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The A20 , or address line 20 , is one of the electrical lines that make up the system bus of an x86 -based computer system. The A20 line in particular is used to transmit the 21st bit on the address bus .
A microprocessor typically has a number of address lines equal to the base-two logarithm of the number of words in its physical address space . For example, a processor with 4 GB of byte-addressable physical space requires 32 lines (log 2 (4 GB) = log 2 (2 32 B) = 32), which are named A0 through A31. The lines are named after the zero-based number of the bit in the address that they are transmitting. The least significant bit is first and is therefore numbered bit 0 and signaled on line A0. A20 transmits bit 20 (the 21st bit) and becomes active once addresses reach 1 MB, or 2 20 .
The Intel 8086 , Intel 8088 , and Intel 80186 processors had 20 address lines, numbered A0 to A19; with these, the processor can access 2 20 bytes, or 1 MB. Internal address registers of such processors only had 16 bits. To access a 20-bit address space, an external memory reference was made up of a 16-bit offset address added to a 16-bit segment number, shifted 4 bits to the left so as to produce a 20-bit physical address. The resulting address is equal to segment × 16 + offset . [ 1 ] There are many combinations of segment and offset that produce the same 20-bit physical address. Therefore, there were various ways to address the same byte in memory. [ 2 ] For example, here are four of the 4096 different segment:offset combinations, all referencing the byte whose physical address is 0x000FFFFF (the last byte in 1 MB-memory space):
Referenced the last way, an increase of one in the offset yields F800:8000 , which is a proper address for the processor, but since it translates to the physical address 0x00100000 (the first byte over 1 MB), the processor would need another address line for actual access to that byte. Since there is no such line on the 8086 line of processors, the 21st bit above, while set, gets dropped, causing the address F800:8000 to "wrap around" [ 1 ] and to actually point to the physical address 0x00000000 .
When IBM designed the IBM PC AT (1984) machine, it decided to use the new higher-performance Intel 80286 microprocessor. The 80286 could address up to 16 MB of system memory in protected mode . However, the CPU was supposed to emulate an 8086's behavior in real mode , its startup mode, so that it could run operating systems and programs that were not written for protected mode. The 80286 did not force the A20 line to zero in real mode, however. Therefore, the combination F800:8000 would no longer point to the physical address 0x00000000 , but to the address 0x00100000 . As a result, programs relying on the address wrap around would no longer work. To remain compatible with such programs, IBM decided to correct the problem on the motherboard .
That was accomplished by inserting a logic gate on the A20 line between the processor and system bus, which got named Gate-A20 . Gate-A20 can be enabled or disabled by software to allow or prevent the address bus from receiving a signal from A20. It is set to non-passing for the execution of older programs that rely on the wrap-around. At boot time, the BIOS first enables Gate-A20 when it counts and tests all of the system memory, and then disables it before transferring control to the operating system.
Originally, the logic gate was a gate connected to the Intel 8042 keyboard controller. [ 1 ] Controlling it was a relatively slow process. Other methods have since been added to allow more efficient multitasking of programs that require this wrap-around with programs that access all of the system memory. There are multiple methods to control the A20 line. [ 3 ]
Disconnecting A20 would not wrap all memory accesses above 1 MB, just those in the 1–2 MB, 3–4 MB, 5–6 MB, etc. ranges. Real-mode software cared only about the area slightly above 1 MB, so the Gate-A20 line was enough.
Enabling the Gate-A20 line is one of the first steps that a protected-mode x86 operating system does in the bootup process, often before control has been passed to the kernel from the bootstrap (in the case of Linux , for example).
Virtual 8086 mode , introduced with the Intel 80386 , allows the A20 wrap-around to be simulated by using the virtual memory facilities of the processor; physical memory may be mapped to multiple virtual addresses. Thus, the memory mapped at the first megabyte of virtual memory may be mapped again in the second megabyte of virtual memory. The operating system may intercept changes to Gate A20 and make corresponding changes to the virtual-memory address space, which also makes irrelevant the efficiency of Gate-A20 line toggling.
Controlling the A20 line was an important feature at one stage in the growth of the IBM PC architecture, as it added access to an additional 65,520 bytes (64 KB − 16 bytes) of memory in real mode , without significant software changes.
In what was arguably a "hack", the A20 gate was originally part of the keyboard controller on the motherboard, which could open or close it depending on what behavior was desired. [ 4 ]
In order to keep full compatibility with the Intel 8086 , the A20 gate was still present in Intel CPUs until 2008. [ 5 ] As the gate was initially closed right after boot, protected-mode operating systems typically opened the A20 gate early during the boot process to never close it again. Such operating systems had no compatibility reasons for keeping it closed, and they gained access to the full range of physical addresses available by opening it.
The Intel 80486 and Pentium added a special pin named A20M# , which when asserted low forces bit 20 of the physical address to be zero for all on-chip cache - or external-memory accesses. It was necessary, since the 80486 introduced an on-chip cache and so masking this bit in external logic was no longer possible. Software still needs to manipulate the gate and must still deal with external peripherals (the chipset ) for that. [ 6 ]
The PC System Design Guide PC 2001 removes compatibility for the A20 line: "If A20M# generation logic is still present in the system, this logic must be terminated such that software writes to I/O port 92, bit 1, do not result in A20M# being asserted to the processor." [ 7 ]
Support for the A20 gate was changed in the Nehalem microarchitecture (some sources incorrectly claim that A20 support was removed). Rather than the CPU having a dedicated A20M# pin that receives the signal whether or not to mask the A20 bit, it has been virtualized so that the information is sent from the peripheral hardware to the CPU using special bus cycles. [ citation needed ] From a software point of view, the mechanism works exactly as before, and an operating system must still program external hardware (which in-turn sends the aforementioned bus cycles to the CPU) to disable the A20 masking. [ citation needed ]
Intel no longer supports the A20 gate, starting with Haswell . Page 271 of the Intel System Programmers Manual Vol. 3A from June 2013 states: "The functionality of A20M# is used primarily by older operating systems and not used by modern operating systems. On newer Intel 64 processors, A20M# may be absent." [ 8 ]
The A20 handler is IBM PC memory manager software that controls access to the high memory area (HMA). Extended-memory managers usually provide this functionality. A20 handlers are named after the 21st address line of the microprocessor, the A20 line.
In DOS , HMA managers such as HIMEM.SYS have the "extra task" of managing A20. HIMEM.SYS provided an API for opening/closing A20. DOS itself could use the area for some of its storage needs, thereby freeing up more conventional memory for programs. That functionality was enabled by the DOS =HIGH or HIDOS =ON directives in the CONFIG.SYS configuration file.
Since 1980, the address wrap was internally used by 86-DOS and MS-DOS to implement the DOS CALL 5 entry point at offset +5 to +9 (which emulates the CP/M-80 -style CALL 5 BDOS API entry point at offset +5 to +7) in the Program Segment Prefix (PSP) (which partially resembles CP/M-80's zero page ). [ 9 ] [ 10 ] This was, in particular, utilized by programs machine-translated from CP/M-80 through assembly language translators [ 9 ] like Seattle Computer Products ' TRANS86 . [ 11 ] The CALL 5 handler this entry point refers to resides at the machine's physical address 0x000000C0 (thereby overlapping the four bytes of the interrupt service routine entry point reserved for INT 30h and the first byte of INT 31h in the x86 real mode interrupt vector table ). [ 12 ] [ 13 ] [ 14 ] However, by the design of CP/M-80, which loaded the operating system immediately above the memory available for the application program to run in, the 8080 / Z80 16-bit target address stored at offset +6 to +7 in the zero page could deliberately also be interpreted as the size of the first memory segment. [ 9 ] In order to emulate this in DOS with its 8086 segment:offset addressing scheme, the far call entry point's 16-bit offset had to match this segment size (i.e. 0xFEF0 ), which is stored at offset +6 to +7 in the PSP, overlapping parts of the CALL 5. [ 13 ] [ 14 ] The only way to reconcile these requirements was to choose a segment value that, when added to 0xFEF0 , results in an address of 0x001000C0 , which, on an 8086, wraps around to 0x000000C0 . [ 15 ] [ 12 ] [ 14 ]
A20 had to be disabled for the wraparound to occur and DOS programs using this interface to work. Newer DOS versions which can relocate parts of themselves into the HMA, typically craft a copy of the entry point at FFFF:00D0 in the HMA (which again resolves to physical 0x001000C0 ), so that the interface can work without regard to the state of A20. [ 14 ] [ 16 ]
One program known to use the CALL 5 interface is the DOS version of the Small-C compiler. [ 17 ] Also, the SPELL utility in Microsoft's Word 3.0 (1987) is one of the programs depending on the CALL 5 interface to be set up correspondingly. [ 18 ] Sun Microsystems ' PC-NFS (1993) requires the CALL 5 fix-up as well. [ 16 ]
Also, to save program space, [ 1 ] a trick was used by some BIOS and DOS programmers, for example, to have one segment that has access to program data (such as from F800:0000 to F800:7FFF , pointing to the physical addresses 0x000F8000–0x000FFFFF ), as well as the I/O data (such as the keyboard buffer) that was located in the first memory segment (with addresses F800:8000 to F800:FFFF pointing to the physical addresses 0x00000000 to 0x00007FFF ).
This trick works for as long as the code isn't executed in low memory , the first 64 KB of RAM, a condition that was always true in older DOS versions without load-high capabilities.
With the DOS kernel relocated into higher memory areas, low memory increasingly became available for programs, causing those depending on the wraparound to fail. [ 19 ] The executable loaders in newer versions of DOS attempt to detect some common types of affected programs and either patch them on-the-fly to function also in low memory [ 20 ] or load them above the first 64 KB before passing execution on to them. [ 20 ] For programs, which are not detected automatically, LOADFIX [ 21 ] or MEMMAX -L [ 21 ] can be used to force programs to be loaded above the first 64 KB.
The trick was utilized by IBM/Microsoft Pascal itself as well as by programs compiled with it, [ 22 ] [ 23 ] [ 10 ] [ 17 ] including Microsoft's MASM . [ 17 ] Other commonly used development utilities using this were executable compressors like Realia's Spacemaker [ 20 ] (written by Robert B. K. Dewar in 1982 and used to compress early versions of the Norton Utilities [ 24 ] [ 25 ] [ 26 ] [ 27 ] ) and Microsoft's EXEPACK [ 19 ] [ 20 ] [ 1 ] [ 28 ] [ 17 ] (written by Reuben Borman in 1985) as well as the equivalent /E[XEPACK] option in Microsoft's LINK 3.02 and higher. [ 19 ] [ 1 ] [ 28 ] [ 26 ] Programs processed with EXEPACK would display a "Packed file is corrupt" error message. [ 1 ] [ 20 ] [ 28 ]
Various third-party utilities exist to modify compressed executables either replacing the problematic uncompression routine(s) through restubbing, or attempting to expand and restore the original file.
Modern Legacy BIOS boot loaders (such as GNU GRUB ) use the A20 line. [ 3 ] UEFI boot loaders use 32-bit protected mode or 64-bit long mode . | https://en.wikipedia.org/wiki/Packed_file_is_corrupt |
PacketVideo Corporation or PV was a San Diego–based company that produced software for wireless multimedia , including the display of video on mobile handsets. The PacketVideo name wasn't actively used after being acquired by Lynx Technology. [ 1 ] [ 2 ]
PV was founded in San Diego , California on 10 August 1998 by James C. Brailean, Cheuk Chan, Osama Al-shaykh, Gene Wen and Mark R Banham . In 2003 PacketVideo sold its infrastructure division to Alcatel. In 2005, PacketVideo was acquired in NextWave Wireless . In 2010, PacketVideo became a wholly owned subsidiary of NTT DoCoMo . Corporate parent NTT DOCOMO sold PacketVideo NorthAmerica and Europe to Lynx Technology on 10 May 2015 and the remaining portion, PacketVideo Japan, exactly one year later on 10 May 2016. [ 1 ]
PV's customers include mobile operators such as Verizon Wireless , NTT DoCoMo and Orange , handset manufacturers, and consumer electronics companies. PV's software is embedded in more than 249 million devices worldwide and more than 248 different products.
Major product groups from PV are: [ 3 ]
PacketVideo has presence in three continents, with its headquarters in San Diego. Major development centers are in San Diego, Chicago , Chandigarh , Charlotte, Tokyo , Tampere , Berlin , Boston , and Basel . Sales and customer support centers are in San Diego, Chicago, Charlotte, Tokyo, Tampere, Nice, and Basel. [ 4 ]
PacketVideo is a member of industry forum and consortiums, [ 5 ] including the Open Handset Alliance , 3rd Generation Partnership Project , Broadcast Mobile Convergence Forum , FLO Forum , International Multimedia Telecommunications Consortium , Mobile DTV Alliance , MPEG Industry Forum , Open Mobile Alliance , and the Digital Living Network Alliance | https://en.wikipedia.org/wiki/PacketVideo |
Packet Forwarding Control Protocol ( PFCP ) is a 3GPP protocol used on the Sx/N4 interface between the control plane and the user plane function, specified in TS 29.244. [ 1 ] It is one of the main protocols introduced in the 5G Next Generation Mobile Core Network (aka 5GC [ 2 ] ), but also used in the 4G/LTE EPC to implement the Control and User Plane Separation (CUPS). [ 3 ] PFCP and the associated interfaces seek to formalize the interactions between different types of functional elements used in the Mobile Core Networks as deployed by most operators providing 4G, as well as 5G, services to mobile subscribers. These two types of components are:
PFCP's scope is similar to that of OpenFlow , however it was engineered to serve the particular use-case of Mobile Core Networks .
PFCP is also used on the interface between the control plane and user plane functions of a disaggregated BNG , as defined by the BroadBand Forum in TR-459 .
Albeit similar to GTP in concepts and implementation, PFCP is complementary to it. It provides the control means for a signaling component of the Control-Plane to manage packet processing and forwarding performed by a User-Plane component. Typical EPC or 5G Packet Gateways are split by the protocol in two functional parts, allowing for a more natural evolution and scalability.
The PFCP protocol is used on the following 3GPP mobile core interfaces:
Note: Sxa and Sxb can be combined, in case a merged SGW/PGW is implemented.
The Control-Plane functional element (e.g. PGW-C, SMF) controls the packet processing and forwarding in the User-Plane functional elements (e.g. PGW-U, UPF), by establishing, modifying or deleting PFCP Sessions.
User plane packets shall be forwarded between the CP and UP functions by encapsulating the user plane packets using GTP-U encapsulation (see 3GPP TS 29.281 [3]). For forwarding data from the UP function to the CP function, the CP function shall provision Packet Detection Rules (PDR) per PFCP session context, with the Packet Detection Information (PDI) identifying the user plane traffic to forward to the CP function and with a Forwarding Action Rule (FAR) set with the Destination Interface "CP function side" and set to perform GTP-U encapsulation and to forward the packets to a GTP-u F-TEID uniquely assigned in the CP function per PFCP session and PDR. The CP function shall then identify the PDN connection and the bearer to which the forwarded data belongs by the Fully Qualified TEID (F-TEID) in the header of the encapsulating GTP-U packet. For forwarding data from the CP function to the UP function, the CP function shall provision one or more PDR(s) per PFCP session context, with the PDI set with the Source Interface "CP function side" and identifying the GTP-u F-TEID uniquely assigned in the UP function per PDR, and with a FAR set to perform GTP-U decapsulation and to forward the packets to the intended destination. URRs and QERs may also be configured.
Per session multiple PDRs, FARs, QoS Enforcement Rules (QER), Usage Reporting Rules (URR) and/or Buffering Action Rules (BAR) are sent.
Here are the main concepts used, organized in their logical association model:
or 12..15
Priority; else (spare 0s)
or 16..(MsgLen+4)
IEs are defined either as having a proprietary encoding, or as grouped. Grouped IEs are simply a list of other IEs, encoded one after the other like in the PFCP Message Payload.
IE Types 0..32767 are 3GPP specific and do not have an Enterprise-ID set. IE Types 32768..65535 can be used by custom implementation and the Enterprise-ID must be set to the IANA SMI Network Management Private Enterprise Codes [ 4 ] of the issuing party.
No session related messages should be exchanged before this procedure.
While the Association-Release is only triggered by the CP, the UP can request it as part of the Association-Update-Request.
The UP may include Usage Report information in the answer, such that an additional Session-Report message would be avoided.
Very similar to GTP-C , PFCP uses UDP . Port 8805 is reserved. [ 5 ]
For reliability, a similar re-transmission strategy as for GTP-C is employed, lost messages being sent N1-times at T1-intervals. Transactions are identified by the 3-byte long Sequence Number, the IP address and port of the communication peer.
The protocol includes an own Heart-beat Request/Response model, which allows monitoring the availability of communication peers and detecting restarts (by use of a Recovery-Timestamp Information Element).
For User-Plane packet exchanges between the Control and User Plane functional elements, GTP-U for the Sx-u interface, or alternatively a simpler UDP or Ethernet encapsulation for the N4-u interface (to be confirmed, as standards are still incomplete). | https://en.wikipedia.org/wiki/Packet_Forwarding_Control_Protocol_(PFCP) |
A packet analyzer (also packet sniffer or network analyzer ) [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ 7 ] [ 8 ] is a computer program or computer hardware such as a packet capture appliance that can analyze and log traffic that passes over a computer network or part of a network. [ 9 ] Packet capture is the process of intercepting and logging traffic. As data streams flow across the network, the analyzer captures each packet and, if needed, decodes the packet's raw data, showing the values of various fields in the packet, and analyzes its content according to the appropriate RFC or other specifications.
A packet analyzer used for intercepting traffic on wireless networks is known as a wireless analyzer - those designed specifically for Wi-Fi networks are Wi-Fi analyzers . [ a ] While a packet analyzer can also be referred to as a network analyzer or protocol analyzer these terms can also have other meanings. Protocol analyzer can technically be a broader, more general class that includes packet analyzers/sniffers. [ 10 ] However, the terms are frequently used interchangeably. [ 11 ]
On wired shared-medium networks , such as Ethernet , Token Ring , and FDDI , depending on the network structure ( hub or switch ), [ 12 ] [ b ] it may be possible to capture all traffic on the network from a single machine. On modern networks, traffic can be captured using a network switch using port mirroring , which mirrors all packets that pass through designated ports of the switch to another port, if the switch supports port mirroring. A network tap is an even more reliable solution than to use a monitoring port since taps are less likely to drop packets during high traffic load.
On wireless LANs , traffic can be captured on one channel at a time, or by using multiple adapters, on several channels simultaneously.
On wired broadcast and wireless LANs, to capture unicast traffic between other machines, the network adapter capturing the traffic must be in promiscuous mode . On wireless LANs, even if the adapter is in promiscuous mode, packets not for the service set the adapter is configured for are usually ignored. To see those packets, the adapter must be in monitor mode . [ citation needed ] No special provisions are required to capture multicast traffic to a multicast group the packet analyzer is already monitoring, or broadcast traffic.
When traffic is captured, either the entire contents of packets or just the headers are recorded. Recording just headers reduces storage requirements, and avoids some privacy legal issues , yet often provides sufficient information to diagnose problems.
Captured information is decoded from raw digital form into a human-readable format that lets engineers review exchanged information. Protocol analyzers vary in their abilities to display and analyze data.
Some protocol analyzers can also generate traffic. These can act as protocol testers. Such testers generate protocol-correct traffic for functional testing, and may also have the ability to deliberately introduce errors to test the device under test 's ability to handle errors. [ 13 ] [ 14 ]
Protocol analyzers can also be hardware-based, either in probe format or, as is increasingly common, combined with a disk array. These devices record packets or packet headers to a disk array.
Packet analyzers can:
Packet capture can be used to fulfill a warrant from a law enforcement agency to wiretap all network traffic generated by an individual. Internet service providers and VoIP providers in the United States must comply with Communications Assistance for Law Enforcement Act regulations. Using packet capture and storage, telecommunications carriers can provide the legally required secure and separate access to targeted network traffic and can use the same device for internal security purposes. Collecting data from a carrier system without a warrant is illegal due to laws about interception. By using end-to-end encryption , communications can be kept confidential from telecommunication carriers and legal authorities. | https://en.wikipedia.org/wiki/Packet_analyzer |
The packet erasure channel is a communication channel model where sequential packets are either received or lost (at a known location). This channel model is closely related to the binary erasure channel .
An erasure code can be used for forward error correction on such a channel.
This article related to telecommunications is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Packet_erasure_channel |
Packeteer, Inc. , founded in 1996 by Robert Packer, Brett Galloway and Bob Luxenberg was an I.T. company based in Cupertino, California that was listed on the NASDAQ . Networking appliances focus on Application Traffic Management and optimization for wide area networks. [ 1 ] They held at least 40 patents for various network optimization methods. [ 2 ] Packeteer was acquired by Blue Coat Systems in 2008. [ 3 ] [ 4 ] [ 5 ]
Packeteer was a contributing member of the Apdex Alliance .
Their main product lines were: | https://en.wikipedia.org/wiki/Packeteer |
Paclitaxel total synthesis in organic chemistry is a major ongoing research effort in the total synthesis of paclitaxel (Taxol). [ 1 ] This diterpenoid is an important drug in the treatment of cancer but, also expensive because the compound is harvested from a scarce resource, namely the Pacific yew ( Taxus brevifolia ). Not only is the synthetic reproduction of the compound itself of great commercial and scientific importance, but it also opens the way to paclitaxel derivatives not found in nature but with greater potential.
The paclitaxel molecule consists of a tetracyclic core called baccatin III and an amide tail. The core rings are conveniently called (from left to right) ring A (a cyclohexene ), ring B (a cyclooctane ), ring C (a cyclohexane ) and ring D (an oxetane ).
The paclitaxel drug development process took over 40 years. The anti-tumor activity of a bark extract of the Pacific yew tree was discovered in 1963 as a follow-up of a US government plant screening program already in existence 20 years before that. The active substance responsible for the anti-tumor activity was discovered in 1969 and structure elucidation was completed in 1971. Robert A. Holton of Florida State University succeeded in the total synthesis of paclitaxel in 1994, a project that he had started in 1982. In 1988 Jean-Noël Denis had also developed a semisynthetic route to paclitaxel starting from 10-deacetylbaccatin III . [ 2 ] This compound is a biosynthetic precursor and is found in larger quantities than paclitaxel itself in Taxus baccata (the european yew). In 1990 Bristol-Myers Squibb bought a licence to the patent for this process which in the years to follow earned Florida State University and Holton (with a 40% take) over 200 million US dollars .
The total synthesis of taxol is called one of the most hotly contested of the 1990s [ 3 ] with around 30 competing research groups by 1992. The number of research groups actually having reported a total synthesis currently stands at 11 with the Holton group (article first accepted for publication) and the Nicolaou group (article first published) first and second in what is called a photo finish.
Some of the efforts are truly synthetic but in others a precursor molecule found in nature is included. The key data are collected below. What all strategies have in common is synthesis of the baccatin molecule followed by last stage addition of the tail, a process (except for one) based on the Ojima lactam .
Ongoing research efforts are directed at the synthesis of taxadiene and taxadienone intermediates. The synthesis of related taxanes decinnamoyltaxinine E and taxabaccatin III has been reported [ 19 ]
The commercial semisynthesis (by Bristol-Myers Squibb ) of paclitaxel starting from 10-deacetylbaccatin III (isolated from the European yew) is based on tail addition of the so-called Ojima lactam to its free hydroxyl group:
Another commercial semisynthesis (by the company Natural Pharmaceuticals ) relies on the isolation of a group of paclitaxel derivatives isolated from primary ornamental taxanes. These derivatives have the same skeleton as paclitaxel except for the organic residue R of the terminal tail amide group which can be phenyl , or propyl or pentyl (among others) whereas in paclitaxel it is an explicit phenyl group. The semisynthesis consists of conversion of the amide group to an amine with Schwartz's reagent through an imine followed by acidic workup and a benzoylation.
In the production process Michigan grown yews which mature in 8 years are periodically topped and dried. This material is shipped to Mexico for a first extraction step (10% paclitaxel content) and then to Canada for further purification to 95% purity. The semisynthesis to final product takes place in China. [ 20 ]
The biosynthetic pathway to paclitaxel has been investigated and consists of approximately 20 enzymatic steps. The complete scheme is still unavailable. The segments that are known are very different from the synthetic pathways tried thus far ( Scheme 1 ). The starting compound is geranylgeranyl diphosphate 2 [ 21 ] which is a dimer of geraniol 1 . This compound already contains all the required 20 carbon atoms for the paclitaxel skeleton. More ring closing through intermediate 3 ( taxadiene ) leads to taxusin 4 . The two main reasons why this type of synthesis is not feasible in the laboratory is that nature does a much better job controlling stereochemistry and a much better job activating a hydrocarbon skeleton with oxygen substituents for which cytochrome P450 is responsible in some of the oxygenations. Intermediate 5 is called 10-deacetylbaccatin III.
A biochemical kilogram-scale production of taxadiene was reported using genetically engineered E. coli in 2011. [ 22 ] | https://en.wikipedia.org/wiki/Paclitaxel_total_synthesis |
A pad abort test is a kind of test of a launch escape system which conducted by setting the system along with the spacecraft still on the ground and let the system activate to carry the spacecraft flying away, then separate in the air and make the spacecraft land safely. The purpose of the test is to determine how well the system could get the crew of a spacecraft to safety in an emergency on the launch pad . As the spacecraft is set still on the ground, the test is also called "zero- altitude abort test" in against "high-altitude abort test".
Section sources. [ 1 ] [ 2 ]
The Mercury program included several pad abort tests for the launch escape system with a boilerplate crew module.
The Apollo program included several pad abort tests for the launch escape system with a boilerplate crew module.
Both tests were conducted at the White Sands Missile Range .
China Manned Space Program included one pad abort test for Shenzhou spacecraft, called "zero-altitude flight test"( Chinese : 零高度飞行试验 ), conducted on October 19, 1998 9:00 am, one year prior to first Shenzhou spacecraft mission with a successful result. [ 3 ]
The Orion pad abort test was conducted on May 6, 2010 at the White Sands Missile Range in New Mexico. [ 4 ] [ 5 ] [ 6 ] The Launch Abort System lifted the Orion Boilerplate to a height of approximately 6000 feet above the ground and landed 6,900 feet downrange about 150 seconds later. [ 7 ] The Abort test resulted in no damage to the test article and the mission was considered a complete success. [ 6 ]
The SpaceX Dragon 2 Pad Abort Test was conducted on May 6, 2015 at approximately 0900 Eastern Daylight Time (EDT). (A video clip released by SpaceX shows the timestamp of the moment of launch as 13:00:00). The vehicle splashed down safely in the ocean to the east of the launchpad 99 seconds later. [ 8 ] A fuel mixture ratio issue was detected after the flight in one of the eight SuperDraco engines, but did not materially affect the flight. [ 9 ] More detailed test results were to be subsequently analyzed by both SpaceX and NASA engineers. [ 10 ]
The pad abort test of Boeing's Starliner craft was conducted at 14:15 UTC on November 4, 2019 at the White Sands Missile Range . [ 11 ] The capsule was lifted to 1,350 m (4,430 ft) and landed with airbags approximately 90 seconds after liftoff. Though the test was deemed a success, one of three main parachutes failed to deploy properly. [ 12 ] [ 13 ]
On 5 July 2018, Indian Space Research Organisation successfully conducted a pad abort test at Satish Dhawan Space Centre, Sriharikota. A first in a series of tests to qualify a crew escape system. [ 14 ]
After a smooth countdown of five hours, the crew escape system, along with the simulated crew module with a mass of 12.6 tonnes, lifted off at 07.00 AM (IST) at the opening of the launch window from its pad at Satish Dhawan Space Centre , Sriharikota. The test was over in 259 seconds, during which the crew escape system along with crew module soared skyward, then arced over the Bay of Bengal and floated back to Earth under its parachutes about 2.9 km from Sriharikota. | https://en.wikipedia.org/wiki/Pad_abort_test |
The Paddle Steamer Preservation Society (PSPS) is a United Kingdom-based registered charity [ 1 ] [ 2 ] and owner of two working paddle steamers ; PS Kingswear Castle and PS Waverley .
In September 1959 a letter by Dr Alan Robinson appeared in The Daily Telegraph newspaper remarking on the rapid decline of the paddle steamer around the shores of the UK and soliciting support for a preservation project. Over the next month a number of letters of support appeared in the Telegraph and following a public meeting on 30 October 1959 the decision was made to form a society. The first meeting was held on 8 November 1959 in Southampton where the name "Paddle Steamer Preservation Society" was adopted, with Dr Alan Robinson as founder. Poet Laureate Sir John Betjeman held the position of Patron of the PSPS from 1960 until his death in 1984.
The Society acquired its first paddle steamer PS Kingswear Castle in 1967 and was given PS Waverley in 1974. Both have been extensively restored and are fully operational.
The Society membership has increased from the 15 persons present at the first meeting to over 3,000 members worldwide, the majority affiliated to one of five PSPS branches that cover the UK.
The PSPS Collection holds in excess of 50,000 objects ranging from posters, souvenirs and paintings through to fittings from long-departed paddle steamers.
In addition to owning two operational paddle steamers the Society also supports other paddle steamer projects including PS Maid of the Loch and PS Medway Queen . | https://en.wikipedia.org/wiki/Paddle_Steamer_Preservation_Society |
A compactor is a machine or mechanism used to reduce the size of material such as waste material or bio mass through compaction . A trash compactor is used in business and public places like hospitals (and in the United States also in homes) to reduce the volume of trash they produce. A baler-wrapper compactor is used for making compact and wrapped bales in order to improve logistics. [ 1 ]
Normally powered by hydraulics , compactors take many shapes and sizes. In landfill sites for example, a large tractor (typically a converted front end loader with some variant of a bulldozer blade attached) with spiked steel wheels called a landfill compactor is used to drive over waste deposited by waste collection vehicles (WCVs).
WCVs themselves incorporate a compacting mechanism which is used to increase the payload of the vehicle and reduce the number of times it has to empty. This usually takes the form of hydraulically powered sliding plates which sweep out the collection hopper and compress the material into what has already been loaded.
Different compactors are used in scrap metal processing, the most familiar being the car crusher . Such devices can be of either the "pancake" type, where a scrap automobile is flattened by a huge descending hydraulically powered plate, or the baling press, where the automobile is compressed from several directions until it resembles a large cube
Many retail and service businesses, such as fast food, restaurants, and hotels, use compactors to reduce the volume of non-recyclable waste as well as curb nuisance such as rodents and smell. In the hospitality industry tolerance for such nuisances is particularly low. These compactors typically come in electric and hydraulic operation, with quite a few loading configurations. Most popular loading configurations fall under the following:
These compactors are almost exclusively of welded steel construction for two reasons: durability under pressure and exposure to the elements, as compactors are installed either completely outdoors or sometimes under a covered loading dock.
As a means to preserve and store forage, baler-wrapper compactors are used to exclude oxygen from the forage and wrap it in air tight film. Without access to air the forage is preserved fresh for longer periods of time.
In the United States, there are also trash compactors, hydraulic or manual, designed for residential use. Likewise, they reduce the volume of garbage . For example, some compactors reduce the volume of polystyrene to 1/30. [ citation needed ]
In the United States, in addition to the waste vehicle and landfill use, there are solar-powered trash compactors that can hold the equivalent of 200 gallons of trash before they need to be emptied. [ 2 ]
The large compactors in garbage trucks can be dangerous for workers, and played a role in the US Civil Rights Movement . The 1968 Memphis sanitation strike took place when two sanitation workers were crushed to death in garbage compactors, after which 700 of their 1300 black coworkers decided to strike. [ 3 ]
Baler-wrapper compactors are used for efficient storage and transport of materials like RDF ( refuse-derived fuel ) and bin waste, as well as compost and saw dust, enabling higher rates of recycling.
In construction , there are three main types of compactor: the plate, the rammer, and the road roller . The roller type compactors are used for compacting crushed rock as the base layer underneath concrete or stone foundations or slabs. The plate compactor, vibrating plate, or tamper, has a large vibrating baseplate and is suited for creating a level grade, while the rammer compactor has a smaller foot. The rammer, or trench rammer, is mainly used to compact the backfill in narrow trenches for water or gas supply pipes etc. Road rollers may also have vibrating rollers.
In plates and rollers, the vibration is provided by rapidly rotating eccentric masses. In smaller plates, the vibration causes a tendency to move forwards, while some larger plates are provided with a directional control. In the rammer the foot is mounted on a sleeve that slides vertically in the leg. Inside the sleeve, a piston is driven up and down by the engine through a reduction gear, crank and connecting rod. Substantial coil springs above and below the piston connect it to the sliding sleeve. The connection between the sleeve and foot is at a small angle so that the whole rammer leans away from the operator. The vibrating motion is therefore slightly off the vertical, and this gives the rammer a tendency to 'walk' forwards. The sliding joint in the leg is protected by a flexible bellows.
In England the name "wacker plate" or just "wacker" is commonly used to refer to plate compactors, derived from the name of Wacker Neuson , a well-known manufacturer of such devices. The name is pronounced in the English style as whacker, as opposed to the correct German vacker . A rammer is colloquially referred to as " Paddy 's Motorbike", due to the traditional resource of Irish construction labourers, and the way that the operator appears to "ride" the hammer holding the handles like a motorcycle. [ citation needed ] | https://en.wikipedia.org/wiki/Paddy's_motorbike |
In chemical graph theory , the Padmakar–Ivan (PI) index is a topological index of a molecule , used in biochemistry . The Padmakar–Ivan index is a generalization introduced by Padmakar V. Khadikar and Iván Gutman [ 1 ] of the concept of the Wiener index , introduced by Harry Wiener . The Padmakar–Ivan index of a graph G is the sum over all edges uv of G of number of edges which are not equidistant from u and v .
Let G be a graph and e = uv an edge of G . Here n e u ( e ∣ G ) {\displaystyle n_{eu}(e\mid G)} denotes the number of edges lying closer to the vertex u than the vertex v , and n e v ( e ∣ G ) {\displaystyle n_{ev}(e\mid G)} is the number of edges lying closer to the vertex v than the vertex u . The Padmakar–Ivan index of a graph G is defined as
The PI index is very important in the study of quantitative structure–activity relationship for the classification models used in the chemical , biological sciences , engineering , and nanotechnology .
The PI index of Dendrimer Nanostar of the following figure can be calculated by [ 2 ] | https://en.wikipedia.org/wiki/Padmakar–Ivan_index |
In mathematics , Padovan polynomials are a generalization of Padovan sequence numbers. These polynomials are defined by: [ 1 ]
The first few Padovan polynomials are:
The Padovan numbers are recovered by evaluating the polynomials P n −3 ( x ) at x = 1.
Evaluating P n −3 ( x ) at x = 2 gives the n th Fibonacci number plus (−1) n . (sequence A008346 in the OEIS )
The ordinary generating function for the sequence is
This polynomial -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Padovan_polynomials |
Paedophagy (literally meaning the "consumption of children") in its general form is the feeding behaviour of fish or other animals whose diet is partially, or primarily the eggs or larvae of other animals. However, P. H. Greenwood, who was the first to describe paedophagia, defines it to be a feeding behaviour evolved among cichlid fishes. [ 1 ] [ 2 ] [ 3 ]
Paedophagy is found in fishes from Lake Victoria in Africa which in total has 200-300 species, [ 4 ] but in regards to paedophages it is known to contain 8 species. [ 1 ] Lake Malawi in Africa has in total 500-1000 species, [ 4 ] but in paedophages contains only several species. Other lakes which contain paegophages include Lake Edward and Lake George , both in Africa, and each contain only one species of paedophage. [ 1 ] From Lake Malawi there are various species of cichlid fish that exhibit paedophagia, they include fishes from the genera Caprichromis , Hemitaeniochromis , and Naevochromis . In Lake Tanganyika species of the genus Haplotaxodon and Greenwoodochromis bellcrossi may also carry out this sort of feeding strategy. [ 5 ]
Mouth brooding is the most common form of parental care in African cichlids, [ 2 ] and has thought to have evolved from the ancestral mode of care known as substrate-guarding. [ 6 ] As mouth brooding is so well known in cichlids , one of the main approaches of paedophages is to steal the brood directly from the mouth of a mother. Upon hatching, development occurs in the mouth until juveniles are well-formed fry, the fry then develop further in the mouth until ready in which they are the released. Typically followed by a phase of parental guarding. [ 2 ] Since the young are kept inside the mothers mouth for an extensive amount of their juvenile life it creates a great opportunity for paedophages, as there is a high probability of a female cichlid to possess young in her mouth.
There are three main methods or behaviours that the predators use to obtain the eggs or young. The first method is voluntary jettisoning of a brood, second being snout-engulfing which forces a brooding female to dislodge her brood from her mouth and lastly, is head-ramming against a brooding female which then causes her to spit out a part of her brood. [ 1 ] Other behaviours include those of the species Plecodus straeleni , which belongs to the family Cichlidae . [ 1 ] When this species exhibits paedophagy, it has been observed circling and waiting outside the bower, which is the spawning location for many cichlid fishes. It waits until the eggs have been laid before attacking the mouth brooder. [ 1 ] However, stealing from the mouth brooding phase is not the only tactic that has been noted, stealing of the fry from the guarding phase of parental care has also been observed. [ 2 ]
This involves juveniles who are being guarded by their parent are approached by a paedophage hunter. The parent will do its best to chase away the predator to protect the offspring, on the other hand, this abrupt movement from the parent distresses the offspring. The offspring then all aggregate together until their mother successfully comes back, where she continues with guarding behaviour. [ 2 ] There are some cases where the fry may try to enter the mother's mouth once she reappeared, but these fry would only be rejected as the threat was over. The only exception to the fry re-entering their mother's mouth is if the mother has been disturbed by the attack and feels it is unsafe, at which point she could carry out a calling movement and all the fry would enter her mouth for a short period of time before being released. [ 2 ]
To obtain the brood without causing serious harm to the mouth brooder, paedophages have features such as protrusible and distensible spacious mouths and deeply embedded teeth that are covered by a thickened oral mucosa. [ 2 ] These large mouths allow the paedophages to engulf the snout of a mouth brooder and discharge the brood, while the teeth adaptation allowed for the paedophage to avoid becoming too heavily attached to the parent which prevents the loss of the brood that the paedophage just obtained. [ 2 ]
Achieving the brood from a brooding parent can take great energy and resources from the paedophage. However, the eggs they obtain are highly nutritious and fairly large when compared to the size of other fish eggs in that they are on average 3.4mm in diameter. [ 7 ] | https://en.wikipedia.org/wiki/Paedophagy |
Paenibacterin is a mixture of antimicrobial lipopeptides isolated from Paenibacillus thiaminolyticus . [ 1 ] It contains three isomeric compounds which differ by the fatty acid side chain. [ 2 ]
This biochemistry article is a stub . You can help Wikipedia by expanding it .
This article about an organic compound is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Paenibacterin |
Paging Network, Inc. , also known as PageNet , was founded in 1981 by entrepreneur George Perrin and ceased in 1999.
The company grew to become the largest wireless messaging company in the world, with more than 10 million pagers in service, and $1 billion in revenues, before the paging industry's rapid decline in the late 1990s.
Based in Dallas , PageNet held the distinction of building and operating the most extensive one-way paging network in the United States, growing to more than 90 offices across the United States. The company extended operations to Canada and Brazil.
The company was known for its low-cost strategy and aggressive marketing tactics, although in its later years it positioned itself as a technology innovator as well.
PageNet's fortunes began to decline in the late 1990s, when the company spent nearly $1 billion to purchase additional spectrum and build out a new network designed to offer advanced services, such as voice paging and two-way paging.
Products developed by Motorola for PageNet's network were unsuccessful, as was a reorganization of the company engineered by McKinsey & Company . Ironically, PageNet had an opportunity to purchase the network that went on to support the successful BlackBerry service, but decided to team with Motorola instead.
As PageNet sank under the weight of its investment, the one-way paging market collapsed—with millions of former paging customers switching to digital cellular and PCS services, which cut prices dramatically while offering new features such as nationwide calling plans and text messaging . Under its last CEO, John P. Frazee, Jr., PageNet was sold to Boston-based Arch Communications in 1999. [ 1 ] That company has since merged with Metrocall to form USA Mobility. [ 2 ]
This article about a telecommunications company is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/PageNet |
The page attribute table ( PAT ) is a processor supplementary capability extension to the page table format of certain x86 and x86-64 microprocessors. Like memory type range registers (MTRRs), they allow for fine-grained control over how areas of memory are cached , and are a companion feature to the MTRRs. [ 1 ]
Unlike MTRRs, which provide the ability to manipulate the behavior of caching for a limited number of fixed physical address ranges, Page Attribute Tables allow for such behavior to be specified on a per-page basis, greatly increasing the ability of the operating system to select the most efficient behavior for any given task. [ 2 ]
The PAT is available on Pentium III and newer CPUs, and on non-Intel CPUs.
This computing article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Page_attribute_table |
A pager , also known as a beeper or bleeper , [ 1 ] is a wireless telecommunications device that receives and displays alphanumeric or voice messages. One-way pagers can only receive messages, while response pagers and two-way pagers can also acknowledge, reply to, and originate messages using an internal transmitter. [ 2 ]
Pagers operate as part of a paging system which includes one or more fixed transmitters (or in the case of response pagers and two-way pagers, one or more base stations ), as well as a number of pagers carried by mobile users. These systems can range from a restaurant system with a single low power transmitter, to a nationwide system with thousands of high-power base stations.
Pagers were developed in the 1950s and 1960s, [ 3 ] and became widely used by the 1980s through the late 1990s and early 2000s. Later in the 21st century, the widespread availability of cellphones and smartphones with text messaging capability has greatly diminished the pager industry. Nevertheless, pagers continue to be used by some emergency services and public safety personnel , because modern pager systems' coverage overlap, combined with use of satellite communications , can make paging systems more reliable than terrestrial based cellular networks in some cases, including during natural and human-made disasters . [ 4 ] This resilience has led public safety agencies to adopt pagers over cellular and other commercial services for critical messaging. [ 5 ] [ 6 ]
The first telephone pager system was patented in 1949 by Al Gross . [ 7 ] Intended for the use of physicians, there was initial resistance to the idea of being permanently on-call, according to Gross. [ 8 ]
One of the first practical paging services was launched in 1950 for physicians in the New York City area. [ 9 ] Physicians paid US$12 per month and carried a 200-gram (7 oz) pager that would receive phone messages within 40 kilometres (25 mi) of a single transmitter tower. The system was manufactured by the Reevesound Company and operated by Telanswerphone. [ 9 ] In 1960, John Francis Mitchell combined elements of Motorola 's walkie-talkie and automobile radio technologies to create the first transistorized pager, [ 10 ] [ 11 ] [ 12 ] and from that time, paging technology continued to advance and pager adoption among emergency personnel was still popular as of July 2016. [ 13 ]
In 1962, the Bell System , the U.S. telephone monopoly, presented its Bellboy radio paging system at the Seattle World's Fair. Bellboy was the first commercial system for personal paging. It also marked one of the first consumer applications of the transistor (invented by Bell Labs in 1947), for which three Bell Labs inventors received a Nobel Prize in Physics in 1956. Solid-state circuitry enabled the Bellboy pager, about the size of a small TV remote device, to fit into a customer's pocket or purse, quite a feat at that time. The Bellboy was a terminal that notified the user when someone was trying to call them. Bell System Bellboy radio pagers each used three reed receiver relays, each relay tuned to one of 33 different frequencies, selectively ringing a particular customer when all three relays were activated at the same time—a precursor of DTMF . [ 14 ] When the person received an audible signal (a buzz) on the pager, the user found a telephone and called the service center, which informed the user of the caller's message.
In the mid-1980s, tone and voice radio paging became popular among emergency responders and professionals. Tone and voice pagers were activated either by a local base station, or through a telephone number assigned to each individual pager. In the 1990s, pagers became popular among the general public as a cheaper, smaller, and more reliable alternative to mobile phones . [ 15 ] The ReFLEX protocol was developed in the mid-1990s.
As prices for mobile phones declined, small form factor phones like the Motorola StarTAC and the Nokia Series 40 line came on the market, cellular connectivity expanded, and digital phones adopted text messaging , most pager customers outside of specialist fields migrated to mobile phones toward the end of the 1990s. While Motorola announced the end of its new pager manufacturing in 2001, [ 16 ] pagers remained in use in large hospital complexes. [ 17 ] First responders in rural areas with inadequate cellular coverage are often issued pagers [ citation needed ] .
The 2005 London bombings resulted in overload of TETRA systems by the emergency services and showed that pagers, with their absence of necessity to transmit an acknowledgement before showing the message, and the related capability to operate on very low signal levels, are not completely outclassed by their successors. [ 18 ] Volunteer firefighters, EMS paramedics and rescue squad members usually carry pagers to alert them of emergency call outs for their department. These pagers receive a special tone from a fire department radio frequency.
Restaurant pagers remain in wide use since the 2000s. Customers are given a portable receiver that would usually vibrate, flash, or beep when a table becomes free or when their meal is ready. [ 19 ] Pagers have been popular with birdwatchers in Great Britain and Ireland since 1991, with companies Rare Bird Alert and Birdnet Information offering news of rare birds sent to pagers that they sell. [ 20 ] [ 21 ]
Today, companies like Visiplex offer similar solutions for onsite pager systems in the medical, education and commercial sectors.
By early 2002, pager usage was rapidly declining in places like North America due to the proliferation of cellular telephones. [ 22 ]
The U.S. paging industry generated $2.1 billion in revenue in 2008, down from $6.2 billion in 2003. [ 23 ] In Canada, 161,500 Canadians paid $18.5 million for pager service in 2013. Telus Communications , one of the three major mobile carriers, announced the end to its Canadian pager service as of 31 March 2015, but rivals Bell , Rogers and PageNet intend to continue service. [ 16 ]
In 2017 the UK National Health Service was thought to have been using over 10% of the remaining pagers in the world (130,000), [ 17 ] with an annual cost of £6.6 million. [ 24 ] Matt Hancock , (then) Secretary of State for Health and Social Care , announced in February 2019 that the 130,000 pagers still in use were to be phased out. [ 25 ] NHSX announced plans in May 2020 to replace pagers and bleepers with "more modern communication tools," accelerated by the pressure placed on the service by the COVID-19 pandemic in England . [ 26 ] In August 2020, a new procurement framework for clinical communications was launched which was intended to phase out pagers by the end of 2021, replacing them with "dedicated clinical-facing communication and tasks management tools" from 25 approved suppliers. [ 27 ]
In Japan, more than ten million pagers were active in 1996. [ 3 ] On 1 October 2019, Japan's last paging service provider shut down radio signals and terminated its service. [ 3 ]
In Russia, the last paging provider was closed in November 2021. [ 28 ]
Many paging network operators now allow numeric and textual pages to be submitted to the paging networks via email. A significant convenience for users given the widespread adoption of email, and commonalities in delivery assurances . This can result in pager messages being delayed or lost. Older forms of message submission using the Telelocator Alphanumeric Protocol involve modem connections directly to a paging network and are less subject to these delays. For this reason, older forms of message submission retain their usefulness for disseminating highly-important alerts to users such as emergency services personnel.
Common paging protocols include TAP , FLEX , ReFLEX , POCSAG , GOLAY, ERMES and NTT. Past paging protocols include Two-tone and 5/6-tone. In the United States, pagers typically receive signals using the FLEX protocol in the 900 MHz band. Commercial paging transmitters typically radiate 1000 watts of effective power , resulting in a much wider coverage area per tower than a mobile phone transmitter, which typically radiates around 0.6 watts per channel. Although 900 MHz FLEX paging networks tend to have stronger in-building coverage than mobile phone networks, commercial paging service providers will work with large institutions to install repeater equipment in the event that service is not available in needed areas of the subscribing institution's buildings. This is especially critical in hospital settings where emergency staff must be able to reliably receive pages to respond to patient needs.
Unlike mobile phones, most one-way pagers do not display any information about whether a signal is being received or about the strength of the received signal. Since one-way pagers do not contain transmitters, one-way paging networks have no way to track whether a message has been successfully delivered to a pager. Because of this, if a one-way pager is turned off or is not receiving a usable signal at the time a message is transmitted, the message will not be received and the sender of the message will not be notified of this fact. In the mid-1990s, some paging companies began offering a service, which allowed a customer to call their pager number and have numeric messages read back to them. This was useful for times when the pager was off or out of the coverage area, as it would know what pages were sent to the subscriber even if the subscriber never actually received the page. Other radio bands used for pagers include the 400 MHz band, the VHF band and the FM commercial broadcast band (88–108&MHz). Other paging protocols used in the VHF, 400 MHz UHF and 900 MHz bands include POCSAG and ERMES. In Canada and the United States, pagers that use the commercial FM band receive a subcarrier, called the Subsidiary Communications Authority , of a broadcast station. On-site paging systems in hospitals, unlike wide area paging systems, are local area services. Hospitals commonly use on-site paging for communication with staff and increasingly for contacting waiting patients when their appointment is due. These offer waiting patients the opportunity to leave the waiting area, but still be contacted.
Paging systems are operated by commercial carriers, often as a subscription service and they are also operated directly by end users as private systems. Commercial carrier systems tend to cover a larger geographical area than private systems, while private systems tend to cover their limited area more thoroughly and deliver messages faster than commercial systems. In all systems, clients send messages to pagers, an activity commonly referred to as paging . System operators often assign unique phone numbers or email addresses to pagers (and pre-defined groups of pagers), enabling clients to page by telephone call, e-mail and SMS. Paging systems also support various types of direct connection protocols, which sacrifice global addressing and accessibility for a dedicated communications link. Automated monitoring and escalation software clients, often used in hospitals, IT departments and alarm companies, tend to prefer direct connections because of the increased reliability. Small paging systems, such as those used in restaurant and retail establishments, often integrate a keyboard and paging system into a single box, reducing both cost and complexity.
Paging systems support several popular direct connection protocols, including TAP , TNPP, SNPP and WCTP , as well as proprietary modem- and socket-based protocols. Additionally, organizations often integrate paging systems with their Voice-mail and PBX systems, conceptually attaching pagers to a telephone extension and set up web portals to integrate pagers into other parts of their enterprise. A paging system alerts a pager (or group of pagers) by transmitting information over an RF channel, including an address and message information. This information is formatted using a paging protocol, such as 2-tone, 5/6-tone, GOLAY, POCSAG , FLEX , ERMES , or NTT. Two-way pagers and response pagers typically use the ReFLEX protocol. [ 29 ]
Modern paging systems typically use multiple base transmitters to modulate the same signal on the same RF channel, a design approach called simulcast . This type of design enables pagers to select the strongest signal from several candidate transmitters using FM capture , thereby improving overall system performance. Simulcast systems often use satellite to distribute identical information to multiple transmitters and GPS at each transmitter to precisely time its modulation relative to other transmitters. The coverage overlap, combined with use of satellite communications, can make paging systems more reliable than terrestrial based cellular networks in some cases, including during natural and human-made disaster. [ 4 ] This resilience has led public safety agencies to adopt pagers over cellular and other commercial services for critical messaging. [ 5 ] [ 6 ]
Pagers themselves vary from very cheap and simple beepers, to more complex personal communications equipment, falling into eight main categories.
Pagers have certain privacy advantages and disadvantages compared with cellular phones. Since a one-way pager is a passive receiver only (it sends no information back to the base station), its location cannot be tracked. However, this can also be disadvantageous, as a message sent to a pager must be broadcast from every paging transmitter in the pager's service area. [ 30 ] Thus, if a pager has nationwide service, a message sent to it could be intercepted by anyone anywhere within the nationwide service area.
On September 17, 2024, a massive attack against Hezbollah members in Lebanon and Syria was committed by Israel, [ 31 ] who simultaneously detonated pagers that they were using. Lebanese Health authorities confirmed 42 deaths and over 3,000 injuries as a result of the explosions. In February 2024, Hezbollah leader Hassan Nasrallah had told the group's members to use pagers instead of cell phones, claiming that Israel had infiltrated their mobile phone network. [ 32 ] [ 33 ] [ 34 ]
As is the case with many new technologies, the functionality of the pager shifted from necessary professional use to a social tool integrated in one's personal life. [ 35 ] : 175 During the rise of the pager, it became the subject of various forms of media, most notably in the 1990s hip-hop scene. Popular artists from the era, including Ice Cube , Method Man , and A Tribe Called Quest , began referencing newly developed mobile technologies such as the pager. A Tribe Called Quest's single "Skypager" directly speaks of the importance of such a wireless communication device, with group member Q-Tip stating that the Skypager "serves an important communicative function for a young professional with a full calendar". [ 35 ] Three 6 Mafia 's "2-Way Freak," [ 36 ] Sir Mix-A-Lot 's " Beepers " [ 37 ] and " Bug a Boo " from Destiny's Child [ 38 ] also make reference to pagers.
Illicit drug dealers used pagers to great effect during the 1990s to conduct commerce, using them to arrange meetings with buyers. Associate superintendent for Miami-Dade County Public Schools in Florida Gul James Fleming once called them "the most dominant symbol of the drug trade" and schools have previously forbidden students from carrying them because of the ease with which they could be "used to arrange illegal drug sales." [ 39 ]
In season one of the TV show The Wire , the drug dealing crew of Avon Barksdale uses pagers to exchange coded messages and coordinate their activities. [ 40 ] | https://en.wikipedia.org/wiki/Pager |
Pagophagia (from Greek: pagos , frost/ice, + phagō , to eat [ 1 ] ) is the compulsive consumption of ice or iced drinks. [ 2 ] It is a form of the disorder known as pica , which in Latin refers to a magpie that eats everything indiscriminately. [ 3 ] Pica's medical definition refers to the persistent consumption of nonnutritive substances, ice in this case, for over a period of at least one month. [ 3 ] However, different studies have included alternative definitions for pagophagia, including "daily consumption of 2–11 full glasses of ice (480–2640 g)" or "the purposeful ingestion of at least one ordinary tray of ice daily for a period in excess of two months." [ 4 ] It has been shown to be associated with iron-deficiency anemia [ 5 ] and responsive to iron supplementation , [ 6 ] [ 7 ] leading some investigators to postulate that some forms of pica may be the result of nutritional deficiency . [ 8 ]
Similarly, folk wisdom also maintained that pica reflected an appetite to compensate for nutritional deficiencies, such as low iron or zinc . In iron deficient pregnant women who experience symptoms of pagophagia, decreased cravings for ice have been observed after iron supplementation. [ 9 ] Later research demonstrated that the substances ingested by those who have pica generally do not provide the mineral or nutrient in which people are deficient. In the long run, as people start consuming more nonfoods compulsively, pica can also cause additional nutritional deficiencies. [ 9 ]
A hypothesis of the neurological basis of pagophagia was proposed in a 2014 study in which those with iron deficiency anemia were shown to have improved response times while performing on a neuropsychological test when given ice to chew on. As a result, the researchers hypothesized that chewing on ice causes vascular changes that allow for increased perfusion of the brain, as well as activation of the sympathetic nervous system , which also increases blood flow to the brain, allowing for increased processing speed and alertness. [ 10 ]
Although some investigators [ 8 ] also hypothesize that chewing ice may lessen pain in glossitis and stomatitis related to iron-deficiency anemia, the specific pathophysiology is still unknown and this hypothesis remains controversial. [ 11 ] The American Dental Association recommends not chewing ice as it can lead to dental injury and suggests that ice should be allowed to melt in the mouth instead. [ 12 ]
The main symptom for pagophagia is intense cravings for chewing ice. Those with pagophagia will find themselves constantly chewing on ice cubes, shaved ice or even frost from the fridge. [ 13 ] Since a common underlying cause of pagophagia is iron-deficiency anemia , many people with the disorder will also experience weakness , fatigue , pallor , sore tongue, dizziness , headache , and cold extremities. [ medical citation needed ] Other symptoms associated with iron deficiency may include brittle nails, cracking at the corner of the mouth, and restless legs syndrome . [ 14 ] Severe cases of iron deficiency can also cause the body to make up for decreased oxygen-carrying capacity of the blood by increasing cardiac output . Thus, palpitations , angina , as well as shortness of breath may also present, specially if there is a preexisting cardiovascular disease or condition. [ 15 ] Excess water intake from any source can lead to hyponatremia and has been noted in at least one case study . [ 16 ]
Although compulsive consumption of ice is frequently associated with a deficiency of iron, the exact etiology of this form of pica is not well-understood. There is one hypothesis that states consumption of ice activates a vasoconstrictive response which causes an increase of blood flow to the brain. Because fatigue is the most common symptom experienced in iron-deficiency anemia due to decreased levels of oxygen delivered to the brain, the increase of blood flow to the brain through consumption of ice is thought to increase alertness and improve the symptoms of fatigue. In support of this hypothesis, individuals with iron-deficient anemia were found to have improved response times on neuropsychological tests than compared to healthy controls when chewing ice. [ 4 ]
Reports have demonstrated the improvement or resolution of pagophagia when given iron supplementation. [ 17 ] People with iron-deficiency anemia who showed symptoms of pagophagia had complete resolution of their symptoms when their iron levels were treated, suggesting the association between serum iron levels and symptoms of pagophagia. In another case, an individual who presented with pagophagia was prescribed 325mg tablets of ferrous sulfate twice daily. The individual was also administered 1000mg of low molecular weight dextran over 1 hour and their symptoms of pagophagia were immediately resolved. [ 14 ] In another case, a woman with iron-deficiency anemia related to gynecological bleeding was admitted and her dietary screening showed consumption of about 80 ice cubes for day for the past 5 years. She was given iron supplementation and her anemia was treated along with the disappearance of pagophagia within two weeks. [ 18 ]
One study looked at the relationship between pagophagia and H. pylori infection in those with iron deficiency anemia. It was found that pagophagia does not increase the risk of H. pylori infections in that specific population. In addition, H. pylori infection and pagophagia did not have a synergistic effect on the development of iron absorption abnormalities in the intestines. [ 19 ]
Pagophagia has been often reported with calcium deficiency but its pathophysiology is unknown. [ 20 ]
In several cases, pagophagia has been associated with certain psychological conditions such as compulsive behavior or depressive disorder where pagophagia was used as a coping mechanism to deal with psychological stress. [ 16 ] Some suggestions for other causes of pagophagia include hunger and gastrointestinal distress related to ways the body attempts to ease the stress. [ 21 ]
Other known risk factors for pica include "stress, cultural factors, learned behavior, low socioeconomic status, underlying mental health disorder, nutritional deficiency, child neglect, pregnancy, epilepsy, [and] familial psychopathology." [ 22 ]
In one case report, a 42-year-old woman presented with complaints of freezer frost and eating ice. She developed a habit of eating 10 to 12 ice cubes and freezer frost each day, and eventually increased her consumption to 25 to 30 ice cubes each day. Her medical assessment revealed no past or family history of any chronic psychiatric disorder or physical disorder. Her hemoglobin, serum calcium , and stool examination were normal. One suspected cause of her pagophagia was psychological stress, the stressor being her son's annual examinations. The woman was previously prescribed venlafaxine 50mg and vitamin B-complex for two to six weeks but with no improvement. The doctor initiated fluoxetine 20mg daily for her and the venlafaxine was tapered off. The dose was increased to 30mg after three weeks and counseling and behavioral treatment was given. Her pagophagia resolved after four months. Along with this case, previous reports have shown selective serotonin reuptake inhibitors effective in treating pagophagia. Counseling and behavioral strategies such as positive and negative reinforcement should be utilized for people with psychiatric conditions. [ 20 ]
Pagophagia may often go undiagnosed as those with the condition may consider it to be harmless and not seek medical help unless the behavior begins to interfere with their lives. However, the disorder is not as harmless as it seems since underlying medical causes that remain undiagnosed may lead to complications. For example, if anemia is not treated properly, the heart will need to exert more force in order to supply adequate oxygen throughout the body which can progress to heart failure . [ 15 ] Other complications of pagophagia include tooth sensitivity and dental injury leading to cracked or chipped teeth. Overconsumption of ice may cause bloating, gas, and stomach pain. Imaging exams such as abdominal x-rays and endoscopy may be ordered if a person presents with abdominal symptoms. [ 23 ]
Due to the relation between pagophagia and iron deficiency anemia, diagnosis begins with obtaining a medical history, a physical exam as well as blood tests that includes a complete blood count and additional tests to determine levels of hemoglobin , hematocrit , serum iron , and ferritin , a protein that helps the body store iron. [ 24 ] In individuals that are anemic, the tests would show results with lower than normal levels which would then confirm the diagnosis. If a blood slide is ordered by the doctor, it may show red blood cells that are smaller and paler than normal cells. [ 25 ] In the case of severe iron deficiency, white blood cell count may also be low. [ 25 ]
A differential diagnosis for psychiatric conditions should be performed in the setting of pagophagia. Schizophrenia and psychosis , other eating disorders, substance use , and autism should be considered in the differential diagnosis. [ 4 ]
When screening for suspected pagophagia, it may be appropriate to include screening for iron deficiency. Screening for pagophagia may help clinicians gather valuable information towards the diagnosis and treatment, especially populations who are at risk, for iron deficiency. Women who are menstruating, pregnant, or lactating may benefit from pagophagia screening because of the high occurrence of iron deficiency in these groups. Other groups at risk due to prevalence of iron deficiency include blood donors, individuals who are post-surgery or trauma, or people who experience malabsorption of iron. [ 4 ] Collecting information during health screening to determine any causes of blood loss, malabsorption of iron from the diet, and any laboratory tests to determine iron deficiency may be appropriate in people who present with symptoms of pagophagia. If iron deficiency is confirmed by laboratory screening, iron replacement therapy can be considered with oral supplementation. Over the counter or prescription formulations of iron containing ferrous gluconate , ferrous sulfate , or ferrous fumarate are available.
In one study of pica in iron deficient versus iron replete blood donors, "pica was reported in 11% of donors with iron depletion/deficiency, compared with 4% of iron-replete donors," with pagophagia accounting for 94% of reported pica cases. [ 26 ] A case series of pagophagia in men with iron-deficiency anemia concluded "that pagophagia occurred in 34% of men with iron-deficiency anemia." Men who were older and had higher platelet counts were less likely to have pagophagia compared to younger men and those with lower platelet counts. [ 27 ]
In women, pica is "most often seen during pregnancy," with estimates of 27.8% of pregnant women experiencing pica, but pica prevalence and manifestation is culturally and geographically heterogenous. [ 22 ] A study of pregnant women in Tehran, Iran found pica in 8.33% of the study population with pagophagia accounting for 76% of observed pica cases. Logistic regression showed a positive correlation between pica in pregnancy with pregnancy complications, lower educational attainment, and use of iron supplementation. [ 28 ] A study of pica in pregnant Mexican-born women living in either the United States or Mexico found differing rates of pagophagy between the two groups. [ 29 ]
A meta-analysis of the prevalence of pica in German children found that 12.3% of German children "have engaged with a pica behavior at some point in their lives," but did not specify the types of pica observed. [ 22 ] Despite pica being observed in young children, it is important to note that it is also a common eating disorder among those who are intellectually impaired. [ 22 ] Thus, proper diagnosis of pica is essential, requiring the children to be at least above two years of age, as it is more common to see children younger than two consuming nonnutritive substances. [ 22 ] In children, pica is usually short term and will disappear spontaneously. [ 22 ] In terms of studies regarding a specific type of pica, a cross-sectional study of American children receiving chronic hemodialysis therapy found that 34.5% of the children studied engaged in pagophagy compared to 12.6% of children who engaged in other forms of pica. [ 30 ] | https://en.wikipedia.org/wiki/Pagophagia |
Pain asymbolia , also called pain dissociation , is a condition in which pain is experienced without unpleasantness . This usually results from injury to the brain, lobotomy , cingulotomy or morphine analgesia . Preexisting lesions of the insula may abolish the aversive quality of painful stimuli while preserving the location and intensity aspects. Typically, patients report that they have pain but are not bothered by it; they recognize the sensation of pain but are mostly or completely immune to suffering from it. The pathophysiology of this disease revolves around a disconnect between the insular cortex secondary to damage and the limbic system , specifically the cingulate gyrus whose prime response to the pain perceived by insular cortex is to tether it with an agonizing emotional response thus signaling the individual of its propensity to inflict actual harm. However, a disconnect is not the only prime causative factor, as damage to these aforementioned cortical structures also results in the same symptomology. [ 1 ] [ 2 ] [ 3 ]
This article about a disease , disorder, or medical condition is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Pain_asymbolia |
In physics , the Painlevé conjecture is a theorem about singularities among the solutions to the n -body problem : there are noncollision singularities for n ≥ 4. [ 1 ] [ 2 ]
The theorem was proven for n ≥ 5 in 1988 by Jeff Xia [ 3 ] [ 4 ] and for n = 4 in 2014 by Jinxin Xue. [ 5 ] [ 6 ]
Solutions ( q , p ) {\displaystyle (\mathbf {q} ,\mathbf {p} )} of the n -body problem q ˙ = M − 1 p , p ˙ = ∇ U ( q ) {\displaystyle {\dot {\mathbf {q} }}=M^{-1}\mathbf {p} ,\;{\dot {\mathbf {p} }}=\nabla U(\mathbf {q} )} (where M are the masses and U denotes the gravitational potential ) are said to have a singularity if there is a sequence of times t n {\displaystyle t_{n}} converging to a finite t ∗ {\displaystyle t^{*}} where ∇ U ( q ( t n ) ) → ∞ {\displaystyle \nabla U\left(\mathbf {q} \left(t_{n}\right)\right)\rightarrow \infty } . That is, the forces and accelerations become infinite at some finite point in time.
A collision singularity occurs if q ( t ) {\displaystyle \mathbf {q} (t)} tends to a definite limit when t → t ∗ , t < t ∗ {\displaystyle t\rightarrow t^{*},t<t^{*}} . If the limit does not exist the singularity is called a pseudocollision or noncollision singularity.
Paul Painlevé showed that for n = 3 any solution with a finite time singularity experiences a collision singularity. However, he failed at extending this result beyond 3 bodies. His 1895 Stockholm lectures end with the conjecture: [ 7 ] [ 8 ]
For n ≥ 4 the n -body problem admits noncollision singularities.
Edvard Hugo von Zeipel proved in 1908 that if there is a collision singularity, then J ( q ( t ) ) {\displaystyle J(\mathbf {q} (t))} tends to a definite limit as t → t ∗ {\displaystyle t\rightarrow t^{*}} , where J ( q ) = ∑ i m i | q i | 2 {\displaystyle J(\mathbf {q} )=\sum _{i}m_{i}|\mathbf {q} _{i}|^{2}} is the moment of inertia . [ 9 ] This implies that a necessary condition for a noncollision singularity is that the velocity of at least one particle becomes unbounded (since the positions q {\displaystyle \mathbf {q} } remain finite up to this point). [ 1 ]
Mather and McGehee managed to prove in 1975 that a noncollision singularity can occur in the co-linear 4-body problem (that is, with all bodies on a line), but only after an infinite number of (regularized) binary collisions. [ 10 ]
Donald G. Saari proved in 1977 that for almost all (in the sense of Lebesgue measure ) initial conditions in the plane or space for 2, 3 and 4-body problems there are singularity-free solutions. [ 11 ]
In 1984, Joe Gerver gave an argument for a noncollision singularity in the planar 5-body problem with no collisions. [ 12 ] He later found a proof for the 3 n body case. [ 13 ]
Finally, in his 1988 doctoral dissertation, Jeff Xia demonstrated a 5-body configuration that experiences a noncollision singularity. [ 3 ] [ 4 ]
Joe Gerver has given a heuristic model for the existence of 4-body singularities. [ 14 ]
In his 2013 doctoral thesis at University of Maryland, Jinxin Xue considered a simplified model for the planar four-body problem case of the Painlevé conjecture. Based on a model of Gerver, he proved that there is a Cantor set of initial conditions which lead to solutions of the Hamiltonian system whose velocities are accelerated to infinity within finite time avoiding all earlier collisions. In 2014, Xue extended his previous work and proved the conjecture for n=4. [ 15 ] [ 5 ] [ 6 ]
Due to the symmetry constraint, Xia's model is only valid for the 5-body problem. Gerver-Xue's model does not have such a constraint, and is likely to be generalized to the general N>4 body problem. | https://en.wikipedia.org/wiki/Painlevé_conjecture |
In the paint and coating industries, paint adhesion testing is often used to determine if the paint or coating will adhere properly to the substrates to which they are applied. Several tests measure the resistance of paints and coatings from substrates: cross-cut test, scrape adhesion, pull-off test , and others. [ 1 ]
The scrape adhesion test measures the determination of the adhesion of organic coatings when applied to smooth, flat panel surfaces. It is helpful in giving relative ratings for a number of coated panels showing significant differences in adhesion. The tested materials are applied uniformly to flat panels, mainly some sort of sheet metal. When the materials have dried, the adhesion is determined by pressing panels under a rounded stylus loaded with increasing weight until the coating is removed from the substrate surface. [ 2 ]
The adhesion of a coating or several coated samples of any paint product is measured by assessing the minimum tensile stress needed to detach or rupture the coating perpendicular to the substrate. Unlike the other methods, this method maximizes the tensile stress, therefore, results may not be comparable. The test is done by securing loading fixtures (dollies) perpendicular to the surface of a coating with an adhesive. Then the testing apparatus is attached to the loading fixture and aligned to apply tension perpendicular to the test surface. The force that is applied gradually increases and is monitored until a plug of coating is detached or a previously specified value is reached. [ 3 ]
The cross-cut test is a method for determining the resistance of paints and coatings to separation from substrates by utilizing a tool to cut a right-angle lattice pattern into the coating, penetrating
to the substrate.
A quick pass/fail test can be accomplished through this method. When testing a multi-coat system, determination of the resistance to separating different layers from one another can be accomplished.
There are two methods described in the ASTM Specification; [ 4 ]
An X-cut is made through the film with a carbide tip tool to the substrate.
Pressure-sensitive tape is applied over the cut.
Tape is smoothed into place using a pencil eraser over the area of the incisions.
Tape is removed by pulling it off rapidly back over itself as close to an angle of 180°.
Adhesion is assessed on a 0 to 5 scale.
A crosshatch pattern is made through the film to the substrate.
Detached flakes of coating are removed by brushing with a soft brush.
Pressure-sensitive tape is applied over the crosshatch cut.
Tape is smoothed into place using a pencil eraser over the area of the incisions.
Tape is removed by pulling it off rapidly back over itself as close to an angle of 180°.
Adhesion is assessed on a 0 to 5 scale.
[0- Greater than 65% area removed & 5 is 0% area removed] | https://en.wikipedia.org/wiki/Paint_adhesion_testing |
Paint by number or painting by numbers kits are self-contained painting sets, designed to facilitate painting a pre-designed image. They generally include brushes , tubs of paint with numbered labels, and a canvas printed with borders and numbers. The user selects the color corresponding to one of the numbers then uses it to fill in a delineated section of the canvas, in a manner similar to a coloring book .
The kits were invented, developed and marketed in 1950 by Max S. Klein, an engineer and owner of the Palmer Paint Company in Detroit, Michigan, United States, and Dan Robbins, a commercial artist. When Palmer Paint introduced crayons to consumers, they also posted images online for a "Crayon by Number" version.
The first patent for the paint-by-number technique was filed in 1923. [ 1 ] Paint by Number in its popular form was created by the Palmer Show Card Paint Company. The owner of the company approached employee Dan Robbins with the idea for the project. After several iterations of the product, the company in 1951 introduced the Craft Master brand, which went on to sell over 12 million kits. [ 1 ] [ 2 ] This public response induced other companies to produce their own versions of painting by number. The Craft Master paint kit box tops proclaimed, "A BEAUTIFUL OIL PAINTING THE FIRST TIME YOU TRY."
Following the death of Max Klein in 1993, his daughter Jacquelyn Schiffman donated the Palmer Paint Co. archives to the Smithsonian Museum of American History . [ 3 ] The archival materials have been placed in the museum's Archives Center where they have been designated collection #544, the "Paint by Number Collection". [ 4 ]
In 1992, Michael O'Donoghue and Trey Speegle organized and mounted a show of O'Donoghue's paint-by-number collection in New York City at the Bridgewater/Lustberg Gallery. After O'Donoghue's death in 1994, the Smithsonian Institution 's National Museum of American History exhibited many key pieces from O'Donoghue's collection, now owned by Speegle, along with works from other collectors in 2001. [ 3 ]
In 2008, a private collector [ who? ] in Massachusetts assembled over 6,000 paint-by-number works dating back to the 1950s from eBay and other American collectors to create the Paint By Number Museum, the world's largest online archive of paint-by-number works. In 2011, the Museum of Modern Art in New York accepted four early designs of paint by number by Max Klein for its Department of Architecture and Design, donated by Jacquelyn Schiffman.
In May 2011, Dan Robbins and Palmer Paint Products, Inc., together developed and brought to market a new 60th-anniversary paint-by-number set. [ 5 ] This collectors set was created in memory of the survivors and those who had lost their lives on September 11, 2001 , and depicts the Twin Towers standing in spirit across the Manhattan skyline.
On April 1, 2019, Dan Robbins died in Sylvania, Ohio, at the age of 93. [ 6 ] [ 7 ] | https://en.wikipedia.org/wiki/Paint_by_number |
Industrial paint robots have been used for decades in automotive paint applications.
Early paint robots were hydraulic versions, which are still in use today but are of inferior quality and safety to the latest electronic offerings. [ 1 ] [ 2 ] [ 3 ] The newest robots are accurate and deliver results with uniform film builds and exact thicknesses.
Originally, industrial paint robots were large and expensive, but robot prices have come down to the point that general industry can now afford the same level of automation used by the large automotive manufacturers.
The selection of modern paint robot varies much more in size and payload to allow many configurations for painting items of all sizes.
Painting robots generally have five or six axis motion, three for the base motions and up to three for applicator orientation. These robots can be used in any explosion hazard Class 1 Division 1 environment.
Industrial paint robots are designed to help standardize the distance and path the automatic sprayer takes, thus eliminating the risk of human error caused by manual spraying. Paint robots are often paired with other automatic painting equipment to maximize the efficiency and consistency of the paint finish. Rotational Bell atomizers, other automatic electrostatic or automatic conventional sprayers are mounted on the robot to provide the highest quality finish. Automatic mixing equipment will usually supply the sprayers with paint. This equipment is designed to regulate pressure and flow, which are extremely important in providing consistent paint finish. Varying levels of automatic mixing equipment can also provide features that cut down on paint waste, and energy costs.
The worlds first painting robot was developed at Trallfa, [ 4 ] a wheelbarrow factory in Bryne, Norway. The development started in 1964 to aid in the painting of the wheelbarrows and to reduce human interaction with toxic paint chemicals. In 1966 the robot was recruited for production in the factory painting the trolleys and wheelbarrows. By 1969 the robot was commercialized as its own product. The first robot, TR2000, was delivered to Swedish Gustavsberg Porcelain for enamelling bath tubs. [ 5 ]
Painting robots have been around since at least 1985. [ 6 ] They were first introduced in the automative industry , including at General Motors' plant in Michigan. [ 7 ]
Industrial robots , including painting ones, were created to keep people out of "dangerous" jobs as well as increase productivity. [ 8 ] Since their creation, robots have been working side by side with people in manufacturing companies. [ 9 ]
In recent years, the painting robot has evolved past industrial use. Many inventors have taken on the idea of creating robots that can create works of art, rather than paint in just a solid color. [ 10 ] Besides making them more creative, others have looked for ways to make the robots affordable and accessible for commercial use in places such as interior wall painting. [ 11 ]
Painting robots are used by vehicle manufacturers to do detailing work on their cars in a consistent and systematic way. Some of these robots are designed with a robotic arm that moves vertically and horizontally, to apply paint on all parts of the car. [ 6 ] A patent granted in 1985 to the Mazda Motor Corporation also includes a door handler (a small mechanical hand) that can open and close doors on a vehicle and paint the interior. [ 6 ]
Companies like FANUC continue to mass-produce industrial painting robots that are then sold to manufacturers for use. [ 12 ] According to FANUC's website, these robots are useful in limiting safety hazard such as the toxicity of paint, reducing wasted materials through consistent application, and increasing productivity. [ 12 ]
Robots are used to paint all different sized automotive parts because they can help provide consistent finish from one part to another. They are used for large exterior parts like doors, hoods, wheels, or bumpers, and also used on small interior components like knobs, consoles and glove boxes.
Finish is also extremely important in the aerospace and defense industry. These parts require very precise specifications for safety and performance reasons. Coatings can provide erosion resistance, anti-static dissipation, and even radar evading stealth. For this reason, consistent finish on all parts is vital to ensure continuity throughout.
Aluminum extrusion can be found in building panels, metal door and window frames, and structural extrusions that are used in the commercial building industry for protecting buildings and increase aesthetic appeal. Many panel and extrusion manufacturers are faced with slim margins. With that, comes pressure to improve quality, continue to reduce costs, produce faster and provide more customization for their consumers. Because of this, many manufacturers in aluminum extrusions and panels are using paint robots and automatic applicators to apply coatings for protection and aesthetics.
Agricultural and construction equipment finish is important because these types of machines face heavy operation in abuse from harsh environments. Coatings help to protect the machines form rust and extend their life cycle. In this industry, product branding plays a big role for many companies trying to differentiate themselves, so high quality finish is a strong factor for many manufacturers.
In order to provide a durable paint coating with strong aesthetic appeal is not an easy task and can involve several layers of different component materials. In an agricultural or construction equipment manufacturer, there are usually multiple pump configurations feeding a plural component proportioning unit that mixes the multiple components of the paint. The proportioner feeds an automatic applicator hooked up to a robot. With several passes with different coatings, consistency is also very important because it minimizes rework and downtime if it is finished right the first time.
Cookware technology continues to evolve using different high performance coatings in order to meet the needs of chefs or people cooking at home. Different types of cookware have unique performance requirements. They need to be able to evenly conduct heat, resist abrasion and impact from repeated utensil use, provide non-stick coatings, provide maximum cleaning ability, and have strong aesthetic appeal. The same pan may need to be coated multiple times with different materials to meet all of its performance requirements.
Paint line robots are very useful paired with an automatic applicator in this environment because each part requires multiple passes with different coatings. The performance of the cookware in each of its specific requirements will hinge solely on the quality of finish of each material. Paint robots provide the same spray pattern and paint path on every pass, minimizing rework for badly finished parts.
There are many different types of containers used in the cosmetic industry . Manufacturers in this industry are concerned with perfect packaging appearance, many using mirror finishes. Any surface imperfections will cause the piece to be rejected or scrapped. The problem is mirror finishes can actually amplify finish imperfections.
In order to reduce rework costs, the base coat needs to be applied to a very consistent and smooth manner with zero variation. This is accomplished by controlling flow rate from the proportioning unit, having fine atomization from the applicator and a very consistent spray pattern provided from a painting robot.
There are multiple ideas people have come up with to increase the presence of painting robots in various industries. One such idea comes from technology professors; an interior wall painting robot. The design aims to make the robots “roller-based” so that it can move freely along walls and apply paint to them. [ 11 ] The hope is to get people out of the toxicity of interior painting and decrease the amount of time it takes to finish walls. [ 11 ] According to the designers, the robot can be made inexpensively as to make it more commercially available.
CloudPainter is a company that designs robots, whose take on the painting robot shifts from simple filling of color to a robot that has “ computational creativity ,” and can paint more detailed and original designs. [ 14 ] The robot has a 3-D printed paint-head with multiple robotic arms and is programmed with artificial intelligence and deep learning . [ 14 ]
A painting robot designed by Shunsuke Kudoh is equipped with fingered hands and stereo vision. It is capable of looking (with a digital camera eye) at an object, then, using its fingers, pick up a paintbrush and copy the object onto a canvas. [ 10 ] The robot is relatively small and can paint small things, such as an apple. [ 10 ]
Ai-Da, a humanoid robot created by Aidan Meller, is prompted by AI algorithms to create paintings using her robotic arm, a paintbrush, and palette. [ 15 ] [ 16 ]
Clockwork, a manicurist robot, uses two 3D cameras to paint a fingernail in about 30 seconds. [ 17 ] [ 18 ] | https://en.wikipedia.org/wiki/Paint_robot |
A paint sealant is a sealant that protects cars from ultraviolet rays and acid rain . Paint sealants protect cars' finishes, and can make cars shiny. There are synthetic sealants and carnauba waxes.
Salt may be a factor that many protective sealants do not defend against, and thus salt water may break down protective layers to get at the metal and corrode it.
Paint sealant works by filling into the pores and irregular surface of the body thereby creating a smooth finish on top. The way it helps is it denies a sticking surface to foreign substance and they come off the car easily without further damaging the car surface. [ 1 ]
This material -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Paint_sealant |
A Gabriel's horn (also called Torricelli's trumpet ) is a type of geometric figure that has infinite surface area but finite volume . The name refers to the Christian tradition where the archangel Gabriel blows the horn to announce Judgment Day . The properties of this figure were first studied by Italian physicist and mathematician Evangelista Torricelli in the 17th century.
These colourful informal names and the allusion to religion came along later. [ 1 ] Torricelli's own name for it is to be found in the Latin title of his paper De solido hyperbolico acuto , written in 1643, a truncated acute hyperbolic solid , cut by a plane. [ 2 ] Volume 1, part 1 of his Opera geometrica published the following year included that paper and a second more orthodox (for the time) Archimedean proof of its theorem about the volume of a truncated acute hyperbolic solid. [ 2 ] [ 3 ] This name was used in mathematical dictionaries of the 18th century, including "Hyperbolicum Acutum" in Harris' 1704 dictionary and in Stone's 1726 one, and the French translation Solide Hyperbolique Aigu in d'Alembert's 1751 one. [ 1 ]
Although credited with primacy by his contemporaries, Torricelli was not the first to describe an infinitely long shape with a finite volume or area. [ 4 ] The work of Nicole Oresme in the 14th century had either been forgotten by, or was unknown to them. [ 4 ] Oresme had posited such things as an infinitely long shape constructed by subdividing two squares of finite total area 2 using a geometric series and rearranging the parts into a figure, infinitely long in one dimension, comprising a series of rectangles. [ 5 ]
Gabriel's horn is formed by taking the graph of y = 1 x , {\displaystyle y={\frac {1}{x}},} with the domain x ≥ 1 {\displaystyle x\geq 1} and rotating it in three dimensions about the x axis. The discovery was made using Cavalieri's principle before the invention of calculus , but today, calculus can be used to calculate the volume and surface area of the horn between x = 1 and x = a , where a > 1 . [ 6 ] Using integration (see Solid of revolution and Surface of revolution for details), it is possible to find the volume V and the surface area A : V = π ∫ 1 a ( 1 x ) 2 d x = π ( 1 − 1 a ) , {\displaystyle V=\pi \int _{1}^{a}\left({\frac {1}{x}}\right)^{2}\,\mathrm {d} x=\pi \left(1-{\frac {1}{a}}\right),} A = 2 π ∫ 1 a 1 x 1 + ( − 1 x 2 ) 2 d x > 2 π ∫ 1 a d x x = 2 π ⋅ [ ln x ] 1 a = 2 π ln a . {\displaystyle A=2\pi \int _{1}^{a}{\frac {1}{x}}{\sqrt {1+\left(-{\frac {1}{x^{2}}}\right)^{2}}}\,\mathrm {d} x>2\pi \int _{1}^{a}{\frac {\mathrm {d} x}{x}}=2\pi \cdot \left[\ln x\right]_{1}^{a}=2\pi \ln a.}
The value a can be as large as required, but it can be seen from the equation that the volume of the part of the horn between x = 1 and x = a will never exceed π ; however, it does gradually draw nearer to π as a increases. Mathematically, the volume approaches π as a approaches infinity. Using the limit notation of calculus, [ 7 ] lim a → ∞ V = lim a → ∞ π ( 1 − 1 a ) = π ⋅ lim a → ∞ ( 1 − 1 a ) = π . {\displaystyle \lim _{a\to \infty }V=\lim _{a\to \infty }\pi \left(1-{\frac {1}{a}}\right)=\pi \cdot \lim _{a\to \infty }\left(1-{\frac {1}{a}}\right)=\pi .}
The surface area formula above gives a lower bound for the area as 2 π times the natural logarithm of a . There is no upper bound for the natural logarithm of a , as a approaches infinity. That means, in this case, that the horn has an infinite surface area. That is to say, [ 7 ] lim a → ∞ A ≥ lim a → ∞ 2 π ln a = ∞ . {\displaystyle \lim _{a\to \infty }A\geq \lim _{a\to \infty }2\pi \ln a=\infty .}
Torricelli's original non-calculus proof used an object, slightly different to the aforegiven, that was constructed by truncating the acute hyperbolic solid with a plane perpendicular to the x axis and extending it from the opposite side of that plane with a cylinder of the same base. [ 8 ] Whereas the calculus method proceeds by setting the plane of truncation at x = 1 {\displaystyle x=1} and integrating along the x axis, Torricelli proceeded by calculating the volume of this compound solid (with the added cylinder) by summing the surface areas of a series of concentric right cylinders within it along the y axis and showing that this was equivalent to summing areas within another solid whose (finite) volume was known. [ 9 ]
In modern terminology this solid was created by constructing a surface of revolution of the function (for strictly positive b ) [ 9 ]
y = { 1 c , where 0 ≤ x ≤ b , 1 x , where b ≤ x . {\displaystyle \quad {}y={\begin{cases}{\dfrac {1}{c}},&{\text{where }}0\leq x\leq b,\\{\dfrac {1}{x}},&{\text{where }}b\leq x.\end{cases}}}
and Torricelli's theorem was that its volume is the same as the volume of the right cylinder with height 1 / b {\displaystyle 1/b} and radius 2 {\displaystyle {\sqrt {2}}} : [ 9 ] [ 8 ]
Theorem. An acute hyperbolic solid, infinitely long, cut by a plane [perpendicular] to the axis, together with the cylinder of the same base, is equal to that right cylinder of which the base is the latus versum (that is, the axis) of the hyperbola, and of which the altitude is equal to the radius of the basis of this acute body.
Torricelli showed that the volume of the solid could be derived from the surface areas of this series of concentric right cylinders whose radii were 1 / b ≥ r ≥ 0 {\displaystyle 1/b\geq r\geq 0} and heights h = 1 / r {\displaystyle h=1/r} . [ 9 ] Substituting in the formula for the surface areas of (just the sides of) these cylinders yields a constant surface area for all cylinders of 2 π r h = 2 π r × 1 / r = 2 π {\displaystyle 2\pi rh=2\pi r\times 1/r=2\pi } . [ 9 ] This is also the area of a circle of radius 2 , {\displaystyle {\sqrt {2}},} and the nested surfaces of the cylinders (filling the volume of the solid) are thus equivalent to the stacked areas of the circles of radius 2 {\displaystyle {\sqrt {2}}} stacked from 0 to 1 / b {\displaystyle 1/b} , and hence the volume of the aforementioned right cylinder, which is known to be V = π r 2 h = π ( 2 ) 2 × 1 / b = 2 π / b {\displaystyle V=\pi r^{2}h=\pi ({\sqrt {2}})^{2}\times 1/b=2\pi /b} : [ 9 ]
Propterea omnes simul superficies cylindricae, hoc est ipsum solidum acutum e b d {\displaystyle ebd} , una cum cylindro basis f e d c {\displaystyle fedc} , aequale erit omnibus circulis simul, hoc est cylindro a c g h {\displaystyle acgh} . Quod erat etc.
(Therefore all the surfaces of the cylinders taken together, that is the acute solid E B D {\displaystyle EBD} itself, is the same as the cylinder of base F E D C {\displaystyle FEDC} , which will be equal to all its circles taken together, that is to cylinder A C G H {\displaystyle ACGH} .)
(The volume of the added cylinder is of course V c = π r 2 × h = π ( 1 / b ) 2 × b = π / b {\displaystyle V_{c}=\pi r^{2}\times h=\pi (1/b)^{2}\times b=\pi /b} and thus the volume of the truncated acute hyperbolic solid alone is V s = V − V c = 2 π / b − π / b = π / b {\displaystyle V_{s}=V-V_{c}=2\pi /b-\pi /b=\pi /b} . If b = 1 {\displaystyle b=1} , as in the modern calculus derivation, V s = π {\displaystyle V_{s}=\pi } .)
In the Opera geometrica this is one of two proofs of the volume of the (truncated) acute hyperbolic solid. [ 3 ] The use of Cavalieri's indivisibles in this proof was controversial at the time and the result shocking (Torricelli later recording that Gilles de Roberval had attempted to disprove it); so when the Opera geometrica was published, the year after De solido hyperbolico acuto , Torricelli also supplied a second proof based upon orthodox Archimedean principles showing that the right cylinder (height 1 / b {\displaystyle 1/b} radius 2 {\displaystyle {\sqrt {2}}} ) was both upper and lower bound for the volume. [ 3 ] Ironically, this was an echo of Archimedes' own caution in supplying two proofs, mechanical and geometrical, in his Quadrature of the Parabola to Dositheus. [ 11 ]
When the properties of Gabriel's horn were discovered, the fact that the rotation of an infinitely large section of the xy plane about the x axis generates an object of finite volume was considered a paradox . While the section lying in the xy plane has an infinite area, any other section parallel to it has a finite area. Thus the volume, being calculated from the "weighted sum" of sections, is finite.
Another approach is to treat the solid as a stack of disks with diminishing radii . The sum of the radii produces a harmonic series that goes to infinity. However, the correct calculation is the sum of their squares. Every disk has a radius r = 1/ x and an area π r 2 or π/ x 2 . The series Σ 1/ x diverges , but the series Σ 1/ x 2 converges . In general, for any real ε > 0 , the series Σ 1/ x 1+ ε converges. (see Particular values of the Riemann zeta function for more detail on this result)
The apparent paradox formed part of a dispute over the nature of infinity involving many of the key thinkers of the time, including Thomas Hobbes , John Wallis , and Galileo Galilei . [ 12 ]
There is a similar phenomenon that applies to lengths and areas in the plane. The area between the curves 1/ x 2 and −1/ x 2 from 1 to infinity is finite, but the lengths of the two curves are clearly infinite.
In lecture 16 of his 1666 Lectiones , Isaac Barrow held that Torricelli's theorem had constrained Aristotle 's general dictum (from De Caelo book 1, part 6) that "there is no proportion between the finite and the infinite". [ 13 ] [ 14 ] Aristotle had himself, strictly speaking, been making a case for the impossibility of the physical existence of an infinite body rather than a case for its impossibility as a geometrical abstract. [ 13 ] Barrow had been adopting the contemporary 17th-century view that Aristotle's dictum and other geometrical axioms were (as he had said in lecture 7) from "some higher and universal science", underpinning both mathematics and physics. [ 15 ] Thus Torricelli's demonstration of an object with a relation between a finite (volume) and an infinite (area) contradicted this dictum, at least in part. [ 15 ] Barrow's explanation was that Aristotle's dictum still held, but only in a more limited fashion when comparing things of the same type, length with length, area with area, volume with volume, and so forth. [ 15 ] It did not hold when comparing things of two different genera (area with volume, for example) and thus an infinite area could be connected to a finite volume. [ 15 ]
Others used Torricelli's theorem to bolster their own philosophical claims, unrelated to mathematics from a modern viewpoint. [ 16 ] Ignace-Gaston Pardies in 1671 used the acute hyperbolic solid to argue that finite humans could comprehend the infinite, and proceeded to offer it as proof of the existences of God and immaterial souls. [ 16 ] [ 17 ] Since finite matter could not comprehend the infinite, Pardies argued, the fact that humans could comprehend this proof showed that humans must be more than matter, and have immaterial souls. [ 17 ] In contrast, Antoine Arnauld argued that because humans perceived a paradox here, human thought was limited in what it could comprehend, and thus is not up to the task of disproving divine, religious, truths. [ 16 ]
Hobbes' and Wallis' dispute was actually within the realm of mathematics: Wallis enthusiastically embracing the new concepts of infinity and indivisibles, proceeding to make further conclusions based upon Torricelli's work and to extend it to employ arithmetic rather than Torricelli's geometric arguments; and Hobbes claiming that since mathematics is derived from real world perceptions of finite things, "infinite" in mathematics can only mean "indefinite". [ 18 ] These led to strongly worded letters by each to the Royal Society and in Philosophical Transactions , Hobbes resorting to namecalling Wallis "mad" at one point. [ 19 ] In 1672 Hobbes tried to re-cast Torricelli's theorem as about a finite solid that was extended indefinitely , in an attempt to hold on to his contention that "natural light" (i.e. common sense) told us that an infinitely long thing must have an infinite volume. [ 19 ] This aligned with Hobbes' other assertions that the use of the idea of a zero-width line in geometry was erroneous, and that Cavalieri's idea of indivisibles was ill-founded. [ 20 ] Wallis argued that there existed geometrical shapes with finite area/volume but no centre of gravity based upon Torricelli, stating that understanding this required more of a command of geometry and logic "than M. Hobs [ sic ] is Master of". [ 21 ] He also restructured the arguments in arithmetical terms as the sums of arithmetic progressions , sequences of arithmetic infinitesimals rather than sequences of geometric indivisibles. [ 22 ]
Oresme had already demonstrated that an infinitely long shape can have a finite area where, as one dimension tends towards infinitely large, another dimension tends towards infinitely small. [ 23 ] In Barrow's own words "the infinite diminution of one dimension compensates for the infinite increase of the other", [ 23 ] in the case of the acute hyperbolic solid by the equation of the Apollonian hyperbola x y = 1 {\textstyle xy=1} . [ 24 ]
Since the horn has finite volume but infinite surface area, there is an apparent paradox that the horn could be filled with a finite quantity of paint and yet that paint would not be sufficient to coat its surface. [ 25 ] However, this paradox is again only an apparent paradox caused by an incomplete definition of "paint", or by using contradictory definitions of paint for the actions of filling and painting. [ 26 ]
One could be postulating a "mathematical" paint that is infinitely divisible (or can be infinitely thinned, or simply zero-width like the zero-width geometric lines that Hobbes took issue with) and capable of travelling at infinite speed, or a "physical" paint with the properties of paint in the real world. [ 26 ] With either one, the apparent paradox vanishes: [ 26 ]
With "mathematical" paint, it does not follow in the first place that an infinite surface area requires an infinite volume of paint, as infinite surface area times zero-thickness paint is indeterminate . [ 26 ]
With physical paint, painting the outside of the solid would require an infinite amount of paint because physical paint has a non-zero thickness. Torricelli's theorem does not talk about a layer of finite width on the outside of the solid, which in fact would have infinite volume. Thus there is no contradiction between infinite volume of paint and infinite surface area to cover. [ 26 ] It is also impossible to paint the interior of the solid, the finite volume of Torricelli's theorem, with physical paint, so no contradiction exists. [ 26 ] This is because physical paint can only fill an approximation of the volume of the solid. [ 27 ] [ 28 ] The molecules do not completely tile 3-dimensional space and leave gaps, and there is a point where the "throat" of the solid becomes too narrow for paint molecules to flow down. [ 26 ] [ 27 ]
Physical paint travels at a bounded speed and would take an infinite amount of time to flow down. [ 29 ] This also applies to "mathematical" paint of zero thickness if one does not additionally postulate it flowing at infinite speed. [ 29 ]
Other different postulates of "mathematical" paint, such as infinite-speed paint that gets thinner at a fast enough rate, remove the paradox too. For volume π {\displaystyle \pi } of paint, as the surface area to be covered A tends towards infinity, the thickness of the paint π / A {\displaystyle \pi /A} tends towards zero. [ 30 ] Like with the solid itself, the infinite increase of the surface area to be painted in one dimension is compensated by the infinite decrease in another dimension, the thickness of the paint.
"Gabriel's wedding cake" is a discrete version of Gabriel's horn, in which the continuous horn shape is approximated by an infinite series of cylinders, but shares the same overall properties as the continuous version; the name derives from the similarity to a multi-tiered wedding cake . It has been used as a teaching tool for students who are not yet familiar with calculus. [ 31 ] [ 32 ]
The converse of Torricelli's acute hyperbolic solid would be a surface of revolution that has a finite surface area but an infinite volume.
In response to Torricelli's theorem, after learning of it from Marin Mersenne , Christiaan Huygens and René-François de Sluse wrote letters to each other about extending the theorem to other infinitely long solids of revolution; which have been mistakenly identified as finding such a converse. [ 33 ]
Jan A. van Maanen, professor of mathematics at the University of Utrecht , reported in the 1990s that he once mis-stated in a conference at Kristiansand that de Sluse wrote to Huygens in 1658 that he had found such a shape: [ 34 ]
evi opera dedicator meansura vasculie, pondere non magni, quod interim helluo nullus ebibat
(I give the measurements of a drinking glass (or vase), that has a small weight, but that even the hardest drinker could not empty.)
to be told in response (by Tony Gardiner and Man-Keung Siu of the University of Hong Kong ) that any surface of rotation with a finite surface area would of necessity have a finite volume. [ 34 ]
Professor van Maanen realized that this was a misinterpretation of de Sluse's letter, and that what de Sluse was actually reporting that the solid "goblet" shape, formed by rotating the cissoid of Diocles and its asymptote about the y axis, had a finite volume (and hence "small weight") and enclosed a cavity of infinite volume. [ 35 ]
Huygens first showed that the area of the rotated two-dimensional shape (between the cissoid and its asymptote) was finite, calculating its area to be 3 times the area of the generating circle of the cissoid, and de Sluse applied Pappus's centroid theorem to show that the solid of revolution thus has finite volume, being a product of that finite area and the finite orbit of rotation. [ 35 ] The area being rotated is finite; de Sluse did not actually say anything about the surface area of the resultant rotated volume. [ 35 ]
Such a converse essentially cannot occur:
First, observe that f is bounded on D . For if lim x → a f ( x ) = ± ∞ {\displaystyle \lim _{x\to a}f(x)=\pm \infty } for some (possibly infinite) a , then there is an open neighbourhood of a on which the solid's surface area is infinite. Hence there is an M > 0 that bounds f on D : | f ( x ) | < M . {\displaystyle |f(x)|<M.}
The volume is then given by V = ∫ D f ( x ) ⋅ π f ( x ) d x ≤ ∫ D M 2 ⋅ 2 π f ( x ) d x ≤ M 2 ⋅ ∫ D 2 π f ( x ) 1 + f ′ ( x ) 2 d x = M 2 ⋅ S < ∞ . {\displaystyle {\begin{aligned}V&=\int _{D}f(x)\cdot \pi f(x)\,\mathrm {d} x\\&\leq \int _{D}{\frac {M}{2}}\cdot 2\pi f(x)\,\mathrm {d} x\\&\leq {\frac {M}{2}}\cdot \int _{D}2\pi f(x){\sqrt {1+f'(x)^{2}}}\,\mathrm {d} x={\frac {M}{2}}\cdot S<\infty .\end{aligned}}} | https://en.wikipedia.org/wiki/Painter's_paradox |
Painting with Fire ( PWF ) is the name given to an immersion process for creating torch fired enamel jewelry . This process is the focal point of torch fired enamel jewelry workshops taught by Barbara A. Lewis , written about in her book, and discussed in Belle Armoire Jewelry , [ 1 ] [ 2 ] [ 3 ] Handcrafted Jewelry , [ 4 ] Bead Trends , [ 5 ] Stringing [ 6 ] and Bead Unique . [ 7 ]
Historically, enameling is the application of glass-on-metal (See vitreous enamel ). Traditional enameling methods, such as Cloisonné and Grisaille , require expensive kilns and often years of training and experience.
The torch firing of enamel, a process that requires a fuel source such as propane or map gas, is inexpensive and accessible to the jewelry artist who has neither the time nor the financial resources to create a traditional enamel studio.
The predominant process for producing torch fired enamel jewelry involves placing a cold and pre-washed metal piece (typically copper) on a tripod, heating the piece with a hand-held gas-fueled torch and sifting enamel onto the heated metal. This method, while less expensive than kiln-fired enameling, can be slow and pose significant safety concerns.
More than 40 years ago, Joseph Spencer of Safety Harbor, Florida , pioneered Multi-Torch Fired Enameling [ 8 ] Barbara Lewis, a long-time ceramic artist and student of Spencer, has applied Spencer's process to develop the Painting with Fire (PWF) Immersion Process.
Unlike the usual tripod-based torch firing methods, the PWF Immersion Process uses a mounted, inexpensive stationary torch and heating the unwashed cold metal in the flame using a welding tig rod (stainless steel mandrel). The heated metal is then immersed directly into the powdered enamel (Thompson Enamel 80 mesh opaque or transparent), then reheating and repeating the immersion process three times – a total of no more than 60–90 seconds per piece. Using Lewis’ patent pending Bead Pulling Station, [ 9 ] the thrice-coated enamel bead is then gently pulled from the mandrel and allowed to fall into a simple bread pan filled with garden vermiculite.
Other kiln and torch firing processes for producing enamel jewelry have typically been limited to pure copper or expensive fine silver. These other methods can be used to enamel sterling silver, but only after completing the laborious process of depletion gilding . With the PWF method, if using transparent enamels in cool colors (blue or green), there is no requirement to heat and dip the oxidized silver into pickling acid. The immersion method involves the same three-times heating and immersion of the sterling piece, attached to the stainless steel mandrel, and coating with transparent enamel.
Lewis’ PWF method also pioneered the enameling of lightweight iron filigree beads. The PWF immersion method allows for artistic variations using multiple combinations of opaque and transparent enamels or reducing the oxygen to create smoky hazes. These variations and other applications of the PWF method are discussed in a " ning " network. [ 10 ] The PWF immersion method is the subject of Torch Fired Enamel Jewelry – A Workshop in Painting with Fire . [ 11 ] | https://en.wikipedia.org/wiki/Painting_with_Fire |
The pair distribution function describes the distribution of distances between pairs of particles contained within a given volume. [ 1 ] Mathematically, if a and b are two particles, the pair distribution function of b with respect to a , denoted by g a b ( r → ) {\displaystyle g_{ab}({\vec {r}})} is the probability of finding the particle b at distance r → {\displaystyle {\vec {r}}} from a , with a taken as the origin of coordinates.
The pair distribution function is used to describe the distribution of objects within a medium (for example, oranges in a crate or nitrogen molecules in a gas cylinder). If the medium is homogeneous (i.e. every spatial location has identical properties), then there is an equal probability density for finding an object at any position r → {\displaystyle {\vec {r}}} :
where V {\displaystyle V} is the volume of the container. On the other hand, the likelihood of finding pairs of objects at given positions (i.e. the two-body probability density) is not uniform. For example, pairs of hard balls must be separated by at least the diameter of a ball. The pair distribution function g ( r → , r → ′ ) {\displaystyle g({\vec {r}},{\vec {r}}')} is obtained by scaling the two-body probability density function by the total number of objects N {\displaystyle N} and the size of the container:
In the common case where the number of objects in the container is large, this simplifies to give:
The simplest possible pair distribution function assumes that all object locations are mutually independent, giving:
where r → {\displaystyle {\vec {r}}} is the separation between a pair of objects. However, this is inaccurate in the case of hard objects as discussed above, because it does not account for the minimum separation required between objects. The hole-correction (HC) approximation provides a better model:
where b {\displaystyle b} is the diameter of one of the objects.
Although the HC approximation gives a reasonable description of sparsely packed objects, it breaks down for dense packing. This may be illustrated by considering a box completely filled by identical hard balls so that each ball touches its neighbours. In this case, every pair of balls in the box is separated by a distance of exactly r = n b {\displaystyle r=nb} where n {\displaystyle n} is a positive whole number. The pair distribution for a volume completely filled by hard spheres is therefore a set of Dirac delta functions of the form:
Finally, it may be noted that a pair of objects which are separated by a large distance have no influence on each other's position (provided that the container is not completely filled). Therefore,
In general, a pair distribution function will take a form somewhere between the sparsely packed (HC approximation) and the densely packed (delta function) models, depending on the packing density f {\displaystyle f} .
Of special practical importance is the radial distribution function , which is independent of orientation. It is a major descriptor for the atomic structure of amorphous materials (glasses, polymers) and liquids. The radial distribution function can be calculated directly from physical measurements like light scattering or x-ray powder diffraction by performing a Fourier Transform .
In Statistical Mechanics the PDF is given by the expression
g a b ( r ) = 1 N a N b ∑ i = 1 N a ∑ j = 1 N b ⟨ δ ( | r i j | − r ) ⟩ {\displaystyle g_{ab}(r)={\frac {1}{N_{a}N_{b}}}\sum \limits _{i=1}^{N_{a}}\sum \limits _{j=1}^{N_{b}}\langle \delta (\vert \mathbf {r} _{ij}\vert -r)\rangle }
When thin films are disordered, as they are in electronic devices, pair distribution is used to view the strain and structure-properties of that material or composition. They have these properties that cannot be exploited in the bulk or crystalline form. There is a method with the radial distribution that is able to view the local structure of a disordered thin film of GeSe 2 {\displaystyle {\ce {GeSe2}}} . But the creators of this method called a need for a better method to view the mid-range order of disordered films. The creation of thin-film Pair Distribution Function (tfPDF) uses a statistical distribution of a material’s mid-range order that enables viewing important details like the disorder. In this technique, 2D data from a scattering method is integrated and Fourier transformed into 1D data that shows the probability of bonds in that material. TfPDF works best when in conjunction with other characterization methods like transmission electron microscopy. Although a developing methodology, tfPDF can give complete structure-property relationships through a reliable characterization technique.
Fischer-Colbrie, Bienenstock, Fuoss, Marcus. Phys. Rev. B (1988) 38, 12388
Jensen, K. M., Billinge, S. J. (2015). IUCrJ, 2(5), 481-489. | https://en.wikipedia.org/wiki/Pair_distribution_function |
In mathematics , a pair of pants is a surface which is homeomorphic to the three-holed sphere . The name comes from considering one of the removed disks as the waist and the two others as the cuffs of a pair of pants .
Pairs of pants are used as building blocks for compact surfaces in various theories. Two important applications are to hyperbolic geometry , where decompositions of closed surfaces into pairs of pants are used to construct the Fenchel-Nielsen coordinates on Teichmüller space , and in topological quantum field theory where they are the simplest non-trivial cobordisms between 1-dimensional manifolds .
A pair of pants is any surface that is homeomorphic to a sphere with three holes, which formally is the result of removing from the sphere three open disks with pairwise disjoint closures. Thus a pair of pants is a compact surface of genus zero with three boundary components .
The Euler characteristic of a pair of pants is equal to −1, and the only other surface with this property is the punctured torus (a torus minus an open disk).
The importance of the pairs of pants in the study of surfaces stems from the following property: define the complexity of a connected compact surface S {\displaystyle S} of genus g {\displaystyle g} with k {\displaystyle k} boundary components to be ξ ( S ) = 3 g − 3 + k {\displaystyle \xi (S)=3g-3+k} , and for a non-connected surface take the sum over all components. Then the only surfaces with negative Euler characteristic and complexity zero are disjoint unions of pairs of pants. Furthermore, for any surface S {\displaystyle S} and any simple closed curve c {\displaystyle c} on S {\displaystyle S} which is not homotopic to a boundary component, the compact surface obtained by cutting S {\displaystyle S} along c {\displaystyle c} has a complexity that is strictly less than S {\displaystyle S} . In this sense, pairs of pants are the only "irreducible" surfaces among all surfaces of negative Euler characteristic.
By a recursion argument, this implies that for any surface there is a system of simple closed curves which cut the surface into pairs of pants. This is called a pants decomposition for the surface, and the curves are called the cuffs of the decomposition. This decomposition is not unique, but by quantifying the argument one sees that all pants decompositions of a given surface have the same number of curves, which is exactly the complexity. [ 1 ] For connected surfaces a pants decomposition has exactly 2 g − 2 + k {\displaystyle 2g-2+k} pants.
A collection of simple closed curves on a surface is a pants decomposition if and only if they are disjoint, no two of them are homotopic and none is homotopic to a boundary component, and the collection is maximal for these properties.
A given surface has infinitely many distinct pants decompositions (we understand two decompositions to be distinct when they are not homotopic). One way to try to understand the relations between all these decompositions is the pants complex associated to the surface . This is a graph with vertex set the pants decompositions of S {\displaystyle S} , and two vertices are joined if they are related by an elementary move, which is one of the two following operations:
The pants complex is connected [ 2 ] (meaning any two pants decompositions are related by a sequence of elementary moves) and has infinite diameter (meaning that there is no upper bound on the number of moves needed to get from one decomposition to the other). In the particular case when the surface has complexity 1, the pants complex is isomorphic to the Farey graph .
The action of the mapping class group on the pants complex is of interest for studying this group. For example, Allen Hatcher and William Thurston have used it to give a proof of the fact that it is finitely presented .
The interesting hyperbolic structures on a pair of pants are easily classified. [ 3 ]
By taking the length of a cuff to be equal to zero, one obtains a complete metric on the pair of pants minus the cuff, which is replaced by a cusp . This structure is of finite volume.
The geometric proof of the classification in the previous paragraph is important for understanding the structure of hyperbolic pants. It proceeds as follows: Given a hyperbolic pair of pants with totally geodesic boundary, there exist three unique geodesic arcs that join the cuffs pairwise and that are perpendicular to them at their endpoints. These arcs are called the seams of the pants.
Cutting the pants along the seams, one gets two right-angled hyperbolic hexagons which have three alternate sides of matching lengths. The following lemma can be proven with elementary hyperbolic geometry. [ 4 ]
So we see that the pair of pants is the double of a right-angled hexagon along alternate sides. Since the isometry class of the hexagon is also uniquely determined by the lengths of the remaining three alternate sides, the classification of pants follows from that of hexagons.
When a length of one cuff is zero one replaces the corresponding side in the right-angled hexagon by an ideal vertex.
A point in the Teichmüller space of a surface S {\displaystyle S} is represented by a pair ( M , f ) {\displaystyle (M,f)} where M {\displaystyle M} is a complete hyperbolic surface and f : S → M {\displaystyle f:S\to M} a diffeomorphism.
If S {\displaystyle S} has a pants decomposition by curves γ i {\displaystyle \gamma _{i}} then one can parametrise Teichmüller pairs by the Fenchel-Nielsen coordinates which are defined as follows. The cuff lengths ℓ i {\displaystyle \ell _{i}} are simply the lengths of the closed geodesics homotopic to the f ( γ i ) {\displaystyle f(\gamma _{i})} .
The twist parameters τ i {\displaystyle \tau _{i}} are harder to define. They correspond to how much one turns when gluing two pairs of pants along γ i {\displaystyle \gamma _{i}} : this defines them modulo ℓ i Z {\displaystyle \ell _{i}\mathbb {Z} } . One can refine the definition (using either analytic continuation [ 5 ] or geometric techniques) to obtain twist parameters valued in R {\displaystyle \mathbb {R} } (roughly, the point is that when one makes a full turn one changes the point in Teichmüller space by precomposing f {\displaystyle f} with a Dehn twist around γ i {\displaystyle \gamma _{i}} ).
One can define a map from the pants complex to Teichmüller space, which takes a pants decomposition to an arbitrarily chosen point in the region where the cuff part of the Fenchel-Nielsen coordinates are bounded by a large enough constant. It is a quasi-isometry when Teichmüller space is endowed with the Weil-Petersson metric , which has proven useful in the study of this metric. [ 6 ]
These structures correspond to Schottky groups on two generators (more precisely, if the quotient of the hyperbolic plane by a Schottky group on two generators is homeomorphic to the interior of a pair of pants then its convex core is an hyperbolic pair of pants as described above, and all are obtained as such).
A cobordism between two n -dimensional closed manifolds is a compact ( n +1)-dimensional manifold whose boundary is the disjoint union of the two manifolds. The category of cobordisms of dimension n +1 is the category with objects the closed manifolds of dimension n , and morphisms the cobordisms between them (note that the definition of a cobordism includes the identification of the boundary to the manifolds). Note that one of the manifolds can be empty; in particular a closed manifold of dimension n +1 is viewed as an endomorphism of the empty set . One can also compose two cobordisms when the end of the first is equal to the start of the second. A n-dimensional topological quantum field theory (TQFT) is a monoidal functor from the category of n -cobordisms to the category of complex vector space (where multiplication is given by the tensor product).
In particular, cobordisms between 1-dimensional manifolds (which are unions of circles) are compact surfaces whose boundary has been separated into two disjoint unions of circles. Two-dimensional TQFTs correspond to Frobenius algebras , where the circle (the only connected closed 1-manifold) maps to the underlying vector space of the algebra, while the pair of pants gives a product or coproduct, depending on how the boundary components are grouped – which is commutative or cocommutative. Further, the map associated with a disk gives a counit (trace) or unit (scalars), depending on grouping of boundary, which completes the correspondence. | https://en.wikipedia.org/wiki/Pair_of_pants_(mathematics) |
In physics , a pair potential is a function that describes the potential energy of two interacting objects solely as a function of the distance between them. [ 1 ]
Some interactions, like Coulomb's law in electrodynamics or Newton's law of universal gravitation in mechanics naturally have this form for simple spherical objects.
For other types of more complex interactions or objects it is useful and common to approximate the interaction by a pair potential, for example interatomic potentials in physics and computational chemistry that use approximations like the Lennard-Jones and Morse potentials.
The total energy of a system of N {\displaystyle N} objects at positions R → i {\displaystyle {\vec {R}}_{i}} , that interact through pair potential v {\displaystyle v} is given by
E = 1 2 ∑ i = 1 N ∑ j ≠ i N v ( | R → i − R → j | ) . {\displaystyle E={\frac {1}{2}}\sum _{i=1}^{N}\sum _{j\neq i}^{N}v\left(\left|{\vec {R}}_{i}-{\vec {R}}_{j}\right|\right)\ .}
Equivalently, this can be expressed as
E = ∑ i = 1 N ∑ j = i + 1 N v ( | R → i − R → j | ) . {\displaystyle E=\sum _{i=1}^{N}\sum _{j=i+1}^{N}v\left(\left|{\vec {R}}_{i}-{\vec {R}}_{j}\right|\right)\ .}
This expression uses the fact that interaction is symmetric between particles i {\displaystyle i} and j {\displaystyle j} .
It also avoids self-interaction by not including the case where i = j {\displaystyle i=j} .
A fundamental property of a pair potential is its range.
It is expected that pair potentials go to zero for infinite distance as particles that are too far apart do not interact.
In some cases the potential goes quickly to zero and the interaction for particles that are beyond a certain distance can be assumed to be zero, these are said to be short-range potentials.
Other potentials, like the Coulomb or gravitational potential, are long range: they go slowly to zero and the contribution of particles at long distances still contributes to the total energy.
The total energy expression for pair potentials is quite simple to use for analytical and computational work.
It has some limitations however, as the computational cost is proportional to the square of number of particles.
This might be prohibitively expensive when the interaction between large groups of objects needs to be calculated.
For short-range potentials the sum can be restricted only to include particles that are close, reducing the cost to linearly proportional to the number of particles.
In some cases it is necessary to calculate the interaction between an infinite number of particles arranged in a periodic pattern.
Pair potentials are very common in physics and computational chemistry and biology; exceptions are very rare. An example of a potential energy function that is not a pair potential is the three-body Axilrod-Teller potential . Another example is the Stillinger-Weber potential for silicon , which includes the angle in a triangle of silicon atoms as an input parameter. [ 2 ] [ 3 ]
Some commonly used pair potentials are listed below. | https://en.wikipedia.org/wiki/Pair_potential |
Pair production is the creation of a subatomic particle and its antiparticle from a neutral boson . Examples include creating an electron and a positron , a muon and an antimuon , or a proton and an antiproton . Pair production often refers specifically to a photon creating an electron–positron pair near a nucleus . As energy must be conserved, for pair production to occur, the incoming energy of the photon must be above a threshold of at least the total rest mass energy of the two particles created. (As the electron is the lightest, hence, lowest mass/energy, elementary particle, it requires the least energetic photons of all possible pair-production processes.) Conservation of energy and momentum are the principal constraints on the process. [ 1 ] All other conserved quantum numbers ( angular momentum , electric charge , lepton number ) of the produced particles must sum to zero – thus the created particles shall have opposite values of each other. For instance, if one particle has electric charge of +1 the other must have electric charge of −1, or if one particle has strangeness of +1 then another one must have strangeness of −1.
The probability of pair production in photon–matter interactions increases with photon energy and also increases approximately as the square of the atomic number (number of protons) of the nearby atom. [ 2 ]
For photons with high photon energy ( MeV scale and higher), pair production is the dominant mode of photon interaction with matter. These interactions were first observed in Patrick Blackett 's counter-controlled cloud chamber , leading to the 1948 Nobel Prize in Physics . [ 3 ] If the photon is near an atomic nucleus, the energy of a photon can be converted into an electron–positron pair:
(Z+) γ → e − + e +
The photon's energy is converted to particle mass in accordance with Einstein's equation, E = mc 2 ; where E is energy , m is mass and c is the speed of light . The photon must have higher energy than the sum of the rest mass energies of an electron and positron (2 × 511 keV = 1.022 MeV, resulting in a photon wavelength of 1.2132 pm ) for the production to occur. (Thus, pair production does not occur in medical X-ray imaging because these X-rays only contain ~ 150 keV.)
The photon must be near a nucleus in order to satisfy conservation of momentum, as an electron–positron pair produced in free space cannot satisfy conservation of both energy and momentum. [ 5 ] Because of this, when pair production occurs, the atomic nucleus receives some recoil . The reverse of this process is electron–positron annihilation .
These properties can be derived through the kinematics of the interaction. Using four vector notation, the conservation of energy–momentum before and after the interaction gives: [ 6 ]
where p ʀ {\displaystyle p_{\text{ʀ}}} is the recoil of the nucleus. Note the modulus of the four vector
is
which implies that ( p γ ) 2 = 0 {\displaystyle (p_{\gamma })^{2}=0} for all cases and ( p e − ) 2 = − m e 2 c 2 {\displaystyle (p_{{\text{e}}^{-}})^{2}=-m_{\text{e}}^{2}c^{2}} . We can square the conservation equation
However, in most cases the recoil of the nucleus is small compared to the energy of the photon and can be neglected. Taking this approximation of p R ≈ 0 {\displaystyle p_{R}\approx 0} and expanding the remaining relation
Therefore, this approximation can only be satisfied if the electron and positron are emitted in very nearly the same direction, that is, θ e ≈ 0 {\displaystyle \theta _{\text{e}}\approx 0} .
This derivation is a semi-classical approximation. An exact derivation of the kinematics can be done taking into account the full quantum mechanical scattering of photon and nucleus .
The energy transfer to electron and positron in pair production interactions is given by
where h {\displaystyle h} is the Planck constant , ν {\displaystyle \nu } is the frequency of the photon and the 2 m e c 2 {\displaystyle 2\,m_{\text{e}}c^{2}} is the combined rest mass of the electron–positron. In general the electron and positron can be emitted with different kinetic energies, but the average transferred to each (ignoring the recoil of the nucleus) is
The exact analytic form for the cross section of pair production must be calculated through quantum electrodynamics in the form of Feynman diagrams and results in a complicated function. To simplify, the cross section can be written as:
where α {\displaystyle \alpha } is the fine-structure constant , r e {\displaystyle r_{\text{e}}} is the classical electron radius , Z {\displaystyle Z} is the atomic number of the material, and P ( E , Z ) {\displaystyle P(E,Z)} is some complex-valued function that depends on the energy and atomic number. Cross sections are tabulated for different materials and energies.
In 2008 the Titan laser , aimed at a 1 millimeter-thick gold target, was used to generate positron–electron pairs in large numbers. [ 7 ]
Pair production is invoked in the heuristic explanation of hypothetical Hawking radiation . According to quantum mechanics , particle pairs are constantly appearing and disappearing as a quantum foam . In a region of strong gravitational tidal forces , the two particles in a pair may sometimes be wrenched apart before they have a chance to mutually annihilate . When this happens in the region around a black hole , one particle may escape while its antiparticle partner is captured by the black hole.
Pair production is also the mechanism behind the hypothesized pair-instability supernova type of stellar explosion, where pair production suddenly lowers the pressure inside a supergiant star , leading to a partial implosion, and then explosive thermonuclear burning. Supernova SN 2006gy is hypothesized to have been a pair production type supernova . | https://en.wikipedia.org/wiki/Pair_production |
Paired-end tags (PET) (sometimes "Paired-End diTags", or simply "ditags") are the short sequences at the 5’ and 3' ends of a DNA fragment which are unique enough that they (theoretically) exist together only once in a genome , therefore making the sequence of the DNA in between them available upon search (if full-genome sequence data is available) or upon further sequencing (since tag sites are unique enough to serve as primer annealing sites). Paired-end tags (PET) exist in PET libraries with the intervening DNA absent, that is, a PET "represents" a larger fragment of genomic or cDNA by consisting of a short 5' linker sequence, a short 5' sequence tag, a short 3' sequence tag, and a short 3' linker sequence. It was shown conceptually that 13 base pairs are sufficient to map tags uniquely. [ 1 ] However, longer sequences are more practical for mapping reads uniquely. The endonucleases (discussed below) used to produce PETs give longer tags (18/20 base pairs and 25/27 base pairs) but sequences of 50–100 base pairs would be optimal for both mapping and cost efficiency. [ 1 ] After extracting the PETs from many DNA fragments, they are linked (concatenated) together for efficient sequencing. On average, 20–30 tags could be sequenced with the Sanger method, which has a longer read length. [ 1 ] Since the tag sequences are short, individual PETs are well suited for next-generation sequencing that has short read lengths and higher throughput. The main advantages of PET sequencing are its reduced cost by sequencing only short fragments, detection of structural variants in the genome, and increased specificity when aligning back to the genome compared to single tags, which involves only one end of the DNA fragment.
PET libraries are typically prepared in two general methods: cloning based and cloning-free based.
Fragmented genomic DNA or complementary DNA (cDNA) of interest is cloned into plasmid vectors . The cloning sites are flanked with adaptor sequences that contain restriction sites for endonucleases (discussed below). Inserts are ligated to the plasmid vectors and individual vectors are then transformed into E. coli making the PET library. PET sequences are obtained by purifying plasmid and digesting with specific endonuclease leaving two short sequences on the ends of the vectors. Under intramolecular (dilute) conditions, vectors are re-circularized and ligated, leaving only the ditags in the vector. The sequences unique to the clone are now paired together. Depending on the next-generation sequencing technique, PET sequences can be left singular, dimerized, or concatenated into long chains. [ 1 ]
Instead of cloning, adaptors containing the endonuclease sequence are ligated to the ends of fragmented genomic DNA or cDNA. The molecules are then self-circularized and digested with endonuclease, releasing the PET. [ 1 ] Before sequencing, these PETs are ligated to adaptors to which PCR primers anneal for amplification.
The advantage of cloning based construction of the library is that it maintains the fragments or cDNA intact for future use. However, the construction process is much longer than the cloning-free method. Variations on library construction have been produced by next-generation sequencing companies to suit their respective technologies. [ 1 ]
Unlike other endonucleases, the MmeI (type IIS) and EcoP15I (type III) restriction endonucleases cut downstream of their target binding sites. MmeI cuts 18/20 base pairs downstream [ 2 ] and EcoP15I cuts 25/27 base pairs downstream. [ 3 ] As these restriction enzymes bind at their target sequences located in the adaptors, they cut and release vectors that contain short sequences of the fragment or cDNA ligated to them, producing PETs. | https://en.wikipedia.org/wiki/Paired-end_tag |
Paired receptors are pairs or clusters of receptor proteins that bind to extracellular ligands but have opposing activating and inhibitory signaling effects. [ 2 ] [ 3 ] [ 4 ] Traditionally, paired receptors are defined as homologous pairs with similar extracellular domains and different cytoplasmic regions, whose genes are located together in the genome as part of the same gene cluster and which evolved through gene duplication . [ 3 ] [ 5 ] Homologous paired receptors often, but not always, have a shared ligand in common. [ 5 ] [ 6 ] More broadly, pairs of receptors have been identified that exhibit paired functional behavior - responding to a shared ligand with opposing intracellular signals - but are not closely homologous or co-located in the genome. [ 4 ] Paired receptors are highly expressed in the cells of the immune system , especially natural killer (NK) and myeloid cells , and are involved in immune regulation. [ 5 ] [ 7 ]
Paired receptors are membrane proteins with extracellular domains that interact with extracellular ligands. The extracellular region may contain multiple repeating protein domains and may be members of either the immunoglobulin or C-type lectin families. [ 5 ] The extracellular domains of homologous paired receptors are typically very similar in sequence but have different binding affinity for their shared ligands, with the inhibitory member of the pair binding more tightly. [ 4 ]
Homologous paired receptors have characteristic differences in their transmembrane and cytoplasmic regions that distinguish the activating and inhibiting members of the pair. Inhibitory receptors have a cytoplasmic sequence typically containing at least one immunoreceptor tyrosine-based inhibitory motif (ITIM). Activating receptors have a truncated cytoplasmic sequence compared to their corresponding inhibitory receptor and feature a positively charged amino acid residue in their transmembrane domain, enabling protein-protein interaction with an adaptor protein that possesses a immunoreceptor tyrosine-based activation motif (ITAM). [ 3 ]
Homologous paired receptors are located in the same gene cluster and are thought to have evolved through gene duplication . [ 3 ] [ 5 ] Sequence features such as the presence of an ITIM-like sequence in the 3' untranslated region of some activating receptors imply that the activating members of the pair likely evolved from the inhibitory members. [ 4 ] [ 9 ] A number of pathogens interact with the inhibitory member of a pair as a means of immune evasion or viral entry , suggesting that activating members with similar binding competencies may be an evolutionary response to this mechanism. [ 4 ] [ 10 ] This hypothesis is known as the "counterbalance theory" [ 11 ] and these evolutionary dynamics represent an evolutionary arms race between pathogens and the host immune system. [ 12 ] The evolutionary pressures on some paired-receptor families have been described as examples of the "Red Queen" effect. [ 5 ]
Including non-paired examples, over 300 potential immune inhibitory receptors have been identified in the human genome . [ 6 ] There are strong indications that paired receptors are rapidly and recently evolving. These genetic regions have high levels of gene polymorphism , and the gene repertoires found in the genomes of closely related lineages vary significantly. [ 5 ] The selective pressure experienced by the host from pathogens is thought to underlie this rapid evolution. [ 4 ] [ 5 ]
Although paired receptors are best characterized as part of the human and mouse immune systems, [ 4 ] they have also been studied in other organisms. The chicken ( Gallus gallus domesticus ) genome contains a number of examples including a very large family, the chicken Ig-like receptors (CHIR) with over 100 members. [ 13 ] Paired receptor evolution has also been studied in Xenopus (clawed frog) species. [ 14 ] [ 15 ] The adaptive immune system is unique to jawed vertebrates , but an example of a paired receptor family has been identified in a jawless vertebrate, termed agnathan paired receptors resembling Ag receptors (APAR) in the hagfish . [ 16 ]
Expression of paired receptors is common in many types of leukocytes , especially myeloid cells and natural killer (NK) cells. [ 4 ] [ 5 ] [ 7 ] Activation of NK cells is a complex regulatory process modulated by a number of different paired receptor families coexpressed in this cell type. [ 7 ] In some cases, only one member of the pair is expressed in a cell type. Expression of the paired members in a single cell type may vary with time, or the proteins may differ in subcellular localization , resulting in variations in signaling. [ 4 ] Expression in NK cells can be stochastic , resulting in unique variations in receptor repertoire. [ 4 ] [ 12 ]
Some paired receptors are expressed outside the immune system, for example in neurons , [ 3 ] [ 12 ] endothelium , and epithelium [ 5 ] but in many examples, wide tissue distribution can be observed. [ 4 ]
Paired receptors transduce extracellular signals through opposing intracellular signaling pathways. Canonically, inhibitory receptors recruit phosphatases through their ITIM motifs, inhibiting the function of cells in which they are expressed. By contrast, activating receptors interact with adaptor proteins such as DAP-12 bearing an ITAM motif, which in turn recruit kinases such as Syk and ZAP70 . [ 5 ]
Ligands for paired receptors can be very diverse. They are often proteins; the best-characterized are the MHC class I molecules, but a number of other endogenous molecules have been described as ligands for at least one family of paired receptors, and in a few cases in the LILR family , even intact bacteria or viruses can serve as ligands. [ 18 ] Lipids such as phosphatidylethanolamine and phosphatidylserine , sugars and sialylated glycans , and nucleic acids can all serve as ligands for some paired receptors. [ 4 ]
The binding affinity of paired receptors' extracellular domains for their ligands is generally fairly weak, with dissociation constants (K d ) in the micromolar (μM) range. However, the inhibitory member of a pair usually binds with higher affinity than the activating member. [ 3 ] [ 4 ] This can produce a competitive inhibition effect, in which the inhibitory member of the pair out-competes its activating counterpart for ligand binding; other mechanisms of interference with activation, such as disrupting dimerization , have also been described. [ 4 ] Thus the net baseline signal from the pair is usually inhibitory, but may be modulated through differences in expression, surface density, subcellular localization, or other factors. [ 4 ]
In NK cells, ligands for inhibitory receptors are often MHC class I (MHC-I) molecules, while those for activating receptors may include signals of abnormality or infection such as proteins from pathogens or tumors , or molecules associated with cell stress . [ 5 ] Endogenous ligands for inhibitory receptors are better characterized than those for activating receptors. [ 3 ] Paired receptor signaling may represent maintenance of homeostasis such that immune responses to normal host cells are inhibited, while responses to abnormal or pathogenic molecules in the environment are activating. NK activation in the absence of inhibitory receptor signals from endogenous ligands is a molecular mechanism for the missing-self hypothesis of NK activation. [ 3 ] [ 5 ] [ 12 ]
A number of examples of molecular mimicry by pathogens, emulating natural endogenous ligands of paired receptors for immune evasion , have been described in the literature. Such interactions are particularly common with the inhibitory members of receptor pairs, bolstering the hypothesis that activating partners are a later evolutionary response to this immune escape strategy. [ 4 ] [ 10 ]
The first described interaction between a paired receptor and a viral protein identified ILT-2 and ILR-4 ( LILRB1 and LILRB2 ) as targets for herpes simplex virus UL18 protein, which resembles an MHC-I molecule. [ 5 ] Variations in susceptibility to mouse cytomegalovirus infection due to differences in Ly49 -family paired receptors among mouse strains are well-characterized, and are attributed to the structural resemblance between the viral protein m157 and MHC-I molecules. [ 5 ] The pathogenic bacterium Escherichia coli K1 exposes surface polysialic acid molecules that serve as a molecular mimic for the native ligand of the inhibitory receptor Siglec-11 , but induces an opposing response through interactions with the paired activating receptor Siglec-16 , exemplifying the benefit of activating receptors as defense mechanisms against molecular mimicry by pathogens. [ 10 ]
Paired receptors are also used as viral entry receptors by a number of viruses and occasionally as entry mechanisms for other pathogens. [ 4 ] Sialylation is common among mammalian cell-surface proteins and a number of pathogens use sialic acid - either self-synthesized or obtained from the host cell - to evade host immunity, including by interacting with inhibitory siglec receptors. [ 5 ]
There are two main groups of paired receptors, distinguished by extracellular regions containing immunoglobulin or C-type lectin domains. Nomenclature within these families is complex and has changed over time as new members were identified. [ 19 ] In general, the example of the LILR family applies; genes designated A represent the inhibitory receptor and genes designated B represent the activating receptor. [ 18 ]
Immunoglobulin-like receptors are members of the immunoglobulin superfamily and have one or more 70-110 residue immunoglobulin domains (Ig) in their extracellular region, typically multiple such domains in tandem. Many of the genes encoding these proteins occur in the leukocyte receptor complex (LRC), a large gene cluster on human chromosome 19 . [ 3 ] Members of this group found in the human genome include:
C-type lectin-like receptors (CLRs) contain one or more C-type lectin (Ca2+ dependent carbohydrate-binding lectin) domains. Example pairs include: | https://en.wikipedia.org/wiki/Paired_receptors |
In mathematics , a pairing is an R - bilinear map from the Cartesian product of two R - modules , where the underlying ring R is commutative .
Let R be a commutative ring with unit , and let M , N and L be R -modules .
A pairing is any R -bilinear map e : M × N → L {\displaystyle e:M\times N\to L} . That is, it satisfies
for any r ∈ R {\displaystyle r\in R} and any m , m 1 , m 2 ∈ M {\displaystyle m,m_{1},m_{2}\in M} and any n , n 1 , n 2 ∈ N {\displaystyle n,n_{1},n_{2}\in N} . Equivalently, a pairing is an R -linear map
where M ⊗ R N {\displaystyle M\otimes _{R}N} denotes the tensor product of M and N .
A pairing can also be considered as an R -linear map Φ : M → Hom R ( N , L ) {\displaystyle \Phi :M\to \operatorname {Hom} _{R}(N,L)} , which matches the first definition by setting Φ ( m ) ( n ) := e ( m , n ) {\displaystyle \Phi (m)(n):=e(m,n)} .
A pairing is called perfect if the above map Φ {\displaystyle \Phi } is an isomorphism of R -modules and the other evaluation map Φ ′ : N → Hom R ( M , L ) {\displaystyle \Phi '\colon N\to \operatorname {Hom} _{R}(M,L)} is an isomorphism also. In nice cases, it suffices that just one of these be an isomorphism, e.g. when R is a field, M,N are finite dimensional vector spaces and L=R .
A pairing is called non-degenerate on the right if for the above map we have that e ( m , n ) = 0 {\displaystyle e(m,n)=0} for all m {\displaystyle m} implies n = 0 {\displaystyle n=0} ; similarly, e {\displaystyle e} is called non-degenerate on the left if e ( m , n ) = 0 {\displaystyle e(m,n)=0} for all n {\displaystyle n} implies m = 0 {\displaystyle m=0} .
A pairing is called alternating if N = M {\displaystyle N=M} and e ( m , m ) = 0 {\displaystyle e(m,m)=0} for all m . In particular, this implies e ( m + n , m + n ) = 0 {\displaystyle e(m+n,m+n)=0} , while bilinearity shows e ( m + n , m + n ) = e ( m , m ) + e ( m , n ) + e ( n , m ) + e ( n , n ) = e ( m , n ) + e ( n , m ) {\displaystyle e(m+n,m+n)=e(m,m)+e(m,n)+e(n,m)+e(n,n)=e(m,n)+e(n,m)} . Thus, for an alternating pairing, e ( m , n ) = − e ( n , m ) {\displaystyle e(m,n)=-e(n,m)} .
Any scalar product on a real vector space V is a pairing (set M = N = V , R = R in the above definitions).
The determinant map (2 × 2 matrices over k ) → k can be seen as a pairing k 2 × k 2 → k {\displaystyle k^{2}\times k^{2}\to k} .
The Hopf map S 3 → S 2 {\displaystyle S^{3}\to S^{2}} written as h : S 2 × S 2 → S 2 {\displaystyle h:S^{2}\times S^{2}\to S^{2}} is an example of a pairing. For instance, Hardie et al. [ 1 ] present an explicit construction of the map using poset models.
In cryptography , often the following specialized definition is used: [ 2 ]
Let G 1 , G 2 {\displaystyle \textstyle G_{1},G_{2}} be additive groups and G T {\displaystyle \textstyle G_{T}} a multiplicative group , all of prime order p {\displaystyle \textstyle p} . Let P ∈ G 1 , Q ∈ G 2 {\displaystyle \textstyle P\in G_{1},Q\in G_{2}} be generators of G 1 {\displaystyle \textstyle G_{1}} and G 2 {\displaystyle \textstyle G_{2}} respectively.
A pairing is a map: e : G 1 × G 2 → G T {\displaystyle e:G_{1}\times G_{2}\rightarrow G_{T}}
for which the following holds:
Note that it is also common in cryptographic literature for all groups to be written in multiplicative notation.
In cases when G 1 = G 2 = G {\displaystyle \textstyle G_{1}=G_{2}=G} , the pairing is called symmetric. As G {\displaystyle \textstyle G} is cyclic , the map e {\displaystyle e} will be commutative ; that is, for any P , Q ∈ G {\displaystyle P,Q\in G} , we have e ( P , Q ) = e ( Q , P ) {\displaystyle e(P,Q)=e(Q,P)} . This is because for a generator g ∈ G {\displaystyle g\in G} , there exist integers p {\displaystyle p} , q {\displaystyle q} such that P = g p {\displaystyle P=g^{p}} and Q = g q {\displaystyle Q=g^{q}} . Therefore e ( P , Q ) = e ( g p , g q ) = e ( g , g ) p q = e ( g q , g p ) = e ( Q , P ) {\displaystyle e(P,Q)=e(g^{p},g^{q})=e(g,g)^{pq}=e(g^{q},g^{p})=e(Q,P)} .
The Weil pairing is an important concept in elliptic curve cryptography ; e.g., it may be used to attack certain elliptic curves (see MOV attack ). It and other pairings have been used to develop identity-based encryption schemes.
Scalar products on complex vector spaces are sometimes called pairings, although they are not bilinear.
For example, in representation theory , one has a scalar product on the characters of complex representations of a finite group which is frequently called character pairing . | https://en.wikipedia.org/wiki/Pairing |
Pairing , sometimes known as bonding , is a process used in computer networking that helps set up an initial linkage between computing devices to allow communications between them. The most common example is used in Bluetooth , [ 1 ] where the pairing process is used to link devices like a Bluetooth headset with a mobile phone .
This computing article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Pairing_(computing) |
In mathematics and particularly in topology , a pairwise Stone space is a bitopological space ( X , τ 1 , τ 2 ) {\displaystyle \scriptstyle (X,\tau _{1},\tau _{2})} that is pairwise compact , pairwise Hausdorff , and pairwise zero-dimensional .
Pairwise Stone spaces are a bitopological version of Stone spaces .
Pairwise Stone spaces are closely related to spectral spaces .
Theorem: [ 1 ] If ( X , τ ) {\displaystyle \scriptstyle (X,\tau )} is a spectral space, then ( X , τ , τ ∗ ) {\displaystyle \scriptstyle (X,\tau ,\tau ^{*})} is a pairwise Stone space, where τ ∗ {\displaystyle \scriptstyle \tau ^{*}} is the de Groot dual topology of τ {\displaystyle \scriptstyle \tau } . Conversely, if ( X , τ 1 , τ 2 ) {\displaystyle \scriptstyle (X,\tau _{1},\tau _{2})} is a pairwise Stone space, then both ( X , τ 1 ) {\displaystyle \scriptstyle (X,\tau _{1})} and ( X , τ 2 ) {\displaystyle \scriptstyle (X,\tau _{2})} are spectral spaces. | https://en.wikipedia.org/wiki/Pairwise_Stone_space |
In numerical analysis , pairwise summation , also called cascade summation , is a technique to sum a sequence of finite- precision floating-point numbers that substantially reduces the accumulated round-off error compared to naively accumulating the sum in sequence. [ 1 ] Although there are other techniques such as Kahan summation that typically have even smaller round-off errors, pairwise summation is nearly as good (differing only by a logarithmic factor) while having much lower computational cost—it can be implemented so as to have nearly the same cost (and exactly the same number of arithmetic operations) as naive summation.
In particular, pairwise summation of a sequence of n numbers x n works by recursively breaking the sequence into two halves, summing each half, and adding the two sums: a divide and conquer algorithm . Its worst-case roundoff errors grow asymptotically as at most O (ε log n ), where ε is the machine precision (assuming a fixed condition number , as discussed below). [ 1 ] In comparison, the naive technique of accumulating the sum in sequence (adding each x i one at a time for i = 1, ..., n ) has roundoff errors that grow at worst as O (ε n ). [ 1 ] Kahan summation has a worst-case error of roughly O (ε), independent of n , but requires several times more arithmetic operations. [ 1 ] If the roundoff errors are random, and in particular have random signs, then they form a random walk and the error growth is reduced to an average of O ( ε log n ) {\displaystyle O(\varepsilon {\sqrt {\log n}})} for pairwise summation. [ 2 ]
A very similar recursive structure of summation is found in many fast Fourier transform (FFT) algorithms, and is responsible for the same slow roundoff accumulation of those FFTs. [ 2 ] [ 3 ]
In pseudocode , the pairwise summation algorithm for an array x of length n ≥ 0 can be written:
For some sufficiently small N , this algorithm switches to a naive loop-based summation as a base case , whose error bound is O(Nε). [ 4 ] The entire sum has a worst-case error that grows asymptotically as O (ε log n ) for large n , for a given condition number (see below).
In an algorithm of this sort (as for divide and conquer algorithms in general [ 5 ] ), it is desirable to use a larger base case in order to amortize the overhead of the recursion. If N = 1, then there is roughly one recursive subroutine call for every input, but more generally there is one recursive call for (roughly) every N /2 inputs if the recursion stops at exactly n = N . By making N sufficiently large, the overhead of recursion can be made negligible (precisely this technique of a large base case for recursive summation is employed by high-performance FFT implementations [ 3 ] ).
Regardless of N , exactly n −1 additions are performed in total, the same as for naive summation, so if the recursion overhead is made negligible then pairwise summation has essentially the same computational cost as for naive summation.
A variation on this idea is to break the sum into b blocks at each recursive stage, summing each block recursively, and then summing the results, which was dubbed a "superblock" algorithm by its proposers. [ 6 ] The above pairwise algorithm corresponds to b = 2 for every stage except for the last stage which is b = N .
Dalton, Wang & Blainey (2014) describe a iterative, "shift-reduce" formulation for pairwise summation. It can be unrolled and sped up using SIMD instructions. The non-unrolled version is: [ 7 ]
Suppose that one is summing n values x i , for i = 1, ..., n . The exact sum is:
(computed with infinite precision).
With pairwise summation for a base case N = 1, one instead obtains S n + E n {\displaystyle S_{n}+E_{n}} , where the error E n {\displaystyle E_{n}} is bounded above by: [ 1 ]
where ε is the machine precision of the arithmetic being employed (e.g. ε ≈ 10 −16 for standard double precision floating point). Usually, the quantity of interest is the relative error | E n | / | S n | {\displaystyle |E_{n}|/|S_{n}|} , which is therefore bounded above by:
In the expression for the relative error bound, the fraction (Σ| x i |/|Σ x i |) is the condition number of the summation problem. Essentially, the condition number represents the intrinsic sensitivity of the summation problem to errors, regardless of how it is computed. [ 8 ] The relative error bound of every ( backwards stable ) summation method by a fixed algorithm in fixed precision (i.e. not those that use arbitrary-precision arithmetic , nor algorithms whose memory and time requirements change based on the data), is proportional to this condition number. [ 1 ] An ill-conditioned summation problem is one in which this ratio is large, and in this case even pairwise summation can have a large relative error. For example, if the summands x i are uncorrelated random numbers with zero mean, the sum is a random walk and the condition number will grow proportional to n {\displaystyle {\sqrt {n}}} . On the other hand, for random inputs with nonzero mean the condition number asymptotes to a finite constant as n → ∞ {\displaystyle n\to \infty } . If the inputs are all non-negative , then the condition number is 1.
Note that the 1 − ε log 2 n {\displaystyle 1-\varepsilon \log _{2}n} denominator is effectively 1 in practice, since ε log 2 n {\displaystyle \varepsilon \log _{2}n} is much smaller than 1 until n becomes of order 2 1/ε , which is roughly 10 10 15 in double precision.
In comparison, the relative error bound for naive summation (simply adding the numbers in sequence, rounding at each step) grows as O ( ε n ) {\displaystyle O(\varepsilon n)} multiplied by the condition number. [ 1 ] In practice, it is much more likely that the rounding errors have a random sign, with zero mean, so that they form a random walk; in this case, naive summation has a root mean square relative error that grows as O ( ε n ) {\displaystyle O(\varepsilon {\sqrt {n}})} and pairwise summation has an error that grows as O ( ε log n ) {\displaystyle O(\varepsilon {\sqrt {\log n}})} on average. [ 2 ]
Pairwise summation is the default summation algorithm in NumPy [ 9 ] and the Julia technical-computing language , [ 10 ] where in both cases it was found to have comparable speed to naive summation (thanks to the use of a large base case).
Other software implementations include the HPCsharp library [ 11 ] for the C# language and the standard library summation [ 12 ] in D . | https://en.wikipedia.org/wiki/Pairwise_summation |
A Pake Doublet (or "Pake Pattern") is a characteristic line shape seen in solid-state nuclear magnetic resonance and electron paramagnetic resonance spectroscopy. It was first described by George Pake .
It arises from dipolar coupling between isolated two spin-1/2 nuclei, or from transitions in quadrupolar nuclei such as deuterium. It is the general shape obtained from an orientationally dependent doublet. The "horns" of the Pake doublet correspond to the situation when the principal axis of the coupling interaction (the internuclear vector in the case dipolar coupling and the principal component of the electric field gradient tensor for quadrupolar nuclei) is perpendicular to the magnetic field. This situation is the most probable and the intensity is much higher. The "feet" of the lineshape correspond to the situation when the principal axis of the coupling interaction is parallel to the magnetic field which is much less statistically relevant.
Pake was the first to describe this lineshape and used it to extract the proton-proton distance from his experiments on a single crystal and powdered hydrates of gypsum (CaSO 4 .2H 2 O). [ 1 ] This made it possible to experimentally determine the internuclear distance between the hydrogen atoms in water.
In solids with vacant positions, dipole coupling is averaged partially due to water diffusion which proceeds according to the symmetry of the solids and the probability distribution of molecules between the vacancies. [ 2 ] In the case the averaged lineshape is used to analyze crystal symmetry , phase transitions , and the degree of molecular disorder in crystalline hydrates, zeolites , clays and biological tissues.
This nuclear magnetic resonance –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Pake_doublet |
Pakistan Atomic Energy Commission ( PAEC ) ( Urdu : ماموریہ جوہری توانائی پاکستان , romanized : māmūrīa jauhrī tawānā'ī pākistān ) is a federally funded independent governmental agency, concerned with research and development of nuclear power , promotion of nuclear science , energy conservation and the peaceful use of nuclear technology . [ 2 ] [ 3 ]
Since its establishment in 1956, the PAEC has overseen the extensive development of nuclear infrastructure to support the economical uplift of Pakistan by founding institutions that focus on development on food irradiation and on nuclear medicine radiation therapy for cancer treatment. [ 4 ] [ 5 ] The PAEC organizes conferences and directs research at the country's leading universities. [ 6 ] Since the 1960s, the PAEC has also been a scientific research partner and sponsor of the European Organization for Nuclear Research (CERN), where Pakistani scientists have contributed to developing particle accelerators and research on high-energy physics . [ 7 ] PAEC scientists regularly visit CERN to join projects led by the European organization. [ 8 ]
Until 2001, the PAEC was the civilian federal oversight agency that manifested the control of atomic radiation , development of nuclear weapons , and their testing . These functions were eventually taken over by the Pakistan Nuclear Regulatory Authority (PNRA), and the National Command Authority under the Prime Minister of Pakistan . [ 9 ]
Following the partition of the British Indian Empire by the United Kingdom in 1947, Pakistan emerged as a Muslim-dominated state. [ 10 ] The turbulent nature of its emergence critically influenced the scientific development of Pakistan. [ 10 ]
The establishment of the Council of Scientific and Industrial Research (PCSIR) in 1951 began Pakistan's research on physical sciences. [ 11 ] In 1953, U.S. President Dwight Eisenhower announced the Atoms for Peace program, of which Pakistan became its earliest partner. [ 12 ] Research at PAEC initially followed a strict non-weapon policy issued by then- Foreign Minister Sir Zafarullah Khan . [ 12 ] In 1955, the Government of Pakistan established a committee of scientists to prepare nuclear energy plans and build an industrial nuclear infrastructure throughout the country. [ 13 ] As the Energy Council Act went into full effect, Prime Minister Huseyn Suhrawardy established the Pakistan Atomic Energy Commission (PAEC) in March 1956. [ 12 ] Its first chair was Nazir Ahmad – an experimental physicist . [ 12 ] Other members of the PAEC included Technical member Salimuzzaman Siddiqui , an organic chemist at the University of Karachi , and Raziuddin Siddiqui , a mathematical physicist at the same university. [ 12 ] Together, they both took charge of the research and development directorates of the commission. [ 13 ] In 1958, Abdus Salam of the University of the Punjab also joined the commission, along with Munir Ahmad Khan who initially lobbied for acquiring an open pool reactor from the United States. [ 13 ]
In 1958, PAEC Chairman Nazir Ahmad proposed to the Pakistan Industrial Development Corporation the building of a heavy water production facility with the capacity to produce 50 kg of heavy water per day at Multan , but this proposal was not acted on. [ 12 ] In 1960, I. H. Usmani was elevated as PAEC's second chair with the transfer of Nazir Ahmad at the Federal Bureau of Statistics . [ 12 ] The Multan Heavy Water Production Facility reactor was built in 1962, financed by local fertilizer companies. [ 14 ] In 1964, PAEC established its first research institute, the Pakistan Institute of Nuclear Science and Technology (PINSTECH), at Nilore , and began negotiation for Pakistan's first commercial nuclear power plant to be built in Karachi . [ 12 ] In 1965, the PAEC reached an agreement with Canadian General Electric to build a CANDU reactor in Karachi. [ 12 ] Financial investment for the Karachi Nuclear Power Plant was provided by the Economic Coordination Committee , and Edward Durell Stone was commissioned to oversee the architectural design of PINSTECH. [ 12 ] From 1965–71, the PAEC sent 600 scientists abroad for training in nuclear sciences. [ 12 ] in 1969, the United Kingdom Atomic Energy Authority , agreed to supply a small scale nuclear reprocessing plant, with the capacity to extract 360 grams of plutonium per year. [ 12 ] In 1973, the PAEC announced the discovery of large uranium deposits in Punjab . [ 12 ]
After India's decisive victory in the Indo-Pakistani War of 1971 , Pakistan retracted its non-weapon policy and the research and development of nuclear weapons began in 1972. [ 12 ] PAEC's senior nuclear engineer Munir Ahmad Khan , was named as PAEC's third chair by Prime Minister Zulfikar Ali Bhutto . [ 15 ] Work began on development of the nuclear fuel cycle infrastructure, and nuclear weapons research in the 1970s. [ 16 ] Key research took place at PINSTECH, where scientists worked on weapon designs and eventual nuclear weapons testing . [ 17 ] The PAEC expanded the crash program with various laboratories, facilities, and directorates researching on developing and testing materials and components for bomb designs , whilst it engineered plants and funded facilities for production of highly enriched uranium (HEU) and plutonium. [ 17 ] In 1976, possible test sites were decided by the PAEC and construction on the sites was completed in 1979. [ 17 ] In 1983, PAEC's efforts reached a milestone when it conducted its first subcritical test on a weapon design; such testing continued until the early 1990s under codename: Kirana-I . [ 17 ]
Following nuclear tests by India earlier in the month, on 28 May 1998, PAEC led the final preparations and conducted Pakistan's first nuclear tests (Codename: Chagai-I ), which was followed by Chagai-II in Kharan Desert on 30 May 1998. In 2001, the PAEC's research was focused back onto civilian and peaceful research with the establishment of the National Command Authority and the Pakistan Nuclear Regulatory Authority . [ 18 ]
Since its establishment in 1956, the PAEC has provided a conspicuous example of the benefits of atomic age technologies for the advancement of agriculture, engineering, biology, and medicine. [ 19 ] [ 20 ] In 1960, the PAEC established its first nuclear medicine centre for cancer treatment at the Jinnah Medical College of the University of Karachi ; the second Medical Isotope Institute was established at the Mayo Hospital of the King Edward Medical University, Lahore . [ 21 ] Physicians and medical researchers were provided with facilities for cancer diagnosis and treatment by the PAEC's funding. [ 21 ]
In 1960, the PAEC established its regional atomic research centre in Lahore , and a metallurgy centre in Karachi in 1963. [ 22 ] Another energy centre was located in Dhaka where many scientists were educated. [ 22 ] In 1967, the PAEC founded the Institute of Engineering and Applied Sciences which became one of the primary technical universities of the country. Many of the PAEC's scientists and engineers served in its faculty. [ 22 ] The PAEC supports its university-level physics program at the Government College University, Lahore where it awards fellowships to the students. The PAEC continues to promotes its program as "peaceful uses of atomic energy commenced for the benefit the scientific community as well as public." [ 23 ]
About its promotion of education, senior scientist, Ishfaq Ahmad quoted: "the PAEC was responsible to send more than 600 scientists to the abroad. [ 12 ] As of present, PAEC maintains its prestigious image, and is now noted as one of the largest science and technology institution of the country. [ 24 ] The PAEC supports research activities and learning programs at the International Centre for Theoretical Physics (ICTP), of which PAEC is also its organizer. [ 25 ] Since 1974, the PAEC has been a key organizer and sponsor of the International Nathiagali Summer College on Physics and Contemporary Needs conference each year where scientists from all over the world are delegated to the country. [ 26 ] The Summer College disseminates the knowledge of advancements in physics, chemistry, biology, astronomy, mathematics, computer science, logic, and philosophy. [ 26 ]
As the emphasis shifted towards concerns for national security interests, the PAEC's important projects were also initiated in this area. [ 18 ] Many notable scientists with international prestige have worked and affiliated with the PAEC. [ 18 ]
PAEC also provided useful services in Pakistan like free religious and science education for more than 2000 poor children, Empowering Pakistani women by giving them basic education especially in suburbs by Hunargah (vocational training centers). PAEC has also established Centers for Retired Employees Welfare (CREW) in Lahore, Islamabad and Karachi for meetings, discussions and problems solving.
PAEC is held responsible for design preparation and proper operational function of Pakistan's commercial nuclear power plants . The PAEC provides lobbying at the governmental level for the safe usage of nuclear power sources; though the nuclear safety regulations , Protection of the nuclear power facilities is managed by the Pakistan Nuclear Regulatory Authority (PNRA). Providing policy guidance to the government, PAEC's studies envision setting up power plants with a capacity of approximately 8800 Megawatts by 2030. [ 27 ]
Under this policy, the KANUPP power plants and CHASHNUPP power plants are expanding and under construction as of 2013. [ 28 ]
Pakistan has a long history of participating in experiments and research undertakings with CERN , and has a long tradition of physicists who are working around the world. [ 29 ] Since the 1960s, Pakistan has been contributing and regularly participating in CERN's projects, theoretical and nuclear experiments. [ 29 ] A prime example would be Abdus Salam ; Salam was the first man to be accredited with all the collaboration with CERN which when he convinced them to give Pakistan stacks of nuclear emulsions exposed for further study of pions , kaons and antiprotons in the 1960s. [ 30 ] Some theoretical physicists from Pakistan had the opportunity to work at CERN through short visits. [ 29 ] During the 1980s, some of the experimental physicists from Pakistan, specialising in the technique of Solid State Nuclear Track Detectors (SSNTD), also benefited from CERN by exposing the stacks in the beam at the Super Proton Synchrotron (SPS). [ 29 ]
In 2005, CERN awarded PAEC with the ATLAS Supplier Award in 2005, in connection with manufacturing and fabrication of various equipment for CERN. [ 31 ]
On 27 June 2011, PAEC and CERN reached an agreement for extending the technical cooperation with CERN's upcoming programmes. [ 31 ] CERN's Director-General Rolf-Dieter Heuer personally paid a visit to Pakistan where he spoke of the importance of science in Pakistan , and the importance of Germany's strategic alliance with Pakistan. [ citation needed ] The agreement was signed in order to extend an earlier agreement, which came into operation in 2003 between CERN and Pakistan for the supply of manufactured equipment for the Large Hadron Collider (LHC) at CERN, along with placement of scientists and engineers from Pakistan to assist in the scientific programme at CERN. [ 31 ]
With the efforts led by the PAEC, CERN made Pakistan an associate member, on 22 June 2014— the first Asian country and the second Muslim country after Turkey . [ 32 ]
In 1997 PAEC chairman Ishfaq Ahmad reached out to CERN to sign a contract between them after elaborate discussions an in-kind contribution worth one million Swiss francs for the construction of eight magnet supports for the Compact Muon Solenoid (CMS) detector. [ 30 ]
For the CMS, the PAEC built magnetic feet and installed 320 Resistive Plate Chambers (RPC), as well as contributing to CMS computing. Several other mechanical components for ATLAS and for the LHC were also built by the PAEC. [ 33 ] It was PAEC's efforts that led the Pakistan Institute of Nuclear Science and Technology (PINSTECH) with CERN's direct cooperation in the area of radioprotection. [ 33 ]
In 2000, CERN signed another agreement which doubled the Pakistani contribution from one to two million Swiss francs. And with this new agreement Pakistan started construction of the resistive plate chambers required for the CMS muon system. While more recently, a protocol has been signed enhancing Pakistan's total contribution to the LHC programme to $10 million. Pakistan with all these efforts is already hoping to become an observer state at CERN. [ 29 ] [ 30 ] In 2006 PAEC and CERN agreed on expanded cooperation, including contributions by PAEC valued at 5 million Swiss francs. [ 34 ]
The PAEC, partnered with Pakistan's leading universities, sent a large team of scientists and engineers to CERN to participate in the Large Hadron Collider on 10 September 2008. [ 35 ] According to the news sources, the team of Pakistani scientists were keenly involved in the development of the Large Hadron Collider— the world's largest and highest-energy particle accelerator . [ 35 ]
The data of the experiment was available for the Pakistani scientists who would examine the data and results would be accumulated afterwards by them. [ 36 ]
On 26 June 2021, 4 scientists of the PAEC were awarded the Team Achievement Award and another scientist was awarded the Young Scientist Award for work in plant mutation breeding and related technologies. [ 37 ] These awards were bestowed in recognition of Pakistan's advancements in the application of nuclear technology for achieving the U.N. Sustainable Development Goals . [ 38 ] The awards were jointly awarded by the International Atomic Energy Agency (IAEA) and the U.N.'s Food and Agriculture Organization . [ 39 ]
The PAEC is chaired by a person appointed by the Government of Pakistan as specified in the government notification. [ 40 ] The PAEC's management is organized by the Government of Pakistan who awards contracts to the potential candidates. [ 40 ] Its full-time members consist of the appointed Chair; a finance member, and two technical members. [ 40 ] Its part-time members are composed of the senior scientists and the chief scientific adviser to the government. [ 40 ]
The PAEC's management are constitutionally bound to meet not less than four times every year for the execution of development projects involving nuclear power stations and the generation of electric power . [ 40 ] The PAEC retains its autonomous management structure under the National Command Authority . [ 41 ] The amendments carried out in 2010, the National Command Authority is now placed again under the Prime Minister of Pakistan . [ 41 ] The Chairman directly reports to the Prime Minister's Secretariat for its policy making and confirmation issues. [ 41 ]
Since 1990, the PAEC has spun off multiple organization, some being partial subsidiaries or where PAEC had minority interests in past. | https://en.wikipedia.org/wiki/Pakistan_Atomic_Energy_Commission |
The Pakistan Institute of Nuclear Science & Technology ( PINSTECH ) is a federally funded research and development laboratory in Nilore , Islamabad , Pakistan . [ 1 ] [ 2 ]
The site was designed by the American architect Edward Durell Stone and its construction was completed in 1965. It has been described as "[maybe] the most architecturally stunning physics complex in the world". [ 3 ]
In response to the war with India in 1971, the lab was repurposed as a primary weapons laboratory from its original civilian mission. [ 3 ] Since the 1990s, the lab has been focused increasingly on civilian mission and it maintains a broad portfolio in providing research opportunities in supercomputing , renewable energy , physical sciences , philosophy , materials science , medicine , environmental science , and mathematics . [ 4 ] [ 5 ]
The Pakistan Institute of Nuclear Science & Technology (PINSTECH) is one of nation's leading research and development Institution affiliated to the national security. [ 6 ] It is a principle national laboratory that has the responsibility by ensuring the safety, security, and reliability of nation's nuclear weapons program by advancing applications in science and technology. : 84 [ 7 ]
The PINSTECH is located in Nilore , about 15 mi (24 km) southeast of Islamabad, and was designed by the American firm, AMF Atomics and Edward Durell Stone who once worded: "This....has been my greatest work. I am proud that it looks like it belongs in this country." : 56–57 [ 7 ] [ 3 ]
Since owned by the Government of Pakistan , its managed by Pakistan Atomic Energy Commission . [ 7 ] The scientific research programs are supported at the laboratory through the Pakistan Institute of Engineering and Applied Sciences , also in Nilore. [ 6 ] The laboratory covers around 400 acres (1.6 km 2 ) area. [ 6 ] [ 3 ]
The establishment of the Pakistan Institute of Nuclear Science & Technology (Pinstech) was embodiment of the Atoms for Peace initiative in 1953 and a long-sought initiative led by Abdus Salam who was lobbying for a professional physical laboratory since 1951. [ 8 ] Budget constraints and lack of interests by the government administration had left a deep impression on Salam who was determined to establish to create an institution to which scientists from the developing countries would come as a right to interact with their peers from industrially advanced countries without permanently leaving their own countries. [ 8 ] Construction of the Pinstech began when Salam who was able to find funding from the United States in 1961. [ 8 ]
Eventually, Salam and I. H. Usmani approached Glenn T. Seaborg for the further funding of the laboratory from the United States government, which stipulated the fund if the Pakistan Atomic Energy Commission were to set up a research reactor of their own at sum of US$ 350,000. : 269 [ 9 ] Contrary to United States' financial pledges, it was reported that the actual cost of building the Pinstech was neared at US$ 6.6 million ($65.9 million in 2024) that was funded and paid by the Pakistani taxpayers in 1965. [ 3 ]
From 1965–69, the Pinstech had an active and direct laboratory-to-laboratory interaction with the American national laboratories such as Oak Ridge , Argonne , Livermore , and Sandia . : 269 [ 9 ] [ 10 ] [ 11 ]
The scientific library of the institute consisted of a large section containing historical references and literatures on the Manhattan Project , brought by Abdus Salam in 1971 prior to start of the nuclear weapons program under Zulfikar Ali Bhutto's administration. : 51–100 [ 12 ]
The Pakistan Atomic Energy Commission (PAEC) hired the laboratory's first director Rafi Muhammad , a professor of physics at the Government College University, Lahore (GCU), who affiliated the Pinstech with the Quaid-i-Azam University in 1967, bearing some special materials testing. [ 13 ] Soon, the scientists from Institute of Theoretical Physics of the Quaid-i-Azam University had an opportunity to seek permanent research employment in physics at the laboratory. [ 8 ]
After the costly war with India in 1971, the re-purposing of the Pinstech Laboratory was difficult since it was never intended to be a weapons laboratory. [ 3 ] Initially, the plutonium pit production at Pinstech was quite difficult together with its tiny research reactor that could never be a source of weapons-grade plutonium. [ 3 ] In spite of its short-comings, the investigations and classified studies on understanding the equation of state on plutonium was started the physicists at the Pinstech laboratory in 1972. [ 3 ] The Pinstech laboratory became a main research and development laboratory when it initiated its ingenious program for the production of plutonium oxide (plutonia) and uranium oxide (Urania) in 1973. : 106 [ 7 ]
The Pinstech laboratory was also a learning center for gaining expertise in nuclear fuel cycle which it provided training to other facilities after learning the very basic knowledge from the European industries prior to 1969. [ 3 ] At the Pinstech laboratory, a pilot plant (New Labs) was built for reprocessing spent reactor fuel into plutonium pit production. [ 3 ] Besides its fundamental and basic programs on physical sciences, the laboratory provided a ground for the Pakistani scientists to design and engineer weapon designs, with many feared that India was rapidly developing a nuclear bomb . [ 7 ]
As Nilore became restricted site, the research efforts were directed towards working on understanding and producing first the reactor-grade plutonium and eventually to military-grade plutonium from the spent fuel rods by undergoing a chemical process, " reprocessing ". : 138 [ 7 ] The design work had carried out on 20 different laboratories at the lab, and it was its New Labs facility of the lab that was able to produce the first batch of the weapon grade plutonium of 239 Pu by 1983. : 191 [ 7 ] This weapon-grade plutonium was the source material that was carried on a nuclear test conducted at the Ras Koh Range on 30 May 1998. : 205 [ 7 ]
The scientists at the Pinstech laboratory initiated the studies on understanding the ingenious nuclear fuel cycle in spite of having basic familiarity. : 115 [ 7 ] In 1973, the lab conducted several studies on understanding the properties of uranium oxide, eventually producing the first fuel bundle in 1976 that was shipped to the Karachi Nuclear Power Plant to keep its grid operations running. : 106 [ 7 ] The Pinstech also took initiatives in learning and understanding the chemistry of uranium hexafluoride , which the technology was transferred to the Islamabad Uranium Conversion Facility in 1974. : 115–116 In addition, the understanding of UF6 eventually led in producing the Zircaloys , which it was also produced at the lab first; and later having it transfer the technology to the Kundian Nuclear Fuel Complex in 1980. : 115–116
As of today, PINSTECH has been shifted to peacetime research in medicine, biology, materials and physics. Its Molybdenum-42 facility was used to medical radioisotopes for treating cancer. Scientists from Nuclear Institute for Agriculture and Biology (NIAB) and Nuclear Institute for Food and Agriculture (NIFA) had been using the PINSTECH facilities to conduct advanced research in both medical and food sciences.
Since its repurposing in 1972, the Pinstech laboratory conducts research into understanding the equation of state of plutonium, its phase diagrams , and its properties . : 200 [ 7 ] In 1987, the Pinstech developed a technology by fabricating a Chromium kF39 and developed an innovative technique, "in-stu leaching", which allowed the extraction of actinides from the uranium ore without the need for conventional milling. : 113 [ 7 ]
The computer scientists at the Pinstech Laboratory had built a supercomputer based on the vintage IBM computer architecture that allowed the physicists at the Pinstech to model the behavior of plutonium without the actual nuclear testing. : 176 [ 7 ] Research work on plutonium is conducted at its special-purpose facility, the New Laboratories, where the weapon-grade nuclear explosives are designed and manufactured. [ 3 ] Much of the work on plutonium is, however, is subjected to classified information. [ 3 ]
The Centralized Analysis Facility (CAF) has been utilized chemistry on plutonium and other areas of actinides sciences are studied and conducts experiments at the Central Diagnostic Laboratory (CDL); both of labs are the most potent facilities in Pakistan. [ 3 ]
Besides its national security mission, the lab promotes applications of radiation and isotope technology in various scientific and technological disciplines to support the nation. [ 3 ] It is also working on important non-nuclear fields, which are crucial for the development of science and technology in the country. In 2020, expansion work was started at Pinstech lab to help its "ability to produce isotopes for medical use, especially for preparation of radiopharmaceuticals for cancer patients while also helping the country in its aspirations in other applications of peaceful use of nuclear technology." [ 1 ]
PINSTECH has particle accelerators and also operates two small nuclear research reactors , a reprocessing plant and another experimental neutron source based on:
The PINSTECH four research directorates and each directorate is headed by an appointed Director-Generals . The following PINSTECH Divisions are listed below:
Physics Research Division (RPD)
The directorate of science consists of four division, and each divisions are headed by deputy director-generals. In 2004, the PINSTECH administration had brought together all of the groups, and were merged into one single Division, known as Physics Research Division (PRD). [ 14 ] Meanwhile, the PINSTECH had also merged Nuclear Physics Division (NPD) and Radiation Physics Division (RPD), Nuclear and Applied Chemistry Divisions as well. The below is the list of research groups working in RPD.
Chemistry Research Division (CRD)
The Directorate of System and Services (DSS, headed by Dr. Matiullah, consists of 5 research divisions that are listed below:
The Directorate of Technology (D-TECH) consists of 3 divisions that are Materials Division (MD), Isotope Application Division (IAD), and the Isotope Production Division (IPD). This is currently overseen by Dr. Gulzar Hussain Zahid, Chief Engineer.
The Directorate of Coordination, headed by Engr. Iqbal Hussain Khan, is an administrative directorate which consists of 3 technical support divisions. Computation, Information, Communication Technologies (CICT)/Management Information System (MIS) Division, The Scientific Information Division (SID), Programme Coordination Division (PCD) are included in this division. | https://en.wikipedia.org/wiki/Pakistan_Institute_of_Nuclear_Science_&_Technology |
While STEM ( Science , technology , engineering and mathematics ) fields all over the world are dominated by men, the number of Pakistani women in 'STEM' is low due to one of the highest gender gaps in STEM fields. [ 1 ] [ 2 ] However, over the time, some Pakistani women have emerged as scientists in fields like Physics , Biology and computer sciences .
Pakistan has one of the highest gender gaps in the world, and it is the third least performer in gender parity according to a report published by World Economic Forum in 2020. [ 3 ] The low literacy rate of women in Pakistan , despite women making almost half the population , is one of the factors in a high gender gap in STEM fields. This literacy rate is even lower in science and technology. [ 4 ] [ 2 ]
According to UNESCO , among students enrolled in bachelor's degrees, 47% are women while 53% are men. The number of women pursuing doctoral studies is only 36%, while the percentage of men is 64%. There is also a significant gender gap in research sector, with women making only 34% of researchers.
Among students in universities, the field of natural sciences is reported to have only 40% women students, while medical sciences have 45%, engineering has 21% and agricultural sciences have only 12%. [ 5 ]
According to the World Economic Forum , only 4.9% of engineering jobs are held by women in Pakistan. The numbers are particularly low in the energy sector with only 3% female engineers in the power transmission sector. The field of artificial intelligence has also seen few numbers of women engineers, with only 22% part of the workforce. [ 6 ]
Efforts have been done by the government of Pakistan as well as women who are part of STEM fields, to reduce the wide gender gap in STEM. Since 2018, the government of Pakistan has worked to improve wage equality and its position on educational attainment index. [ 7 ] Workplace sexual harassment laws have also been made to encourage women to become part of the workforce in both STEM fields as well as non STEM fields. [ 8 ] Many private organizations like Women in tech, Women Engineers Pakistan have been founded to encourage STEM education in women.
Some notable Pakistani women contributing to STEM are: | https://en.wikipedia.org/wiki/Pakistani_women_in_STEM |
Pal-Kal ( Hebrew : פל קל ) was a construction method for concrete ceilings, invented by engineer Eli Ron in the late 1970s (Israel Patent No. 104,101 [ 1 ] ).
The Pal-Kal method offered an easier, faster, and cheaper solution for casting ceilings compared to traditional reinforced concrete slabs. However, certain applications of this method were proven to be extremely dangerous, and the use of non-standard Pal-Kal ceilings was the main cause of the collapse of the Versailles wedding hall disaster .
The basic principle of the Pal-Kal method involved using galvanized steel boxes inside the concrete, replacing the steel rods intended for reinforcement against bending and the upper reinforcement rods. The shape of the concrete poured between the steel boxes was similar to that obtained in a regular ribbed ceiling. In some Pal-Kal ceilings, there was also a thin layer of concrete underneath. The galvanized boxes were placed with the opening facing downwards and with spaces between them. The concrete was poured between and above the boxes. The boxes created air spaces within the ceiling while providing sufficient static thickness. The galvanized steel acted as formwork and also served as reinforcement against bending. In some non-standard Pal-Kal ceilings, the boxes replaced the reinforcement stirrups designed to prevent shearing.
Various versions of the Pal-Kal construction were developed over time, with different combinations of galvanized boxes and different concrete sections, with or without additional steel reinforcement:
Versions 1 and 2 included reinforcement stirrups that provided shear resistance, and such ceilings were considered standard. Versions 3 and 4, without reinforcement stirrups, were non-standard and even hazardous.
Construction process of Pal-Kal ceilings began with the pouring of a very thin layer of non-structural concrete with minimal reinforcement. The role of this concrete was not structural. Above or into this initial concrete layer, the galvanized boxes were inserted in the shape of the letter 'ח' (Chet in Hebrew). Then, additional concrete was poured above the boxes to create the final rigid ceiling. The galvanized steel's function was to ensure better adhesion between it and the concrete.
In 2001, a Pal-Kal ceiling collapsed while guests were dancing on it at the Versailles wedding hall in Jerusalem , resulting in the death of 23 people. The collapse was caused by multiple factors, including the non-standard construction of the ceiling. Shortly before the disaster, a wall supporting the ceiling on the second floor was removed, allowing the ceiling to start sinking. During the wedding, additional weight was added when people were dancing, leading to the sudden collapse of the structure.
Following the disaster, legal actions were taken against those responsible. [ 2 ] The hall owners were found guilty of manslaughter and received two and a half years of imprisonment. Eli Ron, the engineer who invented the Pal-Kal method, and three other engineers were also found guilty of manslaughter. The engineers received a sentence of 22 months, while Eli Ron was sentenced to four years in prison. [ 3 ]
Pal-Kal structures deemed unsafe are forbidden for use and are often demolished. To prevent unnecessary demolitions, safety tests can be conducted on the structure. A Pal-Kal structure that passes this test is as safe as buildings constructed using traditional methods. Nowadays, most municipalities require annual safety checks to detect potential problems in Pal-Kal structures. However, some engineers argue that a single safety test is sufficient and annual checks are unnecessary.
Following the Versailles disaster, other buildings constructed using the Pal-Kal method were inspected, and some of them were closed for use until repairs were completed. In certain buildings, the cost of these repairs reached millions of shekels . [ 4 ] | https://en.wikipedia.org/wiki/Pal-Kal |
Palaeoimmunology or paleo-immunology (" paleo "=ancient, " immuno "=referring to immunology ) is the analysis using histochemical techniques to look at the matrix proteins in historic and pre-historic materials. [ 1 ] Modern immunological assays are used to detect the presence of specific antigens in the sample material. Specimens subject to immunoassays have usually been preserved in a way that has prevented biomolecular targets from degrading. This has either been achieved through natural preservative circumstances, such as accelerated fossilization , [ 2 ] or through artificial mummification . [ 1 ] [ 3 ] [ 4 ] Regardless of the path taken to achieve this state, preservation has occurred before the denaturing of antigenic targets. The purpose of applying immunological assays to archaeological materials is to better understand the biochemical makeup and composition of these pre-historic samples. [ 1 ] [ 2 ] [ 5 ] Antigenic elements within these materials may reveal information regarding the "life" and "death" of the sample being studied. [ 1 ] [ 3 ] [ 4 ] [ 6 ]
Paleo-immunology encompasses a variety of immunoassays performed on a diverse array of archaeological materials. Paleo-immunology is a new, growing field that is still being properly defined. Examples of paleo-immunology as they appear in peer-reviewed literature are as follows:
This immunology article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Palaeoimmunology |
The Palamuru-Rangareddy Lift Irrigation Project (PRLIP) is an irrigation project in the state of Telangana , India . [ 1 ] The project aims to make 12.3 lakh acres of parched lands in erstwhile combined Mahabubnagar district into fertile lands. [ 2 ] The project is built on the Krishna river at a cost of ₹ 35,000 crore in Nagarkurnool district . [ 3 ] [ 4 ] On 16 September 2023, Telangana Chief Minister K. Chandrashekar Rao operationalised the first phase of Palamuru-Rangareddy Lift Irrigation Scheme at Yellur-Narlapur pump house in Nagarkurnool district . [ 5 ] [ 6 ] The project will change the future of six districts viz, Nagarkurnool, Mahabubnagar, Nalgonda, Rangareddy, Vikarabad in South Telangana. [ 7 ] [ 8 ]
Chief Minister Kalvakuntla Chandrashekhar Rao laid the foundation stone of irrigation project on 11 June 2015. [ 9 ] The project aims to divert 70 TMC of flood water from Krishna River at Jurala project. | https://en.wikipedia.org/wiki/Palamuru-Rangareddy_Lift_Irrigation_Scheme |
In general relativity and tensor calculus , the Palatini identity is
where δ Γ ν σ ρ {\displaystyle \delta \Gamma _{\nu \sigma }^{\rho }} denotes the variation of Christoffel symbols and ∇ ρ {\displaystyle \nabla _{\rho }} indicates covariant differentiation . [ 1 ]
The "same" identity holds for the Lie derivative L ξ R σ ν {\displaystyle {\mathcal {L}}_{\xi }R_{\sigma \nu }} . In fact, one has
where ξ = ξ ρ ∂ ρ {\displaystyle \xi =\xi ^{\rho }\partial _{\rho }} denotes any vector field on the spacetime manifold M {\displaystyle M} .
The Riemann curvature tensor is defined in terms of the Levi-Civita connection Γ μ ν λ {\displaystyle \Gamma _{\mu \nu }^{\lambda }} as
Its variation is
While the connection Γ ν σ ρ {\displaystyle \Gamma _{\nu \sigma }^{\rho }} is not a tensor, the difference δ Γ ν σ ρ {\displaystyle \delta \Gamma _{\nu \sigma }^{\rho }} between two connections is , so we can take its covariant derivative
Solving this equation for ∂ μ δ Γ ν σ ρ {\displaystyle \partial _{\mu }\delta \Gamma _{\nu \sigma }^{\rho }} and substituting the result in δ R ρ σ μ ν {\displaystyle \delta {R^{\rho }}_{\sigma \mu \nu }} , all the Γ δ Γ {\displaystyle \Gamma \delta \Gamma } -like terms cancel, leaving only
Finally, the variation of the Ricci curvature tensor follows by contracting two indices, proving the identity | https://en.wikipedia.org/wiki/Palatini_identity |
Palbociclib , sold under the brand name Ibrance among others, is a medication developed by Pfizer for the treatment of HR -positive and HER2 -negative breast cancer . It is a selective inhibitor of the cyclin-dependent kinases CDK4 and CDK6 . [ 5 ] [ 6 ] Palbociclib was the first CDK4/6 inhibitor to be approved as a cancer therapy. [ 7 ]
It is a selective inhibitor of the cyclin-dependent kinases CDK4 and CDK6 . [ 5 ] [ 6 ]
In the G1 phase of the cell cycle , mammalian cells must pass a checkpoint, known as the restriction point "R", in order to complete the cell cycle and divide. CDK4 and CDK6 complex with Cyclin D drive the phosphorylation of the retinoblastoma protein , Rb, which allows the cell to pass R and commit to division . [ 8 ] Regulation of one or more proteins involved in this checkpoint is lost in many cancers. However, by inhibiting CDK4/6, palbociclib ensures that the cyclin D-CDK4/6 complex cannot aid in phosphorylating Rb. This prevents the cell from passing R and exiting G1, and in turn from proceeding through the cell cycle. [ 8 ]
Palbociclib is taken daily orally with food in a cycle of 21 days of active medication, followed by a week of abstinence. Currently, palbociclib is prescribed as a combination therapy with either letrozole or fulvestrant . [ 9 ] Patients should also not consume CYP3A inhibitors or inducers while taking palbociclib. FDA information also cautions against consuming grapefruit products while taking palbociclib, in order to avoid negative interactions . [ 9 ]
The drug was reviewed and approved under the Food and Drug Administration ’s (FDA) accelerated Priority Review and Breakthrough Therapy designation programs on February 3, 2015, as a treatment (in combination with letrozole) for patients with estrogen receptor positive (ER+) advanced breast cancer. [ 10 ] This was an accelerated approval . [ 11 ]
In March 2017, the FDA granted regular approval to palbociclib for hormone receptor (HR) positive, human epidermal growth factor receptor 2 (HER2) negative advanced or metastatic breast cancer , in combination with an aromatase inhibitor . [ 12 ]
A phase III trial , PALOMA-2, was fully enrolled by February 2015 and reported positive results in April 2016. [ 13 ] The results of PALOMA-2 trial, published in November 2016, showed significantly longer progression-free survival in patients on palbociclib in combination with letrozole, compared to patients on letrozole and placebo. Progression-free survival was assessed by radiologically-confirmed disease progression by RECIST criteria or death during the study. At the time of publication, there was insufficient data on overall survival, and a final analysis is planned after a total of 390 deaths occur per protocol and in agreement with regulatory agencies. Of note, it was noted that the addition of palbociclib caused higher rates of myelotoxic events in the study. [ 14 ]
The drug was approved for use in the European Union in November 2016 as a treatment for hormone receptor (HR) positive, human epidermal growth factor receptor 2 (HER2) negative locally advanced or metastatic breast cancer, either in combination with an aromatase inhibitor or, for women who have received prior endocrine therapy , in combination with fulvestrant. In pre- or perimenopausal women, a luteinizing hormone releasing hormone agonist should also be given. [ 15 ]
In December 2017, palbociclib, was accepted for use by the NHS after going through the Scottish Medicines Consortium 's process for medicines used to treat very rare and end-of-life breast cancer. [ 16 ]
A majority of patients taking palbociclib experience neutropenia , a condition where a patient has an abnormally low number of neutrophils . This side effect impacts the immune system , and is thus likely responsible for the second most common side effect, infection . [ 17 ] Leukopenia and anemia are also frequent among patients taking palbociclib. [ 17 ] More than 10% of patients also experience side effects such as fatigue , nausea , diarrhea , respiratory infection , headache , thrombocytopenia , vomiting , and decreased appetite. [ 18 ] [ 17 ] The FDA also indicates that patients should be vigilant to monitor themselves for any sign of pulmonary embolism . The FDA further cautions that women should be aware that the medication can have a harmful effect on a fetus , and thus should not be taken while pregnant. [ 9 ]
FDA- and EMA-approval for palbociclib hinges upon the clinical trials’ results regarding progression-free survival (PFS). However, though data has proven promising (one study [ 19 ] had p-values very close to the significance threshold which, with further clinical trials, may be able to demonstrate statistical significance), there is as of 2019 [update] no significant improvement evident in overall survival (OS) when taking palbociclib. For example, in the PALOMA-2 trial, more than 70% of patients who were treated with palbociclib and letrozole progressed by 40 months. [ 20 ] This has impeded the drug's worldwide acceptance as economic analyses have not found palbociclib to be cost-effective.
De novo resistance to palbociclib implicates a variety of targets both upstream and downstream of the CDK4/6 to Rb pathway. Overexpression of the transcription factor E2F2 is capable of promoting resistance to CDK4/6 inhibition more than just loss of Rb alone (the direct downstream target of CDK4/6). [ 21 ] Palbociclib is less effective in patients whose breast cancer cells overexpress cyclin E1 or E2 , and Brk (breast tumor-related kinase). Brk is an intracellular kinase that is overexpressed in 60% of breast cancers and whose amplification leads to increased phosphorylation of Y88 of the p27 protein, as well as increases the cyclin D and CDK4 activity, thereby rendering the cancer cells more resistant to palbociclib. [ 21 ]
A 2018 study found that mutations in a pathway completely unrelated to the CDK4/6-Rb axis are also implicated in resistance to palbociclib. Loss of the FAT1 tumor suppressor promoted resistance to CDK4/6 inhibitors through the Hippo pathway , a signaling pathway known to function as a tumor suppressor. [ 22 ] Previously, FAT1 had been suggested to be a tumor suppressor and oncogene, though never before explicitly linked to resistance. The team found that FAT1 suppressed cells required significantly higher doses of CDK4/6 inhibitors in order to block proliferation of breast cancer cells in vivo . [ 22 ]
Palbociclib is indicated in HR+, HER2- metastatic breast cancer cells. Because CDK4/6 inhibition acts directly downstream of the endocrine therapy targets, cross-therapy resistance could possibly develop as a result of patient progression on hormone-therapy. In general, however, endocrine-resistant tumors are able to maintain sensitivity to CDK4/6 inhibition, with particular success witnessed with patients given combination therapy of palbociclib with endocrine therapy. [ 20 ] For example, the PALOMA-3 trial which studied the benefit of palbociclib and fulvestrant vs. fulvestrant alone found that the combined treatment regimen improved PFS in both patients with an ESR1 mutation and those with ESR1 wildtype ctDNA. Such results indicate that CDK4/6 inhibitors are effective irrespective of ESR1 mutation status, a marker that otherwise would reveal a patient to be endocrine-resistant. [ 23 ]
Certain manifestations of endocrine therapy resistance may further sensitize the breast cancer to CDK4/6 inhibitors. For example, deficiencies in mismatch repair caused by the MutL mutation in ER+ breast cancer evades CHK2-mediated inhibition of CDK4, thereby leading to endocrine resistance. [ 20 ] CDK4/6 inhibitors, however, have been demonstrated to be highly effective in MutL-defective ER+ breast cancer cells, and MutL bears potential as a biomarker for identifying patients highly suitable for treatment with CDK4/6 inhibitors.
Researchers at the Dana Farber Institute found that breast cancer cells that developed resistance to palbociclib were resensitized to the drug after a seven-day "treatment holiday". [ 24 ] Scientists linked the initial development of resistance to an increase in expression of CDK6 (but not CDK4, the other target of palbociclib), with the specific mechanism of CDK6 upregulation originating from suppression of the TGF-β pathway via the miR-432-5p microRNA . Scientists made this discovery after noticing that, in the lab, all breast cancer cells in the dish were found to acquire resistance at a similar time, a phenomenon contrary to classical models of acquiring resistance in which one or two cells become resistant and then expand to encompass more of the tumor as they divide. These palbociclib-resistance cells also did not contain a particular mutation, but rather became resistant and continued to spread this resistance to neighboring cells via exosomes. While the mechanism of this resistance has not yet been elucidated, it opens an avenue for further research into a completely novel method through which cancer cells acquire resistance. On the other hand, this suggests that patients which seemingly progress on palbociclib could benefit from longer-term treatment following a treatment holiday in which their tumors are "reset".
There are a variety of means through which cancer cells become resistant to palbociclib, with mechanisms of resistance involving multiple targets and processes throughout the pathway in which palbociclib operates. Previous research estimates that breast cancer cells show adaptation against palbociclib as early as 72 hours post-treatment. [ 21 ] Evidence for this was "shown to be mediated by non-canonical activation of cyclin D1/CDK2 complexes, which in turn induced a recovery of cyclin E2 expression and [subsequent] S-phase entry despite CDK4/6 inhibition" upstream of these two targets. [ 21 ] Furthermore, it is estimated that approximately 10% of patients have primary resistance to CDK4/6 inhibitors (resistance prior to drug therapy). [ 25 ] For example, patients who display evidence of functional Rb loss at baseline are not likely to benefit from CDK4/6 inhibition, nor are patients who display baseline evidence of increased cyclin E1 expression, or a high CCNE1/RB ratio. [ 25 ]
The PALOMA-3 trial announced in April 2015 that the addition of palbociclib was superior to fulvestrant alone for progression-free survival . [ 26 ]
In the phase II PALOMA-1 trial reported at the April 2014 annual meeting of the American Association for Cancer Research, the addition of palbociclib to letrozole was shown to significantly slow the progression of advanced cancer (median progression-free survival increased from 10.2 months to 20.2 months), but was not shown to have a statistically significant effect on increasing patients' overall survival times. [ 27 ] [ 28 ] [ 29 ]
Pfizer announce on May 31, 2020, the results of a preplanned efficacy and futility analysis. The results indicate that, when used in combination with post-surgery endocrine therapy, it "is unlikely to show a statistically significant improvement in the primary endpoint of invasive disease-free survival (iDFS)." [ 30 ] The trial was conducted on male and female patients with HR-positive, HER2-negative early stage breast cancer.
According to the NIH National Cancer Institute there are currently 39 active clinical trials testing palbociclib on its own or in combination with other medications. While a majority of these are exploring the further uses of palbociclib to treat breast cancer, other trials are investigating the potential applications of palbociclib to head and neck cancers, non-small cell lung cancer , recurring brain metastasis, squamous cell carcinoma, central nervous system tumors, and other solid tumor types. [ 31 ]
In December 2017, Pfizer announced that the PALOMA-2 trial, an ongoing phase III trial combining palbociclib with letrozole, showed a 44% reduction in risk of disease progression among trial subjects. The trial has also demonstrated greater than a year's improved median progression free survival for patients on the combined therapy (as compared to letrozole on its own). PALOMA-2 median patient follow-up time now exceeds three years, making it the longest traceable data for phase III study of a CDK4/6 inhibitor. [ 7 ]
Palbociclib is currently in Phase 2 clinical trials as a combination treatment with oral SERD ’s for ER+ / HER2- breast cancer. Studies include palbociclib plus G1 Therapeutic’s rintodestrant [ 32 ] and Zentalis’s Zn-c5. [ 33 ]
Palbociclib has several direct competitors currently on the market or in clinical trials. In September 2017, abemaciclib , another selective CDK4/6 inhibitor owned and manufactured by Eli Lilly , was approved for HR-positive, HER2-negative advanced metastatic breast cancer both in combination with fulvestrant and as a monotherapy . In March 2017, the FDA also approved ribociclib , owned by Novartis , as a combination therapy with aromatase inhibitors for indications similar to those of palbociclib and ribociclib. Notably, ribociclib seems to also have an inhibitory effect on Cyclin D3 /CDK6 activity. [ 34 ] G1 Therapeutics [ 35 ] also has a CDK4/6 inhibitor, trilaciclib , which is up for FDA approval (target decision date of February 15, 2021) for use in small cell lung cancer. [ 36 ]
Palbociclib (Ibrance) "can be ordered through select" specialty pharmacies and "sells for $9,850 for 30 days or $118,200 for a year's supply before discounts." [ 37 ] According to a statement by the New York–based Pfizer the price "is not the cost that most patients or payors pay" since most prescriptions are dispensed through health plans, which negotiate discounts for medicines or get government-mandated price concessions. [ 37 ] In the United States specialty pharmacies fill prescriptions for drugs that are usually high cost. [ 38 ] [ 39 ]
Pfizer reported revenue of US$4.753 billion for Ibrance in 2023. [ 40 ]
In February 2017, the National Institute for Health and Care Excellence (NICE) in the United Kingdom published a statement stating that the cost of Ibrance (approximately US$3700/28 days) did not make the added health benefits worth the cost. [ 41 ] It was stated that with the side effects caused by Ibrance, it was not a cost-effective medication for NICE to endorse. [ 42 ] At the time, a year's treatment with palbociclib and a drug such as fulvestrant was priced at US$106,105 (£79,650). [ 42 ] In November 2017 NICE announced that, after negotiation with Pfizer, the price would be discounted, and the drug would be recommended for use. [ 43 ] | https://en.wikipedia.org/wiki/Palbociclib |
The Palearctic or Palaearctic is a biogeographic realm of the Earth, the largest of eight. Confined almost entirely to the Eastern Hemisphere , it stretches across Europe and Asia , north of the foothills of the Himalayas , and North Africa .
The realm consists of several bioregions : the Mediterranean Basin ; North Africa ; North Arabia ; Western , Central and East Asia . The Palaearctic realm also has numerous rivers and lakes, forming several freshwater ecoregions.
Both the eastern and westernmost extremes of the Paleartic span into the Western Hemisphere , including Cape Dezhnyov in Chukotka Autonomous Okrug to the east and Iceland to the west. The term was first used in the 19th century, and is still in use as the basis for zoogeographic classification.
In an 1858 paper for the Proceedings of the Linnean Society , British zoologist Philip Sclater first identified six terrestrial zoogeographic realms of the world: Palaearctic, Aethiopian/ Afrotropic , Indian / Indomalayan , Australasian , Nearctic , and Neotropical . The six indicated general groupings of fauna, based on shared biogeography and large-scale geographic barriers to migration. [ 1 ]
Alfred Wallace adopted Sclater's scheme for his book The Geographical Distribution of Animals , published in 1876. This is the same scheme that persists today, with relatively minor revisions, and the addition of two more realms: Oceania and the Antarctic .
The Palearctic realm includes mostly boreal/subarctic-climate and temperate-climate ecoregions, which stretch from western Europe to the Bering Sea .
The boreal and temperate Euro-Siberian region is the Palearctic's largest biogeographic region, which transitions from tundra in the northern reaches of Russia and Scandinavia to the vast taiga , the boreal coniferous forests which run across the continent. South of the taiga is a belt of temperate broadleaf and mixed forests and temperate coniferous forests . This vast Euro-Siberian region is characterized by many shared plant and animal species, and has many affinities with the temperate and boreal regions of the Nearctic realm of North America . Eurasia and North America were often connected by the Bering land bridge , and have very similar mammal and bird fauna, with many Eurasian species having moved into North America, and fewer North American species having moved into Eurasia. Many zoologists consider the Palearctic and Nearctic to be a single Holarctic realm . The Palearctic and Nearctic also share many plant species, which botanists call the Arcto-Tertiary Geoflora .
The lands bordering the Mediterranean Sea in southern Europe, north Africa, and western Asia are home to the Mediterranean Basin ecoregions, which together constitute the world's largest and most diverse mediterranean climate region of the world, with generally mild, rainy winters and hot, dry summers. The Mediterranean basin's mosaic of Mediterranean forests, woodlands, and scrub are home to 13,000 endemic species. The Mediterranean basin is also one of the world's most endangered biogeographic regions; only 4% of the region's original vegetation remains, and human activities, including overgrazing , deforestation , and conversion of lands for pasture, agriculture, and urbanization, have degraded much of the region. Formerly the region was mostly covered with forests and woodlands, but heavy human use has reduced much of the region to the sclerophyll shrublands known as chaparral , matorral , maquis , or garrigue . Conservation International has designated the Mediterranean basin as one of the world's biodiversity hotspots .
A great belt of deserts , including the Atlantic coastal desert , Sahara Desert, and Arabian Desert , separates the Palearctic and Afrotropic ecoregions. This scheme includes these desert ecoregions in the palearctic realm; other biogeographers identify the realm boundary as the transition zone between the desert ecoregions and the Mediterranean basin ecoregions to the north, which places the deserts in the Afrotropic, while others place the boundary through the middle of the desert.
The Caucasus mountains, which run between the Black Sea and the Caspian Sea , are a particularly rich mix of coniferous, broadleaf, and mixed forests, and include the temperate rain forests of the Euxine-Colchic deciduous forests ecoregion.
Central Asia and the Iranian plateau are home to dry steppe grasslands and desert basins, with montane forests, woodlands, and grasslands in the region's high mountains and plateaux. In southern Asia the boundary of the Palearctic is largely altitudinal. The middle altitude foothills of the Himalaya between about 2,000–2,500 m (6,600–8,200 ft) form the boundary between the Palearctic and Indomalaya ecoregions.
China , Korea and Japan are more humid and temperate than adjacent Siberia and Central Asia, and are home to rich temperate coniferous, broadleaf, and mixed forests, which are now mostly limited to mountainous areas, as the densely populated lowlands and river basins have been converted to intensive agricultural and urban use. East Asia was not much affected by glaciation in the ice ages , and retained 96 percent of Pliocene [ citation needed ] tree genera, while Europe retained only 27 percent. In the subtropical region of southern China and southern edge of the Himalayas, the Palearctic temperate forests transition to the subtropical and tropical forests of Indomalaya , creating a rich and diverse mix of plant and animal species. The mountains of southwest China are also designated as a biodiversity hotspot . In Southeastern Asia, high mountain ranges form tongues of Palearctic flora and fauna in northern Indochina and southern China . Isolated small outposts ( sky islands ) occur as far south as central Myanmar (on Nat Ma Taung , 3,050 m; 10,010 ft), northernmost Vietnam (on Fan Si Pan , 3,140 m; 10,300 ft) and the high mountains of Taiwan .
The realm contains several important freshwater ecoregions as well, including the heavily developed rivers of Europe , the rivers of Russia , which flow into the Arctic , Baltic , Black , and Caspian seas, Siberia 's Lake Baikal , the oldest and deepest lake on the planet, and Japan's ancient Lake Biwa .
One bird family, the accentors (Prunellidae), is endemic to the Palearctic region. The Holarctic has four other endemic bird families: the divers or loons (Gaviidae), grouse (Tetraoninae), auks (Alcidae), and waxwings (Bombycillidae).
There are no endemic mammal orders in the region, but several families are endemic: Calomyscidae ( mouse-like hamsters ), Prolagidae , and Ailuridae ( red pandas ). Several mammal species originated in the Palearctic and spread to the Nearctic during the Ice Age , including the brown bear ( Ursus arctos , known in North America as the grizzly), red deer ( Cervus elaphus ) in Europe and the closely related elk ( Cervus canadensis ) in far eastern Siberia, American bison ( Bison bison ), and reindeer ( Rangifer tarandus , known in North America as the caribou ).
Several large Palearctic animals became extinct from the end of the Pleistocene into historic times, including Irish elk ( Megaloceros giganteus ), aurochs ( Bos primigenius ), woolly rhinoceros ( Coelodonta antiquitatis ), woolly mammoth ( Mammuthus primigenius ), North African elephant ( Loxodonta africana pharaoensis ), Chinese elephant ( Elephas maximus rubridens ), cave bear ( Ursus spelaeus ), Straight tusked elephant ( Palaeoloxodon antiquus ) and European lion ( Panthera leo europaea ). | https://en.wikipedia.org/wiki/Palearctic_realm |
Paleo-inspiration is a paradigm shift that leads scientists and designers to draw inspiration from ancient materials (from art, archaeology , natural history or paleo-environments) to develop new systems or processes , particularly with a view to sustainability .
Paleo-inspiration has already contributed to numerous applications in fields as varied as green chemistry , the development of new artist materials , composite materials , microelectronics , and construction materials . [ 1 ]
While this type of application has been known for a long time, the concept itself was coined by teams from the French National Centre for Scientific Research , the Massachusetts Institute of Technology and the Bern University of Applied Sciences from the term Bioinspiration . They published the concept in a seminal paper published online in 2017 by the journal Angewandte Chemie . [ 2 ]
Different names have been used to designate the corresponding systems, in particular: paleo-inspired, [ 2 ] antiqua-inspired, [ 1 ] antiquity-inspired [ 3 ] or archaeomimetic. [ 4 ] The use of these different names illustrates the extremely large time gap between the sources of inspiration, from millions of years ago when considering palaeontological systems and fossils , to much more recent archaeological or artistic material systems.
Distinct physico-chemical and mechanical properties are sought.
They may concern intrinsic properties of the paleo-inspired materials:
They can also concern processes:
This approach combines several key stages.
Emblematic examples include the microscopic study of the mineral phases present in Roman concretes to reproduce their durability in aggressive environments, particularly in the marine environment. [ 7 ]
A notable discovery is the elucidation of the atomic structure of Maya blue , a composite pigment combining a clay with an organic dye , which has led teams to produce pigments of other colours by combining clays with distinct organic dyes, such as "Maya violet". [ 8 ] | https://en.wikipedia.org/wiki/Paleo-inspiration |
Paleobiology (or palaeobiology ) is an interdisciplinary field that combines the methods and findings found in both the earth sciences and the life sciences . An investigator in this field is known as a paleobiologist .
Paleobiology is closely related to the field of paleontology , although the latter focuses primarily on the study and taxonomic classification of fossil records , while paleobiology incorporates a broader ecological , evolutionary and geological perspectives of the history of life on Earth . It is also not to be confused with geobiology , which focuses more on the contemporary interactions between the modern biosphere and the physical Earth .
Paleobiological research uses biological field research of current biota and of fossil evidence millions of years old to draw parallel and answer questions about the molecular evolution and the evolutionary history of life . In this scientific quest, macrofossils , microfossils and trace fossils are typically analyzed. However, the 21st-century biochemical analysis of DNA and RNA samples offers much promise, as does the biometric construction of phylogenetic trees .
The founder or "father" of modern paleobiology was Baron Franz Nopcsa (1877 to 1933), a Hungarian scientist trained at the University of Vienna. He initially termed the discipline "paleophysiology".
However, credit for coining the word paleobiology itself should go to Professor Charles Schuchert . He proposed the term in 1904 so as to initiate "a broad new science" joining "traditional paleontology with the evidence and insights of geology and isotopic chemistry." [ 1 ]
On the other hand, Charles Doolittle Walcott , a Smithsonian adventurer, has been cited as the "founder of Precambrian paleobiology". Although best known as the discoverer of the mid- Cambrian Burgess shale animal fossils, in 1883 this American curator found the "first Precambrian fossil cells known to science" – a stromatolite reef then known as Cryptozoon algae . In 1899 he discovered the first acritarch fossil cells, a Precambrian algal phytoplankton he named Chuaria . Lastly, in 1914, Walcott reported "minute cells and chains of cell-like bodies" belonging to Precambrian purple bacteria . [ 2 ]
Later 20th-century paleobiologists have also figured prominently in finding Archaean and Proterozoic eon microfossils : In 1954, Stanley A. Tyler and Elso S. Barghoorn described 2.1 billion-year-old cyanobacteria and fungi -like microflora at their Gunflint Chert fossil site. Eleven years later, Barghoorn and J. William Schopf reported finely-preserved Precambrian microflora at their Bitter Springs site of the Amadeus Basin , Central Australia. [ 3 ]
In 1993, Schopf discovered O 2 -producing blue-green bacteria at his 3.5 billion-year-old Apex Chert site in Pilbara Craton , Marble Bar , in the northwestern part of Western Australia . So paleobiologists were at last homing in on the origins of the Precambrian " Oxygen catastrophe ". [ 4 ]
During the early part of the 21st-century, two paleobiologists Anjali Goswami and Thomas Halliday, studied the evolution of mammaliaforms during the Mesozoic and Cenozoic eras (between 299 million to 12,000 years ago). [ 5 ] Additionally, they uncovered and studied the morphological disparity and rapid evolutionary rates of living organisms near the end and in the aftermath of the Cretaceous mass extinction (145 million to 66 million years ago). [ 6 ] [ 7 ]
Books written for the general public on this topic include the following: | https://en.wikipedia.org/wiki/Paleobiology |
Paleobiology is a scientific journal promoting the integration of biology and conventional paleontology , with emphasis placed on biological or paleobiological processes and patterns. It attracts papers of interest to more than one discipline, and occasionally publishes research on recent organisms when this is of interest to paleontologists.
This article about a journal on paleontology is a stub . You can help Wikipedia by expanding it .
See tips for writing articles about academic journals . Further suggestions might be found on the article's talk page . | https://en.wikipedia.org/wiki/Paleobiology_(journal) |
Paleobotany or palaeobotany , also known as paleophytology , is the branch of botany dealing with the recovery and identification of plant fossils from geological contexts, and their use for the biological reconstruction of past environments ( paleogeography ), and the evolutionary history of plants , with a bearing upon the evolution of life in general. It is a component of paleontology and paleobiology . The prefix palaeo- or paleo- means "ancient, old", [ 1 ] and is derived from the Greek adjective παλαιός , palaios . [ 2 ] Paleobotany includes the study of land plants , as well as the study of prehistoric marine photoautotrophs such as photosynthetic algae , seaweeds or kelp . A closely related field is palynology , which is the study of fossilized and extant spores and pollen .
Paleobotany is important in the reconstruction of ancient ecological and climate systems , known as paleoecology and paleoclimatology respectively. It is fundamental to the study of green plant development and evolution . Paleobotany is a historical science much like its adjacent, paleontology. Because of the understanding that paleobotany gives to archeologists, it has become important to the field of archaeology as a whole. primarily for the use of phytoliths in relative dating and in paleoethnobotany . [ 3 ]
The study and discipline of paleobotany was seen as far back as the 19th century. Known as the “Father of Paleobotany”, French botanist Adolphe-Theodore Brongniart was a sufficient figure in this emergence of Paleobotany, known for his work on the relationship between the living and extinct plant life. This work not only progressed paleobotany but also the understanding of the earth and its longevity in actuality and the organic matter that existed over the earth’s timeline. Paleobotany also succeeded in the hands of German paleontologist Ernst Friedrich von Schlothiem , and Czech nobleman and scholar, Kaspar Maria von Sternberg . [ 4 ] [ 5 ]
As paleobotany is the specification of fossilized plant life and the environment in which they thrived in, paleoecology is the study of all once-living organisms and the interactions held in the environments they once existed in, before becoming extinct . [ 6 ]
Paleoecology is a similar study to that of paleontology , but paleoecology uses more methodology from the biological sciences and geological sciences [ 7 ] rather than from an anthropological standpoint as paleontologists do.
Paleopalynology , more commonly known as palynology , is the science and study of ancient palynomorphs: particles sized between 5 and 500 micrometers. [ 8 ] This would be an inclusion of pollen and spores and any other micro-organic matter. Paleopalynology is simply paleobotany on a much smaller scale, the two in close association with each other.
Similar to paleobotany, we can tell a great deal of information about the environment and biome at the time these particles existed prehistorically. These particles also help geologists identify and date the rock strata of sedimentary rocks . It is also used to find natural oils and gas within these rock layers for extraction . [ 9 ] Besides uncovering documentation of our past environmental conditions, palynology can also tell us about animal diets, historical standings of human allergies , and reveal evidence in crime cases. [ citation needed ]
Macroscopic remains of true vascular plants are first found in the fossil record during the Silurian Period of the Paleozoic era. Some dispersed, fragmentary fossils of disputed affinity, primarily spores and cuticles , have been found in rocks from the Ordovician Period in Oman , and are thought to derive from liverwort - or moss -grade fossil plants. [ 10 ]
An important early land plant fossil locality is the Rhynie chert , found outside the village of Rhynie in Scotland . The Rhynie chert is an Early Devonian sinter ( hot spring ) deposit composed primarily of silica . It is exceptional due to its preservation of several different clades of plants, from mosses and lycophytes to more unusual, problematic forms. Many fossil animals, including arthropods and arachnids , are also found in the Rhynie chert, and it offers a unique window into the history of early terrestrial life.
Plant-derived macrofossils become abundant in the Late Devonian including tree trunks, fronds , and roots . The earliest tree was once thought to be Archaeopteris , which bears simple, fern -like leaves spirally arranged on branches atop a conifer -like trunk , [ 11 ] although it is now known to be the recently discovered Wattieza . [ 12 ]
Widespread coal swamp deposits across North America and Europe during the Carboniferous Period contain a wealth of fossils containing arborescent lycopods up to 30 m tall, abundant seed plants , such as conifers and seed ferns , and countless smaller, herbaceous plants .
Angiosperms ( flowering plants ) evolved during the Mesozoic , and flowering plant pollen and leaves first appeared during the Early Cretaceous , approximately 130 million years ago.
A plant fossil is any preserved part of a plant that has long since died. Such fossils may be prehistoric impressions that are many millions of years old, or bits of charcoal that are only a few hundred years old. Prehistoric plants are various groups of plants that lived before recorded history (before about 3500 BC ).
Plant fossils can be preserved in a variety of ways, each of which can give different types of information about the original parent plant. These modes of preservation may be summarised in a paleobotanical context as follows.
Plant fossils almost always represent disarticulated parts of plants; even small herbaceous plants are rarely preserved whole. The few examples of plant fossils that appear to be the remains of whole plants are in fact incomplete as the internal cellular tissue and fine micromorphological detail is normally lost during fossilization. Plant remains can be preserved in a variety of ways, each revealing different features of the original parent plant. [ 13 ]
Because of this, paleobotanists usually assign different taxonomic names to different parts of the plant in different modes of preservation. For instance, in the subarborescent Palaeozoic sphenophytes , an impression of a leaf might be assigned to the genus Annularia , a compression of a cone assigned to Palaeostachya , and the stem assigned to either Calamites or Arthroxylon depending on whether it is preserved as a cast or a petrifaction. All of these fossils may have originated from the same parent plant but they are each given their own taxonomic name. This approach to naming plant fossils originated with the work of Adolphe-Théodore Brongniart . [ 14 ]
For many years this approach to naming plant fossils was accepted by paleobotanists but not formalised within the International Rules of Botanical Nomenclature . [ 15 ] Eventually, Thomas (1935) and Jongmans, Halle & Gothan (1935) proposed a set of formal provisions, the essence of which was introduced into the 1952 International Code of Botanical Nomenclature . [ 16 ] These early provisions allowed fossils representing particular parts of plants in a particular state of preservation to be placed in organ-genera. In addition, a small subset of organ-genera, to be known as form-genera, were recognised based on the artificial taxa introduced by Brongniart mainly for foliage fossils. The concepts and regulations surrounding organ- and form-genera were modified within successive codes of nomenclature, reflecting a failure of the paleobotanical community to agree on how this aspect of plant taxonomic nomenclature should work (a history reviewed by Cleal and Thomas in 2020 [ 17 ] ). The use of organ- and fossil-genera was abandoned with the St Louis Code , and replaced by "morphotaxa". [ 18 ]
The situation in the Vienna Code of 2005 was that any plant taxon whose type is a fossil, except diatoms , can be described as a morphotaxon , a particular part of a plant preserved in a particular way. [ 19 ] Although the name is always fixed to the type specimen, the circumscription (i.e. range of specimens that may be included within the taxon) is defined by the taxonomist who uses the name. Such a change in circumscription could result in an expansion of the range of plant parts or preservation states that could be incorporated within the taxon. For instance, a fossil-genus originally based on compressions of ovules could be used to include the multi-ovulate cupules within which the ovules were originally borne. A complication can arise if, in this case, there was an already named fossil-genus for these cupules. If paleobotanists were confident that the type of the ovule fossil-genus and of the cupule fossil-genus could be included in the same genus, then the two names would compete as to being the correct one for the newly emended genus. In general, there would be competing priority whenever plant parts that had been given different names were discovered to belong to the same species. It appeared that morphotaxa offered no real advantage to paleobotanists over normal fossil-taxa and the concept was abandoned with the 2011 botanical congress and the 2012 International Code of Nomenclature for algae, fungi, and plants .
Some plants have remained almost unchanged throughout earth's geological time scale. Horsetails had evolved by the Late Devonian, [ 20 ] early ferns had evolved by the Mississippian , conifers by the Pennsylvanian . Some plants of prehistory are the same ones around today and are thus living fossils , such as Ginkgo biloba and Sciadopitys verticillata . Other plants have changed radically, or became extinct.
Examples of prehistoric plants are: | https://en.wikipedia.org/wiki/Paleobotany |
Paleoethnobotany (also spelled palaeoethnobotany), or archaeobotany , is the study of past human-plant interactions through the recovery and analysis of ancient plant remains. Both terms are synonymous, though paleoethnobotany (from the Greek words palaios [παλαιός] meaning ancient, ethnos [έθνος] meaning race or ethnicity, and votano [βότανο] meaning plants) is generally used in North America and acknowledges the contribution that ethnographic studies have made towards our current understanding of ancient plant exploitation practices, while the term archaeobotany (from the Greek words archaios [αρχαίος] meaning ancient and votano ) is preferred in Europe and emphasizes the discipline's role within archaeology . [ 1 ] [ 2 ]
As a field of study, paleoethnobotany is a subfield of environmental archaeology . It involves the investigation of both ancient environments and human activities related to those environments, as well as an understanding of how the two co-evolved. Plant remains recovered from ancient sediments within the landscape or at archaeological sites serve as the primary evidence for various research avenues within paleoethnobotany, such as the origins of plant domestication , the development of agriculture , paleoenvironmental reconstructions, subsistence strategies, paleodiets, economic structures, and more. [ 3 ]
Paleoethnobotanical studies are divided into two categories: those concerning the Old World (Eurasia and Africa) and those that pertain to the New World (the Americas). While this division has an inherent geographical distinction to it, it also reflects the differences in the flora of the two separate areas. For example, maize only occurs in the New World, while olives only occur in the Old World. Within this broad division, paleoethnobotanists tend to further focus their studies on specific regions, such as the Near East or the Mediterranean, since regional differences in the types of recovered plant remains also exist.
Plant remains recovered from ancient sediments or archaeological sites are generally referred to as either ‘macrobotanicals’ or ‘microbotanicals.’
Macrobotanical remains are vegetative parts of plants, such as seeds, leaves, stems and chaff , as well as wood and charcoal that can either be observed with the naked eye or the with the use of a low-powered microscope.
Microbotanical remains consist of microscopic parts or components of plants, such as pollen grains , phytoliths and starch granules , that require the use of a high-powered microscope in order to see them.
The study of seeds, wood/charcoal, pollen, phytoliths and starches all require separate training, as slightly different techniques are employed for their processing and analysis. Paleoethnobotanists generally specialize in the study of a single type of macrobotanical or microbotanical remain, though they are familiar with the study of other types and can sometimes even specialize in more than one.
The state of Paleoethnobotany as a discipline today stems from a long history of development that spans more than two hundred years [ specify ] . Its current form is the product of steady progression by all aspects of the field, including methodology, analysis and research. [ vague ]
The study of ancient plant remains began in the 19th century as a result of chance encounters with desiccated and waterlogged material at archaeological sites. In Europe, the first analyses of plant macrofossils were conducted by the botanist C. Kunth (1826) [ 4 ] on desiccated remains from Egyptian tombs and O. Heer (1866) [ 5 ] on waterlogged specimens from lakeside villages in Switzerland, after which point archaeological plant remains became of interest and continued to be periodically studied from different European countries until the mid-20th century. In North America, the first analysis of plant remains occurred slightly later and did not generate the same interest in this type of archaeological evidence until the 1930s when Gilmore (1931) [ 6 ] and Jones (1936) [ 7 ] analysed desiccated material from rock shelters in the American Southwest. All these early studies, in both Europe and North America, largely focused on the simple identification of the plant remains in order to produce a list of the recovered taxa. [ 1 ] [ 2 ]
During the 1950s and 1960s, Paleoethnobotany gained significant recognition as a field of archaeological research with two significant events: the publication of the Star Carr excavations in the UK and the recovery of plant material from archaeological sites in the Near East. Both convinced the archaeological community of the importance of studying plant remains by demonstrating their potential contribution to the discipline; the former produced a detailed paleoenvironmental reconstruction that was integral to the archaeological interpretation of the site and the latter yielded the first evidence for plant domestication, which allowed for a fuller understanding of the archaeological record. Thereafter, the recovery and analysis of plant remains received greater attention as a part of archaeological investigations. [ 1 ] In 1968, the International Work Group for Palaeoethnobotany (IWGP) was founded. [ 8 ]
With the rise of Processual archaeology , the field of Paleoethnobotany began to grow significantly. The implementation in the 1970s of a new recovery method, called flotation, allowed archaeologists to begin systematically searching for plant macrofossils at every type of archaeological site. As a result, there was a sudden influx of material for archaeobotanical study, as carbonized and mineralized plant remains were becoming readily recovered from archaeological contexts. Increased emphasis on scientific analyses also renewed interest in the study of plant microbotanicals, such as phytoliths (1970s) and starches (1980s), while later advances in computational technology during the 1990s facilitated the application of software programs as tools for quantitative analysis. The 1980s and 1990s also saw the publication of several seminal volumes about Paleoethnobotany [ 9 ] [ 10 ] [ 3 ] [ 11 ] [ 12 ] that demonstrated the sound theoretical framework in which the discipline operates. And finally, the popularization of Post-Processual archaeology in the 1990s, helped broaden the range of research topics addressed by paleoethnobotanists, for example 'food-related gender roles'. [ 1 ] [ 2 ]
Paleoethnobotany is a discipline that is ever evolving, even up to the present day. Since the 1990s, the field has continued to gain a better understanding of the processes responsible for creating plant assemblages in the archaeological record and to refine its analytical and methodological approaches accordingly. For example, current studies have become much more interdisciplinary, utilizing various lines of investigation in order to gain a fuller picture of the past plant economies. Research avenues also continue to explore new topics pertaining to ancient human-plant interactions, such as the potential use of plant remains in relation to their mnemonic or sensory properties. [ 1 ] [ 2 ] Interest in plant remains surged in the 2000s alongside the improvement of stable isotope analysis and its application to archaeology, including the potential to illuminate the intensity of agricultural labor, resilience , and long-term social and economic changes. [ 13 ]
Archaeobotany had not been used extensively in Australia until recently. In 2018 a study of the Karnatukul site in the Little Sandy Desert of Western Australia showed evidence of continuous human habitation for around 50,000 years, by analysing wattle and other plant items. [ 14 ] [ 15 ] [ 16 ] [ 17 ]
As organic matter, plant remains generally decay over time due to microbial activity. In order to be recovered in the archaeological record, therefore, plant material must be subject to specific environmental conditions or cultural contexts that prevent their natural degradation. Plant macrofossils recovered as paleoenvironmental, or archaeological specimens result from four main modes of preservation:
In addition to the above-mentioned modes of preservation, plant remains can also be occasionally preserved in a frozen state or as impressions . The former occurs quite rarely, but a famous example comes from Ötzi , the 5,500 year old mummy found frozen in the French Alps, whose stomach contents revealed the plant and meat components of his last meal. [ 29 ] [ 30 ] The latter occurs more regularly, though plant impressions do not actually preserve the macrobotanical remains themselves, but rather their negative imprints in pliable materials like clay, mudbrick or plaster. Impressions often result from the deliberate employment of plant material for decorative or technological purposes (such as the use of leaves to create patterning on ceramics or the use of chaff as temper in the construction of mudbricks ), however, they can also derive from accidental inclusions. Identification of plant impressions is achieved by creating a silicone cast of the imprints and studying them under the microscope. [ 22 ] [ 31 ]
In order to study ancient plant macrobotanical material, Paleoethnobotanists employ a variety of recovery strategies that involve different sampling and processing techniques depending on the kind of research questions they are addressing, the type of plant macrofossils they are expecting to recover and the location from which they are taking samples. [ 2 ]
In general, there are four different types of sampling methods that can be used for the recovery of plant macrofossils from an archaeological site : [ 1 ] [ 32 ]
Each sampling method has its own pros and cons and for this reason, paleoethnobotanists sometimes implement more than one sampling method at a single site. In general, Systematic or Full Coverage sampling is always recommended whenever possible. The practicalities of excavation, however, and/or the type of archaeological site under investigation sometimes limit their use and Judgment sampling tends to occur more often than not. [ 1 ] [ 32 ]
Aside from sampling methods, there are also different types of samples that can be collected, for which the standard, recommended sample size is ~20L for dry sites and 1-5L for waterlogged sites. [ 1 ] [ 32 ]
These different types of samples again serve different research aims. For example, Point/Spot samples can reveal the spatial differentiation of food-related activities, Pinch samples are representative of all activities associated with a specific context, and Column samples can show change or variation or time. [ 1 ] [ 32 ]
The sampling methods and types of samples used for the recovery of microbotanical remains (namely, pollen , phytoliths , and starches ) follows virtually the same practices as outline above, with only some minor differences. First, the required sample size is much smaller: ~50g (a couple of tablespoons) of sediment for each type of microfossil analysis. Secondly, artefacts, such as stone tools and ceramics, can also be sampled for microbotanicals. And third, control samples from unexcavated areas in and around the site should always be collected for analytical purposes. [ 32 ] [ 1 ]
There are several different techniques for the processing of sediment samples. The technique a paleoethnobotanist chooses depends entirely upon the type of plant macrobotanical remains they expect to recover.
Microbotanical remains (namely, pollen , phytoliths and starches ) require completely different processing procedures in order to extract specimens from the sediment matrix. These procedures can be quite expensive, as they involve various chemical solutions, and are always carried out in the laboratory. [ 1 ]
Analysis is the key step in paleoethnobotanical studies that makes the interpretation of ancient plant remains possible. The quality of identifications and the use of different quantification methods are essential factors that influence the depth and breadth of interpretative results.
Plant macrofossils are analyzed under a low-powered stereomicroscope. The morphological features of different specimens, such as size, shape and surface decoration, are compared with images of modern plant material in identification literature, such as seed atlases, as well as real examples of modern plant material from reference collections, in order to make identifications. Based on the type of macrofossils and their level of preservation, identifications are made to various taxonomic levels , mostly family, genus and species. These taxonomic levels reflect varying degrees of identification specificity: families comprise big groups of similar type plants; genera make up smaller groups of more closely related plants within each family, and species consist of the different individual plants within each genus. Poor preservation, however, may require the creation of broader identification categories, such as ‘nutshell’ or ‘cereal grain’, while extremely good preservation and/or the application of analytical technology, such as Scanning Electron Microscopy (SEM) or Morphometric Analysis , may allow even more precise identification down to subspecies or variety level [ 1 ] [ 31 ] [ 35 ]
Desiccated and waterlogged macrofossils often have a very similar appearance with modern plant material, since their modes of preservation do not directly affect the remains. As a result, fragile seed features, such as anthers or wings, and occasionally even color, can be preserved, allowing for very precise identifications of this material. The high temperatures involved in the carbonization of plant remains, however, can sometimes cause the damage to or loss of plant macrofossil features. The analysis of charred plant material, therefore, often includes several family- or genus-level identifications, as well as some specimen categories. Mineralized plant macrofossils can range in preservation from detailed copies to rough casts depending on depositional conditions and the kind of replacing mineral. This type of macrofossil can easily be mistaken for stones by the untrained eye. [ 18 ] [ 20 ] [ 21 ] [ 26 ]
Microbotanical remains follow the same identification principles, but require a high-powered (greater magnification) microscope with transmitted or polarized lighting. Starch and phytolith identifications are also subject to limitations, in terms of taxonomical specificity, based on the state of current reference material for comparison and considerable overlap in specimen morphologies. [ 1 ] [ 35 ] [ 36 ]
After identification, paleoethnobotanists provide absolute counts for all plant macrofossils recovered in each individual sample. These counts constitute the raw analytical data and serve as the basis for any further quantitative methods that may be applied. [ 37 ] Initially, paleoethnobotanical studies mostly involved a qualitative assessment of the plant remains at an archaeological site (presence and absence), but the application of simple statistical methods (non-multivariate) followed shortly thereafter. [ 1 ] [ 37 ] The use of more complex statistics (multivariate), however, is a more recent development. In general, simple statistics allow for observations concerning specimen values across space and over time, [ 37 ] [ 1 ] while more complex statistics facilitate the recognition of patterning within an assemblage, as well as the presentation of large datasets. [ 1 ] [ 38 ] The application of different statistical techniques depends on the quantity of material available. Complex statistics require the recovery of a large number of specimens (usually around 150 from each sample involved in this type of quantitative analysis), whereas simple statistics can be applied regardless of the amount of recovered specimens – though obviously, the more specimens, the more effective the results.
The quantification of microbotanical remains differs slightly from that of macrobotanical remains, mostly due to the high numbers of microbotanical specimens that are usually present in samples. As a result, relative/percentage occurrence sums are usually employed in the quantification of microbotanical remains instead of absolute taxa counts. [ 1 ] [ 36 ]
The work done in Paleoethnobotany is constantly furthering over understanding of ancient plant exploitation practices. The results are disseminated in digital archives, [ 39 ] archaeological excavation reports and at academic conferences, as well as in books and journals related to archaeology, anthropology, plant history, paleoecology , and social sciences. In addition to the use of plants as food, such as paleodiet, subsistence strategies and agriculture, Paleoethnobotany has illuminated many other ancient uses for plants (some examples provided below, though there are many more):
International Associations
Journals
Various knowledge resources | https://en.wikipedia.org/wiki/Paleoethnobotany |
Paleohydrology , or palaeohydrology , is the scientific study of the movement, distribution, and quality of water on Earth during previous periods of its history. The discipline uses indirect evidence to infer changes in deposition rates, the existence of flooding, changes in sea levels, changes in groundwater levels and the erosion of rocks. It also deals with alterations in the floral and faunal assemblages which have come about in previous periods because of changes in hydrology . [ 2 ]
Past hydrological changes on our planet have had enormous effects on the environment. Over most of geologic time, the long-term mean sea level has been higher than today. Only at the Permian - Triassic boundary ~250 million years ago was the long-term mean sea level lower than today. Long term changes in the mean sea level are the result of changes in the oceanic crust , with a downward trend expected to continue in the very long term. [ 3 ] Twenty thousand years ago, the sea level was 120 m (394 ft) lower than at present with vast amounts of water being locked up as ice; in the northern hemisphere, there was twenty times more ice than the present volume. [ 4 ]
The climate of the Sahara , for example, has undergone enormous variations between wet and dry over the last few hundred thousand years, believed to be caused by long-term changes in the North African climate cycle that alters the path of the North African Monsoon . [ 5 ] Paleohydrological studies of sediments in the Fazzan Basin in Libya show that humid conditions once prevailed there that were capable of creating a lake with a surface area of around 76,250 km 2 (29,400 sq mi). [ 6 ] Before the abrupt desertification of North Africa about five thousand years ago, the Sahara was the home of Neolithic men and supported verdant vegetation and diverse wildlife . [ 7 ]
Paleohydrological study usually starts in the field with observations, measurements and the collection of samples; it continues with analysing the samples in the laboratory, recording the data, collating it, modelling systems, time-system analyses and eventually making inferences. A major step is the dating of the material. Methods here include using radioactive isotopes, considering the geological development of the area, the presence or absence of certain organisms and the identification of fossil pollen . Paleohydrology makes use of indirect methods that give an indication of the climatological conditions prevailing at the time. [ 4 ]
Paleo hydrology uses methods that include using direct and indirect climatic data; these can be used to assess the variability in the hydrological cycle. [ 8 ] Direct data encompasses measured and historical information, including streamflow records, flood occurrences, and drought events. In certain regions such as Egypt and China, direct data can extend back thousands of years, offering a rich historical perspective, while globally, it commonly spans approximately two centuries. [ 8 ] Complementing direct data, indirect data—often referred to as proxy data—serves to extend climatic and hydrological insights. For instance, the analysis of tree rings allows for the reconstruction of past precipitation and temperature patterns, while deep-sea sediment cores contribute to predictions of long-term global temperatures. Proxy data is instrumental in providing evidence for prehistoric floods, with its traces commonly preserved in sedimentological deposits within streambeds and botanical evidence. This collective data is crucial for forecasting the frequency and magnitude of floods and droughts in specific geographic areas. [ 8 ]
The methodologies outlined in the methods section facilitate the determination of flood occurrences, magnitude, and ages. Through these techniques, paleoflood data can be extended back over thousands of years, enriching the precision of flood-frequency curves. [ 8 ] This extended historical perspective is invaluable in contemporary flood-frequency analysis, significantly amplifying the effective length of the record. The incorporation of historical flood data enhances the analysis, offering a more comprehensive understanding of the dynamics and patterns involved in flooding events. [ 8 ]
Paleohydrological data serves as a valuable tool in unraveling the climatic variability of the past. Evidence of climatic changes is seen in lake and ocean sediment, as well as in the mass balance of glaciers. Over the last 10,000 years, the climate has undergone significant fluctuations, impacting floods, droughts, and hydrologic patterns. [ 8 ] Understanding this historical climatic variability is crucial for predicting future climate changes. Take, for instance, the Colorado River, a vital freshwater source for the southwestern United States. By analyzing data from past droughts, it becomes evident that recent climatic variability could potentially reduce streamflow by 35 percent. [ 8 ] This knowledge is indispensable for informed future planning, ensuring water availability for the populations that depend on it.
Hydrological fluctuations are linked to the factors causing them, and paleohydrological data can be used to validate climate models. On the orbital time scale, paleohydrological data reflects variations in the Earth's orbit and the cycle of glacial periods and interglacials. For example, variations in the water level of Lake Lisan correlates with data showing temperature fluctuations collected from polar ice core samples. On a shorter time scale, minuscule climatic variations can have large hydrological effects as when excess rainwater entering the North Atlantic was linked with a serious drought in the eastern Mediterranean. The Little Ice Age in northern Europe was linked with drought in East Africa, heavy rains in the African lakes, and persistent El Niño–Southern Oscillation conditions in the Pacific. [ 4 ]
Another application is in the quantification of erosion caused by rivers under differing climatological conditions. Increased erosion rates following deforestation, and pollution resulting from lead-mining activities by the Romans show up in lake sediments. [ 4 ] | https://en.wikipedia.org/wiki/Paleohydrology |
Paleomycology is the study of fossil fungi . [ 1 ] Paleomycology is considered a subdiscipline of paleobotany , centered on mushrooms, fungal spores, and hyphae preserved in sediment layers and rock. [ 2 ] Fungi have been found in the palaeoecological record as far back as the Paleozoic era, with evidence of influencing the evolutionary processes of early flowering plants. [ 3 ]
Interest in fossilized fungi dates back to the early nineteenth century, with the first illustrated collection being curated by Luigi Meschinelli in 1898. It focussed on matching fossils to modern fungi. [ 3 ] Historically, however, paleoecologists tend to place a larger focus on plant and animal macrofossils, partially due to the difficulty and unfamiliarity in identifying fungi physiology and morphology. [ 3 ]
A majority of fossilized fungi remains, such as spores and sclerotia , [ 3 ] are discovered in amber . [ 4 ] Two particular discoveries of fossil fungi, one in the Baltic sea dated to the Eocene and another in the Dominican Republic dated to the Miocene , are is important for comparison across timescales and for the development of the evolutionary record. A sample of amber from the Baltic site preserved a hexapod and the fungi Aspergillus collembolorum, which suggests the presence of parasitic relationships as early as 34 million years ago . [ 4 ] Fossil fungi presents indirect evidence of when symbiotic relationships coevolved, such as saprophytism or commensalism among mycorrhizae or lichen. The presence of wood-rotting fungi in Callixylon whiteanum , one of the oldest identified trees, suggests that saprophytic interactions between plants and fungi evolved when wood first began to develop. [ 2 ]
Fungi require a carbon source for growth and development, which is provided by the decomposition of organic plant and animal matter. Mycorrhizal relationships between plant and fungi are mutualistic: the fungus gains a carbon source, while the plant receives nutrient minerals. Discovery of fungi in the Early Devonian Rhynie chert , when plants were root and leafless, suggests that fungi played a large role in the evolution of plant life into terrestrial ecosystems. [ 3 ]
Fungal endophytes and epiphytes , similarly to mycorrhizae, establish a symbiotic relationship with plant hosts through which they obtain their necessary nutrients, however the lack of fossil endophytes on plant leaves prior to the Cretaceous period suggests that leaves as a fungal habitat were exploited by fungi after flowering plants evolved about 130 million years ago. [ 3 ] The use of fungal epi - and endophytes in the fossil record can be used to determine the evolutionary modifications required to colonize certain ecosystems, as well as to identify the environmental tolerances of fungi, their potential as palaeoclimatological proxies (for instance, the presence of Sporomiella being used to reconstruct megaherbivore extinction), and future use in identifying extinct morphologies. [ 3 ] Evidence of bioeroder fungi has been identified in carbonate substrates (such as in shells) in which organic carbon-containing matter was extracted, indicating the presence of a mutualistic or parasitic relationship between a fungus and host. [ 3 ]
Fungi have not only been identified as bioeroders, but also as part of a food chain. The presence of fungal hyphae and spores in coprolites suggests that arthropods depended on fungi as a food source. [ 3 ]
Fossilized fungal organisms are important to geological evolutionary history. The weathering of rocks and nutrient cycling in mineral media show the impact and spread of microbial fungi in geological processes. [ 3 ] | https://en.wikipedia.org/wiki/Paleomycology |
Paleophycology (also once known as paleoalgology ) is the subdiscipline of paleobotany that deals with the study and identification of fossil algae and their evolutionary relationships and ecology. [ 1 ] [ 2 ]
The field is very important in the science of paleolimnology as the algae leave many indicators of fossil ecosystems. Primary and most familiar are both fossil shells from diatoms and biogeochemical traces of algal pigments in lake sediments. These fossils are clues to changes in nutrient availability and ecology of lakes. [ 3 ] [ 4 ]
Some paleophycologists:
This paleobotany -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Paleophycology |
Paleosalinity (or palaeosalinity) is the salinity of the global ocean or of an ocean basin at a point in geological history.
From Bjerrum plots , it is found that a decrease in the salinity of an aqueous fluid will act to increase the value of the carbon dioxide-carbonate system equilibrium constants, (pK*). This means that the relative proportion of carbonate with respect to carbon dioxide is higher in more saline fluids, e.g. seawater , than in fresher waters. Of crucial importance for paleoclimatology is the observation that an increase in salinity will thus reduce the solubility of carbon dioxide in the oceans. Since there is thought to have been a 120 m depression in sea level at the last glacial maximum due to the extensive formation of ice sheets (which are solely freshwater), this represents a significant fractionation towards saltier seas during glacial periods. Correspondingly, this will cause a net outgassing of carbon dioxide into the atmosphere because of its reduced solubility, acting to increase atmospheric carbon dioxide by 6.5 ‰ . This is thought to partly offset the net decrease of 80-100‰ observed during glacial periods. [ 1 ]
In addition, it is thought that extensive salinity stratification can lead to a reduction in the meridional overturning circulation (MOC) through the slowing of thermohaline circulation . Increased stratification means that there is effectively a barrier to subduction of parcels of water; isopycnals effectively do not outcrop at the surface and are parallel to the surface. The ocean, in this case, can be described as "less ventilated", and this has been implicated in the slowing down of the MOC.
There may exist proxies for salinity, but to date the main way that salinity has been measured has been by directly measuring chlorinity in pore fluids . [ 2 ] Adkins et al. (2002) used pore fluid chlorinity in ODP cores, with the paleo-depth estimated from nearby coral horizons. Chlorinity was measured rather than pure salinity because the major ions in seawater are not constant with depth in the sediment column; for example, sulfate reduction and cation-clay interactions can change overall salinity, whereas chlorinity is not heavily affected.
Adkins' study found that global salinity increased with a global sea level drop of 120 m. Analyzing 18 O data they also found that deep waters were within error of the freezing point, with oceanic waters exhibiting a greater degree of homogeneity in temperatures. In contrast, variations in salinity were much greater than they are today. Modern day salinities are all within 0.5 psu of the global average salinity of 34.7 psu, whereas salinities during the last glacial maximum (LGM) ranged from 35.8 psu in the North Atlantic to 37.1 in the Southern Ocean.
There are some notable differences in the hydrography at the LGM and present day. Today the North Atlantic Deep Water (NADW) is observed to be more saline than Antarctic Bottom Water (AABW), whereas at the last glacial maximum it was observed that the AABW was in fact more saline; a complete reversal. Today the NADW is more salty because of the Gulf Stream ; this could thus indicate a reduction of flow through the Florida Straits due to lowered sea level.
Another observation is that the Southern Ocean was vastly more salty at the LGM than today. This is particularly intriguing given the assumed importance of the Southern Ocean in oceanic dynamical regulation of ice ages. The extreme value of 37.1 psu is assumed to be a consequence of an increased degree of sea ice formation and export. This would account for the increased salinity, but would also account for the lack of oxygen isotopic fractionation ; brine rejection without oxygen isotopic fractionation is thought to be highly characteristic of sea ice formation.
The presence of waters near the freezing point alters the balance of the relative effects of contrasts in salinity and temperature on sea water density. This is described in the equation,
where α {\displaystyle \alpha } is the thermal expansion coefficient and β {\displaystyle \beta } is the haline contraction coefficient . In particular, the ratio β α {\displaystyle {\frac {\beta }{\alpha }}} is crucial. Using the observed temperatures and salinities, in the modern ocean, β α {\displaystyle {\frac {\beta }{\alpha }}} is about 10 whilst at the LGM β α {\displaystyle {\frac {\beta }{\alpha }}} it is estimated to have been closer to 25. The modern thermohaline circulation is thus more controlled by density contrasts due to thermal differences, whereas during the LGM the oceans were more than twice as sensitive to differences in salinity rather than temperature. In this way, the thermohaline circulation can be considered to have been less "thermo" and more "haline". | https://en.wikipedia.org/wiki/Paleosalinity |
Paleostress is a term used in geology (specifically in the fields of structural geology and tectonics ) to indicate mechanical stress that has affected rock formations in the geological past.
In practice, a paleostress tensor may be quantified based on the measurement of certain geological structures (e.g. faults ), whose specific geometries and spatial organization are theoretically linked to the parameters of the tensor (see paleostress inversion ). The latter are quantified through inversion of the structures measured in the field (or potentially on rock samples in the lab). [ citation needed ]
Paleostress is a subset of mechanical stress within geology. Variations in stress fields within the Earth's crust can result in a variety of mechanical responses:
Traditionally, deformations (either folding or fracturing—without dissolution ) are collectively termed mechanical strain .
Both macroscopic and microscopic strain may be elastic , and only exist as long as differential stress exists, or it may be inelastic -- that is the deformation due to a particular stress event remains even after the stress is removed. In the latter case, inelastic deformation, the stress field responsible for the deformation if it can be inferred, is, then, the paleostress . Anderson's classic analysis of faulting serves as a simple application of paleostress analysis in terms of principal components of stress. [ 1 ]
Zoback and Zoback's (1986) synthesis of contemporary stress measurements in North America [ 2 ] was subsequently expanded to a global study [ 3 ] which continues as the World Stress Project.
A number of regional studies of paleostresses has been undertaken, including Europe; [ 4 ] North America; [ 5 ] [ 6 ] and Australia. [ 7 ] | https://en.wikipedia.org/wiki/Paleostress |
Paleostress inversion refers to the determination of paleostress history from evidence found in rocks, based on the principle that past tectonic stress should have left traces in the rocks. [ 1 ] Such relationships have been discovered from field studies for years: qualitative and quantitative analyses of deformation structures are useful for understanding the distribution and transformation of paleostress fields controlled by sequential tectonic events. [ 2 ] Deformation ranges from microscopic to regional scale, and from brittle to ductile behaviour, depending on the rheology of the rock, orientation and magnitude of the stress, etc. Therefore, detailed observations in outcrops, as well as in thin sections , are important in reconstructing the paleostress trajectories.
Inversions require assumptions in order to simplify the complex geological processes. The stress field is assumed to be spatially uniform for a faulted rock mass and temporally stable over the concerned period of time when faulting occurred in that region. In other words, the effect of local fault slip is ignored in the variation in small-scale stress field. Moreover, the maximum shear stress resolved on the fault surface from the known stress field and the slip on each of the fault surface has the same direction and magnitude. [ 3 ] Since the first introduction of the methods by Wallace [ 4 ] and Bott [ 5 ] in the 1950s, similar assumptions have been used throughout the decades.
Anderson [ 6 ] [ 7 ] was the first to utilize conjugate fault systems in interpreting paleostress, including all kinds of conjugate faults (normal, reverse and strike-slip). Regional conjugate fault can be better understood by comparison to a familiar rock mechanics experiment, i.e. the Uniaxial Compressive Strength (UCS) Test. Basics of their mechanisms are similar except the principal stress orientation applied is rotated from perpendicular to parallel to the ground. The conjugate fault model is a simple way to obtain approximate orientations of stress axes, due to the abundance of such structure in the upper brittle crust. Therefore, a number of studies have been carried out by other researchers in assorted structural settings and by correlating with other deformation structures. [ 8 ]
Nonetheless, further development revealed the deficiency of the model:
The geometrical properties of conjugate faults are indicative of the sense of stress, but they may not appear in the actual fault patterns.
There are often oblique pre-existing faults, planes of weaknesses or striations to the fault slip, which do not belong to the conjugate fault sets. Neglecting this considerable amount of data would cause error in analysis.
This ratio provides the relative magnitude of the intermediate stress (σ 2 ) and thus determines the shape of the stress ellipsoid. However, this model does not give an account on the ratio, save for some specific cases.
This method was established by Bott [ 5 ] in 1959, based on the assumption that direction and sense of slip occurs on the fault plane are the same with those of the maximum resolved shear stress, hence, with known orientations and senses of movements on abundant faults, a particular solution T (the reduce stress tensor) is attained. [ 5 ] It gives more comprehensive and accurate results in reconstructing paleostress axes and determining the stress ratio (Φ) than the conjugate fault system. The tensor works by solving for four independent unknowns (three principal axes and Φ) through mathematical computation of observations of faults (i.e. attitude of faults and lineations on fault planes, direction and sense of slip, and other tension fractures).
This method follows four rigorous steps:
Reconstruction of paleostress requires large amount of data to attain accuracy, so it is essential to organize the data in comprehensible format prior to any analysis.
Attitude of fault planes and slickensides is plotted on rose diagrams, such that the geometry is visible. This is particularly useful when the sample size is enormous, it provides the full picture of the region of interest.
Fault movement is resolved into three components (as in 3D), which are vertical transverse, horizontal transverse and lateral components, by trigonometric relation with the measured dips and trends. Net slip is shown more clearly which paves the way to understanding the deformation.
Fault planes are represented by lines in stereonets (equal area lower hemisphere projection), while rakes on them are indicated by dots sitting on the lines. It helps to visualize the geometrical distribution and possible symmetry among individual faults.
This is a concluding step of compiling all the data and check their mechanical compatibility, also could be seen a preliminary step in determining major paleostress orientations. As this is a simple graphical representation of the fault geometry (being the boundaries of dihedra) and sense of slip (shortening direction indicated by black and extension depicted by grey), while it is able to provide good constraints on the orientation of principal stress axes.
The approximation is built upon the assumption that the orientation of maximum principal stress (σ 1 ) most probably passes through the greatest number of P-quadrants. Since fault plane and auxiliary plane perpendicular to striations are considered the same in this method, the model can be directly applied to focal mechanisms of earthquakes. Nonetheless, due to the same reason, this method cannot provide accurate determination of paleostress, as well as the stress ratio.
Stress tensor can be considered as a matrix with nine components being the nine stress vectors acting on a point, in which the three vectors along the diagonal (highlighted in brown) represent the principal axes.
σ i j = ( σ 11 σ 12 σ 13 σ 21 σ 22 σ 23 σ 31 σ 32 σ 33 ) {\displaystyle \sigma _{ij}=\left({\begin{matrix}\color {Brown}{\sigma _{11}}&\sigma _{12}&\sigma _{13}\\\sigma _{21}&\color {Brown}{\sigma _{22}}&\sigma _{23}\\\sigma _{31}&\sigma _{32}&\color {Brown}{\sigma _{33}}\end{matrix}}\right)}
The reduced stress tensor is a mathematical computation approach to determining the three principal axes and the stress ratio, totally four independent unknowns, calculated as eigenvectors and eigenvalue respectively, so that this method is more complete and accurate than the mentioned graphical approaches.
There are a number formulations that can reach the same final results but with distinctive features:
(1) T ϕ = ( x 1 x 2 x 3 y 1 y 2 y 3 z 1 z 2 z 3 ) ( 1 0 0 0 Φ 0 0 0 0 ) ( x 1 y 1 z 1 x 2 y 2 z 2 x 3 y 3 z 3 ) {\displaystyle T_{\phi }=\left({\begin{matrix}x_{1}&x_{2}&x_{3}\\y_{1}&y_{2}&y_{3}\\z_{1}&z_{2}&z_{3}\end{matrix}}\right)\left({\begin{matrix}\color {RubineRed}{1}&0&0\\0&\color {RubineRed}{\Phi }&0\\0&0&\color {RubineRed}{0}\end{matrix}}\right)\left({\begin{matrix}x_{1}&y_{1}&z_{1}\\x_{2}&y_{2}&z_{2}\\x_{3}&y_{3}&z_{3}\end{matrix}}\right)} ,
where stress ratio: Φ = σ 2 − σ 3 σ 1 − σ 3 {\displaystyle {\text{stress ratio: }}\Phi ={\frac {\sigma _{2}-\sigma _{3}}{\sigma _{1}-\sigma _{3}}}} , such that 0 ≤ ϕ ≤ 1 {\displaystyle 0\leq \phi \leq 1} . [ 10 ] This tensor is defined by setting σ 1 , σ 2 and σ 3 as 1, Φ and 0 (highlighted in pink) respectively, due to choosing m = ( σ 1 − σ 3 ) − 1 {\displaystyle m=(\sigma _{1}-\sigma _{3})^{-1}} and n = − m σ 3 {\displaystyle n=-m\sigma _{3}} as the mode of reduction. The advantage of this formulation is the direct correspondence to stress orientation, thus the stress ellipsoid, and the stress ratio.
(2) T ψ = ( c o s ψ α γ α c o s ( ψ + 2 π 3 ) β γ β c o s ( ψ + 4 π 3 ) ) {\displaystyle T_{\psi }=\left({\begin{matrix}cos\psi &\alpha &\gamma \\\alpha &cos(\psi +{\frac {2\pi }{3}})&\beta \\\gamma &\beta &cos(\psi +{\frac {4\pi }{3}})\end{matrix}}\right)}
This formulation is a deviator, which requires more computation to obtain information of the stress ellipsoid despite maintaining a symmetry in mathematical context. [ 11 ]
Minimization aims to reduce the differences between the computed and observed slip directions of fault planes by choosing a function to proceed the least square minimization. Here are a few examples of the functions:
(1) S 1 = ∑ ( s → k , τ → k ) 2 {\displaystyle S_{1}=\sum ({\vec {s}}_{k},{\vec {\tau }}_{k})^{2}}
The very first function used in fault slip analysis does not account on the sense of individual slip, which means altering the sense of a single slip does not affect the result. [ 12 ] However, individual sense of motion is an effective reflection of orientation of stress axes in real situation. Hence, S 1 is the simplest function but include the importance of sense of individual slip.
(2) S 2 = ∑ sin 2 ( s → k , τ → k ) 2 = 1 4 ∑ | s → k − τ → k | τ → k | | 2 {\displaystyle {\begin{alignedat}{2}S_{2}&=\sum \sin ^{2}{\frac {({\vec {s}}_{k},{\vec {\tau }}_{k})}{2}}\\&={\frac {1}{4}}\sum {\left|{\vec {s}}_{k}-{\frac {{\vec {\tau }}_{k}}{\left|{\vec {\tau }}_{k}\right\vert \quad }}\right\vert }^{2}\\\end{alignedat}}}
S 2 is derived from S 1 based on variation in computational process.
(3) S 3 = ∑ min [ tan 2 ( s → k , τ → k ) 2 , 1 ] {\displaystyle S_{3}=\sum \min[\tan ^{2}({\vec {s}}_{k},{\vec {\tau }}_{k})^{2},1]}
S 3 is an improved version of the previous model in two aspects. Regarding the efficiency in computation, which is particularly significant in long iterative processes like this, tangent of angles is preferred to cosine. Moreover, to deal with anomalous data (e.g. faults initiated by another event, error in data collection etc.), an upper limit of the value of the functions of angle could be set to filter deviated data.
(4) S 4 = ∑ | s → k , τ → k | 2 {\displaystyle S_{4}=\sum {\left|{\vec {s}}_{k},{\vec {\tau }}_{k}\right\vert }^{2}}
S 4 resembles S 2 except the unit vector parallel to shear stress is substituted by the predicted shear stress. Therefore, it still produces similar results as other methods, although its physical meaning is less well justified.
The reduced stress tensor should best (hardly perfectly) describe the observed orientations and senses of movement on diversified fault planes in a rock mass. Therefore, by reviewing the fundamental principle of interpreting paleostress from the reduced stress tensor, an assumption is recognized: every fault slip in the rock mass is induced homogeneously by a common stress tensor. This implies the variation in stress orientation and ratio Φ within a rock mass is overlooked yet always present in practical case, due to interaction between discontinuities at any scale.
Hence, the significance of this effect has to be examined to test the validity of the method, by considering the parameter: the difference between the measured slickenside lineation and the theoretical shear stress. The average angular deviation is insignificant when compared with the total of instrumental (measuring tools) and observation (unevenness of fault surfaces and striae) errors in majority of the cases. [ 11 ]
In conclusion, the reduced stress tensor method is validated when
Quantitative analyses cannot stand alone without careful qualitative field observations. The above described analyses are to be carried out after the overall geologic framework is understood e.g. number of paleostress systems, chronological order of successive stress patterns. Also, consistency with other stress markers e.g. stylolites and tension fractures, is required to justify the result.
A piezometer is an instrument used in the measurement of pressure (non-directional) or stress (directional) from strain in rocks at any scale. Referring to the paleostress inversion principle, rock masses under stress should exhibit strain at both macroscopic and microscopic scale, while the latter is found at the grain boundaries (interface between crystal grains at the magnitude below 10 2 μm). Strain is revealed from the change in grain size, orientation of grains or migration of crystal defects, through a number of mechanisms e.g. dynamic recrystallization (DRX).
Since these mechanisms primarily depend on flow stress and their resulted deformation is stable, the strained grain size or grain boundary are often used as an indicator of paleostress in tectonically active regions such as crustal shear zones, orogenic belts and the upper mantle . [ 16 ]
Dynamic recrystallization is one of the crucial mechanisms in reducing grain size in shear setting. [ 17 ] DRX is defined as a nucleation-and-growth process because
are all present in the deformation. This evidence is commonly found in quartz, a typical piezometer, from ductile shear zones. Optical microscope and transmission electron microscope (TEM) are usually utilized in observing the sequential occurrence of subgrain rotation and local grain boundary bulging, and measuring recrystallized grain size. The nucleation process is triggered at boundaries of existing grains only when materials have been deformed to particular critical values.
Grain boundary bulging is the process involving the growth of nuclei at the expense of existing grains and then formation of a 'necklace' structure.
Subgrain rotation is also known as in-situ recrystallization without considerable grain growth. This process happens steadily over the strain history, thus the change in orientation is progressive but not abrupt as grain boundary bulging.
Therefore, grain boundary bulging and subgrain rotation are differentiated as discontinuous and continuous dynamic recrystallization respectively.
The theoretical basis of grain size piezometry was first established by Robert J. Twiss in late 1970s. [ 18 ] By comparing free dislocation energy and grain boundary energy, he derived a static energy balance model applicable to subgrain size . Such relation has been represented by an empirical equation between normalized value of grain size and flow stress , which is universal for various materials:
d is the average grain size;
b is the length of the Burgers vector ;
K is a non-dimensional temperature-dependent constant, which is typically in the order of 10;
μ is the shear modulus ;
σ is the flow stress .
This model does not account for the persistently transforming nature of microstructures seen in dynamic recrystallization, so its inability in determination of recrystallized grain size has led to the latter models.
Unlike the previous model, these models consider the sizes of individual grains vary temporally and spatially, therefore, they derive an average grain size from an equilibrium between nucleation and grain growth . The scaling relation of the grain size is as follows:
where d is the mode of logarithmic grain size, I is the nucleation rate per unit volume, and a is a scaling factor.
Upon this basic theory, there are still plenty of arguments on the details, which are reflected in the assumptions of the models, so there are various modifications.
Derby and Ashby considered boundary bulging nucleation at grain boundary in determining the nucleation rate (I gb ), which opposes to the intracrystalline nucleation suggested by the prior model. Thus this model describes the microstructures of discontinuous DRX (DDRX):
Because of a contrasting assumption that subgrain rotation nucleation in continuous DRX (CDRX) should be considered for the nucleation rate, Shimizu has come up with another model, which has also been tested in laboratory:
Field boundary model [ 21 ]
In the above models, one of the vital factors, especially when the grain size is reduced substantially through dynamic recrystallization, is neglected. The surface energy becomes more significant when grains are sufficiently small, which converts the creep mechanism from dislocation creep to diffusion creep, thus the grains start to grow. Therefore, the determination of the boundary zone between fields of these two creep mechanisms matter to know when the recrystallized grain size tends to stabilize, as to supplement the above model. [ 21 ] The difference between this model and the previous nucleation -and-growth models lies within the assumptions: the field boundary model assumes that grain size reduces in the dislocation creep field, and enlarges in the diffusion creep field, but it is not the case in the previous models.
Quartz is abundant in the crust and contains creep microstructures that are sensitive to deformation conditions in deeper crust. Before starting to infer flow stress magnitude, the mineral has to be calibrated carefully in laboratory. Quartz has been found to exhibit different piezometer relations during different recrystallization mechanisms, which are local grain boundary migration ( dislocation creep ), subgrain rotation (SGR) and the combination of these two, as well as at different grain size. [ 22 ]
Other common minerals used for grain size piezometers are calcite and halite , that have gone through syn-tectonic deformation or manual high-temperature creep, which also demonstrate difference in piezometer relation for distinct recrystallization mechanisms. [ 22 ] | https://en.wikipedia.org/wiki/Paleostress_inversion |
Palaeozoology or paleozoology ( Greek : παλαιόν , palaeon "old" and ζῷον , zoon "animal") is the branch of paleontology and evolutionary biology that specifically deal with the study of prehistoric organisms from the kingdom Animalia and the recovery and identification of their fossil remains from geological (or even archeological ) contexts. The field also extends to the use of these fossil records for reconstructive phylogeny (via comparative anatomy and phylogenetics ) and paleoecology , i.e. the study of ancient natural environments and ecosystems . [ 1 ]
While speculative fossils of earliest animals (in the form of primitive sponges such as Otavia ) can trace back to the late Tonian period of the mid- Neoproterozoic era, definitive macroscopic metazoan remains are mainly found in the fossil record from the Ediacaran period onwards, although they do not become common until after the Cambrian Explosion , and vertebrate fossils do not become common until the Late Devonian period in the latter half of the Paleozoic era. Perhaps the best known macrofossils group is the dinosaurs . Other popularly known animal-derived macrofossils include trilobites , crustaceans , echinoderms , brachiopods , mollusks , bony fishes , sharks , Vertebrate teeth , and shells of numerous invertebrate groups. This is because hard organic parts, such as bones, teeth, and shells resist decay, and are the most commonly preserved and found animal fossils. Exclusively soft-bodied animals — such as jellyfish , flatworms , nematodes , and annelids — are consequently rarely fossilized, as these groups have few mineralized tissues that can survive geological processes, although trace fossils of their existence and activities can be preserved.
Vertebrate paleozoology refers to the use of morphological, temporal, and stratigraphic data to map vertebrate history in evolutionary theory. [ 2 ] Vertebrates are classified as a subphylum of Chordata, a phylum used to classify species adhering to a rod-shaped, flexible body type called a notochord. [ 2 ] They differ from other phyla in that other phyla may have cartilage or cartilage-like tissues forming a sort of skeleton, but only vertebrates possess what we define as bone. [ 2 ]
Classes of vertebrates listed in chronological order from oldest to most recent include heterostracans, osteostracans, coelolepid agnathans, acanthodians, osteichthyan fishes, chondrichthyan fishes, amphibians, reptiles, mammals, and birds. All vertebrates are studied under standard evolutionary generalizations of behavior and life process, although there is controversy over whether population can be accurately estimated from limited fossil resources. [ 2 ]
Evolutionary origins of vertebrates as well as the phylum Chordata have not been scientifically determined. Many believe vertebrates diverged from a common ancestor of chordates and echinoderms. This belief is well supported by the prehistoric marine creature Amphioxus. Amphioxus does not possess bone, making it an invertebrate, but it has common features with vertebrates including a segmented body and a notochord. This could imply that Amphioxus is a transitional form between an early chordate, echinoderm or common ancestor, and vertebrates. [ 2 ]
Quantitative paleozoology is a process of taking a census of fossil types rather than inventory. They differ in that inventory refers to a detailed log of individual fossils, whereas census attempts to group individual fossils to tally the total number of a species. This information can be used to determine which species were most dominant and which had the largest population at a time period or in a geological region. [ 1 ]
In the early 1930s, paleontologists Chester Stock and Hildegarde Howard devised special units for quantitative paleozoology and quantitative paleontology. The first unit used, Number of Identified Species (NISP), specified exact quantity of fossils from a specific species recorded. Stock and Howard determined this unit to be problematic for quantitative purposes as an excess of a small fossil—such as teeth—could exaggerate quantity of the species. There was also an amount of confusion as to whether bone fragments should be assembled and counted as one bone or tallied individually. [ 1 ] Stock and Howard then devised the Minimum Number of Individuals (MNI), which estimated the minimum number of animals needed to produce the fossils recorded. [ 1 ] For example, if five scapulae from a species were found, it might be difficult to determine whether some of them were paired right and left on one individual or whether each came from a different individual, which could alter census, but it could be said that there must be at least three individuals to produce five scapulae. Three would thus be the MNI. [ 1 ] In rare cases where enough of a collection of fossils can be assembled into individuals as to provide an accurate number of individuals, the unit used is Actual Number of Individuals, or ANI. [ 1 ]
Another unit commonly used in quantitative paleozoology is biomass. Biomass is defined as the amount of tissue in an area or from a species. [ 1 ] It is calculated by estimating an average weight based on similar modern species and multiplying it by the MNI. This yields an estimate of how much the entire population of a species may have weighed. [ 1 ] Problems with this measurement include the difference in weight between youngsters and adults, seasonal weight changes due to diet and hibernation, and the difficulty of accurately estimating the weight of a creature with only a skeletal reference. [ 1 ] It is also difficult to determine exact age of fossilized matter within a year or a decade, so a biomass might be grossly exaggerated or under exaggerated if the estimated time frame in which the fossils were alive is incorrect. [ 1 ]
A similar measurement to biomass is meat weight. [ 1 ] To determine meat weight, MNI is multiplied by the amount of meat an individual is thought to have provided, then multiplied by the percentage of that meat thought to be edible. This gives an estimate of "pounds of usable meat" per individual which might have been harvested by prehistoric hunters. [ 1 ] For example, a male Wapiti has an average weight of 400 kg, and in a particular study, the MNI of Wapiti was found to be 10. This would create a biomass of 4,000 kg. If the amount of edible meat is estimated at 50 percent, this would result in a meat weight of 2,000 kg. [ 1 ] The biggest problem with this method is the debate over "percent of usable meat." Different views on which parts of a species are edible and which are not as well as whether or not primitive butchers would have been able to access and prepare different parts have led to controversy. [ 1 ]
Paleozoological data is used in research concerning conservation biology . Conservation biology refers to biological study used for conservation, control, and preservation of various species and ecosystems . In this context, the paleozoological data used is obtained from recently deceased decomposing matter rather than prehistoric matter. [ 3 ]
R. Lee Lyman, Professor and Chair Department of Anthropology at the University of Missouri , [ 4 ] writes that paleozoological research can provide data such as extinction rates and causes and "benchmark" peaks and drops in population which can be used to predict future patterns and to design maximally effective methods of controlling these patterns. [ 3 ] In addition, paleozoological data can be used to compare current to former population and distribution of a species. [ citation needed ] | https://en.wikipedia.org/wiki/Paleozoology |
In mathematics , Paley graphs are undirected graphs constructed from the members of a suitable finite field by connecting pairs of elements that differ by a quadratic residue . The Paley graphs form an infinite family of conference graphs , which yield an infinite family of symmetric conference matrices . Paley graphs allow graph-theoretic tools to be applied to the number theory of quadratic residues, and have interesting properties that make them useful in graph theory more generally.
Paley graphs are named after Raymond Paley . They are closely related to the Paley construction for constructing Hadamard matrices from quadratic residues. [ 1 ] They were introduced as graphs independently by Sachs (1962) and Erdős & Rényi (1963) . Sachs was interested in them for their self-complementarity properties, [ 2 ] while Erdős and Rényi studied their symmetries. [ 3 ]
Paley digraphs are directed analogs of Paley graphs that yield antisymmetric conference matrices . They were introduced by Graham & Spencer (1971) (independently of Sachs, Erdős, and Rényi) as a way of constructing tournaments with a property previously known to be held only by random tournaments: in a Paley digraph, every small subset of vertices is dominated by some other vertex. [ 4 ]
Let q be a prime power such that q = 1 (mod 4). That is, q should either be an arbitrary power of a Pythagorean prime (a prime congruent to 1 mod 4) or an even power of an odd non-Pythagorean prime. This choice of q implies that in the unique finite field F q of order q , the element −1 has a square root.
Now let V = F q and let
If a pair { a , b } is included in E , it is included under either ordering of its two elements. For, a − b = −( b − a ), and −1 is a square, from which it follows that a − b is a square if and only if b − a is a square.
By definition G = ( V , E ) is the Paley graph of order q .
For q = 13, the field F q is just integer arithmetic modulo 13. The numbers with square roots mod 13 are:
Thus, in the Paley graph, we form a vertex for each of the integers in the range [0,12], and connect each such integer x to six neighbors: x ± 1 (mod 13), x ± 3 (mod 13), and x ± 4 (mod 13).
The Paley graphs are self-complementary : the complement of any Paley graph is isomorphic to it. One isomorphism is via the mapping that takes a vertex x to xk (mod q ) , where k is any nonresidue mod q . [ 2 ]
Paley graphs are strongly regular graphs , with parameters
This in fact follows from the fact that the graph is arc-transitive and self-complementary. The strongly regular graphs with parameters of this form (for an arbitrary q ) are called conference graphs , so the Paley graphs form an infinite family of conference graphs. The adjacency matrix of a conference graph, such as a Paley graph, can be used to construct a conference matrix , and vice versa. These are matrices whose coefficients are ±1 , with zero on the diagaonal, that give a scalar multiple of the identity matrix when multiplied by their transpose. [ 5 ]
The eigenvalues of Paley graphs are 1 2 ( q − 1 ) {\displaystyle {\tfrac {1}{2}}(q-1)} (with multiplicity 1) and 1 2 ( − 1 ± q ) {\displaystyle {\tfrac {1}{2}}(-1\pm {\sqrt {q}})} (both with multiplicity 1 2 ( q − 1 ) {\displaystyle {\tfrac {1}{2}}(q-1)} ). They can be calculated using the quadratic Gauss sum or by using the theory of strongly regular graphs. [ 6 ]
If q is prime, the isoperimetric number i ( G ) of the Paley graph satisfies the following bounds:
When q is prime, the associated Paley graph is a Hamiltonian circulant graph .
Paley graphs are quasi-random : the number of times each possible constant-order graph occurs as a subgraph of a Paley graph is (in the limit for large q ) the same as for random graphs, and large sets of vertices have approximately the same number of edges as they would in random graphs. [ 8 ]
Let q be a prime power such that q = 3 (mod 4). Thus, the finite field of order q , F q , has no square root of −1. Consequently, for each pair ( a , b ) of distinct elements of F q , either a − b or b − a , but not both, is a square. The Paley digraph is the directed graph with vertex set V = F q and arc set
The Paley digraph is a tournament because each pair of distinct vertices is linked by an arc in one and only one direction.
The Paley digraph leads to the construction of some antisymmetric conference matrices and biplane geometries .
The six neighbors of each vertex in the Paley graph of order 13 are connected in a cycle; that is, the graph is locally cyclic . Therefore, this graph can be embedded as a Whitney triangulation of a torus , in which every face is a triangle and every triangle is a face. More generally, if any Paley graph of order q could be embedded so that all its faces are triangles, we could calculate the genus of the resulting surface via the Euler characteristic as 1 24 ( q 2 − 13 q + 24 ) {\displaystyle {\tfrac {1}{24}}(q^{2}-13q+24)} . Bojan Mohar conjectures that the minimum genus of a surface into which a Paley graph can be embedded is near this bound in the case that q is a square, and questions whether such a bound might hold more generally. Specifically, Mohar conjectures that the Paley graphs of square order can be embedded into surfaces with genus
where the o(1) term can be any function of q that goes to zero in the limit as q goes to infinity. [ 12 ]
White (2001) finds embeddings of the Paley graphs of order q ≡ 1 (mod 8) that are highly symmetric and self-dual, generalizing a natural embedding of the Paley graph of order 9 as a 3×3 square grid on a torus. However the genus of White's embeddings is higher by approximately a factor of three than Mohar's conjectured bound. [ 13 ] | https://en.wikipedia.org/wiki/Paley_graph |
Paligenosis ( /pɑːliːdʒɛnoʊsɪs/ ) is a cellular program in which mature, quiescent, cells revert to a stem cell-like progenitor state in response to injury as a means to restore tissue damage. In 2018, paligenosis was first formally named and described as a three-stage series of defined molecular and cellular events that appear to be conserved across tissue types and throughout biology. [ 1 ] [ 2 ] As such, it is considered a fundamental cellular process akin to apoptosis , mitosis , and other cellular programs.
Cellular plasticity and regeneration have long been observed in the animal kingdom, with examples such as regeneration of lizard's tail [ 3 ] or salamander's limb [ 4 ] found in scientific literature dating back to the 18th century. The concept of metaplasia was introduced in 1886 to describe a mode of cell plasticity in which cells of a lesion acquire an identity that is unusual within a given tissue while that tissue retains its normal features. [ 5 ] In the 20th century, further investigation detailed examples of regeneration in various organs or species, including amphibian eggs. [ 6 ] [ 7 ] [ 8 ] [ 9 ] [ 10 ] [ 11 ] [ 12 ] [ 13 ] [ 14 ] Much of this early work on regeneration was primarily focused on unidirectional, forward, mitotic processes. However, in 1900, pathologist John George Adami observed that differentiated cells are also able to revert to a pre-mitotic and regenerative state upon injury and speculated that this process is governed by a sequence of energetic and structural changes in the cell. [ 15 ] A more detailed understanding of these changes and related mechanisms did not come until early in the 21st century with the advent of genetic tools and approaches. In 2006, researchers identified some of the first key molecular factors that induce differentiated cells to become reprogrammed as pluripotent stem cells. [ 16 ] Other biomarkers similarly indicative of reversion to a stem cell-like state were reported in the following years. [ 17 ] [ 18 ] [ 19 ] And in 2018, a three-stage series of metabolic changes that govern the cellular shift to a pre-mitotic state and subsequent re-entry into the cell cycle was characterized using the mouse stomach and pancreas as models, but also showing evidence of analogous processes in other organs and in humans. [ 1 ] Pathologist Jason Mills and colleagues named this cellular program paligenosis , which was derived from the Greek pali/n/m (meaning backward or recurrence) + genea (born of, producing) + osis (an action or process). [ 1 ] [ 20 ] [ 21 ]
Paligenosis is defined by three distinct stages of metabolic changes with intervening checkpoints. This stepwise process is governed by specific molecular factors, which are conserved across organs and species.
The first stage of paligenosis is initiated by an injury-induced suppression of mTORC1 , [ 22 ] a regulatory protein complex that activates the translation of proteins. Meanwhile, autophagy and lysosome activity begins to increase, enabling cellular components to be degraded and repurposed. The suppression of mTORC1 is regulated by the DDIT4 protein in healthy cells, making it a gatekeeper and key factor for initiating and regulating this stage. [ 23 ] [ 24 ] The increase in autophagy activity is regulated by increased expression of ATF3 protein upon injury and consequential induction of the lysosomal trafficking RAB7B protein. [ 25 ]
As autodegradation activity reaches its peak, expression levels increase for a pair of metaplasia-associated genes, Sox9 and Cd44v . [ 26 ] mTORC1 activity begins increasing as lysosome and autophagy activity declines. During this stage, mTORC1 is initially suppressed by the protein p53 (also known as TRP53), but healthy cells are able to accumulate IFRD1 protein that eventually facilitates p53 suppression, allowing mTORC1 levels to rise again. [ 23 ] [ 24 ] The modulation of mTORC1 and autophagy in the first two stages thus serves as checkpoints that allow only healthy cells to proliferate. [ 27 ]
In the final stage, mTORC1 activity continues to increase, while lysosome and autophagy activities return to baseline levels. This allows the cell to enter into a proliferative state as it returns to the cell cycle.
Paligenosis is linked to other cellular processes, and research has investigated its role in ribosome biogenesis, [ 28 ] the Hippo pathway, [ 29 ] and a reactive oxygen species pathway. [ 30 ]
Accumulating evidence suggests that the steps of paligenosis are evolutionarily conserved across species and different tissues, indicating that paligenosis is a fundamental biological process. [ 31 ] Paligenosis has been studied most extensively in the mouse stomach, where it is often induced by Heliobacter pylori bacterial infection and marked by the loss of gastric parietal cells and reversion of chief cells to an embryonic-like progenitor state. [ 32 ] [ 33 ] This condition, referred to as atrophic gastritis , is a type of metaplasia known as pseudopyloric or pyloric metaplasia. At the base of pyloric metaplasia, lesions are composed of spasmolytic polypeptide-expressing metaplasia (SPEM) cells. [ 34 ] SPEM cells replace the normal digestive enzyme-secreting chief cells and are accompanied by the expression of several genes and biomarkers that indicate transformation of chief cells to SPEM cells via paligenosis. [ 35 ] [ 36 ] Analogous structural changes accompanied by the presence of paligenosis biomarkers have similarly been identified and studied in other cell environments, including neurons, [ 27 ] the liver, [ 1 ] kidney, [ 1 ] esophagus, [ 37 ] and pancreas, [ 36 ] [ 38 ] often in the context of chronic injury conditions such as acid reflux in the case of Barrett's esophagus . [ 36 ] Studies have also described these indicators of paligenosis not only in mice, but also humans, [ 1 ] [ 39 ] and other organisms including yeast, fruit flies, and axolotls. [ 39 ]
Metaplastic cells are prone to adopting an abnormal state of growth known as dysplasia, eventually giving rise to tumors. [ 40 ] [ 41 ] Paligenosis provides an explanation for how this occurs through what has become known as the cyclical hit model of tumorigenesis. [ 42 ] [ 43 ] In this model, adult differentiated cells that have acquired mutations can be recruited back into a proliferative state via paligenosis. After healing, these cells can redifferentiate. However, under recurrent injury conditions that promote continued cycles of paligenosis, mutations and other chromosomal abnormalities can accumulate leading to loss of capacity for redifferentiation and conversion to uncontrolled cell growth and tumorigenesis. [ 23 ] [ 36 ] Because of this, the resistance of cancer cells to various modes of treatment can often be attributed to cellular plasticity. [ 44 ] [ 45 ] Continued investigation into paligenosis and related processes is thus motivated by the possibility of identifying treatable targets that can be useful for new cancer therapies. [ 46 ] | https://en.wikipedia.org/wiki/Paligenosis |
Palinstrophy is the curl of the vorticity . It is defined as 1 2 ( ∇ × ω ) , {\displaystyle {\frac {1}{2}}\left(\nabla \times \omega \right),} where ω {\displaystyle \omega } is the vorticity.
Palinstrophy is mainly used in turbulence study, where there is a need to quantify how vorticity is transferred from one direction to the others. It is closely related to enstrophy , the latter being more equivalent to the "power" of vorticity. | https://en.wikipedia.org/wiki/Palinstrophy |
The Palisa-Wolf-Star Map or Palisa-Wolf-Star Atlas ( German : Palisa-Wolf-Sternatlas ) is a map series produced between 1900 and 1916 as well as published between 1900 and 1931, which shows the entire starry sky visible in Europe in 210 large-scale sheets.
It was published at the suggestion of the Viennese astronomer Johann Palisa (1848–1925) together with his younger colleague Max Wolf in Heidelberg to facilitate the discovery and tracking of new asteroids. At that time, Palisa had already discovered about 100 of these minor planets through visual observation at the large refractor of the University Observatory in Vienna, while Wolf was the first researcher to use astrophotography for this purpose at the new Heidelberg-Königstuhl State Observatory . The 210 star charts in the format 11 by 9 inches were recorded in Heidelberg and systematically cut out according to celestial coordinates. [ 1 ]
Palisa was not only concerned with facilitating the discovery of the many minor planets to be expected, but also with the possibility of finding "lost" asteroids again and thereby determining their orbits more precisely. The star atlas became an important tool for planetoid researchers for several decades.
What is also remarkable about this work is that two astronomers competing in their field of research were able to decide to cooperate. The "photo pioneer" Wolf surpassed Palisa in the number of discovered asteroids (123 or more than 200) in the following decade, because these small bodies quickly revealed themselves in the sky photographs by a short line trace, while Palisa had to find them at the telescope by comparing them with the star chart.
This space - or spaceflight -related article is a stub . You can help Wikipedia by expanding it .
This astronomy -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Palisa-Wolf-Star_Map |
In histopathology , a palisade is a single layer of relatively long cells, arranged loosely perpendicular to a surface and parallel to each other. [ 1 ] A rosette is a palisade in a halo or spoke-and-wheel arrangement, surrounding a central core or hub. [ 2 ] A pseudorosette is a perivascular radial arrangement of neoplastic cells around a small blood vessel. [ 2 ] Rosettes are characteristic of tumors .
A rosette is a cell formation in a halo or spoke-and-wheel arrangement, surrounding a central core or hub. The central hub may consist of an empty-appearing lumen or a space filled with cytoplasmic processes. The cytoplasm of each of the cells in the rosette is often wedge-shaped with the apex directed toward the central core: the nuclei of the cells participating
in the rosette are peripherally positioned and form a ring or halo around the hub. [ 2 ]
Rosettes may be considered primary or secondary manifestations of tumor architecture. Primary rosettes form as a characteristic growth pattern of a given tumor type whereas secondary rosettes result from the influence of external factors on tumor growth. For example, regressive cell swelling may centripetally displace the cytoplasm as the nucleus is squeezed to the periphery, forming a secondary rosette. Although the presence of primary rosettes may suggest a given diagnosis, usually this finding alone is not considered absolutely pathognomonic for one specific tumor type. [ 2 ]
Loss or gain of genetic information is the main cause of rosette and pseudorosette formation. The cell populations exhibiting neuronal differentiation are believed to secrete surface glycoproteins and glycolipids which mediate cell-to-cell recognition and adhesion. One hypothesis is that these sticky cell surface markers cause the developing cell bodies to cluster or aggregate and their primitive neurites to tangle. As the cells grow, the neurite tangle remains centrally located and the cell bodies are squeezed to the periphery, thus explaining the rosette pattern. Depending upon their location, ependymal cells may display 2 cell poles. A luminal pole projects to the ependymal lining of a ventricle and a "submesenchymal pole" projects toward the surface of the brain demonstrating glial processes and peripherally situated footplates. Frieda and Pollak conceptualize the architecture of ependymomas as a primitive neural tube turned inside out with the submesenchymal poles converging toward a central vessel, thus forming a pseudorosette rather than projecting centrifugally toward the pia . [ 2 ]
True rosettes are mainly found in neuropathologic disorder. Other conditions where they are present include osteosarcoma , non-Hodgkin lymphoma , fibromyxoid sarcoma , medullary thyroid carcinoma , embryonal tumor with abundant neuropil and true rosettes (ETANTR), rhabdomyosarcoma , chronic cholestasis and chronic active hepatitis , tobacco rosette: complex viral disease, malaria, adenocarcinoma in colon and rectum, hyalinizing spindle cell fused with giant rosette, and endometrial stromal sarcoma with hyalinizing giant rosettes. [ 2 ]
Flexner–Wintersteiner rosettes , a spoke-and-wheel shaped cell formation seen in retinoblastoma and certain other ophthalmic tumors, [ 3 ] ) have been described as a form of palisading. [ 4 ]
Unlike the center of the Homer-Wright rosette , the central lumen is devoid of fiber-rich neuropil . The defining feature of this rosette is the central extension of cytoplasmic projections of the surrounding cells. Like the Homer Wright rosette, the Flexner–Wintersteiner rosette represents a specific form of tumor differentiation. [ 5 ] [ 6 ] [ 7 ] [ 8 ] Electron microscopy reveals that the tumor cells forming the Flexner–Wintersteiner rosette have ultrastructural features of primitive photoreceptor cells. [ 9 ] Furthermore, the rosette lumen shows similar staining patterns as in rods and cones , [ 10 ] suggesting that Flexner–Wintersteiner rosettes represent a specific form of retinal differentiation. In addition to being a characteristic finding in retinoblastomas, Flexner–Wintersteiner rosettes may also be found in pinealoblastomas and medulloepitheliomas . [ 5 ]
Flexner–Wintersteiner rosettes were first described in 1891 by Simon Flexner , a professor of experimental pathology at the University of Pennsylvania . Flexner noted characteristic clusters of cells in an infantile eye tumor which he called retinoepithelioma. [ 11 ] [ 12 ] [ 13 ] In 1897, Austrian ophthalmologist Hugo Wintersteiner confirmed Flexner's observations and noted that the cell clusters resembled rods and cones. [ 14 ] These characteristic rosette formations were subsequently recognized as important features of retinoblastomas.
A pseudorosette is a perivascular radial arrangement of neoplastic cells around a small blood vessel. Pseudorosettes are present in neuroblastoma , medulloblastoma , malignant melanoma , ependymoma , Merkel cell carcinoma , neuroendocrine tumor of the skin, seborrheic keratosis , dendritic cell neurofibroma , astroblastoma , large cell neuroendocrine tumor of the cervix, clear cell ependymoma of the spinal cord, celiac disease , nasal tumor of olfactory origin, rosette-forming glioneural tumor (RGNT), oncocytoma , Wilm's tumor , and pheochromocytoma of the urinary bladder. [ 2 ]
A Homer-Wright pseudorosette is a type of pseudorosette in which differentiated tumor cells surround the neuropil . [ 15 ] Examples of tumors containing these are neuroblastoma , medulloblastoma , pinealoblastoma , and primitive neuroectodermal tumors of bone. Homer-Wright rosettes are considered "pseudo" in the sense that they are not true rosettes. Unlike Flexner–Wintersteiner rosettes , which contain an empty lumen, Homer-Wright rosettes contain abundant fibrillary material. They are named for James Homer Wright .
A perivascular pseudorosette consists of a spoke-wheel arrangement of cells with tapered cellular processes radiates around a wall of a centrally placed vessel. The modifier “pseudo” differentiates this pattern from the Homer Wright and Flexner-Wintersteiner rosettes,
perhaps because the central structure is not actually formed by the tumor itself, but instead represents a native, non-neoplastic element. Also, some early investigators argued about the definition of a central lumen, choosing “pseudo” to indicate that the hub was
not a true lumen but contained structures. Nevertheless, this pattern remains extremely diagnostically useful and the modifier unnecessarily leads to confusion. Perivascular pseudorosettes are encountered in most ependymomas regardless of grade or variant. As such, they are significantly more sensitive for the diagnosis of ependymomas than true ependymal rosettes. Unfortunately, perivascular pseudorosettes are also less specific in that they are also encountered in medulloblastomas, PNETs, central neurocytomas,
and less often in glioblastomas, and a rare pediatric tumor, monomorphous pilomyxoid astrocytomas. [ 2 ]
Histologic features of these two tumors are virtually identical, including their tendency to form neuropil-rich rosettes, referred to as pineocytomatous/neurocytic rosettes in central neurocytoma. Both are quite similar to the Homer-Wright rosette, but they are generally larger and more irregular in contour. The cells of the pineocytomatous/neurocytic rosettes are also considered to be much more differentiated than the cells forming Homer-Wright rosettes in that the nuclei are slightly larger, more rounded, much less mitotically active, and paler or less hyperchromatic. In rare cases, these rosettes may aggregate in a sheet of back-to-back clusters resembling fieldstone pavement. [ 2 ]
The neuropathologic diagnosis of brain tumors entails the microscopic examination of conventional formalin-fixed paraffin-embedded tissue samples surgically removed from a radiographically defined lesion. Pathologists rely on visual clues such as pattern recognition when examining the stained tissue with a microscope, much as radiologists rely on grayscale patterns of densities and intensities on images. Some histologic patterns of cellular architecture are distinctive if not pathognomonic whereas others are less specific, but nevertheless considerably narrow the differential diagnosis. The precise biologic bases for some of the observed microscopic patterns are poorly understood though their recognition is nonetheless useful. Rosettes are a commonly encountered neuropathologic histologic architectural pattern seen within certain tumors is the rosette. Although more advanced methods of tissue examination have been developed, such as histochemical and immunohistochemical profiling, genetic analysis, and electron microscopy, the microscopic review of H&E stained material remains a critical component of tumor diagnosis. [ 2 ]
Immunohistochemical evidence of neuronal differentiation is found in nearly all cases with neuronal markers such as synaptophysin, neuronspecific enolase, and neurofilament protein. Some medulloblastomas may also display other forms of differentiation as demonstrated by the presence of the astrocytic marker glial fibrillary acidic protein. Skeletal muscle and melanocytic differentiation are considerably less common and define the medullomyoblastoma and melanotic medulloblastoma variants, respectively. [ 2 ]
Palisades that are generally longer than a rosette or pseudorosette can be seen in neural tumors such as Schwannoma , [ 16 ] [ 17 ] as well as in ameloblastomas . They can also be seen in nodular basal-cell carcinomas . [ 18 ]
Pseudopalisading , a visually similar finding, is the formation of hypercellular zones that typically surrounds necrotic tissue. | https://en.wikipedia.org/wiki/Palisade_(pathology) |
Palivizumab , sold under the brand name Synagis , is a monoclonal antibody produced by recombinant DNA technology used to prevent severe disease caused by respiratory syncytial virus (RSV) infections. [ 2 ] [ 4 ] It is recommended for infants at high-risk for RSV due to conditions such as prematurity or other medical problems including heart or lung diseases. [ 2 ] [ 4 ]
The most common side effects include fever and rash . [ 2 ] [ 4 ]
Palivizumab is a humanized monoclonal antibody (IgG) directed against an epitope in the A antigenic site of the F protein of RSV. In two phase III clinical trials in the pediatric population, palivizumab reduced the risk of hospitalization due to RSV infection by 55% and 45%. [ 5 ] Palivizumab is dosed once a month via intramuscular (IM) injection , to be administered throughout the duration of the RSV season, which in based on past trends has started in Mid-September to Mid-November. [ 2 ] [ 6 ] [ 7 ]
Palivizumab targets the fusion protein of RSV, [ 8 ] inhibiting its entry into the cell and thereby preventing infection. Palivizumab was approved for medical use in 1998. [ 9 ]
Palivizumab is indicated for the prevention of serious lower respiratory tract disease requiring hospitalization caused by the respiratory syncytial virus (RSV) in children at high risk for RSV disease: [ 2 ] [ 4 ] [ 10 ]
The American Academy of Pediatrics has published guidelines for the use of palivizumab. The most recent updates to these recommendations are based on new information regarding RSV seasonality, palivizumab pharmacokinetics, the incidence of bronchiolitis hospitalizations, the effect of gestational age and other risk factors on RSV hospitalization rates, the mortality of children hospitalized with RSV infection, the effect of prophylaxis on wheezing, and palivizumab-resistant RSV isolates. [ 11 ]
All infants younger than one year who were born at <29 weeks (i.e. ≤28 weeks, 6 days) of gestation are recommended to use palivizumab. Infants younger than one year with bronchopulmonary dysplasia (i.e. who were born at <32 weeks gestation and required supplemental oxygen for the first 28 days after birth) and infants younger than two years with bronchopulmonary dysplasia who require medical therapy (e.g. supplemental oxygen, glucocorticoids , diuretics) within six months of the anticipated RSV season are recommended to use palivizumab as prophylaxis. [ 11 ] Taking palivizumab prophylactically decreases the number of RSV infections, decreases wheezing, and may decrease the rate of hospitalization attributed to RSV. [ 12 ] [ 13 ] There are few negative side effects reported. [ 13 ] It is not clear if palivizumab is effective and safe for the other medical conditions that put them at a higher risk for serious cases of RSV such as deficiencies in their immune system. [ 13 ]
Since the risk of RSV decreases after the first year following birth, the use of palivizumab for children more than 12 months of age is generally not recommended with the exception of premature infants who need supplemental oxygen, bronchodilator therapy, or steroid therapy at the time of their second RSV season. [ 11 ]
Decisions regarding palivizumab prophylaxis for children in these groups should be made on a case-by-case basis. [ 11 ]
Because palivizumab is a passive antibody, it is ineffective in the treatment of RSV infection, and its administration is not recommended for this indication. [ 11 ] A 2019 (updated in 2023) Cochrane review found no differences in palivizumab and placebo on outcomes of mortality, length of hospital stay, and adverse events in infants and children aged up to 3 years old with RSV. [ 14 ] Larger RCTs will be required before palivizumab can be recommended as a treatment option. [ 15 ] If an infant has an RSV infection despite the use of palivizumab during the RSV season, monthly doses of palivizumab may be discontinued for the rest of the RSV season due to the low risk of re-hospitalization. [ 11 ] Current studies are in progress to determine new treatments for RSV rather than solely prophylaxis. [ 16 ]
Contraindications for the use of palivizumab include hypersensitivity reactions upon exposure to palivizumab. Serious cases of anaphylaxis have been reported after exposure to palivizumab. Signs of hypersensitivity include hives, shortness of breath, hypotension, and unresponsiveness. No other contraindications for palivizumab have been reported. [ 17 ] Further studies are needed to determine if any drug-drug interactions exist as none have been conducted as of yet.
Palivizumab use may cause side effects, which include, but are not limited to: [ 18 ]
Some more serious side effects include:
Palivizumab has demonstrated a significantly higher affinity and potency in neutralizing both A and B subtypes of RSV when compared with RSV-IGIV. [ 19 ] Treatment with 2.5 mg/kg of palivizumab led to a serum concentration of 25-30 μg/mL in cotton rats and reduced RSV titers by 99% in their lungs. [ 20 ]
Palivizumab is a monoclonal antibody that targets the fusion (F) glycoprotein on the surface of RSV, and deactivates it. [ 20 ] The F protein is a membrane protein responsible for fusing the virus with its target cell and is highly conserved among subgroups of RSV. Deactivating the F protein prevents the virus from fusing with its target's cell membrane and prevents the virus from entering the host cell. [ 20 ] [ 21 ]
A 2008 meta-analysis found that palivizumab absorption was quicker in the pediatric population compared to adults ( k a = 1.01/day vs. k a = 0.373/day). The intramuscular bioavailability of this drug is approximately 70% in healthy young adults. [ 22 ] Current recommendation for RSV immunoprophylaxis is administration of 5 x 15 mg/kg doses of palivizumab to maintain body concentrations above 40 μg/mL. [ 23 ]
The volume of distribution is approximately 4.1 liters. [ 22 ]
Palivizumab has a drug clearance (CL) of approximately 198 ml/day. The half-life of this drug is approximately 20 days with three doses sustaining body concentrations that will last the entire RSV season (5 to 6 months). A 2008 meta-analysis estimated clearance in the pediatric population by considering maturation of CL and body weight which showed a significant reduction compared to adults. [ 22 ]
Palivizumab is a relatively expensive medication, with a 100-mg vial ranging from $904 to $1866. [ 24 ] Multiple studies done by both the manufacturer and independent researchers to determine the cost-effectiveness of palivizumab have found conflicting results. The heterogeneity between these studies makes them difficult to compare. Given that there is no consensus about the cost-effectiveness of palivizumab, usage largely depends on the location of care and individual risk factors. [ 12 ] [ 20 ] [ 25 ]
A 2013 meta-analysis reported that palivizumab prophylaxis was a dominant strategy with an incremental cost-effectiveness ratio of $2,526,203 per quality-adjusted life-year (QALY). It also showed an incremental cost-effectiveness ratio for preterm infants between $5188 and $791,265 per QALY , from the payer perspective. [ 24 ] However, as previously stated, the cost-effectiveness of palivizumab is undecided, and this meta-analysis is only one example of society can benefit from palivizumab prophylaxis.
The disease burden of RSV in young infants and its global prevalence have prompted attempts for vaccine development. As of 2019, there was no approved vaccine for RSV prevention. [ 26 ] A formalin-inactivated RSV vaccine (FIRSV) was studied in the 1960s. The immunized children who were exposed to the virus in the community developed an enhanced form of RSV disease presented by wheezing , fever, and bronchopneumonia . This enhanced form of the disease led to 80% hospitalization in the recipients of FIRSV compared to 5% in the control group. Additionally, 2 fatalities occurred among the vaccine recipients upon reinfection in subsequent years. [ 27 ] Subsequent attempts to develop an attenuated live virus vaccine with optimal immune response and minimal reactogenicity have been unsuccessful. [ 28 ] Further research on animal subjects suggested that intravenously administered immunoglobulin with high RSV neutralizing activity can protect against RSV infection. [ 29 ] In 1995, the U.S. Food and Drug Administration (FDA) approved the use of RespiGam (RSV-IGIV) for the prevention of serious lower respiratory tract infection caused by RSV in children younger than 24 months of age with bronchopulmonary dysplasia or a history of premature birth . [ 30 ] The success of the RSV-IGIV demonstrated efficacy in immunoprophylaxis and prompted research into further technologies. Thus, Palivizumab was developed by AstraZeneca as a monoclonal antibody that was found to be fifty times more potent than its predecessor. This antibody has been widely used for RSV since 1998 when it was approved. [ 31 ]
Palivizumab, originally known as MEDI-493, was developed as an RSV immune prophylaxis tool that was easier to administer and more effective than the current tools of that time (the 1990s). [ 31 ] It was developed over a 10-year period by MedImmune by combining human and mouse DNA. [ 32 ] Specifically, antibody production was stimulated in a mouse model following immunization with RSV. The antibody-producing B cells were isolated from the mouse's spleen and fused with mouse myeloma cell lines. The antibodies were then humanized by cloning and sequencing the DNA from both the heavy and light chains of the monoclonal antibody. Overall, the monoclonal antibody is 95% similar to other human antibodies with the other 5% having DNA origins from the original mouse. [ 20 ] | https://en.wikipedia.org/wiki/Palivizumab |
Palladacycle , as a class of metallacycles , refers to complexes containing at least one carbon- palladium bond. Palladacycles are invoked as intermediates in catalytic or palladium mediated reactions. They have been investigated as pre-catalysts for homogeneous catalysis and synthesis .
In the 1960s, Arthur C. Cope and Robert W. Siekman reported the cyclopalladation reaction between aromatic azobenzenes and palladium(II) dichloride . [ 1 ] The potential of palladacycles as catalysts was highlighted by Herrmann's catalyst in 1990s. Derivatives of tris(o-tolyl)phosphine proved effective in Heck reactions . [ 2 ]
There are two distinct types of palladacycle: four-electron donor (CY) and six-electron donor (YCY) complexes .
The palladacycles can be neutral, cationic, or anionic . Depending on the nature of the coordinating ligands , the neutral palladacycles can be monomers , dimers , or bis-cyclopalladated.
Palladacycles with ring-sizes range from 3 to 10 have been synthesized and characterized, whereas only 5-/6-membered ones are commonly used. Palladacycles of 3-/4-/>6-membered ring-sizes are usually unstable due to their ring strains .
The palladacycles could also be classified by the donor atoms. For example, the Herrmann’s catalyst discussed before is a phosphine -derived palladacycle. Other types of palladacycles such as phosphite palladacycle, imine palladacycle, oxime palladacycle, CS-/CO-palladacycles are also effective in catalytic reactions . Palladacycles derived from 2-aminobiphenyl have been used in a variety of cross-coupling reactions .
Several methods are available for the preparation of palladacycles. A simple and direct method is C–H activation . [ 3 ] The cyclopalladation of aromatic derivatives is usually considered to go through an electrophilic aromatic substitution pathway. [ 4 ] The oxidative addition of aryl halides is another useful method. [ 5 ] However, the accessibility of the aryl halides starting material is a major drawback.
Other types of reactions such as transmetalation [ 6 ] and nucleopalladation [ 7 ] also turned out to be effective methods in the synthesis of palladacycles.
Palladacycles are used as pre-catalysts, usually by the reductive elimination from palladium(II) to the catalytically active palladium(0). In the example of 2-aminobiphenyl palladacycles, a kinetically active 12-electrons Pd(0) species is formed, allowing for further oxidative addition with reactants. [ 8 ] A series of 2-aminobiphenyl bearing various X and L groups were synthesized to better understand the electron/steric effect.
By employing palladacycles as pre-catalysts, high reactivity and selectivity have been achieved in Heck reaction [2] and a variety of cross-coupling reactions , such as Suzuki , [ 9 ] Sonogashira , [ 10 ] Stille , [ 11 ] Buchwald–Hartwig reactions . [ 12 ]
Total synthesis containing palladacycles have been demonstrated. [ 13 ] [ 14 ]
Except their abilities in catalyzing organic reactions, palladacycles have also shown their potential in medicinal and biological chemistry after the success of cis-Pt(NH 3 ) 2 Cl 2 as an anticancer agent . Additionally, they can also be used in CO /SCN- sensing. [ 15 ]
Bruneau, Alexandre; Roche, Maxime; Alami, Mouad; Messaoudi, Samir (2015-02-06). "2-Aminobiphenyl Palladacycles: The "Most Powerful" Precatalysts in C–C and C–Heteroatom Cross-Couplings" . ACS Catalysis . 5 (2): 1386– 1396. doi : 10.1021/cs502011x . ISSN 2155-5435 . | https://en.wikipedia.org/wiki/Palladacycle |
Palladium(II) bis(acetylacetonate) is a compound with formula Pd(C 5 H 7 O 2 ) 2 . This yellow solid is the most common palladium complex of acetylacetonate . This compound is commercially available and used as a catalyst precursor in organic synthesis . The molecule is relatively planar with idealized D 2h symmetry . [ 2 ]
This catalysis article is a stub . You can help Wikipedia by expanding it .
This article about an organic compound is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Palladium(II)_bis(acetylacetonate) |
Palladium(II) nitrate is the inorganic compound with the formula Pd(NO 3 ) 2 .(H 2 O) x where x = 0 or 2. The anhydrous and dihydrate are deliquescent solids. According to X-ray crystallography , both compounds feature square planar Pd(II) with unidentate nitrate ligands. The anhydrous compound, which is a coordination polymer , is yellow. [ 1 ] [ 2 ]
As a solution in nitric acid, Pd(NO 3 ) 2 catalyzes the conversion of alkenes to dinitrate esters. Its pyrolysis affords palladium oxide . [ 3 ]
Hydrated palladium nitrate may be prepared by dissolving palladium oxide hydrate in dilute nitric acid followed by crystallization. The nitrate crystallizes as yellow-brown deliquescent prisms. The anhydrous material is obtained by treating palladium metal with fuming nitric acid . [ 1 ]
This inorganic compound –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Palladium(II)_nitrate |
Palladium hexafluoride is an inorganic chemical compound of palladium metal and fluorine with the chemical formula PdF 6 . [ 1 ] It is reported to be a still hypothetical compound . [ 2 ] This is one of many palladium fluorides .
Fluorination of palladium powder with atomic fluoride at 900–1700 Pa. [ 3 ]
Palladium hexafluoride is predicted to be stable. [ 4 ] The compound is reported to form dark red solid that decomposes to PdF 4 . Palladium hexafluoride is a very powerful oxidizing agent . [ 3 ]
This inorganic compound –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Palladium_hexafluoride |
In organometallic chemistry , palladium-NHC complexes are a family of organopalladium compounds in which palladium forms a coordination complex with N -heterocyclic carbenes (NHCs). They have been investigated for applications in homogeneous catalysis , [ 4 ] particularly cross-coupling reactions . [ 1 ] [ 4 ] [ 5 ]
The synthesis of Pd-NHC complexes follows the methods used for the synthesis of transition metal NHC complexes . The synthesis of Pd-NHC complexes can also be achieved through substitution of a labile ligand L in a Pd-L complex. Labile ligands typically include cyclooctadiene , dibenzylideneacetone , bridging halides , or phosphines . This process can be used in conjunction with the in situ generation of free carbenes. Pd-NHC complexes can also be synthesized through transmetalation with silver-NHC complexes. The transmetallated NHCs can either be isolated for subsequent reaction with palladium in a two-step method, or generated in the presence of palladium in a one-pot reaction. However, generation of Pd-NHC complexes by Ag transmetallation is cost-prohibitive and hampered by Ag complexes’ light sensitivity. [ 4 ]
The utility of palladium-catalyzed cross-coupling reactions is enhanced by the use of N -heterocyclic carbene ligands. Indeed, Pd-NHC complexes have been proven effective in Suzuki-Miyaura , Negishi , Sonogashira , Kumada-Tamao-Corriu , Hiyama , and Stille cross-coupling. Compared to the corresponding Pd-phosphine catalysts, Pd-NHC catalysts can be faster, exhibit broader substrate scope, all with higher turnover numbers. [ 4 ]
In Suzuki-Miyaura cross-couplings , the traditional coupling partners are organobromides and organoboron compounds. While Suzuki-Miyaura cross-couplings typically employ organobromides as coupling partners, organochlorides are more desirable electrophiles for cross-coupling due to their lower cost. The sluggish reactivity of the C-Cl bond is often a problem. With the advent of Pd-NHC complexes, organochlorides have emerged as viable partners in Suzuki-Miyaura cross coupling. [ 4 ] [ 6 ]
The use of NHC-Pd-PEPPSI complexes in Negishi cross-coupling has resulted in high turnover numbers and turnover frequencies. [ 7 ] Additionally, NHC-Pd complexes can be used to couple sp3 centers to sp3 centers in higher yield than their non-NHC Pd analogs. [ 8 ] However, studies of Pd-NHC complexes and their utility in Negishi coupling are currently lacking despite these promising results. [ 4 ]
Pd-NHC complexes used in Sonogashira cross-coupling effect temperature stability in the complex. [ 9 ] As in other Pd-NHC mediated cross-coupling reactions, the use of Pd-NHC complexes also allow higher turnover numbers than their NHC-free counterparts. [ 10 ] NHC-palladacycles permit copper-free Sonogashira reactions to be carried out. [ 11 ] [ 12 ]
The use of Pd-NHC complexes in Heck-Mizoroki cross-coupling permits the use of cheaper, ample supplies of aryl chloride substrates. [ 4 ] Additionally, the activity and stability of the catalyst in Heck-Mizoroki coupling can be enhanced by adjusting the 1,3 substituents on the imidazole ring. [ 13 ] | https://en.wikipedia.org/wiki/Palladium–NHC_complex |
In the Andean mining tradition pallaqueo , palleo [ 1 ] or pirquineo [ 2 ] is the hand selection of rock fragments with ore for further processing . [ 3 ] [ 4 ] Usually, pallaqueo is done in piles of discarded material with little planning, randomly and without authorization. [ 5 ] [ 3 ] However, historically in places like Potosí , Bolivia , pallaqueo has been regarded as an integral part of the mining operation. [ 6 ] [ 7 ] Pallaqueo has the benefit that it can allow for high –or over-all increased– ore grades to be processed. [ 8 ] In some places the selected rocks are then sold to the local mining company , [ 9 ] but this model has the drawback that it could incentivize smuggling of ore from the mine to make it pass as recovered through pallaqueo . [ 5 ] [ 10 ]
The term pallaqueo and palleo are derived from Quechua pállay . [ 11 ] Those that practice pallaqueo are variously referred to as buscones , pallacos , pallaqueros , pallaqueadores and, in Bolivia , palliris . [ 11 ] In some places like La Rinconada in Peru , [ 9 ] this activity is primarily made by women known as pallaqueras , as they are otherwise not allowed to work inside the mines. [ 12 ] [ 11 ] For artisan miners known as pirquineros , pallaqueo is a secondary activity to proper mining. [ 13 ]
The work of pallaqueros and pallaqueras can be physically demanding given uncomfortable stances and – in the high Andes – also because of the cold climate . [ 9 ]
Historically, the term pallaqueros applied sometimes also to any independent miner of surface ores, similar to what is today understood as a pirquinero , [ 14 ] and they were important agents of mineral exploration . [ 7 ] | https://en.wikipedia.org/wiki/Pallaqueo |
A pallet inverter or pile turner is a machine that is used to turn over full pallet loads of packages or products. [ 1 ] [ 2 ] [ 3 ] The term pallet inverter is also used to cover machines that turn the palletised load through 90 degrees only.
The reasons for needing to turn over a pallet are varied. The primary reason is have access to the bottom of the load without having to manually unload all of the boxes or bags. If a pallet or slip sheet is damaged. it can be replaced by inverting the load, replacing it, and re-inverting the load. Sometimes a manufacturer simply needs to turn their products to stop their contents settling. In some industries, it is necessary to transfer goods from one type of pallet to another – for example, when plastic pallets are used for on-site storage and wooden pallets are used for shipping.
Some products require rapid freezing immediately after production and packaging. Processes can utilize freezer spacers between each tier of boxes on a pallet: these promote air flow for controlled and accelerated refrigeration. Prior to shipping, these spacers can be removed using a pallet inverter. This rotates the load ninety degrees to allow easy removal and reuse.
Pallet inverters can be built into production lines or be used as a stand-alone product.
This technology-related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Pallet_inverter |
A palletizer or palletiser is a machine which provides automatic means for stacking cases of goods or products onto a pallet .
Manually placing boxes on pallets can be time consuming and expensive; it can also put unusual stress on workers. [ 1 ] The first mechanized palletizer was designed, built, and installed in 1948 by a company formerly known as Lamson Corp.
There are specific types of palletizers including the row-forming which were introduced in the early 1950s. In row-forming palletizing applications loads are arranged on a row forming area and then moved onto a different area where layer forming takes place. This process repeats until a full layer of goods and products are configured to be placed on a pallet.
The in-line palletizer was developed in the 1970s when higher speeds were needed for palletizing. This palletizer type utilizes a continuous motion flow divider that guides the goods into the desired area on the layer forming platform.
Robotic palletizers were introduced in the early 1980s and have an end of arm tool (end effector) to grab the product from a conveyor or layer table and position it onto a pallet. [ 2 ] Both conventional and robotic palletizers can receive product at a high elevation, typically 7–10.33 feet (2.13–3.15 m), or low "floor level" elevation of 2.5–3.0 feet (0.76–0.91 m). The end of arm tooling has evolved in recent years to accommodate a variation of pack pattern and package types.
Mixed case palletizing is a real-world application variant of the 3D Bin packing problem , where the goal is to stack mixed size cases onto a pallet in such a way it optimizes the space utilization i.e., stack as many cases onto a minimum amount of pallets. Although widespread applications in logistics exist, it remains a challenging problem, and stacking of mixed size products still largely involves manual labour.
Mixed case palletizing is subject to additional challenges as it not only requires robotics to grab the oncoming item i.e., determine the position of the product and robot kinematics to actually pick it up, but also to determine the size and optimal placement position on the pallet. [ 3 ] In recent years, some research has utilized Deep Reinforcement Learning , where robotic agents aim to learn an optimal placement position by stacking many pallets in simulation. Some works apply there learned model in real-world environments. [ 4 ] | https://en.wikipedia.org/wiki/Palletizer |
The Palmer-Bowlus flume , is a class of flumes commonly used to measure the flow of wastewater in sewer pipes and conduits. The Palmer-Bowlus flume has a u-shaped cross-section and was designed to be inserted into, or in line with, pipes and u-channels found in sanitary sewer applications. [ 1 ]
As a long-throated flume, the point of measurement of the Palmer-Bowlus flume is anywhere upstream of the throat ramp greater than D/2 (D=flume size). Montana flume has a single, specified point of measurement in the contracting section at which the level is measured. Unlike most other flumes used for open channel flow measurement, the Palmer-Bowlus flume can be calibrated by theoretical analysis.
The general design of the flume detailed in ASTM D5390: Standard Test Method for Open-Channel Flow Measurement of Water with Palmer-Bowlus Flumes. [ 2 ] It is important to note that unlike the Parshall flume , the standard for the flume does not set out specific sizes and flow rates, but only general characteristics for the class of flume.
18 sizes of Palmer-Bowlus flumes have been developed - in line with the common pipe sizes to which they would be adapted - from 4-inches to 72-inches. In practice, though, it is uncommon to see Palmer-Bowlus flumes greater than 24-inches in size. [ 3 ]
Under average flow conditions, the Palmer-Bowlus flume is accurate to within 3-5%. For lower flow rates - where the depth is low relative to the length of the flume - the accuracy decreases to 5-6%. This error, combined with typical installation / flow meter errors, means that overall site accuracy is somewhat less than other more common flumes. [ 4 ]
Flow in the Palmer-Bowlus Flume transitions from a circular bottom section to a raised trapezoidal throat and then back - accelerating sub-critical flow ( Fr ~0.5) to a supercritical state ( Fr >1) to develop the level-to-flow relationship.
The simplified free-flow discharge can be summarized as
Where
Note that Palmer-Bowlus flumes are proprietary to each manufacturer / throat configuration. The table presented below is for the most common throat configuration - a trapezoidal ramp - and is simplified for the entire flume flow range. For other throat configurations refer to the manufacturer's flow tables. [ 1 ]
Free-Flow – when there is no “back water” to restrict flow through a flume. Only the single depth (primary point of measurement - Ha) needs to be measured to calculate the flow rate. A free flow also induces a hydraulic jump downstream of the flume.
Submerged Flow – when the water surface downstream of the flume is high enough to restrict flow through a flume, the flume is deemed to be submerged. Submergence transitions for Palmer-Bowlus flumes are quite high - 85-90%. [ 5 ] [ 6 ] As a result, corrections for submerged flow in Palmer-Bowlus flumes have not been published. As a result, it is important to set the flume so that it does not experience submerged flow conditions. Although commonly thought of as occurring at higher flow rates, submerged flow can exist at any flow level as it is a function of downstream conditions. In natural stream applications, submerged flow is frequently the result of vegetative growth on the downstream channel banks, sedimentation, or subsidence of the flume.
Unlike other flumes - such as the Parshall , the Palmer-Bowlus flumes is typically only fabricated in two materials:
For standard Palmer-Bowlus flumes with the standard trapezoidal throat ramp: | https://en.wikipedia.org/wiki/Palmer-Bowlus_Flume |
The Palmer drought index , sometimes called the Palmer drought severity index ( PDSI ), or the Palmer Z index , is a regional drought index commonly used for monitoring drought events and studying areal extent and severity of drought episodes. [ 1 ] The index uses precipitation and temperature data to study moisture supply and demand using a simple water balance model. [ 1 ] [ 2 ] [ 3 ] It was developed by meteorologist Wayne Palmer, who first published his method in the 1965 paper Meteorological Drought [ 4 ] for the Office of Climatology of the U.S. Weather Bureau .
The Palmer Drought Index is based on a supply-and-demand model of soil moisture . Supply is comparatively straightforward to calculate, but demand is more complicated as it depends on many factors, not just temperature and the amount of moisture in the soil but also hard-to-calibrate factors including evapotranspiration and recharge rates. Palmer tried to overcome these difficulties by developing an algorithm that approximated them based on the most readily available data, precipitation and temperature.
The index has proven most effective in determining long-term drought, a matter of several months, but it is not as good with conditions over a matter of weeks. It uses a 0 as normal, and drought is shown in terms of negative numbers; for example, negative 2 is moderate drought, negative 3 is severe drought, and negative 4 or less is extreme drought. Palmer's algorithm also is used to describe wet spells, using corresponding positive numbers; for example, 2 is unusually moist, 3 is very moist, and 4 or more is extremely moist. Palmer also developed a formula for standardizing drought calculations for each individual location based on the variability of precipitation and temperature at that location. The Palmer index can therefore be applied to any site for which sufficient precipitation and temperature data is available.
Critics have argued that the utility of the Palmer index is weakened by the arbitrary nature of Palmer's algorithms, including the technique used for standardization and arbitrary designation of drought severity classes and internal temporal memory. [ 5 ] The Palmer index's inability to account for snow and frozen ground also is cited as a weakness. [ 6 ]
The Palmer index is widely used operationally, with Palmer maps published weekly by the United States Government's National Oceanic and Atmospheric Administration . It also has been used by climatologists to standardize global long-term drought analysis. Global Palmer data sets have been developed based on instrumental records beginning in the 19th century. [ 7 ] In addition, dendrochronology has been used to generate estimated Palmer index values for North America for the past 2000 years, allowing analysis of long term drought trends. [ 8 ] It has also been used as a means of explaining the Late Bronze Age collapse .
In the US, regional Palmer maps are featured on the cable channel Weatherscan .
The PDSI is a standardized index that ranges from -10 to +10, with negative values indicating drought conditions and positive values indicating wet conditions. [ 9 ] | https://en.wikipedia.org/wiki/Palmer_drought_index |
Palmetto Pass (often referenced as PAL PASS ) is an electronic toll-collection system used on all toll roads in South Carolina. It was originally administered by the South Carolina Department of Transportation and is now operated by the Connector 2000 Association, which operates the Southern Connector.
Palmetto Pass is now used on one toll road: the Southern Connector (Interstate 185) in Greenville County . Palmetto Pass was formerly used on the Cross Island Parkway ( U.S. Highway 278 ) on Hilton Head Island until tolls were abolished on that road on June 30, 2021. [ 1 ] Drivers are able to go through tolls at speeds up to 45 mph (72 km/h) at the two mainline toll plazas and 5 mph (8.0 km/h) at the ramp tolls on the Southern Connector. The Palmetto Pass has no interoperability agreements with other states or agencies that operate electronic toll collection systems.
As of March 1, 2021 new Palmetto Pass accounts can only be established through the Southern Connector website or agency office.
On February 28, 2021 the Cross Island Parkway stopped issuing new Palmetto Pass accounts in anticipation of an end to tolling on the parkway on June 30, 2021. [ 2 ]
As of January 2, 2024, Palmetto Pass users receive a 10-cent discount on the Southern Connector over cash users at both mainline toll booths. The cost to travel from end to end on the Southern Connector is $4.30 (versus $4.50 for cash users) for two-axle vehicles. Palmetto Pass users pay the same rate as cash payers ($1.50) at the two interchanges with ramp tolls.
On the Cross Island Parkway, Palmetto Pass users previously received a 50-cent discount at the main toll booth (paying .75 cents compared to the $1.25 cash toll rate). | https://en.wikipedia.org/wiki/Palmetto_Pass |
Palmitate mediated localization is a biological process that trafficks a palmitoylated protein to ordered lipid domains. [ 1 ]
One function is thought to cluster proteins to increase the efficiency of protein-protein interactions and facilitate biological processes. In the opposite scenario palmitate mediated localization sequesters proteins away from a non-localized molecule. In theory, disruption of palmitate mediated localization then allows a transient interaction of two molecules through lipid mixing. In the case of an enzyme, palmitate can sequester an enzyme away from its substrate. Disruption of palmitate mediated localization then activates the enzyme by substrate presentation . [ citation needed ]
Palmitate mediated localization is integral to spatial biology ; in particular, lipid partitioning and the formation of lipid rafts . Sequestration of palmitoylated proteins is regulated by cholesterol. Depletion of cholesterol with methyl-beta cyclodextrin disrupts palmitate mediated localization. [ citation needed ] | https://en.wikipedia.org/wiki/Palmitate_mediated_localization |
Palmitoylcarnitine is an ester derivative of carnitine involved in the metabolism of fatty acids . During the tricarboxylic acid cycle (TCA), fatty acids undergo a process known as β-oxidation to produce energy in the form of ATP. β-oxidation occurs primarily within mitochondria, however the mitochondrial membrane prevents the entry of long chain fatty acids (>C10), so the conversion of fatty acids such as palmitic acid is key. [ 1 ] Palmitic acid is brought to the cell and once inside the cytoplasm is first converted to Palmitoyl-CoA. Palmitoyl-CoA has the ability to freely pass the outer mitochondrial membrane, but the inner membrane is impermeable to the Acyl-CoA and thioester forms of various long-chain fatty acids such as palmitic acid. The palmitoyl-CoA is then enzymatically transformed into palmitoylcarnitine via the Carnitine O-palmitoyltransferase family. The palmitoylcarnitine is then actively transferred into the inner membrane of the mitochondria via the carnitine-acylcarnitine translocase . [ 2 ] Once inside the inner mitochondrial membrane, the same Carnitine O-palmitoyltransferase family is then responsible for transforming the palmitoylcarnitine back to the palmitoyl-CoA form.
Palmitoylcarnitine contains the saturated fatty acid known as palmitic acid (C16:0) which is bound to the β-hydroxy group of the carnitine. The core carnitine structure, consisting of butanoate with a quaternary ammonium attached to C4 and hydroxy group at C3, is a common molecular backbone for the transfer of multiple long chain fatty acids in the TCA cycle.
Palmitoylcarnitine is one molecule in a family of ester derivatives of carnitine that are utilized in the TCA cycle to generate energy. The beta oxidation yields 7 NADH, 7 FADH2, and 8 Acetyl-CoA chains. This Acetyl-CoA generates 3 NADH, 1 FADH2, and 1 GTP for every molecule in the TCA cycle. Each NADH generates 2.5 ATP in the ETC and FADH2 generates 1.5 ATP. This totals to 108 ATP, but 2 ATP are consumed to generate the initial Palmitoyl-CoA, leaving a net gain of 106 ATP. [ citation needed ]
Palmitoylcarnitine has demonstrated potential as a diagnostic marker in newborns for the medical condition of primary carnitine deficiency. [ 3 ]
Levels of palmitoylcarnitine (palcar) demonstrated significant correlation with dihydrotestosterone (DHT) and its effects in prostate cancer models, suggesting a similar role between the two molecules. [ 4 ]
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Palmitoylcarnitine |
Palmitoylethanolamide ( PEA ) is an endogenous fatty acid amide , and lipid modulator. [ 2 ]
A main target of PEA is proposed to be the peroxisome proliferator-activated receptor alpha (PPAR-α). [ 3 ] [ 4 ] PEA also has affinity to cannabinoid-like G-coupled receptors GPR55 and GPR119 . [ 5 ] PEA cannot strictly be considered a classic endocannabinoid because it lacks affinity for the cannabinoid receptors CB1 and CB2 . [ 6 ]
In 1975, Czech physicians described the results of a clinical trial [ clarification needed ] looking at joint pain, where the analgesic action of aspirin versus PEA was tested; both drugs were reported to enhance joint movements and decrease pain. [ 7 ] In 1970 the drug manufacturer Spofa in Czechoslovakia introduced Impulsin , a tablet dose of PEA, for the treatment and prophylaxis of influenza and other respiratory infections. [ citation needed ] In Spain, the company Almirall introduced Palmidrol in tablet and suspension forms in 1976, for the same indications. [ citation needed ]
In the mid-1990s, the relationship between anandamide and PEA was described; [ 8 ] [ non-primary source needed ] the expression of mast cell receptors sensitive to the two molecules was demonstrated by Levi-Montalcini and coworkers. [ according to whom? ] [ non-primary source needed ] During this period, more insight into the functions of endogenous fatty acid derivatives emerged, and compounds such as oleamide , palmitoylethanolamide, 2-lineoylglycerol and 2-palmitoylglycerol were explored for their capacity to modulate pain sensitivity and inflammation via what at that time was thought to be the endocannabinoid signalling pathway. [ 9 ] [ 10 ]
Primary reports also have provided evidence that PEA downregulates hyperactive mast cells in a dose-dependent manner, [ 11 ] and that it alleviates pain elicited in mouse models. [ verification needed ] PEA and related compounds such as anandamide also seem to have synergistic effects in models of pain and analgesia. [ 12 ]
In a variety of animal models, PEA seems to have some promise; [ editorializing ] [ citation needed ] researchers have been able to demonstrate relevant clinical efficacy in a variety of disorders, from multiple sclerosis to neuropathic pain. [ 13 ] [ 14 ]
In the mouse forced swimming test , palmitoylethanolamide was comparable to fluoxetine for depression . [ 15 ] An Italian study published in 2011 found that PEA reduced the raised intraocular pressure of glaucoma . [ 16 ] In a spinal trauma model, PEA reduced the resulting neurological deficit via the reduction of mast cell infiltration and activation. PEA in this model also reduced the activation of microglia and astrocytes . [ 17 ] Its activity as an inhibitor of inflammation counteracts reactive astrogliosis induced by beta-amyloid peptide, in a model relevant for neurodegeneration, probably via the PPAR-α mechanism of action. [ 18 ] [ verification needed ] In models of stroke and other CNS trauma, PEA exerted neuroprotective properties. [ 19 ] [ 20 ] [ 21 ] [ 22 ]
Chronic pain and neuropathic pain are indications for which there is high unmet need in the clinic. PEA has been tested in a variety of animal models for chronic and neuropathic pain, because cannabinoids, such as THC , have been proven to be effective in neuropathic pain states. [ 23 ] The analgesic and antihyperalgesic effects of PEA in two models of acute and persistent pain seemed to be explained at least partly via the de novo neurosteroid synthesis. [ 24 ] [ 25 ] In chronic granulomatous pain and inflammation model, PEA could prevent nerve formation and sprouting, mechanical allodynia, and PEA inhibited dorsal root ganglia activation, which is a hallmark for winding up in neuropathic pain. [ 26 ] The mechanism of action of PEA as an analgesic and anti-inflammatory molecule is probably based on different aspects. [ editorializing ] [ citation needed ] PEA inhibits the release of both preformed and newly synthesised mast cell mediators, such as histamine and TNF-alpha . [ 27 ] PEA, as well as its analogue adelmidrol (di-amide derivative of azelaic acid), can both down-regulate mast cells. [ 28 ] PEA reduces the expression of cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) and prevents IkB-alpha degradation and p65 NF-kappaB nuclear translocation, the latter related to PEA as an endogenous PPAR-alpha agonist.
In 2012 it became clear that PEA can also reduce reperfusion injury and the negative impact of shock on various outcome parameters, such as renal dysfunction, ischemic injury and inflammation, most probably via the PPAR-alpha pathway. [ editorializing ] [ citation needed ] Studies have shown that PEA activates PPAR-alpha and TRPV1 receptors that control inflammation and the sensation of pain. [ 29 ] Among the reperfusion and inflammation markers measured PEA could reduce the increase in creatinine, γGT, AST, nuclear translocation of NF-κBp65; kidney MPO activity and MDA levels, nitrotyrosine, PAR and adhesion molecules expression, the infiltration and activation of mast cells and apoptosis. [ 30 ]
The biological responses to PEA dosing in animal models and in humans are being investigated vis-à-vis its involvement in a repair mechanism relevant to patient conditions of chronic inflammation and chronic pain. [ 31 ] [ verification needed ] In a model of visceral pain (inflammation of the urinary bladder ) PEA was able to attenuate the viscero-visceral hyper-reflexia induced by inflammation of the urinary bladder, one of the reasons why PEA is currently explored in the painful bladder syndrome. [ 32 ] In a different model for bladder pain, the turpentine-induced urinary bladder inflammation in the rat, PEA also attenuated a referred hyperalgesia in a dose-dependent way. [ 33 ] Chronic pelvic pain in patients seem to respond favourably to a treatment with PEA. [ 34 ] [ 35 ]
PEA, as an N -acylethanolamine , has physico-chemical properties comparable to anandamide , [ clarification needed ] and, while it is not strictly an endocannabinoid, it is often studied in conjunction with anandamide because of their overlapping synthetic and metabolic pathways. [ non-primary source needed ] N -acylethanolamines such as PEA often act as signaling molecules, activating receptors and regulating a variety of physiological functions. [ non-primary source needed ] PEA is known to activate intracellular, nuclear and membrane-associated receptors, [ non-primary source needed ] and to regulate many physiological functions related to the inflammatory cascade and chronic pain states. [ non-primary source needed ] Endocannabinoid lipids like PEA are widely distributed in nature, in a variety of plant, invertebrate, and mammalian tissues. [ non-primary source needed ]
PEA's mechanism of action sometimes is described as Autacoid Local Injury Antagonism (acronym ALIA), [ 8 ] and PEA under this nomenclature is an ALIAmide . Levi-Montalcini and coworkers presented evidence in 1993 that lipid amides of the N-acylethanolamine type, such as PEA, are potential prototypes of naturally occurring molecules capable of modulating mast cell activation, and her group used the acronym ALIA in that report. [ non-primary source needed ] [ 36 ] An autocoid is a regulating molecule, locally produced. An ALIAmide is an autocoid synthesized on-demand in response to injury, and acts locally to counteract such pathology. Soon after the breakthrough paper of Levi-Montalcini, the mast cell appeared to be an important target for the anti-inflammatory activity of PEA. Since 1993, at least 25 papers have been published on the various effects of PEA on mast cells. These cells are often found in proximity to sensory nerve endings, and their degranulation can enhance the nociceptive signal, the reason why peripheral mast cells are considered to be pro-inflammatory and pro-nociceptive. [ 37 ] PEA's activity is currently seen as a new inroad in the treatment of neuropathic pain and related disorders based on overactivation of glia and glia-related cells, such as in diabetes and glaucoma. [ 38 ] Microglia plays a key role in the winding up phenomenon and central sensitization. [ 39 ] [ 40 ]
The effects of oral dosing of PEA have been explored in humans, and include clinical trials for a variety of pain states, for inflammatory and pain syndromes. [ 35 ] [ 41 ] [ 42 ] [ 43 ] [ 44 ] Daily doses range from 300 to 1200 mg per day. [ 45 ] In a 2017 systematic meta-analysis involving 10 studies including data from 786 patients receiving PEA for pain-related indications and 512 controls, PEA was found to be associated with pain reduction significantly greater than observed in controls ( P < 0.001). [ 46 ] Positive influences have also been observed in dermal applications, specifically atopic eczema, which may be linked to PPAR alpha activation. [ 41 ] [ 47 ] [ verification needed ]
In a 2015 analysis of a double blind placebo controlled study of PEA in sciatic pain, the Numbers Needed to Treat was 1.5. Its positive influence in chronic pain, and inflammatory states such as atopic eczema, seems [ editorializing ] to originate mainly from PPAR alpha activation. [ 41 ] [ 47 ] [ verification needed ] Since 2012 a number of new trials have been published, among which studies in glaucoma. [ 48 ] [ 49 ] PEA also seems [ editorializing ] to be one of the factors responsible for the decrease in pain sensitivity during and after sport, comparable to the endogenous opiates (endorphines). [ 50 ] [ verification needed ]
From a clinical perspective the most important and promising indications for PEA are linked to neuropathic and chronic pain states, such as diabetic neuropathic pain, sciatic pain, CRPS, pelvic pain and entrapment neuropathic pain states. [ 31 ] [ 35 ] [ 42 ] [ 43 ] [ 51 ] [ 52 ] In a blind trial reported in a conference proceeding, patients affected by pain from synovitis or TMJ osteoarthritis (N=25, in total [ clarification needed ] ) were randomly assigned to PEA or ibuprofen groups for two weeks; the decrease in pain reported after two weeks was significantly higher for the PEA-treated group, likewise for improved masticatory function. [ 53 ] [ 54 ] [ better source needed ] In 2012, 20 patients with thalidomide and bortezomib induced neuropathy were reported to have improved nerve functions and less pain after a two-month treatment with PEA. [ 55 ] The authors pointed out that although a placebo effect might play a role in the reported pain relief, the changes in neurophysiological measures clearly indicated that PEA exerted a positive action on the myelinated fibre groups. Sixteen men and fourteen women with two major types of neuropathic pain refractory to analgesic treatment—peripheral diabetic neuropathy (4 men, 7 women) or post-herpetic neuralgia (12 men, 7 women) [ 56 ] —whose symptoms spanned eight pain categories ("burning", "osteoarticular", "piercing", etc. [ 57 ] ) who were under prior treatment with pregabalin were transferred to PEA, after which pregabalin treatment was gradually reintroduced; all were responding well after 45 days, and presented significant decreases in pain scores (without drug-drug interactions). [ verification needed ] [ 58 ]
In 2013, a metareview was published on the clinical efficacy and safety of PEA in the treatment of the common cold and influenza , based on reports from six double-blind, placebo, randomized controlled trials , [ verification needed ] addressing PEA's proposed anti-inflammatory and retinoprotectant effects. [ 59 ]
In 2019, significant increases in fatty acid amides including PEA, arachidonoylethanolamide , and oleoylethanolamide were noted in a Scottish woman with a previously undocumented variant of congenital insensitivity to pain . This was found to be a result of a combination of a hypomorphic single nucleotide polymorphism of fatty acid amide hydrolase (FAAH), alongside a mutation of the pseudogene , FAAH-OUT . The pseudogene was previously considered to be non-coding DNA , FAAH-OUT was found to be capable of modulating the expression of FAAH, making it a possible future target for novel analgesia/anxiolytic drug development. [ 60 ] [ 61 ]
In 2020, PEA has been suggested as a drug that may prove beneficial for the treatment of lung inflammation caused by SARS-CoV-2 infection. [ 62 ] A pharmaceutical company called FSD Pharma have entered PEA into a Phase 1 clinical trial under the name FSD-201, and has approval from the FDA for progressing to Phase 2a for this indication. [ 63 ]
PEA is metabolized by the cellular enzymes fatty acid amide hydrolase (FAAH) and N-acylethanolamine acid amide hydrolase (NAAA), the latter of which has more specificity toward PEA over other fatty acid amides. [ 64 ]
PEA is generally considered safe, and without adverse drug reactions (ADRs) or drug interactions. A 2016 study assessing safety claims in sixteen clinical trials, six case reports/pilot studies and a meta‐analysis of PEA as an analgesic, concluded that for treatment periods up to 49 days, clinical data argued against serious ADRs at an incidence of 1/200 or greater. [ 65 ] A 2016 pooled meta-analysis involving twelve studies found that no serious ADRs were registered and/or reported. [ 66 ] No data on interactions with PEA have been reported. Based on its mechanism, PEA may be considered likely to interact with other PPAR-α agonists used to treat high triglycerides; this remains unconfirmed. | https://en.wikipedia.org/wiki/Palmitoylethanolamide |
The Palmqvist method , or the Palmqvist toughness test , (after Sven Robert Palmqvist ) is a common method to determine the fracture toughness for cemented carbides . In this case, the material's fracture toughness is given by the critical stress intensity factor K Ic . [ 2 ]
The Palmqvist-method uses the lengths of the cracks from a number of Vickers indentions to determine the fracture toughness. The Palmqvist fracture toughness is given by [ 2 ]
where HV is the Vickers hardness in N/mm 2 (or MPa) (i.e., 9.81 x numerical HV), P is the indentation load in N (typically 30 kgf is used) and T is the total crack length (mm) after application of the indenter. | https://en.wikipedia.org/wiki/Palmqvist_method |
A Palmtop PC is an obsolete, approximately pocket calculator -sized, battery-powered computer in a horizontal clamshell design with integrated keyboard and display. It could be used like a modern subnotebook , but was light enough to be comfortably used handheld as well. Most Palmtop PCs were small enough to be stored in a user's shirt or jacket pockets.
Palmtop PCs distinguish from other palmtop computers by using a mostly IBM-compatible PC architecture , and BIOS as well as an Intel-compatible x86 processor. All such devices were DOS -based, with DOS stored in ROM . While many Palmtop PCs came with a number of PDA and office applications pre-installed in ROM, most of them could also run generic, off-the-shelf PC software with no or little modifications. Some could also run other operating systems such as GEOS , Windows 1.0 - 3.0 (in Real mode only), or MINIX 2.0 .
Most Palmtop PCs have been based on a static hardware design for low power consumption, and instant-on/off without the need to reboot. Depending on the model, the battery could power the device for a period ranging from several hours up to several days while running, or between a week and a year in standby mode. Combined with the instant-on/off feature, a battery would typically last from a week up to several months in practical use as PDA.
The first Palmtop PC was the DIP Pocket PC (aka Atari Portfolio ) in 1989. [ 1 ]
Palmtop PCs include:
Some touch-screen computers may also be included in this category:
This computing article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Palmtop_PC |
In probability theory , the Palm–Khintchine theorem , the work of Conny Palm and Aleksandr Khinchin , expresses that a large number of renewal processes , not necessarily Poissonian , when combined ("superimposed") will have Poissonian properties. [ 1 ]
It is used to generalise the behaviour of users or clients in queuing theory . It is also used in dependability and reliability modelling of computing and telecommunications .
According to Heyman and Sobel (2003), [ 1 ] the theorem states that the superposition of a large number of independent equilibrium renewal processes, each with a finite intensity, behaves asymptotically like a Poisson process:
Let { N i ( t ) , t ≥ 0 } , i = 1 , 2 , … , m {\displaystyle \{N_{i}(t),t\geq 0\},i=1,2,\ldots ,m} be independent renewal processes and { N ( t ) , t > 0 } {\displaystyle \{N(t),t>0\}} be the superposition of these processes. Denote by X j m {\displaystyle X_{jm}} the time between the first and the second renewal epochs in process j {\displaystyle j} . Define N j m ( t ) {\displaystyle N_{jm}(t)} the j {\displaystyle j} th counting process, F j m ( t ) = P ( X j m ≤ t ) {\displaystyle F_{jm}(t)=P(X_{jm}\leq t)} and λ j m = 1 / ( E ( ( X j m ) ) ) {\displaystyle \lambda _{jm}=1/(E((X_{jm)}))} .
If the following assumptions hold
1) For all sufficiently large m {\displaystyle m} : λ 1 m + λ m + ⋯ + λ m m = λ < ∞ {\displaystyle \lambda _{1m}+\lambda _{m}+\cdots +\lambda _{mm}=\lambda <\infty }
2) Given ε > 0 {\displaystyle \varepsilon >0} , for every t > 0 {\displaystyle t>0} and sufficiently large m {\displaystyle m} : F j m ( t ) < ε {\displaystyle F_{jm}(t)<\varepsilon } for all j {\displaystyle j}
then the superposition N 0 m ( t ) = N 1 m ( t ) + N m ( t ) + ⋯ + N m m ( t ) {\displaystyle N_{0m}(t)=N_{1m}(t)+N_{m}(t)+\cdots +N_{mm}(t)} of the counting processes approaches a Poisson process as m → ∞ {\displaystyle m\to \infty } . | https://en.wikipedia.org/wiki/Palm–Khintchine_theorem |
The Palos Verdes Peninsula , a coastal region of the Los Angeles metropolitan area , has a long history of landslides and land movements. [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ 7 ] The Palos Verdes Peninsula is home to the cities of Palos Verdes Estates, [ 8 ] Rancho Palos Verdes, [ 9 ] Rolling Hills [ 10 ] and Rolling Hills Estates, [ 11 ] and the unincorporated communities of Academy Hills and Westfield. [ 12 ]
As early as the 1920s, the area was identified as a potentially hazardous landslide area, yet real estate construction and development gained traction in the 1940s and 1950s. [ 13 ] In 2024, the Palos Verdes Peninsula was rocked with another round of landslides. [ 14 ]
In December 2022, a coastal cliff landslide was recorded in Palos Verdes Estates (33.804, -118.394). [ 15 ] [ 16 ]
The city of Rancho Palos Verdes sits on four out of five sub-slides of the Ancient Altamira Landslide Complex, [ 17 ] also referred to as the Greater Portuguese Bend Landslide Complex. [ 18 ] The Complex encompasses four historically active landslide areas within the city limits: Abalone Cove Landslide; Beach Club Landslide; Klondike Canyon Landslide; and Portuguese Bend Landslide; as well as the areas outside of the city’s border of those named landslides. [ 18 ] [ 19 ] [ 17 ] [ 20 ]
The Portuguese Bend landslide was activated in 1956, before Rancho Palos Verdes was incorporated as a city. [ 21 ] Beginning in September 1956 and continuing until early 1957, [ 22 ] the area experienced a landslide concurrent with the construction of a road (the Crenshaw Boulevard extension, south of Crest Road) along the top of an ancient landslide complex. [ 3 ] [ 13 ] [ 23 ] [ 24 ] The impacted areas ranged from several acres to roughly two square miles [ 25 ] [ 23 ] A 1958 video newsreel showed the effects of the landslide’s impact: 140 of the 170 homes in the area were destroyed or displaced. [ 26 ]
In 1961, area homeowners filed a lawsuit against Los Angeles County and won a settlement of roughly $10 million. [ 13 ] [ 27 ]
From 1974 to 1978, an 80 acre landslide [ 28 ] [ 29 ] occurred in the Abalone Cove area. [ 2 ] [ 13 ] [ 25 ] The lower part of the landslide started to move in February 1974. [ 28 ] The "Abalone Cove Slide" was moving so slow that geologists did not verify that it was an actual slide until 1976, after it had damaged roughly twenty homes. [ 30 ] It is estimated that the landslides damaged nearly 50 homes and depressed property values. [ 29 ]
In 1978, residents noticed cracks on Palos Verdes Drive South, and the upper part of the slide may have started to shift. [ 28 ] [ 29 ] That same year, the city restricted building new homes in the areas impacted by the landslides, "Landslide Moratorium Map." [ 2 ] [ 25 ] Since 1980, efforts to control landslide movement have involved removing ground water from the landslide mass. [ 28 ]
The Portuguese Beach Club landslide is a minor slide within the area's landslide complex. [ 17 ] [ 20 ] In 2024, residents of Seaview and the Beach Club filed a lawsuit against the City of Rancho Palos Verdes. [ 6 ] In 2024, the Beach Club area experienced major deformation along Seawall Road, approximately four to five feet across the beach, and potentially into an offshore slide area. [ 31 ]
The Klondike Canyon has been noted for landslides. [ 17 ] [ 20 ] Renewed movement occurred in 1979, [ 32 ] and a Geologic Hazard Abatement Districts was created to study the Klondike Canyon landslides in 1982. [ 32 ]
The Portuguese Bend Landslide is a highly active landslide area that covers approximately 240 acres. [ 33 ] [ 34 ] Since Spring 2023, there has been noticeable land movement and collateral damage in the Portuguese Bend Beach Club, Portuguese Bend Community Association, and Seaview neighborhoods. [ 1 ] [ 19 ] Several miles of trails have closed in the Abalone Cove Reserve, Filiorum Reserve, Forrestal Reserve, and Portuguese Bend Reserve areas. [ 20 ] [ 31 ] In September 2024, more than 200 homeowners had to evacuate the Portuguese Bend and Seaview areas. [ 35 ] Several homes have collapsed or have been made unlivable. [ 36 ] The city issued an evacuation warning for residents; the landslides are moving at a rate of three-fourths to one foot per week. [ 1 ] [ 5 ] [ 35 ] Gas to the Portuguese Bend neighborhood has been shutoff since August 2024. [ 17 ] [ 35 ] For safety reason, local utility companies planned to terminate all electricity for impacted residents. [ 5 ] [ 35 ]
On September 3, 2024, California Governor Gavin Newsom declared a state of emergency in the City of Rancho Palos Verdes. [ 5 ] [ 19 ] [ 35 ] The city has extended a construction moratorium for the landslide areas [ 5 ] [ 34 ] until October 2025. [ 35 ]
In Summer 2024, City officials informed residents that they have identified additional land movements and landslides for Rancho Palos Verdes. [ 21 ] [ 31 ] The new, deeper slide appears to be moving faster and deeper, shifting the city's strategy from individual landslide event response to a broader strategy to address all landslide hazards and issues. [ 31 ]
In 2023, FEMA awarded a $23.3 million grant to Rancho Palos Verdes for the Portuguese Mud/Landslide Community Infrastructure Resilience Project . [ 33 ] [ 36 ] [ 37 ] The goal of the grant is to make improvements in the existing groundwater extraction systems and to install new subsurface water extraction systems. [ 33 ]
The RPV Landslide Complex Working Group meets virtually weekly to plan, coordinate, and implement actions for minimizing land movement and reducing community and property damages. The members of this group include representatives of Abalone Cove Landslide Abatement Districts; California Water Service ; City of Rolling Hills ; Klondike Canyon Landslide Abatement Districts; Los Angeles County Department of Public Works Sanitary Sewer Maintenance ; Los Angeles County Sanitation Districts ; Palos Verdes Peninsula Land Conservancy ; Portuguese Bend Beach Club Homeowners Association; Portuguese Bend Community Association; Rolling Hills Community Association; Seaview Residential Association; Southern California Gas Company ; Southern California Edison ; and area residents. [ 31 ]
In 1979, residents in the Flying Triangle Landslide area noticed cracks in the main road leading to their neighborhood. [ 38 ] The landslide area spanned approximately 90 acres [ 38 ] and damaged and destroyed several homes. [ 3 ] Impacted homeowners received roughly $16 million in compensatory setttlements. [ 38 ]
In 1987, there was a documented landslide in the Flying Triangle area above Portuguese Bend. [ 29 ]
In 2024, Congressman Ted Lieu secured one million dollars for the Rolling Hills Landslide Mitigation Project, which is expected to improve wastewater flow and reduce the risk of additional landslides in the Flying Triangle landslide area within the city boundaries. [ 39 ]
Rollings Hills Estates is located on the northern side of the Palos Verdes Peninsula, an area that has a history of documented landslides. [ 40 ] [ 41 ]
In 1997, employees in a Rolling Hills Estates office park witnessed crumbling walls and buckling sidewalks and had to be evacuated. [ 3 ] [ 42 ]
On July 8, 2023, the Peartree Lane Landslide destroyed several homes in Rolling Hills Estates. [ 43 ] [ 44 ] Townhouses in the area slumped into a canyon. [ 21 ] This land movement may have started in 2022. [ 40 ] | https://en.wikipedia.org/wiki/Palos_Verdes_Peninsula_landslides |
Paludiculture is wet agriculture and forestry on peatlands . [ 1 ] Paludiculture combines the reduction of greenhouse gas emissions from drained peatlands through rewetting with continued land use and biomass production under wet conditions. [ 2 ] “Paludi” comes from the Latin “ palu s ” meaning “swamp, morass” and "paludiculture" as a concept was developed at Greifswald University . [ 3 ] Paludiculture is a sustainable alternative to drainage-based agriculture, intended to maintain carbon storage in peatlands. This differentiates paludiculture from agriculture like rice paddies, which involve draining, and therefore degrading wetlands. [ 4 ]
Peatlands store an enormous amount of carbon. Covering only 3% of the Earth's land surface, they store more than 450 gigatonnes of carbon - more than stored by forests (which cover 30% of the land surface). [ 5 ] [ 6 ] Drained peatlands cause numerous negative environmental impacts such as greenhouse gas emission, nutrient leaching, subsidence and loss of biodiversity . Although only 0.3% of all peatlands are drained, peatland drainage is estimated to be responsible for 6% of all human greenhouse gas emission. [ 7 ] By making soils waterlogged when re-wetting peatlands, decomposition of organic matter (~50% carbon) will almost cease, and hence carbon will no longer escape into the atmosphere as carbon dioxide. [ 8 ] [ 9 ] Peatland rewetting can significantly reduce environmental impacts caused by drainage by restoring hydrological buffering [ 10 ] and reducing the water table's sensitivity to atmospheric evaporative demand. [ 11 ] Due to the drainage of soils for agriculture in many areas, the peat soil depth and water quality has dropped significantly over the years. These problems are mitigated by re-wetting peatlands. As such, they can also make installations against rising sea levels ( levees , pumps) [ 12 ] unnecessary. Wet bogs act as nitrogen sinks, whereas mineralisation and fertilisation from agriculture on drained bogs produces nitrogen run-off into nearby waters. [ 3 ]
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The application of the term "paludiculture" is debated as it is contingent on whether different peatland agricultural practices are considered sustainable. In terms of greenhouse gas emissions, how sustainable a paludiculture practice is deemed to be depends on the greenhouse gas measured, the species of plant and the water table level of the peatland. [ 4 ] "Paludiculture" been used to refer to cultivating native and non-native crops on intact or re-wetted peatlands. In the EU's Common Agricultural Policy , it is defined as the productive land use of wet and rewetted peatlands that preserves the peat soil and thereby minimizes CO 2 emissions and subsidence. [ 17 ] A 2020 review of tropical peatland paludiculture [ 4 ] from the National University of Singapore evaluated wet and re-wetted management pathways in terms of greenhouse gas emissions and carbon sequestration and concluded that commercial paludiculture is only suited to re-wetted peatlands, where it is carbon negative or neutral, as opposed to intact peatlands, where it increases emissions. [ 4 ] After decades of re-wetting, can still contribute to global warming to a greater extent than intact peatlands. [ 18 ] Exceptions where paludiculture on intact peatlands may be sustainable are some traditions of cultivating native crops semi-wild in intact peat swamp forest, or gathering peatland products without active cultivation. The review also suggests that, to be sustainable, paludiculture should only use native vegetation to restore peatlands whilst producing biomass, as opposed to any wetland plants which have the possibility of surviving. This is because using non-native species may create negative peatland conditions for other native plants, and non-native plants tend to have a lower yield and lifespan in undrained or re-wetted peatlands than when grown in their native habitats or drained wetlands. [ 4 ]
Assessments of the sustainability of paludiculture should take into account ecosystem services besides carbon sequestration and how paludiculture can be integrated with traditional farming practices. [ 4 ] Peatlands can provide a number of other ecosystem services e.g. biodiversity conservation and water regulation. It is therefore important to protect this areas and restore degraded areas. To conserve, restore and improve management of peat lands is a cost efficient and relatively easy way to maintain ecosystem services. However, these the ecosystem services are not priced in a market and do not produce economic profit for the local communities. The drainage and cultivation, grazing, as well as peat mining on the other hand give the local communities short-term economic profits. It has therefore been argued that conservation and restoration, which has a significant and common value, needs to be subsidized by the state or the world at large. [ 7 ]
Paludiculture is not focused on nature conservation but on production, but paludiculture and conservation may complement each other in a number of ways. 1) Paludiculture can be the starting point and an intermediate stage in the process of restoring a drained peatland. 2) Paludiculture can lower the cost of the conservation project by e.g. decrease the costs of biomass removal and establishment costs. 3) Areas with paludiculture practice can provide buffer zones around the conserved peat areas. 4) Areas with paludiculture in between conservation areas can provide corridors facilitating species migration. 5) Paludiculture may increase the acceptance by the affected stakeholder to rewet once drained peatland. The support of the local communities in rewetting project are often crucial. [ 3 ]
The effect on greenhouse gas emissions of paludiculture is complex. On the one hand a higher water table will reduce the aerobic decomposition of peat and therefore the carbon dioxide emissions. But on the other hand the increased ground water table may increase anaerobic decomposition of organic matter or methanogenesis and therefore increase the emission of methane (CH 4 ), a short-lived but more potent greenhouse gas than CO 2 . The emissions emanating from rewetted peatland with paludiculture will also be affected by the land-use in terms of type of use (agriculture, forestry, grazing etc.), but also in terms of used species and intensity. Traditional use of peatland has often less impact on the environment than industrial use has, but need not be sustainable in the long run and if used at a larger scale. [ 4 ]
The most obvious way to maintain the ecosystem services that peatland provides is conservation of intact peatlands. This is even more true given the limited success of restoration projects especially in tropical peatlands. The conserved peatland still holds value for humans and hence provides a number of ecosystem services e.g. carbon storage, water storage and discharge. Conserving peatlands also avoids costly investments. Conservation is suggested to be a very cost-effective management practice for peatlands. The most obvious ecosystem services that the conservation management provides - i.e. carbon storage and water storage - are not easily priced on the market. Therefore, peatland conservation may need to be subsidised. [ 7 ]
To rewet peatland and thereby restore the water table level is the first step in the restoration. The intention is to recreate the hydrological function and processes of the peatland. This takes a longer time than may be expected. Studies have found that rewetted previously drained peatland had the hydrological functions - e.g. water storage and discharge capacity - somewhere between a drained and an intact peatland six years after the restoration. [ 4 ]
Undrained peatlands are recommended to be left for conservation and not used for paludiculture. Drained peatlands, on the other hand, can be rewetted and used for paludiculture often using traditional knowledge together with new science. However local communities, especially in the tropics, maintain their livelihood by draining and using the peatland in various ways e.g. agriculture, grazing, and peat mining. [ 7 ] Paludiculture can be a way to restore degraded and drained peatlands as well as maintaining an outcome for the local community. [ 4 ] For example, studies of Sphagnum cultivation on re-wetted peat bogs in Germany shows a significant decrease of greenhouse gas emission compared to a control with irrigated ditches. [ 19 ] The economic feasibility of Sphagnum cultivation on peat bogs are however still unclear. [ 20 ] The basis for paludiculture is however very different in the south, among other things because of higher population and economic pressure on peatland. [ 4 ]
Tropical peatlands extensively occur in Southeast Asia, mainland East Asia, the Caribbean and Central America, South America, and southern Africa. Often located in lowlands, tropical peatlands are uniquely identified by rapid rates of peat soil formation, [ 21 ] under high precipitation and high temperature regimes. [ 22 ] In contrast, a high temperature climate accelerates decomposition rates, causing degraded tropical peatlands to contribute more substantially to global green house gas emissions. [ 23 ] [ 24 ] Although tropical peatlands cover only 587,000 km 2 , they store 119.2 Gigatonnes C at a density per unit area of 203,066 tonnes C km −2 . [ 25 ] For decades, these large carbon stores have succumbed to draining in order to cater for humanity's socio-economic needs. Between 1990 and 2015, cultivation (for management including industrial and small-holder agriculture) had increased from 11 to 50% of forested peatlands in Peninsular Malaysia, Sumatra, and Borneo. [ 4 ] In Malaysia and Indonesia in the last twenty years, peat swamp forests have retreated from covering 77% of peatlands to 36%, endangering many mammals and birds in the region. In 2010, industrial agriculture covers about 3-3.1 million hectares, with oil palm accounting for 2.15 million hectares of this area. [ 26 ] The conversion of natural tropical peatlands into other land uses leads to peat fires and the associated health effects, soil subsidence increasing flood risks, substantial greenhouse gas emissions and loss of biodiversity. [ 27 ] [ 28 ] [ 29 ] [ 30 ] Today efforts are being made to restore degraded tropical peatlands through paludiculture. Paludiculture is researched as a sustainable solution to reduce and reverse the degradation of peat swamp forests, and includes traditional local agricultural practices which predate the use of the term. Commercial paludiculture has not been trialled to the extent that it has in northern peatlands. [ 4 ] Below are examples of paludiculture practices in tropical peatlands.
The Bantu people in Cuvette Central use peatlands for fishing, hunting and gathering, as well as small-scale agriculture near terra firme forests. [ 31 ]
In Indonesia there are three areas that could be the example of paludiculture practices such as beje system in Kutai and Banjar Tribes in East Kalimantan, Nut plantations in Segedong West Kalimantan, and Sago farming in Meranti Island district and Riau Province. [ 32 ] Sago is cultivated semi-wild near rivers in Riau. Jelutong is grown in monocultures and mixed plantings in Central Kalimantanm and in South Sumatra and Jambi, and has been traded since the mid-1800s. This trade has been stiffed by 2006 tariffs and sanctions, [ 33 ] and growing jelutong in monocultures is considered less efficient than crops like smallholder oil palm. [ 4 ]
Besides commercial production, peatland communities in Indonesia have developed less impactful practices for extracting resources. For example, Dayak communities only cultivate peatlands shallower than three meters for small-scale farming of sago and jelutong in coastal areas where the sea inputs nutrients. [ 4 ] In Sumatra, timber harvested in peat swamp forests are transported with wooden sleighs, rails and small canals in a traditional method called ongka which is less destructive than commercial logging transport. [ 34 ] Peat subsidence and CO 2 emissions have still been found present in agroforestry small-holdings in re-wetted peatlands in Jambi and Central Kalimantan, even those with native species. [ 4 ]
In Malaysia, sago plantations are mostly semi-wild, situated near rivers such as in Sarawak, although Malaysia also imports sago from Sumatra to make noodles. [ 4 ] Peatlands are also used by the Jakun people in South East Pahang for hunting, gathering and fishing. [ 35 ]
Mestizo communities in Loreto, Peru use peatlands for hunting and gathering, and sustainably cultivating native palms, which they replant to restore the resource. They are conscious of the limits to the resource and the need to avoid wasteful felling during harvest. [ 36 ]
The greater part of the world's peatlands occur in the northern hemisphere, encompassing both boreal and temperate regions. Global estimates indicate that northern peatlands cover 3,794,000 km2, storing about 450 Gt of C at a density of approximately 118,318 t C km−2 . Peatlands form in poorly drained areas under conditions of high precipitation and low temperature . 66% of northern peatlands are found in Eurasia and 34% in North America. About 60% of these peatlands (2718×103 km2) are perennially frozen, with approximately 2152×103 km2 occurring in Eurasia and 565×103 km2 in North America . In the European Union (25 countries in Europe), peatlands cover approximately 291×103 km2, of which nearly 55% are in Finland and Sweden . Peatlands are more common in Belarus and Ukraine, where they occupy approximately 497×103 km2. Both boreal and temperate peatlands are primarily formed from bryophytes and graminoids, displaying slower rates of accumulation and decomposition comparative to the tropics . Northern peatlands have been drained for agriculture, forestry, and peat mining for fuel and horticulture. Historical uses of intact northern peatlands include fishing, hunting, grazing and gathering berries. Paludiculture is not widely established commercially in northern peatlands and most research projects identified below are ongoing. Many have not yet published peer-reviewed results. Most are focused on Sphagnum and reed farming. Rather than excavating decomposed Sphagnum as peat, non-decomposed reed fibres are harvested in cycles, as a renewable source of biomass. Sphagnum fibres can be used as a growing substrate, packaging to protect plants in transport, or to reintroduce moss when restoring other peatlands.
The University of Greifswald and Belarusian State University are researching reed beds in Naroch National Park as filters to reduce nitrogen and phosphorus run-off from degraded peatlands agriculture into the Baltic. With research scheduled from January 2019 to September 2021, they aim to investigate the potential for harvesting reeds in the area to incentivise reed bed management. [ 16 ]
Paludiculture practices include cultivating Sphagnum and cattail . One of the largest research projects was carried out between 2006 and 2012 by researchers from Université Laval in Quebec, trialling Sphagnum farming in eastern Canada. Their bog site, on the Acadian Peninsula, was previously used for block-cutting peat for fuel and so consisted of ditches of Sphagnum and raised areas of other vegetation. They found that Sphagnum farming could be practiced large-scale in the ditches, although they recommend active irrigation management for more consistent harvests. [ 37 ]
The Finnish Forest Research Institute and Vapo Oy, Finland's largest peat mining company, manage around 10 hectares for experiments in cultivating Sphagnum for restoration and to produce substrates. [ 38 ]
The Greifswald Mire Center lists six research projects for cultivating Sphagnum as a raw material for substrates and restoring moors in Germany: Hankhausen, Drenth, Parovinzialmoor, Ramsloh, Sedelsberg and Südfeld. The Drenth and Parovinzialmoor projects, running from 2015 to 2019, included testing varying irrigation and drainage methods. They found that peat moss can be grown on black peat. [ 39 ] In Sedelsberg, researchers found cultivating Sphagnum on black peat to be "expensive and time-consuming". Researchers at the Südfeld project in 2002 observed a small increase in peat moss, and increasing reeds, cattails, and willows. [ 38 ] Researchers are also investigating reed and cattail cultivation. [ 40 ]
In Mecklenburg -West Pomerania, Greifswald University's ongoing Paludi-Pellets-Project aims to create an efficient biofuel source from sedges, reeds and canary grass in the form of dry pellets. [ 41 ]
Renewable energy company Bord na Móna began peat moss trials in 2012 to restore Sphagnum in raised bogs for potential horticulture. [ 38 ]
Lithuania's first peat moss cultivation trial was in 2011, in Aukštumala Moor in Nemunas Delta Regional Park . Researchers from Vilnius Institute of Botany transplanted sections of Sphagnum from a neighbouring degraded raised bog to the exposed peat surface. They found that 94% of the patches survived and expanded to the exposed peat. [ 38 ]
The ongoing "DESIRE" project is investigating peatland restoration and paludiculture in the Neman River catchment area to reduce nutrient run-off into the Baltic. [ 16 ]
In the ongoing "Omhoog met het Veen - AddMire in the Netherlands" research project, Landscape Noord-Holland aims to investigate the restoration of reed beds and wet heathlands on moors previously converted for agriculture as well as to raise awareness about peat land degradation . The project is intended to promote paludiculture as an alternative income from agriculture. Researchers have rewetted 8 hectares, including for a water storage buffer area for the peat moss experiments. They are measuring the effects of soil erosion and atmospheric nitrogen on the growth of peat moss and the resulting greenhouse gas emissions and soil chemistry. [ 40 ]
Russia has the largest area of peatlands of all the northern circumpolar countries with the world's largest peatland being the West Siberian mire massif and the largest in Europe the Polistovo-Lovatsky mire in northern Russia. [ 42 ] [ 43 ] An estimate derived from the digital soil database of Russia at a geographical scale of 1:5 million, [ 44 ] indicates that the area of soils with a peat depth of more than 30 cm is nearly 2210×10 3 km 2 . Approximately 28% occurs in the zone of seasonally frozen soils, nearly 30% in the zone of sporadic and discontinuous permafrost, and 42% in the zone of continuous permafrost. Peat with a depth of more than 50 cm tends to be dominant in the Northern and Middle Taiga zones, but is uncommon in the Tundra zone.
Ongoing restoration does not seem to include paludiculture. The Wetland International together with the Institute of Forest Science of the Russian Academy of Sciences and the Michael Succow Foundation, implemented a major peatland restoration project in response to the extensive peat fires in the summer of 2010 in the Moscow region. The project was initiated within the framework of co-operation between the Russian Federation and the Federal Republic of Germany to the spearhead the ecological rewetting of peatlands and represents one of the largest peatland ecosystem restoration projects in the world. To date, over 35,000 ha of drained peatlands have been restored using ecological methods with another 10,000 ha currently underway. [ 45 ]
The Database of Potential Paludiculture plants (DPPP) lists more than 1,000 wetland plants, [ 46 ] but only a minor fraction is suitable for paludiculture. Examples for potential and tested paludicultures are provided in the table below.
Fen , oligo-eutrotrophic
Fen, polytrophic
Fen, polytrophic
Native to Tropical Peat Swamp Forests
Raised bog, oligotrophic
Roof greening , miniature models, garden landscaping, top dressing containers and flower beds, lining wire framed hanging baskets, making wreaths, compostable plant pots to reduce plastic use, packaging seedlings for transport and protection when cellar storing root vegetables. Restoring peatlands, e.g. of cutover bog when using the moss layer transfer technique. [ 37 ] | https://en.wikipedia.org/wiki/Paludiculture |
Palynology is the study of microorganisms and microscopic fragments of mega-organisms that are composed of acid-resistant organic material and occur in sediments , sedimentary rocks , and even some metasedimentary rocks. Palynomorphs are the microscopic, acid-resistant organic remains and debris produced by a wide variety of plants , animals , and Protista that have existed since the late Proterozoic . [ 2 ] [ 3 ]
It is the science that studies contemporary and fossil palynomorphs (paleopalynology), including pollen , spores , orbicules , dinocysts , acritarchs , chitinozoans and scolecodonts , together with particulate organic matter (POM) and kerogen found in sedimentary rocks and sediments . Palynology does not include diatoms , foraminiferans or other organisms with siliceous or calcareous tests . The name of the science and organisms is derived from the Greek Ancient Greek : παλύνω , romanized : palynō , "strew, sprinkle" and -logy ) or of "particles that are strewn". [ 3 ] [ 4 ]
Palynology is an interdisciplinary science that stands at the intersection of earth science ( geology or geological science) and biological science ( biology ), particularly plant science ( botany ). Biostratigraphy , a branch of paleontology and paleobotany , involves fossil palynomorphs from the Precambrian to the Holocene for their usefulness in the relative dating and correlation of sedimentary strata . Palynology is also used to date and understand the evolution of many kinds of plants and animals. In paleoclimatology , fossil palynomorphs are studied for their usefulness in understanding ancient Earth history in terms of reconstructing paleoenvironments and paleoclimates. [ 3 ] [ 4 ]
Palynology is quite useful in disciplines such as archeology , in honey production, and criminal and civil law . [ 3 ] [ 4 ] In archaeology, palynology is widely used to reconstruct ancient paleoenvironments and environmental shifts that significantly influenced past human societies and reconstruct the diet of prehistoric and historic humans. Melissopalynology , the study of pollen and other palynomorphs in honey , identifies the sources of pollen in terms of geographical location(s) and genera of plants. This not only provides important information on the ecology of honey bees, it also an important tool in discovering and policing the criminal adultriation and mislabeling of honey and its products. Forensic palynology uses palynomorphs as evidence in criminal and civil law to prove or disprove a physical link between objects, people, and places. [ 4 ] [ 5 ]
Palynomorphs are broadly defined as organic remains, including microfossils , and microscopic fragments of mega-organisms that are composed of acid-resistant organic material and range in size between 5 and 500 micrometres . They are extracted from soils, sedimentary rocks and sediment cores , and other materials by a combination of physical (ultrasonic treatment and wet sieving ) and chemical (acid digestion) procedures to remove the non-organic fraction. Palynomorphs may be composed of organic material such as chitin , pseudochitin and sporopollenin . [ 6 ]
Palynomorphs form a geological record of importance in determining the type of prehistoric life that existed at the time the sedimentary strata was laid down. As a result, these microfossils give important clues to the prevailing climatic conditions of the time. Their paleontological utility derives from an abundance numbering in millions of palynomorphs per gram in organic marine deposits, even when such deposits are generally not fossiliferous . Palynomorphs, however, generally have been destroyed in metamorphic or recrystallized rocks. [ 6 ]
Typical palynomorphs include dinoflagellate cysts , acritarchs , spores , pollen , plant tissue, fungi , scolecodonts (scleroprotein teeth, jaws, and associated features of polychaete annelid worms), arthropod organs (such as insect mouthparts), and chitinozoans . Palynomorph microscopic structures that are abundant in most sediments are resistant to routine pollen extraction. [ 6 ]
A palynofacies is the complete assemblage of organic matter and palynomorphs in a fossil deposit. The term was introduced by the French geologist André Combaz [ wikidata ] in 1964. Palynofacies studies are often linked to investigations of the organic geochemistry of sedimentary rocks . The study of the palynofacies of a sedimentary depositional environment can be used to learn about the depositional palaeoenvironments of sedimentary rocks in exploration geology, often in conjunction with palynological analysis and vitrinite reflectance. [ 7 ] [ 8 ] [ 9 ]
Palynofacies can be used in two ways:
The earliest reported observations of pollen under a microscope are likely to have been in the 1640s by the English botanist Nehemiah Grew , [ 10 ] who described pollen and the stamen, and concluded that pollen is required for sexual reproduction in flowering plants.
By the late 1870s, as optical microscopes improved and the principles of stratigraphy were worked out, Robert Kidston and P. Reinsch were able to examine the presence of fossil spores in the Devonian and Carboniferous coal seams and make comparisons between the living spores and the ancient fossil spores. [ 11 ] Early investigators include Christian Gottfried Ehrenberg ( radiolarians , diatoms and dinoflagellate cysts ), Gideon Mantell ( desmids ) and Henry Hopley White (dinoflagellate cysts).
Quantitative analysis of pollen began with Lennart von Post 's published work. [ 12 ] Although he published in the Swedish language, his methodology gained a wide audience through his lectures. In particular, his Kristiania lecture of 1916 was important in gaining a wider audience. [ 13 ] Because the early investigations were published in the Nordic languages ( Scandinavian languages ), the field of pollen analysis was confined to those countries. [ 14 ] The isolation ended with the German publication of Gunnar Erdtman 's 1921 thesis. The methodology of pollen analysis became widespread throughout Europe and North America and revolutionized Quaternary vegetation and climate change research. [ 13 ] [ 15 ]
Earlier pollen researchers include Früh (1885), [ 16 ] who enumerated many common tree pollen types, and a considerable number of spores and herb pollen grains. There is a study of pollen samples taken from sediments of Swedish lakes by Trybom (1888); [ 17 ] pine and spruce pollen was found in such profusion that he considered them to be serviceable as " index fossils ". Georg F. L. Sarauw studied fossil pollen of middle Pleistocene age ( Cromerian ) from the harbour of Copenhagen . [ 18 ] Lagerheim (in Witte 1905) and C. A.Weber (in H. A. Weber 1918) appear to be among the first to undertake 'percentage frequency' calculations.
The term palynology was introduced by Hyde and Williams in 1944, following correspondence with the Swedish geologist Ernst Antevs , in the pages of the Pollen Analysis Circular (one of the first journals devoted to pollen analysis, produced by Paul Sears in North America). Hyde and Williams chose palynology on the basis of the Greek words paluno meaning 'to sprinkle' and pale meaning 'dust' (and thus similar to the Latin word pollen ). [ 19 ] The archive-based background to the adoption of the term palynology and to alternative names (e.g. paepalology , pollenology ) has been exhaustively explored. [ 20 ] It has been argued there that the word gained general acceptance once used by the influential Swedish palynologist Gunnar Erdtman .
Pollen analysis in North America stemmed from Phyllis Draper , an MS student under Sears at the University of Oklahoma. During her time as a student, she developed the first pollen diagram from a sample that depicted the percentage of several species at different depths at Curtis Bog. This was the introduction of pollen analysis in North America; [ 21 ] pollen diagrams today still often remain in the same format with depth on the y-axis and abundances of species on the x-axis.
Pollen analysis advanced rapidly in this period due to advances in optics and computers. Much of the science was revised by Johannes Iversen and Knut Fægri in their textbook on the subject. [ 22 ]
Chemical digestion follows a number of steps. [ 23 ] Initially the only chemical treatment used by researchers was treatment with potassium hydroxide (KOH) to remove humic substances; defloculation was accomplished through surface treatment or ultra-sonic treatment, although sonification may cause the pollen exine to rupture. [ 14 ] In 1924, the use of hydrofluoric acid (HF) to digest silicate minerals was introduced by Assarson and Granlund, greatly reducing the amount of time required to scan slides for palynomorphs. [ 24 ]
Palynological studies using peats presented a particular challenge because of the presence of well-preserved organic material, including fine rootlets, moss leaflets and organic litter. This was the last major challenge in the chemical preparation of materials for palynological study. Acetolysis was developed by Gunnar Erdtman and his brother to remove these fine cellulose materials by dissolving them. [ 25 ] In acetolysis the specimen is treated with acetic anhydride and sulfuric acid , dissolving cellulistic materials and thus providing better visibility for palynomorphs. [ 26 ]
Some steps of the chemical treatments require special care for safety reasons, in particular the use of HF which diffuses very fast through the skin and, causes severe chemical burns, and can be fatal. [ 27 ]
Another treatment includes kerosene flotation for chitinous materials.
Once samples have been prepared chemically, they are mounted on microscope slides using silicon oil, glycerol or glycerol-jelly and examined using light microscopy or mounted on a stub for scanning electron microscopy .
Researchers will often study either modern samples from a number of unique sites within a given area, or samples from a single site with a record through time, such as samples obtained from peat or lake sediments. More recent studies have used the modern analog technique in which paleo-samples are compared to modern samples for which the parent vegetation is known. [ 28 ]
When the slides are observed under a microscope, the researcher counts the number of grains of each pollen taxon. This record is next used to produce a pollen diagram . These data can be used to detect anthropogenic effects, such as logging, [ 29 ] traditional patterns of land use [ 30 ] or long term changes in regional climate [ 31 ]
Palynology can be applied to problems in many scientific disciplines including geology , botany , paleontology , archaeology , pedology (soil study) , and physical geography : | https://en.wikipedia.org/wiki/Palynology |
Palytoxin , PTX [ 3 ] or PLTX [ 4 ] is an intense vasoconstrictor , [ 1 ] and is considered to be one of the most poisonous non- protein substances known, second only to maitotoxin in terms of toxicity in mice. [ 5 ]
Palytoxin is a polyhydroxylated and partially unsaturated compound (8 double bonds) with a long carbon chain. It has water-soluble and fat-soluble parts, 40 hydroxy groups and 64 chiral centers . Due to chirality and possible double bond cis-trans isomerism , it has over 10 21 alternative stereoisomers . It is thermostable , and treatment with boiling water does not remove its toxicity. It remains stable in aqueous solutions for prolonged periods but rapidly decomposes and loses its toxicity in acidic or alkaline solutions. It has multiple analogues with a similar structure like ostreocin-D, mascarenotoxin-A and -B. [ 3 ]
Palytoxin occurs at least in tropics and subtropics where it is made by Palythoa corals and Ostreopsis dinoflagellates , or possibly by bacteria occurring in these organisms. It can be found in many more species like fish and crabs due to the process of biomagnification . It can also be found in organisms living close to palytoxin producing organisms like sponges , mussels , starfish and cnidaria . [ 3 ]
People are rarely exposed to palytoxin. Exposures have happened in people who have eaten sea animals like fish and crabs, but also in aquarium hobbyists who have handled Palythoa corals incorrectly and in those who have been exposed to certain algal blooms . [ 2 ]
Palytoxin targets the sodium-potassium pump protein by locking it into a position where it allows passive transport of both sodium and potassium ions, thereby destroying the ion gradient that is essential for life. [ 6 ] As palytoxin can affect every type of cell in the body, the symptoms can be very different for the various routes of exposure. [ 2 ]
Palytoxin's planar chemical structure was solved in 1981 by two research groups independently from each other. [ 3 ] Stereochemistry was solved in 1982. [ 7 ] [ 8 ] [ 9 ] Palytoxin carboxylic acid was synthesized by Yoshito Kishi and colleagues in 1989 [ 10 ] and actual palytoxin in 1994 by Kishi and Suh. [ 11 ]
According to an ancient Hawaiian legend, on the island of Maui near the harbor of Hana there was a village of fishermen haunted by a curse. Upon their return from the sea, one of the fishermen would go missing. One day, enraged by another loss, the fishermen assaulted a hunchbacked hermit deemed to be the culprit of the town's misery. While ripping the cloak off the hermit the villagers were shocked because they uncovered rows of sharp and triangular teeth within huge jaws. A shark god had been caught. It was clear that the missing villagers had been eaten by the god on their journeys to the sea. The men mercilessly tore the shark god into pieces, burned him and threw the ashes into a tide pool near the harbor of Hana. Shortly after, a thick brown "moss" started to grow on the walls of the tide pool causing instant death to victims hit by spears smeared with the moss. Thus was the evil of the demon. [ 12 ] [ 13 ] The moss growing in the cursed tide pool became known as " limu-make-o-Hana " which literally means "seaweed of death from Hana." The Hawaiians believed that an ill curse came over them if they tried to collect the deadly "seaweed". [ 14 ] [ 13 ]
Palytoxin was first isolated, named and described from Palythoa toxica by Moore and Scheuer in a study published in 1971. They measured that its molar mass is approximately 3300 g/mol. They also identified it to be the substance that was probably responsible for the toxicity of P. toxica , but it was uncertain at the time if the coral also had other toxic compounds in it. [ 14 ] It was then assessed by Walsh and Bowers that the limu-make-o-Hana was not a seaweed but a zoanthid coral, subsequently described as Palythoa toxica . [ 15 ] Moore and Scheuer were aware of the study that Walsh and Bowers were writing. [ 14 ]
In 1978 by plasmadesorption the mass of the palytoxin was measured to be 2861 g/mol and that it had 8 double bonds . [ 16 ] As palytoxin is such a large molecule, it took some time before the complete structure (including stereochemistry ) was elucidated. Uemura et al. solved its planar chemical structure first and published their results in January 1981. [ 17 ] [ 18 ] [ 19 ] Shortly afterwards Moore and Bartolini solved the same structure and published their results in May 1981. [ 20 ] Forementioned groups solved the structure independently from each other. [ 3 ] Palytoxin's stereochemistry was solved first by Moore et al. in June 1982 [ 7 ] and then by Uemura et al. in December in a study of four parts. [ 8 ] [ 9 ]
Palytoxin carboxylic acid was synthesized in 1989 by the group of Harvard professor Yoshito Kishi . Synthesis happened in 8 parts and then the parts were joined to form the carboxylic acid. [ 10 ] In 1994 Kishi et al. succeeded in making the actual palytoxin from this carboxylic acid. [ 11 ] The accomplishment of palytoxin carboxylic acid synthesis was described as "the Mount Everest of organic synthesis, the largest single molecule that anyone has ever even thought about making" by Crawford in 1989. [ 21 ]
Direct observation of the crystal structure of palytoxin was made in 2022 using microcrystal electron diffraction and an antibody named scFv. Palytoxin is found to fold into a hairpin structure which, according to simulation, would facilitate its binding with the Na + /K + -ATPase. [ 22 ]
Some of the organisms that contain palytoxin or its close analogues are listed below. These are either able to produce these compounds or have been found to contain them in some occasions due to bioaccumulation . [ 23 ]
Such corals are Palythoa caribeaorum , P. mammilosa , P. tuberculosa , P. toxica , P. vestitus , P. aff. margaritae , Zoanthus soanderi and Z. sociatus . [ 24 ]
Such dinoflagellates are Ostreopsis lenticularis , O. siamensis , O. mascarensis and O. ovata . [ 24 ]
Such fish are scrawled filefish , pinktail triggerfish , Ypsiscarus ovifrons , Decapterus macrosoma (shortfin scad), bluestripe herring and Epinephelus sp . [ 24 ]
Such crabs are Lophozozymus pictor , Demania reynaudii and gaudy clown crab . [ 24 ]
Certain bacteria might be able to produce palytoxin and may be the actual producers in some of the organisms listed above. Bacteria that have some evidence of palytoxin or its analogue production include Pseudomonas , Brevibacterium , Acinetobacter , Bacillus cereus , Vibrio sp. ja Aeromonas . [ 3 ]
The toxicity of palytoxin is due to its binding to external part of Na + /K + -ATPase (the sodium – potassium pump), [ 3 ] where it interacts with the natural binding site of ouabain with very high affinity. Na + /K + -ATPase is a transmembrane protein , which is found on the surface of every vertebrate cell. The sodium–potassium pump is necessary for viability of all cells , and this explains the fact that palytoxin affects all cells. [ 24 ] Through this channel, which it forms within the sodium–potassium pump, monovalent positive ions such as sodium and potassium can diffuse freely, thereby destroying the ion gradient of the cell. [ 25 ] [ 26 ] Once palytoxin is bound to the pump, it flips constantly between open and normal conformations . The open conformation is more likely (over 90% probability). If palytoxin detaches, the pump will return to closed conformation. In open conformation, millions of ions diffuse through the pump per second, whereas only about one hundred ions per second are transported through a normally functioning transporter. [ 6 ]
Loss of ion gradient leads to death and hemolysis of red blood cells , for example, and also to violent contractions of heart and other muscle cells . [ 3 ]
First evidence of the mechanism described above was obtained in 1981 and the proposed mechanism was published in 1982. [ 27 ] As the mechanism of action of palytoxin was so unlike any other, it was initially not widely accepted. This was primarily because it was not expected that a pump which provides active transport , could become an ion channel by binding of a compound such as palytoxin. [ 24 ] Therefore, there were some alternative hypotheses, which were reviewed by Frelin and van Renterghem in 1995. [ 28 ] The breakthrough research which is seen as proof for the sodium–potassium pump mechanism was performed in yeast cells ( Saccharomyces cerevisiae ). These cells do not have the sodium–potassium pump, and hence palytoxin does not affect them. But once they were given the DNA to encode for complete sheep Na + /K + -ATPase, they were killed by palytoxin. [ 29 ]
From intravenous (IV) animal studies the toxic dose ( LD 50 ) of palytoxin via IV for humans has been estimated by extrapolation to be between 2.3 and 31.5 micrograms (μg) of palytoxin. [ 3 ] [ 30 ] An acute oral reference dose has been suggested to be 64 μg for a person with weight of 60 kg. [ 3 ] Acute reference dose means a dose that can be safely ingested over a short period of time, usually during one meal or one day. [ 31 ]
In comparison to IV injection, the toxicity of palytoxin in various animals via intramuscular and subcutaneous injections are 2.5 and 4–30 times higher, respectively. Upon ingestion the toxicity in animals has been 200 times less than via IV. [ 2 ] In the table below, there are listed some LD 50 values for partially pure palytoxin obtained from different Palythoa . These values represent the amount of palytoxin required to kill half of the test animals. Values are in micrograms (μg) per kilogram of the animal's weight and have been measured 24 hours after the initial exposure. [ 3 ]
An early toxicological characterization classified palytoxin as "relatively non-toxic" after intragastric administration to rats. The lethal dose (LD 50 ) was greater than 40 μg/kg. The LD 50 after parenteral administration was lower than 1 μg/kg. [ 32 ] However the doubtful purity of this study increased because of uncertainty concerning the toxicological data. In 1974, the structure of palytoxin was not completely elucidated and the molecular weight was a lot higher (3300 Da instead of 2681 Da). A 2004 study discovered an LD 50 of 510 μg/kg after intragastric administration in mice, but histological or biochemical information was missing. (Rhodes and Munday, 2004) Furthermore, palytoxin was not lethal to mice given an oral dose of 200 μg/kg. [ 33 ] It was also found that palytoxin is very toxic after intraperitoneal injection. The LD 50 in mice was less than 1 μg/kg. [ 34 ] As toxin-producing organisms spread to temperate climates and palytoxin-contaminated shellfish were discovered in the Mediterranean Sea [ 35 ] a study was done to better define the toxic effects of palytoxin after oral exposure in mice. Palytoxin was lethal from 600 μg/kg doses. The number of deaths were dose-dependent and the LD 50 calculated to be 767 μg/kg. This is comparable to the LD 50 of 510 μg/kg referred by Munday (2008). The toxicity was not different if the mice had some food in their stomach. The oral toxicity is several times lower than the intraperitoneal toxicity. One of the possible causes of this behavior is that palytoxin is a very big hydrophilic molecule and therefore the absorption could be less efficient through the gastrointestinal tract than through the peritoneum. [ 36 ] A recent study by Fernandez et al. [ 37 ] further investigated on this issue using an in vitro model of intestinal permeability with differentiated monolayers of human colonic Caco-2 cells, confirming that palytoxin was unable to cross the intestinal barrier significantly, despite the damage the toxin exerted on cells and on the integrity of the monolayer. The same study also revealed that palytoxin does not affect tight-junctions on such cells. Palytoxin is most toxic after intravenous injection. The LD 50 in mice is 0.045 μg/kg and in rats 0.089 μg/kg. In other mammals (rabbits, dogs, monkeys and guinea pigs) the LD 50 is ranged between 0.025 and 0.45 μg/kg. They all died in several minutes from heart failure. [ 2 ] The lethal dose for mice by the intratracheal route is above 2 μg/kg in 2 hours. Palytoxin is also very toxic after intramuscular or subcutaneous injection. No toxicity is found after intrarectal administration. Palytoxin is not lethal when topically applied to skin or eyes. [ 33 ] Palytoxin can travel in water vapor and cause poisoning by inhalation.
In this context, despite an increase in reports of palytoxin contaminated seafood in temperate waters (i.e., Mediterranean Sea), there are no validated and accepted protocols for the detection and quantification of this class of biomolecules. However, in recent years, many methodologies have been described with particular attention on the development of new techniques for the ultrasensitive detection of palytoxin in real matrix such as mussels and microalgae (based on LC-MS-MS [ 38 ] or immunoassay [ 39 ] ).
The symptoms of palytoxin poisoning and how quickly they appear depend partially on how much and through what route one has been exposed, e.g. if the poison has been inhaled or if the exposure has happened via skin. [ 2 ]
In some non-lethal cases the symptoms in people have appeared in 6–8 hours after inhalation or skin exposure, and have lasted for 1–2 days. [ 5 ] In different animals the symptoms have appeared in 30–60 minutes after intravenous injection and after 4 hours of eye-exposure. [ 2 ]
The most common complication of severe palytoxin poisoning is rhabdomyolysis . This involves skeletal muscle breakdown and the leakage of intracellular contents into the blood. Other symptoms in humans are bitter/metallic taste, abdominal cramps, nausea, vomiting, diarrhea, mild to acute lethargy , tingling, slow heart rate , kidney failure , impairment of sensation, muscle spasms, tremor myalgia , cyanosis , and respiratory distress. In lethal cases palytoxin usually causes death by cardiac arrest via myocardial injury. [ 3 ] [ 40 ]
Exposure to aerosols of palytoxin analogue ovatoxin-a have resulted mainly in respiratory illness. Other symptoms caused by these aerosols included fever associated with serious respiratory disturbances, such as bronchoconstriction , mild dyspnea, and wheezes, while conjunctivitis was observed in some cases. [ 40 ] [ 3 ]
Clupeotoxism , poisoning after consuming clupeoid fish , is also suggested to be caused by palytoxin. Neurological and gastrointestinal disturbances are associated with clupeotoxism. [ 40 ] Haff disease might be related to palytoxin and is characterized by rhabdomyolysis and gastrointestinal problems. [ 5 ] In addition to ciguatoxins , palytoxin could also be a causative agent of ciguatera seafood poisoning. [ 2 ]
There is no antidote for palytoxin. Only the symptoms can be alleviated. [ 41 ]
Animal studies have shown that vasodilators , such as papaverine and isosorbide dinitrate , can be used as antidotes . The animal experiments only showed benefit if the antidotes were injected into the heart immediately following exposure. [ 32 ]
There have been cases where people died after eating foods containing palytoxin or poisons similar to it. In the Philippines people died after eating Demania crabs. [ 42 ] After eating bluestripe herring some people died in Madagascar. [ 43 ] People who had eaten smoked mackerel and parrotfish experienced near fatal poisoning in Hawaii [ 44 ] and Japan respectively. [ 45 ]
There have been palytoxin poisonings through skin absorption e.g. in people who handled corals without gloves in their home aquariums in Germany [ 46 ] and the USA. [ 2 ]
Cases of inhalation are also known. A man inhaled palytoxin when he tried to kill a Palythoa in his aquarium with boiling water. [ 47 ] In 2018, six people from Steventon, Oxfordshire , England were hospitalized after probable exposure by inhalation to "palytoxins" which were released by coral that was being removed from a personal aquarium. Four firefighters, who responded to the incident, were also hospitalized. The patients presented "flu-like symptoms" and eye-irritation. [ 48 ] Also in 2018, a woman in Cedar Park, Texas was poisoned when she scraped growing algae from Palythoa polyps in her home aquarium. Other members of the family, including children, also reportedly fell ill. The woman described intense flu-like respiratory symptoms and high fever within hours of inhalation and was hospitalized. Confused physicians initially misdiagnosed the palytoxin poisoning to viral infection. The toxin also killed most of the fish in the aquarium. Many aquatic hobbyists purchase the coral for their bright coloring unaware of the toxins present and the danger of the toxin if it is disturbed. [ 49 ] A similar event occurred in the UK in August 2019. [ 50 ]
A formerly unknown derivative of palytoxin, ovatoxin-a, produced as a marine aerosol by the tropical dinoflagellate Ostreopsis ovata caused hundreds of people in Genoa , Italy, to fall ill. In 2005 and 2006 blooms of these algae occurred in the Mediterranean sea. All those affected needed hospitalization. Symptoms were high fever, coughs and wheezes. [ 13 ] | https://en.wikipedia.org/wiki/Palytoxin |
The Pan-African Payment and Settlement System (PAPSS) is a Pan-African real-time gross settlement (RTGS) infrastructure for cross-border payments in distinct local currencies. It was publicly launched on January 13, 2022 [ 1 ] by the African Union (AU) and the African Export-Import Bank (Afreximbank) to compliment trading under the African Continental Free Trade Area (AfCFTA) with further future planned rollout in the Caribbean region by end of 2024. [ 2 ]
PAPSS was first mentioned on the 7 July 2019 [ 3 ] at the 12th Extraordinary Session of The African Union Assembly in Niamey , Niger to support the launch of the operational phase of AfCFTA . [ 4 ] It started as a pilot project among the 6 countries in the West African Monetary Zone (WAMZ) before it became publicly available. [ 3 ] In 2023 several nations of the Caribbean Community [ 5 ] began to implement a pilot framework for using the Pan-African Payment and Settlement System to facilitate trade between the Caribbean and Africa. [ 6 ] [ 7 ] The move coincided with the Afreximbank agreeing to designate the Caribbean region as a diaspora-related sixth region of Africa and opened an office in the Caribbean island of Barbados. PAPSS is slated to be rolled out among Caribbean countries which have already signed the agreement with Afreximbank, and is slated to come on stream in Q4, 2024. [ 8 ]
Here is a simplified overview of how PAPSS works [ 9 ]
On a daily basis, PAPSS settles the balance of all of the transactions among individual African currencies, netting them out prior to midnight. Central Banks then resolve the remaining difference. The payments and settlement process starts again from net zero the next day. [ 11 ]
These are the banks enrolled in PAPSS (December 2024) [ 12 ]
Official website | https://en.wikipedia.org/wiki/Pan-African_Payment_and_Settlement_System |
Pan-Andromeda Archaeological Survey (PAndAS) is a large-scale astronomical survey using the Canada-France-Hawaii Telescope .
The survey is exploring the structure and content of the Andromeda Galaxy (M31) and its neighbour, the Triangulum Galaxy (M33). Clues to the formation of these galaxies may lie within the vast space being studied. PAndAS is searching for this history, hence the term " galactic archaeology ".
The project is headed by Dr. Alan McConnachie at the Herzberg Institute of Astrophysics (NRC-HIA), and involves over twenty five investigators from that institute, as well as from universities in Canada, France, the United States, the United Kingdom, Germany, and Australia. [ 1 ]
This astronomy -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Pan-Andromeda_Archaeological_Survey |
Pan-T antigens are antigens found on all T cells .
They include CD2 , CD3 , CD5 and CD7 . [ 1 ]
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Pan-T_antigens |
Pan-assay interference compounds ( PAINS ) are chemical compounds that often give false positive results in high-throughput screens . [ 1 ] PAINS tend to react nonspecifically with numerous biological targets rather than specifically affecting one desired target. [ 2 ] A number of disruptive functional groups are shared by many PAINS. [ 2 ] [ 3 ] [ 4 ]
While a number of filters have been proposed and are used in virtual screening and computer-aided drug design , [ 5 ] the accuracy of filters with regard to compounds they flag and don't flag has been criticized. [ 6 ]
Common PAINS include toxoflavin , isothiazolones , hydroxyphenyl hydrazones , curcumin , phenol-sulfonamides , rhodanines , enones , quinones , and catechols such as luteolin and various other flavonoids . [ 7 ]
This pharmacology -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Pan-assay_interference_compounds |
In the fields of molecular biology and genetics , a pan-genome ( pangenome or supragenome ) is the entire set of genes from all strains within a clade . More generally, it is the union of all the genomes of a clade. [ 2 ] [ 3 ] [ 4 ] [ 5 ] The pan-genome can be broken down into a "core pangenome" that contains genes present in all individuals, a "shell pangenome" that contains genes present in two or more strains, and a "cloud pangenome" that contains genes only found in a single strain. [ 3 ] [ 4 ] [ 6 ] Some authors also refer to the cloud genome as "accessory genome" containing 'dispensable' genes present in a subset of the strains and strain-specific genes. [ 2 ] [ 3 ] [ 4 ] Note that the use of the term 'dispensable' has been questioned, at least in plant genomes, as accessory genes play "an important role in genome evolution and in the complex interplay between the genome and the environment". [ 5 ] The field of study of pangenomes is called pangenomics. [ 2 ]
The genetic repertoire of a bacterial species is much larger than the gene content of an individual strain. [ 7 ] Some species have open (or extensive) pangenomes, while others have closed pangenomes. [ 2 ] For species with a closed pan-genome, very few genes are added per sequenced genome (after sequencing many strains), and the size of the full pangenome can be theoretically predicted. Species with an open pangenome have enough genes added per additional sequenced genome that predicting the size of the full pangenome is impossible. [ 4 ] Population size and niche versatility have been suggested as the most influential factors in determining pan-genome size. [ 2 ]
Pangenomes were originally constructed for species of bacteria and archaea , but more recently eukaryotic pan-genomes have been developed, particularly for plant species. Plant studies have shown that pan-genome dynamics are linked to transposable elements. [ 8 ] [ 9 ] [ 10 ] [ 11 ] The significance of the pan-genome arises in an evolutionary context, especially with relevance to metagenomics , [ 12 ] but is also used in a broader genomics context. [ 13 ] An open access book reviewing the pangenome concept and its implications, edited by Tettelin and Medini, was published in the spring of 2020. [ 14 ]
The term 'pangenome' was defined with its current meaning by Tettelin et al. in 2005; [ 2 ] it derives 'pan' from the Greek word παν , meaning 'whole' or 'everything', while the genome is a commonly used term to describe an organism's complete genetic material. Tettelin et al. applied the term specifically to bacteria , whose pangenome "includes a core genome containing genes present in all strains and a dispensable genome composed of genes absent from one or more strains and genes that are unique to each strain." [ 2 ]
Is the part of the pangenome that is shared by every genome in the tested set. Some authors have divided the core pangenome in hard core, those families of homologous genes that has at least one copy of the family shared by every genome (100% of genomes) and the soft core or extended core, [ 15 ] those families distributed above a certain threshold (90%). In a study that involves the pangenomes of Bacillus cereus and Staphylococcus aureus , some of them isolated from the international space station, the thresholds used for segmenting the pangenomes were as follows: "Cloud", "Shell", and "Core" corresponding to gene families with presence in <10%, 10–95%, and >95% of the genomes, respectively. [ 16 ]
The core genome size and proportion to the pangenome depends on several factors, but it is especially dependent on the phylogenetic similarity of the considered genomes. For example, the core of two identical genomes would also be the complete pangenome. The core of a genus will always be smaller than the core genome of a species. Genes that belong to the core genome are often related to house keeping functions and primary metabolism of the lineage, nevertheless, the core gene can also contain some genes that differentiate the species from other species of the genus, i.e. that may be related pathogenicity to niche adaptation. [ 17 ]
Is the part of the pangenome shared by the majority of the genomes in a pangenome. [ 18 ] There is not a universally accepted threshold to define the shell genome, some authors consider a gene family as part of the shell pangenome if it shared by more than 50% of the genomes in the pangenome. [ 19 ] A family can be part of the shell by several evolutive dynamics, for example by gene loss in a lineage where it was previously part of the core genome, such is the case of enzymes in the tryptophan operon in Actinomyces , [ 20 ] or by gene gain and fixation of a gene family that was previously part of the dispensable genome such is the case of trpF gene in several Corynebacterium species. [ 21 ]
The cloud genome consists of those gene families shared by a minimal subset of the genomes in the pangenome, [ 22 ] it includes singletons or genes present in only one of the genomes. It is also known as the peripheral genome, or accessory genome. Gene families in this category are often related to ecological adaptation. [ citation needed ]
The pan-genome can be somewhat arbitrarily classified as open or closed based on the alpha value of Heaps' law : N = k n − α {\displaystyle N=kn^{-\alpha }} [ 23 ] [ 15 ]
Usually, the pangenome software can calculate the parameters of the Heap law that best describe the behavior of the data.
An open pangenome occurs when the number of new gene families in one taxonomic lineage keeps increasing without appearing to be asymptotic regardless how many new genomes are added to the pangenome. Escherichia coli is an example of a species with an open pangenome. Any E. coli genome size is in the range of 4000–5000 genes and the pangenome size estimated for this species with approximately 2000 genomes is composed by 89,000 different gene families. [ 24 ] The pangenome of the domain bacteria is also considered to be open.
A closed pangenome occurs in a lineage when only few gene families are added when new genomes are incorporated into the pangenome analysis, and the total amount of gene families in the pangenome seem to be asymptotic to one number. It is believed that parasitism and species that are specialists in some ecological niche tend to have closed pangenomes. Staphylococcus lugdunensis is an example of a commensal bacteria with closed pan-genome. [ 25 ]
The original pangenome concept was developed by Tettelin et al. [ 2 ] when they analyzed the genomes of eight isolates of Streptococcus agalactiae , where they described a core genome shared by all isolates, accounting for approximately 80% of any single genome, plus a dispensable genome consisting of partially shared and strain-specific genes. Extrapolation suggested that the gene reservoir in the S. agalactiae pan-genome is vast and that new unique genes would continue to be identified even after sequencing hundreds of genomes. [ 2 ] The pangenome comprises the entirety of the genes discovered in the sequenced genomes of a given microbial species and it can change when new genomes are sequenced and incorporated into the analysis. [ citation needed ]
The pangenome of a genomic lineage accounts for the intra lineage gene content variability. Pangenome evolves due to: gene duplication, gene gain and loss dynamics and interaction of the genome with mobile elements that are shaped by selection and drift. [ 26 ] Some studies point that prokaryotes pangenomes are the result of adaptive, not neutral evolution that confer species the ability to migrate to new niches. [ 27 ]
The supergenome can be thought of as the real pangenome size if all genomes from a species were sequenced. [ 28 ] It is defined as all genes accessible for being gained by a certain species. It cannot be calculated directly but its size can be estimated by the pangenome size calculated from the available genome data. Estimating the size of the cloud genome can be troubling because of its dependence on the occurrence of rare genes and genomes. In 2011 genomic fluidity was proposed as a measure to categorize the gene-level similarity among groups of sequenced isolates. [ 29 ] In some lineages the supergenomes did appear infinite , [ 30 ] as is the case of the Bacteria domain. [ 31 ]
'Metapangenome' has been defined as the outcome of the analysis of pangenomes in conjunction with the environment where the abundance and prevalence of gene clusters and genomes are recovered through shotgun metagenomes. [ 32 ] The combination of metagenomes with pangenomes, also referred to as "metapangenomics", reveals the population-level results of habitat-specific filtering of the pangenomic gene pool. [ 33 ]
Other authors consider that Metapangenomics expands the concept of pangenome by incorporating gene sequences obtained from uncultivated microorganisms by a metagenomics approach. A metapangenome comprises both sequences from metagenome-assembled genomes ( MAGs ) and from genomes obtained from cultivated microorganisms. [ 34 ] Metapangenomics has been applied to assess diversity of a community, microbial niche adaptation, microbial evolution, functional activities, and interaction networks of the community. [ 35 ] The Anvi'o platform developed a workflow that integrates analysis and visualization of metapangenomes by generating pangenomes and study them in conjunction with metagenomes. [ 32 ]
In 2018, 87% of the available whole genome sequences were bacteria fueling researchers interest in calculating prokaryote pangenomes at different taxonomic levels. [ 22 ] In 2015, the pangenome of 44 strains of Streptococcus pneumoniae bacteria shows few new genes discovered with each new genome sequenced (see figure). In fact, the predicted number of new genes dropped to zero when the number of genomes exceeds 50 (note, however, that this is not a pattern found in all species). This would mean that S. pneumoniae has a 'closed pangenome'. [ 37 ] The main source of new genes in S. pneumoniae was Streptococcus mitis from which genes were transferred horizontally . The pan-genome size of S. pneumoniae increased logarithmically with the number of strains and linearly with the number of polymorphic sites of the sampled genomes, suggesting that acquired genes accumulate proportionately to the age of clones. [ 36 ] Another example of prokaryote pan-genome is Prochlorococcus , the core genome set is much smaller than the pangenome, which is used by different ecotypes of Prochlorococcus . [ 38 ] Open pan-genome has been observed in environmental isolates such as Alcaligenes sp. [ 39 ] and Serratia sp., [ 40 ] showing a sympatric lifestyle. Nevertheless, open pangenome is not exclusive to free living microorganisms, a 2015 study on Prevotella bacteria isolated from humans , compared the gene repertoires of its species derived from different body sites of human. It also reported an open pan-genome showing vast diversity of gene pool. [ 41 ]
Archaea also have some pangenome studies. Halobacteria pangenome shows the following gene families in the pangenome subsets: core (300), variable components (Softcore: 998, Cloud:36531, Shell:11784). [ 42 ]
Eukaryote organisms such as fungi , animals and plants have also shown evidence of pangenomes. In four fungi species whose pangenome has been studied, between 80 and 90% of gene models were found as core genes. The remaining accessory genes were mainly involved in pathogenesis and antimicrobial resistance. [ 43 ]
In animals, the human pangenome is being studied. In 2010 a study estimated that a complete human pan-genome would contain ~19–40 Megabases of novel sequence not present in the extant reference human genome . [ 44 ] The Human Pangenome consortium has the goal to acknowledge the human genome diversity. In 2023, a draft human pangenome reference was published. [ 45 ] It is based on 47 diploid genomes from persons of varied ethnicity. [ 45 ] Plans are underway for an improved reference capturing still more biodiversity from a still wider sample. [ 45 ]
Among plants, there are examples of pangenome studies in model species, both diploid [ 9 ] and polyploid, [ 10 ] and a growing list of crops. [ 46 ] [ 47 ] Pangenomes have shown promise as a tool in plant breeding by accounting for structural variants and SNPs in non-reference genomes, which helps to solve the problem of missing heritability that persists in genome wide association studies . [ 48 ] An emerging plant-based concept is that of pan-NLRome, which is the repertoire of nucleotide-binding leucine-rich repeat (NLR) proteins, intracellular immune receptors that recognize pathogen proteins and confer disease resistance. [ 49 ]
Virus does not necessarily have genes extensively shared by clades such as is the case of 16S in bacteria , and therefore the core genome of the full Virus Domain is empty. Nevertheless, several studies have calculated the pangenome of some viral lineages. The core genome from six species of pandoraviruses comprises 352 gene families only 4.7% of the pangenome, resulting in an open pangenome. [ 50 ]
The number of sequenced genomes is continuously growing "simply scaling up established bioinformatics pipelines will not be sufficient for leveraging the full potential of such rich genomic data sets". [ 51 ] Pan-genome graph constructions are emerging data structure technique designed to represent pangenomes and to efficiently map reads to them. They have been reviewed by Eizenga et al. [ 52 ]
As interest in pangenomes increased, there have been several software tools developed to help analyze this kind of data.
To start a pangenomic analysis the first step is the homogenization of genome annotation. [ 23 ] The same software should be used to annotate all genomes used, such as GeneMark [ 53 ] or RAST. [ 54 ] In 2015, a group reviewed the different kinds of analyses and tools a researcher may have available. [ 55 ] There are seven kinds of software developed to analyze pangenomes: Those dedicated to cluster homologous genes; identify SNPs ; plot pangenomic profiles; build phylogenetic relationships of orthologous genes/families of strains/isolates; function-based searching; annotation and/or curation; and visualization. [ 55 ]
The two most cited software tools for pangenomic analysis at the end of 2014 [ 55 ] were Panseq [ 56 ] and the pan-genomes analysis pipeline (PGAP). [ 57 ] Other options include BPGA – A Pan-Genome Analysis Pipeline for prokaryotic genomes, [ 58 ] GET_HOMOLOGUES, [ 59 ] Roary. [ 60 ] and PanDelos. [ 61 ] In 2015 a review focused on prokaryote pangenomes [ 62 ] and another for plant pan-genomes were published. [ 63 ] Among the first software packages designed for plant pangenomes were PanTools. [ 64 ] and GET_HOMOLOGUES-EST. [ 11 ] [ 59 ] In 2018 panX was released, an interactive web tool that allows inspection of gene families evolutionary history. [ 65 ] panX can display an alignment of genomes, a phylogenetic tree, mapping of mutations and inference about gain and loss of the family on the core-genome phylogeny. In 2019 OrthoVenn 2.0 [ 66 ] allowed comparative visualization of families of homologous genes in Venn diagrams up to 12 genomes. In 2023, BRIDGEcereal was developed to survey and graph indel-based haplotypes from pan-genome through a gene model ID. [ 67 ]
In 2020 Anvi'o [ 1 ] was available as a multiomics platform that contains pangenomic and metapangenomic analyses as well as visualization workflows. In Anvi'o, genomes are displayed in concentrical circles and each radius represents a gene family, allowing for comparison of more than 100 genomes in its interactive visualization. In 2020, a computational comparison of tools for extracting gene-based pangenomic contents (such as GET_HOMOLOGUES, PanDelos, Roary, and others) has been released. [ 68 ] Tools were compared from a methodological perspective, analyzing the causes that lead a given methodology to outperform other tools. The analysis was performed by taking into account different bacterial populations, which are synthetically generated by changing evolutionary parameters. Results show a differentiation of the performance of each tool that depends on the composition of the input genomes. Again in 2020, several tools introduced a graphical representation of the pangenomes showing the contiguity of genes (PPanGGOLiN, [ 46 ] Panaroo [ 65 ] ).
Other software tools for pangenomics include Prodigal, Prokka, PanVis, PanTools, Pangenome Graph Builder (PGGB), PanX, Pagoo, and pgr-tk. [ 69 ] | https://en.wikipedia.org/wiki/Pan-genome |
The PanCam (Panoramic Camera) assembly is a set of two wide angle cameras for multi-spectral stereoscopic panoramic imaging, and a high resolution camera for colour imaging that has been designed to search for textural information or shapes that can be related to the presence of microorganisms on Mars . This camera assembly is part of the science payload on board the European Space Agency 's Rosalind Franklin rover , [ 3 ] tasked to search for biosignatures and biomarkers on Mars. The rover is planned to be launched in August–October 2022 and land on Mars in spring 2023. [ 2 ]
This instrument will provide stereo multispectral images , of the terrain nearby. PanCam are the "eyes" of the rover and its primary navigation system. PanCam will also provide the geological context of the sites being explored and help support the selection of the best sites to carry out exobiology studies, as well as assist in some aspect of atmospheric studies. [ 4 ] This system will also monitor the sample from the drill before it is crushed inside the rover, where the analytical instruments will perform a detailed chemical analysis. [ 4 ]
The Principal Investigator is Professor Andrew Coates of the Mullard Space Science Laboratory , University College London in the United Kingdom.
PanCam design includes the following major components: [ 5 ] | https://en.wikipedia.org/wiki/PanCam |
The Pan Africa Chemistry Network (PACN) connects chemists across Africa . [ 1 ] It was launched in London on 21 November 2007 and in Nairobi on 27 May 2008 by the Royal Society of Chemistry . [ 2 ] The PACN works to connect chemists across Africa and has five centres of excellence in analytical chemistry in Kenya , Ethiopia , Ghana and Nigeria . [ 3 ]
The aim of the PACN is: [ 3 ]
To enable a self-sustaining science base in Africa and to enhance the number of skilled scientists in Africa through networking, skills development and knowledge creation to support an increase in scientific output and its application to challenges.
In partnership with Syngenta , who donated £1 million over five years three PACN Centres of Excellence in Analytical Chemistry were established in Kenya, Ghana and Ethiopia. [ 4 ]
Since December 2011, Procter & Gamble have been working with the PACN and leading scientists and students to exchange knowledge, enhance skills and generate opportunities for innovation in the areas of hygiene, health and waste management. A Collaboration Lab at the University of Lagos in Nigeria was established which includes provision of analytical equipment and internships for Nigerian scientists to apply their knowledge to real life industry challenge. [ 5 ]
The PACN organises a number of events including an annual congress, GC-MS training [ 6 ] and scientific symposia. [ 7 ]
This article about an organization in Africa is a stub . You can help Wikipedia by expanding it .
This article about a chemistry organization is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Pan_Africa_Chemistry_Network |
The Pan American Association of Anatomy ( PAA ) is a public, nonprofit, scientific organization that brings together professionals engaged in the study of Anatomy and related sciences in the American continent.
The Pan American Association of Anatomy (PAA) was created in July 1966 in Mexico City at the 1st Pan American Congress of Anatomy, which was held together with the 3rd National Congress of the Mexican Society of Anatomy. [ 1 ] Its mentor was the Prof. Dr. Liberato J. A. Didio.
The need for a Pan American Association of Anatomy was proposed by Prof. Di Dio during the 74th meeting of the American Association of Anatomy [ 2 ] held in Chicago , USA, in March 1961.
Its objectives include stimulating the development and improvement of teaching and research of morphological sciences on the American continent, facilitating scientific exchange in all its aspects. Since then and through its meetings, it has spread and updated progress of morphological sciences on the American continent.
The PAA is a member of the International Federation of Associations of Anatomists (IFAA). [ 3 ]
The government of the Pan American Association of Anatomy consists of the general assembly (performed with partners in the congress), the board of directors (composed by advisers or delegates from each country) and the executive committee (headed by the president, who is elected by the general assembly).
There are two counselors or delegates for each American country concerned; one as owner and another alternate.
When the mandate of the president of the executive committee is finished, he is named honorary president of the association and he automatically joins the Honorary Presidents Committee of the PAA, which works with the executive committee.
The headquarters of the congresses vary from one congress to another, but they are always within the Americas and in a rotative form. The designation of the host country is resolved at the general assembly by a vote of its partners and it is usually held every 3 years.
Since 2013, the association executive committee has been chaired by Prof. Dr. Manuel Arteaga Martínez, from Mexico (2013–2017). The next Pan-American Congress of Anatomy will be held in Peru , 2017; its president is Prof. Dr. Germán Molina Albornoz, from Peru.
The statutes of the association and the Pan American Congress of Anatomy, adopted by majority vote by the general assembly of the association, can be found on the. [ 4 ]
In 50 years of association life, 18 congresses have been held, with an interval of 3 years (sometimes 2 years) between them. The following countries have hosted at least one congress: Argentina, Brazil, Canada, Costa Rica, Chile, Mexico, Peru, Uruguay, USA and Venezuela.
The Congress covers various topics of morphological sciences and related sciences that have application to the biology and health sciences, especially in medicine and dentistry. It involves research, teaching and medical care. In particular, issues related to development anatomy ( embryology ), microscopic anatomy ( histology and cytology ), human anatomy , veterinary anatomy , comparative anatomy , neuroanatomy , neurobiology , radiological anatomy, clinical anatomy, anthropology , biophysics and biochemistry , etc. are discussed.
In 2009, during the 43rd anniversary of the Pan American Association of Anatomy, the 1st Iberian-Latin-American Terminology Symposium (SILAT) was held, with the purpose of disseminating the International Morphological Terminology . Educational institutions of medical and other health areas which spoke Spanish and Portuguese used it on a daily basis. Its mentor was Prof. Dr. Rolando Cruz Gutiérrez.
Up today, there have been sixteen symposia: four in Costa Rica , two in Brazil , three in Mexico , four in Chile , two in Peru and one in Nicaragua . In these symposia, participants are divided into groups to work with the anatomical, histological and embryological terminology from the Terminology Committee ( FICAT ) of the International Federation of Associations of Anatomists (IFAA). Meetings are held every day. The symposia also develops the presentation of free papers concerning different aspects and considerations of terminology.
These groups of experts review, analyse and discuss the morphological terms; possible errors and defects in the studied structures are also discussed. It was determined that the future meetings are planned in other countries (such as Honduras, Ecuador, Argentina, etc.).
The PAA has the support of various magazines, which are the official organ of publication, showing summaries of scientific congresses communications and other aspects. They are: International Journal of Morphology (Revista Internacional de Morfología), [ 5 ] Brazilian Journal of Morphology Sciences, Venezuelan Magazine of Morphological Sciences and Medical Journal of Costa Rica and Central America.
Headquarters, dates and presidencies:
Headquarters, dates and presidencies: | https://en.wikipedia.org/wiki/Pan_American_Association_of_Anatomy |
Pan Britannica Industries Ltd ( PBI ) was a household and agrochemical formulation company incorporated in 1932 [ 1 ] and based at Britannica House, Stewardstone Road, Waltham Abbey and with a distribution presence in Wisbech in Cambridgeshire . PBI was, in common with many other UK household names, both a manufacturer and marketing organisation for both agricultural and horticultural products.
PBI produced many agro-chemical formulations for farmers, however it was perhaps best known for its product Baby Bio , a liquid plant food that came in a small perfume-shaped bottle. PBI was also the original publisher of the 'Expert' range of gardening books, starting with Be Your Own Gardening Expert written in 1958 by Dr D.G. Hessayon , [ 2 ] [ 3 ] who later became the company's chairman. [ 4 ]
The company was sold to Sumitomo Corporation on 28 September 1990, [ 1 ] [ 5 ] and rebranded as PBI Home & Garden in 1998. [ 6 ] In March 1999 the company was acquired by global conglomerate Bayer . The company has ceased production at Waltham Abbey, the works have been demolished and the site redeveloped for a Tesco supermarket. [ 7 ] The rebranded company, PBI Home and Garden, was dissolved in 2015. [ 8 ]
The company's formulation plant in Waltham Abbey was alleged to be at the centre and therefore the cause of a cancer hotspot. [ 9 ] [ 10 ] This was highlighted by Storyline, an investigative television programme by Carlton Television , in early 1993. Reports of an unusual occurrence of cancer around the plant and subsequent legal action taken by the residents were the basis for this programme. [ 11 ] | https://en.wikipedia.org/wiki/Pan_Britannica_Industries |
The pan amalgamation process is a method to extract silver from ore, using salt and copper(II) sulfate in addition to mercury . The process was widely used from 1609 through the 19th century; it is no longer used.
The patio process had been used to extract silver from ore since its invention in 1557. One drawback of the patio process was the long treatment time, usually weeks. Alvaro Alonso Barba invented the faster pan process (in Spanish the cazo or fondo process) in 1609 in Potosí , Bolivia , in which ore was mixed with salt and mercury (and sometimes copper(II) sulfate ) and heated in shallow copper vessels. The treatment time was reduced to 10 to 20 hours. Whether patio or pan amalgamation was used at a particular location often depended on climate (warmer conditions speeded the patio process) and the availability and cost of fuel to heat the pans. [ 1 ]
The amount of salt and copper(II) sulfate varied from one-quarter to ten pounds of one or the other, or both, per ton of ore treated. The loss of mercury in amalgamation processes was generally one to two times the weight of silver recovered.
The Washoe process, a variation of pan amalgamation, was developed in the 1860s by Almarin B. Paul and others, to work the ore from the Comstock Lode in Nevada , United States (Washoe was an early name for the area and the local tribe who still exists today; see Washoe Valley ). [ 2 ] : 41 In the Washoe process, the copper pans were replaced by iron tanks with mechanical agitators. Each tank ("pan") was circular, and commonly held 1,200 to 1,500 pounds of ore that had been crushed to sand size. Water was added to make a pulp, and 60 to 70 pounds of mercury, along with one-half to three pounds each of salt ( sodium chloride ) and bluestone ( copper(II) sulfate ) were also added. A circular iron plate called a muller was mounted on a vertical shaft and lowered into the pan, and was rotated to provide both agitation and additional grinding. Heat was delivered to the pans by steam pipes. The iron filings worn from the muller and pan proved to be an essential ingredient in the process. [ 3 ] [ 4 ]
A variation of the Washoe process was developed in the Reese River mining district around Austin, Nevada . The Washoe process was found not to work well for ores with arsenic or antimony sulfides , or with galena or sphalerite . In 1869, Carl A. Stetefeldt of Reno found that roasting the ore with salt converted the silver sulfides to silver chlorides , which could then be recovered in amalgamation pans. [ 5 ] The process was introduced in the Reese River District in 1879, with great success.
Other silver-mining districts using the Reese River process included Georgetown, Colorado , Caribou, Colorado , and Silver Cliff, Colorado . [ 6 ] | https://en.wikipedia.org/wiki/Pan_amalgamation |
Pan evaporation is a measurement that combines or integrates the effects of several climate elements: temperature, humidity, rain fall, drought dispersion, solar radiation, and wind. Evaporation is greatest on hot, windy, dry, sunny days; and is greatly reduced when clouds block the sun and when air is cool, calm, and humid. [ 1 ] Pan evaporation measurements enable farmers and ranchers to understand how much water their crops will need. [ 2 ]
An evaporation pan is used to hold water during observations for the determination of the quantity of evaporation at a given location. Such pans are of varying sizes and shapes, the most commonly used being circular or square. [ 3 ] The best known of the pans are the "Class A" evaporation pan and the "Sunken Colorado Pan". [ 4 ] In Europe, India and South Africa, a Symon's Pan (or sometimes Symon's Tank) is used. Often the evaporation pans are automated with water level sensors and a small weather station is located nearby.
A variety of evaporation pans are used throughout the world. There are formulas for converting from one type of pan to another and to measures representative of the environment. [ 5 ] Also, research has been done about the installation practices of evaporation pans so that they can make more reliable and repeatable measurements. [ 6 ]
In the United States, the National Weather Service has standardized its measurements on the Class A evaporation pan , a cylinder with a diameter of 47.5 in (120.7 cm) that has a depth of 10 in (25 cm). The pan rests on a carefully leveled, wooden base and is often enclosed by a chain link fence to prevent animals drinking from it. Evaporation is measured daily as the depth of water (in inches) evaporates from the pan. The measurement day begins with the pan filled to exactly two inches (5 cm) from the pan top. At the end of 24 hours, the amount of water to refill the pan to exactly two inches from its top is measured.
If precipitation occurs in the 24-hour period, it is taken into account in calculating the evaporation. Sometimes precipitation is greater than evaporation, and measured increments of water must be dipped from the pan. Evaporation cannot be measured in a Class A pan when the pan's water surface is frozen.
The Class A Evaporation Pan is of limited use on days with rainfall events of >30mm (203mm rain gauge) unless it is emptied more than once per 24hours. Analysis of the daily rainfall and evaporation readings in areas with regular heavy rainfall events shows that almost without fail, on days with rainfall in excess of 30mm (203mm Rain Gauge) the daily evaporation is spuriously higher than other days in the same month where conditions more receptive to evaporation prevailed.
The most common and obvious error is in daily rainfall events of >55mm (203mm rain gauge) where the Class A Evaporation pan will likely overflow.
The less obvious, and therefore more concerning, is the influence of heavy or intense rainfall causing spuriously high daily evaporation totals without obvious overflow.
The sunken Colorado pan is square, 0.92 m (3 ft) on a side and 0.46 m (18 in.) deep and made of unpainted galvanized iron. As the name suggests, it is buried in the ground to within about 5 cm (2 in.) of its rim. Evaporation from a Sunken Colorado Pan can be compared with a Class A pan using conversion constants. The pan coefficient, on an annual basis, is about 0.8. [ 7 ]
The Symons pan or tank is a standard instrument of the UK Met Office. It is a steel container 1.83 m (6 ft) on a side and 0.61 m (2 ft) deep, sunk into the ground with an above-ground rim of 7.6–10 centimetres (3.0–3.9 in) and is painted black internally. Its evaporation rate is lower than the Class A pan and conversion factors must be used. [ 8 ]
Over the last 50 or so years, pan evaporation has been carefully monitored. For decades, pan evaporation measurements were not analyzed critically for long term trends. But in the 1990s scientists reported that the rate of evaporation was falling. [ 9 ] According to data, the downward trend had been observed all over the world except in a few places where it has increased. [ 10 ] [ 11 ] [ 12 ] [ 13 ]
It is currently theorized that, all other things being equal, as the global climate warms evaporation would increase proportionately and as a result, the hydrological cycle in its most general sense is bound to accelerate. [ 14 ] The downward trend of pan evaporation has since also been linked to a phenomenon called global dimming . [ 15 ] [ 16 ] In 2005 Wild et al. and Pinker et al. found that the "dimming" trend had reversed since about 1990. [ 17 ]
Other theories suggest that measurements have not taken the local environment into account. Since the local moisture level has increased in the local terrain, less water evaporates from the pan. This leads to false measurements and must be compensated for in the data analysis. Models accounting for additional local terrain moisture match global estimates. [ 18 ] In a different view, an analysis of pan trends in records from 154 instruments shows no coherency and pattern of statistically significant trends, with 38% decreasing, 42% no change and 20% increasing. Changes in the local environment are implicated, in which increasing tree density near the pans elevating surface friction and slowing local wind runs, reducing pan evaporation. The evaporation paradox is a result of ongoing changes in the nearby environments. [ 19 ]
Pan evaporation is used to estimate the evaporation from lakes. [ 20 ] There is a correlation between lake evaporation and pan evaporation. [ 21 ] Evaporation from a natural body of water is usually at a lower rate because the body of water does not have metal sides that get hot with the sun, and while light penetration in a pan is essentially uniform, light penetration in natural bodies of water will decrease as depth increases. Most textbooks suggest multiplying the pan evaporation by 0.75 to correct for this. [ citation needed ]
"It is generally agreed that the evaporation from pans has been decreasing for the past half century over many regions of the Earth. However, the significance of this negative trend, as regards terrestrial evaporation, is still somewhat controversial, and its implications for the global hydrologic cycle remain unclear. The controversy stems from the alternative views that these evaporative changes resulted, either from global radiative dimming, or from the complementary relationship between pan and terrestrial evaporation. Actually, these factors are not mutually exclusive but act concurrently." [ 22 ] | https://en.wikipedia.org/wiki/Pan_evaporation |
A pan trap is a type of insect trap used to sample the abundance and diversity of insects, primarily used to capture small Hymenoptera . [ 1 ] Pan traps are typically constructed with a bowl with shallow sides filled with water and soap or a preservative and killing agent. Yellow is the most commonly used color, [ 2 ] but other colors including blue, white, and red are used to target different insect species. [ 3 ]
A pan trap consists of a shallow bowl, typically made of colored plastic, filled with soapy water, salt, propylene glycol, antifreeze , or combinations of other preservatives and killing agents. Salt and propylene glycol are sometimes included as preservatives or to reduce evaporative water loss . Insects fly into the soapy water and are unable to escape and are preserved in the water for research usage. Some traps have been mounted on trees to sample the communities of parasitoid wasps of the invasive beetle, Emerald ash borer . [ 4 ]
The color of pan traps attracts diverse groups of flying insects. Some pollinators confuse the traps with natural flowers, causing the capture of flying pollinator species, including bees . [ 5 ] Some studies have suggested that bee species are more attracted and likely to be captured in blue or white pans compared to yellow pans. [ 3 ] [ 6 ] However, yellow and white pan traps consistently collect the largest number of species. [ 7 ] [ 8 ] | https://en.wikipedia.org/wiki/Pan_trap |
The Panama Canal fence is a term used for a variety of barriers built by the United States in the Panama Canal Zone to control movement in the zone for a variety of enforcement purposes. [ 1 ] [ 2 ] The Canal Zone, primarily consisting of the Panama Canal , a strip of land running from the Pacific Ocean to the Caribbean that was administered by the United States to various degrees until 1999 . The fence was occasionally dubbed a “fence of shame” [ 2 ] and "another Berlin Wall ” [ 2 ] by those opposed to continued United States presence and control of the Canal Zone. [ 3 ]
Panama gained independence [ 4 ] from Colombia with the assistance of the United States and was recognized as a separate state in 1903. [ 5 ] Diplomatic relations were established on November 13, 1903 between the United States and Panama . Both countries signed the Hay-Bunau-Varilla treaty . [ 5 ] [ 6 ] The treaty provided the United States with sovereignty over the Canal Zone. [ 7 ] In exchange, the Republic of Panama [ 6 ] received a $10 million payment and additional annual payments which began with the opening of the canal. In addition to this purchase from Panama, the United States bought the title to all lands in the Canal Zone, [ 8 ] [ 9 ] including a payment of $40 million to the French Canal Company for their properties. [ 10 ] [ 11 ] [ 12 ]
The treaty [ 6 ] granted the Canal Zone, a strip 5 miles (8.0 km) wide on each side of the Panama Canal, in perpetuity to the United States to build, manage, strengthen and defend an inter-oceanic canal. The Canal Zone became a U.S. territory and had its own police, [ 2 ] post offices, courts, television and radio stations. The approval of the treaty was a matter of significant and the continued existence of the canal became a matter of significant popular disapproval among Panamanian nationalists.
According to McPherson (2002) the construction started in the 1950s, after Panamanian students threatened a "patriotic invasion" of the Zone [ 13 ]
A scuffle between Zonian and Panamanian high school students over hosting Panamanian and US flags in the Canal Zone erupted into a protest on January 9, 1964. [ 14 ] This was a result of an ongoing flag hosting dispute between US and Panama, over the period between 1959 and 1964. [ 15 ] This led to series of incidents of civil unrest. [ 14 ] Angry crowds formed along the fenced border between Panama City and the Canal Zone. According to Jackson (1999) [ 2 ] at several points demonstrators stormed into the zone, planting Panamanian flags and began to tear down the fence creating gaps in front of the US District Court and several other spots along the fence. Canal Zone police responded firing shots and tear-gassing protesters pulling or climbing on the fence. [ 16 ]
The riots left four Americans and twenty-two Panamanians dead. The day, January 9, is marked in Panama as Martyrs’ Day and is a national holiday. These events compelled President Roberto Chiari to break diplomatic relations with the United States. Although the diplomatic relations between Panama and the United States were re-established on April 3, 1964, through the joint declaration Moreno-Bunker, these events led to significant Panamanian resent. As part of the Torrijos–Carter Treaties joint administration of the canal began in 1979. On December 31, 1999, the United States handed over full control of the canal to Panama.
The existence and purpose of the various Canal Zone fences remains a matter of significant controversy. [ 17 ] It is generally agreed upon that a fence was built in the 1950s. However, the official and unofficial policies governing the ingress and egress of United States and Panama citizens, which had a significant impact on the functional effect of the fence, remain unknown. | https://en.wikipedia.org/wiki/Panama_Canal_fence |
Panbiogeography , originally proposed by the French-Italian scholar Léon Croizat (1894–1982) in 1958, [ 1 ] [ 2 ] is a cartographical approach to biogeography that plots distributions of a particular taxon or group of taxa on maps, and connects the disjunct distribution areas or collection localities together with lines called tracks , regarding vicariance as the primary mechanism for the distribution of organisms rather than dispersal . While Panbiogeography influenced development of modern biogeography, the ideas in their original form are not considered mainstream biogeographical theory, and the theory was described in 2007 as "almost moribund". [ 3 ]
A track is a representation of the spatial form of a species distribution and can give insights into the spatial processes that generated that distribution. Crossing of an ocean or sea basin or any other major tectonic structure (e.g. a fault zone) by an individual track constitutes a baseline .
Individual tracks are superimposed, and if they coincide according to a specified criterion (e.g. shared baselines or compatible track geometries), the resulting summary lines are considered generalized (or standard) tracks. Generalized tracks suggest the pre-existence of ancestral biotas, which subsequently become fragmented by tectonic and/or climate change. The area where two or more generalized tracks intersect is called node . It means that different ancestral biotic and geological fragments interrelate in space/time, as a consequence of terrain collision, docking, or suturing, thus constituting a composite area. A concentration of numerical, genetical or morphological diversity within a taxon in a given area constitutes a main massing .
Panbiogeography was first conceived by Croizat [ 1 ] [ 2 ] and further applied by researchers in New Zealand and Latin America. [ 4 ] Panbiogeography provides a method for analyzing the geographic (spatial) structure of distributions in order to generate predictions about the evolution of species and other taxa in space and time.
Panbiogeographic key concepts of track, node, baseline, and main massing have shown to be powerful analytical tools, especially following the mathematical formalization of these concepts with the development of quantitative panbiogeography. [ 4 ] Such developments were based on the application of concepts and methods from graph theory , for example minimum spanning trees to depict individual tracks in a more rigorous way, clique analysis to identify standard tracks, and nodal analysis to determine the precise location of panbiogeographic nodes.
Panbiogeography emphasizes the analysis of raw locality and broader distribution data for taxa, and may thus benefit from modern technological advances for the collection, storage, and analysis of such data, as are online biodiversity databases of georeferenced records, [ a ] the Global Positioning System (GPS) and Geographic Information Systems (GIS) technology. Furthermore, panbiogeographers have suggested their paradigm may also be useful to address the critical issue of global biodiversity conservation in a potentially fast and cost-effective way. [ 4 ]
Panbiogeography has generally been dismissed by mainstream biologists, and it has been described as "almost moribund" [ 3 ] and as having "fallen by the wayside" in biogeography following widespread criticism. [ 5 ] Robert H. Cowie, writing in a book review in Heredity stated "Panbiogeography seems to me at best to offer little new insight, at worst to be fundamentally flawed" criticising panbiogeographers for not placing enough emphasis on phylogenetics , which Cowie states is "the underpinning of any biogeographical analysis". [ 6 ] Subsequent researchers have also criticised panbiogeography and argued that the approach is detrimental to biogeography as a scientific discipline. [ 7 ] | https://en.wikipedia.org/wiki/Panbiogeography |
Pancratistatin ( PST ) is a natural compound initially extracted from spider lily , [ 1 ] a Hawaiian native plant of the family Amaryllidaceae [ 2 ] (AMD).
Pancratistatin occurs naturally in Hawaiian spider lily, a flowering plant within the family Amaryllidaceae . Pancratistatin is mostly found in the bulb tissues of spider lilies. It has been shown that the enrichment of atmospheric CO 2 can enhance the production of antiviral secondary metabolites, including pancratistatin, in these plants. [ 3 ] Pancratistatin can be isolated from the tropical bulbs of Hymenocallis littoralis in the order of 100 to 150 mg/kg when bulbs are obtained from the wild type in Hawaii. However, the compound has to be commercially extracted from field- and greenhouse-grown bulbs or from tissue cultures cultivated, for example, in Arizona , which generate lower levels of pancratistatin (a maximum of 22 mg/kg) even in the peak month of October. After October, when the bulb becomes dormant, levels of pancratistatin drop, down to only 4 mg/kg by May. Field-grown bulbs, which show monthly changes in pancratistatin content, generate somewhat smaller amounts (2–5 mg/kg) compared to those grown in greenhouses cultivated over the same period. [ 4 ] There are about 40 different spider lily species worldwide and they are mainly native to the Andes of South America.
Pancratistatin is thought to have potential as a basis for the development of new pharmaceuticals, [ 5 ] particularly in the field of cancer treatment. [ 6 ]
Although there may not be a precise elucidation of pancratistatin biological synthesis, there have been speculations on biosynthesis of narciclasine and lycoricidine that are very similar to pancratistatin in terms of structure. The biosynthesis is accomplished via synthesis from O- methylnorbelladine by para-para phenol coupling to obtain vittatine as an intermediate. Subsequent elimination of two carbon atoms and hydroxylations of vittatine then leads to narciclasine. [ 7 ]
The first total synthesis [ 8 ] of racemic (+/-)-pancratistatin was reported by Samuel Danishefsky and Joung Yon Lee , which involved a very complex and long (40 steps) total synthesis . According to Danishefsky and Joung, there were several weak steps in this synthesis that gave rise to a disappointing low synthetic yield. Amongst the most challenging issues, the Moffatt transposition and the orthoamide problem, which required a blocking maneuver to regiospecifically distinguish the C, hydroxyl group for rearrangement were considered to be the severe cases. However, both Danishevsky and Yon Lee stated that their approach towards the PST total synthesis was not without merit and believed that their work would interest other medicinal scientists to construct a much more practical and efficient way for PST total synthesis. [ 9 ] [ 10 ]
The work of Danishevsky and Joung provided the foundation for another total synthesis of PST, which was propounded by Li, M. in 2006. This method employed a more sophisticated approach, starting out with pinitol that has stereocenters which are exactly the same as the ones in the C-ring of pancratistatin. [ 11 ] Protection of the diol functions of compound 30 gave compound 31. The free hydroxyl of this was subsequently substituted by an azide to give 32. After removal of the silyl function, a cyclic sulfate was installed to obtain product 33. The Staudinger reaction gave the free amine 34 from azide 33. The coupling reaction between 34 and 35 gave compound 36 with a moderate yield. Methoxymethyl protection of both the amide and the free phenol gave compound 37. Treatment of this latter product with t-BuLi followed by addition of cerium chloride gave compound 38. Full deprotection of 38 by BBr 3 and methanol afforded pancratistatin 3 in 12 steps from commercially available pinitol with an overall yield of 2.3% 20. [ 12 ]
The most recent and shortest synthesis of pancratistatin was accomplished by David Sarlah and co workers, completing the asymmetric synthesis of (+)-pancratistatin and (+)-7-deoxypancratistatin in 7 and 6 steps respectively. [ 13 ] The key step of this synthesis was the Nickel catalyzed dearomatization of benzene which directly installed the amine and catachol ring in 98:2 er . Epoxidation then dihydroxylation of the resulting diene afforded the 4 hydroxyl groups. The synthesis was completed by deprotection of the amine and a Cobalt catalyzed CO insertion to furnish the lactam. (+)-7-deoxypancratistatin can then be directly oxidized in a 62% yield to give (+)-pancratistatin. This synthesis yielded multiple grams of the final product which may be essential in the biological evaluation of pancratistatin and analogues.
A very recent approach to a stereocontrolled pancratistatin synthesis was accomplished by Sanghee Kim from the National University of Seoul , in which Claisen rearrangement of dihydropyranethlyene and a cyclic sulfate elimination reaction were employed 21.
The B ring of the phenanthridone (three-membered nitrogen heterocyclic ring) is formed using the Bischler-Napieralski reaction. The n precursor 3 with its stereocenters in the C ring is stereoselectively synthesized from the cis -disubstituted cyclohexene 4. The presence of unsaturated carbonyl in compound 4 suggested the use of a Claisen rearrangement of 3,4-dihydro-2H-pyranylethylene. [ 14 ]
The synthesis starts with the treatment of 6 with excess trimethyl phosphate. This reaction provides phosphate 7 in 97% yield. Using the Horner-Wadsworth-Emmons reaction between 7 and acrolein dimmer 8 in the presence of LHMDS in THF forms ( E )-olefin 5 with very high stereoselectivity in 60% yield. Only less than 1% of ( Z )-olefin was detected in the final product. The Claisen rearrangement of dihydropyranethylene forms the cis-distributed cyclohexene as a single isomer in 78% yield.
The next step of the synthesis involves the oxidation of aldehyde of compound 4 using NaClO 2 to the corresponding carboxylic acid 9 in 90% yield. Iodolactonization of 9 and subsequent treatment with DBU in refluxing benzene gives rise to the bicyclic lacytone in 78% yield. Methanolysis of lactone 10 with NaOMe forms a mixture of hydroxyl ester 11 and its C-4a epimer (pancratistatin numbering). Saponification of the methyl ester 11 with LiOH was followed by a Curtius rearrangement of the resulting acid 12 with diphenylphosphoryl azide in refluxing toluene to afford an isocyanate intermediate, treatment of which with NaOMe/MeOH forms the corresponding carbamate 13 in 82% yield.
The next steps of the synthesis involve the regioselective elimination of the C-3 hydroxyl group and subsequent unsaturation achieved by cyclic sulfate elimination. Diol 16 needs to be treated with thionyl chloride and further oxidation with RuCl 3 provides the cyclic sulfate 17 in 83% yield. [ 15 ] Treatment of cyclic sulfate with DBU yields the desired allylic alcohol 18 (67% yield).
Reaction with OsO 4 forms the single isomer 19 in 88% yield. Peracetylation of 19 (77% yield) accompanied by Banwell’s modified Bischler-Napieralski reaction forms the compound 20 with a small amount of isomer 21 ( 7:1 regioselectivity). The removal of protecting groups with NaOMe/MeOH forms pancratistatin in 83%. | https://en.wikipedia.org/wiki/Pancratistatin |
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