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for application in foods or as part of surface decontamination protocols. == Meat biopreservation == In meat processing, biopreservation has been extensively studied in fermented meat products and ready to eat meat products. The use of native or artificially-introduced microbial population to improve animal health and productivity, and/or to reduce pathogenic organisms, has been termed a probiotic or competitive enhancement approach. Competitive enhancement strategies that have been developed include competitive exclusion, addition of a microbial supplement (probiotic) that improves gastrointestinal health, and adding a limiting, non-host digestible nutrient (prebiotic) that provides an existing (or introduced) commensal microbial population a competitive advantage in the gastrointestinal tract. Each of these approaches utilizes the activities of the native microbial ecosystem against pathogens by capitalizing on the natural microbial competition. Generally speaking, competitive enhancement strategies offer a natural 'green' method to reduce pathogens in the gut of food animals. == Seafood biopreservation == Fishery products are a source of wide variety of valuable nutrients such as proteins, vitamins, minerals, omega-3 fatty acids, taurine, etc. Fishery products, however, are also associated with human intoxication and infection. Approximately 10 to 20% of food-borne illnesses are attributed to fish consumption. Changing consumer demand has driven the appeal of traditional processes applied to seafood (e.g. salting, smoking and canning) lower compared to mild technologies involving lower salt content, lower cooking temperature and vacuum packing (VP)/modified atmosphere packing (MAP). These products, designed as lightly preserved fish products (LPFP), are usually produced from fresh seafood and further processing increases risk of cross contamination. These milder treatments are usually not sufficient to destroy microorganisms, and in some cases psychrotolerant pathogenic and spoilage bacteria can develop during the extended shelf-life of LPFP. Many of these products are also eaten raw, so minimizing the presence and preventing growth of microorganisms is essential for
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the food quality and safety. The microbial safety and stability of food are based on an application of preservative factors called hurdles. The delicate texture and flavor of seafood are very sensitive to the decontamination technologies such as cooking, and more recent mild technologies such as pulsed light, high pressure, ozone, and ultrasound. Chemical preservatives, which are not processes but ingredients, are out of favor with consumers due to natural preservatives demand. An alternative solution that is gaining more and more attention is biopreservation technology. In fish processing, biopreservation is achieved by adding antimicrobials or by increasing the acidity of the fish muscle. Most bacteria stop multiplying when the pH is less than 4.5. Traditionally, acidity has been increased by fermentation, marination or by directly adding acetic, citric or lactic acid to food products. Other preservatives include nitrites, sulphites, sorbates, benzoates and essential oils. The main reason for less documented studies for application of protective microorganisms, bacteriophages or bacteriocins on seafood products for biopreservation compared to dairy or meat products is probably that the early stages of biopreservation have occurred mainly in fermented foodstuffs that are not so developed among seafood products. The selection of potential protective bacteria in seafood products is challenging due to the fact that they need adaptation to the seafood matrix (poor in sugar and their metabolic activities should not change the initial characteristics of the product, i.e. by acidification, and not induce spoilage that could lead to a sensory rejection. Among the microbiota identified in fresh or processed seafood, LAB remains the category that offers the highest potential for direct application as a bioprotective culture or for bacteriocin production. == Commercial applications and products == There has been successful implementation of various phage preparation around the globe. Various applications/delivery methods in food have been developed.
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Bacteriophages and their endolysins can be incorporated into food systems in several ways such as spraying, dipping or immobilization, singly or in combination with other hurdles. The phage preparation LMP-1O2 has been subsequently commercialized as "ListShield" Intralyx, Inc. It has been shown to be effective against 170 different strains of L. monocytogenes, reducing significantly (10 to 1000-fold) the Listeria contamination when sprayed onto ready-to-eat foods, without changing the food general composition, taste, odor or color. The Intralytix company has also commercialized phage-based antimicrobial preparations like SalmoFresh and SalmoLyse for controlling S. enterica. SalmoFresh is prepared with a cocktail of naturally occurring lytic bacteriophages that selectively and specifically kill Salmonella, including strains belonging to the most common/highly pathogenic serotypes Typhimurium, Enteritidis, Heidelberg, Newport, Hadar, Kentucky and Thompson. According to the manufacturer, SalmoFresh is specifically designed for treating foods that are at high risk for Salmonella contamination. In particular, red meat and poultry can be treated prior to grinding for significant reductions in Salmonella contamination. SalmoLyse is a reformulated phage cocktail derived from SalmoFresh in which two of the six phages in the original cocktail have been replaced. Additional bacteriophage preparations have been formulated and referenced to be used to reduce the microbial load of animals prior to slaughter and are commercially available from Omnilytics such as the BacWash product line against Salmonella Omnilytics. Another commercial application has been developed, Listex_ P100 by Micreos in the Netherlands and was granted generally recognized as safe (GRAS) status by the FDA and USDA for use in all food products. Another significant commercial bacteriophage application is ELICOSALI, a wide range of anti-Salmonella and "E. coli" phage cocktail, for treatment of agricultural products developed by Eliava Institute at Tbilisi, Republic of Georgia Eliava Institute. == Safety == Biopreservation judiciously exploits the antimicrobial potential of naturally occurring
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microorganisms in food and/or their metabolites with a long history of safe use. Bacteriocins, bacteriophages and bacteriophage-encoded enzymes fall in this theory. The long and traditional role of lactic acid bacteria on food and feed fermentations is the main factor related to the use of bacteriocins in biopreservation. LAB and their bacteriocins have been consumed unintentionally for ages, laying down a long history of safe use. Their antimicrobial spectrum of inhibition, bactericidal mode of action, relative tolerance to processing conditions (pH, NaCl, heat treatments) and the lack of toxicity towards eukaryotic cells enforces their role as biopreservatives in food. The evaluation of any new antimicrobial actives is done in meat by USDA which relies on the GRAS assessment by FDA among other suitability data. == References ==
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Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus). The parent nucleus transforms or "decays" into a daughter product, with a mass number that is reduced by four and an atomic number that is reduced by two. An alpha particle is identical to the nucleus of a helium-4 atom, which consists of two protons and two neutrons. It has a charge of +2 e and a mass of 4 Da. For example, uranium-238 decays to form thorium-234. While alpha particles have a charge +2 e, this is not usually shown because a nuclear equation describes a nuclear reaction without considering the electrons – a convention that does not imply that the nuclei necessarily occur in neutral atoms. Alpha decay typically occurs in the heaviest nuclides. Theoretically, it can occur only in nuclei somewhat heavier than nickel (element 28), where the overall binding energy per nucleon is no longer a maximum and the nuclides are therefore unstable toward spontaneous fission-type processes. In practice, this mode of decay has only been observed in nuclides considerably heavier than nickel, with the lightest known alpha emitter being the second lightest isotope of antimony, 104Sb. Exceptionally, however, beryllium-8 decays to two alpha particles. Alpha decay is by far the most common form of cluster decay, where the parent atom ejects a defined daughter collection of nucleons, leaving another defined product behind. It is the most common form because of the combined extremely high nuclear binding energy and relatively small mass of the alpha particle. Like other cluster decays, alpha decay is fundamentally a quantum tunneling process. Unlike beta decay, it is governed by the interplay between both the strong nuclear force and the electromagnetic force. Alpha particles have a typical kinetic energy of
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5 MeV (or ≈ 0.13% of their total energy, 110 TJ/kg) and have a speed of about 15,000,000 m/s, or 5% of the speed of light. There is surprisingly small variation around this energy, due to the strong dependence of the half-life of this process on the energy produced. Because of their relatively large mass, the electric charge of +2 e and relatively low velocity, alpha particles are very likely to interact with other atoms and lose their energy, and their forward motion can be stopped by a few centimeters of air. Approximately 99% of the helium produced on Earth is the result of the alpha decay of underground deposits of minerals containing uranium or thorium. The helium is brought to the surface as a by-product of natural gas production. == History == Alpha particles were first described in the investigations of radioactivity by Ernest Rutherford in 1899, and by 1907 they were identified as He2+ ions. By 1928, George Gamow had solved the theory of alpha decay via tunneling. The alpha particle is trapped inside the nucleus by an attractive nuclear potential well and a repulsive electromagnetic potential barrier. Classically, it is forbidden to escape, but according to the (then) newly discovered principles of quantum mechanics, it has a tiny (but non-zero) probability of "tunneling" through the barrier and appearing on the other side to escape the nucleus. Gamow solved a model potential for the nucleus and derived, from first principles, a relationship between the half-life of the decay, and the energy of the emission, which had been previously discovered empirically and was known as the Geiger–Nuttall law. == Mechanism == The nuclear force holding an atomic nucleus together is very strong, in general much stronger than the repulsive electromagnetic forces between the protons. However, the nuclear force is
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also short-range, dropping quickly in strength beyond about 3 femtometers, while the electromagnetic force has an unlimited range. The strength of the attractive nuclear force keeping a nucleus together is thus proportional to the number of the nucleons, but the total disruptive electromagnetic force of proton-proton repulsion trying to break the nucleus apart is roughly proportional to the square of its atomic number. A nucleus with 210 or more nucleons is so large that the strong nuclear force holding it together can just barely counterbalance the electromagnetic repulsion between the protons it contains. Alpha decay occurs in such nuclei as a means of increasing stability by reducing size. One curiosity is why alpha particles, helium nuclei, should be preferentially emitted as opposed to other particles like a single proton or neutron or other atomic nuclei. Part of the reason is the high binding energy of the alpha particle, which means that its mass is less than the sum of the masses of two free protons and two free neutrons. This increases the disintegration energy. Computing the total disintegration energy given by the equation E d i = ( m i − m f − m p ) c 2 , {\displaystyle E_{di}=(m_{\text{i}}-m_{\text{f}}-m_{\text{p}})c^{2},} where mi is the initial mass of the nucleus, mf is the mass of the nucleus after particle emission, and mp is the mass of the emitted (alpha-)particle, one finds that in certain cases it is positive and so alpha particle emission is possible, whereas other decay modes would require energy to be added. For example, performing the calculation for uranium-232 shows that alpha particle emission releases 5.4 MeV of energy, while a single proton emission would require 6.1 MeV. Most of the disintegration energy becomes the kinetic energy of the alpha particle, although to fulfill conservation of
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momentum, part of the energy goes to the recoil of the nucleus itself (see atomic recoil). However, since the mass numbers of most alpha-emitting radioisotopes exceed 210, far greater than the mass number of the alpha particle (4), the fraction of the energy going to the recoil of the nucleus is generally quite small, less than 2%. Nevertheless, the recoil energy (on the scale of keV) is still much larger than the strength of chemical bonds (on the scale of eV), so the daughter nuclide will break away from the chemical environment the parent was in. The energies and ratios of the alpha particles can be used to identify the radioactive parent via alpha spectrometry. These disintegration energies, however, are substantially smaller than the repulsive potential barrier created by the interplay between the strong nuclear and the electromagnetic force, which prevents the alpha particle from escaping. The energy needed to bring an alpha particle from infinity to a point near the nucleus just outside the range of the nuclear force's influence is generally in the range of about 25 MeV. An alpha particle within the nucleus can be thought of as being inside a potential barrier whose walls are 25 MeV above the potential at infinity. However, decay alpha particles only have energies of around 4 to 9 MeV above the potential at infinity, far less than the energy needed to overcome the barrier and escape. === Quantum tunneling === Quantum mechanics, however, allows the alpha particle to escape via quantum tunneling. The quantum tunneling theory of alpha decay, independently developed by George Gamow and by Ronald Wilfred Gurney and Edward Condon in 1928, was hailed as a very striking confirmation of quantum theory. Essentially, the alpha particle escapes from the nucleus not by acquiring enough energy to pass over
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the wall confining it, but by tunneling through the wall. Gurney and Condon made the following observation in their paper on it: It has hitherto been necessary to postulate some special arbitrary 'instability' of the nucleus, but in the following note, it is pointed out that disintegration is a natural consequence of the laws of quantum mechanics without any special hypothesis... Much has been written of the explosive violence with which the α-particle is hurled from its place in the nucleus. But from the process pictured above, one would rather say that the α-particle almost slips away unnoticed. The theory supposes that the alpha particle can be considered an independent particle within a nucleus, that is in constant motion but held within the nucleus by strong interaction. At each collision with the repulsive potential barrier of the electromagnetic force, there is a small non-zero probability that it will tunnel its way out. An alpha particle with a speed of 1.5×107 m/s within a nuclear diameter of approximately 10−14 m will collide with the barrier more than 1021 times per second. However, if the probability of escape at each collision is very small, the half-life of the radioisotope will be very long, since it is the time required for the total probability of escape to reach 50%. As an extreme example, the half-life of the isotope bismuth-209 is 2.01×1019 years. The isotopes in beta-decay stable isobars that are also stable with regards to double beta decay with mass number A = 5, A = 8, 143 ≤ A ≤ 155, 160 ≤ A ≤ 162, and A ≥ 165 are theorized to undergo alpha decay. All other mass numbers (isobars) have exactly one theoretically stable nuclide. Those with mass 5 decay to helium-4 and a proton or a neutron, and those
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with mass 8 decay to two helium-4 nuclei; their half-lives (helium-5, lithium-5, and beryllium-8) are very short, unlike the half-lives for all other such nuclides with A ≤ 209, which are very long. (Such nuclides with A ≤ 209 are primordial nuclides except 146Sm.) Working out the details of the theory leads to an equation relating the half-life of a radioisotope to the decay energy of its alpha particles, a theoretical derivation of the empirical Geiger–Nuttall law. == Uses == Americium-241, an alpha emitter, is used in smoke detectors. The alpha particles ionize air in an open ion chamber and a small current flows through the ionized air. Smoke particles from the fire that enter the chamber reduce the current, triggering the smoke detector's alarm. Radium-223 is also an alpha emitter. It is used in the treatment of skeletal metastases (cancers in the bones). Alpha decay can provide a safe power source for radioisotope thermoelectric generators used for space probes and were used for artificial heart pacemakers. Alpha decay is much more easily shielded against than other forms of radioactive decay. Static eliminators typically use polonium-210, an alpha emitter, to ionize the air, allowing the "static cling" to dissipate more rapidly. == Toxicity == Highly charged and heavy, alpha particles lose their several MeV of energy within a small volume of material, along with a very short mean free path. This increases the chance of double-strand breaks to the DNA in cases of internal contamination, when ingested, inhaled, injected or introduced through the skin. Otherwise, touching an alpha source is typically not harmful, as alpha particles are effectively shielded by a few centimeters of air, a piece of paper, or the thin layer of dead skin cells that make up the epidermis; however, many alpha sources are also accompanied by
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beta-emitting radio daughters, and both are often accompanied by gamma photon emission. Relative biological effectiveness (RBE) quantifies the ability of radiation to cause certain biological effects, notably either cancer or cell-death, for equivalent radiation exposure. Alpha radiation has a high linear energy transfer (LET) coefficient, which is about one ionization of a molecule/atom for every angstrom of travel by the alpha particle. The RBE has been set at the value of 20 for alpha radiation by various government regulations. The RBE is set at 10 for neutron irradiation, and at 1 for beta radiation and ionizing photons. However, the recoil of the parent nucleus (alpha recoil) gives it a significant amount of energy, which also causes ionization damage (see ionizing radiation). This energy is roughly the weight of the alpha (4 Da) divided by the weight of the parent (typically about 200 Da) times the total energy of the alpha. By some estimates, this might account for most of the internal radiation damage, as the recoil nucleus is part of an atom that is much larger than an alpha particle, and causes a very dense trail of ionization; the atom is typically a heavy metal, which preferentially collect on the chromosomes. In some studies, this has resulted in an RBE approaching 1,000 instead of the value used in governmental regulations. The largest natural contributor to public radiation dose is radon, a naturally occurring, radioactive gas found in soil and rock. If the gas is inhaled, some of the radon particles may attach to the inner lining of the lung. These particles continue to decay, emitting alpha particles, which can damage cells in the lung tissue. The death of Marie Curie at age 66 from aplastic anemia was probably caused by prolonged exposure to high doses of ionizing radiation, but it
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is not clear if this was due to alpha radiation or X-rays. Curie worked extensively with radium, which decays into radon, along with other radioactive materials that emit beta and gamma rays. However, Curie also worked with unshielded X-ray tubes during World War I, and analysis of her skeleton during a reburial showed a relatively low level of radioisotope burden. The Russian defector Alexander Litvinenko's 2006 murder by radiation poisoning is thought to have been carried out with polonium-210, an alpha emitter. == References == Alpha emitters by increasing energy (Appendix 1) == Notes == == External links == The LIVEChart of Nuclides - IAEA with filter on alpha decay Alpha decay with 3 animated examples showing the recoil of daughter == See also == Beta decay Gamma decay
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Thermoplasmatota is phylum of Archaea. It is among six other phyla validly published according to the Bacteriological Code. These Archaea can live in acidic environments and have also been found in the South China Sea and Mediterranean grassland soil. == Phylogeny == == See also == List of Archaea genera == References == == External links ==
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"page_id": 78513397,
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"title": "Thermoplasmatota"
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This is a list of selective estrogen receptor modulators (SERMs). == Approved == SERMs that have been approved for medical use include anordrin (+mifepristone (Zi Yun)), bazedoxifene (+conjugated estrogens (Duavee)), broparestrol (Acnestrol), clomifene (Clomid), cyclofenil (Sexovid), lasofoxifene (Fablyn), ormeloxifene (Centron, Novex, Novex-DS, Sevista), ospemifene (Osphena; deaminohydroxytoremifene), raloxifene (Evista), tamoxifen (Nolvadex), and toremifene (Fareston; 4-chlorotamoxifen). == Clinical trials == SERMs that are currently under development and in clinical trials include acolbifene, afimoxifene (4-hydroxytamoxifen; metabolite of tamoxifen), elacestrant, enclomifene ((E)-clomifene), endoxifen (4-hydroxy-N-desmethyltamoxifen; metabolite of tamoxifen), and zuclomifene ((Z)-clomifene). == Non-approved == SERMs that have not been approved for medical use include arzoxifene, brilanestrant, clomifenoxide (clomiphene N-oxide; metabolite of clomifene), droloxifene (3-hydroxytamoxifen), etacstil, fispemifene, GW-7604 (4-hydroxyetacstil; metabolite of etacstil), idoxifene (pyrrolidino-4-iodotamoxifen), levormeloxifene ((L)-ormeloxifene), miproxifene, nafoxidine, nitromifene (CI-628), NNC 45-0095, panomifene, pipendoxifene (ERA-923), trioxifene, and zindoxifene (D-16726). Sivifene (A-007) was initially thought to be a SERM due to its structural similarity to tamoxifen but it was subsequently found not to bind to the estrogen receptor (ER). Tesmilifene (DPPE; YMB-1002, BMS-217380-01) is also structurally related to tamoxifen but similarly does not bind to the ER and is not a SERM. == Structure == SERMs can be variously classified structurally as triphenylethylenes (tamoxifen, clomifene, toremifene, droloxifene, idoxifene, ospemifene, fispemifene, afimoxifene, others), benzothiophenes (raloxifene, arzoxifene), indoles (bazedoxifene, zindoxifene, pipendoxifene), tetrahydronaphthalenes (lasofoxifene, nafoxidine), and benzopyrans (acolbifene, ormeloxifene, levormeloxifene). == References ==
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"page_id": 52626678,
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"title": "List of selective estrogen receptor modulators"
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The pluriblast is a pluripotent population of cells in the embryogenesis of marsupials, called the inner cell mass in eutherians. The pluriblast is distinct from the trophoblast, and gives rise to the germ layers of the embryo, as well as extra embryonic endoderm and extra embryonic mesoderm. Both the pluriblast and trophoblast arise from the totipotent cells of the early conceptus. By definition, the pluriblast does not give rise to trophoblast cells during normal development, although it may retain this potential under experimental conditions. In metatherians (marsupials), the pluriblast forms part of the blastocyst wall and no structure exists that can be described as an inner cell mass. "Inner cell mass" is thus a morphological term peculiar to eutherian mammals, whereas "pluriblast" is a functional term more widely applicable to conserved aspects of mammalian development. == References == == Further reading == Johnson, M. H.; Selwood, L. (1996). "Nomenclature of early development in mammals". Reproduction, Fertility, and Development. 8 (4): 759–764. doi:10.1071/rd9960759. PMID 8870096.
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"page_id": 14943480,
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"title": "Pluriblast"
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Chlorinated polyethylene (PE-C or CPE) is an inexpensive variation of polyethylene, where chlorine is substituted for some of the hydrogen atoms. CPE has a chlorine content from 34 to 44%. Due to its soft, rubbery texture, CPE is added to polyvinyl chloride to increase its impact and weather resistance. Furthermore, it is used for softening PVC foils, without risking plasticizer migration. Chlorinated polyethylene can be crosslinked with peroxides to form an elastomer which is used in cable and rubber industries. When chlorinated polyethylene is added to other polyolefins, it reduces the flammability. Chlorinated polyethylene is sometimes used in power cords as an outer jacket. Chlorinated polyethylene is listed on the Living Building Institute's Red List of materials that cannot be used. == See also == Hypalon Cross-linked polyethylene == References ==
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"page_id": 50529529,
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"title": "Chlorinated polyethylene"
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In quantum field theory, the minimal subtraction scheme, or MS scheme, is a particular renormalization scheme used to absorb the infinities that arise in perturbative calculations beyond leading order, introduced independently by Gerard 't Hooft and Steven Weinberg in 1973. The MS scheme consists of absorbing only the divergent part of the radiative corrections into the counterterms. In the similar and more widely used modified minimal subtraction, or MS-bar scheme ( MS ¯ {\displaystyle {\overline {\text{MS}}}} ), one absorbs the divergent part plus a universal constant that always arises along with the divergence in Feynman diagram calculations into the counterterms. When using dimensional regularization, i.e. d 4 p → μ 4 − d d d p {\displaystyle d^{4}p\to \mu ^{4-d}d^{d}p} , it is implemented by rescaling the renormalization scale: μ 2 → μ 2 e γ E 4 π {\displaystyle \mu ^{2}\to \mu ^{2}{\frac {e^{\gamma _{\rm {E}}}}{4\pi }}} , with γ E {\displaystyle \gamma _{\rm {E}}} the Euler–Mascheroni constant. == References == === Other === Bardeen, W.A.; Buras, A.J.; Duke, D.W.; Muta, T. (1978). "Deep Inelastic Scattering Beyond the Leading Order in Asymptotically Free Gauge Theories" (PDF). Physical Review D. 18 (11): 3998–4017. Bibcode:1978PhRvD..18.3998B. doi:10.1103/PhysRevD.18.3998. Collins, J.C. (1984). Renormalization. Cambridge Monographs on Mathematical Physics. Cambridge University Press. ISBN 978-0-521-24261-5. MR 0778558.
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"page_id": 8324345,
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"title": "Minimal subtraction scheme"
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Degas conductivity is used as an indicator of water quality in the water/steam cycle of power stations. Excessive conductivity values often indicate high corrosion potential, especially with certain ions such as chloride and acetate ions. These can be particularly damaging to the blades in the steam turbine. Degas conductivity is measured after the water sample has flowed through a resin and has had carbon dioxide removed by a degassing process. Specific conductivity and Cation conductivity are the other main types of measurement. == Application of conductivity in steam analysis == Conductivity measurements in the water/steam cycle of power stations are commonly used as indicators of the quality of the water used in the process. Excessive conductivity values often indicate a high corrosion potential, especially in the case of certain ions such as chloride and acetate ions. These can be particularly damaging to the blades in the steam turbine. Typically, there are three major types of conductivity measurements used: Specific conductivity, a measurement that indicates the total dissolved solids in an aqueous solution Cation conductivity, a measurement taken after the water sample has flowed through a resin bed (known as a cation exchanger) Degas conductivity, a measurement taken after the water sample has flowed through a resin and has had carbon dioxide removed by a degassing process Generally, degas conductivity is measured from condensed and cooled samples of primary steam. It may also be relevant for analyzing condensate return, especially in cases where the condensate is returned from a separate plant that used the steam in another process. Above three conductivity measurement gives one of the most robust measurement. Also with three measurement it is possible to calculate: (1) pH of condensate/ Steam and Boiler feed water. (Refer VGB-S-010-T-00;2011-12.EN-ebook) (2) Calculated CO2 values (Refer ASTM D4519 Standard) == Methodology == After
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the ions have been removed from the conditioning of the circulating water (e.g. ammonium NH4+) in the cation exchanger, ions resulting from gaseous components must be removed in order to determine degas conductivity. These are typically gases from the atmosphere which have penetrated into the system through leaks in the water-steam circuit. Of all gases occurring in the atmosphere, typically only carbon dioxide (CO2) dissolves chemically into ions in circulating water. The remaining gases (oxygen, nitrogen, etc.) dissolve physically and do not form ions, and thus do not contribute to conductivity. The chemical reactions of carbon dioxide in water proceed according to the following reaction equation (mass action law): A) CO2 + 2 H2O <--> HCO3 + H3O+ pK = 6.3 B) HCO3− + 2 H2O <--> CO32− pK = 10.3 See the graph showing relative CO2 concentration. After the cation exchanger, the sample pH value is generally 5.5–6, so that means almost only CO2 is present as gas, and only about 6% is carbon carbonate ion CO32−. The bicarbonate ion (HCO3−) is practically absent. However, ionic components of carbon dioxide are far less dangerous to corrosion than the ions of the saline components, e.g. Cl−. In order to obtain a selective conductivity value for these saline-containing ions (with the maximum potential for corrosion), all remaining carbon dioxide must be removed from the sample in order to accurately determine the presence of corrosive ions. There are generally two methods for removing carbon dioxide from the water sample: use of a reboiler to heat the sample and expel the CO2, and use of inert gasses. In the latter method, an inert gas which does not contain CO2 is passed through the sample water, whereby the gas components in the sample water are displaced by the gas components of the inert gas.
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Use of bottled inert gases can be problematic in some industrial applications. Reboilers are very efficient degassing with results over 92%, but they typically require anywhere from 20 to 45 minutes to achieve useful results. Manufacturers of reboiler systems include Swan Analytical, Forbes Marshall, Mettler Toledo, and Sentry Equipment Corp. Working of Degas Cation Conductivity system is explained in attached Animation Some other methods like inert gas method (known as "Gronowski's dynamic method")are also developed, whereby the inert gas is generated in the decarbonation column by passing air through a column filled with soda lime. The removal of the carbon dioxide is carried out in an exchanger column according to the contraflow principle. The inert gas drives the carbon dioxide from the sample water so that no carbonate ion can be formed. What remains in the water sample are salt-like (acid-like) ions and organic components, as well as oxygen and nitrogen which do not form ions in aqueous media. Gronowski's patented degassing method is extremely fast, achieving approximately 94% degassing in 45 seconds, growing up to even greater final efficiency. See the graph, taken from actual test data. == Reasons for measuring a degassed sample of condensed steam == Growth in renewable (but unsteady) energy sources has placed greater burden on modern gas-fired electric plants to cycle on and off to maintain steady and reliable electric production between Renewables and Base Load. These plants utilize a combination of gas (70%) and steam (30%) turbines to produce electricity. Critical for top efficiency is ensuring pure steam reaches the second stage quickly. During the start up of a power plant, the purity of the generated steam determines whether it can be sent to the steam turbine or if it has to be bypassed to the condenser. Traditionally “Cation Conductivity” instruments are used
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"page_id": 52299004,
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to analyze steam quality, but in addition to measuring harmful ionic compounds (e.g. chloride ions), they also include CO2, which as stated above is not significantly harmful to the steam turbine. Furthermore, typical cation conductivity analyzers take 3–4 hours to provide useful indications of steam purity. In many cases, this means the plant never reaches 100% efficiency before it cycles offline. That means a gas-turbine combined cycle plant would be burning fuel at 100%, but only achieving a 70% output and venting the excess heat and exhaust. In the case of a traditional base load power plant, cycling is much less frequent—in some cases, only twice annually for maintenance. Compared with measuring only cation conductivity, the cost savings from an accelerated start-up using degas conductivity is potentially very large. At $0.50/MW-minute ($30/MWH), a 750MW coal plant starting three hours faster each cycle could theoretically generate an additional $133,875 of annual revenue from the same fuel. Based on similar assumptions, the cost savings between different degassing methodologies is significant. If a dynamic system similar to Gronowski's is used, in the nearly 30 minutes of start-up time saved over a reboiler method, the typical combined cycle plant will generate even more income from the same fuel consumed with each and every system start, especially using typical “peak” electricity pricing. Additional benefits are better energy efficiency and reduced emissions of heat and exhaust. Degas Cation conductivity instruments are designed for measurement of all three conductivity Values (Specific, Cation and Degas Cation Conductivity) and also provides output for calculated pH and calculated CO2 in Feed water or Condensate. == References ==
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{
"page_id": 52299004,
"source": null,
"title": "Degas conductivity"
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Kim R. Dunbar is an American inorganic chemist and Distinguished Professor of Chemistry at Texas A&M University. Her research concerns inorganic and coordination chemistry, including molecular magnetism, metals in medicine, supramolecular chemistry Involving anions and anion-pi interactions, and multifunctional materials with organic radicals. == Education and career == Dunbar received her B.S. in chemistry at Westminster College in 1980, followed by her Ph.D. in inorganic chemistry in 1984 at Purdue University studying with professor Richard A. Walton. Dunbar then became a postdoctoral research associate in inorganic chemistry with F. Albert Cotton in 1985–1986 at Texas A&M University, before going on to spend the next twelve years conducting research and teaching at Michigan State University, where she moved through the ranks, ultimately becoming a distinguished professor in 1998. She was recruited back to Texas A&M University in 1999, where she currently holds a Davidson Chair of Science and the Distinguished Professorship of Chemistry. Notably, Dunbar is the first female chair holder of the College of Science at TAMU. In 2015, Dunbar received the American Chemical Society’s (ACS) Award for Distinguished Service in the Advancement of Inorganic Chemistry, the second female recipient of the ACS's top award for inorganic chemistry in its 52-year history. A leader in both chemical research and education, Dunbar is the first female Texas A&M Former Students’ Network (WFSN) Eminent Scholar Award winner. Dunbar was awarded an honorary doctorate degree from her undergraduate alma mater at Westminster College in New Wilmington in 2012. For years Dunbar has served as an Associate editor of the ACS inorganic Chemistry journal. Over the course of her career, she has contributed broadly to the development of inorganic coordination chemistry and materials science which has resulted in over 280 publications to date. == Research == Dunbar's research focuses on many areas including organocyanide
|
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based functional materials, which was featured in an editorial celebrating Women in Chemistry in 2011 published in celebration of the International Year of Chemistry which was the 100th anniversary of Marie Skłodowska's Nobel Prize. Her research, which is based on her major interest in magnets and conductors, interactions with DNA in metal bonded system and conciliation by interactions in anions and aromatic ligands in supramolecular structures and properties allowed her to focus on interfaced problems of metal-based drugs in medicine, alongside synthetic challenges in biological chemistry such as supramolecular anion-𝝅 interactions. Dunbar has extensively studied anion-𝝅 interactions, which describe the special relationship between aromatic molecules and anions. Aromatic systems normally have a high level of electron density and would repel negatively charged particles, however electron deficient ring systems specifically are able to accept the electron density of anions to form a non-covalent interaction. Some important applications of the anion-𝝅 interactions are to purify drinking water by removing nitrate and phosphate ions, catalysis, and biological purposes such as pores, membranes, and fabricated ion routes. Trigonal-bipyramidal cyanide cluster with single-molecule magnets can provide magnetic bistability. They have unique physical properties and can be also applicable in quantum computing. Dunbar's research group focused on introducing magnetically anisotropic metal ions into clusters such as MnIII ions which plays an important role in trigonal-bipyramidal (tbp) molecular geometry for determining magnetic phenomenon. == Selected publications == 1. “A Trigonal-Bipyramidal Cyanide Cluster with Single Molecule-Magnet Behavior: Synthesis, Structure, and Magnetic Properties of {[MnII(tmphen)2]3- [MnIII(CN)6]2}”: C. P. Berlinguette, D. Vaughn, C. Caada-Vilalta, J. R. Galn-Mascars, K. R. Dunbar, Angew. Chem. 2003, 115, 1561 – 1564; Angew. Chem. Int. Ed. 2003, 42, 1523 – 1526. 2. “Novel Binding Interactions of the DNA Fragment d(pGpG) Cross-Linked by the Antitumor Active Compound Tetrakis (m-carboxylato)dirhodium(II,II)”: H. T. Chifotides, K. M. Koshlap, L.
|
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M. Prez, K. R. Dunbar, J. Am. Chem. Soc. 2003, 125, 10714 – 10724. 3. “Anion-p Interactions”: B. L. Schottel, H. T. Chifotides, K. R. Dunbar, Chem. Soc. Rev. 2008, 37, 68 – 83. 4. “Unprecedented Binary Semiconductors Based on TCNQ: Single-Crystal X-ray Studies and Physical Properties of Cu(TCNQX2) X = Cl, Br”: N. Lopez, H. Zhao, A. Ota, A. V. Prosvirin, E. Reinheimer, K. R. Dunbar, Adv. Mater. 2010, 22, 986 – 989. 5. “A Remarkable Family of Rhodium Acetonitrile Compounds Spanning Three Oxidation States and with Nuclearities Ranging from Mononuclear and Dinuclear to One-Dimensional Chains”: M. E. Prater, L. E. Pence, R. Clrac, G. M. Finniss, C. Campana, P. Auban-Senzier, D. Jrome, E. Canadell, K. R. Dunbar, J. Am. Chem. Soc. 1999, 121, 8005 – 8016. 6. Heptacyanotungstate(IV) Anion: A New 5d Transition-Metal Member of the Rare Heptacyanometallate Family of Anions. Francisco J. Birk, Dawid Pinkowicz, and Kim R. Dunbar, Angew. Chem. Int. Ed., 2016, 55, 11368–11371. Frontispiece for Communications 7. A Cobalt-TCNQ Spin-Crossover Bifunctional Material with an Anomalous Conducting Behavior. Xuan Zhang, Zhao-Xi Wang, Haomiao Xie, Ming-Xing Li, Toby J. Woods and Kim R. Dunbar, Chemical Science, (Edge Article) 2016, 7, 1569–1574. 8. Cyanide Single Molecule Magnets Exhibiting Reversible, Solvent Dependent "On" and "Off" Exchange Bias Behavior. Dawid Pinkowicz, Heather I. Southerland, Carolina Avendaño, Andrey Prosvirin, Wolfgang Wernsdorfer, Kasper S. Pedersen, Jan Dreiser, Rodolphe Clérac and Kim R. Dunbar, J. Am. Chem. Soc., 2015, 137, 14406–14422. 9. Metal-organic frameworks as platforms for isolating individual single-molecule magnets in pores. Joshua B. Pyser, Darpandeep Aulakh, Xuan Zhang, Andrey A. Yakovenko, Kim R. Dunbar and Mario Wriedt, J. Am. Chem. Soc., 2015, 37, 9254–9257. 10. Optimizing the Electronic Properties of Photoactive Anticancer Oxypyridine Bridged Dirhodium(II,II) Complexes, Zhanyong Li, Amanda David, Bryan A. Albani, Jean-Philippe Pellois, Claudia Turro, and Kim R.
|
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"title": "Kim Renee Dunbar"
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Dunbar, J. Am. Chem. Soc., 2014, 36, 17058–17070. == Honors and awards == She is the second female recipient of the ACS's top award for inorganic chemistry in its 52-year history and got the first Texas A&M Women Former Students' Network (WFSN) and an honorary doctorate degree from her undergraduate alma mater at Westminster College in New Wilmington in 2012. Her other awards include: ACS Award for Distinguished Service in the Advancement of Inorganic Chemistry, 2015 249th ACS National Meeting & Exposition for coordination compounds as magnetic and conducting materials in inorganic chemistry, Denver, 2015 Inaugural Eminent Scholar Award, Texas A&M University Women Former Students’ Network, 2012 Honorary Degree, Westminster College, PA, 2012 Distinguished Achievement Award in Research, Association of Former Students, Texas A&M, 2012 Inaugural Eminent Scholar Award, Texas A&M University Women Former Students’ Network, 2012 TAMU Association of Former Students Award in Research, 2012 Inaugural Distinguished Achievement Award in Graduate Mentoring, Association of Former Students, 2006 Purdue University Department of Chemistry Distinguished Alumnus Award, 2004 Fellow of American Association for the Advancement of Science and the American Institute of Chemist, 2004 NSF Creativity Grant Extension Award, 1995–1996; 2002–2004 Distinguished Alumni Award, Westminster College, 2000 Distinguished Faculty Award, Michigan State University, 1998 Sigma Xi Research Award, Michigan State University, 1998 Fellow of the Alfred P. Sloan Foundation, 1992–1995 Camille and Henry Dreyfus Teacher-Scholar Award, 1991–1995 University Teaching Award, Michigan State University, 1990 Sigma Xi Thesis Award, Purdue University, 1984 == External links == Publication list as indexed by Google Scholar == References ==
|
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"page_id": 53806334,
"source": null,
"title": "Kim Renee Dunbar"
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Allan McCulloch Campbell (April 27, 1929 – April 19, 2018) was an American microbiologist and geneticist and the Barbara Kimball Browning Professor Emeritus in the Department of Biology at Stanford University. His pioneering work on Lambda phage helped to advance molecular biology in the late 20th century. An important collaborator and member of his laboratory at Stanford University was biochemist Alice del Campillo Campbell, his wife. == Education == Campbell earned his bachelor's degree at the University of California, Berkeley (1950) and master's (1951) and doctoral (1953) degrees from the University of Illinois where he worked with Sol Spiegelman. == Career == From 1953-1957 Campbell was on the faculty of the University of Michigan. During the summers he spent time with Gio ("Joe") Bertani at Caltech and the University of Southern California, at Cold Spring Harbor Laboratory and at the Institut Pasteur with François Jacob. In 1958 he married Alice del Campillo, a Ph.D. student in biochemistry at the University of Michigan. They spent the year after their marriage working in Paris. The two worked closely together throughout their careers, investigating research questions such as the encoding of heat-sensitive endolysin and the biosynthesis and regulation of biotin. Campbell spent the next nine years on the faculty of the University of Rochester, where he made significant discoveries about lambda phage. In 1968 Campbell joined the Department of Biology at Stanford University, where he led his own laboratory. He was appointed to the Barbara Kimball Browning endowed chair in 1992. Campbell was the editor of the Annual Review of Genetics from 1985 to 2012. == Research == Campbell's research has concentrated on the genetics of bacteria and their viruses, especially the integration of viral DNA into host chromosomes. His most prominent discovery was the proposal of the “Campbell model” of virus insertion,
|
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where viral DNA is inserted into the host chromosome, becoming covalently bonded to the bacterial DNA, and then remains dormant until activation. Campbell's research was focused on a specific bacterial virus, phage lambda, and its host bacterium E. coli, but the model provided insights into how extrachromosomal DNA can be inserted and excised in other organisms. This model was proposed in the book Episomes published in 1968, the first comprehensive treatment of plasmid biology. It was described as "a wide-ranging and critical evaluation of the experimental foundation of the episome concept". While study of the regulation of integration and excision of phage lambda in E coli has been a primary focus of his research, Campbell and research associates also studied regulation and expression of E coli genes linked to the lambda insertion location, including the biotin (bio) and galactose (gal) genes. == Background on phage lambda and lysogeny == Early studies on bacterial viruses began after the discovery by Twort and d’Herelle of ‘filterable agents’ which were able to destroy bacteria. These were demonstrated by creating a lawn of bacteria on appropriate media, mixing with these ‘filterable agents’ and then observing areas of destroyed cells seen as cleared circular areas (plaques) on the lawn. These plaques were interpreted as the result of a single agent infecting a bacterial cell, reproducing in the cell and then bursting open to infect surrounding cells, repeating the process until a clear circular area of destroyed cells becomes visible to the unaided eye. These filterable agents were named bacteriophages (eaters of bacteria) or phage for short. The 1940s produced the first pictures of bacterial viruses using electron microscopy produced the first photos of bacterial viruses, and research on the mechanism of infection and reproduction dramatically increased. One of the focal points of this research was
|
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Cold Spring Harbor Laboratory on Long Island, where a ‘phage group’ led by Salvador Luria, Max Delbrück, Alfred Hershey and others met in the summers for research and training of new investigators. In 1951 Esther Lederberg discovered lambda phage, which had an unusual characteristic. While lambda could infect and reproduce in some strains of its host bacterium E. coli, other strains seemed immune to infection. However, when the immune strains were mixed with non-immune strains, occasionally lambda phage could be observed infecting the non-immune strains. Further research suggested that the immune strains contained a dormant copy of the lambda genome which protected it from infection, but that dormant copy could be activated into the active viral state to begin a new round of infection. This dormant phase was called the ‘lysogenic’ state and the actively infectious state was called the ‘lytic’ state. The dormant form of the lambda genome was called the ‘prophage’. Study of phage lambda over the next 50 years provided valuable insights into virus life cycles, the regulation and expression of genetic material, and the mechanism of integration and excision of genetic material into chromosomal locations. Allan Campbell's contribution to the field with the ‘Campbell model’ of integration and excision marked a major step forward in the understanding of this process. == Honors == Campbell was an elected member of the National Academy of Sciences (1971), the American Academy of Arts and Sciences (1971), the American Association for the Advancement of Science (1983) and a fellow of the American Academy of Microbiology. Campbell received the 2004 Abbott-ASM Lifetime Achievement Award from the American Society for Microbiology at the society's 104th general meeting in New Orleans on Monday, May 24, 2004. Campbell delivered the Abbott-ASM Award Lecture and was honored at a dinner ceremony that evening. The award
|
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includes a $20,000 cash prize and a commemorative piece. In honoring Campbell, ASM officials cited his "exceptional insights and achievements in the field of molecular genetics - a career of groundbreaking research that has had a profound influence on several fields, including molecular cloning and gene therapy." == Selected publications == Campbell, Allan M. (1963). "Episomes". In Caspari, E.W.; Thoday, J.M. (eds.). Advances in Genetics. Vol. 11. New York, N.Y.: Academic Press. pp. 101–145. ISBN 9780120176113. {{cite book}}: ISBN / Date incompatibility (help) Campbell, A.; Berg, D.; Botstein, D.; Lederberg, E.M.; Novick, R.P.; Starlinger, P.; Szybalski, W. (1977). "Nomenclature of transposable elements in prokaryotes". DNA insertion elements, plasmids, and episomes. [Cold Spring Harbor, N.Y.]: Cold Spring Harbor Laboratory. pp. 15–22. ISBN 9780879691189. Campbell, A.; Berg, D.; Botstein, D.; Lederberg, E.M.; Novick, R.P.; Starlinger, P.; Szybalski, W. (March 1979). "Nomenclature of transposable elements in prokaryotes". Gene. 5 (3): 197–206. doi:10.1016/0378-1119(79)90078-7. PMID 467979. Campbell, A.; Starlinger, P.; Berg, D.; Botstein, D.; Lederberg, E.M.; Novick, R.P.; Szybalski, W. (July 1979). "Nomenclature of transposable elements in prokaryotes" (PDF). Plasmid. 2 (3): 466–473. doi:10.1016/0147-619X(79)90030-1. PMID 384423. Campbell, Allan (December 2007). "Phage Integration and Chromosome Structure. A Personal History". Annual Review of Genetics. 41 (1): 1–11. doi:10.1146/annurev.genet.41.110306.130240. PMID 17474874. Retrieved 17 September 2021. (Note: After Esther Lederberg's death in November 2006, Campbell published "Phage Integration and Chromosome Structure. A Personal History" with the following dedication: "This chapter is dedicated to the memory of Esther M. Lederberg (1922-2006) whose early work laid some of the ground for the author's research described herein.") == References ==
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François Chollet (French: [fʁɑ̃swa ʃoˈlɛ]; born 20 October 1989) is a French software engineer and artificial intelligence researcher formerly Senior Staff Engineer at Google. Chollet is the creator of the Keras deep-learning library, released in 2015. His research focuses on computer vision, the application of machine learning to formal reasoning, abstraction, and how to achieve greater generality in artificial intelligence (AGI). == Education and career == In 2012, Chollet graduated with a Diplôme d'Ingénieur (Master of Engineering) from ENSTA Paris, a school of the Polytechnic Institute of Paris. In 2015, Chollet started working at Google shortly after releasing Keras. In 2019, he published the Abstraction and Reasoning Corpus for Artificial General Intelligence (ARC-AGI) benchmark, which measures the ability of AI systems to solve novel reasoning problems. In 2024, Chollet launched ARC Prize, a US$1 million competition to solve the ARC-AGI benchmark. He left Google in November 2024 after more than 9 years with the company to found with Zapier co-founder Mike Knoop a new startup focused on developing AGI with program synthesis. In early 2025, Chollet announced the expansion of ARC Prize into a full-fledged non-profit foundation, to further the mission of guiding and accelerating research progress towards artificial general intelligence. == Books and publications == Chollet's research papers in artificial intelligence have been published at major conferences in the field, including the Conference on Computer Vision and Pattern Recognition (CVPR), the Conference on Neural Information Processing Systems (NeurIPS), and the International Conference on Learning Representations (ICLR). Chollet is the author of Xception: Deep Learning with Depthwise Separable Convolutions, which is among the top ten most cited papers in CVPR proceedings at more than 18,000 citations. Chollet is the author of the book Deep Learning with Python, which sold over 100,000 copies, and the co-author with Joseph J. Allaire of
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"title": "François Chollet"
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Deep Learning With R. == Awards == On December 1, 2021, Chollet won the Global Swiss AI Award for breakthroughs in AI. In September 2024, Chollet was named by TIME as one of the 100 most influential people in AI. == Bibliography == Chollet, François (2017). Deep Learning with Python. Manning Publications. ISBN 9781617294433. Chollet, François; Allaire, J. J. (2018). Deep Learning With R. Manning Publications. ISBN 9781617295546. Chollet, François (2019). On the Measure of Intelligence. arXiv:1911.01547. Chollet, François (2021). Deep Learning with Python Second Edition. Manning Publications. ISBN 9781617296864. == References ==
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"title": "François Chollet"
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|
The lacrimal caruncle, or caruncula lacrimalis, is the small, pink, globular nodule at the inner corner (the medial canthus) of the eye. It consists of tissue types of neighbouring eye structures. It may suffer from lesions and allergic inflammation. == Structure == The lacrimal caruncle is found at the medial canthus of the eye. It consists of skin, hair follicles, sebaceous glands, sweat glands, accessory lacrimal tissue and other tissues that are present in the skin and accessory lacrimal glands. Its non-keratinized epithelium resembles the conjunctival epithelium. == Clinical significance == === Lesions === The lacrimal caruncle may have a lesion. This can have any one of a number of causes, which may be difficult to diagnose. Cancer is a rare cause. These lesions include papillomas and oncocytomas. === Allergies === With ocular allergies, the lacrimal caruncle and the plica semilunaris of the conjunctiva may be inflamed and pruritic (itchy) due to histamine release in the tissue and tear film. === Other diagnoses === Sweat glands and oil glands are contained in the caruncle of the eye (lacrimal caruncle in medial canthus). As with all oil glands, lacrimal caruncles can become clogged, causing a pimple, whitehead, or pustule beneath the skin. Clogged oil and sweat glands in the caruncle can affect tear ducts. Treatment for dry eyes due to clogged glands includes refraining from rubbing the eyes and rinsing the eyes with clear water frequently during the day, either with clean hands or a spray faucet. Additionally, one can use a warm damp cloth on the eye, which will help the clogged pore to open up and release some pressure. Anti-bacterial eye drops may also be prescribed. If the pustules enlarge, an oral antibiotic may be prescribed. If lesions such as cysts form, they must be surgically drained; this operation
|
{
"page_id": 8258828,
"source": null,
"title": "Lacrimal caruncle"
}
|
is rarely necessary. If it affects the tear sac it may be dacryocystitis. == References == == Additional images ==
|
{
"page_id": 8258828,
"source": null,
"title": "Lacrimal caruncle"
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Endoreduplication (also referred to as endoreplication or endocycling) is replication of the nuclear genome in the absence of mitosis, which leads to elevated nuclear gene content and polyploidy. Endoreduplication can be understood simply as a variant form of the mitotic cell cycle (G1-S-G2-M) in which mitosis is circumvented entirely, due to modulation of cyclin-dependent kinase (CDK) activity. Examples of endoreduplication characterised in arthropod, mammalian, and plant species suggest that it is a universal developmental mechanism responsible for the differentiation and morphogenesis of cell types that fulfill an array of biological functions. While endoreduplication is often limited to specific cell types in animals, it is considerably more widespread in plants, such that polyploidy can be detected in the majority of plant tissues. Polyploidy and aneuploidy are common phenomena in cancer cells. Given that oncogenesis and endoreduplication likely involve subversion of common cell cycle regulatory mechanisms, a thorough understanding of endoreduplication may provide important insights for cancer biology. == Examples in nature == Endoreduplicating cell types that have been studied extensively in model organisms == Endoreduplication, endomitosis and polytenization == Endoreduplication, endomitosis and polytenization are three different processes resulting in polyploidization of a cell in a regulated manner. In endoreduplication cells skip M phase completely by exiting the mitotic cell cycle in the G2 phase after completing the S phase several times, resulting in a mononucleated polyploid cell. The cell ends up with twice as many copies of each chromosome per repeat of the S phase. Endomitosis is a type of cell cycle variation where mitosis is initiated, but stopped during anaphase and thus cytokinesis is not completed. The cell ends up with multiple nuclei in contrast to a cell undergoing endoreduplication. Therefore depending on how far the cell progresses through mitosis, this will give rise to a mononucleated or binucleated polyploid
|
{
"page_id": 2491663,
"source": null,
"title": "Endoreduplication"
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|
cell. Polytenization arises with under- or overamplification of some genomic regions, creating polytene chromosomes. == Biological significance == Based on the wide array of cell types in which endoreduplication occurs, a variety of hypotheses have been generated to explain the functional importance of this phenomenon. Unfortunately, experimental evidence to support these conclusions is somewhat limited. === Cell differentiation === In developing plant tissues the transition from mitosis to endoreduplication often coincides with cell differentiation and morphogenesis. However it remains to be determined whether endoreduplication and polyploidy contribute to cell differentiation or vice versa. Targeted inhibition of endoreduplication in trichome progenitors results in the production of multicellular trichomes that exhibit relatively normal morphology, but ultimately dedifferentiate and undergo absorption into the leaf epidermis. This result suggests that endoreduplication and polyploidy may be required for the maintenance of cell identity. === Cell/organism size === Cell ploidy often correlates with cell size, and in some instances, disruption of endoreduplication results in diminished cell and tissue size suggesting that endoreduplication may serve as a mechanism for tissue growth. Relative to mitosis, endoreduplication does not require cytoskeletal rearrangement or the production of new cell membrane and it often occurs in cells that have already differentiated. As such it may represent an energetically efficient alternative to cell proliferation among differentiated cell types that can no longer afford to undergo mitosis. While evidence establishing a connection between ploidy and tissue size is prevalent in the literature, contrary examples also exist. === Oogenesis and embryonic development === Endoreduplication is commonly observed in cells responsible for the nourishment and protection of oocytes and embryos. It has been suggested that increased gene copy number might allow for the mass production of proteins required to meet the metabolic demands of embryogenesis and early development. Consistent with this notion, mutation of the
|
{
"page_id": 2491663,
"source": null,
"title": "Endoreduplication"
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Myc oncogene in Drosophila follicle cells results in reduced endoreduplication and abortive oogenesis. However, reduction of endoreduplication in maize endosperm has limited effect on the accumulation of starch and storage proteins, suggesting that the nutritional requirements of the developing embryo may involve the nucleotides that comprise the polyploid genome rather than the proteins it encodes. === Buffering the genome === Another hypothesis is that endoreduplication buffers against DNA damage and mutation because it provides extra copies of important genes. However, this notion is purely speculative and there is limited evidence to the contrary. For example, analysis of polyploid yeast strains suggests that they are more sensitive to radiation than diploid strains. === Stress response === Research in plants suggests that endoreduplication may also play a role in modulating stress responses. By manipulating expression of E2fe (a repressor of endocycling in plants), researchers were able to demonstrate that increased cell ploidy lessens the negative impact of drought stress on leaf size. Given that the sessile lifestyle of plants necessitates a capacity to adapt to environmental conditions, it is appealing to speculate that widespread polyploidization contributes to their developmental plasticity == Genetic control of endoreplication == The best-studied example of a mitosis-to-endoreduplication transition occurs in Drosophila follicle cells and is activated by Notch signaling. Entry into endoreduplication involves modulation of mitotic and S-phase cyclin-dependent kinase (CDK) activity. Inhibition of M-phase CDK activity is accomplished via transcriptional activation of Cdh/fzr and repression of the G2-M regulator string/cdc25. Cdh/fzr is responsible for activation of the anaphase-promoting complex (APC) and subsequent proteolysis of the mitotic cyclins. String/cdc25 is a phosphatase that stimulates mitotic cyclin-CDK complex activity. Upregulation of S-phase CDK activity is accomplished via transcriptional repression of the inhibitory kinase dacapo. Together, these changes allow for the circumvention of mitotic entry, progression through G1, and
|
{
"page_id": 2491663,
"source": null,
"title": "Endoreduplication"
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|
entry into S-phase. The induction of endomitosis in mammalian megakaryocytes involves activation of the c-mpl receptor by the thrombopoietin (TPO) cytokine and is mediated by ERK1/2 signaling. As with Drosophila follicle cells, endoreduplication in megakaryocytes results from activation of S-phase cyclin-CDK complexes and inhibition of mitotic cyclin-CDK activity. Entry into S-phase during endoreduplication (and mitosis) is regulated through the formation of a prereplicative complex (pre-RC) at replication origins, followed by recruitment and activation of the DNA replication machinery. In the context of endoreduplication these events are facilitated by an oscillation in cyclin E-Cdk2 activity. Cyclin E-Cdk2 activity drives the recruitment and activation of the replication machinery, but it also inhibits pre-RC formation, presumably to ensure that only one round of replication occurs per cycle. Failure to maintain control over pre-RC formation at replication origins results in a phenomenon known as "rereplication" which is common in cancer cells. The mechanism by which cyclin E-Cdk2 inhibits pre-RC formation involves downregulation of APC-Cdh1-mediated proteolysis and accumulation of the protein Geminin, which is responsible for sequestration of the pre-RC component Cdt1. Oscillations in Cyclin E-Cdk2 activity are modulated via transcriptional and post-transcriptional mechanisms. Expression of cyclin E is activated by E2F transcription factors that were shown to be required for endoreduplication. Recent work suggests that observed oscillations in E2F and cyclin E protein levels result from a negative-feedback loop involving Cul4-dependent ubiquitination and degradation of E2F. Post-transcriptional regulation of cyclin E-Cdk2 activity involves Ago/Fbw7-mediated proteolytic degradation of cyclin E and direct inhibition by factors such as Dacapo and p57. == Premeiotic endomitosis in unisexual vertebrates == The unisexual salamanders (genus Ambystoma) are the oldest known unisexual vertebrate lineage, having arisen about 5 million years ago. In these polyploid unisexual females, an extra premeiotic endomitotic replication of the genome, doubles the number of chromosomes. As
|
{
"page_id": 2491663,
"source": null,
"title": "Endoreduplication"
}
|
a result, the mature eggs that are produced subsequent to the two meiotic divisions have the same ploidy as the somatic cells of the adult female salamander. Synapsis and recombination during meiotic prophase I in these unisexual females is thought to ordinarily occur between identical sister chromosomes and occasionally between homologous chromosomes. Thus little, if any, genetic variation is produced. Recombination between homeologous chromosomes occurs rarely, if at all. == References ==
|
{
"page_id": 2491663,
"source": null,
"title": "Endoreduplication"
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|
Make People Better is a 2022 documentary film about the use of genetic engineering (called CRISPR gene editing) to enhance two twins girls to be immune to HIV. Directed by Cody Sheehy of Rhumbline Media, it was originated by Samira Kiani, a biotechnologist then at Arizona State University. It focuses on the circumstances involving Chinese biologist He Jiankui who created the first genetically modified humans in 2018. Featured experts included Antonio Regalado, senior editor for biomedicine of MIT Technology Review, who first discovered and revealed the secret experiment, and Benjamin Hurlbut, a bioethicist at the Arizona State University. The film was released on 13 December 2022 by Gravitas Films and Internationally by Cats & Docs. It premiered at Hot Docs Canadian International Documentary Festival, and simultaneously launched on iTunes Store and Amazon Prime Video. The title was taken from James Watson's reply as He asked him, "Do you think that that's [genetically modifying babies is] a good thing to do?" == Background == === Code of the Wild: The Nature of Us === CRISPR (clustered regularly interspaced short palindromic repeats) gene editing is a scientific method by which DNA molecules are cut using an enzyme, CRISPR associated protein 9 (Cas9) so that specific genes can be removed or replaced. The technique, independently developed by Emmanuelle Charpentier and Jennifer Doudna, had been used to make genetically modified organisms and better genes in genetic diseases. Samira Kiani was a researcher on CRISPR gene editing at Arizona State University and teamed up with Cody Sheehy of the Rhumbline Media to make a documentary film on the revolutionary technique. They started a project called Code of the Wild: The Nature of Us in 2018. They first approached expert in the field, George Church at Harvard University, who was popularly known as the "Founding Father
|
{
"page_id": 72746256,
"source": null,
"title": "Make People Better"
}
|
of Genomics", and Antonio Regalado, senior editor for biomedicine of MIT Technology Review, who had been well-versed in the development of the technique. Regalado hinted them that CRISPR gene-edited babies would be born in China "very soon". They further learned from Kiani's former acquaintance Ryan Farrell who was working as a public relations specialist to He Jiankui, associate professor in the Department of Biology of the Southern University of Science and Technology(SUSTech) in Shenzhen, China, that He was running a human germline-editing experiment. They visited He for an interview but received no information on the forthcoming genetically modified babies. === He Jiankui affair === On 25 November 2018, Regalado posted on MIT Technology Review website that He Jiankui was making CRIPSR babies. As it was publicised, He was prompted to announce his experiment and posted the news of the birth of twins, nicknamed Lulu and Nana, on YouTube in five videos the same day. He formally presented the experiment at the Second International Summit on Human Genome Editing organized at the University of Hong Kong on 28 November 2018. He explained that the experiment was to make the babies resistant to HIV infection as they were (as embryos) obtained from an HIV-positive father. He specifically used a mutant gene named CCR5-Δ32 that is known to confer innate resistance to HIV. The twins were born in secrecy in October 2018, and a third baby (revealed in 2022 as Amy) was then almost born, as He reported. Although the People's Daily announced the experimental result as "a historical breakthrough in the application of gene editing technology for disease prevention," the news was met with criticisms from scientists. The Chinese Academy of Medical Sciences publicly condemned the experiment as violation of medical regulations and ethical norms. A group of 122 Chinese scientists jointly
|
{
"page_id": 72746256,
"source": null,
"title": "Make People Better"
}
|
issued a statement that the experiment was unethical, "crazy" and "a huge blow to the global reputation and development of Chinese science". He's university, local authorities, and the Chinese government made a series of investigations, and He was found guilty of violating academic ethics and national laws on the use of human embryos. On 21 January 2019, He was fired by SUSTech and all connections were terminated. On 30 December 2019, the Shenzhen Nanshan District People's Court sentenced He to three years in prison and with a fine of 3 million RMB (US$430,000). == Participants == The film was based on the involvement of the following people: He Jiankui, who made the first CRISPR-edited babies Antonio Regalado, editor of MIT Technology Review who first revealed He's experiment Ryan Farrell, a public relations specialist to He Benjamin Hurlbut, a bioethicist at the Arizona State University == Reception and review == Courtney Small on Point of View Magazine gives a positive review, remarking: "A necessary conversation starter, Make People Better is an intriguing examination of a scientist who was hung out to dry by a community who helped elevate him in the first place." Liz Whittemore on Reel News Daily agrees, commenting that it "does an excellent job of putting scientific advances into perspective." Chris Jones on The Atlanta Mail commented it as "an excellent film for anyone interested in" the understanding of scientific development. However, the film received mostly critical reviews. Beandrea July on The New York Times criticised the film, saying that "a glut of animations and B-roll footage makes the film's visuals feel convoluted, and a flat narrative structure further muddies the waters." She also wrote that the way Sheehy presented the story was clumsy and "deflating the films dramatic tension with so little fanfare that the information’s premature
|
{
"page_id": 72746256,
"source": null,
"title": "Make People Better"
}
|
landing barely registers." She also criticised the film for omitting the news that He was released (in April 2022) while the film was being made. Christopher Cross on Tilt said that the documentary is a narrow-sighted view as the case is not just for scientists, and argues that Sheehy "ignores some of the most glaring facets of a hugely impactful breakthrough. As a thriller, Make People Better is solid, but as a documentary, it's better enjoyed as a Wikipedia article." G. Owen Schaefer, a biomedical ethicist at the National University of Singapore said, "The documentary does not reflect critically on its own title. The origin of the phrase "make people better" is surprising and the film's most clever narrative moment, so I won't spoil it. But does heritable gene editing really make people better? Perhaps instead, it makes better people." == References == == External links == Official website Make People Better at IMDb Rotten Tomatoes profile
|
{
"page_id": 72746256,
"source": null,
"title": "Make People Better"
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Myomeres are blocks of skeletal muscle tissue arranged in sequence, commonly found in aquatic chordates. Myomeres are separated from adjacent myomeres by fascia consisting of connective tissue, known as myosepta. Myomere counts are sometimes used for identifying specimens using meristics, since their number corresponds to the number of vertebrae in the adults. Myomere location varies, with some species containing these only near the tails, while some have them located near the scapular or pelvic girdles. Depending on the species, myomeres could be arranged in an epaxial or hypaxial manner; hypaxial refers to ventral muscles (those of the "stomach" region) and related structures, while epaxial refers to more dorsal muscles (those of the "back"). The horizontal septum divides these two regions in vertebrates from cyclostomes (jawless lamprey and hagfish) to gnathostomes (jawed fish). In terrestrial chordates, which are gnathostomes themselves, the myomeres become fused as well as indistinct, due to the disappearance of myosepta. == Form == Myomeres are overlapping "cones" of muscle fibers bound by connective tissue. The shape of myomeres varies by species. Myomeres are commonly zig-zaged, being muscle fibers shaped like "V" (lancelets), "W" (fishes), or straight (tetrapods). Generally, cyclostome myomeres are arranged in vertical strips while those of jawed fishes are folded in a complex manner due to their evolution of advanced swimming capability. Specifically, myomeres of elasmobranchs and eels are W-shaped, while the myomeres of tetrapods, such as mudpuppies, run vertically and do not display complex folding. Myomeres overlap each other in succession, meaning myomere activation also allows neighboring myomeres to activate. They are innervated by spinal nerves, which pass into each myomere. Myomeres are made up of myoglobin-rich dark muscle as well as white muscle. Dark muscles generally function as slow-twitch muscle fibers while white muscle is composed of fast-twitch fibers. == Function == There
|
{
"page_id": 13108497,
"source": null,
"title": "Myomere"
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|
are three types of myomeres observed in fish-like chordates: amphioxine (lancelet), cyclostomine (jawless fish), and gnathostomine (jawed fish). All myomeres flex the body laterally into concavity to provide force for locomotion. Since myomeres are composed of multinucleated myofibers (contractile cells), force can be generated via muscle contraction that gets transmitted by the intricate connective tissue (myosepta) network. Myomeres compose most of the lateral musculature and provide propulsive force to travel along the line of travel. In this sense, they cause flexion to either side in order to produce locomotor force (the forward swimming motion). Myomeres attach to centra of vertebrae, and neural and haemal spines. The folded shape of each myomere as V- or W-shaped extends over various axial segments, allowing fibers control over a large amount of the body. There are different variations of myomere activation depending on the type of swimming or movement. For example, high loading situations such as fast-starts and turning require almost maximal myomere activation in teleost fish. Further, if swim speeds are lower and movement is in one plane, there is less activation of myomeres. Research has discovered that fish are able to spatially restrict axial myomeres during different swimming behaviors. Some research theorizes that myomeres play additional roles for fish beyond force generation in swimming; microdissection and polarized light microscopy research suggests that anterior myomeres have elongated and reinforced dorsal posterior cones that allow epaxial muscle force to be transmitted to the neurocranium for its elevation, which is a crucial part of suction feeding. == Specific taxa == === Basal chordates === Published information on Pikaia gracilens (a well-known Cambrian fossil) explains evolution of swimming ability in chordates related to myomere shape and function. Specifically, myomeres in this species possessed minimal overlap between successive ones and myosepta dividing them were gently curved. In
|
{
"page_id": 13108497,
"source": null,
"title": "Myomere"
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|
a biomechanical evaluation, it is presumed that Pikaia were not capable of rapid swimming like in living chordates. Several theories for this idea include lacking fast-twitch muscle fibers, ancestral muscle fiber types more like modern slow-twitch fibers, and less tension on myosepta due to less overlap between successive myomeres. === Larval fish and Amphioxus === Larval fish and amphioxus myomeres are V-shaped. They are involved in the specialized notochord of amphioxus. There are muscle cells within myomeres that send, and synapse cytoplasmic extensions of muscle cells with contractile fibrils to the nerve cord surface. In amphioxus, myomeres run longitudinally along the length of the body in a "V"-shape. As sequential contraction for swimming occurs, force from the myomeres is transmitted via connective tissues to the notochord. === Zebrafish === Being model organisms, zebrafish myomeres have been extensively studied. The tail-bending maneuver generated by myomeres in zebrafish requires innervation from motor neurons for both the hypaxial and epaxial muscle regions. It has been found that timing/intensity of neurons firing in these two regions varies, respectively. This process is mediated by a circuit that controls motor neuron activation during swimming behaviors, which, in turn, affects force generation. Similar to this idea, one study found that hypaxial and epaxial myomere activation did not always correlate with myomeric fibers closer to the horizontal septum itself. === Eels === Eel myomeres are W-shaped and cover the entire body. Within these is a mucosal-like matrix that is a-cellular. Superficial to these myomeres is an epithelial layer. Leptocephalus myomeres are also W-shaped and extend from head all the way to the tail. Distinguishing eels can be done through evaluation of the number of myomeres (European has 112-119 while American has 103–11). === Chondrichthyes === The myomeres of some Chondrichthyes, specifically sharks, are W-shaped. Thus, function in Chondrichthyes
|
{
"page_id": 13108497,
"source": null,
"title": "Myomere"
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|
is similar to that of bony fish, where myomeres contribute to propulsive force for locomotion. === Tetrapods === The myomeres of tetrapods run vertically and do not undergo folding like in bony fishes. Further, in higher order vertebrates, myomeres are fused and run longitudinally. Myosepta are not present in amniotes. In salamanders, hypaxial muscles, myomeres, and myosepta run in a straight line mid-laterally to mid-ventrally. Specifically, the orientation of collagen fibers within these myomeres runs mediolateral. It is also theorized that, in salamanders, myosepta increase the amplification of strain of angled muscle fibers. This controls how myomeres bulge during contraction in what is called the 'bulge control hypothesis'. Salamanders in the genus Necturus (mudpuppies) are a salamander species with simply-lain myomeres, unlike the complex nature of bony fishes. Myomeres also play a role in swimming in adult newts. Specifically, epaxial myomeres located opposite to each other at the same longitudinal site alternate rhythmic contraction. During stepping on the ground, the myomeres of the mid-trunk undergo bursts of contraction that are synchronized in contrast to double bursting patterns (in opposite directions) expressed in the anterior and posterior trunks. == References == == Further reading == De Iuliis, Gerardo; Pulerà, Dino (2019). "Vertebrates and Their Kin". The Dissection of Vertebrates. pp. 1–44. doi:10.1016/B978-0-12-410460-0.00001-2. ISBN 978-0-12-410460-0. Myomeres are the segmented paired muscular blocks that extend through the trunk and tail. Alternating contraction of the musculature of the right and left sides of the body exerts forces on the notochord, noted earlier as a laterally flexible rod, that allow the side-to-side locomotory movements characteristic of less derived chordates and vertebrates. Johnston, I.A. (2008). "The biological basis of variability in the texture of fish flesh". Improving Seafood Products for the Consumer. pp. 465–489. doi:10.1533/9781845694586.5.465. ISBN 978-1-84569-019-9. The fillet is made up of segmentally arranged structures
|
{
"page_id": 13108497,
"source": null,
"title": "Myomere"
}
|
called myotomes or myomeres, the shape of which varies along the length of the body. In three dimensions, the myomeres constitute a series of overlapping cones that are bounded by connective tissue sheets or myocommata called myosepta. Typically, a transverse steak through the fillet will cut through several myotomes at different levels. Each myotome contains a lateral superficial strip of dark muscle primarily composed of slow contracting fibre types that are used for sustained swimming activity (Johnston et al., 1977).
|
{
"page_id": 13108497,
"source": null,
"title": "Myomere"
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This article contains a list of the most studied restriction enzymes whose names start with Bd to Bp inclusive. It contains approximately 100 enzymes. The following information is given: Enzyme: Accepted name of the molecule, according to the internationally adopted nomenclature, and bibliographical references. (Further reading: see the section "Nomenclature" in the article "Restriction enzyme".) PDB code: Code used to identify the structure of a protein in the PDB database of protein structures. The 3D atomic structure of a protein provides highly valuable information to understand the intimate details of its mechanism of action. Source: Organism that naturally produces the enzyme. Recognition sequence: Sequence of DNA recognized by the enzyme and to which it specifically binds. Cut: Cutting site and DNA products of the cut. The recognition sequence and the cutting site usually match, but sometimes the cutting site can be dozens of nucleotides away from the recognition site. Isoschizomers and neoschizomers: An isoschizomer is an enzyme that recognizes the same sequence as another. A neoschizomer is a special type of isoschizomer that recognizes the same sequence as another, but cuts in a different manner. A maximum number of 8-10 most common isoschizomers are indicated for every enzyme but there may be many more. Neoschizomers are shown in bold and green color font (e.g.: BamHI). When "None on date" is indicated, that means that there were no registered isoschizomers in the databases on that date with a clearly defined cutting site. Isoschizomers indicated in white font and grey background correspond to enzymes not listed in the current lists: == Whole list navigation == == Restriction enzymes == === Bd - Bp === == Notes ==
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{
"page_id": 27460882,
"source": null,
"title": "List of restriction enzyme cutting sites: Bd–Bp"
}
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In psychology, memory inhibition is the ability not to remember irrelevant information. The scientific concept of memory inhibition should not be confused with everyday uses of the word "inhibition". Scientifically speaking, memory inhibition is a type of cognitive inhibition, which is the stopping or overriding of a mental process, in whole or in part, with or without intention. Memory inhibition is a critical component of an effective memory system. While some memories are retained for a lifetime, most memories are forgotten. According to evolutionary psychologists, forgetting is adaptive because it facilitates selectivity of rapid, efficient recollection. For example, a person trying to remember where they parked their car would not want to remember every place they have ever parked. In order to remember something, therefore, it is essential not only to activate the relevant information, but also to inhibit irrelevant information. There are many memory phenomena that seem to involve inhibition, although there is often debate about the distinction between interference and inhibition. == History == In the early days of psychology, the concept of inhibition was prevalent and influential (e.g., Breese, 1899; Pillsbury, 1908; Wundt, 1902). These psychologists applied the concept of inhibition (and interference) to early theories of learning and forgetting. Starting in 1894, German scientists Muller and Shumann conducted empirical studies that demonstrated how learning a second list of items interfered with memory of the first list. Based on these experiments, Muller argued that the process of attention was based on facilitation. Arguing for a different explanation, Wundt (1902) claimed that selective attention was accomplished by the active inhibition of unattended information, and that to attend to one of several simultaneous stimuli, the others had to be inhibited. American Psychologist Walter Pillsbury combined Muller and Wundt's arguments, claiming that attention both facilitates information that is wanted and
|
{
"page_id": 5506325,
"source": null,
"title": "Memory inhibition"
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inhibits information that is unwanted. In the face of behaviorism during the late 1920s through the 1950s, and through the early growth of cognitive psychology in the late 1950s and early 1960s, inhibition largely disappeared as a theory. Instead, classical interference theory dominated memory research until as late as 1960. By the early 1970s, however, classical interference theory began to decline due to its reliance on associationism, its inability to explain the facts of interference or how interference applies to everyday life, and to newly published reports on proactive and retroactive inhibition. Since the mid-1980s, there has been a renewed interest in understanding the role of inhibition in cognition. Research on a wide variety of psychological processes, including attention, perception, learning and memory, psycholinguistics, cognitive development, aging, learning disabilities, and neuropsychology, suggests that resistance to interference (which implies capacity for inhibition) is an important part of cognition. More recently, researchers suggest that the hippocampus plays a role in the regulation of disliked and competing memories, and fMRI studies have shown hippocampus activity during inhibition processes. == Empirical research == === Part-set cuing effect === The "part-set cuing effect" was initially discovered by Slamecka (1968), who found that providing a portion of to-be-remembered items as test cues often impairs retrieval of the remaining un-cued items compared with performance in a no-cue (free-recall) control condition. Such an effect is intriguing because normally cues are expected to aid recall (e.g., Tulving & Pearlstone, 1966). A prominent figure in retrieval-based inhibition research, Henry L. Roediger III was another one of the first psychologists to propose the idea that retrieving an item reduces the subsequent accessibility of other stored items. Becoming aware of the part-set cueing effect reduces the effect, such that relearning part of a set of previously learned associations can improve recall of
|
{
"page_id": 5506325,
"source": null,
"title": "Memory inhibition"
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the non-relearned associations. === Hasher and Zacks' inhibition account of aging === Using inhibition to explain memory processes began with the work of Hasher and Zacks (1988), which focused on the cognitive costs associated with aging and bridging the attention-memory gap. Hasher and Zacks found that older adults show impairments on tasks that require inhibiting irrelevant information in working memory, and these impairments may lead to problems in a variety of contexts. === Retrieval-induced forgetting === Anderson and Spellman's model of retrieval-induced forgetting suggests that when items compete during retrieval, an inhibitory process will serve to suppress those competitors. For instance, retrieval of one meaning for a word (e.g. the verb meaning of the word sock) will tend to inhibit the dominant meaning of that word (e.g. the noun meaning of sock). In 1995, Anderson and Spellman conducted a three-phase study using their retrieval-induced forgetting model to demonstrate unlearning as inhibition. Study phase: Participants study a list of category-exemplar pairings where some exemplars are semantically similar in that they belong to another category besides the one they are explicitly paired with (e.g. Food-Cracker, Food-Strawberry, Red-Tomato, Red-Blood). Retrieval-practice phase: Participants are cued to practice remembering some of the exemplars given the category cue (e.g. Red-Bl__). Test phase: Given each category as a cue, the participant tries to recall the exemplar (e.g. Food-C__, Food-S__, Red-T__, Red-Bl__). Anderson and Spellman observed that items that shared a semantic relationship with practiced information was less recallable. Using the example from above, recall of items related to practiced information, including tomato and strawberry was lower than recall for cracker, even though strawberry is part of a different pair. This finding suggests that associative competition by explicit category cue is not the only factor in retrieval difficulty. They theorized that the brain suppresses, or inhibits, non-practiced attributes.
|
{
"page_id": 5506325,
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"title": "Memory inhibition"
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This explains why an item that is very similar to tomato, but not from the same pair, also exhibits decreased recall rate. === "Think/no-think" paradigm and intentional inhibition === During the recovered memory debate of the 1990s, cognitive psychologists were dubious about whether specific memories could be repressed. One stumbling block was that repression had not been demonstrated in a research study. In 2001, researchers Anderson and Green claimed to have found laboratory evidence of suppression. They trained their participants with a list of unrelated word pairs (such as ordeal-roach), so they could respond with the second member of the pair (roach) when they saw the other member (ordeal). The more frequently participants had tried to not think about a particular word, the less likely they were to retrieve it on a final memory test. This impairment even occurred when participants were given an "independent probe" test, i.e. given a similar category (insect) instead of the original cue (roach), and asked to fill in the blank on the memory test: insect-r_____. According to Anderson and Green, the fact that participants had a decreased ability to recall items they were told to forget strongly supports the existence of an inhibitory control mechanism and the idea that people have the ability to suppress unwanted memories. Though Anderson & Green's (2001) results have been replicated several times, a group of prominent psychology researchers using the same methodology as the original study were unable to replicate even the basic result (Bulevich, Roediger, Balota, & Butler, 2006). They determined that suppression is not a robust experimental phenomenon in the think/no-think paradigm and suggested that Anderson and Green's findings could be explained by retroactive interference, or simply thinking about X when told to "not think" about Y. == Amnesia for trauma or abuse == Amnesia, the
|
{
"page_id": 5506325,
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"title": "Memory inhibition"
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forgetting of important personal information, usually occurs because of disease or injury to the brain, while psychogenic amnesia, which involves a loss of personal identity and has psychological causes, is rare. Nonetheless, a range of studies have concluded that at least 10% of physical and sexual abuse victims forget the abuse. Some studies claim that the rate of delayed recall of many forms of traumatic experiences (including natural disasters, kidnapping, torture and more) averages among studies at approximately 15%, with the highest rates resulting from child sexual abuse, military combat, and witnessing a family member murdered. A 1996 interview survey of 711 women reported that forgetting and later remembering childhood sexual abuse is not uncommon; more than a quarter of the respondents who reported abuse also reported forgetting the abuse for some period of time and then recalling it on their own. Of those who reported abuse, less than 2% reported that the recall of the abuse was assisted by a therapist or other professional. Other studies show that people who have experienced trauma usually remember it, not forget it. McNally (2001) found that women who report having either repressed or recovered memories of childhood sexual abuse have no worse memory for trauma cue words than women who have never been sexually abused. Similarly, McNally (1998) found that women who were sexually abused as children and who developed PTSD as a result of their abuse will not have any more trouble recalling trauma related words than healthy adult survivors of childhood sexual abuse or women who were never abused as children. Although the rate of recall of previously forgotten traumatic events was shown by Elliot and Briere (1996) to be unaffected by whether or not the victim had a history of being in psychotherapy, individuals who report repressed memories are
|
{
"page_id": 5506325,
"source": null,
"title": "Memory inhibition"
}
|
more susceptible to producing false memories than individuals who could always recall the memory. Williams found that among women with confirmed histories of sexual abuse, approximately 38% did not recall the abuse 17 years later, especially when it was perpetrated by someone familiar to them. Hopper cites several studies which indicate that some abuse victims will have intervals of complete amnesia for their abuse. Peer reviewed and clinical studies have documented the existence of recovered memory; one website lists 43 legal cases where an individual whose claim to have recovered a repressed memory has been accepted by a court. Traumatic amnesia, which allegedly involves the forgetting of specific traumatic events for long periods of time, is highly controversial, as is repression, the psychodynamic explanation of traumatic amnesia. Because these concepts lack good empirical support, psychological scientists are skeptical about the validity of "recovered memories", and argue that some therapists, through suggestive techniques, have (un)knowingly encouraged false memories of victimization. == Evidence against == The idea that subjects can actively inhibit a memory has many critics. MacLeod (2003) challenged the idea of inhibition in cognitive control, arguing that inhibition can be attributed to conflict resolution, which is the error-prone act of choosing between two similar values that do not necessarily have the same pair. Re-examine the pairs from above: Food-Cracker, Food-Strawberry, Red-Tomato, and Red-Blood. Memory inhibition theories suggest that recall of strawberry decreases when recall of tomato decreases because tomato's attributes are inhibited when red-blood is learned. MacLeod argues that inhibition does not take place, but instead is the result of confusion between similar word-pairs like food-tomato and red-strawberry that can lead to errors. This is different from tomato's attributes being inhibited. "In most cases where inhibitory mechanisms have been offered to explain cognitive performance", explains MacLeod, "non-inhibitory mechanisms can accomplish
|
{
"page_id": 5506325,
"source": null,
"title": "Memory inhibition"
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the same goal" (p. 203). == See also == Emotion and memory Interference theory == References == == External links == Anderson's Memory Control Laboratory Daniel Wegner's Thought Suppression Papers Neural Systems Underlying the Suppression of Unwanted Memories Sison, Jo Ann G.; Mather, Mara (2007). "Does remembering emotional items impair recall of same-emotion items?". Psychonomic Bulletin & Review. 14 (2): 282–287. doi:10.3758/BF03194065. PMID 17694914. (emotional part-set cuing effects) Innocence Project: an organization dedicated to exonerating wrongfully convicted individuals
|
{
"page_id": 5506325,
"source": null,
"title": "Memory inhibition"
}
|
The molecular formula C5H7N3 may refer to: Brunfelsamidine, a poisonous plant derivative, which has convulsant and neurotoxic effects 3,4-Diaminopyridine, compound predominantly used as a drug in the treatment of rare muscle diseases
|
{
"page_id": 36963607,
"source": null,
"title": "C5H7N3"
}
|
The molecular formula C16H10O5 (molar mass: 282.24 g/mol, exact mass: 282.052823 u) may refer to: Damnacanthal, an anthraquinone Pseudobaptigenin, an isoflavone
|
{
"page_id": 26346775,
"source": null,
"title": "C16H10O5"
}
|
An Measured Environmental Concentration (MEC) relates to a chemical substance found in an environmental sample. The concentration of the compound may result from direct contamination, transformation and/or metabolization of a different chemical contaminant, natural origin or a combination of these sources. MEC is to be used as a reference in the context of Chemical Safety Assessments (CSA) and should be compared with the respective Predicted Environmental Concentration (PEC) and Predicted No-Effect Concentration (PNEC) in order to decide whether exposure model is valid and the compound related risk is controlled. == References ==
|
{
"page_id": 25625880,
"source": null,
"title": "Measured environmental concentration"
}
|
The molecular formula C23H28N4O3 (molar mass: 408.50 g/mol) may refer to: Etonitazepipne (N-piperidino etonitazene) Isotonitazepyne Protonitazepyne
|
{
"page_id": 74712348,
"source": null,
"title": "C23H28N4O3"
}
|
Sandip Trivedi (Hindi: सन्दिप त्रिवेदी; born 1963) is an Indian theoretical physicist working at Tata Institute for Fundamental Research (TIFR) at Mumbai, India, where had been the director. He is well known for his contributions to string theory, in particular finding (along with Renata Kallosh, Andrei Linde, and Shamit Kachru) the first models of accelerated expansion of the universe in low energy supersymmetric string (see KKLT mechanism). His research areas include string theory, cosmology and particle physics. He is now member of program advisory board of International Center for Theoretical Sciences (ICTS). He is also the recipient of the Infosys Prize 2010 in the category of Physical Sciences. == Education == He completed his master of science (Integrated) in physics from IIT Kanpur in 1985. He was awarded his PhD in 1990 from Caltech, Pasadena, USA. Later he went on to work as a post-doctoral research associate at IAS, Princeton until 1992. == Awards == He won the prestigious Shanti Swarup Bhatnagar Award in the Physical Sciences in 2005. He was the recipient of the Infosys Prize 2010 in the category of Physical Sciences. He is also a recipient of the TWAS Prize in Physics in 2015. == References == == External links == Sandip Trivedi's Home Page at TIFR List of Publications on SPIRES
|
{
"page_id": 21759262,
"source": null,
"title": "Sandip Trivedi"
}
|
Jiaya Jia (Chinese: 贾佳亚) is a Chair Professor of the Department of Computer Science and Engineering at The Hong Kong University of Science and Technology (HKUST). He is an IEEE Fellow, the associate editor-in-chief of one of IEEE’s flagship and premier journals- Transactions on Pattern Analysis and Machine Intelligence (TPAMI), as well as on the editorial board of International Journal of Computer Vision (IJCV). == Early life and education == Jiaya Jia joined CUHK in 2004 as an assistant professor, and was promoted to full professor in 2015. He obtained his PhD degree in computer science jointly from Hong Kong University of Science and Technology and Microsoft Research in 2004. From March 2003 to August 2004, he was a visiting scholar at Microsoft. He conducted collaborative research at Adobe Research in 2007. == Career == Jiaya Jia is a distinguished scientist in the fields of computer vision and artificial intelligence. His research team at HKUST, DV Lab, is one of the largest vision AI research teams in the world and has been making significant contribution to advanced development of computer vision algorithms and technologies with focuses on image/video understanding, detection and segmentation, multi-modal AI, computational imaging, practical optimization, and advanced learning for visual content since 2000. Jiaya Jia has published 200+ top papers and was cited 80,000+ times on Google Scholar with H-Index 110+. 40+ PhDs and fellows from this group are now active in academia and industry, and have become prominent AI tech leaders as professors, directors in major research labs, and founders of several successful startups. Jiaya Jia assumes the position of associate editor-in-chief of IEEE Transactions on Pattern Analysis and Machine Intelligence (TPAMI) since 2021. He is also on the editorial board of International Journal of Computer Vision (IJCV). Jiaya Jia has served as the area chair
|
{
"page_id": 69469471,
"source": null,
"title": "Jiaya Jia"
}
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of ICCV, CVPR, AAAI, ECCV, and several other premium international AI conferences for years. He was on program committees of major conferences in graphics and computational imaging, including ICCP, SIGGRAPH, and SIGGRAPH Asia. == Research == The research areas of Jiaya Jia are computer vision, large X models, and deep learning. Jiaya Jia has made outstanding contributions to computer vision technology, algorithms and engineering, and is among the world's leading experts in the field. His research partners include numerous renowned multinational technology companies, such as Microsoft, Qualcomm, Adobe, Intel, NVIDIA, Amazon, and Lenovo. Jia has cultivated a number of outstanding talents with Master's and PhDs who continue to engage in scientific research and development in computer vision. Many technologies in image analysis and processing developed by Jiaya Jia are still leading in the field worldwide. Wherein, his achievements in image deblurring, filtering, image sparse processing, multi-band image signal fusion and enhancement, large range motion estimation, texture and structure-based layering, etc. have been published in the industry's most influential conferences and publications, and implemented in the real-world applications. These achievements have demonstrated outstanding performance in established systems, and most of which are open source so as to enable wider applications across industries such as aviation, medical imaging, safety management, robotic design, meteorological analysis and many more. == Selected publications == In his over 20 years of research experience, Jiaya Jia has published 200+ top papers that have been cited more than 80,000 times. According to HKUST Website in August 2024, Jiaya Jia has accumulatively published over 200 scientific papers in books, journals and conferences, such as IEEE Transactions on Pattern Analysis and Machine Intelligence (TPAMI), International Journal of Computer Vision (IJCV) "Computer Vision and Pattern Recognition (CVPR)", and "International Conference on Computer Vision (ICCV)". Representative papers include: Jiaya Jia: Mathematical Models
|
{
"page_id": 69469471,
"source": null,
"title": "Jiaya Jia"
}
|
and Practical Solvers for Uniform Motion Deblurring (in Motion Deblurring: Algorithms and Systems), Cambridge University Press, ISBN 9781107044364, 2014; Jiaya Jia: “Matte Extraction” Book: Computer Vision - A Reference Guide, Springer, ISBN 9780387307718 Editor-in-chief: Ikeuchi, Katsushi; Jiaya Jia, Chi-Keung Tang：Image Stitching Using Structure Deformation，IEEE Transactions on Pattern Analysis and Machine Intelligence (TPAMI), Vol. 30, No. 4, 2008; Jiaya Jia, Jian Sun, Chi-Keung Tang, Heung-Yeung Shum：Drag-and-Drop Pasting，ACM Transactions on Graphics (also in SIGGRAPH 2006), Vol. 25, No. 3, 2006. Xiaojuan Qi, Zheng zhe Liu, Renjie Liao, Philip HS Torr, Raquel Urtasun, Jiaya Jia：GeoNet++: Iterative Geometric Neural Network with Edge-Aware Refinement for Joint Depth and Surface Normal Estimation，IEEE Transactions on Pattern Analysis and Machine Intelligence (TPAMI). Accepted. == Selected honors and awards == Associate editor-in-chief of IEEE Transactions on Pattern Analysis and Machine Intelligence (TPAMI) since 2021, the associate editor-in-chief in 42 years since the journal was published; Area chair for CVPR 2021, AAAI 2021, and ICCV 2021; Area chair for CVPR 2020, AAAI 2020, and ECCV 2020; 1st Place of WAD Drivable Area Segmentation Challenge 2018; 1st Place of LSUN'17 Instance and Semantic Segmentation Challenges; 1st Place of COCO Instance Segmentation Challenge 2017; 2nd Place in COCO Detection Challenge 2017; 1st Place of ImageNet Scene Parsing Challenge 2016 with the paper PSPNet presented in CVPR 2017. == References ==
|
{
"page_id": 69469471,
"source": null,
"title": "Jiaya Jia"
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New eugenics, also known as liberal eugenics (a term coined by bioethicist Nicholas Agar), advocates enhancing human characteristics and capacities through the use of reproductive technology and human genetic engineering. Those who advocate new eugenics generally think selecting or altering embryos should be left to the preferences of parents, rather than forbidden (or left to the preferences of the state). New eugenics purports to distinguish itself from the forms of eugenics practiced and advocated in the 20th century, which fell into disrepute after World War II. == New eugenics practices == Eugenics is sometimes broken into the categories of positive eugenics (encouraging reproduction among the designated "fit") and negative eugenics (discouraging or prohibiting reproduction among those designated "unfit"). Both positive and negative eugenic programs were advocated and pursued during the early 20th century. Negative programs were responsible for the compulsory sterilization of hundreds of thousands of persons in many countries, and were included in much of the rhetoric of Nazi eugenic policies of racial hygiene and genocide. According to its proponents, new eugenics belongs in the category of positive eugenics. New eugenics generally supports genetic modification or genetic selection of individuals for traits that are supposed to improve human welfare. The underlying idea is to improve the genetic basis of future generations and reduce incidence of genetic diseases and other undesirable traits. Some of the practices included in new eugenics are: pre-implantation diagnosis and embryo selection, selective breeding, and human embryo engineering and gene therapy. == Ethical status == New eugenics was founded under the liberal ethical values of pluralism, which advocates for the respect of personal autonomy, and egalitarianism, which represents the idea of equality for all people. Arguments used in favor of new eugenics include that it is in the best interest of society that life succeeds rather
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{
"page_id": 1115424,
"source": null,
"title": "New eugenics"
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than fail, and that it is acceptable to ensure that progeny has a chance of achieving this success. Ethical arguments against new eugenics include the claim that creating designer babies is not in the best interest of society as it might create a breach between genetically modified individuals and natural individuals. Additionally, some of these technologies might be economically restrictive, further increasing the socio-economical gap. Dov Fox, a law professor at the University of San Diego, argues that liberal eugenics cannot be justified on the basis of the underlying liberal theory which inspires its name. Instead he favors traditional, coersive eugenics, arguing that reprogenetic technologies like embryo selection, cellular surgery, and human genetic engineering, which aim to enhance general purpose traits in offspring, are not practices a liberal government leaves to the discretion of parents, but practices the state makes compulsory. Fox argues that if the liberal commitment to autonomy is important enough for the state to mandate childrearing practices such as health care and basic education, that very same interest is important enough for the state to mandate safe, effective, and functionally integrated genetic practices that act on analogous all-purpose traits such as resistance to disease and general cognitive functioning. He concludes that the liberal case for compulsory eugenics is a reductio ad absurdum against liberal theory. The United Nations International Bioethics Committee wrote that new eugenics should not be confused with the ethical problems of the 20th century eugenics movements. They have also stated the notion is nevertheless problematic as it challenges the idea of human equality and opens up new ways of discrimination and stigmatization against those who do not want or cannot afford the enhancements. == See also == Biohappiness Directed evolution (transhumanism) Mendelian inheritance Eugenics in France == References == == Further reading ==
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{
"page_id": 1115424,
"source": null,
"title": "New eugenics"
}
|
Noruron (or norea) is a premërgent urea herbicide active ingredient. It is considered obsolete, but may still be used. Introduced in the US in 1062, was used to control grass weeds and broadleaf weeds on crops including broomcorn, cotton, potatoes, sugarcane, spinach, soybeans and sorghum. Noruron is not approved for use in the EU. Noruron is stereochemically racemic, with 5 stereocenters. It is a chiral molecule, and the technical grade stuff is mixed from two racemates. Noruron is applied at 0.75 to 4 kg/ha of active ingredient, typically supplied as wettable powder or granules. It has been sold under the tradename "Herban", a 76% norea wettable powder. == References ==
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{
"page_id": 80020768,
"source": null,
"title": "Noruron"
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The Harvard Computers were a team of women working as skilled workers to process astronomical data at the Harvard College Observatory in Cambridge, Massachusetts, United States. The team was directed by Edward Charles Pickering (1877 to 1919) and, following his death in 1919, by Annie Jump Cannon. The women were challenged to make sense of these patterns by devising a scheme for sorting the stars into categories. Annie Jump Cannon's success at this activity made her famous in her own lifetime, and she produced a stellar classification system that is still in use today. Antonia Maury discerned in the spectra a way to assess the relative sizes of stars, and Henrietta Leavitt showed how the cyclic changes of certain variable stars could serve as distance markers in space. Other computers on the team included Mary Anna Draper, Williamina Fleming, Anna Winlock, and Florence Cushman. Although these women started primarily as calculators, they made significant contributions to astronomy, much of which they published in research articles. == History == In the 19th century, the Harvard College Observatory faced the challenge of working through an overwhelming amount of astronomical data due to improvements in photographic technology. Harvard Observatory's director, Edward Charles Pickering, hired a group of women to analyze the astronomical data. While Pickering was the director of the Harvard Observatory, he hired over eighty women. These women were known as computers. Although Pickering believed that gathering data at astronomical observatories was not the most appropriate work, it seems that several factors contributed to his decision to hire women instead of men. Among them was that men were paid much more than women, so he could employ more staff with the same budget. This was relevant in a time when the amount of astronomical data was surpassing the capacity of the Observatories
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to process it. Although some of Pickering's female staff were astronomy graduates, their wages were similar to those of unskilled workers. They usually earned between 25 and 50 cents per hour (between $8 and $16 in 2024), more than a factory worker but less than a clerical one. Most of the women depended financially on their friends and family members and lived with coworkers to combat the low wages. Although the wages Pickering provided were low, it was common to pay women less than men during the 20th century and does not discount his advocation for women in astronomy. In describing the dedication and efficiency with which the Harvard Computers, including Cushman, undertook this effort, Edward Pickering said, "a loss of one minute in the reduction of each estimate would delay the publication of the entire work by the equivalent of the time of one assistant for two years." Another reason why Pickering decided to hire women over men was he thought allowing women to conduct astronomical research would show the general public that women were capable of higher thinking and worthy of higher education. The first female computer to be hired at the Harvard Observatory was Anna Winlock. Pickering's first hire was Williamina Fleming six years later in 1881. Together, Fleming and Pickering continued to hire female computers through the twentieth century. At times women offered to work at the observatory for free in order to gain experience in a field that was difficult to get into. The computer position was one of the lower class positions at the observatory due to the pay and little chance for promotion. Under the Henry Draper Memorial project, the women were often tasked with measuring the brightness, position, and color of stars. The goal of the project was to photograph the stars
|
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and classify their spectrum. Their work was often segregated from men, so teams of male astronomers would take photographs of the stars in the evening and send them to the women at Harvard for analysis. The work included such tasks as classifying stars by calculating their exact position and movement, predicting the return of comets, and by comparing the photographs to known catalogs and reducing the photographs while accounting for things like atmospheric refraction, parallax, and error in various instruments in order to render the clearest possible image. While the work was repetitive, it still required attention and accuracy. Fleming herself described the work as "so nearly alike that there will be little to describe outside ordinary routine work of measurement, examination of photographs, and of work involved in the reduction of these observations". The work would not have been possible without photographic plate technology. With such technology, dry, color sensitive plates are used to capture photo visual and photo-red magnitudes. The dry plates allowed for longer exposure over longer time intervals, increasing the accuracy of the photographs and range of stars capable of being photographed. The plate technology allowed the women to classify stars more accurately than before. The observatory, with the help of computers, made several breakthroughs in classifying and cataloging the stars. One such accomplishment was the Henry Draper Catalogue. Following the death of Henry Draper (1882), Mary Anna Palmer Draper funded the Mount Wilson Observatory. The work on the catalogue was led by Williamina Fleming. Following the initial classifications done by Fleming (1890), Antonia Maury helped place stars in their correct positions and did further research on the spectra of the stars with Pickering (1901). Henrietta Leavitt discovered a relationship between a Cepheid variable’s brightness and its pulsation period (1908). Annie Jump Cannon and her team
|
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classified an average of 5,000 stars per month from the years 1912–1915. Florence Cushman helped organize and process the data. The catalog was published between 1918 and 1924. Following the death of Pickering (1919), Cannon took control of the projects. An extension to the original works was published between 1925 and 1936, where over 46,850 stars were classified. In the later years of the program, following the publication of the catalog, several women joined and continued to make contributions. Margaret Walton Mayall contributed to the classification of stellar spectra. She later went on to lead the American Association of Variable Star Observers. Helen Sawyer Hogg specialized in cataloging variable stars within globular clusters. Her work helped lay the foundation for understanding stellar evolution and the structure of the universe. Cecilia Payne-Gaposchkin proved that stars are composed primarily of hydrogen and helium. Muriel Mussells Seyfert discovered three new ring nebulae on photographic plates, expanding the catalog of known planetary nebulae. == Notable members == === Mary Anna Palmer Draper === Mary Anna Palmer Draper (1839–1914) was an American astronomer who helped found the Mount Wilson Observatory. Draper was the widow of Dr. Henry Draper, an astronomer who died before completing his work on the chemical composition of stars. She was very involved in her husband's work and wanted to finish his classification of stars after he died. Mary Draper quickly realized the task facing her was far too daunting for one person. She had received correspondence from Mr. Pickering, a close friend of hers and her husband's. Pickering offered to help finish her husband's work, and encouraged her to publish his findings up to the time of his death. Draper agreed to give Pickering the plates her husband had been working on, but took them to Harvard University herself since the
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plates were very small. While at the university, Draper met the Harvard Observatory's current computers and was able to observe some of the observatory's current projects. After some deliberation and much consideration, Draper decided in 1886 to donate money and a telescope of her husband's to the Harvard Observatory in order to photograph the spectra of stars. She had decided this would be the best way to continue her husband's work and erect his legacy in astronomy. She was very insistent on funding the memorial project with her own inheritance, as it would carry on her husband's legacy. She was a dedicated follower of the observatory and a great friend of Pickering's. In 1900, she funded an expedition to see the total solar eclipse occurring that year. === Williamina Fleming === Williamina Fleming (1857–1911) was a Scottish immigrant astronomer who helped with the photographic classification of stellar spectra. Fleming had no prior relation to Harvard, as she was a Scottish immigrant working as Pickering's housemaid. Her first assignment was to improve an existing catalog of stellar spectra, which later led to her appointment as head of the ‘’Henry Draper Catalogue’’ project. Fleming went on to help develop a classification of stars based on their hydrogen content, as well as play a major role in discovering the strange nature of white dwarf stars. Williamina continued her career in astronomy when she was appointed Harvard's Curator of Astronomical Photographs in 1899, also known as Curator of the Photographic Plates. At the age of 42, Fleming became the first woman at the observatory to hold a title of such nature. She remained the only woman curator until the 1950s. Her work also led to her becoming the first female American citizen to be elected to the Royal Astronomical Society in 1907. Throughout her
|
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career, Fleming was able to classify 10,000 spectra and found over 50 nebulae and over 300 stars. Fleming did not retire from working at the observatory, as she died at age 54 from pneumonia. === Antonia Maury === Antonia Maury (1866-1952) was an American astronomer who worked on calculating the orbit of a spectroscopic binary. Maury was the niece of Henry Draper, and after recommendation from Mrs. Draper, was hired as a computer at the age of 22. She was a graduate from Vassar College with honors in physics, astronomy, and philosophy. Pickering was uncomfortable paying the average computer salary to someone with Antonia Maury's achievements, but ultimately ended up hiring her. Maury was first tasked with the spectral measurement of some of the brightest stars. Pickering then tasked Maury with reclassifying some of the stars after the publication of the Henry Draper Catalog. In 1889, Maury studied images of Mizar and found out that it was actually two stars based on two K-lines that became visible for the star every few weeks. Antonia took it upon herself to improve and redesigned the system of classification which was later adopted by the International Astronomical Union. Maury left the observatory in 1891 to begin teaching at the Gilman School in Cambridge Massachusetts. Later, Maury would return to the observatory in 1893 and 1895 to publish many of her observations of stellar spectra. Her work was finished with the help of Pickering and the computing staff and was published in 1897. Maury would return to Harvard College Observatory in 1918 as an adjunct professor. During this time, Maury's work began to be published under her own name due in part to the director Harlow Shapely. She would remain at the observatory until she retired in 1948. === Anna Winlock === Anna Winlock
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(1857–1904) was an American astronomer who helped catalog stars for the Henry Draper Catalogue. Some of the first women who were hired to work as computers had familial connections to the Harvard Observatory’s male staff. For instance, Winlock, one of the first of the Harvard Computers, was the daughter of Joseph Winlock, the third director of the observatory and Pickering’s immediate predecessor. Anna Winlock joined the observatory in 1875 to assist in supporting her family after her father's unexpected passing. She tackled her father's unfinished data analysis, performing the arduous work of mathematically reducing meridian circle observations, which rescued a decade's worth of numbers that had been left in a useless state. Winlock also worked on a stellar cataloging section called the "Cambridge Zone". Working over twenty years on the project, the work done by her team on the Cambridge Zone contributed significantly to the Astronomische Gesellschaft Katalog, which contains information on more than one-hundred thousand stars and is used worldwide by many observatories and their researchers. Within a year of Anna Winlock's hiring, three other women joined the staff: Selina Bond, Rhoda Sauders, and a third, who was likely a relative of an assistant astronomer. In 1886, Anna's younger sister, Louisa Winlock, joined her in the computing room. === Annie Jump Cannon === Annie Jump Cannon (1863–1941) was an American astronomer who make a catalog of the stars, classifying and recording them. Following the death of Pickering in 1901 she took control over the observatory. Pickering hired Cannon, a graduate of Wellesley College, to classify the southern stars. While at Wellesley, she took astronomy courses from one of Pickering's star students, Sarah Frances Whiting. She became the first female assistant to study variable stars at night. She studied the light curve of variable stars which could help suggest the
|
{
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type and causation of variation. Cannon, adding to work done by fellow computer Antonia Maury, greatly simplified [Pickering and Fleming's star classification based on temperature] system, and in 1922, the International Astronomical Union adopted [Cannon's] as the official classification system for stars....During Pickering’s 42-year tenure at the Harvard Observatory, which ended only a year before he died, in 1919, he received many awards, including the Bruce Medal, the Astronomical Society of the Pacific’s highest honor. Craters on the moon and on Mars are named after him. And Annie Jump Cannon’s enduring achievement was dubbed the Harvard—not the Cannon—system of spectral classification. Cannon's Harvard Classification Scheme is the basis of the today's familiar O B A F G K M system. She also categorized the variable stars into tables so they could be identified and compared more easily. These systems connect the color of stars to their temperature. According to Rebecca Dinerstein Knight, Cannon was able to work at a pace of classifying the spectra of 300 stars an hour and therefore was able to classify over 350,000 stars in her lifetime. Cannon was the first female scientist to be recognized for many awards and titles in her field of study. She was the first woman to receive an honorary doctorate from the University of Oxford and the Henry Draper Medal from the National Academy of Sciences, and the first female officer in the American Astronomical Society. Cannon went on to establish her own Annie Jump Cannon Award for women in postdoctoral work. In 1934, Cannon awarded the first Annie Jump Cannon Award to Cecilia Payne-Gaposchkin for her contributions in analyzing stars and the stellar spectrum. The award was given out at an American Astronomical Society meeting, and for winning, Cannon awarded Gaposchkin $50 and a gold pin. === Henrietta Leavitt
|
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=== Henrietta Swan Leavitt (1868-1921) was an American astronomer who worked to measure the distances between galaxies and determine the scale of modeling. Leavitt arrived at the observatory in 1893. She had experience through her college studies, traveling abroad, and teaching. In academia, Leavitt excelled in mathematics courses at Cambridge. When she began working at the observatory she was tasked with measuring star brightness through photometry. She found hundreds of new variable stars after starting to analyze the Great Nebula in Orion and her work was expanded to study the variables of the entire sky with Annie Jump Cannon and Evelyn Leland. With skills gained in photometry, Leavitt compared stars in different exposures. Studying Cepheid variables in the Small Magellanic Cloud, she discovered that their apparent brightness was dependent on their period. Since all those stars were approximately the same distance from Earth, that meant their absolute brightness must depend on their period as well, allowing the use of Cepheid variables as a standard candle for determining cosmic distances. That, in turn, led directly to the modern understanding of the true size of the universe, and Cepheid variables are still an essential rung in the cosmic distance ladder. Pickering published her work with his name as co-author. The legacy she left allowed future scientists to make further discoveries in space. Astronomer Edwin Hubble used Leavitt's method to calculate the distance of the nearest galaxy to the earth, the Andromeda Galaxy. This led to the realization that there are even more galaxies than previously thought. === Florence Cushman === Florence Cushman (1860–1940) was an American astronomer at the Harvard College Observatory who worked on the Henry Draper Catalogue. Cushman was born in Boston, Massachusetts in 1860 and received her early education at Charlestown High School, where she graduated in 1877. In
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1888, she began work at the Harvard College Observatory as an employee of Edward Pickering. Her classifications of stellar spectra contributed to Henry Draper Catalogue between 1918 and 1934. She stayed as an astronomer at the Observatory until 1937 and died in 1940 at the age of 80. Cushman worked at the Harvard College Observatory from 1918 to 1937. Over the course of her nearly fifty-year career, she employed the objective prism method to analyze, classify, and catalog the optical spectra of hundreds of thousands of stars. In the 19th century, the photographic revolution enabled more detailed analysis of the night sky than had been possible with solely eye-based observations. In order to obtain optical spectra for measurement, male astronomers at the Harvard College Observatory expose glass plates on which the astronomical images were captured at night. During the daytime, female assistants like Florence analyzed the resultant spectra by reducing values, computing magnitudes, and cataloging their findings. She is credited with determining the positions and magnitudes of the stars listed in the 1918 edition of the Henry Draper Catalogue, which featured the spectra of roughly 222,000 stars. == See also == Evelyn Leland Cecilia Payne-Gaposchkin Muriel Mussells Seyfert == References == == Further reading == Natasha Geiling; Geiling, Natasha (September 18, 2013). "The Women Who Mapped the Universe And Still Couldn't Get Any Respect". Smithsonian Magazine. == External links == Women Astronomical Computers at the Harvard College Observatory Official Harvard Plate Stacks Website Remarkable Women Stories. The Harvard Astronomical Computers: Stargazers who made history
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Backcrossing is a crossing of a hybrid with one of its parents or an individual genetically similar to its parent, to achieve offspring with a genetic identity closer to that of the parent. It is used in horticulture, animal breeding, and production of gene knockout organisms. Backcrossed hybrids are sometimes described with acronym "BC"; for example, an F1 hybrid crossed with one of its parents (or a genetically similar individual) can be termed a BC1 hybrid, and a further cross of the BC1 hybrid to the same parent (or a genetically similar individual) produces a BC2 hybrid. == Plants == === Advantages === If the recurrent parent is an elite genotype, at the end of the backcrossing programme, an elite genotype is recovered. As no "new" recombination results, the elite combination is not lost. === Disadvantages === It works poorly for quantitative traits. It is more restricted for recessive traits. In practice, sections of genome from the nonrecurrent parents are often still present and can have unwanted traits associated with them. For very wide crosses, limited recombination may maintain thousands of "alien" genes within the elite cultivar. Many backcrosses are required to produce a new cultivar, which can take many years. === Natural backcrossings === York radiate groundsel (Senecio eboracensis) is a naturally occurring hybrid species of Oxford ragwort (Senecio squalidus) and common groundsel (Senecio vulgaris). It is thought to have arisen from a backcrossing of the F1 hybrid with S. vulgaris. Again, the pure tall (TT) and pure dwarf (tt) pea plants when crossed in the parental generation, produce all heterozygote (Tt) tall pea plants in the first filial generation. The cross between first filial heterozygote tall (Tt) pea plant and pure tall (TT) or pure dwarf (tt) pea plant of the parental generation is also an example for
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{
"page_id": 787748,
"source": null,
"title": "Backcrossing"
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the back-crossing between two plants. In this case, the filial generation formed after the back cross may have a phenotype ratio of 1:1 if the cross is made with recessive parent or else all offspring may be having phenotype of dominant trait if the backcross is with a parent having the dominant trait. The former of these traits is also called a test cross. === Artificially recombinant lines === In plants, the term inbred backcross line (IBL) refers to a line (i.e. population) of plants derived from the repeated backcrossing of a line with artificially recombinant DNA with the wild type, operating some kind of selection that can be phenotypical or through a molecular marker (for the production of an introgression line). == Animals == Backcrossing may be deliberately employed in animals to transfer a desirable trait in an animal of inferior genetic background to an animal of preferable genetic background. In gene-knockout experiments in particular, where the knockout is performed on easily cultured stem cell lines, but is required in an animal with a different genetic background, the knockout animal is backcrossed against the animal of the required genetic background. As the figure shows, each time that the mouse with the desired trait (in this case the lack of a gene (i.e. a knockout), indicated by the presence of a positive selectable marker) is crossed with a mouse of a constant genetic background, the average percentage of the genetic material of the offspring that is derived from that constant background increases. The result, after sufficient reiterations, is an animal with the desired trait in the desired genetic background, with the percentage of genetic material from the original stem cells reduced to a minimum (on the order of 0.01%). Due to the nature of meiosis, in which chromosomes derived from
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{
"page_id": 787748,
"source": null,
"title": "Backcrossing"
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each parent are randomly shuffled and assigned to each nascent gamete, the percentage of genetic material deriving from either cell line varies between offspring of a single crossing, but will have an expected value. The genotype of each member of offspring may be assessed to choose not only an individual that carries the desired genetic trait, but also the minimum percentage of genetic material from the original stem cell line. A consomic strain is an inbred strain with one of its chromosomes replaced by the homologous chromosome of another inbred strain via a series of marker-assisted backcrosses. == See also == Introgression Incest == References == == External links == The Plant Breeding and Genomics Community of Practice on eXtension - education and training materials for plant breeders and allied professionals
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{
"page_id": 787748,
"source": null,
"title": "Backcrossing"
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A dense heterarchy is a hierarchical organization in social insect colonies in which the higher levels affect the lower levels and lower levels eventually influence the higher levels. Individual ants within the colony network are likely to have many connections with one another – making the network denser and non-hierarchical. Because there is no highest level within a heterarchy but the heterarchy itself, control is decentralized (not controlled by the queen). Communication between individuals in a dense heterarchy occurs directly between individuals and through stigmergy. Feedback loops of communication can produce emergent properties not obvious when only examining singular activities or communication. == References ==
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{
"page_id": 17302821,
"source": null,
"title": "Dense heterarchy"
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Imaginary time is a mathematical representation of time that appears in some approaches to special relativity and quantum mechanics. It finds uses in certain cosmological theories. Mathematically, imaginary time is real time which has undergone a Wick rotation so that its coordinates are multiplied by the imaginary unit i. Imaginary time is not imaginary in the sense that it is unreal or made-up; it is simply expressed in terms of imaginary numbers. == Origins == In mathematics, the imaginary unit i {\displaystyle i} is − 1 {\displaystyle {\sqrt {-1}}} , such that i 2 {\displaystyle i^{2}} is defined to be − 1 {\displaystyle -1} . A number which is a direct multiple of i {\displaystyle i} is known as an imaginary number.: Chp 4 A number that is the sum of an imaginary number and a real number is known as a complex number. In certain physical theories, periods of time are multiplied by i {\displaystyle i} in this way. Mathematically, an imaginary time period τ {\textstyle \tau } may be obtained from real time t {\textstyle t} via a Wick rotation by π / 2 {\textstyle \pi /2} in the complex plane: τ = i t {\textstyle \tau =it} .: 769 Stephen Hawking popularized the concept of imaginary time in his book The Universe in a Nutshell. "One might think this means that imaginary numbers are just a mathematical game having nothing to do with the real world. From the viewpoint of positivist philosophy, however, one cannot determine what is real. All one can do is find which mathematical models describe the universe we live in. It turns out that a mathematical model involving imaginary time predicts not only effects we have already observed but also effects we have not been able to measure yet nevertheless believe in for
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{
"page_id": 2884904,
"source": null,
"title": "Imaginary time"
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|
other reasons. So what is real and what is imaginary? Is the distinction just in our minds?" In fact, the terms "real" and "imaginary" for numbers are just a historical accident, much like the terms "rational" and "irrational": "...the words real and imaginary are picturesque relics of an age when the nature of complex numbers was not properly understood." == In cosmology == === Derivation === In the Minkowski spacetime model adopted by the theory of relativity, spacetime is represented as a four-dimensional surface or manifold. Its four-dimensional equivalent of a distance in three-dimensional space is called an interval. Assuming that a specific time period is represented as a real number in the same way as a distance in space, an interval d {\displaystyle d} in relativistic spacetime is given by the usual formula but with time negated: d 2 = x 2 + y 2 + z 2 − t 2 {\displaystyle d^{2}=x^{2}+y^{2}+z^{2}-t^{2}} where x {\displaystyle x} , y {\displaystyle y} and z {\displaystyle z} are distances along each spatial axis and t {\displaystyle t} is a period of time or "distance" along the time axis (Strictly, the time coordinate is ( c t ) 2 {\displaystyle (ct)^{2}} where c {\displaystyle c} is the speed of light, however we conventionally choose units such that c = 1 {\displaystyle c=1} ). Mathematically this is equivalent to writing d 2 = x 2 + y 2 + z 2 + ( i t ) 2 {\displaystyle d^{2}=x^{2}+y^{2}+z^{2}+(it)^{2}} In this context, i {\displaystyle i} may be either accepted as a feature of the relationship between space and real time, as above, or it may alternatively be incorporated into time itself, such that the value of time is itself an imaginary number, denoted by τ {\displaystyle \tau } . The equation may then
|
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"page_id": 2884904,
"source": null,
"title": "Imaginary time"
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|
be rewritten in normalised form: d 2 = x 2 + y 2 + z 2 + τ 2 {\displaystyle d^{2}=x^{2}+y^{2}+z^{2}+\tau ^{2}} Similarly its four vector may then be written as ( x 0 , x 1 , x 2 , x 3 ) {\displaystyle (x_{0},x_{1},x_{2},x_{3})} where distances are represented as x n {\displaystyle x_{n}} , and x 0 = i c t {\displaystyle x_{0}=ict} where c {\displaystyle c} is the speed of light and time is imaginary. === Application to cosmology === Hawking noted the utility of rotating time intervals into an imaginary metric in certain situations, in 1971. In physical cosmology, imaginary time may be incorporated into certain models of the universe which are solutions to the equations of general relativity. In particular, imaginary time can help to smooth out gravitational singularities, where known physical laws break down, to remove the singularity and avoid such breakdowns (see Hartle–Hawking state). The Big Bang, for example, appears as a singularity in ordinary time but, when modelled with imaginary time, the singularity can be removed and the Big Bang functions like any other point in four-dimensional spacetime. Any boundary to spacetime is a form of singularity, where the smooth nature of spacetime breaks down.: 769–772 With all such singularities removed from the Universe, it thus can have no boundary and Stephen Hawking speculated that "the boundary condition to the Universe is that it has no boundary".: 85 However, the unproven nature of the relationship between actual physical time and imaginary time incorporated into such models has raised criticisms. Roger Penrose has noted that there needs to be a transition from the Riemannian metric (often referred to as "Euclidean" in this context) with imaginary time at the Big Bang to a Lorentzian metric with real time for the evolving Universe. Also, modern
|
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"page_id": 2884904,
"source": null,
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|
observations suggest that the Universe is open and will never shrink back to a Big Crunch. If this proves true, then the end-of-time boundary still remains.: 769–772 == See also == Euclidean quantum gravity Multiple time dimensions == References == == Further reading == Hawking, Stephen W. (1998). A Brief History of Time (Tenth Anniversary Commemorative ed.). Bantam Books. p. 157. ISBN 978-0-553-10953-5. Gerald D. Mahan. Many-Particle Physics, Chapter 3 A. Zee Quantum field theory in a nutshell, Chapter V.2 == External links == The Beginning of Time — Lecture by Stephen Hawking which discusses imaginary time. Stephen Hawking's Universe: Strange Stuff Explained Archived 2016-03-03 at the Wayback Machine — PBS site on imaginary time.
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}
|
A chimera or chimeric virus is a virus that contains genetic material derived from two or more distinct viruses. It is defined by the Center for Veterinary Biologics (part of the U.S. Department of Agriculture's Animal and Plant Health Inspection Service) as a "new hybrid microorganism created by joining nucleic acid fragments from two or more different microorganisms in which each of at least two of the fragments contain essential genes necessary for replication." The term genetic chimera had already been defined to mean: an individual organism whose body contained cell populations from different zygotes or an organism that developed from portions of different embryos. Chimeric flaviviruses have been created in an attempt to make novel live attenuated vaccines. == Etymology == In mythology, a chimera is a creature such as a hippogriff or a gryphon formed from parts of different animals, thus the name for these viruses. == As a natural phenomenon == Viruses are categorized in two types: In prokaryotes, the great majority of viruses possess double-stranded (ds) DNA genomes, with a substantial minority of single-stranded (ss) DNA viruses and only limited presence of RNA viruses. In contrast, in eukaryotes, RNA viruses account for the majority of the virome diversity although ssDNA and dsDNA viruses are common as well. In 2012, the first example of a naturally-occurring RNA-DNA hybrid virus was unexpectedly discovered during a metagenomic study of the acidic extreme environment of Boiling Springs Lake that is in Lassen Volcanic National Park, California. The virus was named BSL-RDHV (Boiling Springs Lake RNA DNA Hybrid Virus). Its genome is related to a DNA circovirus, which usually infect birds and pigs, and a RNA tombusvirus, which infect plants. The study surprised scientists, because DNA and RNA viruses vary and the way the chimera came together was not understood. Other
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{
"page_id": 5637418,
"source": null,
"title": "Chimera (virus)"
}
|
viral chimeras have also been found, and the group is known as the CHIV viruses ("chimeric viruses"). == As a bioweapon == Combining two pathogenic viruses increases the lethality of the new virus which is why there have been cases where chimeric viruses have been considered for use as a bioweapon. For example, the Soviet Union's Chimera Project attempted in the late 1980s and early 1990s to combine DNA from Venezuelan equine encephalitis virus and Smallpox virus at one location, and Ebola virus and Smallpox virus in another location, even in the face of Boris Yeltsin's decree of 11 April 1992. A combination Smallpox virus and Monkeypox virus has also been studied. == As a medical treatment == Studies have shown that chimeric viruses can also be developed to have medical benefits. The US Food and Drug Administration (FDA) has recently approved the use of chimeric antigen receptor (CAR) to treat relapsed non-Hodgkin Lymphoma. By introducing a chimeric antigen receptor into T cells, the T cells become more efficient at identifying and attacking the tumor cells. Studies are also in progress to create a chimeric vaccine against four types of Dengue virus, however this has not been successful yet. == References ==
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{
"page_id": 5637418,
"source": null,
"title": "Chimera (virus)"
}
|
In particle physics, every type of particle of "ordinary" matter (as opposed to antimatter) is associated with an antiparticle with the same mass but with opposite physical charges (such as electric charge). For example, the antiparticle of the electron is the positron (also known as an antielectron). While the electron has a negative electric charge, the positron has a positive electric charge, and is produced naturally in certain types of radioactive decay. The opposite is also true: the antiparticle of the positron is the electron. Some particles, such as the photon, are their own antiparticle. Otherwise, for each pair of antiparticle partners, one is designated as the normal particle (the one that occurs in matter usually interacted with in daily life). The other (usually given the prefix "anti-") is designated the antiparticle. Particle–antiparticle pairs can annihilate each other, producing photons; since the charges of the particle and antiparticle are opposite, total charge is conserved. For example, the positrons produced in natural radioactive decay quickly annihilate themselves with electrons, producing pairs of gamma rays, a process exploited in positron emission tomography. The laws of nature are very nearly symmetrical with respect to particles and antiparticles. For example, an antiproton and a positron can form an antihydrogen atom, which is believed to have the same properties as a hydrogen atom. This leads to the question of why the formation of matter after the Big Bang resulted in a universe consisting almost entirely of matter, rather than being a half-and-half mixture of matter and antimatter. The discovery of charge parity violation helped to shed light on this problem by showing that this symmetry, originally thought to be perfect, was only approximate. The question about how the formation of matter after the Big Bang resulted in a universe consisting almost entirely of matter remains
|
{
"page_id": 1327,
"source": null,
"title": "Antiparticle"
}
|
an unanswered one, and explanations so far are not truly satisfactory, overall. Because charge is conserved, it is not possible to create an antiparticle without either destroying another particle of the same charge (as is for instance the case when antiparticles are produced naturally via beta decay or the collision of cosmic rays with Earth's atmosphere), or by the simultaneous creation of both a particle and its antiparticle (pair production), which can occur in particle accelerators such as the Large Hadron Collider at CERN. Particles and their antiparticles have equal and opposite charges, so that an uncharged particle also gives rise to an uncharged antiparticle. In many cases, the antiparticle and the particle coincide: pairs of photons, Z0 bosons, π0 mesons, and hypothetical gravitons and some hypothetical WIMPs all self-annihilate. However, electrically neutral particles need not be identical to their antiparticles: for example, the neutron and antineutron are distinct. == History == === Experiment === In 1932, soon after the prediction of positrons by Paul Dirac, Carl D. Anderson found that cosmic-ray collisions produced these particles in a cloud chamber – a particle detector in which moving electrons (or positrons) leave behind trails as they move through the gas. The electric charge-to-mass ratio of a particle can be measured by observing the radius of curling of its cloud-chamber track in a magnetic field. Positrons, because of the direction that their paths curled, were at first mistaken for electrons travelling in the opposite direction. Positron paths in a cloud-chamber trace the same helical path as an electron but rotate in the opposite direction with respect to the magnetic field direction due to their having the same magnitude of charge-to-mass ratio but with opposite charge and, therefore, opposite signed charge-to-mass ratios. The antiproton and antineutron were found by Emilio Segrè and Owen
|
{
"page_id": 1327,
"source": null,
"title": "Antiparticle"
}
|
Chamberlain in 1955 at the University of California, Berkeley. Since then, the antiparticles of many other subatomic particles have been created in particle accelerator experiments. In recent years, complete atoms of antimatter have been assembled out of antiprotons and positrons, collected in electromagnetic traps. === Dirac hole theory === Solutions of the Dirac equation contain negative energy quantum states. As a result, an electron could always radiate energy and fall into a negative energy state. Even worse, it could keep radiating infinite amounts of energy because there were infinitely many negative energy states available. To prevent this unphysical situation from happening, Dirac proposed that a "sea" of negative-energy electrons fills the universe, already occupying all of the lower-energy states so that, due to the Pauli exclusion principle, no other electron could fall into them. Sometimes, however, one of these negative-energy particles could be lifted out of this Dirac sea to become a positive-energy particle. But, when lifted out, it would leave behind a hole in the sea that would act exactly like a positive-energy electron with a reversed charge. These holes were interpreted as "negative-energy electrons" by Paul Dirac and mistakenly identified with protons in his 1930 paper A Theory of Electrons and Protons However, these "negative-energy electrons" turned out to be positrons, and not protons. This picture implied an infinite negative charge for the universe – a problem of which Dirac was aware. Dirac tried to argue that we would perceive this as the normal state of zero charge. Another difficulty was the difference in masses of the electron and the proton. Dirac tried to argue that this was due to the electromagnetic interactions with the sea, until Hermann Weyl proved that hole theory was completely symmetric between negative and positive charges. Dirac also predicted a reaction e− +
|
{
"page_id": 1327,
"source": null,
"title": "Antiparticle"
}
|
p+ → γ + γ, where an electron and a proton annihilate to give two photons. Robert Oppenheimer and Igor Tamm, however, proved that this would cause ordinary matter to disappear too fast. A year later, in 1931, Dirac modified his theory and postulated the positron, a new particle of the same mass as the electron. The discovery of this particle the next year removed the last two objections to his theory. Within Dirac's theory, the problem of infinite charge of the universe remains. Some bosons also have antiparticles, but since bosons do not obey the Pauli exclusion principle (only fermions do), hole theory does not work for them. A unified interpretation of antiparticles is now available in quantum field theory, which solves both these problems by describing antimatter as negative energy states of the same underlying matter field, i.e. particles moving backwards in time. == Elementary antiparticles == == Composite antiparticles == == Particle–antiparticle annihilation == If a particle and antiparticle are in the appropriate quantum states, then they can annihilate each other and produce other particles. Reactions such as e− + e+ → γγ (the two-photon annihilation of an electron-positron pair) are an example. The single-photon annihilation of an electron-positron pair, e− + e+ → γ, cannot occur in free space because it is impossible to conserve energy and momentum together in this process. However, in the Coulomb field of a nucleus the translational invariance is broken and single-photon annihilation may occur. The reverse reaction (in free space, without an atomic nucleus) is also impossible for this reason. In quantum field theory, this process is allowed only as an intermediate quantum state for times short enough that the violation of energy conservation can be accommodated by the uncertainty principle. This opens the way for virtual pair production or
|
{
"page_id": 1327,
"source": null,
"title": "Antiparticle"
}
|
annihilation in which a one particle quantum state may fluctuate into a two particle state and back. These processes are important in the vacuum state and renormalization of a quantum field theory. It also opens the way for neutral particle mixing through processes such as the one pictured here, which is a complicated example of mass renormalization. == Properties == Quantum states of a particle and an antiparticle are interchanged by the combined application of charge conjugation C {\displaystyle C} , parity P {\displaystyle P} and time reversal T {\displaystyle T} . C {\displaystyle C} and P {\displaystyle P} are linear, unitary operators, T {\displaystyle T} is antilinear and antiunitary, ⟨ Ψ | T Φ ⟩ = ⟨ Φ | T − 1 Ψ ⟩ {\displaystyle \langle \Psi |T\,\Phi \rangle =\langle \Phi |T^{-1}\,\Psi \rangle } . If | p , σ , n ⟩ {\displaystyle |p,\sigma ,n\rangle } denotes the quantum state of a particle n {\displaystyle n} with momentum p {\displaystyle p} and spin J {\displaystyle J} whose component in the z-direction is σ {\displaystyle \sigma } , then one has C P T | p , σ , n ⟩ = ( − 1 ) J − σ | p , − σ , n c ⟩ , {\displaystyle CPT\ |p,\sigma ,n\rangle \ =\ (-1)^{J-\sigma }\ |p,-\sigma ,n^{c}\rangle ,} where n c {\displaystyle n^{c}} denotes the charge conjugate state, that is, the antiparticle. In particular a massive particle and its antiparticle transform under the same irreducible representation of the Poincaré group which means the antiparticle has the same mass and the same spin. If C {\displaystyle C} , P {\displaystyle P} and T {\displaystyle T} can be defined separately on the particles and antiparticles, then T | p , σ , n ⟩ ∝ | − p ,
|
{
"page_id": 1327,
"source": null,
"title": "Antiparticle"
}
|
− σ , n ⟩ , {\displaystyle T\ |p,\sigma ,n\rangle \ \propto \ |-p,-\sigma ,n\rangle ,} C P | p , σ , n ⟩ ∝ | − p , σ , n c ⟩ , {\displaystyle CP\ |p,\sigma ,n\rangle \ \propto \ |-p,\sigma ,n^{c}\rangle ,} C | p , σ , n ⟩ ∝ | p , σ , n c ⟩ , {\displaystyle C\ |p,\sigma ,n\rangle \ \propto \ |p,\sigma ,n^{c}\rangle ,} where the proportionality sign indicates that there might be a phase on the right hand side. As C P T {\displaystyle CPT} anticommutes with the charges, C P T Q = − Q C P T {\displaystyle CPT\,Q=-Q\,CPT} , particle and antiparticle have opposite electric charges q and -q. == Quantum field theory == This section draws upon the ideas, language and notation of canonical quantization of a quantum field theory. One may try to quantize an electron field without mixing the annihilation and creation operators by writing ψ ( x ) = ∑ k u k ( x ) a k e − i E ( k ) t , {\displaystyle \psi (x)=\sum _{k}u_{k}(x)a_{k}e^{-iE(k)t},\,} where we use the symbol k to denote the quantum numbers p and σ of the previous section and the sign of the energy, E(k), and ak denotes the corresponding annihilation operators. Of course, since we are dealing with fermions, we have to have the operators satisfy canonical anti-commutation relations. However, if one now writes down the Hamiltonian H = ∑ k E ( k ) a k † a k , {\displaystyle H=\sum _{k}E(k)a_{k}^{\dagger }a_{k},\,} then one sees immediately that the expectation value of H need not be positive. This is because E(k) can have any sign whatsoever, and the combination of creation and annihilation operators has expectation value 1
|
{
"page_id": 1327,
"source": null,
"title": "Antiparticle"
}
|
or 0. So one has to introduce the charge conjugate antiparticle field, with its own creation and annihilation operators satisfying the relations b k ′ = a k † a n d b k ′ † = a k , {\displaystyle b_{k\prime }=a_{k}^{\dagger }\ \mathrm {and} \ b_{k\prime }^{\dagger }=a_{k},\,} where k has the same p, and opposite σ and sign of the energy. Then one can rewrite the field in the form ψ ( x ) = ∑ k + u k ( x ) a k e − i E ( k ) t + ∑ k − u k ( x ) b k † e − i E ( k ) t , {\displaystyle \psi (x)=\sum _{k_{+}}u_{k}(x)a_{k}e^{-iE(k)t}+\sum _{k_{-}}u_{k}(x)b_{k}^{\dagger }e^{-iE(k)t},\,} where the first sum is over positive energy states and the second over those of negative energy. The energy becomes H = ∑ k + E k a k † a k + ∑ k − | E ( k ) | b k † b k + E 0 , {\displaystyle H=\sum _{k_{+}}E_{k}a_{k}^{\dagger }a_{k}+\sum _{k_{-}}|E(k)|b_{k}^{\dagger }b_{k}+E_{0},\,} where E0 is an infinite negative constant. The vacuum state is defined as the state with no particle or antiparticle, i.e., a k | 0 ⟩ = 0 {\displaystyle a_{k}|0\rangle =0} and b k | 0 ⟩ = 0 {\displaystyle b_{k}|0\rangle =0} . Then the energy of the vacuum is exactly E0. Since all energies are measured relative to the vacuum, H is positive definite. Analysis of the properties of ak and bk shows that one is the annihilation operator for particles and the other for antiparticles. This is the case of a fermion. This approach is due to Vladimir Fock, Wendell Furry and Robert Oppenheimer. If one quantizes a real scalar field, then one finds that there is only
|
{
"page_id": 1327,
"source": null,
"title": "Antiparticle"
}
|
one kind of annihilation operator; therefore, real scalar fields describe neutral bosons. Since complex scalar fields admit two different kinds of annihilation operators, which are related by conjugation, such fields describe charged bosons. === Feynman–Stückelberg interpretation === By considering the propagation of the negative energy modes of the electron field backward in time, Ernst Stückelberg reached a pictorial understanding of the fact that the particle and antiparticle have equal mass m and spin J but opposite charges q. This allowed him to rewrite perturbation theory precisely in the form of diagrams. Richard Feynman later gave an independent systematic derivation of these diagrams from a particle formalism, and they are now called Feynman diagrams. Each line of a diagram represents a particle propagating either backward or forward in time. In Feynman diagrams, anti-particles are shown traveling backwards in time relative to normal matter, and vice versa. This technique is the most widespread method of computing amplitudes in quantum field theory today. Since this picture was first developed by Stückelberg, and acquired its modern form in Feynman's work, it is called the Feynman–Stückelberg interpretation of antiparticles to honor both scientists. == See also == == Notes == == References == Feynman, R. P. (1987). "The reason for antiparticles". In R. P. Feynman; S. Weinberg (eds.). The 1986 Dirac memorial lectures. Cambridge University Press. ISBN 0-521-34000-4. Weinberg, S. (1995). The Quantum Theory of Fields, Volume 1: Foundations. Cambridge University Press. ISBN 0-521-55001-7. == External links == Phản hạt at Encyclopedic Dictionary of Vietnam Antimatter at CERN
|
{
"page_id": 1327,
"source": null,
"title": "Antiparticle"
}
|
Iron is a metal with strong redox activity. It exists mainly in the natural environment in two forms: divalent iron (Fe(II)) and trivalent iron (Fe(III)). It is one of the most widely distributed metals on Earth. While dissimilatory iron reduction is an anaerobic microbial process in which Fe(III) serves as a terminal electron acceptor for energy production instead of oxygen. It is a fundamental process in industrial and environmental contexts, playing a key role in processes including bioremediation, electrobiosynthesis, and biogeochemical recycling. Iron reduction occurs through two major mechanisms: abiotic (chemical) reduction and biotic (microbial) reduction. Among these, biologically processes are particularly significant in natural environments and are increasingly leveraged in sustainable technologies for metal recovery and environmental remediation. == Overview of iron-reducing bacteria (IRB) == Iron-reducing bacteria are one of the most important bacterial groups present in various environments. Their main reaction is to reduce ferric iron to ferrous iron. Microorganisms play a vital role in the natural transformation of iron from solute to precipitate. Iron-reducing metabolic pathways can be carried out in aerobic or anaerobic environments, but IRB mainly operate under anaerobic and micro-aerobic conditions. As of 2016, more than 71 facultative IRB have been identified, with morphologies ranging from cocci to comma-shaped and rod-shaped. Under anaerobic conditions, IRB utilize ferric iron (Fe(III)) as a terminal electron acceptor to support the anaerobic degradation of various organic compounds. The consumption of these organic substrates and the production of CO₂ are key indicators of their metabolic activity. Some IRB species, such as Shewanella putrefaciens, Shewanella algae, and certain Pseudomonas spp., are facultative anaerobes capable of utilizing multiple electron acceptors, including oxygen. However, when Fe³⁺ is used as the terminal electron acceptor, their efficiency in oxidizing organic electron donors is significantly reduced. In such cases, compounds like lactate and pyruvate are
|
{
"page_id": 79627568,
"source": null,
"title": "Dissimilatory iron reducing bacteria"
}
|
oxidized to acetate. == Importance in Biogeochemical Cycle == Iron reduction plays a key role in biogeochemical cycles, influencing a variety of environmental processes and the cycling of other elements. For example, processes such as nitrogen and sulfur cycles, anaerobic ammonium oxidation with iron reduction and sulfur-driven iron reduction highlight the interconnectedness of these cycles in terrestrial and aquatic ecosystems. The recognition of microbial iron reduction as a key environmental process marked a significant advancement in our understanding of subsurface biogeochemistry. Microbial iron reduction not only contributes to greenhouse gas formation but also regulates the dynamics of nutrients and contaminants in aquatic systems. In addition, in terrestrial soils, iron redox cycles are closely linked to carbon and nitrogen cycles. By mediating essential biological and chemical reactions, iron reduction is a key driver of soil ecological functions, soil fertility, and nutrient availability. == Historical Background and Discovery == Microbial iron reduction is one of the oldest metabolic processes on Earth. Direct fossil evidence of early microbial life on Earth is scarce. Some microbiological data suggest that both sulfate reduction and iron reduction are the earliest forms of microbial respiration. Furthermore, Fe isotope geochemistry may provide a new method to identify microbial iron reduction early in Earth history. Data from a new study show that the geological record of dissimilatory iron reduction (DIR) extends back to more than 560 million years ago (Myr) and confirms that microorganisms closely related to the last common ancestor could reduce Fe(III). == Metabolic process == === Overall reaction === Dissimilatory iron reduction is an anaerobic process catabolized by bacteria that involves the oxidation of organic acids/H2 and the reduction of extracellular iron. A representative reaction utilizing acetate as the organic acid electron donor and ferric iron ((Fe(III)) as the terminal electron acceptor, while ferrous iron ((Fe(II)),
|
{
"page_id": 79627568,
"source": null,
"title": "Dissimilatory iron reducing bacteria"
}
|
carbon dioxide, and energy are produced, is shown below. A wide variety of organic acids can be used as reductants for dissimilatory iron reduction. This process typically occurs on the cell surface or extracellularly. CH3COO- + 8Fe3+ + 3H2O -> 8Fe2+ + HCO3- + CO2 + 8H+ + 814 kJ/reaction === Electron transport === Bacteria utilize a variety of methods to transfer electrons onto solid state ferric iron. Microorganisms typically form biofilms on the surface of iron minerals due to the role extracellular polymeric substances play in mediated electron transfer. The four primary methods of electron transfer include: 1) direct contact, 2) ligand mediation, 3) electron shuttling, and 4) pili (nanowires). Direct contact involves the physical interaction between the surface of the iron mineral and the bacterial. This process is mediated in Shewanella oneidensis by the MR-1 pathway which directly transfers electrons onto the solid state iron via cytochromes. The MR-1 pathway involves the periplasmic transfer of electrons from the cytoplasmic quinol oxidase protein CymA to an outer membrane c-type cytochrome MtrABC complex; other proteins also play an unknown role in cell surface electron transfer. Ligand-mediated electron transfer involves the use of chelating agents or ligands produced by bacteria to solubilize ferric iron from minerals, increasing its bioavailability. These ligands, often organic acids or siderophores, bind to the iron minerals, forming soluble complexes that are reduced at the cell surface or in the extracellular environment. Electron shuttling involves the use of redox-active compounds that act as intermediates to transfer electrons from the bacterial cell to Fe(III). These shuttles, which can be endogenous or exogenous, cycle between reduced and oxidized states. Common examples include humic substances, flavins and quinones secreted by Shewanella species. After being reduced by the microbes, the shuttle diffuses to the ferric iron mineral, donates electrons, and returns
|
{
"page_id": 79627568,
"source": null,
"title": "Dissimilatory iron reducing bacteria"
}
|
to the cell in its oxidized form to repeat the cycle. This mechanism allows the bacteria to reduce iron at a distance. Pili (also known as nanowires), are electrically conductive appendages that facilitate long-range electron transfer and are produced by some iron-reducing bacteria, such as Geobacter sulfurreducens. These pili are protein filaments and contain aromatic amino acids and cytochromes which enable efficient electron conduction from the cell to distant iron minerals. Nanowires are particularly important in biofilms, where they form a network that increases electron transfer efficiency and supports microbial community interaction. == Phylogenetic diversity and evolutionary relationships == === Distribution of iron-reducing pathways across Bacteria and Archaea === Iron-reducing pathways are phylogenetically widespread, occurring in both Bacteria and Archaea. Most cultured dissimilatory iron-reducing bacteria (DIRB) are affiliated with the class Deltaproteobacteria, including genera such as Geobacter and Shewanella. However, Fe(III) reduction has also been observed in Gammaproteobacteria (e.g., Shewanella alga), Epsilonproteobacteria (e.g., Geospirillum barnesii), and Firmicutes (e.g., Desulfotomaculum reducens). In the archaeal domain, thermophilic species such as Ferroglobus placidus have also demonstrated iron-reducing capabilities. Additionally, organisms like Sinorhodobacter ferrireducens exhibit iron-reducing traits despite falling outside traditional IRB lineages, suggesting horizontal gene transfer or convergent evolution. === Evolutionary origins of ferric iron reduction === Dissimilatory iron reduction is considered one of the earliest respiratory pathways to evolve, possibly predating nitrate and oxygen respiration. Ferric reductases are predicted to have evolved around 3.5 billion years ago, following the formation of Fe(III) via ultraviolet-driven oxidation and anaerobic photosynthesis using Fe²⁺ as an electron donor. Comparative studies of ferric reductase enzymes suggest that iron reduction evolved independently in multiple microbial lineages. For example, the ferric reductase in the archaeon Archaeoglobus fulgidus shares structural features with bacterial flavin reductases but lacks sequence similarity, implying convergent evolution or horizontal gene transfer across domains. Fossilized microbial
|
{
"page_id": 79627568,
"source": null,
"title": "Dissimilatory iron reducing bacteria"
}
|
mats from iron-rich hydrothermal environments also indicate that microbial iron cycling was active in early anoxic ecosystems. These ancient microbial communities may have contributed to Fe(III) accumulation and created conditions favorable for the emergence of iron-reducing pathways. === Sulfate-reducing bacteria (SRB) and Fe(III) reduction === Although sulfate-reducing bacteria (SRB) are primarily associated with the reduction of sulfate (SO₄²⁻), several species have demonstrated the ability to reduce ferric iron. Organisms such as Desulfobulbus propionicus and Desulfotomaculum reducens are capable of using Fe(III) as an electron acceptor under laboratory conditions. These dual capabilities may enable SRB to adapt to fluctuating redox environments in marine sediments, where the availability of sulfate and iron can vary over time. === Evolutionary relationship of IRB and SRB === Phylogenetic studies indicate that IRB and SRB are closely related. Members of the Geobacteraceae family, which includes well-studied IRB, share phylogenetic proximity to sulfate reducers such as Desulfomonile tiedjei and Desulfobulbus spp. Some SRB that reduce Fe(III) possess homologous electron transport components to those found in IRB, supporting a shared ancestry or the possibility of horizontal gene transfer of iron-reducing capabilities. === Similarities in electron transport mechanisms === Both iron-reducing bacteria (IRB) and sulfate-reducing bacteria (SRB) rely on extracellular electron transfer (EET) to access insoluble electron acceptors such as ferric iron (Fe(III)) oxides or metallic iron surfaces. SRB have also been implicated in the corrosion of iron, with evidence suggesting direct electron uptake via semiconductive mineral layers like iron sulfides. These mechanistic similarities may reflect convergent strategies for extracellular respiration. === Ecological interactions and co-occurrence === In natural environments such as coastal sediments and wetlands, IRB and SRB often co-exist. In high-organic-carbon environments like acid sulfate soils, both groups can function simultaneously without outcompeting each other due to the abundance of electron donors and acceptors. Under sulfate-limited conditions,
|
{
"page_id": 79627568,
"source": null,
"title": "Dissimilatory iron reducing bacteria"
}
|
iron reduction may become the dominant anaerobic respiration process. Environmental parameters such as redox potential, iron and sulfate availability, and organic matter content are key factors shaping the spatial distribution and activity of IRB and SRB in marine ecosystems. == Distribution and Environmental Conditions == Iron-reducing bacteria (IRB) inhabit suboxic and anoxic regions, rich in organic matter and iron, which serve as crucial components in their metabolic processes. Despite these specific environmental conditions, IRB inhabit a wide array of terrestrial and aquatic environmental settings. These range from grasslands and riverbeds to continental shelves and deep-sea sediments. However, their primary niche is occupying marine and freshwater sediments, where the combination of nutrient availability and redox conditions support their metabolic activity. While IRB thrive in coastal waters, estuaries, and oceanic sediments, their distribution is highly variable across different environments. For example, open ocean sediments contain decreased iron levels, which contrasts with coastal and continental shelf sediments, and therefore are less suitable for IRB colonization. Within the sediment column itself, IRB can be found primarily in layers near the surface, where the organic matter and iron content foster IRB activity. They can extend deeper down through the sulfate methane transition zone (SMTZ) into the methanic zone as well. The expansive distribution of IRB also extends to a variety of extreme environments including oilfields, polar regions, mines, and hydrothermal vents. The harsh conditions of these environments demonstrate the versatility and adaptability of some IRB, enabling them to persist in specialized and demanding ecological niches. The hydrological cycle plays a crucial role in significantly influencing IRB metabolic processes. Variations in groundwater and especially precipitation, impact IRB-suitable habitats and their metabolic efficiency. Precipitation plays a key role in altering oxygen content in wetlands, which can benefit or prevent iron reduction, depending on the sedimentary depth of
|
{
"page_id": 79627568,
"source": null,
"title": "Dissimilatory iron reducing bacteria"
}
|
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