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604,020 | https://en.wikipedia.org/wiki/Mosaic%20%28genetics%29 | Mosaicism or genetic mosaicism is a condition in which a multicellular organism possesses more than one genetic line as the result of genetic mutation. This means that various genetic lines resulted from a single fertilized egg. Mosaicism is one of several possible causes of chimerism, wherein a single organism is composed of cells with more than one distinct genotype.
Genetic mosaicism can result from many different mechanisms including chromosome nondisjunction, anaphase lag, and endoreplication. Anaphase lagging is the most common way by which mosaicism arises in the preimplantation embryo. Mosaicism can also result from a mutation in one cell during development, in which case the mutation will be passed on only to its daughter cells (and will be present only in certain adult cells). Somatic mosaicism is not generally inheritable as it does not generally affect germ cells.
History
In 1929, Alfred Sturtevant studied mosaicism in Drosophila, a genus of fruit fly. H. J. Muller in 1930 demonstrated that mosaicism in Drosophila is always associated with chromosomal rearrangements, and Schultz in 1936 showed that, in all cases studied, these rearrangements were associated with heterochromatic inert regions. Several hypotheses on the nature of such mosaicism were proposed. One hypothesis assumed that mosaicism appears as the result of a break and loss of chromosome segments. Curt Stern in 1935 assumed that the structural changes in the chromosomes took place as a result of somatic crossing, as a result of which mutations or small chromosomal rearrangements in somatic cells. Thus the inert region causes an increase in mutation frequency or small chromosomal rearrangements in active segments adjacent to inert regions.
In the 1930s, Stern demonstrated that genetic recombination, normal in meiosis, can also take place in mitosis. When it does, it results in somatic (body) mosaics. These organisms contain two or more genetically distinct types of tissue. The term somatic mosaicism was used by CW Cotterman in 1956 in his seminal paper on antigenic variation.
In 1944, M. L. Belgovskii proposed that mosaicism could not account for certain mosaic expressions caused by chromosomal rearrangements involving heterochromatic inert regions. The associated weakening of biochemical activity led to what he called a genetic chimera.
Types
Germline mosaicism
Germline or gonadal mosaicism is a particular form of mosaicism wherein some gametes—i.e., sperm or oocytes—carry a mutation, but the rest are normal. The cause is usually a mutation that occurred in an early stem cell that gave rise to all or part of the gametes.
Somatic mosaicism
Somatic mosaicism (also known as clonal mosaicism) occurs when the somatic cells of the body are of more than one genotype. In the more common mosaics, different genotypes arise from a single fertilized egg cell, due to mitotic errors at first or later cleavages.
Somatic mutation leading to mosaicism is prevalent in the beginning and end stages of human life. Somatic mosaics are common in embryogenesis due to retrotransposition of long interspersed nuclear element-1 (LINE-1 or L1) and Alu transposable elements. In early development, DNA from undifferentiated cell types may be more susceptible to mobile element invasion due to long, unmethylated regions in the genome. Further, the accumulation of DNA copy errors and damage over a lifetime lead to greater occurrences of mosaic tissues in aging humans. As longevity has increased dramatically over the last century, human genome may not have had time to adapt to cumulative effects of mutagenesis. Thus, cancer research has shown that somatic mutations are increasingly present throughout a lifetime and are responsible for most leukemia, lymphomas, and solid tumors.
Trisomies, monosomies, and related conditions
The most common form of mosaicism found through prenatal diagnosis involves trisomies. Although most forms of trisomy are due to problems in meiosis and affect all cells of the organism, some cases occur where the trisomy occurs in only a selection of the cells. This may be caused by a nondisjunction event in an early mitosis, resulting in a loss of a chromosome from some trisomic cells. Generally, this leads to a milder phenotype than in nonmosaic patients with the same disorder.
In rare cases, intersex conditions can be caused by mosaicism where some cells in the body have XX and others XY chromosomes (46, XX/XY). In the fruit fly Drosophila melanogaster, where a fly possessing two X chromosomes is a female and a fly possessing a single X chromosome is a sterile male, a loss of an X chromosome early in embryonic development can result in sexual mosaics, or gynandromorphs. Likewise, a loss of the Y chromosome can result in XY/X mosaic males.
An example of this is one of the milder forms of Klinefelter syndrome, called 46,XY/47,XXY mosaic wherein some of the patient's cells contain XY chromosomes, and some contain XXY chromosomes. The 46/47 annotation indicates that the XY cells have the normal number of 46 total chromosomes, and the XXY cells have a total of 47 chromosomes.
Also monosomies can present with some form of mosaicism. The only non-lethal full monosomy occurring in humans is the one causing Turner's syndrome. Around 30% of Turner's syndrome cases demonstrate mosaicism, while complete monosomy (45, X) occurs in about 50–60% of cases.
Mosaicism isn't necessarily deleterious, though. Revertant somatic mosaicism is a rare recombination event with a spontaneous correction of a mutant, pathogenic allele. In revertant mosaicism, the healthy tissue formed by mitotic recombination can outcompete the original, surrounding mutant cells in tissues such as blood and epithelia that regenerate often. In the skin disorder ichthyosis with confetti, normal skin spots appear early in life and increase in number and size over time.
Other endogenous factors can also lead to mosaicism, including mobile elements, DNA polymerase slippage, and unbalanced chromosome segregation. Exogenous factors include nicotine and UV radiation. Somatic mosaics have been created in Drosophila using X‑ray treatment and the use of irradiation to induce somatic mutation has been a useful technique in the study of genetics.
True mosaicism should not be mistaken for the phenomenon of X-inactivation, where all cells in an organism have the same genotype, but a different copy of the X chromosome is expressed in different cells. The latter is the case in normal (XX) female mammals, although it is not always visible from the phenotype (as it is in calico cats). However, all multicellular organisms are likely to be somatic mosaics to some extent.
Gonosomal mosaicism
Gonosomal mosaicism is a type of somatic mosaicism that occurs very early in the organisms development and thus is present within both germline and somatic cells. Somatic mosaicism is not generally inheritable as it does not usually affect germ cells. In the instance of gonosomal mosaicism, organisms have the potential to pass the genetic alteration, including to potential offspring because the altered allele is present in both somatic and germline cells.
Brain cell mosaicism
A frequent type of neuronal genomic mosaicism is copy number variation. Possible sources of such variation were suggested to be incorrect repairs of DNA damage and somatic recombination.
Mitotic recombination
One basic mechanism that can produce mosaic tissue is mitotic recombination or somatic crossover. It was first discovered by Curt Stern in Drosophila in 1936. The amount of tissue that is mosaic depends on where in the tree of cell division the exchange takes place. A phenotypic character called "twin spot" seen in Drosophila is a result of mitotic recombination. However, it also depends on the allelic status of the genes undergoing recombination. Twin spot occurs only if the heterozygous genes are linked in repulsion, i.e. the trans phase. The recombination needs to occur between the centromeres of the adjacent gene. This gives an appearance of yellow patches on the wild-type background in Drosophila. another example of mitotic recombination is the Bloom's syndrome, which happens due to the mutation in the blm gene. The resulting BLM protein is defective. The defect in RecQ, a helicase, facilitates the defective unwinding of DNA during replication, thus is associated with the occurrence of this disease.
Use in experimental biology
Genetic mosaics are a particularly powerful tool when used in the commonly studied fruit fly, where specially selected strains frequently lose an X or a Y chromosome in one of the first embryonic cell divisions. These mosaics can then be used to analyze such things as courtship behavior, and female sexual attraction.
More recently, the use of a transgene incorporated into the Drosophila genome has made the system far more flexible. The flip recombinase (or FLP) is a gene from the commonly studied yeast Saccharomyces cerevisiae that recognizes "flip recombinase target" (FRT) sites, which are short sequences of DNA, and induces recombination between them. FRT sites have been inserted transgenically near the centromere of each chromosome arm of D. melanogaster. The FLP gene can then be induced selectively, commonly using either the heat shock promoter or the GAL4/UAS system. The resulting clones can be identified either negatively or positively.
In negatively marked clones, the fly is transheterozygous for a gene encoding a visible marker (commonly the green fluorescent protein) and an allele of a gene to be studied (both on chromosomes bearing FRT sites). After induction of FLP expression, cells that undergo recombination will have progeny homozygous for either the marker or the allele being studied. Therefore, the cells that do not carry the marker (which are dark) can be identified as carrying a mutation.
Using negatively marked clones is sometimes inconvenient, especially when generating very small patches of cells, where seeing a dark spot on a bright background is more difficult than a bright spot on a dark background. Creating positively marked clones is possible using the so-called MARCM ("mosaic analysis with a repressible cell marker" system, developed by Liqun Luo, a professor at Stanford University, and his postdoctoral student Tzumin Lee, who now leads a group at Janelia Farm Research Campus. This system builds on the GAL4/UAS system, which is used to express GFP in specific cells. However, a globally expressed GAL80 gene is used to repress the action of GAL4, preventing the expression of GFP. Instead of using GFP to mark the wild-type chromosome as above, GAL80 serves this purpose, so that when it is removed by mitotic recombination, GAL4 is allowed to function, and GFP turns on. This results in the cells of interest being marked brightly in a dark background.
See also
45,X/46,XY mosaicism (X0/XY mosaicism)
References
Further reading
Genetics
Cell biology | Mosaic (genetics) | Biology | 2,430 |
50,934,497 | https://en.wikipedia.org/wiki/Ikee | Ikee was a worm that spread by Secure Shell connections between jailbroken iPhones. It was discovered in 2009 and changed wallpapers to a photo of Rick Astley. The code from Ikee was later used to make a more malicious iPhone malware, called Duh.
History
iPhone owners of Australia reported that smart phones had been infected by a worm that changed their iPhone wallpaper to Rick Astley, a 1980s pop singer. It affected smartphones if the owner did not change their default password after installation of SSH. Once the Ikee worm infected, it would find other iPhones on the mobile network which were vulnerable and infect them as well. The worm wouldn't affect users who hadn't jailbroken or installed SSH on their iPhone. The worm does nothing more than changing the infected user's lock screen wallpaper. The source code of the ikee worm says it was written by Ikex.
Two weeks after the release of Ikee, a malicious worm dubbed "Duh", built off the code of Ikee, was discovered. it acted as a Botnet, communicating with a command and control center. it also attempted to steal banking data from ING Direct.
See also
Brain Test
Dendroid (Malware)
Computer virus
File binder
Individual mobility
Malware
Trojan horse (computing)
Worm (computing)
Mobile operating system
References
IOS malware
Computer worms
Software distribution
Privilege escalation exploits
Online advertising
Privacy | Ikee | Technology | 292 |
25,666,636 | https://en.wikipedia.org/wiki/Quantum%20affine%20algebra | In mathematics, a quantum affine algebra (or affine quantum group) is a Hopf algebra that is a q-deformation of the universal enveloping algebra of an affine Lie algebra. They were introduced independently by and as a special case of their general construction of a quantum group from a Cartan matrix. One of their principal applications has been to the theory of solvable lattice models in quantum statistical mechanics, where the Yang–Baxter equation occurs with a spectral parameter. Combinatorial aspects of the representation theory of quantum affine algebras can be described simply using crystal bases, which correspond to the degenerate case when the deformation parameter q vanishes and the Hamiltonian of the associated lattice model can be explicitly diagonalized.
See also
Quantum enveloping algebra
Quantum KZ equations
Littelmann path model
Yangian
References
Quantum groups
Representation theory
Exactly solvable models
Mathematical quantization | Quantum affine algebra | Physics,Mathematics | 181 |
53,416,251 | https://en.wikipedia.org/wiki/Moenomycin%20family%20antibiotics | First described in 1965, the moenomycins are a family of phosphoglycolipid antibiotics, metabolites of the bacterial genus Streptomyces. Moenomycin A is the founding member of the antibiotic family with the majority discovered by the end of the late 1970s.
Structure
The moenomycins can be reduced to three key structural features
A central 3-phosphoglyceric acid backbone.
A 25-carbon isoprenoid chain connected by an ether linkage to the C2-position of 3-phosphoglyceric acid.
A substituted tetrasaccharide tethered via a phosphodiester linkage to 3-phosphoglyceric acid.
It is the combination of different isoprenoid chains and variously substituted tetrasaccharides that give rise to the diversity of the moenomycin family.
Based on degradation experiments, the defining mark of a moenomycin is the presence of the 25-carbon alcohol moenocinol or diumycinol upon hydrolysis of the lipid tail; these alcohols originate from the L1 or L2 lipid respectively in the figure. These two structures are the only observed lipid tails within the moenomycin family, with AC326-α being the only known for producing diumycinol.
With regards to the tetrasaccharide portion, stereochemistry and functionality can differ at R1 and R2 depending on if this saccharide unit is D-gluco versus D-galacto; there is an axial methyl group in the former case with the exception of moenomycin A12 and C1 where there is instead an axial hydroxyl. The oligosaccharide motif can be deoxygenated, hydroxylated, or glycosylated at the R3 position – notable examples of the pentasaccharide motif include moenomycin A and AC326-α. It is believed the additional glycan can enhance specificity and binding to the target protein, affording increased activity. With the exception of pholipomycin and AC326-α, the R4 saccharide unit is usually the deoxysaccharide. Lastly, in the majority of moenomycins the R5 position is linked to a 2-aminocyclopentane-1,3-dione – a convenient chromophore utilized for structural analysis. For the nosokomycin subfamily, this position forms a carboxamide or carboxylic acid.
Chemical synthesis
Due to the structural complexity of the moenomycins, total synthesis has proved difficult, with only one total synthesis reported so far. Some of the largest challenges include fashioning the glycosidic linkages with stereochemical control and site-specifically decorating the oligosaccharide with pendant functionality. Understanding that the majority of variation within the moenomycin family derives from differences within the oligosaccharide unit, Kahne and lab has designed an efficient and flexible total synthesis of moenomycin A that gives access to analogues as well as other members of the moenomycin family.
Biosynthesis
Extensive exploration into the biosynthesis of the moenomycin family has been conducted to better inform the genetic engineering and biosynthesis of novel moenomycin analogues. Early work on the biosynthesis of the moenomycins focused on the 25-carbon lipid tail derived from moenocinol; the tail was of particular interest given that it appears to break the isoprene rule at C8, containing a quaternary carbon. Feeding studies revealed the moenocinol lipid tail originates from a 15-carbon farnesyl precursor and a 10-carbon geranyl pyrophosphate.
More recently, the biosynthetic gene cluster for moenomycin A was first described in 2007 in Streptomyces ghanaensis. In 2009, the seventeen step biosynthetic pathway was completely characterized, revealing the order of assembly for the molecular scaffold.
Medicinal use
The moenomycins target bacterial peptidoglycan glycosyltransferases, inhibiting cell wall formation, leading to cell death. In general, the antibiotics are particularly potent against gram-positive bacteria with a minimum inhibitory concentration (MIC) between 1–100 (ng/ml). At higher concentrations the moenomycins are also effective against gram-negative bacteria with an MIC between 0.3–150 (μg/ml). In vivo studies using mice models suggest the antibiotics are powerful prophylactic and therapeutic agents, with subcutaneous injection being the most effective mode of delivery.
Moenomycins A and C are commercially used in the formulation of Bambermycins (Flavomycin), a veterinary antibiotic used solely in poultry, swine, and cattle feed.
Due to poor pharmacokinetic properties from the 25-carbon lipid chain, the moenomycins are not used in humans. The pharmacophore is well understood however, allowing the moenomycins to serve as the blueprint for future antibacterials.
Mode of action
General
The moenomycin family functions as an antibiotic by reversibly binding bacterial transglycosylases, essential enzymes that catalyze the extension of the glycan chain of the cell wall to form a stable peptidoglycan layer. The moenomycins mimic and thus compete with the natural substrate of the enzyme, inhibiting growth of the cell wall. Compromise of the wall results in leakage of cell contents, and ultimately cell death. The moenomycins are the only known active site inhibitors of these enzymes, which in lies their promise as human antibiotics given pathogenic bacteria have not yet widely evolved resistance.
Structure-activity relationships
The 25-carbon lipid tail confers to the moenomycins a detergent-like property that allows them to become incorporated into the cytoplasmic membrane of the target bacterial cell. This anchoring presents the oligosaccharide portion of the molecule to the transglycosylase where it can tightly and selectively bind the enzyme, inhibiting cell wall growth. This property however undermines their use in clinical settings. The amphiphilic nature of the moenomycins induce hemolytic activity, provide a long half-life in the blood stream, and creates a tendency to aggregate in aqueous solution. Comparison of moenomycins with an abridged isoprene chain of 10-carbons, show that the oligosaccharide can still tightly bind the enzyme active site, but in vivo the MIC significantly increases since the drug is unable to anchor itself to the cytoplasmic membrane and present its sugar moiety. Further studies are needed to determine the optimal length for favorable pharmacokinetic properties.
In contrast to the lipid portion, the oligosaccharide portion of the moenomycins is relatively well understood. When absent, the chromophore portion can decrease activity by 10-fold, suggesting it is not necessary for recognition but provides additional contacts with the target enzyme.
References
Antibiotics | Moenomycin family antibiotics | Biology | 1,528 |
77,371,207 | https://en.wikipedia.org/wiki/Mahi%20R.%20Singh | Mahi R. Singh (b. 1949) is a professor of physics at Western University researching nanoscience. He was awarded the Fulbright US-Canada Research Chair for 2021-2022.
Early life
Singh was born in 1949 in Hamirpur, India. He received his B.Sc. degree in T.D. College campus; and both M.Sc. (1970) and PhD (1976) degrees from Banaras Hindu University in condensed matter physics.
Academic career
Singh was awarded Humbold Fellow in Stuttgart University from 1979 to 1981. Between 1981 and 1985 he was a Research Associate and Lecturer at McGill University. From 1982 to 1983 he worked in High Magnetic Field Lab, Université Paul Sabatier as a visiting scientist. He also worked as Research Associate at University of North Carolina.
He joined the University of Western Ontario as associate professor in 1985. Currently he is professor in this university. He was also a visiting professor at Texas Center for Superconductivity from June till November in 1992. He also worked as a chief researcher at Superconductors Division of Hitachi, Tokyo between November 1992. During May and August in 2022, he became Fulbright US-Canada Research Chair in Vanderbilt University.
His visiting positions include Texas Center for Superconductivity (1992), University of Oxford (1993-1994), and Dubna and Ioffe Institute Saint Petersburg (2019).
Research
Research topics include:
Nanomaterials and Nanocomposites
Nanophotonics, Plasmonics, and Polaritonics
Graphene and Carbon Nanostructures
Metallic Nanostructures
Second Harmonic Generation
Photonic
Metamaterials
Biomaterials
Selected honors and awards
NIST Visiting Researcher, NIST USA, 2022
Fulbright US-Canada Research Chair, 2020-2021
External Expert for Gerhard Herzberg Canada Gold Medal for Science and Engineering, 2020-2021
Royal Society Visiting Scientist/Professor. 1993-1994
Chief Researcher, Hitachi, Tokyo in 1992–1993
Alexander von Humboldt Award, 1979
References
1949 births
Living people
Canadian physicists
Western University of Health Sciences
Banaras Hindu University alumni
Indian physicists
McGill University
University of North Carolina | Mahi R. Singh | Materials_science | 441 |
1,666,807 | https://en.wikipedia.org/wiki/Dights%20Falls | Dights Falls is a rapid and weir on the Yarra River in Melbourne, Victoria, just downstream of the junction with the Merri Creek. At this point the river narrows and is constricted between 800,000-year-old volcanic, basaltic lava flow and a much older steep, silurian, sedimentary spur. The north side also contains abundant graptolite fossils in sedimentary sandstone.
History
Prior to European settlement, the area was occupied by the Indigenous Wurundjeri tribe of the Kulin nation. The rock falls would have provided the Aboriginal people with a natural river crossing and place to trap migrating fish. It was also a meeting place for many clans where they would trade, settle disputes and exchange brides.
In January 1803, Charles Grimes, the deputy surveyor-general of New South Wales, was sent to Port Phillip to survey the area. Sailing on the schooner Cumberland, under the command of Acting Lieutenant Charles Robbins, the party entered Port Phillip on 20 January 1803. Grimes explored the Yarra by boat for several miles until he reached Dights Falls on 8 February. The event is commemorated by a historic marker on a ridge above the falls to the east: "first white men to discover the river Yarra reaching Yarra Falls on 8th February, 1803. Also to make the first crossing near here with the cattle by the first overlanders John Gardiner, Joseph Hawdon and Captain John Hepburn in December 1836".
In 1839, John Dight, a flour miller previously based in Campell Town, New South Wales, purchased a block of land next to the falls and in 1841, built a water-powered mill there. He built a small weir on the natural bar of basalt boulders to regulate water for the water wheel. The property changed hands several times over the decades until the mill was destroyed by fire in the early 1900s. The site remains one of Melbourne's oldest and most significant industrial sites.
The weir was upgraded in 1895 for the Melbourne Flour Milling Company, which had acquired the former Yarra Falls Roller Mill, which were the largest capacity water-power system in Victoria at the time of construction, and technically Victoria's first hydro-electric plant. It underwent reconstruction work in 1918, 1940, and 1967, following damaging floods.
At the instigation of William Guilfoyle, Director of the Botanic Gardens, the Dight's Falls Pumping Station was built and opened in 1891 under the direction of William Thwaites, located just below the weir on the opposite side of the Yarra to avoid competition with the privately-owned Mill. The Dight's Falls Pumping Scheme supplied much-needed fresh water to the Alexandra Gardens and Royal Botanic Gardens in the Domain Parklands, and from 1893 was used by the Melbourne Hydraulic Power Company for lifts in the City centre, enabling the early construction of Melbourne's distinctive tall buildings. With the eventual transition to mains water at the Gardens and electric lifts in City buildings, the Pumping Station was decommissioned and demolished in 1964.
In 1993, Melbourne Water recognised that the weir was a major obstacle to fish migration up the Yarra River, and installed a fish ladder. Subsequent research found it "is not functioning adequately and will require modifications to improve its efficiency and effectiveness". Melbourne Water have undertaken works from the end of 2010 to replace the weir and construct a new fishway to address this issue.
Current usage
The area can be readily accessed by walkers and cyclists from the Yarra River Trail.
The rapid is often used for canoeing, and has been used many times for the Victorian Canoe Slalom Championships.
Magpies occupy the area, and it is said that the Collingwood Football Club's use of the magpie mascot was inspired by the magpies at Dights Falls.
External links
About the falls.
Information from Parks Victoria.
References
Yarra River
Heritage sites in Melbourne
City of Yarra
City of Boroondara
Weirs | Dights Falls | Environmental_science | 792 |
5,951,578 | https://en.wikipedia.org/wiki/Community%20Coordinated%20Modeling%20Center | The Community Coordinated Modeling Center (CCMC) is a collaborative effort between multiple organizations in the United States to provide information and models relating to space weather research. The partnership includes resources from NASA, the Air Force Materiel Command, Air Force Research Laboratory (AFRL), Air Force Weather Agency (AFWA), NOAA, NSF, and ONR. Quoted from the site's main page, the CCMC is "a multi-agency partnership to enable, support and perform the research and development for next generation space science and space weather models." The CCMC is based at the NASA Goddard Space Flight Center in Greenbelt, Maryland.
References
External links
Community Coordinated Modeling Center Main Page
Space science | Community Coordinated Modeling Center | Astronomy | 144 |
55,149,313 | https://en.wikipedia.org/wiki/Sociedade%20Astron%C3%B4mica%20Brasileira | The Brazilian Astronomical Society (in Portuguese: Sociedade Astronômica Brasileira - SAB) is a professional astronomical society in Brazil, founded in 1974.
According to its statute, the society is obliged to fulfill certain duties:
Congregate Brazil's astronomers;
Uphold the freedom to scientific research and education;
Uphold astronomers' rights and interests;
Support national science's prestige;
Stimulate national astronomy's research and teaching;
Maintain contact with similar institutes and societies, both national and abroad;
Promote scientific meetings, courses and conferences;
Publish and update a scientific bulletin about the society's activities and general news about astronomy.
In addition to symposia, working meetings and contact services, it also holds annual meetings, which have taken place in:
Teaching commission
The Brazilian Astronomical Society Teaching Commission (Comissão de Ensino da Sociedade Astronômica Brasileira - CESAB) is assigned to analyze and correct educational books' potential inaccuracies on astronomy, in cooperation with the Ministry of Education (Ministério da Educação - MEC). The commission is also responsible for the organizing of the Brazilian Astronomy Olympiad and the periodic realization of astronomy courses destinated for teachers, in addition to the frequent production and publishing of articles and texts with the objective to promote and teach astronomy, such as the Brazilian Astronomy Magazine (Revista Brasileira de Astronomia - RBA), published quarterly.
See also
List of Brazilian scientific societies associated with the SBPC
References
External links
Official Site of the Brazilian Astronomical Society (in Portuguese)
Astronomy societies
Astronomy in Brazil | Sociedade Astronômica Brasileira | Astronomy | 322 |
15,958,803 | https://en.wikipedia.org/wiki/Splitting%20principle | In mathematics, the splitting principle is a technique used to reduce questions about vector bundles to the case of line bundles.
In the theory of vector bundles, one often wishes to simplify computations, say of Chern classes. Often computations are well understood for line bundles and for direct sums of line bundles. In this case the splitting principle can be quite useful.
The theorem above holds for complex vector bundles and integer coefficients or for real vector bundles with coefficients. In the complex case, the line bundles or their first characteristic classes are called Chern roots.
The fact that is injective means that any equation which holds in (say between various Chern classes) also holds in .
The point is that these equations are easier to understand for direct sums of line bundles than for arbitrary vector bundles, so equations should be understood in and then pushed down to .
Since vector bundles on are used to define the K-theory group , it is important to note that is also injective for the map in the above theorem.
The splitting principle admits many variations. The following, in particular, concerns real vector bundles and their complexifications:
Symmetric polynomial
Under the splitting principle, characteristic classes for complex vector bundles correspond to symmetric polynomials in the first Chern classes of complex line bundles; these are the Chern classes.
See also
K-theory
Grothendieck splitting principle for holomorphic vector bundles on the complex projective line
References
section 3.1
Raoul Bott and Loring Tu. Differential Forms in Algebraic Topology, section 21.
Characteristic classes
Vector bundles
Mathematical principles | Splitting principle | Mathematics | 316 |
23,227 | https://en.wikipedia.org/wiki/Pisces%20%28constellation%29 | Pisces is a constellation of the zodiac. Its vast bulk – and main asterism viewed in most European cultures per Greco-Roman antiquity as a distant pair of fishes connected by one cord each that join at an apex – are in the Northern celestial hemisphere. Its old astronomical symbol is (♓︎). Its name is Latin for "fishes". It is between Aquarius, of similar size, to the southwest and Aries, which is smaller, to the east. The ecliptic and the celestial equator intersect within this constellation and in Virgo. The Sun passes directly overhead of the equator, on average, at approximately this point in the sky, at the March equinox.
The right ascension/declination 00 is located within the boundaries of Pisces.
Features
The March equinox is currently located in Pisces, due south of Psc, and, due to precession, slowly drifting due west, just below the western fish towards Aquarius.
Stars
Although Pisces is a large constellation, there are only two stars brighter than magnitude 4 in Pisces. It is also the second dimmest of the zodiac constellations.
Alrescha ("the cord"), otherwise Alpha Piscium (α Psc), 309.8 lightyears, class A2, magnitude 3.62, variable binary star
Fumalsamakah ("mouth of the fish"), otherwise Beta Piscium (β Psc), 492 lightyears, class B6Ve, magnitude 4.48
Delta Piscium (δ Psc), 305 lightyears, class K5III, magnitude 4.44. Like other stars near the ecliptic, Delta Piscium is subject to lunar occultations.
Epsilon Piscium (ε Psc), 190 lightyears, class K0III, magnitude 4.27. Has a candidate exoplanet.
Revati ("rich"), otherwise Zeta Piscium (ζ Psc), 148 lightyears, class A7IV, magnitude 5.21. Quintuple star system.
Alpherg ("emptying"), otherwise Eta Piscium (η Psc), 349 lightyears, class G7 IIIa, magnitude 3.62. It is a Gamma Cassiopeiae variable with a weak magnetic field.
Torcular ("thread"), otherwise Omicron Piscium (ο Psc), 258 lightyears, class K0III, magnitude 4.2. It is an evolved red giant star on the horizontal branch.
Omega Piscium (ω Psc), 106 lightyears, class F4IV, magnitude 4.03. It is an F-type star that is either a subgiant or on the main sequence.
Gamma Piscium (γ Psc), 138 lightyears, magnitude 3.70. The star hosts an exoplanet which was discovered in 2021. It has a spectral type of G8 III.
Van Maanen's Star is the closest-known solitary white dwarf to us, with a dim apparent magnitude. It is located about 2° to the south of the star Delta Piscium, with a relatively high proper motion of 2.978″ annually along a position angle of 155.538°. It is closer to the Sun than any other solitary white dwarf. It is too faint to be seen with the naked eye. Like other white dwarfs, it is a very dense star: its mass has been estimated to be about 67% of the Sun's, yet it has only 1% of the Sun's radius. The outer atmosphere has a temperature of approximately 6,110 K, which is relatively cool for a white dwarf. As all white dwarfs steadily radiate away their heat over time, this temperature can be used to estimate its age, thought to be around 3 billion years. It was originally thought to be an F-type star before the properties of white dwarfs were known.
Due to the dimness of these stars, the constellation is essentially invisible in or near any major city due to light pollution.
Deep-sky objects
M74 is a loosely wound (type Sc) spiral galaxy in Pisces, found at a distance of 30 million light years (redshift 0.0022). It has many clusters of young stars and the associated nebulae, showing extensive regions of star formation. It was discovered by Pierre Méchain, a French astronomer, in 1780. A type II-P supernova was discovered in the outer regions of M74 by Robert Evans in June 2003; the star that underwent the supernova was later identified as a red supergiant with a mass of 8 solar masses. It is the brightest member of the M74 Group.
NGC 488 is an isolated face-on prototypical spiral galaxy. Two supernovae have been observed in the galaxy.
NGC 520 is a pair of colliding galaxies located 105 million light-years away.
CL 0024+1654 is a massive galaxy cluster that lenses the galaxy behind it, creating arc-shaped images of the background galaxy. The cluster is primarily made up of yellow elliptical and spiral galaxies, at a distance of 3.6 billion light-years from Earth (redshift 0.4), half as far away as the background galaxy, which is at a distance of 5.7 billion light-years (redshift 1.67).
History and mythology
Pisces originates from some composition of the Babylonian constellations Šinunutu4 "the great swallow" in current western Pisces, and Anunitum the "Lady of the Heaven", at the place of the northern fish. In the first-millennium BC texts known as the Astronomical Diaries, part of the constellation was also called DU.NU.NU (Rikis-nu.mi, "the fish cord or ribbon").
Greco-Roman period
Pisces is associated with the Greek legend that Aphrodite and her son Eros either shape-shifted into forms of fishes to escape, or were rescued by two fishes.
In the Greek version according to Hyginus, Aphrodite and Eros while visiting Syria fled from the monster Typhon by leaping into the Euphrates River and transforming into fishes (Poeticon astronomicon 2.30, citing Diognetus Erythraeus). The Roman variant of the story has Venus and Cupid (counterparts for Aphrodite and Eros) carried away from this danger on the backs of two fishes (Ovid Fasti 2.457ff).
There is also a different origin tale that Hyginus preserved in another work. According to this, an egg rolled into the Euphrates, and some fishes nudged this to shore, after which the doves sat on the egg until Aphrodite (thereafter called the Syrian Goddess) hatched out of it. The fishes were then rewarded by being placed in the skies as a constellation (Fabulae 197). This story is also recorded by the Third Vatican Mythographer.
Modern period
In 1690, the astronomer Johannes Hevelius in his Firmamentum Sobiescianum regarded the constellation Pisces as being composed of four subdivisions:
Piscis Boreus (the North Fish): σ – 68 – 65 – 67 – ψ1 – ψ2 – ψ3 – χ – φ – υ – 91 – τ – 82 – 78 Psc.
Linum Boreum (the North Cord): χ – ρ,94 – VX(97) – η – π – ο – α Psc.
Linum Austrinum (the South Cord): α – ξ – ν – μ – ζ – ε – δ – 41 – 35 – ω Psc.
Piscis Austrinus (the South Fish): ω – ι – θ – 7 – β – 5 – κ,9 – λ – TX(19) Psc.
"Piscis Austrinus" more often refers to a separate constellation in its own right.
In 1754, the botanist and author John Hill proposed to sever a southern zone of Pisces as Testudo (the Turtle). 24 – 27 – YY(30) – 33 – 29 Psc., It would host a natural but quite faint asterism in which the star 20 Psc is the head of the turtle. While Admiral Smyth mentioned the proposal, it was largely neglected by other astronomers, and it is now obsolete.
Western folklore
The Fishes are in the German lore of Antenteh, who owned just a tub and a crude cabin when he met two magical fish. They offered him a wish, which he refused. However, his wife begged him to return to the fish and ask for a beautifully furnished home. This wish was granted, but her desires were not satisfied. She then asked to be a queen and have a palace, but when she asked to become a goddess, the fish became angry and took the palace and home, leaving the couple with the tub and cabin once again. The tub is sometimes recognized as the Great Square of Pegasus.
In non-Western astronomy
The stars of Pisces were incorporated into several constellations in Chinese astronomy. Wai-ping ("Outer Enclosure") was a fence that kept a pig farmer from falling into the marshes and kept the pigs where they belonged. It was represented by Alpha, Delta, Epsilon, Zeta, Mu, Nu, and Xi Piscium. The marshes were represented by the four stars designated Phi Ceti. The northern fish of Pisces was a part of the House of the Sandal, Koui-siou.
See also
List of star names in Pisces
Pisces (Chinese astronomy)
References
Sources
Richard Hinckley Allen, Star Names, Their Lore and Legend, New York, Dover: various dates.
Thomas Wm. Hamilton, Useful Star Names, Strategic Books, 2008.
External links
The Deep Photographic Guide to the Constellations: Pisces
Ian Ridpath's Star Tales – Pisces
Warburg Institute Iconographic Database (medieval and early modern images of Pisces)
Constellations
Equatorial constellations
Constellations listed by Ptolemy | Pisces (constellation) | Astronomy | 2,104 |
41,633,679 | https://en.wikipedia.org/wiki/DSSAT | The Decision Support System for Agrotechnology Transfer (DSSAT) is a set of computer programs for simulating agricultural crop growth. It has been used in over 100 countries by agronomists for evaluating farming methods. One application has been assessing the possible impacts on agriculture of climate change and testing adaptation methods.
DSSAT is built with a modular approach, with different options available to represent such processes as evapotranspiration and soil organic matter accumulation, which facilitates testing different representations of processes important in crop growth. The functionality of DSSAT has also been extended through interfaces with other software such as GIS. DSSAT typically requires input parameters related to soil condition, weather, any management practices such as fertilizer use and irrigation, and characteristics of the crop variety being grown. Many common crops have their characteristics already implemented as DSSAT modules.
DSSAT grew out of the International Benchmark Sites Network for Agrotechnological Transfer (IBSNAT) in the 1980s, with the first official release in 1989. Version 4, released in 2003, introduced a more modular structure and added tools for agricultural economic analysis and risk assessment. Development has continued in affiliation with the International Consortium for Agricultural Systems Applications (ICASA).
Notes
External links
DSSAT website
Agronomy
Environmental science software | DSSAT | Environmental_science | 261 |
665,578 | https://en.wikipedia.org/wiki/Somnolence | Somnolence (alternatively sleepiness or drowsiness) is a state of strong desire for sleep, or sleeping for unusually long periods (compare hypersomnia). It has distinct meanings and causes. It can refer to the usual state preceding falling asleep, the condition of being in a drowsy state due to circadian rhythm disorders, or a symptom of other health problems. It can be accompanied by lethargy, weakness and lack of mental agility.
Somnolence is often viewed as a symptom rather than a disorder by itself. However, the concept of somnolence recurring at certain times for certain reasons constitutes various disorders, such as excessive daytime sleepiness, shift work sleep disorder, and others; and there are medical codes for somnolence as viewed as a disorder.
Sleepiness can be dangerous when performing tasks that require constant concentration, such as driving a vehicle. When a person is sufficiently fatigued, microsleeps may be experienced. In individuals deprived of sleep, somnolence may spontaneously dissipate for short periods of time; this phenomenon is the second wind, and results from the normal cycling of the circadian rhythm interfering with the processes the body carries out to prepare itself to rest.
The word "somnolence" is derived from the Latin "somnus" meaning "sleep".
Causes
Circadian rhythm disorders
Circadian rhythm ("biological clock") disorders are a common cause of drowsiness as are a number of other conditions such as sleep apnea, insomnia and narcolepsy. The body clock disorders are classified as extrinsic (externally caused) or intrinsic. The former type is, for example, shift work sleep disorder, which affects people who work nights or rotating shifts. The intrinsic types include:
Advanced sleep phase disorder (ASPD) – A condition in which patients feel very sleepy and go to bed early in the evening and wake up very early in the morning
Delayed sleep phase disorder (DSPD) – Faulty timing of sleep, peak period of alertness, the core body temperature rhythm, hormonal and other daily cycles such that they occur a number of hours late compared to the norm, often misdiagnosed as insomnia
Non-24-hour sleep–wake disorder – A faulty body clock and sleep-wake cycle that usually is longer than (rarely shorter than) the normal 24-hour period causing complaints of insomnia and excessive sleepiness
Irregular sleep–wake rhythm – Numerous naps throughout the 24-hour period, no main nighttime sleep episode and irregularity from day to day
Physical illness
Sleepiness can also be a response to infection. Such somnolence is one of several sickness behaviors or reactions to infection that some theorize evolved to promote recovery by conserving energy while the body fights the infection using fever and other means. Other causes include:
Anxiety
Brain tumor
Chronic pains
Concussion – a mild traumatic brain injury
Diabetes
Fibromyalgia
Head injury
Hypercalcemia – too much calcium in the blood
Hypermagnesemia
Hyponatremia – low blood sodium
Hypothyroidism – the body doesn't produce enough hormones that control how cells use energy
Meningitis
Mood disorders – depression
Multiple sclerosis
Narcolepsy – disorder of the nervous system
Skull fractures
Sleeping sickness – caused by a specific parasite
Stress
Medicine
Analgesics – mostly prescribed or illicit opiates such as OxyContin or heroin
Anticonvulsants / antiepileptics – such as phenytoin (Dilantin), carbamazepine (Tegretol), Pregabalin (Lyrica) and Gabapentin (Neurontin)
Antidepressants – for instance, sedating tricyclic antidepressants amitriptyline and mirtazapine. Somnolence is less common with SSRIs and SNRIs as well as MAOIs.
Antihistamines – for instance, diphenhydramine (Benadryl, Nytol), doxylamine (Unisom-2), hydroxyzine (Atarax) and promethazine (Phenergan)
Antipsychotics – for example, Lurasidone (Latuda), thioridazine, quetiapine (Seroquel), olanzapine (Zyprexa), risperidone and ziprasidone (Geodon) but not haloperidol
Dopamine agonists used in the treatment of Parkinson's disease – e.g. pergolide, ropinirole and pramipexole.
HIV medications – such as efavirenz
Hypertension medications – such as amlodipine
Hypnotics, or soporific drugs, commonly known as sleeping pills.
Tranquilizers – such as zopiclone (Zimovane), or the benzodiazepines such as diazepam (Valium) or nitrazepam (Mogadon) and the barbiturates, such as amobarbital (Amytal) or secobarbital (Seconal)
Other agents impacting the central nervous system in sufficient or toxic doses
Assessment
Quantifying sleepiness requires a careful assessment. The diagnosis depends on two factors, namely chronicity and reversibility. Chronicity signifies that the patient, unlike healthy people, experiences persistent sleepiness which does not pass. Reversibility stands for the fact that, even if the individual goes to sleep, the sleepiness may not be completely gone after waking up. The problem with the assessment is that patients may only report the consequences of sleepiness: loss of energy, fatigue, weariness, difficulty remembering or concentrating, etc. It is crucial to aim for objective measures to quantify the sleepiness. A good measurement tool is the multiple sleep latency test (MSLT). It assesses the sleep onset latency during the course of one day—often from 8:00 to 16:00. An average sleep onset latency of less than 5 minutes is an indication of pathological sleepiness.
Severity
A number of diagnostic tests, including the Epworth Sleepiness Scale, are available to help ascertain the seriousness and likely causes of abnormal somnolence.
See also
Chronic fatigue syndrome
Decision fatigue
Fibromyalgia
Insomnia
Hypersomnia
Dyssomnia
Fatigue
Narcolepsy
Postprandial somnolence
Restless legs syndrome
Periodic limb movement disorder
Hypnopompic
Hypnagogia
Sleep apnea
References
External links
Symptoms and signs of mental disorders
Sleep
Mental processes
fr:Sommeil#Somnolence | Somnolence | Biology | 1,374 |
25,208,147 | https://en.wikipedia.org/wiki/Solar%20eclipse%20of%20August%2012%2C%202045 | A total solar eclipse will occur at the Moon's descending node of orbit on Saturday, August 12, 2045, with a magnitude of 1.0774. A solar eclipse occurs when the Moon passes between Earth and the Sun, thereby totally or partly obscuring the image of the Sun for a viewer on Earth. A total solar eclipse occurs when the Moon's apparent diameter is larger than the Sun's, blocking all direct sunlight, turning day into darkness. Totality occurs in a narrow path across Earth's surface, with the partial solar eclipse visible over a surrounding region thousands of kilometres wide. Occurring about 7 minutes after perigee (on August 12, 2045, at 17:35 UTC), the Moon's apparent diameter will be near its maximum.
It will be the fourth longest eclipse of the 21st century with a magnitude of 1.0774. It will be visible throughout much of the continental United States, with a path of totality running through northern California, Nevada, Utah, Colorado, Kansas, Oklahoma, Texas, Arkansas, northeastern Louisiana, Mississippi, Alabama, Georgia and Florida. The total eclipse will be greatest over the Bahamas, before continuing over the Turks and Caicos Islands, the Dominican Republic, Haiti, northeastern Venezuela, Trinidad and Tobago, Guyana, Suriname, French Guiana, and northeastern Brazil. A partial solar eclipse will also be visible for parts of the Russian Far East, Hawaii, North America, Central America, the Caribbean, northern and central South America, and West Africa.
The path of totality of this eclipse will be seen over many major cities, including Reno, Salt Lake City, Colorado Springs, Oklahoma City, Tulsa, Jackson, Montgomery, Tallahassee, Tampa, Orlando, Fort Lauderdale, Miami, Nassau, Santo Domingo, Porlamar, Port of Spain, Georgetown, Paramaribo, Belém, São Luís, Joāo Pessoa and Recife. It will also be the second total eclipse visible from Little Rock in 21.3 years. Totality will last for at least 6 minutes along the part of the path that starts at Camden, Alabama, crossing Florida and ending near the southernmost Bahama Islands. The longest duration of totality will be 6 minutes 5.5 seconds at , which is over the Atlantic Ocean east of Fort Lauderdale and south of Freeport, Bahamas.
The solar eclipse of August 21, 2017 had a very similar path of totality over the U.S., about to the northeast, also crossing the Pacific coast and Atlantic coast of the country. This is because when a solar eclipse crosses the U.S. in mid-August at an ascending node (i.e. moves from south to north during odd-numbered saros), the path of the eclipse tracks from coast to coast. When a solar eclipse crosses the U.S. in mid-August at descending node (even numbered saros), the path tracks a large distance southward.
Details of the totality in some places or cities
Images
Animated path: Small dark circle represents umbra, much larger grey circle represents penumbra.
Eclipse details
Shown below are two tables displaying details about this particular solar eclipse. The first table outlines times at which the moon's penumbra or umbra attains the specific parameter, and the second table describes various other parameters pertaining to this eclipse.
Eclipse season
This eclipse is part of an eclipse season, a period, roughly every six months, when eclipses occur. Only two (or occasionally three) eclipse seasons occur each year, and each season lasts about 35 days and repeats just short of six months (173 days) later; thus two full eclipse seasons always occur each year. Either two or three eclipses happen each eclipse season. In the sequence below, each eclipse is separated by a fortnight.
Related eclipses
Eclipses in 2045
An annular solar eclipse on February 16.
A penumbral lunar eclipse on March 3.
A total solar eclipse on August 12.
A penumbral lunar eclipse on August 27.
Metonic
Preceded by: Solar eclipse of October 25, 2041
Followed by: Solar eclipse of May 31, 2049
Tzolkinex
Preceded by: Solar eclipse of July 2, 2038
Followed by: Solar eclipse of September 22, 2052
Half-Saros
Preceded by: Lunar eclipse of August 7, 2036
Followed by: Lunar eclipse of August 18, 2054
Tritos
Preceded by: Solar eclipse of September 12, 2034
Followed by: Solar eclipse of July 12, 2056
Solar Saros 136
Preceded by: Solar eclipse of August 2, 2027
Followed by: Solar eclipse of August 24, 2063
Inex
Preceded by: Solar eclipse of September 1, 2016
Followed by: Solar eclipse of July 24, 2074
Triad
Preceded by: Solar eclipse of October 12, 1958
Followed by: Solar eclipse of June 13, 2132
Solar eclipses of 2044–2047
Saros 136
Metonic series
Tritos series
Inex series
See also
List of solar eclipses in the 21st century
List of solar eclipses visible from the United States
References
External links
http://eclipse.gsfc.nasa.gov/SEplot/SEplot2001/SE2045Aug12T.GIF
2045 in science
2045 08 12
2045 08 12
2045 08 12 | Solar eclipse of August 12, 2045 | Astronomy | 1,082 |
3,275,060 | https://en.wikipedia.org/wiki/PLECS | PLECS (Piecewise Linear Electrical Circuit Simulation) is a software tool for system-level simulations of electrical circuits developed by Plexim. It is especially designed for power electronics but can be used for any electrical network. PLECS includes the possibility to model controls and different physical domains (thermal, magnetic and mechanical) besides the electrical system.
Most circuit simulation programs model switches as highly nonlinear elements. Due to steep voltage and current transient, the simulation becomes slow when switches are commutated. In most simplistic applications, switches are modelled as variable resistors that alternate between a very small and a very large resistance. In other cases, they are represented by a sophisticated semiconductor model.
When simulating complex power electronic systems, however, the processes during switching are of little interest. In these situations it is more appropriate to use ideal switches that toggle instantaneously between a closed and an open circuit. This approach, which is implemented in PLECS, has two major advantages: Firstly, it yields systems that are piecewise-linear across switching instants, thus resolving the otherwise difficult problem of simulating the non-linear discontinuity that occurs in the equivalent-circuit at the switching instant. Secondly, to handle discontinuities at the switching instants, only two integration steps are required (one for before the instant, and one after). Both of these advantages speed up the simulation considerably, without sacrificing accuracy. Thus the software is ideally suited for modelling and simulation of complex drive systems and modular multilevel converters, for example.
In recent years, PLECS has been extended to also support model-based development of controls with automatic code generation. In addition to software, the PLECS product family includes real-time simulation hardware for both hardware-in-the-loop (HIL) testing and rapid control prototyping.
Integration with MATLAB/Simulink or Standalone
The PLECS software is available in two editions: PLECS Blockset for integration with MATLAB®/Simulink®, and PLECS Standalone, a completely independent product.
When using PLECS Blockset, the control loops are usually created in Simulink, while the electrical circuits are modelled in PLECS. PLECS Standalone on the other hand can be operated independently from other software and offers an all-in-one solution for modelling electrical circuits and controls in a single environment. Both editions are interoperable with each other.
The main difference between the two versions is that PLECS Standalone runs faster than PLECS Blockset due to its optimised engine.
Add-on PLECS Coder
A code generator usually converts some intermediate representation of source code into machine code. The PLECS Coder is an add-on to PLECS Blockset and PLECS Standalone. It generates ANSI-C code from a PLECS model which can be compiled to execute on the simulation host or a separate target. The target can be an embedded control platform or a real-time digital simulator. The PLECS Coder can also produce embedded code for specific hardware targets.
Add-on PLECS PIL
In the Model-based design of control loops, Processor-in-the-Loop (PIL) simulation can accelerate the development process. It allows engineers to test their control algorithms on the real hardware inside a virtual circuit simulator. As an add-on to PLECS Blockset and PLECS Standalone, PLECS PIL provides that solution.
Hardware for Real-Time Simulations
The PLECS RT Box is a real-time simulator specially designed for power electronics applications. It is a processing unit for both real-time hardware-in-the-loop (HIL) testing and rapid control prototyping. A PLECS RT Box can be programmed and operated from PLECS. Thus, a software license of PLECS (Blockset or Standalone) and a PLECS Coder license are required to operate the hardware.
References
External links
Electronic circuit simulators
Simulation software
Power electronics | PLECS | Engineering | 832 |
67,130,162 | https://en.wikipedia.org/wiki/Shadow%20rate | The shadow rate is an interest rate in some financial models. It is used to measure the economy when nominal interest rates come close to the zero lower bound. It was created by Fischer Black in his final paper, "Interest Rates as Options".
The shadow rate derives from Fischer Black's insight that currency is an option. If someone has money, the person can either (1) spend it today or (2) not spend it and have money tomorrow. Thus, when loans would return less money than was initially loaned out, investors will choose to "exercise the option" and not loan their money. Thus, the nominal short-term interest rate is always greater than or equal to zero. In Black's model, the shadow nominal short-term rate is what the nominal short-term rate would be if it was allowed to go below the zero lower bound.
When the shadow nominal short-term rate is positive, the nominal short-term rate is equal to the shadow rate. But when the shadow short-term rate is negative — such as during deflation or a bad recession with low inflation — the nominal short-term rate will diverge and stay above zero. In Black's model, even when nominal short-term interest rates stay close to zero, the long-term nominal interest rates can be well above zero. This is because nominal interest rates behave like options and there is some chance that the shadow short-term rate becomes positive in the future.
There is also a shadow real rate. The shadow real short-term rate is equal to the shadow nominal short-term rate minus expected inflation.
Fischer Black published his paper in 1995 and mentioned that the most recent time that the USA had experienced the zero lower bound was the Great Depression. Shadow rate models got renewed interest with the Financial Crisis of 2007–2008 when interest rates plunged to near zero and, even, below zero in some instances.
In contemporary macroeconomic terms, the concept, shadow irate, refers to an expansionary monetary environment during a period of zero ZLB. In such a period, when the central banks implement additional expansionary measures such as quantitative easing (QE), the monetary environment is actually more expansionary than implied by the nominal interest rate alone, and it is possible to calculate what nominal interest rate corresponds to the monetary environment. This interest is known as shadow interest.
Models
Due to the option effect, the shadow short-term rate cannot be observed directly in the market. Economists use models to infer its value from its effect on longer-term interest rates in the yield curve. The value of the shadow short-term rate depends on assumptions about how interest rates move, so different models might calculate different values for it.
Jing Cynthia Wu and Fan Dora Xia's models were published in "Measuring the Macroeconomic Impact of Monetary Policy at the Zero Lower Bound" and in "Negative Interest Rate Policy and Yield Curve". Their rates are also available at the Federal Reserve Bank of Atlanta.
Leo Krippner's model was published in the book Zero Lower Bound Term Structure Modeling: A Practitioner’s Guide. His initial models were done while at the Reserve Bank of New Zealand.
References
Mathematical finance
Monetary policy | Shadow rate | Mathematics | 647 |
27,810,332 | https://en.wikipedia.org/wiki/Bending%20of%20plates | Bending of plates, or plate bending, refers to the deflection of a plate perpendicular to the plane of the plate under the action of external forces and moments. The amount of deflection can be determined by solving the differential equations of an appropriate plate theory. The stresses in the plate can be calculated from these deflections. Once the stresses are known, failure theories can be used to determine whether a plate will fail under a given load.
Bending of Kirchhoff-Love plates
Definitions
For a thin rectangular plate of thickness , Young's modulus , and Poisson's ratio , we can define parameters in terms of the plate deflection, .
The flexural rigidity is given by
Moments
The bending moments per unit length are given by
The twisting moment per unit length is given by
Forces
The shear forces per unit length are given by
Stresses
The bending stresses are given by
The shear stress is given by
Strains
The bending strains for small-deflection theory are given by
The shear strain for small-deflection theory is given by
For large-deflection plate theory, we consider the inclusion of membrane strains
Deflections
The deflections are given by
Derivation
In the Kirchhoff–Love plate theory for plates the governing equations are
and
In expanded form,
and
where is an applied transverse load per unit area, the thickness of the plate is , the stresses are , and
The quantity has units of force per unit length. The quantity has units of moment per unit length.
For isotropic, homogeneous, plates with Young's modulus and Poisson's ratio these equations reduce to
where is the deflection of the mid-surface of the plate.
Small deflection of thin rectangular plates
This is governed by the Germain-Lagrange plate equation
This equation was first derived by Lagrange in December 1811 in correcting the work of Germain who provided the basis of the theory.
Large deflection of thin rectangular plates
This is governed by the Föppl–von Kármán plate equations
where is the stress function.
Circular Kirchhoff-Love plates
The bending of circular plates can be examined by solving the governing equation with
appropriate boundary conditions. These solutions were first found by Poisson in 1829.
Cylindrical coordinates are convenient for such problems. Here is the distance of a point from the midplane of the plate.
The governing equation in coordinate-free form is
In cylindrical coordinates ,
For symmetrically loaded circular plates, , and we have
Therefore, the governing equation is
If and are constant, direct integration of the governing equation gives us
where are constants. The slope of the deflection surface is
For a circular plate, the requirement that the deflection and the slope of the deflection are finite
at implies that . However, need not equal 0, as the limit
of exists as you approach from the right.
Clamped edges
For a circular plate with clamped edges, we have and at the edge of
the plate (radius ). Using these boundary conditions we get
The in-plane displacements in the plate are
The in-plane strains in the plate are
The in-plane stresses in the plate are
For a plate of thickness , the bending stiffness is and we
have
The moment resultants (bending moments) are
The maximum radial stress is at and :
where . The bending moments at the boundary and the center of the plate are
Rectangular Kirchhoff-Love plates
For rectangular plates, Navier in 1820 introduced a simple method for finding the displacement and stress when a plate is simply supported. The idea was to express the applied load in terms of Fourier components, find the solution for a sinusoidal load (a single Fourier component), and then superimpose the Fourier components to get the solution for an arbitrary load.
Sinusoidal load
Let us assume that the load is of the form
Here is the amplitude, is the width of the plate in the -direction, and
is the width of the plate in the -direction.
Since the plate is simply supported, the displacement along the edges of
the plate is zero, the bending moment is zero at and , and
is zero at and .
If we apply these boundary conditions and solve the plate equation, we get the
solution
Where D is the flexural rigidity
Analogous to flexural stiffness EI. We can calculate the stresses and strains in the plate once we know the displacement.
For a more general load of the form
where and are integers, we get the solution
Navier solution
Double trigonometric series equation
We define a general load of the following form
where is a Fourier coefficient given by
.
The classical rectangular plate equation for small deflections thus becomes:
Simply-supported plate with general load
We assume a solution of the following form
The partial differentials of this function are given by
Substituting these expressions in the plate equation, we have
Equating the two expressions, we have
which can be rearranged to give
The deflection of a simply-supported plate (of corner-origin) with general load is given by
Simply-supported plate with uniformly-distributed load
For a uniformly-distributed load, we have
The corresponding Fourier coefficient is thus given by
.
Evaluating the double integral, we have
,
or alternatively in a piecewise format, we have
The deflection of a simply-supported plate (of corner-origin) with uniformly-distributed load is given by
The bending moments per unit length in the plate are given by
Lévy solution
Another approach was proposed by Lévy in 1899. In this case we start with an assumed form of the displacement and try to fit the parameters so that the governing equation and the boundary conditions are satisfied. The goal is to find such that it satisfies the boundary conditions at and and, of course, the governing equation .
Let us assume that
For a plate that is simply-supported along and , the boundary conditions are and . Note that there is no variation in displacement along these edges meaning that and , thus reducing the moment boundary condition to an equivalent expression .
Moments along edges
Consider the case of pure moment loading. In that case and
has to satisfy . Since we are working in rectangular
Cartesian coordinates, the governing equation can be expanded as
Plugging the expression for in the governing equation gives us
or
This is an ordinary differential equation which has the general solution
where are constants that can be determined from the boundary
conditions. Therefore, the displacement solution has the form
Let us choose the coordinate system such that the boundaries of the plate are
at and (same as before) and at (and not and
). Then the moment boundary conditions at the boundaries are
where are known functions. The solution can be found by
applying these boundary conditions. We can show that for the symmetrical case
where
and
we have
where
Similarly, for the antisymmetrical case where
we have
We can superpose the symmetric and antisymmetric solutions to get more general
solutions.
Simply-supported plate with uniformly-distributed load
For a uniformly-distributed load, we have
The deflection of a simply-supported plate with centre with uniformly-distributed load is given by
The bending moments per unit length in the plate are given by
Uniform and symmetric moment load
For the special case where the loading is symmetric and the moment is uniform, we have at ,
The resulting displacement is
where
The bending moments and shear forces corresponding to the displacement are
The stresses are
Cylindrical plate bending
Cylindrical bending occurs when a rectangular plate that has dimensions , where and the thickness is small, is subjected to a uniform distributed load perpendicular to the plane of the plate. Such a plate takes the shape of the surface of a cylinder.
Simply supported plate with axially fixed ends
For a simply supported plate under cylindrical bending with edges that are free to rotate but have a fixed . Cylindrical bending solutions can be found using the Navier and Levy techniques.
Bending of thick Mindlin plates
For thick plates, we have to consider the effect of through-the-thickness shears on the orientation of the normal to the mid-surface after deformation. Raymond D. Mindlin's theory provides one approach for find the deformation and stresses in such plates. Solutions to Mindlin's theory can be derived from the equivalent Kirchhoff-Love solutions using canonical relations.
Governing equations
The canonical governing equation for isotropic thick plates can be expressed as
where is the applied transverse load, is the shear modulus,
is the bending rigidity, is the plate thickness, ,
is the shear correction factor, is the Young's modulus, is the Poisson's
ratio, and
In Mindlin's theory, is the transverse displacement of the mid-surface of the plate
and the quantities and are the rotations of the mid-surface normal
about the and -axes, respectively. The canonical parameters for this theory
are and . The shear correction factor usually has the
value .
The solutions to the governing equations can be found if one knows the corresponding
Kirchhoff-Love solutions by using the relations
where is the displacement predicted for a Kirchhoff-Love plate, is a
biharmonic function such that , is a function that satisfies the
Laplace equation, , and
Simply supported rectangular plates
For simply supported plates, the Marcus moment sum vanishes, i.e.,
Which is almost Laplace`s equation for w[ref 6]. In that case the functions , , vanish, and the Mindlin solution is
related to the corresponding Kirchhoff solution by
Bending of Reissner-Stein cantilever plates
Reissner-Stein theory for cantilever plates leads to the following coupled ordinary differential equations for a cantilever plate with concentrated end load at .
and the boundary conditions at are
Solution of this system of two ODEs gives
where . The bending moments and shear forces corresponding to the displacement
are
The stresses are
If the applied load at the edge is constant, we recover the solutions for a beam under a
concentrated end load. If the applied load is a linear function of , then
See also
Bending
Infinitesimal strain theory
Kirchhoff–Love plate theory
Linear elasticity
Mindlin–Reissner plate theory
Plate theory
Stress (mechanics)
Stress resultants
Structural acoustics
Vibration of plates
References
Continuum mechanics | Bending of plates | Physics | 2,047 |
73,371,360 | https://en.wikipedia.org/wiki/Thomas%20Kurtzman | Thomas Kurtzman is an American physical chemist most notable for his research into the use of convolutional neural networks (CNNs) to improve pharmaceutical design. According to Bioworld, Kurtzman's research "reached the devastating conclusion that 'the entirety'" of apparent deep learning produced over the course of several years by a CNN dataset highly regarded in academia and industry was illusory. The perceived scientific progress, Kurtzman wrote, was due to CNNs' effective learning of the deficiencies in the dataset. "This is alarming," the article continued, "as companies have been built on this research.
During the COVID-19 pandemic, a computational tool Kurtzman developed, GIST, was used to research potential new drugs to treat the illness.
Kurtzman is a professor of chemistry at the Lehman College and the Graduate Center of the City University of New York. His research is conducted at the affiliated Kurtzman Lab and funded by the National Institutes of Health.
He is married to Mor Armony, vice dean for faculty and research at New York University's Stern School of Business.
References
1969 births
Living people
American physical chemists
CUNY Graduate Center faculty
Lehman College faculty | Thomas Kurtzman | Chemistry | 246 |
11,820,625 | https://en.wikipedia.org/wiki/Tyromyces%20calkinsii | Tyromyces calkinsii is a plant pathogen infecting sweetgums.
References
External links
Index Fungorum
USDA ARS Fungal Database
Fungal tree pathogens and diseases
Polyporaceae
Fungus species | Tyromyces calkinsii | Biology | 43 |
13,167,630 | https://en.wikipedia.org/wiki/Accretion%20%28coastal%20management%29 | Accretion is the process of coastal sediment returning to the visible portion of a beach or foreshore after a submersion event. A sustainable beach or foreshore often goes through a cycle of submersion during rough weather and later accretion during calmer periods.
If a coastline is not in a healthy sustainable state, erosion can be more serious, and accretion does not fully restore the original volume of the visible beach or foreshore, which leads to permanent beach loss.
References
Coastal geography
Deposition (geology)
Physical oceanography | Accretion (coastal management) | Physics | 110 |
3,559,509 | https://en.wikipedia.org/wiki/Background%20field%20method | In theoretical physics, background field method is a useful procedure to calculate the effective action of a quantum field theory by expanding a quantum field around a classical "background" value B:
.
After this is done, the Green's functions are evaluated as a function of the background. This approach has the advantage that the gauge invariance is manifestly preserved if the approach is applied to gauge theory.
Method
We typically want to calculate expressions like
where J(x) is a source, is the Lagrangian density of the system, d is the number of dimensions and is a field.
In the background field method, one starts by splitting this field into a classical background field B(x) and a field η(x) containing additional quantum fluctuations:
Typically, B(x) will be a solution of the classical equations of motion
where S is the action, i.e. the space integral of the Lagrangian density. Switching on a source J(x) will change the equations into
.
Then the action is expanded around the background B(x):
The second term in this expansion is zero by the equations of motion. The first term does not depend on any fluctuating fields, so that it can be brought out of the path integral. The result is
The path integral which now remains is (neglecting the corrections in the dots) of Gaussian form and can be integrated exactly:
where "det" signifies a functional determinant and C is a constant. The power of minus one half will naturally be plus one for Grassmann fields.
The above derivation gives the Gaussian approximation to the functional integral. Corrections to this can be computed, producing a diagrammatic expansion.
See also
BF theory
Effective action
Source field
References
Quantum field theory | Background field method | Physics | 357 |
56,397,386 | https://en.wikipedia.org/wiki/Joanna%20Bryson | Joanna Joy Bryson (born 1965) is professor at Hertie School in Berlin. She works on Artificial Intelligence, ethics and collaborative cognition. She has been a British citizen since 2007.
Education
Bryson attended Glenbard North High School and graduated in 1982. She studied Behavioural Science at the University of Chicago, graduating with an AB in 1986. In 1991 she moved to the University of Edinburgh where she completed an MSc in Artificial Intelligence before an MPhil in Psychology. Bryson moved to MIT to complete her PhD, earning a doctorate under Lynn Andrea Stein in 2001 for her thesis "Intelligence by Design: Principles of Modularity and Coordination for Engineering Complex Adaptive Agents". In 1995 she worked for LEGO Futura in Boston, and then in 1998 she worked for LEGO Digital as an AI consultant with Kristinn R. Thórisson on cognitive architectures for autonomous LEGO characters in the Wizard Group. She completed a postdoctoral fellowship in Marc Hauser's Primate Cognitive Neuroscience at the Harvard University in 2002.
Bryson joined the Department of Computer Science at the University of Bath in 2002. At Bath, Bryson founded the Intelligent Systems research group. In 2007 she joined the University of Nottingham as a visiting research fellow in the Methods and Data Institute. During this time, she was a Hans Przibram Fellow at the Konrad Lorenz Institute for Evolution and Cognition. She joined Oxford University as a visiting research fellow in 2010, working with Harvey Whitehouse on the impact of religion on societies.
In 2010 Bryson published Robots Should Be Slaves, which selected as a chapter in Yorick Wilks' "Close Engagements with Artificial Companions: Key Social, Psychological, Ethical and Design Issues". She helped the EPSRC to define the Principles of Robotics in 2010. In 2015 she was a Visiting Academic at the University of Princeton Center for Information Technology Policy, where she remained an affiliate through 2018. She is focussed on "Standardizing Ethical Design for Artificial Intelligence and Autonomous Systems". In 2020 she became Professor of Ethics and Technology at Hertie School of Governance in Berlin.
Public engagements
Bryson's research has appeared in Science and on Reddit. She has consulted The Red Cross on autonomous weapons and contributed to an All Party Parliamentary Group on Artificial Intelligence.
In 2022, Bryson published an article for Wired magazine titled "One Day, AI Will Seem as Human as Anyone. What Then?". In the article she discussed the current limits of and future of AI, how the general public define and think about AI, and how AI interacts with people via Language and touches upon the topics of natural language processing, ethics and Human-computer interaction. Bryson also dissusses the recent EU AI Act.
Honors and awards
In 2017, Bryson won an Outstanding Achievement award from Cognition X. She regularly appears in national media, talking about human-robot relationships and the ethics of AI.
References
Living people
Massachusetts Institute of Technology alumni
Academics of the University of Bath
Academic staff of Hertie School
British women computer scientists
British women engineers
Roboticists
Women roboticists
Artificial intelligence ethicists
Ethics of science and technology
1965 births
21st-century women engineers
American emigrants to the United Kingdom
Naturalised citizens of the United Kingdom
Philosophers of technology
University of Chicago alumni
Alumni of the University of Edinburgh
Lego people | Joanna Bryson | Technology | 646 |
18,381 | https://en.wikipedia.org/wiki/John%20William%20Strutt%2C%203rd%20Baron%20Rayleigh | John William Strutt, 3rd Baron Rayleigh (; 12 November 1842 – 30 June 1919), was an English physicist and mathematician. He spent all of his academic career at the University of Cambridge. Among many honours, he received the Nobel Prize in Physics in 1904 "for his investigations of the densities of the most important gases and for his discovery of argon in connection with these studies". He served as president of the Royal Society from 1905 to 1908 and as chancellor of the University of Cambridge from 1908 to 1919.
Rayleigh provided the first theoretical treatment of the elastic scattering of light by particles much smaller than the light's wavelength, a phenomenon now known as "Rayleigh scattering", which notably explains why the sky is blue. He studied and described transverse surface waves in solids, now known as "Rayleigh waves". He contributed extensively to fluid dynamics, with concepts such as the Rayleigh number (a dimensionless number associated with natural convection), Rayleigh flow, the Rayleigh–Taylor instability, and Rayleigh's criterion for the stability of Taylor–Couette flow. He also formulated the circulation theory of aerodynamic lift. In optics, Rayleigh proposed a well-known criterion for angular resolution. His derivation of the Rayleigh–Jeans law for classical black-body radiation later played an important role in the birth of quantum mechanics (see ultraviolet catastrophe). Rayleigh's textbook The Theory of Sound (1877) is still used today by acousticians and engineers. He introduced the Rayleigh test for circular non-uniformity, of which the Rayleigh plot visualizes.
Early life and education
Strutt was born on 12 November 1842 at Langford Grove, Maypole Road in Maldon, Essex. In his early years he suffered from frailty and poor health. He attended Eton College and Harrow School (each for only a short period), before going on to the University of Cambridge in 1861 where he studied mathematics at Trinity College. He obtained a Bachelor of Arts degree (Senior Wrangler and 1st Smith's Prize) in 1865, and a Master of Arts in 1868. He was subsequently elected to a fellowship of Trinity. He held the post until his marriage to Evelyn Balfour, daughter of James Maitland Balfour, in 1871. He had three sons with her. In 1873, on the death of his father, John Strutt, 2nd Baron Rayleigh, he inherited the Barony of Rayleigh. Rayleigh was elected fellow of the Royal Society on 12 June 1873.
Career
Rayleigh was the second Cavendish Professor of Physics at the University of Cambridge (following James Clerk Maxwell), from 1879 to 1884. He first described dynamic soaring by seabirds in 1883, in the British journal Nature. From 1887 to 1905 he was professor of Natural Philosophy at the Royal Institution.
On this post he carefully and precisely measured atomic mass of oxygen and hydrogen, and by 1892 he moved on to nitrogen. By isolating nitrogen in different ways he discovered a small but significant difference, which indicated a heavier inert gas present in the air besides nitrogen. William Ramsay joined this research topic, and in August they discovered argon.
Around 1900 Rayleigh developed the duplex (combination of two) theory of human sound localisation using two binaural cues, interaural phase difference (IPD) and interaural level difference (ILD) (based on analysis of a spherical head with no external pinnae). The theory posits that we use two primary cues for sound lateralisation, using the difference in the phases of sinusoidal components of the sound and the difference in amplitude (level) between the two ears.
He received the degree of Doctor mathematicae (honoris causa) from the Royal Frederick University on 6 September 1902, when they celebrated the centennial of the birth of mathematician Niels Henrik Abel.
In 1904 he was awarded the Nobel Prize for Physics "for his investigations of the densities of the most important gases and for his discovery of argon in connection with these studies".
During the First World War, he was president of the government's Advisory Committee for Aeronautics, which was located at the National Physical Laboratory, and chaired by Richard Glazebrook.
In 1919, Rayleigh served as president of the Society for Psychical Research. As an advocate that simplicity and theory be part of the scientific method, Rayleigh argued for the principle of similitude.
Rayleigh served as president of the Royal Society from 1905 to 1908. From time to time he participated in the House of Lords; however, he spoke up only if politics attempted to become involved in science.
Personal life and death
Rayleigh married Evelyn Georgiana Mary (née Balfour). He died on 30 June 1919, at his home in Witham, Essex. He was succeeded, as the 4th Lord Rayleigh, by his son Robert John Strutt, another well-known physicist. Lord Rayleigh was buried in the graveyard of All Saints' Church in Terling in Essex.
Religious views
Rayleigh was an Anglican. Though he did not write about the relationship of science and religion, he retained a personal interest in spiritual matters. When his scientific papers were to be published in a collection by the Cambridge University Press, Strutt wanted to include a quotation from the Bible, but he was discouraged from doing so, as he later reported:
Still, he had his wish and the quotation was printed in the five-volume collection of scientific papers. In a letter to a family member, he wrote about his rejection of materialism and spoke of Jesus Christ as a moral teacher:
He held an interest in parapsychology and was an early member of the Society for Psychical Research (SPR). He was not convinced of spiritualism but remained open to the possibility of supernatural phenomena. Rayleigh was the president of the SPR in 1919. He gave a presidential address in the year of his death but did not come to any definite conclusions.
Honours and awards
The lunar crater Rayleigh as well as the Martian crater Rayleigh were named in his honour. The asteroid 22740 Rayleigh was named after him on 1 June 2007. A type of surface waves are known as Rayleigh waves, and the elastic scattering of electromagnetic waves is called Rayleigh scattering. The rayl, a unit of specific acoustic impedance, is also named for him. Rayleigh was also awarded with (in chronological order):
Smith's Prize (1864)
Royal Medal (1882)
Member of the American Philosophical Society (1886)
Matteucci Medal (1894)
Member of the Royal Swedish Academy of Sciences (1897)
Copley Medal (1899)
Nobel Prize in Physics (1904)
Elliott Cresson Medal (1913)
Rumford Medal (1914)
Lord Rayleigh was among the original recipients of the Order of Merit (OM) in the 1902 Coronation Honours list published on 26 June 1902, and received the order from King Edward VII at Buckingham Palace on 8 August 1902.
Sir William Ramsay, his co-worker in the investigation to discover argon described Rayleigh as "the greatest man alive" while speaking to Lady Ramsay during his last illness.
H. M. Hyndman said of Rayleigh that "no man ever showed less consciousness of great genius".
In honour of Lord Rayleigh, the Institute of Acoustics sponsors the Rayleigh Medal (established in 1970) and the Institute of Physics sponsors the John William Strutt, Lord Rayleigh Medal and Prize (established in 2008).
Many of the papers that he wrote on lubrication are now recognized as early classical contributions to the field of tribology. For these contributions, he was named as one of the 23 "Men of Tribology" by Duncan Dowson.
There is a memorial to him by Derwent Wood in St Andrew's Chapel at Westminster Abbey.
Bibliography
The Theory of Sound vol. I (London : Macmillan, 1877, 1894) (alternative link: Bibliothèque Nationale de France OR (Cambridge: University Press, reissued 2011, )
The Theory of Sound vol.II (London : Macmillan, 1878, 1896) (alternative link: Bibliothèque Nationale de France) OR (Cambridge: University Press, reissued 2011, )
Scientific papers (Vol. 1: 1869–1881) (Cambridge : University Press, 1899–1920, reissued by the publisher 2011, )
Scientific papers (Vol. 2: 1881–1887) (Cambridge : University Press, 1899–1920, reissued by the publisher 2011, )
Scientific papers (Vol. 3: 1887–1892) (Cambridge : University Press, 1899–1920, reissued by the publisher 2011, )
Scientific papers (Vol. 4: 1892–1901) (Cambridge : University Press, 1899–1920, reissued by the publisher 2011, )
Scientific papers (Vol. 5: 1902–1910) (Cambridge : University Press, 1899–1920, reissued by the publisher 2011, )
Scientific papers (Vol. 6: 1911–1919) (Cambridge : University Press, 1899–1920, reissued by the publisher 2011, )
See also
References
Further reading
Life of John William Strutt: Third Baron Rayleigh, O.M., F.R.S., (1924) Longmans, Green & Co.
A biography written by his son, Robert Strutt, 4th Baron Rayleigh
External links
About John William Strutt
Lord Rayleigh – the Last of the Great Victorian Polymaths, GEC Review, Volume 7, No. 3, 1992
1842 births
1919 deaths
20th-century British physicists
Acousticians
Alumni of Trinity College, Cambridge
3
British Nobel laureates
Chancellors of the University of Cambridge
De Morgan Medallists
Discoverers of chemical elements
English Anglicans
Experimental physicists
Optical physicists
Fluid dynamicists
Lord-lieutenants of Essex
Members of the Order of Merit
Nobel laureates in Physics
Fellows of the Royal Society
Fellows of the American Academy of Arts and Sciences
Foreign associates of the National Academy of Sciences
Members of the Royal Swedish Academy of Sciences
Members of the Royal Netherlands Academy of Arts and Sciences
Members of the Bavarian Academy of Sciences
Members of the Prussian Academy of Sciences
Members of the Hungarian Academy of Sciences
Members of the French Academy of Sciences
British parapsychologists
People educated at Eton College
People educated at Harrow School
People from Maldon, Essex
Presidents of the Physical Society
Presidents of the Royal Society
Recipients of the Copley Medal
Recipients of the Pour le Mérite (civil class)
Royal Medal winners
Senior Wranglers
John
Members of the Privy Council of the United Kingdom
Burials in Essex
Linear algebraists
Tribologists
Recipients of the Matteucci Medal
Members of the American Philosophical Society
Cavendish Professors of Physics
Members of the Royal Society of Sciences in Uppsala
Scientists of the National Physical Laboratory (United Kingdom) | John William Strutt, 3rd Baron Rayleigh | Chemistry,Materials_science | 2,172 |
11,270,991 | https://en.wikipedia.org/wiki/Ontology%20merging | Ontology merging defines the act of bringing together two conceptually divergent ontologies or the instance data associated to two ontologies. This is similar to work in database merging (schema matching). This merging process can be performed in a number of ways, manually, semi automatically, or automatically. Manual ontology merging although ideal is extremely labour-intensive and current research attempts to find semi or entirely automated techniques to merge ontologies. These techniques are statistically driven often taking into account similarity of concepts and raw similarity of instances through textual string metrics and semantic knowledge. These techniques are similar to those used in information integration employing string metrics from open source similarity libraries.
See also
Ontology mapping
Ontology-based data integration
Ontology (information science)
Data management | Ontology merging | Technology | 155 |
465,001 | https://en.wikipedia.org/wiki/700%20%28number%29 | 700 (seven hundred) is the natural number following 699 and preceding 701.
It is the sum of four consecutive primes (167 + 173 + 179 + 181), the perimeter of a Pythagorean triangle (75 + 308 + 317) and a Harshad number.
Integers from 701 to 799
Nearly all of the palindromic integers between 700 and 800 (i.e. nearly all numbers in this range that have both the hundreds and units digit be 7) are used as model numbers for Boeing Commercial Airplanes.
700s
701 = prime number, sum of three consecutive primes (229 + 233 + 239), Chen prime, Eisenstein prime with no imaginary part
702 = 2 × 33 × 13, pronic number, nontotient, Harshad number
703 = 19 × 37, the 37th triangular number, a hexagonal number, smallest number requiring 73 fifth powers for Waring representation, Kaprekar number, area code for Northern Virginia along with 571, a number commonly found in the formula for body mass index
704 = 26 × 11, Harshad number, lazy caterer number , area code for the Charlotte, NC area.
705 = 3 × 5 × 47, sphenic number, smallest Bruckman-Lucas pseudoprime
706 = 2 × 353, nontotient, Smith number
707 = 7 × 101, sum of five consecutive primes (131 + 137 + 139 + 149 + 151), palindromic number, number of lattice paths from (0,0) to (5,5) with steps (0,1), (1,0) and, when on the diagonal, (1,1).
708 = 22 × 3 × 59, number of partitions of 28 that do not contain 1 as a part
709 = prime number; happy number. It is the seventh in the series 2, 3, 5, 11, 31, 127, 709 where each number is the nth prime with n being the number preceding it in the series, therefore, it is a prime index number.
710s
710 = 2 × 5 × 71, sphenic number, nontotient, number of forests with 11 vertices
711 = 32 × 79, Harshad number, number of planar Berge perfect graphs on 7 nodes. Also the phone number of Telecommunications Relay Service, commonly used by the deaf and hard-of-hearing.
712 = 23 × 89, refactorable number, sum of the first twenty-one primes, totient sum for first 48 integers. It is the largest known number such that it and its 8th power (66,045,000,696,445,844,586,496) have no common digits.
713 = 23 × 31, Blum integer, main area code for Houston, TX. In Judaism there are 713 letters on a Mezuzah scroll.
714 = 2 × 3 × 7 × 17, sum of twelve consecutive primes (37 + 41 + 43 + 47 + 53 + 59 + 61 + 67 + 71 + 73 + 79 + 83), nontotient, balanced number, member of Ruth–Aaron pair (either definition); area code for Orange County, California.
Flight 714 to Sidney is a Tintin graphic novel.
714 is the badge number of Sergeant Joe Friday.
715 = 5 × 11 × 13, sphenic number, pentagonal number, pentatope number ( binomial coefficient ), Harshad number, member of Ruth-Aaron pair (either definition)
The product of 714 and 715 is the product of the first 7 prime numbers (2, 3, 5, 7, 11, 13, and 17)
716 = 22 × 179, area code for Buffalo, NY
717 = 3 × 239, palindromic number
718 = 2 × 359, area code for Brooklyn, NY and Bronx, NY
719 = prime number, factorial prime (6! − 1), Sophie Germain prime, safe prime, sum of seven consecutive primes (89 + 97 + 101 + 103 + 107 + 109 + 113), Chen prime, Eisenstein prime with no imaginary part
720s
720 = 24 × 32 × 5.
6 factorial, highly composite number, Harshad number in every base from binary to decimal, highly totient number.
two round angles (= 2 × 360).
five gross (= 500 duodecimal, 5 × 144).
241-gonal number.
721 = 7 × 103, sum of nine consecutive primes (61 + 67 + 71 + 73 + 79 + 83 + 89 + 97 + 101), centered hexagonal number, smallest number that is the difference of two positive cubes in two ways,
722 = 2 × 192, nontotient, number of odd parts in all partitions of 15, area of a square with diagonal 38
G.722 is a freely available file format for audio file compression. The files are often named with the extension "722".
723 = 3 × 241, side length of an almost-equilateral Heronian triangle
724 = 22 × 181, sum of four consecutive primes (173 + 179 + 181 + 191), sum of six consecutive primes (107 + 109 + 113 + 127 + 131 + 137), nontotient, side length of an almost-equilateral Heronian triangle, the number of n-queens problem solutions for n = 10,
725 = 52 × 29, side length of an almost-equilateral Heronian triangle
726 = 2 × 3 × 112, pentagonal pyramidal number
727 = prime number, palindromic prime, lucky prime,
728 = 23 × 7 × 13, nontotient, Smith number, cabtaxi number, 728!! - 1 is prime, number of cubes of edge length 1 required to make a hollow cube of edge length 12, 72864 + 1 is prime, number of connected graphs on 5 labelled vertices
729 = 272 = 93 = 36.
the square of 27, and the cube of 9, the sixth power of three, and because of these properties, a perfect totient number.
centered octagonal number, Smith number
the number of times a philosopher's pleasure is greater than a tyrant's pleasure according to Plato in the Republic
the largest three-digit cube. (9 x 9 x 9)
the only three-digit sixth power. (3 x 3 x 3 x 3 x 3 x 3)
730s
730 = 2 × 5 × 73, sphenic number, nontotient, Harshad number, number of generalized weak orders on 5 points
731 = 17 × 43, sum of three consecutive primes (239 + 241 + 251), number of Euler trees with total weight 7
732 = 22 × 3 × 61, sum of eight consecutive primes (73 + 79 + 83 + 89 + 97 + 101 + 103 + 107), sum of ten consecutive primes (53 + 59 + 61 + 67 + 71 + 73 + 79 + 83 + 89 + 97), Harshad number, number of collections of subsets of {1, 2, 3, 4} that are closed under union and intersection
733 = prime number, emirp, balanced prime, permutable prime, sum of five consecutive primes (137 + 139 + 149 + 151 + 157)
734 = 2 × 367, nontotient, number of traceable graphs on 7 nodes
735 = 3 × 5 × 72, Harshad number, Zuckerman number, smallest number such that uses same digits as its distinct prime factors
736 = 25 × 23, centered heptagonal number, happy number, nice Friedman number since 736 = 7 + 36, Harshad number
737 = 11 × 67, palindromic number, blum integer.
738 = 2 × 32 × 41, Harshad number.
739 = prime number, strictly non-palindromic number, lucky prime, happy number, prime index prime
740s
740 = 22 × 5 × 37, nontotient, number of connected squarefree graphs on 9 nodes
741 = 3 × 13 × 19, sphenic number, 38th triangular number
742 = 2 × 7 × 53, sphenic number, decagonal number, icosahedral number. It is the smallest number that is one more than triple its reverse. Lazy caterer number . Number of partitions of 30 into divisors of 30.
743 = prime number, Sophie Germain prime, Chen prime, Eisenstein prime with no imaginary part
744 = 23 × 3 × 31, sum of four consecutive primes (179 + 181 + 191 + 193). It is the coefficient of the first degree term of the expansion of Klein's j-invariant, and the zeroth degree term of the Laurent series of the J-invariant. Furthermore, 744 = 3 × 248 where 248 is the dimension of the Lie algebra E8.
745 = 5 × 149 = 24 + 36, number of non-connected simple labeled graphs covering 6 vertices
746 = 2 × 373 = 15 + 24 + 36 = 17 + 24 + 36, nontotient, number of non-normal semi-magic squares with sum of entries equal to 6
747 = 32 × 83 = , palindromic number.
748 = 22 × 11 × 17, nontotient, happy number, primitive abundant number
749 = 7 × 107, sum of three consecutive primes (241 + 251 + 257), blum integer
750s
750 = 2 × 3 × 53, enneagonal number.
751 = prime number, Chen prime, emirp
752 = 24 × 47, nontotient, number of partitions of 11 into parts of 2 kinds
753 = 3 × 251, blum integer
754 = 2 × 13 × 29, sphenic number, nontotient, totient sum for first 49 integers, number of different ways to divide a 10 × 10 square into sub-squares
755 = 5 × 151, number of vertices in a regular drawing of the complete bipartite graph K9,9.
756 = 22 × 33 × 7, sum of six consecutive primes (109 + 113 + 127 + 131 + 137 + 139), pronic number, Harshad number
757 = prime number, palindromic prime, sum of seven consecutive primes (97 + 101 + 103 + 107 + 109 + 113 + 127), happy number.
"The 757" is a local nickname for the Hampton Roads area in the U.S. state of Virginia, derived from the telephone area code that covers almost all of the metropolitan area
758 = 2 × 379, nontotient, prime number of measurement
759 = 3 × 11 × 23, sphenic number, sum of five consecutive primes (139 + 149 + 151 + 157 + 163), a q-Fibonacci number for q=3
760s
760 = 23 × 5 × 19, centered triangular number, number of fixed heptominoes.
761 = prime number, emirp, Sophie Germain prime, Chen prime, Eisenstein prime with no imaginary part, centered square number
762 = 2 × 3 × 127, sphenic number, sum of four consecutive primes (181 + 191 + 193 + 197), nontotient, Smith number, admirable number, number of 1's in all partitions of 25 into odd parts, see also Six nines in pi
763 = 7 × 109, sum of nine consecutive primes (67 + 71 + 73 + 79 + 83 + 89 + 97 + 101 + 103), number of degree-8 permutations of order exactly 2
764 = 22 × 191, telephone number
765 = 32 × 5 × 17, octagonal pyramidal number
a Japanese word-play for Namco;
766 = 2 × 383, centered pentagonal number, nontotient, sum of twelve consecutive primes (41 + 43 + 47 + 53 + 59 + 61 + 67 + 71 + 73 + 79 + 83 + 89)
767 = 13 × 59, Thabit number (28 × 3 − 1), palindromic number.
768 = 28 × 3, sum of eight consecutive primes (79 + 83 + 89 + 97 + 101 + 103 + 107 + 109)
769 = prime number, Chen prime, lucky prime, Proth prime
770s
770 = 2 × 5 × 7 × 11, nontotient, Harshad number
is prime
Famous room party in New Orleans hotel room 770, giving the name to a well known science fiction fanzine called File 770
Holds special importance in the Chabad-Lubavitch Hasidic movement.
771 = 3 × 257, sum of three consecutive primes in arithmetic progression (251 + 257 + 263). Since 771 is the product of the distinct Fermat primes 3 and 257, a regular polygon with 771 sides can be constructed using compass and straightedge, and can be written in terms of square roots.
772 = 22 × 193, 772!!!!!!+1 is prime
773 = prime number, Eisenstein prime with no imaginary part, tetranacci number, prime index prime, sum of the number of cells that make up the convex, regular 4-polytopes
774 = 2 × 32 × 43, nontotient, totient sum for first 50 integers, Harshad number
775 = 52 × 31, member of the Mian–Chowla sequence
776 = 23 × 97, refactorable number, number of compositions of 6 whose parts equal to q can be of q2 kinds
777 = 3 × 7 × 37, sphenic number, Harshad number, palindromic number, 3333 in senary (base 6) counting.
The numbers 3 and 7 are considered both "perfect numbers" under Hebrew tradition.
778 = 2 × 389, nontotient, Smith number
779 = 19 × 41, highly cototient number
780s
780 = 22 × 3 × 5 × 13, sum of four consecutive primes in a quadruplet (191, 193, 197, and 199); sum of ten consecutive primes (59 + 61 + 67 + 71 + 73 + 79 + 83 + 89 + 97 + 101), 39th triangular number,a hexagonal number, Harshad number
780 and 990 are the fourth smallest pair of triangular numbers whose sum and difference (1770 and 210) are also triangular.
781 = 11 × 71. 781 is the sum of powers of 5/repdigit in base 5 (11111), Mertens function(781) = 0, lazy caterer number
782 = 2 × 17 × 23, sphenic number, nontotient, pentagonal number, Harshad number, also, 782 gear used by U.S. Marines
783 = 33 × 29, heptagonal number
784 = 24 × 72 = 282 = , the sum of the cubes of the first seven positive integers, happy number
785 = 5 × 157, Mertens function(785) = 0, number of series-reduced planted trees with 6 leaves of 2 colors
786 = 2 × 3 × 131, sphenic number, admirable number. See also its use in Muslim numerological symbolism.
787 = prime number, sum of five consecutive primes (149 + 151 + 157 + 163 + 167), Chen prime, lucky prime, palindromic prime.
788 = 22 × 197, nontotient, number of compositions of 12 into parts with distinct multiplicities
789 = 3 × 263, sum of three consecutive primes (257 + 263 + 269), Blum integer
790s
790 = 2 × 5 × 79, sphenic number, nontotient, a Harshad number in bases 2, 7, 14 and 16, an aspiring number, the aliquot sum of 1574.
791 = 7 × 113, centered tetrahedral number, sum of the first twenty-two primes, sum of seven consecutive primes (101 + 103 + 107 + 109 + 113 + 127 + 131)
792 = 23 × 32 × 11, number of integer partitions of 21, binomial coefficient , Harshad number, sum of the nontriangular numbers between successive triangular numbers
793 = 13 × 61, Mertens function(793) = 0, star number, happy number
794 = 2 × 397 = 16 + 26 + 36, nontotient
795 = 3 × 5 × 53, sphenic number, Mertens function(795) = 0, number of permutations of length 7 with 2 consecutive ascending pairs
796 = 22 × 199, sum of six consecutive primes (113 + 127 + 131 + 137 + 139 + 149), Mertens function(796) = 0
797 = prime number, Chen prime, Eisenstein prime with no imaginary part, palindromic prime, two-sided prime, prime index prime.
798 = 2 × 3 × 7 × 19, Mertens function(798) = 0, nontotient, product of primes indexed by the prime exponents of 10!
799 = 17 × 47, smallest number with digit sum 25
References
Integers | 700 (number) | Mathematics | 3,658 |
14,517,678 | https://en.wikipedia.org/wiki/Melanin-concentrating%20hormone%20receptor%201 | Melanin-concentrating hormone receptor 1, also known as MCH1, is one of the melanin-concentrating hormone receptors found in all mammals.
The protein encoded by this gene, a member of the G protein-coupled receptor family 1, is an integral plasma membrane protein which binds melanin-concentrating hormone. The encoded protein can inhibit cAMP accumulation and stimulate intracellular calcium flux, and is probably involved in the neuronal regulation of food consumption. Although structurally similar to somatostatin receptors, this protein does not seem to bind somatostatin.
Function
MCH1 is thought to have a number of functions including in the regulation of appetite, and in stress, anxiety and depression.
Selective ligands
Agonists
Melanin concentrating hormone (MCH)
S-36057 - modified MCH 6-13 fragment substituted with 3-iodotyrosine at N-terminus via dioxyoctanoyl linker, used as 125I radioligand for mapping MCH1 in vivo.
LK-184 (Procter & Gamble) is one pick
Antagonists
ATC-0065
ATC-0175
GW-803,430
NGD-4715
SNAP-7941
SNAP-94847
T-226,296
See also
Melanin-concentrating hormone receptor
References
Further reading
External links
G protein-coupled receptors
Human proteins | Melanin-concentrating hormone receptor 1 | Chemistry | 282 |
49,581,858 | https://en.wikipedia.org/wiki/Ralaniten%20acetate | Ralaniten acetate (developmental code name EPI-506) is a first-in-class antiandrogen that targets the N-terminal domain (NTD) of the androgen receptor (AR) developed by ESSA Pharmaceuticals and was under investigation for the treatment of prostate cancer. This mechanism of action is believed to allow the drug to block signaling from the AR and its splice variants. EPI-506 is a derivative of bisphenol A and a prodrug of ralaniten (EPI-002), one of the four stereoisomers of EPI-001, and was developed as a successor of EPI-001. The drug reached phase I/II prior to the discontinuation of its development. It showed signs of efficacy in the form of prostatic specific antigen (PSA) decreases (4–29%) predominantly at higher doses (≥1,280 mg) in some patients but also caused side effects and was discontinued by its developer in favor of next-generation AR NTD inhibitors with improved potency and tolerability.
See also
EPI-7386
N-Terminal domain antiandrogen
References
External links
Ralaniten acetate - AdisInsight
Abandoned drugs
Acetate esters
Alkylating agents
2,2-Bis(4-hydroxyphenyl)propanes
Halohydrins
Nonsteroidal antiandrogens
Organochlorides
Prodrugs | Ralaniten acetate | Chemistry | 299 |
65,841,325 | https://en.wikipedia.org/wiki/EURO%20Advanced%20Tutorials%20in%20Operational%20Research | The EURO Advanced Tutorials in Operational Research are a series of short books devoted to advanced topics in Operational Research that are not available in textbooks. The scope of a Tutorial is to provide more detail about advanced topics in a relevant field to researchers and practitioners. The Book Series was established in 2014 and is published by Springer Science+Business Media. It is an official publication of the Association of European Operational Research Societies.
Renata Mansini, Włodzimierz Ogryczak, M. Grazia Speranza - Linear and Mixed Integer Programming for Portfolio Optimization
Alves, C., Clautiaux, F., de Carvalho, J.V., Rietz, J. - Dual-Feasible Functions for Integer Programming and Combinatorial Optimization
Henggeler Antunes, Carlos, João Alves, Maria, Clímaco, João - Multiobjective Linear and Integer Programming
Lancia, Giuseppe, Serafini, Paolo - Compact Extended Linear Programming Models
Duarte, Abraham, Laguna, Manuel, Marti, Rafael - Metaheuristics for Business Analytics
Zhao, Lima, Huchzermeier, Arnd - Supply Chain Finance
van Wageningen-Kessels, Femke - Traffic Flow Modelling
Doumpos, M., Lemonakis, C., Niklis, D., Zopounidis, C. - Analytical Techniques in the Assessment of Credit Risk
Bigi, G., Castellani, M., Pappalardo, M., Passacantando, M. - Nonlinear Programming Techniques for Equilibria
Vansteenwegen, Pieter, Gunawan, Aldy - Orienteering Problems: Models and Algorithms for Vehicle Routing Problems with Profits
Fajardo, M.D., Goberna, M.A., Rodríguez, M.M.L., Vicente-Pérez, J. - Even Convexity and Optimization
Menoncin, Francesco - Risk Management for Pension Funds
Brandimarte, Paolo - From Shortest Paths to Reinforcement Learning
Maniezzo, Vittorio, Boschetti, Marco Antonio, Stützle, Thomas - Matheuristics
Anjos, Miguel F., Vieira, Manuel V.C. - Facility layout. Mathematical optimization techniques and engineering (Review )
Celso C. Ribeiro, Sebastian Urrutia, Dominique de Werra - Combinatorial Models for Scheduling Sports Tournaments
The editors are
M. Grazia Speranza
Kenneth Sörensen
The past editors are
José Fernando Oliveira (2014-2023)
References
External links
Operations research | EURO Advanced Tutorials in Operational Research | Mathematics | 525 |
6,050,735 | https://en.wikipedia.org/wiki/Step%20potential | In quantum mechanics and scattering theory, the one-dimensional step potential is an idealized system used to model incident, reflected and transmitted matter waves. The problem consists of solving the time-independent Schrödinger equation for a particle with a step-like potential in one dimension. Typically, the potential is modeled as a Heaviside step function.
Calculation
Schrödinger equation and potential function
The time-independent Schrödinger equation for the wave function is
where Ĥ is the Hamiltonian, ħ is the reduced Planck constant, m is the mass, E the energy of the particle. The step potential is simply the product of V0, the height of the barrier, and the Heaviside step function:
The barrier is positioned at x = 0, though any position x0 may be chosen without changing the results, simply by shifting position of the step by −x0.
The first term in the Hamiltonian, is the kinetic energy of the particle.
Solution
The step divides space in two parts: x < 0 and x > 0. In any of these parts the potential is constant, meaning the particle is quasi-free, and the solution of the Schrödinger equation can be written as a superposition of left and right moving waves (see free particle)
where subscripts 1 and 2 denote the regions x < 0 and x > 0 respectively, the subscripts (→) and (←) on the amplitudes A and B denote the direction of the particle's velocity vector: right and left respectively.
The wave vectors in the respective regions being
both of which have the same form as the De Broglie relation (in one dimension)
.
Boundary conditions
The coefficients A, B have to be found from the boundary conditions of the wave function at x = 0. The wave function and its derivative have to be continuous everywhere, so:
Inserting the wave functions, the boundary conditions give the following restrictions on the coefficients
Transmission and reflection
It is useful to compare the situation to the classical case. In both cases, the particle behaves as a free particle outside of the barrier region. A classical particle with energy E larger than the barrier height V0 will be slowed down but never reflected by the barrier, while a classical particle with E < V0 incident on the barrier from the left would always be reflected. Once we have found the quantum-mechanical result we will return to the question of how to recover the classical limit.
To study the quantum case, consider the following situation: a particle incident on the barrier from the left side A→. It may be reflected (A←) or transmitted (B→). Here and in the following assume E > V0.
To find the amplitudes for reflection and transmission for incidence from the left, we set in the above equations A→ = 1 (incoming particle), A← = (reflection), B← = 0 (no incoming particle from the right) and B→ = (transmission ). We then solve for T and R.
The result is:
The model is symmetric with respect to a parity transformation and at the same time interchange k1 and k2. For incidence from the right we have therefore the amplitudes for transmission and reflection
Analysis of the expressions
Energy less than step height (E < V0)
For energies E < V0, the wave function to the right of the step is exponentially decaying over a distance .
Energy greater than step height (E > V0)
In this energy range the transmission and reflection coefficient differ from the classical case. They are the same for incidence from the left and right:
In the limit of large energies E ≫ V0, we have k1 ≈ k2 and the classical result T = 1, R = 0 is recovered.
Thus there is a finite probability for a particle with an energy larger than the step height to be reflected.
Negative steps
In the case of a large positive E, and a small positive step, then T is almost 1.
But, in the case of a small positive E and a large negative V, then R is almost 1.
In other words, a quantum particle reflects off a large potential drop (just as it does off a large potential step). This makes sense in terms of impedance mismatches, but it seems classically counter-intuitive...
Classical limit
The result obtained for R depends only on the ratio E/V0. This seems superficially to violate the correspondence principle, since we obtain a finite probability of reflection regardless of the value of the Planck constant or the mass of the particle. For example, we seem to predict that when a marble rolls to the edge of a table, there can be a large probability that it is reflected back rather than falling off. Consistency with classical mechanics is restored by eliminating the unphysical assumption that the step potential is discontinuous. When the step function is replaced with a ramp that spans some finite distance w, the probability of reflection approaches zero in the limit , where k is the wavenumber of the particle.
Relativistic calculation
The relativistic calculation of a free particle colliding with a step potential can be obtained using relativistic quantum mechanics. For the case of 1/2 fermions, like electrons and neutrinos, the solutions of the Dirac equation for high energy barriers produce transmission and reflection coefficients that are not bounded. This phenomenon is known as the Klein paradox. The apparent paradox disappears in the context of quantum field theory.
Applications
The Heaviside step potential mainly serves as an exercise in introductory quantum mechanics, as the solution requires understanding of a variety of quantum mechanical concepts: wavefunction normalization, continuity, incident/reflection/transmission amplitudes, and probabilities.
A similar problem to the one considered appears in the physics of normal-metal superconductor interfaces. Quasiparticles are scattered at the pair potential which in the simplest model may be assumed to have a step-like shape. The solution of the Bogoliubov-de Gennes equation resembles that of the discussed Heaviside-step potential. In the superconductor normal-metal case this gives rise to Andreev reflection.
See also
Rectangular potential barrier
Finite potential well
Infinite potential well
Delta potential barrier
Finite potential barrier
References
Sources
Quantum Mechanics Demystified, D. McMahon, Mc Graw Hill (USA), 2006,
Quantum Physics of Atoms, Molecules, Solids, Nuclei, and Particles (2nd Edition), R. Eisberg, R. Resnick, John Wiley & Sons, 1985,
Quantum Mechanics, E. Abers, Pearson Ed., Addison Wesley, Prentice Hall Inc, 2004,
Elementary Quantum Mechanics, N.F. Mott, Wykeham Science, Wykeham Press (Taylor & Francis Group), 1972,
Stationary States, A. Holden, College Physics Monographs (USA), Oxford University Press, 1971,
Quantum mechanics, E. Zaarur, Y. Peleg, R. Pnini, Schaum's Outlines, Mc Graw Hill (USA), 1998,
Further reading
The New Quantum Universe, T.Hey, P.Walters, Cambridge University Press, 2009, .
Quantum Field Theory, D. McMahon, Mc Graw Hill (USA), 2008,
Quantum mechanics, E. Zaarur, Y. Peleg, R. Pnini, Schaum's Easy Outlines Crash Course, Mc Graw Hill (USA), 2006,
Quantum mechanical potentials
Schrödinger equation
Quantum models
Scattering theory | Step potential | Physics,Chemistry | 1,533 |
5,342,457 | https://en.wikipedia.org/wiki/SPARCstation%20ZX | The SPARCstation ZX is a computer workstation produced by Sun Microsystems and launched in August 1993. It was end-of-lifed in March 1994. The original price was US$19,995.00.
The SPARCstation ZX was identical to the SPARCstation LX, with the addition of a Sun ZX (also known as LEO) accelerated 3D framebuffer card. This was a double-width, double-decked SBus card providing 24-bit color and a performance of 750,000 3D vectors per second and 310,000 triangle mesh/second.
See also
SPARCstation
SPARCstation LX
References
Sun-4/10/15/30 Handbook
Exciting New Graphics, Imaging And Video Solutions On Sun, SunFLASH, Vol 55 #7
Sun workstations
SPARC microprocessor products | SPARCstation ZX | Technology | 176 |
24,685,572 | https://en.wikipedia.org/wiki/Ssh-keygen | ssh-keygen is a standard component of the Secure Shell (SSH) protocol suite found on Unix, Unix-like and Microsoft Windows computer systems used to establish secure shell sessions between remote computers over insecure networks, through the use of various cryptographic techniques. The ssh-keygen utility is used to generate, manage, and convert authentication keys.
Overview
ssh-keygen is able to generate a key using one of three different digital signature algorithms. With the help of the ssh-keygen tool, a user can create passphrase keys for any of these key types. To provide for unattended operation, the passphrase can be left empty, albeit at increased risk. These keys differ from keys used by the related tool GNU Privacy Guard.
OpenSSH-based client and server programs have been included in Windows 10 since version 1803. The SSH client and key agent are enabled and available by default and the SSH server is an optional Feature-on-Demand.
Key formats supported
Example: ssh-keygen -t rsa
RTFM
Originally, with SSH protocol version 1 (now deprecated) only the RSA algorithm was supported. As of 2016, RSA is still considered strong, but the recommended key length has increased over time.
The SSH protocol version 2 additionally introduced support for the DSA algorithm. DSA is now considered weak and was disabled in OpenSSH 7.0.
Subsequently, OpenSSH added support for a third digital signature algorithm, ECDSA (this key format no longer uses the previous PEM file format for private keys, nor does it depend upon the OpenSSL library to provide the cryptographic implementation).
A fourth format is supported using Ed25519, originally developed by independent cryptography researcher Daniel J. Bernstein.
Command syntax
The syntax of the ssh-keygen command is as follows:
ssh-keygen [options]
Some important options of the ssh-keygen command are as follows:
Files used by the ssh-keygen utility
The ssh-keygen utility generates files for storing public and private keys.
Note : they are stored in $HOME/.ssh/ as follows:
SSH protocol version 2
$HOME/.ssh/id_dsa: The $HOME/.ssh/id_dsa file contains the protocol version 2 DSA authentication identity of the user.
$HOME/.ssh/id_dsa.pub: The $HOME/.ssh/id_dsa.pub file contains the DSA public key for authentication when you are using the SSH protocol version 2. A user should copy its contents in the $HOME/.ssh/authorized_keys file of the remote system where a user wants to log in using DSA authentication.
$HOME/.ssh/id_rsa: The $HOME/.ssh/id_rsa file contains the protocol version 2 RSA authentication identity of the user. This file should not be readable by anyone but the user.
$HOME/.ssh/id_rsa.pub: The $HOME/.ssh/id_rsa.pub file contains the protocol version 2 RSA public key for authentication. The contents of this file should be added to $HOME/.ssh/authorized_keys on all computers where a user wishes to log in using public key authentication.
SSH protocol version 1
$HOME/.ssh/identity: The $HOME/.ssh/identity file contains the RSA private key when using the SSH protocol version 1.
$HOME/.ssh/identity.pub: The $HOME/.ssh/identity.pub file contains the RSA public key for authentication when you are using the SSH protocol version 1. A user should copy its contents in the $HOME/.ssh/authorized_keys file of the remote system where a user wants to log in using RSA authentication.
References
External links
Generating an SSH key, a guide from GitHub
ssh-keygen manual from the OpenBSD project
Linux man page from die.net
Generating SSH Key Pair on Linux and Mac from ifixlinux.com
Operating system security
Unix network-related software
Secure Shell | Ssh-keygen | Technology | 876 |
7,320,339 | https://en.wikipedia.org/wiki/Nitrogen%20rejection%20unit | A nitrogen rejection unit (NRU) selectively removes nitrogen from a gas. The name can be applied to any system that removes nitrogen from natural gas.
For high flow-rate applications, typically above per day at standard pressure, cryogenic processing is the norm. This is a distillation process which utilizes the different volatilities of methane (boiling point of −161.6 °C) and nitrogen (boiling point of −195.69 °C) to achieve separation. In this process, a system of compression and distillation columns drastically reduces the temperature of the gas mixture to a point where methane is liquified and the nitrogen is not. For smaller applications, a series of heat exchangers may be used as an alternative to distillation columns.
For smaller volumes of gas, a system utilizing pressure swing adsorption (PSA) is a more typical method of separation. In PSA, methane and nitrogen can be separated by using an adsorbent with an aperture size very close to the molecular diameter of the larger species, in this case methane (3.8 angstroms). This means nitrogen is able to diffuse through the adsorbent, filling adsorption sites, whilst methane is not. This results in a purified natural gas stream that fits pipeline specifications. The adsorbent can then be regenerated, leaving a highly pure nitrogen stream. PSA is a flexible method for nitrogen rejection, being applied to both small and large flow rates.
The operating conditions of various PSA units are quite variable. Depending on the vendor, high degrees of pretreatment of the gas stream (removal of water vapor and heavy hydrocarbons) may be necessary for the system to operate optimally and without damage to the adsorbent material. Moreover, the degree of hydrocarbon recoveries (75% vs 95%) and purities can vary considerably. The economic viability of any PSA unit will be highly dependent on such factors.
An estimated 25% of the US natural gas reserves contain unacceptably large quantities of nitrogen. Nitrogen is inert and lowers the energy value per volume of natural gas. It also takes up capacity in pipelines that could be used for valuable methane.
Pipeline specifications for nitrogen are extremely variable, though no more than 4% nitrogen is a typical specification.
References
External links
G.I. Dynamics Cryogenic Nitrogen Rejection Technology
California Energy Commission Glossary
Molecular Gate Adsorption Technology
Further reading
Natural gas technology
Industrial gases | Nitrogen rejection unit | Chemistry | 510 |
30,001,250 | https://en.wikipedia.org/wiki/Hit-testing | In computer graphics programming, hit-testing (hit detection, picking, or pick correlation) is the process of determining whether a user-controlled cursor (such as a mouse cursor or touch-point on a touch-screen interface) intersects a given graphical object (such as a shape, line, or curve) drawn on the screen. Hit-testing may be performed on the movement or activation of a mouse or other pointing device.
Hit-testing is used by GUI environments to respond to user actions, such as selecting a menu item or a target in a game based on its visual location. In web programming languages such as HTML, SVG, and CSS, this is associated with the concept of pointer-events (e.g. user-initiated cursor movement or object selection).
Collision detection is a related concept for detecting intersections of two or more different graphical objects, rather than intersection of a cursor with one or more graphical objects.
Algorithm
There are many different algorithms that may be used to perform hit-testing, with different performance or accuracy outcomes. One common hit-test algorithm for axis aligned bounding boxes. A key idea is that the box being tested must be either entirely above, entirely below, entirely to the right or left of the current box. If this is not possible, they are colliding. Example logic is presented in the pseudo-code below:
function HitTest(Rectangle r1, Rectangle r2) returns boolean
{
return not((r1.X + r1.Width < r2.X) or (r1.X > r2.X + r2.Width) or (r1.Y + r1.Height < r2.Y) or (r1.Y > r2.Y + r2.Height));
}
In Python:
def hit_test(r1: Rectangle, r2: Rectangle) -> bool:
"""Return true if it hits else return false."""
return (
not (r1.x + r1.width < r2.x)
or (r1.x > r2.x + r2.width)
or (r1.y + r1.Height < r2.y)
or (r1.y > r2.y + r2.height)
)
See also
Point in polygon
Computational geometry
Collision detection
User interface
References
External links
MSDN: Hit Testing in the Visual Layer
MSDN: Hit Testing Lines and Curves
Articles with example Python (programming language) code
Computer graphics
User interfaces
Video game development | Hit-testing | Technology | 538 |
69,051,116 | https://en.wikipedia.org/wiki/Reverse%20search%20warrant | A reverse search warrant is a type of search warrant used in the United States, in which law enforcement obtains a court order for information from technology companies to identify a group of people who may be suspects in a crime. They differ from traditional search warrants, which typically apply to specific individuals. Geo-fence warrants, which seek data on mobile phone users who were in a specific location at a given time, and keyword warrants, which request information on users who searched specific phrases, are two types of reverse search warrants.
History
Reverse location warrants were first used in 2016, and have become increasingly widely used by United States law enforcement. Google reported that it had received 982 reverse location warrants in 2018, 8,396 in 2019, and 11,554 in 2020. A 2021 transparency report showed that 25% of data requests from law enforcement to Google were geo-fence data requests. Google is the most common recipient of reverse location warrants and the main provider of such data, although companies including Apple, Snapchat, Lyft, and Uber have also received such warrants.
Types
Geo-fence warrant
Geo-fence warrants, also called reverse location warrants, seek to compel data from search engine companies and other technology companies that collect mobile location data, to determine which users may have been in a specific location at a given time.
Keyword warrant
Keyword search warrants seek to compel search engine companies to release data on users who have searched specific phrases—for example, an address that was later the location of a crime. Keyword warrants are comparatively rare but have been used to request data from companies including Google, Microsoft, and Yahoo since at least 2017.
Genealogy database warrants
Companies that collect DNA data have received warrants from law enforcement seeking to access their databases. GEDMatch and Family Tree DNA have cooperated with such requests, while larger companies like Ancestry.com and 23andMe have stated they would fight such attempts by law enforcement. These warrants attempt to connect DNA samples from crime scenes with data belonging to commercial DNA testing companies. Even if a perpetrator of a crime has not submitted their data to such companies, DNA samples belonging to relatives, even quite distant ones, have been used to identify suspects and criminals.
Legality
Some lawyers and privacy experts have argued reverse search warrants are unconstitutional under the Fourth Amendment to the United States Constitution or unauthorized by the Stored Communications Act, notwithstanding the third-party doctrine (there is no reasonable expectation of privacy for information voluntarily given to third parties). The Fourth Amendment specifies that warrants may only be issued "upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized." Some lawyers, legal scholars, and privacy experts have likened reverse search warrants to general warrants, which are not permitted by the Fourth Amendment because they lack specificity in terms of the place to be searched or the items to be seized. Although most judges have authorized geofence warrants, at least two federal judges have ruled that such warrants violate the Fourth Amendment's requirements of probable cause and particularity.
Groups including the New York Civil Liberties Union and the Surveillance Technology Oversight Project joined state senator Zellnor Myrie and assembly member Dan Quart in 2020 to begin work on legislation in New York that would prohibit both geo-fence and keyword warrants. Groups including the Electronic Frontier Foundation have opposed geofence warrants in amicus briefs filed in motions to quash such orders to disclose geofence data.
See also
Dragnet (policing)
References
Internet privacy
Law enforcement terminology
Searches and seizures
Warrants | Reverse search warrant | Engineering | 748 |
33,372,824 | https://en.wikipedia.org/wiki/Tylopilus%20tabacinus | Tylopilus tabacinus is a species of bolete fungus in the family Boletaceae. It is characterized by a tawny-brown cap measuring up to in diameter, and a reticulated stem up to long by thick. A characteristic microscopic feature is the distinctive crystalline substance encrusted on the hyphae in the surface of the cap. The species is known from the eastern United States from Florida north to Rhode Island, and west to Mississippi, and from eastern Mexico. It is a mycorrhizal species, and associates with oak and beech trees.
Taxonomy
The species was first described by American mycologist Charles Horton Peck in 1896 under the name Boletus tabacinus. Peck collected the type specimens in red clay on the bank of a roadside ditch in Alabama. William Alphonso Murrill transferred the species to his then newly described genus Ceriomyces in 1909; this genus has since been subsumed into Boletus. Rolf Singer moved the species to Tylopilus in 1944. Although Singer considered B. tabacinus to be the same species as Boletus pisciodorus, this opinion was contested by William Alphonso Murrill, who, after examining the type specimens of both species, considered them to be distinct. Murrill's conclusion was later corroborated by Alexander H. Smith and Harry D. Thiers in the 1971 monograph of boletes. In 1945, Singer defined the varieties amarus and dubius that he collected in Florida.
Description
The caps of the fruit body initially have a rounded shape, but later become broadly convex and eventually flattened in age; they reach dimensions of wide. The color ranges from yellowish brown to orangish brown to tobacco brown. The cap surface is dry with a somewhat velvet-like texture, although in larger specimens the surface is areolate (divided into small areas by cracks). The cap margin is even and wavy.
The tubes on the underside of the cap (comprising the hymenium) are dark brown to cinnamon-brown. The angular to circular pores are lighter in color than the tubes and number about 1–2 pores per millimeter, while the tubes are up to long. The pore surface is depressed around the stem. The cap flesh is white, but typically stains purplish buff or pinkish buff when cut. The stipe typically measures by thick. When young, it is bulbous, but matures to become more or less equal in width throughout. Its color is roughly the same as the cap, although it tends to be slightly darker in the upper portion, where it is reticulate (covered with a net-like patterns of ridges). The odor of the mushroom has been described variously as "not distinctive, fruity, fishy, or pungent", while the taste is indistinct to slightly bitter. The edibility of the mushroom is unknown. The variety amarus is similar in appearance, but has bitter-tasting flesh, while variety dubius has a lighter colored-cap and less distinctive reticulations on the apex of the stem.
Fruit bodies produce a spore print ranging in color from pinkish brown to reddish brown. The spores measure 10–17 by 3.5–4.5 μm, and are fusoid (somewhat spindle-shaped) to elliptical. Spores have a smooth surface, and a plage (a depressed area where the spore was once attached to the basidium via the sterigma). The spore walls are thin, up to 0.2 μm. They are pale yellow to cream green in a solution of potassium hydroxide, pale yellow-rust in Melzer's reagent, and blue in Methyl blue; without stain, they appear hyaline to pale yellow. The cap cuticle is an interwoven trichodermium—a cellular arrangement whereby the hyphae are of roughly equal length and arranged perpendicularly to the surface. The terminal (end) cells of the trichodermium are 6.5–11.5 μm in diameter, and roughly equal in width throughout their length. They are encrusted with a crystalline substance, a feature that is uncommon in the Boletaceae. The hyphae of the tubes are 5.0–13.0 μm in diameter. Clamp connections are absent from the hyphae.
The basidia (spore-bearing cells) of T. tabacinus are club-shaped and measure 23.5–37.0 by 8.5–13.0 μm. The pleurocystidia (cystidia found on the inner surface of the tubes) are 45.0–60.0 by 6.5–12.5 μm, lanceolate (lance-shaped) to narrowly fusoid-ventricose (enlarged in the middle and somewhat spindle-shaped). Cheilocystidia (cystidia on the outer edges of the tubes) are absent. The caulocystidia (cystidia on the stem) form the reticulations on the stem; they are usually club-shaped and measure 21.0–40.5 by 6.5–10.5 μm.
Similar species
Boletus pisciodorus is similar in form to Tylopilus tabacinus. Unlike, T. tabacinus however, B. pisciodorus has spores that are hyaline in mass, and dark yellowish brown rather than hyaline when viewed with a light microscope. Further, B. pisciodorus has a fishy odor that is apparent in both fresh and dried specimens.
Habitat and distribution
Tylopilus tabacinus forms ectomycorrhizal associations with oaks, and fruit bodies are usually found solitarily, scattered, or in groups on sandy soil under oaks or in mixed oak-pine woods from July to September. In the United States, the mushroom is distributed from Florida north to Rhode Island, and west to Mississippi. It has also been collected from a montane cloud forest of Mexican Beech (Fagus grandifolia var. mexicana) in the state of Hidalgo, Mexico. The occurrence of the mushroom is "occasional to fairly common". The varieties amarus and dubius are rare, known only from their original collection locations in Gainesville, Florida.
See also
List of North American boletes
References
External links
tabacinus
Fungi described in 1896
Fungi of North America
Taxa named by Charles Horton Peck
Fungus species | Tylopilus tabacinus | Biology | 1,346 |
11,899,262 | https://en.wikipedia.org/wiki/Sound%20%28nautical%29 | In nautical terms, the word sound is used to describe the process of determining the depth of water in a tank or under a ship. Tanks are sounded to determine if they are full (for cargo tanks) or empty (to determine if a ship has been holed) and for other reasons. Soundings may also be taken of the water around a ship if it is in shallow water to aid in navigation.
Methods
Tanks may be sounded manually or with electronic or mechanical automated equipment. Manual sounding is undertaken with a sounding line- a rope with a weight on the end. Per the Code of Federal Regulations, most steel vessels with integral tanks are required to have sounding tubes and reinforcing plates under the tubes which the weight strikes when it reaches the bottom of the tank. Sounding tubes are steel pipes which lead upwards from the ships' tanks to a place on deck.
Electronic and mechanical automated sounding may be undertaken with a variety of equipment including float level sensors, capacitance sensors, sonar, etc.
See also
Depth sounding
Sources
Code of Federal Regulations, Title 46
Navigational aids
Oceanography | Sound (nautical) | Physics,Environmental_science | 220 |
5,435,686 | https://en.wikipedia.org/wiki/List%20of%20companion%20plants | This is a list of companion plants, traditionally planted together. Many more are in the list of beneficial weeds. Companion planting is thought by its practitioners to assist in the growth of one or both plants involved in the association. Possible mechanisms include attracting beneficial insects, repelling pests, or providing nutrients such as by fixing nitrogen, shade, or support. Companion plantings can be part of a biological pest control program. A large number of companion plant associations have been proposed; only a few of these have been subjected to scientific testing. Thus where a table column for example states "Helps" or "Helped by", this is to be read as meaning that traditional companion planting involves putting the named plants in that column into an association with the plant named at the left of the row, with the intention of causing the one plant to help or be helped by the other. Mechanisms that have been scientifically verified include using strongly aromatic plants to deter pests; using companions to hide crops from pests; providing plants as nurseries for beneficial insects including predators and parasitoids; trap cropping; and allelopathy, where a plant inhibits the growth of other species.
Vegetables
Fruit
Herbs
Flowers
Other
See also
Push–pull agricultural pest management
Sustainable agriculture
Sustainable landscaping
Sustainable gardening
References
Further reading
Cunningham, Sally Jean. Great Garden Companions: A companion planting system for a beautiful, chemical-free vegetable garden. 1998.
Hylton, W. The Rodale Herb Book, Eighth Printing. Rodale Press. 1974.
External links
Bohnsack, U. Companion Planting Guide.
Companion plants by Professor Stuart B. Hill Department of Entomology Macdonald College
Cass County Extension Companion Planting List
Companion Planting Infographic
+
Lists of plants
Gardening lists
Sustainable agriculture
Sustainable gardening | List of companion plants | Biology | 351 |
67,048,975 | https://en.wikipedia.org/wiki/Storiform%20pattern | A woven or storiform pattern is a histopathologic architectural pattern. The name "storiform" originates , as storiform tissue tends to resemble woven fabric on microscopy.
Storiform fibrosis is a histologic sign of IgG4-related disease, accompanied by a dense lymphoplasmocytic infiltrate, often a partially eosinophilic infiltrate and obliterative phlebitis.
See also
Histopathology, for additional patterns
References
Histopathology | Storiform pattern | Chemistry | 108 |
77,814,305 | https://en.wikipedia.org/wiki/Sh%202-140 | Sharpless 140 is an H II region and emission nebula in the Cepheus constellation, 3,000 light years from the Solar System. It is part of the Cepheus bubble. The surface of the nebula's clouds primarily consists of polycyclic aromatic hydrocarbons.
See also
Sharpless catalog
References
H II regions
Cepheus (constellation)
140 | Sh 2-140 | Astronomy | 73 |
26,633,309 | https://en.wikipedia.org/wiki/Barnes%20zeta%20function | In mathematics, a Barnes zeta function is a generalization of the Riemann zeta function introduced by . It is further generalized by the Shintani zeta function.
Definition
The Barnes zeta function is defined by
where w and aj have positive real part and s has real part greater than N.
It has a meromorphic continuation to all complex s, whose only singularities are simple poles at s = 1, 2, ..., N. For N = w = a1 = 1 it is the Riemann zeta function.
References
Zeta and L-functions | Barnes zeta function | Mathematics | 111 |
21,498,455 | https://en.wikipedia.org/wiki/Delta%200100 | The Delta 0100 series, also Delta 100, 0300 or 300 series, was an American expendable launch system which conducted orbital launches between 1968 and 1972. It was a member of the Delta family of rockets, and the first to be designated using a four digit numerical code. Two variants were flown, individually designated Delta 0300 and Delta 0900.
The Long Tank Thor, a stretched version of the Thor missile, was used as the first stage of the Delta 0100 series. Castor-2 solid rocket boosters were attached to increase thrust at lift-off, three on the 0300 variant, and nine on the 0900. The second stage was a Delta F.
Five 0100 series rockets were launched, three using the 0300 configuration, and two in the 0900 configuration. All launches occurred from Space Launch Complex 2W at Vandenberg AFB. There was one failure, the launch of ITOS E on July 16, 1973. A hydraulic pump malfunction led to loss of pressure to the second stage attitude control thrusters, causing the launch vehicle to tumble out of control and break up in the atmosphere.
The Japanese N-I launch vehicle was derived from the Delta 0300, using a Japanese LE-3 engine on the second stage.
Capabilities
Capacity of the Delta 0100:
Sun-synchronous orbit (SSO), 1450 km × 101.990°: at least .
References
Delta (rocket family) | Delta 0100 | Astronomy | 297 |
5,297,150 | https://en.wikipedia.org/wiki/Strontium%20nitrate | Strontium nitrate is an inorganic compound composed of the elements strontium, nitrogen and oxygen with the formula Sr(NO3)2. This colorless solid is used as a red colorant and oxidizer in pyrotechnics.
Preparation
Strontium nitrate is typically generated by the reaction of nitric acid on strontium carbonate.
2 HNO3 + SrCO3 → Sr(NO3)2 + H2O + CO2
Uses
Like many other strontium salts, strontium nitrate is used to produce a rich red flame in fireworks and road flares. The oxidizing properties of this salt are advantageous in such applications.
Strontium nitrate can aid in eliminating and lessening skin irritations. When mixed with glycolic acid, strontium nitrate reduces the sensation of skin irritation significantly better than using glycolic acid alone.
Biochemistry
As a divalent ion with an ionic radius similar to that of Ca2+ (1.13 Å and 0.99 Å respectively), Sr2+ ions resembles calcium's ability to traverse calcium-selective ion channels and trigger neurotransmitter release from nerve endings. It is thus used in electrophysiology experiments.
In popular culture
In his short story "A Germ-Destroyer", Rudyard Kipling refers to strontium nitrate as the main ingredient of the titular fumigant.
References
Nitrates
Oxidizing agents
Pyrotechnic colorants
Pyrotechnic oxidizers
Strontium compounds | Strontium nitrate | Chemistry | 318 |
45,267,691 | https://en.wikipedia.org/wiki/Orbicella%20franksi | Orbicella franksi, commonly known as boulder star coral, is a colonial stony coral in the family Merulinidae. It is native to shallow waters in the Caribbean Sea, the Gulf of Mexico, the Bahamas, Bermuda and Florida, and is listed as a "near-threatened species" by the International Union for Conservation of Nature.
Taxonomy
Until recently this coral, along with Orbicella faveolata, was thought to be a variety of Orbicella annularis. There is very little morphological difference between them but studies have shown differences in corallite structure, life history, allozymes and distribution. All three members of this species complex used to be placed in the genus Montastraea.
Description
Colonies of Orbicella franksi usually form massive clumps with uneven surfaces, but sometimes forms plates, and in shady positions, may be encrusting. The general colour is orange-brown, greenish-brown or greyish-brown, but the extremities of the lumps are often pale or white. The corallites (the cups in which the polyps sit) are small, measuring across. The growing edges of this coral bear both large and small corallites which is in contrast to the closely related Orbicella faveolata, which has regularly spaced corallites at its growing edges.
Distribution and habitat
Orbicella franksi is native to the Caribbean Sea and the Gulf of Mexico, including Florida, the Bahamas and Bermuda. It typically grows on fore reefs (where it may be the most common species of coral) and its depth range is but it is typically found at depths of between .
Status
Orbicella franksi seems to be more resistant to coral diseases than some members of its genus, but is still susceptible to coral plague, yellow-band disease, black band disease and coral bleaching. The major threats it faces include climate change, ocean acidification and destruction of its reef habitat. The International Union for Conservation of Nature has rated its conservation status as being near threatened.
References
Merulinidae
Coral reefs
Animals described in 1895
ESA threatened species
Taxobox binomials not recognized by IUCN | Orbicella franksi | Biology | 439 |
44,232,885 | https://en.wikipedia.org/wiki/Honda%20UNI-CUB | The Honda UNI-CUB is a concept 2-axis self-balancing personal transporter for use in barrier-free indoor environments, and shown at the Osaka Motor Show 2013.
History
As a successor to the 2009 Honda U3-X, it was demonstrated at the Osaka Motor Show 2013. A launch date has not yet been announced.
Design and operation
Controlled by weight-shifting, similar manner as that of the Segway PT, the unit is fully self-balancing and can move in any direction, including sideways.
There are two wheels, the larger driving wheel for travelling in a forward direction, and a trailing steering wheel at 90 degrees to this one. Both the drive wheel and the steering wheel however are constructed of multiple smaller 'planet' wheels that allow the wheel to be moved laterally. When moving forward the main wheel will be powered and the smaller planet wheels on the steering wheel will rotate to avoid the steering wheel dragging. To turn the steering wheel is rotated. To balance from side to side, or to self-balance laterally, the planet wheels on the drive wheel will be powered appropriately.
Measuring 510 x 315 x 620 mm and weighing 25 kg, the UNI-CUB is powered by a lithium-ion battery and has a 6 km/h top speed and 6 km range. The seat height is 620 mm, while footrests are designed to double as support stands.
References
External links
Details of traction system
UNI-CUB video and information
History and gallery of prototypes
Personal transporters
Japanese inventions
Battery electric vehicles
Mobility devices
One-wheeled balancing robots
Honda concept vehicles
Robotics at Honda | Honda UNI-CUB | Physics | 323 |
3,047,078 | https://en.wikipedia.org/wiki/VMDS | VMDS abbreviates the relational database technology called Version Managed Data Store provided by GE Energy as part of its Smallworld technology platform and was designed from the outset to store and analyse the highly complex spatial and topological networks typically used by enterprise utilities such as power distribution and telecommunications.
VMDS was originally introduced in 1990 as has been improved and updated over the years. Its current version is 6.0.
VMDS has been designed as a spatial database. This gives VMDS a number of distinctive characteristics when compared to conventional attribute only relational databases.
Distributed server processing
VMDS is composed of two parts: a simple, highly scalable data block server called SWMFS (Smallworld Master File Server) and an intelligent client API written in C and Magik. Spatial and attribute data are stored in data blocks that reside in special files called data store files on the server. When the client application requests data it has sufficient intelligence to work out the optimum set of data blocks that are required. This request is then made to SWMFS which returns the data to the client via the network for processing.
This approach is particularly efficient and scalable when dealing with spatial and topological data which tends to flow in larger volumes and require more processing then plain attribute data (for example during a map redraw operation). This approach makes VMDS well suited to enterprise deployment that might involve hundreds or even thousands of concurrent clients.
Support for long transactions
Relational databases support short transactions in which changes to data are relatively small and are brief in terms in duration (the maximum period between the start and the end of a transaction is typically a few seconds or less).
VMDS supports long transactions in which the volume of data involved in the transaction can be substantial and the duration of the transaction can be significant (days, weeks or even months). These types of transaction are common in advanced network applications used by, for example, power distribution utilities.
Due to the time span of a long transaction in this context the amount of change can be significant (not only within the scope of the transaction, but also within the context of the database as a whole). Accordingly, it is likely that the same record might be changed more than once. To cope with this scenario VMDS has inbuilt support for automatically managing such conflicts and allows applications to review changes and accept only those edits that are correct.
Spatial and topological capabilities
As well as conventional relational database features such as attribute querying, join fields, triggers and calculated fields, VMDS has numerous spatial and topological capabilities. This allows spatial data such as points, texts, polylines, polygons and raster data to be stored and analysed.
Spatial functions include: find all features within a polygon, calculate the Voronoi polygons of a set of sites and perform a cluster analysis on a set of points.
Vector spatial data such as points, polylines and polygons can be given topological attributes that allow complex networks to be modelled. Network analysis engines are provided to answer questions such as find the shortest path between two nodes or how to optimize a delivery route (the travelling salesman problem). A topology engine can be configured with a set of rules that define how topological entities interact with each other when new data is added or existing data edited.
Data abstraction
In VMDS all data is presented to the application as objects. This is different from many relational databases that present the data as rows from a table or query result using say JDBC. VMDS provides a data modelling tool and underlying infrastructure as part of the Smallworld technology platform that allows administrators to associate a table in the database with a Magik exemplar (or class). Magik get and set methods for the Magik exemplar can be automatically generated that expose a table's field (or column). Each VMDS row manifests itself to the application as an instance of a Magik object and is known as an RWO (or real world object). Tables are known as collections in Smallworld parlance.
# all_rwos hold all the rwos in the database and is heterogeneous
all_rwos << my_application.rwo_set()
# valve_collection holds the valve collection
valves << all_rwos.select(:collection, {:valve})
number_of_valves << valves.size
Queries are built up using predicate objects:
# find 'open' valves.
open_valves << valves.select(predicate.eq(:operating_status, "open"))
number_of_open_valves << open_valves.size
_for valve _over open_valves.elements()
_loop
write(valve.id)
_endloop
Joins are implemented as methods on the parent RWO. For example, a manager might have several employees who report to him:
# get the employee collection.
employees << my_application.database.collection(:gis, :employees)
# find a manager called 'Steve' and get the first matching element
steve << employees.select(predicate.eq(:name, "Steve").and(predicate.eq(:role, "manager")).an_element()
# display the names of his direct reports. name is a field (or column)
# on the employee collection (or table)
_for employee _over steve.direct_reports.elements()
_loop
write(employee.name)
_endloop
Performing a transaction:
# each key in the hash table corresponds to the name of the field (or column) in
# the collection (or table)
valve_data << hash_table.new_with(
:asset_id, 57648576,
:material, "Iron")
# get the valve collection directly
valve_collection << my_application.database.collection(:gis, :valve)
# create an insert transaction to insert a new valve record into the collection a
# comment can be provide that describes the transaction
transaction << record_transaction.new_insert(valve_collection, valve_data, "Inserted a new valve")
transaction.run()
See also
Smallworld Technical Paper No. 8 - GIS Databases Are Different
List of relational database management systems
List of object-relational database management systems
Spatial database
Multiversion concurrency control
Data management
GIS software | VMDS | Technology | 1,327 |
66,216,792 | https://en.wikipedia.org/wiki/Thiazovivin | Thiazovivin is a drug which acts as a potent and selective inhibitor of the enzyme Rho kinase. It is used alongside a cocktail of other growth factors and modulators in cell culture techniques for the generation of induced pluripotent stem cells, which can then be used for a wide variety of applications.
See also
Rho kinase inhibitor
References
Enzyme inhibitors
Thiazoles
Pyrimidines
Amides
Amines | Thiazovivin | Chemistry | 89 |
51,511,566 | https://en.wikipedia.org/wiki/Weatherbird | The Weatherbird is a cartoon character and a single-panel comic. It is printed on the front of the St. Louis Post-Dispatch and has been in the paper continuously since 1901, making it the longest-running American newspaper cartoon and a mascot of the newspaper.
Cartoonists
The Weatherbird, in its long run, has been drawn by just six cartoonists (three of them, by coincidence, named Martin):
Harry B. Martin (1901 – 1903)
Oscar Chopin (1903 – 1910)
S. Carlisle Martin (1910 – 1932)
Amadee Wohlschlaeger (1932 – 1981)
Albert Schweitzer (1981 – 1986)
Dan Martin (1986 – present ())
The character first appeared on February 11, 1901, Harry B. Martin originated the character, which was originally called "Dickey Bird" ('dicky-bird' is a generic slang term for any small bird). Martin had originally intended to rotate through just a few versions of the bird – one for rain, one for heat, etc. – but readers asked for a new drawing each day, which he then provided.
Martin later moved to New York where he drew the strips It Happened in Birdland (1907–1909) and Inbad the Tailor (1911–1912, for the New York American). Martin became a golf correspondent and an authority on golf (writing 15 books on the subject) and a founder of the American PGA.
Oscar Charles Chopin (1873 – 1932) inherited the Weatherbird from Martin, drawing it until 1910.
S. Carlisle Martin took over the Weatherbird in 1910. He started the tradition of making the Weatherbird comment on the news in addition to the weather, and started a pattern of six words or less for the bird's comments. He was assisted by Carlos Hurd, and drew the Weatherbird until his death in 1932.
In 1912, the Post-Dispatch began running a full-page, multiple-panel color strip on Sunday, titled "Jinx and the Weather Bird Family", and featuring the Weatherbird (called "George" in the strip), his wife, and their mischievous Katzenjammer Kids-like children in various putatively comical escapades. (Jinx was an imp who observed or initiated the hijinks; later the strip was later retitled to just "The Weather Bird Family".) Carlisle Martin drew the strip, but the scripts were by Jean Knott, who later drew and wrote strips in New York. The strip apparently did not last past 1912.
Amadee Wohlschlaeger had the longest tenure as Weatherbird artist: just short of fifty years. Wohlschlaeger was also the Post-Dispatch sports page cartoonist and drew for the Sporting News. Wohlschlaeger recalled that when barely out of his teens "I was doing sports art for the Post and when Carlisle died, I stayed up all night and drew 12 Weatherbirds so I could put them on the feature editor's desk the next morning. The feature editor grabbed me later in the day and said, 'You've got the job. Wohlschlaeger retired in 1981 and lived until age 102, in 2014.
In his nearly half-century-long tenure, Wohlschlaeger's Weatherbird commented on events such as D-Day, the assassination of John F. Kennedy, and the Apollo 11 Moon landing, but his favorite cartoon appeared on October 2, 1944: it showed the Weatherbird dressed in St. Louis Browns uniform and standing on his head, in honor of the Browns' first and only American League pennant.
Albert Schweitzer drew the first Weatherbirds to appear in color consistently. Schweitzer drew the Weatherbird with pink feathers, although he had appeared darkly shaded before. A long-time Post-Dispatch veteran, his retirement came just five years after he took over the strip.
Dan Martin took over the strip in 1986. He eliminated the Weatherbird's emblematic cigars and drew a bird with a bit more of a beak (previous cartoonists had atrophied the beak to the point of flatness). Martin wrote the book The Story of the First 100 Years of the St. Louis Post-Dispatch Weatherbird.
Other manifestations
The Weatherbird inspired the name of John Hartford's "Weatherbird Reel".
Weatherbird brand shoes for children, using pictures of the Weatherbird in advertising, were offered starting in 1901 by the St. Louis-based Peters Shoe Company, later part of International Shoe which continued to base the brand's image on the Weatherbird until 1932 (the brand itself continued at least through the 1950s).
Two of the original windows from the Peters Shoe Company factory, featuring pictures of the Weatherbird, adorn the Weatherbird Cafe in the St. Louis Post-Dispatch office.
A life-size Weatherbird costume is used by the Post-Dispatch for promotions such as meet-and-greets at local bars.
References
Further reading
External links
Fictional birds
American mascots
Magazine mascots
Bird mascots
St. Louis Post-Dispatch
Gag-a-day comics
1901 comics debuts
American comics characters
Comics about anthropomorphic birds
Fictional characters introduced in 1901
Weather prediction
Weather presenters | Weatherbird | Physics | 1,062 |
27,626,494 | https://en.wikipedia.org/wiki/Flood%20Studies%20Report | The Flood Studies Report, published in 1975, is used in relation to rainfall events in the United Kingdom. It has since been replaced by the Flood Estimation Handbook, but the method can still be used.
Calculation procedure
It is possible to use the FSR to predict the depth of rainfall from a storm of a given duration and return period. The FSR includes values for two key variables mapped across the UK: the M5-60 minutes rainfall, and the ratio "r".
M5-60 minutes rainfall is the expected depth of rainfall in millimetres (mm) from a storm lasting 60 minutes (1 hour) with a return period of 5 years (hence M5).
M5-2 days rainfall is the expected depth of rainfall from a storm lasting 2 days (48 hours) with a return period of 5 years.
The dimensionless ratio "r" is the M5-60 minutes value divided by the M5-2 days value.
Factor Z1 is interpolated from figures based on the values of M5-2 days and "r".
Factor Z2 (the growth factor) is found from the M5 rainfall depth, and depends on the return period.
The Areal Reduction Factor (ARF) takes the catchment area into account. For small catchments (below 1 km2) the ARF is not required.
To find the depth of a rainfall of duration D and return period T at a given location in the UK, the following should be carried out:
Find M5-60 minutes rainfall depth and "r" for the location using FSR maps.
Divide this rainfall depth by "r" to get the M5-2 days depth.
Multiply the M5-2 days depth by factor Z1 to find the M5-D depth.
Multiply the M5-D depth by factor Z2 (the growth factor) to find the MT-D depth.
Multiply the MT-D depth by the Areal Reduction Factor (ARF).
Example
Find the depth of rainfall from a storm of duration 6 hours and return period 10 years on a catchment of 5 km2 in Sheffield.
From the FSR maps, the M5-60 minutes rainfall is 20.5mm, and "r" = 0.4.
Divide 20.5mm by 0.4 to get 51.3mm, which is the M5-2 days rainfall depth.
Factor Z1 = 0.64, so multiply 51.3mm by 0.64 to get 32.8mm.
Factor Z2 = 1.16, so multiply 32.8mm by 1.16 to get 38.1mm.
The ARF is 0.96, so multiply 38.1mm by 0.96 to get 36.6mm.
Therefore the expected depth of rainfall from the storm is 36.6mm. The mean intensity of rainfall is given by 36.6mm divided by 6 hours, which is 6.1mm/hour.
Storm profiles
The above method is sufficient for finding the overall depth of rainfall during a storm. However, it is often useful from an engineering perspective to predict the intensity of rainfall during the storm, to allow structures such as drains and sewers to be designed with sufficient capacity for stormwater.
In general, the intensity of a storm is highest at the mid-duration point (known as the peak), and lowest at the start and end of the storm. Therefore, peaked profiles are applied to the storm data to provide a more realistic description of the rainfall intensity during the storm.
Flood Estimation Handbook
The Flood Estimation Handbook was published in 1999 and replaces the FSR. It is based on the percentage runoff equation:
where PR is percentage runoff, PIMP is percentage imperviousness of the catchment, SOIL is the soil index and UCWI is urban catchment wetness index.
References
Hydrology
Environmental engineering
Technical books
Water in the United Kingdom | Flood Studies Report | Chemistry,Engineering,Environmental_science | 794 |
77,534,953 | https://en.wikipedia.org/wiki/NGC%207735 | NGC 7735 is an elliptical galaxy in the constellation of Pegasus. Its velocity with respect to the cosmic microwave background is 9249 ± 36 km/s, which corresponds to a Hubble distance of 136.41 ± 9.57 Mpc (∼445 million light-years). It was discovered by British astronomer John Herschel on 5 September 1828.
One supernova has been observed in NGC 7735: SN 2024we (type Ia, mag 17) was discovered by ASAS-SN on 11 January 2024.
See also
List of NGC objects (7001–7840)
References
External links
7735
072165
Pegasus (constellation)
18280905
Discoveries by John Herschel
+04-55-046
Elliptical galaxies
12744 | NGC 7735 | Astronomy | 154 |
9,347,711 | https://en.wikipedia.org/wiki/Neurokinin%20A | Neurokinin A (NKA), formerly known as Substance K, is a neurologically active peptide translated from the pre-protachykinin gene. Neurokinin A has many excitatory effects on mammalian nervous systems and is also influential on the mammalian inflammatory and pain responses.
Introduction
Neurokinin A (formally known as substance K) is a member of the tachykinin family of neuropeptide neurotransmitters. Tachykinins are important contributors to nociceptive processing, satiety, and smooth muscle contraction. Tachykinins are known to be highly excitatory neurotransmitters in major central neural systems. Neurokinin A is ubiquitous in both the central and peripheral mammalian nervous systems, and seems to be involved in reactions to pain and the inflammatory responses. It is produced from the same preprotachykinin A gene as the neuropeptide substance P. Both substance P and neurokinin A are encoded by the same mRNA, which when alternatively spliced can be translated into either compound. It has various roles in the body of humans and other animals, specifically stimulation of extravascular smooth muscle, vasodilation, hypertensive action, immune system activation, and pain management. The deduced amino acid sequence of neurokinin A is as follows:
His Lys Thr Asp Ser Phe Val Gly Leu Met (HKTDSFVGLM)
with amidation at the C-terminus.
Mechanism of action
Modified from: Sun J, Ramnath RD, Tamizhselvi R, Bhatia M."Neurokinin A engages neurokinin-1 receptor to induce NF-kappaB-dependent gene expression in murine macrophages: implications of ERK1/2 and PI 3-kinase/Akt pathways." Am J Physiol Cell Physiol. 2008 Sep;295(3):C679-91
Like Substance P [SP], Neurokinin A is present in excitatory neurons and secretory cells of the hypothalamic–pituitary–adrenal axis. Additionally both SP neurokinin A is found in the neurosensory system and modulates a wide range of inflammatory and tissue repairing processes . In various tissues, such as the skin, the release of bioactive tachykinins by sensory nerve fibers C, that extend from the dorsal root ganglia into the epidermis, directly influence the activity of keratinocytes. Inflammation, tissue healing and cell proliferation have been linked to both SP and neurokinin A release into surrounding tissues.
Nervous system
The overstimulation of the hypothalamic–pituitary–adrenal axis system and elevated secretion of corticotropin-releasing hormone from the hypothalamus, have been studied in many clinical manifestations of pathological depression. Studies have shown that stress-induced activation of the noradrenergic prefrontal lobe system may be under the control of both endogenously released corticotropin-releasing hormone and SP and neurokinin A. This study directly links the secretion of neurokinin A and SP to certain forms of depression characterized by the corticoid receptor hypothesis of depression.
Inflammatory responses within the central nervous system (CNS) are often the result of traumatic injury or exposure to infectious agents. Inflammation provides a protective immune response to such stresses may also result in progressive damage to the CNS. There is significant evidence to indicate that tachykinins are a major component of the neural inflammatory response at peripheral tissues as well as the CNS. The ability to regulate tachykinin secretion represents an important mechanism for designing potentially useful drugs to treat inflammation. Neurokinin A has been associated with the chemokines interleukin-1 and interleukin-6, both of which are heavily involved in the inflammatory process during infections.
Neuronal tissue can be severely damaged either through physical trauma or intracellular stresses, either chronic or acute. Either of these scenarios can result in calcium overload, protein degradation, the unfolded protein response or an accumulation of DNA damage. Endogenous cellular responses are activated within nerve tissue in response to damage in order to protect cellular, protein, and nucleic acid integrity. A large variety of neuroprotective signaling mechanisms exist, which can be manipulated by drugs to reduce damage from cellular damage in neurons. Tachykinins thus have a number of neuroprotective physiological roles in medical conditions
Immune system
The immune system is a highly integrated system which receives input from many sources, such as sites of injury, nociceptors and white blood cells. Chemical signals therefore are an important component of paracrine, autocrine and endocrine signaling.
Neurokinin A was shown to be a potent chemo attractor for T-cells increasing the migration into infected tissues. This migration is necessary for the pathogen seeking activity of T-cells. Some chemokines trigger the intravascular adhesion of T-cells whereas others direct the migration of leukocytes into and within the extravascular space. Since lymphocytes must be positioned correctly to interact with other cells, the pattern of chemokine receptors and the type and distribution of chemokines in tissues critically influence immune responses. The molecular mechanism behind neurokinin's role as a chemoattractor is currently unclear.
Neurokinin A has an inhibitory effect on the formation of myeloid cells, and appear to be involved in one specific receptor since the effect can be completely abolished by a NK-2 receptor-selective antagonist. The inhibitory effect of neuronkinin A is countered by the excitatory effect of a structurally similar compound: substance P. The opposite effects on myelogenesis by substance P and neurokinin A may represent an important feedback mechanism for maintenance of homeostasis.
Respiratory system
The binding of neurokinin A to the NKR-2 results in bronchoconstriction, mucus production in the lungs and process neurogenic inflammation. This release is propagated through the stimulation of e-NANC nerves in the bronchial epithelium via an axon-reflex mechanism.
Cardiovascular system
Neurokinin has been shown to contribute to both bradycardia and myocardial infarctions through the activation of NK2 receptors.
The dual sensory-motor function of neurokinin A containing afferent neurons is a component of the intracardiac nervous system. Varicose processes of tachykinin-containing nerves are abundant in coronary arteries and in the cardiac ganglia. The diverse responses that are triggered by locally released tachykinins produce beneficial effects such as modulation of ganglion transmission. However, it is also possible that excessive stimulation of cardiac afferents and release of tachykinins, during pathological conditions such as myocardial infarction, could contribute to certain human pathologies.
Receptor
Tachykinins selectively bind and activate the G-protein coupled receptors TACR1(NK1R), TACR2(NK2R), and TACR3(NK3R). Neurokinin A binds to the G-protein coupled receptor ultimately increasing the release of inositol-phosphate and calcium second messengers. Each receptor demonstrates a specific affinity for either neurokinin A or substance P peptides. Both peptides, however, can act as full agonists on either receptor, although their potency is decreased when not bound to their specific receptor.
NK-2 receptor
NK-2 receptors are expressed predominantly in the CNS. Networks involved in emotional processing, such as the prefrontal cortex, cingulate cortex, and amygdala, show the highest concentration of NK-2 receptors. NK-2 receptor antagonists have been theorized to have antidepressant benefits and are presently in clinical trials. As a consequence of its ability to stimulate intestinal smooth muscle, NKA is considered to be specifically active in regulating intestinal motility by its action on NK2 receptors.
Antagonists
MEN 11420 has been demonstrated to be a potent, selective and competitive antagonist of tachykinin NK2 receptors, both in animal and human models. In vivo animal models, MEN 11420 produces an effective and long-lasting blockade of the NK2 receptors expressed in the smooth muscle of the intestinal, genito-urinary and respiratory tract.
History
Neurokinin A was isolated from porcine spinal cord in 1931 by von Euler and Gaddum.
Structure
Tachykinins are a structurally related group of neuropeptides sharing the C-terminal sequence Phe-X-Gly-Leu-Met-NH2. The amino acid sequence of substance P and neurokinin A are well conserved across mammals species. Structure of mammalian neurokinin A was obtained using CD spectropolarimetry and 2D proton NMR. Analysis showed that in water, the peptide adopts an extended conformation while in the presence of micelles (a model cell membrane system), an alpha helical conformation is induced in the central core (Asp4-Met10).
Genetic overview
The pre-protachykinin-1 and pre-protachykinin-2 genes in mice encode four very distinct peptides with varying physiological function. Alternative splicing of the pre-protachykinin-1 gene gives rise to four different peptide precursors (alphatac1, betatac1, deltatac1 und gammatac1), which are further processed into several related peptides including neurokinin A and substance P. The alpha tac1 and beta tac1 precursors encode synthesis of both Substance P and neurokinin A.
Modified from:Nakanishi, Shigetada. "Molecular Mechanisms Of Intercellular Communication In The Hormonal And Neural Systems." IUBMB Life 58.5/6 (2006): 349-357
Mouse models
pre-protachykinin-1 -/- mice show normal fertility and behavioral patterns (litter-mate socialization and pup rearing), but have a reduced sense of anxiety when threatened, compared to both wild-type mice and other mouse models of depression.
Applications
Cancer
Circulating concentrations of neurokinin A is an independent indicator of poor prognosis in certain cancers such as carcinoids. Patients presenting with neurokinin A plasma concentrations of >50 pmol/L showed a poorer 3 year survival rate than patients presenting with neurokinin A concentrations of less than 50 pmol/L. These types of studies show that measuring tachykinin levels in human patients may have clinical relevance.
Patients with Midgut Carcinoid disease (MGC) commonly receive neurokinin A test to determine the progression of their disease. Midgut Carcinoid disease is an uncommon disease with occurrence rates of approximately 1.4 per 100,000 of the population per year. MGC has an unpredictable disease progression depending on the patient, symptoms and progression range from rapid and aggressive to chronic. Treatment is difficult because of the varying degrees of severity, so assessing the extent of the disease is extremely important in effective treatment.
Asthma
The blocking of neuropeptide signaling has come become a novel therapeutic target for suppression of bronchial constriction in asthma patients.
Bronchoconstriction is among the most prominent and extensively studied effects caused by tachykinins. Tachykinins have numerous effects in the respiratory systems especially in asthma patients who are more responsive to tachykinin administration. Through studies with human airways researchers have examined the role tachykinins play in bronchoconstriction, most notably through the receptor NK2, though regulation of NK2 receptors seems to be mediated by the activity of NK1 receptors eluting to complicated inhibition mechanism.
Administration of DNK333 (a dual tachykinin receptor NK1/NK2 antagonist) have shown protective activity against neurokinin A induced bronchoconstriction.
Psychiatric disorders
Neurokinin A is involved in many stress induced neurological disorders, such as depression, schizophrenia and epilepsy.
Affective disorders
Affective disorders are characterized by a frequent, fluctuating alteration in mood, affecting the patient's thoughts, emotions, and behaviors. Affective disorders include depression, anxiety, and bipolar disorder. A number of approaches have been utilized to study the role that neurokinin A plays in the manifestation and continuation of human affective disorders. The measurement of serum peptide levels in depressed patients as well as anxious patients displayed higher plasma levels of tachykinins than their low-anxiety counterparts. In addition to studies of plasma levels of TKs, cerebrospinal fluid (CSF) levels of neurokinin A have also been directly correlated with depression. Under states of depression, neurokinin immunoreactivity is increased in the frontal cortex, and decreased in the striatum. These peptide levels were not found to be normalized by lithium treatment in mice. Elevated levels of tachykinins in CSF have been found in patients with fibromyalgia syndrome, a disorder that is strongly correlated with depression in human patients. Tachykinin ligands have been extensively studied and determined to be functionally linked to the control of affective phenotypes in a complex physiological manner.
Epilepsy
Epilepsy is a broad category of disorders with varying types of severity and presented symptoms. Neurokinins have been experimentally determined as possible predictor in the generation of certain forms of epilepsy. Experimentally when substance P is injected into the rat hippocampus, it significantly lowers the initiation threshold for seizures induced in a dose-dependent manner. Experimental data thus has indicated a pro-convulsant role for the Pre-protachykinin-1 gene and thus substance P and neurokinin A.
Further reading
NCBI
AJPLUNG
Science Direct
Journal of Immunology
References
External links
Journal
Further reading
Peptides | Neurokinin A | Chemistry | 2,941 |
461,525 | https://en.wikipedia.org/wiki/Bricklayer | A bricklayer, which is related to but different from a mason, is a craftsperson and tradesperson who lays bricks to construct brickwork. The terms also refer to personnel who use blocks to construct blockwork walls and other forms of masonry. In British and Australian English, a bricklayer is colloquially known as a "brickie". A stone mason is one who lays any combination of stones, cinder blocks, and bricks in construction of building walls and other works. Bricklaying is a part of masonry.
Bricklaying may also be enjoyed as a hobby. For example, the former British Prime Minister Winston Churchill did bricklaying as a hobby.
Bricklayers occasionally enter competitions where both speed and accuracy are judged. The largest is the "Spec-Mix Bricklayer 500" held annually in Las Vegas, Nevada, USA.
Required training
Professional bricklayers usually go through a formal apprenticeship which includes about three to four years of on-the-job training combined with classroom instruction, though some bricklayers may learn entirely from on-the-job experience. Unions and employers may offer apprenticeships, which allow individuals with little or no experience in bricklaying to learn fundamental skills under a more experienced employee. Contemporary masons in many countries must attend trade school and/or serve apprenticeships in order to complete curricula signifying that they understand fundamental related concepts such as the effects of humidity and water ingress, thermal insulation, and general knowledge regarding the science of construction materials, as well as occupational health and safety.
In fiction and popular culture
Italian-American author John Fante featured hod carriers, bricklayers, and stonemasons prominently in several novels and short stories. This was due to the autobiographical nature of much of Fante's writing; his father, Nick, an Italian-born bricklayer descended from — at least in Fante's fictions — a long line of Italian artisan bricklayers and stonemasons. Fante also spent a significant portion of his youth apprenticed to his father.
In Aleksandr Solzhenitsyn's One Day in the Life of Ivan Denisovich, the title character, a Gulag prisoner, worked as a bricklayer.
The long-running British children's TV series Look and Read featured "Bill the Brickie" ("brickie" being a British and Australian colloquialism for "bricklayer"), who would 'build' words with bricks to demonstrate the use of morphemes, such as '-ed' or '-ing'.
In 2021, Cristiano Ronaldo's mother, Dolores Aveiro, stated in an interview for Sporting Clube de Portugal's official television channel (Sporting TV) that her son would be a bricklayer if he hadn't become a professional football player.
In 2024, The Bricklayer, an American action thriller film directed by Renny Harlin and written by Hanna Weg and Matt Johnson, based on the 2010 novel of the same name by Paul Lindsay, who used the pen name Noah Boyd, was released.
See also
References
.
Artisans
Construction trades workers
Crafts
. | Bricklayer | Engineering | 636 |
352,513 | https://en.wikipedia.org/wiki/Diphosgene | Diphosgene is an organic chemical compound with the formula ClCO2CCl3. This colorless liquid is a valuable reagent in the synthesis of organic compounds. Diphosgene is related to phosgene and has comparable toxicity, but is more conveniently handled because it is a liquid, whereas phosgene is a gas.
Production and uses
Diphosgene is prepared by radical chlorination of methyl chloroformate under UV light:
Cl-CO-OCH3 + 3 Cl2 —(hv)→ Cl-CO-OCCl3 + 3 HCl
Another method is the radical chlorination of methyl formate:
H-CO-OCH3 + 4 Cl2 —(hv)→ Cl-CO-OCCl3 + 4 HCl
Diphosgene converts to phosgene upon heating or upon catalysis with charcoal. It is thus useful for reactions traditionally relying on phosgene. For example, it convert amines into isocyanates, secondary amines into carbamoyl chlorides, carboxylic acids into acid chlorides, and formamides into isocyanides. Diphosgene serves as a source of two equivalents of phosgene:
2 RNH2 + ClCO2CCl3 → 2 RNCO + 4 HCl
With α-amino acids diphosgene gives the acid chloride-isocyanates, OCNCHRCOCl, or N-carboxy-amino acid anhydrides depending on the conditions.
It hydrolyzes to release HCl in humid air.
Diphosgene is used in some laboratory preparations because it is easier to handle than phosgene.
Role in warfare
Diphosgene was originally developed as a pulmonary agent for chemical warfare, a few months after the first use of phosgene. It was used as a poison gas in artillery shells by Germany during World War I. The first recorded battlefield use was in May 1916. Diphosgene was developed because the vapors could destroy the filters of the gas masks in use at the time.
Safety
Diphosgene has a relatively high vapor pressure of 10 mm Hg (1.3 kPa) at 20 °C and decomposes to phosgene around 300 °C. Exposure to diphosgene is similar in hazard to phosgene.
See also
Phosgene
Triphosgene
Carbonyldiimidazole
References
External links
medical care guide.
NATO guide, includes treatment advice
material safety data sheet (PDF, for phosgene and diphosgene treated as one).
MSDS for diphosgene specifically
Pulmonary agents
Chloroformates
Trichloromethyl esters
Carbon oxohalides | Diphosgene | Chemistry | 578 |
47,531,757 | https://en.wikipedia.org/wiki/NGC%20428 | NGC 428 is a barred spiral galaxy in the constellation of Cetus (The Sea Monster), with its spiral structure distorted and warped, possibly the result of the collision of two galaxies. There appears to be a substantial amount of star formation occurring within NGC 428 and it lacks well defined arms — a telltale sign of a galaxy merger. In 2015 the Hubble Space Telescope made a close-up shot of the galaxy with its Advanced Camera for Surveys and its Wide Field and Planetary Camera 2. The structure of NGC 428 has been compared to NGC 5645.
Discoveries
NGC 428 was discovered by William Herschel in December 1786. A type Ia supernova designated SN2013ct was discovered May 11, 2013, within the galaxy by Stuart Parker of the Backyard Observatory Supernova Search (BOSS) project in Australia and New Zealand.
Smoker et al. reported in 1996 on the NGC 428 field, with the HI tail and LSB dwarf 0110+008, assessing star formation properties based on molecule density distributions, and concluded that the tail formation most likely originated through tidal interactions between two galaxies.
Further reading
H-alpha kinematics of S4G spiral galaxies-II. Data description and non-circular motions
Comparative internal kinematics of the HII regions in interacting and isolated galaxies: implications for massive star formation modes
A classical morphological analysis of galaxies in the spitzer survey of stellar structure in galaxies (S4G)
Kinematics of disk galaxies with known masses of their supermassive black holes. Observations Cherepashchuk, A.; Afanas’ev, V.; Zasov, A.; and Katkov, I. Astronomy Reports, 2010, Vol.54(7), pp. 578–589.
See also
Galaxy merger
List of galaxies
References
External links
The galaxy NGC 428 (Location dependent info when to observe the galaxy in the sky)
Supernovae 2013ct in NGC 428
NASA/IPAC Extragalactic Database
Images of NGC 428
Barred spiral galaxies
Magellanic spiral galaxies
Cetus
Galaxies discovered in 1786
0428
004367
00763
IRAS catalogue objects | NGC 428 | Astronomy | 438 |
11,422,078 | https://en.wikipedia.org/wiki/Small%20nucleolar%20RNA%20SNORD72 | In molecular biology, SNORD72 (also known as HBII-240) belongs to the C/D family of snoRNAs.
It is the human orthologue of the mouse MBII-240 and is predicted to guide 2'O-ribose methylation of the large 28S rRNA at residue U4590.
References
External links
Small nuclear RNA | Small nucleolar RNA SNORD72 | Chemistry | 80 |
32,465,788 | https://en.wikipedia.org/wiki/Bjugn%20affair | The Bjugn affair in 1992 in Bjugn Municipality, Norway, started with the arrest of three women and four men and led to one, Ulf Hammern, being charged for allegedly having molested children. He was acquitted 31 January 1994 at Frostating Court of Appeal.
References
External links
http://www.dagbladet.no/magasinet/2002/03/22/320874.html
Trials in Norway | Bjugn affair | Biology | 94 |
1,809,002 | https://en.wikipedia.org/wiki/Stata | Stata (, , alternatively , occasionally stylized as STATA) is a general-purpose statistical software package developed by StataCorp for data manipulation, visualization, statistics, and automated reporting. It is used by researchers in many fields, including biomedicine, economics, epidemiology, and sociology.
Stata was initially developed by Computing Resource Center in California and the first version was released in 1985. In 1993, the company moved to College Station, Texas and was renamed Stata Corporation, now known as StataCorp. A major release in 2003 included a new graphics system and dialog boxes for all commands. Since then, a new version has been released once every two years. The current version is Stata 18, released in April 2023.
Technical overview and terminology
User interface
From its creation, Stata has always employed an integrated command-line interface. Starting with version 8.0, Stata has included a graphical user interface which uses menus and dialog boxes to give access to many built-in commands. The dataset can be viewed or edited in spreadsheet format. From version 11 on, other commands can be executed while the data browser or editor is opened.
Data structure and storage
Until the release of version 16, Stata could only open a single dataset at any one time. Stata allows for flexibility with assigning data types to data. Its compress command automatically reassigns data to data types that take up less memory without loss of information. Stata utilizes integer storage types which occupy only one or two bytes rather than four, and single-precision (4 bytes) rather than double-precision (8 bytes) is the default for floating-point numbers.
Stata's proprietary output language is known as SMCL, which stands for Stata Markup and Control Language and is pronounced "smickle".
Stata's data format is always tabular in format. Stata refers to the columns of tabular data as variables.
Data format compatibility
Stata can import data in a variety of formats. This includes ASCII data formats (such as CSV or databank formats) and spreadsheet formats (including various Excel formats).
Stata's proprietary file formats have changed over time, although not every Stata release includes a new dataset format. Every version of Stata can read all older dataset formats, and can write both the current and most recent previous dataset format, using the saveold command. Thus, the current Stata release can always open datasets that were created with older versions, but older versions cannot read newer format datasets.
Stata can read and write SAS XPORT format datasets natively, using the fdause and fdasave commands.
Some other econometric applications, including gretl, can directly import Stata file formats.
History
Origins
The development of Stata began in 1984, initially by William (Bill) Gould and later by Sean Becketti. The software was originally intended to compete with statistical programs for personal computers such as SYSTAT and MicroTSP. Stata was written, then as now, in the C programming language, initially for PCs running the DOS operating system. The first version was released in 1985 with 44 commands.
Development
There have been 18 major releases of Stata between 1985 and 2024, and additional code and documentation updates between major releases. In its early years, extra sets of Stata programs were sometimes sold as "kits" or distributed as Support Disks. With the release of Stata 6 in 1999, updates began to be delivered to users via the web. The initial release of Stata was for the DOS operating system. Since then, versions of Stata have been released for systems running Unix variants like Linux distributions, Windows, and MacOS. All Stata files are platform-independent.
Hundreds of commands have been added to Stata in its 37-year history. Certain developments have proved to be particularly important and continue to shape the user experience today, including extensibility, platform independence, and the active user community.
Extensibility
The program command was implemented in Stata 1.2, giving users the ability to add their own commands. ado-files followed in Stata 2.1, allowing a user-written program to be automatically loaded into memory. Many user-written ado-files are submitted to the Statistical Software Components Archive hosted by Boston College. StataCorp added an ssc command to allow community-contributed programs to be added directly within Stata. More recent editions of Stata allow users to call Python scripts using commands, as well as allowing Python IDEs like Jupyter Notebooks to import Stata commands. Although Stata does not support R natively, there are user-written extensions to use R scripts in Stata.
User community
A number of important developments were initiated by Stata's active user community. The Stata Technical Bulletin, which often contains user-created commands, was introduced in 1991 and issued six times a year. It was relaunched in 2001 as the peer-reviewed Stata Journal, a quarterly publication containing descriptions of community-contributed commands and tips for the effective use of Stata. In 1994, a listserv began as a hub for users to collaboratively solve coding and technical issues; in 2014, it was converted into a web forum. In 1995, Statacorp began organizing user and developer conferences that meet annually. Only the annual Stata Conference held in the United States is hosted by StataCorp. Other user group meetings are held annually in the United States (the Stata Conference), the UK, Germany, and Italy, and less frequently in several other countries. Local Stata distributors host User Group meetings in their own countries.
Software products
There are four builds of Stata: Stata/MP, Stata/SE, Stata/BE, and Numerics by Stata. Whereas Stata/MP allows for built-in parallel processing of certain commands, Stata/SE and Stata/BE are bottlenecked and limit usage to only one single core. Stata/MP runs certain commands about 2.4 times faster, roughly 60% of theoretical maximum efficiency, when running parallel processes on four CPU cores compared to SE or BE versions. Numerics by Stata allows for web integration of Stata commands.
SE and BE versions differ in the amount of memory datasets may utilize. Though Stata/MP can store 10 to 20 billion observations and up to 120,000 variables, Stata/SE and Stata/BE store up to 2.14 billion observations and handle 32,767 variables and 2,048 variables respectively. The maximum number of independent variables in a model is 65,532 variables in Stata/MP, 10,998 variables in Stata/SE, and 798 variables in Stata/BE.
The pricing and licensing of Stata depends on its intended use: business, government/nonprofit, education, or student. Single user licenses are either renewable annually or perpetual. Other license types include a single license for use by concurrent users, a site license, volume single user for bulk pricing, or a student lab.
Example code
The following set of commands revolve around simple data management.
sysuse auto // Open the included auto dataset
browse // Browse the dataset (opens the Data Editor window)
describe // Describes the dataset and associated variables
summarize // Summary information about numerical variables
codebook make foreign // Summary information about the make (string) and foreign (numeric) variables
browse if missing(rep78) // Browse only observations with missing data for variable rep78
list make if missing(rep78) // List makes of the cars with missing data for variable rep78
The next set of commands move onto descriptive statistics.
summarize price, detail // Detailed summary statistics for variable price
tabulate foreign // One-way frequency table for variable foreign
tabulate rep78 foreign, row // Two-way frequency table for variables rep78 and foreign
summarize mpg if foreign == 1 // Summary information about mpg if the car is foreign (the "==" sign tests for equality)
by foreign, sort: summarize mpg // As above, but using the "by" prefix.
tabulate foreign, summarize(mpg) // As above, but using the tabulate command.
A simple hypothesis test:
ttest mpg, by(foreign) // T-test for difference in means for domestic vs. foreign cars
Graphing data:
twoway (scatter mpg weight) // Scatter plot showing relationship between mpg and weight
twoway (scatter mpg weight), by(foreign, total) // Three graphs for domestic, foreign, and all cars
Linear regression:
generate wtsq = weight^2 // Create a new variable for weight squared
regress mpg weight wtsq foreign, vce(robust) // Linear regression of mpg on weight, wtsq, and foreign
predict mpghat // Create a new variable contained the predicted values of mpg
twoway (scatter mpg weight) (line mpghat weight, sort), by(foreign) // Graph data and fitted line
See also
List of statistical packages
Comparison of statistical packages
Data analysis
Descriptive statistics
stata commands
References
Further reading
External links
Stata Journal
Stata Press
Stata Technical Bulletin
Statistical Software Components Archive
1985 software
Proprietary software programmed in C
Proprietary commercial software for Linux
Science software for Linux
Data mining and machine learning software
Statistical software
Statistical programming languages
Econometrics software
Time series software
Data warehousing
Proprietary cross-platform software
Extract, transform, load tools
Mathematical optimization software
Numerical software | Stata | Mathematics | 2,011 |
29,330,573 | https://en.wikipedia.org/wiki/Stem%20tetrapoda | The Stem Tetrapoda are a cladistically defined group, consisting of all animals more closely related to extant four-legged vertebrates than to their closest extant relatives (the lungfish), but excluding the crown group Tetrapoda. They are thus paraphyletic, though acceptable in phylogenetic nomenclature as the group is defined by strict reference to phylogeny rather than to traits as in traditional systematics. Thus, some finned sarcopterygians are considered to be stem tetrapods.
Content of the group
Stem tetrapods are members of Tetrapodomorpha, the total group and clade that also includes their descendants, the crown tetrapods:
The stem Tetrapoda encompass three distinct grades successively closer to crown group Tetrapoda:
Osteolepiformes, a group of lobe-finned fishes that includes the families Tristichopteridae, Canowindridae, Megalichthyidae, and Osteolepidae
Elpistostegalia, the more advanced lobe-finned fishes (Tristichopteridae) and the "fishapods" (genera such as Panderichthys and Tiktaalik)
Ichthyostegalia, the primarily aquatic primitive labyrinthodonts such as Acanthostega, Ichthyostega, Tulerpeton, and probably loxommatids.
Both Ichthyostegalia and Labyrinthodontia constitute paraphyletic evolutionary grades rather than clades, with amniotes and modern amphibians branching off at some point from the latter. The stem tetrapods may also include one or both of Temnospondyli and Lepospondyli, depending on author. This is due to the uncertain origin of the modern amphibians, whose position in the phylogenetic tree dictates what lineages go in the crown group Tetrapoda. Neither is there for the moment a consensus of the phylogeny of stem tetrapods, nor how Tetrapoda itself should be defined (i.e. as a crown group, or as an apomorphy-based group, using the limb with digits), making the actual content of the group uncertain.
References
Tetrapodomorphs
Tetrapod taxonomy
Paraphyletic groups | Stem tetrapoda | Biology | 478 |
71,570,180 | https://en.wikipedia.org/wiki/Talent%20scheduling | Talent scheduling represents a complex optimization challenge within the fields of computer science and operations research, specifically categorized under combinatorial optimization. Consider, for example, a case involving the production of multiple films, each comprising several scenes that necessitate the participation of one or more actors. Importantly, only one scene can be filmed per day, and the remuneration for the actors is calculated on a daily basis. A critical constraint in this problem is that actors must be engaged for consecutive days; for instance, an actor cannot be contracted for filming on the first and third days without also being hired on the intervening second day. Furthermore, during the entire hiring period, producers are obligated to compensate the actors, even on days when they are not actively participating in filming. The primary objective of talent scheduling is to minimize the total salary expenditure for the actors by optimizing the sequence in which scenes are filmed.
Mathematical formulation
Consider a film shoot composed of shooting days and involving a total of actors. Then we use the day out of days matrix (DODM) to represent the requirements for the various shooting days. The matrix with the entry given by:
Then we define the pay vector , with the th element given by which means rate of pay per day of the th actor. Let v denote any permutation of the n columns of , we have:
is the permutation set of the n shooting days. Then define to be the matrix with its columns permuted according to , we have:
for
Then we use and to represent denote respectively the earliest and latest days in the schedule determined by a which require actor . So we can find actor will be hired for days. But in these days, only days are actually required, which means days are unnecessary, we have:
The total cost of unnecessary days is:
will be the objective function we should minimize.
Proof of strong NP-hardness
It can be proved that the talent scheduling problem is NP-hard by a reduction to the optimal linear arrangement(OLA) problem. Even if we restrict the problem by requiring that each actor is needed for just two days and all actors' salaries are 1, it's still polynomially reducible to the OLA problem. Thus, this problem is unlikely to have pseudo-polynomial algorithm.
Integer programming
The integer programming model is given by:
In this model, means the earliest shooting day for talent , is the latest shooting day for talent , is the scheduling for the project, i.e.
References
Optimal scheduling
NP-complete problems | Talent scheduling | Mathematics,Engineering | 507 |
12,549,840 | https://en.wikipedia.org/wiki/W%20Vision | W Vision (pronounced double vision) was a Japanese Web site claiming to be "the Internet's first real TV station." It preceded by far the now-famous video sites such as YouTube, though it didn't have a user community. Developed by a joint venture between the Impress Group and the Watanabe Productions Group, the Web site provided videos from various content provider and producers, using software including RealPlayer, VDOLive Player, and FutureSplash (now Adobe Flash). The service started in the end of the 1990s, hence the low-quality streaming videos to accommodate the Internet users mostly connecting via dial-up service. The service today is closed.
External links
"W Vision" web site (14 June 1998, archived by the Internet Archive)
Streaming television
Mass media companies of Japan | W Vision | Technology | 166 |
3,333,402 | https://en.wikipedia.org/wiki/Integer%20lattice | In mathematics, the -dimensional integer lattice (or cubic lattice), denoted , is the lattice in the Euclidean space whose lattice points are -tuples of integers. The two-dimensional integer lattice is also called the square lattice, or grid lattice. is the simplest example of a root lattice. The integer lattice is an odd unimodular lattice.
Automorphism group
The automorphism group (or group of congruences) of the integer lattice consists of all permutations and sign changes of the coordinates, and is of order 2n n!. As a matrix group it is given by the set of all n × n signed permutation matrices. This group is isomorphic to the semidirect product
where the symmetric group Sn acts on (Z2)n by permutation (this is a classic example of a wreath product).
For the square lattice, this is the group of the square, or the dihedral group of order 8; for the three-dimensional cubic lattice, we get the group of the cube, or octahedral group, of order 48.
Diophantine geometry
In the study of Diophantine geometry, the square lattice of points with integer coordinates is often referred to as the Diophantine plane. In mathematical terms, the Diophantine plane is the Cartesian product of the ring of all integers . The study of Diophantine figures focuses on the selection of nodes in the Diophantine plane such that all pairwise distances are integers.
Coarse geometry
In coarse geometry, the integer lattice is coarsely equivalent to Euclidean space.
Pick's theorem
Pick's theorem, first described by Georg Alexander Pick in 1899, provides a formula for the area of a simple polygon with all vertices lying on the 2-dimensional integer lattice, in terms of the number of integer points within it and on its boundary.
Let be the number of integer points interior to the polygon, and let be the number of integer points on its boundary (including both vertices and points along the sides). Then the area of this polygon is:
The example shown has interior points and boundary points, so its area is square units.
See also
Regular grid
References
Further reading
Euclidean geometry
Lattice points
Diophantine geometry | Integer lattice | Mathematics | 463 |
3,231,627 | https://en.wikipedia.org/wiki/Lagrangian%20Grassmannian | In mathematics, the Lagrangian Grassmannian is the smooth manifold of Lagrangian subspaces of a real symplectic vector space V. Its dimension is n(n + 1) (where the dimension of V is 2n). It may be identified with the homogeneous space
,
where is the unitary group and the orthogonal group. Following Vladimir Arnold it is denoted by Λ(n). The Lagrangian Grassmannian is a submanifold of the ordinary Grassmannian of V.
A complex Lagrangian Grassmannian is the complex homogeneous manifold of Lagrangian subspaces of a complex symplectic vector space V of dimension 2n. It may be identified with the homogeneous space of complex dimension n(n + 1)
,
where is the compact symplectic group.
As a homogeneous space
To see that the Lagrangian Grassmannian Λ(n) can be identified with , note that is a 2n-dimensional real vector space, with the imaginary part of its usual inner product making it into a symplectic vector space. The Lagrangian subspaces of are then the real subspaces of real dimension n on which the imaginary part of the inner product vanishes. An example is . The unitary group acts transitively on the set of these subspaces, and the stabilizer of is the orthogonal group . It follows from the theory of homogeneous spaces that Λ(n) is isomorphic to as a homogeneous space of .
Topology
The stable topology of the Lagrangian Grassmannian and complex Lagrangian Grassmannian is completely understood, as these spaces appear in the Bott periodicity theorem: , and – they are thus exactly the homotopy groups of the stable orthogonal group, up to a shift in indexing (dimension).
In particular, the fundamental group of is infinite cyclic. Its first homology group is therefore also infinite cyclic, as is its first cohomology group, with a distinguished generator given by the square of the determinant of a unitary matrix, as a mapping to the unit circle. Arnold showed that this leads to a description of the Maslov index, introduced by V. P. Maslov.
For a Lagrangian submanifold M of V, in fact, there is a mapping
which classifies its tangent space at each point (cf. Gauss map). The Maslov index is the pullback via this mapping, in
of the distinguished generator of
.
Maslov index
A path of symplectomorphisms of a symplectic vector space may be assigned a Maslov index, named after V. P. Maslov; it will be an integer if the path is a loop, and a half-integer in general.
If this path arises from trivializing the symplectic vector bundle over a periodic orbit of a Hamiltonian vector field on a symplectic manifold or the Reeb vector field on a contact manifold, it is known as the Conley–Zehnder index. It computes the spectral flow of the Cauchy–Riemann-type operators that arise in Floer homology.
It appeared originally in the study of the WKB approximation and appears frequently in the study of quantization, quantum chaos trace formulas, and in symplectic geometry and topology. It can be described as above in terms of a Maslov index for linear Lagrangian submanifolds.
References
V. I. Arnold, Characteristic class entering in quantization conditions, Funktsional'nyi Analiz i Ego Prilozheniya, 1967, 1,1, 1-14, .
V. P. Maslov, Théorie des perturbations et méthodes asymptotiques. 1972
Assorted source material relating to the Maslov index.
Symplectic geometry
Topology of homogeneous spaces
Mathematical quantization | Lagrangian Grassmannian | Physics | 800 |
7,052,521 | https://en.wikipedia.org/wiki/Tonelli%E2%80%93Hobson%20test | In mathematics, the Tonelli–Hobson test gives sufficient criteria for a function ƒ on R2 to be an integrable function. It is often used to establish that Fubini's theorem may be applied to ƒ. It is named for Leonida Tonelli and E. W. Hobson.
More precisely, the Tonelli–Hobson test states that if ƒ is a real-valued measurable function on R2, and either of the two iterated integrals
or
is finite, then ƒ is Lebesgue-integrable on R2.
References
Integral calculus
Theorems in analysis | Tonelli–Hobson test | Mathematics | 125 |
43,165,864 | https://en.wikipedia.org/wiki/Representation%20on%20coordinate%20rings | In mathematics, a representation on coordinate rings is a representation of a group on coordinate rings of affine varieties.
Let X be an affine algebraic variety over an algebraically closed field k of characteristic zero with the action of a reductive algebraic group G. G then acts on the coordinate ring of X as a left regular representation: . This is a representation of G on the coordinate ring of X.
The most basic case is when X is an affine space (that is, X is a finite-dimensional representation of G) and the coordinate ring is a polynomial ring. The most important case is when X is a symmetric variety; i.e., the quotient of G by a fixed-point subgroup of an involution.
Isotypic decomposition
Let be the sum of all G-submodules of that are isomorphic to the simple module ; it is called the -isotypic component of . Then there is a direct sum decomposition:
where the sum runs over all simple G-modules . The existence of the decomposition follows, for example, from the fact that the group algebra of G is semisimple since G is reductive.
X is called multiplicity-free (or spherical variety) if every irreducible representation of G appears at most one time in the coordinate ring; i.e., .
For example, is multiplicity-free as -module. More precisely, given a closed subgroup H of G, define
by setting and then extending by linearity. The functions in the image of are usually called matrix coefficients. Then there is a direct sum decomposition of -modules (N the normalizer of H)
,
which is an algebraic version of the Peter–Weyl theorem (and in fact the analytic version is an immediate consequence.) Proof: let W be a simple -submodules of . We can assume . Let be the linear functional of W such that . Then .
That is, the image of contains and the opposite inclusion holds since is equivariant.
Examples
Let be a B-eigenvector and X the closure of the orbit . It is an affine variety called the highest weight vector variety by Vinberg–Popov. It is multiplicity-free.
The Kostant–Rallis situation
See also
Algebra representation
Notes
References
Group theory
Representation theory
Representation theory of groups | Representation on coordinate rings | Mathematics | 479 |
14,667,413 | https://en.wikipedia.org/wiki/Glycoside%20hydrolase%20family%201 | Glycoside hydrolase family 1 is a family of glycoside hydrolases. Glycoside hydrolases are a widespread group of enzymes that hydrolyse the glycosidic bond between two or more carbohydrates, or between a carbohydrate and a non-carbohydrate moiety. A classification system for glycoside hydrolases, based on sequence similarity, has led to the definition of >100 different families. This classification is available on the CAZy web site, and also discussed at CAZypedia, an online encyclopedia of carbohydrate active enzymes.
Glycoside hydrolase family 1 CAZY GH_1 comprises enzymes with a number of known activities; beta-glucosidase (); beta-galactosidase (); 6-phospho-beta-galactosidase (); 6-phospho-beta-glucosidase (); lactase-phlorizin hydrolase (), lactase (); beta-mannosidase (); myrosinase ().
Subfamilies
6-phospho-beta-galactosidase
Human proteins containing this domain
GBA3; KL; KLB; LCT; LCTL;
External links
GH1 in CAZypedia
References
Peripheral membrane proteins
EC 3.2.1
Glycoside hydrolase families
Protein families | Glycoside hydrolase family 1 | Biology | 314 |
35,698,290 | https://en.wikipedia.org/wiki/Perpetuant | In mathematical invariant theory, a perpetuant is informally an irreducible covariant of a form or infinite degree. More precisely, the dimension of the space of irreducible covariants of given degree and weight for a binary form stabilizes provided the degree of the form is larger than the weight of the covariant, and the elements of this space are called perpetuants. Perpetuants were introduced and named by . and classified the perpetuants. describes the early history of perpetuants and gives an annotated bibliography.
MacMahon conjectured and Stroh proved that the dimension of the space of perpetuants of degree n>2 and weight w is the coefficient of xw of
For n=1 there is just one perpetuant, of weight 0, and for n=2 the number is given by the coefficient of xw of x2/(1-x2).
There are very few papers after about 1910 discussing perpetuants; is one of the few exceptions. exhibited an explicit base of the space of perpetuants.
References
Invariant theory | Perpetuant | Physics | 238 |
565,694 | https://en.wikipedia.org/wiki/John%20N.%20Little | John N. "Jack" Little is an American electrical engineer and the CEO and co-founder of MathWorks and a co-author of early versions of the company's MATLAB product.
He is a Fellow of the IEEE and a Trustee of the Massachusetts Technology Leadership Council. He holds a Bachelor's degree in Electrical Engineering from the Massachusetts Institute of Technology (1978), and a Master's degree from Stanford University (1980). He is the son of the academic John D. C. Little.
External links
His biography on mathworks.com.
References
Fellows of the IEEE
MIT School of Engineering alumni
Stanford University School of Engineering alumni
Living people
Year of birth missing (living people) | John N. Little | Technology | 141 |
7,865,688 | https://en.wikipedia.org/wiki/Don%20Juanism | Don Juanism or Don Juan syndrome is a non-clinical term for the desire, in a man, to have sex with many different female partners.
The name derives from the Don Juan of opera and fiction. The term satyriasis is sometimes used as a synonym for Don Juanism. The term has also been referred to as the male equivalent of nymphomania in women. These terms no longer apply with any accuracy as psychological or legal categories of psychological disorder.
Analytical psychology
Psychiatrist Carl Jung believed that Don Juanism was an unconscious desire of a man to seek his mother in every woman he encountered. However, he did not see the trait as entirely negative; Jung felt that positive aspects of Don Juanism included heroism, perseverance and strength of will.
Jung argues that related to the mother-complex "are homosexuality and Don Juanism, and sometimes also impotence. In homosexuality, the son's entire heterosexuality is tied to the mother in an unconscious form; in Don Juanism, he unconsciously seeks his mother in every woman he meets....Because of the difference in sex, a son's mother-complex does not appear in pure form. This is the reason why in every masculine mother-complex, side by side with the mother archetype, a significant role is played by the image of the man's sexual counterpart, the anima."
One of Theodore Millon's five narcissist variations is the amorous narcissist which includes histrionic features. According to Millon, the Don Juan or Casanova of our times is erotic and exhibitionistic.
Psychoanalysis
Sigmund Freud explored the connections between mother-fixation and a long series of love-attachments in the first of his articles on the 'Psychology of Love'; while Otto Rank published an article on the Don Juan gestalt in 1922. Otto Fenichel saw Don Juanism as linked to the quest for narcissistic supply, and for proof of achievement (as seen in the number of conquests). He also described what he called the 'Don Juans of Achievement' – people compelled to flee from one achievement to another in an unconscious but never ending quest to overcome an unconscious sense of guilt Sándor Ferenczi stressed the fear of punishment (Hell) in the syndrome, linking it to the Oedipus complex.
Contemporary psychoanalysis stresses the denial of psychic reality and the avoidance of change implicit in Don Juan's (identificatory) pursuit of multiple females.
Cultural references
Aspects of the character are examined by Mozart and his librettist Da Ponte in their opera Don Giovanni, perhaps the best-known artistic work on this subject. To write their opera, Mozart and Da Ponte are known to have consulted with the famous libertine, Giacomo Casanova, the usual historic example of Don Juanism. Although not conclusively established, it is probable that Casanova attended the premiere of this opera, which was likely understood by the audience to be about himself. Charles Rosen saw what he called "the seductive physical power" of Mozart's music as linked to 18th-century libertinism, political fervor and incipient Romanticism, while in a famous passage the philosopher Kierkegaard discusses Mozart's version of the Don Juan story.
Albert Camus has also written on the subject; while Jane Austen was fascinated by the character of Don Juan: "I have seen nobody on the stage who has been a more interesting Character than that compound of Cruelty and Lust".
Anthony Powell in his novel Casanova's Chinese Restaurant distinguishes Don Juan from Casanova: "Don Juan merely liked power. He obviously did not know what sensuality was....Casanova, on the other hand, undoubtedly had his sensuous moments".
In the 4th season Cheers episode "Don Juan is Hell", Diane Chambers writes a sexual history study that suggests Sam Malone as a perfect model for Don Juanism.
See also
References
Further reading
Juliet Mitchell, Mad Men and Medusas (2000)
Analytical psychology
Don Juan
Narcissism | Don Juanism | Biology | 839 |
29,783,201 | https://en.wikipedia.org/wiki/Monte%20Carlo%20methods%20for%20electron%20transport | The Monte Carlo method for electron transport is a semiclassical Monte Carlo (MC) approach of modeling semiconductor transport. Assuming the carrier motion consists of free flights interrupted by scattering mechanisms, a computer is utilized to simulate the trajectories of particles as they move across the device under the influence of an electric field using classical mechanics. The scattering events and the duration of particle flight is determined through the use of random numbers.
Background
Boltzmann transport equation
The Boltzmann transport equation model has been the main tool used in the analysis of transport in semiconductors. The BTE equation is given by:
The distribution function, f, is a dimensionless function which is used to extract all observable of interest and gives a full depiction of electron distribution in both real and k-space. Further, it physically represents the probability of particle occupation of energy k at position r and time t. In addition, due to being a seven-dimensional integro-differential equation (six dimensions in the phase space and one in time) the solution to the BTE is cumbersome and can be solved in closed analytical form under very special restrictions. Numerically, solution to the BTE is employed using either a deterministic method or a stochastic method. Deterministic method solution is based on a grid-based numerical method such as the spherical harmonics approach, whereas the Monte Carlo is the stochastic approach used to solve the BTE.
Monte Carlo method
The semiclassical Monte Carlo method is a statistical method used to yield exact solution to the Boltzmann transport equation which includes complex band structure and scattering processes. This approach is semiclassical for the reason that scattering mechanisms are treated quantum mechanically using the Fermi's Golden Rule, whereas the transport between scattering events is treated using the classical particle notion. The Monte Carlo model in essence tracks the particle trajectory at each free flight and chooses a corresponding scattering mechanism stochastically. Two of the great advantages of semiclassical Monte Carlo are its capability to provide accurate quantum mechanical treatment of various distinct scattering mechanisms within the scattering terms, and the absence of assumption about the form of carrier distribution in energy or k-space. The semiclassical equation describing the motion of an electron is
where F is the electric field, E(k) is the energy dispersion relation, and k is the momentum wave vector. To solve the above equation, one needs strong knowledge of the band structure (E(k)). The E(k) relation describes how the particle moves inside the device, in addition to depicting useful information necessary for transport such as the density of states (DOS) and the particle velocity. A Full-band E(K) relation can be obtained using the semi-empirical pseudopotential method.
Hydrodynamic and drift diffusion method
Both drift diffusion (DD) and the hydrodynamic (HD) models can be derived from the moments of the Boltzmann transport equation (BTE) using simplified approximation valid for long channel devices. The DD scheme is the most classical approach and usually solves the Poisson equation and the continuity equations for carriers considering the drift and diffusion components. In this approach, the charge transit time is assumed to be very large in comparison to the energy relaxation time. On the other hand, the HD method solves
the DD scheme with the energy balance equations obtained from the moments of BTE. Thus, one may capture and calculate physical details such as carrier heating and the velocity overshoot effect. Needless to say, an accurate discretization method is required in HD simulation, since the governing equations are strongly coupled and one has to deal with larger number of variables compared to the DD scheme.
Comparison of semiclassical models
The accuracy of semiclassical models are compared based on the BTE by investigating how they treat the classical velocity overshoot problem, a key short channel effect (SCE) in transistor structures. Essentially, velocity overshoot is a nonlocal effects of scaled devices, which is related to the experimentally observed increase in current drive and transconductance. As the channel length becomes smaller, the velocity is no longer saturated in the high field region, but it overshoots the predicted saturation velocity. The cause of this phenomenon is that the carrier transit time becomes comparable to the energy relaxation time, and therefore the mobile carriers do not have enough time to reach equilibrium with the applied electric field by scattering in the short channel devices. The summary of simulation results (Illinois Tool: MOCA) with DD and HD model is shown in figure beside. In the figure (a), the case when the field is not high enough to cause the velocity overshoot effect in the whole channel region is shown. Note that at such limit, the data from the DD model fit well to the MC model in the non-overshoot region, but the HD model overestimate the velocity in that region. The velocity overshoot is observed only near the drain junction in the MC data and the HD model fits well in that region. From the MC data, it can be noticed that the velocity overshoot effect is abrupt in the high-field region, which is not properly included in the HD model. For high field conditions as shown in the figure (b) the velocity overshoot effect almost all over the channel and the HD results and the MC results are very close in the channel region.
Monte Carlo for semiconductor transport
Band structure
Band structure describes the relationship between energy(E) and wave vector(k). The band structure is used to compute the movement of carriers under the action of the electric field, scattering rate, and final state after the collision. Silicon band structure and its Brillouin zone are shown in figure below, but there is no analytical expression which satisfies entire Brillouin zone. By using some approximation, there are two analytical models for band structure, namely the parabolic and the non-parabolic modes.
Parabolic band structure
For the concept of band structure, parabolic energy bands are generally assumed for simplicity. Electrons reside, at least when close to equilibrium, close to the minima of the E(k) relation. Then the E(k) relation can be extended in a Taylor series as
Because the first derivative vanishes at the band minimum, so the gradient of E(k) is zero at k = 0. Thus,
which yields the definition of the effective mass tensor
This expression is true for semiconductor which has isotropic effective mass, for instance GaAs. In case of silicon, conduction band minima does not lie at k = 0 and the effective mass depends on the crystallographic orientation of the minimum as
where describe longitudinal and transverse effective mass, respectively.
Non-parabolic band structure
For higher applied fields, carriers reside above the minimum and the dispersion relation, E(k), does not satisfy the simple parabolic expression described above. This non-parabolicity is generally described by
where is a coefficient of non-parabolicity given by
where is the electron mass in vacuum, and is the energy gap.
Full band structure
For many applications, non-parabolic band structure provides reasonable approximation. However, in case of very high field transport, which requires the better physical model of the full band structure. For full band approach, numerically generated table of E(k) is used. Full band approach for Monte Carlo simulation was first used by Karl Hess at the University of Illinois at Urbana-Champaign. This approach is based on empirical pseudopotential method suggested by Cohen and Bergstresser [18]. Full band approach is computationally expensive, however, following the advancement of the computational power, it can be used as a more general approach.
Types of Monte Carlo simulation
One-particle Monte Carlo
For this type of simulation, one carrier is injected and the motion is tracked in the domain, until it exits through contact. Another carrier is then injected and the process repeated to simulate an ensemble of trajectories. This approach is mostly useful to study bulk properties, like the steady state drift velocity as a function of field.
Ensemble Monte Carlo
Instead of single carrier, a large ensemble of carriers is simulated at the same time. This procedure is obviously a good candidate for super-computation, since one may apply parallelization and vectorization. Also, it is now possible to perform ensemble averages directly. This approach is suitable for transient simulations.
Self-consistent ensemble Monte Carlo
This method couples the ensemble Monte Carlo procedure to Poisson's equation, and is the most suitable for device simulation. Typically, Poisson's equation is solved at fixed intervals to update the internal field, to reflect the internal redistribution of charge, due to the movement of carriers.
Random flight selection
The probability that the electron will suffer its next collision during dt around t is given by
where P[k(t)]dt is the probability that an electron in the state k suffers a collision during the time dt. Because of the complexity of the integral at the exponent, it is impractical to generate stochastic free flights with the distribution of the equation above. In order to overcome this difficulty, people use a fictitious “self-scattering” scheme. By doing this, the total scattering rate, including this self-scattering, is constant and equal to, say, . By random selection, if self-scattering is selected, k′ after the collision is the same as k and the carrier continues its flight without perturbation. Introducing a constant , the above equation reduces to
Random numbers r can be used very simply to generate stochastic free flights, which duration will then be given by . The computer time used for self-scattering is more than compensated for by the simplification of the calculation of the free-flight duration. To enhance the speed of free flight time calculation, several schemes such as “Constant Technique”, and “Piecewise Technique” are used to minimize the self-scattering events.
Scattering mechanisms
General background in solid-state physics
Important charge transport properties of semiconductor devices such as the deviance from Ohm's law and the saturation of carriers mobility are a direct consequence of scattering mechanisms. It is thus of great importance for a semiconductor device simulation to capture the physics of such mechanisms. The semiconductor Monte Carlo simulation, in this scope, is a very powerful tool for the ease and the precision with which an almost exhaustive array of scattering mechanisms can be included. The duration of the free flights is determined from the scattering rates. At the end of each flight, the appropriate scattering mechanism must be chosen in order to determine the final energy of the scattered carrier, or equivalently, its new momentum and scattering angle. In this sense, one will distinguish two broad types of scattering mechanisms which naturally derive form the classic
kinetic theory of collision between two bodies:
Elastic scattering, where the energy of the particle is conserved after being scattered. Elastic scattering will hence only change the direction of the particle's momentum. Impurity scattering and surface scattering are, with a fair approximation, two good examples of elastic scattering processes.
Inelastic scattering, where energy is transferred between the scattered particle and the scattering center. Electronphonon interactions are essentially inelastic since a phonon of definite energy is either emitted or absorbed by the scattered particle.
Before characterizing scattering mechanisms in greater mathematical details, it is important to note that when running semiconductor Monte Carlo simulations, one has to deal mainly with the following types of scattering events:
Acoustic Phonon: The charge carrier exchanges energy with an acoustic mode of the vibration of atoms in the crystal lattice. Acoustic Phonons mainly arise from thermal excitation of the crystal lattice.
Polar Optical: The charge carrier exchanges energy with one of the polar optical modes of the crystal lattice. These modes are not present in covalent semiconductors. Optical phonons arise from the vibration against each other of atoms of different types when there is more than one atom in the smallest unit cell, and are usually excited by light.
Non-Polar Optical: Energy is exchanged with an optical mode. Non-polar optical phonons must generally be considered in covalent semiconductors and the L-valley of GaAs.
Equivalent Intervalley Phonon: Due to the interaction with a phonon, the charge carrier transitions from initial states to final states which belong to different but equivalent valleys. Typically, this type of scattering mechanism describes the transition of an electron from one X-valley to another X-valley, or from one L-valley to another L-valley.
Non Equivalent Intervalley Phonon: Involves the transition of a charge carrier between valleys of different types.
Piezoelectric Phonon: For low temperatures.
Ionized Impurity: Reflects the deviation of a particle from it ballistic trajectory due to Coulomb interaction with an ionized impurity in the crystal lattice. Because the mass of an electron is relatively small in comparison to the one of an impurity, the Coulomb cross section decreases rapidly with the difference of the modulus of momentum between the initial and final state. Therefore, impurity scattering events are mostly considered for intravalley scattering, intraband scattering and, to a minor extent, interband scattering.
Carrier-Carrier: (electron-electron, hole-hole and electron-hole interactions). When carrier concentration is high, this type of scattering reflects the electrostatic interaction between charge carriers. This problem becomes very quickly computationally intensive with an increasing number of particles in an ensemble simulation. In this scope, Particle-Particle–Particle-Mesh (P3M) algorithms, which distinguish short range and long range interaction of a particle with its surrounding charge gas, have proved efficient in including carrier-carrier interaction in the semiconductor Monte Carlo simulation. Very often, the charge of the carriers is assigned to a grid using a Cloud-in-Cell method, where part of the charge of a given particle is assigned to a given number of closest grid points with a certain weight factor.
Plasmon: Reflects the effect of the collective oscillation of the charge carriers on a given particle.
Inclusion of scattering mechanisms in Monte Carlo
A computationally efficient approach to including scattering in Monte Carlo simulation consists in storing the scattering rates of the individual mechanisms in tables. Given the different scattering rates for a precise particle state, one may then randomly select the scattering process at the end of the free flight. These scattering rates are very often derived using the Born approximation, in which a scattering event is merely a transition between two momentum states of the carrier involved. As discussed in section II-I, the quantum many-body problem arising from the interaction of a carrier with its surrounding environment (phonons, electrons, holes, plasmons, impurities,...) can be reduced to a two-body problem using the quasiparticle approximation, which separates the carrier of interest from the rest of the crystal. Within these approximations,
Fermi's Golden Rule gives, to the first order, the transition probability per unit time for a scattering mechanism from a state to a state :
where H' is the perturbation Hamiltonian representing the collision and E and E′ are respectively the initial and final energies of the system constituted of both the carrier and the electron and phonon gas. The Dirac -function stands for the conservation of energy. In addition, the term , generally referred to as the matrix element, mathematically represents an inner product of the initial and final wave functions of the carrier:
In a crystal lattice, the wavefunctions and are simply Bloch waves. When it is possible, analytic expression of the Matrix elements are commonly found by Fourier expanding the Hamiltonian H', as in the case of Impurity scattering or acoustic phonon scattering. In the important case of a transition from an energy state E to an energy state E' due to a phonon of wave vector q and frequency , the energy and momentum change is:
where R is a reciprocal lattice vector. Umklapp processes (or U-processes) change the momentum of the particle after scattering and are therefore limiting the conduction in semiconductor crystals. Physically, U-processes occur when the final momentum of the particle points out of the first Brillouin zone. Once one knows the scattering probability per unit time from a state k to a state k', it is interesting to determine the scattering rate for a given scattering process. The scattering rate gives the probability per unit time to scatter from a state k to any other state in the reciprocal space. Therefore, the scattering rate is
which can be readily used to determine the free flight time and the scattering process as discussed in section 3-3. It is important to note that this scattering rate will be dependent on the band structure of the material (the dependence arises from the matrix elements).
Selection of scattering mode and scattered trajectory
At the end of a free flight, a scattering mode and angle must be randomly chosen. In order to determine the scattering mechanism, one has to consider all the scattering rates of the mechanisms relevant to the simulation as well as the total scattering rate at the time of scattering Selecting a scattering mechanism then simply results in generating a uniformly distributed random number 0 < r < 1 and referring to the following rules
A computationally efficient approach to selecting the scattering mechanism consists in adding a “void” scattering mechanism so that remains constant over time. If a particle is scattered according to this mechanism, it will keep its ballistic trajectory after scattering takes place. In order to choose a new trajectory, one must first derive the energy (or momentum) of the particle after scattering
where the term accounts for phonon emission or absorption and the term is non-null for inter-valley scattering. The final energy (and the band structure) directly yield the modulus of the new momentum k'. At this point one only needs to choose a new direction (or angle) for the scattered particle. In some simple cases as phonon scattering and a parabolic dispersion relation, the scattering angle is random and evenly distributed on the sphere of radius k'. Using spherical coordinates, the process of choosing the angle is equivalent to randomly picking two angles and . If the angle is distributed with a distribution , then for a uniform distribution of angles, the probability to pick a point of the sphere is
It is possible, in this case, to separate the two variables. Integrating over then over , one finds
The two spherical angles can then be chosen, in the uniform case, by generating two random numbers 0 < r1, r2 < 1 such that
Quantum corrections for Monte Carlo simulation
The current trend of scaling down semiconductor devices has forced physicists to incorporate quantum mechanical issues in order to acquire a thorough understanding of device behavior. Simulating the behavior of nano-scale devices necessitates the use of a full quantum transport model especially for cases when the quantum effects cannot be ignored. This complication, however, can be avoided in the case of practical devices like the modern day MOSFET, by employing quantum corrections within a semi-classical framework. The semi-classical Monte Carlo model can then be employed to simulate the device characteristics. The quantum corrections can be incorporated into a Monte Carlo simulator by simply introducing a quantum potential term which is superimposed onto the classical electrostatic potential seen by the simulated particles. Figure beside pictorially depicts the essential features of this technique. The various quantum approaches available for implementation are described in the following subsections.
Wigner-based correction
The Wigner transport equation forms the basis for the Wigner-based quantum correction.
where, k is the crystal momentum, V is the classical potential, the term on the RHS is the effect of collision, the fourth term on the LHS represents non-local quantum mechanical effects. The standard Boltzmann Transport Equation is obtained when the non-local terms on the LHS disappear in the limit of slow spatial variations. The simplified (for ) quantum corrected BTE then becomes
where the quantum potential is contained in the term (must be an error: was never mentioned).
Effective potential correction
This method for quantum correction was developed by Feynman and Hibbs in 1965. In this method the effective potential is derived by calculating the contribution to the path integral of a particle's quantum fluctuations around its classical path. This calculation is undertaken by a variational method using a trial potential to first order. The effective classical potential in the average point on each path then becomes
Schrödinger-based correction
This approach involves periodical solving of a Schrödinger equation in a simulation with the input being the self-consistent electrostatic potential. The exact energy levels and wavefunctions relating to the electrostatic potential solution are employed to calculate the quantum potential. The quantum correction obtained on the basis of this method can be visualised by the following equation
where Vschr is the quantum correction potential, z is the direction perpendicular to the interface, nq is the quantum density from the Schrödinger equation which is equivalent to the converged Monte Carlo concentration, Vp is the potential from the Poisson solution, V0 is the arbitrary reference potential far away from the quantum region such that the correction goes to null in the region of semi-classical behavior. Even though the above-mentioned potentials for quantum correction differ in their method of calculation and their basic assumptions, yet when it comes to their inclusion into Monte Carlo simulation they are all incorporated the same way.
See also
Monte Carlo method
Semiconductor device
Monte Carlo method for photon transport
Electronic band structure
Method of quantum characteristics
Quantum Monte Carlo
Quasi-Monte Carlo method
References
Monte Carlo methods
Quantum mechanics
Semiconductor analysis | Monte Carlo methods for electron transport | Chemistry | 4,369 |
74,642,799 | https://en.wikipedia.org/wiki/Tourmaline%20Reef | Tourmaline Reef (Spanish: Arrecife de Tourmaline) is a shelf-edge reef located in the Mona Passage off Mayagüez Bay in western Puerto Rico. The reef is one of the best-preserved reefs of its type in Puerto Rico as it is found far away enough from the coast and was selected as one of the first coral reef protection zones under the Puerto Rico Coastal Zone Management Program (Programa de Manejo de la Zona Costanera de Puerto Rico). Tourmaline Reef is located close to Punta Guanajibo, at 7.5 nautical miles from Mayagüez, at depths of up to 10 meters under the ocean surface bordering in waters of moderate to high visibility due to minimal terrigenous or sedimentary deposits.
Conservation
The reef system is protected as the Tourmaline Reef Nature Reserve (Reserva Natural Arrecife de Tourmaline), managed by the Puerto Rico Department of Natural Resources (DRNA) which provides management plans and conservation resources that limit the fishing activities in the area for the purpose of preserving its delicate ecosystem, previously threatened by the overfishing of red grouper (Epinephelus guttatus). The reserve extends between the maritime borders of the municipalities of Mayagüez and Cabo Rojo. The coral cover of the reef is currently at approximately 40% in 2009, a decrease from 60% in 2003. In addition to the coral ecosystem, the reserve also protects tracts of seagrass prairies, important for species such as sea turtles and the West Indian manatee.
References
Coral reefs
Protected areas of Puerto Rico | Tourmaline Reef | Biology | 328 |
14,550,347 | https://en.wikipedia.org/wiki/Bevirimat | Bevirimat (research code MPC-4326) is an anti-HIV drug derived from a betulinic acid-like compound, first isolated from Syzygium claviflorum, a Chinese herb. It is believed to inhibit HIV by a novel mechanism, so-called maturation inhibition. It is not currently U.S. Food and Drug Administration (FDA) approved. It was originally developed by the pharmaceutical company Panacos and reached Phase IIb clinical trials. Myriad Genetics announced on January 21, 2009 the acquisition of all rights to bevirimat for $7M USD. On June 8, 2010 Myriad Genetics announced that it was abandoning their HIV portfolio to focus more on cancer drug development.
Pharmacokinetics
According to the only currently available study, "the mean terminal elimination half-life of bevirimat ranged from 56.3 to 69.5 hours, and the mean clearance ranged from 173.9 to 185.8 mL/hour."
Mechanism of action
Like protease inhibitors, bevirimat and other maturation inhibitors interfere with protease processing of newly translated HIV polyprotein precursor, called gag. Gag is an essential structural protein of the HIV virus. Gag undergoes a chain of interactions both with itself and with other cellular and viral factors to accomplish the assembly of infectious virus particles. HIV assembly is a two-stage process involving an intermediate immature capsid that undergoes a structurally dramatic maturation to yield the infectious particle. This alteration is mediated by the viral protease, which cleaves the Gag polyprotein precursor, allowing the freed parts to reassemble to form the core of the mature virus particle. Bevirimat prevents this viral replication by specifically inhibiting cleavage of the capsid protein (CA) from the SP1 spacer protein. First, bevirimat enters a growing virus particle as it buds from an infected cell and binds to the Gag polypeptide at the CA/SP1 cleavage site. This prevents the protease enzyme from cleaving CA-SP1. As the capsid protein remains bound to SP1, the virus particle core is prevented from compressing into its normal mature shape, which is crucial for infectivity, resulting in the release of an immature, non-infectious particle.
Metabolism
It has been found that bevirimat does not inhibit the cytochrome P450 system or interact with the human P-glycoprotein. Unformulated bevirimat is not well absorbed from the gastrointestinal tract into the blood. Some of the less desirable properties of unformulated bevirimat and its salts include: inadequate bioavailability, poor solubility of the pharmaceutical composition in gastric fluid, insufficient dispersion of bevirimat in gastric fluid, below standard long term safety profile for oral dosage forms, below standard long term chemical and physical stability of the final dosage form, tendency for conversion to metastable forms, lengthy dissolution times for oral dosage forms, and precipitation in gastric or intestinal fluids. Some pharmaceutical compositions of formulated bevirimat have shown to have better properties over unformulated bevirimat. Some of these properties include: improved bioavailability, improved solubility of the composition in gastric fluid, improved dispersion of bevirimat in gastric fluid, improved safety for oral dosage forms, improved chemical and physical stability of the oral dosage form, decreased conversion to metastable forms, and decreased rate of precipitation in gastric fluid. Bevirimat was rapidly absorbed after oral administration, with detectable concentrations present in the plasma within 15 minutes after administration and peak plasma concentrations were achieved approximately one to three hours after administration. The plasma had a mean plasma elimination half-life ranging from 58 to 80 hours. This long half-life of bevirimat supports once-daily dosing. Elimination of bevirimat is primarily via hepatobiliary routes, with renal elimination counting for less than 1% of the dose.
Toxicity and side effects
Preclinical studies have not presented any sign that bevirimat might be associated with any specific safety concerns that would limit its clinical use. In vitro preclinical studies in human cells propose that bevirimat should have low potential for cytotoxicity. There is no evidence of any reproductive or developmental toxicity and it is not immunotoxic. Bevirimat was initially evaluated for safety and pharmacokinetics in a single-dose, randomized, double-blind, placebo-controlled phase clinical study in healthy volunteers. It was administered as an oral solution in doses of 25, 50, 100, and 250 mg. The plasma concentrations were dose-proportional, and the compound was seen to be safe and well tolerated with no dose-limiting toxicities and no serious adverse effects. In one clinical trial, headaches was the most commonly reported side effect of bevirimat, reported by four participants on bevirimat and one on the placebo. The second most common reported side effect was throat discomfort by two participants on bevirimat. No serious adverse effects were reported, all adverse effects reported were mild, and no participants discontinued use of bevirimat because of the adverse effects.
Resistance
In vitro studies have shown that presence of a number of single nucleotide polymorphisms in the CA/SP1 cleavage site have resulted in resistance to bevirimat. However, mutations at these sites were not found in phase I and II clinical trials. Instead, mutations in the glutamine-valine-threonine (QVT) motif of the SP1 peptide are also known to cause bevirimat resistance. In addition, V362I mutations have been shown to confer strong resistance to bevirimat, where the S373P and I376V mutations may confer low resistance to bevirimat. A further complication of the use of bevirimat is that, since bevirimat targets the CA/SP1 cleavage site, it could also be used in the treatment of protease inhibitor resistant patients. Except for A364V, mutations in the CA/SP1 cleavage site have showed to result in fitness deficits when combined with protease inhibitor resistance. This proposes that these mutations may develop slowly. It has been shown that protease inhibitor resistance can result in an increase in the occurrence of mutations within the downstream QVT motif.
Clinical trials
In December 2007, some results of the Phase IIb trial were released. Thomson Financial News reported that, "some patients respond 'very well' to the drug, while another population 'does not respond as well at current dose levels.'" Panacos said it intends to add a group to the study at a higher dosage. The drug manufacturer, Panacos, has stated that success with bevirimat hinges on a patient's particular HIV not having a specific group of genetic mutations in HIV’s Gag protein. When they evaluated the study participants’ virus and found that the participant’s virologic response depended greatly on whether or not the Gag protein of a participant’s virus had polymorphisms—multiple mutations in the protein’s structure. After sampling the virus of 100 patients in the company’s database, they found that about 50 percent did not have Gag polymorphisms, meaning that about 50 percent would likely respond well to the drug.
See also
BMS-955176
References
External links
AIDSmeds Bevirimat
An animation illustrating Bevirimat's mechanism of action
Overview and Publication Listing for Bevirimat from Panacos
Carboxylic acids
Maturation inhibitors
Triterpenes
Experimental antiviral drugs
Cyclopentanes | Bevirimat | Chemistry | 1,613 |
14,190,268 | https://en.wikipedia.org/wiki/Operational%20system | An operational system is a term used in data warehousing to refer to a system that is used to process the day-to-day transactions of an organization. These systems are designed in a manner that processing of day-to-day transactions is performed efficiently and the integrity of the transactional data is preserved.
Synonyms
Sometimes operational systems are referred to as operational databases, transaction processing systems, or online transaction processing systems (OLTP). However, the use of the last two terms as synonyms may be confusing, because operational systems can be batch processing systems as well.
Any enterprise must necessarily maintain a lot of data about its operation.
See also
Data warehouses versus operational systems
Operating system (OS)
Operational data store, a database used for operational reporting, and as a source of data for a data warehouse
Data warehousing
Data management
Business intelligence | Operational system | Technology | 172 |
2,082,726 | https://en.wikipedia.org/wiki/Beck%27s%20monadicity%20theorem | In category theory, a branch of mathematics, Beck's monadicity theorem gives a criterion that characterises monadic functors, introduced by in about 1964. It is often stated in dual form for comonads. It is sometimes called the Beck tripleability theorem because of the older term triple for a monad.
Beck's monadicity theorem asserts that a functor
is monadic if and only if
U has a left adjoint;
U reflects isomorphisms (if U(f) is an isomorphism then so is f); and
C has coequalizers of U-split parallel pairs (those parallel pairs of morphisms in C, which U sends to pairs having a split coequalizer in D), and U preserves those coequalizers.
There are several variations of Beck's theorem: if U has a left adjoint then any of the following conditions ensure that U is monadic:
U reflects isomorphisms and C has coequalizers of reflexive pairs (those with a common right inverse) and U preserves those coequalizers. (This gives the crude monadicity theorem.)
Every diagram in C which is by U sent to a split coequalizer sequence in D is itself a coequalizer sequence in C. In different words, U creates (preserves and reflects) U-split coequalizer sequences.
Another variation of Beck's theorem characterizes strictly monadic functors: those for which the comparison functor is an isomorphism rather than just an equivalence of categories. For this version the definitions of what it means to create coequalizers is changed slightly: the coequalizer has to be unique rather than just unique up to isomorphism.
Beck's theorem is particularly important in its relation with the descent theory, which plays a role in sheaf and stack theory, as well as in the Alexander Grothendieck's approach to algebraic geometry. Most cases of faithfully flat descent of algebraic structures (e.g. those in FGA and in SGA1) are special cases of Beck's theorem. The theorem gives an exact categorical description of the process of 'descent', at this level. In 1970 the Grothendieck approach via fibered categories and descent data was shown (by Jean Bénabou and Jacques Roubaud) to be equivalent (under some conditions) to the comonad approach. In a later work, Pierre Deligne applied Beck's theorem to Tannakian category theory, greatly simplifying the basic developments.
Examples
The forgetful functor from topological spaces to sets is not monadic as it does not reflect isomorphisms: continuous bijections between (non-compact or non-Hausdorff) topological spaces need not be homeomorphisms.
shows that the functor from commutative C*-algebras to sets sending such an algebra A to the unit ball, i.e., the set , is monadic. Negrepontis also deduces Gelfand duality, i.e., the equivalence of categories between the opposite category of compact Hausdorff spaces and commutative C*-algebras can be deduced from this.
The powerset functor from Setop to Set is monadic, where Set is the category of sets. More generally Beck's theorem can be used to show that the powerset functor from Top to T is monadic for any topos T, which in turn is used to show that the topos T has finite colimits.
The forgetful functor from semigroups to sets is monadic. This functor does not preserve arbitrary coequalizers, showing that some restriction on the coequalizers in Beck's theorem is necessary if one wants to have conditions that are necessary and sufficient.
If B is a faithfully flat commutative ring over the commutative ring A, then the functor T from A modules to B modules taking M to B⊗AM is comonadic. This follows from the dual of Becks theorem, as the condition that B is flat implies that T preserves finite limits, while the condition that B is faithfully flat implies that T reflects isomorphisms. A coalgebra over T turns out to be essentially a B-module with descent data, so the fact that T is comonadic is equivalent to the main theorem of faithfully flat descent, saying that B-modules with descent are equivalent to A-modules.
External links
References
pdf
(3 volumes).
Adjoint functors
Category theory | Beck's monadicity theorem | Mathematics | 941 |
17,710,948 | https://en.wikipedia.org/wiki/Ispronicline | Ispronicline (TC-1734, AZD-3480) is an experimental drug which acts as a partial agonist at neural nicotinic acetylcholine receptors. It progressed to phase II clinical trials for the treatment of dementia and Alzheimer's disease, but is no longer under development.
It has also progressed to phase II as a potential treatment for ADHD. With dosages of 50 mg/day showing a significant improvement in ADHD symptoms
Ispronicline is subtype-selective, binding primarily to the α4β2 subtype. It has antidepressant, nootropic and neuroprotective effects.
Early stage clinical trials showed that ispronicline was well tolerated, with the main side effects being dizziness and headache. However, mid-stage clinical trials failed to show sufficient efficacy to continue development as a pharmaceutical drug.
See also
Rivanicline
References
Nootropics
Pyridines
Nicotinic agonists
Stimulants
Ethers
Amines
Isopropyl compounds
Alkene derivatives | Ispronicline | Chemistry | 219 |
1,879,354 | https://en.wikipedia.org/wiki/Telluride%20%28chemistry%29 | The telluride ion is the anion Te2− and its derivatives. It is analogous to the other chalcogenide anions, the lighter O2−, S2−, and Se2−, and the heavier Po2−.
In principle, Te2− is formed by the two-e− reduction of tellurium. The redox potential is −1.14 V.
Te(s) + 2 e− ↔ Te2−
Although solutions of the telluride dianion have not been reported, soluble salts of bitelluride (TeH−) are known.
Organic tellurides
Tellurides also describe a class of organotellurium compounds formally derived from Te2−. An illustrative member is dimethyl telluride, which results from the methylation of telluride salts:
2 CH3I + Na2Te → (CH3)2Te + 2 NaI
Dimethyl telluride is formed by the body when tellurium is ingested. Such compounds are often called telluroethers because they are structurally related to ethers with tellurium replacing oxygen, although the length of the C–Te bond is much longer than a C–O bond. C–Te–C angles tend to be closer to 90°.
Inorganic tellurides
Many metal tellurides are known, including some telluride minerals. These include natural gold tellurides, like calaverite and krennerite (AuTe2), and sylvanite (AgAuTe4). They are minor ores of gold, although they comprise the major naturally occurring compounds of gold. (A few other natural compounds of gold, such as the bismuthide maldonite (Au2Bi) and antimonide aurostibite (AuSb2), are known). Although the bonding in such materials is often fairly covalent, they are described casually as salts of Te2−. Using this approach, Ag2Te is derived from Ag+ and Te2−. Catenated Te anions are known in the form of the polytellurides. They arise by the reaction of telluride dianion with elemental Te:
Te2- + n Te → Ten+12-
Applications
Tellurides have no large scale applications aside from cadmium telluride photovoltaics. Both bismuth telluride and lead telluride are exceptional thermoelectric materials. Some of these thermoelectric materials have been commercialized.
References
Anions | Telluride (chemistry) | Physics,Chemistry | 530 |
28,567,784 | https://en.wikipedia.org/wiki/General%20levelling%20of%20France | The General Levelling of France (niveau général de la France or NGF)
forms a network of benchmarks in mainland France and Corsica, now overseen by the Institut Géographique National. It is now the official levelling network in mainland France. It is made up of two networks:
NGF - IGN69 for mainland France, with the 'zero level' determined by the tide gauge at Marseille
NGF - IGN78 for Corsica, with the 'zero level' determined by the tide gauge at Ajaccio
Topography
Geography of France
Geodesy
Vertical datums | General levelling of France | Mathematics | 119 |
30,834,082 | https://en.wikipedia.org/wiki/MENTAL%20domain | The MENTAL or MLN64 NH2-terminal domain is a membrane-spanning domain that is conserved in two late endosomal proteins in vertebrates, MLN64 and MENTHO. The domain is 170 amino acids long.
Current data indicates that this domain allows for dimerization between MLN64 and MENTHO molecules and with themselves. The domain may also direct cholesterol transport.
References
Protein domains | MENTAL domain | Biology | 85 |
30,639,232 | https://en.wikipedia.org/wiki/Archive%20for%20Mathematical%20Logic | Archive for Mathematical Logic is a peer-reviewed mathematics journal published by Springer Science+Business Media. It was established in 1950 and publishes articles on mathematical logic.
Abstracting and indexing
The journal is abstracted and indexed in:
Mathematical Reviews
Zentralblatt MATH
Scopus
SCImago
According to the Journal Citation Reports, the journal has a 2020 impact factor of 0.287.
References
External links
English-language journals
Mathematical logic journals
Mathematical logic
Academic journals established in 1950
Springer Science+Business Media academic journals
1950 establishments in West Germany | Archive for Mathematical Logic | Mathematics | 107 |
66,175,500 | https://en.wikipedia.org/wiki/Dana%20Carroll | Dana Carroll is an American molecular biologist and biochemist at the University of Utah School of Medicine who has made important contributions to the field of genome editing. He has been a member of the National Academy of Sciences since 2017.
References
Living people
Year of birth missing (living people)
American molecular biologists
Genome editing
United States National Academy of Sciences
Place of birth missing (living people) | Dana Carroll | Engineering,Biology | 77 |
44,613,946 | https://en.wikipedia.org/wiki/MY%20Camelopardalis | MY Camelopardalis (MY Cam) is a binary star system located in the Alicante 1 open cluster, some away in the constellation Camelopardalis. It is one of the most massive known binary star systems and a leading candidate for a massive star merger. MY Cam is the brightest star in Alicante 1.
The system consists of two hot blue O-type stars with one component having a mass of 32 solar masses and the other 38 solar masses.
In 1998, the star was included in a list of suspected variable stars. John Greaves and Patrick Wils proved that it is variable, in 2004. It was given its variable star designation, MY Camelopardalis, in 2008. MY Cam is a contact binary and eclipsing binary, with an orbital period of 1.2 days, and an orbital velocity of . Both stars share a common envelope.
References
Camelopardalis
Common envelope binary stars
Eclipsing binaries
O-type main-sequence stars
Camelopardalis, MY
J03591829+5714137
Emission-line stars
Durchmusterung objects | MY Camelopardalis | Astronomy | 227 |
40,922,605 | https://en.wikipedia.org/wiki/Residential%20Customer%20Equivalent | Residential Customer Equivalent (RCE) is a unit of measures used by the energy industry to denote the typical annual commodity consumption by a single-family residential customer. Also known as "RCE" for short, a single RCE represents 1,000 therms of natural gas or 10,000 kWh of electricity.
RCE is often used to help normalize the size of energy companies. Energy companies serve a number of customers that is typically different from the RCE value consumed by those customers. For example, an LDC or ESCO may serve 50,000 customers but many of those can be commercial or industrial customers, so that same company can be said to serve 400,000 RCE.
References
Energy economics
Equivalent units | Residential Customer Equivalent | Mathematics,Environmental_science | 149 |
33,807,629 | https://en.wikipedia.org/wiki/Hindgut%20fermentation | Hindgut fermentation is a digestive process seen in monogastric herbivores (animals with a simple, single-chambered stomach). Cellulose is digested with the aid of symbiotic microbes including bacteria, archaea, and eukaryotes. The microbial fermentation occurs in the digestive organs that follow the small intestine: the cecum and large intestine. Examples of hindgut fermenters include proboscideans and large odd-toed ungulates such as horses and rhinos, as well as small animals such as rodents, rabbits and koalas.
In contrast, foregut fermentation is the form of cellulose digestion seen in ruminants such as cattle which have a four-chambered stomach, as well as in sloths, macropodids, some monkeys, and one bird, the hoatzin.
Cecum
Hindgut fermenters generally have a cecum and large intestine that are much larger and more complex than those of a foregut or midgut fermenter. Research on small cecum fermenters such as flying squirrels, rabbits and lemurs has revealed these mammals to have a GI tract about 10-13 times the length of their body. This is due to the high intake of fiber and other hard to digest compounds that are characteristic to the diet of monogastric herbivores.
Easily digestible food is processed in the gastrointestinal tract & expelled as regular feces. But in order to get nutrients out of hard to digest fiber, some smaller hindgut fermenters, like lagomorphs (rabbits, hares, pikas), ferment fiber in the cecum (at the small and large intestine junction) and then expel the contents as cecotropes, which are reingested (cecotrophy). The cecotropes are then absorbed in the small intestine to utilize the nutrients.
This process is also beneficial in allowing for restoration of the microflora population, or gut flora. These microbes are found in the gastrointestinal tract and can act as protective agents that strengthen the immune system. Small hindgut fermenters have the ability to expel their microflora, which is useful during the acts of hibernation, estivation and torpor.
Efficiency
While foregut fermentation is generally considered more efficient, and monogastric animals cannot digest cellulose as efficiently as ruminants, hindgut fermentation allows animals to consume small amounts of low-quality forage all day long and thus survive in conditions where ruminants might not be able to obtain nutrition adequate for their needs. While ruminants require a good deal of time resting between meals, hindgut fermenters are able to take in smaller meals more frequently, allowing them to eat and move more readily. The large hindgut fermenters are bulk feeders: they ingest large quantities of low-nutrient food, which they process more rapidly than would be possible for a similarly sized foregut fermenter. The main food in that category is grass, and grassland grazers move over long distances to take advantage of the growth phases of grass in different regions.
Speed
The ability to process food more rapidly than foregut fermenters gives hindgut fermenters an advantage at very large body size, as they are able to accommodate significantly larger food intakes. The largest extant and prehistoric megaherbivores, elephants and indricotheres (a type of rhino), respectively, have been hindgut fermenters. Study of the rates of evolution of larger maximum body mass in different terrestrial mammalian groups has shown that the fastest growth in body mass over time occurred in hindgut fermenters (perissodactyls, rodents and proboscids).
Types
Hindgut fermenters are subdivided into two groups based on the relative size of various digestive organs in relationship to the rest of the system: colonic fermenters tend to be larger species such as horses, and cecal fermenters are smaller animals such as rabbits and rodents. However, in spite of the terminology, colonic fermenters such as horses make extensive use of the cecum to break down cellulose. Also, colonic fermenters typically have a proportionally longer large intestine than small intestine, whereas cecal fermenters have a considerably enlarged cecum compared to the rest of the digestive tract.
Insects
In addition to mammals, several insects are also hindgut fermenters, the best studied of which are the termites, which are characterised by an enlarged "paunch" of the hindgut that also houses the bulk of the gut microbiota. Digestion of wood particles in lower termites is accomplished inside the phagosomes of gut flagellates, but in the flagellate-free higher termites, this appears to be accomplished by fibre-associated bacteria.
See also
Foregut fermentation
Pseudoruminants
Ruminants
Cecotrope
References
Digestive system
Biology terminology | Hindgut fermentation | Biology | 1,070 |
40,254,534 | https://en.wikipedia.org/wiki/Sch%20642305 | Sch 642305 is a chemical compound isolated from Penicillium verrucosum that inhibits bacterial DNA primase.
References
Lactones
Heterocyclic compounds with 2 rings | Sch 642305 | Chemistry | 43 |
38,668,606 | https://en.wikipedia.org/wiki/Kepler-32 | Kepler-32 is an M-type main sequence star located about 1053 light years from Earth, in the constellation of Cygnus. Discovered in January 2012 by the Kepler spacecraft, it shows a 0.58 ± 0.05 solar mass (), a 0.53 ± 0.04 solar radius (), and temperature of 3900.0 K, making it half the mass and radius of the Sun, two-thirds its temperature and 5% its luminosity.
Planetary system
In 2011, 2 planets orbiting around it, were discovered, and two more suspected. The smaller Kepler-32b, orbiting its parent star every 5.90124 days, and Kepler-32c with an orbital period of 8.7522 days. In April 2013, transit-timing variation analysis confirmed 3 other planets to be in the system. However, only very loose constraints of the maximum mass of the planets could be determined.
In 2014, the dynamical simulation shown what the Kepler-32 planetary system have likely undergone a substantial inward migration in the past, producing an observed pattern of lower-mass planets on tightest orbits. Additional yet unobserved gas giant planets on wider orbit are likely necessary for migration of smaller planets to proceed that far inward, although current planetary systems would be unstable if additional planets are located closer than 8.7 AU from the parent star.
References
Cygnus (constellation)
M-type main-sequence stars
952
Planetary systems with five confirmed planets
Planetary transit variables
J19512217+4634273 | Kepler-32 | Astronomy | 313 |
40,474,926 | https://en.wikipedia.org/wiki/WASP-56 | WASP-56 is a sun-like star of spectral type G6 in the constellation of Coma Berenices. It has an apparent magnitude of 11.48. Observations at the Calar Alto Observatory using the lucky imaging technique detected a candidate companion star located 3.4 arc seconds away, however it is not known if this is an actual binary companion or an optical double.
Planetary system
It has a planet that was discovered by transit photometry in 2011 by the SuperWASP program. Fourteen transits were observed over three watching seasons, each lasting 214 minutes and reducing the stars' brightness by 14 millimagnitudes. The planet has around 0.6 times the mass of Jupiter and an orbital period of 4.6 days. The planet possibly has a large core of heavy metals.
References
Coma Berenices
G-type main-sequence stars
Solar analogs
Planetary systems with one confirmed planet
Planetary transit variables
J12132790+2303205 | WASP-56 | Astronomy | 194 |
3,019,076 | https://en.wikipedia.org/wiki/Cartwheel%20Galaxy | The Cartwheel Galaxy (also known as ESO 350-40 or PGC 2248) is a lenticular ring galaxy about 500 million light-years away in the constellation Sculptor. It has a D25 isophotal diameter of , and a mass of about solar masses; its outer ring has a circular velocity of .
It was discovered by Fritz Zwicky in 1941. Zwicky considered his discovery "one of the most complicated structures awaiting its explanation on the basis of stellar dynamics."
The Third Reference Catalogue of Bright Galaxies (RC3) measured a D25 isophotal diameter for the Cartwheel Galaxy at about 60.9 arcseconds, giving it a diameter of based on a redshift-derived distance of .
This diameter is slightly smaller than that of the Andromeda Galaxy.
The large Cartwheel Galaxy is the dominant member of the Cartwheel Galaxy group, consisting of four physically associated spiral galaxies. The three companions are referred to in several studies as G1, the smaller irregular blue Magellanic spiral; G2, the yellow compact spiral with a tidal tail; and G3, a more distant spiral often seen in wide field images.
One supernova has been observed in the Cartwheel Galaxy. SN 2021afdx (type II, mag. 18.8) was discovered by ATLAS on 23 November 2021.
Structures
The structure of the Cartwheel Galaxy is noted to be highly complicated and heavily disturbed. The Cartwheel consists of two rings: the outer ring, the site of massive ongoing star formation due to gas and dust compression; and the inner ring that surrounds the galactic center. A ring of dark absorbing dust is also present in the nucleic ring. Several optical arms or "spokes" are seen connecting the outer ring to the inner. Observations show the presence of both non-thermal radio continuum and optical spokes, but the two do not seem to overlap.
Evolution
The galaxy was once a normal spiral galaxy before it apparently underwent a head-on "bullseye" style collision with a smaller companion approximately 200–300 million years prior to how we see the system today. When the nearby galaxy passed through the Cartwheel Galaxy, the force of the collision caused a powerful gravitational shock wave to expand through the galaxy. Moving at high speed, the shock wave swept up and compressed gas and dust, creating a Starburst region around the galaxy's center portion that went unscathed as it expanded outwards. This explains the bluish ring around the center, which is the brighter portion. It can be noted that the galaxy is beginning to retake the form of a normal spiral galaxy, with arms spreading out from a central core. These arms are often referred to as the cartwheel's “spokes”.
Alternatively, a model based on the gravitational Jeans instability of both axisymmetric (radial) and nonaxisymmetric (spiral) small-amplitude gravity perturbations allows an association between growing clumps of matter and the gravitationally unstable axisymmetric and nonaxisymmetric waves which take on the appearance of a ring and spokes. Based on observational data, however, this theory of ring galaxy evolution does not appear to apply to this specific galaxy.
While most images of the Cartwheel display three galaxies close together, a fourth physically associated companion (also known as G3) is known to be associated with the group through an HI (or neutral hydrogen) tail that connects G3 to the cartwheel. Due to the presence of the HI tail, it is widely believed that G3 is the "bullet" galaxy that plunged through the disk of the cartwheel, creating its current shape, not G1 or G2. This hypothesis makes sense given the size and predicted age of the current structure (~300 million years old as mentioned before). Considering how close G1 and G2 are to the Cartwheel still, it is much more widely believed that the roughly 88 kpc (~287,000 light years) distant G3 is the intruding galaxy.
HI tail mapping is extremely useful in determining “culprit” galaxies in similar cases where the solution is relatively unclear. Hydrogen gas, being the lightest and most abundant gas in galaxies, is easily torn away from parent galaxies through gravitational forces. Evidence of this can be seen in the Jellyfish Galaxy and the Comet Galaxy, which are undergoing a type of gravitational effect called ram pressure stripping, and other galaxies with tidal tails and star forming stellar streams associated with collisions and mergers. Ram pressure stripping will almost always cause trailing-dominant tails of HI gas as a galaxy infalls into a galaxy cluster, while mergers and collisions like the ones involving in Cartwheel galaxy often create leading-dominant tails as the culprit galaxy’s gravity attracts and pulls on the victim galaxy’s gas in the direction of the culprit's motion.
The existing structure of the cartwheel is expected to disintegrate over the next few hundred million years as the remaining gas, dust and stars that haven’t escaped the galaxy begin to infall back towards the center. It is likely that the galaxy will regain a spiral shape after the infall process completes and spiral density waves have a chance to reform. This is only possible if companions G1, G2 and G3 remain distant and do not undergo an additional collision with the cartwheel.
X-ray sources
The unusual shape of the Cartwheel Galaxy may be due to a collision with a smaller galaxy such as one of those in the lower left of the image. The most recent starburst has lit up the Cartwheel rim, which has a diameter larger than that of the Milky Way. Star formation via starburst galaxies, such as the Cartwheel Galaxy, results in the formation of large and extremely luminous stars. When massive stars explode as supernovas, they leave behind neutron stars and black holes. Some of these neutron stars and black holes have nearby companion stars, and become powerful sources of X-rays as they pull matter off their companions (also known as ultra and hyperluminous X-ray sources). The brightest X-ray sources are likely black holes with companion stars, appearing as the white dots that lie along the rim of the X-ray image. The Cartwheel contains an exceptionally large number of these black hole binary X-ray sources, because many massive stars formed in the ring.
References
External links
Galaxy Evolution Simulation:The Cartwheel Galaxy
Cartwheel Galaxy at Constellation Guide
Webb Captures Stellar Gymnastics in The Cartwheel Galaxy nasa.gov
Lenticular galaxies
Peculiar galaxies
Ring galaxies
Sculptor (constellation)
02248
Astronomical objects discovered in 1941 | Cartwheel Galaxy | Astronomy | 1,346 |
59,242,945 | https://en.wikipedia.org/wiki/Operation%20Northern%20Shield | Operation Northern Shield () was an Israeli military operation that took place from 4 December 2018 until 13 January 2019. The operation's declared goal was to locate and destroy Hezbollah tunnels that cross the Blue Line from Lebanon into northern Israel. According to Israel, this operation is part of the ongoing Iran–Israel proxy conflict. On 17 December 2018, United Nations Interim Force in Lebanon (UNIFIL) acknowledged the existence of four tunnels near the Israel–Lebanon border and confirmed that two of them cross the Blue Line in violation of United Nations Security Council Resolution 1701, which helped end the 2006 Lebanon War.
Background
The Israel Defense Forces (IDF) started searching for Hezbollah tunnels into Israel in 2013 after residents of northern Israel reported hearing sounds of digging, but failed to find anything. After the 2014 Gaza War, which saw numerous tunnels dug by Hamas from the Gaza Strip into Israel being uncovered and being utilized in several attacks, the IDF renewed its search for Hezbollah tunnels in northern Israel, and this time found indications that such tunnels existed. A laboratory made up of soldiers from technology and intelligence units was formed to investigate it, based on a similar laboratory investigating Hamas tunnels in southern Israel. A variety of seismic sensors and radar systems were used to locate the tunnels.
The operation was planned two and a half years in advance. After realizing that Hezbollah's tunnels would need to be dealt with in 2015, a team of IDF military engineers, intelligence officers, and technology experts determined that plans should be made for destroying the tunnels. Preparations were made in secrecy, with many participants told they were participating in routine training. Senior officers in the IDF Combat Engineering Corps realized that the hard, rocky terrain of northern Israel, as opposed to the soft, sandy terrain of the area where Hamas tunnels were dug in the south, would pose a challenge that the IDF was not accustomed to. In 2017, it was decided to send 11 Engineering Corps personnel to Europe to learn about hard-rock excavation.
According to a senior Israeli official, the operation was launched in December 2018 due to fears that the details of the planned operation would be leaked. It was feared that Hezbollah might attempt to utilize them and launch a kidnap operation if it discovered that Israel knew about the tunnels.
Events
For the operation, the IDF deployed combat engineering units including the Yahalom special unit, bulldozers and other heavy equipment.
During the first day of the operation, on 4 December, the IDF said it had uncovered a tunnel near the Israeli town of Metula with an estimated length of that "extended more than " into Israel. The Washington Post reported that this tunnel was likely monitored for several years by Israel. While uncovering the first tunnel, the IDF placed a camera inside the tunnel and caught on video two suspected Hezbollah members inside, one of whom was identified by Israel as Dr. Imad "Azaladin" Fahs, who is reportedly known as a "commander for the Hezbollah observation unit on the border with Israel and a commander in the tunnel unit."
Hezbollah claimed that the man spotted in the tunnel is a drug smuggler, and is not among its ranks.
On 6 December 2018, UNIFIL confirmed the existence of the first cross-border tunnel. On the same day, the IDF said it discovered a second tunnel originating from the village of Ramyah near the border, and demanded that UNIFIL reach the tunnel from the Lebanese side and said that "whoever enters the underground perimeter endangers his life".
Also on that day, Israel demanded that Lebanon and UNIFIL destroy the tunnels, saying that it "holds the Lebanese government, the Lebanese Armed Forces and United Nations Interim Force in Lebanon responsible for all events transpiring in and emanating from Lebanon". UNIFIL said that it was "engaged with the parties to pursue urgent follow-up action". According to Al-Manar, the Lebanese Foreign Minister, Gebran Bassil instructed the Lebanese UN envoy to say that Israel is conducting "a diplomatic and political campaign against Lebanon in preparation for attacks against it." As of 8 December 2018, Lebanon has not responded publicly to the Israeli demand, with Lebanese sources telling Asharq Al-Awsat that "all concerned official parties were following up on the issue and they are exerting efforts to address it away from the media or political spotlight" and that Lebanon is working on a UN complaint asserting that Israel's "diplomatic and political campaign against Lebanon that are a precursor to waging attacks against it."
On 11 December 2018, the IDF said it located a third tunnel crossing into Israel. On the same day, UNIFIL confirmed the existence of the second cross-border tunnel.
On 16 December 2018, the IDF said it located a fourth tunnel crossing into Israel, and that as the tunnel had been rigged with explosives anyone entering it from the Lebanese side would be risking their life.
On 17 December 2018, IDF troops placed rolls of concertina wire on the Israeli side of the Blue Line. During placement of the wire, a non-violent confrontation took place between Israeli and Lebanese soldiers. Also on 17 December 2018, UNIFIL acknowledged the existence of four tunnels near the Israel–Lebanon border, and said "UNIFIL at this stage can confirm that two of the tunnels cross the Blue Line" in violations of United Nations Security Council Resolution 1701.
On 19 December 2018, in a special session of the United Nations Security Council, Israel urged the UNSC to condemn Hezbollah and designate it as a terrorist organization. Israel also accused Hezbollah of storing weapons in private homes. Jean-Pierre Lacroix, the UN peacekeeping chief, said UNFIL confirmed four tunnels including two that cross into Israel, a "serious violation" of the 2006 ceasefire resolution (1701). The Lebanese ambassador Amal Mudallali, said that Lebanon takes the matter seriously and remains committed to resolution 1701. However, Mudallali also accused Israel of repeated airspace violations by the Israeli Air Force. While several countries on the council joined Israel in condemning the tunnels, the council took no action at the end of a stormy session.
On 25 December, the IDF announced that it had found a fifth tunnel several days before, and that it had been neutralized with explosives.
On 13 January 2019, the IDF found a sixth tunnel, which it claimed was the largest and most sophisticated discovered. It had electrical lighting, a rail system for moving equipment, garbage disposal, and stairs. The IDF announced that this was the final tunnel, but that it was monitoring other areas along the border where Hezbollah was digging underground infrastructure that had yet to cross into Israel. With this discovery, the IDF announced the conclusion of Operation Northern Shield.
Lebanese view
According to an anonymous Lebanese security source speaking to the Lebanese newspaper Al Joumhouria, the tunnels were "old and deserted", and were exploited by Israel for political ends. Their source stated that Israel had announced the discovery of the tunnels long ago, but was only now using them for political gain.
Hassan Nasrallah, in response to the operation stated that he was surprised that it took so long for Israelis to find the tunnels, and that the operation was an "intelligence failure."
References
Conflicts in 2018
December 2018 events in Israel
Israel–Lebanon border
Iran–Israel proxy conflict
Hezbollah–Israel conflict
Military operations involving Israel
Tunnel warfare
Tunnels in Israel | Operation Northern Shield | Engineering | 1,471 |
5,546,292 | https://en.wikipedia.org/wiki/UNESCO%20Science%20Prize | The UNESCO Science Prize is a biennial scientific prize awarded by the United Nations Educational, Scientific and Cultural Organization (UNESCO) to "a person or group of persons for an outstanding contribution they have made to the technological development of a developing member state or region through the application of scientific and technological research (particularly in the fields of education, engineering and industrial development)."
The candidates for the Science Prize are proposed to the Director-General of UNESCO by the governments of member states or by non-governmental organizations. All proposals are judged by a panel of six scientists and engineers. The prize consists of , an Albert Einstein Silver Medal, and is awarded in odd years to coincide with UNESCO's General Conference.
Past Laureates
1968: Robert Simpson Silver () "for his discovery of a process for the demineralization of sea water."
1970: International Maize and Wheat Improvement Centre () and International Rice Research Institute () "for their work which made it possible to produce, in the space of a few years, improved strains of cereals."
1972: Viktor Kovda () "for his theory on the hydromorphic origin of the soils of the great plains of Asia, Africa, Europe and the Americas" and nine researchers from "for their development of the L-D process designed for recovery of steel from low phosphorus pig iron."
1976: Alfred Champagnat () "for his findings on the low-cost mass production of new proteins from petroleum."
1978: A team of research workers from the Lawes Agricultural Trust () "for their work on synthetic insecticides related to natural pyrethrum."
1980: Leonardo Mata () "for his work on the relationship between malnutrition and infection, particularly in infants" and Vincent Barry's group of scientists from the Medical Research Council (Ireland) () "for their work on the synthesis of an anti-leprosy agent, B-633."
1983: Roger Whitehead () "for his work on the role of maternal nutrition and lactation in infant growth."
1985: A group of six scientists from the Commonwealth Scientific and Industrial Research Organisation () "for their work on the biological control of Salvinia molesta infestations in the Sepik River Basin of Papua New Guinea."
1987: Yuan Longping () "for his work leading to the creation of an hybrid rice with high yield potential."
1989: Johanna Döbereiner () "for her work in exploiting biological nitrogen fixation as the major source of nitrogen in tropical agriculture."
1991: A group of researchers and engineers from the Instituto Tecnológico Venezolano del Petróleo () "for their contribution to the development of hydrocracking distillation and hydrotreatment technology."
1993: Octavio Novaro () for his contribution to the phenomenon of catalysis.
1995: Wang Xuan () "for his contribution to the Chinese photocomposition system".
1997: Marcos Moshinsky () "for his work in nuclear physics."
1999: Atta ur Rahman () "for his work in organic chemistry which has contributed to the development of plant-based therapies for cancer, AIDS and diabetes" and José Leite Lopes () "for his contribution to the development of physics in Latin America."
2001: Baltasar Mena Iniesta (/) "for his ability to relate his research in rheology and new materials to technological applications."
2003: Somchart Soponronnarit () "for research on areas of renewable energy and drying technology."
2005: Alexander Balankin (/) "for his pioneer contributions in development of fractal mechanics and improving exploration techniques for the oil industry".
References
Science and technology awards
Science
Awards established in 1968 | UNESCO Science Prize | Technology | 782 |
42,221,891 | https://en.wikipedia.org/wiki/Russula%20lenkunya | Russula lenkunya is a mushroom in the genus Russula. Found in South Australia, it was first described scientifically by mycologist Cheryl Grgurinovic in 1997.
See also
List of Russula species
References
External links
lenkunya
Fungi of Australia
Fungi described in 1997
Taxa named by Cheryl A. Grgurinovic
Fungus species | Russula lenkunya | Biology | 71 |
42,892,263 | https://en.wikipedia.org/wiki/Amphicarpy | Amphicarpy is a reproductive strategy that occurs with 13 plant families, expressed mostly in species with an annual life cycle. It is characterized by production of two types of fruit, for different ecological roles. It is sometimes restricted to the situation where one fruit type is aerial and the other subterranean (hypogeous), and similar to, but distinguished from, heterocarpy, which latter means a plant that carries two distinct types of fruit or seeds. The word amphicarp is the contraction of the Greek words ἀμφί meaning "of both kinds" and καρπός meaning fruit.
In a typical plant with amphicarpy, one fruit type is underground. These underground fruits usually develop from self-pollinating flowers. The fruits that develop from the aerial flowers may often be the result of cross-pollination.
Plants use this strategy to increase the chance that their genetic material is passed on. It can be referred to as bet hedging in which an organism produces several different phenotypes. Seeds from the underground flowers have low genetic variability (due to their selfing), tend to be larger, and may germinate from within the tissues of the flower, so ensuring that the annual can remain at the site that was suitable to it in the preceding year. Seeds from aerial flowers usually have greater genetic variability, tend to be smaller, and may be spread further. This assists the colonization of new territory, but also helps the exchange of genetic material between populations.
Worldwide, approximately 67 species exhibit amphicarpy, or 0.02% of the known species of flowering plants. Most of these 67 species occur in often disturbed or very stressful circumstances. 31 of the 67 species known to exhibit amphicarpy are in the family Fabaceae. In Israel, a country that harbors many disturbed habitats, with eight out of a total flora of twenty five hundred species, a much higher percentage of 0.32% is amphicarpic. Species that use amphicarpy include Catananche lutea, Gymnarrhena micrantha and Polygala lewtonii. Trifolium polymorphum is a perennial, that combines amphicarpy with vegetative reproduction through stolons. It grows in grasslands where its aerial flowers may not come into seed due to herbivores.
References
Plant reproduction | Amphicarpy | Biology | 484 |
25,008,226 | https://en.wikipedia.org/wiki/Multi-particle%20collision%20dynamics | Multi-particle collision dynamics (MPC), also known as stochastic rotation dynamics (SRD), is a particle-based mesoscale simulation technique for complex fluids which fully incorporates thermal fluctuations and hydrodynamic interactions. Coupling of embedded particles to the coarse-grained solvent is achieved through molecular dynamics.
Method of simulation
The solvent is modelled as a set of point particles of mass with continuous coordinates and velocities . The simulation consists of streaming and collision steps.
During the streaming step, the coordinates of the particles are updated according to
where is a chosen simulation time step which is typically much larger than a molecular dynamics time step.
After the streaming step, interactions between the solvent particles are modelled in the collision step. The particles are sorted into collision cells with a lateral size . Particle velocities within each cell are updated according to the collision rule
where is the centre of mass velocity of the particles in the collision cell and is a rotation matrix. In two dimensions, performs a rotation by an angle or with probability . In three dimensions, the rotation is performed by an angle around a random rotation axis. The same rotation is applied for all particles within a given collision cell, but the direction (axis) of rotation is statistically independent both between all cells and for a given cell in time.
If the structure of the collision grid defined by the positions of the collision cells is fixed, Galilean invariance is violated. It is restored with the introduction of a random shift of the collision grid.
Explicit expressions for the diffusion coefficient and viscosity derived based on Green-Kubo relations are in excellent agreement with simulations.
Simulation parameters
The set of parameters for the simulation of the solvent are:
solvent particle mass
average number of solvent particles per collision box
lateral collision box size
stochastic rotation angle
kT (energy)
time step
The simulation parameters define the solvent properties, such as
mean free path
diffusion coefficient
shear viscosity
thermal diffusivity
where is the dimensionality of the system.
A typical choice for normalisation is . To reproduce fluid-like behaviour, the remaining parameters may be fixed as .
Applications
MPC has become a notable tool in the simulations of many soft-matter systems, including
colloid dynamics
polymer dynamics
vesicles
active systems
liquid crystals
References
Computational fluid dynamics | Multi-particle collision dynamics | Physics,Chemistry | 466 |
37,080,424 | https://en.wikipedia.org/wiki/Gonyostomum | Gonyostomum is a genus of freshwater algae in the class Raphidophyceae. They include the species Gonyostomum semen, which causes nuisance algal blooms.
References
Ochrophyta
Ochrophyte genera | Gonyostomum | Biology | 52 |
21,162,612 | https://en.wikipedia.org/wiki/Fentin%20acetate | Fentin acetate is an organotin compound with the formula (C6H5)3SnO2CCH3. It is a colourless solid that was previously used as a fungicide.
Structure
Most carboxylates of triphenyltin adopt polymeric structures with five-coordinate Sn centers.
References
External links
Acetate esters
Obsolete pesticides
Fungicides
Triphenyltin compounds | Fentin acetate | Biology | 85 |
34,529,648 | https://en.wikipedia.org/wiki/Bloch%27s%20principle | Bloch's principle is a philosophical principle in mathematics
stated by André Bloch.
Bloch states the principle in Latin as: Nihil est in infinito quod non prius fuerit in finito, and explains this as follows: Every proposition in whose statement the actual infinity occurs can be always considered a consequence, almost immediate, of a proposition where it does not occur, a proposition in finite terms.
Bloch mainly applied this principle to the theory of functions of a complex variable. Thus, for example, according to this principle, Picard's theorem corresponds to Schottky's theorem, and Valiron's theorem corresponds to Bloch's theorem.
Based on his Principle, Bloch was able to predict or conjecture several
important results such as the Ahlfors's Five Islands theorem,
Cartan's theorem on holomorphic curves omitting hyperplanes, Hayman's result that an exceptional set of radii is unavoidable in Nevanlinna theory.
In the more recent times several general theorems were proved which can be regarded as rigorous statements in the spirit of the Bloch Principle:
Zalcman's lemma
A family of functions meromorphic on the unit disc is not normal if and only if there exist:
a number
points
functions
numbers
such that
spherically uniformly on compact subsets of where is a nonconstant meromorphic function on
Zalcman's lemma may be generalized to several complex variables. First, define the following:
A family of holomorphic functions on a domain is normal in if every sequence of functions contains either a subsequence which converges to a limit function uniformly on each compact subset of or a subsequence which converges uniformly to on each compact subset.
For every function of class define at each point a Hermitian form
and call it the Levi form of the function at
If function is holomorphic on set
This quantity is well defined since the Levi form is nonnegative for all
In particular, for the above formula takes the form
and coincides with the spherical metric on
The following characterization of normality can be made based on Marty's theorem, which states that a family is normal if and only if the spherical derivatives are locally bounded:
Suppose that the family of functions holomorphic on is not normal at some point Then there exist sequences such that the sequence converges locally uniformly in to a non-constant entire function satisfying
Brody's lemma
Let X be a compact complex analytic manifold, such that every holomorphic map from the complex plane
to X is constant. Then there exists a metric on X such that every holomorphic map from the unit disc with the Poincaré metric to X does not increase distances.
References
Mathematical principles
Philosophy of mathematics | Bloch's principle | Mathematics | 575 |
36,040,822 | https://en.wikipedia.org/wiki/Oil%20dispersant | An oil dispersant is a mixture of emulsifiers and solvents that helps break oil into small droplets following an oil spill. Small droplets are easier to disperse throughout a water volume, and small droplets may be more readily biodegraded by microbes in the water. Dispersant use involves a trade-off between exposing coastal life to surface oil and exposing aquatic life to dispersed oil. While submerging the oil with dispersant may lessen exposure to marine life on the surface, it increases exposure for animals dwelling underwater, who may be harmed by toxicity of both dispersed oil and dispersant. Although dispersant reduces the amount of oil that lands ashore, it may allow faster, deeper penetration of oil into coastal terrain, where it is not easily biodegraded.
History
Torrey Canyon
In 1967, the supertanker Torrey Canyon leaked oil onto the English coastline. Alkylphenol surfactants were primarily used to break up the oil, but proved very toxic in the marine environment; all types of marine life were killed. This led to a reformulation of dispersants to be more environmentally sensitive. After the Torrey Canyon spill, new boat-spraying systems were developed. Later reformulations allowed more dispersant to be contained (at a higher concentration) to be aerosolized.
Exxon Valdez
Alaska had fewer than 4,000 gallons of dispersants available at the time of the Exxon Valdez oil spill, and no aircraft with which to dispense them. The dispersants introduced were relatively ineffective due to insufficient wave action to mix the oil and water, and their use was shortly abandoned.
A report by David Kirby for TakePart found that the main component of the Corexit 9527 formulation used during Exxon Valdez cleanup, 2-butoxyethanol, was identified as "one of the agents that caused liver, kidney, lung, nervous system, and blood disorders among cleanup crews in Alaska following the 1989 Exxon Valdez spill."
Early use (by volume)
Dispersants were applied to a number of oil spills between the years 1967 and 1989.
Deepwater Horizon
During the Deep water Horizon oil spill, an estimated 1.84 million gallons of Corexit was used in an attempt to increase the amount of surface oil and mitigate the damage to coastal habitat. BP purchased all of the world's supply of Corexit soon after the spill began. Nearly half (771,000 gallons) of the dispersants were applied directly at the wellhead. The primary dispersant used were Corexit 9527 and 9500, which were controversial due to toxicity.
In 2012, a study found that Corexit made the oil up to 52 times more toxic than oil alone, and that the dispersant's emulsifying effect makes oil droplets more bio-available to plankton. The Georgia Institute of Technology found that "Mixing oil with dispersant increased toxicity to ecosystems" and made the gulf oil spill worse.
In 2013, in response to the growing body of laboratory-derived toxicity data, some researchers address the scrutiny that should be used when evaluating laboratory test results that have been extrapolated using procedures that are not fully reliable for environmental assessments. Since then, guidance has been published that improves the comparability and relevance of oil toxicity tests.
Rena oil spill
Maritime New Zealand used the oil dispersant Corexit 9500 to help in the cleanup process. The dispersant was applied for only a week, after results proved inconclusive.
Theory
Overview
Surfactants reduce oil-water interfacial tension, which helps waves break oil into small droplets. A mixture of oil and water is normally unstable, but can be stabilized with the addition of surfactants; these surfactants can prevent coalescence of dispersed oil droplets. The effectiveness of the dispersant depends on the weathering of the oil, sea energy (waves), salinity of the water, temperature and the type of oil. Dispersion is unlikely to occur if the oil spreads into a thin layer, because the dispersant requires a particular thickness to work; otherwise, the dispersant will interact with both the water and the oil. More dispersant may be required if the sea energy is low. The salinity of the water is more important for ionic-surfactant dispersants, as salt screens electrostatic interactions between molecules. The viscosity of the oil is another important factor; viscosity can retard dispersant migration to the oil-water interface and also increase the energy required to shear a drop from the slick. Viscosities below 2,000 centipoise are optimal for dispersants. If the viscosity is above 10,000 centipoise, no dispersion is possible.
Requirements
There are five requirements for surfactants to successfully disperse oil:
Dispersant must be on the oil's surface in the proper concentration
Dispersant must penetrate (mix with) the oil
Surfactant molecules must orient at the oil-water interface (hydrophobic in oil and hydrophilic in water)
Oil-water interfacial tension must be lowered (so the oil can be broken up).
Energy must be applied to the mix (for example, by waves)
Effectiveness
The effectiveness of a dispersant may be analyzed with the following equations. The Area refers to the area under the absorbance/wavelength curve, which is determined using the trapezoidal rule. The absorbances are measured at 340, 370, and 400 nm.
Area = 30(Abs340 + Abs370)/2 + 30(Abs340 + Abs400)/2 (1)
The dispersant effectiveness may then be calculated using the equation below.
Effectiveness (%) = Total oil dispersed x 100/(ρoilVoil)
ρoil = density of the test oil (g/L)
Voil = volume of oil added to test flask (L)
Total oil dispersed = mass of oil x 120mL/30mL
Mass of oil = concentration oil x VDCM
VDCM = final volume of DCM-extract of water sample (0.020 L)
Concentration of oil = area determined by Equation (1) / slope of calibration curve
Dispersion models
Developing well-constructed models (accounting for variables such as oil type, salinity and surfactant) are necessary to select the appropriate dispersant in a given situation. Two models exist which integrate the use of dispersants: Mackay's model and Johansen's model. There are several parameters which must be considered when creating a dispersion model, including oil-slick thickness, advection, resurfacing and wave action. A general problem in modeling dispersants is that they change several of these parameters; surfactants lower the thickness of the film, increase the amount of diffusion into the water column and increase the amount of breakup caused by wave action. This causes the oil slick's behavior to be more dominated by vertical diffusion than horizontal advection.
One equation for the modeling of oil spills is:
where
h is the oil-slick thickness
is the velocity of ocean currents in the mixing layer of the water column (where oil and water mix together)
is the wind-driven shear stress
f is the oil-water friction coefficient
E is the relative difference in densities between the oil and water
R is the rate of spill propagation
Mackay's model predicts an increasing dispersion rate, as the slick becomes thinner in one dimension. The model predicts that thin slicks will disperse faster than thick slicks for several reasons. Thin slicks are less effective at dampening waves and other sources of turbidity. Additionally, droplets formed upon dispersion are expected to be smaller in a thin slick and thus easier to disperse in water.
The model also includes:
An expression for the diameter of the oil drop
Temperature dependence of oil movement
An expression for the resurfacing of oil
Calibrations based on data from experimental spills
The model is lacking in several areas: it does not account for evaporation, the topography of the ocean floor or the geography of the spill zone.
Johansen's model is more complex than Mackay's model. It considers particles to be in one of three states: at the surface, entrained in the water column or evaporated. The empirically based model uses probabilistic variables to determine where the dispersant will move and where it will go after it breaks up oil slicks. The drift of each particle is determined by the state of that particle; this means that a particle in the vapor state will travel much further than a particle on the surface (or under the surface) of the ocean. This model improves on Mackay's model in several key areas, including terms for:
Probability of entrainment – depends on wind
Probability of resurfacing – depends on density, droplet size, time submerged and wind
Probability of evaporation – matched with empirical data
Oil dispersants are modeled by Johansen using a different set of entrainment and resurfacing parameters for treated versus untreated oil. This allows areas of the oil slick to be modeled differently, to better understand how oil spreads along the water's surface.
Surfactants
Surfactants are classified into four main types, each with different properties and applications: anionic, cationic, nonionic and zwitterionic (or amphoteric). Anionic surfactants are compounds that contain an anionic polar group. Examples of anionic surfactants include sodium dodecyl sulfate and dioctyl sodium sulfosuccinate. Included in this class of surfactants are sodium alkylcarboxylates (soaps). Cationic surfactats are similar in nature to anionic surfactants, except the surfactant molecules carry a positive charge at the hydrophilic portion. Many of these compounds are quaternary ammonium salts, as well as cetrimonium bromide (CTAB). Non-ionic surfactants are non-charged and together with anionic surfactants make up the majority of oil-dispersant formulations. The hydrophilic portion of the surfactant contains polar functional groups, such as -OH or -NH. Zwitterionic surfactants are the most expensive, and are used for specific applications. These compounds have both positively and negatively charged components. An example of a zwitterionic compound is phosphatidylcholine, which as a lipid is largely insoluble in water.
HLB values
Surfactant behavior is highly dependent on the hydrophilic-lipophilic balance (HLB) value. The HLB is a coding scale from 0 to 20 for non-ionic surfactants, and takes into account the chemical structure of the surfactant molecule. A zero value corresponds to the most lipophilic and a value of 20 is the most hydrophilic for a non-ionic surfactant. In general, compounds with an HLB between one and four will not mix with water. Compounds with an HLB value above 13 will form a clear solution in water. Oil dispersants usually have HLB values from 8–18.
Comparative industrial formulations
Two formulations of different dispersing agents for oil spills, Dispersit and Omni-Clean, are shown below. A key difference between the two is that Omni-Clean uses ionic surfactants and Dispersit uses entirely non-ionic surfactants. Omni-Clean was formulated for little or no toxicity toward the environment. Dispersit, however, was designed as a competitor with Corexit. Dispersit contains non-ionic surfactants, which permit both primarily oil-soluble and primarily water-soluble surfactants. The partitioning of surfactants between the phases allows for effective dispersion.
Degradation and toxicity
Concerns regarding the persistence in the environment and toxicity to various flora and fauna of oil dispersants date back to their early use in the 1960s and 1970s. Both the degradation and the toxicity of dispersants depend on the chemicals chosen within the formulation. Compounds which interact too harshly with oil dispersants should be tested to ensure that they meet three criteria:
They should be biodegradable.
In the presence of oil, they must not be preferentially utilized as a carbon source.
They must be nontoxic to indigenous bacteria.
Methods of use
Dispersants can be delivered in aerosolized form by an aircraft or boat. Sufficient dispersant with droplets in the proper size are necessary; this can be achieved with an appropriate pumping rate. Droplets larger than 1,000 μm are preferred, to ensure they are not blown away by the wind. The ratio of dispersant to oil is typically 1:20.
See also
Nokomis 3
References
Further reading
Environmental chemistry
Environmental issues with water
Oil spill remediation technologies | Oil dispersant | Chemistry,Environmental_science | 2,709 |
1,839,487 | https://en.wikipedia.org/wiki/Glabrousness | Glabrousness (from the Latin glaber meaning "bald", "hairless", "shaved", "smooth") is the technical term for a lack of hair, down, setae, trichomes or other such covering. A glabrous surface may be a natural characteristic of all or part of a plant or animal, or be due to loss because of a physical condition, such as alopecia universalis in humans, which causes hair to fall out or not regrow.
In botany
Glabrousness or otherwise, of leaves, stems, and fruit is a feature commonly mentioned in plant keys; in botany and mycology, a glabrous morphological feature is one that is smooth and may be glossy. It has no bristles or hair-like structures such as trichomes. In anything like the zoological sense, no plants or fungi have hair or wool, although some structures may resemble such materials.
The term "glabrous" strictly applies only to features that lack trichomes at all times. When an organ bears trichomes at first, but loses them with age, the term used is glabrescent.
In the model plant Arabidopsis thaliana, trichome formation is initiated by the GLABROUS1 protein. Knockouts of the corresponding gene lead to glabrous plants. This phenotype has already been used in gene editing experiments and might be of interest as a visual marker for plant research to improve gene editing methods such as CRISPR/Cas9.
In zoology
In varying degrees most mammals have some skin areas without natural hair. In humans, glabrous skin is found on the ventral portion of the fingers, palms, soles of feet and lips, which are all parts of the body most closely associated with interacting with the world around us, as are the labia minora and glans penis. There are four main types of mechanoreceptors in the glabrous skin of humans: Pacinian corpuscles, Meissner's corpuscles, Merkel's discs, and Ruffini corpuscles.
The Naked mole-rat (Heterocephalus glaber) has evolved skin lacking in general, pelagic hair covering, yet has retained long, very sparsely scattered tactile hairs over its body. Glabrousness is a trait that may be associated with neoteny.
Within entomology, the term glabrous is used to refer to those parts of an insect's body with are lacking in setae (bristles) or scales.
See also
Glossary of botanical terms
Glossary of entomology terms
Trichophilia (hair fetishism)
Merkin, a "pubic wig"
References
Plant morphology
Dermatologic terminology | Glabrousness | Biology | 570 |
52,075,391 | https://en.wikipedia.org/wiki/IET%20Software | IET Software is a peer-reviewed scientific journal on software engineering and related issues, published by the Institution of Engineering and Technology (IET) in the United Kingdom.
The journal was previously published under the following titles:
Software & Microsystems (1982–1986, Online , Print )
Software Engineering Journal (1986–1996, Online , Print )
IEE Proceedings - Software (1997–2006. Online , Print )
The journal is listed on the online IEEE Xplore Digital Library. It is indexed by DBLP, EBSCO, Ei Compendex, IET Inspec, ProQuest, Science Citation Index Expanded (SCI-E), SCImago, and Scopus.
See also
IEEE Software magazine
IEEE Transactions on Software Engineering journal
References
External links
IET Software home page
2007 establishments in the United Kingdom
Bimonthly journals
Computer science in the United Kingdom
Computer science journals
English-language journals
Institution of Engineering and Technology academic journals
Academic journals established in 2007
Software engineering publications | IET Software | Technology,Engineering | 200 |
41,649,032 | https://en.wikipedia.org/wiki/Recovery%20effect | The recovery effect is a phenomenon observed in battery usage where the available energy is less than the difference between energy charged and energy consumed. Intuitively, this is because the energy has been consumed from the edge of the battery and the charge has not yet diffused evenly around the battery.
When power is extracted continuously voltage decreases in a smooth curve, but the recovery effect can result in the voltage partially increasing if the current is interrupted.
The KiBaM battery model describes the recovery effect for lead-acid batteries and is also a good approximation to the observed effects in Li-ion batteries. In some batteries, the gains from the recovery life can extend battery life by up to 45% by alternating discharging and inactive periods rather than constantly discharging. The size of the recovery effect depends on the battery load, recovery time and depth of discharge.
Even though the recovery effect phenomenon is prominent in the lead acid battery chemistry, its existence in alkaline, Ni-MH and Li-Ion batteries is still questionable. For instance, a systematic experimental case study shows that an intermittent discharge current in case of alkaline, Ni-MH and Li-ion batteries results in a decreased usable energy output compared to a continuous discharge current of the same average value. This is primarily due to the increased overpotential experienced due to the high peak currents of the intermittent discharge over the continuous discharge current of same average value.
See also
Capacity fading
State of health
State of charge
Smart battery
Battery management system
References
Battery charging
Rechargeable batteries
Scientific phenomena
Phenomena
Physical phenomena | Recovery effect | Physics | 314 |
11,089,355 | https://en.wikipedia.org/wiki/Kalahari%20Meerkat%20Project | The Kalahari Meerkat Project, or KMP, is a long term research project focused on studying the evolutionary causes and ecological consequences of cooperative behaviors in meerkats. The secondary aims of the project are to determine what factors affect the reproductive success of the meerkats and what behavioral and physiological mechanisms control both reproduction and cooperative behavior. The project is also working on monitoring overall plant and animal populations within the reserve and work with the nearby community of Van Zylsrus in the areas of conservation and sustainable use of resources.
Situated at the Kuruman River Reserve in Northern Cape, South Africa, close to the border to Botswana, the project is jointly funded by Cambridge University and the Kalahari Research Trust.
History
The project was founded in the early nineties by researchers (Prof. Tim Clutton-Brock) at Cambridge University. It was originally based on the Kgalagadi Transfrontier Park, but in 1993 moved to the Kuruman River Reserve, an area spanning approximately twenty square miles of semi-arid area of the Kalahari Desert on either side of the mostly dry Kuruman River. The reserve consists primarily of sparsely vegetated fossil dunes that flatten out near the river, which is usually dry. The project is now part of the university's "Large Animal Research Group" headed by Tim Clutton-Brock, FRS, who has headed the Meerkat project since 1993.
Staff
The project usually has 10–15 volunteers who form the main meerkat project staff. They are supervised by a Field Coordinator and a Field Manager. Volunteers come from all over the world and the project is regularly hiring volunteers (see http://www.kalahari-meerkats.com/index.php?id=volunteers). In addition to the core researchers, Earthwatch volunteers aid in collecting research data after being partnered with a staff researcher. There is also usually a South African technician responsible for project logistics, 6–8 post-graduate interns from Europe or South Africa, and a number of doctorate and independent researchers carrying out their own research in the area. There are rarely fewer than 10 people working in the project area at any given time.
The principal investigators of the project are Prof. Tim Clutton-Brock, Professor of Animal Ecology at the University of Cambridge, and Prof. Marta Manser, Professor of Animal Behavior at the University of Zurich.
Subjects
The KMP study encompasses 16 groups of meerkats, with six living exclusively on the reserve and the rest having ranges that extend into the surrounding farmland. Most members of the groups are familiar enough with the human researchers that they are undisturbed by their presence and are relatively easy to touch and collect samples from. Extremely accurate life history records are kept for each meerkat in the study populations, including the recording of births, deaths, pregnancies, lactation and oestrus cycles, changes in social status and group affiliation, and any abnormal behaviors or activities.
The project team offers film crews and wildlife photographers the chance to film the habituated groups of meerkats at the reserve. The KMP meerkats have been the subjects of several documentary programs, including:
Meerkat Manor, a popular Animal Planet docu-drama series focused mostly on The Whiskers, one of the long-term study groups
Ella, A Meerkat's Tale, a 2005 one-hour special from Oxford Scientific Films that follows the life of one young female that breaks the rules and has pups despite being a subordinate female
Meerkats, a 2003 Nigel Marven film
"Life of Mammals", a 2002 episode for Sir David Attenborough's series on BBC
"Walking with Meerkats: Meerkat Madness", a 2001 30-minute National Geographic special produced by Big Wave TV that focuses on the Lazuli research group The title may refer to the BBC production Walking with Dinosaurs and its sister shows Walking with Beasts and Walking with Monsters.
In May 2010, Lapland Studio announced it was releasing a video game entitled Lead the Meerkats for the Nintendo Wii and would be donating proceeds from copies sold on the first day to the project. Clutton-Brock and Evi Bauer, president of the Friends of the Kalahari Meerkat Project, expressed excitement over the games release as a way to educate people about meerkats through a fairly realistic game.
Friends of the Kalahari Meerkat Project
"Friends of the Kalahari Meerkat Project" is a legally independent, but functionally integrated, sponsoring organization of the project that was founded in Switzerland on 23 November 2007. Through this website, the Kalahari Meerkat Project releases information about the meerkats, including life history updates for all of the individual meerkats and the meerkat groups being studied, updates on the current groups, historical information on lost groups, and basic information about meerkats. The project uploads its own photographs and video footage of the meerkats, available for viewing for free.
In April 2008, the site began selling "Friends" packages to offer a way to support the project. The Friends package includes additional project information not published on the site, as well as detailed information comparing the actual project meerkats to their counterparts in Meerkat Manor. On 8 June 2008, the site was expanded to include a virtual store, powered by Zazzle, through which the project offers a variety of custom meerkat items. Proceeds from the items go to support the project and the Friends program.
References
External links
Kalahari Meerkat Project website
Friends of the Kalahari Meerkat Project website
Behavioral ecology
Meerkat Manor
Kalahari Desert | Kalahari Meerkat Project | Biology | 1,165 |
3,727,851 | https://en.wikipedia.org/wiki/NGC%202787 | NGC 2787 is a barred lenticular galaxy approximately 24 million light-years away in the northern constellation of Ursa Major. It was discovered on December 3, 1788 by German-born astronomer William Herschel. J. L. E. Dreyer described it as, "bright, pretty large, a little extended 90°, much brighter middle, mottled but not resolved, very small (faint) star involved to the southeast". The visible galaxy has an angular size of arcminutes or arcminutes and an apparent visual magnitude of 11.8.
This galaxy is small and isolated with a morphological classification of SB(r)0+, which indicates a barred spiral (SB) with a ring around the bar (r). Being a lenticular galaxy, it has the large halo of an elliptical galaxy. The disk is inclined at an angle of to the line of sight from the Earth, with the major axis aligned along a position angle of . The galaxy has an unusually high mass-to-light ratio, much greater than for a typical spiral galaxy. The distribution of the galaxy's neutral hydrogen forms a clumpy ring with a radius of , double that of the visible galaxy, with a mass of . This ring appears misaligned with the central disk.
NGC 2787 contains a low-ionization nuclear emission-line region (LINER) at its core, which is a type of region that is characterized by its spectral line emission from weakly ionized atoms. LINERs are very common within lenticular galaxies, with approximately one-fifth of nearby lenticular galaxies containing LINERs. The supermassive black hole at the center has a mass of . The central region of the galaxy contains dust rings that are tilted with respect to the disk, which may be the result of an encounter with another galaxy.
References
External links
A Galaxy That's All Wound Up
NGC 2787 at ESA/Hubble
Lenticular galaxies
Barred lenticular galaxies
LINER galaxies
Ursa Major
2787
04914
26341 | NGC 2787 | Astronomy | 410 |
16,342,785 | https://en.wikipedia.org/wiki/Wiener%20sausage | In the mathematical field of probability, the Wiener sausage is a neighborhood of the trace of a Brownian motion up to a time t, given by taking all points within a fixed distance of Brownian motion. It can be visualized as a sausage of fixed radius whose centerline is Brownian motion. The Wiener sausage was named after Norbert Wiener by because of its relation to the Wiener process; the name is also a pun on Vienna sausage, as "Wiener" is German for "Viennese".
The Wiener sausage is one of the simplest non-Markovian functionals of Brownian motion. Its applications include stochastic phenomena including heat conduction. It was first described by , and it was used by to explain results of a Bose–Einstein condensate, with proofs published by .
Definitions
The Wiener sausage Wδ(t) of radius δ and length t is the set-valued random variable on Brownian paths b (in some Euclidean space) defined by
is the set of points within a distance δ of some point b(x) of the path b with 0≤x≤t.
Volume
There has been a lot of work on the behavior of the volume (Lebesgue measure) |Wδ(t)| of the Wiener sausage as it becomes thin (δ→0); by rescaling, this is essentially equivalent to studying the volume as the sausage becomes long (t→∞).
showed that in 3 dimensions the expected value of the volume of the sausage is
In dimension d at least 3 the volume of the Wiener sausage is asymptotic to
as t tends to infinity. In dimensions 1 and 2 this formula gets replaced by and respectively. , a student of Spitzer, proved similar results for generalizations of Wiener sausages with cross sections given by more general compact sets than balls.
References
Especially chapter 22.
(Reprint of 1964 edition)
An advanced monograph covering the Wiener sausage.
Mathematical physics
Statistical mechanics
Wiener process | Wiener sausage | Physics,Mathematics | 397 |
40,073,004 | https://en.wikipedia.org/wiki/Flexenclosure | Flexenclosure AB is a Sweden-based developer of hybrid power systems and pre-fabricatedata centres.
History
Founded in 1989, Flexenclosure is a former subsidiary of Pharmadule Emtunga AB. It became an independent company in 2007. Flexenclosure is privately owned. Its major shareholders are Industrifonden, a Swedish investment fund; Pegroco Invest, a privately owned Swedish investment company; Andra AP-fonden (AP2), a Swedish pension fund; and International Finance Corporation (IFC), a private sector global development institution which is a member of the World Bank Group. In May 2013 IFC invested US$24 million in Flexenclosure.
Flexenclosure's headquarters are in Stockholm, with design and manufacturing facilities at Vara in southern Sweden, with subsidiaries in Kenya and India, and overseas offices in Nigeria, Malaysia, Pakistan and the UAE. The company went bankrupt October 2019, e-site division lives on after acquisition of Pegroco under new name.
Products
eSite
eSite is a hybrid power management system that can work as a standalone unit with a backup generator, or with any combination of grid and renewable energy sources to power telecom base station sites.
eCentre
eCentre is a pre-fabricated data centre brand. eCentre is a pre-equipped, self-contained, technical, modular facility for housing and powering data and telecom equipment.
An eCentre can comprise one or a number of different elements including a data centre, switching centre, energy centre, sub-station and Network Operations Centre (NOC).
eCentres are custom-designed and manufactured at Flexenclosure's research, development, design and production facility at Vara, in the south of Sweden, before being transported to their intended location for final assembly and commissioning. eCentres have mostly been installed in West, Central and North African countries such as Nigeria and Mozambique.
References
Data centers
Technology companies of Sweden
Sustainable technologies
Telecommunications companies of Sweden | Flexenclosure | Technology | 417 |
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