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5,270,659 | https://en.wikipedia.org/wiki/Tie%20press | A tie press is a device, based solely on pressure, to flatten neckties. Its use is necessitated by ties usually being of silk or some other textile ill-suited to the heat of ironing.
Tie presses usually operate based on two separate wooden boards which are clamped together with spring-loaded levers. A cardboard cut-out is usually included to retain the shape of the tie during pressing.
Tie presses are particularly useful for bow ties, due to the creasing and thus deformative nature of the bow tie knot, which involves crushing the ends to produce the 'bow' effect. In time, this crushing affects the appearance of the finished knot. This is particularly the case with bow ties with rectangular ends, rather than the 'bow' shaped ends in some bow ties, though both suffer from crushing to some degree or another. Four-in-hand ties, naturally, are also creased, but rarely to the same extent and, as such, usually require less regular pressing.
References
Laundry equipment
Home appliances | Tie press | Physics,Technology | 209 |
19,178,965 | https://en.wikipedia.org/wiki/Fungus | A fungus (: fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as one of the traditional eukaryotic kingdoms, along with Animalia, Plantae, and either Protista or Protozoa and Chromista.
A characteristic that places fungi in a different kingdom from plants, bacteria, and some protists is chitin in their cell walls. Fungi, like animals, are heterotrophs; they acquire their food by absorbing dissolved molecules, typically by secreting digestive enzymes into their environment. Fungi do not photosynthesize. Growth is their means of mobility, except for spores (a few of which are flagellated), which may travel through the air or water. Fungi are the principal decomposers in ecological systems. These and other differences place fungi in a single group of related organisms, named the Eumycota (true fungi or Eumycetes), that share a common ancestor (i.e. they form a monophyletic group), an interpretation that is also strongly supported by molecular phylogenetics. This fungal group is distinct from the structurally similar myxomycetes (slime molds) and oomycetes (water molds). The discipline of biology devoted to the study of fungi is known as mycology (from the Greek , mushroom). In the past, mycology was regarded as a branch of botany, although it is now known that fungi are genetically more closely related to animals than to plants.
Abundant worldwide, most fungi are inconspicuous because of the small size of their structures, and their cryptic lifestyles in soil or on dead matter. Fungi include symbionts of plants, animals, or other fungi and also parasites. They may become noticeable when fruiting, either as mushrooms or as molds. Fungi perform an essential role in the decomposition of organic matter and have fundamental roles in nutrient cycling and exchange in the environment. They have long been used as a direct source of human food, in the form of mushrooms and truffles; as a leavening agent for bread; and in the fermentation of various food products, such as wine, beer, and soy sauce. Since the 1940s, fungi have been used for the production of antibiotics, and, more recently, various enzymes produced by fungi are used industrially and in detergents. Fungi are also used as biological pesticides to control weeds, plant diseases, and insect pests. Many species produce bioactive compounds called mycotoxins, such as alkaloids and polyketides, that are toxic to animals, including humans. The fruiting structures of a few species contain psychotropic compounds and are consumed recreationally or in traditional spiritual ceremonies. Fungi can break down manufactured materials and buildings, and become significant pathogens of humans and other animals. Losses of crops due to fungal diseases (e.g., rice blast disease) or food spoilage can have a large impact on human food supplies and local economies.
The fungus kingdom encompasses an enormous diversity of taxa with varied ecologies, life cycle strategies, and morphologies ranging from unicellular aquatic chytrids to large mushrooms. However, little is known of the true biodiversity of the fungus kingdom, which has been estimated at 2.2 million to 3.8 million species. Of these, only about 148,000 have been described, with over 8,000 species known to be detrimental to plants and at least 300 that can be pathogenic to humans. Ever since the pioneering 18th and 19th century taxonomical works of Carl Linnaeus, Christiaan Hendrik Persoon, and Elias Magnus Fries, fungi have been classified according to their morphology (e.g., characteristics such as spore color or microscopic features) or physiology. Advances in molecular genetics have opened the way for DNA analysis to be incorporated into taxonomy, which has sometimes challenged the historical groupings based on morphology and other traits. Phylogenetic studies published in the first decade of the 21st century have helped reshape the classification within the fungi kingdom, which is divided into one subkingdom, seven phyla, and ten subphyla.
Etymology
The English word fungus is directly adopted from the Latin fungus (mushroom), used in the writings of Horace and Pliny. This in turn is derived from the Greek word sphongos (σφόγγος 'sponge'), which refers to the macroscopic structures and morphology of mushrooms and molds; the root is also used in other languages, such as the German Schwamm ('sponge') and Schimmel ('mold').
The word mycology is derived from the Greek (μύκης 'mushroom') and logos (λόγος 'discourse'). It denotes the scientific study of fungi. The Latin adjectival form of "mycology" (mycologicæ) appeared as early as 1796 in a book on the subject by Christiaan Hendrik Persoon. The word appeared in English as early as 1824 in a book by Robert Kaye Greville. In 1836 the English naturalist Miles Joseph Berkeley's publication The English Flora of Sir James Edward Smith, Vol. 5. also refers to mycology as the study of fungi.
A group of all the fungi present in a particular region is known as mycobiota (plural noun, no singular). The term mycota is often used for this purpose, but many authors use it as a synonym of Fungi. The word funga has been proposed as a less ambiguous term morphologically similar to fauna and flora. The Species Survival Commission (SSC) of the International Union for Conservation of Nature (IUCN) in August 2021 asked that the phrase fauna and flora be replaced by fauna, flora, and funga.
Characteristics
Before the introduction of molecular methods for phylogenetic analysis, taxonomists considered fungi to be members of the plant kingdom because of similarities in lifestyle: both fungi and plants are mainly immobile, and have similarities in general morphology and growth habitat. Although inaccurate, the common misconception that fungi are plants persists among the general public due to their historical classification, as well as several similarities. Like plants, fungi often grow in soil and, in the case of mushrooms, form conspicuous fruit bodies, which sometimes resemble plants such as mosses. The fungi are now considered a separate kingdom, distinct from both plants and animals, from which they appear to have diverged around one billion years ago (around the start of the Neoproterozoic Era). Some morphological, biochemical, and genetic features are shared with other organisms, while others are unique to the fungi, clearly separating them from the other kingdoms:
Shared features:
With other eukaryotes: Fungal cells contain membrane-bound nuclei with chromosomes that contain DNA with noncoding regions called introns and coding regions called exons. Fungi have membrane-bound cytoplasmic organelles such as mitochondria, sterol-containing membranes, and ribosomes of the 80S type. They have a characteristic range of soluble carbohydrates and storage compounds, including sugar alcohols (e.g., mannitol), disaccharides, (e.g., trehalose), and polysaccharides (e.g., glycogen, which is also found in animals).
With animals: Fungi lack chloroplasts and are heterotrophic organisms and so require preformed organic compounds as energy sources.
With plants: Fungi have a cell wall and vacuoles. They reproduce by both sexual and asexual means, and like basal plant groups (such as ferns and mosses) produce spores. Similar to mosses and algae, fungi typically have haploid nuclei.
With euglenoids and bacteria: Higher fungi, euglenoids, and some bacteria produce the amino acid L-lysine in specific biosynthesis steps, called the α-aminoadipate pathway.
The cells of most fungi grow as tubular, elongated, and thread-like (filamentous) structures called hyphae, which may contain multiple nuclei and extend by growing at their tips. Each tip contains a set of aggregated vesicles—cellular structures consisting of proteins, lipids, and other organic molecules—called the Spitzenkörper. Both fungi and oomycetes grow as filamentous hyphal cells. In contrast, similar-looking organisms, such as filamentous green algae, grow by repeated cell division within a chain of cells. There are also single-celled fungi (yeasts) that do not form hyphae, and some fungi have both hyphal and yeast forms.
In common with some plant and animal species, more than one hundred fungal species display bioluminescence.
Unique features:
Some species grow as unicellular yeasts that reproduce by budding or fission. Dimorphic fungi can switch between a yeast phase and a hyphal phase in response to environmental conditions.
The fungal cell wall is made of a chitin-glucan complex; while glucans are also found in plants and chitin in the exoskeleton of arthropods, fungi are the only organisms that combine these two structural molecules in their cell wall. Unlike those of plants and oomycetes, fungal cell walls do not contain cellulose.
Most fungi lack an efficient system for the long-distance transport of water and nutrients, such as the xylem and phloem in many plants. To overcome this limitation, some fungi, such as Armillaria, form rhizomorphs, which resemble and perform functions similar to the roots of plants. As eukaryotes, fungi possess a biosynthetic pathway for producing terpenes that uses mevalonic acid and pyrophosphate as chemical building blocks. Plants and some other organisms have an additional terpene biosynthesis pathway in their chloroplasts, a structure that fungi and animals do not have. Fungi produce several secondary metabolites that are similar or identical in structure to those made by plants. Many of the plant and fungal enzymes that make these compounds differ from each other in sequence and other characteristics, which indicates separate origins and convergent evolution of these enzymes in the fungi and plants.
Diversity
Fungi have a worldwide distribution, and grow in a wide range of habitats, including extreme environments such as deserts or areas with high salt concentrations or ionizing radiation, as well as in deep sea sediments. Some can survive the intense UV and cosmic radiation encountered during space travel. Most grow in terrestrial environments, though several species live partly or solely in aquatic habitats, such as the chytrid fungi Batrachochytrium dendrobatidis and B. salamandrivorans, parasites that have been responsible for a worldwide decline in amphibian populations. These organisms spend part of their life cycle as a motile zoospore, enabling them to propel themselves through water and enter their amphibian host. Other examples of aquatic fungi include those living in hydrothermal areas of the ocean.
around 148,000 species of fungi have been described by taxonomists, but the global biodiversity of the fungus kingdom is not fully understood. A 2017 estimate suggests there may be between 2.2 and 3.8 million species. The number of new fungi species discovered yearly has increased from 1,000 to 1,500 per year about 10 years ago, to about 2,000 with a peak of more than 2,500 species in 2016. In the year 2019, 1,882 new species of fungi were described, and it was estimated that more than 90% of fungi remain unknown. The following year, 2,905 new species were described—the highest annual record of new fungus names. In mycology, species have historically been distinguished by a variety of methods and concepts. Classification based on morphological characteristics, such as the size and shape of spores or fruiting structures, has traditionally dominated fungal taxonomy. Species may also be distinguished by their biochemical and physiological characteristics, such as their ability to metabolize certain biochemicals, or their reaction to chemical tests. The biological species concept discriminates species based on their ability to mate. The application of molecular tools, such as DNA sequencing and phylogenetic analysis, to study diversity has greatly enhanced the resolution and added robustness to estimates of genetic diversity within various taxonomic groups.
Mycology
Mycology is the branch of biology concerned with the systematic study of fungi, including their genetic and biochemical properties, their taxonomy, and their use to humans as a source of medicine, food, and psychotropic substances consumed for religious purposes, as well as their dangers, such as poisoning or infection. The field of phytopathology, the study of plant diseases, is closely related because many plant pathogens are fungi.
The use of fungi by humans dates back to prehistory; Ötzi the Iceman, a well-preserved mummy of a 5,300-year-old Neolithic man found frozen in the Austrian Alps, carried two species of polypore mushrooms that may have been used as tinder (Fomes fomentarius), or for medicinal purposes (Piptoporus betulinus). Ancient peoples have used fungi as food sources—often unknowingly—for millennia, in the preparation of leavened bread and fermented juices. Some of the oldest written records contain references to the destruction of crops that were probably caused by pathogenic fungi.
History
Mycology became a systematic science after the development of the microscope in the 17th century. Although fungal spores were first observed by Giambattista della Porta in 1588, the seminal work in the development of mycology is considered to be the publication of Pier Antonio Micheli's 1729 work Nova plantarum genera. Micheli not only observed spores but also showed that, under the proper conditions, they could be induced into growing into the same species of fungi from which they originated. Extending the use of the binomial system of nomenclature introduced by Carl Linnaeus in his Species plantarum (1753), the Dutch Christiaan Hendrik Persoon (1761–1836) established the first classification of mushrooms with such skill as to be considered a founder of modern mycology. Later, Elias Magnus Fries (1794–1878) further elaborated the classification of fungi, using spore color and microscopic characteristics, methods still used by taxonomists today. Other notable early contributors to mycology in the 17th–19th and early 20th centuries include Miles Joseph Berkeley, August Carl Joseph Corda, Anton de Bary, the brothers Louis René and Charles Tulasne, Arthur H. R. Buller, Curtis G. Lloyd, and Pier Andrea Saccardo. In the 20th and 21st centuries, advances in biochemistry, genetics, molecular biology, biotechnology, DNA sequencing, and phylogenetic analysis have provided new insights into fungal relationships and biodiversity, and have challenged traditional morphology-based groupings in fungal taxonomy.
Morphology
Microscopic structures
Most fungi grow as hyphae, which are cylindrical, thread-like structures 2–10μm in diameter and up to several centimeters in length. Hyphae grow at their tips (apices); new hyphae are typically formed by emergence of new tips along existing hyphae by a process called branching, or occasionally growing hyphal tips fork, giving rise to two parallel-growing hyphae. Hyphae also sometimes fuse when they come into contact, a process called hyphal fusion (or anastomosis). These growth processes lead to the development of a mycelium, an interconnected network of hyphae. Hyphae can be either septate or coenocytic. Septate hyphae are divided into compartments separated by cross walls (internal cell walls, called septa, that are formed at right angles to the cell wall giving the hypha its shape), with each compartment containing one or more nuclei; coenocytic hyphae are not compartmentalized. Septa have pores that allow cytoplasm, organelles, and sometimes nuclei to pass through; an example is the dolipore septum in fungi of the phylum Basidiomycota. Coenocytic hyphae are in essence multinucleate supercells.
Many species have developed specialized hyphal structures for nutrient uptake from living hosts; examples include haustoria in plant-parasitic species of most fungal phyla, and arbuscules of several mycorrhizal fungi, which penetrate into the host cells to consume nutrients.
Although fungi are opisthokonts—a grouping of evolutionarily related organisms broadly characterized by a single posterior flagellum—all phyla except for the chytrids have lost their posterior flagella. Fungi are unusual among the eukaryotes in having a cell wall that, in addition to glucans (e.g., β-1,3-glucan) and other typical components, also contains the biopolymer chitin.
Macroscopic structures
Fungal mycelia can become visible to the naked eye, for example, on various surfaces and substrates, such as damp walls and spoiled food, where they are commonly called molds. Mycelia grown on solid agar media in laboratory petri dishes are usually referred to as colonies. These colonies can exhibit growth shapes and colors (due to spores or pigmentation) that can be used as diagnostic features in the identification of species or groups. Some individual fungal colonies can reach extraordinary dimensions and ages as in the case of a clonal colony of Armillaria solidipes, which extends over an area of more than 900ha (3.5 square miles), with an estimated age of nearly 9,000years.
The apothecium—a specialized structure important in sexual reproduction in the ascomycetes—is a cup-shaped fruit body that is often macroscopic and holds the hymenium, a layer of tissue containing the spore-bearing cells. The fruit bodies of the basidiomycetes (basidiocarps) and some ascomycetes can sometimes grow very large, and many are well known as mushrooms.
Growth and physiology
The growth of fungi as hyphae on or in solid substrates or as single cells in aquatic environments is adapted for the efficient extraction of nutrients, because these growth forms have high surface area to volume ratios. Hyphae are specifically adapted for growth on solid surfaces, and to invade substrates and tissues. They can exert large penetrative mechanical forces; for example, many plant pathogens, including Magnaporthe grisea, form a structure called an appressorium that evolved to puncture plant tissues. The pressure generated by the appressorium, directed against the plant epidermis, can exceed . The filamentous fungus Paecilomyces lilacinus uses a similar structure to penetrate the eggs of nematodes.
The mechanical pressure exerted by the appressorium is generated from physiological processes that increase intracellular turgor by producing osmolytes such as glycerol. Adaptations such as these are complemented by hydrolytic enzymes secreted into the environment to digest large organic molecules—such as polysaccharides, proteins, and lipids—into smaller molecules that may then be absorbed as nutrients. The vast majority of filamentous fungi grow in a polar fashion (extending in one direction) by elongation at the tip (apex) of the hypha. Other forms of fungal growth include intercalary extension (longitudinal expansion of hyphal compartments that are below the apex) as in the case of some endophytic fungi, or growth by volume expansion during the development of mushroom stipes and other large organs. Growth of fungi as multicellular structures consisting of somatic and reproductive cells—a feature independently evolved in animals and plants—has several functions, including the development of fruit bodies for dissemination of sexual spores (see above) and biofilms for substrate colonization and intercellular communication.
Fungi are traditionally considered heterotrophs, organisms that rely solely on carbon fixed by other organisms for metabolism. Fungi have evolved a high degree of metabolic versatility that allows them to use a diverse range of organic substrates for growth, including simple compounds such as nitrate, ammonia, acetate, or ethanol. In some species the pigment melanin may play a role in extracting energy from ionizing radiation, such as gamma radiation. This form of "radiotrophic" growth has been described for only a few species, the effects on growth rates are small, and the underlying biophysical and biochemical processes are not well known. This process might bear similarity to CO2 fixation via visible light, but instead uses ionizing radiation as a source of energy.
Reproduction
Fungal reproduction is complex, reflecting the differences in lifestyles and genetic makeup within this diverse kingdom of organisms. It is estimated that a third of all fungi reproduce using more than one method of propagation; for example, reproduction may occur in two well-differentiated stages within the life cycle of a species, the teleomorph (sexual reproduction) and the anamorph (asexual reproduction). Environmental conditions trigger genetically determined developmental states that lead to the creation of specialized structures for sexual or asexual reproduction. These structures aid reproduction by efficiently dispersing spores or spore-containing propagules.
Asexual reproduction
Asexual reproduction occurs via vegetative spores (conidia) or through mycelial fragmentation. Mycelial fragmentation occurs when a fungal mycelium separates into pieces, and each component grows into a separate mycelium. Mycelial fragmentation and vegetative spores maintain clonal populations adapted to a specific niche, and allow more rapid dispersal than sexual reproduction. The "Fungi imperfecti" (fungi lacking the perfect or sexual stage) or Deuteromycota comprise all the species that lack an observable sexual cycle. Deuteromycota (alternatively known as Deuteromycetes, conidial fungi, or mitosporic fungi) is not an accepted taxonomic clade and is now taken to mean simply fungi that lack a known sexual stage.
Sexual reproduction
Sexual reproduction with meiosis has been directly observed in all fungal phyla except Glomeromycota (genetic analysis suggests meiosis in Glomeromycota as well). It differs in many aspects from sexual reproduction in animals or plants. Differences also exist between fungal groups and can be used to discriminate species by morphological differences in sexual structures and reproductive strategies. Mating experiments between fungal isolates may identify species on the basis of biological species concepts. The major fungal groupings have initially been delineated based on the morphology of their sexual structures and spores; for example, the spore-containing structures, asci and basidia, can be used in the identification of ascomycetes and basidiomycetes, respectively. Fungi employ two mating systems: heterothallic species allow mating only between individuals of the opposite mating type, whereas homothallic species can mate, and sexually reproduce, with any other individual or itself.
Most fungi have both a haploid and a diploid stage in their life cycles. In sexually reproducing fungi, compatible individuals may combine by fusing their hyphae together into an interconnected network; this process, anastomosis, is required for the initiation of the sexual cycle. Many ascomycetes and basidiomycetes go through a dikaryotic stage, in which the nuclei inherited from the two parents do not combine immediately after cell fusion, but remain separate in the hyphal cells (see heterokaryosis).
In ascomycetes, dikaryotic hyphae of the hymenium (the spore-bearing tissue layer) form a characteristic hook (crozier) at the hyphal septum. During cell division, the formation of the hook ensures proper distribution of the newly divided nuclei into the apical and basal hyphal compartments. An ascus (plural asci) is then formed, in which karyogamy (nuclear fusion) occurs. Asci are embedded in an ascocarp, or fruiting body. Karyogamy in the asci is followed immediately by meiosis and the production of ascospores. After dispersal, the ascospores may germinate and form a new haploid mycelium.
Sexual reproduction in basidiomycetes is similar to that of the ascomycetes. Compatible haploid hyphae fuse to produce a dikaryotic mycelium. However, the dikaryotic phase is more extensive in the basidiomycetes, often also present in the vegetatively growing mycelium. A specialized anatomical structure, called a clamp connection, is formed at each hyphal septum. As with the structurally similar hook in the ascomycetes, the clamp connection in the basidiomycetes is required for controlled transfer of nuclei during cell division, to maintain the dikaryotic stage with two genetically different nuclei in each hyphal compartment. A basidiocarp is formed in which club-like structures known as basidia generate haploid basidiospores after karyogamy and meiosis. The most commonly known basidiocarps are mushrooms, but they may also take other forms (see Morphology section).
In fungi formerly classified as Zygomycota, haploid hyphae of two individuals fuse, forming a gametangium, a specialized cell structure that becomes a fertile gamete-producing cell. The gametangium develops into a zygospore, a thick-walled spore formed by the union of gametes. When the zygospore germinates, it undergoes meiosis, generating new haploid hyphae, which may then form asexual sporangiospores. These sporangiospores allow the fungus to rapidly disperse and germinate into new genetically identical haploid fungal mycelia.
Spore dispersal
The spores of most of the researched species of fungi are transported by wind. Such species often produce dry or hydrophobic spores that do not absorb water and are readily scattered by raindrops, for example. In other species, both asexual and sexual spores or sporangiospores are often actively dispersed by forcible ejection from their reproductive structures. This ejection ensures exit of the spores from the reproductive structures as well as traveling through the air over long distances.
Specialized mechanical and physiological mechanisms, as well as spore surface structures (such as hydrophobins), enable efficient spore ejection. For example, the structure of the spore-bearing cells in some ascomycete species is such that the buildup of substances affecting cell volume and fluid balance enables the explosive discharge of spores into the air. The forcible discharge of single spores termed ballistospores involves formation of a small drop of water (Buller's drop), which upon contact with the spore leads to its projectile release with an initial acceleration of more than 10,000g; the net result is that the spore is ejected 0.01–0.02cm, sufficient distance for it to fall through the gills or pores into the air below. Other fungi, like the puffballs, rely on alternative mechanisms for spore release, such as external mechanical forces. The hydnoid fungi (tooth fungi) produce spores on pendant, tooth-like or spine-like projections. The bird's nest fungi use the force of falling water drops to liberate the spores from cup-shaped fruiting bodies. Another strategy is seen in the stinkhorns, a group of fungi with lively colors and putrid odor that attract insects to disperse their spores.
Homothallism
In homothallic sexual reproduction, two haploid nuclei derived from the same individual fuse to form a zygote that can then undergo meiosis. Homothallic fungi include species with an Aspergillus-like asexual stage (anamorphs) occurring in numerous different genera, several species of the ascomycete genus Cochliobolus, and the ascomycete Pneumocystis jirovecii. The earliest mode of sexual reproduction among eukaryotes was likely homothallism, that is, self-fertile unisexual reproduction.
Other sexual processes
Besides regular sexual reproduction with meiosis, certain fungi, such as those in the genera Penicillium and Aspergillus, may exchange genetic material via parasexual processes, initiated by anastomosis between hyphae and plasmogamy of fungal cells. The frequency and relative importance of parasexual events is unclear and may be lower than other sexual processes. It is known to play a role in intraspecific hybridization and is likely required for hybridization between species, which has been associated with major events in fungal evolution.
Evolution
In contrast to plants and animals, the early fossil record of the fungi is meager. Factors that likely contribute to the under-representation of fungal species among fossils include the nature of fungal fruiting bodies, which are soft, fleshy, and easily degradable tissues, and the microscopic dimensions of most fungal structures, which therefore are not readily evident. Fungal fossils are difficult to distinguish from those of other microbes, and are most easily identified when they resemble extant fungi. Often recovered from a permineralized plant or animal host, these samples are typically studied by making thin-section preparations that can be examined with light microscopy or transmission electron microscopy. Researchers study compression fossils by dissolving the surrounding matrix with acid and then using light or scanning electron microscopy to examine surface details.
The earliest fossils possessing features typical of fungi date to the Paleoproterozoic era, some (Ma); these multicellular benthic organisms had filamentous structures capable of anastomosis. Other studies (2009) estimate the arrival of fungal organisms at about 760–1060Ma on the basis of comparisons of the rate of evolution in closely related groups. The oldest fossilizied mycelium to be identified from its molecular composition is between 715 and 810 million years old. For much of the Paleozoic Era (542–251Ma), the fungi appear to have been aquatic and consisted of organisms similar to the extant chytrids in having flagellum-bearing spores. The evolutionary adaptation from an aquatic to a terrestrial lifestyle necessitated a diversification of ecological strategies for obtaining nutrients, including parasitism, saprobism, and the development of mutualistic relationships such as mycorrhiza and lichenization. Studies suggest that the ancestral ecological state of the Ascomycota was saprobism, and that independent lichenization events have occurred multiple times.
In May 2019, scientists reported the discovery of a fossilized fungus, named Ourasphaira giraldae, in the Canadian Arctic, that may have grown on land a billion years ago, well before plants were living on land. Pyritized fungus-like microfossils preserved in the basal Ediacaran Doushantuo Formation (~635 Ma) have been reported in South China. Earlier, it had been presumed that the fungi colonized the land during the Cambrian (542–488.3Ma), also long before land plants. Fossilized hyphae and spores recovered from the Ordovician of Wisconsin (460Ma) resemble modern-day Glomerales, and existed at a time when the land flora likely consisted of only non-vascular bryophyte-like plants. Prototaxites, which was probably a fungus or lichen, would have been the tallest organism of the late Silurian and early Devonian. Fungal fossils do not become common and uncontroversial until the early Devonian (416–359.2Ma), when they occur abundantly in the Rhynie chert, mostly as Zygomycota and Chytridiomycota. At about this same time, approximately 400Ma, the Ascomycota and Basidiomycota diverged, and all modern classes of fungi were present by the Late Carboniferous (Pennsylvanian, 318.1–299Ma).
Lichens formed a component of the early terrestrial ecosystems, and the estimated age of the oldest terrestrial lichen fossil is 415Ma; this date roughly corresponds to the age of the oldest known sporocarp fossil, a Paleopyrenomycites species found in the Rhynie Chert. The oldest fossil with microscopic features resembling modern-day basidiomycetes is Palaeoancistrus, found permineralized with a fern from the Pennsylvanian. Rare in the fossil record are the Homobasidiomycetes (a taxon roughly equivalent to the mushroom-producing species of the Agaricomycetes). Two amber-preserved specimens provide evidence that the earliest known mushroom-forming fungi (the extinct species Archaeomarasmius leggetti) appeared during the late Cretaceous, 90Ma.
Some time after the Permian–Triassic extinction event (251.4Ma), a fungal spike (originally thought to be an extraordinary abundance of fungal spores in sediments) formed, suggesting that fungi were the dominant life form at this time, representing nearly 100% of the available fossil record for this period. However, the relative proportion of fungal spores relative to spores formed by algal species is difficult to assess, the spike did not appear worldwide, and in many places it did not fall on the Permian–Triassic boundary.
Sixty-five million years ago, immediately after the Cretaceous–Paleogene extinction event that famously killed off most dinosaurs, there was a dramatic increase in evidence of fungi; apparently the death of most plant and animal species led to a huge fungal bloom like "a massive compost heap".
Taxonomy
Although commonly included in botany curricula and textbooks, fungi are more closely related to animals than to plants and are placed with the animals in the monophyletic group of opisthokonts. Analyses using molecular phylogenetics support a monophyletic origin of fungi. The taxonomy of fungi is in a state of constant flux, especially due to research based on DNA comparisons. These current phylogenetic analyses often overturn classifications based on older and sometimes less discriminative methods based on morphological features and biological species concepts obtained from experimental matings.
There is no unique generally accepted system at the higher taxonomic levels and there are frequent name changes at every level, from species upwards. Efforts among researchers are now underway to establish and encourage usage of a unified and more consistent nomenclature. Until relatively recent (2012) changes to the International Code of Nomenclature for algae, fungi and plants, fungal species could also have multiple scientific names depending on their life cycle and mode (sexual or asexual) of reproduction. Web sites such as Index Fungorum and MycoBank are officially recognized nomenclatural repositories and list current names of fungal species (with cross-references to older synonyms).
The 2007 classification of Kingdom Fungi is the result of a large-scale collaborative research effort involving dozens of mycologists and other scientists working on fungal taxonomy. It recognizes seven phyla, two of which—the Ascomycota and the Basidiomycota—are contained within a branch representing subkingdom Dikarya, the most species rich and familiar group, including all the mushrooms, most food-spoilage molds, most plant pathogenic fungi, and the beer, wine, and bread yeasts. The accompanying cladogram depicts the major fungal taxa and their relationship to opisthokont and unikont organisms, based on the work of Philippe Silar, "The Mycota: A Comprehensive Treatise on Fungi as Experimental Systems for Basic and Applied Research" and Tedersoo et al. 2018. The lengths of the branches are not proportional to evolutionary distances.
Taxonomic groups
The major phyla (sometimes called divisions) of fungi have been classified mainly on the basis of characteristics of their sexual reproductive structures. , nine major lineages have been identified: Opisthosporidia, Chytridiomycota, Neocallimastigomycota, Blastocladiomycota, Zoopagomycotina, Mucoromycota, Glomeromycota, Ascomycota, and Basidiomycota.
Phylogenetic analysis has demonstrated that the Microsporidia, unicellular parasites of animals and protists, are fairly recent and highly derived endobiotic fungi (living within the tissue of another species). Previously considered to be "primitive" protozoa, they are now thought to be either a basal branch of the Fungi, or a sister group–each other's closest evolutionary relative.
The Chytridiomycota are commonly known as chytrids. These fungi are distributed worldwide. Chytrids and their close relatives Neocallimastigomycota and Blastocladiomycota (below) are the only fungi with active motility, producing zoospores that are capable of active movement through aqueous phases with a single flagellum, leading early taxonomists to classify them as protists. Molecular phylogenies, inferred from rRNA sequences in ribosomes, suggest that the Chytrids are a basal group divergent from the other fungal phyla, consisting of four major clades with suggestive evidence for paraphyly or possibly polyphyly.
The Blastocladiomycota were previously considered a taxonomic clade within the Chytridiomycota. Molecular data and ultrastructural characteristics, however, place the Blastocladiomycota as a sister clade to the Zygomycota, Glomeromycota, and Dikarya (Ascomycota and Basidiomycota). The blastocladiomycetes are saprotrophs, feeding on decomposing organic matter, and they are parasites of all eukaryotic groups. Unlike their close relatives, the chytrids, most of which exhibit zygotic meiosis, the blastocladiomycetes undergo sporic meiosis.
The Neocallimastigomycota were earlier placed in the phylum Chytridiomycota. Members of this small phylum are anaerobic organisms, living in the digestive system of larger herbivorous mammals and in other terrestrial and aquatic environments enriched in cellulose (e.g., domestic waste landfill sites). They lack mitochondria but contain hydrogenosomes of mitochondrial origin. As in the related chrytrids, neocallimastigomycetes form zoospores that are posteriorly uniflagellate or polyflagellate.
Members of the Glomeromycota form arbuscular mycorrhizae, a form of mutualist symbiosis wherein fungal hyphae invade plant root cells and both species benefit from the resulting increased supply of nutrients. All known Glomeromycota species reproduce asexually. The symbiotic association between the Glomeromycota and plants is ancient, with evidence dating to 400 million years ago. Formerly part of the Zygomycota (commonly known as 'sugar' and 'pin' molds), the Glomeromycota were elevated to phylum status in 2001 and now replace the older phylum Zygomycota. Fungi that were placed in the Zygomycota are now being reassigned to the Glomeromycota, or the subphyla incertae sedis Mucoromycotina, Kickxellomycotina, the Zoopagomycotina and the Entomophthoromycotina. Some well-known examples of fungi formerly in the Zygomycota include black bread mold (Rhizopus stolonifer), and Pilobolus species, capable of ejecting spores several meters through the air. Medically relevant genera include Mucor, Rhizomucor, and Rhizopus.
The Ascomycota, commonly known as sac fungi or ascomycetes, constitute the largest taxonomic group within the Eumycota. These fungi form meiotic spores called ascospores, which are enclosed in a special sac-like structure called an ascus. This phylum includes morels, a few mushrooms and truffles, unicellular yeasts (e.g., of the genera Saccharomyces, Kluyveromyces, Pichia, and Candida), and many filamentous fungi living as saprotrophs, parasites, and mutualistic symbionts (e.g. lichens). Prominent and important genera of filamentous ascomycetes include Aspergillus, Penicillium, Fusarium, and Claviceps. Many ascomycete species have only been observed undergoing asexual reproduction (called anamorphic species), but analysis of molecular data has often been able to identify their closest teleomorphs in the Ascomycota. Because the products of meiosis are retained within the sac-like ascus, ascomycetes have been used for elucidating principles of genetics and heredity (e.g., Neurospora crassa).
Members of the Basidiomycota, commonly known as the club fungi or basidiomycetes, produce meiospores called basidiospores on club-like stalks called basidia. Most common mushrooms belong to this group, as well as rust and smut fungi, which are major pathogens of grains. Other important basidiomycetes include the maize pathogen Ustilago maydis, human commensal species of the genus Malassezia, and the opportunistic human pathogen, Cryptococcus neoformans.
Fungus-like organisms
Because of similarities in morphology and lifestyle, the slime molds (mycetozoans, plasmodiophorids, acrasids, Fonticula, and labyrinthulids, now in Amoebozoa, Rhizaria, Excavata, Cristidiscoidea, and Stramenopiles, respectively), water molds (oomycetes) and hyphochytrids (both Stramenopiles) were formerly classified in the kingdom Fungi, in groups like Mastigomycotina, Gymnomycota and Phycomycetes. The slime molds were studied also as protozoans, leading to an ambiregnal, duplicated taxonomy.
Unlike true fungi, the cell walls of oomycetes contain cellulose and lack chitin. Hyphochytrids have both chitin and cellulose. Slime molds lack a cell wall during the assimilative phase (except labyrinthulids, which have a wall of scales), and take in nutrients by ingestion (phagocytosis, except labyrinthulids) rather than absorption (osmotrophy, as fungi, labyrinthulids, oomycetes and hyphochytrids). Neither water molds nor slime molds are closely related to the true fungi, and, therefore, taxonomists no longer group them in the kingdom Fungi. Nonetheless, studies of the oomycetes and myxomycetes are still often included in mycology textbooks and primary research literature.
The Eccrinales and Amoebidiales are opisthokont protists, previously thought to be zygomycete fungi. Other groups now in Opisthokonta (e.g., Corallochytrium, Ichthyosporea) were also at given time classified as fungi. The genus Blastocystis, now in Stramenopiles, was originally classified as a yeast. Ellobiopsis, now in Alveolata, was considered a chytrid. The bacteria were also included in fungi in some classifications, as the group Schizomycetes.
The Rozellida clade, including the "ex-chytrid" Rozella, is a genetically disparate group known mostly from environmental DNA sequences that is a sister group to fungi. Members of the group that have been isolated lack the chitinous cell wall that is characteristic of fungi. Alternatively, Rozella can be classified as a basal fungal group.
The nucleariids may be the next sister group to the eumycete clade, and as such could be included in an expanded fungal kingdom.
Many Actinomycetales (Actinomycetota), a group with many filamentous bacteria, were also long believed to be fungi.
Ecology
Although often inconspicuous, fungi occur in every environment on Earth and play very important roles in most ecosystems. Along with bacteria, fungi are the major decomposers in most terrestrial (and some aquatic) ecosystems, and therefore play a critical role in biogeochemical cycles and in many food webs. As decomposers, they play an essential role in nutrient cycling, especially as saprotrophs and symbionts, degrading organic matter to inorganic molecules, which can then re-enter anabolic metabolic pathways in plants or other organisms.
Symbiosis
Many fungi have important symbiotic relationships with organisms from most if not all kingdoms. These interactions can be mutualistic or antagonistic in nature, or in the case of commensal fungi are of no apparent benefit or detriment to the host.
With plants
Mycorrhizal symbiosis between plants and fungi is one of the most well-known plant–fungus associations and is of significant importance for plant growth and persistence in many ecosystems; over 90% of all plant species engage in mycorrhizal relationships with fungi and are dependent upon this relationship for survival.
The mycorrhizal symbiosis is ancient, dating back to at least 400 million years. It often increases the plant's uptake of inorganic compounds, such as nitrate and phosphate from soils having low concentrations of these key plant nutrients. The fungal partners may also mediate plant-to-plant transfer of carbohydrates and other nutrients. Such mycorrhizal communities are called "common mycorrhizal networks". A special case of mycorrhiza is myco-heterotrophy, whereby the plant parasitizes the fungus, obtaining all of its nutrients from its fungal symbiont. Some fungal species inhabit the tissues inside roots, stems, and leaves, in which case they are called endophytes. Similar to mycorrhiza, endophytic colonization by fungi may benefit both symbionts; for example, endophytes of grasses impart to their host increased resistance to herbivores and other environmental stresses and receive food and shelter from the plant in return.
With algae and cyanobacteria
Lichens are a symbiotic relationship between fungi and photosynthetic algae or cyanobacteria. The photosynthetic partner in the relationship is referred to in lichen terminology as a "photobiont". The fungal part of the relationship is composed mostly of various species of ascomycetes and a few basidiomycetes. Lichens occur in every ecosystem on all continents, play a key role in soil formation and the initiation of biological succession, and are prominent in some extreme environments, including polar, alpine, and semiarid desert regions. They are able to grow on inhospitable surfaces, including bare soil, rocks, tree bark, wood, shells, barnacles and leaves. As in mycorrhizas, the photobiont provides sugars and other carbohydrates via photosynthesis to the fungus, while the fungus provides minerals and water to the photobiont. The functions of both symbiotic organisms are so closely intertwined that they function almost as a single organism; in most cases the resulting organism differs greatly from the individual components. Lichenization is a common mode of nutrition for fungi; around 27% of known fungi—more than 19,400 species—are lichenized. Characteristics common to most lichens include obtaining organic carbon by photosynthesis, slow growth, small size, long life, long-lasting (seasonal) vegetative reproductive structures, mineral nutrition obtained largely from airborne sources, and greater tolerance of desiccation than most other photosynthetic organisms in the same habitat.
With insects
Many insects also engage in mutualistic relationships with fungi. Several groups of ants cultivate fungi in the order Chaetothyriales for several purposes: as a food source, as a structural component of their nests, and as a part of an ant/plant symbiosis in the domatia (tiny chambers in plants that house arthropods). Ambrosia beetles cultivate various species of fungi in the bark of trees that they infest. Likewise, females of several wood wasp species (genus Sirex) inject their eggs together with spores of the wood-rotting fungus Amylostereum areolatum into the sapwood of pine trees; the growth of the fungus provides ideal nutritional conditions for the development of the wasp larvae. At least one species of stingless bee has a relationship with a fungus in the genus Monascus, where the larvae consume and depend on fungus transferred from old to new nests. Termites on the African savannah are also known to cultivate fungi, and yeasts of the genera Candida and Lachancea inhabit the gut of a wide range of insects, including neuropterans, beetles, and cockroaches; it is not known whether these fungi benefit their hosts. Fungi growing in dead wood are essential for xylophagous insects (e.g. woodboring beetles). They deliver nutrients needed by xylophages to nutritionally scarce dead wood. Thanks to this nutritional enrichment the larvae of the woodboring insect is able to grow and develop to adulthood. The larvae of many families of fungicolous flies, particularly those within the superfamily Sciaroidea such as the Mycetophilidae and some Keroplatidae feed on fungal fruiting bodies and sterile mycorrhizae.
As parasites
Many fungi are parasites on plants, animals (including humans), and other fungi. Serious pathogens of many cultivated plants causing extensive damage and losses to agriculture and forestry include the rice blast fungus Magnaporthe oryzae, tree pathogens such as Ophiostoma ulmi and Ophiostoma novo-ulmi causing Dutch elm disease, Cryphonectria parasitica responsible for chestnut blight, and Phymatotrichopsis omnivora causing Texas Root Rot, and plant pathogens in the genera Fusarium, Ustilago, Alternaria, and Cochliobolus. Some carnivorous fungi, like Paecilomyces lilacinus, are predators of nematodes, which they capture using an array of specialized structures such as constricting rings or adhesive nets. Many fungi that are plant pathogens, such as Magnaporthe oryzae, can switch from being biotrophic (parasitic on living plants) to being necrotrophic (feeding on the dead tissues of plants they have killed). This same principle is applied to fungi-feeding parasites, including Asterotremella albida, which feeds on the fruit bodies of other fungi both while they are living and after they are dead.
Some fungi alter the behavior of their animal hosts in ways that spread their spores more effectively (also called "active host transmission"). Examples include Ophiocordyceps unilateralis and possibly the extinct Allocordyceps.
As pathogens
Some fungi can cause serious diseases in humans, several of which may be fatal if untreated. These include aspergillosis, candidiasis, coccidioidomycosis, cryptococcosis, histoplasmosis, mycetomas, and paracoccidioidomycosis. Furthermore, a person with immunodeficiency is more susceptible to disease by genera such as Aspergillus, Candida, Cryptoccocus, Histoplasma, and Pneumocystis. Other fungi can attack eyes, nails, hair, and especially skin, the so-called dermatophytic and keratinophilic fungi, and cause local infections such as ringworm and athlete's foot. Fungal spores are also a cause of allergies, and fungi from different taxonomic groups can evoke allergic reactions.
As targets of mycoparasites
Organisms that parasitize fungi are known as mycoparasitic organisms. About 300 species of fungi and fungus-like organisms, belonging to 13 classes and 113 genera, are used as biocontrol agents against plant fungal diseases. Fungi can also act as mycoparasites or antagonists of other fungi, such as Hypomyces chrysospermus, which grows on bolete mushrooms.
Fungi can also become the target of infection by mycoviruses.
Communication
There appears to be electrical communication between fungi in word-like components according to spiking characteristics.
Possible impact on climate
According to a study published in the academic journal Current Biology, fungi can soak from the atmosphere around 36% of global fossil fuel greenhouse gas emissions.
Mycotoxins
Many fungi produce biologically active compounds, several of which are toxic to animals or plants and are therefore called mycotoxins. Of particular relevance to humans are mycotoxins produced by molds causing food spoilage, and poisonous mushrooms (see above). Particularly infamous are the lethal amatoxins in some Amanita mushrooms, and ergot alkaloids, which have a long history of causing serious epidemics of ergotism (St Anthony's Fire) in people consuming rye or related cereals contaminated with sclerotia of the ergot fungus, Claviceps purpurea. Other notable mycotoxins include the aflatoxins, which are insidious liver toxins and highly carcinogenic metabolites produced by certain Aspergillus species often growing in or on grains and nuts consumed by humans, ochratoxins, patulin, and trichothecenes (e.g., T-2 mycotoxin) and fumonisins, which have significant impact on human food supplies or animal livestock.
Mycotoxins are secondary metabolites (or natural products), and research has established the existence of biochemical pathways solely for the purpose of producing mycotoxins and other natural products in fungi. Mycotoxins may provide fitness benefits in terms of physiological adaptation, competition with other microbes and fungi, and protection from consumption (fungivory). Many fungal secondary metabolites (or derivatives) are used medically, as described under Human use below.
Pathogenic mechanisms
Ustilago maydis is a pathogenic plant fungus that causes smut disease in maize and teosinte. Plants have evolved efficient defense systems against pathogenic microbes such as U. maydis. A rapid defense reaction after pathogen attack is the oxidative burst where the plant produces reactive oxygen species at the site of the attempted invasion. U. maydis can respond to the oxidative burst with an oxidative stress response, regulated by the gene YAP1. The response protects U. maydis from the host defense, and is necessary for the pathogen's virulence. Furthermore, U. maydis has a well-established recombinational DNA repair system which acts during mitosis and meiosis. The system may assist the pathogen in surviving DNA damage arising from the host plant's oxidative defensive response to infection.
Cryptococcus neoformans is an encapsulated yeast that can live in both plants and animals. C.neoformans usually infects the lungs, where it is phagocytosed by alveolar macrophages. Some C.neoformans can survive inside macrophages, which appears to be the basis for latency, disseminated disease, and resistance to antifungal agents. One mechanism by which C.neoformans survives the hostile macrophage environment is by up-regulating the expression of genes involved in the oxidative stress response. Another mechanism involves meiosis. The majority of C.neoformans are mating "type a". Filaments of mating "type a" ordinarily have haploid nuclei, but they can become diploid (perhaps by endoduplication or by stimulated nuclear fusion) to form blastospores. The diploid nuclei of blastospores can undergo meiosis, including recombination, to form haploid basidiospores that can be dispersed. This process is referred to as monokaryotic fruiting. This process requires a gene called DMC1, which is a conserved homologue of genes recA in bacteria and RAD51 in eukaryotes, that mediates homologous chromosome pairing during meiosis and repair of DNA double-strand breaks. Thus, C.neoformans can undergo a meiosis, monokaryotic fruiting, that promotes recombinational repair in the oxidative, DNA damaging environment of the host macrophage, and the repair capability may contribute to its virulence.
Human use
The human use of fungi for food preparation or preservation and other purposes is extensive and has a long history. Mushroom farming and mushroom gathering are large industries in many countries. The study of the historical uses and sociological impact of fungi is known as ethnomycology. Because of the capacity of this group to produce an enormous range of natural products with antimicrobial or other biological activities, many species have long been used or are being developed for industrial production of antibiotics, vitamins, and anti-cancer and cholesterol-lowering drugs. Methods have been developed for genetic engineering of fungi, enabling metabolic engineering of fungal species. For example, genetic modification of yeast species—which are easy to grow at fast rates in large fermentation vessels—has opened up ways of pharmaceutical production that are potentially more efficient than production by the original source organisms. Fungi-based industries are sometimes considered to be a major part of a growing bioeconomy, with applications under research and development including use for textiles, meat substitution and general fungal biotechnology.
Therapeutic uses
Modern chemotherapeutics
Many species produce metabolites that are major sources of pharmacologically active drugs.
Antibiotics
Particularly important are the antibiotics, including the penicillins, a structurally related group of β-lactam antibiotics that are synthesized from small peptides. Although naturally occurring penicillins such as penicillin G (produced by Penicillium chrysogenum) have a relatively narrow spectrum of biological activity, a wide range of other penicillins can be produced by chemical modification of the natural penicillins. Modern penicillins are semisynthetic compounds, obtained initially from fermentation cultures, but then structurally altered for specific desirable properties. Other antibiotics produced by fungi include: ciclosporin, commonly used as an immunosuppressant during transplant surgery; and fusidic acid, used to help control infection from methicillin-resistant Staphylococcus aureus bacteria. Widespread use of antibiotics for the treatment of bacterial diseases, such as tuberculosis, syphilis, leprosy, and others began in the early 20th century and continues to date. In nature, antibiotics of fungal or bacterial origin appear to play a dual role: at high concentrations they act as chemical defense against competition with other microorganisms in species-rich environments, such as the rhizosphere, and at low concentrations as quorum-sensing molecules for intra- or interspecies signaling.
Other
Other drugs produced by fungi include griseofulvin isolated from Penicillium griseofulvum, used to treat fungal infections, and statins (HMG-CoA reductase inhibitors), used to inhibit cholesterol synthesis. Examples of statins found in fungi include mevastatin from Penicillium citrinum and lovastatin from Aspergillus terreus and the oyster mushroom. Psilocybin from fungi is investigated for therapeutic use and appears to cause global increases in brain network integration. Fungi produce compounds that inhibit viruses and cancer cells. Specific metabolites, such as polysaccharide-K, ergotamine, and β-lactam antibiotics, are routinely used in clinical medicine. The shiitake mushroom is a source of lentinan, a clinical drug approved for use in cancer treatments in several countries, including Japan. In Europe and Japan, polysaccharide-K (brand name Krestin), a chemical derived from Trametes versicolor, is an approved adjuvant for cancer therapy.
Traditional medicine
Certain mushrooms are used as supposed therapeutics in folk medicine practices, such as traditional Chinese medicine. Mushrooms with a history of such use include Agaricus subrufescens, Ganoderma lucidum, and Ophiocordyceps sinensis.
Cultured foods
Baker's yeast or Saccharomyces cerevisiae, a unicellular fungus, is used to make bread and other wheat-based products, such as pizza dough and dumplings. Yeast species of the genus Saccharomyces are also used to produce alcoholic beverages through fermentation. Shoyu koji mold (Aspergillus oryzae) is an essential ingredient in brewing shoyu (soy sauce) and sake, and the preparation of miso, while Rhizopus species are used for making tempeh. Several of these fungi are domesticated species that were bred or selected according to their capacity to ferment food without producing harmful mycotoxins (see below), which are produced by very closely related Aspergilli. Quorn, a meat alternative, is made from Fusarium venenatum.
In food
Edible mushrooms include commercially raised and wild-harvested fungi. Agaricus bisporus, sold as button mushrooms when small or Portobello mushrooms when larger, is the most widely cultivated species in the West, used in salads, soups, and many other dishes. Many Asian fungi are commercially grown and have increased in popularity in the West. They are often available fresh in grocery stores and markets, including straw mushrooms (Volvariella volvacea), oyster mushrooms (Pleurotus ostreatus), shiitakes (Lentinula edodes), and enokitake (Flammulina spp.).
Many other mushroom species are harvested from the wild for personal consumption or commercial sale. Milk mushrooms, morels, chanterelles, truffles, black trumpets, and porcini mushrooms (Boletus edulis) (also known as king boletes) demand a high price on the market. They are often used in gourmet dishes.
Certain types of cheeses require inoculation of milk curds with fungal species that impart a unique flavor and texture to the cheese. Examples include the blue color in cheeses such as Stilton or Roquefort, which are made by inoculation with Penicillium roqueforti. Molds used in cheese production are non-toxic and are thus safe for human consumption; however, mycotoxins (e.g., aflatoxins, roquefortine C, patulin, or others) may accumulate because of growth of other fungi during cheese ripening or storage.
Poisonous fungi
Many mushroom species are poisonous to humans and cause a range of reactions including slight digestive problems, allergic reactions, hallucinations, severe organ failure, and death. Genera with mushrooms containing deadly toxins include Conocybe, Galerina, Lepiota and the most infamous, Amanita. The latter genus includes the destroying angel (A.virosa) and the death cap (A.phalloides), the most common cause of deadly mushroom poisoning. The false morel (Gyromitra esculenta) is occasionally considered a delicacy when cooked, yet can be highly toxic when eaten raw. Tricholoma equestre was considered edible until it was implicated in serious poisonings causing rhabdomyolysis. Fly agaric mushrooms (Amanita muscaria) also cause occasional non-fatal poisonings, mostly as a result of ingestion for its hallucinogenic properties. Historically, fly agaric was used by different peoples in Europe and Asia and its present usage for religious or shamanic purposes is reported from some ethnic groups such as the Koryak people of northeastern Siberia.
As it is difficult to accurately identify a safe mushroom without proper training and knowledge, it is often advised to assume that a wild mushroom is poisonous and not to consume it.
Pest control
In agriculture, fungi may be useful if they actively compete for nutrients and space with pathogenic microorganisms such as bacteria or other fungi via the competitive exclusion principle, or if they are parasites of these pathogens. For example, certain species eliminate or suppress the growth of harmful plant pathogens, such as insects, mites, weeds, nematodes, and other fungi that cause diseases of important crop plants. This has generated strong interest in practical applications that use these fungi in the biological control of these agricultural pests. Entomopathogenic fungi can be used as biopesticides, as they actively kill insects. Examples that have been used as biological insecticides are Beauveria bassiana, Metarhizium spp., Hirsutella spp., Paecilomyces (Isaria) spp., and Lecanicillium lecanii. Endophytic fungi of grasses of the genus Epichloë, such as E. coenophiala, produce alkaloids that are toxic to a range of invertebrate and vertebrate herbivores. These alkaloids protect grass plants from herbivory, but several endophyte alkaloids can poison grazing animals, such as cattle and sheep. Infecting cultivars of pasture or forage grasses with Epichloë endophytes is one approach being used in grass breeding programs; the fungal strains are selected for producing only alkaloids that increase resistance to herbivores such as insects, while being non-toxic to livestock.
Bioremediation
Certain fungi, in particular white-rot fungi, can degrade insecticides, herbicides, pentachlorophenol, creosote, coal tars, and heavy fuels and turn them into carbon dioxide, water, and basic elements. Fungi have been shown to biomineralize uranium oxides, suggesting they may have application in the bioremediation of radioactively polluted sites.
Model organisms
Several pivotal discoveries in biology were made by researchers using fungi as model organisms, that is, fungi that grow and sexually reproduce rapidly in the laboratory. For example, the one gene-one enzyme hypothesis was formulated by scientists using the bread mold Neurospora crassa to test their biochemical theories. Other important model fungi are Aspergillus nidulans and the yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe, each of which with a long history of use to investigate issues in eukaryotic cell biology and genetics, such as cell cycle regulation, chromatin structure, and gene regulation. Other fungal models have emerged that address specific biological questions relevant to medicine, plant pathology, and industrial uses; examples include Candida albicans, a dimorphic, opportunistic human pathogen, Magnaporthe grisea, a plant pathogen, and Pichia pastoris, a yeast widely used for eukaryotic protein production.
Others
Fungi are used extensively to produce industrial chemicals like citric, gluconic, lactic, and malic acids, and industrial enzymes, such as lipases used in biological detergents, cellulases used in making cellulosic ethanol and stonewashed jeans, and amylases, invertases, proteases, and xylanases.
See also
Conservation of fungi
Fantastic Fungi
Glossary of mycology
Marine fungi
Fungal infection
Outline of fungi
Outline of lichens
Fungi in art
References
Citations
Cited literature
Further reading
Kolbert, Elizabeth, "Spored to Death" (review of Emily Monosson, Blight: Fungi and the Coming Pandemic, Norton, 253 pp.; and Alison Pouliot, Meetings with Remarkable Mushrooms: Forays with Fungi Across Hemispheres, University of Chicago Press, 278 pp.), The New York Review of Books, vol. LXX, no.14 (21 September 2023), pp. 41–42. "Fungi sicken us and fungi sustain us. In either case, we ignore them at our peril." (p. 42.)
External links
M. C. Cooke (1875), Fungi: Their Nature and Uses, (2009)
---- (1872), Rust, Smut, Mildew, & Mould: An Introduction to the Study of Microscopic Fungi, (2020)
Tree of Life web project: Fungi
Encyclopedia of Life: Fungus
FUNGI in BoDD – Botanical Dermatology Database
Cryptogams
Extant Early Devonian first appearances
Fungi
Taxa described in 1980
Taxa named by Royall T. Moore
Articles containing video clips | Fungus | Biology | 14,503 |
1,390,410 | https://en.wikipedia.org/wiki/Reticular%20cell | A reticular cell is a type of fibroblast that synthesizes collagen alpha-1(III) and uses it to produce extracellular reticular fibers. Reticular cells provide structural support, since they produce and maintain the thin networks of fibers that are a framework for most lymphoid organs.
Reticular cells are found in many organs, including the spleen, lymph nodes and kidneys. They are also found within tissues, such as lymph nodules. There are different types of reticular cells, including epithelial, mesenchymal, and fibroblastic reticular cells. Fibroblastic reticular cells are involved in directing B cells and T cells to specific regions within the tissue whereas epithelial and mesenchymal reticular cells are associated with certain areas of the brain.
See also
List of human cell types derived from the germ layers
Lymph node stromal cell#Fibroblastic reticular cells (FRC)
References
2. Schat, K. A., Kaspers, B., & Kaiser, P. (2014). Structure of the Avian Lymphoid System. In I. Olah, N. Nagy & L. Vervelde (Eds.), Avian Immunology (2nd ed., pp. 11-44). Academic Press.
Cell biology | Reticular cell | Biology | 297 |
4,379,212 | https://en.wikipedia.org/wiki/Commitment%20ordering | Commitment ordering (CO) is a class of interoperable serializability techniques in concurrency control of databases, transaction processing, and related applications. It allows optimistic (non-blocking) implementations. With the proliferation of multi-core processors, CO has also been increasingly utilized in concurrent programming, transactional memory, and software transactional memory (STM) to achieve serializability optimistically. CO is also the name of the resulting transaction schedule (history) property, defined in 1988 with the name dynamic atomicity. In a CO compliant schedule, the chronological order of commitment events of transactions is compatible with the precedence order of the respective transactions. CO is a broad special case of conflict serializability and effective means (reliable, high-performance, distributed, and scalable) to achieve global serializability (modular serializability) across any collection of database systems that possibly use different concurrency control mechanisms (CO also makes each system serializability compliant, if not already).
Each not-CO-compliant database system is augmented with a CO component (the commitment order coordinator—COCO) which orders the commitment events for CO compliance, with neither data-access nor any other transaction operation interference. As such, CO provides a low overhead, general solution for global serializability (and distributed serializability), instrumental for global concurrency control (and distributed concurrency control) of multi-database systems and other transactional objects, possibly highly distributed (e.g., within cloud computing, grid computing, and networks of smartphones). An atomic commitment protocol (ACP; of any type) is a fundamental part of the solution, utilized to break global cycles in the conflict (precedence, serializability) graph. CO is the most general property (a necessary condition) that guarantees global serializability, if the database systems involved do not share concurrency control information beyond atomic commitment protocol (unmodified) messages and have no knowledge of whether transactions are global or local (the database systems are autonomous). Thus CO (with its variants) is the only general technique that does not require the typically costly distribution of local concurrency control information (e.g., local precedence relations, locks, timestamps, or tickets). It generalizes the popular strong strict two-phase locking (SS2PL) property, which in conjunction with the two-phase commit protocol (2PC), is the de facto standard to achieve global serializability across (SS2PL based) database systems. As a result, CO compliant database systems (with any different concurrency control types) can transparently join such SS2PL based solutions for global serializability.
In addition, locking based global deadlocks are resolved automatically in a CO based multi-database environment, a vital side-benefit (including the special case of a completely SS2PL based environment; a previously unnoticed fact for SS2PL).
Furthermore, strict commitment ordering (SCO; Raz 1991c), the intersection of Strictness and CO, provides better performance (shorter average transaction completion time and resulting in better transaction throughput) than SS2PL whenever read-write conflicts are present (identical blocking behavior for write-read and write-write conflicts; comparable locking overhead). The advantage of SCO is especially during lock contention. Strictness allows both SS2PL and SCO to use the same effective database recovery mechanisms.
Two major generalizing variants of CO exist, extended CO (ECO; Raz 1993a) and multi-version CO (MVCO; Raz 1993b). They also provide global serializability without local concurrency control information distribution, can be combined with any relevant concurrency control, and allow optimistic (non-blocking) implementations. Both use additional information for relaxing CO constraints and achieving better concurrency and performance. Vote ordering (VO or Generalized CO (GCO); Raz 2009) is a container schedule set (property) and technique for CO and all its variants. Local VO is necessary for guaranteeing global serializability if the atomic commitment protocol (ACP) participants do not share concurrency control information (have the generalized autonomy property). CO and its variants inter-operate transparently, guaranteeing global serializability and automatic global deadlock resolution together in a mixed, heterogeneous environment with different variants.
Overview
The Commitment ordering (CO; Raz 1990, 1992, 1994, 2009) schedule property has been referred to also as Dynamic atomicity (since 1988), commit ordering, commit order serializability, and strong recoverability (since 1991). The latter is a misleading name since CO is incomparable with recoverability, and the term "strong" implies a special case. This means that a substantial recoverability property does not necessarily have the CO property and vice versa.
In 2009 CO has been characterized as a major concurrency control method, together with the previously known (since the 1980s) three major methods: Locking, Time-stamp ordering, and Serialization graph testing, and as an enabler for the interoperability of systems using different concurrency control mechanisms.
In a federated database system or any other more loosely defined multidatabase system, which are typically distributed in a communication network, transactions span multiple and possibly Distributed databases. Enforcing global serializability in such system is problematic. Even if every local schedule of a single database is still serializable, the global schedule of a whole system is not necessarily serializable. The massive communication exchanges of conflict information needed between databases to reach conflict serializability would lead to unacceptable performance, primarily due to computer and communication latency. The problem of achieving global serializability effectively had been characterized as open until the public disclosure of CO in 1991 by its inventor Yoav Raz (Raz 1991a; see also Global serializability).
Enforcing CO is an effective way to enforce conflict serializability globally in a distributed system since enforcing CO locally in each database (or other transactional objects) also enforces it globally. Each database may use any, possibly different, type of concurrency control mechanism. With a local mechanism that already provides conflict serializability, enforcing CO locally does not cause any other aborts, since enforcing CO locally does not affect the data access scheduling strategy of the mechanism (this scheduling determines the serializability related aborts; such a mechanism typically does not consider the commitment events or their order). The CO solution requires no communication overhead since it uses (unmodified) atomic commitment protocol messages only, already needed by each distributed transaction to reach atomicity. An atomic commitment protocol plays a central role in the distributed CO algorithm, which enforces CO globally by breaking global cycles (cycles that span two or more databases) in the global conflict graph.
CO, its special cases, and its generalizations are interoperable and achieve global serializability while transparently being utilized together in a single heterogeneous distributed environment comprising objects with possibly different concurrency control mechanisms. As such, Commitment ordering, including its special cases, and together with its generalizations (see CO variants below), provides a general, high performance, fully distributed solution (no central processing component or central data structure are needed) for guaranteeing global serializability in heterogeneous environments of multidatabase systems and other multiple transactional objects (objects with states accessed and modified only by transactions; e.g., in the framework of transactional processes, and within Cloud computing and Grid computing). The CO solution scales up with network size and the number of databases without any negative impact on performance (assuming the statistics of a single distributed transaction, e.g., the average number of databases involved with a single transaction, are unchanged).
With the proliferation of Multi-core processors, Optimistic CO (OCO) has also been increasingly utilized to achieve serializability in software transactional memory, and numerous STM articles and patents utilizing "commit order" have already been published (e.g., Zhang et al. 2006).
The commitment ordering solution for global serializability
General characterization of CO
Commitment ordering (CO) is a special case of conflict serializability. CO can be enforced with non-blocking mechanisms (each transaction can complete its task without having its data-access blocked, which allows optimistic concurrency control; however, commitment could be blocked). In a CO schedule, the commitment events' (partial) precedence order of the transactions correspond to the precedence (partial) order of the respective transactions in the (directed) conflict graph (precedence graph, serializability graph), as induced by their conflicting access operations (usually read and write (insert/modify/delete) operations; CO also applies to higher-level operations, where they are conflicting if noncommutative, as well as to conflicts between operations upon multi-version data).
Definition commitment ordering Let be two committed transactions in a schedule, such that is in a conflict with ( precedes ). The schedule has the Commitment ordering (CO) property, if for every two such transactions commits before commits.
The commitment decision events are generated by either a local commitment mechanism or an atomic commitment protocol if different processes need to reach a consensus on whether to commit or abort. The protocol may be distributed or centralized. Transactions may be committed concurrently if the commit partial order allows (if they do not have conflicting operations). Suppose different conflicting operations induce different partial orders of the same transactions. In that case, the conflict graph has cycles, and the schedule will violate serializability when all the transactions on a cycle are committed. In this case, no partial order for commitment events can be found. Thus, cycles in the conflict graph need to be broken by aborting transactions. However, any conflict serializable schedule can be made CO without aborting any transaction by properly delaying commit events to comply with the transactions' precedence partial order.
CO enforcement by itself is not sufficient as a concurrency control mechanism since CO lacks the recoverability property, which should be supported as well.
The distributed CO algorithm
A fully distributed Global commitment ordering enforcement algorithm exists that uses local CO of each participating database, and needs only (unmodified) Atomic commitment protocol messages with no further communication. The distributed algorithm is the combination of local (to each database) CO algorithm processes and an atomic commitment protocol (which can be fully distributed).
Atomic commitment protocol is essential to enforce atomicity of each distributed transaction (to decide whether to commit or abort it; this procedure is always carried out for distributed transactions, independently of concurrency control and CO). A common example of an atomic commitment protocol is the two-phase commit protocol, which is resilient to many types of system failure. In a reliable environment, or when processes usually fail together (e.g., in the same integrated circuit), a simpler protocol for atomic commitment may be used (e.g., a simple handshake of distributed transaction's participating processes with some arbitrary but known special participant, the transaction's coordinator, i.e., a type of one-phase commit protocol). An atomic commitment protocol reaches consensus among participants on whether to commit or abort a distributed (global) transaction that spans these participants. An essential stage in each such protocol is the YES vote (either explicit or implicit) by each participant, which means an obligation of the voting participant to obey the decision of the protocol, either commit or abort. Otherwise, a participant can unilaterally abort the transaction by an explicit NO vote. The protocol commits the transaction only if YES votes have been received from all participants (thus, a missing vote is typically considered a NO). Otherwise, the protocol aborts the transaction. The various atomic commit protocols only differ in their abilities to handle different computing environment failure situations and the amounts of work and other computing resources needed in different situations.
The entire CO solution for global serializability is based on the fact that the atomic commitment protocol eventually aborts this transaction in case of a missing vote for a distributed transaction.
Enforcing global CO
In each database system, a local CO algorithm determines the needed commitment order for that database. By the characterization of CO above, this order depends on the local precedence order of transactions, which results from the local data access scheduling mechanisms. Accordingly, YES votes in the atomic commitment protocol are scheduled for each (unaborted) distributed transaction (in what follows, "a vote" means a YES vote). Suppose a precedence relation (conflict) exists between two transactions. In that case, the second will not be voted on before the first is completed (either committed or aborted), to prevent possible commit order violation by the atomic commitment protocol. Such can happen since the commit order by the protocol is not necessarily the same as the voting order. If no precedence relation exists, both can be voted on concurrently. This vote ordering strategy ensures that also the atomic commitment protocol maintains commitment order, and it is a necessary condition for guaranteeing Global CO (and the local CO of a database; without it both Global CO and Local CO (a property meaning that each database is CO compliant) may be violated).
However, since database systems schedule their transactions independently, it is possible that the transactions' precedence orders in two databases or more are not compatible (no global partial order exists that can embed the respective local partial orders together). With CO, precedence orders are also the commitment orders. When participating databases in the same distributed transaction do not have compatible local precedence orders for that transaction (without "knowing" it; typically no coordination between database systems exists on conflicts, since the needed communication is massive and unacceptably degrades performance) it means that the transaction resides on a global cycle (involving two or more databases) in the global conflict graph. In this case, the atomic commitment protocol will fail to collect all the votes needed to commit that transaction: By the vote ordering strategy above, at least one database will delay its vote for that transaction indefinitely to comply with its own commitment (precedence) order, since it will be waiting to the completion of another, preceding transactions on that global cycle delayed indefinitely by another database with a different order. This means a voting-deadlock situation involving the databases on that cycle.
As a result, the protocol will eventually abort some deadlocked transaction on this global cycle, since each such transaction is missing at least one participant's vote. Selection of the specific transaction on the cycle to be aborted depends on the atomic commitment protocol's abort policies (a timeout mechanism is common, but it may result in more than one needed abort per cycle; both preventing unnecessary aborts and abort time shortening can be achieved by a dedicated abort mechanism for CO). Such abort will break the global cycle involving that distributed transaction. Both deadlocked transactions and possibly others in conflict with the deadlocked (and thus blocked) will be free to be voted on. It is worthwhile noting that each database involved with the voting-deadlock continues to vote regularly on transactions that are not in conflict with its deadlocked transaction, typically almost all the outstanding transactions. Thus, in the case of incompatible local (partial) commitment orders, no action is needed since the atomic commitment protocol resolves it automatically by aborting a transaction that is a cause of incompatibility. This means that the above vote ordering strategy is also a sufficient condition for guaranteeing Global CO.
The following is concluded:
The Vote ordering strategy for Global CO Enforcing Theorem
Let be undecided (neither committed nor aborted) transactions in a database system that enforces CO for local transactions, such that is global and in conflict with ( precedes ). Then, having ended (either committed or aborted) before is voted on to be committed (the vote ordering strategy), in each such database system in a multidatabase environment, is a necessary and sufficient condition for guaranteeing Global CO (the condition guarantees Global CO, which may be violated without it).
Comments:
The vote ordering strategy that enforces global CO is referred to as in (Raz 1992).
The Local CO property of a global schedule means that each database is CO compliant. From the necessity discussion, the part above directly follows that the theorem is also true when replacing "Global CO" with "Local CO" when global transactions are present. Together it means that Global CO is guaranteed if and only if Local CO is guaranteed (which is untrue for Global conflict serializability and Local conflict serializability: Global implies Local, but not the opposite).
Global CO implies Global serializability.
The Global CO algorithm comprises enforcing (local) CO in each participating database system by ordering commits of local transactions (see Enforcing CO locally below) and enforcing the vote ordering strategy in the theorem above (for global transactions).
The exact characterization of voting-deadlocks by global cycles
The above global cycle elimination process by a voting deadlock can be explained in detail by the following observation:
First, it is assumed, for simplicity, that every transaction reaches the ready-to-commit state and is voted on by at least one database (this implies that no blocking by locks occurs).
Define a "wait for vote to commit" graph as a directed graph with transactions as nodes and a directed edge from any first transaction to a second transaction if the first transaction blocks the vote to commit of the second transaction (opposite to conventional edge direction in a wait-for graph). Such blocking happens only if the second transaction conflicts with the first transaction (see above). Thus this "wait for vote to commit" graph is identical to the global conflict graph. A cycle in the "wait for vote to commit" graph means a deadlock in voting. Hence there is a deadlock in voting if there is a cycle in the conflict graph. The local serializability mechanisms eliminate local cycles (confined to a single database). Consequently, only global cycles are left, which are then eliminated by the atomic commitment protocol when it aborts deadlocked transactions with missing (blocked) respective votes.
Secondly, also local commits are dealt with: Note that when enforcing CO, also waiting for a regular local commit of a local transaction can block local commits and votes of other transactions upon conflicts, and the situation for global transactions does not also change without the simplifying assumption above: The final result is the same also with a local commitment for local transactions, without voting in atomic commitment for them.
Finally, blocking by a lock (which has been excluded so far) needs to be considered: A lock blocks a conflicting operation and prevents a conflict from being materialized. Suppose the lock is released only after the transaction end. In that case, it may block indirectly either a vote or a local commit of another transaction (which now cannot get to ready state), with the same effect as a direct blocking of a vote or a local commit. A cycle is generated in the conflict graph only if such blocking by a lock is also represented by an edge. With such added edges representing events of blocking-by-a-lock, the conflict graph is becoming an augmented conflict graph.
Definition: augmented conflict graph
An augmented conflict graph is a conflict graph with added edges: In addition to the original edges a directed edge exists from transaction to transaction if two conditions are met:
is blocked by a data-access lock applied by (the blocking prevents the conflict of with from being materialized and have an edge in the regular conflict graph), and
This blocking will not stop before ends (commits or aborts; true for any locking-based CO)
The graph can also be defined as the union of the (regular) conflict graph with the (reversed edge, regular) wait-for graph
Comments:
Here, unlike the regular conflict graph, which has edges only for materialized conflicts, all materialized, and non-materialized conflicts are represented by edges.
Note that all the new edges are all the (reversed to the conventional) edges of the wait-for graph. The wait-for graph can also be defined as the graph of non-materialized conflicts. By the common conventions, edge direction in a conflict graph defines time order between conflicting operations, which is opposite to the time order defined by an edge in a wait-for graph.
Note that such a global graph contains (has embedded) all the (reversed edge) regular local wait-for graphs and also may include locking based global cycles (which cannot exist in the local graphs). For example, if all the databases on a global cycle are SS2PL based, then all the related vote blocking situations are caused by locks (this is the classical and probably the only global deadlock situation dealt with in the database research literature). This is a global deadlock case where each related database creates a portion of the cycle, but the complete cycle does not reside in any local wait-for graph.
In the presence of CO, the augmented conflict graph is, in fact, a (reversed edge) local-commit and voting wait-for graph: An edge exists from a first transaction, either local or global, to a second, if the second is waiting for the first to end in order to be either voted on (if global) or locally committed (if local). All global cycles (across two or more databases) in this graph generate voting-deadlocks. The graph's global cycles provide complete characterization for voting deadlocks and may include any combination of materialized and non-materialized conflicts. Only cycles of (only) materialized conflicts are also cycles of the regular conflict graph and affect serializability. One or more (lock related) non-materialized conflicts on a cycle prevent it from being a cycle in the regular conflict graph and make it a locking related deadlock. All the global cycles (voting-deadlocks) need to be broken (resolved) to both maintain global serializability and resolve global deadlocks involving data access locking. Indeed they are all broken by the atomic commitment protocol due to missing votes upon a voting deadlock.
Comment: This observation also explains the correctness of Extended CO (ECO) below: Global transactions' voting order must follow the conflict graph order with vote blocking when order relation (graph path) exists between two global transactions. Local transactions are not voted on, and their (local) commits are not blocked upon conflicts. This results in the same voting-deadlock situations and resulting global cycle elimination process for ECO.
The voting-deadlock situation can be summarized as follows:
The CO Voting-Deadlock Theorem
Let a multidatabase environment comprise CO compliant (which eliminates local cycles) database systems that enforce each Global CO (using the condition in the theorem above). A voting-deadlock occurs if and only if a global cycle (spans two or more databases) exists in the Global augmented conflict graph (also blocking by a data-access lock is represented by an edge). Suppose the cycle does not break by any abort. In that case, all the global transactions on it are involved with the respective voting-deadlock. Eventually, each has its vote blocked (either directly or indirectly by a data-access lock); if a local transaction resides on the cycle, eventually, it has its (local) commit blocked.
Comment: A rare situation of a voting deadlock (by missing blocked votes) can happen, with no voting for any transaction on the related cycle by any of the database systems involved with these transactions. This can occur when local sub-transactions are multi-threaded. The highest probability instance of such a rare event involves two transactions on two simultaneous opposite cycles. Such global cycles (deadlocks) overlap with local cycles that are resolved locally and are typically resolved by local mechanisms without involving atomic commitment. Formally it is also a global cycle, but practically it is local (portions of local cycles generate a global one; to see this, split each global transaction (node) to local sub-transactions (its portions confined each to a single database); a directed edge exists between transactions if an edge exists between any respective local sub-transactions; a cycle is local if all its edges originate from a cycle among sub-transactions of the same database, and global if not; global and local can overlap: the same cycle among transactions can result from several different cycles among sub-transactions, and be both local and global).
Also, the following locking based special case is concluded:
The CO Locking-based Global-Deadlock Theorem
In a CO compliant multidatabase system, a locking-based global-deadlock, involving at least one data-access lock (non-materialized conflict), and two or more database systems, is a reflection of a global cycle in the Global augmented conflict graph, which results in a voting-deadlock. Such a cycle is not a cycle in the (regular) Global conflict graph (which reflects only materialized conflicts, so such a cycle does not affect serializability).
Comments:
Any blocking (edge) in the cycle that is not by a data-access lock directly blocks either voting or local commit. All voting-deadlocks are resolved (almost all by Atomic commitment; see comment above), including this locking-based type.
Locking-based global-deadlocks can also be generated in a completely SS2PL-based distributed environment (special case of CO based). All the vote blocking (and voting-deadlocks) are caused by data-access locks. Many research articles have dealt for years with resolving such global deadlocks, but none (except the CO articles) is known (as of 2009) to notice that atomic commitment automatically resolves them. Such automatic resolutions are regularly occurring unnoticed in all existing SS2PL based multidatabase systems, often bypassing dedicated resolution mechanisms.
Voting-deadlocks are the key to the operation of distributed CO.
Global cycle elimination (here voting-deadlock resolution by atomic commitment) and resulting aborted transactions' re-executions are time-consuming, regardless of concurrency control used. If databases schedule transactions independently, global cycles are unavoidable (in a complete analogy to cycles/deadlocks generated in local SS2PL; with distribution, any transaction or operation scheduling coordination results in autonomy violation and is typically in substantial performance penalty). However, their likelihood can be made very low in many cases by implementing database and transaction design guidelines that reduce the number of conflicts involving a global transaction. This, primarily by properly handling hot spots (database objects with frequent access,) and avoiding conflicts by using commutativity when possible (e.g., when extensively using counters, as in finances, and especially multi-transaction accumulation counters, which are typically hot spots).
Atomic commitment protocols are intended and designed to achieve atomicity without considering database concurrency control. They abort upon detecting or heuristically finding (e.g., by a timeout; sometimes mistakenly, unnecessarily) missing votes and typically unaware of global cycles. These protocols can be especially enhanced for CO (including CO's variants below) to prevent unnecessary aborts and accelerate aborts used for breaking global cycles in the global augmented conflict graph (for better performance by earlier release upon transaction-end of computing resources and typically locked data). For example, existing locking based global deadlock detection methods, other than the timeout, can be generalized also to consider local commit and vote direct blocking, besides data access blocking. A possible compromise in such mechanisms is effectively detecting and breaking the most frequent and relatively simple to handle length-2 global cycles, and using timeout for undetected, much less frequent, longer cycles.
Enforcing CO locally
Commitment ordering can be enforced locally (in a single database) by a dedicated CO algorithm, or by any algorithm/protocol that provides any special case of CO. An important such protocol, being utilized extensively in database systems, which generates a CO schedule, is the strong strict two phase locking protocol (SS2PL: "release transaction's locks only after the transaction has been either committed or aborted"; see below). SS2PL is a proper subset of the intersection of 2PL and strictness.
A generic local CO algorithm
A generic local CO algorithm (Raz 1992; Algorithm 4.1) is an algorithm independent of implementation details that enforces exactly the CO property. It does not block data access (nonblocking) and consists of aborting a certain set of transactions (only if needed) upon committing a transaction. It aborts a (uniquely determined at any given time) minimal set of other undecided (neither committed, nor aborted) transactions that run locally and can cause serializability violation in the future (can later generate cycles of committed transactions in the conflict graph; this is the ABORT set of a committed transaction T; after committing T no transaction in ABORT at commit time can be committed, and all of them are doomed to be aborted). This set consists of all undecided transactions with directed edges in the conflict graph to the committed transaction. The size of this set cannot increase when that transaction is waiting to be committed (in the ready state: processing has ended,) and typically decreases in time as its transactions are being decided. Thus, unless real-time constraints exist to complete that transaction, it is preferred to wait with committing that transaction and let this set decrease in size. If another serializability mechanism exists locally (which eliminates cycles in the local conflict graph), or if no cycle involving that transaction exists, the set will be empty eventually, and no abort of a set member is needed. Otherwise, the set will stabilize with transactions on local cycles, and aborting set members will have to occur to break the cycles. Since in the case of CO conflicts generate blocking on commit, local cycles in the augments conflict graph (see above) indicate local commit-deadlocks, and deadlock resolution techniques as in SS2PL can be used (e.g., like timeout and wait-for graph). A local cycle in the augmented conflict graph with at least one non-materialized conflict reflects a locking-based deadlock. The local algorithm above, applied to the local augmented conflict graph rather than the regular local conflict graph, comprises the generic enhanced local CO algorithm, a single local cycle elimination mechanism, for both guaranteeing local serializability and handling locking based local deadlocks. Practically an additional concurrency control mechanism is always utilized, even solely to enforce recoverability. The generic CO algorithm does not affect the local data access scheduling strategy when it runs alongside any other local concurrency control mechanism. It affects only the commit order, and for this reason, it does not need to abort more transactions than those needed to be aborted for serializability violation prevention by any combined local concurrency control mechanism. At most, the net effect of CO may be a delay of commit events (or voting in a distributed environment), to comply with the needed commit order (but not more delay than its special cases, for example, SS2PL, and on average significantly less).
The following theorem is concluded:
The Generic Local CO Algorithm Theorem
When running alone or alongside any concurrency control mechanism in a database system, then
The Generic local CO algorithm guarantees (local) CO (a CO compliant schedule).
The Generic enhanced local CO algorithm guarantees both (local) CO and (local) locking based deadlock resolution. And (when not using a timeout, and no real-time transaction completion constraints are applied) neither algorithm aborts more transactions than the minimum needed (which is determined by the transactions' operations scheduling, out of the scope of the algorithms).
Example: Concurrent programming and Transactional memory
See also Concurrent programming and Transactional memory.
With the proliferation of Multi-core processors, variants of the Generic local CO algorithm have also been increasingly utilized in Concurrent programming, Transactional memory, and especially in Software transactional memory for achieving serializability optimistically by "commit order" (e.g., Ramadan et al. 2009, Zhang et al. 2006, von Parun et al. 2007). Numerous related articles and patents utilizing CO have already been published.
Implementation considerations: The Commitment Order Coordinator (COCO)
A database system in a multidatabase environment is assumed. From a software architecture point of view, a CO component that implements the generic CO algorithm locally, the Commitment Order Coordinator (COCO), can be designed straightforwardly as a mediator between a (single) database system and an atomic commitment protocol component (Raz 1991b). However, the COCO is typically an integral part of the database system. The COCO's functions are to vote to commit on ready global transactions (the processing has ended) according to the local commitment order, to vote to abort on transactions for which the database system has initiated an abort (the database system can initiate abort for any transaction, for many reasons), and to pass the atomic commitment decision to the database system. For local transactions (when can be identified), no voting is needed. For determining the commitment order, the COCO maintains an updated representation of the local conflict graph (or local augmented conflict graph for capturing also locking deadlocks) of the undecided (neither committed nor aborted) transactions as a data structure (e.g., utilizing mechanisms similar to locking for capturing conflicts, but with no data-access blocking). The COCO component has an interface with its database system to receive "conflict," "ready" (the processing has ended; readiness to vote on a global transaction or commit a local one), and "abort" notifications from the database system. It also interfaces with the atomic commitment protocol to vote and receive the atomic commitment protocol's decision on each global transaction. The decisions are delivered from the COCO to the database system through their interface, as well as local transactions' commit notifications, at a proper commit order. The COCO, including its interfaces, can be enhanced, if it implements another variant of CO (see below) or plays a role in the database's concurrency control mechanism beyond voting in atomic commitment.
The COCO also guarantees CO locally in a single, isolated database system with no interface with an atomic commitment protocol.
CO is a necessary condition for global serializability across autonomous database systems.
Suppose databases that participate in distributed transactions (i.e., transactions that span more than a single database) do not use any shared concurrency control information and use unmodified atomic commitment protocol messages (for reaching atomicity). In that case, maintaining (local) commitment ordering or one of its generalizing variants (see below) is a necessary condition for guaranteeing global serializability (a proof technique can be found in (Raz 1992), and a different proof method for this in (Raz 1993a)); it is also a sufficient condition. This is a mathematical fact derived from the definitions of serializability and a transaction. It means that if not complying with CO, then global serializability cannot be guaranteed under this condition (the condition of no local concurrency control information sharing between databases beyond atomic commit protocol messages). Atomic commitment is a minimal requirement for a distributed transaction since it is always needed, which is implied by the transaction definition.
(Raz 1992) defines database autonomy and independence as complying with this requirement without using any additional local knowledge:
Definition: (concurrency control based) autonomous database system
A database system is Autonomous, if it does not share any concurrency control information beyond unmodified atomic commitment protocol messages with any other entity. In addition, it does not use for concurrency control any additional local information beyond conflicts (the last sentence does not appear explicitly but rather implied by further discussion in Raz 1992).
Using this definition, the following is concluded:
The CO and Global serializability Theorem
CO compliance of every autonomous database system (or transactional object) in a multidatabase environment is a necessary condition for guaranteeing Global serializability (without CO, Global serializability may be violated).
CO compliance with every database system is a sufficient condition for guaranteeing Global serializability.
However, the definition of autonomy above implies, for example, that transactions are scheduled in a way that local transactions (confined to a single database) cannot be identified as such by an autonomous database system. This is realistic for some transactional objects but too restrictive and less realistic for general purpose database systems. If autonomy is augmented with the ability to identify local transactions, then compliance with a more general property, Extended commitment ordering (ECO, see below), makes ECO the necessary condition.
Only in (Raz 2009) the notion of Generalized autonomy captures the intended notion of autonomy:
Definition: generalized autonomy
A database system has the Generalized autonomy property if it does not share any other database system any local concurrency information beyond (unmodified) atomic commit protocol messages (however, any local information can be utilized).
This definition is probably the broadest such definition possible in the context of database concurrency control, and it makes CO together with any of its (useful: No concurrency control information distribution) generalizing variants (Vote ordering (VO); see CO variants below) the necessary condition for Global serializability (i.e., the union of CO and its generalizing variants is the necessary set VO, which may also include new unknown useful generalizing variants).
Summary
The Commitment ordering (CO) solution (technique) for global serializability can be summarized as follows:
If each database (or any other transactional object) in a multidatabase environment complies with CO, i.e., arranges its local transactions' commitments and its votes on (global, distributed) transactions to the atomic commitment protocol according to the local (to the database) partial order induced by the local conflict graph (serializability graph) for the respective transactions, then Global CO and Global serializability are guaranteed. A database's CO compliance can be achieved effectively with any local conflict serializability based concurrency control mechanism, neither affecting any transaction's execution process or scheduling nor aborting it. Also, the database's autonomy is not violated. The only low overhead incurred is detecting conflicts (e.g., with locking, but with no data-access blocking; if not already detected for other purposes) and ordering votes and local transactions' commits according to the conflicts.
In case of incompatible partial orders of two or more databases (no global partial order can embed the respective local partial orders together), a global cycle (spans two databases or more) in the global conflict graph is generated. This, together with CO, results in a cycle of blocked votes. A voting-deadlock occurs for the databases on that cycle (however, allowed concurrent voting in each database, typically for almost all the outstanding votes, continue to execute). In this case, the atomic commitment protocol fails to collect all the votes needed for the blocked transactions on that global cycle. Consequently the protocol aborts some transactions with a missing vote. This breaks the global cycle, the voting-deadlock is resolved, and the related blocked votes are free to be executed. Breaking the global cycle in the global conflict graph ensures that global CO and global serializability are maintained. Thus, in the case of incompatible local (partial) commitment orders, no action is needed since the atomic commitment protocol resolves it automatically by aborting a transaction that is a cause for the incompatibility. Furthermore, global deadlocks due to locking (global cycles in the augmented conflict graph with at least one data access blocking) result in voting deadlocks and are resolved automatically by the same mechanism.
Local CO is a necessary condition for guaranteeing Global serializability if the databases involved do not share any concurrency control information beyond (unmodified) atomic commitment protocol messages, i.e., if the databases are autonomous in the context of concurrency control. This means that every global serializability solution for autonomous databases must comply with CO. Otherwise, global serializability may be violated (and thus, is likely to be violated very quickly in a high-performance environment).
The CO solution scales up with network size and the number of databases without performance penalty when it utilizes common distributed atomic commitment architecture.
Distributed serializability and CO
Distributed CO
A distinguishing characteristic of the CO solution to distributed serializability from other techniques is the fact that it requires no conflict information distributed (e.g., local precedence relations, locks, timestamps, tickets), which makes it uniquely effective. It utilizes (unmodified) atomic commitment protocol messages (which are already used) instead.
A common way to achieve distributed serializability in a (distributed) system is by a distributed lock manager (DLM). DLMs, which communicate lock (non-materialized conflict) information in a distributed environment, typically suffer from computer and communication latency, which reduces the performance of the system. CO allows to achieve distributed serializability under very general conditions, without a distributed lock manager, exhibiting the benefits already explored above for multidatabase environments; in particular: reliability, high performance, scalability, the possibility of using optimistic concurrency control when desired, no conflict information related communications over the network (which have incurred overhead and delays), and automatic distributed deadlock resolution.
All distributed transactional systems rely on some atomic commitment protocol to coordinate atomicity (whether to commit or abort) among processes in a distributed transaction. Also, typically recoverable data (i.e., data under transactions' control, e.g., database data; not to be confused with the recoverability property of a schedule) are directly accessed by a single transactional data manager component (also referred to as a resource manager) that handles local sub-transactions (the distributed transaction's portion in a single location, e.g., network node), even if these data are accessed indirectly by other entities in the distributed system during a transaction (i.e., indirect access requires a direct access through a local sub-transaction). Thus recoverable data in a distributed transactional system are typically partitioned among transactional data managers. In such system, these transactional data managers typically comprise the participants in the system's atomic commitment protocol. If each participant complies with CO (e.g., by using SS2PL, or COCOs, or a combination; see above), then the entire distributed system provides CO (by the theorems above; each participant can be considered a separate transactional object), and thus (distributed) serializability. Furthermore: When CO is utilized together with an atomic commitment protocol also distributed deadlocks (i.e., deadlocks that span two or more data managers) caused by data-access locking are resolved automatically. Thus the following corollary is concluded:
The CO Based Distributed Serializability Theorem
Let a distributed transactional system (e.g., a distributed database system) comprise transactional data managers (also called resource managers) that manage all the system's recoverable data. The data managers meet three conditions:
Data partition: Recoverable data are partitioned among the data managers, i.e., each recoverable datum (data item) is controlled by a single data manager (e.g., as common in a Shared nothing architecture; even copies of the same datum under different data managers are physically distinct, replicated).
Participants in atomic commitment protocol: These data managers are the participants in the system's atomic commitment protocol for coordinating distributed transactions' atomicity.
CO compliance: Each such data manager is CO compliant (or some CO variant compliant; see below).
Then
The entire distributed system guarantees (distributed CO and) serializability, and
Data-access-based distributed deadlocks (deadlocks involving two or more data managers with at least one non-materialized conflict) are resolved automatically.
Furthermore: The data managers being CO compliant is a necessary condition for (distributed) serializability in a system meeting conditions 1, 2 above, when the data managers are autonomous, i.e., do not share concurrency control information beyond unmodified messages of atomic commitment protocol.
This theorem also means that when SS2PL (or any other CO variant) is used locally in each transactional data manager, and each data manager has exclusive control of its data, no distributed lock manager (which is often utilized to enforce distributed SS2PL) is needed for distributed SS2PL and serializability. It is relevant to a wide range of distributed transactional applications, which can be easily designed to meet the theorem's conditions.
Distributed optimistic CO (DOCO)
For implementing Distributed Optimistic CO (DOCO), the generic local CO algorithm is utilized in all the atomic commitment protocol participants in the system with no data access blocking and thus with no local deadlocks. The previous theorem has the following corollary:
The Distributed optimistic CO (DOCO) Theorem
If DOCO is utilized, then:
No local deadlocks occur, and
Global (voting) deadlocks are resolved automatically (and all are serializability related (with non-blocking conflicts) rather than locking related (with blocking and possibly also non-blocking conflicts)).
Thus, no deadlock handling is needed.
Examples
Distributed SS2PL
A distributed database system that utilizes SS2PL resides on two remote nodes, A and B. The database system has two transactional data managers (resource managers), one on each node, and the database data are partitioned between the two data managers in a way that each has an exclusive control of its own (local to the node) portion of data: Each handles its own data and locks without any knowledge on the other manager's. For each distributed transaction such data managers need to execute the available atomic commitment protocol.
Two distributed transactions, and , are running concurrently, and both access data x and y. x is under the exclusive control of the data manager on A (B's manager cannot access x), and y under that on B.
reads x on A and writes y on B, i.e., when using notation common for concurrency control.
reads y on B and writes x on A, i.e.,
The respective local sub-transactions on A and B (the portions of and on each of the nodes) are the following:
{| class="wikitable" style="text-align:center;"
|+Local sub-transactions
|-
! !! A !! B
|-
!
| ||
|-
!
| ||
|}
The database system's schedule at a certain point in time is the following:
(also is possible)
holds a read-lock on x and holds read-locks on y. Thus and are blocked by the lock compatibility rules of SS2PL and cannot be executed. This is a distributed deadlock situation, which is also a voting-deadlock (see below) with a distributed (global) cycle of length 2 (number of edges, conflicts; 2 is the most frequent length). The local sub-transactions are in the following states:
is ready (execution has ended) and voted (in atomic commitment)
is running and blocked (a non-materialized conflict situation; no vote on it can occur)
is ready and voted
is running and blocked (a non-materialized conflict; no vote).
Since the atomic commitment protocol cannot receive votes for blocked sub-transactions (a voting-deadlock), it will eventually abort some transaction with a missing vote(s) by timeout, either , or , (or both, if the timeouts fall very close). This will resolve the global deadlock. The remaining transaction will complete running, be voted on, and committed. An aborted transaction is immediately restarted and re-executed.
Comments
The data partition (x on A; y on B) is important since without it, for example, x can be accessed directly from B. If a transaction is running on B concurrently with and and directly writes x, then, without a distributed lock manager the read-lock for x held by on A is not visible on B and cannot block the write of (or signal a materialized conflict for a non-blocking CO variant; see below). Thus serializability can be violated.
Due to data partition, x cannot be accessed directly from B. However, functionality is not limited, and a transaction running on B still can issue a write or read request of x (not common). This request is communicated to the transaction's local sub-transaction on A (which is generated, if does not exist already) which issues this request to the local data manager on A.
Variations
In the scenario above both conflicts are non-materialized, and the global voting-deadlock is reflected as a cycle in the global wait-for graph (but not in the global conflict graph; see Exact characterization of voting-deadlocks by global cycles above). However the database system can utilize any CO variant with exactly the same conflicts and voting-deadlock situation, and same resolution. Conflicts can be either materialized or non-materialized, depending on CO variant used. For example, if SCO (below) is used by the distributed database system instead of SS2PL, then the two conflicts in the example are materialized, all local sub-transactions are in ready states, and vote blocking occurs in the two transactions, one on each node, because of the CO voting rule applied independently on both A and B: due to conflicts is not voted on before ends, and is not voted on before ends, which is a voting-deadlock. Now the conflict graph has the global cycle (all conflicts are materialized), and again it is resolved by the atomic commitment protocol, and distributed serializability is maintained. Unlikely for a distributed database system, but possible in principle (and occurs in a multi-database), A can employ SS2PL while B employs SCO. In this case the global cycle is neither in the wait-for graph nor in the serializability graph, but still in the augmented conflict graph (the union of the two). The various combinations are summarized in the following table:
Comments:
Conflicts and thus cycles in the augmented conflict graph are determined by the transactions and their initial scheduling only, independently of the concurrency control utilized. With any variant of CO, any global cycle (i.e., spans two databases or more) causes a voting deadlock. Different CO variants may differ on whether a certain conflict is materialized or non-materialized.
Some limited operation order changes in the schedules above are possible, constrained by the orders inside the transactions, but such changes do not change the rest of the table.
As noted above, only case 4 describes a cycle in the (regular) conflict graph which affects serializability. Cases 1-3 describe cycles of locking based global deadlocks (at least one lock blocking exists). All cycle types are equally resolved by the atomic commitment protocol. Case 1 is the common Distributed SS2PL, utilized since the 1980s. However, no research article, except the CO articles, is known to notice this automatic locking global deadlock resolution as of 2009. Such global deadlocks typically have been dealt with by dedicated mechanisms.
Case 4 above is also an example for a typical voting-deadlock when Distributed optimistic CO (DOCO) is used (i.e., Case 4 is unchanged when Optimistic CO (OCO; see below) replaces SCO on both A and B): No data-access blocking occurs, and only materialized conflicts exist.
Hypothetical Multi Single-Threaded Core (MuSiC) environment
Comment: While the examples above describe real, recommended utilization of CO, this example is hypothetical, for demonstration only.
Certain experimental distributed memory-resident databases advocate multi single-threaded core (MuSiC) transactional environments. "Single-threaded" refers to transaction threads only, and to serial execution of transactions. The purpose is possible orders of magnitude gain in performance (e.g., H-Store and VoltDB) relatively to conventional transaction execution in multiple threads on a same core. In what described below MuSiC is independent of the way the cores are distributed. They may reside in one integrated circuit (chip), or in many chips, possibly distributed geographically in many computers. In such an environment, if recoverable (transactional) data are partitioned among threads (cores), and it is implemented in the conventional way for distributed CO, as described in previous sections, then DOCO and Strictness exist automatically. However, downsides exist with this straightforward implementation of such environment, and its practicality as a general-purpose solution is questionable. On the other hand, tremendous performance gain can be achieved in applications that can bypass these downsides in most situations.
Comment: The MuSiC straightforward implementation described here (which uses, for example, as usual in distributed CO, voting (and transaction thread) blocking in atomic commitment protocol when needed) is for demonstration only, and has no connection to the implementation in H-Store or any other project.
In a MuSiC environment local schedules are serial. Thus both local Optimistic CO (OCO; see below) and the Global CO enforcement vote ordering strategy condition for the atomic commitment protocol are met automatically. This results in both distributed CO compliance (and thus distributed serializability) and automatic global (voting) deadlock resolution.
Furthermore, also local Strictness follows automatically in a serial schedule. By Theorem 5.2 in (Raz 1992; page 307), when the CO vote ordering strategy is applied, also Global Strictness is guaranteed. Note that serial locally is the only mode that allows strictness and "optimistic" (no data access blocking) together.
The following is concluded:
The MuSiC Theorem
In MuSiC environments, if recoverable (transactional) data are partitioned among cores (threads), then both
OCO (and implied Serializability; i.e., DOCO and Distributed serializability)
Strictness (allowing effective recovery; 1 and 2 implying Strict CO—see SCO below) and
(voting) deadlock resolution
automatically exist globally with unbounded scalability in number of cores used.
Comment: However, two major downsides, which need special handling, may exist:
Local sub-transactions of a global transaction are blocked until commit, which makes the respective cores idle. This reduces core utilization substantially, even if scheduling of the local sub-transactions attempts to execute all of them in time proximity, almost together. It can be overcome by detaching execution from commit (with some atomic commitment protocol) for global transactions, at the cost of possible cascading aborts.
increasing the number of cores for a given amount of recoverable data (database size) decreases the average amount of (partitioned) data per core. This may make some cores idle, while others very busy, depending on data utilization distribution. Also a local (to a core) transaction may become global (multi-core) to reach its needed data, with additional incurred overhead. Thus, as the number of cores increases, the amount and type of data assigned to each core should be balanced according to data usage, so a core is neither overwhelmed to become a bottleneck, nor becoming idle too frequently and underutilized in a busy system. Another consideration is putting in a same core partition all the data that are usually accessed by a same transaction (if possible), to maximize the number of local transactions (and minimize the number of global, distributed transactions). This may be achieved by occasional data re-partition among cores based on load balancing (data access balancing) and patterns of data usage by transactions. Another way to considerably mitigate this downside is by proper physical data replication among some core partitions in a way that read-only global transactions are possibly (depending on usage patterns) completely avoided, and replication changes are synchronized by a dedicated commit mechanism.
CO variants: special cases and generalizations
Special case schedule property classes (e.g., SS2PL and SCO below) are strictly contained in the CO class. The generalizing classes (ECO and MVCO) strictly contain the CO class (i.e., include also schedules that are not CO compliant). The generalizing variants also guarantee global serializability without distributing local concurrency control information (each database has the generalized autonomy property: it uses only local information), while relaxing CO constraints and utilizing additional (local) information for better concurrency and performance: ECO uses knowledge about transactions being local (i.e., confined to a single database), and MVCO uses availability of data versions values. Like CO, both generalizing variants are non-blocking, do not interfere with any transaction's operation scheduling, and can be seamlessly combined with any relevant concurrency control mechanism.
The term CO variant refers in general to CO, ECO, MVCO, or a combination of each of them with any relevant concurrency control mechanism or property (including Multi-version based ECO, MVECO). No other generalizing variants (which guarantee global serializability with no local concurrency control information distribution) are known, but may be discovered.
Strong strict two phase locking (SS2PL)
Strong Strict Two Phase Locking (SS2PL; also referred to as Rigorousness or Rigorous scheduling) means that both read and write locks of a transaction are released only after the transaction has ended (either committed or aborted). The set of SS2PL schedules is a proper subset of the set of CO schedules.
This property is widely utilized in database systems, and since it implies CO, databases that use it and participate in global transactions generate together a serializable global schedule (when using any atomic commitment protocol, which is needed for atomicity in a multi-database environment). No database modification or addition is needed in this case to participate in a CO distributed solution: The set of undecided transactions to be aborted before committing in the local generic CO algorithm above is empty because of the locks, and hence such an algorithm is unnecessary in this case. A transaction can be voted on by a database system immediately after entering a "ready" state, i.e., completing running its task locally. Its locks are released by the database system only after it is decided by the atomic commitment protocol, and thus the condition in the Global CO enforcing theorem above is kept automatically. If a local timeout mechanism is used by a database system to resolve (local) SS2PL deadlocks, then aborting blocked transactions breaks not only potential local cycles in the global conflict graph (real cycles in the augmented conflict graph), but also database system's potential global cycles as a side effect, if the atomic commitment protocol's abort mechanism is relatively slow. Such independent aborts by several entities typically may result in unnecessary aborts for more than one transaction per global cycle. The situation is different for a local wait-for graph based mechanisms: Such cannot identify global cycles, and the atomic commitment protocol will break the global cycle, if the resulting voting deadlock is not resolved earlier in another database.
Local SS2PL together with atomic commitment implying global serializability can also be deduced directly: All transactions, including distributed, obey the 2PL (SS2PL) rules. The atomic commitment protocol mechanism is not needed here for consensus on commit, but rather for the end of phase-two synchronization point. Probably for this reason, without considering the atomic commitment voting mechanism, automatic global deadlock resolution has not been noticed before CO.
Strict CO (SCO)
Strict Commitment Ordering (SCO; (Raz 1991c)) is the intersection of strictness (a special case of recoverability) and CO, and provides an upper bound for a schedule's concurrency when both properties exist. It can be implemented using blocking mechanisms (locking) similar to those used for the popular SS2PL with similar overheads.
Unlike SS2PL, SCO does not block on a read-write conflict but possibly blocks on commit instead. SCO and SS2PL have identical blocking behavior for the other two conflict types: write-read, and write-write. As a result, SCO has shorter average blocking periods, and more concurrency (e.g., performance simulations of a single database for the most significant variant of locks with ordered sharing, which is identical to SCO, clearly show this, with approximately 100% gain for some transaction loads; also for identical transaction loads SCO can reach higher transaction rates than SS2PL before lock thrashing occurs). More concurrency means that with given computing resources more transactions are completed in time unit (higher transaction rate, throughput), and the average duration of a transaction is shorter (faster completion; see chart). The advantage of SCO is especially significant during lock contention.
The SCO Vs. SS2PL Performance Theorem
SCO provides shorter average transaction completion time than SS2PL, if read-write conflicts exist. SCO and SS2PL are identical otherwise (have identical blocking behavior with write-read and write-write conflicts).
SCO is as practical as SS2PL since as SS2PL it provides besides serializability also strictness, which is widely utilized as a basis for efficient recovery of databases from failure. An SS2PL mechanism can be converted to an SCO one for better performance in a straightforward way without changing recovery methods. A description of an SCO implementation can be found in (Perrizo and Tatarinov 1998). See also Semi-optimistic database scheduler.
SS2PL is a proper subset of SCO (which is another explanation why SCO is less constraining and provides more concurrency than SS2PL).
Optimistic CO (OCO)
For implementing Optimistic commitment ordering (OCO) the generic local CO algorithm is utilized without data access blocking, and thus without local deadlocks. OCO without transaction or operation scheduling constraints covers the entire CO class, and is not a special case of the CO class, but rather a useful CO variant and mechanism characterization.
Extended CO (ECO)
General characterization of ECO
Extended Commitment Ordering (ECO; (Raz 1993a)) generalizes CO. When local transactions (transactions confined to a single database) can be distinguished from global (distributed) transactions (transactions that span two databases or more), commitment order is applied to global transactions only. Thus, for a local (to a database) schedule to have the ECO property, the chronological (partial) order of commit events of global transactions only (unimportant for local transactions) is consistent with their order on the respective local conflict graph.
Definition: extended commitment ordering
Let be two committed global transactions in a schedule, such that a directed path of unaborted transactions exists in the conflict graph (precedence graph) from to ( precedes , possibly transitively, indirectly). The schedule has the Extended commitment ordering (ECO) property, if for every two such transactions commits before commits.
A distributed algorithm to guarantee global ECO exists. As for CO, the algorithm needs only (unmodified) atomic commitment protocol messages. In order to guarantee global serializability, each database needs to guarantee also the conflict serializability of its own transactions by any (local) concurrency control mechanism.
The ECO and Global Serializability Theorem
(Local, which implies global) ECO together with local conflict serializability, is a sufficient condition to guarantee global conflict serializability.
When no concurrency control information beyond atomic commitment messages is shared outside a database (autonomy), and local transactions can be identified, it is also a necessary condition.
See a necessity proof in (Raz 1993a).
This condition (ECO with local serializability) is weaker than CO, and allows more concurrency at the cost of a little more complicated local algorithm (however, no practical overhead difference with CO exists).
When all the transactions are assumed to be global (e.g., if no information is available about transactions being local), ECO reduces to CO.
The ECO algorithm
Before a global transaction is committed, a generic local (to a database) ECO algorithm aborts a minimal set of undecided transactions (neither committed, nor aborted; either local transactions, or global that run locally), that can cause later a cycle in the conflict graph. This set of aborted transactions (not unique, contrary to CO) can be optimized, if each transaction is assigned with a weight (that can be determined by transaction's importance and by the computing resources already invested in the running transaction; optimization can be carried out, for example, by a reduction from the Max flow in networks problem (Raz 1993a)). Like for CO such a set is time dependent, and becomes empty eventually. Practically, almost in all needed implementations a transaction should be committed only when the set is empty (and no set optimization is applicable). The local (to the database) concurrency control mechanism (separate from the ECO algorithm) ensures that local cycles are eliminated (unlike with CO, which implies serializability by itself; however, practically also for CO a local concurrency mechanism is utilized, at least to ensure Recoverability). Local transactions can be always committed concurrently (even if a precedence relation exists, unlike CO). When the overall transactions' local partial order (which is determined by the local conflict graph, now only with possible temporary local cycles, since cycles are eliminated by a local serializability mechanism) allows, also global transactions can be voted on to be committed concurrently (when all their transitively (indirect) preceding (via conflict) global transactions are committed, while transitively preceding local transactions can be at any state. This in analogy to the distributed CO algorithm's stronger concurrent voting condition, where all the transitively preceding transactions need to be committed).
The condition for guaranteeing Global ECO can be summarized similarly to CO:
The Global ECO Enforcing Vote ordering strategy Theorem
Let be undecided (neither committed nor aborted) global transactions in a database system that ensures serializability locally, such that a directed path of unaborted transactions exists in the local conflict graph (that of the database itself) from to . Then, having ended (either committed or aborted) before is voted on to be committed, in every such database system in a multidatabase environment, is a necessary and sufficient condition for guaranteeing Global ECO (the condition guarantees Global ECO, which may be violated without it).
Global ECO (all global cycles in the global conflict graph are eliminated by atomic commitment) together with Local serializability (i.e., each database system maintains serializability locally; all local cycles are eliminated) imply Global serializability (all cycles are eliminated). This means that if each database system in a multidatabase environment provides local serializability (by any mechanism) and enforces the vote ordering strategy in the theorem above (a generalization of CO's vote ordering strategy), then Global serializability is guaranteed (no local CO is needed anymore).
Similarly to CO as well, the ECO voting-deadlock situation can be summarized as follows:
The ECO Voting-Deadlock Theorem
Let a multidatabase environment comprise database systems that enforce, each, both Global ECO (using the condition in the theorem above) and local conflict serializability (which eliminates local cycles in the global conflict graph). Then, a voting-deadlock occurs if and only if a global cycle (spans two or more databases) exists in the Global augmented conflict graph (also blocking by a data-access lock is represented by an edge). If the cycle does not break by any abort, then all the global transactions on it are involved with the respective voting-deadlock, and eventually each has its vote blocked (either directly, or indirectly by a data-access lock). If a local transaction resides on the cycle, it may be in any unaborted state (running, ready, or committed; unlike CO no local commit blocking is needed).
As with CO this means that also global deadlocks due to data-access locking (with at least one lock blocking) are voting deadlocks, and are automatically resolved by atomic commitment.
Multi-version CO (MVCO)
Multi-version Commitment Ordering (MVCO; (Raz 1993b)) is a generalization of CO for databases with multi-version resources. With such resources read-only transactions do not block or being blocked for better performance. Utilizing such resources is a common way nowadays to increase concurrency and performance by generating a new version of a database object each time the object is written, and allowing transactions' read operations of several last relevant versions (of each object). MVCO implies One-copy-serializability (1SER or 1SR) which is the generalization of serializability for multi-version resources. Like CO, MVCO is non-blocking, and can be combined with any relevant multi-version concurrency control mechanism without interfering with it. In the introduced underlying theory for MVCO conflicts are generalized for different versions of a same resource (differently from earlier multi-version theories). For different versions conflict chronological order is replaced by version order, and possibly reversed, while keeping the usual definitions for conflicting operations. Results for the regular and augmented conflict graphs remain unchanged, and similarly to CO a distributed MVCO enforcing algorithm exists, now for a mixed environment with both single-version and multi-version resources (now single-version is a special case of multi-version). As for CO, the MVCO algorithm needs only (unmodified) atomic commitment protocol messages with no additional communication overhead. Locking-based global deadlocks translate to voting deadlocks and are resolved automatically. In analogy to CO the following holds:
The MVCO and Global one-copy-serializability Theorem
MVCO compliance of every autonomous database system (or transactional object) in a mixed multidatabase environment of single-version and multi-version databases is a necessary condition for guaranteeing Global one-copy-serializability (1SER).
MVCO compliance of every database system is a sufficient condition for guaranteeing Global 1SER.
Locking-based global deadlocks are resolved automatically.
Comment: Now a CO compliant single-version database system is automatically also MVCO compliant.
MVCO can be further generalized to employ the generalization of ECO (MVECO).
Example: CO based snapshot isolation (COSI)
CO based snapshot isolation (COSI) is the intersection of Snapshot isolation (SI) with MVCO. SI is a multiversion concurrency control method widely utilized due to good performance and similarity to serializability (1SER) in several aspects. The theory in (Raz 1993b) for MVCO described above is utilized later in (Fekete et al. 2005) and other articles on SI, e.g., (Cahill et al. 2008); see also Making snapshot isolation serializable and the references there), for analyzing conflicts in SI in order to make it serializable. The method presented in (Cahill et al. 2008), Serializable snapshot isolation (SerializableSI), a low overhead modification of SI, provides good performance results versus SI, with only small penalty for enforcing serializability. A different method, by combining SI with MVCO (COSI), makes SI serializable as well, with a relatively low overhead, similarly to combining the generic CO algorithm with single-version mechanisms. Furthermore, the resulting combination, COSI, being MVCO compliant, allows COSI compliant database systems to inter-operate and transparently participate in a CO solution for distributed/global serializability (see below). Besides overheads also protocols' behaviors need to be compared quantitatively. On one hand, all serializable SI schedules can be made MVCO by COSI (by possible commit delays when needed) without aborting transactions. On the other hand, SerializableSI is known to unnecessarily abort and restart certain percentages of transactions also in serializable SI schedules.
CO and its variants are transparently interoperable for global serializability
With CO and its variants (e.g., SS2PL, SCO, OCO, ECO, and MVCO above) global serializability is achieved via atomic commitment protocol based distributed algorithms. For CO and all its variants atomic commitment protocol is the instrument to eliminate global cycles (cycles that span two or more databases) in the global augmented (and thus also regular) conflict graph (implicitly; no global data structure implementation is needed). In cases of either incompatible local commitment orders in two or more databases (when no global partial order can embed the respective local partial orders together), or a data-access locking related voting deadlock, both implying a global cycle in the global augmented conflict graph and missing votes, the atomic commitment protocol breaks such cycle by aborting an undecided transaction on it (see The distributed CO algorithm above). Differences between the various variants exist at the local level only (within the participating database systems). Each local CO instance of any variant has the same role, to determine the position of every global transaction (a transaction that spans two or more databases) within the local commitment order, i.e., to determine when it is the transaction's turn to be voted on locally in the atomic commitment protocol. Thus, all the CO variants exhibit the same behavior in regard to atomic commitment. This means that they are all interoperable via atomic commitment (using the same software interfaces, typically provided as services, some already standardized for atomic commitment, primarily for the two phase commit protocol, e.g., X/Open XA) and transparently can be utilized together in any distributed environment (while each CO variant instance is possibly associated with any relevant local concurrency control mechanism type).
In summary, any single global transaction can participate simultaneously in databases that may employ each any, possibly different, CO variant (while concurrently running processes in each such database, and running concurrently with local and other global transactions in each such database). The atomic commitment protocol is indifferent to CO, and does not distinguish between the various CO variants. Any global cycle generated in the augmented global conflict graph may span databases of different CO variants, and generate (if not broken by any local abort) a voting deadlock that is resolved by atomic commitment exactly the same way as in a single CO variant environment. local cycles (now possibly with mixed materialized and non-materialized conflicts, both serializability and data-access-locking deadlock related, e.g., SCO) are resolved locally (each by its respective variant instance's own local mechanisms).
Vote ordering (VO or Generalized CO (GCO); Raz 2009), the union of CO and all its above variants, is a useful concept and global serializability technique. To comply with VO, local serializability (in it most general form, commutativity based, and including multi-versioning) and the vote order strategy (voting by local precedence order) are needed.
Combining results for CO and its variants, the following is concluded:
The CO Variants Interoperability Theorem
In a multi-database environment, where each database system (transactional object) is compliant with some CO variant property (VO compliant), any global transaction can participate simultaneously in databases of possibly different CO variants, and Global serializability is guaranteed (sufficient condition for Global serializability; and Global one-copy-serializability (1SER), for a case when a multi-version database exists).
If only local (to a database system) concurrency control information is utilized by every database system (each has the generalized autonomy property, a generalization of autonomy), then compliance of each with some (any) CO variant property (VO compliance) is a necessary condition for guaranteeing Global serializability (and Global 1SER; otherwise they may be violated).
Furthermore, in such environment data-access-locking related global deadlocks are resolved automatically (each such deadlock is generated by a global cycle in the augmented conflict graph (i.e., a voting deadlock; see above), involving at least one data-access lock (non-materialized conflict) and two database systems; thus, not a cycle in the regular conflict graph and does not affect serializability).
References
(also DEC-TR 841, Digital Equipment Corporation, November 1990)
Yoav Raz (1991a): US patents 5,504,899 (ECO) 5,504,900 (CO) 5,701,480 (MVCO)
Yoav Raz (1991b): "The Commitment Order Coordinator (COCO) of a Resource Manager, or Architecture for Distributed Commitment Ordering Based Concurrency Control", DEC-TR 843, Digital Equipment Corporation, December 1991.
Yoav Raz (1991c): "Locking Based Strict Commitment Ordering, or How to improve Concurrency in Locking Based Resource Managers", DEC-TR 844, December 1991.
Yoav Raz (1993a): "Extended Commitment Ordering or Guaranteeing Global Serializability by Applying Commitment Order Selectivity to Global Transactions." Proceedings of the Twelfth ACM Symposium on Principles of Database Systems (PODS), Washington, DC, pp. 83-96, May 1993. (also DEC-TR 842, November 1991)
Yoav Raz (1993b): "Commitment Ordering Based Distributed Concurrency Control for Bridging Single and Multi Version Resources." Proceedings of the Third IEEE International Workshop on Research Issues on Data Engineering: Interoperability in Multidatabase Systems (RIDE-IMS), Vienna, Austria, pp. 189-198, April 1993. (also DEC-TR 853, July 1992)
Footnotes
External links
Yoav Raz's Commitment ordering page
Data management
Databases
Transaction processing
Concurrency control
Distributed algorithms | Commitment ordering | Technology | 15,915 |
26,862,725 | https://en.wikipedia.org/wiki/Sounding%20board | A sounding board, also known as a tester and abat-voix is a structure placed above and sometimes also behind a pulpit or other speaking platform that helps to project the sound of the speaker. It is usually made of wood. The structure may be specially shaped to assist the projection, for example, being formed as a parabolic reflector. In the typical setting of a church building, the sounding board may be ornately carved or constructed. The term "abat-voix," from the French word for the same thing (abattre (“to beat down”) + voix (“voice”)), is also used in English.
The term “sounding board” is also used figuratively to describe a person who listens to a speech or proposal in order that the speaker may rehearse or explore the proposition more fully.
The term is also used inter-personally to describe one person listening to another, and especially to their ideas. When a person listens and responds with comments, they provide a perspective that otherwise would not be available through introspection or thought alone, and can potentially lead to creative hijack.
See also
Baldachin - canopy over altar or throne
Chhatri
References
Acoustics
Church architecture
Pulpits | Sounding board | Physics | 257 |
3,676,187 | https://en.wikipedia.org/wiki/Augmented%20matrix | In linear algebra, an augmented matrix is a matrix obtained by appending a -dimensional column vector , on the right, as a further column to a -dimensional matrix . This is usually done for the purpose of performing the same elementary row operations on the augmented matrix as is done on the original one when solving a system of linear equations by Gaussian elimination.
For example, given the matrices and column vector , where
the augmented matrix is
For a given number of unknowns, the number of solutions to a system of linear equations depends only on the rank of the matrix of coefficients representing the system and the rank of the corresponding augmented matrix where the components of consist of the right hand sides of the successive linear equations. According to the Rouché–Capelli theorem, any system of linear equations
where is the -component column vector whose entries are the unknowns of the system is inconsistent (has no solutions) if the rank of the augmented matrix is greater than the rank of the coefficient matrix . If, on the other hand, the ranks of these two matrices are equal, the system must have at least one solution. The solution is unique if and only if the rank equals the number of variables . Otherwise the general solution has free parameters where is the difference between the number of variables and the rank. In such a case there as an affine space of solutions of dimension equal to this difference.
The inverse of a nonsingular square matrix of dimension may be found by
appending the identity matrix to the right of to form the dimensional augmented matrix . Applying elementary row operations to transform the left-hand block to the identity matrix , the right-hand block is then the inverse matrix
Example of finding the inverse of a matrix
Let be the square 2×2 matrix
To find the inverse of we form the augmented matrix where is the identity matrix. We then reduce the part of corresponding to to the identity matrix using elementary row operations on .
the right part of which is the inverse .
Existence and number of solutions
Consider the system of equations
The coefficient matrix is
and the augmented matrix is
Since both of these have the same rank, namely 2, there exists at least one solution; and since their rank is less than the number of unknowns, the latter being 3, there are an infinite number of solutions.
In contrast, consider the system
The coefficient matrix is
and the augmented matrix is
In this example the coefficient matrix has rank 2 while the augmented matrix has rank 3; so this system of equations has no solution. Indeed, an increase in the number of linearly independent rows has made the system of equations inconsistent.
Solution of a linear system
As used in linear algebra, an augmented matrix is used to represent the coefficients and the solution vector of each equation set.
For the set of equations
the coefficients and constant terms give the matrices
and hence give the augmented matrix
Note that the rank of the coefficient matrix, which is 3, equals the rank of the augmented matrix, so at least one solution exists; and since this rank equals the number of unknowns, there is exactly one solution.
To obtain the solution, row operations can be performed on the augmented matrix to obtain the identity matrix on the left side, yielding
so the solution of the system is .
References
Marvin Marcus and Henryk Minc, A survey of matrix theory and matrix inequalities, Dover Publications, 1992, . Page 31.
Matrices | Augmented matrix | Mathematics | 677 |
28,239,680 | https://en.wikipedia.org/wiki/Jan%20Vladim%C3%ADr%20Hr%C3%A1sk%C3%BD | Jan Vladimír Hráský (1857–1939) was a Czech architect, builder, engineer, and hydrologist.
Hrásky is known in Slovenia as an original author of building in Neo-Renaissance style of Carniolan Provincial Manor in Ljubljana (1899–1902), where from 1919 is a seat of the University of Ljubljana, and of the National Hall in Celje, where today is a seat of municipality (construction 1895–1896). In the 1890s, he had also designed the railroad bridge in Radeče.
In 1892, the Provincial Theatre (Slovene: Deželno gledališče) in Neo-Renaissance style was built in Ljubljana, today's Ljubljana Opera House, after his and Anton Hruby design. In 1898, he built plans for constructing of water supply tower in Kranj (construction 1909–1911).
External links
1857 births
1939 deaths
Czech architects
Czech engineers
Hydrologists
Architects from Austria-Hungary
Engineers from Austria-Hungary | Jan Vladimír Hráský | Environmental_science | 197 |
20,045,436 | https://en.wikipedia.org/wiki/25%20Scorpii | 25 Scorpii (abbreviated to 25 Sco) is a star in the zodiac constellation of Scorpius, located about 920 light years away from the Sun. Its apparent magnitude is 6.71, so its apparent brightness is at the limit of human eyesight and can only be seen under excellent conditions, according to the Bortle scale. The object is moving closer to the Earth with a heliocentric radial velocity of −1.3 km/s. It is a proposed member of the Scorpius–Centaurus association.
This is an evolved bright giant with a spectral type of K0 II. It is about two times more massive and over twelve times wider than the Sun. The star is radiating 135 times the Sun's luminosity from its photosphere at an effective temperature of about 4,700 K.
References
K-type bright giants
Scorpius–Centaurus association
Scorpius
Scorpii, 25
Durchmusterung objects
151179
082140
6225 | 25 Scorpii | Astronomy | 213 |
66,215,930 | https://en.wikipedia.org/wiki/TC-S%207001 | TC-S 7001 (Azaindole-1) is a drug which acts as a potent and selective inhibitor of the enzyme Rho kinase, with an IC50 of 0.6 nM at ROCK1 and 1.1 nM at ROCK2. It has vasodilatory effects and has been used in research for a variety of applications.
See also
Rho kinase inhibitor
References
Enzyme inhibitors
Pyrrolopyridines
Pyrimidines
Fluoroarenes
Chloroarenes
Aromatic ethers | TC-S 7001 | Chemistry | 107 |
31,417,682 | https://en.wikipedia.org/wiki/Ferroverdin | Ferroverdin refers to three different coordination compounds that were first isolated in 1955 by Chain, Tonolo, and Carilli. It consists of three p-vinylphenyl-3-nitroso-4-hydroxybenzoate ligands complexed with a ferrous ion. Ferroverdin is a green pigment produced in the mycelium of species of Streptomyces. It is claimed to be the “first stable ferrous compound to be found in nature.” There are three types of ferroverdin: A, B, and C. In ferroverdin A, both R groups are hydrogens. In ferroverdin B, R1 is a hydroxyl group (OH) and R2 is a hydrogen (according to a diagram in the paper, the R-groups are on the vinyl group, on the carbon opposite the phenyl; they are respectively trans and cis relative to the phenyl group). In ferroverdin C, R1 is a hydrogen while R2 is a carboxyl group (COOH). Ferroverdin is immune to chelating and oxidizing agents due to the strong interaction between the ligands and ferrous ion. However, it can be broken down by reductive processes.1 The presence of ferroverdin peaks when there are four to eight μg/mL of Fe2+ in the media usually in the form of a salt.
Biological role
Ferroverdin has no antimicrobial or insecticidal activity, and may in fact be a siderophore. Siderophores are responsible for transporting iron (usually as Fe3+) from the medium into the cell to meet the metabolic needs of the organism. The significance of ferroverdin in the transfer pathway of iron remains unknown. Ferroverdin A, B, and C have also been found to inhibit cholesteryl ester transfer protein (CETP) which contributes to high blood pressure in humans.
Structure
The nitrosophenolate chelating group in the three ferroverdins is unusual. Simple synthetic analogues have been made containing 2-nitrosophenol itself. These complexes adopt a facial geometry owing to the binding of alkali metals to the three oxygen centers. Natural ferroverdin has thermodynamic specificity for fac geometry where the ligands have cis arrangements around the bivalent iron atom in low spin. The geometry was determined by 1H NMR which showed the same peak for the three ligands. Even though mer geometry is more sterically favorable, ferroverdin has fac geometry theoretically due to better π stabilization in its d6 orbitals, but further research is being done to provide evidence.
See also
References
Further reading
Chelating agents
Iron complexes
Iron(II) compounds
Pigments
Siderophores | Ferroverdin | Chemistry | 594 |
3,013,792 | https://en.wikipedia.org/wiki/4C%20Entity | The 4C Entity is a digital rights management (DRM) consortium formed by IBM, Intel, Panasonic and Toshiba that has established and licensed interoperable cryptographic protection mechanisms for removable media technologies. 4C Entity was founded in 1999 when Warner Music approached the companies to develop stronger DRM technologies for the then-novel DVD-Audio format after Intel’s CSS DRM technology was hacked.
The group developed and currently lease the Content Protection for Recordable Media (CPRM) and the Content Protection for Prerecorded Media (CPPM) schemes, which use Media Key Block technology and the Cryptomeria cipher along with audio watermarks. 4C Entity has also written the Content Protection System Architecture (CPSA), which describes how content protection solutions work together and the role of each current technology.
CPPM and CPRM are implemented in SD Cards, DVD-Audio, Flash media, and other digital media formats. Like many DRM technologies, 4C Entity and its products have been criticized, with the Associated Press writing that CPRM “spark[ed] privacy concerns.”
References
External links
The 4C Entity
Consortia in the United States
Digital rights management | 4C Entity | Technology | 243 |
11,441,584 | https://en.wikipedia.org/wiki/Cylindrocladiella%20parva | Cylindrocladiella parva is a fungal plant pathogen.
References
Fungal plant pathogens and diseases
Nectriaceae
Fungi described in 1982
Fungus species | Cylindrocladiella parva | Biology | 32 |
16,700,587 | https://en.wikipedia.org/wiki/Particle%20technology | Particle technology is the science and technology of handling and processing particles and powders. It encompasses the production, handling, modification, and use of a wide variety of particulate materials, both wet and dry. Particle handling may include transportation and storage. Particle sizes range from nanometers to centimeters. Particles can be characterized by diverse metrics. The scope of particle technology spans many industries including chemical, petrochemical, agricultural, food, pharmaceuticals, mineral processing, civil engineering, advanced materials, energy, and the environment.
Subjects of particle technology
Particle technology thus deals with:
Behaviour of solids in bulk, including soil mechanics, bulk material handling, silos, conveying, powder metallurgy, nanotechnology;
Size reduction including crushing and grinding;
Increasing size by flocculation, granulation, powder compaction, tableting, and crystallization;
Particle separation, such as sieving, tabling, flotation, magnetic separation, and/or electrostatic precipitation, fluidization, centrifugal separation, and liquid filtration;
Analytical procedures such as particle size analysis.
Particle characterization
Particles are characterized by their individual size and shape, and by the distribution of these properties in bulk quantities. Spherical particles are defined by diameter or radius, and non-spherical particles are defined by the dimensions of their geometric equivalent. The space between particles in bulk means that the bulk density is less than the density of individual particles. The difference between bulk density and particle density may have implications for storage, transportation or other handling of particles. The way in which they move over each other or lock together determines stability or flowability, which is tested by the triaxial shear test.
Particle samples can be visualized using microscopy, most commonly by scanning electron microscopy (SEM) or transmission electron microscopy (TEM). Both SEM and TEM can determine pore structure, surface area and structure of a particle. SEM achieves particle visualization by directing a beam of electrons at the particle sample and creating signals upon interaction with the sample, building a 3D image of the sample's topography and surface structure. TEM uses a similar beam of electrons, but the electrons are directed at a thin slice of the sample to form an image of the electrons that pass through the slice. Particle microscopy can reveal properties or defects in a particle.
Optics can quantify particle size. Measuring light scattering and diffraction caused by a particle are detectable methods of identifying particle size, and are commonly used in the following techniques:
Laser phase Doppler shift: Incident light on a particle is not uniformly distributed, as it is partially reflected and refracted in multiple directions. Particle velocity can be calculated using the Doppler frequency from any signal, while the phase difference between two detectors determines particle size.
Fraunhofer diffraction: When a particle is at least 10 times larger than the laser wavelength and the scattering angle is 30° or smaller, the light intensity distribution pattern can be used to calculate the particle size.
Production and applications
Many industries use particle technologies for particle transportation, separation and fluidization. A variety of production methods are required for particulate materials due to the large differences between them. Three major areas of production techniques and their common applications are listed below.
Size enlargement
Agglomeration is the process of primary particles (of smaller size) coming into contact with each other and forming larger clusters. It occurs in dry powders when particle size is smaller than around 10 μm or when conditions are humid, and in liquids when particles have zero surface charge. It is often induced by Brownian motion in liquids.
Aggregation is another process of forming clusters from particles, but where the particles have stronger bonds due to larger surface area of contact. It occurs mostly in homogenous liquid mixtures.
Crystallization, either in batches or continuous processes, allows the formation of high-purity crystalline particles from solutions. The product usually has particle size in the millimeter range.
Precipitation also forms particulate product from solution. It occurs from two soluble compounds forming an insoluble product in a medium, often aqueous. While the initial particle size of the precipitate formed is only in the nanometer range, the primary particles often spontaneously agglomerate or aggregate to form much larger particles. Polymerization is a special form of precipitation where minimally soluble monomers in an aqueous solution form emulsion droplets with zero solubility.
Granulation is the process of forming granular material from powders or smaller particles. It occurs when a binder liquid is mixed with ingredient particles to form compact clusters. These clusters can be further processed and compressed into tablet form for other applications.
Extrusion forms objects of a fixed cross-sectional shape when the starting material is pushed through a die with the desired cross-section. This technique is often used for plastic, metal and rubber granules. In the food industry, extrusion is also used extensively for making pasta, crouton, cereal, cookie dough, pet food, etc. to achieve uniformity of these items.
Size reduction
Comminution is the mechanical reduction of the size of solid materials. It includes crushing, cutting, grinding, milling, vibrating, and other processes. Crushing and cutting breaks down large pieces of dry or tough material to the centimeter range. Milling can be applied to both dry and wet material, resulting in particle size in the millimeter range.
Atomization is the process of breaking liquids into a spray of much smaller droplets, like an aerosol. The resulting size of these particles or droplets is usually in the nanometer to micrometer range. There are many industrial applications of liquid atomization, including spray drying, film coating, making nano-emulsions, etc. Other applications include fire sprinklers, crop sprayers, dry shampoos, etc.
Emulsification
Emulsification is the process of dispersing particles from two or more immiscible liquids together. Oftentimes, one of the immiscible liquids is aqueous (water as solvent) and the other is organic (oil as solvent). Industrial processes usually involve dispersion of the organic solution into the aqueous solution by mixing with high-energy shears or strong turbulence. Due to the unstable nature of emulsions, surfactants or emulsifiers are required to stabilize the final product to achieve longer shelf life. Common applications of emulsions include food, pharmaceuticals and lubricants. Some examples of food emulsions are milk, mayonnaise, butter, and ice cream. Some examples of pharmaceutical and lubricant emulsions are ointments, creams, oil-soluble vitamins, and some medications.
References
Further reading | Particle technology | Chemistry,Engineering | 1,372 |
47,105,670 | https://en.wikipedia.org/wiki/Thomas%20Henry%20Moray | Thomas Henry Moray (August 28, 1892 - May 18, 1974) was an inventor from Salt Lake City, Utah. He received US patent 2,460,707, "Electrotherapeutic Device", in February 1949, after a process of 17 years in discussions with the patent office.
During the 1920s, Moray worked in the emerging field of radio. After hundreds of experiments designed to improve radio reception, Moray claimed to have discovered a source of energy transmission apparently available everywhere. Using advanced ideas in solid state detectors, he developed a power source which he claimed to produce 50,000 watts. By the early 1930s, dozens of people had reportedly witnessed demonstrations of this technology.
In 1944 Moray was paid $25 a day by the rural electrification administration to perfect his system of drawing electrical energy out of the atmosphere. He claimed his invention produced electricity with no exterior input of energy. The primary component of the device was a non-heated vacuum tube. At the time most vacuum tubes had heaters built inside. The patent office refused to grant his patent, initially, because they claimed that any vacuum tube without a heater would not work. He was never granted a patent for his power supply device. He did have other inventions and was able to obtain a patent for one of those, the Electrotherapeutic device.
References
1892 births
1974 deaths
Free energy conspiracy theories
People from Salt Lake City
20th-century American inventors | Thomas Henry Moray | Technology | 292 |
61,768,618 | https://en.wikipedia.org/wiki/Jeff%20Dozier | Jeff Dozier was an American snow hydrologist, environmental scientist, researcher and academic. He was Distinguished Professor Emeritus and Founding Dean of the Bren School of Environmental Science & Management at the University of California, Santa Barbara.
Dozier's research and teaching focused on snow science, Earth system science, radiative transfer in snow, remote sensing and information systems, image processing, and terrain analysis.
Dozier was a Fellow of the American Geophysical Union and the American Association for the Advancement of Science, a Distinguished Scientist in the Chinese Academy of Sciences, and a recipient of the NASA/Department of Interior William T. Pecora Award and of the NASA Public Service Medal. In 2009, he was awarded the Jim Gray Award from Microsoft. He helped explain optical properties of snow to animators of the film Frozen, which won an Academy Award for Best Animated Feature. He led six expeditions to the Hindu Kush range in Afghanistan, where he made a dozen first ascents, and had a climbing destination, Dozier Dome, in Yosemite National Park named after him.
Early life and education
While Dozier was at the University of California, Berkeley in the early 1960s, he dropped out after a year and a half and went to Europe where he climbed and studied German. He then hitchhiked from Germany to India. His experience during this trip inclined him to learn more about Earth's water and climate. He received his B.A. in geography from California State University, Hayward (now East Bay) in 1968.
Subsequently, he completed the M.Sc. in 1969 and Ph.D. in 1973 in Geography from the University of Michigan. His Ph.D. thesis was entitled 'An evaluation of the variance minimization principle in river channel adjustment,' and a chapter on adjustment of supraglacial streams was published. In 1971, he joined California State University, Hayward as a lecturer and taught there until he moved to the University of California, Santa Barbara in 1974.
In 1974, Dozier went to the Hindu Kush for his sixth climbing expedition. While crossing a steep slope, Dozier realized that he had no idea whether that slope might avalanche. That experience moved his research interest towards Snow and Avalanches.
Career
In 1974, Dozier joined University of California, Santa Barbara as an assistant professor, becoming associate professor in 1980 and Full Professor in 1985. From 1987 to 1990, he worked as a senior member of the technical staff and the Project Scientist for a potential spectroscopy space mission at NASA's Jet Propulsion Laboratory. From 1990 to 1992 he worked at the NASA Goddard Space Flight Center as the Senior Project Scientist at the start of NASA's Earth Observing System, when its configuration was established. In 1992, with Gordon MacDonald and D. James Baker, he co-founded the MEDEA group, which investigated the use of classified data for environmental research, monitoring, and assessment.
In 1994, Dozier founded the Bren School at UCSB and took on the position of its Dean until 2000. He was the chief scientist for the proposed NSF Waters Network from 2008 to 2010 and the principal investigator from 2018 to 2021 of the University of California multicampus Headwaters to Groundwater study, which also included scientists from the Lawrence Livermore and Lawrence Berkeley National Laboratories.
In 2016, Dozier was appointed as the Burges Distinguished Visiting professor at the University of Washington, and in 2018 he served as a Visiting Distinguished Scientist for the Chinese Academy of Sciences. He was an Editor of Geophysical Research Letters from 1991 to 1993.
Research and work
Dozier's research extended from detailed studies of snow hydrology to conception and implementation of remote sensing and information management systems that have facilitated developments in the broader Earth science community. He led interdisciplinary studies in three areas: snow hydrology and biogeochemistry in the mountain environment and its extension to groundwater management in the surrounding lowlands; hydrologic science, environmental engineering, and social science in the water environment; and the integration of environmental science and remote sensing with computer science and technology.
His work in the world's mountains addressed the storage and melting of snow that dominate the hydrologic cycle and have economic and social significance to the people who depend on snowmelt for their water resources. Since mountain environments are rugged, remote, and sometimes uncomfortable, they are difficult to investigate, especially in seasons when snow is widespread. Dozier had insights about the study of mountain snow that continue to yield important benefits for Earth science and its social significance. Shortly after arriving at UC Santa Barbara in 1974, he appreciated that remote sensing from satellites would be the key to measuring snow properties and the energy balance that determines the rates of melting and sublimation, particularly over extensive, inaccessible terrains. His approaches took the view that the information from these satellites would best be interpreted through a rigorous examination of the physics of the sensors, and how the radiation they record interacts with the atmosphere, the ice crystals and liquid water in the snow pack, and the surrounding terrain. Then in the late 1980s and early 1990s, his experience with the EOS Data and Information System and opportunities to work with computer scientists on the National Academy's report on Computing the Future and the Sequoia 2000 project helped him learn how vast amounts of information, which would have to be transmitted and stored to conduct satellite-assisted environmental science, would require thoughtful design and management of very large information systems. Thus, Dozier's research has extended from ground-level studies of energy balance processes to laboratory and field techniques for measuring snow properties, to remote sensing, spatial modeling, and what has become known as environmental informatics.
Dozier's work in remote sensing extended beyond snow. In 1980, he spent a year working for NOAA's National Environmental Satellite, Data, and Information Service in Maryland. There, he and Michael Matson observed tiny bright spots on a satellite image of the Persian Gulf. The image had been captured by the Advanced Very High Resolution Radiometer (AVHRR) instrument on the NOAA-6 satellite, and the spots, they discovered, were campfire-sized flares caused by the burning of methane escaping from oil wells. It marked the first time that such a small fire had been seen from space. He and Matson were intrigued by the possibilities, and Dozier developed a mathematical method to identify small fires in pixels a kilometer in size. This method, published in 1981, became the foundation for nearly all subsequent satellite fire-detection algorithms. Dozier continued work in this area for several years studying thermal infrared remote sensing and how to calculate land surface temperature from space.
Dozier's study of snow and ice properties continued into the 21st century. The work, virtually all undertaken with graduate students, included snow structure and elution of impurities, the spectral signature of snow from instruments on the Landsat and Terra satellites, estimation of fractional snow cover in pixels that also contain soil and vegetation, retrieval of grain size and liquid water from imaging spectroscopy, and estimation of snow water equivalent from synthetic aperture radar and from reconstruction of the snowpack post-melting from calculations of the energy balance.
Awards and honors
1968 - NCGE Medal, Outstanding Geography Major, California State University, East Bay
1988 - Honorary Professor, Institute of Remote Sensing Applications, Chinese Academy of Sciences
1989 - Transactions Prize Paper Award, IEEE Geoscience and Remote Sensing Society
1991 - Fellow, American Geophysical Union
1993 - NASA Public Service Medal
1997 - Moe I. Schneebaum Lecturer, NASA Goddard Space Flight Center
1999 - Fellow, American Association for the Advancement of Science
2005 - William T. Pecora Award, Department of Interior and NASA
2009 - Jim Gray eScience Award, Microsoft Research
2010 - John Nye Lecturer, American Geophysical Union
2014 - For Disney Animation Studios, Academy Award for Best Animated Feature, Frozen
2015 - Best Paper, Western Snow Conference
2016 - Burges Distinguished Visiting professor, University of Washington
2018 - 13th Jeremy Grantham Lecturer, Indian Institute of Science
2018 - Distinguished Scientist, Chinese Academy of Sciences
Selected articles
Dozier, J. (1981). A method for satellite identification of surface temperature fields of subpixel resolution. Remote Sensing of Environment, 11, 221–229.
Dozier, J., & Warren, S. G. (1982). Effect of viewing angle on the infrared brightness temperature of snow. Water Resources Research, 18, 1424–1434.
Dozier, J. (1989). Spectral signature of alpine snow cover from the Landsat Thematic Mapper. Remote Sensing of Environment, 28, 9-22.
Dozier, J., & Frew, J. (1990). Rapid calculation of terrain parameters for radiation modeling from digital elevation data. IEEE Transactions on Geoscience and Remote Sensing, 28, 963–969.
Wan, Z., & Dozier, J. (1996). A generalized split-window algorithm for retrieving land-surface temperature from space. IEEE Transactions on Geoscience and Remote Sensing, 34, 892–905.
Elder, K., Dozier, J., & Michaelsen, J. (1991). Snow accumulation and distribution in an alpine watershed. Water Resources Research, 27, 1541–1552.
Marks, D., & Dozier, J. (1992). Climate and energy exchange at the snow surface in the alpine region of the Sierra Nevada, 2, Snow cover energy balance. Water Resources Research, 28, 3043–3054.
Bales, R. C., Molotch, N. P., Painter, T. H., Dettinger, M. D., Rice, R., & Dozier, J. (2006). Mountain hydrology of the western United States. Water Resources Research, 42, W08432.
Dozier, J., Green, R. O., Nolin, A. W., & Painter, T. H. (2009). Interpretation of snow properties from imaging spectrometry. Remote Sensing of Environment, 113, S25-S37.
Dozier, J., Bair, E. H., & Davis, R. E. (2016). Estimating the spatial distribution of snow water equivalent in the world's mountains. WIREs Water, 3, 461–474.
References
Living people
American environmental scientists
Fellows of the American Association for the Advancement of Science
California State University, East Bay alumni
University of Michigan alumni
University of California, Santa Barbara faculty
1944 births
Avalanche researchers | Jeff Dozier | Environmental_science | 2,137 |
60,476 | https://en.wikipedia.org/wiki/Augmented%20Backus%E2%80%93Naur%20form | In computer science, augmented Backus–Naur form (ABNF) is a metalanguage based on Backus–Naur form (BNF) but consisting of its own syntax and derivation rules. The motive principle for ABNF is to describe a formal system of a language to be used as a bidirectional communications protocol. It is defined by Internet Standard 68 ("STD 68", type case sic), which was , and it often serves as the definition language for IETF communication protocols.
supersedes . updates it, adding a syntax for specifying case-sensitive string literals.
Overview
An ABNF specification is a set of derivation rules, written as
where rule is a case-insensitive nonterminal, the definition consists of sequences of symbols that define the rule, a comment for documentation, and ending with a carriage return and line feed.
Rule names are case-insensitive: <rulename>, <Rulename>, <RULENAME>, and <rUlENamE> all refer to the same rule. Rule names consist of a letter followed by letters, numbers, and hyphens.
Angle brackets (<, >) are not required around rule names (as they are in BNF). However, they may be used to delimit a rule name when used in prose to discern a rule name.
Terminal values
Terminals are specified by one or more numeric characters.
Numeric characters may be specified as the percent sign %, followed by the base (b = binary, d = decimal, and x = hexadecimal), followed by the value, or concatenation of values (indicated by .). For example, a carriage return is specified by %d13 in decimal or %x0D in hexadecimal. A carriage return followed by a line feed may be specified with concatenation as %d13.10.
Literal text is specified through the use of a string enclosed in quotation marks ("). These strings are case-insensitive, and the character set used is (US-)ASCII. Therefore, the string "abc" will match “abc”, “Abc”, “aBc”, “abC”, “ABc”, “AbC”, “aBC”, and “ABC”. RFC 7405 added a syntax for case-sensitive strings: %s"aBc" will only match "aBc". Prior to that, a case-sensitive string could only be specified by listing the individual characters: to match “aBc”, the definition would be %d97.66.99. A string can also be explicitly specified as case-insensitive with a %i prefix.
Operators
White space
White space is used to separate elements of a definition; for space to be recognized as a delimiter, it must be explicitly included. The explicit reference for a single whitespace character is WSP (linear white space), and LWSP is for zero or more whitespace characters with newlines permitted. The LWSP definition in RFC5234 is controversial because at least one whitespace character is needed to form a delimiter between two fields.
Definitions are left-aligned. When multiple lines are required (for readability), continuation lines are indented by whitespace.
Comment
; comment
A semicolon (;) starts a comment that continues to the end of the line.
Concatenation
Rule1 Rule2
A rule may be defined by listing a sequence of rule names.
To match the string “aba”, the following rules could be used:
Alternative
Rule1 / Rule2
A rule may be defined by a list of alternative rules separated by a solidus (/).
To accept the rule fu or the rule bar, the following rule could be constructed:
Incremental alternatives
Rule1 =/ Rule2
Additional alternatives may be added to a rule through the use of =/ between the rule name and the definition.
The rule
is therefore equivalent to
Value range
%c##-##
A range of numeric values may be specified through the use of a hyphen (-).
The rule
is equivalent to
Sequence group
(Rule1 Rule2)
Elements may be placed in parentheses to group rules in a definition.
To match "a b d" or "a c d", the following rule could be constructed:
To match “a b” or “c d”, the following rules could be constructed:
Variable repetition
n*nRule
To indicate repetition of an element, the form <a>*<b>element is used. The optional <a> gives the minimal number of elements to be included (with the default of 0). The optional <b> gives the maximal number of elements to be included (with the default of infinity).
Use *element for zero or more elements, *1element for zero or one element, 1*element for one or more elements, and 2*3element for two or three elements, cf. regular expressions e*, e?, e+ and e{2,3}.
Specific repetition
nRule
To indicate an explicit number of elements, the form <a>element is used and is equivalent to <a>*<a>element.
Use 2DIGIT to get two numeric digits, and 3DIGIT to get three numeric digits. (DIGIT is defined below under "Core rules". Also see zip-code in the example below.)
Optional sequence
[Rule]
To indicate an optional element, the following constructions are equivalent:
Operator precedence
The following operators have the given precedence from tightest binding to loosest binding:
Strings, names formation
Comment
Value range
Repetition
Grouping, optional
Concatenation
Alternative
Use of the alternative operator with concatenation may be confusing, and it is recommended that grouping be used to make explicit concatenation groups.
Core rules
The core rules are defined in the ABNF standard.
Note that in the core rules diagram the CHAR2 charset is inlined in char-val and CHAR3 is inlined in prose-val in the RFC spec. They are named here for clarity in the main syntax diagram.
Example
The (U.S.) postal address example given in the augmented Backus–Naur form (ABNF) page may be specified as follows:
postal-address = name-part street zip-part
name-part = *(personal-part SP) last-name [SP suffix] CRLF
name-part =/ personal-part CRLF
personal-part = first-name / (initial ".")
first-name = *ALPHA
initial = ALPHA
last-name = *ALPHA
suffix = ("Jr." / "Sr." / 1*("I" / "V" / "X"))
street = [apt SP] house-num SP street-name CRLF
apt = 1*4DIGIT
house-num = 1*8(DIGIT / ALPHA)
street-name = 1*VCHAR
zip-part = town-name "," SP state 1*2SP zip-code CRLF
town-name = 1*(ALPHA / SP)
state = 2ALPHA
zip-code = 5DIGIT ["-" 4DIGIT]
Pitfalls
RFC 5234 adds a warning in conjunction to the definition of LWSP as follows:
References
Formal languages
Metalanguages | Augmented Backus–Naur form | Mathematics | 1,521 |
65,940,597 | https://en.wikipedia.org/wiki/Comparison%20of%20user%20features%20of%20messaging%20platforms | Comparison of user features of messaging platforms refers to a comparison of all the various user features of various electronic instant messaging platforms. This includes a wide variety of resources; it includes standalone apps, platforms within websites, computer software, and various internal functions available on specific devices, such as iMessage for iPhones.
This entry includes only the features and functions that shape the user experience for such apps. A comparison of the underlying system components, programming aspects, and other internal technical information, is outside the scope of this entry.
Overview and background
Instant messaging technology is a type of online chat that offers real-time text transmission over the Internet. A LAN messenger operates in a similar way over a local area network. Short messages are typically transmitted between two parties when each user chooses to complete a thought and select "send". Some IM applications can use push technology to provide real-time text, which transmits messages character by character, as they are composed. More advanced instant messaging can add file transfer, clickable hyperlinks, Voice over IP, or video chat.
Non-IM types of chat include multicast transmission, usually referred to as "chat rooms", where participants might be anonymous or might be previously known to each other (for example collaborators on a project that is using chat to facilitate communication). Instant messaging systems tend to facilitate connections between specified known users (often using a contact list also known as a "buddy list" or "friend list"). Depending on the IM protocol, the technical architecture can be peer-to-peer (direct point-to-point transmission) or client-server (an Instant message service center retransmits messages from the sender to the communication device).
By 2010, instant messaging over the Web was in sharp decline, in favor of messaging features on social networks. The most popular IM platforms were terminated, such as AIM which closed down and Windows Live Messenger which merged into Skype. Instant messaging has since seen a revival in popularity in the form of "messaging apps" (usually on mobile devices) which by 2014 had more users than social networks.
As of 2010, social networking providers often offer IM abilities. Facebook Chat is a form of instant messaging, and Twitter can be thought of as a Web 2.0 instant messaging system. Similar server-side chat features are part of most dating websites, such as OkCupid or PlentyofFish. The spread of smartphones and similar devices in the late 2000s also caused increased competition with conventional instant messaging, by making text messaging services still more ubiquitous.
Many instant messaging services offer video calling features, voice over IP and web conferencing services. Web conferencing services can integrate both video calling and instant messaging abilities. Some instant messaging companies are also offering desktop sharing, IP radio, and IPTV to the voice and video features.
The term "Instant Messenger" is a service mark of Time Warner and may not be used in software not affiliated with AOL in the United States. For this reason, in April 2007, the instant messaging client formerly named Gaim (or gaim) announced that they would be renamed "Pidgin".
In the 2010s, more people started to use messaging apps on modern computers and devices like WhatsApp, WeChat, Viber, Facebook Messenger, Telegram, Signal and Line rather than instant messaging on computers like AIM and Windows Live Messenger. For example, WhatsApp was founded in 2009, and Facebook acquired in 2014, by which time it already had half a billion users.
Concepts
Backchannel
Backchannel is the practice of using networked computers to maintain a real-time online conversation alongside the primary group activity or live spoken remarks. The term was coined in the field of linguistics to describe listeners' behaviours during verbal communication. (See Backchannel (linguistics).)
The term "backchannel" generally refers to online conversation about the conference topic or speaker. Occasionally backchannel provides audience members a chance to fact-check the presentation.
First growing in popularity at technology conferences, backchannel is increasingly a factor in education where WiFi connections and laptop computers allow participants to use ordinary chat like IRC or AIM to actively communicate during presentation. More recent research include works where the backchannel is brought publicly visible, such as the ClassCommons, backchan.nl and Fragmented Social Mirror.
Twitter is also widely used today by audiences to create backchannels during broadcasting of content or at conferences. For example, television drama, other forms of entertainment and magazine programs. This practice is often also called live tweeting. Many conferences nowadays also have a hashtag that can be used by the participants to share notes and experiences; furthermore such hashtags can be user generated.
Features
Various platforms and apps are distinguished by their strengths and features in regards to specific functions.
Group messaging
Official channels
Some apps include a feature known as "official channels" which allows companies, especially news media outlets, publications, and other mass media companies, to offer an official channel, which users can join, and thereby receive regular updates, published articles, or news updates from companies or news outlets. Two apps which have a large amount of such channels available are Line and Telegram.
Video group calls
Basic default platforms
Basic platforms which are common across entire categories of mobile devices, computers, or operating systems.
SMS
SMS (short message service) is a text messaging service component of most telephone, Internet, and mobile device systems. It uses standardized communication protocols to enable mobile devices to exchange short text messages. An intermediary service can facilitate a text-to-voice conversion to be sent to landlines.
SMS, as used on modern devices, originated from radio telegraphy in radio memo pagers that used standardized phone protocols. These were defined in 1985 as part of the Global System for Mobile Communications (GSM) series of standards. The first test SMS message was sent on December 3, 1992, when Neil Papwort, a test engineer for Sema Group, used a personal computer to send "Merry Christmas" to the phone of colleague Richard Jarvis. It commercially rolled out to many cellular networks that decade. SMS became hugely popular worldwide as a way of text communication. By the end of 2010, SMS was the most widely used data application, with an estimated 3.5 billion active users, or about 80% of all mobile phone subscribers.
The protocols allowed users to send and receive messages of up to 160 characters (when entirely alpha-numeric) to and from GSM mobiles. Although most SMS messages are sent from one mobile phone to another, support for the service has expanded to include other mobile technologies, such as ANSI CDMA networks and Digital AMPS.
Mobile marketing, a type of direct marketing, uses SMS. According to a 2018 market research report the global SMS messaging business was estimated to be worth over US$100 billion, accounting for almost 50 percent of all the revenue generated by mobile messaging.
A Flash SMS is a type of SMS that appears directly on the main screen without user interaction and is not automatically stored in the inbox. It can be useful in emergencies, such as a fire alarm or cases of confidentiality, as in delivering one-time passwords.
Threaded SMS format
Threaded SMS is a visual styling orientation of SMS message history that arranges messages to and from a contact in chronological order on a single screen.
It was first invented by a developer working to implement the SMS client for the BlackBerry, who was looking to make use of the blank screen left below the message on a device with a larger screen capable of displaying far more than the usual 160 characters, and was inspired by threaded Reply conversations in email.
Visually, this style of representation provides a back-and-forth chat-like history for each individual contact. Hierarchical-threading at the conversation-level (as typical in blogs and on-line messaging boards) is not widely supported by SMS messaging clients. This limitation is due to the fact that there is no session identifier or subject-line passed back and forth between sent and received messages in the header data (as specified by SMS protocol) from which the client device can properly thread an incoming message to a specific dialogue, or even to a specific message within a dialogue.
Most smart phone text-messaging-clients are able to create some contextual threading of "group messages" which narrows the context of the thread around the common interests shared by group members. On the other hand, advanced enterprise messaging applications that push messages from a remote server often display a dynamically changing reply number (multiple numbers used by the same sender), which is used along with the sender's phone number to create session-tracking capabilities analogous to the functionality that cookies provide for web-browsing. As one pervasive example, this technique is used to extend the functionality of many Instant Messenger (IM) applications such that they are able to communicate over two-way dialogues with the much larger SMS user-base. In cases where multiple reply numbers are used by the enterprise server to maintain the dialogue, the visual conversation threading on the client may be separated into multiple threads.
Multimedia Messaging Service
Multimedia Messaging Service (MMS) is a standard way to send messages that include multimedia content to and from a mobile phone over a cellular network. Users and providers may refer to such a message as a PXT, a picture message, or a multimedia message. The MMS standard extends the core SMS (Short Message Service) capability, allowing the exchange of text messages greater than 160 characters in length. Unlike text-only SMS, MMS can deliver a variety of media, including up to forty seconds of video, one image, a slideshow of multiple images, or audio.
The first MMS-capable phones were introduced around 2002 in conjunction with the first GSM network. The Sony Ericsson T68i is widely believed to be the first MMS-capable cell phone, while many more hit North American markets beginning in 2004 and 2005.
The most common use involves sending photographs from camera-equipped handsets. Media companies have utilized MMS on a commercial basis as a method of delivering news and entertainment content, and retailers have deployed it as a tool for delivering scannable coupon codes, product images, videos, and other information.
The 3GPP and WAP groups fostered the development of the MMS standard, which is now continued by the Open Mobile Alliance (OMA).
Content adaptation: Multimedia content created by one brand of MMS phone may not be entirely compatible with the capabilities of the recipient's MMS phone. In the MMS architecture, the recipient MMSC is responsible for providing for content adaptation (e.g., image resizing, audio codec transcoding, etc.), if this feature is enabled by the mobile network operator. When content adaptation is supported by a network operator, its MMS subscribers enjoy compatibility with a larger network of MMS users than would otherwise be available.
Rich Communication Services
Rich Communication Services (RCS) is a communication protocol standard between mobile telephone carriers, based on IP Multimedia Subsystem, developed and defined by the GSM Association (GSMA). It aims to be a replacement of SMS and MMS, with a text-message system that is richer and provides phonebook polling (for service discovery). It is also marketed as Advanced Messaging, and was previously marketed as chat features, joyn, SMSoIP, Message+, and SMS+.
RCS features include high-resolution photo and video sharing, file sharing, typing indicators, read receipts, operation over mobile data or Wi-Fi, and improved group chat functionality. End-to-end encryption is not a feature of RCS specified by GSMA, instead deferring to the individual messaging clients to establish encryption; Google has added support for this feature using RCS in their own text messaging app, Google Messages.
By November 2020, RCS was available globally in Google Messages on Android, provided directly by Google if the operator does not provide RCS. By 2023, there were 800 million active RCS users on Google's platform and 1.2 billion handsets worldwide supporting RCS. Apple added support for RCS in Messages with iOS 18 on September 16, 2024, adding RCS support to all major smartphone manufacturers.
Internet Relay Chat
Internet Relay Chat (IRC) is an application layer protocol that facilitates communication in the form of text. The chat process works on a client/server networking model. IRC clients are computer programs that users can install on their system or web based applications running either locally in the browser or on a third party server. These clients communicate with chat servers to transfer messages to other clients. IRC is mainly designed for group communication in discussion forums, called channels, but also allows one-on-one communication via private messages as well as chat and data transfer, including file sharing.
Client software is available for every major operating system that supports Internet access. As of April 2011, the top 100 IRC networks served more than half a million users at a time, with hundreds of thousands of channels operating on a total of roughly 1,500 servers out of roughly 3,200 servers worldwide. IRC usage has been declining steadily since 2003, losing 60% of its users (from 1 million to about 400,000 in 2012) and half of its channels (from half a million in 2003).
Modern IRC
IRC has changed much over its life on the Internet. New server software has added a multitude of new features.
Services: Network-operated bots to facilitate registration of nicknames and channels, sending messages for offline users and network operator functions.
Extra modes: While the original IRC system used a set of standard user and channel modes, new servers add many new modes for features such as removing color codes from text, or obscuring a user's hostmask ("cloaking") to protect from denial-of-service attacks.
Proxy detection: Most modern servers support detection of users attempting to connect through an insecure (misconfigured or exploited) proxy server, which can then be denied a connection. This proxy detection software is used by several networks, although that real-time list of proxies is defunct since early 2006.
Additional commands: New commands can be such things as shorthand commands to issue commands to Services, to network-operator-only commands to manipulate a user's hostmask.
Encryption: For the client-to-server leg of the connection TLS might be used (messages cease to be secure once they are relayed to other users on standard connections, but it makes eavesdropping on or wiretapping an individual's IRC sessions difficult). For client-to-client communication, SDCC (Secure DCC) can be used.
Connection protocol: IRC can be connected to via IPv4, the old version of the Internet Protocol, or by IPv6, the current standard of the protocol.
, a new standardization effort is under way under a working group called IRCv3, which focuses on more advanced client features like instant notifications, better history support and improved security. , no major IRC networks have fully adopted the proposed standard.
After its golden era during the 1990s and early 2000s (240,000 users on QuakeNet in 2004), IRC has seen a significant decline, losing around 60% of users between 2003 and 2012, with users moving to newer social media platforms like Facebook or Twitter, but also to open platforms like XMPP which was developed in 1999. Certain networks like Freenode have not followed the overall trend and have more than quadrupled in size during the same period. As of 2016, Freenode is the largest IRC network with around 90,000 users.
The largest IRC networks have traditionally been grouped as the "Big Four"—a designation for networks that top the statistics. The Big Four networks change periodically, but due to the community nature of IRC there are a large number of other networks for users to choose from.
Historically the "Big Four" were:
EFnet
IRCnet
Undernet
DALnet
IRC reached 6 million simultaneous users in 2001 and 10 million users in 2003, dropping to 371k in 2018.
, the largest IRC networks are:
freenode – around 90k users at peak hours
IRCnet – around 30k users at peak hours
EFnet – around 18k users at peak hours
Undernet – around 17k users at peak hours
QuakeNet – around 15k users at peak hours
Rizon – around 14k users at peak hours
OFTC – around 13k users at peak hours
DALnet – around 8k users at peak hours
Today, the top 100 IRC networks have around 370k users connected at peak hours.
XMPP
Extensible Messaging and Presence Protocol (XMPP) is a communication protocol for message-oriented middleware based on XML (Extensible Markup Language). It enables the near-real-time exchange of structured yet extensible data between any two or more network entities. Originally named Jabber, the protocol was developed by the eponymous open-source community in 1999 for near real-time instant messaging (IM), presence information, and contact list maintenance. Designed to be extensible, the protocol has been used also for publish-subscribe systems, signalling for VoIP, video, file transfer, gaming, the Internet of Things (IoT) applications such as the smart grid, and social networking services.
Unlike most instant messaging protocols, XMPP is defined in an open standard and uses an open systems approach of development and application, by which anyone may implement an XMPP service and interoperate with other organizations' implementations. Because XMPP is an open protocol, implementations can be developed using any software license and many server, client, and library implementations are distributed as free and open-source software. Numerous freeware and commercial software implementations also exist.
The Internet Engineering Task Force (IETF) formed an XMPP working group in 2002 to formalize the core protocols as an IETF instant messaging and presence technology. The XMPP Working group produced four specifications (RFC 3920, RFC 3921, RFC 3922, RFC 3923), which were approved as Proposed Standards in 2004. In 2011, RFC 3920 and RFC 3921 were superseded by RFC 6120 and RFC 6121 respectively, with RFC 6122 specifying the XMPP address format. In 2015, RFC 6122 was superseded by RFC 7622. In addition to these core protocols standardized at the IETF, the XMPP Standards Foundation (formerly the Jabber Software Foundation) is active in developing open XMPP extensions.
XMPP-based software is deployed widely across the Internet, and by 2003, was used by over ten million people worldwide, according to the XMPP Standards Foundation.
SMS texting apps
Below are apps that are used for texting via SMS. Generally, these apps offer various features for expanded messaging, or group texts; however, all messages are received by others as regular SMS text messages.
Textfree
Textfree (formerly Pinger) is an application made by Pinger that allows users to text and call over the internet for free or for a price. The application runs on iOS, Android, Microsoft Windows and Macintosh devices. Competitors include GOGII, Optini and WhatsApp.
Stand-alone messaging platforms
Below are stand-alone apps that are generally focused upon instant messaging as their core feature; however, almost all of these also include numerous distinct additional features such as group chats, video calls, emojis, etc.
These apps do not use SMS messaging; rather, users of this app receive messages through the app interface, not through SMS texting.
Tango
Tango is a third-party, cross platform messaging application software for smartphones developed by TangoME, Inc. in 2009. The app is free and began as one of the first provider of video calls, voice calls, texting, photo sharing, and games on a 3G network.
As of 2018, Tango has more than 400 million registered users. It was rated by PCMag as "the simplest mobile chat application out there, with a good range of support."
In 2017, Tango entered the live-streaming space, and has become a B2C platform for Live Video Broadcasts. Combining high-quality video streaming, a live messaging chat and a digital economy, Tango is a social community that allows content creators to share their talents and monetize their fans and followers.
Tango is available in many languages including Russian, Spanish, Turkish, Hindi and Vietnamese.
WhatsApp
WhatsApp provides the following features, as detailed below.
Group threads: up to 250 members
Groups and channels: no built-in search function to find official groups and channels. anyone can join groups, if they have the link.
Video calls: up to 3 members.
WhatsApp is an American freeware, cross-platform messaging and Voice over IP (VoIP) service owned by Facebook, Inc. It allows users to send text messages and voice messages, make voice and video calls, and share images, documents, user locations, and other media. WhatsApp's client application runs on mobile devices but is also accessible from desktop computers, as long as the user's mobile device remains connected to the Internet while they use the desktop app. The service requires users to provide a standard cellular mobile number for registering with the service. In January 2018, WhatsApp released a standalone business app targeted at small business owners, called WhatsApp Business, to allow companies to communicate with customers who use the standard WhatsApp client.
The client application was created by WhatsApp Inc. of Mountain View, California, which was acquired by Facebook in February 2014 for approximately US$19.3 billion. It became the world's most popular messaging application by 2015, and has over 2billion users worldwide . It has become the primary means of electronic communication in multiple countries and locations, including Latin America, the Indian subcontinent, and large parts of Europe and Africa.
Telegram
Telegram provides the following features, as detailed below.
Group threads: up to 200,000 members
Groups and channels: provides numerous official channels for various organizations. Has an internal search feature to enable searches to find various official outlets.
Telegram is a cross-platform cloud-based instant messaging, video calling, and VoIP service. It was initially launched for iOS on 14 August 2013 in Russia, and is currently based in Dubai. Telegram client apps are available for Android, iOS, Windows Phone, Windows, macOS and Linux, web interface is also available. As of April 2020, Telegram reached 400 million monthly active users.
Telegram provides end-to-end encrypted calls and optional end-to-end encrypted "secret" chats between two online users on smartphone clients, whereas cloud chats use client-server/ server-client encryption.
Users can send text and voice messages, animated stickers, make voice and video calls, and share an unlimited number of images, documents(2GB per file), user locations, contacts, music, links etc.
SInce March 2017, Telegram introduced its own voice calls. According to Telegram, there is a neural network working to learn various technical parameters about a call to provide better quality of the service for future uses. After a brief initial trial in Western Europe, voice calls are now available for use in most countries.
Telegram announced in April 2020 that they would include group video calls by the end of the year. On 15 August 2020, Telegram added video calling with end-to-end encryption like Signal and WhatsApp, which Zoom does not have yet. Currently offering one-to-one video calls, Telegram has plans to introduce secure group video calls later in 2020. Picture-in-picture mode is also available so that users have the option to simultaneously use the other functions of the app while still remaining on the call and are even able to turn their video off.
Telegram's video and voice calls are secure and end-to-end encrypted.
Google Voice
Google Voice is a telephone service that provides call forwarding and voicemail services, voice and text messaging.
Google Voice provides a U.S. telephone number, chosen by the user from available numbers in selected area codes, free of charge to each user account. Calls to this number are forwarded to telephone numbers that each user must configure in the account web portal. Multiple destinations may be specified that ring simultaneously for incoming calls. Service establishment requires a United States telephone number. A user may answer and receive calls on any of the ringing phones as configured in the web portal. During a received call the user may switch between the configured telephones.
Users may place outbound calls to domestic and international destinations. Calls may be initiated from any of the configured telephones, as well as from a mobile device app, or from the account portal. As of August 2011, users in many other countries also may place outbound calls from the web-based application to domestic and international phone numbers.
Many other Google Voice services—such as voicemail, free text messaging, call history, call screening, blocking of unwanted calls, and voice transcription to text of voicemail messages—are also available to . In terms of product integration, transcribed and audio voicemails, missed call notifications, and/or text messages can optionally be forwarded to an email account of the user's choice. Additionally, text messages can be sent and received via the familiar email or IM interface by reading and writing text messages in numbers in Google Talk respectively (PC-to-Phone texting). Google Voice multi-way videoconferencing (with support for document sharing) is now integrated with Google Hangouts.
The service is configured and maintained by the user in a web-based application, styled after Google's e-mail service, Gmail, or with Android and iOS apps on smart phones or tablets. Google Voice provides free PC-to-phone calling within the United States and Canada, and PC-to-PC voice and video calling worldwide between users of the Google+ Hangouts browser plugin (available for Windows, Intel-based Mac OS X, and Linux).
GroupMe
GroupMe works by downloading the app or accessing the service online, and then forming an account by providing your name, cell phone number and a password, or you can connect through your Facebook or Twitter account. The service then syncs with your contacts and from that point forward the user can make groups, limited to 500 members. An individual who is part of an active group has the ability to turn off notifications for the app; users will still receive the message, but will not be notified about it. Each group is given a label and assigned a unique number. Some of the features of the app include the ability to share photos, videos, locations, create events, and emojis from various packs.
GroupMe has a web client as well as apps for iOS, Android, Windows Phone, and Windows 10.
Those who do not wish to use the app can still send and receive GroupMe messages through SMS (only available in the United States).
Users begin by creating a "group" and adding contacts. When someone sends a message, everyone in the group can see and respond to it. The app allows users to easily attach and send pictures, documents, videos and web-links as well. Users can also send private messages, but only to users who are also active on the GroupMe app.
GroupMe has been used as a means for studying the usage of messaging clients in educational settings. Use cases include facilitating online course discussions, small group work, and other course communications for both in-person and online sections. Though unconventional, using GroupMe to facilitate discussion in an environment where students already interact has been found to encourage rhetorical thinking and overall engagement. Researchers have found alternatives for literacy learning as a "legitimate academic genre", given a student population that communicates in a variety of modes. Research around GroupMe furthers the argument that computer-mediated communication is a valuable space for learning in an increasingly globalized society.
Hike Messenger
Hike Messenger, also called Hike Sticker Chat, is an Indian freeware, cross-platform instant messaging (IM), Voice over IP (VoIP) application which was launched on 12 December 2012 by Kavin Bharti Mittal and is now owned by Hike Private Limited. Hike can work offline through SMS and has multi-platform support. The app registration uses standard one time password (OTP) based authentication process. With abundance of low-cost data, Hike decided to go from a single super app strategy to multiple app approach, so that it can focus more on the core messaging capabilities. It has numerous Hikemoji Stickers which can be customized accordingly.From version 6, the user-interface was revised and the app no longer supports features like news, mobile payment, games or jokes. As per CB Insights, $1.4 billion is the valuation of Hike with more than 100 million registered users until August 2016 and 350 employees working from Bengaluru and Delhi.
KakaoTalk
KakaoTalk, commonly referred to as "KaTalk" in South Korea, is a free mobile instant messaging application for smartphones with free text and free call features, operated by Kakao Corporation. It was launched on March 18, 2010, and is currently available on iOS, Android, Bada OS, BlackBerry, Windows Phone, Nokia Asha, Windows and macOS.
As of May 2017, KakaoTalk had 220 million registered and 49 million monthly active users. It is available in 15 languages. The app is also used by 93% of smartphone owners in South Korea, where it is the number one messaging app.
In addition to free calls and messages, users can share photos, videos, voice messages, location, URL links as well as contact information. Both one-on-one and group chats are available over Wi-Fi, 3G or LTE, and there are no limits to the number of people on a group chat.
Airlines such as Southwest which allow free WhatsApp in flight also have functionality for KaTalk, even though their literature omits to mention same.
The app automatically synchronizes the user's contact list on their smartphones with the contact list on the app to find friends who are on the service. Users can also search for friends by KakaoTalk ID without having to know their phone numbers. The KakaoTalk service also allows its users to export their messages and save them.
KakaoTalk began as a messenger service but has become a platform for the distribution of various third-party content and apps, including hundreds of games, which users can download and play with their friends through the messaging platform. Through the "Plus Friend" feature, users can follow brands, media and celebrities to receive exclusive messages, coupons and other real-time information through KakaoTalk chatrooms. Users can also purchase real-life goods through the messenger's "Gifting" platform.
Besides those listed above, the app has these additional features:
VoiceTalk, free calls and conference calls (with support for up to five people)
Photo, video, location, and contact information sharing
Polling and scheduling feature for members in the chatroom
K-pop & Local Star Friends (Plus Friends)
Walkie-talkie
Customizable themes (for iOS and Android)
Game platform
Stickers and animated emoticons
Plus Mate: You can add your favorite brand, star, or media as your friend to receive a variety of content and benefits.
Kik Messenger
Kik Messenger, commonly called Kik, is a freeware instant messaging mobile app from the Canadian company Kik Interactive, available free of charge on iOS and Android operating systems. It uses a smartphone's data plan or Wi-Fi to transmit and receive messages, photos, videos, sketches, mobile web pages, and other content after users register a username. Kik is known for its features preserving users' anonymity, such as allowing users to register without the need to provide a telephone number or valid email address. However, the application does not employ end-to-end encryption, and the company also logs user IP addresses, which could be used to determine the user's ISP and approximate location. This information, as well as "reported" conversations are regularly surrendered upon request by law enforcement organizations, sometimes without the need for a court order.
Kik was originally intended to be a music-sharing app before transitioning to messaging, briefly offering users the ability to send a limited number of SMS text messages directly from the application. During the first 15 days after Kik's re-release as a messaging app, over 1 million accounts were created. In May 2016, Kik Messenger announced that they had approximately 300 million registered users, and was used by approximately 40% of United States' teenagers.
Kik Messenger announced in October 2019 they had signed a letter of intent with MediaLab AI, followed by the announcement Kik Interactive would be reducing their staff from 100 to just 19. MediaLab owns several mobile apps, most notably Whisper.
A main attraction of Kik that differentiates it from other messaging apps is its anonymity. To register for the Kik service, a user must enter a first and last name, e-mail address, and birth date (which must show that the user is at least 13 years old), and select a username. The Kik registration process does not request or require the entry of a phone number (although the user has the option to enter one), unlike some other messaging services that require a user to provide a functioning mobile phone number.
The New York Times has reported that, according to law enforcement, Kik's anonymity features go beyond those of most widely used apps. As of February 2016, Kik's guide for law enforcement said that the company cannot locate user accounts based on first and last name, e-mail address and/or birth date; the exact username is required to locate a particular account. The guide further said that the company does not have access to content or "historical user data" such as photographs, videos, and the text of conversations, and that photographs and videos are automatically deleted shortly after they are sent. A limited amount of data from a particular account (identified by exact username), including first and last name, birthdate, e-mail address, link to a current profile picture, device-related information, and user location information such as the most recently used IP address, can be preserved for a period of 90 days pending receipt of a valid order from law enforcement. Kik's anonymity has also been cited as a protective safety measure for good faith users, in that "users have screennames; the app doesn't share phone numbers or email addresses."
Kik introduced several new user features in 2015, including a full-screen in-chat browser that allows users to find and share content from the web; a feature allowing users to send previously recorded videos in Kik Messenger for Android and iOS; and "Kik Codes", which assigns each user a unique code similar to a QR code, making it easier to connect and chat with other users. Kik joined the Virtual Global Taskforce, a global anti-child-abuse organization, in March 2015. Kik began using Microsoft's PhotoDNA in March 2015 to premoderate images added by users. That same month, Kik released native video capture allowing users to record up to 15 seconds in the chat window. In October 2015, Kik partnered with the Ad Council as part of an anti-bullying campaign. The campaign was featured on the app and Kik released stickers in collaboration with the campaign. Kik released a feature to send GIFs as emojis in November 2015. Kik added SafePhoto to its safety features in October 2016 which "detects, reports, and deletes known child exploitation images" sent through the platform. Kik partnered with ConnectSafely in 2016 to produce a "parents handbook" and joined The Technology Coalition, an anti-sexual exploitation group including Facebook, Google, Twitter and LinkedIn.
Line
Line (styled in all caps as LINE) is a freeware app for instant communications on electronic devices such as smartphones, tablet computers, and personal computers. Line users exchange texts, images, video and audio, and conduct free VoIP conversations and video conferences. In addition, Line is a platform providing various services including digital wallet as Line Pay, news stream as Line Today, video on demand as Line TV, and digital comic distribution as Line Manga and Line Webtoon. The service is operated by Line Corporation, a Tokyo-based subsidiary of South Korean internet search engine company Naver Corporation.
Line is an application that works on multiple platforms and has access via multiple personal computers (Windows or macOS). The application will also give an option of address book syncing. This application also has a feature to add friends through the use of QR codes, by Line ID, and by shaking phones simultaneously. The application has a direct pop-out message box for reading and replying to make it easy for users to communicate. It also can share photos, videos and music with other users, send the current or any specific location, voice audio, emojis, stickers and emoticons to friends. Users can see a real-time confirmation when messages are sent and received or use a hidden chat feature, which can hide and delete a chat history (from both involved devices and Line servers) after a time set by the user. The application also makes free voice and video calls.
Users can also chat and share media in a group by creating and joining groups that have up to 500 people. Chats also provide bulletin boards on which users can post, like, and comment. This application also has timeline and homepage features that allow users to post pictures, text and stickers on their homepages. Users can also change their Line theme to the theme Line provides in the theme shop for free or users can buy other famous cartoon characters they like. Line also has a feature, called a Snap movie, that users can use to record a stop-motion video and add in provided background music.
In January 2015, Line Taxi was released in Tokyo as a competitor to Uber. Line launched a new android app called "Popcorn buzz" in June 2015. The app facilitates group calls with up to 200 members. In June a new Emoji keyboard was also released for iOS devices, which provides a Line-like experience with the possibility to add stickers. In September 2015 a new Android launcher was released on the Play Store, helping the company to promote its own services through the new user interface.
Signal
Signal is a cross-platform encrypted messaging service developed by the Signal Foundation and Signal Messenger LLC. It uses the Internet to send one-to-one and group messages, which can include files, voice notes, images and videos. It can also be used to make one-to-one voice and video calls, and the Android version can optionally function as an SMS app.
Signal uses standard cellular telephone numbers as identifiers and secures all communications to other Signal users with end-to-end encryption. The apps include mechanisms by which users can independently verify the identity of their contacts and the integrity of the data channel.
Snapchat
Snapchat sends messages referred to as "snaps"; snaps can consist of a photo or a short video, and can be edited to include filters and effects, text captions, and drawings. Snaps can be directed privately to selected contacts, or to a semi-public "Story" or a public "Story" called "Our Story." The ability to send video snaps was added as a feature option in December 2012. By holding down on the photo button while inside the app, a video of up to ten seconds in length can be captured. Spiegel explained that this process allowed the video data to be compressed into the size of a photo. A later update allowed the ability to record up to 60 seconds, but are still segmented into 10 second intervals. After a single viewing, the video disappears by default. On May 1, 2014, the ability to communicate via video chat was added. Direct messaging features were also included in the update, allowing users to send ephemeral text messages to friends and family while saving any needed information by clicking on it. According to CIO, Snapchat uses real-time marketing concepts and temporality to make the app appealing to users. According to Marketing Pro, Snapchat attracts interest and potential customers by combining the AIDA (marketing) model with modern digital technology.
Private message photo snaps can be viewed for a user-specified length of time (1 to 10 seconds as determined by the sender) before they become inaccessible. Users were previously required to hold down on the screen in order to view a snap; this behavior was removed in July 2015 The requirement to hold on the screen was intended to frustrate the ability to take screenshots of snaps; the Snapchat app does not prevent screenshots from being taken but can notify the sender if it detects that it has been saved. However, these notifications can be bypassed through either unauthorized modifications to the app or by obtaining the image through external means. One snap per day can be replayed for free. In September 2015, Snapchat introduced the option to purchase additional replays through in-app purchases. The ability to purchase extra replays was removed in April 2016.
Friends can be added via usernames and phone contacts, using customizable "Snapcodes," or through the "Add Nearby" function, which scans for users near their location who are also in the Add Nearby menu. Spiegel explained that Snapchat is intended to counteract the trend of users being compelled to manage an idealized online identity of themselves, which he says has "taken all of the fun out of communicating."
Viber
Rakuten Viber, or simply Viber, is a cross-platform voice over IP (VoIP) and instant messaging (IM) software application operated by Japanese multinational company Rakuten, provided as freeware for the Android, iOS, Microsoft Windows, macOS and Linux platforms. Users are registered and identified through a cellular telephone number, although the service is accessible on desktop platforms without needing mobile connectivity. In addition to instant messaging it allows users to exchange media such as images and video records, and also provides a paid international landline and mobile calling service called Viber Out. As of 2018, there are over a billion registered users on the network.
Wonder video chat
Wonder is a new style of shared video chat, using a virtual space where users can move between virtual rooms and initiate conversations either with a large group, or within a spontaneous "circle." The chat platforms is entirely browser-based, and does not entail or require the use of any specific app.
Dingtone
Dingtone is an application made by Dingtone that allows users to text and call over the internet for free or for a price. The application runs on Android, IOS, Microsoft Windows and Macintosh devices.
WeChat
WeChat is a Chinese multi-purpose messaging, social media and mobile payment app developed by Tencent. First released in 2011, it became the world's largest standalone mobile app in 2018, with over 1 billion monthly active users. WeChat has been described as China's "app for everything" and a "super app" because of its wide range of functions. WeChat provides text messaging, hold-to-talk voice messaging, broadcast (one-to-many) messaging, video conferencing, video games, sharing of photographs and videos, and location sharing.
WeChat provides text messaging, hold-to-talk voice messaging, broadcast (one-to-many) messaging, video calls and conferencing, video games, photograph and video sharing, as well as location sharing. WeChat also allows users to exchange contacts with people nearby via Bluetooth, as well as providing various features for contacting people at random if desired (if people are open to it). It can also integrate with other social networking services such as Facebook and Tencent QQ. Photographs may also be embellished with filters and captions, and automatic translation service is available.
WeChat supports different instant messaging methods, including text message, voice message, walkie talkie, and stickers. Users can send previously saved or live pictures and videos, profiles of other users, coupons, lucky money packages, or current GPS locations with friends either individually or in a group chat. WeChat's character stickers, such as Tuzki, resemble and compete with those of LINE, a Japanese-South Korean messaging application.
WeChat users can register as a public account (), which enables them to push feeds to subscribers, interact with subscribers and provide them with services. Users can also create an official account, which fall under service, subscription, or enterprise accounts. Once users as individuals or organizations set up a type of account, they cannot change it to another type. By the end of 2014, the number of WeChat official accounts had reached 8 million. Official accounts of organizations can apply to be verified (cost 300 RMB or about US$45). Official accounts can be used as a platform for services such as hospital pre-registrations, visa renewal or credit card service. To create an official account, the applicant must register with Chinese authorities, which discourages "foreign companies".
"Moments" () is WeChat's brand name for its social feed of friends' updates. "Moments" is an interactive platform that allows users to post images, text, and short videos taken by users. It also allows users to share articles and music (associated with QQ Music or other web-based music services). Friends in the contact list can give thumbs up to the content and leave comments. Moments can be linked to Facebook and Twitter accounts, and can automatically post Moments content directly on these two platforms.
In 2017 WeChat had a policy of a maximum of two advertisements per day per Moments user.
Platforms for combining multiple apps
Platforms specifically designed to combined messages from multiple other mobile apps.
Trillian
Trillian is a proprietary multiprotocol instant messaging application created by Cerulean Studios. It is currently available for Microsoft Windows, Mac OS X, Linux, Android, iOS, BlackBerry OS, and the Web. It can connect to multiple IM services, such as AIM, Bonjour, Facebook Messenger, Google Talk (Hangouts), IRC, XMPP (Jabber), VZ, and Yahoo! Messenger networks; as well as social networking sites, such as Facebook, Foursquare, LinkedIn, and Twitter; and email services, such as POP3 and IMAP.
Trillian no longer supports Windows Live Messenger or Skype as these services have combined and Microsoft chose to discontinue Skypekit. They also no longer support connecting to Myspace, and no longer support a distinct connection for Gmail, Hotmail or Yahoo! Mail although these can still be connected to via POP3 or IMAP. Currently, Trillian supports Facebook, Google, Jabber (XMPP), and Olark.
Initially released July 1, 2000, as a freeware IRC client, the first commercial version (Trillian Pro 1.0) was published on September 10, 2002. The program was named after Trillian, a fictional character in The Hitchhiker's Guide to the Galaxy by Douglas Adams. A previous version of the official web site even had a tribute to Douglas Adams on its front page. On August 14, 2009, Trillian "Astra" (4.0) for Windows was released, along with its own Astra network. Trillian 5 for Windows was released in May 2011, and Trillian 6.0 was initially released in February 2017.
Trillian connects to multiple instant messaging services without the need of running multiple clients. Users can create multiple connections to the same service, and can also group connections under separate identities to prevent confusion. All contacts are gathered under the same contact list. Contacts are not bound to their own IM service groups, and can be dragged and dropped freely.
Trillian represents each service with a different-colored sphere. Prior versions used the corporate logos for each service, but these were removed to avoid copyright issues, although some skins still use the original icons. The Trillian designers chose a color-coding scheme based on the underground maps used by the London Underground that uses different colors to differentiate between different lines.
Platforms for specific operating systems
Empathy
Empathy is an instant messaging (IM) and voice over IP (VoIP) client which supports text, voice, video, file transfers, and inter-application communication over various IM communication protocols. It is specifically designed for use with the operating systems BSD, Linux, and other Unix-like systems. It was initially completely XMPP based (similar to Google Talk and Facebook's chat implementations), but others wanted it to use the Telepathy stack. This led to the forking and new name Empathy.
Empathy also provides a collection of reusable graphical user interface widgets for developing instant messaging clients for the GNOME desktop. It is written as extension to the Telepathy framework, for connecting to different instant messaging networks with a unified user interface.
Empathy has been included in the GNOME desktop since its version 2.24, in Ubuntu since version 9.10 (Karmic Koala), and in Fedora since version 12 (Constantine); Empathy has replaced Pidgin as their default messenger application.
Messages for MacOS
Messages (Apple) is an instant messaging software application developed by Apple Inc. for its macOS, iOS, iPadOS, and watchOS operating systems.
The mobile version of Messages on iOS used on iPhone and iPad also supports SMS and MMS due to replacing the older text messaging Text app since iPhone OS 3. Users can tell the difference between a message sent via SMS and one sent over iMessage as the bubbles will appear either green (SMS) or blue (iMessage).
The desktop Messages application replaced iChat as the native OS X instant messaging client with the release of OS X Mountain Lion in July 2012. While it inherits the majority of iChat's features, Messages also brings support for iMessage, Apple's messaging service for iOS, as well as FaceTime integration.
Messages was announced for OS X as a beta application on February 16, 2012 for Macs running Mac OS X 10.7 "Lion". The stable release of Messages was released on July 25, 2012 with OS X Mountain Lion, replacing iChat. In addition to supporting Apple's new iMessage protocol, Messages retained its support for AIM, Yahoo! Messenger, Google Talk and Jabber.
Messages unitizes the newly added Notification Center to notify of incoming messages. The introduction of a new Share button in applications like Safari, Finder and Preview gave users the ability to share links to webpages, photos, and files. Messages also supported dragging and dropping files and photos for sharing. It also supports video calling through Apple's FaceTime and the third-party IM services it supports. With the release of OS X Mountain Lion 10.8.2, Messages gained the ability to send and receive iMessages using an iPhone phone number.
Messages received a major redesign in OS X Yosemite, following the flat design aesthetic introduced in iOS 7. As a part of the new Continuity feature, users can send and receive SMS and MMS messages through paired iPhones running iOS 8 or later.
Social networking mobile apps
A social networking service (also social networking site or social media) is an online platform which people use to build social networks or social relationships with other people who share similar personal or career interests, activities, backgrounds or real-life connections.
Social networking services vary in format and the number of features. They can incorporate a range of new information and communication tools, operating on desktops and on laptops, on mobile devices such as tablet computers and smartphones. They may feature digital photo/video/sharing and diary entries online (blogging). Online community services are sometimes considered social-network services by developers and users, though in a broader sense, a social-network service usually provides an individual-centered service whereas online community services are group-centered. Defined as "websites that facilitate the building of a network of contacts in order to exchange various types of content online," social networking sites provide a space for interaction to continue beyond in person interactions. These computer mediated interactions link members of various networks and may help to both maintain and develop new social and professional relationships
Social networking sites allow users to share ideas, digital photos and videos, posts, and to inform others about online or real-world activities and events with people in their network. While in-person social networking – such as gathering in a village market to talk about events – has existed since the earliest development of towns, the web enables people to connect with others who live in different locations, ranging from across a city to across the world. Depending on the social media platform, members may be able to contact any other member. In other cases, members can contact anyone they have a connection to, and subsequently anyone that contact has a connection to, and so on. The success of social networking services can be seen in their dominance in society today, with Facebook having a massive 2.13 billion active monthly users and an average of 1.4 billion daily active users in 2017. LinkedIn, a career-oriented social-networking service, generally requires that a member personally know another member in real life before they contact them online. Some services require members to have a preexisting connection to contact other members.
MeWe
MeWe is an American alt-tech social media and social networking service owned by Sgrouples, a company based in Culver City, California. MeWe's light approach to content moderation has made it popular among conspiracy theorists, particularly the anti-vaccine movement, as well as American conservatives. The site's interface has been described as similar to that of Facebook, though the company describes MeWe as the "anti-Facebook" due to its focus on data privacy
By 2015, as MeWe neared the end of its beta testing cycle, the press called MeWe's software "not dissimilar to Facebook". Mashable described MeWe as replicating Facebook's features in 2020.
The MeWe site and application has features common to most social media and social networking sites: users can post text and images to a feed, react to others' posts using emoji, post animated GIFs, create specialized groups, post disappearing content, and chat.
Online chat may occur between two or more people or among members of a group. Person-to-person online chat is similar to that in most other social media and social networking sites, and supports text, video calling, and voice calling. "Secret Chat" is limited to the paid subscription tier of MeWe, and uses double ratchet encryption to ensure that chats are private and not visible even to MeWe employees.
MeWe reported in June 2018 that the site had 90,000 active groups, 60,000 of which were "public" and open to all users. Following the influx of Hong Kong users in 2020, MeWe CEO Weinstein announced that the website would provide a Traditional Chinese language version by the end of the year.
User base and content
Although MeWe has not intentionally positioned itself as a social network for conservatives, Mashable noted in November 2020 that its active userbase trends conservative.The platform's choice not to moderate misinformation on the platform has attracted conservatives who felt mainstream social networks were censoring their posts, and those who have been banned from those platforms.
MeetMe
The Meet Group (formerly MeetMe) owns several mobile social networking services including MeetMe, hi5, LOVOO, Growlr, Skout, and Tagged.
The company has millions of mobile daily active users. Its mobile apps are available on iOS, and Android in multiple languages. Through these apps, users can stream live video, send gifts, chat, and share photos. The Meet Group derives revenue from in-app purchases, subscriptions, and advertising. The company has offices in New Hope, Pennsylvania, Philadelphia, San Francisco, Dresden, and Berlin.
The Meet Group has transformed its business from being a predominantly advertising model to now generating the majority of revenue from user pay sources, which include subscriptions and in-app purchases for virtual gifts as part of its video live-streaming product. The company also derives revenue from advertising. In the second quarter of 2018, 60% of revenue was derived from user-pay, versus 26% in the second quarter of 2017. Livestreaming video revenue has become an increasingly important component of revenue and growth, and the product has been rolled out to all of the company's main apps.
myYearbook derives its revenue from three sources: advertising, virtual-currency sales, and monthly subscriptions. Advertising makes up two-thirds of its revenue, with the other sources making up the rest. It has an established sales office based in New York City and Los Angeles.
Nextdoor
Nextdoor is a hyperlocal social networking service for neighborhoods. The company was founded in 2008 and is based in San Francisco, California. Nextdoor launched in the United States in October 2011, and is currently available in 11 countries. Users of Nextdoor are required to submit their real names and addresses (or street without the exact number) to the website; posts made to the website are available only to other Nextdoor members living in the same neighborhood.
Typical platform uses include neighbors reporting on news and events in their "neighborhood" and members asking each other for local service-provider recommendations. "Neighborhood" borders were initially established with Maponics, a provider of geographical information. According to the platform's rules, members whose addresses fall outside the boundaries of existing neighborhoods can establish their own neighborhoods. "Founding" members of neighborhoods determine the name of the neighborhood and its boundaries, although Nextdoor retains the authority to change either of these. A member must attract a minimum of 10 households to establish a new "neighborhood", as of November 2016.
While allowing for "civil debate", the platform prohibits canvassing for votes on forums. The service does however allow separate forums just for political discussions. According to The New York Times, these discussions are "separated from [a user's regular] neighborhood feeds". The company had established these separate forums in 12 markets by 2018. The company has stated it "has no plans" to accept political advertising.
Special-use platforms
U-Report
U-Report is a social messaging tool and data collection system developed by UNICEF to improve citizen engagement, inform leaders, and foster positive change. The program sends SMS polls and alerts to its participants, collecting real-time responses, and subsequently publishes gathered data. Issues polled include health, education, water, sanitation and hygiene, youth unemployment, HIV/AIDS, and disease outbreaks. The program currently has three million participants in forty-one countries.
Platforms that are internal features within major websites
Facebook
Facebook Messenger is an instant messaging service and software application. It began as Facebook Chat in 2008, was revamped in 2010 and eventually became a standalone mobile app in August 2011, while remaining part of the user page on browsers.
Complementing regular conversations, Messenger lets users make one-to-one and group voice and video calls. Its Android app has integrated support for SMS and "Chat Heads", which are round profile photo icons appearing on-screen regardless of what app is open, while both apps support multiple accounts, conversations with optional end-to-end encryption and "Instant Games". Some features, including sending money and requesting transportation, are limited to the United States. In 2017, Facebook added "Messenger Day", a feature that lets users share photos and videos in a story-format with all their friends with the content disappearing after 24 hours; Reactions, which lets users tap and hold a message to add a reaction through an emoji; and Mentions, which lets users in group conversations type @ to give a particular user a notification.
Businesses and users can interact through Messenger with features such as tracking purchases and receiving notifications, and interacting with customer service representatives. Third-party developers can integrate apps into Messenger, letting users enter an app while inside Messenger and optionally share details from the app into a chat. Developers can build chatbots into Messenger, for uses such as news publishers building bots to distribute news. The M virtual assistant (U.S.) scans chats for keywords and suggests relevant actions, such as its payments system for users mentioning money. Group chatbots appear in Messenger as "Chat Extensions". A "Discovery" tab allows finding bots, and enabling special, branded QR codes that, when scanned, take the user to a specific bot.
Instagram
In December 2013, Instagram announced Instagram Direct, a feature that lets users interact through private messaging. Users who follow each other can send private messages with photos and videos, in contrast to the public-only requirement that was previously in place. When users receive a private message from someone they don't follow, the message is marked as pending and the user must accept to see it. Users can send a photo to a maximum of 15 people. The feature received a major update in September 2015, adding conversation threading and making it possible for users to share locations, hashtag pages, and profiles through private messages directly from the news feed. Additionally, users can now reply to private messages with text, emoji or by clicking on a heart icon. A camera inside Direct lets users take a photo and send it to the recipient without leaving the conversation. A new update in November 2016 let users make their private messages "disappear" after being viewed by the recipient, with the sender receiving a notification if the recipient takes a screenshot.
In April 2017, Instagram redesigned Direct to combine all private messages, both permanent and ephemeral, into the same message threads. In May, Instagram made it possible to send website links in messages, and also added support for sending photos in their original portrait or landscape orientation without cropping.
In April 2020, Direct became accessible from the Instagram website.
In August 2020, Facebook started merging Instagram Direct into Facebook Messenger. After the update (which is rolled out to a segment of the user base) the Instagram Direct icon transforms into Facebook Messenger icon.
LinkedIn
The LinkedIn website includes a feature that allows direct messaging by a user to any other user who is on their list of Connections. Additionally, users with Premium membership can send messages to anyone on LinkedIn.
Reddit
In 2017, Reddit developed its own real-time chat software for the site. While some established subreddits have used third-party software to chat about their communities, the company built chat functions that it hopes will become an integral part of Reddit. Individual chat rooms were rolled out in 2017 and community chat rooms for members of a given subreddit were rolled out in 2018.
Twitter
Tweets are publicly visible by default, but senders can restrict message delivery to only their followers. Users can mute users they do not wish to interact with and block accounts from viewing their tweets. Users can tweet via the Twitter website, compatible external applications (such as for smartphones), or by Short Message Service (SMS) available in certain countries. Users may subscribe to other users' tweets—this is known as "following" and subscribers are known as "followers" or "tweeps", a portmanteau of Twitter and peeps. Individual tweets can be forwarded by other users to their own feed, a process known as a "retweet". Users can also "like" (formerly "favorite") individual tweets. Twitter allows users to update their profile via their mobile phone either by text messaging or by apps released for certain smartphones and tablets. Twitter has been compared to a web-based Internet Relay Chat (IRC) client. In a 2009 Time magazine essay, technology author Steven Johnson described the basic mechanics of Twitter as "remarkably simple":
Video conference platforms
Jitsi
Jitsi is a collection of free and open-source multiplatform voice (VoIP), video conferencing and instant messaging applications for the web platform, Windows, Linux, macOS, iOS and Android. The Jitsi project began with the Jitsi Desktop (previously known as SIP Communicator). It is totally free to use, and to host on a business's own server.
With the growth of WebRTC, the project team focus shifted to the Jitsi Videobridge for allowing web-based multi-party video calling. Later the team added Jitsi Meet, a full video conferencing application that includes web, Android, and iOS clients. Jitsi also operates meet.jit.si, a version of Jitsi Meet hosted by Jitsi for free community use. Other projects include: Jigasi, lib-jitsi-meet, Jidesha, and Jitsi.
Jitsi has received support from various institutions such as the NLnet Foundation, the University of Strasbourg and the Region of Alsace and it has also had multiple participations in the Google Summer of Code program.
Jitsi Meet is an open source JavaScript WebRTC application used primarily for video conferencing. In addition to audio and video, screen sharing is available, and new members can be invited via a generated link. The interface is accessible via web browser or with a mobile app. The Jitsi Meet server software can be downloaded and installed on Linux-based computers. Jitsi owner 8x8 maintains a free public-use server for up to 50 participants at meet.jit.si.
Key features of Jitsi Meet
Encrypted communication (secure communication): As of April 2020, one-to-one calls use the P2P mode, which is end-to-end encrypted via DTLS-SRTP between the two participants. Group calls also use DTLS-SRTP encryption, but rely on the Jitsi Videobridge (JVB) as video router, where packets are decrypted temporarily. The Jitsi team emphasizes that "they are never stored to any persistent storage and only live in memory while being routed to other participants in the meeting", and that this measure is necessary due to current limitations of the underlying WebRTC technology.
No need of new client software installation.
Skype
Skype is a proprietary telecommunications application that specializes in providing video chat and voice calls between computers, tablets, mobile devices, the Xbox One console, and smartwatches over the Internet. Skype also provides instant messaging services. Users may transmit text, video, audio and images. Skype allows video conference calls.
In March 2020, Skype was used by 100 million people on a monthly basis and by 40 million people on a daily basis, which was a 70% increase in the number of daily users from the previous month, due to the COVID-19 pandemic.
Registered users of Skype are identified by a unique Skype ID and may be listed in the Skype directory under a Skype username. Skype allows these registered users to communicate through both instant messaging and voice chat. Voice chat allows telephone calls between pairs of users and conference calling and uses proprietary audio codec. Skype's text chat client allows group chats, emoticons, storing chat history, and editing of previous messages. Offline messages were implemented in a beta build of version 5 but removed after a few weeks without notification. The usual features familiar to instant messaging users—user profiles, online status indicators, and so on—are also included.
The Online Number, a.k.a. SkypeIn, service allows Skype users to receive calls on their computers dialed by conventional phone subscribers to a local Skype phone number; local numbers are available for Australia, Belgium, Brazil, Chile, Colombia, Denmark, the Dominican Republic, Estonia, Finland, France, Germany, Hong Kong, Hungary, India, Ireland, Japan, Mexico, Nepal, New Zealand, Poland, Romania, South Africa, South Korea, Sweden, Switzerland, Turkey, the Netherlands, the United Kingdom, and the United States. A Skype user can have local numbers in any of these countries, with calls to the number charged at the same rate as calls to fixed lines in the country.
Skype supports conference calls, video chats, and screen sharing between 25 people at a time for free, which then increased to 50 on 5 April 2019.
Skype does not provide the ability to call emergency numbers, such as 112 in Europe, 911 in North America, 999 in the UK or 100 in India and Nepal. However, as of December 2012, there is limited support for emergency calls in the United Kingdom, Australia, Denmark, and Finland. The U.S. Federal Communications Commission (FCC) has ruled that, for the purposes of section 255 of the Telecommunications Act, Skype is not an "interconnected VoIP provider". As a result, the U.S. National Emergency Number Association recommends that all VoIP users have an analog line available as a backup.
Skype allows users to send instant messages to other users in their contact list. Messages sent to offline users are stored on Skype servers and will be delivered to their recipients as soon as they come online on Skype. Chat history along with the message status will be synchronized across all user devices supported by Skype whenever the user signs in with the same Skype account.
Although Skype allows sending SMS messages, it is not possible to receive SMS messages on Skype so users need a different way to receive responses to the messages they send using Skype. This has been a cause of angst among user who purchase Skype as an alternative to a mobile phone because Microsoft will not refund any purchases even for users who discover this missing feature only after purchasing multi-year contracts. Other than in user complaints on the Microsoft Skype forums, there is no mention on Microsoft or Skype websites that when they say "Send SMS messages," that is just what they mean: users can send but they cannot receive SMS messages.
Skype keeps user instant messaging history on user's local computer, and on Skype's cloud for 30 days. Users cannot control how long their chat histories are stored on Skype's servers but can configure that option individually for every their device. Once user signs into Skype on a new device the conversation history is synced with Skype's cloud and stored locally. Skype allows users to remove or edit individual messages during one hour after sending; this affects messages already received by chat interlocutors as well as not delivered to them yet. Skype allows users to delete all saved conversation histories for the device.
FaceTime
FaceTime is a proprietary videotelephony product developed by Apple Inc. It is available on supported iOS mobile devices running iOS 4 and later and Mac computers that run and later. FaceTime supports any iOS device with a forward-facing camera and any Mac computer equipped with a FaceTime Camera. FaceTime Audio, an audio-only version, is available on any iOS device that supports iOS 7 or newer, and any Mac with a forward-facing camera running and later. FaceTime is included for free in iOS and in macOS from (10.7) onwards.
Apple bought the "FaceTime" name from FaceTime Communications, which changed its name to Actiance in January 2011. On June 7, 2010, Apple CEO Steve Jobs announced FaceTime in conjunction with the iPhone 4 in a keynote speech at the 2010 Apple Worldwide Developers Conference. Support for the fourth generation iPod Touch (the first model of iPod Touch equipped with cameras) was announced in conjunction with the device's release on September 8, 2010. FaceTime for was announced on October 20, 2010.
In May 2011, it was found that FaceTime would work seamlessly over 3G on all iPhone, iPad, and iPod Touch models that supported it. Even though FaceTime worked only over 3G at that time, it now supports 4G LTE calls on networks all over the world, availability being limited to operators' GSM plans.
In 2018, Apple added group video and audio support to FaceTime which can support up to 32 people in iOS 12 and macOS Mojave.
Zoom
Zoom is a videotelephony software program developed by Zoom Video Communications. The free version provides a video chatting service that allows up to 100 devices at once, with a 40-minute time restriction for free accounts having meetings of three or more participants. Users have the option to upgrade by subscribing to one of its plans, with the highest allowing up to 1,000 people concurrently, with no time restriction.
Zoom is compatible with Windows, macOS, iOS, Android, ChromeOS, and Linux. It is noted for its simple interface and usability, specifically for non-tech people. Features include one-on-one meetings, group video conferences, screen sharing, plugins, browser extensions, and the ability to record meetings and have them automatically transcribed. On some computers and operating systems, users are able to select a virtual background, which can be downloaded from different sites, to use as a backdrop behind themselves.
Use of the platform is free for video conferences of up to 100 participants at once, with a 40-minute time limit if there are more than two participants. For longer or larger conferences with more features, paid subscriptions are available, costing $15–20 per month. Features geared towards business conferences, such as Zoom Rooms, are available for $50–100 per month. Up to 49 people can be seen on a screen at once. Zoom has several tiers: Basic, Pro, Business, and Enterprise. Participants do not have to download the app if they are using Google Chrome or Firefox; they can click on a link and join from the browser. Zoom is not compatible with Safari for Macs.
Zoom security features include password-protected meetings, user authentication, waiting rooms, locked meetings, disabling participant screen sharing, randomly generated IDs, and the ability for the host to remove disruptive attendees. As of June 2020, Zoom began offering end-to-end encryption to business and enterprise users, with AES 256 GCM encryption enabled for all users. In October 2020, Zoom added end-to-end encryption for free and paid users. It's available on all platforms, except for the official Zoom web client.
Zoom also offers a transcription service using Otter.ai software that allows businesses to store transcriptions of the Zoom meetings online and search them, including separating and labeling different speakers.
As of July 2020, Zoom Rooms and Zoom Phone also became available as hardware as a service products. Zoom Phone is available for domestic telephone service in 40 countries as of August 2020. Zoom for Home, a category of products designed for home use, became available in August 2020.
Google Duo
Google Duo is a video chat mobile app developed by Google, available on the Android and iOS operating systems. It was announced at Google's developer conference on May 18, 2016, and began its worldwide release on August 16, 2016. It is also available to use via Google's Chrome web browser on desktop and laptop computers.
Google Duo lets users make video calls in high definition. It is optimized for low-bandwidth networks. End-to-end encryption is enabled by default. Duo is based on phone numbers, allowing users to call someone from their contact list. The app automatically switches between Wi-Fi and cellular networks. A "Knock Knock" feature lets users see a live preview of the caller before answering. An update in April 2017 lets users worldwide make audio-only calls.
As of December 1, 2016, Google Duo replaced Hangouts within the suite of Google apps device manufacturers must install in order to gain access to the Google Play Store, with Hangouts instead becoming optional.
In August 2020, it was reported that Google was planning to eventually replace Google Duo with Google Meet, but would continue to support Duo and "invest in building new features" in the long term.
Google Hangouts
Google Hangouts is a cross-platform messaging app developed by Google. Originally a feature of Google+, Hangouts became a stand-alone product in 2013, when Google also began integrating features from Google+ Messenger and Google Talk into Hangouts. In 2017, Google began developing Hangouts into a product aimed at enterprise communication, splitting into two products: Google Meet and Google Chat.
Google has also begun integrating features of Google Voice, its IP telephony product, into Hangouts, stating that Hangouts is designed to be "the future" of Voice. Google began transitioning users from the "classic" version of Hangouts to Meet and Chat in June 2020, and announced in October 2020 that Google Chat would eventually be made free to consumers and fully replace Hangouts, shortly after Google Meet became free as well. Google Hangouts will remain a consumer-level product for people using standard Google accounts.
Google Hangouts has a unique feature in that it allows video calls to be streamed live via YouTube.
Google Meet
Google Meet (formerly known as Hangouts Meet) is a video-communication service developed by Google. It is one of two apps that constitute the replacement for Google Hangouts, the other being Google Chat.
User features of Google Meet include:
Two-way and multi-way audio and video calls with a resolution up to 720p
An accompanying chat
Call encryption between all users
Noise cancelling audio filter
Low-light mode for video
Ability to join meetings through a web browser or through Android or iOS apps
Integration with Google Calendar and Google Contacts for one-click meeting calls
Screen-sharing to present documents, spreadsheets, presentations, or (if using a browser) other browser tabs
Ability to call into meetings using a dial-in number in the US
Hosts being able to deny entry and remove users during a call.
Google Meet uses proprietary protocols for video, audio and data transcoding. However, Google has partnered with the company Pexip to provide interoperability between Google Meet and SIP/H.323-based conferencing equipment and software.
Features for users who use Google Workspace accounts include:
Up to 100 members per call for Google Workspace Starter users, up to 150 for Google Workspace Business users, and up to 250 for Google Workspace Enterprise users
Ability to call into meetings with a dial-in number from selected countries
Password-protected dial-in numbers for Google Workspace Enterprise edition users
Real-time closed captioning based on speech recognition
Background blurring
In March 2020, Google temporarily extended advanced features present in the enterprise edition to anyone using Google Workspace or G Suite for Education editions.
In March 2020, Google rolled out Meet to personal (free) Google accounts.
Free Meet calls can only have a single host and up to 100 participants, compared to the 250-caller limit for Google Workspace users and the 25-participant limit for Hangouts. Unlike business calls with Meet, consumer calls are not recorded and stored, and Google states that consumer data from Meet will not be used for advertisement targeting. While call data is reportedly not being used for advertising purposes, based on an analysis of Meet's privacy policy, Google reserves the right to collect data on call duration, who is participating, and participants' IP addresses.
Users need a Google account to initiate calls and like Google Workspace users, anyone with a Google account is able to start a Meet call from within Gmail.
Marco Polo
Marco Polo (app) is a video messaging and video hosting service mobile app. The app was created in 2014 by Joya Communications, founded by Vlada Bortnik and Michael Bortnik. The app markets itself as a video walkie talkie.
Device-specific platforms
iMessage for iPhones
iMessage is an instant messaging service developed by Apple Inc. and launched in 2011. iMessage functions exclusively on Apple platforms: macOS, iOS, iPadOS, and watchOS.
Core features of iMessage, available on all supported platforms, include sending texts, images, videos, and documents; getting delivery and read statuses (read receipts); and end-to-end encryption (which means no one, including Apple itself, is able to intercept or tamper with sent messages). On all platforms except macOS, the service also allows sending location data and stickers. On iOS and iPadOS, third-party developers can extend iMessage capabilities with custom extensions (an example being quick sharing of recently played songs).
Launched on iOS in 2011, iMessage arrived on macOS (then called OS X) in 2012. In 2020, Apple announced an entirely redesigned version of the macOS Messages app which adds some of the features previously unavailable on the Mac, including location sharing and message effects.
Google Messages
Google Messages is an SMS and instant messaging application developed by Google for its Android mobile operating system. A web interface is also available. Launched in 2014, it has supported Rich Communication Services (RCS) messaging since 2018, marketed as "Chat" features. By April 2020, the app had more than a billion installs which was most likely due to Google's wider roll out of RCS to many different countries without carrier support.
Palringo
Palringo, or The World's Online Festival (WOLF), is a community-oriented messaging and gaming app for iOS and Android. The platform allows users to chat, entertain, and perform on a Stage—live microphone slots for up to 5 people, form and join large groups based on common interests, send instant messages and drop images and voice recordings into conversations. Launched under its original name of Palringo in 2006, the app has 80 million accounts worldwide and offers a range of games along with more than 380,000 groups, some of which have up to 2,500 members. Headquartered in London, WOLF has offices in Newcastle and London, UK, and Amman, Jordan.
Groupware
"Groupware" refers to a number of varied applications that are designed to enable communication amongst members of a team, either within a company, a project, or some other group effort. these applications may incorporate a vast range of features and functions, rather than a single specialized function. Such platforms may include instant messaging, document sharing, visual diagrams, voice conference, and many other team-oriented features.
Microsoft Yammer
Yammer is a freemium enterprise social networking service used for private communication within organizations. Access to a Yammer network is determined by a user's Internet domain so that only individuals with approved email addresses may join their respective networks.
The service began as an internal communication system for the genealogy website Geni.com, and was launched as an independent product in 2008. Microsoft later acquired Yammer in 2012 for US$1.2 billion. Currently Yammer is included in all enterprise plans of Office 365 and Microsoft 365.
Adobe Connect
Adobe Connect (formerly Presedia Publishing System, Macromedia Breeze, and Adobe Acrobat Connect Pro) is a suite of software for remote training, web conferencing, presentation, and desktop sharing. All meeting rooms are organized into 'pods'; with each pod performing a specific role (e.g. chat, whiteboard, note etc.) Adobe Connect was formerly part of the Adobe Acrobat family and has changed names several times.
Google Workspace
Google Workspace, formerly known as G Suite, is a collection of cloud computing, productivity and collaboration tools, software and products developed and marketed by Google. It was first launched in 2006 as Google Apps for Your Domain and rebranded as G Suite in 2016. Google Workspace consists of Gmail, Contacts, Calendar, Meet and Chat for communication; Currents for employee engagement; Drive for storage; and the Google Docs suite for content creation. An Admin Panel is provided for managing users and services. Depending on edition Google Workspace may also include the digital interactive whiteboard Jamboard and an option to purchase such add-ons as the telephony service Voice. The education edition adds a learning platform Google Classroom and as of October 2020 retains the name G Suite for Education.
While most of these services are individually available at no cost to consumers who use their free Google (Gmail) accounts, Google Workspace adds enterprise features such as custom email addresses at a domain (e.g. @yourcompany.com), an option for unlimited Drive storage, additional administrative tools and advanced settings, as well as 24/7 phone and email support.
Being based in Google's data centers, data and information are saved directly and then synchronized to other data centers for backup purposes. Unlike the free, consumer-facing services, Google Workspace users do not see advertisements while using the services, and information and data in Google Workspace accounts do not get used for advertisement purposes. Furthermore, Google Workspace administrators can fine-tune security and privacy settings.
Google Chat
Google Chat is a communication software developed by Google built for teams that provides direct messages and team chat rooms, similar to competitors Slack and Microsoft Teams, along with a group messaging function that allows Google Drive content sharing. It is one of two apps that constitute the replacement for Google Hangouts, the other being Google Meet. Google planned to begin retiring Google Hangouts in October 2019.
The current version is for Google Workspace, (formerly G Suite until October 2020) customers only, with identical features in all packages except a lack of Vault data retention in the Basic package. However, in October 2020, Google announced plans to open Google Chat up to consumers as early as 2021, once Hangouts has been officially retired.
Slack
Slack offers many IRC-style features, including persistent chat rooms (channels) organized by topic, private groups, and direct messaging. Content, including files, conversations, and people, is all searchable within Slack. Users can add emoji buttons to their messages, on which other users can then click to express their reactions to messages.
Slack's free plan allows only the 10,000 most recent messages to be viewed and searched. On March 18, 2020, Slack redesigned its platform to simplify and customize the user experience.
Slack teams allow communities, groups, or teams to join a "workspace" via a specific URL or invitation sent by a team admin or owner. Although Slack was developed for professional and organizational communication, it has been adopted as a community platform, replacing message boards or social media groups.
Public channels allow team members to communicate without the use of email or group SMS (texting). Public channels are open to everyone in the workspace. Private channels allow for private conversation between smaller sub-groups. These private channels can be used to organize large teams. Direct messages allow users to send private messages to specific users rather than a group of people. Direct messages can include up to nine people. Once started, a direct message group can be converted into a private channel.
Slack integrates with many third-party services and supports community-built integrations, including Google Drive, Trello, Dropbox, Box, Heroku, IBM Bluemix, Crashlytics, GitHub, Runscope, Zendesk and Zapier. In December 2015, Slack launched their software application ("app") directory, consisting of over 150 integrations that users can install.
In March 2018, Slack announced a partnership with financial and human capital management firm Workday. This integration allows Workday customers to access Workday features directly from the Slack interface.
Discord
Discord is built to create and manage private and public communities. It gives users access to tools focused around communication like voice and video calls, persistent chat rooms and integrations with other gamer-focused services.
Discord communities are organized into discrete collections of channels called servers. A user can create servers for free, manage their public visibility and create one or more channels within that server.
Starting October 2017, Discord allows game developers and publishers to verify their servers. Verified servers, like verified accounts on social media sites, have badge to mark them as official communities. Verified servers are moderated by the developer's or publisher's own moderation team. Verification was later extended in February 2018 to include esports teams and musical artists.
By the end of 2017, about 450 servers were verified. Approximately 1790 servers are verified as of December 2020.
Discord users can improve the quality of the servers they reside in via the "Server Boost" feature, which improves quality of audio channels, streaming channels, number of emoji slots and other perks in 3 levels. Users can buy boosts to support the servers they choose, for a monthly amount. Possession of "Discord Nitro", the platform's paid subscription, gives a user two extra boosts to use on any server they like.
Channels may be either used for voice chat and streaming or for instant messaging and file sharing. The visibility and access to channels can be customized to limit access from certain users, for example marking a channel "NSFW" (Not Safe For Work) requires that first-time viewers confirm they are over 18 years old and willing to see such content.
Kune
Kune is a free/open source distributed social network focused on collaboration rather than just on communication. That is, it focuses on online real-time collaborative editing, decentralized social networking and web publishing, while focusing on workgroups rather than just on individuals. It aims to allow for the creation of online spaces for collaborative work where organizations and individuals can build projects online, coordinate common agendas, set up virtual meetings, publish on the web, and join organizations with similar interests. It has a special focus on Free Culture and social movements needs. Kune is a project of the Comunes Collective.
All the functionalities of Apache Wave, that is collaborative federated real-time editing, plus
Communication
Chat and chatrooms compatible with Gmail and Jabber through XMPP (with several XEP extensions), as it integrates Emite
Social networking (federated)
Real-time collaboration for groups in:
Documents: as in Google Docs
Wikis
Lists: as in Google Groups but minimizing emails, through waves
Group Tasks
Group Calendar: as in Google Calendar, with ical export
Group Blogs
Web-creation: aiming to publish contents directly on the web (as in WordPress, with a dashboard and public view) (in development)
Bartering: aiming to decentralize bartering as in eBay
Advanced email
Waves: aims to replace most uses of email
Inbox: as in email, all your conversations and documents in all kunes are controlled from your inbox
Email notifications (Projected: replies from email)
Multimedia & Gadgets
Image or Video galleries integrated in any doc
Maps, mindmaps, Twitter streams, etc.
Polls, voting, events, etc.
and more via Apache Wave extensions, easy to program (as in Facebook apps, they run on top of Kune)
See also
Comparison of cross-platform instant messaging clients
Comparison of instant messaging protocols
Comparison of Internet Relay Chat clients
Comparison of LAN messengers
Comparison of VoIP software
List of SIP software
List of video telecommunication services and product brands
References
External links
Comparison articles and overviews
15 Group Messaging Mobile Apps, November 5, 2019, by Sig Ueland, practicalecommerce.com.
The Ultimate Group Text App Guide, Last updated February 17, 2020, snapdesk.app website.
Wikimedia pages
Wikimedia list of conference platforms
Social media
Android Auto software
VoIP software
Mobile applications
Android (operating system) software
IOS software
Instant messaging clients
Cross-platform software
Communication software
Computer-mediated communication
Groupware
Collaborative software
Network software comparisons
user features of messaging platforms
Messaging platforms | Comparison of user features of messaging platforms | Technology | 18,863 |
4,084,346 | https://en.wikipedia.org/wiki/ISO/IEC%2011801 | International standard ISO/IEC 11801 Information technology — Generic cabling for customer premises specifies general-purpose telecommunication cabling systems (structured cabling) that are suitable for a wide range of applications (analog and ISDN telephony, various data communication standards, building control systems, factory automation). It is published by ISO/IEC JTC 1/SC 25/WG 3 of the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC). It covers both balanced copper cabling and optical fibre cabling.
The standard was designed for use within commercial premises that may consist of either a single building or of multiple buildings on a campus. It was optimized for premises that span up to 3 km, up to 1 km2 office space, with between 50 and 50,000 persons, but can also be applied for installations outside this range.
A major revision was released in November 2017, unifying requirements for commercial, home and industrial networks.
Classes and categories
The standard defines several link/channel classes and cabling categories of twisted-pair copper interconnects, which differ in the maximum frequency for which a certain channel performance is required:
Class A: Up to 100 kHz using Category 1 cable and connectors
Class B: Up to 1 MHz using Category 2 cable and connectors
Class C: Up to 16 MHz using Category 3 cable and connectors
Class D: Up to 100 MHz using Category 5e cable and connectors
Class E: Up to 250 MHz using Category 6 cable and connectors
Class EA: Up to 500 MHz using category 6A cable and connectors (Amendments 1 and 2 to ISO/IEC 11801, 2nd Ed.)
Class F: Up to 600 MHz using Category 7 cable and connectors
Class FA: Up to 1 GHz (1000 MHz) using Category 7A cable and connectors (Amendments 1 and 2 to ISO/IEC 11801, 2nd Ed.)
Class BCT-B: Up to 1 GHz (1000 MHz) using with coaxial cabling for BCT applications. (ISO/IEC 11801-1, Edition 1.0 2017-11)
Class I: Up to 2 GHz (2000 MHz) using Category 8.1 cable and connectors (ISO/IEC 11801-1, Edition 1.0 2017-11)
Class II: Up to 2 GHz (2000 MHz) using Category 8.2 cable and connectors (ISO/IEC 11801-1, Edition 1.0 2017-11)
The standard link impedance is 100 Ω. (The older 1995 version of the standard also permitted 120 Ω and 150 Ω in Classes A−C, but this was removed from the 2002 edition.)
The standard defines several classes of optical fiber interconnect:
OM1*: Multimode, 62.5 μm core; minimum modal bandwidth of 200 MHz·km at 850 nm
OM2*: Multimode, 50 μm core; minimum modal bandwidth of 500 MHz·km at 850 nm
OM3: Multimode, 50 μm core; minimum modal bandwidth of 2000 MHz·km at 850 nm
OM4: Multimode, 50 μm core; minimum modal bandwidth of 4700 MHz·km at 850 nm
OM5: Multimode, 50 μm core; minimum modal bandwidth of 4700 MHz·km at 850 nm and 2470 MHz·km at 953 nm
OS1*: Single-mode, maximum attenuation 1 dB/km at 1310 and 1550 nm
OS1a: Single-mode, maximum attenuation 1 dB/km at 1310, 1383, and 1550 nm
OS2: Single-mode, maximum attenuation 0.4 dB/km at 1310, 1383, and 1550 nm
*Grandfathered
OM5
OM5 fiber is designed for wideband applications using SWDM multiplexing of 4–16 carriers (40G=4λ×10G, 100G=4λ×25G, 400G=4×4λ×25G) in the 850–953 nm range.
Category 7
Class F channel and Category 7 cable are backward compatible with Class D/Category 5e and Class E/Category 6. Class F features even stricter specifications for crosstalk and system noise than Class E. To achieve this, shielding was added for individual wire pairs and the cable as a whole. Unshielded cables rely on the quality of the twists to protect from EMI. This involves a tight twist and carefully controlled design. Cables with individual shielding per pair such as Category 7 rely mostly on the shield and therefore have pairs with longer twists.
The Category 7 cable standard was ratified in 2002, and primarily introduced to support 10 gigabit Ethernet over 100 m of copper cabling. It contains four twisted copper wire pairs, just like the earlier standards, terminated either with GG45 electrical connectors or with TERA connectors rated for transmission frequencies of up to 600 MHz.
However, in 2006, Category 6A was ratified for Ethernet to allow 10 Gbit/s while still using the conventional 8P8C connector. Care is required to avoid signal degradation by mixing cable and connectors not designed for that use, however similar. Most manufacturers of active equipment and network cards have chosen to support the 8P8C for their 10 gigabit Ethernet products on copper and not the GG45, ARJ45, or TERA. Therefore, the Category 6 specification was revised to Category 6A to permit this use; products therefore require a Class EA channel (ie, Cat 6A).
some equipment has been introduced which has connectors supporting the Class F (Category 7) channel.
Note, however, that Category 7 is not recognized by the TIA/EIA.
Category 7A
Class FA (Class F Augmented) channels and Category 7A cables, introduced by ISO 11801 Edition 2 Amendment 2 (2010), are defined at frequencies up to 1000 MHz.
The intent of the Class FA was to possibly support the future 40 gigabit Ethernet: 40GBASE-T. Simulation results have shown that 40 gigabit Ethernet may be possible at 50 meters and 100 gigabit Ethernet at 15 meters. In 2007, researchers at Pennsylvania State University predicted that either 32 nm or 22 nm circuits would allow for 100 gigabit Ethernet at 100 meters.
However, in 2016, the IEEE 802.3bq working group ratified the amendment 3 which defines 25GBASE-T and 40GBASE-T on Category 8 cabling specified to 2000 MHz. The Class FA therefore does not support 40G Ethernet.
there is no equipment that has connectors supporting the Class FA (Category 7A) channel.
Category 7A is not recognized in TIA/EIA.
Category 8
Category 8 was ratified by the TR43 working group under ANSI/TIA 568-C.2-1. It is defined up to 2000 MHz and only for distances up to 30 m or 36 m, depending on the patch cords used.
ISO/IEC JTC 1/SC 25/WG 3 developed the equivalent standard ISO/IEC 11801-1:2017/COR 1:2018, with two options:
Class I channel (Category 8.1 cable): minimum cable design U/FTP or F/UTP, fully backward compatible and interoperable with Class EA (Category 6A) using 8P8C connectors;
Class II channel (Category 8.2 cable): F/FTP or S/FTP minimum, interoperable with Class FA (Category 7A) using TERA or GG45.
Abbreviations for twisted pairs
Annex E, Acronyms for balanced cables, provides a system to specify the exact construction for both unshielded and shielded balanced twisted pair cables. It uses three letters—U for unshielded, S for braided shielding, and F for foil shielding—to form a two-part abbreviation in the form of xx/xTP, where the first part specifies the type of overall cable shielding, and the second part specifies shielding for individual cable elements.
Common cable types include U/UTP (unshielded cable); U/FTP (individual pair shielding without the overall screen); F/UTP, S/UTP, or SF/UTP (overall screen without individual shielding); and F/FTP, S/FTP, or SF/FTP (overall screen with individual foil shielding).
2017 edition
In November 2017, a new edition was released by ISO/IEC JTC 1/SC 25 "Interconnection of information technology equipment" subcommittee. It is a major revision of the standard which has unified several prior standards for commercial, home, and industrial networks, as well as data centers, and defines requirements for generic cabling and distributed building networks.
The new series of standards replaces the former 11801 standard and includes six parts:
Versions
ISO/IEC 11801:1995 (Ed. 1)
ISO/IEC 11801:2000 (Ed. 1.1) – Edition 1, Amendment 1
ISO/IEC 11801:2002 (Ed. 2)
ISO/IEC 11801:2008 (Ed. 2.1) – Edition 2, Amendment 1
ISO/IEC 11801:2010 (Ed. 2.2) – Edition 2, Amendment 2
ISO/IEC 11801-1:2017, -1:2017/Cor 1:2018, -2:2017, -3:2017, -3:2017/Amd 1:2021, -3:2017/Cor 1:2018, -4:2017, -4:2017/Cor 1:2018, -5:2017, -5:2017/Cor 1:2018, -6:2017, -6:2017/Cor 1:2018 ( this set is current.)
See also
Ethernet over twisted pair
Twisted pair
TIA/EIA-568
ISO/IEC JTC 1/SC 25
References
Further reading
International standard ISO/IEC 11801: Information technology — Generic cabling for customer premises''.
European standard EN 50173: Information technology — Generic cabling systems. 1995.
11801
Telecommunications | ISO/IEC 11801 | Technology | 2,078 |
5,115,473 | https://en.wikipedia.org/wiki/Allan%20D.%20Emil%20Memorial%20Award | The Allan D. Emil Memorial Award is presented every year at the Congress of the International Astronautical Federation.
It has been presented annually, since 1977, for an outstanding contribution in space science, space technology, space medicine, or space law which involved the participation of more than one nation and/or which furthered the possibility of greater international cooperation in astronautics.
The award consists of a certificate citation and a stipend donated by the Emil family.
Recipients
1977: Charles Stark Draper
1978: Konstantin Bushuyev, Glynn Lunney
1979:
1980: Thomas P. Stafford
1981: Peter Jankowitsch, Leonid I. Sedov
1982: Roger Chevalier
1983: Roy Gibson
1984: Luboš Perek
1985: Hans E.W. Hoffmann
1986: Robert Freitag
1987: Ruedeger Reinhard, Burton Edelson, , Roald Sagdeev,
1988:
1989: Johannes Geiss
1990: Oleg Gazenko, , Karl Klein
1991: Guy Severin,
1992: George Müller, U. Ram Rao
1993: Hubert Curien
1994:
1995: Karl H. Doetsch
1996: Anatoly Grigoriev
1997: James Harford
1998: Alvaro Azcarraga
1999: Edward C. Stone
2000: Marcio Barbosa
2001: Richard Kline
2002: Jean-Claude Husson
2003: Liu Jiyuan
2004: Krishnaswamy Kasturirangan
2005:
2006:
2007: Gerhard Haerendel
2008: Conrad Lautenbacher
2009: Wei Sun
2010:
2011: Kuniaki Shiraki
2012:
2013: Ma Xingrui
2014: K. Radhakrishnan
2015: Virendra Jha
2016: Charles Elachi
2017: Lei Fanpei
2018: Xia Guohong
2019: Joan Vernikos
2020: Kailasavadivoo Sivan
See also
List of space technology awards
External links
Allan D. Emil Memorial Award | IAF
References
Awards established in 1977
Space-related awards | Allan D. Emil Memorial Award | Technology | 404 |
39,240,530 | https://en.wikipedia.org/wiki/Gauge%20group%20%28mathematics%29 | A gauge group is a group of gauge symmetries of the Yang–Mills gauge theory of principal connections on a principal bundle. Given a principal bundle with a structure Lie group , a gauge group is defined to be a group of its vertical automorphisms, that is, its group of bundle automorphisms. This group is isomorphic to the group of global sections of the associated group bundle whose typical fiber is a group which acts on itself by the adjoint representation. The unit element of is a constant unit-valued section of .
At the same time, gauge gravitation theory exemplifies field theory on a principal frame bundle whose gauge symmetries are general covariant transformations which are not elements of a gauge group.
In the physical literature on gauge theory, a structure group of a principal bundle often is called the gauge group.
In quantum gauge theory, one considers a normal subgroup of a gauge group which is the stabilizer
of some point of a group bundle . It is called the pointed gauge group. This group acts freely on a space of principal connections. Obviously, . One also introduces the effective gauge group where is the center of a gauge group . This group acts freely on a space of irreducible principal connections.
If a structure group is a complex semisimple matrix group, the Sobolev completion of a gauge group can be introduced. It is a Lie group. A key point is that the action of on a Sobolev completion of a space of principal connections is smooth, and that an orbit space is a Hilbert space. It is a configuration space of quantum gauge theory.
See also
Gauge symmetry (mathematics)
Gauge theory
Gauge theory (mathematics)
Principal bundle
References
Mitter, P., Viallet, C., On the bundle of connections and the gauge orbit manifold in Yang – Mills theory, Commun. Math. Phys. 79 (1981) 457.
Marathe, K., Martucci, G., The Mathematical Foundations of Gauge Theories (North Holland, 1992) .
Mangiarotti, L., Sardanashvily, G., Connections in Classical and Quantum Field Theory (World Scientific, 2000)
Differential geometry
Gauge theories
Theoretical physics | Gauge group (mathematics) | Physics,Mathematics | 450 |
63,771,951 | https://en.wikipedia.org/wiki/Martellivirales | Martellivirales is an order of viruses.
Taxonomy
The following families are recognized:
Bromoviridae
Closteroviridae
Endornaviridae
Kitaviridae
Mayoviridae
Togaviridae
Virgaviridae
References
Viruses | Martellivirales | Biology | 50 |
16,281,330 | https://en.wikipedia.org/wiki/Laser%20spray%20ionization | Laser spray ionization refers to one of several methods for creating ions using a laser interacting with a spray of neutral particles or ablating material to create a plume of charged particles. The ions thus formed can be separated by m/z with mass spectrometry. Laser spray is one of several ion sources that can be coupled with liquid chromatography-mass spectrometry for the detection of larger molecules.
Types of laser spray ionization
Neutral spray
In one version of the laser spray interface, explosive vaporization and mist formation occur when an aqueous solution effusing from the tip of the stainless steel capillary is irradiated from the opposite side of the capillary by a 10.6 μm infrared laser. Weak ion signals could be detected when the plume was sampled through the ion sampling orifice. When a high voltage (3–4 kV) was applied to the stainless-steel capillary, strong ion signals appeared. The ion abundances were found to be orders of magnitude greater than those obtained by conventional electrospray ionization in the case of aqueous solutions. This approach to laser spray ionization is a hybrid of three basic techniques for the generation of gaseous ions from the condensed phase, i.e., energy-sudden activation, nebulization and the action of an electric field.
Laser spray mass spectrometry can faithfully reflect the solution-phase characteristics of biomolecules. It has been successfully applied to evaluate the binding affinities of protein-DNA.
Laser spray has better ionization efficiency than conventional electrospray ionization (ESI). In particular, the sensitivity became more than one order of magnitude higher in negative ion modes. It was also found that this technique has a potential benefit for the low concentration samples due to condensation effect of the formed droplet by the irradiation of laser. Higher the solvation energies of triply charged metal ions, stronger are the signals for ions.
Laserspray ionization
Laserspray Ionization (LSI) is a newer mass spectrometric technique commonly used with biomolecules, such as proteins. This method is similar to matrix-assisted laser desorption/ionization (MALDI) at atmospheric pressure in that it involves an analyte and matrix mixture. It also contains features from electrospray ionization, in which it produces a similar mass spectra. The mechanism was initially thought to involve laser induced production of highly charge matrix/analyte clusters that upon evaporation of the matrix produces ions by the same mechanism as ESI. LSI's ability to ablate proteins at atmospheric pressure in order to form a multiple of charged ions with a mass resolution of 100,000 when coupled with a quadrupole orbitrap mass spectrometer. The advantages of using LSI includes a solvent-free ionization technique, fast data acquisition, simply to use, and the improved fragmentation through multiple charging.
Laser spray inlet ionization
Due to recent innovations to the laser spray technique, a new method of laser ablation using the spray method has surfaced. Laserspray inlet ionization (LSII) involves a matrix/analyte sample at atmospheric pressure being ablated, and the ionization process will take place in an ion transfer capillary tube located in the mass spectrometer inlet. The LSII method is also known as laserspray ionization vacuum (LSIV).
Applications
Matrix-assisted inlet ionization (MAII) has shown that the laser is not necessary for the ionization process. Ions are formed when matrix-analyte is introduced to the vacuum of a mass spectrometer through an inlet aperture. LSI is a subset of MAII and is now called laserspray inlet ionization (LSII). Laser spray inlet ionization and matrix-assisted inlet ionization can be coupled to a fourier transform ion cyclotron resonance (FT-ICR) mass analyzer to improve detection of peptides and proteins.
References
Chromatography
Ion source | Laser spray ionization | Physics,Chemistry | 828 |
8,628,942 | https://en.wikipedia.org/wiki/NACEVI | NACEVI (NAtional CEnter for VIdeo) is a Czech content delivery network operated by Visual Unity. It is partially financed by the Czech government through the Czech Broadband Forum.
NACEVI serves Windows Media format for audio and video. It is transparent for use of digital rights management. Total streaming capacity is about 10 Gbit/s. Traffic management is optimised for the Czech republic.
Distribution for IPv6 is also available.
External links
NACEVI
Internet technology companies of the Czech Republic | NACEVI | Technology | 101 |
5,235,612 | https://en.wikipedia.org/wiki/Control%20panel%20%28software%29 | Many computer user interfaces use a control panel metaphor to give the user control of software and hardware features. The control panel consists of multiple settings including display settings, network settings, user account settings, and hardware settings. Control panels are also used by web applications for easy graphical configuration. Some services offered by control panels require the user to have admin rights or root access.
Computer history
The term control panel was used for the plugboards in unit record equipment and in the early computers of the 1940s and '50s. In the 1980s, the Xerox Star and the Apple Lisa, which pioneered the first graphical user interface metaphors, controlled user settings by single click selections and variable fields. In 1984 the Apple Macintosh in its initial release made use of fundamental graphic representation of a "control panel board" imitating the operation of slider controls, on/off buttons and radio-select buttons that corresponded to user settings.
Functionality
There are many tasks grouped in a control panel:
Hardware
Color
Color management
Computer displays
Brightness
Contrast
Color calibration
Energy saving
Gamma correction
Screen resolution and orientation
Graphics tablet
Keyboard
Shortcuts and bindings
Language and layout
Text cursor appearance
Mouse and touchpad
Power management
Energy saving
Battery usage
Display brightness
Power button actions
Power plans
Printers and scanners
Sound
Networking
Bluetooth connection and file exchange
Ethernet connection
Internet Accounts
E-mail integration
Social media integration
Wi-Fi connection
System-wide proxy
Security
Certificates and password management
Firewall
Filesystem encryption
Privacy
File indexing and event tracking
Data sharing
System
Login window
System information
Hostname
System time
Calendar system
NTP server
Time zone
Software management
Application management
System update configuration
Software sources
Different types
In Microsoft Windows operating systems, the Control Panel and Settings app are where various computer settings can be modified.
In the classic Mac OS, a control panel served a similar purpose. In macOS, the equivalent to control panels are referred to as System Preferences.
In web hosting, browser-based control panels, such as CPanel and Plesk, are used to manage servers, web services and users.
There are different control panels in free desktops, like GNOME, KDE, Webmin...
See also
Control panel (engineering)
Dashboard (business)
References
User interfaces | Control panel (software) | Technology | 446 |
33,498,023 | https://en.wikipedia.org/wiki/Kappa%20calculus | In mathematical logic, category theory, and
computer science, kappa calculus is a
formal system for defining first-order
functions.
Unlike lambda calculus, kappa calculus has no
higher-order functions; its functions are
not first class objects. Kappa-calculus can be
regarded as "a reformulation of the first-order fragment of typed
lambda calculus".
Because its functions are not first-class objects, evaluation of kappa
calculus expressions does not require
closures.
Definition
The definition below has been adapted from the diagrams on pages 205 and 207 of Hasegawa.
Grammar
Kappa calculus consists of types and expressions, given by the
grammar below:
In other words,
1 is a type
If and are types then is a type.
Every variable is an expression
If is a type then is an expression
If is a type then is an expression
If is a type and e is an expression then is an expression
If and are expressions then is an expression
If x is a variable, is a type, and e is an expression, then is an expression
The and the subscripts of , , and are
sometimes omitted when they can be unambiguously determined from the
context.
Juxtaposition is often used as an abbreviation for a combination of
and composition:
Typing rules
The presentation here uses sequents () rather than hypothetical judgments in order to ease comparison with the simply typed lambda calculus. This requires the additional Var rule, which does not appear in Hasegawa
In kappa calculus an expression has two types: the type of its source and the type of its target. The notation is used to indicate that expression e has source type and target type .
Expressions in kappa calculus are assigned types according to the following rules:
{| cellpadding="9" style="text-align:center;"
| || (Var)
|-
| || (Id)
|-
| || (Bang)
|-
| || (Comp)
|-
|
| (Lift)
|-
|
|(Kappa)
|}
In other words,
Var: assuming lets you conclude that
Id: for any type ,
Bang: for any type ,
Comp: if the target type of matches the source type of they may be composed to form an expression with the source type of and target type of
Lift: if , then
Kappa: if we can conclude that under the assumption that , then we may conclude without that assumption that
Equalities
Kappa calculus obeys the following equalities:
Neutrality: If then and
Associativity: If , , and , then .
Terminality: If and then
Lift-Reduction:
Kappa-Reduction: if x is not free in h
The last two equalities are reduction rules for the calculus,
rewriting from left to right.
Properties
The type can be regarded as the unit type. Because of this, any two functions whose argument type is the same and whose result type is should be equal – since there is only a single value of type both functions must return that value for every argument (Terminality).
Expressions with type can be regarded as "constants" or values of "ground type"; this is because is the unit type, and so a function from this type is necessarily a constant function. Note that the kappa rule allows abstractions only when the variable being abstracted has the type for some . This is the basic mechanism which ensures that all functions are first-order.
Categorical semantics
Kappa calculus is intended to be the internal language of
contextually complete categories.
Examples
Expressions with multiple arguments have source types which are
"right-imbalanced" binary trees. For example, a function f with three
arguments of types A, B, and C and result type D will have type
If we define left-associative juxtaposition as an abbreviation
for , then – assuming that
, , and
– we can apply this function:
Since the expression has source type , it is a "ground value" and may be passed as an argument to another function. If , then
Much like a curried function of type
in lambda calculus, partial
application is possible:
However no higher types (i.e. ) are involved. Note that because the source type of is not , the following expression cannot be well-typed under the assumptions mentioned so far:
Because successive application is used for multiple
arguments it is not necessary to know the arity of a function in
order to determine its typing; for example, if we know that
then the expression
is well-typed as long as has type
for some
and . This property is important when calculating
the principal type of an expression, something
which can be difficult when attempting to exclude higher-order
functions from typed lambda calculi by restricting the grammar of types.
History
Barendregt originally introduced the term
"functional completeness" in the context of combinatory algebra.
Kappa calculus arose out of efforts by Lambek<ref
name="Lambek"/> to formulate an appropriate analogue of functional
completeness for arbitrary categories (see Hermida and Jacobs,<ref
name=HermidaJacobs/> section 1). Hasegawa later developed kappa
calculus into a usable (though simple) programming language including
arithmetic over natural numbers and primitive recursion.<ref
name="Hasegawa"/> Connections to arrows
were later investigated by Power, Thielecke, and others.
Variants
It is possible to explore versions of kappa calculus with
substructural types such as linear, affine,
and ordered types. These extensions require eliminating or
restricting the expression. In such circumstances
the type operator is not a true cartesian product,
and is generally written to make this clear.
References
Logical calculi | Kappa calculus | Mathematics | 1,149 |
9,942,011 | https://en.wikipedia.org/wiki/Fall%20arrest | Fall arrest is the form of fall protection which involves the safe stopping of a person already falling. It is one of several forms of fall protection, forms which also include fall guarding (general protection that prevents persons from entering a fall hazard area e.g., guard rails) and fall restraint (personal protection which prevents persons who are in a fall hazard area from falling in the first place, e.g., fall restraint lanyards).
The U.S. Department of Labor's Occupational Safety and Health Administration specifies under Title 29 of the Code of Federal Regulations that individuals working at height must be protected from fall injury, and fall arrest is one of several forms of fall protection as defined within that Code.
Personal fall arrest system
Fall arrest is of two major types: general fall arrest, such as nets; and personal fall arrest, such as lifelines. The most common manifestation of fall arrest in the workplace is the personal fall arrest system (PFAS or lifeline).
Such a system should include 5 elements referred to as ABCDEs of Fall Arrest:
A – Anchorage a fixed structure or structural adaptation, often including an anchorage connector, to which the other components of the PFAS are rigged.
B – Body Wear a full body harness worn by the worker.
C – Connector a subsystem component connecting the harness to the anchorage – such as a lanyard.
D – Deceleration Device an essential subsystem component designed to dissipate the forces associated with a fall arrest event.
E – Emergency Plan & Equipment a clear and simple approach to rescue of a suspended worker following a fall arrest event. All workers should be familiar with the site-specific plan and able to both comply with and implement it. This includes aiding others, as in recovery of a suspended co-worker before "suspension trauma" sets in.
Each of these elements is critical to the effectiveness of a personal fall arrest system. There are many different combinations of products that are commonly used to assemble a personal fall arrest system, and each must meet strict standards. The specific environment or application generally dictates the combination or combinations that are most appropriate.
Fall protection training
Workers are required to have training in the use of fall protection equipment. This is legislated by Occupational Health and Safety Groups such as OSHA in the USA, and in Canada, the Provincial legislative bodies. Training is required to include instruction on theoretical aspects of using the equipment, and also practical aspects. Typically a fall protection, sometimes called fall arrest class is 8 hours long for general workers, but may include a second 8 hours of training for workers who climb communication towers, or oil derricks. Fall protection training includes information on the use, maintenance, inspection and hazards of using fall protection equipment.
Energy absorption
To arrest a fall in a controlled manner, it is essential that there is sufficient energy absorption capacity in the system. Without this designed energy absorption, the fall can only be arrested by applying large forces to the worker and to the anchorage, which can result in either or both being severely affected.
An analogy for this energy absorption is to consider the difference in dropping an egg onto a stone floor or dropping it into soft mud. Even for the same fall distance and weight of egg (the input energy), there will be more damage with the stone floor as the arrest distance is smaller and so forces must be higher to dissipate the energy. For the soft mud, the arrest distance is longer and so arrest forces are lower but the egg is still stopped and is hopefully undamaged.
Because fall arrest designs require high-rate-energy capacity design methods, fundamental fall arrest design is tedious and esoteric. Thus, most fall arrest parts and systems are designed to the force standards contained in Federal OSHA 29CFR1910.66 appendix c, a force-type design standard which accounts for required energy considerations. The standard mitigates PPE interchangeability problems, allows wide use by designers not versed in high rate energy methods, and it limits the force into the worker to a survivable level.
Actual loads on the user and anchor-anchorage vary widely with user weight, height of fall, geometry, and type of line/rope. Excessive energy into the support and user is avoided by the use of energy absorbing PPE designed for the 1800 lbs maximum of the referenced Federal OSHA standard. (Designers should be cautioned that the force values of the standard are based on high rate energy system design and thus its force values are not necessarily inter-related.)
The most common fall arrest system is the vertical lifeline: a stranded rope that is connected to an anchor above, and to which the user's PPE is attached either directly or through a "shock absorbing" (energy absorbing) lanyard. Once all of the components of the particular lifeline system meet the requirements of the standard, the anchor connection is then referred to as an anchorage, and the system as well as the rope is then called a "lifeline".
Anchors used for lifeline anchorages are designed for force per connecting user, and the standard permits an anchor to deform in order to absorb energy (adhesive anchors have higher design requirements because of aging loss).
The rope can be lifeline rope, which stretches to lengthen the fall distance as it absorbs energy; or static rope, which does not stretch and thus limits the fall distance, but requires the fall energy be absorbed in other devices. It is essential that the PPE be rated for Fall Arrest and PPE used with static line include an energy absorber. While the energy absorbing lanyards hold in excess of when fully absorbed, most limit the load during the fall to under .
Another common system is an HLL (Horizontal Life Line). These are linear anchoring devices, which allow workers to move along the whole length of the anchor, usually without needing to disconnect and fixing points of the anchorage.
It is normally essential to include energy (or shock) absorbers within HLL in addition to those within the workers' PPE. Without such absorbers, the horizontal life line cannot deform significantly when arresting the fall. Because of the geometry of pulling across the horizontal line, this in turn results in large resolved forces being generated within the anchor system, sufficient to cause failure of the anchorage. This can occur even with energy absorbers being included in the PPE of the worker.
The load and horizontal line geometry in horizontal lifelines usually creates falls in excess of the limit of the standard, limiting HLL design to standard-defined "qualified persons". (The recognition of these basic weaknesses have resulted in most temporary "wrapped structure" HLL anchors, which were anchors made from a wire rope wrapped around a structure and its ends fastened together by wire rope clips, being replaced by fixed-point anchors or HLL systems designed by defined "qualified" persons.)
Fall clearance
In arresting a fall in a controlled manner, the distance required to arrest the fall must be considered. Federal OSHA limits the fall distance to unless the specific system is designed by a "qualified person" meeting the requirements of OSHA 29CFR1910.66 appendix c. The user also may not fall so as to strike protrusions or adjoining walls during the fall.
The safe fall distance is a function of the fall factor and the deployment of the "energy absorbers". As a rule of thumb for a factor 2 fall, a fall distance of approx will be required. This is equivalent to 2 stories of a building. If the fall clearance is less than this the worker may strike the ground before his fall is arrested.
Design of HLL systems
The design of an HLL system is a complex process. The designer should always perform a design calculation and the results of this calculation should be presented in any proposal and verified as acceptable. The loads applied to the structure and the fall clearance required should be checked.
See also
Personal protective equipment
Safety harness
References
External links
Fall Arrest Info
Sample Fall Arrest Program
Safety
Occupational safety and health
Construction safety | Fall arrest | Engineering | 1,627 |
1,924,911 | https://en.wikipedia.org/wiki/Gemma%20%28botany%29 | A gemma (English plural gemmas, Latin plural gemmae) is a single cell, or a mass of cells, or a modified bud of tissue, that detaches from the parent and develops into a new individual. This type of asexual reproduction is referred to as fragmentation. It is a means of asexual propagation in plants. These structures are commonly found in fungi, algae, liverworts and mosses, but also in some flowering plants such as pygmy sundews and some species of butterworts. Vascular plants have many other methods of asexual reproduction including bulbils and turions.
In mosses and liverworts
The production of gemmae is a widespread means of asexual reproduction in both liverworts and mosses. In liverworts such as Marchantia, the flattened plant body or thallus is a haploid gametophyte with gemma cups scattered about its upper surface. The gemma cups are cup-like structures containing gemmae. The gemmae are small discs of haploid tissue, and they directly give rise to new gametophytes. They are dispersed from gemma cups by rainfall.
The gemmae are bilaterally symmetrical and are not differentiated into dorsal and ventral surfaces. The mature gemmae fall on the ground and if conditions are suitable their germination starts immediately. The surface of the gemma which comes in contact of the soil gives out many rhizoids. This surface eventually becomes the lower(ventral) surface of the thallus. Meanwhile, the apical cells present in the two lateral notches become active and form two thalli in opposites directions.
Endogenous gemmae are also produced in liverworts, these are ovoid or ellipsoidal shaped, 2 celled at leaf tips or margins. Examples such as Bazzania kokawana (Fossombroniaceae), Endogemma caespiticia and also Riccardia species.
References
External links
Marchantiales – diagrams and micrographs of liverwort gemmae
Plant morphology
Fungal morphology and anatomy
Plant reproduction | Gemma (botany) | Biology | 428 |
44,032,493 | https://en.wikipedia.org/wiki/J.%20A.%20Lindon | James Albert Lindon ( – 16 December 1979) was an English puzzle enthusiast and poet specialising in light verse, constrained writing, and children's poetry.
Lindon was based in Addlestone and Weybridge. His poems often won weekly newspaper competitions, but seldom appeared in anthologies, though poems of his did appear in Yet More Comic and Curious Verse, compiled by J. M. Cohen, published by Penguin Books in 1959. Among his anthologised works are numerous parodies, including spoofs of Dylan Thomas, E. E. Cummings, T. E. Brown, Lewis Carroll, Rudyard Kipling, and Ernest L. Thayer. His palindromic poems appeared occasionally in Word Ways: The Journal of Recreational Linguistics, and several were collected in Howard W. Bergerson's Palindromes and Anagrams. Lindon is also noted as being the world's first writer of vocabularyclept poetry, in which poems are constructed by rearranging the words of an existing poem.
Author Martin Gardner often spoke highly of Lindon's poetry, referring to him as the greatest English writer of comic verse. His skill at wordplay was similarly lauded, with Gardner, Bergerson, Dmitri Borgmann, and others proclaiming him to be among the world's finest palindromists.
In addition to being a poet, Lindon was an accomplished writer and solver of puzzles, especially those in recreational mathematics. He was responsible for most of the pioneering work on antimagic squares.
Bibliography
Lindon's poetry appears in the following anthologies, edited volumes, and journals:
J. M. Cohen, ed. Yet More Comic and Curious Verse. Penguin, 1959.
Worm Runner's Digest. 1959–.
The Guinness Book of Poetry 1958–59. Putnam, 1960.
Martin Gardner. The Annotated Snark. Simon & Schuster, 1962.
Martin Gardner, ed. The Annotated Casey at the Bat: A Collection of Ballads about the Mighty Casey. Dover, 1967.
Word Ways: The Journal of Recreational Linguistics. Greenwood Periodicals et al., 1968–.
Howard W. Bergerson. Palindromes and Anagrams. Dover, 1973.
Oxford Dictionary of Phrase, Saying, and Quotation, Oxford University Press, 1997.
References
1910s births
1979 deaths
Recreational mathematicians
Mathematics popularizers
Palindromists
Anagrammatists
English male poets
20th-century English poets
People from Addlestone
People from Weybridge
20th-century English male writers | J. A. Lindon | Physics,Mathematics | 511 |
360,113 | https://en.wikipedia.org/wiki/Constructive%20proof | In mathematics, a constructive proof is a method of proof that demonstrates the existence of a mathematical object by creating or providing a method for creating the object. This is in contrast to a non-constructive proof (also known as an existence proof or pure existence theorem), which proves the existence of a particular kind of object without providing an example. For avoiding confusion with the stronger concept that follows, such a constructive proof is sometimes called an effective proof.
A constructive proof may also refer to the stronger concept of a proof that is valid in constructive mathematics.
Constructivism is a mathematical philosophy that rejects all proof methods that involve the existence of objects that are not explicitly built. This excludes, in particular, the use of the law of the excluded middle, the axiom of infinity, and the axiom of choice, and induces a different meaning for some terminology (for example, the term "or" has a stronger meaning in constructive mathematics than in classical).
Some non-constructive proofs show that if a certain proposition is false, a contradiction ensues; consequently the proposition must be true (proof by contradiction). However, the principle of explosion (ex falso quodlibet) has been accepted in some varieties of constructive mathematics, including intuitionism.
Constructive proofs can be seen as defining certified mathematical algorithms: this idea is explored in the Brouwer–Heyting–Kolmogorov interpretation of constructive logic, the Curry–Howard correspondence between proofs and programs, and such logical systems as Per Martin-Löf's intuitionistic type theory, and Thierry Coquand and Gérard Huet's calculus of constructions.
A historical example
Until the end of 19th century, all mathematical proofs were essentially constructive. The first non-constructive constructions appeared with Georg Cantor’s theory of infinite sets, and the formal definition of real numbers.
The first use of non-constructive proofs for solving previously considered problems seems to be Hilbert's Nullstellensatz and Hilbert's basis theorem. From a philosophical point of view, the former is especially interesting, as implying the existence of a well specified object.
The Nullstellensatz may be stated as follows: If are polynomials in indeterminates with complex coefficients, which have no common complex zeros, then there are polynomials such that
Such a non-constructive existence theorem was such a surprise for mathematicians of that time that one of them, Paul Gordan, wrote: "this is not mathematics, it is theology".
Twenty five years later, Grete Hermann provided an algorithm for computing which is not a constructive proof in the strong sense, as she used Hilbert's result. She proved that, if exist, they can be found with degrees less than
.
This provides an algorithm, as the problem is reduced to solving a system of linear equations, by considering as unknowns the finite number of coefficients of the
Examples
Non-constructive proofs
First consider the theorem that there are an infinitude of prime numbers. Euclid's proof is constructive. But a common way of simplifying Euclid's proof postulates that, contrary to the assertion in the theorem, there are only a finite number of them, in which case there is a largest one, denoted n. Then consider the number n! + 1 (1 + the product of the first n numbers). Either this number is prime, or all of its prime factors are greater than n. Without establishing a specific prime number, this proves that one exists that is greater than n, contrary to the original postulate.
Now consider the theorem "there exist irrational numbers and such that is rational." This theorem can be proven by using both a constructive proof, and a non-constructive proof.
The following 1953 proof by Dov Jarden has been widely used as an example of a non-constructive proof since at least 1970:
CURIOSA
339. A Simple Proof That a Power of an Irrational Number to an Irrational Exponent May Be Rational.
is either rational or irrational. If it is rational, our statement is proved. If it is irrational, proves our statement.
Dov Jarden Jerusalem
In a bit more detail:
Recall that is irrational, and 2 is rational. Consider the number . Either it is rational or it is irrational.
If is rational, then the theorem is true, with and both being .
If is irrational, then the theorem is true, with being and being , since
At its core, this proof is non-constructive because it relies on the statement "Either q is rational or it is irrational"—an instance of the law of excluded middle, which is not valid within a constructive proof. The non-constructive proof does not construct an example a and b; it merely gives a number of possibilities (in this case, two mutually exclusive possibilities) and shows that one of them—but does not show which one—must yield the desired example.
As it turns out, is irrational because of the Gelfond–Schneider theorem, but this fact is irrelevant to the correctness of the non-constructive proof.
Constructive proofs
A constructive proof of the theorem that a power of an irrational number to an irrational exponent may be rational gives an actual example, such as:
The square root of 2 is irrational, and 3 is rational. is also irrational: if it were equal to , then, by the properties of logarithms, 9n would be equal to 2m, but the former is odd, and the latter is even.
A more substantial example is the graph minor theorem. A consequence of this theorem is that a graph can be drawn on the torus if, and only if, none of its minors belong to a certain finite set of "forbidden minors". However, the proof of the existence of this finite set is not constructive, and the forbidden minors are not actually specified. They are still unknown.
Brouwerian counterexamples
In constructive mathematics, a statement may be disproved by giving a counterexample, as in classical mathematics. However, it is also possible to give a Brouwerian counterexample to show that the statement is non-constructive. This sort of counterexample shows that the statement implies some principle that is known to be non-constructive. If it can be proved constructively that the statement implies some principle that is not constructively provable, then the statement itself cannot be constructively provable.
For example, a particular statement may be shown to imply the law of the excluded middle. An example of a Brouwerian counterexample of this type is Diaconescu's theorem, which shows that the full axiom of choice is non-constructive in systems of constructive set theory, since the axiom of choice implies the law of excluded middle in such systems. The field of constructive reverse mathematics develops this idea further by classifying various principles in terms of "how nonconstructive" they are, by showing they are equivalent to various fragments of the law of the excluded middle.
Brouwer also provided "weak" counterexamples. Such counterexamples do not disprove a statement, however; they only show that, at present, no constructive proof of the statement is known. One weak counterexample begins by taking some unsolved problem of mathematics, such as Goldbach's conjecture, which asks whether every even natural number larger than 4 is the sum of two primes. Define a sequence a(n) of rational numbers as follows:
For each n, the value of a(n) can be determined by exhaustive search, and so a is a well defined sequence, constructively. Moreover, because a is a Cauchy sequence with a fixed rate
of convergence, a converges to some real number α, according to the usual treatment of real numbers in constructive mathematics.
Several facts about the real number α can be proved constructively. However, based on the different meaning of the words in constructive mathematics, if there is a constructive proof that "α = 0 or α ≠ 0" then this would mean that there is a constructive proof of Goldbach's conjecture (in the former case) or a constructive proof that Goldbach's conjecture is false (in the latter case). Because no such proof is known, the quoted statement must also not have a known constructive proof. However, it is entirely possible that Goldbach's conjecture may have a constructive proof (as we do not know at present whether it does), in which case the quoted statement would have a constructive proof as well, albeit one that is unknown at present. The main practical use of weak counterexamples is to identify the "hardness" of a problem. For example, the counterexample just shown shows that the quoted statement is "at least as hard to prove" as Goldbach's conjecture. Weak counterexamples of this sort are often related to the limited principle of omniscience.
See also
Constructivism (philosophy of mathematics)
Errett Bishop - author of the book "Foundations of Constructive Analysis".
Non-constructive algorithm existence proofs
Probabilistic method
References
Further reading
J. Franklin and A. Daoud (2011) Proof in Mathematics: An Introduction. Kew Books, , ch. 4
Hardy, G. H. & Wright, E. M. (1979) An Introduction to the Theory of Numbers (Fifth Edition). Oxford University Press.
Anne Sjerp Troelstra and Dirk van Dalen (1988) "Constructivism in Mathematics: Volume 1" Elsevier Science.
External links
Weak counterexamples by Mark van Atten, Stanford Encyclopedia of Philosophy
Mathematical proofs
Constructivism (mathematics) | Constructive proof | Mathematics | 1,977 |
26,530,729 | https://en.wikipedia.org/wiki/Citrate%20test | The citrate test detects the ability of an organism to use citrate as the sole source of carbon and energy.
Principle
Bacteria are inoculated on a medium containing sodium citrate and a pH indicator such as bromothymol blue. The medium also contains inorganic ammonium salts, which are utilized as sole source of nitrogen. Use of citrate involves the enzyme citrate lyase, which breaks down citrate to oxaloacetate and acetate. Oxaloacetate is further broken down to pyruvate and carbon dioxide (CO2). Production of sodium bicarbonate (NaHCO3) as well as ammonia (NH3) from the use of sodium citrate and ammonium salts results in alkaline pH. This results in a change of the medium's color from green (neutral) to blue (alkaline).
Bacterial colonies are picked up from a straight wire and inoculated into slope of Simmons citrate agar and incubated overnight at 37 °C. Inoculating from a broth culture is not recommended because the inoculum would be too heavy. If the organism has the ability to use citrate, the medium usually changes its color from green to blue, though growth on the medium even without colour change is considered a positive result. An observation of no growth is a negative result.
Examples:
Escherichia coli: Negative
Klebsiella pneumoniae: Positive
Frateuria aurantia: Positive
References
Chemical tests
Microbiology techniques | Citrate test | Chemistry,Biology | 318 |
18,483,642 | https://en.wikipedia.org/wiki/Health%20hazards%20in%20semiconductor%20manufacturing%20occupations | Health hazards in semiconductor manufacturing occupations are a major issue of occupational hygiene due to the chemical hazards required to produce semiconductors in the semiconductor industry. The manifestations of exposure to health hazards during the production process often occurs at a low level and the effects of the toxins may take decades to surface.
Use of toxic materials such as arsine, phosphine and others potentially expose workers to health hazards which include cancer, miscarriages and birth defects.
Protective gear issued to workers protects the products and process from contamination by workers but is not designed to protect workers from contamination by the process, products and materials.
The use of vast variety of toxic chemicals in semiconductor manufacturing makes it difficult to evaluate or pin-point the possibilities of contamination.
There is comparatively extremely low rate of physical accidents in the semiconductor industry.
Semiconductor industry has been ranked the top 5% for workplace health and safety among U.S. companies since 1972.
A Scientific Advisory Committee funded by the Semiconductor Industry Association concluded there was no evidence of increased cancer risk to cleanroom workers, although it could not rule out the possibility that circumstances might exist that could result in increased risk.
Impacts of Health Hazards in Semiconductor Manufacturing on Women
Historically, semiconductor fabrication and the production roles involved in creating integrated circuits have often been the role of women. In the 1980s, it was estimated that 68% of tech production jobs (including semiconductor production) were performed by women. In Southeast Asia, one of the largest producers of semiconductors in the world, over 90% of the production jobs were said to be filled by women during this period. Today, the trend of women dominating production roles in the semiconductor industry continues.
Semiconductor fabrication, as previously stated, has a number of adverse impacts on workers' health. However, these effects are realized to a greater extent in female workers then with men. Digital Equipment, one American producer of semiconductors, found that women working in its factories had twice the chance of experiencing a miscarriage as compared to the general population. Subsequently, Bloomberg reported that the parent company behind Digital Equipment initially pledged to remove the teratogens from their manufacturing processes, however instead decided to outsource production to factories abroad where the regulations and public pressure for the use of these chemicals was less significant. Semiconductor producers continually subvert occupational safety and health regulations by operating abroad in countries where these regulations are lax and even nonexistent, which ultimately occurs at the detriment of the primarily female workers producing the chips.
Many semiconductor fabrication plants are associated with causing loss of eyesight and degradation of vision capabilities in workers. One plant in Hong Kong in the 1970s reported that workers over age 25 were called "Grandma" as they were the most susceptible to eyesight damage from the toxic chemicals involved in semiconductor fabrication. These health impacts can often cause workers to leave semiconductor production jobs earlier than expected, yet unable to easily find other jobs after they fully experience the health impacts of semiconductor fabrication in the first place.
References
Semiconductor device fabrication
Occupational hazards | Health hazards in semiconductor manufacturing occupations | Materials_science | 596 |
34,365,849 | https://en.wikipedia.org/wiki/Ornithocheirus%20buenzeli | "Ornithocheirus" buenzeli (often mis-spelled O. bunzeli) is a pterosaur species known from parts of a humerus (upper arm bone) and part of a lower jaw found in late Cretaceous period (Campanian stage) rocks of the Grünbach Formation, Austria. While it has traditionally been classified in the genus Ornithocheirus, it is more likely an azhdarchid, though due to the fragmentary nature of known fossil remains, it is considered a nomen dubium.
References
Late Cretaceous pterosaurs of Europe
Azhdarchoids
Late Cretaceous reptiles of Europe
Nomina dubia
Fossil taxa described in 1871 | Ornithocheirus buenzeli | Biology | 143 |
19,858,569 | https://en.wikipedia.org/wiki/Conrad%20Roland | Conrad Roland (Konrad Roland Lehmann; 1934 – 25 September 2020) was a German architect and pioneer of the construction of space nets (tensile structures), which primarily are to be found as rope climbing frames on playgrounds. In 1978 he designed and constructed the biggest spacenet of the world until today, the Super Four Mast Spacenet, for the Federal Horticultural Show (BUGA).
Life
Roland was born in München. After his final secondary-school examinations, he completed an apprenticeship as a carpenter. From 1954 until 1963 he studied architecture at Technical University of Munich, at the Illinois Institute of Technology in Chicago and at TU Berlin. During his studies from 1959 till 1961 he was an assistant in Mies van der Rohe's office in Chicago.
In 1963 Roland began to work self-employed in Berlin. He mainly compiled studies, projects and documentations on Hanging-houses and Spacenets. The plans for the construction of a sports stadium in Abu Dhabi, which he developed in co-operation with Jörn-Peter Schmidt-Thomsen in the 1960s, won the tendering competition, but has never been realized.
The subject of spatial net architecture was elaborately covered in his book publication Frei Otto – Spannweiten (1965). A scholarship of the Graham Foundation for Advanced Studies in the Fine Arts, Chicago allowed the work of this monograph. In 1967 Roland worked as guest lecturer in Portsmouth; in 1967 and 1969 he held lectures on “Hanging Houses” in Canada and the United States.
From 1970 onwards the architect devoted himself to the development of the Play-Spacenets. His accomplishments concerning this principle of construction have been honoured with several prizes in and outside the country. In 1974 Roland founded the company “Conrad Roland Spielbau”, which planned and constructed rope play equipment and climbing nets from 1974 until 1985. The succeeding corporation COROCORD Raumnetz GmbH has been carrying the initial letters of his name in the corporate name until today.
Already in 1975 the “Super Two Mast Spacenet” came into being for the Federal Horticultural Show (BUGA) in Mannheim, Germany.
For the BUGA in Düsseldorf in 1987 Roland constructed the biggest Spacenet of the world until today, the “Super Four Mast Spacenet” in Südpark Düsseldorf, which is still in use after remedial maintenance in 2007.
Predominantly, the architect developed Spacenets for playgrounds. In his publication, such as the patent specification for “Spatial Networks” in 1974, Conrad Roland revealed the multitude of applicability of the Spacenets: e.g. multi-level sun terraces, trellis, summer houses, beach and exhibition pavilions or as frame structure for exhibition spaces and sales areas, seat and reclining furniture and also work scaffoldings.
Since 1987 Roland lived in Hawaii.
Bibliography
Conrad Roland: Frei Otto – Spannweiten. Ideen und Versuche zum Leichtbau. Ein Werkstattbericht von Conrad Roland. Ullstein, Berlin, Frankfurt/Main und Wien 1965.
References
External links
https://www.saai.kit.edu/bestand/conrad-roland.php
Conrad-Roland-Trust - http://www.tillaly.com/#/en/contact/
Short biography of Conrad Roland on the pages of the company he founded
1937 births
2020 deaths
20th-century German architects
Structural engineers
Tensile architecture
Tensile membrane structures
Technical University of Munich alumni
Illinois Institute of Technology alumni
21st-century German architects | Conrad Roland | Technology,Engineering | 710 |
2,527,086 | https://en.wikipedia.org/wiki/Isotopes%20of%20neon | Neon (10Ne) possesses three stable isotopes: , , and . In addition, 17 radioactive isotopes have been discovered, ranging from to , all short-lived. The longest-lived is with a half-life of . All others are under a minute, most under a second. The least stable is with a half-life of (). See isotopes of carbon for notes about the measurement. Light radioactive neon isotopes usually decay to fluorine or oxygen, while heavier ones decay to sodium.
List of isotopes
|-id=Neon-15
|
| style="text-align:right" | 10
| style="text-align:right" | 5
|
| []
| 2p
|
| (3/2−)
|
|
|-id=Neon-16
|
| style="text-align:right" | 10
| style="text-align:right" | 6
|
| > [< ]
| 2p
|
| 0+
|
|
|-id=Neon-17
| rowspan=4|
| rowspan=4 style="text-align:right" | 10
| rowspan=4 style="text-align:right" | 7
| rowspan=4|
| rowspan=4|
| β+p ()
|
| rowspan=4|1/2−
| rowspan=4|
| rowspan=4|
|-
| β+α ()
|
|-
| β+ ()
|
|-
| β+pα ()
|
|-id=Neon-18
|
| style="text-align:right" | 10
| style="text-align:right" | 8
|
|
| β+
|
| 0+
|
|
|-id=Neon-19
|
| style="text-align:right" | 10
| style="text-align:right" | 9
|
|
| β+
|
| 1/2+
|
|
|-id=Neon-20
|
| style="text-align:right" | 10
| style="text-align:right" | 10
|
| colspan=3 align=center|Stable
| 0+
| 0.9048(3)
| [, ]
|-id=Neon-21
|
| style="text-align:right" | 10
| style="text-align:right" | 11
|
| colspan=3 align=center|Stable
| 3/2+
|
| [, ]
|-id=Neon-22
|
| style="text-align:right" | 10
| style="text-align:right" | 12
|
| colspan=3 align=center|Stable
| 0+
|
| [, ]
|-id=Neon-23
|
| style="text-align:right" | 10
| style="text-align:right" | 13
|
|
| β−
|
| 5/2+
|
|
|-id=Neon-24
|
| style="text-align:right" | 10
| style="text-align:right" | 14
|
|
| β−
|
| 0+
|
|
|-id=Neon-25
|
| style="text-align:right" | 10
| style="text-align:right" | 15
|
|
| β−
|
| 1/2+
|
|
|-id=Neon-26
| rowspan=2|
| rowspan=2 style="text-align:right" | 10
| rowspan=2 style="text-align:right" | 16
| rowspan=2|
| rowspan=2|
| β− ()
|
| rowspan=2|0+
| rowspan=2|
| rowspan=2|
|-
| β−n ()
|
|-id=Neon-27
| rowspan=3|
| rowspan=3 style="text-align:right" | 10
| rowspan=3 style="text-align:right" | 17
| rowspan=3|
| rowspan=3|
| β− ()
|
| rowspan=3|(3/2+)
| rowspan=3|
| rowspan=3|
|-
| β−n ()
|
|-
| β−2n ?
| ?
|-id=Neon-28
| rowspan=3|
| rowspan=3 style="text-align:right" | 10
| rowspan=3 style="text-align:right" | 18
| rowspan=3|
| rowspan=3|
| β− ()
|
| rowspan=3|0+
| rowspan=3|
| rowspan=3|
|-
| β−n ()
|
|-
| β−2n ()
|
|-id=Neon-29
| rowspan=3|
| rowspan=3 style="text-align:right" | 10
| rowspan=3 style="text-align:right" | 19
| rowspan=3|
| rowspan=3|
| β− ()
|
| rowspan=3|(3/2−)
| rowspan=3|
| rowspan=3|
|-
| β−n ()
|
|-
| β−2n ()
|
|-id=Neon-30
| rowspan=3|
| rowspan=3 style="text-align:right" | 10
| rowspan=3 style="text-align:right" | 20
| rowspan=3|
| rowspan=3|
| β− ()
|
| rowspan=3|0+
| rowspan=3|
| rowspan=3|
|-
| β−n ()
|
|-
| β−2n ()
|
|-id=Neon-31
| rowspan=3|
| rowspan=3 style="text-align:right" | 10
| rowspan=3 style="text-align:right" | 21
| rowspan=3|
| rowspan=3|
| β−
|
| rowspan=3|(3/2−)
| rowspan=3|
| rowspan=3|
|-
| β−n ?
| ?
|-
| β−2n ?
| ?
|-id=Neon-32
| rowspan=3|
| rowspan=3 style="text-align:right" | 10
| rowspan=3 style="text-align:right" | 22
| rowspan=3|#
| rowspan=3|
| β−
|
| rowspan=3|0+
| rowspan=3|
| rowspan=3|
|-
| β−n ?
| ?
|-
| β−2n ?
| ?
|-id=Neon-34
| rowspan=3|
| rowspan=3 style="text-align:right" | 10
| rowspan=3 style="text-align:right" | 24
| rowspan=3|#
| rowspan=3|# [> ]
| β− ?
|
| rowspan=3|0+
| rowspan=3|
| rowspan=3|
|-
| β−2n ?
| ?
|-
| β−n ?
| ?
|-
The isotopic composition refers to that in air.
References
Neon
Neon | Isotopes of neon | Chemistry | 1,540 |
27,211,693 | https://en.wikipedia.org/wiki/Anisotropic%20Network%20Model | The Anisotropic Network Model (ANM) is a simple yet powerful tool made for normal mode analysis of proteins, which has been successfully applied for exploring the relation between function and dynamics for many proteins. It is essentially an Elastic Network Model for the Cα atoms with a step function for the dependence of the force constants on the inter-particle distance.
Theory
The Anisotropic Network Model was introduced in 2000 (Atilgan et al., 2001; Doruker et al., 2000), inspired by the pioneering work of Tirion (1996), succeeded by the development of the Gaussian network model (GNM) (Bahar et al., 1997; Haliloglu et al., 1997), and by the work of Hinsen (1998) who first demonstrated the validity of performing EN NMA at residue level. It represents the biological macromolecule as an elastic mass-and-spring network, to explain the internal motions of a protein subject to a harmonic potential. In the network each node is the Cα atom of the residue and the springs represent the interactions between the nodes. The overall potential is the sum of harmonic potentials between interacting nodes. To describe the internal motions of the spring connecting the two atoms, there is only one degree of freedom. Qualitatively, this corresponds to the compression and expansion of the spring in a direction given by the locations of the two atoms. In other words, ANM is an extension of the Gaussian Network Model to three coordinates per atom, thus accounting for directionality.
The network includes all interactions within a cutoff distance, which is the only predetermined parameter in the model. Information about the orientation of each interaction with respect to the global coordinates system is considered within the force constant matrix (H) and allows prediction of anisotropic motions. Consider a sub-system consisting of nodes i and j, let ri = (xi yi zi) and let rj = (xj yj zj) be the instantaneous positions of atoms i and j. The equilibrium distance between the atoms is represented by sijO and the instantaneous distance is given by sij. For the spring between i and j, the harmonic potential in terms of the unknown spring constant γ, is given by:
The second derivatives of the potential, Vij with respect to the components of ri are evaluated at the equilibrium position, i.e. sijO = sij, are
The above is a direct outcome of one of the key underlying assumptions of ANM – that a given crystal structure is an energetic minimum and does not require energy minimization.
The force constant of the system can be described by the Hessian matrix – (second partial derivative of potential V):
Each element Hi,j is a 3 × 3 matrix which holds the anisotropic information regarding the orientation of nodes i,j. Each such sub matrix (or the "super element" of the Hessian) is defined as
Using the definition of the potential, the Hessian can be expanded as
which can then be written as
Here, the force constant matrix, or the hessian matrix H holds information about the orientation of the nodes, but not about the type of the interaction (such as whether the interaction is covalent or non-covalent, hydrophobic or non-hydrophobic, etc.). In addition, the distance between the interacting nodes is not considered directly. To account for the distance between the interactions we can weight each interaction between nodes i, j by the distance sp. The new off-diagonal elements of the Hessian matrix take the below form, where p is an empirical parameter:
The counterpart of the Kirchhoff matrix Γ of the GNM is simply (1/γ) Η in the ANM. Its decomposition yields 3N − 6 non-zero eigenvalues, and 3N − 6 eigenvectors that reflect the respective frequencies and shapes of the individual modes. The inverse of Η, which holds the desired information about fluctuations is composed of N × N super-elements, each of which scales with the 3 × 3 matrix of correlations between the components of pairs of fluctuation vectors. The Hessian, however is not invertible, as its rank is 3N-6 (6 variables responsible to a rigid body motion). In other words, the eigen values corresponding to the rigid motion are 0, resulting in the determinant being 0, making the matrix not invertible. To obtain a pseudo inverse, a solution to the eigenvalue problem is obtained:
The pseudo-inverse is composed of the 3N − 6 eigenvectors and their respective non-zero eigen values, where λi are the eigenvalues of H sorted by their size from small to large and Ui the corresponding eigenvectors. The eigenvectors (the columns of the matrix U) describe the vibrational direction and the relative amplitude in the different modes.
Comparing ANM and GNM
ANM and GNM are both based on an elastic network model. The GNM has proven itself to accurately describe the vibrational dynamics of proteins and their complexes in numerous studies. Whereas the GNM is limited to the evaluation of the mean squared displacements and cross-correlations between fluctuations, the motion being projected to a mode space of N dimensions, the ANM approach permits us to evaluate directional preferences and thus provides 3-D descriptions of the 3N - 6 internal modes.
It has been observed that GNM fluctuation predictions agree better with experiments than those computed with ANM. The higher performance of GNM can be attributed to its underlying potential, which takes account of orientational deformations, in addition to distance changes.
Evaluation of the model
ANM has been evaluated on a large set of proteins to establish the optimal model parameters that achieve the highest correlation with experimental data and its limits of accuracy and applicability. The ANM is evaluated by comparing the fluctuations predicted from theory and those experimentally observed (B-factors deposited in the PDB). During evaluation, the following observations have been made about the models behavior.
ANM shows insensitivity to the choice of cutoff distance within a certain range, like GNM.
Weighting the interactions by distance improves the correlation.
Residue fluctuations in globular proteins are shown to be more accurately predicted, than those in non-globular proteins.
Significant improvement in agreement with experiments is observed with increase in the resolution of the examined structure.
While understanding how the accuracy of the predicted fluctuations is related to solvent accessibilities, the predictions for buried residues are shown to be in significantly better agreement with the experimental data as compared to the solvent-exposed ones.
Polar/charged residues are more accurately predicted than hydrophobic ones, a possible consequence of the involvement of surface hydrophobic residues in crystal contacts.
Applications of ANM
Recent notable applications of ANM where it has proved to be a promising tool for describing the collective dynamics of the bio-molecular system, include the studies of:
- Hemoglobin, by Chunyan et al., 2003.
- Influenza virus Hemagglutinin A, by Isin et al., 2002.
- Tubulin, by Keskin et al., 2002.
- HIV-1 reverse transcriptase complexed with different inhibitors, by Temiz and Bahar, 2002.
- HIV-1 protease, by Micheletti et al., 2004; Vincenzo et al., 2006.
- DNA-polymerase, by Delarue and Sanejouand, 2002.
- Motor proteins, by Zheng and Brooks, 2005; Zheng and Brooks, 2005; Zheng and Doniach, 2003.
- Membrane proteins including potassium channels, by Shrivastava and Bahar, 2006.
- Rhodopsin, by Rader et al., 2004.
- Nicotinic acetylcholine receptor, by Hung et al., 2005; Taly et al., 2005.
- Auxiliary Activity family 9 and Auxiliary Activity family 10 family of lytic polysaccharide monooxygenases by Arora et al.,2019 and a few more.
ANM web servers
The ANM web server developed by Eyal E, Yang LW, Bahar I. in 2006, presents a web-based interface for performing ANM calculations, the main strengths of which are the rapid computing ability and the user-friendly graphical capabilities for analyzing and interpreting the outputs.
Anisotropic Network Model web server.
ANM server.
References
"Anisotropy of fluctuation dynamics of proteins with an elastic network model", A.R. Atilgan et al., Biophys. J. 80, 505 (2001).
"Anisotropic network model: systematic evaluation and a new web interface", Eyal E, Yang LW, Bahar I. Bioinformatics. 22, 2619–2627, (2006)
"Dynamics of proteins predicted by molecular dynamics simulations and analytical approaches: application to alpha-amylase inhibitor", Doruker, P, Atilgan, AR & Bahar, I, Proteins, 15, 512–524, (2000).
Hinsen, K. (1998) "Analysis of domain motions by approximate normal mode calculations", Proteins, 33, 417–429.
Bahar,I. et al. (1997) "Direct evaluation of thermal fluctuations in proteins using a single-parameter harmonic potential". Fold Des, 2, 173–181
Chennubhotla,C. et al. (2005) "Elastic network models for understanding biomolecular machinery: from enzymes to supramolecular assemblies". Phys Biol, 2, pp. 173–180.
Cui,Q. and Bahar,I. (2006) Normal Mode Analysis: Theory and Applications to Biological and Chemical Systems. Chapman & Hall/CRC, Boca Raton, FL.
Arora et al. (2019) "Structural dynamics of lytic polysaccharide monoxygenases reveals a highly flexible substrate binding region". J Mol Graph Model, 88, 1–10.
See also
Gaussian network model
Molecular modelling | Anisotropic Network Model | Chemistry | 2,105 |
974,908 | https://en.wikipedia.org/wiki/Messier%2096 |
Messier 96 (also known as M96 or NGC 3368) is an intermediate spiral galaxy about 31 million light-years away in the constellation Leo.
Observational history and appearance
It was discovered by French astronomer Pierre Méchain in 1781. After communicating his finding, French astronomer Charles Messier confirmed the finding four days later and added it to his catalogue of nebulous objects.
Finding this object is burdensome with large binoculars. Ideal minimum resolution, in a good sky, is via a telescope of aperture, to reveal its halo with a brighter core region.
This complex galaxy is inclined by an angle of about 53° to the line of sight from the Earth, which is oriented at a position angle of 172°.
Properties
It is categorized as a double-barred spiral galaxy with a small inner bulge through the core along with an outer bulge. The nucleus displays a weak level of activity of the LINER2 type. Variations in ultraviolet emission from the core suggest the presence of a supermassive black hole. Estimates for the mass of this object range from to solar masses ().
On May 9, 1998 a supernova was discovered in this galaxy by Mirko Villi. Designated SN 1998bu, this was a Type Ia supernova explosion. It reached maximum brightness on May 21 at about magnitude 11.6, then steadily faded. Observations of the ejecta a year later showed creation of 0.4 solar masses of iron. The spectrum of the supernova remnant confirmed too radioactive 56Co, which decays into 56Fe.
Messier 96 is about the same mass and size as the Milky Way. It is a very asymmetric galaxy; its dust and gas are unevenly spread throughout its weak spiral arms, and its core is just offset from the midpoint of its extremes. Its arms are also asymmetrical, thought to have been influenced by the gravitational pull of other galaxies within its group.
Messier 96 is being studied as part of a survey of 50 nearby galaxies known as the Legacy ExtraGalactic UV Survey (LEGUS), providing an unprecedented view of star formation within the local universe.
M96 group
M96 is the brightest galaxy within the M96 Group, a group of galaxies in Leo, the other Messier objects of which are M95 and M105. To this are added at least nine other galaxies.
This is the nearest group to the Local Group to combine bright spirals and a bright elliptical galaxy (Messier 105).
See also
List of Messier objects
References
External links
NOAO: M96
SEDS: Spiral Galaxy M96
Intermediate spiral galaxies
Messier 096
Messier 096
096
Messier 096
05882
32192
17810320
Discoveries by Pierre Méchain | Messier 96 | Astronomy | 564 |
321,963 | https://en.wikipedia.org/wiki/Riesel%20number | In mathematics, a Riesel number is an odd natural number k for which is composite for all natural numbers n . In other words, when k is a Riesel number, all members of the following set are composite:
If the form is instead , then k is a Sierpiński number.
Riesel problem
In 1956, Hans Riesel showed that there are an infinite number of integers k such that is not prime for any integer n. He showed that the number 509203 has this property, as does 509203 plus any positive integer multiple of 11184810. The Riesel problem consists in determining the smallest Riesel number. Because no covering set has been found for any k less than 509203, it is conjectured to be the smallest Riesel number.
To check if there are k < 509203, the Riesel Sieve project (analogous to Seventeen or Bust for Sierpiński numbers) started with 101 candidates k. As of December 2022, 57 of these k had been eliminated by Riesel Sieve, PrimeGrid, or outside persons. The remaining 42 values of k that have yielded only composite numbers for all values of n so far tested are
23669, 31859, 38473, 46663, 67117, 74699, 81041, 107347, 121889, 129007, 143047, 161669, 206231, 215443, 226153, 234343, 245561, 250027, 315929, 319511, 324011, 325123, 327671, 336839, 342847, 344759, 362609, 363343, 364903, 365159, 368411, 371893, 384539, 386801, 397027, 409753, 444637, 470173, 474491, 477583, 485557, 494743.
The most recent elimination was in April 2023, when 97139 × 218397548 − 1 was found to be prime by Ryan Propper. This number is 5,538,219 digits long.
As of January 2023, PrimeGrid has searched the remaining candidates up to n = 14,900,000.
Known Riesel numbers
The sequence of currently known Riesel numbers begins with:
509203, 762701, 777149, 790841, 992077, 1106681, 1247173, 1254341, 1330207, 1330319, 1715053, 1730653, 1730681, 1744117, 1830187, 1976473, 2136283, 2251349, 2313487, 2344211, 2554843, 2924861, ...
Covering set
A number can be shown to be a Riesel number by exhibiting a covering set: a set of prime numbers that will divide any member of the sequence, so called because it is said to "cover" that sequence. The only proven Riesel numbers below one million have covering sets as follows:
has covering set {3, 5, 7, 13, 17, 241}
has covering set {3, 5, 7, 13, 17, 241}
has covering set {3, 5, 7, 13, 19, 37, 73}
has covering set {3, 5, 7, 13, 19, 37, 73}
has covering set {3, 5, 7, 13, 17, 241}.
The smallest n for which k · 2n − 1 is prime
Here is a sequence for k = 1, 2, .... It is defined as follows: is the smallest n ≥ 0 such that is prime, or −1 if no such prime exists.
2, 1, 0, 0, 2, 0, 1, 0, 1, 1, 2, 0, 3, 0, 1, 1, 2, 0, 1, 0, 1, 1, 4, 0, 3, 2, 1, 3, 4, 0, 1, 0, 2, 1, 2, 1, 1, 0, 3, 1, 2, 0, 7, 0, 1, 3, 4, 0, 1, 2, 1, 1, 2, 0, 1, 2, 1, 3, 12, 0, 3, 0, 2, 1, 4, 1, 5, 0, 1, 1, 2, 0, 7, 0, 1, ... . The first unknown n is for that k = 23669.
Related sequences are (not allowing n = 0), for odd ks, see or (not allowing n = 0).
Simultaneously Riesel and Sierpiński
A number both Riesel and Sierpiński is a Brier number. The five smallest known examples (and note that some might be smaller, i.e. that the sequence might not be comprehensive) are: 3316923598096294713661, 10439679896374780276373, 11615103277955704975673, 12607110588854501953787, 17855036657007596110949, ... ().
The dual Riesel problem
The dual Riesel numbers are defined as the odd natural numbers k such that |2n - k| is composite for all natural numbers n. There is a conjecture that the set of this numbers is the same as the set of Riesel numbers. For example, |2n - 509203| is composite for all natural numbers n, and 509203 is conjectured to be the smallest dual Riesel number.
The smallest n which 2n - k is prime are (for odd ks, and this sequence requires that 2n > k)
2, 3, 3, 39, 4, 4, 4, 5, 6, 5, 5, 6, 5, 5, 5, 7, 6, 6, 11, 7, 6, 29, 6, 6, 7, 6, 6, 7, 6, 6, 6, 8, 8, 7, 7, 10, 9, 7, 8, 9, 7, 8, 7, 7, 8, 7, 8, 10, 7, 7, 26, 9, 7, 8, 7, 7, 10, 7, 7, 8, 7, 7, 7, 47, 8, 14, 9, 11, 10, 9, 10, 8, 9, 8, 8, ...
The odd ks which k - 2n are all composite for all 2n < k (the de Polignac numbers) are
1, 127, 149, 251, 331, 337, 373, 509, 599, 701, 757, 809, 877, 905, 907, 959, 977, 997, 1019, 1087, 1199, 1207, 1211, 1243, 1259, 1271, 1477, ...
The unknown values of ks are (for which 2n > k)
1871, 2293, 25229, 31511, 36971, 47107, 48959, 50171, 56351, 63431, 69427, 75989, 81253, 83381, 84491, ...
Riesel number base b
One can generalize the Riesel problem to an integer base b ≥ 2. A Riesel number base b is a positive integer k such that gcd(k − 1, b − 1) = 1. (if gcd(k − 1, b − 1) > 1, then gcd(k − 1, b − 1) is a trivial factor of k×bn − 1 (Definition of trivial factors for the conjectures: Each and every n-value has the same factor)) For every integer b ≥ 2, there are infinitely many Riesel numbers base b.
Example 1: All numbers congruent to 84687 mod 10124569 and not congruent to 1 mod 5 are Riesel numbers base 6, because of the covering set {7, 13, 31, 37, 97}. Besides, these k are not trivial since gcd(k + 1, 6 − 1) = 1 for these k. (The Riesel base 6 conjecture is not proven, it has 3 remaining k, namely 1597, 9582 and 57492)
Example 2: 6 is a Riesel number to all bases b congruent to 34 mod 35, because if b is congruent to 34 mod 35, then 6×bn − 1 is divisible by 5 for all even n and divisible by 7 for all odd n. Besides, 6 is not a trivial k in these bases b since gcd(6 − 1, b − 1) = 1 for these bases b.
Example 3: All squares k congruent to 12 mod 13 and not congruent to 1 mod 11 are Riesel numbers base 12, since for all such k, k×12n − 1 has algebraic factors for all even n and divisible by 13 for all odd n. Besides, these k are not trivial since gcd(k + 1, 12 − 1) = 1 for these k. (The Riesel base 12 conjecture is proven)
Example 4: If k is between a multiple of 5 and a multiple of 11, then k×109n − 1 is divisible by either 5 or 11 for all positive integers n. The first few such k are 21, 34, 76, 89, 131, 144, ... However, all these k < 144 are also trivial k (i. e. gcd(k − 1, 109 − 1) is not 1). Thus, the smallest Riesel number base 109 is 144. (The Riesel base 109 conjecture is not proven, it has one remaining k, namely 84)
Example 5: If k is square, then k×49n − 1 has algebraic factors for all positive integers n. The first few positive squares are 1, 4, 9, 16, 25, 36, ... However, all these k < 36 are also trivial k (i. e. gcd(k − 1, 49 − 1) is not 1). Thus, the smallest Riesel number base 49 is 36. (The Riesel base 49 conjecture is proven)
We want to find and proof the smallest Riesel number base b for every integer b ≥ 2. It is a conjecture that if k is a Riesel number base b, then at least one of the three conditions holds:
All numbers of the form k×bn − 1 have a factor in some covering set. (For example, b = 22, k = 4461, then all numbers of the form k×bn − 1 have a factor in the covering set: {5, 23, 97})
k×bn − 1 has algebraic factors. (For example, b = 9, k = 4, then k×bn − 1 can be factored to (2×3n − 1) × (2×3n + 1))
For some n, numbers of the form k×bn − 1 have a factor in some covering set; and for all other n, k×bn − 1 has algebraic factors. (For example, b = 19, k = 144, then if n is odd, then k×bn − 1 is divisible by 5, if n is even, then k×bn − 1 can be factored to (12×19n/2 − 1) × (12×19n/2 + 1))
In the following list, we only consider those positive integers k such that gcd(k − 1, b − 1) = 1, and all integer n must be ≥ 1.
Note: k-values that are a multiple of b and where k−1 is not prime are included in the conjectures (and included in the remaining k with color if no primes are known for these k-values) but excluded from testing (Thus, never be the k of "largest 5 primes found"), since such k-values will have the same prime as k / b.
Conjectured smallest Riesel number base n are (start with n = 2)
509203, 63064644938, 9, 346802, 84687, 408034255082, 14, 4, 10176, 862, 25, 302, 4, 36370321851498, 9, 86, 246, 144, 8, 560, 4461, 476, 4, 36, 149, 8, 144, 4, 1369, 134718, 10, 16, 6, 287860, 4, 7772, 13, 4, 81, 8, 15137, 672, 4, 22564, 8177, 14, 3226, 36, 16, 64, 900, 5392, 4, 6852, 20, 144, 105788, 4, 121, 13484, 8, 187258666, 9, ...
See also
Sierpiński number
Woodall number
Experimental mathematics
BOINC
PrimeGrid
References
Sources
External links
PrimeGrid
The Riesel Problem: Definition and Status
The Prime Glossary: Riesel number
List of primes of the form: k*2^n-1, k<300
List of primes of the form: k*2^n-1, k<300, Project Riesel Prime Search
Riesel and Proth Prime Database
Analytic number theory
Unsolved problems in number theory
Prime numbers | Riesel number | Mathematics | 2,944 |
27,164,904 | https://en.wikipedia.org/wiki/Expressive%20Intelligence%20Studio | The Expressive Intelligence Studio is a research group at the University of California, Santa Cruz, established to conduct research in the field of game design technology. The studio is currently being run by Michael Mateas and Noah Wardrip-Fruin, who work closely with the students in their research.
History
When Michael Mateas formed the group back in 2006, his goal was to "stretch the students into being creative." He did not want the game design program at UCSC to be "just about photo-realistic graphics." Instead he wanted to form an ambitious group of students that grabbed the attention of the gaming industry. According to Noah Wardrip-Fruin, a major benefit for establishing the Expressive Intelligence Studio at UCSC is its proximity to Silicon Valley, where many game companies are located. In 2011, UCSC was listed 7th on Princeton Review's list of top graduate game design programs.
Research
Most of the research done by the Expressive Intelligence Studio is done through major research projects, and focuses primarily on video game AI. PhD students in the program work closely with the advisors on these projects, which have a wide range of topics. Some of these topics include automated support for game generation, automatic generation of autonomous character conversations, story management, and authoring tools for interactive storytelling. This type of research in the field of game design is only being done in a small number of other institutions, such as Massachusetts Institute of Technology, University of Southern California, and Georgia Institute of Technology. According to Mateas, however, the program at the University of California, Santa Cruz Expressive Intelligence Studio strikes a balance between technology and design.
The studio has released several playable games based on research ideas, including Prom Week, the only university-produced finalist in the 2012 Independent Games Festival.
Example EISbot
The EISbot software (short for Expressive Intelligence Studio Bot) is an example for a human-level artificial intelligence which can play Starcraft. It was developed in 2010 for the Conference on Artificial Intelligence and Interactive Digital Entertainment (AIIDE). The AIIDE Starcraft AI Competition is about a game playing agent, who has to win against a human player. EISbot was realized as an agent architecture, which contains submodules for reactive planning, machine learning and case-based reasoning. The reactive planner is the core of EISbot and was realized with A Behavior Language (ABL), which is an action language similar to STRIPS. The behaviors are planned with so called managers who are responsible for subgoals like production, income, tactics and scouting behavior.
See also
Game studies
Interactive storytelling
New media studies
New Media
New Media Art
Game artificial intelligence
References
External links
Expressive Intelligence Studio Blog at UC Santa Cruz
University of California, Santa Cruz
Video game organizations
Video game studies
Game artificial intelligence | Expressive Intelligence Studio | Mathematics | 558 |
5,772,442 | https://en.wikipedia.org/wiki/Karl%20W.%20Giberson | Karl Willard Giberson (born May 13, 1957) is a Canadian physicist, scholar, and author, specializing in the creation–evolution debate (see Creation–evolution controversy). He has held a teaching post since 1984, written several books, and been a member of various academic and scientific organizations. He formerly served as vice president of the BioLogos Foundation.
Education
Giberson holds two bachelor's degrees (in philosophy and in physics/math) from Eastern Nazarene College, and both a master's degree and a PhD in physics from Rice University.
Career
Giberson was a member of the faculty at his alma mater, Eastern Nazarene College, from 1984 to 2011. In that time, he taught courses on physics, astronomy, and science and religion, as well as directing the Honors Scholar Program. His strong support for evolution made him increasingly controversial and played a role in his departure in 2011.
Giberson is also a fellow of the American Scientific Affiliation (ASA). He co-directed the Venice Summer School on Science and Religion, and has lectured on science and religion at Oxford University, the Ettore Majorana Foundation and Centre for Scientific Culture in Sicily, and various colleges and universities in the United States. In 2006, he was invited to speak at the Vatican on "America's Ongoing Hostility to Darwinism" and at the Harvard Club of New York City in 2008.
In early 2009, Giberson became the Executive Vice President of The BioLogos Foundation, founded by Francis Collins. He served briefly as president before leaving the foundation in 2011 to further pursue his passion for writing.
In 2012, Giberson became a faculty member at Stonehill College in Easton, Massachusetts, where he is a scholar-in-residence in science and religion.
In 2013, Giberson was elected to the International Society for Science and Religion (ISSR).
Published works
Giberson is a contributing editor to Books & Culture, where he has published many essays on science. He was the founding editor of Science & Theology News, the leading publication in the field until it ceased publication in 2006, and editor-in-chief of Science & Spirit from 2003 to 2006 for the John Templeton Foundation.
Giberson has published over two hundred articles, reviews, and essays, both technical and popular. In addition to blogging regularly at the Huffington Post, Giberson has written for The New York Times, Salon.com, Discover, Perspectives on Science & Faith, CNN.com, Quarterly Review of Biology, Weekly Standard, Christian History, Christianity Today, Zygon, USA Today and other publications. He has appeared on many radio shows including NPR's Talk of the Nation.
His essay "Say it Ain't So: America's Ongoing Hostility to Religion" appears in the college reader What Matters in America.
Books
Worlds Apart: The Unholy War between Religion and Science, (Church of the Nazarene and Beacon Hill Press, 1993) has, despite controversy, been used at various Nazarene and other evangelical colleges to counter Christian Fundamentalist approaches to "origins".
Species of Origins: America’s Search for a Creation Story (Rowman & Littlefield Publishers, 2002), coauthored with Don Yerxa, garnered recognition as one of the most balanced treatments of the creation–evolution controversy in print. America's leading scholar of creationism, Ronald Numbers, described it as "accessible, accurate, and even-handed." It is used as a textbook and has been translated into Polish for an inclusion in a contemporary philosophy series.
The Oracles of Science: Celebrity Scientists Versus God and Religion (Oxford University Press, 2006), co-authored with Spanish philosopher Mariano Artigas, examines the purported "abuse of science" in the service of secularism by six scientists of this generation: Carl Sagan, Stephen Jay Gould, E.O. Wilson, Richard Dawkins, Steven Weinberg, and Stephen Hawking. The book has been translated into Italian, Spanish and Polish.
Saving Darwin: How to be a Christian and Believe in Evolution (HarperOne, 2008), was recognized by the Washington Post Book World as "One of the best books of 2008."
The Language of Science and Faith: Straight Answers to Genuine Questions (InterVarsity Press, 2011),<ref>Karl Giberson and Francis Collins, "The Language of Science and Faith: Straight Answers to Genuine Questions, InverVarsity Press, 2011 </ref> coauthored with Francis Collins, aims to show Christians why they need not reject science nor God.Quantum Leap: How John Polkinghorne Found God in Science and Religion (Lion UK, 2011), coauthored with Dean Nelson, examines the science-and-religion relationship through the lens of the life of physicist and Anglican priest John Polkinghorne.The Anointed: Evangelical Truth in a Secular Age (Harvard University Press, 2011) coauthored with Randall J. Stephens, explores how intellectual authority is applied and misapplied in Evangelicalism. The authors wrote an op-ed for The New York Times summarizing some of the issues that the book raises.The Wonder of the Universe: Hints of God in Our Fine-Tuned World (IVP Books, 2012), is an exploration of the religious resonances of our modern understanding of cosmology.Seven Glorious Days: A Scientist Retells the Genesis Creation Story (Paraclete Press, 2012), explores what the Biblical creation story would look like if it were written within the framework of modern science.Saving the Original Sinner: How Christians Have Used the Bible's First Man to Oppress, Inspire, and Make Sense of the World'' (Beacon Press, 2015), explains how the idea of the Biblical Adam has evolved throughout the ages and explores the influence that the fall of Adam has had on Western ideas. Giberson contends that the attempts of Evangelical Christians to preserve a literal interpretation of the Biblical creation story have contributed to them becoming intellectually isolated in a variety of fields.
References
External links
KarlGiberson.com
Video (with mp3 available) of discussion about religion and God with Giberson and Robert Wright on Bloggingheads.tv
Living people
American male writers
Eastern Nazarene College alumni
Eastern Nazarene College faculty
Rice University alumni
Canadian evangelicals
1957 births
Theistic evolutionists | Karl W. Giberson | Biology | 1,301 |
1,511,686 | https://en.wikipedia.org/wiki/S%C3%A2nzian%C4%83 | Sânziană is the Romanian name for gentle fairies who play an important part in local folklore, also used to designate the Galium verum or Cruciata laevipes flowers. Under the plural form Sânziene, the word designates an annual festival in the fairies' honor. Etymologically, the name comes from the Latin Sancta Diana, the Roman goddess of the hunt and moon, also celebrated in Roman Dacia (ancient Romania). Diana was known to be the virgin goddess and looked after virgins and women. She was one of the three maiden goddesses, Diana, Minerva and Vesta, who swore never to marry.
People in the western Carpathian Mountains celebrate the Sânziene holiday annually, on June 24. This is similar to the Swedish Midsummer holiday, and is believed to be a pagan celebration of the summer solstice in June. According to the official position of the Romanian Orthodox Church, the customs actually relate to the celebration of Saint John the Baptist's Nativity, which also happens on June 24.
Sânziene rituals
The folk practices of Sânziene imply that the most beautiful maidens in the village dress in white and spend all day searching for and picking flowers, of which one MUST be Galium verum (Lady's bedstraw or Yellow bedstraw) which in Romanian is also named "Sânziànă". Using the flowers they picked during the day, the girls braid floral crowns which they wear upon returning to the village at nightfall. There they meet with their beloved and they dance around a bonfire. The crowns are thrown over the houses, and whenever the crown falls, it is said that someone will die in that house; if the crown stays on the roof of the house, then good harvest and wealth will be bestowed upon the owners. As with other bonfire celebrations, jumping over the embers after the bonfire is not raging anymore is done to purify the person and also to bring health.
Another folk belief is that during the Sânziene Eve night, the heavens open up, making it the strongest night for magic spells, especially for the love spells. Also it is said that the plants harvested during this night will have tremendous magical powers.
It is not a good thing though to be a male and walk at night during Sanziene Eve night, as that is the time when the fairies dance in the air, blessing the crops and bestowing health on people - they do not like to be seen by males, and whoever sees them will be maimed, or the fairies will take their hearing/speech or make them mad.
In some areas of the Carpathians, the villagers then light a big wheel of hay from the ceremonial bonfire and push it down a hill. This has been interpreted as a symbol for the setting sun (from the solstice to come and until the midwinter solstice, the days will be getting shorter).
In cultural references
The consequences of heavens opening on Sânziene are connected by some to paranormal events reported during that period of each year. According to popular beliefs, strange things, both positive and negative, may happen to a person wandering alone on Sânziene night. Strange ethereal activities are believed to happen especially in places such as the Băneasa forest (near the capital of Bucharest) or the Baciu forest (near the city of Cluj-Napoca).
Mircea Eliade's novel, Noaptea de Sânziene (translated as The Forbidden Forest), includes references to the folk belief about skies opening at night, as well as to paranormal events happening in the Băneasa Forest.
In the form Sânziana ("the sânziană"), the word has also come to be used as a female name. It is notably used as such in Vasile Alecsandri's comedy Sânziana şi Pepelea (later an opera by George Stephănescu).
The fairy Sânziene, "the fairy of the summer solstice", is described in a colinda (Romanian folk song) as the "sister of the Sun".
Moldovan band Zdob şi Zdub recorded a song called Sânziene, which tells the story of a search for one's soulmate throughout a midsummer night festival.
See also
Diana (mythology)
Ileana Cosânzeana
Rusalii
References
Further reading
Details about the Sânziene tradition
Details about the Sânziene tradition from the National Museum of Romanian History
External links
Sânziene in Enciclopedia Dacica
Sânziene picture and description
Sânziene celebrated at the National Museum of Romanian History
Fairies
Festivals in Romania
Saint John's Day
June observances
Romanian legendary creatures
Romanian words and phrases
Female legendary creatures
Nature spirits
Summer solstice | Sânziană | Astronomy | 971 |
56,885,735 | https://en.wikipedia.org/wiki/International%20Lunar%20Observatory | The International Lunar Observatory (ILO) is a private scientific and commercial lunar mission by the International Lunar Observatory Association (ILOA Hawai'i) of Kamuela, Hawaii to place a permanent observatory near the South Pole of the Moon to conduct astrophysical studies using an optical telescope and possibly an antenna dish. The mission aims to prove a conceptual design for a lunar observatory that would be reliable, low cost, and fast to implement. A precursor mission, ILO-X consisting of two small imagers (totaling less than 0.6 kg), launched on 15 February 2024 aboard the Intuitive Machines IM-1 mission to the Moon south pole region. It is hoped to be a technology precursor to a future observatories on the Moon, and other commercial initiatives.
The ILO-1 mission is being organized by the International Lunar Observatory Association and the Space Age Publishing Company. It was planned to be launched in 2008 with development by SpaceDev, and was first delayed to 2013. The prime contractors originally were Moon Express, providing the MX-1E lander, and Canadensys Aerospace, providing the optical telescope system. The estimated cost in 2004 was of US$50 million.
Overview
The ILO-1 mission, was later scheduled to be launched in July 2020 with an Electron rocket from New Zealand. The mission was called Moon Express Lunar Scout, and it would have used the MX-1E lander to deliver the observatory on top of the Malapert Mountain, a 5 km tall peak in the Aitken Basin region that has an uninterrupted direct line of sight to Earth, which facilitates communications any time. The original launch of the MX-1E lander with an Electron rocket was cancelled sometime before February 2020; no launch date or launch rocket for the MX-1E has been since announced, leaving the status of it unknown. The ILO-1 flagship payload, and its back up ILO-2, is still being advanced through work by Canadensys Aerospace Corporation (March 2024) while ILOA seeks a different landing provider and partner to land on Malapert Mountain. ILO-1 or ILO-2 may fly with Intuitive Machines to the Moon South Pole region in late 2024 aboard IM-2, or fly with other international or national lunar missions currently under development.
The small robotic ILO-1 observatory is designed to withstand the long lunar nights so it is expected to operate for a few years. Moon Express would have also utilized the mission to explore the Moon's South Pole for mineral resources including water ice. The original plan for the ILO-1 included an optical portion of the system is a Schmidt–Cassegrain telescope. That optical system uses a 7 cm diameter lens, with an 18 cm focal plane, a 13 cm f/5.6 aperture, and 6.4-megapixel resolution. The telescope system would have been "about the size of a shoe-box" with a mass of approximately 2 kg. As of 2024, the instruments for ILO-1 and ILO-2 are under consideration which main goals being astronomy from the Moon and imaging the Milky Way Galaxy Center.
Some collaborators include the National Astronomical Observatory of China (NAOC), Indian Space Research Organisation (ISRO), the newly formed Southeast Asia Principal Operating Partnership, and others.
ILO-X precursor
An ILO-X Precursor instruments were launched on the Intuitive Machines Nova-C IM-1 mission on 15 February 2024. IM-1 landed on the Moon on 22 February, about halfway through the lunar day. Since the lander is unprotected from the cold lunar night, it was only expected to operate until sunset, about seven earth days. ILO-X includes both wide-field and narrow-field imaging systems. The narrow field-of-view imager was named "Ka 'Imi" (To Search) after a student won the Moon Camera Naming Contest held statewide in Hawai'i from March-May 2022. There was an auction to name the wide field-of-view instrument which closed 22 March 2024 and resulted in the winning name Lunar Codex being proposed and accepted. ILOA released its first images from the ILO-X wide field-of-view imager to the public on 29 February 2024 which included one image taken during Deorbit, Descent and Landing (DDL) on 22 February 2024 about 4.2 minutes prior to touchdown which occurred 23:24 UTC, and another image post-landing taken at about 00:30 UTC on 25 February 2024 which shows portions of the lunar landscape, regolith / dust, the Sun, and the IM-1 Odysseus lunar lander. The company received a total of 9 high-resolution and 105 thumbnail images from the ILO-X imagers, but the mission did not fulfill its main astronomy mission goals to capture images of the Milky Way Galaxy or stars in the celestial sky due to off-nominal pointing of the lander.
Objective
The mission's objective is to conduct astrophysical observations from the surface of the Moon, whose lack of atmosphere eliminates much of the need for costly adaptive optics technology. Also, since the Moon's days (about fourteen Earth days) have a dark sky, it allows for nonstop astronomical observations. Disadvantages include micrometeorite impacts, cosmic and solar radiation, lunar dust, and temperature shifts as large as 350 °C. The mission aims to acquire images of galaxies, stars, planets, the Moon and Earth. The project will promote commercial access to the telescope use to schools, scientists and the public at large through the Internet.
See also
List of artificial objects on the Moon
List of missions to the Moon
Lunar Ultraviolet Cosmic Imager, a proposed lunar-based telescope
References
External links
ILO-X and ILO-X Commercial Missions at Canadyensis Aerospace
Photo of the telescope.
History of Lunar-Based Astronomy at Space Age Publishing Co.
Missions to the Moon
Space telescopes
Spacecraft instruments
2020s in spaceflight | International Lunar Observatory | Astronomy | 1,233 |
46,199,120 | https://en.wikipedia.org/wiki/Jan%20Kratochv%C3%ADl | Jan Kratochvíl (born 10 February 1959) is a Czech mathematician and computer scientist whose research concerns graph theory and intersection graphs.
Kratochvíl was born on 10 February 1959 in Prague. He studied at Charles University in Prague, earning a master's degree in 1983 and a Ph.D. in 1987; his dissertation, supervised by Jaroslav Nešetřil, combined graph theory with coding theory. He remained at Charles University as a faculty member, earned his habilitation in 1995, and was promoted to full professor in 2003. From 2003 to 2011 he chaired the department of applied mathematics at Charles University, and from 2012 to 2020 he was the dean of the Faculty of Mathematics and Physics there.
Kratochvíl was the program chair and organizer of the 7th International Symposium on Graph Drawing, in 1999. From 2002 to 2010 he was president of the Czech Mathematical Society. Since March 2021, Kratochvíl is editor-in-chief of Elsevier's Computer Science Review (Impact Factor: 7.7), together with Giuseppe Liotta and Jaroslav Nešetřil.
References
External links
Home page
Google scholar profile
1959 births
Living people
Czech computer scientists
20th-century Czech mathematicians
21st-century Czech mathematicians
Graph theorists
Graph drawing people
Charles University alumni
Academic staff of Charles University
Czechoslovak mathematicians | Jan Kratochvíl | Mathematics | 264 |
4,707,595 | https://en.wikipedia.org/wiki/Iskradata%201680 | Iskradata 1680 was a computer developed by the Iskradata in 1979. Its manufacturer was Iskra Ljubljana. It was the recipient of the IF Product Design Award in 1981.
References
Microcomputers
Computer-related introductions in 1979 | Iskradata 1680 | Technology | 51 |
11,439,473 | https://en.wikipedia.org/wiki/Septoria%20selenophomoides | Septoria selenophomoides is a fungal plant pathogen infecting orchids. It causes leaf spots, starting with small yellowish lesions on the plant's leaves and darkening to brown or black. If the infection develops further, the leaves and fruit fall from the orchid and spread the infection.
References
selenophomoides
Fungal plant pathogens and diseases
Orchid diseases
Fungi described in 1955
Fungus species | Septoria selenophomoides | Biology | 82 |
27,957,076 | https://en.wikipedia.org/wiki/Bite%20inhibition | Bite inhibition, sometimes referred to as a soft mouth (a term which also has a distinct meaning), is a behavior in carnivorans (dogs, cats, etc.) whereby the animal learns to moderate the strength of its bite. It is an important factor in the socialization of pets.
Bite inhibition is typically learned as part of juvenile play behaviors, when the animal is still in the company of its mother and siblings: by biting each other during play, the young animals learn that biting a companion too strongly leads to the abrupt termination of play activities.
Bite inhibition is an important factor in the socialization of pets because many breeds do not innately have the ability to moderate the strength of their bites. In addition to its role in domestication, bite inhibition is also a significant part of the development of dominance hierarchy in wild animals such as wolves.
Evolution of bite inhibition in modern dogs
Modern dogs learn bite inhibition for the same reason that their ancestors, the wolves, did: in order to establish an effective dominance hierarchy. It allows for tranquility in large groups when each individual knows its place. Dominance hierarchies may be formed in groups of canines through intense displays of aggression. However, this type of vying for dominance has only been observed in forced groupings of captive wolves. In the wild, this trend is less common, as wolves tend to group off into family units instead of unrelated adults. Therefore, the alpha male and alpha female would simply be the parents, and the offspring would submit readily. Bite inhibition, then, naturally occurs as the pups learn not to bite their siblings and parents too hard.
Lorenz vs. Schenkel: Interpreting canine aggression
Austrian scientist Konrad Lorenz explains that the inferior animal shows its most vulnerable part to the superior animal as an act of submission. The superior animal could, in theory, kill the other immediately, but instead shows mercy to the inferior animal. Submission was thought to reduce losses for an animal that knows it cannot challenge the other.
A few years later, this idea was challenged by Rudolf Schenkel, who suggests that, contrary to Lorenz's beliefs, the inferior dog is the one with his jaws open near to the superior's neck. The superior canine remains growling and his posture is erect, as though to prepare for an attack. Schenkel suggests that the bite inhibition in this instance is shown by the inferior to show that he does not dare to bite the superior.
Chemicals involved in aggression
Testosterone has a major effect on aggression in animals. Dogs with excess testosterone are found to act out violently, and are far less likely to practice bite inhibition, especially without proper training.
In observations of a wild population of gray wolves, or canis lupus, levels of adrenal glucocorticoid (GCs) were found to be elevated in dominant wolves. GCs affect the stress responses in vertebrates, redirecting energy from systems such as the digestive and reproductive to the senses and heart to eliminate immediate threats.
However, while short-term increases in GCs can be beneficial under stress, long-term increases are harmful to health, as GCs contribute to immune and reproductive system suppression, as well as loss in muscle mass. Therefore, being a dominant individual in the pack has a high cost (and high benefit), while accepting subordination is low cost-low benefit.
Catecholamines, such as epinephrine, or adrenaline, norepinephrine, and dopamine, also have effects on aggression. An increase in catecholamines assist with the body's fight-or-flight response by increasing blood flow to the muscles, decreasing pain sensitivity, and improving attention. Dogs with higher levels of these chemicals tend to be more aggressive, because they are more ready to fight.
Soft mouth
The term "soft mouth" is used by breeders and users of hunting dogs to refer to a behavioral tendency to pick up, hold, and carry quarry gently. It is not a preferred characteristic of terriers and ratters, who are expected to roughly shake and mangle pests such as rats and snakes in order to kill them quickly and efficiently. It is desirable in gundogs such as retrievers and spaniels which are expected to produce quarry intact and in good condition, and is a notoriously difficult behavior to teach to a dog without an inborn temperament to do so. As a result, breeders and users of gun dogs arrived on this term to describe a characteristic important to this enterprise. Dog breeds known for producing more soft-mouthed individuals include Golden Retrievers, Labrador Retrievers, Cocker Spaniels, Poodles, and Gordon Setters, but in any litter some individuals may be much less soft-mouthed than others, as there may be relatively soft-mouthed individuals in a litter of even classically hard-mouthed breeds such as Jack Russell Terriers or Mastiffs.
Training
Bite inhibition is typically learned as part of juvenile play behaviors, when the animal is still in the company of its mother and siblings: by biting each other during play, the young animals learn that biting a companion too strongly leads to the abrupt termination of play activities. This behavior is crucial later in life, as well, when dogs need to maintain the carefully constructed dominance hierarchies. Therefore, a useful method for training a puppy or dog to monitor the strength of its bite would simply be to ignore the dog immediately after the incident occurs. This way, the dog learns that harmful biting will lead to punishment.
A dog's first instinct to unpleasant stimulus is not a bite. A dog will use several techniques to stop a perceived threat before resorting to biting. Therefore, it is important to avoid suppressing important canine communications such as growling and snarling. If a dog learns that a growl is an inappropriate response to a threat, then humans may be encountered with an unexpected bite when they accidentally, for example, step on the dog's tail. Even a dog that would never bite out of anger can snap when met with a painful or threatening stimulus, so training in bite inhibition can be useful to keep them from accidentally hurting another dog or human.
References
Ethology
Dog training and behavior | Bite inhibition | Biology | 1,261 |
12,658,744 | https://en.wikipedia.org/wiki/Paul%20Boltwood | Paul Boltwood (1943 – September 25, 2017) was a Canadian amateur astronomer. He was engaged in developing hardware and software for deep sky imaging and in research of brightness variations in active galactic nuclei. He was also acknowledged for his studies of near-nucleus activity in Comet Hyakutake.
Early life, personal life and education
Paul Boltwood was born in Vancouver, British Columbia in 1943. He first became interested in astronomy around age 12 and had built his own telescope by age 15.
He received a bachelor's degree in mathematics from the University of British Columbia in 1966. He pursued a career in computer software and systems design, with an emphasis on signal and image processing.
Boltwood died on September 25, 2017, aged 73 or 74, in Stittsville, Ontario.
Astronomy
Paul Boltwood founded Boltwood Systems Corporation in 1980, which manufactured cloud sensors for amateur astronomers.
In the early 1990s, he constructed an observatory in his backyard near Ottawa, Ontario, with a CCD camera of his own design. He used the observatory to perform long-term monitoring of several blazars (active galactic nuclei with relativistic jets), including the objects OJ 287 and 3C 66A. His observations were used professional astronomers and he is listed as the co-author of several scientific journal articles.
He made a series of images of the nucleus of the comet Hyakutake, which were released as part of the short film Comet Odyssey.
In 1998, Boltwood won the Sky & Telescope magazine Deep Field Challenge. The contest, proposed by professional astronomer Bradley Schaefer, challenged amateur astronomers to take the deepest image of a designed patch of the sky in the constellation Serpens. Using 20 hours of exposure time on his 16-inch telescope and custom software to add the resulting 767 images together, Boltwood achieved a limiting magnitude of 24.1, a result comparable with those seen in professional observatories. His photo was featured as the Astronomy Picture of the Day on April 14, 1999.
Awards and recognition
In 1995, he was awarded the Chant Medal of the Royal Astronomical Society of Canada. This medal is awarded, not more than once a year, to an amateur astronomer resident in Canada on the basis of the value of the work carried out in astronomy and closely allied fields of the original investigation.
In 2000, he was awarded with the Amateur Achievement Award of the Astronomical Society of the Pacific.
Asteroid 8785 Boltwood was named in his honour.
Selected publications
References
Amateur astronomers
20th-century Canadian astronomers
21st-century Canadian astronomers
1943 births
2017 deaths | Paul Boltwood | Astronomy | 520 |
16,885,228 | https://en.wikipedia.org/wiki/United%20States%20military%20aircraft%20serial%20numbers | In the United States, all military aircraft display a serial number to identify individual aircraft. These numbers are located on the aircraft tail, so they are sometimes referred to unofficially as "tail numbers". On the Northrop Grumman B-2 Spirit bomber, lacking a tail, the number appears on the nose gear door. Individual agencies have each evolved their own system of serial number identification. Aircraft serials are part of the Aircraft Visual Identification System, which also includes the aircraft's tail code and Modex.
History
United States Army Signal Corps
In 1908, the United States government purchased its first heavier than air aircraft. The aircraft, a Wright Model A, was used by the aviation section of the United States Army Signal Corps and was issued with serial number 1. Subsequent aircraft were numbered in sequence.
United States Army Air Service
In 1918, the aviation section of the Army Air Service became the United States Army Air Service (USAAS), but the sequence of numbers started in 1908 continued without change. In 1920, the USAAS became independent from the Signal Corps, and by 1921 the sequence had reached 68000. On 1 July 1921, a new serial system was introduced that was based on the United States Fiscal Year, which continues to the present day. For example, the first aircraft to be procured with the fiscal year 1960 funds was a Boeing B-52H serialized 60-001.
United States Army Air Corps
In 1926, when the USAAS became the United States Army Air Corps (USAAC), the sequence continued unchanged.
United States Army Air Forces
In late June 1941, when the USAAC became the United States Army Air Forces (USAAF), the sequence continued unchanged, and the displayed number, normally shown on the fixed vertical stabilizer's sides, usually omitted the first digit of the year of the contract issuance.
United States Air Force
In 1947, when the USAAF became the United States Air Force (USAF), the sequence continued unchanged. Although USAF was independent of the Army, Army aircraft continued to be allocated in the same numeric sequence until 1967.
United States Army
In 1967, the United States Army continued to use the fiscal year serials, but the numeric element was started at 15000 for each year. In 1971, the sequence was started at 20000 and was not restarted with each fiscal year.
United States Navy and Marine Corps
In 1911, the United States Navy (USN) purchased its first aircraft, a Curtiss Triad pusher floatplane. The Navy allocated a prefix for each manufacturer, and the first aircraft was serialized A-1, with A allocated to Curtiss. Different letters were also allocated to the same manufacturer, but for different types of aircraft, for example, Curtiss amphibians were allocated E. In early 1914, the system was changed to a two-letter type/sub-type system, with each having a sequence starting from 1. A was allocated for heavier-than-air types, for example, AB was a flying boat and AX was an amphibian. All surviving aircraft from the original system were resealed.
In 1917, the individual number sequences were stopped, and a combined sequential numerical system was started at number 51. Prefix letters were retained for a short time, but in 1917 they were replaced with the single letter A for an aeroplane. The numbers were official designating numbers, but became known as Bureau Numbers (BuNos) due to their assignment by the Navy Bureau of Aeronautics. In 1930, the service ceased using the A prefix; the last such serial was A-9204.
In 1935, when the sequence reached 9999, the sequence was restarted at 0001. At the start of the 1940s, so many aircraft were purchased that surviving aircraft from the first sequence could be confused with second-series aircraft, and the sequence was stopped at 7303.
In 1940, the third sequence was started at 00001 (with five digits). When the third sequence reached 99999, it continued with six digits which continues to date.
United States Coast Guard
In 1926, the United States Coast Guard purchased its own aircraft, and they were assigned one or two-digit serial numbers. In 1934, the system was changed to a three-digit number with the first digit indicating an aircraft type. In 1936, this was changed again, and all aircraft (including those withdrawn from use) were allocated serials starting with V101. In 1945, the V prefix was removed and replaced with digit 1 to make four-digit serial numbers, which continues to the present. Since 1969, executive aircraft operated for the Secretary of the Treasury were assigned their own sequence beginning with 1.
Presentation (Army/Air Force)
The early Army aircraft had large black serials marked on the fin or rudder, and in 1917 it was usual to prefix the serial with SC for signal corps, or later AS for aerial service. Later, the prefixes were not always marked and were eventually dropped. From 1942, the serial number was applied to the fin (or boom if a helicopter) — alternatively, the North American A-36 Apache usually had its serial showing on the fuselage instead — with the first digit of the fiscal year being omitted. The serial would not be allowed to be less than four digits (for example B-45 serial number 47-007 was marked 7007), but there was no upper limit (for example YP-59A 42-108783 was marked as 2108783).
When the original fiscal year of a serial became ten years earlier than the current fiscal year, the tail number was often prefixed with a zero, for example, 0-16717 instead of 16717 for UH-1H fiscal serial . This was for disambiguation purposes, to avoid confusion with tail numbers for later fiscal years. The practice was generally abandoned in the 1980s. The notion that it was O for Obsolete is a widespread myth.
In 1956, the fin serials were changed from a minimum of four digits to five digits and in 1957 all serials were limited to five digits (for example KC-135R 58-0001 is marked as 80001). The system is still in use. An aircraft in the first 10 units purchased in the fiscal year is often referred to as "Balls-(number)" – for example, NASA's B-52B, the oldest B-52 in service until its retirement, was known as Balls 8. Aircraft that use the tactical style of marking (for example AF80 020 to the left and below the wing tail code) are also referred to as 'balls'. This is a combination of the two consecutive zeros, one from the last digit in the build year and the other from the first digit in the aircraft number.
In 1969, camouflaged tactical aircraft were marked with a modified presentation with the fiscal year followed by the last three digits of the serial number. Also, the letters AF were often added as a prefix or nearby.
Whatever the serial presentation on the fin, the full fiscal serial is always presented in a technical data block, which is normally on the port (left) side near the cockpit. Often a portion of the aircraft serial number is also painted on the aircraft nose (as is done with helicopters) or on the nose landing gear door (as is done on fighters and bombers) to help ground and aircrew personnel speedily identify a certain aircraft as it approaches while taxiing into or out of parking spots or elsewhere around an airfield.
Presentation (Navy and Marine Corps)
Each Navy and Marine Corps aircraft normally has its Bureau Number plus the type designation marked in small letters on the rear fuselage. Sometimes the last four digits of the serial are painted on the fuselage or vertical stabilizer fin. Sometimes the last three digits are used as the side codes also known as nose numbers or MODEXs (most commonly in the USN P-3C Orion and P-8A Poseidon fleet), but on most operational aircraft this is normally a squadron assigned code instead of a shortened serial number.
See also
Buzz number
Tail code
United Kingdom military aircraft registration number
Notes
Bibliography
Andrade, John M. 1979. US Military Aircraft Designations and Serials since 1909. Midland Counties Publications
External links
Joe Baugher – USAF Serial Listing
Joe Baugher – USN Serial listing
Bureau Numbers of Naval Aircraft
Aircraft markings
Military aircraft designation systems
Serial numbers
United States military aircraft | United States military aircraft serial numbers | Mathematics | 1,695 |
33,529,756 | https://en.wikipedia.org/wiki/Cloud-computing%20comparison | The following is a comparison of cloud-computing software and providers.
IaaS (Infrastructure as a service)
Providers
General
SaaS (Software as a Service)
General
Supported hosts
Supported guests
PaaS (Platform as a service)
Providers
Providers on IaaS
PaaS providers which can run on IaaS providers ("itself" means the provider is both PaaS and IaaS):
References
Cloud computing
Cloud platforms
Computing comparisons | Cloud-computing comparison | Technology | 84 |
64,414,445 | https://en.wikipedia.org/wiki/Ethinylandrostenediol | Ethinylandrostenediol (developmental code name SKF-2856), also known as 17α-ethynyl-5-androstenediol, is a synthetic estrogen, progestogen, and androgen which was never marketed. It is the C17α ethynyl derivative of the androgen precursor and prohormone 5-androstenediol.
Ethinylandrostenediol was first synthesized in the late 1930s and along with its close analogue ethisterone (17α-ethynyltestosterone) was one of the first progestins (synthetic progestogens) to be developed. Ethinylandrostenediol is orally active similarly to ethisterone and shows about half its progestogenic potency. Ethinylandrostenediol was an intermediate in the initial synthesis of ethisterone.
Ethinylandrostenediol shows tissue selectivity in its estrogenic effects in animals and doesn't seem to have estrogenic effects in the uterus. The androgenic activity of ethinylandrostenediol is weak.
An ester of ethinylandrostenediol, ethandrostate (17α-ethynyl-5-androstenediol 3β-cyclohexylpropionate), has been studied clinically in men and women with prostate cancer and breast cancer, respectively.
Notable structural analogues of ethinylandrostenediol include 5-androstenediol, 17α-ethynyl-3β-androstanediol, 17α-ethynyl-3α-androstanediol, ethisterone (17α-ethynyltestosterone), and methandriol (17α-methyl-5-androstenediol), as well as ethinylestradiol (17α-ethynylestradiol or 17α-ethynylestra-1,3,5(10)-triene-3,17β-diol).
References
Abandoned drugs
Ethynyl compounds
Anabolic–androgenic steroids
Androstanes
Antigonadotropins
Diols
Sex hormone esters and conjugates
Progestogens
Synthetic estrogens | Ethinylandrostenediol | Chemistry | 503 |
569,850 | https://en.wikipedia.org/wiki/Roller%20chain | Roller chain or bush roller chain is the type of chain drive most commonly used for transmission of mechanical power on many kinds of domestic, industrial and agricultural machinery, including conveyors, wire- and tube-drawing machines, printing presses, cars, motorcycles, and bicycles. It consists of a series of short cylindrical rollers held together by side links. It is driven by a toothed wheel called a sprocket. It is a simple, reliable, and efficient means of power transmission.
Sketches by Leonardo da Vinci in the 16th century show a chain with a roller bearing. In 1800, James Fussell patented a roller chain on development of his balance lock and in 1880 Hans Renold patented a bush roller chain.
Construction
There are two types of links alternating in the bush roller chain. The first type is inner links, having two inner plates held together by two sleeves or bushings upon which rotate two rollers. Inner links alternate with the second type, the outer links, consisting of two outer plates held together by pins passing through the bushings of the inner links. The "bushingless" roller chain is similar in operation though not in construction; instead of separate bushings or sleeves holding the inner plates together, the plate has a tube stamped into it protruding from the hole which serves the same purpose. This has the advantage of removing one step in assembly of the chain.
The roller chain design reduces friction compared to simpler designs, resulting in higher efficiency and less wear. The original power transmission chain varieties lacked rollers and bushings, with both the inner and outer plates held by pins which directly contacted the sprocket teeth; however this configuration exhibited extremely rapid wear of both the sprocket teeth and the plates where they pivoted on the pins. This problem was partially solved by the development of bushed chains, with the pins holding the outer plates passing through bushings or sleeves connecting the inner plates. This distributed the wear over a greater area; however the teeth of the sprockets still wore more rapidly than is desirable, from the sliding friction against the bushings. The addition of rollers surrounding the bushing sleeves of the chain and provided rolling contact with the teeth of the sprockets resulting in excellent resistance to wear of both sprockets and chain as well. There is even very low friction, as long as the chain is sufficiently lubricated. Continuous, clean, lubrication of roller chains is of primary importance for efficient operation, as is correct tensioning.
Lubrication
Many driving chains (for example, in factory equipment, or driving a camshaft inside an internal combustion engine) operate in clean environments, and thus the wearing surfaces (that is, the pins and bushings) are safe from precipitation and airborne grit, many even in a sealed environment such as an oil bath. Some roller chains are designed to have o-rings built into the space between the outside link plate and the inside roller link plates. Chain manufacturers began to include this feature in 1971 after the application was invented by Joseph Montano while working for Whitney Chain of Hartford, Connecticut. O-rings were included as a way to improve lubrication to the links of power transmission chains, a service that is vitally important to extending their working life. These rubber fixtures form a barrier that holds factory applied lubricating grease inside the pin and bushing wear areas. Further, the rubber o-rings prevent dirt and other contaminants from entering inside the chain linkages, where such particles would otherwise cause significant wear.
There are also many chains that have to operate in dirty conditions, and for size or operational reasons cannot be sealed. Examples include chains on farm equipment, bicycles, and chain saws. These chains will necessarily have relatively high rates of wear.
Many oil-based lubricants attract dirt and other particles, eventually forming an abrasive paste that will compound wear on chains. This problem can be reduced by use of a "dry" PTFE spray, which forms a solid film after application and repels both particles and moisture.
Motorcycle chain lubrication
Chains operating at high speeds comparable to those on motorcycles should be used in conjunction with an oil bath. For modern motorcycles this is not possible, and most motorcycle chains run unprotected. Thus, motorcycle chains tend to wear very quickly relative to other applications. They are subject to extreme forces and are exposed to rain, dirt, sand and road salt.
Motorcycle chains are part of the drive train to transmit the motor power to the back wheel. Properly lubricated chains can reach an efficiency of 98% or greater in the transmission. Unlubricated chains will significantly decrease performance and increase chain and sprocket wear.
Two types of aftermarket lubricants are available for motorcycle chains: spray on lubricants and oil drip feed systems.
Spray lubricants may contain wax or PTFE. While these lubricants use tack additives to stay on the chain they can also attract dirt and sand from the road and over time produce a grinding paste that accelerates component wear.
Oil drip feed systems continuously lubricate the chain and use light oil that does not stick to the chain. Research has shown that oil drip feed systems provide the greatest wear protection and greatest power saving.
Variants
If the chain is not being used for a high wear application (for instance if it is just transmitting motion from a hand-operated lever to a control shaft on a machine, or a sliding door on an oven), then one of the simpler types of chain may still be used. Conversely, where extra strength but the smooth drive of a smaller pitch is required, the chain may be "siamesed"; instead of just two rows of plates on the outer sides of the chain, there may be three ("duplex"), four ("triplex"), or more rows of plates running parallel, with bushings and rollers between each adjacent pair, and the same number of rows of teeth running in parallel on the sprockets to match. Timing chains on automotive engines, for example, typically have multiple rows of plates called strands.
Roller chain is made in several sizes, the most common American National Standards Institute (ANSI) standards being 40, 50, 60, and 80. The first digits indicate the pitch of the chain in eighths of an inch, with the last digit being 0 for standard chain, 1 for lightweight chain, and 5 for bushed chain with no rollers. Thus, a chain with half-inch pitch is a No. 40 while a No. 160 sprocket has teeth spaced 2 inches apart, etc. Metric pitches are expressed in sixteenths of an inch; thus a metric No. 8 chain (08B-1) is equivalent to an ANSI No. 40. Most roller chain is made from plain carbon or alloy steel, but stainless steel is used in food processing machinery or other places where lubrication is a problem, and nylon or brass are occasionally seen for the same reason.
Roller chain is ordinarily hooked up using a master link (also known as a "connecting link"), which typically has one pin held by a horseshoe clip rather than friction fit, allowing it to be inserted or removed with simple tools. Chain with a removable link or pin is also known as "cottered chain", which allows the length of the chain to be adjusted. Half links (also known as "offsets") are available and are used to increase the length of the chain by a single roller. Riveted roller chain has the master link (also known as a "connecting link") "riveted" or mashed on the ends. These pins are made to be durable and are not removable.
Horseshoe clip
A horseshoe clip is the U-shaped spring steel fitting that holds the side-plate of the joining (or "master") link formerly essential to complete the loop of a roller chain. The clip method is losing popularity as more and more chains are manufactured as endless loops not intended for maintenance. Modern motorcycles are often fitted with an endless chain but in the increasingly rare circumstances of the chain wearing out and needing to be replaced, a length of chain and a joining link (with horseshoe clip) will be provided as a spare. Changes in motorcycle suspension are tending to make this use less prevalent.
Common on older motorcycles and older bicycles (e.g. those with hub gears) this clip method cannot be used on bicycles fitted with derailleur gears, as the clip will tend to catch on the gear-changers.
In many cases, an endless chain cannot be replaced easily since it is linked into the frame of the machine (this is the case on the traditional bicycle, amongst other places). However, in some cases, a joining link with horseshoe clip cannot be used or is not preferred in the application either. In this case, a "soft link" is used, placed with a chain riveter and relying solely on friction. With modern materials and tools and skilled application this is a permanent repair having almost the same strength and life of the unbroken chain.
Use
Roller chains are used in low- to mid-speed drives at around 600 to 800 feet per minute; however, at higher speeds, around 2,000 to 3,000 feet per minute, V-belts are normally used due to wear and noise issues.
A bicycle chain is a form of roller chain. Bicycle chains may have a master link, or may require a chain tool for removal and installation. A similar but larger and thus stronger chain is used on most motorcycles although it is sometimes replaced by either a toothed belt or a shaft drive, which offer lower noise level and fewer maintenance requirements.
Some automobile engines use roller chains to drive the camshafts. Very high performance engines often use gear drive, and starting in the early 1960s toothed belts were used by some manufacturers.
Chains are also used in forklifts using hydraulic rams as a pulley to raise and lower the carriage; however, these chains are not considered roller chains, but are classified as lift or leaf chains.
Chainsaw cutting chains superficially resemble roller chains but are more closely related to leaf chains. They are driven by projecting drive links which also serve to locate the chain onto the bar.
A perhaps unusual use of a pair of motorcycle chains is in the Harrier jump jet, where a chain drive from an air motor is used to rotate the movable engine nozzles, allowing them to be pointed downwards for hovering flight, or to the rear for normal forward flight, a system known as "thrust vectoring".
Wear
The effect of wear on a roller chain is to increase the pitch (spacing of the links), causing the chain to grow longer. Note that this is due to wear at the pivoting pins and bushes, not from actual stretching of the metal (as does happen to some flexible steel components such as the hand-brake cable of a motor vehicle).
With modern chains it is unusual for a chain (other than that of a bicycle) to wear until it breaks, since a worn chain leads to the rapid onset of wear on the teeth of the sprockets, with ultimate failure being the loss of all the teeth on the sprocket. The sprockets (in particular the smaller of the two) suffer a grinding motion that puts a characteristic hook shape into the driven face of the teeth. (This effect is made worse by a chain improperly tensioned, but is unavoidable no matter what care is taken). The worn teeth (and chain) no longer provides smooth transmission of power and this may become evident from the noise, the vibration or (in car engines using a timing chain) the variation in ignition timing seen with a timing light. Both sprockets and chain should be replaced in these cases, since a new chain on worn sprockets will not last long. However, in less severe cases it may be possible to save the larger of the two sprockets, since it is always the smaller one that suffers the most wear. Only in very light-weight applications such as a bicycle, or in extreme cases of improper tension, will the chain normally jump off the sprockets.
The lengthening due to wear of a chain is calculated by the following formula:
M = the length of a number of links measured
S = the number of links measured
P = Pitch
In industry, it is usual to monitor the movement of the chain tensioner (whether manual or automatic) or the exact length of a drive chain (one rule of thumb is to replace a roller chain which has elongated 3% on an adjustable drive or 1.5% on a fixed-center drive). A simpler method, particularly suitable for the cycle or motorcycle user, is to attempt to pull the chain away from the larger of the two sprockets, whilst ensuring the chain is taut. Any significant movement (e.g. making it possible to see through a gap) probably indicates a chain worn up to and beyond the limit. Sprocket damage will result if the problem is ignored. Sprocket wear cancels this effect, and may mask chain wear.
Bicycle chain wear
The lightweight chain of a bicycle with derailleur gears can snap (or rather, come apart at the side-plates, since it is normal for the "riveting" to fail first) because the pins inside are not cylindrical, they are barrel-shaped. Contact between the pin and the bushing is not the regular line, but a point which allows the chain's pins to work its way through the bushing, and finally the roller, ultimately causing the chain to snap. This form of construction is necessary because the gear-changing action of this form of transmission requires the chain to both bend sideways and to twist, but this can occur with the flexibility of such a narrow chain and relatively large free lengths on a bicycle.
Chain failure is much less of a problem on hub-geared systems since the chainline does not bend, so the parallel pins have a much bigger wearing surface in contact with the bush. The hub-gear system also allows complete enclosure, a great aid to lubrication and protection from grit.
Chain strength
The most common measure of roller chain's strength is tensile strength. Tensile strength represents how much load a chain can withstand under a one-time load before breaking. Just as important as tensile strength is a chain's fatigue strength. The critical factors in a chain's fatigue strength is the quality of steel used to manufacture the chain, the heat treatment of the chain components, the quality of the pitch hole fabrication of the linkplates, and the type of shot plus the intensity of shot peen coverage on the linkplates. Other factors can include the thickness of the linkplates and the design (contour) of the linkplates. The rule of thumb for roller chain operating on a continuous drive is for the chain load to not exceed a mere 1/6 or 1/9 of the chain's tensile strength, depending on the type of master links used (press-fit vs. slip-fit). Roller chains operating on a continuous drive beyond these thresholds can and typically do fail prematurely via linkplate fatigue failure.
The standard minimum ultimate strength of the ANSI 29.1 steel chain is 12,500 x (pitch, in inches)2.
X-ring and O-Ring chains greatly decrease wear by means of internal lubricants, increasing chain life. The internal lubrication is inserted by means of a vacuum when riveting the chain together.
Chain standards
Standards organizations (such as ANSI and ISO) maintain standards for design, dimensions, and interchangeability of transmission chains. For example, the following table shows data from ANSI standard B29.1-2011 (precision power transmission roller chains, attachments, and sprockets) developed by the American Society of Mechanical Engineers (ASME). See the references for additional information.
For mnemonic purposes, below is another presentation of key dimensions from the same standard, expressed in fractions of an inch (which was part of the thinking behind the choice of preferred numbers in the ANSI standard):
A typical bicycle chain (for derailleur gears) uses narrow -inch-pitch chain. The width of the chain is variable, and does not affect the load capacity. The more sprockets at the rear wheel (historically 3–6, nowadays 7–12 sprockets), the narrower the chain. Chains are sold according to the number of speeds they are designed to work with, for example, "10 speed chain". Hub gear or single speed bicycles use 1/2 x 1/8 inch chains, where 1/8 inch refers to the maximum thickness of a sprocket that can be used with the chain.
Typically chains with parallel shaped links have an even number of links, with each narrow link followed by a broad one. Chains built up with a uniform type of link, narrow at one and broad at the other end, can be made with an odd number of links, which can be an advantage to adapt to a special chainwheel-distance; on the other side such a chain tends to be not so strong.
Roller chains made using ISO standard are sometimes called "isochains".
See also
Self-lubricating chain
References
Bibliography
External links
https://www.leonardodigitale.com/en/browse/Codex-atlanticus/0987-r/
The Complete Guide to Chain
Chain drives
Mechanical power transmission
Mechanical power control | Roller chain | Physics | 3,574 |
12,322,957 | https://en.wikipedia.org/wiki/Monastrol | Monastrol is a cell-permeable small molecule inhibitor discovered by Thomas U. Mayer in the lab of Tim Mitchison. Monastrol was shown to inhibit the kinesin-5 (also known as KIF11, Kinesin Eg5), a motor protein important for spindle bipolarity.
Mechanism of action
Monastrol binds to a long loop that is specific to the Eg5 (also known as KIF11 or kinesin-5) kinesin family, and allosterically inhibits ATPase activity of the kinesin
References
GABAA receptor positive allosteric modulators
GHB receptor agonists
Thioureas
Pyrimidines
3-Hydroxyphenyl compounds | Monastrol | Chemistry | 157 |
9,912,495 | https://en.wikipedia.org/wiki/Simulation%20hypothesis | The simulation hypothesis proposes that what we experience as the world is actually a simulated reality, such as a computer simulation in which we ourselves are constructs. There has been much debate over this topic in the philosophical discourse, and regarding practical applications in computing.
In 2003, philosopher Nick Bostrom proposed the simulation argument, which suggests that if a civilization becomes capable of creating conscious simulations, it could generate so many simulated beings that a randomly chosen conscious entity would almost certainly be in a simulation. The argument presents a trilemma: either such simulations are not created due to technological limitations or self-destruction; or advanced civilizations choose not to create them; or we are almost certainly living in one. This assumes that consciousness is not uniquely tied to biological brains but can arise from any system that implements the right computational structures and processes.
The hypothesis is preceded by many earlier versions, and variations on the idea have also been featured in science fiction, appearing as a central plot device in many stories and films, such as The Matrix (1999).
Origins
Human history is full of thinkers who observed the difference between how things seem and how they might actually be, with dreams, illusions, and hallucinations providing poetic and philosophical metaphors. For example, the "Butterfly Dream" of Zhuangzi from ancient China, or the Indian philosophy of Maya, or in ancient Greek philosophy—Anaxarchus and Monimus likened existing things to a scene-painting and supposed them to resemble the impressions experienced in sleep or madness.
Aztec philosophical texts theorized that the world was a painting or book written by the Teotl.
In the Western philosophical tradition, Plato's allegory of the cave, presented in the 4th century BCE, stands out as an influential example.
René Descartes' evil demon philosophically formalized these epistemic doubts, to be followed by a large literature with subsequent variations like brain in a vat.
In 1969, Konrad Zuse published his book Calculating Space on automata theory, in which he proposes the idea that the universe is fundamentally computational, a concept which became known as digital physics.
Simulation argument
Nick Bostrom's premise:
Bostrom's conclusion:
Expanded argument
Bostrom attempted to assess the probability of our reality being a simulation. His argument states that at least one of the following statements is very likely to be true:
Human civilization or a comparable civilization is unlikely to reach a level of technological maturity capable of producing simulated realities, or such simulations are physically impossible to construct.
A comparable civilization reaching aforementioned technological status will likely not produce a significant number of simulated realities (one that might push the probable existence of digital entities beyond the probable number of "real" entities in a Universe) for any of a number of reasons, such as diversion of computational processing power for other tasks, ethical considerations of holding entities captive in simulated realities, etc.
Any entities with our general set of experiences are almost certainly living in a simulation.
Humans are living in a reality in which post-humans have not developed yet, and current humans are actually living in reality.
Humans will have no way of knowing that they live in a simulation because they will never reach the technological capacity to realize the marks of a simulated reality.
Bostrom's argument rests on the premise that given sufficiently advanced technology, it is possible to represent the populated surface of the Earth without recourse to digital physics; that the qualia experienced by a simulated consciousness are comparable or equivalent to those of a naturally occurring human consciousness, and that one or more levels of simulation within simulations would be feasible given only a modest expenditure of computational resources in the real world.
First, if one assumes that humans will not be destroyed nor destroy themselves before developing such a technology, and that human descendants will have no overriding legal restrictions or moral compunctions against simulating biospheres or their own historical biosphere, then, Bostrom argues it would be unreasonable to count ourselves among the small minority of genuine organisms who, sooner or later, will be vastly outnumbered by artificial simulations.
Epistemologically, it is not impossible for humans to tell whether they are living in a simulation. For example, Bostrom suggests that a window could pop up saying: "You are living in a simulation. Click here for more information". However, imperfections in a simulated environment might be difficult for the native inhabitants to identify and for purposes of authenticity, even the simulated memory of a blatant revelation might be purged programmatically. Nonetheless, should any evidence come to light, either for or against the skeptical hypothesis, it would radically alter the aforementioned probability.
In 2003, Bostrom proposed a trilemma that he called "the simulation argument". Despite its name, the "simulation argument" does not directly argue that humans live in a simulation; instead, it argues that one of three unlikely-seeming propositions is almost certainly true:
"The fraction of human-level civilizations that reach a posthuman stage (that is, one capable of running high-fidelity ancestor simulations) is very close to zero", or
"The fraction of posthuman civilizations that are interested in running simulations of their evolutionary history, or variations thereof, is very close to zero", or
"The fraction of all people with our kind of experiences that are living in a simulation is very close to one".
The trilemma points out that a technologically mature "posthuman" civilization would have enormous computing power; if even a tiny percentage of them were to run "ancestor simulations" (that is, "high-fidelity" simulations of ancestral life that would be indistinguishable from reality to the simulated ancestor), the total number of simulated ancestors, or "Sims", in the universe (or multiverse, if it exists) would greatly exceed the total number of actual ancestors.
Bostrom goes on to use a type of anthropic reasoning to claim that, if the third proposition is the one of those three that is true, and almost all people live in simulations, then humans are almost certainly living in a simulation.
Bostrom claims his argument goes beyond the classical ancient "skeptical hypothesis", claiming that "... we have interesting empirical reasons to believe that a certain disjunctive claim about the world is true", the third of the three disjunctive propositions being that humans are almost certainly living in a simulation. Thus, Bostrom, and writers in agreement with Bostrom such as David Chalmers, argue there might be empirical reasons for the "simulation hypothesis", and that therefore the simulation hypothesis is not a skeptical hypothesis but rather a "metaphysical hypothesis". Bostrom states he personally sees no strong argument as to which of the three trilemma propositions is the true one: "If (1) is true, then we will almost certainly go extinct before reaching posthumanity. If (2) is true, then there must be a strong convergence among the courses of advanced civilizations so that virtually none contains any individuals who desire to run ancestor-simulations and are free to do so. If (3) is true, then we almost certainly live in a simulation. In the dark forest of our current ignorance, it seems sensible to apportion one's credence roughly evenly between (1), (2), and (3)... I note that people who hear about the simulation argument often react by saying, 'Yes, I accept the argument, and it is obvious that it is possibility #n that obtains.' But different people pick a different n. Some think it obvious that (1) is true, others that (2) is true, yet others that (3) is true".
As a corollary to the trilemma, Bostrom states that "Unless we are now living in a simulation, our descendants will almost certainly never run an ancestor-simulation".
Criticism of Bostrom's anthropic reasoning
Bostrom argues that if "the fraction of all people with our kind of experiences that are living in a simulation is very close to one", then it follows that humans probably live in a simulation. Some philosophers disagree, proposing that perhaps "Sims" do not have conscious experiences the same way that unsimulated humans do, or that it can otherwise be self-evident to a human that they are a human rather than a Sim. Philosopher Barry Dainton modifies Bostrom's trilemma by substituting "neural ancestor simulations" (ranging from literal brains in a vat, to far-future humans with induced high-fidelity hallucinations that they are their own distant ancestors) for Bostrom's "ancestor simulations", on the grounds that every philosophical school of thought can agree that sufficiently high-tech neural ancestor simulation experiences would be indistinguishable from non-simulated experiences. Even if high-fidelity computer Sims are never conscious, Dainton's reasoning leads to the following conclusion: either the fraction of human-level civilizations that reach a posthuman stage and are able and willing to run large numbers of neural ancestor simulations is close to zero, or some kind of (possibly neural) ancestor simulation exists.
The hypothesis has received criticism from some physicists, such as Sabine Hossenfelder, who considers that it is physically impossible to simulate the universe without producing measurable inconsistencies, and called it pseudoscience and religion. Cosmologist George F. R. Ellis, who stated that "[the hypothesis] is totally impracticable from a technical viewpoint", and that "late-night pub discussion is not a viable theory". Some scholars categorically reject—or are uninterested in—anthropic reasoning, dismissing it as "merely philosophical", unfalsifiable, or inherently unscientific.
Some critics propose that the simulation could be in the first generation, and all the simulated people that will one day be created do not yet exist, in accordance with philosophical presentism.
The cosmologist Sean M. Carroll argues that the simulation hypothesis leads to a contradiction: if humans are typical, as it is assumed, and not capable of performing simulations, this contradicts the arguer's assumption that it is easy for us to foresee that other civilizations can most likely perform simulations.
Physicist Frank Wilczek raises an empirical objection, saying that the laws of the universe have hidden complexity which is "not used for anything" and the laws are constrained by time and location – all of this being unnecessary and extraneous in a simulation. He further argues that the simulation argument amounts to "begging the question," due to the "embarrassing question" of the nature of the underlying reality in which this universe is simulated. "Okay if this is a simulated world, what is the thing in which it is simulated made out of? What are the laws for that?"
Brian Eggleston has argued that the future humans of our universe cannot be the ones performing the simulation, since the simulation argument considers our universe to be the one being simulated. In other words, it has been argued that the probability that humans live in a simulated universe is not independent of the prior probability that is assigned to the existence of other universes.
Arguments, within the trilemma, against the simulation hypothesis
Some scholars accept the trilemma, and argue that the first or second of the propositions are true, and that the third proposition (the proposition that humans live in a simulation) is false. Physicist Paul Davies uses Bostrom's trilemma as part of one possible argument against a near-infinite multiverse. This argument runs as follows: if there were a near-infinite multiverse, there would be posthuman civilizations running ancestor simulations, which would lead to the untenable and scientifically self-defeating conclusion that humans live in a simulation; therefore, by reductio ad absurdum, existing multiverse theories are likely false. (Unlike Bostrom and Chalmers, Davies (among others) considers the simulation hypothesis to be self-defeating.)
Some point out that there is currently no proof of technology that would facilitate the existence of sufficiently high-fidelity ancestor simulation. Additionally, there is no proof that it is physically possible or feasible for a posthuman civilization to create such a simulation, and therefore for the present, the first proposition must be taken to be true. Additionally there are limits of computation.
Physicist Marcelo Gleiser objects to the notion that posthumans would have a reason to run simulated universes: "...being so advanced they would have collected enough knowledge about their past to have little interest in this kind of simulation. ...They may have virtual-reality museums, where they could go and experience the lives and tribulations of their ancestors. But a full-fledged, resource-consuming simulation of an entire universe? Sounds like a colossal waste of time". Gleiser also points out that there is no plausible reason to stop at one level of simulation, so that the simulated ancestors might also be simulating their ancestors, and so on, creating an infinite regress akin to the "problem of the First Cause".
In 2019, philosopher Preston Greene suggested that it may be best not to find out if we are living in a simulation, since, if it were found to be true, such knowing might end the simulation.
Greene's suggestion is similar to Douglas Adams' humorous idea presented in his 1979 novel The Hitchhiker's Guide to the Galaxy: that if anyone in the Universe should actually work out 'The Meaning of Life, the Universe and Everything', it would instantly disappear and be immediately replaced with something "even more complex and inexplicable".
Economist Robin Hanson argues that a self-interested occupant of a high-fidelity simulation should strive to be entertaining and praiseworthy in order to avoid being turned off or being shunted into a non-conscious low-fidelity part of the simulation. Hanson additionally speculates that someone who is aware that he might be in a simulation might care less about others and live more for today: "your motivation to save for retirement, or to help the poor in Ethiopia, might be muted by realizing that in your simulation, you will never retire and there is no Ethiopia".
Besides attempting to assess whether the simulation hypothesis is true or false, philosophers have also used it to illustrate other philosophical problems, especially in metaphysics and epistemology. David Chalmers has argued that simulated beings might wonder whether their mental lives are governed by the physics of their environment, when in fact these mental lives are simulated separately (and are thus, in fact, not governed by the simulated physics). Chalmers claims that they might eventually find that their thoughts fail to be physically caused, and argues that this means that Cartesian dualism is not necessarily as problematic of a philosophical view as is commonly supposed, though he does not endorse it. Similar arguments have been made for philosophical views about personal identity that say that an individual could have been another human being in the past, as well as views about qualia that say that colors could have appeared differently than they do (the inverted spectrum scenario). In both cases, the claim is that all this would require is hooking up the mental lives to the simulated physics in a different way.
Computationalism
Computationalism is a philosophy of mind theory stating that cognition is a form of computation. It is relevant to the simulation hypothesis in that it illustrates how a simulation could contain conscious subjects, as required by a "virtual people" simulation. For example, it is well known that physical systems can be simulated to some degree of accuracy. If computationalism is correct and if there is no problem in generating artificial consciousness or cognition, it would establish the theoretical possibility of a simulated reality. Nevertheless, the relationship between cognition and phenomenal qualia of consciousness is disputed. It is possible that consciousness requires a vital substrate that a computer cannot provide and that simulated people, while behaving appropriately, would be philosophical zombies. This would undermine Nick Bostrom's simulation argument; humans cannot be a simulated consciousness, if consciousness, as humans understand it, cannot be simulated. The skeptical hypothesis remains intact, however, and humans could still be vatted brains, existing as conscious beings within a simulated environment, even if consciousness cannot be simulated. It has been suggested that whereas virtual reality would enable a participant to experience only three senses (sight, sound and optionally smell), simulated reality would enable all five (including taste and touch).
Some theorists have argued that if the "consciousness-is-computation" version of computationalism and mathematical realism (or radical mathematical Platonism) are true, then consciousness is computation, which in principle is platform independent and thus admits of simulation. This argument states that a "Platonic realm" or ultimate ensemble would contain every algorithm, including those that implement consciousness. Hans Moravec has explored the simulation hypothesis and has argued for a kind of mathematical Platonism according to which every object (including, for example, a stone) can be regarded as implementing every possible computation.
In physics
In physics, the view of the universe and its workings as the ebb and flow of information was first observed by Wheeler. Consequently, two views of the world emerged: the first one proposes that the universe is a quantum computer, while the other one proposes that the system performing the simulation is distinct from its simulation (the universe). Of the former view, quantum-computing specialist Dave Bacon wrote:
In many respects this point of view may be nothing more than a result of the fact that the notion of computation is the disease of our age—everywhere we look today we see examples of computers, computation, and information theory and thus we extrapolate this to our laws of physics. Indeed, thinking about computing as arising from faulty components, it seems as if the abstraction that uses perfectly operating computers is unlikely to exist as anything but a platonic ideal. Another critique of such a point of view is that there is no evidence for the kind of digitization that characterizes computers nor are there any predictions made by those who advocate such a view that have been experimentally confirmed.
Testing the hypothesis physically
A method to test one type of simulation hypothesis was proposed in 2012 in a joint paper by physicists Silas R. Beane from the University of Bonn (now at the University of Washington, Seattle), and Zohreh Davoudi and Martin J. Savage from the University of Washington, Seattle. Under the assumption of finite computational resources, the simulation of the universe would be performed by dividing the space-time continuum into a discrete set of points, which may result in observable effects. In analogy with the mini-simulations that lattice-gauge theorists run today to build up nuclei from the underlying theory of strong interactions (known as quantum chromodynamics), several observational consequences of a grid-like space-time have been studied in their work. Among proposed signatures is an anisotropy in the distribution of ultra-high-energy cosmic rays that, if observed, would be consistent with the simulation hypothesis according to these physicists. In 2017, Campbell et al. proposed several experiments aimed at testing the simulation hypothesis in their paper "On Testing the Simulation Theory".
Reception
Astrophysicist Neil Degrasse Tyson said in a 2018 NBC News interview that he estimated the likelihood of the simulation hypothesis being correct at "better than 50-50 odds", adding "I wish I could summon a strong argument against it, but I can find none". However, in a subsequent interview with Chuck Nice on a YouTube episode of StarTalk, Tyson shared that his friend J. Richard Gott, a professor of astrophysical sciences at Princeton University, made him aware of a strong objection to the simulation hypothesis. The objection claims that the common trait that all hypothetical high-fidelity simulated universes possess is the ability to produce high-fidelity simulated universes. And since our current world does not possess this ability, it would mean that either humans are in the real universe, and therefore simulated universes have not yet been created, or that humans are the last in a very long chain of simulated universes, an observation that makes the simulation hypothesis seem less probable. Regarding this objection, Tyson remarked "that changes my life".
Elon Musk, the CEO of Tesla and SpaceX, stated that the argument for the simulation theory is "quite strong". In a podcast with Joe Rogan, Musk said "If you assume any rate of improvement at all, games will eventually be indistinguishable from reality" before concluding "that it's most likely we're in a simulation". At various other press conferences and events, Musk has also speculated that the likelihood of us living in a simulated reality or computer made by others is about 99.9%, and stated in a 2016 interview that he believed there was "a one in billion chance we're in base reality".
Rizwan Virk, of Massachusetts Institute of Technology is a founder of PlayLabs, and author of the book, "The Simulation Hypothesis". A story about Virk trying on a virtual reality headset and forgetting he was in an empty room makes him wonder if the real world was created by more tech-savvy individuals, other than us.
Other uses in philosophy
Dream argument
There is a long philosophical and scientific history to the underlying thesis that reality is an illusion. This skeptical hypothesis can be traced back to antiquity; for example, to the "Butterfly Dream" of Zhuangzi, or the Indian philosophy of Maya, or in Ancient Greek philosophy Anaxarchus and Monimus likened existing things to a scene-painting and supposed them to resemble the impressions experienced in sleep or madness.
A dream could be considered a type of simulation capable of fooling someone who is asleep. As a result, Bertrand Russell has argued that the "dream hypothesis" is not a logical impossibility, but that common sense as well as considerations of simplicity and inference to the best explanation rule against it. One of the first philosophers to question the distinction between reality and dreams was Zhuangzi, a Chinese philosopher of the 4th century BC. He phrased the problem as the well-known "Butterfly Dream," which went as follows:
Once Zhuangzi dreamt he was a butterfly, a butterfly flitting and fluttering around, happy with himself and doing as he pleased. He didn't know he was Zhuangzi. Suddenly he woke up and there he was, solid and unmistakable Zhuangzi. But he didn't know if he was Zhuangzi who had dreamt he was a butterfly or a butterfly dreaming he was Zhuangzi. Between Zhuangzi and a butterfly there must be some distinction! This is called the Transformation of Things. (2, tr. Burton Watson 1968:49)
The philosophical underpinnings of this argument are also brought up by Descartes, who was one of the first Western philosophers to do so. In Meditations on First Philosophy, he states "... there are no certain indications by which we may clearly distinguish wakefulness from sleep", and goes on to conclude that "It is possible that I am dreaming right now and that all of my perceptions are false".
Chalmers (2003) discusses the dream hypothesis and notes that this comes in two distinct forms:
that he is currently dreaming, in which case many of his beliefs about the world are incorrect;
that he has always been dreaming, in which case the objects he perceives actually exist, albeit in his imagination.
Both the dream argument and the simulation hypothesis can be regarded as skeptical hypotheses. Another state of mind in which some argue an individual's perceptions have no physical basis in the real world is psychosis, though psychosis may have a physical basis in the real world and explanations vary.
In On Certainty, the philosopher Ludwig Wittgenstein has argued that such skeptical hypothesis are unsinnig (i.e. non-sensical), as they doubt knowledge that is required in order to make sense of the hypotheses themselves.
The dream hypothesis is also used to develop other philosophical concepts, such as Valberg's personal horizon: what this world would be internal to if this were all a dream.
Lucid dreaming is characterized as an idea where the elements of dreaming and waking are combined to a point where the user knows they are dreaming, or waking perhaps.
Modern philosophy
A version of the simulation hypothesis was theorized as a part of a philosophical argument on the part of René Descartes, by George Berkeley (1685–1753) with his "immaterialism" (later referred to as subjective idealism by others), and later by Hans Moravec.
René Descartes (1596–1650) and his evil demon concept, sometimes also called his 'evil genius' concept
Aztec philosophical texts theorized that the world was a painting or book written by the Teotl.
Nietzsche, in Beyond Good and Evil chastised philosophers for seeking to find the true world behind the deceptive world of appearances.
It is nothing more than a moral prejudice that truth is worth more than semblance; it is, in fact, the worst proved supposition in the world.... Why might not the world which concerns us—be a fiction?
In popular culture
Science fiction has highlighted themes such as virtual reality, artificial intelligence and computer gaming for more than fifty years.
Simulacron-3 (1964) by Daniel F. Galouye (alternative title: Counterfeit World) tells the story of a virtual city developed as a computer simulation for market research purposes, in which the simulated inhabitants possess consciousness; all but one of the inhabitants are unaware of the true nature of their world. The book was made into a German made-for-TV film called World on a Wire (1973) directed by Rainer Werner Fassbinder and aired on ARD. The film The Thirteenth Floor (1999) was also loosely based on both this book and World on a Wire. "We Can Remember It for You Wholesale" is a short story by American writer Philip K. Dick, first published in The Magazine of Fantasy & Science Fiction in April 1966, and was the basis for the 1990 film Total Recall and its 2012 remake. In Overdrawn at the Memory Bank, a short story made into a 1983 television film, the main character pays to have his mind connected to a simulation.
The same theme was repeated in the 1999 film The Matrix, which depicted a world in which artificially intelligent robots enslaved humanity within a simulation set in the contemporary world. The 2012 play World of Wires was partially inspired by the Bostrom essay on the simulation hypothesis.
The 2012 visual novel Danganronpa 2: Goodbye Despair is set in a simulated reality known as the Neo World Program, which in this instance simulates a class trip to Jabberwock Island which, while initially peaceful, turns into a "killing game" involving the students in the simulation killing each other and trying to not be found guilty. Similarly, 2022's Anonymous;Code explores the idea of the world being a simulation, with an infinite or near-infinite number of "world layers" of simulations running inside other simulations. The main problem with this system is that in some of these "world layers", both above and below the one the characters find themselves living in, the Year 2038 Problem has not been solved, dooming the world to end on January 19, 2038 at 3:14:07 am UTC. The characters have to hack all the way into the highest world layer, the real world that the player lives in, to synchronize all the world layers and solve the Year 2038 problem in all of them.
The 2014 episode of the animated sitcom Rick and Morty, "M. Night Shaym-Aliens!", demonstrates a low-quality simulation that attempts to trap the two titular protagonists, but because the operation is less "realistic" than typically operated "reality", it becomes obvious.
In 2015, Kent Forbes published a documentary named "The Simulation Hypothesis", notably featuring Max Tegmark, Neil degrasse Tyson, Paul Davies and James Gates.
In the 2016 video game No Man's Sky, the universe is a simulated universe run by The Atlas. According to in-game lore, many vastly different iterations of the universe existed, with very different histories and races. As the Atlas AI became more and more corrupted, the universes became more and more similar to each other.
A 2017 episode of the long-running British science fiction series Doctor Who titled "Extremis" features a simulated version of the Twelfth Doctor and his companions. A secret Vatican document describes the truth about the simulated reality by inviting its reader to choose any series of numbers at random. The document lists the same numbers on the next page since the simulated program cannot produce a truly random event. The simulation is finally revealed to be a practice world for aliens intent on real-world domination.
The 2022 Netflix epic period mystery-science fiction 1899 created by Jantje Friese and Baran bo Odar tells the unfinished story of a simulation scenario in which multiple persons find themselves in a circumstance of multiplicities and simultaneities. The storyline involves an amnesia, seemingly to protect the integrity of the simulation, as suggested would be necessary by the philosopher Preston Green.
See also
Calculating Space
Zhuangzi
Advaita Vedanta
Artificial life
Artificial society
Avatamsaka Sutra
Boltzmann brain
Brain in a vat
Computational sociology
Consensus reality
David Icke
Demiurge
Depersonalization-derealization disorder
Digital physics
Interface theory
Experience machine
Fine-tuned universe
Holographic principle
Hyperreality
Margolus–Levitin theorem
Mathematical universe hypothesis
Matrix defense
Maya (religion)
Metaphysics
Metaverse
Mind uploading
Monte Carlo method
Tipler's "Omega point"
OpenWorm, project to simulate the roundworm Caenorhabditis elegans
Perennial philosophy
Phantom time conspiracy theory
Philosophy of artificial intelligence
Philosophy of information
Simulation video game
Social simulation
Theory of knowledge
Virtual reality
Notes
References
Further reading
"Are We Living in a Simulation?" BBC Focus magazine, March 2013, pages 43–45. Interview with physicist Silas Beane of the University of Bonn discussing a proposed test for simulated reality evidence. Three pages, three photos, including one of Beane and a computer-generated scene from the film The Matrix. Publisher: Immediate Media Company, Bristol, UK.
Conitzer, Vincent. "A Puzzle About Further Facts". Open access version of article in Erkenntnis.
Lev, Gid'on. Life in the Matrix. Haaretz Magazine, April 25, 2019, page 6.
Merali, Zeeya. "Do We Live in the Matrix?" Discover, December 2013, pages 24–25. Subtitle: "Physicists have proposed tests to reveal whether we are part of a giant computer simulation".
External links
Are We Living in a Computer Simulation?—Nick Bostrom's Simulation Argument webpage
Arguments in philosophy of mind
Augmented reality
Concepts in epistemology
Concepts in metaphysics
Conspiracy theories
Fiction about virtual reality
Hyperreality
Hypotheses
Internalism and externalism
Limits of computation
Mixed reality
Nick Bostrom
Philosophical debates
Science and technology-related conspiracy theories
Science fiction themes
Thought experiments in philosophy
Virtual reality
Computer simulation | Simulation hypothesis | Physics,Technology | 6,383 |
1,781,347 | https://en.wikipedia.org/wiki/Fusible%20alloy | A fusible alloy is a metal alloy capable of being easily fused, i.e. easily meltable, at relatively low temperatures. Fusible alloys are commonly, but not necessarily, eutectic alloys.
Sometimes the term "fusible alloy" is used to describe alloys with a melting point below . Fusible alloys in this sense are used for solder.
Introduction
Fusible alloys are typically made from low melting metals.
There are 14 low melting metallic elements that are stable for practical handling. These are in 2 distinct groups:
The 5 alkali metals have 1 s electron and melt between +181 (Li) and +28 (Cs) Celsius;
The 9 poor metals have 10 d electrons and from none (Zn, Cd, Hg) to three (Bi) p electrons, they melt between -38 (Hg) and +419 (Zn) Celsius.
From a practical view, low-melting alloys can be divided into the following categories:
Mercury-containing alloys
Only alkali metal-containing alloys
Gallium-containing alloys (but neither alkali metal nor mercury)
Only bismuth, lead, tin, cadmium, zinc, indium, and sometimes thallium-containing alloys
Other alloys (rarely used)
A practical reason here is that the chemical behaviour of alkali metals is very distinct from poor metals. Of the 9 poor metals Hg (mp -38 C) and Ga (mp +29 C) have each their distinct practical issues, and the remaining 7 poor metals from In (mp +156 C) to Zn (mp +419 C) can be viewed together.
Of elements which might be viewed as related but do not share the distinct properties of poor metals:
Po is estimated to melt at 254 C and might be poor metal by properties but is too radioactive (longest halflife 125 years) for practical use;
At same reasoning as Po;
Sb melts at 630 C and is regarded as semimetal rather than poor metal;
Te is also regarded as semimetal not poor metal;
of other metals, next lowest melting point is Pu, but its melting point at 640 Celsius leaves a 220 degree gap between Zn and Pu, thus making the "poor metals" from In to Zn a natural group.
Some reasonably well-known fusible alloys are Wood's metal, Field's metal, Rose metal, Galinstan, and NaK.
Applications
Melted fusible alloys can be used as coolants as they are stable under heating and can give much higher thermal conductivity than most other coolants; particularly with alloys made with a high thermal conductivity metal such as indium or sodium. Metals with low neutron cross-section are used for cooling nuclear reactors.
Such alloys are used for making the fusible plugs inserted in the furnace crowns of steam boilers, as a safeguard in the event of the water level being allowed to fall too low. When this happens the plug, being no longer covered with water, is heated to such a temperature that it melts and allows the contents of the boiler to escape into the furnace. In automatic fire sprinklers the orifices of each sprinkler is closed with a plug that is held in place by fusible metal, which melts and liberates the water when, owing to an outbreak of fire in the room, the temperature rises above a predetermined limit.
Bismuth on solidification expands by about 3.3% by volume. Alloys with at least half of bismuth display this property too. This can be used for mounting of small parts, e.g. for machining, as they will be tightly held.
Low-melting alloys and metallic elements
Well-known alloys
Other alloys
Starting with a table of component elements and selected binary and multiple systems ordered by melting point:
Then organized by practical group and alphabetic symbols of components:
Most of the pairwise phase diagrams of 2 component metal systems have data available for analysis, like at https://himikatus.ru/art/phase-diagr1/diagrams.php
Taking the pairwise alloys of the 7 poor metals other than Hg and Ga, and ordering the pairs (total 21) by alphabetic of these elements Bi, Cd, In, Pb, Sn, Tl, Zn are as follows:
Bi-Cd https://himikatus.ru/art/phase-diagr1/Bi-Cd.php simple eutectic (Bi at 271 C, Cd at 321, eutectic at 146)
Bi-In https://himikatus.ru/art/phase-diagr1/Bi-In.php has ordered phases, eutectic at +72 - in table above
Bi-Pb https://himikatus.ru/art/phase-diagr1/Bi-Pb.php eutectic at +125 - in table above
Bi-Sn https://himikatus.ru/art/phase-diagr1/Bi-Sn.php eutectic at +139 - in table above
Bi-Tl https://himikatus.ru/art/phase-diagr1/Bi-Tl.php an intermetallic alloy and the lower melting eutectic at +188
Bi-Zn https://himikatus.ru/art/phase-diagr1/Bi-Zn.php eutectic at +255
Cd-In https://himikatus.ru/art/phase-diagr1/Cd-In.php eutectic at +128
Cd-Pb https://himikatus.ru/art/phase-diagr1/Cd-Pb.php eutectic at +248
Cd-Sn https://himikatus.ru/art/phase-diagr1/Cd-Sn.php eutectic at +176
Cd-Tl https://himikatus.ru/art/phase-diagr1/Cd-Tl.php eutectic at +204
Cd-Zn https://himikatus.ru/art/phase-diagr1/Cd-Zn.php eutectic at +266
In-Pb https://himikatus.ru/art/phase-diagr1/In-Pb.php is NOT eutectic because Pb solid solution in In only raises melting point
In-Sn https://himikatus.ru/art/phase-diagr1/In-Sn.php eutectic at +120
In-Tl https://himikatus.ru/art/phase-diagr1/In-Tl.php also NOT eutectic because Tl solid solution in In raises melting point
In-Zn https://himikatus.ru/art/phase-diagr1/In-Zn.php eutectic at +143
Pb-Sn https://himikatus.ru/art/phase-diagr1/Pb-Sn.php eutectic at +183 - in table above
Pb-Tl https://himikatus.ru/art/phase-diagr1/Pb-Tl.php also NOT eutectic because the solid solution is higher melting than components
Pb-Zn https://himikatus.ru/art/phase-diagr1/Pb-Zn.php eutectic at +318
Sn-Tl https://himikatus.ru/art/phase-diagr1/Sn-Tl.php eutectic at +168
Sn-Zn https://himikatus.ru/art/phase-diagr1/Sn-Zn.php eutectic at +198 - in table above
Tl-Zn https://himikatus.ru/art/phase-diagr1/Tl-Zn.php eutectic at +292
Considering the binary systems between alkali metals: Li only has appreciable solubility in pair
Li-Na https://himikatus.ru/art/phase-diagr1/Li-Na.php eutectic at +92
The other three alkali metals:
K-Li https://himikatus.ru/art/phase-diagr1/K-Li.php
Li-Rb https://himikatus.ru/art/phase-diagr1/Li-Rb.php
Cs-Li https://himikatus.ru/art/phase-diagr1/Cs-Li.php
practically do not dissolve Li even when liquid and therefore their melting points are not lowered by presence of Li
Na is in liquid phase miscible with all three heavier alkali metals, but on freezing forms intermetallic compounds and eutectics:
K-Na https://himikatus.ru/art/phase-diagr1/K-Na.php eutectic at -12,6 - in table above
Na-Rb https://himikatus.ru/art/phase-diagr1/Na-Rb.php eutectic at -4,5
Cs-Na https://himikatus.ru/art/phase-diagr1/Cs-Na.php eutectic at -31,8
The 3 binary systems between the three heavier alkali metals are all miscible in solid at melting point, but all form poor solid solutions that have melting point minima. This is distinct from eutectic: at eutectic point, two solid phases coexist, and close to eutectic point, the liquidus temperature rises rapidly as just one separates, whereas at poor solid solution melting point minimum, there is a single solid phase, and away from the minimum the liquidus temperature rises only slowly.
K-Rb https://himikatus.ru/art/phase-diagr1/K-Rb.php solid solution minimum mp +34
Cs-K https://himikatus.ru/art/phase-diagr1/Cs-K.php solid solution minimum mp -38 - in table above
Cs-Rb https://himikatus.ru/art/phase-diagr1/Cs-Rb.php solid solution minimum mp +10
See also
Liquid metal
List of elements by melting point
References
Further reading
Weast, R.C., "CRC Handbook of Chemistry and Physics", 55th ed, CRC Press, Cleveland, 1974, p. F-22
External links
Fusible (Low Temp) Alloys
Fusible Alloys. Archived from the original on 2012-10-12.
Jenson, W.B. "Ask the Historian - Onion's fusible alloy"
Coolants | Fusible alloy | Chemistry,Materials_science | 2,272 |
2,934,314 | https://en.wikipedia.org/wiki/Chevalley%E2%80%93Warning%20theorem | In number theory, the Chevalley–Warning theorem implies that certain polynomial equations in sufficiently many variables over a finite field have solutions. It was proved by and a slightly weaker form of the theorem, known as Chevalley's theorem, was proved by . Chevalley's theorem implied Artin's and Dickson's conjecture that finite fields are quasi-algebraically closed fields .
Statement of the theorems
Let be a finite field and be a set of polynomials such that the number of variables satisfies
where is the total degree of . The theorems are statements about the solutions of the following system of polynomial equations
The Chevalley–Warning theorem states that the number of common solutions is divisible by the characteristic of . Or in other words, the cardinality of the vanishing set of is modulo .
The Chevalley theorem states that if the system has the trivial solution , that is, if the polynomials have no constant terms, then the system also has a non-trivial solution .
Chevalley's theorem is an immediate consequence of the Chevalley–Warning theorem since is at least 2.
Both theorems are best possible in the sense that, given any , the list has total degree and only the trivial solution. Alternatively, using just one polynomial, we can take f1 to be the degree n polynomial given by the norm of x1a1 + ... + xnan where the elements a form a basis of the finite field of order pn.
Warning proved another theorem, known as Warning's second theorem, which states that if the system of polynomial equations has the trivial solution, then it has at least solutions where is the size of the finite field and . Chevalley's theorem also follows directly from this.
Proof of Warning's theorem
Remark: If then
so the sum over of any polynomial in of degree less than also vanishes.
The total number of common solutions modulo of is equal to
because each term is 1 for a solution and 0 otherwise.
If the sum of the degrees of the polynomials is less than n then this vanishes by the remark above.
Artin's conjecture
It is a consequence of Chevalley's theorem that finite fields are quasi-algebraically closed. This had been conjectured by Emil Artin in 1935. The motivation behind Artin's conjecture was his observation that quasi-algebraically closed fields have trivial Brauer group, together with the fact that finite fields have trivial Brauer group by Wedderburn's theorem.
The Ax–Katz theorem
The Ax–Katz theorem, named after James Ax and Nicholas Katz, determines more accurately a power of the cardinality of dividing the number of solutions; here, if is the largest of the , then the exponent can be taken as the ceiling function of
The Ax–Katz result has an interpretation in étale cohomology as a divisibility result for the (reciprocals of) the zeroes and poles of the local zeta-function. Namely, the same power of divides each of these algebraic integers.
See also
Combinatorial Nullstellensatz
References
External links
Finite fields
Diophantine geometry
Theorems in algebra | Chevalley–Warning theorem | Mathematics | 644 |
25,421,323 | https://en.wikipedia.org/wiki/Antigen%20retrieval | Antigen retrieval is a non-enzymatic pretreatment for immunostaining to reduce or eliminate the chemical modifications caused by formalin fixation, through high temperature heating or strong alkaline solution (non-heating).
Background
In medicine, most surgically removed tissue samples are fixed in formalin (4% formaldehyde) and embedded in paraffin to preserve the morphology for review by pathologists using stains and microscopy to make a diagnosis. However, formaldehyde can induce chemical modifications that reduce the detectability of proteins (antigens) in immunohistochemistry. Antigen retrieval technique is a non-enzymatic pretreatment for immunostaining to reduce or eliminate these formalin-induced chemical modifications through high temperature heating or strong alkaline solution (non-heating). This process recovers the antigens masked by formalin fixation. As a result, it enables the successful application of immunohistochemistry on formalin fixed paraffin embedded tissue sections. Without antigen retrieval, most immunostains on formalin fixed paraffin embedded tissue sections show no staining.
Antigen retrieval was developed by Dr. Shan-Rong Shi in 1990 and published in 1991. Antigen retrieval techniques (AR) has had a profound impact on medical research and diagnostic pathology, enabling more accurate and reliable staining of tissue samples and improving the diagnostic accuracy of various diseases, including cancer. Antigen retrieval is considered as a milestone in the history of immunohistochemistry. The two primary methods of antigen retrieval are heat-induced AR and non-heating alkaline-induced AR. Both techniques received US patents.
Heat-induced antigen retrieval
Heat-induced antigen retrieval is the most widely used pretreatment in immunohistochemistry for formalin fixed paraffin embedded tissue sections. It requires boiling deparaffinized formalin fixed paraffin embedded tissue sections in either water or various buffer solutions. Due to the limited application of non-heating AR and the prevalence of heat-induced AR, the term "Antigen Retrieval" (AR) is most commonly used to refer to heat-induced AR.
Biochemical studies of the chemical reaction between protein and formalin by Fraenkel—Conrat and co-workers in the 1940s indicated that cross linkages between formalin and protein can be reversed by high-temperature heating or strong alkaline treatment. This observation formed the basis for the development of AR. The mechanism of antigen retrieval is unclear. It believed to reverse cross-links, and allows for restoration of secondary of tertiary structure of the epitope.
Heat-induced antigen retrieval can be performed with microwave ovens, pressure cookers, vegetable steamers, autoclaves, or water baths.
The most important factors for the effectiveness of heat-induced antigen retrieval are the time and temperature of the heating conditions. The chemical composition and pH value of the buffer solution also contribute to the effectiveness of heat-induced antigen retrieval. Thus, the AR-immunohistochemistry protocol must be optimized for each tissue type, fixation method, and antigen using a "test battery" to maximize antigen recovery in formalin fixed paraffin embedded sections.
Non-heating alkaline-induced antigen retrieval
Non-heating alkaline-induced antigen retrieval requires immersing slides in a strong alkaline solution (sodium hydroxide and methanol). It was originally developed for immunostaining on formalin-fixed, routinely acid-decalcified, celloidin-embedded human temporal bone sections. The principle of this method is also based on the study of Fraenkel—Conrat and colleagues as described above. Due to the limited application of non-heating AR, this method is not well-known.
Enzyme digestion
Enzyme digestion, also referred to as protease-induced epitope retrieval by some authors, is an old technique used in immunohistochemistry for formalin fixed paraffin embedded tissue sections before the advent of AR. In enzyme digestion, enzymes such as proteinase K, trypsin, and pepsin are used to restore antibody binding to its epitope. The purported mechanism of action is the cleavage of peptides that mask the epitope, thereby restoring antigenicity.
Disadvantages of enzyme digestion include a low success rate for restoring immunoreactivity and the potential destruction of tissue morphology and the antigen of interest. After the development of AR, enzyme digestion was rarely used in immunohistochemistry for formalin fixed paraffin embedded tissue sections.
Although enzyme digestion and antigen retrieval target the same problem in immunohistochemistry, these two techniques differs in both the mode of action and effectiveness, warranting distinct nomenclature.
Frozen section epitope retrieval
Frozen section epitope retrieval refers to two antigen retrieval methods designed specifically for aldehyde-fixed cryostat frozen tissue sections or cultured cells; the sodium dodecyl sulfate and heating en bloc methods.
The sodium dodecyl sulfate method requires a 5 minute pretreatment using 1% sodium dodecyl sulfate and can produce an increase in staining intensity by immunohistochemistry as well as immunofluorescence.
Heating en bloc takes tissue blocks fixated in paraformaldehyde, heats them in retrieval solutions, and then freezes them using dry ice. Heating is already used in antigen retrieval and has been proven to be widely effective, but previous heating methods have been shown to kill frozen sections. This method proved to enhance immunoreactivity for a wide range of antigens and lower the background staining in some cases.
References
Chemical reactions
Immunohistochemistry
Histology | Antigen retrieval | Chemistry | 1,165 |
5,521,498 | https://en.wikipedia.org/wiki/Araucania%20%28wasp%29 | Araucania is an invalid genus of braconid wasps in the family Braconidae, found in South America. There are at least two described species in Araucania.
The valid genus Araucania Pate 1947, in the family Sapygidae, has nomenclatural precedence over the braconid name, published in 1993, so the latter name must be replaced, following the International Code of Zoological Nomenclature Article 52.2.
Species
Araucania maculipennis Marsh, 1993
Araucania penai Marsh, 1993
References
Further reading
Notes
Parasitic wasps
Braconidae
Hymenoptera of South America | Araucania (wasp) | Biology | 130 |
55,789,686 | https://en.wikipedia.org/wiki/Human%20information%20interaction | Human-information interaction or HII is the formal term for information behavior research in archival science; the term was invented by Nahum Gershon in 1995. HII is not transferable from analog to digital research because nonprofessional researchers greatly emphasize the need for further elaboration of context and scope finding aid elements. Researchers in HII take on many tasks, including helping to design information systems from a biological perspective that conform to the requirements of different segments of society, along with other behaviour intended to improve interaction between humans and information systems. HII is generally considered to be multi-disciplinary as different disciplines have different viewpoints on these interactions and their consequences. HII is considered especially important due to humanity's dependence on information and the technology needed to access it.
References
Information theory
Information science
Interdisciplinary subfields | Human information interaction | Mathematics,Technology,Engineering | 167 |
2,310,294 | https://en.wikipedia.org/wiki/Fetal%20bovine%20serum | Fetal bovine serum (FBS) is the most widely used serum-supplement for the in vitro cell culture of eukaryotic cells. This is due to it having a very low level of antibodies and containing more growth factors, allowing for versatility in many cell culture applications. Fetal bovine serum is derived from the blood drawn from a bovine fetus via a closed system of collection at the slaughterhouse.
The globular protein bovine serum albumin (BSA) is a major component of fetal bovine serum. Besides BSA, fetal bovine serum is a rich source of growth and attachment factors, lipids, hormones, nutrients and electrolytes necessary to support cell growth in culture. It is typically added to basal cell culture medium, such as DMEM or RPMI, at a 5–10% concentration.
Because it is a biological product, FBS is not a fully defined media component, and as such varies in composition between batches. As a result of this and in an attempt to minimize the possibility of transfer of adventitious agents, serum-free and chemically defined media (CDM) have been developed. However, the effectiveness of serum-free media is limited as many cell lines still require serum in order to grow, and many serum-free media formulations can only support the growth of narrowly-defined types of cells.
Production
FBS is a by-product of the meat industry. FBS, as with the vast majority of animal serum used in cell culture, is produced from blood collected at commercial slaughterhouses from cattle that also supply meat intended for human consumption.
The first stage of the production process for FBS is the harvesting of blood from the bovine fetus after the fetus is removed from the slaughtered cow. The fetus dies from the lack of oxygen by remaining in the protective environment of the uterus for a minimum of 15–20 minutes after the cow is dead. The blood is collected aseptically into a sterile container or blood bag and then allowed to clot. The normal method of collection is cardiac puncture. This minimizes the danger of serum contamination with micro-organisms from the fetus itself, and the environment, while maximizing the volume of blood collected. It is then centrifuged to remove the fibrin clot and the remaining blood cells from the clear yellow (straw) colored serum. The serum is frozen prior to further processing that is necessary to make it suitable for cell culture.
The second stage of processing involves filtration, typically using a filtration chain with the final filtration being three sterile 0.1 micron membrane filters. The aseptically processed FBS is subjected to stringent quality control testing and is supplied with a detailed Certificate of Analysis. The certificate gives full test results and information concerning the origin of the serum. Certificates of Analysis vary between commercial suppliers, but each usually includes the following details: filtration statement, country of blood collection, country of manufacture, cell growth performance testing, microbial sterility testing, as well as screening for mycoplasma and virus, endotoxin, hemoglobin, IgG gamma glutamyl transferase and total protein assays. FBS may also be tested for country of collection.
Ethics
Ethical questions have been raised regarding the blood collection process due to the potential suffering caused to the fetus. There has been discussion concerning the methodologies for the collection of fetal bovine serum. The International Serum Industry Association (ISIA) has published literature providing detail on the extensive regulation and processes employed to ensure that serum is collected in an ethical manner. Although the act of slaughter of the dam and the time which passes in the slaughter process prior to harvesting will induce unconsciousness or death of the fetus prior to serum harvesting, it has been postulated that exposure of live unborn calves to oxygen could cause them to gain awareness before being killed, resulting in active debate about the ethics of harvesting serum. While the Industry Association accepts that certain organizations have concerns, they maintain that all collections of serum take place under veterinary supervision in registered slaughterhouses controlled by the competent authority in the country of collection.
Serum use
Fetal bovine serum is commercially available from many manufacturers, and because cells grown in vitro are highly sensitive, customers usually test specific batches to check for suitability for their specific cell type. When changing from batch to batch it is usual to adapt the cells to the new batch of material, for example, by mixing 50% of the old serum with 50% of the new serum and allowing the cells to acclimatize to the new material.
Serum is stored frozen to preserve the stability of components such as growth factors. When serum is thawed, some precipitation may be seen. This is a normal phenomenon, and it does not compromise the quality of serum in any way. The precipitate may be removed by transferring the serum to sterile tubes and centrifuging for 5 minutes at 400 × g. To limit the amount of precipitation, it is recommended that the serum is thawed in a refrigerator at 2-8˚C. The serum should be regularly stirred during this process. Repeated freeze/thaw cycles should be avoided, and it is advisable to dispense the serum into single use aliquots before freezing.
Source history
Serum produced for use in the biotechnology industry and research sectors is highly regulated. The collection and movement of all animal derived products globally is strictly controlled. Veterinary control of animal derived products largely follows the regulations set by the EU (DG SANCO) and the US (USDA). The current regulation governing the importation of animal by-products into the EU is covered by Regulation (EU) 1069/2009 and the implementation document Regulation (EU) 142/2011.
FBS is a product collected worldwide with the main collections being centered in the United States, Australia, New Zealand, Canada, Central America, South America, and Europe.
Global sales
Sales of FBS in 2008 were estimated to be 700,000 liters globally. A 2012 source estimates that about 600,000 liters are made annually, one third of which is suitable for pharmaceutical use under Good Manufacturing Practice. 1 to 3 fetuses are required to produce one liter of serum.
Replacements
Proposed replacements for FBS include:
Bovine ocular fluid, also a byproduct of slaughterhouses. Also contains a variety of mammalian growth factors.
Hydrolyzed sericin, a normally discarded byproduct of silk production. Also supports the growth of skin cells.
Human platelet lysate (HPL), which can be produced from old stock from blood banks. Contains a variety of mammalian growth factors. Human adipose tissue grows better in HPL than in FBS.
Earthworm heat inactivated coelomic fluid, which acts like "blood" in earthworms. Rich in nutrients and growth hormones. Does not contain fibronectin, so an attachment factor must be added.
See also
Chemically defined medium
References
External links
Introduction to Fetal Bovine Serum Class
International Serum Industry Association (ISIA)
Blood
Cattle products
Cell culture reagents | Fetal bovine serum | Chemistry,Biology | 1,452 |
43,216,765 | https://en.wikipedia.org/wiki/Rudder%20%28software%29 | Rudder is an open source audit and configuration management utility to help automate system configuration across large IT infrastructures. Rudder relies on a lightweight local agent installed on each managed machine.
Rudder is produced by Normation, founded in 2010. Its server-side web interface is written in Scala and its local agent is written in C, and are published as free software under the GNU General Public License 3.0.
Features
Host inventory
Feature-complete Web interface
Standardized, reusable policies
Custom Policy editor
Central reporting and historic information for policy applied to hosts
Grouping based on search queries run against inventory
Automatic updating of such groups (dynamic groups)
Dynamic generation of per-host policies (lessens risk of data leaks from shared policy)
Change Request / Validation
REST API
Git backend
History
Rudder was created by the founding team of Normation and first released as free software in October 2011.
Rudder 3.0 was released in February 2015.
Platform support
The following operating systems are supported as a Root server:
Debian Linux 9 and 10
Ubuntu 16.04 LTS, 18.04 LTS and 20.04 LTS
Red Hat Enterprise Linux (RHEL) / CentOS 7 and 8
SUSE Linux Enterprise Server (SLES) 12 et 15
The following operating systems are supported for Rudder Nodes and packages are available for these platforms:
Debian Linux 5 to 10
Ubuntu 10.04 LTS to 20.04 LTS
Red Hat Enterprise Linux (RHEL) / CentOS 3 to 8
SUSE Linux Enterprise Server (SLES) 10 to 15
IBM AIX 5 to 7
Slackware 14
Microsoft Windows Server 2008R2 or higher
See also
CFEngine
Ansible (software)
Bcfg2
Chef (software)
Puppet (software)
Salt (software)
Comparison of open source configuration management software
DevOps
Otter (software)
References
External links
Official website
Configuration management
Virtualization software for Linux
Software using the GNU Affero General Public License
Linux configuration utilities
Linux package management-related software
Unix package management-related software
Remote administration software
Software distribution
Free software programmed in Scala | Rudder (software) | Engineering | 420 |
71,994,467 | https://en.wikipedia.org/wiki/Heinrich%20Leutwyler | Heinrich Leutwyler (born Oct 12, 1938) is a Swiss theoretical physicist, with interests in elementary particle physics, the theory of strong interactions, and quantum field theory.
Early life and education
Leutwyler went to the Gymnasium in Bern and studied physics, mathematics, and astronomy at the University of Bern. After the diploma in 1960 he went to the US, including Princeton. In 1962 he received his PhD under the supervision of John R. Klauder (at Bell Laboratories at the time), for his thesis entitled "Generally covariant Dirac equation and associated Boson Fields."
Career
In 1965 he got his habilitation in Bern, where he became assistant professor in the same year and full professor in 1969, until his retirement in 2000.
In 1983/84 he was dean of the Faculty of Sciences. Leutwyler spent research visits at the Bell Labs in Murray Hill (1963, 1965), at Caltech in Pasadena (1973/74), and at CERN (1969/70, 1983/84, and 1996). Together with Murray Gell-Mann and Harald Fritzsch, Leutwyler was crucially involved in establishing quantum chromodynamics (QCD) as the fundamental theory of strong interactions. Together with Jürg Gasser he performed influential work on chiral perturbation theory, an effective field theory describing QCD at low energies, including the Gasser-Leutwyler coefficients of the effective Lagrangian and the determination of current quark masses.
Leutwyler received an honorary doctorate of the Johannes Gutenberg University Mainz (1995), the Humboldt Award (2000), the Pomeranchuk Prize (2011), and the Sakurai Prize (2023).
Personal life
He is married and has two children.
Publications
Fritzsch, Gellmann, and Leutwyler: Advantages of the color octet gluon picture. In: Physics Letters B, volume 47, 1973, p. 365
Gasser and Leutwyler: Quark masses. In: Physics Reports, volume 87, 1982, p. 77
Gasser and Leutwyler: Chiral Perturbation Theory to One Loop. In: Annals of Physics, volume 158, 1984, p. 142
Gasser and Leutwyler: Chiral Perturbation Theory: Expansions in the Mass of the Strange Quark. In: Nuclear Physics B, volume 250, 1985, p. 465
Leutwyler, On the history of the strong interaction, Erice 2012
References
External links
Webpage at the University of Bern
1938 births
Living people
20th-century American physicists
21st-century American physicists
Swiss physicists
Scientists from Bern
University of Bern alumni
Particle physicists
Humboldt Research Award recipients | Heinrich Leutwyler | Physics | 566 |
10,930,690 | https://en.wikipedia.org/wiki/Finn%20Haldorsen | Finn Haldorsen (5 September 1934 – February 4, 2005) was a Norwegian-born businessman.
Finn Haldorsen was the youngest of 13 children born to Haldor Haldorsen and Anne Serine Haldorsen in
Rubbestadneset, county of Hordaland, Norway. After completing schooling on Bømlo he attended college in Bryne, Norway. Following his military service, he went to work at a steel factory in Manchester, England. He started studying mechanical engineering at the University of Cardiff in Wales. After receiving his honours degree in 1961, he returned to Norway to start work at Wichmann Motorfabrikk AS, his father's engine factory.
Haldorsen was best known for starting the Rubb Group in Norway in 1968. Rubb Group was named for his home town of Rubbestadneset. Haldorsen's goal was to build a fabric covered building that would withstand the harsh Norwegian climate. His success with this effort lead to him moving to England to start Rubb Buildings Ltd. in 1977. When this company was firmly established under the leadership of Bill Wood, he moved to Maine, and established Rubb Inc. in the United States which today is under the leadership of David C. Nickerson.
Haldorsen was married, and had 3 sons and 1 daughter.
References
External links
Zurhaar & Rubb AS
Rubb Buildings Ltd website
1934 births
2005 deaths
People from Bømlo
American company founders
American manufacturing businesspeople
Norwegian company founders
Mechanical engineers
Technology company founders
20th-century American businesspeople | Finn Haldorsen | Engineering | 320 |
7,485,291 | https://en.wikipedia.org/wiki/Leaf%20plate%20montipora | Leaf plate montipora (Montipora capricornis), also known as vase coral, cap coral, or plating montipora, is a type of small polyp stony (SPS) coral in the family Acroporidae.
Description
Montipora capricornis forms flat, plating colonies. The colonies expand by adding to their foundations and further spreading out. The individual polyps appear as small "bumps" on the surface of the skeleton. At night, the polyps emerge from the skeleton to feed on plankton. The polyps are usually transparent with slight patches of color due to zooxanthellae, symbiotic algae living in the coral's tissue.
Habitat
Montipora capricornis is a very common species of coral, particularly in the Indian and Pacific oceans, as well as in reefs in the Red Sea. It usually inhabits the top half of the reef where photosynthesis can occur. Montipora capricornis will "branch out" from their foundation into an area with adequate sunlight. It also lives in coral reefs and enjoys warm sunny temperatures.
Aquarium trade
Montipora capricornis is one of the more common species of SPS coral available on the market. It comes in various color variations, including red, green, and orange. It is considered to be a good beginner's SPS coral, because it is much more tolerant of under-ideal conditions than its relative, Acropora. Montipora capricornis prefers to live in a reef aquarium, if brought into captivity. This Montipora coral prefers a water temperature of a stable . It prefers strong lighting such as that provided by metal halides, but even a modest compact fluorescent lighting system can be sufficient.
References
External links
ReefCorner - Montipora capricornis Database Entry
capricornis
Coral reefs
Cnidarians of the Pacific Ocean
Cnidarians of the Indian Ocean
Fauna of the Red Sea
Marine fauna of Asia
Marine fauna of Oceania
Marine fauna of Southeast Asia
Marine fauna of West Asia
Anthozoa of Australia
Fauna of Western Australia
Animals described in 1985 | Leaf plate montipora | Biology | 437 |
46,605,765 | https://en.wikipedia.org/wiki/Bousfield%20class | In algebraic topology, the Bousfield class of, say, a spectrum X is the set of all (say) spectra Y whose smash product with X is zero: . Two objects are Bousfield equivalent if their Bousfield classes are the same.
The notion applies to module spectra and in that case one usually qualifies a ring spectrum over which the smash product is taken.
See also
Bousfield localization
External links
Ncatlab.org
References
Topology | Bousfield class | Physics,Mathematics | 96 |
25,438,543 | https://en.wikipedia.org/wiki/HD%201461%20b | HD 1461 b is an extrasolar planet, orbiting the 6th magnitude G-type star HD 1461, 76.5 light years away in the constellation Cetus. This planet has a minimum mass 6.4 times that of Earth and orbits at a distance of 0.0634 AU with an eccentricity of less than 0.131. It is currently unknown whether the planet is a gas giant like Uranus or Neptune, or has terrestrial composition like CoRoT-7b. This planet was announced on 13 December 2009 after it was discovered using radial velocity measurements taken at the Keck and Anglo-Australian Observatories.
References
Exoplanets discovered in 2009
Super-Earths
Exoplanets detected by radial velocity
Cetus | HD 1461 b | Astronomy | 151 |
23,219,463 | https://en.wikipedia.org/wiki/Ammonium%20thiocyanate | Ammonium thiocyanate is an inorganic compound with the formula . It is an ammonium salt of thiocyanic acid. It consists of ammonium cations and thiocyanate anions .
Uses
Ammonium thiocyanate is used in the manufacture of herbicides, thiourea, and transparent artificial resins; in matches; as a stabilizing agent in photography; in various rustproofing compositions; as an adjuvant in textile dyeing and printing; as a tracer in oil fields; in the separation of hafnium from zirconium (important for the production of hafnium-free zircalloy for use in nuclear fuel cladding), and in titrimetric analyses.
In May 1945, USAAF General Victor E. Betrandias advanced a proposal to his superior General Arnold to use of ammonium thiocyanate to reduce rice crops in Japan as part of the bombing raids on their country.
Ammonium thiocyanate can also be used to determine the iron content in soft drinks by colorimetry.
Ammonium thiocyanate may also be used to separate quinidine, from liquors, after the isolation of quinine from the neutral, aqueous, sulphate solution. The salt is added to the hot solution and the gummy solid that forms is strained off from the liquid. The solid is then refluxed with methanol, which dissolves most of the impurities, leaving the quinidine thiocyanate as a crystalline solid of 90 - 95% purity. Following separation, (usually by centrifuge) the solid may then be further purified to pharmaceutical quality. (Quinidine is used for the treatment of heart arrhythmia and therefore has considerable value.)
Preparation
Ammonium thiocyanate is made by the reaction of carbon disulfide with aqueous ammonia. Ammonium dithiocarbamate is formed as an intermediate in this reaction, which upon heating, decomposes to ammonium thiocyanate and hydrogen sulfide:
Reactions
Ammonium thiocyanate is stable in air; however, upon heating it isomerizes to thiourea:
The equilibrium mixtures at 150 °C and 180 °C contain 30.3% and 25.3% (by weight) thiourea, respectively. When heated at 200 °C, the dry powder decomposes to ammonia, hydrogen sulfide, and carbon disulfide, leaving a residue of guanidinium thiocyanate.
is weakly acidic due to the ammonium ion; it reacts with alkali hydroxides, such as sodium hydroxide or potassium hydroxide to form sodium thiocyanate or potassium thiocyanate, along with water and ammonia. The thiocyanate anion, specifically, reacts with ferric salts to form a deep-red ferric thiocyanate complex:
Ammonium thiocyanate reacts with several metal ions including copper, silver, zinc, lead, and mercury, forming their thiocyanate precipitates, which may be extracted into organic solvents.
References
A. F. Wells, Structural Inorganic Chemistry, 5th ed., Oxford University Press, Oxford, UK, 1984.
Thiocyanates
Ammonium compounds
Chemical anti-agriculture weapons | Ammonium thiocyanate | Chemistry | 701 |
9,871,104 | https://en.wikipedia.org/wiki/Sharon%20Beder | Sharon Beder is an environmentalist and former professor in the Faculty of Arts at the University of Wollongong in New South Wales, Australia. Her research has focused on how power relationships are maintained and challenged, particularly by corporations and professions. She has written 11 books, and many articles, book chapters and conference papers, as well as designing teaching resources and educational websites.
Early life and family
Beder was born in 1956 in Wellington, New Zealand, granddaughter of Jewish immigrants from Scotland, England and eastern Europe, before the second world war, and daughter of Jacqui and Yoss Beder.
Education
Beder initially trained and worked as a civil engineer in New Zealand before becoming interested in the social, political and philosophical aspects of engineering and then environmental politics. She completed a PhD in Science and Technology Studies at the University of New South Wales in 1989 based on research into the process of engineering decision-making using a case study on the development of Sydney's sewerage system.
Appointments
Before joining the University of Wollongong in 1992, Beder was Environmental Education Co-ordinator at the University of Sydney. She has also been Chairperson of the Environmental Engineering Branch of the Institution of Engineers, Sydney, President of the Society for Social Responsibility in Engineering, and a director of the Earth Foundation Australia.
Awards
Beder was included in a list of "Australia's most influential engineers", published by Engineers Australia in 2004. She was also included in Bulletin Magazine's "Smart 100" in 2003. Her awards include:
High Commendation for IEAust Award for Cultural Change in Engineering Education, 1998
Michael Daley Prize for Excellence in Science, Technology and Engineering Journalism, 1992
Commonwealth Postgraduate Award, 1985-1988
Books
Beder, Sharon. (1989). Toxic Fish and Sewer Surfing. (Allen & Unwin, Sydney)
Beder, Sharon. (1996). The Nature of Sustainable Development. (Scribe Publications, Melbourne)
Beder, Sharon. (1998). The New Engineer: Management and Professional Responsibility in a Changing World. (Macmillan, Melbourne)
Beder, Sharon. (1997). Global Spin: The Corporate Assault on Environmentalism (Green Books, Devon, UK, October 1997, 2nd edition – May 2002, )
Beder, Sharon. (2006). Environmental Principles and Policies (UNSW Press, Sydney, Australia Paperback, , Publication date: September 2006) & EARTHSCAN, London, UK Paperback, , Publication date: October 2006).
Beder, Sharon. (2006). Suiting Themselves: How Corporations Drive the Global Agenda. (Earthscan, London)
Beder, Sharon. (2006). Free Market Missionaries: The Corporate Manipulation of Community Values. (Earthscan, London)
Beder, Sharon. (2009). This Little Kiddy Went to Market: The Corporate Capture of Childhood. (Pluto Press, London)
Beder, Sharon. (2022). Nellie-Roo: The Orphan Joey. (Wildlife Storybooks)
See also
Dioxin controversy
Marine Outfall
Deregulation
Reference Notes
Living people
Australian non-fiction writers
Australian environmentalists
Australian women environmentalists
Non-fiction environmental writers
University of New South Wales alumni
Academic staff of the University of Wollongong
Academic staff of the University of Sydney
Ethics of science and technology
Environmental social scientists
Science and technology studies scholars
20th-century Australian women writers
20th-century Australian writers
21st-century Australian women writers
21st-century Australian writers
1956 births | Sharon Beder | Technology,Environmental_science | 697 |
44,448,550 | https://en.wikipedia.org/wiki/Navitaire | Navitaire LLC is a subsidiary of Amadeus IT Group. Navitaire primarily offers systems for passenger reservations, travel commerce, ancillary revenue and merchandising, as well as revenue accounting and revenue management to airlines and rail companies.
Overview
Navitaire is a subsidiary of Amadeus that provides technology services to the airline and rail industries. Its headquarters are in Minneapolis with offices in London, Manila, Salt Lake City, and Sydney. It has data centers in Minneapolis, Salt Lake City, and Sydney. David Evans has held the role of global managing director since 2013.
Navitaire has approximately 60 clients and 750 employees. it typically works with low-cost carriers (LCC) and hybrid airlines and is the leading passenger service system provider for the LCC market. As of 2014, the firm serves 43% of the top 100 LCCs, and 47% of the top 30 LCCs as measured by seats sold per week. Clients include airlines Wizz Air, Jetstar, Spirit Airlines, Azul Brazilian Airlines, HK Express, and Volaris. The company also works with railway company SNCF and its subsidiary iDTGV.
History
Navitaire was founded as PRA Solutions in 1993 by Accenture. It initially provided airline revenue accounting software and revenue protection software for airlines. The company then developed a direct-distribution platform to book airline reservations, "World Network," an alternative to the global distribution system traditionally used by travel agents to sell airline flights. In 2000, PRA Solutions purchased the Open Skies reservation system from Hewlett Packard, and in 2001, changed its name to Navitaire.
In 2002, the firm implemented codeshare technology for Virgin Blue, and the company later introduced multi-city bookings at the request of Jetstar. Following Hewlett Packard's announcement in 2001 of its plans to discontinue support for the HP3000 hardware that the Open Skies system operated on, Navitaire developed a replacement reservation system called New Skies. The company began converting clients to the new system in 2005. Navitaire was acquired by Amadeus in 2015.
Products and services
Navitaire's passenger service system is New Skies, which was introduced in 2005. It introduced features including a low fare finder and multi-city bookings. The system provides reservations via the Internet, call centers, and through global distribution systems (GDS) using a ticketless model as well as enabling e-ticketing. It also allows integration with other travel services such as travel insurance and car rental, as well as codeshare agreements with other airlines. As of 2010, the firm had 80 such codeshare connections to partner airlines, as well as nine GDS connections.
Navitaire offers additional products and services including Travel Commerce, a platform to aid in ancillary revenue generation and a loyalty system. The company also offers real-time reporting, revenue accounting software and revenue management. It provides a reservations management system for railways called Navitaire Rail, which facilitates multi-channel distribution sales and station check-ins for rail carriers.
Awards
In October 2010, Navitaire was awarded for Best Sales and Distribution Innovation at the 4th Annual Budgies World Low Cost Airlines Awards. The company was awarded Innovation of the Year in the category of Ancillary Revenue & Merchandising at Airline Information's 2013 Mega Awards, after being named a runner-up in the Ancillary Revenue & Merchandising - Most Innovative Technology category at the Mega Awards event held in November 2012. In December 2013, Navitaire received a Tekne Award from Minnesota High Tech Association for its ticketless system and other services. In March 2019, Navitaire became the first passenger revenue accounting provider to be granted ONE Order (00) Capable certification form the International Air Transport Association (IATA).
References
Accenture
Companies based in Minneapolis
Information technology companies of the United States
Computer reservation systems | Navitaire | Technology | 792 |
26,165,899 | https://en.wikipedia.org/wiki/Gamma%20probe | A gamma probe is a handheld device containing a scintillation counter for intraoperative use following injection of a radionuclide to locate sentinel lymph nodes by their radioactivity. It is used primarily for sentinel lymph node mapping and parathyroid surgery. Gamma probes are also used for RSL (radioactive seed localization) to locate small and non-palpable breast lesions.
History
The sentinel node market experienced high growth in the early and mid-1990s, starting with melanoma sentinel node surgical search and breast cancer sentinel node staging; both are currently considered standards of care. The use of a radioactive tracer, rather than a coloured dye, was proposed in 1984.
Clinical use
To locate the draining lymph nodes or sentinel lymph nodes from a breast cancer tumour, a Technetium-99m based radiopharmaceutical is common. This may be a nanocolloid or sestamibi. Although imaging with a gamma camera may also take place, the idea of a small gamma probe is that it can be used to identify lymph nodes (or other sites) with uptake at a much higher resolution during an operation. The probe may be collimated to restrict the field of detection further.
See also
Nuclear medicine
Molecular Imaging
References
External links
Video on SLN
Video on Sentinel Node Mapping in Melanoma
Nuclear medicine
Image sensors
Medical physics
American inventions | Gamma probe | Physics | 289 |
7,555,884 | https://en.wikipedia.org/wiki/Plant%20anatomy | Plant anatomy or phytotomy is the general term for the study of the internal structure of plants. Originally, it included plant morphology, the description of the physical form and external structure of plants, but since the mid-20th century, plant anatomy has been considered a separate field referring only to internal plant structure. Plant anatomy is now frequently investigated at the cellular level, and often involves the sectioning of tissues and microscopy.
Structural divisions
Some studies of plant anatomy use a systems approach, organized on the basis of the plant's activities, such as nutrient transport, flowering, pollination, embryogenesis or seed development. Others are more classically divided into the following structural categories:
Flower anatomy, including study of the calyx, corolla, androecium, and gynoecium
Leaf anatomy, including study of the epidermis, stomata and palisade cells
Stem anatomy, including stem structure and vascular tissues, buds and shoot apex
Fruit/Seed anatomy, including structure of the ovule, seed, pericarp and accessory fruit
Wood anatomy, including structure of the bark, cork, xylem, phloem, vascular cambium, heartwood and sapwood and branch collar
Root anatomy, including structure of the root, root tip, endodermis
History
About 300 BC, Theophrastus wrote a number of plant treatises, only two of which survive, Enquiry into Plants (), and On the Causes of Plants (). He developed concepts of plant morphology and classification, which did not withstand the scientific scrutiny of the Renaissance.
A Swiss physician and botanist, Gaspard Bauhin, introduced binomial nomenclature into plant taxonomy. He published Pinax theatri botanici in 1596, which was the first to use this convention for naming of species. His criteria for classification included natural relationships, or 'affinities', which in many cases were structural.
It was in the late 1600s that plant anatomy became refined into a modern science. Italian doctor and microscopist, Marcello Malpighi, was one of the two founders of plant anatomy. In 1671, he published his Anatomia Plantarum, the first major advance in plant physiogamy since Aristotle. The other founder was the British doctor Nehemiah Grew. He published An Idea of a Philosophical History of Plants in 1672 and The Anatomy of Plants in 1682. Grew is credited with the recognition of plant cells, although he called them 'vesicles' and 'bladders'. He correctly identified and described the sexual organs of plants (flowers) and their parts.
In the eighteenth century, Carl Linnaeus established taxonomy based on structure, and his early work was with plant anatomy. While the exact structural level which is to be considered to be scientifically valid for comparison and differentiation has changed with the growth of knowledge, the basic principles were established by Linnaeus. He published his master work, Species Plantarum in 1753.
In 1802, French botanist Charles-François Brisseau de Mirbel, published (Treatise on Plant Anatomy and Physiology) establishing the beginnings of the science of plant cytology.
In 1812, Johann Jacob Paul Moldenhawer published , describing microscopic studies of plant tissues.
In 1813, a Swiss botanist, Augustin Pyrame de Candolle, published Théorie élémentaire de la botanique, in which he argued that plant anatomy, not physiology, ought to be the sole basis for plant classification. Using a scientific basis, he established structural criteria for defining and separating plant genera.
In 1830, Franz Meyen published Phytotomie, the first comprehensive review of plant anatomy.In 1838, German botanist Matthias Jakob Schleiden, published Contributions to Phytogenesis, stating, "the lower plants all consist of one cell, while the higher plants are composed of (many) individual cells" thus confirming and continuing Mirbel's work.
A German-Polish botanist, Eduard Strasburger, described the mitotic process in plant cells and further demonstrated that new cell nuclei can only arise from the division of other pre-existing nuclei. His Studien über Protoplasma was published in 1876.
Gottlieb Haberlandt, a German botanist, studied plant physiology and classified plant tissue based upon function. On this basis, in 1884, he published (Physiological Plant Anatomy), in which he described twelve types of tissue systems (absorptive, mechanical, photosynthetic, etc.).
British paleobotanists Dunkinfield Henry Scott and William Crawford Williamson described the structures of fossilized plants at the end of the nineteenth century. Scott's Studies in Fossil Botany was published in 1900.
Following Charles Darwin's Origin of Species a Canadian botanist, Edward Charles Jeffrey, who was studying the comparative anatomy and phylogeny of different vascular plant groups, applied the theory to plants using the form and structure of plants to establish a number of evolutionary lines. He published his The Anatomy of Woody Plants in 1917.
The growth of comparative plant anatomy was spearheaded by British botanist Agnes Arber. She published Water Plants: A Study of Aquatic Angiosperms in 1920, Monocotyledons: A Morphological Study in 1925, and The Gramineae: A Study of Cereal, Bamboo and Grass in 1934.
Following World War II, Katherine Esau published, Plant Anatomy (1953), which became the definitive textbook on plant structure in North American universities and elsewhere, it was still in print as of 2006. She followed up with her Anatomy of seed plants in 1960.
See also
Anatomy
Plant morphology
Plant physiology
References
Further reading
General
Crang, R.C.; Lyons-Sobaski, S.; Wise, R.R. (2018) Plant Anatomy: A Concept-Based Approach to the Study of Seed Plants. Springer, New York, 725 pp.
Eames, Arthur Johnson; MacDaniels, Laurence H. (1947). An Introduction to Plant Anatomy 2nd ed. McGraw-Hill, New York, link (1st ed., 1925, link).
Esau, Katherine (1965). Plant Anatomy 2nd ed. Wiley, New York.
Meicenheimer, R. History of Plant Anatomy. Miami University, link.
Specialized
Cutler, D. F.; Gregory, M.; Rudall, P. (eds.) (1960-2014). Anatomy of the Monocotyledons. 10 vols. Oxford University Press.
Goffinet, B.; Buck, W. R.; Shaw, J. (2008). Morphology, anatomy, and classification of the Bryophyta. In: Goffinet, B.; Shaw, J. (eds.). Bryophyte Biology, 2nd ed. Cambridge University Press, pp. 55–138 (1st ed., 2000, link).
Jeffrey, E. C. (1917). The anatomy of woody plants. Chicago, The University of Chicago Press, link.
Metcalfe, C.R.; Chalk, L. (1957). Anatomy of the Dicotyledons: Leaves, stem and wood in relation to taxonomy, with notes on economic uses. 2 vols. Oxford: Clarendon Press. 1500 pp., link (2nd ed., 1979-1998, 4 vols.).
Schoute, J. C. (1938). Anatomy. In: Verdoorn, F. (ed.). Manual of Pteridology. Martinus Nijhoff, The Hague. pp. 65–104. link.
Schweingruber, F. H.; Börner, A.; Schulze, E. (2011-2013). Atlas of Stem Anatomy in Herbs, Shrubs and Trees. Vol. 1, 2011, link. Vol. 2, 2013, link. Springer-Verlag, Berlin, Heidelberg.
External links
Farabee, M.J. (2001) "Plants and their structure" Estrella Mountain Community College, Phoenix, Arizona
Botanical Visual Glossary
Plant anatomy glossary- University of Rhode Island
Branches of botany | Plant anatomy | Biology | 1,656 |
50,534,018 | https://en.wikipedia.org/wiki/Chow%20group%20of%20a%20stack | In algebraic geometry, the Chow group of a stack is a generalization of the Chow group of a variety or scheme to stacks. For a quotient stack , the Chow group of X is the same as the G-equivariant Chow group of Y.
A key difference from the theory of Chow groups of a variety is that a cycle is allowed to carry non-trivial automorphisms and consequently intersection-theoretic operations must take this into account. For example, the degree of a 0-cycle on a stack need not be an integer but is a rational number (due to non-trivial stabilizers).
Definitions
develops the basic theory (mostly over Q) for the Chow group of a (separated) Deligne–Mumford stack. There, the Chow group is defined exactly as in the classical case: it is the free abelian group generated by integral closed substacks modulo rational equivalence.
If a stack X can be written as the quotient stack for some quasi-projective variety Y with a linearized action of a linear algebraic group G, then the Chow group of X is defined as the G-equivariant Chow group of Y. This approach is introduced and developed by Dan Edidin and William A. Graham, as well as Burt Totaro. Later Andrew Kresch (1999) extended the theory to a stack admitting a stratification by quotient stacks.
For higher Chow groups (precursor of motivic homologies) of algebraic stacks, see Roy Joshua's Intersection Theory on Stacks:I and II.
Examples
The calculations depend on definitions. Thus, here, we proceed somehow axiomatically. Specifically, we assume: given an algebraic stack X locally of finite type over a base field k,
(homotopy-invariance) if E is a rank-n vector bundle on X, then .
for each integral substack Z of dimension < p, , a corollary of a localization sequence.
These properties are valid if X is Deligne–Mumford and are expected to hold for any other reasonable theory.
We take X to be the classifying stack , the stack of principal G-bundles for a smooth linear algebraic group G. By definition, it is the quotient stack , where * is viewed as the stack associated to * = Spec k. We approximate it as follows. Given an integer p, choose a representation such that there is a G-invariant open subset U of V on which G acts freely and the complement has codimension . Let be the quotient of by the action . Note the action is free and so is a vector bundle over . By Property 1 applied to this vector bundle,
Then, since , by Property 2,
since .
As a concrete example, let and let it act on by scaling. Then acts freely on . By the above calculation, for each pair of integers n, p such that ,
In particular, for every integer p ≥ 0, . In general, for the hyperplane class h, k-times self-intersection and for negative k and so
where the right-hand side is independent of models used in the calculation (since different hs correspond under the projections between projective spaces.) For , the class , any n, may be thought of as the fundamental class of .
Similarly, we have
where is the first Chern class of h (and c and h are identified when Chow groups and Chow rings of projective spaces are identified). Since , we have that is the free -module generated by .
Virtual fundamental class
The notion originates in the Kuranishi theory in symplectic geometry.
In § 2. of , given a DM stack X and CX the intrinsic normal cone to X, K. Behrend defines the virtual fundamental class of X as
where s0 is the zero-section of the cone determined by the perfect obstruction theory and s0! is the refined Gysin homomorphism defined just as in Fulton's "Intersection theory". The same paper shows that the degree of this class, morally the integration over it, is equal to the weighted Euler characteristic of the Behrend function of X.
More recent (circa 2017) approaches do this type of construction in the context of derived algebraic geometry.
See also
Perfect obstruction theory
Gromov–Witten invariant
Cohomology of a stack
Notes
References
External links
Virtual classes for the working mathematician
The classical number 2875 of lines on the quintic, as a DT invariant
What is the main failure in using Naive Chow group in Artin Stack
Local model of virtual fundamental cycle
https://ncatlab.org/nlab/show/virtual+fundamental+class
On the Virtual Fundamental Class - a slide by Kai Behrend
Algebraic geometry | Chow group of a stack | Mathematics | 974 |
501,758 | https://en.wikipedia.org/wiki/Magnetocrystalline%20anisotropy | In physics, a ferromagnetic material is said to have magnetocrystalline anisotropy if it takes more energy to magnetize it in certain directions than in others. These directions are usually related to the principal axes of its crystal lattice. It is a special case of magnetic anisotropy. In other words, the excess energy required to magnetize a specimen in a particular direction over that required to magnetize it along the easy direction is called crystalline anisotropy energy.
Causes
The spin-orbit interaction is the primary source of magnetocrystalline anisotropy. It is basically the orbital motion of the electrons which couples with crystal electric field giving rise to the first order contribution to magnetocrystalline anisotropy. The second order arises due to the mutual interaction of the magnetic dipoles. This effect is weak compared to the exchange interaction and is difficult to compute from first principles, although some successful computations have been made.
Practical relevance
Magnetocrystalline anisotropy has a great influence on industrial uses of ferromagnetic materials. Materials with high magnetic anisotropy usually have high coercivity, that is, they are hard to demagnetize. These are called "hard" ferromagnetic materials and are used to make permanent magnets. For example, the high anisotropy of rare-earth metals is mainly responsible for the strength of rare-earth magnets. During manufacture of magnets, a powerful magnetic field aligns the microcrystalline grains of the metal such that their "easy" axes of magnetization all point in the same direction, freezing a strong magnetic field into the material.
On the other hand, materials with low magnetic anisotropy usually have low coercivity, their magnetization is easy to change. These are called "soft" ferromagnets and are used to make magnetic cores for transformers and inductors. The small energy required to turn the direction of magnetization minimizes core losses, energy dissipated in the transformer core when the alternating current changes direction.
Thermodynamic theory
The magnetocrystalline anisotropy energy is generally represented as an expansion in powers of the direction cosines of the magnetization. The magnetization vector can be written , where is the saturation magnetization. Because of time reversal symmetry, only even powers of the cosines are allowed. The nonzero terms in the expansion depend on the crystal system (e.g., cubic or hexagonal). The order of a term in the expansion is the sum of all the exponents of magnetization components, e.g., is second order.
Uniaxial anisotropy
More than one kind of crystal system has a single axis of high symmetry (threefold, fourfold or sixfold). The anisotropy of such crystals is called uniaxial anisotropy. If the axis is taken to be the main symmetry axis of the crystal, the lowest order term in the energy is
The ratio is an energy density (energy per unit volume). This can also be represented in spherical polar coordinates with , , and :
The parameter , often represented as , has units of energy density and depends on composition and temperature.
The minima in this energy with respect to satisfy
If ,
the directions of lowest energy are the directions. The axis is called the easy axis. If , there is an easy plane perpendicular to the symmetry axis (the basal plane of the crystal).
Many models of magnetization represent the anisotropy as uniaxial and ignore higher order terms. However, if , the lowest energy term does not determine the direction of the easy axes within the basal plane. For this, higher-order terms are needed, and these depend on the crystal system (hexagonal, tetragonal or rhombohedral).
Hexagonal system
In a hexagonal system the axis is an axis of sixfold rotation symmetry. The energy density is, to fourth
order,
The uniaxial anisotropy is mainly determined by these first two terms. Depending on the values and , there are four different kinds of anisotropy (isotropic, easy axis, easy plane and easy cone):
: the ferromagnet is isotropic.
and : the axis is an easy axis.
and : the basal plane is an easy plane.
and : the basal plane is an easy plane.
: the ferromagnet has an easy cone (see figure to right).
The basal plane anisotropy is determined by the third term, which is sixth-order. The easy directions are projected onto three axes in the basal plane.
Below are some room-temperature anisotropy constants for hexagonal ferromagnets. Since all the values of and are positive, these materials have an easy axis.
Higher order constants, in particular conditions, may lead to first order magnetization processes FOMP.
Tetragonal and rhombohedral systems
The energy density for a tetragonal crystal is
.
Note that the term, the one that determines the basal plane anisotropy, is fourth order (same as the term). The definition of may vary by a constant multiple between publications.
The energy density for a rhombohedral crystal is
.
Cubic anisotropy
In a cubic crystal the lowest order terms in the energy are
If the second term can be neglected, the easy axes are the ⟨100⟩ axes (i.e., the , , and , directions) for and the ⟨111⟩ directions for (see images on right).
If is not assumed to be zero, the easy axes depend on both and . These are given in the table below, along with hard axes (directions of greatest energy) and intermediate axes (saddle points) in the energy). In energy surfaces like those on the right, the easy axes are analogous to valleys, the hard axes to peaks and the intermediate axes to mountain passes.
Below are some room-temperature anisotropy constants for cubic ferromagnets. The compounds involving are ferrites, an important class of ferromagnets. In general the anisotropy parameters for cubic ferromagnets are higher than those for uniaxial ferromagnets. This is consistent with the fact that the lowest order term in the expression for cubic anisotropy is fourth order, while that for uniaxial anisotropy is second order.
Temperature dependence of anisotropy
The magnetocrystalline anisotropy parameters have a strong dependence on temperature. They generally decrease rapidly as the temperature approaches the Curie temperature, so the crystal becomes effectively isotropic. Some materials also have an isotropic point at which . Magnetite (), a mineral of great importance to rock magnetism and paleomagnetism, has an isotropic point at 130 kelvin.
Magnetite also has a phase transition at which the crystal symmetry changes from cubic (above) to monoclinic or possibly triclinic below. The temperature at which this occurs, called the Verwey temperature, is 120 Kelvin.
Magnetostriction
The magnetocrystalline anisotropy parameters are generally defined for ferromagnets that are constrained to remain undeformed as the direction of magnetization changes. However, coupling between the magnetization and the lattice does result in deformation, an effect called magnetostriction. To keep the lattice from deforming, a stress must be applied. If the crystal is not under stress, magnetostriction alters the effective magnetocrystalline anisotropy. If a ferromagnet is single domain (uniformly magnetized), the effect is to change the magnetocrystalline anisotropy parameters.
In practice, the correction is generally not large. In hexagonal crystals, there is no change in . In cubic crystals, there is a small change, as in the table below.
See also
Anisotropy energy
Notes and references
Further reading
Magnetic ordering
Orientation (geometry)
Ferromagnetism | Magnetocrystalline anisotropy | Physics,Chemistry,Materials_science,Mathematics,Engineering | 1,688 |
8,297,574 | https://en.wikipedia.org/wiki/Major%20sublingual%20duct | The excretory ducts of the sublingual gland are from eight to twenty in number. Of the smaller sublingual ducts (ducts of Rivinus), some join the submandibular duct; others open separately into the mouth, on the elevated crest of mucous membrane (plica sublingualis), caused by the projection of the gland, on either side of the frenulum linguae. One or more join to form the major sublingual duct (larger sublingual duct, duct of Bartholin), which opens into the submandibular duct.
References
External links
Histology at medicine.uiowa.edu
Glands of mouth
Saliva | Major sublingual duct | Biology | 145 |
8,057,499 | https://en.wikipedia.org/wiki/George%20Gray%20%28chemist%29 | George William Gray (4 September 1926 – 12 May 2013) was a Professor of Organic Chemistry at the University of Hull who was instrumental in developing the long-lasting materials which made liquid crystal displays possible. He created and systematically developed liquid crystal materials science, and established a method of practical molecular design. Gray was recipient of the 1995 Kyoto Prize in Advanced Technology.
Education and career
Born in Denny, Scotland, Gray was educated at the University of Glasgow and while working as an assistant lecturer at the University College in Hull (then part of the University of London) obtained his PhD in 1953.
He developed his academic career at the college, which became the University of Hull in 1954, from 1946 to 1990. He was appointed senior lecturer in 1960, Professor of Organic Chemistry in 1974, and GF Grant Professor of Chemistry in 1984. He remained an Emeritus Professor at Hull.
In 1990 he joined the chemical company Merck, then became an independent consultant in 1996.
Liquid crystals
In 1973, in conjunction with the Royal Radar Establishment, Gray showed that 4-Cyano-4'-pentylbiphenyl possessed a stable nematic phase at room temperature. This compound and other long-lasting cyano-biphenyls made the twisted nematic display (LCD) popular. Gray wrote the first English book on liquid crystals, "Molecular Structure and Properties of Liquid Crystals", published in 1962.
Gray was recipient of the 1995 Kyoto Prize in Advanced Technology and was made a Commander of the Order of the British Empire (CBE) in 1991. He was elected a Fellow of the Royal Society in 1983, and in 1987 was awarded the Leverhulme Medal of the Royal Society. In 1979 he was awarded the Rank Prize for Opto-electronics and in 1996 the SID Karl Ferdinand Braun Prize. The University of Hull was the first university to be awarded the Queen's Award for Technological Achievement, in 1979, for the liquid crystal joint-development work. Gray has been a Director of the International Liquid Crystal Society. Members of the British Liquid Crystal Society honoured his achievements by establishing the George W. Gray Medal for contributions to liquid crystal research and technology.
In March 2013, the University of Hull celebrated the 40th anniversary of Gray's seminal paper being published on 22 March 1973.
Hull Trains named their first British Rail Class 222 'Pioneer' high-speed train Professor George Gray in recognition of his achievements in the modern history of Hull.
Personal life
In 1953 George Gray married Marjorie Canavan, who died two weeks before her husband. In later life they lived in Furzehill in Wimborne Minster, Dorset. They had three daughters.
References
Further reading
David Dunmur & Tim Sluckin (2011) Soap, Science, and Flat-screen TVs: a history of liquid crystals, pp 201,221–5, Oxford University Press
External links
The History of Liquid Crystals at the University of Hull
George William Gray, Kyoto Prize biography
George William Gray, Kyoto Prize citation
George Gray - Liquid Perfection
Interview With George Gray, The Vega Science Trust
The history of liquid-crystal displays, Hirohisa Kawamoto, Proceedings of the IEEE, Vol. 90, No. 4, April 2002
G. W. Gray, K. J. Harrison, J. A. Nash "New family of nematic liquid crystals for displays" Electronics Lett. 9 (1973) 130
Celebrating 40 years of LCD research, University of Hull
1926 births
2013 deaths
Fellows of the Royal Society
Academics of the University of Hull
Alumni of the University of Glasgow
Alumni of the University of London
Commanders of the Order of the British Empire
People from Denny, Falkirk
Liquid crystals
British organic chemists
20th-century Scottish chemists
Kyoto laureates in Advanced Technology | George Gray (chemist) | Chemistry | 749 |
11,752,492 | https://en.wikipedia.org/wiki/The%20Scary%20Guy | The Scary Guy (sometimes stylized THE SCARY GUY; born December 29, 1953) is a United Kingdom-based American motivational speaker who campaigns worldwide to eliminate hate, violence, prejudice, and bullying in schools and corporations. In addition to being a tattoo shop owner, comic, entertainer, inspirational speaker, and performance artist, The Scary Guy has pierced nose, eyebrows, and ears and covers over 85 percent of his body with tattoos.
Early life
The Scary Guy was born on December 29, 1953, as Earl Kenneth Kaufmann, to his father, Carroll August Kaufmann, and his mother Constance Joan Buckingham. Growing up in New Hope, Minnesota, The Scary Guy graduated in 1972 from Cooper Senior High School and excelled as a voice major at Macalester College, in Saint Paul.
Tattoos
The Scary Guy got his first tattoo at the age of 30 and now has tattoos that cover an estimated 85% of his body. Over the years, his collection has grown as a reflection of his life experiences. They are what he calls, 'modern tribalism', reflecting on various emotional events. One of these is a tattoo of a man called "Yuppiecide", a representation of his former self. Scary Guy's other tattoos represent his love of art and others are chosen simply because The Scary Guy was a computer salesman at one point in his life and they looked "cool".
Bibliography
Hatwood, Mark David. 7 Days and 7 Nights – An Official Biography of The Scary Guy. VisionHeart, Inc. 2008
Videos
The Scary Guy on Firepit Friday
Films
Scary also known as Scary – tattoo therapy, title in German : Scary – Furchterregend (2006) by Uli Kick, Arte, Bayerischer Rundfunk, Filmworks, Südwestrundfunk, Westdeutscher Rundfunk.
See also
Teachers' TV
References
External links
Official website
American social workers
American motivational speakers
American businesspeople
Personal development
1953 births
American tattoo artists
Male tattoo artists
Living people
People from New Hope, Minnesota | The Scary Guy | Biology | 409 |
19,868,716 | https://en.wikipedia.org/wiki/Differential%20pulley | A differential pulley—also called "Weston differential pulley", sometimes "differential hoist", "chain hoist", or colloquially "chain fall"—is used to manually lift very heavy objects like car engines. It is operated by pulling upon the slack section of a continuous chain that wraps around two pulleys on a common shaft. (The two pulleys are joined together such that they rotate as a unit on the single shaft that they share.) The relative sizing of the two connected pulleys determines the maximum weight that can be lifted by hand. If the pulley radii are close enough, then the load will remain in place (and not lower under the force of gravity) until the chain is pulled.
History
The differential pulley was invented in 1854 by Thomas Aldridge Weston from King's Norton, England.
The pulleys were manufactured in collaboration with Richard and George Tangye. According to Richard Tangye's autobiography, the Weston differential pulley evolved from the Chinese windlass, with an endless chain replacing the finite length of rope. He claimed that many engineering firms conceded on the difficulty of efficiently disengaging the chain from the teeth as the pulleys turned, but his firm developed a "pitch" chain which solved the issue. Marketed as "Weston Differential Pulley Blocks with Patent Chain Guides", the pulley had good sales, namely, 3000 sets in 9 months. It was displayed in 5 sizes—from to —at the 1862 International Exhibition in London and received a medal for "original application, practical utility and success".
An ironmonger challenged the Tangyes that the pulley had been in use for 30 years before Weston's patent but the judge, William Page Wood ruled in favour of the Tangyes because the engaging mechanism was substantially different from the one presented as evidence.
The Yale Lock Company acquired the patent rights in 1876.
A dumb pulley can lift very large masses a short distance. It consists of two fixed pulleys of unequal radii that are attached to each other and rotate together, a single pulley bearing the load, and an endless rope looped around the pulleys. To avoid slippage, the rope is usually replaced by a chain, and the connected pulleys by sprockets.
The two sections of chain carrying the single pulley exert opposing and unequal torques on the connected pulleys, such that only the difference of these torques has to be compensated manually by pulling the loose part of the chain.
This leads to a mechanical advantage: the force needed to lift a load is only a fraction of the load's weight. At the same time, the distance the load is lifted is smaller than the length of chain pulled by the same factor. This factor (the mechanical advantage MA) depends on the relative difference of the radii r and R of the connected pulleys:
The effect on the forces and distances (see figure) is quantitatively:
The difference in radii can be made very small, making the mechanical advantage of this pulley system very large.
In the extreme case of zero difference in radii, MA becomes infinite, thus no force (besides friction) is needed to move the chain, but moving the chain will no longer lift the load.
At the other extreme, when r is zero, the system becomes a simple gun tackle with a mechanical advantage of 2.
The same principle is used in a differential windlass, where the connected pulleys are replaced by winches.
Calculation of mechanical advantage
In the above graphic, the four segments of the chain are labelled W, X, Y and Z. The magnitudes of their corresponding forces are FW, FX, FY and FZ, respectively.
Assuming that the chain is massless, FX = 0 because segment X is not supporting any weight.
Taking the system at equilibrium, FW and FY are equal—if they were not, the lower pulley would freely turn until they were.
Next, the downward force acting on the lower pulley equals the upward forces acting on it, so
FL = FW + FY, or 2FW because FW = FY.
Additionally, there is no net torque or moment around the compound pulley, so the clockwise torque is equal to the anticlockwise torque:
FW R + FX r = FY r + FZ R .
Substituting FX and FY from the above equations,
FW R + 0 = FW r + FZ R .
Rearranging gives
FW = FZ · .
As FW = ,
= FZ · .
Finally, the mechanical advantage, = or .
A much simpler method of calculating mechanical advantage can be accomplished by simply counting and comparing the chain link pockets in the two differentially-sized sprockets. Let's call the number of pockets in the two respective sprockets P1 (larger) and P2 (smaller).
In lifting a load, for each full revolution of the double sprocket assembly, P1 chain link pairs (alternate perpendicular links fit between pockets) will be taken up by the larger sprocket while P2 chain link pairs are released by the smaller sprocket, for a net gain of P1 − P2 chain link pairs.
The mechanical advantage would equal the ratio of chain link pairs required for each revolution to the net gain of chain link pairs. Put another way, the mechanical advantage would be the distance of pull required for each unit distance of gain. The mechanical advantage at the differential sprocket pair equals .
Because there is a traveling pulley at the load, this doubles the mechanical advantage of the fixed (anchored) sprocket assembly, leading to a total mechanical advantage of 2 × .
For instance, a 1-ton differential chain fall might have a 15-pocket and a 14-pocket sprocket set. This would provide a total of 2 × , or 30:1 mechanical advantage.
See also
Block and tackle
Hoist
References
Mechanics
Simple machines
Mechanisms (engineering) | Differential pulley | Physics,Technology,Engineering | 1,235 |
243,844 | https://en.wikipedia.org/wiki/Extraterrestrial%20intelligence | Extraterrestrial intelligence (ETI) refers to hypothetical intelligent extraterrestrial life. No such life has ever been verifiably observed to exist. The question of whether other inhabited worlds might exist has been debated since ancient times. The modern form of the concept emerged when the Copernican Revolution demonstrated that the Earth was a planet revolving around the Sun, and other planets were, conversely, other worlds. The question of whether other inhabited planets or moons exist was a natural consequence of this new understanding. It has become one of the most speculative questions in science and is a central theme of science fiction and popular culture.
An alternative name for it is "Extraterrestrial Technological Instantiations" (ETI). The term was coined to avoid the use of terms such as "civilizations" "species" and "intelligence", as those may prove to be ambiguous and open to interpretation, or simply inapplicable in its local context.
Intelligence
Intelligence is, along with the more precise concept of sapience, used to describe extraterrestrial life with similar cognitive abilities as humans. Another interchangeable term is sophoncy, being wise or wiser, first coined by Karen Anderson and published in the 1966 works by her husband Poul Anderson.
Sentience, like consciousness, is a concept sometimes mistakenly used to refer to the concept of intelligence and sapience, since it does not exclude forms of life that are non-sapient (or more broadly non-intelligent or non-conscious).
The term extraterrestrial civilization frames a more particular case of extraterrestrial intelligence. It is the possible long-term result of intelligent and specifically sapient extraterrestrial life.
Probability
The Copernican principle is generalized to the relativistic concept that humans are not privileged observers of the universe. Many prominent scientists, including Stephen Hawking have proposed that the sheer scale of the universe makes it improbable for intelligent life not to have emerged elsewhere. However, Fermi's Paradox highlights the apparent contradiction between high estimates of the probability of the existence of extraterrestrial civilization and humanity's lack of contact with, or evidence for, such civilizations.
So far, there is no observation of extraterrestrial life, including intelligent extraterrestrial life.
The Kardashev scale is a speculative method of measuring a civilization's level of technological advancement, based on the amount of energy a civilization is able to utilize.
The Drake equation is a probabilistic framework used to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way galaxy.
Search for extraterrestrial intelligence
There has been a search for signals from extraterrestrial intelligence for several decades, with no significant results. Active SETI (Active Search for Extra-Terrestrial Intelligence) is the attempt to send messages to intelligent extraterrestrial life. Active SETI messages are usually sent in the form of radio signals. Physical messages like that of the Pioneer plaque may also be considered an active SETI message.
Communication with extraterrestrial intelligence (CETI) is a branch of the search for extraterrestrial intelligence that focuses on composing and deciphering messages that could theoretically be understood by another technological civilization. The best-known CETI experiment was the 1974 Arecibo message composed by Frank Drake and Carl Sagan. There are multiple independent organizations and individuals engaged in CETI research.
The U.S. government's position, in line with that of most relevant experts, is that "chances of contact with an extraterrestrial intelligence are extremely small, given the distances involved." This line of thinking has led some to conclude that first contact might be made with extraterrestrial artificial intelligence, rather than with biological beings.
The Wow! signal remains the best candidate for an extraterrestrial radio signal ever detected, though the fact that no similar signal has ever been observed again makes attribution of the signal to any cause difficult if not impossible.
On 14 June 2022 astronomers working with China's FAST telescope reported the possibility of having detected artificial (presumably alien) signals, but cautions that further studies are required to determine if some kind of natural radio interference may be the source. On 18 June 2022 Dan Werthimer, chief scientist for several SETI-related projects, reportedly noted that “These signals are from radio interference; they are due to radio pollution from earthlings, not from E.T.”
Potential cultural impact of extraterrestrial contact
The potential changes from extraterrestrial contact could vary greatly in magnitude and type, based on the extraterrestrial civilization's level of technological advancement, degree of benevolence or malevolence, and level of mutual comprehension between itself and humanity. Some theories suggest that an extraterrestrial civilization could be advanced enough to dispense with biology, living instead inside of advanced computers. The medium through which humanity is contacted, be it electromagnetic radiation, direct physical interaction, extraterrestrial artefact, or otherwise, may also influence the results of contact. Incorporating these factors, various systems have been created to assess the implications of extraterrestrial contact.
The implications of extraterrestrial contact, particularly with a technologically superior civilization, have often been likened to the meeting of two vastly different human cultures on Earth, a historical precedent being the Columbian Exchange. Such meetings have generally led to the destruction of the civilization receiving contact (as opposed to the "contactor", which initiates contact), and therefore destruction of human civilization is a possible outcome. However, the absence of any such contact to date means such conjecture is largely speculative.
UFOlogy
The extraterrestrial hypothesis is the idea that some UFOs are vehicles containing or sent by extraterrestrial beings (usually called aliens in this context). As an explanation for UFOs, ETI is sometimes contrasted with EDI (extradimensional intelligence), for example by J. Allen Hynek. In 2023, House lawmakers held a hearing to examine how the executive branch handles reports of UFOs.
In culture
The theories and reception of the probability of intelligent life has been a recurring cultural element, particularly of popular culture since the prospect and achievement of spaceflight.
New Mexico has even declared in 2003 the 14th of February as the Extraterrestrial Culture Day.
See also
Extraterrestrial life
Rare Earth hypothesis
Cosmic pluralism
Fermi Paradox
Extraterrestrials in fiction
First contact (science fiction)
Contact (1997 film)
Life origination beyond planets
Messaging to Extra-Terrestrial Intelligence (METI or Active SETI)
Quiet and loud aliens
Sapience
Sentiocentrism
Extraterrestrial: The First Sign of Intelligent Life Beyond Earth, 2021 popular science book by Avi Loeb
References
External links
An astrophysicist's view of UFOs (Adam Frank; New York Times; 30 May 2021)
Extraterrestrial life
Intelligence
Biological hypotheses | Extraterrestrial intelligence | Astronomy,Biology | 1,424 |
9,678 | https://en.wikipedia.org/wiki/Exponential%20function | In mathematics, the exponential function is the unique real function which maps zero to one and has a derivative equal to its value. The exponential of a variable is denoted or , with the two notations used interchangeably. It is called exponential because its argument can be seen as an exponent to which a constant number , the base, is raised. There are several other definitions of the exponential function, which are all equivalent although being of very different nature.
The exponential function converts sums to products: it maps the additive identity to the multiplicative identity , and the exponential of a sum is equal to the product of separate exponentials, . Its inverse function, the natural logarithm, or , converts products to sums: .
Other functions of the general form , with base , are also commonly called exponential functions, and share the property of converting addition to multiplication, . Where these two meanings might be confused, the exponential function of base is occasionally called the natural exponential function, matching the name natural logarithm. The generalization of the standard exponent notation to arbitrary real numbers as exponents, is usually formally defined in terms of the exponential and natural logarithm functions, as . The "natural" base is the unique base satisfying the criterion that the exponential function's derivative equals its value, , which simplifies definitions and eliminates extraneous constants when using exponential functions in calculus.
Quantities which change over time in proportion to their value, for example the balance of a bank account bearing compound interest, the size of a bacterial population, the temperature of an object relative to its environment, or the amount of a radioactive substance, can be modeled using functions of the form , also sometimes called exponential functions; these quantities undergo exponential growth if is positive or exponential decay if is negative.
The exponential function can be generalized to accept a complex number as its argument. This reveals a relation between the multiplication of complex numbers and rotation in the Euclidean plane, Euler's formula : the exponential of an imaginary number is a point on the complex unit circle at angle from the real axis. The identities of trigonometry can thus be translated into identities involving exponentials of imaginary quantities. The complex function is a conformal map from an infinite strip of the complex plane (which periodically repeats in the imaginary direction) onto the whole complex plane except for .
The exponential function can be even further generalized to accept other types of arguments, such as matrices and elements of Lie algebras.
Graph
The graph of is upward-sloping, and increases faster as increases. The graph always lies above the -axis, but becomes arbitrarily close to it for large negative ; thus, the -axis is a horizontal asymptote. The equation means that the slope of the tangent to the graph at each point is equal to its height (its -coordinate) at that point.
Definitions and fundamental properties
There are several different definitions of the exponential function, which are all equivalent, although of very different nature.
One of the simplest definitions is: The exponential function is the unique differentiable function that equals its derivative, and takes the value for the value of its variable.
This "conceptual" definition requires a uniqueness proof and an existence proof, but it allows an easy derivation of the main properties of the exponential function.
Uniqueness: If and are two functions satisfying the above definition, then the derivative of is zero everywhere by the quotient rule. It follows that is constant, and this constant is since .
The exponential function is the inverse function of the natural logarithm. The inverse function theorem implies that the natural logarithm has an inverse function, that satisfies the above definition. This is a first proof of existence. Therefore, one has
for every real number and every positive real number
The exponential function is the sum of a power series:
where is the factorial of (the product of the first positive integers). This series is absolutely convergent for every per the ratio test. So, the derivative of the sum can be computed by term-by-term derivation, and this shows that the sum of the series satisfies the above definition. This is a second existence proof, and shows, as a byproduct, that the exponential function is defined for every , and is everywhere the sum of its Maclaurin series.
The exponential satisfies the functional equation:
This results from the uniqueness and the fact that the function
satisfies the above definition. It can be proved that a function that satisfies this functional equation is the exponential function if its derivative at is and the function is either continuous or monotonic
Positiveness: For every , one has , since the functional equation implies . It results that the exponential function is positive (since , if one would have for some , the intermediate value theorem would imply the existence of some such that . It results also that the exponential function is monotonically increasing.
Extension of exponentiation to positive real bases: Let be a positive real number. The exponential function and the natural logarithm being the inverse each of the other, one has If is an integer, the functional equation of the logarithm implies
Since the right-most expression is defined if is any real number, this allows defining for every positive real number and every real number :
In particular, if is the Euler's number one has (inverse function) and thus This shows the equivalence of the two notations for the exponential function.
The exponential function is the limit
where takes only integer values (otherwise, the exponentiation would require the exponential function to be defined). By continuity of the logarithm, this can be proved by taking logarithms and proving
for example with Taylor's theorem.
General exponential functions
The term "exponential function" is used sometimes for referring to any function whose argument appears in an exponent, such as and However, this name is commonly used for differentiable functions satisfying one of the following equivalent conditions:
There exist some constants and such that for every value of .
There exist some constants and such that for every value of .
For every the value of is independent of that is, for all , and . In words: pairs of arguments with the same difference are mapped into pairs of values with the same ratio.G. Harnett, Quora, 2020, What is the base of an exponential function?
"A (general) exponential function changes by the same factor over equal increments of the input. The factor of change over a unit increment is called the base."Mathebibel "Werden bei einer Exponentialfunktion zur basis die -Werte jeweils um einen festen Zahlenwert vergrössert, so werden die Funktionswerte mit einem konstanten Faktor vervielfacht."
The value of is independent of . This constant value is sometimes called the rate constant of and denoted as ; it equals the constant of the second equivalent condition.G.F. Simmons, Differential Equations and Historical Notes, 1st ed. 1972, p. 15; 3rd ed. 2016, p. 23 "The positive constant is called the rate constant, for its value is clearly a measure of the rate at which the reaction proceeds." . Its reciprocal, the constant value of , is, in some contexts, called the time constant of and denoted as (so, ).
The value of is independent of and This constant value equals the constant of the first equivalent condition and is called the base of the exponential function.
Hierarchy of types
Exponential functions with quantities as elements of domain and codomain. E.g. the lilys in the pond, growing with the same factor during time intervals of equal length. In applications in empirical sciences, notations with and are commonly used. Exponential growth can be modeled by a function with its doubling time. Exponential decay can be modeled by a function with its half-life.
Exponential functions with domain ; see , below.
Exponential functions obeying for all , (changing additions into multiplications; the opposite of the main property of logarithmic functions: changing multiplications into additions) ; equivalent with the condition . Usual form: Sometimes the value of is named the antilog of or the antilogarithm of .
Exponential functions obeying (the function is identical with its own derivative). Usual form:
The (unique) exponential function obeying as well as is called the exponential function; sometimes the natural exponential function or the natural antilogarithm. Symbol: . Usual form: or
Two meanings of 'base'
For exponential functions , to , the -independent value of is called the base of the function . While in expressions (...)(...) and (...)^(...) the value of the first element is called the base of the exponentiation. Example: the exponential function has base , while the expression has base (and exponent ).
Properties
- The Euler number is connected with every exponential function . When argument increases by , changes by factor . For .
- Let be an arbitrary point on the graph in cartesian coordinates of an exponential function with 'time constant' . Then the constant distance on the asymptote of the graph between its intersections with the tangent in and the line through perpendicular to the asymptote, equals .
- The graph of an exponential function in polar coordinates is a logarithmic spiral or equiangular spiral.Ch.-J. de la Vallée Poussin, Cours d'Analyse Infinitésimale, Tome I, 3ième édition 1914, p. 363
More precisely: the graph in polar coordinates of an exponential function with rate constant , is a logarithmic spiral with constant pitch angle (between the directions of the spiral and the polar circle, in an arbitrary point on the spiral) .
- In a logarithmic spiral with pitch angle 45o the length of a radius vector increases by a factor when the polar angle increases by one radian. And by the factor at a 180o switch. See , logarithmic spiral, §Properties, 'Rotating, scaling'.
- An exponential function is determined by two 'points'. With , positive, and determine the exponential function .
Overview
The exponential function arises whenever a quantity grows or decays at a rate proportional to its current value. One such situation is continuously compounded interest, and in fact it was this observation that led Jacob Bernoulli in 1683 to the number
now known as . Later, in 1697, Johann Bernoulli studied the calculus of the exponential function.
If a principal amount of 1 earns interest at an annual rate of compounded monthly, then the interest earned each month is times the current value, so each month the total value is multiplied by , and the value at the end of the year is . If instead interest is compounded daily, this becomes . Letting the number of time intervals per year grow without bound leads to the limit definition of the exponential function,
first given by Leonhard Euler.
This is one of a number of characterizations of the exponential function; others involve series or differential equations.
From any of these definitions it can be shown that is the reciprocal of . For example, from the differential equation definition, when and its derivative using the product rule is for all , so for all .
From any of these definitions it can be shown that the exponential function obeys the basic exponentiation identity. For example, from the power series definition, expanded by the Binomial theorem,
This justifies the exponential notation for .
The derivative (rate of change) of the exponential function is the exponential function itself. More generally, a function with a rate of change proportional to the function itself is expressible in terms of the exponential function. This derivative property leads to exponential growth or exponential decay.
The exponential function extends to an entire function on the complex plane. Euler's formula relates its values at purely imaginary arguments to trigonometric functions. The exponential function also has analogues for which the argument is a matrix, or even an element of a Banach algebra or a Lie algebra.
Derivatives and differential equations
The importance of the exponential function in mathematics and the sciences stems mainly from its property as the unique function which is equal to its derivative and is equal to 1 when . That is,
Functions of the form for constant are the only functions that are equal to their derivative (by the Picard–Lindelöf theorem). Other ways of saying the same thing include:
The slope of the graph at any point is the height of the function at that point.
The rate of increase of the function at is equal to the value of the function at .
The function solves the differential equation .
is a fixed point of derivative as a linear operator on function space.
If a variable's growth or decay rate is proportional to its size—as is the case in unlimited population growth (see Malthusian catastrophe), continuously compounded interest, or radioactive decay—then the variable can be written as a constant times an exponential function of time.
More generally, for any real constant , a function satisfies if and only if for some constant . The constant k'' is called the decay constant, disintegration constant, rate constant, or transformation constant.
Furthermore, for any differentiable function , we find, by the chain rule:
Continued fractions for
A continued fraction for can be obtained via an identity of Euler:
The following generalized continued fraction for converges more quickly:
or, by applying the substitution :
with a special case for :
This formula also converges, though more slowly, for . For example:
Complex exponential
As in the real case, the exponential function can be defined on the complex plane in several equivalent forms.
The most common definition of the complex exponential function parallels the power series definition for real arguments, where the real variable is replaced by a complex one:
Alternatively, the complex exponential function may be defined by modelling the limit definition for real arguments, but with the real variable replaced by a complex one:
For the power series definition, term-wise multiplication of two copies of this power series in the Cauchy sense, permitted by Mertens' theorem, shows that the defining multiplicative property of exponential functions continues to hold for all complex arguments:
The definition of the complex exponential function in turn leads to the appropriate definitions extending the trigonometric functions to complex arguments.
In particular, when ( real), the series definition yields the expansion
In this expansion, the rearrangement of the terms into real and imaginary parts is justified by the absolute convergence of the series. The real and imaginary parts of the above expression in fact correspond to the series expansions of and , respectively.
This correspondence provides motivation for cosine and sine for all complex arguments in terms of and the equivalent power series:
for all
The functions , , and so defined have infinite radii of convergence by the ratio test and are therefore entire functions (that is, holomorphic on ). The range of the exponential function is , while the ranges of the complex sine and cosine functions are both in its entirety, in accord with Picard's theorem, which asserts that the range of a nonconstant entire function is either all of , or excluding one lacunary value.
These definitions for the exponential and trigonometric functions lead trivially to Euler's formula:
We could alternatively define the complex exponential function based on this relationship. If , where and are both real, then we could define its exponential as
where , , and on the right-hand side of the definition sign are to be interpreted as functions of a real variable, previously defined by other means.
For , the relationship holds, so that for real and maps the real line (mod ) to the unit circle in the complex plane. Moreover, going from to , the curve defined by traces a segment of the unit circle of length
starting from in the complex plane and going counterclockwise. Based on these observations and the fact that the measure of an angle in radians is the arc length on the unit circle subtended by the angle, it is easy to see that, restricted to real arguments, the sine and cosine functions as defined above coincide with the sine and cosine functions as introduced in elementary mathematics via geometric notions.
The complex exponential function is periodic with period and holds for all .
When its domain is extended from the real line to the complex plane, the exponential function retains the following properties:
for all
Extending the natural logarithm to complex arguments yields the complex logarithm , which is a multivalued function.
We can then define a more general exponentiation:
for all complex numbers and . This is also a multivalued function, even when is real. This distinction is problematic, as the multivalued functions and are easily confused with their single-valued equivalents when substituting a real number for . The rule about multiplying exponents for the case of positive real numbers must be modified in a multivalued context:
See failure of power and logarithm identities for more about problems with combining powers.
The exponential function maps any line in the complex plane to a logarithmic spiral in the complex plane with the center at the origin. Two special cases exist: when the original line is parallel to the real axis, the resulting spiral never closes in on itself; when the original line is parallel to the imaginary axis, the resulting spiral is a circle of some radius.
Considering the complex exponential function as a function involving four real variables:
the graph of the exponential function is a two-dimensional surface curving through four dimensions.
Starting with a color-coded portion of the domain, the following are depictions of the graph as variously projected into two or three dimensions.
The second image shows how the domain complex plane is mapped into the range complex plane:
zero is mapped to 1
the real axis is mapped to the positive real axis
the imaginary axis is wrapped around the unit circle at a constant angular rate
values with negative real parts are mapped inside the unit circle
values with positive real parts are mapped outside of the unit circle
values with a constant real part are mapped to circles centered at zero
values with a constant imaginary part are mapped to rays extending from zero
The third and fourth images show how the graph in the second image extends into one of the other two dimensions not shown in the second image.
The third image shows the graph extended along the real axis. It shows the graph is a surface of revolution about the axis of the graph of the real exponential function, producing a horn or funnel shape.
The fourth image shows the graph extended along the imaginary axis. It shows that the graph's surface for positive and negative values doesn't really meet along the negative real axis, but instead forms a spiral surface about the axis. Because its values have been extended to , this image also better depicts the 2π periodicity in the imaginary value.
Matrices and Banach algebras
The power series definition of the exponential function makes sense for square matrices (for which the function is called the matrix exponential) and more generally in any unital Banach algebra . In this setting, , and is invertible with inverse for any in . If , then , but this identity can fail for noncommuting and .
Some alternative definitions lead to the same function. For instance, can be defined as
Or can be defined as , where is the solution to the differential equation , with initial condition ; it follows that for every in .
Lie algebras
Given a Lie group and its associated Lie algebra , the exponential map is a map satisfying similar properties. In fact, since is the Lie algebra of the Lie group of all positive real numbers under multiplication, the ordinary exponential function for real arguments is a special case of the Lie algebra situation. Similarly, since the Lie group of invertible matrices has as Lie algebra , the space of all matrices, the exponential function for square matrices is a special case of the Lie algebra exponential map.
The identity can fail for Lie algebra elements and that do not commute; the Baker–Campbell–Hausdorff formula supplies the necessary correction terms.
Transcendency
The function is not in the rational function ring : it is not the quotient of two polynomials with complex coefficients.
If are distinct complex numbers, then are linearly independent over , and hence is transcendental over .
Computation
The Taylor series definition above is generally efficient for computing (an approximation of) . However, when computing near the argument , the result will be close to 1, and computing the value of the difference with floating-point arithmetic may lead to the loss of (possibly all) significant figures, producing a large relative error, possibly even a meaningless result.
Following a proposal by William Kahan, it may thus be useful to have a dedicated routine, often called expm1, which computes directly, bypassing computation of . For example,
one may use the Taylor series:
This was first implemented in 1979 in the Hewlett-Packard HP-41C calculator, and provided by several calculators, operating systems (for example Berkeley UNIX 4.3BSD), computer algebra systems, and programming languages (for example C99).
In addition to base , the IEEE 754-2008 standard defines similar exponential functions near 0 for base 2 and 10: and .
A similar approach has been used for the logarithm; see log1p.
An identity in terms of the hyperbolic tangent,
gives a high-precision value for small values of on systems that do not implement .
See also
Carlitz exponential, a characteristic analogue
Gaussian function
Half-exponential function, a compositional square root of an exponential function
- Used for solving exponential equations
List of exponential topics
List of integrals of exponential functions
Mittag-Leffler function, a generalization of the exponential function
-adic exponential function
Padé table for exponential function – Padé approximation of exponential function by a fraction of polynomial functions
Phase factor
Notes
References
External links
Elementary special functions
Analytic functions
Exponentials
Special hypergeometric functions
E (mathematical constant) | Exponential function | Mathematics | 4,523 |
6,025,673 | https://en.wikipedia.org/wiki/Axial%20symmetry | Axial symmetry is symmetry around an axis; an object is axially symmetric if its appearance is unchanged if rotated around an axis. For example, a baseball bat without trademark or other design, or a plain white tea saucer, looks the same if it is rotated by any angle about the line passing lengthwise through its center, so it is axially symmetric.
Axial symmetry can also be discrete with a fixed angle of rotation, 360°/n for n-fold symmetry.
See also
Axiality (geometry)
Circular symmetry
Reflection symmetry
Rotational symmetry has a more general discussion
Chiral symmetry describes the use in quantum mechanics
References
Rotational symmetry | Axial symmetry | Physics,Mathematics | 127 |
28,921,857 | https://en.wikipedia.org/wiki/Artwork%20%28graphic%20arts%29 | Artwork (also known as art layoutdrawing) is a type of drawing that serves a graphical representation of an image for its reproduction onto a substrate via various processes, such as silkscreen, label making and other printing methods. Transfer of the image often involves a photographic process.
Historically, some types of artworks were prepared on clear polyester drafting film or similar media for strength, durability and dimensional stability. Modern artwork may be stored electronically, such as those created in Adobe Illustrator file format (.ai).
See also
Engineering drawings
Logo
References
Graphic design
Communication design | Artwork (graphic arts) | Engineering | 115 |
1,711,063 | https://en.wikipedia.org/wiki/Aerodynamic%20heating | Aerodynamic heating is the heating of a solid body produced by its high-speed passage through air. In science and engineering, an understanding of aerodynamic heating is necessary for predicting the behaviour of meteoroids which enter the Earth's atmosphere, to ensure spacecraft safely survive atmospheric reentry, and for the design of high-speed aircraft and missiles.
"For high speed aircraft and missiles aerodynamic heating is the conversion of kinetic energy into heat energy as a result of their relative motion in stationary air and the subsequent transfer through the skin into the structure and interior of the vehicle. Some heat is produced by fluid compression at and near stagnation points such as the vehicle nose and wing leading edges. Additional heat is generated from air friction along the skin inside the boundary layer". These two regions of skin heating are shown by van Driest. Boundary layer heating of the skin may be known as kinetic heating.
The effect of skin heating on aircraft wing design
The effects of aerodynamic heating on the temperature of the skin, and subsequent heat transfer into the structure, the cabin, the equipment bays and the electrical, hydraulic and fuel systems, have to be incorporated in the design of supersonic and hypersonic aircraft and missiles.
One of the main concerns caused by aerodynamic heating arises in the design of the wing. For subsonic speeds, two main goals of wing design are minimizing weight and maximizing strength. Aerodynamic heating, which occurs at supersonic and hypersonic speeds, adds an additional consideration in wing structure analysis. An idealized wing structure is made up of spars, stringers, and skin segments. In a wing that normally experiences subsonic speeds, there must be a sufficient number of stringers to withstand the axial and bending stresses induced by the lift force acting on the wing. In addition, the distance between the stringers must be small enough that the skin panels do not buckle, and the panels must be thick enough to withstand the shear stress and shear flow present in the panels due to the lifting force on the wing. However, the weight of the wing must be made as small as possible, so the choice of material for the stringers and the skin is an important factor.
At supersonic speeds, aerodynamic heating adds another element to this structural analysis. At normal speeds, spars and stringers experience a load which is a function of the lift force, first and second moments of inertia, and length of the spar. When there are more spars and stringers, the load in each member is reduced, and the area of the stringer can be reduced to meet critical stress requirements. However, the increase in temperature caused by energy flowing from the air (heated by skin friction at these high speeds) adds another load factor, called a thermal load, to the spars. This thermal load increases the force felt by the stringers, and thus the area of the stringers must be increased in order for the critical stress requirement to be met.
Another issue that aerodynamic heating causes for aircraft design is the effect of high temperatures on common material properties. Common materials used in aircraft wing design, such as aluminum and steel, experience a decrease in strength as temperatures get extremely high. The Young's Modulus of the material, defined as the ratio between stress and strain experienced by the material, decreases as the temperature increases. Young's Modulus is critical in the selection of materials for wing, as a higher value lets the material resist the yield and shear stress caused by the lift and thermal loads. This is because Young's Modulus is an important factor in the equations for calculating the critical buckling load for axial members and the critical buckling shear stress for skin panels. If the Young's Modulus of the material decreases at high temperatures caused by aerodynamic heating, then the wing design will call for larger spars and thicker skin segments in order to account for this decrease in strength as the aircraft goes supersonic. There are some materials that retain their strength at the high temperatures that aerodynamic heating induces. For example, Inconel X-750 was used on parts of the airframe of the X-15, a North American aircraft that flew at hypersonic speeds in 1958. Titanium is another high-strength material, even at high temperatures, and is often used for wing frames of supersonic aircraft. The SR-71 used titanium skin panels painted black to reduce the temperature and corrugated to accommodate expansion. Another important design concept for early supersonic aircraft wings was using a small thickness-to-chord ratio, so that the speed of the flow over the airfoil does not increase too much from the free stream speed. As the flow is already supersonic, increasing the speed even more would not be beneficial for the wing structure. Reducing the thickness of the wing brings the top and bottom stringers closer together, reducing the total moment of inertia of the structure. This increases axial load in the stringers, and thus the area, and weight, of the stringers must be increased. Some designs for hypersonic missiles have used liquid cooling of the leading edges (usually the fuel en route to the engine). The Sprint missile's heat shield needed several design iterations for Mach 10 temperatures.
Reentry vehicles
Heating caused by the very high reentry speeds (greater than Mach 20) is sufficient to destroy the vehicle unless special techniques are used. The early space capsules such as used on Mercury, Gemini, and Apollo were given blunt shapes to produce a stand-off bow shock, allowing most of the heat to dissipate into the surrounding air. Additionally, these vehicles had ablative material that sublimates into a gas at high temperature. The act of sublimation absorbs the thermal energy from the aerodynamic heating and erodes the material rather than heating the capsule. The surface of the heat shield for the Mercury spacecraft had a coating of aluminium with glassfiber in many layers. As the temperature rose to the layers would evaporate and take the heat with it. The spacecraft would become hot but not harmfully so. The Space Shuttle used insulating tiles on its lower surface to absorb and radiate heat while preventing conduction to the aluminium airframe. Damage to the heat shield during liftoff of Space Shuttle Columbia contributed to its destruction upon reentry.
See also
Thermal velocity
References
Further reading
Moore, F.G., Approximate Methods for Weapon Aerodynamics, AIAA Progress in Astronautics and Aeronautics, Volume 186
Chapman, A.J., Heat Transfer, Third Edition, Macmillan Publishing Company, 1974
Bell Laboratories R&D, ABM Research and Development At Bell Laboratories, 1974. Stanley R. Mickelsen Safeguard Complex
Atmospheric entry
Heat transfer
Aerospace engineering
Aerodynamics | Aerodynamic heating | Physics,Chemistry,Engineering | 1,352 |
40,470,121 | https://en.wikipedia.org/wiki/Turpinite | Turpinite, also called Turpenite, is a fictional war gas allegedly developed by the French chemist Eugène Turpin and deployed against the attacking German army during the first months of World War I.
According to contemporary accounts, Turpinite, delivered by artillery shells, silently and suddenly killed any person within of impact with its fumes. Survivors of Turpinite barrages reported a strong chemical smell after an attack. In reality, this smell was a side effect of the explosives used by the French and British militaries during the war. The widespread, sudden deaths caused by artillery were in many cases caused by concussion, which leaves no mark on the victim.
After the war, German scientist Fritz Haber, who pioneered German gas attacks at the Second Battle of Ypres, said German soldiers had reported a strong chemical smell attributed to turpenite. Haber and others investigated, finding the smell was due to incomplete combustion of the picric acid used in British artillery shells. The belief that the French used chemical weapons in 1914 may have contributed to later German use of such weapons.
Bibliography
Max Hastings, Catastrophe 1914: Europe Goes to War. London, Knopf Press, Release Date 24 September 2013, , 640 pp.
References
World War I chemical weapons
Fictional weapons | Turpinite | Chemistry | 262 |
77,358,029 | https://en.wikipedia.org/wiki/Arnold%20Caplan | Arnold Caplan (1942–2024) was a scientist and professor at Case Western Reserve University known for being the father of mesenchymal stem cells (MSCs). His initial work focused on the “Mesengenic process” whereby MSC’s could be preferentially differentiated into the numerous tissues of the mesodermal lineage
Career
He joined Case Western in 1969.
He founded Osiris Therapeutics in 1992.
He has said "by calling them “Mesenchymal Stem Cells,” we are misrepresenting what the cells’ true functions are in the body; instead, he proposes that these cells be renamed “Medicinal Signaling Cells,” to better reflect their main functions in the body: an intelligent source of therapeutic signals for the body to repair and regenerate."
References
1942 births
2024 deaths
Case Western Reserve University faculty
Place of birth missing | Arnold Caplan | Biology | 179 |
24,940,642 | https://en.wikipedia.org/wiki/RoboTuna | The RoboTuna is a robotic fish project involving a series of robotic fish designed and built by a team of scientists at the Massachusetts Institute of Technology (MIT) in the US.
The Project
The project started in 1993. Their aim was to investigate the possibility of constructing a robotic submarine that could reproduce the way tunas swim and see if they could find a superior system of propulsion for the Autonomous Underwater Vehicles (AUVs). Their experiment was a success as they discovered that their fish was both more maneuverable and used less energy than other robotic submarines. The Science Museum in London, UK has one on display in their geophysics and oceanography section .
Improvements
While the early results were successful the RoboTuna was not able to replicate the bursts of acceleration that real tuna were able to manage. Researchers improved the design using a genetic algorithm, in which the best systems will "get to have virtual offspring" according to researcher David Barrett. Early incarnations worked poorly but as the system evolved the RoboTuna's abilities improved. Visualization techniques showed that the system had evolved so that the RoboTuna was taking advantage of vortices that it created. A swish of its tail one way creating a vortex, which was then used by a swish the other way - propelling it off the vortex it had created. This technique not only helps to with normal swimming but explains the impressive standing start speeds of real tuna.
The Researchers
The team involved in the project included: Michael Triantafyllou, David Barrett who built the first RoboTuna (Charlie I) in 1995 for his PhD thesis, and David Beal and Michael Sachinis, who introduced several modifications including a cable-pulley system to produce RoboTuna II.
See also
Tunabot
References
Electromechanical engineering
Robotic animals
Robots of the United States
1995 robots
Massachusetts Institute of Technology
Underwater robots
Tuna | RoboTuna | Engineering,Biology | 372 |
16,384,668 | https://en.wikipedia.org/wiki/SGR%201900%2B14 | |- style="vertical-align: top;"
| Distance
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SGR 1900+14 is a soft gamma repeater (SGR), located in the constellation of Aquila about 20,000 light-years away. It is assumed to be an example of an intensely magnetic star, known as a magnetar. It is thought to have formed after a fairly recent supernova explosion.
An intense gamma-ray burst from this star was detected on August 27, 1998; shortly thereafter a new radio source appeared in that region of the sky. Despite the large distance to this SGR, estimated at 20,000 light years, the burst had large effects on the Earth's atmosphere. The atoms in the ionosphere, which are usually ionized by the Sun's radiation by day and recombine to neutral atoms by night, were ionized at nighttime at levels not much lower than the normal daytime level. The Rossi X-ray Timing Explorer (RXTE), an X-ray satellite, received its strongest signal from this burst at this time, even though it was directed at a different part of the sky, and should normally have been shielded from the radiation.
NASA's Spitzer Space Telescope detected a mysterious ring around SGR 1900+14 at two narrow infrared frequencies in 2005 and 2007. The 2007 Spitzer image showed no discernible change in the ring after two years. The ring measures seven light-years across. The origin of the ring is currently unknown and is the subject of an article in the May 29, 2008 issue of the journal Nature.
References
External links
Image SGR 1900+14
Aquila (constellation)
Soft gamma repeaters
Astronomical X-ray sources
Magnetars | SGR 1900+14 | Astronomy | 349 |
48,940,756 | https://en.wikipedia.org/wiki/NGC%20654 | NGC 654 is an open cluster in the constellation Cassiopeia. It was discovered by William Herschel in 1787. With apparent magnitude 6.5, it can be observed by binoculars. It is located 2,5° northeast of the star Delta Cassiopeiae. In the same low power field can also be seen the open clusters NGC 663 and NGC 659. It surrounds a 7th magnitude yellowish star, an F5Ia supergiant, which is a possible member of the group.
It is 2,400 parsec away. It is a very young cluster, aged approximately 15 million years, but it could be as old as 40 million years, with a time spread of star formation of at least ~20 Myr. The central region of the cluster shows less reddening than the rest of the cluster. One explanation is that between the Solar System and the cluster lie two dust layers, one at 200pc and one more at 1Kpc. Behind the cluster is one more dust layer. The cluster has approx. 80 members, including three Be stars and a few luminous stars like HD 10494 and F5Ia. The earliest spectral type is around B0.
NGC 654 is assumed to form part of the stellar association Cassiopeia OB8, that is located in the Perseus arm of the Milky Way, along with the open clusters M103, NGC 663, NGC 659, and some supergiant stars scattered between them, all of them having similar ages and distances.
Gallery
References
External links
Open clusters
Cassiopeia (constellation)
0654
?
Discoveries by William Herschel | NGC 654 | Astronomy | 334 |
60,525,309 | https://en.wikipedia.org/wiki/Cyber%20Discovery | Cyber Discovery was a United Kingdom initiative to get teenagers interested in cyber security. The initiative was funded £20 million by the UK Department for Digital, Culture, Media and Sport in partnership with SANS Institute Started in 2017, each year the program had followed a similar pattern of 4 (often overlapping) stages.
In the first year of operation, 170 students attended 3 different events in Manchester, Bristol and London in Summer 2018. The events lasted for 2 days and included talks from industry professionals, challenges, and a Capture the Flag competition.
References
Computer security
Digital media | Cyber Discovery | Technology | 112 |
18,276,340 | https://en.wikipedia.org/wiki/Andrew%20Schlafly | Andrew Layton Schlafly (; born April 27, 1961) is an American lawyer and Christian conservative activist. He is the founder and owner of the wiki encyclopedia project Conservapedia. He is the son of the conservative activist and lawyer Phyllis Schlafly.
Schlafly was the lead counsel for the Association of American Physicians and Surgeons' efforts to bring the Patient Protection and Affordable Care Act before the United States Supreme Court.
Early life and education
Schlafly is one of six children. His great-great-grandfather August Schlafly was a Swiss immigrant to the United States. His father Fred Schlafly was an attorney, and his mother Phyllis (née Stewart) spearheaded the movement opposing the Equal Rights Amendment and was founder of the Eagle Forum.
Born and raised in Alton, Illinois, Schlafly graduated from Saint Louis Priory School and later received a B.S.E. in electrical engineering and certificate in engineering physics from Princeton University in 1981.
Career
Engineering
After graduating from Princeton, Schlafly briefly worked as a device physicist for Intel in Santa Clara, California until 1983, when he became a microelectronics engineer at the Johns Hopkins University Applied Physics Laboratory. Schlafly later worked for Bell Labs before enrolling at Harvard Law School.
Legal
Schlafly graduated from Harvard Law School in 1991 with a J.D. in the class that included future U.S. president Barack Obama. From 1989 to 1991, Schlafly was an editor of the Harvard Law Review.
After law school, Schlafly served as an adjunct professor at Seton Hall Law School. In 1992, Schlafly ran as a Republican for the United States House of Representatives seat of Virginia's 11th congressional district; Schlafly came in last place in a field of five candidates in the primary.
Schlafly was an associate for the Wachtell, Lipton, Rosen & Katz law firm in New York City before moving to private practice. Additionally, he is General Counsel at the Association of American Physicians and Surgeons and led its unsuccessful Supreme Court challenge to the Patient Protection and Affordable Care Act. In 2010, Schlafly wrote an article for the Journal of American Physicians and Surgeons about the economic effects of the legislation.
In 2010, Schlafly took the role of lead counsel for a group seeking to recall US Senator Bob Menendez, a Democrat from New Jersey. The group, associated with the Tea Party movement, argued that the US Constitution permits a recall election for federal offices without explicitly so providing. On November 18, 2010, the New Jersey Supreme Court rejected Schlafy's arguments, finding that the New Jersey provision violated the U.S. Constitution. Later that year, Schlafly represented the group RecallND in RecallND v. Jaeger before the North Dakota Supreme Court in another effort to recall Democratic Senator Kent Conrad.
Conservapedia
Schlafly created the wiki-based Conservapedia in November 2006 to counter what he perceived as a liberal bias present in Wikipedia. He felt the need to start the project after reading a student's assignment written using Common Era dating notation, rather than the Anno Domini system that he preferred. Although he was "an early Wikipedia enthusiast", as reported by Shawn Zeller of Congressional Quarterly, Schlafly became concerned about perceived bias after Wikipedia editors repeatedly undid his edits to the article about the 2005 Kansas evolution hearings. Schlafly expressed hope that Conservapedia would become a general resource for American educators and a counterpoint to the liberal bias that he perceived in Wikipedia. The site has been accused of spreading misinformation on scientific subjects, such as HIV/AIDS denialism, the abortion-breast cancer hypothesis, climate change denial, relativity denial, and vaccine/autism connections, and has advocated Young Earth creationism, Barack Obama citizenship conspiracy theories and conspiracy theories that the January 6 United States Capitol attack was staged. Additionally, it features extensive criticisms of atheism, feminism, homosexuality, and the Democratic Party.
In 2009, Schlafly appeared on The Colbert Report to discuss his Conservative Bible Project, a project hosted on Conservapedia that aims to rewrite English translations of the Bible in order to remove or alter terms advancing a "liberal bias".
Dialogue with Richard Lenski
Richard Lenski, an evolutionary biologist known for his work on the E. coli long-term evolution experiment, was contacted by Schlafly in 2008 regarding a set of results that showed one population of E. coli evolved the novel trait of being able to metabolize citrate. Conservapedia supports creationism and objects to evolution, so Schlafly disputed that bacteria could evolve via beneficial mutations. The correspondence was commented on across the Internet. Schlafly was criticized by Lenski on Ars Technica, among other sites, for not reading Lenski's paper properly, for not understanding the experimental data he requested, and for not taking notice of people on Conservapedia itself who considered the paper well researched.
Trademark lawsuit against Saint Louis Brewery
In 2011, Schlafly led a lawsuit on behalf of the family of his activist mother, Phyllis, to block The Saint Louis Brewery from acquiring a trademark on the name "Schlafly". In 2018, the U.S. Federal Circuit Court of Appeals ruled in favor of The Saint Louis Brewery.
Personal life
In 1984, Schlafly married Catherine Kosarek, a medical student and fellow Princeton alum. They live in Far Hills, New Jersey.
References
External links
1961 births
Living people
American people of Swiss descent
American Christian creationists
American critics of atheism
Critics of Wikipedia
Harvard Law School alumni
Johns Hopkins University people
New Jersey lawyers
New Jersey Republicans
People from Alton, Illinois
People from Santa Clara County, California
People from Far Hills, New Jersey
People from Wayne, New Jersey
Princeton University alumni
Seton Hall University School of Law faculty
Virginia Republicans
Activists from California
Male critics of feminism
Wachtell, Lipton, Rosen & Katz people
Relativity critics
20th-century American lawyers
20th-century American people
21st-century American lawyers
Schlafly family | Andrew Schlafly | Physics | 1,267 |
76,361,889 | https://en.wikipedia.org/wiki/Domaine%20Ylang%20Ylang | Domaine Ylang Ylang is the oldest distillery in Mauritius to produce oil from the ylang ylang (Cananga odorata) tree. The plantation of ylang ylang trees alongside the distillery, provided the flowers from which perfume was distilled. The Domaine Ylang Ylang further up the Kestrel Valley commands a view onto the wide lagoon of Vieux Grand Port of Mahebourg and the neighbouring islets on the central east coast of Mauritius.
Although the distillery stopped functioning after 2002 when it had been popular with tourists looking for essential oils and aromatherapy, the laboratory and building can still be seen.
Domaine du Chasseur
In the adjoining Kestrel Valley (also historically known as the Domaine du Chasseur Game Park and Reserve) forest and nature hiking are available for nature-lovers over an area of more than 200 ha where the Mauritius kestrel (Falco punctatus) can be seen. It is an important protected area for many other endemic plants and animal species in Mauritius.
References
Grand Port District
Tourist attractions in Mauritius
Landforms of Mauritius
Environment of Mauritius
Protected areas of Mauritius
Valleys of Africa
Companies of Mauritius
Insular ecology
Important Bird Areas of Mauritius
Biodiversity | Domaine Ylang Ylang | Biology | 241 |
65,402,336 | https://en.wikipedia.org/wiki/Xiaoyu%20Luo | Xiaoyu Luo (, born 1960) is a Chinese and British applied mathematician who studies biomechanics, fluid dynamics, and the interactions of fluid flows with soft biological tissues. She is a professor of applied mathematics at the University of Glasgow.
Education and career
Luo was born in the UK but grew up in Xi'an in a family of artists. After earning bachelor's and master's degrees in theoretical mechanics at Xi'an Jiaotong University, in 1982 and 1985 respectively, she became a lecturer at Xi'an Jiaotong University. There, she studied for a Ph.D. from 1987 until 1990, with a visit to the UK through a joint doctoral program with the University of Sheffield. When she earned her Ph.D. at Xi'an Jiaotong University in 1990, she became the first woman to do so.
She moved to the UK in 1992 to become a postdoctoral researcher at the University of Leeds. She worked as a lecturer in engineering at Queen Mary and Westfield College from 1997 to 2000, and in mechanical engineering at the University of Sheffield from 2000 to 2004, before becoming a senior lecturer in mathematics at the University of Glasgow in 2005. She was promoted to professor in 2008, the first female professor of applied mathematics at Glasgow.
In 2014 she was named a chair professor at Northwestern Polytechnical University in Xi'an. She has also been a visitor to the International Center for Applied Mechanics at Xi'an Jiaotong University.
Recognition
Luo became a Fellow of the Institution of Mechanical Engineers in 2004 and a Fellow of the Royal Society of Edinburgh in 2014.
References
External links
Home page
1960 births
Living people
British mathematicians
21st-century British women mathematicians
Chinese mathematicians
Chinese women mathematicians
Applied mathematicians
Xi'an Jiaotong University alumni
Academic staff of Xi'an Jiaotong University
Academics of Queen Mary University of London
Academics of the University of Sheffield
Academics of the University of Glasgow
Academic staff of the Northwestern Polytechnical University
Fellows of the Institution of Mechanical Engineers
Fellows of the Royal Society of Edinburgh | Xiaoyu Luo | Mathematics | 408 |
5,536,626 | https://en.wikipedia.org/wiki/Digital%20channel%20election | A digital channel election was the process by which television stations in the United States chose which physical radio-frequency TV channel they would permanently use after the analog shutdown in 2009. The process was managed and mandated by the Federal Communications Commission for all full-power TV stations. Low-powered television (LPTV) stations are going through a somewhat different process, and are also allowed to flash-cut to digital.
Process
Stations could choose to keep their initial digital TV channel allocation, do a flash-cut to their former analog TV channel, or attempt to select another channel, often an analog channel or pre-transition digital channel from another station that had been orphaned. Stations on channels 52 to 69 did not have the first option, as the FCC and then the U.S. Congress revoked them from the bandplan.
Many stations have chosen to keep their new channels permanently, after being forced to buy all new transmitters and television antennas. In some cases where the station's current analog tower could not handle the stress of the new digital antenna's weight and wind load, station owners had to construct entirely new broadcast towers in order to comply with the FCC's DTV mandate.
Most broadcasters were bitter at having to purchase digital equipment and broadcast a digital signal when very few homeowners had digital television sets. The FCC allowed broadcasters the opportunity to petition the Federal Communications Commission (FCC) for special temporary authority (STA) to operate their digital facilities at low power, thereby allowing broadcasters additional time in which to purchase their full-power digital facilities. However, the FCC gave a stern July 2006 deadline for all full-power television stations to at least replicate 80% of their current analog coverage area, or run the risk of losing protection from encroachment by other stations.
Most stations made an election in the first round, and most of those received their requested channels. Applicant conflicts with neighboring stations had to request a different channel in the second round. The third and final round occurred in May 2006.
Some stations requested that the FCC assign the best available channel.
Considerations
Aside from the practical considerations above, there are also technical considerations which are based on the physics of the radio spectrum. These affect the radio propagation of DTV just as with other signals.
The low VHF channels from 2 to 6, while requiring the lowest power (up to 100 kW analog video or 20 kW digital), are prone to electromagnetic interference. The ATSC digital TV system has severe problems with susceptibility to impulse noise, bursts of interference which briefly render the entire channel unusable, due to its inability to instantaneously determine where in a video frame to resume display when the signal returns. The result is macroblocking and pixelation of the entire signal whenever impulse noise sources (such as motors, appliances or electrical storms) are active. They also are the lowest in frequency and therefore the longest in wavelength, requiring the largest antennas both to transmit and receive. They are also prone to atmospheric ducting, especially at night when the ground (and the air near it) cools rapidly. Because of the antenna size (a properly-sized VHF TV 2 dipole spans approximately eight feet (2.7 meters)) and the fact that there are only five channels in this band, most set-top antennas are designed to receive the higher TV bands.
Furthermore, channel 6 abuts the FM broadcast band at 88 MHz, possibly causing and receiving interference from adjacent channels. (The FCC refused to remove this band from the bandplan, because taking the high UHF channels instead would bring in more money at auction. This also contradicts what has been done in every other country that has forced a DTV transition, all giving up the VHF bands.) A completely unaddressed issue is the use of HD Radio on 88.1 FM, where the lower sideband overlaps the far upper sideband of digital TV channel 6.
The upper VHF (band III), including channels 7 to 13, is better about the above problems, but still not as good as the UHF band. By keeping these for TV, it also prevents the use of the band for Digital Audio Broadcasting, as is done with local radio stations in Europe.
The UHF band contains 55 channels from 14 to 69, which excludes channel 37 in the U.S. Channels 52 to 69 are unavailable for digital TV, on a permanent basis, leaving only 37 channels. Stations generally try to choose a lower frequency, which causes some crowding and therefore election conflicts on the lowest channels. Still, the UHF band has great advantages over VHF, in large part because of its propagation characteristics and lack of impulse noise. The shorter wavelength also means that smaller antennas are needed, an advantage for both the broadcaster and the viewer. Another advantage is that the great majority of stations use this band, requiring only one type of antenna (and sometimes amplifier) to receive all of those stations. Key disadvantages of UHF operation include the need for greater transmitter power and the reduced coverage area; the edge diffraction of signals around terrestrial obstacles degrades rapidly as frequency is increased.
Effects
Channel elections generally will not affect consumers in the long run, because virtual channel numbering will keep stations appearing on their original analog channel numbers, except the times that a station has trouble transmitting PSIP metadata.
However, most ATSC tuners must re-scan for stations that change their RF channel. On some, this is as simple as manually punching in the new RF channel, at which point the decoder will read the PSIP data and re-map to the proper channel number. However, this may not delete the original mapping, leaving the original "dead" channels interleaved with the new ones (such as 5.1 old, 5.1 new, 5.2 old, 5.2 new), or possibly confusing the receiver (and the user). In many cases, a receiver will not automatically add the new mapping at all if an old one exists. Completely re-scanning will normally solve this, but may not pick up stations that are weak or temporarily off-air during the scan, causing the need to manually enter them (if this is even possible with the given receiver).
Where stations are moving to a different frequency band (such as UHF to VHF), this will affect antenna selection. Many antennas marketed for HDTV use are UHF-only or perform poorly on VHF, while many 82-channel VHF/UHF antennas are a compromise design strongly favoring VHF channels.
References
Digital television
Broadcast engineering | Digital channel election | Engineering | 1,319 |
1,919,022 | https://en.wikipedia.org/wiki/Switched%20fabric | Switched fabric or switching fabric is a network topology in which network nodes interconnect via one or more network switches (particularly crossbar switches). Because a switched fabric network spreads network traffic across multiple physical links, it yields higher total throughput than broadcast networks, such as the early 10BASE5 version of Ethernet and most wireless networks such as Wi-Fi.
The generation of high-speed serial data interconnects that appeared in 2001–2004 which provided point-to-point connectivity between processor and peripheral devices are sometimes referred to as fabrics; however, they lack features such as a message-passing protocol. For example, HyperTransport, the computer processor interconnect technology, continues to maintain a processor bus focus even after adopting a higher speed physical layer. Similarly, PCI Express is just a serial version of PCI; it adheres to PCI's host/peripheral load/store direct memory access (DMA)-based architecture on top of a serial physical and link layer.
Fibre Channel
In the Fibre Channel Switched Fabric (FC-SW-6) topology, devices are connected to each other through one or more Fibre Channel switches. While this topology has the best scalability of the three FC topologies (the other two are Arbitrated Loop and point-to-point), it is the only one requiring switches, which are costly hardware devices.
Visibility among devices (called nodes) in a fabric is typically controlled with Fibre Channel zoning.
Multiple switches in a fabric usually form a mesh network, with devices being on the "edges" ("leaves") of the mesh. Most Fibre Channel network designs employ two separate fabrics for redundancy. The two fabrics share the edge nodes (devices), but are otherwise unconnected. One of the advantages of such setup is capability of failover, meaning that in case one link breaks or a fabric goes out of order, datagrams can be sent via the second fabric.
The fabric topology allows the connection of up to the theoretical maximum of about 16 million devices, limited only by the available address space (224).
239 domains * 256 areas * 256 ports = 15,663,104
See also
Clos network
Fabric Application Interface Standard
InfiniBand
Network traffic control
RapidIO
VPX
References
External links
What is a Switch Fabric
Fibre Channel
Network topology | Switched fabric | Mathematics | 475 |
33,663,228 | https://en.wikipedia.org/wiki/Timeline%20of%20events%20associated%20with%20Anonymous | Anonymous is a decentralised virtual community. They are commonly referred to as an internet-based collective of hacktivists whose goals, like its organization, are decentralized. Anonymous seeks mass awareness and revolution against what the organization perceives as corrupt entities, while attempting to maintain anonymity. Anonymous has had a hacktivist impact. This is a timeline of activities reported to be carried out by the group.
2007
January: Radio host Hal Turner sued several online groups, alleging Anonymous "posted unauthorized copies of his radio shows online, attacked [his] server so as to make it unavailable, and placed unauthorised orders for goods, services and merchandise from third parties in [his] name." The case was dismissed in December for lack of response.
December: A man was arrested in Toronto on charges of luring a child under the age of 14, attempting to invite sexual touching, attempted exposure, and other charges. Police stated that Anonymous, a cyber-vigilante group which trolls for pedophiles and then "outs" them, had targeted the suspect before law enforcement was involved, and cautioned that such interference could impede official investigations.
2008
January 14: Anonymous declared war on the Church of Scientology and bombarded them with DDoS attacks, harassing phone calls, black faxes, and Google bombing.
February–December: Known as Project Chanology, Anonymous organized multiple in-person pickets in front of Churches of Scientology world-wide, starting February 10 and running throughout the year, achieving coordinated pickets in over 100 cities, thousands of protestors, and wearing Guy Fawkes masks.
March 28: The Epilepsy Foundation's forum was salted with posts displaying flashing computer animations with the intention of triggering seizures in photosensitive and pattern-sensitive epileptics. There was some evidence pointing to Anonymous, but Anonymous named other likely culprits including the Church of Scientology seeking to discredit Anonymous. (See also )
June: Anonymous claimed responsibility for attacking and defacing websites and forums of SOHH (Support Online Hip Hop) and AllHipHop, causing the sites to temporarily shut down. They also stole personal information about SOHH employees. (See also .)
September 16: Anonymous declared they hacked the private email account of Sarah Palin. An individual was convicted and sentenced to a year in federal prison. (See also Sarah Palin email hack.)
2009
January: Anonymous targeted California teen McKay Hatch who runs the No Cussing Club, a website against profanity. Hatch's home address, phone number, and other personal information were leaked on the internet, and his family received hate mail, obscene phone calls, bogus pizza deliveries, and pornography through the mail.
June: Anonymous and Pirate Bay set up a website for Iranians to communicate and coordinate online for the 2009 Iranian presidential election protests and the Iranian Green Movement by bypassing the government's internet censorship in Iran.
September 9: Anonymous temporarily shut down the website of the Prime Minister of Australia with a denial-of-service attack as a warning in protest against the government's plan to filter the internet.
2010
January: Anonymous attacked websites of the governments of Tunisia and Zimbabwe over censorship issues related to WikiLeaks.
February 10: Anonymous conducted DDoS attacks against a wide range of Australian government servers in protest of proposed internet filtering legislation which would block some pornography. Australian anti-censorship groups complained that the attack only hurt their cause, and Australian government members dismissed the attack and said that they would just restore the service when the attack finished. (See also February 2010 Australian cyberattacks.)
July: Anonymous flooded the Oregon Tea Party's Facebook page when they found out that OTP had been using part of Anonymous' slogan, "We Are Legion". OTP surrendered, apologized and recanted.
July: In response to Chelsea Manning's imprisonment and treatment after leaking classified information to WikiLeaks, Anonymous threatened to disrupt activities at Marine Corps Brig, Quantico by cyber-attacking communications, exposing private information of personnel, and other harassment methods. Military spokespersons responded that the threat has been referred to law enforcement and counterterrorism officials and requested an investigation.
September: Anonymous targeted major pro-copyright and anti-piracy organizations, law firms, individuals, and entertainment industry websites in retaliation for DDoS attacks on torrent sites. (See also Operation Payback.)
December: Anonymous started DDoS attacks on websites of companies who had withdrawn banking facilities from WikiLeaks including Amazon, PayPal, BankAmerica, Swiss bank PostFinance, MasterCard, and Visa. Over the next year, dozens were arrested and several convicted for their part in the operation. (See also and .)
December: Anonymous promoted sifting through WikiLeaks to identify potentially overlooked cables, making short videos covering the topic, and flooding the internet with them.
2011
January 3: Anonymous got involved during the Tunisian Revolution and engaged in DDoS attacks on key Tunisian websites—including the president, prime minister, ministry of industry, ministry of foreign affairs, and the stock exchange—taking down at least 8 websites and defacing several others. Anonymous distributed information and scripts to help Tunisians bypass government censorship, and Anonymous' own website also came under DDoS attack.
January 9: Anonymous hacked and defaced the website of Fine Gael, an Irish political party.
February 27: As part of the 2011 Wisconsin protests, Anonymous knocked offline the website for the Koch brother's Americans for Prosperity.
Attack on HBGary Federal
On the weekend of February 5–6, 2011, Aaron Barr, the chief executive of the security firm HBGary Federal, announced that his firm had successfully infiltrated the Anonymous group, and although he would not hand over details to the police, he would reveal his findings at a later conference in San Francisco. In retaliation for Aaron Barr's claims, members of the group Anonymous hacked the website of HBGary Federal and replaced the welcome page with a message stating that Anonymous should not be messed with, and that the hacking of the website was necessary to defend itself. Using a variety of techniques, including social engineering and SQL injection, Anonymous went on to take control of the company's e-mail, dumping 68,000 e-mails from the system, erasing files, and taking down their phone system. The leaked emails revealed the reports and company presentations of other companies in computer security such as Endgame systems who promise high quality offensive software, advertising "subscriptions of $2,500,000 per year for access to 0day exploits".
Among the documents exposed was a PowerPoint presentation entitled "The Wikileaks Threat", put together by HBGary Federal along with two other data intelligence firms for Bank of America in December. Within the report, these firms created a list of important contributors to WikiLeaks; they further developed a strategic plan of attack against the site. As TechHerald explains, "the plan included pressing a journalist in order to disrupt his support of the organization, cyber attacks, disinformation, and other potential proactive tactics." The report specifically claims that Glenn Greenwald's support was key to WikiLeaks' ongoing survival.
Anonymous also personally attacked Aaron Barr by taking control of his Twitter account, posting Mr Barr's supposed home address and social security number.
In response to the attacks, founder of HBGary Federal, Greg Hoglund, responded to journalist Brian Krebs, "They didn't just pick on any company, we try to protect the US Government from hackers. They couldn't have chosen a worse company to pick on." After the attacks, Anonymous continued to clog up HBGary Federal fax machines, and made threatening phone calls.
Operation Ouroboros
On February 16, 2011, the group supposedly wrote an open letter to the Westboro Baptist Church, stating: "Cease & desist your protest campaign in the year 2011... close your public Web sites. Should you ignore this warning... the propaganda & detestable doctrine that you promote will be eradicated; the damage incurred will be irreversible, and neither your institution nor your congregation will ever be able to fully recover." On February 19, 2011, the church responded, telling Anonymous to "bring it on" and calling them, among other things, "a puddle of pimple-faced nerds". Anonymous subsequently denied the authenticity of the threat, suggesting that someone from outside Anonymous had made the posting. Due to their website being openly editable by anyone, it is unknown who made the post. Anonymous responded with a press release calling the Westboro Church "professional trolls" stating that they believe that it was a member of the Westboro Church making an attempt to provoke an attack, thus acting as a honeypot which would both allow the church to retaliate against Internet service providers in court, and to gain it further publicity. They also claimed that they had more pressing matters to attend to, namely the support of the protests that led to the 2011 Libyan civil war. That said, Anonymous later suggested tactics for those who wished to attack Westboro nevertheless, avoiding DDoS in favor of sending "prostitutes, preferably male", and in general to "rape their asses in the most unpredictable ways possible".
Anonymous indicated that an attack would be self-defeating, stating: "When Anonymous says we support free speech, we mean it. We count Beatrice Hall among our Anonymous forebears: 'I disapprove of what you say, but I will defend to the death your right to say it.'" Nonetheless, Westboro's website at godhatesfags.com suffered an attack. Another hacktivist by the name of Jester claimed to bring down the websites from the Westboro Baptist Church on his Twitter account.
2011–2012 Operation Empire State Rebellion
On March 14, 2011, Anonymous began releasing emails it said were obtained from Bank of America. According to the group, the files show evidence of "corruption and fraud", and relate to the issue of improper foreclosures. They say that a former employee named Brian Penny from Balboa Insurance, a firm which used to be owned by BofA, appeared to be a reputable insider in the force placed insurance market, a market which, in 2012, began getting more and more coverage from various government and media sources, including the New York Department of Finance, 50 State Attorney General Coalition, the Consumer Financial Protection Bureau, and large class action lawsuits. Balboa Insurance is now owned by Australian Reinsurance company QBE, while Brian privately consults various agencies and institutions on the inside workings of mortgage/insurance tracking systems and force placed insurance while maintaining a blog about his experience as a whistleblower.
Operation Sony
Anonymous announced their intent to attack Sony websites in response to Sony's lawsuit against George Hotz and, specifically due to Sony's gaining access to the IP addresses of all the people who visited George Hotz's blog as part of the libel action, terming it an 'offensive against free speech and internet freedom' Although Anonymous admitted responsibility to subsequent attacks on the Sony websites, Anonymous branch AnonOps denied that they were the cause behind a major outage of the PlayStation Network in April 2011. However, as Anonymous is a leaderless organization, the possibility remains that another branch of the group is responsible for the outage, though screenshots of AnonOps promotion of the attack still exist.
June
June 6: Anonymous claimed to have hacked India's National Informatics Centre in support of Ramdev, defacing it.
June 12: Anonymous claimed responsibility for a DDoS attack of the website of the National Police Corps of Spain, asserting it was a legitimate form of peaceful protest in retaliation for the arrest of three individuals alleged to be associated with acts of cyber civil disobedience attributed to Anonymous.
June 15: The group launched DDoS attacks on ninety-one Malaysian government websites in retaliation for their censoring of websites.
June 20: Members of the group took down the websites of the Orlando, Florida Chamber of Commerce and inserted a message into the website of the Universal Orlando Resort requesting that users "boycott Orlando". The group did so in response to the arrests of members of Food Not Bombs for feeding the homeless in Lake Eola Park against city ordinances. The group had planned and announced the attack on their IRC channel. The group has vowed to take a different Orlando-related website offline every day, and have also targeted the re-election website of Mayor of Orlando Buddy Dyer and the Orlando International Airport. A member of the group left a Guy Fawkes mask outside of the mayor's home; the police are treating the picture taken of the mask as a threat against the mayor. On July 11, the group took down the website of the Roman Catholic Diocese of Orlando and the Rotary Club of Orlando.
June 28: Anonymous announced that within the next 24 hours, it would hack into the website of the Knesset, the legislature of Israel, and knock it offline. It was stated that the planned attacks were a response to alleged hacking attacks by Israeli intelligence such as the Stuxnet virus, a computer virus which allegedly was created by Israeli and U.S. intelligence and targeted the Iranian nuclear program.
Operation Anti-Security
The group collaborated with LulzSec to hack the websites of a number of government and corporate sources and release information from them. As well as targeting American sites, Anonymous also targeted government sites in Tunisia, Anguilla, Brazil, Zimbabwe, Turkey, and Australia. On July 21, Anonymous released two PDFs allegedly taken from NATO.
Operation Facebook
In August 2011, someone created an account on Twitter with the name OP_Facebook and announced the "Operation Facebook". According to the links on the post, Anonymous was going to take down Facebook on November 5, 2011. The date "November 5" is believed to be a reference to V for Vendetta, where the character "V" conducts his plans every fifth of November in memory of Guy Fawkes. This operation isn't assuredly an Anonymous one. There was an earlier OpFacebook that was abandoned, and this was an attempted revival. The plan was contentious and does not appear to be supported by the majority of those who say they are part of Anonymous.
Operation BART
In August 2011, in response to Bay Area Rapid Transit's shutdown of cell phone service in an attempt to disconnect protesters from assembling in response to a police shooting, as well as the shooting itself, Anonymous sent out a mass email/fax bomb to BART personnel and organized multiple mass physical protests at the network's Civic Center station. Anonymous also hacked the BART website, releasing the personal information of 102 BART police officers, as well as account information for about 2,000 customers.
Shooting Sheriffs Saturday
In an event dubbed "Shooting Sheriffs Saturday," Anonymous hacked 70 (mostly rural) law enforcement websites and released 10 GB of leaked emails, training files, informant information and other information. The name is likely a reference to the song "I Shot the Sheriff" by Bob Marley.
Support of Occupy Wall Street
Several contingents of Anonymous have given support to the Occupy Wall Street movement, with members attending local protests and blogs run by members covering the movement.
Operation Syria
In early August, Anonymous hacked the Syrian Defense Ministry website and replaced it with a vector image of the pre-Ba'athist flag, a symbol of the pro-democracy movement in the country, as well as a message supporting the 2011 Syrian uprising and calling on members of the Syrian Army to defect to protect protesters.
Operation DarkNet
In October 2011, the collective campaigned against child pornography protected by anonymous hosting techniques. They temporarily DDoSed 40 child porn sites, published the usernames of over 1500 people frequenting one of those websites, and invited the U.S. Federal Bureau of Investigation and Interpol to follow up.
Opposition to Los Zetas
On October 6, 2011, Anonymous released a video stating that Los Zetas had kidnapped one of the group's members, and threatened that unless the hostage was freed, they would publish personal information about members of the cartel and their collaborators in politics, police, military, and business, which might lead to their prosecution by Mexican authorities, or targeting by rival cartels. The website of Gustavo Rosario Torres, a former Tabasco state prosecutor, was subsequently defaced with a message suggesting his involvement with the organization. According to Anonymous Iberoamerica blog, in early November Los Zetas reportedly freed the kidnapped victim without knowledge of its Anonymous affiliation.
However, following widespread news coverage of the video, reporters did not find evidence of a previous Anonymous action matching the description given, and found little evidence of support among Anonymous members, particularly in Mexico. Reporters noted a lack of details and police reports and that the Veracruz state attorney general couldn't confirm the kidnapping.
Operation Brotherhood Takedown
On November 7, 2011, Anonymous released a warning threat to the Muslim Brotherhood that they would take down major websites belonging to their organization. On November 12 the Muslim Brotherhood released a statement detailing the extent of the attack and that four websites were temporarily taken down. On November 12, 2011, another video was released claiming the attack would continue until November 18.
John Pike incident
In response to the UC Davis pepper-spray incident, Anonymous released the personal information of John Pike, the officer that pepper-sprayed peaceful protestors.
Attack on Stratfor
On December 24, claims were made that Anonymous stole thousands of e-mail addresses and credit card information from security firm Stratfor. Reportedly, Anonymous commented that this is because the data was unencrypted, however some members of Anonymous denied the group was involved. The hackers included Jeremy Hammond, who worked with Anonymous to release Stratfor's 5,543,061 emails to WikiLeaks. The emails revealed Stratfor's surveillance of groups such as Occupy Wall Street and protestors of the Bhopal disaster.
Operation Pharisee
Operation Pharisee was an attack organized via social media such as Facebook, Twitter, and YouTube against the Vatican website for World Youth Day 2011. It was unsuccessful, despite a denial-of-service attack resulting 34 times normal traffic, and well-documented due to the efforts of Imperva, the security firm employed by the Vatican.
Operation Deepthroat
Anonymous, along with 4chan's /b/ board, Reddit, Tumblr and Funnyjunk, teamed together to make a raid on 9gag called Operation Deepthroat. The raid was separated in multiple teams: The first team, the Alpha Team, spammed "horrifying" images of child pornography, gore, furries and scat on 9gag's site, followed by fake accounts made by 4chan, Anonymous, Reddit, Tumblr and Funnyjunk voting the spam up, effectively overloading the servers. The second team, the Gold Team, used the Low Orbit Ion Cannon and the High Orbit Ion Cannon (LOIC and HOIC, respectively), and fired on 9gag, which DDoS'd the entire site down. The third team, the Red Team, was tasked to spread the information of the OP on 4chan, Reddit, Tumblr and Funnyjunk, and also supported the other teams. The fourth and final team, the White Team, was tasked with spamming chat sites such as Omegle and Chatroulette with inappropriate messages, such as "9gag.com is the place for Child Pornography!", in order to tarnish 9gag's "wholesome" and "family-friendly" name. The reason behind this whole operation began when 9gag took several of 4chan's memes and called them theirs, followed by making a legion called the '9gag army', a ripoff of Anonymous. The operation began on December 21, 2011, at 12:00 AM, and ended at 11:59 PM. 9gag was mainly offline for the next few days, except for some servers which managed to protect themselves from the LOIC and HOIC. Prior to the operation, 4chan users used fake accounts to trick 9gaggers into DDoS'ing themselves, saying the coordinates were that of 4chan. The pre-raid attack was mostly ineffective, however, as only a few servers went down.
2012
CSLEA hack
In January 2012, Anonymous hacked the website of the California Statewide Law Enforcement Association to protest police brutality.
Occupy Nigeria
In solidarity with Occupy Nigeria, Anonymous has joined forces with the People's Liberation Front and the Naija Cyber Hactivists of Nigeria. Anonymous promised "a relentless and devastating assault upon the web assets of the Nigerian government" in support of Occupy Nigeria.
This was in protest to the removal of fuel subsidy that the majority of impoverished Nigerians depend upon for their very existence, causing the price of fuel and transportation to skyrocket and therefore extreme hardship for the majority of Nigerians. On January 13, the Nigerian Economic and Financial Crimes Commission website was hacked, with a false report of the arrest of people involved in the oil sector replacing the normal page.
Operation Megaupload
In retaliation for the shut down of the file sharing service Megaupload and the arrest of four workers, Anonymous DDoSed the websites of UMG (the company responsible for the lawsuit against Megaupload), the United States Department of Justice, the United States Copyright Office, the Federal Bureau of Investigation, the MPAA, Warner Brothers Music, the RIAA, and the HADOPI the afternoon of January 19, 2012. The operations by Anonymous were speculated to have been driven further by anger over the House of Representatives' Stop Online Piracy Act (SOPA) and the Senate's Protect Intellectual Property Act (PIPA).
Anti-ACTA activism in Europe
On January 21, 2012, a series of DDoS attacks on Polish government websites took place, for which the Anonymous took responsibility and referred to as "the Polish Revolution". The group via their Twitter account stated it was a revenge for upcoming signing of ACTA agreement by the Polish government. Starting with websites of the Sejm, Polish Prime Minister, President, Ministry of Culture and National Heritage, later on websites of the police, Internal Security Agency, Ministry of Foreign Affairs were also blocked. The presumed attack was further strengthened by the media coverage which resulted in extremely high interest of public opinion, followed up by blackout of popular Polish websites on 24th and protests of thousands of people on January 24 and 25, in major cities of Poland, against signing ACTA. Other suspected targets were the websites of Paweł Graś - the government's spokesman (blocked after Graś denied the attacks ever took place), the website of PSL (blocked after Eugeniusz Kłopotek, a member of the party, supported ACTA on air of the major TV station). Governmental sites in France's presidential website and Austria's Ministry of Justice, Ministry of Internal Affairs, Ministry of Economy and also the website of the Federal Chancellor were also cracked and paralyzed.
Anonymous in Slovenia announced opposition against the Slovenian signing of the ACTA and have posted video threats on various websites against the government officials, as well as against Nova Ljubljanska Banka (commonly known as NLB), accusing the latter of corruption. On February 4, 2012, The NLB was a victim of a cyber attack and was offline for one hour, while public demonstrations were held in the capital of Ljubljana and in Maribor. Some estimated 3000 people gathered in the capital, while around 300 protested in Maribor.
Operation Russia
Unidentified hackers cracked email boxes of some prominent pro-Kremlin activists and officials, including Vasily Yakemenko, head of the Federal Agency for Youth Affairs, Kristina Potupchik, press secretary for Nashi youth movement, and Oleg Khorokhordin, deputy head of the Department for Internal Affairs at the Presidential Administration. Since February 1, links to contents of the mailboxes have been appearing on @OP_Russia Twitter account. The hackers confirmed they consider themselves a part of the Anonymous movement; "We are Anonymous", they stated in an interview. The information discovered enabled many to accuse Yakemenko and his colleagues in paying some influential bloggers, as well as numerous trolls, for publishing stories and commenting in favour of Vladimir Putin on negative press articles on the Internet.
Boston Police Department attacks
On February 3, 2012, Anonymous hacked a website belonging to the Boston Police Department to protest the eviction of Occupy Wall Street protestors. BPD later responded with a sarcastic video of their own.
Preventing vote tampering
In 2012, Anonymous claims to have added a firewall they called The Great Oz, allegedly designed to prevent election tampering in the United States.
Syrian Government E-mail Hack
On February 6, 2012, Anonymous broke into the mail server of the Syrian Ministry of Presidential Affairs, gaining access to some 78 inboxes of Bashar al-Assad's staffers in the process. One of the email files was a document preparing Assad for his December 2011 interview with ABC's Barbara Walters. One of the passwords commonly used by Assad's office accounts was "12345."
In July 2012, Anonymous gave over 2.4 million e-mails to WikiLeaks.
AntiSec Leak and CIA Attack
On Friday, February 10, 2012, Anonymous claimed responsibility for taking down the Central Intelligence Agency's website for more than 5 hours. Several servers went back up while others stayed down. This followed a conversation leak, in which Anonymous took responsibility, between FBI and Scotland Yard officials discussing members of Anonymous being put on trial as well as other topics on the group, which took place a week before. On March 6, 2012, Donncha O'Cearbhaill was charged in connection with the leak. He was released 24-hours later.
Interpol Attack
Following Interpol's announcement on February 28 that they made arrests of 25 suspected members of the hacking activist group Anonymous in Europe and South America, their site went down for a moment.
AIPAC Attack
On March 4, 2012, Anonymous took down the American Israel Public Affairs Committee website. An AIPAC spokesman was questioned on the matter but did not respond. A video titled "Anonymous: Message to AIPAC" was uploaded on YouTube earlier the same day.
Vatican website DDoS Attacks
The official website of the Vatican was brought down temporarily by a DDoS attack from Anonymous on March 7, 2012. Later that day the website recovered. Anonymous has also attempted to take the site down in 2011 but the attempt did not succeed. They claimed that their attack was not targeted against the followers of the Catholic Church but against the Church itself, which Anonymous viewed as corrupt.
On March 12 the Vatican's official website was brought down for a few hours by a second DDoS attack. Anonymous also hacked Vatican Radio and gained access to the Vatican Radio database in protest against the Vatican Radio allegedly using "repeaters with power transmission largely outside the bounds of the law."
Bureau of Justice leak
On March 21, 2012, 1.7GB of data was stolen from the United States Bureau of Justice Statistics by Anonymous. The leak reportedly contained "shiny things such as internal emails and the entire database dump."
Taking down Monsanto's Hungarian website
On March 16 the official website of Monsanto's Hungarian website collapsed and wasn't restored until March 26.
Symantec source code leak
In March 2012, people claiming to be a part of Anonymous leaked the source code for old versions of Norton AntiVirus and Norton Utilities.
April 2012 Chinese attack
In April 2012, Anonymous hacked 485 Chinese government websites, some more than once, to protest the treatment of their citizens. They urged people to "fight for justice, fight for freedom, [and] fight for democracy".
Operation Bahrain and Formula One attacks
On April 21, Anonymous defaced the official site of Formula One, in protest against the 2012 Bahrain Grand Prix. The race was the subject of ongoing controversy, as it was being held during ongoing anti-government protests, with the support of the government. Anonymous posted a press release criticising the decision to hold the race despite the violent crackdowns, and posted data of ticket sales for the event with sensitive information — particularly the credit card numbers of spectators — redacted. Other sites related to the sport and the Bahraini government were also the subject of distributed denial-of-service attack.
Occupy Philippines
On April 21, 2012 busabos of Anonymous Philippines attacked the China University Media Union website, as a retaliation against alleged Chinese hackers who defaced the University of the Philippines website, which claimed that the Scarborough Shoal is Chinese territory. Anonymous left a message that the Scarborough Shoal is the Philippines' territory. On April 25, 2012, busabos of Anonymous #OccupyPhilippines warned that they had not yet started their attack against Chinese websites. The members that can be counted in hand called the cyber attacks were a result of the 2012 Scarborough Shoal standoff.
Operation India
On May 17, 2012, Anonymous launched an attack against the websites of the India Supreme Court and the then-ruling Congress party in reaction to internet service providers blocking popular video sites like Vimeo as well as file-sharing sites like The Pirate Bay.
Operation Quebec
On May 20, 2012, Anonymous launched Opération Québec in reaction to the adoption of Bill 78 by the government of Quebec, an act restricting the freedom of association in this Canadian province after several weeks of student protests. A video was released urging the governing Liberal Party of Quebec to let the citizens protest.
On May 21, the websites of the Liberal Party of Quebec, of the Ministry of Public Security of Quebec as well as a government site on police ethics were DDoSed.
Anonymous then threatened to disrupt the Formula 1 Grand Prix of Canada, to be held between June 7 and 10 in Montreal, the same way they did for the Bahrain Grand Prix. They claimed to have accessed personal information stored in the F1 website.
On May 30, Anonymous leaked a video called "DVD Gouverne (mental)", a 2 hours long footage from Sagard, Quebec where a party for the wife of Paul Desmarais of Power Corporation had been held in 2008. Among the guests were former US president George H. Bush, premier Jean Charest of Quebec, former Canadian prime ministers Jean Chrétien and Brian Mulroney, former Québec premier Lucien Bouchard, former governor general of Canada Adrienne Clarkson, journalist Charlie Rose, singers Robert Charlebois and Hiromi Omura, lyricist Luc Plamondon and conductor Yannick Nézet-Séguin.
Operation Cyprus
An Anonymous video was released on June 8, 2012, claiming that an attack against the government of Cyprus would take place due to reasons of government corruption, media misinformation and the Anti-Counterfeiting Trade Agreement On June 26, DDoS attacks took place against 47 websites of the Republic of Cyprus, which were taken down for 15 hours. The government stated that it was a coordinated attack by Anonymous.
Operation Japan
On June 26, 2012, the website of the Japanese Business Federation, was taken offline, with Anonymous claiming this was part of "Operation Japan". The reason for their action was the new amendments to the copyright laws in Japan. For those found to have illegally copied material such as music, DVDs or Blu-ray discs, fines could run as high as $25,000 and carry a sentence of two years in prison, according to CNET Japan.
Operation Anaheim
On July 25, 2012, Anonymous launched an online protest in response to the Anaheim police shooting. It began with the release of the personal information of some of the top officers, including police chief John Welter.
AAPT attack
In July 2012, Anonymous hacked Australian ISP AAPT and later leaked 40 GB of partially redacted customer data to protest data retention policy.
Attack on the Mexican PRI party
On July 6, 2012, as part of the Yo Soy 132 student protest movement, the Mexican branch of Anonymous defaced the PRI party website, the party that held the power of the country for 70 years and that the 132 movement accused of human rights violations during that period. Anonymous hacked the site leaving slogans against the electoral fraud and the imminent return of the PRI party to power.
Peña's birthday present
On July 20, 2012, a second attack on a PRI related website was performed as part of the Yo Soy 132 student protest movement, by the Mexican branch of Anonymous. This time Anonymous did it on the birthday of president elect Peña Nieto, and as "a gift" they left a picture of Peña next to slogans against electoral fraud and a penis shaped birthday cake.
Operation Myanmar
On August 10, 2012, Anonymous launched a DDoS attack and defacement of more than 100 Myanmar websites, all hackers from all over the world joined this operation as a protest for killing Muslim Rohingya in Myanmar. Myanmar's hackers also made a lot of counterattacks.
Uganda LGBT rights
On August 13, 2012, Anonymous hacked two Uganda government websites to protest the country's strict anti-gay laws.
Hong Kong National Education
In mid-September 2012, Anonymous hackers threatened the Hong Kong government organization, known as National Education Centre. In their online video, Anonymous members claimed responsibility for leaking classified related government documents and taking down the National Education Centre website, after the Hong Kong government has repeatedly ignored months of wide-scale protests against the establishment of a new core Moral and National Education curriculum for children from 6–18 years of age. The new syllabus has come under heavy criticism and international media attention, as it does not award students based on how much factual information is learned, but instead grades and evaluates students based on their level of emotional attachment and approval of the Chinese Communist Party.
Philippine Cybercrime Prevention Act of 2012
busabos of Anonymous Philippines launched a series of attacks against several websites of the Philippine government to protest against the Cybercrime Prevention Act of 2012. The hackers urged for the revisions of the cybercrime law. On September 26, Anonymous defaced several websites, including that of the Bangko Sentral ng Pilipinas and the Philippine National Police. They claim that the law violates freedom of expression and described the law as "most notorious act ever witnessed in the cyber-history". On October 1, they hacked again several government websites in an operation dubbed as "Bloody Monday" and asked for "a revision of the [Cybercrime Law] for the betterment of the Filipino netizens." In February 2014 the Philippine Supreme Court ruled out the online libel to be unconstitutional because of its some provisions.
Release of Westboro Baptist Church Personal Information
Anonymous re-posted the names, addresses, and emails of the prominent members of the Westboro Baptist Church on December 16, 2012, due to announced plans to picket the funerals of the victims of the Sandy Hook Elementary School shooting, followed by saying that God would protect their site. They also caused several DDOS attacks on the site itself, hacked the social media accounts of the members involved, and started a whitehouse.org petition to get the Church legally branded as a Hate Group.
2013
Steubenville rape case
In early 2013, the group released an incriminating video, photographs and tweets from the Steubenville High School football team allegedly involved in a gang rape of an underage girl in rural Ohio. They also released a number of e-mails and photos hacked from the e-mail account of one of the football programs boosters, whom they alleged to have helped cover up the case.
Attack on the Mexican Army website
On January 13, 2013, the SEDENA (the Mexican Army) website was penetrated by the Anonymous branch in Mexico, and all the information found on the vulnerable servers was disclosed (including usernames and passwords). The content of the site was changed for a video with images of the riots that occurred during Peña Nieto's presidential inauguration (on December 1, 2013), and a voice in the background pronounces the Zapatista manifesto. The reason behind the attack was in retaliation for what they called the return of an oppressive government imposed by electoral fraud.
Aaron Swartz Suicide
In January 2013, the group attacked and defaced the United States Sentencing Commission website turning it into a game page repeatedly after which traffic to the website made it crash following the suicide of Reddit co-founder and activist Aaron Swartz. Swartz was accused of stealing materials from the Massachusetts Institute of Technology with intent to distribute them freely.
Federal Reserve
The Federal Reserve was hacked by Anonymous in February 2013.
Operation North Korea
On April 2, 2013, a professional IT webzine BGR carried out an article stating that hacker group Anonymous has started the 'Operation Free Korea.' This calls for 'controversial leader Kim Jong-un [to] resign', 'install free democracy' 'abandon its nuclear ambitions' 'uncensored Internet access' etc. The hackers also proclaimed that if North Korea do not accede to their demand, they will wage "Cyber War." On April 3, 2013, hacker group identifying itself as Anonymous claimed it had stolen all 15,000 user passwords as part of a cyberwar against the DPRK. A few days later, Anonymous claimed to have hacked into the Uriminzokkiri main website, and the Twitter and Flickr pages representing the website.
Instead, a picture posted Thursday on the North's Flickr site shows Kim's face with a pig-like snout and a drawing of Mickey Mouse on his chest. Underneath, the text reads: "Threatening world peace with ICBMs and Nuclear weapons/Wasting money while his people starve to death." It found common ground with its alleged arch-enemy and hacktivist The Jester in which the latter had claimed responsibility for the cyberattacks against Air Koryo and other North Korean websites.
On June 22, 2013, Anonymous claimed that it managed to steal military documents from North Korea, and that the documents would be released on June 25, the day the Korean War started. However, no such documents appear to have been released.
Op Israel
OpIsrael was a coordinated cyber-attack by anti-Israel individuals and Anonymous-affiliated groups that target websites perceived as Israeli The attack, mostly denial of service assaults, was coordinated to coincide with Holocaust Remembrance Day. OpIsrael's stated goal was to "erase Israel from the internet". The attack targeted several government online operations banking and commerce sites, but most of the cyber attacks were repelled, with no significant damage done, although an attack may have succeeded in temporarily taking down the Central Bureau of Statistics site. Media and small business sites were also targeted, and some attacks succeeded in temporarily replacing some of homepages with anti-Israel slogans. However, there were several Facebook pages, Twitter feeds, and web sites from the alleged hackers making false claims to have "caused Israel to lose $5 billion" and "Tel Aviv loses all Internet connection. It was one of Anonymous's biggest failures"
Nir Goldshlager a famous "white hat" hacker and CEO of Break Security Goldshlager, told reporters that OpIsrael hackers "lacked the sophistication and knowledge...while they told many lies to enhance their reputations." Israeli hackers responded to OpIsrael by taking down the OpIsrael website and replacing it with pro-Israel statements and the Israeli national anthem, Hatikvah. In addition, they brought down anti-Israeli sites like Hezbollah's and Islamic Jihad's websites and targeted servers belonging to hackers and broke into the personal computers of the European leaders of the operation and told them to look for the facts and not believe everything they see on the Internet.
2012 Cleveland police shooting incident
In December 2012, Cleveland police fired 137 rounds at a car, killing its two occupants. Anonymous responded in April 2013 by releasing the personal information of the officers involved. 12 officers were later fired or disciplined for their role in the shooting, although criminal charges are still being considered by a grand jury.
Rehtaeh Parsons
In response to the suicide of Rehtaeh Parsons and the lack of action on the part of Canadian authorities, Anonymous threatened to release the personal information of the rapists. However, the group claimed to back down from the threat following pleas from Parsons' mother, Leah. The group has staged protests outside the Royal Canadian Mounted Police headquarters in Halifax.
Sabah Crisis
In March 2013 during the Lahad Datu standoff tension in Sabah due to the clashes between the Royal Army of the Sultanate of Sulu and Malaysian security Forces. A Cyberwar sparks between Philippines and Malaysia. According to the Philippine Cyber Army the Malaysian hackers appeared to have started the attacks and defacement on Philippine websites, posting online threats and videos meaning to send a message to the Filipinos to keep away from the region of Sabah. In response to their attacks the Philippine Cyber Army defaced 175 Malaysian sites (including state-owned pages). The Mcafee Lab Researchers in their 2013 Threats Report placed the Philippine Cyber Army in the list of Global Threats on hacktivism. The Philippine Cyber Army are close to Anonymous.
Philippine Coast Guard incident
On May 9, 2013, a number of Philippine Coast Guard soldiers fired at an unarmed Taiwanese fishing boat, Guang Da Xing No. 28, and killed a Taiwanese fisherman in international waters. On May 10, Hackers recognizing themselves as "AnonTAIWAN" hacked into Philippine Official websites asking for the Philippines' government to apologize to Taiwan's government. They interfered with government official websites of the Philippines, causing inconveniences for the Philippine General Election. Its resulted in great difficulty and delay in making general access through the Philippine government websites at the time of elections.
EDL
In May 2013, Anonymous published the personal information of various English Defence League members online in what Anonymous said was the first part of an attempt to destroy the far right protest movement.
Public NSA documents
On June 7, 2013, Anonymous released what was claimed to be secret documents related to the NSA. In reality, the documents were already publicly available.
Hawthorne dog shooting incident
On June 30, 2013, a Hawthorne, California police officer, Jeffrey Salmon of Torrance, was filmed shooting a dog and arresting his owner. Anonymous responded by issuing a video threat to the police department. The city website also suffered a DDoS attack, although it is unclear if Anonymous was involved.
Nigeria anti-gay laws
On July 4, 2013, Anonymous hacked the national website of Nigeria after the country passed laws that would make homosexuality punishable by up to 14 years in prison.
The GCSB
Anonymous NZ, a New Zealand-based offshoot of Anonymous, carried out its first operation by staging a DDoS on the web site of the Government Communications Security Bureau (GCSB), following the passage of law changes that allowed the electronic intelligence agency to surveil New Zealand citizens. In addition, the web sites of politicians who supported the law changes were also shut down by Anonymous NZ.
Operation Singapore
From August 20, 2013, to November 5, 2013, the group launched attacks on various websites including Ang Mo Kio Town Council, National Museum of Singapore which they leaked 3,600 emails, IP addresses and names from, PAP Community Foundation, and The Straits Times.
National Party-linked websites attacks
Anonymous New Zealand claimed attacks on National Party-linked websites in protest against the GCSB Bill have had no thanks from spied-on internet mogul Kim Dotcom.
Support of anti-PDAF movement
Anonymous Philippines has hacked 115 government websites, prompting Philippine law enforcement agencies to go after them, citing the unnecessary use of hacking. The NBI has been ordered to probe into the hacking of government websites. While a few Senators have downplayed the attacks, they were willing to listen to their grievances, Senator Trillanes IV expressed alarm with the group's capabilities, suggesting the possibility of the group to hack government websites since "it could compromise State operations and data storage."
2014
#OpJustina
In response to the controversial custodial case of Justina Pelletier in which the Boston's Children Hospital alleged her parents of child abuse while Justina was believed to have contracted a mitochondrial disorder, Anonymous performed DDOS attacks against the hospital. As a result, a member was arrested after an unsuccessful flight attempt to Cuba.
Operation Ferguson
Anonymous posted a video warning to the Ferguson, Missouri, police, admonishing them for fatally shooting Mike Brown, an unarmed African American teenager, and swearing revenge if any protesters demonstrating against the police are harmed. The group, which has adopted the Guy Fawkes mask as its symbol and frequently becomes involved in contentious legal matters, said in the video late Sunday Brown's death Saturday is just the latest example of police misconduct having deadly big consequences.
On August 12, a series of doxes were released against Jon Belmar, the St. Louis County Police Chief. There were two reasons for this target. 1) Because he refused to release the name of the officer who shot Mike Brown and 2) Because he challenged Anonymous, calling their threats hollow. A Twitter account affiliated with Anonymous struck back with information regarding Belmar's location, phone number, family members, and their accounts on social media. That same account also released information claiming to be the dox of the officer who shot Brown, but wound up being incorrect.
Operation Hong Kong
Anonymous posted a video warning on News2Share to the Government of the Hong Kong Special Administrative Region on October 1 announcing the engagement of Operation Hong Kong, condemning the government's police's use of force in the ongoing protests. The group stated that it supports the protesters' fight for democracy and promised the government that if the protesters are further harmed or harassed they would attack all web based assets of the Hong Kong Government including but not limited to the taking down of government websites, seizing of government databases, and releasing the personal information on government officials. Anonymous stated that it is time for democracy for the people of Hong Kong and condemns the police for harming the citizens and calls for them to instead protect the citizens.
On October 2, there have been reports that Anonymous have already taken over a few company websites in Hong Kong in accordance to a Hong Kong newspaper Apple Daily.
The Hong Kong Government responded that its servers and web assets are functioning normally, and have arranged to strengthen its cyber defences. The Government further stated that it is prepared against any attempts by Anonymous hackers on its servers and web assets.
Operation Infosurge
November 8, Anonymous Leyte began hacking Philippine government websites to protest the alleged incompetence government officials exhibited in the aftermath of Super Typhoon Yolanda (Haiyan).
More than 10 government websites were defaced by the said group and 33 more were brought rendered inaccessible, for up to 7 hours and a week before, the Department of Trade and Industry (DTI) was reportedly hacked with some 2,000 email addresses, usernames, and password hashes released on Pastebin.
The "Operation Infosurge" was done during the Haiyan Anniversary, which was expected to be a day of prayer and thanksgiving, but turned out to be a day of protest from different "online" groups and organizations in Philippines.
2015
Charlie Hebdo response
In response to the Charlie Hebdo shooting, the Anonymous released a statement offering condolences to the families affected by it and denounced the attacks as an "inhuman assault" on freedom of expression. They also addressed the terrorists: "[a] message for al-Qaeda, the Islamic State, and other terrorists – we are declaring war against you, the terrorists." As such, Anonymous plans to target Jihadist websites and social media accounts linked to supporting Islamic terrorism with the aim of disrupting them and shutting them down.
Gas station hacks
On February 11, Anonymous hacked at least 1 gas station automated tank gauge, changing the online name from "DIESEL" to "WE_ARE_LEGION". Theregister.co.uk stated that a hacker with this kind of access could shut down the entire station by "spoofing the reported fuel level, generating false alarms, and locking the monitoring service out of the system".
Operation Death Eaters
During the week of February 14, Anonymous launched Operation Death Eaters for collating evidence against international pedophile rings and their severe abuse of children to bring them to justice.
Operation Stop Reclamation
On April 2, 2015. The Pro-Philippine Hackers of Anonymous Philippines attacked and defaced a total of 132 Chinese government, educational and commercial websites in response to China's reclamation work in territorial disputes in the South China Sea, parts of which Manila calls the West Philippine Sea.
Operation Anon Down
On July 17, 2015, an Anon in a Guy Fawkes mask was shot and killed by a Royal Canadian Mounted Police (RCMP) officer. As a result, Anonymous websites and YouTube channels vowed revenge, initiating Operation Anon Down. The RCMP website was reported down nationwide on July 19.
Operation StormFront
On July 21, 2015, Anonymous posted a video claiming that due to "Racism, Antisemitism, Islamophobia and Holocaust Denial" they were going to attack the website Stormfront. This website is a white-supremacist website run by former KKK Leader Don Black. The attack was planned for August 1, 2015.
Operation KKK (OPKKK)
Operation KKK says it has identifying data on as many as 1,000 KKK members and supporters. On Oct. 22, 2015, an Anonymous-associated Twitter account announced that the hacking collective had accessed a Klan-associated Twitter account and promised that they would expose about 1,000 Klan members by name. A later news release promised that the operation would release "names and Web sites, new and old" of "more than 1000″ members of the hate group. According to the Daily Dot, Anonymous later released "a few hundred names, Facebook pages, and Google+ accounts."
2016
March 27: Philippines Commission on Elections data breach. Hacker arrested.
December: Anonymous engaged in online activism for a year with DDoS attacks against the Government of Thailand and Ministry of Information and Communication Technology websites to pressure the government to stop pending legislation that would add amendments to the Computer Crime Act and effectively build a Thai version of China's Great Firewall. In December, Anonymous breached the websites of the Thai Police, Ministry of Defence, and Ministry of Tourism and Sports, after which 9 hackers were arrested.
2017
February: A hacker broke into the servers of dark web hosting company Freedom Hosting II, discovered that half of their client's websites were child pornography or other illegal activities, stole information, publicly dumped it, and compromised the company's servers. Security experts later noted that the Tor network had shrunk by 15-20%.
2019
November: Allegedly in retaliation for the siege of the Hong Kong Polytechnic University, Anonymous hacked various Chinese websites, and revealed personal identity information about government employees and corporate data.
December: Anonymous gained access to six email accounts of the Chilean Army and revealed information related to intelligence, operations, finances and international relations from 2015 to 2019.
2020
#PLDTHacked
On May 28, 2020, the Twitter account of PLDT's customer service was hacked by a Filipino anonymous group as a protest to the terrible internet connection serviced by PLDT. The hackers also changed the profile's name to "PLDT Doesn't Care".
The first tweet by the hackers states: "As the pandemic arises, Filipinos need fast internet to communicate with their loved ones. Do your job. The corrupt fear us, the honest support us, the heroic join us. We are Anonymous. We are Legion. We do not forgive. We do not forget . Expect us."
#BlackLivesMatter Movement
Anonymous declared a large hacking sequence on May 28, three days after the murder of George Floyd. An individual claiming to be Anonymous stated that "We are Legion. We do not forgive. We do not forget. Expect us." in a now-deleted video. Anonymous addressed police brutality and vowed that they "will be exposing your many crimes to the world". It is suspected that Anonymous are the cause for the downtime and public suspension of the Minneapolis Police Department website and its parent site, the website of the City of Minneapolis. The webpage belonging to a minor United Nations agency was also turned into a memorial for George Floyd.
BlueLeaks
Anonymous claimed responsibility for stealing and leaking a trove of documents collectively nicknamed 'BlueLeaks'. The 269-gigabyte collection was published by a leak-focused activist group known as Distributed Denial of Secrets.
Bolsonaro hack and support of Julian Assange
In June 4, a group of hackers has released personal information on Brazilian president Jair Bolsonaro and his family and cabinet. Justice minister André Mendonça asked the Federal Police to begin an investigation. Then a parliamentary inquiry by the Brazilian Congress investigating the issue of fake news on the internet issued a report showing that the federal government used R$2 million in public money to fund advertising on several websites, some of them responsible for supporting the president. Anonymous took down Atlanta Police Department's website via DDoS, and defaced websites such as a Filipino governmental webpage and that of Brookhaven National Labs. They expressed support for Julian Assange and press freedom, while briefly "taking a swing" against Facebook, Reddit and Wikipedia for having 'engaged in shady practices behind our prying eyes'. In the case of Reddit, they posted a link to a court document describing the possible involvement of a moderator of a large traffic subreddit (r/news) in an online harassment-related case.
#UgandanLivesMatter
On November 20, 2020, the Uganda Police website was hacked as it was down for a number of days. Anonymous came out and claimed the hack in a tweet in response to the violent crackdown on protesters following the arrest of presidential candidate, popstar Bobi Wine. "Uganda: Police (@PoliceUg) have murdered at least 28 people, arrested 577, and injured dozens more with live ammunition, beatings, tear gas, and water cannons. At a protest challenging President Yoweri Museveni's 34-year reign. UgandaIsBleeding ugandanlivesmatter." read the retweet by Anonymous International account. The first tweet about the hack was done by a claimed member of Anonymous stating that Uganda police force website has been taken offline in response to the violent crackdown on protesters. They should have expected us.. "
2021
#OpsWakeUp21
Anonymous announced cyber-attacks on at least five Malaysian websites including that of Johor and Sabah state governments as well as the International Trade and Industry Ministry. As a result, 11 individuals were nabbed as suspects.
Operation Jane and Epik hack
The Texas Heartbeat Act, a law which bans abortions after six weeks of pregnancy, came into effect in Texas on September 1, 2021. The law relies on private citizens to file civil lawsuits against anyone who performs or induces an abortion, or aids and abets one, once "cardiac activity" in an embryo can be detected via transvaginal ultrasound, which is usually possible beginning at around six weeks of pregnancy. Shortly after the law came into effect, anti-abortion organizations set up websites to collect "whistleblower" reports of suspected violators of the bill.
On September 3, Anonymous announced "Operation Jane", a campaign focused on stymying those who attempted to enforce the law by "exhaust[ing] the investigational resources of bounty hunters, their snitch sites, and online gathering spaces until no one is able to maintain data integrity". On September 11, the group hacked the website of the Republican Party of Texas, replacing it with text about Anonymous, an invitation to join Operation Jane, and a Planned Parenthood donation link.
On September 13, Anonymous released a large quantity of private data belonging to Epik, a domain registrar and web hosting company known for providing services to websites that host far-right, neo-Nazi, and other extremist content. Epik had briefly provided services to an abortion "whistleblower" website run by the anti-abortion Texas Right to Life organization, but the reporting form went offline on September 4 after Epik told the group they had violated their terms of service by collecting private information about third parties. The data included domain purchase and transfer details, account credentials and logins, payment history, employee emails, and unidentified private keys. The hackers claimed they had obtained "a decade's worth of data" which included all customers and all domains ever hosted or registered through the company, and which included poorly encrypted passwords and other sensitive data stored in plaintext. Later on September 13, the Distributed Denial of Secrets (DDoSecrets) organization said they were working to curate the allegedly leaked data for public download, and said that it consisted of "180gigabytes of user, registration, forwarding and other information". Publications including The Daily Dot and The Record by Recorded Future subsequently confirmed the veracity of the hack and the types of data that had been exposed.
Concurrently, the group announced that they have hacked the accounts of German conspiracy theorist Attila Hildmann; as a result one of its Twitter accounts @AnonNewsDE has been suspended and in turn caused reactions from politicians such as the MEP of the German Pirate Party, Patrick Breyer who had recommended the microblogging service Mastodon as an alternative. The hacker collective wrote that the blocking does not restrict the group in its work. The suspension caused the hashtag #FreeAnonNewsDe to be trending on Twitter in Germany.
Hack of Brazilian municipal website
The Brazilian branch of the hacking group hacked the website of the Brumadinho City Hall and left a video to commemorate the dam disaster that occurred on 25 January 2019 which caused the deaths of 270 people.
2022
Operations during the Russian invasion of Ukraine
Anonymous declared that they had launched 'cyber operations' against the Russian Federation, in retaliation for the invasion of Ukraine ordered by Russian president Vladimir Putin. Websites targeted include the state-controlled RT.
Anonymous is also believed to be responsible for hacking several Russian state TV channels; many users on Twitter and TikTok uploaded videos showing channels playing Ukrainian music and displaying pro-Ukraine images, flags, and symbols. They had hacked Russian television services in order to broadcast footage of the war in Ukraine, and systems believed to be related to Russian space agency Roscosmos where they defaced its website and leaked mission files.
A yacht allegedly belonging to Vladimir Putin was reportedly hacked by the group where they changed its call sign to “FCKPTN” and setting its target destination to “hell”. They broadcast a troll face picture through a hacked Russian military radio.
At least 2,500 Russian and Belarusian targets were reportedly hacked by Anonymous. These included more than three hundred websites of Russian government agencies, state media outlets, banks, as well as websites of leading Belarusian banks such as Belarusbank, Priorbank and Belinvestbank. They also hacked a website belonging to Chechnya's regional government. They also warned that “If things continue as they have been in the past few days, the cyber war will be expanded and our measures will be massively increased. This is the final warning to the entire Russian government. Don't mess with Anonymous.”
In response to the seizure of Ukraine's Zaporizhia Nuclear Power Plant by Russia, Anonymous defaced the website of Rosatom and gained access to gigabytes of data which they intended to leak publicly. They had hacked into printers in Russia to spread anti-propaganda messages.
Anonymous leaked 446 GB of data from the Russian Ministry of Culture and had hacked Russian companies Aerogas, Forest, and Petrovsky Fort. From there they leaked around 437,500 emails which they donated to non-profit whistleblower organization Distributed Denial of Secrets. Following that, the hacking collective hacked and leaked 87,500 emails from an engineering firm Neocom Geoservice, which specialises in exploring oil and gas fields and providing drilling support.
In a similar fashion mentioned above, Russian investment company Accent Capital had its computer systems hacked and its 365,000 letters leaked online.
On May 9, 2022, which is the Victory Day in Russia, the video-hosting website RuTube was taken down through cyberattacks, which Anonymous had claimed responsibility later. Network Battalion 65 (NB65), a hacktivist group affiliated with Anonymous, has reportedly hacked Russian payment processor Qiwi. A total of 10.5 terabytes of data including transaction records and customers' credit cards had been exfiltrated. They further infected Qiwi with ransomware and threatened to release more customer records.
Anonymous proceeded to hack Russian firms SOCAR Energoresource and Metprom Group LLC and dump their emails, the latter which was hacked by the Anonymous actors DepaixPorteur, B00daMooda, and Wh1t3Sh4d0w. Anonymous hacked into Vyberi Radio and published more than 1,000,000 emails.
DDoSecrets published 1 terabyte of data obtained from Anonymous, which included millions of files including emails, court files, client data, classified data, photographs, videos, payment information, and more from Rustam Kurmaev and Partners (RKPLaw), which was hacked by Anonymous actors DepaixPorteur and B00daMooda.
Anonymous member "YourAnonSpider" had reportedly hacked into a Russian military UAV (Unmanned Aerial Vehicles) company in which plans and tactics regarding the use of drones in warfare had been stolen.
The collective claimed responsibility for hacking Yandex Taxi on early September 2022 which sent dozens of cars to a location resulting in a traffic jam that lasted up to three hours.
Hack of Australian police emails
The hacking collective leaked 82GB of emails from Australian police in protest of that country's offshore detention of refugees.
2023
Operations during the Israel-Palestinian War
On October 7, Anonymous targeted numerous Israeli systems such as the Iron Dome missile defense system, the government, Israeli websites, and cameras.
Anonymous issued a statement directed to Benjamin Netanyahu and the Israeli government that the international community was outraged by actions that have "resulted in unimaginable devastation, with thousands of innocent lives lost including over 4000 children, and many more injured and displaced".
In March 2024, Anonymous stated that if Israel did not agree in a couple of days to a ceasefire, they would attack, which they did on March 10 attacking Dimona nuclear plant systems by stealing and publishing more than 7 gigabytes of data.
See also
Anonymous (group)
2016 Dyn cyberattack
References
Further reading
How Anonymous Picks Targets, Launches Attacks, and Takes Powerful Organizations Down by Quinn Norton July 3, 2012 Wired.com, includes timeline of events.
The Secret Lives of Dangerous Hackers; 'We Are Anonymous' by Parmy Olson May 31, 2012
Parmy Olson We Are Anonymous timeline on pages 421-431 Hachette Book Group USA
Anonymous (hacker group)
Articles containing video clips
Anonymous
Denial-of-service attacks
Imageboards
Internet culture
Internet events
Internet memes
Social media campaigns
Anonymous | Timeline of events associated with Anonymous | Technology | 12,981 |
8,855,574 | https://en.wikipedia.org/wiki/Thermal%20bridge | A thermal bridge, also called a cold bridge, heat bridge, or thermal bypass, is an area or component of an object which has higher thermal conductivity than the surrounding materials, creating a path of least resistance for heat transfer. Thermal bridges result in an overall reduction in thermal resistance of the object. The term is frequently discussed in the context of a building's thermal envelope where thermal bridges result in heat transfer into or out of conditioned space.
Thermal bridges in buildings may impact the amount of energy required to heat and cool a space, cause condensation (moisture) within the building envelope, and result in thermal discomfort. In colder climates (such as the United Kingdom), thermal heat bridges can result in additional heat losses and require additional energy to mitigate.
There are strategies to reduce or prevent thermal bridging, such as limiting the number of building members that span from unconditioned to conditioned space and applying continuous insulation materials to create thermal breaks.
Concept
Heat transfer occurs through three mechanisms: convection, radiation, and conduction. A thermal bridge is an example of heat transfer through conduction. The rate of heat transfer depends on the thermal conductivity of the material and the temperature difference experienced on either side of the thermal bridge. When a temperature difference is present, heat flow will follow the path of least resistance through the material with the highest thermal conductivity and lowest thermal resistance; this path is a thermal bridge. Thermal bridging describes a situation in a building where there is a direct connection between the outside and inside through one or more elements that possess a higher thermal conductivity than the rest of the envelope of the building.
Identifying Thermal Bridges
Surveying buildings for thermal bridges is performed using passive infrared thermography (IRT) according to the International Organization for Standardization (ISO). Infrared Thermography of buildings can allow thermal signatures that indicate heat leaks. IRT detects thermal abnormalities that are linked to the movement of fluids through building elements, highlighting the variations in the thermal properties of the materials that correspondingly cause a major change in temperature. The drop shadow effect, a situation in which the surrounding environment casts a shadow on the facade of the building, can lead to potential accuracy issues of measurements through inconsistent facade sun exposure. An alternative analysis method, Iterative Filtering (IF), can be used to solve this problem.
In all thermographic building inspections, the thermal image interpretation if performed by a human operator, involving a high level of subjectivity and expertise of the operator. Automated analysis approaches, such as Laser scanning technologies can provide thermal imaging on 3 dimensional CAD model surfaces and metric information to thermographic analyses. Surface temperature data in 3D models can identify and measure thermal irregularities of thermal bridges and insulation leaks. Thermal imaging can also be acquired through the use of unmanned aerial vehicles (UAV), fusing thermal data from multiple cameras and platforms. The UAV uses an infrared camera to generate a thermal field image of recorded temperature values, where every pixel represents radiative energy emitted by the surface of the building.
Thermal Bridging in Construction
Frequently, thermal bridging is used in reference to a building’s thermal envelope, which is a layer of the building enclosure system that resists heat flow between the interior conditioned environment and the exterior unconditioned environment. Heat will transfer through a building’s thermal envelope at different rates depending on the materials present throughout the envelope. Heat transfer will be greater at thermal bridge locations than where insulation exists because there is less thermal resistance. In the winter, when exterior temperature is typically lower than interior temperature, heat flows outward and will flow at greater rates through thermal bridges. At a thermal bridge location, the surface temperature on the inside of the building envelope will be lower than the surrounding area. In the summer, when the exterior temperature is typically higher than the interior temperature, heat flows inward, and at greater rates through thermal bridges. This causes winter heat losses and summer heat gains for conditioned spaces in buildings.
Despite insulation requirements specified by various national regulations, thermal bridging in a building's envelope remain a weak spot in the construction industry. Moreover, in many countries building design practices implement partial insulation measurements foreseen by regulations. As a result, thermal losses are greater in practice that is anticipated during the design stage.
An assembly such as an exterior wall or insulated ceiling is generally classified by a U-factor, in W/m2·K, that reflects the overall rate of heat transfer per unit area for all the materials within an assembly, not just the insulation layer. Heat transfer via thermal bridges reduces the overall thermal resistance of an assembly, resulting in an increased U-factor.
Thermal bridges can occur at several locations within a building envelope; most commonly, they occur at junctions between two or more building elements. Common locations include:
Floor-to-wall or balcony-to-wall junctions, including slab-on-grade and concrete balconies or outdoor patios that extend the floor slab through the building envelope
Roof/Ceiling-to-wall junctions, especially where full ceiling insulation depths may not be achieved
Window-to-wall junctions
Door-to-wall junctions
Wall-to-wall junctions
Wood, steel or concrete members, such as studs and joists, incorporated in exterior wall, ceiling, or roof construction
Recessed luminaries that penetrate insulated ceilings
Windows and doors, especially frames components
Areas with gaps in or poorly installed insulation
Metal ties in masonry cavity walls
Structural elements remain a weak point in construction, commonly leading to thermal bridges that result in high heat loss and low surface temperatures in a room.
Masonry Buildings
While thermal bridges exist in various types of building enclosures, masonry walls experience significantly increased U-factors caused by thermal bridges. Comparing thermal conductivities between different building materials allows for assessment of performance relative to other design options. Brick materials, which are usually used for facade enclosures, typically have higher thermal conductivities than timber, depending on the brick density and wood type. Concrete, which may be used for floors and edge beams in masonry buildings are common thermal bridges, especially at the corners. Depending on the physical makeup of the concrete, the thermal conductivity can be greater than that of brick materials. In addition to heat transfer, if the indoor environment is not adequately vented, thermal bridging may cause the brick material to absorb rainwater and humidity into the wall, which can result in mold growth and deterioration of building envelope material.
Curtain Wall
Similar to masonry walls, curtain walls can experience significantly increased U-factors due to thermal bridging. Curtain wall frames are often constructed with highly conductive aluminum, which has a typical thermal conductivity above 200 W/m·K. In comparison, wood framing members are typically between 0.68 and 1.25 W/m·K. The aluminum frame for most curtain wall constructions extends from the exterior of the building through to the interior, creating thermal bridges.
Impacts of Thermal Bridging
Thermal bridging can result in increased energy required to heat or cool a conditioned space due to winter heat loss and summer heat gain. At interior locations near thermal bridges, occupants may experience thermal discomfort due to the difference in temperature. Additionally, when the temperature difference between indoor and outdoor space is large and there is warm and humid air indoors, such as the conditions experienced in the winter, there is a risk of condensation in the building envelope due to the cooler temperature on the interior surface at thermal bridge locations. Condensation can ultimately result in mold growth with consequent poor indoor air quality and insulation degradation, reducing the insulation performance and causing insulation to perform inconsistently throughout the thermal envelope
Design Methods to Reduce Thermal Bridges
There are several methods that have been proven to reduce or eliminate thermal bridging depending on the cause, location, and the construction type. The objective of these methods is to either create a thermal break where a building component would span from exterior to interior otherwise, or to reduce the number of building components spanning from exterior to interior. These strategies include:
A continuous thermal insulation layer in the thermal envelope, such as with rigid foam board insulation
Lapping of insulation where direct continuity is not possible
Double and staggered wall assemblies
Structural Insulated Panels (SIPs) and Insulating Concrete Forms (ICFs)
Reducing framing factor by eliminating unnecessary framing members, such as implemented with advanced framing
Raised heel trusses at wall-to-roof junctions to increase insulation depth
Quality insulation installation without voids or compressed insulation
Installing double or triple pane windows with gas filler and low-emissivity coating
Installing windows with thermally broken frames made of low conductivity material
Analysis Methods and Challenges
Due to their significant impacts on heat transfer, correctly modeling the impacts of thermal bridges is important to estimate overall energy use. Thermal bridges are characterized by multi-dimensional heat transfer, and therefore they cannot be adequately approximated by steady-state one-dimensional (1D) models of calculation typically used to estimate the thermal performance of buildings in most building energy simulation tools. Steady state heat transfer models are based on simple heat flow where heat is driven by a temperature difference that does not fluctuate over time so that heat flow is always in one direction. This type of 1D model can substantially underestimate heat transfer through the envelope when thermal bridges are present, resulting in lower predicted building energy use.
The currently available solutions are to enable two-dimensional (2D) and three-dimensional (3D) heat transfer capabilities in modeling software or, more commonly, to use a method that translates multi-dimensional heat transfer into an equivalent 1D component to use in building simulation software. This latter method can be accomplished through the equivalent wall method in which a complex dynamic assembly, such as a wall with a thermal bridge, is represented by a 1D multi-layered assembly that has equivalent thermal characteristics.
See also
Damp proofing
List of thermal conductivities
Thermal conduction
Building Science
Thermography
Heat Transfer
References
External links
Design Guide: Solutions to Prevent Thermal Bridging.
Manufactured Structural Thermal Breaks.
EU IEE SAVE Project ASIEPI: topic 'Thermal bridges' - An effective handling of thermal bridges in the EPBD context
Passivhaus Institute: Thermal Bridges in construction - how to avoid them
A bridge too far - ASHRAE Journal article on thermal bridging
International Building Code, 2009: Interior Environment
Online Energy2D simulation of thermal bridge (Java required)
What Defines Thermal Bridge Free Design
Building Envelope Thermal Bridging Guide
Insulators
Thermal protection
Building engineering
Building defects
Low-energy building | Thermal bridge | Materials_science,Engineering | 2,117 |
46,996,238 | https://en.wikipedia.org/wiki/Single-root%20input/output%20virtualization | In virtualization, single root input/output virtualization (SR-IOV) is a specification that allows the isolation of PCI Express resources for manageability and performance reasons.
Details
A single physical PCI Express bus can be shared in a virtual environment using the SR-IOV specification. The SR-IOV offers different virtual functions to different virtual components (e.g. network adapter) on a physical server machine. SR-IOV uses physical and virtual functions to control or configure PCIe devices. Physical functions have the ability to move data in and out of the device while virtual functions are lightweight PCIe functions that support data flowing but also have a restricted set of configuration resources. The virtual or physical functions available to the hypervisor or guest operating system depend on the PCIe device.
The SR-IOV allows different virtual machines (VMs) in a virtual environment to share a single PCI Express hardware interface. In contrast, MR-IOV allows I/O PCI Express to share resources among different VMs on different physical machines.
InfiniBand
A major field of application for SR-IOV is within high-performance computing (HPC). The use of high-performance InfiniBand networking cards is growing within the HPC sector, and there is early research into the use of SR-IOV to allow for the use of InfiniBand within virtual machines such as Xen.
See also
I/O virtualization
References
Hardware virtualization
Computer networking
Peripheral Component Interconnect | Single-root input/output virtualization | Technology,Engineering | 315 |
13,574,236 | https://en.wikipedia.org/wiki/Sodium%20tetradecyl%20sulfate | Sodium tetradecyl sulfate (STS), also known by its INCI name, sodium myristyl sulfate, is a common anionic surfactant. The compound consists of the sodium salt of the micelle-forming sulfate ester of tetradecanol. It is a white, water-soluble solid of low toxicity with many practical uses.
Applications
Medicine
It the active component of the sclerosant drugs Sotradecol and Fibrovein. It is commonly used in the treatment of varicose and spider veins of the leg, during the procedure of sclerotherapy. Being a detergent, its action is on the lipid molecules in the cells of the vein wall, causing inflammatory destruction of the internal lining of the vein and thrombus formation eventually leading to sclerosis of the vein. It is used in concentrations ranging from 0.1% to 3% for this purpose.
It is occasionally used for the treatment of stabilisation of joints that regularly dislocate, particularly in patients with Ehlers-Danlos syndrome.
In the UK, Ireland, Italy, Australia, New Zealand and South Africa, it is sold under the trade-name Fibro-Vein in concentrations of 0.2%, 0.5%, 1.0%, and 3%.
Synthesis
Tetradecyl alcohol is treated with sulfur trioxide followed by neutralization of the resulting pyrosulfuric acid with sodium hydroxide.
References
Organic sodium salts
Sulfate esters
Anionic surfactants | Sodium tetradecyl sulfate | Chemistry | 318 |
4,905,905 | https://en.wikipedia.org/wiki/Carbon%20tetraiodide | Carbon tetraiodide is a tetrahalomethane with the molecular formula . Being bright red, it is a relatively rare example of a highly colored methane derivative. It is only 2.3% by weight carbon, although other methane derivatives are known with still less carbon.
Structure
The tetrahedral molecule features C-I distances of 2.12 ± 0.02 Å. The molecule is slightly crowded with short contacts between iodine atoms of 3.459 ± 0.03 Å, and possibly for this reason, it is thermally and photochemically unstable.
Carbon tetraiodide crystallizes in tetragonal crystal structure (a 6.409, c 9.558 (.10−1 nm)).
It has zero dipole moment due to its symmetrically substituted tetrahedral geometry.
Properties, synthesis, and uses
Carbon tetraiodide is slightly reactive towards water, giving iodoform and I2. It is soluble in nonpolar organic solvents. It decomposes thermally and photochemically to , C2I4. Its synthesis entails AlCl3-catalyzed halide exchange, which is conducted at room temperature:
The product crystallizes from the reaction solution.
Carbon tetraiodide is used as an iodination reagent, often upon reaction with bases. Ketones are converted to 1,1-diiodoalkenes upon treatment with triphenylphosphine (PPh3) and carbon tetraiodide. Alcohols are converted in and to iodide, by a mechanism similar to the Appel reaction. In an Appel reaction, carbon tetrachloride is used to generate alkyl chlorides from alcohols.
Safety considerations
Manufacturers recommend that carbon tetraiodide be stored near . As a ready source of iodine, it is an irritant. Its LD50 on rats is 18 mg/kg. In general, organic compounds should be considered toxic, with the narrow exception of small perfluoroalkanes (essentially inert due to the strength of the C-F bond).
References
Further reading
Inorganic carbon compounds
Nonmetal halides
Iodoalkanes
Halomethanes
Reagents for organic chemistry | Carbon tetraiodide | Chemistry | 469 |
3,209,753 | https://en.wikipedia.org/wiki/Anthrozoology | Anthrozoology, also known as human–animal studies (HAS), is the subset of ethnobiology that deals with interactions between humans and other animals. It is an interdisciplinary field that overlaps with other disciplines including anthropology, ethnology, medicine, psychology, social work, veterinary medicine, and zoology. A major focus of anthrozoologic research is the quantifying of the positive effects of human–animal relationships on either party and the study of their interactions. It includes scholars from fields such as anthropology, sociology, biology, history and philosophy.
Anthrozoology scholars, such as Pauleen Bennett, recognize the lack of scholarly attention given to non-human animals in the past, and to the relationships between human and non-human animals, especially in the light of the magnitude of animal representations, symbols, stories and their actual physical presence in human societies. Rather than a unified approach, the field currently consists of several methods adapted from the several participating disciplines to encompass human–nonhuman animal relationships and occasional efforts to develop sui generis methods.
Areas of study
The interaction and enhancement within captive animal interactions.
Affective (emotional) or relational bonds between humans and animals
Human perceptions and beliefs in respect of other animals
How some animals fit into human societies
How these vary between cultures, and change over times
The study of animal domestication: how and why domestic animals evolved from wild species (paleoanthrozoology)
Captive zoo animal bonds with keepers
The social construction of animals and what it means to be animal
The human–animal bond
Parallels between human–animal interactions and human–technology interactions
The symbolism of animals in literature and art
The history of animal domestication
The intersections of speciesism, racism, and sexism
The place of animals in human-occupied spaces
The religious significance of animals throughout human history
Exploring the cross-cultural ethical treatment of animals
The critical evaluation of animal abuse and exploitation
Mind, self, and personhood in nonhuman animals
The potential human health benefits of companion animal ownership
Human-animal hybrids (where each cell has partly human and partly animal genetic contents)
Human-animal chimeras (where some cells are human and some cells are animal in origin)
Growth of the field
There are currently 23 college programs in HAS or a related field in the United States, Canada, Great Britain, Germany, Israel and the Netherlands, as well as an additional eight veterinary school programs in North America, and over thirty HAS organizations in the US, Canada, Great Britain, Australia, France, Germany, New Zealand, Israel, Sweden, and Switzerland.
In the UK, the University of Exeter runs an MA in Anthrozoology which explores human–animal interactions from anthropological (cross-cultural) perspectives. Human animal interactions (HAI) involving companion animals are also studied by the Waltham Centre for Pet Nutrition, which partners with the US National Institutes of Health to research HAI in relation to child development and aging.
There are now three primary lists for HAS scholars and students—H-Animal, the Human-Animal Studies listserv, and NILAS, as well as the Critical Animal Studies list.
There are now over a dozen journals covering HAS issues, many of them founded in the last decade, and hundreds of HAS books, most of them published in the last decade (see for example, Humanimalia). Brill, Berg, Johns Hopkins, Purdue, Columbia, Reaktion, Palgrave-Macmillan, University of Minnesota, University of Illinois, and Oxford all offer either a HAS series or a large number of HAS books.
In addition, in 2006, Animals and Society Institute (ASI) began hosting the Human-Animal Studies Fellowship, a six-week program in which pre- and post-doctoral scholars work on a HAS research project at a university under the guidance of host scholars and distance peer scholars. Beginning in 2011, ASI has partnered with Wesleyan Animal Studies, who will be hosting the fellowship in conjunction with ASI. There are also a handful of HAS conferences per year, including those organized by ISAZ and NILAS, and the Minding Animals conference, held in 2009 in Australia. Finally, there are more HAS courses being taught now than ever before. The ASI website lists over 300 courses (primarily in North America, but also including Great Britain, New Zealand, Australia, Germany, and Poland) in 29 disciplines at over 200 colleges and universities, not including over 100 law school courses.
See also
Animal behavior
ABMAP
Animal rights
Animal studies
Anthropomorphism
Birds in culture
Cognitive ethology
Companion animal
Critical animal studies
Domestication of the horse
Ethnozoology
Human–animal bonding
Human–canine bond
Intersectionality
Insects in culture
Origin of the domestic dog
Pauleen Bennett
Pet humanization
Service animal
Social grooming
Trans-species psychology
Zooarchaeology
References
External links
Animals and Society Institute
Anthrozoology Research Group
H-Animal
Human-Animal Studies listserve
Humanimalia: a journal of human-animal interface studies
NILAS
Animal rights
Animal welfare
Anthropology
Ethology
Interdisciplinary subfields of sociology
Environmental humanities
Environmental social science
Zoology | Anthrozoology | Biology,Environmental_science | 1,036 |
47,621,173 | https://en.wikipedia.org/wiki/Piezoelectric%20speaker | A piezoelectric speaker (also known as a piezo bender due to its mode of operation, and sometimes colloquially called a "piezo", buzzer, crystal loudspeaker or beep speaker) is a loudspeaker that uses the piezoelectric effect for generating sound. The initial mechanical motion is created by applying a voltage to a piezoelectric material, and this motion is typically converted into audible sound using diaphragms and resonators. The prefix piezo- is Greek for 'press' or 'squeeze'.
Compared to other speaker designs piezoelectric speakers are relatively easy to drive; for example they can be connected directly to TTL outputs, although more complex drivers can give greater sound intensity. Typically they operate well in the range of 1-5 kHz and up to 100 kHz in ultrasound applications.
Usage
Piezoelectric speakers are frequently used to generate sound in digital quartz watches and other electronic devices, and are sometimes used as tweeters in less-expensive speaker systems, such as computer speakers and portable radios. They are also used for producing ultrasound in sonar systems.
Piezoelectric speakers have several advantages over conventional loudspeakers: they are resistant to overloads that would normally destroy most high frequency drivers, and they can be used without a crossover due to their electrical properties. There are also disadvantages: some amplifiers can oscillate when driving capacitive loads like most piezoelectrics, which results in distortion or damage to the amplifier. Additionally, their frequency response, in most cases, is inferior to that of other technologies, especially with regards to bass and midrange. This is why they are generally used in applications where volume and high pitch are more important than sound quality.
Piezoelectric speakers can have extended high frequency output, and this is useful in some specialized circumstances; for instance, sonar applications in which piezoelectric variants are used as both output devices (generating underwater sound) and as input devices (acting as the sensing components of underwater microphones). They have advantages in these applications, not the least of which is simple and solid state construction that resists seawater better than a ribbon or cone based device would.
See also
Buzzer
References
Loudspeakers
Energy conversion
Electrical phenomena | Piezoelectric speaker | Physics | 468 |
18,416,761 | https://en.wikipedia.org/wiki/Key%20Net%20Radio | was a Japanese Internet radio program produced by VisualArt's and the visual novel studio Key in regard to Key and the games the brand produces. Thirty broadcasts were released online from December 13, 2007, to August 30, 2010. The show was hosted by Shinji Orito and Itaru Hinoue of Key, and another woman named Chiro who works for Pekoe, another visual novel studio under VisualArt's. Guests have been known to appear on the show including Jun Maeda and Na-Ga of Key. Each broadcast was recorded and were available via download on Key's official website after being edited by Orito, though Hinoue filled in for Orito on some occasions. The episodes were available for download on the radio show's official blog for the first nine broadcasts, and the first 27 episodes are no longer available for download. The more recent broadcasts could be listened to on VisualArt's' YouTube channel named Visual Channel. Listeners could submit thoughts about the show and any requests they may have for the show, along with submitting questions to the host trio. Key Net Radio'''s mascot is named Kirara and is drawn by Itaru Hinoue.
FormatKey Net Radio was hosted by three people: Shinji Orito, a signature musical composer and co-founder of Key; Itaru Hinoue, a signature art director, character designer, and co-founder of Key; and another woman named Chiro from the visual novel studio Pekoe, also under VisualArt's. The greeting was used by the hosts to address the listeners, and was also used by the listeners as an opening greeting in submissions. For the first six episodes, the show had five corners, or parts, but from the seventh broadcast on two more corners were added to the program. When the show had five corners, each episode started with opening greetings from the hosts and went on to thoughts and impressions that listeners had about the show. This moved on to an informal talk between the hosts, followed by a section where entries previously submitted by listeners concerning their enthusiasm for Key were read by the hosts. The fourth corner concerned answering questions that had been submitted by listeners, and the final corner had Orito playing the flute; listeners could submit suggestions for songs he was to play. The first corner added concerns scary stories that the hosts can tell themselves, or read from submissions by listeners, and was added partly because Hinoue enjoys such stories. The second corner added deals with submissions by listeners describing a new fictional character, and Hinoue will take these submissions and form a new fictional character out of combining elements from multiple submissions together. During the broadcasts, tracks from the soundtracks released under Key Sounds Label play in the background.
Broadcast history
2007–2008
The first broadcast was released on December 13, 2007, and was originally over an hour long, but was cut down to 30 minutes. The main topic of discussion of the first broadcast was Key's products at Comiket 73 held in late December 2007. The second broadcast was an end-of-the-year special released on December 28, 2007, and was longer than the first broadcast at 41:30 minutes. The third broadcast was a New Year Expansion edition released on January 22, 2008, and ran for 43:30 minutes. The fourth broadcast was released on February 25, 2008, covered the then-upcoming OTSU Vol. 2 album release as the main topic, and ran for 39:06 minutes. The fifth broadcast was released on March 19, 2008, and was so long that it was split it into two parts, the first at 38:12 minutes, and the second at 30:40 minutes. The main feature of the fifth broadcast was of having Na-Ga as a guest on the show.
The sixth broadcast was released on April 14, 2008, and ran for 41:26 minutes; this was also the first broadcast not edited by Shinji Orito, but instead was edited by Itaru Hinoue. The seventh broadcast was released on May 17, 2008, and ran for 42:03 minutes; this was the second broadcast edited by Hinoue. The main focus of the seventh broadcast was as a special listener contribution episode. The eighth broadcast was released on May 26, 2008, and ran for 48:37 minutes. The main focus of the eighth broadcast was as a report and discussion of the OTSU #02 and KSL Live World 2008 concerts held in May 2008. The ninth broadcast was released on June 19, 2008, and ran for 54:19 minutes. The main focus of the ninth broadcast was of having Lia as a guest on the show. The tenth broadcast was released on July 11, 2008, and ran for 49:50 minutes. The main focus of the tenth broadcast was of having Jun Maeda as a guest on the show along with giving a report on Little Busters! Ecstasy.
The 11th broadcast was released on August 8, 2008, and ran for 41 minutes. Since the previous two broadcasts had guests on the show, not much time was left to answer questions asked by listeners, so the 11th broadcast was a listener submission special. The 12th broadcast, released on September 19, 2008, ran for 59:20 and was recorded in a bar instead of the normal studio. The 13th broadcast was released on October 15, 2008, and ran for 53:51 minutes. The 13th broadcast focused mainly on information pertaining to Key's then-upcoming visual novel Rewrite, and featured Yūto Tonokawa, a scenario writer for Rewrite, as a guest on the show. The 14th broadcast was released on November 21, 2008, and ran for about 53:06 minutes. The 14th broadcast focused on the impending one-year anniversary of Key Net Radio in December 2008, and answered questions selected out of a lot. The 15th broadcast was released on December 24, 2008, and was released in two parts, the first at 69:04, and the second at 43:21 minutes. The first part focused on looking back and talking about the previous broadcasts, and the second part regarded the goods Key sold at Comiket 75 held in late December 2008.
2009–2010
The 16th broadcast was released on January 21, 2009, and ran for about 41:35 minutes. The broadcast focused on a report regarding Key's involvement at Comiket 75, and giving new information on Key's ten-year anniversary event Key 10th Memorial Fes later held between February 28 and March 1, 2009. The 17th broadcast was released on February 13, 2009, and ran for 28:30 minutes. The episode focused on the many goods to be sold at Key 10th Memorial Fes, and was the shortest broadcast. The 18th broadcast was released on March 19, 2009, and ran for 81:42 minutes. The episode was one of two recordings of the special broadcast Key Net Radio did at Key 10th Memorial Fes on February 28 and March 1, 2009. The 19th broadcast was released on April 9, 2009, and ran for 42:30 minutes. The 19th episode focused on the live broadcast Key Net Radio hosted in Osaka, Japan for two hours on May 6, 2009. The 20th episode was released on May 22, 2009, and ran for 54:03 minutes. The 20th broadcast reported on the live event held in Osaka.
The 21st broadcast was released on July 31, 2009, and ran for 39:30 minutes. The episode was described as a "regular broadcast" reporting on normal Key news and events. The 22nd episode was released on September 24, 2009, and ran for 41:42 minutes. The episode reported on the second VIP (Visual Information Party) event held by VisualArt's and Key on August 28, 2009; Shinji Orito did not participate in this broadcast. The 23rd broadcast was released on December 4, 2009, and ran for 34:40 minutes. This episode mainly focused on the goods Key would be selling at Comiket 77 held in late December 2009. The 24th episode was released on December 29, 2009, and ran for 50:40 minutes. This episode mainly dealt with an overview of the events in 2009 that Key participated in. The 25th broadcast was released on January 28, 2010, and ran for 37:30 minutes. The 25th episode focused on a restructuring of the corners on the show.
The 26th broadcast was released on February 26, 2010, and ran for 46:40 minutes. The episode was described as a "regular broadcast" reporting on normal Key news and events, though also introduced a new corner to the show. The 27th broadcast was released on March 24, 2010, and ran for 55:50 minutes. The episode focused on the Kud Wafter special event held by VisualArt's on April 3, 2010. The 28th broadcast was released on April 26, 2010, and ran for 33:50 minutes. The episode focused on the current state of Key Net Radio and possible changes the show would go through. The 29th episode was released on June 14, 2010, and ran for 1 hour, 1:10 minutes. The episode had the development staff of Kud Wafter on as guests and focused on the development of the game and answering questions from fans to the development staff. The 30th episode was released on August 30, 2010, and ran for 55:30 minutes. This episode was the last to be recorded and later distributed on Key's official website.
Other
An exclusive broadcast entitled Key Net Radio Push!! ver. was included with the August 2008 issue of Push!! sold on June 21, 2008. The main focus of the exclusive episode was of having the scenario writer Kai as a guest on the show. Kai has previously worked with Key on Clannad, though at the time his most recent work was Ram's visual novel 5. A two-CD compilation titled Key Net Radio Vol. 1 bearing the catalog numbers KSLC-0006—0007 containing the radio show's first 15 broadcasts plus an additional special episode was released at Key 10th Memorial Fes on February 28, 2009; it was released for general sale on July 29, 2011. A special radio broadcast was released on April 22, 2009, and ran for 9:50 minutes. The broadcast focused on news regarding the live broadcast held on May 6, 2009. Key Net Radio did another live broadcast on Ustream on May 13, 2010. A third live broadcast was held on Ustream on December 22, 2010. A CD compilation titled Key Net Radio Vol. 2'' containing episodes 16 through 30 of the radio show and the show's theme song "World Link" sung by Kotoko was released on July 29, 2011.
References
External links
Official website
Internet radio
Japanese talk radio programs
2007 radio programme debuts
2010 radio programme endings
Key (company) | Key Net Radio | Technology | 2,187 |
525,062 | https://en.wikipedia.org/wiki/Jo%C5%BEef%20Stefan%20Institute | The Jožef Stefan Institute (JSI) () is the largest research institute in Slovenia. The main research areas are physics, chemistry, molecular biology, biotechnology, information technologies, reactor physics, energy and environment. At the beginning of 2013 the institute had 962 employees, of whom 404 were PhD scientists.
The mission of the Jožef Stefan Institute is the accumulation and dissemination of knowledge at the frontiers of natural science and technology for the benefit of society at large through the pursuit of education, learning, research, and development of high technology at the highest international levels of excellence.
History
The institute was founded by the State Security Administration (Yugoslavia) in 1949 for atomic weapons research. Initially, the Vinča Nuclear Institute in Belgrade was established in 1948, followed by the Ruđer Bošković Institute in Zagreb in 1950 and the Jožef Stefan Institute as an Institute for Physics in the Slovenian Academy of Sciences and Arts. It is named after the distinguished 19th century physicist Josef Stefan (), best known for his work on the Stefan–Boltzmann law of black-body radiation.
IJS is involved in a wide variety of fields of scientific and economic interest. After close to 60 years of scientific achievement, the institute has become part of the image of Slovenia.
Over the last 60 years it has created a number of important institutions, such as the University of Nova Gorica, the Jožef Stefan International Postgraduate School and the Ljubljana Technology park.
Departments
Physics
F1 Theoretical Physics
F2 Low and Medium Energy Physics
F3 Thin Films and Surfaces
F4 Surface Engineering and Optoelectronics
F5 Condensed Matter Physics
F7 Complex Matter
F8 Reactor Physics
Chemistry and Biochemistry
B1 Biochemistry and Molecular Biology
B2 Molecular and Biomedical Sciences
B3 Biotechnology
K1 Inorganic Chemistry and Technology
K3 Physical and Organic Chemistry
K5 Electronic Ceramics
K6 Engineering Ceramics
K7 Nanostructured Materials
K8 Synthesis of Materials K8
K9 Advanced Materials
O2 Environmental Sciences
Electronics and Information Technologies
E1 Automation, Biocybernetics and Robotics
E2 Systems and Control
E3 Artificial Intelligence
E5 Open Computer Systems and Networks
E6 Communication Systems
E7 Computer Systems
E8 Knowledge Technologies
E9 Intelligent Systems
Reactor Engineering and Energetics
R4 Reactor Engineering
Centers
Centre for Knowledge Transfer in Information Technologies
Networking Infrastructure Centre
Reactor Infrastructure Centre
Scientific Information Centre Library
Center for Technology Transfer and Innovation
Campuses
The institute has facilities in two locations. The main facilities and the headquarters are on Jamova 39 in Ljubljana, the other location is the institute's Podgorica Reactor Center located in Brinje, Dol pri Ljubljani near Ljubljana.
Research reactor
The institute's Podgorica Reactor Center is home to a pool type research reactor. The General Atomics TRIGA Mark II reactor is rated for a nominal 250 kW thermal. The reactor was first licensed in 1966 and is expected to continue operation at least into the 2030s.
The Central Radioactive Waste Storage of Slovenia is co-located at the institute's reactor facility. This facility is used for storage of the low and intermediate level solid radioactive waste from the Podgorica Reactor Center and other, non-institute small waste producers such as medical, research, and industrial applications of ionising radiation.
Selection of online services from the institute
VideoLectures.Net Collection of videos of scientific events
AnswerArt Question Answering system
SearchPoint Contextual Web Search
References
External links
Research institutes in Slovenia
Biochemistry research institutes
Organizations established in 1949
Physics research institutes
Biological research institutes
Energy research institutes
Environmental research institutes
Computer science institutes
Nuclear research institutes
Vič District
Scientific organizations in Ljubljana
1949 establishments in Slovenia | Jožef Stefan Institute | Chemistry,Engineering,Environmental_science | 713 |
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