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A smart cosubstrate is a type of cosubstrate used for cofactor regeneration to yield greater productivity and lower environmental impact ( E-factor ). A good example of a smart cosubstrate is a lactonizable diol .
In redox biocatalysis, the nicotinamide cofactor (NAD(P)H or NAD(P)+) can act as an electron donor or acceptor by releasing or accepting a hydride . The cofactor must be used in the reaction either in stoichiometric amounts leading to inhibition and economic issues, or in catalytic amounts coupled with an in situ regeneration system. A common approach catalytic amounts is excess use of sacrificial organic molecules such as isopropanol or ethanol . This approach, however, leads to stoichiometric amounts of waste.
The use of 1,4-butanediol as a smart cosubstrate for cofactor regeneration was the next step towards more sustainable redox biocatalysis (Scheme 1). [ 1 ] The formation of a thermodynamically stable gamma-butyrolactone as a co-product drives the reaction to completion while yielding higher reaction rates. The use of 1,4-butanediol as an intelligent cosubstrate has also been validated in non-aqueous media using a commercial ADH . [ 2 ] [ 3 ]
Biocatalytic cascade reactions currently fall into four different categories:
However, only two types of redox-neutral cascades have been reported for the in situ regeneration of the cofactors: parallel cascades (i.e., bi-substrate — no intermediate — bi- or tri-product) and linear cascades (i.e., single substrate — single intermediate — single product). [ 6 ] [ 7 ] [ 8 ]
The concept of a smart cosubstrate was developed further through the design of a new class of redox-neutral "convergent cascade" reactions. Convergent cascade reactions involve a bi-substrate and a single product without the formation of an intermediate and were developed for the production of epsilon-caprolactone , which consists of a Baeyer-Villiger monooxygenase ; for the oxidation of cyclohexanone ; an alcohol dehydrogenase for oxidation of the "double-smart cosubstrate" 1,6-hexanediol ; and for simultaneous regeneration of the nicotinamide cofactor. [ 9 ] In 2016, two-step optimization of the convergent cascade by Design-of-Experiments and a biphasic system was reported. [ 10 ]
Smart cosubstrates are an elegant solution for thermodynamically limited redox reactions and have many advantages: | https://en.wikipedia.org/wiki/Smart_cosubstrate |
Smart cut is a technological process that enables the transfer of very fine layers of crystalline silicon material onto a mechanical support. It was invented by Michel Bruel of CEA-Leti , and was protected by US patent 5374564. [ 1 ] The application of this technological procedure is mainly in the production of silicon-on-insulator (SOI) wafer substrates.
The role of SOI is to electronically insulate a fine layer of monocrystalline silicon from the rest of the silicon wafer ; an ultra-thin silicon film is transferred to a mechanical support, thereby introducing an intermediate, insulating layer. Semiconductor manufacturers can then fabricate integrated circuits on the top layer of the SOI wafers using the same processes they would use on plain silicon wafers.
The sequence of illustrations pictorially describes the process involved in fabricating SOI wafers using the smart cut technology.
This semiconductor technology-related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Smart_cut |
A smart doorbell is an internet-connected doorbell that notifies the home owner on his or her device (smartphone or any other gadget) when a visitor arrives at the door. It activates when the visitor presses the button of the doorbell, or alternatively, when the doorbell senses a visitor with its built-in motion sensors . The smart doorbell lets the home owner use a smartphone app to watch and talk with the visitor by using the doorbell's built-in high-definition infrared camera and microphone. They can be either battery operated or wired. [ 1 ] Some smart doorbells also allow the user to open the door remotely using a smart lock . [ 2 ]
One of the earliest smart doorbells that entered to the market is the Ring Video Doorbell which was created by entrepreneur Jamie Siminoff in 2013. Since then, several more smart doorbells have been introduced to the market, some of them with additional, unique features. Another major one is Nest Hello . [ 3 ] [ 4 ] [ 5 ] [ 6 ]
Concerns regarding the security of the smart doorbells have been raised. Researchers at Pen Test Partners in the UK have analyzed the Ring smart doorbell and concluded that it is possible for an attacker to gain access to the homeowner's wireless network by unscrewing the Ring, pressing the setup button and accessing the configuration URL. [ 7 ] In another security issue that had been observed, a mix-up of two databases allowed some users of the Ring smart doorbell to view live footage from complete strangers' front porches. [ 8 ] | https://en.wikipedia.org/wiki/Smart_doorbell |
Smart environments link computers and other smart devices to everyday settings and tasks. Smart environments include smart homes , smart cities , and smart manufacturing .
Smart environments are an extension of pervasive computing . According to Mark Weiser , pervasive computing promotes the idea of a world that is connected to sensors and computers. [ 1 ] These sensors and computers are integrated with everyday objects in peoples' lives and are connected through networks. [ 1 ]
Cook and Das, define a smart environment as "a small world where different kinds of smart devices are continuously working to make inhabitants' lives more comfortable." [ 2 ] Smart environments aim to satisfy the experience of individuals from every environment, by replacing hazardous work, physical labor, and repetitive tasks with automated agents.
Poslad [ 3 ] differentiates three different kinds of smart environments for systems, services, and devices: virtual (or distributed) computing environments, physical environments, and human environments, or a hybrid combination of these:
Smart environments encompass a range of features and services across various domains, including smart homes , smart cities , smart health , and smart factories . Some of the key features of smart environments are:
Sensors and Actuators: Smart environments are equipped with an assembly of sensors and actuators that collect data and initiate actions to provide services for the betterment of human life. [ 6 ] [ 7 ]
Interconnected Systems: These environments consist of interconnected systems that enable seamless communication and coordination among various devices and components. [ citation needed ]
Data-Driven Technologies: Smart environments leverage data-driven technologies, such as the Internet of Things (IoT), to obtain information from the physical world, process it, and perform actions accordingly. [ citation needed ]
Efficiency and Sustainability: They are designed to improve efficiency, sustainable practices, and resource management across different settings, such as energy efficiency in smart homes and environmental quality management in smart cities. [ 6 ]
Diverse Requirements: Different types of smart environments have diverse requirements and technology choices, influencing the processing and utilization of data within a specific environment. [ 8 ]
Building a smart environment involves technologies of
The Aware Home Research Initiative at Georgia Tech "is devoted to the multidisciplinary exploration of emerging technologies and services based in the home" and was launched in 1998 as one of the first "living laboratories." [ 9 ] The Mav Home (Managing an Adaptive Versatile Home) project, at UT Arlington , is a smart environment-lab with state-of-the-art algorithms and protocols used to provide a customized, personal environment to the users of this space. The Mav Home project, in addition to providing a safe environment, wants to reduce the energy consumption of the inhabitants. [ 10 ] Other projects include House at the MIT Media Lab and many others. | https://en.wikipedia.org/wiki/Smart_environment |
A smart fluid is a fluid whose properties (e.g. viscosity ) can be changed by applying an electric field or a magnetic field . [ 1 ] [ 2 ] [ 3 ]
The most developed smart fluids today are fluids whose viscosity increases when a magnetic field is applied. Small magnetic dipoles are suspended in a non-magnetic fluid, and the applied magnetic field causes these small magnets to line up and form strings that increase the viscosity. These magnetorheological or MR fluids have been used in the suspension of the 2002 model of the Cadillac Seville STS automobile and more recently, in the suspension of the second-generation Audi TT. Depending on road conditions, the fluid's damping viscosity can be adjusted. This is more expensive than traditional systems, but it provides better (faster) control. Similar systems are being explored to reduce vibration in washing machines , air conditioning compressors , rockets and satellites, and one has even been installed in Japan's National Museum of Emerging Science and Innovation in Tokyo as an earthquake shock absorber .
Some haptic devices whose resistance to touch can be controlled are also based on these MR fluids.
Another major type of smart fluid are electrorheological or ER fluids, whose resistance to flow can be quickly and dramatically altered by an applied electric field (note, the yield stress point is altered rather than the viscosity ). Besides fast acting clutches , brakes , shock absorbers and hydraulic valves , other, more esoteric, applications such as bulletproof vests have been proposed for these fluids.
Other smart fluids change their surface tension in the presence of an electric field. This has been used to produce very small controllable lenses : a drop of this fluid, captured in a small cylinder and surrounded by oil, serves as a lens whose shape can be changed by applying an electric field.
The properties of smart fluids have been known for around sixty years, but were subject to only sporadic investigations up until the 1990s, when they were suddenly the subject of renewed interest, notably culminating with the use of an MR fluid on the suspension of the 2002 model of the Cadillac Seville STS automobile and more recently, on the suspension of the second-generation Audi TT . Other applications include brakes and seismic dampers, which are used in buildings in seismically-active zones to damp the oscillations occurring in an earthquake. Since then it appears that interest has waned a little, possibly due to the existence of various limitations of smart fluids which have yet to be overcome. [ citation needed ] | https://en.wikipedia.org/wiki/Smart_fluid |
Smart glass, also known as switchable glass , dynamic glass , and smart-tinting glass , is a type of glass that can change its optical properties, becoming opaque or tinted, in response to electrical or thermal signals. This can be used to prevent sunlight and heat from entering a building during hot days, improving energy efficiency. [ 1 ] It can also be used to conveniently provide privacy or visibility to a room.
There are two primary classifications of smart glass: active or passive. The most common active glass technologies used today are electrochromic , liquid crystal , and suspended particle devices (SPD). Thermochromic and photochromic are classified as passive technologies. [ 2 ]
When installed in the envelope of buildings, smart glass helps to create climate adaptive building shells , [ 3 ] which benefits include things such as natural light adjustment, visual comfort, UV and infrared blocking, reduced energy use, thermal comfort, resistance to extreme weather conditions, and privacy. [ 4 ] Some smart windows can self-adapt to heat or cool for energy conservation in buildings . [ 5 ] [ 6 ] [ 7 ] Smart windows can eliminate the need for blinds, shades or window treatments. [ 8 ]
Some effects can be obtained by laminating smart film or switchable film onto flat surfaces using glass, acrylic or polycarbonate laminates. [ 9 ] Some types of smart films can be applied to existing glass windows using either a self-adhesive smart film or special glue. [ 10 ] Spray-on methods for applying clear coatings to block heat and conduct electricity are also under development. [ 11 ]
The term "smart window" originated in the 1980s. It was introduced by Swedish material physicist Claes-Göran Granqvist from Chalmers University of Technology , who was brainstorming ideas for making building materials more energy efficient with scientists from Lawrence Berkeley National Laboratory in California . Granqvist used the term to describe a responsive window capable of dynamically changing its tint. [ 4 ]
The following table shows an overview of the different electrically switchable smart glass technologies:
Electrochromic devices change light transmission properties in response to voltage and thus allow control over the amount of light and heat passing through. [ 12 ] In electrochromic windows, the material changes its opacity . A burst of electricity is required for changing its opacity, but the material maintains its shade with little to no additional electrical signals. [ 13 ]
Old electrochromic technologies tend to have a yellow cast in their clear states and blue hues in their tinted states. Darkening occurs from the edges, moving inward, and is a slow process, ranging from many seconds to 20–30 minutes depending on window size. Newer electrochromic technologies eliminate the yellow cast in the clear state and tinting to more neutral shades of gray, tinting evenly rather than from the outside in, and accelerate the tinting speeds to less than three minutes, regardless of the size of the glass. Electrochromic glass maintains visibility in its darkened state and thus preserves visual contact with the outside environment.
Recent advances in electrochromic materials pertaining to transition-metal hydride electrochromics have led to the development of reflective hydrides, which become reflective rather than absorbing, and thus switch states between transparent and mirror-like.
Recent advancements in modified porous nanocrystalline films have enabled the creation of electrochromic display. The single substrate display structure consists of several stacked porous layers printed on top of each other on a substrate modified with a transparent conductor (such as ITO or PEDOT:PSS ). Each printed layer has a specific set of functions. A working electrode consists of a positive porous semiconductor such as titanium dioxide, with adsorbed chromogens . These chromogens change color via reduction or oxidation. A passivator is used as the negative of the image to improve electrical performance. The insulator layer serves the purpose of increasing the contrast ratio and electrically separating the working electrode from the counter electrode . The counter electrode provides a high capacitance to counterbalance the charges inserted/extracted on the SEG electrode (and maintain charge neutrality in the overall device). Carbon is an example of a charge reservoir film. A conducting carbon layer is typically used as the conductive back contact for the counter electrode. In the last printing step, the porous monolith structure is overprinted with a liquid or polymer-gel electrolyte, dried, and then may be incorporated into various encapsulation or enclosures, depending on the application requirements. Displays are very thin, often 30 micrometers. The device can be switched on by applying an electrical potential to the transparent conducting substrate relative to the conductive carbon layer. This causes a reduction of viologen molecules (coloration) to occur inside the working electrode. By reversing the applied potential or providing a discharge path, the device bleaches. A unique feature of the electrochromic monolith is the relatively low voltage (around 1 Volt) needed to color or bleach the viologens . This can be explained by the small over- potentials needed to drive the electrochemical reduction of the surface adsorbed viologens/chromogens.
Most types of smart film require voltage (e.g. 110VAC) to operate, and therefore such types of smart films must be enclosed within glass, acrylic or polycarbonate laminates to provide electrical safety to users. [ citation needed ]
In polymer-dispersed liquid-crystal devices (PDLCs), liquid crystals are dissolved or dispersed into a liquid polymer followed by solidification or curing of the polymer. During the change of the polymer from a liquid to solid, the liquid crystals become incompatible with the solid polymer and form droplets throughout the solid polymer. The curing conditions affect the size of the droplets that in turn affect the final operating properties of the "smart window". Typically, the liquid mix of polymer and liquid crystals is placed between two layers of glass or plastic that include a thin layer of a transparent, conductive material followed by curing of the polymer, thereby forming the basic sandwich structure of the smart window. This structure is in effect a capacitor.
Electrodes from a power supply are attached to the transparent electrodes. With no applied voltage, the liquid crystals are randomly arranged in the droplets, resulting in scattering of light as it passes through the smart window assembly. This results in the translucent, "milky white" appearance. When a voltage is applied to the electrodes, the electric field formed between the two transparent electrodes on the glass causes the liquid crystals to align, allowing light to pass through the droplets with very little scattering and resulting in a transparent state. The degree of transparency can be controlled by the applied voltage. This is possible because at lower voltages, only a few of the liquid crystals align completely in the electric field, so only a small portion of the light passes through while most of the light is scattered. As the voltage is increased, fewer liquid crystals remain out of alignment, resulting in less light being scattered. It is also possible to control the amount of light and heat passing through, when tints and special inner layers are used.
In suspended-particle devices (SPDs), a thin film laminate of rod-like nano-scale particles is suspended in a liquid and placed between two pieces of glass or plastic, or attached to one layer. When no voltage is applied, the suspended particles are randomly organized, thus blocking and absorbing light. When voltage is applied, the suspended particles align and let light pass. Varying the voltage of the film varies the orientation of the suspended particles, thereby regulating the tint of the glazing and the amount of light transmitted. SPDs can be manually or automatically "tuned" to precisely control the amount of light, glare and heat passing through.
Micro-blinds control the amount of light passing through in response to applied voltage. The micro-blinds are composed of rolled thin metal blinds on glass. They are very small and thus practically invisible to the eye. The metal layer is deposited by magnetron sputtering and patterned by laser or lithography process. The glass substrate includes a thin layer of a transparent conducting oxide (TCO) layer. A thin insulator is deposited between the rolled metal layer and the TCO layer for electrical disconnection. With no applied voltage, the micro-blinds are rolled and let light pass through. When there is a potential difference between the rolled metal layer and the transparent conductive layer, the electric field formed between the two electrodes causes the rolled micro-blinds to stretch out and thus block light. The micro-blinds have several advantages including switching speed (milliseconds), UV durability, customized appearance and transmission. The technology of micro-blinds was developed at the National Research Council (Canada) .
Phase-changing polymer (PCP) shows reversible phase transition between amorphous and semicrystalline states. [ 14 ] This change of phase is dominated by temperature change in thermochromic smart glass application, making it completely automatic at no electricity cost. The structure of PCP often consists of two major components: a phase-changing component polymer (let's call it P1) crosslinked with another polymer (P2) which is strongly phase-separated from the former due to different hydrophilicity . Therefore, P1 and P2 are able to form micron-level phase separation after curing. When the temperature is below the phase-transition temperature (Tp) of P1, P1 is semi-crystalline and its refractive index matches with that of P2, thus making the whole structure transparent to visible light. [ 15 ] When the temperature goes above Tp, P1 melts and transitions into amorphous phase which exhibits a large refractive index mismatch with P2, resulting in an opaque appearance. [ 15 ] By smartly selecting the material for P1, a reversed effect of transmittance switch can be observed. For example, if at below Tp the refractive index of the semi-crystalline P1 dismatches that of P2, the film then is opaque; if the amorphous P1 matches P2 with respect to refractive index at above Tp, then the film is transparent at the elevated temperature. One signature application would be that, PCP be coated on the glass window of a warehouse where PCP becomes opaque during hot days to block excessive radiation and cools the room down, thus saving energy from running an air conditioner. [ 16 ]
The expression smart glass can be interpreted in a wider sense to include also glazings that change light transmission properties in response to an environmental signal such as light or temperature.
These types of glazings cannot be controlled manually. In contrast, all electrically switched smart windows can be made to automatically adapt their light transmission properties in response to temperature or brightness by integration with a thermometer or photosensor , respectively.
Smart glass can be used for energy-saving heating and cooling in building by controlling the amount of sunlight which passes through a window. A transparent or haze temperature control film makes the smart film enter a haze state when it is sunny and the indoor temperature is high. When it's sunny and the indoor temperature is low, the smart glass enters a transparent state.
In the office:
Indoor decoration of residence:
Product display and commercial advertisement:
Smart glass can be used as a switchable projection screen on a store window for advertising. Third generation smart film [ clarification needed ] is good for both front and rear projection, and projected images can be viewed from both sides. [ citation needed ]
Uses for other special occasions include:
Eureka Tower in Melbourne has a glass cube which projects 3 m (10 ft) out from the building with visitors inside, suspended almost 300 m (984 ft) above the ground. When one enters, the glass is opaque as the cube moves out over the edge of the building. Once fully extended over the edge, the glass becomes clear.
The Boeing 787 Dreamliner features electrochromic windows which replaced the pull down window shades on existing aircraft. [ 19 ]
NASA is looking into using electrochromics to manage the thermal environment experienced by the newly developed Orion and Altair space vehicles.
Smart glass has been used in some small-production cars including the Ferrari 575 M Superamerica . [ 20 ]
ICE 3 high speed trains use electrochromic glass panels between the passenger compartment and the driver's cabin.
The elevators in the Washington Monument use smart glass in order for passengers to view the commemorative stones inside the monument.
The city's restroom in Amsterdam's Museumplein square features smart glass for ease of determining the occupancy status of an empty stall when the door is shut, and then for privacy when occupied.
Bombardier Transportation has intelligent on-blur windows in the Bombardier Innovia APM 100 operating on Singapore's Bukit Panjang LRT line , to prevent passengers from peering into apartments while the train is moving [ 21 ] and is planning to offer windows using smart glass technology in its Flexity 2 light rail vehicles . [ 22 ]
Chinese phone manufacturer OnePlus demonstrated a phone whose rear cameras are placed behind a pane of electrochromic glass. [ 23 ]
Public toilets in Tokyo use this technology to address safety and privacy concerns. People approaching a restroom are able to confirm that it is empty because they can see through into the interior while the door is unlocked. Once the occupied restroom door is locked, walls of the room are opaque. [ 24 ] [ 25 ]
The Volkswagen ID.7 has a smart glass panoramic sunroof, which can be switched from transparent to opaque electrically. [ 26 ]
University of Toronto has utilized Smart Film Technology on a curtain wall to provide privacy in their swimming pool viewing area. [ 27 ] | https://en.wikipedia.org/wiki/Smart_glass |
A smart home hub , [ 1 ] sometimes also referred to as a smart hub or gateway , [ 2 ] is a control center for a smart home , and enables the components of a smart home to communicate and respond to each other via communication through a central point. [ 3 ] The smart home hub can consist of dedicated computer appliance , software appliance , or software running on computer hardware , and makes it possible to gather configuration , automation and monitoring of a smart house by communicating and controlling different smart devices that consist of for example home appliances , sensors and relays or robots, many of which are commonly categorized under Internet of things .
A smart home can contain one, several, or even no smart home hubs. When using several smart home hubs it is sometimes possible to connect them to each other. Some smart home hubs support a wider selection of components, while others are more specialized for controlling products within certain product groups or using certain wireless technologies (e.g. Wi-Fi , Bluetooth , Z-Wave , and/or Zigbee ).
A smart speaker with a virtual assistant can often be used for speech input to a smart home hub.
Smart home hubs can have software with open source code or use proprietary software with closed source code , and independently of this the application programming interface can be public or closed. Some smart home hubs must run on proprietary hardware, while others (e.g. Home Assistant ) can be installed on generic hardware (e.g. a laptop or single-board computer with Linux ).
Some examples of smart home hubs with closed source code are:
Some examples of smart home hubs based on free and open-source software are:
Some examples of smart home hubs with closed source code but an open application programming interface are:
Various communication protocols can be used between smart home hubs and smart house components. [ 9 ] The protocols can be grouped into wired and wireless technologies.
Some examples of wireless protocols commonly used in smart home hubs are:
There are several cabled bus systems , some of which are built directly into electric panels . Some examples of wired protocols commonly used in smart home hubs are: | https://en.wikipedia.org/wiki/Smart_home_hub |
The term "smart structures" is commonly used for structures which have the ability to adapt to environmental conditions according to the design requirements. As a rule, the adjustments are designed and performed in order to increase the efficiency or safety of the structure. Combining "smart structures" with the "sophistication" achieved in materials science , information technology , measurement science, sensors , actuators , signal processing , nanotechnology , cybernetics , artificial intelligence , and biomimetics , [ 1 ] one can talk about Smart Intelligent Structures. In other words, structures which are able to sense their environment, self-diagnose their condition and adapt in such a way so as to make the design more useful and efficient.
The concept of Smart Intelligent Aircraft Structures offers significant improvements in aircraft total weight, manufacturing cost and, above all, operational cost by an integration of system tasks into the load carrying structure. [ 2 ] It also helps to improve the aircraft's life cycle and reduce its maintenance. [ 3 ] Individual morphing concepts also have the ability to decrease airframe generated noise and hence reduce the effect of air traffic noise near airports. Furthermore, cruise drag reductions have a positive effect on fuel consumption and required take-off fuel load.
Fixed geometry wings are optimized for a single design point, identified through altitude , Mach number , weight , etc. Their development is always a compromise between design and off-design points, referred to a typical mission. This is emphasised for civil aircraft where flight profiles are almost standard. Nevertheless, it may occur to fly at high speeds and low altitude with light weight over a short stretch or to fly at low speeds and high altitude with maximum load for a longer range. The lift coefficient would then range between 0.08 and 0.4, [ 4 ] [ 5 ] with the aircraft experiencing up to 30% weight reduction as the fuel is consumed. [ 6 ] These changes could be compensated by wing camber variations , to pursue optimal geometry for any flight condition, thus improving aerodynamic and structural performance.
Existing aircraft cannot change shape without aerodynamic gaps, something that can be solved with Smart Intelligent Structures. By ensuring the detailed consideration of structural needs throughout the entire lifetime of an aircraft and focusing on the structural integration of needed past capabilities, Smart Intelligent Aircraft Structures will allow aircraft designers to seriously consider conformal morphing technologies. The reduced drag during take-off, cruise and landing for future and ecologically improved civil aircraft wings can be achieved through naturally laminar wing technology, by incorporating a gapless and deformable leading edge device with lift providing capability. Such a morphing structure typically consists of a flexible outer skin and an internal driving mechanism (Figure 1).
Current aircraft designs already employ winglets aimed at increasing the cruise flight efficiency by induced drag reduction. Smart intelligent Structures propose a state of the art technology that incorporates a wingtip active trailing edge , which could be a means of reducing winglet and wing loads at key flight conditions.
Another component of an "intelligent" aircraft structure is the ability to sense and diagnose potential threats to its structural integrity. This differs from conventional non-destructive testing (NDT) by the fact that Structural Health Monitoring (SHM) [ 7 ] uses sensors that are permanently bonded or embedded in the structure. Composite materials , which are highly susceptible to hidden internal flaws which may occur during manufacturing and processing of the material or while the structure is subjected to service loads, require a substantial amount of inspection and defect monitoring at regular intervals. Thus, the increasing use of composite materials for aircraft primary structure aircraft components increases substantially their life cycle cost . According to some estimates, over 25% of the life cycle cost of an aircraft or aerospace structure, which includes pre-production, production, and post-production costs, can be attributed to operation and support, involving inspection and maintenance. With sensing technology reducing in cost, size and weight, and sensor signal processing power continuously increasing, a variety of approaches have been developed allowing integration of such sensing options onto or into structural components .
Although available in principle, none of these SHM technologies have currently achieved a sufficient level of maturity such that SHM could be reliably applied to real engineering structures. A real reduction of life cycle costs related to maintenance and inspections can only be achieved by SHM systems designed as " fail-safe " components and included within a damage tolerance assessment scenario, able to reduce the inspection times (or their intervals) by investigating the structure quickly and reliably and avoiding the time-consuming disassembly of structural parts. [ 8 ]
The advantages of carbon fibre reinforced polymers (CFRPs) over metallic materials in terms of specific stiffness and strength are well known. In the last few years, there has been a sharp increase in the demand for composite materials with integrated multifunctional capabilities for use in aeronautical structures.
However, a major drawback with CFRPs for primary structural applications is their low toughness and damage tolerance. Epoxy resins are brittle and have poor impact strength and resistance to crack propagation , resulting in unsatisfactory levels of robustness and reliability. This results in designs with large margins of safety and complex inspection operations. In addition, by increasing the relative fraction of composite components within new aircraft, challenges regarding electrical conductivity have arisen such as lightning strike protection, static discharge , electrical bonding and grounding , interference shielding and current return through the structure. These drawbacks can be solved by the use of emerging technologies such as nanocomposites , which combine mechanical, electrical and thermal properties. [ 9 ]
Nanoparticle reinforced resins have been found to offer two distinct advantages over current resin systems. [ 10 ] [ 11 ] [ 12 ] [ 13 ] [ 14 ] First of all, they are able to provide an increase in fracture toughness of up to 50% for older liquid resin infusion (LRI) resins and 30% in more advanced systems. Secondly, percolated nanoparticles drastically improve resin conductivity, turning it from a perfect isolator into a semiconductor . While improved damage tolerance properties could directly lead to structural weight savings, the exploitation of electrical properties could also enable a simpler, and hence cheaper, Electrical Structure Network (ESN).
Developing these technologies for future A/C, there is currently (2011 – 2015) a running project, partially funded by the European Commission , called "SARISTU" (Smart Intelligent Aircraft Structures) with a total budget of €51,000,000. This initiative is coordinated by Airbus and brings together 64 partners from 16 European countries. [ 15 ] [ 16 ] SARISTU focuses on the cost reduction of air travel through a variety of individual applications as well as their combination. Specifically, the integration of different conformal morphing concepts in a laminar wing is intended to improve aircraft performance through a 6% drag reduction, with a positive effect on fuel consumption and required take-off fuel load. A side effect will be a decrease of up to 6 dB(A) of the airframe generated noise, thus reducing the impact of air traffic noise in the vicinity of airports. Recent calculations and Computational Fluid Dynamics Analysis indicate that the target is likely to be exceeded but will still need to be offset against a possible weight penalty.
Another expected outcome is to limit the integration cost of Structural Health Monitoring (SHM) systems by moving the system integration as far forward in the manufacturing chain as possible. In this manner, SHM integration becomes a feasible concept to enable in-service inspection cost reductions of up to 1%. Structural Health Monitoring related trials indicate that specific aircraft inspections may gain higher benefits than originally anticipated.
Finally, the incorporation of Carbon Nanotubes into aeronautical resins is expected to enable weight savings of up to 3% when compared to the unmodified skin/stringer/frame system, while a combination of technologies is expected to decrease Electrical Structure Network installation costs by up to 15%. | https://en.wikipedia.org/wiki/Smart_intelligent_aircraft_structure |
A smart key is a vehicular passive entry system developed by Siemens in 1995 and introduced by Mercedes-Benz under the name "Keyless-Go" in 1998 on the W220 S-Class , [ 1 ] after the design patent was filed by Daimler-Benz on May 17, 1997. [ 2 ]
Numerous manufacturers subsequently developed similar passive systems that unlock a vehicle on approach — while the key remains pocketed by the user.
The smart key allows the driver to keep the key fob pocketed when unlocking, locking and starting the vehicle. The key is identified via one of several antennas in the car's bodywork and an ISM band radio pulse generator in the key housing. Depending on the system, the vehicle is automatically unlocked when a button or sensor on the door handle or trunk release is pressed. Vehicles with a smart-key system have a mechanical backup, usually in the form of a spare key blade supplied with the vehicle. Some manufacturers hide the backup lock behind a cover for styling.
Vehicles with a smart-key system can disengage the immobilizer and activate the ignition without inserting a key in the ignition, provided the driver has the key inside the car. On most vehicles, this is done by pressing a starter button or twisting an ignition switch .
When leaving a vehicle that is equipped with a smart-key system, the vehicle is locked by either pressing a button on a door handle, touching a capacitive area on a door handle, or simply walking away from the vehicle. The method of locking varies across models.
Some vehicles automatically adjust settings based on the smart key used to unlock the car. User preferences such as seat positions, steering wheel position, exterior mirror settings, climate control (e.g. temperature) settings, and stereo presets are popular adjustments. Some models, such as the Ford Escape , even have settings to prevent the vehicle from exceeding a maximum speed if it has been started with a certain key.
In 2005, the UK motor insurance research expert Thatcham introduced a standard for keyless entry, requiring the device to be inoperable at a distance of more than 10 cm from the vehicle. [ citation needed ] In an independent test, the Nissan Micra 's system was found to be the most secure, while certain BMW and Mercedes keys failed, being theoretically capable of allowing cars to be driven away while their owners were refueling. [ 3 ] Despite these security vulnerabilities, auto theft rates have decreased 7 percent between 2009 and 2010, and the National Insurance Crime Bureau credits smart keys for this decrease. [ 4 ] [ 5 ]
SmartKeys were developed by Siemens in the mid-1990s and introduced by Mercedes-Benz in 1997 to replace the infrared security system introduced in 1989. Daimler-Benz filed the first patents for SmartKey on February 28, 1997, in German patent offices, with multifunction switchblade key variants following on May 17, 1997. [ 6 ] [ 7 ] [ 8 ] [ 9 ] The device entailed a plastic key to be used in place of the traditional metal key. Electronics that control locking systems and the ignitions made it possible to replace the traditional key with a sophisticated computerized "Key". It is considered a step up from remote keyless entry . The SmartKey adopts the remote control buttons from keyless entry, and incorporates them into the SmartKey fob.
Once inside a Mercedes-Benz vehicle, the SmartKey fob, unlike keyless entry fobs, is placed in the ignition slot where a starter computer verifies the rolling code. Verified in milliseconds, it can then be turned as a traditional key to start the engine. The device was designed with the cooperation of Siemens Automotive and Huf exclusively for Mercedes-Benz, but many luxury manufacturers have implemented similar technology based on the same idea. [ citation needed ] In addition to the SmartKey, Mercedes-Benz now integrates as an option Keyless Go ; this feature allows the driver to keep the SmartKey in their pocket, yet giving them the ability to open the doors, trunk as well as starting the car without ever removing it from their pocket.
The SmartKey's electronics are embedded in a hollow, triangular piece of plastic, wide at the top, narrow at the bottom, squared-off at the tip with a half-inch-long insert piece. The side of the SmartKey also hides a traditional Mercedes-Benz key that can be pulled out from a release at the top. The metal key is used for valet purposes such as locking the glove compartment and/or trunk before the SmartKey is turned over to a parking attendant. Once locked manually, the trunk cannot be opened with the SmartKey or interior buttons. The key fob utilizes a radio-frequency transponder to communicate with the door locks, but it uses infrared to communicate with the engine immobilizer system. The original SmartKeys had a limited frequency and could have only been used in line-of-sight for safety purposes. The driver can also point the smart key at the front driver side door while pushing and holding the unlock button on the SmartKey and the windows and the sunroof will open in order to ventilate the cabin. Similarly, if the same procedure is completed while holding the lock button, the windows and sunroof will close. In cars equipped with the Active Ventilated Seats, the summer opening feature will activate seat ventilation in addition to opening the windows and sunroof. [ citation needed ]
Display Key is a type of smart key developed by BMW that includes a small LCD color touchscreen on it. It performs the standard functions that a key fob would normally do such as locking, unlocking & keyless start, but because of the screen the user can also perform a number of the features from BMW's app. One of which includes commanding the car to self park from the key if your car has self parking capability. The key is currently available for the 3 Series , 4 Series , 5 Series , 6 Series , 7 Ser ies , 8 Series , X3 , X4 , X5 , X6 , and X7 . The key is rechargeable and will last about 3 weeks. It can be charged via a micro USB port on the side or wirelessly on the center console.
Keyless Go (also: Keyless Entry / Go; Passive Entry / Go) is Mercedes' term for an automotive technology which allows a driver to lock and unlock a vehicle without using the corresponding SmartKey buttons. [ 10 ] Once a driver enters a vehicle with an equipped Keyless Go SmartKey or Keyless Go wallet-size card, they have the ability to start and stop the engine, without inserting the SmartKey. A transponder built within the SmartKey allows the vehicle to identify a driver. An additional safety feature is integrated into the vehicle, making it impossible to lock a SmartKey with Keyless Go inside a vehicle.
The system works by having a series of LF ( low frequency 125 kHz) transmitting antennas both inside and outside the vehicle. The external antennas are located in the door handles. When the vehicle is triggered, either by pulling the handle or touching the handle, an LF signal is transmitted from the antennas to the key. The key becomes activated if it is sufficiently close and it transmits its ID back to the vehicle via RF ( Radio frequency >300 MHz) to a receiver located in the vehicle. If the key has the correct ID, the PASE module unlocks the vehicle.
The hardware blocks of a Keyless Entry / Go Electronic control unit ECU are based on its functionality:
The smart key determines if it is inside or outside the vehicle by measuring the strength of the LF fields. In order to start the vehicle, the smart key must be inside the vehicle.
It is important that the vehicle can't be started when the user and therefore the smart key is outside the vehicle. This is especially important at fueling stations where the user is very close to the vehicle. The internal LF field is allowed to overshoot by a maximum of 10 cm to help minimise this risk. Maximum overshoot is usually found on the side windows where there is very little attenuation of the signal.
A second scenario exists under the name "relay station attack" (RSA). The RSA is based on the idea of reducing the long physical distance between the car and the regular car owner's SmartKey. Two relay stations will be needed for this: The first relay station is located nearby the car and the second is close to the SmartKey. So on first view, the Keyless Entry / Go ECU and the SmartKey could communicate together. A third person at the car could pull the door handle and the door would open. However, in every Keyless Entry / Go system provisions exist to avoid a successful two-way communication via RSA. Some of the most known are:
Furthermore, Keyless Entry / Go communicates with other Control Units within the same vehicle. Depending on the electric car architecture, the following are some Control Systems that can be enabled or disabled:
Another possibility is using a motion sensor within the key fob. [ 11 ] [ 12 ]
Dead spots are a result of the maximum overshoot requirement from above. The power delivered to the internal LF antennas has to be tuned to provide the best performance i.e. minimum dead spots and maximum average overshoot. Dead spots are usually near the extremities of the vehicle e.g. the rear parcel shelf.
If the battery in the smart key becomes depleted, it is necessary for there to be a backup method of opening and starting the vehicle. Opening is achieved by an emergency (fully mechanical) key blade usually hidden in the smart key. On many cars emergency starting is achieved by use of an inductive coupling . The user either has to put the key in a slot or hold it near a special area on the cockpit, where there is an inductive coil hidden behind which transfers energy to a matching coil in the dead key fob using inductive charging .
Slots have proven to be problematic, as they can go wrong and the key becomes locked in and cannot be removed. Another problem with the slot is it can't compensate for a fob battery below certain operating threshold. Most smart key batteries are temperature sensitive causing the fob to become intermittent, fully functional, or inoperative all in the same day.
A Keyless Entry / Go system should be able to detect and handle most of the following cases:
A test by ADAC revealed that 20 car models with Keyless Go could be entered and driven away without the key. [ 13 ] [ 14 ] [ 15 ] [ 16 ] In 2014, 6,000 cars (about 17 per day) were stolen using keyless entry in London . [ 17 ] | https://en.wikipedia.org/wiki/Smart_key |
Smart ligands are affinity ligands selected with pre-defined equilibrium ( K d {\displaystyle K_{d}} ), kinetic ( k o f f {\displaystyle k_{off}} , k o n {\displaystyle k_{on}} ) and thermodynamic (ΔH, ΔS) parameters of biomolecular interaction.
Ligands with desired parameters can be selected from large combinatorial libraries of biopolymers using instrumental separation techniques with well-described kinetic behaviour, such as kinetic capillary electrophoresis (KCE), surface plasmon resonance (SPR), microscale thermophoresis (MST), [ 1 ] [ 2 ] etc. Known examples of smart ligands include DNA smart aptamers ; however, RNA and peptide smart aptamers can also be developed.
Smart ligands can find a set of unique applications in biomedical research, drug discovery and proteomic studies. For example, a panel of DNA smart aptamers has been recently used to develop affinity analysis of proteins with ultra-wide dynamic range of measured concentrations. | https://en.wikipedia.org/wiki/Smart_ligand |
Smart materials , also called intelligent or responsive materials, [ 1 ] [ page needed ] are designed materials that have one or more properties that can be significantly changed in a controlled fashion by external stimuli, such as stress , moisture, electric or magnetic fields, light, temperature , pH , or chemical compounds. [ 2 ] [ 3 ] Smart materials are the basis of many applications, including sensors and actuators , or artificial muscles , particularly as electroactive polymers (EAPs). [ 4 ] [ page needed ] [ 5 ] [ page needed ] [ 6 ] [ page needed ] [ 7 ] [ page needed ] [ 8 ] [ page needed ] [ 9 ] [ page needed ]
There are a number of types of smart material, of which are already common. Some examples are as following: | https://en.wikipedia.org/wiki/Smart_material |
A smart number is any synthetic unique identifier that communicates additional information about the entity identified. The smart number is conceptually similar to a superkey as defined in the relational model of database organization, but, is intended to inform end users about status of accounts. The term has fallen out of common usage since using one number to carry so much information is considered bad practice.
Common examples of smart numbers in use today include:
The term smart number may also apply to non-geographic telephone numbers, such as Australia's 13, 1300 and 1800 vanity numbers and freephone numbers . See Intelligent Network . | https://en.wikipedia.org/wiki/Smart_number |
The Smart Onboard Data Interface Module (SMODIM) is an integrated device once used by the United States Army and foreign militaries for live simulated weapons training on military platforms. The SMODIM was the primary component of the Longbow Apache Tactical Engagement Simulation System (LBA TESS) that provides weapons systems training and collective Force-on-Force live training participation. [ 1 ]
TESS was an advanced weapons training system developed for the AH-64 Apache to support force-on-force and force-on-target live training at U.S. Army Combat Training Centers (CTCs), Aviation Home Stations, and deployed locations. [ 2 ] TESS integrates with aircraft and ground vehicles to provide collective opposing force participation in live training.
The Aerial Weapons Scoring System (AWSS) integration with LBA TESS provided the ability to conduct force-on-target engagements using plastic ammunition for 30 mm gun, rockets, and simulated virtual emulated Hellfire missiles. Gunnery scoring was supported by the SMODIM, which transmitted data from the one point to the other. AWSS scored the pilot's live-fire gunnery performance and provided constructive After Action Review (AAR) feedback. [ 3 ] [ 4 ] [ 5 ]
Designed and manufactured by Aerotech,"The SMODIM was fully compatible with the multiple integrated laser engagement system (MILES) and legacy laser-based direct fire weapons simulation. Additionally, it eliminates the requirement for MILES-type lasers by providing the capability to geometrically pair weapon engagements with lasers". [ 6 ]
In 1992, Aerotech was selected by U.S. Army Communications Electronics Command (CECOM) [ 7 ] to provide the real-time casualty assessment (RTCA) interface for the AH-64 Apache Attack Helicopter. This component was called the onboard data interface module (ODIM). As the Army incorporated new technologies, the SMODIM added GPS and telemetry and became the core component of live helicopter training systems at all U.S. Army Combat Training Centers (CTCs) with a fielding of over 240 systems. In 1997, the SMODIM was modified to provide a proof of concept for the upgraded AH-64 (D model) Longbow Apache. In 1998 the "Modular" SMODIM and the longbow tactical engagement simulation system (TESS) training system was fielded to all three CTCs and Aviation Home Stations, and became the U.S. Army's first fully integrated live aviation training system. [ 8 ] Over the following 15 years, the SMODIM has deployed in multiple systems and platforms with over one thousand SMODIMs fielded in the U.S. and abroad. An "Advanced" SMODIM or "ASMODIM" is currently in development due to parts obsolescence and will provide an 80% increased processing performance. Security encryption is in accordance with FIPS 140-2 level 2. Advanced weapon simulation is augmented by digital terrain elevation data ( DTED ) and geometric ranging. Data communication and data transmission upgrades utilize RS-422 and RS-485 full duplex channels, and ARINC 429 technical standards.
The SMODIM includes a built-in GPS receiver, telemetry radio, data recorder, and MIL-STD-1553 mux bus processors. The SMODIM interfaces with the weapons systems and actively tracks, records and transmits data to the ground station or exercise control (EXCON). RTCA feedback is passed directly to the weapons processor and the ground station through the onboard telemetry radio. The SMODIM processes area weapons effects (AWE) data received from the EXCON and computes geometric pairing solutions for weapon engagements using the RF Hellfire, semi-automated laser (SAL) Hellfire, 30 mm chain gun, and rockets. It selects a target from its onboard player/position database in the appropriate weapons impact footprint, then uses the probability-of-hit (Ph) factor to determine the assessment (i.e., 'hit'/'miss'). Via the data link, it then informs the target it has been selected for assessment.
The SMODIM maintains a dynamic position database through player-to-player network communications. The onboard telemetry radio supports simultaneous distribution to multiple locations. The radio acts as a message repeater to overcome line of sight (LOS) interruptions. The SMODIM interfaces with distributed interactive simulation (DIS) networks using SMODIM tracking analysis and recording (SMOTAR), [ 9 ] an advanced software suite that provides visual display and tracking of SMODIM instrumented players. GPS provides real-time position data as players are dynamically simulated, tracked and recorded over tactical maps and aerial photos for after-action review (AAR).
The TESS Aircraft System consists of an "A" kit that becomes part of the aircraft, and a "B" kit that is added to the aircraft for training exercises. [ 10 ] The "A" kit includes the SMODIM Tray Assembly, modified software in the weapons display and systems processors, with cable connection provisions. The "B" kit includes the SMODIM, Eye-Safe Laser Range Finder/Designator (ESLRF/D), TESS Gun Control Unit (TGCU), Aircraft Internal Boresight Subassembly (AIBS), TESS Training Missile (TTM) with Flash Weapon Effects Signature Simulator (FlashWESS), GPS and telemetry antennas.
The SMODIM is qualified with an airworthiness release (AWR) through the Aviation Engineering Directorate (AED). [ 11 ] Environmental and Electromagnetic Interference (EMI) compliance tests include DO-160 , MIL-STD-810 E/F and ADS-37A-PRF.
The SMODIM is used on the following platforms with applicable current contract information:
Other platforms instrumented with the SMODIM include:
The TESS training system and SMODIM are used by the U.S. Army at Aviation Homestations and CTCs ( NTC , JRTC , JMRC ). Permanent TESS training support is provided at Ft Hood , TX since 1998 for the 21st Cavalry Brigade, [ 14 ] and is ongoing through the 166th Aviation Brigade and Foreign Military customers that train there. Permanent field support for TESS is also provided at the CTCs.
The UH-72A LUH Lakota is recently instrumented with the SMODIM and will deploy to Germany at the Joint Multinational Command Training Center (JMTC) to train pilots in combat engagements. [ 15 ] TESS provides the capability to track all LUH aircraft and provide OPFOR aircraft status (alive or killed) to the CTC EXCON. Simulated weapons capability allows Force-on-Force and Force-on-Target training engagements. [ 16 ]
The SMODIM supports U.S. Army Homestation gunnery on digital range training system (DRTS), [ 17 ] Digital Air Ground Integration Range (DAGIR), and Aviation Homestation Interim Package (AHIP) ranges. [ 18 ] Upon proven success, the SMODIM has become a key component of the Tank-Automotive and Armaments Command (TACOM) AHIP modular After Action Review capability. Beginning in September 2013, five AHIP AAR systems that use SMOTAR software suite are being fielded to Ft Knox, KY, Ft Drum, NY, Ft Stewart, GA, Ft Hood, TX, and Grafenwoehr Germany. The objective solution is full integration of ground/air manned platforms and Unmanned Aircraft Systems (UAS) including Gray Eagle, Shadow, Raven, and Puma. [ 19 ]
These programs are contracted by the U.S. Army Training and Doctrine Command (TRADOC), Program Executive Office for Simulation, Training and Instrumentation (PEO STRI), [ 20 ] and Program Manager Training Devices (PM TRADE).
Direct and foreign military sales (FMS) of the aviation TESS are currently in use by: Netherlands, Taiwan, Kuwait, Egypt, United Kingdom, Singapore, and United Arab Emirates. [ 21 ] | https://en.wikipedia.org/wiki/Smart_onboard_data_interface_module |
Smart pipe , related to a mobile network operator (MNO or operator ), refers to an operator’s network which leverages existing or unique service abilities, and the operator’s customer relationships, to provide value beyond that of data connectivity only. The use of the term “smart” refers to the operator’s ability to add value for added, and often unique, types of services and content beyond bandwidth and network speed only.
Among the commonly understood operational models for a MNO are smart pipes, walled gardens , and dumb pipes .
While there is no real industry standard definition of a smart pipe, there are several operators, bloggers, and researchers who have described aspects of a smart pipe which are generally accepted.
Network operator 3 led the way with the release of its X-Series line of devices in 2006. [ 1 ] The X-Series platform bundles a set of services, several of which are unique to 3, and provides unlimited data access in exchange for a fixed monthly premium. While not necessarily a full realization of a smart pipe, 3 is one of the first operators to offer such a combination of bandwidth and value-added services for flat-rate pricing.
In addition to pricing, there is a set of services commonly viewed as parts of a smart pipe, [ 2 ] [ 3 ] [ 4 ] such as:
By exposing these types of services to the mobile ecosystem , network operators can maintain the value of their pipes while enabling entrepreneurs to create new business models and generate entirely new revenue streams.
The need for operators to innovate around a smart pipe is rising as they face rising pressure from media companies [ 2 ] and new technologies, such as Apple’s iPhone , Nokia ’s consumer portal Ovi , and even the open-access policies of the U.S. Federal Communications Commission (FCC) introduced around its upcoming 700 MHz spectrum auction. [ 5 ]
Recently, Arun Sarin , CEO of Vodafone , was criticized for some statements he made about how Vodafone will always have a unique relationship with its subscribers through its billing relationship. [ 6 ] Although Sarin’s point has been true traditionally, as the article points out there are several new threats to that exclusivity such as traditional credit card, Obopay , PayPal Mobile , and existing media companies like Google via the Android platform , Yahoo via Go , and Apple via iPhone . | https://en.wikipedia.org/wiki/Smart_pipe |
A smart plug is a power plug and socket (also known as a wall plug, outlet, or electrical connector) which can be fitted between power cords and sockets to function as a remote-controlled power switch . As such, smart plugs can be used to make "dumb" electrical equipment smart , and thereby enable such devices for home automation or building automation purposes. [ 1 ] [ 2 ]
Smart plugs can, for example, be controlled via a mobile application , a smart home hub or a virtual assistant . [ 3 ] [ 4 ] Examples of protocols used for communication with smart plugs include Wi-Fi , Bluetooth , Zigbee and Z-Wave . Many smart plugs have a built-in ammeter so that electric energy consumption (measured in kilowatt-hours ) of the connected equipment can be monitored. [ 5 ] Smart plugs often have a slim profile so as not to hinder access to neighbouring sockets in a wall outlet or power strip .
This electronics-related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Smart_plug |
Smart polymers , stimuli-responsive polymers or functional polymers are high-performance polymers that change according to the environment they are in.
Such materials can be sensitive to a number of factors, such as temperature , humidity , pH , chemical compounds, the wavelength or intensity of light or an electrical or magnetic field and can respond in various ways, such as altering color or transparency, becoming conductive or permeable to water or changing shape ( shape memory polymers ). Usually, slight changes in the environment are sufficient to induce large changes in the polymer's properties. [ 1 ] [ 2 ] [ 3 ]
Smart polymers appear in highly specialized applications and everyday products alike. They are used for sensors and actuators such as artificial muscles , the production of hydrogels , biodegradable packaging, and to a great extent in biomedical engineering . One example is a polymer that undergoes conformational change in response to pH change, which can be used in drug delivery . [ 4 ] Another is a humidity-sensitive polymer used in self-adaptive wound dressings that automatically regulate moisture balance in and around the wound. [ 5 ] [ 6 ]
The nonlinear response of smart polymers is what makes them so unique and effective. A significant change in structure and properties can be induced by a very small stimulus. Once that change occurs, there is no further change, meaning a predictable all-or-nothing response occurs, with complete uniformity throughout the polymer. Smart polymers may change conformation , adhesiveness or water retention properties, due to slight changes in pH, ionic strength , temperature, ultrasound, or other triggers. For example, Kubota et al designed and loaded ultrasound-responsive hydrogel microbeads with silica nanoparticles that were released under ultrasonic stimulation. [ 7 ]
Another factor in the effectiveness of smart polymers lies in the inherent nature of polymers in general. The strength of each molecule's response to changes in stimuli is the composite of changes of individual monomer units which, alone, would be weak. However, these weak responses, compounded hundreds or thousands of times, create a considerable force for driving biological processes.
The pharmacy industry has been directly related to the polymer’s advances. In this field, polymers are playing a significant role, and their advances are helping entire populations around the world. The human body is a machine with a complex system and works as a response to chemical signals. Polymers play the role of drug delivery technology that can control the release of therapeutic agents in periodic doses. [ 8 ] Polymers are capable of molecular recognition and directing intracellular delivery. [ 8 ] Smart polymers get into the field to play and take advantage of molecular recognition and finally produced awareness systems and polymer carriers to facilitate drug delivery in the body system.
Several polymer systems respond to temperature, undergoing a lower critical solution temperature phase transition. One of the better-studied such polymers is poly(N-isopropylacryamide) , with a transition temperature of approximately 33 °C. Several homologous N- alkyl acrylamides also show LCST behavior, with the transition temperature depending on the length of the hydrophobic side chain. Above their transition temperature, these polymers become insoluble in water. This behavior is believed to be entropy driven.
Currently, the most prevalent use for smart polymers in biomedicine is for specifically targeted drug delivery. Since the advent of timed-release pharmaceuticals , scientists have been faced with the problem of finding ways to deliver drugs to a particular site in the body without having them first degrade in the highly acidic stomach environment. Prevention of adverse effects on healthy bone and tissue is also an important consideration. Researchers have devised ways to use smart polymers to control the release of drugs until the delivery system has reached the desired target. This release is controlled by either a chemical or physiological trigger.
Linear and matrix smart polymers exist with a variety of properties depending on reactive functional groups and side chains. These groups might be responsive to pH, temperature, ionic strength , electric or magnetic fields , and light. Some polymers are reversibly cross-linked by noncovalent bonds that can break and reform depending on external conditions. Nanotechnology has been fundamental in the development of certain nanoparticle polymers such as dendrimers and fullerenes , that have been applied for drug delivery. Traditional drug encapsulation has been done using lactic acid polymers. More recent developments have seen the formation of lattice-like matrices that hold the drug of interest integrated or entrapped between the polymer strands.
Smart polymer matrices release drugs by a chemical or physiological structure-altering reaction, often a hydrolysis reaction resulting in cleavage of bonds and release of drug as the matrix breaks down into biodegradable components. The use of natural polymers has given way to artificially synthesized polymers such as polyanhydrides , polyesters , polyacrylic acids , poly(methyl methacrylates ), poly(phthalaldehyde) , and polyurethanes . Hydrophilic , amorphous , low-molecular-weight polymers containing heteroatoms (i.e., atoms other than carbon) have been found to degrade fastest. Scientists control the rate of drug delivery by varying these properties thus adjusting the rate of degradation.
A graft-and-block copolymer is two different polymers grafted together. A number of patents already exist for various combinations of polymers with different reactive groups. The product exhibits properties of both individual components which adds a new dimension to an intelligent polymer structure and may be useful for certain applications. Cross-linking hydrophobic and hydrophilic polymers result in the formation of micelle-like structures that can protectively assist drug delivery through aqueous medium until conditions at the target location cause the simultaneous breakdown of both polymers.
A graft-and-block approach might be useful for solving problems encountered by the use of a common bioadhesive polymer, polyacrylic acid (PAA). PAA adheres to mucosal surfaces but will swell and degrade rapidly at pH 7.4, resulting in the rapid release of drugs entrapped in its matrix. A combination of PAAc with another polymer that is less sensitive to changes at neutral pH might increase the residence time and slow the release of the drug, thus improving bioavailability and effectiveness.
Hydrogels are polymer networks that do not dissolve in water but swell or collapse in changing aqueous environments. They are useful in biotechnology for phase separation because they are reusable or recyclable . New ways to control the flow, or catch and release of target compounds, in hydrogels, are being investigated. Highly specialized hydrogels have been developed to deliver and release drugs into specific tissues. Hydrogels made from PAAc are especially common because of their bioadhesive properties and tremendous absorbency .
Enzyme immobilization in hydrogels is a fairly well-established process. Reversibly cross-linked polymer networks and hydrogels can be similarly applied to a biological system where the response and release of a drug are triggered by the target molecule itself. Alternatively, the response might be turned on or off by the product of an enzyme reaction. This is often done by incorporating an enzyme, receptor or antibody , that binds to the molecule of interest, into the hydrogel. Once bound, a chemical reaction takes place that triggers a reaction from the hydrogel. The trigger can be oxygen, sensed using oxidoreductase enzymes or a pH-sensing response. An example of the latter is the combined entrapment of glucose oxidase and insulin in a pH-responsive hydrogel. In the presence of glucose, the formation of gluconic acid by the enzyme triggers the release of insulin from the hydrogel.
Two criteria for this technology to work effectively are enzyme stability and rapid kinetics (quick response to the trigger and recovery after removal of the trigger). Several strategies have been tested in type 1 diabetes research, involving the use of similar types of smart polymers that can detect changes in blood glucose levels and trigger the production or release of insulin. Likewise, there are many possible applications of similar hydrogels as drug delivery agents for other conditions and diseases. [ 9 ]
Smart polymers are not just for drug delivery. Their properties make them especially suited for bioseparations . The time and costs involved in purifying proteins might be reduced significantly by using smart polymers that undergo rapid reversible changes in response to a change in medium properties. Conjugated systems have been used for many years in physical and affinity separations and immunoassays . Microscopic changes in the polymer structure are manifested as precipitate formation, which may be used to aid the separation of trapped proteins from solution.
These systems work when a protein or other molecule that is to be separated from a mix, forms a bioconjugate with the polymer and precipitates with the polymer when its environment undergoes a change. The precipitate is removed from the media, thus separating the desired component of the conjugate from the rest of the mixture. Removal of this component from the conjugate depends on the recovery of the polymer and a return to its original state, thus hydrogels are very useful for such processes.
Another approach to controlling biological reactions using smart polymers is to prepare recombinant proteins with built-in polymer binding sites close to ligand or cell binding sites. This technique has been used to control ligand and cell binding activity, based on a variety of triggers including temperature and light.
Smart polymers play an essential part in the technology of self-adaptive wound dressings. The dressing design presents proprietary super-absorbent synthetic smart polymers immobilized in the 3-dimensional fiber matrix with added hydration functionality achieved by embedding hydrogel into the core of the material.
The dressing's mode of action relies on the ability of the polymers to sense and adapt to the changing humidity and fluid content in all areas of the wound simultaneously and to automatically and reversibly switch from absorption to hydration. The smart polymer action ensures the active synchronized response of the dressing material to changes in and around the wound to support the optimal moist healing environment at all times. [ 5 ] [ 6 ]
It has been suggested that polymers might be developed that can learn and self-correct behavior over time. Although this might be a far-distant possibility, there are other more feasible applications that appear to be coming in the near future. One of these is the idea of smart toilets that analyze urine and help identify health problems. In environmental biotechnology , smart irrigation systems have been also proposed. It would be incredibly useful to have a system that turns on and off, and controls fertilizer concentrations, based on soil moisture , pH, and nutrient levels . Many creative approaches to targeted drug delivery systems that self-regulate based on their unique cellular surroundings, are also under investigation.
There are obvious possible problems associated with the use of smart polymers in biomedicine . The most worrisome is the possibility of toxicity or incompatibility of artificial substances in the body, including degradation products and byproducts . However, smart polymers have enormous potential in biotechnology and biomedical applications if these obstacles can be overcome. | https://en.wikipedia.org/wiki/Smart_polymer |
A smart port is most often defined by being a technologically advanced seaport that integrates digitalization , automation , and data-driven solutions to optimize logistics, improve efficiency , enhance security , and reduce environmental impact . It uses technologies like IoT , AI , big data , and blockchain to streamline operations, monitor cargo movements, and improve decision-making in real-time.
A smart port equips the workforce with relevant skills and technology to solve the unique internal and external challenges of the organisation, and to facilitate the efficient movement of goods, delivery of services and smooth flow of information. Using a holistic approach, the smart port achieves results without creating new challenges internally or elsewhere in the supply chain eco-system.
The smart port minimises the negative impacts of its activities on the natural environment and enhances the surrounding communities - economically and socially.
The material benefits of chosen technologies allow the smart port to:
A smart port is not defined by the use of any one particular technology or concept. [ 1 ]
Smart ports employ smart technology solutions to increase efficiency, effectiveness and security by making ports more environmentally sustainable, economically efficient and capable of handling increased port traffic.
Due to the increasing size and volume of container, transport and cruise ships, ports continue to face new challenges with daily traffic and processing. Technologies such as IoT can improve warehouse logistics, inventory management etc. and help automate loading, dispatching and transporting goods.
In smart ports, parking spaces could be optimised and traffic streamlined by making more efficient use of limited space. [ 2 ] Sensors, cameras, drones and other technologies can automatically collect and share information such as weather, traffic and pollution data for port owners and customers. [ 3 ] Optimizing workflow could double capacity without having to additional space or having to invest in new infrastructure and equipment, while simultaneously reducing operation costs. [ 4 ] Making a port "smart" not only means digitally connecting everything inside the port, but also requires multilevel cooperation among government authorities, businesses, local communities and other relevant parties. [ 5 ]
Shared data from smart ports also requires standardisation so that it could be better utilised by people in different countries and locations. [ 5 ] The latest information from international business intelligence provider Visiongain, assesses that Smart Ports Market spending will reach $1.5 bn in 2019. A smart port takes complete advantage of space, produces higher revenues, saves natural resources and benefits from the technology accessible to the logistics community.
Artificial intelligence could assist with security checks and automated screening processes, not only helping to standardise and lower the durations of those tasks, but also making them safer, more reliable and less dependent on human failure. [ 6 ]
In order to remain economically competitive, ports need to efficiently streamline workflow and minimise costs. [ 2 ] If the optimal traffic flow for ships can be determined automatically, the cargo loading and unloading times can be optimised to save time so that more ships and cargo can be cleared in less time. [ 6 ] Local natural resources such as petroleum can also serve as incentives for port development, leading to long-term trade and economic development for an entire area. [ 7 ] At the same time, as automation is potentially able to lower overhead and costs, smart ports can become less financially dependent on political authorities, allowing increased flexibility for private investments and improvements. [ 8 ]
Ports have historically suffered from high levels of environmental pollution . [ 9 ] However, smart ports can limit energy consumption and waste by making use of automation and smart technologies. [ 4 ] [ 5 ] Hamburg , for example, has a system of sensors, cameras and smart lights on roads to help monitor and direct traffic, which can help to optimize traffic and thus lower emissions. [ 2 ] These large public infrastructural development projects typically require significant cooperation from various agencies and government authorities. [ 5 ]
Ports have always served an important function for the transfer of goods. Before the Industrial Revolution , ports had functioned as trade centers and marketplaces that would develop into centers for cross-cultural exchange, social development and demographic settlement.
In the 21st century, as ports merge with big data , artificial intelligence and IoT, the port is beginning to be seen as an interconnected smart environment bringing together different port sectors and even other ports. The whole supply chain is integrated while making autonomous, intelligent choices. [ 10 ]
To help build a network of highly connected and technologically advanced smart ports all over the world, the Hamburg Port Authority started the chainPORT initiative in collaboration with ports like Los Angeles , Montreal , Rotterdam , Antwerp , Barcelona , Felixstowe , Singapore and Busan , to share and disseminate the concept of smart ports. [ 11 ]
The maritime industry has been testing blockchain technology since 2017 and several shipping companies have partnered with tech companies to create blockchain shipping systems to improve maritime logistics. [ 12 ]
IBM has tested the Blockchain technology in Customs Declaration (CusDec) submission. Delays happen in customs declaration submission and border clearing could be minimised if the industry is ready to practice IBM's initiative.
According to 2024 WIPO Technology trends future of transportation report, the scientific community's engagement with smart ports has seen a noticeable uptick in research activity. Since 2016, there has been a marked increase in peer-reviewed journal articles focusing on various aspects of smart port technologies. Besides, the number of published patent families has increased from only 20 in 2016 to over 100 in 2023. [ 13 ]
Since smart ports would have to deal with big data and operate using surveillance, data privacy and security are potential areas of concern. Concerns include questions of who will have access to the data, and how networks can be protected from hacking and sabotage. [ 14 ] [ 15 ] Others criticise the term "smart" as frequently overused and exaggerated by IoT advocates for marketing purposes, while a truly "smart" environment should be able to learn and interact. [ 16 ]
A port ecosystem consists of multiple parties that take on a diverse range of tasks and responsibilities, with each party having different priorities for port development. [ 17 ] Currently, the smart port approach is frequently being promoted by port authorities . However, successfully developing a smart port requires a more holistic multi-stakeholder approach that would require large-scale cooperation on many different levels. [ 18 ] Another problem with automation is the mass replacement of human workers, which has already led to protests in places such as the Port of Los Angeles . [ 19 ]
Some governments have to focus more on providing jobs rather than focusing on smart solutions when the port operation is done by the government.
Automation also cannot be utilised to its full potential if there is a lack of basic infrastructures, such as when there is insufficient capacity for containers or inadequate port area size. In such circumstances, the real cost of implementing smart port technologies can actually outweigh the benefits. [ 20 ] Further, smart solutions are highly capital intensive. This may not be affordable for every port. [ citation needed ] | https://en.wikipedia.org/wiki/Smart_port |
Recent innovations in mobile and sensor technologies allow for creating a digital representation of almost any physical entity and its parameters over time at any place. RFID technologies, for instance, are used to ground digital representations, which are used to track and geo-reference physical entities. In general, physical worlds and digital representations become tightly interconnected, so that manipulations in either would have effect on the other.
Integration of information and communication technologies into products anywhere and anytime enable new forms of mobile marketing in respect to situated marketing communication, dynamic pricing models and dynamic product differentiation models. As Fano and Gershman state: "Technology enables service providers to make the location of their customers the location of their business". [ 1 ]
Smart products are specializations of hybrid products with physical realizations of product categories and digital product descriptions that provide the following characteristics:
The vision of smart products poses questions relevant to various research areas, including marketing , product engineering , computer science , artificial intelligence , economics , communication science , media economics , cognitive science , consumer psychology , innovation management and many more.
Since smart products combine a physical product with additional services, they are a form of product service system .
The term smart product can be confusing as it is used to cover a broad range of different products, ranging from smart home appliances (e.g., smart bathroom scales or smart light bulbs) to smart cars (e.g., Tesla). While these products share certain similarities, they often differ substantially in their capabilities. Raff et al. developed a conceptual framework that distinguishes different smart products based on their capabilities, which features 4 types of smart product archetypes (in ascending order of "smartness") [ 2 ] | https://en.wikipedia.org/wiki/Smart_products |
Smart rubber is a polymeric material that is able to "heal" when torn. Near room temperature this process is reversible and can be cycled several times. Supramolecular self-healing rubber can be processed, re-used, and ultimately recycled. The edges of a tear can be held together, and they will simply re-bond into apparent solidity. This is done by utilizing a hydrogen-bonding polymer , rather than producing a material whose structure would depend on covalent bonding and ionic bonding between chains, which is typical of normal rubber. In this case hydrogen bonding can occur simply by pressing two faces of the substance together, allowing the recovery of a continuous hydrogen bonding network.
Smart rubber will recover its original mechanical strength within several hours of being split and then subsequently recombined. Residual hydrogen bond donors and acceptors responsible for the self-healing properties of the elastomer remain unpaired until the newly exposed surface comes in contact with another complementary surface, allowing formation of new intermolecular hydrogen bonds.
When compared to rubber , which is covalently cross-linked, smart rubber cannot continually hold mechanical stress without undergoing gradual plastic deformation , and strain recovery is typically slow. | https://en.wikipedia.org/wiki/Smart_rubber |
Smart systems are systems (usually computer systems or electronic system ) which are able to incorporate and perform functions of sensing , actuation , and control in order to analyze a situation, based on acquired data and perform decisions in a predictive or adaptive manner , thereby performing smart actions. In most cases the Intelligence /"smartness" of the system can be attributed to autonomous operation based on closed loop control , resource management , and networking capabilities.
Smart systems typically consist of diverse components:
A lot of smart systems evolved from microsystems . They combine technologies and components from microsystems technology (miniaturized electric, mechanical, optical, and fluidic devices) with other disciplines like biology, chemistry, nanoscience , or cognitive sciences .
There are three generations of smart systems:
A major challenge in smart systems technology is the integration of a multitude of diverse components, developed and produced in very different technologies and materials. Focus is on the design and manufacturing of completely new marketable products and services for specialized applications (e.g., in medical technologies), and for mass market applications (e.g., in the automotive industries).
In an industrial context, and when emphasizing the combination of components with the aim of merging their functional and technical abilities into an interoperable system, the term "smart systems integration" is used. This term reflects the industrial requirement and particular challenge of integrating different technologies, component sizes, and materials into one system.
The systems approach calls for integrated design and manufacturing and has to bring together interdisciplinary technological approaches and solutions ( converging technologies ). Manufacturing companies as well as research institutes therefore face challenges in terms of specialized technological know-how, skilled labor, design tools, and equipment needed for the research, design and manufacturing of integrated smart systems.
Smart systems address environmental, societal, and economic challenges like limited resources, climate change, population ageing , and globalization. They are for that reason increasingly used in a large number of sectors. Key sectors in this context are transportation, healthcare, energy, safety and security, logistics, ICT, and manufacturing.
In terms of environmental challenges, smart solutions for energy management and distribution, smart control of electrical drives, smart logistics, or energy-efficient facility management could, by 2020, reduce global emissions by 23%, with an equivalent of 9.2 Gt CO 2 e .
In the automotive sector , smart systems integration will be a key enabler for pre-crash systems and predictive driver assistance features to reach the goal of the Road Safety Action Plan to halve the number of traffic deaths by 2020. Furthermore, smart systems are considered fundamental for sustainable and energy-efficient mobility, e.g., hybrid and electric traction.
Smart systems also considerably contribute to the development of the future Internet of Things , in that they provide smart functionality to everyday objects, e.g., to industrial goods in the supply chain , or to food products in the food supply chain. With the help of active RFID technology, wireless sensors, real-time sense and response capability, energy efficiency, as well as networking functionality, objects will become smart objects. These smart objects could support the elderly and the disabled. The close tracking and monitoring of food products could improve food supply and quality. Smart industrial goods could store information about their origin, destination, components, and use. And waste disposal could become a truly efficient individual recycling process.
Armatix developed a pistol that uses an RFID -active wristwatch to function.
In the healthcare sector, smart systems technology leads to better diagnostic tools, to better treatment and quality of life for patients by simultaneously reducing costs of public healthcare systems. Key developments in this sector are smart miniaturized devices and artificial organs like artificial pancreas or cochlear implants .
For example, Lab-on-a-chip devices have biochemical sensors that detect specific molecular markers in body fluids or tissue. They can include multiple functionalities such as sample taking, sample preparation, and sample pre-treatment, data processing, and storage, implantable systems which can be reabsorbed by the body after use, non-invasive sensors based on transdermal principles, or devices for responsive administration of medication. In healthcare, smart systems often operate autonomously and within networks, because those systems are able to provide real-time monitoring, diagnosis, interaction with other devices, and communication with the patient or physician. | https://en.wikipedia.org/wiki/Smart_system |
Smart thermostats are Wi-Fi thermostats that can be used with home automation and are responsible for controlling a home's heating, ventilation, and air conditioning . They perform similar functions as a programmable thermostat as they allow the user to control the temperature of their home throughout the day using a schedule, but also contain additional features, such as Wi-Fi connectivity, [ 1 ] [ 2 ] that improve upon the issues with programming.
Like other Wi-Fi thermostats, they are connected to the Internet via a Wi-Fi network. They allow users to adjust heating settings from other internet-connected devices, such as a laptop or smartphones . This allows users to control the thermostat remotely. This ease of use is essential for ensuring energy savings : studies have shown that households with programmable thermostats actually have higher energy consumption than those with simple thermostats because residents program them incorrectly or disable them completely. [ 3 ] [ 4 ]
Smart thermostats also record internal/external temperatures, the time the HVAC system has been running and can notify the user if the system's air filter needs to be replaced. This information is typically displayed later on an internet-connected device such as a smartphone.
Manual thermostats (also known as analog thermostats) are the oldest and simplest type of thermostats. These thermostats are set to one temperature and do not change until the user manually adjusts the temperature. [ 5 ]
Programmable thermostats , first introduced over 100 years ago, [ 6 ] are a type of thermostat that allows the user to set a schedule for different temperatures at different times. Most programmable thermostats also have a hold feature which suspends the schedule and effectively turns the thermostat into a manual thermostat. [ 5 ] The idea of the scheduling feature is that users will set a warmer or cooler temperature when the home is unoccupied to save energy and money. Due to this assumed energy savings, some building codes and government programs began requiring the use of programmable thermostats. [ 7 ] Due to the way people use these devices, most programmable thermostats result in more energy use than the basic manual thermostat. [ 8 ]
One of the main objectives of smart thermostats is to reduce the issues involved with using traditional programmable thermostats. In order to understand how smart thermostats take on this task, it is important to understand the issues regarding programmable thermostats and how they affect energy consumption. Between 2008-2009, Florida Power & Light (FPL) provided 400 homeowners with programmable thermostats and monitored their heating and cooling patterns. Out of the 400 participants, 56% of users used the programming feature while the remaining participants did not program the thermostat and left it on "hold". It was determined that the users who used the programming feature actually consumed 12% more energy than the non-programmers. This consumption increase resulted from higher overnight duty cycles associated with lower thermostat setpoints (i.e. lower temperature setting), due to confusion with setting the schedule. This study reveals that programmable thermostats will not necessarily save energy. The smart thermostat attempts to combat this issue by taking the user out of the picture and relying on sensors and computers to save energy. [ 8 ]
Another study conducted on the issue determined that the biggest problem for programmable thermostats was the human using it. The technology inside a programmable thermostat is no doubt one of the most important factors in determining whether or not the thermostat will be successful in saving energy. But an equally important factor is the human who is using the thermostat. Unfortunately, many people who own programmable thermostats do not know how to use the thermostat or are not using all of the features that are offered. One study conducted a number of interviews, surveys, and observations to determine that the vast majority of programmable thermostat owners are not using the thermostats for their intended purpose. An online survey showed that 89% of respondents do not use the schedule feature on their programmable thermostat. Other results from the interviews and surveys show that a large number of people have misconceptions about heating/cooling and the use of programmable thermostats. One misconception is people believing that heating all of the time is more efficient than scheduling the heat to turn off. Another misconception noted in the study is that turning down the thermostat does not substantially reduce energy consumption. These misconceptions reaffirm the idea that the programmable thermostat itself could have all of the necessary tools, but if the user does not use them or uses them incorrectly, then these thermostats will fail at saving energy. [ 7 ]
As a result of these studies and others like them, energy star suspended its labelling of programmable thermostats in December 2009. It became the goal of smart thermostats to address these issues by taking the human out of the picture and creating a thermostat that uses smart computing to truly reduce energy usage and cost. [ 7 ] [ 8 ]
Smart thermostats are similar to programmable thermostats in the sense that they have a scheduling feature that allows users to set different temperatures for different times of the day. In addition to this feature, smart thermostats implement other technologies to reduce the amount of human error involved with using programmable thermostats. Smart thermostats incorporate the use of sensors that determine whether or not the home is occupied and can suspend heating or cooling until the occupant returns. Additionally, smart thermostats utilize Wi-Fi connectivity to give the user access to the thermostat at all times. These additional technologies have proven to make smart thermostats successful in saving users energy and money. [ 5 ]
Development of the smart thermostat began in 2007 with the creation of the ecobee thermostat. The founder of ecobee, Stuart Lombard, wanted to save energy and reduce his family's carbon footprint. After realizing that heating and cooling made up most of his home's energy usage, [ 9 ] Lombard purchased a programmable thermostat in an attempt to reduce total energy usage. Lombard quickly discovered that the programmable thermostat was difficult to use and unreliable. Following difficulties with the programmable thermostat, he set out to create a smart thermostat that saved energy and was easy to use. With that goal, the ecobee company was created in attempt to offer users a thermostat that could truly save energy by fixing the issues with programmable thermostats. [ 10 ]
Following the ecobee, EnergyHub released its version of a smart thermostat in 2009 with the creation of the EnergyHub Dashboard. The co-founder of EnergyHub, Seth Frader-Thompson, got the idea for the Dashboard from his Prius. The Prius had screens on the dashboard that displayed the car's gas mileage in real time. Thompson felt that a house should have something that does the same. With that goal in mind, Thompson created a thermostat that could communicate with a home's furnace and appliances to determine the energy usage and efficiency and how much it was costing. The thermostat also had the capability to turn off appliances or raise and lower the temperature to save energy and cost. Ultimately, the goal of this thermostat was to display energy usage to users and to save energy and money. [ 11 ]
In 2011, Nest Labs developed the Nest Learning Thermostat . The Nest Thermostat attempted to reduce home energy consumption by addressing the problems with programmable thermostats through the use of better technology. This new technology included the implementation of sensors, algorithms, machine learning, and cloud computing. These technologies learn the behaviors and preferences of the occupants, and adjust the temperature up or down to make the occupant comfortable when they are home and to save energy when they are away. Additionally, the Nest Thermostat connects to the home Wi-Fi. This allows users to change the temperature, adjust the schedule, and check energy usage from a smartphone or laptop. All of these features were part of Nest's goal to create an easy to use thermostat that saves users energy and money. [ 12 ]
The programmable schedule feature on the smart thermostat is similar to that on standard programmable thermostats. Users are given the option to program a custom schedule to reduce energy usage when they are away from the home. Studies have shown, though, that manually creating a schedule may lead to more energy usage than just keeping the thermostat at a set temperature. [ 8 ] To avoid this problem, smart thermostats also provide an auto schedule feature. This feature requires the use of algorithms and pattern recognition to create a schedule that results in occupant comfort and energy savings. Upon creating a schedule, the thermostat will continue monitoring occupant behavior to make changes to the auto schedule. By taking the human error out of the scheduling, smart thermostats can create smart schedules that actually save energy. [ 13 ]
In an attempt to mitigate the issues with human error involved with programmable thermostats, the smart thermostat utilizes a sensor that can determine occupancy patterns to automatically change the temperature based on occupant patterns and behaviors. The Nest Learning Thermostat in particular uses passive infrared (PIR) motion sensors inside the unit to sense occupancy in the vicinity of the thermostat. This sensor informs the thermostat whether or not the home is occupied. In the case that the home is not occupied, the thermostat can suspend heating/cooling until the sensor is reactivated by an occupant. This sensor is also used to determine the occupancy patterns to create the auto schedule. A grille member is placed in front of the sensor to visually conceal and protect the PIR motion sensor inside the thermostat. The grille also helps to make the thermostat visually pleasing. [ 2 ] While this sensor technology is important for conserving energy, it is not without flaws. One of the major issues is that the sensor must be activated by someone walking in front of or near the thermostat. It is possible that an occupant could be at home and not pass in front of the sensor. In this case, the thermostat would shut off the heating/cooling and decrease human comfort. [ 14 ]
A major feature of Wi-Fi thermostats (such as smart thermostats) is their ability to connect to the internet. These thermostats are designed with a Wi-Fi module that allows the thermostat to connect to the user's home or office network and interface with a web portal or smartphone application, allowing users to control the thermostat remotely. [ 15 ] The Wi-Fi feature also has the ability to send reports on energy usage and HVAC system performance via the web portal, informing the user on their energy efficiency and how it compares to other smart thermostat users. It also may alert users when a problem arises with their HVAC system or when it is time for equipment maintenance. The thermostat also may use the Wi-Fi connection to display current weather conditions and the weather forecast. [ 1 ]
Another feature offered by some smart thermostats through the internet connection is geofencing. A geofence is a perimeter boundary created around the location of a smartphone or other device, based on GPS signals. The benefit of having a smart thermostat with geofencing capabilities is that it uses a users smartphone location to determine whether the home is occupied. Instead of using a schedule or sensor to determine occupancy, the smart thermostat can rely on the location of the geofence to tell the HVAC system whether it needs to be on or off. [ 16 ] Since most people carry their phones with them, geofencing can be an accurate way to determine occupancy patterns. [ 13 ]
Some smart thermostats, such as the Nest thermostat , can learn when the house is likely to be occupied, and when it is likely to be empty. This allows automatic pre-heating or pre-cooling so the temperature is comfortable when a resident arrives. If the residents or lifestyles change, these smart thermostats will gradually adjust the schedule, maintaining energy savings and comfort.
Motion detectors can determine if someone is home. One smart thermostat that uses motion detectors is the Ecobee4 . [ 17 ]
A wireless network can be used to sense when someone is out of range, thus determining if they're in or nearby their home. This geofencing technique is used by the Honeywell T6 Smart Thermostat.
A Connected thermostat is one that can be controlled through an internet connection, but will not provide analytic information. In recent years Wi-Fi thermostats have risen in popularity, they combine the technology of thermometers and Wi-Fi. So now you can have a thermometer in your home that is displayed on your phone that uses Wi-Fi technology. This technology is being developed right now so it will be available for thermostats in machinery and cars. Google is involved in this push towards technology since it acquired a Wi-Fi temperature company called Nest . [ 18 ] The market of smart thermostats is expected to reach around 3.5 Billion USD by the end of the year 2022. [ citation needed ]
Rather than controlling the temperature of the whole house, zoned systems can control individual rooms. This can increase energy savings, for example by heating or cooling only a Home-office and not the bedrooms and other areas that are empty during the day.
To show that their thermostats save energy and money, numerous smart thermostat producers have conducted models and studies to confirm their savings claims. One popular way that smart thermostat producers calculate energy usage is through energy modeling. In these models, the smart thermostat is compared to a thermostat set at a constant temperature, and savings are calculated. Using this method, ecobee calculated energy savings by correlating how long heating and cooling equipment run to local weather conditions. Energy savings were calculated relative to a constant temperature of 22 °C (72 °F). Upon conducting this model, ecobee determined a 23% savings on heating and cooling costs for those who switch to their smart thermostat. [ 19 ] Using a similar modeling method, Nest claimed a 20% energy savings for homeowners who install a Nest Learning Thermostat. [ 20 ]
To determine energy savings using actual data instead of energy models, in February 2015, Nest conducted a national study of Nest customers in 41 states who had enrolled in Nest's MyEnergy service. In May 2013, Nest acquired MyEnergy, a company that tracks and analyzes utility usage of people enrolled in the program. Upon acquiring MyEnergy, Nest was able to use the historical data to determine the energy savings of those who installed the Nest Learning Thermostat. This study looked at energy usage before and after the installation of a Nest Learning Thermostat and used a weather normalization procedure to prevent unusually cold or warm weather from skewing the data. The study had a sample size of 735 homes for gas usage analysis and 624 homes for electrical analysis. All of these homes were enrolled in the MyEnergy program and had sufficient energy data before and after the installation of a Nest Learning Thermostat. After observing the energy usage for one year, Nest determined that there was an average gas savings of 10% and a cooling savings of 17.5%. The savings varied from house to house depending on how occupants set their thermostat before the installation of a Nest thermostat, along with differences in occupancy patterns, house characteristics, and weather. [ 20 ]
While the results from the MyEnergy study are significantly lower than those from energy modeling, both show a savings in energy usage by switching to a smart thermostat. [ 19 ] [ 20 ]
Since the release of smart thermostats, a number of third party studies have been conducted to determine if smart thermostats actually save energy and how they compare to manual and programmable thermostats with regards to savings. One study conducted an experiment in which 300 standard programmable thermostats were placed in homes and 300 Nest smart thermostats were placed in other homes. It is important to note that the homeowners involved in this study received proper training on how to properly use all of the thermostat functions. This effectively eliminated the issues regarding human error with programmable thermostats. All homes were located within one region of Indiana and had previously undergone home energy assessment. After 1 year of observation, the study concluded that Nest users reduced their heating gas consumption by 12.5% while users of a standard programmable thermostat reduced consumption by 5%. Additionally, it was concluded that Nest and standard programmable thermostat users reduced their cooling electric consumption by 13.9% and 13.1%, respectively. The major factors that allowed Nest to reduce consumption more than other thermostats was its ability to further reduce human error and set more efficient temperatures. The Nest thermostat used sensors and Wi-Fi connectivity to adjust the temperature on its own and provide more savings. This study helps to suggest that smart thermostats are in fact successful in reducing energy consumption. [ 21 ]
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A similar study conducted in 2012 with the ecobee thermostat also concluded that smart thermostats are capable of saving energy. The goal of this pilot program was to determine the gas and electric savings of smart thermostats. This study provided 86 households with 123 ecobee thermostats and monitored the homes for 12 months. The study included 69 houses from Massachusetts and 17 from Rhode Island. The participants either had manual or programmable thermostats before the study was conducted. Gas and electric billing data were provided for 12 months before the study was conducted to use as a baseline. After the 12 months of observation, the study concluded that ecobee thermostats led to an average electricity savings of 16% and an average gas savings of 10%. The gas savings for manual thermostat replacements (10% per thermostat) was found to be larger than for programmable thermostat replacements (8% per thermostat). The difference in electricity savings between homes whose prior equipment was a manual thermostat or programmable thermostat was found to be minimal. [ 1 ]
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Although these studies report differing amounts of savings compared to the internal studies conducted by Nest and ecobee, both of these studies show that smart thermostats have the potential to save energy. This suggests that the technologies added to fix the issues with programmable thermostats have been successful. [ 1 ] [ 21 ]
Although most studies show that smart thermostats show an energy savings, the amount of savings varies. A large discrepancy is seen between energy modeling savings and the savings found using actual data. The energy modeling compares the smart thermostat to a constant set point temperature of 72 °F, but an online survey conducted by Nest showed that most users have a set point temperature that is 10% more efficient. [ 20 ] Therefore, the savings predicted by the energy modeling are going to be higher than real savings.
There are other factors that cause discrepancies even between studies that all look at actual data. Most studies compare total energy consumption of a house from year to year to determine energy savings, as opposed to looking at just the energy that is used for heating and cooling. Due to this, there could be other factors that change the energy consumption of a house, and it might be incorrect to state that the thermostat is responsible for all energy savings in a house. For example, it is possible that other new energy efficient practices/appliances are partially responsible for the savings in addition to the thermostat. [ 20 ]
Another discrepancy to consider is the population of people involved in the study. Some studies, such as the MyEnergy study, involve people who signed up for an energy analysis program. [ 20 ] These people are likely to be more energy conscious and efficient and have better heating and cooling practices. This greater interest in energy efficiency may lead to lower energy savings by switching to a smart thermostat. The most energy-conscious customers are the ones more likely to have had efficient thermostat settings, therefore, the savings that they receive from the smart thermostat may not be as great. [ 1 ]
The weather will also have an impact on the results of a study. Having very high temperatures in the summer and very cold temperatures in the winter will lead to more cooling and heating in those months, requiring more energy. When comparing year to year data, if one year had extreme temperatures, while the following year had moderate temperatures, the savings may look drastic. In reality though, the savings are not from the thermostat, but rather from the change in weather. Studies will try to mitigate this problem through weather normalization procedures. [ 20 ]
While smart thermostats have the potential to save energy consumption, they can create unintended consequences on the broader electrical grid. Smart thermostats tend to operate similarly across a population and can create load synchronization. This load synchronization can create much higher peaks and more rapid changes in heating demand. Particularly in the winter, this heating demand is shifted earlier in the morning, when solar electricity is unavailable, making it more difficult to supply electric heating sources like heat pumps with renewable energy. [ 22 ]
One issue with using a smart thermostat is the unreliability of the motion sensor. One of the main features of the smart thermostat is the ability to change the temperature when the sensor in the thermostat does not sense an occupant. The only sensor that is used though is the sensor in the thermostat. This means that if the home is occupied but no one walks passed the thermostat, the thermostat will think that the home is unoccupied and will change the temperature, potentially leading to occupant discomfort.
One study attempted to address this issue by adding more sensors throughout the house. Instead of using just one sensor in the thermostat, this team experimented with placing motion sensors and door sensors throughout the house to gain better understanding of the occupant's sleeping and occupancy patterns. These sensors communicated with each other and used an algorithm to quickly determine whether the occupants were active, sleeping, or away. The system used historical data to estimate when occupants would be returning and would begin "preheating" the home before they arrived. Additionally, the system would drift further from the set point when it was certain that no one was home. The study compared a standard ("reactive") smart thermostat and the multiple sensor system to a manual thermostat. The study concluded that a reactive smart thermostat with just on sensor saves, on average, 6.8% of energy consumption, while the multiple sensor system saved an average of 28% of energy consumption. This study again shows that, on average, smart thermostats achieve their goal of saving energy. It also shows that smart thermostats are not as well developed as they could be, and the addition of more sensors could result in better performance and energy savings. [ 14 ]
One of the issues with programmable thermostats that smart thermostats try to fix is the confusing user interface. Many owners of programmable thermostats found the controls and directions to be too confusing and opted out of using the scheduling feature completely. Others who used the feature used it incorrectly, due to the confusing directions, and saw an increase in energy usage. [ 7 ] Developers of smart thermostats have attempted to fix this issue by creating simple to use thermostats and providing proper direction. While this is an improvement on programmable thermostats, studies have shown that users desire more intense training from the installer of the thermostat on how to use the technical features. Additionally, many smart thermostats use a web portal where users can adjust the thermostat settings and look at their energy usage history. Again, studies have shown that users want this feature to be improved. Some complain that the web portal is not user friendly and they desire more training on how to use the web features during installation. [ 1 ]
Researchers from the University of Central Florida conducted an experiment to show that hackers could use the Nest thermostat as an entry point into one's home. Upon being connected to the internet, the hackers could use the thermostat to control local network traffic from a remote location. The hacker could also use the thermostat to act as a spy and would know whether or not the home is occupied. The research showed that in order for a hacker to gain access to the thermostat, they would have to gain physical access to the device and upload the malicious firmware via a USB port. This drastically decreases the chances that this type of attack will occur, but it is still possible if a used thermostat is purchased with the firmware already uploaded. The problem that allows this type of attack is with the hardware in the thermostat. Therefore, Nest cannot repair this issue with a simple software update, but rather it would need to build a new thermostat that can prevent this type of attack. [ 15 ] [ 23 ]
According to the 2015 Residential Energy Consumption Survey conducted by the U.S. Energy Information Administration , home heating and cooling account for the highest percentage of residential electrical energy consumption. Air conditioning accounts for 17% of electrical usage while space heating accounts for 15%. [ 9 ] The Residential Energy Consumption Survey from 2009 looked at energy consumption from all energy types (natural gas and electricity). This survey determined that space heating accounted for 42% of all residential energy consumption, while air conditioning accounted for 6%. [ 24 ] This energy usage needed to heat and cool homes is directly linked to climate change , as the energy provided for heating and cooling often comes from the burning of fossil fuels, leading to the release of greenhouse gas emissions . With an added focus on combating climate change and global warming , nations from around the world have begun to take on this issue by limiting greenhouse gas emissions and preventing the rise in global temperature through agreements such as The Paris Agreement . [ 25 ] Any steps taken to reduce residential energy consumption will help to achieve those goals.
Smart thermostats could be a solution to reducing energy consumption, as numerous studies have shown that these thermostats do in fact reduce home energy consumption. [ 1 ] [ 19 ] [ 20 ] [ 21 ] Additionally, the technology within smart thermostats has proven to provide optimal occupant comfort, while still reducing energy consumption. [ 20 ] In addition to providing comfort, these technologies take the human out of the picture. Many sustainable devices rely heavily on how the user uses them. By relying on technology instead of human actions, smart thermostats reduce the amount of human error often experienced with other sustainable devices, such as the programmable thermostat. These factors suggest that installing a smart thermostat is one easy step than many people can take to reduce energy usage and greenhouse gas emissions, ultimately leading to a more sustainable future.
Many housing corporations and smart thermostat developers realize the potential of smart thermostats to save energy, and have developed programs to advance sustainability through smarter technology. Ecobee promotes a sustainable future through its "A Better Tomorrow" program, in which the company donates time, data, and technology to ensure a brighter future. [ 26 ] As part of this program, in January 2018, ecobee donated 776 ecobee thermostats to the Toronto Community Housing Corporation (TCHC) to help the city of Toronto advance their climate change action plan. This donation helps to improve the TCHC's goal of providing healthy, safe, and sustainable homes for the people of Toronto. [ 27 ]
Another popular way that utility companies promote switching to a smart thermostat is through monetary incentives. The San Diego Gas & Electric company currently runs a program that offers participants a $50 e-gift card after switching to a smart thermostat. [ 28 ] The Wisconsin Focus on Energy program partners with utility companies across Wisconsin to offer a $75 check to those who purchase a qualifying smart thermostat. [ 29 ] Austin Energy , a utility company providing electricity to the city of Austin, Texas, offers a $25 rebate for each eligible smart thermostat that is purchased and installed. [ 30 ] Pacific Gas and Electric Company (PG&E) offers smart thermostat rebates in California for residential and multifamily customers. [ 31 ] [ 32 ] Many other companies across the United States offer similar programs to incentive smart thermostats and more sustainable heating and cooling. [ 33 ] [ 34 ]
Upon installing a smart thermostat, there are additional programs that continue to promote sustainability and reduced energy consumption. The Nest Rush Hour Rewards program partners with utility companies across the United States to incentivize customers to set a higher or lower temperature during peak demand periods. Energy rush hours occur when everyone in a particular area turns on their heating or cooling at the same time, such as during a heat wave. This extra demand may require utility companies to run additional power plants, leading to more cost and carbon emissions. To avoid this, the Rush Hour Rewards program incentivizes customers to set a more efficient temperature that will reduce the amount of energy needed to be produced by the utility. [ 35 ]
As more programs like these are created, smart thermostats will play an increasingly important role in reducing residential energy consumption. This reduction will lead to fewer greenhouse gas emissions, helping to create a more sustainable future. | https://en.wikipedia.org/wiki/Smart_thermostat |
Smartdust [ 1 ] is a system of many tiny microelectromechanical systems (MEMS) such as sensors, robots, or other devices, that can detect, for example, light , temperature , vibration , magnetism , or chemicals . They are usually operated on a computer network wirelessly and are distributed over some area to perform tasks, usually sensing through radio-frequency identification . Without an antenna of much greater size the range of tiny smart dust communication devices is measured in a few millimeters and they may be vulnerable to electromagnetic disablement and destruction by microwave exposure.
The concepts for Smart Dust emerged from a workshop at RAND in 1992 and a series of DARPA ISAT studies in the mid-1990s due to the potential military applications of the technology. [ 2 ] The work was strongly influenced by work at UCLA and the University of Michigan during that period, as well as science fiction authors Stanislaw Lem (in novels The Invincible in 1964 and Peace on Earth in 1985), Neal Stephenson and Vernor Vinge . The first public presentation of the concept by that name was at the American Vacuum Society meeting in Anaheim in 1996.
A Smart Dust research proposal [ 3 ] was presented to DARPA written by Kristofer S. J. Pister , Joe Kahn, and Bernhard Boser, all from the University of California, Berkeley , in 1997. The proposal, to build wireless sensor nodes with a volume of one cubic millimeter, was selected for funding in 1998. The project led to a working mote smaller than a grain of rice, [ 4 ] and larger "COTS Dust" devices kicked off the TinyOS effort at Berkeley .
The concept was later expanded upon by Kris Pister in 2001. [ 5 ] A recent review discusses various techniques to take smartdust in sensor networks beyond millimeter dimensions to the micrometre level. [ 6 ]
The Ultra-Fast Systems component of the Nanoelectronics Research Centre at the University of Glasgow is a founding member of a large international consortium which is developing a related concept: smart specks. [ 7 ]
Smart Dust entered the Gartner Hype Cycle on Emerging Technologies in 2003, [ 8 ] and returned in 2013, as the most speculative entrant. [ 9 ]
In 2022, a Nature paper written by Shyamnath Gollakota, Vikram Iyer, Hans Gaensbauer and Thomas Daniel, all from the University of Washington , presented tiny light-weight programmable battery-free wireless sensors that can be dispersed in the wind. [ 10 ] These devices were inspired by Dandelion seeds that can travel as far as a kilometer in dry, windy, and warm conditions.
Dust Networks started a project exploring the application of Smartdust, which included: | https://en.wikipedia.org/wiki/Smartdust |
SmarterChild was a chatbot available on AOL Instant Messenger and Windows Live Messenger (previously MSN Messenger ) networks. [ 1 ] [ 2 ]
SmarterChild was an intelligent agent or "bot" developed by ActiveBuddy , Inc., [ 3 ] with offices in New York and Sunnyvale. [ 4 ] It was widely distributed across global instant messaging networks. [ citation needed ] SmarterChild became very popular, attracting over 30 million Instant Messenger "buddies" on AIM (AOL), MSN and Yahoo Messenger over the course of its lifetime. [ 5 ]
Founded in 2000, ActiveBuddy was the brainchild of Robert Hoffer and Timothy Kay, who later brought seasoned advertising executive Peter Levitan on board as CEO. The concept for conversational instant messaging bots came from the founder's vision to add natural language comprehension functionality to the increasingly popular AIM instant messaging application. [ citation needed ] The original implementation took shape as a demo that Kay programmed in Perl in his Los Altos garage to connect a single buddy name, "ActiveBuddy", to look up stock symbols, and later allow AIM users to play Colossal Cave Adventure , a word-based adventure game, and MIT's Boris Katz Start Question Answering System [ 6 ] but quickly grew to include a wide range of database applications the company called 'knowledge domains' including instant access to news, weather, stock information, movie times, yellow pages listings, and detailed sports data, as well as a variety of tools (personal assistant, calculators, translator, etc.). [ citation needed ] None of the individual domains which the company had named “stocksBuddy”, “sportsBuddy”, etc. ever launched publicly. When Stephen Klein came on board as COO — and eventually CEO — he insisted that all of the disparate test “buddies” be launched together with the company’s highly-developed colloquial chat domain. He suggested using “SmarterChild”, a username coined by Tim Kay which Tim was using to test various things. The bundled domains were launched publicly as SmarterChild (on AIM initially) in June 2001. [ citation needed ] SmarterChild provided information wrapped in fun and quirky conversation. The company generated no revenue from SmarterChild, but used it as a demonstration of the power of what Klein called “conversational computing”. The company subsequently marketed Automated Service Agents—delivering immediate answers to customer service inquiries—-to large corporations, like Comcast, Cingular, TimeWarner Cable, etc. [ 7 ]
SmarterChild's popularity spawned targeted marketing-oriented bots for Radiohead , Austin Powers , Intel , Keebler , The Sporting News and others. [ citation needed ] ActiveBuddy co-founders, Kay and Hoffer, as co-inventors, were issued two controversial U.S. patents in 2002. [ 8 ] [ 9 ]
ActiveBuddy changed its name to Colloquis (briefly Conversagent) and targeted development of consumer-facing enterprise customer service agents, which the company marketed as Automated Service Agents(tm). Microsoft acquired Colloquis in October 2006 [ 10 ] and proceeded to de-commission SmarterChild and kill off the Automated Service Agent business as well.
Robert Hoffer, ActiveBuddy co-founder, licensed the technology from Microsoft after Microsoft abandoned the Colloquis technology. | https://en.wikipedia.org/wiki/SmarterChild |
Smartphone ad hoc networks ( SPANs ; also smart phone ad hoc networks ) are wireless ad hoc networks that use smartphones . Once embedded with ad hoc networking technology, a group of smartphones in close proximity can together create an ad hoc network. Smart phone ad hoc networks use the existing hardware (primarily Bluetooth and Wi-Fi ) in commercially available smartphones to create peer-to-peer networks without relying on cellular carrier networks, wireless access points, or traditional network infrastructure. Wi-Fi SPANs use the mechanism behind Wi-Fi ad-hoc mode, which allows phones to talk directly among each other, through a transparent neighbor and route discovery mechanism. SPANs differ from traditional hub and spoke networks, such as Wi-Fi Direct , in that they support multi-hop routing (ad hoc routing) and relays and there is no notion of a group leader, so peers can join and leave at will without destroying the network.
SPANs are useful under circumstances when the regular network is overloaded or unavailable, such as conferences, music festivals, or natural disasters, and have been popular in Australia and Latin America. [ 1 ] They are popular with youth in the United States as a way to save money, as data sent directly from device to device is free. [ 2 ]
SPANs started being used in Iraq in 2014 to bypass government restrictions on Internet usage, [ 3 ] in the 2014 [ 4 ] and 2019–20 Hong Kong protests , [ 5 ] in 2015 in anti-government protests in Russia . [ 6 ] They have also been used by protestors in Taiwan, Iran, and Syria. [ 7 ]
The ad hoc networking technology operating on Wi-Fi ad hoc mode, at the unlicensed ISM band of 2.4 GHz may result in profit loss by cellular carriers since ISM band is free and unlicensed while cellular carriers operate on licensed band at 900 MHz, 1200 MHz, 1800 MHz, etc. This has the potential to threaten telecommunication operators (telcos). Smart phone mobile ad hoc networks can operate independently and allow communications among smart phones users without the need for any 3G or 4G LTE signals to be present. Wi-Fi ad hoc mode was first implemented on Lucent WaveLAN 802.11a/b on laptop computers. Since Wi-Fi is present and embedded in all smart phones today, this earlier technology was adapted for smartphones.
Smartphone ad hoc networks may be useful in situations that include:
In Apple Inc. iPhones released with iOS version 7.0 and higher, multipeer connectivity [ 9 ] APIs (application programmable interfaces) are enabled and provided to allow Apple iPhones to operate in peer-to-peer ad hoc mesh networking mode. This means iPhones can now talk to each other without using a cellular signal or connection. Currently, Apple uses multipeer to allow one to send photos and large files (up to GB) to peers. This application is called AirDrop and in 2017 had started gaining in popularity. With 700+ millions [ 10 ] of iPhones being used globally, ad hoc peer-to-peer networks will gain pervasive presence almost instantly. [ 11 ]
By merging the Linux Wireless Extension API with parts of the Android software stack , a modified version of Android can enable the ability to harness the ad hoc routing, communications and networking features of the onboard Wi-Fi chip. This empowers millions of Android phones with ad hoc mesh connectivity and networking capabilities. [ 12 ]
Software packages that implement smartphone ad hoc networks include GPL -licensed Serval Project over Bluetooth or WiFi; GPL-licensed Commotion Wireless ; proprietary FireChat over Bluetooth, Bridgefy over Bluetooth, and GPL-licensed Briar over Bluetooth or WiFi. | https://en.wikipedia.org/wiki/Smartphone_ad_hoc_network |
Safety hazards have been noted due to pedestrians walking slowly and without attention to their surroundings because they are focused upon their smartphones . Texting pedestrians may trip over curbs, walk out in front of cars and bump into other walkers. The field of vision of a smartphone user is estimated to be just 5% of a normal pedestrian's. [ 1 ]
Some cities have taken design measures to make the streets safer for inattentive pedestrians, including lights embedded in pavements, and dedicated lanes for smartphone-using pedestrians to use.
The pejorative term smartphone zombie has been used to describe inattentive phone users; [ 2 ] this phrase was sometimes blended to smombie in German [ 3 ] and has seen some English usage. [ 4 ] In Hong Kong such phone users are called dai tau juk ("the head-down tribe"). [ 5 ] A 2017 review considered the popular culture term in regards to the medical diagnoses of internet addiction disorder and other forms of digital media overuse . [ 6 ]
In Chongqing , China, the government constructed a dedicated smartphone-sidewalk in 2014, separating the phone users and the non-phone users. [ 8 ] [ 9 ] [ 10 ] A similar scheme was introduced in Antwerp the following year. [ 11 ]
In Augsburg , Bodegraven and Cologne , ground-level traffic lights embedded in the pavement have been introduced so that they are more visible to preoccupied pedestrians, [ 12 ] [ 13 ] while traffic signals at an intersection in Zagreb cast the red light downwards, producing glare on smartphone screens. [ 14 ]
In Seoul , warning signs have been placed on the pavement at dangerous intersections following over a thousand road accidents caused by smartphones in South Korea in 2014. [ 15 ] The city has also implemented traffic lights embedded into the ground to pass the indication to the pedestrian even if they are fully immersed in their smartphone experience.
An app which uses the phone's camera to make the screen appear transparent can be used to provide some warning of hazards. [ 16 ]
In October 2017, the City of Honolulu, Hawaii introduced a measure to fine pedestrians looking at smartphones while crossing the road. [ 17 ] In 2019, China introduced penalties for "activities affecting other vehicles or pedestrians" and a woman was fined 10 yuan in Wenzhou . [ 18 ]
Science fiction author Ray Bradbury wrote about people being distracted by miniaturised technology in the 1950s, in his stories such as The Pedestrian and Fahrenheit 451 . [ 19 ] [ 20 ] [ 21 ] He wrote in 1958 of observing a couple walking in Beverly Hills , the woman listening to a small transistor radio "oblivious to man and dog, listening to far winds and whispers and soap-opera cries, sleepwalking, helped up and down curbs by a husband who might just as well not have been there". [ 22 ] | https://en.wikipedia.org/wiki/Smartphones_and_pedestrian_safety |
A smartwatch is a portable wearable computer that resembles a wristwatch . Most modern smartwatches are operated via a touchscreen , and rely on mobile apps that run on a connected device (such as a smartphone ) in order to provide core functions.
Early smartwatches were capable of performing basic functions like calculating , displaying digital time, translating text, and playing games. More recent models often offer features comparable to smartphones , including apps, a mobile operating system , Bluetooth and Wi-Fi connectivity, and the ability to function as portable media players or FM radios . Some high-end models have cellular capabilities, allowing users to make and receive phone calls. [ 1 ] [ 2 ] [ 3 ]
While internal hardware varies, most smartwatches have a backlit LCD or OLED electronic visual display [ 4 ] and are powered by a rechargeable lithium-ion battery . They may also incorporate GPS receivers , digital cameras , and microSD card readers, as well as various internal and environmental sensors such as thermometers , accelerometers , altimeters , barometers , gyroscopes , and ambient light sensors . Some smartwatches also function as activity trackers and include body sensors such as pedometers , heart rate monitors , galvanic skin response sensors, and ECG sensors. Software may include maps , health and exercise-related apps, calendars , and various watch faces .
The first digital watch was the Pulsar , introduced by the Hamilton Watch Company in 1972. The "Pulsar" became a brand name, and would later be acquired by Seiko in 1978. In 1982, a Pulsar watch (NL C01) was released which could store 24 digits, likely making it the first watch with user-programmable memory, or the first " memorybank " watch. [ 5 ]
With the introduction of personal computers in the 1980s, Seiko began to develop computers in the form of watches. The Data 2000 watch, named for its ability to store 2000 characters, came with an external keyboard for data entry. Data was synchronised from the keyboard to the watch via electromagnetic coupling (wireless docking). [ 6 ] Its memory was small, at only 112 digits. [ 5 ] It was released in 1984, in gold, silver, and black. [ 7 ]
These models were followed by many others from Seiko during the 1980s, most notably the "RC Series". The RC-1000 Wrist Terminal from Seiko Epson was released in 1984; it was the first Seiko model to interface with a computer [ 6 ] and was priced at around £100. [ 8 ] It featured 2 KB of storage, a two-line, 12-character display, and data transfer with a computer via an RS232C interface. [ 9 ] It was powered by a computer on a chip , and was compatible with most of the popular PCs of that time, including Apple II, II+ and IIe, BBC Micro , [ 10 ] Commodore 64, [ 11 ] IBM PC, NEC 8201, Tandy Color Computer, Model 1000, 1200, 2000 and TRS-80 Model I, III, 4 and 4p. The RC-20 Wrist Computer was released in 1985, [ 12 ] [ 13 ] followed by the RC-4000 and RC-4500.
During the 1980s, Casio began to market a successful line of "computer watches" in addition to its calculator watches , most notably the Casio data bank series. Casio and other companies also produced novelty "game watches", such as the Nelsonic game watches . [ 14 ]
Although pager watches were predicted in the early 1980s, [ 15 ] it took until the end of the decade for them to become more common. Two models were particularly notable: Motorola and Timex produced the Wrist Watch Pager, while AT&T Corporation and Seiko produced the MessageWatch. [ 16 ]
The Timex Datalink , introduced in 1994, was the first watch capable of transferring data wirelessly from a computer. Appointments and contacts created with Microsoft Schedule+ (the predecessor to MS Outlook) could be downloaded to the watch via patterns of visible light , which were displayed by a computer monitor and then detected by the watch's optical sensor. [ citation needed ]
In 1998, Steve Mann designed and built the world's first Linux wristwatch. [ 17 ] He presented it at the IEEE ISSCC on 7 February 2000, where he was dubbed "the father of wearable computing". [ 18 ] The watch later appeared on the cover of Linux Journal in July 2000, in which it was the topic of a featured article. [ 19 ]
Seiko launched the Ruputer in 1998 in Japan, a wristwatch computer with a 3.6 MHz processor. The Ruputer failed to achieve wide success due to its small, hard-to-read screen, cumbersome joystick method of navigation and text input, and poor battery life. [ 20 ] Outside of Japan, this watch was distributed as the Matsucom onHand PC. Despite low demand, it was distributed until 2006, making it a smartwatch with a long life cycle. Ruputer and onHand PC applications are fully compatible with each other. This watch is sometimes considered the first smartwatch, as it was the first to display graphics (albeit in monochrome), and third-party applications (mostly homebrew). [ citation needed ]
In 1999, Samsung launched the world's first watch phone, the SPH-WP10. It had a protruding antenna, monochrome LCD screen, and 90-minute talk time with an integrated speaker and microphone. [ 21 ]
In June 2000, IBM displayed a prototype for the WatchPad , a wristwatch that ran Linux . The original version had only 6 hours of battery life, which was later extended to 12. [ 23 ] It featured 8 MB of memory and ran Linux 2.2. [ 24 ] The device was later upgraded with an accelerometer, vibrating mechanism, and fingerprint sensor. IBM began to collaborate with Citizen Watch Co. to create the "WatchPad". The WatchPad 1.5 features a 320 × 240 QVGA monochrome touch sensitive display and runs Linux 2.4. [ 25 ] [ 26 ] It also features calendar software, Bluetooth , 8 MB of RAM and 16 MB of flash memory. [ 27 ] [ 28 ] Citizen was hoping to market the watch to students and businessmen, with a retail price of around $399. [ 28 ] Epson Seiko introduced their Chrono-bit wristwatch in September 2000. The Chrono-bit watches have a rotating bezel for data input, synchronize PIM data via a serial cable, and can load custom watch faces. [ 29 ]
In 2003, Fossil released the Wrist PDA , a watch that ran the Palm OS and contained 8 MB of RAM and 4 MB of flash memory. [ 30 ] [ 31 ] It contained a built in stylus to assist in using the tiny monochrome display, which had a resolution of 160×160 pixels. Although many reviewers declared the watch revolutionary, it was criticized for its weight (108 grams) and was discontinued in 2005. [ 32 ]
In the same year, Microsoft announced its SPOT smartwatch, which it released in early 2004. [ 33 ] SPOT stands for Smart Personal Objects Technology , an initiative by Microsoft to personalize household electronics and other everyday gadgets. For instance, the company demonstrated coffee makers, weather stations, and alarm clocks featuring built-in SPOT technology. [ 34 ] The device was a standalone smartwatch [ 35 ] that offered information at a glance, in comparison to other devices that required more immersion and interaction. The information included weather, news, stock prices, and sports scores, and was transmitted through FM waves. [ 33 ] It was accessible through a yearly subscription that cost between $39 and $59. [ 34 ]
The Microsoft SPOT Watch had a monochrome 90×126 pixel screen. [ 36 ] Fossil, Suunto, and Tissot also sold smartwatches using SPOT technology. For instance, Fossil's Abacus, which was a variant of the Fossil Wrist PDA, retailed from $130 to $150. [ 37 ] [ 34 ]
Sony Ericsson teamed up with Fossil and released the first watch, MBW-100, that connected to Bluetooth. This watch notified the user when receiving calls and text messages. The watch struggled to gain popularity, however, due to its exclusivity to Sony Ericsson phones. [ 38 ]
In 2009, Hermen van den Burg, CEO of Smartwatch and Burg Wearables, launched Burg , the first smartphone watch with its own SIM card. The watch was "standalone", meaning it did not require tethering to a smartphone. Burg received the award for the Most Innovative Product at the Canton Fair in April 2009. [ 39 ] [ 40 ] [ 41 ] [ 42 ] [ 43 ] [ 44 ] [ excessive citations ] Samsung also launched their S9110 Watch Phone, which featured a 1.76-inch (45 mm) color LCD display and was 11.98 millimetres (0.472 in) thin. [ 21 ]
Sony Ericsson launched the Sony Ericsson LiveView , a wearable watch device which was essentially an external Bluetooth display for an Android smartphone.
Vyzin Electronics Private Limited launched a ZigBee enabled smart watch called VESAG, [ 45 ] which featured cellular connectivity for remote health monitoring. [ 46 ] [ 47 ]
Motorola released MOTOACTV on 6 November 2011. [ 48 ]
Pebble was a smartwatch funded via Kickstarter , which set a fundraising record for the site, raising $10.3 million between 12 April and 18 May 2012. The watch has a 32-millimetre (1.26 in) 144 × 168 pixel black and white memory LCD, using an ultra low-power " transflective LCD " manufactured by Sharp . It features a backlight, vibrating motor, magnetometer , ambient light sensors, and three-axis accelerometer . [ 49 ] [ 50 ] [ 51 ] [ 52 ] [ 53 ] It can communicate with an Android or iOS device using both Bluetooth 2.1 and Bluetooth 4.0 ( Bluetooth Low Energy ) via Stonestreet One's Bluetopia+MFi software stack. [ 54 ] Bluetooth 4.0 support was not initially enabled, but a firmware update in November 2013 enabled it. [ 55 ] The watch is charged using a modified USB -cable that attaches magnetically to the watch, allowing it to maintain water resistance. [ 51 ] The battery was reported in April 2012 to last seven days. [ 56 ] Based on feedback from Kickstarter backers, the developers added water resistance to the device's feature set. [ 57 ] The Pebble has a waterproof rating of 5 atm , which means it can be submerged down to 40 metres (130 ft) and has been tested in both fresh and salt water, allowing one to shower, dive or swim while wearing the watch. [ 58 ]
In 2013, startup Omate announced its TrueSmart watch via a Kickstarter campaign, claiming it was the first smartwatch to capture the full capabilities of a smartphone. The campaign raised over $1 million, making it the 5th most successful Kickstarter at that time. The device made its public debut in early 2014. [ 59 ] Consumer device analyst Avi Greengart, from research firm Current Analysis, suggested that 2013 may be the "year of the smartwatch", as "the components have gotten small enough and cheap enough" and many consumers own smartphones that are compatible with a wearable device. Wearable technology , such as Google Glass , was speculated to evolve into a business worth US$6 billion annually, and a July 2013 media report revealed that the majority of major consumer electronics manufacturers were undertaking work on a smartwatch device at the time of publication. The retail price of a smartwatch could be over US$300, plus data charges, while the minimum cost of smartphone-linked devices may be US$100. [ 60 ] [ 61 ]
As of July 2013, the list of companies that were engaged in smartwatch development activities consisted of Acer , Apple, BlackBerry , Foxconn /Hon Hai, Google , LG , Microsoft , Qualcomm , Samsung, Sony , VESAG and Toshiba . Some notable omissions from this list include HP , HTC , Lenovo , and Nokia . [ 61 ] Science and technology journalist Christopher Mims identified the following points in relation to the future of smartwatches:
Acer's S.T. Liew stated in an interview with gadget website Pocket-Lint that he believed that companies should be researching wearable technology, and that it could grown to "billions of dollars' worth of industry". [ 63 ]
As of 4 September 2013, three new smartwatches had been launched: the Samsung Galaxy Gear , Sony SmartWatch 2 , [ 64 ] and the Qualcomm Toq . [ 65 ] PHTL, a company based in Dallas, Texas , completed a Kickstarter campaign for its HOT Watch smartwatch in September 2013. This device enables users to leave their handsets in their pockets, since it has a speaker for phone calls in both quiet and noisy environments. [ 66 ] In a September 2013 interview, Pebble founder Eric Migicovsky stated that his company was not interested in any acquisition offers. [ 67 ] Two months later, he revealed that his company has sold 190,000 smartwatches, most of which were sold after its Kickstarter campaign closed. [ 68 ]
Motorola Mobility CEO Dennis Woodside confirmed during a December 2013 interview that his company was working on a smartwatch. [ 69 ] Woodside further discussed the difficulties that other companies had experienced with wrist-wearable technologies.
In April 2014, the Samsung Gear 2 was released, one of few smartwatches to be equipped with a digital camera. It has a resolution of two megapixels and can record video in 720p. [ 70 ]
At the 2014 Consumer Electronics Show , a large number of new smartwatches were released from various companies such as Razer Inc . [ 71 ] Archos , [ 72 ] Some called the show a "wrist revolution". [ 73 ] At Google I/O on 25 June 2014, the Android Wear platform was introduced and the LG G Watch and Samsung Gear Live were released. The Wear-based Moto 360 was announced by Motorola in 2014. [ 74 ] At the end of July, Swatch's CEO Nick Hayek announced that they will launch a Swatch Touch with smartwatch technologies in 2015. [ 75 ] In the UK, London's Wearable Technology Show debuted several new models from smartwatch companies.
Samsung's Gear S smartwatch was launched in late August 2014. The model features a curved Super AMOLED display and a built-in 3G modem. TechCrunch ' s Darrell Etherington said that "we’re finally starting to see displays that wrap around the contours of the wrist, rather than sticking out as a traditional flat surface". The corporation commenced selling the Gear S smartwatch in October 2014, alongside the Gear Circle headset accessory. [ 76 ] At IFA 2014, Sony Mobile announced the third generation of its smartwatch series, the Sony Smartwatch 3, powered by Android Wear. [ 77 ] Fashion Entertainments' e-paper watch was also announced at the show. [ 78 ]
On 9 September 2014, Apple Inc. announced its first smartwatch, called Apple Watch, with an early 2015 release date. [ 79 ] On 24 April 2015, Apple Watch began shipping worldwide. [ 80 ] Apple's first wearable attempt was met with considerable criticism during its pre-launch period, with many early technology reviews citing issues with battery life and hardware malfunctions. However, other outlets praised Apple for creating a device with the potential to compete with "traditional watches" [ 81 ] instead of just smartwatches. The watch's screen only wakes when activated by lifting one's wrist, touching the screen, or pressing a button. On 29 October 2014, Microsoft announced the Microsoft Band , a smart fitness tracker and the company's first venture into wrist-worn devices since SPOT (Smart Personal Objects Technology) a decade earlier. The Microsoft Band was released at $199 the following day. [ 82 ]
In October 2015, Samsung unveiled the Samsung Gear S2 . [ 83 ] It features a rotating bezel for ease of use, and an IP68 rating for water resistance up to 1.5 meters deep for 30 minutes. The watch is compatible with industry-standard 20 mm straps.
At the 2016 Consumer Electronics Show, Razer released the Nabu Watch, a dual-screen smartwatch. The first screen integrates an always-on illuminated backlit display and handles standard features such as date and time. The second OLED screen, activated by raising one's wrist, allows access to additional smart features. [ 84 ] Luxury watchmaker TAG Heuer also released TAG Heuer Connected , a smartwatch powered by Android Wear. [ 85 ]
On 31 August 2016, Samsung unveiled the Samsung Gear S3 smartwatch, with improved specifications. There are two models of the watch: the Samsung Gear S3 Classic and the LTE version Samsung Gear S3 Frontier. [ 86 ]
The top smartwatches that debuted at the 2017 Consumer Electronics Show included the Casio WSD-F20, the Misfit Wearables Vapor and the Garmin Fenix 5 series. [ 87 ] On 22 September 2017 Apple released their Apple Watch Series 3 model which offers built in LTE cellular connectivity allowing phone calls, messaging and data without relying on a nearby smartphone connection. [ 88 ]
In 2018, Samsung introduced the Samsung Galaxy Watch series . [ 89 ]
In its September 2018 keynote, Apple introduced a redesigned Apple Watch Series 4. It featured a larger display with smaller bezels, as well as an EKG feature which is built to detect abnormal heart function. [ 90 ]
In Qualcomm's September 2018 presentation, it unveiled its Snapdragon 3100 chip. It is a successor to the Wear 2100, and it includes greater power efficiency, and a separate low power core that can run basic watch functions as well as slightly more advanced functions, such as step tracking. [ citation needed ]
In 2020, the United States Food and Drug Administration granted marketing approval for an Apple Watch app called NightWare. The app aims to improve sleep for people suffering from PTSD -related nightmares, by vibrating when it detects a nightmare in progress based on heart rate monitoring and body movement. [ 91 ]
As of January 2025, smartwatches have advanced significantly, integrating sophisticated health-monitoring features, enhanced connectivity, and practical everyday functionalities. Recent models, such as the Apple Watch Series 10 [ 92 ] and Google Pixel Watch 3, [ 93 ] include innovations like sleep apnea detection and alerts for abnormal pulse rates. Huawei has introduced technology capable of analyzing cough patterns to identify potential pulmonary issues. [ 94 ]
Smartwatches rose in popularity during the 2010s. Today, they are often used as fitness trackers, and smartphone "companions". [ 95 ] [ user-generated source? ] According to a study from statista , smartwatch revenue was estimated to reach $44.15 billion by 2023, and revenue per year was expected to continue to grow to $62.46 billion by 2028. [ 96 ] The top contributors to the market size of market watches include Apple Inc , Fossil Group Inc , Garmin Lt , Google LLC , Huawei Technologies Co , Samsung , and Xiaomi . [ 97 ]
Many smartwatch smartphone models manufactured in the 2010s are completely functional as standalone products. Some are used in sports and feature a GPS tracking unit that can record historical data. For example, after a workout, data can be uploaded onto a computer or online in order to create a log of activities for analysis or sharing. Some watches can provide full GPS support, displaying maps and current coordinates, recording tracks, and bookmarking locations. With Apple, Sony, Samsung, and Motorola introducing smartwatch models, 15 percent of tech consumers [ 98 ] use wearable technologies, which has attracted advertisers. [ 98 ] [ 99 ] Advertising on wearable devices was expected to increase heavily by 2017 as advanced hypertargeting modules were introduced to the devices; companies aim to crate advertisements that are tailored for smartwatches. [ 100 ]
"Sport watch" functionality often includes activity tracker features, as included on GPS watches made for training, diving, and outdoor sports. Functions may include training programs (such as intervals), lap times, speed display, GPS tracking unit, route tracking, dive computer , heart rate monitor compatibility, Cadence sensor compatibility, and compatibility with sport transitions (as in triathlons ). [ 101 ] Other watches can cooperate with a smartphone app to execute their functions. They are paired to a smartphone, usually via Bluetooth . Some of these only work with a phone that runs the same mobile operating system ; others use an OS that is unique to the watch, or otherwise is able to work with most smartphones. Paired, the watch may function as a remote to the phone. This allows the watch to display data such as calls, SMS messages, emails , calendar invitations, and any data that may be made available by relevant phone apps .
From about 2015, several manufacturers began to release smartwatches with LTE support, enabling direct connection to 3G / 4G mobile networks for voice and SMS use, without the need to carry a paired smartphone. [ 102 ]
Tests by UK consumer organization Which? found that ultra-cheap smartwatches and fitness trackers sold online often had serious security flaws, including excessive data collection, insecure data storage, the inability to opt out of data collection, and a lack of a security lock function. Typically, a watch app can request permission to collect and store personally identifiable information, and apps can be rendered unusable if permission is denied. The user cannot know if information is being stored securely, and it cannot be deleted. There is no control over whether the supplier views it or sells it on, for whatever purpose. In many cases, data collected is not encrypted when transmitted to the supplier. [ 103 ]
Which? did not specifically test the functionality of ultra-cheap watches, but noticed during their security audit that some could detect heart rate, blood oxygen measurements, and steps while not being worn or moved. They said that this "suggests [that] they are at best inaccurate and at worst useless". [ 103 ]
In the United Kingdom , a Product Security and Telecoms Infrastructure Act was passed in December 2022, [ 104 ] effective from 2024. The Act, which should cover smartwatches, specifies security standards that manufacturers, importers and distributors (including online marketplaces) of smart devices must meet. [ 103 ]
A 2024 study by the University of Notre Dame found that some smartwatch straps contain high levels of PFAS , chemical compounds that have been classified as toxic or carcinogenic and might penetrate the skin. The researchers recommend replacing straps containing fluoroelastomer with straps made of silicone , which does not contain PFAS. [ 105 ]
Due to faults in the design of current smartwatches, hardware and software designs have sometimes favored certain demographics. For example, smartwatches have more accurate tracking of data for individuals who have lighter skin, compared to individuals who have darker skin. This is due to the method that smartwatches use to monitor heart rate. An article published by the Healthcare Degree describes the most common method, in which devices use optical sensors to track the presence of blood in the wrist, indicating a heart beat. This type of lighting technique is cheaper and simple to use than other methods; however, because the green light used has shorter wavelengths , it is less able to penetrate melanin , the pigment which causes darker skin. This can make heart rate tracking for darker-skinned individuals less accurate. [ 106 ] [ better source needed ]
Social consequences from the increase in popularity of smartwatches include data collection and data privacy concerns. Smartwatches are capable of collecting personal health data such as activity levels, heart rate , sleep patterns , and other metrics. This user data is often collected and stored in the cloud, which can sometimes be accessed by companies and researchers, and used for many purposes. There have been many cases of data misuse. One instance published by the Warren Alpert Medical School involved Fitbit facing a lawsuit in 2011 for selling personal health data to advertisers without user consent. [ 107 ] Another instance occurred when Strava allowed users to share their routes, which led to the accidental revelation of several military base locations throughout the world. [ 107 ]
AsteroidOS is an open source firmware replacement for some Android Wear devices.
Flyme OS is firmware based on the Android operating system, developed by Meizu .
InfiniTime is the default firmware for the PineTime smartwatch, produced by Pine64 . It is a community project based on FreeRTOS , as well as being free software licensed under the GNU General Public License . [ 108 ] It supports Android, desktop Linux, the PinePhone, and SailfishOS as companion devices for features such as music playback, call and text notifications, navigation instructions, and time synchronization. [ 109 ]
As of January 2022, Infinitime version 1.8's additional features include secure Bluetooth pairing, customisable watch faces, a flashlight, basic paint program, stopwatch, alarm clock, countdown timer, step counter, heart rate monitor, a one-player pong clone, a numerical puzzle game and a metronome . Features are under ongoing development, with firmware updates available via GitHub. [ 110 ]
HarmonyOS is an operating system developed by Huawei, intended for the various "smart" devices they manufacture. Starting in 2021, it has seen use in Huawei Watches , replacing its predecessor, LiteOS . [ 111 ]
Sailfish OS is a Linux-based operating system for various platforms, including Sailfish smartwatches.
Tizen is a Linux-based operating system developed for various platforms, including smartwatches. Tizen is a project within the Linux Foundation and is governed by a Technical Steering Group (TSG) composed of Samsung and Intel among others. Samsung released the Samsung Gear 2, Gear 2 Neo, Samsung Gear S, Samsung Gear S2 and Samsung Gear S3, all running Tizen. [ 112 ]
watchOS is a proprietary mobile operating system developed by Apple Inc. to run on the Apple Watch.
Wear OS , previously known as Android Wear, is a smartwatch operating system developed by Google Inc.
In China, since around 2015, smartwatches have become widely used by schoolchildren, and are widely advertised on Chinese television as a safety device for them. [ 113 ] The devices are typically colorful and made of plastic, and they often lack a display unless a button is pressed. While their functionality is limited, they primarily allow children to make and receive calls, display the time, and sometimes measure air temperature. These smartwatches typically cost between US$100 and US$200.
Children's smartwatches are also sold in other countries. [ 114 ] [ 115 ]
Some smartwatches can also help elderly or disabled people, reporting their location to a caretaker if they fall or become lost.
A "smart strap" is a technology that is capable of providing enhanced functionality to smartwatches, through built-in sensors located within the strap. For example, smart strap accessories can add a webcam, [ 116 ] ECG sensor [ 117 ] and biompedance measurement [ 118 ] features. | https://en.wikipedia.org/wiki/Smartwatch |
Smash and Grab is the name given to a technique developed by Charles S. Hoffman and Fred Winston used in molecular biology to rescue plasmids from yeast transformants into Escherichia coli , also known as E. coli, in order to amplify and purify them. [ 1 ] In addition, it can be used to prepare yeast genomic DNA (and DNA from tissue samples) for Southern blot analyses or polymerase chain reaction (PCR). [ citation needed ] | https://en.wikipedia.org/wiki/Smash_and_Grab_(biology) |
In topology , a branch of mathematics , the smash product of two pointed spaces (i.e. topological spaces with distinguished basepoints) ( X, x 0 ) and ( Y , y 0 ) is the quotient of the product space X × Y under the identifications ( x , y 0 ) ~ ( x 0 , y ) for all x in X and y in Y . The smash product is itself a pointed space, with basepoint being the equivalence class of ( x 0 , y 0 ). The smash product is usually denoted X ∧ Y or X ⨳ Y . The smash product depends on the choice of basepoints (unless both X and Y are homogeneous ).
One can think of X and Y as sitting inside X × Y as the subspaces X × { y 0 } and { x 0 } × Y . These subspaces intersect at a single point: ( x 0 , y 0 ), the basepoint of X × Y . So the union of these subspaces can be identified with the wedge sum X ∨ Y = ( X ⨿ Y ) / ∼ {\displaystyle X\vee Y=(X\amalg Y)\;/{\sim }} . In particular, { x 0 } × Y in X × Y is identified with Y in X ∨ Y {\displaystyle X\vee Y} , ditto for X × { y 0 } and X . In X ∨ Y {\displaystyle X\vee Y} , subspaces X and Y intersect in the single point x 0 ∼ y 0 {\displaystyle x_{0}\sim y_{0}} . The smash product is then the quotient
The smash product shows up in homotopy theory , a branch of algebraic topology . In homotopy theory, one often works with a different category of spaces than the category of all topological spaces . In some of these categories the definition of the smash product must be modified slightly. For example, the smash product of two CW complexes is a CW complex if one uses the product of CW complexes in the definition rather than the product topology . Similar modifications are necessary in other categories.
For any pointed spaces X , Y , and Z in an appropriate "convenient" category (e.g., that of compactly generated spaces ), there are natural (basepoint preserving) homeomorphisms
However, for the naive category of pointed spaces, this fails, as shown by the counterexample X = Y = Q {\displaystyle X=Y=\mathbb {Q} } and Z = N {\displaystyle Z=\mathbb {N} } found by Dieter Puppe . [ 1 ] A proof due to Kathleen Lewis that Puppe's counterexample is indeed a counterexample can be found in the book of J. Peter May and Johann Sigurdsson. [ 2 ]
These isomorphisms make the appropriate category of pointed spaces into a symmetric monoidal category with the smash product as the monoidal product and the pointed 0-sphere (a two-point discrete space) as the unit object. One can therefore think of the smash product as a kind of tensor product in an appropriate category of pointed spaces.
Adjoint functors make the analogy between the tensor product and the smash product more precise. In the category of R -modules over a commutative ring R , the tensor functor ( − ⊗ R A ) {\displaystyle (-\otimes _{R}A)} is left adjoint to the internal Hom functor H o m ( A , − ) {\displaystyle \mathrm {Hom} (A,-)} , so that
In the category of pointed spaces , the smash product plays the role of the tensor product in this formula: if A , X {\displaystyle A,X} are compact Hausdorff then we have an adjunction
where M a p s * {\displaystyle \operatorname {Maps_{*}} } denotes continuous maps that send basepoint to basepoint, and M a p s ∗ ( A , Y ) {\displaystyle \mathrm {Maps_{*}} (A,Y)} carries the compact-open topology . [ 3 ]
In particular, taking A {\displaystyle A} to be the unit circle S 1 {\displaystyle S^{1}} , we see that the reduced suspension functor Σ {\displaystyle \Sigma } is left adjoint to the loop space functor Ω {\displaystyle \Omega } : | https://en.wikipedia.org/wiki/Smash_product |
The Smeatonian Society of Civil Engineers was founded in England in 1771. It was the first engineering society to be formed anywhere in the world, and remains the oldest. It was originally known as the Society of Civil Engineers , being renamed following its founder's death. [ 1 ]
The first known formal meeting of civil engineers in Britain took place at the King's Head tavern in Holborn, London, on 15 March 1771, when seven of the leading engineers of the time agreed to establish a Society of Civil Engineers. The leading light of the new Society was John Smeaton who was the first engineer to describe himself as a "Civil Engineer", having coined the term to distinguish himself from the military engineers graduating from the Royal Military Academy at Woolwich . [ 2 ] The other founding members were Thomas Yeoman , Robert Mylne , Joseph Nickalls, John Grundy , John Thompson and James King. In the first year they were joined by John Golborne, William Black, Robert Whitworth and Hugh Henshall , and these eleven were known as the Original Members. [ 3 ]
When the Society was founded its title was the "Society of Civil Engineers". When William Mylne started a new Minute Book in 1822 he used the heading "Engineers' Society" in the reports of each session until 1869, when he changed it to "Smeatonian Society". The Rules and Regulations issued in 1830 bore the title "Smeatonian Society of Civil Engineers" for the first time, which has been its title ever since. [ 4 ] Major Henry Watson was the first military engineer to be elected to membership in 1774. [ 4 ]
Eventually the Smeatonian Society of Civil Engineers became more of a dining club and a group of younger engineers began to demand a better grouping to aid their profession and the Institution of Civil Engineers was formed in 1818.
The unveiling of a memorial stone to Smeaton in Westminster Abbey on 7 November 1994, by Noel Ordman, President, [ 5 ] was described in The Times as 'a triumph for the Smeatonian Society'. [ 6 ] Smeaton is also one of six civil engineers depicted in the Stephenson stained glass window, designed by William Wailes and unveiled in 1862. [ 7 ]
The Society continues to this day, mainly as a dining and discussion club of around sixty senior professional engineers, 'distinguished for their work in the theory or practice of design, manufacture, construction or management in the various fields of engineering', up to eighteen retired Members Emeritus and up to fifteen Honorary Members. The late Prince Philip, Duke of Edinburgh (elected 1953) served as president in 1971 and was an active participant until 2017. Anne, Princess Royal (elected 2017) accepted the invitation to be 2021 president, fifty years after her father, and on 8 September 2021 presided at the Society's two hundred and fiftieth anniversary dinner at Trinity House , Tower Hill . [ 8 ] [ 9 ] Since 1975 the Society has often met at the headquarters of the Institution of Civil Engineers . [ 2 ]
The Latin motto "Omnia in Numero, Pondere et Mensura" was added to the summons card in 1793; it is adapted from Wisdom of Solomon 11:20 "(Thou hast ordered) all things by number, weight and measure". The proposal of the Reverend William Whewell (Honorary Member 1836) at a meeting on 14 June 1843 was accepted, that a Greek motto (probably from Aristotle) should be added to the summons card: "Τεχνη κρατουμεν ὢν φυσει νικωμεθα" "By Art we master what would master us". [ 4 ] Both mottos are still in use.
From 1793 the renewed Society was to be "for promoting and communicating every branch of knowledge useful and necessary to the various and important branches of public and private works in civil engineering". [ 4 ] There were three classes of membership: [ 4 ] First Class - "those who are actually employed in Designing, & forming, Works of different kinds, in the Various Departments of Engineering". Second Class - "Men of Science and Gentlemen of Fame and Fortune" (Honorary Members). Third Class - "Various Artists, whose professions and employments, are necessary & useful thereto as well as connected with Civil Engineering" (Honorary Members).
Women elected include Jean Venables (2003, the 2025 President), Joanna Kennedy (2006), Julia Elton FSA (Honorary 2010), Dame Julia Higgins (2012), Bridget Rosewell (Honorary 2016), Dame Ann Dowling (2017), Dame Helen Atkinson (2017), Dame Judith Hackitt (2018), Faith Wainwright (2019), Sue Kershaw (2021), Michèle Dix (2022), Elaine Martin (2022), Julie Bregulla (2022) and Dame Dervilla Mitchell (2022). [ 10 ]
The following is a list of presidents of the Society from its inception. Honorary Members are shown in italics. In 1793 the Society was reconstituted without a president. The post was reintroduced as an annually elected position in 1841: [ 4 ] | https://en.wikipedia.org/wiki/Smeatonian_Society_of_Civil_Engineers |
Smegma (from Ancient Greek σμῆγμα , smêgma , 'soap') [ 1 ] is shed skin cells , skin oils, and moisture that occurs in male and female mammalian genitalia . In females, it collects around the clitoris and in the folds of the labia minora ; in males, smegma collects under the foreskin .
The accumulation of sebum combined with dead skin cells forms smegma. Smegma clitoridis is defined as the secretion of the apocrine (sweat) and sebaceous (sebum) glands of the clitoris in combination with desquamating epithelial cells. [ 2 ] Glands that are located around the clitoris, the labia minora, and the labia majora secrete sebum .
If smegma is not removed frequently it can lead to clitoral adhesion which can make clitoral stimulation (such as masturbation) painful (clitorodynia). [ 3 ] [ 4 ] [ 5 ] [ 6 ]
In males, smegma helps keep the glans moist and facilitates sexual intercourse by acting as a lubricant. [ 7 ] [ 8 ] [ 9 ]
Smegma was originally thought to be produced by sebaceous glands near the frenulum called Tyson's glands ; however, subsequent studies have failed to find these glands. [ 10 ] Joyce Wright states that smegma is produced from minute microscopic protrusions of the mucosal surface of the foreskin and that living cells constantly grow towards the surface, undergo fatty degeneration, separate off, and form smegma. [ 7 ] Parkash et al. found that smegma contains 26.6% fats and 13.3% proteins, which they judged to be consistent with necrotic epithelial debris. [ 10 ]
Newly produced smegma has a smooth, moist texture. It is thought to be rich in squalene [ 11 ] and contain prostatic and seminal secretions, desquamated epithelial cells , and the mucin content of the urethral glands of Littré . [ 9 ] Smegma contains cathepsin B , lysozymes , [ 12 ] chymotrypsin, neutrophil elastase and cytokines , which aid the immune system. [ 13 ]
According to Wright, the production of smegma, which is low in childhood, increases from adolescence until sexual maturity when the function of smegma for lubrication assumes its full value. From middle-age, production starts to decline and in old age virtually no smegma is produced. [ 7 ] Jakob Øster reported that the incidence of smegma increased from 1% among 6- to 9-year-olds to 8% among 14- to 17-year-olds (amongst those who did not present with phimosis and could be examined). [ 14 ]
The production of smegma, which increases during puberty, can only be of limited significance, as males and females learn to practice good genital hygiene. [ 14 ]
Smegma can cause irritation and inflammation in men, which can increase the risk of penile cancer . In the past some experts used to be concerned smegma itself might cause cancer. [ 15 ]
In healthy animals, smegma helps clean and lubricate the genitals. In veterinary medicine, analysis of this smegma is sometimes used for detection of urogenital tract pathogens, such as Tritrichomonas foetus . [ 16 ] Accumulation of smegma in the equine preputial folds and the urethral fossa and urethral diverticulum can form large "beans" and promote the carriage of Taylorella equigenitalis , the causative agent of contagious equine metritis . [ 17 ] Some equine veterinarians have recommended periodic cleaning of male genitals to improve the health of the animal. [ 18 ] | https://en.wikipedia.org/wiki/Smegma |
Smell training or olfactory training is the act of regularly sniffing or exposing oneself to robust aromas [ 1 ] with the intention of regaining a sense of smell. The stimulating smells used are often selected from major smell categories, such as aromatic, flowery, fruity, and resinous. [ 1 ] Using strong scents, the patient is asked to sniff each different smell for a minimum of 20 seconds, no less than two times per day, for three to six months or more. [ 2 ] [ 3 ] It is used as a rehabilitative therapy to help people who have anosmia or post-viral olfactory dysfunction , a symptom of COVID-19 . [ 4 ] It was considered a promising experimental treatment in a 2017 meta-analysis . [ 1 ]
Along with olfactory implants, [ 5 ] smell training is a promising but experimental treatment option. [ 1 ]
Several individual studies have indicated that smell training can increase olfactory sensitivity. [ 6 ] [ 7 ] [ 8 ] In 2021 a meta-analysis was published that examined research studies of olfactory training for treating loss of smell as a consequence of a viral infection. It found clinically significant improvements and supported its use as a treatment option. [ 9 ] As of March 2021, there have been no studies of smell training's efficacy for children. [ 10 ]
In 2017, the International and European Rhinologic Societies recommended smell training for treating loss of smell due to various conditions. [ 11 ] In 2020, the British Rhinological Society published consensus guidelines for the treatment of smell loss due to COVID-19 . [ 12 ] Although no specific studies were available at that time, the expert panel made recommendations regarding treatment options and concluded that "olfactory training was recommended for all [COVID-19] patients with persistent loss of sense of smell of more than 2 weeks duration." [ 12 ]
Critics such as Richard L. Doty have pointed to the small sample sizes in the studies and the potential for the observed improvements to have been the result of nerve regeneration that would have occurred without intervention as reason to be skeptical. [ 13 ] [ 14 ]
Smell training likely achieves results because the olfactory nerve and olfactory bulb have neural plasticity and are able to regenerate. [ 1 ]
The idea was first written about by Thomas Hummel, a German psychologist at the Dresden University of Technology , in his 2009 paper "Effects of olfactory training in patients with olfactory loss". [ 15 ] In his original study, Hummel instructed patients with olfactory dysfunction to follow a twice-a-day routine for twelve weeks. The routine included inhaling the odor of rose, lemon, clove, and eucalyptus ( phenyl ethyl alcohol , citronellal , eugenol , and eucalyptol respectively) essential oils for ten seconds each. These intense odors each correspond to a different odor category in Henning's odor prism. [ 7 ]
Hummel's paper built on a 1989 study by the Monell Chemical Senses Center in Philadelphia. The study showed that after repeated exposure to androstenone , a chemical which half of all humans cannot detect, some subjects gained the ability to smell it. [ 16 ]
In addition to smell training, other treatments for anosmia that have been researched include systemic steroidal and non-steroidal oral medications, topical medications , and acupuncture . [ 17 ] | https://en.wikipedia.org/wiki/Smell_training |
Smelting is a process of applying heat and a chemical reducing agent to an ore to extract a desired base metal product. [ 1 ] It is a form of extractive metallurgy that is used to obtain many metals such as iron , copper , silver , tin , lead and zinc . Smelting uses heat and a chemical reducing agent to decompose the ore, driving off other elements as gases or slag and leaving the metal behind. The reducing agent is commonly a fossil-fuel source of carbon , such as carbon monoxide from incomplete combustion of coke —or, in earlier times, of charcoal . [ 1 ] The oxygen in the ore binds to carbon at high temperatures, as the chemical potential energy of the bonds in carbon dioxide (CO 2 ) is lower than that of the bonds in the ore.
Sulfide ores such as those commonly used to obtain copper, zinc or lead, are roasted before smelting in order to convert the sulfides to oxides, which are more readily reduced to the metal. Roasting heats the ore in the presence of oxygen from air, oxidizing the ore and liberating the sulfur as sulfur dioxide gas.
Smelting most prominently takes place in a blast furnace to produce pig iron , which is converted into steel . Plants for the electrolytic reduction of aluminium are referred to as aluminium smelters .
Smelters can be classified into two types depending on their business model; custom smelters and integrated smelters. [ 2 ] A custom smelter is a smelter that treats ore on behalf of customers or buy ores. Custom smelters depend on ore concetrates from mines of mines of different ownership. [ 3 ] Integrated smelters depend directly on a specific mining operation and tend to lie next to a mine. [ 2 ]
Smelting involves more than just melting the metal out of its ore. Most ores are the chemical compound of the metal and other elements, such as oxygen (as an oxide ), sulfur (as a sulfide ), or carbon and oxygen together (as a carbonate ). To extract the metal, workers must make these compounds undergo a chemical reaction . Smelting, therefore, consists of using suitable reducing substances that combine with those oxidizing elements to free the metal.
In the case of sulfides and carbonates, a process called " roasting " removes the unwanted carbon or sulfur, leaving an oxide, which can be directly reduced. Roasting is usually carried out in an oxidizing environment. A few practical examples:
Reduction is the final, high-temperature step in smelting, in which the oxide becomes the elemental metal. A reducing environment (often provided by carbon monoxide, made by incomplete combustion in an air-starved furnace) pulls the final oxygen atoms from the raw metal. The carbon source acts as a chemical reactant to remove oxygen from the ore, yielding the purified metal element as a product. The carbon source is oxidized in two stages. First, carbon (C) combusts with oxygen (O 2 ) in the air to produce carbon monoxide (CO). Second, the carbon monoxide reacts with the ore (e.g. Fe 2 O 3 ) and removes one of its oxygen atoms, releasing carbon dioxide (CO 2 ). After successive interactions with carbon monoxide, all of the oxygen in the ore will be removed, leaving the raw metal element (e.g. Fe). [ 6 ] As most ores are impure, it is often necessary to use flux , such as limestone (or dolomite ), to remove the accompanying rock gangue as slag. This calcination reaction emits carbon dioxide.
The required temperature varies both in absolute terms and in terms of the melting point of the base metal. Examples:
Fluxes are materials added to the ore during smelting to catalyze the desired reactions and to chemically bind to unwanted impurities or reaction products. Calcium carbonate or calcium oxide in the form of lime are often used for this purpose, since they react with sulfur, phosphorus, and silicon impurities to allow them to be readily separated and discarded, in the form of slag. Fluxes may also serve to control the viscosity and neutralize unwanted acids.
Flux and slag can provide a secondary service after the reduction step is complete; they provide a molten cover on the purified metal, preventing contact with oxygen while still hot enough to readily oxidize. This prevents impurities from forming in the metal.
The ores of base metals are often sulfides. In recent centuries, reverberatory furnaces have been used to keep the charge being smelted separately from the fuel. Traditionally, they were used for the first step of smelting: forming two liquids, one an oxide slag containing most of the impurities, and the other a sulfide matte containing the valuable metal sulfide and some impurities. Such "reverb" furnaces are today about 40 meters long, 3 meters high, and 10 meters wide. Fuel is burned at one end to melt the dry sulfide concentrates (usually after partial roasting) which are fed through openings in the roof of the furnace. The slag floats over the heavier matte and is removed and discarded or recycled. The sulfide matte is then sent to the converter . The precise details of the process vary from one furnace to another depending on the mineralogy of the ore body.
While reverberatory furnaces produced slags containing very little copper, they were relatively energy inefficient and off-gassed a low concentration of sulfur dioxide that was difficult to capture; a new generation of copper smelting technologies has supplanted them. [ 10 ] More recent furnaces exploit bath smelting, top-jetting lance smelting, flash smelting , and blast furnaces. Some examples of bath smelters include the Noranda furnace, the Isasmelt furnace, the Teniente reactor, the Vunyukov smelter, and the SKS technology. Top-jetting lance smelters include the Mitsubishi smelting reactor. Flash smelters account for over 50% of the world's copper smelters. There are many more varieties of smelting processes, including the Kivset, Ausmelt, Tamano, EAF, and BF.
Of the seven metals known in antiquity , only gold regularly occurs in nature as a native metal . The others – copper , lead , silver , tin , iron , and mercury – occur primarily as minerals, although native copper is occasionally found in commercially significant quantities. These minerals are primarily carbonates , sulfides , or oxides of the metal, mixed with other components such as silica and alumina . Roasting the carbonate and sulfide minerals in the air converts them to oxides. The oxides, in turn, are smelted into the metal. Carbon monoxide was (and is) the reducing agent of choice for smelting. It is easily produced during the heating process, and as a gas comes into intimate contact with the ore.
In the Old World , humans learned to smelt metals in prehistoric times, more than 8000 years ago. The discovery and use of the "useful" metals – copper and bronze at first, then iron a few millennia later – had an enormous impact on human society. The impact was so pervasive that scholars traditionally divide ancient history into Stone Age , Bronze Age , and Iron Age .
In the Americas , pre- Inca civilizations of the central Andes in Peru had mastered the smelting of copper and silver at least six centuries before the first Europeans arrived in the 16th century, while never mastering the smelting of metals such as iron for use with weapon craft. [ 11 ]
Copper was the first metal to be smelted. [ 12 ] How the discovery came about is debated. Campfires are about 200 °C short of the temperature needed, so some propose that the first smelting of copper may have occurred in pottery kilns . [ 13 ] (The development of copper smelting in the Andes, which is believed to have occurred independently of the Old World , may have occurred in the same way. [ 11 ] )
The earliest current evidence of copper smelting, dating from between 5500 BC and 5000 BC, has been found in Pločnik and Belovode, Serbia. [ 14 ] [ 15 ] A mace head found in Turkey and dated to 5000 BC, once thought to be the oldest evidence, now appears to be hammered, native copper. [ 16 ]
Combining copper with tin or arsenic in the right proportions produces bronze , an alloy that is significantly harder than copper. The first copper/arsenic bronzes date from 4200 BC from Asia Minor . The Inca bronze alloys were also of this type. Arsenic is often an impurity in copper ores, so the discovery could have been made by accident. Eventually, arsenic-bearing minerals were intentionally added during smelting. [ citation needed ]
Copper–tin bronzes, harder and more durable, were developed around 3500 BC, also in Asia Minor. [ 17 ]
How smiths learned to produce copper/tin bronzes is unknown. The first such bronzes may have been a lucky accident from tin-contaminated copper ores. However, by 2000 BC, people were mining tin on purpose to produce bronze—which is remarkable as tin is a semi-rare metal, and even a rich cassiterite ore only has 5% tin. [ citation needed ]
The discovery of copper and bronze manufacture had a significant impact on the history of the Old World . Metals were hard enough to make weapons that were heavier, stronger, and more resistant to impact damage than wood, bone, or stone equivalents. For several millennia, bronze was the material of choice for weapons such as swords , daggers , battle axes , and spear and arrow points, as well as protective gear such as shields , helmets , greaves (metal shin guards), and other body armor . Bronze also supplanted stone, wood, and organic materials in tools and household utensils—such as chisels , saws , adzes , nails , blade shears , knives , sewing needles and pins , jugs , cooking pots and cauldrons , mirrors , and horse harnesses . [ citation needed ] Tin and copper also contributed to the establishment of trade networks that spanned large areas of Europe and Asia and had a major effect on the distribution of wealth among individuals and nations. [ citation needed ]
The earliest known cast lead beads were thought to be in the Çatalhöyük site in Anatolia ( Turkey ), and dated from about 6500 BC. [ 18 ] However, recent research has discovered that this was not lead, but rather cerussite and galena, minerals rich in, but distinct from, lead. [ 19 ]
Since the discovery happened several millennia before the invention of writing, there is no written record of how it was made. However, tin and lead can be smelted by placing the ores in a wood fire, leaving the possibility that the discovery may have occurred by accident. [ citation needed ] Recent scholarship however has called this find into question. [ 20 ]
Lead is a common metal, but its discovery had relatively little impact in the ancient world. It is too soft to use for structural elements or weapons, though its high density relative to other metals makes it ideal for sling projectiles. However, since it was easy to cast and shape, workers in the classical world of Ancient Greece and Ancient Rome used it extensively to pipe and store water. They also used it as a mortar in stone buildings. [ 21 ] [ 22 ]
Tin was much less common than lead, is only marginally harder, and had even less impact by itself.
The earliest evidence for iron-making is a small number of iron fragments with the appropriate amounts of carbon admixture found in the Proto-Hittite layers at Kaman-Kalehöyük and dated to 2200–2000 BC. [ 23 ] Souckova-Siegolová (2001) shows that iron implements were made in Central Anatolia in very limited quantities around 1800 BC and were in general use by elites, though not by commoners, during the New Hittite Empire (~1400–1200 BC). [ 24 ]
Archaeologists have found indications of iron working in Ancient Egypt , somewhere between the Third Intermediate Period and 23rd Dynasty (ca. 1100–750 BC). Significantly though, they have found no evidence of iron ore smelting in any (pre-modern) period. In addition, very early instances of carbon steel were in production around 2000 years ago (around the first-century .) in northwest Tanzania , based on complex preheating principles. These discoveries are significant for the history of metallurgy. [ 25 ]
Most early processes in Europe and Africa involved smelting iron ore in a bloomery , where the temperature is kept low enough so that the iron does not melt. This produces a spongy mass of iron called a bloom, which then must be consolidated with a hammer to produce wrought iron . Some of the earliest evidence to date for the bloomery smelting of iron is found at Tell Hammeh , Jordan, radiocarbon-dated to c. 930 BC . [ 26 ]
From the medieval period, an indirect process began to replace the direct reduction in bloomeries. This used a blast furnace to make pig iron , which then had to undergo a further process to make forgeable bar iron. Processes for the second stage include fining in a finery forge . In the 13th century during the High Middle Ages the blast furnace was introduced by China who had been using it since as early as 200 b.c during the Qin dynasty . blast furnace summary | Britannica Puddling was also introduced in the Industrial Revolution .
Both processes are now obsolete, and wrought iron is now rarely made. Instead, mild steel is produced from a Bessemer converter or by other means including smelting reduction processes such as the Corex Process .
Smelting has serious effects on the environment , producing wastewater and slag and releasing such toxic metals as copper , silver, iron, cobalt , and selenium into the atmosphere. [ 27 ] Smelters also release gaseous sulfur dioxide , contributing to acid rain , which acidifies soil and water. [ 28 ]
The smelter in Flin Flon, Canada was one of the largest point sources of mercury in North America in the 20th century. [ 29 ] [ 30 ] Even after smelter releases were drastically reduced, landscape re-emission continued to be a major regional source of mercury. Lakes will likely receive mercury contamination from the smelter for decades, from both re-emissions returning as rainwater and leaching of metals from the soil. [ 29 ]
Air pollutants generated by aluminium smelters include carbonyl sulfide , hydrogen fluoride , polycyclic compounds , lead, nickel , manganese , polychlorinated biphenyls , and mercury . [ 31 ] Copper smelter emissions include arsenic, beryllium , cadmium , chromium , lead, manganese, and nickel. [ 32 ] Lead smelters typically emit arsenic, antimony , cadmium and various lead compounds. [ 33 ] [ 34 ] [ 35 ]
Wastewater pollutants discharged by iron and steel mills includes gasification products such as benzene , naphthalene , anthracene , cyanide , ammonia , phenols and cresols , together with a range of more complex organic compounds known collectively as polycyclic aromatic hydrocarbons (PAH). [ 36 ] Treatment technologies include recycling of wastewater; settling basins , clarifiers and filtration systems for solids removal; oil skimmers and filtration; chemical precipitation and filtration for dissolved metals; carbon adsorption and biological oxidation for organic pollutants; and evaporation. [ 37 ]
Pollutants generated by other types of smelters varies with the base metal ore. For example, aluminum smelters typically generate fluoride , benzo(a)pyrene , antimony and nickel, as well as aluminum. Copper smelters typically discharge cadmium, lead, zinc , arsenic and nickel, in addition to copper. [ 38 ] Lead smelters may discharge antimony , asbestos, cadmium, copper and zinc, in addition to lead. [ 39 ]
Labourers working in the smelting industry have reported respiratory illnesses inhibiting their ability to perform the physical tasks demanded by their jobs. [ 40 ]
In the United States, the Environmental Protection Agency has published pollution control regulations for smelters. | https://en.wikipedia.org/wiki/Smelting |
Smeltmills were water-powered mills used to smelt lead or other metals.
The older method of smelting lead on wind-blown bole hills began to be superseded by artificially-blown smelters. The first such furnace was built by Burchard Kranich at Makeney , Derbyshire in 1554, but produced less good lead than the older bole hill. William Humfrey (the Queen's assay master), and a leading shareholder in the Company of Mineral and Battery Works introduced the ore hearth from the Mendips about 1577. This was initially blown by a foot-blast, but was soon developed into a water-powered smelt mill at Beauchief (now a suburb of Sheffield ).
A typical smelt mill had an orehearth and a slaghearth, the latter being used to reprocess slags from the orehearth in order to recover further lead from the slag
This industry -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Smeltmill |
In organic chemistry , the Smiles rearrangement is an organic reaction and a rearrangement reaction named after British chemist Samuel Smiles. [ 1 ] [ 2 ] It is an intramolecular , nucleophilic aromatic substitution of the type:
where X in the arene compound can be a sulfone , a sulfide , an ether or any substituent capable of dislodging from the arene carrying a negative charge. The terminal functional group in the chain end Y is able to act as a strong nucleophile for instance an alcohol , amine or thiol .
As in other nucleophilic aromatic substitutions the arene requires activation by an electron-withdrawing group preferably in the aromatic ortho position .
In one modification called the Truce–Smiles rearrangement the incoming nucleophile is sufficiently strong that the arene does not require this additional activation, for example when the nucleophile is an organolithium . This reaction is exemplified by the conversion of an aryl sulfone into a sulfinic acid by action of n -butyllithium : [ 3 ]
This particular reaction requires the interaction of the alkyllithium group ortho to the sulfone group akin a directed ortho metalation .
A conceptually related reaction is the Chapman rearrangement .
A radical version of Smiles rearrangement is reported by Stephenson in 2015. [ 4 ]
The Hayashi rearrangement can be considered as the cationic counterpart of Smiles rearrangement. | https://en.wikipedia.org/wiki/Smiles_rearrangement |
In geology, Smith's laws are two rules, formulated by William Smith (1769–1839), which aid in the determination of geological succession . They are fundamental to the production of geological maps .
Both laws were first published by Smith in Strata Identified by Fossils , 1816–1819.
Smith's first law is the Principle of Superposition. This states that newer rock beds will lie on top of older rock beds unless the succession has been overturned. Overturning of the beds causes the succession order to be reversed. This can be caused by folding that is so severe that the beds are moved past the perpendicular. Beds can also be put out of order by an overthrust thrust fault (Jackson, p. 128).
Smith's second law is the Law of Strata identified by fossils. This states that each stratum in the succession contains a distinctive set of fossils. This law allows beds to be identified as belonging to the same stratum even when the horizon between them is not continuous (Jackson, p. 128).
Smith used these new techniques, together with knowledge he had accumulated as a canal engineer and mineral surveyor , to produce geological maps. He started with a hand-produced map of the area around Bath in 1799. In 1815 he published a large-scale map of England, Wales and parts of Scotland. This was the first geological map of Britain (indeed, of any country) and a major milestone in geology (Winchester, p. 195; Jackson, p. 127). In 1819, Smith produced cross-sectional maps showing the underlying geology (Jackson, p. 128).
Smith's map of England and Wales was extensively plagiarised by others, starting with George Bellas Greenough in 1819 (Winchester, pp. 230-234). Smith's laws are still basic to the production of modern geological maps (Jackson, p. 128). | https://en.wikipedia.org/wiki/Smith's_laws |
SmithKline Beecham Clinical Laboratories ( SBCL ) was an American-based medical laboratory company that was acquired by Quest Diagnostics in 1999 for $1.3 billion.
In 1989, SBCL had to pay a $1.5 million fine for illegal laboratory referral kickbacks . [ 1 ]
In 1997, Operation LabScam forced SBCL to agree to pay a $325 million settlement for billing Medicare and Medicaid for tests that physicians were misled into believing were free, violating the 1863 False Claims Act . [ 2 ]
In 1998, a phlebotomist at an SBCL facility in Palo Alto, California was exposed as reusing needles to save money. As a result, over 3,600 patients had to receive testing and counseling for HIV and hepatitis . The incident led to phlebotomy licensure in California . [ 3 ]
This United States corporation or company article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/SmithKline_Beecham_Clinical_Laboratories |
The Smith chart (sometimes also called Smith diagram , Mizuhashi chart ( 水橋チャート ), Mizuhashi–Smith chart ( 水橋スミスチャート ), [ 1 ] [ 2 ] [ 3 ] Volpert–Smith chart ( Диаграмма Вольперта—Смита ) [ 4 ] [ 5 ] or Mizuhashi–Volpert–Smith chart ) is a graphical calculator or nomogram designed for electrical and electronics engineers specializing in radio frequency (RF) engineering to assist in solving problems with transmission lines and matching circuits. [ 6 ] [ 7 ] [ 8 ] [ 9 ] [ 10 ]
It was independently [ 11 ] [ 4 ] [ 12 ] [ 5 ] proposed by Tōsaku Mizuhashi ( 水橋東作 ) in 1937, [ 13 ] and by Amiel R. Volpert [ ru ] ( Амиэ́ль Р. Во́льперт ) [ 14 ] [ 4 ] and Phillip H. Smith in 1939. [ 15 ] [ 16 ] Starting with a rectangular diagram, Smith had developed a special polar coordinate chart by 1936, which, with the input of his colleagues Enoch B. Ferrell and James W. McRae , who were familiar with conformal mappings , was reworked into the final form in early 1937, which was eventually published in January 1939. [ 15 ] [ 9 ] [ 17 ] While Smith had originally called it a " transmission line chart " [ 15 ] [ 16 ] and other authors first used names like " reflection chart ", " circle diagram of impedance ", " immittance chart " or " Z-plane chart ", [ 9 ] early adopters at MIT 's Radiation Laboratory started to refer to it simply as " Smith chart " in the 1940s, [ 9 ] [ 17 ] a name generally accepted in the Western world by 1950. [ 18 ] [ 19 ]
The Smith chart can be used to simultaneously display multiple parameters including impedances , admittances , reflection coefficients , S n n {\displaystyle S_{nn}\,} scattering parameters , noise figure circles, constant gain contours and regions for unconditional stability . [ 20 ] [ 21 ] : 93–103 The Smith chart is most frequently used at or within the unity radius region. However, the remainder is still mathematically relevant, being used, for example, in oscillator design and stability analysis. [ 21 ] : 98–101 While the use of paper Smith charts for solving the complex mathematics involved in matching problems has been largely replaced by software based methods, the Smith chart is still a very useful method of showing [ 22 ] how RF parameters behave at one or more frequencies, an alternative to using tabular information. Thus most RF circuit analysis software includes a Smith chart option for the display of results and all but the simplest impedance measuring instruments can plot measured results on a Smith chart display. [ 23 ]
The Smith chart is a mathematical transformation of the two-dimensional Cartesian complex plane. Complex numbers with positive real parts map inside the circle. Those with negative real parts map outside the circle.
If we are dealing only with impedances with non-negative resistive components, our interest is focused on the area inside the circle. The transformation, for an impedance Smith chart, is:
Γ = Z − Z 0 Z + Z 0 = z − 1 z + 1 , {\displaystyle \Gamma ={\frac {Z-Z_{0}}{Z+Z_{0}}}={\frac {z-1}{z+1}},}
where z = Z / Z 0 , i.e., the complex impedance, Z , normalized by the reference impedance, Z 0 . The impedance Smith chart is then an Argand plot of impedances thus transformed. Impedances with non-negative resistive components will appear inside a circle with unit radius; the origin will correspond to the reference impedance, Z 0 .
The Smith chart is plotted on the complex reflection coefficient plane in two dimensions and may be scaled in normalised impedance (the most common), normalised admittance or both, using different colours to distinguish between them. These are often known as the Z, Y and YZ Smith charts respectively. [ 21 ] : 97 Normalised scaling allows the Smith chart to be used for problems involving any characteristic or system impedance which is represented by the center point of the chart. The most commonly used normalization impedance is 50 ohms . Once an answer is obtained through the graphical constructions described below, it is straightforward to convert between normalised impedance (or normalised admittance) and the corresponding unnormalized value by multiplying by the characteristic impedance (admittance). Reflection coefficients can be read directly from the chart as they are unitless parameters.
The Smith chart has a scale around its circumference or periphery which is graduated in wavelengths and degrees . The wavelengths scale is used in distributed component problems and represents the distance measured along the transmission line connected between the generator or source and the load to the point under consideration. The degrees scale represents the angle of the voltage reflection coefficient at that point. The Smith chart may also be used for lumped-element matching and analysis problems.
Use of the Smith chart and the interpretation of the results obtained using it requires a good understanding of AC circuit theory and transmission-line theory, both of which are prerequisites for RF engineers.
As impedances and admittances change with frequency, problems using the Smith chart can only be solved manually using one frequency at a time, the result being represented by a point . This is often adequate for narrow band applications (typically up to about 5% to 10% bandwidth ) but for wider bandwidths it is usually necessary to apply Smith chart techniques at more than one frequency across the operating frequency band. Provided the frequencies are sufficiently close, the resulting Smith chart points may be joined by straight lines to create a locus .
A locus of points on a Smith chart covering a range of frequencies can be used to visually represent:
The accuracy of the Smith chart is reduced for problems involving a large locus of impedances or admittances, although the scaling can be magnified for individual areas to accommodate these.
A transmission line with a characteristic impedance of Z 0 {\displaystyle Z_{0}\,} may be universally considered to have a characteristic admittance of Y 0 {\displaystyle Y_{0}\,} where
Any impedance, Z T {\displaystyle Z_{\text{T}}\,} expressed in ohms, may be normalised by dividing it by the characteristic impedance, so the normalised impedance using the lower case z T is given by
Similarly, for normalised admittance
The SI unit of impedance is the ohm with the symbol of the upper case Greek letter omega (Ω) and the SI unit for admittance is the siemens with the symbol of an upper case letter S. Normalised impedance and normalised admittance are dimensionless . Actual impedances and admittances must be normalised before using them on a Smith chart. Once the result is obtained it may be de-normalised to obtain the actual result.
Using transmission-line theory, if a transmission line is terminated in an impedance ( Z T {\displaystyle Z_{\text{T}}\,} ) which differs from its characteristic impedance ( Z 0 {\displaystyle Z_{0}\,} ), a standing wave will be formed on the line comprising the resultant of both the incident or f orward ( V F {\displaystyle V_{\text{F}}\,} ) and the r eflected or reversed ( V R {\displaystyle V_{\text{R}}\,} ) waves. Using complex exponential notation:
where
Also
where
The Smith chart is used with one frequency ( ω {\displaystyle \omega } ) at a time, and only for one moment ( t {\displaystyle t} ) at a time, so the temporal part of the phase ( exp ( j ω t ) {\displaystyle \exp(j\omega t)\,} ) is fixed. All terms are actually multiplied by this to obtain the instantaneous phase , but it is conventional and understood to omit it. Therefore,
where A {\displaystyle A\,} and B {\displaystyle B\,} are respectively the forward and reverse voltage amplitudes at the load.
The complex voltage reflection coefficient Γ {\displaystyle \Gamma \,} is defined as the ratio of the reflected wave to the incident (or forward) wave. Therefore,
where C is also a constant.
For a uniform transmission line (in which γ {\displaystyle \gamma \,} is constant), the complex reflection coefficient of a standing wave varies according to the position on the line. If the line is lossy ( α {\displaystyle \alpha \,} is non-zero) this is represented on the Smith chart by a spiral path. In most Smith chart problems however, losses can be assumed negligible ( α = 0 {\displaystyle \alpha =0\,} ) and the task of solving them is greatly simplified. For the loss free case therefore, the expression for complex reflection coefficient becomes
where Γ L {\displaystyle \Gamma _{\text{L}}\,} is the reflection coefficient at the load, and ℓ {\displaystyle \ell \,} is the line length from the load to the location where the reflection coefficient is measured. The phase constant β {\displaystyle \beta \,} may also be written as
where λ {\displaystyle \lambda \,} is the wavelength within the transmission line at the test frequency.
Therefore,
This equation shows that, for a standing wave, the complex reflection coefficient and impedance repeats every half wavelength along the transmission line. The complex reflection coefficient is generally simply referred to as reflection coefficient. The outer circumferential scale of the Smith chart represents the distance from the generator to the load scaled in wavelengths and is therefore scaled from zero to 0.50.
If V {\displaystyle \,V\,} and I {\displaystyle \,I\,} are the voltage across and the current entering the termination at the end of the transmission line respectively, then
and
By dividing these equations and substituting for both the voltage reflection coefficient
and the normalised impedance of the termination represented by the lower case z , subscript T
gives the result:
Alternatively, in terms of the reflection coefficient
These are the equations which are used to construct the Z Smith chart. Mathematically speaking Γ {\displaystyle \,\Gamma \,} and z T {\displaystyle \,z_{\mathsf {T}}\,} are related via a Möbius transformation .
Both Γ {\displaystyle \,\Gamma \,} and z T {\displaystyle \,z_{\mathsf {T}}\,} are expressed in complex numbers without any units. They both change with frequency so for any particular measurement, the frequency at which it was performed must be stated together with the characteristic impedance.
Γ {\displaystyle \,\Gamma \,} may be expressed in magnitude and angle on a polar diagram . Any actual reflection coefficient must have a magnitude of less than or equal to unity so, at the test frequency, this may be expressed by a point inside a circle of unity radius. The Smith chart is actually constructed on such a polar diagram. The Smith chart scaling is designed in such a way that reflection coefficient can be converted to normalised impedance or vice versa. Using the Smith chart, the normalised impedance may be obtained with appreciable accuracy by plotting the point representing the reflection coefficient treating the Smith chart as a polar diagram and then reading its value directly using the characteristic Smith chart scaling. This technique is a graphical alternative to substituting the values in the equations.
By substituting the expression for how reflection coefficient changes along an unmatched loss-free transmission line
for the loss free case, into the equation for normalised impedance in terms of reflection coefficient
and using Euler's formula
yields the impedance-version transmission-line equation for the loss free case: [ 24 ]
where Z i n {\displaystyle \,Z_{\mathsf {in}}\,} is the impedance 'seen' at the input of a loss free transmission line of length ℓ , {\displaystyle \,\ell \,,} terminated with an impedance Z L {\displaystyle \,Z_{\mathsf {L}}\,}
Versions of the transmission-line equation may be similarly derived for the admittance loss free case and for the impedance and admittance lossy cases.
The Smith chart graphical equivalent of using the transmission-line equation is to normalise Z L , {\displaystyle \,Z_{\mathsf {L}}\,,} to plot the resulting point on a Z Smith chart and to draw a circle through that point centred at the Smith chart centre. The path along the arc of the circle represents how the impedance changes whilst moving along the transmission line. In this case the circumferential (wavelength) scaling must be used, remembering that this is the wavelength within the transmission line and may differ from the free space wavelength.
If a polar diagram is mapped on to a cartesian coordinate system it is conventional to measure angles relative to the positive x -axis using a counterclockwise direction for positive angles. The magnitude of a complex number is the length of a straight line drawn from the origin to the point representing it. The Smith chart uses the same convention, noting that, in the normalised impedance plane, the positive x -axis extends from the center of the Smith chart at z T = 1 ± j 0 {\displaystyle \,z_{\mathsf {T}}=1\pm j0\,} to the point z T = ∞ ± j ∞ . {\displaystyle \,z_{\mathsf {T}}=\infty \pm j\infty \,.} The region above the x-axis represents inductive impedances (positive imaginary parts) and the region below the x -axis represents capacitive impedances (negative imaginary parts).
If the termination is perfectly matched, the reflection coefficient will be zero, represented effectively by a circle of zero radius or in fact a point at the centre of the Smith chart. If the termination was a perfect open circuit or short circuit the magnitude of the reflection coefficient would be unity, all power would be reflected and the point would lie at some point on the unity circumference circle.
The normalised impedance Smith chart is composed of two families of circles: circles of constant normalised resistance and circles of constant normalised reactance. In the complex reflection coefficient plane the Smith chart occupies a circle of unity radius centred at the origin. In cartesian coordinates therefore the circle would pass through the points (+1,0) and (−1,0) on the x -axis and the points (0,+1) and (0,−1) on the y -axis.
Since both Γ {\displaystyle \,\Gamma \,} and z T {\displaystyle \,z_{\mathsf {T}}\,} are complex numbers, in general they may be written as:
with a , b , c and d real numbers.
Substituting these into the equation relating normalised impedance and complex reflection coefficient:
gives the following result:
This is the equation which describes how the complex reflection coefficient changes with the normalised impedance and may be used to construct both families of circles. [ 25 ]
The Y Smith chart is constructed in a similar way to the Z Smith chart case but by expressing values of voltage reflection coefficient in terms of normalised admittance instead of normalised impedance. The normalised admittance y T is the reciprocal of the normalised impedance z T , so
Therefore:
and
The Y Smith chart appears like the normalised impedance, type but with the graphic nested circles rotated through 180°, but the numeric scale remaining in its same position (not rotated) as the Z chart.
Similarly taking
for real o ~ {\displaystyle \,{\tilde {o}}\,} and p ~ {\displaystyle \,{\tilde {p}}\,} gives an analogous result, although with more and different minus signs:
The region above the x -axis represents capacitive admittances and the region below the x -axis represents inductive admittances. Capacitive admittances have positive imaginary parts and inductive admittances have negative imaginary parts.
Again, if the termination is perfectly matched the reflection coefficient will be zero, represented by a 'circle' of zero radius or in fact a point at the centre of the Smith chart. If the termination was a perfect open or short circuit the magnitude of the voltage reflection coefficient would be unity, all power would be reflected and the point would lie at some point on the unity circumference circle of the Smith chart.
A point with a reflection coefficient magnitude 0.63 and angle 60° represented in polar form as 0.63 ∠ 60 ∘ {\displaystyle 0.63\angle 60^{\circ }\,} , is shown as point P 1 on the Smith chart. To plot this, one may use the circumferential (reflection coefficient) angle scale to find the ∠ 60 ∘ {\displaystyle \angle 60^{\circ }\,} graduation and a ruler to draw a line passing through this and the centre of the Smith chart. The length of the line would then be scaled to P 1 assuming the Smith chart radius to be unity. For example, if the actual radius measured from the paper was 100 mm, the length OP 1 would be 63 mm.
The following table gives some similar examples of points which are plotted on the Z Smith chart. For each, the reflection coefficient is given in polar form together with the corresponding normalised impedance in rectangular form. The conversion may be read directly from the Smith chart or by substitution into the equation.
In RF circuit and matching problems sometimes it is more convenient to work with admittances (representing conductances and susceptances ) and sometimes it is more convenient to work with impedances (representing resistances and reactances ). Solving a typical matching problem will often require several changes between both types of Smith chart, using normalised impedance for series elements and normalised admittances for parallel elements. For these a dual (normalised) impedance and admittance Smith chart may be used. Alternatively, one type may be used and the scaling converted to the other when required. In order to change from normalised impedance to normalised admittance or vice versa, the point representing the value of reflection coefficient under consideration is moved through exactly 180 degrees at the same radius. For example, the point P1 in the example representing a reflection coefficient of 0.63 ∠ 60 ∘ {\displaystyle 0.63\angle 60^{\circ }\,} has a normalised impedance of z P = 0.80 + j 1.40 {\displaystyle z_{P}=0.80+j1.40\,} . To graphically change this to the equivalent normalised admittance point, say Q1, a line is drawn with a ruler from P1 through the Smith chart centre to Q1, an equal radius in the opposite direction. This is equivalent to moving the point through a circular path of exactly 180 degrees. Reading the value from the Smith chart for Q1, remembering that the scaling is now in normalised admittance, gives y P = 0.30 − j 0.54 {\displaystyle y_{P}=0.30-j0.54\,} . Performing the calculation
manually will confirm this.
Once a transformation from impedance to admittance has been performed, the scaling changes to normalised admittance until a later transformation back to normalised impedance is performed.
The table below shows examples of normalised impedances and their equivalent normalised admittances obtained by rotation of the point through 180°. Again, these may be obtained either by calculation or using a Smith chart as shown, converting between the normalised impedance and normalised admittances planes.
The choice of whether to use the Z Smith chart or the Y Smith chart for any particular calculation depends on which is more convenient. Impedances in series and admittances in parallel add while impedances in parallel and admittances in series are related by a reciprocal equation. If Z TS {\displaystyle Z_{\text{TS}}} is the equivalent impedance of series impedances and Z TP {\displaystyle Z_{\text{TP}}} is the equivalent impedance of parallel impedances, then
For admittances the reverse is true, that is
Dealing with the reciprocals , especially in complex numbers, is more time-consuming and error-prone than using linear addition. In general therefore, most RF engineers work in the plane where the circuit topography supports linear addition. The following table gives the complex expressions for impedance (real and normalised) and admittance (real and normalised) for each of the three basic passive circuit elements : resistance, inductance and capacitance. Using just the characteristic impedance (or characteristic admittance) and test frequency an equivalent circuit can be found and vice versa.
Distributed matching becomes feasible and is sometimes required when the physical size of the matching components is more than about 5% of a wavelength at the operating frequency. Here the electrical behaviour of many lumped components becomes rather unpredictable. This occurs in microwave circuits and when high power requires large components in shortwave, FM and TV broadcasting.
For distributed components the effects on reflection coefficient and impedance of moving along the transmission line must be allowed for using the outer circumferential scale of the Smith chart which is calibrated in wavelengths.
The following example shows how a transmission line, terminated with an arbitrary load, may be matched at one frequency either with a series or parallel reactive component in each case connected at precise positions.
Supposing a loss-free air-spaced transmission line of characteristic impedance Z 0 = 50 Ω {\displaystyle Z_{0}=50\ \Omega } , operating at a frequency of 800 MHz, is terminated with a circuit comprising a 17.5 Ω {\displaystyle \Omega } resistor in series with a 6.5 nanohenry (6.5 nH) inductor. How may the line be matched?
From the table above, the reactance of the inductor forming part of the termination at 800 MHz is
so the impedance of the combination ( Z T {\displaystyle Z_{T}} ) is given by
and the normalised impedance ( z T {\displaystyle z_{T}} ) is
This is plotted on the Z Smith chart at point P 20 . The line OP 20 is extended through to the wavelength scale where it intersects at the point L 1 = 0.098 λ {\displaystyle L_{1}=0.098\lambda \,} . As the transmission line is loss free, a circle centred at the centre of the Smith chart is drawn through the point P 20 to represent the path of the constant magnitude reflection coefficient due to the termination. At point P 21 the circle intersects with the unity circle of constant normalised resistance at
The extension of the line OP 21 intersects the wavelength scale at L 2 = 0.177 λ {\displaystyle L_{2}=0.177\lambda \,} , therefore the distance from the termination to this point on the line is given by
Since the transmission line is air-spaced, the wavelength at 800 MHz in the line is the same as that in free space and is given by
where c {\displaystyle c\,} is the velocity of electromagnetic radiation in free space and f {\displaystyle f\,} is the frequency in hertz. The result gives λ = 375 m m {\displaystyle \lambda =375\ \mathrm {mm} \,} , making the position of the matching component 29.6 mm from the load.
The conjugate match for the impedance at P 21 ( z m a t c h {\displaystyle z_{match}\,} ) is
As the Smith chart is still in the normalised impedance plane, from the table above a series capacitor C m {\displaystyle C_{m}\,} is required where
Rearranging, we obtain
Substitution of known values gives
To match the termination at 800 MHz, a series capacitor of 2.6 pF must be placed in series with the transmission line at a distance of 29.6 mm from the termination.
An alternative shunt match could be calculated after performing a Smith chart transformation from normalised impedance to normalised admittance. Point Q 20 is the equivalent of P 20 but expressed as a normalised admittance. Reading from the Smith chart scaling, remembering that this is now a normalised admittance gives
(In fact this value is not actually used). However, the extension of the line OQ 20 through to the wavelength scale gives L 3 = 0.152 λ {\displaystyle L_{3}=0.152\lambda \,} . The earliest point at which a shunt conjugate match could be introduced, moving towards the generator, would be at Q 21 , the same position as the previous P 21 , but this time representing a normalised admittance given by
The distance along the transmission line is in this case
which converts to 123 mm.
The conjugate matching component is required to have a normalised admittance ( y m a t c h {\displaystyle y_{match}} ) of
From the table it can be seen that a negative admittance would require an inductor, connected in parallel with the transmission line. If its value is L m {\displaystyle L_{m}\,} , then
This gives the result
A suitable inductive shunt matching would therefore be a 6.5 nH inductor in parallel with the line positioned at 123 mm from the load.
The analysis of lumped-element components assumes that the wavelength at the frequency of operation is much greater than the dimensions of the components themselves. The Smith chart may be used to analyze such circuits in which case the movements around the chart are generated by the (normalized) impedances and admittances of the components at the frequency of operation. In this case the wavelength scaling on the Smith chart circumference is not used. The following circuit will be analyzed using a Smith chart at an operating frequency of 100 MHz. At this frequency the free space wavelength is 3 m. The component dimensions themselves will be in the order of millimetres so the assumption of lumped components will be valid. Despite there being no transmission line as such, a system impedance must still be defined to enable normalization and de-normalization calculations and Z 0 = 50 Ω {\displaystyle Z_{0}=50\ \Omega \,} is a good choice here as R 1 = 50 Ω {\displaystyle R_{1}=50\ \Omega \,} . If there were very different values of resistance present a value closer to these might be a better choice.
The analysis starts with a Z Smith chart looking into R 1 only with no other components present. As R 1 = 50 Ω {\displaystyle R_{1}=50\ \Omega \,} is the same as the system impedance, this is represented by a point at the centre of the Smith chart. The first transformation is OP 1 along the line of constant normalized resistance in this case the addition of a normalized reactance of - j 0.80, corresponding to a series capacitor of 40 pF. Points with suffix P are in the Z plane and points with suffix Q are in the Y plane. Therefore, transformations P 1 to Q 1 and P 3 to Q 3 are from the Z Smith chart to the Y Smith chart and transformation Q 2 to P 2 is from the Y Smith chart to the Z Smith chart. The following table shows the steps taken to work through the remaining components and transformations, returning eventually back to the centre of the Smith chart and a perfect 50 ohm match.
A generalization of the Smith chart to a three dimensional sphere, based on the extended complex plane ( Riemann sphere ) and inversive geometry , was proposed by Muller, et al in 2011. [ 26 ]
The chart unifies the passive and active circuit design on little and big circles on the surface of a unit sphere, using a stereographic conformal map of the reflection coefficient's generalized plane. Considering the point at infinity, the space of the new chart includes all possible loads: The north pole is the perfectly matched point, while the south pole is the completely mismatched point. [ 26 ]
The 3D Smith chart has been further extended outside of the spherical surface, for plotting various scalar parameters, such as group delay, quality factors, or frequency orientation. The visual frequency orientation (clockwise vs. counter-clockwise) enables one to differentiate between a negative / capacitance and positive / inductive whose reflection coefficients are the same when plotted on a 2D Smith chart, but whose orientations diverge as frequency increases. [ 27 ] | https://en.wikipedia.org/wiki/Smith_chart |
In mathematics , the Smith conjecture states that if f is a diffeomorphism of the 3-sphere of finite order , then the fixed point set of f cannot be a nontrivial knot .
Paul A. Smith ( 1939 , remark after theorem 4) showed that a non-trivial orientation-preserving diffeomorphism of finite order with fixed points must have a fixed point set equal to a circle, and asked in ( Eilenberg 1949 , Problem 36) if the fixed point set could be knotted. Friedhelm Waldhausen ( 1969 ) proved the Smith conjecture for the special case of diffeomorphisms of order 2 (and hence any even order). The proof of the general case was described by John Morgan and Hyman Bass ( 1984 ) and depended on several major advances in 3-manifold theory, In particular the work of William Thurston on hyperbolic structures on 3-manifolds, and results by William Meeks and Shing-Tung Yau on minimal surfaces in 3-manifolds, with some additional help from Bass, Cameron Gordon , Peter Shalen , and Rick Litherland.
Deane Montgomery and Leo Zippin ( 1954 ) gave an example of a continuous involution of the 3-sphere whose fixed point set is a wildly embedded circle, so the Smith conjecture is false in the topological (rather than the smooth or PL) category. Charles Giffen ( 1966 ) showed that the analogue of the Smith conjecture in higher dimensions is false: the fixed point set of a periodic diffeomorphism of a sphere of dimension at least 4 can be a knotted sphere of codimension 2.
This topology-related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Smith_conjecture |
The Smithsonian Transcription Center is a crowdsourcing transcription project that aims to assist with the preservation and digitization of handwritten material in the Smithsonian Institution . [ 2 ] The Transcription Center cites five reasons why transcription matters: discovery, humanities research, scientific research, education, and readability. [ 3 ] Collections available for transcription include such documents as scientist field notebooks, artist diaries, astronomy logbooks, botany and bumblebee specimens and certified currency proofs. [ 3 ]
The Smithsonian Transcription Center began in June 2013 and spent approximately a year in a beta test phase. [ 4 ] On 12 August 2014 the Transcription Center website was launched to the public. [ 2 ] As well as transcribing, volunteers review the submitted work before it is sent for approval. [ 5 ] The final transcription is then checked by Smithsonian staff and once accepted, both the original images of the work and the transcription are kept on line. [ 6 ]
The Transcriptions Center has an open call for anyone wanting to join in on transcribing documents for their many projects. Researches, educators, history buffs, amateur social scientists, and citizens are welcome to volunteer to transcribe for any of the many projects. [ 3 ] The Transcription Center hopes that it will engage the public by making the Smithsonian Institution collections accessible. [ 3 ] | https://en.wikipedia.org/wiki/Smithsonian_Transcription_Center |
Smog towers or smog free towers (see below for other names) are structures designed as large-scale air purifiers to reduce air pollution particles ( smog ). This approach to the problem of urban air pollution involves air filtration and removal of suspended mechanical particulates such as soot and requires energy or power. Another approach is to remove urban air pollution by a chimney effect in a tall stack or updraft tower, which may be either filtered or released at altitude as with a solar updraft tower and which may not require operating energy beyond what may be produced by the updraft.
The world's first smog-free tower was built by Dutch artist Daan Roosegaarde . It was unveiled in September 2015 in Rotterdam [ 1 ] and later similar structures toured or were installed in [ 2 ] Beijing and Tianjin , China, Kraków , Poland, [ 3 ] Anyang , South Korea [ 4 ] and Abu Dhabi . [ 5 ] The 7-meter (23 ft) tall tower uses patented positive ionisation technology and is expected to clean 30,000 m3 of air per hour. [ 2 ]
In 2016, [ 6 ] [ 7 ] a 100-metre (330 ft) tower has been built in Xi'an , Shaanxi to tackle the city's pollution. [ 8 ] It was funded by the provincial government and costs US$2 million. The running cost is $30000 per year. [ 9 ] It is under testing by researchers at the Institute of Earth Environment of the Chinese Academy of Sciences . [ 10 ]
The experimental demonstration urban updraft tower is cleaning the air in central China with little external energy input. [ 11 ] [ 12 ] A 60-metre urban chimney is surrounded by solar collector. This project was led by Cao Jun Ji, a chemist at the Chinese Academy of Sciences' Key Laboratory of Aerosol Chemistry and Physics. [ 9 ] This work has since been published on, with the performance data and modelling. [ 13 ] [ 14 ]
"I like to tell my students that we don’t need to be medical doctors to save lives ... If we can just reduce the air pollution in major metropolitan areas by 20 percent, for example, we can save tens of thousands of lives each year ... I hope that people will realize that this is a really effective and cheap way to solve the PM2.5 problem." [ 6 ]
“In the case of India, their population is more packed together, so the towers will be more effective in mitigating PM2.5 … At least during the next 10-15 years, they can use them to provide relief to residents while they invest in clean energy technology.” [ 15 ]
— David Pui , Regents Professor and LM Fingerson/TSI Chair in Mechanical Engineering of the University of Minnesota, explained. [ 15 ]
As of 2022 [update] , there are at least eight smog towers in India , some of which are smaller in scale:
In Delhi , India Kurin Systems is developing a 12-metre (40 ft) tall smog tower, called the "Kurin City Cleaner". [ 26 ] It is different from Daan Roosegaarde's Smog Tower in that it won't depend on the ionization technique to clean the air. The H14 grade HEPA Filter, known for being able to clean up to 99.99% of the particulate matter, will be used instead, together with a pre-filter and activated carbon. [ 27 ] It is claimed the tower will filter air for up to 75,000 people within a 3-kilometre (1.9 mi) radius. [ 28 ] and cleaning more than 32 million cubic metres of air every day. [ 29 ] ZNera Space proposed Lutyens' Delhi smog tower network. [ 30 ]
In 2023, some researchers from IIT Bombay conducted a study on the smog tower in Connaught Place, Delhi. They found that the tower's air cleaning efficiency varies with distance. At the source, it operates at 50% efficiency, but this drops to 30% just 50 meters away, and further decreases to slightly over 10% at a distance of 500 meters. They also found that the filter housing was not properly sealed, allowing contaminated air to circumvent the filtration process. [ 31 ]
There are air pollution experts who view smog filtration tower projects with scepticism. For example, Professor Alastair Lewis , Science Director at the NCAS , has argued that static air cleaners, like the prototypes in Beijing and Delhi, cannot process enough city air, quickly enough, to make a meaningful difference to urban pollution. He said that it was "easier [ unbalanced opinion? ] to come up with technologies and schemes that stop harmful emissions at source, rather than to try to capture the resulting pollution once it's free and in the air". [ 32 ]
Noting that the Delhi tower would be powered by (mostly) coal-fired electricity, [ dubious – discuss ] Sunil Dahiya from India's Centre for Research on Energy and Clean Air has commented that "so we will only be adding to pollution elsewhere in the country". [ 33 ] According to The Times , environmentalists said that "given the city[Delhi]'s size and the scale of its pollution, 2.5 million smog towers would be needed to clean its air". [ 34 ] As a refute, "The objective is not to clear entire Delhi's air, it is to create special zones where people can breathe," Anwar Ali Khan, the engineer in charge of the project said. [ 33 ] | https://en.wikipedia.org/wiki/Smog_tower |
A smoke composition is a pyrotechnic composition designed primarily to generate smoke . Smoke compositions are used as obscurants or for generation of signaling smokes. Some are used as a payload of smoke bombs and smoke grenades .
Smoke compositions used as obscurants generate large amount of thick, usually white, smoke.
Zinc chloride smoke is grey-white and consists of tiny particles of zinc chloride . The most common mixture for generating these is a zinc chloride smoke mixture (HC), consisting of hexachloroethane , grained aluminium and zinc oxide . The smoke consists of zinc chloride, zinc oxychlorides, and hydrochloric acid , which absorb the moisture in the air. The smoke also contains traces of organic chlorinated compounds, phosgene , carbon monoxide , and chlorine .
Its toxicity is caused mainly by the content of strongly acidic hydrochloric acid, but also due to thermal effects of reaction of zinc chloride with water. These effects cause lesions of the mucous membranes of the upper airways. Damage of the lower airways can manifest itself later as well, due to fine particles of zinc chloride and traces of phosgene. In high concentrations the smoke can be very dangerous when inhaled. Symptoms include dyspnea , retrosternal pain, hoarseness , stridor , lachrymation , cough , expectoration , and in some cases haemoptysis . Delayed pulmonary edema , cyanosis or bronchopneumonia may develop. The smoke and the spent canisters contain suspected carcinogens .
The prognosis for the casualties depends on the degree of the pulmonary damage. All exposed individuals should be kept under observation for 8 hours. Most affected individuals recover within several days, with some symptoms persisting for up to 1–2 weeks. Severe cases can suffer of reduced pulmonary function for some months, the worst cases developing marked dyspnoea and cyanosis leading to death.
White phosphorus is a popular base for smoke production. It is used in artillery shells, bombs, and grenades.
A colored smoke composition can be used for signalling. These are usually based on a low-temperature burning pyrotechnic composition, mixed with a dye that gets vaporized and creates large, colored smoke particles. The composition is often based on an oxidizer (e.g. potassium chlorate , potassium nitrate , or potassium perchlorate ), a fuel (e.g. lactose ), an optional coolant (e.g. sodium bicarbonate ), and one or more dyes.
Smoke with a suitable composition can be used as a fire suppression agent . A pyrotechnic composition similar to black powder , composed of 15% charcoal and 85% potassium nitrate , generates thick smoke composed of particles of mainly potassium carbonate , which has fire extinguishing properties. Two-kilograms smoke grenades , thrown into burning rooms through plate-glass windows [ why? ] , have been used by some European firefighters . [ 1 ]
Smoke compositions can be used also for creating aerosol of other materials than dyes. Generally the same type of pyrotechnic composition as for colored smokes is used, with the dye being replaced by the desired chemical. The devices usually have the form of smoke bombs .
The best known such application of smoke compositions is in riot control , for dispersion of lachrymatory agents . The agent used is most often CS gas , with less used alternatives CR gas , CN gas and Adamsite .
In agriculture, smoke compositions are used to disperse insecticides and fungicides . Some agents used in this manner are permethrin , cypermethrin , chlorpyrifos , imazalil , etc. [1] , and some fumigation agents.
Smoke compositions can be also used for weather modification , namely cloud seeding , to provide cloud condensation nuclei for the moisture to precipitate. | https://en.wikipedia.org/wiki/Smoke_composition |
Smoke dampers are passive fire protection products used in air conditioning and ventilation ductwork or installed in physical smoke barriers (e.g., walls).
Smoke damper may be used to prevent the spread of smoke from the space of fire origin to other spaces in the same building. A combination of fans and dampers can exhaust smoke from an area while pressurizing the smoke-free areas around the affected area (inhibiting smoke infiltration into additional areas). It may also be used to maintain the required concentration of a fire suppression clean agent in a space, as installed in supply air ducts to restrict the introduction of air into the space, and as installed in return or exhaust air ducts to restrict the depletion of the clean agent from the space. Smoke dampers are usually installed by sheet metal contractors.
Smoke dampers can be activated by the fire alarm system, usually initiated by smoke detectors, or interlocked with a fire suppression system. Smoke dampers close by an electric or pneumatic actuator, or a spring actuator, and can be either manually reset or driven open on a reset signal to the electric or pneumatic actuator.
Combination fire/smoke dampers are also available if a smoke barrier is desired at the same location as a fire barrier.
Fire dampers and smoke dampers are an integral and essential part of a building's passive fire protection system. [ 1 ]
As with any other element of a building's passive fire protection system, smoke dampers need to be maintained, inspected and repaired to ensure they are in working order. The National Fire Protection Association (NFPA) requires the testing, maintenance and repair of smoke dampers as mandated in the Life Safety Code . NFPA 105 states [that] each damper shall be tested and inspected one year after installation. The test and inspection frequency shall then be every 4 years, except in hospitals, where the frequency shall be every 6 years. The code also states that the damper shall be actuated and cycled. The inspections must be document indicating the location of the damper, date of inspection, name of inspector, and deficiencies discovered. [ 2 ]
As with fire damper inspections, smoke damper inspections are required by Authorities Having Jurisdiction (AHJ's). The International Code Council , the Joint Commission , NFPA and State Fire Marshals require these inspections as part of a Building's Life Safety Plan.
NFPA 105 requires that "if a damper is not operable, repairs shall begin as soon as possible". [ 3 ] The repair of smoke dampers is more complicated as compared to fire dampers due to actuator replacement.
According to Underwriter's Laboratory , "smoke dampers certified by UL carry a leakage class rating that indicates the level of air leakage measured through the damper under test conditions." [ 4 ] | https://en.wikipedia.org/wiki/Smoke_damper |
The smoke point , also referred to as the burning point , is the temperature at which an oil or fat begins to produce a continuous bluish smoke that becomes clearly visible, dependent upon specific and defined conditions. [ 1 ] Smoke point values can vary greatly, depending on factors such as the volume of oil utilized, the size of the container, the presence of air currents, the type and source of light as well as the quality of the oil and its acidity content, otherwise known as free fatty acid (FFA) content. [ 2 ] The more FFA an oil contains, the quicker it will break down and start smoking. [ 2 ] [ 3 ] The lower the value of FFA, the higher the smoke point. [ 4 ] However, the FFA content typically represents less than 1% of the total oil and consequently renders smoke point a poor indicator of the capacity of a fat or oil to withstand heat. [ 4 ] [ 5 ] [ 6 ]
The smoke point of an oil correlates with its level of refinement. [ 7 ] [ 8 ] Many cooking oils have smoke points above standard home cooking temperatures: [ 9 ]
Smoke point decreases at a different pace in different oils. [ 10 ]
Considerably above the temperature of the smoke point is the flash point , the point at which the vapours from the oil can ignite in air, given an ignition source.
The following table presents smoke points of various fats and oils.
Hydrolysis and oxidation are the two primary degradation processes that occur in an oil during cooking. [ 10 ] Oxidative stability is how resistant an oil is to reacting with oxygen, breaking down and potentially producing harmful compounds while exposed to continuous heat. Oxidative stability is the best predictor of how an oil behaves during cooking. [ 34 ] [ 35 ] [ 36 ]
The Rancimat method is one of the most common methods for testing oxidative stability in oils. [ 36 ] This determination entails speeding up the oxidation process in the oil (under heat and forced air), which enables its stability to be evaluated by monitoring volatile substances associated with rancidity. It is measured as "induction time" and recorded as total hours before the oil breaks down. Canola oil requires 7.5 hours, for example, whereas extra virgin olive oil (EVOO) and virgin coconut oil will last over a day at 110 °C (230 °F) of continuous heat. [ 9 ] The differing stabilities correlate with lower levels of polyunsaturated fatty acids, which are more prone to oxidation. EVOO is high in monounsaturated fatty acids and antioxidants, conferring stability. Some plant cultivars have been bred to produce "high-oleic" oils with more monounsaturated oleic acid and less polyunsaturated linoleic acid for enhanced stability. [ 9 ]
The oxidative stability does not directly correspond to the smoke point and thus the latter cannot be used as a reference for safe and healthy cooking. [ 37 ] | https://en.wikipedia.org/wiki/Smoke_point |
Smokeless tobacco is a tobacco product that is used by means other than smoking . [ 1 ] Their use involves chewing, sniffing, or placing the product between gum and the cheek or lip. [ 1 ] Smokeless tobacco products are produced in various forms, such as chewing tobacco , snuff , snus , and dissolvable tobacco products. [ 2 ] Smokeless tobacco is widely used in South Asia and this accounts for about 80% of global consumption. [ 3 ] All smokeless tobacco products contain nicotine [ 4 ] and are therefore highly addictive . [ 5 ] Quitting smokeless tobacco use is as challenging as smoking cessation . [ 6 ]
Using smokeless tobacco can cause various harmful effects such as dental disease, oral cancer , oesophagus cancer , and pancreas cancer , coronary heart disease , as well as negative reproductive effects including stillbirth , premature birth and low birth weight . [ 5 ] [ 7 ] Smokeless tobacco poses a lower health risk than traditional combusted products. [ 8 ] However it is not a healthy alternative to cigarette smoking. [ 6 ] The level of risk varies between different types of products (e.g., low nitrosamine Swedish-type snus versus other smokeless tobacco with high nitrosamine levels) and producing regions. [ 9 ] [ 8 ] There is no safe level of smokeless tobacco use. [ 6 ] Globally it contributes to 650 000 deaths each year. [ 10 ]
Smokeless tobacco products typically contain over 3000 constituents, [ 11 ] which includes multiple cancer-causing chemicals. [ 6 ] Approximately 28 chemical constituents present in smokeless tobacco can cause cancer, among which nitrosamine is the most prominent. [ 12 ]
Smokeless tobacco consumption is widespread throughout the world. [ 12 ] Once addicted to nicotine from smokeless tobacco use, many people, particularly young people, expand their tobacco use by smoking cigarettes. [ 6 ] Males are more likely than females to use smokeless tobacco. [ 6 ]
Most smokeless tobacco use involves placing the product between the gum and the cheek or lip. [ 1 ] Smokeless tobacco is a noncombustible tobacco product. [ 1 ]
Types of smokeless tobacco include:
Since there are varied manufacturing methods, products can differ greatly in chemical arrangement and nicotine level. [ 17 ] Smokeless tobacco products typically contain over 3000 constituents which play a part in their taste as well as scent. [ 11 ]
Smokeless tobacco differs depending on the type of product, the types of tobacco used, and the amount of each tobacco type used within a product. Each variable results in different level of nicotine. Furthermore, nicotine is absorbed by the body to different degrees depending on the pH level of the product, which is known as the free nicotine or unionized nicotine level. [ citation needed ]
Below are some measured nicotine levels of various smokeless tobacco products from 2006 and 2007 and their corresponding free nicotine levels as calculated by the Henderson–Hasselbalch equation . [ 18 ]
Various national and international health organizations, including the World Health Organization , the US National Cancer Institute , the UK Royal College of Physicians , stated that, even if it is less dangerous than smoking, using smokeless tobacco is addictive, represents a major health risk, has no safe level use and is not a safe substitute for smoking. [ 19 ] [ 20 ] [ 21 ] [ 22 ]
Using smokeless tobacco can cause a number of adverse health effects such as dental disease, oral cancer, oesophagus cancer, and pancreatic cancer, cardiovascular disease, asthma, and deformities in the female reproductive system. [ 12 ] It also raises the risk of fatal coronary artery disease , fatal stroke and non-fatal ischaemic heart disease [ 5 ] [ 7 ]
Globally it contributes to 650 000 deaths each year with a significant proportion of them in Southeast Asia . [ 10 ]
Quitting smokeless tobacco use is as challenging as smoking cessation . [ 6 ] There is no scientific evidence that using smokeless tobacco can help a person quit smoking. [ 21 ] [ 23 ]
It is not recommended to use any smokeless tobacco product as part of a harm reduction strategy. [ 19 ] [ 23 ] Tobacco companies that sell smokeless tobacco products promote them as harm reduction products and a less harmful substitute to cigarettes. [ 24 ] This creates a false perception of safety while real risk reduction can be achieved by smoking less. [ 19 ]
Smokeless tobacco products vary extensively worldwide in both form and health hazards. The level of health risk varies between different types of products (e.g., low nitrosamine Swedish-type snus versus other smokeless tobacco with high nitrosamine levels from South Asia). [ 9 ] [ 8 ]
Even though smokeless tobacco poses a lower health risk than traditional combusted products, contrary to common belief it is not a "safe" alternative to conventional tobacco. [ 25 ] [ 6 ] There is no safe level of smokeless tobacco use. [ 6 ]
The declines in smokeless tobacco initiation among adolescents and young adults is particularly relevant to improving their health because smokeless tobacco use is often linked to subsequent cigarette initiation. [ 6 ] Smokeless tobacco users can experience negative health consequences at any age. [ 6 ] Youth use of tobacco in any form is unsafe. [ 26 ]
Smokeless tobacco (including products where tobacco is chewed ) is a cause of oral cancer , oesophagus cancer , and pancreas cancer . [ 5 ] Increased risk of oral cancer caused by smokeless tobacco is present in countries such as the United States but particularly prevalent in Southeast Asian countries where the use of smokeless tobacco is common. [ 28 ] [ 29 ]
Smokeless tobacco can cause white or gray patches inside the mouth ( leukoplakia ) that can develop into oral cancer . [ 27 ] [ 12 ]
All tobacco products, including smokeless, contain cancer-causing chemicals. [ 6 ] [ 12 ] These carcinogenic compounds occurring in smokeless tobacco vary widely, and depend upon the kind of product and how it was manufactured. [ 4 ] There are 28 known cancer-causing substances in smokeless tobacco products. [ 4 ]
Carcinogenic compounds in smokeless tobacco belong primarily to three groups of compounds: tobacco-specific nitrosamines (TSNA), N-nitrosoamino acids and N-nitrosamines . Among these TSNAs are the most abundant in smokeless tobacco and the most carcinogenic. [ 4 ] [ 12 ] N-nitrosonornicotine and ketone are group 1 carcinogens to humans. [ 24 ] These two nitrosamines found in smokeless tobacco products are the main agents for the majority of cancers in smokeless tobacco users. [ 24 ]
Products such as 3-(methylnitrosamino)-proprionitrile, nitrosamines, and nicotine initiate the production of reactive oxygen species in smokeless tobacco, eventually leading to fibroblast, DNA, and RNA damage with carcinogenic effects in the mouth of tobacco consumers. [ 12 ] The metabolic activation of nitrosamine in tobacco by cytochrome P450 enzymes may lead to the formation of N-nitrosonornicotine, a major carcinogen, and micronuclei, which are an indicator of genotoxicity. These effects lead to further DNA damage and, eventually, oral cancer. [ 12 ]
Other chemicals found in tobacco can also cause cancer. [ 27 ] These include the radioactive element polonium-210 found in tobacco fertilizer. [ 27 ] Harmful chemicals are also formed when tobacco is cured with heat ( polycyclic aromatic hydrocarbons ). [ 27 ] Furthermore tobacco contains harmful metals such as arsenic , beryllium , cadmium , chromium , cobalt , lead , nickel , and mercury . [ 27 ]
The amounts of nicotine in saliva from using smokeless tobacco could be at amounts that can be toxic to cells in the oral cavity. [ 30 ]
Using smokeless tobacco increases the risk of fatal coronary heart disease and stroke . [ 5 ] [ 7 ] Use of smokeless tobacco also seems to greatly raise the risk of non-fatal ischaemic heart disease among users in Asia, although not in Europe. [ 5 ]
Smokeless tobacco can cause adverse reproductive effects including stillbirth , premature birth , low birth weight . [ 5 ] [ 27 ] Nicotine in smokeless tobacco products that are used during pregnancy can affect how a baby's brain develops before birth. [ 27 ]
Due to the harm caused by smokeless tobacco, it use might lead to the need for management or treatment. Some medications that show some benefits are varenicline and nicotine lozenges . Some behavioural interventions may also help. [ 31 ]
More than 300 million people are using smokeless tobacco worldwide. [ 32 ] People of many regions, including India, Pakistan, other Asian countries, and North America, have a long history of smokeless tobacco use. [ 12 ] Once addicted to nicotine from smokeless tobacco use, many people, particularly young people, expand their tobacco use by smoking cigarettes. [ 6 ] Because young people who use smokeless tobacco can become addicted to nicotine, they may be more likely to also become cigarette smokers. [ 27 ] Youth are particularly susceptible to starting smokeless tobacco use. [ 19 ]
Males were more likely than females to have used smokeless tobacco in the past month. [ 6 ] In 2014, 3.3 percent of people aged 12 or older (an estimated 8.7 million people) used smokeless tobacco in the past month. Past month smokeless tobacco use remained relatively stable between 2002 and 2014. [ 6 ] Past month smokeless tobacco use between 2002 and 2014 was mostly consistent among adults aged 26 or older. [ 6 ] There was more variability in the percentages of young adults aged 18 to 25 and adolescents aged 12 to 17 who used smokeless tobacco between 2002 and 2014. [ 6 ] Smokeless tobacco use for adolescents aged 12 to 17 was higher during the mid-2000s, but the 2014 estimates were closer to the lower levels seen in the early 2000s. [ 6 ] In 2014, an estimated 1.0 million people aged 12 or older used smokeless tobacco for the first time in the past year; this represents 0.5 percent of people who had not previously used smokeless tobacco. [ 6 ] Prevalence of smokeless tobacco types that contain areca nut is increasing in the Western Pacific. [ 11 ]
In 2016 about 2 of every 100 middle school students in the US (2.2%) reported current use of smokeless tobacco. [ 26 ] In 2016 nearly 6 of every 100 high school students in the US (5.8%) reported current use of smokeless tobacco. [ 26 ]
The WHO Framework Convention on Tobacco Control (FCTC) contains a set of common goals, minimum standards for tobacco control policy in the 168 countries which signed it. The FCTC policies are also applicable for smokeless tobacco however they are less implemented in regards to these products. Only 57 countries have policies regulating smokeless tobacco use. 13 countries and the European Union apply a ban for advertising and promoting smokeless tobacco. The sale of smokeless tobacco to minors (Article 16 of FCTC) is restricted only in 13 countries and the WHO-defined Eastern Mediterranean region . 11 countries use taxation and pricing measures (Article 6) to reduce use in the general population. [ 33 ]
In countries where they are applied to smokeless tobacco, FCTC policies had a positive impact on reducing their use. If multiple policies, including large taxes, are implemented, premature deaths can be prevented. However if taxation is higher for smoking products only people might switch to cheaper alternatives like smokeless tobacco. [ 33 ]
The manufacture, distribution and sale of smokeless tobacco is banned completely in Bhutan, Singapore, and Sri Lanka. Partial bans on import and sales on some products are in effect in Australia, Bahrain, Brazil, India, Iran, Tanzania, Thailand, New Zealand, the UK and the European Union. [ 33 ]
Smokeless tobacco was first discussed in the English language in 1683 as a powdered tobacco for breathing into the nose. [ 34 ] People have used it for over a thousand years. [ 34 ] Cigarette manufacturers have penetrated the smokeless tobacco market. [ 35 ]
As long ago as 1986, the advisory committee to the Surgeon General concluded that the use of smokeless tobacco "is not a safe substitute for smoking cigarettes. It can cause cancer and a number of noncancerous oral conditions and can lead to nicotine addiction and dependence". [ 21 ] According to a 2002 report by the Royal College of Physicians , "As a way of using nicotine, the consumption of non-combustible tobacco is of the order of 10–1,000 times less hazardous than smoking, depending on the product". [ 22 ] A panel of experts convened by the National Institutes of Health (NIH) in 2006 stated that the "range of risks, including nicotine addiction, from smokeless tobacco products may vary extensively because of differing levels of nicotine, carcinogens, and other toxins in different products". [ 21 ] In 2010 the National Cancer Institute stated that "because all tobacco products are harmful and cause cancer, the use of all of these products should be strongly discouraged. There is no safe level of tobacco use. People who use any type of tobacco product should be urged to quit". [ 21 ] In 2015 the American Cancer Society stated that "Using any kind of spit or smokeless tobacco is a major health risk. It's less lethal than smoking tobacco, but less lethal is a far cry from safe." [ 20 ] In 2017 the World Health Organization states that "Smokeless tobacco use is a significant part of the overall world tobacco problem." [ 19 ]
Many people who use smokeless tobacco may think it is safer than smoking, but all tobacco products contain toxicants, and use of smokeless tobacco poses its own significant health risks. [ 6 ] In South and South-East Asia these products are considered part of the cultural heritage and there is little enthusiasm for regulation. Around 80% of users live in these regions. [ 36 ] | https://en.wikipedia.org/wiki/Smokeless_tobacco |
According to the Jargon File , smoking clover is a computer display hack , [ 1 ] originally created by Bill Gosper . Several converging lines are drawn on a color monitor in such a way that every pixel struck has its color incremented—altered to the next hue up or down. The color map is then repeatedly rotated.
The result of this is a rainbow -hued, shimmering four-leaf clover . The program has been described as " psychedelic ", and Gosper joked about keeping it a secret from the Food and Drug Administration (FDA) due to its " hallucinogenic properties".
Source code for Linux to reproduce the effect is available on the web. [ 2 ]
This computing article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Smoking_clover |
Smoldyn is an open-source software application for cell-scale biochemical simulations. [ 1 ] [ 2 ] It uses particle-based simulation, meaning that it simulates each molecule of interest individually, in order to capture natural stochasticity and yield nanometer-scale spatial resolution. Simulated molecules diffuse, react, are confined by surfaces, and bind to membranes in similar manners as in real biochemical systems.
Smoldyn was initially released in 2003 as a simulator that represented chemical reactions between diffusing particles in rectilinear volumes. [ 3 ] Further development added support for surfaces, [ 1 ] multiscale simulation [ 4 ] molecules with excluded volume, [ 2 ] rule-based modeling [ 5 ] and C/C++ and Python APIs. [ 6 ] Smoldyn development has been funded by a postdoctoral NSF grant awarded to Steve Andrews, a US DOE contract awarded to Adam Arkin, a grant from the Computational Research Laboratories (Pune, India) awarded to Upinder Bhalla, a MITRE contract and several NIH grants awarded to Roger Brent, and a Simons Foundation grant awarded to Steve Andrews.
Smoldyn has been developed primarily by Steve Andrews, over the course of multiple research and teaching positions. Other contributors have included Nathan Addy, [ 1 ] Martin Robinson, [ 4 ] and Diliwar Singh. [ 6 ]
Smoldyn is primarily a tool for biophysics and systems biology research. It focuses on spatial scales that are between nanometers and microns. The following features descriptions are drawn from the Smoldyn documentation. [ 7 ]
Smoldyn has been refactored twice to run on GPUs, each time offering approximately 200-fold speed improvements. [ 9 ] [ 10 ] However, neither version supports the full range of features that is available in the CPU version. They are not being supported currently. | https://en.wikipedia.org/wiki/Smoldyn |
In statistical physics , the Smoluchowski coagulation equation is a population balance equation introduced by Marian Smoluchowski in a seminal 1916 publication, [ 1 ] describing the time evolution of the number density of particles as they coagulate (in this context "clumping together") to size x at time t .
Simultaneous coagulation (or aggregation) is encountered in processes involving polymerization , [ 2 ] coalescence of aerosols , [ 3 ] emulsication , [ 4 ] flocculation . [ 5 ]
The distribution of particle size changes in time according to the interrelation of all particles of the system. Therefore, the Smoluchowski coagulation equation is an integrodifferential equation of the particle-size distribution. In the case when the sizes of the coagulated particles are continuous variables , the equation involves an integral :
If dy is interpreted as a discrete measure , i.e. when particles join in discrete sizes, then the discrete form of the equation is a summation :
There exists a unique solution for a chosen kernel function . [ 6 ]
The operator , K , is known as the coagulation kernel and describes the rate at which particles of size x 1 {\displaystyle x_{1}} coagulate with particles of size x 2 {\displaystyle x_{2}} . Analytic solutions to the equation exist when the kernel takes one of three simple forms:
known as the constant , additive , and multiplicative kernels respectively. [ 7 ] For the case K = 1 {\displaystyle K=1} it could be mathematically proven that the solution of Smoluchowski coagulation equations have asymptotically the dynamic scaling property. [ 8 ] This self-similar behaviour is closely related to scale invariance which can be a characteristic feature of a phase transition .
However, in most practical applications the kernel takes on a significantly more complex form. For example, the free-molecular kernel which describes collisions in a dilute gas - phase system,
Some coagulation kernels account for a specific fractal dimension of the clusters, as in the diffusion-limited aggregation :
or Reaction-limited aggregation:
where y 1 , y 2 {\displaystyle y_{1},y_{2}} are fractal dimensions of the clusters, k B {\displaystyle k_{B}} is the Boltzmann constant, T {\displaystyle T} is the temperature, W {\displaystyle W} is the Fuchs stability ratio, η {\displaystyle \eta } is the continuous phase viscosity, and γ {\displaystyle \gamma } is the exponent of the product kernel, usually considered a fitting parameter. [ 9 ] For cloud, the kernel for coagulation of cloud particles are usually expressed as:
where r ( x ) {\displaystyle r(x)} and v ( x ) {\displaystyle v(x)} are the radius and fall speed of the cloud particles usually expressed using power law.
Generally the coagulation equations that result from such physically realistic kernels are not solvable, and as such, it is necessary to appeal to numerical methods . Most of deterministic methods can be used when there is only one particle property ( x ) of interest, the two principal ones being the method of moments [ 10 ] [ 11 ] [ 12 ] [ 13 ] [ 14 ] and sectional methods. [ 15 ] In the multi-variate case, however, when two or more properties (such as size, shape, composition, etc.) are introduced, one has to seek special approximation methods that suffer less from curse of dimensionality . Approximation based on Gaussian radial basis functions has been successfully applied to the coagulation equation in more than one dimension. [ 16 ] [ 17 ]
When the accuracy of the solution is not of primary importance, stochastic particle (Monte Carlo) methods are an attractive alternative. Through this method, to compute the coagulation rates for different coagulation events, the simulation entries are virtualized to be equally weighted. The accuracy of this transformation can be adjusted such that just those coagulation events are considered while keeping the number of simulation entries constant. [ 18 ] | https://en.wikipedia.org/wiki/Smoluchowski_coagulation_equation |
The Smoluchowski factor , also known as von Smoluchowski's f-factor is related to inter-particle interactions. It is named after Marian Smoluchowski . [ 1 ]
This physical chemistry -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Smoluchowski_factor |
In algebra , a commutative k -algebra A is said to be 0-smooth if it satisfies the following lifting property: given a k - algebra C , an ideal N of C whose square is zero and a k -algebra map u : A → C / N {\displaystyle u:A\to C/N} , there exists a k -algebra map v : A → C {\displaystyle v:A\to C} such that u is v followed by the canonical map. If there exists at most one such lifting v , then A is said to be 0-unramified (or 0-neat ). A is said to be 0-étale if it is 0-smooth and 0-unramified . The notion of 0-smoothness is also called formal smoothness .
A finitely generated k -algebra A is 0-smooth over k if and only if Spec A is a smooth scheme over k .
A separable algebraic field extension L of k is 0-étale over k . [ 1 ] The formal power series ring k [ [ t 1 , … , t n ] ] {\displaystyle k[\![t_{1},\ldots ,t_{n}]\!]} is 0-smooth only when char k = p > 0 {\displaystyle \operatorname {char} k=p>0} and [ k : k p ] < ∞ {\displaystyle [k:k^{p}]<\infty } (i.e., k has a finite p -basis .) [ 2 ]
Let B be an A -algebra and suppose B is given the I -adic topology, I an ideal of B . We say B is I -smooth over A if it satisfies the lifting property: given an A -algebra C , an ideal N of C whose square is zero and an A -algebra map u : B → C / N {\displaystyle u:B\to C/N} that is continuous when C / N {\displaystyle C/N} is given the discrete topology , there exists an A -algebra map v : B → C {\displaystyle v:B\to C} such that u is v followed by the canonical map. As before, if there exists at most one such lift v , then B is said to be I -unramified over A (or I -neat ). B is said to be I -étale if it is I -smooth and I -unramified . If I is the zero ideal and A is a field , these notions coincide with 0-smooth etc. as defined above.
A standard example is this: let A be a ring , B = A [ [ t 1 , … , t n ] ] {\displaystyle B=A[\![t_{1},\ldots ,t_{n}]\!]} and I = ( t 1 , … , t n ) . {\displaystyle I=(t_{1},\ldots ,t_{n}).} Then B is I -smooth over A .
Let A be a noetherian local k -algebra with maximal ideal m {\displaystyle {\mathfrak {m}}} . Then A is m {\displaystyle {\mathfrak {m}}} -smooth over k {\displaystyle k} if and only if A ⊗ k k ′ {\displaystyle A\otimes _{k}k'} is a regular ring for any finite extension field k ′ {\displaystyle k'} of k {\displaystyle k} . [ 3 ]
This algebra -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Smooth_algebra |
Smooth infinitesimal analysis is a modern reformulation of the calculus in terms of infinitesimals . Based on the ideas of F. W. Lawvere and employing the methods of category theory , it views all functions as being continuous and incapable of being expressed in terms of discrete entities. As a theory, it is a subset of synthetic differential geometry . Terence Tao has referred to this concept under the name "cheap nonstandard analysis." [ 1 ]
The nilsquare or nilpotent infinitesimals are numbers ε where ε ² = 0 is true, but ε = 0 need not be true at the same time. Calculus Made Easy notably uses nilpotent infinitesimals.
This approach departs from the classical logic used in conventional mathematics by denying the law of the excluded middle , e.g., NOT ( a ≠ b ) does not imply a = b . In particular, in a theory of smooth infinitesimal analysis one can prove for all infinitesimals ε , NOT ( ε ≠ 0); yet it is provably false that all infinitesimals are equal to zero. [ 2 ] One can see that the law of excluded middle cannot hold from the following basic theorem (again, understood in the context of a theory of smooth infinitesimal analysis):
Despite this fact, one could attempt to define a discontinuous function f ( x ) by specifying that f ( x ) = 1 for x = 0, and f ( x ) = 0 for x ≠ 0. If the law of the excluded middle held, then this would be a fully defined, discontinuous function. However, there are plenty of x , namely the infinitesimals, such that neither x = 0 nor x ≠ 0 holds, so the function is not defined on the real numbers.
In typical models of smooth infinitesimal analysis, the infinitesimals are not invertible, and therefore the theory does not contain infinite numbers. However, there are also models that include invertible infinitesimals.
Other mathematical systems exist which include infinitesimals, including nonstandard analysis and the surreal numbers . Smooth infinitesimal analysis is like nonstandard analysis in that (1) it is meant to serve as a foundation for analysis , and (2) the infinitesimal quantities do not have concrete sizes (as opposed to the surreals, in which a typical infinitesimal is 1/ω , where ω is a von Neumann ordinal ). However, smooth infinitesimal analysis differs from nonstandard analysis in its use of nonclassical logic , and in lacking the transfer principle . Some theorems of standard and nonstandard analysis are false in smooth infinitesimal analysis, including the intermediate value theorem and the Banach–Tarski paradox . Statements in nonstandard analysis can be translated into statements about limits , but the same is not always true in smooth infinitesimal analysis.
Intuitively, smooth infinitesimal analysis can be interpreted as describing a world in which lines are made out of infinitesimally small segments, not out of points. These segments can be thought of as being long enough to have a definite direction, but not long enough to be curved. The construction of discontinuous functions fails because a function is identified with a curve, and the curve cannot be constructed pointwise. We can imagine the intermediate value theorem's failure as resulting from the ability of an infinitesimal segment to straddle a line. Similarly, the Banach–Tarski paradox fails because a volume cannot be taken apart into points. | https://en.wikipedia.org/wiki/Smooth_infinitesimal_analysis |
In mathematics , a smooth maximum of an indexed family x 1 , ..., x n of numbers is a smooth approximation to the maximum function max ( x 1 , … , x n ) , {\displaystyle \max(x_{1},\ldots ,x_{n}),} meaning a parametric family of functions m α ( x 1 , … , x n ) {\displaystyle m_{\alpha }(x_{1},\ldots ,x_{n})} such that for every α , the function m α {\displaystyle m_{\alpha }} is smooth, and the family converges to the maximum function m α → max {\displaystyle m_{\alpha }\to \max } as α → ∞ {\displaystyle \alpha \to \infty } . The concept of smooth minimum is similarly defined. In many cases, a single family approximates both: maximum as the parameter goes to positive infinity, minimum as the parameter goes to negative infinity; in symbols, m α → max {\displaystyle m_{\alpha }\to \max } as α → ∞ {\displaystyle \alpha \to \infty } and m α → min {\displaystyle m_{\alpha }\to \min } as α → − ∞ {\displaystyle \alpha \to -\infty } . The term can also be used loosely for a specific smooth function that behaves similarly to a maximum, without necessarily being part of a parametrized family.
For large positive values of the parameter α > 0 {\displaystyle \alpha >0} , the following formulation is a smooth, differentiable approximation of the maximum function. For negative values of the parameter that are large in absolute value, it approximates the minimum.
S α {\displaystyle {\mathcal {S}}_{\alpha }} has the following properties:
The gradient of S α {\displaystyle {\mathcal {S}}_{\alpha }} is closely related to softmax and is given by
This makes the softmax function useful for optimization techniques that use gradient descent .
This operator is sometimes called the Boltzmann operator, [ 1 ] after the Boltzmann distribution .
Another smooth maximum is LogSumExp :
This can also be normalized if the x i {\displaystyle x_{i}} are all non-negative, yielding a function with domain [ 0 , ∞ ) n {\displaystyle [0,\infty )^{n}} and range [ 0 , ∞ ) {\displaystyle [0,\infty )} :
The ( n − 1 ) {\displaystyle (n-1)} term corrects for the fact that exp ( 0 ) = 1 {\displaystyle \exp(0)=1} by canceling out all but one zero exponential, and log 1 = 0 {\displaystyle \log 1=0} if all x i {\displaystyle x_{i}} are zero.
The mellowmax operator [ 1 ] is defined as follows:
It is a non-expansive operator. As α → ∞ {\displaystyle \alpha \to \infty } , it acts like a maximum. As α → 0 {\displaystyle \alpha \to 0} , it acts like an arithmetic mean. As α → − ∞ {\displaystyle \alpha \to -\infty } , it acts like a minimum. This operator can be viewed as a particular instantiation of the quasi-arithmetic mean . It can also be derived from information theoretical principles as a way of regularizing policies with a cost function defined by KL divergence. The operator has previously been utilized in other areas, such as power engineering. [ 2 ]
Another smooth maximum is the p-norm :
which converges to ‖ ( x 1 , … , x n ) ‖ ∞ = max 1 ≤ i ≤ n | x i | {\displaystyle \|(x_{1},\ldots ,x_{n})\|_{\infty }=\max _{1\leq i\leq n}|x_{i}|} as p → ∞ {\displaystyle p\to \infty } .
An advantage of the p-norm is that it is a norm . As such it is scale invariant ( homogeneous ): ‖ ( λ x 1 , … , λ x n ) ‖ p = | λ | ⋅ ‖ ( x 1 , … , x n ) ‖ p {\displaystyle \|(\lambda x_{1},\ldots ,\lambda x_{n})\|_{p}=|\lambda |\cdot \|(x_{1},\ldots ,x_{n})\|_{p}} , and it satisfies the triangle inequality .
The following binary operator is called the Smooth Maximum Unit (SMU): [ 3 ]
where ε ≥ 0 {\displaystyle \varepsilon \geq 0} is a parameter. As ε → 0 {\displaystyle \varepsilon \to 0} , | ⋅ | ε → | ⋅ | {\displaystyle |\cdot |_{\varepsilon }\to |\cdot |} and thus max ε → max {\displaystyle \textstyle \max _{\varepsilon }\to \max } .
https://www.johndcook.com/soft_maximum.pdf
M. Lange, D. Zühlke, O. Holz, and T. Villmann, "Applications of lp-norms and their smooth approximations for gradient based learning vector quantization," in Proc. ESANN , Apr. 2014, pp. 271-276.
( https://www.elen.ucl.ac.be/Proceedings/esann/esannpdf/es2014-153.pdf ) | https://en.wikipedia.org/wiki/Smooth_maximum |
Tin(II) hydroxide , Sn(OH) 2 , also known as stannous hydroxide , is an inorganic compound tin(II). The only related material for which definitive information is available is the oxy hydroxide Sn 6 O 4 (OH) 4 , but other related materials are claimed. They are all white solids that are insoluble in water.
Crystals of Sn 6 O 4 (OH) 4 has been characterized by X-ray diffraction. This cluster is obtained from solution of basic solutions of tin(II). The compound consists of an octahedron of Sn centers, each face of which is capped by an oxide or a hydroxide. The structure is reminiscent of the Mo 6 S 8 subunit of the Chevrel phases .. [ 2 ] The structure of pure Sn(OH) 2 is not known. [ 3 ]
Sn(OH) 2 has been claimed to arise from the reaction of (CH 3 ) 3 SnOH with SnCl 2 in an aprotic solvent: [ 3 ]
No crystallographic characterization is available on this material.
Stannous hydroxide adds additional hydroxide ligands to form stannites . [ 4 ] Air easily oxidizes stannous hydroxide to stannic oxide (SnO 2 ). | https://en.wikipedia.org/wiki/Sn6O4(OH)4 |
Tin(IV) bromide is the chemical compound SnBr 4 . It is a colourless low melting solid . [ 1 ]
SnBr 4 crystallises in a monoclinic crystal system with molecular SnBr 4 units that have distorted tetrahedral geometry. [ 2 ] The mean Sn-Br bond length is 242.3 pm. [ 3 ]
SnBr 4 can be prepared by reaction of the elements at standard temperature and pressure (STP): [ 4 ] [ page needed ]
In aqueous solution SnBr 4 dissolves to give a series of octahedral (six-ligated) bromo-aquo complexes. These include SnBr 4 (H 2 O) 2 and cis - and trans - [SnBr 2 (H 2 O) 4 ] 2+ . [ 5 ]
SnBr 4 forms 1:1 and 1:2 complexes with ligands . With trimethylphosphine both SnBr 4 ·P(CH 3 ) 3 and SnBr 4 ·2P(CH 3 ) 3 . [ 6 ]
Tin(IV) bromide undergoes redistribution with tin(IV) chloride as assessed by 119 Sn NMR and Raman spectroscopy . Equilibrium is achieved in seconds at room temperature. By contrast, halide exchange for related germanium and especially silicon halides is slower. [ 7 ] | https://en.wikipedia.org/wiki/SnBr4 |
Tin(II) chloride , also known as stannous chloride , is a white crystalline solid with the formula Sn Cl 2 . It forms a stable dihydrate , but aqueous solutions tend to undergo hydrolysis , particularly if hot. SnCl 2 is widely used as a reducing agent (in acid solution), and in electrolytic baths for tin-plating . Tin(II) chloride should not be confused with the other chloride of tin; tin(IV) chloride or stannic chloride (SnCl 4 ).
SnCl 2 has a lone pair of electrons , such that the molecule in the gas phase is bent. In the solid state, crystalline SnCl 2 forms chains linked via chloride bridges as shown. The dihydrate has three coordinates as well, with one water on the tin and another water on the first. The main part of the molecule stacks into double layers in the crystal lattice , with the "second" water sandwiched between the layers.
Tin(II) chloride dissolves in less than its own mass of water. Dilute solutions are subject to hydrolysis, yielding an insoluble basic salt:
Hydrolysis is prevented in the presence of hydrochloric acid , typically of the same or greater molarity as the stannous chloride. Solutions of SnCl 2 are also unstable towards oxidation by the air:
Oxidation can be prevented by storing the solution over lumps of tin metal. [ 4 ]
Tin(II) chloride acts as a reducing agent for silver and gold salts to the metal, and iron(III) salts to iron(II), for example:
It also reduces copper(II) to copper(I).
Solutions of tin(II) chloride can also serve simply as a source of Sn 2+ ions, which can form other tin(II) compounds via precipitation reactions. For example, reaction with sodium sulfide produces the brown/black tin(II) sulfide :
If alkali is added to a solution of SnCl 2 , a white precipitate of hydrated tin(II) oxide forms initially; this then dissolves in excess base to form a stannite salt such as sodium stannite:
Anhydrous SnCl 2 can be used to make a variety of tin(II) compounds in non-aqueous solvents. For example, the lithium salt of 4-methyl-2,6-di-tert-butylphenol reacts with SnCl 2 in THF to give the yellow linear two-coordinate compound Sn(OAr) 2 (Ar = aryl ). [ 5 ]
Tin(II) chloride also behaves as a weak Lewis acid , forming complexes with ligands such as chloride ion, for example:
Like SnCl 2 (H 2 O) , trichlorostannate ( SnCl − 3 ) ion is pyramidal . Such complexes have a full octet . The lone pair of electrons in such complexes is available for bonding. Therefore, SnCl − 3 itself can serve as a Lewis base or ligand: [ 6 ]
SnCl 2 can be used to make a variety of related compounds containing metal-tin bonds. For example, the reaction with dicobalt octacarbonyl :
Anhydrous SnCl 2 is prepared by the action of dry hydrogen chloride gas on tin metal. The dihydrate is made by a similar reaction, using hydrochloric acid :
The water then carefully evaporated from the acidic solution to produce crystals of SnCl 2 ·2H 2 O. This dihydrate can be dehydrated to anhydration using acetic anhydride . [ 7 ]
A solution of tin(II) chloride containing a little hydrochloric acid is used for the tin-plating of steel, in order to make tin cans . An electric potential is applied, and tin metal is formed at the cathode via electrolysis .
Tin(II) chloride is used as a mordant in textile dyeing because it gives brighter colours with some dyes e.g. cochineal . This mordant has also been used alone to increase the weight of silk.
In recent years, an increasing number of tooth paste brands have been adding Tin(II) chloride as protection against enamel erosion to their formula, e. g. Oral-B or Elmex .
It is used as a catalyst in the production of the plastic polylactic acid (PLA).
It also finds a use as a catalyst between acetone and hydrogen peroxide to form the tetrameric form of acetone peroxide .
Tin(II) chloride also finds wide use as a reducing agent . This is seen in its use for silvering mirrors, where silver metal is deposited on the glass:
A related reduction was traditionally used as an analytical test for Hg 2+ (aq) . For example, if SnCl 2 is added dropwise into a solution of mercury(II) chloride , a white precipitate of mercury(I) chloride is first formed; as more SnCl 2 is added this turns black as metallic mercury is formed.
Stannous chloride is also used by many precious metals refining hobbyists and professionals to test for the presence of gold salts. [ 8 ] When SnCl 2 comes into contact with gold compounds, particularly chloroaurate salts, it forms a bright purple colloid known as purple of Cassius . [ 9 ] A similar reaction occurs with platinum and palladium salts, becoming green and brown respectively. [ 10 ]
When mercury is analyzed using atomic absorption spectroscopy, a cold vapor method must be used, and tin (II) chloride is typically used as the reductant.
In organic chemistry , SnCl 2 is used in the Stephen reduction , whereby a nitrile is reduced (via an imidoyl chloride salt) to an imine which is easily hydrolysed to an aldehyde . [ 11 ]
The reaction usually works best with aromatic nitriles Aryl -CN. A related reaction (called the Sonn-Müller method) starts with an amide, which is treated with PCl 5 to form the imidoyl chloride salt.
The Stephen reduction is less used today, because it has been mostly superseded by diisobutylaluminium hydride reduction.
Additionally, SnCl 2 is used to selectively reduce aromatic nitro groups to anilines . [ 12 ]
SnCl 2 also reduces quinones to hydroquinones .
Stannous chloride is also added as a food additive with E number E512 to some canned and bottled foods, where it serves as a color-retention agent and antioxidant .
SnCl 2 is used in radionuclide angiography to reduce the radioactive agent technetium -99m- pertechnetate to assist in binding to blood cells.
Molten SnCl 2 can be oxidised to form highly crystalline SnO 2 nanostructures. [ 13 ] [ 14 ]
A Stannous reduction is used in nuclear medicine bone scans to remove the negative charge from free pertechnetate when it is bound to MDP for radiopharmaceutical studies. Incomplete reduction due to insufficient tin or accidental insufflation of air leads to the formation of free pertechnetate, a finding which can be seen on bone scans due to its inappropriate uptake in the stomach. [ 15 ]
Stannous Chloride is used for coating SnO 2 Tin Oxide doped conductive iridescent coatings for low e glass. [ 16 ] | https://en.wikipedia.org/wiki/SnCl2 |
Tin(IV) chloride , also known as tin tetrachloride or stannic chloride , is an inorganic compound of tin and chlorine with the formula SnCl 4 . It is a colorless hygroscopic liquid , which fumes on contact with air. It is used as a precursor to other tin compounds. [ 1 ] It was first discovered by Andreas Libavius (1550–1616) and was known as spiritus fumans libavii .
It is prepared from reaction of chlorine gas with tin at 115 °C (239 °F):
Anhydrous tin(IV) chloride solidifies at −33 °C to give monoclinic crystals with the P21/c space group . It is isostructural with SnBr 4 . The molecules adopt near-perfect tetrahedral symmetry with average Sn–Cl distances of 227.9(3) pm. [ 2 ]
Tin(IV) chloride is well known as a Lewis acid . Thus it forms hydrates. The pentahydrate SnCl 4 ·5H 2 O was formerly known as butter of tin . These hydrates consist of cis -[SnCl 4 (H 2 O) 2 ] molecules together with varying amounts of water of crystallization . The additional water molecules link together the molecules of [SnCl 4 (H 2 O) 2 ] through hydrogen bonds . A pentahydrate has also been crystallized. In cis - SnCl 4 (H 2 O) 2 ·3H 2 O , the Sn-Cl bonds are 238.3 pm. [ 3 ] Although the pentahydrate is the most common hydrate, lower hydrates have also been characterised. [ 4 ]
Aside from water, other Lewis bases form adducts with SnCl 4 . These include ammonia and organo phosphines .
The ammonium salt of [SnCl 6 ] 2− is formed from ammonium chloride . It is called "pink salt": [ 5 ]
The analogous reaction with hydrochloric acid gives "hexachlorostannic acid". [ 1 ]
Reaction of the tetrachloride with hydrogen fluoride gives tin tetrafluoride : [ 5 ]
Tin(IV) chloride undergoes redistribution with tin(IV) bromide as assessed by 119 Sn NMR and Raman spectroscopy . Equilibrium is achieved in seconds at room temperature. By contrast, halide exchange for related germanium and especially silicon halides is slower. [ 6 ]
Anhydrous tin(IV) chloride is a major precursor in organotin chemistry . Upon treatment with Grignard reagents , tin(IV) chloride gives tetraalkyltin compounds: [ 7 ]
Anhydrous tin(IV) chloride reacts with tetraorganotin compounds in redistribution reactions :
These organotin halides are useful precursors to catalysts (e.g., dibutyltin dilaurate ) and polymer stabilizers. [ 5 ]
SnCl 4 is used in Friedel–Crafts reactions as a Lewis acid catalyst . [ 1 ] For example, the acetylation of thiophene to give 2-acetylthiophene is promoted by tin(IV) chloride. [ 8 ] Similarly, tin(IV) chloride is useful for nitrations. [ 9 ]
Stannic chloride was used as a chemical weapon in World War I , as it formed an irritating (but non-deadly) dense smoke on contact with air. It was supplanted by a mixture of silicon tetrachloride and titanium tetrachloride near the end of the war due to shortages of tin. [ 10 ] | https://en.wikipedia.org/wiki/SnCl4 |
Tin(II) fluoride , commonly referred to commercially as stannous fluoride [ 1 ] [ 2 ] (from Latin stannum , 'tin'), is a chemical compound with the formula SnF 2 . It is a colourless solid used as an ingredient in toothpastes .
Stannous fluoride is an alternative to sodium fluoride for the prevention of cavities ( tooth decay ). It was first released commercially in 1956, in Crest toothpaste. It was discovered and developed by Joseph Muhler and William Nebergall. In recognition of their innovation, they were inducted into the Inventor's Hall of Fame . [ 1 ]
The fluoride in stannous fluoride helps to convert the calcium mineral hydroxyapatite in teeth into fluorapatite , which makes tooth enamel more resistant to bacteria-generated acid attacks. [ 3 ] The calcium present in plaque and saliva reacts with fluoride to form calcium fluoride on the tooth surface; over time, this calcium fluoride dissolves to allow calcium and fluoride ions to interact with the tooth and form fluoride-containing apatite within the tooth structure. [ 4 ] This chemical reaction inhibits demineralisation and can promote remineralisation of tooth decay. The resulting fluoride-containing apatite is more insoluble, and more resistant to acid and tooth decay. [ 4 ]
In addition to fluoride, the stannous ion has benefits for oral health when incorporated in a toothpaste. At similar fluoride concentrations, toothpastes containing stannous fluoride have been shown to be more effective than toothpastes containing sodium fluoride for reducing the incidence of dental caries and dental erosion , [ 5 ] [ 6 ] [ 7 ] [ 8 ] [ 9 ] as well as reducing gingivitis . [ 10 ] [ 11 ] [ 12 ] [ 13 ] [ 14 ] Some stannous fluoride-containing toothpastes also contain ingredients that allow for better stain removal. [ 15 ] [ 16 ] Stabilised stannous fluoride formulations allow for greater bioavailability of the stannous and fluoride ion, increasing their oral health benefits. [ 17 ] [ 18 ] A systematic review revealed stabilised stannous fluoride-containing toothpastes had a positive effect on the reduction of plaque , gingivitis and staining, with a significant reduction in calculus and halitosis (bad breath) compared to other toothpastes. [ 16 ] A specific formulation of stabilised stannous fluoride toothpastes has shown superior protection against dental erosion and dentine hypersensitivity compared to other fluoride-containing and fluoride-free toothpastes. [ 19 ]
Stannous fluoride was once used under the trade name Fluoristan in the original formulation of the toothpaste brand Crest , though it was later replaced with sodium monofluorophosphate under the trade name Fluoristat. Stabilised stannous fluoride is now the active ingredient in Crest/ Oral B Pro-Health brand toothpaste. Although concerns have been previously raised that stannous fluoride may cause tooth staining, this can be avoided by proper brushing and by using a stabilised stannous fluoride toothpaste. [ 15 ] [ 16 ] Any stannous fluoride staining that occurs due to improper brushing is not permanent, and Crest/Oral B Pro-Health states that its particular formulation is resistant to staining.
SnF 2 can be prepared by evaporating a solution of SnO in 40% HF . [ 20 ]
Readily soluble in water, SnF 2 is hydrolysed. At low concentration, it forms species such as SnOH + , Sn(OH) 2 and Sn(OH) 3 − . At higher concentrations, predominantly polynuclear species are formed, including Sn 2 (OH) 2 2+ and Sn 3 (OH) 4 2+ . [ 21 ] Aqueous solutions readily oxidise to form insoluble precipitates of Sn IV , which are ineffective as a dental prophylactic. [ 22 ] Studies of the oxidation using Mössbauer spectroscopy on frozen samples suggests that O 2 is the oxidizing species. [ 23 ]
SnF 2 acts as a Lewis acid . For example, it forms a 1:1 complex (CH 3 ) 3 NSnF 2 and 2:1 complex [(CH 3 ) 3 N] 2 SnF 2 with trimethylamine , [ 24 ] and a 1:1 complex with dimethylsulfoxide , (CH 3 ) 2 SO·SnF 2 . [ 25 ] In solutions containing the fluoride ion, F − , it forms the fluoride complexes SnF 3 − , Sn 2 F 5 − , and SnF 2 (OH 2 ). [ 26 ] Crystallization from an aqueous solution containing NaF produces compounds containing polynuclear anions, e.g. NaSn 2 F 5 or Na 4 Sn 3 F 10 depending on the reaction conditions, rather than NaSnF 3 . [ 20 ] The compound NaSnF 3 , containing the pyramidal SnF 3 − anion, can be produced from a pyridine–water solution. [ 27 ] Other compounds containing the pyramidal SnF 3 − anion are known, such as Ca(SnF 3 ) 2 . [ 28 ]
SnF 2 is a reducing agent , with a standard reduction potential of E o (Sn IV / Sn II ) = +0.15 V. [ 29 ] Solutions in HF are readily oxidised by a range of oxidizing agents (O 2 , SO 2 or F 2 ) to form the mixed-valence compound Sn 3 F 8 (containing Sn II and Sn IV and no Sn–Sn bonds). [ 20 ]
The monoclinic form contains tetramers, Sn 4 F 8 , where there are two distinct coordination environments for the Sn atoms. In each case, there are three nearest neighbours, with Sn at the apex of a trigonal pyramid, and the lone pair of electrons sterically active. [ 30 ] Other forms reported have the GeF 2 and paratellurite structures. [ 30 ]
In the vapour phase, SnF 2 forms monomers, dimers, and trimers. [ 26 ] Monomeric SnF 2 is a non-linear with an Sn−F bond length of 206 pm. [ 26 ] Complexes of SnF 2 , sometimes called difluorostannylene, with an alkyne and aromatic compounds deposited in an argon matrix at 12 K have been reported. [ 31 ] [ 32 ]
Stannous fluoride can cause redness and irritation if it is inhaled or comes into contact with the eyes. If ingested, it can cause abdominal pains and shock. [ 33 ] Rare but serious allergic reactions are possible; symptoms include itching, swelling, and difficulty breathing. Certain formulations of stannous fluoride in dental products may cause mild tooth discoloration ; this is not permanent and can be removed by brushing, or can be prevented by using a stabilised stannous fluoride toothpaste. [ 15 ] [ 16 ] [ 34 ] | https://en.wikipedia.org/wiki/SnF2 |
Tin(IV) fluoride is a chemical compound of tin and fluorine with the chemical formula SnF 4 . It is a white solid. As reflected by its melting point above 700 °C, the tetrafluoride differs significantly from the other tetrahalides of tin. [ 1 ]
SnF 4 can be prepared by the reaction of tin(IV) chloride with anhydrous hydrogen fluoride : [ 1 ]
When treated with alkali metal fluorides (e.g. KF), tin(IV) fluoride forms hexafluorostannates:
In K 2 SnF 6 , tin adopts an octahedral geometry.
Otherwise, SnF 4 behaves as a Lewis acid forming a variety of adducts with the formula L 2 ·SnF 4 and L·SnF 4 . [ 2 ]
Unlike the heavier tin tetrahalides, which contain tetrahedrally coordinated tin, tin(IV) fluoride contains octahedrally coordinated tin. The octahedra share four corners. There are two terminal, unshared, fluorine atoms trans to one another. [ 3 ] The melting point of SnF 4 is much higher (700 °C) than the other tin(IV) halides: ( SnCl 4 , −33.3 °C; SnBr 4 , 31 °C; SnI 4 , 144 °C). [ 1 ] The structure can also be contrasted with the tetrafluorides of the lighter members of group 14, ( CF 4 , SiF 4 and GeF 4 ), all of which in the solid state form molecular crystals. [ 2 ] | https://en.wikipedia.org/wiki/SnF4 |
Tin(II) iodide , also known as stannous iodide , is the inorganic compound with the formula SnI 2 . It is a red-orange solid. It reacts with iodine to give tin(IV) iodide . [ 1 ]
Tin(II) iodide can be synthesised by heating metallic tin with a mixture iodine in 2 M hydrochloric acid. [ 2 ] [ 1 ]
It crystallizes in a unique motif. According to X-ray crystallography , some Sn(II) centers are bound to six iodide ligands others Sn(II) sites are distorted. [ 3 ] | https://en.wikipedia.org/wiki/SnI2 |
Tin(IV) iodide , also known as stannic iodide , is the chemical compound with the formula Sn I 4 . This tetrahedral molecule crystallizes as a bright orange solid that dissolves readily in nonpolar solvents such as benzene . [ 1 ]
The compound is usually prepared by the reaction of tin and iodine : [ 2 ]
The compound hydrolyses in water. [ 3 ] In hydroiodic acid , it reacts to form a rare example of a hexaiodometallate (here hexaiodostannate(IV)): [ 2 ]
Tin(IV) iodide is an orange solid under standard conditions. [ 3 ] It has a cubic crystal structure with the space group Pa 3 (space group no. 205), the lattice parameter a = 1226 pm and eight formula units per unit cell . [ 4 ] This corresponds approximately to a cubic close packing of iodine atoms in which 1/8 of all tetrahedral gaps are occupied by tin atoms. This leads to discrete tetrahedral SnI 4 molecules. [ 5 ] | https://en.wikipedia.org/wiki/SnI4 |
Tin(II) oxide ( stannous oxide ) is a compound with the formula SnO. It is composed of tin and oxygen where tin has the oxidation state of +2. There are two forms, a stable blue-black form and a metastable red form.
Blue-black SnO can be produced by heating the tin(II) oxide hydrate, SnO· x H 2 O ( x < 1) precipitated when a tin(II) salt is reacted with an alkali hydroxide such as NaOH. [ 4 ] Metastable, red SnO can be prepared by gentle heating of the precipitate produced by the action of aqueous ammonia on a tin(II) salt. [ 4 ] SnO may be prepared as a pure substance in the laboratory, by controlled heating of tin(II) oxalate ( stannous oxalate ) in the absence of air or under a CO 2 atmosphere. This method is also applied to the production of ferrous oxide and manganous oxide . [ 5 ] [ 6 ]
Tin(II) oxide burns in air with a dim green flame to form SnO 2 . [ 4 ]
When heated in an inert atmosphere initially disproportionation occurs giving Sn metal and Sn 3 O 4 which further reacts to give SnO 2 and Sn metal. [ 4 ]
SnO is amphoteric , dissolving in strong acid to give tin(II) salts and in strong base to give stannites containing Sn(OH) 3 − . [ 4 ] It can be dissolved in strong acid solutions to give the ionic complexes Sn(OH 2 ) 3 2+ and Sn(OH)(OH 2 ) 2 + , and in less acid solutions to give Sn 3 (OH) 4 2+ . [ 4 ] Note that anhydrous stannites, e.g. K 2 Sn 2 O 3 , K 2 SnO 2 are also known. [ 7 ] [ 8 ] [ 9 ] SnO is a reducing agent and is thought to reduce copper(I) to metallic clusters in the manufacture of so-called "copper ruby glass". [ 10 ]
Black, α-SnO adopts the tetragonal PbO layer structure containing four coordinate square pyramidal tin atoms. [ 11 ] This form is found in nature as the rare mineral romarchite . [ 12 ] The asymmetry is usually simply ascribed to a sterically active lone pair; however, electron density calculations show that the asymmetry is caused by an antibonding interaction of the Sn(5s) and the O(2p) orbitals. [ 13 ] The electronic structure and chemistry of the lone pair determines most of the properties of the material. [ 14 ]
Non-stoichiometry has been observed in SnO. [ 15 ]
The electronic band gap has been measured between 2.5 eV and 3eV. [ 16 ]
The dominant use of stannous oxide is as a precursor in manufacturing of other, typically divalent, tin compounds or salts. Stannous oxide may also be employed as a reducing agent and in the creation of ruby glass . [ 17 ] It has a minor use as an esterification catalyst.
Cerium(III) oxide in ceramic form, together with Tin(II) oxide (SnO) is used for illumination with UV light. [ 18 ] | https://en.wikipedia.org/wiki/SnO |
Tin(IV) oxide , also known as stannic oxide , is the inorganic compound with the formula SnO 2 . The mineral form of SnO 2 is called cassiterite , and this is the main ore of tin . [ 9 ] With many other names, this oxide of tin is an important material in tin chemistry. It is a colourless, diamagnetic , amphoteric solid.
Tin(IV) oxide crystallises with the rutile structure. As such the tin atoms are six coordinate and the oxygen atoms three coordinate. [ 9 ] SnO 2 is usually regarded as an oxygen-deficient n-type semiconductor . [ 10 ]
Hydrous forms of SnO 2 have been described as stannic acid . Such materials appear to be hydrated particles of SnO 2 where the composition reflects the particle size. [ 11 ]
Tin(IV) oxide occurs naturally. Synthetic tin(IV) oxide is produced by burning tin metal in air. [ 11 ] Annual production is in the range of 10 kilotons. [ 11 ] SnO 2 is reduced industrially to the metal with carbon in a reverberatory furnace at 1200–1300 °C. [ 12 ]
The reaction from tin(IV) oxide with hot carbon monoxide is practiced on a large scale as this carbothermal reduction is used to obtain tin metal from its ores:
Some other reactions relevant to purifying tin from its ores are: [ 13 ]
SnO 2 converts to the monoxide at 1500 °C: [ 13 ]
SnO 2 is insoluble in water. It dissolves in sulfuric acid and in molten sodium hydroxide. It is not amphoteric . Like rutile, it is not attacked by solutions of acid or base.
Dissolution of SnO 2 in sulfuric acid gives the sulfate: [ 11 ]
The latter compound can add additional hydrogen sulfate ligands to give hexahydrogensulfatostannic acid. [ 14 ]
SnO 2 dissolves in molten alkali to give " stannates ," with the nominal formula Na 2 SnO 3 . [ 11 ] Dissolving the solidified SnO 2 /NaOH melt in water gives Na 2 [Sn(OH) 6 ], "preparing salt," which is used in the dye industry. [ 11 ]
In conjunction with vanadium oxide, it is used as a catalyst for the oxidation of aromatic compounds in the synthesis of carboxylic acids and acid anhydrides. [ 9 ]
SnO 2 is used as pigment in the manufacture of glasses, enamels and ceramic glazes . Thousands of tons of SnO 2 are produced annually for this application. Pure SnO 2 gives a milky white colour; other colours are achieved when mixed with other metallic oxides e.g. V 2 O 5 yellow; Cr 2 O 3 pink; and Sb 2 O 5 grey blue. [ 11 ] [ 15 ] This use probably led to the discovery of the pigment lead-tin-yellow , which was produced using tin(IV) oxide as a compound. [ 16 ] The use of tin(IV) oxide has been particularly common in glazes for earthenware , sanitaryware and wall tiles; see the articles tin-glazing and Tin-glazed pottery . Tin oxide remains in suspension in vitreous matrix of the fired glazes, and, with its high refractive index being sufficiently different from the matrix, light is scattered, and hence increases the opacity of the glaze. The degree of dissolution increases with the firing temperature, and hence the extent of opacity diminishes. [ 17 ] Although dependent on the other constituents the solubility of tin oxide in glaze melts is generally low. Its solubility is increased by Na 2 O, K 2 O and B 2 O 3 , and reduced by CaO, BaO, ZnO, Al 2 O 3 , and to a limited extent PbO. [ 18 ]
SnO 2 coatings are valued as transparent conducting oxides (TCOs). Like other TCOs, SnO 2 has significant electrical conductivity but is transparent, an unusual combination of properties. Windows coated with SnO 2 also reflect infrared radiation , which is relevant to temperature control for smart windows . [ 19 ] Coatings can be applied using chemical vapor deposition , vapour deposition techniques that employ SnCl 4 [ 9 ] or organotin trihalides [ 20 ] e.g. butyltin trichloride as the volatile agent. This technique is used to coat glass bottles with a thin (<0.1 μm) layer of SnO 2 , which helps to adhere a subsequent, protective polymer coating such as polyethylene to the glass. [ 9 ]
Thicker layers doped with Sb or F ions are electrically conducting and used in electroluminescent devices and photovoltaics. [ 9 ]
SnO 2 has been evaluated as sensors of combustible gases including carbon monoxide detectors . In these the sensor area is heated to a constant temperature (few hundred °C) and in the presence of a combustible gas the electrical resistivity drops. [ 21 ]
This oxide of tin has been utilized as a mordant in the dyeing process since ancient Egypt. [ 22 ] A German by the name of Kuster first introduced its use to London in 1533 and by means of it alone, the color scarlet was produced there. [ 23 ]
Tin(IV) oxide for this use is sometimes called as "putty powder" [ 24 ] or "jeweler's putty". [ 1 ]
Tin(IV) oxide can be used as a polishing powder, [ 11 ] sometimes in mixtures also with lead oxide, for polishing glass, jewelry, marble and silver. [ 1 ] | https://en.wikipedia.org/wiki/SnO2 |
snRNA-seq , also known as single nucleus RNA sequencing , single nuclei RNA sequencing or sNuc-seq , is an RNA sequencing method for profiling gene expression in cells which are difficult to isolate, such as those from tissues that are archived or which are hard to be dissociated. It is an alternative to single cell RNA seq (scRNA-seq) , as it analyzes nuclei instead of intact cells.
snRNA-seq minimizes the occurrence of spurious gene expression, as the localization of fully mature ribosomes to the cytoplasm means that any mRNAs of transcription factors that are expressed after the dissociation process cannot be translated, and thus their downstream targets cannot be transcribed. [ 1 ] Additionally, snRNA-seq technology enables the discovery of new cell types which would otherwise be difficult to isolate.
The basic snRNA-seq method requires 4 main steps: tissue processing, nuclei isolation, cell sorting, and sequencing. In order to isolate and sequence RNA inside the nucleus, snRNA-seq involves using a quick and mild nuclear dissociation protocol. This protocol allows for minimization of technical issues that can affect studies, especially those concerned with immediate early gene (IEG) behavior.
The resulting dissociated cells are suspended and the suspension gently lysed, allowing the cell nuclei to be separated from their cytoplasmic lysates using centrifugation. [ 2 ] These separated nuclei/cells are sorted using fluorescence-activated cell sorting (FACS) into individual wells, and amplified using microfluidics machinery. [ 2 ] Sequencing occurs as normal and the data can be analyzed as appropriate for its use.
This basic snRNA-seq methodology is capable of profiling RNA from tissues that are preserved or cannot be dissociated, but it does not have high throughput capability due to its reliance on nuclei sorting by FACS. [ 3 ] This technique cannot be scaled easily to profiling large numbers of nuclei or samples. Massively parallel scRNA-seq methods exist and can be readily scaled but their requirement of a single cell suspension as input is not ideal and eliminates some of the flexibility that is available with the snRNA-seq method in regards to the types of tissues and cells that can be examined. [ 3 ] In response, the DroNc-Seq method of massively parallel snRNA-seq with droplet technology was developed by researchers from the Broad Institute of MIT and Harvard. [ 3 ] In this technique, nuclei that have been isolated from their fixed or frozen tissue are encapsulated in droplets with uniquely barcoded beads that are coated with oligonucleotides containing a 30-terminal deoxythymine (dT) stretch. [ 4 ] This coating captures the polyadenylated mRNA content produced when the nuclei are lysed inside the droplets. [ 4 ] The captured mRNA is reverse transcribed into cDNA after emulsion breakage. [ 4 ] Sequencing this cDNA produces the transcriptomes of all the single nuclei being looked at and these can be used for many purposes, including identification of unique cell types. [ 5 ]
The sequencing tools and equipment used in scRNA-seq can be used with modifications for snRNA-seq experiments. Illumina outlines a workflow for the basic snRNA-seq method which can be performed with existing equipment. [ 2 ] DroNc-Seq can be accomplished with microfluidic platforms which are meant for the Drop-seq scRNA-seq method. However, Dolomite Bio has adapted one of their instruments, the automated Nadia platform for scRNA-seq, to be used natively for DroNc-Seq as well. [ 5 ] This instrument could simplify the generation of single nuclei sequencing libraries, as it is being used for its intended purpose.
In regard to data analysis after sequencing, a computational pipeline known as dropSeqPipe was developed by the McCarroll Lab at Harvard. [ 6 ] Although the pipeline was originally developed for use with Drop-seq scRNA-seq data, it can be used with DroNc-Seq data as it also utilizes droplet technology.
snRNA-seq uses isolated nuclei instead of the entire cells to profile gene expression. That is to say, scRNA-seq measures both cytoplasmic and nuclear transcripts, while snRNA-seq mainly measures nuclear transcripts (though some transcripts might be attached to the rough endoplasmic reticulum and partially preserved in nuclear preps). [ 7 ] This allows for snRNA-seq to process only the nucleus and not the entire cell. For this reason, compared to scRNA-seq, snRNA-Seq is more appropriate to profile gene expression in cells that are difficult to isolate (e.g. adipocytes, neurons), as well as preserved tissues. [ 5 ]
Additionally, the nuclei required for snRNA-seq can be obtained quickly and easily from fresh, lightly fixed, or frozen tissues, whereas isolating single cells for single-cell RNA-seq (scRNA-seq) involves extended incubations and processing. This gives researchers the ability to obtain transcriptomes which are not as perturbed during isolation.
In neuroscience, neurons have an interconnected nature which makes it extremely hard to isolate intact single neurons. [ 8 ] As snRNA-seq has emerged as an alternative method of assessing a cell's transcriptome through the isolation of single nuclei, it has been possible to conduct single-neuron studies from postmortem human brain tissue. [ 9 ] snRNA-seq has also enabled the first single neuron analysis of immediate early gene expression (IEGs) associated with memory formation in the mouse hippocampus. [ 1 ] In 2019, Dmitry et al used the method on cortical tissue from ASD patients to identify ASD-associated transcriptomic changes in specific cell types, which is the first cell-type-specific transcriptome assessment in brains affected by ASD. [ 10 ]
Outside of neuroscience, snRNA-seq has also been used in other research areas. In 2019, Haojia et al compared both scRNA-seq and snRNA-seq in a genomic study around the kidney. They found snRNA-seq accomplishes an equivalent gene detection rate to that of scRNA-seq in adult kidney with several significant advantages (including compatibility with frozen samples, reduced dissociation bias and so on ). [ 11 ] In 2019, Joshi et al used snRNA-seq in a human lung biology study in which they found snRNA-seq allowed unbiased identification of cell types from frozen healthy and fibrotic lung tissues. [ 12 ] Adult mammalian heart tissue can be extremely hard to dissociate without damaging cells, which does not allow for easy sequencing of the tissue. However, in 2020, German scientists presented the first report of sequencing an adult mammalian heart by using snRNA-seq and were able to provide practical cell‐type distributions within the heart [ 13 ] | https://en.wikipedia.org/wiki/SnRNA-seq |
snRNP s (pronounced "snurps"), or s mall n uclear r ibo n ucleo p roteins , are RNA - protein complexes that combine with unmodified pre-mRNA and various other proteins to form a spliceosome , a large RNA-protein molecular complex upon which splicing of pre-mRNA occurs. The action of snRNPs is essential to the removal of introns from pre-mRNA , a critical aspect of post-transcriptional modification of RNA, occurring only in the nucleus of eukaryotic cells .
Additionally, U7 snRNP is not involved in splicing at all, as U7 snRNP is responsible for processing the 3′ stem-loop of histone pre-mRNA. [ 1 ]
The two essential components of snRNPs are protein molecules and RNA . The RNA found within each snRNP particle is known as small nuclear RNA , or snRNA , and is usually about 150 nucleotides in length. The snRNA component of the snRNP gives specificity to individual introns by " recognizing " the sequences of critical splicing signals at the 5' and 3' ends and branch site of introns. The snRNA in snRNPs is similar to ribosomal RNA in that it directly incorporates both an enzymatic and a structural role.
SnRNPs were discovered by Michael R. Lerner and Joan A. Steitz . [ 2 ] [ 3 ] Thomas R. Cech and Sidney Altman also played a role in the discovery, winning the Nobel Prize for Chemistry in 1989 for their independent discoveries that RNA can act as a catalyst in cell development.
At least five different kinds of snRNPs join the spliceosome to participate in splicing . They can be visualized by gel electrophoresis and are known individually as: U1, U2, U4, U5, and U6. Their snRNA components are known, respectively, as: U1 snRNA , U2 snRNA , U4 snRNA , U5 snRNA , and U6 snRNA . [ 4 ]
In the mid-1990s, it was discovered that a variant class of snRNPs exists to help in the splicing of a class of introns found only in metazoans , with highly conserved 5' splice sites and branch sites. This variant class of snRNPs includes: U11 snRNA , U12 snRNA , U4atac snRNA , and U6atac snRNA . While different, they perform the same functions as do U1 , U2 , U4 , and U6 , respectively. [ 5 ]
Additionally, U7 snRNP is made of U7 small nuclear RNA and associated proteins and is involved in the processing of the 3′ stem-loop of histone pre-mRNA. [ 1 ]
Small nuclear ribonucleoproteins (snRNPs) assemble in a tightly orchestrated and regulated process that involves both the cell nucleus and cytoplasm . [ 6 ]
The RNA polymerase II transcribes U1 , U2 , U4 , U5 and the less abundant U11 , U12 and U4atac ( snRNAs ) acquire a m7G-cap which serves as an export signal. Nuclear export is mediated by CRM1.
The Sm proteins are synthesized in the cytoplasm by ribosomes translating Sm messenger RNA , just like any other protein. These are stored in the cytoplasm in the form of three partially assembled rings complexes all associated with the pICln protein. They are a 6S pentamer complex of SmD1, SmD2, SmF, SmE and SmG with pICln , a 2-4S complex of SmB, possibly with SmD3 and pICln and the 20S methylosome , which is a large complex of SmD3, SmB, SmD1, pICln and the arginine methyltransferase-5 ( PRMT5 ) protein. SmD3, SmB and SmD1 undergo post-translational modification in the methylosome. [ 7 ] These three Sm proteins have repeated arginine - glycine motifs in the C-terminal ends of SmD1, SmD3 and SmB, and the arginine side chains are symmetrically dimethylated to ω-N G , N G' -dimethyl-arginine. It has been suggested that pICln, which occurs in all three precursor complexes but is absent in the mature snRNPs, acts as a specialized chaperone , preventing premature assembly of Sm proteins.
The snRNAs (U1, U2, U4, U5, and the less abundant U11, U12 and U4atac) quickly interact with the SMN (survival of motor neuron protein); encoded by SMN1 gene) and Gemins 2-8 (Gem-associated proteins: GEMIN2 , GEMIN3 , GEMIN4 , GEMIN5 , GEMIN6 , GEMIN7 , GEMIN8 ) forming the SMN complex . [ 8 ] [ 9 ] It is here that the snRNA binds to the SmD1-SmD2-SmF-SmE-SmG pentamer, followed by addition of the SmD3-SmB dimer to complete the Sm ring around the so-called Sm site of the snRNA. This Sm site is a conserved sequence of nucleotides in these snRNAs, typically AUUUGUGG (where A, U and G represent the nucleosides adenosine , uridine and guanosine , respectively). After assembly of the Sm ring around the snRNA, the 5' terminal nucleoside (already modified to a 7-methylguanosine cap) is hyper-methylated to 2,2,7-trimethylguanosine and the other (3') end of the snRNA is trimmed. This modification, and the presence of a complete Sm ring, is recognized by the snurportin 1 protein.
The completed core snRNP-snurportin 1 complex is transported into the nucleus via the protein importin β . Inside the nucleus, the core snRNPs appear in the Cajal bodies , where final assembly of the snRNPs take place. This consists of additional proteins and other modifications specific to the particular snRNP (U1, U2, U4, U5). The biogenesis of the U6 snRNP occurs in the nucleus, although large amounts of free U6 are found in the cytoplasm. The LSm ring may assemble first, and then associate with the U6 snRNA .
The snRNPs are very long-lived, but are assumed to be eventually disassembled and degraded. Little is known about the degradation process.
Defective function of the survival of motor neuron (SMN) protein in snRNP biogenesis, caused by a genetic defect in the SMN1 gene which codes for SMN, may account for the motor neuron pathology observed in the genetic disorder spinal muscular atrophy . [ 10 ]
Several human and yeast snRNP structures were determined by the cryo-electron microscopy and successive single particle analysis . [ 11 ] Recently, the human U1 snRNP core structure was determined by X-ray crystallography (3CW1, 3PGW), followed by a structure of the U4 core snRNP (2Y9A), which yielded first insights into atomic contacts, especially the binding mode of the Sm proteins to the Sm site. The structure of U6 UsnRNA was solved in complex with a specific protein Prp24 (4N0T), as well as a structure of its 3'- nucleotides bound to the special Lsm2-8 protein ring (4M7A). The PDB codes for the respective structures are mentioned in parentheses. [ 12 ] [ 13 ] The structures determined by single particle electron microscopy analysis are: human U1 snRNP, [ 14 ] human U11/U12 di-snRNP, [ 15 ] human U5 snRNP, U4/U6 di-snRNP, U4/U6∙U5 tri-snRNP. [ 16 ] The further progress determining the structures and functions of snRNPs and spliceosomes continues. [ 17 ]
Autoantibodies may be produced against the body's own snRNPs, most notably the anti-Sm antibodies targeted against the Sm protein type of snRNP specifically in systemic lupus erythematosus (SLE). | https://en.wikipedia.org/wiki/SnRNP |
Tin(IV) sulfide is a compound with the formula SnS2 . A brown, water-insoluble solid, it is a semiconductor with band gap 2.2 eV. [ 5 ] It occurs naturally as the rare mineral berndtite . [ 6 ]
The compound precipitates as a brown solid upon the addition of H 2 S to solutions containing tin(IV) species. This reaction is reversed at low pH . It can also be prepared by heating finely ground Sn with excess sulfur. [ 7 ]
The compound crystallizes in the cadmium iodide motif, with the Sn(IV) situated in "octahedral holes' defined by six sulfide centers. [ 8 ]
The material reacts with sulfide salts to give a series of thiostannates with the formula [SnS 2 ] m [S] 2 n − n . [ 9 ] A simplified equation for this depolymerization reaction is:
Crystalline SnS 2 has a bronze color and is used in decorative coating [ 10 ] where it is known as mosaic gold .
Tin (IV) sulfide has various uses in electrochemistry. It serves as an anode in prototypes of lithium-ion batteries. [ 11 ] Intercalation with organometallic reagents is reversible. [ 12 ]
It has also been evaluated as a component of supercapacitors, which could be used for energy storage. [ 13 ] | https://en.wikipedia.org/wiki/SnS2 |
Tin selenide , also known as stannous selenide, is an inorganic compound with the formula Sn Se . Tin(II) selenide is a narrow band-gap (IV-VI) semiconductor structurally analogous to black phosphorus . It has received considerable interest for possible applications including low-cost photovoltaics , and memory-switching devices. Because of its low thermal conductivity as well as reasonable electrical conductivity, tin selenide is one of the most efficient thermoelectric materials . [ 4 ] [ 5 ]
α-SnSe is classified as a layered metal chalcogenide . [ 6 ] It includes a group 16 anion (Se 2− ) and an electropositive element (Sn 2+ ), and is arranged in a layered structure. Tin(II) selenide (SnSe) crystallizes in the orthorhombic structure that is related to the rock-salt structure. It is isomorphous to germanium selenide (GeSe). [ 7 ] The unit cell encompasses two inverted layers. Each tin atom is covalently bonded to three neighboring selenium atoms, and each selenium atom is covalently bonded to three neighboring tin atoms. [ 8 ] The layers are held together primarily by van der Waals forces . [ 9 ] At temperatures above 800 K its structure changes to rock-salt structure. [ 4 ]
At pressures above 58 GPa, SnSe acts as a superconductor ; this change of conductivity is likely due to a change in the structure to that of CsCl . [ 10 ] Another polymorph is based upon the cubic and orthorhombic crystal system is known as π-SnSe (space group: P213, No. 198). [ 11 ] A γ-SnSe phase has also been reported (space group: Pnma, No. 62). [ 12 ]
Tin(II) selenide can be formed by combining the elements tin and selenium above 350 °C. [ 13 ]
Problems with the composition are encountered during synthesis. Two phases exist—the hexagonal SnSe 2 phase and the orthorhombic SnSe phase. Specific nanostructures can be synthesized, [ 14 ] but few 2D nanostructures have been prepared. Both square SnSe nanostructures and single-layer SnSe nanostructures have been prepared. Historically, phase-controlled synthesis of 2D tin selenide nanostructures is quite difficult. [ 6 ]
Sheet-like nanocrystalline SnSe with an orthorhombic phase has been prepared with good purity and crystallization via a reaction between a selenium alkaline aqueous solution and tin(II) complex at room temperature under atmospheric pressure. [ 15 ] A few-atom-thick SnSe nanowires can be grown inside narrow (~1 nm diameter) single-wall carbon nanotubes by heating the nanotubes with SnSe powder in vacuum at 960 °C. Contrary to the bulk SnSe, they have the cubic crystal structure. [ 2 ]
Tin(II) selenide has been considered for thermoelectric applications. [ 16 ] SnSe has exhibited the highest thermoelectric material efficiency , measured by the unitless ZT parameter, of any known material (~2.62 at 923 K along the b axis and ~2.3 along the c axis). When coupled with the Carnot efficiency for heat conversion, the overall energy conversion efficiency of approximately 25%. Its high efficiency is most likely due to low thermal conductivity of the crystal, the electronic structure may have as important role: SnSe has highly anisotropic valence band structure, which consists of multiple valleys that act as independent channels for very mobile, low effective-mass charge transport within, and heavy-carrier conductivity perpendicular to the layers. [ 17 ] While, historically, lead telluride and silicon-germanium have been used, these materials suffer from high thermal conductivity. [ 18 ]
At room temperature, the crystal structure of SnSe is Pnma . However, at ~750 K, it undergoes a phase transition that results in a higher symmetry Cmcm structure. This phase transition preserves many of the advantageous transport properties of SnSe. The dynamic structural behavior of SnSe involving the reversible phase transition helps to preserve the high power factor. The Cmcm phase, which is structurally related to the low temperature Pnma phase, exhibits a substantially reduced energy gap and enhanced carrier mobilities while maintaining the ultralow thermal conductivity thus yielding the record ZT. Because of SnSe's layered structure, which does not conduct heat well, one end of the SnSe single crystal can get hot while the other remains cool. This idea can be paralleled with the idea of a posture-pedic mattress that does not transfer vibrations laterally. In SnSe, the ability of crystal vibrations (also known as phonons ) to propagate through the material is significantly hampered. This means heat can only travel due to hot carriers (an effect that can be approximated by the Wiedemann–Franz law ), a heat transport mechanism that is much less significant to the total thermal conductivity. Thus the hot end can stay hot while the cold end remains cold, maintaining the temperature gradient needed for thermoelectric device operation. The poor ability to carry heat through its lattice enables the resulting record high thermoelectric conversion efficiency. [ 19 ] The previously reported nanostructured all-scale hierarchical PbTe-4SrTe-2Na (with a ZT of 2.2) exhibits a lattice thermal conductivity of 0.5 W m −1 K −1 . The unprecedentedly high ZT ~2.6 of SnSe arises primarily from an even lower lattice thermal conductivity of 0.23 W m −1 K −1 . [ 20 ] However, in order to take advantage of this ultralow lattice thermal conductivity, the synthesis method must result in macroscale single crystals as p-type polycrystalline SnSe has been shown to have a significantly reduced ZT. [ 21 ] Enhancement in the figure of merit above a relatively high value of 2.5 can have sweeping ramifications for commercial applications especially for materials using less expensive, more Earth-abundant elements that are devoid of lead and tellurium (two materials that have been prevalent in the thermoelectric materials industry for the past couple decades).
Tin selenides may be used for optoelectronic devices, solar cells , memory switching devices, [ 7 ] and anodes for lithium-ion batteries . [ 6 ]
Tin(II) selenide has potential as a solid-state lubricant, due to the nature of its interlayer bonding. [ 22 ] It is not the most stable of the chalcogenide solid-state lubricants, as tungsten diselenide has much weaker interplanar bonding, is highly chemically inert and has high stability in high-temperature, high-vacuum environments. | https://en.wikipedia.org/wiki/SnSe |
Tin telluride is a compound of tin and tellurium (SnTe); is a IV-VI narrow band gap semiconductor and has direct band gap of 0.18 eV. It is often alloyed with lead to make lead tin telluride, which is used as an infrared detector material.
Tin telluride normally forms p-type semiconductor ( Extrinsic semiconductor ) due to tin vacancies and is a low temperature
superconductor. [ 4 ]
SnTe exists in three crystal phases. At Low temperatures, where the concentration of hole carriers is less than 1.5x10 20 cm −3 , Tin Telluride exists in rhombohedral phase also known as α-SnTe.
At room temperature and atmospheric pressure, Tin Telluride exists in NaCl-like cubic crystal phase, known as β-SnTe.
While at 18 kbar pressure, β-SnTe transforms to γ-SnTe, orthorhombic phase , space group Pnma. [ 5 ] This phase change is characterized by 11 percent increase in density and 360 percent increase in resistance for γ-SnTe. [ 6 ]
Tin telluride is a thermoelectric material. Theoretical studies
imply that the n-type performance may be particularly good. [ 7 ]
Generally Pb is alloyed with SnTe in order to access interesting optical and electronic properties, In addition, as a result of Quantum confinement , the band gap of the SnTe increases beyond the bulk band gap, covering the mid-IR wavelength range. The alloyed material has been used in mid- IR photodetectors [ 9 ] and thermoelectric generator . [ 10 ] | https://en.wikipedia.org/wiki/SnTe |
In forest ecology , a snag refers to a standing dead or dying tree , often missing a top or most of the smaller branches. In freshwater ecology it refers to trees, branches, and other pieces of naturally occurring wood found sunken in rivers and streams ; it is also known as coarse woody debris . Snags provide habitat for a wide variety of wildlife but pose hazards to river navigation . When used in manufacturing, especially in Scandinavia , they are often called dead wood and in Finland , kelo wood.
Snags are an important structural component in forest communities, making up 10–20% of all trees present in old-growth tropical, temperate, and boreal forests. [ 1 ] [ 2 ] [ 3 ] Snags and downed coarse woody debris represent a large portion of the woody biomass in a healthy forest. [ 1 ] [ 2 ] [ 3 ]
In temperate forests, snags provide critical habitat for more than 100 species of bird and mammal, and snags are often called 'wildlife trees' by foresters. [ 4 ] [ 5 ] Dead, decaying wood supports a rich community of decomposers like bacteria and fungi , insects , and other invertebrates . These organisms and their consumers , along with the structural complexity of cavities, hollows, and broken tops make snags important habitat for birds, bats, and small mammals, which in turn feed larger mammalian predators. [ 6 ]
Snags are optimal habitat for primary cavity nesters such as woodpeckers which create the majority of cavities used by secondary cavity users in forest ecosystems. Woodpeckers excavate cavities for more than 80 other species and the health of their populations relies on snags. Most snag-dependent birds and mammals are insectivorous and represent a major portion of the insectivorous forest fauna, and are important factors in controlling forest insect populations. [ 6 ] There are many instances in which birds reduced outbreak populations of forest insects, such as woodpeckers affecting outbreaks of southern hardwood borers and Engelmann spruce beetles. [ 6 ]
Snag creation occurs naturally as trees die due to old age, disease, drought, or wildfire. A snag undergoes a series of changes from the time the tree dies until final collapse, and each stage in the decay process has particular value to certain wildlife species. [ 7 ] Snag persistence depends on two factors, the size of the stem, and the durability of the wood of the species concerned. The snags of some large conifers, such as Giant Sequoia and Coast Redwood on the Pacific Coast of North America, and the Alerce of Patagonia, can remain intact for 100 years or more, becoming progressively shorter with age, while other snags with rapidly decaying wood, such as aspen and birch , break up and collapse in 2–10 years.
Snag forests, or complex early seral forests , are ecosystems that occupy potentially forested sites after a stand-replacement disturbance and before re-establishment of a closed-forest canopy. [ 8 ] They are generated by natural disturbances such as wildfire or insect outbreaks that reset ecological succession processes and follow a pathway that is influenced by biological legacies (e.g., large live trees and snags downed logs, seed banks, resprout tissue, fungi, and other live and dead biomass) that were not removed during the initial disturbance. [ 9 ] [ 10 ]
Water hunting birds like the osprey or kingfishers can be found near water, perched in a snag tree, or feeding upon their fish catch.
In freshwater ecology in Australia and the United States, the term snag is used to refer to the trees, branches and other pieces of naturally occurring wood found in a sunken form in rivers and streams. Such snags have been identified as being critical for shelter and as spawning sites for fish , and are one of the few hard substrates available for biofilm growth supporting aquatic invertebrates in lowland rivers flowing through alluvial flood plains. Snags are important as sites for biofilm growth and for shelter and feeding of aquatic invertebrates in both lowland and upland rivers and streams.
In Australia , the role of freshwater snags has been largely ignored until recently, and more than one million snags have been removed from the Murray-Darling basin . Large tracts of the lowland reaches of the Murray-Darling system are now devoid of the snags that native fish like Murray cod require for shelter and breeding. The damage such wholesale snag removal has caused is enormous but difficult to quantify, however some quantification attempts have been made. [ 11 ] Most snags in these systems are river red gum snags. As the dense wood of river red gum is almost impervious to rot it is thought that some of the river red gum snags removed in past decades may have been several thousand years old.
Also known as deadheads , partially submerged snags posed hazards to early riverboat navigation and commerce. If hit, snags punctured the wooden hulls used in the 19th century and early 20th century. Snags were, in fact, the most commonly encountered hazard, especially in the early years of steamboat travel. [ 12 ] As described by a British traveller on the Mississippi in 1858, "We see plenty of snags, which are trees that have floated down; their roots in the water then catch fast in the mud; the stream breaks off the branches, and the sharp end of the tree sticks up, just at the right angles for catching any up-river boat, and often runs right through them, making a large leak, and sinking the unfortunate steamer." [ 13 ]
In the United States, the U.S. Army Corps of Engineers operated " snagboats " such as the W. T. Preston in the Puget Sound of Washington State and the Montgomery in the rivers of Alabama to pull out and clear snags. Starting in 1824, there were successful efforts to remove snags from the Mississippi and its tributaries. [ 12 ] By 1835, a lieutenant reported to the Chief of Engineers that steamboat travel had become much safer, but by the mid-1840s the appropriations for snag removal dried up and snags re-accumulated until after the Civil War. [ 12 ]
In Scandinavia and Finland, snags, invariably pine trees, known in Finnish as kelo and in Swedish as torraka , are collected for the production of different objects, from furniture to entire log houses. Commercial enterprises market them abroad as "dead wood" or in Finland as "kelo wood". They have been especially prized for their silver-grey weathered surface in the manufacture of vernacular or national romantic products. The suppliers of "dead wood" emphasise its age: the wood has developed with dehydration in the dry coldness of the subarctic zones, the tree having stopped growing after some 300–400 years, and the tree has remained upright for another few hundred years. "Dead wood" logs are easier to transport and handle than normal logs due to their lightness. [ citation needed ] | https://en.wikipedia.org/wiki/Snag_(ecology) |
The snake-in-the-box problem in graph theory and computer science deals with finding a certain kind of path along the edges of a hypercube . This path starts at one corner and travels along the edges to as many corners as it can reach. After it gets to a new corner, the previous corner and all of its neighbors must be marked as unusable. The path should never travel to a corner which has been marked unusable.
In other words, a snake is a connected open path in the hypercube where each node connected with path, with the exception of the head (start) and the tail (finish), it has exactly two neighbors that are also in the snake. The head and the tail each have only one neighbor in the snake. The rule for generating a snake is that a node in the hypercube may be visited if it is connected to the current node and it is not a neighbor of any previously visited node in the snake, other than the current node.
In graph theory terminology, this is called finding the longest possible induced path in a hypercube ; it can be viewed as a special case of the induced subgraph isomorphism problem . There is a similar problem of finding long induced cycles in hypercubes, called the coil-in-the-box problem.
The snake-in-the-box problem was first described by Kautz (1958) , motivated by the theory of error-correcting codes . The vertices of a solution to the snake or coil in the box problems can be used as a Gray code that can detect single-bit errors. Such codes have applications in electrical engineering , coding theory , and computer network topologies . In these applications, it is important to devise as long a code as is possible for a given dimension of hypercube . The longer the code, the more effective are its capabilities.
Finding the longest snake or coil becomes notoriously difficult as the dimension number increases and the search space suffers a serious combinatorial explosion . Some techniques for determining the upper and lower bounds for the snake-in-the-box problem include proofs using discrete mathematics and graph theory , exhaustive search of the search space, and heuristic search utilizing evolutionary techniques.
The maximum length for the snake-in-the-box problem is known for dimensions one through eight; it is
Beyond that length, the exact length of the longest snake is not known; the best lengths found so far for dimensions nine through thirteen are
For cycles (the coil-in-the-box problem), a cycle cannot exist in a hypercube of dimension less than two. The maximum lengths of the longest possible cycles are
Beyond that length, the exact length of the longest cycle is not known; the best lengths found so far for dimensions nine through thirteen are
Doubled coils are a special case: cycles whose second half repeats the structure of their first half, also known as symmetric coils . For dimensions two through seven the lengths of the longest possible doubled coils are
Beyond that, the best lengths found so far for dimensions eight through thirteen are
For both the snake and the coil in the box problems, it is known that the maximum length is proportional to 2 n for an n -dimensional box, asymptotically as n grows large, and bounded above by 2 n − 1 . However the constant of proportionality is not known, but is observed to be in the range 0.3 - 0.4 for current best known values. [ 1 ] | https://en.wikipedia.org/wiki/Snake-in-the-box |
The Snake Projection is a continuous map projection typically used as the planar coordinate system for realizing low distortion throughout long linear engineering projects. [ 1 ]
The Snake Projection was originally developed by University College London and Network Rail to provide a continuous low distortion projection for the West Coast Mainline infrastructure works. [ 2 ] The parameters defining each Snake Projection are tailored for the specific project. The most typical use is with large-scale linear engineering projects such as rail infrastructure; however, the projection is equally applicable to any application requiring a low distortion grid along a linear route (for example pipelines and roads). [ 3 ] The name of the projection is derived from the sinuous snake-like nature of the projects it may be designed for. Typical map projection distance distortion characteristics of a Snake Projection are minimal over the whole route within approximately 20 km (12 mi) of the centre line. [ 4 ]
The principal advantage of the projection is that, for the corridor defining the design space, distances measured on the ground have a nearly one-to-one relationship with distances in coordinate space (i.e. no scale factor need be applied to convert between distances in grid and distances on the ground). [ 5 ] The length of the applicable corridor is variable on a project basis; however, when required, the projection can extend over several hundreds of kilometres to achieve grid distortion of less than 20 parts per million along the route. [ 6 ] The main disadvantage is that away from the design corridor, the distortion of the projection is not controlled.
The Snake Projection is suited for engineering purposes due to its low distortion characteristics. An example of its differentiation from mapping grids is the 60 m (200 ft) increase in length of the London to Birmingham section of the HS2 rail line, purely due to the more accurate grid representation compared to the length when using the national mapping coordinate system British National Grid . [ 7 ]
The Snake Projection is the engineering coordinate system used for a significant proportion of primary rail routes in the UK, [ 8 ] including that of the HS2 London to Birmingham high speed line. [ 9 ] For the London to Glasgow West Coast Main Line , the distortion in the Snake Projection used is no greater than 20 parts per million within 5 km (3.1 mi) of either side of the track. [ 10 ]
The Snake Projection algorithm converts between geographical and grid coordinates; however, the method of technical implementation can vary. One method of implementing a Snake Projection is to define using an NTv2 geodetic transformation coupled with a standard parameterised map projection (such as Transverse Mercator ); this is increasing in popularity due to better compatibility with CAD and GIS software. [ 7 ] The global EPSG geodetic coordinate system database features several snake projection definitions through the NTv2 approach. [ 11 ] Other implementations include those published through the SnakeGrid organisation. [ 12 ] | https://en.wikipedia.org/wiki/Snake_Projection |
The Snake Valley Astronomical Association ( SVAA ) is an amateur astronomy club based in Snake Valley , Victoria , Australia . Established in 2005, membership of the SVAA is open to people with an interest in any form of astronomy. As of June 2011 the SVAA has around 30 members.
The original idea to create the SVAA was first discussed by three Snake Valley residents (Ken James, David Johnson, Anthony Baker) and the Shire Mayor (Lysette Ashford) at the 1st Snake Valley Astronomy Camp in 2005. This idea came about due to the dark sky at Snake Valley and the amount of interest shown by attendees at the Astronomy Camp. A public meeting was called in the Snake Valley Hall late in 2005 to investigate interest in the establishment of a club. Twelve people attended that event, and it was decided to go ahead. The first official meeting was held at the Snake Valley Recreation Reserve with 15 people in attendance.
The first Clubroom/Observing location was at the Recreation reserve in 2006 and was 'home' for the next two years. Then in 2008, member Ken James granted the club the use of 3 acres of his property as a Club managed location. A large donation from member Hoerst Bonkhe was forwarded to Mr. James to go towards the construction of a Club meeting room and the possibility of a future Observatory with the stipulation that the Club Room be made available for club members use whilst Mr. James owns the property.
Construction of a Clubroom started immediately in 2008 and the Observatory commenced early in 2016 (Construction of both is now finished). During this time many other donations of Astronomy books, Telescopes, and accessories have built up into a lending library for members.
In 2015 Snake Valley was denoted gold status by the Australian Dark Sky Register. [ 1 ] [ 2 ]
The SVAA holds monthly meetings, which are open to the public. The club also holds astronomy classes. [ 1 ] [ 2 ] Members occasionally do talks and demonstrations for local primary schools, high schools, and other groups. SVAA also runs 2 day basic astronomy competency courses suitable for 'Scouts Australia Astronomer Badge' and other groups.
Members of the SVAA are involved in a variety of interests within astronomy: | https://en.wikipedia.org/wiki/Snake_Valley_Astronomical_Association |
Snake oil is a term used to describe deceptive marketing , health care fraud , or a scam. Similarly, snake oil salesman is a common label used to describe someone who sells, promotes, or is a general proponent of some valueless or fraudulent cure, remedy, or solution. [ 1 ] The term comes from the "snake oil" that used to be sold as a cure-all elixir for many kinds of physiological problems. Many 18th-century European and 19th-century United States entrepreneurs advertised and sold mineral oil (often mixed with various active and inactive household herbs, spices, drugs, and compounds, but containing no snake-derived substances whatsoever) as "snake oil liniment ", making claims about its efficacy as a panacea . Patent medicines that claimed to be panaceas were extremely common from the 18th century until the 20th century, particularly among vendors masking addictive drugs such as cocaine , amphetamine , alcohol , and opium -based concoctions or elixirs , to be sold at medicine shows as medication or products promoting health.
Oil from Chinese water snakes has for centuries been used in Chinese traditional medicine to treat joint pain such as arthritis and bursitis . It has been suggested that the use of snake oil in the United States may have originated with Chinese railway laborers in the mid-19th century, who worked long days of physical toil. Chinese snake oil may have had real benefits due to its high concentration of the omega−3 fatty acid eicosapentaenoic acid (EPA)—more than that of salmon ; the rattlesnake oil later sold by charlatans did not contain a significant amount of omega−3. [ 2 ] In a modern study, erabu sea-snake oil was found to significantly improve the ability of mice to learn mazes, and their swimming endurance, over mice fed lard. [ 2 ] [ 3 ]
Patent medicines originated in England, where a patent was granted to Richard Stoughton's elixir in 1712. [ 4 ] There were no federal regulations in the United States concerning the safety and effectiveness of drugs until the 1906 Pure Food and Drug Act . [ 5 ] Thus, the widespread marketing and availability of dubiously advertised patent medicines without known properties or origin persisted in the US for a much greater number of years than in Europe.
In 18th-century Europe, especially in Britain, viper oil had been commonly recommended for many afflictions, including the ones for which oil from the rattlesnake (pit viper), a type of viper native to America, was subsequently favored to treat rheumatism and skin diseases . [ 6 ] Though there are accounts of oil obtained from the fat of various vipers in the Western world, the claims of its effectiveness as a medicine have never been thoroughly examined, and its efficacy is unknown. It is also likely that much of the snake oil sold by Western entrepreneurs was illegitimate, and did not contain ingredients derived from any kind of snake. Snake oil in the United Kingdom and the United States probably contained modified mineral oil . William Rockefeller Sr. , the father of John D. Rockefeller , peddled literal snake oil. [ 7 ]
A popular trope in Western films, selling snake oil is portrayed as a confidence trick : a traveling salesman purports to be a doctor (with false credentials), selling fake medicines with boisterous marketing hype , and supported by pseudo-scientific evidence. To increase sales, an accomplice in the crowd (a shill or a "toadie") will often attest to the value of the product in an effort to provoke buying enthusiasm. The "doctor" will leave town before his customers realize they have been cheated. This trope is associated with the American Old West . However, the famous judgment that sparked the most controversy happened in 1917, when Stanley's Snake Oil was discovered to contain no actual snake oil, creating the notion that bottles of snake oil (and their salesmen) were essentially a fraud. [ 8 ] That case took place in Rhode Island , and involved snake oil manufactured in Massachusetts , long after and far away from the Old West. [ 9 ] [ better source needed ]
Clark Stanley 's Snake Oil Liniment – produced by Clark Stanley, the "Rattlesnake King" – was tested by the United States government's Bureau of Chemistry , the precursor to the Food and Drug Administration (FDA) in 1916. [ 9 ] It was found to contain: mineral oil, 1% fatty oil (assumed to be tallow ), capsaicin from chili peppers , turpentine , and camphor . [ 4 ]
In 1916, subsequent to the passage of the Pure Food and Drug Act in 1906, Clark Stanley's Snake Oil Liniment was examined by the Bureau of Chemistry, and found to be drastically overpriced and of limited value. As a result, Stanley faced federal prosecution for peddling mineral oil in a fraudulent manner as snake oil. In his 1916 civil hearing instigated by federal prosecutors in the U.S. District Court for Rhode Island, Stanley pleaded nolo contendere (no contest) to the allegations against him, giving no admission of guilt . [ 9 ] His plea was accepted, and as a result, he was fined $20 [ 9 ] (about $578 in 2024). [ 10 ]
The term snake oil has since been established in popular culture as a reference to any worthless concoction sold as medicine, and has been extended to describe a wide-ranging degree of fraudulent goods, services, ideas, and activities such as worthless rhetoric in politics. By further extension, a snake oil salesman is commonly used in English to describe a quack , huckster , or charlatan .
False health products described by medical experts as "snake oil" continue to be marketed during the 21st century, including herbal medicines , dietary supplements , products such as Tibetan singing bowls (when used for healing ) and treatments such as vaginal steaming . The company Goop has been accused of "selling snake oil" in some of its health products and recommendations. [ 11 ] [ 12 ]
During the COVID-19 pandemic , the Xinhua News Agency claimed that the herbal product Shuanghuanglian can prevent or treat infections from coronaviruses , stimulating sales across the United States, Russia, and China. However, the clinical studies on its effectiveness have been inconclusive. [ 13 ] [ 14 ] Su et al. published a report that the herbal substance has been shown in vitro to be cytotoxic "against a clinical isolate of SARS-CoV-2". [ 15 ] However, another government media outlet, People’s Daily , published a contrasting report urging citizens not to purchase the herbal remedy as it had not been recommended for coronavirus antiviral treatment and treatment measures had not passed clinical trials. [ 16 ] | https://en.wikipedia.org/wiki/Snake_oil |
Snappy (previously known as Zippy ) is a fast data compression and decompression library written in C++ by Google based on ideas from LZ77 and open-sourced in 2011. [ 3 ] [ 4 ] It does not aim for maximum compression, or compatibility with any other compression library; instead, it aims for very high speeds and reasonable compression. Compression speed is 250 MB/s and decompression speed is 500 MB/s using a single core of a circa 2011 "Westmere" 2.26 GHz Core i7 processor running in 64-bit mode . The compression ratio is 20–100% lower than gzip . [ 5 ]
Snappy is widely used in Google projects like Bigtable , MapReduce and in compressing data for Google's internal RPC systems. It can be used in open-source projects like MariaDB ColumnStore , [ 6 ] Cassandra , Couchbase , Hadoop , LevelDB , MongoDB , RocksDB , Lucene , Spark, InfluxDB , [ 7 ] and Ceph . [ 8 ] Firefox uses Snappy to compress data in localStorage . [ 9 ] Decompression is tested to detect any errors in the compressed stream. Snappy does not use inline assembler (except some optimizations [ 10 ] ) and is portable.
Snappy encoding is not bit-oriented, but byte-oriented (only whole bytes are emitted or consumed from a stream). The format uses no entropy encoder , like Huffman coding or arithmetic coding .
The first bytes of the stream are the length of uncompressed data, stored as a little-endian varint , [ 11 ] : section 1 which allows for use of a variable-length code . The lower seven bits of each byte are used for data and the high bit is a flag to indicate the end of the length field.
The remaining bytes in the stream are encoded using one of four element types. The element type is encoded in the lower two bits of the first byte ( tag byte ) of the element: [ 12 ]
The copy refers to the dictionary (just-decompressed data). The offset is the shift from the current position back to the already decompressed stream. The length is the number of bytes to copy from the dictionary. The size of the dictionary was limited by the 1.0 Snappy compressor to 32,768 bytes, and updated to 65,536 in version 1.1. [ citation needed ]
The complete official description of the snappy format can be found in the google GitHub repository. [ 11 ]
The text
Wikipedia is a free, web-based, collaborative, multilingual encyclopedia project.
may be compressed to this, shown as hex data with explanations:
The stream starts with the length of the uncompressed data as a varint , so the first byte, with the high bit clear, corresponds to a length of 51 16 =81 bytes. [ 11 ] : section 1
The first block must be a literal, and f042 corresponds thereto: the first byte is broken down as f0 16 ⇒ len−1=111100 2 ;type=00 2 ; type 0 signifies a literal, and a length−1 of 111100 2 =60 means the length is read from the following byte, in this case 42 16 =66. The first 66 bytes of the text (" Wikipedia is a free, web-based, collaborative, multilingual encyclo ") follow. [ 11 ] : 2.1
The next block's header consists of 093f , broken down as 09 16 ⇒ off h =000 2 ,len−4=010 2 ;type=01 2 : type 1 indicates a "copy with 1-byte offset": the length to copy works out to 010 2 +4=6 bytes, and the offset is an 11-bit integer whose top bits are off h and whose low bits are the next byte: 3f , so {off h }{3f 16 }=00000111111 2 =63. [ 11 ] : 2.2,2.2.1
This means to copy 6 bytes, starting 63 bytes ago – since 67 bytes have already been copied this evaluates to copying 6 bytes starting at position 4 (from the fifth byte), which produces " pedia ".
This block has no other content, and thus the following block starts immediately after – 1c 16 ⇒ len−1=000111 2 ;type=00 2 , i.e. a literal of length 000111 2 +1=8. [ 11 ] : 2.1 The final part of the text (" project. ") follows.
In this example, all common substrings with four or more characters were eliminated by the compression process. More common compressors can compress this better. Unlike compression methods such as gzip and bzip2, there is no entropy encoding used to pack alphabet into the bit stream.
The Snappy stream supports inputs with an overall size of up to 4GiB−1, [ 11 ] : section 1 and may add significant overhead to sections which are not or insufficiently compressed, as well as not being self-identifying, and having no data integrity mechanism beyond a simple output size check.
To combat these issues, the Snappy framing format [ 2 ] "Snappy framed" may be used, which breaks the input into chunks of up to 64KiB, [ 2 ] : 4.2,4.3 delimited by 4-byte block headers (a one-byte identifier and three-byte length): [ 2 ] : section 1
Both types of data chunk also contain a CRC-32C checksum of the uncompressed data.
Chunks of types 2-7F 16 are reserved and must result in errors. [ 2 ] : 4.5 Those of types 80 16 -FE 16 may be ignored by the decompressors which do not understand them. [ 2 ] : 4.4,4.6
Snappy distributions include C++ and C bindings. Third party-provided bindings and ports include [ 13 ] C# , Common Lisp , Crystal (programming language) , Erlang , Go , Haskell , Lua , Java , Nim , Node.js , Perl , PHP , Python , R , Ruby , Rust , Smalltalk , and OpenCL . [ 14 ] [ 15 ] A command-line interface program is also available. [ 16 ] | https://en.wikipedia.org/wiki/Snappy_(compression) |
In trigonometry , the Snellius–Pothenot problem is a problem first described in the context of planar surveying . Given three known points A, B, C , an observer at an unknown point P observes that the line segment AC subtends an angle α and the segment CB subtends an angle β ; the problem is to determine the position of the point P . (See figure; the point denoted C is between A and B as seen from P ).
Since it involves the observation of known points from an unknown point, the problem is an example of resection . Historically it was first studied by Snellius , who found a solution around 1615.
Denoting the (unknown) angles ∠ CAP as x and ∠ CBP as y gives:
x + y = 2 π − α − β − C {\displaystyle x+y=2\pi -\alpha -\beta -C}
by using the sum of the angles formula for the quadrilateral PACB . The variable C represents the (known) internal angle in this quadrilateral at point C . (Note that in the case where the points C and P are on the same side of the line AB , the angle ∠ C will be greater than π ).
Applying the law of sines in triangles △ PAC and △ PBC , we can express PC in two different ways:
P C ¯ = A C ¯ sin x sin α = B C ¯ sin y sin β . {\displaystyle {\overline {PC}}={\frac {{\overline {AC}}\sin x}{\sin \alpha }}={\frac {{\overline {BC}}\sin y}{\sin \beta }}.}
A useful trick at this point is to define an auxiliary angle φ such that
tan ϕ = B C sin α A C sin β . {\displaystyle \tan \phi ={\frac {{\rm {BC}}\sin \alpha }{{\rm {AC}}\sin \beta }}.}
(A minor note: one should be concerned about division by zero, but consider that the problem is symmetric, so if one of the two given angles is zero one can, if needed, rename that angle α and call the other (non-zero) angle β , reversing the roles of A and B as well. This will suffice to guarantee that the ratio above is well defined. An alternative approach to the zero angle problem is given in the algorithm below.)
With this substitution the equation becomes
sin x sin y = tan ϕ . {\displaystyle {\frac {\sin x}{\sin y}}=\tan \phi .}
Now two known trigonometric identities can be used, namely
tan ( π 4 − ϕ ) = 1 − tan ϕ tan ϕ + 1 , tan 1 2 ( x − y ) tan 1 2 ( x + y ) = sin x − sin y sin x + sin y , {\displaystyle \tan \left({\tfrac {\pi }{4}}-\phi \right)={\frac {1-\tan \phi }{\tan \phi +1}}\ ,\qquad {\frac {\tan {\tfrac {1}{2}}(x-y)}{\tan {\tfrac {1}{2}}(x+y)}}={\frac {\sin x-\sin y}{\sin x+\sin y}}\ ,}
to put this in the form of the second equation;
tan 1 2 ( x − y ) = tan 1 2 ( α + β + C ) tan ( π 4 − ϕ ) . {\displaystyle \tan {\tfrac {1}{2}}(x-y)=\tan {\tfrac {1}{2}}(\alpha +\beta +C)\tan \left({\tfrac {\pi }{4}}-\phi \right).}
Now these two equations in two unknowns must be solved. Once x and y are known the various triangles can be solved straightforwardly to determine the position of P . [ 1 ] The detailed procedure is shown below.
Given are two lengths AC , BC , and three angles α, β, C , the solution proceeds as follows.
If the coordinates of A : x A , y A {\displaystyle A:x_{A},y_{A}} and C : x C , y C {\displaystyle C:x_{C},y_{C}} are known in some appropriate Cartesian coordinate system then the coordinates of P can be found as well.
By the inscribed angle theorem the locus of points from which AC subtends an angle α is a circle having its center on the midline of AC ; from the center O of this circle, AC subtends an angle 2 α . Similarly the locus of points from which CB subtends an angle β is another circle. The desired point P is at the intersection of these two loci.
Therefore, on a map or nautical chart showing the points A, B, C , the following graphical construction can be used:
This method of solution is sometimes called Cassini's method .
The following solution is based upon a paper by N. J. Wildberger. [ 2 ] It has the advantage that it is almost purely algebraic. The only place trigonometry is used is in converting the angles to spreads . There is only one square root required.
finally: A P ¯ 2 = v 1 R 1 r 2 = v 1 Q 3 r 3 B P ¯ 2 = v 2 R 2 r 1 = v 2 Q 3 r 3 {\displaystyle {\begin{aligned}{\overline {AP}}^{2}&={\frac {v_{1}R_{1}}{r_{2}}}={\frac {v_{1}Q_{3}}{r_{3}}}\\[4pt]{\overline {BP}}^{2}&={\frac {v_{2}R_{2}}{r_{1}}}={\frac {v_{2}Q_{3}}{r_{3}}}\end{aligned}}}
Ventura et al. [ 3 ] solve the planar and three-dimensional Snellius-Pothenot problem via Vector Geometric Algebra and Conformal Geometric Algebra. The authors also characterize the solutions' sensitivity to measurement errors.
When the point P happens to be located on the same circle as A, B, C , the problem has an infinite number of solutions; the reason is that from any other point P' located on the arc APB of this circle the observer sees the same angles α and β as from P ( inscribed angle theorem ). Thus the solution in this case is not uniquely determined.
The circle through ABC is known as the "danger circle", and observations made on (or very close to) this circle should be avoided. It is helpful to plot this circle on a map before making the observations.
A theorem on cyclic quadrilaterals is helpful in detecting the indeterminate situation. The quadrilateral APBC is cyclic iff a pair of opposite angles (such as the angle at P and the angle at C ) are supplementary i.e. iff α + β + C = k π , ( k = 1 , 2 , ⋯ ) {\displaystyle \alpha +\beta +C=k\pi ,(k=1,2,\cdots )} . If this condition is observed the computer/spreadsheet calculations should be stopped and an error message ("indeterminate case") returned.
(Adapted form Bowser, [ 4 ] exercise 140, page 203). A, B, C are three objects such that AC = 435 ( yards ), CB = 320, and ∠ C = 255.8 degrees. From a station P it is observed that ∠ APC = 30 degrees and ∠ CPB = 15 degrees. Find the distances of P from A, B, C . (Note that in this case the points C and P are on the same side of the line AB , a different configuration from the one shown in the figure).
Answer: PA = 790, PB = 777, PC = 502.
A slightly more challenging test case for a computer program uses the same data but this time with ∠ CPB = 0. The program should return the answers 843, 1157 and 837.
The British authority on geodesy, George Tyrrell McCaw (1870–1942) wrote that the proper term in English was Snellius problem , while Snellius-Pothenot was the continental European usage. [ 5 ]
McCaw thought the name of Laurent Pothenot (1650–1732) did not deserve to be included as he had made no original contribution, but merely restated Snellius 75 years later. | https://en.wikipedia.org/wiki/Snellius–Pothenot_problem |
Snf3 is a protein which regulates glucose uptake in yeast. It senses glucose in the environment with high affinity.
Glucose sensing and signaling in budding yeast is similar to the mammalian system in many ways. However, there are also significant differences. Mammalian cells regulate their glucose uptake via hormones (i.e. insulin and glucagon ) or intermediary metabolites . In contrast, yeast as a unicellular organism does not depend on hormones but on nutrients in the medium. The presence of glucose induces a conformational change in the membrane proteins Snf3/Rgt2 or Gpr1, and regulates expression of genes involved in glucose metabolism.
Snf3 is homologous to multiple sugar transporters, it shares high similarity to the glucose transporters of rat brain cells and human HepG2 hepatoma cells, as well as to the arabinose and xylose transporters (AraE and XylE) of Escherichia coli . [ 1 ] Based on this homology and on genetic studies, Snf3 was initially thought to be a high affinity glucose transporter.
Later, it was found that Snf3 is not a glucose transporter, but rather a high affinity glucose sensor. It senses glucose at low concentrations and regulates transcription of the HXT genes, which encode for glucose transporters. If glucose is absent Snf3 is quiescent and transcription of the HXT genes is inhibited by a repressing complex. The complex consisting of several subunits such as Rgt1, Mth1/Std1, Cyc8 and Tup1 binds to the promoters of the HXT genes, thereby blocking their transcription.
Snf3 is able to bind even low amounts of glucose due to its high affinity. The induction of Snf3 by glucose leads to the activation of YckI, a yeast casein kinase . This is followed by the recruitment of Mth1 and Std1 to the C-terminus of Snf3 which facilitates the phosphorylation of the two proteins by YckI. Phosphorylated Mth1 and Std1 are subsequently tagged for proteasome dependent degradation by SCF Grrl , an E3 ubiquitin ligase . Therefore, the inhibitory complex misses two of its key components and cannot be assembled. Thus, repression of the HXT genes is abolished, leading to the expression of the glucose transporters and subsequently glucose import. [ 2 ]
Snf3 is a plasma membrane protein in yeasts that consists of 12 (2x6) transmembrane domains , like the homologous glucose transporters. Its structure is distinct from the homologous transporters in particular by a long C-terminal tail which is predicted to reside in the cytoplasm .
The long C-terminal tail plays an important role in glucose signaling and is probably the signaling domain itself. A soluble version of the C-terminal tail alone is sufficient to induce glucose transport. [ 1 ] [ 2 ] [ 3 ]
All glucose transporters including Snf3 contain an arginine residue situated in a cytoplasmic loop preceding the fifth transmembrane domain. If this position is mutated, Snf3 adopts a state of constant glucose induction irrespective of whether there are nutrients present or not; this suggests an involvement in the glucose sensing process.
The regulation of Snf3 in S. cerevisiae and its downstream events are still poorly understood, but it seems clear that a second glucose sensor Rgt2 influences Snf3 and vice versa. Furthermore, it is unclear whether these two proteins sense the glucose concentration on the outside or inside the cell . Snf3 and Rgt2 influence directly or indirectly several Hxt-transporters which are responsible for the glucose uptake. Low extracellular glucose concentrations are sensed by the Snf3 protein which probably leads to the expression of Hxt2-Genes for high affinity glucose transporters, while Rgt2 senses high glucose concentrations and leads to the expression of low affinity glucose transporters, like Hxt1 Although the downstream pathway is poorly understood it seems that Snf3 and Rgt2 transmit a signal directly or indirectly to Grr1, the DNA binding protein Rgt1, and the two cofactors Ssn6 and Tup1. Also needed for the transcription are the two nuclear proteins Mth1 and Std1. [ 4 ] | https://en.wikipedia.org/wiki/Snf3 |
The Lockheed Martin Sniper is a targeting pod for military aircraft that provides positive target identification, autonomous tracking, GPS coordinate generation, and precise weapons guidance from extended standoff ranges.
The system has been designated AN/AAQ-33 in U.S. military service as the Sniper Advanced Targeting Pod (ATP) . Further variants are the Sniper Extended Range (XR) , as well as the PANTERA export derivative of the Sniper XR. The Lockheed Martin F-35 Lightning II is built with the equivalent of the Sniper XR in its onboard sensors called the AN/AAQ-40 Electro-Optical Targeting System (EOTS) . [ 1 ] The most modern version is the Sniper Advanced Targeting Pod - Sensor Enhancement (ATP-SE) .
The Sniper is a single, lightweight targeting pod with much lower aerodynamic drag than the systems it replaces [ citation needed ] . Its image processing allows aircrews to detect, identify and engage tactical-size targets outside the range of most enemy air defenses, giving it a crucial role in the destruction of enemy air defense missions. It also supports urban engagements beyond jet noise range for counter-insurgency operations. It offers a 3-5X increase in detection range over the older LANTIRN system [ citation needed ] , and is currently flying on U.S. Air Force and multinational F-16 , F-15 , B-1B , CF-18 , Harrier , A-10 , B-52 and Tornado aircraft.
The pod incorporates a high definition mid-wave FLIR , dual-mode laser, visible-light HDTV, laser spot tracker, laser marker, video data link, and a digital data recorder. [ 2 ] Advanced sensors and image processing incorporating image stabilization enable targets to be identified at ranges which minimize exposure to defensive enemy systems. The dual-mode laser offers an eye-safe mode for urban combat and training operations along with a laser-guided bomb designation laser.
The pod's FLIR allows observation and tracking through smoke and clouds, and in low light / no light conditions. The CCD camera supports the same operations in visible light for most daylight conditions.
For target coordination with ground and air forces, a laser spot tracker, a laser marker, and an HDTV quality video down-link to ground-based controllers supports rapid target detection and identification. The Sniper can also provide high-resolution imagery for non-traditional Intelligence, surveillance and reconnaissance (NTISR) missions without occupying the centerline station on small fighter aircraft, and can maintain surveillance even when the aircraft maneuvers. As a result, a second, dedicated fighter aircraft isn't needed to provide protection to a dedicated ISR aircraft, which many small nations cannot afford. [ 3 ]
For ease of maintenance, Sniper's optical bed design, partitioning, and diagnostic capabilities permit two-level maintenance, eliminating costly intermediate-level support. Automated built-in testing allows maintenance personnel to isolate and replace a line replaceable unit in under 20 minutes to restore full mission-capable status.
In August 2001, the U.S. Air Force announced Lockheed Martin's Sniper as the winner of the Advanced Targeting Pod (ATP) competition. The contract provides for pods and associated equipment, spares and support of the F-16 and F-15E aircraft for the entire force, active-duty Air Force and Air National Guard. The U.S. Air Force initial seven-year contract for Sniper ATP has potential value in excess of $843 million. The Sniper ATP has delivered over 125 pods and the U.S. Air Force plans to procure at least 522 Sniper ATPs. The follow-on Advanced Targeting Pod - Sensor Enhancement (ATP-SE) contract was split between the Lockheed Martin Sniper and the LITENING .
In 2014, the USAF declared initial operational capability for the Sniper ATP-SE which included sensor and networking improvements. [ 4 ]
The Sniper is used on the U.S. Air Force B-52H Stratofortress , [ 5 ] B-1B Lancer , F-15E Strike Eagle , F-16 Fighting Falcon , and A-10 Thunderbolt II . It was also used on the British Harrier GR9 [ 6 ] and the Canadian CF-18 Hornet . [ 7 ] In 2016 Lockheed Martin announced that Kuwait would be the first country to use Sniper on the Eurofighter Typhoon. [ 8 ] A team of Lockheed Martin UK , BAE Systems and Leonardo S.p.A. (Selex S&AS at the time) has successfully demonstrated and flown a Sniper ATP on board a Tornado GR4 combat aircraft. [ 9 ]
The Sniper came under fire in 2014 in the aftermath of a deadly airstrike in Afghanistan that saw five American and one Afghan soldier killed when a B-1B bomber equipped with the pod could not detect the infrared strobe lights on the helmets of U.S. troops in a firefight, resulting in the deadliest case of friendly fire between American forces in the course of the Afghanistan War . [ 10 ]
On 27 March 2015, Lockheed Martin was awarded a sole-source contract by the US DOD worth $485 million firm fixed price with minimal cost-plus-fixed-fee, indefinite-delivery/indefinite-quantity to provide multiple Sniper advanced targeting pods to the USAF. [ 11 ]
In 2024, the Ministry of National Defense released footage confirming that the F16V fighter of the Republic of China Air Force used the pod to calibrate the J-16D and H-6K invading ADIZ. [ 12 ] | https://en.wikipedia.org/wiki/Sniper_Advanced_Targeting_Pod |
8.2.6 (May 3, 2019 ; 6 years ago ( 2019-05-03 ) [ 1 ] )
.8.2.3 (April 17, 2019 ; 6 years ago ( 2019-04-17 ) [ 2 ] ) [±]
Snow (stylized in all caps ) is an image messaging and multimedia mobile application created by Camp Mobile , a subsidiary of South Korean internet search giant Naver Corporation . [ 3 ] It features virtual stickers using augmented reality and photographic filters . Pictures and messages sent through Snow are only accessible for a short time.
Snow was launched in September 2015 by Camp Mobile. The company collaborated with different Korean artists. [ 4 ]
In 2016, the app spun off into its own company, named as Snow Corp. [ 5 ] [ 6 ]
In 2018, Snow Corp raised $50M from SoftBank and Sequoia China . It is reported that it plans to use the investment to develop its augmented reality and facial recognition technologies. [ 7 ]
Snow allows users to take pictures or videos (of a maximum duration of 5 minutes) and choose from 1,300 stickers and 50 filters. They can also send them as messages that destroy themselves in 48 hours. Videos could also be saved as GIF files. According to Business Insider , the app functions as a clone of Snapchat . [ 8 ]
This mobile software article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Snow_(app) |
Snow algae are a group of freshwater micro-algae that grow in the alpine and polar regions of the Earth. [ 1 ] Snow algae have been found on every continent but are restricted to areas with temperatures between 0°C-10°C. [ 2 ] Snow algae are pigmented by chlorophyll and carotenoids and can be a variety of colors depending on the individual species, life stage, and topography/geography. [ 3 ] [ 4 ] The pigmentation of snow algae reduces snow and ice albedo , which can stimulate the melting of perennial snow and ice and exacerbate the effects of climate change . [ 5 ] Snow algae are primary producers that form the basis of communities on snow or ice sheets that include microbes, tardigrades , and rotifers . [ 6 ] [ 7 ] Snow algae have also been carried great distances by winds. [ 8 ]
Snow algae produce two main classes of pigment molecules: chlorophylls and carotenoids. [ 9 ] Carotenoids further split into two groups known as primary and secondary carotenoids and typically help give the snow algae cells their visible colors. Primary carotenoids, such as the yellow xanthophyll , are typically used in low concentrations for photosynthesis while still offering some UV protection. [ 10 ] Secondary carotenoids, such as the red astaxanthin , are used for UV protection by the cell and can be found in high or low concentrations depending on the strength of the UV light. [ 11 ]
Different taxa of snow algae produce differing amounts of primary and secondary carotenoids, meaning the color of a snow algae bloom can give some indication of the composition of algae found there. The alga Chlamydomonas nivalis is a very abundant component of red blooms due to its high concentrations of astaxanthin and its derivatives. [ 12 ] Many Chloromonas species are associated with green or orange-yellow snow due to the primary carotenoids they produce. [ 13 ] Similar colors of snow can also vary in composition by region, showing large scale biogeographical trends in the snow algae distribution. [ 14 ]
The algae's life stage may also play a large role in the color of the snow. Many blooms are higher in chlorophylls and primary carotenoids during early stages of the bloom, causing the snow to appear green or yellow. [ 15 ] Later in the summer, the bloom may switch to orange or red due high production of astaxanthin during low nutrient periods and the snow algae’s more stable cyst stage that they use to over-winter. [ 16 ]
Snow algae undergo oxygenic photosynthesis and are primary producers on the snow. This allows other organisms to live on the snow along with the algae and feed on them to obtain energy. Tardigrades and rotifers have been shown to grow preferentially on green blooms but have been found on many different snow algae blooms across the globe. [ 6 ]
Although the trophic webs of snow algae blooms are not generally complex, the microbial communities found in these blooms can play major roles in how nutrients are distributed in the environments they inhabit. These microbial and algal communities cycle globally significant amounts of carbon, nitrogen, iron, and sulfur. [ 7 ]
The pigmentation of snow algae can significantly reduce snow albedo , stimulating the melting of ice and snow on ice sheets. [ 5 ] Larger snow grains allow light to penetrate further into the snow layer which increases light absorbance by snow algae and further reduces the albedo of the snow. [ 5 ] Snow algae drive greater changes in snow albedo later in the summer when algae are more abundant. [ 18 ] The different abundances of pigments present in snow algae, including chlorophyll and carotenoids, lead to differences in light absorption and therefore albedo changes based on algal community composition. [ 19 ] The presence of mineral and organic particle impurities on snow also reduces the albedo of snow, which can sometimes overshadow the effects of snow algal community dynamics on the albedo. [ 19 ] Under warmer conditions snow algae experience more growth, which can further reduce the albedo of snow and ice sheets. This positive feedback loop, similar to the ice-albedo feedback , can exacerbate the melting of perennial snow and ice by climate change. [ 5 ]
This alga -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Snow_algae |
Snow bleaching is a technique used in traditional Japanese textile industry to bleach the fabric using the ozone evaporating from snow. [ 1 ] This technique is used to bleach Echigo-jofu , a type of kimono. This method is based on the fact that ozone is released when snow evaporates due to sunlight. [ 2 ] [ 3 ]
This chemistry -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Snow_bleaching |
Snow hydrology is a scientific study in the field of hydrology which focuses on the composition, dispersion, and movement of snow and ice . Studies of snow hydrology predate the Anno Domini era, although major breakthroughs were not made until the mid eighteenth century.
Snowfall, accumulation and melt are important hydrological processes in watersheds at high altitudes or latitudes. In many western states in the United States, snow melt accounts for a large percentage of the spring runoff that serves as water supply to reservoirs , urban populations and agricultural activities . [ 1 ]
A large portion of snow hydrology groups are pursuing new methods for incorporating snow hydrology into distributed models over complex terrain through theoretical developments, model development and testing with field and remote sensing data sets. Snow hydrology is quite complex and involves both mass and energy balance calculations over a time-varying snow pack which is influenced by spatial location in the watershed, interaction with vegetation and redistribution by winds . Some researchers seek to accurately capture snow dynamics at a point and over a domain as the spatial pattern of snow cover area is readily observable from remote sensing. [ 2 ]
Snow and ice accounts for around 75% of Earth 's entire freshwater volume but lacks the capability of reliable applications. In comparison, the water supplied from rivers and freshwater lakes carries a consistent annual source of water. These natural bodies of water are formed through springs , rainfall and mountainous snow runoff . According to estimates, snow represents about 5% of the precipitation that reaches the Earth's surface. [ 3 ] Due to the large amount of water held within these sources, snow hydrology has been a growing study in the field of river tides and seasonal flow rates .
Despite common belief, snow fall is not the main cause for the destruction of organic matter in cold climates. The most damaging aspect is cold temperature winds that exist above the snow pack surface. Studies have shown the insulating properties of snow defend the plants and small animals in the environment from these frigid winds. “The snow itself is the habitat for various micro-organisms like snow worms and algae.” [ 4 ] Without consistent annual snowfall, many plants would be destroyed due to frost damage. Both ice worms ( Mesenchytraeus Solifugus ) and green algae are unique organisms that can live in glacial and snowy habitats.
Though most of the knowledge in the field of snow hydrology has been discovered in the last two centuries, there is evidence that some understanding existed as early as 500-428BC in the Greek states.
Some of the earliest evidence that supports an ancient technical understanding of snow movement was produced by the Greeks . Anaxagoras, an ancient Greek notes:
The upper class Greeks in these city states were shown to have basic understanding of the cooling properties that snow exhibited. Upper class citizens would have hay lined pits dug beneath their homes and bring snow down from the mountains to fill them. Perishable food items could then be stored in these pits for months at a time.
The Christian Bible contains numerous passages in its text that express a basic understanding of the hydrological cycle. Each of the following verses shows fundamental ideas behind the hydrological processes. [ 6 ]
One of the earliest modern records of the snow hydrology practice, was introduced by the geologist, Antonio Vallisnieri around the time of the 17th century. His work Theorized, “That rivers arising from springs in the Italian Alps came from rain and snowmelt seeping into underground channels." [ 5 ]
The first American research labs were introduced during the 1940s in order to solve the many problems associated with snow movement in the World War II era. These three labs were: [ 7 ]
Currently there are hundreds of snow hydrology labs and sensing devices placed throughout the world. As of 2004, every continent was under observation with the exception of Antarctica . Since then, several sensing devices have been established in the Arctic Circle , allowing for constant observation. [ 8 ] Using these in part with satellite imaging systems has produced an accurate depiction of underlying landmass, which was unknown in the past.
Snow hydrologists focus specifically on movement and composition of snow and ice, within the field of hydrology . The knowledge gained from this career is most commonly used in weather forecasting and ecological/ agricultural jobs, which require knowledge about the effects of snow migration. They retrieve the information they need through depth, density, and composition readings, as well as various remote sensing techniques. Workers in this field can work for government agencies, research firms and public information services.
The study of snow and glacial movement, though now largely dependent on remote sensing devices, still requires in field techniques to accurately determine the validity of the data. These tools and techniques range from simple, such as a depth spike, to complex, such as the core sampling machines used to check for variations in ice composition. Three common types of terrestrial measurements are: [ 9 ]
Remote sensing technology is a recent tool in the field of snow hydrology that was developed in response to a growing outlook in the parametric studies (study of a subject over time) of hydrology formed in the mid 19th century. Compared to the deterministic (concept that there are no random events) approach used in earlier years, this technique created minimal human interaction with the environment and in field equipment. Currently there are thousands of sensing sites around the globe. Each site is capable of receiving data from any number of remote sensing techniques.
The Landsat-MSS is one of the most common used tools. It is capable of detecting and categorizing snow cover into three zones for data calculations. The first zone is an area with 100% snow cover. The second zone is known as the transition zone, which is a mixture of snow covered regions and non snow covered regions. This zone is commonly measured at a 50% snow composition value. The Final zone is snow-free (=aper). The combined reading of these three measurements creates a relatively accurate estimate for the amount of snow within the scanned region. Several detrimental variables for this technique are cloud cover, extreme sunlight and heavy vegetation. [ 10 ]
As of 2004, every continent, with the exception of Antarctica has been under regular surveillance through the use of remote sensing satellites.
Several sensing tools are listed below: [ 11 ]
Meteorology is the scientific study of weather. It is used in weather forecasting to predict atmospheric events prior to their occurrence. Snow hydrology is used to estimate the characteristics of snowfall in different topographical regions. This includes information on snow depth, density, composition and possible runoff patterns. It is also widely used in the study of natural phenomena such as: blizzards , avalanche , ice pellets and hail in order to help foresee natural disasters. [ 12 ]
Glaciology is a similar study to snow hydrology that focuses specially on glacier movement. Glaciers are large masses of ice that are able to slowly migrate over time, through the process of snow accumulation. This study analyzes their past and current growth as well as composition to predict how they have shaped the landmasses they inhabit. Two major studies related to Glaciology are global warming and glacial maximum's ( ice ages ).
In recent years the most predominant topic related to snow hydrology has been global warming . The underlying concept states that human construction and production of emissions , has created a number of gaseous chemical compounds which add to existing greenhouse gases . Gases such as CO 2 and CH 4 trap heat in the atmosphere, adding to global climate change. These gases are usually broken down relatively quickly through environmental processes like photosynthesis ; however, in recent years, studies have shown their atmospheric composition is increasing. [ 13 ] Some studies believe this is a natural part of the Earth's cycle while others claim it is due to the growing amount of fossil fuel emissions and the gradual deforestation of oxygen producing plants. The theory suggests that these changes in temperature, could affect the way ice and snow forms over the Earth's crust, initiating a glacial shifting process, possibly created a rise in sea level from 0.5 meters to 1.5 meters. This change then could influence the salinity of the ocean, causing environmental changes, altering oceanic current and organisms that inhabit it. [ 14 ] | https://en.wikipedia.org/wiki/Snow_hydrology |
Snow pushers (also known as box plows, containment plows, or box style plows) are designed to move snow by pushing it straight ahead. They do this by being constructed with a curved moldboard that lies perpendicular to the direction of travel and a sidewall at either end that keeps the snow contained. For parking lots, runways, laneways, etc. this is an improvement on the traditional windrow plowing, which uses an angled plow to move snow to the side. Snow pushers allow the snow to be moved en masse and completely off site to be piled someplace out of the way.
Although snow pushers did not become widely used until the 1980s, they have been around since the 1970s. Initially, they were not produced by manufacturers, but they were recognized as a good idea by snow removal professionals who either welded their own or contracted to have them fabricated. For a long time, the most common snow pusher design was to take a septic tank or other large steel cylinder and cut it in half, then build a mounting system on the back to attach it to a machine. This type of bare bones construction lasted until the 1990s when various manufacturers began producing them commercially.
Snow pusher designs vary across the industry. They are typically between 3 ft [0.9 m] and 5.5 ft [1.6 m] high and range from 6 ft [1.8 m] to 40 ft [12.2 m] wide. Snow pushers are typically mounted on wheel loaders , skid steers , or backhoes . For wheel loaders and backhoes, they are mounted using a universal mounting system that consists of a set of posts (or plates) between which the machine bucket is placed. Chains are attached to the snow pusher and the bucket and tightened using a chain binder. This system allows for snow pushers to be mounted on any machine without regard for brand-specific mounting brackets. Skid steer loaders can use the universal mounting system; [ 1 ] however, most manufacturers typically offer skid steer snow pushers with a universally accepted quick-attach system. Though the snow pusher might seem like a simple product, there are many variations across the industry in areas such as moldboard height and angle, sidewall support system (post, wedge, or unsupported), trip edge system, shoe thickness, and rubber cutting edge quality, to name a few.
Snow pushers can be divided into two separate families: steel trip edge and fixed rubber edge. Both are used in the same fashion to move snow. Rubber edge snow pushers have a composite material mounted on the bottom of the moldboard which lies flush to the ground and keeps snow from passing under the pusher, getting a cleaner push than otherwise. Rubber edges are able to flex and pass over obstructions under most conditions.
Steel trip edge snow pushers have a spring-loaded steel cutting edge mounted to the bottom of the moldboard that allow them to scrape the pavement. They employ a tripping system to allow them to pass over obstructions such as uneven pavement or raised manhole covers . There are three types of trip edges in use today: compression spring, torsion spring, and composite material springs. Both compression and torsion spring systems work similarly; the steel edge is mounted on a hinge and is held in place by the pressure of the springs; when the edge meets an obstruction the springs compress and allow the edge to flip back and under the pusher and to pass over the obstruction. Composite material trip edges can act like a rubber band when the edge meets an obstruction allowing the steel edge to flip under the pusher and then snap back into place.
During certain conditions where snow may tend to freeze to the ground, a steel edge may tend to clean better than rubber; however, during wet snowfalls a rubber edge will "squeegee" the pavement, leaving it much cleaner than a steel edge can. Also, rubber edges generally contour the ground much more effectively than steel because they flex over humps and into dips. One advantage of steel edges is the reduced drag they create. Rubber edges tend to act like a brake, taking much more power to push than a steel edge when scraping down to bare pavement. Both edges have their advantages and disadvantages, and while some companies have found ways to better contour pavement with a steel edge, their moving components may make them more fragile than continuously welded plows with rubber edges. | https://en.wikipedia.org/wiki/Snow_pusher |
Snow science addresses how snow forms, its distribution, and processes affecting how snowpacks change over time. Scientists improve storm forecasting, study global snow cover and its effect on climate, glaciers, and water supplies around the world. The study includes physical properties of the material as it changes, bulk properties of in-place snow packs, and the aggregate properties of regions with snow cover. In doing so, they employ on-the-ground physical measurement techniques to establish ground truth and remote sensing techniques to develop understanding of snow-related processes over large areas. [ 1 ]
Snow was described in China, as early as 135 BCE in Han Ying's book Disconnection , which contrasted the pentagonal symmetry of flowers with the hexagonal symmetry of snow. [ 3 ] Albertus Magnus proved what may be the earliest detailed European description of snow in 1250. Johannes Kepler attempted to explain why snow crystals are hexagonal in his 1611 book, Strena seu De Nive Sexangula . [ 4 ] In 1675 Friedrich Martens , a German physician, catalogued 24 types of snow crystal. In 1865, Frances E. Chickering published Cloud Crystals - a Snow-Flake Album . [ 5 ] [ 6 ] In 1894, A. A. Sigson photographed snowflakes under a microscope, preceding Wilson Bentley 's series of photographs of individual snowflakes in the Monthly Weather Review .
Ukichiro Nakaya began an extensive study on snowflakes in 1932. From 1936 to 1949, Nakaya created the first artificial snow crystals and charted the relationship between temperature and water vapor saturation , later called the Nakaya Diagram and other works of research in snow, which were published in 1954 by Harvard University Press publishes as Snow Crystals: Natural and Artificial . Teisaku Kobayashi, verified and improves the Nakaya Diagram with the 1960 Kobayashi Diagram , later refined in 1962. [ 7 ] [ 8 ]
Further interest in artificial snowflake genesis continued in 1982 with Toshio Kuroda and Rolf Lacmann, of the Braunschweig University of Technology , publishing Growth Kinetics of Ice from the Vapour Phase and its Growth Forms . [ 9 ] In August 1983, Astronauts synthesized snow crystals in orbit on the Space Shuttle Challenger during mission STS-8 . [ 10 ] By 1988 Norihiko Fukuta et al. confirmed the Nakaya Diagram with artificial snow crystals, made in an updraft [ 11 ] [ 12 ] [ 13 ] and Yoshinori Furukawa demonstrated snow crystal growth in space . [ 14 ]
Snow scientists typically excavate a snow pit within which to make basic measurements and observations. Observations can describe features caused by wind, water percolation, or snow unloading from trees. Water percolation into a snowpack can create flow fingers and ponding or flow along capillary barriers, which can refreeze into horizontal and vertical solid ice formations within the snowpack. Among the measurements of the properties of snowpacks (together with their codes) that the International Classification for Seasonal Snow on the Ground presents are: [ 15 ]
Depth – Depth of snow is measured with a snowboard (typically a piece of plywood painted white) observed during a six-hour period. At the end of the six-hour period, all snow is cleared from the measuring surface. For a daily total snowfall, four six-hour snowfall measurements are summed. Snowfall can be very difficult to measure due to melting, compacting, blowing and drifting. [ 16 ]
Liquid equivalent by snow gauge – The liquid equivalent of snowfall may be evaluated using a snow gauge [ 17 ] or with a standard rain gauge having a diameter of 100 mm (4 in; plastic) or 200 mm (8 in; metal). [ 18 ] Rain gauges are adjusted to winter by removing the funnel and inner cylinder and allowing the snow/freezing rain to collect inside the outer cylinder. Antifreeze liquid may be added to melt the snow or ice that falls into the gauge. [ 19 ] In both types of gauges once the snowfall/ice is finished accumulating, or as its height in the gauge approaches 300 mm (12 in), the snow is melted and the water amount recorded. [ 20 ]
The International Classification for Seasonal Snow on the Ground has a more extensive classification of deposited snow than those that pertain to airborne snow. A list of the main categories (quoted together with their codes) comprises: [ 15 ]
The classification of frozen particulates extends the prior classifications of Nakaya and his successors and are quoted in the following table: [ 15 ]
at −8 °C and below–30 °C
at super-saturation at −3 to −5 °C below −60 °C
at 0 to −3 °C and −8 to −70 °C
at supersaturation at 0 to −3 °C and at −12 to −16 °C
environmental conditions
hexagonal or irregular in shape
accretion of supercooled water droplets
or milky glazed surface
supercooled water, size: >5 mm
mostly small spheroids
Graupel or snow pellets encased in thin ice layer (small hail). Size: both 5 mm
needles pointing into the wind
Thin breakable crust forms on snow surface if process continues long enough.
All are formed in cloud, except for rime, which forms on objects exposed to supercooled moisture, and some plate, dendrites and stellars, which can form in a temperature inversion under clear sky.
Each such layer of a snowpack differs from the adjacent layers by one or more characteristics that describe its microstructure or density, which together define the snow type, and other physical properties. Thus, at any one time, the type and state of the snow forming a layer have to be defined because its physical and mechanical properties depend on them. The International Classification for Seasonal Snow on the Ground lays out the following measurements of snow properties (together with their codes): [ 15 ]
Remote sensing of snowpacks with satellites and other platforms typically includes multi-spectral collection of imagery. Sophisticated interpretation of the data obtained allows inferences about what is observed. The science behind these remote observations has been verified with ground-truth studies of the actual conditions. [ 21 ]
Satellite observations record a decrease in snow-covered areas since the 1960s, when satellite observations began. In some regions such as China, a trend of increasing snow cover has been observed (from 1978 to 2006). These changes are attributed to global climate change, which may lead to earlier melting and less aea coverage. However, in some areas there may be an increase in snow depth because of higher temperatures for latitudes north of 40°. For the Northern Hemisphere as a whole the mean monthly snow-cover extent has been decreasing by 1.3% per decade. [ 22 ]
Satellite observation of snow relies on the usefulness of the physical and spectral properties of snow for analysing remotely sensed data. Dietz, et al. summarize this, as follows: [ 22 ]
The most frequently used methods to map and measure snow extent, snow depth and snow water equivalent employ multiple inputs on the visible–infrared spectrum to deduce the presence and properties of snow. The National Snow and Ice Data Center (NSIDC) uses the reflectance of visible and infrared radiation to calculate a normalized difference snow index, which is a ratio of radiation parameters that can distinguish between clouds and snow. Other researchers have developed decision trees, employing the available data to make more accurate assessments. One challenge to this assessment is where snow cover is patchy, for example during periods of accumulation or ablation and also in forested areas. Cloud cover inhibits optical sensing of surface reflectance, which has led to other methods for estimating ground conditions underneath clouds. For hydrological models, it is important to have continuous information about the snow cover. Applicable techniques involve interpolation, using the known to infer the unknown. Passive microwaves sensors are especially valuable for temporal and spatial continuity because they can map the surface beneath clouds and in darkness. When combined with reflective measurements, passive microwave sensing greatly extends the inferences possible about the snowpack. [ 22 ]
Snow science often leads to predictive models that include snow deposition, snow melt, and snow hydrology—elements of the Earth's water cycle —which help describe global climate change . [ 21 ]
Global climate change models (GCMs) incorporate snow as a factor in their calculations. Some important aspects of snow cover include its albedo (reflectivity of light) and insulating qualities, which slow the rate of seasonal melting of sea ice. As of 2011, the melt phase of GCM snow models were thought to perform poorly in regions with complex factors that regulate snowmelt, such as vegetation cover and terrain. These models compute snow water equivalent (SWE) in some manner, such as: [ 21 ]
SWE = [ –ln( 1 – f c )] / D
where:
Given the importance of snowmelt to agriculture, hydrological runoff models that include snow in their predictions address the phases of accumulating snowpack, melting processes, and distribution of the meltwater through stream networks and into the groundwater. Key to describing the melting processes are solar heat flux, ambient temperature, wind, and precipitation. Initial snowmelt models used a degree-day approach that emphasized the temperature difference between the air and the snowpack to compute snow water equivalent (SWE) as: [ 21 ]
SWE = M ( T a – T m ) when T a ≥ T m
where:
More recent models use an energy balance approach that take into account the following factors to compute the energy available for melt ( Q m ) as: [ 21 ]
Q m = Q * + Q h + Q e + Q g + Q r – Q Θ
where:
Calculation of the various heat flow quantities ( Q ) requires measurement of a much greater range of snow and environmental factors than just temperatures. [ 21 ]
Knowledge gained from science translates into engineering. Four examples are the construction and maintenance of facilities on polar ice caps, the establishment of snow runways, the design of snow tires and ski sliding surfaces . | https://en.wikipedia.org/wiki/Snow_science |
The Snowmass Process is a particle physics community planning exercise sponsored by the Division of Particles and Fields of the American Physical Society . [ 1 ] During this process, scientists develop a collective vision for the next seven to ten years for particle physics research in the US. [ 2 ]
Original planning meetings were held beginning in 1982 in Snowmass, Colorado , [ 3 ] [ 4 ] but that has not been the location since 2005. [ 5 ] [ 6 ] More recent locations of the Snowmass Process include the University of Minnesota (2013) [ 7 ] and the University of Washington (2021), which was delayed until July 2022, due to COVID . [ 8 ]
The modern Snowmass Process consists of a series of small meetings, which culminate in a community-wide meeting. The Snowmass Process solicits reports on progress and plans within "frontiers". Snowmass 2021 identified ten frontiers: "energy; neutrino physics; rare processes and precision measurements; cosmic; theory; accelerator; instrumentation; computation; underground facilities; and community engagement". [ 8 ]
Members of the particle physics community submit Letters of interest [ 9 ] and provide input to contributed whitepapers . [ 8 ] The frontiers use these whitepapers to provide web-based reports based on the material that they receive. The final output of the Snowmass Process is a Snowmass Summary for the Public, a Snowmass Summary Report, and the Snowmass Book. [ 10 ]
The Snowmass Process outcomes of 2013 were used to inform the decisions of the 2014 Particle Physics Project Prioritization Panel . [ 11 ] A newsworthy outcome of the 2021 Snowmass Process was the announcement that the Deep Underground Neutrino Experiment would be pursued in two distinct phases. [ 12 ] [ 13 ]
The outcomes of the Snowmass 2021 process, which extended into 2022, were determined at a final meeting held in July 2022 in Seattle, Washington that had 743 in-person attendees and 654 virtual participants. [ 14 ] Snowmass outcomes were covered in detailed articles by the scientific press. [ 15 ] [ 16 ] The title of the Scientific American article, "Physicists Struggle to Unite Around Future Plans", summed up the problem of convergence of opinion. [ 16 ] The articles report that two major problems stymied the field: lack of observation of new particles and rocketing costs of ongoing projects.
No unexpected particles were observed in the first 15 years of data-taking at the Large Hadron Collider (LHC), the highest energy accelerator on Earth—a disappointment stated by many physicists throughout the Snowmass process, [ 16 ] and reflecting a view that has also been expressed outside of the Snowmass meetings. [ 17 ] Although LHC will continue to run with modest upgrades, this lack of discovery leaves no clear focus for the next decade of high energy searches, and may also point to a "nightmare-scenario" where the Standard Model that forms the present basis of particle physics is complete up to the Planck scale (an energy level far beyond the ability of any conceivable experiment to probe) and particle physics "wheeze[s] to its end". [ 17 ]
However the 2012 the discovery of an expected particle, the Higgs Boson, has given the field hope of finding new physics through precision searches for unexpected Higgs interactions. As a result, during the Snowmass process, physicists argued for precision measurements at a Higgs factory constructed of an electron-positron collider. [ 15 ] [ 16 ] Many Higgs factories are proposed for outside of the US, including at the European center for particle physics, CERN , as well as in China, and so "a surprise at Snowmass 'was the grassroots support for a collider on US soil'" [ 15 ] that grew out of a new US-developed technology called the "cool copper collider". [ 18 ] An alternative if the world-wide competition for an electron-positron machine is too stiff would be to invest in a Muon collider that could act as a Higgs factory with an approach that is unique worldwide. Muon colliders were discussed at the 2013 Snowmass, but shelved due to insufficiently advanced technology. However, at the 2022 final Snowmass meeting there was an "enthusiastic revival" of the concept. [ 15 ]
The possibility of establishing any major new project in the US in the 2023-2033 decade, including a Higgs Factory, is limited due to the rising costs and multi-year delays of existing projects. In particular, at Snowmass, physicists expressed deep concern about the Deep Underground Neutrino Experiment (DUNE) project, which has risen from a base cost of $1.3B in 2015 to $3.1B for a de-scoped instrument. [ 15 ] Cost over-runs and delays of DUNE are problematic due to stiff competition from a similar experiment in Japan, [ 15 ] [ 16 ] leaving physicists to question the value of DUNE results when they are obtained. Worries were expressed by physicists that issues with DUNE were "smoothed over, not smoothed out". [ 15 ] Some physicists at Snowmass suggested that the DUNE project might be cancelled, comparing the ominous cost-growth to the Superconducting Super Collider (SSC) that was cancelled when the cost tripled. [ 16 ]
The whitepapers from the Snowmass process provide input to the 2023 P5 study. The 2023 P5 committee was announced in December 2022. [ 19 ] | https://en.wikipedia.org/wiki/Snowmass_Process |
In hydrology , snowmelt is surface runoff produced from melting snow . It can also be used to describe the period or season during which such runoff is produced. Water produced by snowmelt is an important part of the annual water cycle in many parts of the world, in some cases contributing high fractions of the annual runoff in a watershed. Predicting snowmelt runoff from a drainage basin may be a part of designing water control projects. Rapid snowmelt can cause flooding . If the snowmelt is then frozen, very dangerous conditions and accidents can occur, introducing the need for salt to melt the ice .
There are several energy fluxes involved in the melting of snow. [ 2 ] These fluxes can act in opposing directions, that is either delivering heat to or removing heat from the snowpack . Ground heat flux is the energy delivered to the snowpack from the soil below by conduction . Radiation inputs to the snowpack include net shortwave (solar radiation including visible and ultraviolet light) and longwave ( infrared ) radiation. Net shortwave radiation is the difference in energy received from the sun and that reflected by the snowpack because of the snowpack albedo . Longwave radiation is received by the snowpack from many sources, including ozone, carbon dioxide, and water vapor present in all levels of the atmosphere. Longwave radiation is also emitted by the snowpack in the form near– black-body radiation , where snow has an emissivity between 0.97 and 1.0. [ 3 ] Generally the net longwave radiation term is negative, meaning a net loss of energy from the snowpack. Latent temperature flux is the energy removed from or delivered to the snowpack which accompanies the mass transfers of evaporation , sublimation , or condensation . Sensible heat flux is the heat flux due to convection between the air and snowpack.
Tree trunks absorbing sunlight become warmer than the air and cause earlier melting of snow around them. The snow does not melt slower gradually with distance from the trunk, but rather creates a wall surrounding snow-free ground around it. According to some of sources, North American spring ephermal plants like spring beauty ( Claytonia caroliniana ), trout lily ( Erythronium americanum ) and red trillium ( Trillium erectum L.) benefit from such thaw circles. They can emerge earlier inside these circles, what gives them more time before development of tree canopy foliage cutting off significant portion of the light. They perform nearly all of their yearly photosynthesis during this period. [ 4 ]
Evergreen trees tend to produce larger thaw circles than deciduous trees. This involves largely a different mechanism and spring ephemeral plants don't occur there. [ 4 ]
The snow melts earlier in forest also for example on microtopographic mounds (small elevations) or in wet places like edges of creeks or in seeps . These microsites affect distribution of many herbs too. [ 4 ]
In northern Alaska, the melt-date has advanced by 8 days since the mid-1960s. Decreased snowfall in winter followed by warmer spring conditions seems to be the cause for the advance. [ 5 ] In Europe, the 2012 heat wave has especially been anomalous at higher altitudes. For the first time on record, some of the highest Alpine peaks in Europe were snow-free. Although it would seem that the two were related, the question of how much of this is due to climate change firmly remains a center of debate. [ 6 ]
Increased water runoff due to snowmelt was a cause of many famous floods. One well-known example is the Red River Flood of 1997, when the Red River of the North in the Red River Valley of the United States and Canada flooded. Flooding in the Red River Valley is augmented by the fact that the river flows north through Winnipeg, Manitoba and into Lake Winnipeg . As snow in Minnesota , North Dakota , and South Dakota begins to melt and flow into the Red River, the presence of downstream ice can act as a dam and force upstream water to rise. Colder temperatures downstream can also potentially lead to freezing of water as it flows north, thus augmenting the ice dam problem. Some areas in British Columbia are also prone to snowmelt flooding as well. [ 7 ]
The date of annual melt is of great interest as a potential indicator of climate change. In order to determine whether the earlier disappearance of spring snow cover in northern Alaska is related to global warming versus an appearance of a more natural, continual cycle of the climate, further study and monitoring is necessary. [ 8 ]
Large year-to-year variability complicates the picture and furthers the debate. Inter-annual variability of springtime snow pack comes largely from variability of winter month precipitation which is in turn related to the variability of key patterns of atmospheric circulation.
A study of the mountains in the western United States show a region wide decline in spring snow-pack since the mid-1900s, dominated by loss at low elevations where winter temperatures are near freezing. These losses are an indication of increased temperatures which lead to snow loss via some combination of increased regularity of rain versus snow and increased melting during winter months. These natural variations make it challenging to quantify trends with confidence, to deduce observed changes to predict future climate, or to clearly detect changes in snow-pack due to human impact on warming trends. [ 9 ] | https://en.wikipedia.org/wiki/Snowmelt |
A SNPSTR is a compound genetic marker composed of one or more SNPs and one microsatellite (STR). Autosomal SNPSTRs, which contain an SNP and a microsatellite within 500 base pairs of one another, were discovered in 2002. [ 1 ] More recently a database that contains all SNPSTRs in five model genomes, including human, has been created. [ 2 ]
There has been widespread and growing interest in genetic markers suitable for drawing population genetic inferences about past demographic events and to detect the effects of selection. Single nucleotide polymorphisms ( SNPs ) and microsatellites (or short tandem repeats, STRs) have received great attention in the analysis of human population history, even though they have both disadvantages. It was thus suggested that the combination of these two markers could give rise to better conclusions. | https://en.wikipedia.org/wiki/Snpstr |
In geometry , a snub is an operation applied to a polyhedron . The term originates from Kepler 's names of two Archimedean solids , for the snub cube ( cubus simus ) and snub dodecahedron ( dodecaedron simum ). [ 1 ]
In general, snubs have chiral symmetry with two forms: with clockwise or counterclockwise orientation. By Kepler's names, a snub can be seen as an expansion of a regular polyhedron : moving the faces apart, twisting them about their centers, adding new polygons centered on the original vertices, and adding pairs of triangles fitting between the original edges.
The terminology was generalized by Coxeter , with a slightly different definition, for a wider set of uniform polytopes .
John Conway explored generalized polyhedron operators, defining what is now called Conway polyhedron notation , which can be applied to polyhedra and tilings. Conway calls Coxeter's operation a semi-snub . [ 2 ]
In this notation, snub is defined by the dual and gyro operators, as s = dg , and it is equivalent to an alternation of a truncation of an ambo operator. Conway's notation itself avoids Coxeter's alternation (half) operation since it only applies for polyhedra with even-sided faces.
In 4-dimensions, Conway suggests the snub 24-cell should be called a semi-snub 24-cell because, unlike 3-dimensional snub polyhedra are alternated omnitruncated forms, it is not an alternated omnitruncated 24-cell . It is instead actually an alternated truncated 24-cell . [ 3 ]
Coxeter 's snub terminology is slightly different, meaning an alternated truncation , deriving the snub cube as a snub cuboctahedron , and the snub dodecahedron as a snub icosidodecahedron . This definition is used in the naming of two Johnson solids : the snub disphenoid and the snub square antiprism , and of higher dimensional polytopes, such as the 4-dimensional snub 24-cell , with extended Schläfli symbol s{3,4,3}, and Coxeter diagram .
A regular polyhedron (or tiling), with Schläfli symbol { p , q } {\displaystyle {\begin{Bmatrix}p,q\end{Bmatrix}}} , and Coxeter diagram , has truncation defined as t { p , q } {\displaystyle t{\begin{Bmatrix}p,q\end{Bmatrix}}} , and , and has snub defined as an alternated truncation h t { p , q } = s { p , q } {\displaystyle ht{\begin{Bmatrix}p,q\end{Bmatrix}}=s{\begin{Bmatrix}p,q\end{Bmatrix}}} , and . This alternated construction requires q to be even.
A quasiregular polyhedron , with Schläfli symbol { p q } {\displaystyle {\begin{Bmatrix}p\\q\end{Bmatrix}}} or r { p , q }, and Coxeter diagram or , has quasiregular truncation defined as t { p q } {\displaystyle t{\begin{Bmatrix}p\\q\end{Bmatrix}}} or tr { p , q }, and or , and has quasiregular snub defined as an alternated truncated rectification h t { p q } = s { p q } {\displaystyle ht{\begin{Bmatrix}p\\q\end{Bmatrix}}=s{\begin{Bmatrix}p\\q\end{Bmatrix}}} or htr { p , q } = sr { p , q }, and or .
For example, Kepler's snub cube is derived from the quasiregular cuboctahedron , with a vertical Schläfli symbol { 4 3 } {\displaystyle {\begin{Bmatrix}4\\3\end{Bmatrix}}} , and Coxeter diagram , and so is more explicitly called a snub cuboctahedron , expressed by a vertical Schläfli symbol s { 4 3 } {\displaystyle s{\begin{Bmatrix}4\\3\end{Bmatrix}}} , and Coxeter diagram . The snub cuboctahedron is the alternation of the truncated cuboctahedron , t { 4 3 } {\displaystyle t{\begin{Bmatrix}4\\3\end{Bmatrix}}} , and .
Regular polyhedra with even-order vertices can also be snubbed as alternated truncations, like the snub octahedron , as s { 3 , 4 } {\displaystyle s{\begin{Bmatrix}3,4\end{Bmatrix}}} , , is the alternation of the truncated octahedron , t { 3 , 4 } {\displaystyle t{\begin{Bmatrix}3,4\end{Bmatrix}}} , and . The snub octahedron represents the pseudoicosahedron , a regular icosahedron with pyritohedral symmetry .
The snub tetratetrahedron , as s { 3 3 } {\displaystyle s{\begin{Bmatrix}3\\3\end{Bmatrix}}} , and , is the alternation of the truncated tetrahedral symmetry form, t { 3 3 } {\displaystyle t{\begin{Bmatrix}3\\3\end{Bmatrix}}} , and .
Coxeter's snub operation also allows n- antiprisms to be defined as s { 2 n } {\displaystyle s{\begin{Bmatrix}2\\n\end{Bmatrix}}} or s { 2 , 2 n } {\displaystyle s{\begin{Bmatrix}2,2n\end{Bmatrix}}} , based on n-prisms t { 2 n } {\displaystyle t{\begin{Bmatrix}2\\n\end{Bmatrix}}} or t { 2 , 2 n } {\displaystyle t{\begin{Bmatrix}2,2n\end{Bmatrix}}} , while { 2 , n } {\displaystyle {\begin{Bmatrix}2,n\end{Bmatrix}}} is a regular n- hosohedron , a degenerate polyhedron, but a valid tiling on the sphere with digon or lune -shaped faces.
The same process applies for snub tilings:
Nonuniform polyhedra with all even-valance vertices can be snubbed, including some infinite sets; for example:
Snub star-polyhedra are constructed by their Schwarz triangle (p q r), with rational ordered mirror-angles, and all mirrors active and alternated.
In general, a regular polychoron with Schläfli symbol { p , q , r } {\displaystyle {\begin{Bmatrix}p,q,r\end{Bmatrix}}} , and Coxeter diagram , has a snub with extended Schläfli symbol s { p , q , r } {\displaystyle s{\begin{Bmatrix}p,q,r\end{Bmatrix}}} , and .
A rectified polychoron { p q , r } {\displaystyle {\begin{Bmatrix}p\\q,r\end{Bmatrix}}} = r{p,q,r} , and has snub symbol s { p q , r } {\displaystyle s{\begin{Bmatrix}p\\q,r\end{Bmatrix}}} = sr{p,q,r} , and .
There is only one uniform convex snub in 4-dimensions, the snub 24-cell . The regular 24-cell has Schläfli symbol , { 3 , 4 , 3 } {\displaystyle {\begin{Bmatrix}3,4,3\end{Bmatrix}}} , and Coxeter diagram , and the snub 24-cell is represented by s { 3 , 4 , 3 } {\displaystyle s{\begin{Bmatrix}3,4,3\end{Bmatrix}}} , Coxeter diagram . It also has an index 6 lower symmetry constructions as s { 3 3 3 } {\displaystyle s\left\{{\begin{array}{l}3\\3\\3\end{array}}\right\}} or s{3 1,1,1 } and , and an index 3 subsymmetry as s { 3 3 , 4 } {\displaystyle s{\begin{Bmatrix}3\\3,4\end{Bmatrix}}} or sr{3,3,4}, and or .
The related snub 24-cell honeycomb can be seen as a s { 3 , 4 , 3 , 3 } {\displaystyle s{\begin{Bmatrix}3,4,3,3\end{Bmatrix}}} or s{3,4,3,3}, and , and lower symmetry s { 3 3 , 4 , 3 } {\displaystyle s{\begin{Bmatrix}3\\3,4,3\end{Bmatrix}}} or sr{3,3,4,3} and or , and lowest symmetry form as s { 3 3 3 3 } {\displaystyle s\left\{{\begin{array}{l}3\\3\\3\\3\end{array}}\right\}} or s{3 1,1,1,1 } and .
A Euclidean honeycomb is an alternated hexagonal slab honeycomb , s{2,6,3}, and or sr{2,3,6}, and or sr{2,3 [3] }, and .
Another Euclidean (scaliform) honeycomb is an alternated square slab honeycomb , s{2,4,4}, and or sr{2,4 1,1 } and :
The only uniform snub hyperbolic uniform honeycomb is the snub hexagonal tiling honeycomb , as s{3,6,3} and , which can also be constructed as an alternated hexagonal tiling honeycomb , h{6,3,3}, . It is also constructed as s{3 [3,3] } and .
Another hyperbolic (scaliform) honeycomb is a snub order-4 octahedral honeycomb , s{3,4,4}, and . | https://en.wikipedia.org/wiki/Snub_(geometry) |
In geometry , the order-3 snub heptagonal tiling is a semiregular tiling of the hyperbolic plane. There are four triangles and one heptagon on each vertex . It has Schläfli symbol of sr{7,3} . The snub tetraheptagonal tiling is another related hyperbolic tiling with Schläfli symbol sr{7,4} .
Drawn in chiral pairs, with edges missing between black triangles:
The dual tiling is called an order-7-3 floret pentagonal tiling , and is related to the floret pentagonal tiling .
This semiregular tiling is a member of a sequence of snubbed polyhedra and tilings with vertex figure (3.3.3.3. n ) and Coxeter–Dynkin diagram . These figures and their duals have (n32) rotational symmetry , being in the Euclidean plane for n=6, and hyperbolic plane for any higher n. The series can be considered to begin with n=2, with one set of faces degenerated into digons .
From a Wythoff construction there are eight hyperbolic uniform tilings that can be based from the regular heptagonal tiling.
Drawing the tiles colored as red on the original faces, yellow at the original vertices, and blue along the original edges, there are 8 forms.
This hyperbolic geometry -related article is a stub . You can help Wikipedia by expanding it .
This stereochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Snub_triheptagonal_tiling |
SoRI-20041 is an " antagonist -like" allosteric modulator of amphetamine -induced dopamine release [ 1 ] (in contrast to the related research chemicals SoRI-9804 and SoRI-20040 , which are " agonist -like"). [ 1 ] SoRI-20041 is believed to be the first example of a drug that separately modulates uptake versus release in the dopamine transporter (possibly showing how inward and outward transport represent distinct operational modes of DAT); it produces the same effects as SoRI-20040 and SoRI-9804 in uptake assays and binding assays, inhibiting the re-uptake of dopamine, but does not modulate d-amphetamine- induced DA release by inhibiting that as well, like 'agonists' of the series do. [ 1 ]
This suggests the possibility of simultaneous action and increase of indirect-agonism through the dual action of DRA and DRI efficacy existing together. This increases the inhibition of re-uptake at synaptic dopamine concentrations without interfering in the flow of release of dopamine from amphetaminergic phosphorylation at the affected transporter. This overcomes the obstacle of a compromised binding site that would be rendered unusable through the action of amphetamine. Conventional dopamine re-uptake inhibitors (such as cocaine or methylphenidate ) would otherwise ineffectively target such a site on each specific transporter so affected by amphetamine, making this an example of a DRI that does not have a mutually exclusive functionality against DRA action at individual instances of DAT. | https://en.wikipedia.org/wiki/SoRI-20041 |
In organic chemistry, the Soai reaction is the alkylation of pyrimidine-5-carbaldehyde with diisopropylzinc . The reaction is autocatalytic and leads to rapidly increasing amounts of the same enantiomer of the product. The product pyrimidyl alcohol is chiral and induces that same chirality in further catalytic cycles. Starting with a low enantiomeric excess ("ee") produces a product with very high enantiomeric excess. [ 1 ] The reaction has been studied for clues about the origin of homochirality among certain classes of biomolecules . [ 2 ]
The Japanese chemist Kensō Soai (1950–) discovered the reaction in 1995. [ 3 ] [ 4 ] For his work in "elucidating the origins of chirality and homochirality", Soai received the Chemical Society of Japan award in 2010. [ 5 ]
Other chiral additives can be used as the initial source of asymmetric induction , with the major product of that first reaction being rapidly amplified. For example, Soai's group has demonstrated that even chiral quaternary hydrocarbons, which have no clear Lewis basic site for binding the nucleophile, are nonetheless capable of inducing asymmetric catalysis in the reaction. [ 6 ]
The chiral induction is believed to occur as a result of interactions between the C–H bonds of the alkane and the pi electrons of the aldehyde. [ 6 ]
In another example, Soai and coworkers showed that even [ 15 N]( 2R , 3 S )-bis(dimethylamino)butane, whose chirality results solely due to the difference between 14 N and 15 N (7% isotopic mass difference), gave 45% ee when used as a stoichiometric ligand. [ 7 ] | https://en.wikipedia.org/wiki/Soai_reaction |
A soakage , or soak, is a source of water in Australian deserts .
It is called thus because the water generally seeps into the sand, and is stored below, sometimes as part of an ephemeral river or creek.
Soakages were traditionally important sources of water for Aboriginal Australians in the desert, being the most dependable source in times of drought in Australia .
Aboriginal peoples would scoop out the sand or mud using a coolamon or woomera , often to a depth of several metres, until clean water gathered in the base of the hole. Knowing the precise location of each soakage was extremely valuable knowledge. It is also sometimes called a native well .
Anthropologist Donald Thomson wrote:
For a white man the difficulty in this country is that there is no way in which he can find the wells and soaks unless he does so by chance, and certainly nothing to indicate that the well is there, nor as a rule, even when the terrain and at least its superficial geological formation, the lie of the country, is examined, is there anything to explain the presence of water when he does find it
...
A lifetime of experience, backed by the traditional knowledge that is handed down from generation to generation, enables these people [the Pintupi in this instance] to judge, without having to visit a well that they know, whether it will still contain water and whether, if dry, with the sides fallen in and the well full of debris, it is worth cleaning out. [ 1 ] : 85
Wells were covered to keep them free from fouling by animals. This involved blocking the well with dead branches and uprooted trees. When the wells fell into disrepair, people would bail the well, using the coolamon to throw slush against the wall. This would set like a cement wash and help to hold loose sand, preventing it from falling into the water.
Wells could be up to fifteen feet deep, with small toe holds cut into the walls. [ 1 ] : 23
Donald Thomson writes:
Just before we left, the old men recited to me the names of more than fifty waters – wells, rockholes and claypans ... this, in an area that the early explorers believed to be almost waterless, and where all but a few were, in 1957, still unknown to the white man. And on the eve of our going, Tjappanongo ( Tjapanangka ) produced spear-throwers , on the backs of which were designs deeply incised, more or less geometric in form. Sometimes with a stick, or with his finger, he would point to each well or rock hole in turn and recite its name, waiting for me to repeat it after him. Each time, the group of old men listened intently and grunted in approval – "Eh!" – or repeated the name again and listened once more. This process continued with the name of each water until they were satisfied with my pronunciation, when they would pass on to the next.
I realized that here was the most important discovery of the expedition – that what Tjappanongo and the old men had shown me was really a map, highly conventionalized, like the works on a " message" or "letter" stick of the Aborigines, of the waters of the vast terrain over which the Bindibu hunted. [ 2 ]
In the nineteenth century, both Warburton and Carnegie recorded that they had run down Aboriginal residents with camels and captured and chained them to compel them to reveal their secret sources of water. This action left a lasting impression on Aboriginal residents of desert regions, who would have handed accounts of this down through successive generations. [ 1 ] : 7
In the 1930s, when H. H. Finlayson made his journeys through the desert by camel, he noted that a gelded male camel, after a hard three-and-a-half-day journey in intense heat without water, drank 150 litres (33 imperial gallons) by actual measure without stopping, and fifteen minutes later, another 45 L (10 imp gal).
This sheds light on the resentment built up among the Aboriginal population against explorers for the exploitation and, by enlarging well entrances and digging out springs, the devastation of their precious water supplies to satisfy camel teams. [ 1 ] : 135
Don McLeod (Aboriginal rights activist, see Pilbara ) also tells a story of clashes over soak water at the time of the gold rushes in Western Australia:
During the time of the Laverton rush, the Blackfellows tried to keep their meager water supplies hidden from the knowledge of white prospectors since their horses and camels quickly exhausted the limited soaks.
McLeod relates a story told to him by an old prospector by the name of Long, observing an Aboriginal man and woman:
The man took the throwing stick he was carrying and worked it into the sand. He then broke off a hollow reed and, placing it in the hole he had thus developed, lay down on his stomach and appeared to suck up something through the reed. His companion repeated his movements before they quietly moved on...
Without delay Long, with the aid of a shovel, proved the existence of a soak of sweet water, from which he replenished his supplies...Only a few days later in the same place, another prospector had the same Blackfellow bailed up, threatening to shoot him unless he revealed a source of water. This was certainly not an untypical bush encounter. However, [they were] interrupted by yet another prospector riding a camel. The Blackfellow took advantage of the confusion and threw a spear into the bush and escaped.
On the diggings, a hue and cry was raised over this alleged murderous attack and a party was quickly organised to set out and teach the Blackfellows a lesson – for daring to protect their water. Mustering what guns they could, the punitive party went out to what later became known as Skull Creek, and shot every Blackfellow they could find. The bodies were buried in shallow graves. [ 3 ] | https://en.wikipedia.org/wiki/Soakage_(source_of_water) |
A soap bubble (commonly referred to as simply a bubble ) is an extremely thin film of soap or detergent and water enclosing air that forms a hollow sphere with an iridescent surface. Soap bubbles usually last for only a few seconds before bursting, either on their own or on contact with another object. They are often used for children's enjoyment, but they are also used in artistic performances . Assembling many bubbles results in foam .
When light shines onto a bubble it appears to change colour. Unlike those seen in a rainbow , which arise from differential refraction, the colours seen in a soap bubble arise from light wave interference , reflecting off the front and back surfaces of the thin soap film. Depending on the thickness of the film, different colours interfere constructively and destructively.
Soap bubbles are physical examples of the complex mathematical problem of minimal surface . They will assume the shape of least surface area possible containing a given volume. A true minimal surface is more properly illustrated by a soap film , which has equal pressure on both sides, becoming a surface with zero mean curvature . A soap bubble is a closed soap film: due to the difference in outside and inside pressure, it is a surface of constant mean curvature.
While it has been known since 1884 that a spherical soap bubble is the least-area way of enclosing a given volume of air (a theorem of H. A. Schwarz ), it was not until 2000 that it was proven that two merged soap bubbles provide the optimum way of enclosing two given volumes of air of different size with the least surface area. This has been dubbed the double bubble conjecture . [ 1 ]
Because of these qualities, soap bubble films have been used in practical problem solving applications. Structural engineer Frei Otto used soap bubble films to determine the geometry of a sheet of least surface area that spreads between several points, and translated this geometry into revolutionary tensile roof structures . [ 2 ] A famous example is his West German Pavilion at Expo 67 in Montreal.
The structures that soap films make can not just be enclosed as spheres, but virtually any shape, for example in wire frames. Therefore, many different minimal surfaces can be designed. It is actually sometimes easier to physically make them than to compute them by mathematical modelling . This is why the soap films can be considered as analog computers which can outperform conventional computers, depending on the complexity of the system. [ 3 ] [ 4 ] [ 5 ]
When two bubbles merge, they adopt a shape which makes the sum of their surface areas as small as possible, compatible with the volume of air each bubble encloses. If the bubbles are of equal size, their common wall is flat. If they are not the same size, their common wall bulges into the larger bubble, since the smaller one has a higher internal pressure than the larger one, as predicted by the Young–Laplace equation .
At a point where three or more bubbles meet, they sort themselves out so that only three bubble walls meet along a line. Since the surface tension is the same in each of the three surfaces, the three angles between them must be equal to 120°. Only four bubble walls can meet at a point, with the lines where triplets of bubble walls meet separated by cos −1 (−1/3) ≈ 109.47°. All these rules, known as Plateau's laws , determine how a foam is built from bubbles.
The longevity of a soap bubble is limited by the ease of rupture of the very thin layer of water which constitutes its surface, namely a micrometer -thick soap film .
It is thus sensitive to :
After experiments, researchers found that a solution containing:
gave the longest lasting results as it minimised the Marangoni Effect . [ 6 ]
When a soap bubble is in contact with a solid or a liquid surface wetting is observed. On a solid surface, the contact angle of the bubble depends on the surface energy of the solid. [ 7 ] [ 8 ] A soap bubble has a larger contact angle on a solid surface displaying ultrahydrophobicity than on a hydrophilic surface – see Wetting . On a liquid surface, the contact angle of the soap bubble depends on its size - smaller bubbles have lower contact angles. [ 9 ] [ 10 ]
The gas inside a bubble is less dense than air because it is mostly water vapor. Water vapor is a gas that is formed when water molecules evaporate. When water molecules evaporate, they escape from the liquid state and enter the gas state. In the gas state, water molecules are further apart than they are in the liquid state. This is because water molecules are attracted to each other. When they evaporate, they break away from these attractions and move further apart.
The further apart water molecules are, the less dense they are. This is why water vapor is less dense than air. The gas inside a bubble is mostly water vapor, so it is also less dense than air.
The density of a gas can also be affected by its temperature. As the temperature of a gas increases, the molecules of the gas move faster. This causes them to spread out and become less dense. The opposite is also true. As the temperature of a gas decreases, the molecules of the gas move slower. This causes them to bunch together and become more dense.
The temperature of the gas inside a bubble is affected by the temperature of the water around it. The warmer the water, the warmer the gas inside the bubble. This means that the gas inside a bubble will be less dense if the water is warm than if the water is cold.
Soap bubbles have been used as entertainment for at least 400 years, as evidenced by 17th-century Flemish paintings showing children blowing bubbles with clay pipes. The London-based firm A. & F. Pears created a famous advertising campaign for its soaps in 1886 using a painting by John Everett Millais of a child playing with bubbles. The Chicago company Chemtoy began selling bubble solution in the 1940s, and bubble solution has been popular with children ever since. According to one industry estimate, retailers sell around 200 million bottles annually. Dishwashing liquid with water and additional ingredients such as glycerin and sugar is used as a popular alternative to a ready made bubble solution. [ 11 ]
A bubble is made of transparent water enclosing transparent air. However, the soap film is as thin as the visible light wavelength , resulting in optical interference . This creates iridescence which, together with the bubble's spherical shape and fragility, contributes to its magical effect on children and adults alike. Each colour is the result of varying thicknesses of soap bubble film. Tom Noddy (who featured in the second episode of Marcus du Sautoy 's The Code ) gave the analogy of looking at a contour map of the bubbles' surface. However, it has become a challenge to produce artificially coloured bubbles.
Byron, Melody & Enoch Swetland invented a patented non-toxic bubble (Tekno Bubbles) [ 12 ] that glow under UV lighting. These bubbles look like ordinary high quality "clear" bubbles under normal lighting, but glow when exposed to true UV light. The brighter the UV lighting, the brighter they glow. The family sold them worldwide, but has since sold their company.
Adding coloured dye to bubble mixtures fails to produce coloured bubbles, because the dye attaches to the water molecules as opposed to the surfactant. Therefore, a colourless bubble forms with the dye falling to a point at the base. Dye chemist Dr. Ram Sabnis has developed a lactone dye that sticks to the surfactants, enabling brightly coloured bubbles to be formed. Crystal violet lactone is an example. Another man named Tim Kehoe invented a coloured bubble which loses its colour when exposed to pressure or oxygen, which he is now marketing online as Zubbles , which are non-toxic and non-staining. In 2010, Japanese astronaut Naoko Yamazaki demonstrated that it is possible to create coloured bubbles in microgravity . The reason is that the water molecules are spread evenly around the bubble in the low-gravity environment.
If soap bubbles are blown into air that is below a temperature of −15 °C (5 °F ), they will freeze when they touch a surface . The air inside will gradually diffuse out, causing the bubble to crumble under its own weight. At temperatures below about −25 °C (−13 °F), bubbles will freeze in the air and may shatter when hitting the ground. When a bubble is blown with warm air, the bubble will freeze to an almost perfect sphere at first, but when the warm air cools, and a reduction in volume occurs, there will be a partial collapse of the bubble. A bubble, created successfully at this low temperature, will always be rather small; it will freeze quickly and will shatter if increased further. [ 13 ] Freezing of small soap bubbles happens within 2 seconds after setting on snow (at air temperature around –10...–14 °C). [ 14 ]
Soap bubble performances combine entertainment with artistic achievement. They require a high degree of skill. [ citation needed ] Some performers use common commercially available bubble liquids while others compose their own solutions. Some artists create giant bubbles or tubes, often enveloping objects or even humans. Others manage to create bubbles forming cubes, tetrahedra and other shapes and forms. Bubbles are sometimes handled with bare hands. To add to the visual experience, they are sometimes filled with smoke , vapour or helium and combined with laser lights or fire. Soap bubbles can be filled with a flammable gas such as natural gas and then ignited.
Professional bubble artists include Tom Noddy , Fan Yang and The Amazing Bubble Man .
Bubbles can be effectively used to teach and explore a wide variety of concepts to even young children. Flexibility, colour formation, reflective or mirrored surfaces, concave and convex surfaces, transparency, a variety of shapes (circle, square, triangle, sphere, cube, tetrahedron, hexagon), elastic properties, and comparative sizing, as well as the more esoteric properties of bubbles listed on this page. Bubbles are useful in teaching concepts starting from 2 years old and into college years. A Swiss university professor, Dr. Natalie Hartzell, has theorized that the usage of artificial bubbles for entertainment purposes of young children has shown a positive effect in the region of the child's brain that controls motor skills and is responsible for coordination with children exposed to bubbles at a young age showing measurably better motion skills than those who were not. [ 15 ] | https://en.wikipedia.org/wiki/Soap_bubble |
Soap scum or lime soap is the white solid composed of calcium stearate , magnesium stearate , and similar alkaline earth metal derivatives of fatty acids. These materials result from the addition of soap and other anionic surfactants to hard water . Hard water contains calcium and magnesium ions, which react with the surfactant anion to give these metallic or lime soaps. [ 1 ]
In this reaction, the sodium cation in soap is replaced by calcium to form calcium stearate .
Lime soaps build deposits on fibres, washing machines, and sinks. Synthetic surfactants are less susceptible to the effects of hard water. Most detergents contain builders that prevent the formation of lime soaps. | https://en.wikipedia.org/wiki/Soap_scum |
Sobelivirales is an order of RNA viruses which infect eukaryotes . [ 1 ] Member viruses have a positive-sense single-stranded RNA genome . The name of the group is a portmanteau of member orders " sobe movirus- li ke" and - virales which is the suffix for a virus order . [ 2 ]
The following families are recognized:
This virus -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Sobelivirales |
In mathematics , there is in mathematical analysis a class of Sobolev inequalities , relating norms including those of Sobolev spaces . These are used to prove the Sobolev embedding theorem , giving inclusions between certain Sobolev spaces , and the Rellich–Kondrachov theorem showing that under slightly stronger conditions some Sobolev spaces are compactly embedded in others. They are named after Sergei Lvovich Sobolev .
Let W k,p ( R n ) denote the Sobolev space consisting of all real-valued functions on R n whose weak derivatives up to order k are functions in L p . Here k is a non-negative integer and 1 ≤ p < ∞ . The first part of the Sobolev embedding theorem states that if k > ℓ , p < n and 1 ≤ p < q < ∞ are two real numbers such that
(given n {\displaystyle n} , p {\displaystyle p} , k {\displaystyle k} and ℓ {\displaystyle \ell } this is satisfied for some q ∈ [ 1 , ∞ ) {\displaystyle q\in [1,\infty )} provided ( k − ℓ ) p < n {\displaystyle (k-\ell )p<n} ),
then
and the embedding is continuous: for every f ∈ W k , p ( R n ) {\displaystyle f\in W^{k,p}(\mathbf {R} ^{n})} , one has f ∈ W l , q ( R n ) {\displaystyle f\in W^{l,q}(\mathbf {R} ^{n})} , and
In the special case of k = 1 and ℓ = 0 , Sobolev embedding gives
where p ∗ is the Sobolev conjugate of p , given by
and for every f ∈ W 1 , p ( R n ) {\displaystyle f\in W^{1,p}(\mathbf {R} ^{n})} , one has f ∈ L p ∗ ( R n ) {\displaystyle f\in L^{p^{*}}(\mathbf {R} ^{n})} and
This special case of the Sobolev embedding is a direct consequence of the Gagliardo–Nirenberg–Sobolev inequality . The result should be interpreted as saying that if a function f {\displaystyle f} in L p ( R n ) {\displaystyle L^{p}(\mathbf {R} ^{n})} has one derivative in L p {\displaystyle L^{p}} , then f {\displaystyle f} itself has improved local behavior, meaning that it belongs to the space L p ∗ {\displaystyle L^{p^{*}}} where p ∗ > p {\displaystyle p^{*}>p} . (Note that 1 / p ∗ < 1 / p {\displaystyle 1/p^{*}<1/p} , so that p ∗ > p {\displaystyle p^{*}>p} .) Thus, any local singularities in f {\displaystyle f} must be more mild than for a typical function in L p {\displaystyle L^{p}} .
The second part of the Sobolev embedding theorem applies to embeddings in Hölder spaces C r,α ( R n ) . If n < pk and
with α ∈ (0, 1) then one has the embedding
In other words, for every f ∈ W k , p ( R n ) {\displaystyle f\in W^{k,p}(\mathbf {R} ^{n})} and x , y ∈ R n {\displaystyle x,y\in \mathbf {R} ^{n}} , one has f ∈ C r ( R n ) {\displaystyle f\in C^{r}(\mathbf {R} ^{n})} , in addition,
This part of the Sobolev embedding is a direct consequence of Morrey's inequality . Intuitively, this inclusion expresses the fact that the existence of sufficiently many weak derivatives implies some continuity of the classical derivatives. If α = 1 {\displaystyle \alpha =1} then W k , p ( R n ) ⊂ C r , γ ( R n ) {\displaystyle W^{k,p}(\mathbf {R} ^{n})\subset C^{r,\gamma }(\mathbf {R} ^{n})} for every γ ∈ ( 0 , 1 ) {\displaystyle \gamma \in (0,1)} .
In particular, as long as p k > n {\displaystyle pk>n} , the embedding criterion will hold with r = 0 {\displaystyle r=0} and some positive value of α {\displaystyle \alpha } . That is, for a function f {\displaystyle f} on R n {\displaystyle \mathbb {R} ^{n}} , if f {\displaystyle f} has k {\displaystyle k} derivatives in L p {\displaystyle L^{p}} and p k > n {\displaystyle pk>n} , then f {\displaystyle f} will be continuous (and actually Hölder continuous with some positive exponent α {\displaystyle \alpha } ).
The Sobolev embedding theorem holds for Sobolev spaces W k,p ( M ) on other suitable domains M . In particular ( Aubin 1982 , Chapter 2; Aubin 1976 ), both parts of the Sobolev embedding hold when
If M is a bounded open set in R n with continuous boundary, then W 1,2 ( M ) is compactly embedded in L 2 ( M ) ( Nečas 2012 , Section 1.1.5, Theorem 1.4).
On a compact manifold M with C 1 boundary, the Kondrachov embedding theorem states that if k > ℓ and 1 p − k n < 1 q − ℓ n {\displaystyle {\frac {1}{p}}-{\frac {k}{n}}<{\frac {1}{q}}-{\frac {\ell }{n}}} then the Sobolev embedding
is completely continuous (compact). [ 1 ] Note that the condition is just as in the first part of the Sobolev embedding theorem, with the equality replaced by an inequality, thus requiring a more regular space W k,p ( M ) .
Assume that u is a continuously differentiable real-valued function on R n with compact support . Then for 1 ≤ p < n there is a constant C depending only on n and p such that
with 1 / p ∗ = 1 / p − 1 / n {\displaystyle 1/p^{*}=1/p-1/n} .
The case 1 < p < n {\displaystyle 1<p<n} is due to Sobolev [ 2 ] and the case p = 1 {\displaystyle p=1} to Gagliardo and Nirenberg independently. [ 3 ] [ 4 ] The Gagliardo–Nirenberg–Sobolev inequality implies directly the Sobolev embedding
The embeddings in other orders on R n are then obtained by suitable iteration.
Sobolev's original proof of the Sobolev embedding theorem relied on the following, sometimes known as the Hardy–Littlewood–Sobolev fractional integration theorem. An equivalent statement is known as the Sobolev lemma in ( Aubin 1982 , Chapter 2). A proof is in ( Stein 1970 , Chapter V, §1.3).
Let 0 < α < n and 1 < p < q < ∞ . Let I α = (−Δ) − α /2 be the Riesz potential on R n . Then, for q defined by
there exists a constant C depending only on p such that
If p = 1 , then one has two possible replacement estimates. The first is the more classical weak-type estimate:
where 1/ q = 1 − α / n . Alternatively one has the estimate ‖ I α f ‖ q ≤ C ‖ R f ‖ 1 , {\displaystyle \left\|I_{\alpha }f\right\|_{q}\leq C\|Rf\|_{1},} where R f {\displaystyle Rf} is the vector-valued Riesz transform , cf. ( Schikorra, Spector & Van Schaftingen 2017 ). The boundedness of the Riesz transforms implies that the latter inequality gives a unified way to write the family of inequalities for the Riesz potential.
The Hardy–Littlewood–Sobolev lemma implies the Sobolev embedding essentially by the relationship between the Riesz transforms and the Riesz potentials.
Assume n < p ≤ ∞ . Then there exists a constant C , depending only on p and n , such that
for all u ∈ C 1 ( R n ) ∩ L p ( R n ) , where
Thus if u ∈ W 1, p ( R n ) , then u is in fact Hölder continuous of exponent γ , after possibly being redefined on a set of measure 0.
A similar result holds in a bounded domain U with Lipschitz boundary. In this case,
where the constant C depends now on n , p and U . This version of the inequality follows from the previous one by applying the norm-preserving extension of W 1, p ( U ) to W 1, p ( R n ) . The inequality is named after Charles B. Morrey Jr.
Let U be a bounded open subset of R n , with a C 1 boundary. ( U may also be unbounded, but in this case its boundary, if it exists, must be sufficiently well-behaved.)
Assume u ∈ W k,p ( U ) . Then we consider two cases:
In this case we conclude that u ∈ L q ( U ) , where
We have in addition the estimate
the constant C depending only on k , p , n , and U .
Here, we conclude that u belongs to a Hölder space , more precisely:
where
We have in addition the estimate
the constant C depending only on k , p , n , γ , and U . In particular, the condition k > n / p {\displaystyle k>n/p} guarantees that u {\displaystyle u} is continuous (and actually Hölder continuous with some positive exponent).
If u ∈ W 1 , n ( R n ) {\displaystyle u\in W^{1,n}(\mathbf {R} ^{n})} , then u is a function of bounded mean oscillation and
for some constant C depending only on n . [ 5 ] : §I.2 This estimate is a corollary of the Poincaré inequality .
The Nash inequality, introduced by John Nash ( 1958 ), states that there exists a constant C > 0 , such that for all u ∈ L 1 ( R n ) ∩ W 1,2 ( R n ) ,
The inequality follows from basic properties of the Fourier transform . Indeed, integrating over the complement of the ball of radius ρ ,
because 1 ≤ | x | 2 / ρ 2 {\displaystyle 1\leq |x|^{2}/\rho ^{2}} . On the other hand, one has
which, when integrated over the ball of radius ρ gives
where ω n is the volume of the n -ball . Choosing ρ to minimize the sum of ( 1 ) and ( 2 ) and applying Parseval's theorem:
gives the inequality.
In the special case of n = 1 , the Nash inequality can be extended to the L p case, in which case it is a generalization of the Gagliardo-Nirenberg-Sobolev inequality ( Brezis 2011 , Comments on Chapter 8). In fact, if I is a bounded interval, then for all 1 ≤ r < ∞ and all 1 ≤ q ≤ p < ∞ the following inequality holds
where:
The simplest of the Sobolev embedding theorems, described above, states that if a function f {\displaystyle f} in L p ( R n ) {\displaystyle L^{p}(\mathbb {R} ^{n})} has one derivative in L p {\displaystyle L^{p}} , then f {\displaystyle f} itself is in L p ∗ {\displaystyle L^{p^{*}}} , where
We can see that as n {\displaystyle n} tends to infinity, p ∗ {\displaystyle p^{*}} approaches p {\displaystyle p} . Thus, if the dimension n {\displaystyle n} of the space on which f {\displaystyle f} is defined is large, the improvement in the local behavior of f {\displaystyle f} from having a derivative in L p {\displaystyle L^{p}} is small ( p ∗ {\displaystyle p^{*}} is only slightly larger than p {\displaystyle p} ). In particular, for functions on an infinite-dimensional space, we cannot expect any direct analog of the classical Sobolev embedding theorems.
There is, however, a type of Sobolev inequality, established by Leonard Gross ( Gross 1975 ) and known as a logarithmic Sobolev inequality , that has dimension-independent constants and therefore continues to hold in the infinite-dimensional setting. The logarithmic Sobolev inequality says, roughly, that if a function is in L p {\displaystyle L^{p}} with respect to a Gaussian measure and has one derivative that is also in L p {\displaystyle L^{p}} , then f {\displaystyle f} is in " L p {\displaystyle L^{p}} -log", meaning that the integral of | f | p log | f | {\displaystyle |f|^{p}\log |f|} is finite. The inequality expressing this fact has constants that do not involve the dimension of the space and, thus, the inequality holds in the setting of a Gaussian measure on an infinite-dimensional space. It is now known that logarithmic Sobolev inequalities hold for many different types of measures, not just Gaussian measures.
Although it might seem as if the L p {\displaystyle L^{p}} -log condition is a very small improvement over being in L p {\displaystyle L^{p}} , this improvement is sufficient to derive an important result, namely hypercontractivity for the associated Dirichlet form operator. This result means that if a function is in the range of the exponential of the Dirichlet form operator—which means that the function has, in some sense, infinitely many derivatives in L p {\displaystyle L^{p}} —then the function does belong to L p ∗ {\displaystyle L^{p^{*}}} for some p ∗ > p {\displaystyle p^{*}>p} ( Gross 1975 Theorem 6). | https://en.wikipedia.org/wiki/Sobolev_inequality |
In mathematics , a Sobolev space is a vector space of functions equipped with a norm that is a combination of L p -norms of the function together with its derivatives up to a given order. The derivatives are understood in a suitable weak sense to make the space complete , i.e. a Banach space . Intuitively, a Sobolev space is a space of functions possessing sufficiently many derivatives for some application domain, such as partial differential equations , and equipped with a norm that measures both the size and regularity of a function.
Sobolev spaces are named after the Russian mathematician Sergei Sobolev . Their importance comes from the fact that weak solutions of some important partial differential equations exist in appropriate Sobolev spaces, even when there are no strong solutions in spaces of continuous functions with the derivatives understood in the classical sense.
In this section and throughout the article Ω {\displaystyle \Omega } is an open subset of R n . {\displaystyle \mathbb {R} ^{n}.}
There are many criteria for smoothness of mathematical functions . The most basic criterion may be that of continuity . A stronger notion of smoothness is that of differentiability (because functions that are differentiable are also continuous) and a yet stronger notion of smoothness is that the derivative also be continuous (these functions are said to be of class C 1 {\displaystyle C^{1}} — see Differentiability classes ). Differentiable functions are important in many areas, and in particular for differential equations . In the twentieth century, however, it was observed that the space C 1 {\displaystyle C^{1}} (or C 2 {\displaystyle C^{2}} , etc.) was not exactly the right space to study solutions of differential equations. The Sobolev spaces are the modern replacement for these spaces in which to look for solutions of partial differential equations.
Quantities or properties of the underlying model of the differential equation are usually expressed in terms of integral norms. A typical example is measuring the energy of a temperature or velocity distribution by an L 2 {\displaystyle L^{2}} -norm. It is therefore important to develop a tool for differentiating Lebesgue space functions.
The integration by parts formula yields that for every u ∈ C k ( Ω ) {\displaystyle u\in C^{k}(\Omega )} , where k {\displaystyle k} is a natural number , and for all infinitely differentiable functions with compact support φ ∈ C c ∞ ( Ω ) , {\displaystyle \varphi \in C_{c}^{\infty }(\Omega ),}
where α {\displaystyle \alpha } is a multi-index of order | α | = k {\displaystyle |\alpha |=k} and we are using the notation:
The left-hand side of this equation still makes sense if we only assume u {\displaystyle u} to be locally integrable . If there exists a locally integrable function v {\displaystyle v} , such that
then we call v {\displaystyle v} the weak α {\displaystyle \alpha } -th partial derivative of u {\displaystyle u} . If there exists a weak α {\displaystyle \alpha } -th partial derivative of u {\displaystyle u} , then it is uniquely defined almost everywhere , and thus it is uniquely determined as an element of a Lebesgue space . On the other hand, if u ∈ C k ( Ω ) {\displaystyle u\in C^{k}(\Omega )} , then the classical and the weak derivative coincide. Thus, if v {\displaystyle v} is a weak α {\displaystyle \alpha } -th partial derivative of u {\displaystyle u} , we may denote it by D α u := v {\displaystyle D^{\alpha }u:=v} .
For example, the function
is not continuous at zero, and not differentiable at −1, 0, or 1. Yet the function
satisfies the definition for being the weak derivative of u ( x ) , {\displaystyle u(x),} which then qualifies as being in the Sobolev space W 1 , p {\displaystyle W^{1,p}} (for any allowed p {\displaystyle p} , see definition below).
The Sobolev spaces W k , p ( Ω ) {\displaystyle W^{k,p}(\Omega )} combine the concepts of weak differentiability and Lebesgue norms .
In the one-dimensional case the Sobolev space W k , p ( R ) {\displaystyle W^{k,p}(\mathbb {R} )} for 1 ≤ p ≤ ∞ {\displaystyle 1\leq p\leq \infty } is defined as the subset of functions f {\displaystyle f} in L p ( R ) {\displaystyle L^{p}(\mathbb {R} )} such that f {\displaystyle f} and its weak derivatives up to order k {\displaystyle k} have a finite L p norm . As mentioned above, some care must be taken to define derivatives in the proper sense. In the one-dimensional problem it is enough to assume that the ( k − 1 ) {\displaystyle (k{-}1)} -th derivative f ( k − 1 ) {\displaystyle f^{(k-1)}} is differentiable almost everywhere and is equal almost everywhere to the Lebesgue integral of its derivative (this excludes irrelevant examples such as Cantor's function ).
With this definition, the Sobolev spaces admit a natural norm ,
One can extend this to the case p = ∞ {\displaystyle p=\infty } , with the norm then defined using the essential supremum by
Equipped with the norm ‖ ⋅ ‖ k , p , W k , p {\displaystyle \|\cdot \|_{k,p},W^{k,p}} becomes a Banach space . It turns out that it is enough to take only the first and last in the sequence, i.e., the norm defined by
is equivalent to the norm above (i.e. the induced topologies of the norms are the same).
Sobolev spaces with p = 2 are especially important because of their connection with Fourier series and because they form a Hilbert space . A special notation has arisen to cover this case, since the space is a Hilbert space:
The space H k {\displaystyle H^{k}} can be defined naturally in terms of Fourier series whose coefficients decay sufficiently rapidly, namely,
where f ^ {\displaystyle {\widehat {f}}} is the Fourier series of f , {\displaystyle f,} and T {\displaystyle \mathbb {T} } denotes the 1-torus. As above, one can use the equivalent norm
Both representations follow easily from Parseval's theorem and the fact that differentiation is equivalent to multiplying the Fourier coefficient by i n {\displaystyle in} .
Furthermore, the space H k {\displaystyle H^{k}} admits an inner product , like the space H 0 = L 2 . {\displaystyle H^{0}=L^{2}.} In fact, the H k {\displaystyle H^{k}} inner product is defined in terms of the L 2 {\displaystyle L^{2}} inner product:
The space H k {\displaystyle H^{k}} becomes a Hilbert space with this inner product.
In one dimension, some other Sobolev spaces permit a simpler description. For example, W 1 , 1 ( 0 , 1 ) {\displaystyle W^{1,1}(0,1)} is the space of absolutely continuous functions on (0, 1) (or rather, equivalence classes of functions that are equal almost everywhere to such), while W 1 , ∞ ( I ) {\displaystyle W^{1,\infty }(I)} is the space of bounded Lipschitz functions on I , for every interval I . However, these properties are lost or not as simple for functions of more than one variable.
All spaces W k , ∞ {\displaystyle W^{k,\infty }} are (normed) algebras , i.e. the product of two elements is once again a function of this Sobolev space, which is not the case for p < ∞ . {\displaystyle p<\infty .} (E.g., functions behaving like | x | −1/3 at the origin are in L 2 , {\displaystyle L^{2},} but the product of two such functions is not in L 2 {\displaystyle L^{2}} ).
The transition to multiple dimensions brings more difficulties, starting from the very definition. The requirement that f ( k − 1 ) {\displaystyle f^{(k-1)}} be the integral of f ( k ) {\displaystyle f^{(k)}} does not generalize, and the simplest solution is to consider derivatives in the sense of distribution theory .
A formal definition now follows. Let k ∈ N , 1 ⩽ p ⩽ ∞ . {\displaystyle k\in \mathbb {N} ,1\leqslant p\leqslant \infty .} The Sobolev space W k , p ( Ω ) {\displaystyle W^{k,p}(\Omega )} is defined to be the set of all functions f {\displaystyle f} on Ω {\displaystyle \Omega } such that for every multi-index α {\displaystyle \alpha } with | α | ⩽ k , {\displaystyle |\alpha |\leqslant k,} the mixed partial derivative
exists in the weak sense and is in L p ( Ω ) , {\displaystyle L^{p}(\Omega ),} i.e.
That is, the Sobolev space W k , p ( Ω ) {\displaystyle W^{k,p}(\Omega )} is defined as
The natural number k {\displaystyle k} is called the order of the Sobolev space W k , p ( Ω ) . {\displaystyle W^{k,p}(\Omega ).}
There are several choices for a norm for W k , p ( Ω ) . {\displaystyle W^{k,p}(\Omega ).} The following two are common and are equivalent in the sense of equivalence of norms :
and
With respect to either of these norms, W k , p ( Ω ) {\displaystyle W^{k,p}(\Omega )} is a Banach space. For p < ∞ , W k , p ( Ω ) {\displaystyle p<\infty ,W^{k,p}(\Omega )} is also a separable space . It is conventional to denote W k , 2 ( Ω ) {\displaystyle W^{k,2}(\Omega )} by H k ( Ω ) {\displaystyle H^{k}(\Omega )} for it is a Hilbert space with the norm ‖ ⋅ ‖ W k , 2 ( Ω ) {\displaystyle \|\cdot \|_{W^{k,2}(\Omega )}} . [ 1 ]
It is rather hard to work with Sobolev spaces relying only on their definition. It is therefore interesting to know that by the Meyers–Serrin theorem a function u ∈ W k , p ( Ω ) {\displaystyle u\in W^{k,p}(\Omega )} can be approximated by smooth functions . This fact often allows us to translate properties of smooth functions to Sobolev functions. If p {\displaystyle p} is finite and Ω {\displaystyle \Omega } is open, then there exists for any u ∈ W k , p ( Ω ) {\displaystyle u\in W^{k,p}(\Omega )} an approximating sequence of functions u m ∈ C ∞ ( Ω ) {\displaystyle u_{m}\in C^{\infty }(\Omega )} such that:
If Ω {\displaystyle \Omega } has Lipschitz boundary , we may even assume that the u m {\displaystyle u_{m}} are the restriction of smooth functions with compact support on all of R n . {\displaystyle \mathbb {R} ^{n}.} [ 2 ]
In higher dimensions, it is no longer true that, for example, W 1 , 1 {\displaystyle W^{1,1}} contains only continuous functions. For example, | x | − 1 ∈ W 1 , 1 ( B 3 ) {\displaystyle |x|^{-1}\in W^{1,1}(\mathbb {B} ^{3})} where B 3 {\displaystyle \mathbb {B} ^{3}} is the unit ball in three dimensions. For k > n / p {\displaystyle k>n/p} , the space W k , p ( Ω ) {\displaystyle W^{k,p}(\Omega )} will contain only continuous functions, but for which k {\displaystyle k} this is already true depends both on p {\displaystyle p} and on the dimension. For example, as can be easily checked using spherical polar coordinates for the function f : B n → R ∪ { ∞ } {\displaystyle f:\mathbb {B} ^{n}\to \mathbb {R} \cup \{\infty \}} defined on the n -dimensional unit ball we have:
Intuitively, the blow-up of f at 0 "counts for less" when n is large since the unit ball has "more outside and less inside" in higher dimensions.
Let 1 ⩽ p ⩽ ∞ . {\displaystyle 1\leqslant p\leqslant \infty .} If a function is in W 1 , p ( Ω ) , {\displaystyle W^{1,p}(\Omega ),} then, possibly after modifying the function on a set of measure zero, the restriction to almost every line parallel to the coordinate directions in R n {\displaystyle \mathbb {R} ^{n}} is absolutely continuous ; what's more, the classical derivative along the lines that are parallel to the coordinate directions are in L p ( Ω ) . {\displaystyle L^{p}(\Omega ).} Conversely, if the restriction of f {\displaystyle f} to almost every line parallel to the coordinate directions is absolutely continuous, then the pointwise gradient ∇ f {\displaystyle \nabla f} exists almost everywhere , and f {\displaystyle f} is in W 1 , p ( Ω ) {\displaystyle W^{1,p}(\Omega )} provided f , | ∇ f | ∈ L p ( Ω ) . {\displaystyle f,|\nabla f|\in L^{p}(\Omega ).} In particular, in this case the weak partial derivatives of f {\displaystyle f} and pointwise partial derivatives of f {\displaystyle f} agree almost everywhere. The ACL characterization of the Sobolev spaces was established by Otto M. Nikodym ( 1933 ); see ( Maz'ya 2011 , §1.1.3).
A stronger result holds when p > n . {\displaystyle p>n.} A function in W 1 , p ( Ω ) {\displaystyle W^{1,p}(\Omega )} is, after modifying on a set of measure zero, Hölder continuous of exponent γ = 1 − n p , {\displaystyle \gamma =1-{\tfrac {n}{p}},} by Morrey's inequality . In particular, if p = ∞ {\displaystyle p=\infty } and Ω {\displaystyle \Omega } has Lipschitz boundary, then the function is Lipschitz continuous .
The Sobolev space W 1 , 2 ( Ω ) {\displaystyle W^{1,2}(\Omega )} is also denoted by H 1 ( Ω ) . {\displaystyle H^{1}\!(\Omega ).} It is a Hilbert space, with an important subspace H 0 1 ( Ω ) {\displaystyle H_{0}^{1}\!(\Omega )} defined to be the closure of the infinitely differentiable functions compactly supported in Ω {\displaystyle \Omega } in H 1 ( Ω ) . {\displaystyle H^{1}\!(\Omega ).} The Sobolev norm defined above reduces here to
When Ω {\displaystyle \Omega } has a regular boundary, H 0 1 ( Ω ) {\displaystyle H_{0}^{1}\!(\Omega )} can be described as the space of functions in H 1 ( Ω ) {\displaystyle H^{1}\!(\Omega )} that vanish at the boundary, in the sense of traces ( see below ). When n = 1 , {\displaystyle n=1,} if Ω = ( a , b ) {\displaystyle \Omega =(a,b)} is a bounded interval, then H 0 1 ( a , b ) {\displaystyle H_{0}^{1}(a,b)} consists of continuous functions on [ a , b ] {\displaystyle [a,b]} of the form
where the generalized derivative f ′ {\displaystyle f'} is in L 2 ( a , b ) {\displaystyle L^{2}(a,b)} and has 0 integral, so that f ( b ) = f ( a ) = 0. {\displaystyle f(b)=f(a)=0.}
When Ω {\displaystyle \Omega } is bounded, the Poincaré inequality states that there is a constant C = C ( Ω ) {\displaystyle C=C(\Omega )} such that:
When Ω {\displaystyle \Omega } is bounded, the injection from H 0 1 ( Ω ) {\displaystyle H_{0}^{1}\!(\Omega )} to L 2 ( Ω ) , {\displaystyle L^{2}\!(\Omega ),} is compact . This fact plays a role in the study of the Dirichlet problem , and in the fact that there exists an orthonormal basis of L 2 ( Ω ) {\displaystyle L^{2}(\Omega )} consisting of eigenvectors of the Laplace operator (with Dirichlet boundary condition ).
Sobolev spaces are often considered when investigating partial differential equations. It is essential to consider boundary values of Sobolev functions. If u ∈ C ( Ω ) {\displaystyle u\in C(\Omega )} , those boundary values are described by the restriction u | ∂ Ω . {\displaystyle u|_{\partial \Omega }.} However, it is not clear how to describe values at the boundary for u ∈ W k , p ( Ω ) , {\displaystyle u\in W^{k,p}(\Omega ),} as the n -dimensional measure of the boundary is zero. The following theorem [ 2 ] resolves the problem:
Trace theorem — Assume Ω is bounded with Lipschitz boundary . Then there exists a bounded linear operator T : W 1 , p ( Ω ) → L p ( ∂ Ω ) {\displaystyle T:W^{1,p}(\Omega )\to L^{p}(\partial \Omega )} such that T u = u | ∂ Ω u ∈ W 1 , p ( Ω ) ∩ C ( Ω ¯ ) ‖ T u ‖ L p ( ∂ Ω ) ⩽ c ( p , Ω ) ‖ u ‖ W 1 , p ( Ω ) u ∈ W 1 , p ( Ω ) . {\displaystyle {\begin{aligned}Tu&=u|_{\partial \Omega }&&u\in W^{1,p}(\Omega )\cap C({\overline {\Omega }})\\\|Tu\|_{L^{p}(\partial \Omega )}&\leqslant c(p,\Omega )\|u\|_{W^{1,p}(\Omega )}&&u\in W^{1,p}(\Omega ).\end{aligned}}}
Tu is called the trace of u . Roughly speaking, this theorem extends the restriction operator to the Sobolev space W 1 , p ( Ω ) {\displaystyle W^{1,p}(\Omega )} for well-behaved Ω. Note that the trace operator T is in general not surjective, but for 1 < p < ∞ it maps continuously onto the Sobolev–Slobodeckij space W 1 − 1 p , p ( ∂ Ω ) . {\displaystyle W^{1-{\frac {1}{p}},p}(\partial \Omega ).}
Intuitively, taking the trace costs 1/ p of a derivative. The functions u in W 1,p (Ω) with zero trace, i.e. Tu = 0, can be characterized by the equality
where
In other words, for Ω bounded with Lipschitz boundary, trace-zero functions in W 1 , p ( Ω ) {\displaystyle W^{1,p}(\Omega )} can be approximated by smooth functions with compact support.
For a natural number k and 1 < p < ∞ one can show (by using Fourier multipliers [ 3 ] [ 4 ] ) that the space W k , p ( R n ) {\displaystyle W^{k,p}(\mathbb {R} ^{n})} can equivalently be defined as
with the norm
This motivates Sobolev spaces with non-integer order since in the above definition we can replace k by any real number s . The resulting spaces
are called Bessel potential spaces [ 5 ] (named after Friedrich Bessel ). They are Banach spaces in general and Hilbert spaces in the special case p = 2.
For s ≥ 0 , H s , p ( Ω ) {\displaystyle s\geq 0,H^{s,p}(\Omega )} is the set of restrictions of functions from H s , p ( R n ) {\displaystyle H^{s,p}(\mathbb {R} ^{n})} to Ω equipped with the norm
Again, H s,p (Ω) is a Banach space and in the case p = 2 a Hilbert space.
Using extension theorems for Sobolev spaces, it can be shown that also W k,p (Ω) = H k,p (Ω) holds in the sense of equivalent norms, if Ω is domain with uniform C k -boundary, k a natural number and 1 < p < ∞ . By the embeddings
the Bessel potential spaces H s , p ( R n ) {\displaystyle H^{s,p}(\mathbb {R} ^{n})} form a continuous scale between the Sobolev spaces W k , p ( R n ) . {\displaystyle W^{k,p}(\mathbb {R} ^{n}).} From an abstract point of view, the Bessel potential spaces occur as complex interpolation spaces of Sobolev spaces, i.e. in the sense of equivalent norms it holds that
where:
Another approach to define fractional order Sobolev spaces arises from the idea to generalize the Hölder condition to the L p -setting. [ 6 ] For 1 ⩽ p < ∞ , θ ∈ ( 0 , 1 ) {\displaystyle 1\leqslant p<\infty ,\theta \in (0,1)} and f ∈ L p ( Ω ) , {\displaystyle f\in L^{p}(\Omega ),} the Slobodeckij seminorm (roughly analogous to the Hölder seminorm) is defined by
Let s > 0 be not an integer and set θ = s − ⌊ s ⌋ ∈ ( 0 , 1 ) {\displaystyle \theta =s-\lfloor s\rfloor \in (0,1)} . Using the same idea as for the Hölder spaces , the Sobolev–Slobodeckij space [ 7 ] W s , p ( Ω ) {\displaystyle W^{s,p}(\Omega )} is defined as
It is a Banach space for the norm
If Ω {\displaystyle \Omega } is suitably regular in the sense that there exist certain extension operators, then also the Sobolev–Slobodeckij spaces form a scale of Banach spaces, i.e. one has the continuous injections or embeddings
There are examples of irregular Ω such that W 1 , p ( Ω ) {\displaystyle W^{1,p}(\Omega )} is not even a vector subspace of W s , p ( Ω ) {\displaystyle W^{s,p}(\Omega )} for 0 < s < 1 (see Example 9.1 of [ 8 ] )
From an abstract point of view, the spaces W s , p ( Ω ) {\displaystyle W^{s,p}(\Omega )} coincide with the real interpolation spaces of Sobolev spaces, i.e. in the sense of equivalent norms the following holds:
Sobolev–Slobodeckij spaces play an important role in the study of traces of Sobolev functions. They are special cases of Besov spaces . [ 4 ]
The constant arising in the characterization of the fractional Sobolev space W s , p ( Ω ) {\displaystyle W^{s,p}(\Omega )} can be characterized through the Bourgain-Brezis-Mironescu formula:
and the condition
characterizes those functions of L p ( Ω ) {\displaystyle L^{p}(\Omega )} that are in the first-order Sobolev space W 1 , p ( Ω ) {\displaystyle W^{1,p}(\Omega )} . [ 9 ]
If Ω {\displaystyle \Omega } is a domain whose boundary is not too poorly behaved (e.g., if its boundary is a manifold, or satisfies the more permissive " cone condition ") then there is an operator A mapping functions of Ω {\displaystyle \Omega } to functions of R n {\displaystyle \mathbb {R} ^{n}} such that:
We will call such an operator A an extension operator for Ω . {\displaystyle \Omega .}
Extension operators are the most natural way to define H s ( Ω ) {\displaystyle H^{s}(\Omega )} for non-integer s (we cannot work directly on Ω {\displaystyle \Omega } since taking Fourier transform is a global operation). We define H s ( Ω ) {\displaystyle H^{s}(\Omega )} by saying that u ∈ H s ( Ω ) {\displaystyle u\in H^{s}(\Omega )} if and only if A u ∈ H s ( R n ) . {\displaystyle Au\in H^{s}(\mathbb {R} ^{n}).} Equivalently, complex interpolation yields the same H s ( Ω ) {\displaystyle H^{s}(\Omega )} spaces so long as Ω {\displaystyle \Omega } has an extension operator. If Ω {\displaystyle \Omega } does not have an extension operator, complex interpolation is the only way to obtain the H s ( Ω ) {\displaystyle H^{s}(\Omega )} spaces.
As a result, the interpolation inequality still holds.
Like above , we define H 0 s ( Ω ) {\displaystyle H_{0}^{s}(\Omega )} to be the closure in H s ( Ω ) {\displaystyle H^{s}(\Omega )} of the space C c ∞ ( Ω ) {\displaystyle C_{c}^{\infty }(\Omega )} of infinitely differentiable compactly supported functions. Given the definition of a trace, above, we may state the following
Theorem — Let Ω {\displaystyle \Omega } be uniformly C m regular, m ≥ s and let P be the linear map sending u in H s ( Ω ) {\displaystyle H^{s}(\Omega )} to ( u , d u d n , … , d k u d n k ) | G {\displaystyle \left.\left(u,{\frac {du}{dn}},\dots ,{\frac {d^{k}u}{dn^{k}}}\right)\right|_{G}} where d/dn is the derivative normal to G , and k is the largest integer less than s . Then H 0 s {\displaystyle H_{0}^{s}} is precisely the kernel of P .
If u ∈ H 0 s ( Ω ) {\displaystyle u\in H_{0}^{s}(\Omega )} we may define its extension by zero u ~ ∈ L 2 ( R n ) {\displaystyle {\tilde {u}}\in L^{2}(\mathbb {R} ^{n})} in the natural way, namely
Theorem — Let s > 1 2 . {\displaystyle s>{\tfrac {1}{2}}.} The map u ↦ u ~ {\displaystyle u\mapsto {\tilde {u}}} is continuous into H s ( R n ) {\displaystyle H^{s}(\mathbb {R} ^{n})} if and only if s is not of the form n + 1 2 {\displaystyle n+{\tfrac {1}{2}}} for n an integer.
For f ∈ L p (Ω) its extension by zero,
is an element of L p ( R n ) . {\displaystyle L^{p}(\mathbb {R} ^{n}).} Furthermore,
In the case of the Sobolev space W 1,p (Ω) for 1 ≤ p ≤ ∞ , extending a function u by zero will not necessarily yield an element of W 1 , p ( R n ) . {\displaystyle W^{1,p}(\mathbb {R} ^{n}).} But if Ω is bounded with Lipschitz boundary (e.g. ∂Ω is C 1 ), then for any bounded open set O such that Ω⊂⊂O (i.e. Ω is compactly contained in O), there exists a bounded linear operator [ 2 ]
such that for each u ∈ W 1 , p ( Ω ) : E u = u {\displaystyle u\in W^{1,p}(\Omega ):Eu=u} a.e. on Ω, Eu has compact support within O, and there exists a constant C depending only on p , Ω, O and the dimension n , such that
We call E u {\displaystyle Eu} an extension of u {\displaystyle u} to R n . {\displaystyle \mathbb {R} ^{n}.}
It is a natural question to ask if a Sobolev function is continuous or even continuously differentiable. Roughly speaking, sufficiently many weak derivatives (i.e. large k ) result in a classical derivative. This idea is generalized and made precise in the Sobolev embedding theorem .
Write W k , p {\displaystyle W^{k,p}} for the Sobolev space of some compact Riemannian manifold of dimension n . Here k can be any real number, and 1 ≤ p ≤ ∞. (For p = ∞ the Sobolev space W k , ∞ {\displaystyle W^{k,\infty }} is defined to be the Hölder space C n ,α where k = n + α and 0 < α ≤ 1.) The Sobolev embedding theorem states that if k ⩾ m {\displaystyle k\geqslant m} and k − n p ⩾ m − n q {\displaystyle k-{\tfrac {n}{p}}\geqslant m-{\tfrac {n}{q}}} then
and the embedding is continuous. Moreover, if k > m {\displaystyle k>m} and k − n p > m − n q {\displaystyle k-{\tfrac {n}{p}}>m-{\tfrac {n}{q}}} then the embedding is completely continuous (this is sometimes called Kondrachov's theorem or the Rellich–Kondrachov theorem ). Functions in W m , ∞ {\displaystyle W^{m,\infty }} have all derivatives of order less than m continuous, so in particular this gives conditions on Sobolev spaces for various derivatives to be continuous. Informally these embeddings say that to convert an L p estimate to a boundedness estimate costs 1/ p derivatives per dimension.
There are similar variations of the embedding theorem for non-compact manifolds such as R n {\displaystyle \mathbb {R} ^{n}} ( Stein 1970 ). Sobolev embeddings on R n {\displaystyle \mathbb {R} ^{n}} that are not compact often have a related, but weaker, property of cocompactness . | https://en.wikipedia.org/wiki/Sobolev_space |
In mathematics , sociable numbers are numbers whose aliquot sums form a periodic sequence . They are generalizations of the concepts of perfect numbers and amicable numbers . The first two sociable sequences, or sociable chains, were discovered and named by the Belgian mathematician Paul Poulet in 1918. [ 1 ] In a sociable sequence, each number is the sum of the proper divisors of the preceding number, i.e., the sum excludes the preceding number itself. For the sequence to be sociable, the sequence must be cyclic and return to its starting point.
The period of the sequence, or order of the set of sociable numbers, is the number of numbers in this cycle.
If the period of the sequence is 1, the number is a sociable number of order 1, or a perfect number —for example, the proper divisors of 6 are 1, 2, and 3, whose sum is again 6. A pair of amicable numbers is a set of sociable numbers of order 2. There are no known sociable numbers of order 3, and searches for them have been made up to 5 × 10 7 {\displaystyle 5\times 10^{7}} as of 1970. [ 2 ]
It is an open question whether all numbers end up at either a sociable number or at a prime (and hence 1), or, equivalently, whether there exist numbers whose aliquot sequence never terminates, and hence grows without bound.
As an example, the number 1,264,460 is a sociable number whose cyclic aliquot sequence has a period of 4:
The following categorizes all known sociable numbers as of October 2024 [update] by the length of the corresponding aliquot sequence:
length
sequences
in sequence [ 3 ]
( Perfect number )
( Amicable number )
It is conjectured that if n is congruent to 3 modulo 4 then there is no such sequence with length n .
The 5-cycle sequence is: 12496, 14288, 15472, 14536, 14264
The only known 28-cycle is: 14316, 19116, 31704, 47616, 83328, 177792, 295488, 629072, 589786, 294896, 358336, 418904, 366556, 274924, 275444, 243760, 376736, 381028, 285778, 152990, 122410, 97946, 48976, 45946, 22976, 22744, 19916, 17716 (sequence A072890 in the OEIS ).
These two sequences provide the only sociable numbers below 1 million (other than the perfect and amicable numbers).
The aliquot sequence can be represented as a directed graph , G n , s {\displaystyle G_{n,s}} , for a given integer n {\displaystyle n} , where s ( k ) {\displaystyle s(k)} denotes the
sum of the proper divisors of k {\displaystyle k} . [ 5 ] Cycles in G n , s {\displaystyle G_{n,s}} represent sociable numbers within the interval [ 1 , n ] {\displaystyle [1,n]} . Two special cases are loops that represent perfect numbers and cycles of length two that represent amicable pairs .
It is conjectured that as the number of sociable number cycles with length greater than 2 approaches infinity, the proportion of the sums of the sociable number cycles divisible by 10 approaches 1 (sequence A292217 in the OEIS ). | https://en.wikipedia.org/wiki/Sociable_number |
Social Age [ 1 ] encompasses both societal and technological changes succeeding the Information Age .
It is divergent from the Information Age as it gives more prominence to social factors when adopting and/or extending technology and information. [ 1 ] It further broadens the definition of Attention Age because the Social Age focuses on many forms of societal interactions including online relationships, collaboration and sharing. | https://en.wikipedia.org/wiki/Social_Age |
Social Bonding and Nurture Kinship: Compatibility between Cultural and Biological Approaches is a book on human kinship and social behavior by Maximilian Holland, published in 2012. The work synthesizes the perspectives of evolutionary biology , psychology and sociocultural anthropology towards understanding human social bonding and cooperative behavior. It presents a theoretical treatment that many consider to have resolved longstanding questions about the proper place of genetic (or 'blood') connections in human kinship and social relations, and a synthesis that "should inspire more nuanced ventures in applying Darwinian approaches to sociocultural anthropology". [ 1 ]
The aim of the book is to show that "properly interpreted, cultural anthropology approaches (and ethnographic data) and biological approaches are perfectly compatible regarding processes of social bonding in humans." [ 2 ] Holland's position is based on demonstrating that the dominant biological theory of social behavior ( inclusive fitness theory) is typically misunderstood to predict that genetic ties are necessary for the expression of social behaviors, whereas in fact the theory only implicates genetic associations as necessary for the evolution of social behaviors. Whilst rigorous evolutionary biologists have long understood the distinction between these levels of analysis (see Tinbergen's four questions ), past attempts to apply inclusive fitness theory to humans have often overlooked the distinction between evolution and expression . [ 3 ]
Beyond its central argument, the broader philosophical implications of Holland's work are considered by commentators to be that it both "helps to untangle a long-standing disciplinary muddle" [ 4 ] and "clarifies the relationship between biological and sociocultural approaches to human kinship." [ 5 ] It is claimed that the book "demonstrates that an alternative non-deterministic interpretation of evolutionary biology is more compatible with actual human social behavior and with the frameworks that sociocultural anthropology employs" [ 6 ] and as a consequence, delivers "a convincing, solid and informed blow to the residual genetic determinism that still influences the interpretation of social behaviour." [ 7 ]
The book's form consists of a cumulative argument (using a wide range of supporting evidence) made over nine chapters, with each chapter ending in a brief retrospective summary, and the final chapter containing a recapitulation and summary of the whole, [ 8 ] and drawing some wider conclusions.
Holland begins by tracing transitions in the history of anthropological theories of social behavior and kinship , noting the varying importance with which 'blood ties' have been understood to be a necessary element of human kinship and social relations. He suggests that whilst the mounting ethnographic evidence has led to a move away from the 'blood kinship' concept in recent decades, many sociocultural anthropologists still query the connection between kinship and blood, reproduction or some other apparently biological functions. Meanwhile, many biologists, biological anthropologists and evolutionary psychologists have persisted in viewing human kinship and cooperative behavior as necessarily associated with genetic relationships and 'blood ties'. The current situation has been characterized as "a clash between incommensurate paradigms, holding as they may, completely incompatible ideas about human nature." [ 9 ] Holland argues that a clear resolution to these questions is still outstanding, and would therefore be of value. In closing the introduction, Holland writes; "The approach is not reductive. The claim is rather that a thorough investigation of the 'biological facts' can be useful mainly though allowing a change in focus... away from confusion about the place of genealogy in social ties, and onto a reformulated baseline, built around varied processual aspects of social bonding. " [ 10 ]
The book reviews the background and key elements of Hamilton's inclusive fitness theory from the 1960s onwards, setting out its significant conceptual and heuristic value. Holland notes that Hamilton acknowledged that his earliest and most widely known account (1964) [ 11 ] contained technical inaccuracies. He also notes Hamilton's early speculations about possible proximate mechanisms of the expression of social behavior ( supergenes [ 11 ] as a possible alternative to behaviour-evoking-situations [ 11 ] ) contained errors that have nevertheless remained very influential in popular accounts. Specifically, the supergenes notion (sometimes called the Green-beard effect ) - that organisms may evolve genes that are able to identify identical copies in others and preferentially direct social behaviours towards them - was theoretically clarified and withdrawn by Hamilton in 1987. [ 12 ] However, in the intervening years, the notion that supergenes (or more often, simply individual organisms) have evolved to identify genetic relatives and preferentially cooperate with them took hold, and became the way many biologists came to understand the theory. This persisted, despite Hamilton's 1987 correction. In Holland's view it is the pervasiveness of this longstanding but erroneous perspective, and the suppression of the alternative 'behaviour-evoking-situations' perspective regarding social expression mechanisms, that is largely responsible for the ongoing clash between biological and sociocultural approaches to human kinship.
Holland shows that, in the 1970s and 80s, the first wave of attempts (known as human sociobiology or Darwinian anthropology ) to apply inclusive fitness theory to human social behavior relied on, and further reinforced, this same misinterpretation (above section) about the theory's predictions and the proximate mechanisms of social behavior. Holland also shows that this period of research was burdened with many misplaced assumptions about universal attributes of the human sexes, sexuality and gender roles, apparently projected from the specific cultural values of the researchers themselves. Holland also shows that, following the perceived failures of this early wave, and particularly its methodological agnosticism regarding proximate mechanisms of social behavior, the evolutionary psychology school grew up in its place. Although this latter school typically avoided engaging with the ethnographic data on human kinship, Holland argues that in the few cases where it did so, it repeated the misinterpretation of inclusive fitness theory that characterized the first wave. Holland also notes that Kitcher , in his [ 13 ] 1985 critique of the sociobiological position, suggested that perhaps the expression of social behaviors in humans might quite simply be based on cues of context and familiarity, rather than genetic relatedness per se .
Chapters four and five investigate further the theory and evidence surrounding the proximate mechanisms of social behavior; specifically the question of whether social behaviors are expressed by organisms via behaviour-evoking-situations or via direct detection of actual genetic relatedness. Related questions have been the domain of kin recognition theory. Holland notes that the name 'kin recognition' itself suggests some expectation that a positive identification of genetic relatedness is a prediction of inclusive fitness theory, and is thus expected. Similar points have been made by others; "many behavioural ecologists seem to implicitly assume that specialised mechanisms allowing individuals to distinguish their kin from non-kin must have evolved. [ 14 ] [ 15 ] " Again, the possibility that behaviour-evoking-situations might be the more parsimonious [ 16 ] mechanism of the expression of social behavior, and fully compatible with inclusive fitness theory, has often been underemphasized. However, Holland's review of the evidence notes that field studies in this area quickly established that behaviour-evoking-situations do in fact overwhelmingly mediate social behaviours in those species studied, and that, particularly in mammal species, social bonding and familiarity formed in early developmental contexts (e.g. in burrows or nesting sites) are a common mediating mechanism for social behaviors, independently of genetic relatedness per se . On the basis of the preceding theoretical analysis and review of evidence, at the end of chapter five, Holland argues that;
It is entirely erroneous, both in reference to theory and in reference to the evidence, to claim or suggest that 'the facts of biology' support the claim that organisms have evolved to cooperate with genetic relatives per se . [ 17 ]
Having argued for the above position on the lack of necessity for genetic relatedness per se to mediate social bonding and behavior, Holland suggests that "The further question then is; can we uncover in any greater detail how familiarity and other context-dependent cues operate?". [ 17 ] To discover the extent to which the variety of human kinship behaviors may nevertheless be compatible with this (less deterministic) interpretation of biological theory of social behavior, Holland suggests that a survey of primates' most fundamental social patterns may give clues, especially those of species most closely connected with humans. The variety of primate mating systems , group-membership (' philopatry ') patterns, and life-cycle patterns are reviewed. Holland finds that;
Like other mammals, Catarrhini primate demographics are strongly influenced by ecological conditions, particularly density and distribution of food sources... Cohesive social groups and delayed natal dispersal mean that maternally related individuals, including maternal siblings, face a statistically reliable context of interaction in all Catarrhini primates. This reliable context of interaction with maternally related individuals is extended amongst those species with female philopatry (especially Cercopithecinae). [ 18 ]
As with other social mammals, evidence suggest that the reliability of 'behaviour-evoking-situations' this social context provides has shaped the mechanisms of proximate expression of social bonding and behavior;
Adoption of infants by females (and sometimes males) demonstrates that care-giving and bonding to infants is not mediated by positive powers of discrimination. From the infant's perspective, it will bond with any responsive carer. If not necessarily the actual mother, in natural conditions this will often be a maternal relative (particularly an older sibling), but the context is primary, not the actual relatedness. Similarly, social bonding and social behaviours between maternal siblings (and occasionally between other maternal relatives) is context-driven in primates, and mediated via the care-giver. [ 19 ]
Holland also notes how Bowlby and colleagues' attachment theory was strongly informed by primate bonding patterns and mechanisms, and that in Bowlby's later writing the then emerging inclusive fitness theory was explicitly linked to.
[Bowlby's] work demonstrated that social attachments form on the basis of provision of care, and responsiveness to elicitations for care. The social context of living together and the familiarity this brings, provides the circumstance within which social bonds can form... [ 19 ]
On the basis of combining more recent primate research with the findings of attachment theory, Holland proposes that "In attempting to define more specific forms of the giving of care and nurture which may mediate social bonding we [find] that provision of food is likely to play a part, as well as the more intangible provision of warmth and comfort, and a safe base for sleeping. [ 19 ] "
Holland claims that, while biological theory of social behavior is not deterministic in respect of genetic relatedness vis-a-vis the formation of social bonds and expression of social behaviors, evidence does point to compatibility between a non-reductive interpretation of the theory and how such bonds and behaviors operate in social mammals, primates and in humans. In the final part of the book, Holland explores the extent to which this perspective is also compatible with sociocultural anthropology's ethnographic accounts of human kinship and social behavior, both occasional accounts from the past, as well as more contemporary accounts that have explicitly eschewed the earlier 'blood ties' assumption. Holland finds that;
Many contemporary accounts focus on social bonds formed in childhood and the importance of the performance of acts of care, including food provision, in mediating these bonds. In all cases it is this performance of care which is considered the overriding factor in
mediating social bonds, notwithstanding 'blood ties'. In short, there is strong compatibility between the perspectives on social bonding that emerge from a proper account of biological theory and those documented by ethnographers. [ 20 ]
Holland's concluding chapter gives a summary of his fundamental position;
A crucial implication of this argument taken as a whole is that the expression of the kinds of social behaviours treated by inclusive fitness theory does not require genetic relatedness. Sociobiology and evolutionary psychology's claims that biological science predicts that organisms will direct social behaviour towards relatives are thus both theoretically and empirically erroneous. Such claims and their supporting arguments also give a highly misleading and reductive account of basic biological theory. Properly interpreted, cultural anthropology approaches (and ethnographic data) and biological approaches are perfectly compatible regarding processes of social bonding in humans. Most of all, this requires a focus on the circumstances and processes which lead to social bonding. [ 2 ]
The book notes that, as an outcome of the analysis, Schneider's sociocultural perspective on human kinship is vindicated;
Do the biological facts have some priority or are they but one of the conditions, like ecology, economy, demography, etc., to which kinship systems must adapt? Take note: if the latter is the case, then kinship must be as much rooted in these other conditions as in the biological facts. [ 21 ]
The author supplies several examples of the insight that Schneider's broad approach can provide. The book closes with an example of a clash of cultural perspectives on kinship and family norms, and makes the suggestion that;
Constructing from narrow cultural particulars (Euro-American or otherwise) an essentialised model of 'human nature' does not constitute science; it is closer to cultural colonialism. In any analysis intended to shed light on proposed universals of the human condition, reflexivity is essential, and cultural and biological approaches both surely necessary. [ 22 ]
Kinship theorist and member of the US National Academy of Sciences , Robin Fox wrote of the work:
An excellent and constructive discussion of matters in kinship and its cultural and biological components, handsomely reconciling what have been held to be incompatible positions. [ 23 ] Max Holland gets to the heart of the matter concerning the contentious relationship between kinship categories, genetic relatedness and the prediction of behavior. If he had been in the debate in the 1980s then a lot of subsequent confusion could have been avoided" [ 4 ]
Irwin Bernstein, distinguished research professor in the university of Georgia's Behavioral and Brain Sciences Program made the following comment on Holland's book:
Max Holland has demonstrated extraordinarily thorough scholarship in his exhaustive review of the often contentious discussions of kinship. He has produced a balanced synthesis melding the two approaches exemplified in the biological and sociocultural behavioral positions. His work in reconciling opposing views clearly demonstrates the value of interdisciplinary approaches. This should be the definitive word on the subject. [ 24 ]
Philip Kitcher , John Dewey Professor of Philosophy, and James R. Barker Professorship of Contemporary Civilization at Columbia University , past president of the American Philosophical Association and inaugural winner of the Prometheus Prize, stated of the book:
Max Holland has provided a wide-ranging and deeply-probing analysis of the influence of genetic relatedness and social context on human kinship. He argues that while genetic relatedness may play a role in the evolution of social behavior, it does not determine the forms of such behavior. His discussion is exemplary for its thoroughness, and should inspire more nuanced ventures in applying Darwinian approaches to sociocultural anthropology. [ 1 ]
Kirk Endicott, professor emeritus of anthropology at the university of Dartmouth, wrote that Holland's book was:
A brilliant discussion of the relationship between kinship and social bonding as understood in evolutionary biology and in sociocultural anthropology. Among other contributions, it debunks the common misconception that biological evolution involves individual organisms actively pursuing the goal of increasing the numbers of their genes in successive generations, the measure of their so-called 'individual inclusive fitness'. Holland demonstrates that an alternative non-deterministic interpretation of evolutionary biology is more compatible with actual human social behavior and with the frameworks that sociocultural anthropology employs. [ 25 ]
Janet Carsten, kinship theorist and professor of anthropology at the university of Edinburgh stated that:
This book is a scholarly attempt to get beyond the often sterile oppositions between evolutionary and culturalist approaches to kinship. In bringing together two sides of the debate, it constitutes a valuable contribution to kinship studies. [ 26 ]
In a review for the journal Critique of Anthropology , Nicholas Malone concluded that:
Lucid and effective... Holland has produced a significant work of scholarship that will be of interest to a wide swath of the anthropological community. [ 27 ]
Commenting on the book for the journal Social Analysis , Anni Kajanus found that:
Holland has done an excellent and thorough job in reviewing the disciplinary and interdisciplinary histories of approaches to kinship and social bonds in anthropology, biology, and psychology. Most importantly, he clarifies the different levels of analysis when looking at human behavior in real time and in the evolutionary time frame. This makes the book essential reading for anyone who acknowledges that human relatedness and social bonds are shaped by the
evolved dispositions of our species, their development through the life-course of an individual, and our specific cultural-historical environments... Holland's book goes a long way toward clarifying and therefore advancing these theoretical debates [ 28 ]
An in-depth review of the book by primatologist Augusto Vitale, in the journal Folia Primatologica , found that:
This is, without a doubt, a very significant and important contribution to the on-going discussion about the determinants of sociality in humans as well as in other animals... A painstaking analysis of inclusive fitness, attachment theory and non-human primate social relationships, through a fascinating journey which ends with an anthropological account of social bonds in different cultures... It is a landmark in the field of evolutionary biology, which places genetic determinism in the correct perspective. [ 7 ]
Stuart Semple, evolutionary anthropologist, reviewing the book in the journal Acta Ethologica stated that:
As someone who teaches behavioural ecology to biologists, and primate biology to social and biological anthropologists, I will be strongly recommending this book to all of my advanced undergraduates, masters and PhD students, as well as to my colleagues. Not only does it help to resolve debates that have run for many years, but it is also an outstanding example of what can be achieved by immersing oneself in literature from different fields, while retaining an intellectual openness and exercising incisive analysis. Many of us talk enthusiastically about inter- and multi-disciplinarity, but often this is not much more than lip service. This book is a shining example of what can be achieved when excellent scholars engage fully across disciplinary boundaries. There should be more texts like this. [ 29 ]
In addition to praise for the book's significance, the Folia Primatologica review noted that the book is at times too dense and requires close reading;
The argument here and there becomes too detailed and tortuous, but it is absolutely captivating... [Colleagues] who are less used to extremely detailed theoretical reasoning, will find it difficult at the beginning... [ 7 ] | https://en.wikipedia.org/wiki/Social_Bonding_and_Nurture_Kinship |
The Social Study of Information Systems ( SSIS ) is interested in people developing and using technology and the "culture" of those people. SSIS brings social sciences concepts and methods to study information systems. SSIS studies these phenomena by drawing on and using "lenses" provided by social sciences, including philosophy , sociology , social psychology , organisational theory , political science . Thus, it relates to Social Informatics , Human-centered computing (HCC) , Science and Technology Studies (STS) , Design science .
Key Universities involved in SSIS are: the London School of Economics (LSE), Lancaster University , University of Manchester , University of Warwick , the Massachusetts Institute of Technology (MIT), University of Salford , Case Western Reserve University , the University of Cambridge , University of Edinburgh , Harvard University , and Peking University .
High profile people in the field are Claudio Ciborra , Jannis Kallinikos , Chrisanthi Avgerou & Susan Scott (LSE), Wanda Orlikowski (MIT), Shoshana Zuboff (Harvard), Lucas Introna & Lucy Suchman (Lancaster), Joe Nandhakumar (Warwick), Wendy Currie (Greenwich), Geoff Walsham, Mathew Jones & Michael Barrett (Cambridge), Kalle Lyytinen (Case Western), Rob Kling (Indiana). | https://en.wikipedia.org/wiki/Social_Study_of_Information_Systems |
The Social and Environmental Responsibility World Forum is an initiative organized by the Réseau Alliances in 1993 [ where? ] in partnership with private and public organizations , to encourage social and economic responsibility among businesses .
The initiative was planned for four years (2007–2010), with the goal of creating a permanent cycle of continuous exchanges and communication between actors from all parts of the world.
The work of the Forum was based on concrete projects and actions to formulate to generalize social and environmental responsibility throughout the world. During that period, major events were supposed to take place in Lille to bring together actors and experts in social and environmental responsibility of all nationalities, especially during the international meetings scheduled in October each year.
Developed on economic leaders’ initiative, the Réseau Alliances federates and helps businesses anxious to improve their performance while being more respectful of people and the environment. | https://en.wikipedia.org/wiki/Social_and_Environmental_Responsibility_World_Forum |
Social behavior is behavior among two or more organisms within the same species, it encompasses any behavior in which one member affects another. [ 1 ] [ 2 ] Social behavior can be seen as similar to an exchange of goods, with the expectation that when you give, you will receive something similar in return. [ 3 ] This behavior can be affected by both the qualities of the individual and the environmental (situational) factors. Therefore, social behavior arises as a result of an interaction between the two—the organism and its environment. This means that, in regards to humans, social behavior can be determined by both the individual characteristics of the person, and the situation they are in. [ 4 ]
A major aspect of social behavior is communication, which is the basis for survival and reproduction . [ 5 ] Social behavior is said to be determined by two different processes, that can either work together or oppose one another. The dual-systems model of reflective and impulsive determinants of social behavior came out of the realization that behavior cannot just be determined by one single factor. Instead, behavior can arise by those consciously behaving (where there is an awareness and intent), or by pure impulse. These factors that determine behavior can work in different situations and moments, and can even oppose one another. While at times one can behave with a specific goal in mind, other times they can behave without rational control, and driven by impulse instead. [ 6 ]
There are also distinctions between different types of social behavior, such as mundane versus defensive social behavior. Mundane social behavior is a result of interactions in day-to-day life, and are behaviors learned as one is exposed to those different situations. On the other hand, defensive behavior arises out of impulse, when one is faced with conflicting desires. [ 7 ]
Social behavior constantly changes as one continues to grow and develop, reaching different stages of life. The development of behavior is deeply tied with the biological and cognitive changes one is experiencing at any given time. This creates general patterns of social behavior development in humans. [ 8 ] Just as social behavior is influenced by both the situation and an individual's characteristics, the development of behavior is due to the combination of the two as well—the temperament of the child along with the settings they are exposed to. [ 9 ] [ 7 ]
Culture (parents and individuals that influence socialization in children) play a large role in the development of a child's social behavior, as the parents or caregivers are typically those who decide the settings and situations that the child is exposed to. These various settings the child is placed in (for example, the playground and classroom) form habits of interaction and behavior insomuch as the child being exposed to certain settings more frequently than others. What takes particular precedence in the influence of the setting are the people that the child must interact with their age, sex, and at times culture. [ 7 ]
Emotions also play a large role in the development of social behavior, as they are intertwined with the way an individual behaves. Through social interactions, emotion is understood through various verbal and nonverbal displays, and thus plays a large role in communication. Many of the processes that occur in the brain and underlay emotion often greatly correlate with the processes that are needed for social behavior as well. A major aspect of interaction is understanding how the other person thinks and feels, and being able to detect emotional states becomes necessary for individuals to effectively interact with one another and behave socially. [ 10 ]
As the child continues to gain social information, their behavior develops accordingly. [ 5 ] One must learn how to behave according to the interactions and people relevant to a certain setting, and therefore begin to intuitively know the appropriate form of social interaction depending on the situation. Therefore, behavior is constantly changing as required, and maturity brings this on. A child must learn to balance their own desires with those of the people they interact with, and this ability to correctly respond to contextual cues and understand the intentions and desires of another person improves with age. [ 7 ] That being said, the individual characteristics of the child (their temperament) is important to understanding how the individual learns social behaviors and cues given to them, and this learnability is not consistent across all children. [ 9 ]
When studying patterns of biological development across the human lifespan, there are certain patterns that are well-maintained across humans. These patterns can often correspond with social development, and biological changes lead to respective changes in interactions. [ 8 ]
In pre and post-natal infancy , the behavior of the infant is correlated with that of the caregiver. The development of social behavior is influenced by their mothers' reactions to children's emotional displays. [ 11 ] In infancy, there is already a development of the awareness of a stranger, in which case the individual is able to identify and distinguish between people. [ 8 ]
Come childhood, the individual begins to attend more to their peers, and communication begins to take a verbal form. One also begins to classify themselves on the basis of their gender and other qualities salient about themselves, like race and age. [ 8 ]
When the child reaches school age, one typically becomes more aware of the structure of society in regards to gender, and how their own gender plays a role in this. They become more and more reliant on verbal forms of communication, and more likely to form groups and become aware of their own role within the group. [ 8 ]
By puberty, general relations among same and opposite sex individuals are much more salient, and individuals begin to behave according to the norms of these situations. With increasing awareness of their sex and stereotypes that go along with it, the individual begins to choose how much they align with these stereotypes, and behaves either according to those stereotypes or not. This is also the time that individuals more often form sexual pairs. [ 8 ]
Once the individual reaches child rearing age, one must begin to undergo changes within the own behavior in accordance to major life-changes of a developing family. The potential new child requires the parent to modify their behavior to accommodate a new member of the family. [ 8 ]
Come senescence and retirement , behavior is more stable as the individual has often established their social circle (whatever it may be) and is more committed to their social structure. [ 8 ]
With the advent of the field social cognitive neuroscience came interest in studying social behavior's correlates within the brain to see what is happening beneath the surface as organisms act in a social manner. [ 12 ] Although there is debate on which particular regions of the brain are responsible for social behavior, some have claimed that the paracingulate cortex is activated when one person is thinking about the motives or aims of another, a means of understanding the social world and behaving accordingly. The medial prefrontal lobe has also been seen to have activation during social cognition [ 13 ] Research has discovered through studies on rhesus monkeys that the amygdala , a region known for expressing fear, was activated specifically when the monkeys were faced with a social situation they had never encountered before. This region of the brain was shown to be sensitive to the fear that comes with a novel social situation, inhibiting social interaction. [ 14 ]
Another form of studying the brain regions that may be responsible for social behavior has been through looking at patients with brain injuries who have an impairment in social behavior. Lesions in the prefrontal cortex that occurred in adulthood can affect the functioning of social behavior. When these lesions or a dysfunction in the prefrontal cortex occur in infancy/early on in life, the development of proper moral and social behavior is effected and thus atypical. [ 15 ]
Along with neural correlates, research has investigated what happens within the body (and potentially modulates) social behavior. Vasopressin is a posterior pituitary hormone that is seen to potentially play a role in affiliation for young rats. Along with young rats, vasopressin has also been associated with paternal behavior in prairie voles . Efforts have been made to connect animal research to humans, and found that vasopressin may play a role in the social responses of males in human research. [ 16 ]
Oxytocin has also been seen to be correlated with positive social behavior, and elevated levels have been shown to potentially help improve social behavior that may have been suppressed due to stress. Thus, targeting levels of oxytocin may play a role in interventions of disorders that deal with atypical social behavior. [ 17 ]
Along with vasopressin, serotonin has also been inspected in relation to social behavior in humans. It was found to be associated with human feelings of social connection, and there is a drop in serotonin when one is socially isolated or has feelings of social isolation. Serotonin has also been associated with social confidence. [ 16 ]
Positive affect (emotion) has been seen to have a large impact on social behavior, particularly by inducing more helping behavior, cooperation, and sociability. [ 18 ] Studies have shown that even subtly inducing positive affect within individuals caused greater social behavior and helping. This phenomenon, however, is not one-directional. Just as positive affect can influence social behavior, social behavior can have an influence on positive affect. [ 19 ]
Social behavior has typically been seen as a changing of behaviors relevant to the situation at hand, acting appropriately with the setting one is in. However, with the advent of electronic media , people began to find themselves in situations they may have not been exposed to in everyday life. Novel situations and information presented through electronic media has formed interactions that are completely new to people. While people typically behaved in line with their setting in face-to-face interaction, the lines have become blurred when it comes to electronic media. This has led to a cascade of results, as gender norms started to merge, and people were coming in contact with information they had never been exposed to through face-to-face interaction. A political leader could no longer tailor a speech to just one audience, for their speech would be translated and heard by anyone through the media. People can no longer play drastically different roles when put in different situations, because the situations overlap more as information is more readily available. Communication flows more quickly and fluidly through media, causing behavior to merge accordingly. [ 20 ]
Media has also been shown to have an impact on promoting different types of social behavior, such as prosocial and aggressive behavior. For example, violence shown through the media has been seen to lead to more aggressive behavior in its viewers. [ 21 ] [ 22 ] Research has also been done investigating how media portraying positive social acts, prosocial behavior , could lead to more helping behavior in its viewers. The general learning model was established to study how this process of translating media into behavior works, and why. [ 23 ] [ 24 ] This model suggests a link between positive media with prosocial behavior and violent media with aggressive behavior, and posits that this is mediated by the characteristics of the individual watching along with the situation they are in. This model also presents the notion that when one is exposed to the same type of media for long periods of time, this could even lead to changes within their personality traits, as they are forming different sets of knowledge and may be behaving accordingly. [ 25 ]
In various studies looking specifically at how video games with prosocial content effect behavior, it was shown that exposure influenced subsequent helping behavior in the video-game player. [ 24 ] The processes that underlay this effect point to prosocial thoughts being more readily available after playing a video game related to this, and thus the person playing the game is more likely to behave accordingly. [ 26 ] [ 27 ] These effects were not only found with video games, but also with music, as people listening to songs involving aggression and violence in the lyrics were more likely to act in an aggressive manner. [ 28 ] Likewise, people listening to songs related to prosocial acts (relative to a song with neutral lyrics) were shown to express greater helping behaviors and more empathy afterwards. [ 29 ] [ 30 ] When these songs were played at restaurants, it even led to an increase in tips given (relative to those who heard neutral lyrics). [ 31 ] [ 25 ]
Conformity refers to the behavior that an individual is unconsciously pressured by the group to make his behavior tend to be consistent with the majority of people in the group. [ 32 ] Generally speaking, the larger the group size, the easier it is for individuals to display conformity behaviors. Individuals may submit to the group for two reasons: first, to gain acceptance from the group ( normative social influence ); second, to obtain important information for the group ( informational social influence ). [ 33 ]
Aggression is an important social behavior that can have both negative consequences (in a social interaction) and adaptive consequences (adaptive in humans and other primates for survival). There are many differences in aggressive behavior, and a lot of these differences are sex-difference based. [ 34 ]
Although most animals can communicate nonverbally, humans have the ability to communicate with both verbal and nonverbal behavior. Verbal behavior is the content of one's spoken word. [ 35 ] Verbal and nonverbal behavior intersect in what is known as coverbal behavior, which is nonverbal behavior that contributes to the meaning of verbal speech (i.e. hand gestures used to emphasize the importance of what someone is saying). [ 36 ] Although the spoken words convey meaning in and of themselves, one cannot dismiss the coverbal behaviors that accompany the words, as they place great emphasis on the thought and importance contributing to the verbal speech. [ 37 ] [ 36 ] Therefore, the verbal behaviors and gestures that accompany it work together to make up a conversation . [ 37 ] Although many have posited this idea that nonverbal behavior accompanying speech serves an important role in communication, it is important to note that not all researchers agree. [ 38 ] [ 36 ] However, in most literature on gestures, unlike body language, gestures can accompany speech in ways that bring inner thoughts to life (often thoughts unable to be expressed verbally). [ 39 ] Gestures (coverbal behaviors) and speech occur simultaneously, and develop along the same trajectory within children as well. [ 39 ]
Behaviors that include any change in facial expression or body movement constitute the meaning of nonverbal behavior. [ 40 ] [ 41 ] Communicative nonverbal behavior include facial and body expressions that are intentionally meant to convey a message to those who are meant to receive it. [ 41 ] Nonverbal behavior can serve a specific purpose (i.e. to convey a message), or can be more of an impulse / reflex . [ 41 ] Paul Ekman , an influential psychologist, investigated both verbal and nonverbal behavior (and their role in communication) a great deal, emphasizing how difficult it is to empirically test such behaviors. [ 35 ] Nonverbal cues can serve the function of conveying a message, thought, or emotion both to the person viewing the behavior and the person sending these cues. [ 42 ]
A number of mental disorders affect social behavior. Social anxiety disorder is a phobic disorder characterized by a fear of being judged by others, which manifests itself as a fear of people in general. Due to this pervasive fear of embarrassing oneself in front of others, it causes those affected to avoid interactions with other people. [ 43 ] Attention deficit hyperactivity disorder is a neurodevelopmental disorder mainly identified by its symptoms of inattention , hyperactivity, and impulsivity. Hyperactivity-Impulsivity may lead to hampered social interactions, as one who displays these symptoms may be socially intrusive, unable to maintain personal space, and talk over others. [ 44 ] The majority of children that display symptoms of ADHD also have problems with their social behavior. [ 45 ] [ 46 ] Autism spectrum disorder is a neurodevelopmental disorder that affects the functioning of social interaction and communication. Autistic people may have difficulties in understanding social cues and the emotional states of others. [ 47 ]
Learning disabilities are often defined as a specific deficit in academic achievement ; however, research has shown that with a learning disability can come social skill deficits as well. [ 48 ] | https://en.wikipedia.org/wiki/Social_behavior |
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