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Sapropel (a contraction of Ancient Greek words sapros and pelos , meaning putrefaction and mud (or clay), respectively) is a term used in marine geology to describe dark-coloured sediments that are rich in organic matter . Organic carbon concentrations in sapropels commonly exceed 2 wt.% in weight.
The term sapropel events may also refer to cyclic oceanic anoxic events (OAE), in particular those affecting the Mediterranean Sea with a periodicity of about 21,000 years.
Sapropels have been recorded in the Mediterranean sediments since the closure of the Eastern Tethys Ocean 13.5 million years ago. The formation of sapropel events in the Mediterranean Sea occurs approximately every 21,000 years and last between 3,000 and 5,000 years. The first identification of these events occurred in the mid-20th century. Since then, their formulative conditions of have been investigated.
The occurrence of sapropels has been related to the Earth's orbital parameters ( Milankovitch cycles ). The precession cycles influence the African monsoon , which influences the Mediterranean circulation through increases in freshwater inputs.
Sapropels develop during episodes of reduced oxygen availability in bottom waters, such as an oceanic anoxic event (OAE). Most studies of formational mechanisms infer some degree of reduced deep-water circulation. Oxygen can only reach the deep sea by new deep-water formation and consequent "ventilation" of deep basins. There are two main causes of OAE: reduction in deep-water circulation or raised oxygen demand from upper level.
A reduction in deep-water circulation will eventually lead to a serious decrease in deep-water oxygen concentrations due to biochemical oxygen demand associated with the decay of organic matter. This sinks into the deep sea as a result of export production from surface waters. Oxygen depletion in bottom waters then favors the enhanced preservation of the organic matter during burial by the sediments. Organic-rich sediments may also form in well-ventilated settings that have highly productive surface waters; here the high surface demand simply extracts the oxygen before it can enter the deep circulation current thus depriving the bottom waters of oxygen.
Sapropelic deposits from global ocean anoxic events form important oil source rocks . Detailed process studies of sapropel formation have concentrated on the fairly recent eastern Mediterranean deposits, [ 1 ] the last of which occurred between 9.5 and 5.5 thousand years ago.
The Mediterranean sapropels of the Pleistocene reflect increased density stratification in the isolated Mediterranean basin. They record a higher organic carbon concentration than non-sapropel times; an increase in the δ 15 N and corresponding decrease in δ 13 C tells of rising productivity as a result of nitrogen fixation. [ 2 ] This effect is more pronounced further east in the basin, suggesting that increased precipitation was most pronounced at that end of the sea. [ 2 ]
In the Black Sea , sapropels are distributed at a depth of 500 to 2200 m, and in different morpholithological zones they have different thicknesses. Deep sea sediments are called the sediments formed outside the zone of influence of hydrogenic factors such as wind-driven waves and internal waves as well as of the transgressive and regressive cycles of the Black Sea basin. Here, under the conditions of relative stagnation, can be observed uninterrupted cross-sections because this area was under the sea level during the entire Pleistocene and Holocene . Deep sea organogenic mineral sediments (DSOMS) are those sediments that contain more than 3% organic carbon. The sapropels form a single horizon with constant thickness typical of the Black Sea basin. Analogues of the sapropels on the continental shelf and the upper part of the continental slope are the green aleurite - pelite , oozes with accumulation of plant detritus and decomposed shells of Mytilus galloprovincialis . The transition from aleurite-pelitic oozes to sapropels is facial. The organic matter in the sapropels is of heterogeneous origin. They are composed primarily of planktogenic organisms (about 80%) and continental organic matter (20%). The planktonic organisms are well preserved in most cases under the conditions of the hydrogen sulfide zone. The main components of the sapropels are the dinoflagellate cysts, diatom algae, coccolithophorids , peridiniales . The mineral part of sapropel muds is represented by a poly-component mixture of clay minerals . The minerals illite and montmorillonite predominate, chlorite and kaolinite occur in subordinate quantities. Individual grains of quartz , feldspar , volcanic glass and others are rarely found among them. Carbonate minerals are mainly represented by calcite and dolomite . It is generally accepted that the main source of hydrogen sulfide in the Black Sea today are the processes of anaerobic decomposition of organic matter by sulfate-reducing bacteria (SRB). The organic substance that is fixed at the bottom of the basin in the form of organogenic-mineral sediments (sapropels) is a product of the mass extinction of the plankton biomass as a result of the Black Sea flood . There is an excess of a huge amount of organic matter, which creates favorable conditions for the development of bacterial sulfate reduction. [ 3 ]
Bulgarian Professor Petko Dimitrov is the creator of the idea for the application of sapropel sediments from the bottom of the Black Sea as a natural ecological fertilizer and biological products. [ 5 ] [ 3 ] According to the Romanian tycoon Dinu Patriciu , the sapropel sediments have the potential to be a source of non-conventional energy. [ 6 ] Patriciu has created a marine exploration project in the Black Sea which examines the sapropel sediments of that region. Sediment cores are collected and investigated by several universities and research institutes across the world. [ 6 ] | https://en.wikipedia.org/wiki/Sapropel |
Saprophages are organisms that obtain nutrients by consuming decomposing dead plant or animal biomass. [ 1 ] They are distinguished from detritivores in that saprophages are sessile consumers while detritivores are mobile. [ citation needed ] Typical saprophagic animals include sedentary polychaetes such as amphitrites ( Amphitritinae , worms of the family Terebellidae ) and other terebellids .
The eating of wood, whether live or dead, is known as xylophagy . The activity of animals feeding only on dead wood is called sapro-xylophagy and those animals, sapro-xylophagous.
In food webs , saprophages generally play the roles of decomposers . There are two main branches of saprophages, broken down by nutrient source. There are necrophages which consume dead animal biomass, and thanatophages which consume dead plant biomass. | https://en.wikipedia.org/wiki/Saprophagy |
Saprotrophic bacteria are bacteria that are typically soil-dwelling and utilize saprotrophic nutrition as their primary energy source. They are often associated with soil fungi that also use saprotrophic nutrition and both are classified as saprotrophs. [ 1 ]
A saprotroph is a type of decomposer that feeds exclusively on dead and decaying plant matter. [ 2 ] Saprotrophic organisms include fungi, bacteria, and water molds which are critical to decomposition and nutrient cycling , providing nutrition for consumers at higher trophic levels. They obtain nutrients via absorptive nutrition, in which nutrients are digested by a variety of enzymes and subsequently secreted by the saprotroph. [ 1 ]
Community composition and proliferation rates of saprotrophic indicator bacteria are often considered signals of community health in soil, aquatic, [ 3 ] and bodily systems. [ 4 ]
All saprotrophic bacteria are unicellular prokaryotes , and reproduce asexually through binary fission . [ 2 ] Variation in the turnover times (the rate at which a nutrient is depleted and replaced in a particular nutrient pool) of the bacteria may be due in part to variation in environmental factors including temperature, soil moisture, soil pH, substrate type and concentration, plant genotype, and toxins. [ 5 ] These factors can, in turn, alter the rates of decomposition and soil organic matter turnover, impacting ecosystem productivity . [ 6 ]
When colonizing a new environment, the population of a saprotrophic strain of bacteria initially decreases and then reaches a point of population stabilization. [ 7 ] [ 8 ] While they are common in soil environments, they can persist anywhere with available food resources, such as in aquatic environments, or in fecal matter. [ 8 ] As such, they are a common organism in waste products, where they break down various compounds to obtain nourishment. [ 2 ]
Saprotrophic bacterial growth rate is very sensitive to changes in environmental conditions, making it a good variable to detect rapid and subtle changes in microbial communities. Growth rates are also used to measure interactions between bacteria and fungi, with research suggesting bacterial inhibition of fungal growth as it may exert a competitive pressure on fungi . Under normal soil conditions, bacterial biomass production remains relatively steady, as the growth of microorganisms is balanced by predation and other types of cell death. Studies on bacterial growth rates using leucine or thymidine incorporation suggest the turnover times of soil bacterial communities to be in the order of days to weeks at a temperature of around 20 °C. Other studies have estimated a longer turnover time varying between 107–160 days at 25 °C. This large discrepancy could be due to differences in the methods used for these estimations, as well as differences in the incubation temperatures, which are of utmost importance in determining growth rates. Studies have shown that optimal bacterial growth is achieved at temperatures around 25-30 °C in temperate soils, which is usually much higher than the mean annual temperature. [ citation needed ]
Bacterial growth in the rhizosphere presents a special situation, as it supports the rapid proliferation of bacteria compared with the surrounding soil due to the input of root exudates into the soil. Here, bacterial turnover times are estimated to be in the range of just 12–19 hours, with shorter times exhibited on younger roots. [ citation needed ]
Overall, there has not been sufficient research on bacterial growth rates in soil. This contrasts with our comparatively vast knowledge of bacterial growth rate measurements in aquatic environments. We may blame this disparity on the complexity of the soil matrix, which includes both bacterial and fungal decomposers with different feeding strategies. [ 5 ]
Several environmental factors may impact the activity of saprotrophs, including soil moisture, pH, and the presence of substrates. Soil moisture, indicated by carbon mineralization , is positively correlated with bacterial growth, with bacterial growth increasing as soil moisture content increases. [ citation needed ]
In terms of soil pH, there is a well-known pattern of bacterial dominance in neutral or slightly alkaline soils, though clear evidence for the differential growth of bacteria in soils with different pH is scarce. [ citation needed ]
Compared to fungi, bacteria are considered more competitive in degrading easily available substrates. In addition to quality and type, the concentration of substrate is also important to bacterial growth in soil. For example, a study utilizing the addition of different concentrations of glucose found that bacterial growth increased significantly at low concentrations, and was inhibited at very high concentrations. On the other hand, increased substrate flow in the rhizosphere due to root exudation has been shown to significantly increase bacterial growth rates. Here, there is a plant species and genotype effect on growth, presumably due to different exudation rates. [ 5 ]
Some saprotrophic bacteria are common pathogens in medicine and agriculture, as they move readily between individuals via consumption or other modes of exposure, such as contact with excrement. [ 8 ] For example, certain bacteria may be vectors for food borne illnesses such as Escherichia coli . [ 9 ] Others have the ability to decompose cellulose , and are often found in the rumen of cows, aiding in their digestion by fermenting the cellulose in grass. [ 9 ]
Through saprotrophic nutrition, saprotrophic bacteria release microbial extracellular enzymes (MEEs) into the environment to break down soil organic matter (SOM). MEEs are released when an organism's energy and nutrient needs are not being met. This allows for the monitoring of MEEs as an indicator of nutrient availability in soil. [ 10 ] Some significant MEEs are:
In forest soils, bacteria are important in the decomposition of fungal mycelia and in nitrogen cycle processes, including nitrogen fixation . Additionally, bacteria, alongside fungi, mediate the bulk of biogeochemical processes, determine the availability of mineral nutrients, and determine the fate of carbon in these soils. However, bacteria’s higher demand for nitrogen and inability to translocate nutrients makes them less efficient decomposers than fungi.
Ecosystem disturbances such as fires, insect invasions, and timber harvesting can lead to a slight decrease in bacterial abundance. Furthermore, the bacterial community composition may change in response to changes in nutrient availability and overall chemistry. [ 14 ] | https://en.wikipedia.org/wiki/Saprotrophic_bacteria |
Saprotrophic nutrition / s æ p r ə ˈ t r ɒ f ɪ k , - p r oʊ -/ [ 1 ] or lysotrophic nutrition [ 2 ] [ 3 ] is a process of chemoheterotrophic extracellular digestion involved in the processing of decayed (dead or waste) organic matter . It occurs in saprotrophs , and is most often associated with fungi (e.g. Mucor ) and with soil bacteria . Saprotrophic microscopic fungi are sometimes called saprobes . [ 4 ] Saprotrophic plants or bacterial flora are called saprophytes ( sapro- 'rotten material' + -phyte 'plant'), although it is now believed [ citation needed ] that all plants previously thought to be saprotrophic are in fact parasites of microscopic fungi or of other plants . In fungi, the saprotrophic process is most often facilitated through the active transport of such materials through endocytosis within the internal mycelium and its constituent hyphae . [ 5 ]
Various word roots relating to decayed matter ( detritus , sapro- , lyso- ), to eating and nutrition ( -vore , -phage , -troph ), and to plants or life forms ( -phyte , -obe ) produce various terms, such as detritivore , detritophage, saprotroph, saprophyte , saprophage, and saprobe; their meanings overlap, although technical distinctions (based on physiologic mechanisms) narrow the senses . For example, biologists can make usage distinctions based on macroscopic swallowing of detritus (as in earthworms ) versus microscopic lysis of detritus (as with mushrooms ).
As matter decomposes within a medium in which a saprotroph is residing, the saprotroph breaks such matter down into its composites.
These products are re-absorbed into the hypha through the cell wall by endocytosis and passed on throughout the mycelium complex. This facilitates the passage of such materials throughout the organism and allows for growth and, if necessary, repair. [ 5 ]
In order for a saprotrophic organism to facilitate optimal growth and repair, favourable conditions and nutrients must be present. [ 7 ] Optimal conditions refers to several conditions which optimise the growth of saprotrophic organisms, such as;
The majority of nutrients taken in by such organisms must be able to provide carbon, proteins, vitamins and, in some cases, ions . Due to the carbon composition of the majority of organisms, dead and organic matter provide rich sources of disaccharides and polysaccharides such as maltose and starch , and of the monosaccharide glucose . [ 5 ] | https://en.wikipedia.org/wiki/Saprotrophic_nutrition |
System Activity Report ( sar ) is a Unix System V -derived system monitor command used to report on various system loads, including CPU activity, memory/paging, interrupts, device load, network and swap space utilization. Sar uses / proc filesystem for gathering information. [ 2 ]
Sar was originally developed for the Unix System V operating system; it is available in AIX, HP-UX, Solaris and other System V based operating systems but it is not available for macOS or FreeBSD. Prior to 2013 there was a bsdsar tool, but it is now deprecated. [ 3 ]
Most Linux distributions provide sar utility through the sysstat package.
Additional to sar command, Linux sysstat package in Debian, [ 4 ] RedHat Enterprise Linux and SuSE provides additional reporting tools: | https://en.wikipedia.org/wiki/Sar_(Unix) |
Sara Rietti ( Buenos Aires , 3 December 1930 – Buenos Aires, 28 May 2017), also known as Sara Bartfeld de Rietti , was the first nuclear chemist from Argentina. She was Chief of Staff of the Ministry of Science and Technology during the government of President Raúl Alfonsín . [ 1 ]
Rietti began studying chemistry in 1948 after she had finished her secondary education, graduating in 1954 with her degree in nuclear chemistry. She took her last course at the National Atomic Energy Commission in 1953, a fact that by chance allowed her to be the first nuclear chemist in Argentina. Her thesis was titled Study of the reaction between diboron tetrachloride and diborane. Boranes are chemical compounds known as boron hydrides. These materials cannot receive air or humidity. Because they have to always remain cold, she had to constantly monitor her compounds, including on weekends when she went to her laboratory with her children. In 1963, she finally obtained her doctorate from UBA. [ 2 ] [ 3 ] [ 4 ]
Rietti worked as a researcher at various Argentine universities and state agencies including the Department of Inorganic Chemistry and Physicochemistry at the University of Buenos Aires between 1955 and 1956. She was also a member of the board of directors of the Faculty of Exact and Natural Sciences of the University of Buenos Aires (UBA), where she witnessed the country's security forces breaking into the university during the events known as the Night of the Long Canes on 29 July 1966. [ 2 ] [ 4 ]
On that night, after police detained about 400 intellectuals, Sara and her husband Víctor moved from one police station to the next to free their colleagues from jail. As a result of the nationwide repression, numerous laboratories and libraries were destroyed and many scientists and academics were exiled or fled the country. Sara and Victor decided to remain in Argentina. [ 2 ] [ 4 ]
Rietti worked at the Latin American Publishing Center as director of the Scientific Collection between 1967 and 1969 and served on the board of that publisher between 1972 and 1992. Between 1973 and 1975, she was the coordination director of the National Institute of Industrial Technology . [ 2 ]
In 1983, when science was again allowed to flourish in Argentina, the mathematician Manuel Sadosky appointed her Chief of Staff of the Secretary of Science and Technology, over which he presided, and in 1994 she was appointed academic coordinator of the Graduate Policy and Management of Science and Technology at the UBA. She was also a teacher advisor to the Rectorate there, a position she held until the end of her life. [ 2 ]
Her mother was of Polish descent and her father was Ukrainian. He encouraged her in the sciences when he noticed her abilities in mathematics. Although she preferred philosophy, history or political science, she ultimately followed her father's advice because she had a cousin who had already graduated as a chemist.
While studying at the university, she met Víctor Rietti but was reluctant to establish a personal relationship with him because he was too young and they only saw each other at the university. At his insistence, they got married in 1952, had three children and sixty years later they were still together. [ 4 ] | https://en.wikipedia.org/wiki/Sara_Rietti |
The Sarah Berliner Research Fellowship for Women was established in 1908 by Emile Berliner in honor of his mother, and first awarded in 1909. The fellowship was award biennially and provided $1200 to support a woman studying physics, chemistry, or biology in either America or Europe. The fellowship was open to women holding the degree of doctor of philosophy or otherwise capable of conducting higher research. The first chair of the awarding committee was Christine Ladd-Franklin , [ 1 ] who was also instrumental in the establishment of the fellowship. [ 2 ] In 1911, an increase in funding meant that the fellowship could be offered every year. [ 3 ] | https://en.wikipedia.org/wiki/Sarah_Berliner_Research_Fellowship |
Sarah Elaine B. Petrie is a Canadian and American physical chemist who worked for the research laboratories of Eastman Kodak and became known for her research on the thermal properties of glasses , polymers , and liquid crystals .
Petrie earned a Ph.D. in chemistry in 1957 from the University of Toronto , with the dissertation Dielectric behaviour of vapours adsorbed on porous and non-porous adsorbents , supervised by Robert L. McIntosh. [ 1 ] By the same year she was working for the Kodak Research Laboratories. [ 2 ] In 1977 she was appointed to a panel on polymers in the National Bureau of Standards and as an advisor to the office of chemistry and chemical technology of the National Research Council . [ 3 ] She also served as a councilor to the American Chemical Society Division of Polymer Chemistry from 1979 to 1981. [ 4 ] By 1994, when she served on the Committee on Polymer Science and Engineering of the National Research Council, she was listed as retired from Kodak. [ 5 ]
In 1976, Petrie was named a Fellow of the American Physical Society (APS), after a nomination from the APS Division of Polymer Physics. [ 6 ] | https://en.wikipedia.org/wiki/Sarah_E._Petrie |
Sarah Elizabeth Whitin (born April 18, 1836, died Dec 26, 1917 [ 1 ] ) was sole benefactor of the Whitin Observatory , which she had built on the campus of Wellesley College near Boston. [ 2 ]
She was born Sarah Elizabeth Pratt , daughter of a physician in Hopkinton, Mass. In her childhood, Sarah Elizabeth was fascinated by the stars and on dark nights, would spread out a blanket in the open and, armed with an atlas, would lie in the dark with friends and identify constellations. [ 3 ]
On January 20, 1875, when she was almost 39 years old, Sarah became the second wife of the industrialist John Crane Whitin (1807–1882), owner of the Whitin Machine Works in Whitinsville, Massachusetts . John was almost 30 years her senior and died only seven years later. [ 4 ] After his passing, Sarah was "left with large means" and traveled extensively. [ 3 ]
Sarah Elizabeth Whitin was elected to the Wellesley College Board of Trustees in 1896 and immediately took a keen interest in campus activities, especially the study of astronomy. [ 1 ] In 1896, she became engaged in conversation with the college's first professor of physics and astronomy, Sarah Frances Whiting (they had very similar names but were not related). At the time, the college only had a portable telescope measuring 4 inches, which could be put on a porch roof of College Hall for celestial observations. [ 2 ]
At a campus gathering, Professor Whiting mentioned to Mrs. Whitin that there was a 12-inch refracting telescope still in use in the Olmstead Observatory "which had suddenly become available at a bargain price." Professor Whiting had used the telescope when she taught in Brooklyn, N.Y. and encouraged its purchase for use at a new Wellesley observatory. [ 2 ]
In response to Professor Whiting's suggestions for a new observatory, Whitin wrote "You need not feel that you have made extravagant suggestions. It is only the carrying out of my own ideas as they become broader... My ideas are now way ahead of the little observatory or of my bank account, else it would be far better than it will be!" [ 2 ] [ 5 ]
As told in Wellesley College 1875–1975: A Century of Women, the telescope was bought in 1899. [ 5 ]
In the fall of 1898 [Whitin] proposed to give, and the Trustees voted to accept with gratitude, "a [12-inch] telescope and a simple building to house the instrument." Then at a Trustees meeting the following May, "Mrs. Whitin stated that she now proposes to construct the Observatory of white marble in place of brick." When it was formally opened on October 8, 1900, [President] Hazard could report that it housed "a 12" refractor with micrometer, polarizing photometer, and star and sun spectroscopes. A Rowland concave grating spectroscope, of 6' focus, with its accompanying heliostat , is set up in a room capable of being darkened completely. The library is a beautiful room, and the dome by Warner and Swasey is all that it should be." [ 2 ] [ 5 ]
When the observatory opened October 8, 1900, Professor Whiting became its first director [ 5 ] [ 6 ] and the college received "congratulatory letters from famous women astronomers in Europe." [ 2 ] At the time Professor Whiting described it as "the finest student observatory in the country." [ 5 ] The benefactor was heavily involved in the design of the facility, including the choice of white marble, and the selection of equipment. She also had strong opinions about the floor covering to be placed in the laboratory saying "it will be good for the girls to put their feet on an India rug." [ 2 ] [ 5 ] [ 6 ]
Soon after completion of the observatory, Professor Whiting began exploring plans for an expansion and went back to Mrs. Whitin, as she wrote in the trustee's obituary, which appeared in The Wellesley College News. [ 3 ]
"I knew from the first that it was not large enough for the kind of work we wished to do, and that the nearest college residence hall was too far off for the astronomical staff to be present for the nightly vigil with the stars. Mrs. Whitin herself soon perceived this and of her own initiative began to think of an Observatory House, and an enlargement to the Observatory itself. The beauty and costliness of what was already done seemed difficult to match. Various compromise building materials for the addition were discussed, but after many consultations with the architect, she declared that "marble and copper were good enough," and by 1906 the observatory was doubled with increased equipment, and a house placed beside it, completing a harmonious group, and itself a lovely specimen of domestic architecture." [ 3 ]
Whitin Observatory strategic events, according to Wellesley College archives, follow. [ 2 ] [ 5 ]
In addition to her efforts at the college, Whitin was a board member, and generous supporter, of the Baldwinsville Hospital for the Feeble Minded, for which she built a large school building, as well as the Hospital for the Insane in Worcester, Massachusetts . [ 3 ]
Sarah Elizabeth Whitin remained an active Wellesley Trustee until her illness the last two years of her life. She died on December 26, 1917. [ 1 ] She is buried with her husband (and his first wife) in Pine Grove Cemetery, Whitinsville. [ 4 ] | https://en.wikipedia.org/wiki/Sarah_Elizabeth_Whitin |
Sarah Glaz (born 1947) [ 1 ] is a mathematician and mathematical poet. [ 2 ] Her research specialty is commutative algebra ; she is a professor emeritus of mathematics at the University of Connecticut .
Glaz was born in Bucharest , Romania , and earned a bachelor's degree in 1972 at Tel Aviv University , Israel . [ 3 ] She came to the US for her graduate education in mathematics, completing a Ph.D. in 1977 at Rutgers University . Her dissertation, Finiteness and Differential Properties of Ideals , was supervised by Wolmer Vasconcelos. [ 3 ] [ 4 ]
After postdoctoral research at Case Western Reserve University , Glaz became an assistant professor at Wesleyan University in 1980. She moved to George Mason University in 1988, and again to the University of Connecticut in 1989. She retired as a professor emeritus in 2017. [ 3 ]
Glaz is the author of a book on commutative algebra , Commutative Coherent Rings (Lecture Notes in Mathematics 1371, Springer, 1989). [ 5 ] She is an editor of several other books on commutative algebra. [ 3 ]
In 2017 she published a book of her mathematical poetry named after a poem by Pablo Neruda , Ode to Numbers (Antrim House, 2017). [ 6 ] Her book was a finalist for the 2018 Next Generation Indie Book Awards . [ 7 ]
She is also the editor of an anthology of mathematical poems, Strange Attractors: Poems of Love and Mathematics (with JoAnne Growney, AK Peters/CRC Press, 2008), [ 8 ] and has published translations of poems into English from
Romanian, Portuguese, German, Sanskrit, Sumerian, and Russian. [ 3 ] | https://en.wikipedia.org/wiki/Sarah_Glaz |
In mathematics complex analysis , the Sarason interpolation theorem , introduced by Sarason ( 1967 ), is a generalization of the Caratheodory interpolation theorem and Nevanlinna–Pick interpolation .
This mathematical analysis –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Sarason_interpolation_theorem |
Saratoga Water, also known as Saratoga Spring Water and Saratoga, is a bottled-water company founded in 1872 in Saratoga Springs, New York . [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] Saratoga Spring Water is sold in sparkling and still versions in a cobalt-blue bottle. [ 2 ] [ 6 ] Saratoga Water is a brand of BlueTriton Brands . [ 7 ]
In 1872 a group of Saratoga-based businessmen looking to take advantage of Saratoga’s famous healing waters began bottling a newly discovered spring under the name “ Saratoga Vichy ,” named after the mineral springs of Vichy , France. [ 5 ] [ 8 ]
In 1903, the French Republic sued the Saratoga Water company in French Republic v. Saratoga Vichy Spring Co., over the use of the Vichy name. [ 9 ] The court ruled on behalf of the American company. [ 9 ]
In the mid-1980s, Saratoga Water was bought by Anheuser-Busch . [ 5 ] Evian bought the company from Anheuser-Busch. [ 5 ] Evian shut down the local bottling plant. [ 5 ] [ 3 ] In 2001, Adam Madkour Sr. and a group of local investors purchased the company and re-opened the plant. [ 5 ] In 2021, the brand was sold to BlueTriton Brands. [ 7 ]
In a 2023 New York Times Magazine article titled "The Make-Do Joys of Terrazzo", artist duo Ficus Interfaith describe using the royal blue glass of Saratoga Water bottles as one of the materials they use to make their terrazzo art works. [ 10 ]
In 2024, Saratoga Water launched a line of aluminum bottles . Packaging is among several of the company growth priorities, according to CEO Joey Bergstein. [ 11 ]
In 2025, the brand went viral online after social media influencer Ashton Hall featured the water in his “Morning Routine” videos. [ 12 ] | https://en.wikipedia.org/wiki/Saratoga_Water |
6345
106393
ENSG00000185739
ENSMUSG00000022519
Q86TD4
Q7TQ48
NM_001098814 NM_001323667 NM_001323668
NM_175347 NM_001347162 NM_001361474
NP_001092284 NP_001310596 NP_001310597
NP_001334091 NP_780556 NP_001348403
Sarcalumenin is a protein that in humans is encoded by the SRL gene . [ 5 ] [ 6 ]
Sarcalumenin is a calcium-binding protein that can be found in the sarcoplasmic reticulum of striated muscle . [ 7 ] Sarcalumenin is partially responsible for calcium buffering in the lumen of the sarcoplasmic reticulum and helps out calcium pump proteins. [ 8 ] Additionally, sarcalumenin is necessary for keeping a normal sinus rhythm during both aerobic and anaerobic exercise activity. [ 7 ] Sarcalumenin is a calcium-binding glycoprotein composed of 473 acidic amino acids with a molecular weight of 160 KDa. Together along with other luminal calcium buffer proteins, sarcalumenin plays an important role in regulation of calcium uptake and release during excitation-contraction coupling (ECC) in muscle fibers.
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Sarcalumenin |
Sarcopenia ( ICD-10-CM code M62.84 [ 1 ] ) is a type of muscle loss that occurs with aging and/or immobility . It is characterized by the degenerative loss of skeletal muscle mass, quality, and strength. The rate of muscle loss is dependent on exercise level, co-morbidities, nutrition and other factors. The muscle loss is related to changes in muscle synthesis signalling pathways. It is distinct from cachexia , in which muscle is degraded through cytokine -mediated degradation, although the two conditions may co-exist. Sarcopenia is considered a component of frailty syndrome . [ 2 ] Sarcopenia can lead to reduced quality of life, falls, fracture, and disability. [ 3 ] [ 4 ]
Sarcopenia is a factor in changing body composition . When associated with aging populations, certain muscle regions are expected to be affected first, specifically the anterior thigh and abdominal muscles. [ 3 ] [ 5 ] In population studies, body mass index (BMI) is seen to decrease in aging populations while bioelectrical impedance analysis (BIA) shows body fat proportion rising. [ 6 ]
The hallmark sign of sarcopenia is loss of lean muscle mass, or muscle atrophy . The change in body composition may be difficult to detect due to obesity , changes in fat mass, or edema . Changes in weight, limb, or waist circumference are not reliable indicators of muscle mass changes. Sarcopenia may also cause reduced strength, functional decline and increased risk of falling. Sarcopenia may also have no symptoms until it is severe and is often unrecognized. [ 2 ] Hypertrophy may occur in the upper parts of the body to compensate for this loss of lean muscle mass. [ 3 ] [ 7 ] An early indicator for the onset of sarcopenia can be significant loss of muscle mass in the anterior thigh and abdominal muscles. [ 3 ]
There are many proposed causes of sarcopenia and it is likely the result of multiple interacting factors. Understanding of the causes of sarcopenia is incomplete, however, changes in hormones, immobility, age-related muscle changes, nutrition, and neurodegenerative changes have all been recognized as potential causative factors. [ 8 ]
The degree of sarcopenia is determined by two factors: the initial amount of muscle mass and the rate at which muscle mass declines. Due to variations in these factors across the population, the rate of progression and the threshold at which muscle loss becomes apparent is variable. [ 9 ] Immobility dramatically increases the rate of muscle loss, even in younger people. Other factors that can increase the rate of progression of sarcopenia include decreased nutrient intake, low physical activity, or chronic disease. [ 2 ] Additionally, epidemiological research has indicated that early environmental influences may have long-term effects on muscle health. For example, low birth weight, a marker of a poor early environment, is associated with reduced muscle mass and strength in adult life. [ 10 ] [ 11 ] [ 12 ]
There are multiple theories proposed to explain the mechanisms of muscle changes of sarcopenia including changes in myosatellite cell recruitment, changes in anabolic signaling, protein oxidation, inflammation, and developmental factors. The pathologic changes of sarcopenia include a reduction in muscle tissue quality as reflected in the replacement of muscle fibers with fat, an increase in fibrosis , changes in muscle metabolism, oxidative stress , and degeneration of the neuromuscular junction . [ 13 ] The failure to activate satellite cells upon injury or exercise is also thought to contribute to the pathophysiology of sarcopenia. [ 13 ] Additionally, oxidized proteins can lead to a buildup of lipofuscin and cross-linked proteins causing an accumulation of non-contractile material in the skeletal muscle and contribute to sarcopenic muscle. [ 9 ]
In sarcopenic muscle the distribution of the types of muscle fibers changes with a decrease in type II muscle fibers , or "fast twitch," with little to no decrease in type I muscle fibers , or "slow-twitch" muscle fibers. Deinervated type II fibers are often converted to type I fibers by reinnervation by slow type I fiber motor nerves. [ 14 ] Males are perhaps more susceptible for this aging-related switching of the myofiber type, as a recent research has shown a higher percentage of "slow twitch" muscle fibers in old compared to young males, but not in old compared to young females. [ 15 ]
Aging sarcopenic muscle shows an accumulation of mitochondrial DNA mutations , which has been demonstrated in various other cell types as well. [ 16 ] Clones with mitochondrial mutations build up in certain regions of the muscle, which goes along with an about fivefold increase in the absolute mtDNA copy number, that is, these regions are denser. [ 17 ] An apparent protective factor preventing cells' buildup of damaged mitochondria is sufficient levels of the protein BNIP3 . Deficiency of BNIP3 leads to muscle inflammation and atrophy. [ 18 ]
Furthermore, not every muscle is as susceptible to the atrophic effects of aging. For example, in both humans [ 19 ] and mice [ 20 ] it has been shown that lower leg muscles are not as susceptible to aging as upper leg muscles. This could perhaps be explained by the differential distribution of myofiber type within each muscle group, but this is unknown. [ citation needed ]
Multiple diagnostic criteria have been proposed by various expert groups and continues to be an area of research and debate. Despite the lack of a widely accepted definition, sarcopenia was assigned an ICD-10 code (M62.84) in 2016, recognizing it as a disease state. [ 21 ]
Sarcopenia can be diagnosed when a patient has muscle mass that is at least two standard deviations below the relevant population mean and has a slow walking speed . [ 22 ] The European Working Group on Sarcopenia in Older People (EWGSOP) developed a broad clinical definition for sarcopenia, designated as the presence of low muscle mass and either low muscular strength or low physical performance. [ 8 ] Other international groups have proposed criteria that include metrics on walking speed, distance walked in 6 minutes, or grip strength . [ 21 ] Hand grip strength alone has also been advocated as a clinical marker of sarcopenia that is simple and cost effective and has good predictive power, although it does not provide comprehensive information. [ 23 ]
There are screening tools for sarcopenia that assess patient reported difficulty in doing daily activities such as walking, climbing stairs or standing from a chair and have been shown to predict sarcopenia and poor functional outcomes. [ 24 ]
As sarcopenia is a complex clinical diagnosis, circulating biomarkers have been proposed as proxies for early diagnosis and prediction as well as for follow-up and serial assessment of response to interventions.
Aging and sarcopenia are associated with an increase in inflammatory markers ("inflamm-aging") including: C-reactive protein , tumor necrosis factor , interleukin-8 , interleukin-6 , granulocyte-monocyte colony-stimulating factor , interferons , and serine protease A1 . [ 25 ]
Changes in hormones associated with aging and sarcopenia include a reduction in the sex-hormones testosterone and dehydroepiandrosterone sulfate , [ 26 ] as well as reduced levels of circulating growth hormone and IGF-1 . [ 27 ]
Circulating C-terminal agrin fragments (CAF) have been found to be higher in accelerated sarcopenic patients. [ 28 ]
Lower plasma levels of the amino acids leucine and isoleucine as well as other essential amino acids were found in frail older people compared to non-frail controls. [ 29 ] [ 30 ]
Alanine aminotransferase (ALT) is responsible for the transfer of the α-amino group from an α-amino acid to an α-keto acid, transforming pyruvate to alanine in skeletal muscle. Low circulating ALT is a marker for low muscle mass and sarcopenia, [ 31 ] as well for increased disease activity in patients with inflammatory bowel disease . [ 32 ]
Exercise remains the intervention of choice for sarcopenia, but translation of research findings into clinical practice is challenging. The type, duration and intensity of exercise are variable between studies, preventing a standardized exercise prescription for sarcopenia. [ 33 ] Lack of exercise is a significant risk factor for sarcopenia and exercise can dramatically slow the rate of muscle loss. [ 34 ] Exercise can be an effective intervention because aging skeletal muscle retains the ability to synthesize proteins in response to short-term resistance exercise. [ 35 ] Progressive resistance training in older adults can improve physical performance (gait speed) and muscular strength. [ 36 ] [ 37 ] [ 38 ] Increased exercise can produce greater numbers of cellular mitochondria, increase capillary density, and increase the mass and strength of connective tissue. [ 39 ]
There are currently no approved medications for the treatment of sarcopenia. [ 40 ] Testosterone or other anabolic steroids have also been investigated for treatment of sarcopenia, and seem to have some positive effects on muscle strength and mass, but cause several side effects and raise concerns of prostate cancer in men and virilization in women. [ 41 ] [ 42 ] Additionally, recent studies suggest testosterone treatments may induce adverse cardiovascular events. [ 43 ] [ 44 ] [ 45 ]
DHEA and human growth hormone have been shown to have little to no effect in this setting. Growth hormone increases muscle protein synthesis and increases muscle mass, but does not lead to gains in strength and function in most studies. [ 41 ] This, and the similar lack of efficacy of its effector insulin-like growth factor 1 (IGF-1), may be due to local resistance to IGF-1 in aging muscle, resulting from inflammation and other age changes. [ 41 ]
Other medications under investigation as possible treatments for sarcopenia include ghrelin , vitamin D , angiotensin converting enzyme inhibitors , and eicosapentaenoic acid . [ 41 ] [ 42 ]
Intake of calories and protein are important stimuli for muscle protein synthesis. [ 46 ] Older adults may not utilize protein as efficiently as younger people and may require higher amounts to prevent muscle atrophy. [ 22 ] A number of expert groups have proposed an increase in dietary protein recommendations for older age groups to 1.0–1.2 g/kg body weight per day. [ 47 ] [ 48 ] Ensuring adequate nutrition in older adults is of interest in the prevention of sarcopenia and frailty, since it is a simple, low-cost treatment approach without major side effects. [ 49 ]
A component of sarcopenia is the loss of ability for aging skeletal muscle to respond to anabolic stimuli such as amino acids , especially at lower concentrations. However, aging muscle retains the ability of an anabolic response to protein or amino acids at larger doses. Supplementation with larger doses of amino acids, particularly leucine has been reported to counteract muscle loss with aging. [ 50 ] Exercise may work synergistically with amino acid supplementation. [ 40 ]
β-hydroxy β-methylbutyrate (HMB) is a metabolite of leucine that acts as a signalling molecule to stimulate protein synthesis. [ 22 ] [ 40 ] It is reported to have multiple targets, including stimulating mTOR and decreasing proteasome expression. Its use to prevent the loss of lean body mass in older adults is consistently supported in clinical trials. [ 51 ] [ 52 ] [ 53 ] More research is needed to determine the precise effects of HMB on muscle strength and function in this age group. [ 52 ]
The prevalence of sarcopenia depends on the definition used in each epidemiological study. Estimated prevalence in people between the ages of 60 and 70 is 5–13% and increases to 11–50% in people more than 80 years of age. This equates to >50 million people and is projected to affect >200 million in the next 40 years given the rising population of older adults. [ 8 ]
Sarcopenia is emerging as a major public health concern given the increased longevity of industrialized populations and growing geriatric population. Sarcopenia is a predictor of many adverse outcomes including increased disability, falls and mortality. [ 54 ] [ 55 ] Immobility or bed rest in populations predisposed to sarcopenia can cause dramatic impact on functional outcomes. In the elderly, this often leads to decreased biological reserve and increased vulnerability to stressors known as the " frailty syndrome ". Loss of lean body mass is also associated with increased risk of infection, decreased immunity, and poor wound healing. The weakness that accompanies muscle atrophy leads to higher risk of falls, fractures, physical disability, need for institutional care, reduced quality of life, increased mortality, and increased healthcare costs. [ 22 ] This represents a significant personal and societal burden and its public health impact is increasingly recognized. [ 8 ]
The term sarcopenia stems from Greek σάρξ sarx , "flesh" and πενία penia , "poverty". This was first proposed by Rosenberg in 1989, who wrote that "there may be no single feature of age-related decline that could more dramatically affect ambulation, mobility, calorie intake, and overall nutrient intake and status, independence, breathing, etc". [ citation needed ]
Sarcopenia is distinct from cachexia , in which muscle is degraded through cytokine -mediated degradation, although the two conditions may co-exist. [ citation needed ]
There are significant opportunities to better understand the causes and consequences of sarcopenia and help guide clinical care. This includes elucidation of the molecular and cellular mechanisms of sarcopenia, further refinement of reference populations by ethnic groups, validation of diagnostic criteria and clinical tools, as well as tracking of incidence of hospitalization admissions, morbidity, and mortality. Identification and research on potential therapeutic approaches and timing of interventions is also needed. [ 56 ]
As of 2020 [update] , there are no drugs approved to treat muscle wasting in people with chronic diseases, and there is therefore an unmet need for anabolic drugs with few side effects. One aspect hindering drug approval for treatments for cachexia and sarcopenia is disagreement in endpoints. Several clinical trials have found that selective androgen receptor modulators (SARMs) improve lean mass in humans, but it is not clear whether strength and physical function are also improved. After promising results in a phase II trial, a phase III trial of the SARM ostarine was proven to increase lean body mass but did not show significant improvement in function. [ 57 ] It and other drugs—such as the growth hormone secretagogue anamorelin —have been refused regulatory approval despite significant increases in lean mass due to a lack of evidence that they increased physical performance. Preventing decline in functionality was not considered an acceptable endpoint by the Food and Drug Administration . It is not known how SARMs interact with dietary protein intake and resistance training in people with muscle wasting. [ 58 ] [ 59 ] | https://en.wikipedia.org/wiki/Sarcopenia |
The sarcoplasmic reticulum ( SR ) is a membrane -bound structure found within muscle cells that is similar to the smooth endoplasmic reticulum in other cells . The main function of the SR is to store calcium ions (Ca 2+ ). Calcium ion levels are kept relatively constant, with the concentration of calcium ions within a cell being 10,000 times smaller than the concentration of calcium ions outside the cell. [ 1 ] This means that small increases in calcium ions within the cell are easily detected and can bring about important cellular changes (the calcium is said to be a second messenger ). Calcium is used to make calcium carbonate (found in chalk) and calcium phosphate , two compounds that the body uses to make teeth and bones . This means that too much calcium within the cells can lead to hardening ( calcification ) of certain intracellular structures, including the mitochondria , [ 2 ] leading to cell death. Therefore, it is vital that calcium ion levels are controlled tightly, and can be released into the cell when necessary and then removed from the cell.
The sarcoplasmic reticulum is a network of the tubules that extend throughout muscle cells , wrapping around (but not in direct contact with) the myofibrils (contractile units of the cell). Cardiac and skeletal muscle cells contain structures called transverse tubules (T-tubules) , which are extensions of the cell membrane that travel into the centre of the cell. T-tubules are closely associated with a specific region of the SR, known as the terminal cisternae in skeletal muscle, with a distance of roughly 12 nanometers , separating them. This is the primary site of calcium release. [ 3 ] The longitudinal SR are thinner projects, that run between the terminal cisternae/junctional SR, and are the location where ion channels necessary for calcium ion absorption are most abundant. [ 4 ] These processes are explained in more detail below and are fundamental for the process of excitation-contraction coupling in skeletal , cardiac and smooth muscle .
The SR contains ion channel pumps , within its membrane that are responsible for pumping Ca 2+ into the SR. As the calcium ion concentration within the SR is higher than in the rest of the cell, the calcium ions will not freely flow into the SR, and therefore pumps are required, that use energy, which they gain from a molecule called adenosine triphosphate (ATP) . These calcium pumps are called Sarco(endo)plasmic reticulum Ca 2+ ATPases (SERCA) . There are a variety of different forms of SERCA, with SERCA 2a being found primarily in cardiac and skeletal muscle. [ 5 ]
SERCA consists of 13 structural elements (labelled M1-M10 α-helices in the transmembrane domain, and N, P and A citosolic domains). Calcium ions bind to the M1-M10 transmembrane region, whereas ATP binds to the N domain. When 2 calcium ions, along with a molecule of ATP, bind to the cytosolic side of the pump (i.e. the region of the pump outside the SR), the pump opens. This occurs because ATP (which contains three phosphate groups ) releases a single phosphate group (becoming adenosine diphosphate ). The released phosphate group then binds to the pump (in the P domain), causing the pump to change shape. This shape change causes the cytosolic side of the pump to open, allowing the two Ca 2+ to enter. The cytosolic side of the pump then closes and the sarcoplasmic reticulum side opens, releasing the Ca 2+ into the SR. [ 6 ]
A protein found in cardiac muscle, called phospholamban (PLB) has been shown to prevent SERCA from working. It does this by binding to the SERCA and decreasing its attraction (affinity) to calcium, therefore preventing calcium uptake into the SR. Failure to remove Ca 2+ from the cytosol, prevents muscle relaxation and therefore means that there is a decrease in muscle contraction too. However, molecules such as adrenaline and noradrenaline , can prevent PLB from inhibiting SERCA. When these hormones bind to a receptor, called a beta 1 adrenoceptor , located on the cell membrane, they produce a series of reactions (known as a cyclic AMP pathway ) that produces an enzyme called protein kinase A (PKA) . PKA can add a phosphate to PLB (this is known as phosphorylation), preventing it from inhibiting SERCA and allowing for muscle relaxation. [ 7 ]
Located within the SR is a protein called calsequestrin . This protein can bind to around 50 Ca 2+ , which decreases the amount of free Ca 2+ within the SR (as more is bound to calsequestrin). [ 8 ] Therefore, more calcium can be stored (the calsequestrin is said to be a buffer). It is primarily located within the junctional SR/ luminal space , in close association with the calcium release channel (described below). [ 9 ]
Calcium ion release from the SR, occurs in the junctional SR/ terminal cisternae through a ryanodine receptor (RyR) and is known as a calcium spark . [ 10 ] There are three types of ryanodine receptor, RyR1 (in skeletal muscle ), RyR2 (in cardiac muscle ) and RyR3 (in the brain ). [ 11 ] Calcium release through ryanodine receptors in the SR is triggered differently in different muscles. In cardiac and smooth muscle an electrical impulse ( action potential ) triggers calcium ions to enter the cell through an L-type calcium channel located in the cell membrane (smooth muscle) or T-tubule membrane (cardiac muscle). These calcium ions bind to and activate the RyR, producing a larger increase in intracellular calcium. In skeletal muscle, however, the L-type calcium channel is bound to the RyR. Therefore, activation of the L-type calcium channel, via an action potential, activates the RyR directly, causing calcium release (see calcium sparks for more details). [ 12 ] Also, caffeine (found in coffee) can bind to and stimulate RyR. Caffeine makes the RyR more sensitive to either the action potential (skeletal muscle) or calcium (cardiac or smooth muscle), thereby producing calcium sparks more often (this is partially responsible for caffeine's effect on heart rate). [ 13 ]
Triadin and Junctin are proteins found within the SR membrane, that are bound to the RyR. The main role of these proteins is to anchor calsequestrin (see above) to the ryanodine receptor. At ‘normal’ (physiological) SR calcium levels, calsequestrin binds to the RyR, Triadin and Junctin, which prevents the RyR from opening. [ 14 ] If calcium concentration within the SR falls too low, there will be less calcium bound to the calsequestrin. This means that there is more room on the calsequestrin, to bind to the junctin, triadin and ryanodine receptor, therefore it binds tighter. However, if calcium within the SR rises too high, more calcium binds to the calsequestrin and therefore it binds to the junctin-triadin-RyR complex less tightly. The RyR can therefore open and release calcium into the cell. [ 15 ]
In addition to the effects that PKA had on phospholamban (see above) that resulted in increased relaxation of the cardiac muscle, PKA (as well as another enzyme called calmodulin kinase II ) can also phosphorylate ryanodine receptors. When phosphorylated, RyRs are more sensitive to calcium, therefore they open more often and for longer periods of time. This increases calcium release from the SR, increasing the rate of contraction. [ 16 ] Therefore, in cardiac muscle , activation of PKA , through the cyclic AMP pathway , results in increased muscle contraction (via RyR2 phosphorylation) and increased relaxation (via phospholamban phosphorylation), which increases heart rate.
The mechanism behind the termination of calcium release through the RyR is still not fully understood. Some researchers believe it is due to the random closing of ryanodine receptors (known as stochastic attrition), or the ryanodine receptors becoming inactive after a calcium spark, [ 17 ] while others believe that a decrease in SR calcium, triggers the receptors to close (see calcium sparks for more details).
The breakdown of the sarcoplasmic reticulum, along with the resultant release of calcium, is an important contributor to rigor mortis , the stiffening of muscles after death.
An increase in calcium concentration in the sarcoplasm can also cause muscle stiffness. | https://en.wikipedia.org/wiki/Sarcoplasmic_reticulum |
In mathematics , Sard's theorem , also known as Sard's lemma or the Morse–Sard theorem , is a result in mathematical analysis that asserts that the set of critical values (that is, the image of the set of critical points ) of a smooth function f from one Euclidean space or manifold to another is a null set , i.e., it has Lebesgue measure 0. This makes the set of critical values "small" in the sense of a generic property . The theorem is named for Anthony Morse and Arthur Sard .
More explicitly, [ 1 ] let
be C k {\displaystyle C^{k}} , (that is, k {\displaystyle k} times continuously differentiable ), where k ≥ max { n − m + 1 , 1 } {\displaystyle k\geq \max\{n-m+1,1\}} . Let X ⊂ R n {\displaystyle X\subset \mathbb {R} ^{n}} denote the critical set of f , {\displaystyle f,} which is the set of points x ∈ R n {\displaystyle x\in \mathbb {R} ^{n}} at which the Jacobian matrix of f {\displaystyle f} has rank < m {\displaystyle <m} . Then the image f ( X ) {\displaystyle f(X)} has Lebesgue measure 0 in R m {\displaystyle \mathbb {R} ^{m}} .
Intuitively speaking, this means that although X {\displaystyle X} may be large, its image must be small in the sense of Lebesgue measure: while f {\displaystyle f} may have many critical points in the domain R n {\displaystyle \mathbb {R} ^{n}} , it must have few critical values in the image R m {\displaystyle \mathbb {R} ^{m}} .
More generally, the result also holds for mappings between differentiable manifolds M {\displaystyle M} and N {\displaystyle N} of dimensions m {\displaystyle m} and n {\displaystyle n} , respectively. The critical set X {\displaystyle X} of a C k {\displaystyle C^{k}} function
consists of those points at which the differential
has rank less than m {\displaystyle m} as a linear transformation. If k ≥ max { n − m + 1 , 1 } {\displaystyle k\geq \max\{n-m+1,1\}} , then Sard's theorem asserts that the image of X {\displaystyle X} has measure zero as a subset of M {\displaystyle M} . This formulation of the result follows from the version for Euclidean spaces by taking a countable set of coordinate patches. The conclusion of the theorem is a local statement, since a countable union of sets of measure zero is a set of measure zero, and the property of a subset of a coordinate patch having zero measure is invariant under diffeomorphism .
There are many variants of this lemma, which plays a basic role in singularity theory among other fields. The case m = 1 {\displaystyle m=1} was proven by Anthony P. Morse in 1939, [ 2 ] and the general case by Arthur Sard in 1942. [ 1 ]
A version for infinite-dimensional Banach manifolds was proven by Stephen Smale . [ 3 ]
The statement is quite powerful, and the proof involves analysis. In topology it is often quoted — as in the Brouwer fixed-point theorem and some applications in Morse theory — in order to prove the weaker corollary that “a non-constant smooth map has at least one regular value”.
In 1965 Sard further generalized his theorem to state that if f : N → M {\displaystyle f:N\rightarrow M} is C k {\displaystyle C^{k}} for k ≥ max { n − m + 1 , 1 } {\displaystyle k\geq \max\{n-m+1,1\}} and if A r ⊆ N {\displaystyle A_{r}\subseteq N} is the set of points x ∈ N {\displaystyle x\in N} such that d f x {\displaystyle df_{x}} has rank strictly less than r {\displaystyle r} , then the r -dimensional Hausdorff measure of f ( A r ) {\displaystyle f(A_{r})} is zero. [ 4 ] In particular the Hausdorff dimension of f ( A r ) {\displaystyle f(A_{r})} is at most r . Caveat: The Hausdorff dimension of f ( A r ) {\displaystyle f(A_{r})} can be arbitrarily close to r . [ 5 ] | https://en.wikipedia.org/wiki/Sard's_theorem |
In coding theory , the Sardinas–Patterson algorithm is a classical algorithm for determining in polynomial time whether a given variable-length code is uniquely decodable, named after August Albert Sardinas and George W. Patterson, who published it in 1953. [ 1 ] The algorithm carries out a systematic search for a string which admits two different decompositions into codewords. As Knuth reports, the algorithm was rediscovered about ten years later in 1963 by Floyd , despite the fact that it was at the time already well known in coding theory. [ 2 ]
Consider the code { a ↦ 1 , b ↦ 011 , c ↦ 01110 , d ↦ 1110 , e ↦ 10011 } {\displaystyle \{\,a\mapsto 1,b\mapsto 011,c\mapsto 01110,d\mapsto 1110,e\mapsto 10011\,\}} . This code, which is based on an example by Berstel, [ 3 ] is an example of a code which is not uniquely decodable, since the string
can be interpreted as the sequence of codewords
but also as the sequence of codewords
Two possible decodings of this encoded string are thus given by cdb and babe .
In general, a codeword can be found by the following idea: In the first round, we choose two codewords x 1 {\displaystyle x_{1}} and y 1 {\displaystyle y_{1}} such that x 1 {\displaystyle x_{1}} is a prefix of y 1 {\displaystyle y_{1}} , that is, x 1 w = y 1 {\displaystyle x_{1}w=y_{1}} for some "dangling suffix" w {\displaystyle w} . If one tries first x 1 = 011 {\displaystyle x_{1}=011} and y 1 = 01110 {\displaystyle y_{1}=01110} , the dangling suffix is w = 10 {\displaystyle w=10} . If we manage to find two sequences x 2 , … , x p {\displaystyle x_{2},\ldots ,x_{p}} and y 2 , … , y q {\displaystyle y_{2},\ldots ,y_{q}} of codewords such that x 2 ⋯ x p = w y 2 ⋯ y q {\displaystyle x_{2}\cdots x_{p}=wy_{2}\cdots y_{q}} , then we are finished: For then the string x = x 1 x 2 ⋯ x p {\displaystyle x=x_{1}x_{2}\cdots x_{p}} can alternatively be decomposed as y 1 y 2 ⋯ y q {\displaystyle y_{1}y_{2}\cdots y_{q}} , and we have found the desired string having at least two different decompositions into codewords.
In the second round, we try out two different approaches: the first trial is to look for a codeword that has w as prefix. Then we obtain a new dangling suffix w' , with which we can continue our search. If we eventually encounter a dangling suffix that is itself a codeword (or the empty word ), then the search will terminate, as we know there exists a string with two decompositions. The second trial is to seek for a codeword that is itself a prefix of w . In our example, we have w = 10 {\displaystyle w=10} , and the sequence 1 is a codeword. We can thus also continue with w'=0 as the new dangling suffix.
The algorithm is described most conveniently using quotients of formal languages . In general, for two sets of strings D and N , the (left) quotient N − 1 D {\displaystyle N^{-1}D} is defined as the residual words obtained from D by removing some prefix in N . Formally, N − 1 D = { y ∣ x y ∈ D and x ∈ N } {\displaystyle N^{-1}D=\{\,y\mid xy\in D~{\textrm {and}}~x\in N\,\}} . Now let C {\displaystyle C} denote the (finite) set of codewords in the given code.
The algorithm proceeds in rounds, where we maintain in each round not only one dangling suffix as described above, but the (finite) set of all potential dangling suffixes. Starting with round i = 1 {\displaystyle i=1} , the set of potential dangling suffixes will be denoted by S i {\displaystyle S_{i}} . The sets S i {\displaystyle S_{i}} are defined inductively as follows:
S 1 = C − 1 C ∖ { ε } {\displaystyle S_{1}=C^{-1}C\setminus \{\varepsilon \}} . Here, the symbol ε {\displaystyle \varepsilon } denotes the empty word .
S i + 1 = C − 1 S i ∪ S i − 1 C {\displaystyle S_{i+1}=C^{-1}S_{i}\cup S_{i}^{-1}C} , for all i ≥ 1 {\displaystyle i\geq 1} .
The algorithm computes the sets S i {\displaystyle S_{i}} in increasing order of i {\displaystyle i} . As soon as one of the S i {\displaystyle S_{i}} contains a word from C or the empty word, then the algorithm terminates and answers that the given code is not uniquely decodable. Otherwise, once a set S i {\displaystyle S_{i}} equals a previously encountered set S j {\displaystyle S_{j}} with j < i {\displaystyle j<i} , then the algorithm would enter in principle an endless loop. Instead of continuing endlessly, it answers that the given code is uniquely decodable.
Since all sets S i {\displaystyle S_{i}} are sets of suffixes of a finite set of codewords, there are only finitely many different candidates for S i {\displaystyle S_{i}} . Since visiting one of the sets for the second time will cause the algorithm to stop, the algorithm cannot continue endlessly and thus must always terminate . More precisely, the total number of dangling suffixes that the algorithm considers is at most equal to the total of the lengths of the codewords in the input, so the algorithm runs in polynomial time as a function of this input length. By using a suffix tree to speed the comparison between each dangling suffix and the codewords, the time for the algorithm can be bounded by O( nk ), where n is the total length of the codewords and k is the number of codewords. [ 4 ] The algorithm can be implemented using a pattern matching machine. [ 5 ] The algorithm can also be implemented to run on a nondeterministic Turing machine that uses only logarithmic space ; the problem of testing unique decipherability is NL-complete , so this space bound is optimal. [ 6 ]
A proof that the algorithm is correct , i.e. that it always gives the correct answer, is found in the textbooks by Salomaa [ 7 ] and by Berstel et al. [ 8 ] | https://en.wikipedia.org/wiki/Sardinas–Patterson_algorithm |
The KwaZulu-Natal sardine run of southern Africa occurs from May through July when billions of sardines – or more specifically the Southern African pilchard Sardinops sagax – spawn in the cool waters of the Agulhas Bank and move northward along the east coast of South Africa . Their sheer numbers create a feeding frenzy along the coastline .
The run, containing millions of individual sardines, occurs when a current of cold water heads north from the Agulhas Bank up to Mozambique where it then leaves the coastline and goes further east into the
Fisherman are sometimes observed singing songs while hauling in the fishing nets in typical South African style. It is estimated that the sardine run is the biggest Biomass migration in terms of numbers.
In terms of biomass , researchers estimate the sardine run could rival East Africa's great wildebeest migration. [ 1 ] However, little is known of the phenomenon. It is believed that the water temperature has to drop below 21 °C in order for the migration to take place. In 2003, the sardines failed to 'run' for the third time in 23 years. While 2005 saw a good run, 2006 marked another non-run. [ 2 ]
The shoals are often more than 7 km long, 1.5 km wide and 30 metres deep and are clearly visible from spotter planes or from the surface.
Sardines group together when they are threatened. This instinctual behaviour is a defence mechanism, as lone individuals are more likely to be eaten than when in large groups.
The sardine run is still poorly understood from an ecological point of view.
There have been various hypotheses, sometimes contradictory, that try to explain why and how the run occurs.
A recent interpretation of the causes [ 3 ] is that the sardine run is most likely a seasonal reproductive migration of a genetically distinct subpopulation of sardine that moves along the coast from the eastern Agulhas Bank to the coast of KwaZulu-Natal in most years if not in every year.
Genomic and transcriptomic data indicate that the sardines participating in the run originate from South Africa's cool-temperate Atlantic coast. [ 4 ] These are attracted to temporary cold-water upwelling off the south-east coast, and eventually find themselves trapped in subtropical habitat that is too warm for them.
The migration is restricted to the inshore waters by the preference of sardine for cooler water and the strong and warm offshore Agulhas Current, which flows in the opposite direction to the migration, and is strongest just off the continental shelf.
A band of cooler coastal water and the occurrence of Natal Pulses and break-away eddies make it possible for sardine shoals to overcome their habitat constraints. The importance of these enabling factors is greatest where the continental shelf is narrowest.
The presence of eggs off the KwaZulu-Natal coast suggests that sardine stay there for several months and their return migration during late winter to spring is nearly always unnoticeable because it probably occurs at depths where the water is cooler than at the surface.
In some years there does not appear to be a sardine run. This may be because it is not detected by coastal observers either because it actually does not occur due to high water temperatures and/or other hydrographic barriers, or the migration may occur farther offshore and possibly deeper due to unusual conditions.
Sardine prefer water temperatures between 14 and 20 °C. [ 5 ] Each southern winter the nearshore sea temperature along the South African south east coast drops to within this range. Along the KwaZulu-Natal coast, sardine may be found in water warmer than 20 °C.
It was hypothesized that factors beside temperature may influence the movement of sardine along the KwaZulu-Natal coastline, One of these factors may be predation pressure.
The KwaZulu-Natal coast includes varied oceanographic regions, each influenced by distinct environmental forces. [ 6 ]
These distinct regions may affect sardine distribution and movement.
Some oceanographic variables have been found useful for describing conditions influencing sardine presence. [ 6 ]
Other conditions associated with sardine presence are: [ 6 ]
Favourable:
Unfavourable:
North-easterly and north-westerly winds and north to south currents have a cooling effect upon nearshore sea surface temperatures, but south-easterly winds and increasing air temperatures cause nearshore sea surface temperature warming.
Dolphins (estimated as being up to 18,000 in number, mostly the common dolphin ( Delphinus capensis )) are largely responsible for rounding up the sardines into bait balls. These bait balls can be 10–20 metres in diameter and extend to a depth of 10 metres. The bait balls are short lived and seldom last longer than 10 minutes. Once the sardines are rounded up, sharks (primarily the bronze whaler ), and birds (like the Cape gannet ), and Bryde's whales take advantage of the opportunity. Other whale species, regardless of whether they do or not join the run, may appear in the vicinity such as humpback , southern right , and minke whales . [ 8 ] [ 9 ]
The Cape gannet is the predator species most closely associated with sardine presence along the Eastern Cape and KwaZulu-Natal coastline and is the most useful indicator of sardine run activity.
Sharks and large gamefish presence is also strongly associated with sardine presence during the run, but as they are not as easily observed from the surface they are not as useful a predictor of sardine presence.
The presence of common dolphins inshore along the east coast during winter is significantly associated with sardine presence, and the common dolphin can be considered the third most useful species for predicting sardine presence.
The resident population of bottlenose dolphin does not appear to associate with the sardine run, whereas the migrant stock does. This may explain why the bottlenose dolphin is less likely to predict sardine presence. [ 6 ]
2005 records :
In June and July 2005 the avian and mammal predators included Bryde’s whale ( Balaenoptera edeni ), African penguin ( Spheniscus demersus ), Cape cormorant ( Phalacrocorax capensis ), which were predominantly found in the cooler southern part of the region.
Peak sardine run activity occurred within 4 km of shore at the northward limit of a strip of cool water (<21 °C) stretching along the East Coast. The principal predators at this stage were common dolphins ( Delphinus capensis ) and Cape gannets ( Morus capensis ). [ 10 ]
The recent interest in the sardine run has had significant impact on the local economy. International and domestic divers join local tour operators on sardine run diving expeditions. Such expeditions run from Eastern Cape towns, including East London , Port Saint Johns, and Port Elizabeth. The run has become important to tourism and is considered to be one of the main attractions in KwaZulu-Natal during the winter holiday period. Both local and international tourists are attracted to the spectacle and are provided with opportunities to participate in activities such as dive charters and boat based predator viewing tours.
The KwaZulu-Natal Sharks Board and East Coast Radio, facilitate a ‘Sardine Run Hotline’, which provides information on the position and movement of sardine shoals. Information is also provided on the internet. [ 11 ]
The Sardine Run Association (www.thesardinerunassociation.org) has been formed to provide a link between tour operators , tourists, non-governmental organisations,
scientists, and local and national governments.
The sardine run also supports a small-scale, seasonal beach seine fishery.
The oldest known record of the run is a mention in the Natal Mercury newspaper of 4 August 1853.
More recently, the run has been the subject of natural history documentaries (e.g., the BBC’s Nature's Great Events ) and printed popular media
(e.g., National Geographic ). [ 11 ]
Pilot shoals were netted at Hibberdene on 20 June 2011, while the main shoal was sighted near Port St. Johns . Small pockets of sardines were seen between Mfazazana and Margate . About 25 crates of sardines were hauled out from the first netting at Hibberdene. [ 12 ] A further 33 crates of sardines were netted and were sold at R700 per crate or R30 per dozen sardines. The 58 crates were sold "within minutes". [ 13 ] An attempt was also made to net sardines at Banana Beach . About 500 common dolphins and numerous sharks were noted near Margate. Shark nets had been removed between Umgababa and Port Edward . [ 12 ]
Sardines were netted at Park Rynie on 21 June 2011. Some large nets of 200–300 baskets of sardines were taken. The baskets sold at R600 each. A large gathering of sardine predators was seen off Port Grosvenor on the Wild Coast . Thousands of Cape gannets and dolphins were seen in a continuous line of about 6 km between Brazen Head and just north of the Umtata River . It is suspected that this year's shoal is "massive", and will produce a "bumper run". Shark nets have been removed to the south of Durban . The first shoals were expected to reach Amanzimtoti on 23 June 2011. [ 14 ] The main shoal was still near Port St Johns. [ 15 ]
On 22 June 2011, a "few" baskets were netted at Umgababa beach, and a "handful" of baskets were netted at Warner Beach in the afternoon. Sardines were also netted at Isipingo , where 14 baskets were hauled out. The sardines therefore reached the Amanzimtoti area a day earlier than predicted. [ 16 ]
Rough seas (with waves up to 4.7 m) caused by strong winds associated with a cold front kept the sardines from the shore on 23 June 2011. Pockets of sardines were seen far out to sea off the Bluff . The rough water and far distance of the sardines from shore made it impossible for the fish to be netted. No dolphin or bird activity was seen in the Durban area associated with the sardines. The main shoal was still suspected to be off the Eastern Cape coastline, [ 17 ] with a report of some sardines still seen near Port St Johns on 22 and 23 June 2011. [ 18 ]
Durban beaches were the scene of most netting activity on 27 June 2011. "Hundreds of baskets" of sardines were hauled onto the beaches in 13 nets. The price per basket was R350 in the morning, but later in the afternoon the price had dropped to R120 per basket. [ 19 ] Each net contained in excess of 300 baskets of sardines, with one net containing around 500 baskets. [ 20 ] Sardines were also netted at Umhlanga , Port Shepstone , Margate, Umgababa, and Port Edward . Cape gannets and other seabirds were seen "plunging from considerable heights" to catch the sardines, especially on the South Coast. [ 21 ] Most of the sardines were netted along the Durban beaches as this was the area of calmest waters; swells along the KwaZulu-Natal coastline were around 2.5 m. [ 22 ] Shark nets had been removed from Salt Rock to Port Edward, and bathers were requested to consult with lifeguards before entering the water. [ 20 ] Meanwhile, a baby dolphin washed up on the beach at Scottburgh , with a gash behind its "flipper" (the photo showed a gash between the dorsal fin and the tail) that exposed the spine. The "weeks old" dolphin was taken to a nearby paddling pool, but authorities later euthanased it due to the severity of the injuries. [ 23 ] Speculation was that the dolphin had been injured by a shark, or by a boat propeller; possibly related to the sardine run.
Swells dropped to 1–1.5 m on 28 June 2011, allowing more netting of sardines. Sardines were netted at Amanzimtoti; on the main beach and at Chain Rocks . [ 22 ] A 22-year-old American marine biology student (research diver) named Paulo Edward Stanchi was attacked by a large dusky shark while diving at Aliwal Shoal Marine Protected Area . The group of divers had encountered a pocket of sardines when a 3 m long dusky shark bit Mr Stanchi on his left leg and hands. Mr Stanchi managed to free himself from the shark, and was treated on the diving boat before being transported to Rocky Bay , where medics stabilised him. He was then airlifted to Nkosi Albert Luthuli Hospital , where he underwent surgery. Dusky sharks generally live offshore, but come closer to the shore during the sardine run. The annual sardine run allowed more dusky sharks in the Aliwal Shoal MPA than usual, but there was no reason for them to show any more interest in divers than usual. Mr Stanchi had been wearing split fins with black and grey stripes, and this may have looked like a small shoal of fish to the shark. [ 24 ] [ 25 ] Meanwhile, a woman in her 40s broke her leg in the frenzy at Amanzimtoti when the sardines were netted. The woman is believed to have been trying to get some of the sardines when she "stepped wrong" and fractured her leg. Paramedics stabilized her before transporting her to hospital. [ 26 ]
5 July 2011 was a "quiet day" for the sardine run. "Plenty of birds" were seen diving at Karridene close to the shore. 50 crates of sardines were taken at Umgababa in the early afternoon, while a net of sardines pulled in at Karridene contained some Garrick . More Garrick were caught by fishermen at Karridene, but in general there was little other game fish activity. There was reported to be a "massive shoal" of sardines off Coffee Bay in the Eastern Cape. [ 27 ]
On 15 July 2011, 100 baskets were netted at Pennington . It was difficult to predict the sardines' movements as they were staying offshore. [ 28 ]
On 20 July 2011, 300 baskets of sardines were netted at Pennington in the morning. There were many gannets off Ballito , and "quite a bit of fish" between Park Rynie and Mtwalume. [ 29 ]
A strong cold front hit South Africa towards the end of July, causing land surface temperatures to drop below 10 °C over much of the country. [ 30 ] Heavy snow falls were experienced in high lying areas, including Nottingham Road , Mooi River and Newcastle in the Midlands, while Van Reenen’s Pass was snowed in. [ 31 ] The cold front caused swells of up to 4 meters on the KwaZulu-Natal coast and a 25 to 30 knot wind with rough sea conditions. [ 32 ] A ship called the Phoenix ran aground at Salt Rock, Ballito on 26 July 2011 because of the rough conditions. [ 32 ] This cold front may have put an end to the 2011 Sardine Run.
The 2023 run has been estimated as being the biggest on observed records to date. | https://en.wikipedia.org/wiki/Sardine_run |
Sarepta Therapeutics, Inc. is a medical research and drug development company with corporate offices and research facilities in Cambridge, Massachusetts , United States. Incorporated in 1980 as AntiVirals , [ 2 ] shortly before going public the company changed its name from AntiVirals to AVI BioPharma soon with stock symbol AVII and in July 2012 changed name from AVI BioPharma to Sarepta Therapeutics and SRPT respectively. [ 3 ] As of 2023, the company has four approved drugs (see the Products section below).
Sarepta started in Corvallis, Oregon on January 1, 1980 and was originally named Antivirals Inc. [ 4 ] After occupying several research laboratory spaces in Corvallis, the company opened a production laboratory in Corvallis in February 2002 and was renamed AVI BioPharma Inc. [ 5 ] The company made headlines in 2003 when it announced work on treatments for severe acute respiratory syndrome (SARS) and the West Nile virus . [ 5 ] [ 6 ] In July 2009, the company announced they would move their headquarters from Portland, Oregon , north to Bothell, Washington , near Seattle . [ 7 ] At that time, the company led by president and CEO Leslie Hudson had 83 employees and quarterly revenues of $3.2 million. [ 7 ] AVI had yet to turn a profit and had not yet developed any commercial products as of July 2009. [ 7 ] The company lost $19.7 million in the second quarter of 2009, [ 8 ] and then won an $11.5 million contract with the U.S. Department of Defense 's Defense Threat Reduction Agency in October 2009. [ 9 ] By this time, the company had completed its headquarters move to Bothell. [ 7 ] [ 9 ]
In 2012, the company moved a second time, to Cambridge, Massachusetts. At the time, CEO Chris Garabedian indicated the move was motivated by the need to recruit expertise in rare diseases . [ 10 ] The Corvallis laboratory facility was closed in 2016. The company opened a new Genetic Therapies Center of Excellence in Columbus, Ohio in October, 2021 in order to dramatically advance research into therapeutics for several muscular dystrophies that had begun at Nationwide Children's Hospital several years earlier. [ 11 ]
In June 2017, Sarepta Therapeutics appointed former Allergan executive Doug Ingram as its new CEO to replace Edward Kaye who had announced plans to step down earlier that year. [ 12 ]
In February 2019, Sarepta acquired five gene therapy candidates for $165 million after one of them, MYO-101, produced results with a new gene therapy candidate for patients with Limb-Girdle muscular dystrophy ; two months after receiving a single treatment, muscles from all three patients were producing the protein they couldn't make on their own. [ 13 ]
As of 2022, there are three FDA-approved Duchenne muscular dystrophy drugs in Sarepta Therapeutics' portfolio. [ 14 ] In January 2023, Sarepta partnered with Catalent to manufacture delandistrogene moxeparvovec (SRP-9001). [ 15 ] [ 16 ] [ 17 ]
In June 2023, the FDA approved Sarepta Therapeutics’ fourth therapy, delandistrogene moxeparvovec-rokl, the first gene therapy to treat Duchenne muscular dystrophy (DMD). The product was approved under the accelerated approval pathway for 4-5 year olds with a confirmed DMD diagnosis. Accelerated approval requires that the product be studied further to verify its clinical benefit. [ 18 ]
Its primary products are based on Morpholino oligomers (PMOs), synthetic nucleic acid analogs that were conceived of by James Summerton and invented by Summerton with Dwight Weller, originally developed under the name NeuGene Antisense. Since morpholino oligomers can form sequence-specific double-stranded complexes with RNA they are suitable use in antisense therapy . In one application, translation blocking, a morpholino oligomer binds to messenger RNA produced by a known disease-causing gene to prevent it from being translated into protein. Morpholinos can also work as splice-switching oligos , targeting pre-mRNA to alter splicing and so causing changes in the structure of the mature mRNA (the mechanism of the approved drug eteplirsen). Morpholinos have been tested for a wide range of applications including prevention of cardiac restenosis after angioplasty , treatment of coronary artery bypass grafts, treatment of polycystic kidney disease, redirection of drug metabolism, treatment of some mutations causing Duchenne muscular dystrophy (DMD) , and inhibition of infectious diseases. Their greatest clinical and commercial success thus far has been in the treatment of DMD. A new class of Morpholino oligos, the peptide-linked Morpholinos or PPMO, are linked to an arginine-rich cell-penetrating peptide to enhance their delivery into cells and have entered clinical trials [ 19 ]
The Morpholino drug eteplirsen , targeting exon 51 of the dystrophin mRNA, was approved as a human therapeutic by the FDA in 2016 [ 20 ] and antisense oligonucleotides for Morpholinos targeting other exons are also subsequently approved. [ 21 ] Morpholinos have been used in preclinical studies to inhibit replication of a broad range of viruses, including influenza , West Nile virus , SARS , hepatitis C , dengue fever , Ebola and Calicivirus , all of which are single stranded RNA viruses . They are in advanced development for prevention and treatment of Ebola and Marburg viruses . In March 2013, the Company announced positive results from a non-human primate study of AVI-7288, the drug candidate for treatment of Marburg virus infection. The results showed that intramuscular administration of AVI-7288 resulted in survival rates up to 100 percent in monkeys exposed to this fatal virus. These results are similar to those in previous studies when the drug was given by intravenous injection. [ 22 ]
In December 2019, golodirsen (Vyondys 53) received US FDA approval [ 23 ] for the treatment of cases that can benefit from skipping exon 53 of the dystrophin transcript. The other approved PMO developed by Sarepta is casimersen (AMONDYS45) which is indicated for the treatment of DMD in patients amendable by exon 45 skipping. [ 24 ]
In addition to development of Morpholinos as therapeutics, AVI has conducted six human trials for colorectal and pancreatic cancers using their cancer vaccine AVICINE .
In 2019, Sarepta signed a licensing agrement with Roche for the development, and commercialization outside of USA, for SRP-9001 . [ 25 ] In June 2023, ELEVIDYS (Delandistrogene moxeparvovec) was approved by the FDA for use in 4-5 year old boys with mutations in the DMD gene. [ 26 ] [ 27 ] [ 28 ] The FDA granted accelerated approval to ELEVIDYS, which requires that the product be further studied to verify its clinical benefit. [ 28 ] [ 29 ]
In June 2024, the U.S. Food and Drug Administration expanded approval of delandistrogene moxeparvovec to include individuals with Duchenne muscular dystrophy with a confirmed mutation in the DMD gene who are at least 4 years of age. The FDA granted traditional approval for non-ambulatory patients and accelerated approval for non-ambulatory patients. [ 30 ] | https://en.wikipedia.org/wiki/Sarepta_Therapeutics |
The Sarett oxidation is an organic reaction that oxidizes primary and secondary alcohols to aldehydes and ketones , respectively, using chromium trioxide and pyridine . Unlike the similar Jones oxidation , the Sarett oxidation will not further oxidize primary alcohols to their carboxylic acid form, neither will it affect carbon-carbon double bonds. [ 1 ] Use of the original Sarett oxidation has become largely antiquated however, in favor of other modified oxidation techniques. The unadulterated reaction is still occasionally used in teaching settings and in small scale laboratory research. [ 2 ]
The reaction is named after the American chemist Lewis Hastings Sarett (1917–1999). The first description of its use appears in a 1953 article [ 3 ] co-authored by Sarett that relates to the synthesis of adrenal steroids . The paper proposes the use of the pyridine chromium complex CrO 3 -2C 5 H 5 N to oxidize primary and secondary alcohols. The complex would later become known as the "Sarett Reagent".
Although the Sarett reagent gives good yields of ketones, its conversion of primary alcohols is less efficient. Furthermore, the isolation of products from the reaction solution can be difficult. [ 4 ] These limitations were partially addressed with the introduction of the Collins oxidation . [ 4 ] The active ingredient in both the Sarett reagent is identical to that in the so-called " Collins reagent ", i.e. the pyridine complex (CrO 3 (C 5 H 5 N) 2 . The Collins oxidation varies from the Sarett oxidation only in that it uses methylene chloride as solvent instead of neat pyridine. [ 4 ] The initially proposed methods of executing the Collins and Sarett oxidations were still not ideal however, as the Sarett reagent's hygroscopic , and pyrophoric properties make it difficult to prepare. [ 5 ] This issues lead to an improvement of the Collins oxidation protocol known as the Ratcliffe variant. [ 5 ] [ 6 ]
The Sarett reagent was originally prepared in 1953 by addition of chromium trioxide to pyridine. [ 3 ] The pyridine must be cooled because the reaction is dangerously exothermic. Slowly, the brick-red CrO 3 transform into the bis(pyridine) adduct. Subsequent to the conversion to the Sarett reagent, it is immediately used. [ 3 ]
The specific methods of the reagent's preparation are critical, as improper technique can cause the explosion of the materials. [ 6 ] Some technical improvements to the original methodology have reduced the risks associated with preparation. One such recent improvement reduced the likelihood of explosion by using chromic anhydride granules that would immediately sink below the surface of the cooled pyridine upon addition. [ 2 ] It should also be mentioned that chromium trioxide is a corrosive carcinogen and therefore must be handled with extreme care. [ 7 ]
The original Collins oxidation calls for the Sarett reagent to be removed from the excess pyridine and dissolved in the less basic methylene chloride. [ 4 ] [ 6 ] While the new solvent improves the overall yield of the reaction, it also requires the dangerous transfer of the pyrophoric reagent. The 1970 Ratcliffe variation reduced the risk of explosion by calling for the Sarett reagent to be made in situ . This was achieved by creating the Sarett reagent according to the original protocol using a stirred mixture of pyridine and methylene chloride. [ 5 ]
The Sarett oxidation efficiently oxidizes primary alcohols to aldehydes without further oxidizing them to carboxylic acids. [ 6 ] This key difference from the Jones oxidation is that the Jones oxidation occurs in the presence of water, which adds to the alcohol following oxidation to an aldehyde. [ 6 ] [ 8 ] The Sarett and Collins oxidations occur in the absence of water. [ 6 ] The Sarett oxidation also proceeds under basic conditions , which allows for the use of acid sensitive substrates, such as those containing certain protecting groups . This is dissimilar to other common acidic oxidation reactions such as the Baeyer-Villiger oxidation , which would remove or alter such groups. Additionally, the Sarett reagent is relatively inert towards double bonds and thioether groups. [ 3 ] These groups cannot effectively interact with the chromium of the Sarett reagent, as compared to the chromium in oxidizing complexes used prior to 1953. [ 3 ] | https://en.wikipedia.org/wiki/Sarett_oxidation |
Saridegib , also known as IPI-926 , is an experimental drug candidate undergoing clinical trials for the treatment of various types of cancer, including hard-to-treat hematologic malignancies such as myelofibrosis and ligand-dependent tumors such as chondrosarcoma . [ 1 ] IPI-926 exhibits its pharmacological effect by inhibition of the G protein-coupled receptor smoothened , a component of the hedgehog signaling pathway . [ 2 ] Chemically, it is a semi-synthetic derivative of the alkaloid cyclopamine . The process begins with cyclopamine extracted from harvested Veratrum californicum which is taken through a series of alterations resulting in an analogue of the natural product cyclopamine, making IPI-926 the only compound in development/testing that is not fully synthetic. [ 2 ]
Saridegib is a member of a class of anti-cancer compounds known as hedgehog pathway inhibitors . [ citation needed ] | https://en.wikipedia.org/wiki/Saridegib |
Sarin ( NATO designation GB [short for G-series , "B"]) is an extremely toxic organophosphorus compound . [ 4 ] that has been often used as a chemical weapon due to its extreme potency as a nerve agent .
Sarin is a volatile, colorless and odorless liquid. Exposure can be lethal even at very low concentrations, and death can occur within one to ten minutes after direct inhalation of a lethal dose, [ 5 ] [ 6 ] due to suffocation from respiratory paralysis , unless antidotes are quickly administered. [ 4 ] People who absorb a non-lethal dose and do not receive immediate medical treatment may suffer permanent neurological damage. [ citation needed ]
Sarin is widely considered a weapon of mass destruction . Production and stockpiling of sarin was outlawed as of April 1997 by the Chemical Weapons Convention of 1993, and it is classified as a Schedule 1 substance .
Like some other nerve agents that affect the neurotransmitter acetylcholine , sarin attacks the nervous system by interfering with the degradation of the neurotransmitter acetylcholine at neuromuscular junctions . Death usually occurs as a result of asphyxia due to the inability to control the muscles involved in breathing. [ 7 ]
Initial symptoms following exposure to sarin are a runny nose , tightness in the chest, and constriction of the pupils (miotic action). Soon after, the person will have difficulty breathing and experience nausea and drooling. This progresses to losing control of bodily functions, which may cause the person to vomit, defecate, and urinate. This phase is followed by twitching and jerking. Ultimately, the person becomes comatose and suffocates in a series of convulsive spasms . Common mnemonics for the symptomatology of organophosphate poisoning, including sarin, are the "killer Bs" of bronchorrhea and bronchospasm because they are the leading cause of death, [ 8 ] and SLUDGE – salivation, lacrimation , urination, defecation, gastrointestinal distress, and emesis (vomiting). Death may follow in one to ten minutes after direct inhalation, but may also occur after a delay ranging from hours to several weeks, in cases where exposure is limited but no antidote is applied. [ 7 ]
Sarin has a high volatility (ease with which a liquid can turn into vapour) relative to similar nerve agents, making inhalation very easy, and may even absorb through the skin. A person's clothing can release sarin for about 30 minutes after it has come in contact with sarin gas, which can lead to exposure of other people. [ 9 ]
Treatment measures have been described. [ 9 ] Treatment is typically with the antidotes atropine and pralidoxime . [ 4 ] Atropine, an antagonist to muscarinic acetylcholine receptors , is given to treat the physiological symptoms of poisoning. Since muscular response to acetylcholine is mediated through nicotinic acetylcholine receptors , atropine does not counteract the muscular symptoms. Pralidoxime can regenerate cholinesterases if administered within approximately five hours. Biperiden , a synthetic acetylcholine antagonist , has been suggested as an alternative to atropine due to its better blood–brain barrier penetration and higher efficacy. [ 10 ]
Sarin is a potent inhibitor of acetylcholinesterase , [ 11 ] an enzyme that degrades the neurotransmitter acetylcholine after it is released into the synaptic cleft . In vertebrates, acetylcholine is the neurotransmitter used at the neuromuscular junction, where signals are transmitted between neurons from the peripheral nervous system to muscle fibres. Normally, acetylcholine is released from the neuron to stimulate the muscle, after which it is degraded by acetylcholinesterase , allowing the muscle to relax. A build-up of acetylcholine in the synaptic cleft , due to the inhibition of acetylcholinesterase, means the neurotransmitter continues to act on the muscle fibre, so that any nerve impulses are effectively continually transmitted.
Sarin acts on acetylcholinesterase by forming a covalent bond with the particular serine residue at the active site. Fluoride is the leaving group , and the resulting organo-phosphoester is robust and biologically inactive . [ 12 ] [ 13 ]
Its mechanism of action resembles that of some commonly used insecticides , such as malathion . In terms of biological activity, it resembles carbamate insecticides, such as Sevin , and the medicines pyridostigmine , neostigmine , and physostigmine .
Controlled studies in healthy men have shown that a nontoxic 0.43 mg oral dose administered in several portions over a 3-day interval caused average maximum depressions of 22 and 30%, respectively, in plasma and erythrocyte acetylcholinesterase levels. A single acute 0.5 mg dose caused mild symptoms of intoxication and an average reduction of 38% in both measures of acetylcholinesterase activity. Sarin in blood is rapidly degraded either in vivo or in vitro . Its primary inactive metabolites have in vivo serum half-lives of approximately 24 hours. The serum level of unbound isopropyl methylphosphonic acid (IMPA), a sarin hydrolysis product, ranged from 2–135 μg/L in survivors of a terrorist attack during the first four hours post-exposure. Sarin or its metabolites may be determined in blood or urine by gas or liquid chromatography , while acetylcholinesterase activity is usually measured by enzymatic methods. [ 14 ]
A newer method called "fluoride regeneration" or "fluoride reactivation" detects the presence of nerve agents for a longer period after exposure than the methods described above. Fluoride reactivation is a technique that has been explored since at least the early 2000s. This technique obviates some of the deficiencies of older procedures. Sarin not only reacts with the water in the blood plasma through hydrolysis (forming so-called 'free metabolites'), but also reacts with various proteins to form 'protein adducts'. These protein adducts are not so easily removed from the body, and remain for a longer period of time than the free metabolites. One clear advantage of this process is that the period, post-exposure, for determination of sarin exposure is much longer, possibly five to eight weeks according to at least one study. [ 15 ] [ 16 ]
As a nerve gas, sarin in its purest form is estimated to be 26 times more deadly than cyanide . [ 17 ] The LD 50 of subcutaneously injected sarin in mice is 172 μg/kg. [ 18 ]
Sarin is highly toxic, whether by contact with the skin or breathed in. The toxicity of sarin in humans is largely based on calculations from studies with animals. The lethal concentration of sarin in air is approximately 28–35 mg per cubic meter per minute for a two-minute exposure time by a healthy adult breathing normally (exchanging 15 liters of air per minute, lower 28 mg/m 3 value is for general population). [ 19 ] This number represents the estimated lethal concentration for 50% of exposed victims, the LCt 50 value. The LCt 95 or LCt 100 value is estimated to be 40–83 mg per cubic meter for exposure time of two minutes. [ 20 ] [ 21 ] Calculating effects for different exposure times and concentrations requires following specific toxic load models. In general, brief exposures to higher concentrations are more lethal than comparable long time exposures to low concentrations. [ 22 ] There are many ways to make relative comparisons between toxic substances. The list below compares sarin to some current and historic chemical warfare agents, with a direct comparison to the respiratory LCt 50 :
Sarin is a chiral molecule because it has four chemically distinct substituents attached to the tetrahedral phosphorus center. [ 25 ] The S P form (the (–) optical isomer ) is the more active enantiomer due to its greater binding affinity to acetylcholinesterase . [ 26 ] [ 27 ] The P-F bond is easily broken by nucleophilic agents, such as water and hydroxide. At high p H , sarin decomposes rapidly to nontoxic phosphonic acid derivatives. [ 28 ]
It is almost always manufactured as a racemic mixture (a 1:1 mixture of its enantiomeric forms) as this involves a much simpler synthesis while providing an adequate weapon. [ 26 ] [ 27 ]
A number of production pathways can be used to create sarin. The final reaction typically involves attachment of the isopropoxy group to the phosphorus with an alcoholysis with isopropyl alcohol . Two variants of this final step are common. One is the reaction of methylphosphonyl difluoride with isopropyl alcohol, which produces a racemic mixture of sarin enantiomers with hydrofluoric acid as a byproduct: [ 28 ]
The second process, known as the "Di-Di" process, uses equimolar quantities of methylphosphonyl difluoride (Difluoro) and methylphosphonyl dichloride (Dichloro). This reaction gives sarin, hydrochloric acid and others minors byproducts. The Di-Di process was used by the United States for the production of its unitary sarin stockpile. [ 28 ]
The scheme below shows a generic example that employs the Di-Di method as the final esterification step; in reality, the selection of reagents and reaction conditions dictate both product structure and yield. The choice of enantiomer of the mixed chloro fluoro intermediate displayed in the diagram is arbitrary, but the final substitution is selective for chloro over fluoro as the leaving group . Inert atmosphere and anhydrous conditions ( Schlenk techniques ) are used for synthesis of sarin and other organophosphates. [ 28 ]
As both reactions leave considerable acid in the product, sarin produced in bulk by these methods has a short half life without further processing, and would be corrosive to containers and damaging to weapons systems. Various methods have been tried to resolve these problems. In addition to industrial refining techniques to purify the chemical itself, various additives have been tried to combat the effects of the acid, such as:
Another byproduct of these two chemical processes is diisopropyl methylphosphonate , formed when a second isopropyl alcohol reacts with the sarin itself and from disproportionation of sarin, when distilled incorrectly. The factor of its formation in esterification is that as the concentration of DF-DCl decreases, the concentration of sarin increases, the probability of DIMP formation is greater. DIMP is a natural impurity of sarin, that is almost impossible to be eliminated, mathematically, when the reaction is a 1 mol-1 mol "one-stream". [ 35 ]
This chemical degrades into isopropyl methylphosphonic acid. [ 36 ]
The most important chemical reactions of phosphoryl halides is the hydrolysis of the bond between phosphorus and the fluorine atom. This P-F bond is easily broken by nucleophilic agents, such as water and hydroxide . At high pH , sarin decomposes rapidly to nontoxic phosphonic acid derivatives. [ 37 ] [ 38 ] The initial breakdown of sarin is into isopropyl methylphosphonic acid (IMPA), a chemical that is not commonly found in nature except as a breakdown product of sarin (this is useful for detecting the recent deployment of sarin as a weapon). IMPA then degrades into methylphosphonic acid (MPA), which can also be produced by other organophosphates. [ 39 ]
Sarin with residual acid degrades after a period of several weeks to several months. The shelf life can be shortened by impurities in precursor materials . According to the CIA , some Iraqi sarin had a shelf life of only a few weeks, owing mostly to impure precursors. [ 40 ]
Along with nerve agents such as tabun and VX , sarin can have a short shelf life. Therefore, it is usually stored as two separate precursors that produce sarin when combined. [ 41 ] Sarin's shelf life can be extended by increasing the purity of the precursor and intermediates and incorporating stabilizers such as tributylamine . In some formulations, tributylamine is replaced by diisopropylcarbodiimide (DIC), allowing sarin to be stored in aluminium casings. In binary chemical weapons , the two precursors are stored separately in the same shell and mixed to form the agent immediately before or when the shell is in flight. This approach has the dual benefit of solving the stability issue and increasing the safety of sarin munitions.
Sarin was discovered in 1938 in Wuppertal -Elberfeld in Germany by scientists at IG Farben who were attempting to create stronger pesticides; it is the most toxic of the four G-Series nerve agents made by Germany. The compound, which followed the discovery of the nerve agent tabun , was named in honor of its discoverers: chemist Gerhard S chrader , chemist Otto A mbros , chemist Gerhard R itter [ de ] , and from Heereswaffenamt Hans-Jürgen von der L in de. [ 42 ]
In mid-1939, the formula for the agent was passed to the chemical warfare section of the German Army Weapons Office , which ordered that it be brought into mass production for wartime use. Pilot plants were built, and a production facility was under construction (but was not finished) by the end of World War II . Estimates for total sarin production by Nazi Germany range from 500 kg to 10 tons. [ 43 ]
Though sarin, tabun , and soman were incorporated into artillery shells, Germany did not use nerve agents against Allied targets. Adolf Hitler refused to initiate the use of gases such as sarin as weapons. [ 44 ] | https://en.wikipedia.org/wiki/Sarin |
Sarking is an English word with multiple meanings in roof construction:
In New Zealand, both corrugated metal and asbestos-cement shingle roofs were fitted directly over wooden sarking boards in the historical "bungalow" style of house construction. [ 2 ] [ 3 ] | https://en.wikipedia.org/wiki/Sarking |
In biology , a stolon ( / ˈ s t oʊ l ɒ n / from Latin stolō , genitive stolōnis – "branch"), also known as a runner , is a horizontal connection between parts of an organism. It may be part of the organism, or of its skeleton . Typically, animal stolons are exoskeletons (external skeletons).
In botany , stolons are plant stems which grow at the soil surface or just below ground that form adventitious roots at the nodes , and new plants from the buds . [ 1 ] [ 2 ] Stolons are often called runners . Rhizomes , in contrast, are root-like stems that may either grow horizontally at the soil surface or in other orientations underground. [ 1 ] Thus, not all horizontal stems are called stolons. Plants with stolons are called stoloniferous .
A stolon is a plant propagation strategy and the complex of individuals formed by a mother plant and all its clones produced from stolons form a single genetic individual, a genet . [ citation needed ]
Stolons may have long or short internodes . The leaves along the stolon are usually very small, but in a few cases such as Stachys sylvatica are normal in size. [ 3 ]
Stolons arise from the base of the plant. [ 4 ] In strawberries the base is above the soil surface; in many bulb -forming species and plants with rhizomes, the stolons remain underground and form shoots that rise to the surface at the ends or from the nodes. The nodes of the stolons produce roots, often all around the node and hormones produced by the roots cause the stolon to initiate shoots with normal leaves. [ 5 ] Typically after the formation of the new plant the stolon dies away [ 6 ] in a year or two, while rhizomes persist normally for many years or for the life of the plant, adding more length each year to the ends with active growth. The horizontal growth of stolons results from the interplay of different hormones produced at the growing point and hormones from the main plant, with some studies showing that stolon and rhizome growth are affected by the amount of shady light the plant receives with increased production and branching from plants exposed to mixed shade and sun, while plants in all day sun or all shade produce fewer stolons. [ 7 ]
A number of plants have soil-level or above-ground rhizomes, including Iris species and many orchid species.
T. Holm (1929) restricted the term rhizome to a horizontal, usually subterranean, stem that produces roots from its lower surface and green leaves from its apex, developed directly from the plumule of the embryo. He recognized stolons as axillary, subterranean branches that do not bear green leaves but only membranaceous, scale-like ones. [ 8 ]
A stolon of grasses is defined as a horizontal stem above or on the soil surface that often roots at the internodes. [ 9 ]
In some Cyperus species the stolons end with the growth of tubers; the tubers are swollen stolons that form new plants. [ 10 ]
Some species of crawling plants can also sprout adventitious roots, but are not considered stoloniferous: a stolon is sprouted from an existing stem and can produce a full individual. Examples of plants that extend through stolons include some species from the genera Riccia , Argentina (silverweed), Cynodon , Fragaria , and Pilosella (Hawkweeds), Zoysia japonica , Ranunculus repens . Plants with long, slender stolons are referred to as sarmentose plants. [ 11 ]
Other plants with stolons below the soil surface include many grasses, Ajuga , Mentha , [ 12 ] and Stachys . Several species of Irises have stolons attached to their rhizomes, [ 13 ] including Iris stolonifera .
Lily-of-the-valley ( Convallaria majalis ) has rhizomes that grow stolon-like stems called stoloniferous rhizomes or leptomorph rhizomes. A number of plants have stoloniferous rhizomes including Asters . [ 14 ] These stolon-like rhizomes are long and thin, with long internodes and indeterminate growth with lateral buds at the node, which mostly remain dormant. [ citation needed ]
In potatoes , the stolons [ 15 ] start to grow within 10 days of plants emerging above ground, with tubers usually beginning to form on the end of the stolons. [ 16 ] The tubers are modified stolons [ 17 ] that hold food reserves, with a few buds that grow into stems. Since it is not a rhizome it does not generate roots, but the new stem growth that grows to the surface produces roots. See also BBCH-scale (potato) .
Hydrilla use stolons that produce tubers to spread themselves and to survive dry periods in aquatic habitats. [ 18 ]
Erythronium , commonly called Trout Lily, have white stolons growing from the bulb. Most run horizontally, either underground or along the surface of the ground under leaf litter . A number of bulbous species produce stolons, such as Erythronium propullans . Flowering plants often produce no stolons. [ 19 ]
Convolvulus arvensis is a weed species in agriculture that spreads by under ground stolons that produce rhizomes. [ 20 ]
In studies on grass species, with plants that produce stolons or rhizomes and plants that produce both stolons and rhizomes, morphological and physiological differences were noticed. Stolons have longer internodes and function as means of seeking out light and are used for propagation of the plant, while rhizomes are used as storage organs for carbohydrates and the maintenance of meristem tissue to keep the parent plant alive from one year to the next. [ 21 ]
In mycology , a stolon is defined as an occasionally septate hypha , which connects sporangiophores together. Root-like structures called rhizoids may appear on the stolon as well, anchoring the hyphae to the substrate . The stolon is commonly found in bread molds , and are seen as horizontally expanding across the mold.
Some bryozoans form colonies through the connection of individual units by stolons. Other colonies include sheets and erect colonies. [ 22 ]
Some colonial Cnidaria develop as stolons with interconnected medusoid structures that later separate. [ citation needed ]
Some worm-like animals, such as certain Polychaeta in the genus Myrianida , form stolons containing eggs or sperm which trail behind the main body before detaching to mate with other stolons. [ 23 ]
The worm Megasyllis nipponica takes this to an extreme, developing stolons with their own eyes, antennae, gut, and brain, which detach, seek out, and mate with an opposite-sex stolon to produce fertilized eggs. [ 24 ]
Stolon-based reproduction is thought to have been used by Rangeomorphs in the Ediacaran age. [ 25 ] [ 26 ] | https://en.wikipedia.org/wiki/Sarmentose_(botany) |
The saros ( / ˈ s ɛər ɒ s / ⓘ ) is a period of exactly 223 synodic months , [ a ] 18 years 11 days and 8 hours, [ 2 ] [ 1 ] that can be used to predict eclipses of the Sun and Moon . One saros period after an eclipse, the Sun, Earth , and Moon return to approximately the same relative geometry, a near straight line, and a nearly identical eclipse will occur, in what is referred to as an eclipse cycle . Every eclipse has an associated saros series and all succeeding or preceding eclipses have a different saros series associated with them - as the eclipse of the same series occurs or occurred with a gap of one saros only. Solar and lunar eclipses have different saros series.
A series of eclipses that are separated by one saros is called a saros series . It corresponds to:
The 19 eclipse years means that if there is a solar eclipse (or lunar eclipse ), then after one saros a new moon will take place at the same node of the orbit of the Moon , and under these circumstances another solar eclipse can occur.
The earliest discovered historical record of what is known as the saros is by Chaldean (neo-Babylonian) astronomers in the last several centuries BCE. [ 3 ] [ 4 ] [ 5 ] It was later known to Hipparchus , Pliny [ 6 ] and Ptolemy . [ 7 ]
The name "saros" ( Greek : σάρος ) was applied to the eclipse cycle by Edmond Halley in 1686, [ 8 ] who took it from the Suda , a Byzantine lexicon of the 11th century. The Suda says, "[The saros is] a measure and a number among Chaldeans . For 120 saroi make 2220 years (years of 12 lunar months) according to the Chaldeans' reckoning, if indeed the saros makes 222 lunar months, which are 18 years and 6 months (i.e. years of 12 lunar months)." [ 9 ] The information in the Suda in turn was derived directly or otherwise from the Chronicle of Eusebius of Caesarea , [ 10 ] which quoted Berossus . ( Guillaume Le Gentil claimed that Halley's usage was incorrect in 1756, [ 11 ] but the name continues to be used.) The Greek word apparently either comes from the Babylonian word sāru meaning the number 3600 [ 12 ] or the Greek verb saro (σαρῶ) that means "sweep (the sky with the series of eclipses)". [ 13 ]
The Saros period of 223 lunar months (in Greek numerals , ΣΚΓ′) is in the Antikythera Mechanism user manual on this instrument, made around 150 to 100 BCE in Greece, as seen in the picture. This number is one of a few inscriptions of the mechanism that are visible with the unaided eye. [ 14 ] [ 15 ] Above it, the period of the Metonic cycle and the Callippic cycle are also visible.
The saros, a period of 6585.3211 days (15 common years + 3 leap years + 12.321 days, 14 common years + 4 leap years + 11.321 days, or 13 common years + 5 leap years + 10.321 days), is useful for predicting the times at which nearly identical eclipses will occur. Three periodicities related to lunar orbit, the synodic month , the draconic month , and the anomalistic month coincide almost perfectly each saros cycle. For an eclipse to occur, either the Moon must be located between the Earth and Sun (for a solar eclipse ) or the Earth must be located between the Sun and Moon (for a lunar eclipse ). This can happen only when the Moon is new or full , respectively, and repeat occurrences of these lunar phases result from solar and lunar orbits producing the Moon's synodic period of 29.53059 days. During most full and new moons, however, the shadow of the Earth or Moon falls to the north or south of the other body. Eclipses occur when the three bodies form a nearly straight line. Because the plane of the lunar orbit is inclined to that of the Earth, this condition occurs only when a full or new Moon is near or in the ecliptic plane , that is when the Moon is at one of the two nodes (the ascending or descending node). The period of time for two successive lunar passes through the ecliptic plane (returning to the same node) is termed the draconic month , a 27.21222 day period. The three-dimensional geometry of an eclipse, when the new or full moon is near one of the nodes, occurs every five or six months when the Sun is in conjunction or opposition to the Moon and coincidentally also near a node of the Moon's orbit at that time, or twice per eclipse year . Two eclipses separated by one saros have very similar appearance and duration due to the distance between the Earth and Moon being nearly the same for each event: this is because the saros is also an integer multiple of the anomalistic month of 27.5545 days, the period of the moon with respect to the lines of apsides in its orbit.
After one saros, the Moon will have completed roughly an integer number of synodic, draconic, and anomalistic periods (223, 242, and 239) and the Earth-Sun-Moon geometry will be nearly identical: the Moon will have the same phase and be at the same node and the same distance from the Earth. In addition, because the saros is close to 18 years in length (about 11 days longer), the Earth will be nearly the same distance from the Sun, and tilted to it in nearly the same orientation (same season). [ 16 ] Given the date of an eclipse, one saros later a nearly identical eclipse can be predicted. During this 18-year period, about 40 other solar and lunar eclipses take place, but with a somewhat different geometry. One saros equaling 18.03 years is not equal to a perfect integer number of lunar orbits (Earth revolutions with respect to the fixed stars of 27.32166 days sidereal month ), therefore, even though the relative geometry of the Earth–Sun–Moon system will be nearly identical after a saros, the Moon will be in a slightly different position with respect to the stars for each eclipse in a saros series. The axis of rotation of the Earth–Moon system exhibits a precession period of 18.59992 years.
The saros is not an integer number of days, but contains the fraction of + 1 ⁄ 3 of a day. Thus each successive eclipse in a saros series occurs about eight hours later in the day. In the case of an eclipse of the Sun, this means that the region of visibility will shift westward about 120°, or about one third of the way around the globe, and the two eclipses will thus not be visible from the same place on Earth. In the case of an eclipse of the Moon, the next eclipse might still be visible from the same location as long as the Moon is above the horizon. Given three saros eclipse intervals, the local time of day of an eclipse will be nearly the same. This three saros interval (19,755.96 days) is known as a triple saros or exeligmos ( Greek : "turn of the wheel") cycle.
Each saros series starts with a partial eclipse (Sun first enters the end of the node), and each successive saros the path of the Moon is shifted either northward (when near the descending node) or southward (when near the ascending node) due to the fact that the saros is not an exact integer of draconic months (about one hour short). At some point, eclipses are no longer possible and the series terminates (Sun leaves the beginning of the node). An arbitrary solar saros series was designated as solar saros series 1 by compilers of eclipse statistics. This series has finished, but the eclipse of November 16, 1990 BC ( Julian calendar ) for example is in solar saros series 1. There are different saros series for solar and lunar eclipses. For lunar saros series, the lunar eclipse occurring 58.5 synodic months earlier (February 23, 1994 BC) was assigned the number 1. If there is an eclipse one inex (29 years minus about 20 days) after an eclipse of a particular saros series then it is a member of the next series. For example, the eclipse of October 26, 1961 BC is in solar saros series 2. Saros series, of course, went on before these dates, and it is necessary to extend the saros series numbers backwards to negative numbers even just to accommodate eclipses occurring in the years following 2000 BC (up till the last eclipse with a negative saros number in 1367 BC). For solar eclipses the statistics for the complete saros series within the era between 2000 BC and AD 3000 are given in this article's references. [ 17 ] [ 18 ] It takes between 1226 and 1550 years for the members of a saros series to traverse the Earth's surface from north to south (or vice versa). These extremes allow from 69 to 87 eclipses in each series (most series have 71 or 72 eclipses). From 39 to 59 (mostly about 43) eclipses in a given series will be central (that is, total, annular, or hybrid annular-total). At any given time, approximately 40 different saros series will be in progress.
Saros series, as mentioned, are numbered according to the type of eclipse (lunar or solar). [ 19 ] [ 20 ] In odd numbered series (for solar eclipses) the Sun is near the ascending node, whereas in even numbered series it is near the descending node (this is reversed for lunar eclipse saros series). Generally, the ordering of these series determines the time at which each series peaks, which corresponds to when an eclipse is closest to one of the lunar nodes. For solar eclipses, the 40 series numbered between 117 and 156 are active (series 117 will end in 2054), whereas for lunar eclipses, there are now 41 active saros series (these numbers can be derived by counting the number of eclipses listed over an 18-year (saros) period from the eclipse catalog sites). [ 21 ] [ 22 ]
As an example of a single saros series, this table gives the dates of some of the 72 lunar eclipses for saros series 131. This eclipse series began in AD 1427 with a partial eclipse at the southern edge of the Earth's shadow when the Moon was close to its descending node. In each successive saros, the Moon's orbital path is shifted northward with respect to the Earth's shadow, with the first total eclipse occurring in 1950. For the following 252 years, total eclipses occur, with the central eclipse in 2078. The first partial eclipse after this will occur in the year 2220, and the final partial eclipse of the series will occur in 2707. The total lifetime of lunar saros series 131 is 1280 years. Solar saros 138 interleaves with this lunar saros with an event occurring every 9 years 5 days alternating between each saros series.
Because of the + 1 ⁄ 3 fraction of days in a saros, the visibility of each eclipse will differ for an observer at a given locale. For the lunar saros series 131, the first total eclipse of 1950 had its best visibility for viewers in Eastern Europe and the Middle East because mid-eclipse was at 20:44 UT. The following eclipse in the series occurred about 8 hours later in the day with mid-eclipse at 4:47 UT, and was best seen from North America and South America. The third total eclipse occurred about 8 hours later in the day than the second eclipse with mid-eclipse at 12:43 UT, and had its best visibility for viewers in the Western Pacific, East Asia, Australia and New Zealand. This cycle of visibility repeats from the start to the end of the series, with minor variations. Solar saros 138 interleaves with this lunar saros with an event occurring every 9 years 5 days alternating between each saros series.
For a similar example for solar saros see solar saros 136 .
After a given lunar or solar eclipse, after 9 years and 5 + 1 ⁄ 2 days (a half saros, or sar) an eclipse will occur that is lunar instead of solar, or vice versa, with similar properties. [ 23 ]
For example, if the Moon's penumbra partially covers the southern limb of the Earth during a solar eclipse, 9 years and 5 + 1 ⁄ 2 days later a lunar eclipse will occur in which the Moon is partially covered by the southern limb of the Earth's penumbra. Likewise, 9 years and 5 + 1 ⁄ 2 days after a total solar eclipse or an annular solar eclipse occurs, a total lunar eclipse will also occur. This 9-year period is referred to as a sar . It includes 111 + 1 ⁄ 2 synodic months, or 111 synodic months plus one fortnight . The fortnight accounts for the alternation between solar and lunar eclipse. For a visual example see this chart (each row is one sar apart). | https://en.wikipedia.org/wiki/Saros_(astronomy) |
Sarpa or SARPA (Snake Awareness, Rescue and Protection app) is a snakebite app , an application for mobile devices developed in India to provide rapid, life-saving help for victims of snakebite, which kill an estimated 58,000 people a year in India. [ 1 ] [ 2 ] The app provides information about snakes, gets fast aid for people bitten, and helps in the development of antivenoms. Similar systems developed in India include SnakeHub, Snake Lens, Snakepedia, Serpent and the Big Four Mapping Project. The apps provide rapid response to snakebite incidents, often in remote areas, using a network of volunteers managed by local wildlife departments; their use can save human lives by providing rapid medical care, and also snakes, by helping to avoid interaction between the species. [ 1 ]
This mobile technology related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Sarpa_(snakebite_app) |
Sasaki is a design firm specializing in Architecture , Interior Design , Urban Design , Space Planning, Landscape Architecture , Ecology , Civil Engineering , and Place Branding . [ 1 ] The firm is headquartered in Boston, Massachusetts, but practices on an international scale, with offices in Shanghai, [ 2 ] and Denver, Colorado, [ 3 ] and clients and projects globally.
Sasaki was founded in 1953 by landscape architect Hideo Sasaki while he served as a professor and landscape architecture chair at the Harvard Graduate School of Design . [ 4 ] Sasaki was founded upon collaborative, interdisciplinary design, unprecedented in design practice at the time, [ 5 ] and an emphasis on the integration of land, buildings, people, and their contexts. [ 6 ]
Through the mid to late 1900s, Sasaki designed plazas (including Copley Square ), [ 7 ] [ 8 ] corporate parks, college campuses, and master plans, among other projects. [ 4 ]
The firm includes a team of in house designers, software developers, and data analysts who support the practice. [ 9 ] Today, Sasaki has over 300 employees across its diverse practice areas and between its two offices. [ 10 ] The firm engages in a wide variety of project types, across its many disciplines.
In 2000, in honor of the passing of the firm's founder, the family of Hideo Sasaki together with Sasaki and other financial supporters, established the Sasaki Foundation. [ 11 ] The foundation, which is a separate entity from Sasaki, gives yearly grants, supporting community-led research at Sasaki. [ 12 ] In 2012, Sasaki opened an office in Shanghai to support the firm's work in China and the larger Asia Pacific region. [ 2 ]
In 2018, Sasaki opened the Incubator, a coworking space designed by and located within the Sasaki campus, which houses the Sasaki Foundation as curator of programming. [ 13 ] The 5,000 square-foot space is home to several like-minded non-profits, organizations, and individuals. [ 11 ]
In 2020, Sasaki established a new office in Denver, Colorado, marking the firm's third physical studio location. [ 14 ] Opening an office in Denver, a region where Sasaki has been working since the 1960s, positions Sasaki to deliver on projects across western North America.
In 2007, Sasaki was honored as the American Society of Landscape Architects firm of the year. [ 15 ] In 2012, Sasaki won the American Planning Association firm of the year award. [ 16 ]
Sasaki has earned numerous consecutive Pierre L'Enfant International Planning awards from the American Planning Association. [ 17 ] [ 18 ] [ 19 ] [ 20 ] In 2017, two of the five annual finalists for the Rudy Bruner Award for Urban Excellence were Sasaki projects: the Bruce C. Bolling Municipal Building (Boston, MA) [ 21 ] and the Chicago Riverwalk both were recognized as silver medalists. [ 22 ] Sasaki has been named a top 50 firm by Architect Magazine numerous times. [ 23 ] [ 24 ]
The firm has been recognized by the Boston Society of Landscape Architects (BSLA), Boston Society of Architects (BSA), American Planning Association (APA), American Institute of Architecture (AIA), Society for College and University Planning (SCUP), Urban Land Initiative (ULI), [ 25 ] Dezeen , [ 26 ] and Fast Company , among others.
Notable Sasaki-sponsored research projects include Sea-Change Boston (2016 ASLA Honor Award), [ 27 ] Shifting Gears: An Urbanist's take on autonomous vehicles (2019 Fast Company honorable mention), [ 28 ] Understanding Homelessness, [ 29 ] and Where Design Meets Play. [ 30 ]
Sasaki has a large portfolio of work, which includes: | https://en.wikipedia.org/wiki/Sasaki_(company) |
Satellite crop monitoring is the technology which facilitates real-time crop vegetation index monitoring via spectral analysis [ 1 ] of high resolution satellite images for different fields and crops which enables to track positive and negative dynamics of crop development. [ 2 ] [ 3 ] The difference in vegetation index informs about single-crop development disproportions that speaks for the necessity of additional agriculture works on particular field zones [ 4 ] —that is because satellite crop monitoring belongs to precision agriculture methods.
Satellite crop monitoring technology allows to perform online crop monitoring on different fields, located in different areas, regions, even countries and on different continents. The technology's advantage is a high automation level of sown area condition and its interpretation in an interactive map which can be read by different groups of users. [ 5 ] [ 6 ]
Satellite crop monitoring technology users are: | https://en.wikipedia.org/wiki/Satellite_crop_monitoring |
A satellite data unit (SDU) is an avionics device installed in an aircraft that allows air/ground communication via a satellite network . It is an integral part of an aircraft's SATCOM (satellite communication) system. The device connects with a satellite via ordinary radio frequency (RF) communication and the satellite then connects to a ground station or vice versa . All satellite communication whether audio or data is processed by the SDU. [ 1 ]
The SDU communicates with an onboard MDDU (multi-purpose disk-drive unit) which maintains an updatable table of ground stations near the aircraft's position and the order of preference for selection of which ground station to use which thus guides the choice of satellite. Along with analysing data continuously sent from all ground stations (such as station status and the error rate of signals from each station) the SDU receives information on the aircraft's position and orientation from another onboard system (ADIRU, air data inertial reference unit ) which it passes to the BSU (beam-steering unit) to direct the signal beam from the aircraft to the chosen satellite. [ 1 ]
With the advent of cellphones and the Internet a separate or integrated SDU can be used to offer telephone and Internet services to passengers. [ 1 ] [ 2 ] [ 3 ]
Logs of satellite communication have been used to inform search and rescue agencies of locations of missing aircraft, like Malaysia Airlines Flight 370 whose position was unknown due to loss of radar contact and other communications. Automated SATCOM transmissions suggested it flew about 1,600 km (1,000 mi) off its designated flight path having flown approximately south-southwest rather than the intended approximately north-northeast. [ 4 ]
This technology-related article is a stub . You can help Wikipedia by expanding it .
This aviation -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Satellite_data_unit |
Satellite delay is the noticeable latency due to the limited speed of light , when sending data to and from satellites, especially distant geosynchronous satellites . Bouncing a signal off a geosynchronous satellite takes about a quarter of a second, which is enough to be noticeable, but relaying data between two or three such satellites increases the delay. [ 1 ] | https://en.wikipedia.org/wiki/Satellite_delay |
Satellite formation flying is the coordination of multiple satellites to accomplish the objective of one larger, usually more expensive, satellite. [ 1 ] Coordinating smaller satellites has many benefits over single satellites including simpler designs, faster build times, cheaper replacement creating higher redundancy, unprecedented high resolution, and the ability to view research targets from multiple angles or at multiple times. These qualities make them ideal for astronomy , communications , meteorology , and environmental uses. [ 2 ]
Depending on the application, there are three formations possible: trailing, cluster, and constellation . [ 1 ]
Usually, these formations are made up of numerous small satellites. A micro satellite weighs under 100 kg and a nano satellite weighs under 10kg. Magnetosheric Constellation, for instance, would be composed of 100 micro satellites. [ 3 ]
This technology has become more viable thanks to the development of autonomous flying. With an onboard computer and this algorithm, satellites may autonomously position themselves into a formation. Previously, ground control would have to adjust each satellite to maintain formations. Now, satellites may arrive at and maintain formations with faster response time and have the ability to change the formation for varied resolution of observations. Also, satellites may be launched from different spacecraft and rendezvous on a particular path. This advance was made possible by Dave Folta, John Bristow, and Dave Quinn at NASA ’s Goddard Space Flight Center (GSFC). [ 1 ] | https://en.wikipedia.org/wiki/Satellite_formation_flying |
A satellite navigation ( satnav ) device or GPS device is a device that uses satellites of the Global Positioning System (GPS) or similar global navigation satellite systems (GNSS).
A satnav device can determine the user's geographic coordinates and may display the geographical position on a map and offer routing directions (as in turn-by-turn navigation ).
As of 2023 [update] , four GNSS systems are operational: the original United States' GPS, the European Union's Galileo , Russia's GLONASS , [ 1 ] [ 2 ] and China's BeiDou Navigation Satellite System. The Indian Regional Navigation Satellite System (IRNSS) will follow and Japan's Quasi-Zenith Satellite System ( QZSS ) scheduled for 2023 will augment the accuracy of a number of GNSS.
A satellite navigation device can retrieve location and time information from one or more GNSS systems in all weather conditions, anywhere on or near the Earth's surface. Satnav reception requires an unobstructed line of sight to four or more GNSS satellites, [ 3 ] and is subject to poor satellite signal conditions. In exceptionally poor signal conditions, for example in urban areas, satellite signals may exhibit multipath propagation where signals bounce off structures, or are weakened by meteorological conditions. Obstructed lines of sight may arise from a tree canopy or inside a structure, such as in a building, garage or tunnel. Today, most standalone Satnav receivers are used in automobiles. The Satnav capability of smartphones may use assisted GNSS (A-GNSS) technology, which can use the base station or cell towers to provide a faster Time to First Fix (TTFF), especially when satellite signals are poor or unavailable. However, the mobile network part of the A-GNSS technology would not be available when the smartphone is outside the range of the mobile reception network, while the satnav aspect would otherwise continue to be available.
As with many other technological breakthroughs of the latter 20th century, the modern GNSS system can reasonably be argued to be a direct outcome of the Cold War of the latter 20th century. The multibillion-dollar [ citation needed ] expense of the US and Russian programs was initially justified by military interest. In contrast, the European Galileo was conceived as purely civilian.
In 1960, the US Navy put into service its Transit satellite-based navigation system to aid in naval navigation. The US Navy in the mid-1960s conducted an experiment to track a submarine with missiles with six satellites and orbiting poles and was able to observe satellite changes. [ 4 ] Between 1960 and 1982, as the benefits were shown, the US military consistently improved and refined its satellite navigation technology and satellite system. In 1973, the US military began to plan for a comprehensive worldwide navigational system which eventually became known as the GPS (Global Positioning System).
In 1983, in the wake of the tragedy of the downing of Korean Air Lines Flight 007 , an aircraft which was shot down while in Soviet airspace due to a navigational error, President Ronald Reagan made the navigation capabilities of the existing military GPS system available for dual civilian use. However, civilian use was initially only a slightly degraded " Selective Availability " positioning signal. This new availability of the US military GPS system for civilian use required a certain technical collaboration with the private sector for some time, before it could become a commercial reality. The Macrometer Interferometric Surveyor was the first commercial GNSS-based system for performing geodetic measurements. [ 5 ] [ 6 ]
In 1989, Magellan Navigation Inc. unveiled its Magellan NAV 1000, the world's first commercial handheld GPS receiver. These units initially sold for approximately US$2,900 each.
In 1990, Mazda 's Eunos Cosmo was the first production car in the world with a built-in Satnav system . [ 7 ] In 1991, Mitsubishi introduced Satnav car navigation on the Mitsubishi Debonair (MMCS: Mitsubishi Multi Communication System). [ 8 ] In 1997, a navigation system using Differential GPS was developed as a factory-installed option on the Toyota Prius . [ 9 ] In 2000, the Clinton administration removed the military use signal restrictions, thus providing full commercial access to the US Satnav satellite system.
As GNSS navigation systems became more and more widespread and popular, the pricing of such systems began to fall, and their widespread availability steadily increased. Several additional manufacturers of these systems, such as Garmin (1991), Benefon (1999), Mio (2002) and TomTom (2002) entered the market. Mitac Mio 168 was the first PocketPC to contain a built-in GPS receiver. [ 10 ] Benefon's 1999 entry into the market also presented users with the world's first phone based GPS navigation system. Later, as smartphone technology developed, a GPS chip eventually became standard equipment for most smartphones. To date, ever more popular satellite navigation systems and devices continue to proliferate with newly developed software and hardware applications. It has been incorporated, for example, into cameras.
While the American GPS was the first satellite navigation system to be deployed on a fully global scale, and to be made available for commercial use, this is not the only system of its type. Due to military and other concerns, similar global or regional systems have been, or will soon be deployed by Russia, the European Union, China, India, and Japan.
GNSS devices vary in sensitivity, speed, vulnerability to multipath propagation , and other performance parameters. High-sensitivity receivers use large banks of correlators [ clarification needed ] [ citation needed ] and digital signal processing to search for signals very quickly. This results in very fast times to first fix when the signals are at their normal levels, for example, outdoors. When signals are weak, for example, indoors, the extra processing power can be used to integrate weak signals to the point where they can be used to provide a position or timing solution.
GNSS signals are already very weak when they arrive at the Earth's surface. The GPS satellites only transmit 27 W (14.3 dBW) from a distance of 20,200 km in orbit above the Earth. By the time the signals arrive at the user's receiver, they are typically as weak as −160 dBW , equivalent to 100 attowatts (10 −16 W) [ clarification needed ] . This is well below the thermal noise level in its bandwidth. Outdoors, GPS signals are typically around the −155 dBW level (−125 dBm ).
Conventional GPS receivers integrate the received GPS signals for the same amount of time as the duration of a complete C/A code cycle which is 1 ms. This results in the ability to acquire and track signals down to around the −160 dBW level. High-sensitivity GPS receivers are able to integrate the incoming signals for up to 1,000 times longer than this and therefore acquire signals up to 1,000 times weaker, resulting in an integration gain of 30 dB. A good high-sensitivity GPS receiver can acquire signals down to −185 dBW, and tracking can be continued down to levels approaching −190 dBW.
High-sensitivity GPS can provide positioning in many but not all indoor locations . Signals are either heavily attenuated by the building materials or reflected as in multipath . Given that high-sensitivity GPS receivers may be up to 30 dB more sensitive, this is sufficient to track through 3 layers of dry bricks, or up to 20 cm (8 inches) of steel-reinforced concrete, for example. [ citation needed ] Examples of high-sensitivity receiver chips include SiRFstarIII and MediaTek ʼs MTK II. [ 11 ]
In aviation, the GPS receivers can be "armed" to the approach mode for the destination airport, so that when the aircraft is within 30 nmi (56 km; 35 mi), the receiver sensitivity will automatically change from en route (±5 nm) and RAIM (±2 nm) to terminal (±1 nm), and change again to ±0.3 nm at 2 nmi (3.7 km; 2.3 mi) before reaching the final approach way point. [ 12 ]
A sequential GPS receiver tracks the necessary satellites by typically using one or two hardware channels. [ 13 ] The set will track one satellite at a time, time tag the measurements and combine them when all four satellite pseudoranges have been measured. These receivers are among the least expensive available, but they cannot operate under high dynamics and have the slowest time-to-first-fix (TTFF) performance.
Consumer GNSS navigation devices include:
Dedicated devices have various degrees of mobility. Hand-held , outdoor , or sport receivers have replaceable batteries that can run them for several hours, making them suitable for hiking , bicycle touring and other activities far from an electric power source. Their design is ergonomical , their screens are small, and some do not show color, in part to save power. Some use transflective liquid-crystal displays , allowing use in bright sunlight. Cases are rugged and some are water-resistant.
Other receivers, often called mobile are intended primarily for use in a car, but have a small rechargeable internal battery that can power them for an hour or two [ citation needed ] away from the car. Special purpose devices for use in a car may be permanently installed and depend entirely on the automotive electrical system. Many of them have touch-sensitive screens as input method. Maps may be stored on a memory card . Some offer additional functionality such as a rudimentary music player , image viewer , and video player . [ 14 ]
The pre-installed embedded software of early receivers did not display maps; 21st-century ones commonly show interactive street maps (of certain regions) that may also show points of interest , route information and step-by-step routing directions, often in spoken form with a feature called " text to speech ".
Manufacturers include:
Almost all smartphones now incorporate GNSS receivers [ citation needed ] . This has been driven both by consumer demand and by service suppliers. There are now many phone apps that depend on location services, such as navigational aids, and multiple commercial opportunities, such as localised advertising. In its early development, access to user location services was driven by European and American emergency services to help locate callers. [ 15 ]
All smartphone operating systems offer free mapping and navigational services that require a data connection; some allow the pre-purchase and downloading of maps but the demand for this is diminishing as data connection reliant maps can generally be cached anyway. There are many navigation applications and new versions are constantly being introduced. Major apps include Google Maps Navigation , Apple Maps and Waze , which require data connections, iGo for Android, Maverick and HERE for Windows Phone, which use cached maps and can operate without a data connection. Consequently, almost any smartphone now qualifies as a personal navigation assistant .
The use of mobile phones as navigational devices has outstripped the use of standalone GNSS devices. In 2009, independent analyst firm Berg Insight found that GNSS-enabled GSM/WCDMA handsets in the USA alone numbered 150 million units, [ 16 ] against the sale of only 40 million standalone GNSS receivers. [ 17 ]
Assisted GPS (A-GPS) uses a combination of satellite data and cell tower data to shorten the time to first fix , reduce the need to download a satellite almanac periodically and to help resolve a location when satellite signals are disturbed by the proximity of large buildings. When out of range of a cell tower the location performance of a phone using A-GPS may be reduced. Phones with an A-GPS based hybrid positioning system can maintain a location fix when GPS signals are inadequate by cell tower triangulation and WiFi hotspot locations. Most smartphones download a satellite almanac when online to accelerate a GPS fix when out of cell tower range. [ 18 ]
Some, older, Java -enabled phones lacking integrated GPS may still use external GPS receivers via serial or Bluetooth ) connections, but the need for this is now rare.
By tethering to a laptop , some phones can provide localisation services to a laptop as well. [ 19 ]
Software companies have made available GPS navigation software programs for in-vehicle use on laptop computers. [ 20 ] Benefits of GPS on a laptop include larger map overview, ability to use the keyboard to control GPS functions, and some GPS software for laptops offers advanced trip-planning features not available on other platforms, such as midway stops, capability of finding alternative scenic routes as well as only highway option.
Palms [ 21 ] and Pocket PC 's can also be equipped with GPS navigation. [ 22 ] A pocket PC differs from a dedicated navigation device as it has an own operating system and can also run other applications.
Other GPS devices need to be connected to a computer in order to work. This computer can be a home computer , laptop , PDA , digital camera , or smartphones . Depending on the type of computer and available connectors, connections can be made through a serial or USB cable, as well as Bluetooth , CompactFlash , SD , PCMCIA and the newer ExpressCard . [ 23 ] Some PCMCIA/ExpressCard GPS units also include a wireless modem . [ 24 ]
Devices usually do not come with pre-installed GPS navigation software , thus, once purchased, the user must install or write their own software. As the user can choose which software to use, it can be better matched to their personal taste. It is very common for a PC-based GPS receiver to come bundled with a navigation software suite. Also, software modules are significantly cheaper than complete stand-alone systems (around € 50 to €100). The software may include maps only for a particular region, or the entire world, if software such as Google Maps are used.
Some hobbyists have also made some Satnav devices and open-sourced the plans. Examples include the Elektor GPS units. [ 25 ] [ 26 ] These are based around a SiRFstarIII chip and are comparable to their commercial counterparts. Other chips and software implementations are also available. [ 27 ]
An automotive navigation system takes its location from a GNSS system and, depending on the installed software, may offer the following services:
Aviators use Satnav to navigate and to improve safety and the efficiency of the flight. This may allow pilots to be independent of ground-based navigational aids, enable more efficient routes and provide navigation into airports that lack ground-based navigation and surveillance equipment. There are now some GPS units that allow aviators to get a clearer look in areas where the satellite is augmented to be able to have safe landings in bad visibility conditions. There have now been two new signals made for GPS, the first being made to help in critical conditions in the sky and the other will make GPS more of a robust navigation service. Many aviator services have now made it a required service to use a GPS. [ 28 ] Commercial aviation applications include GNSS devices that calculate location and feed that information to large multi-input navigational computers for autopilot , course information and correction displays to the pilots, and course tracking and recording devices.
Military applications include devices similar to consumer sport products for foot soldiers (commanders and regular soldiers), small vehicles and ships, and devices similar to commercial aviation applications for aircraft and missiles. Examples are the United States military's Commander's Digital Assistant and the Soldier Digital Assistant . [ 29 ] [ 30 ] [ 31 ] [ 32 ] Prior to May 2000 only the military had access to the full accuracy of GPS. Consumer devices were restricted by selective availability (SA), which was scheduled to be phased out but was removed abruptly by President Clinton. [ 33 ] Differential GPS is a method of cancelling out the error of SA and improving GPS accuracy, and has been routinely available in commercial applications such as for golf carts. [ 34 ] GPS is limited to about 15 meter accuracy even without SA. DGPS can be within a few centimeters. [ 35 ]
GPS maps and directions are occasionally imprecise. [ citation needed ] Some people have gotten lost by asking for the shortest route. [ 36 ] [ 37 ] [ 38 ] [ 39 ] Brad Preston, Oregon claims that people are routed into his driveway five to eight times a week because their Satnav shows a street through his property. [ 39 ] Other hazards involve an alley being listed as a street, a lane being identified as a road, [ 40 ] or rail tracks as a road. [ 41 ]
User privacy may be compromised if Satnav equipped handheld devices such as mobile phones upload user geo-location data through associated software installed on the device. User geo-location is currently the basis for navigational apps such as Google Maps, location-based advertising , which can promote nearby shops and may allow an advertising agency to track user movements and habits for future use. Regulatory bodies differ between countries regarding the treatment of geo-location data as privileged or not. Privileged data cannot be stored, or otherwise used, without the user's consent. [ 42 ]
Vehicle tracking systems allow employers to track their employees' location raising questions regarding violation of employee privacy. There are cases where employers continued to collect geo-location data when an employee was off duty in private time. [ 43 ]
Rental car services may use the same technique to geo-fence their customers to the areas they have paid for, charging additional fees for violations. [ 44 ] In 2010, New York Civil Liberties Union filed a case against the Labor Department for firing Michael Cunningham after tracking his daily activity and locations using a Satnav device attached to his car. [ 45 ] Private investigators use planted GPS devices to provide information to their clients on a target's movements. | https://en.wikipedia.org/wiki/Satellite_navigation_device |
Satellite navigation software or GNSS navigation software a category of software that provide positioning services by utilizing data from satellite navigation systems .
Key functions of satellite navigation software usually includes:
Additional functions that extends the capabilities of satellite navigation software includes:
Hardware-wise, a GNSS receiver is needed to interpret satellite signals and compute the user’s location. Nowadays, it is usually a single integrated circuit (IC).
Satellite navigation software is most commonly used on mobile devices, particularly mobile phones , to provide the positioning functionality. However, relying exclusively on GNSS data is not accurate enough due to the limitations of GNSS services, To address this, Assisted GNSS (A-GNSS) is used instead. By leveraging data from nearby cellular towers, Wi-Fi , and Bluetooth connections, A-GNSS enhances accuracy, reduces power consumption, lowers the risk of signal blockage, and effectively mitigates the limitations of GNSS. [ 1 ]
There are many navigation software products available. The primary distinction is whether it is designed for use on land, water or air. [ 2 ] Below is a short-listed software products:
Free and open source
Proprietary (available for free)
Commercial
Navigation software for use on the water has many features in common with land-based GNSS navigation software. It can use electronic navigation chart or raster charts, usually provides user ability to plan routes and set waypoints, and may have live GPS tracking capabilities. In addition, marine navigation software often has option to control external autopilot for automated boat navigation. It may incorporate GRIB weather overlay on the chart, Tide predictions and other related information services of additional use to mariners.
Free and open source
This kind of software usually creates a modern glass cockpit and uses more than just a single GNSS sensor to assist the navigation. Such sensors are Attitude and Heading Reference Systems (AHRS) and Inertial Measurement Unit (IMU) sensors. | https://en.wikipedia.org/wiki/Satellite_navigation_software |
A satellite telephone , satellite phone or satphone is a type of mobile phone that connects to other phones or the telephone network by radio link through satellites orbiting the Earth instead of terrestrial cell sites , as cellphones do. Therefore, they can work in most geographic locations on the Earth's surface, as long as open sky and the line-of-sight between the phone and the satellite are provided. Depending on the architecture of a particular system, coverage may include the entire Earth or only specific regions. Satellite phones provide similar functionality to terrestrial mobile telephones; voice calling , text messaging, and low-bandwidth Internet access are supported through most systems. The advantage of a satellite phone is that it can be used in such regions where local terrestrial communication infrastructures, such as landline and cellular networks, are not available.
Satellite phones are popular on expeditions into remote locations where there is no reliable cellular service, such as recreational hiking, hunting, fishing, and boating trips, as well as for business purposes, such as mining locations and maritime shipping. [ 1 ] Satellite phones rarely get disrupted by natural disasters on Earth or human actions such as war, so they have proven to be dependable communication tools in emergency and humanitarian situations, when the local communications system have been compromised. [ 2 ]
The mobile equipment, also known as a terminal, varies widely. Early satellite phone handsets had a size and weight comparable to that of a late-1980s or early-1990s mobile phone , but usually with a large retractable antenna. More recent satellite phones are similar in size to a regular mobile phone while some prototype satellite phones have no distinguishable difference from an ordinary smartphone . [ 3 ] [ 4 ]
A fixed installation such as one used aboard a ship may include large, rugged, rack-mounted electronics, and a steerable microwave antenna on the mast that automatically tracks the overhead satellites. Smaller installations using VoIP over a two-way satellite broadband service such as BGAN or VSAT bring the costs within the reach of leisure vessel owners. Internet service satellite phones have notoriously poor reception indoors, though it may be possible to get a consistent signal near a window or in the top floor of a building if the roof is sufficiently thin. The phones have connectors for external antennas that can be installed in vehicles and buildings. The systems also allow for the use of repeaters, much like terrestrial mobile phone systems.
In the early 2020s various manufacturers began to integrate satellite messaging connectivity and satellite emergency services into conventional mobile phones for use in remote regions, where there is no reliable terrestrial network.
The first satellite relayed phone calls were achieved early on in the space age, after the first relay test was conducted by Pioneer 1 and the first broadcast by SCORE in 1958 at the end of the year, after Sputnik I became at the beginning of the year the first satellite in history.
MARISAT was the first mobile communications satellite, eventually operated by the first privatized satellite communication INMARSAT organization, which was formed in 1979. [ 5 ]
Satellite phone systems can be classified into two types: systems that use satellites in a high geostationary orbit, 35,786 kilometres (22,236 mi) above the Earth's surface, and systems that use satellites in low Earth orbit (LEO), 640 to 1,120 kilometers (400 to 700 miles) above the Earth. The connection and regular data order and infrastructure order can be found in this image.
Some satellite phones use satellites in geostationary orbit (GSO), which appear at a fixed position in the sky. These systems can maintain near-continuous global coverage with only three or four satellites, reducing the launch costs. The satellites used for these systems are very heavy (about 5000 kg) and expensive to build and launch. The satellites orbit at an altitude of 35,786 kilometres (22,236 mi) above the Earth's surface; a noticeable delay is present while making a phone call or using data services due to the large distance from users. The amount of bandwidth available on these systems is substantially higher than that of the low Earth orbit systems; all three active systems provide portable satellite Internet using laptop-sized terminals with speeds ranging from 60 to 512 kbit per second ( kbps ).
Geostationary satellite phones can only be used at lower latitudes, generally between 70 degrees north of the equator and 70 degrees south of the equator. At higher latitudes the satellite appears at such a low angle in the sky that radio frequency interference from terrestrial sources in the same frequency bands can interfere with the signal.
Another disadvantage of geostationary satellite systems is that in many areas—even where a large amount of open sky is present—the line-of-sight between the phone and the satellite is broken by obstacles such as steep hills and forest. The user will need to find an area with line-of-sight before using the phone. This is not the case with LEO services: even if the signal is blocked by an obstacle, one can wait a few minutes until another satellite passes overhead, but a GSO satellite may drop a call when line of sight is lost.
Satellite phones may use satellites in low Earth orbit (LEO). The advantages include the possibility of providing worldwide wireless coverage with no gaps. LEO satellites orbit the Earth in high-speed, low-altitude orbits with an orbital time of 70–100 minutes, an altitude of 640 to 1,120 kilometers (400 to 700 miles). Since the satellites are not geostationary, they move with respect to the ground. Any given satellite is only in view of a phone for a short time, so the call must be "handed off" electronically to another satellite when one passes beyond the local horizon. Depending on the positions of both the satellite and terminal, a usable pass of an individual LEO satellite will typically last 4–15 minutes on average. [ 6 ] At least one satellite must have line-of-sight to every coverage area at all times to guarantee coverage; thus a constellation of satellites, typically 40 to 70, is required to maintain worldwide coverage.
Both systems, based in the United States, started in the late 1990s, but soon went into bankruptcy after failing to gain enough subscribers to fund launch costs. They are now operated by new owners who bought the assets for a fraction of their original cost and are now both planning to launch replacement constellations supporting higher bandwidth. Data speeds for current networks are between 2200 and 9600 bit/s using a satellite handset.
A third system was announced in 2022 when T-Mobile US and SpaceX announced a partnership to add satellite cellular service to Starlink second generation (Gen2) satellites that are to begin launching to orbit in late 2022. The service is aimed to provide dead-zone cell phone coverage across the US using existing midband PCS spectrum that T-Mobile owns. [ 9 ] Cell coverage will begin with messaging and expand to include voice and limited data services later, with testing to begin in 2023. With Starlink Gen2 satellites in low Earth orbit using existing PCS spectrum, T-Mobile plans to be able to connect ordinary mobile phones to satellites, unlike earlier satellite phones in the market which used specialized radios to connect to geosynchronous-orbit satellites, which have longer communications latencies . [ 10 ] T-Mobile has offered to extend the offering globally if cellular carriers in other countries wish to exchange roaming services via the T-Mobile partnership with SpaceX, with other carriers working with their regulators to enable midband communications landing rights on a country-by-country basis. Bandwidth will be limited to approximately 2 to 4 megabits per second spread across a very large cell coverage area, with thousands of voice calls or millions of text messages simultaneously in an area. The size of a single coverage area has not yet been specified. [ 10 ]
LEO systems have the ability to track a mobile unit's location using Doppler navigation from the satellite. [ 11 ] However, this method can be inaccurate by tens of kilometers. On some Iridium hardware the coordinates can be extracted using AT commands , while recent Globalstar handsets will display them on the screen. [ 12 ]
Most VSAT terminals can be reprogrammed in-field using AT-commands to bypass automatic acquisition of GPS coordinates and instead accept manually injected GPS coordinates.
Satellite phones are usually issued with numbers in a special country calling code .
Inmarsat satellite phones are issued with codes +870. In the past, additional country codes were allocated to different satellites, but the codes +871 to +874 were phased out at the end of 2008 leaving Inmarsat users with the same country code, regardless of which satellite their terminal is registered with. [ 13 ]
Low Earth orbit systems including some of the defunct ones have been allocated number ranges in the International Telecommunication Union 's Global Mobile Satellite System virtual country code +881. Iridium satellite phones are issued with codes +881 6 and +881 7. Globalstar, although allocated +881 8 and +881 9 use U.S. telephone numbers except for service resellers located in Brazil, which use the +881 range.
Small regional satellite phone networks are allocated numbers in the +882 code designated for " international networks " which is not used exclusively for satellite phone networks.
While it is possible to obtain used handsets for the Thuraya, Iridium, and Globalstar networks for approximately US$200 , the newest handsets are quite expensive. The Iridium 9505A, released in 2001, sold in March 2010 for over $1,000. [ 14 ] Satellite phones are purpose-built for one particular network and cannot be switched to other networks. The price of handsets varies with network performance. If a satellite phone provider encounters trouble with its network, handset prices will fall, then increase once new satellites are launched. Similarly, handset prices will increase when calling rates are reduced.
Among the most expensive satellite phones are BGAN terminals, often costing several thousand dollars. [ 15 ] [ 16 ] These phones provide about 0.5 Mbit/s Internet and voice communications. Satellite phones are sometimes subsidised by the provider if one signs a post-paid contract, but subsidies are usually only a few hundred dollars or less.
Since most satellite phones are built under license or the manufacturing of handsets is contracted out to OEMs , operators have a large influence over the selling price. Satellite networks operate under proprietary protocols , making it difficult for manufacturers to independently make handsets.
A startup is proposing the use of standard mobile phone technology in satellites to enable low bandwidth text message with satellites from cheap mobile phones. [ 17 ]
The cost of making voice calls from a satellite phone varies from around $0.15 to $2 per minute, while calling them from landlines and regular mobile phones is more expensive. Costs for data transmissions (particularly broadband data) can be much higher. Rates from landlines and mobile phones range from $3 to $14 per minute with Iridium, Thuraya [ 18 ] and Inmarsat being some of the most expensive networks to call. The receiver of the call pays nothing, unless they are being called via a special reverse-charge service.
Calls between different satellite phone networks are often very expensive, with calling rates of up to $15 per minute.
Calls from satellite phones to landlines are usually around $0.80 to $1.50 per minute unless special offers are used. Such promotions are usually bound to a particular geographic area where traffic is low.
Most satellite phone networks have pre-paid plans, with vouchers ranging from $100 to $5,000.
Some satellite phone networks provide a one-way paging channel to alert users in poor coverage areas (such as indoors) of the incoming call. When the alert is received on the satellite phone it must be taken to an area with better coverage before the call can be accepted.
Globalstar provides a one-way data uplink service, typically used for asset tracking.
Iridium operates a one-way pager service as well as the call alert feature.
In some countries, possession of a satellite phone is illegal. [ 19 ] Their signals will usually bypass local telecoms systems, hindering censorship and wiretapping attempts, which has led some intelligence agencies to believe that satellite phones aid terrorist activity. [ 20 ] It is also common for restrictions to be in place in countries with oppressive governments regimes as a way to both expose subversive agents within their country and maximize the control of the information that makes it past their borders. [ 21 ]
All modern satellite phone networks encrypt voice traffic to prevent eavesdropping. In 2012, a team of academic security researchers reverse-engineered the two major proprietary encryption algorithms in use. [ 37 ] One algorithm (used in GMR-1 phones) is a variant of the A5/2 algorithm used in GSM (used in common mobile phones), and both are vulnerable to cipher-text only attacks. The GMR-2 standard introduced a new encryption algorithm which the same research team also cryptanalysed successfully. Thus satellite phones need additional encrypting if used for high-security applications.
Most mobile telephone networks operate close to capacity during normal times, and large spikes in call volumes caused by widespread emergencies often overload the systems when they are needed most. Examples reported in the media where this has occurred include the 1999 İzmit earthquake , the September 11 attacks , the 2006 Kiholo Bay earthquake , the 2003 Northeast blackouts , Hurricane Katrina , [ 38 ] the 2007 Minnesota bridge collapse , the 2010 Chile earthquake , and the 2010 Haiti earthquake . Reporters and journalists have also been using satellite phones to communicate and report on events in war zones such as Iraq.
Terrestrial cell antennas and networks can be damaged by natural disasters. Satellite telephony can avoid this problem and be useful during natural disasters. Satellite phone networks themselves are prone to congestion as satellites and spot beams cover a large area with relatively few voice channels.
In the early 2020s, manufacturers began to integrate satellite connectivity into smartphone devices for use in remote areas, out of the cellular network range. [ 39 ] [ 40 ] The satellite-to-phone services use L band frequencies, which are compatible with most modern handsets. [ 41 ] [ 42 ] However, due to the antenna limitations in the conventional phones, in the early stages of implementation satellite connectivity is limited to satellite messaging and satellite emergency services. [ 43 ] [ 44 ]
In 2018, Thuraya proposed a mobile phone capable [ 45 ] of both classic cellular plus satellite connectivity, [ 46 ] the X5 Touch, whom to be the world's first bi-types satellite plus cellular smartphone.
Three years later, in 2021, Thuraya launched its second bi-type satellite plus cellular phone, the XT Lite, a reviewed of the X5 model. [ 47 ]
In 2022, the Apple iPhone 14 started supporting sending emergency text messages via Globalstar satellites. Apple later acquires a 20% stake in the company in 2024. [ 48 ] It is however not the first mobile phone to combine both cellular and satellite connectivity. [ 46 ] In 2023, the Apple iPhone 15 added satellite communication with roadside service in the United States. [ 49 ] In 2024, six years after the first bi-technology mobile phone, Thuraya launches the Skyphone, its new edition of 2018's one, [ 50 ] also made for 2G / 3G / 4G and satellite convergence within an Androïd -based phone.
Recent Developments
In recent years, some smartphone manufacturers have started adding satellite communication features directly into their devices. For instance, Apple introduced Emergency SOS via satellite with the iPhone 14, allowing users to send emergency messages when they’re outside of cellular coverage. This feature represents a shift toward making satellite connectivity more accessible to everyday users without requiring a separate satellite phone. [ 51 ]
Accessibility and Market Trends
The demand for reliable communication in remote areas has been steadily growing, especially in the face of natural disasters and the rise of remote work. To meet this need, companies like SpaceX and AST SpaceMobile are working on new satellite networks using low Earth orbit (LEO) satellites. These networks are designed to offer wider coverage and faster connections, potentially making satellite communication more affordable and practical for everyday use. [ 52 ]
In 2022, T-Mobile formed a partnership to use Starlink services via existing LTE spectrum, expected in late 2024. [ 53 ] [ 54 ] [ 55 ] [ 56 ] In 2022, AST SpaceMobile started building a 3GPP standard-based cellular space network to allow existing, unmodified smartphones to connect to satellites in areas with coverage gaps. [ 57 ] [ 58 ]
In 2023, Qualcomm announced Snapdragon Satellite, the service that will allow supported cellphones, starting with Snapdragon 8 Gen 2 chipset, to send and receive text messages via 5G Non-Terrestrial Networks (NTN). [ 59 ]
In 2024, Iridium introduced Project Stardust, a standard-based satellite-to-cellphone service supported via NB-IoT for 5G non-terrestrial networks, which will be used over Iridium's existing low-earth orbit satellites. Scheduled for launch in 2026, the service provides messaging, emergency communications and IoT for devices like cars, smartphones, tablets and related consumer applications. [ 60 ] [ 61 ]
Recent Developments: In recent years, some smartphone manufacturers have started adding satellite communication features directly into their devices. For instance, Apple introduced Emergency SOS via satellite with the iPhone 14, allowing users to send emergency messages when they’re outside of cellular coverage. This feature represents a shift toward making satellite connectivity more accessible to everyday users without requiring a separate satellite phone. [ 62 ]
Accessibility and Market Trends: The demand for reliable communication in remote areas has been steadily growing, especially in the face of natural disasters and the rise of remote work. To meet this need, companies like SpaceX and AST SpaceMobile are working on new satellite networks using low Earth orbit (LEO) satellites. These networks are designed to offer wider coverage and faster connections, potentially making satellite communication more affordable and practical for everyday use. [ 63 ] | https://en.wikipedia.org/wiki/Satellite_phone |
Sativa , [ 1 ] sativus , [ 2 ] and sativum [ 3 ] are Latin botanical adjectives meaning cultivated . It is often associated botanically with plants that promote good health and used to designate certain seed-grown domestic crops. [ 4 ]
Sativa (ending in -a) is the feminine form of the adjective, but masculine (-us) and neuter (-um) endings are also used to agree with the gender of the nouns they modify; for example, the masculine Crocus sativus and neuter Pisum sativum .
Examples of crops incorporating this word and its variations into their Latin name include: | https://en.wikipedia.org/wiki/Sativum |
Satmap Systems Limited is a United Kingdom company founded on 19 October 2005 and based in Leatherhead , Surrey . [ 1 ] Since 2007 it has produced a standalone handheld GPS satellite navigation mapping device for use by walkers, cyclists, mountain rescue , emergency services and the military.
The company closed in 2022.
The Active 10 available since 2007 is sold in four different bundles:
The Active 12 introduced in 2014 is more technically advanced than the Active 10 with a High-Resolution 320x488 pixel HVGA screen, doubled RAM , Bluetooth and a barometric altimeter and it is supplied with a high resolution UK GB 1:50,000 map. It is virtually identical in appearance to the Active 10 but is distinguishable by its orange buttons. [ 2 ]
Accessories include a vehicle mount, silicone protective cases and screen covers. It is necessary to swap the caddy holding the batteries to change the power source. Detailed maps can be loaded on to the device by inserting an SD card into the side, 350 map titles from 13 countries are available including; 1:25,000 and 1:50,000 scale Ordnance Survey maps, Harvey Maps, a 1:16,000 A-Z street maps of London and other UK cities, marine maps, United States , Canada , Australia , Europe and Morocco maps. [ 3 ] | https://en.wikipedia.org/wiki/Satmap |
Satoyasu Iimori (19 October 1885 – 13 October 1982) was a Japanese analytical chemist and a pioneer of radiochemistry. He is so called "the father of radiochemistry in Japan", for his establishment of and contribution to the study of radiochemistry which was not developed at that time in Japan. [ 2 ]
He was an honorary research member of the Institute of Physical and Chemical Research (RIKEN) and also an honorary member of the Chemical Society of Japan as well as the Society of the Analytical Chemistry of Japan . After his retirement as a researcher, he became interested in the synthesis of artificial gemstones. [ 3 ]
He was born in Kanazawa , Ishikawa prefecture , in 1885. In 1906 he entered the Department of Chemistry of Tokyo Imperial University, where he studied under Tamemasa Haga and Kikunae Ikeda. He continued his study in the graduate college of the university, and the Degree of Doctorate of Science was conferred for his research related to cyano-complex compounds of iron.
[ 4 ]
In 1917 he entered the Institute of Physical and Chemical Research (RIKEN), where he started to work in the research of analysis of various minerals. As he appointed to study radiochemistry, he went to U.K. in 1919. He was appointed to join the laboratory of Frederick Soddy, however due to the circumstance of Soddy he studied in the laboratory with Charles Heycock for a while, who was the chemist in the Cambridge University. He joined to work in the laboratory of Frederick Soddy from October 1920 until June 1921, in which his study was focused on the radiochemistry. [ 4 ] After returning to Japan, he led his own laboratory as the chief researcher of RIKEN. Along with working for the research of radiochemistry, the laboratory conducted the research of analytical chemistry, mineralogical chemistry, photochemistry, geochemistry especially of rare elements, luminescence of minerals and ceramics as well. [ 3 ]
During World War II , he contributed to the for search uranium ore, as part of the project "Ni-Goh Kenkyu" (Project NIGO), as his major research was mainly focused on radiochemical minerals. After the war the research of radiochemistry was prohibited by US authority, and he started to develop the field of ceramic materials and retired from RIKEN in 1952. [ 4 ]
While he had his specific interest in the "actinolite" he tried to create it and this creation made him start the various creation of artificial gemstones. They are based on his own idea as a mineralogist. [ 5 ] They were called "IL Stone", which had patented in 1955. He established "Iimori Laboratory, Ltd." to run the business for the creation and trading them. Some of those gemstones were exported mostly to the U.S. in 70's as well as traded in Japan. [ 6 ]
Iimori translated "Isotope" into Japanese as "Doi-genso". Isotope is the concept delivered in Soddy's lecture at the London Chemical Conference in 1918. The lecture was introduced in 1919 at the meeting of chemical laboratory of Tokyo Imperial University, where Iimori proposed to translate the word as " doi genso" in Japanese and it was assented immediately. [ 7 ]
Sci.Pap.I.P.C.R:Scientific papers of the Institute of Physical and Chemical Research | https://en.wikipedia.org/wiki/Satoyasu_Iimori |
Saturate, Aromatic, Resin and Asphaltene (SARA) is an analysis method that divides crude oil components according to their polarizability and polarity. The saturate fraction consists of nonpolar material including linear, branched, and cyclic saturated hydrocarbons ( paraffins ). Aromatics , which contain one or more aromatic rings, are slightly more polarizable. The remaining two fractions, resins and asphaltenes , have polar substituents. The distinction between the two is that asphaltenes are insoluble in an excess of heptane (or pentane) whereas resins are miscible with heptane (or pentane).
There are three main methods to obtain SARA results. One has lately emerged as the most popular. That technology is known as the Iatroscan TLC-FID , and it combines thin-layer chromatography (TLC) with flame ionization detection (FID). It is referred to as IP-143. [ 1 ] Other analysis giving SARA numbers might not correspond to the numbers obtained in IP-143. It is therefore always important to know the analysis method when comparing SARA numbers. [ 2 ]
TLC-FID is the only method that is 100 times more sensitive than any of the older methods and faster, taking 30 seconds for 1 sample instead of 1 day. [ 3 ] In comparison, IP-143 method can take up to 3 days, and it does not offer any analytical precision. | https://en.wikipedia.org/wiki/Saturate,_aromatic,_resin_and_asphaltene |
Saturated absorption spectroscopy measures the transition frequency of an atom or molecule between its ground state and an excited state . In saturated absorption spectroscopy, two counter-propagating, overlapped laser beams are sent through a sample of atomic gas. One of the beams stimulates photon emission in excited atoms or molecules when the laser's frequency matches the transition frequency. By changing the laser frequency until these extra photons appear, one can find the exact transition frequency. This method enables precise measurements at room temperature because it is insensitive to doppler broadening . Absorption spectroscopy measures the doppler-broadened transition, so the atoms must be cooled to millikelvin temperatures to achieve the same sensitivity as saturated absorption spectroscopy.
To overcome the problem of Doppler broadening without cooling down the sample to millikelvin temperatures, a classical pump–probe scheme is used. A laser with a relatively high intensity is sent through the atomic vapor, known as the pump beam. Another counter-propagating weak beam is also sent through the atoms at the same frequency, known as the probe beam. The absorption of the probe beam is recorded on a photodiode for various frequencies of the beams.
Although the two beams are at the same frequency, they address different atoms due to natural thermal motion . If the beams are red-detuned with respect to the atomic transition frequency, then the pump beam will be absorbed by atoms moving towards the beam source, while the probe beam will be absorbed by atoms moving away from that source at the same speed in the opposite direction. If the beams are blue-detuned, the opposite occurs.
If, however, the laser is approximately on resonance, these two beams address the same atoms, those with velocity vectors nearly perpendicular to the direction of laser propagation. In the two-state approximation of an atomic transition, the strong pump beam will cause many of the atoms to be in the excited state; when the number of atoms in the ground state and the excited state are approximately equal, the transition is said to be saturated. When a photon from the probe beam passes through the atoms, there is a good chance that, if it encounters an atom, the atom will be in the excited state and will thus undergo stimulated emission , with the photon passing through the sample. Thus, as the laser frequency is swept across the resonance, a small dip in the absorption feature will be observed at each atomic transition (generally hyperfine resonances ). The stronger the pump beam, the wider and deeper the dips in the Gaussian Doppler-broadened absorption feature become. Under perfect conditions, the width of the dip can approach the natural linewidth of the transition. [ 1 ]
A consequence of this method of counter-propagating beams on a system with more than two states is the presence of crossover lines. When two transitions are within a single Doppler-broadened feature and share a common ground state, a crossover peak at a frequency exactly between the two transitions can occur. This is the result of moving atoms seeing the pump and probe beams resonant with two separate transitions. The pump beam can cause the ground state to be depopulated, saturating one transition, while the probe beam finds much fewer atoms in the ground state because of this saturation, and its absorption falls. These crossover peaks can be quite strong, often stronger than the main saturated absorption peaks. [ 1 ]
According to the description of an atom interacting with the electromagnetic field , the absorption of light by the atom depends on the frequency of the incident photons. More precisely, the absorption is characterized by a Lorentzian of width Γ/2 (for reference, Γ ≈ 2π × 6 MHz for common rubidium D-line transitions [ 2 ] ). If we have a cell of atomic vapour at room temperature, then the distribution of velocity will follow a Maxwell–Boltzmann distribution
where N {\displaystyle N} is the number of atoms, k B {\displaystyle k_{B}} is the Boltzmann constant , and m {\displaystyle m} is the mass of the atom. According to the Doppler effect formula in the case of non-relativistic speeds,
where ω 0 {\displaystyle \omega _{0}} is the frequency of the atomic transition when the atom is at rest (the one which is being probed). The value of v {\displaystyle v} as a function of ω 0 {\displaystyle \omega _{0}} and ω lab {\displaystyle \omega _{\text{lab}}} can be inserted in the distribution of velocities. The distribution of absorption as a function of the pulsation will therefore be proportional to a Gaussian with full width at half maximum
For a rubidium atom at room temperature, [ 3 ]
Therefore, without any special trick in the experimental setup probing the maximum of absorption of an atomic vapour, the uncertainty of the measurement will be limited by the Doppler broadening and not by the fundamental width of the resonance.
As the pump and the probe beam must have the same exact frequency, the most convenient solution is for them to come from the same laser. The probe beam can be made of a reflection of the pump beam passed through neutral density filter to reduce its intensity. To fine-tune the frequency of the laser, a diode laser with a piezoelectric transducer that controls the cavity wavelength can be used. Due to photodiode noise, the laser frequency can be swept across the transition and the photodiode reading averaged over many sweeps.
In real atoms, there are sometimes more than two relevant transitions within the sample's Doppler profile (e.g. in alkali atoms with hyperfine interactions ). This will generate the apparition of other dips in the absorption feature due to these new resonances in addition to crossover resonances. | https://en.wikipedia.org/wiki/Saturated_absorption_spectroscopy |
A saturated compound is a chemical compound (or ion) that resists addition reactions , such as hydrogenation , oxidative addition , and binding of a Lewis base . The term is used in many contexts and classes of chemical compounds. Overall, saturated compounds are less reactive than unsaturated compounds. Saturation is derived from the Latin word saturare , meaning 'to fill'. [ 1 ]
Generally distinct types of unsaturated organic compounds are recognized.
For hydrocarbons:
For organic compounds containing heteroatoms (other than C and H), the list of unsaturated groups is long but some common types are:
Ethane
Propane
1-Octanol
Ethylene
Acetylene
alpha -Linolenic acid , an unsaturated fatty acid
Unsaturated compounds generally carry out typical addition reactions that are not possible with saturated compounds such as alkanes. A saturated organic compound has only single bond between carbon atoms. An important class of saturated compounds are the alkanes . Many saturated compounds have functional groups, e.g., alcohols .
The concept of saturation can be described using various naming systems, formulas , and analytical tests . For instance, IUPAC nomenclature is a system of naming conventions used to describe the type and location of unsaturation within organic compounds. The " degree of unsaturation " is a formula used to summarize and diagram the amount of hydrogen that a compound can bind. Unsaturation can be determined by NMR , mass spectrometry , and IR spectroscopy , or by determining a compound's bromine number or iodine number . [ 2 ]
The terms saturated vs unsaturated are often applied to the fatty acid constituents of fats . The triglycerides (fats) that comprise tallow are derived from the saturated stearic and monounsaturated oleic acids . [ 3 ] Many vegetable oils contain fatty acids with one ( monounsaturated ) or more ( polyunsaturated ) double bonds in them.
In organometallic chemistry , a coordinatively unsaturated complex has fewer than 18 valence electrons and thus is susceptible to oxidative addition or coordination of an additional ligand . Unsaturation is the characteristic of many catalysts . The opposite of coordinatively unsaturated is coordinatively saturated. Complexes that are coordinatively saturated rarely exhibit catalytic properties. [ 4 ] [ 5 ]
In physical chemistry , when referring to surface processes, saturation denotes the degree at which a binding site is fully occupied. For example, base saturation refers to the fraction of exchangeable cations that are base cations. | https://en.wikipedia.org/wiki/Saturated_and_unsaturated_compounds |
A saturated fat is a type of fat in which the fatty acid chains have all single bonds between the carbon atoms. A fat known as a glyceride is made of two kinds of smaller molecules: a short glycerol backbone, and fatty acids that each contain a long linear or branched chain of carbon (C) atoms. Along the chain, some carbon atoms are linked by single bonds (-C-C-) and others are linked by double bonds (-C=C-). [ 1 ] A double bond along the carbon chain can react with a pair of hydrogen atoms to change into a single -C-C- bond, with each H atom now bonded to one of the two C atoms. Glyceride fats without any carbon chain double bonds are called saturated because they are "saturated with" hydrogen atoms, having no double bonds available to react with more hydrogen. Saturated fats are generally solid. [ 2 ] All fats, both saturated and unsaturated, contain 9kcal per gram making them more energy dense than both proteins and carbohydrates. [ 3 ]
Most animal fats are saturated. The fats of plants and fish are generally unsaturated . [ 1 ] Various foods contain different proportions of saturated and unsaturated. Many processed foods like foods deep-fried in hydrogenated oil and sausage are high in saturated fat content. Some store-bought baked goods are as well, especially those containing partially hydrogenated oils . [ 4 ] [ 5 ] [ 6 ] Other examples of foods containing a high proportion of saturated fat and dietary cholesterol include animal fat products such as lard or schmaltz , fatty meats and dairy products made with whole or reduced fat milk like yogurt , ice cream , cheese and butter . [ 7 ] Certain vegetable products have high saturated fat content, such as coconut oil and palm kernel oil . [ 8 ]
Guidelines released by many medical organizations, including the World Health Organization , have advocated for reduction in the intake of saturated fat to promote health and reduce the risk from cardiovascular diseases .
While nutrition labels regularly combine them, the saturated fatty acids appear in different proportions among food groups . Lauric and myristic acids are most commonly found in "tropical" oils (e.g., palm kernel , coconut ) and dairy products. The saturated fat in meat, eggs , cacao, and nuts is primarily the triglycerides of palmitic and stearic acids.
Some common examples of saturated fatty acids:
The effect of saturated fat on heart disease has been extensively studied. [ 22 ] [ 23 ] Saturated fat intake increases low-density lipoprotein cholesterol (LDL-C) concentrations. [ 23 ] [ 24 ] The American Heart Association have stated that "the scientific rationale for decreasing saturated fat in the diet has been and remains based on well-established effects of saturated fat to raise low-density lipoprotein (LDL) cholesterol, a leading cause of atherosclerosis". [ 24 ]
Many health authorities, such as the American Heart Association, [ 24 ] the Academy of Nutrition and Dietetics , [ 25 ] the British Dietetic Association , [ 26 ] the World Heart Federation , [ 27 ] the British National Health Service , [ 28 ] among others, [ 29 ] [ 30 ] advise that saturated fat is a risk factor for cardiovascular diseases. In 2020, the World Health Organization recommended lowering dietary intake of saturated fats to less than 10% of total energy consumption, and increasing intake of unsaturated fats. [ 31 ] There is moderate-quality evidence that reducing the proportion of saturated fat in the diet and replacing it with unsaturated fats or carbohydrates for a period of at least two years leads to a reduction in the risk of cardiovascular disease. [ 22 ]
A 2017 review by the Sax Institute for the National Heart Foundation of Australia found that saturated fat consumption is associated with higher mortality and that replacement of saturated fat with polyunsaturated fat decreases risk of cardiovascular disease events and mortality. [ 32 ] In 2019, the UK Scientific Advisory Committee on Nutrition concluded that higher saturated fat consumption is associated with raised blood cholesterol and increased risk of cardiovascular disease. [ 33 ] [ 34 ]
A 2021 review found that diets high in saturated fat were associated with higher mortality from all causes, as well as from cardiovascular disease. [ 35 ]
A 2023 review by the World Health Organization found convincing evidence that higher saturated fat consumption is associated with higher coronary heart disease incidence and mortality. [ 36 ]
A 2023 review by the Academy of Nutrition and Dietetics found moderate certainty evidence to support reducing saturated fat intake for reduced risk of CVD and CVD events. [ 37 ]
A scoping review for Nordic Nutrition Recommendations 2023 found that partial replacement of saturated fatty acid with omega-6 fatty acid decreases the risk of cardiovascular disease and improves the blood lipid profile. [ 38 ]
A 2024 meta-analysis found that odd-chain and longer-chain saturated fatty acids were negatively associated with the risk of cardiovascular disease, including stroke. [ 39 ]
The consumption of saturated fat is generally considered a risk factor for dyslipidemia , which in turn is a risk factor for some types of cardiovascular disease . [ 40 ] [ 41 ] [ 42 ] [ 43 ] [ 44 ]
Abnormal blood lipid levels – high total cholesterol, high levels of triglycerides, high levels of low-density lipoprotein (LDL) or low levels of high-density lipoprotein (HDL) cholesterol – are associated with increased risk of heart disease and stroke. [ 27 ]
Meta-analyses have found a significant relationship between saturated fat and serum cholesterol levels. [ 24 ] [ 45 ] High total cholesterol levels, which may be caused by many factors, are associated with an increased risk of cardiovascular disease. [ 46 ] [ 47 ]
There are other pathways involving obesity , triglyceride levels, insulin sensitivity , endothelial function , and thrombogenicity , among others, that play a role in cardiovascular disease. Different saturated fatty acids have differing effects on various lipid levels. [ 48 ] There is strong evidence that lauric, myristic, and palmitic acids raise LDL-C, while stearic acid is more neutral. [ 49 ]
A 2022 review of cohort studies found that the risk of type 2 diabetes was not associated with dietary intake of total saturated fats, palmitic acid , and stearic acid . Dietary lauric acid and myristic acid , present in plant oils and also in dairy fat, were associated with reduced risk of diabetes. [ 50 ]
Several reviews of case–control studies have found that saturated fat intake is associated with breast cancer risk and mortality. [ 51 ] [ 52 ] [ 53 ] Observational studies have shown that a diet high in saturated fat is associated with increased prostate cancer risk. [ 54 ]
A 2024 systematic review found that higher levels of myristic acid, palmitic acid and stearic acid are associated with increased cancer risk. [ 55 ]
Recommendations to reduce, limit or replace dietary intake of trans fats and saturated fats, in favor of unsaturated fats, are made by the World Health Organization, [ a ] American Heart Association, [ 24 ] Health Canada, [ 85 ] the US Department of Health and Human Services, [ 86 ] the UK National Health Service, [ 87 ] the UK Scientific Advisory Committee on Nutrition, [ 33 ] the Australian Department of Health and Aging, [ 88 ] the Singapore Ministry of Health, [ 89 ] the Indian Ministry of Health and Family Welfare, [ 90 ] the New Zealand Ministry of Health, [ 91 ] and Hong Kong's Department of Health. [ 92 ]
In 2003, the World Health Organization (WHO) and Food and Agriculture Organization (FAO) expert consultation report concluded: [ 93 ]
The evidence shows that intake of saturated fatty acids is directly related to cardiovascular risk. The traditional target is to restrict the intake of saturated fatty acids to less than 10% of daily energy intake and less than 7% for high-risk groups. If populations are consuming less than 10%, they should not increase that level of intake. Within these limits, the intake of foods rich in myristic and palmitic acids should be replaced by fats with a lower content of these particular fatty acids. In developing countries, however, where energy intake for some population groups may be inadequate, energy expenditure is high and body fat stores are low (BMI <18.5 kg/m 2 ). The amount and quality of fat supply have to be considered keeping in mind the need to meet energy requirements. Specific sources of saturated fat, such as coconut and palm oil, provide low-cost energy and may be an important source of energy for the poor.
A 2004 statement released by the Centers for Disease Control (CDC) determined that "Americans need to continue working to reduce saturated fat intake…" [ 94 ] In addition, reviews by the American Heart Association led the Association to recommend reducing saturated fat intake to less than 7% of total calories according to its 2006 recommendations. [ 95 ] [ 96 ] This concurs with similar conclusions made by the US Department of Health and Human Services , which determined that reduction in saturated fat consumption would positively affect health and reduce the prevalence of heart disease. [ 97 ]
The United Kingdom , National Health Service claims the majority of British people eat too much saturated fat. The British Heart Foundation also advises people to cut down on saturated fat, and to read labels on the food they buy. [ 98 ] [ 99 ] The British Nutrition Foundation have said that based on the totality of available evidence the saturated fatty acids should make up no more than 10% of total dietary energy. [ 100 ]
A 2004 review stated that "no lower safe limit of specific saturated fatty acid intakes has been identified" and recommended that the influence of varying saturated fatty acid intakes against a background of different individual lifestyles and genetic backgrounds should be the focus in future studies. [ 101 ]
Blanket recommendations to lower saturated fat were criticized at a 2010 conference debate of the American Dietetic Association for focusing too narrowly on reducing saturated fats rather than emphasizing increased consumption of healthy fats and unrefined carbohydrates. Concern was expressed over the health risks of replacing saturated fats in the diet with refined carbohydrates, which carry a high risk of obesity and heart disease, particularly at the expense of polyunsaturated fats which may have health benefits. None of the panelists recommended heavy consumption of saturated fats, emphasizing instead the importance of overall dietary quality to cardiovascular health. [ 102 ]
In a 2017 comprehensive review of the literature and clinical trials, the American Heart Association published a recommendation that saturated fat intake be reduced or replaced by products containing monounsaturated and polyunsaturated fats, a dietary adjustment that could reduce the risk of cardiovascular diseases by 30%. [ 24 ]
The two-dimensional illustration has implicit hydrogen atoms bonded to each of the carbon atoms in the polycarbon tail of the myristic acid molecule (there are 13 carbon atoms in the tail; 14 carbon atoms in the entire molecule).
Carbon atoms are also implicitly drawn, as they are portrayed as intersections between two straight lines. "Saturated," in general, refers to a maximum number of hydrogen atoms bonded to each carbon of the polycarbon tail as allowed by the Octet Rule . This also means that only single bonds ( sigma bonds ) will be present between adjacent carbon atoms of the tail. | https://en.wikipedia.org/wiki/Saturated_fat |
In mathematical logic , and particularly in its subfield model theory , a saturated model M is one that realizes as many complete types as may be "reasonably expected" given its size. For example, an ultrapower model of the hyperreals is ℵ 1 {\displaystyle \aleph _{1}} -saturated, meaning that every descending nested sequence of internal sets has a nonempty intersection. [ 1 ]
Let κ be a finite or infinite cardinal number and M a model in some first-order language . Then M is called κ -saturated if for all subsets A ⊆ M of cardinality less than κ , the model M realizes all complete types over A . The model M is called saturated if it is | M |-saturated where | M | denotes the cardinality of M . That is, it realizes all complete types over sets of parameters of size less than | M |. According to some authors, a model M is called countably saturated if it is ℵ 1 {\displaystyle \aleph _{1}} -saturated; that is, it realizes all complete types over countable sets of parameters. [ 2 ] According to others, it is countably saturated if it is countable and saturated. [ 3 ]
The seemingly more intuitive notion—that all complete types of the language are realized—turns out to be too weak (and is appropriately named weak saturation , which is the same as 1-saturation). The difference lies in the fact that many structures contain elements that are not definable (for example, any transcendental element of R is, by definition of the word, not definable in the language of fields ). However, they still form a part of the structure, so we need types to describe relationships with them. Thus we allow sets of parameters from the structure in our definition of types. This argument allows us to discuss specific features of the model that we may otherwise miss—for example, a bound on a specific increasing sequence c n can be expressed as realizing the type { x ≥ c n : n ∈ ω}, which uses countably many parameters. If the sequence is not definable, this fact about the structure cannot be described using the base language, so a weakly saturated structure may not bound the sequence, while an ℵ 1 -saturated structure will.
The reason we only require parameter sets that are strictly smaller than the model is trivial: without this restriction, no infinite model is saturated. Consider a model M , and the type { x ≠ m : m ∈ M }. Each finite subset of this type is realized in the (infinite) model M , so by compactness it is consistent with M , but is trivially not realized. Any definition that is universally unsatisfied is useless; hence the restriction.
Saturated models exist for certain theories and cardinalities:
Both the theory of Q and the theory of the countable random graph can be shown to be ω-categorical through the back-and-forth method . This can be generalized as follows: the unique model of cardinality κ of a countable κ -categorical theory is saturated.
However, the statement that every model has a saturated elementary extension is not provable in ZFC . In fact, this statement is equivalent to [ citation needed ] the existence of a proper class of cardinals κ such that κ < κ = κ . The latter identity is equivalent to κ = λ + = 2 λ for some λ , or κ is strongly inaccessible .
The notion of saturated model is dual to the notion of prime model in the following way: let T be a countable theory in a first-order language (that is, a set of mutually consistent sentences in that language) and let P be a prime model of T . Then P admits an elementary embedding into any other model of T . The equivalent notion for saturated models is that any "reasonably small" model of T is elementarily embedded in a saturated model, where "reasonably small" means cardinality no larger than that of the model in which it is to be embedded. Any saturated model is also homogeneous . However, while for countable theories there is a unique prime model, saturated models are necessarily specific to a particular cardinality. Given certain set-theoretic assumptions, saturated models (albeit of very large cardinality) exist for arbitrary theories. For λ - stable theories, saturated models of cardinality λ exist. | https://en.wikipedia.org/wiki/Saturated_model |
In mathematics , particularly in the subfields of set theory and topology , a set C {\displaystyle C} is said to be saturated with respect to a function f : X → Y {\displaystyle f:X\to Y} if C {\displaystyle C} is a subset of f {\displaystyle f} 's domain X {\displaystyle X} and if whenever f {\displaystyle f} sends two points c ∈ C {\displaystyle c\in C} and x ∈ X {\displaystyle x\in X} to the same value then x {\displaystyle x} belongs to C {\displaystyle C} (that is, if f ( x ) = f ( c ) {\displaystyle f(x)=f(c)} then x ∈ C {\displaystyle x\in C} ). Said more succinctly, the set C {\displaystyle C} is called saturated if C = f − 1 ( f ( C ) ) . {\displaystyle C=f^{-1}(f(C)).}
In topology , a subset of a topological space ( X , τ ) {\displaystyle (X,\tau )} is saturated if it is equal to an intersection of open subsets of X . {\displaystyle X.} In a T 1 space every set is saturated.
Let f : X → Y {\displaystyle f:X\to Y} be a map.
Given any subset S ⊆ X , {\displaystyle S\subseteq X,} define its image under f {\displaystyle f} to be the set: f ( S ) := { f ( s ) : s ∈ S } {\displaystyle f(S):=\{f(s)~:~s\in S\}} and define its preimage or inverse image under f {\displaystyle f} to be the set: f − 1 ( S ) := { x ∈ X : f ( x ) ∈ S } . {\displaystyle f^{-1}(S):=\{x\in X~:~f(x)\in S\}.}
Given y ∈ Y , {\displaystyle y\in Y,} the fiber of f {\displaystyle f} over y {\displaystyle y} is defined to be the preimage: f − 1 ( y ) := f − 1 ( { y } ) = { x ∈ X : f ( x ) = y } . {\displaystyle f^{-1}(y):=f^{-1}(\{y\})=\{x\in X~:~f(x)=y\}.}
Any preimage of a single point in f {\displaystyle f} 's codomain Y {\displaystyle Y} is referred to as a fiber of f . {\displaystyle f.}
A set C {\displaystyle C} is called f {\displaystyle f} -saturated and is said to be saturated with respect to f {\displaystyle f} if C {\displaystyle C} is a subset of f {\displaystyle f} 's domain X {\displaystyle X} and if any of the following equivalent conditions are satisfied: [ 1 ]
Related to computability theory , this notion can be extended to programs. Here, considering a subset A ⊆ N {\displaystyle A\subseteq \mathbb {N} } , this can be considered saturated (or extensional ) if ∀ m , n ∈ N , m ∈ A , ∨ ϕ m = ϕ n ⇒ n ∈ A {\displaystyle \forall m,n\in \mathbb {N} ,m\in A,\vee \phi _{m}=\phi _{n}\Rightarrow n\in A} . In words, given two programs, if the first program is in the set of programs satisfying the property and two programs are computing the same thing, then also the second program satisfies the property. This means that if one program with a certain property is in the set, all programs computing the same function must also be in the set).
In this context, this notion can extend Rice's theorem , stating that:
Let A {\displaystyle A} be a subset such that A ≠ ∅ , A ≠ N , A ⊆ N {\displaystyle A\neq \emptyset ,A\neq \mathbb {N} ,A\subseteq N} . If A {\displaystyle A} is saturated, then A {\displaystyle A} is not recursive.
Let f : X → Y {\displaystyle f:X\to Y} be any function. If S {\displaystyle S} is any set then its preimage C := f − 1 ( S ) {\displaystyle C:=f^{-1}(S)} under f {\displaystyle f} is necessarily an f {\displaystyle f} -saturated set. In particular, every fiber of a map f {\displaystyle f} is an f {\displaystyle f} -saturated set.
The empty set ∅ = f − 1 ( ∅ ) {\displaystyle \varnothing =f^{-1}(\varnothing )} and the domain X = f − 1 ( Y ) {\displaystyle X=f^{-1}(Y)} are always saturated. Arbitrary unions of saturated sets are saturated, as are arbitrary intersections of saturated sets.
Let S {\displaystyle S} and T {\displaystyle T} be any sets and let f : X → Y {\displaystyle f:X\to Y} be any function.
If S {\displaystyle S} or T {\displaystyle T} is f {\displaystyle f} -saturated then f ( S ∩ T ) = f ( S ) ∩ f ( T ) . {\displaystyle f(S\cap T)~=~f(S)\cap f(T).}
If T {\displaystyle T} is f {\displaystyle f} -saturated then f ( S ∖ T ) = f ( S ) ∖ f ( T ) {\displaystyle f(S\setminus T)~=~f(S)\setminus f(T)} where note, in particular, that no requirements or conditions were placed on the set S . {\displaystyle S.}
If τ {\displaystyle \tau } is a topology on X {\displaystyle X} and f : X → Y {\displaystyle f:X\to Y} is any map then set τ f {\displaystyle \tau _{f}} of all U ∈ τ {\displaystyle U\in \tau } that are saturated subsets of X {\displaystyle X} forms a topology on X . {\displaystyle X.} If Y {\displaystyle Y} is also a topological space then f : ( X , τ ) → Y {\displaystyle f:(X,\tau )\to Y} is continuous (respectively, a quotient map ) if and only if the same is true of f : ( X , τ f ) → Y . {\displaystyle f:\left(X,\tau _{f}\right)\to Y.}
This topology-related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Saturated_set |
Saturation arithmetic is a version of arithmetic in which all operations, such as addition and multiplication , are limited to a fixed range between a minimum and maximum value.
If the result of an operation is greater than the maximum, it is set (" clamped ") to the maximum; if it is below the minimum, it is clamped to the minimum. The name comes from how the value becomes "saturated" once it reaches the extreme values; further additions to a maximum or subtractions from a minimum will not change the result.
For example, if the valid range of values is from −100 to 100, the following saturating arithmetic operations produce the following values:
Here is another example for saturating subtraction when the valid range is from 0 to 100 instead:
As can be seen from these examples, familiar properties like associativity and distributivity may fail in saturation arithmetic. [ a ] This makes it unpleasant to deal with in abstract mathematics , but it has an important role to play in digital hardware and algorithms where values have maximum and minimum representable ranges.
Typically, general-purpose microprocessors do not implement integer arithmetic operations using saturation arithmetic; instead, they use the easier-to-implement modular arithmetic , in which values exceeding the maximum value " wrap around " to the minimum value, like the hours on a clock passing from 12 to 1. In hardware, modular arithmetic with a minimum of zero and a maximum of r n − 1, where r is the radix , can be implemented by simply discarding all but the lowest n digits. For binary hardware, which the vast majority of modern hardware is, the radix is 2, and the digits are bits.
However, although more difficult to implement, saturation arithmetic has numerous practical advantages. The result is as numerically close to the true answer as possible; for 8-bit binary signed arithmetic, when the correct answer is 130, it is considerably less surprising to get an answer of 127 from saturating arithmetic than to get an answer of −126 from modular arithmetic. Likewise, for 8-bit binary unsigned arithmetic, when the correct answer is 258, it is less surprising to get an answer of 255 from saturating arithmetic than to get an answer of 2 from modular arithmetic.
Saturation arithmetic also enables overflow of additions and multiplications to be detected consistently without an overflow bit or excessive computation, by simple comparison with the maximum or minimum value (provided the datum is not permitted to take on these values).
Additionally, saturation arithmetic enables efficient algorithms for many problems, particularly in digital signal processing . For example, adjusting the volume level of a sound signal can result in overflow, and saturation causes significantly less distortion to the sound than wrap-around. In the words of researchers G. A. Constantinides et al.: [ 1 ]
When adding two numbers using two's complement representation, overflow results in a "wrap-around" phenomenon. The result can be a catastrophic loss in signal-to-noise ratio in a DSP system. Signals in DSP designs are therefore usually either scaled appropriately to avoid overflow for all but the most extreme input vectors, or produced using saturation arithmetic components.
Saturation arithmetic operations are available on many modern platforms, and in particular was one of the extensions made by the Intel MMX platform, specifically for such signal-processing applications. This functionality is also available in wider versions in the SSE2 and AVX2 integer instruction sets. It is also available in ARM NEON instruction set.
Saturation arithmetic for integers has also been implemented in software for a number of programming languages including C , C++ , such as the GNU Compiler Collection , [ 2 ] LLVM IR, and Eiffel . Support for saturation arithmetic is included as part of the C++26 Standard Library . This helps programmers anticipate and understand the effects of overflow better, and in the case of compilers usually pick the optimal solution.
Saturation is challenging to implement efficiently in software on a machine with only modular arithmetic operations, since simple implementations require branches that create huge pipeline delays. However, it is possible to implement saturating addition and subtraction in software without branches , using only modular arithmetic and bitwise logical operations that are available on all modern CPUs and their predecessors, including all x86 CPUs (back to the original Intel 8086 ) and some popular 8-bit CPUs (some of which, such as the Zilog Z80 , are still in production). On the other hand, on simple 8-bit and 16-bit CPUs, a branching algorithm might actually be faster if programmed in assembly, since there are no pipelines to stall, and each instruction always takes multiple clock cycles. On the x86, which provides overflow flags and conditional moves , very simple branch-free code is possible. [ 3 ]
Although saturation arithmetic is less popular for integer arithmetic in hardware, the IEEE floating-point standard , the most popular abstraction for dealing with approximate real numbers , uses a form of saturation in which overflow is converted into "infinity" or "negative infinity", and any other operation on this result continues to produce the same value. This has the advantage over simple saturation that later operations decreasing the value will not end up producing a misleadingly "reasonable" result, such as in the computation x 2 − y 2 {\textstyle {\sqrt {x^{2}-y^{2}}}} . Alternatively, there may be special states such as "exponent overflow" (and "exponent underflow") that will similarly persist through subsequent operations, or cause immediate termination, or be tested for as in IF ACCUMULATOR OVERFLOW ... as in FORTRAN for the IBM 704 (October 1956). | https://en.wikipedia.org/wiki/Saturation_arithmetic |
A saturation dome is a graphical representation of the combination of vapor and gas that is used in thermodynamics . It can be used to find either the pressure or the specific volume as long as one already has at least one of these properties .
A saturation dome uses the projection of a P– v –T diagram (pressure, specific volume, and temperature ) onto the P– v plane. The points that create the left-hand side of the dome represent the saturated liquid states, while the points on the right-hand side represent the saturated vapor states (commonly referred to as the “dry” region). On the left-hand side of the dome there is compressed liquid and on the right-hand side there is superheated gas. [ 1 ]
Within the dome itself, there is a liquid–vapor mixture. This two-phase region is commonly referred to as the “wet” region. The percentage of liquid and vapor can be calculated using vapor quality. [ 2 ] The triple state line is where the three phases (solid, liquid, and vapor) exist in equilibrium.
The point at the very top of the dome is called the critical point. This point is where the saturated liquid and saturated vapor lines meet. Past this point, it is impossible for a liquid–vapor transformation to occur. [ 3 ] It is also where the critical temperature and critical pressure meet. Beyond this point, it is also impossible to distinguish between the liquid and vapor phases.
A saturation state is the point where a phase change begins or ends. For example, the saturated liquid line represents the point where any further addition of energy will cause a small portion of the liquid to convert to vapor. Likewise, along the saturated vapor line, any removal of energy will cause some of the vapor to condense back into a liquid, producing a mixture. When a substance reaches the saturated liquid line it is commonly said to be at its boiling point. The temperature will remain constant while it is at constant pressure underneath the saturation dome (boiling water stays at a constant of 212F) until it reaches the saturated vapor line. This line is where the mixture has converted completely to vapor. Further heating of the saturated vapor will result in a superheated vapor state. This is because the vapor will be at a temperature higher than the saturation temperature (212F for water) for a given pressure. [ 4 ]
Vapor quality refers to the vapor–liquid mixture that is contained underneath the
dome. This quality is defined as the fraction of the total mixture which is vapor, based on
mass. [ 3 ] A
fully saturated vapor has a quality of 100% while a saturated liquid has a quality of 0%.
Quality can be estimated graphically as it is related to the specific volume, or how far horizontally across the dome the point exists. At the saturated liquid state, the specific volume is denoted as v f , while at the saturated vapor stage it is denoted as v g .
Quality can be calculated by the equation:
x = v − v f v g − v f {\displaystyle x={v-v_{f} \over v_{g}-v_{f}}} [ 5 ] | https://en.wikipedia.org/wiki/Saturation_dome |
Saturation mutagenesis , or site saturation mutagenesis (SSM) , or simply site saturation , is a random mutagenesis technique used in protein engineering , in which a single codon or set of codons is substituted with all possible amino acids at the position. [ 1 ] There are many variants of the site saturation technique, from paired site saturation (saturating two positions in every mutant in the library) to scanning single-site saturation (performing a site saturation at each site in the protein, resulting in a library of size 20 n , where n is the number of peptides in the protein, or n -site saturation , where n sites in a peptide would be site saturated, with a library size of 20 n , where if the length of your peptide is n , you have complete randomization.
Saturation mutagenesis is commonly achieved by site-directed mutagenesis PCR with a randomised codon in the primers (e.g. SeSaM ) [ 2 ] or by artificial gene synthesis , with a mixture of synthesis nucleotides used at the codons to be randomised. [ 3 ]
Different degenerate codons can be used to encode sets of amino acids. [ 1 ] Because some amino acids are encoded by more codons than others, the exact ratio of amino acids cannot be equal. Additionally, it is usual to use degenerate codons that minimise stop codons (which are generally not desired). Consequently, the fully randomised 'NNN' is not ideal, and alternative, more restricted degenerate codons are used. 'NNK' and 'NNS' have the benefit of encoding all 20 amino acids, but still encode a stop codon 3% of the time. Alternative codons such as 'NDT', 'DBK' avoid stop codons entirely, and encode a minimal set of amino acids that still encompass all the main biophysical types (anionic, cationic, aliphatic hydrophobic, aromatic hydrophobic, hydrophilic, small). [ 1 ] In the case there is no restriction to use a single degenerate codon only, it is possible to reduce the bias considerably. [ 4 ] [ 5 ] Several computational tools were developed to allow high level of control over the degenerate codons and their corresponding amino acids. [ 6 ] [ 7 ] [ 8 ]
Saturation mutagenesis is commonly used to generate variants for directed evolution . [ 9 ] [ 10 ] | https://en.wikipedia.org/wiki/Saturation_mutagenesis |
In thermodynamics , the saturation vapor curve is the curve separating the two- phase state and the superheated vapor state in the T–s diagram ( temperature–entropy diagram ).
The saturated liquid curve is the curve separating the subcooled liquid state and the two-phase state in the T–s diagram. [ 1 ]
When used in a power cycle , the fluid expansion depends strongly on the nature of this saturation curve:
This thermodynamics -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Saturation_vapor_curve |
The saturation vapor density (SVD) is the maximum density of water vapor in air at a given temperature. [ 1 ] The concept is related to saturation vapor pressure (SVP). It can be used to calculate exact quantity of water vapor in the air from a relative humidity (RH = % local air humidity measured / local total air humidity possible ) Given an RH percentage, the density of water in the air is given by RH × SVD = Actual Vapor Density . Alternatively, RH can be found by RH = Actual Vapor Density / SVD . As relative humidity is a dimensionless quantity (often expressed in terms of a percentage), vapor density can be stated in units of grams or kilograms per cubic meter.
For low temperatures (below approximately 400 K), SVD can be approximated from the SVP by the ideal gas law : P V = n R T where P is the SVP, V is the volume, n is the number of moles , R is the gas constant and T is the temperature in kelvins . The number of moles is related to density by n = m / M , where m is the mass of water present and M is the molar mass of water [ clarification needed ] (18.01528 grams/mole). Thus, we get P M / R T = m / V = density.
The values shown at hyperphysics-sources [ 2 ] indicate that the saturated vapor density is 4.85 g/m 3 at 273 K, at which the saturated vapor pressure is 4.58 mm of Hg or 610.616447 Pa (760 mm of Hg ≈ 1 atm = 1.01325 * 10 5 Pa). | https://en.wikipedia.org/wiki/Saturation_vapor_density |
Saturation velocity is the maximum velocity a charge carrier in a semiconductor , generally an electron , attains in the presence of very high electric fields . [ 1 ] When this happens, the semiconductor is said to be in a state of velocity saturation . [ 2 ] Charge carriers normally move at an average drift speed proportional to the electric field strength they experience temporally. The proportionality constant is known as mobility of the carrier, which is a material property. A good conductor would have a high mobility value for its charge carrier, which means higher velocity, and consequently higher current values for a given electric field strength. There is a limit though to this process and at some high field value, a charge carrier can not move any faster, having reached its saturation velocity, due to mechanisms that eventually limit the movement of the carriers in the material. [ 3 ]
As the applied electric field increases from that point, the carrier velocity no longer increases because the carriers lose energy through increased levels of interaction with the lattice, by emitting phonons and even photons as soon as the carrier energy is large enough to do so. [ 4 ]
Saturation velocity is a very important parameter in the design of semiconductor devices, especially field effect transistors , which are basic building blocks of almost all modern integrated circuits . Typical values of saturation velocity may vary greatly for different materials, for example for Si it is in the order of 1×10 7 cm/s, for GaAs 1.2×10 7 cm/s, while for 6H-SiC , it is near 2×10 7 cm/s. Typical electric field strengths at which carrier velocity saturates is usually on the order of 10-100 kV/cm. Both saturation field and the saturation velocity of a semiconductor material are typically strong function of impurities, crystal defects and temperature.
For extremely small scale devices, where the high-field regions may be comparable or smaller than the average mean free path of the charge carrier, one can observe velocity overshoot , or hot electron effects which has become more important as the transistor geometries continually decrease to enable design of faster, larger and more dense integrated circuits. [ 5 ] The regime where the two terminals between which the electron moves is much smaller than the mean free path, is sometimes referred as ballistic transport . There have been numerous attempts in the past to build transistors based on this principle without much success. Nevertheless, developing field of nanotechnology , and new materials such as Carbon nanotubes and graphene , offers new hope.
Though in a semiconductor such as Si saturation velocity of a carrier is same as the peak velocity of the carrier, for some other materials with more complex energy band structures, this is not true. In GaAs or InP for example the carrier drift velocity reaches to a maximum as a function of field and then it begins to actually decrease as the electric field applied is increased further. Carriers which have gained enough energy are kicked up to a different conduction band which presents a lower drift velocity and eventually a lower saturation velocity in these materials. This results in an overall decrease of current for higher voltage until all electrons are in the "slow" band and this is the principle behind operation of a Gunn diode , which can display negative differential resistivity. Due to the transfer of electrons to a different conduction band involved, such devices, usually single terminal, are referred to as Transferred electron devices , or TEDs.
When designing semiconductor devices , especially on a sub-micrometre scale as used in modern microprocessors , velocity saturation is an important design characteristic. Velocity saturation greatly affects the voltage transfer characteristics of a field-effect transistor , which is the basic device used in most integrated circuits . If a semiconductor device enters velocity saturation, an increase in voltage applied to the device will not cause a linear increase in current as would be expected by Ohm's law . Instead, the current may only increase by a small amount, or not at all. It is possible to take advantage of this result when trying to design a device that will pass a constant current regardless of the voltage applied, a current limiter in effect. | https://en.wikipedia.org/wiki/Saturation_velocity |
Saturn's hexagon is a persistent approximately hexagonal cloud pattern around the north pole of the planet Saturn , located at about 78°N. [ 1 ] [ 2 ] [ 3 ] The sides of the hexagon are about 14,500 km (9,000 mi) long, [ 4 ] [ 5 ] [ 6 ] [ 7 ] which is about 2,000 km (1,200 mi) longer than the diameter of Earth . [ 8 ] The hexagon may be a bit more than 29,000 km (18,000 mi) wide, [ 9 ] may be 300 km (190 mi) high, and may be a jet stream made of atmospheric gases moving at 320 km/h (200 mph). [ 4 ] [ 5 ] [ 10 ] It rotates with a period of 10h 39m 24s , the same period as Saturn's radio emissions from its interior. [ 11 ] The hexagon does not shift in longitude like other clouds in the visible atmosphere. [ 12 ]
Saturn's hexagon was discovered during the Voyager mission in 1981, and was later revisited by Cassini-Huygens in 2006. During the Cassini mission, the hexagon changed from a mostly blue color to more of a golden color. Saturn's south pole does not have a hexagon, as verified by Hubble observations. It does, however, have a vortex , and there is also a vortex inside the northern hexagon. [ 13 ] Multiple hypotheses for the hexagonal cloud pattern have been developed.
Saturn's polar hexagon was discovered by David Godfrey in 1987 [ 14 ] from piecing together fly-by views from the 1981 Voyager mission , [ 15 ] [ 16 ] and was revisited in 2006 by the Cassini mission . [ 17 ]
Cassini was able to take only thermal infrared images of the hexagon until it passed into sunlight in January 2009. [ 18 ] Cassini was also able to take a video of the hexagonal weather pattern while traveling at the same speed as the planet, therefore recording only the movement of the hexagon. [ 19 ]
After its discovery, and after it came back into the sunlight, amateur astronomers managed to get images showing the hexagon from Earth, even with modest-sized telescopes. [ 20 ] [ self-published source? ]
Between 2012 and 2016, the hexagon changed from a mostly blue color to more of a golden color. [ 21 ] One hypothesis for this is that sunlight is creating haze as the pole is exposed to sunlight due to the change in season. These changes were observed by the Cassini spacecraft. [ 21 ]
One hypothesis, developed at Oxford University, is that the hexagon forms where there is a steep latitudinal gradient in the speed of the atmospheric winds in Saturn's atmosphere. [ 22 ] Similar regular shapes were created in the laboratory when a circular tank of liquid was rotated at different speeds at its centre and periphery. The most common shape was six sided, but shapes with three to eight sides were also produced. The shapes form in an area of turbulent flow between the two different rotating fluid bodies with dissimilar speeds. [ 22 ] [ 23 ] A number of stable vortices of similar size form on the slower (south) side of the fluid boundary and these interact with each other to space themselves out evenly around the perimeter. The presence of the vortices influences the boundary to move northward where each is present and this gives rise to the polygon effect. [ 23 ] Polygons do not form at wind boundaries unless the speed differential and viscosity parameters are within certain margins and so are not present at other likely places, such as Saturn's south pole or the poles of Jupiter.
Other researchers claim that lab studies exhibit vortex streets , a series of spiraling vortices not observed in Saturn's hexagon. Simulations show that a shallow, slow, localized meandering jetstream in the same direction as Saturn's prevailing clouds are able to match the observed behaviors of Saturn's hexagon with the same boundary stability. [ 24 ]
Developing barotropic instability of Saturn's North Polar hexagonal circumpolar jet (Jet) plus North Polar vortex (NPV) system produces a long-living structure akin to the observed hexagon, which is not the case of the Jet-only system, which was studied in this context in a number of papers in literature. The NPV, thus, plays a decisive dynamical role to stabilize hexagon jets. The influence of moist convection, which was recently suggested to be at the origin of Saturn's NPV system in the literature, is investigated in the framework of the barotropic rotating shallow water model and does not alter the conclusions. [ 25 ]
A 2020 mathematical study at the California Institute of Technology found that a stable geometric arrangement of the polygons can occur on any planet when a storm is surrounded by a ring of winds turning in the opposite direction to the storms itself, called an anticyclonic ring, or anticyclonic shielding. [ 26 ] [ 27 ] Such shielding creates a vorticity gradient in the background of a neighbor cyclone, causing mutual rejection between the cyclones (similar to the effect of beta-drift ). Although apparently shielded, the polar cyclone on Saturn cannot hold a polygonal pattern of circumpolar cyclones such as Jupiter's due to the bigger size and slower wind speed of Saturn's polar cyclone, so the side-adjacent vortices and deep barotropic instability (Cassini's wind speed measurements preclude shallower barotropic instability at least at the time of the Cassini encounter), or possibly baroclinic instabilities remain as the most viable explanations for Saturn's sustained hexagon. [ 28 ]
Solar System → Local Interstellar Cloud → Local Bubble → Gould Belt → Orion Arm → Milky Way → Milky Way subgroup → Local Group → Local Sheet → Virgo Supercluster → Laniakea Supercluster → Local Hole → Observable universe → Universe Each arrow ( → ) may be read as "within" or "part of". | https://en.wikipedia.org/wiki/Saturn's_hexagon |
Planetary symbols are used in astrology and traditionally in astronomy to represent a classical planet (which includes the Sun and the Moon) or one of the modern planets. The classical symbols were also used in alchemy for the seven metals known to the ancients , which were associated with the planets , and in calendars for the seven days of the week associated with the seven planets. The original symbols date to Greco-Roman astronomy ; their modern forms developed in the 16th century, and additional symbols would be created later for newly discovered planets.
The seven classical planets, their symbols, days and most commonly associated planetary metals are:
The International Astronomical Union (IAU) discourages the use of these symbols in modern journal articles, and their style manual proposes one- and two-letter abbreviations for the names of the planets for cases where planetary symbols might be used, such as in the headings of tables. [ 1 ] The modern planets with their traditional symbols and IAU abbreviations are:
The symbols of Venus and Mars are also used to represent female and male in biology following a convention introduced by Carl Linnaeus in the 1750s.
The origins of the planetary symbols can be found in the attributes given to classical deities. The Roman planisphere of Bianchini (2nd century, currently in the Louvre , inv. Ma 540) [ 2 ] shows the seven planets represented by portraits of the seven corresponding gods, each a bust with a halo and an iconic object or dress, as follows: Mercury has a caduceus and a winged cap; Venus has a necklace and a shining mirror; Mars has a war-helmet and a spear; Jupiter has a laurel crown and a staff; Saturn has a conical headdress and a scythe; the Sun has rays emanating from his head; and the Moon has a crescent atop her head.
The written symbols for Mercury, Venus, Jupiter, and Saturn have been traced to forms found in late Greek papyri. [ 3 ] [ b ]
Early forms are also found in medieval Byzantine codices which preserve horoscopes. [ 4 ]
A diagram in the astronomical compendium by Johannes Kamateros (12th century) closely resembles the 11th-century forms shown above, with the Sun represented by a circle with a single ray, Jupiter by the letter zeta (the initial of Zeus , Jupiter's counterpart in Greek mythology), Mars by a round shield in front of a diagonal spear, and the remaining classical planets by symbols resembling the modern ones, though without the crosses seen in modern versions of Mercury, Venus, Jupiter and Saturn. [ citation needed ] These crosses first appear in the late 15th or early 16th century. According to Maunder, the addition of crosses appears to be "an attempt to give a savour of Christianity to the symbols of the old pagan gods." [ 5 ] The modern forms of the classical planetary symbols are found in a woodcut of the seven planets in a Latin translation of Abu Ma'shar al-Balkhi 's De Magnis Coniunctionibus printed at Venice in 1506, represented as the corresponding gods riding chariots. [ 6 ]
Earth is not one of the classical planets, as "planets" by definition were "wandering stars" as seen from Earth's surface.
Earth's status as planet is a consequence of heliocentrism in the 16th century.
Nonetheless, there is a pre-heliocentric symbol for the world, now used as a planetary symbol for the Earth. This is a circle crossed by two lines, horizontal and vertical, representing the world divided by four rivers into the four quarters of the world (often translated as the four "corners" of the world): . A variant, now obsolete, had only the horizontal line: . [ 7 ]
A medieval European symbol for the world – the globus cruciger , (the globe surmounted by a Christian cross ) – is also used as a planetary symbol; it resembles an inverted symbol for Venus.
The planetary symbols for Earth are encoded in Unicode at U+1F728 🜨 ALCHEMICAL SYMBOL FOR VERDIGRIS and U+2641 ♁ EARTH .
The crescent shape has been used to represent the Moon since antiquity. In classical antiquity, it is worn by lunar deities ( Selene/Luna , Artemis/Diana , Men , etc.) either on the head or behind the shoulders, with its horns pointing upward.
The representation of the moon as a simple crescent with the horns pointing to the side (as a heraldic crescent increscent or crescent decrescent ) is attested from late Classical times.
The same symbol can be used in a different context not for the Moon itself but for a lunar phase , as part of a sequence of four symbols
for "new moon" (U+1F311 🌑︎), "waxing" (U+263D ☽︎), "full moon" (U+1F315 🌕︎) and "waning" (U+263E ☾︎).
The symbol ☿ for Mercury is a caduceus (a staff intertwined with two serpents), a symbol associated with Mercury / Hermes throughout antiquity. Some time after the 11th century, a cross was added to the bottom of the staff to make it seem more Christian. [ 3 ]
The ☿ symbol has also been used to indicate intersex , transgender , or non-binary gender . [ 8 ] A related usage is for the 'worker' or 'neuter' sex among social insects that is neither male nor (due to its lack of reproductive capacity) fully female, such as worker bees . [ 9 ] It was also once the designated symbol for hermaphroditic or 'perfect' flowers , [ 10 ] but botanists now use ⚥ for these. [ 11 ]
Its Unicode codepoint is U+263F ☿ MERCURY .
The Venus symbol , ♀, consists of a circle with a small cross below it.
It has been interpreted as a depiction of the hand-mirror of the goddess, which may also explain Venus's association with the planetary metal copper, as mirrors in antiquity were made of polished copper, [ 12 ] [ d ] though this is not certain. [ 3 ] In the Greek Oxyrhynchus Papyri 235 , the symbols for Venus and Mercury did not have the cross on the bottom stem, [ 3 ] and Venus appears without the cross (⚲) in Johannes Kamateros (12th century). [ citation needed ]
In botany and biology , the symbol for Venus is used to represent the female sex , alongside the symbol for Mars representing the male sex, [ 13 ] following a convention introduced by Linnaeus in the 1750s. [ 10 ] [ e ] Arising from the biological convention, the symbol also came to be used in sociological contexts to represent women or femininity . This gendered association of Venus and Mars has been used to pair them heteronormatively , describing women and men stereotypically as being so different that they can be understood as coming from different planets, an understanding popularized in 1992 by the book titled Men Are from Mars, Women Are from Venus . [ 14 ] [ 15 ]
Unicode encodes the symbol as U+2640 ♀ FEMALE SIGN , in the Miscellaneous Symbols block. [ f ]
The modern astronomical symbol for the Sun, the circumpunct ( U+2609 ☉ SUN ), was first used in the Renaissance . It possibly represents Apollo's golden shield with a boss ; it is unknown if it traces descent from the nearly identical Egyptian hieroglyph for the Sun.
Bianchini's planisphere , produced in the 2nd century, shows a circlet with rays radiating from it. [ 5 ] [ 2 ] In late Classical times, the Sun is attested as a circle with a single ray. A diagram in Johannes Kamateros' 12th century Compendium of Astrology shows the same symbol. [ 18 ] This older symbol is encoded by Unicode as U+1F71A 🜚 ALCHEMICAL SYMBOL FOR GOLD in the Alchemical Symbols block. Both symbols have been used alchemically for gold, as have more elaborate symbols showing a disk with multiple rays or even a face.
The Mars symbol , ♂, is a depiction of a circle with an arrow emerging from it, pointing at an angle to the upper right in Europe and to the upper left in India. [ 19 ] [ 20 ] It is also the old and obsolete symbol for iron in alchemy. In zoology and botany, it is used to represent the male sex (alongside the astrological symbol for Venus representing the female sex), [ 13 ] following a convention introduced by Linnaeus in the 1750s. [ 10 ]
The symbol dates from at latest the 11th century, at which time it was an arrow across or through a circle, thought to represent the shield and spear of the god Mars; in the medieval form, for example in the 12th-century Compendium of Astrology by Johannes Kamateros, the spear is drawn across the shield. [ 18 ] The Greek Oxyrhynchus Papyri show a different symbol, [ 3 ] perhaps simply a spear. [ 2 ]
Its Unicode codepoint is U+2642 ♂ MALE SIGN ( ♂ ).
The symbol for Jupiter , ♃, was originally a Greek zeta, Ζ , with a stroke indicating that it is an abbreviation (for Zeus , the Greek equivalent of Roman Jupiter).
Its Unicode codepoint is U+2643 ♃ JUPITER .
Salmasius and earlier attestations show that the symbol for Saturn, ♄, derives from the initial letters ( Kappa , rho ) of its ancient Greek name Κρόνος ( Kronos ), with a stroke to indicate an abbreviation . [ 10 ] By the time of Kamateros (12th century), the symbol had been reduced to a shape similar to a lower-case letter eta η, with the abbreviation stroke surviving (if at all) in the curl on the bottom-right end.
Its Unicode codepoint is U+2644 ♄ SATURN .
The symbols for Uranus were created shortly after its discovery in 1781. One symbol, ⛢, invented by J. G. Köhler and refined by Bode , was intended to represent the newly discovered metal platinum ; since platinum, commonly called white gold, was found by chemists mixed with iron, the symbol for platinum combines the alchemical symbols for iron , ♂, and gold , ☉. [ 21 ] [ 22 ] Gold and iron are the planetary metals for the Sun and Mars, and so share their symbols. Several orientations were suggested, but an upright arrow is now universal.
Another symbol, , was suggested by Lalande in 1784. In a letter to Herschel , Lalande described it as "a globe surmounted by the first letter of your name". [ 23 ] The platinum symbol tends to be used by astronomers, and the monogram by astrologers. [ 24 ]
For use in computer systems, the symbols are encoded U+26E2 ⛢ ASTRONOMICAL SYMBOL FOR URANUS and U+2645 ♅ URANUS .
Several symbols were proposed for Neptune to accompany the suggested names for the planet. Claiming the right to name his discovery, Urbain Le Verrier originally proposed to name the planet for the Roman god Neptune [ 25 ] and the symbol of a trident , [ 26 ] while falsely stating that this had been officially approved by the French Bureau des Longitudes . [ 25 ] In October, he sought to name the planet Leverrier , after himself, and he had loyal support in this from the observatory director, François Arago , [ 27 ] who in turn proposed a new symbol for the planet, . [ 28 ] However, this suggestion met with resistance outside France, [ 27 ] and French almanacs quickly reintroduced the name Herschel for Uranus , after that planet's discoverer Sir William Herschel , and Leverrier for the new planet, [ 29 ] though it was used by anglophone institutions. [ 30 ] Professor James Pillans of the University of Edinburgh defended the name Janus for the new planet, and proposed a key for its symbol. [ 26 ] Meanwhile, Struve presented the name Neptune on December 29, 1846, to the Saint Petersburg Academy of Sciences . [ 31 ] In August 1847, the Bureau des Longitudes announced its decision to follow prevailing astronomical practice and adopt the choice of Neptune , with Arago refraining from participating in this decision. [ 32 ] The planetary symbol was Neptune's trident , with the handle stylized either as a crossed , following Mercury, Venus, Jupiter, Saturn, and the asteroids, or as an orb , following the symbols for Uranus, Earth, and Mars. [ 7 ] The crossed variant is the more common today.
For use in computer systems, the symbols are encoded as U+2646 ♆ NEPTUNE and U+2BC9 ⯉ NEPTUNE FORM TWO .
Pluto was almost universally considered a planet from its discovery in 1930 until its re-classification as a dwarf planet (planetoid) by the IAU in 2006. Planetary geologists [ 33 ] and astrologers continue to treat it as a planet. The original planetary symbol for Pluto was , a monogram of the letters P and L. Astrologers generally use a bident with an orb. NASA has used the bident symbol since Pluto's reclassification. These symbols are encoded as U+2647 ♇ PLUTO and U+2BD3 ⯓ PLUTO FORM TWO .
In the 19th century, planetary symbols for the major asteroids were also in use, including 1 Ceres (a reaper's sickle , encoded U+26B3 ⚳ CERES ), 2 Pallas (a lance, U+26B4 ⚴ PALLAS ) and 3 Juno (a sceptre, encoded U+26B5 ⚵ JUNO ).
Encke (1850) used symbols for 5 Astraea , 6 Hebe , 7 Iris , 8 Flora and 9 Metis in the Berliner Astronomisches Jahrbuch . [ 34 ]
In the late 20th century, astrologers abbreviated the symbol for 4 Vesta (the sacred fire of Vesta , encoded U+26B6 ⚶ VESTA ), [ 35 ] and introduced new symbols for 5 Astraea ( , a stylised % sign, shift-5 on QWERTY keyboards for asteroid 5), 10 Hygiea encoded U+2BDA ⯚ HYGIEA ) [ 36 ] and for 2060 Chiron , discovered in 1977 (a key, U+26B7 ⚷ CHIRON ). [ 35 ] Chiron's symbol was adapted as additional centaurs were discovered; symbols for 5145 Pholus and 7066 Nessus have been encoded in Unicode. [ 36 ] The abbreviated Vesta symbol is now universal, and the astrological symbol for Pluto has been used astronomically for Pluto as a dwarf planet. [ 37 ]
In the early 21st century, symbols for the trans-Neptunian dwarf planets have been given Unicode codepoints , particularly Eris (the hand of Eris , ⯰, but also ⯱), Sedna , Haumea , Makemake , Gonggong , Quaoar and Orcus which are in Unicode. All (except Eris, for which the hand of Eris is a traditional Discordian symbol) were devised by Denis Moskowitz, a software engineer in Massachusetts. [ 37 ] [ 38 ]
Other symbols have also been invented by Moskowitz, for some smaller TNOs as well as many planetary moons. (Charon in particular coincidentally matches a symbol already existing in Unicode as an astrological Pluto.) However, these have not been broadly adopted. [ 37 ] [ 39 ]
From 1845 to 1855, many symbols were created for newly discovered asteroids. But by 1851, the spate of discoveries had led to a general abandonment of these symbols in favour of numbering all asteroids instead. [ 41 ] | https://en.wikipedia.org/wiki/Saturn_symbol |
Satya N. Atluri ICCES Medal is a Medal awarded annually by ICCES (International Conference on Computational & Experimental Engineering and Sciences) and Tech Science Press to an individual who has had a significant impact on the world of engineering, the sciences, and commerce, and the well-being of the society at large as a result. This Medal is presented at the Awards Banquet of the annual ICCES Conference . [ 1 ] The recipient of the Medal is invited to deliver a Plenary Lecture, on a topic of her/his choosing, at the ICCES conference. This Medal honors Professor Satya N. Atluri of UCI , who founded ICCES in 1986, and founded the journals, " CMES: Computer Modeling in Engineering & Sciences " (2000), " CMC: Computers, Materials, & Continua " (2004), " MCB: Molecular & Cellular Biomechanics " (2004), " SL: Structural Longevity " (2008), and " ACM: Advances in Computational Mechanics " (2008), all of which are published by Tech Science Press . [ 2 ] All these journals are in the frontier disciplines of engineering and the sciences, and especially at the interfaces of engineering and the sciences. Previously, Professor Atluri founded, and was Editor-in-Chief of the international journal, " Computational Mechanics ", during 1986-2000.
The ICCES conferences are held annually: Tokyo (1986); Atlanta (1988); Melbourne , Australia (1991); Hong Kong (1992); Big Island, Hawaii (1995); San Jose, Costa Rica (1997); Atlanta (1998); Los Angeles (2000); Puerto Vallarta, Mexico (2001); Reno, Nevada (2002); Corfu, Greece (2003); Madeira , Portugal (2004); Chennai, India (2005); Miami (2007); Honolulu (2008); Phuket, Thailand (2009), Las Vegas (2010), and Nanjing, China (2011), Crete, Greece (2012), Seattle , USA (2013), Changwon , South Korea (2014), Reno (2015); Madeira , Portugal (2017), and Tokyo , Japan (2019). All these conferences bring together each year, about 500 of the world’s leading academic, industrial, and government researchers in multidisciplinary engineering, sciences, technologies, and pertinent policies. All aspects of theory, computation, and experimentation are emphasized at these conferences. It is in this spirit that the Satya N. Atluri ICCES Medal honors: 1. Either an individual for her or his multifaceted and exemplary contributions in the broadest sense, and for their impact on society, or 2. An engineering/scientific/technological achievement by a group of individuals, which by its global visibility, benefits the well-being of vast segments of people.
The recent recipients of the Satya N. Atluri Medal include:
2020: Professor Sudhir K. Jain, Director (President) of the Indian Institute of Technology, Gandhi Nagar 2019: Professor Anurag Kumar , Director (i.e., the President) of the Indian Institute of Science, Bangalore, India 2012: Chancellor Henry Yang , University of California, Santa Barbara, USA 2013: Chancellor John A. White , University of Arkansas
2008: Prof. Demosthenes Polyzos, Vice Rector, University of Patras, Greece 2011: Dr. Guangjing Cao, President, Three Gorges Dam Groups, China 2010: Dr. Ratan Naval Tata , Chairman, Tata Sons , Mumbai, India [ 3 ] 2009: Dr. Subra Suresh , Director, National Science Foundation | https://en.wikipedia.org/wiki/Satya_N._Atluri_ICCES_Medal |
In early military engineering , a saucisson ( French for a large, dry-filled sausage ) was a primitive type of fuse , consisting of a long tube or hose of cloth or leather, typically about an inch and half in diameter (37 mm), damp-proofed with pitch and filled with black powder . It was normally laid in a protective wooden trough, and ignited by use of a torch or slow match . Saucissons were used to fire fougasses , petards , mines and camouflets . [ 1 ] [ 2 ]
Very long fascines were also called saucissons . [ citation needed ]
Later, in early 20th century mining jargon , a saucisson referred to the flexible casings used for explosives in mine operations. [ citation needed ]
This explosives -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Saucisson_(pyrotechnics) |
The Saudi Council of Engineers ( SCE ; Arabic : الهيئة السعودية للمهندسين ) is a professional body intended to promote the engineering profession and develop and upgrade its standards and those practicing it. It operates under the supervision of Ministry of Commerce and Investment with headquarters in Riyadh .
The council was established by a royal decree issued by the King Fahd bin Abdul Aziz Al Saud in 2002. The organization's stated responsibilities are:
This Saudi Arabia related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Saudi_Council_of_Engineers |
In 2014 and 2015, a team of Saudi agents allegedly stole proprietary and sensitive personal data from the American social media platform Twitter , in order to unmask anonymous dissidents of Saudi Arabia . Email addresses, phone numbers, internet IP addresses, dates of birth and a history of all the users' activity of Saudi dissidents, opponents and others, were among the stolen materials. [ 1 ]
The United States Department of Justice charged two former Twitter workers and a Saudi intermediary with "acting as illegal agents of Saudi Arabia". Personal data of at least 6,000 Twitter accounts was acquired, according to the complaint. [ 2 ]
Human rights groups ANHRI and Prisoners of Conscience have observed that some anonymous Saudi political activists on Twitter were identified and detained after the infiltration, and suspect that it is related. A Saudi scholar in exile in the United States sued Twitter, alleging that dozens of anonymous political activists he was in contact with have died, were tortured, or remain behind bars as a result of being found to have a connection to him.
With roughly 10 million Twitter users, Saudi Arabia is the service's top Arab market. Not requiring use of real names further made Twitter a leading platform for political dissent in the country. [ 3 ]
Saud al-Qahtani , one of Saudi Crown Prince Mohammed Bin Salman 's top confidants at the time, posted a warning against masked Twitter accounts using his own verified Twitter account in August 2017. Asserting that governments can know the true names of those using Twitter anonymously, he brought up "technical methods" for tracing a person's IP addresses, as well as a "secret I'm not going to reveal." [ 4 ] [ 5 ] Twitter permanently banned al-Qahtani's account in September 2019, claiming "violations of our platform manipulation policies." [ 6 ]
Ali Alzabarah, a Saudi national, and Ahmad Abouammo, a U.S. citizen, were the two former Twitter employees that funneled the data, the complaint asserts. [ 2 ]
Another Saudi national, Ahmed Almutairi, also known as Ahmed Aljbreen, worked as a middleman between Alzabarah, Abouammo, and representatives of the Saudi Royal Family. Almutairi is known for co-founding SMAAT, a Riyadh social-marketing firm that is controlled by the royal family and had a history of running political and commercial influence operations. [ 7 ] [ 8 ]
Bader al-Asaker, a Saudi official who heads the private office of Prince Mohammed and is a board member of Misk Foundation , a philanthropic organization affiliated with MBS , was also involved in the conspiracy, according to the complaint. [ 9 ]
Ali Alzabarah joined Twitter as a site reliability engineer in August 2013. Being involved in keeping the site up, he was given broad access. [ 10 ]
In November 2013, Abouammo, who joined the firm as a member of Twitter's global media team to head the Middle East partnerships, met Alzabarah there. [ 11 ]
In 2014, Abouammo was asked to authenticate an account belonging to a Saudi news personality by a public relations agency representing the Saudi Embassy. This request for a blue checkmark was followed by a request from a US-Saudi business group in Virginia to visit Twitter's headquarters. Bader al-Asaker was to be part of the visit, which was nominally for entrepreneurs. [ 11 ]
On June 13, 2014, al-Asaker traveled to San Francisco to meet Abouammo. [ 12 ]
Months later, Abouammo met al-Asaker in 2014 in London, where he was given a $20,000 watch. A week after returning to Twitter's headquarters, Abouammo accessed the system he used to verify users and obtained information about at least two Saudi dissidents, later passing the data to al-Asaker. That system, according to insiders who have used it, retains information such as email addresses, phone numbers and the latest log-in time – personal information usable to track a user in real life. [ 11 ]
In February 2015, Abouammo got his operators in touch with Alzabarah. Alzabarah's ambitions were straightforward: he wanted to work in a high-ranking job for a "charitable organization run by al-Asaker." [ 11 ]
In May 2015, and within the first week of arriving in San Francisco from Washington, D.C. where he met with al-Asaker, Alzabarah "began to access without authorization private data of Twitter users en masse." Over 6,000 users were compromised in six months, according to the FBI. 33 of those users, the Saudi government has already requested Twitter to provide their personal information through emergency disclosure demands. [ 13 ]
Later in 2015, Abouammo departed Twitter for a position at Amazon in Seattle. Over the next two years, well over $300,000 in bank transfers were made from al-Asaker to Abouammo's various bank accounts. [ 14 ]
On December 2, 2015, Alzabarah reportedly acknowledged to his superiors that he examined user data out of curiosity. His work-owned laptop was taken, and he was removed from the office. He returned to Saudi Arabia the next day after communicating that night with al-Asaker and then Dr. Faisal Al Sudairi, the Saudi consul general in Los Angeles. Alzabarah has not been seen since, according to authorities. [ 15 ]
After arrival in Saudi Arabia, Alzabarah became the CEO of the Misk Initiatives Center, a branch of Mohammed bin Salman 's Misk Foundation , which he created in 2011 and whose secretary-general was al-Asaker. [ 16 ] [ 17 ]
On October 20, 2018, FBI agents in Seattle questioned Abouammo about his efforts on behalf of Saudi officials. In an attempt to hinder the inquiry, Abouammo purportedly lied to the investigators and supplied them with a forged invoice. [ 13 ]
On November 5, 2019, as part of the complaint, federal warrants for both Ali Alzabarah and Almutairi were issued. [ 15 ] Both were accused of operating as undeclared agents of a foreign government. [ 18 ] [ 19 ] On the same day, Abouammo was apprehended in Seattle, WA, and had his first federal court appearance in Seattle on November 6, 2019. [ 2 ]
On February 24, 2021, a federal judge rejected a request to dismiss charges against Abouammo. [ 20 ]
In August 2022, Abouammo was found guilty of acting as a foreign agent without notice to the Attorney General, conspiracy, wire fraud, international money laundering, and falsification of records in a federal investigation. On December 14, 2022 he was sentenced to three and a half years in prison. [ 21 ]
On the condition of anonymity, a business representative of Twitter told The Washington Post in 2019 that access to the instrument panel is now restricted to a small group of "trained and vetted" workers, citing worries about staff safety. [ 22 ]
According to former employees, Twitter did not have plans to handle situations in which a personnel with access to sensitive data built strong ties with foreign powers. A former colleague of Abouammo's said that US, UK, and Israeli security agencies all pressured members of Twitter's media team for private information. [ 11 ]
The departure of Ali Alzabarah didn't cause a stir in Twitter. "One day the general counsel came to me and said there was this crazy thing that happened. They're out of the company," a former Twitter executive remarked. "You can never talk about it," "inside, it was a total nonthing. No one in the rank and file who had ever heard of it. It was a nonissue." [ 11 ]
Omar Abdulaziz , a dissident who was connected to writer Jamal Khashoggi , feels that criticizing the Saudi Arabian regime on social media is now risky. "We were using Twitter ten years ago to expose our opinion on what was really going on there, and we felt safe," he added. "For us, it was a safe platform. That's no longer the case." [ 11 ]
Although Twitter has not revealed the identity of those who may have been unmasked as a result of the claimed attack, human rights groups, such as ANHRI , linked three Saudis detained since 2015 with using Twitter handles @sama7ti, @coluche_ar, and @mahwe13, all critical of the Saudi government. Another human rights organization, Prisoners of Conscience, reported an additional case of a Saudi male who posted critical comments on Twitter under the handle @albna5y and was imprisoned in September 2017. [ 23 ]
Al-Jasser, a Saudi man suspected of running an anonymous Twitter account, was apprehended in early 2018. He was linked to @coluche_ar, one of the accounts obtained by the Twitter breach, according to ANHRI .
Though al-Jasser was reported to have died in jail after being tortured, Saudi officials notified a United Nations team monitoring enforced disappearances in February that he was being kept at Al Ha'ir Prison near Riyadh, according to MENA Rights Group. [ 23 ]
Following a March 2018 arrest and charges that he used a popular parody account to criticize the Saudi government, Abdulrahman al-Sadhan, a 37-year-old Red Crescent relief worker, was convicted by Saudi Arabia's specialized criminal court and sentenced to 20 years in prison followed by an additional 20-year travel restriction. [ 24 ]
Omar Abdulaziz 's account was one of those breached. On February 17, 2016. A message from Twitter's security staff notified him that his and a limited number of other users' personal information had been compromised due to a "bug." "The email address and phone number linked to your account was viewed by another account," said the message. He later filed a lawsuit against the company for allegedly failing to disclose the event. [ 25 ] The accusations are false, according to Twitter. [ 26 ]
In June 2020, Ali al-Ahmed, a Saudi scholar living in exile in the United States, sued Twitter over the 2016 breach, alleging that the company's negligence resulted in the loss and torture of dissidents within Saudi Arabia. al-Ahmed claimed to have been in continuous contact with a number of anonymous Twitter accounts maintained by Saudi state employees and pro-democracy advocates in the period leading up to the breach. Exposing their phone numbers and email addresses, dozens of those who were in direct touch with Ali have died, were tortured or remain behind bars as a result of being found to have a connection to him, he claims. [ 27 ] | https://en.wikipedia.org/wiki/Saudi_infiltration_of_Twitter |
In combinatorial mathematics and extremal set theory , the Sauer–Shelah lemma states that every family of sets with small VC dimension consists of a small number of sets. It is named after Norbert Sauer and Saharon Shelah , who published it independently of each other in 1972. [ 1 ] [ 2 ] The same result was also published slightly earlier and again independently, by Vladimir Vapnik and Alexey Chervonenkis , after whom the VC dimension is named. [ 3 ] In his paper containing the lemma, Shelah gives credit also to Micha Perles , [ 2 ] and for this reason the lemma has also been called the Perles–Sauer–Shelah lemma and the Sauer–Shelah–Perles lemma . [ 4 ] [ 5 ]
Buzaglo et al. call this lemma "one of the most fundamental results on VC-dimension", [ 4 ] and it has applications in many areas. Sauer's motivation was in the combinatorics of set systems, [ 1 ] while Shelah's was in model theory [ 2 ] and that of Vapnik and Chervonenkis was in statistics . [ 3 ] It has also been applied in discrete geometry [ 6 ] and graph theory . [ 7 ]
If F = { S 1 , S 2 , … } {\displaystyle \textstyle {\mathcal {F}}=\{S_{1},S_{2},\dots \}} is a family of sets and T {\displaystyle T} is a set, then T {\displaystyle T} is said to be shattered by F {\displaystyle {\mathcal {F}}} if every subset of T {\displaystyle T} (including the empty set and T {\displaystyle T} itself) can be obtained as the intersection T ∩ S i {\displaystyle T\cap S_{i}} of T {\displaystyle T} with some set S i {\displaystyle S_{i}} in the family. The VC dimension of F {\displaystyle {\mathcal {F}}} is the largest cardinality of a set shattered by F {\displaystyle {\mathcal {F}}} . [ 6 ]
In terms of these definitions, the Sauer–Shelah lemma states that if the VC dimension of F {\displaystyle {\mathcal {F}}} is k {\displaystyle k} , and the union of F {\displaystyle {\mathcal {F}}} has n {\displaystyle n} elements, then F {\displaystyle {\mathcal {F}}} can consist of at most ∑ i = 0 k ( n i ) = O ( n k ) {\displaystyle \sum _{i=0}^{k}{\binom {n}{i}}=O(n^{k})} sets, as expressed using big O notation . Equivalently, if the number of sets in the family, | F | {\displaystyle |{\mathcal {F}}|} , obeys the inequality | F | > ∑ i = 0 k − 1 ( n i ) , {\displaystyle |{\mathcal {F}}|>\sum _{i=0}^{k-1}{\binom {n}{i}},} then F {\displaystyle {\mathcal {F}}} shatters a set of size k {\displaystyle k} . [ 6 ]
The bound of the lemma is tight: Let the family F {\displaystyle {\mathcal {F}}} be composed of all subsets of { 1 , 2 , … , n } {\displaystyle \{1,2,\dots ,n\}} with size less than k {\displaystyle k} . Then the number of sets in F {\displaystyle {\mathcal {F}}} is exactly ∑ i = 0 k − 1 ( n i ) {\textstyle \sum _{i=0}^{k-1}{\binom {n}{i}}} but it does not shatter any set of size k {\displaystyle k} . [ 8 ]
A strengthening of the Sauer–Shelah lemma, due to Pajor (1985) , states that every finite set family F {\displaystyle {\mathcal {F}}} shatters at least | F | {\displaystyle |{\mathcal {F}}|} sets. [ 9 ] This immediately implies the Sauer–Shelah lemma, because only ∑ i = 0 k − 1 ( n i ) {\textstyle \sum _{i=0}^{k-1}{\tbinom {n}{i}}} of the subsets of an n {\displaystyle n} -item universe have cardinality less than k {\displaystyle k} . Thus, when | F | > ∑ i = 0 k − 1 ( n i ) , {\displaystyle |{\mathcal {F}}|>\sum _{i=0}^{k-1}{\binom {n}{i}},} there are not enough small sets to be shattered, so one of the shattered sets must have cardinality at least k {\displaystyle k} . [ 10 ]
For a restricted type of shattered set, called an order-shattered set, the number of shattered sets always equals the cardinality of the set family. [ 11 ]
Pajor's variant of the Sauer–Shelah lemma may be proved by mathematical induction ; the proof has variously been credited to Noga Alon [ 12 ] or to Ron Aharoni and Ron Holzman. [ 11 ]
A different proof of the Sauer–Shelah lemma in its original form, by Péter Frankl and János Pach , is based on linear algebra and the inclusion–exclusion principle . [ 6 ] [ 8 ] This proof extends to other settings such as families of vector spaces and, more generally, geometric lattices . [ 5 ]
The original application of the lemma, by Vapnik and Chervonenkis, was in showing that every probability distribution can be approximated (with respect to a family of events of a given VC dimension) by a finite set of sample points whose cardinality depends only on the VC dimension of the family of events. In this context, there are two important notions of approximation, both parameterized by a number ε {\displaystyle \varepsilon } : a set S {\displaystyle S} of samples, and a probability distribution on S {\displaystyle S} , is said to be an ε {\displaystyle \varepsilon } -approximation of the original distribution if the probability of each event with respect to S {\displaystyle S} differs from its original probability by at most ε {\displaystyle \varepsilon } . A set S {\displaystyle S} of (unweighted) samples is said to be an ε {\displaystyle \varepsilon } -net if every event with probability at least ε {\displaystyle \varepsilon } includes at least one point of S {\displaystyle S} . An ε {\displaystyle \varepsilon } -approximation must also be an ε {\displaystyle \varepsilon } -net but not necessarily vice versa.
Vapnik and Chervonenkis used the lemma to show that set systems of VC dimension d {\displaystyle d} always have ε {\displaystyle \varepsilon } -approximations of cardinality O ( d ε 2 log d ε ) . {\displaystyle O({\tfrac {d}{\varepsilon ^{2}}}\log {\tfrac {d}{\varepsilon }}).} Later authors including Haussler & Welzl (1987) [ 13 ] and Komlós, Pach & Woeginger (1992) [ 14 ] similarly showed that there always exist ε {\displaystyle \varepsilon } -nets of cardinality O ( d ε log 1 ε ) {\displaystyle O({\tfrac {d}{\varepsilon }}\log {\tfrac {1}{\varepsilon }})} , and more precisely of cardinality at most [ 6 ] d ε ln 1 ε + 2 d ε ln ln 1 ε + 6 d ε . {\displaystyle {\tfrac {d}{\varepsilon }}\ln {\tfrac {1}{\varepsilon }}+{\tfrac {2d}{\varepsilon }}\ln \ln {\tfrac {1}{\varepsilon }}+{\tfrac {6d}{\varepsilon }}.} The main idea of the proof of the existence of small ε {\displaystyle \varepsilon } -nets is to choose a random sample x {\displaystyle x} of cardinality O ( d ε log 1 ε ) {\textstyle O({\tfrac {d}{\varepsilon }}\log {\tfrac {1}{\varepsilon }})} and a second independent random sample y {\displaystyle y} of cardinality O ( d ε log 2 1 ε ) {\textstyle O({\tfrac {d}{\varepsilon }}\log ^{2}{\tfrac {1}{\varepsilon }})} , and to bound the probability that x {\displaystyle x} is missed by some large event E {\displaystyle E} by the probability that x {\displaystyle x} is missed and simultaneously the intersection of y {\displaystyle y} with E {\displaystyle E} is larger than its median value. For any particular E {\displaystyle E} , the probability that x {\displaystyle x} is missed while y {\displaystyle y} is larger than its median is very small,
and the Sauer–Shelah lemma (applied to x ∪ y {\displaystyle x\cup y} ) shows that only a small number of distinct events E {\displaystyle E} need to be considered, so by the union bound , with nonzero probability, x {\displaystyle x} is an ε {\displaystyle \varepsilon } -net. [ 6 ]
In turn, ε {\displaystyle \varepsilon } -nets and ε {\displaystyle \varepsilon } -approximations, and the likelihood that a random sample of large enough cardinality has these properties, have important applications in machine learning , in the area of probably approximately correct learning . [ 15 ] In computational geometry , they have been applied to range searching , [ 13 ] derandomization , [ 16 ] and approximation algorithms . [ 17 ] [ 18 ]
Kozma & Moran (2013) use generalizations of the Sauer–Shelah lemma to prove results in graph theory such as that the number of strong orientations of a given graph is sandwiched between its numbers of connected and 2-edge-connected subgraphs. [ 7 ] | https://en.wikipedia.org/wiki/Sauer–Shelah_lemma |
Sauropod neck posture is a subject occasionally debated among scientists, with some favoring postures closer to horizontal whilst others a more upright posture. Research has looked at various avenues of evidence and analysis including: attempting to reconstruct the neutral posture of their necks and estimating range of motion by studying the bones; attempting to reconstruct sauropod metabolism and the energy requirements of sustaining incredibly long necks in various postures; and comparing sauropod neck anatomy to those of living animals. [ 1 ] [ 2 ]
The biomechanics of sauropod skeletons and necks can help determine at what angle the neck was positioned. [ 3 ]
In 2013, a study led by Matthew J. Cobley and published in PLOS ONE focused on the flexibility of the necks of sauropods. They compared the necks of ostriches with sauropod genera to find out how flexible the necks really were. The study noted that previous biomechanics studies found the necks to have been positioned between the extremes of a vertical, and a downward slanted neck. In conclusion, the study found that sauropod neck flexibility should not be based on osteology alone, and if it is, the results should be used with caution. Even though there is a lack of preserved muscle tissue that would determine flexibility, sauropod necks were probably less flexible than previously thought. [ 4 ]
In 2014, Mike P. Taylor analysed the flexibility in the necks of Apatosaurus and Diplodocus . He found that Cobley et al. was incorrect in the fact that vertebrae imply the neck is less flexible than in actuality. Cobley et al. found necks to be much less flexible than in reality when cartilage was added. It was found that the cartilage between the joints would have allowed for the neck to flex far past 90°. However, Taylor noted that while the neck could flex above the vertical, the osteological neutral pose would have been around horizontal, with the habitual pose having the head held upwards in an alert pose. [ 5 ]
Sauropod necks were probably highly muscled to suit their feeding level. Brachiosaurus brancai (now Giraffititan ) was probably a high browser, so it would have been more muscled along the neck than other sauropods like Diplodocus and Dicraeosaurus interpreted as low browsers. The tail and limb length of B. brancai would also need to be greater, to balance out the inclined neck. [ 6 ] However, the question of whether sauropods were endothermic or ectothermic plays a major part in how sauropods were muscled, as endotherms have particularly more intestines and stomach than ectotherms. The amount of gut needed could determine how much food was eaten by sauropods, and therefore at what elevation their heads were held. [ 7 ]
The upright posture of sauropod necks is seen by some as requiring implausibly high blood pressure and heart strength. A 2000 study conducted by Roger Seymour and Harvey Lillywhite found that the blood pressure needed to reach the head with an upright neck would be 700 millimetres of mercury (28 inHg), interpreted as fatal to an endotherm, or highly dangerous to an ectotherm, even with adequate heart musculature. [ 2 ] A later study by Seymour concluded that it would have required half the animal's energy intake to pump the blood to the head. This would disfavor sauropods being high browsers, and instead having lower necks while feeding than commonly portrayed. [ 8 ]
The above work summarily dismisses the hypothesis of secondary hearts in the neck [ 9 ] as evolutionarily implausible, assuming arterial valves could have no role without associated musculature.
A few hypotheses have been generated to solve the dispute over how sauropods held their necks. [ 1 ]
Kent Stevens and Michael Parrish have been the two main supporters of a horizontal neck posture. In 1999, they studied the genera Apatosaurus and Diplodocus , finding the habitual pose of the genera to be slightly declined. They claimed that both sauropods had necks much less flexible than previously thought, with the neck vertebrae of Diplodocus being more inflexible than Apatosaurus . Those two poses would suggest that the sauropods were ground feeders, instead of browsing off taller flora. [ 12 ] Later, in 2005, Stevens and Parrish studied the biomechanics of sauropod necks on a wider variety of sauropods, from the Jurassic: Apatosaurus , Diplodocus , Camarasaurus , Brachiosaurus , Dicraeosaurus , Cetiosaurus , and Euhelopus . All were stated to have a horizontal, or even declining neck. [ 13 ]
However, in 2009 multiple flaws were found with this argument. Michael P. Taylor et al. compared the neck posture of sauropods to that of extant reptiles and other tetrapods , finding these animals' habitual poses to be entirely different from the assumptions of Stevens and Parrish. The latters' errors come mainly from their preconceptions about animals' habitual pose in life, which they simply assumed would naturally match the Osteological Neutral Pose (or ONP). Taylor et al. find the ONP to be, not the actual habitual pose of any examined animal, but an arbitrarily chosen midpoint between the two structural extremes of bone placement. [ 1 ] ONP, then, is merely one place in the range of physically possible motion.
Another, more widely supported hypothesis about sauropod neck posture is that the necks were held at an incline, but not as upright as commonly shown. [ 1 ] Daniela Schwartz et al. in 2006 published a study of the scapula and coracoids, sometimes fused into scapulocoracoids, of sauropod genera. Previously, sauropod shoulder girdles were thought to have been positioned horizontally along the torso, but Schwartz et al. found that the girdles should not have been positioned horizontally, and instead, they would have been angled at an average of 55° to 65°. The study reconstructed the skeletons of Diplodocus , Camarasaurus , and the titanosaur Opisthocoelicaudia , all known from a complete shoulder girdle, with the correct orientation of the scapulocoracoids. For Diplodocus , a 60° shoulder blade would have meant that the neck was more-or-less horizontal, [ 11 ] not too much different from the horizontal pose. [ 12 ] [ 13 ] A juvenile Camarasaurus found by Gilmore was originally described as having the scapulocoracoid in "just the right place", but with it oriented at an angle of 45°, Schwartz et al. criticized the stance. The skeleton found by Schwartz et al. with the angle of the scapulocoracoid is similar to previous reconstruction of the genus by Osborn and Mook, and Jensen. Opisthocoelicaudia was found to have had two possibly poses, both with the scapulocoracoid angled at about 60°. No previous reconstructions, unlike with Camarasaurus , have restored Opisthocoelicaudia similarly. [ 11 ]
Despite skepticism, Euhelopus and Brachiosaurus have been found on anatomical evidence to have held their necks at a vertical angle, which has been treated as impossible for sauropods. Studies have concluded that the blood pressure and energy spent holding necks erect would have been too great to survive; yet Euhelopus and Brachiosaurus , at least, did so anyhow. The energy spent by pumping blood to the head is interpreted as too great for most sauropods, but when they travel often, which has been suggested for those two genera, it would have actually saved energy. The biomechanical evidence favours an upright neck when travelling to spread apart resources. The study finding this conclusion also tested how much energy would have been expended when walking 100 m (330 ft) and standing, both with an upright neck. The approximate conclusion was that an about equal amount of energy would have been used up. Elongated cervical ribs are skeletal evidence for a strong core to support the neck and limit its movement when walking. The study supports the idea that during times of drought and famine, an upright neck was crucial for these sauropods to survive. [ 3 ] | https://en.wikipedia.org/wiki/Sauropod_neck_posture |
In fluid dynamics , Sauter mean diameter ( SMD ) is an average measure of particle size . It was originally developed by German scientist Josef Sauter in the late 1920s. [ 1 ] [ 2 ] It is defined as the diameter of a sphere that has the same volume/surface area ratio as a particle of interest.
Several methods have been devised to obtain a good estimate of the SMD.
The Sauter diameter ( SD , also denoted D [3,2] or d 32 ) for a given particle is defined as:
where d s is the so-called surface diameter and d v is the volume diameter , defined as:
The quantities A p and V p are the ordinary surface area and volume of the particle, respectively.
The equation may be simplified further as:
This is usually taken as the mean of several measurements n , to obtain the Sauter mean diameter (SMD):
This provides intrinsic data that help determine the particle size for fluid problems.
The SMD can be defined as the diameter of a drop having the same volume / surface area ratio as the entire spray.
SMD is especially important in calculations where the active surface area is important. Such areas include catalysis and applications in fuel combustion. | https://en.wikipedia.org/wiki/Sauter_mean_diameter |
Sauvagine is a neuropeptide from the corticotropin-releasing factor (CRF) family of peptides and is orthologous to the mammalian hormone, urocortin 1 , and the teleost fish hormone, urotensin 1. [ 1 ] It is 40 amino acids in length, [ 2 ] and has the sequence XGPPISIDLSLELLRKMIEIEKQEKEKQQAANNRLLLDTI-NH2, with a pyrrolidone carboxylic acid modification at the N-terminal and amidation of the C-terminal isoleucine residue. It was originally isolated from the skin of the frog Phyllomedusa sauvagii . Given its relation to other CRF-related peptides, it exerts similar physiological effects as corticotropin-releasing hormone . [ 3 ] [ 4 ]
Sauvagine belongs to the corticotropin-releasing factor (CRF) family that also includes CRF , urocortin l /urotensin l, urocortin II and urocortin III . [ 5 ] [ 1 ]
Sauvagine has been shown to interact with corticotropin releasing factor receptors 1 and 2 , and (as with other CRF-related peptides) is also bound by the corticotropin-releasing factor binding protein . [ 6 ]
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Sauvagine |
The savannah hypothesis (or savanna hypothesis ) is a hypothesis that human bipedalism evolved as a direct result of human ancestors ' transition from an arboreal lifestyle to one on the savannas . According to the hypothesis, hominins left the woodlands that had previously been their natural habitat millions of years ago and adapted to their new habitat by walking upright.
The idea that a climate-driven retraction of tropical forests forced early hominini into bipedalism has been around for a long time, often implicitly. Some early authors saw savannahs as open grasslands, while others saw a mosaic of environments from woodlands to grasslands. The hypothesis has seen rising criticism since at least the late 1960s. [ 1 ] : 98 The open grasslands version is mostly dismissed; in contrast, the mosaic version still has relatively wide support. However, the transition from forest to savanna probably was more gradual than previously thought.
The fundamental ideas behind it date back to Lamarck , Darwin and Wallace . [ 2 ] [ 3 ] [ 4 ] Also Gustav Steinmann saw reducing rain forest due to climate change as an important driver for bipedalism. [ 5 ] Osborn thought man probably originated from the forests and flood-plains of southern Asia. [ 6 ] Hilzheimer stated it was open landscapes that stimulated development. [ 7 ]
The hypothesis first came to prominence however with the discovery of Australopithecus africanus by Raymond Dart in 1924. In an article on the discovery, published in the journal Nature , Dart wrote:
For the production of man a different apprenticeship was needed to sharpen the wits and quicken the higher manifestations of intellect—a more open veldt country where competition was keener between swiftness and stealth, and where adroitness of thinking and movement played a preponderating role in the preservation of the species. Darwin has said, "no country in the world abounds in a greater degree with dangerous beasts than Southern Africa." and, in my opinion, Southern Africa, by providing a vast open country with occasional wooded belts and a relative scarcity of water, together with a fierce and bitter mammalian competition, furnished a laboratory such as was essential to this penultimate phase of human evolution.
Weinert stated apes are very reluctant to leave the safety of the trees, and the ancestors of modern man did not leave the trees, but the trees left them. [ 9 ] Grabau echoed this by saying "Instead of the apes leaving the trees, the trees left the apes". [ 10 ]
Not everyone agreed with this hypothesis, such as Weidenreich , but he did conclude it was a "widely spread belief". [ 11 ]
The work of Robert Ardrey helped popularize the ideas that Dart had developed with a wide audience.
In the decades following Dart's discovery, more hominid fossils were found in Eastern and Southern Africa, leading researchers to conclude that these were savanna dwellers as well. Much of the academic discussion at the time took for granted that the transition to the savannas was responsible for the emergence of bipedalism, and focused instead on determining particular mechanisms by which this happened. [ 12 ]
One of the proposed mechanisms was the knuckle-walking hypothesis; the claim that early human ancestors walked on all fours when they first emerged into the savannas. This was based on observations of morphological characteristics found in Australopithecus anamensis and Australopithecus afarensis , and posited that knuckle-walking was an example of convergent evolution in chimpanzees and gorillas , which was then lost by the genus Homo . [ 13 ] Paleoanthropologists also posited that the upright posture would have been advantageous to savanna-dwelling hominids, as it allowed them to peer over tall grasses for predators, or in search of prey. [ 14 ] P. E. Wheeler suggested that another advantage lay in reducing the amount of skin exposed to the sun, which helped regulate body temperatures. [ 15 ] The turnover-pulse hypothesis , first described by Elizabeth Vrba seemed to support the savanna hypothesis by suggesting that climate change events resulting in the shrinking of forested areas forced animals out into the open grasslands. [ 12 ]
Robinson investigated adaptive radiation for Australopithecus and saw grass savanna and other more arid environments expanding at this time, thus providing increased opportunity for animals capable of adapting to such conditions. [ 16 ] Monod investigated the role in human evolution of the Sahara during wet periods as a place that was covered with steppes, savannas, and lakes. He saw advantages for the process of hominization in a wooded savanna. [ 17 ]
In analogy with gelada Jolly proposed that "[i]n the basal hominid, therefore, the 'gelada' specialisations would be superimposed upon a behavioural repertoire and post-cranial structure already attuned to some degree of truncal erectness." The transition to bipedality would have been instigated by seed-eating and "probably took place in a dambo -like environment, later shifting to wider floodplains." [ 18 ]
An early critic of the savanna hypothesis was Lovejoy in 1981. He stated "[i]t is more likely that hominids venturing into open habitats were already bipedal and that their regular occupation of savannahs was not possible until intensified social behavior was well developed." [ 19 ]
Kortlandt sought the barrier required for geographic speciation to take place. According to him, the Great Rift Valley , the Nile and the Zambezi acted as a double barrier when a period of desiccation occurred in East Africa. This "must have converted the last-surviving dryopithecine ( Proconsul ) ape there into an upright-walking, drought-adapted, and 'humanoid' type of bush and grassland ape, i.e., in all probability the Homininae, strictly speaking." [ 20 ] This corresponded with the location of some important fossils that had been found until then, such as in 1939 the Australopithecus afarensis in Laetoli by Ludwig Kohl-Larsen and the Paranthropus boisei in the Olduvai Gorge in 1959 by Mary Leakey . This Rift Valley theory became known as the East Side Story by Yves Coppens . [ 21 ]
In the latter parts of the 20th century, new fossil evidence began to emerge which called the savanna hypothesis into question. These newly-discovered remains showed indications that they were still well adapted to climbing trees, even after they had begun to walk upright. [ 22 ] Both humans and chimpanzees tend to walk upright when moving along long branches of trees, increasing their reach. [ 23 ]
In 1993, 4.4 million year old fossil teeth were found in Aramis, Ethiopia , by a group led by Tim D. White attributed to a new species, Australopithecus ramidus , later called Ardipithecus ramidus . The age was thus half a million years older than previously known A. afarensis and had a more monkey-like appearance. [ 24 ] After extensive research, in 2009 in a series of eleven articles in Science , more was published about Ardi. It concluded that Ar. ramidus preferred more wooded areas instead of open grassland, which would not support the climate-driven savannah hypothesis. [ 25 ]
A year later, these conclusions were questioned: "In contrast, we find the environmental context of Ar. ramidus at Aramis to be represented by what is commonly referred to as "tree or bush savanna" with 25% or less woody canopy cover. The habitats involved probably ranged from riparian forest to grassland." [ 26 ]
For Phillip Tobias , the 1994 find of Little Foot , the collection of Australopithecus africanus foot bones demonstrating features consistent with tree-climbing as well as an upright gait, contributed to calling the savannah hypothesis obsolete, stating Open the window and throw out the savannah hypothesis; it's dead and we need a new paradigm. [ 27 ]
In 2000 Brigitte Senut and Martin Pickford found the 6 million year old Orrorin tugenensis in Kenya. The skeleton seems to indicate both bipedalism and good climbing skills. The latter indicates a wooded environment, as does the discovery of black-and-white colobuses . The discovery of impalas points more towards a more open landscape. [ 28 ] It later led Senut to the conclusion that the savannah hypothesis was no longer tenable. [ 29 ] If these fossils are indeed early ancestors of modern man, then the environment of the later Australopithecus is less relevant.
In 2001 the seven-million-year-old Sahelanthropus tchadensis was discovered in Chad . Based on animal finds in the vicinity, this suggests a mosaic of environments from gallery forest at the edge of a lake area to a dominance of large savannah and grassland , although more research was needed to determine this precisely. [ 30 ] The 5.6 million year old Ardipithecus kadabba discovered in 1997 was found in a similar terrain. [ 31 ]
Not everyone was willing to write off the savannah hypothesis. A poor definition of what a savannah actually is contributed to this. Critics of the hypothesis often saw the savannah as open grasslands with sporadic tree growth. However, savannas can have a high tree density and can also be humid. The big difference between savannas and forests is the lack of grasses in the latter. Thure E. Cerling developed a method to determine the forest cover of ancient landscapes, thus no longer requiring a definition of what a savannah is. By distinguishing between the C 3 plants of the tropical forests and the mix of trees and C 4 grasses of the savannah, they investigated the stable carbon isotope of paleosols from some sites in East Africa. They described landscapes varying from forest, woodland / bushland / shrubland , wooded grasslands to grasslands . They concluded that the early hominini lived in a more open environment than Australopithecus , rendering the savannah hypothesis still a plausible possibility. [ 32 ]
Following on from Cerling, Manuel Domínguez-Rodrigo stated that the usual division of landscapes into grassy, wooded and wooded is of little use, because it tells nothing about the evolutionary pressure on mammals. For example, the selection pressure of grass fields in tropical forests is incomparable to the grasslands of savannas. Tropical forests also have many different species of trees, while savannas only have a few species, which hardly carry any fruit. Another factor is that of scale. Paleontologists often only investigate the site itself, an area of several hundred to thousands of meters. These habitats are referred to as biomes , yet, this latter term includes many hundreds of kilometres. According to Domínguez-Rodrigo, the savannah hypothesis can still give a good explanation, although the transition of environment has probably been less abrupt than some earlier authors thought. [ 33 ] | https://en.wikipedia.org/wiki/Savannah_hypothesis |
The Saville reaction is a chemical reaction in which mercury replaces a nitrosyl from a thiol group.
It is used as a method of replacing the nitrosyl from the modified cysteines and thus can serve in research of the redox modification of different proteins. [ 1 ]
This chemical reaction article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Saville_reaction |
Sawdust (or wood dust ) is a by-product or waste product of woodworking operations such as sawing , sanding , milling and routing . It is composed of very small chips of wood . These operations can be performed by woodworking machinery , portable power tools or by use of hand tools . In some manufacturing industries it can be a significant fire hazard and source of occupational dust exposure .
Sawdust, as particulates , is the main component of particleboard . Research on health hazards comes from the field of occupational safety and health , and study of ventilation happens in indoor air quality engineering. Sawdust is an IARC group 1 Carcinogen .
Two waste products, dust and chips, form at the working surface during woodworking operations such as sawing, milling and sanding. These operations both shatter lignified wood cells and break out whole cells and groups of cells. Shattering of wood cells creates dust, while breaking out of whole groups of wood cells creates chips. The more cell-shattering that occurs, the finer the dust particles that are produced. For example, sawing and milling are mixed cell shattering and chip forming processes, whereas sanding is almost exclusively cell shattering. [ 1 ]
A major use of sawdust is for particleboard; coarse sawdust may be used for wood pulp . Sawdust has a variety of other practical uses, including serving as a mulch , as an alternative to clay cat litter , or as a fuel . Until the advent of refrigeration, it was often used in icehouses to keep ice frozen during the summer. It has been used in artistic displays , and as scatter in miniature railroad and other models. It is also sometimes used to soak up liquid spills, allowing the spill to be easily collected or swept aside. As such, it was formerly common on barroom floors. [ 2 ] It is used to make Cutler's resin . Mixed with water and frozen, it forms pykrete , a slow-melting, much stronger form of ice . [ citation needed ]
Sawdust is used in the manufacture of charcoal briquettes . The claim for invention of the first commercial charcoal briquettes goes to Henry Ford who created them from the wood scraps and sawdust produced by his automobile factory. [ 3 ]
Cellulose , fibre starch that is indigestible to humans, and a filler in some low calorie foods, can be and is made from sawdust, as well as from other plant sources. [ 4 ] While there is no documentation [ 5 ] for the persistent rumor, based upon Upton Sinclair 's novel The Jungle , that sawdust was used as a filler in sausage, cellulose derived from sawdust was and is used for sausage casings. [ 6 ] Sawdust-derived cellulose has also been used as a filler in bread. [ 7 ]
When cereals were scarce, sawdust was sometimes an ingredient in kommissbrot . Auschwitz concentration camp survivor, Dr. Miklós Nyiszli , reports in Auschwitz: A Doctor's Eyewitness Account that the subaltern medical staff, who served Dr. Josef Mengele , subsisted on "bread made from wild chestnuts sprinkled with sawdust". [ 8 ]
Airborne sawdust and sawdust accumulations present a number of health and safety hazards. [ 9 ] Wood dust becomes a potential health problem when, for example, the wood particles, from processes such as sanding, become airborne and are inhaled. Wood dust is a known human carcinogen . [ 10 ] [ 11 ] Certain woods and their dust contain toxins that can produce severe allergic reactions. [ 12 ] The composition of sawdust depends on the material it comes from; sawdust produced from natural wood is different from that of sawdust produced from processed wood or wood veneer . [ citation needed ]
Breathing airborne wood dust may cause allergic respiratory symptoms, mucosal and non-allergic respiratory symptoms, and cancer. [ 13 ] In the US, lists of carcinogenic factors are published by the American Conference of Governmental Industrial Hygienists (ACGIH), the Occupational Safety and Health Administration (OSHA), and the National Institute for Occupational Safety and Health (NIOSH). All these organisations recognize wood dust as carcinogenic in relation to the nasal cavities and paranasal sinuses. [ 14 ]
People can be exposed to wood dust in the workplace by breathing it in, skin contact, or eye contact. The OSHA has set the legal limit ( permissible exposure limit ) for wood dust exposure in the workplace as 15 mg/m 3 total exposure and 5 mg/m 3 respiratory exposure over an 8-hour workday. The NIOSH has set a recommended exposure limit (REL) of 1 mg/m 3 over an 8-hour workday. [ 15 ]
Water-borne bacteria digest organic material in leachate, but use up much of the available oxygen. This high biochemical oxygen demand can suffocate fish and other organisms. There is an equally detrimental effect on beneficial bacteria, so it is not at all advisable to use sawdust within home aquariums, as was once done by hobbyists seeking to save some expense on activated carbon . [ 16 ]
Sawdust is flammable and accumulations provide a ready source of fuel. Airborne sawdust can be ignited by sparks or even heat accumulation and result in dust fire or explosions. [ citation needed ]
At sawmills , unless reprocessed into particleboard, burned in a sawdust burner, or used to make heat for other milling operations, sawdust may collect in piles and add harmful leachates into local water systems, creating an environmental hazard . This has placed small sawyers and environmental agencies in a deadlock. [ citation needed ]
Questions about the science behind the determination of sawdust being an environmental hazard remain for sawmill operators (though this is mainly with finer particles), who compare wood residuals to dead trees in a forest. Technical advisors have reviewed some of the environmental studies, but say most lack standardized methodology or evidence of a direct impact on wildlife . They do not take into account large drainage areas , so the amount of material that is getting into the water from the site in relation to the total drainage area is minuscule. [ citation needed ]
Other scientists have a different view, saying the "dilution is the solution to pollution" argument is no longer accepted in environmental science. The decomposition of a tree in a forest is similar to the impact of sawdust, but the difference is of scale. Sawmills may be storing thousands of cubic metres of wood residues in one place, so the issue becomes one of concentration. [ citation needed ]
Of larger concern are substances such as lignins and fatty acids that protect trees from predators while they are alive, but can leach into water and poison wildlife. Those types of things remain in the tree and, as the tree decays, they slowly are broken down. But when sawyers are processing a large volume of wood and large concentrations of these materials permeate into the runoff, the toxicity they cause is harmful to a broad range of organisms. [ 17 ]
Wood flour is finely pulverized wood that has a consistency fairly equal to sand or sawdust, but can vary considerably, with particles ranging in dimensions from a fine powder to roughly that of a grain of rice. Most wood flour manufacturers are able to create batches of wood flour that have the same consistency throughout. All high quality wood flour is made from hardwoods because of its durability and strength. Very low grade wood flour is occasionally made from sapless softwoods such as pine or fir . [ citation needed ]
Wood flour is commonly used as a filler in thermosetting resins such as bakelite , and in linoleum floor coverings. Wood flour is also the main ingredient in wood/plastic composite building products such as decks and roofs. Prior to 1920, wood flour was used as the filler in ¼-inch thick Edison Diamond Discs . [ 18 ]
Wood flour has found a use in plugging small through-wall holes in leaking main condenser ( heat exchanger ) tubes at electrical power generating stations via injecting small quantities of the wood flour into the cooling water supply lines. Some of the injected wood flour clogs the small holes while the remainder exits the station in a relatively environmentally benign fashion. [ citation needed ]
Because of its adsorbent properties it has been used as a cleaning agent for removing grease or oil in various occupations. It has also been noted for its ability to remove lead contamination from water. [ 19 ]
Wood flour can be used as a binder in grain filler compounds. [ citation needed ]
Large quantities of wood flour are frequently to be found in the waste from woodworking and furniture companies. An adaptive reuse to which this material can be directed is composting . [ citation needed ]
Wood flour can be subject to dust explosions if not cared for and disposed of properly. [ citation needed ]
As with all airborne particulates , wood dust particle sizes are classified with regard to effect on the human respiratory system. For this classification, the unit for measurement of particle sizes is the micrometre or micron (μm), where 1 micrometre = 1 micron. Particles below 50 μm are not normally visible to the naked human eye. [ 20 ] Particles of concern for human respiratory health are those <100 μm (where the symbol < means ‘less than’). [ citation needed ]
Zhang (2004) [ 21 ] has defined the size of indoor particulates according to respiratory fraction:
Particles which precipitate in the vicinity of the mouth and eyes, and get into the organism, are defined as the inhalable fraction, that is total dust. Smaller fractions, penetrating into the non-cartilage respiratory tract, are defined as respirable dust. [ 22 ] Dust emitted in the wood industry is characterized by the dimensional disintegration of particles up to 5 μm, and that
is why they precipitate mostly in the nasal cavity, increasing the risk of cancer of the upper respiratory tract. [ 23 ]
The parameter most commonly used to characterize exposures to wood dust in air is total wood dust concentration, in mass per unit volume. In countries that use the metric system, this is usually measured in mg/m 3 (milligram per cubic metre) [ 24 ]
A study to estimate occupational exposure to inhalable wood dust by country, industry, the level of exposure and type of wood dust in 25 member states of the European Union (EU-25) found that in 2000–2003, about 3.6 million workers (2.0% of the employed EU-25 population) were occupationally exposed to inhalable wood dust. The highest exposure levels were estimated to occur in the construction sector and furniture industry. [ 25 ]
Wood dust is known to be a human carcinogen, based on sufficient evidence of carcinogenicity from studies in humans. It has been demonstrated through human epidemiologic studies that exposure to wood dust increases the occurrence of cancer of the nose (nasal cavities and paranasal sinuses). An association of wood dust exposure and cancers of the nose has been observed in numerous case reports, cohort studies, and case control studies specifically addressing nasal cancer. [ 26 ]
To lower the concentration of airborne dust concentrations during woodworking, dust extraction systems are used. These can be divided into two types. The first are local exhaust ventilation systems, the second are room ventilation systems. Use of personal respirators , a form of personal protective equipment , can also isolate workers from dust. [ citation needed ]
Local exhaust ventilation (LEV) systems rely on air pulled with a suction force through piping systems from the point of dust formation to a waste disposal unit. They consist of four elements: dust hoods at the point of dust formation, ventilation ducts, an air cleaning device (waste separator or dust collector) and an air moving device (a fan, otherwise known as an impeller). [ 27 ] The air, containing dust and chips from the woodworking operation, is sucked by an impeller. The impeller is usually built into, or placed close to, the waste disposal unit, or dust collector . [ citation needed ]
Guidelines of performance for woodworking LEV systems exist, and these tie into occupational air quality regulations that exist in many countries. The LEV guidelines often referred to are those set by the ACIAH. [ clarification needed ] [ citation needed ]
Low-volume/high-velocity (LVHV) capture systems are specialised types of LEV that use an extractor hood designed as an integral part of the tool or positioned very close to the operating point of the cutting tool. The hood is designed to provide high capture velocities, often greater than 50 m/s (10,000 fpm) at the contaminant release point. This high velocity is accompanied by airflows often less than 0.02m3/s (50 cfm) resulting from the small face area of the hood that is used. [ 28 ] These systems have come into favour for portable power tools, although adoption of the technology is not widespread. Festool is one manufacturer of portable power tools using LVHV ventilation integrated into the tool design. [ citation needed ]
If suitably designed, general ventilation can also be used as a control of airborne dust. General ventilation can often help reduce skin and clothing contamination, and dust deposition on surfaces. [ 29 ]
″There was once a time when sawmill operators could barely give away their sawdust. They dumped it in the woods or incinerated it just to get rid of the stuff. These days, they have ready markets for sawdust…″, according to a report in 2008. [ 30 ] For example, sawdust is used by biomass power plants as fuel or is sold to dairy farmers as animal bedding. [ 30 ] | https://en.wikipedia.org/wiki/Sawdust |
A saxicolous lichen is a lichen that grows on rock. [ 1 ] [ 2 ] The prefix "sax" from the Latin saxum means "rock" or "stone". [ 3 ]
Saxicolous lichens exhibit very slow growth rates. They may develop on rock substrates for long periods of time, given the absence of external disturbances. [ 4 ] The importance of the mineral composition of the rock substrate, as well as the elemental geochemistry is also important to the distribution of saxicolous lichens, but the relationship between the substrate influence on lichens, either chemical or textural, is still obscure. [ 5 ]
Communities of saxicolous lichens are often species-rich in terms of number. [ 6 ]
This article about lichens or lichenology is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Saxicolous_lichen |
The Saxon Shore ( Latin : litus Saxonicum ) was a military command of the Late Roman Empire , consisting of a series of fortifications on both sides of the English Channel . It was established in the late 3rd century and was led by the " Count of the Saxon Shore ". In the late 4th century, his functions were limited to Britain , while the fortifications in Gaul were established as separate commands. Several well-preserved Saxon Shore forts survive in east and south-east England .
During the latter half of the 3rd century, the Roman Empire faced a grave crisis : Weakened by civil wars, the rapid succession of short-lived emperors, and secession in the provinces, the Romans now faced new waves of attacks by barbarian tribes. Most of Britain had been part of the empire since the mid-1st century. It was protected from raids by native Celtic Britons in the north by the Hadrianic and Antonine Walls , while a fleet of some size was also available.
However, as the frontiers came under increasing external pressure, fortifications were built throughout the Empire in order to protect cities and guard strategically important locations. It is in this context that the forts of the Saxon Shore were constructed. Already in the 230s, under Severus Alexander , several units had been withdrawn from the northern frontier and garrisoned at locations in the south, and had built new forts at Brancaster and Caister-on-Sea in Norfolk and Reculver in Kent. Dover was already fortified in the early 2nd century, and the other forts in this group were constructed in the period between the 270s and 290s.
The only contemporary reference we possess that mentions the name "Saxon Shore" comes in the late 4th-century Notitia Dignitatum , which lists its commander, the Comes Litoris Saxonici per Britanniam (" Count of the Saxon Shore in Britain"), and gives the names of the sites under his command and their respective complements of military personnel. [ 1 ] [ 2 ] However, due to the absence of further evidence, theories have varied among scholars as to the exact meaning of the name, and also the nature and purpose of the chain of forts it refers to.
Two interpretations were put forward as to the meaning of the adjective "Saxon": either a shore attacked by Saxons , or a shore settled by Saxons. Some argue that the latter hypothesis is supported by Eutropius , who states that during the 280s the sea along the coasts of Belgica and Armorica was "infested with Franks and Saxons", and that this was why Carausius was first put in charge of the fleet there, while others believe the term infestation relates to seabourne Saxons and Franks raiding the coasts. [ 3 ] [ non-primary source needed ] It also receives some support from archaeological finds, as artefacts of a Germanic style have been found in burials, while there is evidence of the presence of Saxons in southern England and the northern coasts of Gaul around Boulogne-sur-Mer and Bayeux from the middle of the 5th century onwards, although this timeline coincides with the Anglo-Saxon invasion of Britain. [ 4 ] This, in turn, could mirror a well documented practice of deliberately settling Germanic tribes (Franks became foederati in 358 AD under Emperor Julian) to strengthen Roman defences. Nevertheless, the evidence for extensive Saxon settlement in Britain typically only dates to the 5th century, later than the channel defences of the late 3rd and 4th century associated with the Saxon Shore.
The other interpretation holds that the forts fulfilled a coastal defence role against seaborne invaders, mostly Saxons and Franks, [ 5 ] and acted as bases for the naval units operating against them. This view is reinforced by the parallel chain of fortifications across the Channel on the northern coasts of Gaul , which complemented the British forts, suggesting a unified defensive system, although this could also be accounted for the Saxons having been settled on both sides of the coast as some archeological evidence presented earlier suggests. [ 6 ]
Other scholars like John Cotterill however consider the threat posed by Germanic raiders, at least in the 3rd and early 4th centuries, to be exaggerated. They interpret the construction of the forts at Brancaster, Caister-on-Sea and Reculver in the early 3rd century and their location at the estuaries of navigable rivers as pointing to a different role: fortified points for transport and supply between Britain and Gaul, without any relation (at least at that time) to countering seaborne piracy. [ 7 ] This view is supported by contemporary references to the supplying of the army of Julian the Apostate by Caesar with grain from Britain during his campaign in Gaul in 359, [ 8 ] and their use as secure landing places by Count Theodosius during the suppression of the Great Conspiracy a few years later. [ 9 ] [ non-primary source needed ]
Another theory, proposed by D.A. White, was that the extended system of large stone forts was disproportionate to any threat by seaborne Germanic raiders, and that it was actually conceived and constructed during the secession of Carausius and Allectus (the Carausian Revolt ) in 289–296, and with an entirely different enemy in mind: they were to guard against an attempt at reconquest by the Empire. This view, although widely disputed, has found recent support from archaeological evidence at Pevensey, which dates the fort's construction to the early 290s. [ 10 ]
Whatever their original purpose, it is virtually certain that in the late 4th century the forts and their garrisons were employed in operations against Frankish and Saxon pirates rather than to contain Saxons in Britain itself. Britain was abandoned by Rome in 410, with Armorica following soon after. The forts on both sides continued to be inhabited in the following centuries, and in Britain in particular several continued in use well into the Anglo-Saxon period. [ citation needed ]
The nine forts mentioned in the Notitia Dignitatum for Britain are listed here, from north to south, with their garrisons. [ 1 ]
There are a few other sites that clearly belonged to the system of the British branch of the Saxon Shore (the so-called " Wash – Solent limes "), although they are not included in the Notitia , such as the forts at Walton Castle, Suffolk , which has by now sunk into the sea due to erosion, and at Caister-on-Sea in Norfolk . In the south, Carisbrooke Castle on the Isle of Wight and Clausentum ( Bitterne , in modern Southampton ) are also regarded as westward extensions of the fortification chain. Other sites probably connected to the Saxon Shore system are the sunken fort at Skegness , and the remains of possible signal stations at Thornham in Norfolk, Corton in Suffolk and Hadleigh in Essex. [ 14 ]
Further north on the coast, the precautions took the form of central depots at Lindum ( Lincoln ) and Malton with roads radiating to coastal signal stations. When an alert was relayed to the base, troops could be dispatched along the road. Further up the coast in North Yorkshire, a series of coastal watchtowers (at Huntcliff , Filey , Ravenscar , Goldsborough , and Scarborough ) was constructed, linking the southern defences to the northern military zone of the Wall. [ 15 ] Similar coastal fortifications are also found in Wales , at Cardiff and Caer Gybi . The only fort in this style in the northern military zone is Lancaster, Lancashire , built sometime in the mid-late 3rd century replacing an earlier fort and extramural community, which may reflect the extent of coastal protection on the north-west coast from invading tribes from Ireland.
The Notitia also includes two separate commands for the northern coast of Gaul, both of which belonged to the Saxon Shore system. However, when the list was compiled, in c. 420 AD , Britain had been abandoned by Roman forces. The first command controlled the shores of the province Belgica Secunda (roughly between the estuaries of the Scheldt and the Somme ), under the dux Belgicae Secundae with headquarters at Portus Aepatiaci: [ 16 ]
Although not mentioned in the Notitia , the port of Gesoriacum or Bononia ( Boulogne-sur-Mer ), which until 296 was the main base of the Classis Britannica , would also have come under the dux Belgicae Secundae .
To this group also belongs the Roman fort at Oudenburg in Belgium.
Further west, under the dux tractus Armoricani et Nervicani , were mainly the coasts of Armorica , nowadays Normandy and Brittany . The Notitia lists the following sites: [ 17 ]
Based on citation Hofmann J. Lexicon universale at: https://latin_latin.en-academic.com/28050/GRANNONA_vulgo_GARANDE_vel_GUERANDE Content auto-translated as quote: Grannona commonly known as Garande or Guerande a castle in Britanniae (Brittany ed.), a min. prom. imposing, between the gates of the Loire and Vicinonia. From here is not far from the village of St. Nazarius St. Nazere, notable for the relics of this Martyr and the vet. Monastery, on the Loire in the village of Namnetico, not far from the gate of the river or from the village of Cruciaco le Croisic. Hadr. Vales. Not. Gall.
In addition, there are several other sites where a Roman military presence has been suggested. At Alderney , the fort known as "The Nunnery" is known to date to Roman times, [ 19 ] and the settlement at Longy Common has been cited as evidence of a Roman military establishment, though the archaeological evidence there is, at best, scant. [ 20 ]
Notes
Sources
Media related to Saxon Shore at Wikimedia Commons | https://en.wikipedia.org/wiki/Saxon_Shore |
Saybolt universal viscosity ( SUV ), and the related Saybolt FUROL viscosity ( SFV ), are specific standardised tests producing measures of kinematic viscosity . FUROL is an acronym for fuel and road oil . [ 1 ] Saybolt universal viscosity is specified by the ASTM D2161. Both tests are considered obsolete to other measures of kinematic viscosity, but their results are quoted widely in technical literature.
In both tests, the time taken for 60 ml of the liquid, held at a specific temperature, to flow through a calibrated tube, is measured, using a Saybolt viscometer . [ 2 ] The Saybolt universal viscosity test occurs at 100 °F (38 °C), or more recently, 40 °C (104 °F). The Saybolt FUROL viscosity test occurs at 120 °F (49 °C), or more recently, 50 °C (122 °F), and uses a larger calibrated tube. This provides for the testing of more viscous fluids, with the result being approximately 1 ⁄ 10 of the universal viscosity.
The test results are specified in seconds (s), more often than not referencing the test: Saybolt universal seconds (SUS); seconds, Saybolt universal (SSU); seconds, Saybolt universal viscosity (SSUV); and Saybolt FUROL seconds (SFS); seconds, Saybolt FUROL (SSF). The precise temperature at which the test is performed is often specified as well.
This classical mechanics –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Saybolt_universal_viscosity |
In crystallography , the Sayre equation , named after David Sayre who introduced it in 1952, is a mathematical relationship that allows one to calculate probable values for the phases of some diffracted beams. It is used when employing direct methods to solve a structure. Its formulation is the following:
F h k l = ∑ h ′ k ′ l ′ F h ′ k ′ l ′ F h − h ′ , k − k ′ , l − l ′ {\displaystyle F_{hkl}=\sum _{h'k'l'}F_{h'k'l'}F_{h-h',k-k',l-l'}}
which states how the structure factor for a beam can be calculated as the sum of the products of pairs of structure factors whose indices sum to the desired values of h , k , l {\displaystyle h,k,l} . [ 1 ] [ 2 ] Since weak diffracted beams will contribute a little to the sum, this method can be a powerful way of finding the phase of related beams, if some of the initial phases are already known by other methods.
In particular, for three such related beams in a centrosymmetric structure, the phases can only be 0 or π {\displaystyle \pi } and the Sayre equation reduces to the triplet relationship:
S h ≈ S h ′ S h − h ′ {\displaystyle S_{h}\approx S_{h'}S_{h-h'}}
where the S {\displaystyle S} indicates the sign of the structure factor (positive if the phase is 0 and negative if it is π {\displaystyle \pi } ) and the ≈ {\displaystyle \approx } sign indicates that there is a certain degree of probability that the relationship is true, which becomes higher the stronger the beams are.
This crystallography -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Sayre_equation |
Trimethylstibine is an organoantimony compound with the formula Sb(CH 3 ) 3 . It is a colorless pyrophoric and toxic liquid. [ 2 ] It is synthesized by treatment of antimony trichloride and methyl Grignard reagent . [ 3 ] It is produced by anaerobic bacteria in antimony -rich soils. [ 4 ] In contrast to trimethylphosphine , trimethylstibine is a weaker Lewis base . It is used in the production of some III-V semiconductors .
This article about an organic compound is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Sb(CH3)3 |
Antimony(III) oxide is the inorganic compound with the formula Sb 2 O 3 . It is the most important commercial compound of antimony . It is found in nature as the minerals valentinite and senarmontite. [ 3 ] Like most polymeric oxides , Sb 2 O 3 dissolves in aqueous solutions with hydrolysis . A mixed arsenic-antimony oxide occurs in nature as the very rare mineral stibioclaudetite. [ 4 ] [ 5 ]
Global production of antimony(III) oxide in 2012 was 130,000 tonnes, an increase from 112,600 tonnes in 2002. China produces the largest share followed by US/Mexico, Europe, Japan and South Africa and other countries (2%). [ 6 ]
As of 2010, antimony(III) oxide was produced at four sites in the EU. It is produced via two routes, re-volatilizing of crude antimony(III) oxide and by oxidation of antimony metal.
Oxidation of antimony metal dominates in Europe. Several processes for the production of crude antimony(III) oxide or metallic antimony from virgin material. The choice of process depends on the composition of the ore and other factors. Typical steps include mining, crushing and grinding of ore, sometimes followed by froth flotation and separation of the metal using pyrometallurgical processes (smelting or roasting) or in a few cases (e.g. when the ore is rich in precious metals) by hydrometallurgical processes. These steps do not take place in the EU but closer to the mining location.
Step 1) Crude stibnite is oxidized to crude antimony(III) oxide using furnaces operating at approximately 500 to 1,000 °C. The reaction is the following:
Step 2) The crude antimony(III) oxide is purified by sublimation .
Antimony metal is oxidized to antimony(III) oxide in furnaces. The reaction is exothermic. Antimony(III) oxide is formed through sublimation and recovered in bag filters. The size of the formed particles is controlled by process conditions in furnace and gas flow. The reaction can be schematically described by:
Antimony(III) oxide is an amphoteric oxide . It dissolves in aqueous sodium hydroxide solution to give the meta-antimonite NaSbO 2 , which can be isolated as the trihydrate. Antimony(III) oxide also dissolves in concentrated mineral acids to give the corresponding salts, which hydrolyzes upon dilution with water. [ 7 ] With nitric acid , the trioxide is oxidized to antimony(V) oxide . [ 8 ]
When heated with carbon , the oxide is reduced to antimony metal. With other reducing agents such as sodium borohydride or lithium aluminium hydride , the unstable and very toxic gas stibine is produced. [ 9 ] When heated with potassium bitartrate , a complex salt potassium antimony tartrate , KSb(OH) 2 ·C 4 H 2 O 6 , is formed. [ 8 ]
The structure of Sb 2 O 3 depends on the temperature of the sample. Dimeric Sb 4 O 6 is the high temperature (1560 °C) gas. [ 10 ] Sb 4 O 6 molecules are bicyclic cages, similar to the related oxide of phosphorus(III), phosphorus trioxide . [ 11 ] The cage structure is retained in a solid that crystallizes in a cubic habit. The Sb–O distance is 197.7 pm and the O–Sb–O angle of 95.6°. [ 12 ] This form exists in nature as the mineral senarmontite . [ 11 ] Above 606 °C, the more stable form is orthorhombic , consisting of pairs of -Sb-O-Sb-O- chains that are linked by oxide bridges between the Sb centers. This form exists in nature as the mineral valentinite . [ 11 ]
The annual consumption of antimony(III) oxide in the United States and Europe is approximately 10,000 and 25,000 tonnes , respectively. The main application is as flame retardant synergist in combination with halogenated materials. The combination of the halides and the antimony is key to the flame-retardant action for polymers, helping to form less flammable chars. Such flame retardants are found in electrical apparatuses, textiles, leather, and coatings. [ 13 ]
Other applications:
Antimony(III) oxide has suspected carcinogenic potential for humans. [ 13 ] Its TLV is 0.5 mg/m 3 , as for most antimony compounds. [ 14 ] Before 2021, no other human health hazards were identified for antimony(III) oxide, and no risks to human health and the environment were identified from the production and use of antimony trioxide in daily life. However, the 15th Report on Carcinogens released on December 21, 2021, by the US Department of Health and Human Services categorised antimony(III) oxide as carcinogenic. [ 15 ] | https://en.wikipedia.org/wiki/Sb2O3 |
Antimony tetroxide is an inorganic compound with the formula Sb 2 O 4 . This material, which exists as the mineral cervantite, [ 3 ] is white but reversibly yellows upon heating. The material, with empirical formula SbO 2 , is called antimony tetroxide to signify the presence of two kinds of Sb centers. [ 4 ]
The material forms when Sb 2 O 3 is heated in air: [ 5 ]
At 800 °C, antimony(V) oxide loses oxygen to give the same material:
The material is mixed valence, containing both Sb(V) and Sb(III) centers. Two polymorphs are known, one orthorhombic (shown in the infobox) and one monoclinic. [ 1 ] Both forms feature octahedral Sb(V) centers arranged in sheets with distorted Sb(III) centers bound to four oxides. | https://en.wikipedia.org/wiki/Sb2O4 |
Antimony pentoxide (molecular formula: Sb 2 O 5 ) is a chemical compound of antimony and oxygen . It contains antimony in the +5 oxidation state .
Antimony pentoxide has the same structure as the B form of niobium pentoxide and can be derived from the rutile structure, with antimony coordinated by six oxygen atoms in a distorted octahedral arrangement. The SbO 6 octahedra are corner- and edge-sharing. [ 2 ]
The hydrated oxide is prepared by hydrolysis of antimony pentachloride ; or by acidification of potassium hexahydroxoantimonate(V) . It may also be prepared by oxidation of antimony trioxide with nitric acid . [ 3 ]
Antimony pentoxide finds use as a flame retardant in ABS and other plastics and as a flocculant in the production of titanium dioxide , and is sometimes used in the production of glass, paint and adhesives. [ 4 ] [ 5 ]
It is also used as an ion exchange resin for a number of cations in acidic solution including Na + (especially for their selective retentions), and as a polymerization and oxidation catalyst.
The hydrated oxide is insoluble in nitric acid, but dissolves in a concentrated potassium hydroxide solution to give potassium hexahydroxoantimonate(V), or KSb(OH) 6 . [ 6 ]
When heated to 700 °C (1,290 °F), the yellow hydrated pentoxide converts to an anhydrous white solid with the formula Sb 6 O 13 , containing both antimony(III) and antimony(V) . Heating to 900 °C (1,650 °F) produces a white, insoluble powder of Sb 2 O 4 in both α and β forms. The β form consists of antimony(V) in octahedral interstices and pyramidal Sb III O 4 units. In these compounds, the antimony(V) atom is octahedrally coordinated to six hydroxy groups .
The pentoxide can be reduced to antimony metal by heating with hydrogen or potassium cyanide . [ 7 ] | https://en.wikipedia.org/wiki/Sb2O5 |
Antimony pentasulfide is an inorganic compound of antimony and sulfur , also known as antimony red . It is a nonstoichiometric compound with a variable composition. Its structure is unknown. [ 2 ] Commercial samples are contaminated with sulfur, which may be removed by washing with carbon disulfide in a Soxhlet extractor .
Antimony pentasulfide can be produced by the reaction of antimony with sulfur at a temperature from 250 to 400 °C in an inert atmosphere.
It may be used as a red pigment and is one possible precursor to Schlippe's salt , Na 3 SbS 4 ·9H 2 O , which can be prepared according to the equation:
It is also used in the vulcanization of rubber to produce red rubber.
Like many sulfides , this compound liberates hydrogen sulfide upon treatment with strong acids such as hydrochloric acid . [ 3 ]
Analysis by Mössbauer spectroscopy indicates that this compound is a derivative antimony(III), [ 4 ] explaining the production of antimony(III) chloride , rather than antimony(V) chloride , upon acidification. It is, therefore, not analogous to the phosphorus(V) compound phosphorus pentasulfide . | https://en.wikipedia.org/wiki/Sb2S5 |
Antimony triselenide is the chemical compound with the formula Sb 2 Se 3 . The material exists as the sulfosalt mineral antimonselite ( IMA symbol : Atm [ 2 ] ), which crystallizes in an orthorhombic space group . [ 3 ] In this compound, antimony has a formal oxidation state +3 and selenium −2. The bonding in this compound has covalent character as evidenced by the black color and semiconducting properties of this and related materials. [ 4 ] The low-frequency dielectric constant (ε 0 ) has been measured to be 133 along the c axis of the crystal at room temperature, which is unusually large. [ 5 ] Its band gap is 1.18 eV at room temperature. [ 6 ]
The compound may be formed by the reaction of antimony with selenium and has a melting point of 885 K. [ 4 ]
Sb 2 Se 3 is now being actively explored for application thin-film solar cells. [ 7 ] A record light-to-electricity conversion efficiency of 9.2% has been reported. [ 8 ]
This inorganic compound –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Sb2Se3 |
Antimony telluride is an inorganic compound with the chemical formula Sb 2 Te 3 . As is true of other pnictogen chalcogenide layered materials, it is a grey crystalline solid with layered structure. Layers consist of two atomic sheets of antimony and three atomic sheets of tellurium and are held together by weak van der Waals forces . Sb 2 Te 3 is a narrow-gap semiconductor with a band gap 0.21 eV; it is also a topological insulator , and thus exhibits thickness-dependent physical properties. [ 1 ]
Sb 2 Te 3 has a rhombohedral crystalline structure. [ 8 ] The crystalline material comprises atoms covalently bonded to form 5 atom thick sheets (in order: Te-Sb-Te-Sb-Te), with sheets held together by van der Waals attraction. Due to its layered structure and weak inter-layer forces, bulk antimony telluride may be mechanically exfoliated to isolate single sheets.
Although antimony telluride is a naturally occurring compound, select stoichiometric compounds may be formed by the reaction of antimony with tellurium at 500–900 °C. [ 3 ]
Like other binary chalcogenides of antimony and bismuth , Sb 2 Te 3 has been investigated for its semiconductor properties. It can be transformed into both n -type and p -type semiconductors by doping with an appropriate dopant . [ 3 ]
Doping Sb 2 Te 3 with iron introduces multiple Fermi pockets, in contrast to the single frequency detected for pure Sb 2 Te 3 , and results in reduced carrier density and mobility. [ 9 ]
Sb 2 Te 3 forms the pseudobinary intermetallic system germanium-antimony-tellurium with germanium telluride , GeTe. [ 10 ]
Like bismuth telluride , Bi 2 Te 3 , antimony telluride has a large thermoelectric effect and is therefore used in solid state refrigerators . [ 3 ] | https://en.wikipedia.org/wiki/Sb2Te3 |
Antimony tribromide ( Sb Br 3 ) is a chemical compound containing antimony in its +3 oxidation state.
Antimony tribromide may be made by the reaction of antimony with elemental bromine , or by the reaction of antimony trioxide with hydrobromic acid .
Alternatively, it can be prepared by the action of bromine on a mixture of antimony sulfide and antimony trioxide at 250 °C.
Antimony tribromide has two crystalline forms, both having orthorhombic symmetries. When a warm carbon disulfide solution of SbBr 3 is rapidly cooled, it crystallizes into the needle-like α-SbBr 3 , which then slowly converts to the more stable β form. [ 2 ]
Antimony tribromide hydrolyzes in water to form hydrobromic acid and antimony trioxide:
It can be added to polymers such as polyethylene as a fire retardant . [ 3 ] It is also used in the production of other antimony compounds, in chemical analysis, as a mordant , and in dyeing. [ 4 ] | https://en.wikipedia.org/wiki/SbBr3 |
Antimony trichloride is the chemical compound with the formula SbCl 3 . It is a soft colorless solid with a pungent odor and was known to alchemists as butter of antimony .
Antimony trichloride is prepared by reaction of chlorine with antimony , antimony tribromide , antimony trioxide , or antimony trisulfide . It also may be made by treating antimony trioxide with concentrated hydrochloric acid .
SbCl 3 is readily hydrolysed and samples of SbCl 3 must be protected from moisture. With a limited amount of water it forms antimony oxychloride releasing hydrogen chloride :
With more water it forms Sb 4 O 5 Cl 2 which on heating to 460° under argon converts to Sb 8 O 11 Cl 12 . [ 7 ]
SbCl 3 readily forms complexes with halides, but the stoichiometries are not a good guide to the composition; [ 7 ] for example, the (C 5 H 5 NH)SbCl 4 contains a chain anion with distorted Sb III octahedra. Similarly the salt (C 4 H 9 NH 3 ) 2 SbCl 5 contains a polymeric anion of composition [SbCl 2− 5 ] n with distorted octahedral Sb III . [ 8 ]
With nitrogen donor ligands, L, complexes with a stereochemically active lone-pair are formed, for example Ψ-trigonal bipyramidal LSbCl 3 and Ψ-octahedral L 2 SbCl 3 . [ 9 ]
While SbCl 3 is only a weak Lewis base, [ 7 ] some complexes, such as the carbonyl complexes Fe(CO) 3 (SbCl 3 ) 2 and Ni(CO) 3 SbCl 3 , are known. [ 9 ]
In the gas phase SbCl 3 is pyramidal with a Cl-Sb-Cl angle of 97.2° and a bond length of 233 pm. [ 10 ] In SbCl 3 each Sb has three Cl atoms at 234 pm showing the persistence of the molecular SbCl 3 unit, however there are a further five neighboring Cl atoms, two at 346 pm, one at 361 pm, and two at 374 pm. These eight atoms can be considered as forming a bicapped trigonal prism. These distances can be contrasted with BiCl 3 which has three near neighbors at 250 pm, with two at 324 pm, and three at a mean of 336 pm. The point to note here is that the all eight close neighbours of Bi are closer than the eight closest neighbours of Sb, demonstrating the tendency for Bi to adopt higher coordination numbers. [ 10 ] [ 7 ]
SbCl 3 is a reagent for detecting vitamin A and related carotenoids in the Carr-Price test . The antimony trichloride reacts with the carotenoid to form a blue complex that can be measured by colorimetry .
Antimony trichloride has also been used as an adulterant to enhance the louche effect in absinthe . It has been used in the past to dissolve and remove horn buds from calves without having to cut them off.
It is also used as a catalyst for polymerization, hydrocracking, and chlorination reactions; [ 11 ] a mordant ; and in the production of other antimony salts. Its solution is used as an analytical reagent for chloral, aromatics, and vitamin A . [ 12 ] It has a very potential use as a Lewis acid catalyst in synthetic organic transformation.
A solution of antimony trichloride in liquid hydrogen sulfide is a good conductor, though the applications of such are limited by the very low temperature or high pressure required for hydrogen sulfide to be liquid. [ 13 ]
In episode 2 of the third season of the popular British program All Creatures Great and Small (adapted from chapter six of the book All Things Wise and Wonderful ), several calves died at Kate Billings farm following an episode of nonspecific gastroenteritis , the cause of which was later determined to be ingestion of antimony trichloride present in a topical "butter of antimony" solution painted on to cauterize and remove their horn buds. | https://en.wikipedia.org/wiki/SbCl3 |
Antimony pentachloride is a chemical compound with the formula SbCl 5 . It is a colourless oil, but typical samples are yellowish due to dissolved chlorine . Owing to its tendency to hydrolyse to hydrochloric acid , SbCl 5 is a highly corrosive substance and must be stored in glass or PTFE containers.
Antimony pentachloride is prepared by passing chlorine gas into molten antimony trichloride :
Gaseous SbCl 5 has a trigonal bipyramidal structure. [ 6 ]
This compounds reacts with water to form antimony pentoxide and hydrochloric acid : [ 7 ]
The mono- and tetrahydrates are known, SbCl 5 ·H 2 O and SbCl 5 ·4H 2 O.
This compound forms adducts with many Lewis bases. SbCl 5 is a soft Lewis acid and its ECW model parameters are E A = 3.64 and C A = 10.42. It is used as the standard Lewis acid in the Gutmann scale of Lewis basicity . [ 8 ] [ 9 ]
It is also a strong oxidizing agent . [ 10 ] For example aromatic ethers are oxidized to their radical cations according to the following stoichiometry: [ 11 ]
Antimony pentachloride is used as a polymerization catalyst and for the chlorination of organic compounds.
Antimony pentachloride is a highly corrosive substance that should be stored away from heat and moisture. It is a chlorinating agent and, in the presence of moisture, it releases hydrogen chloride gas. Because of this, it may etch even stainless-steel tools (such as needles), if handled in a moist atmosphere. It should not be handled with non-fluorinated plastics (such as plastic syringes, plastic septa, or needles with plastic fittings), since it melts and carbonizes plastic materials. [ 12 ] | https://en.wikipedia.org/wiki/SbCl5 |
Antimony trifluoride is the inorganic compound with the formula SbF 3 . Sometimes called Swarts' reagent , it is one of two principal fluorides of antimony , the other being SbF 5 . It appears as a white solid. As well as some industrial applications, [ 2 ] it is used as a reagent in inorganic and organofluorine chemistry .
In solid SbF 3 , the Sb centres have octahedral molecular geometry and are linked by bridging fluoride ligands . Three Sb–F bonds are short (192 pm) and three are long (261 pm). Because it is a polymer, SbF 3 is far less volatile than related compounds AsF 3 and SbCl 3 . [ 3 ]
SbF 3 is prepared by treating antimony trioxide with hydrogen fluoride : [ 4 ]
The compound is a mild Lewis acid , hydrolyzing slowly in water. With fluorine, it is oxidized to give antimony pentafluoride .
It is used as a fluorination reagent in organic chemistry . [ 5 ] This application was reported by the Belgian chemist Frédéric Jean Edmond Swarts in 1892, [ 6 ] who demonstrated its usefulness for converting chloride compounds to fluorides . The method involved treatment with antimony trifluoride with chlorine or with antimony pentachloride to give the active species antimony trifluorodichloride (SbCl 2 F 3 ). This compound can also be produced in bulk. [ 7 ] The Swarts reaction is generally applied to the synthesis of organofluorine compounds , but experiments have been performed using silanes . [ 8 ] It was once used for the industrial production of freon . Other fluorine-containing Lewis acids serve as fluorinating agents in conjunction with hydrogen fluoride .
SbF 3 is used in dyeing and in pottery , to make ceramic enamels and glazes.
The lethal minimum dose (guinea pig, oral) is 100 mg/kg. [ 9 ] | https://en.wikipedia.org/wiki/SbF3 |
Antimony pentafluoride is the inorganic compound with the formula Sb F 5 . This colorless, viscous liquid is a strong Lewis acid and a component of the superacid fluoroantimonic acid , formed upon mixing liquid HF with liquid SbF 5 in 1:1 ratio. It is notable for its strong Lewis acidity and the ability to react with almost all known compounds. [ 4 ]
Antimony pentafluoride is prepared by the reaction of antimony pentachloride with anhydrous hydrogen fluoride : [ 5 ]
It can also be prepared from antimony trifluoride and fluorine . [ 6 ]
In the gas phase, SbF 5 adopts a trigonal bipyramidal structure of D 3h point group symmetry (see picture). The material adopts a more complicated structure in the liquid and solid states. The liquid contains polymers wherein each Sb is octahedral, the structure being described with the formula [SbF 4 (μ-F) 2 ] n ((μ-F) denotes the fact that fluoride centres bridge two Sb centers). The crystalline material is a tetramer, meaning that it has the formula [SbF 4 (μ-F)] 4 . The Sb–F bonds are 2.02 Å within the eight-membered Sb 4 F 4 ring; the remaining fluoride ligands radiating from the four Sb centers are shorter at 1.82 Å. [ 7 ] The related species PF 5 and AsF 5 are monomeric in the solid and liquid states, probably due to the smaller sizes of the central atom, which limits their coordination number. BiF 5 is a polymer. [ 8 ]
Antimony pentafluoride is a very strong oxidizing agent. Phosphorus burns on contact with it.
SbF 5 increases the oxidizing power of Fluorine, making it able to oxidize oxygen :
SbF 5 has also been used in the first discovered chemical reaction that produces fluorine gas from fluoride compounds:
The driving force for this reaction is the high affinity of SbF 5 for F − , which is the same property that recommends the use of SbF 5 to generate superacids.
SbF 5 is a strong Lewis acid, exceptionally so toward sources of F − to give the very stable anion [SbF 6 ] − , called hexafluoroantimonate. It is the conjugate base of the superacid fluoroantimonic acid . [SbF 6 ] − is a weakly coordinating anion akin to PF 6 − . Although it is only weakly basic, [SbF 6 ] − does react with additional SbF 5 to give a centrosymmetric adduct :
The [Sb 2 F 11 ] − anion is one of the ions found in HF/SbF 5 Mixture.
SbF 5 is highly corrosive to the skin and the eyes. It is extremely toxic and hazardous to health. Its lethal dose (LD 50 ) is reported to be 270 mg/kg (mouse, subcutaneous) with lowest concentration (LC Lo ) of 15 mg/m 3 or 1.69 ppm (rat, inhalation, 2 hours). Occupational exposure limit set by NIOSH stands at 50 mg/m 3 (5 ppm). It is considered to be Immediately dangerous to life and health at this concentration. Other than that, SbF 5 reacts violently with water along with many other compounds, often releasing dangerous hydrogen fluoride . It is a very strong oxidizer. [ 9 ] [ 10 ] | https://en.wikipedia.org/wiki/SbF5 |
Antimony triiodide is the chemical compound with the formula Sb I 3 . This ruby-red solid is the only characterized "binary" iodide of antimony , i.e. the sole compound isolated with the formula Sb x I y . It contains antimony in its +3 oxidation state. Like many iodides of the heavier main group elements , its structure depends on the phase. Gaseous SbI 3 is a molecular, pyramidal species as anticipated by VSEPR theory . In the solid state, however, the Sb center is surrounded by an octahedron of six iodide ligands, three of which are closer and three more distant. [ 5 ] For the related compound Bi I 3 , all six Bi—I distances are equal. [ 6 ]
It may be formed by the reaction of antimony with elemental iodine , or the reaction of antimony trioxide with hydroiodic acid .
Alternatively, it may be prepared by the interaction of antimony and iodine in boiling benzene or tetrachloroethane .
SbI 3 has been used as a dopant in the preparation of thermoelectric materials. [ 7 ] | https://en.wikipedia.org/wiki/SbI3 |
Antimony tetroxide is an inorganic compound with the formula Sb 2 O 4 . This material, which exists as the mineral cervantite, [ 3 ] is white but reversibly yellows upon heating. The material, with empirical formula SbO 2 , is called antimony tetroxide to signify the presence of two kinds of Sb centers. [ 4 ]
The material forms when Sb 2 O 3 is heated in air: [ 5 ]
At 800 °C, antimony(V) oxide loses oxygen to give the same material:
The material is mixed valence, containing both Sb(V) and Sb(III) centers. Two polymorphs are known, one orthorhombic (shown in the infobox) and one monoclinic. [ 1 ] Both forms feature octahedral Sb(V) centers arranged in sheets with distorted Sb(III) centers bound to four oxides. | https://en.wikipedia.org/wiki/SbO2 |
Antimony oxychloride , known since the 15th century, has been known by a plethora of alchemical names. Since the compound functions as both an emetic and a laxative , it was originally used as a purgative.
Its production was first described by Basil Valentine in Currus Triumphalis Antimonii. In 1659, Johann Rudolf Glauber gave a relatively exact chemical interpretation of the reaction.
Vittorio Algarotti introduced the substance into medicine, and derivatives of his name (algarot, algoroth) were associated with this compound for many years.
The exact composition was unknown for a very long time. The suggestion of SbOCl being a mixture of antimony trichloride and antimony oxide or pure SbOCl were raised. Today the hydrolysis of antimony trichloride is understood; first the SbOCl oxychloride is formed which later forms Sb 4 O 5 Cl 2 .
Neither SbOCl nor the latter compound occur naturally. However, onoratoite is a known Sb-O-Cl mineral, its composition being Sb 8 Cl 2 O 11 . [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ]
Dissolving antimony trichloride in water yields antimony oxychloride: | https://en.wikipedia.org/wiki/SbOCl |
Antimony phosphate , (also called antimony orthophosphate , or antimonous phosphate ) is a chemical compound of antimony and phosphate with formula SbPO 4 . Antimony is in the form Sb(III) with +3 oxidation state. Antimony atoms have a lone pair of electrons.
SbPO 4 occurs as a layered compound. Two-dimensional layers are weakly held together by electrostatic forces. SbPO 4 is one of the most compressible materials, and under pressure compresses more perpendicular to the layers. At standard conditions SbPO 4 crystallises in a monoclinic form [ 2 ] with space group P 2 1 / m . Antimony phosphate has been investigated for use in lithium ion and sodium ion batteries. [ 3 ] [ 4 ]
Antimony atoms are attached to four oxygen atoms. These atoms are arranged as a squarish pyramid with antimony at the apex. Antimony atoms form the top and bottom of the layers. Four oxygen atoms are arranged tetrahedrally around phosphorus. [ 2 ] Antimony to oxygen bond lengths are 1.98 2.04 2.18 and 2.93 Å. the O-Sb-O angles are 87.9 164.8 84.1 and 85.0°. [ 2 ] The structure of SbPO 4 differs from two forms of BiPO 4 , where bismuth associates with five or eight phosphate groups. [ 2 ]
In SbPO 4 the 31 P chemical shift is −18 ppm. The binding energy of the 2p electrons of phosphorus atom as determined by XPS is 133.9 eV. [ 5 ]
When the pressure exceeds 3 GPa, bonds form between the layers, but it retains the monoclinic system. But when the pressure is between 9 and 20 GPa, it transitions to a triclinic form with space group P 1 . [ 6 ] 10.1021/acs.inorgchem.9b02268
The infrared spectrum shows absorption bands at 1145, 1052, and 973, 664, 590, 500, 475, and 372 cm −1 . These are due to vibrations in P-O and Sb-O bonds and also bending in O-P-O bonds. [ 7 ]
Antimony(V) phosphate SbOPO 4 has monoclinic crystals. It has space group C 2 c . The unit cell has dimensions a = 6.791 Å, b = 8.033 Å, c = 7.046 Å, and β = 115.90°, with number of formula per unit cell of Z = 4. It is formed by heating Sb 2 O 5 ·xH 2 O and (NH 4 )H 2 PO 4 . At 1218 K it loses oxygen to become antimony(III) phosphate. [ 8 ]
SbPO 4 may be formed by soaking antimonous oxide in pure phosphoric acid and then filtering the solid, and heating to 600 °C. [ 7 ]
A related method involves heating a water solution of phosphoric acid with antimonous oxide at about 120 °C. [ 9 ]
Yet another procedure involves heating diammonium phosphate with antimonous oxide at 600 °C. [ 9 ]
SbPO 4 reacts with bases such as ammonia , hydrazine and ethylenediamine to form Sb 2 O 3 and hydrogenphosphate salts. [ 7 ]
However intercalation is also claimed with amines. [ 9 ] Intercalation of amines expands the a axis of the crystals, but leaves c, and c dimensions unaltered. The β angle is reduced. This is due to a bilayer of molecules inserting between each layer in the original crystal. [ 9 ]
There are also double salts where phosphate groups are joined to antimony. | https://en.wikipedia.org/wiki/SbPO4 |
Scandium(III) nitrate , Sc(NO 3 ) 3 , is an ionic compound. It is an oxidizer , as all nitrates are. The salt is applied in optical coatings, catalysts, electronic ceramics and the laser industry.
Scandium nitrate can be prepared by the reaction between scandium metal with dinitrogen tetroxide . [ 1 ]
The anhydrous form can also be obtained by the reaction between scandium chloride and dinitrogen pentoxide . [ 2 ] The tetrahydrate can be obtained from the reaction between scandium hydroxide and nitric acid . [ 3 ]
Scandium nitrate is a white solid which dissolves in water and ethanol . [ 4 ] It has multiple hydrated forms, including the dihydrate, trihydrate, and tetrahydrate. The tri- and tetrahydrate exist in the monoclinic crystal system . Upon heating in air to 50 °C, the tetrahydrate transforms into the dihydrate, which at 60 °C further converts to Sc 4 O 3 (NO 3 ) 3 ·6.5H 2 O. At 140–220 °C, Sc 4 O 5 (NO 3 ) 3 is formed. [ 2 ]
Scandium nitrate has been found to form clusters when in an aqueous solution which can affect its behavior and properties in various ways. Small Angle neutron scattering [ 5 ] has been used in experiments to show the clusters can contain as many as 10 scandium ions. This number depends on the concentration of the original scandium nitrate in the solution.
Scandium nitrate has been found to be a successful catalyst in chemical reactions such as Beckmann rearrangement of ketoximes to amides [ 6 ] and the isomerization of allylic alcohols to aldehydes. The catalytic success of scandium nitrate can be increased by modifying its structure in ways such as adding a co catalyst. Scandium nitrate is also the precursor for the synthesis of other scandium based compounds such as scandium oxide or scandium hydroxide. Scandium nitrate has also been investigated for its potential in luminescent materials due to its ability to strongly emit in the blue region of the spectrum. | https://en.wikipedia.org/wiki/Sc(NO3)3 |
Scandium trifluoromethanesulfonate , commonly called scandium triflate , is a chemical compound with formula Sc(SO 3 CF 3 ) 3 , a salt consisting of scandium cations Sc 3+ and triflate SO 3 CF − 3 anions .
Scandium triflate is used as a reagent in organic chemistry as a Lewis acid . [ 1 ] Compared to other Lewis acids, this reagent is stable towards water and can often be used in organic reactions as a true catalyst rather than one used in stoichiometric amounts. The compound is prepared by reaction of scandium oxide with trifluoromethanesulfonic acid .
An example of the scientific use of scandium triflate is the Mukaiyama aldol addition reaction between benzaldehyde and the silyl enol ether of cyclohexanone with an 81% yield . [ 2 ] | https://en.wikipedia.org/wiki/Sc(OSO2CF3)3 |
Scandium(III) oxide or scandia is a inorganic compound with formula Sc 2 O 3 . It is one of several oxides of rare earth elements with a high melting point . It is used in the preparation of other scandium compounds as well as in high-temperature systems (for its resistance to heat and thermal shock ), electronic ceramics , and glass composition (as a helper material).
Scandium(III) oxide adopts a cubic crystal structure ( point group : tetrahedral (T h ), space group : Ia 3 ) containing 6-coordinate metal centres. [ 2 ] Powder diffraction analysis shows Sc−O bond distances of 2.159–2.071 Å. [ 1 ]
Scandium oxide is an insulator with a band gap of 6.0 eV. [ 3 ]
Scandium oxide is the primary form of refined scandium produced by the mining industry. Scandium-rich ores, such as thortveitite (Sc,Y) 2 (Si 2 O 7 ) and kolbeckite ScPO 4 ·2H 2 O are rare, however trace amounts of scandium are present in many other minerals. Scandium oxide is therefore predominantly produced as a by-product from the extraction of other elements.
Scandium oxide is the primary form of refined scandium produced by the mining industry, making it the start point for all scandium chemistry.
Scandium oxide reacts with most acids upon heating, to produce the expected hydrated product. For example, heating in excess aqueous HCl produces hydrated ScCl 3 · n H 2 O . This can be rendered anhydrous by evaporation to dryness in the presence of NH 4 Cl , with the mixture then being purified by removal of NH 4 Cl by sublimation at 300-500 °C. [ 4 ] The presence of NH 4 Cl is required, as the hydrated ScCl 3 · n H 2 O would otherwise form a mixed oxychloride upon drying.
Likewise, it is converted into hydrated scandium(III) triflate (Sc(OTf) 3 · n H 2 O) by a reaction with triflic acid . [ 5 ]
Metallic scandium is produced industrially by the reduction of scandium oxide; this proceeds via conversion to scandium fluoride followed by a reduction with metallic calcium . This process is in some ways similar to the Kroll process for the production of metallic titanium .
Scandium oxide forms scandate salts with alkalis, unlike its higher homologues yttrium oxide and lanthanum oxide (but like lutetium oxide ), for example forming K 3 Sc(OH) 6 with KOH. In this, scandium oxide shows more similarity with aluminium oxide .
Natural scandia, although impure, occurs as mineral kangite . [ 6 ] | https://en.wikipedia.org/wiki/Sc2O3 |
Scandium(III) sulfide is a chemical compound of scandium and sulfur with the chemical formula Sc 2 S 3 . It is a yellow solid.
The crystal structure of Sc 2 S 3 is closely related to that of sodium chloride , in that it is based on a cubic close packed array of anions. Whereas NaCl has all the octahedral interstices in the anion lattice occupied by cations, Sc 2 S 3 has one third of them vacant. The vacancies are ordered, but in a very complicated pattern, leading to a large, orthorhombic unit cell belonging to the space group Fddd. [ 1 ]
Metal sulfides are usually prepared by heating mixtures of the two elements, but in the case of scandium, this method yields scandium monosulfide , ScS. Sc 2 S 3 can be prepared by heating scandium(III) oxide under flowing hydrogen sulfide in a graphite crucible to 1550 °C or above for 2–3 hours. The crude product is then purified by chemical vapor transport at 950 °C using iodine as the transport agent. [ 1 ]
Scandium(III) sulfide can be prepared by reacting scandium(III) chloride with dry hydrogen sulfide at elevated temperature: [ 2 ]
Above 1100 °C, Sc 2 S 3 loses sulfur, forming nonstoichiometric compounds such as Sc 1.37 S 2 . [ 1 ] | https://en.wikipedia.org/wiki/Sc2S3 |
Scandium(III) chloride is the inorganic compound with the formula ScCl 3 . It is a white, high-melting ionic compound , which is deliquescent and highly water-soluble. [ 2 ] This salt is mainly of interest in the research laboratory. Both the anhydrous form and hexahydrate (ScCl 3 •6H 2 O) are commercially available.
ScCl 3 crystallises in the layered BiI 3 motif, which features octahedral scandium centres. [ 3 ] Monomeric ScCl 3 is the predominant species in the vapour phase at 900 K, the dimer Sc 2 Cl 6 accounts for approximately 8%. [ 4 ] The electron diffraction spectrum indicates that the monomer is planar and the dimer has two bridging Cl atoms each Sc being 4 coordinate. [ 4 ]
ScCl 3 is a Lewis acid that absorbs water to give aquo complexes . According to X-ray crystallogrphy , one such hydrate is the salt trans -[ScCl 2 (H 2 O) 4 ]Cl·2H 2 O. [ 5 ] With the less basic ligand tetrahydrofuran , ScCl 3 yields the adduct ScCl 3 (THF) 3 as white crystals. This THF -soluble complex is used in the synthesis of organoscandium compounds . [ 6 ] ScCl 3 has been converted to its dodecyl sulfate salt, which has been investigated as a "Lewis acid-surfactant combined catalyst" (LASC) in aldol-like reactions . [ 7 ]
Scandium(III) chloride was used by Fischer et al. who first prepared metallic scandium by electrolysis of a eutectic melt of scandium(III) chloride and other salts at 700-800 °C. [ 8 ]
ScCl 3 reacts with scandium metal to give a number of chlorides where scandium has an oxidation state <+3, ScCl, Sc 7 Cl 10 , Sc 2 Cl 3 , Sc 5 Cl 8 and Sc 7 Cl 12 . [ 2 ] [ 9 ] For example, reduction of ScCl 3 with scandium metal in the presence of caesium chloride gives the compound CsScCl 3 which contain linear chains of composition Sc II Cl 3 − , containing Sc II Cl 6 octahedra sharing faces. [ 10 ]
Scandium(III) chloride is found in some halide lamps , optical fibers , electronic ceramics, and lasers . [ 11 ] | https://en.wikipedia.org/wiki/ScCl3 |
Scandium(III) fluoride , ScF 3 , is an ionic compound. This salt is slightly soluble in water but dissolves in the presence of excess fluoride to form the ScF 6 3− anion. [ 2 ]
ScF 3 can be produced by reacting scandium and fluorine . [ 3 ] It is also formed during the extraction from the ore thortveitite by the reaction of Sc 2 O 3 with ammonium bifluoride at high temperature: [ 4 ]
The resulting mixture contains a number of metal fluorides and this is reduced by reaction with calcium metal at high temperature. [ 4 ] Further purification steps are required to produce usable metallic scandium. [ 4 ]
Scandium trifluoride exhibits the unusual property of negative thermal expansion , meaning it shrinks when heated. This phenomenon is explained by the quartic oscillation of the fluoride ions. The energy stored in the bending strain of the fluoride ion is proportional to the fourth power of the displacement angle, unlike most other materials where it is proportional to the square of the displacement. A fluorine atom is bound to two scandium atoms, and as temperature increases the fluorine oscillates more perpendicularly to its bonds. This motion draws the scandium atoms together throughout the bulk material, which contracts. [ 5 ] ScF 3 exhibits this property from at least 10 K to 1100 K above which it shows the normal positive thermal expansion; furthermore, the material has cubic symmetry over this entire temperature range, and up to at least 1600 K at ambient pressure. The negative thermal expansion at very low temperatures is quite strong (coefficient of thermal expansion around -14 ppm/K between 60 and 110 K). [ 6 ]
At ambient pressures scandium trifluoride adopts the cubic crystal system, using the perovskite structure with one metal position vacant. [ 7 ] The unit cell dimension is 4.01 Å. [ 7 ] Under pressure scandium trifluoride also forms different crystal structures with rhombohedral, and above 3 GPa tetrahedral. [ 7 ]
Scandium fluoride (ScF₃) features high transparency across UV to IR wavelengths, low optical absorption, and a low refractive index (~1.5). [ 8 ] [ 9 ] It exhibits nonlinear optical properties for frequency conversion and can luminesce when doped with rare-earth ions. [ 10 ] | https://en.wikipedia.org/wiki/ScF3 |
Single-cell genome and epigenome by transposases sequencing (scGET-seq) is a DNA sequencing method for profiling open and closed chromatin . In contrast to single-cell assay for transposase-accessible chromatin with sequencing (scATAC-seq), which only targets active euchromatin , [ 1 ] scGET-seq is also capable of probing inactive heterochromatin . [ 2 ]
This is achieved through the use of TnH, which is created by linking the chromodomain (CD) of heterochromatin protein-1-alpha (HP-1 α {\displaystyle \alpha } ) to the Tn5 transposase . TnH is then able to target histone 3 lysine 9 trimethylation ( H3K9me3 ), a marker for heterochromatin. [ 3 ]
Akin to RNA velocity, which uses the ratio of spliced to unspliced RNA to infer the kinetics of changes in gene expression over the course of cellular development, [ 4 ] the ratio of TnH to Tn5 signals obtained from scGET-seq can be used to calculate chromatin velocity, which measures the dynamics of chromatin accessibility over the course of cellular developmental pathways. [ 2 ]
Transcriptional regulation is tightly linked to chromatin states. Chromatin that is open, or permissive to transcription, make up only 2-3% of the genome , but encompass 94.4% of transcription factor binding sites. [ 5 ] [ 6 ] Conversely, more tightly packed DNA , or heterochromatin , is responsible for genome organization and stability. [ 7 ] Chromatin density also changes over the course of cellular differentiation processes, [ 8 ] but there is a lack of high-throughput sequencing methods for directly assaying heterochromatin.
Many genomic-related diseases such as cancer are highly linked to changes in their epigenome . Cancers in particular are characterized by single-cell heterogeneity, which can drive metastasis and treatment resistance. [ 9 ] [ 10 ] The mechanisms that underlie these processes are still largely unknown, although the advent of single-cell technologies , including single-cell epigenomics , has contributed greatly to their elucidation. [ 11 ]
In 2015, ATAC-seq , which uses the Tn5 transposase to fragment and tag accessible chromatin, or euchromatin , for sequencing, became feasible at the single-cell resolution. [ 12 ] scGET-seq builds upon this technology by also providing information on heterochromatin , providing a more comprehensive look at chromatin structure and dynamics within each cell. [ 13 ]
Sample preparation for scGET-seq starts with obtaining a suspension of nuclei from cells using a method appropriate for the starting material. [ 14 ]
The next step is to produce the TnH transposase . Tn5 is a transposase that cuts and ligates adapters to genomic regions unbound by nucleosomes (open chromatin). [ 15 ] HP-1a is a member of the HP1 family and is able to recognize and specifically bind to H3K9me3 . [ 16 ] [ 17 ] Its chromodomain uses an induced-fit mechanism for recognizing this chromatin modification. [ 18 ] Linking the first 112 amino acids of HP-1a containing the chromodomain to Tn5 using a three poly-tyrosine-glycine-serine (TGS) linker leads to the creation of the TnH transposase , which is capable of targeting heterochromatin marked by H3K9me3 . [ 2 ]
Library preparation is done using a modified protocol for single-cell ATAC-seq , [ 19 ] where the nuclei suspension is sequentially incubated with the Tn5 transposase first, and then TnH. [ 2 ]
The goals of the data analysis are: [ 2 ]
Each of the matrices are filtered of shared regions and then normalized and log2 transformed. Linear dimension reduction is done using principal component analysis (PCA). Groups of cells are identified using a k-NN algorithm [ 21 ] and Leiden algorithm. [ 22 ] Finally, the four matrices are combined using matrix factorization [ 23 ] and UMAP reduction. [ 24 ]
There are two approaches to cell identity annotation: Annotation based on feature annotation of ATAC peaks, [ 25 ] and annotation based on integration with reference scRNA-seq data. [ 26 ]
By using the ratio of Tn5 to TnH signals, quantitative values describing how quickly and in what direction chromatin remodelling is taking place can be calculated (chromatin velocity). [ 2 ] By isolating regions that are most dynamic and identifying which transcription factors bind there, chromatin velocity can be used to infer the dynamic epigenetic processes happening within a given cell and the contributions of various transcription factors to those processes. [ 2 ]
Chromatin remodelling precedes changes in gene expression and enhances the understanding of trajectories and mechanisms of cellular changes. [ 27 ] [ 28 ] Thus, platforms and tools for integration of multimodal data are areas of active research [ 29 ] [ 30 ] [ 31 ] Incorporating temporal and directionality elements through integration of chromatin velocity with RNA velocity has been proposed to reveal even more information about differentiation pathways. [ 32 ] [ 33 ]
scGET-seq has some of the same limitations as scATAC-seq. Both processes require nuclei samples from viable cells, and high cellular viability. [ 13 ] Low cellular viability leads to high background DNA contamination that do not accurately represent authentic biological signals. Additionally, the sparsity and noisy nature of scATAC-seq and scGET-seq data makes analysis challenging, and there is no consensus yet on how to best manage this data [ 34 ]
Another limitation is that scGET-seq still needs the validation of SNVs results by bulk genome sequencing. Even though there is a high correlation of mutations between bulk exome sequencing and scGET-seq results, scGET-seq fails to capture all exome SNVs. [ 2 ] | https://en.wikipedia.org/wiki/ScGET-seq |
Scandium trihydride is an unstable molecular chemical compound with the chemical formula ScH 3 . It has been formed as one of a number of other molecular scandium hydride products at low temperature using laser ablation and identified by infrared spectroscopy. [ 1 ] Scandium trihydride has recently been the subject of Dirac – Hartree–Fock relativistic calculation studies , which investigate the stabilities, geometries, and relative energies of hydrides of the formula MH 3 , MH 2 , or MH.
Scandium trihydride is a quastrigonal planar molecule with three equivalent Sc-H bonds. (C 3v ) structure an equilibrium distance between Sc and hydrogen of 182.0 pm, the bond angle is 119.2 degrees. By weight percent, the composition of scandium trihydride is 6.30% hydrogen and 93.70% scandium. In scandium trihydride, the formal oxidation states of hydrogen and scandium are −1 and +3 respectively, because of the electronegativity of scandium is lower than that of hydrogen. The stability of metal hydrides with the formula MH 3 (M = Sc-Lu) increases as the atomic number of M increases. [ 1 ]
Early theoretical studies of ScH 3 revealed that the molecule is unstable, the bulk substance is likely to be a colourless gas with a low activation energy toward the conversion into trimeric clusters due to the electron deficient nature of the monomer, not unlike the group 13 hydrides. One major difference, is that the dimer is the most stable cluster for group 13 hydrides. This can be attributed to the distortion caused by the d -orbitals. It cannot be made by methods used to synthesise BH 3 or AlH 3 . | https://en.wikipedia.org/wiki/ScH3 |
Scandium triiodide , also known as scandium iodide, is an inorganic compound with the formula ScI 3 and is classified as a lanthanide iodide . This salt is a yellowish powder. [ 1 ] It is used in metal halide lamps together with similar compounds, such as caesium iodide, because of their ability to maximize emission of UV and to prolong bulb life. The maximized UV emission can be tuned to a range that can initiate photopolymerizations . [ 2 ]
Scandium triiodide adopts a structure similar to that of iron trichloride (FeCl 3 ), crystallizing into a rhombohedral lattice. Scandium has a coordination number of 6, while iodine has a coordination number of 3 and is trigonal pyramidal. [ 3 ]
The purest scandium triiodide is obtained through direct reaction of the elements: [ 1 ]
Alternatively, but less effectively, one can produce anhydrous scandium triiodide by dehydrating ScI 3 (H 2 O) 6 . | https://en.wikipedia.org/wiki/ScI3 |
Sca-1 stands for " Stem cells antigen -1" (official gene symbol: Ly6a). It consist of 18-kDa mouse glycosyl phosphatidylinositol -anchored cell surface protein (GPI-AP) of the LY6 gene family . [ 1 ] It is the common biological marker used to identify hematopoietic stem cell (HSC) along with other markers.
This cell biology article is a stub . You can help Wikipedia by expanding it .
This protein -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Sca-1 |
Scabbling —also called scappling —is the process of reducing stone or concrete. In masonry, it refers to shaping a stone to a rough square by use of an axe or hammer . [ 1 ] In Kent, rag-stone masons call this "knobbling". [ 1 ] It was similarly used to shape grindstones .
In modern construction, scabbling is a mechanical process of removing a thin layer of concrete from a structure, typically achieved by compressed air powered machines. A typical scabbling machine uses several heads, each with several carbide or steel tips that peck at the concrete. It operates by pounding a number of tipped rods down onto the concrete surface in rapid succession. It takes several passes with the machine to achieve the desired depth.
Scabbling is used to remove road markings, surface contamination (used in the nuclear industry), to add a decorative or textured pattern to concrete, or to prepare a concrete surface prior to the installation of grout . [ 2 ]
Scarifying machines with flails attached to a drum cage are sometimes referred to as rotary scabblers. These walk behind machines are also referred to as concrete planers.
This architectural element –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Scabbling |
The term S/MAR ( scaffold/matrix attachment region ), otherwise called SAR ( scaffold-attachment region ), or MAR ( matrix-associated region ), are sequences in the DNA of eukaryotic chromosomes where the nuclear matrix attaches. As architectural DNA components that organize the genome of eukaryotes into functional units within the cell nucleus , S/MARs mediate structural organization of the chromatin within the nucleus. These elements constitute anchor points of the DNA for the chromatin scaffold and serve to organize the chromatin into structural domains . Studies on individual genes led to the conclusion that the dynamic and complex organization of the chromatin mediated by S/MAR elements plays an important role in the regulation of gene expression .
It has been known for many years that a polymer meshwork, a so-called " nuclear matrix " or "nuclear-scaffold" is an essential component of eukaryotic nuclei. This nuclear skeleton acts as a dynamic support for many specialized events concerning the readout a spread of genetic information (see below).
S/MARs map to non-random locations in the genome. They occur at the flanks of transcribed regions, in 5´- introns , and also at gene breakpoint cluster regions (BCRs). Being association points for common nuclear structural proteins S/MARs are required for authentic and efficient chromosomal replication and transcription , for recombination and chromosome condensation. S/MARs do not have an obvious consensus sequence. Although prototype elements consist of AT-rich regions several hundred base pairs in length, the overall base composition is definitely not the primary determinant of their activity. Instead, their function requires a pattern of "AT-patches" that confer the propensity for local strand unpairing under torsional strain .
Bioinformatics approaches support the idea that, by these properties, S/MARs not only separate a given transcriptional unit (chromatin domain) from its neighbors, but also provide platforms for the assembly of factors enabling transcriptional events within a given domain. An increased propensity to separate the DNA strands (the so-called 'stress induced duplex destabilization' potential, SIDD ) can serve the formation of secondary structures such as cruciforms or slippage structures , which are recognizable features for a number of enzymes ( DNAses , topoisomerases , poly(ADP-ribosyl) polymerases and enzymes of the histone-acetylation and DNA-methylation apparatus). S/MARs have been classified as either being constitutive (acting as permanent domain boundaries in all cell types) or facultative (cell type- and activity-related) depending on their dynamic properties.
While the number of S/MARs in the human genome has been estimated to approach 64,000 (chromatin domains) plus an additional 10,000 (replication foci), in 2007 still only a minor fraction (559 for all eukaryotes) had met the standard criteria for an annotation in the S/MARt database. [ 1 ]
Current views of the nuclear matrix envision it as a dynamic entity, which changes its properties along the requirements of the cell nucleus—much the same as the cytoskeleton adapts its structure and function to external signals. In retrospect it is of note that the discovery of S/MARs has two major routes:
Subsequent work demonstrated both the constitutive (SAR-like) and the facultative (MAR-like) function of the elements depending on the context. Whereas constitutive S/MARs were found to be associated with a DNase I hypersensitive site in 'all' cell types (whether or not the enclosed domain was transcribed), DNAse I hypersensitivity of the facultative type depended on the transcriptional status. [ 4 ] The major difference between these two functional types of S/MARs is their size: the constitutive elements may extend over several kilobasepairs whereas facultative ones are at the lower size limit around 300 base pairs.
The figure shows our present understanding of these properties and it incorporates the following findings:
As an alternative to viral vectors, which can have unwanted effects in patients body, non-viral methods of gene therapy are being studied. One of such methods uses plasmids with special properties - the so-called episomes . Episomes have the ability to divide together with the rest of eukaryotic genome during mitosis. Compared with standard plasmids they are not epigenetically silenced within nucleus and are not enzymatically destroyed. Episomes acquire this ability through the presence of S/MAR sequence within their construct. [ 7 ]
In 2006, Tetko found a strong correlation of intragenic S/MARs with spatiotemporal expression of genes in Arabidopsis thaliana . [ 8 ] On a genome scale, pronounced tissue- and organ-specific and developmental expression patterns of S/MAR-containing genes have been detected. Notably, transcription factor genes contain a significant higher portion of S/MARs. The pronounced difference in expression characteristics of S/MAR-containing genes emphasizes their functional importance and the importance of structural chromosomal characteristics for gene regulation in plants as well as within other eukaryotes. | https://en.wikipedia.org/wiki/Scaffold/matrix_attachment_region |
In biology, scaffold proteins are crucial regulators of many key signalling pathways . Although scaffolds are not strictly defined in function, they are known to interact and/or bind with multiple members of a signalling pathway, tethering them into complexes . In such pathways, they regulate signal transduction and help localize pathway components (organized in complexes) to specific areas of the cell such as the plasma membrane , the cytoplasm , the nucleus , the Golgi , endosomes , and the mitochondria .
The first signaling scaffold protein discovered was the Ste5 protein from the yeast Saccharomyces cerevisiae . Three distinct domains of Ste5 were shown to associate with the protein kinases Ste11 , Ste7 , and Fus3 to form a multikinase complex. [ 2 ]
Scaffold proteins act in at least four ways: tethering signaling components, localizing these components to specific areas of the cell, regulating signal transduction by coordinating positive and negative feedback signals, and insulating correct signaling proteins from competing proteins. [ 1 ]
This particular function is considered a scaffold's most basic function. Scaffolds assemble signaling components of a cascade into complexes. This assembly may be able to enhance signaling specificity by preventing unnecessary interactions between signaling proteins, and enhance signaling efficiency by increasing the proximity and effective concentration of components in the scaffold complex. A common example of how scaffolds enhance specificity is a scaffold that binds a protein kinase and its substrate, thereby ensuring specific kinase phosphorylation. Additionally, some signaling proteins require multiple interactions for activation and scaffold tethering may be able to convert these interactions into one interaction that results in multiple modifications. [ 3 ] [ 4 ] Scaffolds may also be catalytic as interaction with signaling proteins may result in allosteric changes of these signaling components. [ 5 ] Such changes may be able to enhance or inhibit the activation of these signaling proteins. An example is the Ste5 scaffold in the mitogen-activated protein kinase ( MAPK ) pathway. Ste5 has been proposed to direct mating signaling through the Fus3 MAPK by catalytically unlocking this particular kinase for activation by its MAPKK Ste7. [ 6 ]
Scaffolds localize the signaling reaction to a specific area in the cell, a process that could be important for the local production of signaling intermediates. A particular example of this process is the scaffold, A-kinase anchor proteins (AKAPs), which target cyclic AMP-dependent protein kinase ( PKA ) to various sites in the cell. [ 7 ] This localization is able to locally regulate PKA and results in the local phosphorylation by PKA of its substrates.
Many hypotheses about how scaffolds coordinate positive and negative feedback come from engineered scaffolds and mathematical modeling. In three-kinase signaling cascades, scaffolds bind all three kinases, enhancing kinase specificity and restricting signal amplification by limiting kinase phosphorylation to only one downstream target. [ 3 ] [ 8 ] [ 9 ] These abilities may be related to stability of the interaction between the scaffold and the kinases, the basal phosphatase activity in the cell, scaffold location, and expression levels of the signaling components. [ 3 ] [ 8 ]
Signaling pathways are often inactivated by enzymes that reverse the activation state and/or induce the degradation of signaling components. Scaffolds have been proposed to protect activated signaling molecules from inactivation and/or degradation. Mathematical modeling has shown that kinases in a cascade without scaffolds have a higher probability of being dephosphorylated by phosphatases before they are even able to phosphorylate downstream targets. [ 8 ] Furthermore, scaffolds have been shown to insulate kinases from substrate- and ATP-competitive inhibitors. [ 10 ]
Huntingtin protein co-localizes with ATM repair protein at sites of DNA damage . [ 24 ] Huntingtin is a scaffolding protein in the ATM oxidative DNA damage response complex. [ 24 ] Huntington's disease patients with aberrant huntingtin protein are deficient in repair of oxidative DNA damage . Oxidative DNA damage appears to underlie Huntington's disease pathogenesis . [ 25 ] Huntington's disease is likely caused by the dysfunction of mutant huntingtin scaffold protein in DNA repair leading to increased oxidative DNA damage in metabolically active cells. [ 24 ]
SPIDR (scaffold protein involved in DNA repair ) regulates the stability or assembly of RAD51 and DMC1 on single-stranded DNA. [ 26 ] RAD51 and DMC1 are recombinases that act during mammalian meiosis to mediate strand exchange during the repair of DNA double-strand breaks by homologous recombination . [ 26 ]
On some other instances in biology (not necessarily about cell signaling), the term "Scaffold protein" is used in a broader sense, where a protein holds several things together for any purpose. | https://en.wikipedia.org/wiki/Scaffold_protein |
Scaffolding is a technique used in bioinformatics . It is defined as follows: [ 1 ]
Link together a non-contiguous series of genomic sequences into a scaffold, consisting of sequences separated by gaps of known length. The sequences that are linked are typically contiguous sequences corresponding to read overlaps.
When creating a draft genome, individual reads of DNA are second assembled into contigs , which, by the nature of their assembly, have gaps between them. The next step is to then bridge the gaps between these contigs to create a scaffold. [ 2 ] This can be done using either optical mapping or mate-pair sequencing. [ 3 ]
The sequencing of the Haemophilus influenzae genome marked the advent of scaffolding. That project generated a total of 140 contigs, which were oriented and linked using paired-end reads. The success of this strategy prompted The Institute for Genomic Research to develop the scaffolding program Grouper for their other sequencing projects. Until 2001, Grouper was the only stand-alone scaffolding software. [ 4 ] After the Human Genome Project and Celera proved that it was possible to create a large draft genome, several other similar programs were created. Bambus was created in 2003 and was a rewrite of the original grouper software, but afforded researchers the ability to adjust scaffolding parameters. [ 4 ] This software also allowed for optional use of other linking data, such as contig order in a reference genome.
Algorithms used by assembly software are very diverse, and can be classified as based on iterative marker ordering, or graph based. Graph based applications have the capacity to order and orient over 10,000 markers, compared to the maximum 3000 markers capable of iterative marker applications. [ 5 ] Algorithms can be further classified as greedy, non greedy, conservative, or non conservative. Bambus uses a greedy algorithm, defined as such because it joins together contigs with the most links first. The algorithm used by Bambus 2 removes repetitive contigs before orienting and ordering them into scaffolds. SSPACE also uses a greedy algorithm that begins building its first scaffold with the longest contig provided by the sequence data. SSPACE is the most commonly cited assembly tool in biology publications, likely due to the fact that it is rated as a significantly more intuitive program to install and run than other assemblers. [ 6 ]
In recent years, there has been an advent of new kinds of assemblers capable of integrating linkage data from multiple types of linkage maps. ALLMAPS is the first of such programs and is capable of combining data from genetic maps, created using SNPs or recombination data, with physical maps such as optical or synteny maps. [ 7 ]
Some software, like ABySS and SOAPdenovo, contain gap filling algorithms which, although they do not create any new scaffolds, serve to decrease the gap length between contigs of individual scaffolds. A standalone program, GapFiller, is capable of closing a larger amount of gaps, using less memory than gap filling algorithms contained within assembly programs. [ 8 ]
Utturkar et al. investigated the utility of several different assembly software packages in combination with hybrid sequence data. They concluded that the ALLPATHS-LG and SPAdes algorithms were superior to other assemblers in terms of the number of, maximum length of, and N50 length of contigs and scaffolds. [ 9 ]
Most high-throughput, next generation sequencing platforms produce shorter read lengths compared to Sanger sequencing . These new platforms are able to generate large quantities of data in short periods of time, but until methods were developed for de novo assembly of large genomes from short read sequences, Sanger sequencing remained the standard method of creating a reference genome. [ 10 ] Although Illumina platforms are now able to generate mate pair reads with average lengths of 150bp, they were originally only able to generate reads of 75bp or less, which caused many people in the science community to doubt a reliable reference genome could ever be constructed with short read technology. The increased difficulty of contig and scaffold assembly associated with the new technologies has created a demand for powerful new computer programs and algorithms capable of making sense of the data. [ 11 ]
One strategy that incorporates high-throughput next generation sequencing is hybrid sequencing, wherein several sequencing technologies are used at different levels of coverage, so that they can complement each other with their respective strengths. The release of the SMRT platform, from Pacific Biosciences, marked the beginning of single molecule sequencing and long read tech. It has been shown that 80-100X coverage with SMRT technology, which generates average read with lengths of 5456bp, is usually sufficient to create a finished de novo assembly for prokaryotic organisms. When the funds for that level of coverage are not available to a researcher, they might decide to use a hybrid approach.
Goldberg et al. evaluated the effectiveness of combining high throughput pyrosequencing with traditional Sanger sequencing. They were able to greatly increase N50 contig length and decrease gap length, and even to close one microbial genome with this approach. [ 12 ]
It has been shown that integration of linkage maps can aid de novo assemblies with long range, chromosome scale recombination data, without which, assemblies can be subject to macro ordering errors. Optical mapping is the process of immobilizing the DNA on a slide and digesting it with restriction enzymes. The fragment ends are then fluorescently tagged and stitched back together. For the last two decades, optical mapping has been prohibitively expensive, but recent advances in technology have reduced cost significantly. [ 5 ] [ 13 ] | https://en.wikipedia.org/wiki/Scaffolding_(bioinformatics) |
Scagliola (from the Italian scaglia , meaning "chips") is a type of fine plaster used in architecture and sculpture . The same term identifies the technique for producing columns, sculptures, and other architectural elements that resemble inlays in marble . [ 1 ] The scagliola technique came into fashion in 17th-century [ 2 ] Tuscany as an effective substitute for costly marble inlays, the pietra dura works created for the Medici family in Florence . The use of scagliola declined in the 20th century. [ 3 ]
Scagliola is a composite substance made from plaster of Paris , glue and natural pigments, imitating marble and other hard stones. The material may be veined with colors and applied to a core, or desired pattern may be carved into a previously prepared scagliola matrix. The pattern's indentations are then filled with the colored, plaster-like scagliola composite, and then polished with flax oil for brightness, and wax for protection. The combination of materials and technique provides a complex texture, and richness of color not available in natural veined marbles.
A comparable material is terrazzo . Marmorino is a synonym, but scagliola and terrazzo should not be confused with plaster of Paris , which is one ingredient.
Batches of pigmented plaster, modified with animal glue are applied to molds, armatures and pre-plastered wall planes in a manner that accurately mimics natural stone, breccia and marble. In one technique, veining is created by drawing strands of raw silk saturated in pigment through the plaster mix. Another technique involves trowelling on several layers of translucent renders and randomly cutting back to a previous layer to achieve colour differential similar to jasper .
When dry, the damp surface was pumiced smooth, then buffed with a linen cloth impregnated with Tripoli (a siliceous rottenstone ) and charcoal; finally it was buffed with oiled felt; beeswax was sometimes used for this purpose. Because the colours are integral to the plaster, the pattern is more resistant to scratching than with other techniques, such as painting on wood .
There are two scagliola techniques: in traditional 'Bavarian scagliola' coloured batches of plaster of Paris are worked to a stiff, dough-like consistency. The plaster is modified with the addition of animal glues such as isinglass or hide glue. 'Marezzo scagliola' is worked with the pigmented batches of plaster in a liquid state and relies mainly on the use of Keene's cement, a unique gypsum plaster product in which plaster of Paris was steeped in alum or borate, then burned in a kiln and ground to a fine powder; invented around 1840, it sets to an exceptionally hard state. [ 4 ]
It is typically used without the addition of animal glues. Marezzo scagliola is often called American scagliola because of its widespread use in the United States in the late nineteenth and early twentieth century. Slabs of Marezzo scagliola may be used as table tops. When set, scagliola is hard enough to be turned on a lathe to form vases, balusters and finials.
While there is evidence of scagliola decoration in ancient Roman architecture, scagliola decoration became popular in Italian Baroque buildings in the 17th century, and was imitated throughout Europe until the 19th century. Superb altar frontals using this technique are to be found at the Certosa di Padula in the Campania, Southern Italy.
An early use of scagliola in England is in a fireplace at Ham House , Surrey, which was brought from Italy along with the window sill in the reign of Charles II. This employs the use of a scagliola background which was then cut into to lay in the design.
In 1761, a scagliolista, Domenico Bartoli, from Livorno arrived in London and was employed by William Constable of Burton Constable in Yorkshire. Here he produced two chimneypieces in white marble inlaid with the scagliola embellishments directly into cut matrices in the marble. Apart from the protective edges of altars at Padula this seems to be the first use of this technique.
In 1766 he went into partnership with Johannes Richter, possibly from Dresden, who may have brought a young Pietro Bossi with him. The name Bossi is associated with a family of Northern Italian scagliolisti. Bartoli supplied table tops to Ireland and one chimneypiece at Belvedere House in Dublin could be attributed to Richter. Their styles are very different. There is little evidence that either of them came to Ireland.
Pietro Bossi arrived in Dublin in 1784 and probably died there in 1798. He produced a number of chimneypieces in Dublin of very good quality. Scagliola inlay proved to be desirable in Ireland and there appears to be a continuation long after it became unfashionable in England.
In 1911, Herbert Cescinsky, in English Furniture remarked that scagliola had been popular in Dublin fifty years before. This would explain one at 86, Stephen's Green, clearly an 18th. Century chimneypiece, which has been later embellished in the mid 19th. Century for Crofton Vanderleur, formerly at 4, Parnell Square. A later firm, Sharpe & Emery, Pearce St., Dublin produce a number of examples in the neo-classical Bossi style, sometimes using original chimneypieces.
The correspondence between British Resident in Florence Sir Horace Mann and Horace Walpole describes the process of obtaining a prized scagliola table top. Having received his first top from the Irishman Friar Ferdinando Henrico Hugford (1695–1771) around 1740 Walpole had asked his friend Mann to acquire some more...
(one of these tables is at The Vyne . That table has the arms of Walpole (with his post 1726 Garter Knight embellishments) impaling Shorter - for Prime Minister Sir Robert Walpole and his first wife Catherine Shorter, who died 20 August 1737. He married Maria Skerret in early 1738, thus The Vyne's table could seem have been ordered before c1736-37).
In a letter dated 26 November 1741 Mann writes to Walpole:
Your scagliola table was near finished when behold the stone on which the stuff is put, opened of itself so that all that was done, to his [Hugford's] great mortification is spoilt. He would have been off for beginning again on account of his eyes etc., but I have begged he will do it and he is about it
and on 15 July 1742:
Your scagliola table is almost finished (you remember the first he [Hugford] undertook broke when near done) and is very handsome, but even in this commission my success is not complete, for I cannot persuade the padre [Hugford] to make its companion
and on 30 October 1742:
Your scagliola table is finished, though I have not got it home. The nasty priest [Hugford] will have 25 zecchins [£12 10s] besides many thanks, for the preference given to me, for some simple English have been tampering with him and offered 30 to get it, though it is by no means such a fine performance. The priest wishes I would not take it, as he would make a present of it to the Pope. He leaves Florence for good
and on 11 July 1747:
You bid me get you two scagliola tables, but don't mention the size or any other particulars. The man who made yours is no longer in Florence. Here is a scholar of his [Don Pietro Belloni?], but vastly inferior to him, and so slow in working that he has been almost three years about a pair for a Mr Leson [Joseph Leeson], and requires still six months more. I will endeavour to get somebody to write to the first friar [Hugford] and to engage him to make two tables in his convent and send them to Florence, of which I hope to be able to give you an account by next post.
and on 10 October 1749:
I am glad your scagliola tables please. You must make the greater account of them, as it is impossible to get any more of the same man [Hugford], nor indeed of his disciple here [Belloni], who is a priest too, and has been four years about a pair I bespoke of him, which he tells me plainly he cannot finish in less than two more. They work for diversion and won't be hurried.
In modern times—Tusmore House, Oxfordshire:
The great triumph of the saloon, however, is the use of scagliola, including the richly coloured and figured Sienna shafts of the eight fluted Corinthian columns...and the urns, entablature and balustrade to the second-floor landing which gives access to four plaster-vaulted ante rooms serving the main bedrooms. All this scagliola was produced by Richard Feroze, England's leading contemporary scagliola-maker. [ 5 ]
Italian plasterworkers produced scagliola columns and pilasters for Robert Adam at Syon House (notably the columns in the Anteroom) and at Kedleston Hall (notably the pilasters in the Saloon). In 1816 the Coade Ornamental Stone Manufactory extended their practice to include scagliola; their scagliola was used by Benjamin Dean Wyatt at Apsley House , London. [ 6 ]
In the United States scagliola was popular in the 19th and 20th centuries. Important US buildings featuring scagliola include the Mississippi State Capitol in Jackson, Mississippi (1903), Allen County Courthouse in Fort Wayne, Indiana , Belcourt Castle in Newport, Rhode Island , in the old El Paso County Courthouse (Colorado) in Colorado Springs , in the Kansas State Capitol in Topeka, Kansas , in Shea's Performing Arts Center in Buffalo, New York , and in the Navarro County Courthouse in Corsicana, TX. St. Louis Union Station in St. Louis, Missouri, prominently features scagliola in its magnificent Grand Hall, the Rialto Square Theatre , Joliet, IL, Cathedral of St. Helena in Helena, MT, Congregation Shearith Israel in New York City, Milwaukee Public Library Central Library in Milwaukee, WI and the French Lick Resort Casino , French Lick, IN which recently underwent a major restoration.
Scagliola has historically been considered an Ersatz material and an inexpensive alternative to natural stone. However, it has eventually come to be recognised as an exceptional example of the plasterer's craft and is now prized for its historic value as well as being used in new construction because of its benefits as a plastic material suited to molding in ornate shapes.
Scagliola columns are not generally built of the solid material. Instead scagliola is trowelled onto a canvas which is wrapped around the column's core, and the canvas peeled away when semi-hardened. The scagliola is then surfaced in place. [ 7 ]
The verd antique columns and pilasters in the Anteroom at Syon House are made out of marble not scagliola as it is widely perceived (a beautiful and rare, predominantly green marble that was quarried in Larissa of Greece since antiquity). These columns are not solid. Round sections of marble were painstakingly cut as a veneer of an approximate thickness of 5–6 mm and then glued onto a column core that is hollow and was probably made out of plaster.
On closer inspection the viewer can see the joints of the various sections. The discerning eye will soon realise that they are looking at verd antique veneered marble and not verd antique scagliola. The 3.6 metre high verd antique scagliola columns that can be seen at Dropmore House , Buckinghamshire, are based on the colours and design of this historical work at Syon House. Both research and execution of these new columns were undertaken recently by the contemporary scagliolist Michael Koumbouzis. | https://en.wikipedia.org/wiki/Scagliola |
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Scalability is the property of a system to handle a growing amount of work. One definition for software systems specifies that this may be done by adding resources to the system. [ 1 ]
In an economic context, a scalable business model implies that a company can increase sales given increased resources. For example, a package delivery system is scalable because more packages can be delivered by adding more delivery vehicles. However, if all packages had to first pass through a single warehouse for sorting, the system would not be as scalable, because one warehouse can handle only a limited number of packages. [ 2 ]
In computing, scalability is a characteristic of computers, networks, algorithms , networking protocols , programs and applications. An example is a search engine , which must support increasing numbers of users, and the number of topics it indexes . [ 3 ] Webscale is a computer architectural approach that brings the capabilities of large-scale cloud computing companies into enterprise data centers. [ 4 ]
In distributed systems , there are several definitions according to the authors, some considering the concepts of scalability a sub-part of elasticity , others as being distinct. According to Marc Brooker: "a system is scalable in the range where marginal cost of additional workload is nearly constant." Serverless technologies fit this definition but you need to consider total cost of ownership not just the infra cost. [ 5 ]
In mathematics, scalability mostly refers to closure under scalar multiplication .
In industrial engineering and manufacturing, scalability refers to the capacity of a process, system, or organization to handle a growing workload, adapt to increasing demands, and maintain operational efficiency. A scalable system can effectively manage increased production volumes, new product lines, or expanding markets without compromising quality or performance. In this context, scalability is a vital consideration for businesses aiming to meet customer expectations, remain competitive, and achieve sustainable growth. Factors influencing scalability include the flexibility of the production process, the adaptability of the workforce, and the integration of advanced technologies. By implementing scalable solutions, companies can optimize resource utilization, reduce costs, and streamline their operations. Scalability in industrial engineering and manufacturing enables businesses to respond to fluctuating market conditions, capitalize on emerging opportunities, and thrive in an ever-evolving global landscape. [ citation needed ]
The Incident Command System (ICS) is used by emergency response agencies in the United States. ICS can scale resource coordination from a single-engine roadside brushfire to an interstate wildfire. The first resource on scene establishes command, with authority to order resources and delegate responsibility (managing five to seven officers, who will again delegate to up to seven, and on as the incident grows). As an incident expands, more senior officers assume command. [ 6 ]
Scalability can be measured over multiple dimensions, such as: [ 7 ]
Resources fall into two broad categories: horizontal and vertical. [ 8 ]
Scaling horizontally (out/in) means adding or removing nodes, such as adding a new computer to a distributed software application. An example might involve scaling out from one web server to three. High-performance computing applications, such as seismic analysis and biotechnology , scale workloads horizontally to support tasks that once would have required expensive supercomputers . Other workloads, such as large social networks, exceed the capacity of the largest supercomputer and can only be handled by scalable systems. Exploiting this scalability requires software for efficient resource management and maintenance. [ 7 ]
Scaling vertically (up/down) means adding resources to (or removing resources from) a single node, typically involving the addition of CPUs, memory or storage to a single computer. [ 7 ]
Benefits to scale-up include avoiding increased management complexity, more sophisticated programming to allocate tasks among resources and handling issues such as throughput, latency, and synchronization across nodes. Moreover some applications do not scale horizontally .
Network function virtualization defines these terms differently: scaling out/in is the ability to scale by adding/removing resource instances (e.g., virtual machine), whereas scaling up/down is the ability to scale by changing allocated resources (e.g., memory/CPU/storage capacity). [ 9 ]
Scalability for databases requires that the database system be able to perform additional work given greater hardware resources, such as additional servers, processors, memory and storage. Workloads have continued to grow and demands on databases have followed suit.
Algorithmic innovations include row-level locking and table and index partitioning. Architectural innovations include shared-nothing and shared-everything architectures for managing multi-server configurations.
In the context of scale-out data storage , scalability is defined as the maximum storage cluster size which guarantees full data consistency, meaning there is only ever one valid version of stored data in the whole cluster, independently from the number of redundant physical data copies. Clusters which provide "lazy" redundancy by updating copies in an asynchronous fashion are called 'eventually consistent' . This type of scale-out design is suitable when availability and responsiveness are rated higher than consistency, which is true for many web file-hosting services or web caches ( if you want the latest version, wait some seconds for it to propagate ). For all classical transaction-oriented applications, this design should be avoided. [ 10 ]
Many open-source and even commercial scale-out storage clusters, especially those built on top of standard PC hardware and networks, provide eventual consistency only, such as some NoSQL databases like CouchDB and others mentioned above. Write operations invalidate other copies, but often don't wait for their acknowledgements. Read operations typically don't check every redundant copy prior to answering, potentially missing the preceding write operation. The large amount of metadata signal traffic would require specialized hardware and short distances to be handled with acceptable performance (i.e., act like a non-clustered storage device or database). [ citation needed ]
Whenever strong data consistency is expected, look for these indicators: [ citation needed ]
Indicators for eventually consistent designs (not suitable for transactional applications!) are: [ citation needed ]
It is often advised to focus system design on hardware scalability rather than on capacity. It is typically cheaper to add a new node to a system in order to achieve improved performance than to partake in performance tuning to improve the capacity that each node can handle. But this approach can have diminishing returns (as discussed in performance engineering ). For example: suppose 70% of a program can be sped up if parallelized and run on multiple CPUs instead of one. If α {\displaystyle \alpha } is the fraction of a calculation that is sequential, and 1 − α {\displaystyle 1-\alpha } is the fraction that can be parallelized, the maximum speedup that can be achieved by using P processors is given according to Amdahl's Law :
Substituting the value for this example, using 4 processors gives
Doubling the computing power to 8 processors gives
Doubling the processing power has only sped up the process by roughly one-fifth. If the whole problem was parallelizable, the speed would also double. Therefore, throwing in more hardware is not necessarily the optimal approach.
In distributed systems , you can use Universal Scalability Law (USL) to model and to optimize scalability of your system. USL is coined by Neil J. Gunther and quantifies scalability based on parameters such as contention and coherency. Contention refers to delay due to waiting or queueing for shared resources. Coherence refers to delay for data to become consistent. For example, having a high contention indicates sequential processing that could be parallelized, while having a high coherency suggests excessive dependencies among processes, prompting you to minimize interactions. Also, with help of USL, you can, in advance, calculate the maximum effective capacity of your system: scaling up your system beyond that point is a waste. [ 11 ]
High performance computing has two common notions of scalability: | https://en.wikipedia.org/wiki/Scalability |
The Scalable Coherent Interface or Scalable Coherent Interconnect ( SCI ), is a high-speed interconnect standard for shared memory multiprocessing and message passing. The goal was to scale well, provide system-wide memory coherence and a simple interface; i.e. a standard to replace existing buses in multiprocessor systems with one with no inherent scalability and performance limitations.
The IEEE Std 1596-1992, IEEE Standard for Scalable Coherent Interface (SCI) was approved by the IEEE standards board on March 19, 1992. [ 1 ] It saw some use during the 1990s, but never became widely used and has been replaced by other systems from the early 2000s.
Soon after the Fastbus (IEEE 960) follow-on Futurebus (IEEE 896) project in 1987, some engineers predicted it would already be too slow for the high performance computing marketplace by the time it would be released in the early 1990s.
In response, a "Superbus" study group was formed in November 1987.
Another working group of the standards association of the Institute of Electrical and Electronics Engineers (IEEE) spun off to form a standard targeted at this market in July 1988. [ 2 ] It was essentially a subset of Futurebus features that could be easily implemented at high speed, along with minor additions to make it easier to connect to other systems, such as VMEbus . Most of the developers had their background from high-speed computer buses . Representatives from companies in the computer industry and research community included Amdahl, Apple Computer, BB&N , Hewlett-Packard , CERN, Dolphin Server Technology, Cray Research , Sequent, AT&T, Digital Equipment Corporation, McDonnell Douglas, National Semiconductor, Stanford Linear Accelerator Center, Tektronix, Texas Instruments, Unisys, University of Oslo, University of Wisconsin .
The original intent was a single standard for all buses in the computer. [ 3 ] The working group soon came up with the idea of using point-to-point communication in the form of insertion rings. This avoided the lumped capacitance, limited physical length/speed of light problems and stub reflections in addition to allowing parallel transactions. The use of insertion rings is credited to Manolis Katevenis who suggested it at one of the early meetings of the working group. The working group for developing the standard was led by David B. Gustavson (chair) and David V. James (Vice Chair). [ 4 ]
David V. James was a major contributor for writing the specifications including the executable C-code. [ citation needed ] Stein Gjessing’s group at the University of Oslo used formal methods to verify the coherence protocol and Dolphin Server Technology implemented a node controller chip including the cache coherence logic.
Different versions and derivatives of SCI were implemented by companies like Dolphin Interconnect Solutions , Convex, Data General AViiON (using cache controller and link controller chips from Dolphin), Sequent and Cray Research. Dolphin Interconnect Solutions implemented a PCI and PCI-Express connected derivative of SCI that provides non-coherent shared memory access. This implementation was used by Sun Microsystems for its high-end clusters, Thales Group and several others including volume applications for message passing within HPC clustering and medical imaging.
SCI was often used to implement non-uniform memory access architectures.
It was also used by Sequent Computer Systems as the processor memory bus in their NUMA-Q systems. Numascale developed a derivative to connect with coherent HyperTransport .
The standard defined two interface levels:
This structure allowed new developments in physical interface technology to be easily adapted without any redesign on the logical level.
Scalability for large systems is achieved through a distributed directory-based cache coherence model. (The other popular models for cache coherency are based on system-wide eavesdropping (snooping) of memory transactions – a scheme which is not very scalable.) In SCI each node contains a directory with a pointer to the next node in a linked list that shares a particular cache line.
SCI defines a 64-bit flat address space (16 exabytes) where 16 bits are used for identifying a node (65,536 nodes) and 48 bits for address within the node (256 terabytes). A node can contain many processors and/or memory. The SCI standard defines a packet switched network .
SCI can be used to build systems with different types of switching topologies from centralized to fully distributed switching:
The most common way to describe these multi-dimensional topologies is k-ary n-cubes (or tori). The SCI standard specification mentions several such topologies as examples.
The 2-D torus is a combination of rings in two dimensions. Switching between the two dimensions requires a small switching capability in the node. This can be expanded to three or more dimensions. The concept of folding rings can also be applied to the Torus topologies to avoid any long connection segments.
SCI sends information in packets. Each packet consists of an unbroken sequence of 16-bit symbols. The symbol is accompanied by a flag bit. A transition of the flag bit from 0 to 1 indicates the start of a packet. A transition from 1 to 0 occurs 1 (for echoes) or 4 symbols before the packet end. A packet contains a header with address command and status information, payload (from 0 through optional lengths of data) and a CRC check symbol. The first symbol in the packet header contains the destination node address. If the address is not within the domain handled by the receiving node, the packet is passed to the output through the bypass FIFO. In the other case, the packet is fed to a receive queue and may be transferred to a ring in another dimension. All packets are marked when they pass the scrubber (a node is established as scrubber when the ring is initialized). Packets without a valid destination address will be removed when passing the scrubber for the second time to avoid filling the ring with packets that would otherwise circulate indefinitely.
Cache coherence ensures data consistency in multiprocessor systems. The simplest form applied in earlier systems was based on clearing the cache contents between context switches and disabling the cache for data that were shared between two or more processors. These methods were feasible when the performance difference between the cache and memory were less than one order of magnitude. Modern processors with caches that are more than two orders of magnitude faster than main memory would not perform anywhere near optimal without more sophisticated methods for data consistency. Bus based systems use eavesdropping ( snooping ) methods since buses are inherently broadcast. Modern systems with point-to point links use broadcast methods with snoop filter options to improve performance. Since broadcast and eavesdropping are inherently non-scalable, these are not used in SCI.
Instead, SCI uses a distributed directory-based cache coherence protocol with a linked list of nodes containing processors that share a particular cache line. Each node holds a directory for the main memory of the node with a tag for each line of memory (same line length as the cache line). The memory tag holds a pointer to the head of the linked list and a state code for the line (three states – home, fresh, gone). Associated with each node is also a cache for holding remote data with a directory containing forward and backward pointers to nodes in the linked list sharing the cache line. The tag for the cache has seven states (invalid, only fresh, head fresh, only dirty, head dirty, mid valid, tail valid).
The distributed directory is scalable. The overhead for the directory based cache coherence is a constant percentage of the node’s memory and cache. This percentage is in the order of 4% for the memory and 7% for the cache.
SCI is a standard for connecting the different resources within a multiprocessor computer system, and it is not as widely known to the public as for example the Ethernet family for connecting different systems. Different system vendors implemented different variants of SCI for their internal system infrastructure. These different implementations interface to very intricate mechanisms in processors and memory systems and each vendor has to preserve some degrees of compatibility for both hardware and software.
Gustavson led a group called the Scalable Coherent Interface and Serial Express Users, Developers, and Manufacturers Association and maintained a web site for the technology starting in 1996. [ 3 ] A series of workshops were held through 1999.
After the first 1992 edition, [ 1 ] follow-on projects defined shared data formats in 1993, [ 5 ] a version using low-voltage differential signaling in 1996, [ 6 ] and a memory interface known as Ramlink later in 1996. [ 7 ] In January 1998, the SLDRAM corporation was formed to hold patents on an attempt to define a new memory interface that was related to another working group called SerialExpress or Local Area Memory Port. [ 8 ] [ 9 ] However, by early 1999 the new memory standard was abandoned. [ 10 ]
In 1999 a series of papers was published as a book on SCI. [ 11 ] An updated specification was published in July 2000 by the International Electrotechnical Commission (IEC) of the International Organization for Standardization (ISO) as ISO/IEC 13961. [ 12 ] | https://en.wikipedia.org/wiki/Scalable_Coherent_Interface |
Scalable video multicast is a new wireless multicast technology. In scalable video multicast, the video program subscribers can view the program in accordance with their link conditions. The scalable video multicast has been employed by many standards, such as MBMS , MBS, and DVB-H .
Traditional mobile networks were initially designed for unicast services, and may waste radio network resources by transmitting the same content in multiple copies to different users. With video multicasting, more efficient resource utilization would however be possible. Multicast service is therefore, a significant part of the current mobile services. Examples include the Multicast/Broadcast Service (MBS) over the WiMAX , the Multimedia Broadcast/Multicast Service (MBMS) within the LTE , the Digital Video Broadcasting services (e.g., DVB-T , DVB-H) defined in European Telecommunication Standard (ETS), and the MediaFLO presented by Qualcomm .
In mobile networks, all frames with multicast Receiver Address are transmitted at one of the rates included in a basic rate set. In order to guarantee coverage to all associated users, the transmission rate is typically fixed to one of the low basic rates. This limits the rate at which multicast data can be sent, for example, high-definition video is hard to send via multicast. To address this problem, scalable video multicasting ( SVM ) technology has been proposed. In SVM , video is encoded into one base layer (BL) and several enhancement layers (ELs) by using Scalable Video Coding ( SVC ) technique. The BL ensures the basic video quality of all users and each additional EL further enhances the quality of the video.
This computing article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Scalable_video_multicast |
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