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(the species is unnamed, dubbed C) produce fertile and viable hybrids, but are unable to fertilize eggs of the parent species due to divergence of the alleles that code for bindin proteins: an example of post-zygotic isolation.: 343–344 Populations in sympatry manifest this difference in bindin protein versus those in allopatry.: 343–344 Selection actively acts against the formation of hybrids in both nature (as no documented cases of hybrids have been found) and in the laboratory. Here, the evolution of female egg receptors is thought to pressure bindin evolution in a selective runaway process. This example of reproductive character displacement is highly suggestive of being the result of—and has been cited as strong evidence for—reinforcement.: 343–344 === Fish === In British Columbia, benthic and limnetic morphs of Gasterosteus aculeatus exist together in sympatry in some lakes, while containing only one morph in other lakes. Female benthic morphs in sympatric populations actively discriminate against limnetic males, resulting in low rates of crossing (some gene flow has occurred between the morphs) and low fitness hybrids.: 360 Both selection against hybrids and reproductive character displacement in egg fertilization is observed in Etheostoma lepidum and E. spectabile. === Fungi === A strong case of reinforcement occurring in fungi comes from studies of Neurospora. In crosses between different species in the genera, sympatric pairs show low reproductive success, significantly lower than allopatric pairs. This pattern is observed across small and large geographic scales, with distance correlating with reproductive success. Further evidence of reinforcement in the species was the low fitness detected in the hybrids create from crosses, and that no hybrids have been found in nature, despite close proximity. === Insects === Ethological isolation has been observed between some mosquito species in the Southeast Asian Aedes albopictus group, suggesting—from laboratory experiments of mating trials—that selection
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"page_id": 56754417,
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"title": "Evidence for speciation by reinforcement"
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against hybrids is occurring, in the presence of reproductive character displacement. Female mate discrimination is increased with intermediate migration rates between allopatric populations of Timema cristinae (genus Timema) compared to high rates of migration (where gene flow impedes selection) or low rates (where selection is not strong enough). Where the ranges of the cicada species Magicicada tredecim and M. neotredecim overlap (where they are sympatric), the pitch of M. neotredecim male calling songs is roughly 1.7 kHz compared to 1.1 kHz for those of M. tredecim, with corresponding female song pitch preference differences. In allopatric M. neotredecim populations, the mating call pitch is 1.3–1.5 kHz. The biogeography of the cicadas suggests that M. neotredecim originated after the retreat of the last glacial advance in North America. The song differences of Laupala crickets on the Hawaiian Islands appear to exhibit patterns consistent with character displacement in sympatric populations. A similar pattern exists with Allonemobius fasciatus and A. socius, species of ground crickets in eastern North America. Males in sympatric populations of the damselflies Calopteryx maculata and C. aequabilis are able to discriminate between females of different species better than those in allopatric populations; with females of C. aequabilis in sympatric populations exhibiting lighter wing colors compared to allopatric females—an illustration of reproductive character displacement. Fifteen species of sympatrically distributed Agrodiaetus butterflies with pronounced differences in wing color pattern likely arose as a result of speciation by reinforcement. Phylogenetic patterns indicate the differences arose in allopatry and were reinforced when the distributions came into secondary contact. ==== Drosophila ==== Drosophila is one of the most studied species in speciation research. Dobzhansky and Koller were the first to study isolation between Drosophila species.: 358 Since then, other studies of natural populations such as the D. paulistorum races exhibiting stronger isolation in sympatry versus
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allopatry, or the enhanced isolation found in sympatric populations of D. mojavensis and D. arizonae in southwest America. Rare, sterile hybrids form between D. pseudoobscura and D. persimilis, with sympatric D. pseudoobscura females discriminating against D. persimilis males; more so than allopatric populations. Other Drosophila research on reinforcement has been from laboratory experiments and is discussed below. On the east coast of Australia, D. serrata shares a zone of sympatric overlap with the closely related species D. birchii. The species exhibits reproductive character displacement, with sexual selection operating on the hydrocarbons of the flies cuticle. Reinforcement appears to be driving their speciation in nature, supported by simulated experimental laboratory populations. === Mammals === The deer mice Peromyscus leucopus and P. gossypinus exhibit reproductive character displacement in mating preferences, with heterospecific matings taking place between the species. === Molluscs === Partula suturalis is polymorphic for shell chirality in that it has two forms: sinistral (left-handed) and dextral (right-handed) shells, unlike other monomorphic species on the island of Mo'orea which have only one form (with the exception of P. otaheitana). This polymorphic trait has a direct effect on mate choice and mating behavior; as shown in laboratory mating tests that opposite-coil pairs mate much less often. In areas where P. suturalis lives sympatrically with other sinistral and dextral Partula species, the opposite P. suturalis morph is typically present. Butlin succinctly describes one example of this unique pattern:P. suturalis is sympatric with the dextral P. aurantia and sinistral P. olympia, whose ranges abut but do not overlap; P. suturalis is sinestral in the range of P. aurantia and dextral in the range of P. olympia and does not normally hybridize with either species. However, where their ranges meet there is a sharp transition in the coil of P. suturalis and in this transition
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{
"page_id": 56754417,
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zone it hybridizes with both P. aurantia and P. olympia. The reversal in chirality to sinistrality must have evolved as an isolating mechanism, with patterns of reproductive character displacement suggesting speciation by reinforcement. Satsuma largillierti lives on the western half of Okinawa Island while Satsuma eucosmia lives on the eastern half. Both populations overlap in sympatry along the middle of the island, where the penis length of the species differs significantly in sympatry (a case of reproductive character displacement), but not in allopatry. A similar pattern in snails is found with Lymnaea peregra and L. ovata in the Swiss lake Seealpsee; with mating signal acting as the sympatrically displaced trait. The abalone genus Haliotis has 19 species that occur in sympatry and one that occurs in allopatry. Of the sympatric species, they all contain sperm lysin that drives gamete isolation, but the allopatric species does not.: 343 A similar pattern of sperm lysin differentiation is found in the mussel species Mytilus galloprovincialis and M. trossulus and has likely occurred within the last 200 years due to human-mediated distribution by ships.: 343 === Plants === Plants are thought to provide suitable conditions for reinforcement to occur. This is due to a number of factors such as the unpredictability of pollination, pollen vectors, hybridization, hybrid zones, among others. The study of plants experiencing speciation by reinforcement has largely been overlooked by researchers;: 364 however, there is evidence of its occurrence in them. In the Texas wildflower Phlox drummondii, cis-regulatory mutations of genes that code for anthocyanin pigmentation have caused genetic divergence of two populations. Hybrids (between P. drummondii and P. cuspidata) with maladaptive, intermediate characteristics are under-pollinated; increasing reproductive isolation through reinforcement. The maintenance of the ancestral flower color in the allopatric population is favored weakly by selection, where the derived color
|
{
"page_id": 56754417,
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in the sympatric population is being driven by strong selection. Similarly, in P. pilosa and P. glaberrima, character displacement of petal color has been driven by selection, aided by pollen discrimination. Displacement in flower size has also been observed in the nightshade species Solanum grayi and S. lymholtzianum in sympatry as well as S. rostratum and S. citrullifolium. The bishop pine is divided into two populations distinguished by monoterpene, stomata, and alloenzyme differences; flowering time; and needle color: blue foliage in the northern population and green foliage in the southern populations in California. A small region exists where the species meet in a cline—sustained by selection due to a flowering time divergence, thought to represent reinforcement taking place. Similar patterns of both character displacement in sympatric populations of species have been documented in:: 361 Agrostis tenuis Anthoxanthum odoratum Gilia Costus plants: Costus allenii, C. laevis, and C. guanaiensis; C. pulverulentus and C. scaber A unique case of post-zygotic instead of prezygotic isolation has been observed in both Gossypium and Gilia, suggesting that in plants, post-zygotic isolation's role in reinforcement may play a larger role.: 361 Sympatric populations of Juncus effusus (common rush) exhibits genetic differentiation of plants that flower at different times preventing hybridization. Allochrony may play a role. == Comparative studies == Assortive mating is expected to increase among sympatric populations experiencing reinforcement. This fact allows for the direct comparison of the strength of prezygotic isolation in sympatry and allopatry between different experiments and studies.: 362 Jerry Coyne and H. Allen Orr surveyed 171 species pairs, collecting data on their geographic mode, genetic distance, and strength of both prezygotic and post-zygotic isolation; finding that prezygotic isolation was significantly stronger in sympatric pairs, correlating with the ages of the species.: 362 Additionally, the strength of post-zygotic isolation was not different
|
{
"page_id": 56754417,
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between sympatric and allopatric pairs. This finding lends support the predictions of speciation by reinforcement and correlates well with another later study by Daniel J. Howard.: 363 In his study, 48 studies with observed reproductive character displacement (including plants, insects, crustaceans, molluscs, fish, amphibians, reptiles, birds, and mammals) were analyzed. The cases met several criteria such as the trait in question serving as a reproductive barrier and if there existed clear patterns of sympatry versus allopatry. Out of the 48 candidates, 69 percent (33 cases) found enhanced isolation in sympatry, suggesting that the pattern predicted by reinforcement is common in nature. In addition to Howard's comparative study, he guarded against the potential for positive-result publication bias by surveying 37 studies of hybrid zones. A prediction of reinforcement is that assortive mating should be common in hybrid zones; a prediction that was confirmed in 19 of the 37 cases. A survey of the rates of speciation in fish and their associated hybrid zones found similar patterns in sympatry, supporting the occurrence of reinforcement. One study in the plants Glycine and Silene; however, did not find enhanced isolation. == Laboratory experiments == Laboratory studies that explicitly test for reinforcement are limited.: 357 In general, two types of experiments have been conducted: using artificial selection to mimic natural selection that eliminates the hybrids (often called "destroy-the-hybrids"), and using disruptive selection to select for a trait (regardless of its function in sexual reproduction).: 355–357 Many experiments using the destroy-the-hybrids technique are generally cited as supportive of reinforcement; however, some researchers such as Coyne and Orr and William R. Rice and Ellen E. Hostert contend that they do not truly model reinforcement, as gene flow is completely restricted between two populations.: 356 The table below summarizes some of the laboratory experiments that are often cited
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{
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as testing reinforcement in some form. == References ==
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{
"page_id": 56754417,
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"title": "Evidence for speciation by reinforcement"
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In mycology, the term trama is used in two ways. In the broad sense, it is the inner, fleshy portion of a mushroom's basidiocarp, or fruit body. It is distinct from the outer layer of tissue, known as the pileipellis or cuticle, and from the spore-bearing tissue layer known as the hymenium. In essence, the trama is the tissue that is commonly referred to as the "flesh" of mushrooms and similar fungi. The second use is more specific, and refers to the "hymenophoral trama" that supports the hymenium. It is similarly interior, connective tissue, but it is more specifically the central layer of hyphae running from the underside of the mushroom cap to the lamella or gill, upon which the hymenium rests. Various types have been classified by their structure, including trametoid, cantharelloid, boletoid, and agaricoid, with agaricoid the most common by far. In the agarcoid type, the central trama's hyphae usually run parallel to each other, with a clear boundary area called a sub-hymenium followed by the hymenium itself on the outer layer facing the environment. The word "trama" is Latin for the "weft" or "woof" yarns in the weaving of cloth. This is related to the basidiocarp trama being "filler" tissue and that analogously the woof yarn in weaving is sometimes called "fill". Furthermore, the trama tends to be soft tissue, and in weaving, the woof yarn is not tightly stretched; it therefore need not as a rule be as strong as the warp yarn. == References ==
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{
"page_id": 25428209,
"source": null,
"title": "Trama (mycology)"
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The molecular formula C8H6N2O2 may refer to: Fenadiazole, a hypnotic drug with a unique oxadiazole-based structure Quinoxalinedione, an organic compound; colorless solid that is soluble in polar organic solvents
|
{
"page_id": 23920881,
"source": null,
"title": "C8H6N2O2"
}
|
NCED8 (gene) may refer to: Carlactone synthase, an enzyme All-trans-10'-apo-beta-carotenal 13,14-cleaving dioxygenase, an enzyme
|
{
"page_id": 38338804,
"source": null,
"title": "NCED8"
}
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This is a non-exhaustive list of alternative treatments that have been promoted to treat or prevent cancer in humans but which lack scientific and medical evidence of effectiveness. In many cases, there is scientific evidence that the alleged treatments are not effective, and in some cases, may even be harmful. Unlike accepted cancer treatments, treatments lacking in evidence of efficacy are generally ignored or avoided by the medical community and are often pseudoscientific. Many alternative cancer treatments are considered disproven because they have been investigated with clinical trials and have been shown to be ineffective. == Alternative health systems == Aromatherapy – the use of fragrant substances, such as essential oils, in the belief that smelling them will positively affect health. There is some evidence that aromatherapy improves general well-being, but it has also been promoted for its ability to fight diseases, including cancer. The American Cancer Society states "available scientific evidence does not support claims that aromatherapy is effective in preventing or treating cancer". Ayurvedic medicine – a 2,200-year-old system of traditional medicine which originated on the Indian subcontinent. According to Cancer Research UK, "There is no scientific evidence to prove that Ayurvedic medicine can treat or cure cancer." Germanic New Medicine – a popular medical system devised by Ryke Geerd Hamer (1935–2017), in which all disease is seen as deriving from emotional shock and mainstream medicine is regarded as a conspiracy promulgated by Jews. There is no evidence to support its claims and no biological reason why it should work. Greek cancer cure – A putative cancer cure invented and promoted by microbiologist Hariton-Tzannis Alivizatos. It consisted of intravenous injections of a fluid for which Aliviatos would not reveal the formula. The American Cancer Society concluded that "there is no evidence that any aspect of the diagnostic test
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{
"page_id": 40370421,
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"title": "List of unproven and disproven cancer treatments"
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nor the treatment [...] [is] effective in the treatment of cancer." In addition they state "Nor is there any evidence that.. the intravenous injections are safe." Herbalism – a whole-body approach to promoting health, in which substances are derived from entire plants so as not to disturb what herbalists believe is the delicate chemistry of the plant as a whole. According to Cancer Research UK, "there is currently no strong evidence from studies in people that herbal remedies can treat, prevent or cure cancer". Holistic medicine – a general term for an approach to medicine which encompasses mental and spiritual aspects, and which is manifested in sundry complementary and alternative methods. According to the American Cancer Society, "available scientific evidence does not support claims that these complementary and alternative methods, when used without mainstream or conventional medicine, are effective in treating cancer or any other disease". Homeopathy – a pseudoscientific system of medicine based on ultra-diluted substances. Some proponents promote homeopathy as a cancer cure; however, according to the American Cancer Society "there is no reliable evidence showing that homeopathic remedies can treat cancer in humans". Native American healing – shamanistic forms of medicine traditionally practiced by some indigenous American peoples and which have been claimed as being capable of curing human diseases, including cancer. The American Cancer Society say that while its supportive, community aspects might improve general well-being, "available scientific evidence does not support claims that Native American healing can cure cancer or any other disease". Naturopathy – a system of alternative medicine based on a belief in energy forces in the body and an avoidance of conventional medicine; it is promoted as a treatment for cancer and other ailments. According to the American Cancer Society, "scientific evidence does not support claims that naturopathic medicine can cure cancer
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{
"page_id": 40370421,
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"title": "List of unproven and disproven cancer treatments"
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or any other disease". == Diet-based == Alkaline diet – a restrictive diet of non-acid foods, such as that proposed by Edgar Cayce (1877–1945), based on the claim this will affect the pH of the body generally, so reducing the risk of heart disease and cancer. According to the Canadian Cancer Society, "there is no evidence to support any of these claims." Breuss diet – a diet based on vegetable juice and tea devised by Rudolf Breuss (1899–1990), who claimed it could cure cancer. Physicians have said that, in common with other "cancer diets", there is no evidence of effectiveness and some risk of harm. Budwig protocol (or Budwig diet) – an "anti-cancer" diet developed in the 1950s by Johanna Budwig (1908–2003). The diet is rich in flaxseed oil mixed with cottage cheese, and emphasizes meals high in fruit, vegetables and fiber; it avoids sugar, animal fats, salad oil, meats, butter and especially margarine. Cancer Research UK say, "there is no reliable evidence to show that the Budwig diet [...] helps people with cancer". Fasting and intermittent fasting – not eating or drinking for a period – a practice which has been claimed by some alternative medicine practitioners to help fight cancer, perhaps by "starving" tumors. However, according to the American Cancer Society, "available scientific evidence does not support claims that fasting is effective for preventing or treating cancer in humans". Professional societies in France and the United Kingdom reached similar conclusions. Hallelujah diet – a restrictive "biblical" diet based on raw food, claimed by its inventor to have cured his cancer. Stephen Barrett has written on Quackwatch: "Although low-fat, high-fiber diets can be healthful, the Hallelujah Diet is unbalanced and can lead to serious deficiencies." Harriet Hall at Science-Based Medicine agrees, adding the diet "makes no sense". Ketogenic diet
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"page_id": 40370421,
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– a severe carbohydrate-restricted diet that induces ketosis and is used for the treatment of drug-resistant epilepsy. Advocates assume the diet avoids "fuelling" cancer tumours and say the diet can be used as a substitute for convention treatment, but their claims are not supported by medical evidence. Kousmine diet – a restrictive diet devised by Catherine Kousmine (1904–1992) which emphasized fruit, vegetables, grains, pulses and the use of vitamin supplements. There is no evidence that the diet is an effective cancer treatment. Macrobiotic diet – a restrictive diet based on grains and unrefined foods, and promoted by some as a preventative and cure for cancer. Cancer Research UK states "we don't support the use of macrobiotic diets for people with cancer". McDougall diet – a restrictive low-fat, starch based vegan diet devised by John A. McDougall. The diet is low in fat, high in fiber and contains no cholesterol. McDougall has promoted the diet as an alternative treatment for a number of chronic disorders, including cancer. However, there is no scientific evidence that McDougall's diet is effective. Moerman Therapy – a highly restrictive diet devised by Cornelis Moerman (1893–1988). Its effectiveness is supported by anecdote only – there is no evidence of its worth as a cancer treatment. Superfood – a marketing term applied to certain foods with supposed health-giving properties. Cancer Research UK note that superfoods are often promoted as having an ability to prevent or cure diseases, including cancer; they caution, "a healthy, balanced and varied diet can help to reduce the risk of cancer but it is unlikely that any single food will make a major difference on its own." == Electromagnetic and energy-based == Bioresonance therapy – diagnosis and therapy delivered by attaching an electrical device to the patient, on the basis that cancer cells emit
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{
"page_id": 40370421,
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"title": "List of unproven and disproven cancer treatments"
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certain electromagnetic oscillations. The Memorial Sloan Kettering Cancer Center says that such claims are not supported by any evidence and note that the U.S. Food and Drug Administration has prosecuted many sellers of such devices. Electrohomeopathy (or Mattei cancer cure) – a treatment devised by Count Cesare Mattei (1809–1896), who proposed that different "colors" of electricity could be used to treat cancer. Popular in the late nineteenth century, electrohomeopathy has been described as "utter idiocy". Electro Physiological Feedback Xrroid – an electronic device promoted as being capable of diagnosing and treating cancer and a host of other ailments. However, according to Quackwatch: "The Quantum Xrroid device is claimed to balance 'bio-energetic' forces that the scientific community does not recognize as real. It mainly reflects skin resistance (how easily low-voltage electric currents from the device pass through the skin), which is not related to the body's health." Light therapy – the use of light to treat medical conditions. According to the American Cancer Society, alternative approaches—such as chromotherapy or the use of light boxes—have not been shown to be effective for cancer treatment. Magnetic therapy – the practice of placing magnets on and around the body in order to treat illness. Although this has been promoted as a treatment for cancer and other diseases, the American Cancer Society says, "available scientific evidence does not support these claims". Orgone – a type of life force proposed to exist by Wilhelm Reich (1897–1957) which he claimed could be harnessed to cure diseases, including cancer, perhaps by sitting inside an "orgone accumulator"—a cupboard-like box with metal and organic linings. Quackwatch comments that scientists investigating Reich's ideas have been "unable to find the slightest evidence in Reich's data or elsewhere that such a thing as orgone exists". Polarity therapy – a type of energy medicine
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{
"page_id": 40370421,
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based on the idea that the positive or negative charge of a person's electromagnetic field affects their health. Although it is promoted as effective for curing a number of human ailments, including cancer, the American Cancer Society says "available scientific evidence does not support claims that polarity therapy is effective in treating cancer or any other disease". Rife Frequency Generator – an electronic device purported to cure cancer by transmitting radio waves. Cancer Research UK states, "there is no evidence to show that the Rife machine does what its supporters say it does". Therapeutic Touch (or TT) – contrary to its name, a technique that does not usually involve touching; rather, a practitioner holds their hands close to a patient to affect the "energy" in their body. According to the American Cancer Society, "available scientific evidence does not support any claims that TT can cure cancer or other diseases". Zoetron therapy – therapy based around a large electromagnetic device that emitted a weak field which, it was claimed, could kill cancer cells. Patients were charged US$15,000 up-front for treatment in Mexican clinics. In 2005 criminal charges were brought against the owners of the company making the device for their claims of its worth. Quackwatch says: "there is no scientific evidence or reason to believe that exposure to weak magnetic fields will kill any cells". == Hybrid == Clark's "Cure for All Cancers" – an alternative medicine regime promoted by Hulda Regehr Clark (1928–2009), who (before her death from cancer) claimed it could cure all human diseases, including all cancers. The regime was based on the belief that disease was caused by "parasites", and included herbal remedies, chelation therapy and the use of electronic devices. Quackwatch describes her notions as "absurd". Contreras therapy – treatment offered at the Oasis of Hope
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Hospital in Tijuana, Mexico which includes a number of ineffective treatments including the use of amygdalin and metabolic therapy. The Memorial Sloan Kettering Cancer Center lists "Contreras Therapy" alongside others which "show no evidence of efficacy". Gerson therapy – a predominantly diet regime, generally based on limiting salt, protein and other foods; ingesting large quantities of fruit and vegetables through juicing; augmenting the intake of potassium and iodine; and the use of coffee enemas. According to Cancer Research UK, "available scientific evidence does not support any claims that Gerson therapy can treat cancer [...] Gerson therapy can be very harmful to your health." Gonzalez protocol – a treatment regime devised by Nicholas Gonzalez (1947–2015) based on Gerson therapy. The treatment is a type of metabolic therapy that has no evidence of efficacy. Hoxsey therapy – a treatment consisting of a caustic herbal paste for external cancers or a herbal mixture for "internal" cancers, combined with laxatives, douches, vitamin supplements and dietary changes. A review by the Memorial Sloan Kettering Cancer Center found no evidence that the Hoxsey Therapy was effective as a treatment for cancer. Issels treatment – a regime recommended to be used alongside conventional treatment. It requires removal of metal fillings from the patient's mouth, and adherence to a restrictive diet. Cancer Research UK state: "There is no scientific or medical evidence to back up the claims made by the Issels website". Kelley treatment – a treatment regime devised by William Donald Kelley (1925–2005) based on Gerson therapy, with additional features including prayer and osteopathic manipulation. Famously, Steve McQueen used it for three months before his death. According to the Memorial Sloan Kettering Cancer Center, Kelley treatment is a type of metabolic therapy that shows "no evidence of efficacy". Live blood analysis – in alternative medicine, the practice
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of examining blood samples under a high-powered microscope, claiming this can detect and predict cancer and other illnesses, so leading to a prescription of dietary supplements that are supposed to function as treatment. The practice has been dismissed as quackery by the medical profession. Livingston-Wheeler Therapy – a therapeutic regime that included a restricted diet, various drugs, therapy and the use of enemas. According to the American Cancer Society, "available scientific evidence does not support claims that Livingston-Wheeler therapy was effective in treating cancer or any other disease". Lorraine Day's 10-step program – a regime devised by Lorraine Day based on a restrictive diet and behavioral changes, such as giving up work and ceasing to watch television. Stephen Barrett wrote on Quackwatch, "In my opinion, her advice is untrustworthy and is particularly dangerous to people with cancer". Metabolic therapies – an umbrella term for diet- and enema-based "detoxification" regimes, such as the Gerson therapy, promoted to cure cancer and other disease. The Memorial Sloan Kettering Cancer Center states: "Retrospective reviews of the Gerson, Kelley and Contreras therapies show no evidence of efficacy." Nieper therapy – a regimen devised by Hans Alfred Nieper (1928–1998) which was based on taking a variety of substances, including amygdalin and vitamins, and which Nieper claimed could treat a variety of serious ailments, including cancer. His methods were discredited as both ineffective and unsafe. == Plant- and fungus-based == Actaea racemosa (or black cohosh) – a flowering plant from which dietary supplements are made that are promoted for their claimed health-giving properties. It is of no use preventing or treating cancer. Black cohosh may cause liver damage, and may be unsafe for use by those with hormone-sensitive cancers. Aloe – a genus of flowering succulent plants native to Africa. According to Cancer Research UK, a potentially
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{
"page_id": 40370421,
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deadly product called T-UP is made of concentrated aloe, and promoted as a cancer cure. They say "there is currently no evidence that aloe products can help to prevent or treat cancer in humans". Andrographis paniculata – a herb used in Ayurvedic medicine, and promoted as a dietary supplement for cancer prevention and cure. The Memorial Sloan Kettering Cancer Center has stated that there is no evidence that it helps prevent or cure cancer. Aveloz (also called firestick plant, pencil tree or Euphorbia tirucalli) – a succulent shrub native to parts of Africa and South America. Its sap is promoted as a cancer treatment; however, according to the American Cancer Society, studies suggest that "aveloz sap may actually suppress the immune system, promote tumor growth, and lead to the development of certain types of cancer". Bach flower remedies – preparations devised by Edward Bach (1886–1936) in which tiny amounts of plant material are diluted in a mixture of water and brandy. According to Cancer Research UK, flower remedies are sometimes promoted as being capable of boosting the immune system, but "there is no scientific evidence to prove that flower remedies can control, cure or prevent any type of disease, including cancer". Cannabidiol – a phytocannabinoid extracted from the cannabis plant. Many claims are made for the therapeutic benefit of cannabidiol that are not backed by sound evidence. Some claims—for example that cannabidiol be used to treat cancer—fall into the realm of pseudoscience. Cannabis – Used as a recreational and medicinal drug. Chemicals derived from cannabis have been extensively researched for potential anti-cancer effect and while there has been much laboratory work, claims that cannabis has been proven to cure cancer are—according to Cancer Research UK—"highly misleading". The U.S. National Cancer Institute notes "Cannabis is not approved by the FDA for
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{
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the treatment of any cancer-related symptom or side effect of cancer therapy." Cansema (also called black salve) – a type of paste or poultice often promoted as a cancer cure, especially for skin cancer. According to the American Cancer Society, there is no evidence that this escharotic is effective in treating cancer, and it can be harmful, causing burns and disfigurement. Capsicum – the name given to a group of plants in the nightshade family, well known for producing hot chilli peppers such as the cayenne pepper and the jalapeño. A number of capsicum-based products, including teas and capsules, are promoted for their health benefits, including as a claimed cancer treatment. However, according to the American Cancer Society, "available scientific research does not support claims for the effectiveness of capsicum or whole pepper supplements in preventing or curing cancer at this time". Carctol – a herbal dietary supplement made from ayurvedic herbs. It has been aggressively marketed in the United Kingdom as a cancer treatment, but there is no evidence of its effectiveness. Cassava – a woody shrub native to South America, the root of which is a carbohydrate-rich foodstuff. Cassava root has been promoted as treatment for cancer. However, according to the American Cancer Society, "there is no convincing scientific evidence that cassava or tapioca is effective in preventing or treating cancer". Castor oil – an oil made from the seeds of the castor oil plant. The claim has been made that applying it to the skin can help cure cancer. However, according to the American Cancer Society, "available scientific evidence does not support claims that castor oil on the skin cures cancer or any other disease." Chaparral (or Larrea tridentata) – a plant used to make a herbal remedy which is sold as cancer treatment. Cancer Research UK
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{
"page_id": 40370421,
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"title": "List of unproven and disproven cancer treatments"
}
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state that: "We don't recommend that you take chaparral to treat or prevent any type of cancer." Chlorella – a type of algae promoted for its health-giving properties, including a claimed ability to treat cancer. However, according to the American Cancer Society, "available scientific studies do not support its effectiveness for preventing or treating cancer or any other disease in humans". Echinacea – a group of herbaceous flowering plants in the daisy family, marketed as a herbal supplement that can help combat cancer. According to Cancer Research UK, "there is no scientific evidence to show that echinacea can help treat, prevent or cure cancer in any way." Ellagic acid – a natural phenol found in some foods, especially berries, and which has been marketed as having the ability to prevent and treat a number of human maladies, including cancer. According to the American Cancer Society, such claims are not proven. Essiac – a blended herbal tea devised in the early 20th century and promoted as a cancer cure. The U.S. Food and Drug Administration include Essiac in a list of "Fake Cancer 'Cures' Consumers Should Avoid". Fermented wheat germ extract (FWGE) – a concentrated extract of wheat germ sold with the brand names Avemar and Awge. FWGE is marketed with a number of misleading medical claims, including that it supports the immune system and is useful in the treatment of cancer. Ginger – a root of plants of the Zingiber family, and a popular spice in many types of cuisine. Ginger has been promoted as a cancer treatment for its supposed ability to halt tumor growth; however, according to the American Cancer Society, "available scientific evidence does not support this". Ginseng – a species of perennial plant, the root of which is promoted for its therapeutic value, including a claimed
|
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ability to help fight cancer. However, according to the American Cancer Society, "available scientific evidence does not support claims that ginseng is effective in preventing or treating cancer in humans". Glyconutrients – types of sugar extracted from plants; they are mostly marketed in a product with the brand name "Ambrotose" by Mannatech, Inc. According to the Memorial Sloan Kettering Cancer Center, these products have been "promoted aggressively to cancer patients" on the basis that they can help cellular health and boost the immune system, but "strong scientific evidence to support these claims is lacking". Goldenseal (or Hydrastis canadensis) – an herb from the buttercup family promoted for treating many conditions, including cancer. According to the American Cancer Society, "evidence does not support claims that goldenseal is effective in treating cancer or other diseases. Goldenseal can have toxic side effects, and high doses can cause death." Gotu kola – a swamp plant native to parts of Asia and Africa. Supplements made from it are promoted as cancer treatment; however, according to the American Cancer Society, "available scientific evidence does not support claims of its effectiveness for treating cancer or any other disease in humans". Grapes – fruit, popularized for supposed anti-cancer effect by Johanna Brandt (1876–1964) who championed a "grape diet", and promoted more recently in the form of grape seed extract (GSE). According to the American Cancer Society, "there is very little reliable scientific evidence available at this time that drinking red wine, eating grapes, or following the grape diet can prevent or treat cancer in people". Inonotus obliquus – commonly known as chaga mushroom. Chaga has been used as a folk remedy in Russia and Siberia since the 16th century. According to the Memorial Sloan Kettering Cancer Center, "no clinical trials have been conducted to assess chaga's safety and
|
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efficacy for disease prevention or for the treatment of cancer, cardiovascular disease, or diabetes". They caution that the mushroom extract can interact with other drugs. Juice Plus – a branded line of dietary supplements containing concentrated fruit and vegetable juice extract. In October 2009, Barrie R. Cassileth, chair and chief of integrative medicine at Memorial Sloan Kettering Cancer Center, cautioned that while Juice Plus is being "aggressively promoted to cancer patients based on claims of antioxidant effects", the supplement should not be taken by patients because it can interfere with chemotherapy, nor should it be considered a substitute for fruit and vegetables. Juicing (or juice therapy) – the practice of consuming juice made from raw fruit and vegetables. This has been claimed to bring many benefits such as slowing aging or curing cancer; however, according to the American Cancer Society, "there is no convincing scientific evidence that extracted juices are healthier than whole foods". Kombucha – a kind of fermented tea claimed to cure a variety of human illnesses including AIDS and cancer; however, these purported uses are not backed by evidence. The consumption of kombucha has been associated with adverse effects including muscle inflammation, poisoning and infection. At least one person has died after consuming kombucha, but the death could not be specifically linked to the drink. Laetrile is a trade name for an amygdalin derivitive. It is a glycoside that has been promoted as a cancer cure. It has been found to be ineffective and toxic. Its promotion has been described as "the slickest, most sophisticated, and certainly the most remunerative cancer quack promotion in medical history." Mangosteen – a fruit native to Southeast Asia which is promoted as a "superfruit" and in products such as XanGo juice for treating a variety of human ailments. According to the
|
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American Cancer Society, "there is no reliable evidence that mangosteen juice, puree, or bark is effective as a treatment for cancer in humans". Milk thistle (Silybum marianum) – a biennial plant that grows in many locations over the world. Cancer Research UK say that milk thistle is promoted on the internet for its claimed ability to slow certain kinds of cancer, but that there is no good evidence in support of these claims. Mistletoe – a plant used in anthroposophical medicine, proposed as a cancer cure (in the form of mistletoe extract, called Iscador or Helixor) by Rudolf Steiner (1861–1925), who believed it needed to be harvested when planetary alignment most influenced its potency. According to the American Cancer Society, "available evidence from well-designed clinical trials does not support claims that mistletoe can improve length or quality of life". Modified citrus pectin – a substance chemically extracted from citrus fruits and marketed in dietary supplement form as a treatment for prostate cancer and melanoma. According to Cancer Research UK, it has "not been shown to have any activity in fighting cancer in people". Moxibustion – the practice, used in conjunction with acupuncture or acupressure, of burning dried-up mugwort near the patient. The American Cancer Society comments, "available scientific evidence does not support claims that moxibustion is effective in preventing or treating cancer or any other disease". Mushrooms – promoted on the internet as useful for cancer treatment. According to Cancer Research UK, "there is currently no evidence that any type of mushroom or mushroom extract can prevent or cure cancer". Nerium oleander (or oleander) – one of the most poisonous of commonly grown garden plants, is the basis of an extract which is promoted to treat cancer and other ailments. According to the American Cancer Society, "even a small amount
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of oleander can cause death", and "the effectiveness of oleander has not been proven". Noni juice – juice derived from the fruit of the Morinda citrifolia tree indigenous to Southeast Asia, Australasia, and the Caribbean. Noni juice has been promoted as a cure for cancer. However, The American Cancer Society say "there is no reliable clinical evidence that noni juice is effective in preventing or treating cancer or any other disease in humans". Pau d'arco – a large South American rainforest tree whose bark (sometimes brewed into "lapacho" tea) is promoted as a treatment for many ailments, including cancer. According to the American Cancer Society, "available evidence from well-designed, controlled studies does not support this substance as an effective treatment for cancer in humans". PC-SPES – a herbal supplement marketed (alongside similar supplements PC-CARE, PC-HOPE and PC-PLUS) as a treatment for prostate cancer. It has no medical benefit. Pygeum – an extract made from Prunus africana, the African cherry. Following excitement at the end of the twentieth century about pygeum's therapeutic potential for treating benign prostatic hyperplasia, subsequent research has found it to have no benefit. Rauvolfia serpentina (or snakeroot) – a plant used as the basis of a herbal remedy that some believe may treat cancer. According to the American Cancer Society: "Available scientific evidence does not support claims that Indian snakeroot is effective in treating cancer [...] It also has many dangerous side effects and is likely to increase the risk of cancer." Red clover (Trifolium pratense) – a European species of clover, promoted as a treatment for a variety of health conditions, including cancers. According to the American Cancer Society, "available clinical evidence does not show that red clover is effective in treating or preventing cancer, menopausal symptoms, or any other medical conditions." Saw palmetto (Serenoa repens)
|
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– a type of palm tree found growing in the southeastern United States. Its extract has been promoted as a prostate cancer medicine; however, according to the American Cancer Society, "available scientific studies do not support claims that saw palmetto can prevent or treat prostate cancer in humans". Seasilver – an expensive dietary supplement made mostly from plant extracts and promoted by two U.S. companies. Extravagant claims for its curative powers led to the prosecution and fining of the companies' owners. According to the Memorial Sloan Kettering Cancer Center, "no studies have shown the efficacy of this costly product". Soursop (or graviola) – According to the U.S. Federal Trade Commission soursop extract is among those products for which there is "no credible scientific evidence" of an ability to "prevent, cure, or treat cancer of any kind". Strychnos nux-vomica – a tree native to Asia, the bark of which contains toxic strychnine. Strychnos is promoted within herbal medicine as being a treatment for a wide range of maladies including cancer and heart disease; there is, however, no evidence it is useful for treating any condition. Ukrain – the trademarked name of a drug (sometimes called "celandine") made from Chelidonium majus, a plant in the poppy family. The drug is promoted for its health giving powers and its ability to treat cancer; however, according to the American Cancer Society, "available scientific evidence does not support claims that celandine is effective in treating cancer in humans". Uncaria tomentosa (or cat's claw) – a woody vine found in the tropical jungles of South and Central America, which is promoted as a remedy for cancer and other disease. The American Cancer Society state: "Available scientific evidence also does not support cat's claw's effectiveness in preventing or treating cancer or any other disease. Cat's claw is
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linked to some serious side effects, although the extent of those effects is not known". Venus flytrap – a carnivorous plant, the extract of which has been promoted as a treatment for a variety of human ailments including skin cancer. According to the American Cancer Society, "available scientific evidence does not support claims that extract from the Venus flytrap plant is effective in treating skin cancer or any other type of cancer". Walnuts – large, hard edible seeds of any tree of the genus Juglans. Black walnut has been promoted as a cancer cure on the basis it kills a "parasite" responsible for the disease. There exist walnut hull tinctures made with kerosene or other oil products; one such product which was intended to be used as a cancer treatment, named Todicamp and produced by Todicamp SRL, was recognized as harmful. According to the American Cancer Society, "available scientific evidence does not support claims that hulls from black walnuts remove parasites from the intestinal tract or that they are effective in treating cancer or any other disease". Wheatgrass – a food made from grains of wheat. According to the American Cancer Society, although some wheatgrass champions claim it can "shrink" cancer tumors, "available scientific evidence does not support the idea that wheatgrass or the wheatgrass diet can cure or prevent disease". Wild yam (or Chinese yam) – types of yam, the roots of which are made into creams and dietary supplements that are promoted for a variety of medicinal purposes, including cancer prevention. The American Cancer Society says of these products, "available scientific evidence does not support claims that they are safe or effective." Wilburn Ferguson's solution – a mixture of plants that were supposedly used by the Shuar people for the purpose of shrinking heads, that he claimed was
|
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also effective in treating cancerous tumors. No trials conducted according to modern scientific standards have ever shown that this solution is successful in curing cancer. == Physical procedures == Acupuncture – a mainstay of traditional Chinese medicine, acupuncture attempts to regulate the flow of a supposed energy within the body by means of inserting needles through the skin at certain pre-designated points. Although there is some evidence that suggests acupuncture may help relieve some symptoms associated with cancer, such as treatment side effects, there is no evidence to support claims that acupuncture is an effective treatment for cancer. Applied kinesiology – the practice of diagnosing and treating illness by touching and observing patients to detect meaningful signs in the muscles. Claims have been made that in a session, "spontaneous remission" of cancer can be observed. However, according to the American Cancer Society, "available scientific evidence does not support the claim that applied kinesiology can diagnose or treat cancer or other illness". Chiropractic – the practice of manipulating the spine to treat many human ailments. According to the American Cancer Society, "available scientific evidence does not support claims that chiropractic treatment cures cancer or any other life-threatening illness". Craniosacral therapy (or CST) – a treatment devised by John Upledger in the 1970s. A CST practitioner will massage a patient's scalp in the belief that the precise positioning of their cranial bones can have a profound impact on their health. However, according to the American Cancer Society, "available scientific evidence does not support claims that craniosacral therapy helps in treating cancer or any other disease". Colon cleansing – the practice of cleansing the colon using laxatives and enemas to "detoxify" the body. Coffee enemas in particular are promoted as a cancer therapy. According to the American Cancer Society, "available scientific evidence does
|
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not support claims that colon therapy is effective in treating cancer or any other disease". Cupping – a procedure in which cups are used to create areas of suction on the body. Although claimed by proponents as an alternative cancer treatment, the American Cancer Society say "available scientific evidence does not support claims that cupping has any health benefits". Dance therapy – the use of dance or physical movement to improve physical or mental well-being. The American Cancer Society states, "Few scientific studies have been done to evaluate the effects of dance therapy on health, prevention and recovery from illness. Clinical reports suggest dance therapy may be effective in improving self-esteem and reducing stress. As a form of exercise, dance therapy can be useful for both physical and emotional aspects of quality of life." A Cochrane review found too few studies to draw any conclusions about what effects dance therapy has on psychological or physical outcomes in cancer patients. Ear candling – an alternative medical technique in which lighted candles are placed in the ears for supposed therapeutic effect. The practice has been promoted with extravagant claims it can "purify the blood" or "cure" cancer, but Health Canada has found it has no health benefit; it does, however, carry a serious risk of injury. Psychic surgery – a sleight-of-hand confidence trick in which the practitioner pretends to remove a lump of tissue (typically raw animal entrails bought from a butcher) from a person. No evidence of objective benefit for any medical condition has been found. Reiki – a procedure in which the practitioner might look at, blow on, tap and touch a patient in an attempt to affect the "energy" in their body. Although there is some evidence that reiki sessions are relaxing and so might improve general well-being, Cancer
|
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Research UK say that "there is no scientific evidence to prove that Reiki can prevent, treat or cure cancer or any other disease". Shiatsu – a type of alternative medicine consisting of finger and palm pressure, stretches and other massage techniques. According to Cancer Research UK, "there is no scientific evidence to prove that shiatsu can cure or prevent any type of disease, including cancer." == Spiritual and mental healing == Cancer guided imagery – the practice of attempting to treat cancer in oneself by imagining it away. According to the American Cancer Society, "available scientific evidence does not support claims that imagery can influence the development or progress of cancer". Faith healing – the attempt to cure disease by spiritual means, often by prayer or participation in religious ritual. According to the American Cancer Society, "available scientific evidence does not support claims that faith healing can actually cure physical ailments". Hypnosis – the induction of a deeply relaxed and yet alert mental state. Some practitioners have claimed hypnosis might help boost the immune system. However, according to the American Cancer Society, "available scientific evidence does not support the idea that hypnosis can influence the development or progression of cancer.". Meditation (also Transcendental Meditation and Mindfulness) – mind-body practices in which patients attempt to master their own mental processes. According to the American Cancer Society while meditation "may help to improve the quality of life for people with cancer", "available scientific evidence does not suggest that meditation is effective in treating cancer or any other disease." Neuro-linguistic programming (NLP) – a series of behavioral techniques based on various supposed relationships between language and mental processes. NLP has been promoted as a treatment for HIV/AIDS and cancer, but such claims have no evidence to support them. Anti-cancer psychotherapy – a technique
|
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claiming that a "cancer personality" caused cancer, which could be cured through talk therapy (e.g. that of the Simonton Cancer Center, Bernie Siegel's "Exceptional Cancer Patients" (ECaP) or Deepak Chopra). Evidence is lacking that cancer cures sold or promoted by Deepak Chopra have any value. Qigong – the practice of maintaining a meditative state while making gentle and fluid bodily movements, in an attempt to balance internal life energy. A systematic review of the effect of qigong exercises on cancer treatment concluded "the effectiveness of qigong in cancer care is not yet supported by the evidence from rigorous clinical trials." == Synthetic chemicals and other substances == 714-X – sometimes called "trimethylbicyclonitramineoheptane chloride", is a mixture of chemicals marketed commercially as a cure for many human ailments, including cancer. There is no scientific evidence for any anti-cancer effect from 714-X. Antineoplaston therapy – a form of chemotherapy promoted by the Burzynski Clinic in Texas, United States. The American Cancer Society has found no evidence that antineoplastons have any beneficial effects in cancer, and it has recommended that people do not spend money on antineoplaston treatments. Apitherapy – the use of products derived from bees, such as honey and bee venom, as a therapy. Apitherapy has been promoted for its anti-cancer effects; however, according to the American Cancer Society, "there have been no clinical studies in humans showing that bee venom or other honeybee products are effective in preventing or treating cancer." Cancell (also called Protocel, Sheridan's Formula, Jim's Juice, Crocinic Acid, JS–114, JS–101, 126–F and Entelev) – a formula that has been promoted as a treatment for a wide range of diseases, including cancer. The American Cancer Society and Memorial Sloan Kettering Cancer Center recommend against the use of CanCell, as there is no evidence that it is effective in
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treating any disease, and its proposed method of action is not consistent with modern science. Cell therapy – the practice of injecting cellular material from animals in an attempt to prevent or treat cancer. Although the use of human-to-human cell therapy has some established medical uses, the injection of animal material is, according to the American Cancer Society, not backed by any evidence of effectiveness, and "may in fact be lethal". Caesium chloride – a toxic salt, promoted as a cancer cure (sometimes as "high pH therapy"), on the basis that it targets cancer cells. However, there is no evidence to support these claims, while serious adverse reactions have been reported. These include hypokalemia, arrhythmia and acute cardiac arrest. Chelation therapy – removal of metals from the body by administering chelating agents. Chelation therapy is a legitimate therapy for heavy metal poisoning, but it has also been promoted as an alternative treatment for diseases including cancer. The American Cancer Society says: "Available scientific evidence does not support claims that it is effective for treating other conditions such as cancer. Chelation therapy can be toxic and has the potential to cause kidney damage, irregular heartbeat and even death." Cytokine therapy (or Klehr's autologous tumor therapy) – a so-called immunotherapy with a therapeutic substrate made of cytokines from the cancer patients' blood. The inventor of this method is Nikolaus Walther Klehr, a dermatologist, who practiced it in his private clinics in Salzburg and Munich. The patients were mainly from Slovenia, Poland and other Eastern European countries. Klehr is reported as claiming that his treatment leads to extended lifespan. According to German Cancer Aid, the mechanism of action is unclear and the method's clinical effectiveness unproven. Colloidal silver – liquid containing a suspension of silver particles, marketed as a treatment for cancer and
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other ailments. Quackwatch states that colloidal silver dietary supplements have not been found safe or effective for the treatment of any condition. Ingestion of ionic silver can cause a rare condition called argyria in which silver is reduced to elemental form inside tissues, causing an irreversible blue/gray complexion. Coral calcium – a dietary supplement supposedly made from crushed coral and promoted with claims it could treat a number of diseases including cancer. A consumer advisory issued by the National Center for Complementary and Alternative Medicine stated "Consumers should be aware that claims that coral calcium can treat or cure cancer, multiple sclerosis, lupus, heart disease, or high blood pressure are not supported by existing scientific evidence". DHEA (Dehydroepiandrosterone) – a steroid hormone that has been promoted in supplement form for its claimed cancer prevention properties; there is no scientific evidence to support these claims. Di Bella Therapy – a cocktail of vitamins, drugs and hormones devised by Luigi di Bella (1912–2003) and promoted as a cancer treatment. According to the American Cancer Society: "Available scientific evidence does not support claims that Di Bella therapy is effective in treating cancer. It can cause serious and harmful side effects. ... [These] may include nausea, vomiting, diarrhea, increased blood sugar levels, low blood pressure, sleepiness and neurological symptoms." Dimethyl sulfoxide (or DMSO) – an organosulfur compound that has been promoted as a treatment for cancer since the 1960s. According to the American Cancer Society, "available scientific evidence does not suggest that DMSO is effective in treating cancer in humans". Emu oil – an oil derived from adipose tissue of the emu, and promoted in dietary supplement form with the claimed ability to treat a wide range of diseases, including cancer. These products have been cited by the U.S. Food and Drug Administration as
|
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a prime example of a "rip-off". Gc-MAF (Gc protein-derived macrophage activating factor) – a type of protein that affects the immune system, and which has been promoted as a "miracle cure" for cancer and HIV. According to Cancer Research UK, "there is no solid scientific evidence to show that the treatment is safe or effective". Germanium – a metalloid which has been sold in supplement form with the claim that it is capable of treating leukemia and lung cancer. There is, however, no evidence of benefit, and instead some evidence that such supplements are actively harmful. Hydrazine sulfate – a chemical compound promoted (sometimes as "rocket fuel treatment") for its supposed ability to treat cancer. According to Cancer Research UK, although there is some evidence Hydrazine sulfate might help some people with cancer gain weight, "there is no evidence that it helps to treat cancer". Hyperbaric oxygen therapy – the use of a pressurized oxygen environment as therapy. Hyperbaric oxygen therapy has a number of accepted uses—for example hyperbaric chambers are used for treating decompression sickness. The therapy has also been promoted as a cure-all for a wide range of conditions, including cancer, for which there is no evidence of effectiveness. Insulin potentiation therapy – the practice of injecting insulin, usually alongside a low dose of conventional chemotherapy drugs, in the belief that this improves the overall effect of the treatment. Although it may cause a temporary reduction in tumor size for some patients, there is no evidence that it improves survival time or any other main outcomes. Krebiozen (also known as Carcalon, creatine, substance X, or drug X) – a mineral oil-based liquid sold as an alternative cancer treatment. According to the American Cancer Society: "Available scientific evidence does not support claims that Krebiozen is effective in treating cancer
|
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or any other disease. According to the U.S. Food and Drug Administration (FDA), creatine has been linked to several dangerous side effects." Lipoic acid – an antioxidant available as a dietary supplement and claimed by proponents to be capable of slowing cancer progression. According to the American Cancer Society, "there is no reliable scientific evidence at this time that lipoic acid prevents the development or spread of cancer". Miracle Mineral Supplement (or MMS) – a toxic solution of 28% sodium chlorite in distilled water, is promoted for treating cancer and other ailments. Quackwatch states, "the product, when used as directed, produces an industrial bleach that can cause serious harm to health". Orthomolecular medicine (or Megavitamin therapy) – the use of high doses of vitamins, claimed by proponents to help cure cancer. The view of the medical community is that there is no evidence that these therapies are effective for treating any disease. Oxygen therapy – in alternative medicine, the practice of injecting hydrogen peroxide, oxygenating blood, or administering oxygen under pressure to the rectum, vagina, or other bodily opening. According to the American Cancer Society, "available scientific evidence does not support claims that putting oxygen-releasing chemicals into a person's body is effective in treating cancer", and some of these treatments can be dangerous. Ozone therapy – the application of ozone to the body, either externally or internally. Pangamic acid – a name given to an ill-defined substance peddled by fraudster Ernst T. Krebs, Jr. (1911–1996) with the claim it could cure cancer and various other serious diseases. Sometimes called "vitamin B15", pangamic acid isn't a vitamin and is medically useless. Phosphorylethanolamine – A chemical manufactured in Brazil by Gilberto Chierice and distributed with claims it could cure cancer. In 2015, after courts initially upheld people's rights to try phosphorylethanolamine, subsequent
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opposition from scientific and medical bodies led to a reversal in the law. Subsequent testing has found phosphorylethanolamine to be of no therapeutic benefit. Poly-MVA – a dietary supplement created by Merrill Garnett (1931–), a former dentist turned biochemist. Poly-MVA is promoted as a treatment for a number of diseases including HIV/AIDS and cancer, but there is no medical evidence to support such claims and some concern that the use of Poly-MVA can interfere with the functioning of conventional cancer treatments. Pregnenolone – a steroid which has been promoted online with claims it can treat a variety of diseases including multiple sclerosis, arthritis and cancer, but such claims are not backed by evidence. Protandim – a herbal supplement fraudulently marketed with claims it can cure or prevent a number of serious health conditions, including cancer. Quercetin – a plant pigment used in dietary supplements that have been promoted for their ability to prevent and treat cancer; however, according to the American Cancer society, "there is no reliable clinical evidence that quercetin can prevent or treat cancer in humans". Revici's Guided Chemotherapy – a practice in which a chemical mixture (usually including lipid alcohol and various metals) is given by mouth or injection, supposedly to cure cancer. The practice was devised by Emanuel Revici (1896–1997) and differs from modern chemotherapy despite being named with the same term. According to the American Cancer Society: "Available scientific evidence does not support claims that Revici's guided chemotherapy is effective in treating cancer or any other disease. It may also cause potentially serious side effects." RIGVIR – a virotherapy medication approved by the State Agency of Medicines of the Republic of Latvia. There is no good evidence that RIGVIR is an effective cancer treatment and a number of medical organisations have written to the Latvian
|
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government about the dubious science used to promote it. Its promotion has been described as likely being an instance of cancer quackery. Shark cartilage – a dietary supplement made from ground shark skeleton, and promoted as a cancer treatment perhaps because of the mistaken notion that sharks do not get cancer. The Mayo Clinic conducted research and were "unable to demonstrate any suggestion of efficacy for this shark cartilage product in patients with advanced cancer". Sodium bicarbonate (or baking soda) – the chemical compound with the formula NaHCO3, sometimes promoted as cure for cancer by alternative medical practitioners such as Tullio Simoncini. According to the American Cancer Society: "evidence also does not support the idea that sodium bicarbonate works as a treatment for any form of cancer. There is substantial evidence, however, that these claims are false." Edzard Ernst has called the promotion of sodium bicarbonate as a cancer cure "one of the more sickening alternative cancer scams I have seen for a long time". Urine therapy (or urotherapy) – the practice of attempting to treat cancer—or other illnesses—by drinking, injecting or taking an enema of one's own urine, or by making and taking some derivative substance from it. According to the American Cancer Society, "available scientific evidence does not support claims that urine or urea given in any form is helpful for cancer patients". Vitacor – a type of vitamin supplement devised by Matthias Rath and heavily promoted on the internet, alongside other products from Rath's company under the "Cellular Health" brand, as a claimed treatment for cancer and other human disease; these claims have led to Rath's prosecution. According to Cancer Research UK, "there is no scientific evidence at all to back up the claims that these products work". == See also == List of patent medicines List
|
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of topics characterized as pseudoscience == References ==
|
{
"page_id": 40370421,
"source": null,
"title": "List of unproven and disproven cancer treatments"
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|
The molecular formula C45H38O18 (molar mass: 866.77 g/mol, exact mass: 866.205814 u) may refer to: Arecatannin B1, a condensed tannin found in the betel nut Procyanidin C1, a condensed tannin found in grape Procyanidin C2, a condensed tannin found in grape and barley
|
{
"page_id": 27328755,
"source": null,
"title": "C45H38O18"
}
|
The molecular formula C15H14O may refer to: Diphenylacetone 1,1-Diphenylacetone Dibenzyl ketone Dihydrochalcone Flavan, a backbone of certain flavonoids Isoflavan, a backbone found in isoflavanes Neoflavan
|
{
"page_id": 23986423,
"source": null,
"title": "C15H14O"
}
|
Erica W. Carlson is an American physicist specializing in superconductors, liquid crystals, and strongly correlated materials. She is 150th Anniversary Professor of Physics and Astronomy at Purdue University. As well as for her research, she is known for her work in physics education for quantum physics, and for her introduction of innovative technologies including podcasts and wikis into her physics teaching. == Education and career == Carlson is a 1994 graduate of the California Institute of Technology. She went to the University of California, Los Angeles for graduate study, earning a master's degree in 1995 and completing her Ph.D. in 2000. After postdoctoral research at Boston University, she joined the Purdue faculty in 2003. In 2023, she created a YouTube channel, titled The Quantum Age. On her channel, she discusses many properties of quantum mechanics and quantum materials. The channel is targeted toward upper middle school and high school students. == Recognition == Carlson was named a Fellow of the American Physical Society (APS) in 2015, after a nomination from the APS Division of Condensed Matter Physics, "for theoretical insights into the critical role of electron nematicity, disorder, and noise in novel phases of strongly correlated electron systems and predicting unique characteristics". Purdue University named her as a 150th Anniversary Professor in 2018. == Personal life == Carlson is Christian, and has spoken publicly about combining her religious faith with science. == References == == External links == Carlson research group Erica Carlson publications indexed by Google Scholar
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"title": "Erica Carlson"
}
|
The HERA-B detector was a particle physics experiment at the HERA accelerator at the German national laboratory DESY that collected data from 1993 to 2003. It measured 8 m × 20 m × 9 m and weighed 1000 tons. The HERA-B collaboration consisted of some 250 scientists from 32 institutes in 13 countries. Its primary aim was to measure CP violation in the decays of heavy B mesons in the late 1990s, several years ahead of the Large Hadron Collider and B Factory programs. Unlike most particle physics detectors, the particles were produced not by colliding two circulating beams head-on, nor by slamming the beam into a stationary target, but by moving a thin wire target directly into the waste 'halo' of the circulating proton beam of the HERA accelerator. The beam was unaffected by this 'scraping' but the collision rate produced could be made extremely high, around 5 to 10 million interactions per second (5–10 MHz). The collaboration developed a novel scheme for moving the wires and the vertex detectors very close to the beam (less than one centimetre), using a vacuum chamber and motorised 'arms', had to be developed. == External links == HERA-B webpage HERA-B experiment record on INSPIRE-HEP == References ==
|
{
"page_id": 2883833,
"source": null,
"title": "HERA-B"
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|
The molecular formula C13H18O (molar mass: 190.28 g/mol, exact mass: 190.1358 u) may refer to: Bourgeonal Cyclamen aldehyde Damascenone
|
{
"page_id": 23986430,
"source": null,
"title": "C13H18O"
}
|
Dedifferentiation (pronounced dē-ˌdi-fə-ˌren-chē-ˈā-shən) is a transient process by which cells become less specialized and return to an earlier cell state within the same lineage. This suggests an increase in cell potency, meaning that, following dedifferentiation, a cell may possess the ability to re-differentiate into more cell types than it did before dedifferentiation. This is in contrast to differentiation, where differences in gene expression, morphology, or physiology arise in a cell, making its function increasingly specialized. The loss of specialization observed in dedifferentiation can be noted through changes in gene expression, physiology, function within the organism, proliferative activity, or morphology. While it can be induced in a laboratory setting through processes like direct reprogramming and the production of induced pluripotent stem cells, endogenous dedifferentiation processes also exist as a component of wound healing mechanisms. == History == References to dedifferentiation can be found as far back as 1915, where Charles Manning Child described dedifferentiation as a “return or approach to the embryonic or undifferentiated condition”. While Manning's research was about plants, it helped establish the foundation for our modern-day understanding of dedifferentiation and cell plasticity. Just as plant cells respond to injury by undergoing callus formation via dedifferentiation, some animal models dedifferentiate their cells to form blastema, which are analogous to plant calluses, after limb amputation. In the 1940s C. H. Waddington created the “Epigenetic Landscape”, a diagrammatic representation of cell fate from less differentiated to more differentiated cell types. Here, the concept of a marble moving downhill through various paths is used to represent cell decision-making and cell potency, thus visualizing how cells can take different paths of differentiation to reach a final state. Dedifferentiation would be represented by the marble moving uphill through the pathways it has already taken until it settles somewhere above the most downhill location. In
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"title": "Dedifferentiation"
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our modern-day understanding of dedifferentiation, some controversies remain when defining the boundaries of its definition. Some claim that dedifferentiation is strictly limited to the same cell lineage from which it is derived. However, others say that it can be used to describe a general increase in cell potency. == Mechanisms == The mechanism by which dedifferentiation occurs has not been completely illuminated. The pathways discussed below are found to be closely related to dedifferentiation and regeneration in some species. Because not one pathway has been elucidated as necessary for all dedifferentiation and regeneration, the mechanism may function differently in different species. === Observed markers of dedifferentiation === For dedifferentiation, genes in the extracellular matrix play an important role. For example, MMP, the matrix metalloproteinase, has shown up-regulated activity during early stages of limb regeneration. Matrix Metalloproteinases are responsible for degradation of both non-matrix and matrix proteins. MMP degrades proteins in the extracellular matrix [1] of a cell, resulting in the destabilization of the differentiated cell identity. However, the markers selected to represent dedifferentiation can differ according to the tissue and cell types that are being studied. For example, in mice myotubes, dedifferentiation is marked by a decreased expression of Myogenin, a protein present in differentiated myotubes. === Involved Pathways === Some of the pathways that have shown interaction in dedifferentiation are MSX1, Notch 1, BMP, and Wnt/β-Catenin. MSx1 [2], a gene that is a member of the homeobox [3] family, encodes a transcriptional repressor that can prevent differentiation in epithelial and mesenchymal [4] progenitor cell types. This repressor would be able to keep cells undifferentiated during development. Reduced levels of Msx1 expression resulted in an inability to regenerate tadpole tails. Bone Morphogenic Proteins (BMP [5]) are a group of signaling molecules involved in growth and development in many systems, including
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{
"page_id": 65667328,
"source": null,
"title": "Dedifferentiation"
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|
bone, embryogenesis [6], and homeostasis [7]. The BMP pathway is necessary for dedifferentiation and regeneration in tadpoles. Downregulation of the BMP pathway led to a downregulation of MSx1, resulting in no regeneration in the tadpole. Once BMP expression was restored, Msx1 expression was also restored, and regeneration proceeded.19 Similar studies have shown similar results in mouse digit tip regeneration. The Notch1 [8] pathway has demonstrated importance in the regeneration of frog tadpole tails. Notch1 is a gene in the Notch family of proteins. Notch proteins are part of an intercellular signaling pathway responsible for regulating interactions between cells that are physically next to one another by binding to other notch proteins. Lowered Notch1 expression resulted in no tadpole tail regeneration, and induced Notch1 expression was able to partially rescue tail regeneration in the form of the notochord and spinal cord (but very little musculature.) Moreover, Wnt/Beta-catenin activation has shown promising results in its involvement with dedifferentiation. In both a human epithelial cell transplant into mice and in vitro epithelial cell model, the activated canonical Wnt signaling pathway was found to be necessary for dedifferentiation. When in conjunction with Nanog, the canonical Wnt pathway also induced partial dedifferentiation in zebrafish endothelial cells, as seen by an increase in cell cycle re-entry and loss of cellular adhesion. == Plasticity == Cell plasticity [9] is the idea that cells can switch phenotypes in response to environmental cues. In the context of regeneration, this environmental cue is damage or injury to a limb. Cell plasticity is closely related to dedifferentiation, implying that a cell with ‘plasticity’ can dedifferentiate to change phenotypes. Cell plasticity suggests that cells can change phenotypes slightly; not fully de-differentiating, to serve a better function. A strong example of this is lens regeneration [10] in the newt. == Vertebrates == Across
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"title": "Dedifferentiation"
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|
various vertebrate models that have been used to study cell behavior during wound healing, dedifferentiation is consistently reflected by changes in gene expression, morphology, and proliferative activity that distinguish it from its previously terminally differentiated state. === Zebrafish (Danio rerio) === Upon injury, zebrafish cardiomyocytes have been found to have the capability to differentiate and subsequently rapidly proliferate as a wound healing response. Specifically, resection of up to 20% of the zebrafish ventricle regenerates via the proliferation of already differentiated cardiomyocyte. The cardiomyocytes dedifferentiation is observed through detachment from other cells as well as changes in morphology. === Mice === In mouse myotubes, dedifferentiation was induced upon the suppression of two tumor suppressor genes, encoding the retinoblastoma protein and alternative reading frame protein. These murine primary myotube cells then exhibited a decrease in differentiated cardiomyocyte gene expression, an increase in proliferation, and a change in morphology. Moreover, mouse Schwann cells were shown to have a capability to differentiate when the Ras/Raf/ERK pathway is activated. In this study, the addition of Ras blocks Schwann cell differentiation and induces dedifferentiation. A decrease in Schwann cell gene expression marks this transition. After dedifferentiation, new cells can be generated by re-entering the cell cycle and proliferating, then redifferentiating to myelinate the mice neurons. === Urodeles === Salamanders, including newts and axolotls, are species with the most known regenerative abilities. Adult newts can regenerate limbs, tail, upper and lower jaws, spinal cord, retinas, lenses, optic nerves, intestine, and a portion of its heart ventricle Axolotls share the same abilities, save the retina and lens. These animals are important to the study of dedifferentiation because they use dedifferentiation to create new progenitor cells. This is different from mammalian regeneration, because mammals use preexisting stem cells to replace lost tissues. Dedifferentiation in the newt occurs 4–5 days
|
{
"page_id": 65667328,
"source": null,
"title": "Dedifferentiation"
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after limb amputation and is characterized by cell cycle re-entry and down-regulation of differentiation markers. cell differentiation is determined by what genes the cell expresses, and down-regulation of this expression would make for a less, or “un”, differentiated cell. Re-entry into the cell cycle allows the cell to go through mitosis, dividing to make more cells that would be able to provide new tissue. It has been observed that actinomycin D prevents dedifferentiation in newts == Invertebrates == It is less common to find examples of dedifferentiation (due to a lack of regenerative ability) in most invertebrates. This brief example outlines dedifferentiation in an invertebrate species, and interestingly involves the Msx pathway, as detailed above in the mechanisms section. === Lancelet === Upon amputation, lancelet tails healed and formed a blastema [11] structure, suggesting dedifferentiation of cells to prepare for regeneration Lancelets can regenerate anterior and posterior structures, including neural tube, notochord, fin, and muscle The blastema that is formed expresses PAX3 and PAX7, which is associated with activation of muscle stem cells. This specific invertebrate model seems to be limited in its dedifferentiation abilities with size and age. The older and larger the animal is, the less apt it is [12] for dedifferentiation. == Other Terms Related to Dedifferentiation == === Anaplasia === Anaplasia is defined as cells being in an undifferentiated state and it is often associated with cancer. Often this loss of mature cell markers or morphology can be due to dedifferentiation, but it is sometimes used to refer to cells with incomplete differentiation presenting large variety in size and shape. While its definition can be conflated with dedifferentiation, it is more often perceived as a loss of differentiation leading to abnormal cell activity, including but not limited to tumorigenesis. However, dedifferentiation is often perceived as a
|
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"source": null,
"title": "Dedifferentiation"
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reversion to a different cell type for regenerative purposes. In anaplastic cells, there is often an increase in proliferation and abnormal cellular organization, characteristics that are also present in dedifferentiated cells. === Undifferentiation === Undifferentiated cells have not completed differentiation or specialization, thus retaining their cell potency and oftentimes being highly proliferative. This is often the final cell state after the dedifferentiation process is completed and maintained, as cells become less specialized. === Metaplasia === Metaplasia [13] is not another definition of dedifferentiation, but the two words have very similar implications for cells. Metaplasia refers to the change from a fully differentiated cell type to another. This implies that the cell is able to adapt to environmental stimuli, and that it is possible to reverse embryological commitments in the form of differentiation. The idea of metaplasia depends on the ability for a cell to dedifferentiate. This definition is important to consider when discussing dedifferentiation because the two concepts overlap closely, such that metaplasia may rely on dedifferentiation, or they may share similar pathways. Metaplasia, however, aligns more closely with transdifferentiation, because metaplasia refers more to the idea of a phenotypic transition. === Transdifferentiation === Transdifferentiation [14] refers to the conversion of one cellular phenotype to another. This phrase defines the overview of what dedifferentiation contributes to cell fates; firstly, dedifferentiation brings the cell back up the epigenetic landscape, and then the cell can “roll” down a new valley, thus re-differentiating into a new phenotype. This whole process of the cell fate changing from its original to a new fate is transdifferentiation. However, there is also a second definition of transdifferentiation, in which cells can be directly induced into a new cell type without necessitating dedifferentiation as an intermediate step. == Current Research and Future Implications == Currently, studies and experiments
|
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"title": "Dedifferentiation"
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are being done to test for dedifferentiation-like abilities in mammalian cells, with hopes that this information can provide more insight into possible regenerative abilities in mammals. Dedifferentiation could spark innovation in regenerative medicine because it suggests that one's own cells can change cell fates, which would remove immunological response risks from treatment with allogeneic cells, or cells that are not genetically matched with the patient. A concept that has been explored for mammals is that of inducible dedifferentiation, which would make cells that do not naturally dedifferentiate be able to revert to a pluripotent or progenitor-like state. This is achieved by expressing the appropriate transcription factors in the cell and suppressing others. More information about this as well as the possible risks can be found here [15] . == See also == Dolly (sheep), a female Finn-Dorset sheep and the first mammal that was cloned from an adult somatic cell. Pluripotency == References ==
|
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"page_id": 65667328,
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"title": "Dedifferentiation"
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In biology, translation is the process in living cells in which proteins are produced using RNA molecules as templates. The generated protein is a sequence of amino acids. This sequence is determined by the sequence of nucleotides in the RNA. The nucleotides are considered three at a time. Each such triple results in the addition of one specific amino acid to the protein being generated. The matching from nucleotide triple to amino acid is called the genetic code. The translation is performed by a large complex of functional RNA and proteins called ribosomes. The entire process is called gene expression. In translation, messenger RNA (mRNA) is decoded in a ribosome, outside the nucleus, to produce a specific amino acid chain, or polypeptide. The polypeptide later folds into an active protein and performs its functions in the cell. The polypeptide can also start folding during protein synthesis. The ribosome facilitates decoding by inducing the binding of complementary transfer RNA (tRNA) anticodon sequences to mRNA codons. The tRNAs carry specific amino acids that are chained together into a polypeptide as the mRNA passes through and is "read" by the ribosome. Translation proceeds in three phases: Initiation: The ribosome assembles around the target mRNA. The first tRNA is attached at the start codon. Elongation: The last tRNA validated by the small ribosomal subunit (accommodation) transfers the amino acid. It carries to the large ribosomal subunit which binds it to one of the preceding admitted tRNA (transpeptidation). The ribosome then moves to the next mRNA codon to continue the process (translocation), creating an amino acid chain. Termination: When a stop codon is reached, the ribosome releases the polypeptide. The ribosomal complex remains intact and moves on to the next mRNA to be translated. In prokaryotes (bacteria and archaea), translation occurs in the cytosol, where
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{
"page_id": 262401,
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"title": "Translation (biology)"
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the large and small subunits of the ribosome bind to the mRNA. In eukaryotes, translation occurs in the cytoplasm or across the membrane of the endoplasmic reticulum through a process called co-translational translocation. In co-translational translocation, the entire ribosome–mRNA complex binds to the outer membrane of the rough endoplasmic reticulum (ER), and the new protein is synthesized and released into the ER; the newly created polypeptide can be immediately secreted or stored inside the ER for future vesicle transport and secretion outside the cell. Many types of transcribed RNA, such as tRNA, ribosomal RNA, and small nuclear RNA, do not undergo a translation into proteins. Several antibiotics act by inhibiting translation. These include anisomycin, cycloheximide, chloramphenicol, tetracycline, streptomycin, erythromycin, and puromycin. Prokaryotic ribosomes have a different structure from that of eukaryotic ribosomes, and thus antibiotics can specifically target bacterial infections without harming a eukaryotic host's cells. == Basic mechanisms == The basic process of protein production is the addition of one amino acid at a time to the end of a protein. This operation is performed by a ribosome. A ribosome is made up of two subunits, a small subunit, and a large subunit. These subunits come together before the translation of mRNA into a protein to provide a location for translation to be carried out and a polypeptide to be produced. The choice of amino acid type to add is determined by a messenger RNA (mRNA) molecule. Each amino acid added is matched to a three-nucleotide subsequence of the mRNA. For each such triplet possible, the corresponding amino acid is accepted. The successive amino acids added to the chain are matched to successive nucleotide triplets in the mRNA. In this way, the sequence of nucleotides in the template mRNA chain determines the sequence of amino acids in the generated
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{
"page_id": 262401,
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"title": "Translation (biology)"
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amino acid chain. The addition of an amino acid occurs at the C-terminus of the peptide; thus, translation is said to be amine-to-carboxyl directed. The mRNA carries genetic information encoded as a ribonucleotide sequence from the chromosomes to the ribosomes. The ribonucleotides are "read" by translational machinery in a sequence of nucleotide triplets called codons. Each of those triplets codes for a specific amino acid. The ribosome molecules translate this code to a specific sequence of amino acids. The ribosome is a multisubunit structure containing ribosomal RNA (rRNA) and proteins. It is the "factory" where amino acids are assembled into proteins. Transfer RNAs (tRNAs) are small noncoding RNA chains (74–93 nucleotides) that transport amino acids to the ribosome. The repertoire of tRNA genes varies widely between species, with some bacteria having between 20 and 30 genes while complex eukaryotes could have thousands. tRNAs have a site for amino acid attachment, and a site called an anticodon. The anticodon is an RNA triplet complementary to the mRNA triplet that codes for their cargo amino acid. Aminoacyl tRNA synthetases (enzymes) catalyze the bonding between specific tRNAs and the amino acids that their anticodon sequences call for. The product of this reaction is an aminoacyl-tRNA. The amino acid is joined by its carboxyl group to the 3' OH of the tRNA by an ester bond. When the tRNA has an amino acid linked to it, the tRNA is termed "charged". In bacteria, this aminoacyl-tRNA is carried to the ribosome by EF-Tu, where mRNA codons are matched through complementary base pairing to specific tRNA anticodons. Aminoacyl-tRNA synthetases that mispair tRNAs with the wrong amino acids can produce mischarged aminoacyl-tRNAs, which can result in inappropriate amino acids at the respective position in the protein. This "mistranslation" of the genetic code naturally occurs at low levels
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{
"page_id": 262401,
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in most organisms, but certain cellular environments cause an increase in permissive mRNA decoding, sometimes to the benefit of the cell. The ribosome has two binding sites for tRNA. They are the aminoacyl site (abbreviated A), and the peptidyl site/ exit site (abbreviated P/E). Concerning the mRNA, the three sites are oriented 5' to 3' E-P-A, because ribosomes move toward the 3' end of mRNA. The A-site binds the incoming tRNA with the complementary codon on the mRNA. The P/E-site holds the tRNA with the growing polypeptide chain. When an aminoacyl-tRNA initially binds to its corresponding codon on the mRNA, it is in the A site. Then, a peptide bond forms between the amino acid of the tRNA in the A site and the amino acid of the charged tRNA in the P/E site. The growing polypeptide chain is transferred to the tRNA in the A site. Translocation occurs, moving the tRNA to the P/E site, now without an amino acid; the tRNA that was in the A site, now charged with the polypeptide chain, is moved to the P/E site and the uncharged tRNA leaves, and another aminoacyl-tRNA enters the A site to repeat the process. After the new amino acid is added to the chain, and after the tRNA is released out of the ribosome and into the cytosol, the energy provided by the hydrolysis of a GTP bound to the translocase EF-G (in bacteria) and a/eEF-2 (in eukaryotes and archaea) moves the ribosome down one codon towards the 3' end. The energy required for translation of proteins is significant. For a protein containing n amino acids, the number of high-energy phosphate bonds required to translate it is 4n-1. The rate of translation varies; it is significantly higher in prokaryotic cells (up to 17–21 amino acid residues per
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{
"page_id": 262401,
"source": null,
"title": "Translation (biology)"
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second) than in eukaryotic cells (up to 6–9 amino acid residues per second). === Initiation and termination of translation === Initiation involves the small subunit of the ribosome binding to the 5' end of mRNA with the help of initiation factors (IF). In bacteria and a minority of archaea, initiation of protein synthesis involves the recognition of a purine-rich initiation sequence on the mRNA called the Shine–Dalgarno sequence. The Shine–Dalgarno sequence binds to a complementary pyrimidine-rich sequence on the 3' end of the 16S rRNA part of the 30S ribosomal subunit. The binding of these complementary sequences ensures that the 30S ribosomal subunit is bound to the mRNA and is aligned such that the initiation codon is placed in the 30S portion of the P-site. Once the mRNA and 30S subunit are properly bound, an initiation factor brings the initiator tRNA–amino acid complex, f-Met-tRNA, to the 30S P site. The initiation phase is completed once a 50S subunit joins the 30S subunit, forming an active 70S ribosome. Termination of the polypeptide occurs when the A site of the ribosome is occupied by a stop codon (UAA, UAG, or UGA) on the mRNA, creating the primary structure of a protein. tRNA usually cannot recognize or bind to stop codons. Instead, the stop codon induces the binding of a release factor protein (RF1 & RF2) that prompts the disassembly of the entire ribosome/mRNA complex by the hydrolysis of the polypeptide chain from the peptidyl transferase center of the ribosome. Drugs or special sequence motifs on the mRNA can change the ribosomal structure so that near-cognate tRNAs are bound to the stop codon instead of the release factors. In such cases of 'translational readthrough', translation continues until the ribosome encounters the next stop codon. === Errors in translation === Even though the ribosomes
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are usually considered accurate and processive machines, the translation process is subject to errors that can lead either to the synthesis of erroneous proteins or to the premature abandonment of translation, either because a tRNA couples to a wrong codon or because a tRNA is coupled to the wrong amino acid. The rate of error in synthesizing proteins has been estimated to be between 1 in 105 and 1 in 103 misincorporated amino acids, depending on the experimental conditions. The rate of premature translation abandonment, instead, has been estimated to be of the order of magnitude of 10−4 events per translated codon. === Regulation === The process of translation is highly regulated in both eukaryotic and prokaryotic organisms. Regulation of translation can impact the global rate of protein synthesis which is closely coupled to the metabolic and proliferative state of a cell. To study this process, scientists have used a wide variety of methods such as structural biology, analytical chemistry (mass-spectrometry based), imaging of reporter mRNA translation (in which the translation of a mRNA is linked to an output, such as luminescence or fluorescence), and next-generation sequencing based methods. Other methods such as toeprinting assay can also be used to determine to determine the location of ribosomes of a particular mRNA in vitro, and footprints of other proteins regulating translation. In particular, ribosome profiling, which is a powerful method, enables researchers to take a snapshot of all the proteins being translated at a given time, showing which parts of the mRNA are being translated into proteins by ribosomes at a given time. This method is useful because it looks at all the mRNAs instead of using reporters that would typically look at one specific mRNA at a time. Ribosome profiling provides valuable insights into translation dynamics, revealing the complex interplay
|
{
"page_id": 262401,
"source": null,
"title": "Translation (biology)"
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|
between gene sequence, mRNA structure, and translation regulation. For example, research utilizing this method has revealed that genetic differences and their subsequent expression as mRNAs can also impact translation rate in an RNA-specific manner. Expanding on this concept, a more recent development is single-cell ribosome profiling, a technique that allows us to study the translation process at the resolution of individual cells. This is particularly significant as cells, even those of the same type, can exhibit considerable variability in their protein synthesis. Single-cell ribosome profiling has the potential to shed light on the heterogeneous nature of cells, leading to a more nuanced understanding of how translation regulation can impact cell behavior, metabolic state, and responsiveness to various stimuli or conditions. == Clinical significance == Translational control is critical for the development and survival of cancer. Cancer cells must frequently regulate the translation phase of gene expression, though it is not fully understood why translation is targeted over steps like transcrion. While cancer cells often have genetically altered translation factors, it is much more common for cancer cells to modify the levels of existing translation factors. Several major oncogenic signaling pathways, including the RAS–MAPK, PI3K/AKT/mTOR, MYC, and WNT–β-catenin pathways, ultimately reprogram the genome via translation. Cancer cells also control translation to adapt to cellular stress. During stress, the cell translates mRNAs that can mitigate the stress and promote survival. An example of this is the expression of AMPK in various cancers; its activation triggers a cascade that can ultimately allow the cancer to escape apoptosis (programmed cell death) triggered by nutrition deprivation. Future cancer therapies may involve disrupting the translation machinery of the cell to counter the downstream effects of cancer. == Mathematical modeling of translation == The transcription-translation process description, mentioning only the most basic "elementary" processes, consists of: production
|
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"page_id": 262401,
"source": null,
"title": "Translation (biology)"
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of mRNA molecules (including splicing), initiation of these molecules with help of initiation factors (e.g., the initiation can include the circularization step though it is not universally required), initiation of translation, recruiting the small ribosomal subunit, assembly of full ribosomes, elongation, (i.e. movement of ribosomes along mRNA with production of protein), termination of translation, degradation of mRNA molecules, degradation of proteins. The process of amino acid building to create protein in translation is a subject of various physic models for a long time starting from the first detailed kinetic models such as or others taking into account stochastic aspects of translation and using computer simulations. Many chemical kinetics-based models of protein synthesis have been developed and analyzed in the last four decades. Beyond chemical kinetics, various modeling formalisms such as Totally Asymmetric Simple Exclusion Process, Probabilistic Boolean Networks, Petri Nets and max-plus algebra have been applied to model the detailed kinetics of protein synthesis or some of its stages. A basic model of protein synthesis that takes into account all eight 'elementary' processes has been developed, following the paradigm that "useful models are simple and extendable". The simplest model M0 is represented by the reaction kinetic mechanism (Figure M0). It was generalised to include 40S, 60S and initiation factors (IF) binding (Figure M1'). It was extended further to include effect of microRNA on protein synthesis. Most of models in this hierarchy can be solved analytically. These solutions were used to extract 'kinetic signatures' of different specific mechanisms of synthesis regulation. == Genetic code == It is also possible to translate either by hand (for short sequences) or by computer (after first programming one appropriately, see section below); this allows biologists and chemists to draw out the chemical structure of the encoded protein on paper. First, convert each template DNA base
|
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"page_id": 262401,
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to its RNA complement (note that the complement of A is now U), as shown below. Note that the template strand of the DNA is the one the RNA is polymerized against; the other DNA strand would be the same as the RNA, but with thymine instead of uracil. DNA -> RNA A -> U T -> A C -> G G -> C A=T-> A=U Then split the RNA into triplets (groups of three bases). Note that there are 3 translation "windows", or reading frames, depending on where you start reading the code. Finally, use the table at Genetic code to translate the above into a structural formula as used in chemistry. This will give the primary structure of the protein. However, proteins tend to fold, depending in part on hydrophilic and hydrophobic segments along the chain. Secondary structure can often still be guessed at, but the proper tertiary structure is often very hard to determine. Whereas other aspects such as the 3D structure, called tertiary structure, of protein can only be predicted using sophisticated algorithms, the amino acid sequence, called primary structure, can be determined solely from the nucleic acid sequence with the aid of a translation table. This approach may not give the correct amino acid composition of the protein, in particular if unconventional amino acids such as selenocysteine are incorporated into the protein, which is coded for by a conventional stop codon in combination with a downstream hairpin (SElenoCysteine Insertion Sequence, or SECIS). There are many computer programs capable of translating a DNA/RNA sequence into a protein sequence. Normally this is performed using the Standard Genetic Code, however, few programs can handle all the "special" cases, such as the use of the alternative initiation codons which are biologically significant. For instance, the rare alternative start codon
|
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CTG codes for Methionine when used as a start codon, and for Leucine in all other positions. Example: Condensed translation table for the Standard Genetic Code (from the NCBI Taxonomy webpage). AAs = FFLLSSSSYY**CC*WLLLLPPPPHHQQRRRRIIIMTTTTNNKKSSRRVVVVAAAADDEEGGGG Starts = ---M---------------M---------------M---------------------------- Base1 = TTTTTTTTTTTTTTTTCCCCCCCCCCCCCCCCAAAAAAAAAAAAAAAAGGGGGGGGGGGGGGGG Base2 = TTTTCCCCAAAAGGGGTTTTCCCCAAAAGGGGTTTTCCCCAAAAGGGGTTTTCCCCAAAAGGGG Base3 = TCAGTCAGTCAGTCAGTCAGTCAGTCAGTCAGTCAGTCAGTCAGTCAGTCAGTCAGTCAGTCAG The "Starts" row indicate three start codons, UUG, CUG, and the very common AUG. It also indicates the first amino acid residue when interpreted as a start: in this case it is all methionine. === Translation tables === Even when working with ordinary eukaryotic sequences such as the Yeast genome, it is often desired to be able to use alternative translation tables—namely for translation of the mitochondrial genes. Currently the following translation tables are defined by the NCBI Taxonomy Group for the translation of the sequences in GenBank: == See also == == References == == Further reading == == External links == Virtual Cell Animation Collection: Introducing Translation Translate tool (from DNA or RNA sequence)
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Negligible senescence is a term coined by biogerontologist Caleb Finch to denote organisms that do not exhibit evidence of biological aging (senescence), such as measurable reductions in their reproductive capability, measurable functional decline, or rising death rates with age. There are many species where scientists have seen no increase in mortality after maturity. This may mean that the lifespan of the organism is so long that researchers' subjects have not yet lived up to the time when a measure of the species' longevity can be made. Turtles, for example, were once thought to lack senescence, but more extensive observations have found evidence of decreasing fitness with age. Study of negligibly senescent animals may provide clues that lead to better understanding of the aging process and influence theories of aging. The phenomenon of negligible senescence in some animals is a traditional argument for attempting to achieve similar negligible senescence in humans by technological means. == In vertebrates == Some fish, such as some varieties of sturgeon and rougheye rockfish, and some tortoises and turtles are thought to be negligibly senescent, although recent research on turtles has uncovered evidence of senescence in the wild. The age of a captured fish specimen can be measured by examining growth patterns similar to tree rings on the otoliths (parts of motion-sensing organs). In 2018, naked mole-rats were identified as the first mammal to defy the Gompertz–Makeham law of mortality, and achieve negligible senescence. It has been speculated, however, that this may be simply a "time-stretching" effect primarily due to their very slow (and cold-blooded and hypoxic) metabolism. == In plants == In plants, aspen trees are one example of biological immortality. Each individual tree can live for 40–150 years above ground, but the root system of the clonal colony is long-lived. In some cases, this
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{
"page_id": 23003393,
"source": null,
"title": "Negligible senescence"
}
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is for thousands of years, sending up new trunks as the older trunks die off above ground. One such colony in Utah, given the nickname of "Pando", is estimated to be 80,000 years old, making it possibly the oldest living colony of aspens. The world's oldest known living non-clonal organism was the Methuselah tree of the species Pinus longaeva, the bristlecone pine, growing high in the White Mountains of Inyo County in eastern California, aged 4856–4857 years. This record was superseded in 2012 by another Great Basin bristlecone pine located in the same region as Methuselah, and was estimated to be 5,062 years old. The tree was sampled by Edmund Schulman and dated by Tom Harlan. Ginkgo trees in China resist aging by extensive gene expression associated with adaptable defense mechanisms that collectively contribute to longevity. == In bacteria == Among bacteria, individual organisms are vulnerable and can easily die, but on the level of the colony, bacteria can live indefinitely. The two daughter bacteria resulting from cell division of a parent bacterium can be regarded as unique individuals or as members of a biologically "immortal" colony. The two daughter cells can be regarded as "rejuvenated" copies of the parent cell because damaged macromolecules have been split between the two cells and diluted. See asexual reproduction. Aging and death have been reported for the bacterium Escherichia coli, an organism that reproduces by morphologically symmetrical division. The two progeny cells produced when an E. coli cell divides each have one new pole created by the division and one retained older pole. It was shown that those cell lines that retain older poles over successive cell divisions undergo aging. The old pole cells can be regarded as an aging parent repeatedly reproducing rejuventated offspring. Aging in the old pole cell includes cummulatively
|
{
"page_id": 23003393,
"source": null,
"title": "Negligible senescence"
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|
slowed growth, less offspring biomass production and an increased probability of death. Thus although bacteria divide symmetrically, they do not appear to be immune to the effects of aging. == Maximum life span == Some examples of maximum observed life span of animals thought to be negligibly senescent are: == Cryptobiosis == Some rare organisms, such as tardigrades, usually have short lifespans, but are able to survive for thousands of years—and, perhaps, indefinitely—if they enter into the state of cryptobiosis, whereby their metabolism is reversibly suspended. == Negative senescence == There are also organisms (certain algae, plants, corals, molluscs, sea urchins and lizards) that exhibit negative senescence, whereby mortality chronologically decreases as the organism ages, for all or part of the life cycle, in disagreement with the Gompertz–Makeham law of mortality (see also Late-life mortality deceleration). Furthermore, there are species that have been observed to regress to a larval state and regrow into adults multiple times, such as Turritopsis dohrnii. == See also == Biological immortality DNA damage theory of aging Indefinite lifespan Maximum lifespan Strategies for engineered negligible senescence Societal effects of negligible senescence == References ==
|
{
"page_id": 23003393,
"source": null,
"title": "Negligible senescence"
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Furan-2-ylmethanethiol (2-furanmethanethiol) is an organosulfur compound. It is classified as a furan substituted with a methylthiol group. It is a colourless liquid, but samples can appears yellow upon standing in air. It possesses a strong odour of roasted coffee and a bitter taste. It is a key component of the aroma of roasted coffee. It has been identified as a trigger molecule for parosmia following COVID-19 infection. == Synthesis == Furan-2-ylmethanethiol is prepared by treating furfuryl alcohol with thiourea in hydrochloric acid via an intermediate isothiouronium salt, which is hydrolized to the thiol by heating with sodium hydroxide. == References ==
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{
"page_id": 32964867,
"source": null,
"title": "Furan-2-ylmethanethiol"
}
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Paleoethnobotany (also spelled palaeoethnobotany), or archaeobotany, is the study of past human-plant interactions through the recovery and analysis of ancient plant remains. Both terms are synonymous, though paleoethnobotany (from the Greek words palaios [παλαιός] meaning ancient, ethnos [έθνος] meaning race or ethnicity, and votano [βότανο] meaning plants) is generally used in North America and acknowledges the contribution that ethnographic studies have made towards our current understanding of ancient plant exploitation practices, while the term archaeobotany (from the Greek words archaios [αρχαίος] meaning ancient and votano) is preferred in Europe and emphasizes the discipline's role within archaeology. As a field of study, paleoethnobotany is a subfield of environmental archaeology. It involves the investigation of both ancient environments and human activities related to those environments, as well as an understanding of how the two co-evolved. Plant remains recovered from ancient sediments within the landscape or at archaeological sites serve as the primary evidence for various research avenues within paleoethnobotany, such as the origins of plant domestication, the development of agriculture, paleoenvironmental reconstructions, subsistence strategies, paleodiets, economic structures, and more. Paleoethnobotanical studies are divided into two categories: those concerning the Old World (Eurasia and Africa) and those that pertain to the New World (the Americas). While this division has an inherent geographical distinction to it, it also reflects the differences in the flora of the two separate areas. For example, maize only occurs in the New World, while olives only occur in the Old World. Within this broad division, paleoethnobotanists tend to further focus their studies on specific regions, such as the Near East or the Mediterranean, since regional differences in the types of recovered plant remains also exist. == Macrobotanical vs. microbotanical remains == Plant remains recovered from ancient sediments or archaeological sites are generally referred to as either ‘macrobotanicals’ or ‘microbotanicals.’
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Macrobotanical remains are vegetative parts of plants, such as seeds, leaves, stems and chaff, as well as wood and charcoal that can either be observed with the naked eye or the with the use of a low-powered microscope. Microbotanical remains consist of microscopic parts or components of plants, such as pollen grains, phytoliths and starch granules, that require the use of a high-powered microscope in order to see them. The study of seeds, wood/charcoal, pollen, phytoliths and starches all require separate training, as slightly different techniques are employed for their processing and analysis. Paleoethnobotanists generally specialize in the study of a single type of macrobotanical or microbotanical remain, though they are familiar with the study of other types and can sometimes even specialize in more than one. == History == The state of Paleoethnobotany as a discipline today stems from a long history of development that spans more than two hundred years. Its current form is the product of steady progression by all aspects of the field, including methodology, analysis and research. === Initial work === The study of ancient plant remains began in the 19th century as a result of chance encounters with desiccated and waterlogged material at archaeological sites. In Europe, the first analyses of plant macrofossils were conducted by the botanist C. Kunth (1826) on desiccated remains from Egyptian tombs and O. Heer (1866) on waterlogged specimens from lakeside villages in Switzerland, after which point archaeological plant remains became of interest and continued to be periodically studied from different European countries until the mid-20th century. In North America, the first analysis of plant remains occurred slightly later and did not generate the same interest in this type of archaeological evidence until the 1930s when Gilmore (1931) and Jones (1936) analysed desiccated material from rock shelters in the
|
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"page_id": 327940,
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American Southwest. All these early studies, in both Europe and North America, largely focused on the simple identification of the plant remains in order to produce a list of the recovered taxa. === Establishment of the field === During the 1950s and 1960s, Paleoethnobotany gained significant recognition as a field of archaeological research with two significant events: the publication of the Star Carr excavations in the UK and the recovery of plant material from archaeological sites in the Near East. Both convinced the archaeological community of the importance of studying plant remains by demonstrating their potential contribution to the discipline; the former produced a detailed paleoenvironmental reconstruction that was integral to the archaeological interpretation of the site and the latter yielded the first evidence for plant domestication, which allowed for a fuller understanding of the archaeological record. Thereafter, the recovery and analysis of plant remains received greater attention as a part of archaeological investigations. In 1968, the International Work Group for Palaeoethnobotany (IWGP) was founded. === Expansion and growth === With the rise of Processual archaeology, the field of Paleoethnobotany began to grow significantly. The implementation in the 1970s of a new recovery method, called flotation, allowed archaeologists to begin systematically searching for plant macrofossils at every type of archaeological site. As a result, there was a sudden influx of material for archaeobotanical study, as carbonized and mineralized plant remains were becoming readily recovered from archaeological contexts. Increased emphasis on scientific analyses also renewed interest in the study of plant microbotanicals, such as phytoliths (1970s) and starches (1980s), while later advances in computational technology during the 1990s facilitated the application of software programs as tools for quantitative analysis. The 1980s and 1990s also saw the publication of several seminal volumes about Paleoethnobotany that demonstrated the sound theoretical framework in which
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"page_id": 327940,
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the discipline operates. And finally, the popularization of Post-Processual archaeology in the 1990s, helped broaden the range of research topics addressed by paleoethnobotanists, for example 'food-related gender roles'. === Current state of the field === Paleoethnobotany is a discipline that is ever evolving, even up to the present day. Since the 1990s, the field has continued to gain a better understanding of the processes responsible for creating plant assemblages in the archaeological record and to refine its analytical and methodological approaches accordingly. For example, current studies have become much more interdisciplinary, utilizing various lines of investigation in order to gain a fuller picture of the past plant economies. Research avenues also continue to explore new topics pertaining to ancient human-plant interactions, such as the potential use of plant remains in relation to their mnemonic or sensory properties. Interest in plant remains surged in the 2000s alongside the improvement of stable isotope analysis and its application to archaeology, including the potential to illuminate the intensity of agricultural labor, resilience, and long-term social and economic changes. Archaeobotany had not been used extensively in Australia until recently. In 2018 a study of the Karnatukul site in the Little Sandy Desert of Western Australia showed evidence of continuous human habitation for around 50,000 years, by analysing wattle and other plant items. == Modes of preservation == As organic matter, plant remains generally decay over time due to microbial activity. In order to be recovered in the archaeological record, therefore, plant material must be subject to specific environmental conditions or cultural contexts that prevent their natural degradation. Plant macrofossils recovered as paleoenvironmental, or archaeological specimens result from four main modes of preservation: Carbonized (Charred): Plant remains can survive in the archaeological record when they have been converted into charcoal through exposure to fire under low-oxygen
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conditions. Charred organic material is more resistant to deterioration, since it is only susceptible to chemical breakdown, which takes a long time (Weiner 2010). Due to the essential use of fire for many anthropogenic activities, carbonized remains constitute the most common type of plant macrofossil recovered from archaeological sites. This mode of preservation, however, tends to be biased towards plant remains that come into direct contact with fire for cooking or fuel purposes, as well as those that are more robust, such as cereal grains and nut shells. Waterlogged: Preservation of plant material can also occur when it is deposited in permanently wet, anoxic conditions, because the absence of oxygen prohibits microbial activity. This mode of preservation can occur in deep archaeological features, such as wells, and in lakebed or riverbed sediments adjacent to settlements. A wide range of plant remains are usually preserved as waterlogged material, including seeds, fruit stones, nutshells, leaves, straw and other vegetative matter. Desiccated: Another mode by which plant material can be preserved is desiccation, which only occurs in very arid environments, such as deserts, where the absence of water limits decomposition of organic matter. Desiccated plant remains are a rarer recovery, but an incredibly important source of archaeological information, since all types of plant remains can survive, even very delicate vegetative attributes, such as onion skins and crocus stigmas (saffron), as well as woven textiles, bunches of flowers and entire fruits. Mineralized: Plant material can also preserve in the archaeological record when its soft organic tissues are completely replaced by inorganic minerals. There are two types of mineralization processes. The first, 'biomineralization,' occurs when certain plant remains, such as the fruits of Celtis sp. (hackberry) or nutlets of the Boraginaceae family, naturally produce increased amounts of calcium carbonate or silica throughout their growth, resulting
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in calcified or silicified specimens. The second, 'replacement mineralization,' occurs when plant remains absorb precipitating minerals present in the sediment or organic matter in which they are buried. This mode of preservation by mineralization only occurs under specific depositional conditions, usually involving a high presence of phosphate. Mineralized plant remains, therefore, are most commonly recovered from middens and latrine pits – contexts which often yield plant remains that have passed through the digestive track, such as spices, grape pips and fig seeds. The mineralization of plant material can also occur when remains are deposited alongside metal artefacts, especially those made of bronze or iron. In this circumstance, the soft organic tissues are replaced by the leaching of corrosion products that form over time on the metal objects. In addition to the above-mentioned modes of preservation, plant remains can also be occasionally preserved in a frozen state or as impressions. The former occurs quite rarely, but a famous example comes from Ötzi, the 5,500 year old mummy found frozen in the French Alps, whose stomach contents revealed the plant and meat components of his last meal. The latter occurs more regularly, though plant impressions do not actually preserve the macrobotanical remains themselves, but rather their negative imprints in pliable materials like clay, mudbrick or plaster. Impressions often result from the deliberate employment of plant material for decorative or technological purposes (such as the use of leaves to create patterning on ceramics or the use of chaff as temper in the construction of mudbricks), however, they can also derive from accidental inclusions. Identification of plant impressions is achieved by creating a silicone cast of the imprints and studying them under the microscope. == Recovery methods == In order to study ancient plant macrobotanical material, Paleoethnobotanists employ a variety of recovery strategies that
|
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"page_id": 327940,
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involve different sampling and processing techniques depending on the kind of research questions they are addressing, the type of plant macrofossils they are expecting to recover and the location from which they are taking samples. === Sampling === In general, there are four different types of sampling methods that can be used for the recovery of plant macrofossils from an archaeological site: Full Coverage sampling: involves taking at least one sample from all contexts and features Judgement sampling: entails the sampling of only areas and features most likely to yield ancient plant remains, such as a hearth Random sampling: consists of taking random samples either arbitrarily or via a grid system Systematic sampling: involves taking samples at set intervals during excavation Each sampling method has its own pros and cons and for this reason, paleoethnobotanists sometimes implement more than one sampling method at a single site. In general, Systematic or Full Coverage sampling is always recommended whenever possible. The practicalities of excavation, however, and/or the type of archaeological site under investigation sometimes limit their use and Judgment sampling tends to occur more often than not. Aside from sampling methods, there are also different types of samples that can be collected, for which the standard, recommended sample size is ~20L for dry sites and 1-5L for waterlogged sites. Point/Spot samples: consist of sediment collected only from a particular location Pinch samples: consist of small amounts of sediment that are collected from across the whole context and combined in one bag Column samples: consist of sediment collected from the different stratigraphic layers of a column of sediment that was deliberately left unexcavated These different types of samples again serve different research aims. For example, Point/Spot samples can reveal the spatial differentiation of food-related activities, Pinch samples are representative of all activities associated
|
{
"page_id": 327940,
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with a specific context, and Column samples can show change or variation or time. The sampling methods and types of samples used for the recovery of microbotanical remains (namely, pollen, phytoliths, and starches) follows virtually the same practices as outline above, with only some minor differences. First, the required sample size is much smaller: ~50g (a couple of tablespoons) of sediment for each type of microfossil analysis. Secondly, artefacts, such as stone tools and ceramics, can also be sampled for microbotanicals. And third, control samples from unexcavated areas in and around the site should always be collected for analytical purposes. === Processing === There are several different techniques for the processing of sediment samples. The technique a paleoethnobotanist chooses depends entirely upon the type of plant macrobotanical remains they expect to recover. Dry Screening involves pouring sediment samples through a nest of sieves, usually ranging from 5–0.5 mm. This processing technique is often employed as a means of recovering desiccated plant remains, since the use of water can weaken or damage this type of macrofossil and even accelerate its decomposition. Wet Screening is most often used for waterlogged contexts. It follows the same basic principle as dry screening, expect water is gently sprayed onto the sediment once it has been pour into the nest of sieves in order to help it break up and pass down through the various mesh sizes. The Wash-Over technique was developed in the UK as an effective way of processing waterlogged samples. The sediment is poured into a bucket with water and gently agitated by hand. When the sediment has effectively broken up and the organic matter is suspended, all the contents from the bucket, expect for the heavy inorganic matter at the bottom, is carefully poured out onto a 300μ mesh. The bucket is
|
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then emptied and the organic matter carefully rinsed from the mesh back into the bucket. More water is added before the contents are again poured out through a nest of sieves. Flotation is the most common processing technique employed for the recovery of carbonized plant remains. It uses water as a mechanism for separating charred and organic material from the sediment matrix, by capitalizing on their buoyancy properties. When a sediment sample is slowly added to agitated water, the stones, sand, shells and other heavy material within the sediment sink to the bottom (heavy fraction or heavy residue), while the charred and organic material, which is less dense, float to the surface (light fraction or flot). This floating material can either be scooped off or spilled over into a fine-mesh sieve (usually ~300 μm). Both the heavy and light fractions are then left to dry before being examined for archaeological remains. Plant macrofossils are mostly contained within the light fraction, though some denser specimens, such as pulses or mineralized grape endosperms, are also sometimes found in the heavy fraction. Thus, each fraction must be sorted to extract all plant material. A microscope is used in order to aid the sorting of the light fractions, while heavy fractions are sorted with the naked eye. Flotation can be undertaken manually with buckets or by machine-assistance, which circulates the water through a series of tanks by means of a pump. Small-scale, manual flotation can also be used in the laboratory on waterlogged samples. Microbotanical remains (namely, pollen, phytoliths and starches) require completely different processing procedures in order to extract specimens from the sediment matrix. These procedures can be quite expensive, as they involve various chemical solutions, and are always carried out in the laboratory. == Analysis == Analysis is the key step in
|
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paleoethnobotanical studies that makes the interpretation of ancient plant remains possible. The quality of identifications and the use of different quantification methods are essential factors that influence the depth and breadth of interpretative results. === Identification === Plant macrofossils are analyzed under a low-powered stereomicroscope. The morphological features of different specimens, such as size, shape and surface decoration, are compared with images of modern plant material in identification literature, such as seed atlases, as well as real examples of modern plant material from reference collections, in order to make identifications. Based on the type of macrofossils and their level of preservation, identifications are made to various taxonomic levels, mostly family, genus and species. These taxonomic levels reflect varying degrees of identification specificity: families comprise big groups of similar type plants; genera make up smaller groups of more closely related plants within each family, and species consist of the different individual plants within each genus. Poor preservation, however, may require the creation of broader identification categories, such as ‘nutshell’ or ‘cereal grain’, while extremely good preservation and/or the application of analytical technology, such as Scanning Electron Microscopy (SEM) or Morphometric Analysis, may allow even more precise identification down to subspecies or variety level Desiccated and waterlogged macrofossils often have a very similar appearance with modern plant material, since their modes of preservation do not directly affect the remains. As a result, fragile seed features, such as anthers or wings, and occasionally even color, can be preserved, allowing for very precise identifications of this material. The high temperatures involved in the carbonization of plant remains, however, can sometimes cause the damage to or loss of plant macrofossil features. The analysis of charred plant material, therefore, often includes several family- or genus-level identifications, as well as some specimen categories. Mineralized plant macrofossils can
|
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range in preservation from detailed copies to rough casts depending on depositional conditions and the kind of replacing mineral. This type of macrofossil can easily be mistaken for stones by the untrained eye. Microbotanical remains follow the same identification principles, but require a high-powered (greater magnification) microscope with transmitted or polarized lighting. Starch and phytolith identifications are also subject to limitations, in terms of taxonomical specificity, based on the state of current reference material for comparison and considerable overlap in specimen morphologies. === Quantification === After identification, paleoethnobotanists provide absolute counts for all plant macrofossils recovered in each individual sample. These counts constitute the raw analytical data and serve as the basis for any further quantitative methods that may be applied. Initially, paleoethnobotanical studies mostly involved a qualitative assessment of the plant remains at an archaeological site (presence and absence), but the application of simple statistical methods (non-multivariate) followed shortly thereafter. The use of more complex statistics (multivariate), however, is a more recent development. In general, simple statistics allow for observations concerning specimen values across space and over time, while more complex statistics facilitate the recognition of patterning within an assemblage, as well as the presentation of large datasets. The application of different statistical techniques depends on the quantity of material available. Complex statistics require the recovery of a large number of specimens (usually around 150 from each sample involved in this type of quantitative analysis), whereas simple statistics can be applied regardless of the amount of recovered specimens – though obviously, the more specimens, the more effective the results. The quantification of microbotanical remains differs slightly from that of macrobotanical remains, mostly due to the high numbers of microbotanical specimens that are usually present in samples. As a result, relative/percentage occurrence sums are usually employed in the quantification of
|
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microbotanical remains instead of absolute taxa counts. == Research results == The work done in Paleoethnobotany is constantly furthering over understanding of ancient plant exploitation practices. The results are disseminated in digital archives, archaeological excavation reports and at academic conferences, as well as in books and journals related to archaeology, anthropology, plant history, paleoecology, and social sciences. In addition to the use of plants as food, such as paleodiet, subsistence strategies and agriculture, Paleoethnobotany has illuminated many other ancient uses for plants (some examples provided below, though there are many more): Production of bread/pastry in the widest sense Production of beverages Extraction of oils and dyes Agricultural regimes (irrigation, manuring, and sowing) Economic practices (production, storage, and trade) Building materials Fuel Symbolic use in ritual activities == See also == == References == == Bibliography == == External links == International Associations Association of Environmental Archaeology (AEA) International Work Group for Palaeoethnobotany (IWGP) Journals Vegetation History and Archaeobotany, exclusively publishing archaeobotanical/palaeoethnobotanical research, official publishing organ of the IWGP Archaeological and Anthropological Sciences Environmental Archaeology Interdisciplinaria Archaeologica (IANSA) Various knowledge resources ArchBotLit, Kiel University Digital Plant Atlas, Groningen University Integrated Archaeobotanical Research Project (IAR), originally hosted at the University of Sheffield Terry B. Ball, "Phytolith Literature Review" Steve Archer, "About Phytoliths" Alwynne B. Beaudoin, "The Dung File"
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The Gesellschaft zur Erhaltung alter und gefährdeter Haustierrassen or GEH is a German national association for the conservation of historic and endangered domestic animal breeds. == History == The GEH was founded on 5 December 1981 in the Rottal, in Lower Bavaria in southern Germany. It has about 2100 members. Since it was founded, no domestic livestock breed has become extinct in Germany. == Activities == The GEH co-operates with other national and international organisations for the conservation of biodiversity. It publishes an annual Rote Liste or red list of endangered breeds of livestock, which attributes one of four categories of conservation risk to domestic breeds of cattle, dogs, goats, horses, pigs, rabbits and sheep, of chickens, ducks, geese and turkeys, and of bees; listing of domestic pigeon breeds is in preparation. Some breeds from outside Germany are listed separately. The four levels of risk are: I: extrem gefährdet, "extremely endangered" II: stark gefährdet, "seriously endangered" III: gefährdet, "endangered" Vorwarnstufe, "alert" The risk level is calculated using a formula that takes into account five criteria: the number of breeding animals or breeding females; the percentage of pure-bred matings; the five-year trend in breed numbers; the number of breeders or herds; and the interval between generations of the animal. The GEH also publishes, in conjunction with the Bund Deutscher Rassegeflügelzüchter, the German national association of poultry breeders, a separate list of the historic poultry breeds and colour varieties that were raised in Germany before 1930. The same levels of conservation risk are assigned as in the main red list. == Endangered breed of the year == Since 1984 the GEH has each year named one or more animal breeds as "endangered breed of the year". To date, these have been: 1984 (1984): Kärntner Brillenschaf or Jezersko–Solčava (sheep) 1986 (1986): Murnau-Werdenfelser (cattle)
|
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"page_id": 43581700,
"source": null,
"title": "Gesellschaft zur Erhaltung alter und gefährdeter Haustierrassen"
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1987 (1987): Schwäbisch Hällisches (pig) 1988 (1988): Schleswig Coldblood (horse) 1989 (1989): Waldschaf (sheep) 1990 (1990): Angeln Saddleback (pig) 1991 (1991): Rhönschaf (sheep) 1992 (1992): Hinterwälder (cattle) 1993 (1993): Thüringer Wald Ziege (goat) 1994 (1994): Westphalian (chicken) 1994 (1994): Diepholzer Gans (goose) 1994 (1994): Pomeranian duck 1995 (1995): Bentheim Black Pied (pig) 1996 (1996): Schleswig Coldblood (horse) 1997 (1997): Rotes Höhenvieh (cattle) 1998 (1998): Weiße gehörnte Heidschnucke (sheep) 1998 (1998): Altdeutscher Hütehund (dog) 1999 (1999): Mangalica (pig) 2000 (2000): Rottaler (horse) 2001 (2001): Bayerische Landgans (goose) 2001 (2001): Bergischer Kräher (chicken) 2001 (2001): Bergische Schlotterkamm (chicken) 2001 (2001): Krüper (chicken) 2002 (2002): Angeln (cattle), old breeding goals 2003 (2003): Großspitz and Mittelspitz (dog) 2003 (2003): Deutscher Pinscher (dog) 2004 (2004): Leutstettener (horse) 2004 (2004): European Dark Bee 2005 (2005): Bentheimer Landschaf (sheep) 2006 (2006): Deutsches Sattelschwein (pig) 2007 (2007): Murnau-Werdenfelser (cattle) 2008 (2008): Bronzepute (turkey) 2009 (2009): Alpines Steinschaf (sheep) 2010 (2010): Meißner Widder (rabbit) 2011 (2011): Limpurger (cattle) 2012 (2012): Deutscher Sperber (chicken) 2013 (2013): Leineschaf (sheep), original type 2014 (2014): Dülmener (horse) 2015 (2015): Deutsche Karakul (sheep) 2016 (2016): Original Braunvieh (cattle) 2016 (2016): Glan cattle (cattle) 2016 (2016): Deutsches Schwarzbuntes Niederungsrind (German Black Pied, cattle) 2017 (2017): Deutsche Pekingente, German Pekin (duck) 2017 (2017): Orpington Duck 2017 (2017): Warzenente (duck) 2018 (2018): Altwürttemberger (horse) 2019 (2019): Mangalica (pig) 2020 (2020): Pustertaler Sprinzen and Old German herding dogs == Note == == References ==
|
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"page_id": 43581700,
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Ceruminous glands are specialized sweat glands located subcutaneously in the external auditory canal, in the outer third. Ceruminous glands are simple, coiled, tubular glands made up of an inner secretory layer of cells and an outer myoepithelial layer of cells. They are classed as apocrine glands. The glands drain into larger ducts, which then drain into the guard hairs that reside in the external auditory canal. Here they produce cerumen, or earwax, by mixing their secretion with sebum and dead epidermal cells. Cerumen keeps the eardrum pliable, lubricates and cleans the external auditory canal, waterproofs the canal, kills bacteria, and serves as a barrier to trap foreign particles (dust, fungal spores, etc.) by coating the guard hairs of the ear, making them sticky. These glands are capable of developing both benign and malignant tumors. The benign tumors include ceruminous adenoma, ceruminous pleomorphic adenoma, and ceruminous syringocystadenoma papilliferum. The malignant tumors include ceruminous adenocarcinoma, adenoid cystic carcinoma, and mucoepidermoid carcinoma. == See also == List of specialized glands within the human integumentary system List of distinct cell types in the adult human body == References == == External links == Anatomy Atlases - Ceruminous Gland
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"page_id": 11403524,
"source": null,
"title": "Ceruminous gland"
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The quinhydrone electrode may be used to measure the hydrogen ion concentration (pH) of a solution containing an acidic substance. == Principles and operation == Quinones form a quinhydrone cocrystal by formation of hydrogen bonding between ρ-quinone and ρ-hydroquinone. An equimolar mixture of ρ-quinones and ρ-hydroquinone in contact with an inert metallic electrode, such as antimony, forms what is known as a quinhydrone electrode. Such devices can be used to measure the pH of solutions. Quinhydrone electrodes provide fast response times and high accuracy. However, it can only measure pH in the range of 1 to 9 and the solution must not contain a strong oxidizing or reducing agent. A platinum wire electrode is immersed in a saturated aqueous solution of quinhydrone, in which there is the following equilibrium C6H6O2 ⇌ C6H4O2 + 2H+ +2e−. The potential difference between the platinum electrode and a reference electrode is dependent on the activity, a H + {\displaystyle a_{H^{+}}} , of hydrogen ions in the solution. E = E 0 + R T 2 F ln a H + {\displaystyle E=E^{0}+{\frac {RT}{2F}}\ln a_{H^{+}}} (Nernst equation) == Limitations == The quinhydrone electrode provides an alternative to the most commonly used glass electrode. however, it is not reliable above pH 8 (at 298 K) and cannot be used with solutions that contain a strong oxidizing or reducing agent. == References ==
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{
"page_id": 9765126,
"source": null,
"title": "Quinhydrone electrode"
}
|
In theoretical physics, the problem of time is a conceptual conflict between quantum mechanics and general relativity. Quantum mechanics regards the flow of time as universal and absolute, whereas general relativity regards the flow of time as malleable and relative. This problem raises the question of what time really is in a physical sense and whether it is truly a real, distinct phenomenon. It also involves the related question of why time seems to flow in a single direction, despite the fact that no known physical laws at the microscopic level seem to require a single direction. == Time in quantum mechanics == In classical mechanics, a special status is assigned to time in the sense that it is treated as a classical background parameter, external to the system itself. This special role is seen in the standard Copenhagen interpretation of quantum mechanics: all measurements of observables are made at certain instants of time and probabilities are only assigned to such measurements. Furthermore, the Hilbert space used in quantum theory relies on a complete set of observables which commute at a specific time.: 759 == Time in general relativity == In general relativity time is no longer a unique background parameter, but a general coordinate. The field equations of general relativity are not parameterized by time but formulated in terms of spacetime. Many of the issues related to the problem of time exist within general relativity. At the cosmic scale, general relativity shows a closed universe with no external time. These two very different roles of time are incompatible. == Impact on quantum gravity == Quantum gravity describes theories that attempt to reconcile or unify quantum mechanics and general relativity, the current theory of gravity. The problem of time is central to these theoretical attempts. It remains unclear how time
|
{
"page_id": 42598658,
"source": null,
"title": "Problem of time"
}
|
is related to quantum probability, whether time is fundamental or a consequence of processes, and whether time is approximate, among other issues. Different theories try different answers to the questions but no clear solution has emerged. == The frozen formalism problem == The most commonly discussed aspect of the problem of time is the frozen formalism problem. The non-relativistic equation of quantum mechanics includes time evolution: i ℏ ∂ ∂ t ψ ( t ) = H ψ ( t ) , {\displaystyle i\hbar {\frac {\partial }{\partial t}}\psi (t)=H\psi (t),} where H {\displaystyle H} is an energy operator characterizing the system and the wave function ψ ( t ) {\displaystyle \psi (t)} over space evolves in time, t. In general relativity the energy operator becomes a constraint in the Wheeler–DeWitt equation: H ^ ( x ) | ψ ⟩ = 0 , {\displaystyle {\hat {H}}(x)|\psi \rangle =0,} where the operator varies throughout space, but the wavefunction here, called the wavefunction of the universe, is constant. Consequently this cosmic universal wavefunction is frozen and does not evolve. Somehow, at a smaller scale, the laws of physics, including a concept of time, apply within the universe while the cosmic level is static.: 762 == Proposed solutions to the problem of time == Work started by Don Page and William Wootters suggests that the universe appears to evolve for observers on the inside because of energy entanglement between an evolving system and a clock system, both within the universe. In this way the overall system can remain timeless while parts experience time via entanglement. The issue remains an open question closely related to attempted theories of quantum gravity. In other words, time is an entanglement phenomenon, which places all equal clock readings (of correctly prepared clocks – or any objects usable as clocks)
|
{
"page_id": 42598658,
"source": null,
"title": "Problem of time"
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|
into the same history. In 2013, at the Istituto Nazionale di Ricerca Metrologica (INRIM) in Turin, Italy, Ekaterina Moreva, together with Giorgio Brida, Marco Gramegna, Vittorio Giovannetti, Lorenzo Maccone, and Marco Genovese performed the first experimental test of Page and Wootters' ideas. They confirmed for photons that time is an emergent phenomenon for internal observers of a quantum system but is absent for external observers, which is consistent with the predictions of the Wheeler–DeWitt equation. Consistent discretizations approach developed by Jorge Pullin and Rodolfo Gambini have no constraints. These are lattice approximation techniques for quantum gravity. In the canonical approach, if one discretizes the constraints and equations of motion, the resulting discrete equations are inconsistent: they cannot be solved simultaneously. To address this problem, one uses a technique based on discretizing the action of the theory and working with the discrete equations of motion. These are automatically guaranteed to be consistent. Most of the hard conceptual questions of quantum gravity are related to the presence of constraints in the theory. Consistent discretized theories are free of these conceptual problems and can be straightforwardly quantized, providing a solution to the problem of time. It is a bit more subtle than this. Although without constraints and having "general evolution", the latter is only in terms of a discrete parameter that isn't physically accessible. The way out is addressed in a way similar to the Page–Wootters approach. The idea is to pick one of the physical variables to be a clock and ask relational questions. These ideas, where the clock is also quantum mechanical, have actually led to a new interpretation of quantum mechanics — the Montevideo interpretation of quantum mechanics. This new interpretation solves the problems of the use of environmental decoherence as a solution to the problem of measurement in quantum
|
{
"page_id": 42598658,
"source": null,
"title": "Problem of time"
}
|
mechanics by invoking fundamental limitations, due to the quantum mechanical nature of clocks, in the process of measurement. These limitations are very natural in the context of generally covariant theories as quantum gravity where the clock must be taken as one of the degrees of freedom of the system itself. They have also put forward this fundamental decoherence as a way to resolve the black hole information paradox. In certain circumstances, a matter field is used to de-parametrize the theory and introduce a physical Hamiltonian. This generates physical time evolution, not a constraint. Reduced phase-space quantization constraints are solved first and then quantized. This approach was considered for some time to be impossible, as it seems to require first finding the general solution to Einstein's equations. However, with the use of ideas involved in Dittrich's approximation scheme (built on ideas of Carlo Rovelli) a way to explicitly implement, at least in principle, a reduced phase-space quantization was made viable. Avshalom Elitzur and Shahar Dolev argue that quantum-mechanical experiments such as the "quantum liar" provide evidence of inconsistent histories, and that spacetime itself may therefore be subject to change affecting entire histories. Elitzur and Dolev also believe that an objective passage of time and relativity can be reconciled and that it would resolve many of the issues with the block universe and the conflict between relativity and quantum mechanics. One solution to the problem of time proposed by Lee Smolin is that there exists a "thick present" of events, in which two events in the present can be causally related to each other, but in contrast to the block-universe view of time in which all time exists eternally. Marina Cortês and Lee Smolin argue that certain classes of discrete dynamical systems demonstrate time asymmetry and irreversibility, which is consistent with an
|
{
"page_id": 42598658,
"source": null,
"title": "Problem of time"
}
|
objective passage of time. == Weyl time in scale-invariant quantum gravity == Motivated by the Immirzi ambiguity in loop quantum gravity and the near-conformal invariance of the standard model of elementary particles, Charles Wang and co-workers have argued that the problem of time may be related to an underlying scale invariance of gravity–matter systems. Scale invariance has also been proposed to resolve the hierarchy problem of fundamental couplings. As a global continuous symmetry, scale invariance generates a conserved Weyl current according to Noether’s theorem. In scale-invariant cosmological models, this Weyl current naturally gives rise to a harmonic time. In the context of loop quantum gravity, Charles Wang et al. suggest that scale invariance may lead to the existence of a quantized time. == Thermal time hypothesis == The thermal time hypothesis is a possible solution to the problem of time in classical and quantum theory as has been put forward by Carlo Rovelli and Alain Connes. Physical time flow is modeled as a fundamental property of the theory, a macroscopic feature of thermodynamical origin. == See also == Hořava–Lifshitz gravity De Donder–Weyl theory == References == == Further reading == The Order of Time by Carlo Rovelli Time Reborn by Lee Smolin The Singular Universe and the Reality of Time by Lee Smolin and Roberto Mangabeira Unger
|
{
"page_id": 42598658,
"source": null,
"title": "Problem of time"
}
|
The molecular formula C28H48O2 (molar mass: 416.68 g/mol, exact mass: 416.3654 u) may refer to: β-Tocopherol γ-Tocopherol
|
{
"page_id": 37749002,
"source": null,
"title": "C28H48O2"
}
|
The Stuart–Landau equation describes the behavior of a nonlinear oscillating system near the Hopf bifurcation, named after John Trevor Stuart and Lev Landau. In 1944, Landau proposed an equation for the evolution of the magnitude of the disturbance, which is now called as the Landau equation, to explain the transition to turbulence based on a phenomenological argument and an attempt to derive this equation from hydrodynamic equations was done by Stuart for plane Poiseuille flow in 1958. The formal derivation to derive the Landau equation was given by Stuart, Watson and Palm in 1960. The perturbation in the vicinity of bifurcation is governed by the following equation d A d t = σ A − l 2 A | A | 2 . {\displaystyle {\frac {dA}{dt}}=\sigma A-{\frac {l}{2}}A|A|^{2}.} where A = | A | e i ϕ {\displaystyle A=|A|e^{i\phi }} is a complex quantity describing the disturbance, σ = σ r + i σ i {\displaystyle \sigma =\sigma _{r}+i\sigma _{i}} is the complex growth rate, l = l r + i l i {\displaystyle l=l_{r}+il_{i}} is a complex number and l r {\displaystyle l_{r}} is the Landau constant. The evolution of the actual disturbance is given by the real part of A ( t ) {\displaystyle A(t)} i.e., by | A | cos ϕ {\displaystyle |A|\cos \phi } . Here the real part of the growth rate is taken to be positive, i.e., σ r > 0 {\displaystyle \sigma _{r}>0} because otherwise the system is stable in the linear sense, that is to say, for infinitesimal disturbances ( | A | {\displaystyle |A|} is a small number), the nonlinear term in the above equation is negligible in comparison to the other two terms in which case the amplitude grows in time only if σ r > 0 {\displaystyle \sigma
|
{
"page_id": 57409796,
"source": null,
"title": "Stuart–Landau equation"
}
|
_{r}>0} . The Landau constant is also taken to be positive, l r > 0 {\displaystyle l_{r}>0} because otherwise the amplitude will grow indefinitely (see below equations and the general solution in the next section). The Landau equation is the equation for the magnitude of the disturbance, d | A | 2 d t = 2 σ r | A | 2 − l r | A | 4 , {\displaystyle {\frac {d|A|^{2}}{dt}}=2\sigma _{r}|A|^{2}-l_{r}|A|^{4},} which can also be re-written as d | A | d t = σ r | A | − l r 2 | A | 3 . {\displaystyle {\frac {d|A|}{dt}}=\sigma _{r}|A|-{\frac {l_{r}}{2}}|A|^{3}.} Similarly, the equation for the phase is given by d ϕ d t = σ i − l i 2 | A | 2 . {\displaystyle {\frac {d\phi }{dt}}=\sigma _{i}-{\frac {l_{i}}{2}}|A|^{2}.} For non-homogeneous systems, i.e., when A {\displaystyle A} depends on spatial coordinates, see Ginzburg–Landau equation. Due to the universality of the equation, the equation finds its application in many fields such as hydrodynamic stability, Belousov–Zhabotinsky reaction, etc. == General solution == The Landau equation is linear when it is written for the dependent variable | A | − 2 {\displaystyle |A|^{-2}} , d | A | − 2 d t + 2 σ r | A | − 2 = l r . {\displaystyle {\frac {d|A|^{-2}}{dt}}+2\sigma _{r}|A|^{-2}=l_{r}.} The general solution for σ r ≠ 0 {\displaystyle \sigma _{r}\neq 0} of the above equation is | A ( t ) | − 2 = l r 2 σ r + ( | A ( 0 ) | − 2 − l r 2 σ r ) e − 2 σ r t . {\displaystyle |A(t)|^{-2}={\frac {l_{r}}{2\sigma _{r}}}+\left(|A(0)|^{-2}-{\frac {l_{r}}{2\sigma _{r}}}\right)e^{-2\sigma _{r}t}.} As t → ∞ {\displaystyle t\rightarrow \infty } , the magnitude of the disturbance
|
{
"page_id": 57409796,
"source": null,
"title": "Stuart–Landau equation"
}
|
| A | {\displaystyle |A|} approaches a constant value that is independent of its initial value, i.e., | A | m a x → ( 2 σ r / l r ) 1 / 2 {\displaystyle |A|_{\mathrm {max} }\rightarrow (2\sigma _{r}/l_{r})^{1/2}} when t ≫ 1 / σ r {\displaystyle t\gg 1/\sigma _{r}} . The above solution implies that | A | {\displaystyle |A|} does not have a real solution if l r < 0 {\displaystyle l_{r}<0} and σ r > 0 {\displaystyle \sigma _{r}>0} . The associated solution for the phase function ϕ ( t ) {\displaystyle \phi (t)} is given by ϕ ( t ) − ϕ ( 0 ) = σ i t − l i 2 l r ln [ 1 + | A ( 0 ) | 2 l r 2 σ r ( e 2 σ r t − 1 ) ] . {\displaystyle \phi (t)-\phi (0)=\sigma _{i}t-{\frac {l_{i}}{2l_{r}}}\ln \left[1+{\frac {|A(0)|^{2}l_{r}}{2\sigma _{r}}}(e^{2\sigma _{r}t}-1)\right].} As t ≫ 1 / σ r {\displaystyle t\gg 1/\sigma _{r}} , the phase varies linearly with time, ϕ ∼ ( σ i / σ r − l i / l r ) σ r t . {\displaystyle \phi \sim (\sigma _{i}/\sigma _{r}-l_{i}/l_{r})\sigma _{r}t.} It is instructive to consider a hydrodynamic stability case where it is found that, according to the linear stability analysis, the flow is stable when R e ≤ R e c r {\displaystyle Re\leq Re_{\mathrm {cr} }} and unstable otherwise, where R e {\displaystyle Re} is the Reynolds number and the R e c r {\displaystyle Re_{\mathrm {cr} }} is the critical Reynolds number; a familiar example that is applicable here is the critical Reynolds number, R e c r ≈ 50 {\displaystyle Re_{\mathrm {cr} }\approx 50} , corresponding to the transition to Kármán vortex street in
|
{
"page_id": 57409796,
"source": null,
"title": "Stuart–Landau equation"
}
|
the problem of flow past a cylinder. The growth rate σ r {\displaystyle \sigma _{r}} is negative when R e < R e c r {\displaystyle Re<Re_{\mathrm {cr} }} and is positive when R e > R e c r {\displaystyle Re>Re_{\mathrm {cr} }} and therefore in the neighbourhood R e → R e c r {\displaystyle Re\rightarrow Re_{\mathrm {cr} }} , it may written as σ r = const . × ( R e − R e c r ) {\displaystyle \sigma _{r}={\text{const}}.\times (Re-Re_{\mathrm {cr} })} wherein the constant is positive. Thus, the limiting amplitude is given by | A | m a x ∝ R e − R e c r . {\displaystyle |A|_{\mathrm {max} }\propto {\sqrt {Re-Re_{\mathrm {cr} }}}.} == Negative Landau constant == When the Landau constant is negative, l r < 0 {\displaystyle l_{r}<0} , we must include a negative term of higher order to arrest the unbounded increase of the perturbation. In this case, the Landau equation becomes d | A | 2 d t = 2 σ r | A | 2 − l r | A | 4 − β r | A | 6 , β r > 0. {\displaystyle {\frac {d|A|^{2}}{dt}}=2\sigma _{r}|A|^{2}-l_{r}|A|^{4}-\beta _{r}|A|^{6},\quad \beta _{r}>0.} The limiting amplitude then becomes | A | m a x → | l r | 2 β r ± l r 2 4 β r 2 + 2 | l r | σ r β r , as t ≫ 1 / σ r {\displaystyle |A|_{\mathrm {max} }\rightarrow {\frac {|l_{r}|}{2\beta _{r}}}\pm {\sqrt {{\frac {l_{r}^{2}}{4\beta _{r}^{2}}}+{\frac {2|l_{r}|\sigma _{r}}{\beta _{r}}}}},\quad {\text{as}}\quad t\gg 1/\sigma _{r}} where the plus sign corresponds to the stable branch and the minus sign to the unstable branch. There exists a value of a critical value R e c r ′ {\displaystyle Re_{\mathrm
|
{
"page_id": 57409796,
"source": null,
"title": "Stuart–Landau equation"
}
|
{cr} }'} where the above two roots are equal ( σ r = − | l r | / 8 β r {\displaystyle \sigma _{r}=-|l_{r}|/8\beta _{r}} ) such that R e c r ′ < R e c r {\displaystyle Re_{\mathrm {cr} }'<Re_{\mathrm {cr} }} , indicating that the flow in the region R e c r ′ < R e < R e c r {\displaystyle Re_{\mathrm {cr} }'<Re<Re_{\mathrm {cr} }} is metastable, that is to say, in the metastable region, the flow is stable to infinitesimal perturbations, but not to finite amplitude perturbations. == See also == Landau's phase transition theory Ginzburg–Landau theory == References ==
|
{
"page_id": 57409796,
"source": null,
"title": "Stuart–Landau equation"
}
|
The Hosoya index, also known as the Z index, of a graph is the total number of matchings in it. The Hosoya index is always at least one, because the empty set of edges is counted as a matching for this purpose. Equivalently, the Hosoya index is the number of non-empty matchings plus one. The index is named after Haruo Hosoya. It is used as a topological index in chemical graph theory. Complete graphs have the largest Hosoya index for any given number of vertices; their Hosoya indices are the telephone numbers. == History == This graph invariant was introduced by Haruo Hosoya in 1971. It is often used in chemoinformatics for investigations of organic compounds. In his article, "The Topological Index Z Before and After 1971," on the history of the notion and the associated inside stories, Hosoya writes that he introduced the Z index to report a good correlation of the boiling points of alkane isomers and their Z indices, basing on his unpublished 1957 work carried out while he was an undergraduate student at the University of Tokyo. == Example == A linear alkane, for the purposes of the Hosoya index, may be represented as a path graph without any branching. A path with one vertex and no edges (corresponding to the methane molecule) has one (empty) matching, so its Hosoya index is one; a path with one edge (ethane) has two matchings (one with zero edges and one with one edges), so its Hosoya index is two. Propane (a length-two path) has three matchings: either of its edges, or the empty matching. n-butane (a length-three path) has five matchings, distinguishing it from isobutane which has four. More generally, a matching in a path with k {\displaystyle k} edges either forms a matching in the first k
|
{
"page_id": 14221581,
"source": null,
"title": "Hosoya index"
}
|
− 1 {\displaystyle k-1} edges, or it forms a matching in the first k − 2 {\displaystyle k-2} edges together with the final edge of the path. This case analysis shows that the Hosoya indices of linear alkanes obey the recurrence governing the Fibonacci numbers, and because they also have the same base case they must equal the Fibonacci numbers. The structure of the matchings in these graphs may be visualized using a Fibonacci cube. The largest possible value of the Hosoya index, on a graph with n {\displaystyle n} vertices, is given by the complete graph K n {\displaystyle K_{n}} . The Hosoya indices for the complete graphs are the telephone numbers These numbers can be expressed by a summation formula involving factorials, as ∑ k = 0 ⌊ n / 2 ⌋ n ! 2 k ⋅ k ! ⋅ ( n − 2 k ) ! . {\displaystyle \sum _{k=0}^{\lfloor n/2\rfloor }{\frac {n!}{2^{k}\cdot k!\cdot \left(n-2k\right)!}}.} Every graph that is not complete has a smaller Hosoya index than this upper bound. == Algorithms == The Hosoya index is #P-complete to compute, even for planar graphs. However, it may be calculated by evaluating the matching polynomial mG at the argument 1. Based on this evaluation, the calculation of the Hosoya index is fixed-parameter tractable for graphs of bounded treewidth and polynomial (with an exponent that depends linearly on the width) for graphs of bounded clique-width. The Hosoya index can be efficiently approximated to any desired constant approximation ratio using a fully-polynomial randomized approximation scheme. == Notes == == References == Roberto Todeschini, Viviana Consonni (2000) "Handbook of Molecular Descriptors", Wiley-VCH, ISBN 3-527-29913-0
|
{
"page_id": 14221581,
"source": null,
"title": "Hosoya index"
}
|
An ecosystem, short for ecological system, is defined as a collection of interacting organisms within a biophysical environment.: 458 Ecosystems are never static, and are continually subject to both stabilizing and destabilizing processes. Stabilizing processes allow ecosystems to adequately respond to destabilizing changes, or perturbations, in ecological conditions, or to recover from degradation induced by them: yet, if destabilizing processes become strong enough or fast enough to cross a critical threshold within that ecosystem, often described as an ecological 'tipping point', then an ecosystem collapse (sometimes also termed ecological collapse) occurs. Ecosystem collapse does not mean total disappearance of life from the area, but it does result in the loss of the original ecosystem's defining characteristics, typically including the ecosystem services it may have provided. Collapse of an ecosystem is effectively irreversible more often than not, and even if the reversal is possible, it tends to be slow and difficult. Ecosystems with low resilience may collapse even during a comparatively stable time, which then typically leads to their replacement with a more resilient system in the biosphere. However, even resilient ecosystems may disappear during the times of rapid environmental change, and study of the fossil record was able to identify how certain ecosystems went through a collapse, such as with the Carboniferous rainforest collapse or the collapse of Lake Baikal and Lake Hovsgol ecosystems during the Last Glacial Maximum. Today, the ongoing Holocene extinction is caused primarily by human impact on the environment, and the greatest biodiversity loss so far had been due to habitat degradation and fragmentation, which eventually destroys entire ecosystems if left unchecked. There have been multiple notable examples of such an ecosystem collapse in the recent past, such as the collapse of the Atlantic northwest cod fishery. More are likely to occur without a change in
|
{
"page_id": 58458383,
"source": null,
"title": "Ecosystem collapse"
}
|
course, since estimates show that 87% of oceans and 77% of the land surface have been altered by humanity, with 30% of global land area is degraded and a global decline in ecosystem resilience. Deforestation of the Amazon rainforest is the most dramatic example of a massive, continuous ecosystem and a biodiversity hotspot being under the immediate threat from habitat destruction through logging, and the less-visible, yet ever-growing and persistent threat from climate change. Biological conservation can help to preserve threatened species and threatened ecosystems alike. However, time is of the essence. Just as interventions to preserve a species have to occur before it falls below viable population limits, at which point an extinction debt occurs regardless of what comes after, efforts to protect ecosystems must occur in response to early warning signals, before the tipping point to a regime shift is crossed. Further, there is a substantial gap between the extent of scientific knowledge how extinctions occur, and the knowledge about how ecosystems collapse. While there have been efforts to create objective criteria used to determine when an ecosystem is at risk of collapsing, they are comparatively recent, and are not yet as comprehensive. While the IUCN Red List of threatened species has existed for decades, the IUCN Red List of Ecosystems has only been in development since 2008. == Definition == Ecosystem collapse has been defined as a "transformation of identity, loss of defining features, and replacement by a novel ecosystem", and involves the loss of "defining biotic or abiotic features", including the ability to sustain the species which used to be associated with that ecosystem. According to another definition, it is "a change from a baseline state beyond the point where an ecosystem has lost key defining features and functions, and is characterised by declining spatial extent,
|
{
"page_id": 58458383,
"source": null,
"title": "Ecosystem collapse"
}
|
increased environmental degradation, decreases in, or loss of, key species, disruption of biotic processes, and ultimately loss of ecosystem services and functions". Ecosystem collapse has also been described as "an analogue of species extinction", and in many cases, it is irreversible, with a new ecosystem appearing instead, which may retain some characteristics of the previous ecosystem, yet has agreatly altered structure and function. There are exceptions where an ecosystem can be recovered past the point of a collapse, but by definition, will always be far more difficult to reverse than allowing a disturbed yet functioning ecosystem to recover, requiring active intervention and/or a prolonged period of time even if it can be reversed. == Drivers == While collapse events can occur naturally with disturbances to an ecosystem—through fires, landslides, flooding, severe weather events, disease, or species invasion—there has been a noticeable increase in human-caused disturbances over the past fifty years. The combination of environmental change and the presence of human activity is increasingly detrimental to ecosystems of all types, as our unrestricted actions often increase the risk of abrupt (and potentially irreversible) changes post-disturbance; when a system would otherwise have been able to recover. Some behaviors that induce transformation are: human intervention in the balance of local diversity (through introduction of new species or overexploitation), alterations in the chemical balance of environments through pollution, modifications of local climate or weather with anthropogenic climate change, and habitat destruction or fragmentation in terrestrial/marine systems. For instance, overgrazing was found to cause land degradation, specifically in Southern Europe, which is another driver of ecological collapse and natural landscape loss. Proper management of pastoral landscapes can mitigate risk of desertification. Despite the strong empirical evidence and highly visible collapse-inducing disturbances, anticipating collapse is a complex problem. The collapse can happen when the ecosystem's distribution
|
{
"page_id": 58458383,
"source": null,
"title": "Ecosystem collapse"
}
|
decreases below a minimal sustainable size, or when key biotic processes and features disappear due to environmental degradation or disruption of biotic interactions. These different pathways to collapse can be used as criteria for estimating the risk of ecosystem collapse. Although states of ecosystem collapse are often defined quantitatively, few studies adequately describe transitions from pristine or original state towards collapse. == Geological record == In another example, 2004 research demonstrated how during the Last Glacial Maximum (LGM), alternations in the environment and climate led to a collapse of Lake Baikal and Lake Hovsgol ecosystems, which then drove species evolution. The collapse of Hovsgol's ecosystem during the LGM brought forth a new ecosystem, with limited biodiversity in species and low levels of endemism, in Hovsgol during the Holocene. That research also shows how ecosystem collapse during LGM in Lake Hovsgol led to higher levels of diversity and higher levels of endemism as a byproduct of subsequent evolution. In the Carboniferous period, coal forests, great tropical wetlands, extended over much of Euramerica (Europe and America). This land supported towering lycopsids which fragmented and collapsed abruptly. The collapse of the rainforests during the Carboniferous has been attributed to multiple causes, including climate change and volcanism. Specifically, at this time climate became cooler and drier, conditions that are not favourable to the growth of rainforests and much of the biodiversity within them. The sudden collapse in the terrestrial environment made many large vascular plants, giant arthropods, and diverse amphibians to go extinct, allowing seed-bearing plants and amniotes to take over (but smaller relatives of the affected ones survived also). == Historic examples of collapsed ecosystems == The Rapa Nui subtropical broadleaf forests in Easter Island, formerly dominated by an endemic Palm, are considered collapsed due to the combined effects of overexplotaition, climate change
|
{
"page_id": 58458383,
"source": null,
"title": "Ecosystem collapse"
}
|
and introduced exotic rats. The Aral Sea was an endorheic lake between Kazakhstan and Uzbekistan. It was once considered one of the largest lakes in the world but has been shrinking since the 1960s after the rivers that fed it were diverted for large scale irrigation. By 1997, it had declined to 10% of its original size, splitting into much smaller hypersaline lakes, while dried areas have transformed into desert steppes. The regime shift in the northern Benguela upwelling ecosystem is considered an example of ecosystem collapse in open marine environments. Prior to the 1970s sardines were the dominant vertebrate consumers, but overfishing and two adverse climatic events (Benguela Niño in 1974 and 1984) lead to an impoverished ecosystem state with high biomass of jellyfish and pelagic goby. Another notable example is the collapse of the Grand Banks cod in the early 1990s, when overfishing reduced fish populations to 1% of their historical levels. == Currently Collapsing == Not currently considered collapsed, but well on the way if there is no intervention. Northerns Savannas of Australia, The Kimberley and the Cape York Peninsula. Both are considered some of the largest intact ecosystems, with the Kimberley containing 2,000 native plants and the Cape containing roughly 3,000. Both home hundreds of birds, mammals, reptiles, and insects alike. Due to fire-promoting weeds the landscape has changed from woodlands to grasslands over the years. Added pressures from climate change, over grazing, and forestry has started to make a significant decline. The Northern Mangroves in Australia continue to lose nutrients and landmass. Approximately 7,400 hectares (18,286 acres) of the mangroves were lost in the largest die back recorded between 2015-2016. The Great Barrier Reef recorded its first bleaching event in 1998, and the largest bleaching spread occurred in 2020. It is recorded that roughly 50%
|
{
"page_id": 58458383,
"source": null,
"title": "Ecosystem collapse"
}
|
of the coral has been lost, as of 2023. As the coral bleaches, it is not only dying, but the organisms that rely on it for survival are being impacted as well. It is assumed the Great Barrier Reef supports over 9,000 organisms. The continued decline of the Great Barrier Reef is due to many factors, the largest being Climate Change and pollution. World Heritage Site: Shark Bay is considered the most venerable according to the Climate Change Vulnerability Index. The ecosystem supports the community but decline due to global warming and climate change have heavily affected this. The sea grass is not sustainable with changing climates and that is the main source of habitat for the fish and marine life. Great Salt Lake of Utah is considered a keystone ecosystem and economic dependent factor for the state of Utah. It has lost over 73% of its water and 60% surface area since 1850. Unless drastic measures are taken, the lake is expected to completely dry up and cause irreparable damage that will impact the wellbeing of the wildlife, public health, environmental decline, and economic decline. == Contemporary risk == There are two tools commonly used together to assess risks to ecosystems and biodiversity: generic risk assessment protocols and stochastic simulation models. The most notable of the two tactics is risk assessment protocol, particularly because of the IUCN Red List of Ecosystems (RLE), which is widely applicable to many ecosystems even in data-poor circumstances. However, because using this tool is essentially comparing systems to a list of criteria, it is often limited in its ability to look at ecosystem decline holistically; and is thus often used in conjunction with simulation models that consider more aspects of decline such as ecosystem dynamics, future threats, and social-ecological relationships. The IUCN RLE is
|
{
"page_id": 58458383,
"source": null,
"title": "Ecosystem collapse"
}
|
a global standard that was developed to assess threats to various ecosystems on local, regional, national, and global scales, as well as to prompt conservation efforts in the face of the unparalleled decline of natural systems in the last decade. And though this effort is still in the earlier stages of implementation, the IUCN has a goal to assess the risk of collapse for all of the world's ecosystems by 2025. The concept of ecosystem collapse is used in the framework to establish categories of risk for ecosystems, with the category Collapsed used as the end-point of risk assessment. Other categories of threat (Vulnerable, Endangered and Critically Endangered) are defined in terms of the probability or risk of collapse. A paper by Bland et al. suggests four aspects for defining ecosystem collapse in risk assessments: qualitatively defining initial and collapsed states describing collapse and recovery transitions identifying and selecting indicators of collapse setting quantitative collapse thresholds. === Early detection and monitoring === Scientists can predict tipping points for ecosystem collapse. The most frequently used model for predicting food web collapse is called R50, which is a reliable measurement model for food web robustness. However, there are others: i.e. marine ecosystem assessments can use RAM Legacy Stock Assessment Database. In one example, 154 different marine fish species were studied to establish the relationship between pressures on fish populations such as overfishing and climate change, these populations; traits like growth rate, and the risk of ecosystem collapse. The measurement of "critical slowing down" (CSD) is one approach for developing early warning signals for a potential or likely onset of approaching collapse. It refers to increasingly slow recovery from perturbations. In 2020, one paper suggested that once a 'point of no return' is reached, breakdowns do not occur gradually but rapidly and that
|
{
"page_id": 58458383,
"source": null,
"title": "Ecosystem collapse"
}
|
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