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20,938,380 | https://en.wikipedia.org/wiki/Blue%20Oak%20Ranch%20Reserve | The Blue Oak Ranch Reserve, a unit of the University of California Natural Reserve System, is an ecological reserve and biological field station in Santa Clara County, California. It is located on in the Diablo Range, northwest of Mount Hamilton, at elevation.
The land, part of the 19th century Mexican land grant of Rancho Cañada de Pala, was donated to the University of California on December 1, 2007 by the Blue Oak Ranch Trust, an anonymous benefactor.
Overnight accommodations for academic researchers and educational groups may be made by permission only.
Flora
Flora of Blue Oak Ranch Reserve includes:
purple needle grass (Nassella pulchra)
barley (Hordeum)
bluegrass (Poa spp.)
three-awn (Aristida spp.)
melic (Melica sspspp
wildrye (Elymus and Leymus spp.)
Invasive introduced species
yellow starthistle (Centaurea solstitialis)
medusahead grass (Taeniatherum caput-medusae)
Italian thistle (Carduus pycnocephalus)
tocalote (Centaurea melitensis)
Canada thistle (Cirsium arvense)
bull thistle (Cirsium vulgare)
Plant communities
valley oak woodland
black oak woodland
coast live oak woodland
riparian forest
chamise chaparral
Diablan sage scrub
non-native annual grassland
wildflower field
native perennial grassland
Fauna
Fauna of Blue Oak Ranch Reserve includes:
Western toad
Pacific tree frog
Pacific chorus frog
red-legged frog
California newt
California tiger salamander
Western pond turtle
red-winged blackbird
pied-billed grebe
Canada goose
American coot
wood duck
Invasive fish
sunfish
largemouth bass
mosquitofish
See also
Quercus douglasii — Blue oak
California oak woodlands — a plant community within the ranch
California interior chaparral and woodlands — the plant community that the ranch is within
California chaparral and woodlands ecoregion — ecoregion of the Mediterranean forests, woodlands, and scrub Biome, that the ranch is within
List of California native plants
Restoration ecology
References
External links
Blue Oak Ranch Reserve official site
Blue Oak Reserve: University of California Natural Reserve System
University of California Natural Reserve System
Protected areas of Santa Clara County, California
Diablo Range
Natural history of the California Coast Ranges
Ecological restoration
Environment of the San Francisco Bay Area
California chaparral and woodlands
Ranches in California
University of California, Berkeley | Blue Oak Ranch Reserve | Chemistry,Engineering | 477 |
51,566,149 | https://en.wikipedia.org/wiki/Journal%20of%20Medical%20Biochemistry | The Journal of Medical Biochemistry is a quarterly peer-reviewed open access medical journal covering research in medical biochemistry, clinical chemistry, and related disciplines. It was established in 1982 as Jugoslovenska medicinska biohemija, obtaining its current name in 2007. It is published by Walter de Gruyter on behalf of the Society of Medical Biochemists of Serbia.
The journal exhibited unusual levels of self-citation and its journal impact factor of 2019 was suspended from the Journal Citation Reports in 2020, a sanction which hit 34 journals in total.
Editors-in-chief
The following persons are or have been editors-in-chief of the journal:
Neda Longino (1982–1988)
Ernest Suchanek (1988–1992)
Nada Majkić-Singh (1992–present)
Abstracting and indexing
The journal is abstracted and indexed in:
References
External links
Biochemistry journals
De Gruyter academic journals
English-language journals
Open access journals
Quarterly journals
Academic journals established in 1982 | Journal of Medical Biochemistry | Chemistry | 202 |
20,022,028 | https://en.wikipedia.org/wiki/Forgotten%20Chicago | Forgotten Chicago is an organization that seeks to discover and document little-known elements of Chicago's infrastructure, architecture, neighborhoods, and general cityscape, existing or historical.
The organization exposes many of these often-overlooked elements of Chicago's built environment to a wide audience to increase interest in their preservation. In addition to conducting research and publishing articles on its website, Forgotten Chicago also leads neighborhood walking tours and holds free presentations at area libraries. Forgotten Chicago has received many accolades including being named one of Chicago Magazine's 171 best Chicago websites in February 2008 and is featured in the Chicago Tribune, The Northwest Indiana Times, Time Out Chicago, and local radio.
Their web presence underwent a major re-design in January 2009 with feature improvements, revised and updated content, and more ways for the public to get involved with the organization through Twitter and Facebook.
See also
Forgotten NY
References
External links
Forgotten Chicago
Forgotten Chicago message board
Forgotten Chicago Twitter
History websites of the United States
History of Chicago
Historic preservation organizations in the United States
Architectural history
Cultural heritage of the United States
Urban exploration in the United States
Organizations based in Chicago | Forgotten Chicago | Engineering | 223 |
67,592,296 | https://en.wikipedia.org/wiki/Cold%20data | In computer storage, cold data refers to data that is rarely accessed, therefore considered "cold".
Cold data is the opposite of hot data, which is data that is frequently accessed.
Uses
To optimize storage costs, cold data can be stored on lower performing and less expensive storage media. For example, solid state disks may be used for storing hot data, while cold data can be moved to hard drives, optical discs, tapes, or migrated to cloud storage.
See also
References
Data storage
Computer data storage
Backup | Cold data | Engineering | 105 |
4,894,360 | https://en.wikipedia.org/wiki/List%20of%20CAS%20numbers%20by%20chemical%20compound | This is a list of CAS numbers by chemical formulas and chemical compounds, indexed by formula.The CAS number is a unique number applied to a specific chemical by the Chemical Abstracts Service (CAS).This list complements alternative listings to be found at list of inorganic compounds and glossary of chemical formulae.
A
B
C
D
E
F
G
H
I
K
L
M
N
O
P
R
S
T
U
V
W
X
Y
Z
See also
References
External links
PubChem Search
Webelements
ATSDR Toxic Substances
Common Chemistry – Most common substances from Chemical Abstracts Service
CAS numbers list from ChemSynthesis service
Chemical compounds
ro:Număr registru CAS | List of CAS numbers by chemical compound | Physics,Chemistry | 133 |
49,781,600 | https://en.wikipedia.org/wiki/NhaD%20family | The NhaD family (TC# 2.A.62) belongs to the Ion Transporter (IT) Superfamily. A representative list of proteins belonging to the NhaD family can be found in the Transporter Classification Database.
The NhaD Na+/H+ antiporter has been characterized from two Vibrio species: V. parahaemolyticus and V. cholerae and in the haloalkaliphile, Alkalimonas amylolytica. These proteins and their homologues are 400-500 aas long and exhibit 10-13 TMSs. They catalyze Na+/H+ and Li+/H+ antiport. They exhibit activity at basic pH (8-10) with no activity at pH 7.5. The Amylolytica antiporter has low Na+ affinity and has optimal activity at 600 mM Na+. Homologues are found in Pseudomonadota of all groups, Flavobacteriia, and Chlamydia. Distant homologues of the IT superfamily are ubiquitous.
The generalized reaction catalyzed by NhaD is:nH+ (in) + mNa+ (out) ⇌ nH+ (out) + mNa+ (in).
See also
Sodium-Proton antiporter
Antiporter
Transporter Classification Database
Further reading
Barrero-Gil, Javier; Rodríguez-Navarro, Alonso; Benito, Begoña (2007-01-01). "Cloning of the PpNHAD1 transporter of Physcomitrella patens, a chloroplast transporter highly conserved in photosynthetic eukaryotic organisms". Journal of Experimental Botany 58(11): 2839–2849. doi:10.1093/jxb/erm094. ISSN 0022-0957. PMID 17617660.
Kurz, Matthias; Brünig, Anika N. S.; Galinski, Erwin A. (2006-01-01). "NhaD type sodium/proton-antiporter of Halomonas elongata: a salt stress response mechanism in marine habitats?". Saline Systems 2: 10.doi:10.1186/1746-1448-2-10. ISSN 1746-1448.PMC 1552076. PMID 16872527.
Liu, Jun; Xue, Yanfen; Wang, Quanhui; Wei, Yi; Swartz, Talia H.; Hicks, David B.; Ito, Masahiro; Ma, Yanhe; Krulwich, Terry A. (2005-11-01). "The activity profile of the NhaD-type Na+(Li+)/H+ antiporter from the soda Lake Haloalkaliphile Alkalimonas amylolytica is adaptive for the extreme environment". Journal of Bacteriology 187 (22): 7589–7595.doi:10.1128/JB.187.22.7589-7595.2005. ISSN 0021-9193.
Melo, Ana M. P.; Felix, Nuno A. M.; Carita, João N.; Saraiva, Lígia M.; Teixeira, Miguel (2006-09-29)."The Na+/H+ antiporter of the thermohalophilic bacterium Rhodothermus marinus". Biochemical and Biophysical Research Communications 348 (3): 1011–1017.doi:10.1016/j.bbrc.2006.07.134. ISSN 0006-291X.PMID 16904646.
Zhong, Nai-Qin; Han, Li-Bo; Wu, Xiao-Min; Wang, Li-Li; Wang, Fang; Ma, Yan-He; Xia, Gui-Xian (2012-06-01). "Ectopic expression of a bacterium NhaD-type Na+/H+ antiporter leads to increased tolerance to combined salt/alkali stresses". Journal of Integrative Plant Biology 54 (6): 412–421. doi:10.1111/j.1744-7909.2012.01129.x. ISSN 1744-7909. PMID 22583823.
References
Protein families
Membrane proteins
Transmembrane proteins
Transmembrane transporters
Transport proteins
Integral membrane proteins | NhaD family | Biology | 922 |
71,925,011 | https://en.wikipedia.org/wiki/Side%20effects%20of%20radiotherapy%20on%20fertility | The side effects of radiotherapy on fertility are a growing concern to patients undergoing radiotherapy as cancer treatments. Radiotherapy is essential for certain cancer treatments and often is the first point of call for patients. Radiation can be divided into two categories: ionising radiation (IR) and non-ionising radiation (NIR). IR is more dangerous than NIR and a source of this radiation is X-rays used in medical procedures, for example in radiotherapy.
IR can have varying impacts which depend on many factors including age, irradiation field and treatment dose and duration. Where the radiotherapy is directed is important as IR to the pelvis will affect the ovary and uterus or testis. Whereas cranial irradiation will disrupt the hypothalamic-pituitary-gonadal axis (HPG-A), causing subsequent disruption of hormone secretion.
In females, IR can have long-term effects on fertility, specifically on ovarian insufficiency, pubertal arrest and subsequent infertility.
In males, the use of radiotherapy can disrupt the endocrine system leading to altered spermatogenesis and consequently a decrease in sperm count, sperm motility, sperm morphology and sperm viability.
The rapid evolution of radiotherapy technologies has had the benefit of more effective and accurate treatments with less side effects.
Impacts of radiotherapy on female fertility
Radiation therapy can have a significant impact on female fertility. The damage induced varies greatly and is determined by factors such as the age of the patient along with the dose and duration of treatment given. Estimates suggest that less than 2Gy of radiation could destroy half of a female’s immature oocytes. Female ovaries are estimated to store over 1,000,000 primordial follicles at birth which decrease in number and quality with increasing age via processes such as apoptosis. Radiation therapy greatly accelerates this decline. Permanent damage occurs with follicular atrophy and reduced follicle numbers. Consequently these changes lead to uterine dysfunction due to changes in ovarian hormone production which can result in early menopause and risk of infertility.
Hormonal disruption includes female patients experiencing decrease LH (luteinising hormone) secretion and attenuated LH surges leading to increased risk of ovarian failure. LH plays an important role in proper sexual development. Further potential endocrinopathies include hypogonadism and hyperprolactinemia. Studies now suggest that the stage of follicular development may determine how much damage is induced.
Radiation therapy has been seen to also have a direct impact on the uterus, leading to changes to its vascular supply, volume and elasticity. Necrosis, atrophy and fibrosis have also all been observed in the endometrium and myometrium. Changes such as these have significant consequences in regard to pregnancy outcomes; studies suggest cancer patients receiving radiation have a higher chance of experiencing miscarriages or having low birth weight, premature children. The likelihood of perinatal infant mortality and low birth weight are significantly related to radiation dose.
Impacts of radiotherapy on male fertility
Male fertility can be greatly impacted by radiotherapy of the reproductive system. Spermatogenesis is a process by which male sperm cells are produced. This process can take up to 70 days to complete. Some of the cells involved in this process can be damaged by the use of radiotherapy. Cells called spermatogonia are the most heavily impacted by radiotherapy. These are the cells that go on to divide to produce spermatozoa, or what are commonly known as sperm cells. Spermatogonia are the most impacted by radiotherapy because they are more radiosensitive than other types of cells such as spermatozoa. This means that the whole spermatogenic process is impacted by radiotherapy.
In addition to the damage of spermatogonia, the cells which produce a hormone called testosterone are also impaired by radiotherapy. Testosterone is the main male hormone in the body. These cells are called Leydig cells and they are found in the testes. However, Leydig cells are far more resistant to radiation than other cells in the testes and only become damaged by high levels of radiotherapy. These cells are more sensitive when the radiotherapy takes place in childhood. Damaged Leydig cells reduce the levels of testosterone in the body, which in turn increases the levels of another hormone called LH. Clinically, the monitoring of these two hormones can be indicative of Leydig cell function and health.
In combination, these two processes can lead to male fertility being compromised and can sometimes result in infertility.
Long-term effects of childhood radiotherapy on fertility
The number of childhood cancer survivors is increasing due to technological and diagnostic advancements. However as a result, there is increasing concern of the long-term effects of cancer treatments, such as radiotherapy treatment. A significant issue associated with childhood radiotherapy includes infertility.
Prepubescent males who experience radiotherapy to their testes, can result in reduced spermatogenesis. This can be through damage to the germ cells, the sertoli cells and/or Leydig cells. Both the dosage and the timing of the treatment can determine the extent of disruption to spermatogenesis. In prepubescent males, low doses (>1-3Gy) can cause short-term oligospermia or azoospermia, while higher doses (>2-3 Gy) can cause permanent azoospermia.
Moreover, testicular radiation or central nervous system (CNS) radiation in prepubertal males can affect testosterone levels and cause hypoandrogenism. Testicular radiation damages the androgen-producing Leydig cells while CNS radiation impairs the hypothalamic-pituitary-gonadal (HPG) axis, reducing gonadotropin production.
In prepubescent females, high radiation dose to the pelvic region can also have adverse side effects on fertility. Long-term effects include early onset menopause, ovarian failure and inability to complete puberty. Where pregnancy occurs in these individuals, there are high risks associated with the health of the offspring due to pregnancy complications. These include low birth weight, miscarriage and premature labour.
Prevention and treatment of infertility caused by radiotherapy
In modern medicine there are multiple options to limit the effect of cancer treatment on fertility. One of the preventative measures in females is transposition of gonadal organs further from local therapeutic agents with a success rate over 90%. Another less invasive method used for many years is lead shielding of gonadal region in both males and females as a protective measure against radiotherapy.
In prepubescent males novel techniques such as testicular tissue extraction and cryopreservation as well as in vitro maturation of spermatogonia which can then be transferred to native tissue after the treatment are being heavily researched. The most common solution is cryopreservation of sperms in post pubertal males and cryopreservation of oocytes or embryos for females with smaller age constrain compared to males who can then utilise multiple assisted reproductive techniques (ART) methods such as intrauterine insemination, IVF or ICSI as an alternative resource for preservation of fertility.
Future approach to this problem focuses on cytoprotective strategies using hormonal treatment to alter HPG-A to guard reproductive organs from radiotherapy. By disrupting the gametogenesis or decreasing the sensitivity of germ cells scientists could acquire quiescent state less susceptible to side effects of cancer treatment.
References
Radiation therapy
Fertility
Infertility
Cryopreservation | Side effects of radiotherapy on fertility | Chemistry | 1,586 |
22,700 | https://en.wikipedia.org/wiki/Omphalos%20hypothesis | The Omphalos hypothesis is one attempt to reconcile the scientific evidence that the Earth is billions of years old with a literal interpretation of the Genesis creation narrative, which implies that the Earth is only a few thousand years old. It is based on the religious belief that the universe was created by a divine being, within the past six to ten thousand years (in keeping with flood geology), and that the presence of objective, verifiable evidence that the universe is older than approximately ten millennia is due to the creator introducing false evidence that makes the universe appear significantly older.
The idea was named after the title of an 1857 book, Omphalos by Philip Henry Gosse, in which Gosse argued that for the world to be "functional", God must have created the Earth with mountains and canyons, trees with growth rings, Adam and Eve with fully grown hair, fingernails, and navels (ὀμφαλός omphalos is Greek for "navel"), and all living creatures with fully formed evolutionary features, etc., and that, therefore, no empirical evidence about the age of the Earth or universe can be taken as reliable.
Various supporters of Young Earth creationism have given different explanations for their belief that the universe is filled with false evidence of the universe's age, including a belief that some things needed to be created at a certain age for the ecosystems to function, or their belief that the creator was deliberately planting deceptive evidence.
The idea was widely rejected in the 19th century, when Gosse published his aforementioned book. It saw some revival in the 20th century by some Young Earth creationists, who extended the argument to include visible light that appears to originate from far-off stars and galaxies (addressing the "starlight problem").
Development of the idea
Pre-scientific sources
Stories of the beginning of human life based on the creation story in Genesis have been published for centuries. The 4th-century theologian Ephrem the Syrian described a world in which divine creation instantly produced fully grown organisms:
19th-century thinkers
By the 19th century, scientific evidence of the Earth's age had been collected, and it disagreed with a literal reading of the biblical accounts. This evidence was rejected by some writers at the time, such as François-René de Chateaubriand. Chateaubriand wrote in his 1802 book, Génie du christianisme (Part I Book IV Chapter V), that "God might have created, and doubtless did create, the world with all the marks of antiquity and completeness which it now exhibits." In modern times, Rabbi Dovid Gottlieb supported a similar position, saying that the objective scientific evidence for an old universe is strong, but wrong, and that the traditional Jewish calendar is correct.
In the middle of the 19th century, the disagreement between scientific evidence about the age of the Earth and the Western religious traditions was a significant debate among intellectuals. Gosse published Omphalos in 1857 to explain his answer to this question. He concluded that the religious tradition was correct. Gosse began with the earlier idea that the Earth contained mature organisms at the instant they were created, and that these organisms had false signs of their development, such as hair on mammals, which grows over time. He extended this idea of creating a single mature organism to creating mature systems, and concluded that fossils were an artifact of the creation process and merely part of what was necessary to make creation work. Therefore, he reasoned, fossils and other signs of the Earth's age could not be used to prove its age.
Other contemporary proposals for reconciling the stories of creation in Genesis with the scientific evidence included the interval theory or gap theory of creation, in which a large interval of time passed in between the initial creation of the universe and the beginning of the Six Days of Creation. This idea was put forward by Archbishop John Bird Sumner of Canterbury in Treatise on the Records of Creation. Another popular idea, promoted by the English theologian John Pye Smith, was that the Garden of Eden described the events of only one small location. A third proposal, by French naturalist Georges-Louis Leclerc, Comte de Buffon, held that the six "days" of the creation story were arbitrary and large ages rather than 24-hour periods.
Theologians rejected Gosse's proposal on the grounds that it seemed to make the divine creator tell lies—either lying in the scriptures, or lying in nature. Scientists rejected it on the grounds that it disagreed with uniformitarianism, an explanation of geology that was widely supported at the time, and the impossibility of testing or falsifying the idea.
Modern creationists
Some modern creationists still argue against scientific evidence in the same way. For instance, John D. Morris, president of the Institute for Creation Research wrote in 1990 about the "appearance of age", saying that: "...what [God] created was functionally complete right from the start—able to fulfill the purpose for which it was created".
He does not extend this idea to the geological record, preferring to believe that it was all created in the Flood, but others such as Gerald E. Aardsma go further, with his idea of "virtual history". This appears to suggest that events after the creation have changed the "virtual history" we now see, including the fossils:
Criticisms
Beginning of false creation
Although Gosse's original Omphalos hypothesis specifies a popular creation story, others have proposed that the idea does not preclude creation as recently as five minutes ago, including memories of times before this created in situ. This idea is sometimes called Last Thursdayism by its opponents, as in "the world might as well have been created last Thursday."
Scientifically, the concept is both unverifiable and unfalsifiable through any conceivable scientific study—in other words, it is impossible to conclude the truth of the hypothesis, since it requires the empirical data itself to have been arbitrarily created to look the way it does at every observable level of detail.
Deceptive creator
From a religious viewpoint, it can be interpreted as God having created a "fake" universe, such as illusions of light emitted from supernovae that never really happened, or volcanic mountains that were never really volcanoes in the first place and that never actually experienced erosion.
In a rebuttal of the claim that God might have implanted a false history of the age of the universe to test our faith in the truth of the Torah, Rabbi Natan Slifkin, an author whose works have been banned by several Haredi rabbis for going against the tenets of the Talmud, writes:
Similar formulations
Five-minute hypothesis
The five-minute hypothesis is a skeptical hypothesis put forth by the philosopher Bertrand Russell, that proposes that the universe sprang into existence five minutes ago from nothing, with human memory and all other signs of history included. It is a commonly used example of how one may maintain extreme philosophical skepticism with regard to memory and trust in evidentially derived historical chronology.
Borges's Tlön, Uqbar, Orbis Tertius
Jorge Luis Borges, in his 1940 work, Tlön, Uqbar, Orbis Tertius, describes a fictional world in which some essentially follow as a religious belief a philosophy much like Russell's discussion on the logical extreme of Gosse's theory:
Borges had earlier written a short essay, "The Creation and P. H. Gosse" that explored the rejection of Gosse's Omphalos. Borges argued that its unpopularity stemmed from Gosse's explicit (if inadvertent) outlining of what Borges characterized as absurdities in the Genesis story.
See also
"A Clockwork Origin"
Age of the universe
Boltzmann brain
Christian mythology
Conflict thesis
Dark City (1998 film)
Kabbalah
Omphalos (story)
Russell's teapot
Strata (novel)
References
External links
Mirror of the defunct "The Church Of Last Thursdayism" webpage (stored at www.archive.org)
Archived Usenet Post containing the FAQ of "The Church of Last Thursdayism" (stored by Google.com)
"The Church of Last Thursday" home
Concepts in epistemology
Creationism
Skepticism
Genesis creation narrative | Omphalos hypothesis | Biology | 1,678 |
64,068,598 | https://en.wikipedia.org/wiki/Telluride%20oxide | The telluride oxides or oxytellurides are double salts that contain both telluride and oxide anions (Te2− and O2−). They are in the class of mixed anion compounds.
Compounds that can be mistakenly called "telluride oxides" are tellurium dioxide and tellurite.
Some of these are under investigation as photovoltaic materials, e.g. oxygen doped zinc telluride.
Structure
Due to the different size and chemical nature of Te2− and O2− the ions occupy different positions in the crystal structure. Some of these structures are layered.
Many of the crystal systems are tetragonal. One unusual structure has stacked tubes made from tellurium, with nested tubes of antimony oxide, which contain alkali metal.
List
References
Tellurides
Oxides | Telluride oxide | Chemistry | 174 |
5,347,314 | https://en.wikipedia.org/wiki/Blumeria%20graminis | Blumeria graminis (commonly called barley powdery mildew or corn mildew) is a fungus that causes powdery mildew on grasses, including cereals. It is the only species in the genus Blumeria. It has also been called Erysiphe graminis and (by its anamorph) Oidium monilioides or Oidium tritici.
Systematics
Previously B. graminis was included within the genus Erysiphe, but molecular studies have placed it into a clade of its own. In 1975, it was moved to the new monospecific genus Blumeria. Blumeria differs from Erysiphe in its digitate haustoria and in details of the conidial wall. Blumeria is also considered to be phylogenetically distinct from Erisiphe as it solely infects the true grasses of Poaceae.
Eight special forms or formae speciales (ff.spp.) of B. graminis have been distinguished, each of which is parasitic on a particular genus or pareticular genera of grasses. Those that infect crop plants are B. g. f.sp. , which causes powdery mildew of wheat and infects other grasses in the genera Triticum and Aegilops, f.sp. on barley, f.sp. on oats and f.sp. on rye. Other formae speciales are pathogenic on wild grasses, including on grasses in the genera Agropyron and Elymus, on Bromus spp., on Poa spp. and on Lolium spp. (ryegrass).
Morphology
The mycelium can cover the plant surface almost completely, especially the upper sides of leaves. Ascocarp is dark brown, globose with filamentous appendages, asci oblong. Ascospores hyaline, ellipsoid, 20–30 x 10–13 μm in size. Anamorph produces on hyaline conidiophores catenate conidia of oblong to cylindrical shape, not including fibrosin bodies, 32–44 x 12–15 μm in size. Haustoria are palmate.
B. graminis is unique among the Erysiphales by having conidia with a primary germ tube and finger-shaped ("digitate") appressoria.
Taxonomy
The genus name of Blumeria is in honour of Samuel Blumer (b. 1895), a Swiss botanist (Mycology), Phytopathology, from the University of Bern (Universität Bern).
The genus was circumscribed by Golovin ex Speer in Sydowia Vol.27 on page 2 in 1975.
Ecology
B. graminis asexually produces conidia and sexually forms ascospores.
Conidia are mainly distributed by wind, pests, or human activities. The water initiating ascospores are hypothesized to be dispersed not only by wind but also by splashing water-droplets.
It is biotrophic, and does not grow on synthetic media. Relatively cool and humid conditions are favourable for its growth. Its relatively great genetic variability enables it often to infect previously resistant plant varieties.
Genetics and Evolution
Genetics
The genomes of B. g. f. sp. hordei and B. g. f. sp. tritici have recently been sequenced.
Sequencing of the genome of the wheat powdery mildew B. g. f. sp. tritici, has allowed inference of important aspects of its evolution. It has been seen that it is the most repetitive fungal genome sequenced with 90% transposable elements. Additionally, 6540 genes were annotated, from which 437 encoded candidate secretor proteins and 165 for non-secreted candidate secretor proteins. These were shown to be subject to positive selection, due to their implication in the gene-for-gene relationship to defeat plant disease resistance.
The ability to infect tetraploid- as well as domesticated hexaploid wheat, was seen to be the result of mildew genomes being mosaics of ancient haplogroups that existed before wheat domestication. This has allowed wheat powdery mildew to maintain genetic flexibility, variability and thus a great potential for pathogen variation. It is hypothesized that this mosacisism can be maintained through clonal reproduction in populations with a small effective size or quasi-clonal reproduction in populations with large effective size.
Evolution of Blumeria graminis f.sp. tritici
Wheat powdery mildew is an obligate biotroph with a poorly understood evolutionary history. Sequencing its genome in 2013, many aspects of the evolution of its parasitism were unveiled. Obligate biotrophy has appeared multiple times in evolution in both ascomycetes like B. graminis and basidiomycetes, thus different selective pressure must have acted in the different organisms through time.
It has been seen that B. g. f.sp. triticis genome is a mosaic of haplogroups with different divergence times, which explains its unique pathogen adaptability. Haplogroup Hold (diverged 40-80 mya) allows for the infection of wild tetraploid wheat and Hyoung (diverged 2-10 mya) allows for the infection of both domesticated hexaploid wheat species.
Additionally, it has been seen that there is a positive selective pressure acting on genes that code for candidate secretor proteins and non-secreted candidate secretor proteins, indicating that these might participate in the gene-for-gene relationship of plant disease resistance.
Pathology
Powdery mildew of wheat is relatively easy to diagnose due to the characteristic little white spots of cotton-like mycelia. These can appear on the upper and lower epidermis of the leaves. As the disease progresses they become a light tan color. B. g. f. sp. tritici is an obligate parasite which means it only grows on living tissue. Though present throughout wheat growing regions, it especially favors the eastern seaboard of the United States as well as coastal regions of the United Kingdom.
Hosts and symptoms
Triticum spp. (wheat) is the only host of B. g. f. sp. tritici. Signs on the foliage of wheat are white, powdery mycelium and conidia. As the disease progresses, the patches turn gray and small dark black or brown cleistothecia form in the mycelium mass. Symptoms progress from lower to upper leaves. Symptoms of powdery mildew are chlorotic areas surrounding the infected areas. The lower leaf surface corresponding to the mycelial mat will also show chlorosis. Lower leaves are commonly the most infected because of higher humidity around them.
Disease cycle
B. g. f. sp. tritici has a polycyclic life cycle typical of its phylum, Ascomycota. Powdery mildew of wheat overwinters as cleistothecia dormant in plant debris. Under warmer conditions, however, the fungus can overwinter as asexual conidia or mycelium on living host plants. It can persist between seasons most likely as ascospores in wheat debris left in the field. Ascospores are sexual spores produced from the cleistothecia. These spores, as well as conidia, serve as the primary inoculum and are dispersed by wind. Neither spore requires free water to germinate, only high relative humidity. Wheat powdery mildew thrives in cool humid conditions and cloudy weather increases chances of disease.
When conidia land on a wheat leaf's hydrophobic surface cuticle, they release proteins which facilitate active transport of lightweight anions between leaf and fungus even before germination. This process helps Blumeria recognize that it is on the correct host and directs growth of the germ tube.
Both ascospores and conidia germinate directly with a germ tube. Conidia can recognize the host plant and within one minute of initial contact, the direction of germ tube growth is determined. The development of appressoria then begins infection following the growth of a germ tube. After initial infection, the fungus produces haustoria inside of the wheat cells and mycelium grows on the plant's outer surface. Powdery mildew of wheat produces conidia during the growing season as often as every 7 to 10 days. These conidia function as secondary inoculum as growth and reproduction repeat throughout the growing season.
Environment
Powdery mildew of wheat thrives in cool, humid climates and proliferates in cloudy weather conditions. The pathogen can also be an issue in drier climates if wheat fields are irrigated. Ideal temperatures for growth and reproduction of the pathogen are between and with growth ceasing above . Dense, genetically similar plantings provide opportune conditions for growth of powdery mildew.
Management
Controlling the disease involves eliminating conducive conditions as much as possible by altering planting density and carefully timing applications and rates of nitrogen. Since nitrogen fertilizers encourage dense leafy growth, nitrogen should be applied at precise rates, less than 70 pounds per acre, to control decrease severity. Crop rotation with non-host plants is another way to keep mildew infection to a minimum, however the aerial nature of conidia and ascospore dispersal makes it of limited use. Wheat powdery mildew can also be controlled by eliminating the presence of volunteer wheat in agricultural fields as well as tilling under crop residues.
Chemical control is possible with fungicides such as triadimefon and propiconazole. Another chemical treatment involves treating wheat with a silicon solution or calcium silicate slag. Silicon helps the plant cells defend against fungal attack by degrading haustoria and by producing callose and papilla. With silicon treatment, epidermal cells are less susceptible to powdery mildew of wheat.
Milk has long been popular with home gardeners and small-scale organic growers as a treatment for powdery mildew. Milk is diluted with water (typically 1:10) and sprayed on susceptible plants at the first sign of infection, or as a preventative measure, with repeated weekly application often controlling or eliminating the disease. Studies have shown milk's effectiveness as comparable to some conventional fungicides, and better than benomyl and fenarimol at higher concentrations. Milk has proven effective in treating powdery mildew of summer squash, pumpkins, grapes, and roses. The exact mechanism of action is unknown, but one known effect is that ferroglobulin, a protein in whey, produces oxygen radicals when exposed to sunlight, and contact with these radicals is damaging to the fungus.
Another way to control wheat powdery mildew is breeding in genetic resistance, using "R genes" (resistance genes) to prevent infection. There are at least 25 loci on the wheat genome that encode resistance to powdery mildew. If the particular variety of wheat has only one loci for resistance, the pathogen may be controlled only for a couple years. If, however, the variety of wheat has multiple loci for resistance, the crop may be protected for around 15 years. Because finding these loci can be difficult and time-consuming, molecular markers are used to facilitate combining resistant genomes. One organization working towards identifying these molecular markers is the . With these markers established, researchers will then be able to determine the most effective combination of resistance genes.
is an HSP70 a family of heat shock proteins in Arabidopsis. The ortholog in barley (Hordeum vulgare) is disclosed by Molitor et al., 2011. They find that it is transcribed in response to B. graminis infection, is protective against Bg infection, and that prophylactic infection with Piriformospora indica produces systemic induced resistsance to Bg.
Importance
Powdery mildew can be found in all wheat growing areas of the United States but usually will be most severe in the east and southeast. It is more common in areas with a humid or semi-arid environment where wheat is grown. Powdery mildew has become a more important disease in some areas because of increased application of nitrogen fertilizer, which favors the development of the fungus. Severe symptoms of powdery mildew can cause stunting of wheat. If unmanaged, this disease can reduce yields significantly by reducing photosynthetic areas and causes non-seed producing tillers. Powdery mildew causes reduced kernel size and lower yields. The sooner powdery mildew begins to develop and how high on the plant it develops by flowering the larger the yield loss. Yield Losses up to 45 percent have been shown in Ohio on susceptible varieties when plants are infected early and weather favors disease.
References
Pietro D. Spanu et al., Genome Expansion and Gene Loss in Powdery Mildew Fungi Reveal Functional Tradeoffs in Parasitism, in: Science. December 10, 2010
British Erysiphales
NIAES, Microbial Systematics Lab page on Blumeria
Costamilan, 2005
Fungi described in 1815
Leotiomycetes
Cereal diseases
Fungal plant pathogens and diseases
Fungus species | Blumeria graminis | Biology | 2,749 |
47,881,049 | https://en.wikipedia.org/wiki/Theo%20Rasing | Theodorus "Theo" Henricus Maria Rasing (born 26 May 1953) is a Dutch professor of experimental physics at Radboud University Nijmegen. His expertise lies in the field of magneto-optics. He was a winner of the 2008 Spinoza Prize.
Career
Rasing was born on 26 May 1953 in Didam. In 1976 he obtained a cum laude degree in physics from Radboud University Nijmegen. He obtained his doctorate from the same university in 1982. In 1997 he became professor at Radboud University Nijmegen.
In 2008 he was one of four winners of the Dutch Spinoza Prize and received a 1,5 million euro grant. In 2013 Rasing won a 2,5 million euro Advanced Grant by the European Research Council for a research proposal titled 'magnetisation at its fastest'.
Rasing was elected a member of the Royal Netherlands Academy of Arts and Sciences in 2010. In the same year he was made a Knight of the Order of the Netherlands Lion. Rasing was elected a member of the Academia Europaea in 2013.
In February 2015 the Dutch newspaper de Volkskrant listed Rasing second on a list of funds obtained by researchers.
References
External links
Profile on Radboud University Nijmegen
1953 births
Living people
20th-century Dutch physicists
European Research Council grantees
Experimental physicists
Knights of the Order of the Netherlands Lion
Magneticians
Members of Academia Europaea
Members of the Royal Netherlands Academy of Arts and Sciences
Optical physicists
People from Montferland
Radboud University Nijmegen alumni
Academic staff of Radboud University Nijmegen
Spinoza Prize winners | Theo Rasing | Physics | 333 |
2,989,336 | https://en.wikipedia.org/wiki/DBc | dBc (decibels relative to the carrier) is the power ratio of a signal to a carrier signal, expressed in decibels. For example, phase noise is expressed in dBc/Hz at a given frequency offset from the carrier. dBc can also be used as a measurement of Spurious-Free Dynamic Range (SFDR) between the desired signal and unwanted spurious outputs resulting from the use of signal converters such as a digital-to-analog converter or a frequency mixer.
If the dBc figure is positive, then the relative signal strength is greater than the carrier signal strength. If the dBc figure is negative, then the relative signal strength is less than carrier signal strength.
Although the decibel (dB) is permitted for use alongside SI units, the dBc is not.
Example
If a carrier (reference signal) has a power of , and noise signal has power of .
Power of reference signal expressed in decibel is :
Power of noise expressed in decibel is :
The calculation of dBc difference between noise signal and reference signal is then as follows:
It is also possible to compute the dBc power of noise signal with respect to reference signal directly as logarithm of their ratio as follows:
.
References
External links
Encyclopedia of Laser Physics and Technology
Units of measurement
Radio frequency propagation
Telecommunications engineering
Logarithmic scales of measurement | DBc | Physics,Mathematics,Engineering | 280 |
101,336 | https://en.wikipedia.org/wiki/High-temperature%20superconductivity | High-temperature superconductivity (high-c or HTS) is superconductivity in materials with a critical temperature (the temperature below which the material behaves as a superconductor) above , the boiling point of liquid nitrogen. They are only "high-temperature" relative to previously known superconductors, which function at colder temperatures, close to absolute zero. The "high temperatures" are still far below ambient (room temperature), and therefore require cooling. The first breakthrough of high-temperature superconductor was discovered in 1986 by IBM researchers Georg Bednorz and K. Alex Müller. Although the critical temperature is around , this new type of superconductor was readily modified by Ching-Wu Chu to make the first high-temperature superconductor with critical temperature . Bednorz and Müller were awarded the Nobel Prize in Physics in 1987 "for their important break-through in the discovery of superconductivity in ceramic materials". Most high-c materials are type-II superconductors.
The major advantage of high-temperature superconductors is that they can be cooled using liquid nitrogen, in contrast to the previously known superconductors that require expensive and hard-to-handle coolants, primarily liquid helium. A second advantage of high-c materials is they retain their superconductivity in higher magnetic fields than previous materials. This is important when constructing superconducting magnets, a primary application of high-c materials.
The majority of high-temperature superconductors are ceramic materials, rather than the previously known metallic materials. Ceramic superconductors are suitable for some practical uses but they still have many manufacturing issues. For example, most ceramics are brittle, which makes the fabrication of wires from them very problematic. However, overcoming these drawbacks is the subject of considerable research, and progress is ongoing.
The main class of high-temperature superconductors is copper oxides combined with other metals, especially the rare-earth barium copper oxides (REBCOs) such as yttrium barium copper oxide (YBCO). The second class of high-temperature superconductors in the practical classification is the iron-based compounds.
Magnesium diboride is sometimes included in high-temperature superconductors: It is relatively simple to manufacture, but it superconducts only below , which makes it unsuitable for liquid nitrogen cooling.
History
Superconductivity was discovered by Kamerlingh Onnes in 1911, in a metal solid. Ever since, researchers have attempted to observe superconductivity at increasing temperatures with the goal of finding a room-temperature superconductor. By the late 1970s, superconductivity was observed in several metallic compounds (in particular Nb-based, such as NbTi, Nb3Sn, and Nb3Ge) at temperatures that were much higher than those for elemental metals and which could even exceed .
In 1986, at the IBM research lab near Zürich in Switzerland, Bednorz and Müller were looking for superconductivity in a new class of ceramics: the copper oxides, or cuprates.
Bednorz encountered a particular copper oxide whose resistance dropped to zero at a temperature around . Their results were soon confirmed by many groups, notably Paul Chu at the University of Houston and Shoji Tanaka at the University of Tokyo.
In 1987, Philip W. Anderson gave the first theoretical description of these materials, based on the resonating valence bond (RVB) theory, but a full understanding of these materials is still developing today. These superconductors are now known to possess a d-wave pair symmetry. The first proposal that high-temperature cuprate superconductivity involves d-wave pairing was made in 1987 by N. E. Bickers, Douglas James Scalapino and R. T. Scalettar, followed by three subsequent theories in 1988 by Masahiko Inui, Sebastian Doniach, Peter J. Hirschfeld and Andrei E. Ruckenstein, using spin-fluctuation theory, and by Claudius Gros, Didier Poilblanc, Maurice T. Rice and FC. Zhang, and by Gabriel Kotliar and Jialin Liu identifying d-wave pairing as a natural consequence of the RVB theory. The confirmation of the d-wave nature of the cuprate superconductors was made by a variety of experiments, including the direct observation of the d-wave nodes in the excitation spectrum through angle resolved photoemission spectroscopy (ARPES), the observation of a half-integer flux in tunneling experiments, and indirectly from the temperature dependence of the penetration depth, specific heat and thermal conductivity.
As of 2021, the superconductor with the highest transition temperature at ambient pressure is the cuprate of mercury, barium, and calcium, at around . There are other superconductors with higher recorded transition temperaturesfor example lanthanum superhydride at , but these only occur at very high pressures.
The origin of high-temperature superconductivity is still not clear, but it seems that instead of electron–phonon attraction mechanisms, as in conventional superconductivity, one is dealing with genuine electronic mechanisms (e.g. by antiferromagnetic correlations), and instead of conventional, purely s-wave pairing, more exotic pairing symmetries are thought to be involved (d-wave in the case of the cuprates; primarily extended s-wave, but occasionally d-wave, in the case of the iron-based superconductors).
In 2014, evidence showing that fractional particles can happen in quasi two-dimensional magnetic materials, was found by École Polytechnique Fédérale de Lausanne (EPFL) scientists lending support for Anderson's theory of high-temperature superconductivity.
Selected list of superconductors
Properties
The "high-temperature" superconductor class has had many definitions.
The label high-c should be reserved for materials with critical temperatures greater than the boiling point of liquid nitrogen. However, a number of materialsincluding the original discovery and recently discovered pnictide superconductorshave critical temperatures below but nonetheless are commonly referred to in publications as high-c class.
A substance with a critical temperature above the boiling point of liquid nitrogen, together with a high critical magnetic field and critical current density (above which superconductivity is destroyed), would greatly benefit technological applications. In magnet applications, the high critical magnetic field may prove more valuable than the high c itself. Some cuprates have an upper critical field of about 100 tesla. However, cuprate materials are brittle ceramics that are expensive to manufacture and not easily turned into wires or other useful shapes. Furthermore, high-temperature superconductors do not form large, continuous superconducting domains, rather clusters of microdomains within which superconductivity occurs. They are therefore unsuitable for applications requiring actual superconductive currents, such as magnets for magnetic resonance spectrometers. For a solution to this (powders), see HTS wire.
There has been considerable debate regarding high-temperature superconductivity coexisting with magnetic ordering in YBCO, iron-based superconductors, several ruthenocuprates and other exotic superconductors, and the search continues for other families of materials. HTS are Type-II superconductors, which allow magnetic fields to penetrate their interior in quantized units of flux, meaning that much higher magnetic fields are required to suppress superconductivity. The layered structure also gives a directional dependence to the magnetic field response.
All known high-c superconductors are Type-II superconductors. In contrast to Type-I superconductors, which expel all magnetic fields due to the Meissner effect, Type-II superconductors allow magnetic fields to penetrate their interior in quantized units of flux, creating "holes" or "tubes" of normal metallic regions in the superconducting bulk called vortices. Consequently, high-c superconductors can sustain much higher magnetic fields.
Cuprates
Cuprates are layered materials, consisting of superconducting layers of copper oxide, separated by spacer layers.
Cuprates generally have a structure close to that of a two-dimensional material. Their superconducting properties are determined by electrons moving within weakly coupled copper-oxide (CuO2) layers. Neighbouring layers contain ions such as lanthanum, barium, strontium, or other atoms which act to stabilize the structures and dope electrons or holes onto the copper-oxide layers. The undoped "parent" or "mother" compounds are Mott insulators with long-range antiferromagnetic order at sufficiently low temperatures. Single band models are generally considered to be enough to describe the electronic properties.
The cuprate superconductors adopt a perovskite structure. The copper-oxide planes are checkerboard lattices with squares of O2− ions with a Cu2+ ion at the centre of each square. The unit cell is rotated by 45° from these squares. Chemical formulae of superconducting materials generally contain fractional numbers to describe the doping required for superconductivity. There are several families of cuprate superconductors and they can be categorized by the elements they contain and the number of adjacent copper-oxide layers in each superconducting block. For example, YBCO and BSCCO can alternatively be referred to as "Y123" and Bi2201/Bi2212/Bi2223 depending on the number of layers in each superconducting block (). The superconducting transition temperature has been found to peak at an optimal doping value (=0.16) and an optimal number of layers in each superconducting block, typically =3.
Possible mechanisms for superconductivity in the cuprates continue to be the subject of considerable debate and further research. Certain aspects common to all materials have been identified. Similarities between the antiferromagnetic the low-temperature state of undoped materials and the superconducting state that emerges upon doping, primarily the x2−y2 orbital state of the Cu2+ ions, suggest that electron–electron interactions are more significant than electron–phonon interactions in cupratesmaking the superconductivity unconventional. Recent work on the Fermi surface has shown that nesting occurs at four points in the antiferromagnetic Brillouin zone where spin waves exist and that the superconducting energy gap is larger at these points. The weak isotope effects observed for most cuprates contrast with conventional superconductors that are well described by BCS theory.
Similarities and differences in the properties of hole-doped and electron doped cuprates:
Presence of a pseudogap phase up to at least optimal doping.
Different trends in the Uemura plot relating transition temperature to the superfluid density. The inverse square of the London penetration depth appears to be proportional to the critical temperature for a large number of underdoped cuprate superconductors, but the constant of proportionality is different for hole- and electron-doped cuprates. The linear trend implies that the physics of these materials is strongly two-dimensional.
Universal hourglass-shaped feature in the spin excitations of cuprates measured using inelastic neutron diffraction.
Nernst effect evident in both the superconducting and pseudogap phases.
The electronic structure of superconducting cuprates is highly anisotropic (see the crystal structure of YBCO or BSCCO). Therefore, the Fermi surface of HTSC is very close to the Fermi surface of the doped CuO2 plane (or multi-planes, in case of multi-layer cuprates) and can be presented on the 2‑D reciprocal space (or momentum space) of the CuO2 lattice. The typical Fermi surface within the first CuO2 Brillouin zone is sketched in Fig. 1 (left). It can be derived from the band structure calculations or measured by angle resolved photoemission spectroscopy (ARPES). Fig. 1 (right) shows the Fermi surface of BSCCO measured by ARPES. In a wide range of charge carrier concentration (doping level), in which the hole-doped HTSC are superconducting, the Fermi surface is hole-like (i.e. open, as shown in Fig. 1). This results in an inherent in-plane anisotropy of the electronic properties of HTSC. In 2018, the full three dimensional Fermi surface structure was derived from soft x-ray ARPES.
Iron-based
Iron-based superconductors contain layers of iron and a pnictogensuch as arsenic or phosphorus, a chalcogen, or a crystallogen. This is currently the family with the second highest critical temperature, behind the cuprates. Interest in their superconducting properties began in 2006 with the discovery of superconductivity in LaFePO at and gained much greater attention in 2008 after the analogous material LaFeAs(O,F) was found to superconduct at up to under pressure.
The highest critical temperatures in the iron-based superconductor family exist in thin films of FeSe, where a critical temperature in excess of was reported in 2014.
Since the original discoveries several families of iron-based superconductors have emerged:
LnFeAs(O,F) or LnFeAsO1−x (Ln=lanthanide) with c up to , referred to as 1111 materials. A fluoride variant of these materials was subsequently found with similar c values.
(Ba,K)Fe2As2 and related materials with pairs of iron-arsenide layers, referred to as 122 compounds. c values range up to . These materials also superconduct when iron is replaced with cobalt.
LiFeAs and NaFeAs with c up to around . These materials superconduct close to stoichiometric composition and are referred to as 111 compounds.
FeSe with small off-stoichiometry or tellurium doping.
LaFeSiH with c around in its stoichiometric composition. This superconducting crystallogenide has oxide and fluoride variants LaFeSiOx and LaFeSiFx.
Most undoped iron-based superconductors show a tetragonal-orthorhombic structural phase transition followed at lower temperature by magnetic ordering, similar to the cuprate superconductors. However, they are poor metals rather than Mott insulators and have five bands at the Fermi surface rather than one.
The phase diagram emerging as the iron-arsenide layers are doped is remarkably similar, with the superconducting phase close to or overlapping the magnetic phase. Strong evidence that the c value varies with the As–Fe–As bond angles has already emerged and shows that the optimal c value is obtained with undistorted FeAs4 tetrahedra. The symmetry of the pairing wavefunction is still widely debated, but an extended s-wave scenario is currently favoured.
Magnesium diboride
Magnesium diboride is occasionally referred to as a high-temperature superconductor because its c value of is above that historically expected for BCS superconductors. However, it is more generally regarded as the highest c conventional superconductor, the increased c resulting from two separate bands being present at the Fermi level.
Carbon-based
In 1991 Hebard et al. discovered Fulleride superconductors, where alkali-metal atoms are intercalated into C60 molecules.
In 2008 Ganin et al. demonstrated superconductivity at temperatures of up to for Cs3C60.
P-doped Graphane was proposed in 2010 to be capable of sustaining high-temperature superconductivity.
On 31st of December 2023 "Global Room-Temperature Superconductivity in Graphite" was published in the journal "Advanced Quantum Technologies" claiming to demonstrate superconductivity at room temperature and ambient pressure in Highly oriented pyrolytic graphite with dense arrays of nearly parallel line defects.
Nickelates
In 1999, Anisimov et al. conjectured superconductivity in nickelates, proposing nickel oxides as direct analogs to the cuprate superconductors. Superconductivity in an infinite-layer nickelate, Nd0.8Sr0.2NiO2, was reported at the end of 2019 with a superconducting transition temperature between . This superconducting phase is observed in oxygen-reduced thin films created by the pulsed laser deposition of Nd0.8Sr0.2NiO3 onto SrTiO3 substrates that is then reduced to Nd0.8Sr0.2NiO2 via annealing the thin films at in the presence of CaH2. The superconducting phase is only observed in the oxygen reduced film and is not seen in oxygen reduced bulk material of the same stoichiometry, suggesting that the strain induced by the oxygen reduction of the Nd0.8Sr0.2NiO2 thin film changes the phase space to allow for superconductivity.
Of important is further to extract access hydrogen from the reduction with CaH2, otherwise topotactic hydrogen may prevent superconductivity.
Cuprates
The structure of cuprates which are superconductors are often closely related to perovskite structure, and the structure of these compounds has been described as a distorted, oxygen deficient multi-layered perovskite structure. One of the properties of the crystal structure of oxide superconductors is an alternating multi-layer of CuO2 planes with superconductivity taking place between these layers. The more layers of CuO2, the higher c. This structure causes a large anisotropy in normal conducting and superconducting properties, since electrical currents are carried by holes induced in the oxygen sites of the CuO2 sheets. The electrical conduction is highly anisotropic, with a much higher conductivity parallel to the CuO2 plane than in the perpendicular direction. Generally, critical temperatures depend on the chemical compositions, cations substitutions and oxygen content. They can be classified as superstripes; i.e., particular realizations of superlattices at atomic limit made of superconducting atomic layers, wires, dots separated by spacer layers, that gives multiband and multigap superconductivity.
Yttrium–barium cuprate
An yttrium–barium cuprate, YBa2Cu3O7−x (or Y123), was the first superconductor found above liquid nitrogen boiling point. There are two atoms of Barium for each atom of Yttrium.
The proportions of the three different metals in the YBa2Cu3O7 superconductor are in the mole ratio of 1 to 2 to 3 for yttrium to barium to copper, respectively: this particular superconductor has also often been referred to as the 123 superconductor.
The unit cell of YBa2Cu3O7 consists of three perovskite unit cells, which is pseudocubic, nearly orthorhombic. The other superconducting cuprates have another structure: they have a tetragonal cell.
Each perovskite cell contains a Y or Ba atom at the center: Ba in the bottom unit cell, Y in the middle one, and Ba in the top unit cell. Thus, Y and Ba are stacked in the sequence [Ba–Y–Ba] along the c-axis. All corner sites of the unit cell are occupied by Cu, which has two different coordinations, Cu(1) and Cu(2), with respect to oxygen. There are four possible crystallographic sites for oxygen: O(1), O(2), O(3) and O(4). The coordination polyhedra of Y and Ba with respect to oxygen are different. The tripling of the perovskite unit cell leads to nine oxygen atoms, whereas YBa2Cu3O7 has seven oxygen atoms and, therefore, is referred to as an oxygen-deficient perovskite structure. The structure has a stacking of different layers: (CuO)(BaO)(CuO2)(Y)(CuO2)(BaO)(CuO). One of the key feature of the unit cell of YBa2Cu3O7−x (YBCO) is the presence of two layers of CuO2. The role of the Y plane is to serve as a spacer between two CuO2 planes. In YBCO, the Cu–O chains are known to play an important role for superconductivity. c is maximal near when x ≈ 0.15 and the structure is orthorhombic. Superconductivity disappears at x ≈ 0.6, where the structural transformation of YBCO occurs from orthorhombic to tetragonal.
Other cuprates
The preparation of other cuprates is more difficult than the YBCO preparation.
They also have a different crystal structure: they are tetragonal where YBCO is orthorhombic.
Problems in these superconductors arise because of the existence of three or more phases having a similar layered structure.
Moreover, the crystal structure of other tested cuprate superconductors are very similar. Like YBCO, the perovskite-type feature and the presence of simple copper oxide (CuO2) layers also exist in these superconductors. However, unlike YBCO, Cu–O chains are not present in these superconductors. The YBCO superconductor has an orthorhombic structure, whereas the other high-c superconductors have a tetragonal structure.
There are three main classes of superconducting cuprates: bismuth-based, thallium-based and mercury-based.
The second cuprate by practical importance is currently BSCCO, a compound of Bi–Sr–Ca–Cu–O. The content of bismuth and strontium creates some chemical issues.
It has three superconducting phases forming a homologous series as Bi2Sr2Can−1CunO4+2n+x (n=1, 2 and 3).
These three phases are Bi-2201, Bi-2212 and Bi-2223, having transition temperatures of , and , respectively, where the numbering system represent number of atoms for Bi Sr, Ca and Cu respectively. The two phases have a tetragonal structure which consists of two sheared crystallographic unit cells. The unit cell of these phases has double Bi–O planes which are stacked in a way that the Bi atom of one plane sits below the oxygen atom of the next consecutive plane. The Ca atom forms a layer within the interior of the CuO2 layers in both Bi-2212 and Bi-2223; there is no Ca layer in the Bi-2201 phase. The three phases differ with each other in the number of cuprate planes; Bi-2201, Bi-2212 and Bi-2223 phases have one, two and three CuO2 planes, respectively. The c axis lattice constants of these phases increases with the number of cuprate planes (see table below). The coordination of the Cu atom is different in the three phases. The Cu atom forms an octahedral coordination with respect to oxygen atoms in the 2201 phase, whereas in 2212, the Cu atom is surrounded by five oxygen atoms in a pyramidal arrangement. In the 2223 structure, Cu has two coordinations with respect to oxygen: one Cu atom is bonded with four oxygen atoms in square planar configuration and another Cu atom is coordinated with five oxygen atoms in a pyramidal arrangement.
Cuprate of Tl–Ba–Ca: The first series of the Tl-based superconductor containing one Tl–O layer has the general formula TlBa2Can−1CunO2n+3, whereas the second series containing two Tl–O layers has a formula of Tl2Ba2Can−1CunO2n+4 with n =1, 2 and 3. In the structure of Tl2Ba2CuO6 (Tl-2201), there is one CuO2 layer with the stacking sequence (Tl–O) (Tl–O) (Ba–O) (Cu–O) (Ba–O) (Tl–O) (Tl–O). In Tl2Ba2CaCu2O8 (Tl-2212), there are two Cu–O layers with a Ca layer in between. Similar to the Tl2Ba2CuO6 structure, Tl–O layers are present outside the Ba–O layers. In Tl2Ba2Ca2Cu3O10 (Tl-2223), there are three CuO2 layers enclosing Ca layers between each of these. In Tl-based superconductors, c is found to increase with the increase in CuO2 layers. However, the value of c decreases after four CuO2 layers in TlBa2Can−1CunO2n+3, and in the Tl2Ba2Can−1CunO2n+4 compound, it decreases after three CuO2 layers.
Cuprate of Hg–Ba–Ca The crystal structure of HgBa2CuO4 (Hg-1201), HgBa2CaCu2O6 (Hg-1212) and HgBa2Ca2Cu3O8 (Hg-1223) is similar to that of Tl-1201, Tl-1212 and Tl-1223, with Hg in place of Tl. It is noteworthy that the c of the Hg compound (Hg-1201) containing one CuO2 layer is much larger as compared to the one-CuO2-layer compound of thallium (Tl-1201). In the Hg-based superconductor, c is also found to increase as the CuO2 layer increases. For Hg-1201, Hg-1212 and Hg-1223, the values of c are 94, 128, and the record value at ambient pressure , respectively, as shown in table below. The observation that the c of Hg-1223 increases to under high pressure indicates that the c of this compound is very sensitive to the structure of the compound.
Preparation and manufacturing
The simplest method for preparing ceramic superconductors is a solid-state thermochemical reaction involving mixing, calcination and sintering.
The appropriate amounts of precursor powders, usually oxides and carbonates, are mixed thoroughly using a Ball mill. Solution chemistry processes such as coprecipitation, freeze-drying and sol–gel methods are alternative ways for preparing a homogeneous mixture. These powders are calcined in the temperature range from for several hours. The powders are cooled, reground and calcined again. This process is repeated several times to get homogeneous material. The powders are subsequently compacted to pellets and sintered. The sintering environment such as temperature, annealing time, atmosphere and cooling rate play a very important role in getting good high-c superconducting materials. The YBa2Cu3O7−x compound is prepared by calcination and sintering of a homogeneous mixture of Y2O3, BaCO3 and CuO in the appropriate atomic ratio. Calcination is done at , whereas sintering is done at in an oxygen atmosphere. The oxygen stoichiometry in this material is very crucial for obtaining a superconducting YBa2Cu3O7−x compound. At the time of sintering, the semiconducting tetragonal YBa2Cu3O6 compound is formed, which, on slow cooling in oxygen atmosphere, turns into superconducting YBa2Cu3O7−x. The uptake and loss of oxygen are reversible in YBa2Cu3O7−x. A fully oxygenated orthorhombic YBa2Cu3O7−x sample can be transformed into tetragonal YBa2Cu3O6 by heating in a vacuum at temperature above .
The preparation of Bi-, Tl- and Hg-based high-c superconductors is more difficult than the YBCO preparation. Problems in these superconductors arise because of the existence of three or more phases having a similar layered structure. Thus, syntactic intergrowth and defects such as stacking faults occur during synthesis and it becomes difficult to isolate a single superconducting phase. For Bi–Sr–Ca–Cu–O, it is relatively simple to prepare the Bi-2212 (c ≈ 85 K) phase, whereas it is very difficult to prepare a single phase of Bi-2223 (c ≈ 110 K). The Bi-2212 phase appears only after few hours of sintering at , but the larger fraction of the Bi-2223 phase is formed after a long reaction time of more than a week at . Although the substitution of Pb in the Bi–Sr–Ca–Cu–O compound has been found to promote the growth of the high-c phase, a long sintering time is still required.
Ongoing research
The question of how superconductivity arises in high-temperature superconductors is one of the major unsolved problems of theoretical condensed matter physics. The mechanism that causes the electrons in these crystals to form pairs is not known. Despite intensive research and many promising leads, an explanation has so far eluded scientists. One reason for this is that the materials in question are generally very complex, multi-layered crystals (for example, BSCCO), making theoretical modelling difficult.
Improving the quality and variety of samples also gives rise to considerable research, both with the aim of improved characterisation of the physical properties of existing compounds, and synthesizing new materials, often with the hope of increasing c. Technological research focuses on making HTS materials in sufficient quantities to make their use economically viable as well as in optimizing their properties in relation to applications.
Metallic hydrogen has been proposed as a room-temperature superconductor, some experimental observations have detected the occurrence of the Meissner effect. LK-99, copper-doped lead-apatite, has also been proposed as a room-temperature superconductor.
Theoretical models
There have been two representative theories for high-temperature or unconventional superconductivity.
Firstly, weak coupling theory suggests superconductivity emerges from antiferromagnetic spin fluctuations in a doped system.
According to this theory, the pairing wave function of the cuprate HTS should have a dx2-y2 symmetry. Thus, determining whether the pairing wave function has d-wave symmetry is essential to test the spin fluctuation mechanism. That is, if the HTS order parameter (a pairing wave function like in Ginzburg–Landau theory) does not have d-wave symmetry, then a pairing mechanism related to spin fluctuations can be ruled out. (Similar arguments can be made for iron-based superconductors but the different material properties allow a different pairing symmetry.) Secondly, there was the interlayer coupling model, according to which a layered structure consisting of BCS-type (s-wave symmetry) superconductors can enhance the superconductivity by itself. By introducing an additional tunnelling interaction between each layer, this model successfully explained the anisotropic symmetry of the order parameter as well as the emergence of the HTS. Thus, in order to solve this unsettled problem, there have been numerous experiments such as photoemission spectroscopy, NMR, specific heat measurements, etc. Up to date the results were ambiguous, some reports supported the d symmetry for the HTS whereas others supported the s symmetry. This muddy situation possibly originated from the indirect nature of the experimental evidence, as well as experimental issues such as sample quality, impurity scattering, twinning, etc.
This summary makes an implicit assumption: superconductive properties can be treated by mean-field theory. It also fails to mention that in addition to the superconductive gap, there is a second gap, the pseudogap. The cuprate layers are insulating, and the superconductors are doped with interlayer impurities to make them metallic. The superconductive transition temperature can be maximized by varying the dopant concentration. The simplest example is La2CuO4, which consist of alternating CuO2 and LaO layers which are insulating when pure. When 8% of the La is replaced by Sr, the latter act as dopants, contributing holes to the CuO2 layers, and making the sample metallic. The Sr impurities also act as electronic bridges, enabling interlayer coupling. Proceeding from this picture, some theories argue that the basic pairing interaction is still interaction with phonons, as in the conventional superconductors with Cooper pairs. While the undoped materials are antiferromagnetic, even a few percent of impurity dopants introduce a smaller pseudogap in the CuO2 planes which is also caused by phonons. The gap decreases with increasing charge carriers, and as it nears the superconductive gap, the latter reaches its maximum. The reason for the high transition temperature is then argued to be due to the percolating behaviour of the carriersthe carriers follow zig-zag percolative paths, largely in metallic domains in the CuO2 planes, until blocked by charge density wave domain walls, where they use dopant bridges to cross over to a metallic domain of an adjacent CuO2 plane. The transition temperature maxima are reached when the host lattice has weak bond-bending forces, which produce strong electron–phonon interactions at the interlayer dopants.
D symmetry in YBCO
An experiment based on flux quantization of a three-grain ring of YBa2Cu3O7 (YBCO) was proposed to test the symmetry of the order parameter in the HTS. The symmetry of the order parameter could best be probed at the junction interface as the Cooper pairs tunnel across a Josephson junction or weak link.
It was expected that a half-integer flux, that is, a spontaneous magnetization could only occur for a junction of d symmetry superconductors. But, even if the junction experiment is the strongest method to determine the symmetry of the HTS order parameter, the results have been ambiguous. John R. Kirtley and C. C. Tsuei thought that the ambiguous results came from the defects inside the HTS, so that they designed an experiment where both clean limit (no defects) and dirty limit (maximal defects) were considered simultaneously. In the experiment, the spontaneous magnetization was clearly observed in YBCO, which supported the d symmetry of the order parameter in YBCO. But, since YBCO is orthorhombic, it might inherently have an admixture of s symmetry. So, by tuning their technique further, they found that there was an admixture of s symmetry in YBCO within about 3%. Also, they found that there was a pure dx2−y2 order parameter symmetry in the tetragonal Tl2Ba2CuO6.
Spin-fluctuation mechanism
Despite all these years, the mechanism of high-c superconductivity is still highly controversial, mostly due to the lack of exact theoretical computations on such strongly interacting electron systems. However, most rigorous theoretical calculations, including phenomenological and diagrammatic approaches, converge on magnetic fluctuations as the pairing mechanism for these systems. The qualitative explanation is as follows:
In a superconductor, the flow of electrons cannot be resolved into individual electrons, but instead consists of many pairs of bound electrons, called Cooper pairs. In conventional superconductors, these pairs are formed when an electron moving through the material distorts the surrounding crystal lattice, which in turn attracts another electron and forms a bound pair. This is sometimes called the "water bed" effect. Each Cooper pair requires a certain minimum energy to be displaced, and if the thermal fluctuations in the crystal lattice are smaller than this energy the pair can flow without dissipating energy. This ability of the electrons to flow without resistance leads to superconductivity.
In a high-c superconductor, the mechanism is extremely similar to a conventional superconductor, except, in this case, phonons virtually play no role and their role is replaced by spin-density waves. Just as all known conventional superconductors are strong phonon systems, all known high-c superconductors are strong spin-density wave systems, within close vicinity of a magnetic transition to, for example, an antiferromagnet. When an electron moves in a high-c superconductor, its spin creates a spin-density wave around it. This spin-density wave in turn causes a nearby electron to fall into the spin depression created by the first electron (water-bed effect again). Hence, again, a Cooper pair is formed. When the system temperature is lowered, more spin density waves and Cooper pairs are created, eventually leading to superconductivity. Note that in high-c systems, as these systems are magnetic systems due to the Coulomb interaction, there is a strong Coulomb repulsion between electrons. This Coulomb repulsion prevents pairing of the Cooper pairs on the same lattice site. The pairing of the electrons occur at near-neighbor lattice sites as a result. This is the so-called d-wave pairing, where the pairing state has a node (zero) at the origin.
Examples
Examples of high-c cuprate superconductors include YBCO and BSCCO, which are the most known materials that achieve superconductivity above the boiling point of liquid nitrogen.
See also
References
External links
High-temperature superconductors
Correlated electrons
Unsolved problems in physics | High-temperature superconductivity | Physics,Materials_science | 7,992 |
2,440,792 | https://en.wikipedia.org/wiki/Podosome | Podosomes are conical, actin-rich structures found as appendages on the outer surface of the plasma membrane of animal cells. Their size ranges from approximately 0.5 μm to 2.0 μm in diameter. While usually situated on the periphery of the cellular membrane, these unique structures display a polarized pattern of distribution in migrating cells, situating at the front border between the lamellipodium and lamellum. Their primary purpose is connected to cellular motility and invasion; therefore, they serve as both sites of attachment and degradation along the extracellular matrix. Many different specialized cells exhibit these dynamic structures such as invadopodia, (invasive cancer cells), osteoclasts, vascular smooth muscle cells, endothelial cells, and certain immune cells such as macrophages and dendritic cells.
Characteristics
A podosome consists of a core rich in actin surrounded by adhesion and scaffolding proteins. The actin filaments within these structures are highly regulated by many actin nucleators, polymerization activators, actin binding and crosslinking proteins, kinases, small GTPases, and scaffold proteins; therefore, total actin turnover occurs within seconds. To distinguish podosomes from others types of cellular adhesions, the protein Tks5 and WASP (Wiskott–Aldrich syndrome protein) are used as markers alongside actin, cortactin and the Arp2/3 complex to localize and isolate these protrusions because Tks5 and WASP are unique to the podosome when compared with other actin-based cellular structures.
In their outward structure, the podosomes demonstrate two distinct features: an actin core and a ring complex. Within the core, coordinators of actin nucleation are found. Specifically, the Arp2/3 complex and WASP when close to the plasma membrane or cortactin when further away comprise this group of proteins. Emanating radially from the dense core of actin are actin filaments reaching to the plasma membrane and between neighboring podosomes.
In the ring complex, integrins and integrin-associated proteins serve to connect the cytoskeleton to cell surface integrins forming the outward protrusion. Initial research suggested that the superstructure of podosomes were cylindrical, but new advances in bioimaging techniques have altered that perception and show the ring complex to display a polygonal form. These finding were made possible through the application of Bayesian blinking and bleaching analytics to data gained from standard widefield microscopy using cells that expressed fluorescently tagged proteins specific to the podosome ring complex.
Typically, the podosome size falls between 0.5 um and 2.0 um in diameter and depth. The lifetime of the structure is only minutes in duration, much shorter than observed in invadopodia.
Function
Podosomes are thought to be intimately connected to cellular motility within tissue microenvironments through coordinating degradation of the extracellular matrix with cellular movement. The migration of cells is essential to proper embryonic development and, in maturity, to wound healing and the inflammatory response. Examples of these motile cell behaviors include: transendothelial migration of dendritic cells, migration of aortic endothelial cells for arterial vessel remodeling, and tissue infiltration by macrophages. Aberrations in cell migration lie beneath pathologies involving development, vasculature, and immunity. Consequently, podosomes are present in cell types associated with tissue remodeling and the immune system.
Patients who suffer from Wiskott–Aldrich syndrome demonstrate, through their immune cells, continued evidence of the role podosomes fulfill in cell motility. These patients do not possess fully formed WASP that has been shown to localize in podosomes and to be integral to their formation from previous studies. The dendritic cells and macrophages of these patients’ immune systems do not manifest podosome formations and demonstrate defects in cellular movement within tissue microenvironments. Some researchers suspect that podosomes may be implicated in the migration of neural crest cells. Patients who exhibit Frank–ter Haar syndrome are known to be mutant for the podosome specific protein Tks4 and demonstrate defects in neural crest cell migration.
Adding to the known functionalities of podosomes, research suggests that these dynamic structures also exhibit mechanosensory attributes. Initial formation of podosomes seems to be influenced by the structure and composition of the underlying substratum including the presence and distribution of specific ligands. Various integrin receptors monitor the mechanical properties of the cellular microenvironment and can influence and initiate formation of a podosome. Once fully formed, the integrity of the matrix substratum dictates the lifespan of the podosome with increased stiffness leading to longer endurance and closer spacing between podosome sites.
Some studies indicates also a putative role for podosomes even in the regulation of bone marrow stem cell's function. Podosomes have been shown to be widely present in vitro on mesodermal progenitor cells (MPCs), cell capable of differentiating into mesenchymal stromal cells.
It has been proposed that podosomes are important in the mobilisation of MPCs in the event of physiological need.
Role in osteoclasts
Osteoclasts are large, multinucleated bone cells that conduct the process of bone resorption. In this remodeling process, podosomes play an integral role. During the maturation of osteoclast precursors, groups of podosomes form higher ordered ring structures which ultimately coalesce into a band about the cell periphery. The resulting arrangement of podosomes is highly interconnected through a dense, radial network of actin filaments that extend between and onto neighboring podosomes.
Accumulation of F-actin, vinculin, paxillin, and α-actin within the podosomes of the coalescent band signals the development of a fully matured osteoclast. Upon initiation of bone resorption, the band of podosomes disassembles leaving behind a mesh primarily composed of F-actin which functions as the ‘sealing zone.’ This sealing zone becomes the site of osteoclast attachment to the bone matrix. Inhibition of bone resorption through drug intervention results in the lack of the podosome band during early osteoclast differentiation and ultimate absence of a sealing zone.
History
In the early 1980s, chicken embryo fibroblasts were transformed using the Rous sarcoma virus (RSV) containing the oncogene v-src. This transformation elicited the relocalization of vinculin and α-actin in the cytoskeleton from focal adhesions forming circular clusters. Later in 1985, it was shown using the same cells that these protein clusters were localized to protrusions in the ventral plasma membrane, were substratum adhesion sites; therefore, these structures were termed podosomes indicating their foot-like character in cells. In 1989, it was demonstrated that these podosomes played a role in matrix degradation. To reflect this newly discovered destructive nature the name invadopodia was given to these dynamic structures.
Because both terms invadopodia and podosomes were initially used to reference the identical structures in identical cell lines, there exists confusion about the nomenclature. Typically, when these structures are found in normal cells, they are referred to as podosomes, and when in cancer cells, invadopodia.
References
External links
MBInfo - Podosomes
MBInfo - Podosome Assembly
Podosomes and Invadopodia at Scirus Topic Pages
Cell anatomy
Membrane biology | Podosome | Chemistry | 1,629 |
14,285,885 | https://en.wikipedia.org/wiki/Formate%E2%80%93tetrahydrofolate%20ligase | In enzymology, a formate—tetrahydrofolate ligase () is an enzyme that catalyzes the chemical reaction
ATP + formate + tetrahydrofolate ADP + phosphate + 10-formyltetrahydrofolate
The 3 substrates of this enzyme are ATP, formate, and tetrahydrofolate, whereas its 3 products are ADP, phosphate, and 10-formyltetrahydrofolate.
This enzyme belongs to the family of ligases, specifically those forming generic carbon-nitrogen bonds. This enzyme participates in glyoxylate and dicarboxylate metabolism and one carbon pool by folate.
In eukaryotes the FTHFS activity is expressed by a multifunctional enzyme, C-1-tetrahydrofolate synthase (C1-THF synthase), which also catalyses the dehydrogenase and cyclohydrolase activities. Two forms of C1-THF syntheses are known, one is located in the mitochondrial matrix, while the second one is cytoplasmic. In both forms the FTHFS domain consists of about 600 amino acid residues and is located in the C-terminal section of C1-THF synthase. In prokaryotes FTHFS activity is expressed by a monofunctional homotetrameric enzyme of about 560 amino acid residues.
Nomenclature
The systematic name of this enzyme class is formate:tetrahydrofolate ligase (ADP-forming). Other names in common use include:
formyltetrahydrofolate synthetase,
10-formyltetrahydrofolate synthetase,
tetrahydrofolic formylase, and
tetrahydrofolate formylase.
Examples
Human genes encoding formate-tetrahydrofolate ligases include:
MTHFD1 – cytoplasmic
MTHFD1L – mitochondrial
Structural studies
As of late 2007, 3 structures have been solved for this class of enzymes, with PDB accession codes , , and .
The crystal structure of N(10)-formyltetrahydrofolate synthetase from Moorella thermoacetica shows that the subunit is composed of three domains organised around three mixed beta-sheets. There are two cavities between adjacent domains. One of them was identified as the nucleotide binding site by homology modelling. The large domain contains a seven-stranded beta-sheet surrounded by helices on both sides. The second domain contains a five-stranded beta-sheet with two alpha-helices packed on one side while the other two are a wall of the active site cavity. The third domain contains a four-stranded beta-sheet forming a half-barrel. The concave side is covered by two helices while the convex side is another wall of the large cavity. Arg 97 is likely involved in formyl phosphate binding. The tetrameric molecule is relatively flat with the shape of the letter X, and the active sites are located at the end of the subunits far from the subunit interface.
Related enzymes
The reverse reaction converting 10-formyltetrahydrofolate to tetrahydrofolate is performed by formyltetrahydrofolate dehydrogenase.
References
Further reading
Protein families
EC 6.3.4
Enzymes of known structure | Formate–tetrahydrofolate ligase | Biology | 701 |
45,586,556 | https://en.wikipedia.org/wiki/Academic%20Torrents | Academic Torrents is a website which enables the sharing of research data using the BitTorrent protocol. The site was founded in November 2013, and is a project of the Institute for Reproducible Research (a 501(c)3 U.S. non-profit corporation).
The project is said to be similar to LOCKSS but with a focus on "offering researchers the opportunity to distribute the hosting of their papers and datasets to authors and readers, providing easy access to scholarly works and simultaneously backing them up on computers around the world."
Notable datasets
Developing Human Connectome Project
The developing Human Connectome Project related to the Human Connectome Project uses the platform. "Researchers from three leading British institutions are using BitTorrent to share over 150 GB of unique high-resolution brain scans of unborn babies with colleagues worldwide... The researchers opted to go for the Academic Torrents tracker, which specializes in sharing research data"
CrossRef metadata
The site hosts public metadata releases from Crossref which contain over 120+ million metadata records for scholarly work, each with a DOI. This was done so to allow the community to work with the entire database programmatically instead of using their API. "The sheer number of records means that, though anyone can use these records anytime, downloading them all via our APIs can be quite time-consuming. We hope this saves the research community valuable time during this crisis."
See also
Digital library
Digital preservation
References
BitTorrent websites
Creative Commons-licensed works
Open-access archives
Scholarly communication
Open science
Collaborative software
Open data
Academic publishing
Data publishing
Institutional repository software
501(c)(3) organizations
Access to Knowledge movement
American digital libraries
Foundations based in the United States
Metascience-related organizations | Academic Torrents | Technology | 354 |
80,754 | https://en.wikipedia.org/wiki/Division%20by%20two | In mathematics, division by two or halving has also been called mediation or dimidiation. The treatment of this as a different operation from multiplication and division by other numbers goes back to the ancient Egyptians, whose multiplication algorithm used division by two as one of its fundamental steps.
Some mathematicians as late as the sixteenth century continued to view halving as a separate operation, and it often continues to be treated separately in modern computer programming.
Performing this operation is simple in decimal arithmetic, in the binary numeral system used in computer programming, and in other even-numbered bases. To divide an odd number by 2 use the mathematical solution ((N-1)÷2)+0.5. For example, if N=7, then ((7-1)÷2)+0.5=3.5, so 7÷2=3.5.
Binary
In binary arithmetic, division by two can be performed by a bit shift operation that shifts the number one place to the right.
This is a form of strength reduction optimization. For example, 1101001 in binary (the decimal number 105), shifted one place to the right, is 110100 (the decimal number 52): the lowest order bit, a 1, is removed. Similarly, division by any power of two 2k may be performed by right-shifting k positions. Because bit shifts are often much faster operations than division, replacing a division by a shift in this way can be a helpful step in program optimization. However, for the sake of software portability and readability, it is often best to write programs using the division operation and trust in the compiler to perform this replacement. An example from Common Lisp:
(setq number #b1101001) ; #b1101001 — 105
(ash number -1) ; #b0110100 — 105 >> 1 ⇒ 52
(ash number -4) ; #b0000110 — 105 >> 4 ≡ 105 / 2⁴ ⇒ 6
The above statements, however, are not always true when dealing with dividing signed binary numbers. Shifting right by 1 bit will divide by two, always rounding down. However, in some languages, division of signed binary numbers round towards 0 (which, if the result is negative, means it rounds up). For example, Java is one such language: in Java, -3 / 2 evaluates to -1, whereas -3 >> 1 evaluates to -2. So in this case, the compiler cannot optimize division by two by replacing it by a bit shift, when the dividend could possibly be negative.
Binary floating point
In binary floating-point arithmetic, division by two can be performed by decreasing the exponent by one (as long as the result is not a subnormal number). Many programming languages provide functions that can be used to divide a floating point number by a power of two. For example, the Java programming language provides the method java.lang.Math.scalb for scaling by a power of two, and the C programming language provides the function ldexp for the same purpose.
Decimal
The following algorithm is for decimal. However, it can be used as a model to construct an algorithm for taking half of any number N in any even base.
Write out N, putting a zero to its left.
Go through the digits of N in overlapping pairs, writing down digits of the result from the following table.
Example: 1738/2=?
Write 01738. We will now work on finding the result.
01: even digit followed by 1, write 0.
17: odd digit followed by 7, write 8.
73: odd digit followed by 3, write 6.
38: odd digit followed by 8, write 9.
Result: 0869.
From the example one can see that 0 is even.
If the last digit of N is odd digit one should add 0.5 to the result.
See also
One half
Median, a value that splits a set of data values into two equal subsets
Bisection, the partition of a geometric object into two equal halves
Dimidiation, a heraldic method of joining two coats of arms by splitting their designs into halves
References
Division (mathematics)
Elementary arithmetic
Binary arithmetic
Parity (mathematics)
2 (number) | Division by two | Mathematics | 871 |
1,447,904 | https://en.wikipedia.org/wiki/Kerr%E2%80%93Newman%20metric | The Kerr–Newman metric describes the spacetime geometry around a mass which is electrically charged and rotating. It is a vacuum solution which generalizes the Kerr metric (which describes an uncharged, rotating mass) by additionally taking into account the energy of an electromagnetic field, making it the most general asymptotically flat and stationary solution of the Einstein–Maxwell equations in general relativity. As an electrovacuum solution, it only includes those charges associated with the magnetic field; it does not include any free electric charges.
Because observed astronomical objects do not possess an appreciable net electric charge (the magnetic fields of stars arise through other processes), the Kerr–Newman metric is primarily of theoretical interest.
The model lacks description of infalling baryonic matter, light (null dusts) or dark matter, and thus provides an incomplete description of stellar mass black holes and active galactic nuclei. The solution however is of mathematical interest and provides a fairly simple cornerstone for further exploration.
The Kerr–Newman solution is a special case of more general exact solutions of the Einstein–Maxwell equations with non-zero cosmological constant.
History
In December of 1963, Roy Kerr and Alfred Schild found the Kerr–Schild metrics that gave all Einstein spaces that are exact linear perturbations of Minkowski space. In early 1964, Kerr looked for all Einstein–Maxwell spaces with this same property. By February of 1964, the special case where the Kerr–Schild spaces were charged (including the Kerr–Newman solution) was known but the general case where the special directions were not geodesics of the underlying Minkowski space proved very difficult. The problem was given to George Debney to try to solve but was given up by March 1964. About this time Ezra T. Newman found the solution for charged Kerr by guesswork.
In 1965, Ezra "Ted" Newman found the axisymmetric solution of Einstein's field equation for a black hole which is both rotating and electrically charged. This formula for the metric tensor is called the Kerr–Newman metric. It is a generalisation of the Kerr metric for an uncharged spinning point-mass, which had been discovered by Roy Kerr two years earlier.
Four related solutions may be summarized by the following table:
{| class="wikitable"
|-
!
! Non-rotating (J = 0)
! Rotating (J ∈ )
|-
! Uncharged (Q = 0)
| Schwarzschild
| Kerr
|-
! Charged (Q ∈ )
| Reissner–Nordström
| Kerr-Newman
|-
|}
where Q represents the body's electric charge and J represents its spin angular momentum.
Overview of the solution
Newman's result represents the simplest stationary, axisymmetric, asymptotically flat solution of Einstein's equations in the presence of an electromagnetic field in four dimensions. It is sometimes referred to as an "electrovacuum" solution of Einstein's equations.
Any Kerr–Newman source has its rotation axis aligned with its magnetic axis. Thus, a Kerr–Newman source is different from commonly observed astronomical bodies, for which there is a substantial angle between the rotation axis and the magnetic moment. Specifically, neither the Sun, nor any of the planets in the Solar System have magnetic fields aligned with the spin axis. Thus, while the Kerr solution describes the gravitational field of the Sun and planets, the magnetic fields arise by a different process.
If the Kerr–Newman potential is considered as a model for a classical electron, it predicts an electron having not just a magnetic dipole moment, but also other multipole moments, such as an electric quadrupole moment. An electron quadrupole moment has not yet been experimentally detected; it appears to be zero.
In the G = 0 limit, the electromagnetic fields are those of a charged rotating disk inside a ring where the fields are infinite. The total field energy for this disk is infinite, and so this G = 0 limit does not solve the problem of infinite self-energy.
Like the Kerr metric for an uncharged rotating mass, the Kerr–Newman interior solution exists mathematically but is probably not representative of the actual metric of a physically realistic rotating black hole due to issues with the stability of the Cauchy horizon, due to mass inflation driven by infalling matter. Although it represents a generalization of the Kerr metric, it is not considered as very important for astrophysical purposes, since one does not expect that realistic black holes have a significant electric charge (they are expected to have a minuscule positive charge, but only because the proton has a much larger momentum than the electron, and is thus more likely to overcome electrostatic repulsion and be carried by momentum across the horizon).
The Kerr–Newman metric defines a black hole with an event horizon only when the combined charge and angular momentum are sufficiently small:
An electron's angular momentum J and charge Q (suitably specified in geometrized units) both exceed its mass M, in which case the metric has no event horizon. Thus, there can be no such thing as a black hole electron — only a naked spinning ring singularity. Such a metric has several seemingly unphysical properties, such as the ring's violation of the cosmic censorship hypothesis, and also appearance of causality-violating closed timelike curves in the immediate vicinity of the ring.
A 2009 paper by Russian theorist Alexander Burinskii considered an electron as a generalization of the previous models by Israel (1970) and Lopez (1984), which truncated the "negative" sheet of the Kerr-Newman metric, obtaining the source of the Kerr-Newman solution in the form of a relativistically rotating disk. Lopez's truncation regularized the Kerr-Newman metric by a cutoff at :, replacing the singularity by a flat regular space-time, the so called "bubble". Assuming that the Lopez bubble corresponds to a phase transition similar to the Higgs symmetry breaking mechanism, Burinskii showed that a gravity-created ring singularity forms by regularization the superconducting core of the electron model and should be described by the supersymmetric Landau-Ginzburg field model of phase transition:
By omitting Burinsky's intermediate work, we come to the recent new proposal: to consider the truncated by Israel and Lopez negative sheet of the KN solution as the sheet of the positron.
This modification unites the KN solution with the model of QED, and shows the important role of the Wilson lines formed by frame-dragging of the vector potential.
As a result, the modified KN solution acquires a strong interaction with Kerr's gravity caused by the additional energy contribution of the electron-positron vacuum and creates the Kerr–Newman relativistic circular string of Compton size.
Limiting cases
The Kerr–Newman metric can be seen to reduce to other exact solutions in general relativity in limiting cases. It reduces to
the Kerr metric as the charge Q goes to zero;
the Reissner–Nordström metric as the angular momentum J (or a = ) goes to zero;
the Schwarzschild metric as both the charge Q and the angular momentum J (or a) are taken to zero; and
Minkowski space if the mass M, the charge Q, and the rotational parameter a are all zero.
Alternately, if gravity is intended to be removed, Minkowski space arises if the gravitational constant G is zero, without taking the mass and charge to zero. In this case, the electric and magnetic fields are more complicated than simply the fields of a charged magnetic dipole; the zero-gravity limit is not trivial.
The metric
The Kerr–Newman metric describes the geometry of spacetime for a rotating charged black hole with mass M, charge Q and angular momentum J. The formula for this metric depends upon what coordinates or coordinate conditions are selected. Two forms are given below: Boyer–Lindquist coordinates, and Kerr–Schild coordinates. The gravitational metric alone is not sufficient to determine a solution to the Einstein field equations; the electromagnetic stress tensor must be given as well. Both are provided in each section.
Boyer–Lindquist coordinates
One way to express this metric is by writing down its line element in a particular set of spherical coordinates, also called Boyer–Lindquist coordinates:
where the coordinates are standard spherical coordinate system, and the length scales:
have been introduced for brevity. Here rs is the Schwarzschild radius of the massive body, which is related to its total mass-equivalent M by
where G is the gravitational constant, and rQ is a length scale corresponding to the electric charge Q of the mass
where ε0 is the vacuum permittivity.
Electromagnetic field tensor in Boyer–Lindquist form
The electromagnetic potential in Boyer–Lindquist coordinates is
while the Maxwell tensor is defined by
In combination with the Christoffel symbols the second order equations of motion can be derived with
where is the charge per mass of the test particle.
Kerr–Schild coordinates
The Kerr–Newman metric can be expressed in the Kerr–Schild form, using a particular set of Cartesian coordinates, proposed by Kerr and Schild in 1965. The metric is as follows.
Notice that k is a unit vector. Here M is the constant mass of the spinning object, Q is the constant charge of the spinning object, η is the Minkowski metric, and a = J/M is a constant rotational parameter of the spinning object. It is understood that the vector is directed along the positive z-axis, i.e. . The quantity r is not the radius, but rather is implicitly defined by the relation
Notice that the quantity r becomes the usual radius R
when the rotational parameter a approaches zero. In this form of solution, units are selected so that the speed of light is unity (c = 1). In order to provide a complete solution of the Einstein–Maxwell equations, the Kerr–Newman solution not only includes a formula for the metric tensor, but also a formula for the electromagnetic potential:
At large distances from the source (R ≫ a), these equations reduce to the Reissner–Nordström metric with:
In the Kerr–Schild form of the Kerr–Newman metric, the determinant of the metric tensor is everywhere equal to negative one, even near the source.
Electromagnetic fields in Kerr–Schild form
The electric and magnetic fields can be obtained in the usual way by differentiating the four-potential to obtain the electromagnetic field strength tensor. It will be convenient to switch over to three-dimensional vector notation.
The static electric and magnetic fields are derived from the vector potential and the scalar potential like this:
Using the Kerr–Newman formula for the four-potential in the Kerr–Schild form, in the limit of the mass going to zero, yields the following concise complex formula for the fields:
The quantity omega () in this last equation is similar to the Coulomb potential, except that the radius vector is shifted by an imaginary amount. This complex potential was discussed as early as the nineteenth century, by the French mathematician Paul Émile Appell.
Irreducible mass
The total mass-equivalent M, which contains the electric field-energy and the rotational energy, and the irreducible mass Mirr are related by
which can be inverted to obtain
In order to electrically charge and/or spin a neutral and static body, energy has to be applied to the system. Due to the mass–energy equivalence, this energy also has a mass-equivalent; therefore M is always higher than Mirr. If for example the rotational energy of a black hole is extracted via the Penrose processes, the remaining mass–energy will always stay greater than or equal to Mirr.
Important surfaces
Setting to 0 and solving for gives the inner and outer event horizon, which is located at the Boyer–Lindquist coordinate
Repeating this step with gives the inner and outer ergosphere
Equations of motion
For brevity, we further use nondimensionalized quantities normalized against , , and , where reduces to and to , and the equations of motion for a test particle of charge become
with for the total energy and for the axial angular momentum. is the Carter constant:
where is the poloidial component of the test particle's angular momentum, and the orbital inclination angle.
and
with and for particles are also conserved quantities.
is the frame dragging induced angular velocity. The shorthand term is defined by
The relation between the coordinate derivatives and the local 3-velocity is
for the radial,
for the poloidial,
for the axial and
for the total local velocity, where
is the axial radius of gyration (local circumference divided by 2π), and
the gravitational time dilation component. The local radial escape velocity for a neutral particle is therefore
References
Bibliography
External links
co-authored by Ezra T. Newman himself
SR Made Easy, chapter 11: Charged and Rotating Black Holes and Their Thermodynamics
Exact solutions in general relativity
Equations
Metric tensors | Kerr–Newman metric | Mathematics,Engineering | 2,653 |
3,346,091 | https://en.wikipedia.org/wiki/No%20Kidding%21 | No Kidding! International is an international non-profit social club created for singles and couples who have never had children regardless of the reason. Such people are generally described as "childless" by society at large, but some of their members who are childless by choice prefer the term "childfree" in order to highlight the voluntary nature of their circumstance. The first chapter of this organization was begun by Jerry Steinberg (the "Founding Non-Father" of No Kidding!) in Vancouver, British Columbia, in 1984. There are numerous chapters in Canada, the United States and several other countries.
The stated purpose of No Kidding! is to give childless and childfree adults a place to share common interests not involving children, as well as to provide the opportunity to make new like-minded friends. Anyone who has never been a parent, regardless of the reason, is permitted to join. The club organizes a wide range of activities, including biking, hiking, wine and cheese parties, dinners, Sunday brunches, community theater, and concerts.
The organization has annual conventions where people from all over the U.S. and Canada gather. Conventions were held annually between 2002 and 2006. So far, conventions have been held in Las Vegas, New Orleans, Seattle, Philadelphia and Toronto. In 2010, the convention was in Houston.
The group's founder, as well as representatives of various No Kidding! chapters, have made numerous appearances in international media, as well as in local newspapers, radio shows and TV programs.
See also
Kidding Aside, a British childfree movement
References
External links
Official website
Organizations established in 1984
Organizations based in Vancouver
1984 establishments in British Columbia
Voluntary childlessness | No Kidding! | Biology | 336 |
1,115,593 | https://en.wikipedia.org/wiki/United%20States%20Department%20of%20Defense%20aerospace%20vehicle%20designation | Joint Regulation 4120.15E: Designating and Naming Military Aerospace Vehicles is the current system for designating all aircraft, helicopters, rockets, missiles, spacecraft, and other aerial vehicles in military use by the United States Armed Forces.
History
United States Department of Defense Directive 4120.15 "Designating and Naming Military Aircraft, Rockets, and Guided Missiles" was originally issued November 24, 1971 and named the Air Force as the Executive Agent empowered to carry out the directive. Directive 4120.15 was implemented by Air Force Regulation (AFR) 82-1/Army Regulation (AR) 70-50/Naval Material Command Instruction (NAVMATINST) 8800.4A on March 27, 1974. The Joint Regulation designation system was heavily based upon the 1962 US Tri-Service aircraft designation system but also took control of the previously separate designation system for missiles and drones.
The current version was enacted by Joint Regulation 4120.15E Designating and Naming Military Aerospace Vehicles and was implemented via Air Force Instruction (AFI) 16-401, Army Regulation (AR) 70-50, Naval Air Systems Command Instruction (NAVAIRINST) 13100.16 November 3, 2020. The list of US military aircraft was kept via 4120.15-L Model Designation of Military Aerospace Vehicles 31 August 2018 until its transition to data.af.mil.
Overview
There are two basic components to a craft's identity: its vehicle designation and its popular name. A vehicle designation is sometimes referred to as a Mission Design Series (MDS), referring to the three main parts of the designation that combine to form a unique profile for each vehicle. The first letters (up to four) signify the type of craft and its mission. The design number, preceded by a dash "-", essentially signifies the product design of the aircraft (i.e. design 16 in F-16A). The series number identifies the specific "production model of a particular design number" with subsequent series indicating major revisions or changes. Finally, there may be variant and block identifiers which clarify the exact configuration of the vehicle.
The popular name is a matter of less specific construction, but is aimed at providing an official common name which eases identification and communication regarding the vehicle. The popular name is not used in official internal publications (an official internal report would refer to the "F-16" and "AIM-9" but not mention the names "Fighting Falcon" or "Sidewinder"). The popular name may be based on the manufacturer's internal name for the craft but all popular names must have the manufacturer's permission and be approved by the DoD. Pilots often have their own nicknames for their aircraft which may bear only coincidental resemblance (if that) to the official popular name, although some pilot nicknames are similar or even derived from the official popular name (such as "Bug" and "Super Bug" for the F/A-18 Hornet and F/A-18E/F Super Hornet).
There are seven potential components of a system's MDS designation as well as three potential components which are not included in the MDS.
Aircraft designation
Status prefix
Modified mission symbols
Many craft have been designed for more specific missions than their basic mission symbol would indicate, and many design series have been designed for different missions than the original design, and may or may not still maintain capability for the original mission. The modified mission symbol provides the services the ability to accurately indicate a craft's mission without losing commonality with the basic design MDS. If utilized, the modified mission symbol is placed as a prefix directly in front of the basic mission symbol (but after any applicable status prefix, see above). Modified mission symbols are not used for rockets and missiles. Currently authorized modified mission symbols are:
Basic mission symbol
The basic mission symbol is the heart of the mission part of the designation. No designation is without it, and some designations consist of only a basic mission symbol for the mission part, such as the F-14 or C-130. The following are the officially authorized basic mission symbols:
A Attack. Attack craft are designed to directly attack enemy land or sea targets, interdict enemy movements and support, and strike precision targets. Examples are the A-6 Intruder and A-10 Thunderbolt II.
B Bomber. Bombers are designed to attack strategic and tactical targets with heavy bomb loads and missiles. They carry heavy loads of free-fall and stand-off weaponry. Examples are the B-52 Stratofortress and B-2A Spirit.
C Cargo. Transports are designed to carry cargo and passengers to provide tactical logistical support and strategic mobility to other forces. Examples are the C-2 Greyhound and C-130 Hercules.
E Electronic. Electronics craft are designed explicitly to fulfill electronic specialty missions such as ECM, ACC, AEW, and communications. Examples are the E-2 Hawkeye and E-3 Sentry.
F Fighter. Fighters are designed to intercept and engage enemy aircraft and missiles. It is also a catch-all for multi-mission aircraft, even if it is primarily designed for ground-attack purpose. Examples are the F-22 Raptor and F-16 Fighting Falcon.
L Laser. Laser craft are those that are primarily designed to employ laser weaponry against air and ground targets. This is a very new designation, and only applies to the AL-1 airborne laser (ABL) program.
O Observation. Observation craft are designed to maintain observation over land, primarily territory either held by enemy forces or susceptible to infiltration. Unlike reconnaissance craft, they loiter over area providing observation over time. Examples are the O-1 Bird Dog and OV-10 Bronco.
P Patrol. Patrol craft are designed for maritime reconnaissance missions, including anti-submarine warfare. Example is the P-3 Orion.
R Reconnaissance: Reconnaissance craft are designed to conduct reconnaissance through photographic and electrical means, example SR-71.
S Anti-submarine: Anti-submarine warfare (ASW) craft are designed to locate and attack enemy submarines. Example is the S-3 Viking.
T Trainer: Trainers are aircraft used to train aircrews. Examples are the T-6 Texan II and T-45 Goshawk.
U Utility: Utility craft are utilized for miscellaneous missions and base support, like the U-3A. The U designation has also been used to obfuscate an aircraft's true purpose or capabilities, like with the U-2.
X Research: Research craft are designed for experimental and developmental research programs. Unlike the X mission modifier, the X basic mission symbol is used for craft solely designed for this purpose, with no operational mission intended or feasible. Examples are the entire series of X-planes from the Bell X-1 on.
Vehicle type symbols
For non-standard vehicle types (vehicles other than piloted, fixed-wing and self-propelled aircraft which are wholly supported by aerodynamic lift from liftoff to touchdown), a final symbol is added after the basic mission symbol to identify the vehicle type. Current applicable symbols are as follow:
D UAV Control Segment. Equipment used to control unmanned aircraft. An example is the MD-1A, used to launch, control, and recover the MQ-1 and MQ-9 drones.
G Glider. A glider is a fixed-wing aircraft designed to use air currents for normal lift, although it may have an engine. An example is the TG-15A training glider.
H Helicopter. A helicopter is any rotary-wing aircraft, like the UH-60.
Q Unmanned. An unmanned aerial vehicle (UAV) is any aircraft without capacity for a human pilot, but not applied to missiles or rockets. Examples include MQ-1 Predator and RQ-11.
S Spaceplane. A spaceplane is a vehicle designed to fly beyond earth's atmosphere and return. This vehicle code was poorly chosen, as it conflicts with the mission code S (Anti-Submarine Warfare). "ES" could equally designate a spaceplane designed specifically for electronic warfare or an anti-submarine plane modified for that purpose.
V V/STOL. A Vertical and/or Short Takeoff and Landing aircraft is designed to take-off and land vertically, but not rely on rotary-wing lift for flight. This includes vectored thrust aircraft such as the AV-8 Harrier and tiltrotors such as the V-22 Osprey. It also applies to aircraft of the normal fixed-wing configuration that are capable of taking off and landing in a short runway space, such as the OV-10 Bronco.
Z Lighter than air. A lighter than air craft is designed to remain aloft through buoyancy of lighter than air gases. Such craft include blimps and balloons. An example is the SZ-1A.
Design number
The design number is separated from the earlier components by a dash. Design numbers run consecutively from 1 to 999.
Series
The series letter follows the design number and progresses consecutively starting with A. In the event the series letter "Z" is used, the design number will progress to the next unused number and series will begin again at "A". To avoid confusion, series "I" and "O" are not used.
Additional Components
Configuration/Component number
Configuration/component numbers signify changes that "affect performance, tactics, or integral components of a weapon system." They appear to the right of the series symbol and are separated from the series symbol by a dash.
Block number
The block number specifies a group of aircraft produced to the same specifications by the manufacturer. Block numbers are assigned in multiples of 5 (01, 05, 10). An example is F-16C Block 25.
Serial number
Serial numbers are located on the tail and identify a specific aircraft. For example, MH-53M Pave Low IV serial number 68-10357 was the Pave Low which carried the mission commanders during the Sơn Tây raid. For more information on serial numbering of military aircraft, see United States military aircraft serial numbers.
Rockets/missiles
Status prefix
Status prefix is an optional prefix not always used for vehicles in regular service. If used, it is the first letter in the MDS. Authorized current status prefixes are:
e Digitally developed. Vehicles that are developed in a digital environment.
C Captive. Only used for rockets and missiles, C applies to rockets/missiles that are designed to be carried in their launch environment but are incapable of being launched/fired. They may contain guidance and control electronics but the engine and warhead are typically inert or ballasted.
D Dummy. Only used for rockets and missiles which are non-flying, primarily for ground training. All guidance, control electronics, engine, and warhead are inert or ballasted.
J Temporary Special Test. Applied to craft involved with special testing of temporarily installed equipment. The J prefix is used for aircraft that can be reasonably returned to their original configuration following tests. An example is aircraft used as testbeds for new electronics, but which will or may not retain that equipment after tests are complete.
N Permanent Special Test. Applied to craft involved with special testing on a permanent basis, with modifications to their configuration that make return to original configuration impractical. Many military aircraft transferred to NASA for aeronautical research carry this designation.
X Experimental. Applied to craft which are not yet accepted for service, or to prototypes for which standard configuration has not been finalized. Most prototypes of the past carried this prefix, but it should not be confused with craft given an X basic mission symbol. The X status prefix is for designs for other missions, but at an experimental stage of the design process.
Y Prototype. Originally applied to demonstration craft where configuration had been determined, but from the 1970s on applied to all prototypes of aircraft intended for production.
Z Planning. Applied to designs in the planning/pre-development phase.
Rocket/missile launch environment
All rockets and missiles contain a symbol to indicate the launch method, be it from the air, ground, sea, etc. The following are the currently authorized symbols for launch environments. These are not used for other aerospace vehicles.
A Air-launched. The missile is launched from an airborne vehicle. Example is the AIM-9 Sidewinder dogfighting missile.
B Multiple. The missile can be launched from various environments. The BGM-109 Tomahawk, for instance, can launch from a ground unit, aircraft, or ship-mounted launcher.
C Coffin. Stored in an unhardened container horizontally or less than 45 degree angle and either launched horizontally or raised vertical for launch. Coffin launchers may be either on land or at sea. An example is the CGM-16 ICBM.
F Individual. The missile is launched by an individual soldier in the field, otherwise referred to as man-portable. Example is the FIM-92 Stinger, a light man-portable surface-to-air missile (SAM).
G Ground. The missile is launched directly from the ground surface, including runways.
H Silo-Stored. The missile stored vertically in a silo but raised to ground level for launch. An example is the Atlas-F.
L Silo-Launched. The missile is launched from its storage silo, below ground.
M Mobile. The missile is launched from a mobile ground vehicle or movable platform.
P Pad. Like a traditional space rocket, the missile is stored and launched from an unprotected or partially protected ground facility.
R Ship. The missile is launched from a ship or barge.
S Space. The missile is launched from a spacecraft. This is so far used only for the upper stage of another rocket like the SSB-8 Centaur.
U Underwater. The missile is launched from a submarine or underwater device.
Rocket/missile mission symbol
Rockets and missiles are assigned a single mission symbol, which usually denotes the intended target type of the missile. For most types of missile, the combination of launch environment and mission symbols form a from-to combination (surface-to-air, ship-to-submarine) that gives one a good idea of the potential uses for the missile.
C Transport. Applies to vehicles designed to carry cargo and deliver it to a location. This can also be used to designate a carrier for electronics or weapons systems.
D Decoy. Applies to vehicles that function as decoys for defeating enemy anti-aircraft and anti-missile defenses.
E Electronics. Applies to vehicles that carry out electronic missions such as communications or countermeasures.
G Ground. Applies to vehicles designed to attack surface targets, including vehicles.
I Intercept. Applies to vehicles designed to attack aerial targets, in an offensive or defensive capacity.
L Launch detection/surveillance. Applies to vehicles designed to detect launch of missiles and track and identify enemy aircraft and missiles. This also applies to detection and monitoring of space launches and re-entry.
M Scientific/Calibration. Applies to vehicles designed to collect scientific data.
N Navigation. Applies to vehicles which provide navigational assistance.
Q Drone. Applies to a vehicle designed to be remotely controlled. Ballistic/semi-ballistic vehicles, cruise missiles, and artillery projectiles are not considered drones.
S Space support. Applies to vehicles designed to support space programs and activities.
T Training. Applies to aircraft used in training.
U Underwater Attack. Applies to vehicles designed to attack submarines and underwater targets.
W Weather. Applies to vehicles designed to obtain weather data and collect aerial samples.
Vehicle type symbol
For rockets and missiles, the vehicle type symbol identifies the basic vehicle type and will be the final symbol in the mission part of the MDS.
B Booster. Boosters are primary or auxiliary propulsion units for other vehicles.
M Guided Missile. Guided missiles are unmanned vehicles flying a path controlled by a guidance system.
N Probe. Probes are non-orbital unmanned vehicles designed primarily to collect data within the aerospace environment.
R Rocket. Rockets are single-use unmanned vehicles without guidance after launch.
S Satellite. Satellites are space vehicles which orbit the earth and used to collect and transmit various data.
Design number
The design number is separated from the earlier components by a dash. Design numbers run consecutively from 1 to 999.
Series
The series letter follows the design number and progresses consecutively starting with A. In the event the series letter "Z" is used, the design number will progress to the next unused number and series will begin again at "A". To avoid confusion, series "I" and "O" are not used.
Additional Components
Configuration/Component number
Configuration/component numbers signify changes that "affect performance, tactics, or integral components of a weapon system." They appear to the right of the series symbol and are separated from the series symbol by a dash.
Block number
The block number specifies a group of aircraft produced to the same specifications by the manufacturer. Block numbers are assigned in multiples of 5 (01, 05, 10).
Serial number
Serial numbers are located on the tail and identify a specific rocket/missile. For more information on serial numbering of military aircraft, see United States military aircraft serial numbers.
Exceptions
The F-117 Nighthawk does not currently have any air-to-air capabilities but was not designated A-117. There has been conjecture and anecdotal reports concerning purported air-to-air capabilities targeted toward destroying Soviet AWACS craft.
The OA-1K Sky Warden is designated as a new version of the unrelated A-1 Skyraider of which the last version was the A-1J.
Although the mission letters of the AV-8 Harrier's designation are correct, the series number was already used in the Ryan XV-8 ("Fleep") if following the system, the Harrier would have been named AV-12.
The "FB-111" was originally a fighter that was adapted to the bomber role. Thus it should have been designated BF-111.
The CC-130J Hercules referred to the stretched C-130J-30 Hercules. The -30 suffix was not supportable in the system, so a modified mission letter had to be added. Hence, the CC-130J is a cargo aircraft "modified" for the cargo role. This was later dropped. The CC-130J should not be confused with the CC-130 Hercules operated by the Royal Canadian Air Force. The first "C" identifies the aircraft as a Canadian asset. Canada later acquired C-130Js as CC-130Js.
Many manufacturers have used non-standard modifiers for commercial purposes; for instance, the Spanish F/A-18 Hornets were 'designated' EF-18 by McDonnell Douglas (the E standing for España , the native name for Spain, and AH-64D Apache helicopters were designated 'WAH-64' by licensed manufacturer Westland. Non-standard series letters, especially ones the U.S. Air Force has no intention of progressing to, are often used to designate the intended country of use, such as I (Israel - e.g. F-15I), J (Japan), K (South Korea or United Kingdom), S (Saudi Arabia) and SG (Singapore).
See also
United States military aircraft designation systems
1962 United States Tri-Service aircraft designation system
1963 United States Tri-Service missile and drone designation system
List of U.S. DoD aircraft designations
List of US DoD MDS designators for missiles, rockets, probes, boosters, and satellites
List of undesignated military aircraft of the United States
Notes
References
External links
Current Designations of U.S. Military Aerospace Vehicles, Andreas Parsch
United States Military Aircraft Designations, Vic Flintham
Guided missiles
Rocketry
Designation
Military aircraft designation systems
Naming conventions
United States military aircraft | United States Department of Defense aerospace vehicle designation | Engineering | 3,993 |
16,119,760 | https://en.wikipedia.org/wiki/Autonomously%20replicating%20sequence | An autonomously replicating sequence (ARS) contains the origin of replication in the yeast genome. It contains four regions (A, B1, B2, and B3), named in order of their effect on plasmid stability. The A-Domain is highly conserved, any mutation abolishes origin function. Mutations on B1, B2, and B3 will diminish, but not prevent functioning of the origin.
Element A is highly conserved, consisting of the consensus sequence:
(where Y is either pyrimidine and R is either purine). When this element is mutated, the ARS loses all activity.
As seen above the ARS are considerably A-T rich which makes it easy for replicative proteins to disrupt the H-bonding in that area. ORC protein complex (origin recognition complex) is bound at the ARS throughout the cell cycle, allowing replicative proteins access to the ARS.
Mutational analysis for the yeast ARS elements have shown that any mutation in the B1, B2 and B3 regions result in a reduction of function of the ARS element. A mutation in the A region results in a complete loss of function.
Melting of DNA occurs within domain B2, induced by attachment of ARS binding factor 1 to B3.
A1 and B1 domain binds with origin recognition complex.
To identify these sequences, yeast mutants unable to synthesize histidine were transformed with plasmids containing the His gene and random fragments of the yeast genome. If the genome fragment contained an origin of replication, cells were able to grow in a medium lacking histidine. These sequences were termed autonomously replicating sequences, because they were replicated and inherited by progeny without integrating into the host chromosome.
References
Genomics techniques | Autonomously replicating sequence | Chemistry,Biology | 356 |
63,002,132 | https://en.wikipedia.org/wiki/Pimodivir | Pimodivir (VX-787, JNJ-63623872) is an antiviral drug which was developed as a treatment for influenza. It acts as an inhibitor of influenza virus polymerase basic protein 2, and has shown promising results in Phase II clinical trials. However, in late 2021, Janssen announced that the clinical development of pimidivir had been halted due to lack of benefit over standard of care.
See also
Baloxavir marboxil
Favipiravir
Galidesivir
Nitazoxanide
Oseltamivir
Peramivir
Remdesivir
Ribavirin
Triazavirin
Umifenovir
Zanamivir
References
Anti–RNA virus drugs
Antiviral drugs | Pimodivir | Biology | 155 |
14,520,624 | https://en.wikipedia.org/wiki/Jay%20Nunamaker | Jay F. Nunamaker Jr. (born August 27, 1937) is Regents Professor and Soldwedel Professor at the University of Arizona. Regents Professor is the highest faculty rank bestowed at the university, an honor reserved for the top 3% of scholars.
He founded both the MIS department (ranked top 5 in the country by U.S. News & World Report for the past 20 years) in 1974, and the Center for the Management of Information in 1985 at the University of Arizona.
Biography
Nunamaker has served as major professor to over 80 doctoral students from 1968–present. Students that currently hold, or have held, positions at Harvard, University of Michigan, Indiana University, University of Iowa, University of Florida, University of Georgia, University of Washington, Carnegie Mellon University, Texas A&M University, University of Hawaii, and other top MIS institutions.
Jay Nunamaker has been featured in the July 1997 Forbes magazine issue on technology as one of eight key innovators in information technology.
In 2002, he was the recipient of the LEO (lifetime achievement) Award from the Association of Information Systems, at ICIS in Barcelona, Spain.
In a 2005 article in Communications of the Association for Information Systems, he was recognized as one of the most productive information systems researchers, ranking no. 4 to 6 for the period from 1991-2003 based on the number of papers in top IS journals.
Work
His multidisciplinary research is built on a foundation of computer supported collaboration, decision support, deception detection and determination of intent.
Nunamaker's research has led to major breakthroughs in collaboration, decision support systems, and automated systems analysis and design, and he is known for testing his theories and systems in the “real world.”
He built the first operational decision support center in 1985; there are over 2,500 decision centers in industry, government and universities using the GroupSystems software developed at the University of Arizona.
His research on group support systems addresses behavioral as well as engineering issues and focuses on theory as well as implementation.
Publications
His publications span more than 250 papers and seven books, and editorial positions on major journals, in computer science and engineering, information management, communication, security informatics.
References
Further reading
External links
Website at arizona.edu.
1937 births
Living people
Information systems researchers
University of Pittsburgh alumni
Carnegie Mellon University alumni
Case Western Reserve University alumni
Purdue University faculty
University of Arizona faculty | Jay Nunamaker | Technology | 489 |
36,033,336 | https://en.wikipedia.org/wiki/Tree%20Trunks%20%28Adventure%20Time%29 | "Tree Trunks" is the fourth episode of the first season of the American animated television series Adventure Time. The episode was written and storyboarded by Bert Youn and Sean Jimenez, from a story by Merriwether Williams and Tim McKeon. It originally aired on Cartoon Network on April 12, 2010. The episode guest stars Polly Lou Livingston as the titular Tree Trunks.
The series follows the adventures of Finn (voiced by Jeremy Shada), a human boy, and his best friend and adoptive brother Jake (voiced by John DiMaggio), a dog with magical powers to change shape and grow and shrink at will. In this episode, Tree Trunks joins Finn and Jake who go on a quest to fulfill her desire of picking a proposed legendary "crystal gem apple" in an evil forest. The three eventually find the tree, and Tree Trunks eats the apple, only to apparently explode and be transported to a crystal dimension.
Tree Trunks was voiced by Polly Lou Livingston, a friend of series creator Pendleton Ward's mother. Ward asked Livingston to appear on his show several years after he last saw her. The original ending called for Tree Trunks to simply explode, but a new ending was amended to explain what happened to her. This served as the genesis for the second season episode "Crystals Have Power". The episode was viewed by 1.847 million viewers and received a 1.2 rating among adults between the ages of 18 and 49. The episode received largely positive reviews from critics, with many commenting on the episode's ending.
Plot
Finn and Jake are invited to the elephant Tree Trunks' house for apple pie. The group begins talking about what they wish they could do if they could achieve anything, and Tree Trunks notes that she wants to pick the rare Crystal Gem Apple, which is located in the Evil Forest. Finn and Jake decide to make her wish come true. When they reach the Evil Forest, they encounter a wall of flesh and try to fight it, but because Tree Trunks is naive, she begins putting stickers on it. After defeating the monster, Tree Trunks walks away, following a skeleton butterfly. She is attacked by sign zombies and begins having a tea party with them, not knowing they want to kill her. Finn and Jake fight off the Sign Zombies and continue their adventure, until they encounter a brain beast. Finn goes to fight it, but Tree Trunks' "adventurer's instincts" tell her to put on makeup and seduce the brain beast with her womanly charms. Jake has to leap in to save Tree Trunks while Finn attacks the monster's magic gem weak spot.
Finn, enraged, tells Tree Trunks that she is putting herself in danger. Dejected and crying, she leaves, only to find the Crystal Gem Apple in the heart of the forest. Unfortunately, a Crystal Guardian appears and begins copying Finn and Jake's actions, blocking every attempt to fight it physically. Finn and Jake realize that they have to fight the Crystal Guardian "Tree Trunks-style" by putting on makeup and tricking the monster into letting Tree Trunks take a bite of the Crystal Gem Apple. She bites the apple, pauses for a second, then explodes, leaving Finn, Jake, and the Crystal Guardian shocked and staring at each other in horror. In a final enigmatic scene, Tree Trunks is seen walking in front of a crystal background laughing happily.
Production
"Tree Trunks" was written and storyboarded by Bert Youn and Sean Jimenez from a story by Merriwether Williams and Tim McKeon, and directed by Larry Leichliter. Although the episode was the fourth aired, it was really the sixteenth produced; this is why Tree Trunks appears in the later season one episode "Evicted!" despite her vanishing at the end of this entry. The episode features the introduction of the titular character, played by Polly Lou Livingston. Livingston was a friend of Pendleton Ward's mother, Bettie Ward, and knew Pendleton when he was a young child. After having not seen her for eight years, he approached her, asking if she would like to play the voice of a character on Adventure Time. She noted that she "nearly fainted" when asked, and was surprised he still remembered her. Bettie claimed it was due to her unforgettable Southern drawl.
Originally, the episode called for Tree Trunks to simply explode. The ending, featuring her walking in a strange crystal dimension, was added after the story board was submitted. Thus, this action was the genesis for the season two sequel "Crystals Have Power", which saw the return of Tree Trunks. The unedited version of the episode, featuring Tree Trunks simply exploding, was featured, however, on the Adventure Time: My Two Favorite People DVD. Episode composer Casey James Basichis used a variety of basses and saws to create the whimsical music featured in the episode. He later called the resulting sound a "folksy massacre". Basichis sought to continue the "fun and experimental spirit" in other episodes that focus on Tree Trunks.
Reception
"Tree Trunks" first aired on Cartoon Network on April 12, 2010. The episode was viewed by 1.847 million viewers and scored a Nielsen rating of 1.2/2. This means it was seen by 1.2 percent of all households and 2 percent of all households watching television at the time of the episode's airing. In addition, 1.242 million kids aged 6–11 watched the episode, which marked an increase in 171 percent from the previous year. The episode first saw physical release as part of the 2011 Adventure Time: My Two Favorite People DVD, which included 12 episodes from the series' first two seasons. It was later re-leased as part of the complete first season DVD in July 2012.
Francis Rizzo III of DVD Talk rhetorically asked, "If anyone would like to explain just what the hell happened at the end of 'Tree Trunks' I'm all ears." However, he noted that "If [Adventure Time] was a lesser show, episodes like that could possibly make one walk away shaking your head, but somehow it was simply another quirky bit of personality for a show bursting at the seams with it." A review from the Dayton Examiner wrote that "Tree Trunks makes a hysterical character by just being absurd". They praised the fact that, in the episode, she often says lines "that have vague sexual overtones (some of them failing to even be vague)". The review enjoyed the way the episode was able to convey the message of "following your dreams" in such an absurd way. The review also praised the "priceless" twist ending, calling it "the absolute best moment in the episode and one of [their] personal favorites in the entirety of Adventure Time".
Explanatory notes
References
External links
2010 American television episodes
Adventure Time season 1 episodes
Apples in culture
Crystals
Elephants in popular culture
Television episodes set in forests | Tree Trunks (Adventure Time) | Chemistry,Materials_science | 1,406 |
42,255,617 | https://en.wikipedia.org/wiki/Phagoptosis | Phagoptosis (cell death by phagocytosis) is a type of cell death caused by the cell being phagocytosed (i.e. eaten) by another cell, and therefore this form of cell death is prevented by blocking phagocytosis.
Phagocytosis of an otherwise-viable cell may occur because the cell is recognised as stressed, activated, senescent, damaged, pathogenic or non-self, or is misrecognised. Cells are phagocytosed as a result of: i) expressing eat-me signals on their surface, ii) losing don’t-eat-me signals, and/or iii) binding of opsonins. It is clear that otherwise-viable cells can expose/bind such phagocytosis-promoting signals as a result of cell stress, activation or senescence. Phagoptosis is probably the most common form of cell death in the body as it is responsible for erythrocyte turnover. And there is increasing evidence that it mediates physiological death of neutrophils, T cells, platelets and stem cells, and thereby regulates inflammation, immunity, clotting and neurogenesis. Phagoptosis is a major form of host defence against pathogens and cancer cells. However, recent evidence indicates that excessive phagoptosis may kill host cells in inflammatory conditions, contributing to haemophagic conditions, and neuronal loss in the inflamed brain.
Mechanism
Phagoptosis is normally caused by: the cell exposing on its surface so-called "eat-me" signals, and/or the cell no longer exposing "don't-eat-me" signals and/or the cell being opsonised i.e. binding soluble proteins that tag the cell for phagocytosis. For example, phosphatidylserine is an "eat-me" signal that, when exposed on the surface of a cell, triggers phagocytes (i.e. cells that eat other cells) to eat that cell. Phosphatidylserine is normally found on the inside of healthy cells, but can become exposed on the surface of dying, activated or stressed cells. Phagocytosis of such cells requires specific receptors on the phagocyte that recognise either phosphatidylserine directly or opsonins bound to the phosphatidylserine or other "eat-me" signals, such as calreticulin. "Don't-eat-me" signals include CD47, which when expressed on the surface of a cell, inhibit phagocytosis of that cell, by activating SIRP-alpha receptors on the phagocyte. Opsonins are normally soluble proteins, which when bound to the surface of a cell induce phagocytes to phagocytose that cell. Opsonins include Mfge8, Gas6, Protein S, antibodies and complement factors C1q and C3b.
Functions
Phagoptosis has multiple functions including removal and disposal of: pathogenic cells, aged cells, damaged cells, stressed cells and activated cells. Pathogenic cells such as bacteria can be opsonised by antibodies or complement factors, enabling their phagocytosis and phagoptosis by macrophages and neutrophils. "Aged" erythrocytes and neutrophils, as well as "activated" platelets, neutrophils and T-cells, are thought to be phagocytosed alive by macrophages.
Development. Phagoptosis removes excess cells during development in the worm, C. elegans. During mammalian development multiple cells undergo programmed cell senescence and are then phagocytosed by macrophages. Brain macrophages (microglia) can regulate the number of neural precursor cells in the developing brain by phagocytosing these otherwise viable precursors and thus limiting neurogenesis.
Turnover of blood cells. Red blood cells (erythrocytes) live for roughly 4 months in the blood before being phagocytosed by macrophages. Old erythrocytes do not die, but rather display changes in the cell surface that enable macrophages to recognise them as old or damaged, including exposure of phosphatidylserine, desialylation of glycoproteins, loss or changed conformation of the "don't-eat-me" signal CD47, and exposure of novel antigens that bind endogenous antibodies. Neutrophils have a daily rhythm of entry and exit from the blood, driven by neutrophil “aging” in the circulation, causing decreased expression of CD62L and increased expression of CXCR4, which directs the “aged” neutrophils to the bone marrow, where they are phagocytosed by macrophages. However, it is still unclear how or why neutrophils turnover at such an enormous rate. Antigen recognition causes phosphatidylserine exposure on activated T-cells, which is recognized by Tim-4 on macrophages, inducing phagoptosis of the activated T-cells, and thus the contraction phase of the adaptive response.
Host defence against pathogens. Phagocytosis of otherwise-viable pathogens, such as bacteria, can be mediated by neutrophils, monocytes, macrophages, microglia and dendritic cells, and is central to host defence against pathogens. Dendritic cells can phagocytose viable neutrophils, and present antigens derived from bacteria or cancer cell debris previously phagocytosed by the neutrophils. Thus phagoptosis can contribute to host defence in a variety of ways.
Host defence against cancer. It has been known for some time that animals defend themselves against cancer by antibody-mediated or antibody-independent phagocytosis of viable tumour cells by macrophages. Recognition of viable cancer cells for phagocytosis may be based on the expression of novel antigens, senescence markers, phosphatidylserine or calreticulin. More recently it has become clear that most human cancer cells overexpress CD47 on their surface to prevent themselves being phagocytosed, and that if this ‘don’t-eat-me’ signalling is blocked then a variety of cancers can be cleared from the body. Thus it would appear that phagoptosis is an important defence against cancer, but that tumour cells can suppress this, and blocking this suppression is an attractive therapeutic option.
Pathological phagoptosis of blood cells. Hemophagocytosis is a clinical condition, found in many infectious and inflammatory disorders, where activated macrophages have engulfed apparently viable blood cells, resulting in reduced white or red cell count (cytopenia). IFN-γ (and possibly other cytokines) appears to drive hemophagocytosis during infection by directly stimulating phagoptosis of blood cells by macrophages. Hemophagocytic lymphohistiocytosis (HLH) is characterized by excessive engulfment of hematopoietic stem cells (HSCs) by bone marrow macrophages, and this has been found to result from down regulation of CD47 expression on HSCs, enabling macrophages to eat them alive.
Pathological phagoptosis in the brain. Microglial phagocytosis of stressed-but-viable neurons occurs under inflammatory conditions, and may contribute to neuronal loss in brain pathologies [2].
References
Cellular processes | Phagoptosis | Biology | 1,582 |
67,615,206 | https://en.wikipedia.org/wiki/Hydroxyarchaeol | Hydroxyarchaeol is a core lipid unique to archaea, similar to archaeol, with a hydroxide functional group at the carbon-3 position of one of its ether side chains. It is found exclusively in certain taxa of methanogenic archaea, and is a common biomarker for methanogenesis and methane-oxidation. Isotopic analysis of hydroxyarchaeol can be informative about the environment and substrates for methanogenesis.
Discovery
Hydroxyarchaeol was first identified by Dennis G. Sprott and colleagues in 1990 from Methanosaeta concilii by a combination of TLC, NMR and mass spectrometric analysis.
Structure and function
The lipid consists of a glycerol backbone with two C20 phytanyl ether chains attached, one of which has a hydroxyl (-OH) group attached at the C3 carbon. It is one of the major core lipids of methanogenic archaea alongside archaeol, forming the basis of their cell membrane. The two major forms are sn-2- and sn-3-hydroxyarchaeol, depending on if the hydroxyl group is on the sn-2 or sn-3 phytanyl chain of the glycerol backbone.
Methanogen biomarker
Use of hydroxyarchaeol as a biomarker was a primary way to identify methanogens in the environment, though it has become supplementary to metagenomic and 16S rRNA techniques for identifying phylogeny. While hydroxyarchaeol has only been identified in methanogenic archaea, not all methanogens count it among their core lipids. Other methanogens may contain different derivatives of archaeol, including cyclic archaeol and caldarchaeol based on taxonomic differences. Hydroxyarchaeol has been identified in many different taxa, including within the orders Methanococcales, Methanosarcinales, which contains the genus Methanosaeta, and a genus from the order Methanobacteriales. There is evidence that there is a taxonomic preference for the sn-2 vs sn-3 form based on phylogeny, as a mix of the two forms do not tend to appear in the same organism, but the reason for this difference is not well understood. Because of the hydroxyl group, which is prone to degradation over time, hydroxyarchaeol has not been observed in ancient samples, and thus is thought to indicate modern sources of methanogens .
Measurement techniques
Original measurements of hydroxyarchaeol were done using TLC and NMR, but have become dominated by gas-chromatograph/mass spectrometry. For most methods, extraction of the core lipid is typically done using variations of a Bligh-Dyer method, which makes use of the various polarities and miscibility of dichloromethane (DCM), methanol, and water. Acidic conditions using trichloroacetic acid (TCA) during extraction and additional cleanup of samples with polar solvents such as DCM is often needed to better isolate the lipids of interest.
GC-MS
Prior to GC-MS analysis, the intact hydroxyarchaeol lipid is typically hydrolyzed to the core lipid component and derivatized by adding trimethyl silyl (TMS) groups to the free hydroxyl functional groups. This allows for the lipid to volatilize in the GC and reach the MS analyzer. Because hydroxyarchaeol has multiple sites that can be modified after TMS derivatization, the observed mass spectra can be either the mono- or di-TMS derivative, and need to be compared to authentic standards to properly identify and quantify. For identification and quantification, the mass spectrometer typically utilizes a quadrupole mass analyzer, but isotopic analysis uses an isotope-ratio mass spectrometer (IRMS) that has higher mass resolution and sensitivity.
δ13C Isotope ratio analysis
The relative isotopic ratio of carbon (δ13C) found in hydroxyarchaeol is used to identify what the methane-associated organism is using as a carbon source. Carbon sources in the environment will have a measurable δ13C signature that can be matched with the biomarkers found in an organism, which will gain the isotopic signature of its food source. Since archaea that make hydroxyarchaeol can harness a number of carbon sources, including dissolved inorganic carbon (DIC), methanol, trimethylamine, and methane, this is a useful way to determine which is the primary source of energy, or if there is a mixture of use in the environment.
Case Study
Hydroxyarchaeol has been found in peat bogs and methane seeps in the deep ocean as a marker of both methanogens and methanotrophs. The deep sea sediment hydroxyarchaeol had very depleted δ13C at methane seeps. Both the methane and DIC present also had depleted δ13C values, but not as a perfect match to the identified biomarker. By modeling the isotopic ratio of DIC and methane to the isotopic ratio of the biomarkers, the researchers could estimate the relative contribution to biosynthesis and metabolic pathways that each source had for the organism. The model could predict a relative contribution that matched well with actual measurements, indicating there was mixed metabolism occurring at these sites, with specific biosynthetic pathways using different proportions of carbon derived from each source. This method made use of hydroxyarchaeol in the bulk sample to target the metabolism of a specific group of microbes without need for exhaustive separations of different organisms, making it useful for environmental analysis.
References
Glycerol ethers
Lipids
Biomarkers | Hydroxyarchaeol | Chemistry,Biology | 1,249 |
7,482,420 | https://en.wikipedia.org/wiki/Proline%20%28data%20page%29 |
References
Chemical data pages
Chemical data pages cleanup | Proline (data page) | Chemistry | 10 |
4,529,580 | https://en.wikipedia.org/wiki/William%20Champion%20%28metallurgist%29 | William Champion (1709–1789) is credited with patenting a process in Great Britain to distill zinc metal from calamine using charcoal in a smelter.
Background
After Abraham Darby I had left the Bristol Brass Company to form his own new copper works at Coalbrookdale, fellow Quaker Nehemiah Champion took over leadership. Nehemiah had three sons: John (1705–1794); Nehemiah (1709–1782); and the youngest William (1710–1789).
Early life and patent
As a young man, William Champion toured Europe to learn the art of brass making, returning to become a junior partner in the Bristol Brass Company in 1730. He then experimented for six years to develop a process to create zinc – then known as spelter. Using a scaled-up process similar to that used at the Zawar mines in India where this process was available centuries before William Champion rediscovered it, since the 12th century AD, he overcame the difficulties of zinc vaporising at 907 °C by introducing a condensing vapour into the process through distillation. He obtained a patent for his method in July 1738, and his system remained in production for over 100 years.
Under the Bristol Brass Company, from 1738 within works established at the Old Market, by September 1742 he had produced of zinc per charge from six crucibles located in the furnace, at a cost of around £7,000. However, he had now created two sets of enemies:
The local residents, who in September 1742 reported Champion to the city council. They sought assurance that Champion would cease metal smelting at the site immediately.
The zinc importers and traders. When he started his experimentations, spelter sold at £260 per ton. By 1750, this had reduced to £48, resulting in a loss to the traders who were trying to force Champion out of business.
Warmley Works
In 1742 father Nehemiah – a widower – married a widow, Martha Vandewall, the sister of Thomas Goldney III. The Goldney family owned land in Warmley, and in 1746 backed by the Goldney family, William left the Bristol Brass Company and began to construct the Warmley Works. With tools and manufacturing equipment supplied by the Darby Ironworks at Coalbrookdale, over the next few years Warmley Works became the biggest metal processing plant in the world, with outputs of zinc, copper, brass and other metals. After the death of his father in 1747, William was joined in the business by his brother Nehemiah, and sister Rachael as a shareholder.
In February 1750, William applied to the House of Commons for some form of recompense for the losses he had suffered in making the first home produced zinc, which he hoped would allow extension of his patented process. Although a committee reported agreed that the patent should be extended through an act of Parliament, a counter petition by the powerful lobby of the merchants of Bristol delayed the passage, and William later abandoned the legal process. However, William continued to expand the business through development at both the Warmley site, as well as new furnaces at Kingswood, a forge at Kelston near the River Avon, and a battery mill at Bitton on the River Boyd. By 1754, he had:
His brother John Champion developed a refined process and patented in 1758 the calcination of zinc sulfide (zinc blende) to oxide for use in the retort process. The English zinc industry was concentrated in and around Bristol and Swansea.
Docks and Bristol floating harbour
By 1765, with excess capital on his hands, William commenced development of a new dock at Rownham on the eastern bank of the River Avon, which would be capable of holding 36 large ships. However, after the increased cost of construction depleted his resources, and with a distinct lack of trade, he sold the dock in 1770 to the Merchant Venturers for £1,770, who renamed it The Merchants' Dock. During the dock's construction, William had also proposed creating a complete floating harbour at Bristol, by building lock gates on the River Avon where it junctioned with the River Frome. However, the plan was abandoned due to an estimated cost of £37,000.
Downfall
By 1767, the Warmley Company claimed to have a capital of £200,000 and to give employment to about 2,000 people. Further, William had taken out additional patents covering: the refining of copper by using wrought iron pipes to remove arsenic from the smelt; using pit coal instead of charcoal to make brass wire; using zinc sulphide instead of calamine to make his brass.
The company had been formed before the Bubble Act 1720, and in 1767 petitioned Parliament to change its status to incorporation. In return, the partners offered to invest another £200,000 worth of capital, including £30,000 into the production of brass pins. This brought about the combined wrath of other metal companies formed under the Bubble Act 1720, as well as the pin makers of Gloucester, who petitioned that such an investment was 50% greater than their existing facilities. In April 1767 the Commons issued a warrant that gave authority for the preparation of a charter of incorporation, but this was countered by the competitors. After lengthy legal proceeding, a second warrant was issued by the Attorney General in October 1767. This led to a further counter-petition, which claimed that the Warmley Company would become a monopoly. By March 1768, the opposition had won and no further steps were taken to obtain a charter of incorporation.
Due to the collapse of the process to incorporate, in April 1768 William's partners discovered that he had tried to withdraw part of his capital without permission, and he was instantly dismissed from the company. Because he could not pay his debts William Champion was declared bankrupt. He died in 1789.
Legacy
Now a debt-encased and loss-making enterprise, on 11 March 1769 the Warmley Works were offered for sale in Felix Farley's Bristol Journal. Sold to the Harford & Bristol Copper Company, they also obtained the rights to Champion's patents. Using the process but winding down the operations until 1809, they later sold the Bitton Battery Mill in 1825 for use as a paper mill.
Because of the American War of Independence, the price of tar greatly increased, which was used at the time as a sealant on ships. On 29 April 1780 an advert appeared in Sarah Farley's Journal offering for sale a process of making English tar, from the estate of the deceased William Champion. Later, a tar works was established within Bristol Harbour.
See also
National Smelting Company
References
P. K. Stembridge, The Goldney family: a Bristol Dynasty (Bristol Record Society 1998), 46–51.
A. Raistrick, Quakers in Science and Industry (1950; Sessions Book Trust, York 1993), 192–6.
Engineers from Bristol
English Quakers
English metallurgists
Zinc
Copper alloys
1709 births
1789 deaths | William Champion (metallurgist) | Chemistry | 1,407 |
15,396,145 | https://en.wikipedia.org/wiki/HUGO%20Gene%20Nomenclature%20Committee | The HUGO Gene Nomenclature Committee (HGNC) is a committee of the Human Genome Organisation (HUGO) that sets the standards for human gene nomenclature. The HGNC approves a unique and meaningful name for every known human gene, based on a query of experts. In addition to the name, which is usually 1 to 10 words long, the HGNC also assigns a symbol (a short group of characters) to every gene. As with an SI symbol, a gene symbol is like an abbreviation but is more than that, being a second unique name that can stand on its own just as much as substitute for the longer name. It may not necessarily "stand for" the initials of the name, although many gene symbols do reflect that origin.
Purpose
Full gene names, and especially gene abbreviations and symbols, are often not specific to a single gene. A marked example is CAP which can refer to any of 6 different genes (BRD4 , CAP1 , HACD1 , LNPEP , SERPINB6 , and SORBS1 ).
The HGNC short gene names, or gene symbols, unlike previously used or published symbols, are specifically assigned to one gene only. This can result in less common abbreviations being selected but reduces confusion as to which gene is referred to.
Naming guidelines
The HGNC published its latest human gene naming guidelines in 2020. These may be summarized as:
gene symbols must be unique
symbols should only contain Latin letters and Arabic numerals
symbols should not contain punctuation or "G" for gene
symbols do not contain any reference to the species they are encoded in, i.e. "H/h" for human
The HGNC states that "gene nomenclature should evolve with new technology rather than be restrictive, as sometimes occurs when historical and single gene nomenclature systems are applied." The HGNC has also issued guides to specific locus types such as endogenous retroviral loci, structural variants and non-coding RNAs.
Naming procedure
When assigning new gene nomenclature the HGNC make efforts to contact authors who have published on the human gene in question by email, and their responses to the proposed nomenclature are requested. HGNC also coordinates with the related Mouse and Rat Genomic Nomenclature Committees, other database curators, and experts for given specific gene families or sets of genes.
Revision
The gene name revision procedure is similar to the naming procedure, but changing a standardized gene name after establishment of a consensus can create confusion, therefore the merit of this is controversial. For this reason the HGNC aims to change a gene name only if agreement for that change can be reached among a majority of researchers working on that gene.
See also
Human Genome Organisation (HUGO)
Human Genome Project
Human genome
Gene
Gene nomenclature
A complete list of all HGNC-approved gene symbols for protein-coding genes:
List of human protein-coding genes 1
List of human protein-coding genes 2
List of human protein-coding genes 3
List of human protein-coding genes 4
References
External links
HGNC homepage
HUGO homepage
Biological nomenclature
Genetics databases
Genetics in the United Kingdom
Genetics organizations
Science and technology in Cambridgeshire
South Cambridgeshire District | HUGO Gene Nomenclature Committee | Biology | 642 |
52,872,753 | https://en.wikipedia.org/wiki/Digvijai%20Singh | Digvijai Singh (11 December 1934 – 20 July 2018) was an Indian mechanical engineer and a former vice chancellor of the University of Roorkee before its reconstitution as the Indian Institute of Technology, Roorkee. He was also a former vice chairman of the All India Council for Technical Education (AICTE) and a former director of Central Road Research Institute. He is known for his studies on dynamics of single track vehicles and Fluid film lubrication and was an elected fellow of all the three major Indian science academies viz. Indian National Science Academy, Indian Academy of Sciences, and the National Academy of Sciences, India as well as the Indian National Academy of Engineering. The Council of Scientific and Industrial Research, the apex agency of the Government of India for scientific research, awarded him the Shanti Swarup Bhatnagar Prize for Science and Technology, one of the highest Indian science awards for his contributions to Engineering Sciences in 1978.
Biography
Born on 11 December 1934 in the Indian state of Uttar Pradesh, Digvijai Singh graduated in science from Allahabad University in 1953 before graduating in mechanical engineering from University of Roorkee (present-day Indian Institute of Technology, Roorkee) in 1956 and did another bachelor's degree in civil engineering in 1957 at the same institution before joining the university as a lecturer in 1958. Subsequently, he took a sabbatical to move to the US where he completed his master's degree (MS) in 1962 as well as a doctoral degree (PhD) in 1964 at the University of Wisconsin. On his return to India, he resumed his service at University of Roorkee and served as a professor, head of the department of mechanical and industrial engineering, dean of academics and dean of research and industrial liaison till 1990 when he was appointed as the director of the Central Road Research Institute. In 1996, he was made the vice chairman of the All India Council for Technical Education and after a service of 4 years, he became the vice chancellor of Roorkee University in 2000. He oversaw the transition of the university to an Indian Institute of Technology in 2001 and became the director of the IIT. He superannuated from service after handing over the charge to Prem Vrat in December 2001.
Legacy
Singh's early researches during his doctoral studies were funded by Harley-Davidson and were focused on single-track vehicles. Later, on Volkswagen and University of Stuttgart sponsorship, he worked on vehicle dynamics and tyre-pavement interaction and these studies assisted in improving the design of scooters as well as in the indigenization of their manufacturing. His work on welding technology covered weld pool solidification, effects of welding parameters on molten metal transfer, spatter, heat affected zones, changes in crystallographic structures, and solute redistribution and he proposed protocols for the analytical prediction and measurement of residual stresses in and around spot welds. Later in his career, he shifted his focus to tribological studies and contributed to widening the understanding of fluid film lubrication as well as hydrostatic and hydrodynamic lubrication. He also headed a research group engaged in the studies of Pavement management systems. His researches have been documented in 160 peer-reviewed articles; the online article repository of Indian Academy of Sciences has listed 49 of them. He has also mentored 19 doctoral and several master's scholars in their studies.
Singh sat in the board of directors of the International Road Federation from 1991 to 1994 and, as a founder member of the World Interchange Network, he served as a director of the organization from 1993 to 1996. He was the secretary of the Association of Academies and Societies of Sciences in Asia (AASSA) during 1993–94 and was a member of the Science and Engineering Council of the Department of Science and Technology during 1983–88 and 2000–03. He has been associated with several global and national bodies as a member; governing body of the Technology Information, Forecasting and Assessment Council (1997–99), committees of World Road Association, Central Board of Railway Research (1986–89, 1998-2000), National Accreditation Board for Testing and Calibration laboratories (1998-2000), Committee on Auto-Fuel Policy (2001–02) and Apex Committee on Road Construction and Transportation Equipment (2001–04) are some of them. He was a member of the board of governors of the Engineering Council of India (2002–07) and presided the Tribology Society of India from 1998 to 2000. He was the Lead Person of the Fly Ash Mission (FAM) of the Department of Science and Technology and chaired its Technology Advisory Group during 1993–99. He was also the chairman of programme advisory committee on the National Science and Technology Management System (1997–2003) and served as the national coordinator of the engineering sciences section of the Indo-Russian Integrated long term programme of cooperation in Science and Technology. He was closely associated with the Indian National Academy of Engineering; he has chaired the Engineering Education Forum of the academy and is a member of its Forum on Engineering Interventions for Disaster Mitigation.
Death
Professor D. V. Singh died in New Delhi on 20 July 2018.
Awards and honors
The Council of Scientific and Industrial Research awarded Singh the Shanti Swarup Bhatnagar Prize, one of the highest Indian science awards in 1978. He received two honors from the Institution of Engineers (India); the Mechanical Engineering Design Award in 1997 and the Eminent Engineering Personality Award in 2003. The Indian National Academy of Engineering awarded him the Jaikrishna Memorial Award in 2003; INAE would honor him again in 2015 with the Lifetime Achievement Award. In between, he received the Distinguished Alumnus Award of the Indian Institute of Technology, Roorkee in 2007 and the Lifetime Achievement Award of Tribology Society of India in 2011. He is also a recipient of the Silver Jubilee Award of IMDA.
The Indian Academy of Sciences elected him as a fellow in 1981 and he became an elected fellow of the Indian National Science Academy in 1983 and the National Academy of Sciences, India in 1990. He was also an elected fellow of the Indian National Academy of Engineering. He has held the National Professorship of the University Grants Commission of India and the award orations delivered by him include Dr. Guru Prasad Chatterjee Memorial Lecture of the Indian National Science Academy.
Selected bibliography
See also
Hydrostatics
Fluid dynamics
Notes
References
1934 births
2018 deaths
Recipients of the Shanti Swarup Bhatnagar Award in Engineering Science
Fellows of the Indian Academy of Sciences
Fellows of the Indian National Science Academy
Scientists from Uttar Pradesh
Fellows of the National Academy of Sciences, India
Indian mechanical engineers
University of Allahabad alumni
IIT Roorkee alumni
University of Wisconsin–Madison alumni
Heads of universities and colleges in India
Tribologists
Fellows of the Indian National Academy of Engineering | Digvijai Singh | Materials_science | 1,369 |
68,906,231 | https://en.wikipedia.org/wiki/List%20of%20Mersenne%20primes%20and%20perfect%20numbers | Mersenne primes and perfect numbers are two deeply interlinked types of natural numbers in number theory. Mersenne primes, named after the friar Marin Mersenne, are prime numbers that can be expressed as for some positive integer . For example, is a Mersenne prime as it is a prime number and is expressible as . The exponents corresponding to Mersenne primes must themselves be prime, although the vast majority of primes do not lead to Mersenne primes—for example, .
Perfect numbers are natural numbers that equal the sum of their positive proper divisors, which are divisors excluding the number itself. So, is a perfect number because the proper divisors of are , and , and .
Euclid proved that every prime expressed as has a corresponding perfect number . For example, the Mersenne prime leads to the corresponding perfect number . In 1747, Leonhard Euler completed what is now called the Euclid–Euler theorem, showing that these are the only even perfect numbers. As a result, there is a one-to-one correspondence between Mersenne primes and even perfect numbers, so a list of one can be converted into a list of the other.
It is currently an open problem whether there are infinitely many Mersenne primes and even perfect numbers. The density of Mersenne primes is the subject of the Lenstra–Pomerance–Wagstaff conjecture, which states that the expected number of Mersenne primes less than some given is , where is Euler's number, is Euler's constant, and is the natural logarithm. It is widely believed, but not proven, that no odd perfect numbers exist; numerous restrictive conditions have been proven, including a lower bound of .
The following is a list of all 52 currently known () Mersenne primes and corresponding perfect numbers, along with their exponents . The largest 18 of these have been discovered by the distributed computing project Great Internet Mersenne Prime Search, or GIMPS; their discoverers are listed as "GIMPS / name", where the name is the person who supplied the computer that made the discovery. New Mersenne primes are found using the Lucas–Lehmer test (LLT), a primality test for Mersenne primes that is efficient for binary computers. Due to this efficiency, the largest known prime number has often been a Mersenne prime.
All possible exponents up to the 48th () have been tested and verified by GIMPS . Ranks 49 and up are provisional, and may change in the unlikely event that additional primes are discovered between the currently listed ones. Later entries are extremely long, so only the first and last six digits of each number are shown, along with the number of decimal digits.
Notes
References
External links
List on GIMPS, with the full values of large numbers
A technical report on the history of Mersenne numbers, by Guy Haworth
Mathematical tables
Primes
List
List | List of Mersenne primes and perfect numbers | Mathematics | 624 |
78,623,990 | https://en.wikipedia.org/wiki/GAARlandia | The Greater Antilles + Aves Ridge, also known as GAARlandia, is a hypothesized land bridge which is proposed to have connected the Greater Antilles to South America around 33 million years ago (mya). Animal and plant species are thought to have colonized the Caribbean Islands through dispersal and vicariance, and the most prominent vicariance hypothesis involves colonization via GAARlandia. Proponents of the hypothesis cite studies of individual lineages, while critics point to a lack of geological evidence.
Hypothesis
The GAARlandia hypothesis was introduced by Ross MacPhee and Manuel Iturralde-Vinent in 1994. It posits that the North American and South American plates compressed the Caribbean plate for 2 million years during the Eocene–Oligocene boundary (33 million years ago), which led the presently-submerged Aves Ridge in the eastern Caribbean Sea to rise and connect South America with Puerto Rico via an unbroken land bridge; Puerto Rico is posited to have been further connected via dry land to Hispaniola, Cuba and eastern Jamaica. During this period the ice sheet expanded on Antarctica, causing the global sea level to drop. MacPhee and Iturralde-Vinent proposed that the ancestors of the non-flying land vertebrates that inhabit, or used to inhabit, the Greater Antilles arrived from South America by walking along this bridge rather than through oceanic dispersal.
Debate
The GAARlandia hypothesis is controversial in the scientific community. It has been supported by studies of individual lineages, but simultaneous colonization by multiple lineages is yet to be proven. Alonso et al. (2011) firmly argued in favor of the hypothesis: they found out in a phylogenetic research that the common ancestor of the toads of the genus Peltophryne, which do not tolerate saltwater, arrived on the Greater Antilles 33 million years ago–exactly when GAARlandia is supposed to have connected the present-day islands to South America. Other taxa found to have arrived at the time GAARlandia is said to have existed include cichlids, Eleutherodactylus and Osteopilus frogs, butterflies, Polistinae wasps, spiders with limited dispersal ability, extinct primates and Megalocnidae sloths, multiple bat groups, and hystricognath rodents.
Ali & Hedges (2021) have found "weak and non-existent" support for GAARlandia, respectively, in the colonization record of land vertebrates and the geological and seismic data. They conclude that oceanic dispersal is "the best available explanation" for the origin of all Greater Antillean species, including plants and invertebrates.
Weaver et al. posit that GAARlandia might have enabled Limia, freshwater fish endemic to the islands, to reach the Antilles through a combination of dispersal, vicariance, and island hopping. Weaver et al. note, however, limias and all other native Antillean species are tolerant of saltwater, and conclude that intolerant species (such as primary division freshwater fish and caecilians) would have colonized the islands as well if a land bridge had been sufficient. Weaver et al. note that mammals which may have walked across GAARlandia, including megalonychid sloths, were capable of crossing short stretches of saltwater as well.
References
Biological hypotheses
Former landforms
Eocene South America
Oligocene South America
Natural history of the Greater Antilles
Natural history of South America
Biology controversies
Eocene Caribbean
Oligocene Caribbean | GAARlandia | Biology | 710 |
47,226,980 | https://en.wikipedia.org/wiki/Penicillium%20qii | Penicillium qii is a species of the genus of Penicillium which was isolated from plant leaves in China.
References
qii
Fungus species | Penicillium qii | Biology | 33 |
6,311,700 | https://en.wikipedia.org/wiki/Salt%20spray%20test | The salt spray test (or salt fog test) is a standardized and popular corrosion test method, used to check corrosion resistance of materials and surface coatings. Usually, the materials to be tested are metallic (although stone, ceramics, and polymers may also be tested) and finished with a surface coating which is intended to provide a degree of corrosion protection to the underlying metal.
Salt spray testing is an accelerated corrosion test that produces a corrosive attack to coated samples in order to evaluate (mostly comparatively) the suitability of the coating for use as a protective finish. The appearance of corrosion products (rust or other oxides) is evaluated after a predetermined period of time. Test duration depends on the corrosion resistance of the coating; generally, the more corrosion resistant the coating is, the longer the period of testing before the appearance of corrosion or rust.
The salt spray test is one of the most widespread and long-established corrosion tests. ASTMB117 was the first internationally recognized salt spray standard, originally published in 1939. Other important relevant standards are ISO9227, JISZ2371 and ASTMG85.
Application
Salt spray testing is popular because it is relatively inexpensive, quick, well standardized, and reasonably repeatable. Although there may be a weak correlation between the duration in salt spray test and the expected life of a coating in certain coatings such as hot-dip galvanized steel, this test has gained worldwide popularity due to low cost and quick results. Most salt spray chambers today are not being used to predict the corrosion resistance of a coating, but to maintain coating processes such as pre-treatment and painting, electroplating, galvanizing, and the like, on a comparative basis. For example, pre-treated + painted components must pass 96 hours Neutral Salt Spray, to be accepted for production. Failure to meet this requirement implies instability in the chemical process of the pre-treatment, or the paint quality, which must be addressed immediately so that the upcoming batches are of the desired quality. The longer the accelerated corrosion test, the longer the process remains out of control, and larger is the loss in the form of non-conforming batches.
The principal application of the salt spray test is, therefore, enabling quick comparisons to be made between actual and expected corrosion resistance. Most commonly, the time taken for oxides to appear on the samples under test is compared to expectations, to determine whether the test is passed or failed. For this reason, the salt spray test is most often deployed in a quality audit role, where, for example, it can be used to check the effectiveness of a production process, such as the surface coating of a metallic part.
The salt spray test has little application in predicting how materials or surface coatings will resist corrosion in the real world, because it does not create, replicate or accelerate real-world corrosive conditions. Cyclic corrosion testing is better suited to this.
Testing equipment
The apparatus for testing consists of a closed testing cabinet/chamber, where a salt water (5% NaCl) solution is atomized by means of spray nozzle(s) using pressurized air. This produces a corrosive environment of dense salt water fog (also referred to as a mist or spray) in the chamber, so that test samples exposed to this environment are subjected to severely corrosive conditions. Chamber volumes vary from supplier to supplier. If there is a minimum volume required by a particular salt spray test standard, this will be clearly stated and should be complied with. There is a general historical consensus that larger chambers can provide a more homogeneous testing environment.
Variations to the salt spray test solutions depend upon the materials to be tested. The most common test for steel based materials is the Neutral Salt Spray test (often abbreviated to NSS) which reflects the fact that this type of test solution is prepared to a neutral pH of 6.5 to 7.2. To maintain a neutral pH, hydrochloric acid or sodium hydroxide are added to reduce or increase pH into the required range. Results are represented generally as testing hours in NSS without appearance of corrosion products (e.g. 720 h in NSS according to ISO 9227). Synthetic seawater solutions are also commonly specified by some companies and standards. Other test solutions have other chemicals added including acetic acid (often abbreviated to ASS) and acetic acid with copper chloride (often abbreviated to CASS) each one chosen for the evaluation of decorative coatings, such as electroplated copper-nickel-chromium, electroplated copper-nickel or anodized aluminum. These acidified test solutions generally have a pH of 3.1 to 3.3
Some sources do not recommend using ASS or CASS test cabinets interchangeably for NSS tests, due to the risk of cross-contamination. It is claimed that a thorough cleaning of the cabinet after CASS test is very difficult. ASTM does not address this issue, but ISO 9227 does not recommend it and if it is to be done, advocates a thorough cleaning.
Although the majority of salt spray tests are continuous, i.e.; the samples under test are exposed to the continuous generation of salt fog for the entire duration of the test, a few do not require such exposure. Such tests are commonly referred to as modified salt spray tests. ASTM G85 is an example of a test standard which contains several modified salt spray tests which are variations to the basic salt spray test.
Modified salt spray tests
ASTM G85 is the most popular global test standard covering modified salt spray tests. There are five such tests altogether, referred to in ASTM G85 as annexes A1 through to A5. Many of these modified tests originally arose within particular industry sector, in order to address the need for a corrosion test capable of replicating the effects of naturally occurring corrosion and accelerate these effects.
This acceleration arises through the use of chemically altered salt spray solutions, often combined with other test climates and in most cases, the relatively rapid cycling of these test climates over time. Although popular in certain industries, modified salt spray testing has in many cases been superseded by cyclic corrosion testing (CCT)
The type of environmental test chambers used for modified salt spray testing to ASTM G85 are generally similar to the chambers used for testing to ASTM B117, but will often have some additional features, such as an automatic climate cycling control system.
ASTM G85 Annex A1 – Acetic Acid Salt Spray Test (non-cyclic)
This test can be used to determine the relative resistance to corrosion of decorative chromium plating on steel and zinc based die casting when exposed to an acetic acid salt spray climate at an elevated temperature. This test is also referred to as an ASS test.
Test specimens are placed in an enclosed chamber and exposed to a continuous indirect spray of salt water solution, prepared in accordance with the requirements of the test standard and acidified (pH 3.1–3.3) by the addition of acetic acid. This spray is set to fall-out on to the specimens at a rate of 1–2 ml/80 cm2/hour, in a chamber temperature of 35 °C. This climate is maintained under constant steady state conditions. The test duration is variable.
ASTM G85 Annex A2 – Acidified Salt Fog Test (cyclic).
This test can be used to test the relative resistance to corrosion of aluminium alloys when exposed to a changing climate of acetic acid salt spray, followed by air drying, followed by high humidity, all at an elevated temperature. This test is also referred to as a MASTMAASIS test.
Test specimens are placed in an enclosed chamber, and exposed to a changing climate that comprises the following 3 part repeating cycle. 0.75 hours exposure to a continuous indirect spray of salt water solution, prepared in accordance with the requirements of the test standard and acidified (pH 2.8–3.0) by the addition of acetic acid. This spray is set to fall-out on to the specimens at a rate of 1–2 ml/80 cm2/hour. This is followed by a 2 hour exposure to an air drying (purge) climate. This is followed by 3.25 hours exposure to a high humidity climate which gradually rises to between 65% RH and 95% RH. The entire test cycle is at a constant chamber temperature of 49 °C. The number of cycle repeats and therefore the test duration is variable.
ASTM G85 Annex A3 – Seawater Acidified Test (cyclic)
This test can be used to test the relative resistance to corrosion of coated or uncoated aluminium alloys and other metals, when exposed to a changing climate of acidified synthetic seawater spray, followed by a high humidity, both at an elevated temperature. This test is also referred to as a SWAAT test.
Test specimens are placed in an enclosed chamber, and exposed to a changing climate that comprises the following 2 part repeating cycle. First, a 30 minute exposure to a continuous indirect spray of synthetic seawater solution, prepared in accordance with the requirements of the test standard and acidified (pH 2.8–3.0) by the addition of acetic acid. This spray is set to fall-out on to the specimens at a rate of 1–2 ml/80 cm2/hour. This is followed by a 90 minute exposure to a high humidity climate (above 98% RH). The entire test cycle is at a constant chamber temperature of 49 °C (may be reduced to 24–35 °C for organically coated specimens). The number of cycle repeats and therefore the test duration is variable.
ASTM G85 Annex A4 – Salt Spray Test (cyclic)
This test can be used to test the relative resistance to corrosion of product samples that are likely to encounter a combined /salt spray/acid rain environment during their usual service life.
Test specimens are placed in an enclosed chamber, and exposed to 1 of 2 possible changing climate cycles. In either case, the exposure to salt spray may be salt water spray or synthetic sea water prepared in accordance with the requirements of the test standard. The most appropriate test cycle and spray solutions are to be agreed between parties.
The first climate cycle comprises a continuous indirect spray of neutral (pH 6.5–7.2) salt water/synthetic seawater solution, which falls-out on to the specimens at a rate of 1–2 ml/80 cm2/hour. During this spraying, the chamber is dosed with gas at a rate of 35 cm3/minute/m3 of chamber volume, for 1 hour in every 6 hours of spraying. The entire test cycle is at a constant chamber temperature of 35 °C. The number of cycle repeats and therefore the test duration is variable.
The second climate cycle comprises 0.5 hours of continuous indirect spray of neutral (pH 6.5–7.2) salt water/synthetic seawater solution, which falls-out on to the specimens at a rate of 1–2 ml/80 cm2/hour. This is followed by 0.5 hours of dosing with gas at a rate of 35 cm3/minute/m3 of chamber volume. This is followed by 2 hours of high humidity soak. The entire test cycle is at a constant chamber temperature of 35 °C. The number of cycle repeats and therefore the test duration is variable.
ASTM G85 Annex A5 – Dilute Electrolyte Salt Fog/Dry Test (cyclic)
This test can be used to test the relative resistance to corrosion of paints on steel when exposed to a changing climate of dilute salt spray at ambient temperature, followed by air drying at elevated temperature.
It is a popular test in the surface coatings industry, where it is also referred to as the PROHESION test.
Test specimens are placed in an enclosed chamber, and exposed to a changing climate with the following 2-part cycle.
First, a 1-hour exposure to a continuous indirect spray of salt water solution, prepared in accordance with the requirements of the test standard and acidified (pH 3.1–3.3) by the addition of acetic acid.
This spray is set to fall on the specimens at a rate of 1–2 ml/80 cm2/hour, in an ambient chamber temperature (21–27 °C). This is followed by a 1-hour exposure to an air drying (purge) climate at 35 °C.
The cycle repeats until the desired duration has been achieved.
Standardization
Chamber construction, testing procedure and testing parameters are standardized under national and international standards, such as ASTM B 117 and ISO 9227. These standards describe the necessary information to carry out this test; testing parameters such as temperature, air pressure of the sprayed solution, preparation of the spraying solution, concentration, pH, etc. Daily checking of testing parameters is necessary to show compliance with the standards, so records shall be maintained accordingly. ASTM B117 and ISO 9227 are widely used as reference standards. Testing cabinets are manufactured according to the specified requirements here.
However, these testing standards neither provide information of testing periods for the coatings to be evaluated, nor the appearance of corrosion products in form of salts. Requirements are agreed between customer and manufacturer. In the automotive industry requirements are specified under material specifications. Different coatings have different behavior in salt spray test and consequently, test duration will differ from one type of coating to another. For example, a typical electroplated zinc and yellow passivated steel part lasts 96 hours in salt spray test without white rust. Electroplated zinc-nickel steel parts can last more than 720 hours in NSS test without red rust (or 48 hours in CASS test without red rust) Requirements are established in test duration (hours) and coatings shall comply with minimum testing periods.
Artificial seawater which is sometimes used for Salt Spray Testing can be found at ASTM International. The standard for Artificial Seawater is ASTM D1141-98 which is the standard practice for the preparation of substitute ocean water.
Uses
Typical coatings that can be evaluated with this method are:
Phosphated (pre-treated) surfaces (with subsequent paint/primer/lacquer/rust preventive)
Zinc and zinc-alloy plating (see also electroplating). See ISO 4042 for guidance
Electroplated chromium, nickel, copper, tin
Coatings not applied electrolytically, such as zinc flake coatings according to ISO 10683
Organic coatings, such as rust preventives
Paint Coating
Hot-dip galvanized surfaces are not generally tested in a salt spray test (see ISO 1461 or ISO 10684). Hot-dip galvanizing produces zinc carbonates when exposed to a natural environment, thus protecting the coating metal and reducing the corrosion rate. The zinc carbonates are not produced when a hot-dip galvanized specimen is exposed to a salt spray fog, therefore this testing method does not give an accurate measurement of corrosion protection. ISO 9223 gives the guidelines for proper measurement of corrosion resistance for hot-dip galvanized specimens.
Painted surfaces with an underlying hot-dip galvanized coating can be tested according to this method. See ISO 12944-6.
Testing periods range from a few hours (e.g. 8 or 24 hours of phosphated steel) to more than a month (e.g. 720 hours of zinc-nickel coatings, 1000 hours of certain zinc flake coatings).
Bibliography
Metal Finishing. Guidebook and directory issue. Published by Metal Finishing Magazine, 1996
See also
Corrosion
Corrosion engineering
Cyclic corrosion testing
Environmental chamber
Japanese Industrial Standards
ASTM International
International Organization for Standardization
Further reading
ASTM G85 Modified Salt Spray Test standard
Deutsches Institut für Normung e.V. DIN 50021 Sprühnebelprüfungen mit verschiedenen Natriumchloridlösungen. Beuth Verlag GmbH, 1988. This standard has been superseded by ISO 9227 and it is only mentioned for bibliographic purposes
ISO International Organization for Standardization. ISO 9227 Corrosion tests in artificial atmospheres—Salt spray tests, 2006
ISO International Organization for Standardization. ISO 4628-3 Paints and varnishes. Evaluation of degradation of coatings. Designation of quantity and size of defects, and of intensity of uniform changes in appearance. Part 3 Assessment of degree of rusting
MIL-STD-810 Environmental Engineering Considerations and Laboratory Tests
ASTM B117 Test Conditions, Method & Application
References
Corrosion
Metallurgical processes
Measuring instruments
Coatings
Environmental testing
ISO standards | Salt spray test | Chemistry,Materials_science,Technology,Engineering | 3,349 |
33,980,091 | https://en.wikipedia.org/wiki/Recover%20%28command%29 | In computing, recover is a primitive file system error recovery utility included in MS-DOS / IBM PC DOS versions prior to DOS 6.0 and a number of other operating systems.
Overview
Typing recover at the DOS command-line invoked the program file or (depending on the DOS version). recover proceeded under the assumption that all directory information included on a disk or disk partition was hopelessly corrupted, but that the FAT and non-directory areas might still contain useful information (though there might be additional bad disk sectors not recorded in the FAT).
The program removed all subdirectories and all entries in the root directory, and then created new files with names such as "" in the root directory, corresponding to the valid allocation chains that were found in the FAT area (excluding disk clusters that were tested and found to have hardware errors). A formerly bootable disk would no longer be bootable after recover had executed. The range of circumstances in which recover was genuinely useful was quite limited, and well-meaning DOS users sometimes created havoc by running recover under the misconception that it was a file undelete utility.
In DOS version 5, another mode of operation was added: specifying a single filename on the command line would cause the program to test all the disk sectors used to store the file, and shorten the file by omitting sectors which tested bad.
DR DOS 6.0 includes an implementation of the command. The command is also available on SISNE plus and IBM OS/2. The FreeDOS version was developed by Imre Leber and is licensed under the GPL.
See also
Chkdsk
Scandisk
Norton Utilities
List of DOS commands
References
Further reading
External links
recover | Microsoft Docs
Open source RECOVER implementation that comes with MS-DOS v2.0
Disk file systems
External DOS commands
IBM PC compatibles
Microsoft free software
OS/2 commands | Recover (command) | Technology | 383 |
10,374,398 | https://en.wikipedia.org/wiki/NGC%204650A | NGC 4650A is a polar-ring lenticular galaxy located in the constellation Centaurus. It should not be confused with the spiral galaxy NGC 4650, which shares almost the same radial distance as NGC 4650A. The real distance between both galaxies is
only about 6 times the optical radius of NGC 4650.
References
External links
Hubble Heritage site: Pictures and description
Centaurus
4650A
42951
Polar-ring galaxies
Lenticular galaxies | NGC 4650A | Astronomy | 92 |
72,422,117 | https://en.wikipedia.org/wiki/U%20Sagittarii | U Sagittarii is a variable star in the southern constellation of Sagittarius, abbreviated U Sgr. It is a classical Cepheid variable that ranges in brightness from an apparent visual magnitude of 6.28 down to 7.15, with a pulsation period of 6.745226 days. At its brightest, this star is dimly visible to the naked eye. The distance to this star is approximately 2,080 light years based on parallax measurements, and it is drifting further away with a radial velocity of 2 km/s.
The variability of this star was announced by J. Schmidt in 1866, who found a preliminary period of 6.74784 days. It was later determined to be a variable of the Cepheid type. In 1925, P. Doig assumed that the star is a member of the open cluster Messier 25 (M25), but actual evidence of its membership would not be available until 1932 when P. Hayford made radial velocity measurements of the cluster. Membership in this cluster is now reasonably established, and as such this Cepheid serves as one of the anchors for the cosmic distance scale since the distance to the cluster can be determined independently from the star. Indeed, new research indicates U Sgr's host cluster (M25) may constitute a ternary (triple) star cluster together with NGC 6716 and Collinder 394.
This is an evolved G-type supergiant star with a typical stellar classification of G1Ib. It appears to be making its third traversal of the instability strip with its period changing at the rate of . Elemental abundances are similar to those in the Sun. It has an estimated 6.6 times the mass of the Sun and 56 times the Sun's radius. The star is radiating over 4,000 times the Sun's luminosity from its photosphere at an effective temperature of 5,802 K.
References
Further reading
Classical Cepheid variables
G-type supergiants
Sagittarius (constellation)
6947
Durchmusterung objects
170764
90836 | U Sagittarii | Astronomy | 433 |
22,537,012 | https://en.wikipedia.org/wiki/List%20of%20fastest%20computers | This is a historical list of fastest computers and includes computers and supercomputers which were considered the fastest in the world at the time they were built.
a. An asterisk (*) denotes Rmaxthe highest score measured using the LINPACK benchmarks suite.
See also
History of supercomputing
Timeline of instructions per second (IPS)
TOP500 § Systems ranked No. 1 since 1976 (FLOPS)
References
Computer Speeds From Instruction Mixes (pre-1960 to 1971)
TOP500 #1 systems since 1993 – TOP500.org
History of computing hardware
Fastest computers
Fastest computers
Fastest computers | List of fastest computers | Technology | 123 |
71,972,809 | https://en.wikipedia.org/wiki/Caitlin%20Casey | Caitlin M Casey is an observational astronomer and associate professor at the University of Texas at Austin. She is known for her work in extragalactic astrophysics; she works on the formation and evolution of massive galaxies in the early Universe.
Education and career
Casey's interest in astronomy began as a child when she was given the opportunity to visit the planetarium in Rock Bridge High School in her hometown of Columbia, Missouri.
Casey completed her bachelor's degrees in physics, astronomy and applied mathematics from the University of Arizona in 2007. She attributes her decision to attend Arizona from first attending their Astronomy Camp during high school. She then obtained her Ph.D. in Astronomy from the University of Cambridge in 2010 under a Gates Cambridge Scholarship. While in Cambridge she served as president of the Gates Scholars' Society from 2009-2010. Casey was subsequently a NASA Hubble Postdoctoral Fellow at the Institute for Astronomy, University of Hawai’i at Mānoa, and then she spent two years as a postdoc at the University of California, Irvine as a McCue Postdoctoral Fellow of Cosmology. Casey became assistant professor in the Department of Astronomy at the University of Texas at Austin in 2015. Since 2021, Casey is an associate professor.
Career and research
Casey is known for her research on galaxy formation and evolution, specifically on the most massive and luminous galaxies in the Universe. While in Hawaii, she examined the formation of starburst galaxies, research that was conducted with the largest spectroscopic survey using the W.M. Keck Observatory of submillimeter-luminous galaxies detected by the Herschel Space Observatory. While at the University of California, Irvine Casey authored a review paper on star-forming galaxies. Casey is principal investigator of the COSMOS-Web Survey and the Cosmic Evolution Survey. This work is a collaborative effort with Jeyhan Kartaltepe. The COSMOS-Web Survey is a James Webb Space Telescope NIRCam imaging program that aims to reveal the sources of cosmic reionization and was the telescope's largest allocated project in its first year of observations. She presented the initial results of her research with the COSMOS-Web survey in 2023.
Casey is an advocate for equity in STEM, creating the TAURUS program, a summer research experience for marginalized students in the summer of 2016. This program is hosted at the University of Texas at Austin at the McDonald Observatory and allows under-represented undergraduate students to get involved with astronomical research. Casey created a workshop designed to spread awareness about bullying, microaggressions and harassment for academic researchers with her colleague Kartik Sheth called The Ethical Gray Zone in 2013.
Selected publications
Honors and awards
Casey received the 2018 Newton Lacy Pierce Prize awarded by the American Astronomical Society for impactful work in observational astronomy achieved before age 36. In 2019 she was awarded a Cottrell Scholar Award from the Research Corporation for Science Advancement.
References
External links
Living people
Scientists from Columbia, Missouri
Rock Bridge High School alumni
University of Arizona alumni
Alumni of the University of Cambridge
University of Texas at Austin faculty
Women astronomers
Year of birth missing (living people) | Caitlin Casey | Astronomy | 623 |
21,438,345 | https://en.wikipedia.org/wiki/Design%20knowledge | There is a large body of knowledge that designers call upon and use during the design process to match the ever-increasing complexity of design problems. Design knowledge can be classified into two categories: product knowledge and design process knowledge.
Product Knowledge
Product knowledge has been fairly studied and a number of modeling techniques have been developed. Most of them are tailored to specific products or specific aspects of the design activities. For example, geometric modeling is used mainly for supporting detailed design, while knowledge modeling is working for supporting conceptual designs. Based on these techniques, a design repository project at NIST attempts to model three fundamental facets of an artifact representation: the physical layout of the artifact (form), an indication of the overall effect that the artifact creates (function), and a causal account of the operation of the artifact (behavior). The recent NIST research effort towards the development of the basic foundations of the next generation of CAD systems suggested a core representation for design information called the NIST core product model (CPM) and a set of derived models defined as extensions of the CPM (e.g.). The NIST core product model has been developed to unify and integrate product or assembly information. The CPM
provides a base-level product model that is: not tied to any vendor software; open; non-proprietary; expandable; independent of any one product development process; capable of capturing the engineering context that is most commonly shared in product development activities. The core model focuses on artifact representation including function, form, behavior, material, physical and functional decompositions, and relationships among these concepts. The entity-relationship data model influences the model heavily; accordingly, it consists of two sets of classes, called object and relationship, equivalent to the UML class and association class, respectively.
Design Process Knowledge
Design process knowledge can be described in two levels: design activities and design rationale. The importance of representation for design rationale has been recognized but it is a more complex issue that extends beyond artifact function. The design structure matrix (DSM) has been used for modeling design process (activities) and some related research efforts have been conducted. For example, a web-based prototype system for modeling the product development process using a multi-tiered DSM is developed at MIT. However, few research endeavors have been found on design rationale.
Representation Scenarios
In terms of representation scenarios, design knowledge can also be categorized into off-line and on-line knowledge. Design process knowledge can be categorized into ontologies.
Off-line Knowledge
Offline Knowledge refers to existing knowledge representation, including design knowledge in handbook and design ‘‘know-how’’, etc.; the latter refers to the new design knowledge created in the course of design activities by designers themselves. For the off-line knowledge, there are two representation approaches. One is to highly abstract and categorize existing knowledge including experiences into a series of design principles, rationales and constraints. TRIZ is a good instance of this approach. The other is to represent a collection of design knowledge into a certain case for description. Case-based design is an example of this approach. The key issue is on the computerization of the
design knowledge representation. For instance, researchers at the Engineering Design Centre at Lancaster University, UK established a unique knowledge representation methodology and knowledge base vocabulary based on the theory of domains, design principles and computer modeling. They developed a software tool for engineering knowledge management. The tool provides an engineering system designer with the capability to search a knowledge base of past solutions, and other known technologies to explored viable alternatives for product design.
On-line Knowledge
On-line knowledge representation is capturing the dynamic design knowledge in a certain format for design re-use and archive. A few research efforts have been found in this area. Blessing proposes the process-based support system (PROSUS) based on a model of the design process rather than the product. It uses a design matrix to represent the design process as a structured set of issues and activities. Together with the common product data model (CPDM), PROSUS supports the capture of all outputs of the design activity.
Ontologies
Ontologies are being used for product representation (e.g.). Research suggests that there is a need to provide computer support that will supply clear and complete design knowledge and also facilitate designer intervention and customization during the decision-making activities in the design process. For example, WebCADET is a design support system that uses distributed Web-based AI tools. It uses the AI as text approach, where knowledge-based systems (KBSs) can be seen as a medium to facilitate the communication of design knowledge between designers. The system can provide support for designers when searching for design knowledge.
References
Design | Design knowledge | Engineering | 955 |
1,568,646 | https://en.wikipedia.org/wiki/HD%20187123 | HD 187123 is a single, yellow-hued star with two exoplanetary companions in the northern constellation of Cygnus. It has an apparent visual magnitude of 7.83, making it an 8th magnitude star that is too faint to be visible with the naked eye. However, it should be easy target with binoculars or small telescope. The system is located at a distance of 150 light years from the Sun based on parallax measurements, but is drifting closer with a radial velocity of −17 km/s.
This is an ordinary G-type main-sequence star with a stellar classification of G2V. The physical properties of this star are sufficiently similar to the Sun that it has been considered a solar analog, although the metallicity is higher. It is estimated to be five or six billion years old and is spinning with a projected rotational velocity of 2 km/s. The star has a similar mass to the Sun but is slightly larger with 117% of the Sun's radius. It is radiating 1.44 times the luminosity of the Sun from its photosphere at an effective temperature of 5,853 K.
Planetary system
In 1998 the California and Carnegie Planet Search team, after following a suggestion by Kevin Apps, a Briton who at the time was an undergraduate student found a possible planet orbiting the star. There were also indications of another, more distant body orbiting the star and this claim was published in 2006. This planet was confirmed in 2009. The presence of water has been detected in the atmosphere of HD 187123 b with high confidence.
See also
List of extrasolar planets
List of exoplanets discovered before 2000 - HD 187123 b
List of exoplanets discovered between 2000–2009 - HD 187123 c
References
External links
G-type main-sequence stars
Solar analogs
Planetary systems with two confirmed planets
Cygnus (constellation)
Durchmusterung objects
187123
097336 | HD 187123 | Astronomy | 394 |
1,013,989 | https://en.wikipedia.org/wiki/Tola%20%28unit%29 | The tola ( / ; also transliterated as tolah or tole) is a traditional Ancient Indian and South Asian unit of mass, now standardised as 180 grains () or exactly troy ounce. It was the base unit of mass in the British Indian system of weights and measures introduced in 1833, although it had been in use for much longer. It was also used in Aden and Zanzibar: in the latter, one tola was equivalent to 175.90 troy grains (0.97722222 British tolas, or 11.33980925 grams).
The tola is a Vedic measure, with the name derived from the Sanskrit (from the root ) meaning "weighing" or "weight". One tola was traditionally the weight of 100 Ratti (ruttee) seeds, and its exact weight varied according to locality. However, it is also a convenient mass for a coin: several pre-colonial coins, including the currency of Akbar the Great (1556–1605), had a mass of "one tola" within slight variation. The first rupee (; rupayā), minted by Sher Shah Suri (1540–45), had a mass of 178 troy grains, or about 1% less than the British tola. The British East India Company issued a silver rupee coin of 180 troy grains, and this became the practical standard mass for the tola well into the 20th century.
The British tola of 180 troy grains (from 1833) can be seen as more of a standardisation than a redefinition: the previous standard in the Bengal Presidency, the system of "sicca weights", was the mass of one Murshidabad rupee, 179.666 troy grains. For the larger weights used in commerce (in the Bengal Presidency), the variation in the pre-1833 standards was found to be greater than the adjustment.
The tola formed the base for units of mass under the British Indian system, and was also the standard measure of gold and silver bullion. Although the tola has been officially replaced by metric units since 1956, it is still in current use, and is a popular denomination for gold bullion bars in Bangladesh, India, Nepal, Pakistan and Singapore, with a ten tola bar being the most commonly traded. In Nepal, minting of tola size gold coins continue up to the present, even though the currency of Nepal is called rupee and has no official connection to the tola. It is also used in most gold markets (bazars/souks) in the United Arab Emirates and in all the Cooperation Council for the Arab States of the Gulf (GCC) countries.
Tola is still used as a measure of charas (Indian hashish). On the black market, however, one tola equals a mass of approximately and not the actual mass of one tola.
See also
Troy ounce
References
External links
Tola to Gram Calculator
Tola unit converter
Units of mass
Customary units in India | Tola (unit) | Physics,Mathematics | 623 |
10,875,756 | https://en.wikipedia.org/wiki/Lie%27s%20third%20theorem | In the mathematics of Lie theory, Lie's third theorem states that every finite-dimensional Lie algebra over the real numbers is associated to a Lie group . The theorem is part of the Lie group–Lie algebra correspondence.
Historically, the third theorem referred to a different but related result. The two preceding theorems of Sophus Lie, restated in modern language, relate to the infinitesimal transformations of a group action on a smooth manifold. The third theorem on the list stated the Jacobi identity for the infinitesimal transformations of a local Lie group. Conversely, in the presence of a Lie algebra of vector fields, integration gives a local Lie group action. The result now known as the third theorem provides an intrinsic and global converse to the original theorem.
Historical notes
The equivalence between the category of simply connected real Lie groups and finite-dimensional real Lie algebras is usually called (in the literature of the second half of 20th century) Cartan's or the Cartan-Lie theorem as it was proved by Élie Cartan. Sophus Lie had previously proved the infinitesimal version: local solvability of the Maurer-Cartan equation, or the equivalence between the category of finite-dimensional Lie algebras and the category of local Lie groups.
Lie listed his results as three direct and three converse theorems. The infinitesimal variant of Cartan's theorem was essentially Lie's third converse theorem. In an influential book Jean-Pierre Serre called it the third theorem of Lie. The name is historically somewhat misleading, but often used in connection to generalizations.
Serre provided two proofs in his book: one based on Ado's theorem and another recounting the proof by Élie Cartan.
Proofs
There are several proofs of Lie's third theorem, each of them employing different algebraic and/or geometric techniques.
Algebraic proof
The classical proof is straightforward but relies on Ado's theorem, whose proof is algebraic and highly non-trivial. Ado's theorem states that any finite-dimensional Lie algebra can be represented by matrices. As a consequence, integrating such algebra of matrices via the matrix exponential yields a Lie group integrating the original Lie algebra.
Cohomological proof
A more geometric proof is due to Élie Cartan and was published by . This proof uses induction on the dimension of the center and it involves the Chevalley-Eilenberg complex.
Geometric proof
A different geometric proof was discovered in 2000 by Duistermaat and Kolk. Unlike the previous ones, it is a constructive proof: the integrating Lie group is built as the quotient of the (infinite-dimensional) Banach Lie group of paths on the Lie algebra by a suitable subgroup. This proof was influential for Lie theory since it paved the way to the generalisation of Lie third theorem for Lie groupoids and Lie algebroids.
See also
Lie group integrator
References
External links
Encyclopaedia of Mathematics (EoM) article
Lie algebras
Lie groups
Theorems about algebras | Lie's third theorem | Mathematics | 618 |
43,592 | https://en.wikipedia.org/wiki/John%20Herschel | Sir John Frederick William Herschel, 1st Baronet (; 7 March 1792 – 11 May 1871) was an English polymath active as a mathematician, astronomer, chemist, inventor and experimental photographer who invented the blueprint and did botanical work.
Herschel originated the use of the Julian day system in astronomy. He named seven moons of Saturn and four moons of Uranus – the seventh planet, discovered by his father Sir William Herschel. He made many contributions to the science of photography, and investigated colour blindness and the chemical power of ultraviolet rays. His Preliminary Discourse (1831), which advocated an inductive approach to scientific experiment and theory-building, was an important contribution to the philosophy of science.
Early life and work on astronomy
Herschel was born in Slough, Buckinghamshire, the son of Mary Baldwin and astronomer Sir William Herschel. He was the nephew of astronomer Caroline Herschel. He studied shortly at Eton College and St John's College, Cambridge, graduating as Senior Wrangler in 1813. It was during his time as an undergraduate that he became friends with the mathematicians Charles Babbage and George Peacock. He left Cambridge in 1816 and started working with his father. He took up astronomy in 1816, building a reflecting telescope with a mirror in diameter, and with a focal length. Between 1821 and 1823 he re-examined, with James South, the double stars catalogued by his father. He was one of the founders of the Royal Astronomical Society in 1820. For his work with his father, he was presented with the Gold Medal of the Royal Astronomical Society in 1826 (which he won again in 1836), and with the Lalande Medal of the French Academy of Sciences in 1825, while in 1821 the Royal Society bestowed upon him the Copley Medal for his mathematical contributions to their Transactions. Herschel was made a Knight of the Royal Guelphic Order in 1831. He also seemed to be aware of Indian thought and mathematics introduced to him by George Everest as claimed by Mary Boole:
He stated in his historical article Mathematics in Brewster's Cyclopedia:
Herschel served as president of the Royal Astronomical Society three times: 1827–1829, 1839–1841 and 1847–1849.
Herschel's A preliminary discourse on the study of natural philosophy, published early in 1831 as part of Dionysius Lardner's Cabinet cyclopædia, set out methods of scientific investigation with an orderly relationship between observation and theorising. He described nature as being governed by laws which were difficult to discern or to state mathematically, and the highest aim of natural philosophy was understanding these laws through inductive reasoning, finding a single unifying explanation for a phenomenon. This became an authoritative statement with wide influence on science, particularly at the University of Cambridge where it inspired the student Charles Darwin with "a burning zeal" to contribute to this work.
He was elected as a member to the American Philosophical Society in 1854.
Herschel published a catalogue of his astronomical observations in 1864, as the General Catalogue of Nebulae and Clusters, a compilation of his own work and that of his father's, expanding on the senior Herschel's Catalogue of Nebulae. A further complementary volume was published posthumously, as the General Catalogue of 10,300 Multiple and Double Stars.
Herschel correctly considered astigmatism to be due to irregularity of the cornea and theorised that vision could be improved by the application of some animal jelly contained in a capsule of glass against the cornea. His views were published in an article entitled Light in 1828 and the Encyclopædia Metropolitana in 1845.
Discoveries of Herschel include the galaxies NGC 7, NGC 10, NGC 25, and NGC 28.
Visit to South Africa
He declined an offer from the Duke of Sussex that they travel to South Africa on a Navy ship.
Herschel had his own inherited money and he paid £500 for passage on the S.S. Mountstuart Elphinstone. He, his wife, their three children and his 20 inch telescope departed from Portsmouth on 13 November 1833.
The voyage to South Africa was made to catalogue the stars, nebulae, and other objects of the southern skies. This was to be a completion as well as extension of the survey of the northern heavens undertaken initially by his father William Herschel. He arrived in Cape Town on 15 January 1834 and set up a private telescope at Feldhausen (site of present day Grove Primary School) at Claremont, a suburb of Cape Town. Amongst his other observations during this time was that of the return of Comet Halley. Herschel collaborated with Thomas Maclear, the Astronomer Royal at the Cape of Good Hope and the members of the two families became close friends. During this time, he also witnessed the Great Eruption of Eta Carinae (December 1837).
In addition to his astronomical work, however, this voyage to a far corner of the British empire also gave Herschel an escape from the pressures under which he found himself in London, where he was one of the most sought-after of all British men of science. While in southern Africa, he engaged in a broad variety of scientific pursuits free from a sense of strong obligations to a larger scientific community. It was, he later recalled, probably the happiest time in his life. A village in the contemporary province of Eastern Cape is named after him.
Herschel combined his talents with those of his wife, Margaret, and between 1834 and 1838 they produced 131 botanical illustrations of fine quality, showing the Cape flora. Herschel used a camera lucida to obtain accurate outlines of the specimens and left the details to his wife. Even though their portfolio had been intended as a personal record, and despite the lack of floral dissections in the paintings, their accurate rendition makes them more valuable than many contemporary collections. Some 112 of the 132 known flower studies were collected and published as Flora Herscheliana in 1996. The book also included work by Charles Davidson Bell and Thomas Bowler.
As their home during their stay in the Cape, the Herschels had selected 'Feldhausen' ("Field Houses"), an old estate on the south-eastern side of Table Mountain. Here John set up his reflector to begin his survey of the southern skies.
Herschel, at the same time, read widely. Intrigued by the ideas of gradual formation of landscapes set out in Charles Lyell's Principles of Geology, he wrote to Lyell on 20 February 1836 praising the book as a work that would bring "a complete revolution in [its] subject, by altering entirely the point of view in which it must thenceforward be contemplated" and opening a way for bold speculation on "that mystery of mysteries, the replacement of extinct species by others." Herschel himself thought catastrophic extinction and renewal "an inadequate conception of the Creator" and by analogy with other intermediate causes, "the origination of fresh species, could it ever come under our cognizance, would be found to be a natural in contradistinction to a miraculous process". He prefaced his words with the couplet:
Taking a gradualist view of development and referring to evolutionary descent from a proto-language, Herschel commented:
The document was circulated, and Charles Babbage incorporated extracts in his ninth and unofficial Bridgewater Treatise, which postulated laws set up by a divine programmer. When HMS Beagle called at Cape Town, Captain Robert FitzRoy and the young naturalist Charles Darwin visited Herschel on 3 June 1836. Later on, Darwin would be influenced by Herschel's writings in developing his theory advanced in The Origin of Species. In the opening lines of that work, Darwin writes that his intent is "to throw some light on the origin of species – that mystery of mysteries, as it has been called by one of our greatest philosophers," referring to Herschel. However, Herschel ultimately rejected the theory of natural selection.
Herschel returned to England in 1838, was created a baronet, of Slough in the County of Buckingham, and published Results of Astronomical Observations made at the Cape of Good Hope in 1847. In this publication he proposed the names still used today for the seven then-known satellites of Saturn: Mimas, Enceladus, Tethys, Dione, Rhea, Titan, and Iapetus. In the same year, Herschel received his second Copley Medal from the Royal Society for this work. A few years later, in 1852, he proposed the names still used today for the four then-known satellites of Uranus: Ariel, Umbriel, Titania, and Oberon. A stone obelisk, erected in 1842 and now in the grounds of The Grove Primary School, marks the site where his 20-ft reflector once stood.
Photography
Herschel made numerous important contributions to photography. He made improvements in photographic processes, particularly in inventing the cyanotype process, which became known as blueprints, and variations, such as the chrysotype. In 1839, he made a photograph on glass, which still exists, and experimented with some colour reproduction, noting that rays of different parts of the spectrum tended to impart their own colour to a photographic paper. Herschel made experiments using photosensitive emulsions of vegetable juices, called phytotypes, also known as anthotypes, and published his discoveries in the Philosophical Transactions of the Royal Society of London in 1842. He collaborated in the early 1840s with Henry Collen, portrait painter to Queen Victoria. Herschel originally discovered the platinum process on the basis of the light sensitivity of platinum salts, later developed by William Willis.
Herschel coined the term photography in 1839. Herschel was also the first to apply the terms negative and positive to photography.
Herschel discovered sodium thiosulfate to be a solvent of silver halides in 1819, and informed Talbot and Daguerre of his discovery that this "hyposulphite of soda" ("hypo") could be used as a photographic fixer, to "fix" pictures and make them permanent, after experimentally applying it thus in early 1839.
Herschel's ground-breaking research on the subject was read at the Royal Society in London in March 1839 and January 1840.
Other aspects of Herschel's career
Herschel wrote many papers and articles, including entries on meteorology, physical geography and the telescope for the eighth edition of the Encyclopædia Britannica. He also translated the Iliad of Homer.
In 1823, Herschel published his findings on the optical spectra of metal salts.
Herschel invented the actinometer in 1825 to measure the direct heating power of the Sun's rays, and his work with the instrument is of great importance in the early history of photochemistry.
Herschel proposed a correction to the Gregorian calendar, making years that are multiples of 4000 common years rather than leap years, thus reducing the average length of the calendar year from 365.2425 days to 365.24225. Although this is closer to the mean tropical year of 365.24219 days, his proposal has never been adopted because the Gregorian calendar is based on the mean time between vernal equinoxes (currently days).
Herschel was elected a Foreign Honorary Member of the American Academy of Arts and Sciences in 1832, and in 1836, a foreign member of the Royal Swedish Academy of Sciences.
In 1835, the New York Sun newspaper wrote a series of satiric articles that came to be known as the Great Moon Hoax, with statements falsely attributed to Herschel about his supposed discoveries of animals living on the Moon, including batlike winged humanoids.
Several locations are named for him: the village of Herschel in western Saskatchewan, Canada, site of the discovery of Dolichorhynchops herschelensis, a type of plesiosaur; Mount Herschel in Antarctica; the crater J. Herschel on the Moon; and the settlement of Herschel, Eastern Cape and the Herschel Girls' School in Cape Town, South Africa.
While it is commonly accepted that Herschel Island, in the Arctic Ocean, part of the Yukon Territory, was named after him, the entries in the expedition journal of Sir John Franklin state that the latter wished to honour the Herschel family, of which John Herschel's father, Sir William Herschel, and his aunt, Caroline Herschel, are as notable as John.
Family
Herschel married Margaret Brodie Stewart (1810–1884) on 3 March 1829 at St. Marlyebone Church in London, and was father of the following children:
Caroline Emilia Mary Herschel (31 March 1830 – 29 January 1909), who married the soldier and politician Alexander Hamilton-Gordon
Isabella Herschel (5 June 1831 – 1893)
Sir William James Herschel, 2nd Bt. (9 January 1833 – 1917),
Margaret Louisa Herschel (1834–1861), an accomplished artist
Alexander Stewart Herschel (1836–1907), FRS, FRAS
Col. John Herschel FRS, FRAS, (1837–1921) surveyor
Maria Sophia Herschel (1839–1929)
Amelia Herschel (1841–1926) married Sir Thomas Francis Wade, diplomat and sinologist
Julia Herschel (1842–1933) married on 4 June 1878 to Captain (later Admiral) John Fiot Lee Pearse Maclear
Matilda Rose Herschel (1844–1914), a gifted artist, married William Waterfield (Indian Civil Service)
Francisca Herschel (1846–1932)
Constance Anne Herschel (1855–20 June 1939), mathematician and scientist who became lecturer in natural sciences at Girton College, Cambridge
Death
Herschel died on 11 May 1871 at age 79 at Collingwood, his home near Hawkhurst in Kent. On his death, he was given a national funeral and buried in Westminster Abbey.
His obituary by Henry W Field of London was read to the American Philosophical Society on 1 December 1871.
Arms
Bibliography
In chronological order
,
(The Encyclopædia Metropolitana was published in 30 vols. from 1817–1845)
In Popular Culture
Sir John Herschel served as the basis for the character of the same name in the radio-musical series Pulp Musicals. Played by Curt Mega, the series features a highly fictionalized version of Herschel.
References
Works cited
Further reading
On Herschel's relationship with Charles Babbage, William Whewell, and Richard Jones, see
External links
Biographical information
R. Derek Wood (2008), 'Fourteenth March 1839, Herschel's Key to Photography'
Herschel Museum of Astronomy
Science in the Making Herschel's papers in the Royal Society's archives
Wikisource copy of a notice from 1823 concerning the star catalogue, published in Astronomische Nachrichten
1792 births
1871 deaths
19th-century English astronomers
Photographers from Buckinghamshire
19th-century English photographers
Alumni of St John's College, Cambridge
Baronets in the Baronetage of the United Kingdom
Burials at Westminster Abbey
English Christians
English people of German descent
Fellows of the American Academy of Arts and Sciences
Fellows of the Royal Astronomical Society
Fellows of the Royal Society
Honorary members of the Saint Petersburg Academy of Sciences
Masters of the Mint
Members of the Royal Swedish Academy of Sciences
People educated at Eton College
People from Slough
Pioneers of photography
Presidents of the Royal Astronomical Society
Proto-evolutionary biologists
Recipients of the Copley Medal
Recipients of the Gold Medal of the Royal Astronomical Society
Recipients of the Pour le Mérite (civil class)
Rectors of the University of Aberdeen
Royal Medal winners
Senior Wranglers
Spectroscopists
John
Recipients of the Lalande Prize
Translators of Homer
Wynberg, Cape Town | John Herschel | Physics,Chemistry,Biology | 3,176 |
70,571,059 | https://en.wikipedia.org/wiki/Azov%20Lubricants%20and%20Oils | Azov Lubricants and Oils (AZMOL British Petrochemicals) is a petrochemical company located in Berdiansk, Zaporizhzhia Oblast. Today AZMOL British Petrochemicals is the largest producer of lubricants in Ukraine.
Awards
Order of the Red Banner
See also
XADO
WD-40
Carl Bechem GmbH
References
Companies established in 1937
Recipients of the Order of the Red Banner
Berdiansk
Companies based in Zaporizhzhia Oblast
Petrochemical companies
Petrochemical industry
1937 in Ukraine
History of Zaporizhzhia Oblast | Azov Lubricants and Oils | Chemistry | 128 |
357,715 | https://en.wikipedia.org/wiki/The%20First%20%2420%20Million%20Is%20Always%20the%20Hardest | The First $20 Million Is Always the Hardest is a 2002 film based on the novel of the same name by technology-culture writer Po Bronson. The film stars Adam Garcia and Rosario Dawson. The screenplay was written by Jon Favreau and Gary Tieche.
Plot
Andy Kasper is a marketer who quits his job in search of something more fulfilling. He gets hired at LaHonda Research Institute, where Francis Benoit assigns him to design the PC99, a $99 PC. He moves into a run-down boarding house where he meets his neighbor Alisa, an artist. He puts together a team of unassigned LaHonda employees. The team includes: Salman Fard, a short, foreign man with an accent who is hacking into CIA files when Andy meets him; Curtis "Tiny" Russell, a massively obese, anthropophobic man; and Darrell, a tall, blond, pierced, scary, germaphobic, deep-voiced man with personal space issues who regularly refers to himself in the third person.
The team finds many non-essential parts but cannot come close to the $99 mark. It is Salman's idea to put all the software on the internet, eliminating the need for a hard drive, RAM, a CD-ROM drive, a floppy drive, and anything that holds information. The computer has been reduced to a microprocessor, a monitor, a mouse, a keyboard, and the internet, but it is still too expensive. Having seen the rest of his team watching a hologram of an attractive lady the day before, in a dream Andy is inspired to eliminate the monitor in favor of the cheaper holographic projector. The last few hundred dollars come off when Darrell suggests using virtual reality gloves in place of a mouse and keyboard. Tiny then writes a "hypnotizer" code to link the gloves, the projector, and the internet, and they're done.
But immediately before he finishes, the whole team (except for Tiny, who is still writing the code) quits LaHonda after being told that there are no more funds for their project, but sign a non-exclusive patent waiver, meaning that LaHonda will share the patent rights to any technology they had developed up to that point. After leaving LaHonda, they pitch their product to numerous companies, but do not get accepted, mainly because the prototype emagi (electronic magic) was ugly, and something always seemed to go wrong during the demonstration of their product.
Alisa, whose relationship with Andy has been growing steadily, helps improve the emagi's looks, which helps the team with their callback with executive. They agree to give her 51% of their company in exchange for getting their product manufactured and for getting Andy's Porsche bought back, which he had had to sell in order to raise money to build a new emagi after leaving LaHonda. Unfortunately, she then sells the patent rights to the emagi to Francis Benoit, who plans to sell the emagi at $999 a piece and reap a huge profit.
The team interrupts the meeting in which Benoit is going to introduce the emagi to the world and introduces an even newer computer he and his team developed and manufactured at LaHonda, which was in a state of disaster when they arrived. It was a small silver tube that projected a hologram and lasers which would detect where the hands were, eliminating the need even for virtual reality gloves. Andy then reminds Benoit of the non-exclusive patent waiver, which had been Benoit's idea in the first place.
Cast
Adam Garcia as Andy Kasper
Rosario Dawson as Alisa
Anjul Nigam as Salman Fard
Ethan Suplee as Curtis "Tiny" Russell
Jake Busey as Darrell
Enrico Colantoni as Francis Benoit
Gregory Jbara as Hank
Dan Butler as Lloyd
Linda Hart as Mrs. 'B'
Shiva Rose as Torso
Chandra West as Robin
Rob Benedict as Willy
Heather Paige Kent as Claudia Goss
John Rothman as Ben
Reggie Lee as Suit
Reception
Box office
Opening Weekend Gross was $2,535 (USA) (30 June 2002) (2 Screens (NY, LA)
The feature received limited release in New York and Los Angeles. Its domestic gross was just $5,491, making it one of the greatest flops in movie history.
Critical response
References
External links
The First $20 Million Is Always the Hardest at the AFI Catalog of Feature Films
The First $20 Million Is Always the Hardest at tcmdb
The First $20 Million Is Always the Hardest at Allmovie
The First $20 Million Is Always the Hardest at Metacritic
The First $20 Million Is Always the Hardest at Rotten Tomatoes
2002 films
Films about computing
2002 comedy films
American comedy films
Films set in the San Francisco Bay Area
Films shot in San Francisco
Films directed by Mick Jackson
Films with screenplays by Jon Favreau
2000s English-language films
2000s American films | The First $20 Million Is Always the Hardest | Technology | 1,004 |
29,482,098 | https://en.wikipedia.org/wiki/Comparison%20of%20IPv6%20support%20in%20operating%20systems | This is a comparison of operating systems in regard to their support of the IPv6 protocol.
Notes
Operating systems that support neither DHCPv6 nor SLAAC cannot automatically configure unicast IPv6 addresses.
Operating systems that support neither DHCPv6 nor ND RDNSS cannot automatically configure name servers in an IPv6-only environment.
References
External links
ISOC IPv6 FAQ with OS tips
IPv6
Computing comparisons
IPv6 support | Comparison of IPv6 support in operating systems | Technology | 103 |
56,608,953 | https://en.wikipedia.org/wiki/Floristic%20Quality%20Assessment | Floristic Quality Assessment (FQA) is a tool used in the United States to assess an area's ecological integrity based on its plant species composition. Floristic Quality Assessment was originally developed in order to assess the likelihood that impacts to an area "would be irreversible or irretrievable...to make standard comparisons among various open land areas, to set conservation priorities, and to monitor site management or restoration efforts." The concept was developed by Gerould Wilhelm in the 1970s in a report on the natural lands of Kane County, Illinois. In 1979 Wilhelm and Floyd Swink codified this "scoring system"
for the 22-county Chicago Region.
Coefficient of conservatism
Each plant species in a region is assigned a coefficient of conservatism, also known as a C-value, ranging between 0 and 10. A plant species with a higher score (e.g. 10) has a lower tolerance to environmental degradation such as overgrazing or development and therefore is naturally restricted to undisturbed, remnant habitats. Non-native plants are either assigned a C-value of 0 or are excluded from assessments. In the Chicago Region, 84% of the native plant species have a C-value of 4 or greater. Plants with a C-value of 4 or greater rarely naturally move from a remnant area to surrounding degraded land. For example, the federally endangered Dalea foliosa has a C-value of 10.
C-values are assigned within specific ecological and geographic regions by botanical experts familiar with the species' autecology within the respective regions. , there were more than 50 different FQA databases ranging from the Gulf Coastal Plain to western Washington, though most databases represented regions in the eastern and central United States and Canada.
The mean C-value () is calculated based on an inventory of plants. An area with a native mean C-value of 3.5 or higher likely has "sufficient floristic quality to be of at least marginal natural area quality." Remnant natural areas with mean C-values of 4.0 or greater are unmitigable.
Floristic Quality Index
The Floristic Quality Index (FQI, or Rating Index according to Swink and Wilhelm) is calculated by multiplying the mean C value by the square root of the total number of species:
For example, the FQI for Nelson Lake Marsh was 78 in 1994 and that for Russell R. Kirt Prairie was about 30 in 1999.
References
External links
Universal FQA
Biodiversity
Environmental conservation
Community ecology
Measurement of biodiversity
Index numbers
Summary statistics for categorical data | Floristic Quality Assessment | Mathematics,Biology | 528 |
63,771,242 | https://en.wikipedia.org/wiki/Bamfordvirae | Bamfordvirae is a kingdom of viruses. This kingdom is recognized for its use of double jelly roll major capsid proteins. It was formerly known as the PRD1-adenovirus lineage. The kingdom is named after Dennis H. Bamford who first promoted the evolutionary unity of all viruses encoding double jelly-roll major capsid proteins.
Taxonomy
Source:
The following phyla are recognized:
Nucleocytoviricota
Preplasmiviricota
There also exists an unassigned family:
Yaraviridae
References | Bamfordvirae | Biology | 110 |
47,684,045 | https://en.wikipedia.org/wiki/Dihydrotanshinone%20I | Dihydrotanshinone I (DI) is a naturally occurring compound extracted from Salvia miltiorrhiza Bunge, also known as Chinese sage, red sage root, and the Chinese herbal Dan Shen. It belongs to a class of lipophilic abietane diterpenoids and has been reported to have cytotoxicity to a variety of tumor cells, as well as antiviral effects in vitro. Since they were first discovered, over 40 related compounds and over 50 hydrophilic compounds have been isolated from Dan Shen.
References
Diketones | Dihydrotanshinone I | Chemistry | 120 |
51,255,248 | https://en.wikipedia.org/wiki/Cyclododecanone | Cyclododecanone is an organic compound with the formula (CH2)11CO. It is a cyclic ketone that exists as a white solid at room temperature. Like its smaller analogs but unlike the larger ones, it has a camphor-like odor.
History and synthesis
It was first obtained by Ružička et al. in 1926 by ketonic decarboxylation. A higher-yield method by acyloin condensation was devised by Prelog et al. in 1947.
It is now industrially produced by the oxidation of cyclododecane via cyclododecanol.
Uses
Cyclododecanone is oxidized on an industrial scale to give the corresponding dicarboxylic acid 1,12-dodecanedioic acid and laurolactam, which are precursors to certain specialized nylons. It is also precursor to cyclohexadecanone, which is used in some fragrances.
Hydrazone formation with pimagedine leads to a hypoglycemic formula. Notice that the shape of the molecule can be made to appear like a pharmacy cross symbol.
References
Perfume ingredients
Macrocycles
Mammalian pheromones
Cycloalkanones
Twelve-membered rings | Cyclododecanone | Chemistry | 260 |
1,476,870 | https://en.wikipedia.org/wiki/ShmooCon | ShmooCon was an American hacker convention organized by The Shmoo Group. There were typically 40 different talks and presentations on a variety of subjects related to computer security and cyberculture. Multiple events were held at the convention related to cryptography and computer security such as Shmooganography, Hack Fortress, a locksport village hosted by TOOOL DC, and Ghost in the Shellcode.
Venues, dates, and attendance
Each conference venue and date has been included for easy reference.
Research presented at ShmooCon
ShmooCon seeks to select talks that are original research and have not been presented at other conventions.
Charitable efforts
Every year ShmooCon supported multiple charities, such as the Electronic Frontier Foundation and Hackers for Charity, by sponsoring T-shirt sales. Attendees were provided the opportunity to donate a fixed amount of money for a charity in exchange for a T-shirt. ShmooCon also had a long-standing program, Shmooze-A-Student, where attendees could opt to cover an undergraduate college student's ticket fee and stipend when purchasing their own ticket.
References
External links
ShmooCon website
ShmooCon "find a room" mailing list
Hacker conventions
Recurring events established in 2005 | ShmooCon | Technology | 253 |
30,708,936 | https://en.wikipedia.org/wiki/Chromium%20acetate%20hydroxide | Chromium acetate hydroxide is the coordination complex with the formula [Cr2(OH)3(OAc)3]4. A dark violet solid, it crystallizes as the triacontatetrahydrate (34 molecules of water of crystallization). It is water soluble.
Structure
The complex is a tetramer of binuclear Cr2(OH)3(OAc)3. The subunits are linked by acetate and hydroxide ligands. The oxidation state of chromium is III, which explains the stability of the complex since octahedral d3 ions give kinetically robust complexes. Overall, the complex's structure is unusual compared to other transition metal carboxylate complexes.
See also
Chromium(II) acetate
Chromium(III) acetate
References
External links
http://www.chemicalbook.com/ChemicalProductProperty_EN_CB9726110.htm
http://www.chemicalbook.com/CAS%5Cmol%5C39430-51-8.mol
https://web.archive.org/web/20120119193658/http://www.sigmaaldrich.com/catalog/ProductDetail.do?D7=0&N5=SEARCH_CONCAT_PNO%7CBRAND_KEY&N4=318108%7CALDRICH&N25=0&QS=ON&F=SPEC
Chromium(III) compounds
Acetates
Hydroxides
Coordination complexes
Reducing agents
Chromium–oxygen compounds | Chromium acetate hydroxide | Chemistry | 342 |
72,486,551 | https://en.wikipedia.org/wiki/Amanita%20betulae | Amanita betulae is a species of Amanita found in growing in birch and mixed hardwood in Europe
References
External links
betulae
Fungi of Europe
Fungi described in 2009
Fungus species | Amanita betulae | Biology | 40 |
3,235,310 | https://en.wikipedia.org/wiki/Panic%20buying | Panic buying (alternatively hyphenated as panic-buying; also known as panic purchasing) occurs when consumers buy unusually large amounts of a product in anticipation of, or after, a disaster or perceived disaster, or in anticipation of a large price increase, or shortage.
Panic buying during various health crises is influenced by "(1) individuals' perception of the threat of a health crisis and scarcity of products; (2) fear of the unknown, which is caused by emotional pressure and uncertainty; (3) coping behaviour, which views panic buying as a venue to relieve anxiety and regain control over the crisis; and (4) social psychological factors, which account for the influence of the social network of an individual".
Panic buying is a type of herd behavior. It is of interest in consumer behavior theory, the broad field of economic study dealing with explanations for "collective action such as fads and fashions, stock market movements, runs on nondurable goods, buying sprees, hoarding, and banking panics".
Panic buying can lead to genuine shortages regardless of whether the risk of a shortage is real or perceived without merit; the latter scenario is an example of self-fulfilling prophecy.
Examples
Panic buying occurred before, during, or following:
The First (1914–1918) and Second World Wars (1939–1945).
The 1918–1919 global influenza pandemic ("Spanish flu") led to the panic buying of quinine and other remedies for influenza and its symptoms from pharmacists and doctors' surgeries. Sales of Vicks VapoRub increased from $900,000 to $2.9 million in a year.
In the First Austrian Republic in 1922, hyperinflation and the rapid depreciation of the Austrian krone led to panic buying and food hoarding, which continued until a rescue backed by the League of Nations prevented an economic collapse.
Bengal famine of 1943.
1962 Cuban Missile Crisis led to panic buying of canned foods in the United States.
The 1973 toilet paper panic in the United States.
The 1979 oil crisis led to panic buying of oil, led by Japan.
The 1985 arrival of New Coke led many consumers to panic buy the original Coke.
Year 2000 problem – food.
2001 – panic buying of metals, gold and oil on international commodity markets following the September 11 attacks.
Between January and February 2003, during the SARS outbreak, several rounds of panic buying of various products (including salt, rice, vinegar, vegetable oil, antibiotics, face masks, and traditional Chinese medicine) took place in the Chinese province of Guangdong and in neighboring areas such as Hainan and Hong Kong.
2000 and 2005 UK fuel protests.
2005 Jilin chemical plant explosions – water, food.
2008–2016 United States ammunition shortage – panic buying by gun owners who feared tougher gun control laws under President Barack Obama was one cause of ammunition shortages.
In September 2013 during the Venezuelan economic crisis, the Venezuelan government temporarily took over the Aragua-based Paper Manufacturing Company toilet paper plant to manage the "production, marketing and distribution" of toilet paper following months of depleted stocks of basic goods—including toilet paper—and foodstuffs, such as rice and cooking oil. Blame for the shortages was placed on "ill-conceived government policies such as price controls on basic goods and tight restrictions on foreign currency" and hoarding.
Dakazo – Amid decreased support before the 2013 Venezuelan municipal elections, Venezuelan president Nicolás Maduro announced the military occupation of stores on 8 November 2013, proclaiming "Leave nothing on the shelves!" The announcement of lowered prices sparked looting in multiple cities across Venezuela. By the end of the Dakazo, many Venezuelan stores were left empty of their goods. A year later in November 2014, some stores still remained empty following the Dakazo.
In September 2021, panic buying of petrol led to empty fuel filling stations across the United Kingdom. A lack of tanker drivers was blamed, with Brexit being the primary cause according to most Road Haulage Association respondents.
In November 2021, panic buying of groceries took place in the British Columbia Interior and Fraser Valley owing to the impacts of the 2021 Pacific Northwest floods.
On March 3, 2022, panic buying of IKEA kit furniture and home appliances occurred in Russia due to the company's decision to close their 17 Russian stores in light of the 2022 Russian invasion of Ukraine. Extensive queues were reported in IKEA's Moscow and Saint Petersburg stores, and customers attempted to enter from the exit doors when entrance doors were closed.
In May 2023, the Malaysian states of Penang and Kedah experienced panic buying of bottled water due to an interruption in tap water supply lasting less than 24 hours.
In August 2023, after the discharge of radioactive water of the Fukushima Daiichi Nuclear Power Plant, people in China began panic buying salt and radiation detectors because of the public anxiety towards the radioactive water released. Consumers in South Korea also began hoarding salt and seafood.
In August 2024, Japanese consumers began panic buying rice due to supply shortages, megaquake warnings, and typhoons.
In October 2024, American consumers purchased large quantities of toilet paper and paper towels during the 2024 United States port strike, despite these products not being among those affected by labor action. At the end of the same month, due to the Spanish floods, water bottles and other products ran out in the supermarkets Mercadona and Consum, in Valencia.
In December 2024, after Yoon Suk Yeol, the president of South Korea, declared martial law, South Korean consumers began panic buying food, water, and other essential goods.
COVID-19 pandemic
Panic buying became a major international phenomenon between February and March 2020 during the early onset of the COVID-19 pandemic, and continued in smaller, more localized waves throughout during sporadic lockdowns across the world. Stores around the world were depleted of items such as face masks, food, bottled water, milk, toilet paper, hand sanitizer, rubbing alcohol, antibacterial wipes and painkillers. As a result, many retailers rationed the sale of these items.
Online retailers such as eBay and Amazon began to pull certain items listed for sale by third parties such as toilet paper, face masks, pasta, canned vegetables, hand sanitizer and antibacterial wipes over price gouging concerns. As a result, Amazon restricted the sale of these items and others (such as thermometers and ventilators) to healthcare professionals and government agencies. Additionally, panic renting of self-storage units took place during the onset of the pandemic.
The massive buyouts of toilet paper caused bewilderment and confusion from the public. Images of empty shelves of toilet paper were shared on social media in many countries around the world, e.g. Australia, United States, the United Kingdom, Canada, Singapore, Hong Kong and Japan. In Australia, two women were charged over a physical altercation over toilet paper at a supermarket. The severity of the panic buying drew criticism; particularly from Prime Minister of Australia Scott Morrison, calling for Australians to "stop it".
Research on this specific social phenomenon of toilet paper hoarding suggested that social media had played a crucial role in stimulating mass-anxiety and panic. Social media research found that many people posting about toilet paper panic buying were negative, either expressing anger or frustration over the frantic situation. This high amount of negative viral posts could act as an emotional trigger of anxiety and panic, spontaneously spreading fear and fueling psychological reactions in midst of the crisis. It may have triggered a snowball effect in the public, encouraged by the images and videos of empty shelves and people fighting over toilet rolls.
Gallery
See also
Panic selling
Revenge buying
Stock market crash
Economic bubble
Mass hysteria
Hoarding
Panic room
References
Financial problems
Investment
Consumer behaviour
Scarcity | Panic buying | Biology | 1,594 |
59,020,460 | https://en.wikipedia.org/wiki/Leontovich%20boundary%20condition | The Shchukin-Leontovich boundary condition is a boundary condition in classical electrodynamics that relates to the tangential components of the electric Et and magnetic Ht fields on the surface of well-conducting bodies.
Definition
As originally formulated by Soviet physicists Alexander Shchukin and Mikhail Leontovich, the boundary condition is given as
where and represent the tangential components of the electric and magnetic fields, is the effective surface impedance, and is a unit normal pointing into the conducting material. This condition is accurate when the conductivity of the conductor is large, which is the case for most metals. More generally, for cases when the radii of curvature of the conducting surface is large with respect to the skin depth, the resulting fields on the interior can be well approximated by plane waves, thus giving rise to the Shchukin-Leontovitch condition. A generalization of the Shchukin-Leontovich impedance boundary condition for a flat surface of a uniform half-space with an arbitrary dielectric constant, presented as a one-sided non-local relation, was formulated in.
Applications
The Shchukin-Leontovich boundary condition is useful in many scattering problems where one material is a metal with large (but finite) conductivity. As the condition provides a relationship between the electric and magnetic fields at the surface of the conductor, without knowledge of the fields within, the task of finding the total fields is considerably simplified.
References
Boundary conditions
Electrodynamics | Leontovich boundary condition | Materials_science,Mathematics | 304 |
28,802,840 | https://en.wikipedia.org/wiki/Cantharellus%20californicus | Cantharellus californicus, also called the California golden chanterelle, mud puppy, or oak chanterelle, is a fungus native to California, United States. It is a member of the genus Cantharellus along with other popular edible chanterelles. It is generally similar in appearance to C. cibarius and C. formosus except for its large size at maturity.
Description
The pileus (cap) of C. californicus is wide, exceptionally , and yellow-orange in color (although adhering leaf litter may cause a mottled color); it may become brownish with age. The hymenium is folded into decurrent ridges (false gills) and cross-veins, which deepen with age. The color of these ridges is usually similar to the cap but paler. The stipe (stem) is long and wide, with coloration similar to the hymenium. The spores are creamy yellow, elliptical, and smooth.
individual specimens up to are reported, making it the largest-known species of chanterelle. Their unusual size is due in part to their capacity for indeterminate growth, making C. californicus specimens actively grow for far longer than most other mushrooms.
Similar species
Several other species of chanterelle may be found in western North America:
C. cascadensis – bright yellow fading to white in center of cap, associated with conifers
C. cibarius var. roseocanus – false gills tend to be as dark or darker than cap
C. formosus – smaller size, narrower stem, associated with conifers
C. subalbidus – whitish overall color
Additionally, Hygrophoropsis aurantiaca, Chroogomphus tomentosus, and species in the genera Craterellus, Gomphus, Omphalotus, and Polyozellus may have a somewhat similar appearance to C. californicus. Omphalotus olivascens, the western jack-o'-lantern mushroom, is poisonous and has been mistaken for chanterelles.
Distribution and habitat
Cantharellus californicus forms a mycorrhizal association with oaks, particularly coast live oak in the woodlands of Coastal California. It has also been found in association with interior live oak, California black oak, canyon live oak, tanoak, and possibly Pacific madrone and manzanita. C. californicus is a popular wild edible in the San Francisco Bay Area, and is most common between November and April.
In culture
It became the official state mushroom of California in 2024.
References
External links
californicus
Edible fungi of California
Fungi described in 2008
Fungi without expected TNC conservation status
Fungus species
Mycorrhizal associates of oaks
Symbols of California | Cantharellus californicus | Biology | 572 |
61,159,333 | https://en.wikipedia.org/wiki/Warming%20stripes | Warming stripes (sometimes referred to as climate stripes, climate timelines or stripe graphics) are data visualization graphics that use a series of coloured stripes chronologically ordered to visually portray long-term temperature trends. Warming stripes reflect a "minimalist" style, conceived to use colour alone to avoid technical distractions to intuitively convey global warming trends to non-scientists.
The initial concept of visualizing historical temperature data has been extended to involve animation, to visualize sea level rise and predictive climate data, and to visually juxtapose temperature trends with other data such as atmospheric concentration, global glacier retreat, precipitation, progression of ocean depths, aviation emission's percentage contribution to global warming, biodiversity loss, soil moisture deviations, and fine particulate matter concentrations. In less technical contexts, the graphics have been embraced by climate activists, used as cover images of books and magazines, used in fashion design, projected onto natural landmarks, and used on athletic team uniforms, music festival stages, and public infrastructure.
Background, publication and content
In May 2016, to make visualizing climate change easier for the general public, University of Reading climate scientist Ed Hawkins created an animated spiral graphic of global temperature change as a function of time, a representation said to have gone viral. Jason Samenow wrote in The Washington Post that the spiral graph was "the most compelling global warming visualization ever made", before it was featured in the opening ceremony of the 2016 Summer Olympics.
Separately, by 10 June 2017, Ellie Highwood, also a climate scientist at the University of Reading, had completed a crocheted "global warming blanket" that was inspired by "temperature blankets" representing temperature trends in respective localities. Hawkins provided Highwood with a more user friendly colour scale to avoid the muted colour differences present in Highwood's blanket. Independently, in November 2015, University of Georgia estuarine scientist Joan Sheldon made a "globally warm scarf" having 400 blue, red and purple rows, but could not contact Hawkins until 2022. Both Highwood and Sheldon credit as their original inspirations, "sky blankets" and "sky scarves" which are based on daily sky colours.
On 22 May 2018, Hawkins published graphics constituting a chronologically ordered series of blue and red vertical stripes that he called warming stripes. Hawkins, a lead author for the IPCC 6th Assessment Report, received the Royal Society's 2018 Kavli Medal, in part "for actively communicating climate science and its various implications with broad audiences".
As described in a BBC article, in the month the big meteorological agencies release their annual climate assessments, Hawkins experimented with different ways of rendering the global data and "chanced upon the coloured stripes idea". When he tried out a banner at the Hay Festival, according to the article, Hawkins "knew he'd struck a chord". The National Centre for Atmospheric Science (UK), with which Hawkins is affiliated, states that the stripes "paint a picture of our changing climate in a compelling way. Hawkins swapped out numerical data points for colours which we intuitively react to".
Others have called Hawkins' warming stripes "climate stripes" or "climate timelines".
Warming stripe graphics are reminiscent of colour field painting, a style prominent in the mid 20th century, which strips out all distractions and uses only colour to convey meaning. Colour field pioneer artist Barnett Newman said he was "creating images whose reality is self-evident", an ethos that Hawkins is said to have applied to the problem of climate change.
Collaborating with Berkeley Earth scientist Robert Rohde, on 17 June 2019 Hawkins published for public use, a large set of warming stripes on ShowYourStripes.info. Individualized warming stripe graphics were published for the globe, for most countries, as well as for certain smaller regions such as states in the US or parts of the UK, since different parts of the world are warming more quickly than others.
Data sources and data visualization
Warming stripe graphics are defined with various parameters, including:
source of dataset (meteorological organization)
geographical scope of measurement (global, country, state, etc.)
time period (year range, for horizontal "axis")
temperature range (range of anomaly (deviation) about a reference or baseline temperature)
colour palette (usually, shades of blue and red),
colour scale (assignment of colours to represent respective ranges of temperature anomaly),
temperature boundaries (temperature above which a stripe is red and below which is blue, usually determined by an average annual temperature over a "reference period" or "baseline" of usually 30 years).
Hawkins' original graphics use the eight most saturated blues and reds from the ColorBrewer 9-class single hue palettes, which optimize colour palettes for maps and are noted for their colourblind-friendliness. Hawkins said the specific colour choice was an aesthetic decision ("I think they look just right"), also selecting baseline periods to ensure equally dark shades of blue and red for aesthetic balance. Hawkins chose the 1971-2000 average as a boundary between reds and blues because the average global temperature in that reference period represented the mid-point in the warming to date.
A Republik analysis said that "this graphic explains everything in the blink of an eye", attributing its effect mainly to the chosen colors, which "have a magical effect on our brain, (letting) us recognize connections before we have even actively thought about them". The analysis concluded that colors other than blue and red "don't convey the same urgency as (Hawkins') original graphic, in which the colors were used in the classic way: blue=cold, red=warm."
ShowYourStripes.info cites dataset sources Berkeley Earth, NOAA, UK Met Office, MeteoSwiss, DWD (Germany), specifically explaining that the data for most countries comes from the Berkeley Earth temperature dataset, except that for the US, UK, Switzerland & Germany the data comes from respective national meteorological agencies.
For each country-level #ShowYourStripes graphic (Hawkins, June 2019), the average temperature in the 1971–2000 reference period is set as the boundary between blue (cooler) and red (warmer) colours, the colour scale varying +/- 2.6 standard deviations of the annual average temperatures between 1901 and 2000. Hawkins noted in 2019 that the graphic for the Arctic "broke the colour scale" since it is warming more than twice as fast as the global average, and reported that the 2023 global average was so extreme that a new, darker shade of red was required.
For statistical and geographic reasons, it is expected that graphics for small areas will show more year-to-year variation than those for large regions. Year-to-year changes reflected in graphics for localities result from weather variability, whereas global warming over centuries reflects climate change.
The NOAA website warns that the graphics "shouldn't be used to compare the rate of change at one location to another", explaining that "the highest and lowest values on the colour scale may be different at different locations". Further, a certain colour in one graphic will not necessarily correspond to the same temperature in other graphics.
A climate change denier generated a warming stripes graphic that misleadingly affixed Northern Hemisphere readings over one period to global readings over another period, and omitted readings for the most recent thirteen years, with some of the data being 29-year-smoothed—to give the false impression that recent warming is routine. Calling the graphic "imposter warming stripes", meteorologist Jeff Berardelli described it in January 2020 as "a mishmash of data riddled with gaps and inconsistencies" with an apparent objective to confuse the public.
Applications and influence
After Hawkins' first publication of warming stripe graphics in May 2018, broadcast meteorologists in multiple countries began to show stripe-decorated neckties, necklaces, pins and coffee mugs on-air, reflecting a growing acceptance of climate science among meteorologists and a willingness to communicate it to audiences. In 2019, the United States House Select Committee on the Climate Crisis used warming stripes in its committee logo, showing horizontally oriented stripes behind a silhouette of the United States Capitol, and three US Senators wore warming stripe lapel pins at the 2020 State of the Union Address.
On 17 June 2019, Hawkins initiated a social media campaign with hashtag #ShowYourStripes that encourages people to download their regions' graphics from ShowYourStripes.info, and to post them. The campaign was backed by U.N. Climate Change, the World Meteorological Organization and the Intergovernmental Panel on Climate Change. Called "a new symbol for the climate emergency" by French magazine L'EDN, the graphics have been embraced by climate activists, used as cover images of books and magazines, used in fashion design, projected onto natural landmarks, and used on athletic team uniforms, music festival stages, and public infrastructure. More specifically, warming stripes have been applied to knit-it-yourself scarves, a vase, neckties, cufflinks, bath towels, vehicles, and a music festival stage, as well as on the side of Freiburg, Germany, streetcars, as municipal murals in Córdoba, Spain, Anchorage, Alaska, and Jersey, on face masks during the COVID-19 pandemic, in an action logo of the German soccer club 1. FSV Mainz 05, on the side of the Climate Change Observatory in Valencia, on the side of a power station turbine house in Reading, Berkshire, on tech-themed shirts, on designer dresses, on the uniforms of Reading Football Club, on Leipzig's Sachsen Bridge, on a biomethane-powered bus, as a stage backdrop at the 2022 Glastonbury Festival, on the racer uniforms and socks and webpage banner of the Climate Classic bicycle race, on the World Bank's Climate Explainer Series, projected onto the White Cliffs of Dover, on an Envision Racing electric race car, and on numerous bridges and towers noted by Climate Central. Remarking that "infiltrating popular culture is a means of triggering a change of attitude that will lead to mass action", Hawkins surmised that making the graphics available for free has made them used more widely. Hawkins further said that any merchandise-related profits are donated to charity.
Through a campaign led by nonprofit Climate Central using hashtag #MetsUnite, more than 100 TV meteorologists—the scientists most laymen interact with more than any other—featured warming stripes and used the graphics to focus audience attention during broadcasts on summer solstices beginning in 2018 with the "Stripes for the Solstice" effort.
On 24 June 2019, Hawkins tweeted that nearly a million stripe graphics had been downloaded by visitors from more than 180 countries in the course of their first week.
In 2018, the German Weather Service's meteorological training journal Promet showed a warming stripes graphic on the cover of the issue titled "Climate Communication". By September 2019, the Met Office, the UK's national weather service, was using both a climate spiral and a warming stripe graphic on its "What is climate change?" webpage. Concurrently, the cover of the 21–27 September 2019 issue of The Economist, dedicated to "The climate issue," showed a warming stripe graphic, as did the cover of The Guardian on the morning of the 20 September 2019 climate strikes. The environmental initiative Scientists for Future (2019) included warming stripes in its logo. The Science Information Service (Germany) noted in December 2019 that warming stripes were a "frequently used motif" in demonstrations by the School strike for the climate and Scientists for Future, and were also on the roof of the German Maritime Museum in Bremerhaven. Also in December 2019, Voilà Information Design said that warming stripes "have replaced the polar bear on a melting iceberg as the icon of the climate crisis".
On 18 January 2020, a 20-metre-wide artistic light-show installation of warming stripes was opened at the Gendarmenmarkt in Berlin, with the Berlin-Brandenburg Academy of Sciences building being illuminated in the same way. The cover of the "Climate Issue" (fall 2020) of the Space Science and Engineering Center's Through the Atmosphere journal was a warming stripes graphic, and in June 2021 the WMO used warming stripes to "show climate change is here and now" in its statement that "2021 is a make-or-break year for climate action". The November 2021 UN Climate Change Conference (COP26) exhibited an immersive "climate canopy" sculpture consisting of hanging, blue and red color-coded, vertical lighted bars with fabric fringes.
On 27 September 2019, the Fachhochschule (University of Applied Science) Potsdam announced that warming stripes graphics had won in the science category of an international competition recognising innovative and understandable visualisations of climate change, the jury stating that the graphics make an "impact through their innovative, minimalist design".
Hawkins was appointed Member of the Order of the British Empire (MBE) in the 2020 New Year Honours "For services to Climate Science and to Science Communication".
In April 2022, textiles from haute couture fashion designer Lucy Tammam with warming stripes won the Best Customer Engagement Campaign title in the Sustainable Fashion 2022 awards by Drapers fashion magazine.
In October 2022, the front cover of Greta Thunberg's The Climate Book features warming stripes.
In May 2024, Hawkins received the Royal Geographical Society's Geographical Engagement Award for his work in developing warming stripes.
Extensions of warming stripes
In 2018, University of Reading post-doctoral research assistant Emanuele Bevacqua juxtaposed vertical-stripe graphics for concentration and for average global temperature (August), and "circular warming stripes" depicting average global temperature with concentric coloured rings (November).
In March 2019, German engineer Alexander Radtke extended Hawkins' historical graphics to show predictions of future warming through the year 2200, a graphic that one commentator described as making the future "a lot more visceral". Radtke bifurcated the graphic to show diverging predictions for different degrees of human action in reducing greenhouse gas emissions.
On or before 30 May 2019, UK-based software engineer Kevin Pluck designed animated warming stripes that portray the unfolding of the temperature increase, allowing viewers to experience the change from an earlier stable climate to recent rapid warming.
By June 2019, Hawkins vertically stacked hundreds of warming stripe graphics from corresponding world locations and grouped them by continent to form a comprehensive, composite graphic, "Temperature Changes Around the World (1901–2018)".
On 1 July 2019, Durham University geography research fellow Richard Selwyn Jones published a Global Glacier Change graphic, modeled after and credited as being inspired by Hawkins' #ShowYourStripes graphics, allowing global warming and global glacier retreat to be visually juxtaposed. Jones followed on 8 July 2019 with a stripe graphic portraying global sea level change using only shades of blue. Separately, NOAA displayed a graphic juxtaposing annual temperatures and precipitation, researchers from the Netherlands used stripe graphics to represent progression of ocean depths, and the Institute of Physics used applied the graphic to represent aviation emission's percentage contribution to global warming.
In 2023, University of Derby professor Miles Richardson created sequenced stripes to illustrate biodiversity loss, and the German Meteorological Service represented soil moisture deviations using sequenced green and brown stripes. In August 2024, the website airqualitystripes.info published shareable "air quality stripes" graphics for world cities, using blue, yellow, orange, red and black stripes to represent fine particulate matter (PM2.5) concentrations over time.
Critical response
Some warned that warming stripes of individual countries or states, taken out of context, could advance the idea that global temperatures are not rising, though research meteorologist J. Marshall Shepherd said that "geographic variations in the graphics offer an outstanding science communication opportunity". Meteorologist and #MetsUnite coordinator Jeff Berardelli said that "local stripe visuals help us tell a nuanced story—the climate is not changing uniformly everywhere".
Others say the charts should include axes or legends, though the website FAQ page explains the graphics were "specifically designed to be as simple as possible, and to start conversations... (to) fill a gap and enable communication with minimal scientific knowledge required to understand their meaning". J. Marshall Shepherd, former president of the American Meteorological Society, lauded Hawkins' approach, writing that "it is important not to miss the bigger picture. Science communication to the public has to be different" and commending Hawkins for his "innovative" approach and "outstanding science communication" effort.
In The Washington Post, Matthew Cappucci wrote that the "simple graphics ... leave a striking visual impression" and are "an easily accessible way to convey an alarming trend", adding that "warming tendencies are plain as day". Greenpeace spokesman Graham Thompson remarked that the graphics are "like a really well-designed logo while still being an accurate representation of very important data".
CBS News contributor Jeff Berardelli noted that the graphics "aren't based on future projections or model assumptions" in the context of stating that "science is not left or right. It's simply factual."
A September 2019 editorial in The Economist hypothesized that "to represent this span of human history (1850–2018) as a set of simple stripes may seem reductive"—noting those years "saw world wars, technological innovation, trade on an unprecedented scale and a staggering creation of wealth"—but concluded that "those complex histories and the simplifying stripes share a common cause," namely, fossil fuel combustion.
Informally, warming stripes have been said to resemble "tie-dyed bar codes" and a "work of art in a gallery".
See also
Climate change art
Climate communication
Color field
Craftivism
Data and information visualization
Environmental communication
Instrumental temperature record
Scientific consensus on climate change
The Tempestry Project
Notes
References
Further reading
— clickable map of warming stripes for each county in 48 contiguous US states
— Survey of climate change visualizations
External links
ShowYourStripes.info — warming stripes portraying historical data for multiple locations
Climate change in art
Climate communication
Climatology
Climate and weather statistics
Scientific visualization
Data and information visualization | Warming stripes | Physics | 3,738 |
1,573,097 | https://en.wikipedia.org/wiki/Dimethoxyethane | Dimethoxyethane, also known as glyme, monoglyme, dimethyl glycol, ethylene glycol dimethyl ether, dimethyl cellosolve, and DME, is a colorless, aprotic, and liquid ether that is used as a solvent, especially in batteries. Dimethoxyethane is miscible with water.
Production
Monoglyme is produced industrially by the reaction of dimethylether with ethylene oxide:
CH3OCH3 + CH2CH2O → CH3OCH2CH2OCH3
Applications as solvent and ligand
Together with a high-permittivity solvent (e.g. propylene carbonate), dimethoxyethane is used as the low-viscosity component of the solvent for electrolytes of lithium batteries. In the laboratory, DME is used as a coordinating solvent.
Dimethoxyethane is often used as a higher-boiling-point alternative to diethyl ether and tetrahydrofuran. Dimethoxyethane acts as a bidentate ligand for some metal cations. It is therefore often used in organometallic chemistry. Grignard reactions and hydride reductions are typical application. It is also suitable for palladium-catalyzed reactions including Suzuki reactions and Stille couplings. Dimethoxyethane is also a good solvent for oligo- and polysaccharides.
Sodium naphthalide dissolved in dimethoxyethane is used as a PTFE etching solution that removes fluorine atoms from the surface, which get replaced by oxygen, hydrogen, and water. This physically etches the surface as well to prepare the surface for better adhesion.
References
External links
Clariant Glymes Homepage www.glymes.com
1,2-Dimethoxyethane - chemical product info: properties, production, applications.
International Chemical Safety Card 1568
Chemical hazard links
Glycol ethers
Ether solvents
Ligands
Hazardous air pollutants | Dimethoxyethane | Chemistry | 430 |
48,009,311 | https://en.wikipedia.org/wiki/Coprococcus | Coprococcus is a genus of anaerobic cocci which are part of the human faecal microbiota. Despite the depletion of Coprococcus was found in colon cancer, there is no evidence for its protective role against colon cancer .
Three species have been described:
Coprococcus catus Holdeman and Moore 1974
Coprococcus comes Holdeman and Moore 1974
Coprococcus eutactus Holdeman and Moore 1974
C. comes may seem to play a role in cases of resistance against blood pressure medicine.
Etymology
'kopros' - excrement, faeces; 'kokkos' - berry; 'Coprococcus' - faecal coccus
References
Gut flora bacteria
Lachnospiraceae
Bacteria genera | Coprococcus | Biology | 157 |
61,950,060 | https://en.wikipedia.org/wiki/KaVo%20Kerr | KaVo Kerr was a dental equipment manufacturer group that was sold formerly to Envista. The group stemmed from a joint venture set up in 2016 between KaVo (KaVo Dental GmbH), which was established in 1909 in Berlin, Germany, and Kerr Corporation, which was founded in 1891 in Detroit, Michigan, as well as a division of Danaher Corporation headquartered in Brea, California.
In December 2019, Danaher spun off its dental segment into an independent publicly-traded company - Envista Holdings Corporation. Envista will employ 12,000 people worldwide.
History
Kerr
Kerr was established in 1891 in Detroit, Michigan by brothers Robert and John Kerr as The Detroit Dental Manufacturing Company and started to offer its products and services to the European market in 1893. The company officially changed its name to The KERR Manufacturing Company in 1939.
The company established its first factory in Europe in Scafati, Italy in 1959. Kerr acquired part of the McShirley line of products in 1971. Later in 1978, the Sybron Dental Product Division was formed.
In 2001, Kerr acquired Hawe Neos company in the aim of enhancing its offer of prophylaxis consumables. In 2006, Kerr became part of Danaher Corporation. In 2014, Kerr acquired DUX Dental and Vettec Inc. In 2015, Total Care, Axis SybronEndo and Kerr reorganized into a unilateral organization: Kerr Dental.
KaVo
KaVo was established in 1909 in Berlin, Germany by Alois Kaltenbach as KaVo Dental GmbH. By 1919, Richard Voigt joined the Kavo and the number of the employees expanded to 300 by 1939. In 1946, the headquarters were moved from Potsdam to the Upper Swabian town of Biberach an der Riss. In 1959, the company opened a dental technology factory in Leutkirch. In 2004, it was purchased by Danaher Corporation. In the same year, KaVo acquired Gendex. In 2005, KaVo acquired Pelton & Crane, a dental operatory equipment manufacturer with a 100-year history in North America, and joined the KaVo Kerr family along with DEXIS. In 2007, i-CAT was acquired by Kavo, formerly Soredex imaging brands in 2009. In 2012, Aribex, which is best known for the NOMAD handheld and portable X-ray systems, was acquired by KaVo Dental Group.
In September 2021, Envista announced that KaVo will be sold to Planmeca for $455 million.
See also
PaloDEx
:de:KaVo Dental (German)
References
External links
Official website
Danaher Corporation
Dental companies of the United States
Companies based in Brea, California | KaVo Kerr | Biology | 550 |
23,857,440 | https://en.wikipedia.org/wiki/STAAD | STAAD or (STAAD.Pro) is a structural analysis and design software application originally developed by Research Engineers International (REI) in 1997. In late 2005, Research Engineers International was bought by Bentley Systems. STAAD stands for STructural Analysis And Design.
STAAD.Pro is one of the most widely used structural analysis and design software products worldwide. It can apply more than 90 international steel, concrete, timber and aluminium design codes.
It can make use of various forms of analysis from the traditional static analysis to more recent analysis methods like p-delta analysis, geometric non-linear analysis, Pushover analysis (Static-Non Linear Analysis) or a buckling analysis. It can also make use of various forms of dynamic analysis methods from time history analysis to response spectrum analysis. The response spectrum analysis feature is supported for both user defined spectra as well as a number of international code specified spectra.
Additionally, STAAD.Pro is interoperable with applications such as RAM Connection, AutoPIPE, SACS and many more engineering design and analysis applications to further improve collaboration between the different disciplines involved in a project. STAAD can be used for analysis and design of all types of structural projects from plants, buildings, and bridges to towers, tunnels, metro stations, water/wastewater treatment plants and more.
Important Features
Analytical Modeling
Analytical model can be created using the ribbon-based user interface, by editing the command file or by importing several other files types like dxf, cis/2 etc. The model geometry can even be generated from the data of macro-enabled applications (like Microsoft Excel, Microstation etc.) by using Macros.
Physical Modeling
Physical modeling has been a significant feature included in the program. STAAD.Pro Physical Modeler takes advantage of physical modeling to simplify modeling of a structure, which in turn more accurately reflects the process of building a model. Beams and surfaces are placed in the model on the scale of which they would appear in the physical world. A column may span multiple floors and a surface represents an entire floor of a building, for example. A joint is then generated anywhere two physical objects meet in the model (as well as at the free ends of cantilevered members, for convenience).
STAAD Building Planner
STAAD Building Planner is a module that enables seamless generation of building models that can be analyzed and designed thereafter in the program itself. Operations like defining geometry, making changes in the geometric specifications are matters of only few clicks in this workflow.
Steel AutoDrafter
Steel AutoDrafter workflow extracts planar drawings and material take-off from a structural steel model prepared in STAAD.Pro. It produces excellent quality plans at any level and sections in any of the orthogonal directions.
STAAD.Beava
The general philosophy governing the design of bridges is that, subject to a set of loading rules and constraints, the worst effects due to load application should be established and designed against. The process of load application can be complex as governing rules can impose interdependent parameters such as loaded length on a lane, lane factors, and load intensity. To obtain the maximum design effects, engineers have to try many loading situations on a trial and error basis.
This leads to the generation of many live load application instances (and a large volume of output data) that then must be combined with dead load and other effects, as well. Bridge Deck is used to minimize the load application process while complying with national code requirements.
The program is based on the use of influence surfaces, which are generated by STAAD.Pro as part of the loading process. An influence surface for a given effect on a bridge deck relates its value to movement of a unit load over the point of interest. The influence surface is a three-dimensional form of an influence line for a single member (or, in other words, it is a 2D influence function).
STAAD.Pro will automatically generate influence surfaces for effects such as bending moments for elements, deflection in all the degrees of freedom of nodes, and support reactions. The user then instruct the program to utilize the relevant influence surfaces and, with due regards to code requirements, optimize load positions to obtain the maximum desired effects.
Advanced Concrete Design
The Advanced Concrete Design workflow provides direct access for STAAD.Pro models to leverage the power of the RCDC application. This is a standalone application, which is operated outside the STAAD.Pro environment, but requires a model and results data from a suitable analysis.
The model should typically be formed from beams and columns (plates are currently not supported). RCDC can be used to design the following objects: Pile Caps, Footings, Columns and walls, Beams, Slabs.
As the projects progresses, each design created in RCDC is retained and displayed when RCDC is re-entered, so that previous designs can be recalled and/or continued.
Detailed drawings and BBS of excellent quality can be generated as required and they are quite ready to be sent for execution.
Advanced Slab Design
The STAAD.Pro Advanced Slab Design workflow is an integrated tool that works from within the STAAD.Pro environment. Concrete slabs can be defined, and the data can be transferred to RAM Concept.
The data passed into RAM Concept includes the geometry, section and material properties, loads and combination information, and analysis results.
Earthquake Mode
Eurocode 8: Part 1 contains specific requirements and recommendations for building structures that are to be constructed in seismic regions. Essentially, these fundamental requirements have been provided to ensure that the structures can sustain the seismic loads without collapse and also – where required– avoid suffering unacceptable damage and can continue to function after an exposure to a seismic event.
This STAAD.Pro workflow is used to check if the structure conforms to the basic geometric recommendations made in Eurocode 8 (EC8). This workflow is in addition to the normal post-processing workflow which gives the various analysis results. These checks are intended to give you a "feel" for the structure and are not mandatory to proceed to the design phase.
OpenSTAAD Macro Editor
OpenSTAAD is a library of exposed functions enabling engineers access STAAD.Pro’s internal functions and routines as well as its graphical commands. With OpenSTAAD, one can use VBA macros to perform such tasks as automating repetitive modeling or post-processing tasks or embedding customized design routines. Following an open architecture paradigm, OpenSTAAD was built using ATL, COM, and COM+ standards as specified by Microsoft. This allows OpenSTAAD to be used in a macro application like Microsoft Excel or Autodesk AutoCAD. OpenSTAAD can also be used to link STAAD data to Web-based applications using ActiveX, HTML, and ASP. Through the in-built Macro Editor, one can leverage the functionalities of OpenSTAAD and automate the analysis and design workflows, thereby eliminating the chance of occurrence of potential errors due to manual intervention and reducing the required time for execution of the whole workflow (as compared to the manual execution time), to a large extent.
References
External links
Bentley.com
reisoftwareth.com
Computer-aided engineering software
Structural analysis
Structural engineering | STAAD | Engineering | 1,480 |
9,025,384 | https://en.wikipedia.org/wiki/List%20of%20UN%20numbers%203201%20to%203300 | UN numbers from UN3201 to UN3300 as assigned by the United Nations Sub-Committee of Experts on the Transport of Dangerous Goods are as follows:
UN 3201 to UN 3300
See also
Dangerous goods
Lists of UN numbers
References
External links
UN Dangerous Goods List
ADR Dangerous Goods List 2021
ADR Dangerous Goods substances
Lists of UN numbers | List of UN numbers 3201 to 3300 | Chemistry,Technology | 70 |
6,503,797 | https://en.wikipedia.org/wiki/Ground%20granulated%20blast-furnace%20slag | Ground granulated blast-furnace slag (GGBS or GGBFS) is obtained by quenching molten iron slag (a by-product of iron and steel-making) from a blast furnace in water or steam, to produce a glassy, granular product that is then dried and ground into a fine powder. Ground granulated blast furnace slag is a latent hydraulic binder forming calcium silicate hydrates (C-S-H) after contact with water. It is a strength-enhancing compound improving the durability of concrete. It is a component of metallurgic cement ( in the European norm ). Its main advantage is its slow release of hydration heat, allowing limitation of the temperature increase in massive concrete components and structures during cement setting and concrete curing, or to cast concrete during hot summer.
Production and composition
The chemical composition of a slag varies considerably depending on the composition of the raw materials in the iron production process. Silicate and aluminate impurities from the ore and coke are combined in the blast furnace with a flux which lowers the viscosity of the slag. In the case of pig iron production, the flux consists mostly of a mixture of limestone and forsterite or in some cases dolomite. In the blast furnace the slag floats on top of the iron and is decanted for separation. Slow cooling of slag melts results in an unreactive crystalline material consisting of an assemblage of Ca-Al-Mg silicates. To obtain a good slag reactivity or hydraulicity, the slag melt needs to be rapidly cooled or quenched below 800 °C in order to prevent the crystallization of merwinite and melilite. In order to cool and fragment the slag, a granulation process can be applied in which molten slag is subjected to jet streams of water or air under pressure. Alternatively, in the pelletization process, the liquid slag is partially cooled with water and subsequently projected into the air by a rotating drum. In order to obtain a suitable reactivity, the obtained fragments are ground to reach the same fineness as Portland cement.
The main components of blast furnace slag are CaO (30-50%), SiO2 (28-38%), Al2O3 (8-24%), MnO, and MgO (1-18%). In general increasing the CaO content of the slag results in raised slag basicity and an increase in compressive strength. The MgO and Al2O3 content show the same trend up to respectively 10-12% and 14%, beyond which no further improvement can be obtained. Several compositional ratios or so-called hydraulic indices have been used to correlate slag composition with hydraulic activity; the latter being mostly expressed as the binder compressive strength.
The glass content of slags suitable for blending with Portland cement typically varies between 90 and 100% and depends on the cooling method and the temperature at which cooling is initiated. The glass structure of the quenched glass largely depends on the proportions of network-forming elements such as Si and Al over network-modifiers such as Ca, Mg and to a lesser extent Al. Increased amounts of network-modifiers lead to higher degrees of network depolymerization and reactivity.
Common crystalline constituents of blast-furnace slags are merwinite and melilite. Other minor components which can form during progressive crystallization are belite, monticellite, rankinite, wollastonite and forsterite. Minor amounts of reduced sulphur are commonly encountered as oldhamite.
Applications
GGBS is used to make durable concrete structures in combination with ordinary Portland cement and/or other pozzolanic materials. GGBS has been widely used in Europe, and increasingly in the United States and in Asia (particularly in Japan and Singapore) for its superiority in concrete durability, extending the lifespan of buildings.
Two major uses of GGBS are in the production of quality-improved slag cement, namely Portland Blastfurnace cement (PBFC) and high-slag blast-furnace cement (HSBFC), with GGBS content ranging typically from 30 to 70%; and in the production of ready-mixed or site-batched durable concrete.
Concrete made with GGBS cement sets more slowly than concrete made with ordinary Portland cement, depending on the amount of GGBS in the cementitious material, but also continues to gain strength over a longer period in production conditions. This results in lower heat of hydration and lower temperature rises, and makes avoiding cold joints easier, but may also affect construction schedules where quick setting is required.
Use of GGBS significantly reduces the risk of damages caused by alkali–silica reaction (ASR), provides higher resistance to chloride ingress — reducing the risk of reinforcement corrosion — and provides higher resistance to attacks by sulfate and other chemicals.
GGBS cement uses
GGBS cement can be added to concrete in the concrete manufacturer's batching plant, along with Portland cement, aggregates and water. The normal ratios of aggregates and water to cementitious material in the mix remain unchanged. GGBS is used as a direct replacement for Portland cement, on a one-to-one basis by weight. Replacement levels for GGBS vary from 30% to up to 85%. Typically 40% to 50% is used in most instances.
The use of GGBS in addition to Portland cement in concrete in Europe is covered in the concrete standard EN 206:2013. This standard establishes two categories of additions to concrete along with ordinary Portland cement: nearly inert additions (Type I) and pozzolanic or latent hydraulic additions (Type II). GGBS cement falls in the latter category. As GGBS cement is slightly less expensive than Portland cement, concrete made with GGBS cement will be similarly priced to that made with ordinary Portland cement.
It is used partially as per mix ratio.
Architectural and engineering benefits
Durability
GGBS cement is routinely specified in concrete to provide protection against both sulfate attack and chloride attack. GGBS has now effectively replaced sulfate-resisting Portland cement (SRPC) on the market for sulfate resistance because of its superior performance and greatly reduced cost compared to SRPC. Most projects in Dublin's docklands, including Spencer Dock, are using GGBS in subsurface concrete for sulfate resistance.
Bulk Electrical Resistivity is a test method that can measure the resistivity of concrete samples. (ASTM 1876–19) The higher electrical resistivity can be an indication of higher ion transfer resistivity and thus higher durability. By replacing up to 50% GGBS in concrete, researchers have shown that some durability properties can be significantly improved.
To protect against chloride attack, GGBS is used at a replacement level of 50% in concrete. Instances of chloride attack occur in reinforced concrete in marine environments and in road bridges where the concrete is exposed to splashing from road de-icing salts. In most NRA projects in Ireland GGBS is now specified in structural concrete for bridge piers and abutments for protection against chloride attack. The use of GGBS in such instances will increase the life of the structure by up to 50% had only Portland cement been used, and precludes the need for more expensive stainless steel reinforcing.
GGBS is also routinely used to limit the temperature rise in large concrete pours. The more gradual hydration of GGBS cement generates both lower temperature peak and less total overall heat than Portland cement. This reduces thermal gradients in the concrete, which prevents the occurrence of microcracking which can weaken the concrete and reduce its durability, and was used for this purpose in the construction of the Jack Lynch Tunnel in Cork.
Appearance
In contrast to the stony grey of concrete made with Portland cement, the near-white color of GGBS cement permits architects to achieve a lighter color for exposed fair-faced concrete finishes, at no extra cost. To achieve a lighter color finish, GGBS is usually specified at replacement levels of between 50% and 70%, although levels as high as 85% can be used. GGBS cement also produces a smoother, more defect-free surface, due to the fineness of the GGBS particles. Dirt does not adhere to GGBS concrete as easily as concrete made with Portland cement, reducing maintenance costs. GGBS cement prevents the occurrence of efflorescence, the staining of concrete surfaces by calcium carbonate deposits. Due to its much lower lime content and lower permeability, GGBS is effective in preventing efflorescence when used at replacement levels of 50%-to-60%.
Strength
Concrete containing GGBS cement has a higher ultimate strength than concrete made with Portland cement. It has a higher proportion of the strength-enhancing calcium silicate hydrates (CSH) than concrete made with Portland cement only, and a reduced content of free lime, which does not contribute to concrete strength. Concrete made with GGBS continues to gain strength over time, and has been shown to double its 28-day strength over periods of 10 to 12 years.
The optimum dosage of Ground granulated blast-furnace slag (GGBS) for replacement in concrete was reported to be 20-30% by mass to provide higher compressive strength compared to the concrete made with only cement.
Sustainability
Since GGBS is a by-product of steel manufacturing process, its use in concrete is recognized by LEED, as well as Building Environmental Assessment Method (BEAM) Plus in Hong Kong, etc. as improving the sustainability of the project and will therefore add points towards LEED and BEAM Plus certifications. In this respect, GGBS can also be used for superstructure in addition to the cases where the concrete is in contact with chlorides and sulfates — provided that the slower setting time for casting of the superstructure is justified.
Notes
External links
The Concrete Society, Cementitious Materials: The effect of GGBS, fly ash, silica fume and limestone fines on the properties of concrete Cementitious materials
References
Amorphous solids
Glass compositions
Cement
Concrete
Materials | Ground granulated blast-furnace slag | Physics,Chemistry,Engineering | 2,110 |
61,183,286 | https://en.wikipedia.org/wiki/C7H6Cl2 | {{DISPLAYTITLE:C7H6Cl2}}
The molecular formula C7H6Cl2 may refer to:
Benzal chloride
Dichlorotoluene | C7H6Cl2 | Chemistry | 38 |
17,087,685 | https://en.wikipedia.org/wiki/Slingshot%20%28water%20vapor%20distillation%20system%29 | Slingshot is a water purification device created by inventor Dean Kamen. Powered by a Stirling engine running on a combustible fuel source, it claims to be able to produce drinking water from almost any source by means of vapor compression distillation, requires no filters, and can operate using cow dung as fuel.
The name of the machine is a reference to the slingshot used by David to defeat Goliath.
Technical characteristics
In his TEDMED 2010 presentation, Kamen announced several goals for and characteristics of the machine:
five years of operation without overhaul or maintenance
use less than a kilowatt of power (lower than the power consumption of a microwave oven)
generate 1000 litres of pure water/day, enough for 100 people for hygiene and cooking
meets the U.S. pharmacopoeic standard for water for injections
requires no pre-treatment, pipelines, engineers, consumables (osmosis membranes, charcoal, etc.), or installation permits
History
Kamen came to develop the device on the basis of statistics that showed lack of access to clean water as a public health crisis. Statistics from the World Health Organization show that there are 900 million people worldwide without a readily available supply of drinking water and that some 3.5 million people die annually because of diseases resulting from the consumption of unsanitary water. Despite the fact that over two-thirds of the Earth's surface is covered with water, only 1% of it is potable.
Kamen sought to develop a technology that would transform the 97% of water that is undrinkable into water that can be used and consumed on the spot, readily and inexpensively. The device takes contaminated water and runs it through a vapor compression distiller that produces clean water, producing 250 gallons daily (~946 litres), enough for 100 people. The test devices have been used with "anything that looks wet", including polluted river water, saline ocean water and raw sewage. In a demonstration at a technology conference in October 2004, Kamen ran his own urine through the machine and drank the clean water that came out.
Kamen built two machines — a power generator that would output one kilowatt from "anything that burns", and the water distiller, which uses the electricity. In 2005, the power generator was tested for six months in a village in Bangladesh and generated enough electricity to light 70 energy-efficient light bulbs. The hand-made prototype cost each.
By the end of 2005, a team of 200 at DEKA had produced 30 units, each the size of a compact refrigerator. A pair of Slingshot devices ran successfully for a month in a village in Honduras during the summer of 2006. While the initial devices cost hundreds of thousands of dollars, Kamen hopes that increased economies of scale will allow production machines to be made available for $2,000 each.
In 2008, Kamen demonstrated the device on The Colbert Report.
In his TEDMED 2010 presentation, Kamen lamented throughout that when he asked for "a few million dollars" over a few months, no large global health organizations supported the development. Later in the presentation, he announced a partnership with The Coca-Cola Company.
In 2011, field tests of Slingshot in five towns in Ghana proved their effectiveness and durability.
In October 2012, Kamen and Coca-Cola CEO Muhtar Kent announced at the Clinton Global Initiative that in collaboration with DEKA Research, Africare and Inter-American Development Bank, they will start bringing the Slingshot to rural parts of Latin America and Africa. The first initiative will be testing the Slingshot technology in health centers and schools in remote communities in Latin America in 2013.
Proposed development
Kamen hopes to send thousands of the units with local village entrepreneurs, in much the same way independent cell phone businesses have thrived and gradually changed the face of many impoverished areas around the globe. Future target price for the device is in the $1,000 to $2,000 range.
As of 2020, the product does not seem to be in commercial production or wide use. Kamen invented the Coca-Cola Freestyle soda dispenser in return for the Coca-Cola corporation to release the Slingshot world wide. The systems were instead distributed as a component of EKOCENTER kiosks, of which only 150 have been deployed worldwide.
See also
Biosand filter, a point-of-use water treatment system adapted from traditional slow sand filters
LifeStraw, designed by Vestergaard Frandsen
LifeSaver bottle, designed by Michael Pritchard
Tata Swach
Sono arsenic filter, developed by Abul Hussam of George Mason University
References
External links
Focus Forward 3-minute film
Dean Kamen’s Slingshot water purifier and Stirling generator tech — low cost water and power for the developing world
To Build a Better World
Slingshot article and Tedmed video
SlingShot documentary film (2014) Director: Paul Lazarus (IMDB listing)
American inventions
Water filters
Water technology
Water treatment | Slingshot (water vapor distillation system) | Chemistry,Engineering,Environmental_science | 1,005 |
12,388,613 | https://en.wikipedia.org/wiki/Streaming%20current | A streaming current and streaming potential are two interrelated electrokinetic phenomena studied in the areas of surface chemistry and electrochemistry. They are an electric current or potential which originates when an electrolyte is driven by a pressure gradient through a channel or porous plug with charged walls.
The first observation of the streaming potential is generally attributed to the German physicist Georg Hermann Quincke in 1859.
Applications
Streaming currents in well-defined geometries are a sensitive method to characterize the zeta potential of surfaces, which is important in the fields of colloid and interface science. In geology, measurements of related spontaneous potential are used for evaluations of formations. Streaming potential has to be considered in design for flow of poorly conductive fluids (e.g., gasoline lines) because of the danger of buildup of high voltages. The streaming current monitor (SCM) is a fundamental tool for monitoring coagulation in wastewater treatment plants. The degree of coagulation of raw water may be monitored by the use of an SCM to provide a positive feedback control of coagulant injection. As the streaming current of the wastewater increases, more coagulant agent is injected into the stream. The higher levels of coagulant agent cause the small colloidal particles to coagulate and sediment out of the stream. Since less colloid particles are in the wastewater stream, the streaming potential decreases. The SCM recognizes this and subsequently reduces the amount of coagulant agent injected into the wastewater stream. The implementation of SCM feedback control has led to a significant materials cost reduction, one that was not realized until the early 1980s. In addition to monitoring capabilities, the streaming current could, in theory, generate usable electrical power. This process, however, has yet to be applied as typical streaming potential mechanical to electrical efficiencies are around 1%.
Origin
Adjacent to the channel walls, the charge-neutrality of the liquid is violated due to the presence of the electrical double layer: a thin layer of counterions attracted by the charged surface.
The transport of counterions along with the pressure-driven fluid flow gives rise to a net charge transport: the streaming current. The reverse effect, generating a fluid flow by applying a potential difference, is called electroosmotic flow.
Measurement method
A typical setup to measure streaming currents consists of two reversible electrodes placed on either side of a fluidic geometry across which a known pressure difference is applied. When both electrodes are held at the same potential, the streaming current is measured directly as the electric current flowing through the electrodes. Alternatively, the electrodes can be left floating, allowing a streaming potential to build up between the two ends of the channel.
A streaming potential is defined as positive when the electric potential is higher on the high pressure end of the flow system than on the low pressure end.
The value of streaming current observed in a capillary is usually related to the zeta potential through the relation:
.
The conduction current, which is equal in magnitude to the streaming current at steady state, is:
At steady state, the streaming potential built up across the flow system is given by:
Symbols:
Istr - streaming current under short-circuit conditions, A
Ustr - streaming potential at zero net current conditions, V
Ic - conduction current, A
εrs - relative permittivity of the liquid, dimensionless
ε0 - electrical permittivity of vacuum, F·m−1
η - dynamic viscosity of the liquid, kg·m−1·s−1
ζ - zeta potential, V
ΔP - pressure difference, Pa
L - capillary length, m
a - capillary radius, m
KL - specific conductivity of the bulk liquid, S·m−1
The equation above is usually referred to as the Helmholtz–Smoluchowski equation.
The above equations assume that:
the double layer is not too large compared to the pores or capillaries (i.e., ), where κ is the reciprocal of the Debye length
there is no surface conduction (which typically may become important when the zeta potential is large, e.g., |ζ| > 50 mV)
there is no electrical double layer polarization
the surface is homogeneous in properties
there is no axial concentration gradient
the geometry is that of a capillary/tube.
Literature
J. Lyklema, Fundamentals of Interface and Colloid Science
F.H.J. van der Heyden et al., Phys. Rev. Lett. 95, 116104 (2005)
C. Werner et al., J. Colloid Interface Sci. 208, 329 (1998)
Mansouri et al. The Journal of Physical Chemistry C, 112(42), 16192 (2008)
References
Electric current
Colloidal chemistry | Streaming current | Physics,Chemistry | 979 |
35,777,877 | https://en.wikipedia.org/wiki/C25H38O2 | The molecular formula C25H38O2 (molar mass: 370.57 g/mol, exact mass: 370.2872 u) may refer to:
CBD-DMH, or DMH-CBD
Dimethylheptylpyran
JWH-051
Penmesterol, or penmestrol
Variecolol | C25H38O2 | Chemistry | 78 |
585,185 | https://en.wikipedia.org/wiki/Chemical%20Abstracts%20Service | Chemical Abstracts Service (CAS) is a division of the American Chemical Society. It is a source of chemical information and is located in Columbus, Ohio, United States.
Print periodicals
Chemical Abstracts is a periodical index that provides numerous tools such as SciFinder as well as tagged keywords, summaries, indexes of disclosures, and structures of compounds in recently published scientific documents. Approximately 8,000 journals, technical reports, dissertations, conference proceedings, and new books, available in at least 50 different languages, are monitored yearly, as are patent specifications from 27 countries and two international organizations. Chemical Abstracts ceased print publication on January 1, 2010.
Databases
The two principal databases that support the different products are CAplus and Registry.
CAS References
CAS References consists of bibliographic information and abstracts for all articles in chemical journals worldwide, and chemistry-related articles from all scientific journals, patents, and other scientific publications.
Registry
, the CAS Registry contains information on more than 200 million organic and inorganic substances, and about 70 million protein and nucleic acid sequences. The sequence information comes from CAS and GenBank, produced by the National Institutes of Health. The chemical information is produced by CAS, and is prepared by the CAS Registry System, which identifies each compound with a specific CAS registry number, index name, and graphic representation of its chemical structure.
The assignment of chemical names is done according to the chemical nomenclature rules for CA index names, which is slightly different from the internationally standard IUPAC names, according to the rules of IUPAC.
Products
CAS databases are available via two principal database systems, STN, and SciFinder.
STN
STN (Scientific & Technical Information Network) International is operated jointly by CAS and FIZ Karlsruhe, and is intended primarily for information professionals, using a command language interface. In addition to CAS databases, STN also provides access to many other databases, similar to Dialog.
SciFinder
SciFinder is a database of chemical and bibliographic information. Originally it was available only as a client application (for both Windows and MacOS operating systems), a web version was released in 2008. By that time it had a graphical interface, and was able to do graphical searches for chemical structures and reactions (the first database to allow such functions), as well as keyword searches for literature in chemistry and related disciplines. SciFinder Scholar was a very similar a product developed for academic institutions, but discontinued in 2023.
In 2017 the ACS released SciFinder-n as a web-only product with the same data content and improved user interface and search functions.
SciFinder is considered as the best source of chemical information worldwide, with substantially larger number of relevant information sources than Web of Science or Scopus with Reaxys. However, due to its unique and unusual search functions, substantial training is needed in order to fully take advantage of SciFinder capabilities.
CASSI
CASSI stands for Chemical Abstracts Service Source Index. Since 2009, this formerly print and CD-ROM compilation is available as a free online resource to look up and confirm publication information. The online CASSI Search Tool provides titles and abbreviations, CODEN, ISSN, publisher, and date of first issue (history) for a selected journal. Also included is its language of text and language of summaries.
The range is from 1907 to the present, including both serial and non-serial scientific and technical publications. The database is updated quarterly. Beyond CASSI lists abbreviated journal titles from early chemical literature and other historical reference sources.
History
Chemical Abstracts (CA) began as a volunteer effort and developed from there. The use of volunteer abstractors was phased out in 1994. Chemical Abstracts has been associated with the American Chemical Society in one way or another since 1907.
For many years, beginning in 1909, the offices of Chemical Abstracts were housed in various places on the Columbus, Ohio campus of Ohio State University, including McPherson Laboratory and Watts Hall. In 1965, CAS moved to a new site on the west bank of the Olentangy River, just north of The Ohio State campus. This campus became well known in the Columbus area and famous as the site of many Columbus Symphony Orchestra pop concerts. In 2009, the campus consisted of three buildings.
In 1907, William A. Noyes had enlarged the Review of American Chemical Research, an abstracting publication begun by Arthur Noyes in 1895 that was the forerunner of Chemical Abstracts. When it became evident that a separate publication containing these abstracts was needed, Noyes became the first editor of the new publication, Chemical Abstracts.
E. J. Crane became the first Director of Chemical Abstracts Service when it became an American Chemical Society division in 1956. Crane had been CA editor since 1915, and his dedication was a key factor in its long-term success.
Dale B. Baker became the CAS Director upon Crane's retirement in 1958. According to CAS, his visionary view of CAS' potential "led to expansion, modernization, and the forging of international alliances with other information organizations." CAS was an early leader in the use of computer technology to organize and disseminate information.
The CAS Chemical Registry System was introduced in 1965. CAS developed a unique registry number to identify chemical substances. Agencies such as the U.S. Environmental Protection Agency and local fire departments around the world now rely on these numbers for the definite identification of substances. According to the ACS, this is the largest chemical substance database in the world.
In 1965, CAS left their offices at OSU for a new headquarters north of campus. Ground was broken in 1971 for an expansion to the building designed by architects Brubaker/Brandt to accommodate the review of 400,000 new research reports printed each year. The 5-story 142,000 square foot building opened in May 1973.
In 2007, the ACS designated its Chemical Abstracts Service subdivision an ACS National Historic Chemical Landmark in recognition of its significance as a comprehensive repository of research in chemistry and related sciences.
In 2021, CAS rebranded along with a change in logo. The organization updated their mission to be more focused on dynamic responsiveness due to ongoing changes within scientific industries and communities.
In 2022, CAS announced the release of almost half a million CAS registry numbers under an open license in their Common Chemistry project.
See also
Beilstein database
Chemical database
ChemInform
ChemSpider
SPRESI database
FIZ Karlsruhe
Google Scholar
Inorganic Crystal Structure Database
List of academic databases and search engines
List of chemical databases
List of open-access journals
List of scientific journals
PubChem
References
External links
American Chemical Society
Chemical databases
Chemistry journals
Bibliographic databases and indexes
1907 establishments in Ohio
Companies based in the Columbus, Ohio metropolitan area | Chemical Abstracts Service | Chemistry | 1,345 |
5,763,642 | https://en.wikipedia.org/wiki/Barkcloth | Barkcloth or bark cloth is a versatile material that was once common in Asia, Africa, and the Pacific. Barkcloth comes primarily from trees of the family Moraceae, including Broussonetia papyrifera, Artocarpus altilis, Artocarpus tamaran, and Ficus natalensis. It is made by beating sodden strips of the fibrous inner bark of these trees into sheets, which are then finished into a variety of items. Many texts that mention "paper clothing" are actually referring to barkcloth.
Some modern cotton-based fabrics are also named "barkcloth" for their resemblance to these traditional fabrics.
Traditional
Austronesia
Before the development of woven textiles, barkcloth made from trees belonging to the mulberry family (Moraceae) were an important aspect of the pre-Austronesian and Austronesian material culture during the Neolithic period. Stone barkcloth beaters, in particular, are considered part of the "Austronesian toolkit." They have been found in abundance in the Pearl River basin in Southern China, which is considered to be part of the homelands of the Austronesian peoples before they started migrating into islands during the Austronesian expansion (c.3000 to 1500 BC). The oldest example, found in the Dingmo Site in Guangxi, has been dated back to ~5900 BC. They were spread along with Austronesian voyagers into Island Southeast Asia, Oceania (with the notable exception of Micronesia), and Madagascar. Genetic studies on the paper mulberry populations in the Pacific have all confirmed close genealogical ties to populations in Taiwan and Southern China.
Though they exist in abundance in archaeological sites in Island Southeast Asia, barkcloth have largely disappeared in the region as they were replaced by woven textiles. But they survived until around the 19th century in the outlying regions of the Austronesian expansion, particularly in Island Melanesia and Polynesia, as well as the interior highlands of Borneo. Some communities in Southeast Asia are reviving this practice. At Monbang traditional village on Alor Island, Indonesia, tourists can see members of the Kabola ethnic group wear barkcloth and dance traditional dances.
Uganda
Barkcloth has been manufactured in Buganda, Uganda, for centuries and is Uganda's sole representative on the UNESCO Intangible Cultural Heritage Lists.
Vietnam
The production of barkcloth may have originated in Southeastern China, in a region adjacent to Vietnam. South East China was the origins to the ancestors of many people, including those who migrated to Vietnam. Throughout ancient Vietnam, the bark-cloth was widely made; this practice of producing barkcloth has survived in modern times in a few rural areas in Vietnam.
Modern cotton "barkcloth"
Today, what is commonly called barkcloth is a soft, thick, slightly textured fabric, so named because it has a rough surface like that of tree bark. This barkcloth is usually made of densely woven cotton fibers. Historically, the fabric has been used in home furnishings, such as curtains, drapery, upholstery, and slipcovers. It is often associated with 1940s through 1960s home fashions, particularly in tropical, abstract, "atomic" and "boomerang" prints, the last two themes being expressed by images of atoms with electrons whirling, and by the boomerang shape which was very popular in mid-century cocktail tables and fabrics and influenced by the Las Vegas "Atomic City" era. Waverly, a famed design house for textiles and wall coverings between 1923 and 2007, called their version of this fabric rhino cloth, possibly for the rough, nubbly surface. American barkcloth shot through with gold Lurex threads was called Las Vegas cloth, and contained as much as 65% rayon as well, making it a softer, more flowing fabric than the stiffer all-cotton rhino cloth or standard cotton barkcloth.
See also
Cedar bark textile
Lacebark
Osnaburg
Tapa cloth
Bast shoe
Bast fibre
References
External links
Bark Cloth − Then and Now: Amazing Discoveries, Cummings, Patricia L., Quilters' Muse Virtual Museum
Tapa: Situating Pacific Barkcloth in Time and Place Tapa: Situating Pacific Barkcloth in Time and Place A three-year AHRC funded research project at the for Textile Conservation Centre for Textile Conservation that aims to transform our understanding of Pacific barkcloth manufacture using a multidisciplinary approach
Woven fabrics
1950s fashion
1960s fashion
Indigenous textiles
Plant products | Barkcloth | Chemistry | 895 |
7,455,244 | https://en.wikipedia.org/wiki/Telephone%20numbers%20in%20the%20Americas | All countries in the Americas use codes that start with "5", with the exception of the countries of the North American Numbering Plan, such as Canada and the United States, which use country code 1, and Greenland and Aruba with country codes starting with the digit "2", which mostly is used by countries in Africa.
See also
Telephone numbering plan
National conventions for writing telephone numbers
List of country calling codes
List of international call prefixes
List of North American Numbering Plan area codes
Area codes in the Caribbean
:Category:Telephone numbers by country
International telecommunications
Telecommunications in Central America
Telecommunications in the Caribbean
Telecommunications in North America
Telecommunications in South America
Telephone numbers | Telephone numbers in the Americas | Mathematics | 130 |
21,926,877 | https://en.wikipedia.org/wiki/Graphics%20BBS | Graphics BBS (GBBS) was a bulletin board system server developed from 1989 to 1992 by Eric Anderson as part of his thesis at Chisholm Institute of Technology. Although it had superior graphics capabilities compared to RIP, it was harder to integrate into existing BBS's, and so was ultimately less popular.
GBBS allowed sending graphics defined by BASIC commands, as well as GIF images. Since the images were cached between sessions, each image only needed to be downloaded once, so these connections were often as fast as a text BBS.
The software was primarily used around Melbourne until the Internet killed the old bulletin boards.
References
Bulletin board system software | Graphics BBS | Technology | 134 |
15,722,493 | https://en.wikipedia.org/wiki/Los%20Angeles%20Air%20Route%20Traffic%20Control%20Center | The Los Angeles Air Route Traffic Control Center is an air traffic control center located in Palmdale, California, United States. Located adjacent to United States Air Force Plant 42 and the Palmdale Regional Airport, it is one of 22 Air Route Traffic Control Centers (ARTCC) operated by the United States Federal Aviation Administration (FAA).
The Los Angeles ARTCC controls en route air traffic over southern and central California, southern Nevada, southwestern Utah, western Arizona, and portions of the Pacific Ocean Air Defense Identification Zone (ADIZ), with the exception of military airspace and lower-level airspace controlled by local airport towers and Terminal Control Centers (TRACON).
History
The Los Angeles Air Route Traffic Control Center was established on March 15, 1937, being the fifth ARTCC established in the United States. The Los Angeles ARTCC was originally located in Burbank. In 1943, it was moved to Downtown Los Angeles on 7th Street and Flower Street. In 1946, it was again moved to just south of Los Angeles International Airport (LAX) in Inglewood on Manchester Boulevard. On March 1, 1963, the Los Angeles ARTCC was moved to its present location in Palmdale on 25th Street East and Avenue P, being located adjacent to United States Air Force Plant 42 and the Palmdale Regional Airport.
Operations
The Los Angeles ARTCC controls of airspace over southern and central California, southern Nevada, southwestern Utah, and western Arizona. It controls airspace from the surface up to FL600 (60,000 feet). Around 40 percent of the ARTCC's airspace is composed of special use airspace (SUA) which is used by the United States Armed Forces. The ARTCC's airspace is divided into six areas, simply named Areas A through F, which are further subdivided into 20 low level sectors and 16 high altitude sectors.
As of 2019, the ARTCC employs over 500 people, 320 of whom are air traffic controllers. , Lisa Jones is the acting air traffic manager. The United States Department of Homeland Security provides security for the ARTCC.
The Los Angeles ARTCC is the 10th busiest ARTCC in the United States. Between January 1, 2022 and December 31, 2022, the Los Angeles ARTCC handled 2,271,937 aircraft operations.
Airports
A total of 97 airports are located within the Los Angeles ARTCC. Additionally, there are also 8 Terminal Control Centers (TRACON): Bakersfield, High Desert, Nellis, Las Vegas, Santa Barbara, Southern California, and Yuma.
See also
List of airports in the Los Angeles area
References
Bibliography
External links
Los Angeles Center Weather Service Unit (CWSU) (NWS/FAA)
Air traffic control centers
Air traffic control in the United States
Buildings and structures in Palmdale, California
WAAS reference stations
Aviation in California
Transportation in Palmdale, California | Los Angeles Air Route Traffic Control Center | Technology | 571 |
37,036,135 | https://en.wikipedia.org/wiki/Tabeo | The Tabeo is a discontinued tablet computer developed by Toys "R" Us that runs on a version of the Android 4.0 operating system. Tabeo is officially at "End of Life" status, meaning the company is no longer providing support for the original Tabeo and Tabeo E2. Though some of the E2 devices seem to have been sold in Mexico, this seems to have happened to devices that were returned to the reseller. Tabeo is no longer fulfilling warranty repair or replacements, as the company has not produced a new device in 3 years. The company is also no longer providing assistance with any issues that may arise with the device, as the device is considerably Out of Warranty. All support has been discontinued.It was specifically designed with children in mind, allows parents to implement parental controls, and has 50 apps pre-installed. More than 6000 other apps, all considered to be safe for children, are available on the Tabeo App Store. It has a 7-inch screen and 4 gigabytes of built-in storage space, but is capable of supporting SDHC cards with up to 32 gigabytes of space. It was released on October 21, 2012.
Lawsuit
Fuhu Inc., producer of the Nabi tablet for children, sued Toys "R" Us before the Tabeo was released, claiming that the company had stolen its trade secrets, breached its contract, and committed fraud; and accusing the company of unfair competition. In October 2011, Toys "R" Us had made a deal with Fuhu for exclusive rights to distribute the Nabi tablet. However, Toys "R" Us barely advertised the device and did not order many units, eventually ending the deal in January 2012. Fuhu claimed that it did not know why Toys "R" Us did this until the Tabeo was announced. The lawsuit aimed to prevent the release of the Tabeo, and asked for any Tabeos that had been produced to be turned over to Fuhu, along with additional monetary damages.
References
Tablet computers
Toys "R" Us | Tabeo | Technology | 418 |
71,337,783 | https://en.wikipedia.org/wiki/N%20%3D%201%20supersymmetric%20Yang%E2%80%93Mills%20theory | In theoretical physics, more specifically in quantum field theory and supersymmetry, supersymmetric Yang–Mills, also known as super Yang–Mills and abbreviated to SYM, is a supersymmetric generalization of Yang–Mills theory, which is a gauge theory that plays an important part in the mathematical formulation of forces in particle physics. It is a special case of 4D N = 1 global supersymmetry.
Super Yang–Mills was studied by Julius Wess and Bruno Zumino in which they demonstrated the supergauge-invariance of the theory and wrote down its action, alongside the action of the Wess–Zumino model, another early supersymmetric field theory.
The treatment in this article largely follows that of Figueroa-O'Farrill's lectures on supersymmetry and of Tong.
While N = 4 supersymmetric Yang–Mills theory is also a supersymmetric Yang–Mills theory, it has very different properties to supersymmetric Yang–Mills theory, which is the theory discussed in this article. The supersymmetric Yang–Mills theory was studied by Seiberg and Witten in Seiberg–Witten theory. All three theories are based in super Minkowski spaces.
The supersymmetric Yang–Mills action
Preliminary treatment
A first treatment can be done without defining superspace, instead defining the theory in terms of familiar fields in non-supersymmetric quantum field theory.
Spacetime and matter content
The base spacetime is flat spacetime (Minkowski space).
SYM is a gauge theory, and there is an associated gauge group to the theory. The gauge group has associated Lie algebra .
The field content then consists of
a -valued gauge field
a -valued Majorana spinor field (an adjoint-valued spinor), known as the 'gaugino'
a -valued auxiliary scalar field .
For gauge-invariance, the gauge field is necessarily massless. This means its superpartner is also massless if supersymmetry is to hold. Therefore can be written in terms of two Weyl spinors which are conjugate to one another: , and the theory can be formulated in terms of the Weyl spinor field instead of .
Supersymmetric pure electromagnetic theory
When , the conceptual difficulties simplify somewhat, and this is in some sense the simplest gauge theory. The field content is simply a (co-)vector field , a Majorana spinor and a auxiliary real scalar field .
The field strength tensor is defined as usual as .
The Lagrangian written down by Wess and Zumino is then
This can be generalized to include a coupling constant , and theta term , where is the dual field strength tensor
and is the alternating tensor or totally antisymmetric tensor. If we also replace the field with the Weyl spinor , then a supersymmetric action can be written as
This can be viewed as a supersymmetric generalization of a pure gauge theory, also known as Maxwell theory or pure electromagnetic theory.
Supersymmetric Yang–Mills theory (preliminary treatment)
In full generality, we must define the gluon field strength tensor,
and the covariant derivative of the adjoint Weyl spinor,
To write down the action, an invariant inner product on is needed: the Killing form is such an inner product, and in a typical abuse of notation we write simply as , suggestive of the fact that the invariant inner product arises as the trace in some representation of .
Supersymmetric Yang–Mills then readily generalizes from supersymmetric Maxwell theory. A simple version is
while a more general version is given by
Superspace treatment
Superspace and superfield content
The base superspace is super Minkowski space.
The theory is defined in terms of a single adjoint-valued real superfield , fixed to be in Wess–Zumino gauge.
Supersymmetric Maxwell theory on superspace
The theory is defined in terms of a superfield arising from taking covariant derivatives of :
.
The supersymmetric action is then written down, with a complex coupling constant , as
where h.c. indicates the Hermitian conjugate of the preceding term.
Supersymmetric Yang–Mills on superspace
For non-abelian gauge theory, instead define
and . Then the action is
Symmetries of the action
Supersymmetry
For the simplified Yang–Mills action on Minkowski space (not on superspace), the supersymmetry transformations are
where .
For the Yang–Mills action on superspace, since is chiral, then so are fields built from . Then integrating over half of superspace, , gives a supersymmetric action.
An important observation is that the Wess–Zumino gauge is not a supersymmetric gauge, that is, it is not preserved by supersymmetry. However, it is possible to do a compensating gauge transformation to return to Wess–Zumino gauge. Then, after a supersymmetry transformation and the compensating gauge transformation, the superfields transform as
Gauge symmetry
The preliminary theory defined on spacetime is manifestly gauge invariant as it is built from terms studied in non-supersymmetric gauge theory which are gauge invariant.
The superfield formulation requires a theory of generalized gauge transformations. (Not supergauge transformations, which would be transformations in a theory with local supersymmetry).
Generalized abelian gauge transformations
Such a transformation is parametrized by a chiral superfield , under which the real superfield transforms as
In particular, upon expanding and appropriately into constituent superfields, then contains a vector superfield while contains a scalar superfield , such that
The chiral superfield used to define the action,
is gauge invariant.
Generalized non-abelian gauge transformations
The chiral superfield is adjoint valued. The transformation of is prescribed by
,
from which the transformation for can be derived using the Baker–Campbell–Hausdorff formula.
The chiral superfield is not invariant but transforms by conjugation:
,
so that upon tracing in the action, the action is gauge-invariant.
Extra classical symmetries
Superconformal symmetry
As a classical theory, supersymmetric Yang–Mills theory admits a larger set of symmetries, described at the algebra level by the superconformal algebra. Just as the super Poincaré algebra is a supersymmetric extension of the Poincaré algebra, the superconformal algebra is a supersymmetric extension of the conformal algebra which also contains a spinorial generator of conformal supersymmetry .
Conformal invariance is broken in the quantum theory by trace and conformal anomalies.
While the quantum supersymmetric Yang–Mills theory does not have superconformal symmetry, quantum N = 4 supersymmetric Yang–Mills theory does.
R-symmetry
The R-symmetry for supersymmetry is a symmetry of the classical theory, but not of the quantum theory due to an anomaly.
Adding matter
Abelian gauge
Matter can be added in the form of Wess–Zumino model type superfields . Under a gauge transformation,
,
and instead of using just as the Lagrangian as in the Wess–Zumino model, for gauge invariance it must be replaced with
This gives a supersymmetric analogue to QED. The action can be written
For flavours, we instead have superfields , and the action can be written
with implicit summation.
However, for a well-defined quantum theory, a theory such as that defined above suffers a gauge anomaly. We are obliged to add a partner to each chiral superfield (distinct from the idea of superpartners, and from conjugate superfields), which has opposite charge. This gives the action
Non-Abelian gauge
For non-abelian gauge, matter chiral superfields are now valued in a representation of the gauge group:
.
The Wess–Zumino kinetic term must be adjusted to .
Then a simple SQCD action would be to take to be the fundamental representation, and add the Wess–Zumino term:
.
More general and detailed forms of the super QCD action are given in that article.
Fayet–Iliopoulos term
When the center of the Lie algebra is non-trivial, there is an extra term which can be added to the action known as the Fayet–Iliopoulos term.
References
Supersymmetric quantum field theory | N = 1 supersymmetric Yang–Mills theory | Physics | 1,766 |
1,635,646 | https://en.wikipedia.org/wiki/Monocropping | In agriculture, monocropping is the practice of growing a single crop year after year on the same land. Maize, soybeans, and wheat are three common crops often monocropped. Monocropping is also referred to as continuous cropping, as in "continuous corn." Monocropping allows for farmers to have consistent crops throughout their entire farm. They can plant only the most profitable crop, use the same seed, pest control, machinery, and growing method on their entire farm, which may increase overall farm profitability.
Diversity can be added both in time, as with a crop rotation or sequence, or in space, with a polyculture or intercropping (see table below). Note that the distinction between monoculture and polyculture is not the same as between monocropping and intercropping. The first two describe diversity in space, as does intercropping. Monocropping and crop rotation describe diversity over time. This is frequently a source of confusion, even in scientific journal articles.
Strategy
Monocropping as an agricultural strategy tends to emphasize the use of expensive specialized farm equipment—an important component in realizing its efficiency goals. This can lead to an increased dependency and reliance on expensive machinery that cannot be produced locally and may need to be financed. This can make a significant change in the economics of farming in regions that are accustomed to self-sufficiency in agricultural production. In addition, political complications may ensue when these dependencies extend across national boundaries.
The controversies surrounding monocropping are complex, but traditionally the core issues concern the balance between its advantages in increasing short-term food production—especially in hunger-prone regions—and its disadvantages with respect to long-term land stewardship and the fostering of local economic independence and ecological sustainability. Advocates of monocropping believe polyculture production would be costly and unable to feed everyone, while critics of monocropping dispute these claims and attribute them to corporate special interest groups, citing the damage that monocropping causes to societies and the environment. Many farmers practice neither monocropping nor polyculture, but divide their farms into large plots and rotate crops between the plots to get some of the benefits purported of both systems.
Difficulties
A difficulty with monocropping is that the solution to one problem—whether economic, environmental or political—may result in a cascade of other problems. For example, a well-known concern is pesticides and fertilizers seeping into surrounding soil and groundwater from extensive monocropped acreage in the U.S. and abroad. This issue, especially with respect to the pesticide DDT, played an important role in focusing public attention on ecology and pollution issues during the 1960s when Rachel Carson published her landmark book Silent Spring.
Journalist Michael Pollan argues that monocropping not only depletes fertile land, but it results in overproduction of certain agricultural crops. Corn is a primary example, as its overproduction drove its pricing downward. The overproduction for low prices drives many small farms out of business, as many small farms cannot compete with government-subsidized agricultural productions. This ironically, as Pollan argues, leads to "food deserts" in which farmers produce a certain crop that is modified to be inedible and serve another purpose; this, coupled with low government payments, drives farmers and their families into hunger.
Soil depletion is also a negative effect of mono-cropping. Crop rotation plays an important role in replenishing soil nutrients, especially atmospheric nitrogen converted to usable forms by nitrogen-fixing bacteria that form a relationship with legumes such as soybeans. Some legumes can also be used as cover crops or planted in fallow fields. In addition, monocropping encourages pesticide resistance and pest evolution and so rotating crops performs an important role in preventing pathogen and pest build-up. There are however a few diseases which are less severe in a monocropping system, like take-all in wheat, as the population of an organism which feeds on the disease causing pathogen grows over repeated years of the presence of the pathogen.
Soil ecology
While economically a very efficient system, allowing for specialization in equipment and crop production, monocropping is also controversial, as it damages the soil ecology (including depletion or reduction in diversity of soil nutrients) and provide an unbuffered niche for parasitic species, increasing crop vulnerability to opportunistic insects, plants, and microorganisms. The result is a more fragile ecosystem with an increased dependency on pesticides and artificial fertilizers. The concentrated presence of a single cultivar, genetically adapted with a single resistance strategy, presents a situation in which an entire crop can be wiped out very quickly by a single opportunistic species. An example of this would be the Great Famine of Ireland in 1845–1849.
Deforestation
Under certain circumstances monocropping can lead to deforestation or the displacement of indigenous peoples. For example, since 1970 the Amazon Rainforest has lost nearly one fifth of its forest cover. A main cause of this deforestation is local farmers clearing land for more crops. In Colombia, the need for more farming land is causing the displacement of large populations of peasants.
See also
Intensive farming
Monoculture
References
Intensive farming
Agricultural terminology
Agricultural soil science
Crops | Monocropping | Chemistry | 1,092 |
470,284 | https://en.wikipedia.org/wiki/Transcortin | Transcortin, also known as corticosteroid-binding globulin (CBG) or serpin A6, is a protein produced in the liver in animals. In humans it is encoded by the SERPINA6 gene. It is an alpha-globulin.
Function
This gene encodes an alpha-globulin protein with corticosteroid-binding properties. This is the major transport protein for glucocorticoids and progestins in the blood of most vertebrates. The gene localizes to a chromosomal region containing several closely related serine protease inhibitors (serpins).
Binding
Transcortin binds several steroid hormones at high rates:
Cortisol - Approximately 90% of the cortisol in circulation is bound to transcortin. (The rest is bound to serum albumin.) Cortisol is thought to be biologically active only when it is not bound to transcortin.
Cortisone
Deoxycorticosterone (DOC)
Corticosterone - About 78% of serum corticosterone is bound to transcortin.
Aldosterone - Approximately 17% of serum aldosterone is bound to transcortin, while another 47% is bound to serum albumin. The remaining 36% is free.
Progesterone - Approximately 18% of serum progesterone is bound to transcortin, while another 80% of it is bound to serum albumin. The remaining 2% is free.
17α-Hydroxyprogesterone
In addition, approximately 4% of serum testosterone is bound to transcortin. A similarly small fraction of serum estradiol is bound to transcortin as well.
Synthesis
Transcortin is produced by the liver and is increased by estrogens.
Clinical significance
Mutations in this gene are rare. Only four mutations have been described, often in association with fatigue and chronic pain. This mechanism for these symptoms is not known. This condition must be distinguished from secondary hypocortisolism. Exogenous hydrocortisone does not appear to improve the fatigue.
Hepatic synthesis of corticosteroid-binding globulin more than doubles in pregnancy; that is, bound plasma cortisol in term pregnancy is approximately 2 to 3 times that of nonpregnant women.
See also
Serpin
Circaseptan, 7-day biological cycle
References
Further reading
External links
The MEROPS online database for peptidases and their inhibitors: I04.954
Glycoproteins | Transcortin | Chemistry | 533 |
8,555,091 | https://en.wikipedia.org/wiki/Copper%28II%29%20azide | Copper(II) azide is a medium density explosive with the molecular formula .
Uses
Copper azide is very explosive and is too sensitive for any practical use unless handled in solution.
Preparation
Copper azide can be prepared by a metathesis reaction between water-soluble sources of and azide ions. (Spectator ions omitted in reaction below).
It can be destroyed by concentrated nitric acid to form non-explosive products, these being nitrogen, nitrogen oxides and copper(II) nitrate.
References
Azides
Copper(II) compounds
Explosive chemicals | Copper(II) azide | Chemistry | 110 |
48,258,936 | https://en.wikipedia.org/wiki/Debiasing | Debiasing is the reduction of bias, particularly with respect to judgment and decision making. Biased judgment and decision making is that which systematically deviates from the prescriptions of objective standards such as facts, logic, and rational behavior or prescriptive norms. Biased judgment and decision making exists in consequential domains such as medicine, law, policy, and business, as well as in everyday life. Investors, for example, tend to hold onto falling stocks too long and sell rising stocks too quickly. Employers exhibit considerable discrimination in hiring and employment practices, and some parents continue to believe that vaccinations cause autism despite knowing that this link is based on falsified evidence. At an individual level, people who exhibit less decision bias have more intact social environments, reduced risk of alcohol and drug use, lower childhood delinquency rates, and superior planning and problem solving abilities.
Debiasing can occur within the decision maker. For example, a person may learn or adopt better strategies by which to make judgments and decisions. Debiasing can also occur as a result of changes in external factors, such as changing the incentives relevant to a decision or the manner in which the decision is made.
There are three general approaches to debiasing judgment and decision making, and the costly errors with which biased judgment and decision making is associated: changing incentives, nudging, and training. Each approach has strengths and weaknesses. For more details, see Morewedge and colleagues (2015).
General approaches
Incentives
Changing incentives can be an effective means to debias judgment and decision making. This approach is generally derived from economic theories suggesting that people act in their self-interest by seeking to maximize their utility over their lifetime. Many decision making biases may occur simply because they are more costly to eliminate than to ignore. Making people more accountable for their decisions (increasing incentives), for example, can increase the extent to which they invest cognitive resources in making decisions, leading to less biased decision making when people generally have an idea of how a decision should be made. However, "bias" might not be the appropriate term for these types of decision making errors. These "strategy-based" errors occur simply because the necessary effort outweighs the benefit. If a person makes a suboptimal choice based on an actual bias, then incentives may exacerbate the issue. An incentive in this case may simply cause the person to perform the suboptimal behavior more enthusiastically.
Incentives can be calibrated to change preferences toward more beneficial behavior. Price cuts on healthy foods increase their consumption in school cafeterias, and soda taxes appear to reduce soda consumption by the public. People often are willing to use incentives to change their behavior through the means of a commitment device. Shoppers, for example, were willing to forego a cash back rebate on healthy food items if they did not increase the percentage of healthy foods in their shopping baskets.
Incentives can backfire when they are miscalibrated or are weaker than social norms that were preventing undesirable behavior. Large incentives can also lead people to choke under pressure.
Nudges
Nudges, changes in information presentation or the manner by which judgments and decisions are elicited, is another means to debiasing. People may choose healthier foods if they are better able to understand their nutritional contents, and may choose lower-calorie meals if they are explicitly asked if they would like to downsize their side orders. Other examples of nudges include changing which option is the default option to which people will be assigned if they do not choose an alternative option, placing a limit on the serving size of soda, or automatically enrolling employees in a retirement savings program.
Training
Training can effectively debias decision makers over the long term. Training, to date, has received less attention by academics and policy makers than incentives and nudges because initial debiasing training efforts resulted in mixed success (see Fischhoff, 1982 in Kahneman et al.). Decision makers could be effectively debiased through training in specific domains. For example, experts can be trained to make very accurate decisions when decision making entails recognizing patterns and applying appropriate responses in domains such as firefighting, chess, and weather forecasting. Evidence of more general debiasing, across domains and different kinds of problems, however, was not discovered until recently. The reason for the lack of more domain-general debiasing was attributed to experts failing to recognize the underlying "deep structure" of problems in different formats and domains. Weather forecasters are able to predict rain with high accuracy, for example, but show the same overconfidence in their answers to basic trivia questions as other people. An exception was graduate training in scientific fields heavily reliant on statistics such as psychology.
Experiments by Morewedge and colleagues (2015) have found interactive computer games and instructional videos can result in long-term debiasing at a general level. In a series of experiments, training with interactive computer games that provided players with personalized feedback, mitigating strategies, and practice, reduced six cognitive biases by more than 30% immediately and by more than 20% as long as three months later. The biased reduced were anchoring, bias blind spot, confirmation bias, fundamental attribution error, projection bias, and representativeness.
Training in reference class forecasting may also improve outcomes. Reference class forecasting is a method for systematically debiasing estimates and decisions, based on what Daniel Kahneman calls the outside view. As pointed out by Kahneman in Thinking, Fast and Slow (p. 252), one of the reasons reference class forecasting is effective for debiasing is that, in contrast to conventional forecasting methods, it takes into account the so-called "unknown unknowns." According to Kahneman, reference class forecasting is effective for debiasing and "has come a long way" in practical implementation since he originally proposed the idea with Amos Tversky (p. 251).
Sometimes effective strategies
Incentives
Paying people for optimal behavior through bonuses or by providing discounts (e.g., to exercise, to take their medication, to trade in fuel inefficient vehicles such as the "cash for clunkers" program).
Taxing people for suboptimal behavior (e.g., drinking soda, smoking tobacco, and weed).
Nudges
Using default effect to nudge people towards decisions optimal for the decision maker or society.
Commitment devices that makes it more costly to make suboptimal decisions (e.g., Schwartz et al., 2014).
Reframing choice options in ways that make important attributes salient. Labeling hamburger meat 25% fat, for example, makes people more sensitive to fat content than labeling it 75% lean.
Presenting information in formats that make critical information easier to evaluate, such as displaying nutritional value using a "traffic light" system.
Training
Providing people with personalized feedback regarding the direction and degree to which they exhibit bias.
Teaching a "consider-the-alternative" strategy, such as considering a plausible alternative reason for an event than cause one suspects.
Teaching people statistical reasoning and normative rules of which they are unaware.
Encouraging people to take the perspective of a person who will experience the consequences of their decision can reduce bias. Participants who were shown a "morphed" image of their face to resemble themselves upon retirement were more likely to save money for the future rather than elect to receive it in the present.
Encourage, incentivize, or make mandatory the use of reference class forecasting. Reference class forecasting was made mandatory in Great Britain and Denmark for large government infrastructure projects with the explicit purpose of eliminating optimism bias.
See also
Cognitive bias mitigation
Cognitive bias modification
Cognitive vulnerability
Reference class forecasting
References
Decision-making
Cognitive biases
Behavioral economics
Bias
Heuristics | Debiasing | Biology | 1,605 |
31,936,536 | https://en.wikipedia.org/wiki/Landscape%20and%20Urban%20Planning | Landscape and Urban Planning is a monthly peer-reviewed academic journal published by Elsevier. It covers landscape science (including landscape planning, design, and architecture), urban and regional planning, landscape and ecological engineering, landscape and urban ecology, and other practice-oriented fields. The editors-in-chief are Joan I. Nassauer (University of Michigan) and Peter H. Verburg (Vrije Universiteit Amsterdam).
History
The journal was established in 1974 as Landscape Planning under founding editor-in-chief Arnold E. Weddle. In 1986, the journal was renamed and merged with the journal Urban Ecology. In 1988, the journal also incorporated Reclamation and Revegetation Research.
Editors-in-chief
Landscape and Urban Planning
The following persons are or have been editor-in-chief of Landscape and Urban Planning:
Urban Ecology
The following persons have been editor-in-chief of Urban Ecology:
Amos Rapoport (University of Wisconsin–Milwaukee): April 1981–1986
Royce LaNier (University of Wisconsin–Milwaukee): 1975–March 1981
Reclamation and Revegetation Research
The following persons have been editor-in-chief of Reclamation and Revegetation Research:
Mohan K. Wali (University of North Dakota): 1982–1988
Edward M. Watkin (Mine Waste Reclamation, Guelph, Ontario): 1983–1988
Abstracting and indexing
The journal is abstracted and indexed in:
According to the Journal Citation Reports, the journal has a 2022 impact factor of 9.1.
References
External links
Landscape ecology
Landscape architecture
Urban planning
Urban design
English-language journals
Monthly journals
Elsevier academic journals
Hybrid open access journals
Academic journals established in 1974
Urban studies and planning journals | Landscape and Urban Planning | Engineering | 342 |
10,129,659 | https://en.wikipedia.org/wiki/Ducci%20sequence | A Ducci sequence is a sequence of n-tuples of integers, sometimes known as "the Diffy game", because it is based on sequences.
Given an n-tuple of integers , the next n-tuple in the sequence is formed by taking the absolute differences of neighbouring integers:
Another way of describing this is as follows. Arrange n integers in a circle and make a new circle by taking the difference between neighbours, ignoring any minus signs; then repeat the operation. Ducci sequences are named after Enrico Ducci (1864–1940), the Italian mathematician who discovered in the 1930s that every such sequence eventually becomes periodic.
Ducci sequences are also known as the Ducci map or the n-number game. Open problems in the study of these maps still remain.
Properties
From the second n-tuple onwards, it is clear that every integer in each n-tuple in a Ducci sequence is greater than or equal to 0 and is less than or equal to the difference between the maximum and minimum members of the first n-tuple. As there are only a finite number of possible n-tuples with these constraints, the sequence of n-tuples must sooner or later repeat itself. Every Ducci sequence therefore eventually becomes periodic.
If n is a power of 2 every Ducci sequence eventually reaches the n-tuple (0,0,...,0) in a finite number of steps.
If n is not a power of two, a Ducci sequence will either eventually reach an n-tuple of zeros or will settle into a periodic loop of 'binary' n-tuples; that is, n-tuples of form , is a constant, and .
An obvious generalisation of Ducci sequences is to allow the members of the n-tuples to be any real numbers rather than just integers. For example,
this 4-tuple converges to (0, 0, 0, 0) in four iterations:
The properties presented here do not always hold for these generalisations. For example, a Ducci sequence starting with the n-tuple (1, q, q2, q3) where q is the (irrational) positive root of the cubic does not reach (0,0,0,0) in a finite number of steps, although in the limit it converges to (0,0,0,0).
Examples
Ducci sequences may be arbitrarily long before they reach a tuple of zeros or a periodic loop. The 4-tuple sequence starting with (0, 653, 1854, 4063) takes 24 iterations to reach the zeros tuple.
This 5-tuple sequence enters a period 15 binary 'loop' after 7 iterations.
The following 6-tuple sequence shows that sequences of tuples whose length is not a power of two may still reach a tuple of zeros:
If some conditions are imposed on any "power of two"-tuple Ducci sequence, it would take that power of two or lesser iterations to reach the zeros tuple. It is hypothesized that these sequences conform to a rule.
Modulo two form
When the Ducci sequences enter binary loops, it is possible to treat the sequence in modulo two. That is:
This forms the basis for proving when the sequence vanish to all zeros.
Cellular automata
The linear map in modulo 2 can further be identified as the cellular automata denoted as rule 102 in Wolfram code and related to rule 90 through the Martin-Odlyzko-Wolfram map. Rule 102 reproduces the Sierpinski triangle.
Other related topics
The Ducci map is an example of a difference equation, a category that also include non-linear dynamics, chaos theory and numerical analysis. Similarities to cyclotomic polynomials have also been pointed out. While there are no practical applications of the Ducci map at present, its connection to the highly applied field of difference equations led to conjecture that a form of the Ducci map may also find application in the future.
References
External links
Ducci Sequence
Integer Iterations on a Circle at Cut-the-Knot
Sequences and series
Number theory | Ducci sequence | Mathematics | 859 |
1,810,648 | https://en.wikipedia.org/wiki/Happy%20slapping | Happy slapping was a fad originating in the United Kingdom around 2005, in which one or more people attack a victim for the purpose of recording the assault (commonly with a camera phone or a smartphone). Though the term usually refers to relatively minor acts of violence such as hitting or slapping the victim, more serious crimes such as the murder of a retired care worker, and sexual assault were also occasionally classified as "happy slapping" by the BBC.
Use with video technology
The general availability and affordability of mobile phones with integrated video cameras for the first time in the mid 2000s, in addition to their ease of use, meant that, compared to in previous decades, little if any planning was required to carry out and film such an attack. Similarly, the end product was more easily watched and circulated for entertainment than ever before, spreading through informal networks of person to person sharing. Contemporary media commentators suggested that the craze was inspired by such television shows as Jackass, Dirty Sanchez and Bumfights.
History
"Happy slapping" started in the south London Borough of Lewisham, in a format known as "Slap Happy TV", where a happy-slapping video would be recorded, and then watched by dozens of people like a TV show, but in the form of a montage. Videos of Happy Slapping were commonly circulated via Bluetooth on mobile phones. The first newspaper article to use the phrase "happy slapping" was "Bullies film fights by phone", published in The Times Educational Supplement on 21 January 2005, in which reporter Michael Shaw described teachers' accounts of the craze in London schools.
Gary Martin, writing on "The Phrase Finder" website described the phenomenon as: "Unprovoked attacks on individuals made in order to record the event, and especially the victim's shock and surprise, on video phones."
Martin wrote that happy slapping "began as a youth craze in the UK in late 2004. Children or passers by are slapped or otherwise mugged by one or more of a gang while others record the event on video and then distribute it by phone or Internet. Initially the attacks were, as the phrase would have us believe, fairly minor pranks ... As the craze spread the attacks became more vicious—often serious assaults known in legal circles as grievous bodily harm."
Legal consequences
Denmark
When the international media attention surrounding attacks abroad reached a high point, a girl was sentenced to eight months in prison. She was sentenced on a number of counts including previous crimes.
A common punishment in 2007 was a fine or up to 40 days in prison, suspended if the attacker has no previous record. The attacker shall be liable to a fine or imprisonment for any term which does not exceed 3 years. Happy slapping is judged as "simple battery" as defined by section 244 of the Danish Criminal Code.
France
In February 2007, an amendment aimed at criminalising "happy slapping" was added to a law "on the prevention of delinquency" by the Parliament of France based on a proposal from then Interior Minister Nicolas Sarkozy. The anti-happy-slapping clause appears as the last part of Article 44, which also deals with ambushing law enforcement personnel. The law equates filming or photographing certain classes of violent crimes, including severe beatings and rape, with being an accomplice of such crimes. The law makes it illegal to broadcast the images of such crimes, punishable by up to 5 years in prison and/or a €75,000 fine.
The law does not apply to those who took the above actions in order to obtain evidence in court, or as professional journalism. Professional journalism is delimited in France by the "press card", which is awarded by a commission representing journalist unions and press organisations. As defined by law, a professional journalist is one whose main activity is professional paid journalism.
The bill was signed into law on 5 March 2007, despite some organisations, including Reporters Without Borders, and the French chapter of Wikimedia, arguing that this clause created a legal discrimination in criminal law between professional journalists and ordinary citizens practising journalism. Specifically, it was argued that citizens filming incidents of police brutality and publishing such information online could be intimidated by law enforcement into remaining silent, or prosecuted for their actions. This criticism was relayed by the international media.
French President Nicolas Sarkozy declared to Reporters Without Borders that "the spirit of the law is not to infringe [on] freedom of information. However, if the least doubt subsist[s], then I'm in favour of a clarification of the law."
United Kingdom
In March 2008, a teenage girl who filmed the fatal beating of a man on her mobile phone was sentenced to two years' detention in the first prosecution of its kind in the United Kingdom. The judge stated that the courts had to make an example of such youths. She had pleaded guilty at Leeds Crown Court in February 2008 to aiding and abetting the murder of Gavin Waterhouse, 29, from Keighley, West Yorkshire. Mark Masters, 19, from Keighley, and Sean Thompson, 17, from Bradford, were sentenced to seven and six years, respectively, after admitting to murder. Waterhouse died from a ruptured spleen after being beaten in September 2007.
Just before the attack, the girl was handed a mobile phone by one of the attackers and told to "video this", prosecutors said. She approached Waterhouse, asked for money, and recorded the subsequent attack. She was sentenced to serve a two-year detention training order. Police said they were satisfied with the court's decision. The Crown Prosecutor said "this is the first time a suspect in England and Wales has been successfully prosecuted for aiding and abetting murder or manslaughter, for the filming of an inaptly called 'happy slapping' incident".
Media-reported incidents
United Kingdom: On 9 May 2005, a 16-year-old Plant Hill Arts College student was beaten up and left unconscious in a vicious "happy slapping" attack in Blackley, Manchester. Footage of the attack was circulated on students' phones.
United Kingdom, 18 June 2005: Police arrested three 14-year-old boys for the suspected rape of an 11-year-old girl who attended their school in Stoke Newington, London. Authorities were alerted when school staff saw footage from the students' phones.
United Kingdom, 7 December 2005: Singer Myleene Klass was happy-slapped in Bermondsey, South London.
United Kingdom, December 2005: A 15-year-old-girl, Chelsea O'Mahoney (her name was initially withheld, although this decision was reversed during sentencing) and her co-defendants Reece Sargeant, 21, Darren Case, 18, and David Blenman, 17, were all convicted of the manslaughter of David Morley in London. Barry Lee, 20, and another 17-year-old were cleared of all charges. According to press reports, "The 15-year-old girl had told Morley that she was making a documentary about 'happy slapping' before her gang of friends kicked him to death."
Sweden, 1 September 2006: A 16-year-old boy happy slapped and hospitalised a 15-year-old boy in the city of Örebro. Hours later, the victim's 17-year-old sister stabbed and killed the assailant with a hunting knife and claimed self-defence. The happy slapping was filmed and distributed online. The incidents were considered gang-related.
Australia, 23 October 2006: Police in Victoria launched an investigation into the production and distribution of a DVD, Cunt: The Movie, featuring footage of several youths sexually assaulting a girl and setting her hair on fire. DVD copies were allegedly sold at the Werribee Secondary College for AU$10.
United Kingdom, 26 January 2007: Andrew Elvin, 17, was jailed for life, with a minimum custodial sentence of twelve years, for the murder of Luke Salisbury, who died three days after being attacked by Elvin on 2 March 2006. Caine Hallett, 18, was sentenced to five years for manslaughter for the same incident, while Danielle Reeves, 18, faced a retrial in May 2007 for manslaughter.
United Kingdom, 14 February 2007: Eight youths set upon a 31-year-old man, Curtis Mulcare, in Brighton, who turned out to be an amateur boxer. Two of the youths were hospitalised by the intended victim and four were arrested for causing an affray.
United Kingdom, July 2007: Anthony Anderson, 27, of Hartlepool, urinated on a dying woman while a friend made a video of the incident. He is reported to have yelled "This is YouTube material!"
United Kingdom, November 2007: Emily Nakanda, 15, a contestant in the TV show The X Factor, withdrew from the competition after a happy-slapping video in which Nakanda allegedly attacks a teenage girl was discovered on the internet.
United Kingdom, May 2008: A teenage girl fell to her death from an attic window while trying to escape a "happy slapping" girl gang. Her primary assailant was sentenced to 8 years incarceration while another was ordered detained at a psychiatric facility without a time limit.
United Kingdom, August 2009: Ekram Haque, a retired care worker was assaulted and killed by two teens as he left his house of worship. Haque's attack was the subject of a BBC3 episode of Our Crime.
In fiction
In the 2006 Doctor Who episode "School Reunion", the Doctor comments on the kids at the school being very well-behaved, expecting them to be "happy-slapping hoodies with ASBOs and ringtones".
A group of British teenagers in the 2008 movie Eden Lake film the torturing and burning of a young boy.
In the 2009 film Harry Brown, a teenager films the murder of an elderly man, which Michael Caine's character uses as evidence to inflict pain on the teenager.
In episode 1 of series 2 of the British political satire The Thick of It, Hugh tells Glenn to happy slap Ollie while Hugh takes a picture of it on Ollie's phone.
In Coronation Street in November 2013, Simon Barlow was the victim of a happy-slapping incident by Faye Windass and Grace Piper. He was attacked, forced into one of his cousin Amy's dresses, and almost had lipstick applied to him. Grace filmed while Faye attacked him.
In 2011, Canadian filmmaker Christos Sourligas directed a film, also called Happy Slapping, about this phenomenon. The film was shot entirely on iPhone 4S by the cast. It was re-edited in 2014 with new material to accommodate the selfie-obsessed market.
See also
Knockout game
References
External links
How I unwittingly helped to start the Happy Slaps panic
Happy Slaps: Fact and Fiction
Counterculture of the 2000s
Youth culture in the United Kingdom
Crimes
Abuse
Harassment and bullying
2000s fads and trends
Crime in the United Kingdom
Filmed killings
Slapping | Happy slapping | Biology | 2,253 |
74,991,098 | https://en.wikipedia.org/wiki/Xiaomi%20Civi | Xiaomi Civi and Xiaomi Civi 1S are mid-level youth smartphones of Xiaomi. Xiaomi Civi was presented on September 27, 2021, and Civi 1S on April 21, 2022. Xiaomi Civi is the successor of Xiaomi Mi CC9. The main differences between the models are the processor and the silver colour in the 1S.
Design
The screen is made of Corning Gorilla Glass 5. The back panel is made of glass. The side part is made of aluminium.
By design, the models are similar to Vivo smartphones.
The USB-C connector, speaker, microphone and slot for 2 SIM-cards are located below. On top are the second microphone and IR port. On the right side are the volume buttons and the smartphone lock button.
Xiaomi Civi was sold in 3 colors: Black, Blue and Pink.
Xiaomi Civi 1S was sold in 4 colors: Black, Blue, Pink and Silver.
Specifications
Platform
Xiaomi Civi received a Qualcomm Snapdragon 778G processor, and Civi 1S —Snapdragon 778G+. Both are paired with an Adreno 642L GPU.
Battery
The battery received a volume of 4500 mAh and support for fast charging at 55 W.
Camera
Smartphones received a main triple camera 64 MP, f/1.79 (wide-angle) + 8 MP, f/2.2 with a viewing angle of 120° (ultra-wide) + 2 MP, f/2.4 (macro ) with phase detection autofocus and the ability to record video in 4K@30fps resolution. The front camera received a resolution of 32 MP (wide-angle), autofocus and the ability to record video in 1080p@30fps resolution.
Screen
Screen AMOLED, 6.55", FullHD+ (2400 × 1080) with pixel density 402 ppi, aspect ratio 20:9, display refresh rate 120 Hz, support.
References
Android (operating system) devices
Civi
Mobile phones with infrared transmitter
Mobile phones introduced in 2021
Discontinued smartphones | Xiaomi Civi | Technology | 442 |
20,790,476 | https://en.wikipedia.org/wiki/Harren%20Jhoti | Harren Jhoti (born 1962) is an Indian-born British structural biologist whose main interest has been rational drug design and discovery. He is president and chief executive officer (CEO) of biotechnology company Astex Pharmaceuticals ("Astex") which is located in Cambridge, United Kingdom.
Career
Jhoti co-founded Astex with Tom Blundell and Chris Abell in 1999. He pioneered the development of fragment-based drug discovery (FBDD), an approach now widely used in industry and academia, which identifies small molecules with potential therapeutic potential as part of the drug discovery process. Jhoti was Astex's chief scientific officer until November 2007 when he was appointed CEO. In 2013, Astex was acquired for around USD $900 million and now operates as a wholly owned subsidiary of Otsuka Pharmaceutical Co. Ltd, headquartered in Tokyo, Japan.
Prior to Astex, Jhoti was head of structural biology at GlaxoWellcome (now GSK). Before founding Astex in 1999, he was head of structural biology and bioinformatics at GlaxoWellcome in the UK (1991-1999). Prior to GlaxoWellcome, Jhoti was a post-doctoral scientist at the University of Oxford.
Jhoti received both his BSc (Hons) in biochemistry in 1985 and PhD in protein crystallography in 1989 from the University of London.
Honours, fellowships and awards
Jhoti's scientific achievements have been recognised by the Royal Society, the Royal Society of Chemistry, the Royal Society of Biology and the Academy of Medical Sciences. He has also received the UK BioIndustry Association (BIA)'s Lifetime Achievement Award (2018) and the European Federation for Medicinal Chemistry's Prous Institute-Overton and Meyer Award for New Technologies in Drug Discovery (2012). Jhoti has previously been recognised as the Royal Society of Chemistry's Entrepreneur of the Year Entrepreneur of the Year (2007). He has also served on the board of the BIA between 2013-2015.
Jhoti has been published in Nature and Science, and was featured in Time magazine after Astex was named a Technology Pioneer by the World Economic Forum in 2005.
Jhoti was appointed Officer of the Order of the British Empire (OBE) in the 2023 New Year Honours for services to cancer research and drug discovery.
References
Living people
Fellows of the Royal Society
Fellows of the Royal Society of Biology
Fellows of the Royal Society of Chemistry
Fellows of the Academy of Medical Sciences (United Kingdom)
1962 births
Structural biologists
Indian emigrants to England
Naturalised citizens of the United Kingdom
21st-century Indian biologists
British biologists
Officers of the Order of the British Empire
Alumni of Queen Mary University of London
Alumni of Birkbeck, University of London | Harren Jhoti | Chemistry | 585 |
221,277 | https://en.wikipedia.org/wiki/Kernel%20panic | A kernel panic (sometimes abbreviated as KP) is a safety measure taken by an operating system's kernel upon detecting an internal fatal error in which either it is unable to safely recover or continuing to run the system would have a higher risk of major data loss. The term is largely specific to Unix and Unix-like systems. The equivalent on Microsoft Windows operating systems is a stop error, often called a "blue screen of death".
The kernel routines that handle panics, known as panic() in AT&T-derived and BSD Unix source code, are generally designed to output an error message to the console, dump an image of kernel memory to disk for post-mortem debugging, and then either wait for the system to be manually rebooted, or initiate an automatic reboot. The information provided is of a highly technical nature and aims to assist a system administrator or software developer in diagnosing the problem. Kernel panics can also be caused by errors originating outside kernel space. For example, many Unix operating systems panic if the init process, which runs in user space, terminates.
History
The Unix kernel maintains internal consistency and runtime correctness with assertions as the fault detection mechanism. The basic assumption is that the hardware and the software should perform correctly and a failure of an assertion results in a panic, i.e. a voluntary halt to all system activity. The kernel panic was introduced in an early version of Unix and demonstrated a major difference between the design philosophies of Unix and its predecessor Multics. Multics developer Tom van Vleck recalls a discussion of this change with Unix developer Dennis Ritchie:
I remarked to Dennis that easily half the code I was writing in Multics was error recovery code. He said, "We left all that stuff out. If there's an error, we have this routine called panic, and when it is called, the machine crashes, and you holler down the hall, 'Hey, reboot it.
The original panic() function was essentially unchanged from Fifth Edition UNIX to the VAX-based UNIX 32V and output only an error message with no other information, then dropped the system into an endless idle loop. As the Unix codebase was enhanced, the panic() function was also enhanced to dump various forms of debugging information to the console.
Causes
A panic may occur as a result of a hardware failure or a software bug in the operating system. In many cases, the operating system is capable of continued operation after an error has occurred. If the system is in an unstable state, rather than risking security breaches and data corruption, the operating system stops in order to prevent further damage, which helps to facilitate diagnosis of the error and may restart automatically.
After recompiling a kernel binary image from source code, a kernel panic while booting the resulting kernel is a common problem if the kernel was not correctly configured, compiled or installed. Add-on hardware or malfunctioning RAM could also be sources of fatal kernel errors during start up, due to incompatibility with the OS or a missing device driver. A kernel may also go into panic() if it is unable to locate a root file system. During the final stages of kernel userspace initialization, a panic is typically triggered if the spawning of init fails. A panic might also be triggered if the init process terminates, as the system would then be unusable.
The following is an implementation of the Linux kernel final initialization in kernel_init():
static int __ref kernel_init(void *unused)
{
...
/*
* We try each of these until one succeeds.
*
* The Bourne shell can be used instead of init if we are
* trying to recover a really broken machine.
*/
if (execute_command) {
if (!run_init_process(execute_command))
return 0;
pr_err("Failed to execute %s. Attempting defaults...\n",
execute_command);
}
if (!run_init_process("/sbin/init") ||
!run_init_process("/etc/init") ||
!run_init_process("/bin/init") ||
!run_init_process("/bin/sh"))
return 0;
panic("No init found. Try passing init= option to kernel. "
"See Linux Documentation/init.txt for guidance.");
}
Operating system specifics
Linux
Kernel panics appear in Linux like in other Unix-like systems; however, serious but non-fatal errors can generate another kind of error condition, known as a kernel oops. In this case, the kernel normally continues to run after killing the offending process. As an oops could cause some subsystems or resources to become unavailable, they can later lead to a full kernel panic.
On Linux, a kernel panic causes keyboard LEDs to blink as a visual indication of a critical condition.
macOS
When a kernel panic occurs in Mac OS X 10.2 through 10.7, the computer displays a multilingual message informing the user that they need to reboot the system. Prior to 10.2, a more traditional Unix-style panic message was displayed; in 10.8 and later, the computer automatically reboots and the message is only displayed as a skippable warning afterward. The format of the message varies from version to version:
10.0–10.1: The system displays text on the screen, giving details about the error, and becomes unresponsive.
10.2: Rolls down a black transparent curtain then displays a message on a white background informing the user that they should restart the computer. The message is shown in English, French, German and Japanese.
10.3–10.5: Similar to 10.2, but the background of the error message is dark grey.
10.6–10.7: The text has been revised and now includes a Spanish translation.
10.8 and later: The computer becomes unresponsive before it immediately reboots. After restarting, it shows a message for a few seconds informing the user that a problem caused the computer to restart, before continuing to boot. The message now includes a Chinese translation.
If five new kernel panics occur within three minutes of the first one, the Mac will display a prohibitory sign for thirty seconds, and then shut down; this is known as a "recurring kernel panic".
In all versions above 10.2, the text is superimposed on a standby symbol and is not full screen. Debugging information is saved in NVRAM and written to a log file on reboot. In 10.7 there is a feature to automatically restart after a kernel panic. In some cases, on 10.2 and later, white text detailing the error may appear in addition to the standby symbol.
See also
Core dump
Blue screen of death
Fatal system error
Screen of death
Machine-check exception (MCE)
Reliability, availability and serviceability (RAS)
References
Computer errors
Operating system kernels
Screens of death | Kernel panic | Technology | 1,483 |
7,817,474 | https://en.wikipedia.org/wiki/Vapor%E2%80%93liquid%20equilibrium | In thermodynamics and chemical engineering, the vapor–liquid equilibrium (VLE) describes the distribution of a chemical species between the vapor phase and a liquid phase.
The concentration of a vapor in contact with its liquid, especially at equilibrium, is often expressed in terms of vapor pressure, which will be a partial pressure (a part of the total gas pressure) if any other gas(es) are present with the vapor. The equilibrium vapor pressure of a liquid is in general strongly dependent on temperature. At vapor–liquid equilibrium, a liquid with individual components in certain concentrations will have an equilibrium vapor in which the concentrations or partial pressures of the vapor components have certain values depending on all of the liquid component concentrations and the temperature. The converse is also true: if a vapor with components at certain concentrations or partial pressures is in vapor–liquid equilibrium with its liquid, then the component concentrations in the liquid will be determined dependent on the vapor concentrations and on the temperature. The equilibrium concentration of each component in the liquid phase is often different from its concentration (or vapor pressure) in the vapor phase, but there is a relationship. The VLE concentration data can be determined experimentally or approximated with the help of theories such as Raoult's law, Dalton's law, and Henry's law.
Such vapor–liquid equilibrium information is useful in designing columns for distillation, especially fractional distillation, which is a particular specialty of chemical engineers. Distillation is a process used to separate or partially separate components in a mixture by boiling (vaporization) followed by condensation. Distillation takes advantage of differences in concentrations of components in the liquid and vapor phases.
In mixtures containing two or more components, the concentrations of each component are often expressed as mole fractions. The mole fraction of a given component of a mixture in a particular phase (either the vapor or the liquid phase) is the number of moles of that component in that phase divided by the total number of moles of all components in that phase.
Binary mixtures are those having two components. Three-component mixtures are called ternary mixtures. There can be VLE data for mixtures with even more components, but such data is often hard to show graphically. VLE data is a function of the total pressure, such as 1 atm or at the pressure the process is conducted at.
When a temperature is reached such that the sum of the equilibrium vapor pressures of the liquid components becomes equal to the total pressure of the system (it is otherwise smaller), then vapor bubbles generated from the liquid begin to displace the gas that was maintaining the overall pressure, and the mixture is said to boil. This temperature is called the boiling point of the liquid mixture at the given pressure. (It is assumed that the total pressure is held steady by adjusting the total volume of the system to accommodate the specific volume changes that accompany boiling.) The boiling point at an overall pressure of 1 atm is called the normal boiling point of the liquid mixture.
Thermodynamic description of vapor–liquid equilibrium
The field of thermodynamics describes when vapor–liquid equilibrium is possible, and its properties. Much of the analysis depends on whether the vapor and liquid consist of a single component, or if they are mixtures.
Pure (single-component) systems
If the liquid and vapor are pure, in that they consist of only one molecular component and no impurities, then the equilibrium state between the two phases is described by the following equations:
;
; and
where and are the pressures within the liquid and vapor, and are the temperatures within the liquid and vapor, and and are the molar Gibbs free energies (units of energy per amount of substance) within the liquid and vapor, respectively. In other words, the temperature, pressure and molar Gibbs free energy are the same between the two phases when they are at equilibrium.
An equivalent, more common way to express the vapor–liquid equilibrium condition in a pure system is by using the concept of fugacity. Under this view, equilibrium is described by the following equation:
where and are the fugacities of the liquid and vapor, respectively, at the system temperature and pressure . It is often convenient to use the quantity , the dimensionless fugacity coefficient, which is 1 for an ideal gas.
Multicomponent systems
In a multicomponent system, where the vapor and liquid consist of more than one type of compounds, describing the equilibrium state is more complicated. For all components in the system, the equilibrium state between the two phases is described by the following equations:
;
; and
where and are the temperature and pressure for each phase, and and are the partial molar Gibbs free energy also called chemical potential (units of energy per amount of substance) within the liquid and vapor, respectively, for each phase. The partial molar Gibbs free energy is defined by:
where is the (extensive) Gibbs free energy, and is the amount of substance of component .
Boiling-point diagrams
Binary mixture VLE data at a certain overall pressure, such as 1 atm, showing mole fraction vapor and liquid concentrations when boiling at various temperatures can be shown as a two-dimensional graph called a boiling-point diagram. The mole fraction of component 1 in the mixture can be represented by the symbol . The mole fraction of component 2, represented by , is related to in a binary mixture as follows:
In multi-component mixtures in general with n components, this becomes:
The preceding equilibrium equations are typically applied for each phase (liquid or vapor) individually, but the result can be plotted in a single diagram. In a binary boiling-point diagram, temperature () (or sometimes pressure) is graphed vs. . At any given temperature (or pressure) where both phases are present, vapor with a certain mole fraction is in equilibrium with liquid with a certain mole fraction. The two mole fractions often differ. These vapor and liquid mole fractions are represented by two points on the same horizontal isotherm (constant ) line. When an entire range of temperatures vs. vapor and liquid mole fractions is graphed, two (usually curved) lines result. The lower one, representing the mole fraction of the boiling liquid at various temperatures, is called the bubble point curve. The upper one, representing the mole fraction of the vapor at various temperatures, is called the dew point curve.
These two curves necessarily meet where the mixture becomes purely one component, namely where (and , pure component 2) or (and , pure component 1). The temperatures at those two points correspond to the boiling points of each of the two pure components.
For certain pairs of substances, the two curves also coincide at some point strictly between and . When they meet, they meet tangently; the dew-point temperature always lies above the boiling-point temperature for a given composition when they are not equal. The meeting point is called an azeotrope for that particular pair of substances. It is characterized by an azeotrope temperature and an azeotropic composition, often expressed as a mole fraction. There can be maximum-boiling azeotropes, where the azeotrope temperature is at a maximum in the boiling curves, or minimum-boiling azeotropes, where the azeotrope temperature is at a minimum in the boiling curves.
If one wants to represent a VLE data for a three-component mixture as a boiling point "diagram", a three-dimensional graph can be used. Two of the dimensions would be used to represent the composition mole fractions, and the third dimension would be the temperature. Using two dimensions, the composition can be represented as an equilateral triangle in which each corner represents one of the pure components. The edges of the triangle represent a mixture of the two components at each end of the edge. Any point inside the triangle represents the composition of a mixture of all three components. The mole fraction of each component would correspond to where a point lies along a line starting at that component's corner and perpendicular to the opposite edge. The bubble point and dew point data would become curved surfaces inside a triangular prism, which connect the three boiling points on the vertical temperature "axes". Each face of this triangular prism would represent a two-dimensional boiling-point diagram for the corresponding binary mixture. Due to their three-dimensional complexity, such boiling-point diagrams are rarely seen. Alternatively, the three-dimensional curved surfaces can be represented on a two-dimensional graph by the use of curved isotherm lines at graduated intervals, similar to iso-altitude lines on a map. Two sets of such isotherm lines are needed on such a two-dimensional graph: one set for the bubble point surface and another set for the dew point surface.
K values and relative volatility values
The tendency of a given chemical species to partition itself
preferentially between liquid and vapor phases is the Henry's law constant. There can be VLE data for mixtures of four or more components, but such a boiling-point diagram is hard to show in either tabular or graphical form. For such multi-component mixtures, as well as binary
mixtures, the vapor–liquid equilibrium data are represented in terms of values (vapor–liquid distribution ratios) defined by
where and are the mole fractions of component in the phases and respectively.
For Raoult's law
For modified Raoult's law
where is the activity coefficient, is the partial pressure and is the pressure.
The values of the ratio are correlated empirically or theoretically in terms of temperature, pressure and phase compositions in the form of equations, tables or graph such as the DePriester charts.
For binary mixtures, the ratio of the values for the two components is called the relative volatility denoted by
which is a measure of the relative ease or difficulty of separating the two components. Large-scale industrial distillation is rarely undertaken if the relative volatility is less than 1.05 with the volatile component being and the less volatile component being .
values are widely used in the design calculations of continuous distillation columns for distilling multicomponent mixtures.
Vapor–liquid equilibrium diagrams
For each component in a binary mixture, one could make a vapor–liquid equilibrium diagram. Such a diagram would graph liquid mole fraction on a horizontal axis and vapor mole fraction on a vertical axis. In such VLE diagrams, liquid mole fractions for components 1 and 2 can be represented as and respectively, and vapor mole fractions of the corresponding components are commonly represented as and . Similarly for binary mixtures in these VLE diagrams:
Such VLE diagrams are square with a diagonal line running from the () corner to the () corner for reference.
These types of VLE diagrams are used in the McCabe–Thiele method to determine the number of equilibrium stages (or theoretical plates) needed to distill a given composition binary feed mixture into one distillate fraction and one bottoms fraction. Corrections can also be made to take into account the incomplete efficiency of each tray in a distillation column when compared to a theoretical plate.
Raoult's law
At boiling and higher temperatures the sum of the individual component partial pressures becomes equal to the overall pressure, which can symbolized as .
Under such conditions, Dalton's law would be in effect as follows:
Then for each component in the vapor phase:
where = partial pressure of component 1, = partial pressure of component 2, etc.
Raoult's law is approximately valid for mixtures of components between which there is very little interaction other than the effect of dilution by the other components. Examples of such mixtures includes mixtures of alkanes, which are non-polar, relatively inert compounds in many ways, so there is little attraction or repulsion between the molecules. Raoult's law states that for components 1, 2, etc. in a mixture:
where , , etc. are the vapor pressures of components 1, 2, etc. when they are pure, and , , etc. are mole fractions of the corresponding component in the liquid.
Recall from the first section that vapor pressures of liquids are very dependent on temperature. Thus the pure vapor pressures for each component are a function of temperature (): For example, commonly for a pure liquid component, the Clausius–Clapeyron relation may be used to approximate how the vapor pressure varies as a function of temperature. This makes each of the partial pressures dependent on temperature also regardless of whether Raoult's law applies or not. When Raoult's law is valid these expressions become:
At boiling temperatures if Raoult's law applies, the total pressure becomes:
At a given such as 1 atm and a given liquid composition, can be solved for to give the liquid mixture's boiling point or bubble point, although the solution for may not be mathematically analytical (i.e., may require a numerical solution or approximation). For a binary mixture at a given , the bubble point can become a function of (or ) and this function can be shown on a two-dimensional graph like a binary boiling point diagram.
At boiling temperatures if Raoult's law applies, a number of the preceding equations in this section can be combined to give the following expressions for vapor mole fractions as a function of liquid mole fractions and temperature:
Once the bubble point 's as a function of liquid composition in terms of mole fractions have been determined, these values can be inserted into the above equations to obtain corresponding vapor compositions in terms of mole fractions. When this is finished over a complete range of liquid mole fractions and their corresponding temperatures, one effectively obtains a temperature function of vapor composition mole fractions. This function effectively acts as the dew point function of vapor composition.
In the case of a binary mixture, and the above equations can be expressed as:
For many kinds of mixtures, particularly where there is interaction between components beyond simply the effects of dilution, Raoult's law does not work well for determining the shapes of the curves in the boiling point or VLE diagrams. Even in such mixtures, there are usually still differences in the vapor and liquid equilibrium concentrations at most points, and distillation is often still useful for separating components at least partially. For such mixtures, empirical data is typically used in determining such boiling point and VLE diagrams. Chemical engineers have done a significant amount of research trying to develop equations for correlating and/or predicting VLE data for various kinds of mixtures which do not obey Raoult's law well.
See also
Continuous distillation
Dortmund Data Bank (includes a collection of VLE data)
Fenske equation
Flash evaporation
DECHEMA model
Hand boiler
Van Laar equation
Margules activity model
Pervaporation
Supercooling
Superheated steam
External links
Distillation Principals by Ming T. Tham, University of Newcastle upon Tyne (scroll down to Relative Volatility)
Introduction to Distillation: Vapor Liquid Equilibria
VLE Thermodynamics (Chemical Engineering Dept., Prof. Richard Rowley, Brigham Young University)
NIST Standard Reference Database 103b (Describes the extensive VLE database available from NIST)
Some VLE data sets and diagrams for mixtures of 30 common components, a small subset of the Dortmund Data Bank
Where can I get the vapor-liquid phase equilibrium data? Reference to the various phase equilibrium data sources
Can. J. Chem. Eng. ternary and multicomponent systems from binary ones
George Schlowsky, Alan Erickson, and Thomas A. Schafer, Modular Process Systems, Inc., Operations & Maintenance - Generating your own VLE Data, Chemical Engineering, March 1995, McGraw-Hill, Inc.
References
Chemical engineering thermodynamics
Equilibrium chemistry
Distillation
Phases of matter | Vapor–liquid equilibrium | Physics,Chemistry,Engineering | 3,227 |
29,039 | https://en.wikipedia.org/wiki/SH3%20domain | The SRC Homology 3 Domain (or SH3 domain) is a small protein domain of about 60 amino acid residues. Initially, SH3 was described as a conserved sequence in the viral adaptor protein v-Crk. This domain is also present in the molecules of phospholipase and several cytoplasmic tyrosine kinases such as Abl and Src. It has also been identified in several other protein families such as: PI3 Kinase, Ras GTPase-activating protein, CDC24 and cdc25. SH3 domains are found in proteins of signaling pathways regulating the cytoskeleton, the Ras protein, and the Src kinase and many others. The SH3 proteins interact with adaptor proteins and tyrosine kinases. Interacting with tyrosine kinases, SH3 proteins usually bind far away from the active site. Approximately 300 SH3 domains are found in proteins encoded in the human genome. In addition to that, the SH3 domain was responsible for controlling protein-protein interactions in the signal transduction pathways and regulating the interactions of proteins involved in the cytoplasmic signaling.
Structure
The SH3 domain has a characteristic beta-barrel fold that consists of five or six β-strands arranged as two tightly packed anti-parallel β sheets. The linker regions may contain short helices. The SH3-type fold is an ancient fold found in eukaryotes as well as prokaryotes.
Peptide binding
The classical SH3 domain is usually found in proteins that interact with other proteins and mediate assembly of specific protein complexes, typically via binding to proline-rich peptides in their respective binding partner. Classical SH3 domains are restricted in humans to intracellular proteins, although the small human MIA family of extracellular proteins also contain a domain with an SH3-like fold.
Many SH3-binding epitopes of proteins have a consensus sequence that can be represented as a regular expression or Short linear motif:
-X-P-p-X-P-
1 2 3 4 5
with 1 and 4 being aliphatic amino acids, 2 and 5 always and 3 sometimes being proline. The sequence binds to the hydrophobic pocket of the SH3 domain. More recently, SH3 domains that bind to a core consensus motif R-x-x-K have been described. Examples are the C-terminal SH3 domains of adaptor proteins like Grb2 and Mona (a.k.a. Gads, Grap2, Grf40, GrpL etc.). Other SH3 binding motifs have emerged and are still emerging in the course of various molecular studies, highlighting the versatility of this domain.
SH3 interactomes
SH3 domain-mediated protein-protein interaction networks, i.e., SH3 interactomes, revealed that worm SH3 interactome resembles the analogous yeast network because it is significantly enriched for proteins with roles in endocytosis. Nevertheless, orthologous SH3 domain-mediated interactions are highly rewired between worm and yeast.
Proteins with SH3 domain
Signal transducing adaptor proteins
CDC24
Cdc25
PI3 kinase
Phospholipase
Ras GTPase-activating protein
Vav proto-oncogene
GRB2
p54 S6 kinase 2 (S6K2)
SH3D21
ARMH3 (potentially)
STAC3
Some myosins
SH3 and multiple ankyrin repeat domains: SHANK1, SHANK2, SHANK3
YAP1
ARHGAP12
vexin (VXN)
TANGO1
Integrase
Focal Adhesion Kinase (FAK, PTK2)
Proline-rich tyrosine kinase (Pyk2, CADTK, PTK2beta)
TRIP10 (cip4)
See also
Src homology 2 domain-containing
Structural domain
References
External links
Nash Lab Protein Interaction Domains in Signal Transduction - The SH3 domain
GENEART - Screen your protein against all human SH3 domains in a single phage display cycle
Protein domains
Protein superfamilies | SH3 domain | Biology | 836 |
69,540,685 | https://en.wikipedia.org/wiki/ChoKyun%20Rha | ChoKyun Rha (October 5, 1933 – March 2, 2021) was a Korean-born American food technologist, inventor, and professor of biomaterials science and engineering at the Massachusetts Institute of Technology (MIT). She was the first Asian woman awarded tenure at MIT.
Early life
ChoKyun Rha was born in Seoul, the daughter of SaeJin Rha and Young Soon Choi Rha. Her father was a physician and dean of the medical school at Seoul National University. She moved to the United States in 1956, and attended Miami University in Ohio, before enrolling at MIT as an undergraduate. She finished a bachelor's degree in 1962, with a senior thesis on the storage of dried scallions. She stayed at MIT to earn master's degrees in 1964 and 1966, and completed a doctoral degree in 1967, with a dissertation titled "Thermal Sterilization of Flexibly Packaged Foods".
Career
Rha was a professor of biomaterials science and engineering at MIT, until her retirement in 2006. In 1980, she became the first Asian woman to earn tenure at MIT. She helped establish Genzyme, a biotechnology firm, and founded and directed the Malaysia-MIT Biotechnology Partnership Program. She endowed a professorship in industrial biotechnology at MIT. She was a co-founder of Women’s World Banking, a microfinancing program.
Rha's research focused on biochemistry and biotechnology for food and other applications. Her work was published in academic journalist including Journal of Food Science, Nature Biotechnology, Applied Microbiology and Biotechnology, Bioresource Technology, Biotechnology Letters, and British Journal of Nutrition. She earned her first of several patents in 1988, with a process for encapsulation. As part of her work in Malaysia, she developed several patented products derived from palm oil.
Publications
"Evaluation of cheese texture" (1978, with Cho Lee and Em Imoto)
"Microstructure of soybean protein aggregates and its relation to the physical and textural properties of the curd" (1978, with Cho Lee)
"Single-Cell Protein: Engineering, Economics, and Utilization in Foods" (1980, with C. L. Cooney and S. R. Tannenbaum)
"Improved detergent-based recovery of polyhydroxyalkanoates (PHAs)" (2011, with Yung-Han Yang, Christopher Brigham, Laura Willis, and Anthony Sinskey)
Theory, Determination and Control of Physical Properties of Food Materials (book edited by Rha, 2012)
Characterization of chitosan film" (2012, with Carlos A. Kienzle-Sterzer and Dolores Rodriguez Sanchez)
"Characterization of an extracellular lipase and its chaperone from Ralstonia eutropha H16" (2013, with Jingnan Lu, Christopher Brigham, and Anthony Sinskey)
Personal life
ChoKyun Rha married fellow MIT professor Anthony Sinskey, and the couple frequently collaborated on research. She had two sons, Tong-ik Lee Sinskey and Taeminn Song, both of whom graduated from MIT. Rha died in 2021, in Boston, aged 87 years.
References
1933 births
2021 deaths
Academics from Seoul
South Korean emigrants to the United States
American women scientists
Massachusetts Institute of Technology faculty
Massachusetts Institute of Technology alumni
Food technology
Biotechnologists | ChoKyun Rha | Biology | 680 |
1,025,034 | https://en.wikipedia.org/wiki/Dakuten%20and%20handakuten | The , colloquially , is a diacritic most often used in the Japanese kana syllabaries to indicate that the consonant of a mora should be pronounced voiced, for instance, on sounds that have undergone rendaku (sequential voicing).
The , colloquially , is a diacritic used with kana for morae pronounced with or to indicate that they should instead be pronounced with .
Glyphs
The dakuten resembles a quotation mark, while the handakuten is a small circle, similar to a degree sign, both placed at the top right corner of a kana character:
Both the dakuten and handakuten glyphs are drawn identically in hiragana and katakana scripts. The combining characters are rarely used in full-width Japanese characters, as Unicode and all common multibyte Japanese encodings provide precomposed glyphs for all possible dakuten and handakuten character combinations in the standard hiragana and katakana ranges. However, combining characters are required in half-width kana, which does not provide any precomposed characters in order to fit within a single byte.
The similarity between the dakuten and quotation marks (") is not a problem, as written Japanese uses corner brackets (「」).
Phonetic shifts
The following table summarizes the phonetic shifts indicated by the dakuten and handakuten. Literally, morae with dakuten are , while those without are . However, the handakuten (lit. "half-muddy mark") does not follow this pattern.
(Yellow shading indicates non-standard use.)
Handakuten on ka, ki, ku, ke, ko (rendered as ) represent the sound of ng in singing (), which is an allophone of in many dialects of Japanese. They are not used in normal Japanese writing, but may be used by linguists and in dictionaries (or to represent characters in fiction who speak that way). This is called . Another rare application of handakuten is on the r-series, to mark them as explicitly l: , and so forth. This is only done in technical or pedantic contexts, as many Japanese speakers cannot tell the difference between r and l. Additionally, linguists sometimes use to represent in cases when speaker pronounces at the beginning of a word as a moraic nasal.
In katakana only, the dakuten may also be added to the character u and a small vowel character to create a sound, as in ヴァ va. However, a hiragana version of this character also exists, with somewhat sporadic compatibility across platforms (). As does not exist in Japanese, this usage applies only to some modern loanwords and remains relatively uncommon, and e.g. Venus is typically transliterated as (bīnasu) instead of (vīnasu). Japanese speakers, however, pronounce both the same, with or , an occasional allophone of intervocalic .
An even less common method is to add dakuten to the w-series, reviving the mostly obsolete characters for () and (). is represented by using /u/, as above; becomes despite its normally being silent. Precomposed characters exist for this method as well ( ), although most IMEs do not have a convenient way to enter them.
In Ainu texts, handakuten can be used with the katakana to make it a /t͡s/ sound, ce [t͡se] (which is interchangeable with ), and is used with small fu to represent a final p, . In addition, handakuten can be combined with either katakana or (tsu and to) to make a [tu̜] sound, or .
In Miyakoan, handakuten can be used with (normally [i]) to represent the vowel .
In informal writing, dakuten is occasionally used on vowels to indicate a shocked or strangled articulation; for example, on or . Dakuten can also be occasionally used with to indicate a guttural hum, growl, or similar sound.
Kana iteration marks
The dakuten can also be added to hiragana and katakana iteration marks, indicating that the previous kana is repeated with voicing:
Both signs are relatively rare, but can occasionally be found in personal names such as Misuzu () or brand names such as Isuzu (いすゞ). In these cases the pronunciation is identical to writing the kana out in full. A longer, multi-character iteration mark called the kunojiten (), only used in vertical writing, may also have a dakuten added ().
Other communicative representations
Representations of Dakuten
Representations of Handakuten
Voiced morae and semi-voiced morae do not have independent names in radiotelephony and are signified by the unvoiced name followed by "ni dakuten" or "ni handakuten".
Full Braille representation
History
The kun'yomi pronunciation of the character (daku in on'yomi) is nigori; hence the dakuten may also be called the nigori-ten. This character, meaning "muddy", stems from historical Chinese phonology, where consonants were traditionally classified as "fully clear" (, voiceless unaspirated obstruent), "partly clear" (, voiceless aspirated obstruent), "fully muddy" (, voiced obstruent) and "partly muddy" (, voiced sonorant) (see Middle Chinese § Initials and w:zh:清濁音). Unlike in Chinese where "clear" and "muddy" were phonological, in Japanese, these terms are purely orthographic: a is simply a kana with a "muddy mark", or a dakuten; a or is simply a kana with a "half muddy mark", or a handakuten; a is any other kana without either of these marks. In fact, the "partly clear/half muddy" consonant in Japanese would be considered "fully clear" in Chinese, while "clear" Japanese consonants such as , , , and would be "partly muddy" in Chinese. Meiji-era descriptions of the Japanese "sound" system (either the actual phonology, or the orthography) in terms of "clear" and "muddy" always referenced the kana spelling and the two diacritics dakuten and handakuten.
Dakuten were used sporadically since the start of written Japanese; their use tended to become more common as time went on. The modern practice of using dakuten in all cases of voicing in all writing only came into being in the Meiji period.
The handakuten is an innovation by Portuguese Jesuits, who first used it in the Rakuyōshū. These Jesuits needed to accurately transcribe Japanese sounds, which the Japanese tended to neglect by making no distinction between /h/, /b/ and /p/ in their own writing.
See also
Tsu (kana)
Sokuon
Dagesh (Hebrew diacritic)
References
External links
and on Japanese Wikipedia
(Trans.: Phonetic Kana with Dakuten) and (Trans.: Phonetic Kana with Handakuten)
Kana
Japanese phonology
Japanese writing system terms
Diacritics | Dakuten and handakuten | Mathematics | 1,544 |
69,074,412 | https://en.wikipedia.org/wiki/American%20Center%20for%20Mobility | The American Center for Mobility (ACM) is a vehicular automation research center and federally designated automated vehicle proving ground located in Ypsilanti Township, Michigan.
History
Founded in December 2017 on the site of the Willow Run manufacturing complex, the American Center for Mobility began as a joint initiative of the State of Michigan, partnering with Ann Arbor SPARK, Business Leaders for Michigan, the Michigan Department of Transportation, the Michigan Economic Development Corporation, the University of Michigan, and Ypsilanti Township as a way of accelerating autonomous vehicle research regionally and nationally.
Portions of the US Highway 12 alignment and ramps to the former manufacturing complex were repurposed for creation of a test track. Additional roadways and connections were constructed on the site of the complex.
Features
The test track includes a curved tunnel, highway loop, an off-road course, two double overpasses, along with various intersections and roundabouts. The track is branded as "Powered by Intertek" as Intertek serves as operations and maintenance partner.
In January of 2020 ACM opened its Technology Park, designed to serve as an incubation hub for startups and offices onsite for partners, as well as event and demonstration space.
In addition to the test track and research center in Ypsilanti, ACM also operates the Detroit Smart Parking Center in Detroit in partnership with Ford, Bedrock, and Bosch.
References
Road test tracks
2017 establishments in Michigan
Self-driving cars | American Center for Mobility | Engineering | 293 |
11,172,587 | https://en.wikipedia.org/wiki/HEPPS%20%28buffer%29 | HEPPS (EPPS) is a buffering agent used in biology and biochemistry. The pKa of HEPPS is 8.00. It is ones of Good's buffers.
Research on mice with Alzheimer's disease-like amyloid beta plaques has shown that HEPPS can cause the plaques to break up, reversing some of the symptoms in the mice. HEPPS was reported to dissociate amyloid beta oligomers in patients' plasma samples enabling blood diagnosis of Alzheimer's disease.
See also
CAPSO
CHES
HEPES
References
Buffer solutions
Sulfonic acids
Piperazines
Primary alcohols | HEPPS (buffer) | Chemistry,Biology | 128 |
78,590,623 | https://en.wikipedia.org/wiki/Diradicaloid | Biradicaloids or diradicaloids are molecules with two radical electrons that have significant interaction with each other. The two unpaired electrons are coupled and can either form a singlet ground state (antiferromagnetic coupling) or a triplet ground state (ferromagnetic coupling) (Figure 1).
This is in contrast to "disbiradicals," where the two radical electrons have no significant interaction and act independently as isolated radical species. Diradicals are characterized by their diradical character, commonly quantified using an indicator . In the limit of fully degenerate frontier molecular orbitals, approaches a value of 1, representing 100% diradical character. However, diradicaloids have a small gap between the highest occupied molecular orbital (HOMO) and the lowest occupied molecular orbital (LUMO) and thus can be described as having incomplete diradical character, generally corresponding to a value of between 0.20 and 0.80. Diradicals have historically been characterized as transient species describing the transition state of a bond breaking and/or making process, but recently, the introduction of steric strain to prevent bond formation and substitution of carbon atoms with main-group elements have been found to significantly stabilize diradical species, leading to their isolation and structural characterization. However, these modifications decrease diradical character, leading these species to be more properly designated as diradicaloids. Diradicaloids have found applications in small molecule activation, molecular switching, nonlinear optics, and spintronics.
Theoretical description
Electronic structure
Due to the coupling interaction between the radical electrons in a diradical(oid) species, they cannot be simply described as the union of two independent radical centers. Both the open-shell singlet and triplet states must be considered to fully describe the electronic structure of diradical(oid) species.
The triplet state wavefunction can be described as a single electronic configuration with a single Slater determinant. However, when the frontier molecular orbitals are degenerate or nearly degenerate, the lowest-energy singlet state wavefunction must account for multiple electronic configurations (see electronic correlation). Thus, is most accurately represented as a combination of Slater determinants. Here, the configuration interaction (CI) coefficients and define the contribution of each determinant to the total wavefunction, where refers to the HOMO and refers to the LUMO:
When , and are degenerate, and the singlet wavefunction describes a perfect diradical. As the HOMO-LUMO gap increases, the wavefunction approaches that of a classical closed-shell species; approaches 1 and approaches 0 so that the lowest-energy singlet state is dominated by the doubly occupied HOMO.
To gain a more intuitive understanding of the diradical nature of the wavefunction, the triplet and singlet wavefunctions can be represented using a localized orbital basis, where and are the two localized orbitals (Figure 2). Assuming and are orthogonal, the overlap integral becomes 0. The HOMO can be decomposed into the in-phase overlap of and , while the LUMO can be decomposed into the out-of-phase overlap of and :
Consequently, the singlet wavefunction can be expressed as the combination of a covalent contribution and an ionic contribution . The covalent component represents the electron configuration in which both localized orbitals are singly occupied; this corresponds to diradical character. The ionic component represents the electron configuration in which one localized orbital is doubly occupied, leaving the other localized orbital empty; this corresponds to zwitterionic character:
where and
When , and ; thus, this situation describes 100% diradical character. As the HOMO-LUMO gap increases, approaches 1 and approaches 0, which results in ; thus, this situation reduces to the complete delocalization of the electrons over the two-orbital system, which is equivalent to the electron configuration of the closed-shell species.
Indicators of diradical character
The CI coefficients and can be used to provide a quantification of diradical character. Some common indicators are listed below:
All of the above indicators () effectively describe how much greater the relative weight of the covalent contribution is to the singlet wavefunction compared to the ionic contribution. Thus, the greater the values of these indicators, the greater the diradical character. In the limit of 100% diradical character, these indicators approach a value of 1; in the limit of 100% classical closed-shell character, these indicators approach a value of 0.
Natural orbital (NO) occupation numbers are also another theoretical indicator of diradical character. The occupancy of the lowest unoccupied NO is equal to the indicator and ranges from 0 to 1; the closer the calculated occupancy is to 1, the greater the predicted diradical character. On the other hand, the occupancy of the highest occupied NO ranges from 1 to 2; the closer the calculated occupancy is to 1, the greater the predicted diradical character. These natural orbital occupancy numbers can be calculated using almost all computational methods and therefore can often be obtained with less computational cost than calculating using CI methods.
A small singlet-triplet energy gap can also indicate increased diradical character. Lastly, if the calculated A-B distance (where A and B are the two radical centers) is elongated compared to the sum of the covalent radii (the typical A-B distance of a closed-shell molecule) but is shorter than the sum of the van der Waals radii, this may also suggest the presence of a diradicaloid. Incorporating sterically bulky substituents and introducing ring strain in heterocycles can help to prevent bond formation and/or generate elongated bonds.
Synthesis
Cyclobutane-1,3-diyl analogues
Cyclobutane-1,3-diyl
Cyclobutane-1,3-diyl is the planar four-membered carbon ring species with radical character localized at the 1 and 3 positions. The singlet cyclobutane-1,3-diyl is predicted to be the transition state for the ring inversion of bicyclobutane, proceeding via homolytic cleavage of the transannular carbon-carbon bond (Figure 3).
A 1,3-dimethyl substituted derivative in the triplet state was detected by electron paramagnetic resonance spectroscopy; the diradical species was generated via irradiation of the precursor diazo compound below 25 K in a solid matrix (Figure 4). However, the all-carbon cyclobutane-1,3-diyl is very short-lived and quickly reacts to form the bicyclobutane isomer.
1,3-diphospha-cyclobutane-2,4-diyl
In 1995, Niecke and coworkers reported the first synthesis of a phosphorus analog of cyclobutane-1,3-diyl, [ClC(μ-PMes*)]2. This species consists of a [P2C2]-four-membered heterocycle with radical character centered on the two carbon atoms. The heterocycle was synthesized from the reaction of aryl(dichloromethylene)phosphene (aryl = Mes*, supermesityl) with n-butyllithium in a 2:1 ratio, followed by elimination of LiCl (Figure 5). X-ray diffraction revealed that that the [P2C2] unit exists in the planar four-membered ring form, rather than as the bicyclic isomer. MCSCF calculations predicted a singlet ground state. In addition, the calculated CI wavefunction has contributions from both the doubly occupied HOMO state and the doubly occupied LUMO state; this corresponded to occupation of the HOMO with 1.6 electrons, indicating considerable diradical character. The diphosphacyclobutane heterocycle is thermally stable, and transannular C-C bond formation is thermally forbidden according to the Woodward-Hoffmann rules. Heating at 100 °C in toluene led to the cleavage of the P-C bond, likely generating a ring-opened carbene intermediate that subsequently performed intramolecular C-H activation.
Another synthetic route was developed by Yoshifuji and Ito to access a wider variety of substituents at phosphorus (Figure 7). 2 equivalents of Mes*-substituted phosphaalkyne can be reacted with the lithiated compound of the first substituent on phosphorus, forming the anionic [P2C2] four-membered ring. This intermediate can then be alkylated to attach the second phosphorus substituent. This two-step synthetic pathway allows for the synthesis of unsymmetrically substituted 1,3-diphospha-cyclobutane-2,4-diyls. The substituents on carbon are limited to Mes*, however, due to the limitation of the phosphaalkyne starting material. Most diradicaloids of this type can be handled in air and display high kinetic stability due to the steric protection provided by the Mes* substituents on the carbon radical centers.
1,3-diaza-2,4-dipnicta-cyclobutane-2,4-diyl
These diradical species consist of a [Pn1(μ-NR)2Pn2] heterocyclic core (Pn = pnictogen) where the radical sites are centered on the pnictogen atoms. The presence of a nitrogen atom in the heterocycle is thought to stabilize the planar form relative to the bicyclic isomer. This is believed to result from the inability of Pn-Pn bond formation in the bicyclobutane form to energetically compensate for the increase in Pn-N-Pn angle strain; consequently, the planar form, which allows for larger Pn-N-Pn angles, is more stable. The lack of electron delocalization found in calculations suggests that aromaticity from the presence of 6π electrons does not play a significant role in stabilization of the planar isomers.
In 2011, Schulz and coworkers synthesized the first example of a [P2N2] four-membered ring diradicaloid (here, Pn = phosphorus) with meta-terphenyl and hypersilyl substituents on the nitrogen atoms. The synthetic route begins with the chlorinated P2N2 heterocycle, which is then reduced to the diradicaloid with relatively mild titanium(II) or titanium(III) reducing agents (Figure 8). The bulky terphenyl and hypersilyl groups provide kinetic stabilization, preventing dimerization. The terphenyl-substituted diradicaloid is almost indefinitely stable under argon atmosphere at ambient temperatures as a solid and in solvent. The crystal structure reveals a planar [P2N2] four-membered ring and a long distance between the two phosphorus atoms (2.6186 Å compared to 2.22 Å, the sum of covalent radii), indicating no significant transannular interactions. Computations also support the diradical character of this species and predict a singlet ground state. The calculated CI wavefunction has contributions from both the doubly occupied HOMO state and the doubly occupied LUMO state; this corresponds to occupation of the HOMO with 1.7 electrons, indicating considerable diradical character.
Using a similar synthetic route, the arsenic analogue was also synthesized from the chlorinated precursor; reduction using magnesium metal generated the arsenic centered diradicaloid. The crystal structure confirmed a long As-As distance, and EPR spectroscopy indicated a singlet ground state. A mixed phosphorus-arsenic diradicaloid was also reported in 2015, the first with different radical centers. The crystal structure revealed a kite-shaped planar four membered ring with a transannular As-P distance of 2.790 Å, which is shorter than the sum of van der Waals radii (3.65 Å) but longer than the sum of covalent radii (2.32 Å).
Heavier derivatives (where Pn = antimony and bismuth) were observed in situ but could not be isolated due to rapid decomposition to the allyl analogues in the presence of magnesium; however, the corresponding diradicaloids could be trapped through [2+2] cycloadditions with alkynes, thereby providing evidence for their existence. Calculations suggest that the antimony and bismuth-centered diradicaloids have higher diradical character than the lighter pnictogen analogues due to the singlet-triplet energy gap decreasing with heavier, larger pnictogens.
Other hetero-cyclobutane-1,3-diyls
In 2002, Bertrand and coworkers synthesized the first 1,3-diphospha-2,4-dibora-cyclobutane-2,4-diyl, in which the diradical character is localized on the boron atoms. In 2009, Schnöckel and coworkers reported the synthesis of a heavier aluminum-centered diradical analog. A silicon-centered diradical (1,3-diaza-2,4-disilacyclobutane-2,4-diyl) is also known, synthesized by Sekiguchi and coworkers in 2011. An analog in which the nitrogen atoms are replaced with carbon, as well as an all-silicon cyclobutane-1,3-diyl, have been synthesized. In 2004, Power and coworkers reported the synthesis of a germanium-centered diradical, the heavier analog of Sekiguchi's silicon diradical. The corresponding tin-centered diradicals have also been synthesized by Lappert and coworkers in 2004. In 2017, N-heterocyclic carbene-stabilized phosphorus-centered diradicals were reported; like the Niecke-type diradicaloid, the core heterocycle is a [P2C2] four-membered ring, but the radical centers are located on phosphorus rather than carbon. Lastly, one of the first hetero-cyclobutanediyl derivates synthesized is N2S2, disulfur dinitride, but its diradical character has been widely discussed in the literature and is still disputed today.
Cyclopentane-1,3-diyl analogues
Cyclopentane-1,3-diyl
Cyclopentane-1,3-diyl is the planar five-membered carbon ring species with radical character localized at the 1 and 3 positions. The triplet diradical was detected by EPR spectroscopy; the diradical species was generated via irradiation of the precursor diazo compound at 5.5 K in a solid matrix (Figure 11). Due to its very short lifetime, all-carbon cyclopentane-1,3-diyl cannot be isolated, but heating cyclopentane-1,3-diyl leads to the formation of a transannular C-C bond, producing the housane isomer. While the triplet state is predicted to be an energy minimum, the singlet state is predicted to be the transition state for housane inversion.
Hetero-cyclopentane-1,3-diyls
Five-membered diradicals with radical character localized on pnictogen atoms can be synthesized via the insertion of carbon monoxide and isonitriles into the corresponding pnictogen-centered cyclobutane-1,3-diyls. In 2015, Schulz and coworkers reported the first stable cyclopentane-1,3-diyl species generated from the ring expansion of terphenyl-substituted diphosphadiazanediyl using carbon monoxide (Figure 12). The computed structural data support an almost planar five-membered ring, and the HOMO/LUMO contributions to the CI wavefunction indicate an occupation of the HOMO with 1.44 electrons, suggesting diradical character. Experimentally, additions of phosphaalkyne and elemental sulfur across the phosphorus atom are consistent with diradicaloid reactivity.
Isonitriles can also insert into the same diphosphadiazanediyls to form the corresponding heterocyclic 5-membered diradicaloids (Figure 13a). The insertion reaction is sensitive to the steric bulk of the substituent on the isonitrile; for example, the terphenyl-substituted isonitrile was unable to undergo the insertion reaction, while the smaller 2,6-dimethylphenyl isonitrile was able to insert into the P-N bond.
Isonitrile insertion was also explored with mixed phosphorus-nitrogen and phosphorus-arsenic centered 4-membered ring diradicaloids. With the latter compound, the isonitrile selectively inserts into the arsenic-nitrogen bond over the phosphorus-nitrogen bond (Figure 13b). The resulting five-membered ring species was characterized via X-ray structural analysis, confirming the above connectivity (Figure 14). Calculations revealed a substantial diradical character (=0.24), which agrees with the experimentally observed activation of triple bonds.
Other main group diradicaloids
Diradicaloid 6-membered heterocycles have been reported. In 2020, a cyclic alkylaminocarbene-stabilized 9,10-diboraanthracene was synthesized. EPR spectroscopy and quantum calculations indicated a singlet diradical ground state, and the incorporation of boron atoms was demonstrated to lower the HOMO-LUMO band gap. In 2021, a cyclic germanium-centered diradicaloid with a [C4Ge2] framework was isolated. Calculations indicated a singlet diradical ground state, and the ability of the germanium species to split dihydrogen at room temperature further supported its diradical character.
A 1,2-diborete diradicaloid containing a highly strained [B2C2] framework was reported by Braunschweig and coworkers in 2022. In 2024, the first diborepin diradicals, in which the boron radical sites are disjointed, were synthesized by Gilliard and coworkers.
Reactivity
Diradicaloids, depending on the reaction conditions and extent of diradical character, can display both closed-shell and open-shell reactivity. Closed-shell reactivity (e.g., pericyclic reactions) is best understood using the delocalized molecular orbital picture, while open-shell reactivity (e.g., radical additions) is best understood using the localized atomic orbital picture.
Closed-shell reactivity
For example, the phosphorus-centered diradicaloid [P(μ-NTer)2]2 can undergo concerted pericyclic reactions with single bonds (H2), double bonds (alkenes, aldehydes), and triple bonds (alkynes, nitriles) (Figure 15). Only the cis-addition products are observed, which is consistent with a concerted mechanism.
From a molecular orbital perspective, the formation of new bonds at phosphorus occurs through the interaction of the antibonding HOMO of the diradicaloid with the antibonding LUMO of the reacting partner or the interaction of the bonding LUMO of the diradicaloid with the bonding HOMO of the reacting partner, both of which are symmetry-allowed.
Interestingly, H2 addition is reversible; below 50 °C, H2 addition is observed, and above 60 °C, H2 release occurs to regenerate the original diradicaloid species.
Diradicaloids can also react as nucleophiles or electrophiles from their zwitterionic resonance forms. For example, [P(μ-NTer)2]2 has been shown to react with both Lewis basic N-heterocyclic carbenes as well as Lewis acidic gold(I) chloride (Figure 17).
Open-shell reactivity
For example, the phosphorus-centered diradicaloid [P(μ-NTer)2]2 can undergo stepwise radical addition reactions with alkyl bromides (Figure 18). The trans-addition products were exclusively formed, which is consistent with a stepwise radical abstraction followed by radical recombination mechanism.
Applications
Hetero-cyclopentane-1,3-diyls have been shown to display molecular switching behavior; this property relies on the ability to use external stimuli to switch a molecule between two different stable states, thereby allowing for easy modulation of special reactivity and/or other properties. Diradicaloids can serve as molecular switches if certain external stimuli can reversibly toggle between the planar isomer, which displays diradical character and corresponding reactivity, and the bicyclic housane isomer, which is a closed shell species.
For example, the concept of switchable diradicals was demonstrated using the hetero-cyclopentane-1,3-diyl with phosphorus-phosphorus centered radicals (Figure 19). Upon exposure to red light, the planar five-membered ring diradical isomerizes to the bicyclic housane species. After irradiation, the thermally induced reverse reaction occurs, breaking the transannular bond to regenerate the planar diradicaloid species. Thus, the activation chemistry of the diradical can be switched "off" via irradiation and can be switched back "on" via stopping irradiation. This switching could be repeated several times without degradation of the diradicaloid.
References
Molecular machines
Radicals | Diradicaloid | Physics,Chemistry,Materials_science,Technology | 4,647 |
1,674,279 | https://en.wikipedia.org/wiki/Concrete%20bridge | Concrete bridges are a type of bridge, constructed out of concrete. They started to appear widely in the early 20th century.
History
Unreinforced concrete has been used in bridge construction since antiquity: the Romans incorporated concrete cores into a number of their masonry bridges and aqueducts, along with constructing spanning water conduits of concrete. From the late 18th century cast iron framed bridges may have had an unreinforced cast concrete deck, or had their structure encased in concrete, for example the Homersfield Bridge, constructed between 1869 and 1870, between the English counties of Suffolk and Norfolk. In 1873, Frenchman Joseph Monier obtained a French patent for a method of iron-wire reinforced concrete bridge construction; his first iron-wire reinforced concrete bridge was constructed across the moat of the marquis de Tillièrein's :fr:Château de Chazelet, in 1875. This and all later bridges made according to Monier's system patterned the construction of previously used stone bridges. Their main structural unit was an arch barrel. All barrel sections were reinforced similarly, regardless of the forces acting on it.
The longest steel reinforced bridge, in 2024, is the Tian'e Longtan Bridge, Guangxi Zhuang, China.
The US's longest unreinforced concrete span, is the arch of the, 1910, Rocky River Bridge in Cleveland, Ohio.
Early extant examples include:
Finland
Savisilta "clay bridge", Ylivieska, the second oldest concrete bridge in Finland. (reinforced concrete, constructed 1912).
France
Pont du jardin des plantes, Grenoble, foorbridge (cast concrete, constructed 1855)
Bridge across the moat at Château de Chazelet (iron-wire reinforced concrete, constructed 1875)
United Kingdom
Homersfield Bridge, River Waveney, England (cast and wrought iron reinforced, span , constructed 1869-1870)
Axmouth Bridge, on the River Axe at Seaton, Devon (unreinforced, middle span , opened 1877)
Glenfinnan Viaduct, Scotland (unreinforced, twenty-one spans, constructed 1897–1901)
Waterloo Bridge (reinforced cast concrete, longest span , opened 1942)
United States
Alvord Lake Bridge, Golden Gate Park, San Francisco (reinforced concrete, span, 1889).
Walnut Lane Bridge, Philadelphia, PA (unreinforced concrete, span, 1908)
Rocky River Bridge, Cleveland, Ohio (unreinforced concrete, span, 1910)
References
Bridges | Concrete bridge | Engineering | 510 |
1,553,120 | https://en.wikipedia.org/wiki/Delphi%20%28online%20service%29 | Delphi Forums is a U.S. online service provider and since the mid-1990s has been a community internet forum site. It started as a nationwide dialup service in 1983. Delphi Forums remains active as of 2025.
History
The company that became Delphi was founded by Wes Kussmaul as Kussmaul Encyclopedia in 1981 and featured an encyclopedia, e-mail, and a primitive chat. Newswires, bulletin boards and better chat were added in early 1982.
Kussmaul recalled:
Delphi was actually launched in October 1981, at Jerry Milden's Northeast Computer Show, as the Kussmaul Encyclopedia--the world's first commercially available computerized encyclopedia. (Frank Greenagle's Arête Encyclopedia was announced at about the same time, but you couldn't buy it until much later.) The Kussmaul Encyclopedia was actually a complete home computer system (your choice of Tandy Color Computer or Apple II) with a 300-bps modem that dialed up to a VAX computer hosting our online encyclopedia database. We sold the system for about the same price and terms as Britannica. People wandered around in it and were impressed with the ease with which they could find information. We had a wonderful cross-referencing system that turned every occurrence of a word that was the name of an entry in the encyclopedia into a hypertext link—in 1981...
In November 1982, Wes hired Glenn McIntyre as a software engineer primarily doing internal systems. Glenn brought in colleagues Kip Bryan and Dan Bruns. Kip wrote the software that became Delphi Conference and Delphi Forums. Dan upon finishing his MBA at Harvard, become President and subsequently CEO when Wes moved on to form Global Villages.
On March 15, 1983, the Delphi name was first used by General Videotex Corporation. Forums were text-based, and accessed via Telenet, Sprintnet, Tymnet, Uninet, and Datapac. In 1984, it had 4 million members.
Delphi was extended to Argentina in 1985, through a partnership with the Argentine IT company Siscotel S.A.
Delphi partnered with ASCII Corp. of Japan to open online services in 1991.
Delphi provided national consumer access to the Internet in 1992. Features included E-mail (July 1992), FTP, Telnet, Usenet, text-based Web access (November 1992), MUDs, Finger, and Gopher. "To a lot of people at the time, we seemed to be in an enviable position" says Dan Bruns, Delphi's CEO. "But we didn't have a lot of financing to fuel our growth..."
In 1993, Delphi was sold to Rupert Murdoch's News Corporation. News Corporation recognized that there would be growth in consumer use of the internet and attempted to use Delphi as its vehicle. It had 125,000 text-based customers in 1995 and had 150 employees. Murdoch hired away IBM's director of high-performance computing and communications, Alan Baratz, in 1994 to run Delphi. Under Baratz, Delphi acquired space in Cross Point, an office complex in Lowell, Massachusetts constructed for Wang Laboratories, and built a large state-of-the-art server farm. Bruns and General Manager Rusty Williams stayed on. Delphi peaked with 500,000 paid subscribers and about 600 employees.
By 1995, Delphi had lost many of its subscribers, and Bruns left Delphi. In 1996, NewsCorp decided to exit the online business, was laying off almost half of Delphi's employees and wanted to sell or close Delphi. Dan Bruns and some of Delphi's original investors bought Delphi from NewsCorp for an undisclosed amount. With only 50,000 paying subscribers left, Delphi was back to its pre-NewsCorp size. "We were on the same growth slope, but this time we were going down instead of up," he says. "It felt a little poetic."
In 1996, Delphi launched a free, ad-supported managed-content website with associated message boards and chat rooms, under the management of a team led by Dan Bruns and which included Bill Louden, who had headed GEnie during its heyday. For a period of time, both text-based and web-based community services were available. After a year as a managed content site, Delphi reinvented itself as a community-driven service that allowed anyone to create an online community.
Prospero Technologies was formed in January 2000 as the merger of Delphi Forums and Wellengaged. Webpages for forums were discontinued.
In 2001, Rob Brazell purchased Delphi Forums, merged it with eHow and Idea Exchange, and formed Blue Frogg Enterprises. The Delphi.com domain was sold to Delphi Corporation, the auto parts manufacturer. Prospero was sold to Inforonics.
In 2002, Prospero reacquired Delphi Forums, joining it with Talk City to form Delphi Forums LLC.
In 2008, online community developer Mzinga acquired Littleton-based Prospero Technologies LLC, which was then owned by Bruce Buckland, chairman and CEO of Mallory Ventures. In March 2009, a Forrester Research analyst reported on Twitter that Mzinga was having financial difficulties after it had completed a second round of layoffs. On September 1, 2011, Mzinga sold Delphiforums back to early owner Dan Bruns.
In January 2012, Delphi Forums resigned from the Better Business Bureau in protest of their support for the Stop Online Piracy Act (SOPA).
In February 2013, Delphi Forums celebrated its 30th anniversary. Delphi owner Dan Bruns said, "It's true that the Delphi that launched in 1983 was very different from today's internet," Bruns said, "but one thing remains the same: places like Delphi Forums provide a friendly, comfortable setting for people to share common interests and passions and to build lasting friendships. If we keep that simple truth in mind, we have a terrific legacy to build on going forward."
During 2014, Delphi Forums began a beta test of a new forum interface, called Zeta. The current long-time format, now called Classic, also remains, and hosts may use either interface.
Additional sources
Delphi Forums History Project
Boston Globe: Zitner, Aaron May 04, 1995 Delphi will move to N.Y., Lowell
See also
Stellar Conquest
References
Internet service providers of the United States
Internet forums
Pre–World Wide Web online services
Communications in Massachusetts
History of computing
History of the Internet | Delphi (online service) | Technology | 1,368 |
60,064,660 | https://en.wikipedia.org/wiki/Sergey%20Bozhevolnyi | Sergey I. Bozhevolnyi (Russian: Сергей Иосифович Божевольный, born June 19, 1955) is a Russian-Danish physicist. He is currently a professor and the leader for the Centre for Nano Optics at the University of Southern Denmark.
Education and career
Bozhevolnyi was raised in the village of , Yeysky District, Krasnodar Krai, USSR and grew up in a family of teachers of physics and mathematics. In 1978 he graduated from Moscow Institute of Physics and Technology with a Master of Science degree in physics. In 1981, he earned a PhD-degree from the same university with the thesis entitled "Study of electro-optical modulators and deflectors based on diffuse waveguides in LiNbO₃". In 1998, he earned a Doctor of Science Degree at Aarhus University, Denmark, with his thesis entitled "Subwavelength apertureless light confinement".
1981–1989 Lecturer, Senior Lecturer, Associate Professor of the , Russia
1990–1991 Head of Section of Optical Technologies, Institute of Microelectronics, Russian Academy of Sciences, Yaroslavl, Russia
1987,1991 — visiting scientist, since 1992 lecturer and associate professor, since 2003 full professor at the Department of Physics and Nanotechnology, Aalborg University, Denmark
1998–2001 Lecturer at the Center for Microelectronics, Technical University of Denmark, Denmark
2001–2004 Chief Technical Officer, Micro Managed Photons A / S, Denmark
since 2008 Professor of nano-optics, since 2013 head of the Center for Nano Optics at the University of Southern Denmark, Odense, Denmark
In 2006, together with professor Alexander Tishchenko at Jean Monnet University, he founded the Laboratory of Nano-Optics and Plasmonics in Moscow Institute of Physics and Technology
Since 2017, Bozhevolnyi is on the list of the most Highly Cited Researchers ( Clarivate / Thomson-Reuters).
Publications
Professor Bozhevolnyi has authored and co-authored more than 600 peer-reviewed articles with 13 patents and 14 book chapters. His h-index was 84 (Web of Science) and 100 (Google Scholar) as of November 28, 2024.
Awards
2007 Elected Fellow of the Optical Society of America for his "pioneering contributions to near-field optics and plasmonics, including nonlinear phenomena and surface plasmon localization and guiding in nanostructures."
2009 Best Scientist of the year from the Danish newspaper "Fyens Stiftstidendes Forskerpris"
2011 Selected as a member of the Danish Academy of Natural Sciences (DNA)
2019 Willum Kann-Rasmussen Prize (for outstanding contributions to the development of technical and natural sciences)
2019 Danish Optical Society Senior Award (for outstanding contribution to near-field optics and fundamental efforts in the development of nano-optics in Denmark, 2019)
2019 Selected as a member of the Danish Academy of Technical Sciences (ATV)
2020 Recipient of the EPS-QEOD Prize for "Research in Laser Science and Applications" (for seminal contributions to surface-plasmon polaritons and the developments of plasmonic metasurfaces)
2024 Knighted in Order of the Dannebrog by His Majesty the King on October 23, 2024
References
External links
Metamaterials scientists
1955 births
Living people
21st-century Danish physicists
Russian physicists
Optical physicists
Fellows of Optica (society)
Moscow Institute of Physics and Technology alumni
Academic staff of the University of Southern Denmark
Russian emigrants to Denmark | Sergey Bozhevolnyi | Materials_science | 739 |
2,526,933 | https://en.wikipedia.org/wiki/Isotopes%20of%20europium | Naturally occurring europium (63Eu) is composed of two isotopes, 151Eu and 153Eu, with 153Eu being the most abundant (52.2% natural abundance). While 153Eu is observationally stable (theoretically can undergo alpha decay with half-life over 5.5×1017 years), 151Eu was found in 2007 to be unstable and undergo alpha decay. The half-life is measured to be (4.62 ± 0.95(stat.) ± 0.68(syst.)) × 1018 years which corresponds to 1 alpha decay per two minutes in every kilogram of natural europium. Besides the natural radioisotope 151Eu, 36 artificial radioisotopes have been characterized, with the most stable being 150Eu with a half-life of 36.9 years, 152Eu with a half-life of 13.516 years, 154Eu with a half-life of 8.593 years, and 155Eu with a half-life of 4.7612 years. The majority of the remaining radioactive isotopes, which range from 130Eu to 170Eu, have half-lives that are less than 12.2 seconds. This element also has 18 metastable isomers, with the most stable being 150mEu (t1/2 12.8 hours), 152m1Eu (t1/2 9.3116 hours) and 152m5Eu (t1/2 96 minutes).
The primary decay mode before the most abundant stable isotope, 153Eu, is electron capture, and the primary mode after is beta decay. The primary decay products before 153Eu are isotopes of samarium and the primary products after are isotopes of gadolinium.
List of isotopes
|-id=Europium-130
| 130Eu
| style="text-align:right" | 63
| style="text-align:right" | 67
| 129.96357(54)#
| 1.1(5) ms[0.9(+5−3) ms]
|
|
| 2+#
|
|
|-id=Europium-131
| 131Eu
| style="text-align:right" | 63
| style="text-align:right" | 68
| 130.95775(43)#
| 17.8(19) ms
|
|
| 3/2+
|
|
|-id=Europium-132
| rowspan=2|132Eu
| rowspan=2 style="text-align:right" | 63
| rowspan=2 style="text-align:right" | 69
| rowspan=2|131.95437(43)#
| rowspan=2|100# ms
| β+
| 132Sm
| rowspan=2|
| rowspan=2|
| rowspan=2|
|-
| p
| 131Sm
|-id=Europium-133
| 133Eu
| style="text-align:right" | 63
| style="text-align:right" | 70
| 132.94924(32)#
| 200# ms
| β+
| 133Sm
| 11/2−#
|
|
|-id=Europium-134
| rowspan=2|134Eu
| rowspan=2 style="text-align:right" | 63
| rowspan=2 style="text-align:right" | 71
| rowspan=2|133.94651(21)#
| rowspan=2|0.5(2) s
| β+
| 134Sm
| rowspan=2|
| rowspan=2|
| rowspan=2|
|-
| β+, p (rare)
| 133Pm
|-id=Europium-135
| rowspan=2|135Eu
| rowspan=2 style="text-align:right" | 63
| rowspan=2 style="text-align:right" | 72
| rowspan=2|134.94182(32)#
| rowspan=2|1.5(2) s
| β+
| 135Sm
| rowspan=2|11/2−#
| rowspan=2|
| rowspan=2|
|-
| β+, p
| 134Pm
|-id=Europium-136
| rowspan=2|136Eu
| rowspan=2 style="text-align:right" | 63
| rowspan=2 style="text-align:right" | 73
| rowspan=2|135.93960(21)#
| rowspan=2|3.3(3) s
| β+ (99.91%)
| 136Sm
| rowspan=2|(7+)
| rowspan=2|
| rowspan=2|
|-
| β+, p (.09%)
| 135Pm
|-id=Europium-136m
| rowspan=2 style="text-indent:1em" | 136mEu
| rowspan=2 colspan="3" style="text-indent:2em" | 0(500)# keV
| rowspan=2|3.8(3) s
| β+ (99.91%)
| 136Sm
| rowspan=2|(3+)
| rowspan=2|
| rowspan=2|
|-
| β+, p (.09%)
| 135Pm
|-id=Europium-137
| 137Eu
| style="text-align:right" | 63
| style="text-align:right" | 74
| 136.93557(21)#
| 8.4(5) s
| β+
| 137Sm
| 11/2−#
|
|
|-id=Europium-138
| 138Eu
| style="text-align:right" | 63
| style="text-align:right" | 75
| 137.93371(3)
| 12.1(6) s
| β+
| 138Sm
| (6−)
|
|
|-id=Europium-139
| 139Eu
| style="text-align:right" | 63
| style="text-align:right" | 76
| 138.929792(14)
| 17.9(6) s
| β+
| 139Sm
| (11/2)−
|
|
|-id=Europium-140
| rowspan=2|140Eu
| rowspan=2 style="text-align:right" | 63
| rowspan=2 style="text-align:right" | 77
| rowspan=2|139.92809(6)
| rowspan=2|1.51(2) s
| β+ (95.1(7)%)
| rowspan=2|140Sm
| rowspan=2|1+
| rowspan=2|
| rowspan=2|
|-
| EC (4.9(7)%)
|-id=Europium-140m
| rowspan=2 style="text-indent:1em" | 140mEu
| rowspan=2 colspan="3" style="text-indent:2em" | 210(15) keV
| rowspan=2|125(2) ms
| IT (99%)
| 140Eu
| rowspan=2|5−#
| rowspan=2|
| rowspan=2|
|-
| β+(1%)
| 140Sm
|-id=Europium-141
| 141Eu
| style="text-align:right" | 63
| style="text-align:right" | 78
| 140.924931(14)
| 40.7(7) s
| β+
| 141Sm
| 5/2+
|
|
|-id=Europium-141m
| rowspan=2 style="text-indent:1em" | 141mEu
| rowspan=2 colspan="3" style="text-indent:2em" | 96.45(7) keV
| rowspan=2|2.7(3) s
| IT (86%)
| 141Eu
| rowspan=2|11/2−
| rowspan=2|
| rowspan=2|
|-
| β+ (14%)
| 141Sm
|-id=Europium-142
| rowspan=2|142Eu
| rowspan=2 style="text-align:right" | 63
| rowspan=2 style="text-align:right" | 79
| rowspan=2|141.92343(3)
| rowspan=2|2.36(10) s
| β+ (89.9(16)%)
| rowspan=2|142Sm
| rowspan=2|1+
| rowspan=2|
| rowspan=2|
|-
| EC (11.1(16)%)
|-
|-id=Europium-142m
| style="text-indent:1em" | 142mEu
| colspan="3" style="text-indent:2em" | 460(30) keV
| 1.223(8) min
| β+
| 142Sm
| 8−
|
|
|-id=Europium-143
| 143Eu
| style="text-align:right" | 63
| style="text-align:right" | 80
| 142.920298(12)
| 2.59(2) min
| β+
| 143Sm
| 5/2+
|
|
|-id=Europium-143m
| style="text-indent:1em" | 143mEu
| colspan="3" style="text-indent:2em" | 389.51(4) keV
| 50.0(5) μs
|
|
| 11/2−
|
|
|-id=Europium-144
| 144Eu
| style="text-align:right" | 63
| style="text-align:right" | 81
| 143.918817(12)
| 10.2(1) s
| β+
| 144Sm
| 1+
|
|
|-id=Europium-144m
| style="text-indent:1em" | 144mEu
| colspan="3" style="text-indent:2em" | 1127.6(6) keV
| 1.0(1) μs
|
|
| (8−)
|
|
|-id=Europium-145
| 145Eu
| style="text-align:right" | 63
| style="text-align:right" | 82
| 144.916265(4)
| 5.93(4) d
| β+
| 145Sm
| 5/2+
|
|
|-id=Europium-145m
| style="text-indent:1em" | 145mEu
| colspan="3" style="text-indent:2em" | 716.0(3) keV
| 490 ns
|
|
| 11/2−
|
|
|-id=Europium-146
| 146Eu
| style="text-align:right" | 63
| style="text-align:right" | 83
| 145.917206(7)
| 4.61(3) d
| β+
| 146Sm
| 4−
|
|
|-id=Europium-146m
| style="text-indent:1em" | 146mEu
| colspan="3" style="text-indent:2em" | 666.37(16) keV
| 235(3) μs
|
|
| 9+
|
|
|-id=Europium-147
| rowspan=2|147Eu
| rowspan=2 style="text-align:right" | 63
| rowspan=2 style="text-align:right" | 84
| rowspan=2|146.916746(3)
| rowspan=2|24.1(6) d
| β+ (99.99%)
| 147Sm
| rowspan=2|5/2+
| rowspan=2|
| rowspan=2|
|-
| α (.0022%)
| 143Pm
|-id=Europium-148
| rowspan=2|148Eu
| rowspan=2 style="text-align:right" | 63
| rowspan=2 style="text-align:right" | 85
| rowspan=2|147.918086(11)
| rowspan=2|54.5(5) d
| β+ (100%)
| 148Sm
| rowspan=2|5−
| rowspan=2|
| rowspan=2|
|-
| α (9.39×10−7%)
| 144Pm
|-id=Europium-149
| 149Eu
| style="text-align:right" | 63
| style="text-align:right" | 86
| 148.917931(5)
| 93.1(4) d
| EC
| 149Sm
| 5/2+
|
|
|-id=Europium-150
| 150Eu
| style="text-align:right" | 63
| style="text-align:right" | 87
| 149.919702(7)
| 36.9(9) y
| β+
| 150Sm
| 5(−)
|
|
|-id=Europium-150m
| rowspan=3 style="text-indent:1em" | 150mEu
| rowspan=3 colspan="3" style="text-indent:2em" | 42.1(5) keV
| rowspan=3|12.8(1) h
| β− (89%)
| 150Gd
| rowspan=3|0−
| rowspan=3|
| rowspan=3|
|-
| β+ (11%)
| 150Sm
|-
| IT (≤5×10−8%)
| 150Eu
|-id=Europium-151
| 151Eu
| style="text-align:right" | 63
| style="text-align:right" | 88
| 150.9198502(26)
| 4.62×1018 y
| α
| 147Pm
| 5/2+
| 0.4781(6)
|
|-id=Europium-151m
| style="text-indent:1em" | 151mEu
| colspan="3" style="text-indent:2em" | 196.245(10) keV
| 58.9(5) μs
| IT
| 151Eu
| 11/2−
|
|
|-id=Europium-152
| rowspan=3|152Eu
| rowspan=3 style="text-align:right" | 63
| rowspan=3 style="text-align:right" | 89
| rowspan=3|151.9217445(26)
| rowspan=3|13.537(6) y
| EC (72.09%)
| 152Sm
| rowspan=3|3−
| rowspan=3|
| rowspan=3|
|-
| β− (27.9%)
| 152Gd
|-
| β+ (0.027%)
| 152Sm
|-id=Europium-152m1
| rowspan=2 style="text-indent:1em" | 152m1Eu
| rowspan=2 colspan="3" style="text-indent:2em" | 45.5998(4) keV
| rowspan=2|9.3116(13) h
| β− (72%)
| 152Gd
| rowspan=2|0−
| rowspan=2|
| rowspan=2|
|-
| β+ (28%)
| 152Sm
|-id=Europium-152m2
| style="text-indent:1em" | 152m2Eu
| colspan="3" style="text-indent:2em" | 65.2969(4) keV
| 0.94(8) μs
|
|
| 1−
|
|
|-id=Europium-152m3
| style="text-indent:1em" | 152m3Eu
| colspan="3" style="text-indent:2em" | 78.2331(4) keV
| 165(10) ns
|
|
| 1+
|
|
|-id=Europium-152m4
| style="text-indent:1em" | 152m4Eu
| colspan="3" style="text-indent:2em" | 89.8496(4) keV
| 384(10) ns
|
|
| 4+
|
|
|-id=Europium-152m5
| style="text-indent:1em" | 152m5Eu
| colspan="3" style="text-indent:2em" | 147.86(10) keV
| 96(1) min
|
|
| 8−
|
|
|-id=Europium-153
| 153Eu
| style="text-align:right" | 63
| style="text-align:right" | 90
| 152.9212303(26)
| colspan=3 align=center|Observationally Stable
| 5/2+
| 0.5219(6)
|
|-id=Europium-154
| rowspan=2|154Eu
| rowspan=2 style="text-align:right" | 63
| rowspan=2 style="text-align:right" | 91
| rowspan=2|153.9229792(26)
| rowspan=2|8.593(4) y
| β− (99.98%)
| 154Gd
| rowspan=2|3−
| rowspan=2|
| rowspan=2|
|-
| EC (.02%)
| 154Sm
|-id=Europium-154m1
| style="text-indent:1em" | 154m1Eu
| colspan="3" style="text-indent:2em" | 68.1702(4) keV
| 2.2(1) μs
| IT
| 154Eu
| 2+
|
|
|-id=Europium-154m2
| style="text-indent:1em" | 154m2Eu
| colspan="3" style="text-indent:2em" | 145.3(3) keV
| 46.3(4) min
| IT
| 154Eu
| (8−)
|
|
|-
| 155Eu
| style="text-align:right" | 63
| style="text-align:right" | 92
| 154.9228933(27)
| 4.7611(13) y
| β−
| 155Gd
| 5/2+
|
|
|-id=Europium-156
| 156Eu
| style="text-align:right" | 63
| style="text-align:right" | 93
| 155.924752(6)
| 15.19(8) d
| β−
| 156Gd
| 0+
|
|
|-id=Europium-157
| 157Eu
| style="text-align:right" | 63
| style="text-align:right" | 94
| 156.925424(6)
| 15.18(3) h
| β−
| 157Gd
| 5/2+
|
|
|-id=Europium-158
| 158Eu
| style="text-align:right" | 63
| style="text-align:right" | 95
| 157.92785(8)
| 45.9(2) min
| β−
| 158Gd
| (1−)
|
|
|-id=Europium-159
| 159Eu
| style="text-align:right" | 63
| style="text-align:right" | 96
| 158.929089(8)
| 18.1(1) min
| β−
| 159Gd
| 5/2+
|
|
|-id=Europium-160
| 160Eu
| style="text-align:right" | 63
| style="text-align:right" | 97
| 159.93197(22)#
| 38(4) s
| β−
| 160Gd
| 1(−)
|
|
|-id=Europium-161
| 161Eu
| style="text-align:right" | 63
| style="text-align:right" | 98
| 160.93368(32)#
| 26(3) s
| β−
| 161Gd
| 5/2+#
|
|
|-id=Europium-162
| 162Eu
| style="text-align:right" | 63
| style="text-align:right" | 99
| 161.93704(32)#
| 10.6(10) s
| β−
| 162Gd
|
|
|
|-
| 163Eu
| style="text-align:right" | 63
| style="text-align:right" | 100
| 162.93921(54)#
| 7.7(4) s
| β−
| 163Gd
| 5/2+#
|
|
|-id=Europium-163m
| style="text-indent:1em" | 163mEu
| colspan="3" style="text-indent:2em" | 964.5(10) keV
| 911(24) ns
|
|
| (13/2−)
|
|
|-id=Europium-164
| 164Eu
| style="text-align:right" | 63
| style="text-align:right" | 101
| 163.94299(64)#
| 4.16(19) s
| β−
| 164Gd
|
|
|
|-id=Europium-165
| 165Eu
| style="text-align:right" | 63
| style="text-align:right" | 102
| 164.94572(75)#
|
| β−
| 165Gd
| 5/2+#
|
|
|-id=Europium-166
| rowspan=2|166Eu
| rowspan=2 style="text-align:right" | 63
| rowspan=2 style="text-align:right" | 103
| rowspan=2|165.94997(86)#
| rowspan=2|
| β− (99.37%)
| 166Gd
| rowspan=2|
| rowspan=2|
| rowspan=2|
|-
| β−, n (0.63%)
| 165Gd
|-id=Europium-167
| rowspan=2|167Eu
| rowspan=2 style="text-align:right" | 63
| rowspan=2 style="text-align:right" | 104
| rowspan=2|166.95321(86)#
| rowspan=2|
| β− (98.05%)
| 167Gd
| rowspan=2|5/2+#
| rowspan=2|
| rowspan=2|
|-
| β−, n (1.95%)
| 166Gd
|-id=Europium-168
| rowspan=2|168Eu
| rowspan=2 style="text-align:right" | 63
| rowspan=2 style="text-align:right" | 105
| rowspan=2|
| rowspan=2|
| β− (96.05%)
| 168Gd
| rowspan=2|
| rowspan=2|
| rowspan=2|
|-
| β−, n (3.95%)
| 167Gd
|-id=Europium-169
| rowspan=2|169Eu
| rowspan=2 style="text-align:right" | 63
| rowspan=2 style="text-align:right" | 106
| rowspan=2|
| rowspan=2|
| β− (85.38%)
| 169Gd
| rowspan=2|
| rowspan=2|
| rowspan=2|
|-
| β−, n (14.62%)
| 168Gd
|-id=Europium-170
| rowspan=2|170Eu
| rowspan=2 style="text-align:right" | 63
| rowspan=2 style="text-align:right" | 107
| rowspan=2|
| rowspan=2|
| β−
| 170Gd
| rowspan=2|
| rowspan=2|
| rowspan=2|
|-
| β−, n
| 169Gd
Europium-155
Europium-155 is a fission product with a half-life of 4.76 years. It has a maximum decay energy of 252 keV. In a thermal reactor (almost all current nuclear power plants), it has a low fission product yield, about half of one percent as much as the most abundant fission products.
155Eu's large neutron capture cross section (about 3900 barns for thermal neutrons, 16000 resonance integral) means that most of even the small amount produced is destroyed in the course of the nuclear fuel's burnup. Yield, decay energy, and half-life are all far less than that of 137Cs and 90Sr, so 155Eu is not a significant contributor to nuclear waste.
Some 155Eu is also produced by successive neutron capture on 153Eu (nonradioactive, 350 barns thermal, 1500 resonance integral, yield is about 5 times as great as 155Eu) and 154Eu (half-life 8.6 years, 1400 barns thermal, 1600 resonance integral, fission yield is extremely small because beta decay stops at 154Sm). However, the differing cross sections mean that both 155Eu and 154Eu are destroyed faster than they are produced.
154Eu is a prolific emitter of gamma radiation.
References
Isotope masses from:
Isotopic compositions and standard atomic masses from:
Half-life, spin, and isomer data selected from the following sources.
Europium
Europium | Isotopes of europium | Chemistry | 5,720 |
25,851,959 | https://en.wikipedia.org/wiki/Wild%20arc | In geometric topology, a wild arc is an embedding of the unit interval into 3-dimensional space not equivalent to the usual one in the sense that there does not exist an ambient isotopy taking the arc to a straight line segment.
found the first example of a wild arc. found another example, called the Fox-Artin arc, whose complement is not simply connected.
Fox-Artin arcs
Two very similar wild arcs appear in the article. Example 1.1 (page 981) is most generally referred to as the Fox-Artin wild arc. The crossings have the regular sequence over/over/under/over/under/under when following the curve from left to right.
The left end-point 0 of the closed unit interval is mapped by the arc to the left limit point of the curve, and 1 is mapped to the right limit point. The range of the arc lies in the Euclidean space or the 3-sphere .
Fox-Artin arc variant
Example 1.1* has the crossing sequence over/under/over/under/over/under. According to , page 982: "This is just the chain stitch of knitting extended indefinitely in both directions."
This arc cannot be continuously deformed to produce Example 1.1 in or , despite its similar appearance.
Also shown here is an alternative style of diagram for the arc in Example 1.1*.
See also
Wild knot
Alexander horned sphere
Further reading
Geometric topology | Wild arc | Mathematics | 296 |
20,067,629 | https://en.wikipedia.org/wiki/Bridging%20model | In computer science, a bridging model is an abstract model of a computer which provides a conceptual bridge between the physical implementation of the machine and the abstraction available to a programmer of that machine; in other words, it is intended to provide a common level of understanding between hardware and software engineers.
A successful bridging model is one which can be efficiently implemented in reality and efficiently targeted by programmers; in particular, it should be possible for a compiler to produce good code from a typical high-level language. The term was introduced by Leslie Valiant's 1990 paper A Bridging Model for Parallel Computation, which argued that the strength of the von Neumann model was largely responsible for the success of computing as a whole. The paper goes on to develop the bulk synchronous parallel model as an analogous model for parallel computing.
References
Computer architecture
Theoretical computer science | Bridging model | Mathematics,Technology,Engineering | 174 |
12,197,312 | https://en.wikipedia.org/wiki/Chromatin%20remodeling | Chromatin remodeling is the dynamic modification of chromatin architecture to allow access of condensed genomic DNA to the regulatory transcription machinery proteins, and thereby control gene expression. Such remodeling is principally carried out by 1) covalent histone modifications by specific enzymes, e.g., histone acetyltransferases (HATs), deacetylases, methyltransferases, and kinases, and 2) ATP-dependent chromatin remodeling complexes which either move, eject or restructure nucleosomes. Besides actively regulating gene expression, dynamic remodeling of chromatin imparts an epigenetic regulatory role in several key biological processes, egg cells DNA replication and repair; apoptosis; chromosome segregation as well as development and pluripotency. Aberrations in chromatin remodeling proteins are found to be associated with human diseases, including cancer. Targeting chromatin remodeling pathways is currently evolving as a major therapeutic strategy in the treatment of several cancers.
Overview
The transcriptional regulation of the genome is controlled primarily at the preinitiation stage by binding of the core transcriptional machinery proteins (namely, RNA polymerase, transcription factors, and activators and repressors) to the core promoter sequence on the coding region of the DNA. However, DNA is tightly packaged in the nucleus with the help of packaging proteins, chiefly histone proteins to form repeating units of nucleosomes which further bundle together to form condensed chromatin structure. Such condensed structure occludes many DNA regulatory regions, not allowing them to interact with transcriptional machinery proteins and regulate gene expression. To overcome this issue and allow dynamic access to condensed DNA, a process known as chromatin remodeling alters nucleosome architecture to expose or hide regions of DNA for transcriptional regulation.
By definition, chromatin remodeling is the enzyme-assisted process to facilitate access of nucleosomal DNA by remodeling the structure, composition and positioning of nucleosomes.
Classification
Access to nucleosomal DNA is governed by two major classes of protein complexes:
Covalent histone-modifying complexes.
ATP-dependent chromatin remodeling complexes.
Covalent histone-modifying complexes
Specific protein complexes, known as histone-modifying complexes catalyze addition or removal of various chemical elements on histones. These enzymatic modifications include acetylation, methylation, phosphorylation, and ubiquitination and primarily occur at N-terminal histone tails. Such modifications affect the binding affinity between histones and DNA, and thus loosening or tightening the condensed DNA wrapped around histones, e.g., Methylation of specific lysine residues in H3 and H4 causes further condensation of DNA around histones, and thereby prevents binding of transcription factors to the DNA that lead to gene repression. On the contrary, histone acetylation relaxes chromatin condensation and exposes DNA for TF binding, leading to increased gene expression.
Known modifications
Well characterized modifications to histones include:
Methylation
Both lysine and arginine residues are known to be methylated. Methylated lysines are the best understood marks of the histone code, as specific methylated lysine match well with gene expression states. Methylation of lysines H3K4 and H3K36 is correlated with transcriptional activation while demethylation of H3K4 is correlated with silencing of the genomic region. Methylation of lysines H3K9 and H3K27 is correlated with transcriptional repression. Particularly, H3K9me3 is highly correlated with constitutive heterochromatin.
Acetylation - by HAT (histone acetyl transferase); deacetylation - by HDAC (histone deacetylase)
Acetylation tends to define the 'openness' of chromatin as acetylated histones cannot pack as well together as deacetylated histones.
Phosphorylation
Ubiquitination
However, there are many more histone modifications, and sensitive mass spectrometry approaches have recently greatly expanded the catalog.
Histone code hypothesis
The histone code is a hypothesis that the transcription of genetic information encoded in DNA is in part regulated by chemical modifications to histone proteins, primarily on their unstructured ends. Together with similar modifications such as DNA methylation it is part of the epigenetic code.
Cumulative evidence suggests that such code is written by specific enzymes which can (for example) methylate or acetylate DNA ('writers'), removed by other enzymes having demethylase or deacetylase activity ('erasers'), and finally readily identified by proteins ('readers') that are recruited to such histone modifications and bind via specific domains, e.g., bromodomain, chromodomain. These triple action of 'writing', 'reading' and 'erasing' establish the favorable local environment for transcriptional regulation, DNA-damage repair, etc.
The critical concept of the histone code hypothesis is that the histone modifications serve to recruit other proteins by specific recognition of the modified histone via protein domains specialized for such purposes, rather than through simply stabilizing or destabilizing the interaction between histone and the underlying DNA. These recruited proteins then act to alter chromatin structure actively or to promote transcription.
A very basic summary of the histone code for gene expression status is given below (histone nomenclature is described here):
ATP-dependent chromatin remodeling
ATP-dependent chromatin-remodeling complexes regulate gene expression by either moving, ejecting or restructuring nucleosomes. These protein complexes have a common ATPase domain and energy from the hydrolysis of ATP allows these remodeling complexes to reposition nucleosomes (often referred to as "nucleosome sliding") along the DNA, eject or assemble histones on/off of DNA or facilitate exchange of histone variants, and thus creating nucleosome-free regions of DNA for gene activation. Also, several remodelers have DNA-translocation activity to carry out specific remodeling tasks.
All ATP-dependent chromatin-remodeling complexes possess a sub unit of ATPase that belongs to the SNF2 superfamily of proteins. In association to the sub unit's identity, two main groups have been classified for these proteins. These are known as the SWI2/SNF2 group and the imitation SWI (ISWI) group. The third class of ATP-dependent complexes that has been recently described contains a Snf2-like ATPase and also demonstrates deacetylase activity.
Known chromatin remodeling complexes
There are at least four families of chromatin remodelers in eukaryotes: SWI/SNF, ISWI, NuRD/Mi-2/CHD, and INO80 with first two remodelers being very well studied so far, especially in the yeast model. Although all of remodelers share common ATPase domain, their functions are specific based on several biological processes (DNA repair, apoptosis, etc.). This is due to the fact that each remodeler complex has unique protein domains (Helicase, bromodomain, etc.) in their catalytic ATPase region and also has different recruited subunits.
Specific functions
Several in-vitro experiments suggest that ISWI remodelers organize nucleosome into proper bundle form and create equal spacing between nucleosomes, whereas SWI/SNF remodelers disorder nucleosomes.
The ISWI-family remodelers have been shown to play central roles in chromatin assembly after DNA replication and maintenance of higher-order chromatin structures.
INO80 and SWI/SNF-family remodelers participate in DNA double-strand break (DSB) repair and nucleotide-excision repair (NER) and thereby plays crucial role in TP53 mediated DNA-damage response.
NuRD/Mi-2/CHD remodeling complexes primarily mediate transcriptional repression in the nucleus and are required for the maintenance of pluripotency of embryonic stem cells.
Significance
In normal biological processes
Chromatin remodeling plays a central role in the regulation of gene expression by providing the transcription machinery with dynamic access to an otherwise tightly packaged genome. Further, nucleosome movement by chromatin remodelers is essential to several important biological processes, including chromosome assembly and segregation, DNA replication and repair, embryonic development and pluripotency, and cell-cycle progression. Deregulation of chromatin remodeling causes loss of transcriptional regulation at these critical check-points required for proper cellular functions, and thus causes various disease syndromes, including cancer.
Response to DNA damage
Chromatin relaxation is one of the earliest cellular responses to DNA damage. Several experiments have been performed on the recruitment kinetics of proteins involved in the response to DNA damage. The relaxation appears to be initiated by PARP1, whose accumulation at DNA damage is half complete by 1.6 seconds after DNA damage occurs. This is quickly followed by accumulation of chromatin remodeler Alc1, which has an ADP-ribose–binding domain, allowing it to be quickly attracted to the product of PARP1. The maximum recruitment of Alc1 occurs within 10 seconds of DNA damage. About half of the maximum chromatin relaxation, presumably due to action of Alc1, occurs by 10 seconds. PARP1 action at the site of a double-strand break allows recruitment of the two DNA repair enzymes MRE11 and NBS1. Half maximum recruitment of these two DNA repair enzymes takes 13 seconds for MRE11 and 28 seconds for NBS1.
Another process of chromatin relaxation, after formation of a DNA double-strand break, employs γH2AX, the phosphorylated form of the H2AX protein. The histone variant H2AX constitutes about 10% of the H2A histones in human chromatin. γH2AX (phosphorylated on serine 139 of H2AX) was detected at 20 seconds after irradiation of cells (with DNA double-strand break formation), and half maximum accumulation of γH2AX occurred in one minute. The extent of chromatin with phosphorylated γH2AX is about two million base pairs at the site of a DNA double-strand break.
γH2AX does not, by itself, cause chromatin decondensation, but within seconds of irradiation the protein "Mediator of the DNA damage checkpoint 1" (MDC1) specifically attaches to γH2AX. This is accompanied by simultaneous accumulation of RNF8 protein and the DNA repair protein NBS1 which bind to MDC1 as MDC1 attaches to γH2AX. RNF8 mediates extensive chromatin decondensation, through its subsequent interaction with CHD4 protein, a component of the nucleosome remodeling and deacetylase complex NuRD. CHD4 accumulation at the site of the double-strand break is rapid, with half-maximum accumulation occurring by 40 seconds after irradiation.
The fast initial chromatin relaxation upon DNA damage (with rapid initiation of DNA repair) is followed by a slow recondensation, with chromatin recovering a compaction state close to its pre-damage level in ~ 20 min.
Cancer
Chromatin remodeling provides fine-tuning at crucial cell growth and division steps, like cell-cycle progression, DNA repair and chromosome segregation, and therefore exerts tumor-suppressor function. Mutations in such chromatin remodelers and deregulated covalent histone modifications potentially favor self-sufficiency in cell growth and escape from growth-regulatory cell signals - two important hallmarks of cancer.
Inactivating mutations in SMARCB1, formerly known as hSNF5/INI1 and a component of the human SWI/SNF remodeling complex have been found in large number of rhabdoid tumors, commonly affecting pediatric population. Similar mutations are also present in other childhood cancers, such as choroid plexus carcinoma, medulloblastoma and in some acute leukemias. Further, mouse knock-out studies strongly support SMARCB1 as a tumor suppressor protein. Since the original observation of SMARCB1 mutations in rhabdoid tumors, several more subunits of the human SWI/SNF chromatin remodeling complex have been found mutated in a wide range of neoplasms.
The SWI/SNF ATPase BRG1 (or SMARCA4) is the most frequently mutated chromatin remodeling ATPase in cancer. Mutations in this gene were first recognized in human cancer cell lines derived from lung. In cancer, mutations in BRG1 show an unusually high preference for missense mutations that target the ATPase domain. Mutations are enriched at highly conserved ATPase sequences, which lie on important functional surfaces such as the ATP pocket or DNA-binding surface. These mutations act in a genetically dominant manner to alter chromatin regulatory function at enhancers and promoters.
Inactivating mutations in BCL7A in Diffuse large B-cell lymphoma (DLBCL) and in other haematological malignancies
PML-RARA fusion protein in acute myeloid leukemia recruits histone deacetylases. This leads to repression of genes responsible for myelocytes to differentiate, leading to leukemia.
Tumor suppressor Rb protein functions by the recruitment of the human homologs of the SWI/SNF enzymes BRG1, histone deacetylase and DNA methyltransferase. Mutations in BRG1 are reported in several cancers causing loss of tumor suppressor action of Rb.
Recent reports indicate DNA hypermethylation in the promoter region of major tumor suppressor genes in several cancers. Although few mutations are reported in histone methyltransferases yet, correlation of DNA hypermethylation and histone H3 lysine-9 methylation has been reported in several cancers, mainly in colorectal and breast cancers.
Mutations in Histone Acetyl Transferases (HAT) p300 (missense and truncating type) are most commonly reported in colorectal, pancreatic, breast and gastric carcinomas. Loss of heterozygosity in coding region of p300 (chromosome 22q13) is present in large number of glioblastomas.
Further, HATs have diverse role as transcription factors beside having histone acetylase activity, e.g., HAT subunit, hADA3 may act as an adaptor protein linking transcription factors with other HAT complexes. In the absence of hADA3, TP53 transcriptional activity is significantly reduced, suggesting role of hADA3 in activating TP53 function in response to DNA damage.
Similarly, TRRAP, the human homolog to yeast Tra1, has been shown to directly interact with c-Myc and E2F1, known oncoproteins.
Cancer genomics
Rapid advance in cancer genomics and high-throughput ChIP-chip, ChIP-Seq and Bisulfite sequencing methods are providing more insight into role of chromatin remodeling in transcriptional regulation and role in cancer.
Therapeutic intervention
Epigenetic instability caused by deregulation in chromatin remodeling is studied in several cancers, including breast cancer, colorectal cancer, pancreatic cancer. Such instability largely cause widespread silencing of genes with primary impact on tumor-suppressor genes. Hence, strategies are now being tried to overcome epigenetic silencing with synergistic combination of HDAC inhibitors or HDI and DNA-demethylating agents.
HDIs are primarily used as adjunct therapy in several cancer types. HDAC inhibitors can induce p21 (WAF1) expression, a regulator of p53's tumor suppressoractivity. HDACs are involved in the pathway by which the retinoblastoma protein (pRb) suppresses cell proliferation. Estrogen is well-established as a mitogenic factor implicated in the tumorigenesis and progression of breast cancer via its binding to the estrogen receptor alpha (ERα). Recent data indicate that chromatin inactivation mediated by HDAC and DNA methylation is a critical component of ERα silencing in human breast cancer cells.
Approved usage:
Vorinostat was licensed by the U.S. FDA in October 2006 for the treatment of cutaneous T cell lymphoma (CTCL).
Romidepsin (trade name Istodax) was licensed by the US FDA in Nov 2009 for cutaneous T-cell lymphoma (CTCL).
Phase III Clinical trials:
Panobinostat (LBH589) is in clinical trials for various cancers including a phase III trial for cutaneous T cell lymphoma (CTCL).
Valproic acid (as Mg valproate) in phase III trials for cervical cancer and ovarian cancer.
Started pivotal phase II clinical trials:
Belinostat (PXD101) has had a phase II trial for relapsed ovarian cancer, and reported good results for T cell lymphoma.
HDAC inhibitors.
Current front-runner candidates for new drug targets are Histone Lysine Methyltransferases (KMT) and Protein Arginine Methyltransferases (PRMT).
Other disease syndromes
ATRX-syndrome (α-thalassemia X-linked mental retardation) and α-thalassemia myelodysplasia syndrome are caused by mutations in ATRX, a SNF2-related ATPase with a PHD finger domain.
CHARGE syndrome, an autosomal dominant disorder, has been linked recently to haploinsufficiency of CHD7, which encodes the CHD family ATPase CHD7.
Senescence
Chromatin architectural remodeling is implicated in the process of cellular senescence, which is related to, and yet distinct from, organismal aging. Replicative cellular senescence refers to a permanent cell cycle arrest where post-mitotic cells continue to exist as metabolically active cells but fail to proliferate. Senescence can arise due to age associated degradation, telomere attrition, progerias, pre-malignancies, and other forms of damage or disease. Senescent cells undergo distinct repressive phenotypic changes, potentially to prevent the proliferation of damaged or cancerous cells, with modified chromatin organization, fluctuations in remodeler abundance, and changes in epigenetic modifications. Senescent cells undergo chromatin landscape modifications as constitutive heterochromatin migrates to the center of the nucleus and displaces euchromatin and facultative heterochromatin to regions at the edge of the nucleus. This disrupts chromatin-lamin interactions and inverts of the pattern typically seen in a mitotically active cell. Individual Lamin-Associated Domains (LADs) and Topologically Associating Domains (TADs) are disrupted by this migration which can affect cis interactions across the genome. Additionally, there is a general pattern of canonical histone loss, particularly in terms of the nucleosome histones H3 and H4 and the linker histone H1. Histone variants with two exons are upregulated in senescent cells to produce modified nucleosome assembly which contributes to chromatin permissiveness to senescent changes. Although transcription of variant histone proteins may be elevated, canonical histone proteins are not expressed as they are only made during the S phase of the cell cycle and senescent cells are post-mitotic. During senescence, portions of chromosomes can be exported from the nucleus for lysosomal degradation which results in greater organizational disarray and disruption of chromatin interactions.
Chromatin remodeler abundance may be implicated in cellular senescence as knockdown or knockout of ATP-dependent remodelers such as NuRD, ACF1, and SWI/SNP can result in DNA damage and senescent phenotypes in yeast, C. elegans, mice, and human cell cultures. ACF1 and NuRD are downregulated in senescent cells which suggests that chromatin remodeling is essential for maintaining a mitotic phenotype. Genes involved in signaling for senescence can be silenced by chromatin confirmation and polycomb repressive complexes as seen in PRC1/PCR2 silencing of p16. Specific remodeler depletion results in activation of proliferative genes through a failure to maintain silencing. Some remodelers act on enhancer regions of genes rather than the specific loci to prevent re-entry into the cell cycle by forming regions of dense heterochromatin around regulatory regions.
Senescent cells undergo widespread fluctuations in epigenetic modifications in specific chromatin regions compared to mitotic cells. Human and murine cells undergoing replicative senescence experience a general global decrease in methylation; however, specific loci can differ from the general trend. Specific chromatin regions, especially those around the promoters or enhancers of proliferative loci, may exhibit elevated methylation states with an overall imbalance of repressive and activating histone modifications. Proliferative genes may show increases in the repressive mark H3K27me3 while genes involved in silencing or aberrant histone products may be enriched with the activating modification H3K4me3. Additionally, upregulating histone deacetylases, such as members of the sirtuin family, can delay senescence by removing acetyl groups that contribute to greater chromatin accessibility. General loss of methylation, combined with the addition of acetyl groups results in a more accessible chromatin conformation with a propensity towards disorganization when compared to mitotically active cells. General loss of histones precludes addition of histone modifications and contributes changes in enrichment in some chromatin regions during senescence.
See also
Epigenetics
Histone
Nucleosomes
Chromatin
Histone acetyltransferase
Transcription factors
CAF-1 (Chromatin assembly factor-1) - histone chaperone that execute a coordinating role in сhromatin remodeling.
References
Further reading
External links
MBInfo - Chromatin
MBInfo - DNA Packaging
YouTube - Chromatin, Histones and Modifications
YouTube - Epigenetics Overview
Gene expression
Cancer
Epigenetics
Nuclear organization | Chromatin remodeling | Chemistry,Biology | 4,840 |
22,446,301 | https://en.wikipedia.org/wiki/Hebeloma%20aminophilum | Hebeloma aminophilum, commonly known as the ghoul fungus, is a species of mushroom in the family Hymenogastraceae. Found in Western Australia, it gets its common name from the propensity of the fruiting bodies to spring out of decomposing animal remains.
Taxonomy
The ghoul fungus was first described by mycologists R.N. Hilton and Orson K. Miller, Jr. in 1987. The holotype collection consisted of about 100 specimens that were fruiting around the bones of a decomposing kangaroo carcass that had been dumped some months before.
Etymology
The generic name is derived from the Ancient Greek Hebe, "youth", and -loma, a fringe (pertaining to the fungal veil), referring to how the fungal veil is only seen in immature specimens. It gets its common name of ghoul fungus from its habit of growing around animal carcasses.
Description
The dull pinkish brown or cream cap is in diameter, convex initially before flattening out with age. There is a slight umbo, and the cap margin is inrolled when young. A thin white veil rapidly disappears in young mushrooms. The cap surface is sticky initially. The adnate (or sometimes adnexed) gills are pale pink to pinkish brown and up to 1 cm deep. With age, they can be encrusted with clumps of spores. The cylindrical stipe is high, 1–1.2 cm in diameter and has a thickened base and lacks a ring. The thick flesh is cream or pale yellow, with a bitter taste and a stale smell. The spore print is pinkish brown, and the oval spores measure 8.5 by 4.9 μm. The mycelium is white.
Similar species
Similar species include the introduced poisonpie (Hebeloma crustuliniforme), which has been recorded in pine plantations, the native western Australian poisonpie (H. westraliense), which does not grow near carcasses, and the Australian white webcap (Cortinarius austroalbidus), which is paler and smells of curry.
Distribution and habitat
An uncommon fungus, H. aminophilum is found in southern Western Australia, southeastern South Australia and Victoria. Fruiting bodies arise in eucalyptus woodland in the vicinity of sheep, reptile and bird carcasses. The habit of growing from flesh gives it the term sarcophilous.
See also
List of Hebeloma species
References
Ammonia fungi
aminophilum
Fungi described in 1987
Fungi native to Australia
Fungus species | Hebeloma aminophilum | Chemistry,Biology | 529 |
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