), and cloud storage.
== Customers ==
In August 2007, the company announced a technology and services agreement with Microsoft under which Limelight will help improve the performance, scalability, and reliability of Internet delivery of media content and online services, including video, music, games, software, and social media, across Microsoft's global Internet properties. In March 2008, the company was the infrastructure provider for the webcast of Oprah's "A New Earth" classroom series, featuring author Eckhart Tolle. The live event drew over 800,000 users. The server crashed during the event because of an error in the programming code; the crash was widely misreported as a failure of network infrastructure.
In May 2008, NBC announced that the company would be the content delivery network for the 2008 Summer Olympics webcast on NBCOlympics.com. Ultimately, the company delivered "more than 50 million unique visitors, resulting in 1.3 billion page views, 70 million video streams, and 600 million minutes of video watched" for NBCOlympics.com, using Microsoft Silverlight technology.
In June 2008, the company was the primary source of content delivery services for the online debut of Disney's Camp Rock. The 24-hour online event saw more than 863,000 total plays for the movie. In January 2009, the company delivered the inauguration of U.S. President Barack Obama to 2.5 million Internet viewers around the world, resulting in more than 9 million simultaneous multimedia streams overall flowing through the company's network. Later that year, in March, the company was the exclusive mobile content delivery provider for CBS' coverage of the 2009 NCAA tournament. Limelight Networks' technology was used to deliver coverage of the college basketball games to the Apple iPhone.
In 2012, Limelight helped deliver sporting events like the Wimbledon Tennis Championships, the Indian Cricket League, the European Championship and the RBS Six Nations’ rugby championships and helped several broadcasters deliver the 2012 Summer Games.
Described and Captured Media Program, a non profit educational organization uses Edgio to accelerate distribution by caching videos on servers as close to the user as possible.
In February 2017 Limelight was one of three content delivery networks to stream the NFL's Super Bowl.
== Acquisitions ==
May 2009, the company acquired Kiptronic, Inc., a privately held provider of device-optimized content delivery solutions and dynamic advertising insertion. It exists today as the Orchestrate Video offering.
April 2010, the company acquired EyeWonder, Inc., a privately held provider of rich media advertising (or "interactive digital advertising") founded in 1999 for $110 million. As part of the purchase of EyeWonder, Limelight Networks, Inc. also purchased chors GmbH. Both of these businesses, which consisted of the EyeWonder business unit, were later sold to DG.
August 2011 the company acquired Delve Networks, Inc., a privately held provider of cloud-based video publishing and analytics services. It exists today as the Orchestrate Video offering.
May 2011, the company acquired AcceloWeb for $20 million. It exists today as the Orchestrate Performance offering.
May 2011, the company acquired Clickability, a web content management system company, for $10 million. On December 23, 2013, Upland Software announced that they had acquired Clickability from Limelight.
September 2021, the company acquired Moov Corporation, doing business as Layer0, a provider of sub-second web apps and APIs through an all-in-one Jamstack platform.
June 2022, the company acquired Edgecast from Yahoo! Inc. for approximately $300 million.
== Patent lawsuits ==
In June 2006, Limelight Networks was sued by Akamai Technologies and the Massachusetts Institute of Technology over alleged patent infringement. In April 2009, the District Court for the District of Massachusetts ruled that Limelight Networks did not infringe, overturning the February 2008 finding of a Boston jury. Similarly, in December 2007, Limelight Networks was sued by Level 3 Communications over alleged intellectual property and patent infringement. In January 2009, a jury ruled that Limelight Networks did not infringe. Akamai Technologies appealed part of the decision. On April 20, 2011, the United States Court of Appeals for the Federal Circuit granted the petition by Akamai Technologies for rehearing en banc its appeal in Akamai Technologies, Inc. v. Limelight Networks, Inc. The order vacated the earlier opinion of December 20, 2010. The order includes a request to file new briefs addressing this question: If separate entities each perform separate steps of a method claim, under what circumstances would that claim be directly infringed and to what extent would each of the parties be liable?
On August 31, 2012, the Court of Appeals for the Federal Circuit issued its opinion in the case. The Court of Appeals stated that the trial court determined that Limelight did not directly infringe on Akamai's patent. A slim majority in this three-way divided opinion also announced a revised legal theory of induced infringement, remanded the case to the trial court giving Akamai an opportunity for a new trial to attempt to prove induced infringement. On December 28, 2012, Limelight filed a petition asking the Supreme Court to review the decision of the Federal Circuit regarding the standard for induced infringement in cases where multiple parties may perform various steps of a patented claim. Akamai filed a cross petition asking the Court to also review the standard for direct infringement in those cases. On June 24, 2013, the Supreme Court asked the Solicitor General to weigh in on the petition for certiorari. In June 2014, the Supreme Court reached a unanimous decision rejecting Akamai's claim of "induced infringement".
On July 1, 2016, it was announced that the Massachusetts District Court entered the final judgment in the case, with Limelight paying $51M in total damages to Akamai (to be reflected in Limelight's 2016 Q2 earnings).
== See also ==
Streaming media
== References ==
== External links == | Wikipedia/Limelight_Networks |
A backbone or core network is a part of a computer network which interconnects networks, providing a path for the exchange of information between different LANs or subnetworks. A backbone can tie together diverse networks in the same building, in different buildings in a campus environment, or over wide areas. Normally, the backbone's capacity is greater than the networks connected to it.
A large corporation that has many locations may have a backbone network that ties all of the locations together, for example, if a server cluster needs to be accessed by different departments of a company that are located at different geographical locations. The pieces of the network connections (for example: Ethernet, wireless) that bring these departments together is often mentioned as network backbone. Network congestion is often taken into consideration while designing backbones.
One example of a backbone network is the Internet backbone.
== History ==
The theory, design principles, and first instantiation of the backbone network came from the telephone core network when traffic was purely voice. The core network was the central part of a telecommunications network that provided various services to customers who were connected by the access network. One of the main functions was to route telephone calls across the PSTN.
Typically the term referred to the high capacity communication facilities that connect primary nodes. A core network provided paths for the exchange of information between different sub-networks.
In the United States, local exchange core networks were linked by several competing interexchange networks; in the rest of the world, the core network has been extended to national boundaries.
Core networks usually had a mesh topology that provided any-to-any connections among devices on the network. Many main service providers would have their own core/backbone networks that are interconnected. Some large enterprises have their own core/backbone network, which are typically connected to the public networks.
Backbone networks create links that allow long-distance transmission, usually 10 to 100 miles, and in certain cases - up to 150 miles. This makes backbone network essential to providing long-haul wireless solutions to provide internet service, especially to remote areas.
== Functions ==
Core networks typically provided the following functionality:
Aggregation: The highest level of aggregation in a service provider network. The next level in the hierarchy under the core nodes is the distribution networks and then the edge networks. Customer-premises equipment (CPE) do not normally connect to the core networks of a large service provider.
Authentication: The function to decide whether the user requesting a service from the telecom network is authorized to do so within this network or not.
Call control and switching: call control or switching functionality decides the future course of call based on the call signaling processing. E.g. switching functionality may decide based on the "called number" that the call be routed towards a subscriber within this operator's network or with number portability more prevalent to another operator's network.
Charging: This functionality of the collation and processing of charging data generated by various network nodes. Two common types of charging mechanisms found in present-day networks are prepaid charging and postpaid charging. See Automatic Message Accounting
Service invocation: The core network performs the task of service invocation for its subscribers. Service invocation may happen based on some explicit action (e.g. call transfer) by user or implicitly (call waiting). It's important to note however that service execution may or may not be a core network functionality as third-party networks and nodes may take part in actual service execution.
Gateways: Gateways shall be present in the core network to access other networks. Gateway functionality is dependent on the type of network it interfaces with.
Physically, one or more of these logical functionalities may simultaneously exist in a given core network node.
Besides the above-mentioned functionalities, the following also formed part of a telecommunications core network:
O&M: Network operations center and operations support systems to configure and provision the core network nodes. Number of subscribers, peak hour call rate, nature of services, geographical preferences are some of the factors that impact the configuration. Network statistics collection, alarm monitoring and logging of various network nodes actions also happens in the O&M center. These stats, alarms and traces form important tools for a network operator to monitor the network health and performance and improvise on the same.
Subscriber database: The core network also hosts the subscriber database (e.g. HLR in GSM systems). The subscriber database is accessed by core network nodes for functions like authentication, profiling, service invocation etc.
== Distributed backbone ==
A distributed backbone is a backbone network that consists of a number of connectivity devices connected to a series of central connectivity devices, such as hubs, switches, or routers, in a hierarchy. This kind of topology allows for simple expansion and limited capital outlay for growth, because more layers of devices can be added to existing layers. In a distributed backbone network, all of the devices that access the backbone share the transmission media, as every device connected to this network is sent all transmissions placed on that network.
Distributed backbones, in all practicality, are in use by all large-scale networks. Applications in enterprise-wide scenarios confined to a single building are also practical, as certain connectivity devices can be assigned to certain floors or departments. Each floor or department possesses a LAN and a wiring closet with that workgroup's main hub or router connected to a bus-style network using backbone cabling. Another advantage of using a distributed backbone is the ability for network administrator to segregate workgroups for ease of management.
There is the possibility of single points of failure, referring to connectivity devices high in the series hierarchy. The distributed backbone must be designed to separate network traffic circulating on each individual LAN from the backbone network traffic by using access devices such as routers and bridges.
== Collapsed backbone ==
A conventional backbone network spans distance to provide interconnectivity across multiple locations. In most cases, the backbones are the links while the switching or routing functions are done by the equipment at each location. It is a distributed architecture.
A collapsed backbone (also known as inverted backbone or backbone-in-a-box) is a type of backbone network architecture. In the case of a collapsed backbone, each location features a link back to a central location to be connected to the collapsed backbone. The collapsed backbone can be a cluster or a single switch or router. The topology and architecture of a collapsed backbone is a star or a rooted tree.
The main advantages of the collapsed backbone approach are
ease of management since the backbone is in a single location and in a single box, and
since the backbone is essentially the back plane or internal switching matrix of the box, proprietary, high performance technology can be used.
However, the drawback of the collapsed backbone is that if the box housing the backbone is down or there are reachability problem to the central location, the entire network will crash. These problems can be minimized by having redundant backbone boxes as well as having secondary/backup backbone locations.
== Parallel backbone ==
There are a few different types of backbones that are used for an enterprise-wide network. When organizations are looking for a very strong and trustworthy backbone they should choose a parallel backbone. This backbone is a variation of a collapsed backbone in that it uses a central node (connection point). Although, with a parallel backbone, it allows for duplicate connections when there is more than one router or switch. Each switch and router are connected by two cables. By having more than one cable connecting each device, it ensures network connectivity to any area of the enterprise-wide network.
Parallel backbones are more expensive than other backbone networks because they require more cabling than the other network topologies. Although this can be a major factor when deciding which enterprise-wide topology to use, the expense of it makes up for the efficiency it creates by adding increased performance and fault tolerance. Most organizations use parallel backbones when there are critical devices on the network. For example, if there is important data, such as payroll, that should be accessed at all times by multiple departments, then your organization should choose to implement a parallel backbone to make sure that the connectivity is never lost.
== Serial backbone ==
A serial backbone is the simplest kind of backbone network. Serial backbones consist of two or more internet working devices connected to each other by a single cable in a daisy-chain fashion. A daisy chain is a group of connectivity devices linked together in a serial fashion. Hubs are often connected in this way to extend a network. However, hubs are not the only device that can be connected in a serial backbone. Gateways, routers, switches and bridges more commonly form part of the backbone. The serial backbone topology could be used for enterprise-wide networks, though it is rarely implemented for that purpose.
== See also ==
Backhaul
Core router
Network service provider
== References ==
== External links ==
IPv6 Backbone Network Topology | Wikipedia/Network_backbone |
Showtime (also known as Paramount+ with Showtime) is an American premium television network and the flagship property of Showtime Networks, a sub-division of the Paramount Media Networks division of Paramount Global. Showtime's programming includes original television series produced exclusively for the linear network and developed for the co-owned Paramount+ streaming service, theatrically released and independent motion pictures, documentaries, and occasional stand-up comedy specials, made-for-TV movies, and softcore adult programming.
Headquartered at Paramount Plaza in the northern part of New York City's Broadway district, Showtime operates eight 24-hour, linear multiplex channels and formerly a standalone traditional subscription video on demand service; the channel's programming catalog and livestreams of its primary linear East and West Coast feeds are also available via an ad-free subscription tier of Paramount+ of the same name, which is also sold a la carte through Apple TV Channels, Prime Video Channels, The Roku Channel and YouTube Primetime Channels. (Subscribers of Paramount+'s Prime Video add-on also receive access to the East Coast feeds of Showtime's seven multiplex channels.) It is a sister premium television network to The Movie Channel and Flix.
In addition, the Showtime brand has been licensed for use by a number of channels and platforms worldwide including Showtime Arabia (it has been merged into OSN) in the Middle East and North Africa, and the now defunct Showtime Movie Channels in Australia. As of September 2018, Showtime's programming was available to approximately 28.567 million American households which subscribed to a multichannel television provider (28.318 million of which receive Showtime's primary channel at a minimum).
== History ==
=== Early years (1976–1982) ===
Showtime was launched on July 1, 1976, on Times-Mirror Cable systems in Escondido, Long Beach, and Palos Verdes, California through the conversion of 10,000 subscribers of the previous Channel One franchise. Exactly a week later Showtime launched on Viacom Cablevision's system in Dublin, California; the channel was originally owned by Viacom. The first program to be broadcast on Showtime was Celebration, a concert special featuring performances by Rod Stewart, Pink Floyd, and ABBA. By the end of its first year on the air, Showtime had 55,000 subscribers nationwide. On March 7, 1978, Showtime became a nationally distributed service when it was uplinked to satellite, becoming a competitor with Time Inc.'s HBO and other pay cable networks.
In 1979, Viacom sold 50% of Showtime to the TelePrompTer Corporation. On July 4, 1981, Showtime began a 24-hour programming schedule (rival HBO followed suit in December of the same year). In 1982, Group W Cable, a subsidiary of Westinghouse Electric Corporation (which acquired TelePrompTer the previous year), sold its 50% stake in Showtime back to Viacom for $75 million. The sale of Group W's stake in the channel happened shortly after the company began a partnership with Walt Disney Productions (now The Walt Disney Company) to develop a competing premium service, The Disney Channel. Group W left the joint venture in September, due to disagreements over creative control and financial obligations. In 1982 Showtime broadcast its first made-for-cable movie Falcon's Gold and its first original series and children's program Faerie Tale Theatre.
=== Formation of Showtime Networks and ownership by Viacom (1982–2005) ===
In August 1982, MCA Inc. (then the owner of Universal Pictures), Gulf+Western (then the owner of Paramount Pictures) and Warner Communications agreed to acquire The Movie Channel (TMC). The three companies combined acquired a controlling 75% interest in the service (with each holding a 25% ownership stake) from Warner-Amex Satellite Entertainment. The deal was spurred by the studios wanting to increase their share of revenue for licensing rights to their films to premium television services, as well as concerns that HBO's dominance of that market and its pre-buying of pay cable rights to films prior to their theatrical release would result in that service holding undue negotiating power for the television rights, resulting in a lower than suitable licensing fee rate the studios would be paid for individual films. The three companies announced an agreement in to acquire interests in TMC on November 11, 1982. In late December of the same year, the U.S. Department of Justice launched a routine preliminary inquiry into the proposed partnership. The Department of Justice had blocked a similar attempt by MCA, Gulf+Western, 20th Century Fox, and Columbia Pictures to create a competing pay service, Premiere, in an antitrust case ruling two years earlier in January 1981.
On January 7, 1983, Viacom International (adding itself as a partner) drafted an amendment to the proposal to consolidate The Movie Channel with Showtime. Under the revised proposal, the four studios would each own a 22.58% stake in the two networks, with American Express owning a 9.68% minority interest. In addition, the consortium would appoint a management team separate from those employed by the two channels–which continued to operate as separate services–to operate the joint venture. However the deal ran into regulatory hurdles because Warner, Universal, and Paramount received 50% of their respective total revenue from film releases and licensing fees from premium services. Also Showtime and TMC combined would control about 30% of the pay cable marketplace, creating an oligopoly with HBO (which in conjunction with Cinemax controlled 60% of the market).
After a four-month investigation resulted in the Department of Justice filing a civil antitrust lawsuit against the five parties to block the Showtime-TMC merger on June 10, 1983, the Department asked Warner and American Express to restructure the deal during hearings for the case. The Department's decision–citing concerns, including some expressed by HBO management, that combining the assets of Showtime and TMC would stifle competition in the sale of their programming and that of other pay cable services to cable providers–was despite the fact that under the original proposal, MCA, Gulf+Western and Warner had each agreed to continue licensing films released by their respective movie studios to competing pay television networks.
The partners involved in the merger would also set standard prices for films that were acquired for broadcast on The Movie Channel and Showtime, either those produced by the studio partners or by unassociated film studios. To address the Justice Department's concerns over the deal, the four partners submitted a revised proposal for consideration on July 19 which included guarantees of conduct agreeing that Paramount, Universal, and Warner Bros. would not receive higher residual licensing payments for films acquired by Showtime and The Movie Channel than those paid by other studios, and that all four partners would not permit the two channels in the venture to pay lower fees for films produced by three studio partners than those paid by smaller pay television services for the same films.
After the revised proposal was rejected on July 28, Warner Communications and American Express restructured the purchase to include only Viacom as a partner, bowing Gulf+Western and MCA out from the partnership. The changes – which Justice Department officials acknowledged would "prevent any anti-competitive effect from arising" following the merger, by allowing other premium services to enter the market should the venture significantly raise licensing fee prices for films–led the Justice Department to drop its challenge to the merger agreement on August 12; the department formally approved the deal the following day on August 13. When the deal was completed on September 6, 1983, the operations of The Movie Channel and Showtime were folded into a new holding company, Showtime/The Movie Channel, Inc., which was majority owned by Viacom (controlling 50% of the venture's common stock as well as investing $40 million in cash), with Warner Communications (which owned 31%), and Warner-Amex (which owned the remaining 19% interest) as minority partners.
As the consolidation of its operations with The Movie Channel was ongoing, in 1983, Showtime increased its national distribution on cable providers when competing premium service Spotlight ceased operations, effectively absorbing that channel's subscriber base.
In 1984 the network's first major promotional campaign, "We Make Excitement" (also referred to, particularly in bumpers and program introductions, as "Showtime Excitement") was created by the J. Walter Thompson company and utilizing an adapted version of the Pointer Sisters song "I'm So Excited". The campaign lasted into 1986 and coincided with both the exclusivity deal signed with Paramount for films (see below) and a graphical upgrade to the network's presentation to include computer-generated graphics.
On August 10, 1985, after Time Inc. and cable provider Tele-Communications Inc. (TCI) jointly submitted a bid to buy the company for $900 million and the assumption of $500 million in debt as well as an earlier offer by American Express the previous month to buy out Warner's share of the company (under a clause in the agreement that allowed either company the option of buying out their partner's stake in Warner-Amex), Warner Communications exercised an option to acquire American Express' 50% share of Warner-Amex Cable Communications for $450 million. Among the options, barring that it chose to sell Viacom a 50% interest in the company for $450 million, the deal originally excluded Warner-Amex's 19% interest in Showtime-The Movie Channel, Inc.; that interest would have reverted to Warner, which intended to operate Warner-Amex as a wholly owned subsidiary.
Two weeks later on August 26, Viacom acquired Warner Communications and Warner-Amex's combined 50% ownership interest in Showtime/The Movie Channel, Inc. as well as full ownership of the Warner-Amex and public shareholder interests in MTV Networks for $671.7 million, giving Viacom exclusive ownership of both networks and once again making it the sole owner of Showtime through its $500 million cash payment and acquisition of 1.625 million shares from Warner for the latter's 31% stake in Showtime/The Movie Channel and Warner-Amex's 19% interest in the unit and its 60% interest in MTV Networks (Viacom owned Showtime alone or jointly with other companies–TelePrompTer Corporation, and later briefly, its successor Group W Cable–from the time it launched in July 1976). The buyout, part of an option given by Warner in its purchase of American Express' interest in MTV, was exercised in part to finance much of the buyout of Showtime/The Movie Channel without borrowing any money (ironically, Warner Communications would eventually acquire rivals HBO and Cinemax, when the company merged with Time Inc. in 1990 to form Time Warner, which is now known as Warner Bros. Discovery). The subsidiary was renamed Showtime Networks, Inc. in 1988.
Also in 1988, the company formed Showtime Event Television (now Showtime PPV) as a pay-per-view distributor of special event programming. In 1990, Showtime ventured into acquiring and premiering independent films exclusively for the channel as part of the 30-Minute Movie short film anthology series. One of its first premieres, 12:01 PM, was nominated for an Academy Award;1992's Session Man won an Academy Award for Best Live Action Short Film. In the years that followed, Showtime expanded its acquisitions into the realm of feature-length fare, including the Adrian Lyne-directed 1997 remake of Lolita.
On March 1, 1994, Showtime and The Movie Channel in conjunction with rivals HBO and Cinemax implemented a cooperative content advisory system to provide to parents specific information about pay-cable programming content that may be unsuitable for their children; the development of the system—inspired by the advisory ratings featured in program guides distributed by the major premium cable services—was in response to concerns from parents and advocacy groups about violent content on television, allowing Showtime Networks and other premium services discretionary authority to assign individual ratings corresponding to the objectionable content depicted in specific programs (and categorized based on violence, profanity, sexuality or miscellaneous mature material). A revised system—centered around ten content codes of two to three letters in length—was implemented by Showtime and the other participating premium services on June 10, 1994.
In 1997, the channel's first major rebrand since the 1980s was introduced, with a new logo emphasizing the "SHO" part of the network's name within a circle (intended to be a spotlight), playing into the channel's common acronym in listings services like TV Guide. A new slogan, "No Limits" (in reference to the fact that as a premium channel, Showtime could push the boundaries of programming without censorship, as well as offer the type of exciting programming that appealed to subscribers), and a bold red-and-black color scheme was instituted, with promotions and bumpers feature surrealistic imagery; the campaign was created by the newly formed in-house marketing and advertising agency, "Red Group".
In 2000, Showtime launched "Showtime Interactive 24.7", a service that provided DVD-style interaction of its entertainment offerings. The following year in 2001, Showtime became one of the first cable networks to launch a high definition simulcast feed (with Star Trek: Insurrection becoming the first film on the network to be broadcast in HD); Showtime also began to provide Dolby Digital 5.1 surround sound on select programs.
=== Under CBS Corporation ownership (2005–2019) ===
On June 14, 2005, Viacom decided to separate itself into two companies (only five years after the company's acquisition of CBS), both of which would be controlled by Viacom parent National Amusements, amid stagnation of the company's stock price. When the split was completed on December 31, 2005, the original Viacom was restructured as CBS Corporation and kept Showtime Networks along with the original Viacom's broadcasting assets (which included the CBS television network, UPN and the company's broadcast group, which became CBS Television Stations), Paramount Television (now the separate arms CBS Studios for network and cable production, and CBS Media Ventures for production of first-run syndicated programs and off-network series distribution), advertising firm Viacom Outdoor (renamed CBS Outdoor), Simon & Schuster, and Paramount Parks (which was later sold to Cedar Fair, L.P. on June 30, 2006). A new company that assumed the Viacom name took Paramount Pictures, the MTV Networks and BET Networks cable divisions, and Famous Music (the latter of which was sold to Sony-ATV Music Publishing (CBS once owned its sister company) in May 2007).
=== Re-merger with Viacom; co-branding with Paramount+ (2019–present) ===
On August 13, 2019, the announcement was made that CBS and Viacom would merge into a new entity known as ViacomCBS (now known as Paramount Global). Viacom CEO Bob Bakish would be president and CEO of the new company, while Ianniello would become chairman and CEO of CBS and oversee CBS-branded assets. Shari Redstone would also serve as chairperson of ViacomCBS. On October 29, 2019, National Amusements approved the re-merger deal. It closed on December 4, 2019. As part of the new structure the Showtime Networks unit and its assets—Showtime, The Movie Channel and Flix—became part of the Premium Network Group division of ViacomCBS Domestic Media Networks, along with BET and temporarily Pop TV (which was transferred to the Youth & Entertainment Group division the following month, later named MTV Entertainment Group), to be overseen by SNI CEO David Nevins. ViacomCBS renamed itself as Paramount Global on February 16, 2022; the company's domestic networks division became Paramount Media Networks on the same day.
On January 30, 2023, Paramount Global announced plans to fully integrate the Showtime direct-to-consumer service (which was sold directly to streaming-only consumers) with the premium tier of the Paramount+ streaming service; the combined service would be branded as Paramount+ with Showtime, replacing a streaming bundle of the same name that launched in August 2022. The merger commenced on June 27, 2023, with the cable-specific Showtime Anytime TV Everywhere app (which was offered to subscribers of the linear Showtime television service) ceasing operations on December 14, and the standalone Showtime app being discontinued on April 30, 2024; the primary Showtime channel was rebranded as Paramount+ with Showtime on January 8, 2024, although the former name remains in use as a standalone brand for its multiplex channels and for marketing of the network's original programs.
== Channels ==
=== Background ===
In 1991, after HBO and Cinemax debuted the first premium television multiplex service in the United States, Showtime followed with the testing of its own secondary service–Showtime 2–on October 1 of that year. In April 1994, Showtime announced the creation of a new themed multiplex service, consisting of five channels: Spanish service Showtime En Espanol; family-oriented Showtime Family Television; action-oriented service Showtime Action Television; a service featuring comedy films and series called Showtime Comedy Television; and an all-movie channel called Showtime Film Festival. This planned extension to the multiplex did not come to fruition–although a third multiplex service, Showtime 3, would make its debut in 1996.
The multiplex would eventually expand over time with the launch of the action film channel Showtime Extreme on March 10, 1998, followed by the debut of the science fiction channel Showtime Beyond in September 1999; the Showtime Unlimited name for the Showtime multiplex, TMC and Flix came into use around this time. Three additional themed channels made their debut in March 2001: Showtime Family Zone (which carries films intended for family audiences), Showtime Next (a channel featuring films and series that appeal toward adults between the ages of 18 and 34 years old) and Showtime Women (a channel featuring movies, specials,
and Showtime original programs that appeal toward a female audience). The programming format of Showtime 3 was overhauled five months later on July 1, 2001, to focus on theatrical movie releases and Showtime's original made-for-cable films, that under the new name Showcase.
Showtime Family Zone, Showtime Next and Showtime Women do not have distribution by most pay television providers as extensive as the other Showtime multiplex channels. The availability of either of the three channels on cable providers varies depending on the market; Dish Network only carries Showtime Family Zone, and DirecTV carries Showtime Next and Showtime Family Zone, but not Showtime Women.
=== List of Showtime channels ===
Depending on the service provider, Paramount+ with Showtime provides up to sixteen multiplex channels–eight 24-hour multiplex channels, all of which are simulcast in both standard definition and high definition–as well as a video on demand service (Paramount+ with Showtime On Demand). Paramount+ with Showtime broadcasts its primary and multiplex channels on both Eastern and Pacific Time Zone schedules. The respective coastal feeds of each channel are usually packaged together (though most cable providers only offer the east and west coast feeds of the main Paramount+ with Showtime channel), resulting in the difference in local airtimes for a particular movie or program between two geographic locations being three hours at most.
Subscribers to the separate premium film service The Movie Channel, which is also owned by Paramount, do not necessarily have to subscribe to the linear Paramount+ with Showtime service in order to receive TMC; both The Movie Channel and co-owned fellow movie service Flix are typically sold together in a package (although in the case of Flix, this depends on the channel's provider availability), though DirecTV and Dish Network alternately sell TMC through a separate film tier. For unexplained reasons, live feeds of The Movie Channel and Flix have not been included alongside the other Showtime multiplex channels on its proprietary streaming services (including the Paramount+ premium tier) or its add-on tiers that are sold through live-TV streaming providers (such as Hulu, YouTube TV and DirecTV Stream), restricting their distribution to traditional cable, satellite and telco/fiber optic television providers. From 1999 to 2005, the package encompassing Showtime and its sister networks was marketed as "Showtime Unlimited"; the broader tier sometimes included the Sundance Channel (now Sundance TV) during this period, by way of the stake Showtime Networks held in the network from its 1996 inception until Sundance's 2008 purchase by Rainbow Media (now AMC Networks).
== Other services ==
=== Showtime HD ===
Showtime HD is a high definition simulcast feed of Showtime that broadcasts in the 1080i resolution format. In addition to its main channel, all of Showtime's multiplex channels also broadcast in the format, though availability of all of the HD feeds varies by provider. Showtime HD is available through virtually all providers which carry Showtime, along with Showtime's streaming services. Films shown on Showtime's HD simulcast feeds are broadcast in their domestic aspect ratio if that version is provided by the studios that maintain pay television distribution rights with the channel.
=== Showtime on Demand ===
Showtime operates a subscription video-on-demand television service called Showtime on Demand, which is available at no additional charge to Showtime subscribers. Showtime on Demand offers feature films, episodes of Showtime's original series, adult programming and sports events. Showtime on Demand's rotating program selection incorporates select new titles that are added each Friday, alongside existing program titles held over from the previous one to two weeks. The service began to be test marketed in 2001 and was officially launched in July 2002.
=== Showtime Anytime ===
On October 27, 2010, Showtime launched Showtime Anytime, a website that featured around 400 hours of streaming program content available in standard or high definition that was accessible to subscribers of the Showtime television service with TV Everywhere login. Content available on the service included Showtime original programming, feature films, comedy specials, documentaries and sports programming. It was available nationally to Showtime subscribers of satellite provider AT&T DirecTV, and regionally by Comcast Xfinity; Spectrum; Optimum; Cox Communications; CenturyLink Prism; Grande Communications; Mediacom; AT&T U-verse; and Verizon FIOS. The Showtime Anytime app (which was offered as a free download) was initially released on the iOS App Store for the iPad and iPhone on October 3, 2011. On October 1, 2012, an Android app became available through the Google Play platform for Android devices.
In September 2017, it was discovered that the Showtime Anytime website was injected with code that mined the cryptocurrency Monero using the viewer's CPU, which would potentially cause degraded performance for other websites and applications. The code was removed as soon as it was discovered.
The Anytime app and website viewing were shut down in December 2023.
=== SHO Sync ===
On September 22, 2011, Showtime launched Showtime Social, a second screen interactive app providing interactivity with Showtime programs including viewer-participant polls and trivia questions as well as real-time aggregation of Twitter, Facebook and blog comments about particular Showtime programs; the app utilizes Automated Content Recognition technology to generate interactive content regardless of whether it is being watched live, on-demand or by DVR; the app also displays heat maps depicting viewer reactions throughout the duration of an episode at the conclusion of the program. The app–which was renamed SHO Sync on September 13, 2012–was originally released for Apple iOS devices (iPad and iPhone), with an app for LG-manufactured Smart TVs being released on August 15, 2013.
On July 9, 2015, Showtime announced it would discontinue SHO Sync, immediately discontinuing support of the iPad app with the iPhone and LG apps to be discontinued at a later date. However, the channel hinted that the core interactive functions of SHO Sync may be restored in a different form, with the possibility of being incorporated into Showtime Anytime and the Showtime over-the-top streaming service.
=== Streaming service ===
On June 3, 2015, then-Showtime parent CBS Corporation announced that it would launch an over-the-top subscription video on demand service that would be distributed as a standalone offering without the requirement of having an existing television subscription to use (in the manner of competitor HBO's OTT offering, HBO Now). The service, which used the same branding as the linear television channel, was officially launched on July 7, 2015 (coinciding with the season premieres of Ray Donovan and Masters of Sex on July 12). The service was initially available for purchase through Apple Inc. (to Apple TV and iOS devices), Hulu, Roku, PlayStation Vue, and Amazon Prime as well as through Showtime's website (SHO.com).
The Showtime streaming service was identical to Showtime Anytime; it offered a back catalog of episodes of various past and present Showtime original series (with new episodes of Showtime original series being made available for streaming the same day as their original broadcast on the main linear Showtime channel), feature films and documentaries, and sports events and analysis programs. Subscriptions were also available over Amazon Prime (Amazon Channels), Hulu, The Roku Channel, and Apple TV (Apple TV Channels) as add-ons. Unlike HBO Now, Showtime also provided live streams of the East and West Coast television feeds of the linear Showtime channel (live streams of Showtime's multiplex services, and sister networks The Movie Channel, The Movie Channel Xtra, and Flix were not available on the service; live streams of Showtime's multiplex channels were available for Amazon Prime users as part of the Showtime add-on subscription).
==== Absorption into Paramount+ ====
The Showtime streaming service co-existed with Paramount Global's flagship streaming service Paramount+, and became part of a bundle offer with the service. In August 2022, the Paramount+ apps were updated with the ability to upgrade a subscription to the "Paramount+ with Showtime" bundle, and for subscribers to the bundle to access Showtime content from within the Paramount+ apps. Showtime would continue to be offered as a standalone service and application. However, in September, the company was in talks of moving the entire Showtime content within Paramount+. By December 2022, Paramount CEO Bob Bakish said that it "didn't make sense to run Showtime as a 100% stand-alone organization".
On January 30, 2023, Paramount Global confirmed the two services would be fully merged in the near future in the United States, with both the Showtime service and the current Paramount+ Premium tier to be rebranded "Paramount+ with Showtime", echoing similar integrations in other international markets. The "Showtime" brand will remain active as a distinct programming imprint. On May 20, 2023, Paramount Global announced that the merger of both services would take place on June 27, with the standalone Showtime app being shut down on April 30, 2024. The primary Showtime channel was rebranded as Paramount+ with Showtime on January 8, 2024, although the former name remains in use as a standalone brand for its multiplex channels.
== Programming ==
Paramount+ with Showtime's programming schedule currently consists largely of theatrically released feature films—which occupy much of the service's daily schedule, varying in quantity depending on channel—and original series targeted at adult audiences (including, as of June 2020, dramas like Shameless, Homeland, Yellowjackets, Billions, The Chi, The L Word: Generation Q, and Penny Dreadful: City of Angels; comedies such as Black Monday, Our Cartoon President and Kidding; and docuseries including The Circus and Vice). In addition, Showtime has documentary films, boxing matches, sports-centric magazine series, occasional original stand-up comedy specials, and short-form behind-the-scenes specials centered mainly on theatrical films (either running in their initial theatrical or Showtime Networks broadcast window).
Since the early 1980s, Showtime has run an adult-oriented late night programming block on its main channel called "Showtime After Hours" (which was briefly branded as "Showtime Late Night" during the mid-1990s) each night after 12:00 a.m. Eastern Time; programs featured within the block include feature films, series produced specifically for broadcast during the block and occasional stand-up comedy specials. Softcore erotica programming has previously aired during the "After Hours" block, though adult films have been absent from Showtime's primary channel since the mid-2000s; the network began broadcasting a limited amount of original erotica series (such as Beach Heat: Miami) on its main channel in 2010, after having been removed for most of the previous decade. The network's multiplex channels Showtime 2 and Showtime Extreme also occasionally feature adult films during the overnight hours, though this has become less commonplace since late 2011.
Until the formation of Showtime Family Zone in 2001, Showtime heavily incorporated programming (both American and foreign) aimed at children and teenagers as part of its daytime schedule; in particular, the main channel ran a late afternoon block of teen-oriented series on Sundays (such as Ready or Not, Chris Cross and Degrassi High), as well as a morning block of shows aimed at younger children (such as OWL/TV, A Bunch of Munsch and The Busy World of Richard Scarry) during the early and mid-1990s, and a weekday mid-afternoon and Sunday morning film block called "Showtime Familytime" that ran during the 1980s and 1990s.
The main Showtime network also carried, unusually for a premium channel, news programming; the now-defunct All News Channel (partially owned by Viacom) produced 90-second long news updates that aired during Showtime's primetime promotional breaks in the early 1990s (ANC also produced news updates for fellow Viacom network VH1), in part as a response to the first Gulf War.
=== Original programming ===
Showtime has become known in recent years for the network's original television programs, the most popular of which include the crime drama Dexter, the dark comedy drama Weeds, family dramas Ray Donovan and Shameless and the drama/thriller series Homeland. Other notable past and present original series include Stargate SG-1 (which ran on Showtime for its first five seasons, before moving to the Sci-Fi Channel (now Syfy) for the remainder of its run); Dead Like Me; Californication; Gigolos; Nurse Jackie; The Tudors; Brotherhood; Soul Food; Queer as Folk; The L Word; The Big C; Penn & Teller: Bullshit!; and United States of Tara. In mid-2017, the channel aired the critically acclaimed third season of David Lynch's TV series Twin Peaks. From 2007 to 2013, multiplex service Showtime 2 broadcast an original program exclusive to that channel, the seasonal late night reality series Big Brother: After Dark, a companion to sister broadcast network CBS' American adaptation of Big Brother; the program moved to TVGN (which has since been renamed Pop) starting with the June 26, 2013, premiere of Big Brother's 15th season.
Showtime formerly produced its own original made-for-cable movies, originally branded as "Showtime Original Movies" until 1994 and "Showtime Original Pictures" thereafter until the channel discontinued producing television films in 2007. Showtime is also one of only two premium cable services (alongside Disney Channel during its existence as a premium channel prior to 1997) that has produced original movies aimed at family audiences; these films were originally broadcast under the separate banner "Showtime Original Pictures for Kids" from 1995 to 1997 and "Showtime Original Pictures for All Ages" from 1997 to 2005.
==== Showtime After Hours ====
A signature feature of Showtime was a late-night block known as Showtime After Hours, which featured softcore pornographic films and original series. Showtime did not have set start or end times for the block, as they varied depending on the mainstream feature films–and original series on certain nights–that aired prior to and following it, and also depended on the number of programs and programs in particular that were scheduled to air within the block. Programs that aired under the Showtime After Hours banner carried either a TV-MA or R rating (usually the former), primarily for strong sexual content and nudity. The block had often been the subject of both scrutiny in the media and a source of humor in popular culture, with references to Showtime's late night programming being featured in various films and television shows.
=== Movie library ===
As of 2025, Showtime–and sister channels The Movie Channel and Flix–maintains exclusive first-run film licensing agreements with Amblin Partners (including releases produced in conjunction with DreamWorks Pictures, which maintains a pay television licensing agreement for its other releases with Showtime rivals HBO and Cinemax, and Participant), and Bleecker Street.
Despite being corporately reunited with Paramount Pictures in 2019 as a result of the ViacomCBS merger, Paramount maintains an existing output deal with MGM+ (formerly Epix, which Paramount co-owned with Lionsgate and MGM from its 2009 launch until 2018) until the end of 2025. New films from Paramount Pictures will not be able to air on Showtime until 2026 unless further negotiations are made. Showtime subscribers though certain providers are able to stream certain recent Paramount Pictures films through included Paramount+ subscriptions.
Showtime also shows sub-runs – runs of films that have already received broadcast or syndicated television airings – of theatrical films distributed by IFC Films, Sony Pictures (including content from Columbia Pictures, TriStar Pictures, Screen Gems, Revolution Studios and Morgan Creek Productions), Warner Bros. Pictures (including content from New Line Cinema), Universal Pictures (including content from subsidiary Focus Features), Open Road Films, Screen Media, Oscilloscope (select films), Summit Entertainment (for films released prior to 2013), Paramount Pictures (for films released prior to 2020), A24 (for films released prior to 2024), Amblin Partners (including DreamWorks Pictures, for films released prior to 2025) Metro-Goldwyn-Mayer (including content from subsidiary United Artists), Lionsgate (sub-run rights with the latter two studios are for films released prior to 2015), and Walt Disney Studios Motion Pictures (including content from Pixar, 20th Century Studios, Walt Disney Animation Studios, Walt Disney Pictures, and Marvel Studios).
The window between a film's initial release in theaters and its initial screening on Showtime and sister channels The Movie Channel and Flix is wider than the grace period leading to a film's initial broadcast on HBO/Cinemax, Starz/Encore, and Epix. Films that Showtime has pay cable rights to will usually run on The Movie Channel and Flix during the period of its term of licensing.
==== Former first-run contracts ====
Within years of its launch, Showtime entered into licensing agreements with several movie studios. Following Viacom's 1983 acquisition of a joint stake in The Movie Channel, Paramount Pictures (then owned by Gulf+Western) signed a five-year exclusive first-run distribution agreement with Showtime and The Movie Channel to carry the studio's films through 1989. On July 15, 1987, HBO signed a five-year deal with Paramount Pictures to broadcast 85 of their films released from May 1988 onward; in May 1989, after it signed a licensing deal with HBO, Paramount Pictures filed a lawsuit against Showtime Networks, Viacom and its parent National Amusements over Showtime's alleged refusal to pay a total of $88 million in fees for five films (that underperformed in their theatrical release) to reduce the minimum liability for its 75-film package from Paramount. After Paramount Pictures was purchased by Viacom in 1994, Showtime (which was also owned by Viacom at the time) signed a seven-year distribution deal with Paramount which took effect in January 1998, following the expiration of Paramount Pictures' contract with HBO.
In 1986, Showtime signed an agreement with Buena Vista Motion Pictures Group; its contract with Walt Disney Pictures expired after 1992, while output deals with Touchstone Pictures and Hollywood Pictures expired after 1996. Rival pay channel Starz signed a deal with Disney in 1994, carrying only Touchstone Pictures and Hollywood Pictures films released from January 1997 onward early on. Also in 1986, Showtime signed an agreement with Orion Pictures for an exclusive first-run film output deal, that coincides with owner Viacom purchasing a minority stake in Showtime. By 1989, Showtime had already made exclusive deals with Carolco Pictures (signed in 1988), Atlantic Entertainment Group, Cannon Films (both signed in 1986), Universal Pictures, De Laurentiis Entertainment Group, Imagine Entertainment (signed in 1986), and Weintraub Films.
On April 13, 1990, Showtime signed an exclusive first-run film output deal with New Line Cinema; the deal expired after 1995. In July 1993, Encore signed an output deal with New Line Cinema, broadcasting its films released between 1994 and 2004. On November 22, 1993, Showtime signed exclusive first-run premium cable rights with Metro-Goldwyn-Mayer (renewing an existing pact with the studio) and United Artists, which were renewed for nine additional years in 2000. On March 5, 1996, Showtime announced a seven-year output deal with Phoenix Pictures (as part of an agreement that also included the purchase of an 11% equity interest), broadcasting titles from that studio released between 1996 and 2002. During that time, Showtime also maintained output deals with TriStar Pictures (between 1994 and 1999), Dimension Films (between 1997 and 2003), Castle Rock Entertainment (which expired after 1999), PolyGram Filmed Entertainment (which expired after 2001), and Artisan Entertainment. In 2006, Showtime entered into a partial deal with Rogue Pictures to broadcast select films released by the studio (especially those originally produced for home video release).
On December 4, 2008, Showtime signed a four-year exclusive first-run distribution deal with Summit Entertainment, broadcasting 42 films that were released by that studio between 2009 and 2012. On May 27, 2011, rival premium channel HBO had signed an output deal with Summit Entertainment, allowing films that were released between 2013 and 2017 to be broadcast on HBO. Showtime formerly had a deal with The Weinstein Company (since 2009, including releases by Dimension Films). Netflix assumed the rights to The Weinstein Company's films starting in 2016.
==== Paramount Pictures, Lionsgate, and MGM ====
The future of Showtime was put into question after negotiations to renew film output deals with Paramount Pictures (which was separated from Showtime following the December 2005 split of Viacom and CBS into two separate companies, with CBS Corporation taking ownership of Showtime; the companies would however re-merge 14 years later), Metro-Goldwyn-Mayer, and Lions Gate Entertainment broke down, due to the failure between the studios and Showtime to agree on licensing fees for movies from the channel's three largest film distributors. All three studios then entered into a joint venture, Studio 3 Partners, to form Epix as a competitor to Showtime, HBO and Starz; Epix debuted in May 2009 as a broadband Internet service, with the television channel launching on October 30 of that year.
==== A24 ====
From November 13, 2019 to December 31, 2023, Showtime was the exclusive premium cable broadcaster for films distributed by A24 (excluding titles part of A24's already-existing partnership with Apple Inc.) through an output deal made between the two entities.
=== Sports programming ===
Showtime has broadcast a limited amount of sports programming, which is produced by the channel's Showtime Sports division. Showtime also operates Showtime Sports PPV (formerly Showtime Sports & Entertainment Television or SSET), which formerly broadcast boxing matches and has broadcast other select event programming for pay-per-view. Beginning in March 1986, Showtime's sports programming consisted largely of boxing matches produced under the banner Showtime Championship Boxing; in 2001, the network launched ShoBox: The New Generation, focusing primarily on up-and-coming boxers. In 2004, Showtime began broadcasting all domestic fights telecast on the channel in high definition.
In December 2006, Showtime announced a deal to broadcast mixed martial arts matches from the then-newly formed Elite Xtreme Combat (or EliteXC), an MMA organization formed by Showtime Networks and ProElite, Inc., with all events broadcast under the banner ShoXC; the league folded two years later in 2008.
In 2008, Showtime acquired Inside the NFL, the longest-running program in the history of HBO, from HBO after it had cancelled the seasonal analysis and interview program in February of that year; Inside the NFL moved to Showtime that September. In 2021, Inside the NFL moved to Paramount+.
In February 2009, mixed martial arts promotion Strikeforce announced a three-year broadcast agreement with Showtime, allowing it to broadcast up to 16 events per year, as well as a deal with sister network CBS for an option to produce up to four events for that network; Strikeforce ended its run on Showtime when the league folded in January 2013. In addition to broadcasting big-ticket Strikeforce events on Showtime, the promotion also announced it would produce ShoMMA: Strikeforce Challengers, an event series highlighting up-and-coming fighters.
In 2010, Showtime debuted another original sports insider program, Inside NASCAR, focusing on interviews and analysis from around the NASCAR circuit. In 2011, Showtime expanded its MMA programming by televising events produced by M-1 Global, the Russian PTC company of popular Strikeforce fighter Fedor Emelianenko. In November 2012, Showtime debuted a sports-themed spinoff of CBS' long-running newsmagazine 60 Minutes, titled 60 Minutes Sports.
From 2012 to 2015, Showtime also aired an hour-long program called Jim Rome on Showtime, featuring the CBS Sports Radio host's commentary and interviews with personalities in the sports world.
On February 9, 2021, it was announced that Showtime would be the exclusive home of Bellator MMA beginning with Bellator 255 on April 2 (the ViacomCBS merger made Bellator and Showtime corporate siblings). It was the first time mixed martial arts aired on Showtime since Strikeforce was absorbed by the UFC.
Showtime Sports ceased operations on December 31, 2023, and sports programming has been moved to the CBS Sports branding.
== International ==
Outside of the United States, several pay television networks have used the Showtime name and former logo through licensing agreements with Showtime Networks for a while such as Showtime Australia, Showtime Arabia, Showtime Scandinavia and Spain's Showtime Extreme (now XTRM). Showtime launched a South African version as part of the new TopTV satellite provider's package on May 1, 2010.
In January 2015, CBS announced an exclusive Canadian brand and content licensing agreement with domestic broadcaster Bell Media, under which Showtime programming would air exclusively on Bell's services including The Movie Network and CraveTV (later consolidated under the Crave name); prior to this, The Movie Network and now-defunct counterpart Movie Central had been licensing Canadian rights to current Showtime programming. Later that year, Chinese streamer PPTV agreed to a multiyear license to stream CBS and Showtime series in the country, giving 400 million users access to select Showtime series from CBS.
Showtime programming is also distributed in selected countries/territories through localized versions of Paramount+, including Australia, Latin America, the United Kingdom, and Ireland.
=== SkyShowtime ===
SkyShowtime is a joint-venture between Paramount Global's Showtime and Comcast's Sky which combines programming from the corporations' Paramount+ and Peacock services. SkyShowtime launched in European markets where Sky does not operate their satellite and cable services.
== Notes ==
== References ==
== External links ==
Paramount+ with Showtime | Wikipedia/Showtime_(TV_network) |
A New Kind of Science is a book by Stephen Wolfram, published by his company Wolfram Research under the imprint Wolfram Media in 2002. It contains an empirical and systematic study of computational systems such as cellular automata. Wolfram calls these systems simple programs and argues that the scientific philosophy and methods appropriate for the study of simple programs are relevant to other fields of science.
== Contents ==
=== Computation and its implications ===
The thesis of A New Kind of Science (NKS) is twofold: that the nature of computation must be explored experimentally, and that the results of these experiments have great relevance to understanding the physical world.
=== Simple programs ===
The basic subject of Wolfram's "new kind of science" is the study of simple abstract rules—essentially, elementary computer programs. In almost any class of a computational system, one very quickly finds instances of great complexity among its simplest cases (after a time series of multiple iterative loops, applying the same simple set of rules on itself, similar to a self-reinforcing cycle using a set of rules). This seems to be true regardless of the components of the system and the details of its setup. Systems explored in the book include, among others, cellular automata in one, two, and three dimensions; mobile automata; Turing machines in 1 and 2 dimensions; several varieties of substitution and network systems; recursive functions; nested recursive functions; combinators; tag systems; register machines; and reversal-addition. For a program to qualify as simple, there are several requirements:
Its operation can be completely explained by a simple graphical illustration.
It can be completely explained in a few sentences of human language.
It can be implemented in a computer language using just a few lines of code.
The number of its possible variations is small enough so that all of them can be computed.
Generally, simple programs tend to have a very simple abstract framework. Simple cellular automata, Turing machines, and combinators are examples of such frameworks, while more complex cellular automata do not necessarily qualify as simple programs. It is also possible to invent new frameworks, particularly to capture the operation of natural systems. The remarkable feature of simple programs is that a significant proportion of them can produce great complexity. Simply enumerating all possible variations of almost any class of programs quickly leads one to examples that do unexpected and interesting things. This leads to the question: if the program is so simple, where does the complexity come from? In a sense, there is not enough room in the program's definition to directly encode all the things the program can do. Therefore, simple programs can be seen as a minimal example of emergence. A logical deduction from this phenomenon is that if the details of the program's rules have little direct relationship to its behavior, then it is very difficult to directly engineer a simple program to perform a specific behavior. An alternative approach is to try to engineer a simple overall computational framework, and then do a brute-force search through all of the possible components for the best match.
Simple programs are capable of a remarkable range of behavior. Some have been proven to be universal computers. Others exhibit properties familiar from traditional science, such as thermodynamic behavior, continuum behavior, conserved quantities, percolation, sensitive dependence on initial conditions, and others. They have been used as models of traffic, material fracture, crystal growth, biological growth, and various sociological, geological, and ecological phenomena. Another feature of simple programs is that, according to the book, making them more complicated seems to have little effect on their overall complexity. A New Kind of Science argues that this is evidence that simple programs are enough to capture the essence of almost any complex system.
=== Mapping and mining the computational universe ===
In order to study simple rules and their often-complex behavior, Wolfram argues that it is necessary to systematically explore all these computational systems and document what they do. He further argues that this study should become a new branch of science, like physics or chemistry. The basic goal of this field is to understand and characterize the computational universe using experimental methods.
The proposed new branch of scientific exploration admits many different forms of scientific production. For instance, qualitative classifications are often the results of initial forays into the computational jungle. On the other hand, explicit proofs that certain systems compute this or that function are also admissible. Some forms of production are also in some ways unique to this field of study—for example, the discovery of computational mechanisms that emerge in different systems but in bizarrely different forms.
Another type of production involves the creation of programs for the analysis of computational systems. In the NKS framework, these themselves should be simple programs, and subject to the same goals and methodology. An extension of this idea is that the human mind is itself a computational system, and hence providing it with raw data in as effective a way as possible is crucial to research. Wolfram believes that programs and their analysis should be visualized as directly as possible, and exhaustively examined by the thousands or more. Since this new field concerns abstract rules, it can in principle address issues relevant to other fields of science. But in general, Wolfram's idea is that novel ideas and mechanisms can be discovered in the computational universe, where they can be represented in their simplest forms, and then other fields can choose among these discoveries for those they find relevant.
=== Systematic abstract science ===
While Wolfram advocates simple programs as a scientific discipline, he also argues that its methodology will revolutionize other fields of science. The basis of his argument is that the study of simple programs is the minimal possible form of science, grounded equally in both abstraction and empirical experimentation. Every aspect of the methodology NKS advocates is optimized to make experimentation as direct, easy, and meaningful as possible while maximizing the chances that the experiment will do something unexpected. Just as this methodology allows computational mechanisms to be studied in their simplest forms, Wolfram argues that the process of doing so engages with the mathematical basis of the physical world, and therefore has much to offer the sciences.
Wolfram argues that the computational realities of the universe make science hard for fundamental reasons. But he also argues that by understanding the importance of these realities, we can learn to use them in our favor. For instance, instead of reverse engineering our theories from observation, we can enumerate systems and then try to match them to the behaviors we observe. A major theme of NKS is investigating the structure of the possibility space. Wolfram argues that science is far too ad hoc, in part because the models used are too complicated and unnecessarily organized around the limited primitives of traditional mathematics. Wolfram advocates using models whose variations are enumerable and whose consequences are straightforward to compute and analyze.
=== Philosophical underpinnings ===
==== Computational irreducibility ====
Wolfram argues that one of his achievements is in providing a coherent system of ideas that justifies computation as an organizing principle of science. For instance, he argues that the concept of computational irreducibility (that some complex computations are not amenable to short-cuts and cannot be "reduced"), is ultimately the reason why computational models of nature must be considered in addition to traditional mathematical models. Likewise, his idea of intrinsic randomness generation—that natural systems can generate their own randomness, rather than using chaos theory or stochastic perturbations—implies that computational models do not need to include explicit randomness.
==== Principle of computational equivalence ====
Based on his experimental results, Wolfram developed the principle of computational equivalence (PCE): the principle says that systems found in the natural world can perform computations up to a maximal ("universal") level of computational power. Most systems can attain this level. Systems, in principle, compute the same things as a computer. Computation is therefore simply a question of translating input and outputs from one system to another. Consequently, most systems are computationally equivalent. Proposed examples of such systems are the workings of the human brain and the evolution of weather systems.
The principle can be restated as follows: almost all processes that are not obviously simple are of equivalent sophistication. From this principle, Wolfram draws an array of concrete deductions that he argues reinforce his theory. Possibly the most important of these is an explanation of why we experience randomness and complexity: often, the systems we analyze are just as sophisticated as we are. Thus, complexity is not a special quality of systems, like the concept of "heat", but simply a label for all systems whose computations are sophisticated. Wolfram argues that understanding this makes possible the "normal science" of the NKS paradigm.
=== Applications and results ===
NKS contains a number of specific results and ideas, and they can be organized into several themes. One common theme of examples and applications is demonstrating how little complexity it takes to achieve interesting behavior, and how the proper methodology can discover this behavior.
First, there are several cases where NKS introduces what was, during the book's composition, the simplest known system in some class that has a particular characteristic. Some examples include the first primitive recursive function that results in complexity, the smallest universal Turing machine, and the shortest axiom for propositional calculus. In a similar vein, Wolfram also demonstrates many simple programs that exhibit phenomena like phase transitions, conserved quantities, continuum behavior, and thermodynamics that are familiar from traditional science. Simple computational models of natural systems like shell growth, fluid turbulence, and phyllotaxis are a final category of applications that fall in this theme.
Another common theme is taking facts about the computational universe as a whole and using them to reason about fields in a holistic way. For instance, Wolfram discusses how facts about the computational universe inform evolutionary theory, SETI, free will, computational complexity theory, and philosophical fields like ontology, epistemology, and even postmodernism.
Wolfram suggests that the theory of computational irreducibility may explain how free will is possible in a nominally deterministic universe. He posits that the computational process in the brain of the being with free will is so complex that it cannot be captured in a simpler computation, due to the principle of computational irreducibility. Thus, while the process is indeed deterministic, there is no better way to determine the being's will than, in essence, to run the experiment and let the being exercise it.
The book also contains a number of results—both experimental and analytic—about what a particular automaton computes, or what its characteristics are, using some methods of analysis.
The book contains a new technical result in describing the Turing completeness of the Rule 110 cellular automaton. Very small Turing machines can simulate Rule 110, which Wolfram demonstrates using a 2-state 5-symbol universal Turing machine. Wolfram conjectures that a particular 2-state 3-symbol Turing machine is universal. In 2007, as part of commemorating the book's fifth anniversary, Wolfram's company offered a $25,000 prize for proof that this Turing machine is universal. Alex Smith, a computer science student from Birmingham, UK, won the prize later that year by proving Wolfram's conjecture.
== Reception ==
Periodicals gave A New Kind of Science coverage, including articles in The New York Times, Newsweek, Wired, and The Economist. Some scientists, including Cosma Shalizi and Scott Aaronson, criticized the book and perceived a fatal flaw—that simple systems such as cellular automata are not complex enough to describe the degree of complexity in evolved systems, and observed that Wolfram ignored the research categorizing the complexity of systems. Although critics accept Wolfram's result showing universal computation, they view it as minor and dispute Wolfram's claim of a paradigm shift. Others found that the work contained valuable insights and refreshing ideas. Wolfram addressed his critics in a series of blog posts.
=== Scientific philosophy ===
A tenet of NKS is that the simpler the system, the more likely a version of it will recur in a wide variety of more complicated contexts. Therefore, NKS argues that systematically exploring the space of simple programs will lead to a base of reusable knowledge. But many scientists believe that of all possible parameters, only some actually occur in the universe. For instance, of all possible permutations of the symbols making up an equation, most will be essentially meaningless. NKS has also been criticized for asserting that the behavior of simple systems is somehow representative of all systems.
=== Methodology ===
A common criticism of NKS is that it does not follow established scientific methodology. For instance, NKS does not establish rigorous mathematical definitions, nor does it attempt to prove theorems; and most formulas and equations are written in Mathematica rather than standard notation. Along these lines, NKS has also been criticized for being heavily visual, with much information conveyed by pictures that lack formal meaning. It has also been criticized for not using modern research in the field of complexity, particularly works on complexity from a rigorous mathematical perspective. And it has been criticized for misrepresenting chaos theory.
=== Utility ===
NKS has been criticized for not providing specific results that are immediately applicable to ongoing scientific research. There has also been criticism, implicit and explicit, that the study of simple programs has little connection to the physical universe and hence is of limited value. Steven Weinberg has pointed out that no real-world system has been satisfactorily explained using Wolfram's methods. Mathematician Steven G. Krantz wrote, "Just because Wolfram can cook up a cellular automaton that seems to produce the spot pattern on a leopard, may we safely conclude that he understands the mechanism by which the spots are produced on the leopard, or why the spots are there, or what function (evolutionary or mating or camouflage or other) they perform?"
=== Principle of computational equivalence (PCE) ===
The principle of computational equivalence (PCE) has been criticized for being vague, unmathematical, and not making directly verifiable predictions. It has also been criticized for being contrary to the spirit of research in mathematical logic and computational complexity theory, which seek to make fine-grained distinctions between levels of computational sophistication, and for wrongly conflating different kinds of universality property. Moreover, critics such as Ray Kurzweil have argued that it ignores the distinction between hardware and software; while two computers may be equivalent in power, it does not follow that any two programs they might run are also equivalent. Others suggest it is little more than a rechristening of the Church–Turing thesis.
=== The fundamental theory (NKS Chapter 9) ===
Wolfram's speculations of a direction toward a fundamental theory of physics have been criticized as vague and obsolete. Scott Aaronson, Professor of Computer Science at University of Texas Austin, also claims that Wolfram's methods cannot be compatible with both special relativity and Bell's theorem violations, and hence cannot explain the observed results of Bell tests.
Edward Fredkin and Konrad Zuse pioneered the idea of a computable universe, the former by writing a line in his book on how the world might be like a cellular automaton, later further developed by Fredkin using a toy model called Salt. It has been claimed that NKS tries to take these ideas as its own, but Wolfram's model of the universe is a rewriting network, not a cellular automaton, as Wolfram himself has suggested a cellular automaton cannot account for relativistic features such as no absolute time frame. Jürgen Schmidhuber has also charged that his work on Turing machine-computable physics was stolen without attribution, namely his idea on enumerating possible Turing-computable universes.
In a 2002 review of NKS, the Nobel laureate and elementary particle physicist Steven Weinberg wrote, "Wolfram himself is a lapsed elementary particle physicist, and I suppose he can't resist trying to apply his experience with digital computer programs to the laws of nature. This has led him to the view (also considered in a 1981 paper by Richard Feynman) that nature is discrete rather than continuous. He suggests that space consists of a set of isolated points, like cells in a cellular automaton, and that even time flows in discrete steps. Following an idea of Edward Fredkin, he concludes that the universe itself would then be an automaton, like a giant computer. It's possible, but I can't see any motivation for these speculations, except that this is the sort of system that Wolfram and others have become used to in their work on computers. So might a carpenter, looking at the moon, suppose that it is made of wood."
=== Natural selection ===
Wolfram's claim that natural selection is not the fundamental cause of complexity in biology has led journalist Chris Lavers to say that Wolfram does not understand the theory of evolution.
=== Originality ===
NKS has been heavily criticized as not original or important enough to justify its title and claims.
The authoritative manner in which NKS presents a vast number of examples and arguments has been criticized as leading the reader to believe that each of these is original to Wolfram; in particular, one of the most substantial new technical results presented in the book, that the rule 110 cellular automaton is Turing complete, was not proven by Wolfram. Wolfram credits the proof to his research assistant Matthew Cook. But the book's notes section acknowledges many of the discoveries made by these other scientists, citing their names together with historical facts, although not in the form of a traditional bibliography section. Additionally, the idea that very simple rules often generate great complexity is already an established idea in science, particularly in chaos theory and complex systems.
== See also ==
Digital physics
Scientific reductionism
Calculating Space
Marcus Hutter's "Universal Artificial Intelligence" algorithm
== References ==
== External links ==
A New Kind of Science free E-Book
What We've Learned from NKS YouTube playlist — extensive discussion of each NKS chapter; (As of 2022, Stephen Wolfram discusses the NKS chapters in view of recent developments. Wolfram Physics Project) | Wikipedia/A_New_Kind_of_Science |
"A Mathematical Theory of Communication" is an article by mathematician Claude E. Shannon published in Bell System Technical Journal in 1948. It was renamed The Mathematical Theory of Communication in the 1949 book of the same name, a small but significant title change after realizing the generality of this work. It has tens of thousands of citations, being one of the most influential and cited scientific papers of all time, as it gave rise to the field of information theory, with Scientific American referring to the paper as the "Magna Carta of the Information Age", while the electrical engineer Robert G. Gallager called the paper a "blueprint for the digital era". Historian James Gleick rated the paper as the most important development of 1948, placing the transistor second in the same time period, with Gleick emphasizing that the paper by Shannon was "even more profound and more fundamental" than the transistor.
It is also noted that "as did relativity and quantum theory, information theory radically changed the way scientists look at the universe". The paper also formally introduced the term "bit" and serves as its theoretical foundation.
== Publication ==
The article was the founding work of the field of information theory. It was later published in 1949 as a book titled The Mathematical Theory of Communication (ISBN 0-252-72546-8), which was published as a paperback in 1963 (ISBN 0-252-72548-4). The book contains an additional article by Warren Weaver, providing an overview of the theory for a more general audience.
== Contents ==
This work is known for introducing the concepts of channel capacity as well as the noisy channel coding theorem.
Shannon's article laid out the basic elements of communication:
An information source that produces a message
A transmitter that operates on the message to create a signal which can be sent through a channel
A channel, which is the medium over which the signal, carrying the information that composes the message, is sent
A receiver, which transforms the signal back into the message intended for delivery
A destination, which can be a person or a machine, for whom or which the message is intended
It also developed the concepts of information entropy, redundancy and the source coding theorem, and introduced the term bit (which Shannon credited to John Tukey) as a unit of information. It was also in this paper that the Shannon–Fano coding technique was proposed – a technique developed in conjunction with Robert Fano.
== References ==
== External links ==
(PDF) "A Mathematical Theory of Communication" by C. E. Shannon (reprint with corrections) hosted by the Harvard Mathematics Department, at Harvard University
Original publications: The Bell System Technical Journal 1948-07: Vol 27 Iss 3. AT & T Bell Laboratories. 1948-07-01. pp. 379–423., The Bell System Technical Journal 1948-10: Vol 27 Iss 4. AT & T Bell Laboratories. 1948-10-01. pp. 623–656.
Khan Academy video about "A Mathematical Theory of Communication" | Wikipedia/The_Mathematical_Theory_of_Communication |
Hard science and soft science are colloquial terms used to compare scientific fields on the basis of perceived methodological rigor, exactitude, and objectivity. In general, the formal sciences and natural sciences are considered hard science, whereas the social sciences and other sciences are described as soft science.
Precise definitions vary, but features often cited as characteristic of hard science include producing testable predictions, performing controlled experiments, relying on quantifiable data and mathematical models, a high degree of accuracy and objectivity, higher levels of consensus, faster progression of the field, greater explanatory success, cumulativeness, replicability, and generally applying a purer form of the scientific method. A closely related idea (originating in the nineteenth century with Auguste Comte) is that scientific disciplines can be arranged into a hierarchy of hard to soft on the basis of factors such as rigor, "development", and whether they are basic or applied.
Philosophers and historians of science have questioned the relationship between these characteristics and perceived hardness or softness. The more "developed" hard sciences do not necessarily have a greater degree of consensus or selectivity in accepting new results. Commonly cited methodological differences are also not a reliable indicator. For example, social sciences such as psychology and sociology use mathematical models extensively, but are usually considered soft sciences. However, there are some measurable differences between hard and soft sciences. For example, hard sciences make more extensive use of graphs, and soft sciences are more prone to a rapid turnover of buzzwords.
The metaphor has been criticised for unduly stigmatizing soft sciences, creating an unwarranted imbalance in the public perception, funding, and recognition of different fields.
== History of the terms ==
The origin of the terms "hard science" and "soft science" is obscure. The earliest attested use of "hard science" is found in an 1858 issue of the Journal of the Society of Arts, but the idea of a hierarchy of the sciences can be found earlier, in the work of the French philosopher Auguste Comte (1798‒1857). He identified astronomy as the most general science, followed by physics, chemistry, biology, then sociology. This view was highly influential, and was intended to classify fields based on their degree of intellectual development and the complexity of their subject matter.
The modern distinction between hard and soft science is often attributed to a 1964 article published in Science by John R. Platt. He explored why he considered some scientific fields to be more productive than others, though he did not actually use the terms themselves. In 1967, sociologist of science Norman W. Storer specifically distinguished between the natural sciences as hard and the social sciences as soft. He defined hardness in terms of the degree to which a field uses mathematics and described a trend of scientific fields increasing in hardness over time, identifying features of increased hardness as including better integration and organization of knowledge, an improved ability to detect errors, and an increase in the difficulty of learning the subject.
== Empirical support ==
In the 1970s sociologist Stephen Cole conducted a number of empirical studies attempting to find evidence for a hierarchy of scientific disciplines, and was unable to find significant differences in terms of core of knowledge, degree of codification, or research material. Differences that he did find evidence for included a tendency for textbooks in soft sciences to rely on more recent work, while the material in textbooks from the hard sciences was more consistent over time. After he published in 1983, it has been suggested that Cole might have missed some relationships in the data because he studied individual measurements, without accounting for the way multiple measurements could trend in the same direction, and because not all the criteria that could indicate a discipline's scientific status were analysed.
In 1984, Cleveland performed a survey of 57 journals and found that natural science journals used many more graphs than journals in mathematics or social science, and that social science journals often presented large amounts of observational data in the absence of graphs. The amount of page area used for graphs ranged from 0% to 31%, and the variation was primarily due to the number of graphs included rather than their sizes. Further analyses by Smith in 2000, based on samples of graphs from journals in seven major scientific disciplines, found that the amount of graph usage correlated "almost perfectly" with hardness (r=0.97). They also suggested that the hierarchy applies to individual fields, and demonstrated the same result using ten subfields of psychology (r=0.93).
In a 2010 article, Fanelli proposed that we expect more positive outcomes in "softer" sciences because there are fewer constraints on researcher bias. They found that among research papers that tested a hypothesis, the frequency of positive results was predicted by the perceived hardness of the field. For example, the social sciences as a whole had a 2.3-fold increased odds of positive results compared to the physical sciences, with the biological sciences in between. They added that this supported the idea that the social sciences and natural sciences differ only in degree, as long as the social sciences follow the scientific approach.
In 2013, Fanelli tested whether the ability of researchers in a field to "achieve consensus and accumulate knowledge" increases with the hardness of the science, and sampled 29,000 papers from 12 disciplines using measurements that indicate the degree of scholarly consensus. Out of the three possibilities (hierarchy, hard/soft distinction, or no ordering), the results supported a hierarchy, with physical sciences performing the best followed by biological sciences and then social sciences. The results also held within disciplines, as well as when mathematics and the humanities were included.
== Criticism ==
Critics of the concept argue that soft sciences are implicitly considered to be less "legitimate" scientific fields, or simply not scientific at all. An editorial in Nature stated that social science findings are more likely to intersect with everyday experience and may be dismissed as "obvious or insignificant" as a result. Being labelled a soft science can affect the perceived value of a discipline to society and the amount of funding available to it. In the 1980s, mathematician Serge Lang successfully blocked influential political scientist Samuel P. Huntington's admission to the US National Academy of Sciences, describing Huntington's use of mathematics to quantify the relationship between factors such as "social frustration" (Lang asked Huntington if he possessed a "social-frustration meter") as "pseudoscience". During the late 2000s recessions, social science was disproportionately targeted for funding cuts compared to mathematics and natural science. Proposals were made for the United States' National Science Foundation to cease funding disciplines such as political science altogether. Both of these incidents prompted critical discussion of the distinction between hard and soft sciences.
The perception of hard vs soft science is influenced by gender bias with a higher proportion of women in a given field leading to a "soft" perception even within STEM fields. This perception of softness is accompanied by a devaluation of the field's worth.
== See also ==
Academic field
Demarcation problem
Exact sciences
Hard and soft science fiction
History of science
Methodological dualism
Non-science
Philosophy of social science
Positivism dispute
STEM fields
== Notes ==
== References == | Wikipedia/Hard_Science |
Brian Wilson (born 1933 in Newton-le-Willows, Lancashire) is a British systems scientist and honorary professor at Cardiff University, known for his development of soft systems methodology (SSM) and enterprise modelling.
== Biography ==
After graduating from University of Nottingham with a B.Sc. and Ph.D. in electrical engineering, nuclear power engineering and control system design, Wilson joined the United Kingdom Atomic Energy Authority where he studied the control and spatial stability of gas-cooled reactors and power plants. In 1966, he left the world of nuclear power engineering and control system design, and became a founder member of the Department of Systems Engineering at the University of Lancaster.
Wilson has had an association with Cardiff University for a number of years, in a variety of roles, and has recently been conferred as an honorary professor in the Department of Computer Science.
He left the University of Lancaster in 1992 and built his own consultancy company, Brian Wilson & Associates, where he continued to develop and apply his particular brand of SSM, leading to the uses of SSM in enterprise model building.
== Work ==
During his time at the University of Lancaster, Wilson was involved in the development of a particular form of business analysis known as soft systems methodology (SSM). This development was driven by the action research programme carried out in that department, in which his particular interest was the application of SSM to information and organisation-based analysis. The work appeared in the book, Systems: Concepts, methodologies and Applications, (editions 1 & 2), published by John Wiley.
He has 40 years of experience of tackling organisation-based problems of various kinds and he has undertaken projects in the pharmaceutical industry, the Met Office, the Office of Government Commerce (OGC), the Ministry of Defence (MoD), the Police, the National Health Service and a variety of other organisations in both private and public sectors.
His most recent work has been focused with the development of SSM-based models to bring about the integration of children's services within Tameside; to contribute to the MOD's "Carrier Strike" programme and to explore the organisation of the detection and containment of illegal importation and use of nuclear and radiological materials as part of the anti-terrorist programme, "Cyclamen". Also, a contribution was made to the development of an "enterprise" architecture for information assurance in the public sector and to the development of new information support across a number of publishing companies within Hachette Livre.
== Publications ==
Books:
1980, Systems: Concepts, methodologies and Applications, John Wiley.
2001, Soft Systems Methodology—Conceptual model building and its contribution, J.H.Wiley.
Papers:
2006, Deriving Information Requirements
== References ==
== External links ==
Brian Wilson at koiosgroup.com. | Wikipedia/Brian_Wilson_(systems_scientist) |
This list of life sciences comprises the branches of science that involve the scientific study of life – such as microorganisms, plants, and animals including human beings. This science is one of the two major branches of natural science, the other being physical science, which is concerned with non-living matter. Biology is the overall natural science that studies life, with the other life sciences as its sub-disciplines.
Some life sciences focus on a specific type of organism. For example, zoology is the study of animals, while botany is the study of plants. Other life sciences focus on aspects common to all or many life forms, such as anatomy and genetics. Some focus on the micro-scale (e.g. molecular biology, biochemistry) other on larger scales (e.g. cytology, immunology, ethology, pharmacy, ecology). Another major branch of life sciences involves understanding the mind – neuroscience. Life sciences discoveries are helpful in improving the quality and standard of life and have applications in health, agriculture, medicine, and the pharmaceutical and food science industries. For example, it has provided information on certain diseases which has overall aided in the understanding of human health.
== Basic life science branches ==
Biology – scientific study of life
Anatomy – study of form and function, in plants, animals, and other organisms
Histology – the study of tissues
Neuroscience – the study of the nervous system
Astrobiology – the study of the formation and presence of life in the universe
Biotechnology – study of combination of both the living organism and technology
Biochemistry – the study of the chemical reactions required for life to exist and function, usually focused on the cellular level
Quantum biology – the study of quantum phenomena in organisms
Bioinformatics – developing of methods or software tools for storing, retrieving, organizing and analyzing biological data to generate useful biological knowledge
Biophysics – study of biological processes by applying the theories and methods that have been traditionally used in the physical sciences
Biomechanics – the study of the mechanics of living beings
Botany – study of plants
Agrostology – the study of grasses and grass-like species
Phycology – the study of algae
Cell biology (cytology) – study of the cell as a complete unit, and the molecular and chemical interactions that occur within a living cell
Developmental biology – the study of the processes through which an organism forms, from zygote to full structure
Ecology – study of the interactions of living organisms with one another and with the non-living elements of their environment
Enzymology – study of enzymes
Evolutionary biology – study of the origin and descent of species over time
Evolutionary developmental biology – the study of the evolution of development including its molecular control
Genetics – the study of genes and heredity
Immunology – the study of the immune system
Marine biology – the study of ocean organisms
Biological oceanography – the study of life in the oceans and their interaction with the environment
Microbiology – the study of microscopic organisms (microorganisms) and their interactions with other living organisms
Aerobiology – study of the movement and transportation of microorganisms in the air
Bacteriology – study of bacteria
Virology – study of viruses and virus-like agents
Molecular biology – the study of biology and biological functions at the molecular level, some cross over with biochemistry, genetics, and microbiology
Structural biology – a branch of molecular biology, biochemistry, and biophysics concerned with the molecular structure of biological macro-molecules
Mycology – the study of fungi
Paleontology – the study of prehistoric organisms
Parasitology – the study of parasites, their hosts, and the relationship between them
Pathology – study of the causes and effects of disease or injury
Human biology – the biological study of human beings
Pharmacology – study of drug action
Biological (or physical) anthropology – the study of humans, non-human primates, and hominids
Biolinguistics – the study of the biology and evolution of language
Physiology – the study of the functioning of living organisms and the organs and parts of living organisms
Population biology – the study of groups of conspecific organisms
Population dynamics – the study of short-term and long-term changes in the size and age composition of populations, and the biological and environmental processes influencing those changes. Population dynamics deals with the way populations are affected by birth and death rates, and by immigration and emigration, and studies topics such as ageing populations or population decline.
Synthetic biology – the design and construction of new biological entities such as enzymes, genetic circuits and cells, or the redesign of existing biological systems
Systems biology – the study of the integration and dependencies of various components within a biological system, with particular focus upon the role of metabolic pathways and cell-signaling strategies in physiology
Theoretical biology – use of abstractions and mathematical models to study biological phenomena
Toxicology – the study of poisons
Zoology – the study of (generally non-human) animals
Ethology – the study of animal behavior
== Applied life science branches and derived concepts ==
Agriculture – science and practice of cultivating plants and livestock
Agronomy – science of cultivating plants for resources
Biocomputers – systems of biologically derived molecules, such as DNA and proteins, are used to perform computational calculations involving storing, retrieving, and processing data. The development of biological computing has been made possible by the expanding new science of nanobiotechnology.
Biocontrol – bioeffector-method of controlling pests (including insects, mites, weeds and plant diseases) using other living organisms.
Bioengineering – study of biology through the means of engineering with an emphasis on applied knowledge and especially related to biotechnology
Bioelectronics – field at the convergence of electronics and biological sciences. The electrical state of biological matter significantly affects its structure and function, compare for instance the membrane potential, the signal transduction by neurons, the isoelectric point (IEP) and so on. Micro- and nano-electronic components and devices have increasingly been combined with biological systems like medical implants, biosensors, lab-on-a-chip devices etc. causing the emergence of this new scientific field.
Biomaterials – any matter, surface, or construct that interacts with biological systems. As a science, biomaterials is about fifty years old. The study of biomaterials is called biomaterials science. It has experienced steady and strong growth over its history, with many companies investing large amounts of money into the development of new products. Biomaterials science encompasses elements of medicine, biology, chemistry, tissue engineering and materials science.
Biomedical science – healthcare science, also known as biomedical science, is a set of applied sciences applying portions of natural science or formal science, or both, to develop knowledge, interventions, or technology of use in healthcare or public health. Such disciplines as medical microbiology, clinical virology, clinical epidemiology, genetic epidemiology and pathophysiology are medical sciences.
Biomonitoring – measurement of the body burden of toxic chemical compounds, elements, or their metabolites, in biological substances. Often, these measurements are done in blood and urine.
Biopolymer – polymers produced by living organisms; in other words, they are polymeric biomolecules. Since they are polymers, biopolymers contain monomeric units that are covalently bonded to form larger structures. There are three main classes of biopolymers, classified according to the monomeric units used and the structure of the biopolymer formed: polynucleotides (RNA and DNA), which are long polymers composed of 13 or more nucleotide monomers; polypeptides, which are short polymers of amino acids; and polysaccharides, which are often linear bonded polymeric carbohydrate structures.
Biotechnology – manipulation of living matter, including genetic modification and synthetic biology
Conservation biology – the management of nature and of Earth's biodiversity with the aim of protecting species, their habitats, and ecosystems from excessive rates of extinction and the erosion of biotic interactions. It is an interdisciplinary subject drawing on natural and social sciences, and the practice of natural resource management.
Environmental health – multidisciplinary field concerned with environmental epidemiology, toxicology, and exposure science.
Fermentation technology – study of use of microorganisms for industrial manufacturing of various products like vitamins, amino acids, antibiotics, beer, wine, etc.
Food science – applied science devoted to the study of food. Activities of food scientists include the development of new food products, design of processes to produce and conserve these foods, choice of packaging materials, shelf-life studies, study of the effects of food on the human body, sensory evaluation of products using panels or potential consumers, as well as microbiological, physical (texture and rheology) and chemical testing.
Genomics – application of recombinant DNA, DNA sequencing methods, and bioinformatics to sequence, assemble, and analyze the function and structure of genomes (the complete set of DNA within a single cell of an organism). The field includes efforts to determine the entire DNA sequence of organisms and fine-scale genetic mapping. The field also includes studies of intragenomic phenomena such as heterosis, epistasis, pleiotropy and other interactions between loci and alleles within the genome. In contrast, the investigation of the roles and functions of single genes is a primary focus of molecular biology or genetics and is a common topic of modern medical and biological research. Research of single genes does not fall into the definition of genomics unless the aim of this genetic, pathway, and functional information analysis is to elucidate its effect on, place in, and response to the entire genome's networks.
Health sciences – sciences which focus on health, or health care, as core parts of their subject matter. These two subject matters relate to multiple academic disciplines, both STEM disciplines, as well as emerging patient safety disciplines (such as social care research), and are both relevant to current health science knowledge.
Medical devices – A medical device is an instrument, apparatus, implant, in vitro reagent, or similar or related article that is used to diagnose, prevent, or treat disease or other conditions, and does not achieve its purposes through chemical action within or on the body (which would make it a drug). Whereas medicinal products (also called pharmaceuticals) achieve their principal action by pharmacological, metabolic or immunological means, medical devices act by other means like physical, mechanical, or thermal means.
Medical imaging – the technique and process used to create images of the human body (or parts and function thereof) for clinical or physiological research purposes
Immunotherapy – the "treatment of disease by inducing, enhancing, or suppressing an immune response". Immunotherapies designed to elicit or amplify an immune response are classified as activation immunotherapies, while immunotherapies that reduce or suppress are classified as suppression immunotherapies.
Kinesiology – scientific study of human movement. Kinesiology, also known as human kinetics, addresses physiological, mechanical, and psychological mechanisms. Applications of kinesiology to human health include: biomechanics and orthopedics; strength and conditioning; sport psychology; methods of rehabilitation, such as physical and occupational therapy; and sport and exercise. Individuals who have earned degrees in kinesiology can work in research, the fitness industry, clinical settings, and in industrial environments. Studies of human and animal motion include measures from motion tracking systems, electrophysiology of muscle and brain activity, various methods for monitoring physiological function, and other behavioral and cognitive research techniques.
Optogenetics – a neuromodulation technique employed in neuroscience that uses a combination of techniques from optics and genetics to control and monitor the activities of individual neurons in living tissue—even within freely-moving animals—and to precisely measure the effects of those manipulations in real-time. The key reagents used in optogenetics are light-sensitive proteins. Spatially-precise neuronal control is achieved using optogenetic actuators like channelrhodopsin, halorhodopsin, and archaerhodopsin, while temporally-precise recordings can be made with the help of optogenetic sensors like Clomeleon, Mermaid, and SuperClomeleon.
Pharmacogenomics – field of science and technology that analyses how genetic makeup affects an individual's response to drugs. Pharmacogenomics (a portmanteau of pharmacology and genomics) deals with the influence of genetic variation on drug response in patients by correlating gene expression or single-nucleotide polymorphisms with a drug's efficacy or toxicity.
Pharmacology – branch of medicine and biology concerned with the study of drug action, where a drug can be broadly defined as any human-made, natural, or endogenous (within the body) molecule which exerts a biochemical and/or physiological effect on the cell, tissue, organ, or organism. More specifically, it is the study of the interactions that occur between a living organism and chemicals that affect normal or abnormal biochemical function. If substances have medicinal properties, they are considered pharmaceuticals.
Proteomics – the large-scale study of proteins, particularly their structures and functions. Proteins are vital parts of living organisms, as they are the main components of the physiological metabolic pathways of cells. The proteome is the entire set of proteins, produced or modified by an organism or system. This varies with time and distinct requirements, or stresses, that a cell or organism undergoes.
== See also ==
Outline of biology
Divisions of pharmacology
Control theory
== References ==
== Further reading ==
Magner, Lois N. (2002). A history of the life sciences (Rev. and expanded 3rd ed.). New York: M. Dekker. ISBN 0824708245. | Wikipedia/Bioscience |
The Sciences of the Artificial (1969) is a book by Herbert A. Simon in the domain of the learning sciences and artificial intelligence; it is especially influential in design theory. The book is themed around how artificial phenomena ought to be categorized, discussing as to whether such phenomena belong within the domain of 'science'.
It has been reviewed many times in scientific literature—including as a special column in The Journal of the Learning Sciences.
The book was followed by two later editions—in 1981 and in 1996—in which Simon broadened the scope of his discussions.
== Background ==
During the 1950s and 1960s, an expanse of literature was published that demonstrated broad interest in treating design as a rigorous and systematic discipline in hopes of establishing design as a science. Primarily through the fields of operational research and Organisation & Methods, these academics purposed to make design compatible with the related disciplines of management science and operations management.
This trend would bring about the "design methods movement" of the 1960s, serving as the backdrop under which Simon wrote the article "Architecture of Complexity" (1962), which would later become The Sciences of the Artificial (1969). In his work, Simon had the broader intention of unifying the social sciences.
== Overview ==
The theme of the book is how ought artificial phenomena be categorized, discussing as to whether such phenomena belong within the domain of 'science'.
Intending to demonstrate that it is possible for there to be an empirical science of 'artificial' phenomena in addition to that of 'natural' phenomena, Simon argues that designed systems are a valid field of study. The distinction Simon provides between the 'artificial' and the 'natural' is that artificial things are synthetic, and characterized in terms of functions, goals, and adaptation.
Simon characterizes an artificial system as an interface that links two environments—inner and outer. Therefore, artificial systems are susceptible to change because they are contingent upon their environment, i.e. the circumstances in which they are in. Moreover, these environments exist in the realm of 'natural science', while the interface is the realm of 'artificial science'.
To Simon, science of the 'artificial' is the science of 'design'; the sciences of the artificial are relevant to "all fields that create designs to perform tasks or fulfill goals and functions." Moreover:Engineering, medicine, business, architecture, and painting are concerned not with the necessary but with the contingent – not with how things are but with how they might be – in short, with design.: xi Such fields also include those of cognitive psychology, linguistics, economics, management/administration, and education. As such, Simon explores the commonalities of artificial systems including economic systems, business firms, artificial intelligence, complex engineering projects, and social plans.
The book ultimately provides an information-processing theory of humanity's thinking processes as an operational, empirically based alternative to behaviorism.
== References == | Wikipedia/The_Sciences_of_the_Artificial |
In sociology, social complexity is a conceptual framework used in the analysis of society. In the sciences, contemporary definitions of complexity are found in systems theory, wherein the phenomenon being studied has many parts and many possible arrangements of the parts; simultaneously, what is complex and what is simple are relative and change in time.
Contemporary usage of the term complexity specifically refers to sociologic theories of society as a complex adaptive system, however, social complexity and its emergent properties are recurring subjects throughout the historical development of social philosophy and the study of social change.
Early theoreticians of sociology, such as Ferdinand Tönnies, Émile Durkheim, and Max Weber, Vilfredo Pareto and Georg Simmel, examined the exponential growth and interrelatedness of social encounters and social exchanges. The emphases on the interconnectivity among social relationships, and the emergence of new properties within society, is found in the social theory produced in the subfields of sociology. Social complexity is a basis for the connection of the phenomena reported in microsociology and macrosociology, and thus provides an intellectual middle-range for sociologists to formulate and develop hypotheses. Methodologically, social complexity is theory-neutral, and includes the phenomena studied in microsociology and the phenomena studied in macrosociology.
== Theoretic background ==
In 1937, the sociologist Talcott Parsons continued the work of the early theoreticians of sociology with his work on action theory; and by 1951, Parson had developed action theory into formal systems theory in The Social System (1951). In the following decades, the synergy between general systems thinking and the development of social system theories is carried forward by Robert K. Merton in discussions of theories of the middle-range and social structure and agency. From the late 1970s until the early 1990s, sociological investigation concerned the properties of systems in which the strong correlation of sub-parts leads to the observation of autopoetic, self-organizing, dynamical, turbulent, and chaotic behaviours that arise from mathematical complexity, such as the work of Niklas Luhmann.
One of the earliest usages of the term "complexity", in the social and behavioral sciences, to refer specifically to a complex system is found in the study of modern organizations and management studies. However, particularly in management studies, the term often has been used in a metaphorical rather than in a qualitative or quantitative theoretical manner. By the mid-1990s, the "complexity turn" in social sciences begins as some of the same tools generally used in complexity science are incorporated into the social sciences. By 1998, the international, electronic periodical, Journal of Artificial Societies and Social Simulation, had been created. In the last several years, many publications have presented overviews of complexity theory within the field of sociology. Within this body of work, connections also are drawn to yet other theoretical traditions, including constructivist epistemology and the philosophical positions of phenomenology, postmodernism and critical realism.
== Methodologies ==
Methodologically, social complexity is theory-neutral, meaning that it accommodates both local and global approaches to sociological research. The very idea of social complexity arises out of the historical-comparative methods of early sociologists; obviously, this method is important in developing, defining, and refining the theoretical construct of social complexity. As complex social systems have many parts and there are many possible relationships between those parts, appropriate methodologies are typically determined to some degree by the research level of analysis differentiated by the researcher according to the level of description or explanation demanded by the research hypotheses.
At the most localized level of analysis, ethnographic, participant- or non-participant observation, content analysis and other qualitative research methods may be appropriate. More recently, highly sophisticated quantitative research methodologies are being developed and used in sociology at both local and global levels of analysis. Such methods include (but are not limited to) bifurcation diagrams, network analysis, non-linear modeling, and computational models including cellular automata programming, sociocybernetics and other methods of social simulation.
=== Complex social network analysis ===
Complex social network analysis is used to study the dynamics of large, complex social networks. Dynamic network analysis brings together traditional social network analysis, link analysis and multi-agent systems within network science and network theory. Through the use of key concepts and methods in social network analysis, agent-based modeling, theoretical physics, and modern mathematics (particularly graph theory and fractal geometry), this method of inquiry brought insights into the dynamics and structure of social systems. New computational methods of localized social network analysis are coming out of the work of Duncan Watts, Albert-László Barabási, Nicholas A. Christakis, Kathleen Carley and others.
New methods of global network analysis are emerging from the work of John Urry and the sociological study of globalization, linked to the work of Manuel Castells and the later work of Immanuel Wallerstein. Since the late 1990s, Wallerstein increasingly makes use of complexity theory, particularly the work of Ilya Prigogine. Dynamic social network analysis is linked to a variety of methodological traditions, above and beyond systems thinking, including graph theory, traditional social network analysis in sociology, and mathematical sociology. It also links to mathematical chaos and complex dynamics through the work of Duncan Watts and Steven Strogatz, as well as fractal geometry through Albert-László Barabási and his work on scale-free networks.
=== Computational sociology ===
The development of computational sociology involves such scholars as Nigel Gilbert, Klaus G. Troitzsch, Joshua M. Epstein, and others. The foci of methods in this field include social simulation and data-mining, both of which are sub-areas of computational sociology. Social simulation uses computers to create an artificial laboratory for the study of complex social systems; data-mining uses machine intelligence to search for non-trivial patterns of relations in large, complex, real-world databases. The emerging methods of socionics are a variant of computational sociology.
Computational sociology is influenced by a number of micro-sociological areas as well as the macro-level traditions of systems science and systems thinking. The micro-level influences of symbolic interaction, exchange, and rational choice, along with the micro-level focus of computational political scientists, such as Robert Axelrod, helped to develop computational sociology's bottom-up, agent-based approach to modeling complex systems. This is what Joshua M. Epstein calls generative science. Other important areas of influence include statistics, mathematical modeling and computer simulation.
=== Sociocybernetics ===
Sociocybernetics integrates sociology with second-order cybernetics and the work of Niklas Luhmann, along with the latest advances in complexity science. In terms of scholarly work, the focus of sociocybernetics has been primarily conceptual and only slightly methodological or empirical. Sociocybernetics is directly tied to systems thought inside and outside of sociology, specifically in the area of second-order cybernetics.
== Areas of application ==
In the first decade of the 21st century, the diversity of areas of application has grown as more sophisticated methods have developed. Social complexity theory is applied in studies of social cooperation and public goods; altruism; education; global civil society collective action and social movements; social inequality; workforce and unemployment; policy analysis; health care systems; and innovation and social change, to name a few. A current international scientific research project, the Seshat: Global History Databank, was explicitly designed to analyze changes in social complexity from the Neolithic Revolution until the Industrial Revolution.
As a middle-range theoretical platform, social complexity can be applied to any research in which social interaction or the outcomes of such interactions can be observed, but particularly where they can be measured and expressed as continuous or discrete data points. One common criticism often cited regarding the usefulness of complexity science in sociology is the difficulty of obtaining adequate data. Nonetheless, application of the concept of social complexity and the analysis of such complexity has begun and continues to be an ongoing field of inquiry in sociology. From childhood friendships and teen pregnancy to criminology and counter-terrorism, theories of social complexity are being applied in almost all areas of sociological research.
In the area of communications research and informetrics, the concept of self-organizing systems appears in mid-1990s research related to scientific communications. Scientometrics and bibliometrics are areas of research in which discrete data are available, as are several other areas of social communications research such as sociolinguistics. Social complexity is also a concept used in semiotics.
== See also ==
== References ==
== Further reading ==
Byrne, David (1998). Complexity Theory and the Social Sciences. London: Routledge.
Byrne, D., & Callaghan, G. (2013). Complexity theory and the social sciences: The state of the art. Routledge.
Castellani, Brian and Frederic William Hafferty (2009). Sociology and Complexity Science: A New Area of Inquiry (Series: Understanding Complex Systems XV). Berlin, Heidelberg: Springer-Verlag.
Eve, Raymond, Sara Horsfall and Mary E. Lee (1997). Chaos, Complexity and Sociology: Myths, Models, and Theories. Thousand Oaks, CA: Sage Publications.
Jenks, Chris and John Smith (2006). Qualitative Complexity: Ecology, Cognitive Processes and the Re-Emergence of Structures in Post-Humanist Social Theory. New York, NY: Routledge.
Kiel, L. Douglas (ed.) (2008). Knowledge Management, Organizational Intelligence, Learning and Complexity. UNESCO (EOLSS): Paris, France.
Kiel, L. Douglas and Euel Elliott (eds.) (1997). Chaos Theory in the Social Sciences: Foundations and Applications. The University of Michigan Press: Ann Arbor, MI.
Leydesdorff, Loet (2001). A Sociological Theory of Communication: The Self-Organization of the Knowledge-Based Society. Parkland, FL: Universal Publishers.
Urry, John (2005). "The Complexity Turn." Theory, Culture and Society, 22(5): 1–14. | Wikipedia/Sociology_and_complexity_science |
The Center for Advanced Study in the Behavioral Sciences (CASBS) is an interdisciplinary research institution at Stanford University designed to advance the frontiers of knowledge about human behavior and society, and contribute to the resolution of some of the world’s greatest challenges. It incubates initiatives designed to address major questions about human behavior and society, sponsors projects focused on challenges facing societies and the world, and offers a residential postdoctoral fellowship program for selected scientists and scholars studying social, behavioral, and policy issues. Fellows are drawn from a variety of fields, including "the five core social and behavioral disciplines of anthropology, economics, political science, psychology, and sociology". In recent decades, the Center has also hosted legal scholars, humanists, public policy practitioners, philosophers, and technical experts among others. CASBS fellows over the years include 30 Nobel laureates, 52 MacArthur fellows, and one U.S. Supreme Court justice.
It is one of the (currently ten) members of Some Institutes for Advanced Study (SIAS). Its campus is 19,600 square feet (1,820 m2) with ample space for hosting groups of researchers. It has 54 studies, meeting rooms, a conference hall, a kitchen, and dining room with a private chef.
Sarah Soule started as director of the center in September 2023.
== History ==
The center was founded in 1954 by the Ford Foundation. The American educator Ralph W. Tyler served as the center's first director from 1954 to 1966. Political scientist Margaret Levi was the director of the center from 2014 until 2022.
The CASBS buildings were designed by William Wurster, a local architect.
Earlier, fellow selection was a closed process; new fellows were nominated by former fellows. However, since 2007, the center opened up the fellow selection process to applications. In 2008, it became an integral part of Stanford University and functions as one of the university's independent research institutes.
== Fellows ==
Each class of fellows numbers about 40 people. In the first 40 years of its existence it supported about 2,000 scientists and scholars.
=== Notable fellows ===
The institute has been home to notable scholars, including:
== References ==
== External links ==
Center for Advanced Study website
List of CASBS Fellows | Wikipedia/Center_for_Advanced_Study_in_the_Behavioral_Sciences |
Systematics is the name given by John Godolphin Bennett (1897–1974) to a branch of systems science that he developed in the mid-twentieth century. Also referred to as the theory of Multi-Term Systems or Bennettian Systematics, it focuses on types, levels, and degrees of complexity in systems, the qualities emergent at these levels, and the ability to represent and practically deal with ("understand") complexity using abstract models. Thus to understand the notions of sameness and difference requires a system or universe of discourse with a minimum of two terms or elements. To understand the concept of relatedness requires three, and so on.
Bennettian Systematics evolved through various stages of formulation as described in his major, four-volume work The Dramatic Universe (initially published 1955-1966) and in various articles in Systematics: The Journal of the Institute for the Comparative Study of History, Philosophy and the Sciences, published from 1963 to 1974. Bennettian Systematics has been further refined and advanced by students such as A. G. E. Blake, Anthony Hodgson, Kenneth Pledge, Henri Bortoft, Richard Heath and others.
== Overview ==
Bennett has described his discipline of Systematics in quite general terms as "the study of systems and their application to the problem of understanding ourselves and the world." He notes in this general context 4 branches of Systematics:
Pure Systematics – seeks "to identify and describe the universal properties or attributes common to all systems".
Formal Systematics – studies "the properties of systems without reference to the nature of the terms. It consists mainly of the investigation of possible modes of connectedness which evidently can be very complex for systems with more than three or four terms".
Applied Systematics – "the study of systems occurring in our experience and is chiefly directed to the identification of the terms and their characteristics".
Practical Systematics – focuses on "the application of the understanding gained through the study of systems to the problems that arise in all departments of life".
Bennett's use of the term "Systematics" is basically synonymous with what today falls under the terms "systemics", "systemology", "systems science", and "systems theory". However, his own specific work under the name "Systematics" takes approaches that are still unfamiliar to many current systems specialists, making his work a specialty in a much broader field. In addition, the use of the term "systematics" in biology to refer to the classification of types and forms of organisms creates ambiguity and rather overwhelms the term's current viability within general systemology. Thus reference can be made simply to "Bennettian Systems" (or Systemics or Systematics), or to "Multi-Term Systems" to describe his work and its continuations.
Formal Bennettian systems are defined around and focus on the idea of logical or qualitative complexity rather than quantitative complexity. There is thus a possible analogy to the philosophical program of logical atomism. ("Quantitative complexity", as contrasted with "qualitative", results from the presence in a practical setting of two or more actual components of the same qualitative type. However, in practical Systematics, the quantity or amount of a component also has concrete qualitative effects, and the two categories cannot always be separated.)
Thus in formal Systematics, Bennettian systems are abstract, and each system represents a qualitative or logical "type" or level analogous to the logical levels used by Bertrand Russell in his Theory of Types.
Each formal level consists of qualitatively independent but mutually relevant "terms" that constitute a "universe of discourse" specific to that level, and terminology suitable at one level can cause category confusion when used in other contexts.
Every multi-term system so-defined has its special system-level attribute or characteristic emergent quality, such as "dynamism" for the triad, or "significance" for the pentad. The emergence of these qualities, according to the work of Anthony Blake in what he calls Lattice Systematics, is mysterious but not random and occurs within a process involving both increasing "spiritualization" of will and increasing specification or "materialization" of function.
The logical level of the system depends on the number of the qualitatively different but mutually relevant terms in the system. Bennettian systems thus increase in qualitative complexity, and display new emergent qualities, in a quantized, progressive series as the number of qualitatively distinct terms within the system increases.
Conversely, the "terms" of a given formal system correlate in a general way with the specific degree, type, or level of the system they occur in, so that the terms of a dyad are characterized as "poles", those of a triad as "impulses", those of a tetrad as "sources", those of a pentad as "limits," and so on.
Each system beyond the first contains subsystems and all systems, theoretically, are embedded in supersystems with a higher number of terms.
In practical Systematics, Bennett carried this process of elaboration up to the 12-term system as best he could within the constraints of the very limited technical vocabulary currently available to make such distinctions. Beyond the 12-term system he spoke of "societies".
Bennett correlates the logical levels or leaps of qualitative complexity with what he calls the "concrete" or "qualitative" significance of number, perhaps again analogous to what Russell calls "relation number" in Principia Mathematica and in looser reference to Pythagorean traditions, although Bennett was at pains to distinguish what he was doing from various kinds of mere "numerology".
The series of Bennettian systems includes the monad, dyad, triad, tetrad, and so on, open-endedly. Systems progress in complexity from the monad up, and from vague wholeness to increasingly articulate structure that reaches into society, history and the ontological fabric of the cosmos.
=== Practical and applied Bennettian systems ===
The series of Multi-Term Systems can serve in applications as simplified but progressively complex outer checklists to ascertain the objective diagnostic completeness of a survey and analysis of a system or situation. Conversely, the system models can be used "inwardly" as an aid to subjectively assessing one's own impartiality, wisdom and adequacy of comprehension. They thus can point toward real structures and processes in the outer world of fact as well as, logically, those structures and processes in the inner world of values and human capacities.
The Enneagram of Process of Gurdjieff is a central but partial part of the Bennettian Systematics of the ennead.
=== History ===
Systematics came in part out of the Pythagorean historical tradition but was influenced by twentieth century movements such as A. N. Whitehead's philosophy of organism, C. S. Peirce's pragmatism, and Bertrand Russell's logical atomism, theory of types, and logic of relations. However, it was independent of Bertalanffy's general systems theory and other systems thinking work. The strongest personal influence was from Gurdjieff and his writings. Gurdjieff had taught the significance of the 'law of three' and the 'law of seven' in a meta-scientific context, but Bennett proposed that there was a 'law' for every integral number, and that this could help people understand practical things such as management and education.
Parallels can be drawn between Bennettian Systematics and the work of C. G. Jung and Marie Louise von Franz on number as archetypal, as well as with the philosophies of engineers such as Buckminster Fuller and Arthur Young.
=== Programme ===
Bennettian Systematics has an integrative programme. Throughout all cultures and throughout all disciplines there are discernible threads of meaning associated with multi-term systems that might otherwise be missed. Bennettian Systematics links with understanding which is connected with structural unity and how insight from one area of experience can be transferred to another without distortion. A journal called Systematics was launched by Bennett’s Institute for the Comparative Study of History, Philosophy and the Sciences in 1963 to publish a diversity of articles relating to this programme. Systematics also led into the development of a new learning system called structural communication, which later became a broad methodology called logovisual thinking (LVT).
== See also ==
John G. Bennett
Systemics
Systemography
Systems philosophy
Systems science
Systems theory
== References ==
== Further reading ==
John G. Bennett, General systematics in: Systematics, Vol 1 No. 1, June 1963.
John G. Bennett: The Dramatic Universe, Vols. I – IV, 1955-66.
John G. Bennett (ed. David Seamon): Elementary Systematics – a tool for understanding wholes, 1970.
Systematics: The Journal of the Institute for the Comparative Study of History, Philosophy and the Sciences (1963-1974).
== External links ==
Systematics.org website about Systematics, with many links.
Duversity.org. A website with further materials.
Meaninggames. A compendium of sources related to Bennettian Systematics.
LOGOVISUAL THINKING website.
Deeper Dialogue, a discussion group. | Wikipedia/Systematics_–_study_of_multi-term_systems |
Autonomous agency theory (AAT) is a viable system theory (VST) which models autonomous social complex adaptive systems. It can be used to model the relationship between an agency and its environment(s), and these may include other interactive agencies. The nature of that interaction is determined by both the agency's external and internal attributes and constraints. Internal attributes may include immanent dynamic "self" processes that drive agency change.
== History ==
Stafford Beer coined the term viable systems in the 1950s, and developed it within his management cybernetics theories. He designed his viable system model as a diagnostic tool for organisational pathologies (conditions of social ill-health). This model involves a system concerned with operations and their direct management, and a meta-system that "observes" the system and controls it. Beer's work refers to Maturana's concept of autopoiesis, which explains why living systems actually live. However, Beer did not make general use of the concept in his modelling process.
In the 1980s Eric Schwarz developed an alternative model from the principles of complexity science. This not only embraces the ideas of autopoiesis (self-production), but also autogenesis (self-creation) which responds to a proposition that living systems also need to learn to maintain their viability. Self-production and self-creation are both networks of processes that connect an operational system of agency structure from which behaviour arises, an observing relational meta-system, this itself observed by an "existential" meta-meta-system. As such Schwarz' VST constitutes a different paradigm from that of Beer.
AAT is a development of Schwarz' paradigm through the addition of propositions setting it in a knowledge context.
== Development ==
AAT is a generic modelling approach that has the capacity to anticipate future potentials for behaviour. Such anticipation occurs because behaviour in the agency as a living system is "structure determined", where the structure itself of the agency is responsible for that anticipation. This is like anticipating the behaviour of both a tiger or a giraffe when faced with food options. The tiger has a structure that allows it to have speed, strength and sharp inbuilt weapons to kill moving prey, but the giraffe has a structure that allows it to acquire its food in high places in a way the tiger could not duplicate. Even if a giraffe has the speed to chase prey, it does not have the resources to kill and eat it.
Agency generic structure is a substructure defined by three systems that are, in general terms, referred to as:
existential (pattern of thematic relevance that is the consequence of experience);
noumenal (representing the nature of a phenomenal effect subjectively through conceptual relationships)
phenomenal (maintaining patterns of context related structural relevance connected with action, and constituting an origin for experience).
These generic systems are ontologically distinct; their natures being determined by the context in which the autonomous agency exists. The substructure also maintains a superstructure that is constructed through context related propositional theory. Superstructural theory may include attributes of collective identity, cognition, emotion, personality; purpose and intention; self-reference, self-awareness, self-reflection, self-regulation and self-organisation. The substructural systems are connected by autopoietic and autogenetic networks of processes as shown in Figure 1 below.
The terminology becomes simplified when the existential system is taken to be culture, and it is recognised that Piaget's concept of operative intelligence is equivalent to autopoiesis, and his figurative intelligence to autogenesis. The noumenal system now becomes a personality system, and autonomous agency theory now becomes cultural agency theory (CAT). This is normally used to model plural situations like organisations or a nation states, when its personality system is taken to have normative characteristics (see also Normative personality), that is, driven by cultural norms as represented in Figure 2 below. This has developed further through mindset agency theory enabling agency behaviour to be anticipated.
A feature of this modelling approach is that the properties of the cultural system act as an attractor for the agency as a whole, providing constraint for the properties of its personality and operative systems. This attraction ceases with cultural instability, when CAT reduces to instrumentality with no capacity to learn. Another feature is driven by possibilities of recursion permitted using Beer's proposition of viability law: every viable system contains and is contained in a viable system.
== Cultural agency theory ==
Cultural agency theory (CAT) as a development of AAT. It is principally used to model organisational contexts that have at least potentially stable cultures. The existential system of AAT becomes the cultural system, the figurative system becomes a normative personality, and the operative system now represents the organisational structure that facilitates and constrains behaviour.
The cultural system may be regarded as a (second-order) "observer" of the instrumental couple that occurs between the normative personality and the operative system. The function of this couple is to manifest figurative attributes of the personality, like goals or ideology, operatively consequently influencing behaviour. This instrumental nature occurs through feedforward processes such that personality attributes can be processed for operative action. Where there are issues in doing this, feedback processes create imperatives for adjustment. This is like having a goal, and finding that it cannot be implemented, thereby having to reconsider the goal. This instrumental couple can also be seen in terms of the operative system and its first-order "observing" system, the normative personality. So, while personality is a first-order "observer" of CAT's operative system, it is ultimately directed by its second-order cultural "observer" system.
A development of this has occurred using trait theory from psychology. Unlike other trait theories of personality, this adopts epistemic traits that centres on values, an approach that tends to be more stable (since basic values tend to be stable) in terms of personality testing and retesting, than other approaches that use (for instance) agency preferences (like Myers-Briggs Type Indicator) that may change between test and retest. This trait theory for the normative personality is called mindset agency theory, and is a development of Maruyama's Mindscape Theory.
The cognitive process by which personality is represented through epistemic trait functions (called types), can be explained through both instrumental and epistemic rationality, where instrumental rationality (also referred to as utilitarian, and related to the expectations about the behaviour of other human beings or objects in the environment given some cognitive basis for those expectation) is independent of, if constrained by, epistemic rationality (related to the formation of beliefs in an unbiased manner, normally set in terms of believable propositions: due to their being strongly supported by evidence, as opposed to being agnostic towards propositions that are unsupported by "sufficient" evidence, whatever this means). Applications of CAT could be found in social, political and economic sciences, for instance, recent studies analyzed Donald Trump and Theresa May's personalities.
== Higher orders of autonomous agency ==
Stafford Beer's (1979) viable system model is a well-known diagnostic model that comes out of his management cybernetics paradigm. Related to this is the idea of first-order and second-order cybernetics. Cybernetics is concerned with feedforward and feedback processes, and first-order cybernetics is concerned with this relationship between the system and its environment. Second-order cybernetics is concerned with the relationship between the system and its internal meta-system (that some refer to as "the observer" of the system). Von Foerster has referred to second-order cybernetics as the "cybernetics of cybernetics". While attempts to explore higher orders of cybernetics have been made, no development into a general theory of higher cybernetic orders has emerged from this paradigm.
In contrast, extending the principles of autonomous agency theory, a generic model has been formulated for the generation of higher cybernetic orders, developed using the concepts of recursion and incursion as proposed by Dubois. The model is reflective, for instance, of processes of knowledge creation for community learning and symbolic convergence theory. This nth-order theory of cybernetics links with "the cybernetics of cybernetics" by assigning to its second-order cybernetic concept inferences that may arise from any higher-order cybernetics that may exist, if unperceived. The network of processes in this general representation of higher cybernetic orders is expressed in terms of orders of autopoiesis, so that for instance autogenesis may be seen as a second-order of autopoiesis.
== See also ==
Agency (philosophy)
Autogenesis, a thermodynamic synergy in living systems
Cybernetics
Second-order cybernetics
== References == | Wikipedia/Autonomous_agency_theory |
Reversal theory is a structural, phenomenological theory of personality, motivation, and emotion in the field of psychology. It focuses on the dynamic qualities of normal human experience to describe how a person regularly reverses between psychological states, reflecting their motivational style, the meaning they attach to a situation at a given time, and the emotions they experience.
== Introduction ==
Unlike many theories related to personality, reversal theory does not consist of static traits (trait theory), but rather a set of dynamic motivational states. As people cycle through states, they will see different things as important, experience different emotions, react differently, and look for quite different rewards. Motivation drives orientation, styles, perspective, and desires. The theory emphasizes the changeability of human nature.
Hundreds of empirical papers have been published testing, or using, one or another idea from the theory. It has also generated over twenty books, many standardized questionnaires, its own journal, and various training techniques used in a number of countries. Workshops have been developed for self-development, leadership, creativity, and salesmanship among other topics. Other previous and current applications of the theory include risk-taking, violence, creativity, humor, sexual behavior, ritual, terrorism, advertising, fantasy, and so on.
The Reversal Theory Society has its own journal, the Journal of Motivation, Emotion, and Personality. A number of instruments have been created to measure reversal theory phenomena. Many of these focus on state dominance – which states are more prevalent for a person over time. While others attempt to capture the phenomena of the reversals themselves – how people's states shift in specific situations.
== Origins ==
Reversal theory was initially developed primarily by British psychologist Dr. Michael Apter and psychiatrist Dr. Ken Smith in the mid-1970s. The starting point was Smith's recognition of a personality dimension which he believed had been largely overlooked but was of critical importance in understanding certain kinds of pathology. He coined the terms 'telic' and 'paratelic' to describe the endpoints of this dimension, which could be described in less precise language as the dimension of serious to playful. Apter made a fundamental change to this idea by suggesting that we were not dealing here with enduring traits but with passing states.
Apter's suggestion was that in everyday life people moved backward and forward between two opposite states, which were alternative ways of seeing the world. The dimension was really a dichotomy. In the normal way of things, people were playful and serious in turn. (Such alternations are widespread in all kinds of different systems in the real world and known in cybernetics as 'bistable states'. Examples would be teeter-totters (seesaws), toggle switches, and Gestalt reversal figures.) In emphasizing this kind of dynamic, they would be challenging the emphasis placed in personality theory on enduring traits. To them, people were more like waves than the rocks that they broke on.
== Conceptual framework ==
=== States ===
The theory distinctively proposes that human experience is structurally organized into metamotivational domains, of which four have been identified. Each domain consists of a pair of opposing values or motives so that only one of each pair can be experienced in any given moment. Each pair in a domain represents two opposite forms of motivation – only one state in each pair can be active at a time. Humans reverse between the states in each pair depending on a number of factors, including our inherent tendency to adopt one style over the other.
==== Serious/Playful (Telic/Paratelic) ====
==== Conforming/Rebellious ====
The first four motivational states are referred to as the somatic pairs. This is due to the significance of their interaction, e.g. Serious-rebelliousness (organizing a protest march) is noticeably different from playful rebelliousness (telling a joke in a business meeting).
==== Mastery/Sympathy ====
==== Self/Other (Autic/Alloic) ====
The last four motivational states are referred to as the transactional pairs. This is due to the significance of their interaction, e.g. self-mastery (running a marathon) is noticeably different from others-mastery (training someone to run a marathon).
=== Reversals ===
The primary emphasis of reversal theory lies in the concept of reversals – by "triggering" a reversal between states, we can change the meaning attributed to the situation. E.g., what seemed serious before, can suddenly feel exciting with the right change in situation or mindset. Reversals can be created by changing a situation, reframing it, role-playing, or using specific symbols or props that invoke a specific state (e.g., a toy can help trigger the Playful state; the image of a traffic sign may invoke the Conforming state).
Reversals can occur as a result of frustration, or by the passing of time (called satiation).
Reversal theory links the motivational states above to emotion by proposing that if one is in a state and things are going well, positive emotions result; if the needs of the state are not fulfilled, negative emotions result.
=== Synergy ===
Cognitive synergy is what happens when one experiences opposite qualities attached to the same thing at the same time. Examples would include works of art, metaphors, jokes, toys, and so on. Thus, a representational painting is both a three-dimensional scene and a flat canvas with paint on it. Being aware of both these aspects is what gives it a special synergic quality in experience. But reversal theory offers an interesting perspective on the phenomenon: When perceived in the serious (telic) state synergies tend to be a nuisance, while in the playful (paratelic) state they are usually intriguing and fun.
=== Bistability ===
This the basis for the principle of homeostasis that is found in many fields of study, including many theories found in psychology. Figure 1 (above) demonstrates this principle. The idea that humans are always looking for a perfect medium state of arousal and anything too extreme in either direction is not to be desired, i.e., boredom or anxiety.
Reversal theory proposes an altogether different view of arousal, which is what is called bistability. Bistability emphasizes polarity in the hedonic tone, and this is represented by the curves of the "butterfly curves" figure. It demonstrates that arousal is experienced in each state in a different – indeed opposite way and has its own unique range of emotions. In the serious (telic) state, represented by the solid curve, this range is from relaxation to anxiety, and in the playful paratelic) state, represented by the dashed curve, from boredom to excitement.
In the serious state, one becomes anxious as threatening or demanding events raise arousal levels, but pleasantly relaxed when a task is completed. In the paratelic state, one becomes pleasantly excited as one becomes more emotionally involved and aroused, but bored if there is a lack of stimulation. It will be seen from this that reversal theory gives a very different interpretation of arousal from optimal arousal theory, with its famous inverted u-curve. This enables it, among other things, to make sense of the fact that some activities involve very high arousal and intense pleasure (sexual behavior, for example, and playing or watching a sport) – something which optimal arousal theory has no satisfactory way of dealing with. It also introduces a certain dynamic into the situation through the possibility of sudden changes in experience, and it will have been noticed that as arousal gets higher or lower, so the effect of reversal from one curve to the other becomes more dramatic.
The world is seen differently – there is a different experiential structure in each case. One aspect of this is what reversal theory calls 'the protective frame'. This reversal within arousal explains such phenomena as why people indulge in dangerous sports, why people commit recreational violence, the nature of sexual perversion and sexual dysfunction, the attraction of military combat, and the nature of post-traumatic stress disorder. For example, people gratuitously confront themselves with risk in dangerous sports like parachuting and rock-climbing, in order to achieve high (not moderate) arousal. This high arousal may be experienced as anxiety, but if the danger is overcome (and thereby a protective frame set up), then there will be a switch to the playful (in the moment) curve, and this will result in excitement as intense as the anxiety had been – and hopefully longer-lasting.
=== Dominance ===
Reversal theory introduced the term dominance to make the motivational styles a testable factor in psychometrics, so as to expand its application regions. Dominance means the tendency that an individual has to be one kind of person or another over time. An individual may reverse into a Playful (paretelic) state, but if he or she is Serious (telic) dominant, he or she will easily reverse into Serious states. This term distinguished the reversal theory from the traditional trait theory, namely, one's personality is not a permanent asset but a reversing tendency changing in accordance to the environment, etc.
=== Parapathic emotions and the protective frame ===
All high arousal emotions will be experienced pleasantly in the form of excitement when the individual is in the paratelic state – even the most otherwise unpleasant emotions. Such paradoxical emotions are referred to in the theory as 'parapathic emotions'. So it is possible to have, for example, parapathic anxiety, as in riding a roller coaster. Parapathic emotions arise when the ongoing experience involves what the theory calls a 'protective frame'. Sometimes this makes negative emotions enjoyable, like fear in a horror movie, but this can also make psychologically difficult situations bearable. The frame can be imagined as an emotional safety bubble. Sometimes this frame, which can be physical or psychological, may serve as what can be imagined an emotional safety bubble.
=== Psychodiversity ===
Humans are complex and act in accordance with many, even contradictory values. The needs they produce may vary, but any attempt to structure them (linear, hierarchical, etc.) is left wanting. The normally-functioning person, then, is able to access all the states at different times, and, over time, obtain all the different satisfactions that are available in these various states. Such a well-rounded person may be said to display psychodiversity.
The term can be understood by analogy with the biological concept of biodiversity. A biodiverse ecology is one that contains many different species. It is healthy in that, if the climate changes, at least some species will survive to start rebuilding the ecology. Likewise, a person who displays psychodiversity is able to survive personal problems and thrive in different and changing environments.
== Scientific application ==
Reversal theory has attracted widespread interest among the research community, especially of psychologists, and more than 500 papers and book chapters have been written, along with almost 30 books. There have been some 70 graduate dissertations, mainly doctoral.
The theory has been used in the elucidation of a wide diversity of topics and one of the main strengths of the theory is its comprehensiveness and potential for integration. Here, in no special order, are some of the topics that have been worked on:
Stress, addiction, anxiety, depression, delinquency, hooliganism, personality disorder, boredom, gambling, crime, violence, leadership, teamwork, creativity, risk-taking, teaching, dieting, humor, aesthetics, play, sport, exercise, design, advertising, corporate culture, consumer behavior, hotel management, sexual behavior, religious faith, ritual, spying, and marital relations.
== Practical application ==
=== Sport psychology ===
Following the publication of John Kerr's Counseling Athletes: Applying Reversal Theory, reversal theory has started to be recognized as a useful approach to training, exercise, and sport, although it is difficult to know how many athletes and coaches are actually using it. Kerr and others have reported it being used in a variety of sports, including soccer, figure skating, golf, and martial arts. Graham Winter, a coach for three Australian Olympic teams, utilizes reversal theory for the psychological health of his athletes.
=== Future ===
The recent rise in interest in personal measurement ("the measured self"), advances in the technology enabling/supporting personal measurement (e.g., smartphones, wearable technology), and developments in modeling and analyzing repeatedly-measured experiences (i.e., ecological momentary assessment, experience sampling, and multilevel modeling) the idea (reversals and the theory) provides a framework and sets of hypotheses regarding change over time. At present, such measurement is at the descriptive stage, and the application of reversal theory can move this body of work toward more predictive science.
Biological and medical researchers have begun to develop instrumentation that allows the tracking of physiological variables in real-time from individual subjects in their natural settings. Psychologists are beginning to look at the possibilities opened up to them by this technology, and reversal theory is perfectly positioned to take advantage of it. For example, using the recent "Reversal Theory State Measure" to study the causes of reversals, the relative frequency of reversal in different people ('reversibility'), the biases among the eight states in different people, and so on. There are many ongoing areas of application for this such as telehealth.
== Instrumentation ==
Since the formulation of reversal theory, dozens of psychometric instruments have been developed to test the motivational styles. An early instrument was The Telic Dominance Scale (TDS) developed by Murgatroyd, Rushton, Apter & Ray in 1978. This scale was aimed primarily at assessing Telic Dominance.
The Apter Motivational Style Inventory (AMSP) is a research instrument that assesses dominant styles. A commercial version is used for training and development by practitioners educated by Apter Solutions.
Others include the Apter Leadership Profile [System] (ALPS), which utilizes a 360-degree measurement of leaders' motivational micro-climates, and how they interact with their direct reports. The Reversal Theory State Measure (RTSM), a more recently developed tool system, utilizes technology to measure ongoing motivational state changes over time.
== Society, journal, and conference ==
A society for researchers and practitioners in reversal theory was set up in 1983. The society has organized regular biennial conferences since then. In 2013, an open-access journal was launched: Journal of Motivation, Emotion and Personality: Reversal Theory Studies.
The Reversal Theory Society's presidents have been:
1983-1985 Stephen Murgatroyd
1985-1987 Michael Cowles
1987-1989 John Kerr
1989-1991 Stephen Murgatroyd
1991-1993 Kathleen O'Connell
1993-1995 Sven Svebak
1995-1997 Ken Heskin
1997-1999 Mark McDermott and Murray Griffin
1999-2001 Kathy LaFreniere
2001-2003 George V. Wilson
2003-2005 Richard Mallows
2005-2007 Koenraad Lindner
2007-2009 Joanne Hudson
2009-2011 Tony Young
2011-2013 Jennifer Tucker
2013-2015 Fabien D. Legrand
2015-2017 Kenneth M. Kramer
2017-2019 Joanne Hudson
2019-2021 Jay Lee
2021-2023 Nathalie Duriez
== References ==
== Further reading == | Wikipedia/Reversal_theory |
An ecosystem (or ecological system) is a system formed by organisms in interaction with their environment.: 458 The biotic and abiotic components are linked together through nutrient cycles and energy flows.
Ecosystems are controlled by external and internal factors. External factors—including climate and what parent materials form the soil and topography—control the overall structure of an ecosystem, but are not themselves influenced by it. By contrast, internal factors both control and are controlled by ecosystem processes. include decomposition, the types of species present, root competition, shading, disturbance, and succession. While external factors generally determine which resource inputs an ecosystem has, the availability of said resources within the ecosystem is controlled by internal factors.
Ecosystems are dynamic entities—they are subject to periodic disturbances and are always in the process of recovering from some past disturbance. The tendency of an ecosystem to remain close to its equilibrium state, is termed its resistance. The capacity of a system to absorb disturbance and reorganize while undergoing change so as to retain essentially the same function, structure, identity, and feedbacks is termed its ecological resilience.
Ecosystems can be studied through a variety of approaches—theoretical studies, studies monitoring specific ecosystems over long periods of time, those that look at differences between ecosystems to elucidate how they work and direct manipulative experimentation. Biomes are general classes or categories of ecosystems. However, there is no clear distinction between biomes and ecosystems. Ecosystem classifications are specific kinds of ecological classifications that consider all four elements of the definition of ecosystems: a biotic component, an abiotic complex, the interactions between and within them, and the physical space they occupy. Biotic factors of the ecosystem are living things; such as plants, animals, and bacteria, while abiotic are non-living components; such as water, soil and atmosphere.
Plants allow energy to enter the system through photosynthesis, building up plant tissue. Animals play an important role in the movement of matter and energy through the system, by feeding on plants and on one another. They also influence the quantity of plant and microbial biomass present. By breaking down dead organic matter, decomposers release carbon back to the atmosphere and facilitate nutrient cycling by converting nutrients stored in dead biomass back to a form that can be readily used by plants and microbes.
Ecosystems provide a variety of goods and services upon which people depend, and may be part of. Ecosystem goods include the "tangible, material products" of ecosystem processes such as water, food, fuel, construction material, and medicinal plants. Ecosystem services, on the other hand, are generally "improvements in the condition or location of things of value". These include things like the maintenance of hydrological cycles, cleaning air and water, the maintenance of oxygen in the atmosphere, crop pollination and even things like beauty, inspiration and opportunities for research. Many ecosystems become degraded through human impacts, such as soil loss, air and water pollution, habitat fragmentation, water diversion, fire suppression, and introduced species and invasive species. These threats can lead to abrupt transformation of the ecosystem or to gradual disruption of biotic processes and degradation of abiotic conditions of the ecosystem. Once the original ecosystem has lost its defining features, it is considered "collapsed". Ecosystem restoration can contribute to achieving the Sustainable Development Goals.
== Definition ==
An ecosystem (or ecological system) consists of all the organisms and the abiotic pools (or physical environment) with which they interact.: 5 : 458 The biotic and abiotic components are linked together through nutrient cycles and energy flows.
"Ecosystem processes" are the transfers of energy and materials from one pool to another.: 458 Ecosystem processes are known to "take place at a wide range of scales". Therefore, the correct scale of study depends on the question asked.: 5
=== Origin and development of the term ===
The term "ecosystem" was first used in 1935 in a publication by British ecologist Arthur Tansley. The term was coined by Arthur Roy Clapham, who came up with the word at Tansley's request. Tansley devised the concept to draw attention to the importance of transfers of materials between organisms and their environment.: 9 He later refined the term, describing it as "The whole system, ... including not only the organism-complex, but also the whole complex of physical factors forming what we call the environment". Tansley regarded ecosystems not simply as natural units, but as "mental isolates". Tansley later defined the spatial extent of ecosystems using the term "ecotope".
G. Evelyn Hutchinson, a limnologist who was a contemporary of Tansley's, combined Charles Elton's ideas about trophic ecology with those of Russian geochemist Vladimir Vernadsky. As a result, he suggested that mineral nutrient availability in a lake limited algal production. This would, in turn, limit the abundance of animals that feed on algae. Raymond Lindeman took these ideas further to suggest that the flow of energy through a lake was the primary driver of the ecosystem. Hutchinson's students, brothers Howard T. Odum and Eugene P. Odum, further developed a "systems approach" to the study of ecosystems. This allowed them to study the flow of energy and material through ecological systems.: 9
== Processes ==
=== External and internal factors ===
Ecosystems are controlled by both external and internal factors. External factors, also called state factors, control the overall structure of an ecosystem and the way things work within it, but are not themselves influenced by the ecosystem. On broad geographic scales, climate is the factor that "most strongly determines ecosystem processes and structure".: 14 Climate determines the biome in which the ecosystem is embedded. Rainfall patterns and seasonal temperatures influence photosynthesis and thereby determine the amount of energy available to the ecosystem.: 145
Parent material determines the nature of the soil in an ecosystem, and influences the supply of mineral nutrients. Topography also controls ecosystem processes by affecting things like microclimate, soil development and the movement of water through a system. For example, ecosystems can be quite different if situated in a small depression on the landscape, versus one present on an adjacent steep hillside.: 39 : 66
Other external factors that play an important role in ecosystem functioning include time and potential biota, the organisms that are present in a region and could potentially occupy a particular site. Ecosystems in similar environments that are located in different parts of the world can end up doing things very differently simply because they have different pools of species present.: 321 The introduction of non-native species can cause substantial shifts in ecosystem function.
Unlike external factors, internal factors in ecosystems not only control ecosystem processes but are also controlled by them.: 16 While the resource inputs are generally controlled by external processes like climate and parent material, the availability of these resources within the ecosystem is controlled by internal factors like decomposition, root competition or shading. Other factors like disturbance, succession or the types of species present are also internal factors.
=== Primary production ===
Primary production is the production of organic matter from inorganic carbon sources. This mainly occurs through photosynthesis. The energy incorporated through this process supports life on earth, while the carbon makes up much of the organic matter in living and dead biomass, soil carbon and fossil fuels. It also drives the carbon cycle, which influences global climate via the greenhouse effect.
Through the process of photosynthesis, plants capture energy from light and use it to combine carbon dioxide and water to produce carbohydrates and oxygen. The photosynthesis carried out by all the plants in an ecosystem is called the gross primary production (GPP).: 124 About half of the gross GPP is respired by plants in order to provide the energy that supports their growth and maintenance.: 157 The remainder, that portion of GPP that is not used up by respiration, is known as the net primary production (NPP).: 157 Total photosynthesis is limited by a range of environmental factors. These include the amount of light available, the amount of leaf area a plant has to capture light (shading by other plants is a major limitation of photosynthesis), the rate at which carbon dioxide can be supplied to the chloroplasts to support photosynthesis, the availability of water, and the availability of suitable temperatures for carrying out photosynthesis.: 155
=== Energy flow ===
Energy and carbon enter ecosystems through photosynthesis, are incorporated into living tissue, transferred to other organisms that feed on the living and dead plant matter, and eventually released through respiration.: 157 The carbon and energy incorporated into plant tissues (net primary production) is either consumed by animals while the plant is alive, or it remains uneaten when the plant tissue dies and becomes detritus. In terrestrial ecosystems, the vast majority of the net primary production ends up being broken down by decomposers. The remainder is consumed by animals while still alive and enters the plant-based trophic system. After plants and animals die, the organic matter contained in them enters the detritus-based trophic system.
Ecosystem respiration is the sum of respiration by all living organisms (plants, animals, and decomposers) in the ecosystem. Net ecosystem production is the difference between gross primary production (GPP) and ecosystem respiration. In the absence of disturbance, net ecosystem production is equivalent to the net carbon accumulation in the ecosystem.
Energy can also be released from an ecosystem through disturbances such as wildfire or transferred to other ecosystems (e.g., from a forest to a stream to a lake) by erosion.
In aquatic systems, the proportion of plant biomass that gets consumed by herbivores is much higher than in terrestrial systems. In trophic systems, photosynthetic organisms are the primary producers. The organisms that consume their tissues are called primary consumers or secondary producers—herbivores. Organisms which feed on microbes (bacteria and fungi) are termed microbivores. Animals that feed on primary consumers—carnivores—are secondary consumers. Each of these constitutes a trophic level.
The sequence of consumption—from plant to herbivore, to carnivore—forms a food chain. Real systems are much more complex than this—organisms will generally feed on more than one form of food, and may feed at more than one trophic level. Carnivores may capture some prey that is part of a plant-based trophic system and others that are part of a detritus-based trophic system (a bird that feeds both on herbivorous grasshoppers and earthworms, which consume detritus). Real systems, with all these complexities, form food webs rather than food chains which present a number of common, non random properties in the topology of their network.
=== Decomposition ===
The carbon and nutrients in dead organic matter are broken down by a group of processes known as decomposition. This releases nutrients that can then be re-used for plant and microbial production and returns carbon dioxide to the atmosphere (or water) where it can be used for photosynthesis. In the absence of decomposition, the dead organic matter would accumulate in an ecosystem, and nutrients and atmospheric carbon dioxide would be depleted.: 183
Decomposition processes can be separated into three categories—leaching, fragmentation and chemical alteration of dead material. As water moves through dead organic matter, it dissolves and carries with it the water-soluble components. These are then taken up by organisms in the soil, react with mineral soil, or are transported beyond the confines of the ecosystem (and are considered lost to it).: 271–280 Newly shed leaves and newly dead animals have high concentrations of water-soluble components and include sugars, amino acids and mineral nutrients. Leaching is more important in wet environments and less important in dry ones.: 69–77
Fragmentation processes break organic material into smaller pieces, exposing new surfaces for colonization by microbes. Freshly shed leaf litter may be inaccessible due to an outer layer of cuticle or bark, and cell contents are protected by a cell wall. Newly dead animals may be covered by an exoskeleton. Fragmentation processes, which break through these protective layers, accelerate the rate of microbial decomposition.: 184 Animals fragment detritus as they hunt for food, as does passage through the gut. Freeze-thaw cycles and cycles of wetting and drying also fragment dead material.: 186
The chemical alteration of the dead organic matter is primarily achieved through bacterial and fungal action. Fungal hyphae produce enzymes that can break through the tough outer structures surrounding dead plant material. They also produce enzymes that break down lignin, which allows them access to both cell contents and the nitrogen in the lignin. Fungi can transfer carbon and nitrogen through their hyphal networks and thus, unlike bacteria, are not dependent solely on locally available resources.: 186
==== Decomposition rates ====
Decomposition rates vary among ecosystems. The rate of decomposition is governed by three sets of factors—the physical environment (temperature, moisture, and soil properties), the quantity and quality of the dead material available to decomposers, and the nature of the microbial community itself.: 194 Temperature controls the rate of microbial respiration; the higher the temperature, the faster the microbial decomposition occurs. Temperature also affects soil moisture, which affects decomposition. Freeze-thaw cycles also affect decomposition—freezing temperatures kill soil microorganisms, which allows leaching to play a more important role in moving nutrients around. This can be especially important as the soil thaws in the spring, creating a pulse of nutrients that become available.: 280
Decomposition rates are low under very wet or very dry conditions. Decomposition rates are highest in wet, moist conditions with adequate levels of oxygen. Wet soils tend to become deficient in oxygen (this is especially true in wetlands), which slows microbial growth. In dry soils, decomposition slows as well, but bacteria continue to grow (albeit at a slower rate) even after soils become too dry to support plant growth.: 200
=== Dynamics and resilience ===
Ecosystems are dynamic entities. They are subject to periodic disturbances and are always in the process of recovering from past disturbances.: 347 When a perturbation occurs, an ecosystem responds by moving away from its initial state. The tendency of an ecosystem to remain close to its equilibrium state, despite that disturbance, is termed its resistance. The capacity of a system to absorb disturbance and reorganize while undergoing change so as to retain essentially the same function, structure, identity, and feedbacks is termed its ecological resilience. Resilience thinking also includes humanity as an integral part of the biosphere where we are dependent on ecosystem services for our survival and must build and maintain their natural capacities to withstand shocks and disturbances. Time plays a central role over a wide range, for example, in the slow development of soil from bare rock and the faster recovery of a community from disturbance.: 67
Disturbance also plays an important role in ecological processes. F. Stuart Chapin and coauthors define disturbance as "a relatively discrete event in time that removes plant biomass".: 346 This can range from herbivore outbreaks, treefalls, fires, hurricanes, floods, glacial advances, to volcanic eruptions. Such disturbances can cause large changes in plant, animal and microbe populations, as well as soil organic matter content. Disturbance is followed by succession, a "directional change in ecosystem structure and functioning resulting from biotically driven changes in resource supply.": 470
The frequency and severity of disturbance determine the way it affects ecosystem function. A major disturbance like a volcanic eruption or glacial advance and retreat leave behind soils that lack plants, animals or organic matter. Ecosystems that experience such disturbances undergo primary succession. A less severe disturbance like forest fires, hurricanes or cultivation result in secondary succession and a faster recovery.: 348 More severe and more frequent disturbance result in longer recovery times.
From one year to another, ecosystems experience variation in their biotic and abiotic environments. A drought, a colder than usual winter, and a pest outbreak all are short-term variability in environmental conditions. Animal populations vary from year to year, building up during resource-rich periods and crashing as they overshoot their food supply. Longer-term changes also shape ecosystem processes. For example, the forests of eastern North America still show legacies of cultivation which ceased in 1850 when large areas were reverted to forests.: 340 Another example is the methane production in eastern Siberian lakes that is controlled by organic matter which accumulated during the Pleistocene.
=== Nutrient cycling ===
Ecosystems continually exchange energy and carbon with the wider environment. Mineral nutrients, on the other hand, are mostly cycled back and forth between plants, animals, microbes and the soil. Most nitrogen enters ecosystems through biological nitrogen fixation, is deposited through precipitation, dust, gases or is applied as fertilizer.: 266 Most terrestrial ecosystems are nitrogen-limited in the short term making nitrogen cycling an important control on ecosystem production.: 289 Over the long term, phosphorus availability can also be critical.
Macronutrients which are required by all plants in large quantities include the primary nutrients (which are most limiting as they are used in largest amounts): Nitrogen, phosphorus, potassium.: 231 Secondary major nutrients (less often limiting) include: Calcium, magnesium, sulfur. Micronutrients required by all plants in small quantities include boron, chloride, copper, iron, manganese, molybdenum, zinc. Finally, there are also beneficial nutrients which may be required by certain plants or by plants under specific environmental conditions: aluminum, cobalt, iodine, nickel, selenium, silicon, sodium, vanadium.: 231
Until modern times, nitrogen fixation was the major source of nitrogen for ecosystems. Nitrogen-fixing bacteria either live symbiotically with plants or live freely in the soil. The energetic cost is high for plants that support nitrogen-fixing symbionts—as much as 25% of gross primary production when measured in controlled conditions. Many members of the legume plant family support nitrogen-fixing symbionts. Some cyanobacteria are also capable of nitrogen fixation. These are phototrophs, which carry out photosynthesis. Like other nitrogen-fixing bacteria, they can either be free-living or have symbiotic relationships with plants.: 360 Other sources of nitrogen include acid deposition produced through the combustion of fossil fuels, ammonia gas which evaporates from agricultural fields which have had fertilizers applied to them, and dust.: 270 Anthropogenic nitrogen inputs account for about 80% of all nitrogen fluxes in ecosystems.: 270
When plant tissues are shed or are eaten, the nitrogen in those tissues becomes available to animals and microbes. Microbial decomposition releases nitrogen compounds from dead organic matter in the soil, where plants, fungi, and bacteria compete for it. Some soil bacteria use organic nitrogen-containing compounds as a source of carbon, and release ammonium ions into the soil. This process is known as nitrogen mineralization. Others convert ammonium to nitrite and nitrate ions, a process known as nitrification. Nitric oxide and nitrous oxide are also produced during nitrification.: 277 Under nitrogen-rich and oxygen-poor conditions, nitrates and nitrites are converted to nitrogen gas, a process known as denitrification.: 281
Mycorrhizal fungi which are symbiotic with plant roots, use carbohydrates supplied by the plants and in return transfer phosphorus and nitrogen compounds back to the plant roots. This is an important pathway of organic nitrogen transfer from dead organic matter to plants. This mechanism may contribute to more than 70 Tg of annually assimilated plant nitrogen, thereby playing a critical role in global nutrient cycling and ecosystem function.
Phosphorus enters ecosystems through weathering. As ecosystems age this supply diminishes, making phosphorus-limitation more common in older landscapes (especially in the tropics).: 287–290 Calcium and sulfur are also produced by weathering, but acid deposition is an important source of sulfur in many ecosystems. Although magnesium and manganese are produced by weathering, exchanges between soil organic matter and living cells account for a significant portion of ecosystem fluxes. Potassium is primarily cycled between living cells and soil organic matter.: 291
=== Function and biodiversity ===
Biodiversity plays an important role in ecosystem functioning.: 449–453 Ecosystem processes are driven by the species in an ecosystem, the nature of the individual species, and the relative abundance of organisms among these species. Ecosystem processes are the net effect of the actions of individual organisms as they interact with their environment. Ecological theory suggests that in order to coexist, species must have some level of limiting similarity—they must be different from one another in some fundamental way, otherwise, one species would competitively exclude the other. Despite this, the cumulative effect of additional species in an ecosystem is not linear: additional species may enhance nitrogen retention, for example. However, beyond some level of species richness,: 331 additional species may have little additive effect unless they differ substantially from species already present.: 324 This is the case for example for exotic species.: 321
The addition (or loss) of species that are ecologically similar to those already present in an ecosystem tends to only have a small effect on ecosystem function. Ecologically distinct species, on the other hand, have a much larger effect. Similarly, dominant species have a large effect on ecosystem function, while rare species tend to have a small effect. Keystone species tend to have an effect on ecosystem function that is disproportionate to their abundance in an ecosystem.: 324
An ecosystem engineer is any organism that creates, significantly modifies, maintains or destroys a habitat.
== Study approaches ==
=== Ecosystem ecology ===
Ecosystem ecology is the "study of the interactions between organisms and their environment as an integrated system".: 458 The size of ecosystems can range up to ten orders of magnitude, from the surface layers of rocks to the surface of the planet.: 6
The Hubbard Brook Ecosystem Study started in 1963 to study the White Mountains in New Hampshire. It was the first successful attempt to study an entire watershed as an ecosystem. The study used stream chemistry as a means of monitoring ecosystem properties, and developed a detailed biogeochemical model of the ecosystem. Long-term research at the site led to the discovery of acid rain in North America in 1972. Researchers documented the depletion of soil cations (especially calcium) over the next several decades.
Ecosystems can be studied through a variety of approaches—theoretical studies, studies monitoring specific ecosystems over long periods of time, those that look at differences between ecosystems to elucidate how they work and direct manipulative experimentation. Studies can be carried out at a variety of scales, ranging from whole-ecosystem studies to studying microcosms or mesocosms (simplified representations of ecosystems). American ecologist Stephen R. Carpenter has argued that microcosm experiments can be "irrelevant and diversionary" if they are not carried out in conjunction with field studies done at the ecosystem scale. In such cases, microcosm experiments may fail to accurately predict ecosystem-level dynamics.
=== Classifications ===
Biomes are general classes or categories of ecosystems.: 14 However, there is no clear distinction between biomes and ecosystems. Biomes are always defined at a very general level. Ecosystems can be described at levels that range from very general (in which case the names are sometimes the same as those of biomes) to very specific, such as "wet coastal needle-leafed forests".
Biomes vary due to global variations in climate. Biomes are often defined by their structure: at a general level, for example, tropical forests, temperate grasslands, and arctic tundra.: 14 There can be any degree of subcategories among ecosystem types that comprise a biome, e.g., needle-leafed boreal forests or wet tropical forests. Although ecosystems are most commonly categorized by their structure and geography, there are also other ways to categorize and classify ecosystems such as by their level of human impact (see anthropogenic biome), or by their integration with social processes or technological processes or their novelty (e.g. novel ecosystem). Each of these taxonomies of ecosystems tends to emphasize different structural or functional properties. None of these is the "best" classification.
Ecosystem classifications are specific kinds of ecological classifications that consider all four elements of the definition of ecosystems: a biotic component, an abiotic complex, the interactions between and within them, and the physical space they occupy. Different approaches to ecological classifications have been developed in terrestrial, freshwater and marine disciplines, and a function-based typology has been proposed to leverage the strengths of these different approaches into a unified system.
== Human interactions with ecosystems ==
Human activities are important in almost all ecosystems. Although humans exist and operate within ecosystems, their cumulative effects are large enough to influence external factors like climate.: 14
=== Ecosystem goods and services ===
Ecosystems provide a variety of goods and services upon which people depend. Ecosystem goods include the "tangible, material products" of ecosystem processes such as water, food, fuel, construction material, and medicinal plants. They also include less tangible items like tourism and recreation, and genes from wild plants and animals that can be used to improve domestic species.
Ecosystem services, on the other hand, are generally "improvements in the condition or location of things of value". These include things like the maintenance of hydrological cycles, cleaning air and water, the maintenance of oxygen in the atmosphere, crop pollination and even things like beauty, inspiration and opportunities for research. While material from the ecosystem had traditionally been recognized as being the basis for things of economic value, ecosystem services tend to be taken for granted.
The Millennium Ecosystem Assessment is an international synthesis by over 1000 of the world's leading biological scientists that analyzes the state of the Earth's ecosystems and provides summaries and guidelines for decision-makers. The report identified four major categories of ecosystem services: provisioning, regulating, cultural and supporting services. It concludes that human activity is having a significant and escalating impact on the biodiversity of the world ecosystems, reducing both their resilience and biocapacity. The report refers to natural systems as humanity's "life-support system", providing essential ecosystem services. The assessment measures 24 ecosystem services and concludes that only four have shown improvement over the last 50 years, 15 are in serious decline, and five are in a precarious condition.: 6–19
The Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) is an intergovernmental organization established to improve the interface between science and policy on issues of biodiversity and ecosystem services. It is intended to serve a similar role to the Intergovernmental Panel on Climate Change.
Ecosystem services are limited and also threatened by human activities. To help inform decision-makers, many ecosystem services are being assigned economic values, often based on the cost of replacement with anthropogenic alternatives. The ongoing challenge of prescribing economic value to nature, for example through biodiversity banking, is prompting transdisciplinary shifts in how we recognize and manage the environment, social responsibility, business opportunities, and our future as a species.
=== Degradation and decline ===
As human population and per capita consumption grow, so do the resource demands imposed on ecosystems and the effects of the human ecological footprint. Natural resources are vulnerable and limited. The environmental impacts of anthropogenic actions are becoming more apparent. Problems for all ecosystems include: environmental pollution, climate change and biodiversity loss. For terrestrial ecosystems further threats include air pollution, soil degradation, and deforestation. For aquatic ecosystems threats also include unsustainable exploitation of marine resources (for example overfishing), marine pollution, microplastics pollution, the effects of climate change on oceans (e.g. warming and acidification), and building on coastal areas.
Many ecosystems become degraded through human impacts, such as soil loss, air and water pollution, habitat fragmentation, water diversion, fire suppression, and introduced species and invasive species.: 437
These threats can lead to abrupt transformation of the ecosystem or to gradual disruption of biotic processes and degradation of abiotic conditions of the ecosystem. Once the original ecosystem has lost its defining features, it is considered collapsed (see also IUCN Red List of Ecosystems). Ecosystem collapse could be reversible and in this way differs from species extinction. Quantitative assessments of the risk of collapse are used as measures of conservation status and trends.
=== Management ===
When natural resource management is applied to whole ecosystems, rather than single species, it is termed ecosystem management. Although definitions of ecosystem management abound, there is a common set of principles which underlie these definitions: A fundamental principle is the long-term sustainability of the production of goods and services by the ecosystem; "intergenerational sustainability [is] a precondition for management, not an afterthought". While ecosystem management can be used as part of a plan for wilderness conservation, it can also be used in intensively managed ecosystems (see, for example, agroecosystem and close to nature forestry).
=== Restoration and sustainable development ===
Integrated conservation and development projects (ICDPs) aim to address conservation and human livelihood (sustainable development) concerns in developing countries together, rather than separately as was often done in the past.: 445
== See also ==
Complex system
Earth science
Ecoregion
Ecological resilience
Ecosystem-based adaptation
Artificialization
Ecosystem structure
=== Types ===
The following articles are types of ecosystems for particular types of regions or zones:
Ecosystems grouped by condition
Agroecosystem
Closed ecosystem
Depauperate ecosystem
Novel ecosystem
Reference ecosystem
=== Instances ===
Ecosystem instances in specific regions of the world:
Greater Yellowstone Ecosystem
Leuser Ecosystem
Longleaf pine Ecosystem
Tarangire Ecosystem
== References ==
== External links ==
Media related to Ecosystems at Wikimedia Commons
The dictionary definition of ecosystem at Wiktionary
Wikidata: topic (Scholia)
Biomes and ecosystems travel guide from Wikivoyage | Wikipedia/Ecological_systems |
Cybernetics: Or Control and Communication in the Animal and the Machine is a book written by Norbert Wiener and published in 1948. It is the first public usage of the term "cybernetics" to refer to self-regulating mechanisms. The book laid the theoretical foundation for servomechanisms (whether electrical, mechanical or hydraulic), automatic navigation, analog computing, artificial intelligence, neuroscience, and reliable communications.
A second edition with minor changes and two additional chapters was published in 1961.
== Reception ==
The book aroused a considerable amount of public discussion and comment at the time of publication, unusual for a predominantly technical subject.
"[A] beautifully written book, lucid, direct, and, despite its complexity, as readable by the layman as the trained scientist, if the former is willing to forego attempts to understand mathematical formulas."
"One of the most influential books of the twentieth century, Cybernetics has been acclaimed as one of the 'seminal works' comparable in ultimate importance to Galileo or Malthus or Rousseau or Mill."
"Its scope and implications are breathtaking, and leaves the reviewer with the conviction that it is a major contribution to contemporary thought."
"Cybernetics... is worthwhile for its historical value alone. But it does much more by inspiring the contemporary roboticist to think broadly and be open to innovative applications."
The public interest aroused by this book inspired Wiener to address the sociological and political issues raised in a book targeted at the non-technical reader, resulting in the publication in 1950 of The Human Use of Human Beings.
== Table of contents ==
Introduction
1. Newtonian and Bergsonian Time
2. Groups and Statistical Mechanics
3. Time Series, Information, and Communication
4. Feedback and Oscillation
5. Computing Machines and the Nervous System
6. Gestalt and Universals
7. Cybernetics and Psychopathology
8. Information, Language, and Society
=== Supplementary chapters in the second edition ===
9. On Learning and Self-Reproducing Machines
10. Brain Waves and Self-Organising Systems
== Synopsis ==
=== Introduction ===
Wiener recounts that the origin of the ideas in this book is a ten-year-long series of meetings at the Harvard Medical School where medical scientists and physicians discussed scientific method with mathematicians, physicists and engineers. He details the interdisciplinary nature of his approach and refers to his work with Vannevar Bush and his differential analyzer (a primitive analog computer), as well as his early thoughts on the features and design principles of future digital calculating machines. He traces the origins of cybernetic analysis to the philosophy of Leibniz, citing his work on universal symbolism and a calculus of reasoning.
=== Newtonian and Bergsonian Time ===
The theme of this chapter is an exploration of the contrast between time-reversible processes governed by Newtonian mechanics and time-irreversible processes in accordance with the Second Law of Thermodynamics. In the opening section he contrasts the predictable nature of astronomy with the challenges posed in meteorology, anticipating future developments in Chaos theory. He points out that in fact, even in the case of astronomy, tidal forces between the planets introduce a degree of decay over cosmological time spans, and so strictly speaking Newtonian mechanics do not precisely apply.
=== Groups and Statistical Mechanics ===
This chapter opens with a review of the – entirely independent and apparently unrelated – work of two scientists in the early 20th century: Willard Gibbs and Henri Lebesgue. Gibbs was a physicist working on a statistical approach to Newtonian dynamics and thermodynamics, and Lebesgue was a pure mathematician working on the theory of trigonometric series. Wiener suggests that the questions asked by Gibbs find their answer in the work of Lebesgue. Wiener claims that the Lebesgue integral had unexpected but important implications in establishing the validity of Gibbs' work on the foundations of statistical mechanics. The notions of average and measure in the sense established by Lebesgue were urgently needed to provide a rigorous proof of Gibbs' ergodic hypothesis.
The concept of entropy in statistical mechanics is developed, and its relationship to the way the concept is used in thermodynamics. By an analysis of the thought experiment Maxwell's demon, he relates the concept of entropy to that of information.
=== Time Series, Information, and Communication ===
This is one of the more mathematically intensive chapters in the book. It deals with the transmission or recording of a varying analog signal as a sequence of numerical samples, and lays much of the groundwork for the development of digital audio and telemetry over the past six decades. It also examines the relationship between bandwidth, noise, and information capacity, as developed by Wiener in collaboration with Claude Shannon. This chapter and the next one form the core of the foundational principles for the developments of automation systems, digital communications and data processing which have taken place over the decades since the book was published.
=== Feedback and Oscillation ===
This chapter lays down the foundations for the mathematical treatment of negative feedback in automated control systems. The opening passage illustrates the effect of faulty feedback mechanisms by the example of patients with various forms of ataxia. He then discusses railway signalling, the operation of a thermostat, and a steam engine centrifugal governor. The rest of the chapter is mostly taken up with the development of a mathematical formulation of the operation of the principles underlying all of these processes. More complex systems are then discussed such as automated navigation, and the control of non-linear situations such as steering on an icy road. He concludes with a reference to the homeostatic processes in living organisms.
=== Computing Machines and the Nervous System ===
This chapter opens with a discussion of the relative merits of analog computers and digital computers (which Wiener referred to as analogy machines and numerical machines), and maintains that digital machines will be more accurate, electronic implementations will be superior to mechanical or electro-mechanical ones, and that the binary system is preferable to other numerical scales. After discussing the need to store both the data to be processed and the algorithms which are employed for processing that data, and the challenges involved in implementing a suitable memory system, he goes on to draw the parallels between binary digital computers and the nerve structures in organisms.
Among the mechanisms that he speculated for implementing a computer memory system was "a large array of small condensers [ie capacitors in today's terminology] which could be rapidly charged or discharged", thus prefiguring the essential technology of modern dynamic random-access memory chips.
Virtually all of the principles which Wiener enumerated as being desirable characteristics of calculating and data processing machines have been adopted in the design of digital computers, from the early mainframes of the 1950s to the latest microchips.
=== Gestalt and Universals ===
This brief chapter is a philosophical enquiry into the relationship between the physical events in the central nervous system and the subjective experiences of the individual. It concentrates principally on the processes whereby nervous signals from the retina are transformed into a representation of the visual field. It also explores the various feedback loops involved in the operation of the eyes: the homeostatic operation of the iris to control light levels, the adjustment of the lens to bring objects into focus, and the complex set of reflex movements to bring an object of attention into the detailed vision area of the fovea.
The chapter concludes with an outline of the challenges presented by attempts to implement a reading machine for the blind.
=== Cybernetics and Psychopathology ===
Wiener opens this chapter with the disclaimers that he is neither a psychopathologist nor a psychiatrist, and that he is not asserting that mental problems are failings of the brain to operate as a computing machine. However, he suggests that there might be fruitful lines of enquiry opened by considering the parallels between the brain and a computer. (He employed the archaic-sounding phrase "computing machine", because at the time of writing the word "computer" referred to a person who is employed to perform routine calculations). He then discussed the concept of 'redundancy' in the sense of having two or three computing mechanisms operating simultaneously on the same problem, so that errors may be recognised and corrected.
=== Information, Language, and Society ===
Starting with an outline of the hierarchical nature of living organisms, and a discussion of the structure and organisation of colonies of symbiotic organisms, such as the Portuguese Man o' War, this chapter explores the parallels with the structure of human societies, and the challenges faced as they scale and complexity of society increases.
The chapter closes with speculation about the possibility of constructing a chess-playing machine, and concludes that it would be conceivable to build a machine capable of a standard of play better than most human players but not at expert level. Such a possibility seemed entirely fanciful to most commentators in the 1940s, bearing in mind the state of computing technology at the time, although events have turned out to vindicate the prediction – and even to exceed it.
=== On Learning and Self-Reproducing Machines ===
Starting with an examination of the learning process in organisms, Wiener expands the discussion to John von Neumann's theory of games, and the application to military situations. He then speculates about the manner in which a chess-playing computer could be programmed to analyse its past performances and improve its performance. This proceeds to a discussion of the evolution of conflict, as in the examples of matador and bull, or mongoose and cobra, or between opponents in a tennis game. He discusses various stories such as The Sorcerer's Apprentice, which illustrate the view that the literal-minded reliance on "magical" processes may turn out to be counter-productive or catastrophic. The context of this discussion was to draw attention to the need for caution in delegating to machines the responsibility for warfare strategy in an age of Nuclear weapons. The chapter concludes with a discussion of the possibility of self-replicating machines and the work of Professor Dennis Gabor in this area.
=== Brain Waves and Self-Organising Systems ===
This chapter opens with a discussion of the mechanism of evolution by natural selection, which he refers to as "phylogenetic learning", since it is driven by a feedback mechanism caused by the success or otherwise in surviving and reproducing; and modifications of behaviour over a lifetime in response to experience, which he calls "ontogenetic learning". He suggests that both processes involve non-linear feedback, and speculates that the learning process is correlated with changes in patterns of the rhythms of the waves of electrical activity that can be observed on an electroencephalograph. After a discussion of the technical limitations of earlier designs of such equipment, he suggests that the field will become more fruitful as more sensitive interfaces and higher performance amplifiers are developed and the readings are stored in digital form for numerical analysis, rather than recorded by pen galvanometers in real time - which was the only available technique at the time of writing. He then develops suggestions for a mathematical treatment of the waveforms by Fourier analysis, and draws a parallel with the processing of the results of the Michelson–Morley experiment which confirmed the constancy of the velocity of light, which in turn led Albert Einstein to develop the theory of Special Relativity. As with much of the other material in this book, these pointers have been both prophetic of future developments and suggestive of fruitful lines of research and enquiry.
== Influence ==
The book provided a foundation for research into electronic engineering, computing (both analog and digital), servomechanisms, automation, telecommunications and neuroscience. It also created widespread public debates on the technical, philosophical and sociological issues it discussed. And it inspired a wide range of books on various subjects peripherally related to its content.
The book introduced the word 'cybernetics' itself into public discourse.
Maxwell Maltz titled his pioneering self-development work "Psycho-Cybernetics" in reference to the process of steering oneself towards a pre-defined goal by making corrections to behaviour. Much of the personal development industry and the Human potential movement is said to be derived from Maltz's work.
Cybernetics became a surprise bestseller and was widely read beyond the technical audience that Wiener had expected. In response he wrote The Human Use of Human Beings in which he further explored the social and psychological implications in a format more suited to the non-technical reader.
In 1954, Marie Neurath produced a children's book Machines which seem to Think [1], which introduced the concepts of Cybernetics, control systems and negative feedback in an accessible format.
== References == | Wikipedia/Cybernetics:_Or_Control_and_Communication_in_the_Animal_and_the_Machine |
Systemography (SGR) is a process where phenomena regarded as complex are purposefully represented as a constructed model of a general system. It may be used in three different ways: conceptualization, analysis, and simulation. The work of Jean-Louis Le Moigne is associated with systemography.
Systemography modeling consists of building, simultaneously, the process' operational, informational and decisional systemographs in modeling phase. Ettore Bresciani Filho (2001) recommends the following order in systemography modeling:
Define the border of the system to be modeled, characterizing the border's processors responsible for the system's inputs and outputs.
Build the operational systemograph of the production system, disposing in a block diagram the production process' different stages, representing each with an operational processor.
Build the informational systemograph of the production system, disposing in a block diagram the different stages of the information's generation, transformation and communication, representing each with an informational processor.
Build the decisional systemograph of the production system, disposing in a block diagram the different stages of the decision's process representing each one with decisional processors.
Classify the processors of the systemographs in categories, types and levels; building a comparative table of processors.
Identify the possible forces fields influences, such as culture and organizational climate.
Relate the problems in priority order, applying problem analysis techniques to identify and find solutions for each one of them.
Use mathematical methods for the modeling the processors as the system as a whole.
Propose the solution of the problems in the form of recommendations and procedures to be adopted.
To systemograph consists, in a few words, in building a model, physical or mathematical, static or dynamic, analytical or numeric of a phenomenon that can be noticed as complex by the analyzer that intends to model it.
The elaboration of the operational systemographs (presenting the operations involved in the process), of the informational systemographs (where the information flow is highlighted) and of the decisional systemographs (where the decisions are shown) allows, during the activity analysis, to evaluate it and to improve it.
These systemographs allow to observe and to eliminate redundancies and cycles that are (or not) important for the process, providing its systemic visualization, identifying points to allow its rationalization, increase of flexibility, and activation.
== History ==
The systemography was studied and presented theoretically by Jean-Louis LeMoigne (1990; 1994) in his Théorie du Système Général (1994). Bresciani Filho presents, in his works and through his students, a practical use of the systemography concepts, particularly for systems of production and of information.
== See also ==
== Notes ==
== References ==
[1]
[2]
BRESCIANI FILHO, Ettore. Método de estudo de sistema – sistemografia. Texto Didático – Unicamp – Universidade Estadual de Campinas e PUC – Pontifícia Universidade Católica de Campinas: texto publicado na Revista do Instituto de Informática da PUC Campinas, em 2001.
DURAND, Daniel. La systémique. Collection Que sais-je?, n. 1795. 9. ed. Paris: PUF – Presses Universitaires de France, 2002. 127 p.
FERREIRA, Vitorio Henrique. Reorganização do atendimento ao cliente em uma empresa de saneamento básico. Dissertação (Mestrado em Gerenciamento de Sistemas de Informação). Campinas: Pontifícia Universidade Católica de Campinas, Instituto de Informática, 1999. 109 p.
KINTSCHNER, Fernando Ernesto. Método de reorganização de processos com apoio na engenharia de sistemas. Tese (Doutorado em Engenharia Mecânica). Campinas: Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica, 2003. 146 p. Disponível em <http://libdigi.unicamp.br/document/?code=vtls000293075>. Accesso em: 25 March 2010.
KINTSCHNER, Fernando Ernesto. Metodologia de reestruturação da área de administração de materiais em empresa industrial. Dissertação (Mestrado em Gerenciamento de Sistemas de Informação). Campinas: Pontifícia Universidade Católica de Campinas, Instituto de Informática, 1998. 53 p.
LE MOIGNE, Jean-Louis. La modélisation des systèmes complexes. Afcet Systèmes. Paris: Dunod, 1990. 178 p.
LE MOIGNE, Jean-Louis. La théorie du système général: théorie de la modélisation. 4. ed. Paris: PUF – Presses Universitaires de France, 1994. 338 p.
POUVREAU David (2013). "Une histoire de la 'systémologie générale' de Ludwig von Bertalanffy – Généalogie, genèse, actualisation et postérité d'un projet herméneutique", Doctoral Thesis (1138 pages), Ecole des Hautes Etudes en Sciences Sociales (EHESS), Paris : http://tel.archives-ouvertes.fr/tel-00804157
SALLES, Valério Maronni. Gestão de projetos de infra-estrutura para implantação de sistemas de informação. Dissertação (Mestrado em Gerenciamento de Sistemas de Informação). Campinas: Pontifícia Universidade Católica de Campinas, Instituto de Informática, 2003. 127 p.
SILVA, Íris Bento. Modelo de sistema integrado de produto e processo com melhoria contínua da qualidade. Tese(Doutorado em Engenharia Mecânica). Campinas: Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica, 2000. 239 p. Disponível em: <http://libdigi.unicamp.br/document/?code=vtls000203984>. Accesso em: 25 March 2010.
THIMMIG, Rolando Antonio. Reorganização do sistema de matrículas de uma faculdade. Dissertação (Mestrado em Gerenciamento de Sistemas de Informação). Campinas: Pontifícia Universidade Católica de Campinas, Instituto de Informática, 2000. 147 p.
THIMMIG, Rolando Antonio. Aplicação da sistemografia para a elaboração da proposta de um método de acreditação de instituição de saúde. Tese(Doutorado em Engenharia Mecânica – área de Concentração: Materiais e Processos de Fabricação). Campinas: Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica, 2008. 228 p. Disponível em <http://libdigi.unicamp.br/document/?code=vtls000437590>. Accesso em: 25 March 2010. | Wikipedia/Systemography |
The viable systems approach (VSA) is a systems theory in which the observed entities and their environment are interpreted through a systemic viewpoint, starting with the analysis of fundamental elements and finally considering more complex related systems (von Bertalanffy, 1968). The assumption is that each entity/system is related to other systems, placed at higher level of observation, called supra-systems, whose traits can be detected in their own subsystems (principle of system hierarchy).
The fundamental unit of analysis is a system made up of many parts or structures (Parsons, 1971). In this sense, every entity (a firm, or simply an individual, a consumer, or a community) as a system can be considered a micro-environment, made up of a group of interlinked sub-components which aim towards a common goal (this is the condition, for the aggregate, to be qualified as a system).
The viable system model was first proposed by Anthony Stafford Beer. In general terms, a viable system is finalized toward its vitality throughout viable behavior based upon consonant and resonant relationships (Barile, 2000; Golinelli, 2000, 2005, 2010; Barile, 2008, 2009).
== Systems thinking ==
Systems thinking contributed in a significant manner to the creation of a new conception of phenomenological reality, as a synthesis of philosophical, sociological, mathematical, physical and biological approaches, influencing culture and its prevalent values founded on the axiomatic corpus of Cartesian thought, has set off a paradigm revolution, moving on from a reductionist-mechanistic approach to reality, and modifying the traditional investigation model. Having rapidly spread to all areas of study, the systems approach has become the result of reflection, theoretical contribution, and formalisation, creating an epistemological approach to research and to the study of a complex reality.
The origins of systems theory go back to the 1950s when a group of scholars from various scientific and social fields (von Bertalanffy in 1956, and others) developed an interdisciplinary theory based on the concept of systems. Their systems viewpoint rejected the idea that certain phenomena could be fully understood exclusively through an analytical approach, especially when the investigated subject consisted of complex phenomenon characterized by significant interaction among its components, as with the firm. In such a case, full understanding could be achieved through a global vision of the subject in question—a systemic vision—by applying a research method of this organized complexity.
Systems thinking comes from the shift in attention from the part to the whole, implying a perception of reality as an integrated and interacting unicuum of phenomena, where the individual properties of the single parts become indistinct, while the relationships between the parts themselves and the events they produce through their interaction, become more important (in other words we may say that "system elements are rationally connected"; Luhmann, 1990).
The systems approach does not coincide with the holistic approach and is not in opposition to the analytical-reductionist approach. Rather, it is an approach which, placing itself within a continuum with reductionism and holism at its extremities, is able to reconcile the two. From the analysis of the elementary components of a phenomenon, it is always possible to arrive at, and then explain, a phenomenon in its entirety (von Bertalanffy, 1968).
== Description ==
The VSA is a scientific approach to business theory that has become increasingly prominent in Italian academic circles in the past decade. Based upon system theory, VSA focuses on the analysis of relationships among socio-economic entities in search of viable interacting conditions (Barile, 2000; Golinelli, 2000). According to VSA, every entity (a business or an individual) can be considered a system of many parts or structures (Parsons, 1971), made up of a group of interlinked sub-components, with the aim of realising a common goal.
The viable systems approach proposes a deep analysis of the structure/systems dichotomy, proposing that every system represents a recognisable entity emerging from a specific changing structure (set of individual elements with assigned roles, activities and tasks performing in compliance with rules and constraints). Since a system originates from its structure, its evolution derives from the dynamic activation of static existing basic relationships. A structure can be studied (what it is? How it is made?), a system should only be interpreted (how does it work? What logics does it follow?)". This means that the static structure brings up the recognition of various possible systems dependant on the finalities and final goal; e.g., a human being is composed by many components assembled within a physical structure, but in the dynamic view man and women may be eating, sleeping, playing tennis or bridge, and all of these are different possible system behaviors.
Another important VSA proposal is represented in the following figure, derived from Beer's first conceptualization of the decision making area and operating structure. Basically, VSA advances upon Stafford Beer's proposal, based upon the distribution of numerous managerial and operative decisions within the operating structure area. The management system can limit the real decision making to strategic and high level issues, involving every decision maker. In a similar way, we may say that the operating area of a human being involves the decision of going to jog, requiring the person to wear a sport outfit and running shoes; on the other hand, the decision about pursuing higher education, starting a new venture, or practicing within an existing business, may be relegated within the higher control system.
In addition, the viable systems approach introduces the conceptual matrix. This is based upon an iterative process of conception and realization of a viable system. It starts from an idea that needs to be framed within a logical model, then expressed in a physical structure. Once the physical structure is defined it can relate with external resources and systems, embracing them within an extended structure that, via its dynamics, can give birth to numerous specific structures and eventually end up to be a viable system. This recursive process may represent the development of a business just as much as an industrial district.
== VSA origins ==
Starting from this theoretical basis, the VSA has integrated several multidisciplinary contributions, applying them to the observation of complex entities. Principally, it has developed its theory around several key concepts derived by other disciplines: from system thinking (open system aspects), from natural and ecological sciences (particularly the organic aspects of homeostasis and equifinality; Hannan and Freeman, 1977); from chemical and biological disciplines (deepening concepts such as autopoiesis; Maturana and Varela, 1975), from sociology and psychology (an enlightening theory was cognitivism; Clark, 1993), and from information technology (specifically we refer to IT roots based on cybernetics studies; Beer, 1975). VSA enables an analysis of the relationships that exist among an enterprise's internal components, as well as an analysis of the relationships between enterprises and other systemic entities in its environmental context.
According to VSA, an enterprise develops as an open system that is characterised by:
many components (both tangible and intangible);
interdependence and communication among these components;
activation of these relationships in order to pursue the system's goal.
=== Key concepts ===
Some founding concepts of the VSA should be made clear to the reader (Golinelli 2000, 2005, 2008, 2009; Golinelli et al., 2002; Barile 2000, 2006, 2008, 2009a):
a viable system lives; that is, its aim is to survive within a context which is populated by other (viable) systems;
every context is subjectively perceived by a viable system's top management (the decision-maker) from analyzing its environment (a macro-system in which the decision maker is submerged) distinguishing and identifying its relevant supra-systems (resources owners) in relation with its objective;
context defines the potential of viable systems, within which are a few higher-level systems (relevant supra-systems) able to constrain top management decisions;
the system's structural definition and the level of consonance between its evolved components (interacting supra and sub systems), define a given system's effectiveness
a viable system has the capability of dynamically adjusting (auto-regulating) its structure: hence we may refer consonance to the system's attempt to correctly interpret contextual signals, and resonance to the expression of the associated adaptive behavior; a system is stable if it satisfies external expectations and needs displayed by relevant supra-systems.
=== Fundamental concepts ===
== VSA applications ==
Decision making
Competition
Social and human behaviour
Complexity
Organization strategy
Marketing design and management
Service science
Managerial systems
== See also ==
Service-dominant logic
Viable system theory
== References ==
ASHBY, H.R. (1958), "General Systems Theory as a New Discipline", in General Systems (Yearbook of the Society for the Advancement of General Systems Theory), vol.3, pp. 1–6.
BARILE, S., (2000), eds., Contributi sul pensiero sistemico, Arnia, Salerno.
BARILE, S., SAVIANO, M., PELS, J., POLESE, F., CARRUBBO, L. (2014) "The contribution of VSA and SDl. Perspectives to Strategic Thinking in Emerging Economies", Managing Service Quality, Vol.24, n.6, pp. 565–591.
BEER, S. (1972), Brain of the Firm, The Penguin Press, London.
CAPRA, F. (1997), The Web of Life, Flamingo, London.
CLARK, A. (1993), Associative Engines, MIT Press, Boston.
GOLINELLI, G.M. (2010), Viable Systems Approach – Governing Business Dynamics, Kluwer/CEDAM, Padova.
LUHMANN, N. (1990), Soziale Sisteme – Grundriß einer Allgemeinen Theorie, Suhrkamp Verlag, Frankfurt.
MATURNANA, H.R. and VARELA, F.J. (1975), Autopoietic Systems, BLC Report 9, University of Illinois.
PARSONS, T. (1971), The System of Modern Societies, Prentice-Hall, Englewood Cliffs.
VON BERTALANFFY, L. (1968), General System Theory – Foundations, Development, Applications, George Braziller, New York.
WIENER, N., Cybernetics, MIT Press, 1948.
== Further reading ==
BARABÁSI, A.L. (2002), Linked – The New Science of Networks, Perseus, Cambridge.
BARILE, S. (2008), L'impresa come Sistema – Contributi sull'Approccio Sistemico Vitale, II ed., Giappichelli, Torino.
BARILE, S. (2009a), Management Sistemico Vitale, Giappichelli, Torino.
BARILE, S. (2009b), "The dynamic of Information Varieties in the Processes of Decision Making", Proceedings of the 13th WMSCI - World Multi-Conference on Systemics, Cybernetics and Informatics, Orlando, July.
BARILE, S., PELS, J., POLESE, F., SAVIANO, M. (2012), "An Introduction to the Viable Systems Approach and its Contribution to Marketing" in Journal of Business Market Management, Vol.5, No.2, pp. 54–78, http://www.jbm-online.net/index.php/jbm/article/view/14.
BARILE, S. (Ed.) (2013), Contributions to theoretical and practical advances in management. A Viable Systems Approach (VSA), Vol. II, Roma, ARACNE.
BARILE, S. and POLESE, F. (2010), "Linking Viable Systems Approach and Many-to-Many Network Approach to Service-Dominant Logic and Service Science", in International Journal of Quality and Service Science, vol.2, n.1, pp. 23–42.
BARILE, S. and SAVIANO, M. (2011), "Foundations of systems thinking: the structure-system paradigm", in VARIOUS AUTHORS, Contributions to theoretical and practical advances in management. A Viable Systems Approach (VSA). ASVSA, Associazione per la Ricerca sui Sistemi Vitali, International Printing Srl, Avellino, pp. 1–26.
BARILE, S., PELS, J., POLESE, F., SAVIANO, M. (2012), "An Introduction to the Viable Systems Approach and its Contribution to Marketing", in Journal of Business, Market, Management, vol.5, n.2, pp. 54–78.
BEER, S. (1975), "Preface", in H.R., MATURNANA and F.J. VARELA, Autopoietic Systems, BLC Report 9, University of Illinois.
CAPRA, F. (2002), The Hidden Connections, HarperCollins, London.
CHRISTOPHER, W.F. (2007), Holistic Management – Managing What Matters for Company Success, Wiley-Interscience. Hoboken.
GOLINELLI, G., PASTORE, A., GATTI, M., MASSARONI, E. and VAGNANI, G. (2002), "The Firm as a Viable System – Managing Inter-Organisational Relationships", in Sinergie, n.58, pp. 65–98.
GOLINELLI, G.M. (2000), L'approccio Sistemico al Governo dell'Impresa – L'Impresa Sistema Vitale, I ed., CEDAM, Padova.
GOLINELLI, G.M. (2001), "Firm as a Viable System", in Symphonya. Emerging Issues in Management (www.unimib.it/symphonya), n. 2., pp.
GOLINELLI, G.M. (2005), L'approccio Sistemico al Governo dell'Impresa. – L'Impresa Sistema Vitale, II ed., CEDAM, Padova.
GOLINELLI, G.M. (2008), L'approccio Sistemico al Governo dell'Impresa – Verso la Scientificazione dell'Azione di Governo, vol.II, II ed., CEDAM, Padova.
GOLINELLI, G.M. (2010), Viable Systems Approach (VSA), Governing Business Dynamics, Kluwer Cedam, Padova.
GOLINELLI, G.M., GATTI, M., VAGNANI, G. and GATTI, C. (2001), "Managing The Firm as a Viable System", Euram (European Academy of Management) Proceedings: European Management Research – Trends and Challenges, IESE, Barcelona, April 20–21.
GUMMESSON, E. (2008), Total Relationship Marketing, Butterworth-Heinemann, Oxford.
GUMMESSON, E., MELE, C. and POLESE, F. (2009), "Service Science, S-D logic and Network Theory – Integrating the Perspectives for a New Research Agenda", in E., GUMMESSON, C., MELE and F., POLESE, Service Science, S-D Logic and Network Theory, Giappichelli, Napoli, pp. 1–6.
HANNAN, M.T. and FREEMAN, J. (1977), "The Population Ecology of Organizations", American Journal of Sociology, vol.82, n.5, pp. 929–964.
SPOHRER, J., ANDERSON, L., PASS, N. and AGER, T. (2008), "Service Science and Service Dominant Logic", Otago Forum 2, pp. 4–18.
SPOHRER, J., MAGLIO, P.P., BAILEY, J. and GRUHL, D. (2007), "Steps Toward a Science of Service Systems", Computer, pp. 71–77.
VARGO, S.L. and LUSCH, R. (2008), "Service-Dominant Logic – Continuing the Evolution", Journal of the Academy of Marketing Science, vol.36, pp. 1–10.
VARGO, S.L. and LUSCH, R.F. (2004), "Evolving to a New Dominant Logic for Marketing", Journal of Marketing, vol.68, pp. 1–17.
VON BERTALANFFY, L. (1956), "General System Theory", in F.E., EMERY (eds.), General System, (Yearbook of the Society for the Advancement of General System Theory).
VON BERTALANFFY, L. (1962), Modern Theories of Development, Harper, New York.
WEICK, K. E. (1995), Sensemaking in Organizations. Sage, Thousand Oaks. | Wikipedia/Viable_systems_approach |
Viable system theory (VST) concerns cybernetic processes in relation to the development/evolution of dynamical systems: it can be used to explain living systems, which are considered to be complex and adaptive, can learn, and are capable of maintaining an autonomous existence, at least within the confines of their constraints. These attributes involve the maintenance of internal stability through adaptation to changing environments. One can distinguish between two strands such theory: formal systems and principally non-formal system. Formal viable system theory is normally referred to as viability theory, and provides a mathematical approach to explore the dynamics of complex systems set within the context of control theory. In contrast, principally non-formal viable system theory is concerned with descriptive approaches to the study of viability through the processes of control and communication, though these theories may have mathematical descriptions associated with them.
== History ==
The concept of viability arose with Stafford Beer in the 1950s through his paradigm of management systems. Its formal relative, viability theory began its life in 1976 with the mathematical interpretation of a book by Jacques Monod published in 1971 and entitled Chance and Necessity, and which concerned processes of evolution. Viability theory is concerned with dynamic adaptation of uncertain evolutionary systems to environments defined by constraints, the values of which determine the viability of the system. Both formal and non-formal approaches ultimately concern the structure and evolutionary dynamics of viability in complex systems.
An alternative non-formal paradigm arose in the late 1980s through the work of Eric Schwarz, which increases the dimensionality of Beer's paradigm
== Beer viable system theory ==
The viable system theory of Beer is most well known through his viable system model and is concerned with viable organisations capable of evolving. Through both internal and external analysis it is possible to identify the relationships and modes of behaviour that constitute viability. The model is underpinned by the realisation that organisations are complex, and recognising the existence of complexity is inherent to processes of analysis. Beer's management systems paradigm is underpinned by a set of propositions, sometimes referred to as cybernetic laws. Sitting within this is his viable systems model (VSM) and one of its laws is a principle of recursion, so that just as the model can be applied to divisions in a department, it can also be applied to the departments themselves. This is permitted through Beer's viability law which states that every viable system contains and is contained in a viable system. The cybernetic laws are applied to all types of human activity systems like organisations and institutions.
Now, paradigms are concerned with not only theory but also modes of behaviour within inquiry. One significant part of Beer's paradigm is the development of his Viable Systems Model (VSM) that addresses problem situations in terms of control and communication processes, seeking to ensure system viability within the object of attention. Another is Beer's Syntegrity protocol which centres on the means by which effective communications in complex situations can occur. VSM has been used successfully to diagnose organisational pathologies (conditions of social ill-health). The model involves not only an operative system that has both structure (e.g., divisions in an organisation or departments in a division) from which behaviour emanates that is directed towards an environment, but also a meta-system, which some have called the observer of the system. The system and meta-system are ontologically different, so that for instance where in a production company the system is concerned with production processes and their immediate management, the meta-system is more concerned with the management of the production system as a whole. The connection between the system and meta-system is explained through Beer's Cybernetic map. Beer considered that viable social systems should be seen as living systems. Humberto Maturana used the term or autopoiesis (self-production) to explain biological living systems, but was reluctant to accept that social systems were living.
== Schwarz viable system theory ==
The viable system theory of Schwarz is more directed towards the explicit examination of issues of complexity than is that of Beer. The theory begins with the idea of dissipative systems. While all isolated systems conserve energy, in non-isolated systems, one can distinguish between conservative systems (in which the kinetic energy is conserved) and dissipative systems (where the total kinetic and potential energy is conserved, but where part of the energy is changed in form and lost). If dissipated systems are far from equilibrium they "try" to recover equilibrium so quickly that they form dissipative structures to accelerate the process. Dissipative systems can create structured spots where entropy locally decreases and so negentropy locally increases to generate order and organisation. Dissipative systems involve far-from-equilibrium process that are inherently dynamically unstable, though they survive through the creation of order that is beyond the thresholds of instability.
Schwarz explicitly defined the living system in terms of its metastructure involving a system, a metasystem and a meta-meta-system, this latter being an essential attribute. As with Beer, the system is concerned with operative attributes. Schwarz's meta-system is essentially concerned with relationships, and the meta-meta system is concerned with all forms of knowledge and its acquisition. Thus, where in Beer's theory learning processes can only be discussed in terms of implicit processes, in Schwarz's theory they can be discussed in explicit terms.
Schwarz's living system model is a summary of much of the knowledge of complex adaptive systems, but succinctly compressed as a graphical generic metamodel. It is this capacity of compression that establishes it as a new theoretical structure that is beyond the concept of autopoiesis/self-production proposed by Humberto Maturana, through the concept of autogenesis. While the concept of autogenesis has not had the collective coherence that autopoiesis has, Schwarz clearly defined it as a network of self-creation processes and firmly integrated it with relevant theory in complexity in a way not previously done. The outcome illustrates how a complex and adaptive viable system is able to survive - maintaining an autonomous durable existence within the confines of its own constraints. The nature of viable systems is that they should have at least potential independence in their processes of regulation, organisation, production, and cognition. The generic model provides a holistic relationship between the attributes that explains the nature of viable systems and how they survive. It addresses the emergence and possible evolution of organisations towards complexity and autonomy intended to refer to any domain of system (e.g., biological, social, or cognitive).
Systems in general, but also human activity systems, are able to survive (in other words they become viable) when they develop:
(a) patterns of self-organisation that lead to self-organisation through morphogenesis and complexity;
(b) patterns for long term evolution towards autonomy;
(c) patterns that lead to the functioning of viable systems.
This theory was intended to embrace the dynamics of dissipative systems using three planes.
Plane of energy.
Plane of information.
Plane of totality.
Each of the three planes (illustrated in Figure 1 below) is an independent ontological domain, interactively connected through networks of processes, and it shows the basic ontological structure of the viable system.
Connected with this is an evolutionary spiral of self-organisation (adapted from Schwarz's 1997 paper), shown in Figure 2 below.
Here, there are 4 phases or modes that a viable system can pass through. Mode 3 occurs with one of three possible outcomes (trifurcation): system death when viability is lost; more of the same; and metamorphosis when the viable system survives because it changes form.
The dynamic process that viable living systems have, as they move from stability to instability and back again, is explained in Table 1, referring to aspects of both Figures 1 and 2.
Schwarz's VST has been further developed, set within a social knowledge context, and formulated as autonomous agency theory.
== See also ==
Systems theory
Viable systems approach
== References == | Wikipedia/Viable_system_theory |
Family therapy (also referred to as family counseling, family systems therapy, marriage and family therapy, couple and family therapy) is a branch of psychotherapy focused on families and couples in intimate relationships to nurture change and development. It tends to view change in terms of the systems of interaction between family members.
The different schools of family therapy have in common a belief that, regardless of the origin of the problem, and regardless of whether the clients consider it an "individual" or "family" issue, involving families in solutions often benefits clients. This involvement of families is commonly accomplished by their direct participation in the therapy session. The skills of the family therapist thus include the ability to influence conversations in a way that catalyses the strengths, wisdom, and support of the wider system.
In the field's early years, many clinicians defined the family in a narrow, traditional manner usually including parents and children. As the field has evolved, the concept of the family is more commonly defined in terms of strongly supportive, long-term roles and relationships between people who may or may not be related by blood or marriage.
The conceptual frameworks developed by family therapists, especially those of
family systems theorists, have been applied to a wide range of human behavior, including organisational dynamics and the study of greatness.
== History and theoretical frameworks ==
Formal interventions with families to help individuals and families experiencing various kinds of problems have been a part of many cultures, probably throughout history. These interventions have sometimes involved formal procedures or rituals, and often included the extended family as well as non-kin members of the community (see for example Ho'oponopono). Following the emergence of specialization in various societies, these interventions were often conducted by particular members of a community – for example, a chief, priest, physician, and so on – usually as an ancillary function.
Family therapy as a distinct professional practice within Western cultures can be argued to have had its origins in the social work movements of the 19th century in the United Kingdom and the United States. As a branch of psychotherapy, its roots can be traced somewhat later to the early 20th century with the emergence of the child guidance movement and marriage counseling. The formal development of family therapy dates from the 1940s and early 1950s with the founding in 1942 of the American Association of Marriage Counselors (the precursor of the AAMFT), and through the work of various independent clinicians and groups – in the United Kingdom (John Bowlby at the Tavistock Clinic), the United States (Donald deAvila Jackson, John Elderkin Bell, Nathan Ackerman, Christian Midelfort, Theodore Lidz, Lyman Wynne, Murray Bowen, Carl Whitaker, Virginia Satir, Ivan Boszormenyi-Nagy), and in Hungary, D.L.P. Liebermann – who began seeing family members together for observation or therapy sessions. There was initially a strong influence from psychoanalysis (most of the early founders of the field had psychoanalytic backgrounds) and social psychiatry, and later from learning theory and behavior therapy – and significantly, these clinicians began to articulate various theories about the nature and functioning of the family as an entity that was more than a mere aggregation of individuals.
The movement received an important boost starting in the early 1950s through the work of anthropologist Gregory Bateson and colleagues – Jay Haley, Donald D. Jackson, John Weakland, William Fry, and later, Virginia Satir, Ivan Boszormenyi-Nagy, Paul Watzlawick and others – at Palo Alto in the United States, who introduced ideas from cybernetics and general systems theory into social psychology and psychotherapy, focusing in particular on the role of communication (see Bateson Project). This approach eschewed the traditional focus on individual psychology and historical factors – that involve so-called linear causation and content – and emphasized instead feedback and homeostatic mechanisms and "rules" in here-and-now interactions – so-called circular causation and process – that were thought to maintain or exacerbate problems, whatever the original cause(s). (See also systems psychology and systemic therapy.) This group was also influenced significantly by the work of US psychiatrist, hypnotherapist, and brief therapist Milton H. Erickson – especially his innovative use of strategies for change, such as paradoxical directives The members of the Bateson Project (like the founders of a number of other schools of family therapy, including Carl Whitaker, Murray Bowen, and Ivan Boszormenyi-Nagy) had a particular interest in the possible psychosocial causes and treatment of schizophrenia, especially in terms of the putative "meaning" and "function" of signs and symptoms within the family system. The research of psychiatrists and psychoanalysts Lyman Wynne and Theodore Lidz on communication deviance and roles (e.g., pseudo-mutuality, pseudo-hostility, schism and skew) in families of people with schizophrenia also became influential with systems-communications-oriented theorists and therapists. A related theme, applying to dysfunction and psychopathology more generally, was that of the "identified patient" or "presenting problem" as a manifestation of or surrogate for the family's, or even society's, problems. (See also double bind; family nexus.)
By the mid-1960s, a number of distinct schools of family therapy had emerged. From those groups that were most strongly influenced by cybernetics and systems theory, there came MRI Brief Therapy, and slightly later, strategic therapy, Salvador Minuchin's structural family therapy and the Milan systems model. Partly in reaction to some aspects of these systemic models, came the experiential approaches of Virginia Satir and Carl Whitaker, which downplayed theoretical constructs, and emphasized subjective experience and unexpressed feelings (including the subconscious), authentic communication, spontaneity, creativity, total therapist engagement, and often included the extended family. Concurrently and somewhat independently, there emerged the various intergenerational therapies of Murray Bowen, Ivan Boszormenyi-Nagy, James Framo, and Norman Paul, which present different theories about the intergenerational transmission of health and dysfunction, but which all deal usually with at least three generations of a family (in person or conceptually), either directly in therapy sessions, or via "homework", "journeys home", etc. Psychodynamic family therapy – which, more than any other school of family therapy, deals directly with individual psychology and the unconscious in the context of current relationships – continued to develop through a number of groups that were influenced by the ideas and methods of Nathan Ackerman, and also by the British School of Object Relations and John Bowlby's work on attachment. Multiple-family group therapy, a precursor of psychoeducational family intervention, emerged, in part, as a pragmatic alternative form of intervention – especially as an adjunct to the treatment of serious mental disorders with a significant biological basis, such as schizophrenia – and represented something of a conceptual challenge to some of the systemic (and thus potentially "family-blaming") paradigms of pathogenesis that were implicit in many of the dominant models of family therapy. The late 1960s and early 1970s saw the development of network therapy (which bears some resemblance to traditional practices such as Ho'oponopono) by Ross Speck and Carolyn Attneave, and the emergence of behavioral marital therapy (renamed behavioral couples therapy in the 1990s) and behavioral family therapy as models in their own right.
By the late 1970s, the weight of clinical experience – especially in relation to the treatment of serious mental disorders – had led to some revision of a number of the original models and a moderation of some of the earlier stridency and theoretical purism. There were the beginnings of a general softening of the strict demarcations between schools, with moves toward rapprochement, integration, and eclecticism – although there was, nevertheless, some hardening of positions within some schools. These trends were reflected in and influenced by lively debates within the field and critiques from various sources, including feminism and post-modernism, that reflected in part the cultural and political tenor of the times, and which foreshadowed the emergence (in the 1980s and 1990s) of the various post-systems constructivist and social constructionist approaches. While there was still debate within the field about whether, or to what degree, the systemic-constructivist and medical-biological paradigms were necessarily antithetical to each other (see also Anti-psychiatry; Biopsychosocial model), there was a growing willingness and tendency on the part of family therapists to work in multi-modal clinical partnerships with other members of the helping and medical professions.
From the mid-1980s to the present, the field has been marked by a diversity of approaches that partly reflect the original schools, but which also draw on other theories and methods from individual psychotherapy and elsewhere – these approaches and sources include: brief therapy, structural therapy, constructivist approaches (e.g., Milan systems, post-Milan/collaborative/conversational, reflective), Bring forthism approach (e.g. Dr. Karl Tomm's IPscope model and Interventive interviewing), solution-focused therapy, narrative therapy, a range of cognitive and behavioral approaches, psychodynamic and object relations approaches, attachment and emotionally focused therapy, intergenerational approaches, network therapy, and multisystemic therapy (MST). Multicultural, intercultural, and integrative approaches are being developed, with Vincenzo Di Nicola weaving a synthesis of family therapy and transcultural psychiatry in his model of cultural family therapy, A Stranger in the Family: Culture, Families, and Therapy. Many practitioners claim to be eclectic, using techniques from several areas, depending upon their own inclinations and/or the needs of the client(s), and there is a growing movement toward a single "generic" family therapy that seeks to incorporate the best of the accumulated knowledge in the field and which can be adapted to many different contexts; however, there are still a significant number of therapists who adhere more or less strictly to a particular, or limited number of, approach(es).
The Liberation Based Healing framework for family therapy offers a complete paradigm shift for working with families while addressing the intersections of race, class, gender identity, sexual orientation and other socio-political identity markers. This theoretical approach and praxis is informed by critical pedagogy, feminism, critical race theory, and decolonizing theory. This framework necessitates an understanding of the ways colonization, cis-heteronormativity, patriarchy, white supremacy and other systems of domination impact individuals, families and communities and centers the need to disrupt the status quo in how power operates. Traditional Western models of family therapy have historically ignored these dimensions and when white, male privilege has been critiqued, largely by feminist theory practitioners, it has often been to the benefit of middle-class, white women's experiences. While an understanding of intersectionality is of particular significance in working with families with violence, a liberatory framework examines how power, privilege and oppression operate within and across all relationships. Liberatory practices are based on the principles of critical consciousness, Accountability and Empowerment. These principles guide not only the content of the therapeutic work with clients but also the supervisory and training process of therapists. Dr. Rhea Almeida developed the cultural context model as a way to operationalize these concepts into practice through the integration of culture circles, sponsors, and a socio-educational process within the therapeutic work.
Ideas and methods from family therapy have been influential in psychotherapy generally: a survey of over 2,500 US therapists in 2006 revealed that of the 10 most influential therapists of the previous quarter-century, three were prominent family therapists and that the marital and family systems model was the second most utilized model after cognitive behavioral therapy.
== Techniques ==
Family therapy uses a range of counseling and other techniques including:
Structural therapy – identifies and re-orders the organisation of the family system
Strategic therapy – looks at patterns of interactions between family members
Systemic/Milan therapy – focuses on belief systems
Narrative therapy – restorying of dominant problem-saturated narrative, emphasis on context, separation of the problem from the person
Transgenerational therapy – transgenerational transmission of unhelpful patterns of belief and behaviour
IPscope model and Interventive Interviewing
Communication theory
Psychoeducation
Psychotherapy
Relationship counseling
Relationship education
Systemic coaching
Systems theory
Reality therapy
the genogram
The number of sessions depends on the situation, but the average is 5–20 sessions. A family therapist usually meets several members of the family at the same time. This has the advantage of making differences between the ways family members perceive mutual relations as well as interaction patterns in the session apparent both for the therapist and the family. These patterns frequently mirror habitual interaction patterns at home, even though the therapist is now incorporated into the family system. Therapy interventions usually focus on relationship patterns rather than on analyzing impulses of the unconscious mind or early childhood trauma of individuals as a Freudian therapist would do – although some schools of family therapy, for example psychodynamic and intergenerational, do consider such individual and historical factors (thus embracing both linear and circular causation) and they may use instruments such as the genogram to help to elucidate the patterns of relationship across generations.
The distinctive feature of family therapy is its perspective and analytical framework rather than the number of people present at a therapy session. Specifically, family therapists are relational therapists: They are generally more interested in what goes on between individuals rather than within one or more individuals, although some family therapists – in particular those who identify as psychodynamic, object relations, intergenerational, or experiential family therapists (EFTs) – tend to be as interested in individuals as in the systems those individuals and their relationships constitute. Depending on the conflicts at issue and the progress of therapy to date, a therapist may focus on analyzing specific previous instances of conflict, as by reviewing a past incident and suggesting alternative ways family members might have responded to one another during it, or instead proceed directly to addressing the sources of conflict at a more abstract level, as by pointing out patterns of interaction that the family might have not noticed.
Family therapists tend to be more interested in the maintenance and/or solving of problems rather than in trying to identify a single cause. Some families may perceive cause-effect analyses as attempts to allocate blame to one or more individuals, with the effect that for many families a focus on causation is of little or no clinical utility. It is important to note that a circular way of problem evaluation is used as opposed to a linear route. Using this method, families can be helped by finding patterns of behaviour, what the causes are, and what can be done to better their situation.
== Evidence base ==
Family therapy has an evolving evidence base. A summary of current evidence is available via the UK's Association of Family Therapy. Evaluation and outcome studies can also be found on the Family Therapy and Systemic Research Centre website. The website also includes quantitative and qualitative research studies of many aspects of family therapy.
According to a 2004 French government study conducted by French Institute of Health and Medical Research, family and couples therapy was the second most effective therapy after Cognitive behavioral therapy. The study used meta-analysis of over a hundred secondary studies to find some level of effectiveness that was either "proven" or "presumed" to exist. Of the treatments studied, family therapy was presumed or proven effective at treating schizophrenia, bipolar disorder, anorexia and alcohol dependency.
== Concerns and criticism ==
In a 1999 address to the Coalition of Marriage, Family and Couples Education conference in Washington, D.C., University of Minnesota Professor William Doherty said:
I take no joy in being a whistle blower, but it's time. I am a committed marriage and family therapist, having practiced this form of therapy since 1977. I train marriage and family therapists. I believe that marriage therapy can be very helpful in the hands of therapists who are committed to the profession and the practice. But there are a lot of problems out there with the practice of therapy – a lot of problems.
Doherty suggested questions prospective clients should ask a therapist before beginning treatment:
"Can you describe your background and training in marital therapy?"
"What is your attitude toward salvaging a troubled marriage versus helping couples break up?"
"What is your approach when one partner is seriously considering ending the marriage and the other wants to save it?"
"What percentage of your practice is marital therapy?"
"Of the couples you treat, what percentage would you say work out enough of their problems to stay married with a reasonable amount of satisfaction with the relationship." "What percentage break up while they are seeing you?" "What percentage do not improve?" "What do you think makes the differences in these results?"
== Licensing and degrees ==
Family therapy practitioners come from a range of professional backgrounds, and some are specifically qualified or licensed/registered in family therapy (licensing is not required in some jurisdictions and requirements vary from place to place). In the United Kingdom, family therapists will have a prior relevant professional training in one of the helping professions usually psychologists, psychotherapists, or counselors who have done further training in family therapy, either a diploma or an M.Sc. In the United States there is a specific degree and license as a marriage and family therapist; however, psychologists, nurses, psychotherapists, social workers, or counselors, and other licensed mental health professionals may practice family therapy. In the UK, family therapists who have completed a four-year qualifying programme of study (MSc) are eligible to register with the professional body the Association of Family Therapy (AFT), and with the UK Council for Psychotherapy (UKCP).
A master's degree is required to work as a Marriage and Family Therapist (MFT) in some American states. Most commonly, MFTs will first earn a M.S. or M.A. degree in marriage and family therapy, counseling, psychology, family studies, or social work. After graduation, prospective MFTs work as interns under the supervision of a licensed professional and are referred to as an MFTi.
Prior to 1999 in California, counselors who specialized in this area were called Marriage, Family and Child Counselors. Today, they are known as Marriage and Family Therapists (MFT), and work variously in private practice, in clinical settings such as hospitals, institutions, or counseling organizations.
Marriage and family therapists in the United States and Canada often seek degrees from accredited Masters or Doctoral programs recognized by the Commission on Accreditation for Marriage and Family Therapy Education (COAMFTE), a division of the American Association of Marriage and Family Therapy.
Requirements vary, but in most states about 3000 hours of supervised work as an intern are needed to sit for a licensing exam. MFTs must be licensed by the state to practice. Only after completing their education and internship and passing the state licensing exam can a person call themselves a Marital and Family Therapist and work unsupervised.
License restrictions can vary considerably from state to state. Contact information about licensing boards in the United States are provided by the Association of Marital and Family Regulatory Boards.
There have been concerns raised within the profession about the fact that specialist training in couples therapy – as distinct from family therapy in general – is not required to gain a license as an MFT or membership of the main professional body, the AAMFT.
=== Values and ethics ===
Since issues of interpersonal conflict, power, control, values, and ethics are often more pronounced in relationship therapy than in individual therapy, there has been debate within the profession about the different values that are implicit in the various theoretical models of therapy and the role of the therapist's own values in the therapeutic process, and how prospective clients should best go about finding a therapist whose values and objectives are most consistent with their own. An early paper on ethics in family therapy written by Vincenzo Di Nicola in consultation with a bioethicist asked basic questions about whether strategic interventions "mean what they say" and if it is ethical to invent opinions offered to families about the treatment process, such as statements saying that half of the treatment team believes one thing and half believes another. Specific issues that have emerged have included an increasing questioning of the longstanding notion of therapeutic neutrality, a concern with questions of justice and self-determination, connectedness and independence, functioning versus authenticity, and questions about the degree of the therapist's pro-marriage/family versus pro-individual commitment.
The American Association for Marriage and Family Therapy requires members to adhere to a code of ethics, including a commitment to "continue therapeutic relationships only so long as it is reasonably clear that clients are benefiting from the relationship."
== Founders and key influences ==
Some key developers of family therapy are:
== Summary of theories and techniques ==
(references:)
== Journals ==
Australian and New Zealand Journal of Family Therapy
Contemporary Family Therapy
Family Process
Family Relations
Family Relations, Interdisciplinary Journal of Applied Family Studies ISSN 0197-6664
Journal of Family Therapy
Marriage Fitness
Murmurations: Journal of Transformative Systemic Practice
Sexual and Relationship Therapy
Journal of Marital & Family Therapy
Families, Systems and Health
== See also ==
== Footnotes ==
== Further reading ==
Deborah Weinstein, The Pathological Family: Postwar America and the Rise of Family Therapy. Ithaca, NY: Cornell University Press, 2013.
Satir, V., Banmen, J., Gerber, J., & Gomori, M. (1991). The Satir Model: Family Therapy and Beyond. Palo Alto, CA: Science and Behavior Books.
The Systemic Thinking and Practice Series. Routledge
Gehring, T. M., Debry, M. & Smith, P. K. (Eds.). (2016). The Family System Test FAST. Theory and application. Hove: Brunner-Routledge. | Wikipedia/Family_systems_therapy |
Media, or mediums, are the core types of material (or related other tools) used by an artist, composer, designer, etc. to create a work of art. For example, a visual artist may broadly use the media of painting or sculpting, which themselves have more specific media within them, such as watercolor paints or marble.
The following is a list of artistic categories and the media used within each category:
== Architecture ==
Cement, concrete, mortar
Cob
Glass
Metal
Stone, brick
Wood
== Carpentry ==
Adhesives
Wood (timber)
== Ceramics ==
Bone china
Clay
Glaze
Porcelain
Pottery
Terracotta
Tile
== Drawing ==
=== Common drawing materials ===
=== Common supports (surfaces) for drawing ===
=== Common drawing tools and methods ===
== Electronic ==
Graphic art software and 3D computer graphics
Word processors and desktop publishing software
Digital photography and digital cinematography
Specialized input devices (e.g. variable pressure sensing tablets and touchscreens)
Digital printing
Programming languages
== Film ==
Animation
Cel animation
Computer animation
Cutout animation
Drawn-on-film animation
Stop motion
Live action
Puppet film
Video art
Single-channel video
Video installation
Film, as a form of mass communication, is itself also considered a medium in the sense used by fields such as sociology and communication theory (see also mass media). These two definitions of medium, while they often overlap, are different from one another: television, for example, utilizes the same types of artistic media as film, but may be considered a different medium from film within communication theory.
== Food ==
A chef's tools and equipment, including ovens, stoves, grills, and griddles. Specialty equipment may be used, including salamanders, French tops, woks, tandoors, and induction burners.
== Glass ==
Glassblowing, Glass fusing, colouring and marking methods.
== Installation ==
Installation art is a site-specific form of sculpture that can be created with any material. An installation can occupy a large amount of space, create an ambience, transform/disrupt the space, exist in the space. One way to distinguish an installation from a sculpture (this may not apply to every installation) is to try to imagine it in a different space. If the objects present difficulties in a different space than the original, it is probably an installation.
== Literature ==
=== Traditional writing media ===
Digital word processor
Internet websites
Letterpress printing
Computer printers
Marker
Pen and ink or quill
Pencil
=== Common bases for writing ===
Card stock
Paper, ruled paper
Vellum
== Natural world ==
Floral design
Rock
Soil
Vegetation
Water
== Painting ==
=== Common paint media ===
=== Uncommon paint media ===
=== Supports for painting ===
=== Common tools and methods ===
Action painting
Aerosol paint
Airbrush
Batik
Brush
Cloth
Paint roller or paint pad
Palette knife
Sponge
Pencil
Finger
=== Mural techniques ===
Muralists use many of the same media as panel painters, but due to the scale of their works, use different techniques. Some such techniques include:
Aerosol paint
Digital painting
Fresco
Image projector
Marouflage
Mosaic
Pouncing
=== Graphic narrative media ===
Comics creators use many of the same media as traditional painters.
== Performing arts ==
The performing arts are a form of entertainment that may be created by the artist's own body, face, and presence as a medium. There are many genres of performance; dance, theatre and re-enactment are a few examples. Performance art is a performance that may not present a conventional formal linear narrative.
== Photography ==
In photography, a photosensitive surface is used to capture an optical still image, usually utilizing a lens to focus light. Some photographic media include:
Digital image sensor
Photographic film
Potassium dichromate
Potassium ferricyanide and ferric ammonium citrate
Silver nitrate
== Printmaking ==
In the art of printmaking, "media" tends to refer to the technique used to create a print. Common media include:
== Sculpture ==
In sculpting, a solid structure and textured surface is shaped or combined using substances and components, to form a three-dimensional object. The size of a sculptured work can be built very big and could be considered as architecture, although more commonly a large statue or bust, and can be crafted very small and intricate as jewellery, ornaments and decorative reliefs.
=== Materials ===
==== Carving media ====
==== Casting media ====
Cement
Ceramics
Metal
Plaster
Plastic
Synthetic resin
Wax
==== Modeling media ====
Clay
Papier-mâché
Plaster
Polystyrene
Sand
Styrofoam
==== Assembled media ====
==== Finishing materials ====
Acids to create a patina (corrosive)
Glaze
Polychrome
Wax
=== Tools ===
== Sound ==
The art of sound can be singular or a combination of speech or objects and crafted instruments, to create sounds, rhythms and music for a range of sonic hearing purposes. See also music and sound art.
== Technical products ==
The use of technical products as an art medium is a merging of applied art and science, that may involve aesthetics, efficiency and ergonomics using various materials.
== Textiles ==
In the art of textiles a soft and flexible material of fibers or yarn is formed by spinning wool, flax, cotton, or other material on a spinning wheel and crocheting, knitting, macramé (knotting), weaving, or pressing fibres together (felt) to create a work.
== See also ==
== References ==
== External links ==
Media (artists' materials) — definition from the Getty Art & Architecture Thesaurus.
Artistic Medium, Internet Encyclopedia of Philosophy | Wikipedia/Art_materials |
Smoothed-particle hydrodynamics (SPH) is a computational method used for simulating the mechanics of continuum media, such as solid mechanics and fluid flows. It was developed by Gingold and Monaghan and Lucy in 1977, initially for astrophysical problems. It has been used in many fields of research, including astrophysics, ballistics, volcanology, and oceanography. It is a meshfree Lagrangian method (where the co-ordinates move with the fluid), and the resolution of the method can easily be adjusted with respect to variables such as density.
== Method ==
=== Advantages ===
By construction, SPH is a meshfree method, which makes it ideally suited to simulate problems dominated by complex boundary dynamics, like free surface flows, or large boundary displacement.
The lack of a mesh significantly simplifies the model implementation and its parallelization, even for many-core architectures.
SPH can be easily extended to a wide variety of fields, and hybridized with some other models, as discussed in Modelling Physics.
As discussed in section on weakly compressible SPH, the method has great conservation features.
The computational cost of SPH simulations per number of particles is significantly less than the cost of grid-based simulations per number of cells when the metric of interest is related to fluid density (e.g., the probability density function of density fluctuations). This is the case because in SPH the resolution is put where the matter is.
=== Limitations ===
Setting boundary conditions in SPH such as inlets and outlets and walls is more difficult than with grid-based methods. In fact, it has been stated that "the treatment of boundary conditions is certainly one of the most difficult technical points of the SPH method". This challenge is partly because in SPH the particles near the boundary change with time. Nonetheless, wall boundary conditions for SPH are available.
The computational cost of SPH simulations per number of particles is significantly larger than the cost of grid-based simulations per number of cells when the metric of interest is not (directly) related to density (e.g., the kinetic-energy spectrum). Therefore, overlooking issues of parallel speedup, the simulation of constant-density flows (e.g., external aerodynamics) is more efficient with grid-based methods than with SPH.
== Examples ==
=== Fluid dynamics ===
Smoothed-particle hydrodynamics is being increasingly used to model fluid motion as well. This is due to several benefits over traditional grid-based techniques. First, SPH guarantees conservation of mass without extra computation since the particles themselves represent mass. Second, SPH computes pressure from weighted contributions of neighboring particles rather than by solving linear systems of equations. Finally, unlike grid-based techniques, which must track fluid boundaries, SPH creates a free surface for two-phase interacting fluids directly since the particles represent the denser fluid (usually water) and empty space represents the lighter fluid (usually air). For these reasons, it is possible to simulate fluid motion using SPH in real time. However, both grid-based and SPH techniques still require the generation of renderable free surface geometry using a polygonization technique such as metaballs and marching cubes, point splatting, or 'carpet' visualization. For gas dynamics it is more appropriate to use the kernel function itself to produce a rendering of gas column density (e.g., as done in the SPLASH visualisation package).
One drawback over grid-based techniques is the need for large numbers of particles to produce simulations of equivalent resolution. In the typical implementation of both uniform grids and SPH particle techniques, many voxels or particles will be used to fill water volumes that are never rendered. However, accuracy can be significantly higher with sophisticated grid-based techniques, especially those coupled with particle methods (such as particle level sets), since it is easier to enforce the incompressibility condition in these systems. SPH for fluid simulation is being used increasingly in real-time animation and games where accuracy is not as critical as interactivity.
Recent work in SPH for fluid simulation has increased performance, accuracy, and areas of application:
B. Solenthaler, 2009, develops Predictive-Corrective SPH (PCISPH) to allow for better incompressibility constraints
M. Ihmsen et al., 2010, introduce boundary handling and adaptive time-stepping for PCISPH for accurate rigid body interactions
K. Bodin et al., 2011, replace the standard equation of state pressure with a density constraint and apply a variational time integrator
R. Hoetzlein, 2012, develops efficient GPU-based SPH for large scenes with Fluids v.3
N. Akinci et al., 2012, introduce a versatile boundary handling and two-way SPH-rigid coupling technique that is completely based on hydrodynamic forces; the approach is applicable to different types of SPH solvers
M. Macklin et al., 2013 simulates incompressible flows inside the Position Based Dynamics framework, for bigger timesteps
N. Akinci et al., 2013, introduce a versatile surface tension and two-way fluid-solid adhesion technique that allows simulating a variety of interesting physical effects that are observed in reality
J. Kyle and E. Terrell, 2013, apply SPH to Full-Film Lubrication
A. Mahdavi and N. Talebbeydokhti, 2015, propose a hybrid algorithm for implementation of solid boundary condition and simulate flow over a sharp crested weir
S. Tavakkol et al., 2016, develop curvSPH, which makes the horizontal and vertical size of particles independent and generates uniform mass distribution along curved boundaries
W. Kostorz and A. Esmail-Yakas, 2020, propose a general, efficient and simple method for evaluating normalization factors near piecewise-planar boundaries
Colagrossi et al., 2019, study flow around a cylinder close to a free-surface and compare with other techniques
=== Astrophysics ===
Smoothed-particle hydrodynamics's adaptive resolution, numerical conservation of physically conserved quantities, and ability to simulate phenomena covering many orders of magnitude make it ideal for computations in theoretical astrophysics.
Simulations of galaxy formation, star formation, stellar collisions, supernovae and meteor impacts are some of the wide variety of astrophysical and cosmological uses of this method.
SPH is used to model hydrodynamic flows, including possible effects of gravity. Incorporating other astrophysical processes which may be important, such as radiative transfer and magnetic fields is an active area of research in the astronomical community, and has had some limited success.
=== Solid mechanics ===
Libersky and Petschek
extended SPH to Solid Mechanics. The main advantage of SPH in this application is the possibility of dealing with larger local distortion than grid-based methods.
This feature has been exploited in many applications in Solid Mechanics: metal forming, impact, crack growth, fracture, fragmentation, etc.
Another important advantage of meshfree methods in general, and of SPH in particular, is that mesh dependence problems are naturally avoided given the meshfree nature of the method. In particular, mesh alignment is related to problems involving cracks and it is avoided in SPH due to the isotropic support of the kernel functions. However, classical SPH formulations suffer from tensile instabilities
and lack of consistency.
Over the past years, different corrections have been introduced to improve the accuracy of the SPH solution, leading to the RKPM by Liu et al.
Randles and Libersky
and Johnson and Beissel
tried to solve the consistency problem in their study of impact phenomena.
Dyka et al.
and Randles and Libersky
introduced the stress-point integration into SPH and Ted Belytschko et al.
showed that the stress-point technique removes the instability due to spurious singular modes, while tensile instabilities can be avoided by using a Lagrangian kernel. Many other recent studies can be found in the literature devoted to improve the convergence of the SPH method.
Recent improvements in understanding the convergence and stability of SPH have allowed for more widespread applications in Solid Mechanics. Other examples of applications and developments of the method include:
Metal forming simulations.
SPH-based method SPAM (Smoothed Particle Applied Mechanics) for impact fracture in solids by William G. Hoover.
Modified SPH (SPH/MLSPH) for fracture and fragmentation.
Taylor-SPH (TSPH) for shock wave propagation in solids.
Generalized coordinate SPH (GSPH) allocates particles inhomogeneously in the Cartesian coordinate system and arranges them via mapping in a generalized coordinate system in which the particles are aligned at a uniform spacing.
== Numerical tools ==
=== Interpolations ===
The Smoothed-Particle Hydrodynamics (SPH) method works by dividing the fluid into a set of discrete moving elements
i
,
j
{\displaystyle i,j}
, referred to as particles. Their Lagrangian nature allows setting their position
r
i
{\displaystyle \mathbf {r} _{i}}
by integration of their velocity
v
i
{\displaystyle \mathbf {v} _{i}}
as:
d
r
i
d
t
=
v
i
.
{\displaystyle {\frac {\mathrm {d} {\boldsymbol {r}}_{i}}{\mathrm {d} t}}={\boldsymbol {v}}_{i}.}
These particles interact through a kernel function with characteristic radius known as the "smoothing length", typically represented in equations by
h
{\displaystyle h}
. This means that the physical quantity of any particle can be obtained by summing the relevant properties of all the particles that lie within the range of the kernel, the latter being used as a weighting function
W
{\displaystyle W}
. This can be understood in two steps. First an arbitrary field
A
{\displaystyle A}
is written as a convolution with
W
{\displaystyle W}
:
A
(
r
)
=
∫
A
(
r
′
)
W
(
|
r
−
r
′
|
,
h
)
d
V
(
r
′
)
.
{\displaystyle A({\boldsymbol {r}})=\int A\left({\boldsymbol {r^{\prime }}}\right)W(|{\boldsymbol {r}}-{\boldsymbol {r^{\prime }}}|,h)\,\mathrm {d} V\!\left({\boldsymbol {r'}}\right).}
The error in making the above approximation is order
h
2
{\displaystyle h^{2}}
. Secondly, the integral is approximated using a Riemann summation over the particles:
A
(
r
)
=
∑
j
V
j
A
j
W
(
|
r
−
r
j
|
,
h
)
,
{\displaystyle A({\boldsymbol {r}})=\sum _{j}V_{j}A_{j}W(|{\boldsymbol {r}}-{\boldsymbol {r}}_{j}|,h),}
where the summation over
j
{\displaystyle j}
includes all particles in the simulation.
V
j
{\displaystyle V_{j}}
is the volume of particle
j
{\displaystyle j}
,
A
j
{\displaystyle A_{j}}
is the value of the quantity
A
{\displaystyle A}
for particle
j
{\displaystyle j}
and
r
{\displaystyle {\boldsymbol {r}}}
denotes position. For example, the density
ρ
i
{\displaystyle \rho _{i}}
of particle
i
{\displaystyle i}
can be expressed as:
ρ
i
=
ρ
(
r
i
)
=
∑
j
m
j
W
i
j
,
{\displaystyle \rho _{i}=\rho ({\boldsymbol {r}}_{i})=\sum _{j}m_{j}W_{ij},}
where
m
j
=
ρ
j
V
j
{\displaystyle m_{j}=\rho _{j}V_{j}}
denotes the particle mass and
ρ
j
{\displaystyle \rho _{j}}
the particle density, while
W
i
j
=
W
j
i
{\displaystyle W_{ij}=W_{ji}}
is a short notation for
W
(
|
r
i
−
r
j
|
,
h
)
{\displaystyle W(|{\boldsymbol {r}}_{i}-{\boldsymbol {r}}_{j}|,h)}
. The error done in approximating the integral by a discrete sum depends on
h
{\displaystyle h}
, on the particle size (i.e.
V
j
1
/
d
{\displaystyle V_{j}^{1/d}}
,
d
{\displaystyle d}
being the space dimension), and on the particle arrangement in space. The latter effect is still poorly known.
Kernel functions commonly used include the Gaussian function, the quintic spline and the Wendland
C
2
{\displaystyle C^{2}}
kernel. The latter two kernels are compactly supported (unlike the Gaussian, where there is a small contribution at any finite distance away), with support proportional to
h
{\displaystyle h}
. This has the advantage of saving computational effort by not including the relatively minor contributions from distant particles.
Although the size of the smoothing length can be fixed in both space and time, this does not take advantage of the full power of SPH. By assigning each particle its own smoothing length and allowing it to vary with time, the resolution of a simulation can be made to automatically adapt itself depending on local conditions. For example, in a very dense region where many particles are close together, the smoothing length can be made relatively short, yielding high spatial resolution. Conversely, in low-density regions where individual particles are far apart and the resolution is low, the smoothing length can be increased, optimising the computation for the regions of interest.
=== Discretization of governing equations ===
For particles of constant mass, differentiating the interpolated density
ρ
i
{\displaystyle \rho _{i}}
with respect to time yields
d
ρ
i
d
t
=
∑
j
m
j
(
v
i
−
v
j
)
⋅
∇
W
i
j
,
{\displaystyle {\frac {d\rho _{i}}{dt}}=\sum _{j}m_{j}\left({\boldsymbol {v}}_{i}-{\boldsymbol {v}}_{j}\right)\cdot \nabla W_{ij},}
where
∇
W
i
j
=
−
∇
W
j
i
{\displaystyle \nabla W_{ij}=-\nabla W_{ji}}
is the gradient of
W
i
j
{\displaystyle W_{ij}}
with respect to
r
i
{\displaystyle {\boldsymbol {r}}_{i}}
. Comparing this equation with the continuity equation in the Lagrangian description (using material derivatives),
d
ρ
d
t
=
−
ρ
∇
⋅
v
,
{\displaystyle {\frac {d\rho }{dt}}=-\rho \nabla \cdot {\boldsymbol {v}},}
it is apparent that its right-hand side is an approximation of
−
ρ
∇
⋅
v
{\displaystyle -\rho \nabla \cdot \mathbf {v} }
; hence one defines a discrete divergence operator as follows:
D
i
{
v
j
}
=
−
1
ρ
i
∑
j
m
j
(
v
i
−
v
j
)
⋅
∇
W
i
j
.
{\displaystyle \operatorname {D} _{i}\left\{{\boldsymbol {v}}_{j}\right\}=-{\frac {1}{\rho _{i}}}\sum _{j}m_{j}\left({\boldsymbol {v}}_{i}-{\boldsymbol {v}}_{j}\right)\cdot \nabla W_{ij}.}
This operator gives an SPH approximation of
∇
⋅
v
{\displaystyle \nabla \cdot \mathbf {v} }
at the particle
i
{\displaystyle i}
for a given set of particles with given masses
m
j
{\displaystyle m_{j}}
, positions
{
r
j
}
{\displaystyle \left\{\mathbf {r} _{j}\right\}}
and velocities
{
v
j
}
{\displaystyle \left\{\mathbf {v} _{j}\right\}}
.
The other important equation for a compressible inviscid fluid is the Euler equation for momentum balance:
d
v
d
t
=
−
1
ρ
∇
p
+
g
{\displaystyle {\frac {d{\boldsymbol {v}}}{dt}}=-{\frac {1}{\rho }}\nabla p+{\boldsymbol {g}}}
Similarly to continuity, the task is to define a discrete gradient operator in order to write
d
v
i
d
t
=
−
1
ρ
G
i
{
p
j
}
+
g
{\displaystyle {\frac {d{\boldsymbol {v}}_{i}}{dt}}=-{\frac {1}{\rho }}\operatorname {\mathbf {G} } _{i}\left\{p_{j}\right\}+{\boldsymbol {g}}}
One choice is
G
i
{
p
j
}
=
ρ
i
∑
j
m
j
(
p
i
ρ
i
2
+
p
j
ρ
j
2
)
∇
W
i
j
,
{\displaystyle \operatorname {\mathbf {G} } _{i}\left\{p_{j}\right\}=\rho _{i}\sum _{j}m_{j}\left({\frac {p_{i}}{\rho _{i}^{2}}}+{\frac {p_{j}}{\rho _{j}^{2}}}\right)\nabla W_{ij},}
which has the property of being skew-adjoint with the divergence operator above, in the sense that
∑
i
V
i
v
i
⋅
G
i
{
p
j
}
=
−
∑
i
V
i
p
i
D
i
{
v
j
}
,
{\displaystyle \sum _{i}V_{i}{\boldsymbol {v}}_{i}\cdot \operatorname {\mathbf {G} } _{i}\left\{p_{j}\right\}=-\sum _{i}V_{i}p_{i}\operatorname {D} _{i}\left\{{\boldsymbol {v}}_{j}\right\},}
this being a discrete version of the continuum identity
∫
v
⋅
grad
p
=
−
∫
p
div
⋅
v
.
{\displaystyle \int {\boldsymbol {v}}\cdot \operatorname {grad} p=-\int p\operatorname {div} \cdot {\boldsymbol {v}}.}
This property leads to nice conservation properties.
Notice also that this choice leads to a symmetric divergence operator and antisymmetric gradient. Although there are several ways of discretizing the pressure gradient in the Euler equations, the above antisymmetric form is the most acknowledged one. It supports strict conservation of linear and angular momentum. This means that a force that is exerted on particle
i
{\displaystyle i}
by particle
j
{\displaystyle j}
equals the one that is exerted on particle
j
{\displaystyle j}
by particle
i
{\displaystyle i}
including the sign change of the effective direction, thanks to the antisymmetry property
∇
W
i
j
=
−
∇
W
j
i
{\displaystyle \nabla W_{ij}=-\nabla W_{ji}}
.
Nevertheless, other operators have been proposed, which may perform better numerically or physically.
For instance, one drawback of these operators is that while the divergence
D
{\displaystyle \operatorname {D} }
is zero-order consistent (i.e. yields zero when applied to a constant vector field), it can be seen that the gradient
G
{\displaystyle \operatorname {\mathbf {G} } }
is not. Several techniques have been proposed to circumvent this issue, leading to renormalized operators (see e.g.).
=== Variational principle ===
The above SPH governing equations can be derived from a least action principle, starting from the Lagrangian of a particle system:
L
=
∑
j
m
j
(
1
2
v
j
2
−
e
j
+
g
⋅
r
j
)
{\displaystyle {\mathcal {L}}=\sum _{j}m_{j}\left({\tfrac {1}{2}}{\boldsymbol {v}}_{j}^{2}-e_{j}+{\boldsymbol {g}}\cdot {\boldsymbol {r}}_{j}\right)}
,
where
e
j
{\displaystyle e_{j}}
is the particle specific internal energy. The Euler–Lagrange equation of variational mechanics reads, for each particle:
d
d
t
∂
L
∂
v
i
=
∂
L
∂
r
i
.
{\displaystyle {\frac {\mathrm {d} }{\mathrm {d} t}}{\frac {\partial {\mathcal {L}}}{\partial {\boldsymbol {v}}_{i}}}={\frac {\partial {\mathcal {L}}}{\partial {\boldsymbol {r}}_{i}}}.}
When applied to the above Lagrangian, it gives the following momentum equation:
m
i
d
v
i
d
t
=
−
∑
j
m
j
∂
e
j
∂
r
i
+
m
i
g
=
−
∑
j
m
j
∂
e
j
∂
ρ
j
∂
ρ
j
∂
r
i
+
m
i
g
{\displaystyle m_{i}{\frac {\mathrm {d} {\boldsymbol {v}}_{i}}{\mathrm {d} t}}=-\sum _{j}m_{j}{\frac {\partial e_{j}}{\partial {\boldsymbol {r}}_{i}}}+m_{i}{\boldsymbol {g}}=-\sum _{j}m_{j}{\frac {\partial e_{j}}{\partial \rho _{j}}}{\frac {\partial \rho _{j}}{\partial {\boldsymbol {r}}_{i}}}+m_{i}{\boldsymbol {g}}}
where the chain rule has been used, since
e
j
{\displaystyle e_{j}}
depends on
ρ
j
{\displaystyle \rho _{j}}
, and the latter, on the position of the particles.
Using the thermodynamic property
d
e
=
(
p
/
ρ
2
)
d
ρ
{\displaystyle \mathrm {d} e=\left(p/\rho ^{2}\right)\mathrm {d} \rho }
we may write
m
i
d
v
i
d
t
=
−
∑
j
m
j
p
j
ρ
j
2
∂
ρ
j
∂
r
i
+
m
i
g
,
{\displaystyle m_{i}{\frac {\mathrm {d} {\boldsymbol {v}}_{i}}{\mathrm {d} t}}=-\sum _{j}m_{j}{\frac {p_{j}}{\rho _{j}^{2}}}{\frac {\partial \rho _{j}}{\partial {\boldsymbol {r}}_{i}}}+m_{i}{\boldsymbol {g}},}
Plugging the SPH density interpolation and differentiating explicitly
∂
ρ
j
∂
r
i
{\displaystyle {\tfrac {\partial \rho _{j}}{\partial {\boldsymbol {r}}_{i}}}}
leads to
d
v
i
d
t
=
−
∑
j
m
j
(
p
i
ρ
i
2
+
p
j
ρ
j
2
)
∇
W
i
j
+
g
,
{\displaystyle {\frac {\mathrm {d} {\boldsymbol {v}}_{i}}{\mathrm {d} t}}=-\sum _{j}m_{j}\left({\frac {p_{i}}{\rho _{i}^{2}}}+{\frac {p_{j}}{\rho _{j}^{2}}}\right)\nabla W_{ij}+{\boldsymbol {g}},}
which is the SPH momentum equation already mentioned, where we recognize the
G
{\displaystyle \operatorname {\mathbf {G} } }
operator. This explains why linear momentum is conserved, and allows conservation of angular momentum and energy to be conserved as well.
=== Time integration ===
From the work done in the 80's and 90's on numerical integration of point-like particles in large accelerators, appropriate time integrators have been developed with accurate conservation properties on the long term; they are called symplectic integrators. The most popular in the SPH literature is the leapfrog scheme, which reads for each particle
i
{\displaystyle i}
:
v
i
n
+
1
/
2
=
v
i
n
+
a
i
n
Δ
t
2
,
r
i
n
+
1
=
r
i
n
+
v
i
i
+
1
/
2
Δ
t
,
v
i
n
+
1
=
v
i
n
+
1
/
2
+
a
i
i
+
1
Δ
t
2
,
{\displaystyle {\begin{aligned}{\boldsymbol {v}}_{i}^{n+1/2}&={\boldsymbol {v}}_{i}^{n}+{\boldsymbol {a}}_{i}^{n}{\frac {\Delta t}{2}},\\{\boldsymbol {r}}_{i}^{n+1}&={\boldsymbol {r}}_{i}^{n}+{\boldsymbol {v}}_{i}^{i+1/2}\Delta t,\\{\boldsymbol {v}}_{i}^{n+1}&={\boldsymbol {v}}_{i}^{n+1/2}+{\boldsymbol {a}}_{i}^{i+1}{\frac {\Delta t}{2}},\end{aligned}}}
where
Δ
t
{\displaystyle \Delta t}
is the time step, superscripts stand for time iterations while
a
i
{\displaystyle {\boldsymbol {a}}_{i}}
is the particle acceleration, given by the right-hand side of the momentum equation.
Other symplectic integrators exist (see the reference textbook). It is recommended to use a symplectic (even low-order) scheme instead of a high order non-symplectic scheme, to avoid error accumulation after many iterations.
Integration of density has not been studied extensively (see below for more details).
Symplectic schemes are conservative but explicit, thus their numerical stability requires stability conditions, analogous to the Courant-Friedrichs-Lewy condition (see below).
=== Boundary techniques ===
In case the SPH convolution shall be practiced close to a boundary, i.e. closer than s · h, then the integral support is truncated. Indeed, when the convolution is affected by a boundary, the convolution shall be split in 2 integrals,
A
(
r
)
=
∫
Ω
(
r
)
A
(
r
′
)
W
(
|
r
−
r
′
|
,
h
)
d
r
′
+
∫
B
(
r
)
−
Ω
(
r
)
A
(
r
′
)
W
(
|
r
−
r
′
|
,
h
)
d
r
′
,
{\displaystyle A({\boldsymbol {r}})=\int _{\Omega ({\boldsymbol {r}})}A\left({\boldsymbol {r^{\prime }}}\right)W(|{\boldsymbol {r}}-{\boldsymbol {r^{\prime }}}|,h)d{\boldsymbol {r^{\prime }}}+\int _{B({\boldsymbol {r}})-\Omega ({\boldsymbol {r}})}A\left({\boldsymbol {r^{\prime }}}\right)W(|{\boldsymbol {r}}-{\boldsymbol {r^{\prime }}}|,h)d{\boldsymbol {r^{\prime }}},}
where B(r) is the compact support ball centered at r, with radius s · h, and Ω(r) denotes the part of the compact support inside the computational domain, Ω ∩ B(r). Hence, imposing boundary conditions in SPH is completely based on approximating the second integral on the right hand side. The same can be of course applied to the differential operators computation,
∇
A
(
r
)
=
∫
Ω
(
r
)
A
(
r
′
)
∇
W
(
r
−
r
′
,
h
)
d
r
′
+
∫
B
(
r
)
−
Ω
(
r
)
A
(
r
′
)
∇
W
(
r
−
r
′
,
h
)
d
r
′
.
{\displaystyle \nabla A({\boldsymbol {r}})=\int _{\Omega ({\boldsymbol {r}})}A\left({\boldsymbol {r^{\prime }}}\right)\nabla W({\boldsymbol {r}}-{\boldsymbol {r^{\prime }}},h)d{\boldsymbol {r^{\prime }}}+\int _{B({\boldsymbol {r}})-\Omega ({\boldsymbol {r}})}A\left({\boldsymbol {r^{\prime }}}\right)\nabla W({\boldsymbol {r}}-{\boldsymbol {r^{\prime }}},h)d{\boldsymbol {r^{\prime }}}.}
Several techniques has been introduced in the past to model boundaries in SPH.
==== Integral neglect ====
The most straightforward boundary model is neglecting the integral,
∫
B
(
r
)
−
Ω
(
r
)
A
(
r
′
)
∇
W
(
r
−
r
′
,
h
)
d
r
′
≃
0
,
{\displaystyle \int _{B({\boldsymbol {r}})-\Omega ({\boldsymbol {r}})}A\left({\boldsymbol {r^{\prime }}}\right)\nabla W({\boldsymbol {r}}-{\boldsymbol {r^{\prime }}},h)d{\boldsymbol {r^{\prime }}}\simeq {\boldsymbol {0}},}
such that just the bulk interactions are taken into account,
∇
A
i
=
∑
j
∈
Ω
i
V
j
A
j
∇
W
i
j
.
{\displaystyle \nabla A_{i}=\sum _{j\in \Omega _{i}}V_{j}A_{j}\nabla W_{ij}.}
This is a popular approach when free-surface is considered in monophase simulations.
The main benefit of this boundary condition is its obvious simplicity. However, several consistency issues shall be considered when this boundary technique is applied. That's in fact a heavy limitation on its potential applications.
==== Fluid Extension ====
Probably the most popular methodology, or at least the most traditional one, to impose boundary conditions in SPH, is Fluid Extension technique. Such technique is based on populating the compact support across the boundary with so-called ghost particles, conveniently imposing their field values.
Along this line, the integral neglect methodology can be considered as a particular case of fluid extensions, where the field, A, vanish outside the computational domain.
The main benefit of this methodology is the simplicity, provided that the boundary contribution is computed as part of the bulk interactions. Also, this methodology has been deeply analyzed in the literature.
On the other hand, deploying ghost particles in the truncated domain is not a trivial task, such that modelling complex boundary shapes becomes cumbersome. The 2 most popular approaches to populate the empty domain with ghost particles are Mirrored-Particles and Fixed-Particles.
==== Boundary Integral ====
The newest Boundary technique is the Boundary Integral methodology. In this methodology, the empty volume integral is replaced by a surface integral, and a renormalization:
∇
A
i
=
1
γ
i
(
∑
j
∈
Ω
i
V
j
A
j
∇
W
i
j
+
∑
j
∈
∂
Ω
i
S
j
A
j
n
j
W
i
j
)
,
{\displaystyle \nabla A_{i}={\frac {1}{\gamma _{i}}}\left(\sum _{j\in \Omega _{i}}V_{j}A_{j}\nabla W_{ij}+\sum _{j\in \partial \Omega _{i}}S_{j}A_{j}{\boldsymbol {n}}_{j}W_{ij}\right),}
γ
i
=
∑
j
∈
Ω
i
V
j
W
i
j
,
{\displaystyle \gamma _{i}=\sum _{j\in \Omega _{i}}V_{j}W_{ij},}
with nj the normal of the generic j-th boundary element. The surface term can be also solved considering a semi-analytic expression.
== Modelling physics ==
=== Hydrodynamics ===
==== Weakly compressible approach ====
Another way to determine the density is based on the SPH smoothing operator itself. Therefore, the density is estimated from the particle distribution utilizing the SPH interpolation. To overcome undesired errors at the free surface through kernel truncation, the density formulation can again be integrated in time.
The weakly compressible SPH in fluid dynamics is based on the discretization of the Navier–Stokes equations or Euler equations for compressible fluids. To close the system, an appropriate equation of state is utilized to link pressure
p
{\displaystyle p}
and density
ρ
{\displaystyle \rho }
. Generally, the so-called Cole equation
(sometimes mistakenly referred to as the "Tait equation") is used in SPH. It reads
p
=
ρ
0
c
2
γ
(
(
ρ
ρ
0
)
γ
−
1
)
+
p
0
,
{\displaystyle p={\frac {\rho _{0}c^{2}}{\gamma }}\left(\left({\frac {\rho }{\rho _{0}}}\right)^{\gamma }-1\right)+p_{0},}
where
ρ
0
{\displaystyle \rho _{0}}
is the reference density and
c
{\displaystyle c}
the speed of sound. For water,
γ
=
7
{\displaystyle \gamma =7}
is commonly used. The background pressure
p
0
{\displaystyle p_{0}}
is added to avoid negative pressure values.
Real nearly incompressible fluids such as water are characterized by very high speeds of sound of the order
10
3
m
/
s
{\displaystyle 10^{3}\mathrm {m/s} }
. Hence, pressure information travels fast compared to the actual bulk flow, which leads to very small Mach numbers
M
{\displaystyle M}
. The momentum equation leads to the following relation:
δ
ρ
ρ
0
≈
|
v
|
2
c
2
=
M
2
{\displaystyle {\frac {\delta \rho }{\rho _{0}}}\approx {\frac {|{\boldsymbol {v}}|^{2}}{c^{2}}}=M^{2}}
where
ρ
{\displaystyle \rho }
is the density change and
v
{\displaystyle v}
the velocity vector.
In practice a value of c smaller than the real one is adopted to avoid time steps too small in the time integration scheme. Generally a numerical speed of sound is adopted such that density variation smaller than 1% are allowed. This is the so-called weak-compressibility assumption.
This corresponds to a Mach number smaller than 0.1, which implies:
c
=
10
v
max
{\displaystyle c=10v_{\text{max}}}
where the maximum velocity
v
max
{\displaystyle v_{\text{max}}}
needs to be estimated, for e.g. by Torricelli's law or an educated guess. Since only small density variations occur, a linear equation of state can be adopted:
p
=
c
2
(
ρ
−
ρ
0
)
{\displaystyle p=c^{2}\left(\rho -\rho _{0}\right)}
Usually the weakly-compressible schemes are affected by a high-frequency spurious noise on the pressure and density fields.
This phenomenon is caused by the nonlinear interaction of acoustic waves and by fact that the scheme is explicit in time and centered in space
.
Through the years, several techniques have been proposed to get rid of this problem. They can be classified in three different groups:
the schemes that adopt density filters,
the models that add a diffusive term in the continuity equation,
the schemes that employ Riemann solvers to model the particle interaction.
===== Density filter technique =====
The schemes of the first group apply a filter directly on the density field to remove the spurious numerical noise. The most used filters are the MLS (moving least squares) and the Shepard filter
which can be applied at each time step or every n time steps. The more frequent is the use of the filtering procedure, the more regular density and pressure fields are obtained. On the other hand, this leads to an increase of the computational costs. In long time simulations, the use of the filtering procedure may lead to the disruption of the hydrostatic pressure component and to an inconsistency between the global volume of fluid and the density field. Further, it does not ensure the enforcement of the dynamic free-surface boundary condition.
===== Diffusive term technique =====
A different way to smooth out the density and pressure field is to add a diffusive term inside the continuity equation (group 2) :
d
ρ
i
d
t
=
∑
j
m
j
(
v
i
−
v
j
)
⋅
∇
W
i
j
+
D
i
(
ρ
)
,
{\displaystyle {\displaystyle {\frac {d\rho _{i}}{dt}}=\sum _{j}m_{j}\left({\boldsymbol {v}}_{i}-{\boldsymbol {v}}_{j}\right)\cdot \nabla W_{ij}+{\mathcal {D}}_{i}(\rho ),}}
The first schemes that adopted such an approach were described in Ferrari
and in Molteni
where the diffusive term was modeled as a Laplacian of the density field. A similar approach was also used in Fatehi and Manzari
.
In Antuono et al.
a correction to the diffusive term of Molteni was proposed to remove some inconsistencies close to the free-surface. In this case the adopted diffusive term is equivalent to a high-order differential operator on the density field.
The scheme is called δ-SPH and preserves all the conservation properties of the SPH without diffusion (e.g., linear and angular momenta, total energy,
see
) along with a smooth and regular representation of the density and pressure fields.
In the third group there are those SPH schemes which employ numerical fluxes obtained through Riemann solvers to model the particle interactions.
===== Riemann solver technique =====
For an SPH method based on Riemann solvers, an inter-particle Riemann problem is constructed along a unit vector
e
i
j
=
−
r
i
j
/
r
i
j
{\displaystyle \mathbf {e} _{ij}=-\mathbf {r} _{ij}/r_{ij}}
pointing from particle
i
{\displaystyle i}
to particle
j
{\displaystyle j}
. In this Riemann problem the initial left and right states are on particles
i
{\displaystyle i}
and
j
{\displaystyle j}
, respectively. The
L
{\displaystyle L}
and
R
{\displaystyle R}
states are
{
(
ρ
L
,
U
L
,
P
L
)
=
(
ρ
i
,
v
i
⋅
e
i
j
,
P
i
)
(
ρ
R
,
U
R
,
P
R
)
=
(
ρ
j
,
v
j
⋅
e
i
j
,
P
j
)
.
{\displaystyle {\begin{cases}(\rho _{L},U_{L},P_{L})=(\rho _{i},\mathbf {v} _{i}\cdot \mathbf {e} _{ij},P_{i})\\(\rho _{R},U_{R},P_{R})=(\rho _{j},\mathbf {v} _{j}\cdot \mathbf {e} _{ij},P_{j}).\end{cases}}}
The solution of the Riemann problem results in three waves emanating from the discontinuity. Two waves, which can be shock or rarefaction wave, traveling with the smallest or largest wave speed. The middle wave is always a contact discontinuity and separates two intermediate states, denoted by
(
ρ
L
∗
,
U
L
∗
,
P
L
∗
)
{\displaystyle (\rho _{L}^{\ast },U_{L}^{\ast },P_{L}^{\ast })}
and
(
ρ
R
∗
,
U
R
∗
,
P
R
∗
)
{\displaystyle (\rho _{R}^{\ast },U_{R}^{\ast },P_{R}^{\ast })}
. By assuming that the intermediate state satisfies
U
L
∗
=
U
R
∗
=
U
∗
{\displaystyle U_{L}^{\ast }=U_{R}^{\ast }=U^{\ast }}
and
P
L
∗
=
P
R
∗
=
P
∗
{\displaystyle P_{L}^{\ast }=P_{R}^{\ast }=P^{\ast }}
, a linearized Riemann solver for smooth flows or with only moderately strong shocks can be written as
{
U
∗
=
U
¯
+
1
2
(
P
L
−
P
R
)
ρ
¯
c
0
P
∗
=
P
¯
+
1
2
ρ
¯
c
0
(
U
L
−
U
R
)
,
{\displaystyle {\begin{cases}U^{\ast }={\overline {U}}+{\frac {1}{2}}{\frac {(P_{L}-P_{R})}{{\bar {\rho }}c_{0}}}\\P^{\ast }={\overline {P}}+{\frac {1}{2}}{\bar {\rho }}c_{0}{(U_{L}-U_{R})},\end{cases}}}
where
U
¯
=
(
U
L
+
U
R
)
/
2
{\displaystyle {\overline {U}}=(U_{L}+U_{R})/2}
and
P
¯
=
(
P
L
+
P
R
)
/
2
{\displaystyle {\overline {P}}=(P_{L}+P_{R})/2}
are inter-particle averages. With the solution of the Riemann problem, i.e.
U
∗
{\displaystyle U^{\ast }}
and
P
∗
{\displaystyle P^{\ast }}
, the discretization of the SPH method is
d
ρ
i
d
t
=
2
ρ
i
∑
j
m
j
ρ
j
(
v
i
−
v
∗
)
⋅
∇
i
W
i
j
,
{\displaystyle {\frac {d\rho _{i}}{dt}}=2\rho _{i}\sum _{j}{\frac {m_{j}}{\rho _{j}}}(\mathbf {v} _{i}-\mathbf {v} ^{\ast })\cdot \nabla _{i}W_{ij},}
d
v
i
d
t
=
−
2
∑
j
m
j
(
P
∗
ρ
i
ρ
j
)
∇
i
W
i
j
.
{\displaystyle {\frac {d\mathbf {v} _{i}}{dt}}=-2\sum _{j}m_{j}\left({\frac {P^{\ast }}{\rho _{i}\rho _{j}}}\right)\nabla _{i}W_{ij}.}
where
v
∗
=
U
∗
e
i
j
+
(
v
¯
i
j
−
U
¯
e
i
j
)
{\displaystyle \mathbf {v} ^{\ast }=U^{\ast }\mathbf {e} _{ij}+({\overline {\mathbf {v} }}_{ij}-{\overline {U}}\mathbf {e} _{ij})}
. This indicates that the inter-particle average velocity and pressure are simply replaced by the solution of the Riemann problem. By comparing both it can be seen that the intermediate velocity and pressure from the inter-particle averages amount to implicit dissipation, i.e. density regularization and numerical viscosity, respectively.
Since the above discretization is very dissipative a straightforward modification is to apply a limiter to decrease the implicit numerical dissipations introduced by limiting the intermediate pressure by
P
∗
=
P
¯
+
1
2
β
ρ
¯
(
U
L
−
U
R
)
,
{\displaystyle P^{\ast }={\overline {P}}+{\frac {1}{2}}\beta {\overline {\rho }}{(U_{L}-U_{R})},}
where the limiter is defined as
β
=
min
(
η
max
(
U
L
−
U
R
,
0
)
,
c
¯
)
.
{\displaystyle \beta =\min {\big (}\eta \max(U_{L}-U_{R},0),{\overline {c}}{\big )}.}
Note that
β
{\displaystyle \beta }
ensures that there is no dissipation when the fluid is under the action of an expansion wave, i.e.
U
L
<
U
R
{\displaystyle U_{L}<U_{R}}
, and that the parameter
η
{\displaystyle \eta }
, is used to modulate dissipation when the fluid is under the action of a compression wave, i.e.
U
L
≥
U
R
{\displaystyle U_{L}\geq U_{R}}
. Numerical experiments found the
η
=
3
{\displaystyle \eta =3}
is generally effective. Also note that the dissipation introduced by the intermediate velocity is not limited.
==== Incompressible approach ====
==== Viscosity modelling ====
In general, the description of hydrodynamic flows require a convenient treatment of diffusive processes to model the viscosity in the Navier–Stokes equations. It needs special consideration because it involves the Laplacian differential operator. Since the direct computation does not provide satisfactory results, several approaches to model the diffusion have been proposed.
Artificial viscosity
Introduced by Monaghan and Gingold
the artificial viscosity was used to deal with high Mach number fluid flows. It reads
Π
i
j
=
{
−
α
c
¯
i
j
ϕ
i
j
+
β
ϕ
i
j
2
ρ
¯
i
j
v
i
j
⋅
r
i
j
<
0
0
v
i
j
⋅
r
i
j
≥
0
{\displaystyle \Pi _{ij}={\begin{cases}{\dfrac {-\alpha {\bar {c}}_{ij}\phi _{ij}+\beta \phi _{ij}^{2}}{{\bar {\rho }}_{ij}}}&\quad {\boldsymbol {v}}_{ij}\cdot {\boldsymbol {r}}_{ij}<0\\0&\quad {\boldsymbol {v}}_{ij}\cdot {\boldsymbol {r}}_{ij}\geq 0\end{cases}}}
Here,
α
{\displaystyle \alpha }
is controlling a volume viscosity while
β
{\displaystyle \beta }
acts similar to the Neumann Richtmeyr artificial viscosity. The
ϕ
i
j
{\displaystyle \phi _{ij}}
is defined by
ϕ
i
j
=
h
v
i
j
⋅
r
i
j
‖
r
i
j
‖
2
+
η
h
2
,
{\displaystyle \phi _{ij}={\frac {h{\boldsymbol {v}}_{ij}\cdot {\boldsymbol {r}}_{ij}}{\Vert {\boldsymbol {r}}_{ij}\Vert ^{2}+\eta _{h}^{2}}},}
where ηh is a small fraction of h (e.g. 0.01h) to prevent possible numerical infinities at close distances.
The artificial viscosity also has shown to improve the overall stability of general flow simulations. Therefore, it is applied to inviscid problems in the following form
Π
i
j
=
α
h
c
v
i
j
⋅
r
i
j
‖
r
i
j
‖
2
+
η
h
2
.
{\displaystyle \Pi _{ij}=\alpha hc{\frac {{\boldsymbol {v}}_{ij}\cdot {\boldsymbol {r}}_{ij}}{\Vert {\boldsymbol {r}}_{ij}\Vert ^{2}+\eta _{h}^{2}}}.}
It is possible to not only stabilize inviscid simulations but also to model the physical viscosity by this approach. To do so
α
h
c
=
2
(
n
+
2
)
μ
ρ
{\displaystyle \alpha hc=2(n+2){\frac {\mu }{\rho }}}
is substituted in the equation above, where
n
{\displaystyle n}
is the number of spatial dimensions of the model. This approach introduces the bulk viscosity
ζ
=
5
3
μ
{\displaystyle \zeta ={\frac {5}{3}}\mu }
.
Morris
For low Reynolds numbers the viscosity model by Morris
was proposed.
[
ν
Δ
v
]
i
j
=
2
ν
m
j
ρ
j
r
i
j
⋅
∇
w
h
,
i
j
‖
r
i
j
‖
2
+
η
h
2
v
i
j
.
{\displaystyle [\nu \Delta {\boldsymbol {v}}]_{ij}=2\nu {\frac {m_{j}}{\rho _{j}}}\,{\frac {{\boldsymbol {r}}_{ij}\cdot \nabla w_{h,ij}}{\Vert {\boldsymbol {r}}_{ij}\Vert ^{2}+\eta _{h}^{2}}}\,{\boldsymbol {v}}_{ij}.}
LoShao
==== Additional physics ====
Surface tension
Heat transfer
Turbulence
==== Multiphase extensions ====
=== Astrophysics ===
Often in astrophysics, one wishes to model self-gravity in addition to pure hydrodynamics. The particle-based nature of SPH makes it ideal to combine with a particle-based gravity solver, for instance tree gravity code, particle mesh, or particle-particle particle-mesh.
=== Solid mechanics and fluid-structure interaction (FSI) ===
==== Total Lagrangian formulation for solid mechanics ====
To discretize the governing equations of solid dynamics, a correction matrix
B
0
{\displaystyle \mathbb {B} ^{0}}
is first introduced to reproducing rigid-body rotation as
where
∇
a
0
W
a
=
∂
W
(
|
r
a
b
0
|
,
h
)
∂
|
r
a
b
0
|
e
a
b
0
{\displaystyle \nabla _{a}^{0}W_{a}={\frac {\partial W\left(|\mathbf {r} _{ab}^{0}|,h\right)}{\partial |\mathbf {r} _{ab}^{0}|}}\mathbf {e} _{ab}^{0}}
stands for the gradient of the kernel function evaluated at the initial reference configuration.
Note that subscripts
a
{\displaystyle a}
and
b
{\displaystyle b}
are used to denote solid particles, and smoothing length
h
{\displaystyle h}
is identical to that in the discretization of fluid equations.
Using the initial configuration as the reference, the solid density is directly evaluated as
where
J
=
det
(
F
)
{\displaystyle J=\det(\mathbb {F} )}
is the Jacobian determinant of deformation tensor
F
{\displaystyle \mathbb {F} }
.
We can now discretize the momentum equation in the following form
where inter-particle averaged first Piola-Kirchhoff stress
P
~
{\displaystyle {\tilde {\mathbb {P} }}}
is defined as
Also
f
a
F
:
p
{\displaystyle \mathbf {f} _{a}^{F:p}}
and
f
a
F
:
v
{\displaystyle \mathbf {f} _{a}^{F:v}}
correspond to the fluid pressure and viscous forces acting on the solid particle
a
{\displaystyle a}
, respectively.
==== Fluid-structure coupling ====
In fluid-structure coupling, the surrounding solid structure is behaving as a moving boundary for fluid, and the no-slip boundary condition is imposed at the fluid-structure interface. The interaction forces
f
i
S
:
p
{\displaystyle \mathbf {f} _{i}^{S:p}}
and
f
i
S
:
v
{\displaystyle \mathbf {f} _{i}^{S:v}}
acting on a fluid particle
i
{\displaystyle i}
, due to the presence of the neighboring solid particle
a
{\displaystyle a}
, can be obtained as
and
Here, the imaginary pressure
p
a
d
{\displaystyle p_{a}^{d}}
and velocity
v
a
d
{\displaystyle \mathbf {v} _{a}^{d}}
are defined by
where
n
S
{\displaystyle \mathbf {n} ^{S}}
denotes the surface normal direction of the solid structure,
and the imaginary particle density
ρ
a
d
{\displaystyle \rho _{a}^{d}}
is calculated through the equation of state.
Accordingly, the interaction forces
f
a
F
:
p
{\displaystyle \mathbf {f} _{a}^{F:p}}
and
f
a
F
:
v
{\displaystyle \mathbf {f} _{a}^{F:v}}
acting on a solid particle
a
{\displaystyle a}
are given by
and
The anti-symmetric property of the derivative of the kernel function will ensure the momentum conservation for each pair of interacting particles
i
{\displaystyle i}
and
a
{\displaystyle a}
.
=== Others ===
The discrete element method, used for simulating granular materials, is related to SPH.
== Variants of the method ==
== References ==
== Further reading ==
Hoover, W. G. (2006); Smooth Particle Applied Mechanics: The State of the Art, World Scientific.
Stellingwerf, R. F.; Wingate, C. A.; "Impact Modelling with SPH", Memorie della Societa Astronomia Italiana, Vol. 65, p. 1117 (1994).
Amada, T.; Imura, M.; Yasumuro, Y.; Manabe, Y.; and Chihara, K. (2004); "Particle-based fluid simulation on GPU", in Proceedings of ACM Workshop on General-purpose Computing on Graphics Processors (August, 2004, Los Angeles, California).
Desbrun, M.; and Cani, M.-P. (1996). "Smoothed Particles: a new paradigm for animating highly deformable bodies" in Proceedings of Eurographics Workshop on Computer Animation and Simulation (August 1996, Poitiers, France).
Hegeman, K.; Carr, N. A.; and Miller, G. S. P.; "Particle-based fluid simulation on the GPU", in Proceedings of International Conference on Computational Science (Reading, UK, May 2006), Lecture Notes in Computer Science v. 3994/2006 (Springer-Verlag).
Kelager, M. (2006) Lagrangian Fluid Dynamics Using Smoothed Particle Hydrodynamics, MSc Thesis, Univ. Copenhagen.
Kolb, A.; and Cuntz, N. (2005); "Dynamic particle coupling for GPU-based fluid simulation", in Proceedings of the 18th Symposium on Simulation Techniques (2005) pp. 722–727.
Liu, G. R.; and Liu, M. B.; Smoothed Particle Hydrodynamics: a meshfree particle method, Singapore: World Scientific (2003).
Monaghan, Joseph J. (1992). "Smoothed Particle Hydrodynamics", Annual Review of Astronomy and Astrophysics (1992). 30 : 543–74.
Muller, M.; Charypar, D.; and Gross, M.; "Particle-based Fluid Simulation for Interactive Applications", in Breen, D; and Lin, M. (eds.), Proceedings of Eurographics/SIGGRAPH Symposium on Computer Animation (2003).
Vesterlund, M.; Simulation and Rendering of a Viscous Fluid Using Smoothed Particle Hydrodynamics, MSc Thesis, Umea University, Sweden.
Violeau, D.; Fluid Mechanics and the SPH method, Oxford University Press (2012).
== External links ==
First large simulation of star formation using SPH
SPHERIC (SPH rEsearch and engineeRing International Community)
ITVO is the web-site of The Italian Theoretical Virtual Observatory created to query a database of numerical simulation archive.
SPHC Image Gallery depicts a wide variety of test cases, experimental validations, and commercial applications of the SPH code SPHC.
A derivation of the SPH model starting from Navier-Stokes equations
=== Software ===
Algodoo is a 2D simulation framework for education using SPH
AQUAgpusph is the free (GPLv3) SPH of the researchers, by the researchers, for the researchers
dive solutions is a commercial web-based SPH engineering software for CFD purposes
DualSPHysics is a mostly open source SPH code based on SPHysics and using GPU computing. The open source components are available under the LGPL.
FLUIDS v.1 is a simple, open source (Zlib), real-time 3D SPH implementation in C++ for liquids for CPU and GPU.
Fluidix is a GPU-based particle simulation API available from OneZero Software
GADGET [1] is a freely available (GPL) code for cosmological N-body/SPH simulations
GPUSPH SPH simulator with viscosity (GPLv3)
Pasimodo is a program package for particle-based simulation methods, e.g. SPH
LAMMPS is a massively parallel, open-source classical molecular dynamics code that can perform SPH simulations
Physics Abstraction Layer is an open source abstraction system that supports real time physics engines with SPH support
PreonLab is a commercial engineering software developed by FIFTY2 Technology implementing an implicit SPH method
Punto is a freely available visualisation tool for particle simulations
pysph Open Source Framework for Smoothed Particle Hydrodynamics in Python (New BSD License)
Py-SPHViewer Open Source python visualisation tool for Smoothed Particle Hydrodynamics simulations.
RealFlow Commercial SPH solver for the cinema industry.
RheoCube is a commercial SaaS product by Lorenz Research for the study and prediction of complex-fluid rheology and stability
SimPARTIX is a commercial simulation package for SPH and Discrete element method (DEM) simulations from Fraunhofer IWM
SPH-flow
SPHERA
SPHinXsys is an open source multi-physics, multi-resolution SPH library. It provides C++ APIs for physical accurate simulation and aims to model coupled industrial dynamic systems including fluid, solid, multi-body dynamics and beyond.
SPHysics is an open source SPH implementation in Fortran
SPLASH is an open source (GPL) visualisation tool for SPH simulations
SYMPLER: A freeware SYMbolic ParticLE simulatoR from the University of Freiburg.
Nauticle is a general-purpose computational tool for particle-based numerical methods.
NDYNAMICS is a commercial fluid simulation software based on implicit SPH developed by CENTROID LAB currently used for internal/external flooding/nuclear/chemical engineering applications. | Wikipedia/Smoothed_particle_hydrodynamics |
The Energy Citations Database (ECD) was created in 2001 in order to make scientific literature citations, and electronic documents, publicly accessible from U.S. Department of Energy (DOE), and its predecessor agencies, at no cost to the user. This database also contains all the unclassified materials from Energy Research Abstracts. Classified materials are not available to the public. ECD does include the unclassified, unlimited distribution scientific and technical reports from the Department of Energy and its predecessor agencies, the Atomic Energy Commission and the Energy Research and Development Administration. The database is usually updated twice per week.
ECD provides free access to over 2.6 million science research citations with continued growth through regular updates. There are over 221,000 electronic documents, primarily from 1943 forward, available via the database. Citations and documents are made publicly available by the Regional Federal Depository Libraries. These institutions maintain and make available DOE research literature, providing access to non‑electronic documents prior to 1994, and electronic access to more recent documents.
ECD was created and developed by DOE's Office of Scientific and Technical Information with the science-attentive citizen in mind. It contains energy and energy‑related scientific and technical information collected by the DOE and its predecessor agencies.
== Scope ==
Topics, or subjects, and Department of Energy disciplines of interest in Energy Citations Database (ECD) are wide-ranging. Scientific and technical research encompass chemistry, physics, materials, environmental science, geology, engineering, mathematics, climatology, oceanography, computer science, and related disciplines. It includes bibliographic citations to report scientific literature, conference papers, journal articles, books, dissertations, and patents.
=== Stated capabilities ===
Bibliographic citations for scientific and technical information dating from 1943 to the present day. Search capabilities include full text, bibliographic citation, title, creator/author, subject, identifier numbers, publication date, system entry date, resource/document type, research organization, sponsoring organization, and/or any combination of these.
Commensurate with the above search capabilities is sorting results by various means.
Results can be sorted by relevance, publication date, system entry date, resource/document type, title, research organization, sponsoring organization, or the unique Office of Scientific Information (OSTI) Identifier. Furthermore, acquiring a count of search results, combined with a link to the actual results is available.
ability to receive weekly Alerts in topics of interest;
information about acquiring a non-electronic document
== Research and database in predecessor agencies ==
Since the late 1940s, the Office of Scientific and Technical Information (OSTI) and its predecessor organizations have been responsible for the management of scientific and technical information (STI) for the Department of Energy (DOE) and its predecessor agencies, the Atomic Energy Commission (AEC) and the Energy Research and Development Administration (ERDA). Growth and development of STI management has incorporated planning, developing, maintaining, and administering all services and facilities required to accomplish the dissemination of scientific and technical information for the encouragement of scientific progress.
=== Atomic Energy Commission ===
In 1942, the Manhattan Project was established by the United States Army to conduct atomic research with the goal of ending World War II. This research was performed in a manner that helped to cement the ongoing bond between basic scientific research and national security. After the war, the authority to continue this research was transferred from the Army to the United States Atomic Energy Commission (AEC) through the Atomic Energy Act of 1946. This Act was signed into law by President Harry S. Trumanun on August 1, 1946, and entrusted the AEC with the government monopoly in the field of atomic research and development.
=== Energy Reorganization Act ===
The Energy Reorganization Act of 1974 abolished the Atomic Energy Commission and established the Energy Research and Development Administration (ERDA). ERDA was created to achieve two goals:
First was to focus the Federal Government's energy research and development activities within a unified agency whose major function would be to promote the speedy development of various energy technologies. The second, was to separate nuclear licensing and regulatory functions from the development and production of nuclear power and weapons.
=== Department of Energy ===
To achieve a major Federal energy reorganization, the Department of Energy (DOE) was activated on October 1, 1977. DOE became the twelfth cabinet-level department in the Federal Government and brought together for the first time most of the government's energy programs and defense responsibilities that included the design, construction, and testing of nuclear weapons.
== Features section ==
The Energy Citations Database features noteworthy topics of discussion in the features section.
=== SciDAC ===
SciDAC is a specially designed program within the Office of Science of the U.S. Department of Energy. It enables scientific discovery through advanced computing (SciDAC), and is driven by a spirit of collaboration. Discipline scientists, applied mathematicians, and computer scientists are working together to maximize use of the most sophisticated high-power computers for scientific discovery. Research results are promulgated through the SciDAC review magazine. Supercomputer Modeling and Visualization is covered in the Spring 2010 issue of this magazine.
== Regional Federal Depository Libraries ==
There are nearly 1,250 depository libraries throughout the United States and its territories. Access to all documents (hundreds of thousands) is no-fee access. Expert assisted searches are available, on site.
Federal depository libraries have been established by Congress to ensure that the American public has access to its Government's information. The Federal Depository Library Program (FDLP) involves the acquisition, format conversion, and distribution of depository materials to libraries throughout the United States and the coordination of Federal depository libraries in the 50 states, the District of Columbia and U.S. territories.
The U.S. Government Printing Office administers the FDLP.
=== Federal depository library coverage ===
Coverage generally encompasses:
Health and Nutrition
Laws, Statistics, and Presidential Materials
Science and Technology
Business and Careers
Education
History
World Maps
Available formats are publications, journals, electronic resources, microfiche, microfilm and various other formats encompassing hundreds of thousands of topics.
== References ==
This article incorporates public domain material from websites or documents of the United States Department of Energy.
This article incorporates public domain material from websites or documents of the United States government. | Wikipedia/Energy_Citations_Database |
Chipmunk2D is a 2-dimensional real-time rigid body physics engine written by Scott Lembcke that is designed to be portable, lightweight, fast, and easy to use. Prior to version 7, two main versions of the library existed. Chipmunk2D Free was written purely in C99, and freely available under the terms of the MIT License. Chipmunk2D Pro was a proprietary upgrade designed for development on mobile devices. It included several high-level subroutines in Objective-C, and floating-point optimizations for the ARM processor. However, after version 7 the project was fully open-sourced.
Aside from Objective-C, there are official bindings for Ruby, and third party interfaces exist for Python, Haskell, OCaml, and others. Chipmunk is endorsed by a number of game libraries, including Aerosol, Gosu, and Cocos2d.
== Features ==
Chipmunk supports multiple collision primitives attached to one rigid body, and bodies may be joined by constraints. It has a flexible collision detection system with layers, exclusion groups and collision callbacks. Callbacks are defined based on user definable "collision types" and may reject collisions and even override the calculation of friction and elasticity coefficients.
Version 7 of the library introduced "Autogeometry", an image tracing feature that transforms a raster graphic into a polygonal shape usable by the library. This feature is currently only available in the Objective-C version of the library.
Chipmunk has been widely used on the iPhone, Mac/Windows/Linux, and other platforms, including Nintendo Wii and Sony PSP.
== See also ==
Box2D
== References ==
== External links ==
Official website
Chipmunk Forums
Chipmunks Ruby Bindings, with more functionality wrapped.
chipmunk-ffi, a more up-to-date Ruby interface using Nice-FFI.
Demos of Chipmunk on YouTube | Wikipedia/Chipmunk_physics_engine |
In vehicle dynamics, a tire model is a type of multibody simulation used to simulate the behavior of tires. In current vehicle simulator models, the tire model is the weakest and most difficult part to simulate.
Tire models can be classified on their accuracy and complexity, in a spectrum that goes from more simple empirical models to more complex physical models that are theoretically grounded. Empirical models include Hans B. Pacejka's Magic Formula, while physically based models include brush models (although they are still quite simplified), and more complex and detailed physical models include RMOD-K, FTire and Hankook. Theoretically-based models can be in turn classified from more approximative to more complex ones, going for example from the solid model, to the rigid ring model, to the flexural (elastic) ring model (like the Fiala model), and the most complex ones based on finite element methods.
Brush models were very popular in the 1960s and '70s, after which Pacejka's models became widespread for many applications.
== Classification by purpose ==
=== Driving dynamics models ===
Brush model (Dugoff, Fancher and Segel, 1970)
Hohenheim tire model (physical approach [1])
Pacejka Magic Formula Tire (Bakker, Nyborg and Pacejka, 1987)
TameTire (semi-physical approach)
TMeasy (semi-physical approach)
Stretched string tire model (Fiala 1954)
=== Comfort models ===
BRIT (Brush and Ring Tire)
CDTire (Comfort and Durability Tire)
Ctire (Comfort tire)
Dtire (Dynamical Nonlinear Spatial Tire Model)
FTire (Flexible Structure Tire Model)
RMOD-K (Comfort and Durability Tire)
SWIFT (Short Wavelength Intermediate Frequency Tire) (Besselink, Pacejka, Schmeitz, & Jansen, 2005)
== Applications ==
Fully physics-based tire models have been typically too computational expensive to be run in realtime driving simulations. For example, to since CDTire/3D, a physics-based tire model, cannot be run in realtime, for realtime applications typically an equivalent semi-empirical "magic formula" type of model, called CDTire/Realtime, is derived from it through experiments and a regression algorithm.
In 2016, a slightly less accurate version of FTire, a physics-based tire model, was adapted to be run in real time. This realtime version of FTire was shown in 2018 to run on a 2,7 GHz 12 Core Intel Xeon E5 (2014, 22 nm process, about $2000), with 900 contact road/contact patch elements, a sample frequency of 4.0 kHz including thermal and wear simulation.
The typical tire model sampling rate used in automotive simulators is 1 kHz. However, running at higher frequencies, like 2 kHz, might mitigate lowered numerical stability in some scenarios, and might increase the model accuracy in frequency domain above
about 250 Hz.
== See also ==
Contact patch
Self aligning torque
Slip (vehicle dynamics)
Thermal analysis
Heat transfer
== References ==
== Further reading ==
Egbert, Bakker; Nyborg, Lars; Pacejka, Hans B. (1987). "Tyre modelling for use in vehicle dynamics studies" (PDF). Society of Automotive Engineers. A new way of representing tyre data obtained from measurements in pure cornering and pure braking conditions.
Hans Pacejka (2012) Tire and Vehicle Dynamics, third edition (first edition 2002)
Lugner, P., & Plöchl, M. (2005). Tyre model performance test: first experiences and results. Vehicle System Dynamics, 43(sup1), 48-62.
Xu Wang (2020) Automotive Tire Noise and Vibrations: Analysis, Measurement and Simulation, ch.10
FTire physical tire model to run with rFpro driving simulation software, at rFpro official Vimeo and youtube channels, Jan 29, 2020
Romano, L., Bruzelius, F., & Jacobson, B. (2020) Brush tyre models for large camber angles and steering speeds, in Vehicle System Dynamics, 1-52.
VEHICLE DYNAMICS LIBRARY OFFERS EXPANDED SUPPORT FOR COSIN’S FTIRE MODEL, MODELON, AUGUST 1, 2017
Février, P., Hague, O. B., Schick, B., & Miquet, C. (2010) Advantages of a thermomechanical tire model for vehicle dynamics, ATZ worldwide, 112(7), 33-37.
== External links ==
Tire models at Project Chrono
Tires For Heavy Trucks by PneusQuebec
Tire Modeling; Extracting Results from a Large Data Set at YouTube | Wikipedia/Tire_model |
The Tokamak Game Physics SDK is an open-source physics engine.
At its beginnings, Tokamak was free for non commercial uses only. Since May 2007, it has become open sourced under a BSD License. Now it can be used under BSD or Zlib license, in order to make the source code exchange with other physics engine possible.
== Features ==
Tokamak features a unique iterative method for solving constraints. This is claimed to allow developers to make trade-offs between accuracy and speed and provides more predictable processor and memory usage. Tokamak's constraint solver does not
involve solving large matrices, thereby avoiding memory bandwidth limitations on some game consoles.
The SDK supports a variety of joint types and joint limits and a realistic friction model. Tokamak is optimized for stacking large numbers of objects - a frequently requested feature by game developers. Tokamak provides collision detection for primitives (box, sphere, capsule), combinations of primitives, and arbitrary static triangle meshes. Lightweight 'rigid particles' provide particle effects in games at minimal cost.
Tokamak also supports "Breakage Constructing models" which will break when a collision occurs. Fragments of the original model will automatically be spawned by Tokamak's built-in breakage functionality.
collision detection✔
Particle system?
Rigid body dynamics?
== See also ==
Physics Abstraction Layer
== External links ==
Tokamak web site Archived 2016-03-30 at the Wayback Machine
Tokamak sourceforge project page | Wikipedia/Tokamak_physics_engine |
Computer animation physics or game physics are laws of physics as they are defined within a simulation or video game, and the programming logic used to implement these laws. Game physics vary greatly in their degree of similarity to real-world physics. Sometimes, the physics of a game may be designed to mimic the physics of the real world as accurately as is feasible, in order to appear realistic to the player or observer. In other cases, games may intentionally deviate from actual physics for gameplay purposes. Common examples in platform games include the ability to start moving horizontally or change direction in mid-air and the double jump ability found in some games. Setting the values of physical parameters, such as the amount of gravity present, is also a part of defining the game physics of a particular game.
There are several elements that form components of simulation physics including the physics engine, program code that is used to simulate Newtonian physics within the environment, and collision detection, used to solve the problem of determining when any two or more physical objects in the environment cross each other's path.
== Physics simulations ==
There are two central types of physics simulations: rigid body and soft-body simulators. In a rigid body simulation objects are grouped into categories based on how they should interact and are less performance intensive. Soft-body physics involves simulating individual sections of each object such that it behaves in a more realistic way.
== Particle systems ==
A common aspect of computer games that model some type of conflict is the explosion. Early computer games used the simple expedient of repeating the same explosion in each circumstance. However, in the real world an explosion can vary depending on the terrain, altitude of the explosion, and the type of solid bodies being impacted. Depending on the processing power available, the effects of the explosion can be modeled as the split and shattered components propelled by the expanding gas. This is modelled by means of a particle system simulation. A particle system model allows a variety of other physical phenomena to be simulated, including smoke, moving water, precipitation, and so forth. The individual particles within the system are modelled using the other elements of the physics simulation rules, with the limitation that the number of particles that can be simulated is restricted by the computing power of the hardware. Thus explosions may need to be modelled as a small set of large particles, rather than the more accurate huge number of fine particles.
== Ragdoll physics ==
This is a procedural animation and simulation technique to display the movement of a character when killed. It treats the character's body as a series of rigid bones connected together with hinges at the joints. The simulation models what happens to the body as it collapses to the ground. More sophisticated physics models of creature movement and collision interactions require greater level of computing power and a more accurate simulation of solids, liquids, and hydrodynamics. The modelled articulated systems can then reproduce the effects of skeleton, muscles, tendons, and other physiological components. Some games, such as Boneworks and Half-Life 2, apply forces to individual joints that allow ragdolls to move and behave like humanoids with fully procedural animations. This allows to, for example, knock an enemy down or grab each individual joint and move it around and the physics-based animation would adapt accordingly, which wouldn't be possible with conventional means. This method is called active ragdolls and is often used in combination with inverse kinematics.
== Projectiles ==
Projectiles, such as arrows or bullets, often travel at very high speeds. This creates problems with collisions - sometimes the projectile travels so fast that it simply goes past a thin object without ever detecting that it has collided with it. Before, this was solved with ray-casting, which does not require the creation of a physical projectile. However, simply shooting a ray in the direction that the weapon is aiming at is not particularly realistic, which is why modern games often create a physical projectile that can be affected by gravity and other forces. This projectile uses a form of continuous collision detection to make sure that the above-stated problem will not occur (at the cost of inferior performance), since more complex calculations are required to perform such a task.
Games such as FIFA 14 require accurate projectile physics for objects such as the soccer ball. In FIFA 14, developers were required to fix code related to the drag coefficient which was inaccurate in previous games, leading to a much more realistic simulation of a real ball.
== Books ==
Eberly, David H. (2003). Game Physics. Morgan Kaufmann. ISBN 978-1-55860-740-8.
Millington, Ian (2007). Game Physics Engine Development. Morgan Kaufmann. ISBN 978-0-12-369471-3.
Bourg, David M. (2001). Physics for Game Developers. O'Reilly Media. ISBN 978-0-596-00006-6.
Szauer, Gabor (2017). Game Physics Cookbook. Packt Publishing. ISBN 978-1787123663.
Conger, David (2004). Physics Modeling for Game Programmers. Course Technology PTR. ISBN 978-1592000937.
== See also ==
Physics engine
Physics game
Real-time simulation
== References ==
== External links ==
"Math and Physics". GameDev. Archive. Archived from the original on February 22, 2011.
"Physics Engines List". Database. Digital Rune. Mar 30, 2015 [2010]. Archived from the original on March 9, 2016. | Wikipedia/Game_physics |
Ragdoll physics is a type of procedural animation used by physics engines, which is often used as a replacement for traditional static death animations in video games and animated films. As computers increased in power, it became possible to do limited real-time physical simulations, which made death animations more realistic.
Early video games used manually created animations for a character’s death sequences. This had the advantage of low CPU utilization, as the data needed to animate a "dying" character was chosen from a set number of pre-drawn frames. In contrast, a ragdoll is a collection of multiple rigid bodies (each of which is ordinarily tied to a bone in the graphics engine's skeletal animation system) tied together by a system of constraints that restrict how the bones may move relative to each other. When the character dies, their body begins to collapse to the ground, honouring these restrictions on each of the joints' motion, which often looks more realistic.
The term ragdoll comes from the problem that the articulated systems, due to the limits of the solvers used, tend to have little or zero joint/skeletal muscle stiffness, leading to a character collapsing much like a toy rag doll, often into comically improbable or compromising positions. Modern use of ragdoll physics goes beyond death sequences.
== History ==
The Jurassic Park licensed game Jurassic Park: Trespasser exhibited ragdoll physics in 1998 but received very polarised opinions; most were negative, as the game had a large number of bugs. It was remembered, however, for being a pioneer in video game physics.
There are fighting games where the player controls one part of the body of the fighter and the rest follows along, such as Rag Doll Kung Fu, as well as racing games such as the FlatOut series.
Recent procedural animation technologies, such as those found in NaturalMotion's Euphoria software, have allowed the development of games that rely heavily on the suspension of disbelief facilitated by realistic whole-body muscle/nervous ragdoll physics as an integral part of the immersive gaming experience, as opposed to the antiquated use of canned-animation techniques. This is seen in Grand Theft Auto IV, Grand Theft Auto V, Red Dead Redemption, Max Payne 3 and Red Dead Redemption 2 as well as titles such as LucasArts' Star Wars: The Force Unleashed and Puppet Army Faction's Kontrol, which feature 2D powered ragdoll locomotion on uneven or moving surfaces.
== Approaches ==
Ragdolls have been implemented using Featherstone's algorithm and spring-damper contacts. An alternative approach uses constraint solvers and idealized contacts.
While the constrained-rigid-body approach to ragdolls is the most common, other "pseudo-ragdoll" techniques have been used:
Verlet integration: used by Hitman: Codename 47 and popularized by Thomas Jakobsen, this technique models each character bone as a point connected to an arbitrary number of other points via simple constraints. Verlet constraints are much simpler and faster to solve than most of those in a fully modelled rigid body system, resulting in much less CPU consumption for characters.
Inverse kinematics post-processing: used in Halo: Combat Evolved, this technique relies on playing a pre-set death animation and then using inverse kinematics to force the character into a possible position after the animation has completed. This means that, during an animation, a character could wind up clipping through world geometry, but after it has come to rest, all of its bones will be in valid space. Limitations can force body parts to move through each other in unnatural ways; for instance, a character's hand may lay on top of their chest in a death animation, but the hand is then moved through the chest to the ground underneath by inverse kinematics.
Blended ragdoll: this technique was used in Halo 2, Halo 3, Call of Duty 4: Modern Warfare, Left 4 Dead, Medal of Honor: Airborne, Team Fortress 2, and Uncharted: Drake's Fortune. It works by playing a pre-made animation, then binding the ragdoll to the last frame of the animation. Occasionally the ragdolling player model will appear to stretch out and spin around in multiple directions, as though the character were made of rubber. This erratic behavior has been observed to occur in games that use certain versions of the Havok engine, such as Halo 2 and Fable II.
Active ragdoll: used primarily in Unreal Engine games such as Unreal Tournament 3 and Killing Floor 2. It works by playing a pre-made animation, but constraining the output of that animation to what a physical system would allow. This helps alleviate the ragdoll feeling of characters suddenly going limp, offering correct environmental interaction as well. This requires both animation processing and physics processing, thus making it even slower than a traditional ragdoll alone, though the benefits of the extra visuals seem to overshadow the reduction in processing speed. See also: Euphoria (software)
Procedural animation: traditionally used in non-realtime media (film/TV/etc), this technique (used in the Medal of Honor series starting from European Assault onward) employs the use of multi-layered physical models in non-playing characters (bones / muscle / nervous systems), and deformable scenic elements from "simulated materials" in vehicles, etc. By removing the use of pre-made animation, each reaction seen by the player is unique, whilst still deterministic.
== See also ==
Cartoon physics
Joint constraints
Stair Dismount
Turbo Dismount
Lugaru
== References == | Wikipedia/Ragdoll_physics |
Star Wars: The Force Unleashed is a 2008 action-adventure game developed and published by LucasArts, and part of The Force Unleashed multimedia project. It was initially developed for the PS2, PS3, Wii, and Xbox 360 consoles and on iOS, second-generation N-Gage, NDS, PSP, and Java-equipped mobile phone handhelds. The game was released in North America on September 16, 2008, in Australia and Southeast Asia on September 17, and in Europe on September 19. LucasArts released downloadable content for the PS3 and Xbox 360 consoles. An Ultimate Sith Edition of the game, containing both new and previously released downloadable content, was released in November 2009, and later ported to Mac OS X and Windows. An enhanced remaster of the Wii version, developed by Aspyr, was released for the Nintendo Switch on April 20, 2022.
The project bridges the first two Star Wars trilogies, acting as an origin story for both the united Rebel Alliance and the Galactic Civil War depicted in the original trilogy. The game introduces a new protagonist named "Starkiller", a powerful Force user trained as Darth Vader's secret apprentice, who is tasked with hunting down Jedi survivors of the Great Jedi Purge while trying to keep his existence a secret. However, after he is tasked with planting the seeds of what would become the Rebel Alliance, which Vader plans to take advantage of to overthrow the Emperor, Starkiller begins to question his morality and to redeem himself slowly. Following The Walt Disney Company's acquisition of Lucasfilm in 2012, the game became part of the non-canonical Star Wars Legends continuity in 2014, and an alternative origin for the Rebel Alliance and the Galactic Civil War was given in other forms of Star Wars media, such as Star Wars Rebels.
Star Wars: The Force Unleashed received generally positive reviews from critics, praising its story, voice acting, physics, art, and soundtrack, but criticism for its linear gameplay and technical issues. The game was a bestseller in the United States and Australia, with over 1,000,000 copies sold in its debut month. As of February 2010, the game had sold over 7,000,000 copies, and was the fastest-selling Star Wars video game of its time. A sequel, Star Wars: The Force Unleashed II, was released in October 2010.
== Gameplay ==
The Force Unleashed is a third-person action game in which the player's character's weapons are the Force and a lightsaber. Developers treated the main character's lightsaber like another Force power, and wanted to ensure "something visceral and cool" happened with each button-push. The game has a combo system for stringing lightsaber attacks and for combining lightsaber attacks with Force powers. Experience points earned by killing enemies and finding artifacts can be used to increase Starkiller's powers and traits. The gameplay is intended to be easy to learn; the development team included "horrible" gamers to help ensure the game's accessibility. Players can casually run and gun through the game, but the game rewards those who take a stealthy, more tactical approach. The game includes enemies that are easy to overcome; game difficulty arises from presenting these enemies in large numbers that can wear down the player's character. Additionally, enemies learn from the player's character's attacks; using the same attack on different characters can sometimes lead to the player's character doing less damage. The enemies, which number over 50, have various strengths and weaknesses; developers faced the difficulty of effectively placing them throughout the game's varied environments. Players must also carefully manage their automatically-regenerating Force energy when using exceptionally strong Force abilities, as overuse of them can drop the Force meter below zero to a negative level, incurring Force debt that disables all Force powers for a period of time until the auto-regeneration removes the debt; the more Force debt incurred, the longer the player will be without Force abilities.
=== Version differences ===
The Force Unleashed has different features across platforms. The PS3 and Xbox 360 versions, powered by the Ronin engine, utilize high-definition graphics and advanced dynamic destruction effects. These versions also support downloadable content in two expansions, expanding the game's plot. The Nintendo versions use motion controls to implement Starkiller's attacks, with the Wii version using the Wii Remote to execute lightsaber attacks and the Nunchuk to wield Force powers, while the Nintendo DS version utilizes the touchscreen to execute attacks, where single actions can be executed by tapping a certain region of the screen (with each region corresponding to a particular action, such as jumping or Force pushing), while more advanced attacks can be performed by dragging the stylus across neighboring regions of the screen.
The PS2 and PSP versions are identical in content to the Wii version, which is different than the PS3 and Xbox 360 versions. Since these versions don't support or use DLC, they exclusively intersperse certain levels with 3 of the 5 Jedi trials that Starkiller completes at the Jedi temple in Coruscant to hone his abilities, which are all included in a DLC pack for the PS3 and Xbox 360 versions. The PSP version also exclusively features five additional "historical" bonus levels that re-enact pivotal scenes and duels throughout the Star Wars saga, as well as special scenarios that can be played with as different Star Wars characters who have the same abilities in the standard single-player mode. The Nintendo DS version utilizes 3-D graphics like all other major versions, but lacks voice acting.
The Wii and handheld versions support multiplayer. Players duel against each other as famous Jedi and Sith in the Star Wars saga in the Wii version,. The handheld versions utilize wireless multiplayer for a 4-player battle mode.
The Switch version is a port of the Wii version with numerous differences. It retains the motion controls from the Wii version, allowing players to use the Joy-Con controllers to perform various actions like swinging the lightsaber and using Force powers. While the graphical improvements are minor, it benefits from a stable 60 FPS performance, an improvement over some older versions with frame rate issues. This version includes the Jedi Temple missions, originally DLC on other platforms. However, some iconic moments from the Xbox 360 and PS3 versions, like bringing down a Star Destroyer with the Force, are simplified or presented as cutscenes. It includes a local multiplayer mode, a feature in the Wii version. Players can customize their lightsaber with different colors, hilts, and combat crystals, though some specific features from other versions, like the unstable kyber crystal, are not present.
== Plot ==
Shortly into the Galactic Empire's rule, Imperial spies locate a Jedi survivor of the Great Purge named Kento Marek on Kashyyyk. Darth Vader arrives as the planet is invaded and eliminates any Wookiee resistance between him and the fugitive Jedi. Reaching Kento's home, Vader easily defeats him in a lightsaber duel but senses someone far more powerful nearby. Initially believing it to be Kento's Jedi Master, Vader prepares to execute the defiant Jedi until his lightsaber is suddenly force-pulled from his hand by Kento's son, Galen. Sensing the boy's strong connection to the Force, Vader kills Kento and an Imperial squadron after they try to execute Galen and secretly takes him as his apprentice, with only a select few knowing of his existence.
Years later, an adult Galen (given the alias "Starkiller") completes his Sith training. He's sent by Vader to eliminate several Jedi survivors across the galaxy in preparation for assassinating the Emperor so that the duo can rule the galaxy together. Starkiller travels aboard his ship, the Rogue Shadow, alongside training droid PROXY (who is programmed to try and kill Starkiller) and Imperial pilot Juno Eclipse. Starkiller's targets include Rahm Kota, a Clone Wars veteran and leader of a militia; Kazdan Paratus, insane after years of isolation on Raxus Prime; and Shaak Ti, who's hiding on Felucia. Two of these three Jedi masters, Kota and Ti, inform Starkiller that they have foreseen that soon Vader will no longer be his master before he finishes them (with Ti committing suicide instead). After the latter's death, Starkiller returns to Vader again, but the Emperor arrives, his spies having uncovered Starkiller's existence. To prove his loyalty to the Emperor, Vader appears to kill his apprentice by stabbing him and hurling him through space.
Unbeknownst to the Emperor, Vader has Starkiller recovered and resuscitated. Vader sends Starkiller to foster a rebellion among the Empire's enemies, hoping to distract the Emperor's spies for Vader to overthrow him. Starkiller rescues Juno, arrested and branded a traitor to the Empire, and escapes with her and PROXY. Looking for allies to aid his mission, Starkiller finds an alive Kota on Cloud City, rendered blind from Starkiller's earlier victory over him and reduced to alcoholism, and rescues him from Imperial forces.
The group travels to Kashyyyk to locate Kota's contact, senator Bail Organa. Starkiller discovers his old home and meets his father's spirit, who expresses remorse for Starkiller's upbringing under Vader. To gain Bail's trust, Starkiller rescues his captive daughter Princess Leia Organa, and liberates the enslaved Wookiees at her request. Starkiller learns from Kota that Bail went missing on Felucia, after searching for Shaak Ti in the hope that she would rescue Leia. Starkiller travels to Felucia to find Bail, discovering that he'd been captured by Shaak Ti's former apprentice Maris Brood, who succumbed to the Dark Side after her master's death. Starkiller defeats Brood but spares her life, and convinces Bail to join the rebellion.
To convince more dissidents to do the same, Vader suggests that Starkiller attack a Star Destroyer facility on Raxus Prime to show that the Empire is vulnerable. Juno learns Starkiller is still serving Vader and chastises him, but agrees to keep silent. On Raxus Prime, Starkiller is attacked by PROXY, who attempts to fulfill his programming by killing him. Still, Starkiller defeats him, destroys the facility, and pulls a falling Star Destroyer out of the sky using the Force. Bail meets with fellow senators Mon Mothma and Garm Bel Iblis on Corellia to formally organize a rebellion, only for Vader to arrive and arrest them and Kota. After overpowering Starkiller, Vader reveals that he was merely a tool to lure out the Empire's enemies, and had never intended to use him to overthrow the Emperor. Starkiller escapes after PROXY sacrifices himself by attacking Vader.
Juno rescues Starkiller, who uses the Force to see that Kota and the senators are being held on the Death Star. After Juno kisses him and he bids farewell, Starkiller battles his way through the station to reach the Emperor's throne room. Vader confronts him, but Starkiller defeats his former master and faces the Emperor, who tries to goad him into killing Vader so Starkiller can take his place. Kota tries to attack the Emperor, but is subdued with Force lightning. At this point, the player must choose between saving Kota (Light Side) or killing Vader (Dark Side).
If the player chooses the Light Side, Starkiller defeats the Emperor, but spares him at Kota's urging. The Emperor unleashes Force lightning at Kota, but Starkiller absorbs it, sacrificing himself to allow Kota and the senators to escape on the Rogue Shadow. The Emperor and Vader become concerned that Starkiller has become a martyr to inspire the newly-formed Rebel Alliance. On Kashyyyk, the senators proceed with the rebellion and Leia chooses Starkiller's family crest as their symbol. Kota tells Juno that among Starkiller's dark thoughts, Juno herself was one bright spot that he held onto right until his death.
If the player chooses the Dark Side, Starkiller kills Vader and is congratulated by the Emperor, who commands him to kill Kota to sever his ties to the Jedi and become a Sith Lord. Starkiller instead attacks the Emperor, who foils his attempt and then crushes him with the Rogue Shadow, severely injuring Starkiller and killing Juno, Kota, and the senators. Starkiller later awakens to find his body being grafted with armor to continue serving the Emperor, though he assures Starkiller that he'll be replaced once he finds a new apprentice just as Vader before him.
=== Downloadable content ===
Three DLC levels for the game were released for the PS3, Xbox 360, and computer versions of the game. The first one is set during the events of the main story and explores more of Starkiller's background, while the second and third ones expand upon the non-canonical Dark Side ending of the game, taking place in their own alternate timeline. All three DLC packs are included on-disc in the Ultimate Sith Edition for all abovementioned three platforms.
The Coruscant DLC depicts Starkiller, at some point before traveling to Kashyyyk, deciding to visit the abandoned Jedi Temple to learn more about his identity and connection to the Force. After fighting his way past the Imperial security forces, he reaches the old Council Chambers, where he meets Kento Marek's spirit who tells him that he needs to pass three Jedi trials. Upon doing so, Starkiller is faced with a mysterious Sith warrior, revealed to be a dark reflection of himself created by his own fear. Following his defeat, Starkiller finds a holocron left by Marek, who reveals himself as his father and implores him to return to the light side. Starkiller then returns to the Rogue Shadow to resume his current mission.
The Tatooine and Hoth DLC's are set during alternate depictions of A New Hope and The Empire Strikes Back, respectively, and present Starkiller as the Emperor's trusted assassin, referred to as "Lord Starkiller".
In the Tatooine DLC, he's tasked with retrieving the Death Star plans stolen by the Rebel Alliance, which have been tracked to Tatooine. He visits Jabba the Hutt, who has knowledge on the plans' whereabouts, revealing that they're in the possession of two droids at Mos Eisley. When Starkiller refuses to work for him, Jabba attempts to have Starkiller eaten by his rancor. Killing the beast, Starkiller escapes from Jabba's palace after massacring Jabba's mercenaries, including Boba Fett. At Mos Eisley, Starkiller kills Jedi Master Obi-Wan Kenobi after a duel which allows the droids to board the Millennium Falcon, though Starkiller manages to place a tracking device on the ship before it takes off.
In the Hoth DLC, Starkiller partakes in the Battle of Hoth, where the Empire attacks the weakened Rebel Alliance base. During the battle, Starkiller infiltrates the base with orders to capture Luke Skywalker, who had begun training as a Jedi. Starkiller finds and defeats Skywalker in the base's hangar, severing his right hand. When the Falcon tries to take off, Starkiller seizes the ship with the Force while goading Skywalker to give into the Dark Side to rescue his friends. Skywalker attacks Starkiller with Force lightning, causing him to let go of the ship and congratulate Skywalker for embracing the Dark Side, planning to make him his apprentice the same way that Vader did to him.
== Cast and characters ==
Sam Witwer as Galen Marek / Starkiller — The forbidden child of a Jedi, Starkiller was adopted by his father's killer, Darth Vader, who, aware of his strong connection to the Force, raised him to be his secret apprentice. Once his training is complete, Starkiller is dispatched by his master to kill several prominent Jedi who survived the Great Jedi Purge. Although initially acting as a villain, Starkiller is "really just [a] damaged kid." Developers decided not to give Starkiller a name in the game, but the novelization reveals his real name as "Galen Marek". Although Starkiller starts as Vader's apprentice, a focus of the game is to allow the character to evolve into "something more heroic, something greater." Audio director David Collins saw a resemblance between Starkiller concept art and his friend, Witwer; Collins asked for Witwer's headshot and an audition reel, and a few weeks later Witwer sat for a 45-minute audition. Witwer secured the role by demonstrating to developers his deep understanding of the character; in portraying Starkiller, Witwer brought many new ideas about the character and imbued him with a sense of humanity. Developers tried not to make Starkiller so evil that players would have difficulty connecting to him, aiming to strike a balance between loyalty to his master and his growing sense of disillusionment with the Empire. The character's name is an homage to "Anakin Starkiller," the original name of the character that eventually became Luke Skywalker. Witwer also voiced Emperor Palpatine.
Matt Sloan as Darth Vader — A powerful Dark Lord of the Sith, high-ranking enforcer of the Empire, and Starkiller's master, who discovers Starkiller as a child and trains him. In training Starkiller by having him hunt the few remaining Jedi survivors, Vader intends to prepare him to overthrow the Emperor, although there are "twists and turns" in this scheme. The events depicted in The Force Unleashed are pivotal to Darth Vader's history and development, depicting him as being largely responsible for the events leading to the Galactic Civil War, depicted in the original Star Wars trilogy.
Nathalie Cox as Juno Eclipse — Rogue Shadow’s pilot and Starkiller's love interest. Eclipse was not originally part of the game; early concepts had the apprentice as an older character who develops a connection with a young Princess Leia. Star Wars creator George Lucas, uncomfortable with this idea, encouraged the developers to create a love interest. The apprentice, who has had limited interaction with women when the game begins, does not at first know how to act around her. Her introduction early in the game allows the relationship with Starkiller to develop, and her inclusion helps "recapture that rich ensemble feel of the original Star Wars". According to Sean Williams, who wrote the novelization, the romantic storyline is the key to The Force Unleashed. The name "Juno Eclipse" was originally proposed as a name for the character eventually called "Asajj Ventress" — it was ultimately rejected as insufficiently villainous. The Force Unleashed project lead Haden Blackman brought the name back for the mythic quality of the name "Juno" and the duality suggested by an "eclipse." Cox, in addition to strongly resembling the character's concept art, had "integrity and poise" appropriate to Juno Eclipse that helped the actor secure the role.
Cully Fredricksen as General Rahm Kota — A Jedi Master and Clone Wars veteran who provides Starkiller with additional insight into the Force and helps connect him to his Jedi heritage. Developers realized early that Starkiller would require insight into the Force from someone other than Darth Vader; after rejecting the idea of this coming from the spirit of Qui-Gon Jinn or some version of Darth Plagueis, they decided to fill this role with one of Starkiller's Jedi opponents. The character was conceived as a "tough-as-nails" contrast to the more traditional image of a Jedi represented by Jinn and Obi-Wan Kenobi. Senior concept artist Amy Beth Christianson drew upon samurai influences for Kota's appearance. The character changed little after being conceived; Fredricksen's own traits made the character tougher. Fredricksen was the first actor cast for the project.
Adrienne Wilkinson as Maris Brood — A Zabrak survivor of the Jedi Purge and Shaak Ti's apprentice. After her master's death at Starkiller's hands, Brood falls to the dark side and uses Felucia's inhabitants to wage war on the Imperial forces trying to occupy the planet. The character was originally conceived as a pirate captain, and Christianson's early art included Brood's distinctive lightsaber tonfas. Wilkinson brought strength to her performance, leading to an expansion of the role with more dialogue.
David W. Collins as PROXY — Starkiller's droid sidekick, designed to constantly test his lightsaber and Force abilities, as well as deliver important messages through holographic projection. Collins said PROXY has C-3PO's innocence but also is "really dangerous." The companion trade paperback describes the conflict between PROXY's primary programming to kill Starkiller and its self-imposed desire to help him; PROXY is eager to please Starkiller, but does not know how dangerous it can be or that there is a conflict between its programming and Starkiller's wishes. Trying to avoid having PROXY's dialogue become too reminiscent of either C-3PO or the villainous HK-47 of Knights of the Old Republic, developers focused on PROXY's friendly naïvety.
Jimmy Smits as Bail Organa — Smits voices the character he played in the prequels trilogy: a Galactic Senator from Alderaan and Princess Leia's adoptive father who becomes a founding member of the Rebel Alliance.
Tom Kane as Kento Marek / Captain Ozzik Sturn
Larry Drake as Kazdan Paratus
Susan Eisenberg as Shaak Ti
Catherine Taber as Princess Leia Organa
David W. Collins as Jabba the Hutt
Dee Bradley Baker as Boba Fett
Rob Rackstraw as Obi-Wan Kenobi
Lloyd Floyd as Luke Skywalker
== Development ==
=== Concept ===
Game planning began in summer 2004. Initially, about six developers started with a "clean slate" to conceptualize a new Star Wars game; the small group of engineers, artists, and designers spent more than a year brainstorming ideas for what might make a good game. Over 100 initial concepts were whittled down to 20 to 25 that included making the game the third entry in the Knights of the Old Republic series or having the protagonist be a Wookiee "superhero", Darth Maul, a bounty hunter, a smuggler, a mercenary or the last member of the Skywalker family living 500 years after the events of Return of the Jedi. The decision to focus on the largely unexplored period between Revenge of the Sith and A New Hope helped energize the design team. Consumer feedback helped the developers narrow in on seven concepts, and elements from those seven went into The Force Unleashed's overall concept.
Production was greatly aided by concept art, which was intended to bridge the two Star Wars trilogies visually, convey the impression of a "lived-in" universe, show how the galaxy changes under Imperial rule, and to seem familiar yet new. An off-hand comment about the Force in the game being powerful enough "to pull a Star Destroyer out of the sky" inspired an image by senior concept artist Amy Beth Christenson that became an important part of the developers' idea pitches and evolved into a major moment in the game. These illustrations also inspired the creation of dozens of simple, three-dimensional animations. Eventually, a one-minute previsualization video highlighting the idea of "kicking someone's ass with the Force" helped convince the designers that The Force Unleashed would be "a great game"; George Lucas, upon seeing the one-minute video, told the designers to "go make that game". Once the concept was solidified, the development team grew from ten to twenty people. The idea of "reimagining" the Force as "amped up" in The Force Unleashed aligned with LucasArts' overall goal of harnessing the power of the latest video game consoles to "dramatically" change gaming, specifically through the use of simulation-based gameplay.
=== Story ===
In April 2005, after several months of planning, the LucasArts team received Lucas' encouragement to create a game centered on Darth Vader's secret apprentice in the largely unexplored period between Revenge of the Sith and A New Hope, drawing the two trilogies together. LucasArts spent six months developing the story. Lucas spent hours discussing with the developers the relationship between Darth Vader and Emperor Palpatine and provided feedback on what Vader would want out of and how he would motivate an apprentice. Lucas Licensing reviewed many game details to ensure they fit into canon. Focus group feedback indicated that, while hunting down Jedi at Vader's order would be fun, the character should be redeemed, in keeping with a major Star Wars motif. Before the game's release, Lucasfilm claimed it would "unveil new revelations about the Star Wars galaxy" with a "redemption" motif. The story progresses through a combination of scripted events, in-game cinematics, cutscenes, and dialogue.
Looking over many unexplored already existing characters, the creative team considered bringing Darth Plagueis, Emperor Palpatine's enigmatic master only mentioned in Revenge of the Sith, into the game's story through various methods: one was for Plagueis' spirit to serve as the guide for Vader's secret apprentice to provide players with information about their character's powers, another had Plagueis as the story's MacGuffin by having Vader send his apprentice to search for Plagueis to resurrect his beloved Padmé Amidala, making Vader's apprentice actually a reincarnated Plagueis or having a redeemed Plagueis become the apprentice's mentor. Knight and the developers explored different possible looks for Plagueis, depicting him as a human resembling actor Michael Gambon, a zombie, a time traveler, a cyborg, etc. Although the game introduces new characters, developers felt the presence of characters already part of Star Wars would help anchor the game within the official continuity.
=== Technology ===
During pre-production, about 30 people were on the project team. LucasArts spent several years developing the tools and technology to create The Force Unleashed. Prototyping, level construction, marketing, and public relations took about a year. Until late 2006, the production team was ascertaining "how many polygons, lights, [and] characters" next-generation platforms supported; a year of full production began in early 2007. A series of quickly-produced "play blast" videos helped the developers focus on mechanics, the user interface, and finishing moves. Development of the Xbox 360 version came first; PlayStation 3 development started when the production team had enough development kits. Making the game run on both the PlayStation 3 and Xbox 360 was "a monumental task".
The game is based on LucasArts' proprietary "Ronin" game engine but also integrates third-party technology: Havok for rigid body physics, Pixelux Entertainment's "Digital Molecular Matter" (DMM) for dynamically destructible objects, and NaturalMotion's Euphoria for realistic non-player character artificial intelligence. The focus of employing Euphoria to develop The Force Unleashed caused LucasArts to "sideline" Indiana Jones and the Staff of Kings, an Indiana Jones title that had been in development since two years ago, for a while until development on the Star Wars title concluded. LucasArts' programmers had to overcome technical hurdles to get Havok-, DMM- and Euphoria-coded components to interact. Developers also had to strike a balance between realistic and entertaining physics. LucasArts initially opted not to release a personal computer version of The Force Unleashed, stating that doing the game well would be too processor-intensive for typical PCs and that scaling down the game's procedural physics for the PC platform would "fundamentally" change The Force Unleashed's gameplay. However, LucasArts later announced Windows and Mac versions of the game, developed in conjunction with Aspyr Media, for release in Fall 2009.
Lacking Havok, Euphoria, and DMM, Krome's Wii version relies on the company's in-house physics engine. Some character animations may be ragdoll while others are preset; in developing the game, Krome tried to blur the distinction between the two. The lighting system in the Wii version is more advanced than that in the PS2 version, which Krome also built; the PS2 includes more graphic details than the PSP version.
=== ILM collaboration and cast performance ===
The Force Unleashed is intended to make players think they are "actually, finally, in a Star Wars movie". It is the first game on which LucasArts and Industrial Light & Magic (ILM) collaborated since they both relocated to the Letterman Digital Arts Center in San Francisco, California. This collaboration allowed the companies to co-develop tools to make film-quality effects. LucasArts worked with ILM's Zeno tool framework and helped ILM build its Zed game editor. Lucas said having the two companies working together in the same building was "a great collaboration".
It took Senior Manager of Voice and Audio Darragh O'Farrell four months to cast The Force Unleashed. ILM's face- and motion-capture "CloneCam" technology recorded actors' voice and physical performances. This led to a change in LucasArts' casting process: for the first time, actors needed to match characters' age and gender. Actors performed their lines together, rather than in isolation, to better understand their characters' interaction. Consequently, the script's dialogue was reduced while reliance on characters' expressions — captured through the CloneCam — increased. CloneCam technology had previously been used in producing the Pirates of the Caribbean movies.
=== Music ===
LucasArts music supervisor Jesse Harlin said the music matches the game's motif of redemption and goal of bridging the gap between Revenge of the Sith and A New Hope:
We had to make sure that the game's score started off rooted within the Prequel Trilogy feel of ethnic percussion and sweeping themes that spoke to the nobility and grandeur of the old Jedi Order. As the game progresses, however, the Empire gains more control, the Jedi are hunted, and the ordered control of the Prequels gives way to the more romantic temperament of the Original Trilogy.
The game's soundtrack includes material composed by John Williams for the films in addition to material created specifically for The Force Unleashed. Jesse Harlin composed the game's main theme, while Mark Griskey composed the score. Griskey made use of several motifs from the film scores as well as Harlin's main theme. The 90-minute soundtrack was recorded by the Skywalker Symphony Orchestra and mixed at Skywalker Sound in Lucas Valley in September and October 2007. During gameplay, a proprietary engine combines "musical elements according to the pace, plot, and environment of the game at any given moment", resulting in a unique musical experience. A promotional soundtrack album was made available online through Tracksounds.com in 2008.
== Other media ==
=== Print works ===
Sean Williams' novelization was released in the United States on August 19, 2008. It spent one week as #1 on both Publishers Weekly's and The New York Times' hardcover fiction bestsellers lists, slipping to #7 and #9, respectively, the following week. It also reached #15 on USA Today's bestsellers list.
Williams took on the writing project in part because of the "catchy description" of The Force Unleashed being "Episode 3.5" of the Star Wars saga. The novel focuses on the dark side of the Force and its practitioners; Williams found it "interesting" to portray the Jedi as "bad guys." The author most enjoyed developing the character of Juno Eclipse, exploring the "feminine" side of The Force Unleashed in a way the video game does not. Williams also said that while the game allows the player to "do" Starkiller's actions, the novel allows readers to experience Starkiller's thoughts about those actions, adding another dimension to the story.
Dark Horse's The Force Unleashed graphic novel was published August 18, 2008. Newsarama called the graphic novel a "solid story" that matches the video game source material in both structure and plot. IGN gave the graphic novel a score of 6.9/10 (6.4/10 for art, 7.5/10 for the writing), praising the overall story but faulting inconsistency in the art and questioning whether the comic medium was the best way to convey the story.
=== Merchandise ===
At Toy Fair 2007, Hasbro showed seven figures from their action figure line based on the game. Lego released a model of the Starkiller's ship, the Rogue Shadow.
=== Expansion ===
Two weeks after the game's release, LucasArts announced development on two downloadable expansion packs for the game's PS3 and Xbox 360 versions. The first expansion added "skins" that allow the player's character to appear as Star Wars figures other than Starkiller, such as Obi-Wan Kenobi, Anakin Skywalker, Qui-Gon Jinn, Jango Fett, C-3PO, Luke Skywalker, Darth Maul, Darth Sion, Mace Windu, Plo Koon, Kit Fisto and Ki-Adi-Mundi. The skins chosen to be part of the expansion were based in part on fans' feedback, and many skins of such prior Star Wars characters were also implemented as cheat codes for the Wii, PlayStation 2 and PlayStation Portable versions of the game with no additional downloads required. The second expansion pack added a new mission expanding Starkiller's background. Although a moment in the game's main story was considered as a "jumping off point" for the expansion, LucasArts decided instead to make the new mission instantly accessible to players. The mission's location — the Jedi Temple on Coruscant — appears in the Wii, PlayStation 2 and PlayStation Portable versions of The Force Unleashed, but was cut during planning from the PS3 and Xbox 360 platforms.
The Tatooine Downloadable Content, released August 27, 2009, is the first of two expansions that occur in an "Infinities" storyline, an alternate history in which Starkiller kills Vader and becomes Palpatine's assassin. The second Infinities expansion, which takes place on Hoth, was originally only available as part of the Ultimate Sith Edition, which also includes all previous downloadable content. However, the Hoth expansion was later made available for download on the PlayStation Network and Xbox Live.
== Reception ==
1.738 million unit sales of The Force Unleashed across all platforms made it the third best-selling game globally in the third quarter of 2008; as of July 2009, it had sold six million copies. The Force Unleashed was both the fastest-selling Star Wars game and LucasArts' fastest-selling game. The Force Unleashed won a Writers Guild of America award for Best Video Game Writing. During the 12th Annual Interactive Achievement Awards, the Academy of Interactive Arts & Sciences awarded The Force Unleashed with "Outstanding Achievement in Adapted Story".
=== PlayStation 3, Xbox 360 and PC ===
The Force Unleashed received mixed to fairly positive reviews. Electronic Gaming Monthly said the game is "ambitious--yet dissatisfying"; however, GameSpot said the game "gets more right than it does wrong". GameSpot said the PC port of the game retained all of the game's strengths and weaknesses, but that the port failed to take advantage of the PC platform.
GameSpot called the game's story "more intimate and more powerful" than the Star Wars franchise's prequel trilogy; X-Play identified the game's story as one of the game's "few bright spots" and said the game's visuals successfully convey Star Wars' "classic used universe" feel. GamePro and GameSpot praised the game's art and physics, and GamePro also commended Starkiller's "cool powers". IGN praised the game's voice acting, particularly Witwer's performance as Starkiller. The Washington Times identified Mark Griskey's soundtrack as "another star" of the game, and Tracksounds called it "the most entertaining Star Wars score since Return of the Jedi". Time called The Force Unleashed the seventh best video game of 2008. The game received GameSpot's 2008 award for Best Use of a Creative License and was nominated for Best Voice Acting. Gaming Target selected the game as one of their "40 Games We'll Still Be Playing From 2008".
Conversely, Entertainment Weekly called The Force Unleashed the second-worst game of 2008 and GameTrailers called it the most disappointing game that year; it was also a nominee for GameSpot's Most Disappointing Game recognition. Official Xbox Magazine cited the game's linear gameplay and lack of multiplayer as reasons the game falls short of being "an all-engrossing Star Wars experience". GamesTM suggested that allowing players to take a hack-and-slash approach means many "will never view the title's full potential". IGN and X-Play criticized some boss battles and enemies' behavior; GamePro also faulted "disappointing" boss battles and the game's "uneven" combat. Rather than feeling more powerful as the game progresses, GamePro felt that increases in Starkiller's powers were dampened by increasingly difficult enemy abilities and positions; X-Play commented that despite a good level-up system, Starkiller and his enemies are "pretty much on even ground most of the time". Wired, X-Play, and GameSpot criticized the game's third-person camera and the sequence that requires the player to make Starkiller pull a Star Destroyer out of the sky. Wired.com speculated that LucasArts could have recognized the frustration of the Star Destroyer sequence and removed it, but left it in because they hyped the sequence before the game's release. Wired.com and GameSpot further criticized the load times and abrupt gameplay-cinematic transitions. GameSpot also faulted "loose" targeting and some visual and audio glitches. IGN, which also identified problems with targeting, speculated that DMM's processor intensiveness limited its use throughout the game, detracting from players' ability to feel immersed. GameTrailers and IGN were disappointed with the lack of variety within and between levels. X-Play, pointing to "Default Text" as the bonus objective description in the Xbox 360 version's final mission and other glitches, said it seems the developers one day "just stopped working on the game". GameSpot cited the port's lack of visual options and poor framerate as evidence the PC edition had been rushed.
IGN described the Jedi Academy expansion as "pretty decent". GameSpot said LucasArts seems to have acknowledged some of the game's criticisms in developing the Tatooine expansion, but IGN called the level's boss fights "a joke" in light of the player's high Force powers. IGN found the level design in The Ultimate Sith Edition's Hoth scenario uninteresting, and called the boss fight against Luke Skywalker tough but "not nearly as fun" as it could have been.
The demo was the fourth most-played Xbox Live game during the week of August 25, trailing Grand Theft Auto IV, Halo 3, and Call of Duty 4: Modern Warfare; it was the ninth most-played Xbox Live title throughout all of 2008. The week it was released, The Force Unleashed was the sixth most-played game on Xbox Live, and it rose to fifth the following week. In its first week on sale in Australia, the PS3 and Xbox 360 versions of The Force Unleashed were the top and second-best sellers, respectively. In the United States, the PlayStation 3 and Xbox 360 version sold 325,000 and 610,000 copies, respectively, in September 2008; that month, the Xbox 360 version was the best-selling game and the PlayStation 3 version was the fifth best-selling game for their respective consoles.
=== Other platforms ===
Nintendo Power praised the story and the number of lightsaber combos but criticized the game's easiness and hack-and-slash gameplay. It also praised the Wii version for its story and Force powers, but criticized the game's lightsaber controls and linear gameplay. GameSpot noticed visual glitches and problematic audio compression that detracted from the Wii version's "mature and exciting" story, adding that the reduced number of Force-manipulable objects helps mitigate the targeting problems experienced on other platforms. Referring to the Wii remote and nunchuck controls, GameSpot also speculated that The Force Unleashed is "possibly the most waggle-heavy" Wii game. Zero Punctuation criticized the Wii version's graphics and compared lightsaber combat to "trying to follow an aerobics routine with both your arms tied to different windmills". The ability to upgrade Starkiller's abilities in the PS2 version, according to IGN, is not as "robust" as it should be, and the game's targeting system is sometimes frustrating. IGN said the PS2's real-time cutscene rendering made Starkiller seem emotionless, and that pre-rendered cutscenes would have been better. GameSpot found the DS version's plot interesting but the storytelling itself "lackluster". While the DS version is easy, with Starkiller killing enemies "like a hot knife through butter", GameSpot said the player's sense of power is not matched by a sense of freedom. GameSpot called the PSP version's camera "unwieldy", but added that smaller and less cluttered environments make the targeting system less frustrating than on other platforms. The Wii version was a nominee for multiple Wii-specific awards from IGN in its 2008 video game awards, including Best Story and Best Voice Acting.
In the week of its release, the Wii version was the sixth bestselling game in Australia and was second to Wii Fit among games for that platform. The PS2 version was the eighth bestseller in Australia, and both the PS2 and PSP versions were the top sellers on their respective platforms. The DS version was eighth most sold among DS games in Australia. In the United States, the Wii version sold 223,000 copies in September 2008, making it the ninth best-selling game that month. In the United States, the PlayStation 2 version was the 14th best-selling game in September 2008, selling over 100,000 copies.
== Further reading ==
Williams, Sean (August 19, 2008). Star Wars: The Force Unleashed. Del Rey Books. ISBN 978-0345502858.
== Notes ==
== References ==
== External links ==
Official website
Star Wars: The Force Unleashed on Wookieepedia, a Star Wars wiki
Star Wars: The Force Unleashed at MobyGames
Star Wars: The Force Unleashed at IMDb | Wikipedia/Star_Wars:_The_Force_Unleashed |
The Open Dynamics Engine (ODE) is a physics engine written in C/C++. Its two main components are a rigid body dynamics simulation engine and a collision detection engine. It is free software licensed both under the BSD license and the LGPL.
ODE was started in 2001 and has already been used in many applications and games, such as Assetto Corsa, BloodRayne 2, Call of Juarez, S.T.A.L.K.E.R., Titan Quest, World of Goo, X-Moto and OpenSimulator.
== Overview ==
The Open Dynamics Engine is used for simulating the dynamic interactions between bodies in space. It is not tied to any particular graphics package although it includes a basic one called drawstuff. It supports several geometries: box, sphere, capsule (cylinder capped with hemispheres), triangle mesh, cylinder and heightmap.
== Simulation ==
Higher level environments that allow non-programmers access to ODE include Player Project, Webots, Opensimulator, anyKode Marilou and CoppeliaSim.
ODE is a popular choice for robotics simulation applications, with scenarios such as mobile robot locomotion and simple grasping. ODE has some drawbacks in this field, for example the method of approximating friction and poor support for joint-damping.
== See also ==
OPAL – the Open Physics Abstraction Layer, originally built on top of ODE
Physics Abstraction Layer – The original Physics Abstraction Layer
Newton Game Dynamics
Bullet – another open source physics engine used in commercial games and movies
Chipmunk – a similar physics engine intended for 2D applications
Vortex (software)
Project Chrono
== References ==
== External links ==
Bitbucket: ODE project page
Open Dynamics Engine (ODE) Community Wiki Archived 2016-03-03 at the Wayback Machine
(Old) Official ODE Homepage
(Obsolete) Python-ODE Bindings (pyode)
The ode4j project, a Java port of ODE
The ODE.NET project, a C# wrapper for ODE Archived 2016-09-15 at the Wayback Machine | Wikipedia/Open_Dynamics_Engine |
Newton Game Dynamics is an open-source physics engine for realistically simulating rigid bodies in games and other real-time applications. Its solver is deterministic and not based on traditional LCP or iterative methods.
Newton Game Dynamics is actively developed by Julio Jerez. Currently a new version which will take advantage of multi-core CPUs and GPUs is being developed.
== Games that used Newton ==
This is a select list of games using Newton Game Dynamics.
Amnesia: Rebirth
Amnesia: A Machine for Pigs
Amnesia: The Dark Descent
Amnesia: The Bunker
b4n92uid theBall
City Bus Simulator
Future Pinball – a 3D pinball editing and gaming application
Mount & Blade
Nicktoons Winners Cup Racing
Overclocked: A History of Violence
Penumbra: Overture
Penumbra: Black Plague
Penumbra: Requiem
SOMA
Steam Brigade
SALVATIONLAND
== Engines which incorporated Newton ==
A list of game engines using Newton Game Dynamics:
HPL Engine 1, 2, and 3
== See also ==
Physics Abstraction Layer (PAL)
Open Dynamics Engine (ODE)
Project Chrono
== External links ==
Github repository with latest development changes
Official Newton Game Dynamics homepage
== References == | Wikipedia/Newton_Game_Dynamics |
Vortex Studio is a simulation software platform developed by CM Labs Simulations. It features a real-time physics engine that simulates rigid body dynamics, collision detection, contact determination, and dynamic reactions. It also contains model import and preparation tools, an image generator, and networking tools for distributed simulation which is accessed through a desktop editor via a GUI. Vortex adds accurate physical motion and interactions to objects in visual-simulation applications for operator training, mission planning, product concept validation, heavy machinery and robotics design and testing, haptics devices, immersive and virtual reality (VR) environments.
The Vortex Studio content creation platform and the C++ SDK have several modules that simulate physics-based particles, sensors, floating bodies, cable systems, earthmoving operations, grasping, and vehicles (wheeled or tracked). Vortex has modular architecture: developers can integrate their projects into 3D visualisation frameworks and deploy them in environments that contain software-in-the-loop (SIL), MATLAB, hardware-in-the-loop (HIL), and motion platform components.
== History ==
Vortex Studio is developed by CM Labs Simulations Inc., a private company established in Montreal in 2001. CM Labs was created when the management of MathEngine Canada Inc. purchased a portion of the business from MathEngine PLC, the parent company in the UK. MathEngine Canada Inc. was originally the research and development team responsible for creating the Karma physics simulation engine for computer games. That team and underlying technology came Lateral Logic Inc, founded in 1994 in Montreal, which had developed rigid-body dynamics and collision detection engines for use in custom simulators sold to Sisu AB for forestry harvester operator training and to Nokia for product demonstration. Lateral Logic was acquired by MathEngine in 1999.
CM Labs shifted its focus away from gaming. It now supports two distinct markets, visual simulation for training (VST), targeting Vortex at robotics and heavy-equipment operator training in both commercial and military applications, and heavy equipment prototyping and engineering, targeting mostly manufacturers and academia.
Vortex Studio has been under active development ever since the initial launch of the software in 2001. It usually has three releases per year (a, b and c).
== Use ==
Vortex has been used for commercial, military, and academic projects. It has been used to simulate vehicles, robotics, and heavy equipment in construction, mining, forestry, marine, subsea, planetary, academic, and military environments. It has also been used to simulate the movements and behaviour of animals and insects for scientific purposes. Sample examples are:
The Explosive Ordnance Disposal (EOD) robot simulator developed by the European Aeronautic Defence and Space Company (EADS) for training purposes. EADS uses Vortex to model the physical behaviour of the robot as it maneuvers in its simulated environment, interacting with other objects while processing user commands.
A driverless vehicle designed by Carnegie Mellon University’s Red Team Racing for the DARPA Grand Challenge that uses Vortex for preplanning and onboard navigation to “accurately simulate the vehicle as it navigates the terrain, including both local area constraints and global path planning objectives.”
Heavy-equipment operator training simulators such as tower crane, mobile crane, crawler crane, and concrete pump for the Operating Engineers Training Institute of Ontario and the International Union of Operating Engineers – Local 721. These simulators are used to prepare operators for proper equipment use and accident avoidance.
Georgia State University’s AnimatLab project, which is a simulation software environment that models how the body and nervous system dynamically interact in a Vortex-governed virtual physical world where relevant neural and physical parameters can be observed and manipulated.
== See also ==
Game physics
Robotics simulator
== References ==
== Further reading ==
Bourg, David M. (2001). Physics for Game Developers. O’Reilly.
Coutinho, Murilo G. (2001). Dynamic Simulations of Multibody Systems. Springer-Verlag.
Kuipers, Jack B. (1998). Quaternions and Rotation Sequences. Princeton University Press.
Lanczos, Cornelius (1986). The Variational Principles of Mechanics. Dover Books.
== External links ==
A Virtual Highway for Road Warriors, MT2 2008 Volume 13, Issue 6 Archived 2012-12-16 at the Wayback Machine
The Daily Commercial News, May 12, 2008 Archived February 19, 2012, at the Wayback Machine
Visual Interactive Simulation Lecture, Spring 2005, Physics Engines | Wikipedia/Vortex_(physics_engine) |
In physics, a force is an influence that can cause an object to change its velocity unless counterbalanced by other forces. In mechanics, force makes ideas like 'pushing' or 'pulling' mathematically precise. Because the magnitude and direction of a force are both important, force is a vector quantity. The SI unit of force is the newton (N), and force is often represented by the symbol F.
Force plays an important role in classical mechanics. The concept of force is central to all three of Newton's laws of motion. Types of forces often encountered in classical mechanics include elastic, frictional, contact or "normal" forces, and gravitational. The rotational version of force is torque, which produces changes in the rotational speed of an object. In an extended body, each part applies forces on the adjacent parts; the distribution of such forces through the body is the internal mechanical stress. In the case of multiple forces, if the net force on an extended body is zero the body is in equilibrium.
In modern physics, which includes relativity and quantum mechanics, the laws governing motion are revised to rely on fundamental interactions as the ultimate origin of force. However, the understanding of force provided by classical mechanics is useful for practical purposes.
== Development of the concept ==
Philosophers in antiquity used the concept of force in the study of stationary and moving objects and simple machines, but thinkers such as Aristotle and Archimedes retained fundamental errors in understanding force. In part, this was due to an incomplete understanding of the sometimes non-obvious force of friction and a consequently inadequate view of the nature of natural motion. A fundamental error was the belief that a force is required to maintain motion, even at a constant velocity. Most of the previous misunderstandings about motion and force were eventually corrected by Galileo Galilei and Sir Isaac Newton. With his mathematical insight, Newton formulated laws of motion that were not improved for over two hundred years.
By the early 20th century, Einstein developed a theory of relativity that correctly predicted the action of forces on objects with increasing momenta near the speed of light and also provided insight into the forces produced by gravitation and inertia. With modern insights into quantum mechanics and technology that can accelerate particles close to the speed of light, particle physics has devised a Standard Model to describe forces between particles smaller than atoms. The Standard Model predicts that exchanged particles called gauge bosons are the fundamental means by which forces are emitted and absorbed. Only four main interactions are known: in order of decreasing strength, they are: strong, electromagnetic, weak, and gravitational.: 2–10 : 79 High-energy particle physics observations made during the 1970s and 1980s confirmed that the weak and electromagnetic forces are expressions of a more fundamental electroweak interaction.
== Pre-Newtonian concepts ==
Since antiquity the concept of force has been recognized as integral to the functioning of each of the simple machines. The mechanical advantage given by a simple machine allowed for less force to be used in exchange for that force acting over a greater distance for the same amount of work. Analysis of the characteristics of forces ultimately culminated in the work of Archimedes who was especially famous for formulating a treatment of buoyant forces inherent in fluids.
Aristotle provided a philosophical discussion of the concept of a force as an integral part of Aristotelian cosmology. In Aristotle's view, the terrestrial sphere contained four elements that come to rest at different "natural places" therein. Aristotle believed that motionless objects on Earth, those composed mostly of the elements earth and water, were in their natural place when on the ground, and that they stay that way if left alone. He distinguished between the innate tendency of objects to find their "natural place" (e.g., for heavy bodies to fall), which led to "natural motion", and unnatural or forced motion, which required continued application of a force. This theory, based on the everyday experience of how objects move, such as the constant application of a force needed to keep a cart moving, had conceptual trouble accounting for the behavior of projectiles, such as the flight of arrows. An archer causes the arrow to move at the start of the flight, and it then sails through the air even though no discernible efficient cause acts upon it. Aristotle was aware of this problem and proposed that the air displaced through the projectile's path carries the projectile to its target. This explanation requires a continuous medium such as air to sustain the motion.
Though Aristotelian physics was criticized as early as the 6th century, its shortcomings would not be corrected until the 17th century work of Galileo Galilei, who was influenced by the late medieval idea that objects in forced motion carried an innate force of impetus. Galileo constructed an experiment in which stones and cannonballs were both rolled down an incline to disprove the Aristotelian theory of motion. He showed that the bodies were accelerated by gravity to an extent that was independent of their mass and argued that objects retain their velocity unless acted on by a force, for example friction. Galileo's idea that force is needed to change motion rather than to sustain it, further improved upon by Isaac Beeckman, René Descartes, and Pierre Gassendi, became a key principle of Newtonian physics.
In the early 17th century, before Newton's Principia, the term "force" (Latin: vis) was applied to many physical and non-physical phenomena, e.g., for an acceleration of a point. The product of a point mass and the square of its velocity was named vis viva (live force) by Leibniz. The modern concept of force corresponds to Newton's vis motrix (accelerating force).
== Newtonian mechanics ==
Sir Isaac Newton described the motion of all objects using the concepts of inertia and force. In 1687, Newton published his magnum opus, Philosophiæ Naturalis Principia Mathematica. In this work Newton set out three laws of motion that have dominated the way forces are described in physics to this day. The precise ways in which Newton's laws are expressed have evolved in step with new mathematical approaches.
=== First law ===
Newton's first law of motion states that the natural behavior of an object at rest is to continue being at rest, and the natural behavior of an object moving at constant speed in a straight line is to continue moving at that constant speed along that straight line. The latter follows from the former because of the principle that the laws of physics are the same for all inertial observers, i.e., all observers who do not feel themselves to be in motion. An observer moving in tandem with an object will see it as being at rest. So, its natural behavior will be to remain at rest with respect to that observer, which means that an observer who sees it moving at constant speed in a straight line will see it continuing to do so.: 1–7
=== Second law ===
According to the first law, motion at constant speed in a straight line does not need a cause. It is change in motion that requires a cause, and Newton's second law gives the quantitative relationship between force and change of motion.
Newton's second law states that the net force acting upon an object is equal to the rate at which its momentum changes with time. If the mass of the object is constant, this law implies that the acceleration of an object is directly proportional to the net force acting on the object, is in the direction of the net force, and is inversely proportional to the mass of the object.: 204–207
A modern statement of Newton's second law is a vector equation:
F
=
d
p
d
t
,
{\displaystyle \mathbf {F} ={\frac {\mathrm {d} \mathbf {p} }{\mathrm {d} t}},}
where
p
{\displaystyle \mathbf {p} }
is the momentum of the system, and
F
{\displaystyle \mathbf {F} }
is the net (vector sum) force.: 399 If a body is in equilibrium, there is zero net force by definition (balanced forces may be present nevertheless). In contrast, the second law states that if there is an unbalanced force acting on an object it will result in the object's momentum changing over time.
In common engineering applications the mass in a system remains constant allowing as simple algebraic form for the second law. By the definition of momentum,
F
=
d
p
d
t
=
d
(
m
v
)
d
t
,
{\displaystyle \mathbf {F} ={\frac {\mathrm {d} \mathbf {p} }{\mathrm {d} t}}={\frac {\mathrm {d} \left(m\mathbf {v} \right)}{\mathrm {d} t}},}
where m is the mass and
v
{\displaystyle \mathbf {v} }
is the velocity.: 9-1,9-2 If Newton's second law is applied to a system of constant mass, m may be moved outside the derivative operator. The equation then becomes
F
=
m
d
v
d
t
.
{\displaystyle \mathbf {F} =m{\frac {\mathrm {d} \mathbf {v} }{\mathrm {d} t}}.}
By substituting the definition of acceleration, the algebraic version of Newton's second law is derived:
F
=
m
a
.
{\displaystyle \mathbf {F} =m\mathbf {a} .}
=== Third law ===
Whenever one body exerts a force on another, the latter simultaneously exerts an equal and opposite force on the first. In vector form, if
F
1
,
2
{\displaystyle \mathbf {F} _{1,2}}
is the force of body 1 on body 2 and
F
2
,
1
{\displaystyle \mathbf {F} _{2,1}}
that of body 2 on body 1, then
F
1
,
2
=
−
F
2
,
1
.
{\displaystyle \mathbf {F} _{1,2}=-\mathbf {F} _{2,1}.}
This law is sometimes referred to as the action-reaction law, with
F
1
,
2
{\displaystyle \mathbf {F} _{1,2}}
called the action and
−
F
2
,
1
{\displaystyle -\mathbf {F} _{2,1}}
the reaction.
Newton's third law is a result of applying symmetry to situations where forces can be attributed to the presence of different objects. The third law means that all forces are interactions between different bodies. and thus that there is no such thing as a unidirectional force or a force that acts on only one body.
In a system composed of object 1 and object 2, the net force on the system due to their mutual interactions is zero:
F
1
,
2
+
F
2
,
1
=
0.
{\displaystyle \mathbf {F} _{1,2}+\mathbf {F} _{2,1}=0.}
More generally, in a closed system of particles, all internal forces are balanced. The particles may accelerate with respect to each other but the center of mass of the system will not accelerate. If an external force acts on the system, it will make the center of mass accelerate in proportion to the magnitude of the external force divided by the mass of the system.: 19-1
Combining Newton's second and third laws, it is possible to show that the linear momentum of a system is conserved in any closed system. In a system of two particles, if
p
1
{\displaystyle \mathbf {p} _{1}}
is the momentum of object 1 and
p
2
{\displaystyle \mathbf {p} _{2}}
the momentum of object 2, then
d
p
1
d
t
+
d
p
2
d
t
=
F
1
,
2
+
F
2
,
1
=
0.
{\displaystyle {\frac {\mathrm {d} \mathbf {p} _{1}}{\mathrm {d} t}}+{\frac {\mathrm {d} \mathbf {p} _{2}}{\mathrm {d} t}}=\mathbf {F} _{1,2}+\mathbf {F} _{2,1}=0.}
Using similar arguments, this can be generalized to a system with an arbitrary number of particles. In general, as long as all forces are due to the interaction of objects with mass, it is possible to define a system such that net momentum is never lost nor gained.: ch.12
=== Defining "force" ===
Some textbooks use Newton's second law as a definition of force. However, for the equation
F
=
m
a
{\displaystyle \mathbf {F} =m\mathbf {a} }
for a constant mass
m
{\displaystyle m}
to then have any predictive content, it must be combined with further information.: 12-1 Moreover, inferring that a force is present because a body is accelerating is only valid in an inertial frame of reference.: 59 The question of which aspects of Newton's laws to take as definitions and which to regard as holding physical content has been answered in various ways,: vii which ultimately do not affect how the theory is used in practice. Notable physicists, philosophers and mathematicians who have sought a more explicit definition of the concept of force include Ernst Mach and Walter Noll.
== Combining forces ==
Forces act in a particular direction and have sizes dependent upon how strong the push or pull is. Because of these characteristics, forces are classified as "vector quantities". This means that forces follow a different set of mathematical rules than physical quantities that do not have direction (denoted scalar quantities). For example, when determining what happens when two forces act on the same object, it is necessary to know both the magnitude and the direction of both forces to calculate the result. If both of these pieces of information are not known for each force, the situation is ambiguous.: 197
Historically, forces were first quantitatively investigated in conditions of static equilibrium where several forces canceled each other out. Such experiments demonstrate the crucial properties that forces are additive vector quantities: they have magnitude and direction. When two forces act on a point particle, the resulting force, the resultant (also called the net force), can be determined by following the parallelogram rule of vector addition: the addition of two vectors represented by sides of a parallelogram, gives an equivalent resultant vector that is equal in magnitude and direction to the transversal of the parallelogram. The magnitude of the resultant varies from the difference of the magnitudes of the two forces to their sum, depending on the angle between their lines of action.: ch.12
Free-body diagrams can be used as a convenient way to keep track of forces acting on a system. Ideally, these diagrams are drawn with the angles and relative magnitudes of the force vectors preserved so that graphical vector addition can be done to determine the net force.
As well as being added, forces can also be resolved into independent components at right angles to each other. A horizontal force pointing northeast can therefore be split into two forces, one pointing north, and one pointing east. Summing these component forces using vector addition yields the original force. Resolving force vectors into components of a set of basis vectors is often a more mathematically clean way to describe forces than using magnitudes and directions. This is because, for orthogonal components, the components of the vector sum are uniquely determined by the scalar addition of the components of the individual vectors. Orthogonal components are independent of each other because forces acting at ninety degrees to each other have no effect on the magnitude or direction of the other. Choosing a set of orthogonal basis vectors is often done by considering what set of basis vectors will make the mathematics most convenient. Choosing a basis vector that is in the same direction as one of the forces is desirable, since that force would then have only one non-zero component. Orthogonal force vectors can be three-dimensional with the third component being at right angles to the other two.: ch.12
=== Equilibrium ===
When all the forces that act upon an object are balanced, then the object is said to be in a state of equilibrium.: 566 Hence, equilibrium occurs when the resultant force acting on a point particle is zero (that is, the vector sum of all forces is zero). When dealing with an extended body, it is also necessary that the net torque be zero. A body is in static equilibrium with respect to a frame of reference if it at rest and not accelerating, whereas a body in dynamic equilibrium is moving at a constant speed in a straight line, i.e., moving but not accelerating. What one observer sees as static equilibrium, another can see as dynamic equilibrium and vice versa.: 566
==== Static ====
Static equilibrium was understood well before the invention of classical mechanics. Objects that are not accelerating have zero net force acting on them.
The simplest case of static equilibrium occurs when two forces are equal in magnitude but opposite in direction. For example, an object on a level surface is pulled (attracted) downward toward the center of the Earth by the force of gravity. At the same time, a force is applied by the surface that resists the downward force with equal upward force (called a normal force). The situation produces zero net force and hence no acceleration.
Pushing against an object that rests on a frictional surface can result in a situation where the object does not move because the applied force is opposed by static friction, generated between the object and the table surface. For a situation with no movement, the static friction force exactly balances the applied force resulting in no acceleration. The static friction increases or decreases in response to the applied force up to an upper limit determined by the characteristics of the contact between the surface and the object.
A static equilibrium between two forces is the most usual way of measuring forces, using simple devices such as weighing scales and spring balances. For example, an object suspended on a vertical spring scale experiences the force of gravity acting on the object balanced by a force applied by the "spring reaction force", which equals the object's weight. Using such tools, some quantitative force laws were discovered: that the force of gravity is proportional to volume for objects of constant density (widely exploited for millennia to define standard weights); Archimedes' principle for buoyancy; Archimedes' analysis of the lever; Boyle's law for gas pressure; and Hooke's law for springs. These were all formulated and experimentally verified before Isaac Newton expounded his three laws of motion.: ch.12
==== Dynamic ====
Dynamic equilibrium was first described by Galileo who noticed that certain assumptions of Aristotelian physics were contradicted by observations and logic. Galileo realized that simple velocity addition demands that the concept of an "absolute rest frame" did not exist. Galileo concluded that motion in a constant velocity was completely equivalent to rest. This was contrary to Aristotle's notion of a "natural state" of rest that objects with mass naturally approached. Simple experiments showed that Galileo's understanding of the equivalence of constant velocity and rest were correct. For example, if a mariner dropped a cannonball from the crow's nest of a ship moving at a constant velocity, Aristotelian physics would have the cannonball fall straight down while the ship moved beneath it. Thus, in an Aristotelian universe, the falling cannonball would land behind the foot of the mast of a moving ship. When this experiment is actually conducted, the cannonball always falls at the foot of the mast, as if the cannonball knows to travel with the ship despite being separated from it. Since there is no forward horizontal force being applied on the cannonball as it falls, the only conclusion left is that the cannonball continues to move with the same velocity as the boat as it falls. Thus, no force is required to keep the cannonball moving at the constant forward velocity.
Moreover, any object traveling at a constant velocity must be subject to zero net force (resultant force). This is the definition of dynamic equilibrium: when all the forces on an object balance but it still moves at a constant velocity. A simple case of dynamic equilibrium occurs in constant velocity motion across a surface with kinetic friction. In such a situation, a force is applied in the direction of motion while the kinetic friction force exactly opposes the applied force. This results in zero net force, but since the object started with a non-zero velocity, it continues to move with a non-zero velocity. Aristotle misinterpreted this motion as being caused by the applied force. When kinetic friction is taken into consideration it is clear that there is no net force causing constant velocity motion.: ch.12
== Examples of forces in classical mechanics ==
Some forces are consequences of the fundamental ones. In such situations, idealized models can be used to gain physical insight. For example, each solid object is considered a rigid body.
=== Gravitational force or Gravity ===
What we now call gravity was not identified as a universal force until the work of Isaac Newton. Before Newton, the tendency for objects to fall towards the Earth was not understood to be related to the motions of celestial objects. Galileo was instrumental in describing the characteristics of falling objects by determining that the acceleration of every object in free-fall was constant and independent of the mass of the object. Today, this acceleration due to gravity towards the surface of the Earth is usually designated as
g
{\displaystyle \mathbf {g} }
and has a magnitude of about 9.81 meters per second squared (this measurement is taken from sea level and may vary depending on location), and points toward the center of the Earth. This observation means that the force of gravity on an object at the Earth's surface is directly proportional to the object's mass. Thus an object that has a mass of
m
{\displaystyle m}
will experience a force:
F
=
m
g
.
{\displaystyle \mathbf {F} =m\mathbf {g} .}
For an object in free-fall, this force is unopposed and the net force on the object is its weight. For objects not in free-fall, the force of gravity is opposed by the reaction forces applied by their supports. For example, a person standing on the ground experiences zero net force, since a normal force (a reaction force) is exerted by the ground upward on the person that counterbalances his weight that is directed downward.: ch.12
Newton's contribution to gravitational theory was to unify the motions of heavenly bodies, which Aristotle had assumed were in a natural state of constant motion, with falling motion observed on the Earth. He proposed a law of gravity that could account for the celestial motions that had been described earlier using Kepler's laws of planetary motion.
Newton came to realize that the effects of gravity might be observed in different ways at larger distances. In particular, Newton determined that the acceleration of the Moon around the Earth could be ascribed to the same force of gravity if the acceleration due to gravity decreased as an inverse square law. Further, Newton realized that the acceleration of a body due to gravity is proportional to the mass of the other attracting body. Combining these ideas gives a formula that relates the mass (
m
⊕
{\displaystyle m_{\oplus }}
) and the radius (
R
⊕
{\displaystyle R_{\oplus }}
) of the Earth to the gravitational acceleration:
g
=
−
G
m
⊕
R
⊕
2
r
^
,
{\displaystyle \mathbf {g} =-{\frac {Gm_{\oplus }}{{R_{\oplus }}^{2}}}{\hat {\mathbf {r} }},}
where the vector direction is given by
r
^
{\displaystyle {\hat {\mathbf {r} }}}
, is the unit vector directed outward from the center of the Earth.
In this equation, a dimensional constant
G
{\displaystyle G}
is used to describe the relative strength of gravity. This constant has come to be known as the Newtonian constant of gravitation, though its value was unknown in Newton's lifetime. Not until 1798 was Henry Cavendish able to make the first measurement of
G
{\displaystyle G}
using a torsion balance; this was widely reported in the press as a measurement of the mass of the Earth since knowing
G
{\displaystyle G}
could allow one to solve for the Earth's mass given the above equation. Newton realized that since all celestial bodies followed the same laws of motion, his law of gravity had to be universal. Succinctly stated, Newton's law of gravitation states that the force on a spherical object of mass
m
1
{\displaystyle m_{1}}
due to the gravitational pull of mass
m
2
{\displaystyle m_{2}}
is
F
=
−
G
m
1
m
2
r
2
r
^
,
{\displaystyle \mathbf {F} =-{\frac {Gm_{1}m_{2}}{r^{2}}}{\hat {\mathbf {r} }},}
where
r
{\displaystyle r}
is the distance between the two objects' centers of mass and
r
^
{\displaystyle {\hat {\mathbf {r} }}}
is the unit vector pointed in the direction away from the center of the first object toward the center of the second object.
This formula was powerful enough to stand as the basis for all subsequent descriptions of motion within the Solar System until the 20th century. During that time, sophisticated methods of perturbation analysis were invented to calculate the deviations of orbits due to the influence of multiple bodies on a planet, moon, comet, or asteroid. The formalism was exact enough to allow mathematicians to predict the existence of the planet Neptune before it was observed.
=== Electromagnetic ===
The electrostatic force was first described in 1784 by Coulomb as a force that existed intrinsically between two charges.: 519 The properties of the electrostatic force were that it varied as an inverse square law directed in the radial direction, was both attractive and repulsive (there was intrinsic polarity), was independent of the mass of the charged objects, and followed the superposition principle. Coulomb's law unifies all these observations into one succinct statement.
Subsequent mathematicians and physicists found the construct of the electric field to be useful for determining the electrostatic force on an electric charge at any point in space. The electric field was based on using a hypothetical "test charge" anywhere in space and then using Coulomb's Law to determine the electrostatic force.: 4-6–4-8 Thus the electric field anywhere in space is defined as
E
=
F
q
,
{\displaystyle \mathbf {E} ={\mathbf {F} \over {q}},}
where
q
{\displaystyle q}
is the magnitude of the hypothetical test charge. Similarly, the idea of the magnetic field was introduced to express how magnets can influence one another at a distance. The Lorentz force law gives the force upon a body with charge
q
{\displaystyle q}
due to electric and magnetic fields:
F
=
q
(
E
+
v
×
B
)
,
{\displaystyle \mathbf {F} =q\left(\mathbf {E} +\mathbf {v} \times \mathbf {B} \right),}
where
F
{\displaystyle \mathbf {F} }
is the electromagnetic force,
E
{\displaystyle \mathbf {E} }
is the electric field at the body's location,
B
{\displaystyle \mathbf {B} }
is the magnetic field, and
v
{\displaystyle \mathbf {v} }
is the velocity of the particle. The magnetic contribution to the Lorentz force is the cross product of the velocity vector with the magnetic field.: 482
The origin of electric and magnetic fields would not be fully explained until 1864 when James Clerk Maxwell unified a number of earlier theories into a set of 20 scalar equations, which were later reformulated into 4 vector equations by Oliver Heaviside and Josiah Willard Gibbs. These "Maxwell's equations" fully described the sources of the fields as being stationary and moving charges, and the interactions of the fields themselves. This led Maxwell to discover that electric and magnetic fields could be "self-generating" through a wave that traveled at a speed that he calculated to be the speed of light. This insight united the nascent fields of electromagnetic theory with optics and led directly to a complete description of the electromagnetic spectrum.
=== Normal ===
When objects are in contact, the force directly between them is called the normal force, the component of the total force in the system exerted normal to the interface between the objects.: 264 The normal force is closely related to Newton's third law. The normal force, for example, is responsible for the structural integrity of tables and floors as well as being the force that responds whenever an external force pushes on a solid object. An example of the normal force in action is the impact force on an object crashing into an immobile surface.: ch.12
=== Friction ===
Friction is a force that opposes relative motion of two bodies. At the macroscopic scale, the frictional force is directly related to the normal force at the point of contact. There are two broad classifications of frictional forces: static friction and kinetic friction.: 267
The static friction force (
F
s
f
{\displaystyle \mathbf {F} _{\mathrm {sf} }}
) will exactly oppose forces applied to an object parallel to a surface up to the limit specified by the coefficient of static friction (
μ
s
f
{\displaystyle \mu _{\mathrm {sf} }}
) multiplied by the normal force (
F
N
{\displaystyle \mathbf {F} _{\text{N}}}
). In other words, the magnitude of the static friction force satisfies the inequality:
0
≤
F
s
f
≤
μ
s
f
F
N
.
{\displaystyle 0\leq \mathbf {F} _{\mathrm {sf} }\leq \mu _{\mathrm {sf} }\mathbf {F} _{\mathrm {N} }.}
The kinetic friction force (
F
k
f
{\displaystyle F_{\mathrm {kf} }}
) is typically independent of both the forces applied and the movement of the object. Thus, the magnitude of the force equals:
F
k
f
=
μ
k
f
F
N
,
{\displaystyle \mathbf {F} _{\mathrm {kf} }=\mu _{\mathrm {kf} }\mathbf {F} _{\mathrm {N} },}
where
μ
k
f
{\displaystyle \mu _{\mathrm {kf} }}
is the coefficient of kinetic friction. The coefficient of kinetic friction is normally less than the coefficient of static friction.: 267–271
=== Tension ===
Tension forces can be modeled using ideal strings that are massless, frictionless, unbreakable, and do not stretch. They can be combined with ideal pulleys, which allow ideal strings to switch physical direction. Ideal strings transmit tension forces instantaneously in action–reaction pairs so that if two objects are connected by an ideal string, any force directed along the string by the first object is accompanied by a force directed along the string in the opposite direction by the second object. By connecting the same string multiple times to the same object through the use of a configuration that uses movable pulleys, the tension force on a load can be multiplied. For every string that acts on a load, another factor of the tension force in the string acts on the load. Such machines allow a mechanical advantage for a corresponding increase in the length of displaced string needed to move the load. These tandem effects result ultimately in the conservation of mechanical energy since the work done on the load is the same no matter how complicated the machine.: ch.12
=== Spring ===
A simple elastic force acts to return a spring to its natural length. An ideal spring is taken to be massless, frictionless, unbreakable, and infinitely stretchable. Such springs exert forces that push when contracted, or pull when extended, in proportion to the displacement of the spring from its equilibrium position. This linear relationship was described by Robert Hooke in 1676, for whom Hooke's law is named. If
Δ
x
{\displaystyle \Delta x}
is the displacement, the force exerted by an ideal spring equals:
F
=
−
k
Δ
x
,
{\displaystyle \mathbf {F} =-k\Delta \mathbf {x} ,}
where
k
{\displaystyle k}
is the spring constant (or force constant), which is particular to the spring. The minus sign accounts for the tendency of the force to act in opposition to the applied load.: ch.12
=== Centripetal ===
For an object in uniform circular motion, the net force acting on the object equals:
F
=
−
m
v
2
r
r
^
,
{\displaystyle \mathbf {F} =-{\frac {mv^{2}}{r}}{\hat {\mathbf {r} }},}
where
m
{\displaystyle m}
is the mass of the object,
v
{\displaystyle v}
is the velocity of the object and
r
{\displaystyle r}
is the distance to the center of the circular path and
r
^
{\displaystyle {\hat {\mathbf {r} }}}
is the unit vector pointing in the radial direction outwards from the center. This means that the net force felt by the object is always directed toward the center of the curving path. Such forces act perpendicular to the velocity vector associated with the motion of an object, and therefore do not change the speed of the object (magnitude of the velocity), but only the direction of the velocity vector. More generally, the net force that accelerates an object can be resolved into a component that is perpendicular to the path, and one that is tangential to the path. This yields both the tangential force, which accelerates the object by either slowing it down or speeding it up, and the radial (centripetal) force, which changes its direction.: ch.12
=== Continuum mechanics ===
Newton's laws and Newtonian mechanics in general were first developed to describe how forces affect idealized point particles rather than three-dimensional objects. In real life, matter has extended structure and forces that act on one part of an object might affect other parts of an object. For situations where lattice holding together the atoms in an object is able to flow, contract, expand, or otherwise change shape, the theories of continuum mechanics describe the way forces affect the material. For example, in extended fluids, differences in pressure result in forces being directed along the pressure gradients as follows:
F
V
=
−
∇
P
,
{\displaystyle {\frac {\mathbf {F} }{V}}=-\mathbf {\nabla } P,}
where
V
{\displaystyle V}
is the volume of the object in the fluid and
P
{\displaystyle P}
is the scalar function that describes the pressure at all locations in space. Pressure gradients and differentials result in the buoyant force for fluids suspended in gravitational fields, winds in atmospheric science, and the lift associated with aerodynamics and flight.: ch.12
A specific instance of such a force that is associated with dynamic pressure is fluid resistance: a body force that resists the motion of an object through a fluid due to viscosity. For so-called "Stokes' drag" the force is approximately proportional to the velocity, but opposite in direction:
F
d
=
−
b
v
,
{\displaystyle \mathbf {F} _{\mathrm {d} }=-b\mathbf {v} ,}
where:
b
{\displaystyle b}
is a constant that depends on the properties of the fluid and the dimensions of the object (usually the cross-sectional area), and
v
{\displaystyle \mathbf {v} }
is the velocity of the object.: ch.12
More formally, forces in continuum mechanics are fully described by a stress tensor with terms that are roughly defined as
σ
=
F
A
,
{\displaystyle \sigma ={\frac {F}{A}},}
where
A
{\displaystyle A}
is the relevant cross-sectional area for the volume for which the stress tensor is being calculated. This formalism includes pressure terms associated with forces that act normal to the cross-sectional area (the matrix diagonals of the tensor) as well as shear terms associated with forces that act parallel to the cross-sectional area (the off-diagonal elements). The stress tensor accounts for forces that cause all strains (deformations) including also tensile stresses and compressions.: 133–134 : 38-1–38-11
=== Fictitious ===
There are forces that are frame dependent, meaning that they appear due to the adoption of non-Newtonian (that is, non-inertial) reference frames. Such forces include the centrifugal force and the Coriolis force. These forces are considered fictitious because they do not exist in frames of reference that are not accelerating.: ch.12 Because these forces are not genuine they are also referred to as "pseudo forces".: 12-11
In general relativity, gravity becomes a fictitious force that arises in situations where spacetime deviates from a flat geometry.
== Concepts derived from force ==
=== Rotation and torque ===
Forces that cause extended objects to rotate are associated with torques. Mathematically, the torque of a force
F
{\displaystyle \mathbf {F} }
is defined relative to an arbitrary reference point as the cross product:
τ
=
r
×
F
,
{\displaystyle {\boldsymbol {\tau }}=\mathbf {r} \times \mathbf {F} ,}
where
r
{\displaystyle \mathbf {r} }
is the position vector of the force application point relative to the reference point.: 497
Torque is the rotation equivalent of force in the same way that angle is the rotational equivalent for position, angular velocity for velocity, and angular momentum for momentum. As a consequence of Newton's first law of motion, there exists rotational inertia that ensures that all bodies maintain their angular momentum unless acted upon by an unbalanced torque. Likewise, Newton's second law of motion can be used to derive an analogous equation for the instantaneous angular acceleration of the rigid body:
τ
=
I
α
,
{\displaystyle {\boldsymbol {\tau }}=I{\boldsymbol {\alpha }},}
where
I
{\displaystyle I}
is the moment of inertia of the body
α
{\displaystyle {\boldsymbol {\alpha }}}
is the angular acceleration of the body.: 502
This provides a definition for the moment of inertia, which is the rotational equivalent for mass. In more advanced treatments of mechanics, where the rotation over a time interval is described, the moment of inertia must be substituted by the tensor that, when properly analyzed, fully determines the characteristics of rotations including precession and nutation.: 96–113
Equivalently, the differential form of Newton's second law provides an alternative definition of torque:
τ
=
d
L
d
t
,
{\displaystyle {\boldsymbol {\tau }}={\frac {\mathrm {d} \mathbf {L} }{\mathrm {dt} }},}
where
L
{\displaystyle \mathbf {L} }
is the angular momentum of the particle.
Newton's third law of motion requires that all objects exerting torques themselves experience equal and opposite torques, and therefore also directly implies the conservation of angular momentum for closed systems that experience rotations and revolutions through the action of internal torques.
=== Yank ===
The yank is defined as the rate of change of force: 131
Y
=
d
F
d
t
{\displaystyle \mathbf {Y} ={\frac {\mathrm {d} \mathbf {F} }{\mathrm {d} t}}}
The term is used in biomechanical analysis, athletic assessment and robotic control. The second ("tug"), third ("snatch"), fourth ("shake"), and higher derivatives are rarely used.
=== Kinematic integrals ===
Forces can be used to define a number of physical concepts by integrating with respect to kinematic variables. For example, integrating with respect to time gives the definition of impulse:
J
=
∫
t
1
t
2
F
d
t
,
{\displaystyle \mathbf {J} =\int _{t_{1}}^{t_{2}}{\mathbf {F} \,\mathrm {d} t},}
which by Newton's second law must be equivalent to the change in momentum (yielding the Impulse momentum theorem).
Similarly, integrating with respect to position gives a definition for the work done by a force:: 13-3
W
=
∫
x
1
x
2
F
⋅
d
x
,
{\displaystyle W=\int _{\mathbf {x} _{1}}^{\mathbf {x} _{2}}{\mathbf {F} \cdot {\mathrm {d} \mathbf {x} }},}
which is equivalent to changes in kinetic energy (yielding the work energy theorem).: 13-3
Power P is the rate of change dW/dt of the work W, as the trajectory is extended by a position change
d
x
{\displaystyle d\mathbf {x} }
in a time interval dt:: 13-2
d
W
=
d
W
d
x
⋅
d
x
=
F
⋅
d
x
,
{\displaystyle \mathrm {d} W={\frac {\mathrm {d} W}{\mathrm {d} \mathbf {x} }}\cdot \mathrm {d} \mathbf {x} =\mathbf {F} \cdot \mathrm {d} \mathbf {x} ,}
so
P
=
d
W
d
t
=
d
W
d
x
⋅
d
x
d
t
=
F
⋅
v
,
{\displaystyle P={\frac {\mathrm {d} W}{\mathrm {d} t}}={\frac {\mathrm {d} W}{\mathrm {d} \mathbf {x} }}\cdot {\frac {\mathrm {d} \mathbf {x} }{\mathrm {d} t}}=\mathbf {F} \cdot \mathbf {v} ,}
with
v
=
d
x
/
d
t
{\displaystyle \mathbf {v} =\mathrm {d} \mathbf {x} /\mathrm {d} t}
the velocity.
=== Potential energy ===
Instead of a force, often the mathematically related concept of a potential energy field is used. For instance, the gravitational force acting upon an object can be seen as the action of the gravitational field that is present at the object's location. Restating mathematically the definition of energy (via the definition of work), a potential scalar field
U
(
r
)
{\displaystyle U(\mathbf {r} )}
is defined as that field whose gradient is equal and opposite to the force produced at every point:
F
=
−
∇
U
.
{\displaystyle \mathbf {F} =-\mathbf {\nabla } U.}
Forces can be classified as conservative or nonconservative. Conservative forces are equivalent to the gradient of a potential while nonconservative forces are not.: ch.12
=== Conservation ===
A conservative force that acts on a closed system has an associated mechanical work that allows energy to convert only between kinetic or potential forms. This means that for a closed system, the net mechanical energy is conserved whenever a conservative force acts on the system. The force, therefore, is related directly to the difference in potential energy between two different locations in space, and can be considered to be an artifact of the potential field in the same way that the direction and amount of a flow of water can be considered to be an artifact of the contour map of the elevation of an area.: ch.12
Conservative forces include gravity, the electromagnetic force, and the spring force. Each of these forces has models that are dependent on a position often given as a radial vector
r
{\displaystyle \mathbf {r} }
emanating from spherically symmetric potentials. Examples of this follow:
For gravity:
F
g
=
−
G
m
1
m
2
r
2
r
^
,
{\displaystyle \mathbf {F} _{\text{g}}=-{\frac {Gm_{1}m_{2}}{r^{2}}}{\hat {\mathbf {r} }},}
where
G
{\displaystyle G}
is the gravitational constant, and
m
n
{\displaystyle m_{n}}
is the mass of object n.
For electrostatic forces:
F
e
=
q
1
q
2
4
π
ε
0
r
2
r
^
,
{\displaystyle \mathbf {F} _{\text{e}}={\frac {q_{1}q_{2}}{4\pi \varepsilon _{0}r^{2}}}{\hat {\mathbf {r} }},}
where
ε
0
{\displaystyle \varepsilon _{0}}
is electric permittivity of free space, and
q
n
{\displaystyle q_{n}}
is the electric charge of object n.
For spring forces:
F
s
=
−
k
r
r
^
,
{\displaystyle \mathbf {F} _{\text{s}}=-kr{\hat {\mathbf {r} }},}
where
k
{\displaystyle k}
is the spring constant.: ch.12
For certain physical scenarios, it is impossible to model forces as being due to a simple gradient of potentials. This is often due a macroscopic statistical average of microstates. For example, static friction is caused by the gradients of numerous electrostatic potentials between the atoms, but manifests as a force model that is independent of any macroscale position vector. Nonconservative forces other than friction include other contact forces, tension, compression, and drag. For any sufficiently detailed description, all these forces are the results of conservative ones since each of these macroscopic forces are the net results of the gradients of microscopic potentials.: ch.12
The connection between macroscopic nonconservative forces and microscopic conservative forces is described by detailed treatment with statistical mechanics. In macroscopic closed systems, nonconservative forces act to change the internal energies of the system, and are often associated with the transfer of heat. According to the Second law of thermodynamics, nonconservative forces necessarily result in energy transformations within closed systems from ordered to more random conditions as entropy increases.: ch.12
== Units ==
The SI unit of force is the newton (symbol N), which is the force required to accelerate a one kilogram mass at a rate of one meter per second squared, or kg·m·s−2.The corresponding CGS unit is the dyne, the force required to accelerate a one gram mass by one centimeter per second squared, or g·cm·s−2. A newton is thus equal to 100,000 dynes.
The gravitational foot-pound-second English unit of force is the pound-force (lbf), defined as the force exerted by gravity on a pound-mass in the standard gravitational field of 9.80665 m·s−2. The pound-force provides an alternative unit of mass: one slug is the mass that will accelerate by one foot per second squared when acted on by one pound-force. An alternative unit of force in a different foot–pound–second system, the absolute fps system, is the poundal, defined as the force required to accelerate a one-pound mass at a rate of one foot per second squared.
The pound-force has a metric counterpart, less commonly used than the newton: the kilogram-force (kgf) (sometimes kilopond), is the force exerted by standard gravity on one kilogram of mass. The kilogram-force leads to an alternate, but rarely used unit of mass: the metric slug (sometimes mug or hyl) is that mass that accelerates at 1 m·s−2 when subjected to a force of 1 kgf. The kilogram-force is not a part of the modern SI system, and is generally deprecated, sometimes used for expressing aircraft weight, jet thrust, bicycle spoke tension, torque wrench settings and engine output torque.
See also Ton-force.
== Revisions of the force concept ==
At the beginning of the 20th century, new physical ideas emerged to explain experimental results in astronomical and submicroscopic realms. As discussed below, relativity alters the definition of momentum and quantum mechanics reuses the concept of "force" in microscopic contexts where Newton's laws do not apply directly.
=== Special theory of relativity ===
In the special theory of relativity, mass and energy are equivalent (as can be seen by calculating the work required to accelerate an object). When an object's velocity increases, so does its energy and hence its mass equivalent (inertia). It thus requires more force to accelerate it the same amount than it did at a lower velocity. Newton's second law,
F
=
d
p
d
t
,
{\displaystyle \mathbf {F} ={\frac {\mathrm {d} \mathbf {p} }{\mathrm {d} t}},}
remains valid because it is a mathematical definition.: 855–876 But for momentum to be conserved at relativistic relative velocity,
v
{\displaystyle v}
, momentum must be redefined as:
p
=
m
0
v
1
−
v
2
/
c
2
,
{\displaystyle \mathbf {p} ={\frac {m_{0}\mathbf {v} }{\sqrt {1-v^{2}/c^{2}}}},}
where
m
0
{\displaystyle m_{0}}
is the rest mass and
c
{\displaystyle c}
the speed of light.
The expression relating force and acceleration for a particle with constant non-zero rest mass
m
{\displaystyle m}
moving in the
x
{\displaystyle x}
direction at velocity
v
{\displaystyle v}
is:: 216
F
=
(
γ
3
m
a
x
,
γ
m
a
y
,
γ
m
a
z
)
,
{\displaystyle \mathbf {F} =\left(\gamma ^{3}ma_{x},\gamma ma_{y},\gamma ma_{z}\right),}
where
γ
=
1
1
−
v
2
/
c
2
.
{\displaystyle \gamma ={\frac {1}{\sqrt {1-v^{2}/c^{2}}}}.}
is called the Lorentz factor. The Lorentz factor increases steeply as the relative velocity approaches the speed of light. Consequently, the greater and greater force must be applied to produce the same acceleration at extreme velocity. The relative velocity cannot reach
c
{\displaystyle c}
.: 26 : §15–8
If
v
{\displaystyle v}
is very small compared to
c
{\displaystyle c}
, then
γ
{\displaystyle \gamma }
is very close to 1 and
F
=
m
a
{\displaystyle \mathbf {F} =m\mathbf {a} }
is a close approximation. Even for use in relativity, one can restore the form of
F
μ
=
m
A
μ
{\displaystyle F^{\mu }=mA^{\mu }}
through the use of four-vectors. This relation is correct in relativity when
F
μ
{\displaystyle F^{\mu }}
is the four-force,
m
{\displaystyle m}
is the invariant mass, and
A
μ
{\displaystyle A^{\mu }}
is the four-acceleration.
The general theory of relativity incorporates a more radical departure from the Newtonian way of thinking about force, specifically gravitational force. This reimagining of the nature of gravity is described more fully below.
=== Quantum mechanics ===
Quantum mechanics is a theory of physics originally developed in order to understand microscopic phenomena: behavior at the scale of molecules, atoms or subatomic particles. Generally and loosely speaking, the smaller a system is, the more an adequate mathematical model will require understanding quantum effects. The conceptual underpinning of quantum physics is different from that of classical physics. Instead of thinking about quantities like position, momentum, and energy as properties that an object has, one considers what result might appear when a measurement of a chosen type is performed. Quantum mechanics allows the physicist to calculate the probability that a chosen measurement will elicit a particular result. The expectation value for a measurement is the average of the possible results it might yield, weighted by their probabilities of occurrence.
In quantum mechanics, interactions are typically described in terms of energy rather than force. The Ehrenfest theorem provides a connection between quantum expectation values and the classical concept of force, a connection that is necessarily inexact, as quantum physics is fundamentally different from classical. In quantum physics, the Born rule is used to calculate the expectation values of a position measurement or a momentum measurement. These expectation values will generally change over time; that is, depending on the time at which (for example) a position measurement is performed, the probabilities for its different possible outcomes will vary. The Ehrenfest theorem says, roughly speaking, that the equations describing how these expectation values change over time have a form reminiscent of Newton's second law, with a force defined as the negative derivative of the potential energy. However, the more pronounced quantum effects are in a given situation, the more difficult it is to derive meaningful conclusions from this resemblance.
Quantum mechanics also introduces two new constraints that interact with forces at the submicroscopic scale and which are especially important for atoms. Despite the strong attraction of the nucleus, the uncertainty principle limits the minimum extent of an electron probability distribution and the Pauli exclusion principle prevents electrons from sharing the same probability distribution. This gives rise to an emergent pressure known as degeneracy pressure. The dynamic equilibrium between the degeneracy pressure and the attractive electromagnetic force give atoms, molecules, liquids, and solids stability.
=== Quantum field theory ===
In modern particle physics, forces and the acceleration of particles are explained as a mathematical by-product of exchange of momentum-carrying gauge bosons. With the development of quantum field theory and general relativity, it was realized that force is a redundant concept arising from conservation of momentum (4-momentum in relativity and momentum of virtual particles in quantum electrodynamics). The conservation of momentum can be directly derived from the homogeneity or symmetry of space and so is usually considered more fundamental than the concept of a force. Thus the currently known fundamental forces are considered more accurately to be "fundamental interactions".: 199–128
While sophisticated mathematical descriptions are needed to predict, in full detail, the result of such interactions, there is a conceptually simple way to describe them through the use of Feynman diagrams. In a Feynman diagram, each matter particle is represented as a straight line (see world line) traveling through time, which normally increases up or to the right in the diagram. Matter and anti-matter particles are identical except for their direction of propagation through the Feynman diagram. World lines of particles intersect at interaction vertices, and the Feynman diagram represents any force arising from an interaction as occurring at the vertex with an associated instantaneous change in the direction of the particle world lines. Gauge bosons are emitted away from the vertex as wavy lines and, in the case of virtual particle exchange, are absorbed at an adjacent vertex. The utility of Feynman diagrams is that other types of physical phenomena that are part of the general picture of fundamental interactions but are conceptually separate from forces can also be described using the same rules. For example, a Feynman diagram can describe in succinct detail how a neutron decays into an electron, proton, and antineutrino, an interaction mediated by the same gauge boson that is responsible for the weak nuclear force.
== Fundamental interactions ==
All of the known forces of the universe are classified into four fundamental interactions. The strong and the weak forces act only at very short distances, and are responsible for the interactions between subatomic particles, including nucleons and compound nuclei. The electromagnetic force acts between electric charges, and the gravitational force acts between masses. All other forces in nature derive from these four fundamental interactions operating within quantum mechanics, including the constraints introduced by the Schrödinger equation and the Pauli exclusion principle. For example, friction is a manifestation of the electromagnetic force acting between atoms of two surfaces. The forces in springs, modeled by Hooke's law, are also the result of electromagnetic forces. Centrifugal forces are acceleration forces that arise simply from the acceleration of rotating frames of reference.: 12-11 : 359
The fundamental theories for forces developed from the unification of different ideas. For example, Newton's universal theory of gravitation showed that the force responsible for objects falling near the surface of the Earth is also the force responsible for the falling of celestial bodies about the Earth (the Moon) and around the Sun (the planets). Michael Faraday and James Clerk Maxwell demonstrated that electric and magnetic forces were unified through a theory of electromagnetism. In the 20th century, the development of quantum mechanics led to a modern understanding that the first three fundamental forces (all except gravity) are manifestations of matter (fermions) interacting by exchanging virtual particles called gauge bosons. This Standard Model of particle physics assumes a similarity between the forces and led scientists to predict the unification of the weak and electromagnetic forces in electroweak theory, which was subsequently confirmed by observation.
=== Gravitational ===
Newton's law of gravitation is an example of action at a distance: one body, like the Sun, exerts an influence upon any other body, like the Earth, no matter how far apart they are. Moreover, this action at a distance is instantaneous. According to Newton's theory, the one body shifting position changes the gravitational pulls felt by all other bodies, all at the same instant of time. Albert Einstein recognized that this was inconsistent with special relativity and its prediction that influences cannot travel faster than the speed of light. So, he sought a new theory of gravitation that would be relativistically consistent. Mercury's orbit did not match that predicted by Newton's law of gravitation. Some astrophysicists predicted the existence of an undiscovered planet (Vulcan) that could explain the discrepancies. When Einstein formulated his theory of general relativity (GR) he focused on Mercury's problematic orbit and found that his theory added a correction, which could account for the discrepancy. This was the first time that Newton's theory of gravity had been shown to be inexact.
Since then, general relativity has been acknowledged as the theory that best explains gravity. In GR, gravitation is not viewed as a force, but rather, objects moving freely in gravitational fields travel under their own inertia in straight lines through curved spacetime – defined as the shortest spacetime path between two spacetime events. From the perspective of the object, all motion occurs as if there were no gravitation whatsoever. It is only when observing the motion in a global sense that the curvature of spacetime can be observed and the force is inferred from the object's curved path. Thus, the straight line path in spacetime is seen as a curved line in space, and it is called the ballistic trajectory of the object. For example, a basketball thrown from the ground moves in a parabola, as it is in a uniform gravitational field. Its spacetime trajectory is almost a straight line, slightly curved (with the radius of curvature of the order of few light-years). The time derivative of the changing momentum of the object is what we label as "gravitational force".
=== Electromagnetic ===
Maxwell's equations and the set of techniques built around them adequately describe a wide range of physics involving force in electricity and magnetism. This classical theory already includes relativity effects. Understanding quantized electromagnetic interactions between elementary particles requires quantum electrodynamics (QED). In QED, photons are fundamental exchange particles, describing all interactions relating to electromagnetism including the electromagnetic force.
=== Strong nuclear ===
There are two "nuclear forces", which today are usually described as interactions that take place in quantum theories of particle physics. The strong nuclear force is the force responsible for the structural integrity of atomic nuclei, and gains its name from its ability to overpower the electromagnetic repulsion between protons.: 940
The strong force is today understood to represent the interactions between quarks and gluons as detailed by the theory of quantum chromodynamics (QCD). The strong force is the fundamental force mediated by gluons, acting upon quarks, antiquarks, and the gluons themselves. The strong force only acts directly upon elementary particles. A residual is observed between hadrons (notably, the nucleons in atomic nuclei), known as the nuclear force. Here the strong force acts indirectly, transmitted as gluons that form part of the virtual pi and rho mesons, the classical transmitters of the nuclear force. The failure of many searches for free quarks has shown that the elementary particles affected are not directly observable. This phenomenon is called color confinement.: 232
=== Weak nuclear ===
Unique among the fundamental interactions, the weak nuclear force creates no bound states. The weak force is due to the exchange of the heavy W and Z bosons. Since the weak force is mediated by two types of bosons, it can be divided into two types of interaction or "vertices" — charged current, involving the electrically charged W+ and W− bosons, and neutral current, involving electrically neutral Z0 bosons. The most familiar effect of weak interaction is beta decay (of neutrons in atomic nuclei) and the associated radioactivity.: 951 This is a type of charged-current interaction. The word "weak" derives from the fact that the field strength is some 1013 times less than that of the strong force. Still, it is stronger than gravity over short distances. A consistent electroweak theory has also been developed, which shows that electromagnetic forces and the weak force are indistinguishable at a temperatures in excess of approximately 1015 K. Such temperatures occurred in the plasma collisions in the early moments of the Big Bang.: 201
== See also ==
Contact force – Force between two objects that are in physical contact
Force control – Force control is given by the machine
Force gauge – Instrument for measuring force
Orders of magnitude (force) – Comparison of a wide range of physical forces
Parallel force system – Situation in mechanical engineering
Rigid body – Physical object which does not deform when forces or moments are exerted on it
Specific force – Concept in physics
== References ==
== External links ==
"Classical Mechanics, Week 2: Newton's Laws". MIT OpenCourseWare. Retrieved 2023-08-09.
"Fundamentals of Physics I, Lecture 3: Newton's Laws of Motion". Open Yale Courses. Retrieved 2023-08-09. | Wikipedia/Force_vector |
AGX Dynamics (previously known as AGX Multiphysics) is a proprietary real-time physics engine developed by Algoryx Simulation AB that simulates rigid body dynamics, collision detection, dry frictional contacts, jointed systems, motors, fluids, deformable materials, hydraulics, hydrodynamics, cable systems and wires. AGX targets several domains, such as virtual reality real-time simulator applications for training and marketing; computer aided engineering and virtual prototyping; movie visual effects; and education. For education, components of AGX are used in the end-user software product Algodoo also developed and sold by Algoryx. Users of AGX simulate e.g. granular systems, construction equipment, forestry machines, mining processes and machines, biomechanics, industrial robots, ship and anchor handling processes and cranes. AGX is often integrated with 3D visualization frameworks such as OpenSceneGraph, OGRE, Unity and Unreal Engine and often also with actual hardware and control systems of the real-world version of the simulator. AGX is integrated in many 3D modeling and CAD systems, including Algoryx Momentum for ANSYS Discovery (formerly SpaceClaim).
AGX has been under active development since 2007. It usually has about 3 major releases per year.
== History ==
AGX is developed by Algoryx Simulation AB, a private limited company established in Umeå, Sweden in 2007, as a spin-off from Umeå University. In February 2011, Algoryx was selected for the list of Top-20 companies to represent Swedish Innovation, by the Swedish Institute, a Swedish government agency. In March 2011, Algoryx was ranked as one of Sweden's most promising young high tech companies by business magazine Affärsvärlden and tech news paper Ny Teknik. In May 2011, Algoryx was selected by Red Herring for the Top 100 list of the most innovative companies in Europe.
== References ==
== External links ==
Official homepage
Homepage of Algoryx Simulation AB
Homepage of physics education software Algodoo | Wikipedia/AGX_Multiphysics |
AGX Dynamics (previously known as AGX Multiphysics) is a proprietary real-time physics engine developed by Algoryx Simulation AB that simulates rigid body dynamics, collision detection, dry frictional contacts, jointed systems, motors, fluids, deformable materials, hydraulics, hydrodynamics, cable systems and wires. AGX targets several domains, such as virtual reality real-time simulator applications for training and marketing; computer aided engineering and virtual prototyping; movie visual effects; and education. For education, components of AGX are used in the end-user software product Algodoo also developed and sold by Algoryx. Users of AGX simulate e.g. granular systems, construction equipment, forestry machines, mining processes and machines, biomechanics, industrial robots, ship and anchor handling processes and cranes. AGX is often integrated with 3D visualization frameworks such as OpenSceneGraph, OGRE, Unity and Unreal Engine and often also with actual hardware and control systems of the real-world version of the simulator. AGX is integrated in many 3D modeling and CAD systems, including Algoryx Momentum for ANSYS Discovery (formerly SpaceClaim).
AGX has been under active development since 2007. It usually has about 3 major releases per year.
== History ==
AGX is developed by Algoryx Simulation AB, a private limited company established in Umeå, Sweden in 2007, as a spin-off from Umeå University. In February 2011, Algoryx was selected for the list of Top-20 companies to represent Swedish Innovation, by the Swedish Institute, a Swedish government agency. In March 2011, Algoryx was ranked as one of Sweden's most promising young high tech companies by business magazine Affärsvärlden and tech news paper Ny Teknik. In May 2011, Algoryx was selected by Red Herring for the Top 100 list of the most innovative companies in Europe.
== References ==
== External links ==
Official homepage
Homepage of Algoryx Simulation AB
Homepage of physics education software Algodoo | Wikipedia/AGX_Multiphysics_(physics_engine) |
Direct numerical control (DNC), also known as distributed numerical control (also DNC), is a common manufacturing term for networking CNC machine tools. On some CNC machine controllers, the available memory is too small to contain the machining program (for example machining complex surfaces), so in this case the program is stored in a separate computer and sent directly to the machine, one block at a time. If the computer is connected to a number of machines it can distribute programs to different machines as required. Usually, the manufacturer of the control provides suitable DNC software. However, if this provision is not possible, some software companies provide DNC applications that fulfill the purpose. DNC networking or DNC communication is always required when CAM programs are to run on some CNC machine control.
Wireless DNC is also used in place of hard-wired versions. Controls of this type are very widely used in industries with significant sheet metal fabrication, such as the automotive, appliance, and aerospace industries.
== History ==
=== 1950s-1970s ===
Programs had to be walked to NC controls, generally on paper tape. NC controls had paper tape readers precisely for this purpose. Many companies were still punching programs on paper tape well into the 1980s, more than twenty-five years after its elimination in the computer industry.
=== 1980s ===
The focus in the 1980s was mainly on reliably transferring NC programs between a host computer and the control. The Host computers would frequently be Sun Microsystems, HP, Prime, DEC or IBM type computers running a variety of CAD/CAM software. DNC companies offered machine tool links using rugged proprietary terminals and networks. For example, DLog offered an x86 based terminal, and NCPC had one based on the 6809. The host software would be responsible for tracking and authorising NC program modifications. Depending on program size, for the first time operators had the opportunity to modify programs at the DNC terminal. No time was lost due to broken tapes, and if the software was correctly used, an operator running incorrect or out of date programs became a thing of the past.
Older controls frequently had no port capable of receiving programs such as an RS-232 or RS-422 connector. In these cases, a device known as a Behind The Reader or BTR card was used. The connection between the control's tape reader and the internal processor was interrupted by a microprocessor based device which emulated the paper tape reader's signals, but which had a serial port connected to the DNC system. As far as the control was concerned, it was receiving from the paper tape unit as it always had; in fact it was the BTR or Reader Emulation card which was transmitting. A switch was frequently added to permit the paper tape reader to be used as a backup.
=== 1990s to present ===
The PC explosion in the late 1980s and early 1990s signalled the end of the road for proprietary DNC terminals. With some exceptions, CNC manufacturers began migrating to PC-based controls running DOS, Windows or OS/2 which could be linked in to existing networks using standard protocols. Customers began migrating away from expensive minicomputer and workstation based CAD/CAM toward more cost-effective PC-based solutions. Users began to demand more from their DNC systems than secure upload/download and editing. PC-based systems which could accomplish these tasks based on standard networks began to be available at minimal or no cost. In some cases, users no longer needed a DNC "expert" to implement shop floor networking, and could do it themselves. However, the task can still be a challenge based on the CNC Control wiring requirements, parameters and NC program format.
To remain competitive, therefore, DNC companies moved their offerings upmarket into DNC Networking, Shop Floor Control or SFC, Manufacturing Execution Systems or MES. These terms encompass concepts such as real-time Machine Monitoring, Graphics, Tool Management, Traveler Management and Scheduling. Instead of merely acting as a repository for programs, DNC systems aim to give operators at the machine an integrated view of all the information (both textual and graphical) they require in order to carry out a manufacturing operation, and give management timely information as to the progress of each step. DNC systems are frequently directly integrated with corporate CAD/CAM, ERP and Computer-aided Process Planning CAPP systems.
== Special protocols ==
A challenge when interfacing into machine tools is that in some cases special protocols are used. Two well-known examples are Mazak's Mazatrol and Heidenhain's LSV2 protocol. Many DNC systems offer support for these protocols. Another protocol is DNC2 which is found on Fanuc controls. DNC2 allows advanced interchange of data with the control, such as tooling offsets, tool life information and machine status as well as automated transfer without operator intervention.
== Machine monitoring ==
One of the issues involved in machine monitoring is whether or not it can be accomplished automatically in a practical way. In the 1980s monitoring was typically done by having a menu on the DNC terminal where the operator had to manually indicate what was being done by selecting from a menu, which has obvious drawbacks. There have been advances in passive monitoring systems where the machine condition can be determined by hardware attached in such a way as not to interfere with machine operations (and potentially void warranties). Many modern controls allow external applications to query their status using a special protocol. MTConnect is one prominent attempt to augment the existing world of proprietary systems with an open-source, industry-standard protocol using XML schemas. The end goal being to achieve higher levels of manufacturing business intelligence and workflow automation.
== Alternatives ==
Smaller facilities will typically use a portable PC or laptop to avoid the expense of a fully networked DNC system. In the past Facit Walk Disk and a similar device from Mazak were very popular.
== Footnotes == | Wikipedia/Direct_numerical_control |
Transform, clipping, and lighting (T&L or TCL) is a term used in computer graphics.
== Overview ==
Transformation is the task of producing a two-dimensional view of a three-dimensional scene. Clipping means only drawing the parts of the scene that will be present in the picture after rendering is completed. Lighting is the task of altering the colour of the various surfaces of the scene on the basis of lighting information.
== Hardware ==
Hardware T&L had been used by arcade game system boards since 1993, and by home video game consoles since the Sega Genesis's Virtua Processor (SVP), Sega Saturn's SCU-DSP and Sony PlayStation's GTE in 1994 and the Nintendo 64's RSP in 1996, though it wasn't traditional hardware T&L, but still software T&L running on a coprocessor instead of the main CPU, and could be used for rudimentary programmable pixel and vertex shaders as well. More traditional hardware T&L would appear on consoles with the GameCube and Xbox in 2001 (the PS2 still using a vector coprocessor for T&L). Personal computers implemented T&L in software until 1999, as it was believed faster CPUs would be able to keep pace with demands for ever more realistic rendering. However, 3D computer games of the time were producing increasingly complex scenes and detailed lighting effects much faster than the increase of CPU processing power.
Nvidia's GeForce 256 was released in late 1999 and introduced hardware support for T&L to the consumer PC graphics card market. It had faster vertex processing not only due to the T&L hardware, but also because of a cache that avoided having to process the same vertex twice in certain situations. While DirectX 7.0 (particularly Direct3D 7) was the first release of that API to support hardware T&L, OpenGL had supported it much longer and was typically the purview of older professionally oriented 3D accelerators which were designed for computer-aided design (CAD) instead of games.
Aladdin's ArtX integrated graphics chipset also featured T&L hardware, being released in November 1999 as part of the Aladdin VII motherboards for socket 7 platform.
S3 Graphics launched the Savage 2000 accelerator in late 1999, shortly after GeForce 256, but S3 never developed working Direct3D 7.0 drivers that would have enabled hardware T&L support.
== Usefulness ==
Hardware T&L did not have broad application support in games at the time (mainly due to Direct3D games transforming their geometry on the CPU and not being allowed to use indexed geometries), so critics contended that it had little real-world value. Initially, it was only somewhat beneficial in a few OpenGL-based 3D first-person shooter titles of the time, most notably Quake III Arena. 3dfx and other competing graphics card companies contended that a fast CPU would make up for the lack of a T&L unit.
ATI's initial response to GeForce 256 was the dual-chip Rage Fury MAXX. By using two Rage 128 chips, each rendering an alternate frame, the card was able to somewhat approach the performance of SDR memory GeForce 256 cards, but the GeForce 256 DDR still retained the top speed. ATI was developing their own GPU at the time known as the Radeon which also implemented hardware T&L.
3dfx's Voodoo5 5500 did not have a T&L unit but it was able to match the performance of the GeForce 256, although the Voodoo5 was late to market and by its release it could not match the succeeding GeForce 2 GTS.
STMicroelectronics' PowerVR Kyro II, released in 2001, was able to rival the costlier ATI Radeon DDR and NVIDIA GeForce 2 GTS in benchmarks of the time, despite not having hardware transform and lighting. As more and more games were optimised for hardware transform and lighting, the KYRO II lost its performance advantage and is not supported by most modern games.
Futuremark's 3DMark 2000 heavily utilized hardware T&L, which resulted in the Voodoo 5 and Kyro II both scoring poorly in the benchmark tests, behind budget T&L video cards such as the GeForce 2 MX and Radeon SDR.
== Industry standardization ==
By 2000, only ATI with their comparable Radeon 7xxx series, would remain in direct competition with Nvidia's GeForce 256 and GeForce 2. By the end of 2001, all discrete graphics chips would have hardware T&L.
Support of hardware T&L assured the GeForce and Radeon of a strong future, unlike its Direct3D 6 predecessors which relied upon software T&L. While hardware T&L does not add new rendering features, the extra performance allowed for much more complex scenes and an increasing number of games recommended it anyway to run at optimal performance. GPUs that support T&L in hardware are usually considered to be in the DirectX 7.0 generation.
After hardware T&L had become standard in GPUs, the next step in computer 3D graphics was DirectX 8.0 with fully programmable vertex and pixel shaders. Nonetheless, many early games using DirectX 8.0 shaders, such as Half-Life 2, made that feature optional so DirectX 7.0 hardware T&L GPUs could still run the game. For instance, the GeForce 256 was supported in games up until approximately 2006, in games such as Star Wars: Empire at War.
== References == | Wikipedia/Transform_and_lighting |
The governing equations of a mathematical model describe how the values of the unknown variables (i.e. the dependent variables) change when one or more of the known (i.e. independent) variables change.
Physical systems can be modeled phenomenologically at various levels of sophistication, with each level capturing a different degree of detail about the system. A governing equation represents the most detailed and fundamental phenomenological model currently available for a given system.
For example, at the coarsest level, a beam is just a 1D curve whose torque is a function of local curvature. At a more refined level, the beam is a 2D body whose stress-tensor is a function of local strain-tensor, and strain-tensor is a function of its deformation. The equations are then a PDE system. Note that both levels of sophistication are phenomenological, but one is deeper than the other. As another example, in fluid dynamics, the Navier-Stokes equations are more refined than Euler equations.
As the field progresses and our understanding of the underlying mechanisms deepens, governing equations may be replaced or refined by new, more accurate models that better represent the system's behavior. These new governing equations can then be considered the deepest level of phenomenological model at that point in time.
== Mass balance ==
A mass balance, also called a material balance, is an application of conservation of mass to the analysis of physical systems. It is the simplest governing equation, and it is simply a budget (balance calculation) over the quantity in question:
== Differential equation ==
=== Physics ===
The governing equations in classical physics that are
lectured
at universities are listed below.
=== Classical continuum mechanics ===
The basic equations in classical continuum mechanics are all balance equations, and as such each of them contains a time-derivative term which calculates how much the dependent variable change with time. For an isolated, frictionless / inviscid system the first four equations are the familiar conservation equations in classical mechanics.
Darcy's law of groundwater flow has the form of a volumetric flux caused by a pressure gradient. A flux in classical mechanics is normally not a governing equation, but usually a defining equation for transport properties. Darcy's law was originally established as an empirical equation, but is later shown to be derivable as an approximation of Navier-Stokes equation combined with an empirical composite friction force term. This explains the duality in Darcy's law as a governing equation and a defining equation for absolute permeability.
The non-linearity of the material derivative in balance equations in general, and the complexities of Cauchy's momentum equation and Navier-Stokes equation makes the basic equations in classical mechanics exposed to establishing of simpler approximations.
Some examples of governing differential equations in classical continuum mechanics are
=== Biology ===
A famous example of governing differential equations within biology is
== Sequence of states ==
A governing equation may also be a state equation, an equation describing the state of the system, and thus actually be a constitutive equation that has "stepped up the ranks" because the model in question was not meant to include a time-dependent term in the equation. This is the case for a model of an oil production plant which on the average operates in a steady state mode. Results from one thermodynamic equilibrium calculation are input data to the next equilibrium calculation together with some new state parameters, and so on. In this case the algorithm and sequence of input data form a chain of actions, or calculations, that describes change of states from the first state (based solely on input data) to the last state that finally comes out of the calculation sequence.
== See also ==
Constitutive equation
Mass balance
Master equation
Mathematical model
Primitive equations
== References == | Wikipedia/Governing_equations |
Finite-difference time-domain (FDTD) or Yee's method (named after the Chinese American applied mathematician Kane S. Yee, born 1934) is a numerical analysis technique used for modeling computational electrodynamics.
== History ==
Finite difference schemes for time-dependent partial differential equations (PDEs) have been employed for many years in computational fluid dynamics problems, including the idea of using centered finite difference operators on staggered grids in space and time to achieve second-order accuracy.
The novelty of Yee's FDTD scheme, presented in his seminal 1966 paper, was to apply centered finite difference operators on staggered grids in space and time for each electric and magnetic vector field component in Maxwell's curl equations.
The descriptor "Finite-difference time-domain" and its corresponding "FDTD" acronym were originated by Allen Taflove in 1980.
Since about 1990, FDTD techniques have emerged as primary means to computationally model many scientific and engineering problems dealing with electromagnetic wave interactions with material structures. Current FDTD modeling applications range from near-DC (ultralow-frequency geophysics involving the entire Earth-ionosphere waveguide) through microwaves (radar signature technology, antennas, wireless communications devices, digital interconnects, biomedical imaging/treatment) to visible light (photonic crystals, nanoplasmonics, solitons, and biophotonics). In 2006, an estimated 2,000 FDTD-related publications appeared in the science and engineering literature (see Popularity). As of 2013, there are at least 25 commercial/proprietary FDTD software vendors; 13 free-software/open-source-software FDTD projects; and 2 freeware/closed-source FDTD projects, some not for commercial use (see External links).
=== Development of FDTD and Maxwell's equations ===
An appreciation of the basis, technical development, and possible future of FDTD numerical techniques for Maxwell's equations can be developed by first considering their history. The following lists some of the key publications in this area.
== FDTD models and methods ==
When Maxwell's differential equations are examined, it can be seen that the change in the E-field in time (the time derivative) is dependent on the change in the H-field across space (the curl). This results in the basic FDTD time-stepping relation that, at any point in space, the updated value of the E-field in time is dependent on the stored value of the E-field and the numerical curl of the local distribution of the H-field in space.
The H-field is time-stepped in a similar manner. At any point in space, the updated value of the H-field in time is dependent on the stored value of the H-field and the numerical curl of the local distribution of the E-field in space. Iterating the E-field and H-field updates results in a marching-in-time process wherein sampled-data analogs of the continuous electromagnetic waves under consideration propagate in a numerical grid stored in the computer memory.
This description holds true for 1-D, 2-D, and 3-D FDTD techniques. When multiple dimensions are considered, calculating the numerical curl can become complicated. Kane Yee's seminal 1966 paper proposed spatially staggering the vector components of the E-field and H-field about rectangular unit cells of a Cartesian computational grid so that each E-field vector component is located midway between a pair of H-field vector components, and conversely. This scheme, now known as a Yee lattice, has proven to be very robust, and remains at the core of many current FDTD software constructs.
Furthermore, Yee proposed a leapfrog scheme for marching in time wherein the E-field and H-field updates are staggered so that E-field updates are conducted midway during each time-step between successive H-field updates, and conversely. On the plus side, this explicit time-stepping scheme avoids the need to solve simultaneous equations, and furthermore yields dissipation-free numerical wave propagation. On the minus side, this scheme mandates an upper bound on the time-step to ensure numerical stability. As a result, certain classes of simulations can require many thousands of time-steps for completion.
=== Using the FDTD method ===
To implement an FDTD solution of Maxwell's equations, a computational domain must first be established. The computational domain is simply the physical region over which the simulation will be performed. The E and H fields are determined at every point in space within that computational domain. The material of each cell within the computational domain must be specified. Typically, the material is either free-space (air), metal, or dielectric. Any material can be used as long as the permeability, permittivity, and conductivity are specified.
The permittivity of dispersive materials in tabular form cannot be directly substituted into the FDTD scheme.
Instead, it can be approximated using multiple Debye, Drude, Lorentz or critical point terms.
This approximation can be obtained using open fitting programs and does not necessarily have physical meaning.
Once the computational domain and the grid materials are established, a source is specified. The source can be current on a wire, applied electric field or impinging plane wave.
In the last case FDTD can be used to simulate light scattering from arbitrary shaped objects, planar periodic structures at various incident angles, and photonic band structure of infinite periodic structures.
Since the E and H fields are determined directly, the output of the simulation is usually the E or H field at a point or a series of points within the computational domain. The simulation evolves the E and H fields forward in time.
Processing may be done on the E and H fields returned by the simulation. Data processing may also occur while the simulation is ongoing.
While the FDTD technique computes electromagnetic fields within a compact spatial region, scattered and/or radiated far fields can be obtained via near-to-far-field transformations.
=== Strengths of FDTD modeling ===
Every modeling technique has strengths and weaknesses, and the FDTD method is no different.
FDTD is a versatile modeling technique used to solve Maxwell's equations. It is intuitive, so users can easily understand how to use it and know what to expect from a given model.
FDTD is a time-domain technique, and when a broadband pulse (such as a Gaussian pulse) is used as the source, then the response of the system over a wide range of frequencies can be obtained with a single simulation. This is useful in applications where resonant frequencies are not exactly known, or anytime that a broadband result is desired.
Since FDTD calculates the E and H fields everywhere in the computational domain as they evolve in time, it lends itself to providing animated displays of the electromagnetic field movement through the model. This type of display is useful in understanding what is going on in the model, and to help ensure that the model is working correctly.
The FDTD technique allows the user to specify the material at all points within the computational domain. A wide variety of linear and nonlinear dielectric and magnetic materials can be naturally and easily modeled.
FDTD allows the effects of apertures to be determined directly. Shielding effects can be found, and the fields both inside and outside a structure can be found directly or indirectly.
FDTD uses the E and H fields directly. Since most EMI/EMC modeling applications are interested in the E and H fields, it is convenient that no conversions must be made after the simulation has run to get these values.
=== Weaknesses of FDTD modeling ===
Since FDTD requires that the entire computational domain be gridded, and the grid spatial discretization must be sufficiently fine to resolve both the smallest electromagnetic wavelength and the smallest geometrical feature in the model, very large computational domains can be developed, which results in very long solution times. Models with long, thin features, (like wires) are difficult to model in FDTD because of the excessively large computational domain required. Methods such as eigenmode expansion can offer a more efficient alternative as they do not require a fine grid along the z-direction.
There is no way to determine unique values for permittivity and permeability at a material interface.
Space and time steps must satisfy the CFL condition, or the leapfrog integration used to solve the partial differential equation is likely to become unstable.
FDTD finds the E/H fields directly everywhere in the computational domain. If the field values at some distance are desired, it is likely that this distance will force the computational domain to be excessively large. Far-field extensions are available for FDTD, but require some amount of postprocessing.
Since FDTD simulations calculate the E and H fields at all points within the computational domain, the computational domain must be finite to permit its residence in the computer memory. In many cases this is achieved by inserting artificial boundaries into the simulation space. Care must be taken to minimize errors introduced by such boundaries. There are a number of available highly effective absorbing boundary conditions (ABCs) to simulate an infinite unbounded computational domain. Most modern FDTD implementations instead use a special absorbing "material", called a perfectly matched layer (PML) to implement absorbing boundaries.
Because FDTD is solved by propagating the fields forward in the time domain, the electromagnetic time response of the medium must be modeled explicitly. For an arbitrary response, this involves a computationally expensive time convolution, although in most cases the time response of the medium (or Dispersion (optics)) can be adequately and simply modeled using either the recursive convolution (RC) technique, the auxiliary differential equation (ADE) technique, or the Z-transform technique. An alternative way of solving Maxwell's equations that can treat arbitrary dispersion easily is the pseudo-spectral spatial domain (PSSD), which instead propagates the fields forward in space.
=== Grid truncation techniques ===
The most commonly used grid truncation techniques for open-region FDTD modeling problems are the Mur absorbing boundary condition (ABC), the Liao ABC, and various perfectly matched layer (PML) formulations. The Mur and Liao techniques are simpler than PML. However, PML (which is technically an absorbing region rather than a boundary condition per se) can provide orders-of-magnitude lower reflections. The PML concept was introduced by J.-P. Berenger in a seminal 1994 paper in the Journal of Computational Physics. Since 1994, Berenger's original split-field implementation has been modified and extended to the uniaxial PML (UPML), the convolutional PML (CPML), and the higher-order PML. The latter two PML formulations have increased ability to absorb evanescent waves, and therefore can in principle be placed closer to a simulated scattering or radiating structure than Berenger's original formulation.
To reduce undesired numerical reflection from the PML additional back absorbing layers technique can be used.
== Popularity ==
Notwithstanding both the general increase in academic publication
throughput during the same period and the overall expansion of interest
in all Computational electromagnetics (CEM) techniques, there are
seven primary reasons for the tremendous expansion of interest in FDTD
computational solution approaches for Maxwell's equations:
FDTD does not require a matrix inversion. Being a fully explicit computation, FDTD avoids the difficulties with matrix inversions that limit the size of frequency-domain integral-equation and finite-element electromagnetics models to generally fewer than 109 electromagnetic field unknowns. FDTD models with as many as 109 field unknowns have been run; there is no intrinsic upper bound to this number.
FDTD is accurate and robust. The sources of error in FDTD calculations are well understood, and can be bounded to permit accurate models for a very large variety of electromagnetic wave interaction problems.
FDTD treats impulsive behavior naturally. Being a time-domain technique, FDTD directly calculates the impulse response of an electromagnetic system. Therefore, a single FDTD simulation can provide either ultrawideband temporal waveforms or the sinusoidal steady-state response at any frequency within the excitation spectrum.
FDTD treats nonlinear behavior naturally. Being a time-domain technique, FDTD directly calculates the nonlinear response of an electromagnetic system. This allows natural hybriding of FDTD with sets of auxiliary differential equations that describe nonlinearities from either the classical or semi-classical standpoint. One research frontier is the development of hybrid algorithms which join FDTD classical electrodynamics models with phenomena arising from quantum electrodynamics, especially vacuum fluctuations, such as the Casimir effect.
FDTD is a systematic approach. With FDTD, specifying a new structure to be modeled is reduced to a problem of mesh generation rather than the potentially complex reformulation of an integral equation. For example, FDTD requires no calculation of structure-dependent Green functions.
Parallel-processing computer architectures have come to dominate supercomputing. FDTD scales with high efficiency on parallel-processing CPU-based computers, and extremely well on recently developed GPU-based accelerator technology.
Computer visualization capabilities are increasing rapidly. While this trend positively influences all numerical techniques, it is of particular advantage to FDTD methods, which generate time-marched arrays of field quantities suitable for use in color videos to illustrate the field dynamics.
Taflove has argued that these factors combine to suggest that FDTD will remain one of
the dominant computational electrodynamics techniques (as well as potentially other multiphysics problems).
== See also ==
Computational electromagnetics
Eigenmode expansion
Beam propagation method
Finite-difference frequency-domain
Finite element method
Scattering-matrix method
Discrete dipole approximation
== References ==
== Further reading ==
== External links ==
Free software/Open-source software FDTD projects:
FDTD++: advanced, fully featured FDTD software, along with sophisticated material models and predefined fits as well as discussion/support forums and email support
openEMS (Fully 3D Cartesian & Cylindrical graded mesh EC-FDTD Solver, written in C++, using a Matlab/Octave-Interface)
pFDTD (3D C++ FDTD codes developed by Se-Heon Kim)
JFDTD (2D/3D C++ FDTD codes developed for nanophotonics by Jeffrey M. McMahon)
WOLFSIM Archived 2008-07-02 at the Wayback Machine (NCSU) (2-D)
Meep (MIT, 2D/3D/cylindrical parallel FDTD)
(Geo-) Radar FDTD
bigboy (unmaintained, no release files. must get source from cvs)
Parallel (MPI&OpenMP) FDTD codes in C++ (developed by Zs. Szabó)
FDTD code in Fortran 90
FDTD code in C for 2D EM Wave simulation
Angora (3D parallel FDTD software package, maintained by Ilker R. Capoglu)
GSvit (3D FDTD solver with graphics card computing support, written in C, graphical user interface XSvit available)
gprMax (Open Source (GPLv3), 3D/2D FDTD modelling code in Python/Cython developed for GPR but can be used for general EM modelling.)
Freeware/Closed source FDTD projects (some not for commercial use):
EMTL (Electromagnetic Template Library) (Free С++ library for electromagnetic simulations. The current version implements mainly the FDTD). | Wikipedia/Finite_difference_time-domain_method |
Bidirectional texture function (BTF) is a 6-dimensional function depending on planar texture coordinates (x,y) as well as on view and illumination spherical angles. In practice this function is obtained as a set of several thousand color images of material sample taken during different camera and light positions.
The BTF is a representation of the appearance of texture as a function of viewing and illumination direction. It is an image-based representation, since the geometry of the surface is unknown and not measured. BTF is typically captured by imaging the surface at a sampling of the hemisphere of possible viewing and illumination directions. BTF measurements are collections of images. The term BTF was first introduced in and similar terms have since been introduced including BSSRDF and SBRDF (spatial BRDF). SBRDF has a very similar definition to BTF, i.e. BTF is also a spatially varying BRDF.
To cope with a massive BTF data with high redundancy, many compression methods were proposed.
Application of the BTF is in photorealistic material rendering of objects in virtual reality systems and for visual scene analysis, e.g., recognition of complex real-world materials using bidirectional feature histograms or 3D textons.
Biomedical and biometric applications of the BTF include recognition of skin texture.
== See also ==
BSDF == BRDF + BTDF, a 4+1 dimensional function of the scattering distribution from a single point/pixel/vertex.
Columbia Utrecht Reflectance and Texture Database
BTF Database Bonn and Measurement Lab
CVPR 2010 BTF Modeling Tutorial
BTFbase - BTF compression based on a multi-level vector quantization (free BTF shader)
UTIA BTF Database - a new source of publicly available bidirectional texture function measurements
== References == | Wikipedia/Bidirectional_texture_function |
Imagine was the name of a cutting-edge 3D modeling and ray tracing program, originally for the Amiga computer and later also for MS-DOS and Microsoft Windows.
It was created by Impulse, Inc. It used the .iob extension for its objects. Imagine was a derivative of the software TurboSilver, which was also for the Amiga and written by Impulse.
CAD-Technologies continued the distribution of the Amiga version. Starting with version 5.1, new updates were available for free for current customers as part of the Amiga Constant Upgrade Program (ACUP) up until presumed Imagine 6.0 release.
== Versions ==
=== Amiga ===
1990 - Imagine
1992 - Imagine 2.0
1993 - Imagine 2.9
1994 - Imagine 3.0
1995 - Imagine 3.1
1995 - Imagine 3.2
1995 - Imagine 3.3
1995 - Imagine 4.0
1996 - Imagine 5.0
1998 - Imagine 5.1 and 5.1a (first ACUP release)
1998 - Imagine 5.13
2000 - Imagine 5.17
2006 - Imagine 5.19 (last public release)
=== MS-DOS ===
1993 - Imagine 2.0
1994 - Imagine 3.0
1995 - Imagine 4.0
=== Windows ===
1996 - Imagine 1.0
1997 - Imagine 1.3.4 (first CUP release)
1999 - Imagine 1.9
1999 - Imagine 2.0
1999 - Imagine 2.1.2
2000 - Imagine 2.1.3
2000 - Imagine 2.1.4 (no bones)
2002 - Imagine 2.1.5
2002 - Imagine 2.1.6 (additional effects (*.ifx files))
2002 - Imagine 2.1.7
2002 - Imagine 2.1.8 (additional effect (FireRing.ifx file))
2004 - Imagine 2.1.9 (last public release, added Volumetric)
== See also ==
Sculpt 3D
== References ==
== External links ==
Program for reading IOB files Archived 2017-10-12 at the Wayback Machine
Aminet Imagine traces
Imagine 3D fan site | Wikipedia/Imagine_(3D_modeling_software) |
ColorGraphics Weather Systems was a computer graphics company that pioneered the use of computer graphics for displaying weather forecasts on local television. Formed in 1979 by Terry Kelly and Richard Daly, it is now part of Weather Central, another of Kelly's companies.
== History ==
After graduating from the University of Wisconsin–Madison in 1971 with a degree in meteorology, Terry Kelly took a job with Madison, Wisconsin, television station WKOW calculating weather predictions. Over the next two years he introduced a number of new techniques to the industry, including using magnets to represent high and low points, color markers on a whiteboard for graphics, and later hand-photographing satellite cloud imagery with a Bolex camera to produce the first cloud-movement animations.
Kelly and several of his colleagues also produced weather forecasting software. In 1974 he was promoted to chief meteorologist at WKOW, and at the same time started Weather Central to sell and operate their software for smaller organizations such as ski resorts and local highway departments.
ColorGraphics was formed in 1979 as a partnership between Kelly and Richard Daly. Kelly and Daly had both worked in the University of Wisconsin's Space Science and Engineering department, developers of the McIDAS weather display system. McIDAS used downloaded satellite cloud cover images and superimposed them on locally generated maps. Designed for the National Weather Service, McIDAS was a high-end system well beyond the budget of a television station.
Kelly's idea was to adapt the McIdas concept for lower cost home computer systems that were appearing in the late 1970s. Their first system, "LiveLine", was based on the Apple II. Its graphics system could not be genlocked, so a TV camera had to be pointed at the screen to send the video into the production systems. This initial system was soon replaced by a similar one running on Cromemco computers using a modified version of their Dazzler color-graphics card. In spite of its simplicity and low resolution, the fast production and "high tech" look caught on, and by the mid-1980s the system was almost universal, replacing bluescreen systems on cardboard maps that had previously been used. The company noted that 70% of the top 50 TV markets were using the system by 1982. By 1984 80% of all television stations in the country were using ColorGraphics system, built on Cromemco microcomputers, to generate weather, news, and sports graphics.
In 1982 the company was purchased by Dynatech Corporation, an expanding electronics company. Dynatech purchased Cromemco in 1987 and rolled the two companies together, before divesting all of its media properties in the early 1990s. Kelly and Daly purchased the rights back from Dynatech in 1994, operating under the Weather Central name. In 1995 they introduced the new "GENESIS" platform on Silicon Graphics computers, which later moved onto Hewlett-Packard workstations.
== References ==
=== Notes ===
=== Bibliography ===
Nelson, Mike (2007). Colorado Weather Almanac. Big Earth Publishing. ISBN 978-1555664015.
== External links ==
Weather Central, Inc. | Wikipedia/ColorGraphics_Weather_Systems |
HOOPS Visualize is a 3D computer graphics software designed to render graphics across both mobile and desktop platforms. HOOPS Visualize provides 3D Graphics API to render CAD models. It's part of the HOOPS 3D Application Framework SDK. Since June 2018 it's licensed via Siemens PLM Software.
== History ==
The HOOPS 3D Graphics System was originally developed in the mid-1980s in the CADIF Lab at Cornell University. Ithaca Software later formed to commercialize the technology. Subsequently, HOOPS was widely adopted for Computer-Aided Design (CAD), Computer-Aided Manufacturing (CAM) and Computer-Aided Engineering (CAE) software.
In 1993, Autodesk, Inc. acquired Ithaca Software. In 1996, HOOPS was spun out of Autodesk by Tech Soft 3D, Inc., which continues to develop and sell the HOOPS 3D Graphics System under the name HOOPS Visualize. The software is made available free of charge to educational institutions.
== Overview ==
The program features a unified API that allows users to add interactive 3D visualization to both desktop and mobile applications. HOOPS Visualize provides a hierarchical scene management engine capable of handling a range of graphics entities, together with a graphics pipeline and interaction handling algorithms. It includes clash detection, multi-plane sectioning, and large model visualization, along with many other features.
Features include:
Retained-mode graphics system with a supporting database
Data is structured hierarchically in a scene graph
Able to use many different contexts for rendering, including DirectX, OpenGL, as well as software and hardcopy
Interfaces with C, C++, C#, and Java
Out-of-core rendering mode for visualizing large point-cloud datasets
Integrates with other engineering SDKs like ACIS, Parasolid, RealDWG, and HOOPS Exchange, as well as industry standard CAD formats
PMI support, mark-up, model trees, point clouds
Compatible with all major graphical user interfaces
Platform independent input architecture
== Technical Overview ==
Internally it uses OpenGL or DirectX (Windows). Tech Soft 3D has developed its own framework for event handling.
The graphics kernel (Core Graphics) is based on the hierarchichal scene graph data structures.
== File formats ==
== References == | Wikipedia/HOOPS_3D_Graphics_System |
The Application Programming Interface for Windows (APIW) Standard is a specification of the Microsoft Windows 3.1 API drafted by Willows Software. It is the successor to previously proposed Public Windows Interface standard. It was created in an attempt to establish a vendor-neutral, platform-independent, open standard of the 16-bit Windows API not controlled by Microsoft.
== Creation ==
By the end of 1990, Windows 3.0 was the top-selling software. The various graphical Windows applications had already started to reduce training time and enhance productivity on personal computers. At the same time, various Unix and Unix-based operating systems dominated technical workstations and departmental servers. The idea of a consistent application environment across heterogeneous environments was compelling to both enterprise customers and software developers.
On May 5, 1993, Sun Microsystems announced Windows Application Binary Interface (WABI), a product to run Windows software on Unix, and the Public Windows Interface (PWI) initiative, an effort to standardize a subset of the popular 16-bit Windows APIs. The PWI consortium's aims were stated as turning the proprietary Windows API into an "open, publicly available specification" and for the evolution of this specification to be the responsibility of "a neutral body". The consortium, counting Sun, IBM, Hewlett Packard and Novell among its members, proposed PWI to various companies and organizations including X/Open, IEEE and Unix International. The previous day, Microsoft had announced SoftPC, a Windows to Unix product created by Insignia Solutions as part of a program where Microsoft licensed their Windows source code to select third parties, which in the following year became known as Windows Interface Source Environment (WISE). Later that month, Microsoft also announced Windows NT, a version of Windows designed to run on workstations and servers.
== ECMA involvement ==
In February 1994, the PWI Specification Committee sent a draft specification to X/Open—who rejected it in March, after being threatened by Microsoft's assertion of intellectual property rights (IPR) over the Windows APIs—and the European Computer Manufacturers' Association (ECMA). In September, now part of an ECMA delegation, they made an informational presentation about the project at the ISO SC22 plenary meeting in The Hague, Netherlands. Their goal was to make it an ISO standard in order to force Microsoft to comply with it (in Windows) or risk not being able sell to European or Asian governments who can only buy ISO standards-compliant products.
In April 1995, Willows Software, Inc. (formerly Multiport, Inc.) a Saratoga, California-based Canopy-funded company, that had been working on Windows to Unix technologies (inherited from then defunct Hunter Systems, Inc.) since early 1993, joined the ad hoc ECMA group. This group became Technical Committee 37 in August (about the time Windows 95 was released). Willows vowed to complete a full draft specification by the end of the year. In October, the draft specification was completed under the name Application Programming Interface for Windows (APIW). This was accepted as ECMA-234 in December and was put on the fast-track program to become an ISO standard.
== ISO delay ==
Again, Microsoft claimed intellectual property over Windows APIs and ISO put the standard on hold pending proof of their claims. The delay lasted until November 1997, when, hearing no response from Microsoft, ISO announced they were pushing through with the standard. However, there is no record of it ever being approved as an ISO standard.
== See also ==
Willows Toolkit for UNIX – American software companyPages displaying short descriptions of redirect targets
Willows RT for Embedded Systems – American software companyPages displaying short descriptions of redirect targets
Novell Corsair – Linux distribution of the late 1990s and early 2000sPages displaying short descriptions of redirect targets
Caldera Network Desktop – Linux distribution of the late 1990s and early 2000sPages displaying short descriptions of redirect targets
== References == | Wikipedia/Application_Programming_Interface_for_Windows |
Artificial intelligence art usually means visual artwork generated (or enhanced) through the use of artificial intelligence (AI) programs.
Artists began to create AI art in the mid to late 20th century, when the discipline was founded. Throughout its history, AI has raised many philosophical concerns related to the human mind, artificial beings, and also what can be considered art in human–AI collaboration. Since the 20th century, people have used AI to create art, some of which has been exhibited in museums and won awards.
During the AI boom of the 2020s, text-to-image models such as Midjourney, DALL-E, Stable Diffusion, and FLUX.1 became widely available to the public, allowing users to quickly generate imagery with little effort. Commentary about AI art in the 2020s has often focused on issues related to copyright, deception, defamation, and its impact on more traditional artists, including technological unemployment.
== History ==
=== Early history ===
Automated art dates back at least to the automata of ancient Greek civilization, when inventors such as Daedalus and Hero of Alexandria were described as designing machines capable of writing text, generating sounds, and playing music. Creative automatons have flourished throughout history, such as Maillardet's automaton, created around 1800 and capable of creating multiple drawings and poems.
Also in the 19th century, Ada Lovelace, writes that "computing operations" could be used to generate music and poems, now referred to as "The Lovelace Effect," where a computer's behavior is viewed as creative. Lovelace also discusses a concept known as "The Lovelace Objection," where she argues that a machine has "no pretensions whatever to originate anything."
In 1950, with the publication of Alan Turing's paper "Computing Machinery and Intelligence", there was a shift from defining machine intelligence in abstract terms to evaluating whether a machine can mimic human behavior and responses convincingly. Shortly after, the academic discipline of artificial intelligence was founded at a research workshop at Dartmouth College in 1956. Since its founding, researchers in the field have explored philosophical questions about the nature of the human mind and the consequences of creating artificial beings with human-like intelligence; these issues have previously been explored by myth, fiction, and philosophy since antiquity.
=== Artistic history ===
Since the founding of AI in the 1950s, artists have used artificial intelligence to create artistic works. These works were sometimes referred to as algorithmic art, computer art, digital art, or new media art.
One of the first significant AI art systems is AARON, developed by Harold Cohen beginning in the late 1960s at the University of California at San Diego. AARON uses a symbolic rule-based approach to generate technical images in the era of GOFAI programming, and it was developed by Cohen with the goal of being able to code the act of drawing. AARON was exhibited in 1972 at the Los Angeles County Museum of Art. From 1973 to 1975, Cohen refined AARON during a residency at the Artificial Intelligence Laboratory at Stanford University. In 2024, the Whitney Museum of American Art exhibited AI art from throughout Cohen's career, including re-created versions of his early robotic drawing machines.
Karl Sims has exhibited art created with artificial life since the 1980s. He received an M.S. in computer graphics from the MIT Media Lab in 1987 and was artist-in-residence from 1990 to 1996 at the supercomputer manufacturer and artificial intelligence company Thinking Machines. In both 1991 and 1992, Sims won the Golden Nica award at Prix Ars Electronica for his videos using artificial evolution. In 1997, Sims created the interactive artificial evolution installation Galápagos for the NTT InterCommunication Center in Tokyo. Sims received an Emmy Award in 2019 for outstanding achievement in engineering development.
In 1999, Scott Draves and a team of several engineers created and released Electric Sheep as a free software screensaver. Electric Sheep is a volunteer computing project for animating and evolving fractal flames, which are distributed to networked computers which display them as a screensaver. The screensaver used AI to create an infinite animation by learning from its audience. In 2001, Draves won the Fundacion Telefónica Life 4.0 prize for Electric Sheep.
In 2014, Stephanie Dinkins began working on Conversations with Bina48. For the series, Dinkins recorded her conversations with BINA48, a social robot that resembles a middle-aged black woman. In 2019, Dinkins won the Creative Capital award for her creation of an evolving artificial intelligence based on the "interests and culture(s) of people of color."
In 2015, Sougwen Chung began Mimicry (Drawing Operations Unit: Generation 1), an ongoing collaboration between the artist and a robotic arm. In 2019, Chung won the Lumen Prize for her continued performances with a robotic arm that uses AI to attempt to draw in a manner similar to Chung. In 2018, an auction sale of artificial intelligence art was held at Christie's in New York where the AI artwork Edmond de Belamy sold for US$432,500, which was almost 45 times higher than its estimate of US$7,000–10,000. The artwork was created by Obvious, a Paris-based collective.
In 2024, Japanese film generAIdoscope was released. The film was co-directed by Hirotaka Adachi, Takeshi Sone, and Hiroki Yamaguchi. All video, audio, and music in the film were created with artificial intelligence.
In 2025, Japanese anime television series Twins Hinahima was released. The anime was produced and animated with AI assistance during the process of cutting and conversion of photographs into anime illustrations and later retouched by art staff. Most of the remaining parts such as characters and logos were hand-drawn with various software.
=== Technical history ===
Deep learning, characterized by its multi-layer structure that attempts to mimic the human brain, first came about in the 2010s and causing a significant shift in the world of AI art. During the deep learning era, there are mainly these types of designs for generative art: autoregressive models, diffusion models, GANs, normalizing flows.
In 2014, Ian Goodfellow and colleagues at Université de Montréal developed the generative adversarial network (GAN), a type of deep neural network capable of learning to mimic the statistical distribution of input data such as images. The GAN uses a "generator" to create new images and a "discriminator" to decide which created images are considered successful. Unlike previous algorithmic art that followed hand-coded rules, generative adversarial networks could learn a specific aesthetic by analyzing a dataset of example images.
In 2015, a team at Google released DeepDream, a program that uses a convolutional neural network to find and enhance patterns in images via algorithmic pareidolia. The process creates deliberately over-processed images with a dream-like appearance reminiscent of a psychedelic experience. Later, in 2017, a conditional GAN learned to generate 1000 image classes of ImageNet, a large visual database designed for use in visual object recognition software research. By conditioning the GAN on both random noise and a specific class label, this approach enhanced the quality of image synthesis for class-conditional models.
Autoregressive models were used for image generation, such as PixelRNN (2016), which autoregressively generates one pixel after another with a recurrent neural network. Immediately after the Transformer architecture was proposed in Attention Is All You Need (2018), it was used for autoregressive generation of images, but without text conditioning.
The website Artbreeder, launched in 2018, uses the models StyleGAN and BigGAN to allow users to generate and modify images such as faces, landscapes, and paintings.
In the 2020s, text-to-image models, which generate images based on prompts, became widely used, marking yet another shift in the creation of AI generated artworks.
In 2021, using the influential large language generative pre-trained transformer models that are used in GPT-2 and GPT-3, OpenAI released a series of images created with the text-to-image AI model DALL-E 1. It was an autoregressive generative model with essentially the same architecture as GPT-3. Along with this, later in 2021, EleutherAI released the open source VQGAN-CLIP based on OpenAI's CLIP model. Diffusion models, generative models used to create synthetic data based on existing data, were first proposed in 2015, but they only became better than GANs in early 2021. Latent diffusion model was published in December 2021 and became the basis for the later Stable Diffusion (August 2022).
In 2022, Midjourney was released, followed by Google Brain's Imagen and Parti, which were announced in May 2022, Microsoft's NUWA-Infinity, and the source-available Stable Diffusion, which was released in August 2022. DALL-E 2, a successor to DALL-E, was beta-tested and released (with the further successor DALL-E 3 being released in 2023). Stability AI has a Stable Diffusion web interface called DreamStudio, plugins for Krita, Photoshop, Blender, and GIMP, and the Automatic1111 web-based open source user interface. Stable Diffusion's main pre-trained model is shared on the Hugging Face Hub.
Ideogram was released in August 2023, this model is known for its ability to generate legible text.
In 2024, Flux was released. This model can generate realistic images and was integrated into Grok, the chatbot used on X (formerly Twitter), and Le Chat, the chatbot of Mistral AI. Flux was developed by Black Forest Labs, founded by the researchers behind Stable Diffusion. Grok later switched to its own text-to-image model Aurora in December of the same year. Several companies, along with their products, have also developed an AI model integrated with an image editing service. Adobe has released and integrated the AI model Firefly into Premiere Pro, Photoshop, and Illustrator. Microsoft has also publicly announced AI image-generator features for Microsoft Paint. Along with this, some examples of text-to-video models of the mid-2020s are Runway's Gen-2, Google's VideoPoet, and OpenAI's Sora, which was released in December 2024.
== Tools and processes ==
=== Imagery ===
There are many tools available to the artist when working with diffusion models. They can define both positive and negative prompts, but they are also afforded a choice in using (or omitting the use of) VAEs, LoRAs, hypernetworks, IP-adapter, and embedding/textual inversions. Artists can tweak settings like guidance scale (which balances creativity and accuracy), seed (to control randomness), and upscalers (to enhance image resolution), among others. Additional influence can be exerted during pre-inference by means of noise manipulation, while traditional post-processing techniques are frequently used post-inference. People can also train their own models.
In addition, procedural "rule-based" generation of images using mathematical patterns, algorithms that simulate brush strokes and other painted effects, and deep learning algorithms such as generative adversarial networks (GANs) and transformers have been developed. Several companies have released apps and websites that allow one to forego all the options mentioned entirely while solely focusing on the positive prompt. There also exist programs which transform photos into art-like images in the style of well-known sets of paintings.
There are many options, ranging from simple consumer-facing mobile apps to Jupyter notebooks and web UIs that require powerful GPUs to run effectively. Additional functionalities include "textual inversion," which refers to enabling the use of user-provided concepts (like an object or a style) learned from a few images. Novel art can then be generated from the associated word(s) (the text that has been assigned to the learned, often abstract, concept) and model extensions or fine-tuning (such as DreamBooth).
==== Impact and applications ====
AI has the potential for a societal transformation, which may include enabling the expansion of noncommercial niche genres (such as cyberpunk derivatives like solarpunk) by amateurs, novel entertainment, fast prototyping, increasing art-making accessibility, and artistic output per effort or expenses or time—e.g., via generating drafts, draft-definitions, and image components (inpainting). Generated images are sometimes used as sketches, low-cost experiments, inspiration, or illustrations of proof-of-concept-stage ideas. Additional functionalities or improvements may also relate to post-generation manual editing (i.e., polishing), such as subsequent tweaking with an image editor.
=== Prompt engineering and sharing ===
Prompts for some text-to-image models can also include images and keywords and configurable parameters, such as artistic style, which is often used via keyphrases like "in the style of [name of an artist]" in the prompt /or selection of a broad aesthetic/art style. There are platforms for sharing, trading, searching, forking/refining, or collaborating on prompts for generating specific imagery from image generators. Prompts are often shared along with images on image-sharing websites such as Reddit and AI art-dedicated websites. A prompt is not the complete input needed for the generation of an image; additional inputs that determine the generated image include the output resolution, random seed, and random sampling parameters.
==== Related terminology ====
Synthetic media, which includes AI art, was described in 2022 as a major technology-driven trend that will affect business in the coming years. Harvard Kennedy School researchers voiced concerns about synthetic media serving as a vector for political misinformation soon after studying the proliferation of AI art on the X platform. Synthography is a proposed term for the practice of generating images that are similar to photographs using AI.
== Impact ==
=== Bias ===
A major concern raised about AI-generated images and art is sampling bias within model training data leading towards discriminatory output from AI art models. In 2023, University of Washington researchers found evidence of racial bias within the Stable Diffusion model, with images of a "person" corresponding most frequently with images of males from Europe or North America.
Looking more into the sampling bias found within AI training data, in 2017, researchers at Princeton University used AI software to link over 2 million words, finding that European names were viewed as more "pleasant" than African-Americans names, and that the words "woman" and "girl" were more likely to be associated with the arts instead of science and math, "which were most likely connected to males." Generative AI models typically work based on user-entered word-based prompts, especially in the case of diffusion models, and this word-related bias may lead to biased results.
Along with this, generative AI can perpetuate harmful stereotypes regarding women. For example, Lensa, an AI app that trended on TikTok in 2023, was known to lighten black skin, make users thinner, and generate hypersexualized images of women. Melissa Heikkilä, a senior reporter at MIT Technology Review, shared the findings of an experiment using Lensa, noting that the generated avatars did not resemble her and often depicted her in a hypersexualized manner. Experts suggest that such outcomes can result from biases in the datasets used to train AI models, which can sometimes contain imbalanced representations, including hypersexual or nude imagery.
In 2024, Google's chatbot Gemini's AI image generator was criticized for perceived racial bias, with claims that Gemini deliberately underrepresented white people in its results. Users reported that it generated images of white historical figures like the Founding Fathers, Nazi soldiers, and Vikings as other races, and that it refused to process prompts such as "happy white people" and "ideal nuclear family". Google later apologized for "missing the mark" and took Gemini's image generator offline for updates. This prompted discussions about the ethical implications of representing historical figures through a contemporary lens, leading critics to argue that these outputs could mislead audiences regarding actual historical contexts. In addition to the well-documented representational issues such as racial and gender bias, some scholars have also pointed out deeper conceptual assumptions that shape how we perceive AI-generated art. For instance, framing AI strictly as a passive tool overlooks how cultural and technological factors influence its outputs. Others suggest viewing AI as part of a collaborative creative process, where both human and machine contribute to the artistic result.
=== Copyright ===
Legal scholars, artists, and media corporations have considered the legal and ethical implications of artificial intelligence art since the 20th century. Some artists use AI art to critique and explore the ethics of using gathered data to produce new artwork.
In 1985, intellectual property law professor Pamela Samuelson argued that US copyright should allocate algorithmically generated artworks to the user of the computer program. A 2019 Florida Law Review article presented three perspectives on the issue. In the first, artificial intelligence itself would become the copyright owner; to do this, Section 101 of the US Copyright Act would need to be amended to define "author" as a computer. In the second, following Samuelson's argument, the user, programmer, or artificial intelligence company would be the copyright owner. This would be an expansion of the "work for hire" doctrine, under which ownership of a copyright is transferred to the "employer." In the third situation, copyright assignments would never take place, and such works would be in the public domain, as copyright assignments require an act of authorship.
In 2022, coinciding with the rising availability of consumer-grade AI image generation services, popular discussion renewed over the legality and ethics of AI-generated art. A particular topic is the inclusion of copyrighted artwork and images in AI training datasets, with artists objecting to commercial AI products using their works without consent, credit, or financial compensation. In September 2022, Reema Selhi, of the Design and Artists Copyright Society, stated that "there are no safeguards for artists to be able to identify works in databases that are being used and opt out." Some have claimed that images generated with these models can bear resemblance to extant artwork, sometimes including the remains of the original artist's signature. In December 2022, users of the portfolio platform ArtStation staged an online protest against non-consensual use of their artwork within datasets; this resulted in opt-out services, such as "Have I Been Trained?" increasing in profile, as well as some online art platforms promising to offer their own opt-out options. According to the US Copyright Office, artificial intelligence programs are unable to hold copyright, a decision upheld at the Federal District level as of August 2023 followed the reasoning from the monkey selfie copyright dispute.
OpenAI, the developer of DALL-E, has its own policy on who owns generated art. They assign the right and title of a generated image to the creator, meaning the user who inputted the prompt owns the image generated, along with the right to sell, reprint, and merchandise it.
In January 2023, three artists—Sarah Andersen, Kelly McKernan, and Karla Ortiz—filed a copyright infringement lawsuit against Stability AI, Midjourney, and DeviantArt, claiming that it is legally required to obtain the consent of artists before training neural nets on their work and that these companies infringed on the rights of millions of artists by doing so on five billion images scraped from the web. In July 2023, U.S. District Judge William Orrick was inclined to dismiss most of the lawsuits filed by Andersen, McKernan, and Ortiz, but allowed them to file a new complaint. Also in 2023, Stability AI was sued by Getty Images for using its images in the training data. A tool built by Simon Willison allowed people to search 0.5% of the training data for Stable Diffusion V1.1, i.e., 12 million of the 2.3 billion instances from LAION 2B. Artist Karen Hallion discovered that her copyrighted images were used as training data without their consent.
In March 2024, Tennessee enacted the ELVIS Act, which prohibits the use of AI to mimic a musician's voice without permission. A month later in that year, Adam Schiff introduced the Generative AI Copyright Disclosure Act which, if passed, would require that AI companies to submit copyrighted works in their datasets to the Register of Copyrights before releasing new generative AI systems. In November 2024, a group of artists and activists shared early access to OpenAI’s unreleased video generation model, Sora, via Huggingface. The action, accompanied by a statement, criticized the exploitative use of artists’ work by major corporations.'
=== Deception ===
As with other types of photo manipulation since the early 19th century, some people in the early 21st century have been concerned that AI could be used to create content that is misleading and can be made to damage a person's reputation, such as deepfakes. Artist Sarah Andersen, who previously had her art copied and edited to depict Neo-Nazi beliefs, stated that the spread of hate speech online can be worsened by the use of image generators. Some also generate images or videos for the purpose of catfishing.
AI systems have the ability to create deepfake content, which is often viewed as harmful and offensive. The creation of deepfakes poses a risk to individuals who have not consented to it. This mainly refers to deepfake pornography which is used as revenge porn, where sexually explicit material is disseminated to humiliate or harm another person. AI-generated child pornography has been deemed a potential danger to society due to its unlawful nature.
After winning the 2023 "Creative" "Open competition" Sony World Photography Awards, Boris Eldagsen stated that his entry was actually created with artificial intelligence. Photographer Feroz Khan commented to the BBC that Eldagsen had "clearly shown that even experienced photographers and art experts can be fooled". Smaller contests have been affected as well; in 2023, a contest run by author Mark Lawrence as Self-Published Fantasy Blog-Off was cancelled after the winning entry was allegedly exposed to be a collage of images generated with Midjourney.
In May 2023, on social media sites such as Reddit and Twitter, attention was given to a Midjourney-generated image of Pope Francis wearing a white puffer coat. Additionally, an AI-generated image of an attack on the Pentagon went viral as part of a hoax news story on Twitter.
In the days before March 2023 indictment of Donald Trump as part of the Stormy Daniels–Donald Trump scandal, several AI-generated images allegedly depicting Trump's arrest went viral online. On March 20, British journalist Eliot Higgins generated various images of Donald Trump being arrested or imprisoned using Midjourney v5 and posted them on Twitter; two images of Trump struggling against arresting officers went viral under the mistaken impression that they were genuine, accruing more than 5 million views in three days. According to Higgins, the images were not meant to mislead, but he was banned from using Midjourney services as a result. As of April 2024, the tweet had garnered more than 6.8 million views.
In February 2024, the paper Cellular functions of spermatogonial stem cells in relation to JAK/STAT signaling pathway was published using AI-generated images. It was later retracted from Frontiers in Cell and Developmental Biology because the paper "does not meet the standards".
To mitigate some deceptions, OpenAI developed a tool in 2024 to detect images that were generated by DALL-E 3. In testing, this tool accurately identified DALL-E 3-generated images approximately 98% of the time. The tool is also fairly capable of recognizing images that have been visually modified by users post-generation.
=== Income and employment stability ===
As generative AI image software such as Stable Diffusion and DALL-E continue to advance, the potential problems and concerns that these systems pose for creativity and artistry have risen. In 2022, artists working in various media raised concerns about the impact that generative artificial intelligence could have on their ability to earn money, particularly if AI-based images started replacing artists working in the illustration and design industries. In August 2022, digital artist R. J. Palmer stated that "I could easily envision a scenario where using AI, a single artist or art director could take the place of 5–10 entry level artists... I have seen a lot of self-published authors and such say how great it will be that they don’t have to hire an artist." Scholars Jiang et al. state that "Leaders of companies like Open AI and Stability AI have openly stated that they expect generative AI systems to replace creatives imminently." A 2022 case study found that AI-produced images created by technology like DALL-E caused some traditional artists to be concerned about losing work, while others use it to their advantage and view it as a tool.
AI-based images have become more commonplace in art markets and search engines because AI-based text-to-image systems are trained from pre-existing artistic images, sometimes without the original artist's consent, allowing the software to mimic specific artists' styles. For example, Polish digital artist Greg Rutkowski has stated that it is more difficult to search for his work online because many of the images in the results are AI-generated specifically to mimic his style. Furthermore, some training databases on which AI systems are based are not accessible to the public.
The ability of AI-based art software to mimic or forge artistic style also raises concerns of malice or greed. Works of AI-generated art, such as Théâtre D'opéra Spatial, a text-to-image AI illustration that won the grand prize in the August 2022 digital art competition at the Colorado State Fair, have begun to overwhelm art contests and other submission forums meant for small artists. The Netflix short film The Dog & the Boy, released in January 2023, received backlash online for its use of artificial intelligence art to create the film's background artwork. Within the same vein, Disney released Secret Invasion, a Marvel TV show with an AI-generated intro, on Disney+ in 2023, causing concern and backlash regarding the idea that artists could be made obsolete by machine-learning tools.
AI art has sometimes been deemed to be able to replace traditional stock images. In 2023, Shutterstock announced a beta test of an AI tool that can regenerate partial content of other Shutterstock's images. Getty Images and Nvidia have partnered with the launch of Generative AI by iStock, a model trained on Getty's library and iStock's photo library using Nvidia's Picasso model.
=== Power usage ===
Researchers from Hugging Face and Carnegie Mellon University reported in a 2023 paper that generating one thousand 1024×1024 images using Stable Diffusion's XL 1.0 base model requires 11.49 kWh of energy and generates 1,594 grams (56.2 oz) of carbon dioxide, which is roughly equivalent to driving an average gas-powered car a distance of 4.1 miles (6.6 km). Comparing 88 different models, the paper concluded that image-generation models used on average around 2.9 kWh of energy per 1,000 inferences.
== Analysis of existing art using AI ==
In addition to the creation of original art, research methods that use AI have been generated to quantitatively analyze digital art collections. This has been made possible due to the large-scale digitization of artwork in the past few decades. According to CETINIC and SHE (2022), using artificial intelligence to analyze already-existing art collections can provide new perspectives on the development of artistic styles and the identification of artistic influences.
Two computational methods, close reading and distant viewing, are the typical approaches used to analyze digitized art. Close reading focuses on specific visual aspects of one piece. Some tasks performed by machines in close reading methods include computational artist authentication and analysis of brushstrokes or texture properties. In contrast, through distant viewing methods, the similarity across an entire collection for a specific feature can be statistically visualized. Common tasks relating to this method include automatic classification, object detection, multimodal tasks, knowledge discovery in art history, and computational aesthetics. Synthetic images can also be used to train AI algorithms for art authentication and to detect forgeries.
Researchers have also introduced models that predict emotional responses to art. One such model is ArtEmis, a large-scale dataset paired with machine learning models. ArtEmis includes emotional annotations from over 6,500 participants along with textual explanations. By analyzing both visual inputs and the accompanying text descriptions from this dataset, ArtEmis enables the generation of nuanced emotional predictions.
== Other forms of art ==
AI has also been used in arts outside of visual arts. Generative AI has been used in video game production beyond imagery, especially for level design (e.g., for custom maps) and creating new content (e.g., quests or dialogue) or interactive stories in video games. AI has also been used in the literary arts, such as helping with writer's block, inspiration, or rewriting segments. In the culinary arts, some prototype cooking robots can dynamically taste, which can assist chefs in analyzing the content and flavor of dishes during the cooking process.
== See also ==
== References == | Wikipedia/AI-generated_imagery |
Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the landforms and features themselves, or a description or depiction in maps.
Topography is a field of geoscience and planetary science and is concerned with local detail in general, including not only relief, but also natural, artificial, and cultural features such as roads, land boundaries, and buildings. In the United States, topography often means specifically relief, even though the USGS topographic maps record not just elevation contours, but also roads, populated places, structures, land boundaries, and so on.
Topography in a narrow sense involves the recording of relief or terrain, the three-dimensional quality of the surface, and the identification of specific landforms; this is also known as geomorphometry. In modern usage, this involves generation of elevation data in digital form (DEM). It is often considered to include the graphic representation of the landform on a map by a variety of cartographic relief depiction techniques, including contour lines, hypsometric tints, and relief shading.
== Etymology ==
The term topography originated in ancient Greece and continued in ancient Rome, as the detailed description of a place. The word comes from the Greek τόπος (topos, "place") and -γραφία (-graphia, "writing"). In classical literature this refers to writing about a place or places, what is now largely called 'local history'. In Britain and in Europe in general, the word topography is still sometimes used in its original sense.
Detailed military surveys in Britain (beginning in the late eighteenth century) were called Ordnance Surveys, and this term was used into the 20th century as generic for topographic surveys and maps. The earliest scientific surveys in France were the Cassini maps after the family who produced them over four generations. The term "topographic surveys" appears to be American in origin. The earliest detailed surveys in the United States were made by the "Topographical Bureau of the Army", formed during the War of 1812, which became the Corps of Topographical Engineers in 1838. After the work of national mapping was assumed by the United States Geological Survey in 1878, the term topographical remained as a general term for detailed surveys and mapping programs, and has been adopted by most other nations as standard.
In the 20th century, the term topography started to be used to describe surface description in other fields where mapping in a broader sense is used, particularly in medical fields such as neurology.
== Objectives ==
An objective of topography is to determine the position of any feature or more generally any point in terms of both a horizontal coordinate system such as latitude, longitude, and altitude. Identifying (naming) features, and recognizing typical landform patterns are also part of the field.
A topographic study may be made for a variety of reasons: military planning and geological exploration have been primary motivators to start survey programs, but detailed information about terrain and surface features is essential for the planning and construction of any major civil engineering, public works, or reclamation projects.
== Techniques ==
There are a variety of approaches to studying topography. Which method(s) to use depends on the scale and size of the area under study, its accessibility, and the quality of existing surveys.
=== Field survey ===
Surveying helps determine accurately the terrestrial or three-dimensional space position of points and the distances and angles between them using leveling instruments such as theodolites, dumpy levels and clinometers.
GPS and other global navigation satellite systems (GNSS) are also used.
Work on one of the first topographic maps was begun in France by Giovanni Domenico Cassini, the great Italian astronomer.
Even though remote sensing has greatly sped up the process of gathering information, and has allowed greater accuracy control over long distances, the direct survey still provides the basic control points and framework for all topographic work, whether manual or GIS-based.
In areas where there has been an extensive direct survey and mapping program (most of Europe and the Continental U.S., for example), the compiled data forms the basis of basic digital elevation datasets such as USGS DEM data. This data must often be "cleaned" to eliminate discrepancies between surveys, but it still forms a valuable set of information for large-scale analysis.
The original American topographic surveys (or the British "Ordnance" surveys) involved not only recording of relief, but identification of landmark features and vegetative land cover.
=== Remote sensing ===
Remote sensing is a general term for geodata collection at a distance from the subject area.
==== Passive sensor methodologies ====
Besides their role in photogrammetry, aerial and satellite imagery can be used to identify and delineate terrain features and more general land-cover features. Certainly they have become more and more a part of geovisualization, whether maps or GIS systems. False-color and non-visible spectra imaging can also help determine the lie of the land by delineating vegetation and other land-use information more clearly. Images can be in visible colours and in other spectrum.
==== Photogrammetry ====
Photogrammetry is a measurement technique for which the co-ordinates of the points in 3D of an object are determined by the measurements made in two photographic images (or more) taken starting from different positions, usually from different passes of an aerial photography flight. In this technique, the common points are identified on each image. A line of sight (or ray) can be built from the camera location to the point on the object. It is the intersection of its rays (triangulation) which determines the relative three-dimensional position of the point. Known control points can be used to give these relative positions absolute values. More sophisticated algorithms can exploit other information on the scene known a priori (for example, symmetries in certain cases allowing the rebuilding of three-dimensional co-ordinates starting from one only position of the camera).
==== Active sensor methodologies ====
Satellite RADAR mapping is one of the major techniques of generating Digital Elevation Models (see below). Similar techniques are applied in bathymetric surveys using sonar to determine the terrain of the ocean floor. In recent years, LIDAR (LIght Detection And Ranging), a remote sensing technique that uses a laser instead of radio waves, has increasingly been employed for complex mapping needs such as charting canopies and monitoring glaciers.
== Forms of topographic data ==
Terrain is commonly modelled either using vector (triangulated irregular network or TIN) or gridded (raster image) mathematical models. In the most applications in environmental sciences, land surface is represented and modelled using gridded models. In civil engineering and entertainment businesses, the most representations of land surface employ some variant of TIN models. In geostatistics, land surface is commonly modelled as a combination of the two signals – the smooth (spatially correlated) and the rough (noise) signal.
In practice, surveyors first sample heights in an area, then use these to produce a Digital Land Surface Model in the form of a TIN. The DLSM can then be used to visualize terrain, drape remote sensing images, quantify ecological properties of a surface or extract land surface objects. The contour data or any other sampled elevation datasets are not a DLSM. A DLSM implies that elevation is available continuously at each location in the study area, i.e. that the map represents a complete surface. Digital Land Surface Models should not be confused with Digital Surface Models, which can be surfaces of the canopy, buildings and similar objects. For example, in the case of surface models produces using the lidar technology, one can have several surfaces – starting from the top of the canopy to the actual solid earth. The difference between the two surface models can then be used to derive volumetric measures (height of trees etc.).
=== Raw survey data ===
Topographic survey information is historically based upon the notes of surveyors. They may derive naming and cultural information from other local sources (for example, boundary delineation may be derived from local cadastral mapping). While of historical interest, these field notes inherently include errors and contradictions that later stages in map production resolve.
=== Remote sensing data ===
As with field notes, remote sensing data (aerial and satellite photography, for example), is raw and uninterpreted. It may contain holes (due to cloud cover for example) or inconsistencies (due to the timing of specific image captures). Most modern topographic mapping includes a large component of remotely sensed data in its compilation process.
=== Topographic mapping ===
In its contemporary definition, topographic mapping shows relief. In the United States, USGS topographic maps show relief using contour lines. The USGS calls maps based on topographic surveys, but without contours, "planimetric maps."
These maps show not only the contours, but also any significant streams or other bodies of water, forest cover, built-up areas or individual buildings (depending on scale), and other features and points of interest.
While not officially "topographic" maps, the national surveys of other nations share many of the same features, and so they are often called "topographic maps."
Existing topographic survey maps, because of their comprehensive and encyclopedic coverage, form the basis for much derived topographic work. Digital Elevation Models, for example, have often been created not from new remote sensing data but from existing paper topographic maps. Many government and private publishers use the artwork (especially the contour lines) from existing topographic map sheets as the basis for their own specialized or updated topographic maps.
Topographic mapping should not be confused with geological mapping. The latter is concerned with underlying structures and processes to the surface, rather than with identifiable surface features.
=== Digital elevation modeling ===
The digital elevation model (DEM) is a raster-based digital dataset of the topography (hypsometry and/or bathymetry) of all or part of the Earth (or a telluric planet). The pixels of the dataset are each assigned an elevation value, and a header portion of the dataset defines the area of coverage, the units each pixel covers, and the units of elevation (and the zero-point). DEMs may be derived from existing paper maps and survey data, or they may be generated from new satellite or other remotely sensed radar or sonar data.
=== Topological modeling ===
A geographic information system (GIS) can recognize and analyze the spatial relationships that exist within digitally stored spatial data. These topological relationships allow complex spatial modelling and analysis to be performed. Topological relationships between geometric entities traditionally include adjacency (what adjoins what), containment (what encloses what), and proximity (how close something is to something else).
reconstitute a sight in synthesized images of the ground,
determine a trajectory of overflight of the ground,
calculate surfaces or volumes,
trace topographic profiles,
== Topography in other fields ==
Topography has been applied to different science fields. In neuroscience, the neuroimaging discipline uses techniques such as EEG topography for brain mapping. In ophthalmology, corneal topography is used as a technique for mapping the surface curvature of the cornea. In tissue engineering, atomic force microscopy is used to map nanotopography.
In human anatomy, topography is superficial human anatomy.
In mathematics the concept of topography is used to indicate the patterns or general organization of features on a map or as a term referring to the pattern in which variables (or their values) are distributed in a space.
== Topographers ==
Topographers are experts in topography. They study and describe the surface features of a place or region.
== See also ==
Cartography
Digital elevation model
Fall line (topography)
Geomorphology
Global Relief Model
Hypsography
Marine topography
Sea-surface topography
Topographic map
Orography
== References == | Wikipedia/Topographical |
The Discovery of Grounded Theory is a 1967 book (ISBN 0-202-30260-1) by Barney Glaser and Anselm Strauss on grounded theory.
After their success with Awareness of Dying, Glaser and Strauss decided to write a book on methodology. The Discovery of Grounded Theory was meant to invite and motivate people to use the newly developed methodology. Unlike later works, it does not provide much advice on how to put the theory into practice.
The authors had several goals in mind when writing the book:
Legitimize qualitative research. Having a reference book by established authors helped students defend qualitative studies, which were not widely accepted at the time.
Criticize functionalists like Talcott Parsons, and his student Robert K. Merton, who in turn had been a teacher of Barney Glaser.
Demonstrate the possibility of building theories from data, something that many qualitative researchers doubt to this day, instead choosing to stick with mere ethnographic descriptions.
== References ==
Legewie, Heiner & Schervier-Legewie, Barbara (September 2004). "Forschung ist harte Arbeit, es ist immer ein Stück Leiden damit verbunden. Deshalb muss es auf der anderen Seite Spaß machen". Anselm Strauss interviewed by Heiner Legewie and Barbara Schervier-Legewie. Forum: Qualitative Social Research On-line Journal, 5(3), Art. 22. Interview as MP3 audio (English) / edited German translation of interview. Accessed on May 20, 2005.
Glaser, Barney G. and Strauss, Anselm L. (1967) The discovery of grounded theory: strategies for qualitative research. Chicago.: Aldine. | Wikipedia/The_Discovery_of_Grounded_Theory |
Qualitative research is a type of research that aims to gather and analyse non-numerical (descriptive) data in order to gain an understanding of individuals' social reality, including understanding their attitudes, beliefs, and motivation. This type of research typically involves in-depth interviews, focus groups, or field observations in order to collect data that is rich in detail and context. Qualitative research is often used to explore complex phenomena or to gain insight into people's experiences and perspectives on a particular topic. It is particularly useful when researchers want to understand the meaning that people attach to their experiences or when they want to uncover the underlying reasons for people's behavior. Qualitative methods include ethnography, grounded theory, discourse analysis, and interpretative phenomenological analysis. Qualitative research methods have been used in sociology, anthropology, political science, psychology, communication studies, social work, folklore, educational research, information science and software engineering research.
== Background ==
Qualitative research has been informed by several strands of philosophical thought and examines aspects of human life, including culture, expression, beliefs, morality, life stress, and imagination. Contemporary qualitative research has been influenced by a number of branches of philosophy, for example, positivism, postpositivism, critical theory, and constructivism.
The historical transitions or 'moments' in qualitative research, together with the notion of 'paradigms' (Denzin & Lincoln, 2005), have received widespread popularity over the past decades. However, some scholars have argued that the adoptions of paradigms may be counterproductive and lead to less philosophically engaged communities.
== Approaches to inquiry ==
The use of nonquantitative material as empirical data has been growing in many areas of the social sciences, including pedagogy, development psychology and cultural psychology. Several philosophical and psychological traditions have influenced investigators' approaches to qualitative research, including phenomenology, social constructionism, symbolic interactionism, and positivism.
=== Philosophical traditions ===
Phenomenology refers to the philosophical study of the structure of an individual's consciousness and general subjective experience. Approaches to qualitative research based on constructionism, such as grounded theory, pay attention to how the subjectivity of both the researcher and the study participants can affect the theory that develops out of the research. The symbolic interactionist approach to qualitative research examines how individuals and groups develop an understanding of the world. Traditional positivist approaches to qualitative research seek a more objective understanding of the social world. Qualitative researchers have also been influenced by the sociology of knowledge and the work of Alfred Schütz, Peter L. Berger, Thomas Luckmann, and Harold Garfinkel.
=== Sources of data ===
Qualitative researchers use different sources of data to understand the topic they are studying. These data sources include interview transcripts, videos of social interactions, notes, verbal reports and artifacts such as books or works of art. The case study method exemplifies qualitative researchers' preference for depth, detail, and context. Data triangulation is also a strategy used in qualitative research. Autoethnography, the study of self, is a qualitative research method in which the researcher uses his or her personal experience to understand an issue.
Grounded theory is an inductive type of research, based on ("grounded" in) a very close look at the empirical observations a study yields. Thematic analysis involves analyzing patterns of meaning. Conversation analysis is primarily used to analyze spoken conversations. Biographical research is concerned with the reconstruction of life histories, based on biographical narratives and documents. Narrative inquiry studies the narratives that people use to describe their experience.
== Data collection ==
Qualitative researchers may gather information through observations, note-taking, interviews, focus groups (group interviews), documents, images and artifacts.
=== Interviews ===
Research interviews are an important method of data collection in qualitative research. An interviewer is usually a professional or paid researcher, sometimes trained, who poses questions to the interviewee, in an alternating series of usually brief questions and answers, to elicit information. Compared to something like a written survey, qualitative interviews allow for a significantly higher degree of intimacy, with participants often revealing personal information to their interviewers in a real-time, face-to-face setting. As such, this technique can evoke an array of significant feelings and experiences within those being interviewed. Sociologists Bredal, Stefansen and Bjørnholt identified three "participant orientations", that they described as "telling for oneself", "telling for others" and "telling for the researcher". They also proposed that these orientations implied "different ethical contracts between the participant and researcher".
=== Participant observation ===
In participant observation ethnographers get to understand a culture by directly participating in the activities of the culture they study. Participant observation extends further than ethnography and into other fields, including psychology. For example, by training to be an EMT and becoming a participant observer in the lives of EMTs, Palmer studied how EMTs cope with the stress associated with some of the gruesome emergencies they deal with.
=== Recursivity ===
In qualitative research, the idea of recursivity refers to the emergent nature of research design. In contrast to standardized research methods, recursivity embodies the idea that the qualitative researcher can change a study's design during the data collection phase.
Recursivity in qualitative research procedures contrasts to the methods used by scientists who conduct experiments. From the perspective of the scientist, data collection, data analysis, discussion of the data in the context of the research literature, and drawing conclusions should be each undertaken once (or at most a small number of times). In qualitative research however, data are collected repeatedly until one or more specific stopping conditions are met, reflecting a nonstatic attitude to the planning and design of research activities. An example of this dynamism might be when the qualitative researcher unexpectedly changes their research focus or design midway through a study, based on their first interim data analysis. The researcher can even make further unplanned changes based on another interim data analysis. Such an approach would not be permitted in an experiment. Qualitative researchers would argue that recursivity in developing the relevant evidence enables the researcher to be more open to unexpected results and emerging new constructs.
== Data analysis ==
Qualitative researchers have a number of analytic strategies available to them.
=== Coding ===
In general, coding refers to the act of associating meaningful ideas with the data of interest. In the context of qualitative research, interpretative aspects of the coding process are often explicitly recognized and articulated; coding helps to produce specific words or short phrases believed to be useful abstractions from the data.
=== Pattern thematic analysis ===
Data may be sorted into patterns for thematic analyses as the primary basis for organizing and reporting the study findings.
=== Content analysis ===
According to Krippendorf, "Content analysis is a research technique for making replicable and valid inference from data to their context" (p. 21). It is applied to documents and written and oral communication. Content analysis is an important building block in the conceptual analysis of qualitative data. It is frequently used in sociology. For example, content analysis has been applied to research on such diverse aspects of human life as changes in perceptions of race over time, the lifestyles of contractors, and even reviews of automobiles.
== Issues ==
=== Computer-assisted qualitative data analysis software (CAQDAS) ===
Contemporary qualitative data analyses can be supported by computer programs (termed computer-assisted qualitative data analysis software). These programs have been employed with or without detailed hand coding or labeling. Such programs do not supplant the interpretive nature of coding. The programs are aimed at enhancing analysts' efficiency at applying, retrieving, and storing the codes generated from reading the data. Many programs enhance efficiency in editing and revising codes, which allow for more effective work sharing, peer review, data examination, and analysis of large datasets.
Common qualitative data analysis software includes:
ATLAS.ti
Dedoose (mixed methods)
MAXQDA (mixed methods)
NVivo
QDA MINER
A criticism of quantitative coding approaches is that such coding sorts qualitative data into predefined (nomothetic) categories that are reflective of the categories found in objective science. The variety, richness, and individual characteristics of the qualitative data are reduced or, even, lost.
To defend against the criticism that qualitative approaches to data are too subjective, qualitative researchers assert that by clearly articulating their definitions of the codes they use and linking those codes to the underlying data, they preserve some of the richness that might be lost if the results of their research boiled down to a list of predefined categories. Qualitative researchers also assert that their procedures are repeatable, which is an idea that is valued by quantitatively oriented researchers.
Sometimes researchers rely on computers and their software to scan and reduce large amounts of qualitative data. At their most basic level, numerical coding schemes rely on counting words and phrases within a dataset; other techniques involve the analysis of phrases and exchanges in analyses of conversations. A computerized approach to data analysis can be used to aid content analysis, especially when there is a large corpus to unpack.
=== Trustworthiness ===
A central issue in qualitative research is trustworthiness (also known as credibility or, in quantitative studies, validity). There are many ways of establishing trustworthiness, including member check, interviewer corroboration, peer debriefing, prolonged engagement, negative case analysis, auditability, confirmability, bracketing, and balance. Data triangulation and eliciting examples of interviewee accounts are two of the most commonly used methods of establishing the trustworthiness of qualitative studies.
Transferability of results has also been considered as an indicator of validity.
=== Limitations of qualitative research ===
Qualitative research is not without limitations. These limitations include participant reactivity, the potential for a qualitative investigator to over-identify with one or more study participants, "the impracticality of the Glaser-Strauss idea that hypotheses arise from data unsullied by prior expectations," the inadequacy of qualitative research for testing cause-effect hypotheses, and the Baconian character of qualitative research. Participant reactivity refers to the fact that people often behave differently when they know they are being observed. Over-identifying with participants refers to a sympathetic investigator studying a group of people and ascribing, more than is warranted, a virtue or some other characteristic to one or more participants. Compared to qualitative research, experimental research and certain types of nonexperimental research (e.g., prospective studies), although not perfect, are better means for drawing cause-effect conclusions.
Glaser and Strauss, influential members of the qualitative research community, pioneered the idea that theoretically important categories and hypotheses can emerge "naturally" from the observations a qualitative researcher collects, provided that the researcher is not guided by preconceptions. The ethologist David Katz wrote "a hungry animal divides the environment into edible and inedible things....Generally speaking, objects change...according to the needs of the animal." Karl Popper carrying forward Katz's point wrote that "objects can be classified and can become similar or dissimilar, only in this way--by being related to needs and interests. This rule applied not only to animals but also to scientists." Popper made clear that observation is always selective, based on past research and the investigators' goals and motives and that preconceptionless research is impossible.
The Baconian character of qualitative research refers to the idea that a qualitative researcher can collect enough observations such that categories and hypotheses will emerge from the data. Glaser and Strauss developed the idea of theoretical sampling by way of collecting observations until theoretical saturation is obtained and no additional observations are required to understand the character of the individuals under study. Bertrand Russell suggested that there can be no orderly arrangement of observations such that a hypothesis will jump out of those ordered observations; some provisional hypothesis usually guides the collection of observations.
== In psychology ==
=== Community psychology ===
Autobiographical narrative research has been conducted in the field of community psychology. A selection of autobiographical narratives of community psychologists can be found in the book Six Community Psychologists Tell Their Stories: History, Contexts, and Narrative.
=== Educational psychology ===
Edwin Farrell used qualitative methods to understand the social reality of at-risk high school students. Later he used similar methods to understand the reality of successful high school students who came from the same neighborhoods as the at-risk students he wrote about in his previously mentioned book.
=== Health psychology ===
In the field of health psychology, qualitative methods have become increasingly employed in research on understanding health and illness and how health and illness are socially constructed in everyday life. Since then, a broad range of qualitative methods have been adopted by health psychologists, including discourse analysis, thematic analysis, narrative analysis, and interpretative phenomenological analysis. In 2015, the journal Health Psychology published a special issue on qualitative research.
=== Industrial and organizational psychology ===
According to Doldor and colleagues organizational psychologists extensively use qualitative research "during the design and implementation of activities like organizational change, training needs analyses, strategic reviews, and employee development plans."
=== Occupational health psychology ===
Although research in the field of occupational health psychology (OHP) has predominantly been quantitatively oriented, some OHP researchers have employed qualitative methods. Qualitative research efforts, if directed properly, can provide advantages for quantitatively oriented OHP researchers. These advantages include help with (1) theory and hypothesis development, (2) item creation for surveys and interviews, (3) the discovery of stressors and coping strategies not previously identified, (4) interpreting difficult-to-interpret quantitative findings, (5) understanding why some stress-reduction interventions fail and others succeed, and (6) providing rich descriptions of the lived lives of people at work. Some OHP investigators have united qualitative and quantitative methods within a single study (e.g., Elfering et al., [2005]); these investigators have used qualitative methods to assess job stressors that are difficult to ascertain using standard measures and well validated standardized instruments to assess coping behaviors and dependent variables such as mood.
=== Social media psychology ===
Since the advent of social media in the early 2000s, formerly private accounts of personal experiences have become widely shared with the public by millions of people around the world. Disclosures are often made openly, which has contributed to social media's key role in movements like the #metoo movement.
The abundance of self-disclosure on social media has presented an unprecedented opportunity for qualitative and mixed methods researchers; mental health problems can now be investigated qualitatively more widely, at a lower cost, and with no intervention by the researchers. To take advantage of these data, researchers need to have mastered the tools for conducting qualitative research.
== Academic journals ==
Consumption Markets & Culture
Journal of Consumer Research
Qualitative Inquiry
Qualitative Market Research
Qualitative Research
The Qualitative Report
== See also ==
== References ==
== Further reading ==
Adler, P. A. & Adler, P. (1987). : context and meaning in social inquiry / edited by Richard Jessor, Anne Colby, and Richard A. Shweder OCLC 46597302
Baškarada, S. (2014) "Qualitative Case Study Guidelines", in The Qualitative Report, 19(40): 1-25. Available from [1]
Boas, Franz (1943). "Recent anthropology". Science. 98 (2546): 311–314, 334–337. Bibcode:1943Sci....98..334B. doi:10.1126/science.98.2546.334. PMID 17794461.
Creswell, J. W. (2003). Research design: Qualitative, quantitative, and mixed method approaches. Thousand Oaks, CA: Sage Publications.
Denzin, N. K., & Lincoln, Y. S. (2000). Handbook of qualitative research ( 2nd ed.). Thousand Oaks, CA: Sage Publications.
Denzin, N. K., & Lincoln, Y. S. (2011). The SAGE Handbook of qualitative research ( 4th ed.). Los Angeles: Sage Publications.
DeWalt, K. M. & DeWalt, B. R. (2002). Participant observation. Walnut Creek, CA: AltaMira Press.
Fischer, C.T. (Ed.) (2005). Qualitative research methods for psychologists: Introduction through empirical studies. Academic Press. ISBN 0-12-088470-4.
Franklin, M. I. (2012), "Understanding Research: Coping with the Quantitative-Qualitative Divide". London/New York. Routledge
Giddens, A. (1990). The consequences of modernity. Stanford, CA: Stanford University Press.
Gubrium, J. F. and J. A. Holstein. (2000). "The New Language of Qualitative Method." New York: Oxford University Press.
Gubrium, J. F. and J. A. Holstein (2009). "Analyzing Narrative Reality." Thousand Oaks, CA: Sage.
Gubrium, J. F. and J. A. Holstein, eds. (2000). "Institutional Selves: Troubled Identities in a Postmodern World." New York: Oxford University Press.
Hammersley, M. (2008) Questioning Qualitative Inquiry, London, Sage.
Hammersley, M. (2013) What is qualitative research?, London, Bloomsbury.
Holliday, A. R. (2007). Doing and Writing Qualitative Research, 2nd Edition. London: Sage Publications
Holstein, J. A. and J. F. Gubrium, eds. (2012). "Varieties of Narrative Analysis." Thousand Oaks, CA: Sage.
Kaminski, Marek M. (2004). Games Prisoners Play. Princeton University Press. ISBN 0-691-11721-7.
Mahoney, J; Goertz, G (2006). "A Tale of Two Cultures: Contrasting Quantitative and Qualitative Research". Political Analysis. 14 (3): 227–249. CiteSeerX 10.1.1.135.3256. doi:10.1093/pan/mpj017.
Malinowski, B. (1922/1961). Argonauts of the Western Pacific. New York: E. P. Dutton.
Miles, M. B. & Huberman, A. M. (1994). Qualitative Data Analysis. Thousand Oaks, CA: Sage.
Pamela Maykut, Richard Morehouse. 1994 Beginning Qualitative Research. Falmer Press.
Pernecky, T. (2016). Epistemology and Metaphysics for Qualitative Research. London, UK: Sage Publications.
Patton, M. Q. (2002). Qualitative research & evaluation methods ( 3rd ed.). Thousand Oaks, CA: Sage Publications.
Pawluch D. & Shaffir W. & Miall C. (2005). Doing Ethnography: Studying Everyday Life. Toronto, ON Canada: Canadian Scholars' Press.
Racino, J. (1999). Policy, Program Evaluation and Research in Disability: Community Support for All." New York, NY: Haworth Press (now Routledge imprint, Francis and Taylor, 2015).
Ragin, C. C. (1994). Constructing Social Research: The Unity and Diversity of Method, Pine Forge Press, ISBN 0-8039-9021-9
Riessman, Catherine K. (1993). "Narrative Analysis." Thousand Oaks, CA: Sage.
Rosenthal, Gabriele (2018). Interpretive Social Research. An Introduction. Göttingen, Germany: Universitätsverlag Göttingen.
Savin-Baden, M. and Major, C. (2013). "Qualitative research: The essential guide to theory and practice." London, Rutledge.
Silverman, David, (ed), (2011), "Qualitative Research: Issues of Theory, Method and Practice". Third Edition. London, Thousand Oaks, New Delhi, Sage Publications
Stebbins, Robert A. (2001) Exploratory Research in the Social Sciences. Thousand Oaks, CA: Sage.
Taylor, Steven J., Bogdan, Robert, Introduction to Qualitative Research Methods, Wiley, 1998, ISBN 0-471-16868-8
Van Maanen, J. (1988) Tales of the field: on writing ethnography, Chicago: University of Chicago Press.
Wolcott, H. F. (1995). The art of fieldwork. Walnut Creek, CA: AltaMira Press.
Wolcott, H. F. (1999). Ethnography: A way of seeing. Walnut Creek, CA: AltaMira Press.
Ziman, John (2000). Real Science: what it is, and what it means. Cambridge, Uk: Cambridge University Press.
== External links ==
Qualitative Philosophy
C.Wright Mills, On intellectual Craftsmanship, The Sociological Imagination,1959
Participant Observation, Qualitative research methods: a Data collector's field guide
Analyzing and Reporting Qualitative Market Research
Overview of available QDA Software
=== Videos ===
Qualitative analysis, with a focus on interview data on YouTube
Living Theory Approach to Qualitative Action Research on YouTube
Yale University series by Leslie Curry on YouTube | Wikipedia/Qualitative_methods |
The Network Time Protocol (NTP) is a networking protocol for clock synchronization between computer systems over packet-switched, variable-latency data networks. In operation since before 1985, NTP is one of the oldest Internet protocols in current use. NTP was designed by David L. Mills of the University of Delaware.
NTP is intended to synchronize participating computers to within a few milliseconds of Coordinated Universal Time (UTC).: 3 It uses the intersection algorithm, a modified version of Marzullo's algorithm, to select accurate time servers and is designed to mitigate the effects of variable network latency. NTP can usually maintain time to within tens of milliseconds over the public Internet, and can achieve better than one millisecond accuracy in local area networks under ideal conditions. Asymmetric routes and network congestion can cause errors of 100 ms or more.
The protocol is usually described in terms of a client–server model, but can as easily be used in peer-to-peer relationships where both peers consider the other to be a potential time source.: 20 Implementations send and receive timestamps using the User Datagram Protocol (UDP) on port number 123.: 16 They can also use broadcasting or multicasting, where clients passively listen to time updates after an initial round-trip calibrating exchange. NTP supplies a warning of any impending leap second adjustment, but no information about local time zones or daylight saving time is transmitted.
The current protocol is version 4 (NTPv4), which is backward compatible with version 3.
== Clock synchronization algorithm ==
A typical NTP client regularly polls one or more NTP servers. The client must compute its time offset and round-trip delay. Time offset θ is positive or negative (client time > server time) difference in absolute time between the two clocks. It is defined by
θ
=
(
t
1
−
t
0
)
+
(
t
2
−
t
3
)
2
,
{\displaystyle \theta ={\frac {(t_{1}-t_{0})+(t_{2}-t_{3})}{2}},}
and the round-trip delay δ by
δ
=
(
t
3
−
t
0
)
−
(
t
2
−
t
1
)
,
{\displaystyle \delta ={(t_{3}-t_{0})-(t_{2}-t_{1})},}
where
t0 is the client's timestamp of the request packet transmission,
t1 is the server's timestamp of the request packet reception,
t2 is the server's timestamp of the response packet transmission and
t3 is the client's timestamp of the response packet reception.: 19
To derive the expression for the offset, note that for the request packet,
t
0
+
θ
+
δ
/
2
=
t
1
{\displaystyle t_{0}+\theta +\delta /2=t_{1}}
and for the response packet,
t
3
+
θ
−
δ
/
2
=
t
2
{\displaystyle t_{3}+\theta -\delta /2=t_{2}}
Solving for θ yields the definition of the time offset.
The values for θ and δ are passed through filters and subjected to statistical analysis ("mitigation"). Outliers are discarded and an estimate of time offset is derived from the best three remaining candidates. The clock frequency is then adjusted to reduce the offset gradually ("discipline"), creating a feedback loop.: 20
Accurate synchronization is achieved when both the incoming and outgoing routes between the client and the server have symmetrical nominal delay. If the routes do not have a common nominal delay, a systematic bias exists of half the difference between the forward and backward travel times. A number of approaches have been proposed to measure asymmetry, but among practical implementations only chrony seems to have one included.
== History ==
In 1979, network time synchronization technology was used in what was possibly the first public demonstration of Internet services running over a trans-Atlantic satellite network, at the National Computer Conference in New York. The technology was later described in the 1981 Internet Engineering Note (IEN) 173 and a public protocol was developed from it that was documented in RFC 778. The technology was first deployed in a local area network as part of the Hello routing protocol and implemented in the Fuzzball router, an experimental operating system used in network prototyping, where it ran for many years.
Other related network tools were available both then and now. They include the Daytime and Time protocols for recording the time of events, as well as the ICMP Timestamp messages and IP Timestamp option (RFC 781). More complete synchronization systems, although lacking NTP's data analysis and clock disciplining algorithms, include the Unix daemon timed, which uses an election algorithm to appoint a server for all the clients; and the Digital Time Synchronization Service (DTSS), which uses a hierarchy of servers similar to the NTP stratum model.
In 1985, NTP version 0 (NTPv0) was implemented in both Fuzzball and Unix, and the NTP packet header and round-trip delay and offset calculations, which have persisted into NTPv4, were documented in RFC 958. Despite the relatively slow computers and networks available at the time, accuracy of better than 100 milliseconds was usually obtained on Atlantic spanning links, with accuracy of tens of milliseconds on Ethernet networks.
In 1988, a much more complete specification of the NTPv1 protocol, with associated algorithms, was published in RFC 1059. It drew on the experimental results and clock filter algorithm documented in RFC 956 and was the first version to describe the client–server and peer-to-peer modes. In 1991, the NTPv1 architecture, protocol and algorithms were brought to the attention of a wider engineering community with the publication of an article by David L. Mills in the IEEE Transactions on Communications.
In 1989, RFC 1119 was published defining NTPv2 by means of a state machine, with pseudocode to describe its operation. It introduced a management protocol and cryptographic authentication scheme which have both survived into NTPv4, along with the bulk of the algorithm. However the design of NTPv2 was criticized for lacking formal correctness by the DTSS community, and the clock selection procedure was modified to incorporate Marzullo's algorithm for NTPv3 onwards.
In 1992, RFC 1305 defined NTPv3. The RFC included an analysis of all sources of error, from the reference clock down to the final client, which enabled the calculation of a metric that helps choose the best server where several candidates appear to disagree. Broadcast mode was introduced.
In subsequent years, as new features were added and algorithm improvements were made, it became apparent that a new protocol version was required. In 2010, RFC 5905 was published containing a proposed specification for NTPv4. Following the retirement of Mills from the University of Delaware, the reference implementation is currently maintained as an open source project led by Harlan Stenn. On the IANA side, a ntp (network time protocols) work group is in charge of reviewing proposed drafts.
The protocol has significantly progressed since NTPv4. As of 2022, three RFC documents describing updates to the protocol have been published, not counting the numerous peripheral standards such as Network Time Security. Mills had mentioned plans for a "NTPv5" on his page, but one was never published. An unrelated draft termed "NTPv5" by M. Lichvar of chrony was initiated in 2020 and includes security, accuracy, and scaling changes.
=== SNTP ===
As NTP replaced the use of the old Time Protocol, some use cases nevertheless found the full protocol too complicated. In 1992, Simple Network Time Protocol (SNTP) was defined to fill this niche. The SNTPv3 standard describes a way to use NTPv3, such that no storage of state over an extended period is needed. The topology becomes essentially the same as with the Time Protocol, as only one server is used. In 1996, SNTP was updated to SNTPv4 with some features of the then-in-development NTPv4. The current version of SNTPv4 was merged into the main NTPv4 standard in 2010. SNTP is fully interoperable with NTP since it does not define a new protocol.: §14 However, the simple algorithms provide times of reduced accuracy and thus it is inadvisable to sync time from an SNTP source.
== Clock strata ==
NTP uses a hierarchical, semi-layered system of time sources. Each level of this hierarchy is termed a stratum and is assigned a number starting with zero for the reference clock at the top. A server synchronized to a stratum n server runs at stratum n + 1. The number represents the distance from the reference clock and is used to prevent cyclical dependencies in the hierarchy. Stratum is not always an indication of quality or reliability; it is common to find stratum 3 time sources that are higher quality than other stratum 2 time sources. A brief description of strata 0, 1, 2 and 3 is provided below.
Stratum 0
These are high-precision timekeeping devices such as atomic clocks, GNSS (including GPS) or other radio clocks, or a PTP-synchronized clock. They generate a very accurate pulse per second signal that triggers an interrupt and timestamp on a connected computer. Stratum 0 devices are also known as reference clocks. NTP servers cannot advertise themselves as stratum 0. A stratum field set to 0 in NTP packet indicates an unspecified stratum.: 21
Stratum 1
These are computers whose system time is synchronized to within a few microseconds of their attached stratum 0 devices. Stratum 1 servers may peer with other stratum 1 servers for sanity check and backup. They are also referred to as primary time servers.
Stratum 2
These are computers that are synchronized over a network to stratum 1 servers. Often a stratum 2 computer queries several stratum 1 servers. Stratum 2 computers may also peer with other stratum 2 computers to provide more stable and robust time for all devices in the peer group.
Stratum 3
These are computers that are synchronized to stratum 2 servers. They employ the same algorithms for peering and data sampling as stratum 2, and can themselves act as servers for stratum 4 computers, and so on.
The upper limit for stratum is 15; stratum 16 is used to indicate that a device is unsynchronized. The NTP algorithms on each computer interact to construct a Bellman–Ford shortest-path spanning tree, to minimize the accumulated round-trip delay to the stratum 1 servers for all the clients.: 20
In addition to stratum, the protocol is able to identify the synchronization source for each server in terms of a reference identifier (refid).
For servers on stratum 2 and below, the refid is an encoded form of the upstream time server's IP address. For IPv4, this is simply the 32-bit address; for IPv6, it would be the first 32 bits of the MD5 hash of the source address. Refids serve to detect and prevent timing loops to the first degree.
The refid field is filled with status words in the case of kiss-o'-death (KoD) packets, which tell the client to stop sending requests so that the server can rest. Some examples are INIT (initialization), STEP (step time change), and RATE (client requesting too fast). The program output may additionally use codes not transmitted in the packet to indicate error, such as XFAC to indicate a network disconnection.
The IANA maintains a registry for refid source names and KoD codes. Informal assignments can still appear.
== Software implementations ==
=== Reference implementation ===
The NTP reference implementation, along with the protocol, has been continuously developed for over 20 years. Backwards compatibility has been maintained as new features have been added. It contains several sensitive algorithms, especially to discipline the clock, that can misbehave when synchronized to servers that use different algorithms. The software has been ported to almost every computing platform, including personal computers. It runs as a daemon called ntpd under Unix or as a service under Windows. Reference clocks are supported and their offsets are filtered and analysed in the same way as remote servers, although they are usually polled more frequently.: 15–19 This implementation was audited in 2017, finding 14 potential security issues.
=== Windows Time ===
All Microsoft Windows versions since Windows 2000 include the Windows Time service (W32Time), which has the ability to synchronize the computer clock to an NTP server.
W32Time was originally implemented for the purpose of the Kerberos version 5 authentication protocol, which required time to be within 5 minutes of the correct value to prevent replay attacks. The network time server in Windows 2000 Server (and Windows XP) does not implement NTP disciplined synchronization, only locally disciplined synchronization with NTP/SNTP correction.
Beginning with Windows Server 2003 and Windows Vista, the NTP provider for W32Time became compatible with a significant subset of NTPv3. Microsoft states that W32Time cannot reliably maintain time synchronization with one second accuracy. If higher accuracy is desired, Microsoft recommends using a newer version of Windows or different NTP implementation.
Beginning with Windows 10 version 1607 and Windows Server 2016, W32Time can be configured to reach time accuracy of 1 s, 50 ms or 1 ms under certain specified operating conditions.
=== OpenNTPD ===
In 2004, Henning Brauer of OpenBSD presented OpenNTPD, an NTPv3/SNTPv4 implementation with a focus on security and encompassing a privilege separated design. Whilst it is aimed more closely at the simpler generic needs of OpenBSD users, it also includes some protocol security improvements while still being compatible with existing NTP servers. The simpler code base sacrifices accuracy, deemed unnecessary in this use case. A portable version is available in Linux package repositories.
=== NTPsec ===
NTPsec is a fork of the reference implementation that has been systematically security-hardened. The fork point was in June 2015 and was in response to a series of compromises in 2014. The first production release shipped in October 2017. Between removal of unsafe features, removal of support for obsolete hardware, and removal of support for obsolete Unix variants, NTPsec has been able to pare away 75% of the original codebase, making the remainder easier to audit. A 2017 audit of the code showed eight security issues, including two that were not present in the original reference implementation, but NTPsec did not suffer from eight other issues that remained in the reference implementation.
=== chrony ===
chrony is an independent NTP implementation mainly sponsored by Red Hat, who uses it as the default time program in their distributions. Being written from scratch, chrony has a simpler codebase allowing for better security and lower resource consumption. It does not however compromise on accuracy, instead syncing faster and better than the reference ntpd in many circumstances. It is versatile enough for ordinary computers, which are unstable, go into sleep mode or have intermittent connection to the Internet. It is also designed for virtual machines, a more unstable environment.
chrony has been evaluated as "trustworthy", with only a few incidents. It is able to achieve improved precision on LAN connections, using hardware timestamping on the network adapter. Support for Network Time Security (NTS) was added on version 4.0. chrony is available under GNU General Public License version 2, was created by Richard Curnow in 1997 and is currently maintained by Miroslav Lichvar.
=== ntpd-rs ===
ntpd-rs is a security-focused implementation of the NTP protocol, founded by the Internet Security Research Group as part of their Prossimo initiative for the creation of memory safe Internet infrastructure. ntpd-rs is implemented in Rust programming language which offers memory safety guarantees in addition to the Real-time computing capabilities which are required for an NTP implementation. ntpd-rs is used in security-sensitive environments such as the Let's Encrypt non-profit Certificate Authority. Support for NTS is available. ntpd-rs is part of the "Pendulum" project which also includes a Precision Time Protocol implementation "statime". Both projects are available under Apache and MIT software licenses.
=== Others ===
Ntimed was started by Poul-Henning Kamp of FreeBSD in 2014 and abandoned in 2015. The implementation was sponsored by the Linux Foundation.
systemd-timesyncd is the SNTP client built into systemd. It is used by Debian since version "bookworm" and the downstream Ubuntu.
== Leap seconds ==
On the day of a leap second event, ntpd receives notification from either a configuration file, an attached reference clock, or a remote server. Although the NTP clock is actually halted during the event, because of the requirement that time must appear to be strictly increasing, any processes that query the system time cause it to increase by a tiny amount, preserving the order of events. If a negative leap second should ever become necessary, it would be deleted with the sequence 23:59:58, 00:00:00, skipping 23:59:59.
An alternative implementation, called leap smearing, consists in introducing the leap second incrementally during a period of 24 hours, from noon to noon in UTC time. This implementation is used by Google (both internally and on their public NTP servers), Amazon AWS, and Facebook. chrony supports leap smear in smoothtime and leapsecmode configurations, but such use is not to be mixed with a public NTP pool as leap smear is non-standard and will throw off client calculation in a mix.
== Security concerns ==
Because adjusting system time is generally a privileged operation, part or all of NTP code has to be run with some privileges in order to support its core functionality. Only a few other security problems have been identified in the reference implementation of the NTP codebase, but those that appeared in 2009 were cause for significant concern. The protocol has been undergoing revision and review throughout its history. The codebase for the reference implementation has undergone security audits from several sources for several years.
A stack buffer overflow exploit was discovered and patched in 2014. Apple was concerned enough about this vulnerability that it used its auto-update capability for the first time. On systems using the reference implementation, which is running with root user's credential, this could allow unlimited access. Some other implementations, such as OpenNTPD, have smaller code base and adopted other mitigation measures like privilege separation, are not subject to this flaw.
A 2017 security audit of three NTP implementations, conducted on behalf of the Linux Foundation's Core Infrastructure Initiative, suggested that both NTP and NTPsec were more problematic than chrony from a security standpoint.
NTP servers can be susceptible to man-in-the-middle attacks unless packets are cryptographically signed for authentication. The computational overhead involved can make this impractical on busy servers, particularly during denial of service attacks. NTP message spoofing from a man-in-the-middle attack can be used to alter clocks on client computers and allow a number of attacks based on bypassing of cryptographic key expiration. Some of the services affected by fake NTP messages identified are TLS, DNSSEC, various caching schemes (such as DNS cache), Border Gateway Protocol (BGP), Bitcoin and a number of persistent login schemes.
NTP has been used in distributed denial of service attacks. A small query is sent to an NTP server with the return IP address spoofed to be the target address. Similar to the DNS amplification attack, the server responds with a much larger reply that allows an attacker to substantially increase the amount of data being sent to the target. To avoid participating in an attack, NTP server software can be upgraded or servers can be configured to ignore external queries.
=== Secure extensions ===
NTP itself includes support for authenticating servers to clients. NTPv3 supports a symmetric key mode, which is not useful against MITM. The public key system known as "autokey" in NTPv4 adapted from IPSec offers useful authentication, but is not practical for a busy server. Autokey was also later found to suffer from several design flaws, with no correction published, save for a change in the message authentication code. Autokey should no longer be used.
Network Time Security (NTS) is a secure version of NTPv4 with TLS and AEAD. The main improvement over previous attempts is that a separate "key establishment" server handles the heavy asymmetric cryptography, which needs to be done only once. If the server goes down, previous users would still be able to fetch time without fear of MITM. NTS is supported by several NTP servers including Cloudflare and Netnod. It can be enabled on chrony, NTPsec, and ntpd-rs.
Microsoft also has an approach to authenticate NTPv3/SNTPv4 packets using a Windows domain identity, known as MS-SNTP. This system is implemented in the reference ntpd and chrony, using samba for the domain connection.
== NTP packet header format ==
LI (Leap Indicator): 2 bits
Warning of leap second insertion or deletion:
0 = no warning
1 = last minute has 61 seconds
2 = last minute has 59 seconds
3 = unknown (clock unsynchronized)
VN (Version Number): 3 bits
NTP version number, typically 4.
Mode: 3 bits
Association mode:
0 = reserved
1 = symmetric active
2 = symmetric passive
3 = client
4 = server
5 = broadcast
6 = control
7 = private
Stratum: 8 bits
Indicates the distance from the reference clock.
0 = invalid
1 = primary server
2–15 = secondary
16 = unsynchronized
Poll: 8 bits
Maximum interval between successive messages, in log₂(seconds). Typical range is 6 to 10.
Precision: 8 bits
Signed log₂(seconds) of system clock precision (e.g., –18 ≈ 1 microsecond).
Root Delay: 32 bits
Total round-trip delay to the reference clock, in NTP short format.
Root Dispersion: 32 bits
Total dispersion to the reference clock, in NTP short format.
Reference ID: 32 bits
Identifies the specific server or reference clock; interpretation depends on Stratum.
Reference Timestamp: 64 bits
Time when the system clock was last set or corrected, in NTP timestamp format.
Origin Timestamp (org): 64 bits
Time at the client when the request departed, in NTP timestamp format.
Receive Timestamp (rec): 64 bits
Time at the server when the request arrived, in NTP timestamp format.
Transmit Timestamp (xmt): 64 bits
Time at the server when the response left, in NTP timestamp format.
Extension Field: variable
Optional field(s) for NTP extensions (see , Section 7.5).
Key Identifier: 32 bits
Unsigned integer designating an MD5 key shared by the client and server.
Message Digest (MD5): 128 bits
MD5 hash covering the packet header and extension fields, used for authentication.
=== Timestamps ===
The 64-bit binary fixed-point timestamps used by NTP consist of a 32-bit part for seconds and a 32-bit part for fractional second, giving a time scale that rolls over every 232 seconds (136 years) and a theoretical resolution of 2−32 seconds (233 picoseconds). NTP uses an epoch of January 1, 1900. Therefore, the first rollover occurs on February 7, 2036.
NTPv4 introduces a 128-bit date format: 64 bits for the second and 64 bits for the fractional-second. The most-significant 32 bits of this format is the Era Number which resolves rollover ambiguity in most cases. According to Mills, "The 64-bit value for the fraction is enough to resolve the amount of time it takes a photon to pass an electron at the speed of light. The 64-bit second value is enough to provide unambiguous time representation until the universe goes dim."
== See also ==
Allan variance – Measure of frequency stability in clocks and oscillators
Clock network – Set of clocks that synchronized to same time
International Atomic Time – Time standard based on atomic clocks
IRIG timecode – Standard formats for transferring time information
NITZ – Mechanism for time synchronisation on mobile devices
NTP pool – Networked computers providing time synchronization
Ntpdate – Software to synchronize computer time
Precision Time Protocol – Network time synchronization protocol
== Notes ==
== References ==
== Further reading ==
Definitions of Managed Objects for Network Time Protocol Version 4 (NTPv4). doi:10.17487/RFC5907. RFC 5907.
Network Time Protocol (NTP) Server Option for DHCPv6. doi:10.17487/RFC5908. RFC 5908.
== External links ==
Official website
Official Stratum One Time Servers list
IETF NTP working group
Microsoft Windows accurate time guide and more
Time and NTP paper
NTP Survey 2005
Current NIST leap seconds file compatible with ntpd
David L. Mills, A Brief History of NTP Time: Confessions of an Internet Timekeeper (PDF), retrieved 7 February 2021 | Wikipedia/Simple_Network_Time_Protocol |
Transaction Capabilities Application Part, from ITU-T recommendations Q.771-Q.775 or ANSI T1.114 is a protocol for Signalling System 7 networks. Its primary purpose is to facilitate multiple concurrent dialogs between the same sub-systems on the same machines, using Transaction IDs to differentiate these, similar to the way TCP ports facilitate multiplexing connections between the same IP addresses on the Internet.
TCAP uses ASN.1 BER encoding, as well as the protocols it encapsulates, namely MAP in mobile phone networks or INAP in Intelligent Networks.
== Overview ==
TCAP messages are sent over the wire between machines. TCAP primitives are sent between the application and the local TCAP stack. All TCAP messages are primitives but there are primitives that are not messages. In other words, some are only transferred inside the local machine. A TCAP primitive is made up of one or more TCAP components.
An ITU-T TCAP primitive may be one of the following types:
A Begin primitive has an Originating Transaction ID (up to 4 bytes). A Continue primitive has an Originating Transaction ID and a Destination Transaction ID. End and Abort primitives only have a Destination Transaction ID. Each primitive has both an optional component and (optional) dialogue portions. The component portion for the unidirectional primitive is mandatory.
The dialogue portion carries dialogue or unidialogue control PDUs. For MAP and INAP, dialogue PDU is used which performs establishment and release of dialogues for the application context provided in the primitives. Following primitives are defined for the dialogue PDU:
Each ITU-T TCAP component may be one of the following types:
Invoke components have a signed 7 bit InvokeID which is present in all the other components to identify which invoke they relate to.
TCAP is based on the OSI defined ROSE, Remote Operations Services Element protocol.
== Transaction ID ==
The transaction ID is a TCAP reference for a set of TCAP operations that are performed within a single dialog. When machine A starts a TCAP dialog with another machine B, A sends a Begin message to B. This Begin message contains an Originating Transaction ID, which is the Transaction ID reference for A. When machine B replies to A with a Continue message, it includes A's Transaction ID as the Destination Transaction ID. Furthermore, B includes its own Transaction ID as the Originating Transaction ID.
As the TCAP dialog goes on, each Continue message includes the Transaction ID of the destination machine as the Destination Transaction ID and the Transaction ID of the originating machine as the Originating Transaction ID. When either machine wants to close the dialog, it sends an End message or an Abort message to the other machine. This message contains the Destination Transaction ID only.
== Invoke ID ==
Invoke ID is a TCAP reference for a specific TCAP operation and must be unique within a dialog.
== Decoded TCAP Message ==
This is a MO-SMS sent by a MAP layer and the hex stream is taken from TCAP layer.
62 74 48 04 00 02 00 30 6B 1A 28 18 06 07 00 11 86 05 01 01 01 A0 0D 60 0B A1 09 06 07 04 00 00
01 00 19 02 6C 50 A1 4E 02 01 01 02 01 2E 30 46 80 05 70 31 42 44 44 84 06 A1 70 91 92 55 55 04
35 2F 09 00 70 97 92 62 23 04 00 90 20 11 80 01 24 00 27 43 50 7A 0E A2 A3 CB 20 71 79 4E 07 B1
C3 EE 73 3D 7C 2E 83 D2 20 74 D8 5E 06 95 ED 65 39 68 5E 2E BB 01 00
According to tag length values, this can be decoded as below.
'--> 62|74 <- Start of Tcap begin message
|
'--> 48|04:00 02 00 30 <- Transaction ID
|
'--> 6B|1A <- Start of Dialog portion
|
'--> 28|18
|
'--> 06|07:00 11 86 05 01 01 01
|
'--> A0|0D
|
'--> 60|0B
|
'--> A1|09
|
'--> 06|07:04 00 00 01 00 19 02 <- Application context
|
'--> 6C|50 <- Start of component portion
|
'--> A1|4E
|
'--> 02|01:01 <- Component Id (invoke id)
|
'--> 02|01:2E <- Operation Code
|
'--> 30|46 <- Start of parameter buffer
|
'--> 80|05:70 31 42 44 44 <- SM-RP-DA(BCD)
|
'--> 84|06:A1 70 91 92 55 55 <- SM-RP-OA(BCD)
|
'--> 04|35:2F 09 00 70 97 92 62 23 04 00 90 20 11 80 01 24 00 27 43 50 7A 0E A2 A3 CB 20 71 79 4E 07 B1 C3 EE 73 3D 7C 2E 83 D2 20 74 D8 5E 06 95 ED 65 39 68 5E 2E BB 01 <- SM-RP-UI
== External links ==
ITU Q.771: Functional description of transaction capabilities
ITU Q.772: Transaction capabilities information element definitions
ITU Q.773: Transaction capabilities formats and encoding
ITU Q.774: Transaction capabilities procedures
ITU Q.775: Guidelines for using transaction capabilities
[1]: TCAP ASN1 specification | Wikipedia/Transaction_Capabilities_Application_Part |
The eDonkey Network (also known as the eDonkey2000 network or eD2k) is a decentralized, mostly server-based, peer-to-peer file-sharing network created in 2000 by US developers Jed McCaleb and Sam Yagan that is best suited to share big files among users, and to provide long term availability of files. Like most sharing networks, it is decentralized, as there is no central hub for the network; also, files are not stored on a central server but are exchanged directly between users based on the peer-to-peer principle.
The server part of the network is proprietary freeware. There are two families of server software for the eD2k network: the original one from MetaMachine, written in C++, closed-source and proprietary, and no longer maintained; and eserver, written in C, also closed-source and proprietary, although available free of charge and for several operating systems and computer architectures. The eserver family is currently in active development and support, and almost all eD2k servers as of 2008 run this server software.
There are many programs that act as the client part of the network. Most notably, eDonkey2000, the original client by MetaMachine, closed-source but freeware, and no longer maintained but very popular in its day; and eMule, a free program for Windows written in Visual C++ and licensed under the GNU GPL.
The original eD2k protocol has been extended by subsequent releases of both eserver and eMule programs, generally working together to decide what new features the eD2k protocol should support. However, the eD2k protocol is not formally documented (especially in its current extended state), and it can be said that in practice the eD2k protocol is what eMule and eserver do together when running, and also how eMule clients communicate among themselves. As eMule is open source, its code is freely available for peer-review of the workings of the protocol. Examples of eD2k protocol extensions are "peer exchange among clients", "protocol obfuscation" and support for files larger than four gigabytes, etc. The other eD2k client programs, given time, generally follow suit adopting these protocol extensions.
eDonkey client programs connect to the network to share files. eDonkey servers act as communication hubs for the clients, allowing users to locate files within the network. Clients and servers are available for Windows, macOS, Linux, and other Unix-like operating systems. By running an eDonkey server program on a machine connected to the Internet, any user can add a server to the network. As the number of servers and their addresses change frequently, client programs update their server lists regularly.
== Features ==
=== Hash identification ===
Files on the eDonkey network are uniquely identified using MD4 root hash of an MD4 hash list of the file. This treats files with identical content but different names as the same, and files with different contents but same name as different.
Files are divided in full chunks of 9,728,000 bytes (9500 KiB) plus a remainder chunk, and a separate 128-bit MD4 checksum is computed for each. That way, if a transmission error is detected, only one chunk is corrupted instead of the whole file. Furthermore, valid downloaded chunks are available for sharing before the rest of the file is downloaded, speeding up the distribution of large files throughout the network. A file's identification checksum is computed by concatenating the chunks' MD4 checksums in order and hashing the result. In cryptographic terms, the list of MD4 checksums is a hash list, and the file identification checksum is the root hash, also called top hash or master hash.
It is possible for a malicious user to create two different chunks with the same checksum due to MD4 being vulnerable to collision attacks.
=== Search ===
The eDonkey network supports searching of files by name and a number of secondary characteristics such as size, extension, bitrate, etc. The Lugdunum versions of eserver (eDonkey server software) support complex Boolean searches like 'one AND two AND (three OR four) AND ("five four three" OR "two one") NOT seven'.
To ease file searching, some websites list the checksums of sought-after files in the form of an eD2k link. Some of these websites also have lists of active servers for users to update.
== History ==
In 2004, the eDonkey network overtook FastTrack to become the most widely used file sharing network on the Internet. While figures vary from hour to hour, it is believed, as of mid-2005, to host on average approximately two to three million users sharing 500 million to two billion files via 100 to 200 servers. The network's most popular server was at one time Razorback2, which usually hosted about one million users. Sometime around February 21, 2006, the Razorback2 servers were raided and seized by the Federal Belgian Police. DonkeyServer No1 and DonkeyServer No2 currently combine for over one and a half million users. However, around July 16, 2007, both servers together with several others were shut down after a temporary injunction was issued.
By 2007, BitTorrent had overcome eDonkey network as the most widely used file sharing network on the Internet. In 2009, it was reported that eDonkey is still the second most popular P2P protocol but is rapidly declining.
== Successor protocols ==
The original eDonkey network relied on central servers run by users willing to donate the necessary bandwidth and processing/disk usage overhead. Such servers could be subject to heavy traffic and, consequently, more vulnerable to attacks.
To overcome this problem, MetaMachine, the developer of the original eDonkey client, developed Overnet as a successor to the eDonkey protocol. The eMule Project also developed a Kademlia network of their own (called Kad) to overcome the reliance on central servers. In addition, eMule includes a pure P2P client source-exchange capability, allowing a client with a ‘High ID’ (i. e., with incoming eD2k connections not blocked by a firewall) to continue downloading (and uploading) files with a high number of sources for days, even after complete disconnection from the original Kad or eD2k servers that handled the original requests. (eMule does not query secondary servers when told to disconnect from the server). This source-exchange capability is designed to reduce the load on servers by two thirds or more for files that have a large number of seeds, or sources (other clients) for the files. The original eDonkey client by MetaMachine does not support source exchanges.
== Legal action ==
=== Legal action against eDonkey 2000 ===
On September 13, 2006, MetaMachine Inc., the developer of the eDonkey2000 client, agreed to pay $30 million to avoid potential copyright infringement lawsuits brought by the RIAA. In accordance with the agreement, eDonkey is to discontinue distribution of their software as well as to take measures to prevent the use of previous copies of their software for file sharing.
=== Confiscation of Razorback 2 ===
Razorback2 was a server of the eDonkey network, known for being able to handle 1 million users simultaneously.
On 21 February 2006, several servers (including Razorback2), located in a Belgian datacenter, were confiscated by the Belgian police, and their operator, who lives in Switzerland, was arrested. This was done after a local judge authorized the confiscation at the datacenter in Zaventem near Brussels, after a denouncement of the Motion Picture Association of America (MPAA), in collaboration with the International Federation of the Phonographic Industry.
The MPAA Chairman and CEO Dan Glickman, described this raid as a "major victory":
This is a major victory in our fight to cut off the supply of illegal materials being circulated on the Internet via peer-to-peer networks. By shaving the illegal traffic of copyrighted works facilitated by Razorback2, we are depleting other illegal networks of their ability to supply Internet pirates with copyrighted works which is a positive step in our international effort to fight piracy.
Besides having Razorback's equipment confiscated and their site shut down, copyright enforcement entities such as MPAA and IFPI have set up several "Razorback2" fake servers online, with the purpose of mimicking the original servers but which yield no useful results, hampering file-sharing traffic. Afterwards, the Swiss anti-piracy tech firm Logistep SA was hired to help further intimidate and prosecute filesharing users.
=== eDonkey poisoning ===
Servers have appeared on the eDonkey network that censor shared content searches and information about files by the type of the file (such as video or MP3) or by keywords. These servers report large numbers of users (up to 1.5 million) connected to them, thus raising the number of users in the network to 10–13 million; however, it is impossible to determine how many people are actually connected to them. Such servers often disseminate advertisements disguised as commonly searched-for music/video files.
== Server software ==
The main server software used for the eD2k network is known as Lugdunum server. It was created by reverse engineering edonkey protocol and redesigned from scratch. (MetaMachine abandoned development of eD2k server software and revealed the source code to Lugdunum in late 2002, but was never used). Lugdunum has extended the eD2k protocol while maintaining backward compatibility. Lugdunum server software is gratis, but not open source. The stated reason for not opening the source is to prevent the easy creation of fake servers and to prevent attacking the server itself.
In September 2007, a new server software was announced on the eMule web site forums, called satan-edonkey-server. Given the shut down of major eMule servers due to legal action against them just days earlier, the new server was accepted with suspicion. It was feared that the software may transmit information about the clients to unknown third parties. Some trusted eMule developers received the source code of satan-edonkey-server and stated that no spy-code is built in. The satan server software was created by reverse engineering edonkey protocol. The software comes in two versions (C++ and Java). Satan-eDonkey-server software is also gratis.
A Java version of the server side can be found in [1], which was written in 2012.
== Client software ==
Numerous clients, including several that are free software, are available for the eDonkey/eDonkey2000 network:
aMule: a successful fork from lMule, it fully copied the interface and feel of eMule, and now it shares code with eMule project.
eDonkey2000: an original MetaMachine client, since discontinued
eMule: a free Windows client, can also be run on Linux (under Wine); numerous mods are also available
eMule Plus is a free (GPL) Windows client loosely based on eMule, but doesn't have KAD or obfuscation support while adding other features such as automated fake checks and enhanced GUI. eMule Plus has no direct association with the original eMule.
Hydranode: a free, multi-network, cross-platform, core-GUI-separated client
iMule: an anonymous eMule using the I2P network
JMule: a free open source multi platform java client.
Jubster: a multi-network client for Windows
lMule (Linux Mule): A very raw eDonkey client based in eMule, targeted to Linux platforms.
Lphant: an eDonkey and BitTorrent, cross-platform, core-GUI-separated client that runs on the Microsoft .NET and Mono platforms
eAnt: a successful fork from Lphant with significant improvements made to keep the source code open. Currently inactive.
MLDonkey: a free, multi-network, cross-platform client
Morpheus: a file sharing client for Windows
Pruna (formerly, MediaVAMP): a Korean-language client based on eMule
Shareaza: a free open source multi-network file-sharing client that supports the Gnutella2 and Gnutella P2P networks, as well the BitTorrent protocol, additionally to eD2k. It allows network-spanning search of content and has web browser integration to operate as a download manager. Supports user profiles, remote file browsing, chat and advanced search filtering.
xMule (X11 Mule): a fork from lMule. Deviating from copying eMule, it has more controls than lMule but is less user-friendly. Discontinued in January 2009.
qMule: a multi-protocol, cross-platform client for eDonkey and BitTorrent networks. Based on libed2k, libtorrent-rasterbar and Qt.
== Tools and libraries ==
libed2k: Cross platform C++ eDonkey protocol library. Inspired by libtorrent_rasterbar.
== See also ==
Comparison of file-sharing applications
Kad network
Overnet
== References ==
== External links ==
pDonkey project Archived 2009-01-13 at the Wayback Machine – eDonkey protocol description | Wikipedia/EDonkey_network |
Peer Name Resolution Protocol (PNRP) is a peer-to-peer protocol designed by Microsoft. PNRP enables dynamic name publication and resolution, and requires IPv6.
PNRP was first mentioned during a presentation at a P2P conference in November 2001. It appeared in July 2003 in the Advanced Networking Pack for Windows XP, and was later included in the Service Pack 2 for Windows XP. PNRP 2.0 was introduced with Windows Vista and was available for download for Windows XP Service Pack 2 users. PNRP 2.1 is included in Windows Vista SP1, Windows Server 2008 and Windows XP SP3. PNRP v2 is not available for Windows XP Professional x64 Edition or any edition of Windows Server 2003.
Windows Remote Assistance in Windows 7 uses PNRP, Teredo and IPv6 when connecting using the Easy Connect option.
The design of PNRP is covered by US Patent #7,065,587, issued on June 20, 2006.
Support for PNRP was removed in Windows 10 with version 1909.
== PNRP services ==
The PNRP is a distributed name resolution protocol allowing Internet hosts to publish "peer names" and corresponding IPv6 addresses and optionally other information. Other hosts can then resolve the peer name, retrieve the corresponding addresses and other information, and establish peer-to-peer connections.
With PNRP, peer names are composed of an "authority" and a "qualifier". The authority is identified by a secure hash of an associated public key, or by a place-holder (the number zero) if the peer name is "unsecured". The qualifier is a string, allowing an authority to have different peer names for different services.
If a peer name is secure, the PNRP name records are signed by the publishing authority, and can be verified using its public key. Unsecured peer names can be published by anybody, without possible verification.
Multiple entities can publish the same peer name. For example, if a peer name is associated with a group, any group member can publish addresses for the peer name.
Peer names are published and resolved within a specified scope. The scope can be a local link, a site (e.g. a campus), or the whole Internet.
== PNRP and Distributed Hash Tables ==
Internally, PNRP uses an architecture similar to distributed hash table systems such as Chord or Pastry. The peer name is hashed to produce a 128-bit peer identifier, and a DHT-like algorithm is used to retrieve the location of the host publishing that identifier. There are however some significant differences.
DHT systems like Chord or Pastry store the indices of objects (hashes) at the node whose identifier is closest to the hash, and the routing algorithm is designed to find that node. In contrast, PNRP always store the hash on the node that publishes the identifier. A node will thus have as many entries in the routing system as the number of identifiers that it publishes. The PNRP design arguably trades increased security and robustness for higher routing cost.
Most DHT systems assume that only one node publishes a specific index. In contrast, PNRP allows multiple hosts to publish the same name. The internal index is in fact composed of the 128-bit hash of the peer name and a 128-bit location identifier, derived from an IPv6 address of the node.
PNRP does not use a routing table, but rather a cache of PNRP entries. New cache entries are acquired as a side effect of ongoing traffic. The cache maintenance algorithm ensures that each node maintains adequate knowledge of the "cloud". It is designed to ensure that the time to resolve a request varies as the logarithm of the size of the cloud.
== See also ==
Features new to Windows Vista
Link-Local Multicast Name Resolution (LLMNR)
Multicast DNS (mDNS)
Network Basic Input/Output System (NetBIOS)
Windows Vista networking technologies
Zero-configuration networking
== References ==
== External links ==
Microsoft Peer-to-Peer Networking blog on how Windows features use PNRP
PNRPv2 protocol specification at MSDN
Microsoft PNRP documentation (API) at MSDN
MSDN-Article by Justin Smith, featuring PNRP
Windows Peer-to-Peer Networking at Microsoft TechNet
Advanced Networking Pack for Windows XP at Microsoft.com
Distributed Peer-to-peer Name Resolution Slide deck presented by Christian Huitema at the O'Reilly P2P conference in November 2001.
U.S. patent 7,065,587, U.S. patent 7,418,479, U.S. patent 7,962,651, U.S. patent 20,020,143,989, U.S. patent 7,065,587, U.S. patent 7,068,789, U.S. patent 7,496,648 | Wikipedia/Peer_Name_Resolution_Protocol |
Constrained Application Protocol (CoAP) is a specialized UDP-based Internet application protocol for constrained devices, as defined in RFC 7252 (published in 2014). It enables those constrained devices called "nodes" to communicate with the wider Internet using similar protocols.
CoAP is designed for use between devices on the same constrained network (e.g., low-power, lossy networks), between devices and general nodes on the Internet, and between devices on different constrained networks both joined by an internet. CoAP is also being used via other mechanisms, such as SMS on mobile communication networks.
CoAP is an application-layer protocol that is intended for use in resource-constrained Internet devices, such as wireless sensor network nodes. CoAP is designed to easily translate to HTTP for simplified integration with the web, while also meeting specialized requirements such as multicast support, very low overhead, and simplicity. Multicast, low overhead, and simplicity are important for Internet of things (IoT) and machine-to-machine (M2M) communication, which tend to be embedded and have much less memory and power supply than traditional Internet devices have. Therefore, efficiency is very important. CoAP can run on most devices that support UDP or a UDP analogue.
The Internet Engineering Task Force (IETF) Constrained RESTful Environments Working Group (CoRE) has done the major standardization work for this protocol. In order to make the protocol suitable to IoT and M2M applications, various new functions have been added.
== Specification ==
The core of the protocol is specified in RFC 7252. Various extensions have been proposed, particularly:
RFC 7641 (2015) Observing Resources in the Constrained Application Protocol
RFC 7959 (2016) Block-Wise Transfers in the Constrained Application Protocol (CoAP)
RFC 8323 (2018) CoAP (Constrained Application Protocol) over TCP, TLS, and WebSockets
RFC 8974 (2021) Extended Tokens and Stateless Clients in the Constrained Application Protocol (CoAP)
== Message formats ==
CoAP makes use of two message types, requests and responses, using a simple, binary header format. CoAP is by default bound to UDP and optionally to DTLS, providing a high level of communications security. When bound to UDP, the entire message must fit within a single datagram. When used with 6LoWPAN as defined in RFC 4944, messages should fit into a single IEEE 802.15.4 frame to minimize fragmentation.
The smallest CoAP message is 4 bytes in length, if the token, options and payload fields are omitted, i.e. if it only consists of the CoAP header. The header is followed by the token value (0 to 8 bytes) which may be followed by a list of options in an optimized type–length–value format. Any bytes after the header, token and options (if any) are considered the message payload, which is prefixed by the one-byte "payload marker" (0xFF). The length of the payload is implied by the datagram length.
=== CoAP fixed-size header ===
The first 4 bytes are mandatory in all CoAP datagrams, they constitute the fixed-size header.
These fields can be extracted from these 4 bytes in C via these macros:
==== Version (ver) (2 bits) ====
Indicates the CoAP version number.
==== Type (2 bits) ====
This describes the datagram's message type for the two message type context of Request and Response.
Request
0 : Confirmable : This message expects a corresponding acknowledgement message.
1 : Non-confirmable : This message does not expect a confirmation message.
Response
2 : Acknowledgement : This message is a response that acknowledge a confirmable message
3 : Reset : This message indicates that it had received a message but could not process it.
==== Token length (4 bits) ====
Indicates the length of the variable-length Token field, which may be 0–8 bytes in length.
==== Request/response code (8 bits) ====
The three most significant bits form a number known as the "class", which is analogous to the class of HTTP status codes. The five least significant bits form a code that communicates further detail about the request or response. The entire code is typically communicated in the form class.code .
You can find the latest CoAP request/response codes at [1], though the below list gives some examples:
==== Message ID (16 bits) ====
Used to detect message duplication and to match messages of type acknowledgement/reset to messages of type confirmable/non-confirmable.
=== Token ===
Every request carries a token (but it may be zero length) whose value was generated by the client. The server must echo every token value without any modification back to the client in the corresponding response. It is intended for use as a client-local identifier to match requests and responses, especially for concurrent requests.
Matching requests and responses is not done with the message ID because a response may be sent in a different message than the acknowledgement (which uses the message ID for matching). For example, this could be done to prevent retransmissions if obtaining the result takes some time. Such a detached response is called "separate response". In contrast, transmitting the response directly in the acknowledgement is called "piggybacked response" which is expected to be preferred for efficiency reasons.
=== Option ===
Option delta:
0 to 12: For delta between 0 and 12: Represents the exact delta value between the last option ID and the desired option ID, with no option delta extended value
13: For delta from 13 to 268: Option delta extended is an 8-bit value that represents the option delta value minus 13
14: For delta from 269 to 65,804: Option delta extended is a 16-bit value that represents the option delta value minus 269
15: Reserved for payload marker, where the option delta and option length are set together as 0xFF.
Option length:
0 to 12: For option length between 0 and 12: Represents the exact length value, with no option length extended value
13: For option length from 13 to 268: Option length extended is an 8-bit value that represents the option length value minus 13
14: For option length from 269 to 65,804: Option length extended is a 16-bit value that represents the option length value minus 269
15: Reserved for future use. It is an error for the option length field to be set to 0xFF.
Option value:
Size of option value field is defined by option length value in bytes.
Semantic and format this field depends on the respective option.
== Active protocol implementations ==
== Proxy implementations ==
There exist proxy implementations which provide forward or reverse proxy functionality for the CoAP protocol and also implementations which translate between protocols like HTTP and CoAP.
The following projects provide proxy functionality:
Squid 3.1.9 with transparent HTTP-CoAP mapping module
jcoap Proxy
Californium cf-proxy2
CoAPthon
FreeCoAP
libcoap
== Projects using CoAP ==
== Inactive protocol implementations ==
== CoAP group communication ==
In many CoAP application domains it is essential to have the ability to address several CoAP resources as a group, instead of addressing each resource individually
(e.g. to turn on all the CoAP-enabled lights in a room with a single CoAP request triggered by toggling the light switch).
To address this need, the IETF has developed an optional extension for CoAP in the form of an experimental RFC: Group Communication for CoAP - RFC 7390
This extension relies on IP multicast to deliver the CoAP request to all group members.
The use of multicast has certain benefits such as reducing the number of packets needed to deliver the request to the members.
However, multicast also has its limitations such as poor reliability and being cache-unfriendly.
An alternative method for CoAP group communication that uses unicasts instead of multicasts relies on having an intermediary where the groups are created.
Clients send their group requests to the intermediary, which in turn sends individual unicast requests to the group members, collects the replies from them, and sends back an aggregated reply to the client.
== Security ==
CoAP defines four security modes:
NoSec, where DTLS is disabled
PreSharedKey, where DTLS is enabled, there is a list of pre-shared keys, and each key includes a list of which nodes it can be used to communicate with. Devices must support the AES cipher suite.
RawPublicKey, where DTLS is enabled and the device uses an asymmetric key pair without a certificate, which is validated out of band. Devices must support the AES cipher suite and Elliptic Curve algorithms for key exchange.
Certificate, where DTLS is enabled and the device uses X.509 certificates for validation.
Research has been conducted on optimizing DTLS by implementing security associates as CoAP resources rather than using DTLS as a security wrapper for CoAP traffic. This research has indicated that improvements of up to 6.5 times none optimized implementations.
In addition to DTLS, RFC8613 defines the Object Security for Constrained RESTful Environments (OSCORE) protocol which provides security for CoAP at the application layer.
== Security issues ==
Although the protocol standard includes provisions for mitigating the threat of DDoS amplification attacks, these provisions are not implemented in practice, resulting in the presence of over 580,000 targets primarily located in China and attacks up to 320 Gbit/s.
== See also ==
Internet of Things
OMA Lightweight M2M
Web of Things
Static Context Header Compression (SCHC)
== References ==
== External links ==
RFC 7252 "The Constrained Application Protocol (CoAP)"
coap.me – CoAP test server run by University of Bremen | Wikipedia/Constrained_Application_Protocol |
According to the redundancy theory of truth (also known as the disquotational theory of truth), asserting that a statement is true is completely equivalent to asserting the statement itself. For example, asserting the sentence "'Snow is white' is true" is equivalent to asserting the sentence "Snow is white". The philosophical redundancy theory of truth is a deflationary theory of truth.
== Overview ==
Redundancy theorists infer from this premise that truth is a redundant concept—in other words, that "truth" is merely a word that it is conventional to use in certain contexts but not one that points to anything in reality. The theory is commonly attributed to Frank P. Ramsey, who argued that the use of words like fact and truth was nothing but a roundabout way of asserting a proposition, and that treating these words as separate problems in isolation from judgment was merely a "linguistic muddle", though there remains some debate as to the correct interpretation of his position (Le Morvan 2004).
Redundancy theorists begin by inquiring into the function of the predicate "__is true" in sentences like "'Snow is white' is true". They reason that asserting the longer sentence is equivalent to asserting the shorter sentence "Snow is white". From this they infer that nothing is added to the assertion of the sentence "Snow is white" by quoting it, appending the predicate "__is true", and then asserting the result.
Most predicates attribute properties to their subjects, but the redundancy theory denies that the predicate is true does so. Instead, it treats the predicate is true as empty, adding nothing to an assertion except to convert its use to its mention. That is, the predicate "___is true" merely asserts the proposition contained in the sentential clause to which it is applied but does not ascribe any additional property to that proposition or sentence, and in Ramsey's British lexicon, "is true" is redundant.
Hence, redundancy theory of truth claims that the whole issue of truth is an illusion, caused by our use of the predicate..."is true" which allegedly is redundant, i.e without meaning.
== Precursors ==
Gottlob Frege was probably the first philosophical logician to express something very close to the idea that the predicate "is true" does not express anything above and beyond the statement to which it is attributed. In 1892, he wrote:
One can, indeed, say: "The thought that 5 is a prime number is true." But closer examination shows that nothing more has been said than in the simple sentence "5 is a prime number." The truth claim arises in each case from the form of the declarative sentence, and when the latter lacks its usual force, e.g., in the mouth of an actor upon the stage, even the sentence "The thought that 5 is a prime number is true" contains only a thought, and indeed the same thought as the simple "5 is a prime number."
In 1918, he argued:
It is worthy of notice that the sentence "I smell the scent of violets" has the same content as the sentence "it is true that I smell the scent of violets". So it seems, then, that nothing is added to the thought by my ascribing to it the property of truth.
== Ramsey's approach ==
Ramsey's paper "Facts and Propositions" (1927) is frequently cited as the precipitating contribution to the current of thought that came to be called the redundancy theory of truth. He wrote, "But before we proceed further with the analysis of judgment, it is necessary to say something about truth and falsehood, in order to show that there is really no separate problem of truth but merely a linguistic muddle" (p. 38).
Starting in a context of discussion that is concerned with analyzing judgment, in effect, the matter of asserting or denying propositions, Ramsey turns to the question of truth and falsehood, and suggests that these words add nothing of substance to the analysis of judgment already in progress:
Truth and falsity are ascribed primarily to propositions. The proposition to which they are ascribed may be either explicitly given or described.
Suppose first that it is explicitly given; then it is evident that 'It is true that Caesar was murdered' means no more than that Caesar was murdered, and 'It is false that Caesar was murdered' means that Caesar was not murdered.
In the course of his argument, Ramsey observes that there are many different ways of asserting what is really the same proposition, at least so far as the abstract logical meanings of sentences are concerned. In his first examples, he uses the verbal forms (1) 'It is true that ___' and (2) 'It is false that ___', for the sake of concreteness filling in the blanks with the sentential clause 'Caesar was murdered'. He says that assertions mediated by these forms are not distinct in meaning from the corresponding direct assertions.
They are phrases we sometimes use for emphasis or for stylistic reasons, or to indicate the position occupied by the statement in our argument.
So also we can say 'It is a fact that he was murdered' or 'That he was murdered is contrary to fact'.
In the same context and by the same token, Ramsey cites the verbal forms (3) 'It is a fact that ___' and (4) '___ is contrary to fact' as further examples of dispensable, otiose, redundant, or purely stylistic verbiage.
In the second case in which the proposition is described and not given explicitly we have perhaps more of a problem, for we get statements from which we cannot in ordinary language eliminate the words 'true' and 'false'.
The strategy of Ramsey's argument is to demonstrate that certain figures of speech—those in which truth and falsehood seem to figure as real properties of propositions, or as logical values that constitute real objects, however abstract, of discussion and thought—can always be eliminated in favor of paraphrases that do not reify truth and falsehood as nouns, or even use true and false as adjectives. The plausibility of this tactic is fairly evident in the case of verbal forms that introduce direct or indirect quotations, but its feasibility is less clear in the case of propositions whose contents are not given in full, but only by indirect or partial description.
Thus if I say 'He is always right', I mean that the propositions he asserts are always true, and there does not seem to be any way of expressing this without using the word 'true'.
But suppose we put it thus 'For all p, if he asserts p, p is true', then we see that the propositional function p is true is simply the same as p, as e.g. its value 'Caesar was murdered is true' is the same as 'Caesar was murdered'.
The type of propositional function that Ramsey is referring to here is a function that takes a proposition as input and gives a proposition as output. In this case, the propositional function of interest is one that takes any proposition p and returns a proposition of the form 'p is true'.
We have in English to add 'is true' to give the sentence a verb, forgetting that ' p ' already contains a (variable) verb.
This may be made clearer by supposing for a moment that only one form of proposition is in question, say the relational form aRb; then 'He is always right' could be expressed by 'For all a, R, b, if he asserts aRb, then aRb ', to which 'is true' would be an obviously superfluous addition.
When all forms of proposition are included the analysis is more complicated but not essentially different; and it is clear that the problem is not as to the nature of truth and falsehood, but as to the nature of judgment or assertion, for what is difficult to analyse in the above formulation is 'He asserts aRb '.
It is, perhaps, also immediately obvious that if we have analysed judgment we have solved the problem of truth; for taking the mental factor in a judgment (which is often itself called a judgment), the truth or falsity of this depends only on what proposition it is that is judged, and what we have to explain is the meaning of saying that the judgment is a judgment that a has R to b, i.e. is true if aRb, false if not. We can, if we like, say that it is true if there exists a corresponding fact that a has R to b, but this is essentially not an analysis but a periphrasis, for 'The fact that a has R to b exists' is no different from ' a has R to b '.
== Variants ==
A variant of redundancy theory is the disquotational theory, which uses a modified form of Tarski's T-schema: To say that "'P' is true" is to say that P. Yet another version of deflationism is the prosentential theory of truth, first developed by Dorothy Grover, Joseph Camp, and Nuel Belnap as an elaboration of Ramsey's claims. They argue that sentences like "That's true", when said in response to "It's raining", are prosentences (see pro-form), expressions that merely repeat the content of other expressions. In the same way that it means the same as my dog in the sentence My dog was hungry, so I fed it, That's true is supposed to mean the same as It's raining—if you say the latter and I then say the former. These variations do not necessarily follow Ramsey in asserting that truth is not a property, but rather can be understood to say that, for instance, the assertion "P" may well involve a substantial truth, and the theorists in this case are minimalizing only the redundancy or prosentence involved in the statement such as "that's true."
Proponents of pragmatic, constructivist and consensus theories would differ with all these conclusions, however, and instead assert that the second person making the statement "that's true" is actually participating in further verifying, constructing and/or achieving consensus on the proposed truth of the matter—e.g., the proposition that "it's raining".
Redundancy theory does not apply to representations that are not analogous to sentences and they do not apply to many other things that are commonly judged to be true or otherwise. Consider the analogy between the sentence "Snow is white" and the person Snow White, both of which can be true in a sense. To say "'Snow is white' is true" is to say "Snow is white", but to say "Snow White is true" is, obviously, not to say "Snow White."
== See also ==
Coherentism
Confirmation holism
Disquotational principle
Truth
Truth theory
=== Related topics ===
== Notes ==
== References ==
Le Morvan, Pierre (2004), "Ramsey on Truth and Truth on Ramsey", British Journal for the History of Philosophy 12(4), 705–718. PDF text.
Ramsey, F. P. (1927), "Facts and Propositions", Aristotelian Society Supplementary Volume 7, 153–170. Reprinted, pp. 34–51 in F. P. Ramsey, Philosophical Papers, David Hugh Mellor (ed.), Cambridge University Press, Cambridge, UK, 1990.
Ramsey, F. P. (1990), Philosophical Papers, David Hugh Mellor (ed.), Cambridge University Press, Cambridge, UK.
== External links ==
John M. Vickers (2004), "Ramsey on Judgment: The Theory of 'Facts and Propositions'", Dialectica 58(4), 499. Eprint.
""Prosentential Theory of Truth"". Internet Encyclopedia of Philosophy. | Wikipedia/Redundancy_theory_of_truth |
Mobility models characterize the movements of mobile users with respect to their location, velocity and direction over a period of time. These models play a vital role in the design of Mobile Ad Hoc Networks(MANET). Most of the times simulators play a significant role in testing the features of mobile ad hoc networks. Simulators like (NS, QualNet, etc.) allow the users to choose the mobility models as these models represent the movements of nodes or users. As the mobile nodes move in different directions, it becomes imperative to characterize their movements vis-à-vis to standard models. The mobility models proposed in literature have varying degrees of realism i.e. from random patterns to realistic patterns. Thus these models contribute significantly while testing the protocols for mobile ad hoc networks.
== Background and terminology ==
The study of large and complex networks is possible by experimenting on a simulator rather than on analytical studies. The relatively new form of networks like Mobile Ad Hoc Networks(MANET), Vehicular Ad Hoc Networks (VANET), etc. are characterized by nodes which are autonomous and dynamic in nature. Thus it becomes very essential to capture their movements so that the corresponding simulations results are nearer to reality. Mobility models are basically classified as stochastic, detailed, Hybrid and Trace based Realistic models.
The stochastic models are based on random movements and the nodes are free to move in any direction. Example include Random waypoint model, Random walk and Random direction model.
The detailed models are tailored for specific scenarios. This could include meetings, library and classroom scenarios. Example includes Street random waypoint (STRAW),
The Hybrid models try to strike a balance between realism (Detailed models) and freedom of movements(Stochastic models). Examples include Reference point group mobility model, Manhattan mobility model and Freeway mobility model.
The Real trace models contain a collection of movements of realistic users based on specific scenarios. Example includes CRAWDAD.
== Mobility models ==
For mobility modelling, the behavior or activity of a user's movement can be described using both analytical and simulation models. The input to analytical mobility models are simplifying assumptions regarding the movement behaviors of users. Such models can provide performance parameters for simple cases through mathematical calculations. In contrast, simulation models consider more detailed and realistic mobility scenarios. Such models can derive valuable solutions for more complex cases. Typical mobility
models include
Random waypoint model
Random walk model
Random direction model
Street random waypoint
Reference point group model (RPGM)
Manhattan mobility model
Freeway mobility model
== Metrics for Mobility Models ==
Mobility model metrics are useful to study the impact of mobility models on the performances of mobile ad hoc networks. Metrics are usually classified as mobility metrics, connectivity graph metrics and protocol performance metrics.
The mobility metrics usually speaks about the mobility patterns. These include spatial dependence, temporal dependence, relative speed and geographic restrictions.
The connectivity graph metrics speaks about the number of link changes, link duration, path duration and path availability.
The protocol performance metrics speaks about throughput and routing overhead.
== See also ==
Mobility management
Mobile ad hoc network (MANET)
Radio propagation models
Network simulation
Network simulator
Network traffic simulation
Radio resource management (RRM)
Traffic generation model
== References == | Wikipedia/Mobility_model |
In computer network research, network simulation is a technique whereby a software program replicates the behavior of a real network. This is achieved by calculating the interactions between the different network entities such as routers, switches, nodes, access points, links, etc. Most simulators use discrete event simulation in which the modeling of systems in which state variables change at discrete points in time. The behavior of the network and the various applications and services it supports can then be observed in a test lab; various attributes of the environment can also be modified in a controlled manner to assess how the network/protocols would behave under different conditions.
== Network simulator ==
A network simulator is a software program that can predict the performance of a computer network or a wireless communication network. Since communication networks have become tool complex for traditional analytical methods to provide an accurate understanding of system behavior, network simulators are used. In simulators, the computer network is modeled with devices, links, applications, etc., and the network performance is reported. Simulators come with support for the most popular technologies and networks in use today such as 5G, Internet of Things (IoT), Wireless LANs, mobile ad hoc networks, wireless sensor networks, vehicular ad hoc networks, cognitive radio networks, LTE
== Simulations ==
Most of the commercial simulators are GUI driven, while some network simulators are CLI driven. The network model/configuration describes the network (nodes, routers, switches, links) and the events (data transmissions, packet error, etc.). Output results would include network-level metrics, link metrics, device metrics etc. Further, drill down in terms of simulations trace files would also be available. Trace files log every packet, every event that occurred in the simulation and is used for analysis. Most network simulators use discrete event simulation, in which a list of pending "events" is stored, and those events are processed in order, with some events triggering future events—such as the event of the arrival of a packet at one node triggering the event the arrival of that packet at a downstream node.
== Network emulation ==
Network emulation allows users to introduce real devices and applications into a test network (simulated) that alters packet flow in such a way as to mimic the behavior of a live network. Live traffic can pass through the simulator and be affected by objects within the simulation.
The typical methodology is that real packets from a live application are sent to the emulation server (where the virtual network is simulated). The real packet gets 'modulated' into a simulation packet. The simulation packet gets demodulated into a real packet after experiencing effects of loss, errors, delay, jitter etc., thereby transferring these network effects into the real packet. Thus it is as-if the real packet flowed through a real network but in reality it flowed through the simulated network.
Emulation is widely used in the design stage for validating communication networks prior to deployment.
== List of network simulators ==
There are both free/open-source and proprietary network simulators available. Examples of notable open source network simulators / emulators include:
ns Simulator
GloMoSim
SimGrid
There are also some notable commercial network simulators.
== Uses of network simulators ==
Network simulators provide a cost-effective method for
5G, 6G coverage, capacity, throughput and latency analysis
Network R & D (More than 70% of all Network Research paper reference a network simulator)
Defense applications such as UHF/VHF/L-Band Radio based MANET Radios, Dynamic TDMA MAC, PHY Waveforms etc.
IOT, VANET simulations
UAV network/drone swarm communication simulation
Machine Learning for communication networks
Education: Online courses, Lab experimentation, and R & D. Most universities use a network simulator for teaching / R & D since it is too expensive to buy hardware equipment
There are a wide variety of network simulators, ranging from the very simple to the very complex. Minimally, a network simulator must enable a user to
Model the network topology specifying the nodes on the network and the links between those nodes
Model the application flow (traffic) between the nodes
Providing network performance metrics such as throughput, latency, error, etc., as output
Evaluate protocol and device designs
Log radio measurements, packet and events for drill-down analyses and debugging
== See also ==
Network emulation
Traffic generation model
== References == | Wikipedia/Network_simulator |
A communication channel refers either to a physical transmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio channel in telecommunications and computer networking. A channel is used for information transfer of, for example, a digital bit stream, from one or several senders to one or several receivers. A channel has a certain capacity for transmitting information, often measured by its bandwidth in Hz or its data rate in bits per second.
Communicating an information signal across distance requires some form of pathway or medium. These pathways, called communication channels, use two types of media: Transmission line-based telecommunications cable (e.g. twisted-pair, coaxial, and fiber-optic cable) and broadcast (e.g. microwave, satellite, radio, and infrared).
In information theory, a channel refers to a theoretical channel model with certain error characteristics. In this more general view, a storage device is also a communication channel, which can be sent to (written) and received from (reading) and allows communication of an information signal across time.
== Examples ==
Examples of communications channels include:
A connection between initiating and terminating communication endpoints of a telecommunication circuit.
A single path provided by a transmission medium via either
physical separation, such as by multipair cable or
separation, such as by frequency-division or time-division multiplexing.
A path for conveying electrical or electromagnetic signals, usually distinguished from other parallel paths.
A data storage device which can communicate a message over time.
The portion of a storage medium, such as a track or band, that is accessible to a given reading or writing station or head.
A buffer from which messages can be put and got.
In a communications system, the physical or logical link that connects a data source to a data sink.
A specific radio frequency, pair or band of frequencies, usually named with a letter, number, or codeword, and often allocated by international agreement, for example:
Marine VHF radio uses some 88 channels in the VHF band for two-way FM voice communication. Channel 16, for example, is 156.800 MHz. In the US, seven additional channels, WX1 - WX7, are allocated for weather broadcasts.
Television channels such as North American TV Channel 2 at 55.25 MHz, Channel 13 at 211.25 MHz. Each channel is 6 MHz wide. This was based on the bandwidth required by analog television signals. Since 2006, television broadcasting has switched to digital modulation (digital television) which uses image compression to transmit a television signal in a much smaller bandwidth, so each of these physical channels has been divided into multiple virtual channels each carrying a DTV channel.
Original Wi-Fi uses 13 channels in the ISM bands from 2412 MHz to 2484 MHz in 5 MHz steps.
The radio channel between an amateur radio repeater and an amateur radio operator uses two frequencies often 600 kHz (0.6 MHz) apart. For example, a repeater that transmits on 146.94 MHz typically listens for a ham transmitting on 146.34 MHz.
All of these communication channels share the property that they transfer information. The information is carried through the channel by a signal.
== Channel models ==
Mathematical models of the channel can be made to describe how the input (the transmitted signal) is mapped to the output (the received signal). There exist many types and uses of channel models specific to the field of communication. In particular, separate models are formulated to describe each layer of a communication system.
A channel can be modeled physically by trying to calculate the physical processes which modify the transmitted signal. For example, in wireless communications, the channel can be modeled by calculating the reflection from every object in the environment. A sequence of random numbers might also be added to simulate external interference or electronic noise in the receiver.
Statistically, a communication channel is usually modeled as a tuple consisting of an input alphabet, an output alphabet, and for each pair (i, o) of input and output elements, a transition probability p(i, o). Semantically, the transition probability is the probability that the symbol o is received given that i was transmitted over the channel.
Statistical and physical modeling can be combined. For example, in wireless communications the channel is often modeled by a random attenuation (known as fading) of the transmitted signal, followed by additive noise. The attenuation term is a simplification of the underlying physical processes and captures the change in signal power over the course of the transmission. The noise in the model captures external interference or electronic noise in the receiver. If the attenuation term is complex it also describes the relative time a signal takes to get through the channel. The statistical properties of the attenuation in the model are determined by previous measurements or physical simulations.
Communication channels are also studied in discrete-alphabet modulation schemes. The mathematical model consists of a transition probability that specifies an output distribution for each possible sequence of channel inputs. In information theory, it is common to start with memoryless channels in which the output probability distribution only depends on the current channel input.
A channel model may either be digital or analog.
=== Digital channel models ===
In a digital channel model, the transmitted message is modeled as a digital signal at a certain protocol layer. Underlying protocol layers are replaced by a simplified model. The model may reflect channel performance measures such as bit rate, bit errors, delay, delay variation, etc. Examples of digital channel models include:
Binary symmetric channel (BSC), a discrete memoryless channel with a certain bit error probability
Binary asymmetric channel (BAC), similar to BSC but the probability of a flip from 0 to 1 and vice-versa is unequal
Binary bursty bit error channel model, a channel with memory
Binary erasure channel (BEC), a discrete channel with a certain bit error detection (erasure) probability
Packet erasure channel, where packets are lost with a certain packet loss probability or packet error rate
Arbitrarily varying channel (AVC), where the behavior and state of the channel can change randomly
=== Analog channel models ===
In an analog channel model, the transmitted message is modeled as an analog signal. The model can be a linear or non-linear, time-continuous or time-discrete (sampled), memoryless or dynamic (resulting in burst errors), time-invariant or time-variant (also resulting in burst errors), baseband, passband (RF signal model), real-valued or complex-valued signal model. The model may reflect the following channel impairments:
Noise model, for example
Additive white Gaussian noise (AWGN) channel, a linear continuous memoryless model
Phase noise model
Interference model, for example crosstalk (co-channel interference) and intersymbol interference (ISI)
Distortion model, for example a non-linear channel model causing intermodulation distortion (IMD)
Frequency response model, including attenuation and phase-shift
Group delay model
Modelling of underlying physical layer transmission techniques, for example a complex-valued equivalent baseband model of modulation and frequency response
Radio frequency propagation model, for example
Log-distance path loss model
Fading model, for example Rayleigh fading, Ricean fading, log-normal shadow fading and frequency selective (dispersive) fading
Doppler shift model, which combined with fading results in a time-variant system
Ray tracing models, which attempt to model the signal propagation and distortions for specified transmitter-receiver geometries, terrain types, and antennas
Propagation graph, models signal dispersion by representing the radio propagation environment by a graph.
Mobility models, which also causes a time-variant system
== Types ==
Digital (discrete) or analog (continuous) channel
Transmission medium, for example a fiber-optic cable
Multiplexed channel
Computer network virtual channel
Simplex communication, duplex communication or half-duplex communication channel
Return channel
Uplink or downlink (upstream or downstream channel)
Broadcast channel, unicast channel or multicast channel
== Channel performance measures ==
These are examples of commonly used channel capacity and performance measures:
Spectral bandwidth in Hertz
Symbol rate in baud, symbols/s
Digital bandwidth in bit/s measures: gross bit rate (signalling rate), net bit rate (information rate), channel capacity, and maximum throughput
Channel utilization
Spectral efficiency
Signal-to-noise ratio in decibel measures: signal-to-interference ratio, Eb/N0
Bit error rate (BER), packet error rate (PER)
Latency in seconds: propagation time, transmission time, round-trip delay, end-to-end delay
Packet delay variation
Eye pattern
== Multi-terminal channels, with application to cellular systems ==
In networks, as opposed to point-to-point communication, the communication media can be shared between multiple communication endpoints (terminals). Depending on the type of communication, different terminals can cooperate or interfere with each other. In general, any complex multi-terminal network can be considered as a combination of simplified multi-terminal channels. The following channels are the principal multi-terminal channels first introduced in the field of information theory:
A point-to-multipoint channel, also known as broadcasting medium (not to be confused with broadcasting channel): In this channel, a single sender transmits multiple messages to different destination nodes. All wireless channels except directional links can be considered as broadcasting media, but may not always provide broadcasting service. The downlink of a cellular system can be considered as a point-to-multipoint channel, if only one cell is considered and inter-cell co-channel interference is neglected. However, the communication service of a phone call is unicasting.
Multiple access channel: In this channel, multiple senders transmit multiple possible different messages over a shared physical medium to one or several destination nodes. This requires a channel access scheme, including a media access control (MAC) protocol combined with a multiplexing scheme. This channel model has applications in the uplink of cellular networks.
Relay channel: In this channel, one or several intermediate nodes (called relay, repeater or gap filler nodes) cooperate with a sender to send the message to an ultimate destination node.
Interference channel: In this channel, two different senders transmit their data to different destination nodes. Hence, the different senders can have a possible crosstalk or co-channel interference on the signal of each other. The inter-cell interference in cellular wireless communications is an example of an interference channel. In spread-spectrum systems like 3G, interference also occurs inside the cell if non-orthogonal codes are used.
A unicast channel is a channel that provides a unicast service, i.e. that sends data addressed to one specific user. An established phone call is an example.
A broadcast channel is a channel that provides a broadcasting service, i.e. that sends data addressed to all users in the network. Cellular network examples are the paging service as well as the Multimedia Broadcast Multicast Service.
A multicast channel is a channel where data is addressed to a group of subscribing users. LTE examples are the physical multicast channel (PMCH) and multicast broadcast single frequency network (MBSFN).
== References == | Wikipedia/Channel_model |
Complexity characterizes the behavior of a system or model whose components interact in multiple ways and follow local rules, leading to non-linearity, randomness, collective dynamics, hierarchy, and emergence.
The term is generally used to characterize something with many parts where those parts interact with each other in multiple ways, culminating in a higher order of emergence greater than the sum of its parts. The study of these complex linkages at various scales is the main goal of complex systems theory.
The intuitive criterion of complexity can be formulated as follows: a system would be more complex if more parts could be distinguished, and if more connections between them existed.
As of 2010, a number of approaches to characterizing complexity have been used in science; Zayed et al.
reflect many of these. Neil Johnson states that "even among scientists, there is no unique definition of complexity – and the scientific notion has traditionally been conveyed using particular examples..." Ultimately Johnson adopts the definition of "complexity science" as "the study of the phenomena which emerge from a collection of interacting objects".
== Overview ==
Definitions of complexity often depend on the concept of a "system" – a set of parts or elements that have relationships among them differentiated from relationships with other elements outside the relational regime. Many definitions tend to postulate or assume that complexity expresses a condition of numerous elements in a system and numerous forms of relationships among the elements. However, what one sees as complex and what one sees as simple is relative and changes with time.
Warren Weaver posited in 1948 two forms of complexity: disorganized complexity, and organized complexity.
Phenomena of 'disorganized complexity' are treated using probability theory and statistical mechanics, while 'organized complexity' deals with phenomena that escape such approaches and confront "dealing simultaneously with a sizable number of factors which are interrelated into an organic whole". Weaver's 1948 paper has influenced subsequent thinking about complexity.
The approaches that embody concepts of systems, multiple elements, multiple relational regimes, and state spaces might be summarized as implying that complexity arises from the number of distinguishable relational regimes (and their associated state spaces) in a defined system.
Some definitions relate to the algorithmic basis for the expression of a complex phenomenon or model or mathematical expression, as later set out herein.
== Disorganized vs. organized ==
One of the problems in addressing complexity issues has been formalizing the intuitive conceptual distinction between the large number of variances in relationships extant in random collections, and the sometimes large, but smaller, number of relationships between elements in systems where constraints (related to correlation of otherwise independent elements) simultaneously reduce the variations from element independence and create distinguishable regimes of more-uniform, or correlated, relationships, or interactions.
Weaver perceived and addressed this problem, in at least a preliminary way, in drawing a distinction between "disorganized complexity" and "organized complexity".
In Weaver's view, disorganized complexity results from the particular system having a very large number of parts, say millions of parts, or many more. Though the interactions of the parts in a "disorganized complexity" situation can be seen as largely random, the properties of the system as a whole can be understood by using probability and statistical methods.
A prime example of disorganized complexity is a gas in a container, with the gas molecules as the parts. Some would suggest that a system of disorganized complexity may be compared with the (relative) simplicity of planetary orbits – the latter can be predicted by applying Newton's laws of motion. Of course, most real-world systems, including planetary orbits, eventually become theoretically unpredictable even using Newtonian dynamics; as discovered by modern chaos theory.
Organized complexity, in Weaver's view, resides in nothing else than the non-random, or correlated, interaction between the parts. These correlated relationships create a differentiated structure that can, as a system, interact with other systems. The coordinated system manifests properties not carried or dictated by individual parts. The organized aspect of this form of complexity with regard to other systems, rather than the subject system, can be said to "emerge," without any "guiding hand".
The number of parts does not have to be very large for a particular system to have emergent properties. A system of organized complexity may be understood in its properties (behavior among the properties) through modeling and simulation, particularly modeling and simulation with computers. An example of organized complexity is a city neighborhood as a living mechanism, with the neighborhood people among the system's parts.
== Sources and factors ==
There are generally rules which can be invoked to explain the origin of complexity in a given system.
The source of disorganized complexity is the large number of parts in the system of interest, and the lack of correlation between elements in the system.
In the case of self-organizing living systems, usefully organized complexity comes from beneficially mutated organisms being selected to survive by their environment for their differential reproductive ability or at least success over inanimate matter or less organized complex organisms. See e.g. Robert Ulanowicz's treatment of ecosystems.
Complexity of an object or system is a relative property. For instance, for many functions (problems), such a computational complexity as time of computation is smaller when multitape Turing machines are used than when Turing machines with one tape are used. Random Access Machines allow one to even more decrease time complexity (Greenlaw and Hoover 1998: 226), while inductive Turing machines can decrease even the complexity class of a function, language or set (Burgin 2005). This shows that tools of activity can be an important factor of complexity.
== Varied meanings ==
In several scientific fields, "complexity" has a precise meaning:
In computational complexity theory, the amounts of resources required for the execution of algorithms is studied. The most popular types of computational complexity are the time complexity of a problem equal to the number of steps that it takes to solve an instance of the problem as a function of the size of the input (usually measured in bits), using the most efficient algorithm, and the space complexity of a problem equal to the volume of the memory used by the algorithm (e.g., cells of the tape) that it takes to solve an instance of the problem as a function of the size of the input (usually measured in bits), using the most efficient algorithm. This allows classification of computational problems by complexity class (such as P, NP, etc.). An axiomatic approach to computational complexity was developed by Manuel Blum. It allows one to deduce many properties of concrete computational complexity measures, such as time complexity or space complexity, from properties of axiomatically defined measures.
In algorithmic information theory, the Kolmogorov complexity (also called descriptive complexity, algorithmic complexity or algorithmic entropy) of a string is the length of the shortest binary program that outputs that string. Minimum message length is a practical application of this approach. Different kinds of Kolmogorov complexity are studied: the uniform complexity, prefix complexity, monotone complexity, time-bounded Kolmogorov complexity, and space-bounded Kolmogorov complexity. An axiomatic approach to Kolmogorov complexity based on Blum axioms (Blum 1967) was introduced by Mark Burgin in the paper presented for publication by Andrey Kolmogorov. The axiomatic approach encompasses other approaches to Kolmogorov complexity. It is possible to treat different kinds of Kolmogorov complexity as particular cases of axiomatically defined generalized Kolmogorov complexity. Instead of proving similar theorems, such as the basic invariance theorem, for each particular measure, it is possible to easily deduce all such results from one corresponding theorem proved in the axiomatic setting. This is a general advantage of the axiomatic approach in mathematics. The axiomatic approach to Kolmogorov complexity was further developed in the book (Burgin 2005) and applied to software metrics (Burgin and Debnath, 2003; Debnath and Burgin, 2003).
In information theory, information fluctuation complexity is the fluctuation of information about information entropy. It is derivable from fluctuations in the predominance of order and chaos in a dynamic system and has been used as a measure of complexity in many diverse fields.
In information processing, complexity is a measure of the total number of properties transmitted by an object and detected by an observer. Such a collection of properties is often referred to as a state.
In physical systems, complexity is a measure of the probability of the state vector of the system. This should not be confused with entropy; it is a distinct mathematical measure, one in which two distinct states are never conflated and considered equal, as is done for the notion of entropy in statistical mechanics.
In dynamical systems, statistical complexity measures the size of the minimum program able to statistically reproduce the patterns (configurations) contained in the data set (sequence). While the algorithmic complexity implies a deterministic description of an object (it measures the information content of an individual sequence), the statistical complexity, like forecasting complexity, implies a statistical description, and refers to an ensemble of sequences generated by a certain source. Formally, the statistical complexity reconstructs a minimal model comprising the collection of all histories sharing a similar probabilistic future and measures the entropy of the probability distribution of the states within this model. It is a computable and observer-independent measure based only on the internal dynamics of the system and has been used in studies of emergence and self-organization.
In mathematics, Krohn–Rhodes complexity is an important topic in the study of finite semigroups and automata.
In network theory, complexity is the product of richness in the connections between components of a system, and defined by a very unequal distribution of certain measures (some elements being highly connected and some very few, see complex network).
In software engineering, programming complexity is a measure of the interactions of the various elements of the software. This differs from the computational complexity described above in that it is a measure of the design of the software. Halstead complexity measures, cyclomatic complexity, time complexity, and parameterized complexity are closely linked concepts.
In model theory, U-rank is a measure of the complexity of a complete type in the context of stable theories.
In bioinformatics, linguistic sequence complexity is a measure of the vocabulary richness of a genetic text in gene sequences
In statistical learning theory, the Vapnik–Chervonenkis dimension is a measure of the size (capacity, complexity, expressive power, richness, or flexibility) of a class of sets.
In computational learning theory, Rademacher complexity is a measure of richness of a class of sets with respect to a probability distribution.
In sociology, social complexity is a conceptual framework used in the analysis of society.
In combinatorial game theory, measures of game complexity involve understanding game positions, possible outcomes, and computation required for various game scenarios.
Other fields introduce less precisely defined notions of complexity:
A complex adaptive system has some or all of the following attributes:
The number of parts (and types of parts) in the system and the number of relations between the parts is non-trivial – however, there is no general rule to separate "trivial" from "non-trivial";
The system has memory or includes feedback;
The system can adapt itself according to its history or feedback;
The relations between the system and its environment are non-trivial or non-linear;
The system can be influenced by, or can adapt itself to, its environment;
The system is highly sensitive to initial conditions.
Peak complexity is the concept that human societies address problems by adding social and economic complexity, but that process is subject to diminishing marginal returns
== Study ==
Complexity has always been a part of our environment, and therefore many scientific fields have dealt with complex systems and phenomena. From one perspective, that which is somehow complex – displaying variation without being random – is most worthy of interest given the rewards found in the depths of exploration.
The use of the term complex is often confused with the term complicated. In today's systems, this is the difference between myriad connecting "stovepipes" and effective "integrated" solutions. This means that complex is the opposite of independent, while complicated is the opposite of simple.
While this has led some fields to come up with specific definitions of complexity, there is a more recent movement to regroup observations from different fields to study complexity in itself, whether it appears in anthills, human brains or social systems. One such interdisciplinary group of fields is relational order theories.
== Topics ==
=== Behaviour ===
The behavior of a complex system is often said to be due to emergence and self-organization. Chaos theory has investigated the sensitivity of systems to variations in initial conditions as one cause of complex behaviour.
=== Mechanisms ===
Recent developments in artificial life, evolutionary computation and genetic algorithms have led to an increasing emphasis on complexity and complex adaptive systems.
=== Simulations ===
In social science, the study on the emergence of macro-properties from the micro-properties, also known as macro-micro view in sociology. The topic is commonly recognized as social complexity that is often related to the use of computer simulation in social science, i.e. computational sociology.
=== Systems ===
Systems theory has long been concerned with the study of complex systems (in recent times, complexity theory and complex systems have also been used as names of the field). These systems are present in the research of a variety of disciplines, including biology, economics, social studies and technology. Recently, complexity has become a natural domain of interest of real-world socio-cognitive systems and emerging systemics research. Complex systems tend to be high-dimensional, non-linear, and difficult to model. In specific circumstances, they may exhibit low-dimensional behaviour.
=== Data ===
In information theory, algorithmic information theory is concerned with the complexity of strings of data.
Complex strings are harder to compress. While intuition tells us that this may depend on the codec used to compress a string (a codec could be theoretically created in any arbitrary language, including one in which the very small command "X" could cause the computer to output a very complicated string like "18995316"), any two Turing-complete languages can be implemented in each other, meaning that the length of two encodings in different languages will vary by at most the length of the "translation" language – which will end up being negligible for sufficiently large data strings.
These algorithmic measures of complexity tend to assign high values to random noise. However, under a certain understanding of complexity, arguably the most intuitive one, random noise is meaningless and so not complex at all.
Information entropy is also sometimes used in information theory as indicative of complexity, but entropy is also high for randomness. In the case of complex systems, information fluctuation complexity was designed so as not to measure randomness as complex and has been useful in many applications. More recently, a complexity metric was developed for images that can avoid measuring noise as complex by using the minimum description length principle.
=== Classification Problems ===
There has also been interest in measuring the complexity of classification problems in supervised machine learning. This can be useful in meta-learning to determine for which data sets filtering (or removing suspected noisy instances from the training set) is the most beneficial and could be expanded to other areas. For binary classification, such measures can consider the overlaps in feature values from differing classes, the separability of the classes, and measures of geometry, topology, and density of manifolds.
For non-binary classification problems, instance hardness is a bottom-up approach that first seeks to identify instances that are likely to be misclassified (assumed to be the most complex). The characteristics of such instances are then measured using supervised measures such as the number of disagreeing neighbors or the likelihood of the assigned class label given the input features.
=== In molecular recognition ===
A recent study based on molecular simulations and compliance constants describes molecular recognition as a phenomenon of organisation.
Even for small molecules like carbohydrates, the recognition process can not be predicted or designed even assuming that each individual hydrogen bond's strength is exactly known.
=== The law of requisite complexity ===
Deriving from the law of requisite variety, Boisot and McKelvey formulated the ‘Law of Requisite Complexity’, that holds that, in order to be efficaciously adaptive, the internal complexity of a system must match the external complexity it confronts.
=== Positive, appropriate and negative complexity ===
The application in project management of the Law of Requisite Complexity, as proposed by Stefan Morcov, is the analysis of positive, appropriate and negative complexity.
=== In project management ===
Project complexity is the property of a project which makes it difficult to understand, foresee, and keep under control its overall behavior, even when given reasonably complete information about the project system.
=== In systems engineering ===
Maik Maurer considers complexity as a reality in engineering. He proposed a methodology for managing complexity in systems engineering :
1. Define the system.
2. Identify the type of complexity.
3. Determine the strategy.
4. Determine the method.
5. Model the system.
6. Implement the method.
== Applications ==
Computational complexity theory is the study of the complexity of problems – that is, the difficulty of solving them. Problems can be classified by complexity class according to the time it takes for an algorithm – usually a computer program – to solve them as a function of the problem size. Some problems are difficult to solve, while others are easy. For example, some difficult problems need algorithms that take an exponential amount of time in terms of the size of the problem to solve. Take the travelling salesman problem, for example. It can be solved, as denoted in Big O notation, in time
O
(
n
2
2
n
)
{\displaystyle O(n^{2}2^{n})}
(where n is the size of the network to visit – the number of cities the travelling salesman must visit exactly once). As the size of the network of cities grows, the time needed to find the route grows (more than) exponentially.
Even though a problem may be computationally solvable in principle, in actual practice it may not be that simple. These problems might require large amounts of time or an inordinate amount of space. Computational complexity may be approached from many different aspects. Computational complexity can be investigated on the basis of time, memory or other resources used to solve the problem. Time and space are two of the most important and popular considerations when problems of complexity are analyzed.
There exist a certain class of problems that although they are solvable in principle they require so much time or space that it is not practical to attempt to solve them. These problems are called intractable.
There is another form of complexity called hierarchical complexity. It is orthogonal to the forms of complexity discussed so far, which are called horizontal complexity.
== Emerging applications in other fields ==
The concept of complexity is being increasingly used in the study of cosmology, big history, and cultural evolution with increasing granularity, as well as increasing quantification.
=== Application in cosmology ===
Eric Chaisson has advanced a cosmological complexity metric which he terms Energy Rate Density. This approach has been expanded in various works, most recently applied to measuring evolving complexity of nation-states and their growing cities.
== See also ==
== References ==
== Further reading ==
Chapouthier G. (2024) Complexity in Mosaic Form: from living beings to ethics, EPJ Web Conf., v.300, n° 01006, doi=10.1051/epjconf/202430001006
== External links ==
Complexity Measures – an article about the abundance of not-that-useful complexity measures.
Exploring Complexity in Science and Technology Archived 2011-03-05 at the Wayback Machine – Introductory complex system course by Melanie Mitchell
Santa Fe Institute focusing on the study of complexity science: Lecture Videos
UC Four Campus Complexity Videoconferences – Human Sciences and Complexity | Wikipedia/complexity |
Assembly theory is a framework developed to quantify the complexity of molecules and objects by assessing the minimal number of steps required to assemble them from fundamental building blocks. Proposed by chemist Lee Cronin and his team, the theory assigns an assembly index to molecules, which serves as a measurable indicator of their structural complexity. Cronin and colleagues argue that this approach allows for experimental verification and has applications in understanding selection processes, evolution, and the identification of biosignatures in astrobiology. However, the usefulness of the approach has been disputed.
== Background ==
The hypothesis was proposed by chemist Leroy Cronin in 2017 and developed by the team he leads at the University of Glasgow, then extended in collaboration with a team at Arizona State University led by astrobiologist Sara Imari Walker, in a paper released in 2021.
Assembly theory conceptualizes objects not as point particles, but as entities defined by their possible formation histories. This allows objects to show evidence of selection, within well-defined boundaries of individuals or selected units. Combinatorial objects are important in chemistry, biology and technology, in which most objects of interest (if not all) are hierarchical modular structures. For any object an 'assembly space' can be defined as all recursively assembled pathways that produce this object. The 'assembly index' is the number of steps on a shortest path producing the object. For such shortest path, the assembly space captures the minimal memory, in terms of the minimal number of operations necessary to construct an object based on objects that could have existed in its past.
The assembly is defined as "the total amount of selection necessary to produce an ensemble of observed objects"; for an ensemble containing
N
T
{\displaystyle N_{T}}
objects in total,
N
{\displaystyle N}
of which are unique, the assembly
A
{\displaystyle A}
is defined to be
A
=
∑
i
=
1
N
e
a
i
(
n
i
−
1
N
T
)
{\displaystyle A=\mathop {\sum } \limits _{i=1}^{N}{e}^{{a}_{i}}\left({\frac {{n}_{i}-1}{{N}_{\rm {T}}}}\right)}
,
where
n
i
{\displaystyle n_{i}}
denotes 'copy number', the number of occurrences of objects of type
i
=
{
1
,
2
,
…
,
N
}
{\displaystyle i=\{1,2,\dots ,N\}}
having assembly index
a
i
{\displaystyle a_{i}}
.
For example, the word 'abracadabra' contains 5 unique letters (a, b, c, d and r) and is 11 symbols long. It can be assembled from its constituents as a + b --> ab + r --> abr + a --> abra + c --> abrac + a --> abraca + d --> abracad + abra --> abracadabra, because 'abra' was already constructed at an earlier stage. Because this requires at least 7 steps, the assembly index is 7. The word ‘abracadrbaa’, of the same length, for example, has no repeats so has an assembly index of 10.
Take two binary strings
C
=
[
01010101
]
{\displaystyle C=[01010101]}
and
D
=
[
00010111
]
{\displaystyle D=[00010111]}
as another example. Both have the same length
N
=
8
{\displaystyle N=8}
bits, both have the same Hamming weight
N
1
=
N
/
2
=
4
{\displaystyle N_{1}=N/2=4}
. However, the assembly index of the first string is
a
(
C
)
=
3
{\displaystyle a(C)=3}
("01" is assembled, joined with itself into "0101", and joined again with "0101" taken from the assembly pool), while the assembly index of the second string is
a
(
D
)
=
6
{\displaystyle a(D)=6}
, since in this case only "01" can be taken from the assembly pool.
In general, for K subunits of an object O the assembly index is bounded by
log
2
(
K
)
≤
a
O
≤
K
−
1
{\displaystyle \log _{2}(K)\leq a_{O}\leq K-1}
.
Once a pathway to assemble an object is discovered, the object can be reproduced. The rate of discovery of new objects can be defined by the expansion rate
k
d
{\displaystyle k_{\text{d}}}
, introducing a discovery timescale
τ
d
≈
1
/
k
d
{\displaystyle \tau _{\text{d}}\approx 1/k_{\text{d}}}
.
To include copy number
n
i
{\displaystyle n_{i}}
in the dynamics of assembly theory, a production timescale
τ
p
≈
1
/
k
p
{\displaystyle \tau _{\text{p}}\approx 1/k_{\text{p}}}
is defined, where
k
p
{\displaystyle k_{\text{p}}}
is the production rate of a specific object
i
{\displaystyle i}
.
Defining these two distinct timescales
τ
d
{\displaystyle \tau _{\text{d}}}
, for the initial discovery of an object, and
τ
p
{\displaystyle \tau _{\text{p}}}
, for making copies of existing objects, allows to determine the regimes in which selection is possible.
While other approaches can provide a measure of complexity, the researchers claim that assembly theory's molecular assembly number is the first to be measurable experimentally. Molecules with a high assembly index are very unlikely to form abiotically, and the probability of abiotic formation goes down as the value of the assembly index increases. The assembly index of a molecule can be obtained directly via spectroscopic methods. This method could be implemented in a fragmentation tandem mass spectrometry instrument to search for biosignatures.
The theory was extended to map chemical space with molecular assembly trees, demonstrating the application of this approach in drug discovery, in particular in research of new opiate-like molecules by connecting the "assembly pool elements through the same pattern in which they were disconnected from their parent compound(s)".
It is difficult to identify chemical signatures that are unique to life. For example, the Viking lander biological experiments detected molecules that could be explained by either living or natural non-living processes.
It appears that only living samples can produce assembly index measurements above ~15. However, 2021, Cronin first explained how polyoxometalates could have large assembly indexes >15 in theory due to autocatalysis.
== Critical views ==
Chemist Steven A. Benner has publicly criticized various aspects of assembly theory. Benner argues that it is transparently false that non-living systems, and with no life intervention, cannot contain molecules that are complex but people would be misled in thinking that because it was published in Nature journals after peer review, these papers must be right.
A paper published in the Journal of Molecular Evolution concludes that "the hype around Assembly Theory reflects rather unfavorably both on the authors and the scientific publication system in general". The author concludes that what "assembly theory really does is to detect and quantify bias caused by higher-level constraints in some well-defined rule-based worlds"; one "can use assembly theory to check whether something unexpected is going on in a very broad range of computational model worlds or universes".
Another paper authored by a group of chemists and planetary scientists published in the Journal of the Royal Society Interface demonstrated that abiotic chemical processes have the potential to form crystal structures of great complexity — values exceeding the proposed abiotic/biotic divide of MA index = 15. They conclude that "while the proposal of a biosignature based on a molecular assembly index of 15 is an intriguing and testable concept, the contention that only life can generate molecular structures with MA index ≥ 15 is in error".
Two papers published in 2024 argue that assembly theory provides no insights beyond those already available using algorithmic complexity and Claude Shannon's information theory.
== See also ==
List of interstellar and circumstellar molecules
Smallest grammar problem
Word problem for groups
== References ==
== Further reading ==
Cronin, Leroy; Walker, Sara Imari (3 June 2016). "Beyond prebiotic chemistry". Science. 352 (6290): 1174–1175. Bibcode:2016Sci...352.1174C. doi:10.1126/science.aaf6310. ISSN 0036-8075. PMID 27257242. S2CID 206649123.
Cronin, Leroy; Krasnogor, Natalio; Davis, Benjamin G.; Alexander, Cameron; Robertson, Neil; Steinke, Joachim H. G.; Schroeder, Sven L. M.; Khlobystov, Andrei N.; Cooper, Geoff; Gardner, Paul M.; Siepmann, Peter (2006). "The imitation game—a computational chemical approach to recognizing life". Nature Biotechnology. 24 (10): 1203–1206. doi:10.1038/nbt1006-1203. ISSN 1546-1696. PMID 17033651. S2CID 4664573.
Ball, Philip (4 May 2023). "A New Theory for the Assembly of Life in the Universe". Quanta Magazine. | Wikipedia/Assembly_theory |
The Zero-Force Evolutionary Law (ZFEL) is a theory proposed by Daniel McShea and Robert Brandon regarding the evolution of diversity and complexity. Under the ZFEL, diversity is understood as the variation among organisms and complexity as the variation among the parts within an organism. A part is understood as a system that is to some degree internally integrated and isolated from its surroundings. In a multicellular organism, for example, a cell is a part, and therefore complexity is the number of different cell types. Like the theory of relativity, the theory has a special and general formulation. The special formulation states that in the absence of natural selection, an evolutionary system with variation and heredity will tend spontaneously to diversify and complexify.
The general formulation states that evolutionary systems have a tendency to diversify and complexify, but that these processes may be amplified or constrained by other forces, including natural selection. The mechanism of the ZFEL is the inherently error-prone process of replication and reproduction. In the absence of selection, errors tend to accumulate, with the result that individuals within a population tend to become more different from each other (diversity) and parts within an individual tend to become more different from each other (complexity). Both of these tendencies can be overcome by selection, including stabilizing or negative selection, with the result that diversity or complexity often does not change, or even decreases. What the ZFEL offers is not so much a prediction as a null expectation, telling us what will happen in evolution when selection is absent. It is the analogue of Newton's law of momentum, which tells us the trajectory of a moving object in the absence of forces (a straight line).
== See also ==
Constructive neutral evolution
Evolution of biological complexity
Neutral theory of molecular evolution
== References == | Wikipedia/Zero-Force_Evolutionary_Law |
The model of hierarchical complexity (MHC) is a framework for scoring how complex a behavior is, such as verbal reasoning or other cognitive tasks. It quantifies the order of hierarchical complexity of a task based on mathematical principles of how the information is organized, in terms of information science. This model was developed by Michael Commons and Francis Richards in the early 1980s.
== Overview ==
The model of hierarchical complexity (MHC) is a formal theory and a mathematical psychology framework for scoring how complex a behavior is. Developed by Michael Lamport Commons and colleagues, it quantifies the order of hierarchical complexity of a task based on mathematical principles of how the information is organized, in terms of information science. Its forerunner was the general stage model.
Behaviors that may be scored include those of individual humans or their social groupings (e.g., organizations, governments, societies), animals, or machines. It enables scoring the hierarchical complexity of task accomplishment in any domain. It is based on the very simple notions that higher order task actions:
are defined in terms of the next lower ones (creating hierarchy);
organize the next lower actions;
organize lower actions in a non-arbitrary way (differentiating them from simple chains of behavior).
It is cross-culturally and cross-species valid. The reason it applies cross-culturally is that the scoring is based on the mathematical complexity of the hierarchical organization of information. Scoring does not depend upon the content of the information (e.g., what is done, said, written, or analyzed) but upon how the information is organized.
The MHC is a non-mentalistic model of developmental stages. It specifies 16 orders of hierarchical complexity and their corresponding stages. It is different from previous proposals about developmental stage applied to humans; instead of attributing behavioral changes across a person's age to the development of mental structures or schema, this model posits that task sequences of task behaviors form hierarchies that become increasingly complex. Because less complex tasks must be completed and practiced before more complex tasks can be acquired, this accounts for the developmental changes seen in an individual persons' performance of complex tasks. For example, a person cannot perform arithmetic until the numeral representations of numbers are learned, or a person cannot operationally multiply the sums of numbers until addition is learned. However, as much as natural intelligence helps human to understand some numbers, it does not play a complete role in multiplying large numbers without learning additions.
The creators of the MHC claim that previous theories of stage have confounded the stimulus and response in assessing stage by simply scoring responses and ignoring the task or stimulus. The MHC separates the task or stimulus from the performance. The participant's performance on a task of a given complexity represents the stage of developmental complexity.
Previous stage theories were unsatisfying to Commons and Richards because the theories did not show the existence of the stages more than describing sequential changes in human behavior. This led them to create a list of two concepts they felt a successful developmental theory should address. The two ideas they wanted to study were (1) the hierarchical complexity of the task to be solved and (2) the psychology, sociology, and anthropology of the task performance (and the development of the performance).
== Vertical complexity of tasks performed ==
One major basis for this developmental theory is task analysis. The study of ideal tasks, including their instantiation in the real world, has been the basis of the branch of stimulus control called psychophysics. Tasks are defined as sequences of contingencies, each presenting stimuli and each requiring a behavior or a sequence of behaviors that must occur in some non-arbitrary fashion. The complexity of behaviors necessary to complete a task can be specified using the horizontal complexity and vertical complexity definitions described below. Behavior is examined with respect to the analytically-known complexity of the task.
Tasks are quantal in nature. They are either completed correctly or not completed at all. There is no intermediate state (tertium non datur). For this reason, the model characterizes all stages as P-hard and functionally distinct. The orders of hierarchical complexity are quantized like the electron atomic orbitals around the nucleus: each task difficulty has an order of hierarchical complexity required to complete it correctly, analogous to the atomic Slater determinant. Since tasks of a given quantified order of hierarchical complexity require actions of a given order of hierarchical complexity to perform them, the stage of the participant's task performance is equivalent to the order of complexity of the successfully completed task. The quantal feature of tasks is thus particularly instrumental in stage assessment because the scores obtained for stages are likewise discrete.
Every task contains a multitude of subtasks. When the subtasks are carried out by the participant in a required order, the task in question is successfully completed. Therefore, the model asserts that all tasks fit in some configured sequence of tasks, making it possible to precisely determine the hierarchical order of task complexity. Tasks vary in complexity in two ways: either as horizontal (involving classical information); or as vertical (involving hierarchical information).
=== Horizontal complexity ===
Classical information describes the number of "yes–no" questions it takes to do a task. For example, if one asked a person across the room whether a penny came up heads when they flipped it, their saying "heads" would transmit 1 bit of "horizontal" information. If there were 2 pennies, one would have to ask at least two questions, one about each penny. Hence, each additional 1-bit question would add another bit. Let us say they had a four-faced top with the faces numbered 1, 2, 3, and 4. Instead of spinning it, they tossed it against a backboard as one does with dice in a game of craps. Again, there would be 2 bits. One could ask them whether the face had an even number. If it did, one would then ask if it were a 2. Horizontal complexity, then, is the sum of bits required by just such tasks as these.
=== Vertical complexity ===
Hierarchical complexity refers to the number of recursions that the coordinating actions must perform on a set of primary elements. Actions at a higher order of hierarchical complexity: (a) are defined in terms of actions at the next lower order of hierarchical complexity; (b) organize and transform the lower-order actions (see Figure 2); (c) produce organizations of lower-order actions that are qualitatively new and not arbitrary, and cannot be accomplished by those lower-order actions alone. Once these conditions have been met, we say the higher-order action coordinates the actions of the next lower order.
To illustrate how lower actions get organized into more hierarchically complex actions, let us turn to a simple example. Completing the entire operation 3 × (4 + 1) constitutes a task requiring the distributive act. That act non-arbitrarily orders adding and multiplying to coordinate them. The distributive act is therefore one order more hierarchically complex than the acts of adding and multiplying alone; it indicates the singular proper sequence of the simpler actions. Although simply adding results in the same answer, people who can do both display a greater freedom of mental functioning. Additional layers of abstraction can be applied. Thus, the order of complexity of the task is determined through analyzing the demands of each task by breaking it down into its constituent parts.
The hierarchical complexity of a task refers to the number of concatenation operations it contains, that is, the number of recursions that the coordinating actions must perform. An order-three task has three concatenation operations. A task of order three operates on one or more tasks of vertical order two and a task of order two operates on one or more tasks of vertical order one (the simplest tasks).
== Stages of development ==
Stage theories describe human organismic and/or technological evolution as systems that move through a pattern of distinct stages over time. Here development is described formally in terms of the model of hierarchical complexity (MHC).
=== Formal definition of stage ===
Since actions are defined inductively, so is the function h, known as the order of the hierarchical complexity. To each action A, we wish to associate a notion of that action's hierarchical complexity, h(A). Given a collection of actions A and a participant S performing A, the stage of performance of S on A is the highest order of the actions in A completed successfully at least once, i.e., it is: stage (S, A) = max{h(A) | A ∈ A and A completed successfully by S}. Thus, the notion of stage is discontinuous, having the same transitional gaps as the orders of hierarchical complexity. This is in accordance with previous definitions.
Because MHC stages are conceptualized in terms of the hierarchical complexity of tasks rather than in terms of mental representations (as in Piaget's stages), the highest stage represents successful performances on the most hierarchically complex tasks rather than intellectual maturity.
=== Stages of hierarchical complexity ===
The following table gives descriptions of each stage in the MHC.
== Relationship with Piaget's theory ==
The MHC builds on Piagetian theory but differs from it in many ways; notably the MHC has additional higher stages. In both theories, one finds:
Higher-order actions defined in terms of lower-order actions. This forces the hierarchical nature of the relations and makes the higher-order tasks include the lower ones and requires that lower-order actions are hierarchically contained within the relative definitions of the higher-order tasks.
Higher-order of complexity actions organize those lower-order actions. This makes them more powerful. Lower-order actions are organized by the actions with a higher order of complexity, i.e., the more complex tasks.
What Commons et al. (1998) have added includes:
Higher-order-of-complexity actions organize those lower-order actions in a non-arbitrary way.
This makes it possible for the model's application to meet real world requirements, including the empirical and analytic. Arbitrary organization of lower order of complexity actions, possible in the Piagetian theory, despite the hierarchical definition structure, leaves the functional correlates of the interrelationships of tasks of differential complexity formulations ill-defined.
Moreover, the model is consistent with the neo-Piagetian theories of cognitive development. According to these theories, progression to higher stages or levels of cognitive development is caused by increases in processing efficiency and working memory capacity. That is, higher-order stages place increasingly higher demands on these functions of information processing, so that their order of appearance reflects the information processing possibilities at successive ages.
The following dimensions are inherent in the application:
Task and performance are separated.
All tasks have an order of hierarchical complexity.
There is only one sequence of orders of hierarchical complexity.
Hence, there is structure of the whole for ideal tasks and actions.
There are transitional gaps between the orders of hierarchical complexity.
Stage is defined as the most hierarchically complex task solved.
There are discrete gaps in Rasch scaled stage of performance.
Performance stage is different task area to task area.
There is no structure of the whole—horizontal décalage—for performance. It is not inconsistency in thinking within a developmental stage. Décalage is the normal modal state of affairs.
== Orders and corresponding stages ==
The MHC specifies 16 orders of hierarchical complexity and their corresponding stages, positing that each of Piaget's substages, in fact, are robustly hard stages. The MHC adds five postformal stages to Piaget's developmental trajectory: systematic stage 12, metasystematic stage 13, paradigmatic stage 14, cross-paradigmatic stage 15, and meta-cross-paradigmatic stage 16. It may be the Piaget's consolidate formal stage is the same as the systematic stage. The sequence is as follows: (0) calculatory, (1) automatic, (2) sensory & motor, (3) circular sensory-motor, (4) sensory-motor, (5) nominal, (6) sentential, (7) preoperational, (8) primary, (9) concrete, (10) abstract, (11) formal, and the five postformal: (12) systematic, (13) metasystematic, (14) paradigmatic, (15) cross-paradigmatic, and (16) meta-cross-paradigmatic. The first four stages (0–3) correspond to Piaget's sensorimotor stage at which infants and very young children perform. Adolescents and adults can perform at any of the subsequent stages. MHC stages 4 through 5 correspond to Piaget's pre-operational stage; 6 through 8 correspond to his concrete operational stage; and 9 through 11 correspond to his formal operational stage.
More complex behaviors characterize multiple system models. The four highest stages in the MHC are not represented in Piaget's model. The higher stages of the MHC have extensively influenced the field of positive adult development. Some adults are said to develop alternatives to, and perspectives on, formal operations; they use formal operations within a "higher" system of operations. Some theorists call the more complex orders of cognitive tasks "postformal thought", but other theorists argue that these higher orders cannot exactly be labelled as postformal thought.
Jordan (2018) argued that unidimensional models such as the MHC, which measure level of complexity of some behavior, refer to only one of many aspects of adult development, and that other variables are needed (in addition to unidimensional measures of complexity) for a fuller description of adult development.
== Empirical research using the model ==
The MHC has a broad range of applicability. Its mathematical foundation permits it to be used by anyone examining task performance that is organized into stages. It is designed to assess development based on the order of complexity which the actor utilizes to organize information. The model thus allows for a standard quantitative analysis of developmental complexity in any cultural setting. Other advantages of this model include its avoidance of mentalistic explanations, as well as its use of quantitative principles which are universally applicable in any context.
The following practitioners can use the MHC to quantitatively assess developmental stages:
Cross-cultural developmentalists
Animal developmentalists
Evolutionary psychologists
Organizational psychologists
Developmental political psychologists
Learning theorists
Perception researchers
Historians of science
Educators
Therapists
Anthropologists
=== List of examples ===
In one representative study, Commons, Goodheart, and Dawson (1997) found, using Rasch analysis (Rasch, 1980), that hierarchical complexity of a given task predicts stage of a performance, the correlation being r = 0.92. Correlations of similar magnitude have been found in a number of the studies. The following are examples of tasks studied using the model of hierarchical complexity or Kurt W. Fischer's similar skill theory:
As of 2014, people and institutes from all the major continents of the world, except Africa, have used the model of hierarchical complexity. Because the model is very simple and is based on analysis of tasks and not just performances, it is dynamic. With the help of the model, it is possible to quantify the occurrence and progression of transition processes in task performances at any order of hierarchical complexity.
== Criticisms ==
The descriptions of stages 13–15 have been described as insufficiently precise.
== See also ==
== References ==
== Literature ==
== External links ==
Behavioral Development Bulletin
Society for Research in Adult Development | Wikipedia/Model_of_hierarchical_complexity |
Holism in science, holistic science, or methodological holism is an approach to research that emphasizes the study of complex systems. Systems are approached as coherent wholes whose component parts are best understood in context and in relation to both each other and to the whole. Holism typically stands in contrast with reductionism, which describes systems by dividing them into smaller components in order to understand them through their elemental properties.
The holism-individualism dichotomy is especially evident in conflicting interpretations of experimental findings across the social sciences, and reflects whether behavioural analysis begins at the systemic, macro-level (ie. derived from social relations) or the component micro-level (ie. derived from individual agents).
== Overview ==
David Deutsch calls holism anti-reductionist and refers to the concept of thinking as the only legitimate way to think about science in as a series of emergent, or higher level phenomena. He argues that neither approach is purely correct.
Two aspects of Holism are:
The way of doing science, sometimes called "whole to parts", which focuses on observation of the specimen within its ecosystem first before breaking down to study any part of the specimen.
The idea that the scientist is not a passive observer of an external universe but rather a participant in the system.
Proponents claim that Holistic science is naturally suited to subjects such as ecology, biology, physics and the social sciences, where complex, non-linear interactions are the norm. These are systems where emergent properties arise at the level of the whole that cannot be predicted by focusing on the parts alone, which may make mainstream, reductionist science ill-equipped to provide understanding beyond a certain level. This principle of emergence in complex systems is often captured in the phrase ′the whole is greater than the sum of its parts′. Living organisms are an example: no knowledge of all the chemical and physical properties of matter can explain or predict the functioning of living organisms. The same happens in complex social human systems, where detailed understanding of individual behaviour cannot predict the behaviour of the group, which emerges at the level of the collective. The phenomenon of emergence may impose a theoretical limit on knowledge available through reductionist methodology, arguably making complex systems natural subjects for holistic approaches.
Science journalist John Horgan has expressed this view in the book The End of Science. He wrote that a certain pervasive model within holistic science, self-organized criticality, for example, "is not really a theory at all. Like punctuated equilibrium, self-organized criticality is merely a description, one of many, of the random fluctuations, the noise, permeating nature." By the theorists' own admissions, he said, such a model "can generate neither specific predictions about nature nor meaningful insights. What good is it, then?"
One of the reasons that holistic science attracts supporters is that it seems to offer a progressive, 'socio-ecological' view of the world, but Alan Marshall's book The Unity of Nature offers evidence to the contrary; suggesting holism in science is not 'ecological' or 'socially-responsive' at all, but regressive and repressive.
== Examples in various fields of science ==
=== Physical science ===
==== Agriculture ====
Permaculture takes a systems level approach to agriculture and land management by attempting to copy what happens in the natural world. Holistic management integrates ecology and social sciences with food production. It was originally designed as a way to reverse desertification. Organic farming is sometimes considered a holistic approach.
==== In physics ====
Richard Healey offered a modal interpretation and used it to present a model account of the puzzling correlations which portrays them as resulting from the operation of a process that violates both spatial and spatiotemporal separability. He argued that, on this interpretation, the nonseparability of the process is a consequence of physical property holism; and that the resulting account yields genuine understanding of how the correlations come about without any violation of relativity theory or Local Action. Subsequent work by Clifton, Dickson and Myrvold cast doubt on whether the account can be squared with relativity theory’s requirement of Lorentz invariance but leaves no doubt of an spatially entangled holism in the theory. Paul Davies and John Gribbin further observe that Wheeler's delayed choice experiment shows how the quantum world displays a sort of holism in time as well as space.
In the holistic approach of David Bohm, any collection of quantum objects constitutes an indivisible whole within an implicate and explicate order. Bohm said there is no scientific evidence to support the dominant view that the universe consists of a huge, finite number of minute particles, and offered instead a view of undivided wholeness: "ultimately, the entire universe (with all its 'particles', including those constituting human beings, their laboratories, observing instruments, etc.) has to be understood as a single undivided whole, in which analysis into separately and independently existent parts has no fundamental status".
==== Chaos and complexity ====
Scientific holism holds that the behavior of a system cannot be perfectly predicted, no matter how much data is available. Natural systems can produce surprisingly unexpected behavior, and it is suspected that behavior of such systems might be computationally irreducible, which means it would not be possible to even approximate the system state without a full simulation of all the events occurring in the system. Key properties of the higher level behavior of certain classes of systems may be mediated by rare "surprises" in the behavior of their elements due to the principle of interconnectivity, thus evading predictions except by brute force simulation.
==== Ecology ====
Holistic thinking can be applied to ecology, combining biological, chemical, physical, economic, ethical, and political insights. The complexity grows with the area, so that it is necessary to reduce the characteristic of the view in other ways, for example to a specific time of duration.
==== Medicine ====
In primary care the term "holistic," has been used to describe approaches that take into account social considerations and other intuitive judgements. The term holism, and so-called approaches, appear in psychosomatic medicine in the 1970s, when they were considered one possible way to conceptualize psychosomatic phenomena. Instead of charting one-way causal links from psyche to soma, or vice versa, it aimed at a systemic model, where multiple biological, psychological and social factors were seen as interlinked.
Other, alternative approaches in the 1970s were psychosomatic and somatopsychic approaches, which concentrated on causal links only from psyche to soma, or from soma to psyche, respectively. At present it is commonplace in psychosomatic medicine to state that psyche and soma cannot really be separated for practical or theoretical purposes.
The term systems medicine first appeared in 1992 and takes an integrative approach to all of the body and environment.
=== Social science ===
==== Economics ====
Some economists use a causal holism theory in their work. That is they view the discipline in the manner of Ludwig Wittgenstein and claim that it can't be defined by necessary and sufficient conditions.
==== Education reform ====
The Taxonomy of Educational Objectives identifies many levels of cognitive functioning, which it is claimed may be used to create a more holistic education. In authentic assessment, rather than using computers to score multiple choice tests, a standards based assessment uses trained scorers to score open-response items using holistic scoring methods. In projects such as the North Carolina Writing Project, scorers are instructed not to count errors, or count numbers of points or supporting statements. The scorer is instead instructed to judge holistically whether "as a whole" is it more a "2" or a "3". Critics question whether such a process can be as objective as computer scoring, and the degree to which such scoring methods can result in different scores from different scorers.
==== Anthropology ====
Anthropology is holistic in two senses. First, it is concerned with all human beings across times and places, and with all dimensions of humanity (evolutionary, biophysical, sociopolitical, economic, cultural, psychological, etc.) Further, many academic programs following this approach take a "four-field" approach to anthropology that encompasses physical anthropology, archeology, linguistics, and cultural anthropology or social anthropology.
Some anthropologists disagree, and consider holism to be an artifact from 19th century social evolutionary thought that inappropriately imposes scientific positivism upon cultural anthropology.
The term "holism" is additionally used within social and cultural anthropology to refer to a methodological analysis of a society as a whole, in which component parts are treated as functionally relative to each other. One definition says: "as a methodological ideal, holism implies ... that one does not permit oneself to believe that our own established institutional boundaries (e.g. between politics, sexuality, religion, economics) necessarily may be found also in foreign societies."
==== Psychology of perception ====
A major holist movement in the early twentieth century was gestalt psychology. The claim was that perception is not an aggregation of atomic sense data but a field, in which there is a figure and a ground. Background has holistic effects on the perceived figure. Gestalt psychologists included Wolfgang Koehler, Max Wertheimer, Kurt Koffka. Koehler claimed the perceptual fields corresponded to electrical fields in the brain. Karl Lashley did experiments with gold foil pieces inserted in monkey brains purporting to show that such fields did not exist. However, many of the perceptual illusions and visual phenomena exhibited by the gestaltists were taken over (often without credit) by later perceptual psychologists. Gestalt psychology had influence on Fritz Perls' gestalt therapy, although some old-line gestaltists opposed the association with counter-cultural and New Age trends later associated with gestalt therapy. Gestalt theory was also influential on phenomenology. Aron Gurwitsch wrote on the role of the field of consciousness in gestalt theory in relation to phenomenology. Maurice Merleau-Ponty made much use of holistic psychologists such as work of Kurt Goldstein in his "Phenomenology of Perception."
==== Teleological psychology ====
Alfred Adler believed that the individual (an integrated whole expressed through a self-consistent unity of thinking, feeling, and action, moving toward an unconscious, fictional final goal), must be understood within the larger wholes of society, from the groups to which he belongs (starting with his face-to-face relationships), to the larger whole of mankind. The recognition of our social embeddedness and the need for developing an interest in the welfare of others, as well as a respect for nature, is at the heart of Adler's philosophy of living and principles of psychotherapy.
Edgar Morin, the French philosopher and sociologist, can be considered a holist based on the transdisciplinary nature of his work.
== Skeptical reception ==
According to skeptics, the phrase "holistic science" is often misused by pseudosciences. In the book Science and Pseudoscience in Clinical Psychology it's noted that "Proponents of pseudoscientific claims, especially in organic medicine, and mental health, often resort to the "mantra of holism" to explain away negative findings. When invoking the mantra, they typically maintain that scientific claims can be evaluated only within the context of broader claims and therefore cannot be evaluated in isolation." This is an invocation of Karl Popper's demarcation problem and in a posting to Ask a Philosopher Massimo Pigliucci clarifies Popper by positing, "Instead of thinking of science as making progress by inductive generalization (which doesn’t work because no matter how many times a given theory may have been confirmed thus far, it is always possible that new, contrary, data will emerge tomorrow), we should say that science makes progress by conclusively disconfirming theories that are, in fact, wrong."
Victor J. Stenger states that "holistic healing is associated with the rejection of classical, Newtonian physics. Yet, holistic healing retains many ideas from eighteenth and nineteenth century physics. Its proponents are blissfully unaware that these ideas, especially superluminal holism, have been rejected by modern physics as well".
Some quantum mystics interpret the wave function of quantum mechanics as a vibration in a holistic ether that pervades the universe and wave function collapse as the result of some cosmic consciousness. This is a misinterpretation of the effects of quantum entanglement as a violation of relativistic causality and quantum field theory.
== See also ==
== References ==
== Further reading ==
Article "Patterns of Wholeness: Introducing Holistic Science" by Brian Goodwin, from the journal Resurgence
Article "From Control to Participation" by Brian Goodwin, from the journal Resurgence
Freire, Olival (2005). "Science and exile: David Bohm, the cold war, and a new interpretation of quantum mechanics". Historical Studies in the Physical and Biological Sciences. 36: 1–34. arXiv:physics/0508184. Bibcode:2005physics...8184F. doi:10.1525/hsps.2005.36.1.1. | Wikipedia/Holism_in_science |
A complex system is a system composed of many components which may interact with each other. Examples of complex systems are Earth's global climate, organisms, the human brain, infrastructure such as power grid, transportation or communication systems, complex software and electronic systems, social and economic organizations (like cities), an ecosystem, a living cell, and, ultimately, for some authors, the entire universe.
The behavior of a complex system is intrinsically difficult to model due to the dependencies, competitions, relationships, and other types of interactions between their parts or between a given system and its environment. Systems that are "complex" have distinct properties that arise from these relationships, such as nonlinearity, emergence, spontaneous order, adaptation, and feedback loops, among others. Because such systems appear in a wide variety of fields, the commonalities among them have become the topic of their independent area of research. In many cases, it is useful to represent such a system as a network where the nodes represent the components and links represent their interactions.
The term complex systems often refers to the study of complex systems, which is an approach to science that investigates how relationships between a system's parts give rise to its collective behaviors and how the system interacts and forms relationships with its environment. The study of complex systems regards collective, or system-wide, behaviors as the fundamental object of study; for this reason, complex systems can be understood as an alternative paradigm to reductionism, which attempts to explain systems in terms of their constituent parts and the individual interactions between them.
As an interdisciplinary domain, complex systems draw contributions from many different fields, such as the study of self-organization and critical phenomena from physics, of spontaneous order from the social sciences, chaos from mathematics, adaptation from biology, and many others. Complex systems is therefore often used as a broad term encompassing a research approach to problems in many diverse disciplines, including statistical physics, information theory, nonlinear dynamics, anthropology, computer science, meteorology, sociology, economics, psychology, and biology.
== Types of systems ==
Complex systems can be:
Complex adaptive systems which have the capacity to change.
Polycentric systems : “where many elements are capable of making mutual adjustments for ordering their relationships with one another within a general system of rules where each element acts with independence of other elements”.
Disorganised systems involving localized interactions of multiple entities that do not form a coherent whole. Disorganised systems are linked to self-organisation processes.
Hierarchic systems which are analyzable into successive sets of subsystems. They can also be called nested or embedded systems.
Cybernetic systems involve information feedback loops.
== Key concepts ==
=== Adaptation ===
Complex adaptive systems are special cases of complex systems that are adaptive in that they have the capacity to change and learn from experience. Examples of complex adaptive systems include the international trade markets, social insect and ant colonies, the biosphere and the ecosystem, the brain and the immune system, the cell and the developing embryo, cities, manufacturing businesses and any human social group-based endeavor in a cultural and social system such as political parties or communities.
=== Decomposability ===
A system is decomposable if the parts of the system (subsystems) are independent from each other, for exemple the model of a perfect gas consider the relations among molecules negligeable.
In a nearly decomposable system, the interactions between subsystems are weak but not negligeable, this is often the case in social systems. Conceptually, a system is nearly decomposable if the variables composing it can be separated into classes and subclasses, if these variables are independent for many functions but affect each other, and if the whole system is greater than the parts.
== Features ==
Complex systems may have the following features:
Complex systems may be open
Complex systems are usually open systems – that is, they exist in a thermodynamic gradient and dissipate energy. In other words, complex systems are frequently far from energetic equilibrium: but despite this flux, there may be pattern stability, see synergetics.
Complex systems may exhibit critical transitions
Critical transitions are abrupt shifts in the state of ecosystems, the climate, financial and economic systems or other complex systems that may occur when changing conditions pass a critical or bifurcation point. The 'direction of critical slowing down' in a system's state space may be indicative of a system's future state after such transitions when delayed negative feedbacks leading to oscillatory or other complex dynamics are weak.
Complex systems may be nested
The components of a complex system may themselves be complex systems. For example, an economy is made up of organisations, which are made up of people, which are made up of cells – all of which are complex systems. The arrangement of interactions within complex bipartite networks may be nested as well. More specifically, bipartite ecological and organisational networks of mutually beneficial interactions were found to have a nested structure. This structure promotes indirect facilitation and a system's capacity to persist under increasingly harsh circumstances as well as the potential for large-scale systemic regime shifts.
Dynamic network of multiplicity
As well as coupling rules, the dynamic network of a complex system is important. Small-world or scale-free networks which have many local interactions and a smaller number of inter-area connections are often employed. Natural complex systems often exhibit such topologies. In the human cortex for example, we see dense local connectivity and a few very long axon projections between regions inside the cortex and to other brain regions.
May produce emergent phenomena
Complex systems may exhibit behaviors that are emergent, which is to say that while the results may be sufficiently determined by the activity of the systems' basic constituents, they may have properties that can only be studied at a higher level. For example, empirical food webs display regular, scale-invariant features across aquatic and terrestrial ecosystems when studied at the level of clustered 'trophic' species. Another example is offered by the termites in a mound which have physiology, biochemistry and biological development at one level of analysis, whereas their social behavior and mound building is a property that emerges from the collection of termites and needs to be analyzed at a different level.
Relationships are non-linear
In practical terms, this means a small perturbation may cause a large effect (see butterfly effect), a proportional effect, or even no effect at all. In linear systems, the effect is always directly proportional to cause. See nonlinearity.
Relationships contain feedback loops
Both negative (damping) and positive (amplifying) feedback are always found in complex systems. The effects of an element's behavior are fed back in such a way that the element itself is altered.
== History ==
In 1948, Dr. Warren Weaver published an essay on "Science and Complexity", exploring the diversity of problem types by contrasting problems of simplicity, disorganized complexity, and organized complexity. Weaver described these as "problems which involve dealing simultaneously with a sizable number of factors which are interrelated into an organic whole."
While the explicit study of complex systems dates at least to the 1970s, the first research institute focused on complex systems, the Santa Fe Institute, was founded in 1984. Early Santa Fe Institute participants included physics Nobel laureates Murray Gell-Mann and Philip Anderson, economics Nobel laureate Kenneth Arrow, and Manhattan Project scientists George Cowan and Herb Anderson. Today, there are over 50 institutes and research centers focusing on complex systems.
Since the late 1990s, the interest of mathematical physicists in researching economic phenomena has been on the rise. The proliferation of cross-disciplinary research with the application of solutions originated from the physics epistemology has entailed a gradual paradigm shift in the theoretical articulations and methodological approaches in economics, primarily in financial economics. The development has resulted in the emergence of a new branch of discipline, namely "econophysics", which is broadly defined as a cross-discipline that applies statistical physics methodologies which are mostly based on the complex systems theory and the chaos theory for economics analysis.
The 2021 Nobel Prize in Physics was awarded to Syukuro Manabe, Klaus Hasselmann, and Giorgio Parisi for their work to understand complex systems. Their work was used to create more accurate computer models of the effect of global warming on the Earth's climate.
== Applications ==
=== Complexity in practice ===
The traditional approach to dealing with complexity is to reduce or constrain it. Typically, this involves compartmentalization: dividing a large system into separate parts. Organizations, for instance, divide their work into departments that each deal with separate issues. Engineering systems are often designed using modular components. However, modular designs become susceptible to failure when issues arise that bridge the divisions.
=== Complexity of cities ===
Jane Jacobs described cities as being a problem in organized complexity in 1961, citing Dr. Weaver's 1948 essay. As an example, she explains how an abundance of factors interplay into how various urban spaces lead to a diversity of interactions, and how changing those factors can change how the space is used, and how well the space supports the functions of the city. She further illustrates how cities have been severely damaged when approached as a problem in simplicity by replacing organized complexity with simple and predictable spaces, such as Le Corbusier's "Radiant City" and Ebenezer Howard's "Garden City". Since then, others have written at length on the complexity of cities.
=== Complexity economics ===
Over the last decades, within the emerging field of complexity economics, new predictive tools have been developed to explain economic growth. Such is the case with the models built by the Santa Fe Institute in 1989 and the more recent economic complexity index (ECI), introduced by the MIT physicist Cesar A. Hidalgo and the Harvard economist Ricardo Hausmann.
Recurrence quantification analysis has been employed to detect the characteristic of business cycles and economic development. To this end, Orlando et al. developed the so-called recurrence quantification correlation index (RQCI) to test correlations of RQA on a sample signal and then investigated the application to business time series. The said index has been proven to detect hidden changes in time series. Further, Orlando et al., over an extensive dataset, shown that recurrence quantification analysis may help in anticipating transitions from laminar (i.e. regular) to turbulent (i.e. chaotic) phases such as USA GDP in 1949, 1953, etc. Last but not least, it has been demonstrated that recurrence quantification analysis can detect differences between macroeconomic variables and highlight hidden features of economic dynamics.
=== Complexity and education ===
Focusing on issues of student persistence with their studies, Forsman, Moll and Linder explore the "viability of using complexity science as a frame to extend methodological applications for physics education research", finding that "framing a social network analysis within a complexity science perspective offers a new and powerful applicability across a broad range of PER topics".
=== Complexity in healthcare research and practice ===
Healthcare systems are prime examples of complex systems, characterized by interactions among diverse stakeholders, such as patients, providers, policymakers, and researchers, across various sectors like health, government, community, and education. These systems demonstrate properties like non-linearity, emergence, adaptation, and feedback loops. Complexity science in healthcare frames knowledge translation as a dynamic and interconnected network of processes—problem identification, knowledge creation, synthesis, implementation, and evaluation—rather than a linear or cyclical sequence. Such approaches emphasize the importance of understanding and leveraging the interactions within and between these processes and stakeholders to optimize the creation and movement of knowledge. By acknowledging the complex, adaptive nature of healthcare systems, complexity science advocates for continuous stakeholder engagement, transdisciplinary collaboration, and flexible strategies to effectively translate research into practice.
=== Complexity and biology ===
Complexity science has been applied to living organisms, and in particular to biological systems. Within the emerging field of fractal physiology, bodily signals, such as heart rate or brain activity, are characterized using entropy or fractal indices. The goal is often to assess the state and the health of the underlying system, and diagnose potential disorders and illnesses.
=== Complexity and chaos theory ===
Complex systems theory is related to chaos theory, which in turn has its origins more than a century ago in the work of the French mathematician Henri Poincaré. Chaos is sometimes viewed as extremely complicated information, rather than as an absence of order. Chaotic systems remain deterministic, though their long-term behavior can be difficult to predict with any accuracy. With perfect knowledge of the initial conditions and the relevant equations describing the chaotic system's behavior, one can theoretically make perfectly accurate predictions of the system, though in practice this is impossible to do with arbitrary accuracy.
The emergence of complex systems theory shows a domain between deterministic order and randomness which is complex. This is referred to as the "edge of chaos".
When one analyzes complex systems, sensitivity to initial conditions, for example, is not an issue as important as it is within chaos theory, in which it prevails. As stated by Colander, the study of complexity is the opposite of the study of chaos. Complexity is about how a huge number of extremely complicated and dynamic sets of relationships can generate some simple behavioral patterns, whereas chaotic behavior, in the sense of deterministic chaos, is the result of a relatively small number of non-linear interactions. For recent examples in economics and business see Stoop et al. who discussed Android's market position, Orlando who explained the corporate dynamics in terms of mutual synchronization and chaos regularization of bursts in a group of chaotically bursting cells and Orlando et al. who modelled financial data (Financial Stress Index, swap and equity, emerging and developed, corporate and government, short and long maturity) with a low-dimensional deterministic model.
Therefore, the main difference between chaotic systems and complex systems is their history. Chaotic systems do not rely on their history as complex ones do. Chaotic behavior pushes a system in equilibrium into chaotic order, which means, in other words, out of what we traditionally define as 'order'. On the other hand, complex systems evolve far from equilibrium at the edge of chaos. They evolve at a critical state built up by a history of irreversible and unexpected events, which physicist Murray Gell-Mann called "an accumulation of frozen accidents". In a sense chaotic systems can be regarded as a subset of complex systems distinguished precisely by this absence of historical dependence. Many real complex systems are, in practice and over long but finite periods, robust. However, they do possess the potential for radical qualitative change of kind whilst retaining systemic integrity. Metamorphosis serves as perhaps more than a metaphor for such transformations.
=== Complexity and network science ===
A complex system is usually composed of many components and their interactions. Such a system can be represented by a network where nodes represent the components and links represent their interactions. For example, the Internet can be represented as a network composed of nodes (computers) and links (direct connections between computers). Other examples of complex networks include social networks, financial institution interdependencies, airline networks, and biological networks.
== Notable scholars ==
== See also ==
== References ==
== Further reading ==
Complexity Explained.
L.A.N. Amaral and J.M. Ottino, Complex networks – augmenting the framework for the study of complex system, 2004.
Chu, D.; Strand, R.; Fjelland, R. (2003). "Theories of complexity". Complexity. 8 (3): 19–30. Bibcode:2003Cmplx...8c..19C. doi:10.1002/cplx.10059.
Walter Clemens, Jr., Complexity Science and World Affairs, SUNY Press, 2013.
Gell-Mann, Murray (1995). "Let's Call It Plectics". Complexity. 1 (5): 3–5. Bibcode:1996Cmplx...1e...3G. doi:10.1002/cplx.6130010502.
A. Gogolin, A. Nersesyan and A. Tsvelik, Theory of strongly correlated systems , Cambridge University Press, 1999.
Nigel Goldenfeld and Leo P. Kadanoff, Simple Lessons from Complexity Archived 2017-09-28 at the Wayback Machine, 1999
Kelly, K. (1995). Out of Control, Perseus Books Group.
Orlando, Giuseppe Orlando; Pisarchick, Alexander; Stoop, Ruedi (2021). Nonlinearities in Economics. Dynamic Modeling and Econometrics in Economics and Finance. Vol. 29. doi:10.1007/978-3-030-70982-2. ISBN 978-3-030-70981-5. S2CID 239756912.
Syed M. Mehmud (2011), A Healthcare Exchange Complexity Model
Preiser-Kapeller, Johannes, "Calculating Byzantium. Social Network Analysis and Complexity Sciences as tools for the exploration of medieval social dynamics". August 2010
Donald Snooks, Graeme (2008). "A general theory of complex living systems: Exploring the demand side of dynamics". Complexity. 13 (6): 12–20. Bibcode:2008Cmplx..13f..12S. doi:10.1002/cplx.20225.
Stefan Thurner, Peter Klimek, Rudolf Hanel: Introduction to the Theory of Complex Systems, Oxford University Press, 2018, ISBN 978-0198821939
SFI @30, Foundations & Frontiers (2014).
== External links ==
"The Open Agent-Based Modeling Consortium".
"Complexity Science Focus". Archived from the original on 2017-12-05. Retrieved 2017-09-22.
"Santa Fe Institute".
"The Center for the Study of Complex Systems, Univ. of Michigan Ann Arbor". Archived from the original on 2017-12-13. Retrieved 2017-09-22.
"INDECS". (Interdisciplinary Description of Complex Systems)
"Introduction to Complexity – Free online course by Melanie Mitchell". Archived from the original on 2018-08-30. Retrieved 2018-08-29.
Jessie Henshaw (October 24, 2013). "Complex Systems". Encyclopedia of Earth.
Complex systems in scholarpedia.
Complex Systems Society
(Australian) Complex systems research network.
Complex Systems Modeling based on Luis M. Rocha, 1999.
CRM Complex systems research group
The Center for Complex Systems Research, Univ. of Illinois at Urbana-Champaign
Institute for Cross-Disciplinary Physics and Complex Systems (IFISC) | Wikipedia/Complex_systems_theory |
Terence Kemp McKenna (November 16, 1946–April 3, 2000) was an American ethnobotanist and mystic who advocated for the responsible use of naturally occurring psychedelic plants and mushrooms. He spoke and wrote about a variety of subjects, including psychedelic drugs, plant-based entheogens, shamanism, metaphysics, alchemy, language, philosophy, culture, technology, ethnomycology, environmentalism, and the theoretical origins of human consciousness. He was called the "Timothy Leary of the '90s", "one of the leading authorities on the ontological foundations of shamanism", and the "intellectual voice of rave culture".
McKenna formulated a concept about the nature of time based on fractal patterns he claimed to have discovered in the I Ching, which he called novelty theory, proposing that this predicted the end of time, and a transition of consciousness in the year 2012. His promotion of novelty theory and its connection to the Maya calendar is credited as one of the factors leading to the widespread beliefs about the 2012 phenomenon. Novelty theory is considered pseudoscience.
== Biography ==
=== Early life ===
Terence McKenna was born and raised in Paonia, Colorado,
with Irish ancestry on his father's side of the family.
As a youth, McKenna had a hobby of fossil-hunting from which he acquired a deep scientific appreciation of nature. At the age of 14, he became interested in psychology after reading Carl Jung's book Psychology and Alchemy. At the age of 14, McKenna first became aware of magic mushrooms when he read the article "Seeking the Magic Mushroom" from the May 13, 1957 edition of LIFE magazine. He began smoking cannabis as a teenager.
At age 16 McKenna moved to Los Altos, California to live with family friends for a year. He finished high school in Lancaster, California. In 1963, he was introduced to the literary world of psychedelics through The Doors of Perception and Heaven and Hell by Aldous Huxley and certain issues of The Village Voice which published articles on psychedelics.
McKenna said that one of his early psychedelic experiences with morning glory seeds showed him "that there was something there worth pursuing."
=== Studying and traveling ===
In 1965, McKenna enrolled in the University of California, Berkeley and was accepted into the Tussman Experimental College. While in college in 1967 he began studying shamanism through the study of Tibetan folk religion. That same year, which he called his "opium and kabbala phase", he traveled to Jerusalem where he met Kathleen Harrison, an ethnobotanist who later became his wife.
In 1969, McKenna traveled to Nepal led by his interest in Tibetan painting and hallucinogenic shamanism. He sought out shamans of the Tibetan Bon tradition, trying to learn more about the shamanic use of visionary plants. During his time there, he also studied the Tibetan language and worked as a hashish smuggler, until "one of his Bombay-to-Aspen shipments fell into the hands of U. S. Customs." He then wandered through southeast Asia viewing ruins, and spent time as a professional butterfly collector in Indonesia.
After his mother's death from cancer in 1970, McKenna, his brother Dennis, and three friends traveled to the Colombian Amazon in search of oo-koo-hé, a plant preparation containing dimethyltryptamine (DMT). Instead of oo-koo-hé they found fields full of gigantic Psilocybe cubensis mushrooms, which became the new focus of the expedition. In La Chorrera, at the urging of his brother, McKenna was the subject of a psychedelic experiment in which the brothers attempted to "bond harmine DNA with their own neural DNA" (harmine is another psychedelic compound they used synergistically with the mushrooms), through the use of a set specific vocal techniques. They hypothesised this would give them access to the collective memory of the human species, and would manifest the alchemists' Philosopher's Stone which they viewed as a "hyperdimensional union of spirit and matter". McKenna claimed the experiment put him in contact with "Logos": an informative, divine voice he believed was universal to visionary religious experience. McKenna also often referred to the voice as "the mushroom", and "the teaching voice" amongst other names. The voice's reputed revelations and his brother's simultaneous peculiar psychedelic experience prompted him to explore the structure of an early form of the I Ching, which led to his "Novelty Theory".
During their stay in the Amazon, McKenna also became romantically involved with his interpreter, Ev.
In 1972, McKenna returned to U.C. Berkeley to finish his studies and in 1975, he graduated with a degree in ecology, shamanism, and conservation of natural resources. In the autumn of 1975, after parting with his girlfriend Ev earlier in the year, McKenna began a relationship with his future wife and the mother of his two children, Kathleen Harrison.
Soon after graduating, McKenna and Dennis published a book inspired by their Amazon experiences, The Invisible Landscape: Mind, Hallucinogens and the I Ching. The brothers' experiences in the Amazon were the main focus of McKenna's book True Hallucinations, published in 1993. McKenna also began lecturing locally around Berkeley and started appearing on some underground radio stations.
=== Psilocybin mushroom cultivation ===
McKenna, along with his brother Dennis, developed a technique for cultivating psilocybin mushrooms using spores they brought to America from the Amazon. In 1976, the brothers published what they had learned in the book Psilocybin: Magic Mushroom Grower's Guide, under the pseudonyms "O.T. Oss" and "O.N. Oeric". McKenna and his brother were the first to come up with a reliable method for cultivating psilocybin mushrooms at home. As ethnobiologist Jonathan Ott explains, "[the] authors adapted San Antonio's technique (for producing edible mushrooms by casing mycelial cultures on a rye grain substrate; San Antonio 1971) to the production of Psilocybe [Stropharia] cubensis. The new technique involved the use of ordinary kitchen implements, and for the first time the layperson was able to produce a potent entheogen in his [or her] own home, without access to sophisticated technology, equipment, or chemical supplies." When the 1986 revised edition was published, the Magic Mushroom Grower's Guide had sold over 100,000 copies.
=== Mid- to later life ===
==== Public speaking ====
In the early 1980s, McKenna began to speak publicly on the topic of psychedelic drugs, becoming one of the pioneers of the psychedelic movement. His main focus was on the naturally occurring psychedelics such as psilocybin mushrooms (which were the catalyst for his career), ayahuasca, cannabis, and the plant derivative DMT. He conducted lecture tours and workshops promoting natural psychedelics as a way to explore universal mysteries, stimulate the imagination, and re-establish a harmonious relationship with nature. Though associated with the New Age and Human Potential Movements, McKenna himself had little patience for New Age sensibilities. He repeatedly stressed the importance and primacy of the "felt presence of direct experience", as opposed to dogma.
In addition to psychedelic drugs, McKenna spoke on a wide array of subjects, including shamanism; metaphysics; alchemy; language; culture; self-empowerment; environmentalism, techno-paganism; artificial intelligence; evolution; extraterrestrials; science and scientism; the Web; and virtual reality.
It's clearly a crisis of two things: of consciousness and conditioning. These are the two things that the psychedelics attack. We have the technological power, the engineering skills to save our planet, to cure disease, to feed the hungry, to end war. But we lack the intellectual vision, the ability to change our minds. We must decondition ourselves from 10,000 years of bad behavior, and it's not easy.
McKenna soon became a fixture of popular counterculture with Timothy Leary once introducing him as "one of the five or six most important people on the planet" and with comedian Bill Hicks' referencing him in his stand-up act and building an entire routine around his ideas. McKenna also became a popular personality in the psychedelic rave/dance scene of the early 1990s, with frequent spoken word performances at raves and contributions to psychedelic and goa trance albums by The Shamen, Spacetime Continuum, Alien Project, Capsula, Entheogenic, Zuvuya, Shpongle, and Shakti Twins. In 1994 he appeared as a speaker at the Starwood Festival, documented in the book Tripping by Charles Hayes.
McKenna published several books in the early-to-mid-1990s including: The Archaic Revival; Food of the Gods; and True Hallucinations. Hundreds of hours of McKenna's public lectures were recorded either professionally or bootlegged and have been produced on cassette tape, CD and MP3. Segments of his talks have gone on to be sampled by many musicians and DJ's.
McKenna was a colleague and close friend of chaos mathematician Ralph Abraham, and author and biologist Rupert Sheldrake. He conducted several public and many private debates with them from 1982 until his death. These debates were known as trialogues and some of the discussions were later published in the books: Trialogues at the Edge of the West and The Evolutionary Mind.
==== Botanical Dimensions ====
In 1985, McKenna founded Botanical Dimensions with his then-wife, Kathleen Harrison. Botanical Dimensions is a nonprofit ethnobotanical preserve on the Big Island of Hawaii, established to collect, protect, propagate, and understand plants of ethno-medical significance and their lore, and appreciate, study, and educate others about plants and mushrooms felt to be significant to cultural integrity and spiritual well-being. The 19-acre (7.7 ha) botanical garden is a repository containing thousands of plants that have been used by indigenous people of the tropical regions, and includes a database of information related to their purported healing properties. McKenna was involved until 1992, when he retired from the project, following his and Kathleen's divorce earlier in the year. Kathleen still manages Botanical Dimensions as its president and projects director.
After their divorce, McKenna moved to Hawaii permanently, where he built a modernist house and created a gene bank of rare plants near his home. Previously, he had split his time between Hawaii and Occidental, CA.
=== Death ===
McKenna was a longtime sufferer of migraines, but on 22 May 1999 he began to have unusually extreme and painful headaches. He then collapsed due to a seizure. McKenna was diagnosed with glioblastoma multiforme, a highly aggressive form of brain cancer. For the next several months he underwent various treatments, including experimental gamma knife radiation treatment. According to Wired magazine, McKenna was worried that his tumor may have been caused by his psychedelic drug use, or his 35 years of daily cannabis smoking; however, his doctors assured him there was no causal relation.
In late 1999, McKenna described his thoughts concerning his impending death to interviewer Erik Davis:
I always thought death would come on the freeway in a few horrifying moments, so you'd have no time to sort it out. Having months and months to look at it and think about it and talk to people and hear what they have to say, it's a kind of blessing. It's certainly an opportunity to grow up and get a grip and sort it all out. Just being told by an unsmiling guy in a white coat that you're going to be dead in four months definitely turns on the lights. ... It makes life rich and poignant. When it first happened, and I got these diagnoses, I could see the light of eternity, à la William Blake, shining through every leaf. I mean, a bug walking across the ground moved me to tears.
McKenna died on April 3, 2000, at the age of 53.
=== Library fire and insect collection ===
McKenna's library of over 3,000 rare books and personal notes was destroyed in a fire in Monterey, California on February 7, 2007. An index of McKenna's library was preserved by his brother Dennis.
McKenna studied Lepidoptera and entomology in the 1960s, and his studies included hunting for butterflies, primarily in Colombia and Indonesia, creating a large collection of insect specimens. After McKenna's death, his daughter, the artist and photographer Klea McKenna, preserved his insect collection, turning it into a gallery installation, then publishing The Butterfly Hunter, a book of 122 insect photos from a set of over 2,000 specimens McKenna collected between 1969 and 1972, alongside maps of his collecting routes through rainforests in Southeast Asia and South America. McKenna's insect collection was consistent with his interest in Victorian-era explorers and naturalists, and his worldview based on close observation of nature. In the 1970s, when he was still collecting, he became quite squeamish and guilt-ridden about the necessity of killing butterflies in order to collect and classify them, according to McKenna's daughter, this led him to cease his entomological studies.
== Thought ==
=== Psychedelics ===
Terence McKenna advocated the exploration of altered states of mind via the ingestion of naturally occurring psychedelic substances; for example, and in particular, as facilitated by the ingestion of high doses of psychedelic mushrooms, ayahuasca, and DMT, which he believed was the apotheosis of the psychedelic experience.
He was less enthralled with synthetic drugs, stating, "I think drugs should come from the natural world and be use-tested by shamanically orientated cultures ... one cannot predict the long-term effects of a drug produced in a laboratory."
McKenna always stressed the responsible use of psychedelic substances, saying: "Experimenters should be very careful. One must build up to the experience. These are bizarre dimensions of extraordinary power and beauty. There is no set rule to avoid being overwhelmed, but move carefully, reflect a great deal, and always try to map experiences back onto the history of the race and the philosophical and religious accomplishments of the species. All the compounds are potentially dangerous, and all compounds, at sufficient doses or repeated over time, involve risks. The library is the first place to go when looking into taking a new compound."
He also recommended, and often spoke of taking, what he called "heroic doses", which he defined as five grams of dried psilocybin mushrooms, taken alone, on an empty stomach, in silent darkness, and with eyes closed. He believed that when taken this way one could expect a profound visionary experience, believing it is only when "slain" by the power of the mushroom that the message becomes clear.
Although McKenna avoided giving his allegiance to any one interpretation (part of his rejection of monotheism), he was open to the idea of psychedelics as being "trans-dimensional travel". He proposed that DMT sent one to a "parallel dimension" and that psychedelics literally enabled an individual to encounter "higher dimensional entities", or what could be ancestors, or spirits of the Earth, saying that if you can trust your own perceptions it appears that you are entering an "ecology of souls". McKenna also put forward the idea that psychedelics were "doorways into the Gaian mind", suggesting that "the planet has a kind of intelligence, it can actually open a channel of communication with an individual human being" and that the psychedelic plants were the facilitators of this communication.
==== Machine elves ====
McKenna spoke of hallucinations while on DMT in which he met intelligent entities he described as "self-transforming machine elves".
==== Psilocybin panspermia speculation ====
In a more radical version of biophysicist Francis Crick's hypothesis of directed panspermia, McKenna speculated on the idea that psilocybin mushrooms may be a species of high intelligence, which may have arrived on this planet as spores migrating through space and which are attempting to establish a symbiotic relationship with human beings. He postulated that "intelligence, not life, but intelligence may have come here [to Earth] in this spore-bearing life form". He said, "I think that theory will probably be vindicated. I think in a hundred years if people do biology they will think it quite silly that people once thought that spores could not be blown from one star system to another by cosmic radiation pressure," and also believed that "few people are in a position to judge its extraterrestrial potential, because few people in the orthodox sciences have ever experienced the full spectrum of psychedelic effects that are unleashed".
==== Opposition to organized religion ====
McKenna was opposed to Christianity and most forms of organized religion or guru-based forms of spiritual awakening, favouring shamanism, which he believed was the broadest spiritual paradigm available, stating that:
What I think happened is that in the world of prehistory all religion was experiential, and it was based on the pursuit of ecstasy through plants. And at some time, very early, a group interposed itself between people and direct experience of the 'Other.' This created hierarchies, priesthoods, theological systems, castes, ritual, taboos. Shamanism, on the other hand, is an experiential science that deals with an area where we know nothing. It is important to remember that our epistemological tools have developed very unevenly in the West. We know a tremendous amount about what is going on in the heart of the atom, but we know absolutely nothing about the nature of the mind.
==== Technological singularity ====
During the final years of his life and career, McKenna became very engaged in the theoretical realm of technology. He was an early proponent of the technological singularity and in his last recorded public talk, Psychedelics in the age of intelligent machines, he outlined ties between psychedelics, computation technology, and humans. He also became enamored with the Internet, calling it "the birth of [the] global mind", believing it to be a place where psychedelic culture could flourish.
==== Admired writers ====
Either philosophically or religiously, he expressed admiration for Marshall McLuhan, Alfred North Whitehead, Pierre Teilhard de Chardin, Carl Jung, Plato, Gnostic Christianity, and Alchemy, while regarding the Greek philosopher Heraclitus as his favorite philosopher.
McKenna also expressed admiration for the works of writers Aldous Huxley, James Joyce, whose book Finnegans Wake he called "the quintessential work of art, or at least work of literature of the 20th century," science fiction writer Philip K. Dick, who he described as an "incredible genius", fabulist Jorge Luis Borges, with whom McKenna shared the belief that "scattered through the ordinary world there are books and artifacts and perhaps people who are like doorways into impossible realms, of impossible and contradictory truth" and Vladimir Nabokov. McKenna once said that he would have become a Nabokov lecturer if he had never encountered psychedelics.
=== "Stoned ape" theory of human evolution ===
McKenna's hypothesis concerning the influence of psilocybin mushrooms on human evolution is known as "the 'stoned ape' theory."
In his 1992 book Food of the Gods, McKenna proposed that the transformation from humans' early ancestors Homo erectus to the species Homo sapiens mainly involved the addition of the mushroom Psilocybe cubensis in the diet, an event that according to his theory took place about 100,000 BCE (when he believed humans diverged from the genus Homo). McKenna based his theory on the effects, or alleged effects, produced by the mushroom while citing studies by Roland Fischer et al. from the late 1960s to early 1970s.
McKenna stated that, due to the desertification of the African continent at that time, human forerunners were forced from the shrinking tropical canopy into search of new food sources. He believed they would have been following large herds of wild cattle whose dung harbored the insects that, he proposed, were undoubtedly part of their new diet, and would have spotted and started eating Psilocybe cubensis, a dung-loving mushroom often found growing out of cowpats.
McKenna's hypothesis was that low doses of psilocybin improve visual acuity, particularly edge detection, meaning that the presence of psilocybin in the diet of early pack hunting primates caused the individuals who were consuming psilocybin mushrooms to be better hunters than those who were not, resulting in an increased food supply and in turn a higher rate of reproductive success. Then at slightly higher doses, he contended, the mushroom acts to sexually arouse, leading to a higher level of attention, more energy in the organism, and potential erection in the males, rendering it even more evolutionarily beneficial, as it would result in more offspring. At even higher doses, McKenna proposed that the mushroom would have acted to "dissolve boundaries", promoting community bonding and group sexual activities. Consequently, there would be a mixing of genes, greater genetic diversity, and a communal sense of responsibility for the group offspring. At these higher doses, McKenna also argued that psilocybin would be triggering activity in the "language-forming region of the brain", manifesting as music and visions, thus catalyzing the emergence of language in early hominids by expanding "their arboreally evolved repertoire of troop signals". He also pointed out that psilocybin would dissolve the ego and "religious concerns would be at the forefront of the tribe's consciousness, simply because of the power and strangeness of the experience itself."
According to McKenna, access to and ingestion of mushrooms was an evolutionary advantage to humans' omnivorous hunter-gatherer ancestors, also providing humanity's first religious impulse. He believed that psilocybin mushrooms were the "evolutionary catalyst" from which language, projective imagination, the arts, religion, philosophy, science, and all of human culture sprang.
==== Criticism ====
McKenna's "stoned ape" theory has not received attention from the scientific community and has been criticized for a relative lack of citation to any of the paleoanthropological evidence informing our understanding of human origins. His ideas regarding psilocybin and visual acuity have been criticized as misrepresentations of Fischer et al.'s findings, who published studies of visual perception parameters other than acuity. Criticism has also noted a separate study on psilocybin-induced transformation of visual space, wherein Fischer et al. stated that psilocybin "may not be conducive to the survival of the organism". There is a lack of scientific evidence that psilocybin increases sexual arousal, and even if it does, it would not necessarily entail an evolutionary advantage. Others have pointed to civilizations such as the Aztecs, who used psychedelic mushrooms (at least among the Priestly class), that did not reflect McKenna's model of how psychedelic-using cultures would behave, for example, by carrying out human sacrifice. There are also examples of Amazonian tribes such as the Jivaro and the Yanomami who use ayahuasca ceremoniously and who are known to engage in violent behaviour. This, it has been argued, indicates the use of psychedelic plants does not necessarily suppress the ego and create harmonious societies.
=== Archaic revival ===
One of the main themes running through McKenna's work, and the title of his second book, was the idea that Western civilization was undergoing what he called an "archaic revival".
His hypothesis was that Western society has become "sick" and is undergoing a "healing process": In the same way that the human body begins to produce antibodies when it feels itself to be sick, humanity as a collective whole (in the Jungian sense) was creating "strategies for overcoming the condition of disease" and trying to cure itself, by what he termed as "a reversion to archaic values". McKenna pointed to phenomena including surrealism, abstract expressionism, body piercing and tattooing, psychedelic drug use, sexual permissiveness, jazz, experimental dance, rave culture, rock and roll and catastrophe theory, amongst others, as his evidence that this process was underway. This idea is linked to McKenna's "stoned ape" theory of human evolution, with him viewing the "archaic revival" as an impulse to return to the symbiotic and blissful relationship he believed humanity once had with the psilocybin mushroom.
In differentiating his idea from the "New Age", a term that he felt trivialized the significance of the next phase in human evolution, McKenna stated that: "The New Age is essentially humanistic psychology '80s-style, with the addition of neo-shamanism, channeling, crystal and herbal healing. The archaic revival is a much larger, more global phenomenon that assumes that we are recovering the social forms of the late neolithic, and reaches far back in the 20th century to Freud, to surrealism, to abstract expressionism, even to a phenomenon like National Socialism which is a negative force. But the stress on ritual, on organized activity, on race/ancestor-consciousness – these are themes that have been worked out throughout the entire 20th century, and the archaic revival is an expression of that."
=== Novelty theory and Timewave Zero ===
Novelty theory is a pseudoscientific idea that purports to predict the ebb and flow of novelty in the universe as an inherent quality of time, proposing that time is not a constant but has various qualities tending toward either "habit" or "novelty". Habit, in this context, can be thought of as entropic, repetitious, or conservative; and novelty as creative, disjunctive, or progressive phenomena. McKenna's idea was that the universe is an engine designed for the production and conservation of novelty and that as novelty increases, so does complexity. With each level of complexity achieved becoming the platform for a further ascent into complexity.
The basis of the theory was conceived in the mid-1970s after McKenna's experiences with psilocybin mushrooms at La Chorrera in the Amazon led him to closely study the King Wen sequence of the I Ching.
In Asian Taoist philosophy, opposing phenomena are represented by the yin and yang. Both are always present in everything, yet the amount of influence of each varies over time. The individual lines of the I Ching are made up of both Yin (broken lines) and Yang (solid lines).
When examining the King Wen sequence of 64 hexagrams, McKenna noticed a pattern. He analysed the "degree of difference" between the hexagrams in each successive pair and claimed he found a statistical anomaly, which he believed suggested that the King Wen sequence was intentionally constructed, with the sequence of hexagrams ordered in a highly structured and artificial way, and that this pattern codified the nature of time's flow in the world. With the degrees of difference as numerical values, McKenna worked out a mathematical wave form based on the 384 lines of change that make up the 64 hexagrams. He was able to graph the data and this became the Novelty Time Wave.
Peter J. Meyer (Peter Johann Gustav Meyer), in collaboration with McKenna, studied and developed novelty theory, working out a mathematical formula and developing the Timewave Zero software (the original version of which was completed by July 1987), enabling them to graph and explore its dynamics on a computer. The graph was fractal: It exhibited a pattern in which a given small section of the wave was found to be identical in form to a larger section of the wave. McKenna called this fractal modeling of time "temporal resonance", proposing it implied that larger intervals, occurring long ago, contained the same amount of information as shorter, more recent, intervals. He suggested the up-and-down oscillation of the wave shows an ongoing wavering between habit and novelty respectively. With each successive iteration trending, at an increasing level, towards infinite novelty. So according to novelty theory, the pattern of time itself is speeding up, with a requirement of the theory being that infinite novelty will be reached on a specific date.
McKenna believed that events in history could be identified that would help him locate the time wave end date and attempted to find the best-fit of the graph to the data field of human history. The last harmonic of the wave has a duration of 67.29 years. Population growth, peak oil, and pollution statistics were some of the factors that pointed him to an early twenty-first century end date and when looking for a particularly novel event in human history as a signal that the final phase had begun McKenna picked the dropping of the atomic bomb on Hiroshima. This adjusted his graph to reach zero in mid-November 2012. When he later discovered that the end of the 13th baktun in the Maya calendar had been correlated by Western Maya scholars as December 21, 2012, he adopted their end date instead.
McKenna saw the universe, in relation to novelty theory, as having a teleological attractor at the end of time, which increases interconnectedness and would eventually reach a singularity of infinite complexity. He also frequently referred to this as "the transcendental object at the end of time." When describing this model of the universe he stated that: "The universe is not being pushed from behind. The universe is being pulled from the future toward a goal that is as inevitable as a marble reaching the bottom of a bowl when you release it up near the rim. If you do that, you know the marble will roll down the side of the bowl, down, down, down – until eventually it comes to rest at the lowest energy state, which is the bottom of the bowl. That's precisely my model of human history. I'm suggesting that the universe is pulled toward a complex attractor that exists ahead of us in time, and that our ever-accelerating speed through the phenomenal world of connectivity and novelty is based on the fact that we are now very, very close to the attractor." Therefore, according to McKenna's final interpretation of the data and positioning of the graph, on December 21, 2012, we would have been in the unique position in time where maximum novelty would be experienced. An event he described as a "concrescence", a "tightening 'gyre'" with everything flowing together. Speculating that "when the laws of physics are obviated, the universe disappears, and what is left is the tightly bound plenum, the monad, able to express itself for itself, rather than only able to cast a shadow into physis as its reflection...It will be the entry of our species into 'hyperspace', but it will appear to be the end of physical laws, accompanied by the release of the mind into the imagination."
Novelty theory is considered to be pseudoscience. Among the criticisms are the use of numerology to derive dates of important events in world history, the arbitrary rather than calculated end date of the time wave and the apparent adjustment of the eschaton from November 2012 to December 2012 in order to coincide with the Maya calendar. Other purported dates do not fit the actual time frames: the date claimed for the emergence of Homo sapiens is inaccurate by 70,000 years, and the existence of the ancient Sumer and Egyptian civilisations contradict the date he gave for the beginning of "historical time". Some projected dates have been criticized for having seemingly arbitrary labels, such as the "height of the age of mammals" and McKenna's analysis of historical events has been criticised for having a eurocentric and cultural bias.
==== The Watkins Objection ====
The British mathematician Matthew Watkins of Exeter University conducted a mathematical analysis of the Time Wave, and claimed there were mathematical flaws in its construction.
== Critical reception ==
Judy Corman, vice president of the Phoenix House of New York, attacked McKenna for popularizing "dangerous substances". In a 1993 letter to The New York Times, he wrote that: "surely the fact that Terence McKenna says that the psilocybin mushroom 'is the megaphone used by an alien, intergalactic Other to communicate with mankind' is enough for us to wonder if taking LSD has done something to his mental faculties." The same year, in his True Hallucinations review for The New York Times, Peter Conrad wrote: "I suffered hallucinatory agonies of my own while reading his shrilly ecstatic prose".
Reviewing Food of the Gods, Richard Evans Schultes wrote in American Scientist that the book was "a masterpiece of research and writing" and that it "should be read by every specialist working in the multifarious fields involved with the use of psychoactive drugs". Concluding that, "[i]t is, without question, destined to play a major role in our future considerations of the role of the ancient use of psychoactive drugs, the historical shaping of our modern concerns about drugs and perhaps about man's desire for escape from reality with drugs."
In 1994, Tom Hodgkinson wrote for The New Statesman and Society, that "to write him off as a crazy hippie is a rather lazy approach to a man not only full of fascinating ideas but also blessed with a sense of humor and self-parody".
In a 1992 issue of Esquire magazine, Mark Jacobson wrote of True Hallucinations that, "it would be hard to find a drug narrative more compellingly perched on a baroquely romantic limb than this passionate Tom-and-Huck-ride-great-mother-river-saga of brotherly bonding," adding "put simply, Terence is a hoot!"
Wired called him a "charismatic talking head" who was "brainy, eloquent, and hilarious", and Jerry Garcia of the Grateful Dead also said that he was "the only person who has made a serious effort to objectify the psychedelic experience".
== Publications ==
=== Books ===
McKenna, Terence; McKenna, Dennis (1975). The Invisible Landscape: Mind, Hallucinogens, and the I Ching. New York: Seabury. ISBN 978-0-8164-9249-7.
McKenna, Terence; McKenna, Dennis (1976). Psilocybin: Magic Mushroom Grower's Guide. Under the pseudonyms OT Oss and ON Oeric. Berkeley, CA: And/Or Press. ISBN 978-0-915904-13-6.
McKenna, Terence (1991). The Archaic Revival: Speculations on Psychedelic Mushrooms, the Amazon, Virtual Reality, UFOs, Evolution, Shamanism, the Rebirth of the Goddess, and the End of History. San Francisco: Harper San Francisco. ISBN 978-0-06-250613-9.
McKenna, Terence (1992a). Food of the Gods: The Search for the Original Tree of Knowledge – A Radical History of Plants, Drugs, and Human Evolution. New York: Bantam. ISBN 978-0-553-07868-8.
McKenna, Terence (1992b). Synesthesia. Illustrated by Ely, Timothy C. New York: Granary Books. OCLC 30473682.
Sheldrake, Rupert; McKenna, Terence; Abraham, Ralph H. (1992). Trialogues at the Edge of the West: Chaos, Creativity, and the Resacralization of the World. Forward by Houston, Jean. Bear & Company. ISBN 978-0-939680-97-9.
McKenna, Terence (1993). True Hallucinations: Being an Account of the Author's Extraordinary Adventures in the Devil's Paradise. San Francisco: Harper San Francisco. ISBN 978-0-06-250545-3.
Sheldrake, Rupert; McKenna, Terence; Abraham, Ralph H. (1998). The Evolutionary Mind: Conversations on Science, Imagination & Spirit. Monkfish Book Publishing. ISBN 978-0-9749359-7-3.
=== Spoken word ===
History Ends in Green: Gaia, Psychedelics and the Archaic Revival, 6 audiocassette set, Mystic Fire audio, 1993, ISBN 978-1-56176-907-0 (recorded at the Esalen Institute, 1989)
TechnoPagans at the End of History (transcription of rap with Mark Pesce from 1998)
Psychedelics in the Age of Intelligent Machines (1999) (DVD) HPX/SurrealStudio
Conversations on the Edge of Magic (1994) (CD & Cassette) ACE
Rap-Dancing into the Third Millennium (1994) (Cassette) (Re-issued on CD as The Quintessential Hallucinogen) ACE
Packing For the Long Strange Trip (1994) (Audio Cassette) ACE
Global Perspectives and Psychedelic Poetics (1994) (Cassette) Sound Horizons Audio-Video, Inc.
The Search for the Original Tree of Knowledge (1992) (Cassette) Sounds True
The Psychedelic Society (DVD & Video Cassette) Sound Photosynthesis
True Hallucinations Workshop (Audio/Video Cassette) Sound Photosynthesis
The Vertigo at History's Edge: Who Are We? Where Have We Come From? Where Are We Going? (DVD & Video/Audio Cassette) Sound Photosynthesis
Ethnobotany and Shamanism (DVD & Video/Audio Cassette) Sound Photosynthesis
Shamanism, Symbiosis and Psychedelics Workshop (Audio/Video Cassette) Sound Photosynthesis
Shamanology (Audio Cassette) Sound Photosynthesis
Shamanology of the Amazon (w/ Nicole Maxwell) (Audio/Video Cassette) Sound Photosynthesis
Beyond Psychology (1983) (Audio Cassette) Sound Photosynthesis
Understanding & the Imagination in the Light of Nature Parts 1 & 2 (DVD & Video/Audio Cassette) Sound Photosynthesis
Ethnobotany (a complete course given at The California Institute of Integral Studies) (Audio Cassette) Sound Photosynthesis
Non-ordinary States of Reality Through Vision Plants (Audio Cassette) Sound Photosynthesis
Mind & Time, Spirit & Matter: The Complete Weekend in Santa Fe (Audio/Video Cassette) Sound Photosynthesis
Forms and Mysteries: Morphogenetic Fields and Psychedelic Experiences (w/ Rupert Sheldrake) (DVD & Video/Audio Cassette) Sound Photosynthesis
UFO: The Inside Outsider (DVD & Video/Audio Cassette) Sound Photosynthesis
A Calendar for The Goddess (DVD & Video/Audio Cassette) Sound Photosynthesis
A Magical Journey: Including Hallucinogens and Culture, Time and The I Ching, and The Human Future (Video Cassette) TAP/Sound Photosynthesis
Aliens and Archetypes (Video Cassette) TAP/Sound Photosynthesis
Angels, Aliens and Archetypes 1987 Symposium: Shamanic Approaches to the UFO, and Fairmont Banquet Talk (DVD & Video/Audio Cassette) Sound Photosynthesis
Botanical Dimensions (Audio Cassette) Sound Photosynthesis
Conference on Botanical Intelligence (w/ Joan Halifax, Andy Weil, & Dennis McKenna) (Audio Cassette) Sound Photosynthesis
Coping With Gaia's Midwife Crisis (Audio Cassette) Sound Photosynthesis
Dreaming Awake at the End of Time (DVD & Video/Audio Cassette) Sound Photosynthesis
Evolving Times (DVD, CD & Video/Audio Cassette) Sound Photosynthesis
Food of the Gods (Audio/Video Cassette) Sound Photosynthesis
Food of the Gods 2: Drugs, Plants and Destiny (Video Cassette) Sound Photosynthesis
Hallucinogens in Shamanism & Anthropology at Bridge Psychedelic Conf.1991 (w/ Ralph Metzner, Marlene Dobkin De Rios, Allison Kennedy & Thomas Pinkson) (Audio Cassette) Sound Photosynthesis
Finale – Bridge Psychedelic Conf.1991 (Audio/Video Cassette) Sound Photosynthesis
Man and Woman at the End of History (w/ Riane Eisler) (Audio Cassette) Sound Photosynthesis
Plants, Consciousness, and Transformation (1995) (Audio Cassette) Sound Photosynthesis
Metamorphosis (w/ Rupert Sheldrake & Ralph Abraham) (1995) (Video Cassette) Mystic Fire/Sound Photosynthesis
Nature is the Center of the Mandala (Audio Cassette) Sound Photosynthesis
Opening the Doors of Creativity (1990) (DVD & Video/Audio Cassette) Sound Photosynthesis
Places I Have Been (CD & Audio Cassette) Sound Photosynthesis
Plants, Visions and History Lecture (Audio/Video Cassette) Sound Photosynthesis
Psychedelics Before and After History (DVD & Video/Audio Cassette) Sound Photosynthesis
Sacred Plants As Guides: New Dimensions of the Soul (at the Jung Society Clairemont, California) (DVD & Video/Audio Cassette) Sound Photosynthesis
Seeking the Stone (Video Cassette) Sound Photosynthesis
Shamanism: Before and Beyond History – A Weekend at Ojai (w/ Ralph Metzner) (Audio/Video Cassette) Sound Photosynthesis
Shedding the Monkey (Audio Cassette) Sound Photosynthesis
State of the Stone '95 (Audio Cassette) Sound Photosynthesis
The Ethnobotany of Shamanism Introductory Lecture: The Philosophical Implications of Psychobotony: Past, Present and Future (at CIIS) (Audio/Video Cassette) Sound Photosynthesis
The Ethnobotany of Shamanism Workshop: Psychedelics Before and After History (at CIIS) (Audio Cassette) Sound Photosynthesis
The Grammar of Ecstasy – the World Within the Word (Audio Cassette) Sound Photosynthesis
The Light at the End of History (Audio/Video Cassette) Sound Photosynthesis
The State of the Stone Address: Having Archaic and Eating it Too (Audio Cassette) Sound Photosynthesis
The Taxonomy of Illusion (at UC Santa Cruz) (DVD & Video/Audio Cassette) Sound Photosynthesis
This World ...and Its Double (DVD & Video/Audio Cassette) Sound Photosynthesis
Trialogues at the Edge of the Millennium (w/ Rupert Sheldrake & Ralph Abraham) (at UC Santa Cruz) (1998) (Video Cassette) Trialogue Press
=== Discography ===
Re : Evolution with The Shamen (1992)
Dream Matrix Telemetry with Zuvuya (1993)
Alien Dreamtime with Spacetime Continuum & Stephen Kent (2003)
"Reclaim Your Mind" with Mark Pontius (2020)
=== Filmography ===
== See also ==
== Notes ==
== References ==
== External links ==
Terence McKenna at IMDb
Botanical Dimensions
Dunning, Brian (June 30, 2020). "Skeptoid #734: The Stoned Ape Theory". Skeptoid.
Erowid's Terence McKenna Vault
Official website
Psychedelic Salon, Over 100 podcasts of Terence McKenna lectures
Tao of Terence Archived August 11, 2016, at the Wayback Machine, a 12-part series of essays on McKenna by Tao Lin at Vice
Terence McKenna Bibliography Archived July 7, 2015, at the Wayback Machine, list of references to books, articles, audio, video, interviews and translations by and about Terence McKenna
Terrence McKenna's True Hallucinations Documentary by Peter Bergmann
The Transcendental Object At The End Of Time Documentary by Peter Bergmann | Wikipedia/Novelty_theory |
Thorngate's postulate of commensurate complexity, also referred to as Thorngate's impostulate of theoretical simplicity is the description of a phenomenon in social science theorizing. Karl E. Weick maintains that research in the field of social psychology can – at any one time – achieve only two of the three meta-theoretical virtues of "Generality", "Accuracy" and "Simplicity." One of these aspects therefore must always be subordinated to the others. The postulate is named for the Canadian social psychologist Warren Thorngate of the University of Alberta, whose work is quoted by Weick.
Thorngate described the problem this way:
'“In order to increase both generality and accuracy, the complexity of our theories must necessarily be increased.”
== Background ==
The postulate was a response to the debate among sociologists – mainly between Kenneth J. Gergen and Barry R. Schlenker – revolving around the meaning of sociological research. Whilst Schlenker appeared to maintain the position, that context only superficially influenced social behavior, Gergen appeared to maintain that context penetrated everything in social behavior, rendering observations as specific to the very situation observed. Thus, simplifying the discussion, the observation of social behavior would be no more than collecting historical data, since context would never be the same and the results would remain unique. In fact, sociology would be some specialized kind of historical research. Considering this, Thorngate writes
It is impossible for a theory of social behaviour to be simultaneously general, simple or parsimonious, and accurate.
The statement was confirmed by Gergen:
The more general a simple theory, the less accurate it will be in predicting specifics.
== Weick's Interpretation ==
Weick represents this model “as a clockface with general at 12:00, accurate at 4:00, and simple at 8:00 to drive home the point that an explanation that satisfies any two characteristics is least able to satisfy the third characteristic.”
According to Weick, research operates in this continuum:
if research that aims to be accurate and simple (6-o'clock), results would not be generally applicable.
if research that aims to be general and simple (10-o'clock), results would not be accurate and
if research that aims to be general and accurate (2-o'clock), results would not be simple any more.
Basically, Weick maintains, that there is a "trade-off" between these three virtues in such a way that only two can be achieved at any given time. Research therefore must operate in different modes to capture reality in sufficient precision and granularity. The postulate therefore becomes descriptive of research and prescriptive of research methodology.
== Criticism ==
Though confirming the postulate in general, Fred Dickinson, Carol Blair and Brian L. Ott criticized Weicks use of the word "accurate". Accuracy is hard to achieve, especially if the topic is difficult to qualify, e. g. in researching memory. They suggest replacing the term "accurate" with "interpretive utility".
== Sources == | Wikipedia/Thorngate's_postulate_of_commensurate_complexity |
A hyperbolic geometric graph (HGG) or hyperbolic geometric network (HGN) is a special type of spatial network where (1) latent coordinates of nodes are sprinkled according to a probability density function into a
hyperbolic space of constant negative curvature and (2) an edge between two nodes is present if they are close according to a function of the metric (typically either a Heaviside step function resulting in deterministic connections between vertices closer than a certain threshold distance, or a decaying function of hyperbolic distance yielding the connection probability). A HGG generalizes a random geometric graph (RGG) whose embedding space is Euclidean.
== Mathematical formulation ==
Mathematically, a HGG is a graph
G
(
V
,
E
)
{\displaystyle G(V,E)}
with a vertex set V (cardinality
N
=
|
V
|
{\displaystyle N=|V|}
) and an edge set E constructed by considering the nodes as points placed onto a 2-dimensional hyperbolic space
H
ζ
2
{\displaystyle \mathbb {H} _{\zeta }^{2}}
of constant negative Gaussian curvature,
−
ζ
2
{\displaystyle -\zeta ^{2}}
and cut-off radius
R
{\displaystyle R}
, i.e. the radius of the Poincaré disk which can be visualized using a hyperboloid model.
Each point
i
{\displaystyle i}
has hyperbolic polar coordinates
(
r
i
,
θ
i
)
{\displaystyle (r_{i},\theta _{i})}
with
0
≤
r
i
≤
R
{\displaystyle 0\leq r_{i}\leq R}
and
0
≤
θ
i
<
2
π
{\displaystyle 0\leq \theta _{i}<2\pi }
.
The hyperbolic law of cosines allows to measure the distance
d
i
j
{\displaystyle d_{ij}}
between two points
i
{\displaystyle i}
and
j
{\displaystyle j}
,
cosh
(
ζ
d
i
j
)
=
cosh
(
ζ
r
i
)
cosh
(
ζ
r
j
)
{\displaystyle \cosh(\zeta d_{ij})=\cosh(\zeta r_{i})\cosh(\zeta r_{j})}
−
sinh
(
ζ
r
i
)
sinh
(
ζ
r
j
)
cos
(
π
−
|
π
−
|
θ
i
−
θ
j
|
|
⏟
Δ
)
.
{\displaystyle -\sinh(\zeta r_{i})\sinh(\zeta r_{j})\cos {\bigg (}\underbrace {\pi \!-\!{\bigg |}\pi -|\theta _{i}\!-\!\theta _{j}|{\bigg |}} _{\Delta }{\bigg )}.}
The angle
Δ
{\displaystyle \Delta }
is the (smallest) angle between the two
position vectors.
In the simplest case, an edge
(
i
,
j
)
{\displaystyle (i,j)}
is established iff (if and only if) two nodes are within a certain neighborhood radius
r
{\displaystyle r}
,
d
i
j
≤
r
{\displaystyle d_{ij}\leq r}
, this corresponds to an influence threshold.
=== Connectivity decay function ===
In general, a link will be established with a probability depending on the distance
d
i
j
{\displaystyle d_{ij}}
.
A connectivity decay function
γ
(
s
)
:
R
+
→
[
0
,
1
]
{\displaystyle \gamma (s):\mathbb {R} ^{+}\to [0,1]}
represents the probability of assigning an edge to a pair of nodes at distance
s
{\displaystyle s}
.
In this framework, the simple case of hard-code neighborhood like in random geometric graphs is referred to as truncation decay function.
== Generating hyperbolic geometric graphs ==
Krioukov et al. describe how to generate hyperbolic geometric graphs with uniformly random node distribution (as well as generalized versions) on a disk of radius
R
{\displaystyle R}
in
H
ζ
2
{\displaystyle \mathbb {H} _{\zeta }^{2}}
. These graphs yield a power-law distribution for the node degrees. The angular coordinate
θ
{\displaystyle \theta }
of each point/node is chosen uniformly random from
[
0
,
2
π
]
{\displaystyle [0,2\pi ]}
, while the density function for the radial coordinate r is chosen according to the probability distribution
ρ
{\displaystyle \rho }
:
ρ
(
r
)
=
α
sinh
(
α
r
)
cosh
(
α
R
)
−
1
{\displaystyle \rho (r)=\alpha {\frac {\sinh(\alpha r)}{\cosh(\alpha R)-1}}}
The growth parameter
α
>
0
{\displaystyle \alpha >0}
controls the distribution: For
α
=
ζ
{\displaystyle \alpha =\zeta }
, the distribution is uniform in
H
ζ
2
{\displaystyle \mathbb {H} _{\zeta }^{2}}
, for smaller values the nodes are distributed more towards the center of the disk and for bigger values more towards the border. In this model, edges between nodes
u
{\displaystyle u}
and
v
{\displaystyle v}
exist iff
d
u
v
<
R
{\displaystyle d_{uv}<R}
or with probability
γ
(
d
u
v
)
{\displaystyle \gamma (d_{uv})}
if a more general connectivity decay function is used. The average degree is controlled by the radius
R
{\displaystyle R}
of the hyperbolic disk. It can be shown, that for
α
/
ζ
>
1
/
2
{\displaystyle \alpha /\zeta >1/2}
the node degrees follow a power law distribution with exponent
γ
=
1
+
2
α
/
ζ
{\displaystyle \gamma =1+2\alpha /\zeta }
.
The image depicts randomly generated graphs for different values of
α
{\displaystyle \alpha }
and
R
{\displaystyle R}
in
H
1
2
{\displaystyle \mathbb {H} _{1}^{2}}
. It can be seen how
α
{\displaystyle \alpha }
has an effect on the distribution of the nodes and
R
{\displaystyle R}
on the connectivity of the graph. The native representation where the distance variables have their true hyperbolic values is used for the visualization of the graph, therefore edges are straight lines.
=== Quadratic complexity generator ===
Source:
The naive algorithm for the generation of hyperbolic geometric graphs distributes the nodes on the hyperbolic disk by choosing the angular and radial coordinates of each point are sampled randomly. For every pair of nodes an edge is then inserted with the probability of the value of the connectivity decay function of their respective distance. The pseudocode looks as follows:
V
=
{
}
,
E
=
{
}
{\displaystyle V=\{\},E=\{\}}
for
i
←
0
{\displaystyle i\gets 0}
to
N
−
1
{\displaystyle N-1}
do
θ
←
U
[
0
,
2
π
]
{\displaystyle \theta \gets U[0,2\pi ]}
r
←
1
α
acosh
(
1
+
(
cosh
α
R
−
1
)
U
[
0
,
1
]
)
{\displaystyle r\gets {\frac {1}{\alpha }}{\text{acosh}}(1+(\cosh \alpha R-1)U[0,1])}
V
=
V
∪
{
(
r
,
θ
)
}
{\displaystyle V=V\cup \{(r,\theta )\}}
for every pair
(
u
,
v
)
∈
V
×
V
,
u
≠
v
{\displaystyle (u,v)\in V\times V,u\neq v}
do
if
U
[
0
,
1
]
≤
γ
(
d
u
v
)
{\displaystyle U[0,1]\leq \gamma (d_{uv})}
then
E
=
E
∪
{
(
u
,
v
)
}
{\displaystyle E=E\cup \{(u,v)\}}
return
V
,
E
{\displaystyle V,E}
N
{\displaystyle N}
is the number of nodes to generate, the distribution of the radial coordinate by the probability density function
ρ
{\displaystyle \rho }
is achieved by using inverse transform sampling.
U
{\displaystyle U}
denotes the uniform sampling of a value in the given interval. Because the algorithm checks for edges for all pairs of nodes, the runtime is quadratic. For applications where
N
{\displaystyle N}
is big, this is not viable any more and algorithms with subquadratic runtime are needed.
=== Sub-quadratic generation ===
To avoid checking for edges between every pair of nodes, modern generators use additional data structures that partition the graph into bands. A visualization of this shows a hyperbolic graph with the boundary of the bands drawn in orange. In this case, the partitioning is done along the radial axis. Points are stored sorted by their angular coordinate in their respective band. For each point
u
{\displaystyle u}
, the limits of its hyperbolic circle of radius
R
{\displaystyle R}
can be (over-)estimated and used to only perform the edge-check for points that lie in a band that intersects the circle. Additionally, the sorting within each band can be used to further reduce the number of points to look at by only considering points whose angular coordinate lie in a certain range around the one of
u
{\displaystyle u}
(this range is also computed by over-estimating the hyperbolic circle around
u
{\displaystyle u}
).
Using this and other extensions of the algorithm, time complexities of
O
(
n
log
log
n
+
m
)
{\displaystyle {\mathcal {O}}(n\log \log n+m)}
(where
n
{\displaystyle n}
is the number of nodes and
m
{\displaystyle m}
the number of edges) are possible with high probability.
== Findings ==
For
ζ
=
1
{\displaystyle \zeta =1}
(Gaussian curvature
K
=
−
1
{\displaystyle K=-1}
), HGGs form an ensemble of networks for which is possible to express the degree distribution analytically as closed form for the limiting case of large number of nodes. This is worth mentioning since this is not true for many ensembles of graphs.
== Applications ==
HGGs have been suggested as promising model for social networks where the hyperbolicity appears through a competition between similarity and popularity of an individual.
== References == | Wikipedia/Hyperbolic_Geometric_Graph |
In network science, reciprocity is a measure of the likelihood of vertices in a directed network to be mutually linked. Like the clustering coefficient, scale-free degree distribution, or community structure, reciprocity is a quantitative measure used to study complex networks.
== Motivation ==
In real network problems, people are interested in determining the likelihood of occurring double links (with opposite directions) between vertex pairs. This problem is fundamental for several
reasons. First, in the networks that transport information or material (such as email networks, World Wide Web (WWW), World Trade Web, or Wikipedia ), mutual links facilitate the transportation process. Second, when analyzing directed networks, people often treat them as undirected ones for simplicity; therefore, the information obtained from reciprocity studies helps to estimate the error introduced when a directed network is treated as undirected (for example, when measuring the clustering coefficient). Finally, detecting nontrivial patterns of reciprocity can reveal possible mechanisms and organizing principles that shape the observed network's topology.
== Definitions ==
=== Traditional definition ===
A traditional way to define the reciprocity
r
{\displaystyle r}
is using the ratio of the number of links pointing in both directions
L
<
−
>
{\displaystyle L^{<->}}
to the total number of links L
r
=
L
<
−
>
L
{\displaystyle r={\frac {L^{<->}}{L}}}
With this definition,
r
=
1
{\displaystyle r=1}
is for a purely bidirectional network while
r
=
0
{\displaystyle r=0}
for a purely unidirectional one. Real networks have an intermediate value between 0 and 1.
However, this definition of reciprocity has some defects. It cannot tell the relative difference of reciprocity compared with purely random network with the same number of vertices and edges. The useful information from reciprocity is not the value itself, but whether mutual links occur more or less often than expected by chance. Besides, in those networks containing self-linking loops (links starting and ending at the same vertex), the self-linking loops should be excluded when calculating
L
{\displaystyle L}
.
=== Garlaschelli and Loffredo's definition ===
In order to overcome the defects of the above definition, Garlaschelli and Loffredo defined reciprocity as the correlation coefficient between the entries of the adjacency matrix of a directed graph (
a
i
j
=
1
{\displaystyle a_{ij}=1}
if a link from
i
{\displaystyle i}
to
j
{\displaystyle j}
exists, and
a
i
j
=
0
{\displaystyle a_{ij}=0}
if not):
ρ
≡
∑
i
≠
j
(
a
i
j
−
a
¯
)
(
a
j
i
−
a
¯
)
∑
i
≠
j
(
a
i
j
−
a
¯
)
2
{\displaystyle \rho \equiv {\frac {\sum _{i\neq j}(a_{ij}-{\bar {a}})(a_{ji}-{\bar {a}})}{\sum _{i\neq j}(a_{ij}-{\bar {a}})^{2}}}}
,
where the average value
a
¯
≡
∑
i
≠
j
a
i
j
N
(
N
−
1
)
=
L
N
(
N
−
1
)
{\displaystyle {\bar {a}}\equiv {\frac {\sum _{i\neq j}a_{ij}}{N(N-1)}}={\frac {L}{N(N-1)}}}
.
a
¯
{\displaystyle {\bar {a}}}
measures the ratio of observed to possible directed links (link density), and self-linking loops are now excluded from
L
{\displaystyle L}
since
i
{\displaystyle i}
is not equal to
j
{\displaystyle j}
.
The definition can be written in the following simple form:
ρ
=
r
−
a
¯
1
−
a
¯
{\displaystyle \rho ={\frac {r-{\bar {a}}}{1-{\bar {a}}}}}
The new definition of reciprocity gives an absolute quantity which directly allows one to distinguish between reciprocal (
ρ
>
0
{\displaystyle \rho >0}
) and antireciprocal (
ρ
<
0
{\displaystyle \rho <0}
) networks, with mutual links occurring more and less often than random respectively.
If all the links occur in reciprocal pairs,
ρ
=
1
{\displaystyle \rho =1}
; if
r
=
0
{\displaystyle r=0}
,
ρ
=
ρ
m
i
n
{\displaystyle \rho =\rho _{min}}
.
ρ
m
i
n
≡
−
a
¯
1
−
a
¯
{\displaystyle \rho _{min}\equiv {\frac {-{\bar {a}}}{1-{\bar {a}}}}}
This is another advantage of using
ρ
{\displaystyle \rho }
, since it incorporates the idea that complete antireciprocality is more statistically significant in networks with larger density, while it must be regarded as a less pronounced effect in sparser networks.
== References == | Wikipedia/Reciprocity_in_network |
Complex Networks is an American media and entertainment company for youth culture, based in New York City. It was founded as a bi-monthly magazine, Complex, by fashion designer Marc Eckō. Complex Networks reports on popular and emerging trends in style, sneakers, food, music, sports and pop culture. Complex Networks reached over 90 million unique users per month in 2013 across its owned and operated and partner sites, socials and YouTube channels. The print magazine ceased publication with the December 2016/January 2017 issue. Complex currently has 6.02 million subscribers and 1.8 billion total views on YouTube. As of 2019, the company's yearly revenue was estimated to be US$200 million, 15% of which came from commerce.
Complex Networks has been named by Business Insider as one of the Most Valuable Startups in New York, and Most Valuable Private Companies in the World. In 2012, the company launched Complex TV, an online broadcasting platform.
In 2016, it became a joint-venture of Verizon and Hearst. Subsequently in 2021, BuzzFeed, Inc. announced the acquisition of the company. In 2024, NTWRK acquired Complex Networks from BuzzFeed for $108 million.
== History ==
Complex was established in 2002 by the founder of the Eckō Unltd. brand, Marc Eckō, as a print magazine aimed at providing young men a report of the latest in hip hop, fashion and pop culture without regard to race. The name Complex evolved from a slogan developed to promote the Eckō Unltd. website: "Ecko.complex". The idea was to create a men's magazine that combined Eckō's streetwear and hip hop attitude along with the style of Japanese men's magazines by providing consumer guides. This was achieved by creating a magazine in two sections: one traditional magazine, and the other a shopping guide.
In 2005, Complex was joined by senior publishing executive turned future CEO, Rich Antoniello and the former senior editor of Vibe magazine, Noah Callahan-Bever, who became editor-in-chief and chief content officer a year later. By 2006, Complex had begun to turn a profit which allowed the magazine to consider an expansion of their online presence. In April 2007, Complex soft-launched a media network with four websites: NahRight, Nice Kicks, SlamxHype and MoeJackson.
=== Complex ===
In September 2007, Complex launched Complex Media in order to fully capitalize on the trend toward digital content. In 2010, ad sales grew 154%. According to comScore, Complex got 12 million unique hits in March 2012. This encouraged large brands such as Coors, AT&T, Ford, McDonald's, Nike, Adidas and Apple to advertise within the collective. Complex now includes over 100 sites.
In 2011, Complex acquired Pigeons & Planes, an indie music and rap blog, and brought their total sites to 51 with monthly traffic of 25 million uniques. In 2012, Complex launched Four Pins, a humorous menswear site, edited by Fuck Yeah Menswear author Lawrence Schlossman; Sneaker Report, a performance footwear site; and First We Feast, a food culture site edited by former Time Out New York food editor Chris Schonberger. In 2013, Complex launched the dance music site Do Androids Dance and Green Label, a branded content site presented by Mountain Dew. That year, Complex also acquired the sneakerhead culture magazine and website Sole Collector.
On November 4, 2013, Complex premiered a new logo and cover design on Instagram that would appear online, as well as on the December 2013 Eminem cover issue.
In 2013, Complex partnered with Mountain Dew to launch "Green Label" an entertainment and culture website. In 2014, Complex launched an NBA-themed website called "Triangle Offense" in a partnership with Bacardi rum.
In August 2014, Complex ranked #3 in the United States in a ComScore survey of unique visitors between the ages of 18 and 34 with 20.3 million in that demographic per month. In January 2015, it announced its acquisition of Collider, the online source for movies, television, breaking news, incisive content, and imminent trends. Collider.com reaches over 3 million monthly unique readers (comScore, December 2014) powered by a team of ten writers, including founder and Editor in Chief Steve Weintraub. In February 2018, Complex sold Collider.com to former head-of-video Marc Fernandez.
In 2015, Do Androids Dance was merged into Complex. In 2016, Four Pins was closed.
=== Funding ===
In 2009, Complex raised $12.8 million from Accel Partners and Austin Ventures. In September 2013, it secured $25 million in a second round of funding from Iconix Brand Group, who own Rocawear, Starter, Eckō Unltd. and Umbro, among others.
=== Verizon Hearst Media Partners subsidiary ===
On April 18, 2016, Complex was acquired by a joint venture of Hearst Communications and Verizon Communications, Verizon Hearst Media Partners. The venture emphasized a goal of building "a portfolio of the emerging digital brands of the future for the millennial and Gen-Z audience", and proposed that Complex would develop content for Verizon-owned AOL and go90.
After a failure to reach expectations, on June 29, 2018, Verizon announced that go90 would shut down.
== Covers ==
Complex became known early on for its double-sided covers and split format. Complex covers often combined celebrities from across music, film and sports. Some of Complex's early covers included Nas (May 2002), Tony Hawk and Xzibit (June/July 2002), Ludacris and Dale Earnhardt Jr. (April/May 2003), and Mos Def and David Bowie (August/September 2003). In 2007, Complex gave Kim Kardashian her first-ever magazine shoot and cover.
Complex has since expanded to interactive digital covers. In September 2019, the American rapper Kid Cudi and the Japanese designer Nigo were interviewed by Complex and also appeared jointly on a digital cover and told the stories of their careers and rise in the entertainment and streetwear industries.
== Complex shows ==
Complex TV launched in 2012 as an online broadcaster of original content. Nathan Brown, a long-time video development and production executive, serves as general manager of Complex TV and Video. In December 2013, a subsidiary of Complex TV, Complex News, was launched, focusing on day-to-day news. In 2014, Pluto.tv added Complex Media as a content partner. Complex Content Studio is supported by an 18-person editorial team.
According to WNIP source, "by 2016, Complex Networks had shifted 80% of its content budget to video and was launching dozens of individual shows under Complex's YouTube channel and a number of spin-off properties".
On November 10, 2017, a block of Complex TV series began airing on the U.S. cable network Fuse under the Complex x Fuse banner.
Complex Networks has produced more than two dozen original shows, which include Hot Ones and Desus vs. Mero.
== Podcasts ==
Complex Networks launched three original podcasts at the end of 2019 in collaboration with a Swedish podcast firm Acast. Watch Less, covering such topics as movies and pop culture, hosted by Khris 'Khal' Davenport and Frazier Tharpe. The Complex Sports Podcast (formerly Load Management), hosted by Zach 'Chopz' Frydenlund, Zion Olojede, and Adam Caparell discusses sports and sports culture. The Complex Sneakers Podcast covers the history and present day of sneaker culture and is hosted by Joe La Puma, Matthew Welty, and Brendan Dunne.
== ComplexCon ==
Launch and Development (2015–2016): ComplexCon, an annual cultural festival and exhibition, was launched in 2016 by Complex Networks in partnership with ReedPop. It was co-created by Marc Eckō and Aaron Levant, combining Complex’s influence in youth culture with Reed Exhibitions’ event expertise. Designed as a "cultural World’s Fair", ComplexCon merges music, art, fashion, food, and technology into an interactive experience. Eckō provided creative direction and industry connections, while Levant focused on execution and logistics.
Inaugural Event (2016): The first ComplexCon took place on November 5–6, 2016, at the Long Beach Convention Center, attracting 35,000 attendees. Eckō recruited Takashi Murakami to design the event’s visual identity and Pharrell Williams as Cultural Director. The event featured concerts, brand exhibitions, streetwear pop-ups, art installations, and panels, with Eckō moderating discussions and shaping content.
In Spring 2016, the first two-day event took place at the Long Beach Convention and Entertainment Center in Long Beach, CA in November 2016 and featured performances by Snoop Dogg, Skrillex, Kid Cudi, and more. In 2019 the festival was held twice. The first event took place at McCormick Place in Chicago, IL in collaboration with a focus on local artists, designers, and musicians. The second festival occurred in the traditional Long Beach, CA location and included appearances by Selena Gomez, LL Cool J, Lil Kim, Offset, Kid Cudi, Lil Yachty, Timothée Chalamet, Yara Shahidi and Tyga. These virtual and in-person events have drawn in large crowds of young adults who relate and connect with the growing streetwear and rising hip-hop artists.
In 2024, Complex Networks was acquired by NTWRK, led by Aaron Levant, with plans for continued experiential marketing initiatives. That same year, ComplexCon launched its first international edition in Hong Kong, followed by an announced return in 2025.
ComplexCon remains a flagship event for Complex Networks, recognized for influencing global street culture through its blend of commerce, entertainment, and community engagement.
== ComplexLand ==
In lieu of ComplexCon during the COVID-19 pandemic, Complex Networks launched a five-day virtual festival named "ComplexLand" in December 2020. The game took place in a video game format where users could visit virtual shops and order products that would be shipped to them in real life. Players could also access video content such as panels and performances. The event included virtual appearances by T-Pain, Fat Joe, Lil Yachty, Jack Harlow, and Donatella Versace. The interactive experience was accessible through web browser and was developed by Jam3 in WebGl.
== The Complex Shop ==
In December 2019, Complex Networks launched an online store called the Complex Shop. At launch, the store included items from 70 different clothing brands, including some exclusive collaborations.
The store also carries merchandise from Complex's various brands and content.
The Complex Shop has partnered with the Google News Initiative to measure audience engagement and consumer behavior. They also partnered with Neighborhood Spot and UNION x Dodgers to sell branded products.
== Brand partnerships ==
In 2013, Digiday stated Complex was one of the publishers that "acts like an agency" based on their branded content and brand partnerships. In 2013 alone, Complex created an average of 47 pieces of content a month on behalf of major brands, including McDonald's, Gillette, Levi's, Toyota, Adidas and others. It also partnered with PepsiCo to launch GreenLabel.com, a Mountain Dew-branded lifestyle site that's staffed by Complex's editorial employees. Green Label currently attracts over twice as much traffic as MountainDew.com. Later in 2013, Complex worked with Dr. Pepper to a series of videos aimed at young males featuring producer/songwriter The-Dream.
== Awards ==
== Controversies ==
=== Kim Kardashian photo ===
In 2009, AnimalNewYork.com reported that Complex had posted a digitally unenhanced version of April/May issue cover star Kim Kardashian. Complex swapped the enhanced image on their site, but not before the unenhanced version had gone viral. Kardashian responded to the incident on her blog, saying: "So what: I have a little cellulite. What curvy girl doesn't!?" She went on to say that she was "proud" of her body, posting behind-the-scenes pictures of the shoot on her website. The incident was covered by a variety of online publications including Huffington Post, NY Daily News, Business Insider, Gawker, and others.
=== Wale threatens Complex staff ===
On December 11, 2013, Complex writer Insanul Ahmed received a call from rapper Wale complaining that his latest album, The Gifted, had not been included on Complex's "50 Best Albums of 2013" list. A portion of the conversation was recorded and posted on the Complex website and on Complex TV on December 13. Wale could be heard threatening: "Get the security ready." According to Complex, Wale refused requests to meet, but he did post a humorous Instagram video that day which made light of the situation. Wale, later appearing on Hot97, said that his fall-out with Kid Cudi had something to do with the snub, and that he was not "begging Williamsburg hipsters" to like his music. Wale was referring to the October/November 2010 issue of Complex in which Kid Cudi said: "We don't fuck with you musically." The quote quickly went viral.
== See also ==
Ego Trip
Stüssy
The Hundreds
Vice Media
Supreme
Virgil Abloh
== References ==
== External links ==
Official website | Wikipedia/Complex_Networks |
A small-world network is a graph characterized by a high clustering coefficient and low distances. In an example of the social network, high clustering implies the high probability that two friends of one person are friends themselves. The low distances, on the other hand, mean that there is a short chain of social connections between any two people (this effect is known as six degrees of separation). Specifically, a small-world network is defined to be a network where the typical distance L between two randomly chosen nodes (the number of steps required) grows proportionally to the logarithm of the number of nodes N in the network, that is:
L
∝
log
N
{\displaystyle L\propto \log N}
while the global clustering coefficient is not small.
In the context of a social network, this results in the small world phenomenon of strangers being linked by a short chain of acquaintances. Many empirical graphs show the small-world effect, including social networks, wikis such as Wikipedia, gene networks, and even the underlying architecture of the Internet. It is the inspiration for many network-on-chip architectures in contemporary computer hardware.
A certain category of small-world networks were identified as a class of random graphs by Duncan Watts and Steven Strogatz in 1998. They noted that graphs could be classified according to two independent structural features, namely the clustering coefficient, and average node-to-node distance (also known as average shortest path length). Purely random graphs, built according to the Erdős–Rényi (ER) model, exhibit a small average shortest path length (varying typically as the logarithm of the number of nodes) along with a small clustering coefficient. Watts and Strogatz measured that in fact many real-world networks have a small average shortest path length, but also a clustering coefficient significantly higher than expected by random chance. Watts and Strogatz then proposed a novel graph model, currently named the Watts and Strogatz model, with (i) a small average shortest path length, and (ii) a large clustering coefficient. The crossover in the Watts–Strogatz model between a "large world" (such as a lattice) and a small world was first described by Barthelemy and Amaral in 1999. This work was followed by many studies, including exact results (Barrat and Weigt, 1999; Dorogovtsev and Mendes; Barmpoutis and Murray, 2010).
== Properties of small-world networks ==
Small-world networks tend to contain cliques, and near-cliques, meaning sub-networks which have connections between almost any two nodes within them. This follows from the defining property of a high clustering coefficient. Secondly, most pairs of nodes will be connected by at least one short path. This follows from the defining property that the mean-shortest path length be small. Several other properties are often associated with small-world networks. Typically there is an over-abundance of hubs – nodes in the network with a high number of connections (known as high degree nodes). These hubs serve as the common connections mediating the short path lengths between other edges. By analogy, the small-world network of airline flights has a small mean-path length (i.e. between any two cities you are likely to have to take three or fewer flights) because many flights are routed through hub cities. This property is often analyzed by considering the fraction of nodes in the network that have a particular number of connections going into them (the degree distribution of the network). Networks with a greater than expected number of hubs will have a greater fraction of nodes with high degree, and consequently the degree distribution will be enriched at high degree values. This is known colloquially as a fat-tailed distribution. Graphs of very different topology qualify as small-world networks as long as they satisfy the two definitional requirements above.
Network small-worldness has been quantified by a small-coefficient,
σ
{\displaystyle \sigma }
, calculated by comparing clustering and path length of a given network to an Erdős–Rényi model with same degree on average.
σ
=
C
C
r
L
L
r
{\displaystyle \sigma ={\frac {\frac {C}{C_{r}}}{\frac {L}{L_{r}}}}}
if
σ
>
1
{\displaystyle \sigma >1}
(
C
≫
C
r
{\textstyle C\gg C_{r}}
and
L
≈
L
r
{\textstyle L\approx {L_{r}}}
), network is small-world. However, this metric is known to perform poorly because it is heavily influenced by the network's size.
Another method for quantifying network small-worldness utilizes the original definition of the small-world network comparing the clustering of a given network to an equivalent lattice network and its path length to an equivalent random network. The small-world measure (
ω
{\displaystyle \omega }
) is defined as
ω
=
L
r
L
−
C
C
ℓ
{\displaystyle \omega ={\frac {L_{r}}{L}}-{\frac {C}{C_{\ell }}}}
Where the characteristic path length L and clustering coefficient C are calculated from the network you are testing, Cℓ is the clustering coefficient for an equivalent lattice network and Lr is the characteristic path length for an equivalent random network.
Still another method for quantifying small-worldness normalizes both the network's clustering and path length relative to these characteristics in equivalent lattice and random networks. The Small World Index (SWI) is defined as
SWI
=
L
−
L
ℓ
L
r
−
L
ℓ
×
C
−
C
r
C
ℓ
−
C
r
{\displaystyle {\text{SWI}}={\frac {L-L_{\ell }}{L_{r}-L_{\ell }}}\times {\frac {C-C_{r}}{C_{\ell }-C_{r}}}}
Both ω′ and SWI range between 0 and 1, and have been shown to capture aspects of small-worldness. However, they adopt slightly different conceptions of ideal small-worldness. For a given set of constraints (e.g. size, density, degree distribution), there exists a network for which ω′ = 1, and thus ω aims to capture the extent to which a network with given constraints as small worldly as possible. In contrast, there may not exist a network for which SWI = 1, thus SWI aims to capture the extent to which a network with given constraints approaches the theoretical small world ideal of a network where C ≈ Cℓ and L ≈ Lr.
== Examples of small-world networks ==
Small-world properties are found in many real-world phenomena, including websites with navigation menus, food webs, electric power grids, metabolite processing networks, networks of brain neurons,
voter networks, telephone call graphs, and airport networks. Cultural networks and word co-occurrence networks have also been shown to be small-world networks.
Networks of connected proteins have small world properties such as power-law obeying degree distributions. Similarly transcriptional networks, in which the nodes are genes, and they are linked if one gene has an up or down-regulatory genetic influence on the other, have small world network properties.
== Examples of non-small-world networks ==
In another example, the famous theory of "six degrees of separation" between people tacitly presumes that the domain of discourse is the set of people alive at any one time. The number of degrees of separation between Albert Einstein and Alexander the Great is almost certainly greater than 30 and this network does not have small-world properties. A similarly constrained network would be the "went to school with" network: if two people went to the same college ten years apart from one another, it is unlikely that they have acquaintances in common amongst the student body.
Similarly, the number of relay stations through which a message must pass was not always small. In the days when the post was carried by hand or on horseback, the number of times a letter changed hands between its source and destination would have been much greater than it is today. The number of times a message changed hands in the days of the visual telegraph (circa 1800–1850) was determined by the requirement that two stations be connected by line-of-sight.
Tacit assumptions, if not examined, can cause a bias in the literature on graphs in favor of finding small-world networks (an example of the file drawer effect resulting from the publication bias).
== Network robustness ==
It is hypothesized by some researchers, such as Albert-László Barabási, that the prevalence of small world networks in biological systems may reflect an evolutionary advantage of such an architecture. One possibility is that small-world networks are more robust to perturbations than other network architectures. If this were the case, it would provide an advantage to biological systems that are subject to damage by mutation or viral infection.
In a small world network with a degree distribution following a power-law, deletion of a random node rarely causes a dramatic increase in mean-shortest path length (or a dramatic decrease in the clustering coefficient). This follows from the fact that most shortest paths between nodes flow through hubs, and if a peripheral node is deleted it is unlikely to interfere with passage between other peripheral nodes. As the fraction of peripheral nodes in a small world network is much higher than the fraction of hubs, the probability of deleting an important node is very low. For example, if the small airport in Sun Valley, Idaho was shut down, it would not increase the average number of flights that other passengers traveling in the United States would have to take to arrive at their respective destinations. However, if random deletion of a node hits a hub by chance, the average path length can increase dramatically. This can be observed annually when northern hub airports, such as Chicago's O'Hare airport, are shut down because of snow; many people have to take additional flights.
By contrast, in a random network, in which all nodes have roughly the same number of connections, deleting a random node is likely to increase the mean-shortest path length slightly but significantly for almost any node deleted. In this sense, random networks are vulnerable to random perturbations, whereas small-world networks are robust. However, small-world networks are vulnerable to targeted attack of hubs, whereas random networks cannot be targeted for catastrophic failure.
== Construction of small-world networks ==
The main mechanism to construct small-world networks is the Watts–Strogatz mechanism.
Small-world networks can also be introduced with time-delay, which will not only produce fractals but also chaos under the right conditions, or transition to chaos in dynamics networks.
Soon after the publication of Watts–Strogatz mechanism, approaches have been developed by Mashaghi and co-workers to generate network models that exhibit high degree correlations, while preserving the desired degree distribution and small-world properties. These approaches are based on edge-dual transformation and can be used to generate analytically solvable small-world network models for research into these systems.
Degree–diameter graphs are constructed such that the number of neighbors each vertex in the network has is bounded, while the distance from any given vertex in the network to any other vertex (the diameter of the network) is minimized. Constructing such small-world networks is done as part of the effort to find graphs of order close to the Moore bound.
Another way to construct a small world network from scratch is given in Barmpoutis et al., where a network with very small average distance and very large average clustering is constructed. A fast algorithm of constant complexity is given, along with measurements of the robustness of the resulting graphs. Depending on the application of each network, one can start with one such "ultra small-world" network, and then rewire some edges, or use several small such networks as subgraphs to a larger graph.
Small-world properties can arise naturally in social networks and other real-world systems via the process of dual-phase evolution. This is particularly common where time or spatial constraints limit the addition of connections between vertices The mechanism generally involves periodic shifts between phases, with connections being added during a "global" phase and being reinforced or removed during a "local" phase.
Small-world networks can change from scale-free class to broad-scale class whose connectivity distribution has a sharp cutoff following a power law regime due to constraints limiting the addition of new links. For strong enough constraints, scale-free networks can even become single-scale networks whose connectivity distribution is characterized as fast decaying. It was also shown analytically that scale-free networks are ultra-small, meaning that the distance scales according to
L
∝
log
log
N
{\displaystyle L\propto \log \log N}
.
== Applications ==
=== Applications to sociology ===
The advantages to small world networking for social movement groups are their resistance to change due to the filtering apparatus of using highly connected nodes, and its better effectiveness in relaying information while keeping the number of links required to connect a network to a minimum.
The small world network model is directly applicable to affinity group theory represented in sociological arguments by William Finnegan. Affinity groups are social movement groups that are small and semi-independent pledged to a larger goal or function. Though largely unaffiliated at the node level, a few members of high connectivity function as connectivity nodes, linking the different groups through networking. This small world model has proven an extremely effective protest organization tactic against police action. Clay Shirky argues that the larger the social network created through small world networking, the more valuable the nodes of high connectivity within the network. The same can be said for the affinity group model, where the few people within each group connected to outside groups allowed for a large amount of mobilization and adaptation. A practical example of this is small world networking through affinity groups that William Finnegan outlines in reference to the 1999 Seattle WTO protests.
=== Applications to earth sciences ===
Many networks studied in geology and geophysics have been shown to have characteristics of small-world networks. Networks defined in fracture systems and porous substances have demonstrated these characteristics. The seismic network in the Southern California region may be a small-world network. The examples above occur on very different spatial scales, demonstrating the scale invariance of the phenomenon in the earth sciences.
=== Applications to computing ===
Small-world networks have been used to estimate the usability of information stored in large databases. The measure is termed the Small World Data Transformation Measure. The greater the database links align to a small-world network the more likely a user is going to be able to extract information in the future. This usability typically comes at the cost of the amount of information that can be stored in the same repository.
The Freenet peer-to-peer network has been shown to form a small-world network in simulation, allowing information to be stored and retrieved in a manner that scales efficiency as the network grows.
Nearest Neighbor Search solutions like HNSW use small-world networks to efficiently find the information in large item corpuses.
=== Small-world neural networks in the brain ===
Both anatomical connections in the brain and the synchronization networks of cortical neurons exhibit small-world topology.
Structural and functional connectivity in the brain has also been found to reflect the small-world topology of short path length and high clustering. The network structure has been found in the mammalian cortex across species as well as in large scale imaging studies in humans. Advances in connectomics and network neuroscience, have found the small-worldness of neural networks to be associated with efficient communication.
In neural networks, short pathlength between nodes and high clustering at network hubs supports efficient communication between brain regions at the lowest energetic cost. The brain is constantly processing and adapting to new information and small-world network model supports the intense communication demands of neural networks. High clustering of nodes forms local networks which are often functionally related. Short path length between these hubs supports efficient global communication. This balance enables the efficiency of the global network while simultaneously equipping the brain to handle disruptions and maintain homeostasis, due to local subsystems being isolated from the global network. Loss of small-world network structure has been found to indicate changes in cognition and increased risk of psychological disorders.
In addition to characterizing whole-brain functional and structural connectivity, specific neural systems, such as the visual system, exhibit small-world network properties.
A small-world network of neurons can exhibit short-term memory. A computer model developed by Sara Solla had two stable states, a property (called bistability) thought to be important in memory storage. An activating pulse generated self-sustaining loops of communication activity among the neurons. A second pulse ended this activity. The pulses switched the system between stable states: flow (recording a "memory"), and stasis (holding it). Small world neuronal networks have also been used as models to understand seizures.
== See also ==
Barabási–Albert model – Scale-free network generation algorithm
Climate as complex networks – Conceptual model to generate insight into climate science
Dual-phase evolution – Process that drives self-organization within complex adaptive systems
Dunbar's number – Suggested cognitive limit important in sociology and anthropology
Erdős number – Closeness of someone's association with mathematician Paul Erdős
Erdős–Rényi (ER) model – Two closely related models for generating random graphs
Local World Evolving Network Models
Percolation theory – Mathematical theory on behavior of connected clusters in a random graph
Network science – Academic field - mathematical theory of networks
Scale-free network – Network whose degree distribution follows a power law
Six degrees of Kevin Bacon – Parlor game on degrees of separation
Small-world experiment – Experiments examining the average path length for social networks
Social network – Social structure made up of a set of social actors
Watts–Strogatz model – Method of generating random small-world graphs
Network on a chip – Electronic communication subsystem on an integrated circuit – systems on chip modeled on small-world networks
Zachary's karate club
== References ==
== Further reading ==
=== Books ===
=== Journal articles ===
== External links ==
Dynamic Proximity Networks by Seth J. Chandler, The Wolfram Demonstrations Project.
Small-World Networks entry on Scholarpedia (by Mason A. Porter) | Wikipedia/Small_world_networks |
In network theory, multidimensional networks, a special type of multilayer network, are networks with multiple kinds of relations.
Increasingly sophisticated attempts to model real-world systems as multidimensional networks have yielded valuable insight in the fields of social network analysis, economics, urban and international transport, ecology, psychology, medicine, biology, commerce, climatology, physics, computational neuroscience, operations management, and finance.
== Terminology ==
The rapid exploration of complex networks in recent years has been dogged by a lack of standardized naming conventions, as various groups use overlapping and contradictory terminology to describe specific network configurations (e.g., multiplex, multilayer, multilevel, multidimensional, multirelational, interconnected). To fully leverage the dataset information on the directional nature of the communications, some authors consider only direct networks without any labels on vertices, and introduce the definition of edge-labeled multigraphs which can cover many multidimensional situations. The term "fully multidimensional" has also been used to refer to a multipartite edge-labeled multigraph. Multidimensional networks have also recently been reframed as specific instances of multilayer networks.
In this case, there are as many layers as there are dimensions, and the links between nodes within each layer are simply all the links for a given dimension.
== Definition ==
=== Unweighted multilayer networks ===
In elementary network theory, a network is represented by a graph
G
=
(
V
,
E
)
{\displaystyle G=(V,E)}
in which
V
{\displaystyle V}
is the set of nodes and
E
{\displaystyle E}
the links between nodes, typically represented as a tuple of nodes
u
,
v
∈
V
{\displaystyle u,v\in V}
. While this basic formalization is useful for analyzing many systems, real world networks often have added complexity in the form of multiple types of relations between system elements. An early formalization of this idea came through its application in the field of social network analysis (see, e.g., and papers on relational algebras in social networks) in which multiple forms of social connection between people were represented by multiple types of links.
To accommodate the presence of more than one type of link, a multidimensional network is represented by a triple
G
=
(
V
,
E
,
D
)
{\displaystyle G=(V,E,D)}
, where
D
{\displaystyle D}
is a set of dimensions (or layers), each member of which is a different type of link, and
E
{\displaystyle E}
consists of triples
(
u
,
v
,
d
)
{\displaystyle (u,v,d)}
with
u
,
v
∈
V
{\displaystyle u,v\in V}
and
d
∈
D
{\displaystyle d\in D}
.
Note that as in all directed graphs, the links
(
u
,
v
,
d
)
{\displaystyle (u,v,d)}
and
(
v
,
u
,
d
)
{\displaystyle (v,u,d)}
are distinct.
By convention, the number of links between two nodes in a given dimension is either 0 or 1 in a multidimensional network. However, the total number of links between two nodes across all dimensions is less than or equal to
|
D
|
{\displaystyle |D|}
.
=== Weighted multilayer networks ===
In the case of a weighted network, this triplet is expanded to a quadruplet
e
=
(
u
,
v
,
d
,
w
)
{\displaystyle e=(u,v,d,w)}
, where
w
{\displaystyle w}
is the weight on the link between
u
{\displaystyle u}
and
v
{\displaystyle v}
in the dimension
d
{\displaystyle d}
.
Further, as is often useful in social network analysis, link weights may take on positive or negative values. Such signed networks can better reflect relations like amity and enmity in social networks. Alternatively, link signs may be figured as dimensions themselves, e.g.
G
=
(
V
,
E
,
D
)
{\displaystyle G=(V,E,D)}
where
D
=
{
−
1
,
0
,
1
}
{\displaystyle D=\{-1,0,1\}}
and
E
=
{
(
u
,
v
,
d
)
;
u
,
v
∈
V
,
d
∈
D
}
{\displaystyle E=\{(u,v,d);u,v\in V,d\in D\}}
This approach has particular value when considering unweighted networks.
This conception of dimensionality can be expanded should attributes in multiple dimensions need specification. In this instance, links are n-tuples
e
=
(
u
,
v
,
d
1
…
d
n
−
2
)
{\displaystyle e=(u,v,d_{1}\dots d_{n-2})}
. Such an expanded formulation, in which links may exist within multiple dimensions, is uncommon but has been used in the study of multidimensional time-varying networks.
=== General formulation in terms of tensors ===
Whereas unidimensional networks have two-dimensional adjacency matrices of size
V
×
V
{\displaystyle V\times V}
, in a multidimensional network with
D
{\displaystyle D}
dimensions, the adjacency matrix becomes a multilayer adjacency tensor, a four-dimensional matrix of size
(
V
×
D
)
×
(
V
×
D
)
{\displaystyle (V\times D)\times (V\times D)}
. By using index notation, adjacency matrices can be indicated by
A
j
i
{\displaystyle A_{j}^{i}}
, to encode connections between nodes
i
{\displaystyle i}
and
j
{\displaystyle j}
, whereas multilayer adjacency tensors are indicated by
M
j
β
i
α
{\displaystyle M_{j\beta }^{i\alpha }}
, to encode connections between node
i
{\displaystyle i}
in layer
α
{\displaystyle \alpha }
and node
j
{\displaystyle j}
in layer
β
{\displaystyle \beta }
. As in unidimensional matrices, directed links, signed links, and weights are all easily accommodated by this framework.
In the case of multiplex networks, which are special types of multilayer networks where nodes can not be interconnected with other nodes in other layers, a three-dimensional matrix of size
(
V
×
V
)
×
D
{\displaystyle (V\times V)\times D}
with entries
A
i
j
α
{\displaystyle A_{ij}^{\alpha }}
is enough to represent the structure of the system by encoding connections between nodes
i
{\displaystyle i}
and
j
{\displaystyle j}
in layer
α
{\displaystyle \alpha }
.
== Multidimensional network-specific definitions ==
=== Multi-layer neighbors ===
In a multidimensional network, the neighbors of some node
v
{\displaystyle v}
are all nodes connected to
v
{\displaystyle v}
across dimensions.
=== Multi-layer path length ===
A path between two nodes in a multidimensional network can be represented by a vector r
=
(
r
1
,
…
r
|
D
|
)
{\displaystyle =(r_{1},\dots r_{|D|})}
in which the
i
{\displaystyle i}
th entry in r is the number of links traversed in the
i
{\displaystyle i}
th dimension of
G
{\displaystyle G}
. As with overlapping degree, the sum of these elements can be taken as a rough measure of a path length between two nodes.
=== Network of layers ===
The existence of multiple layers (or dimensions) allows to introduce the new concept of network of layers, peculiar of multilayer networks. In fact, layers might be interconnected in such a way that their structure can be described by a network, as shown in the figure.
The network of layers is usually weighted (and might be directed), although, in general, the weights depends on the application of interest. A simple approach is, for each pair of layers, to sum all of the weights in the connections between their nodes to obtain edge weights that can be encoded into a matrix
q
α
β
{\displaystyle q_{\alpha \beta }}
. The rank-2 adjacency tensor, representing the underlying network of layers in the space
R
L
×
L
{\displaystyle \mathbb {R} ^{L\times L}}
is given by
Ψ
δ
γ
=
∑
α
,
β
=
1
L
q
α
β
E
δ
γ
(
α
β
)
{\displaystyle \Psi _{\delta }^{\gamma }=\sum \limits _{\alpha ,\beta =1}^{L}q_{\alpha \beta }E_{\delta }^{\gamma }(\alpha \beta )}
where
E
δ
γ
(
α
β
)
{\displaystyle E_{\delta }^{\gamma }(\alpha \beta )}
is the canonical matrix with all components equal to zero except for the entry corresponding to row
α
{\displaystyle \alpha }
and column
β
{\displaystyle \beta }
, that is equal to one. Using the tensorial notation, it is possible to obtain the (weighted) network of layers from the multilayer adjacency tensor as
Ψ
δ
γ
=
M
j
δ
i
γ
U
i
j
{\displaystyle \Psi _{\delta }^{\gamma }=M_{j\delta }^{i\gamma }U_{i}^{j}}
.
== Centrality measures ==
=== Degree ===
In a non-interconnected multidimensional network, where interlayer links are absent, the degree of a node is represented by a vector of length
|
D
|
:
k
=
(
k
i
1
,
…
k
i
|
D
|
)
{\displaystyle |D|:\mathbf {k} =(k_{i}^{1},\dots k_{i}^{|D|})}
. Here
|
D
|
{\displaystyle |D|}
is an alternative way to denote the number of layers
L
{\displaystyle L}
in multilayer networks. However, for some computations it may be more useful to simply sum the number of links adjacent to a node across all dimensions. This is the overlapping degree:
∑
α
=
1
|
D
|
k
i
α
{\displaystyle \sum _{\alpha =1}^{|D|}k_{i}^{\alpha }}
. As with unidimensional networks, distinction may similarly be drawn between incoming links and outgoing links.
If interlayer links are present, the above definition must be adapted to account for them, and the multilayer degree is given by
k
i
=
M
j
β
i
α
U
α
β
u
j
=
∑
α
,
β
=
1
L
∑
j
=
1
N
M
j
β
i
α
{\displaystyle k^{i}=M_{j\beta }^{i\alpha }U_{\alpha }^{\beta }u^{j}=\sum _{\alpha ,\beta =1}^{L}\sum _{j=1}^{N}M_{j\beta }^{i\alpha }}
where the tensors
U
α
β
{\displaystyle U_{\alpha }^{\beta }}
and
u
j
{\displaystyle u^{j}}
have all components equal to 1. The heterogeneity in the number of connections of a node across the different layers can be taken into account through the participation coefficient.
=== Versatility as multilayer centrality ===
When extended to interconnected multilayer networks, i.e. those systems where nodes are connected across layers, the concept of centrality is better understood in terms of versatility. Nodes that are not central in each layer might be the most important for the multilayer systems in certain scenarios. For instance, this is the case where two layers encode different networks with only one node in common: it is very likely that such a node will have the highest centrality score because it is responsible for the information flow across layers.
==== Eigenvector versatility ====
As for unidimensional networks, eigenvector versatility can be defined as the solution of the eigenvalue problem given by
M
j
β
i
α
Θ
i
α
=
λ
1
Θ
j
β
{\displaystyle M_{j\beta }^{i\alpha }\Theta _{i\alpha }=\lambda _{1}\Theta _{j\beta }}
, where Einstein summation convention is used for sake of simplicity. Here,
Θ
j
β
=
λ
1
−
1
M
j
β
i
α
Θ
i
α
{\displaystyle \Theta _{j\beta }=\lambda _{1}^{-1}M_{j\beta }^{i\alpha }\Theta _{i\alpha }}
gives the multilayer generalization of Bonacich's eigenvector centrality per node per layer. The overall eigenvector versatility is simply obtained by summing up the scores across layers as
θ
i
=
Θ
i
α
u
α
{\displaystyle \theta _{i}=\Theta _{i\alpha }u^{\alpha }}
.
==== Katz versatility ====
As for its unidimensional counterpart, the Katz versatility is obtained as the solution
Φ
j
β
=
[
(
δ
−
a
M
)
−
1
]
j
β
i
α
U
i
α
{\displaystyle \Phi _{j\beta }=[(\delta -aM)^{-1}]_{j\beta }^{i\alpha }U_{i\alpha }}
of the tensorial equation
Φ
j
β
=
a
M
j
β
i
α
Φ
i
α
+
b
u
j
β
{\displaystyle \Phi _{j\beta }=aM_{j\beta }^{i\alpha }\Phi _{i\alpha }+bu_{j\beta }}
, where
δ
j
β
i
α
=
δ
j
i
δ
β
α
{\displaystyle \delta _{j\beta }^{i\alpha }=\delta _{j}^{i}\delta _{\beta }^{\alpha }}
,
a
{\displaystyle a}
is a constant smaller than the largest eigenvalue and
b
{\displaystyle b}
is another constant generally equal to 1. The overall Katz versatility is simply obtained by summing up the scores across layers as
ϕ
i
=
Φ
i
α
u
α
{\displaystyle \phi _{i}=\Phi _{i\alpha }u^{\alpha }}
.
==== HITS versatility ====
For unidimensional networks, the HITS algorithm has been originally introduced by Jon Kleinberg to rate Web Pages. The basic assumption of the algorithm is that relevant pages, named authorities, are pointed by special Web pages, named hubs. This mechanism can be mathematically described by two coupled equations which reduce to two eigenvalue problems. When the network is undirected, Authority and Hub centrality are equivalent to eigenvector centrality.
These properties are preserved by the natural extension of the equations proposed by Kleinberg to the case of interconnected multilayer networks, given by
(
M
M
t
)
j
β
i
α
Γ
i
α
=
λ
1
Γ
j
β
{\displaystyle (MM^{t})_{j\beta }^{i\alpha }\Gamma _{i\alpha }=\lambda _{1}\Gamma _{j\beta }}
and
(
M
t
M
)
j
β
i
α
Υ
i
α
=
λ
1
Υ
j
β
{\displaystyle (M^{t}M)_{j\beta }^{i\alpha }\Upsilon _{i\alpha }=\lambda _{1}\Upsilon _{j\beta }}
, where
t
{\displaystyle t}
indicates the transpose operator,
Γ
i
α
{\displaystyle \Gamma _{i\alpha }}
and
Υ
i
α
{\displaystyle \Upsilon _{i\alpha }}
indicate hub and authority centrality, respectively. By contracting the hub and authority tensors, one obtains the overall versatilities as
γ
i
=
Γ
i
α
u
α
{\displaystyle \gamma _{i}=\Gamma _{i\alpha }u^{\alpha }}
and
υ
i
=
Υ
i
α
u
α
{\displaystyle \upsilon _{i}=\Upsilon _{i\alpha }u^{\alpha }}
, respectively.
==== PageRank versatility ====
PageRank, originally introduced to rank web pages, can also be considered as a measure of centrality for interconnected multilayer networks.
It is worth remarking that PageRank can be seen as the steady-state solution of a special Markov process on the top of the network. Random walkers explore the network according to a special transition matrix and their dynamics is governed by a random walk master equation. It is easy to show that the solution of this equation is equivalent to the leading eigenvector of the transition matrix.
Random walks have been defined also in the case of interconnected multilayer networks and edge-colored multigraphs (also known as multiplex networks). For interconnected multilayer networks, the transition tensor governing the dynamics of the random walkers within and across layers is given by
R
j
β
i
α
=
r
T
j
β
i
α
+
(
1
−
r
)
N
L
u
j
β
i
α
,
{\displaystyle R_{j\beta }^{i\alpha }=rT_{j\beta }^{i\alpha }+{\frac {(1-r)}{NL}}u_{j\beta }^{i\alpha },}
, where
r
{\displaystyle r}
is a constant, generally set to 0.85,
N
{\displaystyle N}
is the number of nodes and
L
{\displaystyle L}
is the number of layers or dimensions. Here,
R
j
β
i
α
{\displaystyle R_{j\beta }^{i\alpha }}
might be named Google tensor and
u
j
β
i
α
{\displaystyle u_{j\beta }^{i\alpha }}
is the rank-4 tensor with all components equal to 1.
As its unidimensional counterpart, PageRank versatility consists of two contributions: one encoding a classical random walk with rate
r
{\displaystyle r}
and one encoding teleportation across nodes and layers with rate
1
−
r
{\displaystyle 1-r}
.
If we indicate by
Ω
i
α
{\displaystyle \Omega _{i\alpha }}
the eigentensor of the Google tensor
R
j
β
i
α
{\displaystyle R_{j\beta }^{i\alpha }}
, denoting the steady-state probability to find the walker in node
i
{\displaystyle i}
and layer
α
{\displaystyle \alpha }
, the multilayer PageRank is obtained by summing up over layers the eigentensor:
ω
i
=
Ω
i
α
u
α
{\displaystyle \omega _{i}=\Omega _{i\alpha }u^{\alpha }}
== Triadic closure and clustering coefficients ==
Like many other network statistics, the meaning of a clustering coefficient becomes ambiguous in multidimensional networks, due to the fact that triples may be closed in different dimensions than they originated. Several attempts have been made to define local clustering coefficients, but these attempts have highlighted the fact that the concept must be fundamentally different in higher dimensions: some groups have based their work off of non-standard definitions, while others have experimented with different definitions of random walks and 3-cycles in multidimensional networks.
== Community discovery ==
While cross-dimensional structures have been studied previously, they fail to detect more subtle associations found in some networks. Taking a slightly different take on the definition of "community" in the case of multidimensional networks allows for reliable identification of communities without the requirement that nodes be in direct contact with each other.
For instance, two people who never communicate directly yet still browse many of the same websites would be viable candidates for this sort of algorithm.
=== Modularity maximization ===
A generalization of the well-known modularity maximization method for community discovery has been originally proposed by Mucha et al. This multiresolution method assumes a three-dimensional tensor representation of the network connectivity within layers, as for edge-colored multigraphs, and a three-dimensional tensor representation of the network connectivity across layers. It depends on the resolution parameter
γ
{\displaystyle \gamma }
and the weight
ω
{\displaystyle \omega }
of interlayer connections. In a more compact notation, making use of the tensorial notation, modularity can be written as
Q
∝
S
i
α
a
B
j
β
i
α
S
a
j
β
{\displaystyle Q\propto S_{i\alpha }^{a}B_{j\beta }^{i\alpha }S_{a}^{j\beta }}
, where
B
j
β
i
α
=
M
j
β
i
α
−
P
j
β
i
α
{\displaystyle B_{j\beta }^{i\alpha }=M_{j\beta }^{i\alpha }-P_{j\beta }^{i\alpha }}
,
M
j
β
i
α
{\displaystyle M_{j\beta }^{i\alpha }}
is the multilayer adjacency tensor,
P
j
β
i
α
{\displaystyle P_{j\beta }^{i\alpha }}
is the tensor encoding the null model and the value of components of
S
a
i
α
{\displaystyle S_{a}^{i\alpha }}
is defined to be 1 when a node
i
{\displaystyle i}
in layer
α
{\displaystyle \alpha }
belongs to a particular community, labeled by index
a
{\displaystyle a}
, and 0 when it does not.
=== Tensor decomposition ===
Non-negative matrix factorization has been proposed to extract the community-activity structure of temporal networks. The multilayer network is represented by a three-dimensional tensor
T
i
j
τ
{\displaystyle T_{ij}^{\tau }}
, like an edge-colored multigraph, where the order of layers encode the arrow of time. Tensor factorization by means of Kruskal decomposition is thus applied to
T
i
j
τ
{\displaystyle T_{ij}^{\tau }}
to assign each node to a community across time.
=== Statistical inference ===
Methods based on statistical inference, generalizing existing approaches introduced for unidimensional networks, have been proposed. Stochastic block model is the most used generative model, appropriately generalized to the case of multilayer networks.
As for unidimensional networks, principled methods like minimum description length can be used for model selection in community detection methods based on information flow.
== Structural reducibility ==
Given the higher complexity of multilayer networks with respect to unidimensional networks, an active field of research is devoted to simplify the structure of such systems by employing some kind of dimensionality reduction.
A popular method is based on the calculation of the quantum Jensen-Shannon divergence between all pairs of layers, which is then exploited for its metric properties to build a distance matrix and hierarchically cluster the layers. Layers are successively aggregated according to the resulting hierarchical tree and the aggregation procedure is stopped when the objective function, based on the entropy of the network, gets a global maximum. This greedy approach is necessary because the underlying problem would require to verify all possible layer groups of any size, requiring a huge number of possible combinations (which is given by the Bell number and scales super-exponentially with the number of units). Nevertheless, for multilayer systems with a small number of layers, it has been shown that the method performs optimally in the majority of cases.
== Other multilayer network descriptors ==
=== Degree correlations ===
The question of degree correlations in unidimensional networks is fairly straightforward: do nodes of similar degree tend to connect to each other? In multidimensional networks, what this question means becomes less clear. When we refer to a node's degree, are we referring to its degree in one dimension, or collapsed over all? When we seek to probe connectivity between nodes, are we comparing the same nodes across dimensions, or different nodes within dimensions, or a combination? What are the consequences of variations in each of these statistics on other network properties? In one study, assortativity was found to decrease robustness in a duplex network.
=== Path dominance ===
Given two multidimensional paths, r and s, we say that r dominates s if and only if:
∀
d
∈
⟨
1
,
|
D
|
⟩
,
r
l
≤
s
l
{\displaystyle \forall d\in \langle 1,|D|\rangle ,r_{l}\leq s_{l}}
and
∃
i
{\displaystyle \exists i}
such that
r
l
<
s
l
{\displaystyle r_{l}<s_{l}}
.
=== Shortest path discovery ===
Among other network statistics, many centrality measures rely on the ability to assess shortest paths from node to node. Extending these analyses to a multidimensional network requires incorporating additional connections between nodes into the algorithms currently used (e.g., Dijkstra's). Current approaches include collapsing multi-link connections between nodes in a preprocessing step before performing variations on a breadth-first search of the network.
=== Multidimensional distance ===
One way to assess the distance between two nodes in a multidimensional network is by comparing all the multidimensional paths between them and choosing the subset that we define as shortest via path dominance: let
M
P
(
u
,
v
)
{\displaystyle MP(u,v)}
be the set of all paths between
u
{\displaystyle u}
and
v
{\displaystyle v}
. Then the distance between
u
{\displaystyle u}
and
v
{\displaystyle v}
is a set of paths
P
⊆
M
P
{\displaystyle P\subseteq MP}
such that
∀
p
∈
P
,
∄
p
′
∈
M
P
{\displaystyle \forall p\in P,\nexists p'\in MP}
such that
p
′
{\displaystyle p'}
dominates
p
{\displaystyle p}
. The length of the elements in the set of shortest paths between two nodes is therefore defined as the multidimensional distance.
=== Dimension relevance ===
In a multidimensional network
G
=
(
V
,
E
,
D
)
{\displaystyle G=(V,E,D)}
, the relevance of a given dimension (or set of dimensions)
D
′
{\displaystyle D'}
for one node can be assessed by the ratio:
Neighbors
(
v
,
D
′
)
Neighbors
(
v
,
D
)
{\displaystyle {\frac {{\text{Neighbors}}(v,D')}{{\text{Neighbors}}(v,D)}}}
.
=== Dimension connectivity ===
In a multidimensional network in which different dimensions of connection have different real-world values, statistics characterizing the distribution of links to the various classes are of interest. Thus it is useful to consider two metrics that assess this: dimension connectivity and edge-exclusive dimension connectivity. The former is simply the ratio of the total number of links in a given dimension to the total number of links in every dimension:
|
{
(
u
,
v
,
d
)
∈
E
|
u
,
v
∈
V
}
|
|
E
|
{\displaystyle {\frac {|\{(u,v,d)\in E|u,v\in V\}|}{|E|}}}
. The latter assesses, for a given dimension, the number of pairs of nodes connected only by a link in that dimension:
|
{
(
u
,
v
,
d
)
∈
E
|
u
,
v
∈
V
∧
∀
j
∈
D
,
j
≠
d
:
(
u
,
v
,
j
)
∉
E
}
|
|
{
(
u
,
v
,
d
)
∈
E
|
u
,
v
∈
V
}
|
{\displaystyle {\frac {|\{(u,v,d)\in E|u,v\in V\wedge \forall j\in D,j\neq d:(u,v,j)\notin E\}|}{|\{(u,v,d)\in E|u,v\in V\}|}}}
.
=== Burst detection ===
Burstiness is a well-known phenomenon in many real-world networks, e.g. email or other human communication networks. Additional dimensions of communication provide a more faithful representation of reality and may highlight these patterns or diminish them. Therefore, it is of critical importance that our methods for detecting bursty behavior in networks accommodate multidimensional networks.
== Diffusion processes on multilayer networks ==
Diffusion processes are widely used in physics to explore physical systems, as well as in other disciplines as social sciences, neuroscience, urban and international transportation or finance. Recently, simple and more complex diffusive processes have been generalized to multilayer networks. One result common to many studies is that diffusion in multiplex networks, a special type of multilayer system, exhibits two regimes: 1) the weight of inter-layer links, connecting layers each other, is not high enough and the multiplex system behaves like two (or more) uncoupled networks; 2) the weight of inter-layer links is high enough that layers are coupled each other, raising unexpected physical phenomena. It has been shown that there is an abrupt transition between these two regimes.
In fact, all network descriptors depending on some diffusive process, from centrality measures to community detection, are affected by the layer-layer coupling. For instance, in the case of community detection, low coupling (where information from each layer separately is more relevant than the overall structure) favors clusters within layers, whereas high coupling (where information from all layer simultaneously is more relevant than the each layer separately) favors cross-layer clusters.
=== Random walks ===
As for unidimensional networks, it is possible to define random walks on the top of multilayer systems. However, given the underlying multilayer structure, random walkers are not limited to move from one node to another within the same layer (jump), but are also allowed to move across layers (switch).
Random walks can be used to explore a multilayer system with the ultimate goal to unravel its mesoscale organization, i.e. to partition it in communities, and have been recently used to better understand navigability of multilayer networks and their resilience to random failures, as well as for exploring efficiently this type of topologies.
In the case of interconnected multilayer systems, the probability to move from a node
i
{\displaystyle i}
in layer
α
{\displaystyle \alpha }
to node
j
{\displaystyle j}
in layer
β
{\displaystyle \beta }
can be encoded into the rank-4 transition tensor
T
j
β
i
α
{\displaystyle T_{j\beta }^{i\alpha }}
and the discrete-time walk can be described by the master equation
p
j
β
(
t
+
1
)
=
∑
α
=
1
L
∑
i
=
1
N
T
j
β
i
α
p
i
α
(
t
)
=
∑
α
=
1
L
∑
i
=
1
N
(
T
t
)
j
β
i
α
p
i
α
(
0
)
{\displaystyle p_{j\beta }(t+1)=\sum _{\alpha =1}^{L}\sum _{i=1}^{N}T_{j\beta }^{i\alpha }p_{i\alpha }(t)=\sum _{\alpha =1}^{L}\sum _{i=1}^{N}(T^{t})_{j\beta }^{i\alpha }p_{i\alpha }(0)}
where
p
i
α
(
t
)
{\displaystyle p_{i\alpha }(t)}
indicates the probability of finding the walker in node
i
{\displaystyle i}
in layer
α
{\displaystyle \alpha }
at time
t
{\displaystyle t}
.
There are many different types of walks that can be encoded into the transition tensor
T
j
β
i
α
{\displaystyle T_{j\beta }^{i\alpha }}
, depending on how the walkers are allowed to jump and switch. For instance, the walker might either jump or switch in a single time step without distinguishing between inter- and intra-layer links (classical random walk), or it can choose either to stay in the current layer and jump, or to switch layer and then jump to another node in the same time step (physical random walk). More complicated rules, corresponding to specific problems to solve, can be found in the literature. In some cases, it is possible to find, analytically, the stationary solution of the master equation.
=== Classical diffusion ===
The problem of classical diffusion in complex networks is to understand how a quantity will flow through the system and how much time it will take to reach the stationary state. Classical diffusion in multiplex networks has been recently studied by introducing the concept of supra-adjacency matrix, later recognized as a special flattening of the multilayer adjacency tensor. In tensorial notation, the diffusion equation on the top of a general multilayer system can be written, concisely, as
d
X
j
β
(
t
)
d
t
=
−
L
j
β
i
α
X
i
α
(
t
)
{\displaystyle {\frac {dX_{j\beta }(t)}{dt}}=-L_{j\beta }^{i\alpha }X_{i\alpha }(t)}
where
X
i
α
(
t
)
{\displaystyle X_{i\alpha }(t)}
is the amount of diffusing quantity at time
t
{\displaystyle t}
in node
i
{\displaystyle i}
in layer
α
{\displaystyle \alpha }
. The rank-4 tensor governing the equation is the Laplacian tensor, generalizing the combinatorial Laplacian matrix of unidimensional networks. It is worth remarking that in non-tensorial notation, the equation takes a more complicated form.
Many of the properties of this diffusion process are completely understood in terms of the second smallest eigenvalue of the Laplacian tensor. It is interesting that diffusion in a multiplex system can be faster than diffusion in each layer separately, or in their aggregation, provided that certain spectral properties are satisfied.
=== Information and epidemics spreading ===
Recently, how information (or diseases) spread through a multilayer system has been the subject of intense research.
== Multilayer network analysis software ==
Several software programs focusing on the analysis and visualization of multilayer networks have been introduced. Some popular solutions include multinet (C++ / Python / R), MuxViz (R), Pymnet (Python), with each software typically specializing in different analytical functions. However, most software currently face issues such as processing very large multilayer networks, while the interoperability between software also needs improvement.
== References == | Wikipedia/Multidimensional_network |
Random graph theory of gelation is a mathematical theory for sol–gel processes. The theory is a collection of results that generalise the Flory–Stockmayer theory, and allow identification of the gel point, gel fraction, size distribution of polymers, molar mass distribution and other characteristics for a set of many polymerising monomers carrying arbitrary numbers and types of reactive functional groups.
The theory builds upon the notion of the random graph, introduced by mathematicians Paul Erdős and Alfréd Rényi, and independently by Edgar Gilbert in the late 1950s, as well as on the generalisation of this concept known as the random graph with a fixed degree sequence. The theory has been originally developed to explain step-growth polymerisation, and adaptations to other types of polymerisation now exist. Along with providing theoretical results the theory is also constructive. It indicates that the graph-like structures resulting from polymerisation can be sampled with an algorithm using the configuration model, which makes these structures available for further examination with computer experiments.
== Premises and degree distribution ==
At a given point of time, degree distribution
u
(
n
)
{\displaystyle u(n)}
, is the probability that a randomly chosen monomer has
n
{\displaystyle n}
connected neighbours. The central idea of the random graph theory of gelation is that a cross-linked or branched polymer can be studied separately at two levels: 1) monomer reaction kinetics that predicts
u
(
n
)
{\displaystyle u(n)}
and 2) random graph with a given degree distribution. The advantage of such a decoupling is that the approach allows one to study the monomer kinetics with relatively simple rate equations, and then deduce the degree distribution serving as input for a random graph model. In several cases the aforementioned rate equations have a known analytical solution.
=== One type of functional groups ===
In the case of step-growth polymerisation of monomers carrying functional groups of the same type (so called
A
1
+
A
2
+
A
3
+
⋯
{\displaystyle A_{1}+A_{2}+A_{3}+\cdots }
polymerisation) the degree distribution is given by:
u
(
n
,
t
)
=
∑
m
=
n
∞
(
m
n
)
c
(
t
)
n
(
1
−
c
(
t
)
)
m
−
n
f
m
,
{\displaystyle u(n,t)=\sum _{m=n}^{\infty }{\binom {m}{n}}c(t)^{n}{\big (}1-c(t){\big )}^{m-n}f_{m},}
where
c
(
t
)
=
μ
t
1
+
μ
t
{\displaystyle c(t)={\frac {\mu t}{1+\mu t}}}
is bond conversion,
μ
=
∑
m
=
1
k
m
f
m
{\displaystyle \mu =\sum _{m=1}^{k}mf_{m}}
is the average functionality, and
f
m
{\displaystyle f_{m}}
is the initial fractions of monomers of functionality
m
{\displaystyle m}
. In the later expression unit reaction rate is assumed without loss of generality. According to the theory, the system is in the gel state when
c
(
t
)
>
c
g
{\displaystyle c(t)>c_{g}}
, where the gelation conversion is
c
g
=
∑
m
=
1
∞
m
f
m
∑
m
=
1
∞
(
m
2
−
m
)
f
m
{\displaystyle c_{g}={\frac {\sum _{m=1}^{\infty }mf_{m}}{\sum _{m=1}^{\infty }(m^{2}-m)f_{m}}}}
. Analytical expression for average molecular weight and molar mass distribution are known too. When more complex reaction kinetics are involved, for example chemical substitution, side reactions or degradation, one may still apply the theory by computing
u
(
n
,
t
)
{\displaystyle u(n,t)}
using numerical integration. In which case,
∑
n
=
1
∞
(
n
2
−
2
n
)
u
(
n
,
t
)
>
0
{\displaystyle \sum _{n=1}^{\infty }(n^{2}-2n)u(n,t)>0}
signifies that the system is in the gel state at time t (or in the sol state when the inequality sign is flipped).
=== Two types of functional groups ===
When monomers with two types of functional groups A and B undergo step growth polymerisation by virtue of a reaction between A and B groups, a similar analytical results are known. See the table on the right for several examples. In this case,
f
m
,
k
{\displaystyle f_{m,k}}
is the fraction of initial monomers with
m
{\displaystyle m}
groups A and
k
{\displaystyle k}
groups B. Suppose that A is the group that is depleted first. Random graph theory states that gelation takes place when
c
(
t
)
>
c
g
{\displaystyle c(t)>c_{g}}
, where the gelation conversion is
c
g
=
ν
10
ν
11
+
(
ν
20
−
ν
10
)
(
ν
02
−
ν
01
)
{\displaystyle c_{g}={\frac {\nu _{10}}{\nu _{11}+{\sqrt {(\nu _{20}-\nu _{10})(\nu _{02}-\nu _{01})}}}}}
and
ν
i
,
j
=
∑
m
,
k
=
1
∞
m
i
k
j
f
m
,
k
{\displaystyle \nu _{i,j}=\sum _{m,k=1}^{\infty }m^{i}k^{j}f_{m,k}}
. Molecular size distribution, the molecular weight averages, and the distribution of gyration radii have known formal analytical expressions. When degree distribution
u
(
n
,
l
,
t
)
{\displaystyle u(n,l,t)}
, giving the fraction of monomers in the network with
n
{\displaystyle n}
neighbours connected via A group and
l
{\displaystyle l}
connected via B group at time
t
{\displaystyle t}
is solved numerically, the gel state is detected when
2
μ
μ
11
−
μ
μ
02
−
μ
μ
20
+
μ
02
μ
20
−
μ
11
2
>
0
{\displaystyle 2\mu \mu _{11}-\mu \mu _{02}-\mu \mu _{20}+\mu _{02}\mu _{20}-\mu _{11}^{2}>0}
, where
μ
i
,
j
=
∑
n
,
l
=
1
∞
n
i
l
j
u
(
n
,
l
,
t
)
{\displaystyle \mu _{i,j}=\sum _{n,l=1}^{\infty }n^{i}l^{j}u(n,l,t)}
and
μ
=
μ
01
=
μ
10
{\displaystyle \mu =\mu _{01}=\mu _{10}}
.
=== Generalisations ===
Known generalisations include monomers with an arbitrary number of functional group types, crosslinking polymerisation, and complex reaction networks.
== References == | Wikipedia/Random_graph_theory_of_gelation |
The field of complex networks has emerged as an important area of science to generate novel insights into nature of complex systems The application of network theory to climate science is a young and emerging field. To identify and analyze patterns in global climate, scientists model climate data as complex networks.
Unlike most real-world networks where nodes and edges are well defined, in climate networks, nodes are identified as the sites in a spatial grid of the underlying global climate data set, which can be represented at various resolutions. Two nodes are connected by an edge depending on the degree of statistical similarity (that may be related to dependence) between the corresponding pairs of time-series taken from climate records.
The climate network approach enables novel insights into the dynamics of the climate system over different spatial and temporal scales.
== Construction of climate networks ==
Depending upon the choice of nodes and/or edges, climate networks may take many different forms, shapes, sizes and complexities.
Tsonis et al. introduced the field of complex networks to climate. In their model, the nodes for the network were constituted by a single variable (500 hPa) from NCEP/NCAR Reanalysis datasets. In order to estimate the edges between nodes, correlation coefficient at zero time lag between all possible pairs of nodes were estimated. A pair of nodes was considered to be connected, if their correlation coefficient is above a threshold of 0.5.
Steinhaeuser and team introduced the novel technique of multivariate networks in climate by constructing networks from several climate variables separately and capture their interaction in multivariate predictive model. It was demonstrated in their studies that in context of climate, extracting predictors based on cluster attributes yield informative precursors to improve predictive skills.
Kawale et al. presented a graph based approach to find dipoles in pressure data. Given the importance of teleconnection, this methodology has potential to provide significant insights.
Imme et al. introduced a new type of network construction in climate based on temporal probabilistic graphical model, which provides an alternative viewpoint by focusing on information flow within network over time.
Agarwal et al. proposed advanced linear and nonlinear methods to construct and investigate climate networks at different timescales. Climate networks constructed using SST datasets at different timescale averred that multi-scale analysis of climatic processes holds the promise of better understanding the system dynamics that may be missed when processes are analyzed at one timescale only
== Applications of climate networks ==
Climate networks enable insights into the dynamics of climate system over many spatial scales. The local degree centrality and related measures have been used to identify super-nodes and to associate them to known dynamical interrelations in the atmosphere, called teleconnection patterns. It was observed that climate networks possess “small world” properties owing to the long-range spatial connections.
Steinhaeuser et al. applied complex networks to explore the multivariate and multi-scale dependence in climate data. Findings of the group suggested a close similarity of observed dependence patterns in multiple variables over multiple time and spatial scales.
Tsonis and Roeber investigated the coupling architecture of the climate network. It was found that the overall network emerges from intertwined subnetworks. One subnetwork is operating at higher altitudes and other is operating in the tropics, while the equatorial subnetwork acts as an agent linking the 2 hemispheres . Though, both networks possess Small World Property, the 2 subnetworks are significantly different from each other in terms of network properties like degree distribution.
Donges et al. applied climate networks for physics and nonlinear dynamical interpretations in climate. The team used measure of node centrality, betweenness centrality (BC) to demonstrate the wave-like structures in the BC fields of climate networks constructed from monthly averaged reanalysis and atmosphere-ocean coupled general circulation model (AOGCM) surface air temperature (SAT) data.
== Teleconnection path ==
Teleconnections are spatial patterns in the atmosphere that link weather and climate anomalies over large distances across the globe. Teleconnections have the characteristics that they are persistent, lasting for 1 to 2 weeks, and often much longer, and they are recurrent, as similar patterns tend to occur repeatedly. The presence of teleconnections is associated with changes in temperature, wind, precipitation, atmospheric variables of greatest societal interest.
== Computational issues and challenges ==
There are numerous computational challenges that arise at various stages of the network construction and analysis process in field of climate networks:
Calculating the pair-wise correlations between all grid points is a non-trivial task.
Computational demands of network construction, which depends upon the resolution of spatial grid.
Generation of predictive models from the data poses additional challenges.
Inclusion of lag and lead effects over space and time is a non-trivial task.
== See also ==
Community structure
Network theory
Network science
Teleconnection
Climatology
== References == | Wikipedia/Climate_networks |
In ecology, r/K selection theory relates to the selection of combinations of traits in an organism that trade off between quantity and quality of offspring. The focus on either an increased quantity of offspring at the expense of reduced individual parental investment of r-strategists, or on a reduced quantity of offspring with a corresponding increased parental investment of K-strategists, varies widely, seemingly to promote success in particular environments. The concepts of quantity or quality offspring are sometimes referred to as "cheap" or "expensive", a comment on the expendable nature of the offspring and parental commitment made. The stability of the environment can predict if many expendable offspring are made or if fewer offspring of higher quality would lead to higher reproductive success. An unstable environment would encourage the parent to make many offspring, because the likelihood of all (or the majority) of them surviving to adulthood is slim. In contrast, more stable environments allow parents to confidently invest in one offspring because they are more likely to survive to adulthood.
The terminology of r/K-selection was coined by the ecologists Robert MacArthur and E. O. Wilson in 1967 based on their work on island biogeography; although the concept of the evolution of life history strategies has a longer history (see e.g. plant strategies).
The theory was popular in the 1970s and 1980s, when it was used as a heuristic device, but lost importance in the early 1990s, when it was criticized by several empirical studies. A life-history paradigm has replaced the r/K selection paradigm, but continues to incorporate its important themes as a subset of life history theory. Some scientists now prefer to use the terms fast versus slow life history as a replacement for, respectively, r versus K reproductive strategy.
== Overview ==
In r/K selection theory, selective pressures are hypothesised to drive evolution in one of two generalized directions: r- or K-selection. These terms, r and K, are drawn from standard ecological formula as illustrated in the simplified Verhulst model of population dynamics:
d
N
d
t
=
r
N
(
1
−
N
K
)
{\displaystyle {\frac {{\text{d}}N}{{\text{d}}t}}=r\ N\left(1-{\frac {\ N\ }{K}}\right)}
where N is the population, r is the maximum growth rate, K is the carrying capacity of the local environment, and d N / d t (the derivative of population size N with respect to time t) is the rate of change in population with time. Thus, the equation relates the growth rate of the population N to the current population size, incorporating the effect of the two constant parameters r and K.
(Note that when the population size is greater than the carrying capacity then 1 - N/K is negative, which indicates a population decline or negative growth.) The choice of the letter K came from the German Kapazitätsgrenze (capacity limit), while r came from rate.
=== r-selection ===
r-selected species are those that emphasize high growth rates, typically exploit less-crowded ecological niches, and produce many offspring, each of which has a relatively low probability of surviving to adulthood (i.e., high r, low K). A typical r species is the dandelion (genus Taraxacum).
In unstable or unpredictable environments, r-selection predominates due to the ability to reproduce rapidly. There is little advantage in adaptations that permit successful competition with other organisms, because the environment is likely to change again. Among the traits that are thought to characterize r-selection are high fecundity, small body size, early maturity onset, short generation time, and the ability to disperse offspring widely.
Organisms whose life history is subject to r-selection are often referred to as r-strategists or r-selected. Groups of organisms known for exhibiting r-selected traits are bacteria, diatoms, insects, grasses, cephalopods, fowl, and rodents.
=== K-selection ===
By contrast, K-selected species display traits associated with living at densities close to carrying capacity and typically are strong competitors in such crowded niches, that invest more heavily in fewer offspring, each of which has a relatively high probability of surviving to adulthood (i.e., low r, high K). In scientific literature, r-selected species are occasionally referred to as "opportunistic" whereas K-selected species are described as "equilibrium".
In stable or predictable environments, K-selection predominates as the ability to compete successfully for limited resources is crucial and populations of K-selected organisms typically are very constant in number and close to the maximum that the environment can bear (unlike r-selected populations, where population sizes can change much more rapidly).
Traits that are thought to be characteristic of K-selection include large body size, long life expectancy, and the production of fewer offspring, which often require extensive parental care until they mature. Organisms whose life history is subject to K-selection are often referred to as K-strategists or K-selected. Organisms with K-selected traits include large organisms such as elephants, sharks, humans, and whales, but also smaller long-lived organisms such as Arctic terns, parrots, and eagles.
=== Continuous spectrum ===
Although some organisms are identified as primarily r- or K-strategists, the majority of organisms do not follow this pattern. For instance, trees have traits such as longevity and strong competitiveness that characterise them as K-strategists. In reproduction, however, trees typically produce thousands of offspring and disperse them widely, traits characteristic of r-strategists.
Similarly, reptiles such as sea turtles display both r- and K-traits: Although sea turtles are large organisms with long lifespans (provided they reach adulthood), they produce large numbers of unnurtured offspring.
The r/K dichotomy can be re-expressed as a continuous spectrum using the economic concept of discounted future returns, with r-selection corresponding to large discount rates and K-selection corresponding to small discount rates.
== Ecological succession ==
In areas of major ecological disruption or sterilisation (such as after a major volcanic eruption, as at Krakatoa or Mount St. Helens), r- and K-strategists play distinct roles in the ecological succession that regenerates the ecosystem. Because of their higher reproductive rates and ecological opportunism, primary colonisers typically are r-strategists and they are followed by a succession of increasingly competitive flora and fauna. The ability of an environment to increase energetic content, through photosynthetic capture of solar energy, increases with the increase in complex biodiversity as r species proliferate to reach a peak possible with K strategies.
Eventually a new equilibrium is approached (sometimes referred to as a climax community), with r-strategists gradually being replaced by K-strategists which are more competitive and better adapted to the emerging micro-environmental characteristics of the landscape. Traditionally, biodiversity was considered maximized at this stage, with introductions of new species resulting in the replacement and local extinction of endemic species. However, the intermediate disturbance hypothesis posits that intermediate levels of disturbance in a landscape create patches at different levels of succession, promoting coexistence of colonizers and competitors at the regional scale.
== Application ==
While usually applied at the level of species, r/K selection theory is also useful in studying the evolution of ecological and life history differences between subspecies, for instance the African honey bee, A. m. scutellata, and the Italian bee, A. m. ligustica. At the other end of the scale, it has also been used to study the evolutionary ecology of whole groups of organisms, such as bacteriophages. Other researchers have proposed that the evolution of human inflammatory responses is related to r/K selection.
Some researchers, such as Lee Ellis, J. Philippe Rushton, and Aurelio José Figueredo, have attempted to apply r/K selection theory to various human behaviors, including crime, sexual promiscuity, fertility, IQ, and other traits related to life history theory. Rushton developed "differential K theory" to attempt to explain variations in behavior across human races. Differential K theory has been debunked as being devoid of empirical basis, and has also been described as a key example of scientific racism.
== Status ==
Although r/K selection theory became widely used during the 1970s, it also began to attract more critical attention. In particular, a review in 1977 by the ecologist Stephen C. Stearns drew attention to gaps in the theory, and to ambiguities in the interpretation of empirical data for testing it.
In 1981, a review of the r/K selection literature by Parry demonstrated that there was no agreement among researchers using the theory about the definition of r- and K-selection, which led him to question whether the assumption of a relation between reproductive expenditure and packaging of offspring was justified. A 1982 study by Templeton and Johnson showed that in a population of Drosophila mercatorum under K-selection the population actually produced a higher frequency of traits typically associated with r-selection. Several other studies contradicting the predictions of r/K selection theory were also published between 1977 and 1994.
When Stearns reviewed the status of the theory again in 1992, he noted that from 1977 to 1982 there was an average of 42 references to the theory per year in the BIOSIS literature search service, but from 1984 to 1989 the average dropped to 16 per year and continued to decline. He concluded that r/K theory was a once useful heuristic that no longer serves a purpose in life history theory.
More recently, the panarchy theories of adaptive capacity and resilience promoted by C. S. Holling and Lance Gunderson have revived interest in the theory, and use it as a way of integrating social systems, economics, and ecology.
Writing in 2002, Reznick and colleagues reviewed the controversy regarding r/K selection theory and concluded that:
The distinguishing feature of the r- and K-selection paradigm was the focus on density-dependent selection as the important agent of selection on organisms' life histories. This paradigm was challenged as it became clear that other factors, such as age-specific mortality, could provide a more mechanistic causative link between an environment and an optimal life history (Wilbur et al. 1974; Stearns 1976, 1977). The r- and K-selection paradigm was replaced by new paradigm that focused on age-specific mortality (Stearns, 1976; Charlesworth, 1980). This new life-history paradigm has matured into one that uses age-structured models as a framework to incorporate many of the themes important to the r–K paradigm.
Alternative approaches are now available both for studying life history evolution (e.g. Leslie matrix for an age-structured population) and for density-dependent selection (e.g. variable density lottery model).
== See also ==
Evolutionary game theory
Life history theory
Minimax/maximin strategy
Ruderal species
Semelparity and iteroparity
Survivorship curve
Trivers–Willard hypothesis
== References == | Wikipedia/R/K_selection_theory |
In animal husbandry, feed conversion ratio (FCR) or feed conversion rate is a ratio or rate measuring of the efficiency with which the bodies of livestock convert animal feed into the desired output. For dairy cows, for example, the output is milk, whereas in animals raised for meat (such as beef cows, pigs, chickens, and fish) the output is the flesh, that is, the body mass gained by the animal, represented either in the final mass of the animal or the mass of the dressed output. FCR is the mass of the input divided by the output (thus mass of feed per mass of milk or meat). In some sectors, feed efficiency, which is the output divided by the input (i.e. the inverse of FCR), is used. These concepts are also closely related to efficiency of conversion of ingested foods (ECI).
== Background ==
Feed conversion ratio (FCR) is the ratio of inputs to outputs; it is the inverse of "feed efficiency" which is the ratio of outputs to inputs. FCR is widely used in hog and poultry production, while FE is used more commonly with cattle. Being a ratio the FCR is dimensionless, that is, it is not affected by the units of measurement used to determine the FCR.
FCR a function of the animal's genetics and age, the quality and ingredients of the feed, and the conditions in which the animal is kept, and storage and use of the feed by the farmworkers.
As a rule of thumb, the daily FCR is low for young animals (when relative growth is large) and increases for older animals (when relative growth tends to level out). However FCR is a poor basis to use for selecting animals to improve genetics, as that results in larger animals that cost more to feed; instead residual feed intake (RFI) is used which is independent of size. RFI uses for output the difference between actual intake and predicted intake based on an animal's body weight, weight gain, and composition.
The outputs portion may be calculated based on weight gained, on the whole animal at sale, or on the dressed product; with milk it may be normalized for fat and protein content.
As for the inputs portion, although FCR is commonly calculated using feed dry mass, it is sometimes calculated on an as-fed wet mass basis, (or in the case of grains and oilseeds, sometimes on a wet mass basis at standard moisture content), with feed moisture resulting in higher ratios.
== Conversion ratios for livestock ==
Animals that have a low FCR are considered efficient users of feed. However, comparisons of FCR among different species may be of little significance unless the feeds involved are of similar quality and suitability.
=== Beef cattle ===
As of 2013 in the US, an FCR calculated on live weight gain of 4.5–7.5 was in the normal range with an FCR above 6 being typical. Divided by an average carcass yield of 62.2%, the typical carcass weight FCR is above 10. As of 2013 FCRs had not changed much compared to other fields in the prior 30 years, especially compared to poultry which had improved feed efficiency by about 250% over the last 50 years.
=== Dairy cattle ===
The dairy industry traditionally didn't use FCR but in response to increasing concentration in the dairy industry and other livestock operations, the EPA updated its regulations in 2003 controlling manure and other waste releases produced by livestock operators.: 11–11 In response the USDA began issuing guidance to dairy farmers about how to control inputs to better minimize manure output and to minimize harmful contents, as well as optimizing milk output.
In the US, the price of milk is based on the protein and fat content, so the FCR is often calculated to take that into account. Using an FCR calculated just on the weight of protein and fat, as of 2011 an FCR of 13 was poor, and an FCR of 8 was very good.
Another method for dealing with pricing based on protein and fat, is using energy-corrected milk (ECM), which adds a factor to normalize assuming certain amounts of fat and protein in a final milk product; that formula is (0.327 x milk mass) + (12.95 x fat mass) + (7.2 x protein mass).
In the dairy industry, feed efficiency (ECM/intake) is often used instead of FCR (intake/ECM); an FE less than 1.3 is considered problematic.
FE based simply on the weight of milk is also used; an FE between 1.30 and 1.70 is normal.
=== Pigs ===
Pigs have been kept to produce meat for 5,000 to 9,000 years. As of 2011, pigs used commercially in the UK and Europe had an FCR, calculated using weight gain, of about 1 as piglets and ending about 3 at time of slaughter. As of 2012 in Australia and using dressed weight for the output, a FCR calculated using weight of dressed meat of 4.5 was fair, 4.0 was considered "good", and 3.8, "very good".
The FCR of pigs is greatest up to the period, when pigs weigh 220 pounds. During this period, their FCR is 3.5. Their FCR begins increasing gradually after this period. For instance, in the US as of 2012, commercial pigs had FCR calculated using weight gain, of 3.46 for while they weighed between 240 and 250 pounds, 3.65 between 250 and 260 pounds, 3.87 between 260 and 270 lbs, and 4.09 between 280 and 270 lbs.
Because FCR calculated on the basis of weight gained gets worse after pigs mature, as it takes more and more feed to drive growth, countries that have a culture of slaughtering pigs at very high weights, like Japan and Korea, have poor FCRs.
=== Sheep ===
Some data for sheep illustrate variations in FCR. A FCR (kg feed dry matter intake per kg live mass gain) for lambs is often in the range of about 4 to 5 on high-concentrate rations, 5 to 6 on some forages of good quality, and more than 6 on feeds of lesser quality. On a diet of straw, which has a low metabolizable energy concentration, FCR of lambs may be as high as 40. Other things being equal, FCR tends to be higher for older lambs (e.g. 8 months) than younger lambs (e.g. 4 months).
=== Poultry ===
As of 2011 in the US, broiler chickens has an FCR of 1.6 based on body weight gain, and mature in 39 days. At around the same time the FCR based on weight gain for broilers in Brazil was 1.8. The global average in 2013 is around 2.0 for weight gain (live weight) and 2.8 for slaughtered meat (carcass weight).
For hens used in egg production in the US, as of 2011 the FCR was about 2, with each hen laying about 330 eggs per year. When slaughtered, the world average layer flock as of 2013 yields a carcass FCR of 4.2, still much better than the average backyard chicken flock (FCR 9.2 for eggs, 14.6 for carcass).
From the early 1960s to 2011 in the US broiler growth rates doubled and their FCRs halved, mostly due to improvements in genetics and rapid dissemination of the improved chickens. The improvement in genetics for growing meat created challenges for farmers who breed the chickens that are raised by the broiler industry, as the genetics that cause fast growth decreased reproductive abilities.
=== Carnivorous fish ===
In aquaculture, the fish feed for carnivorous fish commonly includes fish-derived products in the form of fishmeal and fish oil. There are therefore two ratios to be reported:
The regular feed conversion ratio, i.e. output fish mass divided by total feed mass.
The conversion ratio only taking into account the fish-based component of fish feed, called the FIFO ratio (or Fish In – Fish Out ratio). FIFO is fish in (the mass of harvested fish used to feed farmed fish) divided by fish out (mass of the resulting farmed fish).
FIFO is a way of expressing the contribution from harvested wild fish used in aquafeed compared with the amount of edible farmed fish, as a ratio. The fish used in fishmeal and fish oil production are not used for human consumption, but with their use as fishmeal and fish oil in aquafeed they contribute to global food production.
Fishmeal and fish oil inclusion rates in aquafeeds have shown a continual decline over time as aquaculture grows and more feed is produced, but with a finite annual supply of fishmeal and fish oil. Calculations have shown that the overall fed aquaculture FIFO declined from 0.63 in 2000 to 0.33 in 2010, and 0.22 in 2015. In 2015, therefore, approximately 4.55 kg of farmed fish was produced for every 1 kg of wild fish harvested and used in feed. (For Salmon & Trout, the FIFO ratios for 2000, 2010, and 2015 are: 2.57, 1.38, 0.82.)
As of 2015 farm-raised Atlantic salmon had a commodified feed supply with four main suppliers, and an FCR of around 1. Tilapia is about 1.5, and as of 2013 farmed catfish had a FCR of about 1.
It is possible for fish to have an FCR below 1 despite obvious energy losses in feed-to-meat conversion. Fish feed tends to be dry food with higher energy density than water-rich fish flesh.
=== Herbivorous and omnivorous fish ===
For herbivorous and omnivorous fish like Chinese carp and tilapia, the plant-based feed yields much lower FCR compared to carnivorous kept on a partially fish-based diet, despite a decrease in overall resource use. The edible (fillet) FCR of tilapia is around 4.6 and the FCR of Chinese carp is around 4.9.
=== Rabbits ===
In India, rabbits raised for meat had an FCR of 2.5 to 3.0 on high grain diet and 3.5 to 4.0 on natural forage diet, without animal-feed grain.
=== Global averages by species and production systems ===
In a global study, FAO estimated various feed conversion ratios, taking into account the diversity of feed material consumed by livestock. At global level, ruminants require 133 kg of dry matter per kg of protein while monogastrics require 30 kg. However, when considering human edible feed only, ruminants require 5.9 kg of feed to produce 1 kg of animal protein, while monogastrics require 15.8 kg. When looking at meat only, ruminants consume an average of 2.8 kg of human edible feed per kg of meat produced, while monogastrics need 3.2 kg. Finally, when accounting for the protein content of the feed, ruminant need an average of 0.6 kg of edible plant protein to produce 1 kg of animal protein while monogastric need 2 kg. This means that ruminants make a positive net contribution to the supply of edible protein for humans at global level.
== Feed conversion ratios of meat alternatives ==
Many alternatives to conventional animal meat sources have been proposed for higher efficiency, including insects, meat analogues, and cultured meats.
=== Insects ===
Although there are few studies of the feed conversion ratios of edible insects, the house cricket (Acheta domesticus) has been shown to have a FCR of 0.9 - 1.1 depending on diet composition. A more recent work gives an FCR of 1.9–2.4. Reasons contributing to such a low FCR include the whole body being used for food, the lack of internal temperature control (insects are poikilothermic), high fecundity and rate of maturation.
=== Meat analogue ===
If one treats tofu as a meat, the FCR reaches as low as 0.29. The FCRs for less watery forms of meat analogues are unknown.
=== Cultured meat ===
Although cultured meat has a potentially much lower land footprint required, its FCR is closer to poultry at around 4 (2-8). It has a high need for energy inputs.
== See also ==
Entomophagy
Food vs. feed
Life-cycle assessment
== References == | Wikipedia/Feed_conversion_ratio |
Species distribution modelling (SDM), also known as environmental (or ecological) niche modelling (ENM), habitat modelling, predictive habitat distribution modelling, and range mapping uses ecological models to predict the distribution of a species across geographic space and time using environmental data. The environmental data are most often climate data (e.g. temperature, precipitation), but can include other variables such as soil type, water depth, and land cover. SDMs are used in several research areas in conservation biology, ecology and evolution. These models can be used to understand how environmental conditions influence the occurrence or abundance of a species, and for predictive purposes (ecological forecasting). Predictions from an SDM may be of a species’ future distribution under climate change, a species’ past distribution in order to assess evolutionary relationships, or the potential future distribution of an invasive species. Predictions of current and/or future habitat suitability can be useful for management applications (e.g. reintroduction or translocation of vulnerable species, reserve placement in anticipation of climate change).
There are two main types of SDMs. Correlative SDMs, also known as climate envelope models, bioclimatic models, or resource selection function models, model the observed distribution of a species as a function of environmental conditions. Mechanistic SDMs, also known as process-based models or biophysical models, use independently derived information about a species' physiology to develop a model of the environmental conditions under which the species can exist.
The extent to which such modelled data reflect real-world species distributions will depend on a number of factors, including the nature, complexity, and accuracy of the models used and the quality of the available environmental data layers; the availability of sufficient and reliable species distribution data as model input; and the influence of various factors such as barriers to dispersal, geologic history, or biotic interactions, that increase the difference between the realized niche and the fundamental niche. Environmental niche modelling may be considered a part of the discipline of biodiversity informatics.
== History ==
A. F. W. Schimper used geographical and environmental factors to explain plant distributions in his 1898 Pflanzengeographie auf physiologischer Grundlage (Plant Geography Upon a Physiological Basis) and his 1908 work of the same name. Andrew Murray used the environment to explain the distribution of mammals in his 1866 The Geographical Distribution of Mammals. Robert Whittaker's work with plants and Robert MacArthur's work with birds strongly established the role the environment plays in species distributions. Elgene O. Box constructed environmental envelope models to predict the range of tree species. His computer simulations were among the earliest uses of species distribution modelling.
The adoption of more sophisticated generalised linear models (GLMs) made it possible to create more sophisticated and realistic species distribution models. The expansion of remote sensing and the development of GIS-based environmental modelling increase the amount of environmental information available for model-building and made it easier to use.
== Correlative vs mechanistic models ==
=== Correlative SDMs ===
SDMs originated as correlative models. Correlative SDMs model the observed distribution of a species as a function of geographically referenced climatic predictor variables using multiple regression approaches. Given a set of geographically referred observed presences of a species and a set of climate maps, a model defines the most likely environmental ranges within which a species lives. Correlative SDMs assume that species are at equilibrium with their environment and that the relevant environmental variables have been adequately sampled. The models allow for interpolation between a limited number of species occurrences.
For these models to be effective, it is required to gather observations not only of species presences, but also of absences, that is, where the species does not live. Records of species absences are typically not as common as records of presences, thus often "random background" or "pseudo-absence" data are used to fit these models. If there are incomplete records of species occurrences, pseudo-absences can introduce bias. Since correlative SDMs are models of a species’ observed distribution, they are models of the realized niche (the environments where a species is found), as opposed to the fundamental niche (the environments where a species can be found, or where the abiotic environment is appropriate for the survival). For a given species, the realized and fundamental niches might be the same, but if a species is geographically confined due to dispersal limitation or species interactions, the realized niche will be smaller than the fundamental niche.
Correlative SDMs are easier and faster to implement than mechanistic SDMs, and can make ready use of available data. Since they are correlative however, they do not provide much information about causal mechanisms and are not good for extrapolation. They will also be inaccurate if the observed species range is not at equilibrium (e.g. if a species has been recently introduced and is actively expanding its range).
=== Mechanistic SDMs ===
Mechanistic SDMs are more recently developed. In contrast to correlative models, mechanistic SDMs use physiological information about a species (taken from controlled field or laboratory studies) to determine the range of environmental conditions within which the species can persist. These models aim to directly characterize the fundamental niche, and to project it onto the landscape. A simple model may simply identify threshold values outside of which a species can't survive. A more complex model may consist of several sub-models, e.g. micro-climate conditions given macro-climate conditions, body temperature given micro-climate conditions, fitness or other biological rates (e.g. survival, fecundity) given body temperature (thermal performance curves), resource or energy requirements, and population dynamics. Geographically referenced environmental data are used as model inputs. Because the species distribution predictions are independent of the species’ known range, these models are especially useful for species whose range is actively shifting and not at equilibrium, such as invasive species.
Mechanistic SDMs incorporate causal mechanisms and are better for extrapolation and non-equilibrium situations. However, they are more labor-intensive to create than correlational models and require the collection and validation of a lot of physiological data, which may not be readily available. The models require many assumptions and parameter estimates, and they can become very complicated.
Dispersal, biotic interactions, and evolutionary processes present challenges, as they aren’t usually incorporated into either correlative or mechanistic models.
Correlational and mechanistic models can be used in combination to gain additional insights. For example, a mechanistic model could be used to identify areas that are clearly outside the species’ fundamental niche, and these areas can be marked as absences or excluded from analysis. See for a comparison between mechanistic and correlative models.
== Niche models (correlative) ==
There are a variety of mathematical methods that can be used for fitting, selecting, and evaluating correlative SDMs. Models include "profile" methods, which are simple statistical techniques that use e.g. environmental distance to known sites of occurrence such as BIOCLIM and DOMAIN; "regression" methods (e.g. forms of generalized linear models); and "machine learning" methods such as maximum entropy (MAXENT). Ten machine learning techiniques used in SDM can be seen in. An incomplete list of models that have been used for niche modelling includes:
=== Profile techniques ===
BIOCLIM
DOMAIN
Ecological niche factor analysis (ENFA)
Mahalanobis distance
Isodar analysis
=== Regression-based techniques ===
Generalized linear model (GLM)
Generalized additive model (GAM)
Multivariate adaptive regression splines (MARS)
Maxlike
Favourability Function (FF)
=== Machine learning techniques ===
MAXENT
Artificial neural networks (ANN)
Genetic Algorithm for Rule Set Production (GARP)
Boosted regression trees (BRT)/gradient boosting machines (GBM)
Random forest (RF)
Support vector machines (SVM)
XGBoost (XGB)
Furthermore, ensemble models can be created from several model outputs to create a model that captures components of each. Often the mean or median value across several models is used as an ensemble. Similarly, consensus models are models that fall closest to some measure of central tendency of all models—consensus models can be individual model runs or ensembles of several models.
== Niche modelling software (correlative) ==
SPACES is an online Environmental niche modeling platform that allows users to design and run dozens of the most prominent methods in a high performance, multi-platform, browser-based environment.
MaxEnt is the most widely used method/software uses presence only data and performs well when there are few presence records available.
ModEco implements various methods.
DIVA-GIS has an easy to use (and good for educational use) implementation of BIOCLIM
The Biodiversity and Climate Change Virtual Laboratory (BCCVL) is a "one stop modelling shop" that simplifies the process of biodiversity and climate impact modelling. It connects the research community to Australia's national computational infrastructure by integrating a suite of tools in a coherent online environment. Users can access global climate and environmental datasets or upload their own data, perform data analysis across six different experiment types with a suite of 17 different methods, and easily visualize, interpret and evaluate the results of the models. Experiments types include: Species Distribution Model, Multispecies Distribution Model, Species Trait Model (currently under development), Climate Change Projection, Biodiverse Analysis and Ensemble Analysis. Example of BCCVL SDM outputs can be found here
Another example is Ecocrop, which is used to determine the suitability of a crop to a specific environment. This database system can also project crop yields and evaluate the impact of environmental factors such as climate change on plant growth and suitability.
Most niche modelling methods are available in the R packages 'dismo', 'biomod2' and 'mopa'..
Software developers may want to build on the openModeller project.
The Collaboratory for Adaptation to Climate Change adapt.nd.edu Archived 2012-08-06 at the Wayback Machine has implemented an online version of openModeller that allows users to design and run openModeller in a high-performance, browser-based environment to allow for multiple parallel experiments without the limitations of local processor power.
== See also ==
Biogeography
Ecosystem model
Quantum evolution
== References ==
== Further reading ==
Pearson, R.G. (2007). "Species' distribution modeling for conservation educators and practitioners" (PDF). Lessons in Conservation. 3: 54–89. S2CID 40254248. Archived from the original (PDF) on 2019-02-26.
Elith J.; Leathwick J.R. (2009). "Species distribution models: ecological explanation and prediction across space and time". Annual Review of Ecology, Evolution, and Systematics. 40: 677–697. doi:10.1146/annurev.ecolsys.110308.120159. S2CID 86460963.
Candela L.; Castelli D.; Coro G.; Pagano P.; Sinibaldi F. (2013). "Species distribution modeling in the cloud". Concurrency and Computation: Practice and Experience. 28 (4): 1056–1079. doi:10.1002/cpe.3030. S2CID 45203952. Archived from the original on May 30, 2020.
== External links ==
Climate Envelope Modeling Working Group - Online gathering place for scientists, practitioners, managers, and developers to discuss, support, and develop climate Environmental Niche Modeling tools and platforms
BioVeL Ecological Niche Modeling (ENM) - online tool with workflows to generate ecological niche models
EUBrazilOpenBio SpeciesLab Virtual Research Environment - online working environment to support the production of ecological niche modeling by (i) simplifying access to occurrence points and environmental parameters and (ii) offering a powerful version of openModeller benefitting from a distributed computing infrastructure;
openModeller - open source niche modelling library
Lifemapper 2.0 - video of presentation by Aimee Stewart, Kansas University, at O'Reilly Where 2.0 Conference 2008
AquaMaps - global predictive maps for marine species
Ecological Modelling - International Journal on Ecological Modelling and Systems Ecology | Wikipedia/Species_distribution_modelling |
An ecological network is a representation of the biotic interactions in an ecosystem, in which species (nodes) are connected by pairwise interactions (links). These interactions can be trophic or symbiotic. Ecological networks are used to describe and compare the structures of real ecosystems, while network models are used to investigate the effects of network structure on properties such as ecosystem stability.
== Properties ==
Historically, research into ecological networks developed from descriptions of trophic relationships in aquatic food webs; however, recent work has expanded to look at other food webs as well as webs of mutualists. Results of this work have identified several important properties of ecological networks.
Complexity (linkage density): the average number of links per species. Explaining the observed high levels of complexity in ecosystems has been one of the main challenges and motivations for ecological network analysis, since early theory predicted that complexity should lead to instability.
Connectance: the proportion of possible links between species that are realized (links/species2). In food webs, the level of connectance is related to the statistical distribution of the links per species. The distribution of links changes from (partial) power-law to exponential to uniform as the level of connectance increases. The observed values of connectance in empirical food webs appear to be constrained by the variability of the physical environment, by habitat type, which will reflect on an organism's diet breadth driven by optimal foraging behaviour. This ultimately links the structure of these ecological networks to the behaviour of individual organisms.
Degree distribution: the degree distribution of an ecological network is the cumulative distribution for the number of links each species has. The degree distributions of food webs have been found to display the same universal functional form. The degree distribution can be split into its two component parts, links to a species' prey (aka. in degree) and links to a species' predators (aka- out degree). Both the in degree and out degree distributions display their own universal functional forms. As there is a faster decay of the out-degree distribution than the in degree distribution we can expect that on average in a food web a species will have more in links than out links.
Clustering: the proportion of species that are directly linked to a focal species. A focal species in the middle of a cluster may be a keystone species, and its loss could have large effects on the network.
Compartmentalization: the division of the network into relatively independent sub-networks. Some ecological networks have been observed to be compartmentalized by body size and by spatial location. Evidence also exists which suggests that compartmentalization in food webs appears to result from patterns of species' diet contiguity and adaptive foraging
Nestedness: the degree to which species with few links have a sub-set of the links of other species, rather than a different set of links. In highly nested networks, guilds of species that share an ecological niche contain both generalists (species with many links) and specialists (species with few links, all shared with the generalists). In mutualistic networks, nestedness is often asymmetrical, with specialists of one guild linked to the generalists of the partner guild. The level of nestedness is determined not by species features but overall network depictors (e.g. network size and connectance) and can be predicted by a dynamic adaptive model with species rewiring to maximize individual fitness or the fitness of the whole community.
In-block nestedness: Also called compound structures, some ecological networks combine compartmentalization at large network scales with nestedness within compartments.
Network motif: Motifs are unique sub-graphs composed of n-nodes found embedded in a network. For instance there exist thirteen unique motif structures containing three species, some of these correspond to familiar interaction modules studied by population ecologists such as food chains, apparent competition, or intraguild predation. Studies investigating motif structures of ecological networks, by examining patterns of under/over representation of certain motifs compared to a random graph, have found that food webs have particular motif structures
Trophic coherence: The tendency of species to specialise on particular trophic levels leads to food webs displaying a significant degree of order in their trophic structure, known as trophic coherence, which in turn has important effects on properties such as stability and prevalence of cycles.
== Stability and Optimisation ==
The relationship between ecosystem complexity and stability is a major topic of interest in ecology. Use of ecological networks makes it possible to analyze the effects of the network properties described above on the stability of an ecosystem. Ecosystem complexity was once thought to reduce stability by enabling the effects of disturbances, such as species loss or species invasion, to spread and amplify through the network. However, other characteristics of network structure have been identified that reduce the spread of indirect effects and thus enhance ecosystem stability. The relationship between complexity and stability can even be inverted in food webs with sufficient trophic coherence, so that increases in biodiversity would make a community more stable rather than less.
Once ecological networks are described as transportation networks where the food flows along the predation links, one can extend the concept of allometric scaling to them. In doing so one could find that spanning trees are characterized by universal scaling relations, thereby suggesting that ecological network could be the product of an optimisation procedure.
Interaction strength may decrease with the number of links between species, damping the effects of any disturbance and cascading extinctions are less likely in compartmentalized networks, as effects of species losses are limited to the original compartment. Furthermore, as long as the most connected species are unlikely to go extinct, network persistence increases with connectance and nestedness. No consensus on the links between network nestedness and community stability in mutualistic species has however been reached among several investigations in recent years. Recent findings suggest that a trade-off between different types of stability may exist. The nested structure of mutual networks was shown to promote the capacity of species to persist under increasingly harsh circumstances. Most likely, because the nested structure of mutualistic networks helps species to indirectly support each other when circumstances are harsh. This indirect facilitation helps species to survive, but it also means that under harsh circumstances one species cannot survive without the support of the other. As circumstances become increasingly harsh, a tipping point may therefore be passed at which the populations of a large number of species may collapse simultaneously.
== Other applications ==
Additional applications of ecological networks include exploration of how the community context affects pairwise interactions. The community of species in an ecosystem is expected to affect both the ecological interaction and coevolution of pairs of species. Related, spatial applications are being developed for studying metapopulations, epidemiology, and the evolution of cooperation. In these cases, networks of habitat patches (metapopulations) or individuals (epidemiology, social behavior), make it possible to explore the effects of spatial heterogeneity.
== See also ==
Biological network
Consumer-resource systems
Food web
Pollination network
Recycling (ecological)
== Notes ==
== References ==
=== Specific ===
=== General === | Wikipedia/Ecological_network |
Resource selection functions (RSFs) are a class of functions that are used in spatial ecology to assess which habitat characteristics are important to a specific population or species of animal, by assessing a probability of that animal using a certain resource proportional to the availability of that resource in the environment.
== Modeling ==
Resource Selection Functions require two types of data: location information for the wildlife in question, and data on the resources available across the study area. Resources can include a broad range of environmental and geographical variables, including categorical variables such as land cover type, or continuous variables such as average rainfall over a given time period. A variety of methods are used for modeling RSFs, with logistic regression being commonly used.
RSFs can be fit to data where animal presence is known, but absence is not, such as for species where several individuals within a study area are fitted with a GPS collar, but some individuals may be present without collars.
When this is the case, buffers of various distances are generated around known presence points, with a number of available points generated within each buffer, which represent areas where the animal could have been, but it is unknown whether they actually were. These models can be fit using binomial generalized linear models or binomial generalized linear mixed models, with the resources, or environmental and geographic data, as explanatory variables.
== Scale ==
Resource selection functions can be modeled at a variety of spatial scales, depending on the species and the scientific question being studied. (insert one more sentence on scale)
Most RSFs address one of the following scales, which were defined by Douglas Johnson in 1980 and are still used today:
First order selection: The entire range of a species
Second order selection: The home range of an individual or group of animals
Third order selection: Resource or habitat usage within an individual's or group's home range
Fourth order selection: The procurement of specific resources, such as food, at specific sites
== References == | Wikipedia/Resource_selection_function |
Marxian class theory asserts that an individual's position within a class hierarchy is determined by their role in the production process, and argues that political and ideological consciousness is determined by class position. A class is those who share common economic interests, are conscious of those interests, and engage in collective action which advances those interests. Within Marxian class theory, the structure of the production process forms the basis of class construction.
To Marx, a class is a group with intrinsic tendencies and interests that differ from those of other groups within society, the basis of a fundamental antagonism between such groups. For example, it is in the laborer's best interest to maximize wages and benefits and in the capitalist's best interest to maximize profit at the expense of such, leading to a contradiction within the capitalist system, even if the laborers and capitalists themselves are unaware of the clash of interests.
Marxian class theory has been open to a range of alternate positions, most notably from scholars such as E. P. Thompson and Mario Tronti. Both Thompson and Tronti suggest class consciousness within the production process precedes the formation of productive relationships. In this sense, Marxian class theory often relates to discussion over pre-existing class struggles.
== Origins of Karl Marx's theory ==
Karl Marx's class theory derives from a range of philosophical schools of thought including left Hegelianism, Scottish Empiricism, and Anglo-French political-economics. Marx's view of class originated from a series of personal interests relating to social alienation and human struggle, whereby the formation of class structure relates to acute historical consciousness. Political-economics also contributed to Marx's theories, centering on the concept of "origin of income" where society is divided into three sub-groups: Rentiers, Capitalist, and Worker. This construction is based on David Ricardo's theory of capitalism. Marx strengthened this with a discussion over verifiable class relationships.
Marx sought to define class as embedded in productive relations rather than social status. His political and economic thought developed towards an interest in production as opposed to distribution, and this henceforth became a central theme in his concept of class.
== Class structure ==
Marx distinguishes one class from another on the basis of two criteria: ownership of the means of production and control of the labor power of others. From this, Marx states "Society as a whole is more and more splitting up into two great hostile camps, into two great classes directly facing each other":
I. Capitalists, or bourgeoisie, own the means of production and purchase the labor power of others
II. Workers, or proletariat, do not own any means of production or the ability to purchase the labor power of others. Rather, they sell their own labor power.
Class is thus determined by property relations, not by income or status. These factors are determined by distribution and consumption, which mirror the production and power relations of classes.
The Manifesto of the Communist Party describes two additional classes that “decay and finally disappear in the face of Modern Industry”:
III. A small, transitional class known as the petite bourgeoisie own sufficient means of production but do not purchase labor power. Marx's Communist Manifesto fails to properly define the petite bourgeoisie beyond “smaller capitalists” (Marx and Engels, 1848, 25).
IV. The “dangerous class”, or Lumpenproletariat, “the social scum, that passively rotting mass thrown off by the lowest layers of the old society.”
== Conflict as the nature of class relations ==
"The history of all hitherto existing society is the history of class struggles… Freeman and slave, patrician and plebeian, lord and serf, guild-master and journeyman, in a word, oppressor and oppressed, stood in constant opposition to one another, carried on an uninterrupted, now hidden, now open fight, a fight that each time ended, either in a revolutionary reconstruction of society at large, or in the common ruin of the contending classes.... The modern bourgeois society that has sprouted from the ruins of feudal society has not done away with class antagonisms. It has but established new classes, new conditions of oppression, new forms of struggle in place of the old ones. Our epoch, the epoch of the bourgeoisie, possesses, however, this distinctive feature: it has simplified class antagonisms. Society as a whole is more and more splitting up into two great hostile camps, into two great classes directly facing each other: Bourgeoisie and Proletariat.” – Communist Manifesto
Marx established conflict as the key driving force of history and the main determinant of social trajectories (Kingston). However, in order to understand the nature of “class conflict,” we must first understand that such conflict arises from a unified class interest, also known as class consciousness. Class consciousness is an aspect of Marxist theory, referring to the self-awareness of social classes, the capacity to act in its own rational interests, or measuring the extent to which an individual is conscious of the historical tasks their class (or class allegiance) sets for them.
Moreover, by definition, the objective interests of classes are fundamentally in opposition; consequently, these opposing interests and consciousnesses eventually lead to class conflict.
Marx first saw the development of class conflict confined to individual factories and capitalists. However, given the maturation of capitalism, the life conditions of bourgeoisie and proletariat began to grow more disparate. This increased polarization and homogenization within classes fostered an environment for individual struggles to become more generalized. When increasing class conflict is manifested at the societal level, class consciousness and common interests are also increased. Consequently, when class consciousness is augmented, policies are organized to ensure the duration of such interest for the ruling class. Here begins the use of the struggle for political power and classes become political forces.
Since the distribution of political power is determined by power over production, or power over capital, it is no surprise that the bourgeois class uses their wealth to legitimatize and protect their property and consequent social relations. Thus the ruling class is those who hold the economic power and make the decisions (Dahrendorf).
== Class structure of capitalism ==
In Marxist theory, the capitalist stage of production consists of two main classes: the bourgeoisie, the capitalists who own the means of production, and the much larger proletariat (or 'working class') who must sell their own labour power (See also: wage labour). This is the fundamental economic structure of work and property (See also: wage labour), a state of inequality that is normalised and reproduced through cultural ideology. Thus the proletariat, in itself, is forced into a subservient position by the power of capital, which has stripped the means of production from them. As the proletariat becomes conscious of its situation and power, organizes itself, and takes collective political action it becomes a class for itself which has the revolutionary potential to become the ruling class.
Max Weber critiqued historical materialism, positing that stratification is not based purely on economic inequalities but on other status and power differentials. Social class pertaining broadly to material wealth may be distinguished from status class based on honour, prestige, religious affiliation, and so on. The conditions of capitalism and its class system came together due to a variety of "elective affinities".
Marxists explain the history of "civilized" societies in terms of a war of classes between those who control production and those who produce the goods or services in society. In the Marxist view of capitalism, this is a conflict between capitalists (bourgeoisie) and wage-workers (the proletariat). For Marxists, class antagonism is rooted in the situation that control over social production necessarily entails control over the class which produces goods—in capitalism this is the exploitation of workers by the bourgeoisie.
Marx himself argued that it was the goal of the proletariat itself to displace the capitalist system with socialism, changing the social relationships underpinning the class system and then developing into a future communist society in which: "..the free development of each is the condition for the free development of all." (Communist Manifesto) This would mark the beginning of a classless society in which human needs rather than profit would be motive for production. In a society with democratic control and production for use, there would be no class, no state and no need for money.
For Marx, class has three primary facts:
Objective factors
A class shares a common relationship to the means of production. That is, all people in one class make their living in a common way in terms of ownership of the things that produce social goods. A class may own things, own land, own people, be owned, own nothing but their labor. A class will extract tax, produce agriculture, enslave and work others, be enslaved and work, or work for a wage.
Subjective factors
The members will necessarily have some perception of their similarity and common interest. Marx termed this Class consciousness. Class consciousness is not simply an awareness of one's own class interest (for instance, the maximisation of shareholder value; or, the maximization of the wage with the minimization of the working day), class consciousness also embodies deeply shared views of how society should be organized legally, culturally, socially and politically.
Reproduction of class relations
Class as a set of social relationships that is reproduced from one generation to the next.
The first criterion divides a society into the owners and non-owners of means of production. In capitalism, these are capitalist (bourgeoisie) and proletariat. Finer divisions can be made, however: the most important subgroup in capitalism being petite bourgeoisie (small bourgeoisie), people who possess their own means of production but utilize it primarily by working on it themselves rather than hiring others to work on it. They include self-employed artisans, small shopkeepers, and many professionals. Jon Elster has found mention in Marx of 15 classes from various historical periods.
Vladimir Lenin has defined classes as "large groups of people differing from each other by the place they occupy in a historically determined system of social production, by their relation (in most cases fixed and formulated in law) to the means of production, by their role in the social organization of labor, and, consequently, by the dimensions of the share of social wealth of which they dispose and the mode of acquiring it."
== Proletarianisation ==
The most important transformation of society for Marxists has been the massive and rapid growth of the proletariat over the last two hundred and fifty years. Starting with agricultural and domestic textile laborers in England and Flanders, more and more occupations only provide a living through wages or salaries. Private manufacturing, leading to self-employment, is no longer as viable as it was before the industrial revolution, because automation made manufacturing very cheap. Many people who once controlled their own labor-time were converted into proletarians through industrialization. Today groups which in the past subsisted on stipends or private wealth—like doctors, academics or lawyers—are now increasingly working as wage laborers. Marxists call this process proletarianization, and point to it as the major factor in the proletariat being the largest class in current societies in the rich countries of the "first world."
== Prediction of socialist revolution ==
Marx predicts revolution in capitalist society into socialist society because of eventual discontent. The socialization of labor, in the growth of large-scale production, capitalist interest groups and organizations, as well as in the enormous increase in the dimensions and power of finance capital provides the principal material foundation for the unavoidable arrival of socialism. The physical, intellectual and moral perpetrator of this transformation is the proletariat. The proletariat's struggle against the bourgeoisie inevitably becomes a political struggle with the goal of political conquest by the proletariat. With the domination of the proletariat, the socialization of production cannot help but lead to the means of production becoming the property of society. The direct consequences of this transformation are a drop in labor productivity, a shorter working day, and the replacement of small-scale unified production by collective and improved labor conditions.
Capitalism breaks for all time the ties between producer and owner, once held by the bond of class conflict. Now a new union will be formed based on the conscious application of science and the concentration of collective labor.
He also extended this redistribution to the structure of power in families. Marx imagined that with socialism women's status would increase, leading to the break-up of the patriarchal family.
"Modern industry, by assigning as it does, an important part in the socially organized process of production, outside the domestic sphere, to women, to young persons, and to children of both sexes, creates a new economic foundation for a higher form of the family and of the relations between the sexes… Moreover, it is obvious that the fact of the collective working group being composed of individuals of both sexes and all ages, must necessarily, under suitable conditions, become a source of human development; although in its spontaneously developed, brutal, capitalistic form, where the laborer exists for the process of production, and not the process of production for the laborer, that fact is a pestiferous source of corruption and slavery." (Capital, Vol. I, Chapter 13).
== Objective and subjective factors in class in Marxism ==
Marxism has a rather heavily defined dialectic between objective factors (i.e., material conditions, the social structure) and subjective factors (i.e. the conscious organization of class members). While most forms of Marxism analyses sees people's class based on objective factors (class structure), major Marxist trends have made greater use of subjective factors in understanding the history of the working class. E.P. Thompson's The Making of the English Working Class is a definitive example of this "subjective" Marxist trend. Thompson analyses the English working class as a group of people with shared material conditions coming to a positive self-consciousness of their social position. This feature of social class is commonly termed class consciousness in Marxism, a concept which became famous with Georg Lukács' History and Class Consciousness (1923). It is seen as the process of a "class in itself" moving in the direction of a "class for itself", a collective agent that changes history rather than simply being a victim of the historical process. In Lukács' words, the proletariat was the "subject–object of history", and the first class which could separate false consciousness (inherent to the bourgeois's consciousness), which reified economic laws as universal (whereas they are only a consequence of historic capitalism).
== Transnational capitalist class ==
Globalization theorists, such as William I. Robinson, Leslie Sklair, Kees Van Der Pijl, and Jerry Harris, argue that today a transnational capitalist class has emerged.
== See also ==
Capitalist mode of production
Economic inequality
Exploitation (Marxism)
Mode of production
Relations of production
Superstructure
Surplus labor
Surplus value
== References ==
Blackledge, Paul (2011). "Why workers can change the world". Socialist Review 364. London. Archived from the original on 10 December 2011.
Dahrendorf, Ralf. Class and Class Conflict in Industrial Society. Stanford, Calif.: Stanford University Press, 1959.
David McLellan, ed., "Capital." The Marx-Engels Reader, 1977. Oxford University Press: Great Britain.
Kingston, Paul W. The Classless Society. Stanford, Calif.: Stanford University Press, 2000.
Marx & Engels. The Communist Manifesto. New York: Penguin group, 1998.
Youth for International Socialism- NewYouth.com | Wikipedia/Marxian_class_theory |
A fishery is an area with an associated fish or aquatic population which is harvested for its commercial or recreational value. Fisheries can be wild or farmed. Population dynamics describes the ways in which a given population grows and shrinks over time, as controlled by birth, death, and migration. It is the basis for understanding changing fishery patterns and issues such as habitat destruction, predation and optimal harvesting rates. The population dynamics of fisheries is used by fisheries scientists to determine sustainable yields.
The basic accounting relation for population dynamics is the BIDE (Birth, Immigration, Death, Emigration) model, shown as:
N1 = N0 + B − D + I − E
where N1 is the number of individuals at time 1, N0 is the number of individuals at time 0, B is the number of individuals born, D the number that died, I the number that immigrated, and E the number that emigrated between time 0 and time 1. While immigration and emigration can be present in wild fisheries, they are usually not measured.
A fishery population is affected by three dynamic rate functions:
Birth rate or recruitment. Recruitment means reaching a certain size or reproductive stage. With fisheries, recruitment usually refers to the age a fish can be caught and counted in nets.
Growth rate. This measures the growth of individuals in size and length. This is important in fisheries where the population is often measured in terms of biomass.
Mortality. This includes harvest mortality and natural mortality. Natural mortality includes non-human predation, disease and old age.
If these rates are measured over different time intervals, the harvestable surplus of a fishery can be determined. The harvestable surplus is the number of individuals that can be harvested from the population without affecting long term stability (average population size). The harvest within the harvestable surplus is called compensatory mortality, where the harvest deaths are substituting for the deaths that would otherwise occur naturally. Harvest beyond that is additive mortality, harvest in addition to all the animals that would have died naturally.
Care is needed when applying population dynamics to real world fisheries. Over-simplistic modelling of fisheries has resulted in the collapse of key stocks.
== History ==
The first principle of population dynamics is widely regarded as the exponential law of Malthus, as modelled by the Malthusian growth model. The early period was dominated by demographic studies such as the work of Benjamin Gompertz and Pierre François Verhulst in the early 19th century, who refined and adjusted the Malthusian demographic model. A more general model formulation was proposed by F.J. Richards in 1959, by which the models of Gompertz, Verhulst and also Ludwig von Bertalanffy are covered as special cases of the general formulation.
== Population size ==
The population size (usually denoted by N) is the number of individual organisms in a population.
The effective population size (Ne) was defined by Sewall Wright, who wrote two landmark papers on it (Wright 1931, 1938). He defined it as "the number of breeding individuals in an idealized population that would show the same amount of dispersion of allele frequencies under random genetic drift or the same amount of inbreeding as the population under consideration". It is a basic parameter in many models in population genetics. Ne is usually less than N (the absolute population size).
Small population size results in increased genetic drift. Population bottlenecks are when population size reduces for a short period of time.
Overpopulation may indicate any case in which the population of any species of animal may exceed the carrying capacity of its ecological niche.
== Virtual population analysis ==
Virtual population analysis (VPA) is a cohort modeling technique commonly used in fisheries science for reconstructing historical fish numbers at age using information on death of individuals each year. This death is usually partitioned into catch by fisheries and natural mortality. VPA is virtual in the sense that the population size is not observed or measured directly but is inferred or back-calculated to have been a certain size in the past in order to support the observed fish catches and an assumed death rate owing to non-fishery related causes.
== Minimum viable population ==
The minimum viable population (MVP) is a lower bound on the population of a species, such that it can survive in the wild. More specifically MVP is the smallest possible size at which a biological population can exist without facing extinction from natural disasters or demographic, environmental, or genetic stochasticity. The term "population" refers to the population of a species in the wild.
As a reference standard, MVP is usually given with a population survival probability of somewhere between ninety and ninety-five percent and calculated for between one hundred and one thousand years into the future.
The MVP can be calculated using computer simulations known as population viability analyses (PVA), where populations are modelled and future population dynamics are projected.
== Maximum sustainable yield ==
In population ecology and economics, the maximum sustainable yield or MSY is, theoretically, the largest catch that can be taken from a fishery stock over an indefinite period. Under the assumption of logistic growth, the MSY will be exactly at half the carrying capacity of a species, as this is the stage at when population growth is highest. The maximum sustainable yield is usually higher than the optimum sustainable yield.
This logistic model of growth is produced by a population introduced to a new habitat or with very poor numbers going through a lag phase of slow growth at first. Once it reaches a foothold population it will go through a rapid growth rate that will start to level off once the species approaches carrying capacity. The idea of maximum sustained yield is to decrease population density to the point of highest growth rate possible. This changes the number of the population, but the new number can be maintained indefinitely, ideally.
MSY is extensively used for fisheries management. Unlike the logistic (Schaefer) model, MSY in most modern fisheries models occurs at around 30-40% of the unexploited population size. This fraction differs among populations depending on the life history of the species and the age-specific selectivity of the fishing method.
However, the approach has been widely criticized as ignoring several key factors involved in fisheries management and has led to the devastating collapse of many fisheries. As a simple calculation, it ignores the size and age of the animal being taken, its reproductive status, and it focuses solely on the species in question, ignoring the damage to the ecosystem caused by the designated level of exploitation and the issue of bycatch. Among conservation biologists it is widely regarded as dangerous and misused.
== Recruitment ==
Recruitment is the number of new young fish that enter a population in a given year. The size of fish populations can fluctuate by orders of magnitude over time, and five to 10-fold variations in abundance are usual. This variability applies across time spans ranging from a year to hundreds of years. Year to year fluctuations in the abundance of short lived forage fish can be nearly as great as the fluctuations that occur over decades or centuries. This suggests that fluctuations in reproductive and recruitment success are prime factors behind fluctuations in abundance. Annual fluctuations often seem random, and recruitment success often has a poor relationship to adult stock levels and fishing effort. This makes prediction difficult.
The recruitment problem is the problem of predicting the number of fish larvae in one season that will survive and become juvenile fish in the next season. It has been called "the central problem of fish population dynamics" and “the major problem in fisheries science". Fish produce huge volumes of larvae, but the volumes are very variable and mortality is high. This makes good predictions difficult.
According to Daniel Pauly, the definitive study was made in 1999 by Ransom Myers. Myers solved the problem "by assembling a large base of stock data and developing a complex mathematical model to sort it out. Out of that came the conclusion that a female in general produced three to five recruits per year for most fish.”
== Fishing effort ==
Fishing effort is a measure of the anthropogenic work input used to catch fish. A good measure of the fishing effort will be approximately proportional to the amount of fish captured. Different measures are appropriate for different kinds of fisheries. For example, the fishing effort exerted by a fishing fleet in a trawl fishery might be measured by summing the products of the engine power for each boat and time it spent at sea (KW × days). For a gill-net fishery the effort might be measured by summing the products of the length of each set net and the time it was set in the water (Km × soak time). In fisheries where boats spend a lot of time looking for fish, a measure based on search time may be used.
== Overfishing ==
The notion of overfishing hinges on what is meant by an acceptable level of fishing.
A current operational model used by some fisheries for predicting acceptable levels is the Harvest Control Rule (HCR). This formalizes and summarizes a management strategy which can actively adapt to subsequent feedback. The HCR is a variable over which the management has some direct control and describes how the harvest is intended to be controlled by management in relation to the state of some indicator of stock status. For example, a harvest control rule can describe the various values of fishing mortality which will be aimed at for various values of the stock abundance. Constant catch and constant fishing mortality are two types of simple harvest control rules.
Biological overfishing occurs when fishing mortality has reached a level where the stock biomass has negative marginal growth (slowing down biomass growth), as indicated by the red area in the figure. Fish are being taken out of the water so quickly that the replenishment of stock by breeding slows down. If the replenishment continues to slow down for long enough, replenishment will go into reverse and the population will decrease.
Economic or bioeconomic overfishing additionally considers the cost of fishing and defines overfishing as a situation of negative marginal growth of resource rent. Fish are being taken out of the water so quickly that the growth in the profitability of fishing slows down. If this continues for long enough, profitability will decrease.
== Metapopulation ==
A metapopulation is a group of spatially separated populations of the same species which interact at some level. The term was coined by Richard Levins in 1969. The idea has been most broadly applied to species in naturally or artificially fragmented habitats. In Levins' own words, it consists of "a population of populations".
A metapopulation generally consists of several distinct populations together with areas of suitable habitat which are currently unoccupied. Each population cycles in relative independence of the other populations and eventually goes extinct as a consequence of demographic stochasticity (fluctuations in population size due to random demographic events); the smaller the population, the more prone it is to extinction.
Although individual populations have finite life-spans, the population as a whole is often stable because immigrants from one population (which may, for example, be experiencing a population boom) are likely to re-colonize habitat which has been left open by the extinction of another population. They may also emigrate to a small population and rescue that population from extinction (called the rescue effect).
== Age class structure ==
Age can be determined by counting growth rings in fish scales, otoliths, cross-sections of fin spines for species with thick spines such as triggerfish, or teeth for a few species. Each method has its merits and drawbacks. Fish scales are easiest to obtain, but may be unreliable if scales have fallen off of the fish and new ones grown in their places. Fin spines may be unreliable for the same reason, and most fish do not have spines of sufficient thickness for clear rings to be visible. Otoliths will have stayed with the fish throughout its life history, but obtaining them requires killing the fish. Also, otoliths often require more preparation before ageing can occur.
An age class structure with gaps in it, for instance a regular bell curve for the population of 1-5 year-old fish, excepting a very low population for the 3-year-olds, implies a bad spawning year 3 years ago in that species.
Often fish in younger age class structures have very low numbers because they were small enough to slip through the sampling nets, and may in fact have a very healthy population.
== Population cycle ==
A population cycle occurs where populations rise and fall over a predictable period of time. There are some species where population numbers have reasonably predictable patterns of change although the full reasons for population cycles is one of the major unsolved ecological problems. There are a number of factors which influence population change such as availability of food, predators, diseases and climate.
== Trophic cascades ==
Trophic cascades occur when predators in a food chain suppress the abundance of their prey, thereby releasing the next lower trophic level from predation (or herbivory if the intermediate trophic level is an herbivore). For example, if the abundance of large piscivorous fish is increased in a lake, the abundance of their prey, zooplanktivorous fish, should decrease, large zooplankton abundance should increase, and phytoplankton biomass should decrease. This theory has stimulated new research in many areas of ecology. Trophic cascades may also be important for understanding the effects of removing top predators from food webs, as humans have done in many places through hunting and fishing activities.
Classic examples
In lakes, piscivorous fish can dramatically reduce populations of zooplanktivorous fish, zooplanktivorous fish can dramatically alter freshwater zooplankton communities, and zooplankton grazing can in turn have large impacts on phytoplankton communities. Removal of piscivorous fish can change lake water from clear to green by allowing phytoplankton to flourish.
In the Eel River, in Northern California, fish (steelhead and roach) consume fish larvae and predatory insects. These smaller predators prey on midge larvae, which feed on algae. Removal of the larger fish increases the abundance of algae.
In Pacific kelp forests, sea otters feed on sea urchins. In areas where sea otters have been hunted to extinction, sea urchins increase in abundance and decimate kelp
A recent theory, the mesopredator release hypothesis, states that the decline of top predators in an ecosystem results in increased populations of medium-sized predators (mesopredators).
== Basic models ==
The classic population equilibrium model is Verhulst's 1838 growth model:
d
N
d
t
=
r
N
(
1
−
N
K
)
{\displaystyle {\frac {dN}{dt}}=rN\left(1-{\frac {N}{K}}\right)}
where N(t) represents number of individuals at time t, r the intrinsic growth rate and K is the carrying capacity, or the maximum number of individuals that the environment can support.
The individual growth model, published by von Bertalanffy in 1934, can be used to model the rate at which fish grow. It exists in a number of versions, but in its simplest form it is expressed as a differential equation of length (L) over time (t):
L
′
(
t
)
=
r
B
(
L
∞
−
L
(
t
)
)
{\displaystyle L'(t)=r_{B}\left(L_{\infty }-L(t)\right)}
where rB is the von Bertalanffy growth rate and L∞ the ultimate length of the individual.
Schaefer published a fishery equilibrium model based on the Verhulst model with an assumption of a bi-linear catch equation, often referred to as the Schaefer short-term catch equation:
H
(
E
,
X
)
=
q
E
X
{\displaystyle H(E,X)=qEX\!}
where the variables are; H, referring to catch (harvest) over a given period of time (e.g. a year); E, the fishing effort over the given period; X, the fish stock biomass at the beginning of the period (or the average biomass), and the parameter q represents the catchability of the stock. Assuming the catch to equal the net natural growth in the population over the same period (
X
˙
=
0
{\displaystyle {\dot {X}}=0}
), the equilibrium catch is a function of the long term fishing effort E:
H
(
E
)
=
q
K
E
(
1
−
q
E
r
)
{\displaystyle H(E)=qKE\left(1-{\frac {qE}{r}}\right)}
r and K being biological parameters representing intrinsic growth rate and natural equilibrium biomass respectively.
The Baranov catch equation of 1918 is perhaps the most used equation in fisheries modelling. It gives the catch in numbers as a function of initial population abundance N0 and fishing F and natural mortality M:
C
=
F
F
+
M
(
1
−
e
−
(
F
+
M
)
T
)
N
0
{\displaystyle C={\frac {F}{F+M}}\left(1-e^{-(F+M)T}\right)N_{0}}
where T is the time period and is usually left out (i.e. T=1 is assumed). The equation assumes that fishing and natural mortality occur simultaneously and thus "compete" with each other. The first term expresses the proportion of deaths that are caused by fishing, and the second and third term the total number of deaths.
The Ricker model is a classic discrete population model which gives the expected number (or density) of individuals Nt + 1 in generation t + 1 as a function of the number of individuals in the previous generation,
N
t
+
1
=
N
t
e
r
(
1
−
N
t
/
k
)
{\displaystyle N_{t+1}=N_{t}e^{r(1-{N_{t}}/{k})}}
Here r is interpreted as an intrinsic growth rate and k as the carrying capacity of the environment. The Ricker model was introduced in the context of the fisheries by Ricker (1954).
The Beverton–Holt model, introduced in the context of fisheries in 1957, is a classic discrete-time population model which gives the expected number n t+1 (or density) of individuals in generation t + 1 as a function of the number of individuals in the previous generation,
n
t
+
1
=
R
0
n
t
1
+
n
t
/
M
.
{\displaystyle n_{t+1}={\frac {R_{0}n_{t}}{1+n_{t}/M}}.}
Here R0 is interpreted as the proliferation rate per generation and K = (R0 − 1) M is the carrying capacity of the environment.
== Predator–prey equations ==
The classic predator–prey equations are a pair of first order, non-linear, differential equations used to describe the dynamics of biological systems in which two species interact, one a predator and one its prey. They were proposed independently by Alfred J. Lotka in 1925 and Vito Volterra in 1926.
An extension to these are the competitive Lotka–Volterra equations, which provide a simple model of the population dynamics of species competing for some common resource.
In the 1930s Alexander Nicholson and Victor Bailey developed a model to describe the population dynamics of a coupled predator–prey system. The model assumes that predators search for prey at random, and that both predators and prey are assumed to be distributed in a non-contiguous ("clumped") fashion in the environment.
In the late 1980s, a credible, simple alternative to the Lotka–Volterra predator-prey model (and its common prey dependent generalizations) emerged, the ratio dependent or Arditi–Ginzburg model. The two are the extremes of the spectrum of predator interference models. According to the authors of the alternative view, the data show that true interactions in nature are so far from the Lotka–Volterra extreme on the interference spectrum that the model can simply be discounted as wrong. They are much closer to the ratio dependent extreme, so if a simple model is needed one can use the Arditi-Ginzburg model as the first approximation.
== See also ==
== References ==
== Further reading ==
Berryman, Alan (2002) Population Cycles. Oxford University Press US. ISBN 0-19-514098-2
de Vries, Gerda; Hillen, Thomas; Lewis, Mark; Schonfisch, Birgitt and Muller, Johannes (2006) A Course in Mathematical Biology SIAM. ISBN 978-0-89871-612-2
Haddon, Malcolm (2001) Modelling and quantitative methods in fisheries Chapman & Hall. ISBN 978-1-58488-177-3
Hilborn, Ray and Walters, Carl J (1992) Quantitative Fisheries Stock Assessment Springer. ISBN 978-0-412-02271-5
McCallum, Hamish (2000) Population Parameters Blackwell Publishing. ISBN 978-0-86542-740-2
Prevost E and Chaput G (2001) Stock, recruitment and reference points Institute National de la Recherche Agronomique. ISBN 2-7380-0962-X.
Plagányi, Éva, Models for an ecosystem approach to fisheries. FAO Fisheries Technical Paper. No. 477. Rome, FAO. 2007. 108p [1]
Quinn, Terrance J. II and Richard B. Deriso (1999) Quantitative Fish Dynamics.Oxford University Press ISBN 0-19-507631-1
Sparre, Per and Hart, Paul J B (2002) Handbook of Fish Biology and Fisheries, Chapter13: Choosing the best model for fisheries assessment. Blackwell Publishing. ISBN 0-632-06482-X
Turchin, P. 2003. Complex Population Dynamics: a Theoretical/Empirical Synthesis. Princeton, NJ: Princeton University Press. | Wikipedia/Population_dynamics_of_fisheries |
The metabolic theory of ecology (MTE) is the ecological component of the more general Metabolic Scaling Theory and Kleiber's law. It posits that the metabolic rate of organisms is the fundamental biological rate that governs most observed patterns in ecology. MTE is part of a larger set of theory known as metabolic scaling theory that attempts to provide a unified theory for the importance of metabolism in driving pattern and process in biology from the level of cells all the way to the biosphere.
MTE is based on an interpretation of the relationships between body size, body temperature, and metabolic rate across all organisms. Small-bodied organisms tend to have higher mass-specific metabolic rates than larger-bodied organisms. Furthermore, organisms that operate at warm temperatures through endothermy or by living in warm environments tend towards higher metabolic rates than organisms that operate at colder temperatures. This pattern is consistent from the unicellular level up to the level of the largest animals and plants on the planet.
In MTE, this relationship is considered to be the primary constraint that influences biological processes (via their rates and times) at all levels of organization (from individual up to ecosystem level). MTE is a macroecological theory that aims to be universal in scope and application.
== Fundamental concepts in MTE ==
=== Metabolism ===
Metabolic pathways consist of complex networks, which are responsible for the processing of both energy and material. The metabolic rate of a heterotroph is defined as the rate of respiration in which energy is obtained by oxidation of a carbon compound. The rate of photosynthesis on the other hand, indicates the metabolic rate of an autotroph. According to MTE, both body size and temperature affect the metabolic rate of an organism. Metabolic rate scales as 3/4 power of body size, and its relationship with temperature is described by the Van't Hoff-Arrhenius equation over the range of 0 to 40 °C.
=== Stoichiometry ===
From the ecological perspective, stoichiometry is concerned with the proportion of elements in both living organisms and their environment. In order to survive and maintain metabolism, an organism must be able to obtain crucial elements and excrete waste products. As a result, the elemental composition of an organism would be different from the exterior environment. Through metabolism, body size can affect stoichiometry. For example, small organism tend to store most of their phosphorus in rRNA due to their high metabolic rate, whereas large organisms mostly invest this element inside the skeletal structure. Thus, concentration of elements to some extent can limit the rate of biological processes. Inside an ecosystem, the rate of flux and turn over of elements by inhabitants, combined with the influence of abiotic factors, determine the concentration of elements.
== Theoretical background ==
Metabolic rate scales with the mass of an organism of a given species according to Kleiber's law where B is whole organism metabolic rate (in watts or other unit of power), M is organism mass (in kg), and Bo is a mass-independent normalization constant (given in a unit of power divided by a unit of mass. In this case, watts per kilogram):
B
=
B
o
M
3
/
4
{\displaystyle B=B_{o}M^{3/4}\,}
At increased temperatures, chemical reactions proceed faster. This relationship is described by the Boltzmann factor, where E is activation energy in electronvolts or joules, T is absolute temperature in kelvins, and k is the Boltzmann constant in eV/K or J/K:
e
−
E
k
T
{\displaystyle e^{-{\frac {E}{k\,T}}}}
While Bo in the previous equation is mass-independent, it is not explicitly independent of temperature. To explain the relationship between body mass and temperature, building on earlier work showing that the effects of both body mass and temperature could be combined multiplicatively in a single equation, the two equations above can be combined to produce the primary equation of the MTE, where bo is a normalization constant that is independent of body size or temperature:
B
=
b
o
M
3
/
4
e
−
E
k
T
{\displaystyle B=b_{o}M^{3/4}e^{-{\frac {E}{k\,T}}}}
According to this relationship, metabolic rate is a function of an organism's body mass and body temperature. By this equation, large organisms have higher metabolic rates (in watts) than small organisms, and organisms at high body temperatures have higher metabolic rates than those that exist at low body temperatures. However, specific metabolic rate (SMR, in watts/kg) is given by
S
M
R
=
(
B
/
M
)
=
b
o
M
−
1
/
4
e
−
E
k
T
{\displaystyle SMR=(B/M)=b_{o}M^{-1/4}e^{-{\frac {E}{k\,T}}}}
Hence SMR for large organisms are lower than small organisms.
== Past debate over mechanisms and the allometric exponent ==
Researchers have debated two main aspects of this theory, the pattern and the mechanism. Past debated have focused on the question whether metabolic rate scales to the power of 3⁄4 or 2⁄3w, or whether either of these can even be considered a universal exponent. In addition to debates concerning the exponent, some researchers also disagree about the underlying mechanisms generating the scaling exponent. Various authors have proposed at least eight different types of mechanisms that predict an allometric scaling exponent of either 2⁄3 or 3⁄4. The majority view is that while the 3⁄4 exponent is indeed the mean observed exponent within and across taxa, there is intra- and interspecific variability in the exponent that can include shallower exponents such as2⁄3. Past debates on the exact value of the exponent are settled in part because the observed variability in the metabolic scaling exponent is consistent with a 'relaxed' version of metabolic scaling theory where additional selective pressures lead to a constrained set of variation around the predicted optimal 3⁄4 exponent.
Much of past debate have focused on two particular types of mechanisms. One of these assumes energy or resource transport across the external surface area of three-dimensional organisms is the key factor driving the relationship between metabolic rate and body size. The surface area in question may be skin, lungs, intestines, or, in the case of unicellular organisms, cell membranes. In general, the surface area (SA) of a three dimensional object scales with its volume (V) as SA = cV2⁄3, where c is a proportionality constant. The Dynamic Energy Budget model predicts exponents that vary between 2⁄3 – 1, depending on the organism's developmental stage, basic body plan and resource density. DEB is an alternative to metabolic scaling theory, developed before the MTE. DEB also provides a basis for population, community and ecosystem level processes to be studied based on energetics of the constituent organisms. In this theory, the biomass of the organism is separated into structure (what is built during growth) and reserve (a pool of polymers generated by assimilation). DEB is based on the first principles dictated by the kinetics and thermodynamics of energy and material fluxes, has a similar number of parameters per process as MTE, and the parameters have been estimated for over 3000 animal species "Add my Pet". Retrieved 23 August 2022. While some of these alternative models make several testable predictions, others are less comprehensive and of these proposed models only DEB can make as many predictions with a minimal set of assumptions as metabolic scaling theory.
In contrast, the arguments for a 3⁄4 scaling factor are based on resource transport network models, where the limiting resources are distributed via some optimized network to all resource consuming cells or organelles. These models are based on the assumption that metabolism is proportional to the rate at which an organism's distribution networks (such as circulatory systems in animals or xylem and phloem in plants) deliver nutrients and energy to body tissues. Larger organisms are necessarily less efficient because more resource is in transport at any one time than in smaller organisms: size of the organism and length of the network imposes an inefficiency due to size. It therefore takes somewhat longer for large organisms to distribute nutrients throughout the body and thus they have a slower mass-specific metabolic rate. An organism that is twice as large cannot metabolize twice the energy—it simply has to run more slowly because more energy and resources are wasted being in transport, rather than being processed. Nonetheless, natural selection appears to have minimized this inefficiency by favoring resource transport networks that maximize rate of delivery of resources to the end points such as cells and organelles. This selection to maximize metabolic rate and energy dissipation results in the allometric exponent that tends to D/(D+1), where D is the primary dimension of the system. A three dimensional system, such as an individual, tends to scale to the 3/4 power, whereas a two dimensional network, such as a river network in a landscape, tends to scale to the 2/3 power.
Despite past debates over the value of the exponent, the implications of metabolic scaling theory and the extensions of the theory to ecology (metabolic theory of ecology) the theory might remain true regardless of its precise numerical value.
== Implications of the theory ==
The metabolic theory of ecology's main implication is that metabolic rate, and the influence of body size and temperature on metabolic rate, provide the fundamental constraints by which ecological processes are governed. If this holds true from the level of the individual up to ecosystem level processes, then life history attributes, population dynamics, and ecosystem processes could be explained by the relationship between metabolic rate, body size, and body temperature. While different underlying mechanisms make somewhat different predictions, the following provides an example of some of the implications of the metabolism of individuals.
=== Organism level ===
Small animals tend to grow fast, breed early, and die young. According to MTE, these patterns in life history traits are constrained by metabolism. An organism's metabolic rate determines its rate of food consumption, which in turn determines its rate of growth. This increased growth rate produces trade-offs that accelerate senescence. For example, metabolic processes produce free radicals as a by-product of energy production. These in turn cause damage at the cellular level, which promotes senescence and ultimately death. Selection favors organisms which best propagate given these constraints. As a result, smaller, shorter lived organisms tend to reproduce earlier in their life histories.
=== Population and community level ===
MTE has profound implications for the interpretation of population growth and community diversity. Classically, species are thought of as being either r selected (where populations tend to grow exponentially, and are ultimately limited by extrinsic factors) or K selected (where population size is limited by density-dependence and carrying capacity). MTE explains this diversity of reproductive strategies as a consequence of the metabolic constraints of organisms. Small organisms and organisms that exist at high body temperatures tend to be r selected, which fits with the prediction that r selection is a consequence of metabolic rate. Conversely, larger and cooler bodied animals tend to be K selected. The relationship between body size and rate of population growth has been demonstrated empirically, and in fact has been shown to scale to M−1/4 across taxonomic groups. The optimal population growth rate for a species is therefore thought to be determined by the allometric constraints outlined by the MTE, rather than strictly as a life history trait that is selected for based on environmental conditions.
Regarding density, MTE predicts carrying capacity of populations to scale as M-3/4, and to exponentially decrease with increasing temperature. The fact that larger organisms reach carrying capacity sooner than smaller one is intuitive, however, temperature can also decrease carrying capacity due to the fact that in warmer environments, higher metabolic rate of organisms demands a higher rate of supply. Empirical evidence in terrestrial plants, also suggests that density scales as -3/4 power of the body size.
Observed patterns of diversity can be similarly explained by MTE. It has long been observed that there are more small species than large species. In addition, there are more species in the tropics than at higher latitudes. Classically, the latitudinal gradient in species diversity has been explained by factors such as higher productivity or reduced seasonality. In contrast, MTE explains this pattern as being driven by the kinetic constraints imposed by temperature on metabolism. The rate of molecular evolution scales with metabolic rate, such that organisms with higher metabolic rates show a higher rate of change at the molecular level. If a higher rate of molecular evolution causes increased speciation rates, then adaptation and ultimately speciation may occur more quickly in warm environments and in small bodied species, ultimately explaining observed patterns of diversity across body size and latitude.
MTE's ability to explain patterns of diversity remains controversial. For example, researchers analyzed patterns of diversity of New World coral snakes to see whether the geographical distribution of species fit within the predictions of MTE (i.e. more species in warmer areas). They found that the observed pattern of diversity could not be explained by temperature alone, and that other spatial factors such as primary productivity, topographic heterogeneity, and habitat factors better predicted the observed pattern. Extensions of metabolic theory to diversity that include eco-evolutionary theory show that an elaborated metabolic theory can account for differences in diversity gradients by including feedbacks between ecological interactions (size-dependent competition and predation) and evolutionary rates (speciation and extinction)
=== Ecosystem processes ===
At the ecosystem level, MTE explains the relationship between temperature and production of total biomass. The average production to biomass ratio of organisms is higher in small organisms than large ones. This relationship is further regulated by temperature, and the rate of production increases with temperature. As production consistently scales with body mass, MTE provides a framework to assess the relative importance of organismal size, temperature, functional traits, soil and climate on variation in rates of production within and across ecosystems. Metabolic theory shows that variation in ecosystem production is characterized by a common scaling relationship, suggesting that global change models can incorporate the mechanisms governing this relationship to improve predictions of future ecosystem function.
== See also ==
Allometry
Constructal theory
Dynamic energy budget theory
Ecology
Evolutionary physiology
Occupancy-abundance relationship
== References == | Wikipedia/Metabolic_theory_of_ecology |
The Goodwin model, sometimes called Goodwin's class struggle model, is a model of endogenous economic fluctuations first proposed by the American economist Richard M. Goodwin in 1967. It combines aspects of the Harrod–Domar growth model with the Phillips curve to generate endogenous cycles in economic activity (output, unemployment and wages) unlike most modern macroeconomic models in which movements in economic aggregates are driven by exogenously assumed shocks. Since Goodwin's publication in 1967, the model has been extended and applied in various ways.
== Model ==
The model is derived from the following assumptions:
there is steady growth of labour productivity (e.g. by technological improvement);
there is steady growth of the labour force (e.g. by births);
there are only two factors of production: labour and capital;
workers completely consume their wages, and capitalists completely invest their profits;
the capital-output ratio is constant (i.e. a fixed amount of output can always be turned into the same amount of capital);
real wages change according to a linearized Phillips curve, where wages rise when close to full employment.
The model uses the variables
q is output
k is (homogeneous) capital
w is the wage rate
a is labour productivity
n is the labour force
which are all functions of time (although the time subscripts have been suppressed for convenience) and the constants
α is the rate of growth of labour productivity
β is the rate of growth of the labour force
γ is used to define the real wage change curve
ρ is also used to define the real wage change curve
σ is the capital-output ratio.
A number of derived quantities are helpful to define the model.
The amount of employed labour is given by
l
=
q
a
{\displaystyle l={\frac {q}{a}}}
,
the employment ratio is given by
v
=
l
n
{\displaystyle v={\frac {l}{n}}}
,
the workers' share in the output is given by
u
=
w
l
q
=
w
a
{\displaystyle u={\frac {wl}{q}}={\frac {w}{a}}}
,
and the share of the capitalists in the output (
s
{\displaystyle s}
for surplus) is given by
s
=
1
−
u
{\displaystyle s=1-u}
.
The model is then defined by a set of differential equations.
Firstly, the change in labour productivity is defined by
a
˙
a
=
α
{\displaystyle {\frac {\dot {a}}{a}}=\alpha }
,
that is, steady growth, with
a
t
=
a
0
e
α
t
{\displaystyle a_{t}=a_{0}e^{\alpha t}}
.
(Note that
x
˙
{\displaystyle {\dot {x}}}
is the derivative over time
d
x
/
d
t
{\displaystyle {dx}/{dt}}
.)
The labour force changes according to
n
˙
n
=
β
{\displaystyle {\frac {\dot {n}}{n}}=\beta }
,
again, steady growth, with
n
t
=
n
0
e
β
t
{\displaystyle n_{t}=n_{0}e^{\beta t}}
.
Real wages change according to
w
˙
w
=
−
γ
+
ρ
v
{\displaystyle {\frac {\dot {w}}{w}}=-\gamma +\rho v}
,
that is, the real wage change curve is modelled as linear.
Note that to correctly model the assumptions,
γ
{\displaystyle \gamma }
and
ρ
{\displaystyle \rho }
must be picked to ensure that real wages increase when
v
{\displaystyle v}
is near 1.
In other words, if the labor market is 'tight' (employment is already high) there is upward pressure on wages and vice versa in a 'lax' labor market.
Capital changes according to
k
˙
=
q
s
{\displaystyle {\dot {k}}=qs}
,
as the surplus is assumed to be completely invested by the capitalist.
Lastly, output changes according to
q
˙
q
=
s
σ
{\displaystyle {\frac {\dot {q}}{q}}={\frac {s}{\sigma }}}
,
that is, in proportion to the surplus invested.
Note that
q
˙
q
=
k
˙
k
=
1
−
u
σ
{\displaystyle {\frac {\dot {q}}{q}}={\frac {\dot {k}}{k}}={\frac {1-u}{\sigma }}}
by the assumption that k and q grow at the same rate by assumption of full utilization of capital and constant returns to scale.
=== Solution ===
The defining equations can be solved for
u
˙
{\displaystyle {\dot {u}}}
and
v
˙
{\displaystyle {\dot {v}}}
,
which gives the two differential equations
v
˙
=
v
(
−
1
σ
u
+
1
σ
−
α
−
β
)
{\displaystyle {\dot {v}}=v(-{\frac {1}{\sigma }}u+{\frac {1}{\sigma }}-\alpha -\beta )}
u
˙
=
u
(
ρ
v
−
γ
−
α
)
{\displaystyle {\dot {u}}=u(\rho v-\gamma -\alpha )}
.
These are the key equations of the model and in fact are the Lotka–Volterra equations, which are used in biology to model predator-prey interaction.
These equations have two fixed points. The first is when
u
=
0
{\displaystyle u=0}
and
v
=
0
{\displaystyle v=0}
and the second is when
u
=
1
−
(
α
+
β
)
σ
{\displaystyle u=1-(\alpha +\beta )\sigma }
v
=
γ
+
α
ρ
{\displaystyle v={\frac {\gamma +\alpha }{\rho }}}
,
which determines the center of a family of cyclic trajectories.
Since the model cannot be solved explicitly, it is instructive to analyze the trajectory of the economy in terms of a phase diagram.
The two lines defining the center of the cycle divide the positive orthant into four regions. The figure below indicates with arrows the movement of the economy in each region. For example, the north-western region (high employment, low labor's share in output) the economy is moving north-east (employment is rising, worker's share is increasing). Once it crosses the u* line it will begin moving south-west.
The figure below illustrates the movement of potential output (output at full employment), actual output and wages over time.
As can be seen the Goodwin model can generate endogenous fluctuations in economic activity without relying on extraneous assumptions of outside shocks, whether on the demand or supply side.
== Statistics ==
== See also ==
Business cycle
Richard M. Goodwin
Harrod–Domar model
Marxian economics
Phillips curve
== Notes ==
== References ==
Goodwin, Richard M. (1967), "A Growth Cycle", in C.H. Feinstein, editor, Socialism, Capitalism and Economic Growth. Cambridge: Cambridge University Press.
Goodwin, Richard M., Chaotic Economic Dynamics, Oxford University Press, 1990.
Flaschel, Peter, The Macrodynamics of Capitalism - Elements for a Synthesis of Marx, Keynes and Schumpeter. Second edition, Springer Verlag Berlin 2010. Chapter 4.3. | Wikipedia/Goodwin_model_(economics) |
The Nicholson–Bailey model was developed in the 1930s to describe the population dynamics of a coupled host-parasitoid system.a It is named after Alexander John Nicholson and Victor Albert Bailey. Host-parasite and prey-predator systems can also be represented with the Nicholson-Bailey model. The model is closely related to the Lotka–Volterra model, which describes the dynamics of antagonistic populations (preys and predators) using differential equations.
The model uses (discrete time) difference equations to describe the population growth of host-parasite populations. The model assumes that parasitoids search for hosts at random, and that both parasitoids and hosts are assumed to be distributed in a non-contiguous ("clumped") fashion in the environment. In its original form, the model does not allow for stable coexistence. Subsequent refinements of the model, notably adding density dependence on several terms, allowed this coexistence to happen.
== Equations ==
=== Derivation ===
The model is defined in discrete time. It is usually expressed as
H
t
+
1
=
k
H
t
e
−
a
P
t
P
t
+
1
=
c
H
t
(
1
−
e
−
a
P
t
)
{\displaystyle {\begin{array}{rcl}H_{t+1}&=&kH_{t}e^{-aP_{t}}\\P_{t+1}&=&cH_{t}\left(1-e^{-aP_{t}}\right)\end{array}}}
with H the population size of the host, P the population size of the parasitoid, k the reproductive rate of the host, a the searching efficiency of the parasitoid, and c the average number of viable eggs that a parasitoid lays on a single host.
This model can be explained based on probability.
e
−
a
P
t
{\displaystyle e^{-aP_{t}}}
is the probability that the host will survive
P
t
{\displaystyle P_{t}}
predators; whereas
1
−
e
−
a
P
t
{\displaystyle 1-e^{-aP_{t}}}
is that they will not, bearing in mind the parasitoid eventually will hatch into larva and escape.
=== Analysis of the Nicholson–Bailey model ===
When
0
<
k
<
1
{\displaystyle 0<k<1}
,
(
H
¯
,
P
¯
)
=
(
0
,
0
)
{\displaystyle ({\bar {H}},{\bar {P}})=(0,0)}
is the unique non-negative fixed point and all non-negative solutions converge to
(
0
,
0
)
{\displaystyle (0,0)}
. When
k
=
1
{\displaystyle k=1}
, all non-negative solutions lie on level curves of the function
z
=
H
+
P
−
ln
(
P
)
{\displaystyle z=H+P-{\text{ln}}(P)}
and converge to a fixed point on the
P
{\displaystyle P}
-axis. When
k
>
1
{\displaystyle k>1}
, this system admits one unstable positive fixed point, at
H
¯
=
k
ln
(
k
)
(
k
−
1
)
a
c
P
¯
=
ln
(
k
)
a
.
{\displaystyle {\begin{array}{rcl}{\bar {H}}&=&{\frac {k\,{\text{ln}}(k)}{(k-1)\,ac}}\\{\bar {P}}&=&{\frac {{\text{ln}}(k)}{a}}\end{array}}.}
It has been proven that all positive solutions whose initial conditions are not equal to
(
H
¯
,
P
¯
)
{\displaystyle ({\bar {H}},{\bar {P}})}
are unbounded and exhibit oscillations with infinitely increasing amplitude.
=== Variations ===
Density dependence can be added to the model, by assuming that the growth rate of the host decreases at high abundances. The equation for the parasitoid is unchanged, and the equation for the host is modified:
H
t
+
1
=
H
t
e
r
(
1
−
H
t
/
K
)
e
−
a
P
t
P
t
+
1
=
c
H
t
(
1
−
e
−
a
P
t
)
{\displaystyle {\begin{array}{rcl}H_{t+1}&=&H_{t}e^{r(1-H_{t}/K)}e^{-aP_{t}}\\P_{t+1}&=&cH_{t}\left(1-e^{-aP_{t}}\right)\end{array}}}
The host rate of increase k is replaced by r, which becomes negative when the host population density reaches K.
== See also ==
Lotka–Volterra inter-specific competition equations
Population dynamics
== Notes ==
^a Parasitoids encompass insects that place their ova inside the eggs or larva of other creatures (generally other insects as well).
== References ==
== Further reading ==
Hopper, J. L. (1987). "Opportunities and Handicaps of Antipodean Scientists: A. J. Nicholson and V. A. Bailey on the Balance of Animal Populations". Historical Records of Australian Science. 7 (2): 179–188. doi:10.1071/hr9880720179.
== External links ==
Nicholson–Bailey model
Nicholson-Bailey model with density dependence
Nicholson-Bailey spatial model | Wikipedia/Nicholson–Bailey_model |
In theoretical ecology and nonlinear dynamics, consumer-resource models (CRMs) are a class of ecological models in which a community of consumer species compete for a common pool of resources. Instead of species interacting directly, all species-species interactions are mediated through resource dynamics. Consumer-resource models have served as fundamental tools in the quantitative development of theories of niche construction, coexistence, and biological diversity. These models can be interpreted as a quantitative description of a single trophic level.
A general consumer-resource model consists of M resources whose abundances are
R
1
,
…
,
R
M
{\displaystyle R_{1},\dots ,R_{M}}
and S consumer species whose populations are
N
1
,
…
,
N
S
{\displaystyle N_{1},\dots ,N_{S}}
. A general consumer-resource model is described by the system of coupled ordinary differential equations,
d
N
i
d
t
=
N
i
g
i
(
R
1
,
…
,
R
M
)
,
i
=
1
,
…
,
S
,
d
R
α
d
t
=
f
α
(
R
1
,
…
,
R
M
,
N
1
,
…
,
N
S
)
,
α
=
1
,
…
,
M
{\displaystyle {\begin{aligned}{\frac {\mathrm {d} N_{i}}{\mathrm {d} t}}&=N_{i}g_{i}(R_{1},\dots ,R_{M}),&&\qquad i=1,\dots ,S,\\{\frac {\mathrm {d} R_{\alpha }}{\mathrm {d} t}}&=f_{\alpha }(R_{1},\dots ,R_{M},N_{1},\dots ,N_{S}),&&\qquad \alpha =1,\dots ,M\end{aligned}}}
where
g
i
{\displaystyle g_{i}}
, depending only on resource abundances, is the per-capita growth rate of species
i
{\displaystyle i}
, and
f
α
{\displaystyle f_{\alpha }}
is the growth rate of resource
α
{\displaystyle \alpha }
. An essential feature of CRMs is that species growth rates and populations are mediated through resources and there are no explicit species-species interactions. Through resource interactions, there are emergent inter-species interactions.
Originally introduced by Robert H. MacArthur and Richard Levins, consumer-resource models have found success in formalizing ecological principles and modeling experiments involving microbial ecosystems.
== Models ==
=== Niche models ===
Niche models are a notable class of CRMs which are described by the system of coupled ordinary differential equations,
d
N
i
d
t
=
N
i
g
i
(
R
)
,
i
=
1
,
…
,
S
,
d
R
α
d
t
=
h
α
(
R
)
+
∑
i
=
1
S
N
i
q
i
α
(
R
)
,
α
=
1
,
…
,
M
,
{\displaystyle {\begin{aligned}{\frac {\mathrm {d} N_{i}}{\mathrm {d} t}}&=N_{i}g_{i}(\mathbf {R} ),&&\qquad i=1,\dots ,S,\\{\frac {\mathrm {d} R_{\alpha }}{\mathrm {d} t}}&=h_{\alpha }(\mathbf {R} )+\sum _{i=1}^{S}N_{i}q_{i\alpha }(\mathbf {R} ),&&\qquad \alpha =1,\dots ,M,\end{aligned}}}
where
R
≡
(
R
1
,
…
,
R
M
)
{\displaystyle \mathbf {R} \equiv (R_{1},\dots ,R_{M})}
is a vector abbreviation for resource abundances,
g
i
{\displaystyle g_{i}}
is the per-capita growth rate of species
i
{\displaystyle i}
,
h
α
{\displaystyle h_{\alpha }}
is the growth rate of species
α
{\displaystyle \alpha }
in the absence of consumption, and
−
q
i
α
{\displaystyle -q_{i\alpha }}
is the rate per unit species population that species
i
{\displaystyle i}
depletes the abundance of resource
α
{\displaystyle \alpha }
through consumption. In this class of CRMs, consumer species' impacts on resources are not explicitly coordinated; however, there are implicit interactions.
==== MacArthur consumer-resource model (MCRM) ====
The MacArthur consumer-resource model (MCRM), named after Robert H. MacArthur, is a foundational CRM for the development of niche and coexistence theories. The MCRM is given by the following set of coupled ordinary differential equations:
d
N
i
d
t
=
τ
i
−
1
N
i
(
∑
α
=
1
M
w
α
c
i
α
R
α
−
m
i
)
,
i
=
1
,
…
,
S
,
d
R
α
d
t
=
r
α
K
α
(
K
α
−
R
α
)
R
α
−
∑
i
=
1
S
N
i
c
i
α
R
α
,
α
=
1
,
…
,
M
,
{\displaystyle {\begin{aligned}{\frac {\mathrm {d} N_{i}}{\mathrm {d} t}}&=\tau _{i}^{-1}N_{i}\left(\sum _{\alpha =1}^{M}w_{\alpha }c_{i\alpha }R_{\alpha }-m_{i}\right),&&\qquad i=1,\dots ,S,\\{\frac {\mathrm {d} R_{\alpha }}{\mathrm {d} t}}&={\frac {r_{\alpha }}{K_{\alpha }}}\left(K_{\alpha }-R_{\alpha }\right)R_{\alpha }-\sum _{i=1}^{S}N_{i}c_{i\alpha }R_{\alpha },&&\qquad \alpha =1,\dots ,M,\end{aligned}}}
where
c
i
α
{\displaystyle c_{i\alpha }}
is the relative preference of species
i
{\displaystyle i}
for resource
α
{\displaystyle \alpha }
and also the relative amount by which resource
α
{\displaystyle \alpha }
is depleted by the consumption of consumer species
i
{\displaystyle i}
;
K
α
{\displaystyle K_{\alpha }}
is the steady-state carrying capacity of resource
α
{\displaystyle \alpha }
in absence of consumption (i.e., when
c
i
α
{\displaystyle c_{i\alpha }}
is zero);
τ
i
{\displaystyle \tau _{i}}
and
r
α
−
1
{\displaystyle r_{\alpha }^{-1}}
are time-scales for species and resource dynamics, respectively;
w
α
{\displaystyle w_{\alpha }}
is the quality of resource
α
{\displaystyle \alpha }
; and
m
i
{\displaystyle m_{i}}
is the natural mortality rate of species
i
{\displaystyle i}
. This model is said to have self-replenishing resource dynamics because when
c
i
α
=
0
{\displaystyle c_{i\alpha }=0}
, each resource exhibits independent logistic growth. Given positive parameters and initial conditions, this model approaches a unique uninvadable steady state (i.e., a steady state in which the re-introduction of a species which has been driven to extinction or a resource which has been depleted leads to the re-introduced species or resource dying out again). Steady states of the MCRM satisfy the competitive exclusion principle: the number of coexisting species is less than or equal to the number of non-depleted resources. In other words, the number of simultaneously occupiable ecological niches is equal to the number of non-depleted resources.
==== Externally supplied resources model ====
The externally supplied resource model is similar to the MCRM except the resources are provided at a constant rate from an external source instead of being self-replenished. This model is also sometimes called the linear resource dynamics model. It is described by the following set of coupled ordinary differential equations:
d
N
i
d
t
=
τ
i
−
1
N
i
(
∑
α
=
1
M
w
α
c
i
α
R
α
−
m
i
)
,
i
=
1
,
…
,
S
,
d
R
α
d
t
=
r
α
(
κ
α
−
R
α
)
−
∑
i
=
1
S
N
i
c
i
α
R
α
,
α
=
1
,
…
,
M
,
{\displaystyle {\begin{aligned}{\frac {\mathrm {d} N_{i}}{\mathrm {d} t}}&=\tau _{i}^{-1}N_{i}\left(\sum _{\alpha =1}^{M}w_{\alpha }c_{i\alpha }R_{\alpha }-m_{i}\right),&&\qquad i=1,\dots ,S,\\{\frac {\mathrm {d} R_{\alpha }}{\mathrm {d} t}}&=r_{\alpha }(\kappa _{\alpha }-R_{\alpha })-\sum _{i=1}^{S}N_{i}c_{i\alpha }R_{\alpha },&&\qquad \alpha =1,\dots ,M,\end{aligned}}}
where all the parameters shared with the MCRM are the same, and
κ
α
{\displaystyle \kappa _{\alpha }}
is the rate at which resource
α
{\displaystyle \alpha }
is supplied to the ecosystem. In the eCRM, in the absence of consumption,
R
α
{\displaystyle R_{\alpha }}
decays to
κ
α
{\displaystyle \kappa _{\alpha }}
exponentially with timescale
r
α
−
1
{\displaystyle r_{\alpha }^{-1}}
. This model is also known as a chemostat model.
==== Tilman consumer-resource model (TCRM) ====
The Tilman consumer-resource model (TCRM), named after G. David Tilman, is similar to the externally supplied resources model except the rate at which a species depletes a resource is no longer proportional to the present abundance of the resource. The TCRM is the foundational model for Tilman's R* rule. It is described by the following set of coupled ordinary differential equations:
d
N
i
d
t
=
τ
i
−
1
N
i
(
∑
α
=
1
M
w
α
c
i
α
R
α
−
m
i
)
,
i
=
1
,
…
,
S
,
d
R
α
d
t
=
r
α
(
K
α
−
R
α
)
−
∑
i
=
1
S
N
i
c
i
α
,
α
=
1
,
…
,
M
,
{\displaystyle {\begin{aligned}{\frac {\mathrm {d} N_{i}}{\mathrm {d} t}}&=\tau _{i}^{-1}N_{i}\left(\sum _{\alpha =1}^{M}w_{\alpha }c_{i\alpha }R_{\alpha }-m_{i}\right),&&\qquad i=1,\dots ,S,\\{\frac {\mathrm {d} R_{\alpha }}{\mathrm {d} t}}&=r_{\alpha }(K_{\alpha }-R_{\alpha })-\sum _{i=1}^{S}N_{i}c_{i\alpha },&&\qquad \alpha =1,\dots ,M,\end{aligned}}}
where all parameters are shared with the MCRM. In the TCRM, resource abundances can become nonphysically negative.
==== Microbial consumer-resource model (MiCRM) ====
The microbial consumer resource model describes a microbial ecosystem with externally supplied resources where consumption can produce metabolic byproducts, leading to potential cross-feeding. It is described by the following set of coupled ODEs:
d
N
i
d
t
=
τ
i
−
1
N
i
(
∑
α
=
1
M
(
1
−
l
α
)
w
α
c
i
α
R
α
−
m
i
)
,
i
=
1
,
…
,
S
,
d
R
α
d
t
=
κ
α
−
r
R
α
−
∑
i
=
1
S
N
i
c
i
α
R
α
+
∑
i
=
1
S
∑
β
=
1
M
N
i
D
α
β
l
β
w
β
w
α
c
i
β
R
β
,
α
=
1
,
…
,
M
,
{\displaystyle {\begin{aligned}{\frac {\mathrm {d} N_{i}}{\mathrm {d} t}}&=\tau _{i}^{-1}N_{i}\left(\sum _{\alpha =1}^{M}(1-l_{\alpha })w_{\alpha }c_{i\alpha }R_{\alpha }-m_{i}\right),&&\qquad i=1,\dots ,S,\\{\frac {\mathrm {d} R_{\alpha }}{\mathrm {d} t}}&=\kappa _{\alpha }-rR_{\alpha }-\sum _{i=1}^{S}N_{i}c_{i\alpha }R_{\alpha }+\sum _{i=1}^{S}\sum _{\beta =1}^{M}N_{i}D_{\alpha \beta }l_{\beta }{\frac {w_{\beta }}{w_{\alpha }}}c_{i\beta }R_{\beta },&&\qquad \alpha =1,\dots ,M,\end{aligned}}}
where all parameters shared with the MCRM have similar interpretations;
D
α
β
{\displaystyle D_{\alpha \beta }}
is the fraction of the byproducts due to consumption of resource
β
{\displaystyle \beta }
which are converted to resource
α
{\displaystyle \alpha }
and
l
α
{\displaystyle l_{\alpha }}
is the "leakage fraction" of resource
α
{\displaystyle \alpha }
governing how much of the resource is released into the environment as metabolic byproducts.
== Symmetric interactions and optimization ==
=== MacArthur's Minimization Principle ===
For the MacArthur consumer resource model (MCRM), MacArthur introduced an optimization principle to identify the uninvadable steady state of the model (i.e., the steady state so that if any species with zero population is re-introduced, it will fail to invade, meaning the ecosystem will return to said steady state). To derive the optimization principle, one assumes resource dynamics become sufficiently fast (i.e.,
r
α
≫
1
{\displaystyle r_{\alpha }\gg 1}
) that they become entrained to species dynamics and are constantly at steady state (i.e.,
d
R
α
/
d
t
=
0
{\displaystyle {\mathrm {d} }R_{\alpha }/{\mathrm {d} }t=0}
) so that
R
α
{\displaystyle R_{\alpha }}
is expressed as a function of
N
i
{\displaystyle N_{i}}
. With this assumption, one can express species dynamics as,
d
N
i
d
t
=
τ
i
−
1
N
i
[
∑
α
∈
M
∗
r
α
−
1
K
α
w
α
c
i
α
(
r
α
−
∑
j
=
1
S
N
j
c
j
α
)
−
m
i
]
,
{\displaystyle {\frac {\mathrm {d} N_{i}}{\mathrm {d} t}}=\tau _{i}^{-1}N_{i}\left[\sum _{\alpha \in M^{\ast }}r_{\alpha }^{-1}K_{\alpha }w_{\alpha }c_{i\alpha }\left(r_{\alpha }-\sum _{j=1}^{S}N_{j}c_{j\alpha }\right)-m_{i}\right],}
where
∑
α
∈
M
∗
{\displaystyle \sum _{\alpha \in M^{\ast }}}
denotes a sum over resource abundances which satisfy
R
α
=
r
α
−
∑
j
=
1
S
N
j
c
j
α
≥
0
{\displaystyle R_{\alpha }=r_{\alpha }-\sum _{j=1}^{S}N_{j}c_{j\alpha }\geq 0}
. The above expression can be written as
d
N
i
/
d
t
=
−
τ
i
−
1
N
i
∂
Q
/
∂
N
i
{\displaystyle \mathrm {d} N_{i}/\mathrm {d} t=-\tau _{i}^{-1}N_{i}\,\partial Q/\partial N_{i}}
, where,
Q
(
{
N
i
}
)
=
1
2
∑
α
∈
M
∗
r
α
−
1
K
α
w
α
(
r
α
−
∑
j
=
1
S
c
j
α
N
j
)
2
+
∑
i
=
1
S
m
i
N
i
.
{\displaystyle Q(\{N_{i}\})={\frac {1}{2}}\sum _{\alpha \in M^{\ast }}r_{\alpha }^{-1}K_{\alpha }w_{\alpha }\left(r_{\alpha }-\sum _{j=1}^{S}c_{j\alpha }N_{j}\right)^{2}+\sum _{i=1}^{S}m_{i}N_{i}.}
At un-invadable steady state
∂
Q
/
∂
N
i
=
0
{\displaystyle \partial Q/\partial N_{i}=0}
for all surviving species
i
{\displaystyle i}
and
∂
Q
/
∂
N
i
>
0
{\displaystyle \partial Q/\partial N_{i}>0}
for all extinct species
i
{\displaystyle i}
.
=== Minimum Environmental Perturbation Principle (MEPP) ===
MacArthur's Minimization Principle has been extended to the more general Minimum Environmental Perturbation Principle (MEPP) which maps certain niche CRM models to constrained optimization problems. When the population growth conferred upon a species by consuming a resource is related to the impact the species' consumption has on the resource's abundance through the equation,
q
i
α
(
R
)
=
−
a
i
(
R
)
b
α
(
R
)
∂
g
i
∂
R
α
,
{\displaystyle q_{i\alpha }(\mathbf {R} )=-a_{i}(\mathbf {R} )b_{\alpha }(\mathbf {R} ){\frac {\partial g_{i}}{\partial R_{\alpha }}},}
species-resource interactions are said to be symmetric. In the above equation
a
i
{\displaystyle a_{i}}
and
b
α
{\displaystyle b_{\alpha }}
are arbitrary functions of resource abundances. When this symmetry condition is satisfied, it can be shown that there exists a function
d
(
R
)
{\displaystyle d(\mathbf {R} )}
such that:
∂
d
∂
R
α
=
−
h
α
(
R
)
b
α
(
R
)
.
{\displaystyle {\frac {\partial d}{\partial R_{\alpha }}}=-{\frac {h_{\alpha }(\mathbf {R} )}{b_{\alpha }(\mathbf {R} )}}.}
After determining this function
d
{\displaystyle d}
, the steady-state uninvadable resource abundances and species populations are the solution to the constrained optimization problem:
min
R
d
(
R
)
s.t.,
g
i
(
R
)
≤
0
,
i
=
1
,
…
,
S
,
R
α
≥
0
,
α
=
1
,
…
,
M
.
{\displaystyle {\begin{aligned}\min _{\mathbf {R} }&\;d(\mathbf {R} )&&\\{\text{s.t.,}}&\;g_{i}(\mathbf {R} )\leq 0,&&\qquad i=1,\dots ,S,\\&\;R_{\alpha }\geq 0,&&\qquad \alpha =1,\dots ,M.\end{aligned}}}
The species populations are the Lagrange multipliers for the constraints on the second line. This can be seen by looking at the KKT conditions, taking
N
i
{\displaystyle N_{i}}
to be the Lagrange multipliers:
0
=
N
i
g
i
(
R
)
,
i
=
1
,
…
,
S
,
0
=
∂
d
∂
R
α
−
∑
i
=
1
S
N
i
∂
g
i
∂
R
α
,
α
=
1
,
…
,
M
,
0
≥
g
i
(
R
)
,
i
=
1
,
…
,
S
,
0
≤
N
i
,
i
=
1
,
…
,
S
.
{\displaystyle {\begin{aligned}0&=N_{i}g_{i}(\mathbf {R} ),&&\qquad i=1,\dots ,S,\\0&={\frac {\partial d}{\partial R_{\alpha }}}-\sum _{i=1}^{S}N_{i}{\frac {\partial g_{i}}{\partial R_{\alpha }}},&&\qquad \alpha =1,\dots ,M,\\0&\geq g_{i}(\mathbf {R} ),&&\qquad i=1,\dots ,S,\\0&\leq N_{i},&&\qquad i=1,\dots ,S.\end{aligned}}}
Lines 1, 3, and 4 are the statements of feasibility and uninvadability: if
N
¯
i
>
0
{\displaystyle {\overline {N}}_{i}>0}
, then
g
i
(
R
)
{\displaystyle g_{i}(\mathbf {R} )}
must be zero otherwise the system would not be at steady state, and if
N
¯
i
=
0
{\displaystyle {\overline {N}}_{i}=0}
, then
g
i
(
R
)
{\displaystyle g_{i}(\mathbf {R} )}
must be non-positive otherwise species
i
{\displaystyle i}
would be able to invade. Line 2 is the stationarity condition and the steady-state condition for the resources in nice CRMs. The function
d
(
R
)
{\displaystyle d(\mathbf {R} )}
can be interpreted as a distance by defining the point in the state space of resource abundances at which it is zero,
R
0
{\displaystyle \mathbf {R} _{0}}
, to be its minimum. The Lagrangian for the dual problem which leads to the above KKT conditions is,
L
(
R
,
{
N
i
}
)
=
d
(
R
)
−
∑
i
=
1
S
N
i
g
i
(
R
)
.
{\displaystyle L(\mathbf {R} ,\{N_{i}\})=d(\mathbf {R} )-\sum _{i=1}^{S}N_{i}g_{i}(\mathbf {R} ).}
In this picture, the unconstrained value of
R
{\displaystyle \mathbf {R} }
that minimizes
d
(
R
)
{\displaystyle d(\mathbf {R} )}
(i.e., the steady-state resource abundances in the absence of any consumers) is known as the resource supply vector.
== Geometric perspectives ==
The steady states of consumer resource models can be analyzed using geometric means in the space of resource abundances.
=== Zero net-growth isoclines (ZNGIs) ===
For a community to satisfy the uninvisibility and steady-state conditions, the steady-state resource abundances (denoted
R
⋆
{\displaystyle \mathbf {R} ^{\star }}
) must satisfy,
g
i
(
R
⋆
)
≤
0
,
{\displaystyle g_{i}(\mathbf {R} ^{\star })\leq 0,}
for all species
i
{\displaystyle i}
. The inequality is saturated if and only if species
i
{\displaystyle i}
survives. Each of these conditions specifies a region in the space of possible steady-state resource abundances, and the realized steady-state resource abundance is restricted to the intersection of these regions. The boundaries of these regions, specified by
g
i
(
R
⋆
)
=
0
{\displaystyle g_{i}(\mathbf {R} ^{\star })=0}
, are known as the zero net-growth isoclines (ZNGIs). If species
i
=
1
,
…
,
S
⋆
{\displaystyle i=1,\dots ,S^{\star }}
survive, then the steady-state resource abundances must satisfy,
g
1
(
R
⋆
)
,
…
,
g
S
⋆
(
R
⋆
)
=
0
{\displaystyle g_{1}(\mathbf {R} ^{\star }),\ldots ,g_{S^{\star }}(\mathbf {R} ^{\star })=0}
. The structure and locations of the intersections of the ZNGIs thus determine what species and feasibly coexist; the realized steady-state community is dependent on the supply of resources and can be analyzed by examining coexistence cones.
=== Coexistence cones ===
The structure of ZNGI intersections determines what species can feasibly coexist but does not determine what set of coexisting species will be realized. Coexistence cones determine what species determine what species will survive in an ecosystem given a resource supply vector. A coexistence cone generated by a set of species
i
=
1
,
…
,
S
⋆
{\displaystyle i=1,\ldots ,S^{\star }}
is defined to be the set of possible resource supply vectors which will lead to a community containing precisely the species
i
=
1
,
…
,
S
⋆
{\displaystyle i=1,\ldots ,S^{\star }}
.
To see the cone structure, consider that in the MacArthur or Tilman models, the steady-state non-depleted resource abundances must satisfy,
K
=
R
⋆
+
∑
i
=
1
S
N
i
C
i
,
{\displaystyle \mathbf {K} =\mathbf {R} ^{\star }+\sum _{i=1}^{S}N_{i}\mathbf {C} _{i},}
where
K
{\displaystyle \mathbf {K} }
is a vector containing the carrying capacities/supply rates, and
C
i
=
(
c
i
1
,
…
,
c
i
M
⋆
)
{\displaystyle \mathbf {C} _{i}=(c_{i1},\ldots ,c_{iM^{\star }})}
is the
i
{\displaystyle i}
th row of the consumption matrix
c
i
α
{\displaystyle c_{i\alpha }}
, considered as a vector. As the surviving species are exactly those with positive abundances, the sum term becomes a sum only over surviving species, and the right-hand side resembles the expression for a convex cone with apex
R
⋆
{\displaystyle \mathbf {R} ^{\star }}
and whose generating vectors are the
C
i
{\displaystyle \mathbf {C} _{i}}
for the surviving species
i
{\displaystyle i}
.
== Complex ecosystems ==
In an ecosystem with many species and resources, the behavior of consumer-resource models can be analyzed using tools from statistical physics, particularly mean-field theory and the cavity method. In the large ecosystem limit, there is an explosion of the number of parameters. For example, in the MacArthur model,
O
(
S
M
)
{\displaystyle O(SM)}
parameters are needed. In this limit, parameters may be considered to be drawn from some distribution which leads to a distribution of steady-state abundances. These distributions of steady-state abundances can then be determined by deriving mean-field equations for random variables representing the steady-state abundances of a randomly selected species and resource.
=== MacArthur consumer resource model cavity solution ===
In the MCRM, the model parameters can be taken to be random variables with means and variances:
⟨
c
i
α
⟩
=
μ
/
M
,
var
(
c
i
α
)
=
σ
2
/
M
,
⟨
m
i
⟩
=
m
,
var
(
m
i
)
=
σ
m
2
,
⟨
K
α
⟩
=
K
,
var
(
K
α
)
=
σ
K
2
.
{\displaystyle \langle c_{i\alpha }\rangle =\mu /M,\quad \operatorname {var} (c_{i\alpha })=\sigma ^{2}/M,\quad \langle m_{i}\rangle =m,\quad \operatorname {var} (m_{i})=\sigma _{m}^{2},\quad \langle K_{\alpha }\rangle =K,\quad \operatorname {var} (K_{\alpha })=\sigma _{K}^{2}.}
With this parameterization, in the thermodynamic limit (i.e.,
M
,
S
→
∞
{\displaystyle M,S\to \infty }
with
S
/
M
=
Θ
(
1
)
{\displaystyle S/M=\Theta (1)}
), the steady-state resource and species abundances are modeled as a random variable,
N
,
R
{\displaystyle N,R}
, which satisfy the self-consistent mean-field equations,
0
=
R
(
K
−
μ
S
M
⟨
N
⟩
−
R
+
σ
K
2
+
S
M
σ
2
⟨
N
2
⟩
Z
R
+
σ
2
S
M
ν
R
)
,
0
=
N
(
μ
⟨
R
⟩
−
m
−
σ
2
χ
N
+
σ
2
⟨
R
2
⟩
+
σ
m
2
Z
N
)
,
{\displaystyle {\begin{aligned}0&=R(K-\mu {\tfrac {S}{M}}\langle N\rangle -R+{\sqrt {\sigma _{K}^{2}+{\tfrac {S}{M}}\sigma ^{2}\langle N^{2}\rangle }}Z_{R}+\sigma ^{2}{\tfrac {S}{M}}\nu R),\\0&=N(\mu \langle R\rangle -m-\sigma ^{2}\chi N+{\sqrt {\sigma ^{2}\langle R^{2}\rangle +\sigma _{m}^{2}}}Z_{N}),\end{aligned}}}
where
⟨
N
⟩
,
⟨
N
2
⟩
,
⟨
R
⟩
,
⟩
R
2
⟩
{\displaystyle \langle N\rangle ,\langle N^{2}\rangle ,\langle R\rangle ,\rangle R^{2}\rangle }
are all moments which are determined self-consistently,
Z
R
,
Z
N
{\displaystyle Z_{R},Z_{N}}
are independent standard normal random variables, and
ν
=
⟨
∂
N
/
∂
m
⟩
{\displaystyle \nu =\langle \partial N/\partial m\rangle }
and
χ
=
⟨
∂
R
/
∂
K
⟩
{\displaystyle \chi =\langle \partial R/\partial K\rangle }
are average susceptibilities which are also determined self-consistently.
This mean-field framework can determine the moments and exact form of the abundance distribution, the average susceptibilities, and the fraction of species and resources that survive at a steady state.
Similar mean-field analyses have been performed for the externally supplied resources model, the Tilman model, and the microbial consumer-resource model. These techniques were first developed to analyze the random generalized Lotka–Volterra model.
== See also ==
Theoretical ecology
Community (ecology)
Competition (biology)
Lotka–Volterra equations
Competitive Lotka–Volterra equations
Generalized Lotka–Volterra equation
Random generalized Lotka–Volterra model
== References ==
== Further reading ==
Cui, Wenping; Robert Marsland III; Mehta, Pankaj (2024). "Les Houches Lectures on Community Ecology: From Niche Theory to Statistical Mechanics". arXiv:2403.05497 [q-bio.PE].
Stefano Allesina's Community Ecology course lecture notes: https://stefanoallesina.github.io/Theoretical_Community_Ecology/ | Wikipedia/Consumer-resource_model |
Functional ecology is a branch of ecology that focuses on the roles, or functions, that species play in the community or ecosystem in which they occur. In this approach, physiological, anatomical, and life history characteristics of the species are emphasized. The term "function" is used to emphasize certain physiological processes rather than discrete properties, describe an organism's role in a trophic system, or illustrate the effects of natural selective processes on an organism. This sub-discipline of ecology represents the crossroads between ecological patterns and the processes and mechanisms that underlie them.
Researchers use two different tools in functional ecology: screening, which involves measuring a trait across a number of species, and empiricism, which provides quantitative relationships for the traits measured in screening. Functional ecology often emphasizes an integrative approach, using organism traits and activities to understand community dynamics and ecosystem processes, particularly in response to the rapid global changes occurring in Earth's environment.
Functional ecology sits at the nexus of several disparate disciplines and serves as the unifying principle between evolutionary ecology, evolutionary biology, genetics and genomics, and traditional ecological studies. It explores such areas as "[species'] competitive abilities, patterns of species co-occurrence, community assembly, and the role of different traits on ecosystem functioning".
== History ==
The notion that ecosystems' functions can be affected by their constituent parts has its origins in the 19th century. Charles Darwin's On The Origin of Species is one of the first texts to directly comment on the effect of biodiversity on ecosystem health by noting a positive correlation between plant density and ecosystem productivity. In his influential 1927 work, Animal Ecology, Charles Elton proposed classifying an ecosystem based on the how its members utilize resources. By the 1950s, Elton's model of ecosystems was widely accepted, where organisms that shared similarities in resource use occupied the same 'guild' within an ecosystem.
Beginning in the 1970s, an increased interest in functional classification revolutionized functional ecology. 'Guilds' would be re-termed 'functional groups', and classification schemes began to focus more on interactions between species and trophic levels. Functional ecology became widely understood to be the study of ecological processes that concern the adaptations of organism within the ecosystem. In the 1990s, biodiversity became better understood as the diversity of species' ecological functions within an ecosystem, rather than simply a great number of different species present. Finally, in the 2000s researchers began using functional classification schemes to examine ecosystems' and organisms' responses to drastic change and disturbance, and the impact of function loss on the health of an ecosystem.
== Functional Diversity ==
Functional diversity is widely considered to be "the value and the range of those species and organismal traits that influence ecosystem functioning" In this sense, the use of the term "function" may apply to individuals, populations, communities, trophic levels, or evolutionary process (i.e. considering the function of adaptations). Functional diversity was conceived as an alternative classification to schemes using genetic diversity or physiological diversity to measure the ecological importance of species in an environment, as well as a way to understand how biodiversity affects specific ecosystem functions, where in this context, 'biodiversity' refers to the diversity of ecosystem functions present in a given system. Understanding ecosystems via functional diversity is as powerful as it is broadly applicable and gives insight into observable patterns in ecosystems, such as species occurrence, species competitive abilities, and the influence of biological communities on ecosystem functioning.
=== Impact on Ecosystem Health ===
A key interest of modern research in Functional Ecology is the impact of functional diversity on ecosystem health. Unsurprisingly, biodiversity has a positive impact on the productivity of an ecosystem. Increased functional diversity increases both the capacity of the ecosystem to regulate the flux of energy and matter through the environment (Ecosystem Functions) as well as the ecosystem's ability to produce resources beneficial to humans such as air, water, and wood (Ecosystem Services). Ecosystem Functions are drastically reduced with decreases in the diversity of genes, species and functional groups present within an ecosystem. In fact, reductions in functional diversity broadly impact the survivability of organisms in an environment regardless of functional group, trophic level, or species, implying that the organization and interaction of communities in an ecosystem has a profound impact on its ability to function and self-sustain. Furthermore, diversity improves environmental stability. The greater an ecosystem's diversity, the more resilient it is to changes in species composition (e.g. extinction events or invasive species) and extraneous changes to environmental conditions (e.g. logging, farming, and pollution). Moreover, the benefits that diversity provides to an environment scale non-linearly with the amount of diversity.
Unfortunately, this relationship also acts in the opposite direction. The loss of diversity non-linearly disrupts ecosystems (even stable ones); this negative impact is especially detrimental when the loss is across trophic levels. For, example, the loss of a single tertiary predator can have cascading effects on the food chain, resulting in reduction of plant biomass and genetic diversity. This in turn can alter the "vegetation structure, fire frequency, and even disease epidemics in a range of ecosystems". The effects of diversity on ecosystems are so powerful, that they can rival the impact of climate change and other global ecosystem stressors.
Alternatively, in rare situations, diversity has been shown to retard ecological productivity. In experimentally concocted microscopic environments, a diverse culture of bacteria was unable to out-produce a homogeneous culture of an 'efficient' control strain. However, the statistical validity and setup of these experiments have been questioned, and require further investigation to carry substantial merit. In general, the current consensus that diversity is beneficial to ecosystem health has much more theoretical and empirical support and is more widely applicable.
=== Scaling ===
Most models of complex functional diversity are only effective in a small range of spatial scales. However, by defining the functional trait probability density as a "function representing the distribution of probabilities of observing each possible trait value in a given ecological unit," the results of many models can be generalized to larger scales. At larger spatial scales, more environmental heterogeneity may increase opportunities for species to exploit more functional groups. Consistent with this conclusion, tests of theoretical models predict that the net effects of biodiversity on ecosystem functions grow stronger over time, over larger spatial scales, and with more heterogeneous natural resources. However, these results are expected to underestimate the actual relationshipm impling that large space and time scales coupled with diverse resources are more than necessary to sustain an ecosystem.
== Applications of Functional Ecology ==
A functional approach to understanding and dealing with environments provides numerous benefits to our understanding of biology and its applications in our lives. While the concept of functional ecology is still in its infancy, it has been widely applied throughout biological studies to better understand organisms, environments, and their interactions.
=== Species Detection and Classification ===
The notions of functional ecology have beneficial implications for species detection and classification. When detecting species, ecologically important traits, such as plant height, influence the probability of detection during field surveys. When holistically analyzing an environment, the systematic error of imperfect species detection can lead to incorrect trait-environment evolutionary conclusions as well as poor estimates of functional trait diversity and environmental role. For example, if small species of insects are less likely to be detected, researchers may conclude that they are much more scarce (and thus less impactful) in the environment than larger species of insects. This 'detection filtering' has major consequences on functional packaging and the defining functional groups in an ecosystem. Thankfully, correlations between environmental change and evolutionary adaptation are much larger than the effects of imperfect species detection. Nevertheless, approaching ecosystems with theoretical maps of functional relationships between species and groups can reduce the likelihood of improper detection and improve the robustness of any biological conclusions drawn.
=== Functional traits ===
A functional approach to defining traits can even help species classification. Trait focused schemes of taxonomy have long been used to classify species, but the number and type of 'trait' to consider is widely debated. Considering more traits in a classification scheme will separate species into more specific functional groups, but may lead to an overestimation of total functional diversity in the environment. However, considering too few traits runs the risk of classifying species as functionally redundant, when they are in fact vital to the health of the ecosystem. So, before one can classify organisms by traits, the definition of 'trait' must be settled. Rather than define traits as proxies for organism performance, as Darwin did, modern ecologists favor a more robust definition of traits often referred to as "functional traits". Under this paradigm, functional traits are defined as morpho-physiophenological traits which impact fitness indirectly via their effects on growth, reproduction and survival. Notice that is definition is not specific to species. Since larger biological organizations grow, reproduce and sustain just as individual organisms do, functional traits can be used to describe ecosystem processes and properties as well. To distinguish between functional traits at different scales, the classification scheme adopts the following nomenclature. Individual organisms have Ecophysiological traits and life-history traits; populations have demographic traits; communities have response traits; and ecosystems have effect traits. At each level, functional traits can directly and indirectly influence functional traits in the levels above or below them. For example, when averaged over an ecosystem, individual plants' heights can contribute to ecosystem productivity or efficiency.
=== Genomics ===
Functional Ecology is closely intertwined with genomics. Understanding the functional niches that organisms occupy in an ecosystem can provide clues to genetic differences between members of a genus. On the other hand, discovering the traits/functions that genes encode for yields insight into the roles that organisms perform in their environment. This kind of genomic study is referred to as genomic ecology or ecogenomics. Genomic ecology can classify traits on cellular and physiological levels leading to a more refined classification system. In addition, once genetic markers for functional traits in individuals are identified, predictions about the functional diversity and composition of an ecosystem can be made from the genetic data of a few species in a process called "reverse ecology". Reverse ecology can contribute to better taxonomy of organisms as well. Rather than defining species by genetic proximity alone, organisms can be additionally classified by the functions they serve in the same ecology.
This application of reverse ecology has proven especially useful in the classification of bacteria. Researchers were able to identify the correspondence between genetic variation and ecological niche function in the genus Agrobacterium and their greater biological implication on species distinction and diversity in the ecosystem. The researchers found that 196 genes specific to Agrobacterium fabrum coded for metabolic pathways specific to plants which allowed for the use of plant-specific compounds and sugars to avoid iron deficiency. This trait, unique to Agrobacterium fabrum, allowed it to avoid competition with closely related bacteria in Agrobacterium found within the same environment. Thus, understanding the genetics of Agrobacterium fabrum allowed researchers to infer that it evolved into the niche (i.e. ecological role) of a plant so that it could avoid competing with its close relatives. If this process can be shown to generalize, then the ecological functions of other organisms can be inferred simply from genetic information.
However, reverse ecology and genomic ecology face several hurdles before they can be accepted as rigorous and mainstream approaches to taxonomy or ecology. One of the major challenges is that technologies for the sequencing and comparison of transcriptomic data do not exist, making the acquisition of transcriptomic data dependent on environmental conditions. Additionally, as studied environments increase in complexity, transcriptomic data becomes harder to collect. Furthermore, the functions that many discovered genes encode for are still unknown making it difficult if not impossible to infer ecological function from a genome. Testing hypotheses concerning what functions given genes encode for is difficult experimentally and is expensive and time-consuming.
=== De-extinction ===
Functional ecology also has broad applications to the science of and debate over de-extinction, the resurrection of extinct species. Function ecology can be applied to strategically assess the resurrection of extinct species to maximize its impact on an environment. To avoid reintroducing a species that is rendered functionally redundant by one of its ancestors, a functional analysis of global ecosystems can be performed to determine which ecosystems would benefit most from the added functional diversity of the reintroduced species. These considerations are important because, while many species currently being considered for de-extinction are terrestrial, they are also functionally redundant in their former ecosystems. However, many extinct marine species have been identified as functionally unique in their environments, even today, which makes a strong case for their reintroduction. In fact, while some functions have been recovered by evolution, as is the case with many extinct terrestrial species, some functional gaps have widened over time. Reintroducing extinct species has the potential to close these gaps, making richer, more balanced ecosystems.
Furthermore, before a species goes extinct in the classical sense of the word, keeping a functional perspective in mind can avoid "functional extinction". Functional extinction is defined as "the point at which a species fails to perform its historical functional role". Endangered species such as species of tigers, tuna and sea otters usually qualify for this threshold. If functional ecology is considered, new species (not necessarily extinct) can be introduced into ecosystem where a species has become functionally extinct before any de-extinction action ever needs to be taken. This can be a key transformative process in ecological preservation and restoration because functional extinction can have cascading effects on the health of an ecosystem. For example, species that engineer ecosystems such as beavers are particularly unique functionally; their absence from an ecosystem could be devastating.
While functional arguments for reintroduction of extinct species may paint thoughtful reintroduction as an ecological boon, the ethical and practical debate over de-extinction has not left functional approaches unscathed. The main critique of functional arguments in favor of de-extinction are largely focused on contentions that ecological functions are often ambiguously defined and that it is unclear what functions must be present to define an ecosystem. These arguments suggest that reintroducing an extinct species could be drastically harm an ecosystem if conclusions about its function or the functions of the species it is intended to replace are incorrect. Additionally, even if an extinct species' function is well understood de-extinction could be equally harmful if the function served by the extinct species is no longer needed by the ecosystem.
== Journals ==
The scientific journal Functional Ecology is published by the British Ecological Society since 1986
== See also ==
Community ecology
== References == | Wikipedia/Functional_ecology |
The competitive Lotka–Volterra equations are a simple model of the population dynamics of species competing for some common resource. They can be further generalised to the generalized Lotka–Volterra equation to include trophic interactions.
== Overview ==
The form is similar to the Lotka–Volterra equations for predation in that the equation for each species has one term for self-interaction and one term for the interaction with other species. In the equations for predation, the base population model is exponential. For the competition equations, the logistic equation is the basis.
The logistic population model, when used by ecologists often takes the following form:
d
x
d
t
=
r
x
(
1
−
x
K
)
.
{\displaystyle {dx \over dt}=rx\left(1-{x \over K}\right).}
Here x is the size of the population at a given time, r is inherent per-capita growth rate, and K is the carrying capacity.
=== Two species ===
Given two populations, x1 and x2, with logistic dynamics, the Lotka–Volterra formulation adds an additional term to account for the species' interactions. Thus the competitive Lotka–Volterra equations are:
d
x
1
d
t
=
r
1
x
1
(
1
−
(
x
1
+
α
12
x
2
K
1
)
)
d
x
2
d
t
=
r
2
x
2
(
1
−
(
x
2
+
α
21
x
1
K
2
)
)
.
{\displaystyle {\begin{aligned}{dx_{1} \over dt}&=r_{1}x_{1}\left(1-\left({x_{1}+\alpha _{12}x_{2} \over K_{1}}\right)\right)\\[0.5ex]{dx_{2} \over dt}&=r_{2}x_{2}\left(1-\left({x_{2}+\alpha _{21}x_{1} \over K_{2}}\right)\right).\end{aligned}}}
Here, α12 represents the effect species 2 has on the population of species 1 and α21 represents the effect species 1 has on the population of species 2. These values do not have to be equal. Because this is the competitive version of the model, all interactions must be harmful (competition) and therefore all α-values are positive. Also, note that each species can have its own growth rate and carrying capacity. A complete classification of this dynamics, even for all sign patterns of above coefficients, is available, which is based upon equivalence to the 3-type replicator equation.
=== N species ===
This model can be generalized to any number of species competing against each other. One can think of the populations and growth rates as vectors, α's as a matrix. Then the equation for any species i becomes
d
x
i
d
t
=
r
i
x
i
(
1
−
∑
j
=
1
N
α
i
j
x
j
K
i
)
{\displaystyle {\frac {dx_{i}}{dt}}=r_{i}x_{i}\left(1-{\frac {\sum _{j=1}^{N}\alpha _{ij}x_{j}}{K_{i}}}\right)}
or, if the carrying capacity is pulled into the interaction matrix (this doesn't actually change the equations, only how the interaction matrix is defined),
d
x
i
d
t
=
r
i
x
i
(
1
−
∑
j
=
1
N
α
i
j
x
j
)
{\displaystyle {\frac {dx_{i}}{dt}}=r_{i}x_{i}\left(1-\sum _{j=1}^{N}\alpha _{ij}x_{j}\right)}
where N is the total number of interacting species. For simplicity all self-interacting terms αii are often set to 1.
=== Possible dynamics ===
The definition of a competitive Lotka–Volterra system assumes that all values in the interaction matrix are positive or 0 (αij ≥ 0 for all i, j). If it is also assumed that the population of any species will increase in the absence of competition unless the population is already at the carrying capacity (ri > 0 for all i), then some definite statements can be made about the behavior of the system.
The populations of all species will be bounded between 0 and 1 at all times (0 ≤ xi ≤ 1, for all i) as long as the populations started out positive.
Smale showed that Lotka–Volterra systems that meet the above conditions and have five or more species (N ≥ 5) can exhibit any asymptotic behavior, including a fixed point, a limit cycle, an n-torus, or attractors.
Hirsch proved that all of the dynamics of the attractor occur on a manifold of dimension N−1. This essentially says that the attractor cannot have dimension greater than N−1. This is important because a limit cycle cannot exist in fewer than two dimensions, an n-torus cannot exist in less than n dimensions, and chaos cannot occur in less than three dimensions. So, Hirsch proved that competitive Lotka–Volterra systems cannot exhibit a limit cycle for N < 3, or any torus or chaos for N < 4. This is still in agreement with Smale that any dynamics can occur for N ≥ 5.
More specifically, Hirsch showed there is an invariant set C that is homeomorphic to the (N−1)-dimensional simplex
Δ
N
−
1
=
{
x
i
:
x
i
≥
0
,
∑
i
x
i
=
1
}
{\displaystyle \Delta _{N-1}=\left\{x_{i}:x_{i}\geq 0,\sum _{i}x_{i}=1\right\}}
and is a global attractor of every point excluding the origin. This carrying simplex contains all of the asymptotic dynamics of the system.
To create a stable ecosystem the αij matrix must have all positive eigenvalues. For large-N systems Lotka–Volterra models are either unstable or have low connectivity. Kondoh and Ackland and Gallagher have independently shown that large, stable Lotka–Volterra systems arise if the elements of αij (i.e. the features of the species) can evolve in accordance with natural selection.
== 4-dimensional example ==
A simple 4-dimensional example of a competitive Lotka–Volterra system has been characterized by Vano et al. Here the growth rates and interaction matrix have been set to
r
=
[
1
0.72
1.53
1.27
]
α
=
[
1
1.09
1.52
0
0
1
0.44
1.36
2.33
0
1
0.47
1.21
0.51
0.35
1
]
{\displaystyle r={\begin{bmatrix}1\\0.72\\1.53\\1.27\end{bmatrix}}\quad \alpha ={\begin{bmatrix}1&1.09&1.52&0\\0&1&0.44&1.36\\2.33&0&1&0.47\\1.21&0.51&0.35&1\end{bmatrix}}}
with
K
i
=
1
{\displaystyle K_{i}=1}
for all
i
{\displaystyle i}
. This system is chaotic and has a largest Lyapunov exponent of 0.0203. From the theorems by Hirsch, it is one of the lowest-dimensional chaotic competitive Lotka–Volterra systems. The Kaplan–Yorke dimension, a measure of the dimensionality of the attractor, is 2.074. This value is not a whole number, indicative of the fractal structure inherent in a strange attractor. The coexisting equilibrium point, the point at which all derivatives are equal to zero but that is not the origin, can be found by inverting the interaction matrix and multiplying by the unit column vector, and is equal to
x
¯
=
(
α
)
−
1
[
1
1
1
1
]
=
[
0.3013
0.4586
0.1307
0.3557
]
.
{\displaystyle {\overline {x}}=\left(\alpha \right)^{-1}{\begin{bmatrix}1\\1\\1\\1\end{bmatrix}}={\begin{bmatrix}0.3013\\0.4586\\0.1307\\0.3557\end{bmatrix}}.}
Note that there are always 2N equilibrium points, but all others have at least one species' population equal to zero.
The eigenvalues of the system at this point are 0.0414±0.1903i, −0.3342, and −1.0319. This point is unstable due to the positive value of the real part of the complex eigenvalue pair. If the real part were negative, this point would be stable and the orbit would attract asymptotically. The transition between these two states, where the real part of the complex eigenvalue pair is equal to zero, is called a Hopf bifurcation.
A detailed study of the parameter dependence of the dynamics was performed by Roques and Chekroun in.
The authors observed that interaction and growth parameters leading respectively to extinction of three species, or coexistence of two, three or four species, are for the most part arranged in large regions with clear boundaries. As predicted by the theory, chaos was also found; taking place however over much smaller islands of the parameter space which causes difficulties in the identification of their location by a random search algorithm. These regions where chaos occurs are, in the three cases analyzed in, situated at the interface between a non-chaotic four species region and a region where extinction occurs. This implies a high sensitivity of biodiversity with respect to parameter variations in the chaotic regions. Additionally, in regions where extinction occurs which are adjacent to chaotic regions, the computation of local Lyapunov exponents revealed that a possible cause of extinction is the overly strong fluctuations in species abundances induced by local chaos.
== Spatial arrangements ==
=== Background ===
There are many situations where the strength of species' interactions depends on the physical distance of separation. Imagine bee colonies in a field. They will compete for food strongly with the colonies located near to them, weakly with further colonies, and not at all with colonies that are far away. This doesn't mean, however, that those far colonies can be ignored. There is a transitive effect that permeates through the system. If colony A interacts with colony B, and B with C, then C affects A through B. Therefore, if the competitive Lotka–Volterra equations are to be used for modeling such a system, they must incorporate this spatial structure.
=== Matrix organization ===
One possible way to incorporate this spatial structure is to modify the nature of the Lotka–Volterra equations to something like a
reaction–diffusion system. It is much easier, however, to keep the format of the equations the same and instead modify the interaction matrix. For simplicity, consider a five species example where all of the species are aligned on a circle, and each interacts only with the two neighbors on either side with strength α−1 and α1 respectively. Thus, species 3 interacts only with species 2 and 4, species 1 interacts only with species 2 and 5, etc. The interaction matrix will now be
α
i
j
=
[
1
α
1
0
0
α
−
1
α
−
1
1
α
1
0
0
0
α
−
1
1
α
1
0
0
0
α
−
1
1
α
1
α
1
0
0
α
−
1
1
]
.
{\displaystyle \alpha _{ij}={\begin{bmatrix}1&\alpha _{1}&0&0&\alpha _{-1}\\\alpha _{-1}&1&\alpha _{1}&0&0\\0&\alpha _{-1}&1&\alpha _{1}&0\\0&0&\alpha _{-1}&1&\alpha _{1}\\\alpha _{1}&0&0&\alpha _{-1}&1\end{bmatrix}}.}
If each species is identical in its interactions with neighboring species, then each row of the matrix is just a permutation of the first row. A simple, but non-realistic, example of this type of system has been characterized by Sprott et al. The coexisting equilibrium point for these systems has a very simple form given by the inverse of the sum of the row
x
¯
i
=
1
∑
j
=
1
N
α
i
j
=
1
α
−
1
+
1
+
α
1
.
{\displaystyle {\overline {x}}_{i}={\frac {1}{\sum _{j=1}^{N}\alpha _{ij}}}={\frac {1}{\alpha _{-1}+1+\alpha _{1}}}.}
=== Lyapunov functions ===
A Lyapunov function is a function of the system f = f(x) whose existence in a system demonstrates stability. It is often useful to imagine a Lyapunov function as the energy of the system. If the derivative of the function is equal to zero for some orbit not including the equilibrium point, then that orbit is a stable attractor, but it must be either a limit cycle or n-torus - but not a strange attractor (this is because the largest Lyapunov exponent of a limit cycle and n-torus are zero while that of a strange attractor is positive). If the derivative is less than zero everywhere except the equilibrium point, then the equilibrium point is a stable fixed point attractor. When searching a dynamical system for non-fixed point attractors, the existence of a Lyapunov function can help eliminate regions of parameter space where these dynamics are impossible.
The spatial system introduced above has a Lyapunov function that has been explored by Wildenberg et al. If all species are identical in their spatial interactions, then the interaction matrix is circulant. The eigenvalues of a circulant matrix are given by
λ
k
=
∑
j
=
0
N
−
1
c
j
γ
k
j
{\displaystyle \lambda _{k}=\sum _{j=0}^{N-1}c_{j}\gamma ^{kj}}
for k = 0N − 1 and where
γ
=
e
i
2
π
/
N
{\displaystyle \gamma =e^{i2\pi /N}}
the Nth root of unity. Here cj is the jth value in the first row of the circulant matrix.
The Lyapunov function exists if the real part of the eigenvalues are positive (Re(λk) > 0 for k = 0, …, N/2). Consider the system where α−2 = a, α−1 = b, α1 = c, and α2 = d. The Lyapunov function exists if
Re
(
λ
k
)
=
Re
(
1
+
α
−
2
e
i
2
π
k
(
N
−
2
)
/
N
+
α
−
1
e
i
2
π
k
(
N
−
1
)
/
N
+
α
1
e
i
2
π
k
/
N
+
α
2
e
i
4
π
k
/
N
)
=
1
+
(
α
−
2
+
α
2
)
cos
(
4
π
k
N
)
+
(
α
−
1
+
α
1
)
cos
(
2
π
k
N
)
>
0
{\displaystyle {\begin{aligned}\operatorname {Re} (\lambda _{k})&=\operatorname {Re} \left(1+\alpha _{-2}e^{i2\pi k(N-2)/N}+\alpha _{-1}e^{i2\pi k(N-1)/N}+\alpha _{1}e^{i2\pi k/N}+\alpha _{2}e^{i4\pi k/N}\right)\\&=1+(\alpha _{-2}+\alpha _{2})\cos \left({\frac {4\pi k}{N}}\right)+(\alpha _{-1}+\alpha _{1})\cos \left({\frac {2\pi k}{N}}\right)>0\end{aligned}}}
for k = 0, …, N − 1. Now, instead of having to integrate the system over thousands of time steps to see if any dynamics other than a fixed point attractor exist, one need only determine if the Lyapunov function exists (note: the absence of the Lyapunov function doesn't guarantee a limit cycle, torus, or chaos).
Example: Let α−2 = 0.451, α−1 = 0.5, and α2 = 0.237. If α1 = 0.5 then all eigenvalues are negative and the only attractor is a fixed point. If α1 = 0.852 then the real part of one of the complex eigenvalue pair becomes positive and there is a strange attractor. The disappearance of this Lyapunov function coincides with a Hopf bifurcation.
=== Line systems and eigenvalues ===
It is also possible to arrange the species into a line. The interaction matrix for this system is very similar to that of a circle except the interaction terms in the lower left and upper right of the matrix are deleted (those that describe the interactions between species 1 and N, etc.).
α
i
j
=
[
1
α
1
0
0
0
α
−
1
1
α
1
0
0
0
α
−
1
1
α
1
0
0
0
α
−
1
1
α
1
0
0
0
α
−
1
1
]
{\displaystyle \alpha _{ij}={\begin{bmatrix}1&\alpha _{1}&0&0&0\\\alpha _{-1}&1&\alpha _{1}&0&0\\0&\alpha _{-1}&1&\alpha _{1}&0\\0&0&\alpha _{-1}&1&\alpha _{1}\\0&0&0&\alpha _{-1}&1\end{bmatrix}}}
This change eliminates the Lyapunov function described above for the system on a circle, but most likely there are other Lyapunov functions that have not been discovered.
The eigenvalues of the circle system plotted in the complex plane form a trefoil shape. The eigenvalues from a short line form a sideways Y, but those of a long line begin to resemble the trefoil shape of the circle. This could be due to the fact that a long line is indistinguishable from a circle to those species far from the ends.
== Notes == | Wikipedia/Competitive_Lotka–Volterra_equations |
The Arditi–Ginzburg equations describe ratio-dependent predator–prey dynamics. Where N is the population of a prey species and P that of a predator, the population dynamics are described by the following two equations:
d
N
d
t
=
f
(
N
)
N
−
g
(
N
P
)
P
d
P
d
t
=
e
g
(
N
P
)
P
−
u
P
{\displaystyle {\begin{aligned}{\frac {dN}{dt}}&=f(N)\,N-g{\left(\!{\tfrac {N}{P}}\!\right)}P\\[4pt]{\frac {dP}{dt}}&=e\,g{\left(\!{\tfrac {N}{P}}\!\right)}P-uP\end{aligned}}}
Here f(N) captures any change in the prey population not due to predator activity including inherent birth and death rates. The per capita effect of predators on the prey population (the harvest rate) is modeled by a function g which is a function of the ratio N/P of prey to predators. Predators receive a reproductive payoff, e, for consuming prey, and die at rate u. Making predation pressure a function of the ratio of prey to predators contrasts with the prey-dependent Lotka–Volterra equations, where the per capita effect of predators on the prey population is simply a function of the magnitude of the prey population g(N). Because the number of prey harvested by each predator decreases as predators become more dense, ratio-dependent predation is a way of incorporating predator intraspecific competition for food. Ratio-dependent predation may account for heterogeneity in large-scale natural systems in which predator efficiency decreases when prey is scarce. The merit of ratio-dependent versus prey-dependent models of predation has been the subject of much controversy, especially between the biologists Lev R. Ginzburg and Peter A. Abrams. Ginzburg purports that ratio-dependent models more accurately depict predator-prey interactions while Abrams maintains that these models make unwarranted complicating assumptions. A later review critically examines the claims made about ratio-dependent predation to find that the added value of the ratio-dependent predation models is unclear and concludes that "As empirical evidence is often lacking on both functional responses and the importance of functional responses for population dynamics, there is no need to strongly favor one limit model over the others."
A recent ecology undergraduate textbook devotes about equal space to Lotka-Volterra and Arditi-Ginzburg equations.
Neither prey-dependent nor ratio-dependent models can claim universal accuracy but the issue is to identify which is least wrong.
== See also ==
Lotka–Volterra equation
Population dynamics
== References ==
== Further reading ==
Tyutyunov, Yu. V.; Titova, L. I. (1 May 2020). "From Lotka–Volterra to Arditi–Ginzburg: 90 Years of Evolving Trophic Functions". Biology Bulletin Reviews. 10 (3): 167–185. doi:10.1134/S207908642003007X. ISSN 2079-0872. | Wikipedia/Arditi–Ginzburg_equations |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.