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The Ship and Ocean Industries Research and Development Center ( SOIC ; Chinese : 船舶暨海洋產業研發中心 ; pinyin : Chuánbó Jì Hǎiyáng Chǎnyè Yánfā Zhōngxīn ) is a Taiwanese government owned naval architecture and maritime research institute founded in 1976.
The prime mission of SOIC is to support Taiwan ’s maritime industry . To further this mission it provides marine engineering planning, ship and ocean platform design, technical services, and knowledge integration services to private and public organizations and companies. [ 2 ] SOIC has designed vessels for shipping giants, local industry, the Republic of China Navy , and the Coast Guard Administration . [ 3 ]
SOIC was founded as United Ship Design and Development Center (USDDC) on 1 July 1976. The first chairman was Chieh-Jen Chiang. The first ship designed by USDDC was a 6,100 DWT log carrier. [ 3 ] In 2012 the institute changed its name to Ship and Ocean Industries R&D Center to better communicate the scope of its activities. [ 4 ]
In the 21st century SOIC has been involved in projects to advance Taiwan's offshore wind power industry. [ 5 ] [ 6 ]
The Yacht Industry Department of SOIC is the only government supported R&D center for yacht materials and design in the world. [ 7 ] | https://en.wikipedia.org/wiki/Ship_and_Ocean_Industries_R&D_Center |
The Ship and Offshore Structural Mechanics Laboratory ( SSML ) is a laboratory in the Department of Naval Architecture and Ocean Engineering of Pusan National University . The SSML develops methods useful for strength analysis and structural design of marine structures. The methods developed should be helpful for achievement of high performance of the structural system. The Laboratory has the facilities for numerical and experimental studies. This includes mechanical testing equipment (static and dynamic loading machines) and high-speed computers with non-linear finite element programmes.
Sloshing loads can cause structural damage in the insulation structures of the LNG cargo tanks and also their internal structures such as stiffeners and equipment like LNG pump towers. Structural failure of insulation structures leads to a catastrophic situation of the vessel. LS-DYNA3D numerical simulations and fracture testing are being undertaken on the material and insulation box / panel structure models.
Steel stiffened panels are important in a variety of marine and land-based applications including ships, offshore platforms and box girder bridges. Aluminum panels are used for building high speed ships. Numerical and experimental studies on buckling and ultimate strength of steel and aluminum stiffened panels are being undertaken.
Ship collisions and grounding continue to occur regardless of continuous efforts to prevent such accidents. With the increasing demand for safety at sea and for protection of the environment, it is of crucial importance to be able to reduce the probability of accidents, assess their consequences and ultimately minimize or prevent potential damages to the ships and the marine environment. Numerical and experimental studies on collision and grounding of ships are being undertaken.
Failures in ship structures, including total losses, continue to occur worldwide, in spite of ongoing continuous efforts to prevent them. Such failures can have enormous costs associated with them, including lost lives in some cases. One of the possible causes of marine casualties is the inability of aging ships to withstand rough seas and weather, because the ship's structural safety becomes reduced during later life although it is quite adequate at the design stage and perhaps some 15 years beyond. Condition assessment scheme (CAS) is being developed.
The axial crushing of a square section steel tube was done by impact loading. The test was carried out using the drop hammer machine. Based on the test results, mean crushing strength and effective crashing distance of plated structures under impact have been evaluated. The results could be useful for structural design of vessels and automobiles against collision accidents. The detailed results were published in Journal of Ship Research, Vol.41, No.2, 1997.
Collapse tests on nine mild steel corrugated bulkhead models having five bays of corrugations were carried out, varying the corrugation angle, the plate thickness and the type of loading (axial compression and / or lateral pressure). The detailed results were published in Journal of Ship Research, Vol.41, No.4, 1997.
A total of six double skinned structural models, namely four mild steel models and two aluminum alloy models, have been tested in a quasi-static loading condition, varying the plate thickness and the initial colliding location. The mild steel models were designed to represent side or bottom structures typical in double hull tankers or LNG carriers. The aluminum alloy models were designed to examine the internal mechanics in collision and grounding of aluminum alloy hull vessels for future designs. A same type indentor with a conical shape regarded as a striking body was used for the tests of all models.
[ 1 ]
http://saos.edmgr.com http://www.kosori.org | https://en.wikipedia.org/wiki/Ship_and_Offshore_Structural_Mechanics_Laboratory |
A ship model basin is a basin or tank used to carry out hydrodynamic tests with ship models , for the purpose of designing a new (full sized) ship, or refining the design of a ship to improve the ship's performance at sea. It can also refer to the organization (often a company) that owns and operates such a facility.
An engineering firm acts as a contractor to the relevant shipyards , and provides hydrodynamic model tests and numerical calculations to support the design and development of ships and offshore structures.
The eminent English engineer William Froude published a series of influential papers on ship designs for maximising stability in the 1860s. The Institution of Naval Architects eventually commissioned him to identify the most efficient hull shape. He validated his theoretical models with extensive empirical testing, using scale models for the different hull dimensions. He established a formula (now known as the Froude number ) by which the results of small-scale tests could be used to predict the behaviour of full-sized hulls. He built a sequence of 3, 6 and (shown in the picture) 12 foot scale models and used them in towing trials to establish resistance and scaling laws. His experiments were later vindicated in full-scale trials conducted by the Admiralty and as a result the first ship model basin was built, at public expense, at his home in Torquay . Here he was able to combine mathematical expertise with practical experimentation to such good effect that his methods are still followed today. [ 1 ]
Inspired by Froude's successful work, shipbuilding company William Denny and Brothers completed the world's first commercial example of a ship model basin in 1883. The facility was used to test models of a variety of vessels and explored various propulsion methods, including propellers, paddles and vane wheels. Experiments were carried out on models of the Denny-Brown stabilisers and the Denny hovercraft to gauge their feasibility. Tank staff also carried out research and experiments for other companies: Belfast-based Harland & Wolff decided to fit a bulbous bow on the liner Canberra after successful model tests in the Denny Tank. [ 2 ]
The hydrodynamic test facilities present at a model basin site include at least a towing tank and a cavitation tunnel and workshops. Some ship model basins have further facilities such as a maneuvering and seakeeping basin and an ice tank .
A towing tank is a basin, several metres wide and hundreds of metres long, equipped with a towing carriage that runs on two rails on either side. The towing carriage can either tow the model or follow the self-propelled model, and is equipped with computers and devices to register or control, respectively, variables such as speed, propeller thrust and torque, rudder angle etc. The towing tank serves for resistance and propulsion tests with towed and self-propelled ship models to determine how much power the engine will have to provide to achieve the speed laid down in the contract between shipyard and ship owner. The towing tank also serves to determine the maneuvering behaviour in model scale. For this, the self-propelled model is exposed to a series of zig-zag maneuvers at different rudder angle amplitudes. Post-processing of the test data by means of system identification results in a numerical model to simulate any other maneuver like Dieudonné spiral test or turning circles. Additionally, a towing tank can be equipped with a PMM ( planar motion mechanism ) or a CPMC (computerized planar motion carriage) to measure the hydrodynamic forces and moments on ships or submerged objects under the influence of oblique inflow and enforced motions. The towing tank can also be equipped with a wave generator to carry out seakeeping tests, either by simulating natural (irregular) waves or by exposing the model to a wave packet that yields a set of statistics known as response amplitude operators (acronym RAO ), that determine the ship's likely real-life sea-going behavior when operating in seas with varying wave amplitudes and frequencies (these parameters being known as sea states ). Modern seakeeping test facilities can determine these RAO statistics, with the aid of appropriate computer hardware and software, in a single test.
A cavitation tunnel is used to investigate propellers . This is a vertical water circuit with large diameter pipes. At the top, it carries the measuring facilities. A parallel inflow is established. With or without a ship model, the propeller, attached to a dynamometer , is brought into the inflow, and its thrust and torque is measured at different ratios of propeller speed (number of revolutions) to inflow velocity. A stroboscope synchronized with the propeller speed serves to visualize cavitation as if the cavitation bubble would not move. By this, one can observe if the propeller would be damaged by cavitation. To ensure similarity to the full-scale propeller, the pressure is lowered, and the gas content of the water is controlled.
Ship model basins manufacture their ship models from wood or paraffin with a computerized milling machine . Some of them also manufacture their model propellers. Equipping the ship models with all drives and gauges and manufacturing equipment for non-standard model tests are the main tasks of the workshops.
This is a test facility that is wide enough to investigate arbitrary angles between waves and the ship model, and to perform maneuvers like turning circles, for which the towing tank is too narrow. However, some important maneuvers like the spiral test still require even more space and still have to be simulated numerically after system identification.
An ice tank is used to develop ice breaking vessels , this tank fulfills similar purposes as the towing tank does for open water vessels. Resistance and required engine power as well as maneuvering behaviour are determined depending on the ice thickness. Also ice forces on offshore structures can be determined. Ice layers are frozen with a special procedure to scale down the ice crystals to model scale.
Additionally, these companies or authorities have CFD software and experience to simulate the complicated flow around ships and their rudders and propellers numerically. Today's state of the art does not yet allow software to replace model tests in their entirety by CFD calculations. One reason, but not the only one, is that elementization is still expensive. Also the lines design of some of the ships is carried out by the specialists of the ship model basin, either from the beginning or by optimizing the initial design obtained from the shipyard. The same applies to the design of propellers.
The ship model basins worldwide are organized in the ITTC [ 3 ] ( International Towing Tank Conference ) to standardize their model test procedures.
Some of the most significant ship model basins are: | https://en.wikipedia.org/wiki/Ship_model_basin |
Ship of Harkinian is an unofficial open source port of the 1998 Nintendo 64 video game The Legend of Zelda: Ocarina of Time that runs on Microsoft Windows , Linux , macOS , Wii U , and Nintendo Switch . It has also been ported to the Android operating system by a third party developer .
It was first released in March 2022 for Windows, four months after Ocarina of Time 's source code was decompiled and released. Since then, Ship of Harkinian has received ports to Linux and macOS, and homebrew ports to Wii U and Nintendo Switch.
Updates to Ship of Harkinian have attracted media attention, as they often integrate options and features which aren't present in any official release of Ocarina of Time .
The title of the project is an allusion to the philosophical thought experiment Ship of Theseus , as well as the name of the King from The Legend of Zelda CD-i games , who was infamous for the internet memes spawned from the games.
In November 2021, after 21 months of development, the Zelda Reverse Engineering Team (ZRET) successfully decompiled the executable to The Legend of Zelda: Ocarina of Time into human-readable code. While the decompilation project was principally carried out for the sake of documenting the game's creation and backend functionality, it also made possible the potential creation of source ports of Ocarina of Time , which would allow the game to be recompiled and run on platforms it wasn't originally developed for. Speaking to Ars Technica , ZRET member Rozlette stated that source ports were "outside the scope of what we do". [ 2 ]
In June 2020, developers Jack Walker and Kenix discussed the potential of a PC port of Ocarina of Time based on the ZRET decompilation project's work; at the time, Ocarina of Time 's decompilation was only 17% complete. Development on what would later become Ship of Harkinian began in November 2021, coinciding with the decompilation project reaching completion. [ 3 ]
In January 2022, a group of community developers named Harbour Masters released footage and screenshots of Ocarina of Time running natively on Microsoft Windows , in a widescreen aspect ratio not supported by the original Nintendo 64 release. The project was titled "Ship of Harkinian", a reference to Zelda: Wand of Gamelon . Speaking to Video Games Chronicle , Kenix, now part of Harbour Masters, estimated the project was "approximately 90%" complete. [ 4 ]
Prior to Ship of Harkinian's release, Harbour Masters showcased various experimental game modifications to Ocarina of Time , such as gyroscopic aiming and 4K texture support. [ 5 ]
Ship of Harkinian launched for Windows in March 2022. [ 6 ]
In May 2022, Harbour Masters announced the release of a Linux port of Ship of Harkinian via "Ship of Harkinian Direct", an online video parody presentation of Nintendo Direct . Additional features noted in this Direct include save states , an integrated cheat menu, accessibility options , and support for running the game at 60 frames per second. [ 7 ]
Two months later, in July 2022, an additional Ship of Harkinian Direct was released, announcing the release of Ship of Harkinian for macOS and Wii U . Additional features promoted in this Direct include a graphic interface for rebinding controls, a "randomizer" which randomizes various elements of the game to enhance replayability, and the ability to set an arbitrary framerate (up to 250FPS). [ 8 ]
Ship of Harkinian received Nintendo Switch support in the September 2022 "Zhora Alfa" update. [ 9 ]
In April 2023, a new Ship of Harkinian Direct was released, announcing custom texture and model support. Multiplayer functionality was added to the port; a second player can take control of Ivan the Fairy, described as a fairy "who likes to play tricks", whose abilities can either help or hinder the main player. [ 10 ]
Harbour Masters have expressed intent to create a source port for The Legend of Zelda: Majora's Mask shortly after ZRET completes their decompilation of the game. [ 4 ] [ 11 ]
In November 2023, Harbour Masters revealed that they had fully decompiled Majora's Mask , and are currently working on a PC port provisionally called 2Ship2Harkinian, [ 12 ] with its first version being released on 26 May 2024.
In December 2024, Harbour Masters released the first version of StarShip , a PC port of Star Fox 64 . [ 13 ]
Reception to Ship of Harkinian has been generally positive.
Ship of Harkinian has been favorably compared against the Nintendo Classics version of Ocarina of Time . Nick Rodriguez of Screen Rant deemed Ship of Harkinian "significantly better than the current Switch version in almost every regard", [ 14 ] with The Verge 's Derek Hill expressing similar sentiment: "As long as Nintendo is content putting out alarmingly low-quality versions of their classic games for shockingly high prices, Ship of Harkinian is proof that the unofficial option is sometimes the best option." [ 3 ]
Some outlets expressed apprehension over Ship of Harkinian, fearing that Nintendo's perceived litigiousness could jeopardize the project. In discussing Ship of Harkinian's long-term prospects, GameSpot writer Jenny Zheng remarked that that Ship of Harkinian's "odds aren't great", while characterizing Nintendo as "notoriously copyright-lawsuit-happy". [ 15 ] Luke Plunkett of Kotaku referred to Ship of Harkinian's legality as "murky", but noted that other projects built off of reverse engineering efforts were still active as of writing. [ 16 ] In a statement to GamesRadar+ , Harbour Masters contributor Kenix defended the legality of Ship of Harkinian: "The [Ocarina of Time] assets will be ripped from a user's own ROM that they must provide and then be exported into an archive compatible with the Ship of Harkinian. None of Nintendo's own property is involved in the process." [ 17 ] Harbour Masters encouraged users to support official releases of Ocarina of Time , and offered a unique role on their Discord server to those who can provide proof of ownership. [ 18 ] | https://en.wikipedia.org/wiki/Ship_of_Harkinian |
Shiplap is a type of wooden board used commonly as exterior siding in the construction of residences, barns, sheds, and outbuildings.
Shiplap is either rough-sawn 25 mm (1 in) or milled 19 mm ( 3 ⁄ 4 in) pine or similarly inexpensive wood between 76 and 254 mm (3 and 10 in) wide with a 9.5–12.7 mm ( 3 ⁄ 8 – 1 ⁄ 2 in) rabbet on opposite sides of each edge. [ 1 ] The rabbet allows the boards to overlap in this area. The profile of each board partially overlaps that of the board next to it creating a channel that gives shadow line effects, provides excellent weather protection and allows for dimensional movement.
Useful for its strength as a supporting member, and its ability to form a relatively tight seal when lapped, shiplap is usually used as a type of siding for buildings that do not require extensive maintenance and must withstand cold and aggressive climates. Rough-sawn shiplap is attached vertically in post and beam construction, usually with 51–65 mm (6d–8d) common nails , while milled versions, providing a tighter seal, are more commonly placed horizontally, more suited to two-by-four frame construction .
Small doors and shutters such as those found in barns and sheds are often constructed of shiplap cut directly from the walls, with only thin members framing or crossing the back for support. Shiplap is also used indoors for the rough or rustic look that it creates when used as paneling or a covering for a wall or ceiling. Shiplap is often used to describe any rabbeted siding material that overlaps in a similar fashion.
In interior design , shiplap is a style of wooden wall siding characterized by long planks, normally painted white, that are mounted horizontally with a slight gap between them in a manner that evokes exterior shiplap walls. A disadvantage of the style is that the gaps are prone to accumulating dust. [ 2 ]
Installing shiplap horizontally in a room can help carry the eye around the space, making it feel larger. Installing it vertically helps emphasize the height of the room, making it feel taller. Rectangular shiplap pieces can be placed in a staggered zig-zag layout to add texture and enhance the size of the room. [ 3 ] Shiplap can also be installed on the ceiling, to draw the eye upwards. [ 4 ] | https://en.wikipedia.org/wiki/Shiplap |
Shipping container architecture is a form of architecture that uses steel intermodal containers (shipping containers) as the main structural element . It is also referred to as cargotecture or arkitainer , portmanteau words formed from " cargo " and " architecture ". This form of architecture is often associated with the tiny-house movement as well as the sustainable living movement.
The use of containers as building materials has been growing in popularity due to their strength, wide availability, low cost, and eco-friendliness. [ 1 ] [ 2 ]
Due to their shape and material, shipping containers have the ability to be customized in many different ways and can be modified to fit various purposes. Standardized dimensions and various interlocking mechanisms make these containers modular , allowing them to be easily combined into larger structures that follow modular design . This also simplifies any extensions to the structure as new containers can easily be added on to create larger structures. When empty, shipping containers can be stacked up to 12 units high.
Because shipping containers are designed to be stacked in high columns and to carry heavy loads, they are also strong and durable. They are designed to resist harsh environments, such as those on ocean-going vessels . Shipping containers conform to standard shipping sizes, which makes pre-fabricated modules easily transportable by ship , truck , or rail .
Shipping container construction is still less expensive than conventional construction, despite metal fabrication and welding being considered specialized labor (which usually increases construction costs). Unlike wood-frame construction , attachments must be welded or drilled to the outer skin, which is more time-consuming, and requires different job site equipment.
As a result of their widespread use, new and used shipping containers are available globally. This availability makes building tiny or container houses more affordable. Depending on the desired specifications and materials used, a container home will often cost less compared to a traditional house [ 3 ]
Shipping container construction requires fewer resources, meaning the quantity of traditional building materials needed (e.g. bricks and cement) are reduced. When upcycling shipping containers, thousands of kilograms of steel are saved. For example, a 12-metre-long (39 ft) shipping container weighs over 3,500 kilograms (7,700 lb).
Containers used for human occupancy in an environment with extreme temperature variations will normally have to be better insulated than most brick, block , or wood structures because steel conducts heat very well. Humidity can also affect steel structures, so when moist interior air condenses against the steel, it becomes humid and forms rust if the steel is not sealed and insulated.
While in service, containers may be damaged by friction , handling collisions , and the force of heavy loads overhead during ship transits. Additionally, although the two ends of a container are extremely strong, the roof is not. In the case of a 20-foot-long (6.1 m) container, the roof is built and tested only to withstand a 300 kg (660 lb) load, applied to an area of 61 cm by 30.5 cm (2 ft by 1 ft) in the weakest part of the roof. [ 4 ] Companies inspect containers, and condemn them if they present cracked welds, twisted frames, or pin holes, among other faults.
Shipping containers possess the capacity to be organized into modular arrangements, thereby creating expansive structures. Nevertheless, deviating from the established standard dimensions, typically 20 feet (6.1 m) or 40 feet (12 m) in length, can engender inefficiencies in terms of both temporal and financial resources. Containers surpassing the 40 ft (12 m) length threshold may encounter challenges during navigation within residential vicinities.
The transportation and construction of shipping container structures can be expensive due to size and weight, and often require the use of cranes or forklifts . This is in contrast to more traditional construction materials like brick or lumber , which can be handled manually and used for construction even at elevated heights.
Obtaining building permits for shipping container homes can be troublesome in regions where municipalities are not familiar with shipping container architecture, because the use of steel for construction is usually for industrial rather than residential structures. In the United States , some shipping container homes have been built outside of various city zoning areas, where no building permits are required.
To meet Australian government shipping quarantine requirements, most container floors are treated with insecticides containing copper (23–25%), chromium (38–45%) and arsenic (30–37%) when manufactured. Chromium and arsenic are known carcinogens . If shipping containers are repurposed for human habitation, these floors should be safely removed, disposed, and replaced. Because shipping containers can carry a wide variety of industrial cargo, spillages or contamination may also occur inside the container, and will have to be cleaned before habitation. Before human habitation, ideally all internal surfaces should be abrasive blasted to bare metal, and re-painted with a non-toxic paint system. Solvents released from paint, and sealants used in manufacture, might also be harmful to human health.
The use, size, location and appearance of structures based on shipping containers vary widely.
When futurist Stewart Brand needed a place to assemble the material he would use to write How Buildings Learn , he converted a shipping container into an office space in the early 1990s. The conversion process is described in How Buildings Learn itself.
In 2000, the firm Urban Space Management completed a project called Container City I in the Trinity Buoy Wharf area of London . The firm has gone on to complete additional container-based building projects, with more underway. In 2006, the Dutch company Tempohousing finished, in Amsterdam , the biggest container village in the world: 1,000 student homes from modified shipping containers from China. [ 5 ]
In 2002, standard ISO shipping containers began to be modified for use as stand-alone on-site wastewater treatment plants. This use of containers creates a cost-effective, modular, and customizable solution to on-site wastewater treatment, eliminating the need for construction of a separate building to house the treatment system. [ 6 ]
In 2006, Southern California Architect Peter DeMaria designed the first two-story shipping container home in the U.S., as an approved structural system under the strict guidelines of the nationally recognized Uniform Building Code (UBC). Named the Redondo Beach House, it inspired the creation of Logical Homes , a cargo container–based pre-fabricated home company. In 2007, Logical Homes created its flagship project, the Aegean, for the Computer Electronics Show in Las Vegas , Nevada.
In 2006, Village Underground constructed a series of not-for-profit artists' workspaces in Shoreditch , London. Developing the concept further, Auro Foxcroft constructed recycled shipping container architecture that incorporated retired London Underground carriages.
In 2007, entrepreneur Brian McCarthy developed prototypes of shipping container housing for maquiladora workers in Mexico. [ 7 ]
Hybrid Cargotecture Development (HCD), headquartered in Sri Lanka, is a leader in the field of containerized construction. Known for its eco-friendly approach, the company specializes in transforming upcycled shipping containers into luxury homes, chalets, offices, and resorts. With a focus on innovation and sustainability, HCD has pioneered hybrid designs that combine the durability of shipping containers with modern, high-end finishes.
HCD has completed several notable projects within Sri Lanka, including containerized housing solutions for resorts and eco-tourism initiatives. The company has also expanded internationally, exporting container homes and offices to markets in Australia, the USA, Canada, and Germany. These projects highlight the versatility and global appeal of containerized housing, particularly for sustainable and fast-construction solutions.
HCD continues to contribute to the container home industry by addressing housing and commercial needs while promoting environmental sustainability through the use of repurposed materials.
In 2010, German architect and production designer Stefan Beese used six 12-metre-long (39 ft) shipping containers to create a large viewing deck and VIP lounge area for the Voodoo Music Experience , New Orleans , as a substitute for typical grand stand scaffolding . The containers double as storage space for other festival components throughout the year. The two top containers are cantilevered 2.7 metres (8.9 ft) on each side, creating two balconies that are prime viewing locations. Each container was perforated with cutouts spelling the word "VOODOO".
In the United Kingdom, walls of containers filled with sand have been used as large sandbags to protect against flying debris from exploding ceramic insulators in electricity substations .
In October 2013, two barges owned by Google with superstructures made out of shipping containers received media attention amid speculation about their purpose. [ 8 ]
Empty shipping containers are commonly used as market stalls and warehouses in the countries of the former USSR .
The biggest shopping mall or organized market in Europe is made up of alleys formed by stacked containers, on 69 hectares (170 acres) of land, between the airport and the central part of Odesa , Ukraine . Informally named " Tolchok ", and officially known as the Seventh-Kilometer Market , it has 16,000 vendors and employs 1,200 security guards and maintenance workers.
In Central Asia , the Dordoy Bazaar in Bishkek , Kyrgyzstan is almost entirely composed of double-stacked containers. It is popular with travelers coming from Kazakhstan and Russia for the cheap prices and plethora of knock off designers.
In 2011, the Cashel Mall in Christchurch , New Zealand reopened in a series of shipping containers, months after it had been destroyed in the earthquake that devastated the city's central business district. [ 9 ] Starbucks Coffee has also built a store using shipping containers. [ 10 ] A pop-up shopping mall called Boxpark was also created in Shoreditch , London, in 2011, followed by other locations in the Greater London area. [ 11 ] A pop-up shopping mall, Common Ground, was created in Seoul , South Korea in 2016. [ 12 ]
Shipping containers have also been used as:
The abundance and relative cheapness of these containers during the last decade comes from the deficit in manufactured goods coming from North America in the last two decades. These manufactured goods come to North America from Asia and, to a lesser extent, Europe, in containers that often have to be shipped back empty, or "deadhead", at considerable expense. It is often cheaper to buy new containers in Asia than to ship old ones back. Therefore, new applications are sought for the used containers that have reached their North American destination.
Containers have been utilized by architects and individuals to build diverse structures, including homes , offices , apartments , schools , dormitories , artists studios , and emergency shelters . Additionally, containers have found use as swimming pools and temporary secure spaces on construction sites and other venues.
CONEX containers were developed by Malcom McLean to standardize the intermodal shipping unit. CONEX containers may or may not meet the requirements of local building codes. As they are not field erected, a registered engineer or architect must verify that the containers comply with the structural requirements of the building code. The 2021 ICC [ 25 ] code was amended to address CONEX containers.
Phillip C. Clark filed for a United States patent on November 23, 1987, described as "Method for converting one or more steel shipping containers into a habitable building at a building site and the product thereof". This patent was granted August 8, 1989 as patent 4854094. The patent documentation shows what are possibly the earliest recorded plans for constructing shipping container housing and shelters by laying out some very basic architectural concepts. Regardless, the patent may not have represented novel invention at its time of filing. Paul Sawyers previously described extensive shipping container buildings used on the set of the 1985 film Space Rage Breakout on Prison Planet .
Other examples of earlier container architecture concepts include a 1977 report entitled "Shipping Containers as Structural Systems", [ 26 ] investigating the feasibility of using 20-foot (6.1 m) shipping containers as structural elements by the US military .
During the 1991 Gulf War , containers saw considerable nonstandard uses, not only as makeshift shelters, but also for housing of US soldiers. The shipping containers were equipped with air conditioning units and provided shelter as well as protection from artillery shelling.
It has been rumored that some shipping containers were used for transportation of Iraqi prisoners of war , with holes cut in the containers to allow for ventilation. Containers continue to be used for military shelters, often additionally fortified by adding sandbags to the side walls, to protect against weapons such as rocket-propelled grenades ("RPGs").
Shipping container architecture has inspired the reality television series Containables ( DIY ) and Container Homes ( HGTV ), in addition to being featured in episodes of Grand Designs ( Channel 4 ) and Amazing Interiors ( Netflix ). | https://en.wikipedia.org/wiki/Shipping_container_architecture |
A shipping container clinic is a type of shipping container architecture using intermodal containers (shipping containers) as the structural element of a medical clinic that can be easily deployed to remote regions of the world. Shipping containers are ideal because of their inherent strength, wide availability and relatively low cost. In addition, and most relevant, shipping containers can be deployed anywhere in the world with the clinic already assembled within the container. This means pop-up clinics can be operational within days after deployment.
Several organizations have developed the concept of shipping container clinics.
In 2005, Hospitals of Hope produced a "Clinic In A Can" in a 45-foot trailer that was sent to Les Cayes , Haiti to provide medical relief. [ 1 ] The 45 foot trailer is converted into five medical rooms, with each one being approximately 70 square feet. The container has since helped Hospitals of Hope provide care to over 30,000 residents of Haiti. In 2006, Pulitzer Prize winning author, Laurie Garrett , worked with Rensselaer Polytechnic Institute to create a prototype "Doc In A Box" based on Garrett's conceptual framework. [ 2 ] [ 3 ]
In June 2010, Hospitals of Hope sent two "Clinic In A Cans" to Haiti in partnership with Heart to Heart International in response to an earthquake. [ 4 ] The containers were both 40 feet long and cost around $12,000 to build. In November 2010, Containers 2 Clinics sent a prototype clinic to be used on site at Grace Children's Hospital in Port-au-Prince , Haiti . [ 5 ] [ 6 ]
In April 2011, a three-unit Clinic In A Can was shipped to Haiti in partnership with Aslan Youth Ministries. [ 7 ] This small hospital will be operated by Aslan Youth Ministries, an organization working in the north-east of Haiti. With a fault line running under where they work, steel shipping containers are safer than a concrete structure.
In August 2012, Clinics4All established its Global Clinic Donation Program (GCDP) to provide medical clinics free of charge to third-world governments through their respective departments or Ministries of Health as a means of improving access to healthcare in medically under-served and remote areas, particularly for children and women. [ citation needed ]
In March 2013, Clinic In A Can shipped a solar powered clinic to Mirebalais , Haiti in partnership with Global Vision Citadelle Ministries, as well as a radiology Clinic In A Can to Freetown , Sierra Leone . [ 8 ] [ 9 ] In July 2013, Arkitainer opened its doors as a UK based company specialising in the use of shipping containers for various community based projects. A recent proposal for a residential community complete with clinics, schooling and vocational training for Cape Town is currently underway. [ citation needed ]
Since 2017, Cipla, one of South Africa's largest pharmaceutical companies, has deployed moveable clinics to deprived areas to help with South Africa's COVID-19 vaccination program. As part of the Cipla Foundation's Sha’p Left project, these containers have been used as Centralised Chronic Medicine Dispensing and Distribution (CCMDD) points across South Africa, with the bulk of the projects in Gauteng and KwaZulu-Natal. [ 10 ] | https://en.wikipedia.org/wiki/Shipping_container_clinic |
Shire plc was a UK -founded Jersey -registered specialty biopharmaceutical company. Originating in the United Kingdom with an operational base in the United States, its brands and products included Vyvanse , Lialda , and Adderall XR . Shire was acquired by Takeda Pharmaceutical Company on 8 January 2019.
Shire was a global biotechnology company focused on serving people with rare diseases and other highly specialized conditions. The company's products were available in more than 100 countries across core therapeutic areas including Hematology , Immunology , Neuroscience , Lysosomal Storage Disorders , Gastrointestinal / Internal Medicine / Endocrine and Hereditary Angioedema; a growing franchise in Oncology; and an emerging, innovative pipeline in Ophthalmics .
The original corporate headquarters was located in Basingstoke , Hampshire, England. Main offices are located in Dublin , Ireland, the United States in Cambridge , Massachusetts, and Chicago , Illinois, and in Zug, Switzerland . In addition, Shire owns manufacturing sites in Lexington , Massachusetts, and Social Circle , Georgia. Shire's headquarters in Lexington, Massachusetts, will be integrated with Takeda's new U.S. headquarters, which is being relocated from Deerfield, Illinois , to the Boston area.
Shire was founded in 1986 in the UK by five entrepreneurs: Harry Stratford , Dennis Stephens, Peter Moriarty, Geoff Hall and Dr Jim Murray. [ 6 ] Under the management of Rolf Stahel , Shire was first listed on the London Stock Exchange in 1996. Shire's initial products were calcium supplements ( Calcichew-D 3 ) for patients seeking to treat or prevent osteoporosis . In 1997 the company acquired Pharmavene for £105 million in order to access Pharmavene's drug delivery methods. [ 7 ] Later in the same year Shire acquired Richwood Pharmaceutical Company, forming Shire-Richwood Inc. [ 8 ]
In 2001 the company acquired Biochem Canada. [ 9 ] Shire's next acquisition didn't come until 2005 when it acquired Transkaryotic Therapeutics [ 10 ] and two years later – in 2007 – New River Pharmaceuticals Inc, for a then company record of $2.6 billion. [ 11 ] With the purchase of New River, Shire gained access and ownership of Vyvanse . A year later the company acquired the German company Jerini , for $521 million. Jerini focused on treating hereditary angioedema . [ 12 ]
In 2008, in reaction to new taxation measures announced by the UK government in the treatment of royalties on patents, the company moved its tax domicile to Dublin , Ireland. [ 13 ]
2010 saw a change in company strategy, with the company seeking to expand through mergers and acquisitions - culminating in the company becoming one of the most acquisitive in the industry. In 2010 the company acquired Movetis , a Belgian company focusing on gastrointestinal products for $565 million, [ 14 ] a year later it acquired regenerative medicine manufacturer Advanced BioHealing. [ 15 ] In 2012 the company acquired FerroKin BioSciences for $325 million along with FerroKins lead iron chelator - FBS0701. [ 16 ] 2013 saw the company complete its highest number of acquisitions with Lotus Tissue Repair, Inc. (lead compound, ABH001), [ 17 ] SARcode Bioscience Inc., [ 18 ] with the last being ViroPharma . Shire changed the name of ViroPharma to Shire Viropharma Inc. upon acquisition and on their final day of trading the company was valued at $3.3 billion. [ 19 ] At $4.2 billion, ViroPharma set a new company record. [ 20 ] In 2014 Shire acquired two rare disease drug companies: Fibrotech [ 21 ] with its antifibrotic compounds for $75 million, and Lumena, a company researching rare gastro-intestinal and hepatic compounds, for $260 million. [ 22 ]
In 2015, NPS Pharmaceuticals was acquired for $5.2 billion, bringing along its rare disease drugs Gattex and Natpara . [ 23 ] On their final day of trading, NPS had a market capitalisation of $4.99 billion. The company also acquired, later in the same year, Meritage Pharma for $245 million, Foresight Biotherapeutics for $300 million [ 24 ] and Dyax for $6.5 billion. [ 25 ] [ 26 ] The purchases bolstered Shires gastro-intestinal and rare disease sectors, with Phase-III-ready treatment - Budesonide - for the treatment of eosinophilic esophagitis . As well as expanding the company's pipeline with a late-stage treatment candidate for infectious conjunctivitis with lead candidate FST-100 and increasing the company's rare disease catalogue with Dyax's portfolio of plasma kallikrein inhibitors against hereditary angioedema (led by the approved drug Kalbitor and the Phase III DX-2930). In January 2016, the company made its most significant purchase, with the $32 billion acquisition of Baxalta (which had been spun-off from Baxter the previous year [ 27 ] ), creating the largest global biotech company focused solely on rare diseases. [ 28 ]
In April 2018, Shire agreed to sell its oncology business to French pharmaceutical company Servier for £1.7billion. [ 29 ]
On 20 June 2014, Shire rejected a takeover attempt by AbbVie . AbbVie offered £46.11 per share (£27.3 billion or $46.5 billion in total). [ 30 ] On 8 July, the offer was increased to $51.5 billion. [ 31 ] On 18 July, it was announced that AbbVie would acquire Shire for $54.8 billion. [ 32 ] On 15 October, news broke suggesting AbbVie was reconsidering their proposed takeover deal due to changes in US "Tax Inversion" law [ 33 ] and on 16 October AbbVie's board recommended that shareholders vote against the deal. [ 34 ] This news sent Shire's share price down over 27%; however, AbbVie would be subject to a $1.6 billion break-up fee, payable to Shire. [ 35 ] On 21 October, the merger was called off. [ 36 ]
In April 2018, reported that Takeda Pharmaceutical Company had an approach to acquire Shire. Days later Shire announced they had rejected all three Takeda bids. The first bid valued the business at £41 billion (£28 per Shire shares paid in Takeda shares plus £16 per share in cash), the second £43 billion (£28.75 per Shire shares paid in Takeda shares plus £16.75 per share in cash) and the third £44 billion (£28 per Shire shares paid in Takeda shares plus £17.75 per share in cash). [ 37 ] Reuters also reported interest from Allergan [ 38 ] however they ruled themselves out a day later. [ 39 ] A day later Takeda increased their offer with a fourth bid, to £26 per Shire shares paid in Takeda shares plus £21 per share in cash - giving a total value of £44.3 billion ($62.1 billion). [ 40 ] On 24 April, Takeda submitted an enhanced fifth bid for the company. [ 41 ] On 25 April, Shire said that they will recommend the revised £45.8 billion ($64 billion) offer to their shareholders. The enhanced offer included a more generous cash component, with the deal offering £21.76 ($30.33) in cash for each Shire ordinary share. [ 42 ] [ 43 ] [ 44 ] The same day, GlaxoSmithKline ruled out making any form of counter-bid. [ 45 ] On 8 May 2018, an agreement was finally reached in which Shire was sold to Takeda in a $62 billion deal. [ 46 ] [ 47 ] Takeda's acquisition of Shire closed on 8 January 2019. [ 48 ]
The Annual Revenue figures in the following table were drawn from the company's 2015 preliminary results. [ 49 ]
In July 2014, Shire licensed the rights to the investigational Hunter syndrome compound, AGT-182, from ArmaGen for up to $225 million. [ 50 ]
The Annual Revenue figures in the following Table were drawn from the company's 2015 preliminary results. [ 49 ]
Flemming Ørnskov , was the company's chief executive officer through 8 January 2019 with Takeda's acquisition of Shire. [ 51 ] Ginger Gregory as chief human resources officer, Jeffrey Poulton as CFO , and Philip Vickers as head of R&D . [ 52 ] James Bowling vacated his position as interim CFO in the aftermath of the collapse of the AbbVie inversion deal. [ 53 ] The chair of Shire's board of directors was Susan Kilsby. [ 54 ]
In September 2014, Shire reached a $56.5 million settlement with the U.S. Department of Justice for alleged violations of the False Claims Act . The Justice Department alleged that Shire had improperly marketed and promoted Adderall XR, Daytrana, Vyvane, Pentasa, and Lialda during various periods between 2004 and 2010. The allegations included claims that Shire had made exaggerated and false statements regarding product safety, promoted medications for non- FDA approved off-label use, and marketed products on unsubstantiated claims of beneficial side effects, including reductions in criminality, traffic accidents, sexually transmitted infections , and divorce rates. [ 55 ] [ 56 ] [ 57 ]
In August 2017, Shire reached a $350 million settlement with the Department of Justice for violations of the same act, regarding the unlawful promotion of Shire's product Dermagraft. [ 58 ] [ 59 ] | https://en.wikipedia.org/wiki/Shire_(pharmaceutical_company) |
" Shirt-sleeve environment " is a term used in aircraft design to describe the interior of an aircraft in which no special clothing need be worn. Early aircraft had no internal pressurization , so the crews of those that reached the stratosphere had to be garbed to withstand the low temperature and pressure of the air outside. Respirator masks needed to cover the mouth and nose. Silk socks were worn to retain heat. Sometimes leather clothing , such as boots, were electrically heated. When jet fighter aircraft reached still higher altitudes, something similar to a space suit had to be worn, and pilots of the highest reconnaissance aircraft wore real space suits.
Commercial jet airliners fly in the stratosphere, but because they are pressurized, they could be said to have a shirt-sleeve environment. Crews of the US Apollo spacecraft always began the flight phases of launch , docking , and re-entry in space suits, although they could remove them for many hours. The Soviets tried to perfect this to save weight. This worked well, until an accidental depressurization on entry resulted in the deaths of an entire Soyuz crew . Protocols were changed shortly thereafter to require at least partial spacesuits . Early Soyuz spacecraft had no provision for space suits in the re-entry module , although the orbital module was intended for use as an airlock . Thus these operated in a shirt-sleeve environment except for spacewalks .
This term is also used in science fiction to describe an alien planet with an atmosphere breathable by humans without special equipment. [ 1 ]
The Space Shuttle 's Spacelab Habitable module was an area with expanded volume for astronauts to work in a shirt sleeve environment and had space for equipment racks and related support equipment for operations in Low Earth orbit . [ 2 ]
One of the goals for MOLAB rover was to achieve a shirt-sleeve environment (compared to the Lunar Roving Vehicle which was open to space and required the use of space suits to operate). [ 3 ] One of the considerations was the habitable volume that could be occupied. [ 3 ] | https://en.wikipedia.org/wiki/Shirt-sleeve_environment |
A shit flow diagram , also known as an SFD or excreta flow diagram , is a tool used to visually depict the management of human waste within urban sanitation systems . It distinguishes between safely and unsafely managed human excreta through color-coded arrows, providing insights into areas needing sanitation improvements. Initially developed through international collaboration, SFDs are commonly employed in urban sanitation planning and policy formulation, especially in low- and middle-income countries. Their creation involves data collection, stakeholder engagement, and systematic analysis. While SFDs offer valuable visual representations, their accuracy can be limited by data reliability issues and technical constraints, which ongoing methodological developments aim to address.
A shit flow diagram visually represents the flow of human excreta through various stages of the sanitation chain in urban areas, highlighting safe versus unsafe management practices. An SFD employs colored arrows to illustrate how excreta moves through containment, emptying, transport, treatment , and disposal or reuse stages. Green arrows indicate excreta flows that are safely managed—effectively contained, properly transported, adequately treated, and safely disposed of or reused—while red arrows represent unsafe management, such as inadequate containment, improper transport, lack of treatment, or unsafe environmental discharge, posing significant health and environmental risks. The width of each arrow in the diagram proportionally reflects the percentage of the population's excreta represented by that particular flow, clearly communicating the relative scale of safe and unsafe sanitation practices. [ 1 ]
The primary stages represented in an SFD include containment of excreta at the source (e.g., pit latrines , septic tanks , sewer systems ), emptying and transporting excreta or fecal sludge , the subsequent treatment process to reduce harmful pathogens and pollutants, and finally, disposal or reuse, indicating whether excreta are safely managed or unsafely discharged into the environment. Through this visualization, authorities can readily identify specific points in the sanitation service chain that require intervention, facilitating targeted improvements and enabling effective monitoring towards achieving safely managed sanitation. [ 2 ]
The shit flow diagram emerged as a practical tool for visualizing and communicating urban sanitation issues in low- and middle-income countries. Developed through the collaborative efforts of organizations such as the Sustainable Sanitation Alliance (SuSanA), Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ), the World Bank , the Swiss Federal Institute of Aquatic Science and Technology (EAWAG), and the Bill and Melinda Gates Foundation , the SFD has gained traction for its ability to clearly and concisely represent complex sanitation data, aiding decision-making and advocacy among diverse stakeholders. [ 3 ] [ 4 ]
Early prototypes of fecal waste flow diagrams were developed independently before the formalization of the SFD concept. Notable examples include those created for Kumasi, Ghana , in 1993 and Dakar, Senegal , in 2011, where the term "sanitation cityscape" was initially employed. [ 5 ] [ 6 ] The importance of analytical tools to comprehensively address sanitation issues, including underlying policy, regulatory, institutional, and financial challenges, was strongly emphasized during the second Fecal Sludge Management Conference (FSM2) held in Durban, South Africa , in 2012. [ 7 ] Subsequently, the Water and Sanitation Program (WSP) of the World Bank conducted a comprehensive 12-city study in 2012-13. [ 8 ] [ 9 ] In 2014, the SFD Promotion Initiative was established with a grant from the Bill and Melinda Gates Foundation, leading to further refinement and standardization of the methodology. This initiative developed comprehensive manuals, tools, and procedural guidelines to ensure consistency and comparability in SFD production worldwide. It also introduced the concept of assessing the enabling environment, which encompasses policies, regulatory frameworks, and institutional capacities necessary for sustainable sanitation services. [ 4 ] [ 10 ] [ 9 ]
Developing a shit flow diagram involves several methodological steps, combining primary data collection, literature reviews, stakeholder consultations, and data analysis. Initially, an extensive literature review is conducted to gather existing secondary data from government reports, academic publications, and international sanitation assessments. This secondary data provides baseline information and highlights potential data gaps or inconsistencies that need further validation. [ 11 ]
Primary data collection is undertaken through field observations and key informant interviews. Field observations typically involve examining the condition of sanitation infrastructure, the frequency and methods of emptying, transport logistics, and the operational status of treatment facilities. Key informant interviews, often conducted with local government officials, sanitation service providers , and community representatives, provide valuable insights into local practices, institutional arrangements, and operational challenges. [ 12 ]
Data collected through these methods is then systematically analyzed to map the sanitation service chain accurately. This analysis includes assessing the proportion of excreta that is safely managed at each stage, identifying potential leakage points, and determining the percentage of excreta flows that are unsafely discharged into the environment. Specialized tools, such as the SFD Graphic Generator, are used to visually represent the analyzed data, ensuring clarity and consistency across different diagrams and locations. [ 13 ] [ 14 ]
Throughout this process, engaging with stakeholders, authorities, and participants is essential to validate findings, foster ownership of the results, and encourage actionable insights for local improvements. Regular consultations and workshops are often held to review preliminary results, refine data accuracy, and discuss potential interventions for identified issues. [ 15 ] [ 16 ]
Babati, Tanzania : Babati experiences rapid urban growth but faces significant sanitation management challenges. Approximately 82% of housing units have sanitation facilities, yet only 31% of the fecal sludge generated is safely managed onsite. A major issue is inadequate containment, with around 69% of fecal waste unsafely discharged into the environment or improperly contained, posing significant risks to groundwater quality . The town lacks centralized sewerage and fecal sludge treatment facilities, forcing reliance on onsite sanitation systems. Data collection and analysis using the shit flow diagram methodology revealed gaps between reported sanitation access and actual conditions. This analysis prompted local authorities to recognize the importance of implementing effective fecal sludge management, rather than attempting to introduce a central sewer system prematurely. [ 17 ]
Kampala, Uganda : An SFD revealed that Greater Kampala relies heavily on onsite sanitation systems, with approximately 99% of its population using septic tanks, ventilated improved pit latrines, or traditional pit latrines. A significant challenge is the low rate of fecal sludge emptying: a study found that 53% of septic tanks have never been emptied, despite high accessibility to emptying services. Additionally, only about 35% of fecal sludge produced is collected and delivered to the Lubigi fecal sludge treatment plant. The treatment plant, operating at its maximum capacity, uses manual screening, grit removal, and drying beds. The city's existing sewage infrastructure primarily serves commercial and institutional users rather than residential ones. Addressing these issues requires substantial infrastructure investments to improve the fecal sludge management system, expand treatment capacity, and enhance emptying services. [ 18 ]
Alappuzha, India : Alappuzha , also called Alleppey, located in Kerala, India , faces significant sanitation challenges due to its flat topography, proximity to the Arabian Sea and Vembanad Lake , and a high groundwater table. Despite universal access to toilets, the municipality lacks facilities for treating sewage or fecal sludge, causing severe environmental contamination. Most onsite sanitation systems, including septic tanks and pit latrines, are inadequately designed and irregularly emptied, leading to untreated waste contaminating local groundwater and canals. Tests indicated widespread contamination, with E. coli detected in the majority of water samples. Additionally, the town's canals suffer from eutrophication due to nutrient-rich seepage from improperly managed sanitation systems, negatively affecting tourism, one of Alappuzha's key economic activities. The SFD for Alappuzha clearly highlights these issues, emphasizing the urgent need for improved fecal sludge management and infrastructure investments to safeguard environmental and public health. [ 19 ]
Guwahati, India : In Guwahati , sanitation sustainability is complicated by frequent seasonal flooding and poor sanitation infrastructure design. Despite a high reported coverage of improved sanitation facilities (93.4%), actual management practices differ significantly, leading to regular shifts between improved and unimproved sanitation statuses depending on seasonal flooding. Many latrines become flooded or inaccessible during monsoons , forcing residents to resort to "sanitation stacking," where multiple sanitation methods, including open defecation , are used simultaneously depending on seasonal and environmental conditions. Additionally, many septic tanks discharge effluent directly into marshlands , severely compromising environmental safety. Shit flow diagrams for the area reveal that, although officially considered "improved," nearly half of the sanitation systems (approximately 46%) safely manage fecal sludge, highlighting significant discrepancies between official classifications and actual on-the-ground sanitation practices. [ 20 ]
Shit flow diagrams face several challenges and limitations. Reliable data collection is often hampered by limited local technical capacity, unclear definitions of sanitation containment systems, and insufficient performance data, particularly regarding onsite sanitation. Informal sanitation practices, inadequate record-keeping, and discrepancies between reported and actual conditions can significantly impact the accuracy and reliability of SFDs. Additionally, widespread improper disposal practices and insufficient reliable data on treatment outcomes make it challenging to accurately evaluate sanitation safety. [ 21 ]
Proposed improvements for SFDs include refining methodologies to better differentiate between types of sanitation systems and management practices, developing clearer guidelines for data collection and interpretation, and enhancing local capacity through targeted training programs. Furthermore, expanding the use of digital and mobile tools to streamline data collection and analysis is anticipated to improve the accuracy and efficiency of SFD generation. Integrating environmental considerations alongside public health criteria will also enhance the utility of SFDs for comprehensive urban sanitation planning. [ 22 ] | https://en.wikipedia.org/wiki/Shit_flow_diagram |
In electrical engineering , a shmoo plot is a graphical display of the response of a component or system varying over a range of conditions or inputs.
The origin of the shmoo plot is unclear. It is referenced in a 1966 IEEE paper. [ 1 ] Another early reference is in manuals for IBM 2365 Processor Storage . [ 2 ]
The invention of the shmoo plot is sometimes credited to VLSI Hall Of Fame inductee Robert Huston (1941–2006). [ 3 ] But this is unlikely because Huston did not begin working as a test engineer until 1967. [ 4 ]
The plot takes its name from the Shmoo , a fictional species created by Al Capp in the cartoon Li'l Abner . These small, blob-like creatures have shapes similar to the "working" volumes that would be enclosed by shmoo plots drawn against three independent variables (such as voltage, temperature, and response speed).
Semiconductor chips do not usually exhibit "shmoo" shape plots. [ citation needed ] Historically, testing of magnetic core memory arrays produced the "shmoo" shape and the term continued into the semiconductor era.
Shmoo plots are often used to represent the results of the testing of complex electronic systems such as computers or integrated circuits such as DRAMs , ASICs or microprocessors. The plot usually shows the range of conditions in which the device under test operates (in adherence with some remaining set of specifications).
For example, when testing semiconductor memory : voltages , temperature , and refresh rates can be varied over specified ranges and only certain combinations of these factors will allow the device to operate. Plotted on independent axes (voltage, temperature, refresh rates), the range of working values will enclose a three-dimensional, usually oddly-shaped volume. Other examples of conditions and inputs that can be varied include frequency , temperature , timing parameters, system- or component-specific variables, and even varying knobs tweakable during silicon chip fabrication producing parts of varying quality which are then used in the process.
Often one 'knob' or variable is plotted on one axis against another knob or variable on another axis, producing a two-dimensional graph. This allows the test engineer to visually observe the operating ranges of the device under test. This process of varying the conditions and inputs to the component or system may sometimes be referred to as 'shmooing' but more officially known as electrical testing or qualification. Automatic test equipment often contains software features that allow automated shmooing of a part.
Automated test equipment have traditionally generated a two-dimensional, ASCII form of the shmoo plot that uses an "X" to represent functional points and blank space for non-functional points. In modern times plots with two colors (e.g. red/green) or even multi colored plots in form of digital spread sheet documents and alike became also common, even if the traditional form is still in use. [ 5 ] For testing efficiency sometimes only the border of interest (where a certain value changes its state) is backed up with data in the diagrams thus (often reasonably) assuming the areas outside those transition will stay at those state. [ 6 ]
If sufficiently-wide ranges of the two independent variables were to be tested, a normal shmoo plot would show an operating envelope of some shape not unlike Al Capp's Shmoo , but in practice, this might damage the device under test , and finer-grained views are of much more interest, particularly focusing on published component margins (e.g., - 5% Vcc). When this is done, the operating envelope typically extends to the border of the plot in one or more directions.
One example of such “shmooing” is the procedure for optimising the two operating variables of the Read Only Storage (ROS) in the IBM S/360 Model 65 Central Processing Unit (CPU). While the CPU is running a diagnostic test program the ROS bias voltage and time delay are varied and the points where the ROS generates errors are manually plotted on a graphical shmoo plot (see illustration). To pass the test the shmoo plot must be large enough to contain a rectangle which represents the minimum permissible error-free range of bias voltage and time delay. The optimum ROS bias voltage and time delay will be indicated by a point at the centre of the rectangle.
Sometimes a shmoo plot has an unusual and surprising shape, and while it is difficult to determine the exact cause, it is sometimes due to some unusual defect (perhaps in only part of a circuit) coupled with otherwise normal operation. In other cases, it might be an artifact of the electrical testing setup or the test program used, in particular a race condition . As such, a shmoo plot can be a useful test setup verification tool.
A limitation of the technique is that the extended duration of testing of the device may cause additional internal device heating, resulting in a skewing of the data (later tested cells on the plot may perform worse than earlier ones). One way of avoiding this is to exercise the device thoroughly in a similar manner immediately before the actual shmoo test. | https://en.wikipedia.org/wiki/Shmoo_plot |
Shneider-Miles scattering (also referred to as collisional scattering [ 1 ] or quasi-Rayleigh scattering [ 2 ] ) is the quasi - elastic scattering of electromagnetic radiation by charged particles in a small-scale medium with frequent particle collisions. Collisional scattering typically occurs in coherent microwave scattering of high neutral density, low ionization degree microplasmas such as atmospheric pressure laser-induced plasmas. [ 3 ] Shneider-Miles scattering is characterized by a 90° phase shift between the incident and scattered waves and a scattering cross section proportional to the square of the incident driving frequency ( ω 2 {\displaystyle \omega ^{2}} ). Scattered waves are emitted in a short dipole radiation pattern. [ 1 ] The variable phase shift present in semi-collisional scattering regimes allows for determination of a plasma's collisional frequency through coherent microwave scattering .
Mikhail Shneider and Richard Miles first described the phenomenon mathematically in their 2005 work on microwave diagnostics of small plasma objects. [ 4 ] The scattering regime was experimentally demonstrated and formally named by Adam R. Patel and Alexey Shashurin and has been applied in the coherent microwave scattering diagnosis of small laser-induced plasma objects. [ 1 ]
A plasma, consisting of neutral particles, ions, and unbound electrons, responds to the oscillating electric field of incident electromagnetic radiation primarily through the motion of electrons (ions and neutral particles can often be regarded as stationary due to their larger mass). If the frequency of the incident radiation is sufficiently low and the plasma frequency is sufficiently high (corresponding to the Rayleigh scattering regime), the electrons will travel until the plasma object becomes polarized, counteracting the incident electric field and preventing further movement until the incident field reverses direction. If the frequency of the incident radiation is sufficiently high and the plasma frequency is sufficiently low (corresponding to the Thomson scattering regime), electrons will only travel a short distance before the electric field reverses direction, making collisions with other particles unlikely during a given oscillation.
If the frequency on the incident radiation is intermediate and a high density of neutral particles and ions is present, electrons will travel far enough to collide many times with other particles but not far enough to significantly polarize the plasma object. This characterizes the collisional scattering regime. The linear oscillation of unbound electrons in a relatively-small space gives rise to a short-dipole radiation pattern.
This is analogous to a spring-mass-damper system , where the polarization of the plasma object creates the restoring force and the drag due to collisions with other particles creates the damping force. The phase shift of the scattered wave is 90º in the Shneider-Miles regime due to the drag force being dominant.
Note that, in this context, Rayleigh scattering is regarded as ω 4 {\displaystyle \omega ^{4}} volumetric small particle scattering rather than an even broader short-dipole approximation of the radiation. Otherwise, Thomson scattering would fall under the banner of "Rayleigh". Mie scattering experiences a similar ambiguity.
The scattering cross section of an object ( σ {\displaystyle \sigma } ) is defined by the time-averaged power of the scattered wave ( ⟨ P s ⟩ {\displaystyle \langle P_{s}\rangle } ) divided by the intensity of the incident wave ( I I {\displaystyle I_{I}} ): σ = ⟨ P s ⟩ I I {\displaystyle \sigma ={\frac {\langle P_{s}\rangle }{I_{I}}}} .
Starting with the assumptions that a plasma object is small relative to the incident wavelength, thin relative to the skin depth, unmagnetized, and homogenous, the scattering cross-section of the plasma object can be determined by the following equation, where e {\displaystyle e} is the electron charge, m {\displaystyle m} is the electron mass, N e {\displaystyle N_{e}} is the number of unbound electrons in the plasma object, ξ {\displaystyle \xi } is the geometrically-determined depolarization factor, [ 5 ] ω {\displaystyle \omega } is the incident wave circular frequency, ω p {\displaystyle \omega _{p}} is the plasma frequency , and ν m {\displaystyle \nu _{m}} is the effective momentum-transfer collisional frequency (not to be confused with collisional frequency). [ 6 ] [ 7 ]
σ = e 4 6 π m 2 ϵ 0 2 c 4 N e 4 ω 4 ( ξ ω p 2 − ω 2 ) 2 + ( ν m ω ) 2 {\displaystyle \sigma ={\frac {e^{4}}{6\pi m^{2}\epsilon _{0}^{2}c^{4}}}{\frac {N_{e}^{4}\omega ^{4}}{(\xi \omega _{p}^{2}-\omega ^{2})^{2}+(\nu _{m}\omega )^{2}}}} [ 1 ]
(The above equation is derived from the Drude-Lorentz-Sommerfeld model. It neglects transient effects of electron motion and is only qualitatively applicable to Rayleigh scattering due to neglecting evanescence effects - strict consideration of boundary conditions is often required to capture the case of negative permittivity. [ 8 ] ). The total cross section can related to the cross section of an individual electron ( σ e {\displaystyle \sigma _{e}} ) according to the equation σ e = σ / N e 2 {\displaystyle \sigma _{e}=\sigma /N_{e}^{2}} , since the electron motion will be in phase assuming that the plasma object is small relative to the incident wavelength.
The scattering regime is determined by the dominant term in the denominator. Collisional scattering refers to the assumption that ν m ω ≫ | ξ ω p 2 − ω | {\displaystyle \nu _{m}\omega \gg |\xi \omega _{p}^{2}-\omega |} , allowing the total scattering cross section to be expressed as:
σ c o l l i s i o n a l = e 4 6 π m 2 ϵ 0 2 c 4 N e 4 ω 2 ν m 2 {\displaystyle \sigma _{collisional}={\frac {e^{4}}{6\pi m^{2}\epsilon _{0}^{2}c^{4}}}{\frac {N_{e}^{4}\omega ^{2}}{\nu _{m}^{2}}}} [ 1 ]
The collisional scattering cross-section can also be expressed in terms of the Thomson scattering cross section ( σ T h o m p s o n {\displaystyle \sigma _{Thompson}} ), which is independent of the plasma geometry and collisional frequency according to the following equation.
σ c o l l i s i o n a l = σ T h o m p s o n ( ω ν m ) 2 {\displaystyle \sigma _{collisional}=\sigma _{Thompson}({\frac {\omega }{\nu _{m}}})^{2}} [ 1 ] | https://en.wikipedia.org/wiki/Shneider-Miles_scattering |
In oceanography , geomorphology , and geoscience , a shoal is a natural submerged ridge , bank , or bar that consists of, or is covered by, sand or other unconsolidated material, and rises from the bed of a body of water close to the surface or above it, which poses a danger to navigation. Shoals are also known as sandbanks , sandbars , or gravelbars . Two or more shoals that are either separated by shared troughs or interconnected by past or present sedimentary and hydrographic processes are referred to as a shoal complex . [ 1 ] [ 2 ]
The term shoal is also used in a number of ways that can be either similar to, or quite different from, how it is used in geologic, geomorphic, and oceanographic literature. Sometimes, the term refers to either any relatively shallow place in a stream , lake , sea , or other body of water; a rocky area on the seafloor within an area mapped for navigation purposes; or a growth of vegetation on the bottom of a deep lake, that occurs at any depth, or is used as a verb for the process of proceeding from a greater to a lesser depth of water. [ 2 ]
Shoals are characteristically long and narrow (linear) ridges. They can develop where a stream , river , or ocean current promotes deposition of sediment and granular material , resulting in localized shallowing (shoaling) of the water. Marine shoals also develop either by the in-place drowning of barrier islands as the result of episodic sea level rise or by the erosion and submergence of inactive delta lobes .
Shoals can appear as a coastal landform in the sea , where they are classified as a type of ocean bank , or as fluvial landforms in rivers, streams, and lakes .
A shoal–sandbar may seasonally separate a smaller body of water from the sea, such as:
The term bar can apply to landform features spanning a considerable range in size, from a length of a few meters in a small stream to marine depositions stretching for hundreds of kilometers along a coastline, often called barrier islands .
They are typically composed of sand , although they could be of any granular matter that the moving water has access to and is capable of shifting around (for example, soil , silt , gravel , cobble , shingle , or even boulders ). The grain size of the material comprising a bar is related to the size of the waves or the strength of the currents moving the material, but the availability of material to be worked by waves and currents is also important.
Wave shoaling is the process when surface waves move towards shallow water, such as a beach, they slow down, their wave height increases and the distance between waves decreases. This behavior is called shoaling , and the waves are said to shoal. The waves may or may not build to the point where they break , depending on how large they were to begin with, and how steep the slope of the beach is. In particular, waves shoal as they pass over submerged sandbanks or reefs. This can be treacherous for boats and ships.
Shoaling can also refract waves, so the waves change direction. For example, if waves pass over a sloping bank which is shallower at one end than the other, then the shoaling effect will result in the waves slowing more at the shallow end. Thus, the wave fronts will refract, changing direction like light passing through a prism. Refraction also occurs as waves move towards a beach if the waves come in at an angle to the beach, or if the beach slopes more gradually at one end than the other.
Sandbars, also known as a trough bars, form where the waves are breaking, because the breaking waves set up a shoreward current with a compensating counter-current along the bottom. Sometimes this occurs seaward of a trough (marine landform).
Sand carried by the offshore moving bottom current is deposited where the current reaches the wave break. [ 3 ] Other longshore bars may lie further offshore, representing the break point of even larger waves, or the break point at low tide.
In Russian tradition of geomorphology , a peresyp is a sandbar that rises above the water level (like a spit ) and separates a liman or a lagoon from the sea. Unlike tombolo bars, a peresyp seldom forms a contiguous strip and usually has one or several channels that connect the liman and the sea. [ 4 ]
A harbor or river bar is a sedimentary deposit formed at a harbor entrance or river mouth by the deposition of freshwater sediment or by the action of waves on the sea floor or on up-current beaches.
Where beaches are suitably mobile, or the river's suspended or bed loads are large enough, deposition can build up a sandbar that completely blocks a river mouth and dams the river. It can be a seasonally natural process of aquatic ecology , causing the formation of estuaries and wetlands in the lower course of the river. This situation will persist until the bar is eroded by the sea, or the dammed river develops sufficient head to break through the bar.
The formation of harbor bars that prevent access for boats and shipping can be the result of:
In a nautical sense, a bar is a shoal, similar to a reef : a shallow formation of (usually) sand that is a navigation or grounding hazard, with a depth of water of 6 fathoms (11 meters) or less. It therefore applies to a silt accumulation that shallows the entrance to or course of a river, or creek. A bar can form a dangerous obstacle to shipping, preventing access to the river or harbor in poor weather conditions or at some states of the tide .
In addition to longshore bars discussed above that are relatively small features of a beach , the term shoal can be applied to larger geological units that form off a coastline as part of the process of coastal erosion, such as spits and baymouth bars that form across the front of embayments and rias . A tombolo is a bar that forms an isthmus between an island or offshore rock and a mainland shore.
In places of reentrance along a coastline (such as inlets , coves , rias, and bays), sediments carried by a longshore current will fall out where the current dissipates, forming a spit. An area of water isolated behind a large bar is called a lagoon. Over time, lagoons may silt up, becoming salt marshes .
In some cases, shoals may be precursors to beach expansion and dunes formation, providing a source of windblown sediment to augment such beach or dunes landforms. [ 5 ]
Since prehistoric times, humans have chosen some shoals as a site of habitation. In some early cases, the locations provided easy access to exploit marine resources. [ 6 ] In modern times, these sites are sometimes chosen for the water amenity or view, but many such locations are prone to storm damage. [ 7 ] [ 8 ]
An area in Northwest Alabama is commonly referred to as " The Shoals " by local inhabitants, and one of the cities, Muscle Shoals , is named for such landform and its abundance of Mussels . | https://en.wikipedia.org/wiki/Shoal |
Shock is an abrupt discontinuity in the flow field and it occurs in flows when the local flow speed exceeds the local sound speed . [ 1 ] More specifically, it is a flow whose Mach number exceeds 1.
Shock is formed due to coalescence of various small pressure pulses. Sound waves are pressure waves and it is at the speed of the sound wave the disturbances are communicated in the medium. When an object is moving in a flow field the object sends out disturbances which propagate at the speed of sound and adjusts the remaining flow field accordingly. [ clarification needed ] However, if the object itself happens to travel at speed greater than sound, then the disturbances created by the object would not have traveled and communicated to the rest of the flow field and this results in an abrupt change of property, which is termed as shock in gas dynamics terminology.
Shocks are characterized by discontinuous changes in flow properties such as velocity , pressure , temperature , etc. Typically, shock thickness is of a few mean free paths (of the order of 10 −8 m). Shocks are irreversible occurrences in supersonic flows (i.e. the entropy increases).
Where, the index 1 refers to upstream properties, and the index 2 refers to down stream properties. The subscript 0 refers to total or stagnation properties. T is temperature, M is the mach number, P is pressure, ρ is density, and γ is the ratio of specific heats . | https://en.wikipedia.org/wiki/Shock_(fluid_dynamics) |
In mechanics and physics , shock is a sudden acceleration caused, for example, by impact , drop, kick, earthquake , or explosion . Shock is a transient physical excitation.
Shock describes matter subject to extreme rates of force with respect to time. Shock is a vector that has units of an acceleration (rate of change of velocity). The unit g (or g ) represents multiples of the standard acceleration of gravity and is conventionally used.
A shock pulse can be characterised by its peak acceleration, the duration, and the shape of the shock pulse (half sine, triangular, trapezoidal, etc.). The shock response spectrum is a method for further evaluating a mechanical shock. [ 1 ]
Shock measurement is of interest in several fields such as
Shocks are usually measured by accelerometers but other transducers and high speed imaging are also used. [ 12 ] A wide variety of laboratory instrumentation is available; stand-alone shock data loggers are also used.
Field shocks are highly variable and often have very uneven shapes. Even laboratory controlled shocks often have uneven shapes and include short duration spikes; Noise can be reduced by appropriate digital or analog filtering. [ 13 ] [ 14 ]
Governing test methods and specifications provide detail about the conduct of shock tests. Proper placement of measuring instruments is critical. Fragile items and packaged goods respond with variation to uniform laboratory shocks; [ 15 ] Replicate testing is often called for. For example, MIL-STD-810 G Method 516.6 indicates: at least three times in both directions along each of three orthogonal axes".
Shock testing typically falls into two categories, classical shock testing and pyroshock or ballistic shock testing. Classical shock testing consists of the following shock impulses: half sine , haversine, sawtooth wave , and trapezoid . Pyroshock and ballistic shock tests are specialized and are not considered classical shocks. Classical shocks can be performed on Electro Dynamic (ED) Shakers, Free Fall Drop Tower or Pneumatic Shock Machines. A classical shock impulse is created when the shock machine table changes direction abruptly. This abrupt change in direction causes a rapid velocity change which creates the shock impulse. Testing the effects of shock are sometimes conducted on end-use applications: for example, automobile crash tests .
Use of proper test methods and Verification and validation protocols are important for all phases of testing and evaluation.
Mechanical shock has the potential for damaging an item (e.g., an entire light bulb ) or an element of the item (e.g. a filament in an Incandescent light bulb ):
When laboratory testing, field experience, or engineering judgement indicates that an item could be damaged by mechanical shock, several courses of action might be considered: [ 17 ] | https://en.wikipedia.org/wiki/Shock_(mechanics) |
The Shock and Vibration Information Analysis Center ( SAVIAC ) is a U.S. Government organization established by the U.S. Navy Office of Naval Research on 20 December 1946. SAVIAC's purpose is to promulgate information on the transient and vibratory response of structures and materials. This broad field includes such technical areas as the testing, analysis and design of structural or mechanical systems subjected to dynamic conditions and loading such as vibration , blast , impact , and shock for various agencies in the U. S. Government including NASA , the Department of Energy (DOE), and the Department of Defense (DOD). The organization sponsored the professional journal Shock and Vibration Journal and currently sponsors and publishes the professional journal Journal of Critical Technology in Shock and Vibration. SAVIAC also sponsored and published a series of monograms addressing different aspects of shock and vibration. In 2012 SAVIAC became inactive as a result of new Department of Defense cost-cutting regulations limiting DoD sponsorship and participation of conferences and workshops. SAVIAC has been succeeded by an industrially-funded and managed "Shock and Vibration Exchange" SAVE .
SAVIAC assembled and promoted a yearly symposium . The annual Shock and Vibration Symposium was the leading forum for the structural dynamics and vibration community to present and discuss new developments and ongoing research. The Symposium, established in 1947, includes both classified and unclassified sessions. The classified sessions allow critical technology and classified (up to secret level) research to be presented in closed forums of cleared U.S. government and government contractor researchers. Topics covered at the symposium include shock-ship testing, water shock, weapons effects ( air blast , ground shock, cratering, penetration ), shock physics, earthquake engineering , structural dynamics , and shock and vibration instrumentation and experiment techniques. Over 200 technical papers were typically presented. Panel discussions addressed topics such as new software developments or accelerometer isolation problems. Tutorials provide up-to-date technology overviews by leading specialists. Since 2012 the Shock and Vibration Symposium has continued under the management and sponsorship of SAVE.
References:
Henry C. Pusey (Editor). "50 Years of Shock and Vibration Technology." SAVIAC Monogram SVM-15, Shock and Vibration Information Analysis Center, 1996. | https://en.wikipedia.org/wiki/Shock_and_Vibration_Information_Analysis_Center |
A shock data logger or vibration data logger is a measurement instrument that is capable of autonomously recording shocks or vibrations over a defined period of time. Digital data is usually in the form of acceleration and time. The shock and vibration data can be retrieved (or transmitted), viewed and evaluated after it has been recorded.
In contrast with a shock data logger, a shock detector is used to indicate whether or not the threshold of specified shock has occurred.
A logger comprises sensors such as accelerometers , storage media, a processor and power supply. The sensors measure and store shocks either as the entire waveform, summary data, or an indication of whether a threshold value was observed . Some devices have accelerometers built into the unit while others can use external accelerometers. The processor processes the measured data and saves it on the storage media together with the associated measurement times. This allows the measurement data to be retrieved after the measurements have been completed, either directly on the logger or via an interface to a computer. Some have an RFID interface. [ 1 ] Software is used to present the measured data in the form of tables or graphs and provides functions for the evaluation of the measurement data.
The shock and vibration data is either recorded continuously over a defined time period or on an event-driven basis where the recording of data is determined by certain criteria. Employing such an event-based measurement method allows the recording of specific shocks that exceed a critical length of time or strength. Some have wireless capability such as Bluetooth transmissions to smartphones. [ 2 ]
Acceleration loggers usually use non-volatile storage media for recording the measurement data. These may be hard disc drives or EEPROMs for instance. Such devices will not lose the data when the device is powered down. This also means that the measured data will remain stored in the event of a power failure.
Shocks and impacts are often described by the peak acceleration expressed in g-s (sometimes called g-forces ). The form of the shock pulse and particularly the pulse duration are equally important. For example, a short 1 ms 300 g shock has little damage potential and is not usually of interest but a 20 ms 300 g shock might be critical. Use of shock response spectrum analysis is also useful.
The mounting location also affects the response of most shock detectors. A shock on a rigid item such as a sports helmet or a rigid package might respond to a field shock with a jagged shock pulse which, without proper filtering is difficult to characterize. A shock on a cushioned item usually has a smoother shock pulse., and thus more consistent responses from shock detector.
Shocks are vector quantities with the direction of the shock often being important to the item of interest.
A shock data logger can be evaluated:
separately in a laboratory physical test , perhaps on an instrumented shock machine;
or mounted to its intended item in a testing laboratory with controlled fixturing and controlled input shocks;
or in the field with uncontrolled and more highly variable input shocks.
Use of proper test methods , calibration , and Verification and validation protocols are important for all phases of evaluation.
Shock loggers can be used to monitor fragile and valuable goods during transit and to measure the transportation shock and vibration environment. [ 3 ] [ 4 ] The loggers can be rigidly attached to the goods, packaging, or transport vehicles so that they can record the shocks and vibrations acting upon them. Some large items may have several shock sensors to measure different locations. The measured data reveals whether the goods in transit have been subjected to potentially damaging conditions. Based on this data, the options may be:
Shock and vibration data from multiple replicate shipments can be used to:
compare the shipment severity of different routings or of logistics providers; [ 5 ] or develop composite data to be used in package testing protocols. The shock handling data is often most useful converted from accelerations to drop heights or other means of quantifying the severity of impacts. Several means of statistical analysis of drops and impacts are available. [ 6 ] Vibration data is often most useful in power spectral density format which can be used in to control random vibration testing in a laboratory.
Among other applications, acceleration sensors are used to: | https://en.wikipedia.org/wiki/Shock_and_vibration_data_logger |
Shock chlorination is a process used in many swimming pools, water wells , springs , and other water sources to reduce the bacterial and algal residue in the water. Shock chlorination is performed by mixing a large amount of sodium hypochlorite , which can be in the form of a powder or a liquid such as chlorine bleach , into the water. The common advice is that the amount added must raise the level of chlorine to 10X the level (in parts per million) of chloramines present in the pool water; this is "shocking". A lesser ratio is termed superchlorinating . [ 1 ] Water that is being shock chlorinated should not be swum in or drunk until the sodium hypochlorite count in the water goes down to three ppm or less which is generally more than 6 hours. [ 2 ] Commercial sodium hypochlorite should not be mixed with commercial calcium hypochlorite , as there is a risk of explosion. [ citation needed ] Although a verb for superchlorination , [ 3 ] "shock" is often misunderstood (through marketing and sales language) to be a unique type of product.
While "shocking" pools to reduce the buildup of chloramines works with inorganic, ammonia-based chloramines, in two studies it was found ineffective with the organic chloramines present in all pool water e.g. with creatinine , an organic component in human sweat . Indeed, superchlorination produces free chlorine that reacts with organic contaminants to form a variety of disinfection byproducts (DBPs) which are hazardous to swimmer health e.g. one of the worst DBPs is the noxious and volatile trichloramine (NCl 3 ), well known for irritating the eyes nearby a pool. It has been pointed out that ozone is an excellent alternative, a much more effective oxidizer than chlorine shock. [ 3 ] | https://en.wikipedia.org/wiki/Shock_chlorination |
A shock detector , shock indicator , or impact monitor is a device which indicates whether a physical shock or impact has occurred. These usually have a binary output ( go/no-go ) and are sometimes called shock overload devices . Shock detectors can be used on shipments of fragile valuable items to indicate whether a potentially damaging drop or impact may have occurred. They are also used in sports helmets to help estimate if a dangerous impact may have occurred. [ 1 ]
By contrast, a shock data logger is a data acquisition system for analysis and recording of shock pulses.
Shocks and impacts are often specified by the peak acceleration expressed in g-s (sometimes called g-forces ). The form of the shock pulse and particularly the duration are equally important. [ 1 ] For example, a short 1 ms 300 g shock has little damage potential and is not usually of interest but a 20 ms 300 g shock might be critical. Depending on the use, the response to this time sensitivity of a shock detector needs to be matched to the sensitivity of the item it is intended to monitor.
The mounting location also affects the response of most shock detectors. A shock on a rigid item such as a sports helmet or a rigid package might respond to a field shock with a jagged shock pulse which, without proper filtering is difficult to characterize. A shock on a cushioned item usually has a smoother shock pulse., and thus more consistent responses from shock detector.
Shocks are vector quantities with the direction of the shock being important to the item of interest, Shock detectors also can be highly sensitive to the direction of the input shock. [ 1 ]
A shock detector can be evaluated:
Use of proper test methods and verification and validation protocols are important for all phases of evaluation.
A wide variety of technologies are available ranging from simple analog indicators to more sophisticated electronics. Usually a device provides an optical indication of a triggered event but sometimes electrical or RFID signals can be provided. Hundreds of shock detectors are described in patents listed in patent classification 01P15/00: "Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration" [ 3 ]
Analogue constructions include:
More sophisticated electronic systems use accelerometers and associated microelectromechanical systems . [ 1 ]
A shock detector can be mounted on a package (inside or outside) or directly on the product being shipped. Mounting on the package is usually done to detect excessive handling such as high drop heights while mounting on the product is done to more closely indicate product damage. [ 4 ]
Some shipments need more than one shock detector to better monitor all directions of impacts. [ 4 ] Large or long items sometimes have shock detectors at both ends of the shipping container.
The shock detector indicates whether the goods in transit were likely to have been subjected to potentially damaging conditions. Based on this data, the options may be: [ 4 ]
Shock and impact are not the only hazards that can cause damage; vibration , puncture, and compression can also cause damage yet would not trigger a shock detector.
Personal protective equipment such as helmets are sometimes equipped with impact monitors. [ 5 ] [ 6 ] These are intended to help managers know if an excessive impact has occurred and help direct needed rest or medical attention. Research is continuing, including specialized mouthguards to help classify head impacts. [ 7 ]
Crash sensors on bicycle helmets can detect a crash and call for assistance. Fall sensors are available to senior citizens to call for help when a fall is detected. [ 8 ]
A related use of an impact detector is as automobile air bag sensor. These sophisticated sensors are used to trigger the protective air bag system used on current vehicles. [ 9 ]
Active hard-drive protection systems sense impacts to laptop computers to help minimize damage from drops.
Some emergency locator beacons , such as Emergency Locator Transmitters , are activated by a specified shock or impact.
Shock detectors are used to indicate if a significant impact has occurred: This helps determine the need for follow-up actions. Variability is always present and must be accounted for in the analysis:
Of course, it is best when the shock detector properly signals when damage or injury is likely and when it is not. It is very possible to have false positive signals where a shock detector is triggered but there is no damage to a product or no injury to a person. Likewise false negatives are also possible. [ 13 ]
No Damage or Injury
Shock detectors are intended to indicate a single severe shock or impact. In some instances a series of lesser shocks might cause damage or injury [ 14 ] but would not trigger a shock detector. | https://en.wikipedia.org/wiki/Shock_detector |
Shock diamonds (also known as Mach diamonds or thrust diamonds , and less commonly Mach disks ) are a formation of standing wave patterns that appear in the supersonic exhaust plume of an aerospace propulsion system, such as a supersonic jet engine , rocket , ramjet , or scramjet , when it is operated in an atmosphere. The "diamonds" are actually a complex flow field made visible by abrupt changes in local density and pressure as the exhaust passes through a series of standing shock waves and expansion fans . The physicist Ernst Mach was the first to describe a strong shock normal to the direction of fluid flow, the presence of which causes the diamond pattern. [ 1 ] : 48
Shock diamonds form when the supersonic exhaust from a propelling nozzle is slightly over-expanded, meaning that the static pressure of the gases exiting the nozzle is less than the ambient air pressure . The higher ambient pressure compresses the flow, and since the resulting pressure increase in the exhaust gas stream is adiabatic , a reduction in velocity causes its static temperature to be substantially increased. [ 2 ] The exhaust is typically over-expanded at low altitudes, where air pressure is higher.
As the flow exits the nozzle, ambient air pressure will compress the flow. [ 2 ] The external compression is caused by oblique shock waves inclined at an angle to the flow. The compressed flow is alternately expanded by Prandtl-Meyer expansion fans , and each "diamond" is formed by the pairing of an oblique shock with an expansion fan. When the compressed flow becomes parallel to the center line, a shock wave perpendicular to the flow forms, called a normal shock wave or Mach disk . This locates the first shock diamond, and the space between it and the nozzle is called the "zone of silence". [ 3 ] The distance from the nozzle to the first shock diamond can be approximated by
x = 0.67 D 0 P 0 P 1 , {\displaystyle x=0.67D_{0}{\sqrt {\frac {P_{0}}{P_{1}}}},}
where x is the distance, D 0 is the nozzle diameter, P 0 is chamber pressure, and P 1 is atmospheric pressure. [ 3 ]
As the exhaust passes through the normal shock wave, its temperature increases, igniting excess fuel and causing the glow that makes the shock diamonds visible. [ 2 ] The illuminated regions either appear as disks or diamonds , giving them their name.
Eventually the flow expands enough so that its pressure is again below ambient, at which point the expansion fan reflects from the contact discontinuity (the outer edge of the flow). The reflected waves, called the compression fan, cause the flow to compress. [ 2 ] If the compression fan is strong enough, another oblique shock wave will form, creating a second Mach disk and shock diamond. The pattern of disks and diamonds would repeat indefinitely if the gases were ideal and frictionless; [ 2 ] however, turbulent shear at the contact discontinuity causes the wave pattern to dissipate with distance. [ 4 ]
Diamond patterns can similarly form when a nozzle is under-expanded (exit pressure higher than ambient) in lower atmospheric pressure at higher altitudes. In this case, the expansion fan is first to form, followed by the oblique shock. [ 2 ]
Shock diamonds are most commonly associated with jet and rocket propulsion, but they can form in other systems.
When artillery pieces are fired, gas exits the cannon muzzle at supersonic speeds and produces a series of shock diamonds. The diamonds cause a bright muzzle flash which can expose the location of gun emplacements to the enemy. It was found that when the ratio between the flow pressure and atmospheric pressure is close, which can be achieved with a flash suppressor , the shock diamonds were greatly minimized. Adding a muzzle brake to the end of the muzzle balances the pressures and prevents shock diamonds. [ 1 ] : 41
Some radio jets , powerful jets of plasma that emanate from quasars and radio galaxies , are observed to have regularly-spaced knots of enhanced radio emissions. [ 1 ] : 68 The jets travel at supersonic speed through a thin "atmosphere" of gas in space, [ 1 ] : 51 so it is hypothesized that these knots are shock diamonds. [ 5 ] [ 6 ] | https://en.wikipedia.org/wiki/Shock_diamond |
Shock hardening is a process used to strengthen metals and alloys , wherein a shock wave produces atomic-scale defects in the material's crystalline structure. As in cold work , these defects interfere with the normal processes by which metallic materials yield ( plasticity ), making materials stiffer, but more brittle . When compared to traditional cold work, such an extremely rapid process results in a different class of defect, producing a much harder material for a given change in shape. If the shock wave applies too great a force for too long, however, the rarefaction front that follows it can form voids in the material due to hydrostatic tension, weakening the material and often causing it to spall . Since voids nucleate at large defects, such as oxide inclusions and grain boundaries , high-purity samples with a large grain size (especially single crystals) are able to withstand greater shock without spalling, and can therefore be made much harder.
Shock hardening has been observed in many contexts:
Explosive forging uses the detonation of a high explosive charge to create a shockwave. This effect is used to harden rail track cast components [ 1 ] and, coupled with the Misnay-Schardin effect , in the operation of explosively forged penetrators . Greater hardening can be achieved by using a lower quantity of an explosive with greater brisance , so that the force applied is greater but the material spends less time in hydrostatic tension.
Laser shock , similar to inertial confinement fusion , uses the ablation plume caused by a laser pulse to apply force to the laser's target. [ 2 ] The rebound from the expelled matter can create very high pressures, and the pulse length of lasers is often quite short, meaning that good hardening can be achieved with little risk of spallation . Surface effects can also be achieved by laser treatment, including amorphization .
Light-gas guns have been used to study shock hardening. Although too labor-intensive for widespread industrial application, they do provide a versatile research testbed. They allow precise control of both magnitude and profile of the shock wave through adjustments to the projectile's muzzle velocity and density profile, respectively. Studies of various projectile types have been crucial in overturning a prior theory that spallation occurs at a threshold of pressure, independent of time. Instead, experiments show longer-lasting shocks of a given magnitude produce more material damage. | https://en.wikipedia.org/wiki/Shock_hardening |
The term shock polar is generally used with the graphical representation of the Rankine–Hugoniot equations in either the hodograph plane or the pressure ratio-flow deflection angle plane. The polar itself is the locus of all possible states after an oblique shock . The shock polar was first introduced by Adolf Busemann in 1929. [ 1 ]
The minimum angle, θ {\displaystyle \theta } , which an oblique shock can have is the Mach angle μ = sin − 1 ( 1 / M ) {\displaystyle \mu =\sin ^{-1}(1/M)} , where M {\displaystyle M} is the initial Mach number before the shock and the greatest angle corresponds to a normal shock. The range of shock angles is therefore sin − 1 ( 1 / M ) ≤ θ ≤ π / 2 {\displaystyle \sin ^{-1}(1/M)\leq \theta \leq \pi /2} . To calculate the pressures for this range of angles, the Rankine–Hugoniot equations are solved for pressure: p p 0 = 1 + 2 γ γ + 1 ( M 2 sin 2 θ − 1 ) {\displaystyle {\frac {p}{p_{0}}}=1+{\frac {2\gamma }{\gamma +1}}\left(M^{2}\sin ^{2}\theta -1\right)} To calculate the possible flow deflection angles, the relationship between shock angle θ {\displaystyle \theta } and φ {\displaystyle \varphi } is used: tan φ = 2 cot θ M 2 sin 2 θ − 1 2 + M 2 ( γ + cos 2 θ ) . {\displaystyle \tan \varphi =2\cot \theta {\frac {M^{2}\sin ^{2}\theta -1}{2+M^{2}(\gamma +\cos 2\theta )}}.} Where γ {\displaystyle \gamma } is the ratio of specific heats and φ {\displaystyle \varphi } is the flow deflection angle.
One of the primary uses of shock polars is in the field of shock wave reflection. A shock polar is plotted for the conditions before the incident shock, and a second shock polar is plotted for the conditions behind the shock, with its origin located on the first polar, at the angle through which the incident shock wave deflects the flow. Based on the intersections between the incident shock polar and the reflected shock polar, conclusions as to which reflection patterns are possible may be drawn. Often, it is used to graphically determine whether regular shock reflection is possible, or whether Mach reflection occurs. [ 2 ] [ 3 ] | https://en.wikipedia.org/wiki/Shock_polar |
A shock tube is an instrument used to replicate and direct blast waves at a sensor or model in order to simulate explosions and their effects, usually on a smaller scale. Shock tubes (and related impulse facilities such as shock tunnels, expansion tubes, and expansion tunnels) can also be used to study aerodynamic flow under a wide range of temperatures and pressures that are difficult to obtain in other types of testing facilities. Shock tubes are also used to investigate compressible flow phenomena and gas phase combustion reactions. More recently, shock tubes have been used in biomedical research to study how biological specimens are affected by blast waves. [ 1 ] [ 2 ]
A shock wave inside a shock tube may be generated by a small explosion (blast-driven) or by the buildup of high pressures which cause diaphragm(s) to burst and a shock wave to propagate down the shock tube (compressed-gas driven).
An early study of compression driven shock tubes was published in 1899 by French scientist Paul Vieille , though the apparatus was not called a shock tube until the 1940s. [ 3 ] In the 1930s it was rediscovered by W. H. Payman and WCF Shepherd of English Safety in Mines Research Board in order to study underground methane explosions, but the term was not coined until Bleakney et al. publication of 1949. [ 4 ] [ 5 ]
In the 1940s, interest revived and shock tubes were increasingly used to study the flow of fast moving gases over objects, the chemistry and physical dynamics of gas phase combustion reactions. The modern version of the shock tube was developed during WWII at Princeton University by a group led by Walker Bleakney , [ 6 ] who published overviews of their studies in 1946 and 1949.
In 1966, Duff and Blackwell [ 7 ] described a type of shock tube driven by high explosives. These ranged in diameter from 0.6 to 2 m and in length from 3 m to 15 m. The tubes themselves were constructed of low-cost materials and produced shock waves with peak dynamic pressures of 7 MPa to 200 MPa and durations of a few hundred microseconds to several milliseconds.
Both compression-driven and blast-driven shock tubes are currently used for scientific as well as military applications. Compressed-gas driven shock tubes are more easily obtained and maintained in laboratory conditions; however, the shape of the pressure wave is different from a blast wave in some important respects and may not be suitable for some applications. Blast-driven shock tubes generate pressure waves that are more realistic to free-field blast waves. However, they require facilities and expert personnel for handling high explosives. Also, in addition to the initial pressure wave, a jet effect caused by the expansion of compressed gases (compression-driven) or production of rapidly expanding gases (blast-driven) follows and may transfer momentum to a sample after the blast wave has passed. More recently, laboratory scale shock tubes driven by fuel-air mixtures have been developed that produce realistic blast waves and can be operated in more ordinary laboratory facilities. [ 8 ] Because the molar volume of gas is much less, the jet effect is a fraction of that for compressed-gas driven shock tubes. To date, the smaller size and lower peak pressures generated by these shock tubes make them most useful for preliminary, nondestructive testing of materials, validation of measurement equipment such as high speed pressure transducers, and for biomedical research as well as military applications.
A simple shock tube is a tube, rectangular or circular in cross-section, usually constructed of metal, in which a gas at low pressure and a gas at high pressure are separated using some form of diaphragm . See, for instance, texts by Soloukhin, Gaydon and Hurle, and Bradley. [ 9 ] [ 10 ] [ 11 ] The diaphragm suddenly bursts open under predetermined conditions to produce a wave propagating through the low pressure section. The shock that eventually forms increases the temperature and pressure of the test gas and induces a flow in the direction of the shock wave. Observations can be made in the flow behind the incident front or take advantage of the longer testing times and vastly enhanced pressures and temperatures behind the reflected wave.
The low-pressure gas, referred to as the driven gas, is subjected to the shock wave. The high pressure gas is known as the driver gas. The corresponding sections of the tube are likewise called the driver and driven sections. The driver gas is usually chosen to have a low molecular weight , (e.g., helium or hydrogen ) for safety reasons, with high speed of sound , but may be slightly diluted to 'tailor' interface conditions across the shock. To obtain the strongest shocks the pressure of the driven gas is well below atmospheric pressure (a partial vacuum is induced in the driven section before detonation).
The test begins with the bursting of the diaphragm. [ 12 ] Several methods are commonly used to burst the diaphragm.
The bursting diaphragm produces a series of pressure waves , each increasing the speed of sound behind them, so that they compress into a shock propagating through the driven gas. This shock wave increases the temperature and pressure of the driven gas and induces a flow in the direction of the shock wave but at lower velocity than the lead wave. Simultaneously, a rarefaction wave, often referred to as the Prandtl-Meyer wave, travels back in to the driver gas.
The interface, across which a limited degree of mixing occurs, separates driven and driver gases is referred to as the contact surface and follows, at a lower velocity, the lead wave.
A 'Chemical Shock Tube' involves separating driver and driven gases by a pair of diaphragms designed to fail after pre-determined delays with an end 'dump tank' of greatly increased cross-section. This allows an extreme rapid reduction (quench) in temperature of the heated gases.
In addition to measurements of rates of chemical kinetics shock tubes have been used to measure dissociation energies and molecular relaxation rates [ 14 ] [ 15 ] [ 16 ] [ 17 ] they have been used in aerodynamic tests. The fluid flow in the driven gas can be used much as a wind tunnel , allowing higher temperatures and pressures therein [ 18 ] replicating conditions in the turbine sections of jet engines . However, test times are limited to a few milliseconds, either by the arrival of the contact surface or the reflected shock wave.
They have been further developed into shock tunnels , with an added nozzle and dump tank. The resultant high temperature hypersonic flow can be used to simulate atmospheric re-entry of spacecraft or hypersonic craft, again with limited testing times. [ 19 ]
Shock tubes have been developed in a wide range of sizes. The size and method of producing the shock wave determine the peak and duration of the pressure wave it produces. Thus, shock tubes can be used as a tool used to both create and direct blast waves at a sensor or an object in order to imitate actual explosions and the damage that they cause on a smaller scale, provided that such explosions do not involve elevated temperatures and shrapnel or flying debris. Results from shock tube experiments can be used to develop and validate numerical model of the response of a material or object to an ambient blast wave without shrapnel or flying debris. Shock tubes can be used to experimentally determine which materials and designs would be best suited to the job of attenuating ambient blast waves without shrapnel or flying debris. The results can then be incorporated into designs to protect structures and people that might be exposed to an ambient blast wave without shrapnel or flying debris. Shock tubes are also used in biomedical research to find out how biological tissues are affected by blast waves.
There are alternatives to the classical shock tube; for laboratory experiments at very high pressure, shock waves can also be created using high-intensity short-pulse lasers. [ 20 ] [ 21 ] [ 22 ] [ 23 ] | https://en.wikipedia.org/wiki/Shock_tube |
Shock waves are common in astrophysical environments. [ 1 ]
Because of the low ambient density , most astronomical shocks are collisionless . This means that the shocks are not formed by two-body Coulomb collisions , since the mean free path for these collisions is too large, often exceeding the size of the system. Such shocks were first theorised by Frederic de Hoffmann and Edward Teller , [ 2 ] who studied shock waves in magnetized fluids with infinite conductivity. The precise mechanism for energy dissipation and entropy generation at such shocks is still under investigation, but it is widely accepted that the general mechanism driving these shocks consists of wave particle interaction and plasma instabilities , that operate on the scale of plasma skin depth , which is typically much shorter than the mean free path.
It is known that collisionless shocks are associated with extremely high energy particles , although it has not been definitively established if the high energy photons observed are emitted by protons , electrons or both. The energetic particles are in general believed to be accelerated by the Fermi acceleration mechanism. It is usually agreed that shocks caused by supernova remnants expanding in the interstellar medium accelerate the cosmic rays measured above the Earth's atmosphere. [ 3 ]
Shock waves in stellar environments, such as shocks inside a core collapse supernova explosion often become radiation mediated shocks. Such shocks are formed by photons colliding with the electrons of the matter, and the downstream of these shocks is dominated by radiation energy density rather than thermal energy of matter.
An important type of astrophysical shock is the relativistic shock, in which the shock velocity is a non-negligible fraction of the speed of light. These shocks are unique to astrophysical environments, and can be either collisionless or radiation mediated. Relativistic shocks are theoretically expected in gamma ray bursts , active galactic nucleus jets and in some types of supernovae. | https://en.wikipedia.org/wiki/Shock_waves_in_astrophysics |
The Shockley diode equation , or the diode law , named after transistor co-inventor William Shockley of Bell Labs , models the exponential current–voltage (I–V) relationship of semiconductor diodes in moderate constant current forward bias or reverse bias :
where
The equation is called the Shockley ideal diode equation when the ideality factor n {\displaystyle n} equals 1, thus n {\displaystyle n} is sometimes omitted. The ideality factor typically varies from 1 to 2 (though can in some cases be higher), depending on the fabrication process and semiconductor material . The ideality factor was added to account for imperfect junctions observed in real transistors, mainly due to carrier recombination as charge carriers cross the depletion region .
The thermal voltage V T {\displaystyle V_{\text{T}}} is defined as:
where
For example, it is approximately 25.852 mV at 300 K (27 °C; 80 °F).
The reverse saturation current I S {\displaystyle I_{\text{S}}} is not constant for a given device, but varies with temperature; usually more significantly than V T {\displaystyle V_{\text{T}}} , so that V D {\displaystyle V_{\text{D}}} typically decreases as T {\displaystyle T} increases.
Under reverse bias , the diode equation's exponential term is near 0, so the current is near the somewhat constant − I S {\displaystyle -I_{\text{S}}} reverse current value (roughly a picoampere for silicon diodes or a microampere for germanium diodes, [ 1 ] although this is obviously a function of size).
For moderate forward bias voltages the exponential becomes much larger than 1, since the thermal voltage is very small in comparison. The − 1 {\displaystyle -1} in the diode equation is then negligible, so the forward diode current will approximate
The use of the diode equation in circuit problems is illustrated in the article on diode modeling .
Internal resistance causes "leveling off" of a real diode's I–V curve at high forward bias. The Shockley equation doesn't model this, but adding a resistance in series will.
The reverse breakdown region (particularly of interest for Zener diodes ) is not modeled by the Shockley equation.
The Shockley equation doesn't model noise (such as Johnson–Nyquist noise from the internal resistance, or shot noise ).
The Shockley equation is a constant current (steady state) relationship, and thus doesn't account for the diode's transient response , which includes the influence of its internal junction and diffusion capacitance and reverse recovery time .
Shockley derives an equation for the voltage across a p-n junction in a long article published in 1949. [ 2 ] Later he gives a corresponding equation for current as a function of voltage under additional assumptions, which is the equation we call the Shockley ideal diode equation. [ 3 ] He calls it "a theoretical rectification formula giving the maximum rectification", with a footnote referencing a paper by Carl Wagner , Physikalische Zeitschrift 32 , pp. 641–645 (1931).
To derive his equation for the voltage, Shockley argues that the total voltage drop can be divided into three parts:
He shows that the first and the third of these can be expressed as a resistance times the current: I D R 1 . {\displaystyle I_{\text{D}}R_{1}.} As for the second, the difference between the quasi-Fermi levels at the junction, he says that we can estimate the current flowing through the diode from this difference. He points out that the current at the p terminal is all holes, whereas at the n terminal it is all electrons, and the sum of these two is the constant total current. So the total current is equal to the decrease in hole current from one side of the diode to the other. This decrease is due to an excess of recombination of electron-hole pairs over generation of electron-hole pairs. The rate of recombination is equal to the rate of generation when at equilibrium, that is, when the two quasi-Fermi levels are equal. But when the quasi-Fermi levels are not equal, then the recombination rate is e ( ϕ p − ϕ n ) / V T {\displaystyle e^{(\phi _{\text{p}}-\phi _{\text{n}})/V_{\text{T}}}} times the rate of generation. We then assume that most of the excess recombination (or decrease in hole current) takes place in a layer going by one hole diffusion length L p {\displaystyle L_{\text{p}}} into the n material and one electron diffusion length L n {\displaystyle L_{\text{n}}} into the p material, and that the difference between the quasi-Fermi levels is constant in this layer at V J . {\displaystyle V_{\text{J}}.} Then we find that the total current, or the drop in hole current, is
where
and g {\displaystyle g} is the generation rate. We can solve for V J {\displaystyle V_{\text{J}}} in terms of I D {\displaystyle I_{\text{D}}} :
and the total voltage drop is then
When we assume that R 1 {\displaystyle R_{1}} is small, we obtain V = V J {\displaystyle V=V_{\text{J}}} and the Shockley ideal diode equation.
The small current that flows under high reverse bias is then the result of thermal generation of electron–hole pairs in the layer. The electrons then flow to the n terminal, and the holes to the p terminal. The concentrations of electrons and holes in the layer is so small that recombination there is negligible.
In 1950, Shockley and coworkers published a short article describing a germanium diode that closely followed the ideal equation. [ 4 ]
In 1954, Bill Pfann and W. van Roosbroek (who were also of Bell Telephone Laboratories) reported that while Shockley's equation was applicable to certain germanium junctions, for many silicon junctions the current (under appreciable forward bias) was proportional to e V J / A V T , {\displaystyle e^{V_{\text{J}}/AV_{\text{T}}},} with A having a value as high as 2 or 3. [ 5 ] This is the ideality factor n {\displaystyle n} above.
Feynman gave a derivation using the Brownian ratchet in The Feynman Lectures on Physics I.46. [ 6 ]
In 1981, Alexis de Vos and Herman Pauwels showed that a more careful analysis of the quantum mechanics of a junction, under certain assumptions, gives a current versus voltage characteristic of the form
in which A is the cross-sectional area of the junction, and F i is the number of incoming photons per unit area, per unit time, with energy over the band-gap energy, and F o ( V ) is outgoing photons, given by [ 7 ]
The factor of 2 multiplying the outgoing flux is needed because photons are emitted from both sides, but the incoming flux is assumed to come from just one side.
Although the analysis was done for photovoltaic cells under illumination, it applies also when the illumination is simply background thermal radiation, provided that a factor of 2 is then used for this incoming flux as well. The analysis gives a more rigorous expression for ideal diodes in general, except that it assumes that the cell is thick enough that it can produce this flux of photons. When the illumination is just background thermal radiation, the characteristic is
Note that, in contrast to the Shockley law, the current goes to infinity as the voltage goes to the gap voltage hν g /q . This of course would require an infinite thickness to provide an infinite amount of recombination.
This equation was recently revised to account for the new temperature scaling in the revised current I S {\displaystyle I_{\text{S}}} using a recent model [ 8 ] for 2D materials based Schottky diode . | https://en.wikipedia.org/wiki/Shockley_diode_equation |
Shockwave cosmology [ 1 ] [ 2 ] is a non-standard cosmology proposed by Joel Smoller and Blake Temple in 2003. In this model, the “ big bang ” is an explosion inside a black hole , producing the expanding volume of space and matter that includes the observable universe . [ 3 ]
Smoller and Temple integrate shock waves into Einstein's general relativity . [ 3 ] This produces a universe that "looks essentially identical to the aftermath of the big bang" according to cosmologists Barnes and Lewis. They explain that Smoller and Temple's version is distinguished from the big bang only by there being a shockwave at the leading edge of an explosion – one that, for Smoller and Temple's model, must be beyond the observable universe. However, Barnes and Lewis do not support shockwave cosmology because they see it as not testable; they point out that there is no explosion in the standard theory of the Big Bang. [ 4 ]
From Smoller and Temple's calculations, we are still inside an expanding black hole . The configuration of 'flat' spacetime (see Minkowski space) inside a black hole, also occurs during the moments of the formation of a black hole from a collapsing star. [ 5 ] [ 3 ]
Eventually, according to shockwave cosmology, the mass of our expanding volume of space and matter will fall in density as it expands. At some point, the event horizon of the black hole will cease to be. An outside observer will then see it appear as a white hole . The matter would then continue to expand. [ 3 ]
In related work, Smoller, Temple, and Vogler propose that this shockwave may have resulted in our part of the universe having a lower density than that surrounding it, causing the accelerated expansion normally attributed to dark energy . [ 6 ] [ 7 ]
They also propose that this related theory could be tested: a universe with dark energy should give a figure for the cubic correction to redshift versus luminosity C = −0.180 at a = a whereas for Smoller, Temple, and Vogler's alternative C should be positive rather than negative. They give a more precise calculation for their wave model alternative as: the cubic correction to redshift versus luminosity at a = a is C = 0.359. [ 6 ]
Although shockwave cosmology produces a universe that "looks essentially identical to the aftermath of the big bang", [ 4 ] cosmologists consider that it needs further development before it could be considered as a more advantageous model than the big bang theory (or standard model) in explaining the universe. In particular, and especially for the proposed alternative to dark energy, it would need to explain big bang nucleosynthesis , the quantitative details of the microwave background anisotropies, the Lyman-alpha forest , and galaxy surveys . [ 7 ] | https://en.wikipedia.org/wiki/Shockwave_cosmology |
Shodex is the brand name of HPLC columns and is best known for polymer-based columns. The product range covers aqueous and organic Size Exclusion Chromatography columns for large (bio-)molecules, columns for the routine analysis of sugars and organic acids, and a variety of Reversed Phase and HILIC columns. Additionally they offer Ion Chromatography (IC) and Ion Exchange columns.
Shodex HPLC Columns are manufactured in Japan by Resonac (formerly known as Showa Denko ), one of the largest Japanese chemical companies and listed in the Nikkei 225 index . They produce around 260 different columns, most packed with polymer-based particles, and have been doing so since 1974.
The portfolio includes standard analytical columns, semi-micro columns, and preparative columns. Also size exclusion chromatography calibration standards are available (Pullulan, Polystyrene, Polymethylmethacrylate)
Shodex is distributed worldwide by the different sales offices and by a range of local distributors. | https://en.wikipedia.org/wiki/Shodex |
Shollar water is bottled water from the Shollar spring in Şollar , Azerbaijan , or water pumped to the city of Baku from the Shollar spring.
Baku is the capital and largest city of Azerbaijan , as well as the largest city in the Caspian Sea and of the Caucasus region . Despite its grandeur, in the 19th century its water was salty and seldom clean, contributing to diseases such as cholera , diphtheria , scarlet fever , typhoid , and spotted fever. Faced with constant interruptions and unsanitary supply of water, the people of Baku sought "a reliable, healthy source of water". [ 1 ] When all known solutions had been exhausted, Baku's city planners sought international expertise. After years of research and deliberation, a decision to construct a pipeline to direct water from the Caucasus Mountains to Baku was made. Water from this pipeline became known as "Shollar water".
In the late 19th century, access to drinking water was a serious problem for most people living in Baku. Alternatives such as desalination plants or a pipeline from the Kura River were too costly, and were abandoned. [ 2 ] While in Paris, Haji Zeynalabdin Taghiyev , an Azeri national, industrial magnate, and philanthropist , conceived an idea to build a pipeline from the foothills of the Caucasus Mountains to Baku. In 1899, Taghiyev hired William Lindley , a British civil engineer who had designed multiple water and sewerage systems for more than thirty cities across Europe. Tasked with trying to find a plentiful source of water, Lindley chose the springs near Guba , in the Caucasus Mountains.
Baku's municipal government was primarily opposed to the idea of constructing a pipeline, but Taghiyev insisted, saying, "As long as the Shahdagh Mountain [had] ice on its peak …Shollar will never run out." [ 3 ]
Lindley spent the year of 1899 completing exploratory works near Quba Uyezd's rich springs and rivers. Water was found in Shollar , located on the highlands between Qusar and Khazri . His project was supported by Alimardan Topchubashov , a member of the Duma . Topchubashov supplied 25,000 rubles for Lindley's project. [ citation needed ]
In 1901, the Duma provided another 182,000 rubles for the project. Work began on 3 January 1904. However, the project was slowed due to the revolution between 1905 and 1907. On 5 May 1909, the Duma created the Department of Construction of the Water Conduit, and Lindley was named an engineer. [ citation needed ]
Construction of the pipeline began in January 1917. [ citation needed ]
The Baku-Shollar water conduct passes through the hills of in Guba and ends in Baku. The conduit has a length of 110 miles south and cost 27 million men to construct. Soon after its construction, the pipeline supplied 3 million buckets of water a day to Baku residents. To this day, the Shollar pipeline remains a vital source of water to central Baku. Reliable and clean, this water source has helped increase Baku's population from a few thousand to over 2.5 million.
When constructed, the Baku-Shollar water conduit was the longest in the country.
There are three Shollar Water Towers in Sovetsky settlement of Baku. According to residents, these monuments were taken under state control. These towers were built in the 19th century due to the construction of Shollar water pipeline. From each of this tower people were provided by Shollar water. These towers were functioned till the 1950s.
Access to dependable and clean drinking water remains a major issue for the majority of cities within Azerbaijan . In particular, the Absheron peninsula lacks a source of potable water, as its groundwater is contaminated and polluted. Azerbaijan imports bottled drinking water from other nations such as Iran , Turkey , and the United Arab Emirates , but the country actually has enough domestic water sources to avoid importing water, according to Parviz Moin , an Iranian fluid dynamicist.
Moin conducted research on whether Shollar water could be used as a source in the bottled water operation. After Moin took a sample from the Shollar spring and sent it to Germany for testing, German scientists confirmed that the Shollar water was an "excellent source of drinking [water]." [ 4 ]
Modern water bottling from the Shollar pipeline began on 1 July 1997. Using Taghiyev's original pipeline and local workers, the operation sells water throughout Azerbaijan. The company even expanded its resources and currently bottles soft drinks, including cola and orange-flavored soda. [ 5 ]
[ 6 ] [ 7 ] [ 8 ] [ 9 ] [ 10 ] [ 11 ] [ 12 ] [ 13 ] [ 14 ] | https://en.wikipedia.org/wiki/Shollar_water |
Shoolery's rule , which is named after James Nelson Shoolery , is a good approximation of the chemical shift δ of methylene groups in proton nuclear magnetic resonance . We can calculate shift of the CH 2 protons in a A–CH 2 –B structure using the formula
where 0.23 ppm is the chemical shift of methane and the empirical adjustments S are based on the identities of the A and B groups:
Shoolery's rule is a particular instance of a general class of rules of the form
with two substituents on methylene resulting in two parameters S A {\displaystyle S_{A}} and S B {\displaystyle S_{B}} . [ 1 ]
This nuclear magnetic resonance –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Shoolery's_rule |
The shooting ratio or Bertolo code in filmmaking and television production is the ratio between the total duration of its footage created for possible use in a project and that which appears in its final cut. [ 1 ]
A film with a shooting ratio of 2:1 would have shot twice the amount of footage than was used in the film. In real terms this means that 120 minutes of footage would have been shot to produce a film of 60 minutes in length.
While shooting ratios can vary greatly between productions, a typical shooting ratio for a production using film stock will be between 6:1 and 10:1, whereas a similar production using video is likely to be much higher. This is a direct result of the significant difference in price between video tape stock and film stock and the necessary processing. Although the decisions, styles and preferences of the filmmakers can affect the shooting ratio of a project greatly, the nature of the production (genre, form, single camera, multi-camera, etc.) greatly affects the typical range of the ratios seen – documentary films typically have the highest (often exceeding 100:1 following the rise of video and digital media) and animated films have the lowest (typically as close to 1:1 as possible, since the creation of footage frame by frame makes the time costs of animation extremely high compared to live action). Animated productions will often shoot acting reference (by animators of themselves and or others), location reference, and performance reference (taken of voice actors), but these pieces of reference footage are not regarded as counting towards the shooting ratio, as they were never intended to appear in the projects they were created for. Audition footage, screen tests , and location reference are similarly not counted towards a narrative film's shooting ratio, live action or animated, for the same reason. Since a documentary may potentially use any footage that is shot at any point for any reason, documentary productions do not have similar exceptions. Head slates, tail slates, and outtakes are counted live action shooting ratios because, although the footage is not intended for use in the final picture, it is contained on the same reels and masters as the footage that is intended for final picture. Animated and visual effects projects typically do not include slates as part of the shooting ratio, since they virtually are instantaneous and zero-cost to create in digital formats.
In modern productions, due to the ubiquity of digital filmmaking, shooting ratios are less limited by price of stock and storage, since the vast majority of productions are now entirely or partially digital. Shooting ratios instead defined and limited by the expense (in time, labor, and money, and memory) of actually shooting and editing the film, rather than cost of raw media.
This article related to film or motion picture terminology is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Shooting_ratio |
A shop drawing is a drawing or set of drawings produced by the contractor , supplier , manufacturer, subcontractor , consultants, or fabricator . [ 1 ] Shop drawings are typically required for prefabricated components. Examples of these include: elevators, structural steel, trusses, pre-cast concrete, windows, appliances, cabinets, air handling units, and millwork . Also critical are the installation and coordination shop drawings of the MEP trades such as sheet metal ductwork, piping, plumbing, fire protection, and electrical. Shop drawings are produced by contractors and suppliers under their contract with the owner. The shop drawing is the manufacturer’s or the contractor’s drawn version of information shown in the construction documents. [ 1 ] The shop drawing normally shows more detail than the construction documents. It is drawn to explain the fabrication and/or installation of the items to the manufacturer’s production crew or contractor's installation crews. The style of the shop drawing is usually very different from that of the architect’s drawing. The shop drawing’s primary emphasis is on the particular product or installation and excludes notation concerning other products and installations, unless integration with the subject product is necessary. [ 1 ]
The shop drawings should include information for the architect and engineer to compare to the specifications and drawings. The shop drawing should address the appearance, performance, and prescriptive descriptions in the specifications and construction drawings. [ 2 ] The shop drawing often is more detailed than the information shown in the construction documents to give the architect and engineer the opportunity to review the fabricator’s version of the product, prior to fabrication. References to the construction documents, drawings, and specifications assist the architect and engineer in their review of the shop drawings. Attachment of manufacturer’s material specifications, “catalog cut sheets,” and other manufacturer’s information may be helpful to accompany these drawings. Because shop drawings facilitate the architect’s and engineer’s approval of the product, they should be as clear and complete as possible.
Notes concerning changes or differences from the original documents should be made on the shop drawing for the architect’s and engineer’s approval. Ultimately, they are responsible for changes in these drawings and should have the opportunity to analyze any modifications. A dialogue should occur between the fabricator and the architect and engineer about any areas needing clarification. Successful installations are the result of collaboration between the designer, fabricator, and contractor. [ 2 ]
Dimensions, manufacturing conventions, and special fabrication instructions should be included on the shop drawing. It should be clear to fabrication personnel what will be manufactured from the shop drawings alone. The construction documents are rarely used as a reference in fabrication, with the fabricators relying on the shop drawing for all information. [ 2 ]
Most jobsite dimensions, such as the dimensions between two surfaces on the jobsite, need to be verified. A dimension may be shown on the construction drawings, but the actual dimension may vary, from very small to large increments, depending on jobsite conditions. It is extremely important that the fabricated item arrive on the jobsite ready to be installed without field modification. Special care must be taken by the contractor to measure and verify dimensions. In new construction, plan dimensions usually are sufficient for ordering many fabricated items such as structural steel or precast concrete . [ 2 ]
In remodeling and renovation work, it is essential that field dimensions be verified prior to fabrication. Some fabricators, such as cabinet and casework suppliers, prefer not to rely on the contractor’s verification and will verify the dimensions with their own personnel. [ 2 ]
millwork and casework, find application in projects including commercial offices, retail stores, parks, hotels, shopping malls, restaurants, upholstery for furniture items, lightings, display counters, racks and shelves, mantelpieces etc.
Some fabricators and manufacturers will provide symbols, data, or instructions concerning installation. This can include a list of other materials, such as fasteners or adhesives , appropriate but not included for the product.
Third party review may be required for major building systems. An example of this would be a commercial chiller which would be furnished by the mechanical contractor, but would require electrical connections, plumbing, rigging, insulation and commissioning. Various third parties will need to review the installation information and confirm they are furnishing compatible equipment and proper layout of services. Review of installation information for major equipment should be reviewed with field supervisors including the project superintendent, trade foremen and field engineer. Installation of major equipment will dictate structural clearances and temporary openings. [ 2 ]
Some fabrications will require a sample submittal with the shop drawing, primarily for color and texture selection of finishes. [ 2 ]
Problems with design coordination, such as time consumption and ineffectiveness related to the current 2D paper-based process, are some of the top concerns of a general contractor, since late conflict correction increases the potential for errors in the field. In order to address this issue, there have been an increasing number of Architecture, Engineering and Construction (AEC) firms utilizing building information models (BIM) in their coordination and clash detection processes, which according to practitioners, allows for increased coordination and fewer field problems. Leite et al. [ 3 ] compared types of clashes identified in a manual coordination process (overlay of 2D drawings on a light table by pairs of subcontractors) and through automatic clash detection using a Building Information Model (BIM). The automatic clash detection identified several clashes that were missed by the subcontractors, who were performing this task manually. Also, the manual clash detection identified clashes which could not possibly be found by the automatic clash detection software, since one of the clashing objects (e.g. cable trays) was not modeled in the BIM. This study also included site observations of field detected clashes, some of which were not identified in either manual or automatic processes. Leite noted that the combination of clashes identified in coordination meetings, those automatically detected, as well as those identified in the field enable identification of objects that need to be modeled in order to capture the largest possible number of clashes. This paper was limited to the comparison of types of clashes identified in each of the three methods during a specific project. Although their results cannot be generalized, they still provide insight towards the need to identify what needs to be modeled in a BIM for MEP coordination prior to the start of the coordination process.
Because writing comments on eight to ten copies is a tedious process and an inefficient use of the architect and engineer's time, they will frequently specify other
methods for distributing comments. Quick review is essential during the approval process. [ 4 ] Any method that facilitates this, while providing ample opportunity for comment and complete distribution, should be considered. Although a procedure may be specified in the contract drawings, most architects and engineers are open to suggestions and innovations that speed up the process.
Shop drawings are required, in various forms, depending upon the practice of the
architect and engineer. A specific number of copies may be required by the
specification. An example distribution of the completed and corrected shop
drawings may include the:
Corrections are made by the architect and engineer, and the shop drawing is corrected by the supplier, then the appropriate number of copies is distributed. This method can be time consuming, as the shop drawing is not approved until the corrections are made on it. [ 4 ]
The architect and engineer make comments on the reproducible, then copies are distributed. This method facilitates the timely approval and distribution of the shop drawing. Review comments usually are obvious on the reproducible copy. When sepia copies are used,
the reproduction of the sepia often is not as clear as a normal blue-line print. [ 4 ]
When the supplier and designer have compatible CAD software or when universal file formats such as IFC , PDF or DWG are utilized, the review can be made from a CD, email or FTP transfer. Comments can be made by the designer in a bold font or changes can be boxed for emphasis.
Popular CAD platforms used for generating shop drawings are Advance Steel, AutoCAD , Revit , CATIA , Creo Elements/Pro , Inventor , Solidworks and Tekla Structures .
Concrete reinforcing is one of the many items requiring specialized shop drawings for the fabrication of the material. Concrete reinforcing is custom-fabricated from 60-foot-long reinforcing bars . [ 5 ] The reinforcing bars are cut to length and bent to specific configurations. The shop drawing and the accompanying “cut sheet” lists the quantity, sizes, lengths, and shapes of the reinforcing bar. [ 5 ] This information is provided for review by the structural engineer to ensure that sufficient reinforcing is being supplied; fabrication of the bar by the supplier’s shop; an inventory list for the contractor, upon delivery the typical project has thousands of pieces of reinforcing steel that need to be organized for storage and installation; and placement by the ironworker. The Concrete Reinforcing Steel Institute (CRSI) has developed standard symbols, graphics, and formats for shop drawings and cut sheets that generally are used by reinforcing steel fabricators. [ 5 ] Each fabricator, has particular style for shop drawings and cut sheets, depending on the drafts people and Computer-aided design systems. Examples of software used are Advance Concrete, AutoCAD , MicroStation , ProConcrete and Tekla Structures . | https://en.wikipedia.org/wiki/Shop_drawing |
Shop fitting ( shopfitting ) is the trade of fitting out retail and service shops and stores with equipment, fixtures and fittings. The trade applies to all kinds of outlets from small corner shops to hypermarkets . A shop fitter executes planning, designs shop layout and installs equipment and services. A shop fitting firm typically incorporates professional expertise in interior design , manufacturing of bespoke furniture, signage and fittings (with own or outsourced facilities) and purchasing of retail equipment.
A shop fitting cycle begins with a survey and measurement of available space and preparing design drawings for submission to the client. Alternatively, the client may have their own drawings prepared by an independent interior designer. The shop fitter arranges for purchase of standard equipment and merchandise or production of bespoke furniture, delivers and physically installs them—until the shop is ready for daily operation.
There are different requirements to the different branches and types of shop. Fashion shop design requires up-to-the-minute awareness of current trends in colour and style to create stores that will draw customers in.
'Shopfitting system' refers to a product range made to satisfy the needs of shopfitters and ultimately retailers for display and merchandising goods. A shopfitting system can be adapted from combinations of standardized components for a particular retail application. A manufacturer would normally launch new shopfitting systems on a 2-year basis. Leading manufacturers would offer design oriented systems, followers would reinterpret them making the display solution achievable with as many as existing items as possible, hoping that retailers will choose their product because of the cheap price.
Shopfitting systems are usually connected to a "modular" concept, meaning that each item has more than one use. This economically goes into the rules of "network", where one element has the value of three, if added to another element, because 1x1=1 but 2x2=4: an extra item designed and compatible with others, has very high value.
Shop fitting is a profession that involves the fit-out of retail outlets like corner shops, department stores, convenience stores, supermarkets and hypermarkets with equipment, fixtures and fittings. It’s carried out by a shop fitter who executes all planning, design, layout and installation of equipment and services. A shop fitter brings interior design expertise and assists in the design of bespoke furniture, fittings and signage and also with the buying of retail equipment.
The process begins with a survey of the retail premises and measurement of available space. The next stage is the preparation of design, which is then submitted to the client for review and approval. Some clients provide their own design drawings that are prepared by another interior designer. Finally, the shop fitter arranges for the purchase of standard equipment and the production of the bespoke furniture, which is delivered and installed – ready for the shop operation.
Shop fitting is a precision orientated profession that requires intricacy and exceptional attention to detail in order to meet client requirements. Visual elements heavily impact customer behaviour hence why shop fitting is now at the forefront of attracting new customers to stores across the globe. [ 1 ] | https://en.wikipedia.org/wiki/Shop_fitting |
Shore power or shore supply is the provision of shoreside electrical power to a ship at berth while its main and auxiliary engines are shut down. [ 1 ] While the term denotes shore as opposed to off-shore , it is sometimes applied to aircraft or land-based vehicles (such as campers, heavy trucks with sleeping compartments and tour buses ), which may plug into grid power when parked for idle reduction .
The source for land-based power may be grid power from an electric utility company, but also possibly an external remote generator. These generators may be powered by diesel or renewable energy sources such as wind or solar .
Shore power saves consumption of fuel that would otherwise be used to power vessels while in port, and eliminates the air pollution associated with consumption of that fuel. A port city may have anti-idling laws that require ships to use shore power. Use of shore power may facilitate maintenance of the ship's engines and generators, and reduces noise.
The amount of power required can be relatively large, for example for visiting Cruise Ships to cold-iron the port of Flåm in Norway fitted a system capable of supplying 16 Megavolt-amperes [ 2 ]
" Cold ironing " is specifically a shipping industry term that came into use when all ships had coal -fired engines. When a ship tied up at port, there was no need to continue to feed the fire and the iron engines would cool down, eventually going completely cold – hence the term "cold ironing". Commercial ships can use shore-supplied power for services such as cargo handling, pumping, ventilation and lighting while in port, they need not run their own diesel engines, reducing air pollution emissions. Examples are ferries and cruise ships for hotel electric power, and a salmon feeder ship uses shore power while at the salmon farm. [ 3 ]
On small private boats , electrical power supply on board is usually provided by 12 or 24 volt DC batteries [ 4 ] whilst at sea unless the vessel has a generator. When the vessel is berthed in a marina or harbourside, mains electricity is often offered via a shore power connection. [ 5 ] This allows the vessel to use a battery charger to recharge batteries and also to run mains-powered AC devices such as TV, washing machine, cooking appliances and air conditioning. The power is usually provided from a power pedestal on the dock which is often metered or has a card payment system if electricity is not provided free of charge. The vessel connects to the supply using a suitable shore power cable. [ 6 ]
Shore power, as it relates to the trucking industry, is commonly referred to as "Truck Stop Electrification" (TSE). The US Environmental Protection Agency estimates that trucks plugging in versus idling on diesel fuel could save as much as $3240 annually. [ 7 ] As of 2009 [update] there were 138 truck stops [ 8 ] in the USA that offer on-board systems (also called Shore power) or off-board systems (also called single system electrification) for an hourly fee. Auxiliary power units offer another alternative to both idling and shore power for trucks.
Similar to shore power for ships, a ground power unit (GPU) may be used to supply electric power for an aircraft on the ground, to sustain interior lighting, ventilation and other requirements before starting of the main engines or the aircraft auxiliary power unit (APU). It is also used by aircraft with APUs if the airport authority does not permit the usage of APUs whilst parked, or if the carrier wishes to save on the use of jet fuel (which APUs use). This may be a self-contained engine-generator set, or it may convert commercial power to the voltage and frequency needed for the aircraft (for example 115 V 400 Hz).
Shore power may be a grid connection for passenger trains laying over between runs. [ 9 ] Similarly buses may be connected when not in use. [ citation needed ] | https://en.wikipedia.org/wiki/Shore_power |
Shoring is the process of temporarily supporting a building, vessel, structure, or trench with shores ( props ) when in danger of collapse or during repairs or alterations. Shoring comes from shore , a timber or metal prop. [ 1 ] Shoring may be vertical, angled, or horizontal.
In this method, inclined members called rakers are used to give temporary lateral support to an unsafe wall. One or more timbers slope between the face of the structure to be supported and the ground. [ 2 ] The most effective support is given if the raker meets the wall at an angle of 60 to 70 degrees. A wall-plate is typically used to increase the area of support.
Shoring is commonly used when installing the foundation of a building. A shoring system such as piles and lagging or shotcrete will support the surrounding loads until the underground levels of the building are constructed. Commonly used shoring equipment includes post shores, shoring beams, and timber jacks.
During excavation, shoring systems speed up excavation and provide safety for workers since trenches can be prone to collapse. In this case, shoring should not be confused with shielding . Shoring is designed to prevent collapse where shielding is only designed to protect workers when collapses occur.
Concrete-structure and stone-building shoring, in these cases also referred to as falsework , provides temporary support until the concrete becomes hard and achieves the desired strength to support loads.
Hydraulic shoring is the use of hydraulic pistons that can be pumped outward until they press up against the trench walls. They are typically combined with steel plate or plywood, either being 1-1/8" thick plywood, or special heavy Finland Form (FINFORM) 7/8″ thick.
Beam and plate steel I-beams are driven into the ground and steel plates are slid in amongst them. A similar method that uses wood planks is called soldier boarding. Hydraulics tend to be faster and easier; the other methods tend to be used for longer term applications or larger excavations.
Soil nailing is a technique in which soil slopes, excavations or retaining walls are reinforced by the insertion of relatively slender elements – normally steel reinforcing bars. The bars are usually installed into a pre-drilled hole and then grouted into place or drilled and grouted simultaneously. They are usually installed untensioned at a slight downward inclination. A rigid or flexible facing (often sprayed concrete) or isolated soil nail heads may be used at the surface.
Shoring is used on board when damage has been caused to a vessel's integrity, and to hold leak-stopping devices in place to reduce or stop incoming water. Generally consists of timber 100 mm x 100 mm and used in conjunction with wedges, to further jam shoring in place, pad pieces to spread the load and dogs to hold it together. Also used on board is mechanical shoring as a quick, temporary solution, however it isn't favoured due to its inability to move with the vessel.
This consists of a timber member jammed on a pad piece on either the deck or deck head depending on water levels in the compartment and a strong point, this is called the proud. Then there is a horizontal timber cut to size to fit between this and what it is shoring up, e.g. a splinter box, bulkhead or door. Timber wedges are then used to tighten up the structure if necessary.
This is to support a hatch or splint box on the deck, consisting of a vertical timber between the deck and deck head, with two wedges used opposing each other to tighten it. Pad pieces are used to spread the load on weak structures.
Shoring is a term used in the process of air freight container and pallet (ULD) buildup, e.g. making sure that the cargo placed in containers and on pallets is packed securely and efficiently. Specifically, shoring is done to affix cargo to the ULD and adapt different form factors of cargo items to maximize the use of the available ULD volume.
Typically, wooden beams and various forms of boards are used. Most often, shoring material is re-used but as the airfreight industry uses high-quality timber, shoring material often disappears and is a non-insignificant cost of cargo transport. | https://en.wikipedia.org/wiki/Shoring |
Chlorinated paraffins (CPs) are complex mixtures of polychlorinated n -alkanes ( paraffin wax ). The chlorination degree of CPs can vary between 30 and 70 wt% . CPs are subdivided according to their carbon chain length into short-chain CPs (SCCPs, C 10–13 ), medium-chain CPs (MCCPs, C 14–17 ) and long-chain CPs (LCCPs, C >17 ). Depending on chain length and chlorine content, CPs are colorless or yellowish liquids or solids. [ 1 ]
Chlorinated paraffins are synthesized by reaction of chlorine gas with unbranched paraffin fractions (<2 % isoparaffins, <100 ppm aromatics ) at a temperature of 80–100 °C. [ 2 ] The radical substitution may be promoted by UV-light . [ 3 ] [ 1 ]
When the desired degree of chlorination is achieved, residues of hydrochloric acid and chlorine are blown off with nitrogen . Epoxidized vegetable oil, glycidyl ether or organophosphorous compounds may be added to the final product for improved stability at high temperatures. [ 4 ] [ 5 ]
Commercial products have been classified as substances of unknown or variable composition. CPs are complex mixtures of chlorinated n-alkanes containing thousands of homologues and isomers [ 6 ] which are not completely separated by standard analytical methods. [ 7 ]
CPs are produced in Europe, North America, Australia, Brazil, South Africa and Asia. [ 8 ] In China, where most of the world production capacity is located, 600,000 tons of chlorinated paraffins were produced in 2007. [ 9 ] Production and use volumes of CPs exceeded 1,000,000 tons in 2013. [ 10 ]
Production of CPs for industrial use started in the 1930s, [ 11 ] with global production in 2000 being about 2 million tonnes. [ 12 ] Currently, over 200 CP formulations are in use for a wide range of industrial applications, such as flame retardants and plasticisers , as additives in metal working fluids, in sealants, paints, adhesives, textiles, leather fat and coatings. [ 13 ] [ 1 ]
Short-chain CPs are classified as persistent and their physical properties ( octanol-water partition coefficient (logK OW ) 4.4–8, depending on the chlorination degree) imply a high potential for bioaccumulation . SCCPs are classified as toxic to aquatic organisms, and carcinogenic to rats and mice. Therefore, it was concluded that SCCPs have PBT and vPvB properties and they were added to the Candidate List of substances of very high concern for Authorisation under REACH Regulation . [ 14 ] SCCPs (average chain length of C 12 , chlorination degree 60 wt% ) were categorised in group 2B as possibly carcinogenic to humans from the International Agency for Research on Cancer (IARC). [ 15 ] In 2017, it was agreed to globally ban SCCPs under the Stockholm Convention on Persistent Organic Pollutants , effective December 2018. However, also MCCPs are toxic to the aquatic environment and persistent; MCCPs in soil, biota, and most of the sediment cores show increasing time trends over the last years to decades; MCCP concentrations in sediment close to local sources exceed toxicity thresholds such as the PNEC . [ 10 ] In July 2021 also MCCPs were added to the Candidate List of Substances of Very High Concern (SVHC) under the REACH Regulation.
Chlorinated paraffins have been detected in marine life such as cetaceans (whales) and bivalves (molluscs). Of particular concern is fetal accumulation in whales, with the chemicals beginning to build-up in the offspring before they are even born. [ 16 ] | https://en.wikipedia.org/wiki/Short-chain_chlorinated_paraffins |
Short-path distillation is a distillation technique that involves the distillate traveling a short distance, often only a few centimeters, and is normally done at reduced pressure. [ 1 ] [ 2 ] Short-path distillation systems often have a variety of names depending on the manufacturer of the system and what compounds are being distilled within them. A classic example would be a distillation involving the distillate traveling from one glass bulb to another, without the need for a condenser separating the two chambers. This technique is often used for compounds which are unstable at high temperatures or to purify small amounts of compound. The advantage is that the heating temperature can be considerably lower at reduced pressure than the boiling point of the liquid at standard pressure, and the distillate only has to travel a short distance before condensing. A short path ensures that little compound is lost on the sides of the apparatus. The Kugelrohr is a kind of a short path distillation apparatus which can contain multiple chambers to collect distillate fractions. To increase the evaporation rate without increasing temperature there are several modern techniques that increase the surface area of the liquid such as thin film , wiped film or 'wiper' film , and rolled film all of which involve mechanically spreading a film of the liquid over a large surface . [ 3 ] | https://en.wikipedia.org/wiki/Short-path_distillation |
Short-term conflict alert ( STCA ) is an automated warning system for air traffic controllers (ATCO). It is a ground-based safety net intended to assist the controller in preventing collision between aircraft by generating, in a timely manner, an alert of a potential or actual infringement of separation minima. [ 1 ]
ICAO Doc 4444 requires that radar systems should provide for the display of safety-related alerts including the presentation of actual and predicted conflict. [ 2 ] It is worth mentioning that ICAO Doc 4444 does neither provide definitions of the term STCA nor conflict alert . Instead the term STCA is ambiguously used in ATC community to identify such alerts as well as for data processing systems providing the alert function.
As an implementation STCA is part of the predictive safety net functions. It uses surveillance information derived from radars , ADS-B or multilateration as well as environmental data and optional flight plan information in order to predict the movement of aircraft. This process is usually working unnoticeably to the air traffic controller unless a (potential) separation infringement is identified. In this case STCA will generate an alarm to inform the air traffic controller about the hazardous situation identifying the conflicting aircraft. [ 3 ] Due to the uncertainty of trajectory prediction the look ahead time of STCA system is typically limited to approx. 2 minutes. [ 4 ] Extending the look ahead time is not beneficial as more and more nuisance alerts will be generated.
In addition to STCA, other ground-based safety net functions are typically implemented to support the ATCO. These in include
The equivalent system on board an aircraft is TCAS . This system alerts pilots to possible conflicts, and suggests remedial actions, in the form of a climb or descent. Unlike TCAS, STCA does not normally suggest remedial action. If action is required, the controller will normally give a turn command to the aircraft, eliminating the possibility that his command will contradict that given by TCAS. [ 5 ]
Other concepts of air safety are: | https://en.wikipedia.org/wiki/Short-term_conflict_alert |
A short-term exposure limit ( STEL ) is the acceptable average exposure over a short period of time, usually 15 minutes as long as the time-weighted average is not exceeded.
STEL is a term used in exposure assessment , occupational health , industrial hygiene and toxicology . The STEL may be a legal limit in the United States for exposure of an employee to a chemical substance . The Occupational Safety and Health Administration (U.S. OSHA) has set OSHA-STELs for 1,3-butadiene , [ 1 ] benzene [ 2 ] and ethylene oxide . [ 3 ] For chemicals, STEL assessments are usually done for 15 minutes and expressed in parts per million (ppm), or sometimes in milligrams per cubic meter (mg/m 3 ). [ 4 ]
The American Conference of Governmental Industrial Hygienists publishes a more extensive list of STELs as threshold limit values (TLV-STEL). [ 5 ] | https://en.wikipedia.org/wiki/Short-term_exposure_limit |
Short Message Peer-to-Peer ( SMPP ) in the telecommunications industry is an open, industry standard protocol designed to provide a flexible data communication interface for the transfer of short message [ 1 ] data between External Short Messaging Entities (ESMEs), Routing Entities (REs) and SMSC . [ 2 ]
SMPP is often used to allow third parties (e.g. value-added service providers like news organizations) to submit messages, often in bulk, but it may be used for SMS peering as well. SMPP is able to carry short messages including EMS , voicemail notifications, Cell Broadcasts , WAP messages including WAP Push messages (used to deliver MMS notifications), USSD messages and others. Because of its versatility and support for non- GSM SMS protocols, like UMTS , IS-95 (CDMA), CDMA2000 , ANSI-136 (TDMA) and iDEN , SMPP is the most commonly used protocol for short message exchange outside SS7 networks.
SMPP (Short Message Peer-to-Peer) was originally designed by Aldiscon , a small Irish company that was later acquired by Logica (since 2016, after a number of changes Mavenir ). The protocol was originally created by a developer, Ian J Chambers, to test the functionality of the SMSC without using SS7 test equipment to submit messages.
In 1995 the ETSI included the SMPP protocol into the technical report TR 03.39. [ 3 ]
In 1999 Logica formally handed over SMPP to the SMPP Developers Forum, later renamed as The SMS Forum.
The SMS Forum disbanded in 2007, with this announcement: "The SMS Forum, a non-profit organization with a mission to develop, foster and promote SMS (short message service) to the benefit of the global wireless industry will disband by July 27, 2007." [ 4 ] As part of the original handover terms, SMPP ownership returned to Mavenir.
SMPP uses the client–server model of operation, despite "peer-to-peer" in the name. The Short Message Service Center (SMSC) usually acts as a server, awaiting connections from ESMEs. When SMPP is used for SMS peering, the sending MC usually acts as a client.
The protocol is based on pairs of request/response PDUs ( protocol data units , or packets) exchanged over OSI layer 4 ( TCP session or X.25 SVC3) connections. [ 5 ] The well-known port assigned by the IANA for SMPP when operating over TCP is 2775, but multiple arbitrary port numbers are often used in messaging environments.
Before exchanging any messages, a bind command must be sent and acknowledged. The bind command determines in which direction will be possible to send messages; bind_transmitter only allows client to submit messages to the server, bind_receiver means that the client will only receive the messages, and bind_transceiver (introduced in SMPP 3.4) allows message transfer in both directions. [ 6 ] In the bind command the ESME identifies itself using system_id, system_type and password; the address_range field designed to contain ESME address is usually left empty. The bind command contains interface_version parameter to specify which version of SMPP protocol will be used.
Message exchange may be synchronous, where each peer waits for a response for each PDU being sent, or asynchronous, where multiple requests can be issued without waiting and acknowledged in a skew order by the other peer; the number of unacknowledged requests is called a window ; for the best performance both communicating sides must be configured with the same window size.
The SMPP standard has evolved during the time. The most commonly used versions of SMPP are:
The applicable version is passed in the interface_version parameter of a bind command.
The SMPP PDUs are binary encoded for efficiency. They start with a header which may be followed by a body:
Each PDU starts with a header. The header consists of 4 fields, each of length of 4 octets:
All numeric fields in SMPP use the big endian order, which means that the first octet is the Most Significant Byte (MSB).
This is an example of the binary encoding of a 60-octet submit_sm PDU. The data is shown in Hex octet values as a single dump and followed by a header and body break-down of that PDU.
This is best compared with the definition of the submit_sm PDU from the SMPP specification in order to understand how the encoding matches the field by field definition.
The value break-downs are shown with decimal in parentheses and Hex values after that. Where you see one or several hex octets appended, this is because the given field size uses 1 or more octets encoding.
Again, reading the definition of the submit_sm PDU from the spec will make all this clearer.
Note that the text in the short_message field must match the data_coding. When the data_coding is 8 (UCS2), the text must be in UCS-2BE (or its extension, UTF-16BE ). When the data_coding indicates a 7-bit encoding, each septet is stored in a separate octet in the short_message field (with the most significant bit set to 0). SMPP 3.3 data_coding exactly copied TP-DCS values of GSM 03.38 , which make it suitable only for GSM 7-bit default alphabet, UCS2 or binary messages; SMPP 3.4 introduced a new list of data_coding values:
The meaning of the data_coding=4 or 8 is the same as in SMPP 3.3. Other values in the range 1-15 are reserved in SMPP 3.3. Unfortunately, unlike SMPP 3.3, where data_coding=0 was unambiguously GSM 7-bit default alphabet, for SMPP 3.4 and higher the GSM 7-bit default alphabet is missing in this list, and data_coding=0 may differ for various Short message service centers —it may be ISO-8859-1 , ASCII , GSM 7-bit default alphabet, UTF-8 or even configurable per ESME. When using data_coding=0 , both sides (ESME and SMSC) must be sure they consider it the same encoding. Otherwise it is better not to use data_coding=0 . It may be tricky to use the GSM 7-bit default alphabet, some Short message service centers requires data_coding=0 , others e.g. data_coding=241 .
Despite its wide acceptance, the SMPP has a number of problematic features:
Although data_coding value in SMPP 3.3 are based on the GSM 03.38 , since SMPP 3.4 there is not a standardized data_coding value for the GSM default alphabet ( GSM 03.38 ). It is further ambiguous whether the 7-bit characters are packed, as in GSM, allowing sending 160 characters in 140 octets, or whether each 7-bit character is encoded as an entire octet (with the high bit set to zero, as with ASCII).
According to SMPP 3.4 and 5.0 the value data_coding=0 means ″SMSC Default Alphabet″. Which encoding it really is, depends on the type of the SMSC and its configuration.
One of the encodings in CDMA standard C.R1001 is Shift-JIS used for Japanese. SMPP 3.4 and 5.0 specifies three encodings for Japanese (JIS, ISO-2022-JP and Extended Kanji JIS), but none of them is identical with CDMA MSG_ENCODING 00101. It seems that the Pictogram encoding (data_coding=9) is used to carry the messages in Shift-JIS in SMPP.
When a submit_sm fails, the SMSC returns a submit_sm_resp with non-zero value of command_status and ″empty″ message_id.
For the best compatibility, any SMPP implementation should accept both variants of negative submit_sm_resp regardless of the version of SMPP standard used for the communication.
The original intention of error scenarios was that no body would be returned in the PDU response. This was the standard behavior exhibited on all Aldiscon/Logica SMSC and also in most of the other vendors. When SMPP 3.4 was being taken on by the WAP forum, several clarifications were requested on whether a body should be included with NACKed response and measures were taken to clarify this in several places in the specification including the submit_sm section and also in the bind_transceiver section. What should have been done was to add the clarification that we eventually added in V5.0.. that bodies are not supposed to be included in error responses. Some vendors have been very silly in their implementations including bodies on rejected bind_transmitter responses but not on bind_transceiver responses etc. The recommendation I would make to vendors.. as suggested above.. accept both variants. But its also wise to allow yourself issue NACKed submit_sm_resp and deliver_sm_resp PDUs with and without an empty body. In the case of these two PDUs, that empty body will look like a single NULL octet at the end of the stream. The reason you may need this ability to include what I call dummy bodies with NACKed requests is that the other side of the equation may be unable or unwilling to change their implementation to tolerate the missing body. (I worked on three versions of SMPP specification in Aldiscon/Logica and designed the ESME solution for Openmind Networks)
The only way to pass delivery receipts in SMPP 3.3 is to put information in a text form to the short_message field; however, the format of the text is described in Appendix B of SMPP 3.4, although SMPP 3.4 may (and should) use receipted_message_id and message_state TLVs for the purpose. While SMPP 3.3 states that Message ID is a C-Octet String (Hex) of up to 8 characters (plus terminating '\0'), the SMPP 3.4 specification states that the id field in the Delivery Receipt Format is a C-Octet String (Decimal) of up to 10 characters. This splits SMPP implementations to 2 groups:
The SMPP 3.4 specification does however state that the delivery receipt format is SMSC vendor specific, and therefore the format included in the specification is merely one possibility. As noted above, when using SMPP 3.4 receipted_message_id and message_state TLVs should be used to convey the outcome of a message.
Since introduction of TLV parameters in version 3.4, the SMPP may be regarded an extensible protocol. In order to achieve the highest possible degree of compatibility and interoperability any implementation should apply the Internet robustness principle : ″Be conservative in what you send, be liberal in what you accept″. It should use a minimal set of features which are necessary to accomplish a task. And if the goal is communication and not quibbling, each implementation should overcome minor nonconformities with standard:
Information applicable to one version of SMPP can often be found in another version of SMPP, for example with the case of SMPP 3.4 describing the only mechanism of delivery receipts in SMPP 3.3 described above.
The SMPP protocol is designed on a clear-text binary protocol which needs to be considered if using for potentially sensitive information such as one-time passwords via SMS. There are, however, implementations of SMPP over SSL/TLS if required. [ 7 ] | https://en.wikipedia.org/wiki/Short_Message_Peer-to-Peer |
A Short Message Service Center ( SMSC ) is a network element in the mobile telephone network. Its purpose is to store, forward, convert and deliver Short Message Service (SMS) messages.
The full designation of an SMSC according to 3GPP is Short Message Service - Service Center (SMS-SC). 8522076203
SMS can be directed in several ways:
The tasks of an SMSC can be described as
When a user sends a text message (SMS message) to another user, the message gets stored in the SMSC (Short Message Service Center), which delivers it to the destination user when they are available. This is a store and forward option.
An SMS center (SMSC) is responsible for handling the SMS operations of a wireless network.
SMSCs can be used to interface with other applications, for example a spreadsheet can interface with the SMSC allowing messages to be sent SMS from an Excel spreadsheet , or to send an SMS from Excel. Inbound messages to a long number or short code can also be passed through the SMSC allowing m2m communications or Telematics.
An SMS message is stored temporarily in the SMS center if the recipient mobile phone is unavailable. It is possible on most mobile handsets to specify an expiry period after which the SMS message will be deleted from the SMS center. Once deleted, the SMS message will no longer be available for dispatch to the recipient mobile phone (even if it comes on line). The validity period should be regarded by the handset user as a request, as the SMSC itself can be configured to ignore or otherwise handle message delivery schedules.
The SMS sender needs to set a flag in the SMS message to notify the SMS center that they want the status report about the delivery of this SMS message. This is usually done by changing a setting on the mobile handset. | https://en.wikipedia.org/wiki/Short_Message_service_center |
SOAP (Short Oligonucleotide Analysis Package) is a suite of bioinformatics software tools from the BGI Bioinformatics department enabling the assembly, alignment, and analysis of next generation DNA sequencing data. It is particularly suited to short read sequencing data .
All programs in the SOAP package may be used free of charge and are distributed under the GPL open source software license.
The SOAP suite of tools can be used to perform the following genome assembly tasks:
SOAPaligner (SOAP2) is specifically designed for fast alignment of short reads and performs favorably with respect to similar alignment tools such as Bowtie and MAQ. [ 1 ]
SOAPdenovo is a short read de novo assembler utilizing De Bruijn graph construction. It is optimized for short reads such as that generated by Illumina and is capable of assembling large genomes such as the human genome. [ 2 ] SOAPdenovo was used to assemble the genome of the giant panda . [ 3 ] This was upgraded to SOAPdenovo2, which was optimized for large genomes and included the widely used GapCloser module. [ 4 ]
SOAPdenovo-Trans is a de novo transcriptome assembler designed specifically for RNA-Seq that was created for the 1000 Plant Genomes project. [ 5 ]
SOAPindel is a tool to find insertions and deletions from next generation paired-end sequencing data, providing a list of candidate indels with quality scores. [ 6 ]
SOAPsnp is a consensus sequence builder. This tool uses the output from SOAPaligner to generate a consensus sequence which enables SNPs to be called on a newly sequenced individual.
SOAPsv is a tool to find structural variations using whole genome assembly. [ 7 ]
SOAPnuke is a tool for integrated quality control and preprocessing of datasets from genomic, small RNA , Digital Gene Expression , and metagenomic experiments. [ 8 ]
The first release of SOAP consisted only of the sequence alignment tool SOAPaligner . [ 9 ]
SOAP v2 [ 1 ] extended and improved on SOAP v1 by significantly improving the performance of the SOAPaligner tool. Alignment time was reduced by a factor of 20-30, while memory usage was reduced by a factor of 3. Support was added for compressed file formats.
The SOAP suite was expanded then to include the new tools: SOAPdenovo 1&2, SOAPindel, SOAPsnp, and SOAPsv.
SOAP v3 extended the alignment tool by being the first short-read alignment tool to utilize GPU processors. [ 10 ] As a result of these improvements, SOAPalign significantly outperformed competing aligners Bowtie and BWA in terms of speed. | https://en.wikipedia.org/wiki/Short_Oligonucleotide_Analysis_Package |
A short circuit (sometimes abbreviated to short or s/c ) is an electrical circuit that allows a current to travel along an unintended path with no or very low electrical impedance . This results in an excessive current flowing through the circuit.
The opposite of a short circuit is an open circuit , which is an infinite resistance (or very high impedance ) between two nodes.
A short circuit is an abnormal connection between two nodes of an electric circuit intended to be at different voltages . This results in an electric current limited only by the Thévenin equivalent resistance of the rest of the network which can cause circuit damage, overheating , fire or explosion . Although usually the result of a fault , there are cases where short circuits are caused intentionally, for example, for the purpose of voltage-sensing crowbar circuit protectors .
In circuit analysis , a short circuit is defined as a connection between two nodes that forces them to be at the same voltage. In an 'ideal' short circuit, this means there is no resistance and thus no voltage drop across the connection. In real circuits, the result is a connection with almost no resistance. In such a case, the current is limited only by the resistance of the rest of the circuit.
A common type of short circuit occurs when the positive and negative terminals of a battery or a capacitor are connected with a low- resistance conductor , like a wire . With a low resistance in the connection, a high current will flow, causing the delivery of a large amount of energy in a short period of time.
A high current flowing through a battery can cause a rapid increase of temperature, potentially resulting in an explosion with the release of hydrogen gas and electrolyte (an acid or a base ), which can burn tissue and cause blindness or even death. Overloaded wires will also overheat causing damage to the wire's insulation, or starting a fire.
In electrical devices, unintentional short circuits are usually caused when a wire's insulation breaks down, or when another conducting material is introduced, allowing charge to flow along a different path than the one intended.
In mains circuits, short circuits may occur between two phases , between a phase and neutral or between a phase and earth (ground). Such short circuits are likely to result in a very high current and therefore quickly trigger an overcurrent protection device. However, it is possible for short circuits to arise between neutral and earth conductors and between two conductors of the same phase. Such short circuits can be dangerous, particularly as they may not immediately result in a large current and are therefore less likely to be detected. Possible effects include unexpected energisation of a circuit presumed to be isolated. To help reduce the negative effects of short circuits, power distribution transformers are deliberately designed to have a certain amount of leakage reactance . The leakage reactance (usually about 5 to 10% of the full load impedance) helps limit both the magnitude and rate of rise of the fault current .
A short circuit may lead to formation of an electric arc . The arc, a channel of hot ionized plasma , is highly conductive and can persist even after significant amounts of original material from the conductors has evaporated. Surface erosion is a typical sign of electric arc damage. Even short arcs can remove significant amounts of material from the electrodes. The temperature of the resulting electrical arc is very high (tens of thousands of degrees), causing the metal on the contact surfaces to melt, pool and migrate with the current, as well as to escape into the air as fine particulate matter. [ 1 ]
Within milliseconds, a short circuit can deliver a fault current that is hundreds or thousands of times higher than the normal operating current of the system. [ 2 ] Damage from short circuits can be reduced or prevented by employing fuses , circuit breakers , or other overload protection , which disconnect the power in reaction to excessive current. Overload protection must be chosen according to the current rating of the circuit. Circuits for large home appliances require protective devices set or rated for higher currents than lighting circuits. Wire gauges specified in building and electrical codes are chosen to ensure safe operation in conjunction with the overload protection. An overcurrent protection device must be rated to safely interrupt the maximum prospective short-circuit current .
In an improper installation, the overcurrent from a short circuit may cause ohmic heating of the circuit parts with poor conductivity (faulty joints in wiring, faulty contacts in power sockets, or even the site of the short circuit itself). Such overheating is a common cause of fires . An electric arc, if it forms during the short circuit, produces high amount of heat and can cause ignition of combustible substances as well.
In industrial and utility distribution systems, dynamic forces generated by high short-circuit currents cause conductors to spread apart. Busbars, cables, and apparatus can be damaged by the forces generated in a short circuit.
In electronics , the ideal model (infinite gain ) of an operational amplifier is said to produce a virtual short circuit between its input terminals because no matter what the output voltage is, the difference of potential between its input terminals is zero. If one of the input terminals is connected to the ground, then the other one is said to provide a virtual ground because its potential is (ideally) identical to that of the ground. [ 3 ] [ 4 ] An ideal operational amplifier also has infinite input impedance , so unlike a real short circuit, no current flows between the terminals of the virtual short. [ 5 ] | https://en.wikipedia.org/wiki/Short_circuit |
Short Course Immune Induction Therapy or SCIIT , is a therapeutic strategy employing rapid, specific, short term-modulation of the immune system using a therapeutic agent to induce T-cell non-responsiveness, also known as operational tolerance. [ 1 ] [ 2 ] As an alternative strategy to immunosuppression and antigen-specific tolerance inducing therapies, the primary goal of SCIIT is to re-establish or induce peripheral immune tolerance in the context of autoimmune disease and transplant rejection through the use of biological agents (compare also tolerogenic therapy ). In recent years, SCIIT has received increasing attention in clinical and research settings as an alternative to immunosuppressive drugs currently used in the clinic, drugs which put the patients at risk of developing infection , cancer , and cardiovascular disease . [ 3 ]
Immune tolerance can be defined as the ability of the immune system to distinguish between self and non-self, or harmless and harmful. T-cells are able to distinguish between self and non-self largely through their T-cell receptor , or TCR. Immune tolerance is maintained by central and peripheral tolerance . During central tolerance , T-cells are selected in the thymus and allowed to enter the periphery based on the ability of the T-cell to recognize self-peptides (via its TCR) being presented in the context of self-MHC. If the TCR binds the peptide-MHC complex with high affinity, the T cell is deleted from the host. In a healthy individual, this process eliminates the majority of T-cells that are self-reactive, although a few T-cells will escape thymic deletion. However, these potentially self-reactive cells in the periphery are held in check by a number of regulatory mechanisms such as active suppression by regulatory T cells( Tregs ), clonal anergy , deletion, and ignorance. [ 4 ] While autoimmunity is thought to result from the breakdown of central and peripheral tolerance, undesirable immune responses such as transplant organ rejection occur when the immune system is working properly and recognizes the transplanted organ as being non-self, leading to rejection of the transplanted tissue. In this context, manipulating the immune system to recognize the transplanted organ as self for the induction of immunological tolerance would be beneficial for the establishment of transplant tolerance. [ 3 ]
As autoimmunity and organ transplant rejection are inextricably linked to T-cell activation and differentiation, it is apposite that T-cells are the primary target of modern tolerance induction strategies. Current strategies for the treatment of T-cell mediated pathologies employ long-term, broad immunosuppressive drugs, which are moderately effective in limiting T-cell responses but carry unfavorable side effects, such as organ toxicity, risk of infection, and cancer. [ 3 ] Due to the adverse risks associated with immunosuppressive drugs, it became apparent that the ideal strategy would be antigen-specific: a therapy that was able to inhibit the antigen-specific T-cell response, but would still leave the remainder of the immune system intact to defend against infection. [ 4 ] These strategies employed the use of soluble peptide tolerance and oral peptide tolerance to great efficacy in experimental settings, however, all have failed to translate into the clinic. One reason for the failure of these strategies is that T-cell mediated organ destruction is now understood to be a complex event involving epitope spreading to multiple tissue-specific antigens and cryptic epitopes. Thus, at any given stage of disease or rejection, the T-cell response is likely to be heterogenic, involving multiple TCR specificities, leading to difficulties in prescribing the antigen, dosing, and timing of administration required to induce tolerance. While antigen-specific tolerance induction is an attractive strategy, [ 5 ] it's limited by a lack of knowledge, and because of its stringent requirements, a slightly broader approach is more practical.
SCIIT attempts to occupy the middle ground of immuno-therapeutics by avoiding the dangerous side effects of general immunosuppressive therapy, while alleviating the stringent demands of antigen-specific tolerance induction. SCIIT aims to achieve this by targeting receptor-ligand interactions that provide signals that are critical for the survival, activation, and function of T-cells in the periphery.
T-cell receptor stimulation is the primary signal required for the activation and differentiation of T-cells. Recognition of specific antigen through the interaction of the TCR with its cognate antigen/MHC complex leads to a cascade of effects ultimately leading to T cell-mediated immunity. It is with good reason that some of the most promising tolerance inducing therapies have targeted the TCR and its co-receptors.
The most promising therapy to make use of targeting the T-cell through its receptor is the class of monoclonal antibodies specific for CD3 . The CD3 chains compose the signaling arm of the TCR, translating the strength of binding affinity of the TCR/peptide-MHC complex to downstream cytoplasmic signals. [ 6 ] Initial studies involving αCD3 as a therapy used Fc receptor (FCR)-binding monoclonal antibodies, which proved to be very efficacious. A short, 5-day course of FcR-binding, anti-CD3 antibody treatment was able to re-establish peripheral tolerance in animal models of autoimmune disease, thereby completely reversing disease. The mechanism of action caused systemic depletion of T-cells from the blood and sites of inflammation. While effective, the FcR-binding antibodies deliver strong stimulatory signals to the T-cell, leading to activation-induced-cell-death, and largely depleting T-cells from the periphery and site of inflammation . This effect was transient, and mice were able to mount normal immune responses to exogenous antigens within weeks of treatment. However, treatment with FcR-binding anti-CD3 antibody such as OKT3 induced strong stimulation of T-cells, leading to T-cell cytokine release, which resulted in a number of symptoms when administered to patients. [ 7 ] In lieu of this, a mutant version of the antibody was developed that lacked the ability to bind FcR. This mutant form of the anti-CD3 acts by only delivering a partial signal to the T-cell, leading to inactivation, deletion, and anergy induction. Results from a clinical trial in 2000 showed that treatment with the modified form of anti-CD3 preserved islet function in new-onset Type 1 diabetics. Data from follow up studies suggest that anti-CD3 antibody treatment caused not only anergy induction and transient depletion of T cells, but an increase in CD4+ and CD8+ Foxp3+Tregs. [ 5 ] While promising, islet function gradually decreased over time in human patients treated with anti-CD3 antibodies, and data suggest that the mitogenic capabilities of anti-CD3 antibodies may overcome their therapeutic utility. [ 5 ] [ 8 ] Although current clinical trials are ongoing to improve the efficacy of anti-CD3 antibody treatment, alternative targets within the TCR may provide a better therapeutic T cell target.
Although it is not thought to directly target components of the TCR/CD3 complex, Alemtuzumab , or Campath-1H, has been utilized because of its strong ability to deplete T cells, in many cases for up to 3 years. It is a monoclonal antibody that targets CD52 , a protein that is expressed on the surface of mature lymphocytes . Originally approved for B cell cancers, its use has spread to off-label indications. [ 9 ] One such indication includes renal transplantation, whereby its use remains controversial. This is not because the antibody is not extremely efficient at immune-suppressing patients, but due to the inherent risk of patients developing serious complications. [ 10 ] [ 11 ] Furthermore, the use of Alemtuzumab in transplantation may also be a question related to reimbursement, as it is comparably cheaper to other drugs used to treat clinical episodes of transplant rejection, and it can significantly shorten the duration of a patient's hospital visit. [ 9 ] Alemtuzumab is now being tested in clinical trials for the treatment of autoimmune diseases, such as Multiple Sclerosis, where it has shown considerable promise at preventing multiple sclerosis symptoms in Relapsing-Remitting patients. However, many patients treated with alemtuzumab went on to develop other autoimmune diseases, [ 11 ] especially those involving the thymus, as well as a plethora of infections. In general, the data suggest that alemtuzumab is excellent at inducing immune suppression. However, as a SCITT agent, it appears to overstep the required immune modulation, placing patients at unnecessary risk.
Antibodies directed against the αβ chains of the TCR have also been shown to be efficacious for the induction and restoration of immunological tolerance in animal models of autoimmunity [ 12 ] and transplantation. [ 13 ] Like anti-CD3 antibodies, the administration of anti-TCR αβ antibodies has generally been met with favorable effects in the treatment of autoimmune disease. Treatment of mice with anti-TCR αβ antibody at the time of Experimental autoimmune encephalomyelitis (EAE) disease induction completely prevented disease onset, while treatment during chronic EAE disease caused disease remission. [ 12 ] Anti-TCR αβ antibody treatment induces tolerance through a number of mechanisms including the functional blockade of T cells at the site of inflammation, transient T-cell depletion, upregulation of Th2 cytokines, [ 14 ] and an increase in the regulatory NKT cell population. [ 12 ] In transplantation, the use of anti-TCR αβ antibody treatment may be more efficacious than anti-CD3 antibody treatment, and its potential for prolonging allograft survival has been demonstrated in multiple animal models of transplantation, such as renal allografts, [ 15 ] heterotopic heart transplants, [ 14 ] and corneal transplants. [ 16 ] While this has yet to be defined completely, this is likely the combined result of preserving γδ T cells and the lack of mitogenic effects observed when peripheral blood monocytes are incubated with anti-αβ TCR antibodies. The ability for anti-αβ TCR antibodies to modulate T cells without inducing significant cytokine release is likely due in part because the αβ TCR lacks immunoreceptor tyrosine-based activation motifs (ITAM's). [ 6 ] The ability for targeting the αβ TCR with monoclonal antibodies to prevent renal transplant rejection is currently the focus of the phase 2 clinical trial.
Due to the activation, depletion, and immunosuppression following the administration of T-cell depleting therapies, there is a risk of infection to the patient. The most common infection is caused by the reactivation of latent Epstein–Barr virus infection. [ 5 ] [ 17 ] EBV reactivation in the context of T-cell depleting strategies can result in serious complications, such as post-transplant lymphoproliferative disorder, which can have fatal consequences. [ 10 ] However, in a European clinical study using anti-CD3 antibody treatment, patients previously infected with EBV had a transient incidence of EBV reactivation during treatment. The infection was self-limiting and did not return during the 4 years following treatment cessation, nor was it associated with any severe complications. [ 5 ] | https://en.wikipedia.org/wiki/Short_course_immune_induction_therapy |
Short integer solution (SIS) and ring-SIS problems are two average -case problems that are used in lattice-based cryptography constructions. Lattice-based cryptography began in 1996 from a seminal work by Miklós Ajtai [ 1 ] who presented a family of one-way functions based on SIS problem. He showed that it is secure in an average case if the shortest vector problem S V P γ {\displaystyle \mathrm {SVP} _{\gamma }} (where γ = n c {\displaystyle \gamma =n^{c}} for some constant c > 0 {\displaystyle c>0} ) is hard in a worst-case scenario.
Average case problems are the problems that are hard to be solved for some randomly selected instances. For cryptography applications, worst case complexity is not sufficient, and we need to guarantee cryptographic construction are hard based on average case complexity.
A full rank lattice L ⊂ R n {\displaystyle {\mathfrak {L}}\subset \mathbb {R} ^{n}} is a set of integer linear combinations of n {\displaystyle n} linearly independent vectors { b 1 , … , b n } {\displaystyle \{b_{1},\ldots ,b_{n}\}} , named basis :
where B ∈ R n × n {\displaystyle B\in \mathbb {R} ^{n\times n}} is a matrix having basis vectors in its columns.
Remark: Given B 1 , B 2 {\displaystyle B_{1},B_{2}} two bases for lattice L {\displaystyle {\mathfrak {L}}} , there exist unimodular matrices U 1 {\displaystyle U_{1}} such that B 1 = B 2 U 1 − 1 , B 2 = B 1 U 1 {\displaystyle B_{1}=B_{2}U_{1}^{-1},B_{2}=B_{1}U_{1}} .
Definition: Rotational shift operator on R n ( n ≥ 2 ) {\displaystyle \mathbb {R} ^{n}(n\geq 2)} is denoted by rot {\displaystyle \operatorname {rot} } , and is defined as:
Micciancio introduced cyclic lattices in his work in generalizing the compact knapsack problem to arbitrary rings. [ 2 ] A cyclic lattice is a lattice that is closed under rotational shift operator. Formally, cyclic lattices are defined as follows:
Definition: A lattice L ⊆ Z n {\displaystyle {\mathfrak {L}}\subseteq \mathbb {Z} ^{n}} is cyclic if ∀ x ∈ L : rot ( x ) ∈ L {\displaystyle \forall {\boldsymbol {x}}\in {\mathfrak {L}}:\operatorname {rot} ({\boldsymbol {x}})\in {\mathfrak {L}}} .
Examples: [ 3 ]
consider the quotient polynomial ring R = Z [ x ] / ( x n − 1 ) {\displaystyle R=\mathbb {Z} [x]/(x^{n}-1)} , and let p ( x ) {\displaystyle p(x)} be some polynomial in R {\displaystyle R} , i.e. p ( x ) = ∑ i = 0 n − 1 a i x i {\displaystyle p(x)=\sum _{i=0}^{n-1}a_{i}x^{i}} where a i ∈ Z {\displaystyle a_{i}\in \mathbb {Z} } for i = 0 , … , n − 1 {\displaystyle i=0,\ldots ,n-1} .
Define the embedding coefficient Z {\displaystyle \mathbb {Z} } -module isomorphism ρ {\displaystyle \rho } as:
Let I ⊂ R {\displaystyle I\subset R} be an ideal. The lattice corresponding to ideal I ⊂ R {\displaystyle I\subset R} , denoted by L I {\displaystyle {\mathfrak {L}}_{I}} , is a sublattice of Z n {\displaystyle \mathbb {Z} ^{n}} , and is defined as
Theorem: L ⊂ Z n {\displaystyle {\mathfrak {L}}\subset \mathbb {Z} ^{n}} is cyclic if and only if L {\displaystyle {\mathfrak {L}}} corresponds to some ideal I {\displaystyle I} in the quotient polynomial ring R = Z [ x ] / ( x n − 1 ) {\displaystyle R=\mathbb {Z} [x]/(x^{n}-1)} .
proof: ⇐ ) {\displaystyle \Leftarrow )} We have:
Let ( a 0 , … , a n − 1 ) {\displaystyle (a_{0},\ldots ,a_{n-1})} be an arbitrary element in L {\displaystyle {\mathfrak {L}}} . Then, define p ( x ) = ∑ i = 0 n − 1 a i x i ∈ I {\displaystyle p(x)=\sum _{i=0}^{n-1}a_{i}x^{i}\in I} . But since I {\displaystyle I} is an ideal, we have x p ( x ) ∈ I {\displaystyle xp(x)\in I} . Then, ρ ( x p ( x ) ) ∈ L I {\displaystyle \rho (xp(x))\in {\mathfrak {L}}_{I}} . But, ρ ( x p ( x ) ) = rot ( a 0 , … , a n − 1 ) ∈ L I {\displaystyle \rho (xp(x))=\operatorname {rot} (a_{0},\ldots ,a_{n-1})\in {\mathfrak {L}}_{I}} . Hence, L {\displaystyle {\mathfrak {L}}} is cyclic.
⇒ ) {\displaystyle \Rightarrow )}
Let L ⊂ Z n {\displaystyle {\mathfrak {L}}\subset \mathbb {Z} ^{n}} be a cyclic lattice. Hence ∀ ( a 0 , … , a n − 1 ) ∈ L : rot ( a 0 , … , a n − 1 ) ∈ L {\displaystyle \forall (a_{0},\ldots ,a_{n-1})\in {\mathfrak {L}}:\operatorname {rot} (a_{0},\ldots ,a_{n-1})\in {\mathfrak {L}}} .
Define the set of polynomials I := { ∑ i = 0 n − 1 a i x i ∣ ( a 0 , … , a n − 1 ) ∈ L } {\displaystyle I:=\left\{\sum _{i=0}^{n-1}a_{i}x^{i}\mid (a_{0},\ldots ,a_{n-1})\in {\mathfrak {L}}\right\}} :
Hence, I ⊂ R {\displaystyle I\subset R} is an ideal, and consequently, L = L I {\displaystyle {\mathfrak {L}}={\mathfrak {L}}_{I}} .
Let f ( x ) ∈ Z [ x ] {\displaystyle f(x)\in \mathbb {Z} [x]} be a monic polynomial of degree n {\displaystyle n} . For cryptographic applications, f ( x ) {\displaystyle f(x)} is usually selected to be irreducible. The ideal generated by f ( x ) {\displaystyle f(x)} is:
The quotient polynomial ring R = Z [ x ] / ( f ( x ) ) {\displaystyle R=\mathbb {Z} [x]/(f(x))} partitions Z [ x ] {\displaystyle \mathbb {Z} [x]} into equivalence classes of polynomials of degree at most n − 1 {\displaystyle n-1} :
where addition and multiplication are reduced modulo f ( x ) {\displaystyle f(x)} .
Consider the embedding coefficient Z {\displaystyle \mathbb {Z} } -module isomorphism ρ {\displaystyle \rho } . Then, each ideal in R {\displaystyle R} defines a sublattice of Z n {\displaystyle \mathbb {Z} ^{n}} called ideal lattice .
Definition: L I {\displaystyle {\mathfrak {L}}_{I}} , the lattice corresponding to an ideal I {\displaystyle I} , is called ideal lattice. More precisely, consider a quotient polynomial ring R = Z [ x ] / ( p ( x ) ) {\displaystyle R=\mathbb {Z} [x]/(p(x))} , where ( p ( x ) ) {\displaystyle (p(x))} is the ideal generated by a degree n {\displaystyle n} polynomial p ( x ) ∈ Z [ x ] {\displaystyle p(x)\in \mathbb {Z} [x]} . L I {\displaystyle {\mathfrak {L}}_{I}} , is a sublattice of Z n {\displaystyle \mathbb {Z} ^{n}} , and is defined as:
Remark: [ 5 ]
The Short Integer Solution (SIS) problem is an average case problem that is used in lattice-based cryptography constructions. Lattice-based cryptography began in 1996 from a seminal work by Ajtai [ 1 ] who presented a family of one-way functions based on the SIS problem. He showed that it is secure in an average case if S V P γ {\displaystyle \mathrm {SVP} _{\gamma }} (where γ = n c {\displaystyle \gamma =n^{c}} for some constant c > 0 {\displaystyle c>0} ) is hard in a worst-case scenario. Along with applications in classical cryptography, the SIS problem and its variants are utilized in several post-quantum security schemes including CRYSTALS-Dilithium and Falcon . [ 7 ] [ 8 ]
Let A ∈ Z q n × m {\displaystyle A\in \mathbb {Z} _{q}^{n\times m}} be an n × m {\displaystyle n\times m} matrix with entries in Z q {\displaystyle \mathbb {Z} _{q}} that consists of m {\displaystyle m} uniformly random vectors a i ∈ Z q n {\displaystyle {\boldsymbol {a_{i}}}\in \mathbb {Z} _{q}^{n}} : A = [ a 1 | ⋯ | a m ] {\displaystyle A=[{\boldsymbol {a_{1}}}|\cdots |{\boldsymbol {a_{m}}}]} . Find a nonzero vector x ∈ Z m {\displaystyle {\boldsymbol {x}}\in \mathbb {Z} ^{m}} such that for some norm ‖ ⋅ ‖ {\displaystyle \|\cdot \|} :
A solution to SIS without the required constraint on the length of the solution ( ‖ x ‖ ≤ β {\displaystyle \|{\boldsymbol {x}}\|\leq \beta } ) is easy to compute by using Gaussian elimination technique. We also require β < q {\displaystyle \beta <q} , otherwise x = ( q , 0 , … , 0 ) ∈ Z m {\displaystyle {\boldsymbol {x}}=(q,0,\ldots ,0)\in \mathbb {Z} ^{m}} is a trivial solution.
In order to guarantee f A ( x ) {\displaystyle f_{A}({\boldsymbol {x}})} has non-trivial, short solution, we require:
Theorem: For any m = poly ( n ) {\displaystyle m=\operatorname {poly} (n)} , any β > 0 {\displaystyle \beta >0} , and any sufficiently large q ≥ β n c {\displaystyle q\geq \beta n^{c}} (for any constant c > 0 {\displaystyle c>0} ), solving SIS n , m , q , β {\displaystyle \operatorname {SIS} _{n,m,q,\beta }} with nonnegligible probability is at least as hard as solving the GapSVP γ {\displaystyle \operatorname {GapSVP} _{\gamma }} and SIVP γ {\displaystyle \operatorname {SIVP} _{\gamma }} for some γ = β ⋅ O ( n ) {\displaystyle \gamma =\beta \cdot O({\sqrt {n}})} with a high probability in the worst-case scenario.
The SIS problem solved over an ideal ring is also called the Ring-SIS or R-SIS problem. [ 2 ] [ 9 ] This problem considers a quotient polynomial ring R q = Z q [ x ] / ( f ( x ) ) {\displaystyle R_{q}=\mathbb {Z} _{q}[x]/(f(x))} with f ( x ) = x n − 1 {\displaystyle f(x)=x^{n}-1} for some integer n {\displaystyle n} and with some norm ‖ ⋅ ‖ {\displaystyle \|\cdot \|} . Of particular interest are cases where there exists integer k {\displaystyle k} such that n = 2 k {\displaystyle n=2^{k}} as this restricts the quotient to cyclotomic polynomials. [ 10 ]
We then define the problem as follows:
Select m {\displaystyle m} independent uniformly random elements a i ∈ R q {\displaystyle a_{i}\in R_{q}} . Define vector a → := ( a 1 , … , a m ) ∈ R q m {\displaystyle {\vec {\boldsymbol {a}}}:=(a_{1},\ldots ,a_{m})\in R_{q}^{m}} . Find a nonzero vector z → := ( z 1 , … , z m ) ∈ R m {\displaystyle {\vec {\boldsymbol {z}}}:=(z_{1},\ldots ,z_{m})\in R^{m}} such that:
Recall that to guarantee existence of a solution to SIS problem, we require m ≈ n log q {\displaystyle m\approx n\log q} . However, Ring-SIS problem provide us with more compactness and efficacy: to guarantee existence of a solution to Ring-SIS problem, we require m ≈ log q {\displaystyle m\approx \log q} .
Definition: The nega-circulant matrix of b {\displaystyle b} is defined as:
When the quotient polynomial ring is R = Z [ x ] / ( x n + 1 ) {\displaystyle R=\mathbb {Z} [x]/(x^{n}+1)} for n = 2 k {\displaystyle n=2^{k}} , the ring multiplication a i . p i {\displaystyle a_{i}.p_{i}} can be efficiently computed by first forming rot ( a i ) {\displaystyle \operatorname {rot} (a_{i})} , the nega-circulant matrix of a i {\displaystyle a_{i}} , and then multiplying rot ( a i ) {\displaystyle \operatorname {rot} (a_{i})} with ρ ( p i ( x ) ) ∈ Z n {\displaystyle \rho (p_{i}(x))\in Z^{n}} , the embedding coefficient vector of p i {\displaystyle p_{i}} (or, alternatively with σ ( p i ( x ) ) ∈ Z n {\displaystyle \sigma (p_{i}(x))\in Z^{n}} , the canonical coefficient vector.
Moreover, R-SIS problem is a special case of SIS problem where the matrix A {\displaystyle A} in the SIS problem is restricted to negacirculant blocks: A = [ rot ( a 1 ) | ⋯ | rot ( a m ) ] {\displaystyle A=[\operatorname {rot} (a_{1})|\cdots |\operatorname {rot} (a_{m})]} . [ 10 ]
The SIS problem solved over a module lattice is also called the Module-SIS or M-SIS problem. Like R-SIS, this problem considers the quotient polynomial ring R = Z [ x ] / ( f ( x ) ) {\displaystyle R=\mathbb {Z} [x]/(f(x))} and R q = Z q [ x ] / ( f ( x ) ) {\displaystyle R_{q}=\mathbb {Z} _{q}[x]/(f(x))} for f ( x ) = x n − 1 {\displaystyle f(x)=x^{n}-1} with a special interest in cases where n {\displaystyle n} is a power of 2. Then, let M {\displaystyle M} be a module of rank d {\displaystyle d} such that M ⊆ R d {\displaystyle M\subseteq R^{d}} and let ‖ ⋅ ‖ {\displaystyle \|\cdot \|} be an arbitrary norm over R q m {\displaystyle R_{q}^{m}} .
We then define the problem as follows:
Select m {\displaystyle m} independent uniformly random elements a i ∈ R q d {\displaystyle a_{i}\in R_{q}^{d}} . Define vector a → := ( a 1 , … , a m ) ∈ R q d × m {\displaystyle {\vec {\boldsymbol {a}}}:=(a_{1},\ldots ,a_{m})\in R_{q}^{d\times m}} . Find a nonzero vector z → := ( z 1 , … , z m ) ∈ R m {\displaystyle {\vec {\boldsymbol {z}}}:=(z_{1},\ldots ,z_{m})\in R^{m}} such that:
While M-SIS is a less compact variant of SIS than R-SIS, the M-SIS problem is asymptotically at least as hard as R-SIS and therefore gives a tighter bound on the hardness assumption of SIS. This makes assuming the hardness of M-SIS a safer, but less efficient underlying assumption when compared to R-SIS. [ 10 ] | https://en.wikipedia.org/wiki/Short_integer_solution_problem |
Short interspersed nuclear elements ( SINEs ) are non-autonomous, non-coding transposable elements (TEs) that are about 100 to 700 base pairs in length. [ 1 ] They are a class of retrotransposons , DNA elements that amplify themselves throughout eukaryotic genomes , often through RNA intermediates. SINEs compose about 13% of the mammalian genome. [ 2 ]
The internal regions of SINEs originate from tRNA and remain highly conserved, suggesting positive pressure to preserve structure and function of SINEs. [ 3 ] While SINEs are present in many species of vertebrates and invertebrates, SINEs are often lineage specific, making them useful markers of divergent evolution between species. Copy number variation and mutations in the SINE sequence make it possible to construct phylogenies based on differences in SINEs between species. SINEs are also implicated in certain types of genetic disease in humans and other eukaryotes .
In essence, short interspersed nuclear elements are genetic parasites which have evolved very early in the history of eukaryotes to utilize protein machinery within the organism as well as to co-opt the machinery from similarly parasitic genomic elements. The simplicity of these elements make them remarkably successful at persisting and amplifying (through retrotransposition) within the genomes of eukaryotes. These "parasites" which have become ubiquitous in genomes can be very deleterious to organisms as discussed below. However, eukaryotes have been able to integrate short-interspersed nuclear elements into different signaling, metabolic and regulatory pathways and SINEs have become a great source of genetic variability. They seem to play a particularly important role in the regulation of gene expression and the creation of RNA genes . This regulation extends to chromatin re-organization and the regulation of genomic architecture. The different lineages, mutations, and activities among eukaryotes make short-interspersed nuclear elements a useful tool in phylogenetic analysis.
SINEs are classified as non-LTR retrotransposons because they do not contain long terminal repeats (LTRs) . [ 4 ] There are three types of SINEs common to vertebrates and invertebrates: CORE-SINEs, V-SINEs, and AmnSINEs. [ 3 ] SINEs have 50-500 base pair internal regions which contain a tRNA-derived segment with A and B boxes that serve as an internal promoter for RNA polymerase III . [ 5 ] [ 3 ]
SINEs are characterized by their different modules, which are essentially a sectioning of their sequence. SINEs can, but do not necessarily have to possess a head, a body, and a tail. The head is at the 5' end of short-interspersed nuclear elements and is evolutionarily derived from an RNA synthesized by RNA Polymerase III such as ribosomal RNAs and tRNAs; the 5' head is indicative of which endogenous element that SINE was derived from and was able to parasitically utilize its transcriptional machinery. [ 1 ] For example, the 5' of the Alu SINE is derived from 7SL RNA , a sequence transcribed by RNA Polymerase III, giving rise to the RNA element of SRP, an abundant ribonucleoprotein. [ 6 ] The body of SINEs possess an unknown origin but often share much homology with a corresponding LINE which thus allows SINEs to parasitically co-opt endonucleases coded by LINEs (which recognize certain sequence motifs). Lastly, the 3′ tail of SINEs is composed of short simple repeats of varying lengths; these simple repeats are sites where two (or more) short-interspersed nuclear elements can combine to form a dimeric SINE. [ 7 ] Short-interspersed nuclear elements which only possess a head and tail are called simple SINEs whereas short-interspersed nuclear elements which also possess a body or are a combination of two or more SINEs are complex SINEs. [ 1 ]
Short-interspersed nuclear elements are transcribed by RNA polymerase III which is known to transcribe ribosomal RNA and tRNA , two types of RNA vital to ribosomal assembly and mRNA translation . [ 8 ] SINEs, like tRNAs and many small-nuclear RNAs possess an internal promoter and thus are transcribed differently than most protein-coding genes. [ 1 ] In other words, short-interspersed nuclear elements have their key promoter elements within the transcribed region itself. Though transcribed by RNA polymerase III, SINEs and other genes possessing internal promoters, recruit different transcriptional machinery and factors than genes possessing upstream promoters. [ 9 ]
Changes in chromosome structure influence gene expression primarily by affecting the accessibility of genes to transcriptional machinery. The chromosome has a very complex and hierarchical system of organizing the genome. This system of organization, which includes histones , methyl groups, acetyl groups, and a variety of proteins and RNAs allows different domains within a chromosome to be accessible to polymerases, transcription factors , and other associated proteins to different degrees. [ 10 ] Furthermore, the shape and density of certain areas of a chromosome can affect the shape and density of neighboring (or even distant regions) on the chromosome through interaction facilitated by different proteins and elements. Non-coding RNAs such as short-interspersed nuclear elements, which have been known to associate with and contribute to chromatin structure, can thus play huge role in regulating gene expression. [ 11 ] Short-interspersed-nuclear-elements similarly can be involved in gene regulation by modifying genomic architecture.
In fact Usmanova et al. 2008 suggested that short-interspersed nuclear elements can serve as direct signals in chromatin rearrangement and structure. The paper examined the global distribution of SINEs in mouse and human chromosomes and determined that this distribution was very similar to genomic distributions of genes and CpG motifs . [ 12 ] The distribution of SINEs to genes was significantly more similar than that of other non-coding genetic elements and even differed significantly from the distribution of long-interspersed nuclear elements. [ 12 ] This suggested that the SINE distribution was not a mere accident caused by LINE-mediated retrotransposition but rather that SINEs possessed a role in gene-regulation. Furthermore, SINEs frequently contain motifs for YY1 polycomb proteins. [ 12 ] YY1 is a zinc-finger protein that acts as a transcriptional repressor for a wide-variety of genes essential for development and signaling. [ 13 ] Polycomb protein YY1 is believed to mediate the activity of histone deacetylases and histone acetyltransferases to facilitate chromatin re-organization; this is often to facilitate the formation of heterochromatin (gene-silencing state). [ 14 ] Thus, the analysis suggests that short-interspersed nuclear elements can function as a ‘signal-booster' in the polycomb-dependent silencing of gene-sets through chromatin re-organization. [ 12 ] In essence, it is the cumulative effect of many types of interactions that leads to the difference between euchromatin , which is not tightly packed and generally more accessible to transcriptional machinery, and heterochromatin , which is tightly packed and generally not accessible to transcriptional machinery; SINEs seem to play an evolutionary role in this process.
In addition to directly affecting chromatin structure, there are a number of ways in which SINEs can potentially regulate gene expression. For example, long non-coding RNA can directly interact with transcriptional repressors and activators, attenuating or modifying their function. [ 15 ] This type of regulation can occur in different ways: the RNA transcript can directly bind to the transcription factor as a co-regulator; also, the RNA can regulate and modify the ability of co-regulators to associate with the transcription factor. [ 15 ] For example, Evf-2, a certain long non-coding RNA, has been known to function as a co-activator for certain homeobox transcription factors which are critical to nervous system development and organization. [ 16 ] Furthermore, RNA transcripts can interfere with the functionality of the transcriptional complex by interacting or associating with RNA polymerases during the transcription or loading processes. [ 15 ] Moreover, non-coding RNAs like SINEs can bind or interact directly with the DNA duplex coding the gene and thus prevent its transcription. [ 15 ]
Also, many non-coding RNAs are distributed near protein-coding genes, often in the reverse direction. This is especially true for short-interspersed nuclear elements as seen in Usmanova et al. These non-coding RNAs, which lie adjacent to or overlap gene-sets provide a mechanism by which transcription factors and machinery can be recruited to increase or repress the transcription of local genes. The particular example of SINEs potentially recruiting the YY1 polycomb transcriptional repressor is discussed above. [ 12 ] Alternatively, it also provides a mechanism by which local gene expression can be curtailed and regulated because the transcriptional complexes can hinder or prevent nearby genes from being transcribed. There is research to suggest that this phenomenon is particularly seen in the gene-regulation of pluripotent cells. [ 17 ]
In conclusion, non-coding RNAs such as SINEs are capable of affecting gene expression on a multitude of different levels and in different ways. Short-interspersed nuclear elements are believed to be deeply integrated into a complex regulatory network capable of fine-tuning gene expression across the eukaryotic genome.
The RNA transcribed from the short-interspersed nuclear element does not code for any protein product but is nonetheless reverse-transcribed and inserted back into an alternate region in the genome. For this reason, short interspersed nuclear elements are believed to have co-evolved with long interspersed nuclear element (LINEs), as LINEs do in fact encode protein products which enable them to be reverse- transcribed and integrated back into the genome. [ 4 ] SINEs are believed to have co-opted the proteins coded by LINEs which are contained in 2 reading frames. Open reading frame 1 (ORF 1) encodes a protein which binds to RNA and acts as a chaperone to facilitate and maintain the LINE protein-RNA complex structure. [ 18 ] Open reading frame 2 (ORF 2) codes a protein which possesses both endonuclease and reverse transcriptase activities. [ 19 ] This enables the LINE mRNA to be reverse-transcribed into DNA and integrated into the genome based on the sequence-motifs recognized by the protein's endonuclease domain.
LINE-1 (L1) is transcribed and retrotransposed most frequently in the germ-line and during early development; as a result SINEs move around the genome most during these periods. SINE transcription is down-regulated by transcription factors in somatic cells after early development, though stress can cause up-regulation of normally silent SINEs. [ 20 ] SINEs can be transferred between individuals or species via horizontal transfer through a viral vector . [ 21 ]
SINEs are known to share sequence homology with LINES which gives a basis by which the LINE machinery can reverse transcribe and integrate SINE transcripts. [ 22 ] Alternately, some SINEs are believed to use a much more complex system of integrating back into the genome; this system involves the use random double-stranded DNA breaks (rather than the endonuclease coded by related long-interspersed nuclear elements creating an insertion-site). [ 22 ] These DNA breaks are utilized to prime reverse transcriptase, ultimately integrating the SINE transcript back into the genome. [ 22 ] SINEs nonetheless depend on enzymes coded by other DNA elements and are thus known as non-autonomous retrotransposons as they depend on the machinery of LINEs, which are known as autonomous retrotransposons. [ 23 ]
The theory that short-interspersed nuclear elements have evolved to utilize the retrotransposon machinery of long-interspersed nuclear elements is supported by studies which examine the presence and distribution of LINEs and SINEs in taxa of different species. [ 24 ] For example, LINEs and SINEs in rodents and primates show very strong homology at the insertion-site motif. [ 24 ] Such evidence is a basis for the proposed mechanism in which integration of the SINE transcript can be co-opted with LINE-coded protein products. This is specifically demonstrated by a detailed analysis of over 20 rodent species profiled LINEs and SINEs, mainly L1s and B1s respectively; these are families of LINEs and SINEs found at high frequencies in rodents along with other mammals. [ 24 ] The study sought to provide phylogenetic clarity within the context of LINE and SINE activity.
The study arrived at a candidate taxa believed to be the first instance of L1 LINE extinction; it expectedly discovered that there was no evidence to suggest that B1 SINE activity occurred in species which did not have L1 LINE activity. [ 24 ] Also, the study suggested that B1 short-interspersed nuclear element silencing in fact occurred before L1 long-interspersed nuclear element extinction; this is due to the fact that B1 SINEs are silenced in the genus most-closely related to the genus which does not contain active L1 LINEs (though the genus with B1 SINE silencing still contains active L1 LINEs). [ 24 ] Another genus was also found which similarly contained active L1 long-interspersed nuclear elements but did not contain B1 short-interspersed nuclear elements; the opposite scenario, in which active B1 SINEs were present in a genus which did not possess active L1 LINEs was not found. [ 24 ] This result was expected and strongly supports the theory that SINEs have evolved to co-opt the RNA-binding proteins, endonucleases, and reverse-transcriptases coded by LINEs. In taxa which do not actively transcribe and translate long-interspersed nuclear elements protein-products, SINEs do not have the theoretical foundation by which to retrotranspose within the genome. The results obtained in Rinehart et al. are thus very supportive of the current model of SINE retrotransposition.
Insertion of a SINE upstream of a coding region may result in exon shuffling or changes to the regulatory region of the gene. Insertion of a SINE into the coding sequence of a gene can have deleterious effects and unregulated transposition can cause genetic disease . The transposition and recombination of SINEs and other active nuclear elements is thought to be one of the major contributions of genetic diversity between lineages during speciation. [ 21 ]
Short-interspersed nuclear elements are believed to have parasitic origins in eukaryotic genomes. These SINEs have mutated and replicated themselves a large number of times on an evolutionary time-scale and thus form many different lineages. Their early evolutionary origin has caused them to be ubiquitous in many eukaryotic lineages.
Alu elements , short-interspersed nuclear element of about 300 nucleotides, are the most common SINE in humans, with >1,000,000 copies throughout the genome, which is over 10 percent of the total genome; this is not uncommon among other species. [ 25 ] Alu element copy number differences can be used to distinguish between and construct phylogenies of primate species. [ 21 ] Canines differ primarily in their abundance of SINEC_Cf repeats throughout the genome, rather than other gene or allele level mutations. These dog-specific SINEs may code for a splice acceptor site, altering the sequences that appear as exons or introns in each species. [ 26 ]
Apart from mammals, SINEs can reach high copy numbers in a range of species, including nonbony vertebrates (elephant shark) and some fish species (coelacanths). [ 27 ] In plants, SINEs are often restricted to closely related species and have emerged, decayed, and vanished frequently during evolution. [ 28 ] Nevertheless, some SINE families such as the Au-SINEs [ 29 ] and the Angio-SINEs [ 30 ] are unusually widespread across many often unrelated plant species.
There are >50 human diseases associated with SINEs. [ 20 ] When inserted near or within the exon, SINEs can cause improper splicing, become coding regions, or change the reading frame , often leading to disease phenotypes in humans and other animals. [ 26 ] Insertion of Alu elements in the human genome is associated with breast cancer , colon cancer , leukemia , hemophilia , Dent's disease , cystic fibrosis , neurofibromatosis , and many others. [ 4 ]
The role of short-interspersed nuclear elements in gene regulation within cells has been supported by multiple studies. One such study examined the correlation between a certain family of SINEs with microRNAs (in zebrafish ). [ 31 ] The specific family of SINEs being examined was the Anamnia V-SINEs; this family of short interspersed nuclear elements is often found in the untranslated region of the 3' end of many genes and is present in vertebrate genomes. [ 31 ] The study involved a computational analysis in which the genomic distribution and activity of the Anamnia V-SINEs in Danio rerio zebrafish was examined; furthermore, these V-SINEs potential to generate novel microRNA loci was analyzed. [ 31 ] It was found that genes which were predicted to possess V-SINEs were targeted by microRNAs with significantly higher hybridization E-values (relative to other areas in the genome). [ 31 ] The genes that had high hybridization E-values were genes particularly involved in metabolic and signaling pathways. [ 31 ] Almost all miRNAs identified to have a strong ability to hybridize to putative V-SINE sequence motifs in genes have been identified (in mammals) to have regulatory roles. [ 31 ] These results which establish a correlation between short-interspersed nuclear elements and different regulatory microRNAs strongly suggest that V-SINEs have a significant role in attenuating responses to different signals and stimuli related to metabolism, proliferation and differentiation. Many other studies must be undertaken to establish the validity and extent of short-interspersed nuclear element retrotransposons' role in regulatory gene-expression networks. In conclusion, though not much is known about the role and mechanism by which SINEs generate miRNA gene loci it is generally understood that SINEs have played a significant evolutionary role in the creation of "RNA-genes", this is also touched upon above in SINEs and pseudogenes.
With such evidence suggesting that short-interspersed nuclear elements have been evolutionary sources for microRNA loci generation it is important to further discuss the potential relationships between the two as well as the mechanism by which the microRNA regulates RNA degradation and more broadly, gene expression. A microRNA is a non-coding RNA generally 22 nucleotides in length. [ 32 ] This non-protein coding oligonucleotide is usually transcribed from a longer nuclear DNA sequence by RNA polymerase II which is also responsible for the transcription of most mRNAs and snRNAs in eukaryotes. [ 33 ] However, some research suggests that some microRNAs that possess upstream short-interspersed nuclear elements are transcribed by RNA polymerase III which is widely implicated in ribosomal RNA and tRNA, two transcripts vital to mRNA translation. [ 34 ] This provides an alternate mechanism by which short-interspersed nuclear elements could be interacting with or mediating gene-regulatory networks involving microRNAs.
The genomic regions producing miRNA can be independent RNA-genes often being anti-sense to neighboring protein-coding genes, or can be found within the introns of protein-coding genes. [ 35 ] The co-localization of microRNA and protein-coding genes provides a mechanistic foundation by which microRNA regulates gene-expression. Furthermore, Scarpato et al. reveals (as discussed above) that genes predicted to possess short-interspersed nuclear elements (SINEs) through sequence analysis were targeted and hybridized by microRNAs significantly greater than other genes. [ 31 ] This provides an evolutionarily path by which the parasitic SINEs were co-opted and utilized to form RNA-genes (such as microRNAs) which have evolved to play a role in complex gene-regulatory networks.
The microRNAs are transcribed as part of longer RNA strands of generally about 80 nucleotides which through complementary base-pairing are able to form hairpin loop structures [ 36 ] These structures are recognized and processed in the nucleus by the nuclear protein DiGeorge Syndrome Critical Region 8 (DGCR8) which recruits and associates with the Drosha protein. [ 37 ] This complex is responsible for cleaving some of the hair-pin structures from the pre-microRNA which is transported to the cytoplasm. The pre-miRNA is processed by the protein DICER into a double stranded 22 nucleotide. [ 38 ] Thereafter, one of the strands is incorporated into a multi-protein RNA-induced silencing complex (RISC). [ 39 ] Among these proteins are proteins from the Argonaute family which are critical to the complex's ability to interact with and repress the translation of the target mRNA. [ 40 ]
Understanding the different ways in which microRNA regulates gene-expression, including mRNA-translation and degradation is key to understanding the potential evolutionary role of SINEs in gene-regulation and in the generation of microRNA loci. This, in addition to SINEs' direct role in regulatory networks (as discussed in SINEs as long non-coding RNAs) is crucial to beginning to understand the relationship between SINEs and certain diseases. Multiple studies have suggested that increased SINE activity is correlated with certain gene-expression profiles and post-transcription regulation of certain genes. [ 41 ] [ 42 ] [ 43 ] In fact, Peterson et al. 2013 demonstrated that high SINE RNA expression correlates with post-transcriptional downregulation of BRCA1 , a tumor suppressor implicated in multiple forms of cancer, namely breast cancer. [ 43 ] Furthermore, studies have established a strong correlation between transcriptional mobilization of SINEs and certain cancers and conditions such as hypoxia; this can be due to the genomic instability caused by SINE activity as well as more direct-downstream effects. [ 42 ] SINEs have also been implicated in countless other diseases. In essence, short-interspersed nuclear elements have become deeply integrated in countless regulatory, metabolic and signaling pathways and thus play an inevitable role in causing disease. Much is still to be known about these genomic parasites but it is clear they play a significant role within eukaryotic organisms.
The activity of SINEs however has genetic vestiges which do not seem to play a significant role, positive or negative, and manifest themselves in the genome as pseudogenes . SINEs however should not be mistaken as RNA pseudogenes. [ 1 ] In general, pseudogenes are generated when processed mRNAs of protein-coding genes are reverse-transcribed and incorporated back into the genome (RNA pseudogenes are reverse transcribed RNA genes). [ 44 ] Pseudogenes are generally functionless as they descend from processed RNAs independent of their evolutionary-context which includes introns and different regulatory elements which enable transcription and processing. These pseudogenes, though non-functional may in some cases still possess promoters, CpG islands, and other features which enable transcription; they thus can still be transcribed and may possess a role in the regulation of gene expression (like SINEs and other non-coding elements). [ 44 ] Pseudogenes thus differ from SINEs in that they are derived from transcribed- functional RNA whereas SINEs are DNA elements which retrotranspose by co-opting RNA genes transcriptional machinery. However, there are studies which suggest that retro-transposable elements such as short-interspersed nuclear elements are not only capable of copying themselves in alternate regions in the genome but are also able to do so for random genes too. [ 45 ] [ 46 ] Thus SINEs can be playing a vital role in the generation of pseudogenes, which themselves are known to be involved in regulatory networks. This is perhaps another means by which SINEs have been able to influence and contribute to gene-regulation. | https://en.wikipedia.org/wiki/Short_interspersed_nuclear_element |
In crystallography , short range order refers to the regular and predictable arrangement (i.e. crystalline lattice) of atoms over a short distance, usually with one or two atom spacings. However, this regularity described by short-range order does not necessarily apply to a larger area. [ 1 ] Examples of materials with short range order include amorphous materials such as wax , glass and liquids [ 2 ] as well as the collagen fibrils of the stroma in the cornea. [ 3 ]
Besides ordering of atoms, short-range ordering of vacancies are also possible. Example of systems with short-range ordering of oxygen-vacancies include oxygen-deficient stoichiometries of the superconductors YBa 2 Cu 2 O 7−δ , Nd 2− x Ce x CuO 4− y ; as well as perovskites and novel bismuth sillenites . [ 4 ] [ 5 ] [ 6 ] [ 7 ] [ 8 ] | https://en.wikipedia.org/wiki/Short_range_order |
The short time duty (or short time operation ) indicates an operating mode of increased performance but for a shorter length of time. Commonly it is also referred to the maximum load (the performance) at which and the related maximum length of time a device can be operated without to failure.
The load can be a maximum power , temperature , revolution speed , torque , acceleration or whatever can influence the mechanical or chemical properties of the device for its correct function: for instance an electrical motor can be driven at a higher revolution speed than for normal (constant) operation (nominal revolution speed), but after a short time it should be driven down or switched out in order to prevent from damage; another example can be the operating temperature of a simple oven which can be raised to the maximum allowed but only for a short time to avoid that the oven begins to burn. Generally at all performances a part of the input energy will be dissipated as heat. The higher the operation power the higher the heat to dissipate. If the performance is too high, the device will not be able to dissipate the heat to its environment and its temperature will raise proportionally to the energy surplus. If the temperature raises too much the mechanical and chemical properties of the device will begin to change causing permanent deformations for plastical material or fractures for brittle materials. Being the energy the product of power and time, either the power (or any to it related physical value) as by normal operation/duty or the time as by short-time duty have to be limited.
A common application is the high current measure (typically up to 10 or 20 A) with multimeters . The maximum time length of short time duty (typically 10 to 30 seconds) is indicated near the corresponding socket (usually the left one) as well as the time to be waited for, before each of such measures might be repeated (typically "each 15 minutes"). Another common application is inflation with air compressors: those become very hot, if used for a too long time and have to be shut down after a certain time (for small compressors such that of the picture a typical time is 10 minutes).
Only in some cases there is a built-in device protection in form for instance of a fusible in electrical devices (for instance in a halogen lamp to prevent damage from use of too high power bulbs) or in form for instance of a pressure relief valve in hydraulic devices (e.g. a pressure cooker ); many others have no protection (most hair-dryers ) and the user realizes that the duty short time is over after for example the overheating has already damaged the device.
Many producers indicates this short time duty only in the instruction handbook of the device, other indicates it on the very device. At this time (2007) there is no international identifier for this property. In Germany for instance it is indicated with KB (Kurzzeitbetrieb = shor time operating/operation [ 1 ] ) and the time in minutes, in France there is no abbreviation but it is referred to as service temporaire , in Spanish it is indicated with servicio temporal , in Italian with servizio di durata limitata , and so on. [ 2 ]
The concept of short time duty is easy to understand when referred to human beings in medical applications both somatic (body) as well as psychological (mind). The analogy with devices is useful to better understand both type of applications and should not be underestimated as if human beings were much better than their machines or devices: in this case a short time duty prevents from diseases .
The best example is the radiation exposure ( X-rays , gamma-radiation or particle radiation ) for which a maximum short-time-, as well as a cumulative year-, and a life-dose are well defined for every type of radiation in order to avoid cancer (e.g. maximum number of dental X-rays per year). In this case the maximum load of the definition is represented by the dose (see also Radiation Safety ). A controversial field is the uses of mobile (cellular) phones, for which there are no proven damages.
Another simple example of well defined short time duty are the exposure times of sunscreen lotions (in this the case the load is also the electromagnetic radiation dose but its energy is just weaker and its frequency is shorter, i.e. ultra-violet light UV ). A last good example are allergies : in this case the load is the concentration of the allergic substance and the short time duty is depending on many factors like age, genetics, medical condition and so on.
Besides this somatic examples many everyday situations can influence the correct operating of human beings: a stressing situation (an annoying noise or even mobbing at work) can be tolerated for a certain short time "duty" (some seconds or days depending on its impact and on patience), but thereafter it can make irritable or bear to a serious depression.
The human body has also some built-in protections but only to a moderate extent (there is no fusible which can be simply exchanged in case of overload). The best protection for human beings is on the one side health education, which is equivalent to a handbook of its own body (body side), and love, friendship and politeness in case of human relations (mind side).
All human beings have a similar resistance to most biological agents and exposures with some exceptions (e.g. UV-rays short time duty or allergies) but the human gene sequences are remarkably homogeneous, so that there is a quite good standardisation and all human beings recognize their similars as such and automatically know which short time duties they can withstand. Only by psychological aspects the short time duty is very different from human being to human being depending on their culture and religion (to sneeze in a far east country will rapidly irritate the companionship while just causing commiseration in a west country). | https://en.wikipedia.org/wiki/Short_time_duty |
An important question in statistical mechanics is the dependence of model behaviour on the dimension of the system. The shortcut model [ 1 ] [ 2 ] was introduced in the course of studying this dependence. The model interpolates between discrete regular lattices of integer dimension.
The behaviour of different processes on discrete regular lattices have been studied quite extensively. They show a rich diversity of behaviour, including a non-trivial dependence on the dimension of the regular lattice. [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ 7 ] [ 8 ] [ 9 ] [ 10 ] [ 11 ] In recent years the study has been extended from regular lattices to complex networks . The shortcut model has been used in studying several processes and their dependence on dimension.
Usually, dimension is defined based on the scaling exponent of some property in the appropriate limit. One property one could use [ 2 ] is the scaling of volume with distance. For regular lattices Z d {\displaystyle \textstyle \mathbf {Z} ^{d}} the number of nodes j {\displaystyle \textstyle j} within a distance r ( i , j ) {\displaystyle \textstyle r(i,j)} of node i {\displaystyle \textstyle i} scales as r ( i , j ) d {\displaystyle \textstyle r(i,j)^{d}} .
For systems which arise in physical problems one usually can identify some physical space relations among the vertices. Nodes which are linked directly will have more influence on each other than nodes which are separated by several links. Thus, one could define the distance r ( i , j ) {\displaystyle \textstyle r(i,j)} between nodes i {\displaystyle \textstyle i} and j {\displaystyle \textstyle j} as the length of the shortest path connecting the nodes.
For complex networks one can define the volume as the number of nodes j {\displaystyle \textstyle j} within a distance r ( i , j ) {\displaystyle \textstyle r(i,j)} of node i {\displaystyle \textstyle i} , averaged over i {\displaystyle \textstyle i} , and the dimension may be defined as the exponent which determines the scaling behaviour of the volume with distance. For a vector n → = ( n 1 , … , n d ) ∈ Z d {\displaystyle \textstyle {\vec {n}}=(n_{1},\dots ,n_{d})\in \mathbf {Z} ^{d}} , where d {\displaystyle \textstyle d} is a positive integer, the Euclidean norm ‖ n → ‖ {\displaystyle \textstyle \|{\vec {n}}\|} is defined as the Euclidean distance from the origin to n → {\displaystyle \textstyle {\vec {n}}} , i.e.,
However, the definition which generalises to complex networks is the L 1 {\displaystyle \textstyle L^{1}} norm,
The scaling properties hold for both the Euclidean norm and the L 1 {\displaystyle \textstyle L^{1}} norm. The scaling relation is
where d is not necessarily an integer for complex networks. k {\displaystyle \textstyle k} is a geometric constant which depends on the complex network. If the scaling relation Eqn. holds, then one can also define the surface area S ( r ) {\displaystyle \textstyle S(r)} as the number of nodes which are exactly at a distance r {\displaystyle \textstyle r} from a given node, and S ( r ) {\displaystyle \textstyle S(r)} scales as
A definition based on the complex network zeta function [ 1 ] generalises the definition based on the scaling property of the volume with distance [ 2 ] and puts it on a mathematically robust footing.
The shortcut model starts with a network built on a one-dimensional regular lattice. One then adds edges to create shortcuts that join remote parts of the lattice to one another. The starting network is a one-dimensional lattice of N {\displaystyle \textstyle N} vertices with periodic boundary conditions. Each vertex is joined to its neighbors on either side, which results in a system with N {\displaystyle \textstyle N} edges. The network is extended by taking each node in turn and, with probability p {\displaystyle \textstyle p} , adding an edge to a new location m {\displaystyle \textstyle m} nodes distant.
The rewiring process allows the model to interpolate between a one-dimensional regular lattice and a two-dimensional regular lattice. When the rewiring probability p = 0 {\displaystyle \textstyle p=0} , we have a one-dimensional regular lattice of size N {\displaystyle \textstyle N} . When p = 1 {\displaystyle \textstyle p=1} , every node is connected to a new location and the graph is essentially a two-dimensional lattice with m {\displaystyle \textstyle m} and N / m {\displaystyle \textstyle N/m} nodes in each direction. For p {\displaystyle \textstyle p} between 0 {\displaystyle \textstyle 0} and 1 {\displaystyle \textstyle 1} , we have a graph which interpolates between the one and two dimensional regular lattices. The graphs we study are parametrized by
One application using the above definition of dimension was to the
extensiveness of statistical mechanics systems with a power law potential where the interaction varies with the distance r {\displaystyle \textstyle r} as 1 / r α {\displaystyle \textstyle 1/r^{\alpha }} . In one dimension the system properties like the free energy do not behave extensively when 0 ≤ α ≤ 1 {\displaystyle \textstyle 0\leq \alpha \leq 1} , i.e., they increase faster than N as N → ∞ {\displaystyle \textstyle N\rightarrow \infty } , where N is the number of spins in the system.
Consider the Ising model with the Hamiltonian (with N spins)
where s i {\displaystyle \textstyle s_{i}} are the spin variables, r ( i , j ) {\displaystyle \textstyle r(i,j)} is the distance between node i {\displaystyle \textstyle i} and node j {\displaystyle \textstyle j} , and J ( r ( i , j ) ) {\displaystyle \textstyle J(r(i,j))} are the couplings between the spins. When the J ( r ( i , j ) ) {\displaystyle \textstyle J(r(i,j))} have the behaviour 1 / r α {\displaystyle \textstyle 1/r^{\alpha }} , we have the power law potential. For a general complex network the condition on the exponent α {\displaystyle \textstyle \alpha } which preserves extensivity of the Hamiltonian was studied. At zero temperature, the energy per spin is proportional to
and hence extensivity requires that ρ {\displaystyle \textstyle \rho } be finite. For a general complex network ρ {\displaystyle \textstyle \rho } is proportional to the Riemann zeta function ζ ( α − d + 1 ) {\displaystyle \textstyle \zeta (\alpha -d+1)} . Thus, for the potential to be extensive, one requires
Other processes which have been studied are self-avoiding random walks, and the scaling of the mean path length with the network size. These studies lead to the interesting result that the dimension transitions sharply as the shortcut probability increases from zero. [ 12 ] The sharp transition in the dimension has been explained in terms of the combinatorially large
number of available paths for points separated by distances large compared to 1. [ 13 ]
The shortcut model is useful for studying the dimension dependence of different processes. The processes studied include the behaviour of the power law potential as a function of the dimension, the behaviour of self-avoiding random walks, and the scaling of the mean path length. It may be useful to compare the shortcut model with the small-world network , since the definitions have a lot of similarity. In the small-world network also one starts with a regular lattice and adds shortcuts with probability p {\displaystyle \textstyle p} . However, the shortcuts are not constrained to connect to a node a fixed distance ahead. Instead, the other end of the shortcut can connect to any randomly chosen node. As a result, the small world model tends to a random graph rather than a two-dimensional graph as the shortcut probability is increased. | https://en.wikipedia.org/wiki/Shortcut_model |
Shortcuts to adiabaticity (STA) are fast control protocols to drive the dynamics of system without relying on the adiabatic theorem . The concept of STA was introduced in a 2010 paper by Xi Chen et al. [ 1 ] Their design can be achieved using a variety of techniques. [ 2 ] [ 3 ] A universal approach is provided by counterdiabatic driving, [ 4 ] also known as transitionless quantum driving. [ 5 ] Motivated by one of authors systematic study of dissipative Landau-Zener transition, the key idea was demonstrated earlier by a group of scientists from China, Greece and USA in 2000, as steering an eigenstate to destination. [ 6 ] Counterdiabatic driving has been demonstrated in the laboratory using a time-dependent quantum oscillator . [ 7 ]
The use of counterdiabatic driving requires to diagonalize the system Hamiltonian, limiting its use in many-particle systems. In the control of trapped quantum fluids, the use of symmetries such as scale invariance and the associated conserved quantities has allowed to circumvent this requirement. [ 8 ] [ 9 ] [ 10 ] STA have also found applications in finite-time quantum thermodynamics to suppress quantum friction. [ 11 ] Fast nonadiabatic strokes of a quantum engine have been implemented using a three-dimensional interacting Fermi gas . [ 12 ] [ 13 ]
The use of STA has also been suggested to drive a quantum phase transition . [ 14 ] In this context, the Kibble-Zurek mechanism predicts the formation of topological defects . While the implementation of counterdiabatic driving across a phase transition requires complex many-body interactions, feasible approximate controls can be found. [ 15 ] [ 16 ] [ 17 ]
Outside of physics, STA have been applied to population genetics to derive a formalism to admit finite time control of the speed and trajectory in evolving populations, with an eye towards manipulating large populations of organisms causing human disease as an evolutionary therapy method, or toward more efficient directed evolution . [ 18 ]
This quantum mechanics -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Shortcuts_to_adiabaticity |
In computer science , the shortest common supersequence of two sequences X and Y is the shortest sequence which has X and Y as subsequences . This is a problem closely related to the longest common subsequence problem . Given two sequences X = < x 1 ,...,x m > and Y = < y 1 ,...,y n >, a sequence U = < u 1 ,...,u k > is a common supersequence of X and Y if items can be removed from U to produce X and Y .
A shortest common supersequence (SCS) is a common supersequence of minimal length. In the SCS problem, two sequences X and Y are given, and the task is to find a shortest possible common supersequence of these sequences. In general, an SCS is not unique.
For two input sequences, an SCS can be formed from a longest common subsequence (LCS) easily. For example, the longest common subsequence of X [ 1.. m ] = a b c b d a b {\displaystyle [1..m]=abcbdab} and Y [ 1.. n ] = b d c a b a {\displaystyle [1..n]=bdcaba} is Z [ 1.. L ] = b c b a {\displaystyle [1..L]=bcba} . By inserting the non-LCS symbols into Z while preserving their original order, we obtain a shortest common supersequence U [ 1.. S ] = a b d c a b d a b {\displaystyle [1..S]=abdcabdab} . In particular, the equation L + S = m + n {\displaystyle L+S=m+n} holds for any two input sequences.
There is no similar relationship between shortest common supersequences and longest common subsequences of three or more input sequences. (In particular, LCS and SCS are not dual problems .) However, both problems can be solved in O ( n k ) {\displaystyle O(n^{k})} time using dynamic programming, where k {\displaystyle k} is the number of sequences, and n {\displaystyle n} is their maximum length. For the general case of an arbitrary number of input sequences, the problem is NP-hard . [ 1 ]
The closely related problem of finding a minimum-length string which is a superstring of a finite set of strings S = { s 1 , s 2 ,..., s n } is also NP-hard. [ 2 ] Several constant factor approximations have been proposed throughout the years, and the current best known algorithm has an approximation factor of 2.475. [ 3 ] However, perhaps the simplest solution is to reformulate the problem as an instance of weighted set cover in such a way that the weight of the optimal solution to the set cover instance is less than twice the length of the shortest superstring S . One can then use the O(log( n ))-approximation for weighted set-cover to obtain an O(log( n ))-approximation for the shortest superstring (note that this is not a constant factor approximation).
For any string x in this alphabet, define P ( x ) to be the set of all strings which are substrings of x . The instance I of set cover is formulated as follows:
The instance I can then be solved using an algorithm for weighted set cover, and the algorithm can output an arbitrary concatenation of the strings x for which the weighted set cover algorithm outputs P ( x ). [ 4 ]
Consider the set S = { abc, cde, fab }, which becomes the universe of the weighted set cover instance. In this case, M = { abcde, fabc }. Then the set of subsets of the universe is
which have costs 3, 3, 3, 5, and 4, respectively. | https://en.wikipedia.org/wiki/Shortest_common_supersequence |
Shortest seek first (or shortest seek time first ) is a secondary storage scheduling algorithm to determine the motion of the disk read-and-write head in servicing read and write requests.
This is an alternative to the first-come first-served (FCFS) algorithm. The drive maintains an incoming buffer of requests, and tied with each request is a cylinder number of the request. Lower cylinder numbers indicate the cylinder is closer to the spindle, while higher numbers indicate the cylinder is further away. The shortest seek first algorithm determines which request is closest to the current position of the head, and services that request next.
The shortest seek first algorithm has the benefit of simplicity, in that overall arm movement is reduced, resulting in a lower average response time.
However, since the buffer is always getting new requests, these can skew the service time of requests that may be furthest away from the disk head's current location, if the new requests are all close to the current location; in fact, starvation may result, with the faraway requests never being able to make progress. [ 1 ]
The elevator algorithm is one alternative for reducing arm movement and response time, and ensuring consistent servicing of requests.
This computing article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Shortest_seek_first |
In mathematics , and particularly in the theory of formal languages , shortlex is a total ordering for finite sequences of objects that can themselves be totally ordered. In the shortlex ordering, sequences are primarily sorted by cardinality (length) with the shortest sequences first, and sequences of the same length are sorted into lexicographical order . [ 1 ] Shortlex ordering is also called radix , length-lexicographic , military , or genealogical ordering. [ 2 ]
In the context of strings on a totally ordered alphabet, the shortlex order is identical to the lexicographical order, except that shorter strings precede longer strings. For example, the shortlex order of the set of strings on the English alphabet (in its usual order) is [ ε, a, b, c, ..., z, aa, ab, ac, ..., zz, aaa, aab, aac, ..., zzz, ... ], where ε denotes the empty string .
The strings in this ordering over a fixed finite alphabet can be placed into one-to-one order-preserving correspondence with the natural numbers , giving the bijective numeration system for representing numbers. [ 3 ] The shortlex ordering is also important in the theory of automatic groups . [ 4 ]
This algebra -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Shortlex_order |
Shorts in Motion: The Art of Seduction is a Canadian anthology of 10 original two-minute mobile shorts for video cell phones, by directors, artists and personalities, including: Ann Marie Fleming , Mark McKinney , Guy Maddin , Isabella Rossellini , Theodore Ushev and Denis Villeneuve . The series is presented by Bravo!FACT and co-produced by marblemedia and the National Film Board of Canada (NFB). [ 1 ] It was one of the NFB's first ventures into mobile media. [ 2 ] Rossellini is the only non-Canadian director.
Shorts in Motion: The Art of Seduction integrates quizzes, advice columns and guides as well as downloads of all 10 Micro Movies which can be played back on mobile phones. For a further level of audience interaction, the ability to create and send e-cards via users' cell phones was also implemented.
The Art of Seduction was named Best Made for Mobile Video Service at the GSM Global Mobile Awards (Barcelona, 2007) and Best Original Content for Mobile at the Banff World Television Award (Banff, 2007). [ 3 ] It was also nominated for an International Interactive Emmy . | https://en.wikipedia.org/wiki/Shorts_in_Motion:_The_Art_of_Seduction |
In lipidomics , the process of shotgun lipidomics (named by analogy with shotgun sequencing ) uses analytical chemistry to investigate the biological function, significance, and sequelae of alterations in lipids and protein constituents mediating lipid metabolism, trafficking, or biological function in cells. [ 1 ] [ 2 ] Lipidomics has been greatly facilitated by recent advances in, and novel applications of, electrospray ionization mass spectrometry (ESI/MS). [ 3 ]
Lipidomics is a research field that studies the pathways and networks of cellular lipids in biological systems (i.e., lipidomes) on a large scale. It involves the identification and quantification of the thousands of cellular lipid molecular species and their interactions with other lipids, proteins, and other moieties in vivo. Investigators in lipidomics examine the structures, functions, interactions, and dynamics of cellular lipids and the dynamic changes that occur during pathophysiologic perturbations. Lipidomic studies play an essential role in defining the biochemical mechanisms of lipid-related disease processes through identifying alterations in cellular lipid metabolism, trafficking and homeostasis. The two major platforms currently used for lipidomic analyses are HPLC-MS and shotgun lipidomics.
Shotgun lipidomics was developed by Richard W. Gross and Xianlin Han, by employing ESI intrasource separation techniques. Individual molecular species of most major and many minor lipid classes can be fingerprinted and quantitated directly from biological lipid extracts without the need for chromatographic purification.
Shotgun lipidomics is fast, highly sensitive, and it can identify hundreds of lipids missed by other methods — all with a much smaller tissue sample so that specific cells or minute biopsy samples can be examined. | https://en.wikipedia.org/wiki/Shotgun_lipidomics |
In genetics , shotgun sequencing is a method used for sequencing random DNA strands. It is named by analogy with the rapidly expanding, quasi-random shot grouping of a shotgun .
The chain-termination method of DNA sequencing ("Sanger sequencing") can only be used for short DNA strands of 100 to 1000 base pairs . Due to this size limit, longer sequences are subdivided into smaller fragments that can be sequenced separately, and these sequences are assembled to give the overall sequence.
In shotgun sequencing, [ 1 ] [ 2 ] DNA is broken up randomly into numerous small segments, which are sequenced using the chain termination method to obtain reads . Multiple overlapping reads for the target DNA are obtained by performing several rounds of this fragmentation and sequencing. Computer programs then use the overlapping ends of different reads to assemble them into a continuous sequence. [ 1 ]
Shotgun sequencing was one of the precursor technologies that was responsible for enabling whole genome sequencing .
For example, consider the following two rounds of shotgun reads:
In this extremely simplified example, none of the reads cover the full length of the original sequence, but the four reads can be assembled into the original sequence using the overlap of their ends to align and order them. In reality, this process uses enormous amounts of information that are rife with ambiguities and sequencing errors. Assembly of complex genomes is additionally complicated by the great abundance of repetitive sequences , meaning similar short reads could come from completely different parts of the sequence.
Many overlapping reads for each segment of the original DNA are necessary to overcome these difficulties and accurately assemble the sequence. For example, to complete the Human Genome Project , most of the human genome was sequenced at 12X or greater coverage ; that is, each base in the final sequence was present on average in 12 different reads. Even so, current methods have failed to isolate or assemble reliable sequence for approximately 1% of the ( euchromatic ) human genome, as of 2004. [ 3 ]
Whole genome shotgun sequencing for small (4000- to 7000-base-pair) genomes was first suggested in 1979. [ 1 ] The first genome sequenced by shotgun sequencing was that of cauliflower mosaic virus , published in 1981. [ 4 ] [ 5 ]
Broader application benefited from pairwise end sequencing , known colloquially as double-barrel shotgun sequencing . As sequencing projects began to take on longer and more complicated DNA sequences, multiple groups began to realize that useful information could be obtained by sequencing both ends of a fragment of DNA. Although sequencing both ends of the same fragment and keeping track of the paired data was more cumbersome than sequencing a single end of two distinct fragments, the knowledge that the two sequences were oriented in opposite directions and were about the length of a fragment apart from each other was valuable in reconstructing the sequence of the original target fragment.
History . The first published description of the use of paired ends was in 1990 [ 6 ] as part of the sequencing of the human HGPRT locus, although the use of paired ends was limited to closing gaps after the application of a traditional shotgun sequencing approach. The first theoretical description of a pure pairwise end sequencing strategy, assuming fragments of constant length, was in 1991. [ 7 ] At the time, there was community consensus that the optimal fragment length for pairwise end sequencing would be three times the sequence read length. In 1995 Roach et al. [ 8 ] introduced the innovation of using fragments of varying sizes, and demonstrated that a pure pairwise end-sequencing strategy would be possible on large targets. The strategy was subsequently adopted by The Institute for Genomic Research (TIGR) to sequence the genome of the bacterium Haemophilus influenzae in 1995, [ 9 ] and then by Celera Genomics to sequence the Drosophila melanogaster (fruit fly) genome in 2000, [ 10 ] and subsequently the human genome.
To apply the strategy, a high-molecular-weight DNA strand is sheared into random fragments, size-selected (usually 2, 10, 50, and 150 kb), and cloned into an appropriate vector . The clones are then sequenced from both ends using the chain termination method yielding two short sequences. Each sequence is called an end-read or read 1 and read 2 and two reads from the same clone are referred to as mate pairs . Since the chain termination method usually can only produce reads between 500 and 1000 bases long, in all but the smallest clones, mate pairs will rarely overlap.
The original sequence is reconstructed from the reads using sequence assembly software. First, overlapping reads are collected into longer composite sequences known as contigs . Contigs can be linked together into scaffolds by following connections between mate pairs. The distance between contigs can be inferred from the mate pair positions if the average fragment length of the library is known and has a narrow window of deviation. Depending on the size of the gap between contigs, different techniques can be used to find the sequence in the gaps. If the gap is small (5-20kb) then the use of polymerase chain reaction (PCR) to amplify the region is required, followed by sequencing. If the gap is large (>20kb) then the large fragment is cloned in special vectors such as bacterial artificial chromosomes (BAC) followed by sequencing of the vector.
Proponents of this approach argue that it is possible to sequence the whole genome at once using large arrays of sequencers, which makes the whole process much more efficient than more traditional approaches. Detractors argue that although the technique quickly sequences large regions of DNA, its ability to correctly link these regions is suspect, particularly for eukaryotic genomes with repeating regions. As sequence assembly programs become more sophisticated and computing power becomes cheaper, it may be possible to overcome this limitation. [ 11 ]
Coverage (read depth or depth) is the average number of reads representing a given nucleotide in the reconstructed sequence. It can be calculated from the length of the original genome ( G ), the number of reads( N ), and the average read length( L ) as N × L / G {\displaystyle N\times L/G} . For example, a hypothetical genome with 2,000 base pairs reconstructed from 8 reads with an average length of 500 nucleotides will have 2x redundancy. This parameter also enables one to estimate other quantities, such as the percentage of the genome covered by reads (sometimes also called coverage). A high coverage in shotgun sequencing is desired because it can overcome errors in base calling and assembly. The subject of DNA sequencing theory addresses the relationships of such quantities.
Sometimes a distinction is made between sequence coverage and physical coverage . Sequence coverage is the average number of times a base is read (as described above). Physical coverage is the average number of times a base is read or spanned by mate paired reads. [ 12 ]
Although shotgun sequencing can in theory be applied to a genome of any size, its direct application to the sequencing of large genomes (for instance, the human genome ) was limited until the late 1990s, when technological advances made practical the handling of the vast quantities of complex data involved in the process. [ 13 ] Historically, full-genome shotgun sequencing was believed to be limited by both the sheer size of large genomes and by the complexity added by the high percentage of repetitive DNA (greater than 50% for the human genome) present in large genomes. [ 14 ] It was not widely accepted that a full-genome shotgun sequence of a large genome would provide reliable data. For these reasons, other strategies that lowered the computational load of sequence assembly had to be utilized before shotgun sequencing was performed. [ 14 ] In hierarchical sequencing, also known as top-down sequencing, a low-resolution physical map of the genome is made prior to actual sequencing. From this map, a minimal number of fragments that cover the entire chromosome are selected for sequencing. [ 15 ] In this way, the minimum amount of high-throughput sequencing and assembly is required.
The amplified genome is first sheared into larger pieces (50-200kb) and cloned into a bacterial host using BACs or P1-derived artificial chromosomes (PAC). Because multiple genome copies have been sheared at random, the fragments contained in these clones have different ends, and with enough coverage (see section above) finding the smallest possible scaffold of BAC contigs that covers the entire genome is theoretically possible. This scaffold is called the minimum tiling path .
Once a tiling path has been found, the BACs that form this path are sheared at random into smaller fragments and can be sequenced using the shotgun method on a smaller scale. [ 16 ]
Although the full sequences of the BAC contigs is not known, their orientations relative to one another are known. There are several methods for deducing this order and selecting the BACs that make up a tiling path. The general strategy involves identifying the positions of the clones relative to one another and then selecting the fewest clones required to form a contiguous scaffold that covers the entire area of interest. The order of the clones is deduced by determining the way in which they overlap. [ 17 ] Overlapping clones can be identified in several ways. A small radioactively or chemically labeled probe containing a sequence-tagged site (STS) can be hybridized onto a microarray upon which the clones are printed. [ 17 ] In this way, all the clones that contain a particular sequence in the genome are identified. The end of one of these clones can then be sequenced to yield a new probe and the process repeated in a method called chromosome walking.
Alternatively, the BAC library can be restriction-digested . Two clones that have several fragment sizes in common are inferred to overlap because they contain multiple similarly spaced restriction sites in common. [ 17 ] This method of genomic mapping is called restriction or BAC fingerprinting because it identifies a set of restriction sites contained in each clone. Once the overlap between the clones has been found and their order relative to the genome known, a scaffold of a minimal subset of these contigs that covers the entire genome is shotgun-sequenced. [ 15 ]
Because it involves first creating a low-resolution map of the genome, hierarchical shotgun sequencing is slower than whole-genome shotgun sequencing, but relies less heavily on computer algorithms than whole-genome shotgun sequencing. The process of extensive BAC library creation and tiling path selection, however, make hierarchical shotgun sequencing slow and labor-intensive. Now that the technology is available and the reliability of the data demonstrated, [ 14 ] the speed and cost efficiency of whole-genome shotgun sequencing has made it the primary method for genome sequencing.
The classical shotgun sequencing was based on the Sanger sequencing method: this was the most advanced technique for sequencing genomes from about 1995–2005. The shotgun strategy is still applied today, however using other sequencing technologies, such as short-read sequencing and long-read sequencing .
Short-read or "next-gen" sequencing produces shorter reads (anywhere from 25–500bp) but many hundreds of thousands or millions of reads in a relatively short time (on the order of a day). [ 18 ] This results in high coverage, but the assembly process is much more computationally intensive. These technologies are vastly superior to Sanger sequencing due to the high volume of data and the relatively short time it takes to sequence a whole genome. [ 19 ]
Having reads of 400-500 base pairs length is sufficient to determine the species or strain of the organism where the DNA comes from, provided its genome is already known, by using for example a k -mer based taxonomic classifier software. With millions of reads from next generation sequencing of an environmental sample, it is possible to get a complete overview of any complex microbiome with thousands of species, like the gut flora . Advantages over 16S rRNA amplicon sequencing are: not being limited to bacteria; strain-level classification where amplicon sequencing only gets the genus; and the possibility to extract whole genes and specify their function as part of the metagenome. [ 20 ] The sensitivity of metagenomic sequencing makes it an attractive choice for clinical use . [ 21 ] It however emphasizes the problem of contamination of the sample or the sequencing pipeline. [ 22 ]
This article incorporates public domain material from NCBI Handbook . National Center for Biotechnology Information . | https://en.wikipedia.org/wiki/Shotgun_sequencing |
Shotgun surgery is an anti-pattern in software development which occurs when a developer adds features to an application codebase which span a multiplicity of implementors or implementations in a single change. This is common practice in many programming scenarios, as a great amount of programming effort is usually expended on adding new features to increase the value of programming assets. As a consequence, these new features may require adding code in several places simultaneously where the code itself looks very similar and may only have slight variations. Owing to the fast-paced nature of commercial software development, there may not be sufficient time to remodel (or refactor ) a system to support the new features trivially. As a consequence, the practice of copy-and-paste programming is prevalent; the code is written in a single place then simply copied to all other places where that implementation is required (with any required changes applied in-place).
This practice is generally frowned on by the refactoring community as a direct violation of the abstraction principle , also known as the Once and Only Once rule – ultimately any change to the new functionality may require widespread changes. Further, any potential software bug in this new feature will be replicated many-fold and can make bug fixing particularly difficult and tedious. Even in the absence of copied code, the implementations are guaranteed to be very similar and just as prone to requirements change or bug fixing. This form of software development tends to favour short-term improvement (in the form of additional features) at the cost of long-term maintainability and stability.
The canonical example of this practice is logging which generally adds prologue code to many functions simultaneously, for example:
Could be transformed to:
Here a single requirement has added similar code to several functions simultaneously. As such any change in requirements here (namely adding line numbers to the log) would now require a considerable effort. Shotgun surgery is not synonymous with cut and paste coding, as highlighted by this trivial example. The practice of copying code can be viewed as a "means to an end", where shotgun surgery is merely an "end" (i.e. there are many ways to reach the same conclusion).
The concerns with this style are by-and-large the same as those for any duplication in a software system; that is, duplicating the same logic in many places can vastly increase the costs of making changes to the same logic later. Some of the aforementioned costs are measurable, others are not (at least not trivially). There is also some evidence that this anti-pattern is correlated with higher defect rates. [ 1 ]
Typically some combination of the following is to be expected:
Of these the most insidious are the psychological effects (e.g. see broken windows theory ) which can exponentially lead to software rot . [ citation needed ] When uncontrolled this can cause entire codebases to become unmaintainable. Generally the only solution to this problem is to completely rewrite the code [ citation needed ] (at substantial cost).
Aspect-oriented programming (AOP) aims at reducing these forms of invasive modifications in favour of adopting an "aspect" or "concern". The solutions take the form of boilerplate code which can be applied over a domain of functions simultaneously (through the process of weaving ) which vastly reduces the amount of duplicated code. The use of domain-specific languages is also becoming more widespread where light-weight compilers are written to generate most of the duplicated code on the behalf of the programmer. Both methods fall into the broader categories of code generation and automation. | https://en.wikipedia.org/wiki/Shotgun_surgery |
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Shotokuvirae is a kingdom of viruses . [ 1 ]
The kingdom, Shotokuvirae, was named after Japan's Empress Shotoku (718-770 AD), who reigned over Japan twice, first as Empress Koken and later as Empress Shotoku, and who created the world's earliest written record of a plant virus disease, which was a poem to her followers about a geminivirus eupatorium yellow vein virus infection of a eupatorium plant, which she had described as having turned yellow. [ 2 ]
The following phyla are recognized: [ 1 ]
This virus -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Shotokuvirae |
Shovelware is a type of video game or software bundle known more for the quantity of what is included than for its quality or usefulness. [ 1 ]
The metaphor implies that the creators showed little care for the quality of the original software, as if the new compilation or version had been created by indiscriminately adding titles "by the shovel" in the same way someone would shovel bulk material into a pile. The term "shovelware" is coined by semantic analogy to phrases like shareware and freeware , which describe methods of software distribution. It first appeared in the early 1990s when large amounts of shareware demo programs were copied onto CD-ROMs and advertised in magazines or sold at computer flea markets. [ 1 ]
Computer Gaming World wrote in 1990 that for "those who do not wish to wait" for software that used the new CD-ROM format, The Software Toolworks and Access Software planned to release "game packs of several classic titles". [ 2 ] By 1993 the magazine referred to software repackaged on CD-ROM as "shovelware", describing one collection from Access as having a "rather dusty menu" and another from The Software Toolworks ("the reigning king of software repackaging efforts") as including games that were "mostly mediocre even in their prime"; the one exception, Chessmaster 2000 , used "stunning CGA graphics ". [ 3 ] In 1994 the magazine described shovelware as "old and/or weak programs shoveled onto a CD to turn a quick buck". [ 4 ]
The capacity of a CD-ROM was 450–700 times that of the floppy disk , and 6–16 times larger than the hard disks with which personal computers were commonly outfitted in 1990. This outsized capacity meant that very few users would install the discs' entire contents, encouraging producers to fill them by including as much existing content as possible, often without regard to the quality of the material. Advertising the number of titles on the disc often took precedence over the quality of the content. Software reviewers, displeased with huge collections of inconsistent quality, dubbed this practice "shovelware" in the early 1990s. Additionally, some CD-ROM computer games had software that did not fill the disc to capacity, which enabled game companies to bundle demo versions of other products on the same disc.
The prevalence of shovelware has decreased due to the practice of downloading individual programs from a crowdsourced or curated app store becoming the predominant mode of software distribution . It continues in some cases with bundled or pre-installed software , where many extra programs of dubious quality and functionality are included with a piece of hardware.
Low-budget, poor-quality video games, released in the hopes of being purchased by unsuspecting customers, are often referred to as "shovelware". This can lead to discoverability issues when a platform has no type of quality control. [ 5 ]
Some developers and publishers have become well-known as creators of shovelware. Blast! Entertainment , a defunct video game developer and publisher, was known for releasing licensed shovelware games based on movies, television shows and books [ 6 ] such as An American Tail , Beverly Hills Cop , Jumanji , and Lassie , the majority of which received negative reception. [ citation needed ] Another defunct European publisher, Phoenix Games, was known for its line of value-priced titles for the PlayStation 2 , Wii , DS , and PC. [ 7 ] A number of their in-house games are adaptations of low-budget animated mockbusters , which largely function as interactive "activity centre" games with minimal actual gameplay. Games made by other studios, including Mere Mortals , but published by Phoenix, have a similarly poor reputation. [ 8 ]
The Nintendo Wii became known for large amounts of shovelware, including ports of PlayStation 2 games which had previously only been released in Europe. [ 9 ] Data Design Interactive became known for creating shovelware for the Wii. Their games Ninjabread Man , Anubis II , Rock 'n' Roll Adventures , and Myth Makers: Trixie in Toyland all used the exact same gameplay and level layouts, but changed the art and character design to make them appear to be unique properties. [ 10 ] [ 11 ] The eShop on Nintendo's later console, the Nintendo Switch , has also become notorious for featuring an abundance of low-quality games and software. [ 12 ] [ 13 ]
Asset flips are a subset of shovelware that largely or entirely use pre-made assets in order to release games en masse. Called fake games by Valve Corporation , 173 were removed from Steam in one 2017 purge that included several sock puppets of Silicon Echo Studios. [ 14 ] | https://en.wikipedia.org/wiki/Shovelware |
The shower-curtain effect in physics describes the phenomenon of a shower curtain being blown inward when a shower is running. The problem of identifying the cause of this effect has been featured in Scientific American magazine, with several theories given to explain the phenomenon but no definite conclusion.
The shower-curtain effect may also be used to describe the observation of how nearby phase front distortions of an optical wave are more severe than remote distortions of the same amplitude. [ jargon ]
Also called chimney effect or stack effect , observes that warm air (from the hot shower) rises out over the shower curtain as cooler air (near the floor) pushes in under the curtain to replace the rising air. By pushing the curtain in towards the shower, the (short range) vortex and Coandă effects become more significant. However, the shower-curtain effect persists when cold water is used, implying that this is not the sole mechanism. [ 1 ]
The most popular explanation given for the shower-curtain effect is Bernoulli's principle . [ 1 ] Bernoulli's principle states that an increase in velocity results in a decrease in pressure. This theory presumes that the water flowing out of a shower head causes the air through which the water moves to start flowing in the same direction as the water. This movement would be parallel to the plane of the shower curtain. If air is moving across the inside surface of the shower curtain, Bernoulli's principle says the air pressure there will drop. This would result in a pressure differential between the inside and outside, causing the curtain to move inward. It would be strongest when the gap between the bather and the curtain is smallest, resulting in the curtain attaching to the bather. [ 2 ] [ citation needed ]
A computer simulation of a typical bathroom found that none of the above theories pan out in their analysis, but instead found that the spray from the shower-head drives a horizontal vortex . This vortex has a low-pressure zone in the centre, which sucks the curtain. [ 3 ] [ 1 ]
David Schmidt of the University of Massachusetts was awarded the 2001 Ig Nobel Prize in Physics for his partial solution to the question of why shower curtains billow inwards. He used a computational fluid dynamics code to achieve the results. Professor Schmidt is adamant that this was done "for fun" in his own free time without the use of grants. [ 4 ]
The Coandă effect , also known as "boundary layer attachment", is the tendency of a moving fluid to adhere to an adjacent wall. [ 1 ]
A hot shower will produce steam that condenses on the shower side of the curtain, lowering the pressure there. In a steady state the steam will be replaced by new steam delivered by the shower but in reality the water temperature will fluctuate and lead to times when the net steam production is negative. [ citation needed ]
Colder dense air outside and hot less dense air inside causes higher air pressure on the outside to force the shower curtain inwards to equalise the air pressure, this can be observed simply when the bathroom door is open allowing cold air into the bathroom.
Many shower curtains come with features to reduce the shower-curtain effect. They may have adhesive suction cups on the bottom edges of the curtain, which are then pushed onto the sides of the shower when in use. Others may have magnets at the bottom, though these are not effective on acrylic or fiberglass tubs.
It is possible to use a telescopic shower curtain rod to block the curtain on its lower part and to prevent it from sucking inside.
Hanging the curtain rod higher or lower, or especially further away from the shower head, can reduce the effect. A convex shower rod can also be used to hold the curtain against the inside wall of a tub.
A weight can be attached to a long string and the string attached to the curtain rod in the middle of the curtain (on the inside). Hanging the weight low against the curtain just above the rim of the shower pan or tub makes it an effective billowing deterrent without allowing the weight to hit the pan or tub and damage it.
There are a few alternative solutions that either attach to the shower curtain directly, attach to the shower rod or attach to the wall. | https://en.wikipedia.org/wiki/Shower-curtain_effect |
Shpolskii systems are low-temperature host–guest systems – they are typically rapidly frozen solutions of polycyclic aromatic hydrocarbons in suitable low molecular weight normal alkanes. The emission and absorption spectra of lowest energy electronic transitions in the Shpolskii systems exhibit narrow lines instead of the inhomogeneously broadened features normally associated with spectra of chromophores in liquids and amorphous solids. The effect was first described by Eduard Shpolskii in the 1950s [ 1 ] and 1960's [ 2 ] [ 3 ] [ 4 ] in the journals Transactions of the U.S.S.R. Academy of Sciences and Soviet Physics Uspekhi .
Subsequent detailed studies of concentration and speed of cooling behavior of Shpolskii systems by L. A. Nakhimovsky and coauthors led to a hypothesis that these systems are metastable segregational solid solutions formed when one or more chromophores replace two or more molecules in the host crystalline lattice. The solid state quasi-equilibrium solubility in most Shpolskii systems is very low. When the Shpolskii effect is manifested, the solid state solubility increases two to three orders of magnitude. [ 5 ] [ 6 ] Isothermic annealing of the supersaturated rapidly frozen solutions of dibenzofuran in heptane was performed, and it was shown that the return of the metastable system to equilibrium in time reasonable for laboratory observation required the annealing temperature to be close to the melting temperature of the metastable frozen solution. [ 7 ] Thus the Shpolskii systems are an example of a persistent metastable state.
A good match between the chromophore and the host lattice leads to a uniform environment for all the chromophores and hence greatly reduces the inhomogeneous broadening of the electronic transition's pure electronic and vibronic lines. In addition to the weak inhomogeneous broadening of the transitions, the quasi-lines observed at very low temperatures are phonon -less transitions. [ 8 ] Since phonons originate in the lattice, an additional requirement is weak chromophore-lattice coupling. Weak coupling increases the probability of phonon-less transitions and hence favors the narrow zero phonon lines . [ 9 ] The weak coupling is usually expressed in terms of the Debye-Waller factor , where a maximum value of one indicates no coupling between the chromophore and the lattice phonons. The narrow lines characteristic of the Shpolskii systems are only observed at cryogenic temperatures because at higher temperatures many phonons are active in the lattice and all of the amplitude of the transition shifts to the broad phonon sideband . The original observation of the Shpolskii effect was made at liquid nitrogen temperature (77 kelvins ), but using temperatures close to that of liquid helium (4.2 K) yields much sharper spectral lines and is the usual practice.
Low molecular weight normal alkanes absorb light at energies higher than the absorption of all pi-pi electronic transitions of aromatic hydrocarbons. They interact weakly with the chromophores and crystallize when frozen. The length of the alkanes is often chosen to approximately match at least one of the dimensions of the chromophore, and are usually in the size range between n-pentane and n-dodecane. | https://en.wikipedia.org/wiki/Shpolskii_matrix |
Shq1p is a protein involved in the rRNA processing pathway . It was discovered by Pok Yang in the Chanfreau laboratory at UCLA . Depletion of Shq1p has led to decreased level of various H/ACA box snoRNAs (H/ACA box snoRNAs are responsible for pseuduridylation of pre-rRNA) and certain pre-rRNA intermediates. [ 1 ]
During the synthesis of eukaryotic ribosomes , four mature ribosomal RNAs (the 5S, 5.8S, 18S, and 25S) must be synthesized. Three of these rRNAs (5.8S, 18S, and 25S) come from a single pre-rRNA known as the 35S. Although many of the intermediates in this rRNA processing pathway have been identified in the last thirty years, there are still a number of proteins involved in this process whose specific function is unknown.
Shq1, a protein thought to play a role in the stabilization and/or production of box H/ACA snoRNA , is still uncharacterized. It has been proposed that Shq1, along with Naf1p, is involved in the initial steps of the biogenesis of H/ACA box snoRNPs (box H/ACA snoRNAs form complexes with proteins , thereby forming snoRNPs ) because of its association with certain snoRNP proteins during the snoRNP ’s maturation, while showing very little association with the mature snoRNP complex. [ 1 ] Despite the known involvement of Shq1 in H/ACA box snoRNP's production, the exact function of this protein in the overall rRNA processing pathway is still unknown. | https://en.wikipedia.org/wiki/Shq1 |
Shredding refers to the process in bioinformatics of taking assembled gene sequences and disassembling them into short sequences of usually 500 to 750 base pairs (bp). This is generally done for the purpose of taking the short shredded sequences and reapplying various analysis and bioinformatic techniques. Being able to cut DNA samples and then run them through gel electrophoresis to study each strand in order to help find cures for diseases or illnesses is also another purpose.
The most common tool or enzyme used to shred DNA into fragments is CAS9 . Clustered regularly interspaces short palindromic repeats(CRISPR) - Cas9 allows genetic material to be either altered, removed or added at specific locations. CRISPR-Cas 9 consists of guide RNA (gRNA) and the enzyme(Cas9). This enzyme is able to cut DNA the exactly as wanted without making a mistake. There are also many other enzymes that help with shredding such as CASX or CAS3. CAS3 is a shredding tool but is not as accurate as CAS9 and may lead to random DNA strands being deleted.
DNA (deoxyribonucleic acid) was first found by Rosalind Franklin . She discovered that DNA exists in species by taking multiple x-rays until she found an "X" looking diagram. She did not actually know much about it other than it exists. She died a few years later due to a massive amount of exposure to x-rays. James Watson and Francis Cricket then used Rosalind's discovery and looked further into it. They discovered the structure of DNA. They were the first to know that DNA has a double helix after the analysis of the x-rays.
With time, DNA fragments were discovered. They first studied DNA on very simplistic organisms. This is because the human DNA strand is very complex compared to an organism like a fruit fly, which has much simpler genes. The scientists did various experiments using simplistic genes and worked their way into much harder genes. They did various cutting to specific genes to see what would occur.
The process of shredding was used successfully several times during the analysis phase of the human genome project . [ 1 ] The first phase of the human genome project is called the "shotgun phase". During this phase human chromosomes are 1). Divided into DNA segments of equal size and then 2). Subdivided into even smaller DNA segments. The overall goal is to get DNA segments into small sizes in order to be able to test run them.
This bioinformatics-related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Shredding_(disassembling_genomic_data) |
In category theory , a branch of mathematics , certain unusual functors are denoted f ! {\displaystyle f_{!}} and f ! , {\displaystyle f^{!},} with the exclamation mark used to indicate that they are exceptional in some way. They are thus accordingly sometimes called shriek maps, with " shriek " being slang for an exclamation mark, though other terms are used, depending on context.
Shriek notation is used in two senses:
In algebraic geometry , these arise in image functors for sheaves , particularly Verdier duality , where f ! {\displaystyle f_{!}} is a "less usual" functor.
In algebraic topology , these arise particularly in fiber bundles , where they yield maps that have the opposite of the usual variance. They are thus called wrong way maps , Gysin maps , as they originated in the Gysin sequence , or transfer maps . A fiber bundle F → E → B , {\displaystyle F\to E\to B,} with base space B , fiber F , and total space E , has, like any other continuous map of topological spaces, a covariant map ( pushforward ) on homology H ∗ ( E ) → H ∗ ( B ) {\displaystyle H_{*}(E)\to H_{*}(B)} and a contravariant map ( pullback ) on cohomology H ∗ ( B ) → H ∗ ( E ) . {\displaystyle H^{*}(B)\to H^{*}(E).} However, it also has a covariant map on cohomology, corresponding in de Rham cohomology to " integration along the fiber ", and a contravariant map on homology, corresponding in de Rham cohomology to "pointwise product with the fiber". The composition of the "wrong way" map with the usual map gives a map from the homology of the base to itself, analogous to a unit/counit of an adjunction ; compare also Galois connection .
These can be used in understanding and proving the product property for the Euler characteristic of a fiber bundle . [ 1 ] | https://en.wikipedia.org/wiki/Shriek_map |
Shrink-fitting is a technique in which an interference fit is achieved by a relative size change after assembly. This is usually achieved by heating or cooling one component before assembly and allowing it to return to the ambient temperature after assembly, employing the phenomenon of thermal expansion to make a joint. For example, the thermal expansion of a piece of a metallic drainpipe allows a builder to fit the cooler piece to it. As the adjoined pieces reach the same temperature, the joint becomes strained and stronger.
Other examples are the fitting of a wrought iron tyre around the rim of a wooden cart wheel by a wheelwright , or of a steel tyre to the wheel of a railway engine or rolling stock. In both cases the tyre will be heated and expands to slightly greater than the wheel's diameter , and is fitted around it. After cooling, the tyre contracts, binding tightly in place. The bombard Mons Meg was assembled from longitudinal staves of iron held in place by shrink-fitted iron hoops. [ 1 ]
A common method used in industry is the use of induction shrink fitting which refers to the use of induction heating technology to pre-heat metal components between 150˚C and 300˚C thereby causing them to expand and allow for the insertion or removal of another component. Other methods of shrink-fitting include compression shrink fitting, which uses a cryogen such as liquid nitrogen to cool the insert, and shape memory coupling , which is achieved by means of a phase transition .
This article about a mechanical engineering topic is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Shrink-fitting |
A shrink tunnel or heat tunnel is a heated tunnel mounted over or around a conveyor system . Items (such as packaging ) have shrink film loosely applied; with heat, the film shrinks to fit snugly around the wrapped object. [ 1 ]
Several types of shrink tunnels are available. [ 3 ] [ 4 ] [ 5 ] The heat source can be based on heating element (electrical resistance), infrared heater , steam, or gas flame. Often forced air is used to improve convection , sometimes focusing the heat on one component of the item.
Tunnels are available with or without a conveyor system. Some are built into a production line or are integral with machinery that also applies the shrink film. Others are movable by hand or by castors. A shrink tunnel, referred to as an oven, may be equipped with an integrated conveyor of two different kinds: the roller conveyor or the belt conveyor . Roller conveyors can be used with polyolefin , PVC , and shrink polyethylene films. The space in between the rollers is filled with hot air from the bottom of the tunnel to shrink the film layer around the object, creating a sealed package. When used with polyolefin and PVC based films the rollers are called "live" or spinning. When used with polyethylene films the rollers are called "dead" or not spinning. The tunnels with Teflon mesh belts and polymer mesh belts are used for smaller packages, or when the package may have an instability and need a stable platform.
Some heat shrink tunnels have two or more zones for heating and controlled cooling. | https://en.wikipedia.org/wiki/Shrink_tunnel |
A shrub or bush is a small to medium-sized perennial woody plant . Unlike herbaceous plants , shrubs have persistent woody stems above the ground. Shrubs can be either deciduous or evergreen. They are distinguished from trees by their multiple stems and shorter height , less than 6–10 m (20–33 ft) tall. [ 1 ] [ 2 ] Small shrubs, less than 2 metres (6.6 feet) tall are sometimes termed as subshrubs . Many botanical groups have species that are shrubs, and others that are trees and herbaceous plants instead.
Some define a shrub as less than 6 m (20 ft) and a tree as over 6 m. Others use 10 m (33 ft) as the cutoff point for classification. [ 2 ] Many trees do not reach this mature height because of hostile, less than ideal growing conditions, and resemble shrub-sized plants. Others in such species have the potential to grow taller in ideal conditions. For longevity, most shrubs are classified between perennials and trees. Some only last about five years in good conditions. Others, usually larger and more woody, live beyond 70. On average, they die after eight years. [ 3 ]
Shrubland is the natural landscape dominated by various shrubs; there are many distinct types around the world, including fynbos , maquis , shrub-steppe , shrub swamp and moorland . In gardens and parks, an area largely dedicated to shrubs (now somewhat less fashionable than a century ago) is called a shrubbery , shrub border or shrub garden. There are many garden cultivars of shrubs, bred for flowering, for example rhododendrons , and sometimes even leaf colour or shape.
Compared to trees and herbaceous plants, a small number of shrubs have culinary usage. [ citation needed ] Apart from the several berry -bearing species (using the culinary rather than botanical definition), few are eaten directly, and they are generally too small for much timber use unlike trees. Those that are used include several perfumed species such as lavender and rose , and a wide range of plants with medicinal uses. Tea and coffee are on the tree-shrub boundary; [ 4 ] they are normally harvested from shrub-sized plants, but these would be large enough to become small trees if left to grow instead.
Shrubs are perennial woody plants, and therefore have persistent woody stems above ground (compare with succulent stems of herbaceous plants ). [ 2 ] Usually, shrubs are distinguished from trees by their height and multiple stems. Some shrubs are deciduous (e.g. hawthorn ) and others evergreen (e.g. holly ). [ 2 ] Ancient Greek philosopher Theophrastus divided the plant world into trees, shrubs and herbs. [ 5 ] Small, low shrubs, generally less than 2 m (6.6 ft) tall, such as lavender , periwinkle and most small garden varieties of rose , are often termed as subshrubs . [ 6 ] [ 7 ]
Most definitions characterize shrubs as possessing multiple stems with no main trunk below. [ 2 ] This is because the stems have branched below ground level. There are exceptions to this, with some shrubs having main trunks, but these tend to be very short and divide into multiple stems close to ground level without a reasonable length beforehand. Many trees can grow in multiple stemmed forms also while being tall enough to be trees, such as oak or ash . [ 2 ]
An area of cultivated shrubs in a park or a garden is known as a shrubbery . [ 8 ] When clipped as topiary , suitable species or varieties of shrubs develop dense foliage and many small leafy branches growing close together. [ 9 ] Many shrubs respond well to renewal pruning , in which hard cutting back to a " stool ", removes everything but vital parts of the plant, resulting in long new stems known as "canes". [ 10 ] Other shrubs respond better to selective pruning to dead or unhealthy, or otherwise unattractive parts to reveal their structure and character. [ 11 ]
Shrubs in common garden practice are generally considered broad-leaved plants , though some smaller conifers such as mountain pine and common juniper are also shrubby in structure. Species that grow into a shrubby habit may be either deciduous or evergreen . [ 12 ]
In botany and ecology , a shrub is more specifically used to describe the particular physical canopy structure or plant life-form of woody plants which are less than 8 metres (26 ft) high and usually multiple stems arising at or near the surface of the ground. For example, a descriptive system widely adopted in Australia is based on structural characteristics based on life-form, plus the height and amount of foliage cover of the tallest layer or dominant species . [ 13 ]
For shrubs that are 2–8 metres (6.6–26.2 ft) high, the following structural forms are categorized:
For shrubs less than 2 metres (6.6 ft) high, the following structural forms are categorized:
Those marked with * can also develop into tree form if in ideal conditions. | https://en.wikipedia.org/wiki/Shrub |
Shu Jie Lam is a Malaysian-Chinese research chemist specialising in biomolecular engineering . She is researching star polymers designed to attack superbugs as antibiotics . [ 1 ] [ 2 ] [ 3 ] [ 4 ]
This biographical article about a chemist is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Shu_Jie_Lam |
The A. V. Shubnikov Institute of Crystallography is a scientific institute of the Department of Physical Sciences of the Russian Academy of Sciences (RAS) located in Moscow, Russia. [ 1 ] The institute was created by the order of the Presidium of the Academy of Sciences of the USSR on 16 November 1943. The first director of the Institute was a corresponding member of the Academy of Sciences of the USSR Alexei Vasilievich Shubnikov . In 1969, the institute was awarded the Order of the Red Banner of Labour .
Areas of scientific interest: | https://en.wikipedia.org/wiki/Shubnikov_Institute_of_Crystallography_RAS |
In mathematics, a shuffle algebra is a Hopf algebra with a basis corresponding to words on some set, whose product is given by the shuffle product X ⧢ Y of two words X , Y : the sum of all ways of interlacing them. The interlacing is given by the riffle shuffle permutation .
The shuffle algebra on a finite set is the graded dual of the universal enveloping algebra of the free Lie algebra on the set.
Over the rational numbers, the shuffle algebra is isomorphic to the polynomial algebra in the Lyndon words .
The shuffle product occurs in generic settings in non-commutative algebras ; this is because it is able to preserve the relative order of factors being multiplied together - the riffle shuffle permutation . This can be held in contrast to the divided power structure , which becomes appropriate when factors are commutative.
The shuffle product of words of lengths m and n is a sum over the ( m + n )! / m ! n ! ways of interleaving the two words, as shown in the following examples:
It may be defined inductively by [ 1 ]
where ε is the empty word , a and b are single elements, and u and v are arbitrary words.
The shuffle product was introduced by Eilenberg & Mac Lane (1953) . The name "shuffle product" refers to the fact that the product can be thought of as a sum over all ways of riffle shuffling two words together: this is the riffle shuffle permutation . The product is commutative and associative . [ 2 ]
The shuffle product of two words in some alphabet is often denoted by the shuffle product symbol ⧢ ( Unicode character U+29E2 SHUFFLE PRODUCT , derived from the Cyrillic letter ⟨ш⟩ sha ).
The closely related infiltration product was introduced by Chen, Fox & Lyndon (1958) . It is defined inductively on words over an alphabet A by
For example:
The infiltration product is also commutative and associative. [ 3 ] | https://en.wikipedia.org/wiki/Shuffle_algebra |
The Shukhov cracking process is a thermal cracking process invented by Vladimir Shukhov and Sergei Gavrilov.
Shukhov designed and built the first thermal cracking device for the petrochemical industry . His patent (Shukhov cracking process – patent of Russian Empire No. 12926 from November 27, 1891) on cracking was used to invalidate Standard Oil 's patents ( Burton process – Patent of United States No. 1,049,667 on January 7, 1913) on oil refineries .
In 1937 the Shukhov cracking process was superseded by catalytic cracking . It is still in use today to produce diesel .
This article related to natural gas, petroleum or the petroleum industry is a stub . You can help Wikipedia by expanding it .
This chemical process -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Shukhov_cracking_process |
The Shulva Sutras or Śulbasūtras ( Sanskrit : शुल्बसूत्र; śulba : "string, cord, rope") are sutra texts belonging to the Śrauta ritual and containing geometry related to fire-altar construction.
The Shulba Sutras are part of the larger corpus of texts called the Shrauta Sutras , considered to be appendices to the Vedas . They are the only sources of knowledge of Indian mathematics from the Vedic period . Unique Vedi (fire-altar) shapes were associated with unique gifts from the Gods. For instance, "he who desires heaven is to construct a fire-altar in the form of a falcon"; "a fire-altar in the form of a tortoise is to be constructed by one desiring to win the world of Brahman" and "those who wish to destroy existing and future enemies should construct a fire-altar in the form of a rhombus". [ 1 ]
The four major Shulba Sutras, which are mathematically the most significant, are those attributed to Baudhayana , Manava , Apastamba and Katyayana . [ 2 ] Their language is late Vedic Sanskrit , pointing to a composition roughly during the 1st millennium BCE . [ 2 ] The oldest is the sutra attributed to Baudhayana, possibly compiled around 800 BCE to 500 BCE. [ 2 ] Pingree says that the Apastamba is likely the next oldest; he places the Katyayana and the Manava third and fourth chronologically, on the basis of apparent borrowings. [ 3 ] According to mathematical historian Kim Plofker , the Katyayana was composed after "the great grammatical codification of Sanskrit by Pāṇini in probably the mid-fourth century BCE", but she places the Manava in the same period as the Baudhayana. [ 4 ]
With regard to the composition of Vedic texts, Plofker writes,
The Vedic veneration of Sanskrit as a sacred speech, whose divinely revealed texts were meant to be recited, heard, and memorized rather than transmitted in writing, helped shape Sanskrit literature in general. ... Thus texts were composed in formats that could be easily memorized: either condensed prose aphorisms ( sūtras, a word later applied to mean a rule or algorithm in general) or verse, particularly in the Classical period. Naturally, ease of memorization sometimes interfered with ease of comprehension. As a result, most treatises were supplemented by one or more prose commentaries ..." [ 5 ]
There are multiple commentaries for each of the Shulba Sutras, but these were written long after the original works. The commentary of Sundararāja on the Apastamba, for example, comes from the late 15th century CE [ 6 ] and the commentary of Dvārakãnātha on the Baudhayana appears to borrow from Sundararāja. [ 7 ] According to philosopher Frits Staal , certain aspects of the tradition described in the Shulba Sutras would have been "transmitted orally", and he points to places in southern India where the fire-altar ritual is still practiced and an oral tradition preserved. [ 8 ] The fire-altar tradition largely died out in India, however, and Plofker warns that those pockets where the practice remains may reflect a later Vedic revival rather than an unbroken tradition. [ 4 ] Archaeological evidence of the altar constructions described in the Shulba Sutras is sparse. A large falcon-shaped fire altar ( śyenaciti ), dating to the second century BCE, was found in the, 1957-59, excavations by G. R. Sharma at Kausambi , [ 9 ] but this altar does not conform to the dimensions prescribed by the Shulba Sutras. [ 3 ] [ 10 ]
The content of the Shulba Sutras is likely older than the works themselves. [ citation needed ] The Satapatha Brahmana and the Taittiriya Samhita , whose contents date to the late second millennium or early first millennium BCE, describe altars whose dimensions appear to be based on the right triangle with legs of 15 pada and 36 pada , one of the triangles listed in the Baudhayana Shulba Sutra. [ 11 ] [ 12 ]
The origin of the mathematics in the Shulba Sutras is not known. It is possible, as proposed by mathematical historian Radha Charan Gupta , that the geometry was developed to meet the needs of ritual. [ 13 ] Some scholars go farther: Staal hypothesizes a common ritual origin for Indian and Greek geometry, citing similar interest and approach to doubling and other geometric transformation problems. [ 14 ] Seidenberg, followed by Bartel Leendert van der Waerden , sees a ritual origin for mathematics more broadly, postulating that the major advances, such as discovery of the Pythagorean theorem, occurred in only one place, and diffused from there to the rest of the world. [ 15 ] [ 16 ] Van der Waerden mentions that author of Sulbha sutras existed before 600 BCE and could not have been influenced by Greek geometry. [ 17 ] [ 18 ] While, historian, Carl Benjamin Boyer mentions Old Babylonian mathematics (c. 2000 BCE–1600 BCE) as a possible origin, the c. 1800 BCE Plimpton 322 tablet containing a table of triplets, however also states that Shulba sutras contain a formula not found in Babylon sources. [ 19 ] [ 1 ] Abraham Seidenberg argues that either "Old Babylonia got the theorem of Pythagoras from India or that Old Babylonia and India got it from a third source". Seidenberg suggests that this source might be Sumerian and may predate 1700 BC. [ 20 ] In contrast, Pingree cautions that "it would be a mistake to see in [the altar builders'] works the unique origin of geometry; others in India and elsewhere, whether in response to practical or theoretical problems, may well have advanced as far without their solutions having been committed to memory or eventually transcribed in manuscripts." [ 21 ] Plofker also raises the possibility that "existing geometric knowledge [was] consciously incorporated into ritual practice". [ 22 ]
The sutras contain statements of the Pythagorean theorem , both in the case of an isosceles right triangle and in the general case, as well as lists of Pythagorean triples . [ 23 ] In Baudhayana, for example, the rules are given as follows:
1.9. The diagonal of a square produces double the area [of the square]. [...] 1.12. The areas [of the squares] produced separately by the lengths of the breadth of a rectangle together equal the area [of the square] produced by the diagonal. 1.13. This is observed in rectangles having sides 3 and 4, 12 and 5, 15 and 8, 7 and 24, 12 and 35, 15 and 36. [ 24 ]
Similarly, Apastamba's rules for constructing right angles in fire-altars use the following Pythagorean triples: [ 25 ] [ 26 ]
In addition, the sutras describe procedures for constructing a square with area equal either to the sum or to the difference of two given squares. Both constructions proceed by letting the largest of the squares be the square on the diagonal of a rectangle, and letting the two smaller squares be the squares on the sides of that rectangle. The assertion that each procedure produces a square of the desired area is equivalent to the statement of the Pythagorean theorem. Another construction produces a square with area equal to that of a given rectangle. The procedure is to cut a rectangular piece from the end of the rectangle and to paste it to the side so as to form a gnomon of area equal to the original rectangle. Since a gnomon is the difference of two squares, the problem can be completed using one of the previous constructions. [ 27 ]
The Baudhayana Shulba sutra gives the construction of geometric shapes such as squares and rectangles. [ 28 ] It also gives, sometimes approximate, geometric area-preserving transformations from one geometric shape to another. These include transforming a square into a rectangle , an isosceles trapezium , an isosceles triangle , a rhombus , and a circle , and transforming a circle into a square. [ 28 ] In these texts approximations, such as the transformation of a circle into a square, appear side by side with more accurate statements. As an example, the statement of circling the square is given in Baudhayana as:
2.9. If it is desired to transform a square into a circle, [a cord of length] half the diagonal [of the square] is stretched from the centre to the east [a part of it lying outside the eastern side of the square]; with one-third [of the part lying outside] added to the remainder [of the half diagonal], the [required] circle is drawn. [ 29 ]
and the statement of squaring the circle is given as:
2.10. To transform a circle into a square, the diameter is divided into eight parts; one [such] part after being divided into twenty-nine parts is reduced by twenty-eight of them and further by the sixth [of the part left] less the eighth [of the sixth part]. 2.11. Alternatively, divide [the diameter] into fifteen parts and reduce it by two of them; this gives the approximate side of the square [desired]. [ 29 ]
The constructions in 2.9 and 2.10 give a value of π as 3.088, while the construction in 2.11 gives π as 3.004. [ 30 ]
Altar construction also led to an estimation of the square root of 2 as found in three of the sutras. In the Baudhayana sutra it appears as:
2.12. The measure is to be increased by its third and this [third] again by its own fourth less the thirty-fourth part [of that fourth]; this is [the value of] the diagonal of a square [whose side is the measure]. [ 29 ]
which leads to the value of the square root of two as being:
Indeed, an early method for calculating square roots can be found in some Sutras [ citation needed ] , the method involves the recursive formula: x ≈ x − 1 + 1 2 ⋅ x − 1 {\displaystyle {\sqrt {x}}\approx {\sqrt {x-1}}+{\frac {1}{2\cdot {\sqrt {x-1}}}}} for large values of x, which bases itself on the non-recursive identity a 2 + r ≈ a + r 2 ⋅ a {\displaystyle {\sqrt {a^{2}+r}}\approx a+{\frac {r}{2\cdot a}}} for values of r extremely small relative to a .
It has also been suggested, for example by Bürk [ 33 ] that this approximation of √2 implies knowledge that √2 is irrational . In his translation of Euclid's Elements , Heath outlines a number of milestones necessary for irrationality to be considered to have been discovered, and points out the lack of evidence that Indian mathematics had achieved those milestones in the era of the Shulba Sutras. [ 34 ] | https://en.wikipedia.org/wiki/Shulba_Sutras |
A shunt is a device that is designed to provide a low-resistance path for an electrical current in a circuit . It is typically used to divert current away from a system or component in order to prevent overcurrent . Electrical shunts are commonly used in a variety of applications including power distribution systems, electrical measurement systems, automotive and marine applications.
One example is in miniature Christmas lights which are wired in series . When the filament burns out in one of the incandescent light bulbs , the full line voltage appears across the burnt out bulb. A shunt resistor , which has been connected in parallel across the filament before it burnt out, will then short out to bypass the burnt filament and allow the rest of the string to light. If too many lights burn out however, a shunt will also burn out, requiring the use of a multimeter to find the point of failure.
In photovoltaics , the term is widely used to describe an unwanted short circuit between the front and back surface contacts of a solar cell , usually caused by wafer damage.
A gas -filled tube can also be used as a shunt, particularly in a lightning arrester . Neon , like other noble gases , has a high breakdown voltage , so that normally current will not flow across it. However, a direct lightning strike (such as on a radio tower antenna ) will cause the shunt to arc and conduct the massive amount of electricity to ground , protecting transmitters and other equipment.
Another older form of lightning arrester employs a simple narrow spark gap, over which an arc will jump when a high voltage is present. While a low cost solution, its high triggering voltage offers almost no protection for modern solid-state electronic devices powered by the protected circuit.
Capacitors are used as shunts to redirect high-frequency noise to ground before it can propagate to the load or other circuit components.
The term shunt is used in filter and similar circuits with a ladder topology to refer to the components connected between the line and common. The term is used in this context to distinguish the shunt components connected between the signal and return lines from the components connected in series along the signal line. More generally, the term shunt can be used for a component connected in parallel with another. For instance, shunt m-derived half section is a common filter section from the image impedance method of filter design. [ 1 ]
Where devices are vulnerable to reverse polarity of a signal or power supply, a diode may be used to protect the circuit. If connected in series with the circuit it simply prevents reversed current, but if connected in parallel it can shunt the reversed supply, causing a fuse or other current limiting circuit to open.
All semiconductor diodes have a threshold voltage – typically between 0.5 volt and 1 volt – that must be exceeded before significant current will flow through the diode in the normally allowed direction. Two anti-parallel shunt diodes (one to conduct current in each direction) can be used to limit the signal flowing past them to no more than their threshold voltages, in order to protect later components from overload.
When a circuit must be protected from overvoltage and there are failure modes in the power supply that can produce such overvoltages, the circuit may be protected by a device commonly called a crowbar circuit . When this device detects an overvoltage it causes a short circuit between the power supply and its return. This will cause both an immediate drop in voltage (protecting the device) and an instantaneous high current which is expected to open a current sensitive device (such as a fuse or circuit breaker ). This device is called a crowbar as it is likened to dropping an actual crowbar across a set of bus bars (exposed electrical conductors).
On warships, it is common to install battle short shunts across fuses for essential equipment before entering combat. This bypasses overcurrent protection at a time when removing power to the equipment is not an appropriate reaction. [ citation needed ]
As an introduction to the next chapter, this figure shows that the term "shunt resistor" should be understood in the context of what it shunts.
In this example the resistor R L would be understood as "the shunt resistor" (to the load L), because this resistor would pass current around the load L. R L is connected in parallel with the load L.
However, the series resistors R M1 and R M2 are low Ohmic resistors (like in the photo) meant to pass current around the instruments M1 and M2, and function as shunt resistors to those instruments. R M1 and R M2 are connected in parallel with M1 and M2. If seen without the instruments these two resistors would be considered series resistors in this circuit.
An ammeter shunt allows the measurement of current values too large to be directly measured by a particular ammeter. In this case, a separate shunt, a resistor of very low but accurately known resistance , is placed in parallel with a voltmeter , so that virtually all of the current to be measured will flow through the shunt (provided that the very high internal resistance of the voltmeter takes such a low portion of the current that it can be considered negligible). The resistance is chosen so that the resultant voltage drop is measurable but low enough not to disrupt the circuit . The voltage across the shunt is proportional to the current flowing through it, and so the measured voltage can be scaled to directly display the current value. [ 2 ] [ 3 ]
Shunts are rated by maximum current and voltage drop at that current. For example, a 500 A, 75 mV shunt would have a resistance of 150 micro ohm , a maximum allowable current of 500 amps and at that current the voltage drop would be 75 millivolts . By convention, most shunts are designed to drop 50 mV, 75 mV or 100 mV when operating at their full rated current and most ammeters consist of a shunt and a voltmeter with full-scale deflections of 50, 75, or 100 mV. All shunts have a derating factor for continuous (more than 2 minutes) use, 66% being the most common, so the example shunt should not be operated above 330 A (and 50 mV drop) longer than that.
This limitation is due to thermal limits at which a shunt will no longer operate correctly. For manganin , a common shunt material, at 80 °C thermal drift begins to occur, at 120 °C thermal drift is a significant problem where error, depending on the design of the shunt, can be several percent and at 140 °C the manganin alloy becomes permanently damaged due to annealing resulting in the resistance value drifting up or down. [ citation needed ]
If the current being measured is also at a high voltage potential this voltage will be present in the connecting leads too and in the reading instrument itself. [ 2 ] Sometimes, the shunt is inserted in the return leg ( grounded side) to avoid this problem. Some alternatives to shunts can provide isolation from the high voltage by not directly connecting the meter to the high voltage circuit. Examples of devices that can provide this isolation are Hall effect current sensors and current transformers (see clamp meters ). Current shunts are considered more accurate and cheaper than Hall effect devices. Common accuracy specifications of such devices are ±0.1%, ±0.25% or ±0.5%.
The Thomas-type double manganin walled shunt and MI type (improved Thomas-type design) were used by NIST and other standards laboratories as the legal reference of an ohm until superseded in 1990 by the quantum Hall effect . Thomas-type shunts are still used as secondary standards to take very accurate current measurements, as using quantum Hall effect is a time-consuming process. The accuracy of these types of shunts is measured in the ppm and sub-ppm scale of drift per year of set resistance. [ 4 ]
Where the circuit is grounded (earthed) on one side, a current measuring shunt can be inserted either in the ungrounded conductor or in the grounded conductor. A shunt in the ungrounded conductor must be insulated for the full circuit voltage to ground; the measuring instrument must be inherently isolated from ground or must include a resistive voltage divider or an isolation amplifier between the relatively high common-mode voltage and lower voltages inside the instrument. A shunt in the grounded conductor may not detect leakage current that bypasses the shunt, but it will not experience high common-mode voltage to ground. The load is removed from a direct path to ground, which may create problems for control circuitry, result in unwanted emissions, or both. | https://en.wikipedia.org/wiki/Shunt_(electrical) |
The Shunt equation (also known as the Berggren equation) quantifies the extent to which venous blood bypasses oxygenation in the capillaries of the lung . “Shunt” and “ dead space “ are terms used to describe conditions where either blood flow or ventilation do not interact with each other in the lung, as they should for efficient gas exchange to take place. These terms can also be used to describe areas or effects where blood flow and ventilation are not properly matched, though both may be present to varying degrees. Some references refer to “shunt-effect” or “dead space-effect” to designate the ventilation/perfusion mismatch states that are less extreme than absolute shunt or dead space.
The following equation relates the percentage of blood flow that is not exposed to inhaled gas, called the shunt fraction Q s / Q t {\displaystyle Q_{s}/Q_{t}} , to the content of oxygen in venous, arterial, and pulmonary capillary blood.
The blood entering the pulmonary system will have oxygen flux Q t ⋅ C v O 2 {\displaystyle Q_{t}\cdot Cv_{O_{2}}} , where C v O 2 {\displaystyle Cv_{O_{2}}} is oxygen content of the venous blood and Q t {\displaystyle Q_{t}} is the total cardiac output .
Similarly, the blood emerging from the pulmonary system will have oxygen flux Q t ⋅ C a O 2 {\displaystyle Q_{t}\cdot Ca_{O_{2}}} , where C a O 2 {\displaystyle Ca_{O_{2}}} is oxygen content of the arterial blood.
This will be made up of blood which bypassed the lungs ( Q s {\displaystyle Q_{s}} ) and blood which went through the pulmonary capillaries ( Q c {\displaystyle Q_{c}} ).
We can express this as Q t = Q s + Q c {\displaystyle Q_{t}=Q_{s}+Q_{c}} .
We can solve for Q c {\displaystyle Q_{c}} : Q c = Q t − Q s {\displaystyle Q_{c}=Q_{t}-Q_{s}} .
If we add the oxygen content of Q s to Q c we get the oxygen content of Q t :
Q t ⋅ C a O 2 = Q s ⋅ C v O 2 + ( Q t − Q s ) ⋅ C c O 2 {\displaystyle Q_{t}\cdot Ca_{O_{2}}=Q_{s}\cdot Cv_{O_{2}}+(Q_{t}-Q_{s})\cdot Cc_{O_{2}}} Substitute Q c as above, C CO2 is the oxygen content of pulmonary alveolar capillary blood (i.e. End-pulmonary-capillary Oxygen Content).
Q t ⋅ C a O 2 = Q s ⋅ C v O 2 + Q t ⋅ C c O 2 − Q s ⋅ C c O 2 {\displaystyle Q_{t}\cdot Ca_{O_{2}}=Qs\cdot Cv_{O_{2}}+Q_{t}\cdot Cc_{O_{2}}-Qs\cdot Cc_{O_{2}}} Multiply out the brackets. Q s ⋅ C c O 2 − Q s ⋅ C v O 2 = Q t ⋅ C c O 2 − Q t ⋅ C a O 2 {\displaystyle Q_{s}\cdot Cc_{O_{2}}-Qs\cdot Cv_{O_{2}}=Q_{t}\cdot Cc_{O_{2}}-Qt\cdot Ca_{O_{2}}} Get the Q s terms and the Q t terms on the same side. Q s ⋅ ( C c O 2 − C v O 2 ) = Q t ⋅ ( C c O 2 − C a O 2 ) {\displaystyle Q_{s}\cdot (Cc_{O_{2}}-Cv_{O_{2}})=Q_{t}\cdot (Cc_{O_{2}}-Ca_{O_{2}})} Factor out the Q terms. Q s Q t = C c O 2 − C a O 2 C c O 2 − C v O 2 {\displaystyle {\dfrac {Q_{s}}{Q_{t}}}={\dfrac {Cc_{O_{2}}-Ca_{O_{2}}}{Cc_{O_{2}}-Cv_{O_{2}}}}} Divide by Q t and by ( C CO2 - C VO2 ).
The above equation requires measurement of the end-pulmonary-capillary oxygen content (Cc O2 ) which is difficult to obtain and it is assumed to be equal to the alveolar oxygen content. [ 3 ] This is based on the assumption that, if an alveolus is receiving air, then it is perfectly oxygenated. The following equation, provides the ratio of the pulmonary blood flow divided by the systemic blood flow and relates to any type of shunt (intracardiac or extracardiac) using variables that can be easily attained in a cardiac catheterization laboratory. Note that the abbreviations are different from the aforementioned equation to reflect the most widely used terminology in cardiovascular medicine.
Q p : Q s = P V O 2 − M V O 2 P V 02 − P A 02 {\displaystyle Qp:Qs={\frac {PVO2-MVO2}{PV02-PA02}}}
Based on the Fick principle :
By applying the Fick principle for the systemic and pulmonary flow, we can calculate the Qs and Qp as follows:
Qs = systemic oxygen consumption / (Pulmonary Vein oxygen content - Mixed Venous oxygen content)
Qp = pulmonary oxygen consumption / (Pulmonary Artery oxygen content - Pulmonary Vein oxygen content)
The pulmonary oxygen consumption is the net effect of the oxygen that the lung provides to the blood from the atmosphere minus the oxygen that is consumed by the lungs to keep them functional. Since all our oxygen is provided to our body form our lungs, the systemic oxygen consumption is the opposite number of the pulmonary oxygen consumption. We can formulate this as follows:
pulmonary oxygen consumption = -1 * systemic oxygen consumption
In the Qp formula above, let us substitute pulmonary oxygen consumption for systemic oxygen consumption:
Qp = pulmonary oxygen consumption / (Pulmonary Artery oxygen content - Pulmonary Vein oxygen content) = -1 * systemic oxygen consumption / (Pulmonary Artery oxygen content - Pulmonary Vein oxygen content) <=>
Qp = systemic oxygen consumption / (Pulmonary Vein oxygen content - Pulmonary Artery oxygen content)
Now we can divide Qp/Qs and the equation simplifies as the systemic oxygen consumption term cancels out:
Qp:Qs = Pulmonary vein oxygen content - Mixed venous oxygen content Pulmonary vein oxygen content - Pulmonary artery oxygen content {\displaystyle {\text{Qp:Qs}}={\frac {\text{Pulmonary vein oxygen content - Mixed venous oxygen content}}{\text{Pulmonary vein oxygen content - Pulmonary artery oxygen content}}}}
Oxygen content is difficult to measure but we can easily measure oxygen saturation . Using the fact that each gram of hemoglobin can carry 1.34 mL of O2, the oxygen content of the blood (either arterial or venous) can be estimated by the following formula: Oxygen Content of blood = [ Hb ] ( g/dl ) × 1.34 ( mL O 2 / g of Hb ) × O 2 saturation fraction + 0.0032 × P O 2 ( torr ) {\displaystyle {\text{Oxygen Content of blood}}=\left[{\text{Hb}}\right]\left({\text{g/dl}}\right)\ \times \ 1.34\left({\text{mL}}\ {\ce {O2}}/{\text{g of Hb}}\right)\times \ O_{2}^{\text{saturation fraction}}+\ 0.0032\ \times \ P_{{\ce {O2}}}({\text{torr}})} PO2 is the partial pressure of oxygen and reflects the amount of oxygen gas dissolved in the blood. The term 0.0032 * P02 in the equation is very small and therefore negligible. In other words, very little oxygen is transferred diluted in the blood; the vast majority of oxygen is carried by hemoglobin. This term can be omitted and the oxygen content of blood equation simplifies into the following:
Oxygen content of blood = [Hb](gr/dl) * 1.34(ml02/gr of Hb) * Oxygen saturation
Let's call the [Hb](gr/dl) * 1.34(ml02/gr of Hb) a constant variable x, therefore:
Mixed Venous oxygen content = [Hb](gr/dl) * 1.34(ml02/gr of Hb) * MV02 = x * MV02
Pulmonary artery oxygen content = [Hb](gr/dl) * 1.34(ml02/gr of Hb) * PA02 = x * PA02
Pulmonary vein oxygen content = [Hb](gr/dl) * 1.34(ml02/gr of Hb) * PV02 = x * PV02
Using the above, we can substitute the oxygen content with oxygen consumption in the Qp / Qs formula as follows:
Qp / Qs = (Pulmonary Vein oxygen content - Mixed Venous oxygen content) / (Pulmonary Vein oxygen content - Pulmonary Artery oxygen content) <=>
Qp / Qs = (x * PV02 - x * MV02) / (x * PV02 - x * PA02) <=>
Qp / Qs = [x * (PV02 - MV02)] / [x * (PV02 - PA02)] <=>
Qp / Qs = (PV02 - MV02) / (PV02 - PA02)
In echocardiography, we can measure the Velocity Time Integral (VTI) . This is a clinical Doppler ultrasound measurement of blood flow, equivalent to the area under the velocity time curve. Based on the Bernoulli equation for incompressible fluids , the product of VTI (cm/stroke) and the cross sectional area of any cardiac structure (cm 2 ) yields a stroke volume (cm 3 /stroke), which can be used to calculate cardiac output.
Qp = VTI RVOT × π × (d RVOT / 2)² <=> Qp = VTI RVOT × 0.785 × d RVOT ²
Qs = VTI LVOT × π × (d LVOT / 2)² <=> Qs = VTI LVOT × 0.785 × d LVOT ²
Where:
d RVOT - Right ventricular outflow tract diameter
VTI RVOT - Velocity time integral of the right ventricular outflow tract before the pulmonary valve
d LVOT - Left ventricular outflow tract diameter
VTI LVOT - Velocity time integral of left ventricular outflow tract before the aortic valve
π – The constant π as, for ease of calculations, we theorize that the cross sectional area is almost circular
Based on the above, a shunt can be quantified by measuring the flow ratio of the pulmonary cardiac output (Qp) to the systemic cardiac output (Qs).
Qp/Qs = (VTI RVOT × 0.785 × d RVOT ²) / (VTI LVOT × 0.785 × d LVOT ²) <=>
Qp/Qs = (VTI RVOT × d RVOT ²) / (VTI LVOT × d LVOT ²) | https://en.wikipedia.org/wiki/Shunt_equation |
A shutdown valve (also referred to as SDV or emergency shutdown valve , ESV , ESD , or ESDV ; or safety shutoff valve ) is an actuated valve designed to stop the flow of a hazardous fluid upon the detection of a dangerous event. This provides protection against possible harm to people, equipment or the environment.
Shutdown valves form part of a safety instrumented system . The process of providing automated safety protection upon the detection of a hazardous event is called functional safety .
Shutdown valves are primarily associated with the petroleum industry although other industries may also require this type of protection system. ESD valves are required by law on any equipment placed on an offshore drilling rig to prevent catastrophic events like the BP Horizon explosion in the Gulf of Mexico in 2010.
A safety shutoff valve should be fail-safe , that is close upon failure of any element of the input control system (such as temperature controllers, steam pressure controllers), air pressure , fuel pressure, current from a flame detector , or current from other safety devices such as low water cutoff, and high pressure cutoff.
A blowdown valve ( BDV ) is a type of shutdown valve designed to depressurize a pressure vessel by directing vapour to a flare , vent or blowdown stack in an emergency. BDVs fail-safe to the open position upon failure of the control system. [ 1 ] The type of valve, type of actuation and performance measurement are similar to an ESD valve.
For fluids, metal seated ball valves are used as shut-down valves (SDV's). Use of metal seated ball valves leads to overall lower costs when taking into account lost production and inventory , and valve repair costs resulting from the use of soft seated ball valves which have a lower initial cost.
Straight-through flow valves, such as rotary-shaft ball valves, are typically high-recovery valves. High recovery valves are valves that lose little energy due to little flow turbulence . Flow paths are straight through. Rotary control valves, butterfly valve and ball valves are good examples.
For air intake shut down, two distinct types are commonly utilized, i.e. butterfly valves and swing gate or guillotine valves. Because diesel engines ignite fuel using compression instead of an electronic ignition, shutting off the fuel source to a diesel engine will not necessarily stop the engine from running. When an external hydrocarbon, such as methane gas, is present in the atmosphere, it can be sucked into a diesel engine causing overspeed or over revving , potentially leading to a catastrophic failure and explosion. When actuated, ESD valves stop the flow of air and prevent these failures.
As shutdown valves form part of a SIS it is necessary to operate the valve by means of an actuator. These actuators are normally fail safe fluid power type. Typical examples of these are:
In addition to the fluid type, actuators also vary in the manner in which the energy is stored to operate the valve on demand as follows:
The type of actuation required depends upon the application, site facilities and also the physical space available although the majority of actuators used for shutdown valves are of the spring return type due to the fail safe nature of spring return systems.
In a solenoid -operated safety shutoff valve, a spring action closes the valve instantly when an electric current fails and the solenoid ceases to be energized. The solenoid circuit is generally arranged so that it is broken upon failure of any element of the system. This valve cannot be re-opened until the solenoid is again energized. The coil of the valve solenoid must be connected in series with all of the elements. For this to operate, fuel, air and steam pressure can be converted to electrical signals by means of bellows , a bourdon tube , or a diaphragm-operated mercury switch .
However, sudden closing of a valve in a piping system may lead to water hammer or implosion so in special cases there may be additional items connected to the shutoff valve, such as a pressure relief valve or an aerator valve.
For shutdown valves used in safety instrumented systems it is essential to know that the valve is capable of providing the required level of safety performance and that the valve will operate on demand. The required level of performance is dictated by the Safety Requirements Specification, where eventually a Safety Integrity Level (SIL) is indicated. In order to maintain the level of performance required during the valve lifetime, the Safety Maintenance Manual prescription shall be fulfilled: one of the possible requests is to test the valve. Among the others 2 types of testing methods are:
The performance standard of ESDVs may include the specification and testing of a closure time (e.g. to close in less than 10 seconds) and the specification and measurement of an acceptable leakage rate of fluid through the closed valve. [ 2 ] | https://en.wikipedia.org/wiki/Shutdown_valve |
A shuttle is a tool designed to neatly and compactly store a holder that carries the thread of the weft yarn while weaving with a loom . Shuttles are thrown or passed back and forth through the shed , between the yarn threads of the warp in order to weave in the weft.
The simplest shuttles, known as "stick shuttles", are made from a flat, narrow piece of wood with notches on the ends to hold the weft yarn. More complicated shuttles incorporate bobbins or pirns .
In the United States, shuttles are often made of wood from the flowering dogwood , because it is hard, resists splintering, and can be polished to a very smooth finish. In the United Kingdom shuttles were usually made of boxwood, cornel, or persimmon. | https://en.wikipedia.org/wiki/Shuttle_(weaving) |
Shuttle catalysis is used to describe catalytic reactions where a chemical entity of a donor molecule is transferred to an acceptor molecule. [ 1 ] In these reactions, while the number of chemical bonds of each reactant changes, the types and total number of chemical bonds remain constant over the course of the reaction. In contrast to many organic reactions which exothermicity practically renders them irreversible , reactions operated under shuttle catalysis are often reversible . [ 2 ] However, the position of the equilibrium can be driven to the product side through Le Chatelier’s principle. The driving forces for this equilibrium shift are typically the formation of a gas/precipitation, the use of high ground-state energy reactants or the formation of stabilized products or the excess equivalents of a reactant. [ 3 ]
The relocation of shuttled entities is often mediated by a transition metal catalyst, which serves to functionalize or defunctionalize a compound of interest. An advantage to this process is that it excludes the process of handling toxic or reactive raw chemical entities. However, these reactions require the development of catalytic systems that can efficiently deliver the shuttled entities between the reactants under mild conditions through a sequence of elementary steps .
Transfer hydrogenation has been extensively studied to reduce various functional groups without requiring hazardous pressurized H 2 . [ 4 ]
In 1999, Chul-Ho Jun and Hyuk Lee reported the first example of hydroacylation through shuttle catalysis. [ 5 ] In this example, 3-methyl-2-aminopyridine was used to activate the acyl group as well as coordinate to the rhodium catalyst, promoting C–C bond cleavage to eventually enable aldehyde transfer from a ketone to an alkene. The driving force of this reaction is the excess presence of alkenes and the formation of stable styrenes /extrusion of volatile ethylene . This method doesn’t require the use of toxic and self-reacting aldehydes such as acetaldehyde in the traditional hydroacylation procedures.
Hydroformylation is a classical transition-metal catalyzed reaction, and it has been widely employed in industrial settings. However, a drawback of this reaction is the requirement of the hazardous mixture of H 2 /CO. For that reason, a process to replace H 2 /CO gas with a non-hazardous aldehyde is sought after.
In 1999, Christian P. Lenges and Maurice Brookhart reported isovaleraldehyde as a suitable surrogate for H 2 /CO transfer to 3,3-dimethyl-1-butene by using a rhodium(I) catalyst. [ 6 ] [ 7 ]
The reverse of this process was rendered catalytic by Vy M. Dong and co-workers in 2015. [ 8 ] [ 9 ] They performed dehydroformylation on aldehydes to achieve the corresponding alkenes. For this transformation, they used either norbornene or norbornadiene as a H 2 /CO acceptor, promoting reactivity through strain-release.
To replace the use of toxic hydrocyanide (HCN) gas or surrogates such as acetone cyanohydrin , Bill Morandi and co-workers developed a hydrocyanation strategy using shuttle catalysis. [ 10 ] In this example, they use isovaleronitrile as a HCN surrogate under nickel/aluminum co-catalyzed conditions to afford hydrocyanation reactions of various alkenes. The use of isovaleronitrile allows careful control of HCN concentration, and the formation of volatile isobutylene is the driving force for the reaction.
Other chemical entities including arenes , [ 11 ] CO/HCl, [ 12 ] HMgBr, [ 13 ] H 2 Zn, [ 14 ] H 2 O, [ 15 ] carbene, [ 16 ] silylene, [ 17 ] sulfenium [ 18 ] have also been shuttled under this catalysis platform. | https://en.wikipedia.org/wiki/Shuttle_catalysis |
A shuttle vector is a vector (usually a plasmid ) constructed so that it can propagate in two different host species. [ 1 ] Therefore, DNA inserted into a shuttle vector can be tested or manipulated in two different cell types. The main advantage of these vectors is they can be manipulated in E. coli , then used in a system which is more difficult or slower to use (e.g. yeast).
Shuttle vectors include plasmids that can propagate in eukaryotes and prokaryotes (e.g. both Saccharomyces cerevisiae and Escherichia coli ) or in different species of bacteria (e.g. both E. coli and Rhodococcus erythropolis ). There are also adenovirus shuttle vectors, which can propagate in E. coli and mammals.
Shuttle vectors are frequently used to quickly make multiple copies of the gene in E. coli (amplification). They can also be used for in vitro experiments and modifications (e.g. mutagenesis , PCR ).
One of the most common types of shuttle vectors is the yeast shuttle vector. [ 2 ] Almost all commonly used S. cerevisiae vectors are shuttle vectors. Yeast shuttle vectors have components that allow for replication and selection in both E. coli cells and yeast cells. The E. coli component of a yeast shuttle vector includes an origin of replication and a selectable marker, e.g. antibiotic resistance , beta lactamase , beta galactosidase. The yeast component of a yeast shuttle vector includes an autonomously replicating sequence (ARS), a yeast centromere (CEN), and a yeast selectable marker (e.g. URA3 , a gene that encodes an enzyme for uracil synthesis, Lodish et al. 2007). | https://en.wikipedia.org/wiki/Shuttle_vector |
The Shvab–Zeldovich formulation is an approach to remove the chemical-source terms from the conservation equations for energy and chemical species by linear combinations of independent variables, when the conservation equations are expressed in a common form. Expressing conservation equations in common form often limits the range of applicability of the formulation. The method was first introduced by V. A. Shvab in 1948 [ 1 ] and by Yakov Zeldovich in 1949. [ 2 ]
For simplicity, assume combustion takes place in a single global irreversible reaction
∑ i = 1 N ν i ′ ℜ i → ∑ i = 1 N ν i ″ ℜ i {\displaystyle \sum _{i=1}^{N}\nu _{i}'\Re _{i}\rightarrow \sum _{i=1}^{N}\nu _{i}''\Re _{i}}
where ℜ i {\displaystyle \Re _{i}} is the ith chemical species of the total N {\displaystyle N} species and ν i ′ {\displaystyle \nu _{i}'} and ν i ″ {\displaystyle \nu _{i}''} are the stoichiometric coefficients of the reactants and products, respectively. Then, it can be shown from the law of mass action that the rate of moles produced per unit volume of any species ω {\displaystyle \omega } is constant and given by
ω = w i W i ( ν i ″ − ν i ′ ) {\displaystyle \omega ={\frac {w_{i}}{W_{i}(\nu _{i}''-\nu _{i}')}}}
where w i {\displaystyle w_{i}} is the mass of species i produced or consumed per unit volume and W i {\displaystyle W_{i}} is the molecular weight of species i.
The main approximation involved in Shvab–Zeldovich formulation is that all binary diffusion coefficients D {\displaystyle D} of all pairs of species are the same and equal to the thermal diffusivity . In other words, Lewis number of all species are constant and equal to one. This puts a limitation on the range of applicability of the formulation since in reality, except for methane, ethylene, oxygen and some other reactants, Lewis numbers vary significantly from unity. The steady, low Mach number conservation equations for the species and energy in terms of the rescaled independent variables [ 3 ]
α i = Y i / [ W i ( ν i ″ − ν i ′ ) ] and α T = ∫ T r e f T c p d T ∑ i = 1 N h i 0 W i ( ν i ′ − ν i ″ ) {\displaystyle \alpha _{i}=Y_{i}/[W_{i}(\nu _{i}''-\nu _{i}')]\quad {\text{and}}\quad \alpha _{T}={\frac {\int _{T_{ref}}^{T}c_{p}\,\mathrm {d} T}{\sum _{i=1}^{N}h_{i}^{0}W_{i}(\nu _{i}'-\nu _{i}'')}}}
where Y i {\displaystyle Y_{i}} is the mass fraction of species i, c p = ∑ i = 1 N Y i c p , i {\displaystyle c_{p}=\sum _{i=1}^{N}Y_{i}c_{p,i}} is the specific heat at constant pressure of the mixture, T {\displaystyle T} is the temperature and h i 0 {\displaystyle h_{i}^{0}} is the formation enthalpy of species i, reduce to
∇ ⋅ [ ρ v α i − ρ D ∇ α i ] = ω , ∇ ⋅ [ ρ v α T − ρ D ∇ α T ] = ω {\displaystyle {\begin{aligned}\nabla \cdot [\rho {\boldsymbol {v}}\alpha _{i}-\rho D\nabla \alpha _{i}]=\omega ,\\\nabla \cdot [\rho {\boldsymbol {v}}\alpha _{T}-\rho D\nabla \alpha _{T}]=\omega \end{aligned}}}
where ρ {\displaystyle \rho } is the gas density and v {\displaystyle {\boldsymbol {v}}} is the flow velocity. The above set of N + 1 {\displaystyle N+1} nonlinear equations, expressed in a common form, can be replaced with N {\displaystyle N} linear equations and one nonlinear equation. Suppose the nonlinear equation corresponds to α 1 {\displaystyle \alpha _{1}} so that
∇ ⋅ [ ρ v α 1 − ρ D ∇ α 1 ] = ω {\displaystyle \nabla \cdot [\rho {\boldsymbol {v}}\alpha _{1}-\rho D\nabla \alpha _{1}]=\omega }
then by defining the linear combinations β T = α T − α 1 {\displaystyle \beta _{T}=\alpha _{T}-\alpha _{1}} and β i = α i − α 1 {\displaystyle \beta _{i}=\alpha _{i}-\alpha _{1}} with i ≠ 1 {\displaystyle i\neq 1} , the remaining N {\displaystyle N} governing equations required become
∇ ⋅ [ ρ v β i − ρ D ∇ β i ] = 0 , ∇ ⋅ [ ρ v β T − ρ D ∇ β T ] = 0. {\displaystyle {\begin{aligned}\nabla \cdot [\rho {\boldsymbol {v}}\beta _{i}-\rho D\nabla \beta _{i}]=0,\\\nabla \cdot [\rho {\boldsymbol {v}}\beta _{T}-\rho D\nabla \beta _{T}]=0.\end{aligned}}}
The linear combinations automatically removes the nonlinear reaction term in the above N {\displaystyle N} equations.
Shvab–Zeldovich–Liñán formulation was introduced by Amable Liñán in 1991 [ 4 ] [ 5 ] for diffusion-flame problems where the chemical time scale is infinitely small ( Burke–Schumann limit ) so that the flame appears as a thin reaction sheet. The reactants can have Lewis number that is not necessarily equal to one.
Suppose the non-dimensional scalar equations for fuel mass fraction Y F {\displaystyle Y_{F}} (defined such that it takes a unit value in the fuel stream), oxidizer mass fraction Y O {\displaystyle Y_{O}} (defined such that it takes a unit value in the oxidizer stream) and non-dimensional temperature T {\displaystyle T} (measured in units of oxidizer-stream temperature) are given by [ 6 ]
where ω = D a Y F Y O e − E / R T {\displaystyle \omega =Da\,Y_{F}Y_{O}e^{-E/RT}} is the reaction rate, D a {\displaystyle Da} is the appropriate Damköhler number , S {\displaystyle S} is the mass of oxidizer stream required to burn unit mass of fuel stream, q {\displaystyle q} is the non-dimensional amount of heat released per unit mass of fuel stream burnt and e − E / R T {\displaystyle e^{-E/RT}} is the Arrhenius exponent. Here, L e F {\displaystyle Le_{F}} and L e O {\displaystyle Le_{O}} are the Lewis number of the fuel and oxygen, respectively and D T {\displaystyle D_{T}} is the thermal diffusivity . In the Burke–Schumann limit , D a → ∞ {\displaystyle Da\rightarrow \infty } leading to the equilibrium condition
In this case, the reaction terms on the right-hand side become Dirac delta functions . To solve this problem, Liñán introduced the following functions
where S ~ = S L e O / L e F {\displaystyle {\tilde {S}}=SLe_{O}/Le_{F}} , T 0 {\displaystyle T_{0}} is the fuel-stream temperature and T s {\displaystyle T_{s}} is the adiabatic flame temperature , both measured in units of oxidizer-stream temperature. Introducing these functions reduces the governing equations to
where L e m = L e O ( S + 1 ) / ( S ~ + 1 ) {\displaystyle Le_{m}=Le_{O}(S+1)/({\tilde {S}}+1)} is the mean (or, effective) Lewis number. The relationship between Z {\displaystyle Z} and Z ~ {\displaystyle {\tilde {Z}}} and between H {\displaystyle H} and H ~ {\displaystyle {\tilde {H}}} can be derived from the equilibrium condition.
At the stoichiometric surface (the flame surface), both Y F {\displaystyle Y_{F}} and Y O {\displaystyle Y_{O}} are equal to zero, leading to Z = Z s = 1 / ( S + 1 ) {\displaystyle Z=Z_{s}=1/(S+1)} , Z ~ = Z ~ s = 1 / ( S ~ + 1 ) {\displaystyle {\tilde {Z}}={\tilde {Z}}_{s}=1/({\tilde {S}}+1)} , H = H s = ( T f − T 0 ) / ( T s − T 0 ) − 1 {\displaystyle H=H_{s}=(T_{f}-T_{0})/(T_{s}-T_{0})-1} and H ~ = H ~ s = ( T f − T 0 ) / ( T s − T 0 ) − 1 / L e F {\displaystyle {\tilde {H}}={\tilde {H}}_{s}=(T_{f}-T_{0})/(T_{s}-T_{0})-1/Le_{F}} , where T f {\displaystyle T_{f}} is the flame temperature (measured in units of oxidizer-stream temperature) that is, in general, not equal to T s {\displaystyle T_{s}} unless L e F = L e O = 1 {\displaystyle Le_{F}=Le_{O}=1} . On the fuel stream, since Y F − 1 = Y O = T − T 0 = 0 {\displaystyle Y_{F}-1=Y_{O}=T-T_{0}=0} , we have Z − 1 = Z ~ − 1 = H = H ~ = 0 {\displaystyle Z-1={\tilde {Z}}-1=H={\tilde {H}}=0} . Similarly, on the oxidizer stream, since Y F = Y O − 1 = T − 1 = 0 {\displaystyle Y_{F}=Y_{O}-1=T-1=0} , we have Z = Z ~ = H − ( 1 − T 0 ) / ( T s − T 0 ) = H ~ − ( 1 − T 0 ) / ( T s − T 0 ) − 1 / L e O + 1 / L e F = 0 {\displaystyle Z={\tilde {Z}}=H-(1-T_{0})/(T_{s}-T_{0})={\tilde {H}}-(1-T_{0})/(T_{s}-T_{0})-1/Le_{O}+1/Le_{F}=0} .
The equilibrium condition defines [ 7 ]
The above relations define the piecewise function Z ( Z ~ ) {\displaystyle Z({\tilde {Z}})}
where L e m = Z ~ s / Z s = ( S + 1 ) / ( S / L e F + 1 ) {\displaystyle Le_{m}={\tilde {Z}}_{s}/Z_{s}=(S+1)/(S/Le_{F}+1)} is a mean Lewis number. This leads to a nonlinear equation for Z ~ {\displaystyle {\tilde {Z}}} . Since H − H ~ {\displaystyle H-{\tilde {H}}} is only a function of Y F {\displaystyle Y_{F}} and Y O {\displaystyle Y_{O}} , the above expressions can be used to define the function H ( Z ~ , H ~ ) {\displaystyle H({\tilde {Z}},{\tilde {H}})}
With appropriate boundary conditions for H ~ {\displaystyle {\tilde {H}}} , the problem can be solved.
It can be shown that Z ~ {\displaystyle {\tilde {Z}}} and H ~ {\displaystyle {\tilde {H}}} are conserved scalars, that is, their derivatives are continuous when crossing the reaction sheet, whereas Z {\displaystyle Z} and H {\displaystyle H} have gradient jumps across the flame sheet. | https://en.wikipedia.org/wiki/Shvab–Zeldovich_formulation |
Shwartzman phenomenon is a rare reaction of a body to particular types of toxins , called endotoxins , which cause thrombosis in the affected tissue . A clearing of the thrombosis results in a reticuloendothelial blockade , which prevents re-clearing of the thrombosis caused by a repeat introduction of the toxin. That will cause tissue necrosis . Shwartzman phenomenon is usually observed during delivery or abortion, when foreign bodies are introduced into the tissues of the female reproductive system .
The Shwartzman phenomenon is named for Gregory Shwartzman , the doctor at Mount Sinai Hospital in New York City who was the first to develop the concept of immune system hypersensitivity in the 1920s. This reaction was experimented using Neisseria meningitidis endotoxin. [ 1 ] A related observation was made by Giuseppe Sanarelli leading to the term Sanarelli-Shwartzman phenomenon, however many modern works use more generic terms such as disseminated intravascular coagulation . [ 2 ]
This is notably seen with Neisseria meningitidis . [ 3 ] | https://en.wikipedia.org/wiki/Shwartzman_phenomenon |
Tetramethylsilane (abbreviated as TMS ) is the organosilicon compound with the formula Si(CH 3 ) 4 . It is the simplest tetraorganosilane. Like all silanes , the TMS framework is tetrahedral. TMS is a building block in organometallic chemistry but also finds use in diverse niche applications.
TMS is a by-product of the production of methyl chlorosilanes, SiCl x (CH 3 ) 4− x , via the direct process of reacting methyl chloride with silicon. The more useful products of this reaction are those for x = 1 ( trimethylsilyl chloride ), 2 ( dimethyldichlorosilane ), and 3 ( methyltrichlorosilane ). [ 1 ]
TMS undergoes deprotonation upon treatment with butyllithium to give (H 3 C) 3 SiCH 2 Li . The latter, trimethylsilylmethyl lithium, is a relatively common alkylating agent .
In chemical vapor deposition , TMS is the precursor to silicon dioxide or silicon carbide , depending on the deposition conditions. In the formation of silicon carbide, carbosilanes , such as 1,3,5,7-tetramethyl-1,3,5,7-tetrasilaadamantane , are observed as intermediates. [ 2 ]
Tetramethylsilane is the accepted internal standard for calibrating chemical shift for 1 H , 13 C and 29 Si NMR spectroscopy in organic solvents (where TMS is soluble). In water, where it is not soluble, sodium salts of DSS, 2,2-dimethyl-2-silapentane-5-sulfonate , are used instead. Because of its high volatility, TMS can easily be evaporated, which is convenient for recovery of samples analyzed by NMR spectroscopy. [ 3 ]
Because all twelve hydrogen atoms in a tetramethylsilane molecule are equivalent, its 1 H NMR spectrum consists of a singlet. [ 4 ] The chemical shift of this singlet is assigned as δ 0, and all other chemical shifts are determined relative to it. The majority of compounds studied by 1 H NMR spectroscopy absorb downfield of the TMS signal, thus there is usually no interference between the standard and the sample. Similarly, all four carbon atoms in a tetramethylsilane molecule are equivalent. [ 4 ] In a fully decoupled 13 C NMR spectrum, the carbon in the tetramethylsilane appears as a singlet, allowing for easy identification. The chemical shift of this singlet is also set to be δ 0 in the 13 C spectrum, and all other chemical shifts are determined relative to it. | https://en.wikipedia.org/wiki/Si(CH3)4 |
Disilyne is a low valent silicon compound with the chemical formula Si 2 R 2 where oxidation state of Si is +1. Several isomers are possible, but none are sufficiently stable to be of practical value. Substituted disilynes contain a formal silicon–silicon triple bond and as such are sometimes written R 2 Si 2 (where R is a substituent group). They are the silicon analogues of alkynes .
The term silyne has two diverse meanings. Some chemists use it to refer to compounds containing a silicon–silicon triple bond, [ 1 ] by analogy to the carbon–carbon triple bond in alkynes , whereas others use the term to refer to compounds containing a silicon–carbon triple bond [ 2 ] by analogy to silene, which often refers to compounds containing silicon–carbon double bonds. [ 3 ] The term polysilyne can refer to the layer polymer (SiH) n or substituted derivatives. [ 1 ]
The first substituted disilyne to be isolated and characterised by X-ray crystallography is one with an additional trisubstituted silicon group on each silicon of the disilyne core. The structure R′ 2 R′′Si−Si≡Si−SiR′′R′ 2 , where R′ = HC(SiMe 3 ) 2 and R′′ = HCMe 2 , is an emerald green crystalline compound reported in 2004. [ 4 ]
It was prepared by the reduction of the related tetrabrominated precursor by potassium graphite (KC 8 ). It is air- and moisture-sensitive but is a stable solid up to 128 °C.
The geometry of disilynes is unlike that of analogous carbon structures. Whereas substituted alkynes , such as 2-butyne , are linear, having a 180° bond angle at each end of the carbon–carbon triple bond, the Si−Si≡Si−Si chain is bent to 137° at each end. The four silicon atoms in the chain are however perfectly coplanar, with the first and fourth silicon atoms trans to one another. The central triple bond length is 206 pm, which is around 4% shorter than the typical bond-length of Si–Si double bonds (214 pm)) and the Si–Si single bonds are 237 pm. The color is attributed to a weak π–π * transition.
Calculations show a bond order of 2.6. An alternative calculation of the bond order by a different group describes the bonding as essentially due to only two electron pairs, with the third pair in a non-bonding orbital . [ 5 ] [ 6 ] [ 7 ] Reaction of this compound with phenylacetylene produced a 1,2-di silabenzene . [ 8 ] Other workers [ 9 ] have also reported another related compound which contains a hexasila-3-yne chain:
In this compound, the Si–Si triple bond length was calculated as 207 pm.
Triple bonded compounds of the heavier members of group 14 have also been prepared; lead , [ 10 ] and tin [ 11 ] and germanium ( digermyne ) [ 12 ] The cores of the disilyne, digermyne, distannyne, and diplumbyne have similarly bent geometries. These findings are generally consistent with the absence of conventional triple bonds. | https://en.wikipedia.org/wiki/Si2H2 |
Disilane is a chemical compound with general chemical formula Si 2 R 6 that was first identified in 1902 by Henri Moissan and Samuel Smiles (1877–1953) where R = H. Moissan and Smiles reported disilane as being among the products formed by the action of dilute acids on metal silicides. Although these reactions had been previously investigated by Friedrich Woehler and Heinrich Buff between 1857 and 1858, Moissan and Smiles were the first to explicitly identify disilane. They referred to disilane as silicoethane . Higher members of the homologous series Si n H 2 n +2 formed in these reactions were subsequently identified by Carl Somiesky (sometimes spelled "Karl Somieski") and Alfred Stock .
At standard temperature and pressure , disilane is a colourless, acrid gas. Disilane and ethane have similar structures, although disilane is much more reactive. Other compounds of the general formula Si 2 X 6 (X = hydrogen , halogen , alkyl , aryl , and mixtures of these groups) are called disilanes. Disilane is a group 14 hydride .
Disilane is usually prepared by the hydrolysis of magnesium silicide . This reaction produces silane , disilane, and even trisilane . The method has been abandoned for the production of silane, but it remains viable for generating disilane. [ 3 ] The presence of traces of disilane is responsible for the spontaneous flammability of silane produced by hydrolysis by this method (analogously diphosphine is often the spontaneously pyrophoric contaminant in samples of phosphine ).
It also arises by thermal decomposition disilane via both photochemical [ 4 ] and thermal decomposition of silane.
The reduction of Si 2 Cl 6 with lithium aluminium hydride affords disilane in modest yield. [ 5 ]
Disilane and silane thermally decompose around 640 °C, depositing amorphous silicon . This chemical vapor deposition process is relevant to the manufacture of photovoltaic devices . [ 3 ] Specifically it is utilized in the production of silicon wafers . [ 6 ]
More generally, diorganosilanes are produced by reductive coupling of silyl chlorides , e.g.
Disilane gas can be used to control pressure of Si vapors during process of graphene growth by thermal decomposition of SiC . Pressure of Si vapors influences quality of produced graphene. [ 7 ] | https://en.wikipedia.org/wiki/Si2H6 |
The pyroxenes (commonly abbreviated Px ) are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks . Pyroxenes have the general formula XY(Si,Al) 2 O 6 , [ 1 ] where X represents ions of calcium (Ca), sodium (Na), iron (Fe(II)) or magnesium (Mg) and more rarely zinc , manganese or lithium , and Y represents ions of smaller size, such as chromium (Cr), aluminium (Al), magnesium (Mg), cobalt (Co), manganese (Mn), scandium (Sc), titanium (Ti), vanadium (V) or even iron (Fe(II) or Fe(III)). Although aluminium substitutes extensively for silicon in silicates such as feldspars and amphiboles , the substitution occurs only to a limited extent in most pyroxenes. They share a common structure consisting of single chains of silica tetrahedra . Pyroxenes that crystallize in the monoclinic system are known as clinopyroxenes and those that crystallize in the orthorhombic system are known as orthopyroxenes .
The name pyroxene is derived from the Ancient Greek words for 'fire' ( πυρ , pur ) and 'stranger' ( ξένος , xénos ). Pyroxenes were so named due to their presence in volcanic lavas , where they are sometimes found as crystals embedded in volcanic glass ; it was assumed they were impurities in the glass, hence the name meaning "fire stranger". However, they are simply early-forming minerals that crystallized before the lava erupted.
The upper mantle of Earth is composed mainly of olivine and pyroxene minerals. Pyroxene and feldspar are the major minerals in basalt , andesite , and gabbro rocks. [ 2 ] [ 3 ]
Pyroxenes are the most common single-chain silicate minerals. (The only other important group of single-chain silicates, the pyroxenoids , are much less common.) Their structure consists of parallel chains of negatively-charged silica tetrahedra bonded together by metal cations. In other words, each silicon ion in a pyroxene crystal is surrounded by four oxygen ions forming a tetrahedron around the relatively small silicon ion. Each silicon ion shares two oxygen ions with neighboring silicon ions in the chain. [ 4 ]
The tetrahedra in the chain all face in the same direction, so that two oxygen ions are located on one face of the chain for every oxygen ion on the other face of the chain. The oxygen ions on the narrower face are described as apical oxygen ions. Pairs of chains are bound together on their apical sides by Y cations, with each Y cation surrounded by six oxygen ions. The resulting pairs of single chains have sometimes been likened to I-beams . The I-beams interlock, with additional X cations bonding the outer faces of the I-beams to neighboring I-beams and providing the remaining charge balance. This binding is relatively weak and gives pyroxenes their characteristic cleavage . [ 4 ]
The chain silicate structure of the pyroxenes offers much flexibility in the incorporation of various cations and the names of the pyroxene minerals are primarily defined by their chemical composition.
Pyroxene minerals are named according to the chemical species occupying the X (or M2) site, the Y (or M1) site, and the tetrahedral T site. Cations in Y (M1) site are closely bound to 6 oxygens in octahedral coordination. Cations in the X (M2) site can be coordinated with 6 to 8 oxygen atoms, depending on the cation size. As of 1989 [update] , twenty mineral names are recognised by the International Mineralogical Association's Commission on New Minerals and Mineral Names and 105 previously used names have been discarded. [ 5 ]
A typical pyroxene has mostly silicon in the tetrahedral site and predominately ions with a charge of +2 in both the X and Y sites, giving the approximate formula XYT 2 O 6 . The names of the common calcium–iron–magnesium pyroxenes are defined in the 'pyroxene quadrilateral'. The enstatite-ferrosilite series ( [Mg,Fe]SiO 3 ) includes the common rock-forming mineral hypersthene , contains up to 5 mol.% calcium and exists in three polymorphs, orthorhombic orthoenstatite and protoenstatite and monoclinic clinoenstatite (and the ferrosilite equivalents). Increasing the calcium content prevents the formation of the orthorhombic phases and pigeonite ( [Mg,Fe,Ca][Mg,Fe]Si 2 O 6 ) only crystallises in the monoclinic system. There is not complete solid solution in calcium content and Mg-Fe-Ca pyroxenes with calcium contents between about 15 and 25 mol.% are not stable with respect to a pair of exolved crystals. This leads to a miscibility gap between pigeonite and augite compositions. There is an arbitrary separation between augite and the diopside-hedenbergite ( CaMgSi 2 O 6 − CaFeSi 2 O 6 ) solid solution. The divide is taken at >45 mol.% Ca. As the calcium ion cannot occupy the Y site, pyroxenes with more than 50 mol.% calcium are not possible. A related mineral wollastonite has the formula of the hypothetical calcium end member ( Ca 2 Si 2 O 6 ) but important structural differences mean that it is instead classified as a pyroxenoid.
Magnesium, calcium and iron are by no means the only cations that can occupy the X and Y sites in the pyroxene structure. A second important series of pyroxene minerals are the sodium-rich pyroxenes, corresponding to the 'pyroxene triangle' nomenclature. The inclusion of sodium, which has a charge of +1, into the pyroxene implies the need for a mechanism to make up the "missing" positive charge. In jadeite and aegirine this is added by the inclusion of a +3 cation (aluminium and iron(III) respectively) on the Y site. Sodium pyroxenes with more than 20 mol.% calcium, magnesium or iron(II) components are known as omphacite and aegirine-augite . With 80% or more of these components the pyroxene is classified using the quadrilateral diagram.
A wide range of other cations that can be accommodated in the different sites of pyroxene structures.
In assigning ions to sites, the basic rule is to work from left to right in this table, first assigning all silicon to the T site and then filling the site with the remaining aluminium and finally iron(III); extra aluminium or iron can be accommodated in the Y site and bulkier ions on the X site.
Not all the resulting mechanisms to achieve charge neutrality follow the sodium example above, and there are several alternative schemes:
In nature, more than one substitution may be found in the same mineral. | https://en.wikipedia.org/wiki/Si2O6 |
Trinitite , also known as atomsite or Alamogordo glass , [ 1 ] [ 2 ] is the glassy residue left on the desert floor after the plutonium -based Trinity nuclear bomb test on July 16, 1945, near Alamogordo, New Mexico . The glass is primarily composed of arkosic sand composed of quartz grains and feldspar (both microcline and smaller amount of plagioclase with small amount of calcite , hornblende and augite in a matrix of sandy clay ) [ 3 ] that was melted by the atomic blast. It was first academically described in American Mineralogist in 1948. [ 4 ]
It is usually a light green, although red trinitite was also found in one section of the blast site, [ 4 ] and rare pieces of black trinitite formed. [ 5 ] It is mildly radioactive but safe to handle. [ 6 ] [ 7 ] [ 8 ] Pieces of the material remain at the Trinity site as of 2018 [update] , [ 9 ] although most of it was bulldozed and buried by the United States Atomic Energy Commission in 1953. [ 10 ]
In 2005 it was theorized by Los Alamos National Laboratory scientist Robert E. Hermes and independent investigator William Strickfaden that much of the glass was formed by sand which was drawn up inside the fireball and then rained down in a liquid form. [ 11 ] [ 12 ] In a 2010 article in Geology Today , Nelson Eby of University of Massachusetts Lowell and Robert Hermes describe trinitite:
Contained within the glass are melted bits of the first atomic bomb and the support structures and various radionuclides formed during the detonation. The glass itself is marvelously complex at the tens to hundreds of micrometre scale, and besides glasses of varying composition also contains unmelted quartz grains. Air transport of the melted material led to the formation of spheres and dumbbell shaped glass particles. Similar glasses are formed during all ground level nuclear detonations and contain forensic information that can be used to identify the atomic device. [ 13 ]
This was supported by a 2011 study based on nuclear imaging and spectrometric techniques. [ 14 ] Green trinitite is theorised by researchers to contain material from the bomb's support structure, while red trinitite contains material originating from copper electrical wiring. [ 15 ]
An estimated 4,300 gigajoules (4.3 × 10 19 erg) of heat energy went into forming the glass. As the temperature required to melt the sand into the observed glass form was about 1,470 °C (2,680 °F), this was estimated to have been the minimum temperature the sand was exposed to. [ 16 ] Material within the blast fireball was superheated for an estimated 2–3 seconds before solidification. [ 17 ] Relatively volatile elements such as zinc are found in decreasing quantities the closer the trinitite was formed to the centre of the blast. The higher the temperature, the more these volatile elements evaporated and were not captured as the material solidified. [ 18 ]
The detonation left large quantities of trinitite scattered around the crater, [ 19 ] with Time writing in September 1945 that the site took the appearance of "[a] lake of green jade," while "[t]he glass takes strange shapes—lopsided marbles, knobbly sheets a quarter-inch thick, broken, thin-walled bubbles, green, wormlike forms." [ 2 ] The presence of rounded, beadlike forms suggests that some material melted after being thrown into the air and landed already formed, rather than remaining at ground level and being melted there. [ 15 ] Other trinitite which formed on the ground contains inclusions of infused sand. [ 17 ] This trinitite cooled rapidly on its upper surface, while the lower surface was superheated. [ 20 ]
The chaotic nature of trinitite's creation has resulted in variations in both structure and composition. [ 17 ] The glass has been described as "a layer 1 to 2 centimeters thick, with the upper surface marked by a very thin sprinkling of dust which fell upon it while it was still molten. At the bottom is a thicker film of partially fused material, which grades into the soil from which it was derived. The color of the glass is a pale bottle green, and the material is extremely vesicular with the size of the bubbles ranging to nearly the full thickness of the specimen." [ 3 ] The most common form of trinitite is green fragments of 1–3 cm thick, smooth on one side and rough on the other; this is the trinitite that cooled after landing still-molten on the desert floor. [ 22 ] [ 20 ]
Around 30% of trinitite is void space, although quantities vary greatly between samples. Trinitite exhibits various other defects such as cracks. [ 17 ] In trinitite that cooled after landing, the smooth upper surface contains large numbers of small vesicles while the lower rough layer has lower vesicle density but larger vesicles. [ 20 ] It is primarily alkaline. [ 22 ]
One of the more unusual isotopes found in trinitite is a barium neutron activation product, the barium in the Trinity device coming from the slow explosive lens employed in the device, known as Baratol . [ 21 ] Quartz is the only surviving mineral in most trinitite. [ 17 ] Trinitite no longer contains sufficient radiation to be harmful unless swallowed. [ 2 ] It still contains the radionuclides 241 Am , 137 Cs and 152 Eu owing to the Trinity test using a plutonium bomb . [ 22 ]
There are two forms of trinitite glass with differing refraction indices . The lower-index glass is composed largely of silicon dioxide , with the higher-index variant having mixed components. Red trinitite exists in both variants and contains glass rich in copper, iron, and lead as well as metallic globules. [ 4 ] Black trinitite's colour is as a result of being rich in iron. [ 5 ]
In a study published in 2021 a sample of red trinitite was found to contain a previously undiscovered complex quasicrystal , the oldest known manmade quasicrystal, with a symmetry group in the shape of an icosahedron . [ 23 ] It is composed of iron, silicon, copper and calcium. [ 19 ] The quasicrystal's structure displays fivefold rotational symmetry . [ 23 ] The quasicrystal research was led by geologist Luca Bindi of the University of Florence and Paul Steinhardt , after he theorised red trinitite was likely to contain quasicrystals as they often contain elements that rarely combine. [ 19 ] [ 24 ] The structure has a formula of Si 61 Cu 30 Ca 7 Fe 2 . [ 23 ] A single 10 μm grain was detected after ten months of work examining six small samples of red trinitite. [ 19 ] [ 24 ] [ 25 ]
A 2010 study in the open access journal Proceedings of the National Academy of Sciences examined trinitite's potential value to the field of nuclear forensics . [ 26 ] Prior to this research, it was assumed trinitite's components fused identically and their original composition could not be discerned. The study demonstrated that glass from nuclear detonations could provide information about the device and associated components, such as packaging. [ 27 ]
During the 2010s millions of dollars of research was undertaken examining trinitite to better understand what information such glasses held that could be used to understand the nuclear explosion that created them. [ 28 ] The researchers theorized that trinitite analysis may be useful for forensically identifying perpetrators of a future nuclear attack. [ 27 ] [ 29 ]
Researchers involved with the discovery of the quasicrystal speculated their work could improve efforts to investigate nuclear weapons proliferation since quasicrystals do not decay, unlike other evidence produced by nuclear weapons testing. [ 23 ] Trinitite has been chosen as a research subject partly because the nuclear test was well-documented. [ 18 ] A 2015 study in the Journal of Radioanalytical and Nuclear Chemistry funded by the National Nuclear Security Administration describes a method by which trinitite-like glass could be deliberately synthesized for use as test subjects for new nuclear forensic techniques. [ 17 ] Laser ablation was first successfully used to identify the isotopic signature unique to the uranium within the bomb from a sample of trinitite, demonstrating this faster method's effectiveness. [ 30 ]
Trinitite was not initially considered remarkable in the context of the nuclear test and ongoing war, but when the war ended visitors began to notice the glass and collect it as souvenirs. [ 2 ] For a time it was believed that the desert sand had simply melted from the direct radiant thermal energy of the fireball and was not particularly dangerous. Thus, it was marketed as suitable for use in jewelry in 1945 [ 31 ] [ 32 ] and 1946. [ 2 ] It is now illegal to take the remaining material from the site, much of which has been removed by the US government and buried elsewhere in New Mexico; however, material that was taken prior to this prohibition is still in the hands of collectors and available legally in mineral shops. [ 2 ] [ 28 ] Counterfeit trinitite is also on the market; trinitite's authenticity requires scientific analysis. [ 33 ] [ 5 ] There are samples in the National Museum of Nuclear Science and History , Smithsonian National Museum of Natural History , [ 2 ] the New Mexico Farm and Ranch Heritage Museum , [ 34 ] and the Corning Museum of Glass ; [ 35 ] the National Atomic Testing Museum houses a paperweight containing trinitite. [ 36 ] In the United Kingdom Science Museum Group 's collection contains a trinitite sample, [ 37 ] as does the Canadian War Museum [ 38 ] in Canada.
The SETI Institute , which seeks to find and research signs of intelligent life elsewhere in space, stated in 2021 that trinitite was to be included in their library of objects connected to "transformational moments" of potential interest to intelligent extraterrestrials . [ 39 ] The sculpture Trinity Cube by Trevor Paglen , exhibited in 2019 at the Museum of Contemporary Art San Diego as part of a themed collection of Paglen's art titled Sights Unseen, is partially made from trinitite. [ 40 ] The c.1988 artwork Trinitite, Ground Zero, Trinity Site, New Mexico by photographer Patrick Nagatani is housed at the Denver Art Museum . [ 41 ]
Occasionally, the name trinitite is broadly applied to all glassy residues of nuclear bomb testing, not just the Trinity test. [ 42 ] Black vitreous fragments of fused sand that had been solidified by the heat of a nuclear explosion were created by French testing at the Reggane site in Algeria . [ 43 ] Following the atomic bombing of Hiroshima , it was discovered in 2016 that between 0.6% and 2.5% of sand on local beaches was fused glass spheres formed during the bombing. Like trinitite, the glass contains material from the local environment, including materials from buildings destroyed in the attack. The material has been called hiroshimaite . [ 44 ] Kharitonchiki (singular: kharitonchik, Russian: харитончик ) is an analog of trinitite found in Semipalatinsk Test Site in Kazakhstan at ground zeroes of Soviet atmospheric nuclear tests. The porous black material is named after one of the leading Russian nuclear weapons scientists, Yulii Borisovich Khariton . [ 45 ]
Trinitite, in common with several similar naturally occurring minerals, is a melt glass . [ 46 ] While trinitite and materials of similar formation processes such as lavinite are anthropogenic, fulgurites , found in many thunderstorm -prone regions and in deserts , are naturally-formed, glassy materials and are generated by lightning striking sediments such as sand. [ 19 ] Impactite , a material similar to trinitite, can be formed by meteor impacts. The Moon's geology includes many rocks formed by one or more large impacts in which increasingly volatile elements are found in lower amounts the closer they are to the point of impact, similar to the distribution of volatile elements in trinitite. [ 18 ] | https://en.wikipedia.org/wiki/Si61Cu30Ca7Fe2 |
Amphibole ( / ˈ æ m f ə b oʊ l / AM -fə-bohl ) is a group of inosilicate minerals , forming prism or needlelike crystals, [ 1 ] composed of double chain SiO 4 tetrahedra , linked at the vertices and generally containing ions of iron and/or magnesium in their structures. Its IMA symbol is Amp. [ 2 ] Amphiboles can be green, black, colorless, white, yellow, blue, or brown. The International Mineralogical Association currently classifies amphiboles as a mineral supergroup, within which are two groups and several subgroups. [ 3 ]
Amphiboles crystallize into two crystal systems, monoclinic and orthorhombic . [ 4 ] In chemical composition and general characteristics they are similar to the pyroxenes . The chief differences from pyroxenes are that (i) amphiboles contain essential hydroxyl (OH) or halogen (F, Cl) and (ii) the basic structure is a double chain of tetrahedra (as opposed to the single chain structure of pyroxene). Most apparent, in hand specimens, is that amphiboles form oblique cleavage planes (at around 120 degrees), whereas pyroxenes have cleavage angles of approximately 90 degrees. Amphiboles are also specifically less dense than the corresponding pyroxenes. [ 5 ] Amphiboles are the primary constituent of amphibolites . [ 6 ]
Like pyroxenes, amphiboles are classified as inosilicate (chain silicate) minerals. However, the pyroxene structure is built around single chains of silica tetrahedra while amphiboles are built around double chains of silica tetrahedra. In other words, as with almost all silicate minerals, each silicon ion is surrounded by four oxygen ions. In amphiboles, some of the oxygen ions are shared between silicon ions to form a double chain structure as depicted below. These chains extend along the [001] axis of the crystal. One side of each chain has apical oxygen ions, shared by only one silicon ion, and pairs of double chains are bound to each other by metal ions that connect apical oxygen ions. The pairs of double chains have been likened to I-beams . Each I-beam is bonded to its neighbor by additional metal ions to form the complete crystal structure. Large gaps in the structure may be empty or partially filled by large metal ions, such as sodium, but remain points of weakness that help define the cleavage planes of the crystal. [ 7 ]
Amphiboles are minerals of either igneous or metamorphic origin. Amphiboles are more common in intermediate to felsic igneous rocks than in mafic igneous rocks, [ 8 ] because the higher silica and dissolved water content of the more evolved magmas favors formation of amphiboles rather than pyroxenes. [ 9 ] The highest amphibole content, around 20%, is found in andesites . [ 10 ] Hornblende is widespread in igneous and metamorphic rocks and is particularly common in syenites and diorites . Calcium is sometimes a constituent of naturally occurring amphiboles. Amphiboles of metamorphic origin include those developed in limestones by contact metamorphism ( tremolite ) and those formed by the alteration of other ferromagnesian minerals (such as hornblende as an alteration product of pyroxene). [ 11 ] Pseudomorphs of amphibole after pyroxene are known as uralite . [ 12 ]
The name amphibole derives from Greek amphíbolos ( ἀμφίβολος , lit. ' double entendre ' ), implying ambiguity. The name was used by René Just Haüy to include tremolite, actinolite and hornblende . The group was so named by Haüy in allusion to the protean variety, in composition and appearance, assumed by its minerals. This term has since been applied to the whole group. Numerous sub-species and varieties are distinguished, the more important of which are tabulated below in two series. The formulae of each will be seen to be built on the general double-chain silicate formula RSi 4 O 11 . [ 13 ]
Four of the amphibole minerals are commonly called asbestos . These are: anthophyllite, riebeckite, the cummingtonite/grunerite series, and the actinolite/tremolite series. The cummingtonite/grunerite series is often termed amosite or "brown asbestos", and riebeckite is known as crocidolite or "blue asbestos". These are generally called amphibole asbestos. [ 14 ] Mining, manufacture and prolonged use of these minerals can cause serious illnesses. [ 15 ] [ 16 ]
The more common amphiboles are classified as shown in the following table: [ 17 ]
Orthorhombic series
Monoclinic series
Certain amphibole minerals form solid solution series, at least at elevated temperature. Ferrous iron usually substitutes freely for magnesium in amphiboles to form continuous solid solution series between magnesium-rich and iron-rich endmembers. These include the cummington (magnesium) to grunerite (iron) endmembers, where the dividing line is placed at 30% magnesium. [ 18 ]
In addition, the orthoamphiboles, anthophyllite and gedrite, which differ in their aluminium content, form a continuous solid solution at elevated temperature. As the amphibole cools, the two end members exsolve to form very thin layers (lamellae). [ 18 ]
Hornblende is highly variable in composition, and includes at least five solid solution series: magnesiohornblende-ferrohornblende ( Ca 2 [(Mg,Fe) 4 Al]Si 7 AlO 22 (OH) 2 ), tschermakite-ferrotschermakite ( Ca 2 [(Mg,Fe) 3 Al 2 ]Si 6 Al 2 O 22 (OH) 2 ), edenite-ferroedenite ( NaCa 2 (Mg,Fe) 5 Si 7 AlO 22 (OH) 2 ), pargasite-ferropargasite ( NaCa 2 [(Mg,Fe) 4 Al]Si 6 Al 2 O 22 (OH) 2 ) and magnesiohastingstite-hastingsite ( NaCa 2 [(Mg,Fe) 4 Fe 3+ ]Si 6 Al 2 O 22 (OH) 2 ). In addition, titanium, manganese, or chromium can substitute for some of the cations and oxygen, fluorine, or chlorine for some of the hydroxide. The different chemical types are almost impossible to distinguish even by optical or X-ray methods, and detailed chemical analysis using an electron microprobe is required. [ 12 ]
Glaucophane to riebeckite form yet another solid solution series, which also extends towards hornblende and arfvedsonite. [ 19 ]
There is not a continuous series between calcic clinoamphiboles, such as hornblende, and low-calcium amphiboles, such as orthoamphiboles or the cummingtonite-grunerite series. Compositions intermediate in calcium are almost nonexistent in nature. [ 20 ] However, there is a solid solution series between hornblende and tremolite-actinolite at elevated temperature. A miscibility gap exists at lower temperatures, and, as a result, hornblende often contains exsolution lamellae of grunerite. [ 21 ]
On account of the wide variations in chemical composition, the different members vary considerably in properties and general appearance.
Anthophyllite occurs as brownish, fibrous or lamellar masses with hornblende in mica - schist at Kongsberg in Norway and some other localities. An aluminous related species is known as gedrite and a deep green Russian variety containing little iron as kupfferite . [ 13 ]
Hornblende is an important constituent of many igneous rocks. It is also an important constituent of amphibolites formed by metamorphism of basalt . [ 22 ]
Actinolite is an important and common member of the monoclinic series, forming radiating groups of acicular crystals of a bright green or greyish-green color. It occurs frequently as a constituent of greenschists . The name (from Greek ἀκτίς, ἀκτῖνος/aktís, aktînos , a 'ray' and λίθος/líthos , a 'stone') is a translation of the old German word Strahlstein (radiated stone). [ 13 ] [ 23 ]
Glaucophane , crocidolite , riebeckite and arfvedsonite form a somewhat special group of alkali-amphiboles. The first two are blue fibrous minerals, with glaucophane occurring in blueschists and crocidolite (blue asbestos) in ironstone formations, both resulting from dynamo-metamorphic processes. The latter two are dark green minerals, which occur as original constituents of igneous rocks rich in sodium, such as nepheline - syenite and phonolite . [ 13 ] [ 24 ]
Pargasite is a rare magnesium-rich variety of hornblende [ 12 ] with essential sodium , usually found in ultramafic rocks. For instance, it occurs in uncommon mantle xenoliths , carried up by kimberlite . It is hard, dense, black and usually automorphic , with a red-brown pleochroism in petrographic thin section . [ 25 ] | https://en.wikipedia.org/wiki/Si8O22 |
Aurosilane is an inorganic compound with a chemical formula of SiAu 4 . In this compound, gold acts as an electron acceptor with a valence of -1. Aurosilane has been isolated as a type of gold silane . [ 1 ] Its unit cell parameters are a=5.658, c=5.605 A. [ 2 ] The LUMO and the four Si-Au bonding orbitals of SiAu 4 are similar to those of SiH 4 . [ 3 ]
In addition, silicon can also form other compounds with gold such as Si 3 Au 3 [ 4 ]
This inorganic compound –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/SiAu4 |
Silicon tetrabromide , also known as tetrabromosilane, is the inorganic compound with the formula SiBr 4 . [ 1 ] This colorless liquid has a suffocating odor due to its tendency to hydrolyze with release of hydrogen bromide . [ 2 ] The general properties of silicon tetrabromide closely resemble those of the more commonly used silicon tetrachloride . [ 2 ]
The properties of the tetrasilanes , all of which are tetrahedral, are significantly affected by nature of the halide . These trends apply also to the mixed halides. Melting points , boiling points , and bond lengths increase with the atomic mass of the halide. The opposite trend is observed for the Si-X bond energies .
Covalently saturated silicon complexes like SiBr 4 , along with tetrahalides of germanium (Ge) and tin (Sn), are Lewis acids . [ 5 ] Although silicon tetrahalides obey the octet rule , they add Lewis basic ligands to give adducts with the formula SiBr 4 L and SiBr 4 L 2 (where L is a Lewis base). [ 6 ] [ 7 ] [ 8 ] The Lewis acidic properties of the tetrahalides tend to increase as follows: SiI 4 < SiBr 4 < SiCl 4 < SiF 4 . This trend is attributed to the relative electronegativities of the halogens. [ 7 ] [ 4 ]
The strength of the Si-X bonds decrease in the order: Si-F > Si-Cl > Si-Br > Si-I. [ 4 ] [ 3 ]
Silicon tetrabromide is synthesized by the reaction of silicon with hydrogen bromide at 600 °C. [ 9 ]
Side products include dibromosilane (SiH 2 Br 2 ) and tribromosilane (SiHBr 3 ). [ 9 ]
It can also be produced by treating silicon-copper mixture with bromine: [ 10 ]
Like other halosilanes, SiBr 4 can be converted to hydrides, alkoxides , amides , and alkyls , i.e., products with the following functional groups: Si-H, Si-OR, Si-NR 2 , Si-R, and Si-X bonds respectively. [ 2 ]
Silicon tetrabromide can be readily reduced by hydrides or complex hydrides. [ 3 ]
Reactions with alcohols and amines proceed as follows: [ 3 ]
Grignard reactions with metal alkyl halides are particularly important reactions due to their production of organosilicon compounds which can be converted to silicones . [ 3 ]
Redistribution reactions occur between two different silicon tetrahalides (as well as halogenated polysilanes) when heated to 100 ˚C, resulting in various mixed halosilanes. [ 2 ] [ 4 ] The melting points and boiling points of these mixed halosilanes generally increase as their molecular weights increase. [ 11 ] (Can occur with X= H, F, Cl, Br, and I)
Silicon tetrabromide hydrolyzes readily when exposed to air causing it to fume: [ 12 ]
Silicon tetrabromide is stable in the presence of oxygen at room temperature, but bromosiloxanes form at 670–695 ˚C . [ 12 ]
Due to its close similarity to silicon tetrachloride, there are few applications unique to SiBr 4 . The pyrolysis of SiBr 4 does have the advantage of depositing silicon at faster rates than that of SiCl 4 , however SiCl 4 is usually preferred due to its availability in high purity. [ 13 ] Pyrolysis of SiBr 4 followed by treatment with ammonia yields silicon nitride (Si 3 N 4 ) coatings, a hard compound used for ceramics, sealants, and the production of many cutting tools. [ 13 ] | https://en.wikipedia.org/wiki/SiBr4 |
Tetramethyl orthosilicate (TMOS) is the chemical compound with the formula Si(OCH 3 ) 4 . This molecule consists of four methoxy groups bonded to a silicon atom. The basic properties are similar to the more popular tetraethyl orthosilicate , which is usually preferred because the product of hydrolysis , ethanol , is less toxic than methanol .
Tetramethyl orthosilicate hydrolyzes to SiO 2 :
In organic synthesis , Si(OCH 3 ) 4 has been used to convert ketones and aldehydes to the corresponding ketals and acetals , respectively. [ 2 ]
The hydrolysis of Si(OCH 3 ) 4 produces insoluble SiO 2 and CH 3 OH (methanol). Even at low concentrations inhalation causes lung lesions, and at slightly higher concentrations eye contact with the vapor causes blindness [ citation needed ] . Worse, at low concentrations (200 ppm/15 min) the damage is often insidious, with onset of symptoms hours after exposure. [ 3 ] The mode of action is the precipitation of silica in the eyes and/or lungs [ citation needed ] . Contrary to common information, including several erroneous MSDS sheets, the methanol produced is only a risk through chronic exposure and is a comparatively small concern. The mechanisms of methanol toxicity are well established, methanol causes blindness via conversion to formaldehyde, then to toxic formic acid in the liver; methanol splashes to the eye cause only moderate and reversible eye irritation. [ 4 ] | https://en.wikipedia.org/wiki/SiC4H12O4 |
Silicon tetrachloride or tetrachlorosilane is the inorganic compound with the formula SiCl 4 . It is a colorless volatile liquid that fumes in air. It is used to produce high purity silicon and silica for commercial applications. It is a part of the chlorosilane family.
Silicon tetrachloride is prepared by the chlorination of various silicon compounds such as ferrosilicon , silicon carbide , or mixtures of silicon dioxide and carbon. The ferrosilicon route is most common. [ 3 ]
In the laboratory, SiCl 4 can be prepared by treating silicon with chlorine at 600 °C (1,112 °F): [ 1 ]
It was first prepared by Jöns Jakob Berzelius in 1823. [ 4 ]
Brine can be contaminated with silica when the production of chlorine is a byproduct of a metal refining process from metal chloride ore. In rare occurrences, the silicon dioxide in silica is converted to silicon tetrachloride when the contaminated brine is electrolyzed . [ 5 ]
Like other chlorosilanes or silanes , silicon tetrachloride reacts readily with water :
The reaction can be noticed on exposure of the liquid to air, as SiCl 4 vapour produces fumes as it reacts with moisture to give a cloud-like aerosol of silica and hydrochloric acid . [ 6 ] In contrast, carbon tetrachloride is not readily hydrolyzed.
With alcohols it reacts to give orthosilicate esters :
At higher temperatures homologues of silicon tetrachloride can be prepared by the reaction:
In fact, the chlorination of silicon is accompanied by the formation of hexachlorodisilane Si 2 Cl 6 . A series of compounds containing up to six silicon atoms in the chain can be separated from the mixture using fractional distillation . [ 1 ]
Silicon tetrachloride is a classic electrophile in its reactivity. [ 7 ] It forms a variety of organosilicon compounds upon treatment with Grignard reagents and organolithium compounds :
Reduction with hydride reagents affords silane .
Silicon tetrachloride is used as an intermediate in the manufacture of polysilicon , a hyper-pure form of silicon, [ 3 ] since it has a boiling point convenient for purification by repeated fractional distillation . It is reduced to trichlorosilane (HSiCl 3 ) by hydrogen gas in a hydrogenation reactor, and either directly used in the Siemens process or further reduced to silane (SiH 4 ) and injected into a fluidized bed reactor . Silicon tetrachloride reappears in both these two processes as a by-product and is recycled in the hydrogenation reactor. Vapor phase epitaxy of reducing silicon tetrachloride with hydrogen at approximately 1250 °C was done:
The produced polysilicon is used as wafers in large amounts by the photovoltaic industry for conventional solar cells made of crystalline silicon and also by the semiconductor industry.
Silicon tetrachloride can also be hydrolysed to fumed silica . High purity silicon tetrachloride is used in the manufacture of optical fibres. This grade should be free of hydrogen containing impurities like trichlorosilane. Optical fibres are made using processes like MCVD and OFD where silicon tetrachloride is oxidized to pure silica in the presence of oxygen.
As a feedstock in production of fused silica .
Pollution from the production of silicon tetrachloride has been reported in China associated with the increased demand for photovoltaic cells that has been stimulated by subsidy programs. [ 12 ] | https://en.wikipedia.org/wiki/SiCl4 |
Chlorotrifluorosilane is an inorganic gaseous compound with formula SiClF 3 composed of silicon , fluorine and chlorine . It is a silane that substitutes hydrogen with fluorine and chlorine atoms.
By heating a mixture of anhydrous aluminium chloride and sodium hexafluorosilicate to between 190 and 250 °C a mixture of gases containing chlorotrifluorosilane is given off. These are condensed at -196 °C degrees and fractionally distilled at temperatures up to -78 °C. [ 2 ]
SiClF 3 can be made by reacting silicon tetrachloride and silicon tetrafluoride gases at 600 °C, producing a mixture of fluorochlorosilanes including about one quarter SiClF 3 . [ 3 ]
SiClF 3 can be made by reacting silicon tetrachloride with antimony trifluoride . An antimony pentachloride catalyst assists. The products are distilled to separate it out from tetrafluorosilane and dichlorodifluorosilane . [ 4 ] [ 5 ] [ 6 ]
At high temperatures above 500 °C silicon tetrafluoride can react with phosphorus trichloride to yield some SiClF 3 . This is unusual because SiF 4 is very stable. [ 7 ]
Silicon tetrachloride can react with trifluoro(trichloromethyl)silane to yield SiClF 3 and CCl 3 SiCl 3 . [ 8 ]
2-Chloroethyltrifluorosilane or 1,2-dichloroethyltrifluorosilane can be disassociated by an infrared laser to yield SiClF 3 and C 2 H 4 ( ethylene ) or vinyl chloride . By tuning the laser to a vibration frequency of a particular isotope of silicon, different isotopomers can be selectively broken up in order to have a product that only concentrates one isotope of silicon. So silicon-30 can be increased to 80% by using the 934.5 cm −1 line in a CO 2 laser . [ 9 ]
The first published preparation of SiClF 3 by Schumb and Gamble was by exploding hexafluorodisilane in chlorine: Si 2 F 6 + Cl 2 → 2SiClF 3 . Other products of this explosion may include amorphous silicon, SiCl 2 F 2 and SiF 4 . [ 10 ]
Chlorine reacts with silicon tetrafluoride in the presence of aluminium chips at 500-600 °C to make mostly silicon tetra chloride and some SiClF 3 . [ 11 ]
Mercuric chloride when heated with SiF 3 Co(CO) 4 breaks the bond to form a 90% yield of SiClF 3 . [ 12 ]
The combination of SiF 4 and chlorodimethylphosphine yields some SiClF 3 . [ 13 ]
Trifluorosilane SiHF 3 reacts with gaseous chlorine to yield SiClF 3 and HCl. [ 14 ]
Bond length for Si–Cl is 1.996 Å and for Si–F is 1.558 Å. The bond angle ∠FSiCl = 110.2° and ∠FSiF = 108.7°. [ 4 ] The bond length between silicon and chlorine is unusually short, indicating a 31% double bond. This can be explained by the more ionic fluoride bonds withdrawing some charge allowing a partial positive charge on the chlorine. [ 15 ]
The molecular dipole moment is 0.636 Debye . [ 4 ]
Between 129.18 and 308.83 K the vapour pressure in mm Hg at temperature T in K is given by log 10 P = 102.6712 -2541.6/T -43.347 log 10 T + 0.071921T -0.000045231 T 2 . [ 16 ]
The heat of formation of chlorotrifluorosilane is -315.0 kcal/mol at 298K. [ 17 ]
Chlorotrifluorosilane is hydrolysed by water to produce silica.
Chlorotrifluorosilane reacts with trimethylstannane ((CH 3 ) 3 SnH) at room temperature to make trifluorosilane in about 60 hours. [ 18 ]
Proposed uses include a dielectric gas with a high breakdown voltage, and low global warming potential , a precursor for making fluorinated silica soot, and a vapour deposition gas.
Chlorotrifluorosilane can form an addition compound with pyridine with formula SiClF 3 .2py (py=pyridine) [ 19 ] An addition compound with trimethylamine exists. [ 20 ] [ 21 ] This addition compound is made by mixing trimethylamine vapour with Chlorotrifluorosilane and condensing out a solid at -78 °C. If this was allowed to soak in trimethylamine liquid for over eight hours, a diamine complex formed (2Me 3 N·SiClF 3 ). [ 21 ] At 0° the disassociation pressure of the monoamine complex was 23 mm Hg. [ 21 ]
SiClF 3 − is a trigonal bipyramidal shape with a Cl and F atom on the axis. It is formed when gamma rays hit the neutral molecule. [ 22 ]
Chlorotetrafluorosilicate (IV) (SiClF 4 − ) can form a stable a pale yellow crystalline compound tetraethylammonium chlorotetrafluorosilicate. [ 23 ] | https://en.wikipedia.org/wiki/SiClF3 |
SiC–SiC matrix composite is a particular type of ceramic matrix composite (CMC) which have been accumulating interest mainly as high temperature materials for use in applications such as gas turbines , as an alternative to metallic alloys . CMCs are generally a system of materials that are made up of ceramic fibers or particles that lie in a ceramic matrix phase. In this case, a SiC/SiC composite is made by having a SiC ( silicon carbide ) matrix phase and a fiber phase incorporated together by different processing methods. Outstanding properties of SiC/SiC composites include high thermal , mechanical , and chemical stability while also providing high strength to weight ratio . [ 1 ]
SiC/SiC composites are mainly processed through three different methods. However, these processing methods are often subjected to variations in order to create the desired structure or property: [ 1 ]
Mechanical properties of CMCs, including SiC–SiC composites can vary depending on the properties of their various components, namely, the fiber, matrix, and interphases. For example, the size, composition, crystallinity, or alignment of the fibers will dictate the properties of the composite. The interplay between matrix microcracking and fiber-matrix debonding often dominates the failure mechanism of SiC/SiC composites. This results in SiC/SiC composites having non-brittle behavior despite being fully ceramic. Additionally, creep rates at high temperatures are also extremely low, but still dependent on its various constituents. [ 1 ] [ 6 ]
SiC–SiC composites have a relatively high thermal conductivity and can operate at very high temperatures due to their inherently high creep and oxidation resistance. Residual porosity and stoichiometry of the material can vary its thermal conductivity, with increasing porosity leading to lower thermal conductivity and presence of Si–O–C phase also leading to lower thermal conductivity. In general, a typical well processed SiC–SiC composite can achieve a thermal conductivity of around 30 W/m-K at 1,000 °C (1,830 °F). [ 1 ]
Since SiC–SiC composites are generally sought for in high temperature applications, their oxidation resistance is of high importance. The oxidation mechanism for SiC–SiC composites vary depending on the temperature range, with operation in the higher temperature range (>1000 °C) being more beneficial than at lower temperatures (<1000 °C). In the former case, passive oxidation generates a protective oxide layer wheres in the latter case, oxidation degrades the fiber-matrix interface. Nonetheless, oxidation is an issue and environmental barrier coatings are being investigated to address this issue. [ 1 ]
Silicon carbide (SiC) ceramic matrix composites (CMCs) are a specific application of
engineering ceramic materials used to enhance aerospace applications such as turbine engine
components and thermal protection systems . Due to exhibiting high temperature capabilities, low
density, and resistance to oxidation and corrosion, SiC/SiC CMCs are largely used in aerospace
applications. The use of SiC/SiC CMCs on rotating engine components reduce the complexity of
design and engine structure weight, providing improved performance and fuel emissions. The
implementation of SiC/SiC ceramic matrix components will improve aircraft and space vehicle
performance and fuel efficiency, reducing additional harm to the environment in a cost-effective
manner.
Additional applications of SiC/SiC CMCs include combustion and turbine section components of
aero-propulsion and land-based gas turbine engines, thermal protection systems, thruster nozzles,
reusable rocket nozzles , and turbopump components for space vehicles.
With the development and implementation of future SiC/SiC CMCs, the SiC fiber creep and
rupture properties must be examined. Defects such as grain size , impurities, porosity, and surface
toughness all contribute to SiC fiber creep and rupture. Due to relatively low toughness, low
damage tolerance, and large variability in mechanical properties, CMCs have been limited to less
critical components. In the future, the implementation of greater SiC/SiC CMCs into aerospace
applications is hindered by lack of understanding of ceramic material characteristics,
degradation, mechanisms, and interactions to prevent component life and broaden component
design. | https://en.wikipedia.org/wiki/SiC–SiC_matrix_composite |
Chlorotrifluorosilane is an inorganic gaseous compound with formula SiClF 3 composed of silicon , fluorine and chlorine . It is a silane that substitutes hydrogen with fluorine and chlorine atoms.
By heating a mixture of anhydrous aluminium chloride and sodium hexafluorosilicate to between 190 and 250 °C a mixture of gases containing chlorotrifluorosilane is given off. These are condensed at -196 °C degrees and fractionally distilled at temperatures up to -78 °C. [ 2 ]
SiClF 3 can be made by reacting silicon tetrachloride and silicon tetrafluoride gases at 600 °C, producing a mixture of fluorochlorosilanes including about one quarter SiClF 3 . [ 3 ]
SiClF 3 can be made by reacting silicon tetrachloride with antimony trifluoride . An antimony pentachloride catalyst assists. The products are distilled to separate it out from tetrafluorosilane and dichlorodifluorosilane . [ 4 ] [ 5 ] [ 6 ]
At high temperatures above 500 °C silicon tetrafluoride can react with phosphorus trichloride to yield some SiClF 3 . This is unusual because SiF 4 is very stable. [ 7 ]
Silicon tetrachloride can react with trifluoro(trichloromethyl)silane to yield SiClF 3 and CCl 3 SiCl 3 . [ 8 ]
2-Chloroethyltrifluorosilane or 1,2-dichloroethyltrifluorosilane can be disassociated by an infrared laser to yield SiClF 3 and C 2 H 4 ( ethylene ) or vinyl chloride . By tuning the laser to a vibration frequency of a particular isotope of silicon, different isotopomers can be selectively broken up in order to have a product that only concentrates one isotope of silicon. So silicon-30 can be increased to 80% by using the 934.5 cm −1 line in a CO 2 laser . [ 9 ]
The first published preparation of SiClF 3 by Schumb and Gamble was by exploding hexafluorodisilane in chlorine: Si 2 F 6 + Cl 2 → 2SiClF 3 . Other products of this explosion may include amorphous silicon, SiCl 2 F 2 and SiF 4 . [ 10 ]
Chlorine reacts with silicon tetrafluoride in the presence of aluminium chips at 500-600 °C to make mostly silicon tetra chloride and some SiClF 3 . [ 11 ]
Mercuric chloride when heated with SiF 3 Co(CO) 4 breaks the bond to form a 90% yield of SiClF 3 . [ 12 ]
The combination of SiF 4 and chlorodimethylphosphine yields some SiClF 3 . [ 13 ]
Trifluorosilane SiHF 3 reacts with gaseous chlorine to yield SiClF 3 and HCl. [ 14 ]
Bond length for Si–Cl is 1.996 Å and for Si–F is 1.558 Å. The bond angle ∠FSiCl = 110.2° and ∠FSiF = 108.7°. [ 4 ] The bond length between silicon and chlorine is unusually short, indicating a 31% double bond. This can be explained by the more ionic fluoride bonds withdrawing some charge allowing a partial positive charge on the chlorine. [ 15 ]
The molecular dipole moment is 0.636 Debye . [ 4 ]
Between 129.18 and 308.83 K the vapour pressure in mm Hg at temperature T in K is given by log 10 P = 102.6712 -2541.6/T -43.347 log 10 T + 0.071921T -0.000045231 T 2 . [ 16 ]
The heat of formation of chlorotrifluorosilane is -315.0 kcal/mol at 298K. [ 17 ]
Chlorotrifluorosilane is hydrolysed by water to produce silica.
Chlorotrifluorosilane reacts with trimethylstannane ((CH 3 ) 3 SnH) at room temperature to make trifluorosilane in about 60 hours. [ 18 ]
Proposed uses include a dielectric gas with a high breakdown voltage, and low global warming potential , a precursor for making fluorinated silica soot, and a vapour deposition gas.
Chlorotrifluorosilane can form an addition compound with pyridine with formula SiClF 3 .2py (py=pyridine) [ 19 ] An addition compound with trimethylamine exists. [ 20 ] [ 21 ] This addition compound is made by mixing trimethylamine vapour with Chlorotrifluorosilane and condensing out a solid at -78 °C. If this was allowed to soak in trimethylamine liquid for over eight hours, a diamine complex formed (2Me 3 N·SiClF 3 ). [ 21 ] At 0° the disassociation pressure of the monoamine complex was 23 mm Hg. [ 21 ]
SiClF 3 − is a trigonal bipyramidal shape with a Cl and F atom on the axis. It is formed when gamma rays hit the neutral molecule. [ 22 ]
Chlorotetrafluorosilicate (IV) (SiClF 4 − ) can form a stable a pale yellow crystalline compound tetraethylammonium chlorotetrafluorosilicate. [ 23 ] | https://en.wikipedia.org/wiki/SiF3Cl |
Silicon tetrafluoride or tetrafluorosilane is a chemical compound with the formula Si F 4 . This colorless gas is notable for having a narrow liquid range: its boiling point is only 4 °C above its melting point. It was first prepared in 1771 by Carl Wilhelm Scheele by dissolving silica in hydrofluoric acid , [ 5 ] and later synthesized by John Davy in 1812. [ 6 ] It is a tetrahedral molecule and is corrosive. [ 7 ]
Volcanic plumes contain significant amounts of silicon tetrafluoride. Production can reach several tonnes per day. [ 8 ] Some amounts are also emitted from spontaneous coal fires. [ 9 ] The silicon tetrafluoride is partly hydrolysed and forms hexafluorosilicic acid .
SiF 4 is a by-product of the production of phosphate fertilizers wet process production , resulting from the attack of HF (derived from fluorapatite protonolysis) on silicates , which are present as impurities in the phosphate rocks . [ 10 ] The hydrofluoric acid and silicon dioxide (SiO 2 ) react to produce hexafluorosilicic acid : [ 10 ]
In the laboratory, the compound is prepared by heating barium hexafluorosilicate (Ba[SiF 6 ]) above 300 °C (572 °F) whereupon the solid releases volatile SiF 4 , leaving a residue of BaF 2 .
Alternatively, sodium hexafluorosilicate ( Na 2 [SiF 6 ] ) may also be thermally decomposed at 400 °C (752 °F)—600 °C (1,112 °F) (optionally in inert nitrogen gas atmosphere) [ 11 ] : 8
This volatile compound finds limited use in microelectronics and organic synthesis . [ 12 ]
It is also used in production of fluorosilicic acid (see above). [ 7 ]
Staying in the 1980s, as part of the Low-Cost Solar Array Project by Jet Propulsion Laboratory , [ 13 ] it was investigated as a potentially cheap feedstock for polycrystalline silicon production in fluidized bed reactors . [ 14 ] Few methods using it for the said production process were patented. [ 11 ] [ 15 ]
In 80s the Ethyl Corporation came up with a process that uses hexafluorosilicic acid and sodium aluminium hydride (NaAlH 4 ) (or other alkali metal hydride) to produce silane (SiH 4 ). [ 16 ]
In 2001 it was listed by New Jersey authorities as a hazardous substance that is corrosive and may severely irritate or even burn skin and eyes. [ 7 ] It is fatal if inhaled. [ 3 ] | https://en.wikipedia.org/wiki/SiF4 |
Silylidyne is a chemical substance occurring as a molecule found in stars and probably existing in interstellar space, or as a monolayer on the surface of solid silicon . The SiH molecule is a radical , and can be made experimentally by striking an electric arc to silicon on a low pressure hydrogen gas. [ 1 ]
As a surface layer, silicon hydrides form when the silicon is cleaned with hydrofluoric acid. These hydrides decompose to SiH when heated to 750 K. [ 2 ] Other ways to coat a silicon surface in hydrogen is via reaction with atomic hydrogen , or hot silane . [ 3 ] A (111) crystal face will become covered in the pure monohydride, but other faces on a silicon crystal will also have the dihydride and trihydride groups. [ 3 ]
The silylidyne group, not to be confused with silylidyne, is a ≡SiH group that is bonded with a triple bond. The hydrogen can be substituted by other groups to make a more generic family of silylidynes. It is known as a ligand on molybdenum.
Silylidyne in space was first noticed in sun spots in 1933. Later on it was found on the solar disk, photosphere, and in cool stars. Mira variable stars of type M or S may have emission lines of SiH. In even cooler brown dwarfs and planets, SiH is not found, but instead silicon takes form as silicon monoxide at low pressures, and SiH 4 at high pressures. Minute amounts of SiH as a transient species may be found in these bodies as SiO and SiH 4 react with water. [ 4 ]
The Si-H bond strength is 80 kcal/mol. [ 3 ]
The most prominent spectral band is due to A 2 Δ → X 2 Π transitions. Higher level excited states are the B 2 Σ − and C 2 Σ + , D 2 Δ, E 2 Σ + . [ 4 ]
The life time of the molecules in the A state is 530 nanoseconds. They decay to the X ground state. [ 4 ] | https://en.wikipedia.org/wiki/SiH |
Trichlorosilane (TCS) is an inorganic compound with the formula HCl 3 Si. It is a colourless, volatile liquid. Purified trichlorosilane is the principal precursor to ultrapure silicon in the semiconductor industry. In water, it rapidly decomposes to produce a siloxane polymer while giving off hydrochloric acid . Because of its reactivity and wide availability, it is frequently used in the synthesis of silicon-containing organic compounds. [ 2 ]
Trichlorosilane is produced by treating powdered metallurgical grade silicon with blowing hydrogen chloride at 300 °C in a hydrochlorination process. [ 3 ] Hydrogen is also produced, as described in the chemical equation :
Yields of 80-90% can be achieved. The main byproducts are silicon tetrachloride ( chemical formula SiCl 4 ), hexachlorodisilane (Si 2 Cl 6 ) and dichlorosilane (H 2 SiCl 2 ), from which trichlorosilane can be separated by distillation .
It is also produced from silicon tetrachloride in a direct chlorination process: [ 4 ] [ 5 ]
Both methods are widely used. The first method is cheaper but yield is hard to control. The second method doesn't require as much control, but needs twice as much capital investment and consumes 120 to 200 kWh/kg compared to 65-90 kWh/kg for the first method. The distillation of TCS purifies it substantially and with it, most of the impurities in the silicon are removed. [ 6 ]
Trichlorosilane is the basic ingredient used in the production of purified polysilicon .
It can be used in a chemical vapor deposition process called the Siemens process . [ 7 ] [ 8 ]
Via hydrosilylation , trichlorosilane is a precursor to other useful organosilicon compounds:
Some useful products of this or similar reactions include octadecyltrichlorosilane (OTS), perfluoroctyltrichlorosilane (PFOTCS), and perfluorodecyltrichlorosilane (FDTS). These reagents used in surface science and nanotechnology to form self-assembled monolayers . Such layers containing fluorine decrease surface energy and reduce sticking. This effect is usually exploited as coating for MEMS and microfabricated stamps for a nanoimprint lithography (NIL) and in injection molding tools. [ 9 ]
Trichlorosilane is a reagent in the conversion of benzoic acids to toluene derivatives. In the first step of a two-pot reaction, the carboxylic acid is first converted to the trichlosilylbenzyl compound. In the second step, the benzylic silyl derivative is converted to the toluene derivative with base. [ 10 ]
Trichlorosilane is highly reactive, and may respond violently (and even explosively) to many compounds. [ 11 ] This also includes water , potentially producing silicon dioxide , chlorine , hydrogen , hydrogen chloride (and its aqueous form hydrochloric acid ), and heat. Trichlorosilane can cause hazardous chemical reactions with moisture and humidity alone, and should be handled and stored under inert gas . [ 11 ] Spills of trichlorosilane may be neutralized using a 1-1 ratio of sodium hydroxide , or a 2-1 ratio of sodium bicarbonate to trichlorosilane. [ 12 ] Fires can be extinguished using alcohol-resistant aqueous film-forming foam (AR-AFFF). [ 11 ] [ 12 ] | https://en.wikipedia.org/wiki/SiHCl3 |
Silicon tetraiodide is the chemical compound with the formula Si I 4 . It is a tetrahedral molecule with Si-I bond lengths of 2.432(5) Å. [ 1 ]
SiI 4 is a precursor to silicon amides of the formula Si(NR 2 ) 4 (R = alkyl). [ 2 ] It has also been of interest in the manufacture and etching of silicon in microelectronics .
This compound is produced by treating silicon-copper mixture with iodine: [ 3 ]
It reacts quickly with water and moisture in the air.
It can also be made on a large scale by reaction of silicon or silicon carbide with iodine on heating to about 200 °C. Of more academic interest is the reaction of silane with iodine vapour at 130 - 150 °C, as this produces a series of compounds ranging from iodosilane SiH 3 I to diiodosilane SiH 2 I 2 and triiodosilane SiHI 3 as well. These compounds are colourless liquids at room temperature. [ 4 ] The last one can be readily distinguished from the similar carbon compound, iodoform which is a yellow solid at room temperature.
This inorganic compound –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/SiI4 |
Silicon monoxide is the chemical compound with the formula SiO where silicon is present in the oxidation state +2. In the vapour phase, it is a diatomic molecule. [ 1 ] It has been detected in stellar objects [ 2 ] and has been described as the most common oxide of silicon in the universe. [ 3 ]
When SiO gas is cooled rapidly, it condenses to form a brown/black polymeric glassy material, (SiO) n , which is available commercially and used to deposit films of SiO. Glassy (SiO) n is air and moisture sensitive. [ clarification needed ] [ citation needed ]
Its surface readily oxidizes in air at room temperature , giving an SiO 2 surface layer that protects the material from further oxidation . However, (SiO) n irreversibly disproportionates into SiO 2 and Si in a few hours between 400 °C and 800 °C and very rapidly between 1,000 °C and 1,440 °C, although the reaction does not go to completion. [ 4 ]
The first precise report on the formation of SiO was in 1887 [ 5 ] by the chemist Charles F. Maybery (1850–1927) at the Case School of Applied Science in Cleveland . Maybery claimed that SiO formed as an amorphous greenish-yellow substance with a vitreous luster when silica was reduced with charcoal in the absence of metals in an electric furnace. [ 6 ] The substance was always found at the interface between the charcoal and silica particles.
By investigating some of the chemical properties of the substance, its specific gravity, and a combustion analysis, Maybery deduced that the substance must be SiO. The equation representing the partial chemical reduction of SiO 2 with C can be represented as:
Complete reduction of SiO 2 with twice the amount of carbon yields elemental silicon and twice the amount of carbon monoxide. In 1890, the German chemist Clemens Winkler (the discoverer of germanium) was the first to attempt to synthesize SiO by heating silicon dioxide with silicon in a combustion furnace. [ 7 ]
However, Winkler was not able to produce the monoxide since the temperature of the mixture was only around 1000 °C. The experiment was repeated in 1905 by Henry Noel Potter (1869–1942), a Westinghouse engineer. Using an electric furnace, Potter was able to attain a temperature of 1700 °C and observe the generation of SiO. [ 5 ] Potter also investigated the properties and applications of the solid form of SiO. [ 8 ] [ 9 ]
Because of the volatility of SiO, silica can be removed from ores or minerals by heating them with silicon to produce gaseous SiO in this manner. [ 1 ] However, due to the difficulties associated with accurately measuring its vapor pressure, and because of the dependency on the specifics of the experimental design, various values have been reported in the literature for the vapor pressure of SiO (g). For the p SiO above molten silicon in a quartz (SiO 2 ) crucible at the melting point of silicon, one study yielded a value of 0.002 atm. [ 10 ] For the direct vaporization of pure, amorphous SiO solid, 0.001 atm has been reported. [ 11 ] For a coating system, at the phase boundary between SiO 2 and a silicide, 0.01 atm was reported. [ 12 ]
Silica itself, or refractories containing SiO 2 , can be reduced with H 2 or CO at high temperatures, e.g.: [ 13 ]
As the SiO product volatilizes off (is removed), the equilibrium shifts to the right, resulting in the continued consumption of SiO 2 . Based on the dependence of the rate of silica weight loss on the gas flow rate normal to the interface, the rate of this reduction appears to be controlled by convective diffusion or mass transfer from the reacting surface. [ 14 ] [ 15 ]
Silicon monoxide molecules have been trapped in an argon matrix cooled by helium. In these conditions, the SiO bond length is between 148.9 pm [ 3 ] and 151 pm. [ 16 ] This bond length is similar to the length of Si=O double bonds (148 pm) in the matrix-isolated linear molecule SiO 2 (O=Si=O), suggestive of the absence of a triple bond as in carbon monoxide . [ 3 ] However, the SiO triple bond has a calculated bond length of 150 pm and a bond energy of 794 kJ/mol, which are also very close to those reported for SiO. [ 16 ] In the carbon analogues the formal double bonds of carbon dioxide (116 pm) is also close to the triple bond length of carbon monoxide (112.8 pm); in light of this the observed bond length of SiO may be consistent with at least some triple-bond character in the diatomic molecule. The SiO double bond structure is, notably, an exception to Lewis' octet rule for molecules composed of the light main group elements, whereas the SiO triple bond satisfies this rule. That anomaly not withstanding, the observation that monomeric SiO is short-lived and that (SiO) 'n' oligomers with 'n' = 2,3,4,5 are known, [ 17 ] all having closed ring structures in which the silicon atoms are connected through bridging oxygen atoms (i.e. each oxygen atom is singly bonded to two silicon atoms; no Si-Si bonds), suggests the Si=O double bond structure, with a hypovalent silicon atom, is likely for the monomer. [ 3 ]
Condensing molecular SiO in argon matrix together with fluorine , chlorine or carbonyl sulfide (COS), followed by irradiation with light, produces the planar molecules OSiF 2 (with Si-O distance 148 pm) and OSiCl 2 (Si-O 149 pm), and the linear molecule OSiS (Si-O 149 pm, Si-S 190 pm). [ 3 ]
Matrix-isolated molecular SiO reacts with oxygen atoms generated by microwave discharge to produce molecular SiO 2 which has a linear structure.
When metal atoms (such as Na , Al , Pd , Ag , and Au ) are co-deposited with SiO, triatomic molecules are produced with linear (AlSiO and PdSiO), non-linear (AgSiO and AuSiO), and ring (NaSiO) structures. [ 3 ]
Potter reported SiO solid as yellowish-brown in color and as being an electrical and thermal insulator. The solid burns in oxygen and decomposes water with the liberation of hydrogen. It dissolves in warm alkali hydroxides and in hydrofluoric acid. Even though Potter reported the heat of combustion of SiO to be 200 to 800 calories higher than that of an equilibrium mixture of Si and SiO 2 (which could, arguably, be used as evidence that SiO is a unique chemical compound), [ 18 ] some studies characterized commercially available solid silicon monoxide materials as an inhomogeneous mixture of amorphous SiO 2 and amorphous Si with some chemical bonding at the interface of the Si and SiO 2 phases. [ 19 ] [ 20 ] Recent spectroscopic studies in a correlation with Potter's report suggest that commercially available solid silicon monoxide materials can not be considered as an inhomogeneous mixture of amorphous SiO 2 and amorphous Si . [ 21 ]
Interstellar SiO was first reported in 1971 after detection in the giant molecular cloud Sgr B2 . [ 22 ] SiO is used as a molecular tracer of shocked gas in protostellar outflows. [ 23 ] | https://en.wikipedia.org/wiki/SiO |
Silicon dioxide , also known as silica , is an oxide of silicon with the chemical formula SiO 2 , commonly found in nature as quartz . [ 5 ] [ 6 ] In many parts of the world, silica is the major constituent of sand . Silica is one of the most complex and abundant families of materials , existing as a compound of several minerals and as a synthetic product. Examples include fused quartz , fumed silica , opal , and aerogels . It is used in structural materials , microelectronics , and as components in the food and pharmaceutical industries. All forms are white or colorless, although impure samples can be colored.
Silicon dioxide is a common fundamental constituent of glass .
In the majority of silicon dioxides, the silicon atom shows tetrahedral coordination , with four oxygen atoms surrounding a central Si atom ( see 3-D Unit Cell ). Thus, SiO 2 forms 3-dimensional network solids in which each silicon atom is covalently bonded in a tetrahedral manner to 4 oxygen atoms. [ 8 ] [ 9 ] In contrast, CO 2 is a linear molecule. The starkly different structures of the dioxides of carbon and silicon are a manifestation of the double bond rule . [ 10 ]
Based on the crystal structural differences, silicon dioxide can be divided into two categories: crystalline and non-crystalline (amorphous). In crystalline form, this substance can be found naturally occurring as quartz , tridymite (high-temperature form), cristobalite (high-temperature form), stishovite (high-pressure form), and coesite (high-pressure form). On the other hand, amorphous silica can be found in nature as opal and diatomaceous earth . Quartz glass is a form of intermediate state between these structures. [ 11 ]
All of these distinct crystalline forms always have the same local structure around Si and O. In α-quartz the Si–O bond length is 161 pm, whereas in α-tridymite it is in the range 154–171 pm. The Si–O–Si angle also varies between a low value of 140° in α-tridymite, up to 180° in β-tridymite. In α-quartz, the Si–O–Si angle is 144°. [ 12 ]
Alpha quartz is the most stable form of solid SiO 2 at room temperature. The high-temperature minerals, cristobalite and tridymite, have both lower densities and indices of refraction than quartz. The transformation from α-quartz to beta-quartz takes place abruptly at 573 °C. Since the transformation is accompanied by a significant change in volume, it can easily induce fracturing of ceramics or rocks passing through this temperature limit. [ 13 ] The high-pressure minerals, seifertite , stishovite, and coesite, though, have higher densities and indices of refraction than quartz. [ 14 ] Stishovite has a rutile -like structure where silicon is 6-coordinate. The density of stishovite is 4.287 g/cm 3 , which compares to α-quartz, the densest of the low-pressure forms, which has a density of 2.648 g/cm 3 . [ 15 ] The difference in density can be ascribed to the increase in coordination as the six shortest Si–O bond lengths in stishovite (four Si–O bond lengths of 176 pm and two others of 181 pm) are greater than the Si–O bond length (161 pm) in α-quartz. [ 16 ] The change in the coordination increases the ionicity of the Si–O bond. [ 17 ]
Faujasite silica, another polymorph, is obtained by the dealumination of a low-sodium, ultra-stable Y zeolite with combined acid and thermal treatment. The resulting product contains over 99% silica, and has high crystallinity and specific surface area (over 800 m 2 /g). Faujasite-silica has very high thermal and acid stability. For example, it maintains a high degree of long-range molecular order or crystallinity even after boiling in concentrated hydrochloric acid . [ 18 ]
Molten silica exhibits several peculiar physical characteristics that are similar to those observed in liquid water : negative temperature expansion, density maximum at temperatures ~5000 °C, and a heat capacity minimum. [ 19 ] Its density decreases from 2.08 g/cm 3 at 1950 °C to 2.03 g/cm 3 at 2200 °C. [ 20 ]
The molecular SiO 2 has a linear structure like CO 2 . It has been produced by combining silicon monoxide (SiO) with oxygen in an argon matrix.
The dimeric silicon dioxide, (SiO 2 ) 2 has been obtained by reacting O 2 with matrix isolated dimeric silicon monoxide, (Si 2 O 2 ). In dimeric silicon dioxide there are two oxygen atoms bridging between the silicon atoms with an Si–O–Si angle of 94° and bond length of 164.6 pm and the terminal Si–O bond length is 150.2 pm. The Si–O bond length is 148.3 pm, which compares with the length of 161 pm in α-quartz. The bond energy is estimated at 621.7 kJ/mol. [ 21 ]
SiO 2 is most commonly encountered in nature as quartz , which comprises more than 10% by mass of the Earth's crust. [ 22 ] Quartz is the only polymorph of silica stable at the Earth's surface. Metastable occurrences of the high-pressure forms coesite and stishovite have been found around impact structures and associated with eclogites formed during ultra-high-pressure metamorphism . The high-temperature forms of tridymite and cristobalite are known from silica-rich volcanic rocks . In many parts of the world, silica is the major constituent of sand . [ 23 ]
Even though it is poorly soluble, silica occurs in many plants such as rice . Plant materials with high silica phytolith content appear to be of importance to grazing animals, from chewing insects to ungulates . Silica accelerates tooth wear, and high levels of silica in plants frequently eaten by insects may have developed as a defense mechanism against predation. [ 24 ] [ 25 ]
Silica is also the primary component of rice husk ash , which is used, for example, in filtration and as supplementary cementitious material (SCM) in cement and concrete manufacturing. [ 26 ]
Silicification in and by cells has been common in the biological world and it occurs in bacteria, protists, plants, and animals (invertebrates and vertebrates). [ 27 ]
Prominent examples include:
About 95% of the commercial use of silicon dioxide (sand) is in the construction industry, e.g. in the production of concrete ( Portland cement concrete ). [ 22 ]
Certain deposits of silica sand, with desirable particle size and shape and desirable clay and other mineral content, were important for sand casting of metallic products. [ 33 ] The high melting point of silica enables it to be used in such applications such as iron casting; modern sand casting sometimes uses other minerals for other reasons.
Crystalline silica is used in hydraulic fracturing of formations which contain tight oil and shale gas . [ 34 ]
Silica is the primary ingredient in the production of most glass . As other minerals are melted with silica, the principle of freezing point depression lowers the melting point of the mixture and increases fluidity. The glass transition temperature of pure SiO 2 is about 1475 K. [ 35 ] When molten silicon dioxide SiO 2 is rapidly cooled, it does not crystallize, but solidifies as a glass. [ 36 ] Because of this, most ceramic glazes have silica as the main ingredient. [ 37 ]
The structural geometry of silicon and oxygen in glass is similar to that in quartz and most other crystalline forms of silicon and oxygen, with silicon surrounded by regular tetrahedra of oxygen centres. The difference between the glass and crystalline forms arises from the connectivity of the tetrahedral units: Although there is no long-range periodicity in the glassy network, ordering remains at length scales well beyond the SiO bond length. One example of this ordering is the preference to form rings of 6-tetrahedra. [ 38 ]
The majority of optical fibers for telecommunications are also made from silica. It is a primary raw material for many ceramics such as earthenware , stoneware , and porcelain .
Silicon dioxide is used to produce elemental silicon . The process involves carbothermic reduction in an electric arc furnace : [ 39 ]
Fumed silica , also known as pyrogenic silica, is prepared by burning SiCl 4 in an oxygen-rich hydrogen flame to produce a "smoke" of SiO 2 . [ 15 ]
It can also be produced by vaporizing quartz sand in a 3000 °C electric arc. Both processes result in microscopic droplets of amorphous silica fused into branched, chainlike, three-dimensional secondary particles which then agglomerate into tertiary particles, a white powder with extremely low bulk density (0.03-0.15 g/cm 3 ) and thus high surface area. [ 40 ] The particles act as a thixotropic thickening agent, or as an anti-caking agent, and can be treated to make them hydrophilic or hydrophobic for either water or organic liquid applications.
Silica fume is an ultrafine powder collected as a by-product of the silicon and ferrosilicon alloy production. It consists of amorphous (non-crystalline) spherical particles with an average particle diameter of 150 nm, without the branching of the pyrogenic product. The main use is as pozzolanic material for high performance concrete. Fumed silica nanoparticles can be successfully used as an anti-aging agent in asphalt binders. [ 41 ]
Silica, either colloidal, precipitated, or pyrogenic fumed, is a common additive in food production. It is used primarily as a flow or anti- caking agent in powdered foods such as spices and non-dairy coffee creamer, or powders to be formed into pharmaceutical tablets. [ 40 ] It can adsorb water in hygroscopic applications. Colloidal silica is used as a fining agent for wine, beer, and juice, with the E number reference E551 . [ 22 ]
In cosmetics, silica is useful for its light-diffusing properties [ 42 ] and natural absorbency. [ 43 ]
Diatomaceous earth , a mined product, has been used in food and cosmetics for centuries. It consists of the silica shells of microscopic diatoms ; in a less processed form it was sold as tooth powder . [ 44 ] [ 45 ] Manufactured or mined hydrated silica is used as the hard abrasive in toothpaste .
Silicon dioxide is widely used in the semiconductor technology:
Because silicon dioxide is a native oxide of silicon it is more widely used compared to other semiconductors like gallium arsenide or indium phosphide .
Silicon dioxide could be grown on a silicon semiconductor surface. [ 46 ] Silicon oxide layers could protect silicon surfaces during diffusion processes , and could be used for diffusion masking. [ 47 ] [ 48 ]
Surface passivation is the process by which a semiconductor surface is rendered inert, and does not change semiconductor properties as a result of interaction with air or other materials in contact with the surface or edge of the crystal. [ 49 ] [ 50 ] The formation of a thermally grown silicon dioxide layer greatly reduces the concentration of electronic states at the silicon surface . [ 50 ] SiO 2 films preserve the electrical characteristics of p–n junctions and prevent these electrical characteristics from deteriorating by the gaseous ambient environment. [ 48 ] Silicon oxide layers could be used to electrically stabilize silicon surfaces. [ 47 ] The surface passivation process is an important method of semiconductor device fabrication that involves coating a silicon wafer with an insulating layer of silicon oxide so that electricity could reliably penetrate to the conducting silicon below. Growing a layer of silicon dioxide on top of a silicon wafer enables it to overcome the surface states that otherwise prevent electricity from reaching the semiconducting layer. [ 49 ] [ 51 ]
The process of silicon surface passivation by thermal oxidation (silicon dioxide) is critical to the semiconductor industry . It is commonly used to manufacture metal–oxide–semiconductor field-effect transistors (MOSFETs) and silicon integrated circuit chips (with the planar process ). [ 49 ] [ 51 ]
Hydrophobic silica is used as a defoamer component .
In its capacity as a refractory , it is useful in fiber form as a high-temperature thermal protection fabric. [ 52 ]
Silica is used in the extraction of DNA and RNA due to its ability to bind to the nucleic acids under the presence of chaotropes . [ 53 ]
Silica aerogel was used in the Stardust spacecraft to collect extraterrestrial particles. [ 54 ]
Pure silica (silicon dioxide), when cooled as fused quartz into a glass with no true melting point, can be used as a glass fibre for fibreglass.
Silicon dioxide is mostly obtained by mining, including sand mining and purification of quartz .
Quartz is suitable for many purposes, while chemical processing is required to make a purer or otherwise more suitable (e.g. more reactive or fine-grained) product. [ 55 ] [ 56 ]
Precipitated silica or amorphous silica is produced by the acidification of solutions of sodium silicate . The gelatinous precipitate or silica gel , is first washed and then dehydrated to produce colorless microporous silica. [ 15 ] The idealized equation involving a trisilicate and sulfuric acid is:
Approximately one billion kilograms/year (1999) of silica were produced in this manner, mainly for use for polymer composites – tires and shoe soles. [ 22 ]
Thin films of silica grow spontaneously on silicon wafers via thermal oxidation , producing a very shallow layer of about 1 nm or 10 Å of so-called native oxide. [ 57 ] Higher temperatures and alternative environments are used to grow well-controlled layers of silicon dioxide on silicon, for example at temperatures between 600 and 1200 °C, using so-called dry oxidation with O 2
or wet oxidation with H 2 O. [ 58 ] [ 59 ]
The native oxide layer is beneficial in microelectronics , where it acts as electric insulator with high chemical stability. It can protect the silicon, store charge, block current, and even act as a controlled pathway to limit current flow. [ 60 ]
Many routes to silicon dioxide start with an organosilicon compound, e.g., HMDSO, [ 61 ] TEOS. Synthesis of silica is illustrated below using tetraethyl orthosilicate (TEOS). [ 62 ] Simply heating TEOS at 680–730 °C results in the oxide:
Similarly TEOS combusts around 400 °C:
TEOS undergoes hydrolysis via the so-called sol-gel process . The course of the reaction and nature of the product are affected by catalysts, but the idealized equation is: [ 63 ]
Being highly stable, silicon dioxide arises from many methods. Conceptually simple, but of little practical value, combustion of silane gives silicon dioxide. This reaction is analogous to the combustion of methane:
However the chemical vapor deposition of silicon dioxide onto crystal surface from silane had been used using nitrogen as a carrier gas at 200–500 °C. [ 64 ]
Silicon dioxide is a relatively inert material (hence its widespread occurrence as a mineral). Silica is often used as inert containers for chemical reactions. At high temperatures, it is converted to silicon by reduction with carbon.
Fluorine reacts with silicon dioxide to form SiF 4 and O 2 whereas the other halogen gases (Cl 2 , Br 2 , I 2 ) are unreactive. [ 15 ]
Most forms of silicon dioxide are attacked ("etched") by hydrofluoric acid (HF) to produce hexafluorosilicic acid : [ 12 ]
Stishovite does not react to HF to any significant degree. [ 65 ] HF is used to remove or pattern silicon dioxide in the semiconductor industry.
Silicon dioxide acts as a Lux–Flood acid , being able to react with bases under certain conditions. As it does not contain any hydrogen, non-hydrated silica cannot directly act as a Brønsted–Lowry acid . While silicon dioxide is only poorly soluble in water at low or neutral pH (typically, 2 × 10 −4 M for quartz up to 10 −3 M for cryptocrystalline chalcedony ), strong bases react with glass and easily dissolve it. Therefore, strong bases have to be stored in plastic bottles to avoid jamming the bottle cap, to preserve the integrity of the recipient, and to avoid undesirable contamination by silicate anions. [ 66 ]
Silicon dioxide dissolves in hot concentrated alkali or fused hydroxide, as described in this idealized equation: [ 15 ]
Silicon dioxide will neutralise basic metal oxides (e.g. sodium oxide , potassium oxide , lead(II) oxide , zinc oxide , or mixtures of oxides, forming silicates and glasses as the Si-O-Si bonds in silica are broken successively). [ 12 ] As an example the reaction of sodium oxide and SiO 2 can produce sodium orthosilicate , sodium silicate, and glasses, dependent on the proportions of reactants: [ 15 ]
Examples of such glasses have commercial significance, e.g. soda–lime glass , borosilicate glass , lead glass . In these glasses, silica is termed the network former or lattice former. [ 12 ] The reaction is also used in blast furnaces to remove sand impurities in the ore by neutralisation with calcium oxide , forming calcium silicate slag .
Silicon dioxide reacts in heated reflux under dinitrogen with ethylene glycol and an alkali metal base to produce highly reactive, pentacoordinate silicates which provide access to a wide variety of new silicon compounds. [ 67 ] The silicates are essentially insoluble in all polar solvent except methanol .
Silicon dioxide reacts with elemental silicon at high temperatures to produce SiO: [ 12 ]
The solubility of silicon dioxide in water strongly depends on its crystalline form and is three to four times higher for amorphous silica than quartz; as a function of temperature, it peaks around 340 °C (644 °F). [ 68 ] This property is used to grow single crystals of quartz in a hydrothermal process where natural quartz is dissolved in superheated water in a pressure vessel that is cooler at the top. Crystals of 0.5–1 kg can be grown for 1–2 months. [ 12 ] These crystals are a source of very pure quartz for use in electronic applications. [ 15 ] Above the critical temperature of water 647.096 K (373.946 °C; 705.103 °F) and a pressure of 22.064 megapascals (3,200.1 psi) or higher, water is a supercritical fluid and solubility is once again higher than at lower temperatures. [ 69 ]
Silica ingested orally is essentially nontoxic, with an LD 50 of 5000 mg/kg (5 g/kg). [ 22 ] A 2008 study following subjects for 15 years found that higher levels of silica in water appeared to decrease the risk of dementia . An increase of 10 mg/day of silica in drinking water was associated with a reduced risk of dementia of 11%. [ 70 ]
Inhaling finely divided crystalline silica dust can lead to silicosis , bronchitis , or lung cancer , as the dust becomes lodged in the lungs and continuously irritates the tissue, reducing lung capacities. [ 71 ] When fine silica particles are inhaled in large enough quantities (such as through occupational exposure), it increases the risk of systemic autoimmune diseases such as lupus [ 72 ] and rheumatoid arthritis compared to expected rates in the general population. [ 73 ]
Silica is an occupational hazard for people who do sandblasting or work with powdered crystalline silica products. Amorphous silica, such as fumed silica, may cause irreversible lung damage in some cases but is not associated with the development of silicosis. Children, asthmatics of any age, those with allergies , and the elderly (all of whom have reduced lung capacity ) can be affected in less time. [ 74 ]
Crystalline silica is an occupational hazard for those working with stone countertops because the process of cutting and installing the countertops creates large amounts of airborne silica. [ 75 ] Crystalline silica used in hydraulic fracturing presents a health hazard to workers. [ 34 ]
In the body, crystalline silica particles do not dissolve over clinically relevant periods. Silica crystals inside the lungs can activate the NLRP3 inflammasome inside macrophages and dendritic cells and thereby result in production of interleukin , a highly pro-inflammatory cytokine in the immune system. [ 76 ] [ 77 ] [ 78 ]
Regulations restricting silica exposure 'with respect to the silicosis hazard' specify that they are concerned only with silica, which is both crystalline and dust-forming. [ 79 ] [ 80 ] [ 81 ] [ 82 ] [ 83 ] [ 84 ]
In 2013, the U.S. Occupational Safety and Health Administration reduced the exposure limit to 50 μg /m 3 of air. Prior to 2013, it had allowed 100 μg/m 3 and in construction workers even 250 μg/m 3 . [ 34 ] In 2013, OSHA also required the "green completion" of fracked wells to reduce exposure to crystalline silica and restrict the exposure limit. [ 34 ]
SiO 2 , more so than almost any material, exists in many crystalline forms. These forms are called polymorphs .
Inhaling finely divided crystalline silica can lead to severe inflammation of the lung tissue, silicosis , bronchitis , lung cancer , and systemic autoimmune diseases , such as lupus and rheumatoid arthritis . Inhalation of amorphous silicon dioxide, in high doses, leads to non-permanent short-term inflammation, where all effects heal. [ 100 ]
This extended list enumerates synonyms for silicon dioxide; all of these values are from a single source; values in the source were presented capitalized. [ 101 ] | https://en.wikipedia.org/wiki/SiO2 |
SiRF Technology, Inc. was an American pioneer in the commercial use of GPS technology for consumer applications. The company was founded in 1995 and was headquartered in San Jose, California . Notable and founding members included Sanjai Kohli , [ 2 ] Dado Banatao , and Kanwar Chadha. [ citation needed ] The company was acquired by British firm CSR plc in 2009, who were in turn subsequently acquired by American company Qualcomm on 13 August 2015. [ 3 ] [ 4 ]
SiRF manufactured a range of patented GPS chipsets and software for consumer navigation devices and systems. The chips are based on ARM controllers integrated with low-noise radio receivers to decode GPS signals at very low signal levels (typically -160 dBm ). SiRF chips also support SBAS to allow for differentially corrected positions.
SiRFstarIII architecture is designed to be useful in wireless and handheld location-based services (LBS) applications, for 2G, 2.5G, 3G asynchronous networks. The SiRFstarIII family comprises the GRF3w RF IC, the GSP3f digital section, and the GSW3 software that is API compatible with GSW2 and SiRFLoc. The chips have been adopted by major GPS manufacturers, including Sony, Micro Technologies, Garmin, TomTom and Magellan.
SiRFatlas IV is a multifunction location system processor and is meant for entry-level Personal Navigation Devices (PNDs). The SiRFatlas IV is a cheaper version of the very popular, but rather expensive SiRFPrima platform. [ 5 ] [ 6 ] Has GPS/Galileo baseband, LCD touch-screen controller, video input, 10-bit ADC and a high-speed USB 2.0.
SiRFstarV chips, launched in 2012, are capable of tracking NAVSTAR , GLONASS , Galileo , Compass , SBAS , and future GNSS signals. The SiRFusion platform integrates positioning from GNSS, terrestrial radio solutions such as Wi-Fi and cellular, and MEMS sensors including accelerometers, gyroscopes, and compasses. SiRFusion can then combine this real-time information with cellular base station and Wi-Fi access point location data, ephemeribased aiding information from the CSR Positioning Center (CPC) to generate accurate and reliable position updates.
On 10 February 2009, UK wireless chip company CSR announced it was buying SiRF in a share deal worth $136 million. [ 7 ] | https://en.wikipedia.org/wiki/SiRF |
SiRFstarIII is a range of high sensitivity GPS microcontroller chips manufactured by SiRF Technology . GPS microcontroller chips interpret signals from GPS satellites and determine the position of the GPS receiver. It was announced in 2004. [ 1 ] [ 2 ]
SiRFstarIII features: [ 3 ] | https://en.wikipedia.org/wiki/SiRFstarIII |
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