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allows for understanding that everyone lies somewhere on a particular personality dimension, the dichotomous (nominal categorical and ordinal) approaches only seek to confirm that a particular person either has or does not have a particular mental disorder. Expert witnesses particularly are trained to help courts in translating the data into the legal (e.g. 'guilty' vs. 'not guilty') dichotomy, which apply to law, sociology and ethics. == In linguistics == In linguistics, the range of dialects spoken over a geographical area that differ slightly between neighboring areas is known as a dialect continuum. A language continuum is a similar description for the merging of neighboring languages without a clear defined boundary. Examples of dialect or language continuums include the varieties of Italian or German; and the Romance languages, Arabic languages, or Bantu languages. == References == == External links == Continuity and infinitesimals, John Bell, Stanford Encyclopedia of Philosophy
|
{
"page_id": 20646034,
"source": null,
"title": "Continuum (measurement)"
}
|
Why Zebras Don't Get Ulcers is a 1994 (2nd ed. 1998, 3rd ed. 2004) book by Stanford University biologist Robert M. Sapolsky. The book includes the subtitle "A Guide to Stress, Stress-related Diseases, and Coping" on the front cover of its third edition. == Background and synopsis == The title derives from Sapolsky's premise that for animals such as zebras, stress is generally episodic (e.g., running away from a lion), while for humans, stress is often chronic (e.g., worrying about losing one's job). Therefore, many wild animals are less susceptible than humans to chronic stress-related disorders such as ulcers, hypertension, decreased neurogenesis and increased hippocampal neuronal atrophy. However, chronic stress occurs in some social primates (Sapolsky studies baboons) for individuals on the lower side of the social dominance hierarchy. Sapolsky focuses on the effects of glucocorticoids on the human body, arguing that such hormones may be useful to animals in the wild escaping their predators, (see Fight-or-flight response) but the effects on humans, when secreted at high quantities or over long periods of time, are much less desirable. Sapolsky relates the history of endocrinology, how the field reacted at times of discovery, and how it has changed through the years. While most of the book focuses on the biological machinery of the body, the last chapter of the book focuses on self-help. Why Zebras Don't Get Ulcers argues that social phenomena such as child abuse and the chronic stress of poverty affect biological stress, leading to increased risk of disease and disability. == Reception == The book received mostly positive reviews. Kirkus Reviews called it an "entertaining explanation of how stress affects the body and what we can do to counteract its effects." Barry Keverne wrote in a review for New Scientist: "Everyone can benefit from reading Why Zebras Don't
|
{
"page_id": 5769363,
"source": null,
"title": "Why Zebras Don't Get Ulcers"
}
|
Get Ulcers and gain insights into the workings of the body and mind, and why some of us are more vulnerable than others to stress-related illness." == References == == External links == Stress: Portrait of a Killer Archived 2016-03-17 at the Wayback Machine, National Geographic documentary based on Why Zebras Don't Get Ulcers "Why Zebras Don't Get Ulcers: Stress and Health", lecture by Robert Sapolsky "Why Zebras Don't Get Ulcers", NPR segment from December 3, 1999 from Fresh Air
|
{
"page_id": 5769363,
"source": null,
"title": "Why Zebras Don't Get Ulcers"
}
|
Photoexcitation is the production of an excited state of a quantum system by photon absorption. The excited state originates from the interaction between a photon and the quantum system. Photons carry energy that is determined by the wavelengths of the light that carries the photons. Objects that emit light with longer wavelengths, emit photons carrying less energy. In contrast to that, light with shorter wavelengths emit photons with more energy. When the photon interacts with a quantum system, it is therefore important to know what wavelength one is dealing with. A shorter wavelength will transfer more energy to the quantum system than longer wavelengths. On the atomic and molecular scale photoexcitation is the photoelectrochemical process of electron excitation by photon absorption, when the energy of the photon is too low to cause photoionization. The absorption of the photon takes place in accordance with Planck's quantum theory. Photoexcitation plays a role in photoisomerization and is exploited in different techniques: Dye-sensitized solar cells makes use of photoexcitation by exploiting it in cheaper inexpensive mass production solar cells. The solar cells rely on a large surface area in order to catch and absorb as many high energy photons as possible. Shorter wavelengths are more efficient for the energy conversion compared to longer wavelengths, since shorter wavelengths carry photons that are more energy rich. Light containing shorter wavelengths therefore cause a longer and less efficient conversion of energy in dye-sensitized solar cells. Photochemistry Luminescence Optically pumped lasers use photoexcitation in a way that the excited atoms in the lasers get an enormous direct-gap gain needed for the lasers. The density that is needed for the population inversion in the compound Ge, a material often used in lasers, must become 1020 cm−3, and this is acquired via photoexcitation. The photoexcitation causes the electrons in atoms
|
{
"page_id": 3147924,
"source": null,
"title": "Photoexcitation"
}
|
to go to an excited state. The moment the amount of atoms in the excited state is higher than the amount in the normal ground state, the population inversion occurs. The inversion, like the one caused with germanium, makes it possible for materials to act as lasers. Photochromic applications. Photochromism causes a transformation of two forms of a molecule by absorbing a photon. For example, the BIPS molecule(2H-l-benzopyran-2,2-indolines) can convert from trans to cis and back by absorbing a photon. The different forms are associated with different absorption bands. In a cis-form of BIPS, the transient absorption band has a value of 21050 cm−1, in contrast to the band from the trans-form, that has a value of 16950 cm−1. The results were optically visible, where the BIPS in gels turned from a colorless appearance to a brown or pink color after repeatedly being exposed to a high energy UV pump beam. High energy photons cause a transformation in the BIPS molecule making the molecule change its structure. On the nuclear scale photoexcitation includes the production of nucleon and delta baryon resonances in nuclei. == References ==
|
{
"page_id": 3147924,
"source": null,
"title": "Photoexcitation"
}
|
In mechanics, friction torque is the torque caused by the frictional force that occurs when two objects in contact move. Like all torques, it is a rotational force that may be measured in newton meters or pounds-feet. == Engineering == Friction torque can be disruptive in engineering. There are a variety of measures engineers may choose to take to eliminate these disruptions. Ball bearings are an example of an attempt to minimize the friction torque. Friction torque can also be an asset in engineering. Bolts and nuts, or screws are often designed to be fastened with a given amount of torque, where the friction is adequate during use or operation for the bolt, nut, or screw to remain safely fastened. This is true with such applications as lug nuts retaining wheels to vehicles, or equipment subjected to vibration with sufficiently well-attached bolts, nuts, or screws to prevent the vibration from shaking them loose. == Examples == When a cyclist applies the brake to the forward wheel, the bicycle tips forward due to the frictional torque between the wheel and the ground. When a golf ball hits the ground it begins to spin in part because of the friction torque applied to the golf ball from the friction between the golf ball and the ground. == References == == See also == Torque Force Engineering
|
{
"page_id": 11733139,
"source": null,
"title": "Friction torque"
}
|
Homological mirror symmetry is a mathematical conjecture made by Maxim Kontsevich. It seeks a systematic mathematical explanation for a phenomenon called mirror symmetry first observed by physicists studying string theory. == History == In an address to the 1994 International Congress of Mathematicians in Zürich, Kontsevich (1994) speculated that mirror symmetry for a pair of Calabi–Yau manifolds X and Y could be explained as an equivalence of a triangulated category constructed from the algebraic geometry of X (the derived category of coherent sheaves on X) and another triangulated category constructed from the symplectic geometry of Y (the derived Fukaya category). Edward Witten originally described the topological twisting of the N=(2,2) supersymmetric field theory into what he called the A and B model topological string theories. These models concern maps from Riemann surfaces into a fixed target—usually a Calabi–Yau manifold. Most of the mathematical predictions of mirror symmetry are embedded in the physical equivalence of the A-model on Y with the B-model on its mirror X. When the Riemann surfaces have empty boundary, they represent the worldsheets of closed strings. To cover the case of open strings, one must introduce boundary conditions to preserve the supersymmetry. In the A-model, these boundary conditions come in the form of Lagrangian submanifolds of Y with some additional structure (often called a brane structure). In the B-model, the boundary conditions come in the form of holomorphic (or algebraic) submanifolds of X with holomorphic (or algebraic) vector bundles on them. These are the objects one uses to build the relevant categories. They are often called A and B branes respectively. Morphisms in the categories are given by the massless spectrum of open strings stretching between two branes. The closed string A and B models only capture the so-called topological sector—a small portion of the full string
|
{
"page_id": 2164886,
"source": null,
"title": "Homological mirror symmetry"
}
|
theory. Similarly, the branes in these models are only topological approximations to the full dynamical objects that are D-branes. Even so, the mathematics resulting from this small piece of string theory has been both deep and difficult. The School of Mathematics at the Institute for Advanced Study in Princeton devoted a whole year to Homological Mirror Symmetry during the 2016-17 academic year. Among the participants were Paul Seidel from MIT, Maxim Kontsevich from IHÉS, and Denis Auroux, from UC Berkeley. == Examples == Only in a few examples have mathematicians been able to verify the conjecture. In his seminal address, Kontsevich commented that the conjecture could be proved in the case of elliptic curves using theta functions. Following this route, Alexander Polishchuk and Eric Zaslow provided a proof of a version of the conjecture for elliptic curves. Kenji Fukaya was able to establish elements of the conjecture for abelian varieties. Later, Kontsevich and Yan Soibelman provided a proof of the majority of the conjecture for nonsingular torus bundles over affine manifolds using ideas from the SYZ conjecture. In 2003, Paul Seidel proved the conjecture in the case of the quartic surface. In 2002 Hausel & Thaddeus (2002) explained SYZ conjecture in the context of Hitchin system and Langlands duality. == Hodge diamond == The dimensions hp,q of spaces of harmonic (p,q)-differential forms (equivalently, the cohomology, i.e., closed forms modulo exact forms) are conventionally arranged in a diamond shape called the Hodge diamond. These (p,q)-Betti numbers can be computed for complete intersections using a generating function described by Friedrich Hirzebruch. For a three-dimensional manifold, for example, the Hodge diamond has p and q ranging from 0 to 3: Mirror symmetry translates the dimension number of the (p, q)-th differential form hp,q for the original manifold into hn-p,q of that for the
|
{
"page_id": 2164886,
"source": null,
"title": "Homological mirror symmetry"
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|
counter pair manifold. Namely, for any Calabi–Yau manifold the Hodge diamond is unchanged by a rotation by π radians and the Hodge diamonds of mirror Calabi–Yau manifolds are related by a rotation by π/2 radians. In the case of an elliptic curve, which is viewed as a 1-dimensional Calabi–Yau manifold, the Hodge diamond is especially simple: it is the following figure. In the case of a K3 surface, which is viewed as 2-dimensional Calabi–Yau manifold, since the Betti numbers are {1, 0, 22, 0, 1}, their Hodge diamond is the following figure. In the 3-dimensional case, usually called the Calabi–Yau manifold, a very interesting thing happens. There are sometimes mirror pairs, say M and W, that have symmetric Hodge diamonds with respect to each other along a diagonal line. M's diamond: W's diamond: M and W correspond to A- and B-model in string theory. Mirror symmetry not only replaces the homological dimensions but also the symplectic structure and complex structure on the mirror pairs. That is the origin of homological mirror symmetry. In 1990-1991, Candelas et al. 1991 had a major impact not only on enumerative algebraic geometry but on the whole mathematics and motivated Kontsevich (1994). The mirror pair of two quintic threefolds in this paper have the following Hodge diamonds. == See also == Mirror symmetry conjecture - more mathematically based article Topological quantum field theory Category theory Floer homology Fukaya category Derived category Quintic threefold == References == Candelas, Philip; de la Ossa, Xenia C.; Green, Paul S.; Parkes, Linda (1991). "A pair of Calabi-Yau manifolds as an exactly soluble superconformal theory". Nuclear Physics B. 359 (1): 21–74. Bibcode:1991NuPhB.359...21C. doi:10.1016/0550-3213(91)90292-6. MR 1115626. Kontsevich, Maxim (1994). "Homological algebra of mirror symmetry". arXiv:alg-geom/9411018. Kontsevich, Maxim; Soibelman, Yan (2000). "Homological Mirror Symmetry and torus fibrations". arXiv:math.SG/0011041. Seidel, Paul (2003). "Homological
|
{
"page_id": 2164886,
"source": null,
"title": "Homological mirror symmetry"
}
|
mirror symmetry for the quartic surface". arXiv:math.SG/0310414. Hausel, Tamas; Thaddeus, Michael (2002). "Mirror symmetry, Langlands duality, and the Hitchin system". Inventiones Mathematicae. 153 (1): 197–229. arXiv:math.DG/0205236. Bibcode:2003InMat.153..197H. doi:10.1007/s00222-003-0286-7. S2CID 11948225.
|
{
"page_id": 2164886,
"source": null,
"title": "Homological mirror symmetry"
}
|
Propynylidyne is a chemical compound that has been identified in interstellar space. == Structure == === Linear (l-C3H) === μD=3.551 Debye 2Π electronic ground state ==== Simulated spectrum ==== A rotational spectrum of the 2Π electronic ground state of l-C3H can be made using the PGopher software (a Program for Simulating Rotational Structure, C. M. Western, University of Bristol, http://pgopher.chm.bris.ac.uk) and molecular constants extracted from the literature. These constants include μ=3.551 Debye and others provided by Yamamoto et al. 1990, given in units of MHz: B=11189.052, D=0.0051365, ASO=432834.31, γ=-48.57, p=-7.0842, and q=-13.057. A selection rule of ΔJ=0,1 was applied, with S=0.5. The resulting simulation for the rotational spectrum of C3H at a temperature of 30 K agree well with observations. The simulated spectrum is shown in the figure at right with the approximate atmospheric transmission overplotted in blue. All of the strongest simulated lines with J < 8.5 are observed by Yamamoto et al. === Cyclic (c-C3H) === μD=2.4 Debye electronic ground state == Chemistry == The molecule C3H has been observed in cold, dense molecular clouds. The dominant formation and destruction mechanisms are presented below, for a typical cloud with temperature 10K. The relative contributions of each reaction have been calculated using rates and abundances from the UMIST database for astrochemistry. === Dominant formation reactions === === Dominant destruction reactions === === Contribution to carbon-chain molecule production === The C3H molecule provides the dominant pathway to the production of C4H+, and thereby all other CnH (n>3) molecules via the reactions: C3H + C+ → C4+ + H C4+ + H2 → C4H+ + H These reactions produce the majority of C4H+, which is necessary for the production of higher-order carbon-chain molecules. Compared to the competing reaction, C3H3+ + C → C4H2+ + H, also shown right, the destruction of
|
{
"page_id": 19990682,
"source": null,
"title": "Propynylidyne"
}
|
C3H provides a much faster pathway for hydrocarbon growth. Other molecules in the C3H family, C2H and C3H2, do not significantly contribute to the production of carbon-chain molecules, rather forming endpoints in this process. The production of C2H and C3H2 essentially inhibits larger carbon-chain molecule formation, since neither they nor the products of their destruction are recycled into the hydrocarbon chemistry. == First astronomical detection == The first confirmation of the existence of the interstellar molecule C3H was announced by W.M Irvine et al. at the January 1985 meeting of the American Astronomical Society. The group detected C3H in both the spectrum of the evolved carbon star IRC+10216 and in the molecular cloud TMC-1. These results were formally published in July of the same year by Thaddeus et al. A 1987 paper by W.M. Irvine provides a comparison of detections for 39 molecules observed in cold (Tk ≅10K), dark clouds, with particular emphasis paid to tri-carbon species, including C3H. == Subsequent astronomical detections == Later reports of astronomical detections of the C3H radical are given in chronological order below. In 1987, Yamamoto et al. report measurements of the rotational spectra of the cyclic C3H radical (c-C3H) in the laboratory and in interstellar space towards TMC-1. This publication marks the first terrestrial measurement of C3H. Yamamoto et al. precisely determine molecular constants and identify 49 lines in the c-C3H rotational spectrum. Both fine and hyperfine components are detected toward TMC-1, and the column density for the line of sight toward TMC-1 is estimated to be 6x1012cm−2, which is comparable to the linear C3H radical (l-C3H). M.L Marconi and A. Korth et al. reported a likely detection of C3H within the ionopause of Comet Halley in 1989. Using the heavy ion analyzer (PICCA) on board the Giotto spacecraft they determined that C3H
|
{
"page_id": 19990682,
"source": null,
"title": "Propynylidyne"
}
|
was responsible for producing a peak at 37amu detected within ~4500 km of the comet nucleus. Marconi et al. argue that a gas phase progenitor molecule for C3H is unlikely to exist within the ionopause and suggest that desorption from circumnuclear CHON dust grains may have instead produced the observed C3H. In 1990, Yamamoto et al. detected C3H toward IRC + 10216 using the Nobeyama Radio Observatory's 45-m radio telescope. They determine an upper limit for the column density of the ν4 state 3x1012cm−2. From additional laboratory measurements they determine an extremely low vibrationally excited state for the C3H radical: ν4(2Σμ)=610197(1230) MHz, caused by the Renner-Teller effect in the ν4 (CCH bending) state. J.G. Mangum and A. Wootten report new detections of c-C3H towards 13 of 19 observed Galactic molecular clouds. They measure relative abundance of C3H to C3H2: N(c-C3H)/N(C3H2) = 9.04±2.87 x 10−2. This ratio does not change systematically for warmer sources, which they suggest provides evidence that the two ring molecules have a common precursor in C3H3+. L.A. Nyman et al. present a molecular line survey of the carbon star IRAS 15194-5115 using the 15m Swedish-ESO Submillimetre Telescope to probe the 3 and 1.3 mm bands. Comparing the molecular abundances with those of IRC + 10216, they find C3H to have similar abundances in both sources. In 1993, M. Guelin et al. map the emission from the 95 GHz and 98 GHz lines of the C3H radicals in IRC+10216. This reveals a shell-like distribution of the C3H emission and time-dependent chemistry. The close correspondence between the emission peaks of C3H and the species <noautolink>MgNC</noautolink> and C4H suggests a fast common formation mechanism, suggested to be desorption from dust grains. Turner et al. survey 10 hydrocarbon species, including l-C3H and c-C3H in three translucent clouds and TMC-1 and L183.
|
{
"page_id": 19990682,
"source": null,
"title": "Propynylidyne"
}
|
Abundances are measured or estimated for each. The mean cyclic-to-linear abundance ratio for C3H is found to be 2.7, although a large variation in this ratio is observed from source to source. In 2004, N. Kaifu et al. completed the first spectral line survey toward TMC-1 in the frequency range 8.8-50.0 GHz with the 45-m radio telescope at Nobeyama Radio Observatory. They detected 414 lines of 38 molecular species including c-C3H and compiled spectral charts and improved molecular constants for several carbon-chain molecules. Martin et al. made the first spectral line survey towards an extragalactic source, targeting the starburst galaxy NGC253 across the frequency range 129.1-175.2 GHz. Approximately 100 spectral features were identified as transitions from 25 different molecular species, including a tentative first extra-galactic detection of C3H. == References ==
|
{
"page_id": 19990682,
"source": null,
"title": "Propynylidyne"
}
|
The molecular formula C20H26N4O (molar mass: 338.45 g/mol, exact mass: 338.2107 u) may refer to: Lisuride
|
{
"page_id": 24053915,
"source": null,
"title": "C20H26N4O"
}
|
The molecular formula C16H17N3O may refer to: Ergine Isoergine
|
{
"page_id": 24053920,
"source": null,
"title": "C16H17N3O"
}
|
A quantum heterostructure is a heterostructure in a substrate (usually a semiconductor material), where size restricts the movements of the charge carriers forcing them into a quantum confinement. This leads to the formation of a set of discrete energy levels at which the carriers can exist. Quantum heterostructures have sharper density of states than structures of more conventional sizes. Quantum heterostructures are important for fabrication of short-wavelength light-emitting diodes and diode lasers, and for other optoelectronic applications, e.g. high-efficiency photovoltaic cells. Examples of quantum heterostructures confining the carriers in quasi-two, -one and -zero dimensions are: Quantum wells Quantum wires Quantum dots == References == == See also == http://www.ecse.rpi.edu/~schubert/Light-Emitting-Diodes-dot-org/chap04/chap04.htm Kitaev's periodic table
|
{
"page_id": 3147940,
"source": null,
"title": "Quantum heterostructure"
}
|
Phyllis Jean Stabeno is a physical oceanographer known for her research on the movement of water in polar regions. She has led award-winning research projects in the Arctic and was noted for a distinguished scientific career by the National Oceanic and Atmospheric Administration. == Education and career == Stabeno received her Ph.D. in 1982 from Oregon State University. As of 2021, she works at the National Oceanic and Atmospheric Administration (NOAA) within the Pacific Marine Environmental Laboratory. == Research == Stabeno is known for her research on the water masses of the Arctic, long-term changes in the movement of water in the region, and the implications of these changes in the face of global climate change. Her early research examined currents off California and Oregon. She used current data from moorings and buoys that were tracked by satellites to characterize the movement of water in the vicinity of Kodiak Island, Alaska. She subsequently expanded to using satellite-tracked buoys to examine water movement in the Bering Sea, and conducted studies on the changes in the water movement in the region, especially in response to climate change. She has used moorings deployed on the continental shelf to track the Alaska Coastal Current and followed the movement of eggs and larvae from walleye pollock. Her work includes investigations into the Gulf of Alaska, the region near select Aleutian Islands, and the North Pacific Ocean. In the Bering Sea, her research has revealed warming of waters on the Bering Sea shelf, the physical oceanography of the Bering Sea, and an integration of data from the Bering Sea that spans multiple decades. == Selected publications == Hunt Jr, George L.; Stabeno, Phyllis; Walters, Gary; Sinclair, Elizabeth; Brodeur, Richard D.; Napp, Jeffery M.; Bond, Nicholas A. (2002-12-01). "Climate change and control of the southeastern Bering Sea
|
{
"page_id": 69208231,
"source": null,
"title": "Phyllis Stabeno"
}
|
pelagic ecosystem". Deep Sea Research Part II: Topical Studies in Oceanography. Ecology of the SE Bering Sea. 49 (26): 5821–5853. Bibcode:2002DSRII..49.5821H. doi:10.1016/S0967-0645(02)00321-1. ISSN 0967-0645. S2CID 55222333. Bond, N. A.; Overland, J. E.; Spillane, M.; Stabeno, P. (2003). "Recent shifts in the state of the North Pacific". Geophysical Research Letters. 30 (23): 2183. Bibcode:2003GeoRL..30.2183B. doi:10.1029/2003GL018597. ISSN 1944-8007. S2CID 130532536. Stabeno, P. J; Bond, N. A; Hermann, A. J; Kachel, N. B; Mordy, C. W; Overland, J. E (2004-05-01). "Meteorology and oceanography of the Northern Gulf of Alaska". Continental Shelf Research. 24 (7): 859–897. Bibcode:2004CSR....24..859S. doi:10.1016/j.csr.2004.02.007. ISSN 0278-4343. Stabeno, P. J.; Bond, N. A.; Kachel, N. B.; Salo, S. A.; Schumacher, J. D. (2001). "On the temporal variability of the physical environment over the south-eastern Bering Sea". Fisheries Oceanography. 10 (1): 81–98. doi:10.1046/j.1365-2419.2001.00157.x. ISSN 1365-2419. == Awards and honors == Stabeno was the lead investigator for the Bering Ecosystem Study (BEST) and Bering Sea Integrated Ecosystem Research Plan (BSIERP) programs which won the Department of Commerce Gold Medal in 2015. In 2019 she received a Distinguished Career Award in Scientific Achievement from NOAA. == References == == External links == Phyllis Stabeno publications indexed by Google Scholar Causes and implications of record low sea ice extent in the Bering Sea in 2018 on YouTube May 16, 2019
|
{
"page_id": 69208231,
"source": null,
"title": "Phyllis Stabeno"
}
|
4,5-Dihydroxy-2,3-pentanedione (DPD) is an organic compound that occurs naturally but exists as several related structures. The idealized formula for this species is CH3C(O)C(O)CH(OH)CH2OH, but it is known to exist as several other forms resulting from cyclization. It is not stable at room temperature as a pure material, which has further complicated its analysis. The (S)-stereoisomer occurs naturally. It is typically hydrated, i.e., one keto group has added water to give the geminal diol. DPD is produced by degradation of S-adenosylhomocysteine by the action of the enzyme S-ribosylhomocysteinase. The compound probably does not exist as depicted above, but as an equilibrium mixture of three hydrates. DPD reacts with boric acid to form a borate diester known as autoinducer-2 (AI-2). AI-2 is a signaling molecule used for bacterial quorum sensing. It is produced and recognized by many Gram-negative and Gram-positive bacteria. AI-2 is synthesized by the reaction of DPD with boric acid and is recognized by the two-component sensor kinase LuxPQ in Vibrionaceae. == References ==
|
{
"page_id": 49481896,
"source": null,
"title": "4,5-Dihydroxy-2,3-pentanedione"
}
|
The Journal of Experimental Marine Biology and Ecology is a peer-reviewed bimonthly journal which publishes work on the biochemistry, physiology, behaviour, and genetics of marine plants and animals in relation to their ecology. According to the Journal Citation Reports, the journal has a 2015 impact factor of 1.796. == References ==
|
{
"page_id": 49023145,
"source": null,
"title": "Journal of Experimental Marine Biology and Ecology"
}
|
Generalized multidimensional scaling (GMDS) is an extension of metric multidimensional scaling, in which the target space is non-Euclidean. When the dissimilarities are distances on a surface and the target space is another surface, GMDS allows finding the minimum-distortion embedding of one surface into another. GMDS is an emerging research direction. Currently, main applications are recognition of deformable objects (e.g. for three-dimensional face recognition) and texture mapping. == References == Bronstein AM, Bronstein MM, Kimmel R (January 2006). "Generalized multidimensional scaling: a framework for isometry-invariant partial surface matching". Proc. Natl. Acad. Sci. U.S.A. 103 (5): 1168–72. Bibcode:2006PNAS..103.1168B. doi:10.1073/pnas.0508601103. PMC 1360551. PMID 16432211.
|
{
"page_id": 4196522,
"source": null,
"title": "Generalized multidimensional scaling"
}
|
β-Hydroxy β-methylbutyryl-coenzyme A (HMB-CoA), also known as 3-hydroxyisovaleryl-CoA, is a metabolite of L-leucine that is produced in the human body. Its immediate precursors are β-hydroxy β-methylbutyric acid (HMB) and β-methylcrotonoyl-CoA (MC-CoA). It can be metabolized into HMB, MC-CoA, and HMG-CoA in humans. == Metabolic pathway == == Notes == == References ==
|
{
"page_id": 51447977,
"source": null,
"title": "Β-Hydroxy β-methylbutyryl-CoA"
}
|
Deuterated solvents are a group of compounds where one or more hydrogen atoms are substituted by deuterium atoms. These isotopologues of common solvents are often used in nuclear magnetic resonance spectroscopy. == Examples == Heavy water Deuterated acetone Deuterated benzene Deuterated chloroform Deuterated dichloromethane Deuterated DMF Deuterated DMSO Deuterated ethanol Deuterated methanol Deuterated THF == References ==
|
{
"page_id": 22743210,
"source": null,
"title": "Deuterated solvent"
}
|
The Beard and Chuang model is a well known and leading theoretical force balance model used to derive the rotational cross-sections of raindrops in their equilibrium state by employing Chebyshev polynomials in series. The radius-vector of the raindrop's surface r ( θ ) {\displaystyle r(\theta )} in vertical angular direction θ {\displaystyle \theta } is equal to r ( θ ) = a [ 1 + ∑ c n c o s ( n θ ) ] {\displaystyle r(\theta )=a[1+\sum c_{n}cos(n\theta )]} , where shape coefficients c n ⋅ 10 4 {\displaystyle c_{n}\cdot 10^{4}} are defined for the raindrops with different equivolumetric diameter as in following table == Applications == The description of raindrop shape has some rather practical uses. Understanding rain is particularly important with regard to the propagation of electromagnetic signals. A portion of atmosphere that has rain in it, or a rain cell, has the characteristic of attenuating and de-polarizing EM signals that pass through it. The attenuation of such a signal is approximately proportional to the square of the frequency of the signal, and the de-polarization is proportional to the shape distribution of raindrops in the rain cell. == References ==
|
{
"page_id": 18483373,
"source": null,
"title": "Beard and Chuang model"
}
|
The molecular formula C11H14N2O2 (molar mass: 206.241 g/mol) may refer to: 4-Hydroxy-5-methoxytryptamine Pheneturide Phenylethylmalonamide
|
{
"page_id": 61540526,
"source": null,
"title": "C11H14N2O2"
}
|
The molecular formula C19H23N3O2 (molar mass : 325.41 g/mol) may refer to: ABT-670, a potent, orally bioavailable dopamine agonist Ergometrine, a primary ergot and morning glory alkaloid Ergometrinine, an ergot alkaloid
|
{
"page_id": 24053935,
"source": null,
"title": "C19H23N3O2"
}
|
Bardsey Bird and Field Observatory is a bird observatory on Bardsey Island, off the Welsh coast. It was founded in 1953 by a group of ornithologists from the West Midland Bird Club (who were represented on the observatory's management committee), the West Wales Field Society, and local people. The West Midlands Bird club not only saw a possibility for a new bird observatory, but an opportunity for studying the complex ecology of a small island. The observatory's main objective is to monitor and census the breeding and migratory birds which use the island. Observatory staff undertake a daily census, with a log of the day's sightings taken each evening. Spring and summer are particularly intensive times when the populations of breeding landbirds and seabirds are counted. BBFO is one of two fully accredited observatory in Wales and is 1 of 20 accredited bird observatories around the coast of the UK and Ireland. It is recognised by the Bird Observatories Council. Bardsey Island or Ynys Enlli is of great conservation importance and is designated as a National Nature Reserve (NNR), Site of Special Scientific Interest (SSSI), Special Protection Area (SPA), Environmentally Sensitive Area (ESA), Llyn Peninsula Special Area of Conservation (SAC) and Area of Outstanding Natural Beauty. It is part of the Llyn Peninsula Heritage Coast. Steven Stansfield is the current Warden and Director of Operations and has been resident on the island since January 1998 and is the longest serving member of staff at the Observatory. Bardsey Bird Observatory and Field Centre is a registered charity. == See also == Eifion Jones == References == == External links == Bardsey Lodge & Bird Observatory
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In physics, a quantum (pl.: quanta) is the minimum amount of any physical entity (physical property) involved in an interaction. The fundamental notion that a property can be "quantized" is referred to as "the hypothesis of quantization". This means that the magnitude of the physical property can take on only discrete values consisting of integer multiples of one quantum. For example, a photon is a single quantum of light of a specific frequency (or of any other form of electromagnetic radiation). Similarly, the energy of an electron bound within an atom is quantized and can exist only in certain discrete values. Atoms and matter in general are stable because electrons can exist only at discrete energy levels within an atom. Quantization is one of the foundations of the much broader physics of quantum mechanics. Quantization of energy and its influence on how energy and matter interact (quantum electrodynamics) is part of the fundamental framework for understanding and describing nature. == Origin == The modern concept of the quantum in physics originates from December 14, 1900, when Max Planck reported his findings to the German Physical Society. He showed that modelling harmonic oscillators with discrete energy levels resolved a longstanding problem in the theory of blackbody radiation.: 15 In his report, Planck did not use the term quantum in the modern sense. Instead, he used the term Elementarquantum to refer to the "quantum of electricity", now known as the elementary charge. For the smallest unit of energy, he employed the term Energieelement, "energy element", rather than calling it a quantum. Shortly afterwards, in a paper published in Annalen der Physik, Planck introduced the constant h, which he termed the "quantum of action" (elementares Wirkungsquantum) in 1906. In this paper, Planck also reported more precise values for the elementary charge and the
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Avogadro–Loschmidt number, the number of molecules in one mole of substance. The constant h is now known as the Planck constant. After his theory was validated, Planck was awarded the Nobel Prize in Physics for his discovery in 1918. In 1905 Albert Einstein suggested that electromagnetic radiation exists in spatially localized packets which he called "quanta of light" (Lichtquanta). Einstein was able to use this hypothesis to recast Planck's treatment of the blackbody problem in a form that also explained the voltages observed in Philipp Lenard's experiments on the photoelectric effect.: 23 Shortly thereafter, the term "energy quantum" was introduced for the quantity hν. == Quantization == While quantization was first discovered in electromagnetic radiation, it describes a fundamental aspect of energy not just restricted to photons. In the attempt to bring theory into agreement with experiment, Max Planck postulated that electromagnetic energy is absorbed or emitted in discrete packets, or quanta. == See also == Introduction to quantum mechanics History of quantum mechanics == References == == Further reading == Hoffmann, Banesh (1959). The Strange story of the quantum: An account for the general reader of the growth of the ideas underlying our present atomic knowledge (2 ed.). New York: Dover. ISBN 978-0-486-20518-2. {{cite book}}: ISBN / Date incompatibility (help) Mehra, Jagdish; Rechenberg, Helmut; Mehra, Jagdish; Rechenberg, Helmut (2001). The historical development of quantum theory. 4: Pt.1, the fundamental equations of quantum mechanics, 1925-1926 (1. softcover print ed.). New York Heidelberg: Springer. ISBN 978-0-387-95178-2. M. Planck, A Survey of Physical Theory, transl. by R. Jones and D.H. Williams, Methuen & Co., Limited., London 1925 (Dover edition 17 May 2003, ISBN 978-0486678672) including the Nobel lecture. Rodney, Brooks (14 December 2010) Fields of Color: The theory that escaped Einstein. Allegra Print & Imaging. ISBN 979-8373308427
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The Gibilmanna Observatory is a research station used for a diverse range of studies set up and run by the Istituto Nazionale di Geofisica e Vulcanologia (INGV) and it is located on Cozzo Timpa Rossa at 1005 m.a.s.l. near Cefalù, a town in the district of Palermo, Italy. It is one of the 120 stations of the Italian Magnetic Network measuring Earth magnetism field in Italy, and in 2005 INGV's Centro Nazionale Terremoti (CNT) selected it to set up the OBS Lab aimed at designing, manufacturing and managing the Ocean-Bottom Seismometer with Hydrophone (OBS/H), later deployed for monitoring the Marsili submarine volcano in the Tyrrhenian Sea. In addition, the observatory is one of the 110 Data Collection Platform (D.C.P.) stations of the Aeronautica Militare Italiana for automatic weather data gathering and transmission to the METEOSAT satellite. Since 1976 this station has also been equipped for Ionospheric research and it is the most southern station of its kind in Europe. Real time ionograms are recorded by the INGV own developed AIS-INGV ionosonde installed at the station and reported on the INGV ionospheric website. == References == Istituto Nazionale di Geofisica e Vulcanologia "IGNV". Retrieved on 17 May 2015 Italian Magnetic Network "INGV". Retrieved on 17 May 2015 D'Anna G. et al. (2009), "Il Nuovo OBS/H dell'INGV", Quaderni di Geofisica, 29 Aeronautica Militare Italiana "La rete osservativa". Retrieved on 17 May 2015 Ionospheric Station of Gibilmanna "Latest Ionogram". Retrieved on 17 May 2015
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An ecotone is a transitional area between two plant communities, where these meet and integrate. Examples include areas between grassland and forest, estuaries and lagoon, freshwater and sea water etc. An ecotone may be narrow or wide, and it may be local (the zone between a field and forest) or regional (the transition between forest and grassland ecosystems). An ecotone may appear on the ground as a gradual blending of the two communities across a broad area, or it may manifest itself as a sharp boundary line. == Etymology == The word ecotone was coined (and its etymology given) in 1904 in "The Development and Structure of Vegetation" (Lincoln, Nebraska: Botanical Seminar) by Frederic E. Clements. It is formed as a combination of ecology plus -tone, from the Greek tonos or tension – in other words, a place where ecologies are in tension. == Features == There are several distinguishing features of an ecotone. First, an ecotone can have a sharp vegetation transition, with a distinct line between two communities. For example, a change in colors of grasses or plant life can indicate an ecotone. Second, a change in physiognomy (physical appearance of a plant species) can be a key indicator. Water bodies, such as estuaries, can also have a region of transition, and the boundary is characterized by the differences in heights of the macrophytes or plant species present in the areas because this distinguishes the two areas' accessibility to light. Scientists look at color variations and changes in plant height. Third, a change of species can signal an ecotone. There will be specific organisms on one side of an ecotone or the other. Other factors can illustrate or obscure an ecotone, for example, migration and the establishment of new plants. These are known as spatial mass effects, which
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are noticeable because some organisms will not be able to form self-sustaining populations if they cross the ecotone. If different species can survive in both communities of the two biomes, then the ecotone is considered to have species richness; ecologists measure this when studying the food chain and success of organisms. Lastly, the abundance of introduced species in an ecotone can reveal the type of biome or efficiency of the two communities sharing space. Because an ecotone is the zone in which two communities integrate, many different forms of life have to live together and compete for space. Therefore, an ecotone can create a diverse ecosystem. == Formation == Changes in the physical environment may produce a sharp boundary, as in the example of the interface between areas of forest and cleared land. Elsewhere, a more gradually blended interface area will be found, where species from each community will be found together as well as unique local species. Mountain ranges often create such ecotones, due to the wide variety of climatic conditions experienced on their slopes. They may also provide a boundary between species due to the obstructive nature of their terrain. Mont Ventoux in France is a good example, marking the boundary between the flora and fauna of northern and southern France. Most wetlands are ecotones. The spatial variation of ecotones often form due to disturbances, creating patches that separate patches of vegetation. Different intensity of disturbances can cause landslides, land shifts, or movement of sediment that can create these vegetation patches and ecotones. Plants in competition extend themselves on one side of the ecotone as far as their ability to maintain themselves allows. Beyond this competitors of the adjacent community take over. As a result, the ecotone represents a shift in dominance. Ecotones are particularly significant for mobile
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animals, as they can exploit more than one set of habitats within a short distance. The ecotone contains not only species common to the communities on both sides; it may also include a number of highly adaptable species that tend to colonize such transitional areas. The phenomenon of increased variety of plants as well as animals at the community junction is called the edge effect and is essentially due to a locally broader range of suitable environmental conditions or ecological niches. == Ecotones and ecoclines == An ecotone is often associated with an ecocline: a "physical transition zone" between two systems. The ecotone and ecocline concepts are sometimes confused: an ecocline can signal an ecotone chemically (ex: pH or salinity gradient), or microclimatically (hydrothermal gradient) between two ecosystems. In contrast: an ecocline is a variation of the physicochemical environment dependent of one or two physico-chemical factors of life, and thus presence/absence of certain species. An ecocline can be a thermocline, chemocline (chemical gradient), halocline (salinity gradient) or pycnocline (variations in density of water induced by temperature or salinity). ecocline transitions are less distinct (less clear-cut), have more stable conditions within, hence a higher plant species richness. an ecotone describes a variation in species prevalence and is often not strictly dependent on a major physical factor separating one ecosystem from another, with resulting habitat variability. An ecotone is often unobtrusive and harder to measure. an ecotone is the area where two communities interact. Ecotones can be easily identified by distinct change in soil gradient and soil composition between two communities. ecotone transitions are more clear-cut (distinct), conditions are less stable, hence they have a low species richness. == Examples == The Kra ecotone between 11°N and 13°N latitude just north of the Kra Isthmus that connects the Thai-Malay Peninsula with mainland
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Asia is an example of a regional scale ecotone. It marks the transition zone between the moist deciduous forest in the mainland Southeast Asia biogeographical region in the north and the wet seasonal dipterocarp forest in the Sundaland region in the south. It has been shown to be the biogeographical transition between Indochinese and Sundaic faunas. Approximately 152 species of bird were found to have northern or southern range limits between these latitudes. Population genetics studies have also found that the Kra ecotone is the major physical barrier that limits gene flow in the honeybees Apis cerana and Apis dorsata and the stingless bees Trigona collina and Trigona pagdeni. The Wallace Line running through the Lombok Strait between the Indonesian islands of Bali and Lombok is a faunal boundary that separates the Indomalayan realm from Wallacea. It is named for Alfred Russel Wallace, who first observed the abrupt boundary between the two biomes in 1859. Biologists believe it was the depth of the Lombok Strait itself that kept the animals on either side isolated from one another. However, it has been found that some flightless animals such as certain weevil species have, in the past, been involved in several transgression events in which species from land east of the Wallace Line relocated to Bali. When sea levels dropped during the Pleistocene ice age, the islands of Bali, Java and Sumatra were all connected to one another and to the mainland of Asia. They shared the Asian fauna. The Lombok Strait's deep water kept Lombok and the Lesser Sunda archipelago isolated from the Asian mainland. These islands were, instead, colonized by Australasian fauna. Mbam Djerem National Park's ecotone in Cameroon is up to 1,000 km wide in places and differences within species are believed to be precursors to speciation. General examples
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of ecotones include salt marshes and riparian zones. == See also == Cline (biology) - Ecocline Ecotype Phylogenetic niche conservatism Plant functional type Satoyama Biogeographic realm == References == == External links ==
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Iron oxide nanoparticles are iron oxide particles with diameters between about 1 and 100 nanometers. The two main forms are composed of magnetite (Fe3O4) and its oxidized form maghemite (γ-Fe2O3). They have attracted extensive interest due to their superparamagnetic properties and their potential applications in many fields (although cobalt and nickel are also highly magnetic materials, they are toxic and easily oxidized) including molecular imaging. Applications of iron oxide nanoparticles include terabit magnetic storage devices, catalysis, sensors, superparamagnetic relaxometry, high-sensitivity biomolecular magnetic resonance imaging, magnetic particle imaging, magnetic fluid hyperthermia, separation of biomolecules, and targeted drug and gene delivery for medical diagnosis and therapeutics. These applications require coating of the nanoparticles by agents such as long-chain fatty acids, alkyl-substituted amines, and diols. They have been used in formulations for supplementation. == Structure == Magnetite has an inverse spinel structure with oxygen forming a face-centered cubic crystal system. In magnetite, all tetrahedral sites are occupied by Fe3+ and octahedral sites are occupied by both Fe3+ and Fe2+. Maghemite differs from magnetite in that all or most of the iron is in the trivalent state (Fe3+) and by the presence of cation vacancies in the octahedral sites. Maghemite has a cubic unit cell in which each cell contains 32 oxygen ions, 211⁄3 Fe3+ ions and 22⁄3 vacancies. The cations are distributed randomly over the 8 tetrahedral and 16 octahedral sites. == Magnetic properties == Due to its 4 unpaired electrons in 3d shell, an iron atom has a strong magnetic moment. Ions Fe2+ have also 4 unpaired electrons in 3d shell and Fe3+ have 5 unpaired electrons in 3d shell. Therefore, when crystals are formed from iron atoms or ions Fe2+ and Fe3+ they can be in ferromagnetic, antiferromagnetic, or ferrimagnetic states. In the paramagnetic state, the individual atomic magnetic moments are
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randomly oriented, and the substance has a zero net magnetic moment if there is no magnetic field. These materials have a relative magnetic permeability greater than one and are attracted to magnetic fields. The magnetic moment drops to zero when the applied field is removed. But in a ferromagnetic material, all the atomic moments are aligned even without an external field. A ferrimagnetic material is similar to a ferromagnet but has two different types of atoms with opposing magnetic moments. The material has a magnetic moment because the opposing moments have different strengths. If they have the same magnitude, the crystal is antiferromagnetic and possesses no net magnetic moment. When an external magnetic field is applied to a ferromagnetic material, the magnetization (M) increases with the strength of the magnetic field (H) until it approaches saturation. Over some range of fields the magnetization has hysteresis because there is more than one stable magnetic state for each field. Therefore, a remanent magnetization will be present even after removing the external magnetic field. A single domain magnetic material (e. g. magnetic nanoparticles) that has no hysteresis loop is said to be superparamagnetic. The ordering of magnetic moments in ferromagnetic, antiferromagnetic, and ferrimagnetic materials decreases with increasing temperature. Ferromagnetic and ferrimagnetic materials become disordered and lose their magnetization beyond the Curie temperature T C {\displaystyle T_{C}} and antiferromagnetic materials lose their magnetization beyond the Néel temperature T N {\displaystyle T_{N}} . Magnetite is ferrimagnetic at room temperature and has a Curie temperature of 850 K. Maghemite is ferrimagnetic at room temperature, unstable at high temperatures, and loses its susceptibility with time. (Its Curie temperature is hard to determine). Both magnetite and maghemite nanoparticles are superparamagnetic at room temperature. This superparamagnetic behavior of iron oxide nanoparticles can be attributed to their size. When the
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size gets small enough (<10 nm), thermal fluctuations can change the direction of magnetization of the entire crystal. A material with many such crystals behaves like a paramagnet, except that the moments of entire crystals are fluctuating instead of individual atoms. Furthermore, the unique superparamagnetic behavior of iron oxide nanoparticles allows them to be manipulated magnetically from a distance. In the latter sections, external manipulation will be discussed in regards to biomedical applications of iron oxide nanoparticles. Forces are required to manipulate the path of iron oxide particles. A spatially uniform magnetic field can result in a torque on the magnetic particle, but cannot cause particle translation; therefore, the magnetic field must be a gradient to cause translational motion. The force on a point-like magnetic dipole moment m due to a magnetic field B is given by the equation: F m = ∇ ( m ⋅ B ) {\displaystyle \mathbf {F} _{m}=\mathbf {\nabla } \left(\mathbf {m} \cdot \mathbf {B} \right)} In biological applications, iron oxide nanoparticles will be translate through some kind of fluid, possibly bodily fluid, in which case the aforementioned equation can be modified to: F m = { V χ 2 μ 0 ∇ | B | 2 in a weak magnetic field 1 2 ∇ ( m s a t ⋅ B ) in a strong magnetic field {\displaystyle \mathbf {F} _{m}={\begin{cases}{\frac {V\chi }{2\mu _{0}}}\mathbf {\nabla } \left|\mathbf {B} \right|^{2}&\qquad {\text{in a weak magnetic field}}\\{\frac {1}{2}}\mathbf {\nabla } \left(\mathbf {m} _{sat}\cdot \mathbf {B} \right)&\qquad {\text{in a strong magnetic field}}\end{cases}}} Based on these equations, there will be the greatest force in the direction of the largest positive slope of the energy density scalar field. Another important consideration is the force acting against the magnetic force. As iron oxide nanoparticles translate toward the magnetic field source, they experience
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Stokes' drag force in the opposite direction. The drag force is expressed below. F d = 6 π η R v {\displaystyle \mathbf {F} _{d}=6\pi \,\eta \,R\,v\,} In this equation, η is the fluid viscosity, R is the hydrodynamic radius of the particle, and 𝑣 is the velocity of the particle. == Synthesis == The preparation method has a large effect on shape, size distribution, and surface chemistry of the particles. It also determines to a great extent the distribution and type of structural defects or impurities in the particles. All these factors affect magnetic behavior. Recently, many attempts have been made to develop processes and techniques that would yield "monodisperse colloids" consisting of nanoparticles uniform in size and shape. === Coprecipitation === By far the most employed method is coprecipitation. This method can be further divided into two types. In the first, ferrous hydroxide suspensions are partially oxidized with different oxidizing agents. For example, spherical magnetite particles of narrow size distribution with mean diameters between 30 and 100 nm can be obtained from a Fe(II) salt, a base and a mild oxidant (nitrate ions). The other method consists in ageing stoichiometric mixtures of ferrous and ferric hydroxides in aqueous media, yielding spherical magnetite particles homogeneous in size. In the second type, the following chemical reaction occurs: 2 Fe3+ + Fe2+ + 8 OH− → Fe3O4↓ + 4 H2O Optimum conditions for this reaction are pH between 8 and 14, Fe3+/Fe2+ ratio of 2:1 and a non-oxidizing environment. Being highly susceptibile to oxidation, magnetite (Fe3O4) is transformed to maghemite (γFe2O3) in the presence of oxygen: 2 Fe3O4 + O2 → 2 γFe2O3 The size and shape of the nanoparticles can be controlled by adjusting pH, ionic strength, temperature, nature of the salts (perchlorates, chlorides, sulfates, and nitrates), or the Fe(II)/Fe(III)
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concentration ratio. === Microemulsions === A microemulsion is a stable isotropic dispersion of 2 immiscible liquids consisting of nanosized domains of one or both liquids in the other stabilized by an interfacial film of surface-active molecules. Microemulsions may be categorized further as oil-in-water (o/w) or water-in-oil (w/o), depending on the dispersed and continuous phases. Water-in-oil is more popular for synthesizing many kinds of nanoparticles. The water and oil are mixed with an amphiphillic surfactant. The surfactant lowers the surface tension between water and oil, making the solution transparent. The water nanodroplets act as nanoreactors for synthesizing nanoparticles. The shape of the water pool is spherical. The size of the nanoparticles will depend on size of the water pool to a great extent. Thus, the size of the spherical nanoparticles can be tailored and tuned by changing the size of the water pool. === High-temperature decomposition of organic precursors === The decomposition of iron precursors in the presence of hot organic surfactants results in samples with good size control, narrow size distribution (5-12 nm) and good crystallinity; and the nanoparticles are easily dispersed. For biomedical applications like magnetic resonance imaging, magnetic cell separation or magnetorelaxometry, where particle size plays a crucial role, magnetic nanoparticles produced by this method are very useful. Viable iron precursors include Fe(Cup)3, Fe(CO)5, or Fe(acac)3 in organic solvents with surfactant molecules. A combination of Xylenes and Sodium Dodecylbenezensulfonate as a surfactant are used to create nanoreactors for which well dispersed iron(II) and iron (III) salts can react. == Biomedical applications == Magnetite and maghemite are preferred in biomedicine because they are biocompatible and potentially non-toxic to humans. Iron oxide is easily degradable and therefore useful for in vivo applications. Results from exposure of a human mesothelium cell line and a murine fibroblast cell line to seven industrially
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important nanoparticles showed a nanoparticle specific cytotoxic mechanism for uncoated iron oxide. Solubility was found to strongly influence the cytotoxic response. Labelling cells (e.g. stem cells, dendritic cells) with iron oxide nanoparticles is an interesting new tool to monitor such labelled cells in real time by magnetic resonance tomography. Some forms of Iron oxide nanoparticle have been found to be toxic and cause transcriptional reprogramming. Iron oxide nanoparticles are used in cancer magnetic nanotherapy that is based on the magneto-spin effects in free-radical reactions and semiconductor material ability to generate oxygen radicals, furthermore, control oxidative stress in biological media under inhomogeneous electromagnetic radiation. The magnetic nanotherapy is remotely controlled by external electromagnetic field reactive oxygen species (ROS) and reactive nitrogen species (RNS)-mediated local toxicity in the tumor during chemotherapy with antitumor magnetic complex and lesser side effects in normal tissues. Magnetic complexes with magnetic memory that consist of iron oxide nanoparticles loaded with antitumor drug have additional advantages over conventional antitumor drugs due to their ability to be remotely controlled while targeting with a constant magnetic field and further strengthening of their antitumor activity by moderate inductive hyperthermia (below 40 °C). The combined influence of inhomogeneous constant magnetic and electromagnetic fields during nanotherapy has initiated splitting of electron energy levels in magnetic complex and unpaired electron transfer from iron oxide nanoparticles to anticancer drug and tumor cells. In particular, anthracycline antitumor antibiotic doxorubicin, the native state of which is diamagnetic, acquires the magnetic properties of paramagnetic substances. Electromagnetic radiation at the hyperfine splitting frequency can increase the time that radical pairs are in the triplet state and hence the probability of dissociation and so the concentration of free radicals. Free radicals in cancer cells induce changes in mechanochemical tumor heterogeneity by modifying bonds which influence the spatial arrangement of molecules
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in cell structures. The translation of the magnetic force exerted on the tumor and its microenvironment by magnetic nanoparticles into biochemical signaling pathways is known as the magneto-mechanochemical effect. This leads to the formation of regions with different biomechanical and biochemical properties within the tumor. The reactivity of magnetic particles depends on their spin state. The experimental data was received about correlation between the frequency of electromagnetic field radiation with magnetic properties and quantity paramagnetic centres of complex. It is possible to control the kinetics of malignant tumor. Cancer cells are then particularly vulnerable to an oxidative assault and induction of high levels of oxidative stress locally in tumor tissue, that has the potential to destroy or arrest the growth of cancer cells and can be thought as therapeutic strategy against cancer. Multifunctional magnetic complexes with magnetic memory can combine cancer magnetic nanotherapy, tumor targeting and medical imaging functionalities in theranostics approach for personalized cancer medicine. Yet, the use of inhomogeneous stationary magnetic fields to target iron oxide magnetic nanoparticles can result in enhanced tumor growth. Magnetic force transmission through magnetic nanoparticles to the tumor due to the action of the inhomogeneous stationary magnetic field reflects mechanical stimuli converting iron-induced reactive oxygen species generation to the modulation of biochemical signals. Iron oxide nanoparticles may also be used in magnetic hyperthermia as a cancer treatment method. In this method, the ferrofluid which contains iron oxide is injected to the tumor and then heated up by an alternating high frequency magnetic field. The temperature distribution produced by this heat generation may help to destroy cancerous cells inside the tumor. The use of superparamagnetic iron oxide (SPIO) can also be used as a tracer in sentinel node biopsy instead of radioisotope. == See also == Neuroregeneration Regenerative medicine == References == == External
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links == Media related to Magnetite nanoparticles at Wikimedia Commons
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Disodium enneaborate is the traditional name for a salt of sodium, boron, oxygen, and hydrogen, with elemental formula Na2B9H22O20 or Na2B9O9·11H2O. It is the sodium borate with the highest boron/sodium ratio. == Structure == The correct formula has since been determined to be (Na+)2[B8O11(OH)4]2−·B(OH)3·2H2O. The anion is a linear polymer with repeating unit [−B8O11(OH)4−]2−. Sodium cations, water molecules, and undissociated boric acid molecules B(OH)3 lie between the chains, held by numerous hydrogen bonds. The compound crystallizes in the monoclinic crystal system with space group P21/n. The cell parameters are a = 1021.3 pm, b = 1294.0 pm, c = 1245.7 pm, β = 93.070°, V = 1.6440 nm3, and Z = 2. The sodium cations occur in groups of four with interatomic distances of 378.30 pm and 379.32 pm. == Reactions == Upon heating, disodium enneaborate initially becomes amorphous and then crystallizes as anhydrous disodium octaborate α-Na2B8O13 along with amorphous B2O3. Notably, the former contains octaborate fundamental building blocks that are topologically equivalent to those in the enneaborate. == References ==
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A supercentenarian, sometimes hyphenated as super-centenarian, is a person who is 110 or older. This age is achieved by about one in 1,000 centenarians. Supercentenarians typically live a life free of significant age-related diseases until shortly before the maximum human lifespan is reached. == Etymology == The term "supercentenarian" has been used since 1832 or earlier. Norris McWhirter, editor of The Guinness Book Of Records, used the term in association with age claims researcher A. Ross Eckler Jr. in 1976, and the term was further popularised in 1991 by William Strauss and Neil Howe in their book Generations. The term "semisupercentenarian", has been used to describe someone aged 105–109. Originally the term "supercentenarian" was used to mean someone well over the age of 100, but 110 years and over became the cutoff point of accepted criteria for demographers. == Incidence == The Gerontology Research Group maintains a top 30–40 list of oldest verified living people. The researchers estimate, based on a 0.15% to 0.25% survival rate of centenarians until the age of 110, that there should be between 300 and 450 living supercentenarians in the world. A study conducted in 2010 by the Max Planck Institute for Demographic Research found 663 validated supercentenarians, living and dead, and showed that the countries with the highest total number (not frequency) of supercentenarians (in decreasing order) were the United States, Japan, England plus Wales, France, and Italy. The first verified supercentenarian in human history was Dutchman Geert Adriaans Boomgaard (1788–1899), and it was not until the 1980s that the oldest verified age surpassed 115. == History == While claims of extreme age have persisted from the earliest times in history, the earliest supercentenarian accepted by Guinness World Records is Dutchman Thomas Peters (reportedly c. 1745–1857). However, Peters's age cannot be reliably verified due
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to an absence of any documents recording his early life. Other scholars, such as French demographer Jean-Marie Robine, consider Geert Adriaans Boomgaard, also of the Netherlands, who turned 110 in 1898, to be the first verifiable case, as the alleged evidence for Peters has apparently been lost. The evidence for the 112 years of Englishman William Hiseland (reportedly 1620–1732) does not meet the standards required by Guinness World Records. Church of Norway records, the accuracy of which is subject to dispute, also show what appear to be several supercentenarians who lived in the south-central part of present-day Norway during the 16th and 17th centuries, including Johannes Torpe (1549–1664), and Knud Erlandson Etun (1659–1770), both residents of Valdres, Oppland. In 1902, Margaret Ann Neve, born in 1792, became the first verified female supercentenarian. Jeanne Calment of France, who died in 1997 aged 122 years, 164 days, had the longest human lifespan documented. The oldest man ever verified is Jiroemon Kimura of Japan, who died in 2013 aged 116 years and 54 days. Ethel Caterham (born 21 August 1909) of the United Kingdom is the world's oldest living person, aged 115 years, 266 days. João Marinho Neto (born 5 October 1912) of Brazil is the world's oldest living man, aged 112 years, 221 days. == Research into centenarians == Research into centenarians helps scientists understand how an ordinary person might live longer. Organisations that research centenarians and supercentenarians include the GRG, LongeviQuest, and the Supercentenarian Research Foundation. In May 2021, whole genome sequencing analysis of 81 Italian semi-supercentenarians and supercentenarians were published, along with 36 control group people from the same region who were simply of advanced age. == Morbidity == Research on the morbidity of supercentenarians has found that they remain free of major age-related diseases (e.g., stroke, cardiovascular disease, dementia,
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cancer, Parkinson's disease and diabetes) until the very end of life when they die of exhaustion of organ reserve, which is the ability to return organ function to homeostasis. About 10% of supercentenarians survive until the last three months of life without major age-related diseases, as compared to only 4% of semi-supercentenarians and 3% of centenarians. By measuring the biological age of various tissues from supercentenarians, researchers may be able to identify the nature of those that are protected from ageing effects. According to a study of 30 different body parts from a 112-year-old female supercentenarian, along with younger controls, the cerebellum is protected from ageing, according to an epigenetic biomarker of tissue age known as the epigenetic clock—the reading is about 15 years younger than expected in a centenarian. These findings could explain why the cerebellum exhibits fewer neuropathological hallmarks of age-related dementia as compared to other brain regions. A 2021 genomic study identified genetic characteristics that protect against age-related diseases, particularly variants that improve DNA repair. Five variants were found to be significant, affecting STK17A (increased expression) and COA1 (reduced expression) genes. Supercentenarians also had an unexpectedly low level of somatic mutations. == See also == List of notable supercentenarians == References == == External links == "Supercentenarian". Merriam-Webster.com Dictionary. Merriam-Webster. Gerontology Research Group International Database on Longevity Supercentenarian Research Foundation New England Supercentenarian Study European Supercentenarian Organisation
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"page_id": 329915,
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"title": "Supercentenarian"
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Carla Restrepo is a professor in the biology department of the University of Puerto Rico, Río Piedras Campus. Her research focuses on the study of tropical landscapes, including the processes underlying their large-scale dynamics. == Education == Restrepo received her B.S. in biology at the University of Valle in Cali, Colombia, in 1984. In 1990, Restrepo received an M.S. in zoology at the University of Florida, where she also received her Ph.D. in 1995. == Awards == Restrepo has received a number of prizes, honors, and grants in the course of her career. 1988: Jessie Smith Noyes Fellowship to attend Organization for Tropical Studies course 1989–1992: National Science Foundation Minority Graduate Fellowship 1990: Marcia Tucker Travel Award, American Ornithologists' Union, USA 1993: Graduate School Travel Award, University of Florida, FL 1995: Department of Zoology Travel Award, University of Florida, FL 1995: College of Liberal Arts and Sciences Dissertation Fellowship, University of Florida, FL 1996–1998: National Science Foundation Minority Postdoctoral Research Fellowship 2010: Elective Member of the American Ornithologist’s Union 2019: Fulbright scholarship == Research == Her main areas of research are landscape ecology, ecosystems, landslides and their impact on ecosystem diversity, changes in land cover and carbon budgets, forest fragmentation and phenotypic plasticity, and seed dispersal in fragmented landscapes. == Recent publications == Sutton, L. and C. Restrepo. 2013. Natural disasters, diverse economy and livelihoods in the Sierra de Las Minas, Guatemala. Journal of Latin American Geography 12: 137-164. Delgado, D., A. Galindo, M.E. Perez, T. Giray, and C. Restrepo. 2012. Forecasting the influence of climate change on agroecosystem services: Impacts on honey yields in a small-island developing state. Psyche: A Journal of Entomology, doi:10.1155/2012/951215. Ramos-Scharron, C., E. Castellanos, and C. Restrepo. 2012. The role of shallow landslides in the downslope transfer of organic matter and its implications on the
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"page_id": 62064828,
"source": null,
"title": "Carla Restrepo"
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residence time of carbon in a tropical mountain system. Journal of Geophysical Research - Biogeosciences 117, G03016. doi:10.1029/2011JG001838 Xu, L., T. Hanson, E. Bedrick, and C. Restrepo. 2010. Hypothesis tests on mixture model components with application to ecological and agricultural data. Journal of Agricultural, Biological, and Environmental Statistics 15:308–326. DOI: 10.1007/s13253-010-0020-z Restrepo, C., L. Walker, A. Shiels, R. Bussman, L. Claessens, S. Fisch, P. Lozano, G. Negi, L. Paolini, G. Poveda, C. Ramos-Scharron, M. Richter, E. Velazquez. 2009. Landsliding and its multi-scale influence on mountainscapes. BioScience 59:685-698. Restrepo, C. and N. Arango. 2008. Discontinuities in the Geographical Range Size of North American Birds and Butterflies: A Biogeographical Test of the Textural Discontinuity Hypothesis. Pages 101-135 in C. Allen, G. Peterson, and C. S. Holling (eds.). Cross-scale Structure and Discontinuities in Ecosystems and other Complex Systems. Columbia University Press, New York, New York, US. Delgado-Acevedo, J. and C. Restrepo. 2008. The effect of habitat loss on body size, allometry, and bilateral asymmetry in two Eleutherodactylus species of Puerto Rico. Conservation Biology 22:773-782 Doi: 10.1111/j.1523-1739.2008.00930.x Allen, A., B. T. Milne, W. Pockman, A. Tyler, and C. Restrepo. 2008. Allometry, growth, and population regulation of the desert shrub Larrea tridentata. Functional Ecology 22:197-204. DOI: 10.1111/j.1365- 2435.2007.01376.x Acevedo, M. and C. Restrepo. 2008. Land-use change and the large-scale organization of bird assemblages in the island of Puerto Rico. Diversity and Distributions 14:114-122. Cuervo, A. and C. Restrepo. 2007. Assemblage and population-level consequences of forest fragmentation on bilateral asymmetry in tropical montane birds. Biological Journal of the Linnean Society 92:119-133. == References ==
|
{
"page_id": 62064828,
"source": null,
"title": "Carla Restrepo"
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A savanna or savannah is a mixed woodland-grassland (i.e. grassy woodland) biome and ecosystem characterised by the trees being sufficiently widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach the ground to support an unbroken herbaceous layer consisting primarily of grasses. Four savanna forms exist; savanna woodland where trees and shrubs form a light canopy, tree savanna with scattered trees and shrubs, shrub savanna with distributed shrubs, and grass savanna where trees and shrubs are mostly nonexistent. Savannas maintain an open canopy despite a high tree density. It is often believed that savannas feature widely spaced, scattered trees. However, in many savannas, tree densities are higher and trees are more regularly spaced than in forests. The South American savanna types cerrado sensu stricto and cerrado dense typically have densities of trees similar to or higher than that found in South American tropical forests, with savanna ranging from 800 to 3300 trees per hectare (trees/ha) and adjacent forests with 800–2000 trees/ha. Similarly Guinean savanna has 129 trees/ha, compared to 103 for riparian forest, while Eastern Australian sclerophyll forests have average tree densities of approximately 100 per hectare, comparable to savannas in the same region. Savannas are also characterised by seasonal water availability, with the majority of rainfall confined to one season. They are associated with several types of biomes, and are frequently in a transitional zone between forest and desert or grassland, though mostly a transition between desert to forest. Savanna covers approximately 20% of the Earth's land area. Unlike the prairies in North America and steppes in Eurasia, which feature cold winters, savannas are mostly located in areas having warm to hot climates, such as in Africa, Australia, South America, and India. == Etymology == The word derives from the Spanish sabana,
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"title": "Savanna"
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which is itself a loanword from Taíno, which means "treeless grassland" in the West Indies. The letter b in Spanish, when positioned in the middle of a word, is pronounced almost like an English v; hence the change of grapheme when transcribed into English. The word originally entered English as the Zauana in a description of the ilands of the kinges of Spayne from 1555. This was equivalent in the orthography of the times to zavana (see history of V). Peter Martyr reported it as the local name for the plain around Comagre, the court of the cacique Carlos in present-day Panama. The accounts are inexact, but this is usually placed in present-day Madugandí or at points on the nearby Guna Yala coast opposite Ustupo or on Point Mosquitos. These areas are now either given over to modern cropland or jungle. == Distribution == Many grassy landscapes and mixed communities of trees, shrubs, and grasses were described as savanna before the middle of the 19th century, when the concept of a tropical savanna climate became established. The Köppen climate classification system was strongly influenced by effects of temperature and precipitation upon tree growth, and oversimplified assumptions resulted in a tropical savanna classification concept which considered it as a "climatic climax" formation. The common usage to describe vegetation now conflicts with a simplified yet widespread climatic concept. The divergence has sometimes caused areas such as extensive savannas north and south of the Congo and Amazon Rivers to be excluded from mapped savanna categories. In different parts of North America, the word "savanna" has been used interchangeably with "barrens", "prairie", "glade", "grassland" and "oak opening". Different authors have defined the lower limits of savanna tree coverage as 5–10% and upper limits range as 25–80% of an area. Two factors common to all
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savanna environments are rainfall variations from year to year, and dry season wildfires. In the Americas, e.g. in Belize, Central America, savanna vegetation is similar from Mexico to South America and to the Caribbean. The distinction between woodland and savanna is vague and therefore the two can be combined into a single biome as both woodlands and savannas feature open-canopied trees with crowns not usually interlinking (mostly forming 25–60% cover). Over many large tropical areas, the dominant biome (forest, savanna or grassland) can not be predicted only by the climate, as historical events plays also a key role, for example, fire activity. In some areas, indeed, it is possible for there to be multiple stable biomes. The annual rainfall ranges from 500 mm (19.69 in) to 1,270 mm (50.00 in) per year, with the precipitation being more common in six or eight months of the year, followed by a period of drought. Savannas may at times be classified as forests. In climatic geomorphology it has been noted that many savannas occur in areas of pediplains and inselbergs. It has been posited that river incision is not prominent but that rivers in savanna landscapes erode more by lateral migration. Flooding and associated sheet wash have been proposed as dominant erosion processes in savanna plains. == Ecology == The savannas of tropical America comprise broadleaved trees such as Curatella, Byrsonima, and Bowdichia, with grasses such as Leersia and Paspalum. Bean relative Prosopis is common in the Argentinian savannas. In the East African savannas, Acacia, Combretum, baobabs, Borassus, and Euphorbia are a common vegetation genera. Drier savannas there feature spiny shrubs and grasses, such as Andropogon, Hyparrhenia, and Themeda. Wetter savannas include Brachystegia trees and Pennisetum purpureum, and elephant grass type. West African savanna trees include Anogeissus, Combretum, and Strychnos. Indian savannas are
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"page_id": 198843,
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mostly cleared, but the reserved ones feature Acacia, Mimosa, and Zizyphus over a grass cover comprising Sehima and Dichanthium. The Australian savanna is abundant with sclerophyllous evergreen vegetation, which include the eucalyptus, as well as Acacia, Bauhinia, Pandanus with grasses such as Heteropogon and kangaroo grass (Themeda). Animals in the African savanna generally include the giraffe, elephant, buffalo, zebra, gnu, hippopotamus, rhinoceros, and antelope, where they rely on grass and/or tree foliage to survive. In the Australian savanna, mammals in the family Macropodidae predominate, such as kangaroos and wallabies, though cattle, horses, camels, donkeys and the Asian water buffalo, among others, have been introduced by humans. == Threats == It is estimated that less than three percent of savanna ecosystems can be classified as highly intact. Reasons for savanna degradation are manifold, as outlined below. === Changes in fire management === Savannas are subject to regular wildfires and the ecosystem appears to be the result of human use of fire. For example, Native Americans created the Pre-Columbian woodlands of North America by periodically burning where fire-resistant plants were the dominant species. Fire-stick farming appears to have been responsible for the widespread occurrence of savanna in tropical Australia and New Guinea, and savannas in India are a result of human fire use. The maquis shrub savannas of the Mediterranean region were likewise created and maintained by anthropogenic fire. Intentional controlled burns typically create fires confined to the herbaceous layer that do little long term damage to mature trees. This prevents more catastrophic wildfires that could do much more damage. However, these fires either kill or suppress tree seedlings, thus preventing the establishment of a continuous tree canopy which would prevent further grass growth. Prior to European settlement aboriginal land use practices, including fire, influenced vegetation and may have maintained and modified
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{
"page_id": 198843,
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"title": "Savanna"
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savanna flora. It has been suggested by many authors that aboriginal burning created a structurally more open savanna landscape. Aboriginal burning certainly created a habitat mosaic that probably increased biodiversity and changed the structure of woodlands and geographic range of numerous woodland species. It has been suggested by many authors that with the removal or alteration of traditional burning regimes many savannas are being replaced by forest and shrub thickets with little herbaceous layer. The consumption of herbage by introduced grazers in savanna woodlands has led to a reduction in the amount of fuel available for burning and resulted in fewer and cooler fires. The introduction of exotic pasture legumes has also led to a reduction in the need to burn to produce a flush of green growth because legumes retain high nutrient levels throughout the year, and because fires can have a negative impact on legume populations which causes a reluctance to burn. === Grazing and browsing animals === The closed forest types such as broadleaf forests and rainforests are usually not grazed owing to the closed structure precluding grass growth, and hence offering little opportunity for grazing. In contrast the open structure of savannas allows the growth of a herbaceous layer and is commonly used for grazing domestic livestock. As a result, much of the world's savannas have undergone change as a result of grazing by sheep, goats and cattle, ranging from changes in pasture composition to woody plant encroachment. The removal of grass by grazing affects the woody plant component of woodland systems in two major ways. Grasses compete with woody plants for water in the topsoil and removal by grazing reduces this competitive effect, potentially boosting tree growth. In addition to this effect, the removal of fuel reduces both the intensity and the frequency of fires
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{
"page_id": 198843,
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which may control woody plant species. Grazing animals can have a more direct effect on woody plants by the browsing of palatable woody species. There is evidence that unpalatable woody plants have increased under grazing in savannas. Grazing also promotes the spread of weeds in savannas by the removal or reduction of the plants which would normally compete with potential weeds and hinder establishment. In addition to this, cattle and horses are implicated in the spread of the seeds of weed species such as prickly acacia (Acacia nilotica) and stylo (Stylosanthes species). Alterations in savanna species composition brought about by grazing can alter ecosystem function, and are exacerbated by overgrazing and poor land management practices. Introduced grazing animals can also affect soil condition through physical compaction and break-up of the soil caused by the hooves of animals and through the erosion effects caused by the removal of protective plant cover. Such effects are most likely to occur on land subjected to repeated and heavy grazing. The effects of overstocking are often worst on soils of low fertility and in low rainfall areas below 500 mm, as most soil nutrients in these areas tend to be concentrated in the surface so any movement of soils can lead to severe degradation. Alteration in soil structure and nutrient levels affects the establishment, growth and survival of plant species and in turn can lead to a change in woodland structure and composition. That being said, impact of grazing animals can be reduced. Looking at Elephant impact on Savannas, the overall impact is reduced in the presence of rainfall and fences. === Tree clearing === Large areas of Australian and South American savannas have been cleared of trees, and this clearing continues today. For example, land clearing and fracking threaten the Northern Territory, Australia savanna,
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{
"page_id": 198843,
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"title": "Savanna"
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and 480,000 ha of savanna were being cleared annually in Queensland in the 2000s, primarily to improve pasture production. Substantial savanna areas have been cleared of woody vegetation and much of the area that remains today is vegetation that has been disturbed by either clearing or thinning at some point in the past. Clearing is carried out by the grazing industry in an attempt to increase the quality and quantity of feed available for stock and to improve the management of livestock. The removal of trees from savanna land removes the competition for water from the grasses present, and can lead to a two to fourfold increase in pasture production, as well as improving the quality of the feed available. Since stock carrying capacity is strongly correlated with herbage yield, there can be major financial benefits from the removal of trees, such as assisting with grazing management: regions of dense tree and shrub cover harbors predators, leading to increased stock losses, for example, while woody plant cover hinders mustering in both sheep and cattle areas. A number of techniques have been employed to clear or kill woody plants in savannas. Early pastoralists used felling and girdling, the removal of a ring of bark and sapwood, as a means of clearing land. In the 1950s arboricides suitable for stem injection were developed. War-surplus heavy machinery was made available, and these were used for either pushing timber, or for pulling using a chain and ball strung between two machines. These two new methods of timber control, along with the introduction and widespread adoption of several new pasture grasses and legumes promoted a resurgence in tree clearing. The 1980s also saw the release of soil-applied arboricides, notably tebuthiuron, that could be utilised without cutting and injecting each individual tree. In many ways "artificial"
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"page_id": 198843,
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"title": "Savanna"
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clearing, particularly pulling, mimics the effects of fire and, in savannas adapted to regeneration after fire as most Queensland savannas are, there is a similar response to that after fire. Tree clearing in many savanna communities, although causing a dramatic reduction in basal area and canopy cover, often leaves a high percentage of woody plants alive either as seedlings too small to be affected or as plants capable of re-sprouting from lignotubers and broken stumps. A population of woody plants equal to half or more of the original number often remains following pulling of eucalypt communities, even if all the trees over 5 metres are uprooted completely. === Exotic plant species === A number of exotic plants species have been introduced to savannas around the world. Amongst the woody plant species are serious environmental weeds such as Prickly Acacia (Acacia nilotica), Rubbervine (Cryptostegia grandiflora), Mesquite (Prosopis spp.), Lantana (Lantana camara and L. montevidensis) and Prickly Pear (Opuntia spp.). A range of herbaceous species have also been introduced to these woodlands, either deliberately or accidentally including Rhodes grass and other Chloris species, Buffel grass (Cenchrus ciliaris), Giant rat's tail grass (Sporobolus pyramidalis) parthenium (Parthenium hysterophorus) and stylos (Stylosanthes spp.) and other legumes. These introductions have the potential to significantly alter the structure and composition of savannas worldwide, and have already done so in many areas through a number of processes including altering the fire regime, increasing grazing pressure, competing with native vegetation and occupying previously vacant ecological niches. Other plant species include: white sage, spotted cactus, cotton seed, rosemary. === Climate change === Human induced climate change resulting from the greenhouse effect may result in an alteration of the structure and function of savannas. Some authors have suggested that savannas and grasslands may become even more susceptible to woody plant encroachment
|
{
"page_id": 198843,
"source": null,
"title": "Savanna"
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as a result of greenhouse induced climate change. However, a recent case described a savanna increasing its range at the expense of forest in response to climate variation, and potential exists for similar rapid, dramatic shifts in vegetation distribution as a result of global climate change, particularly at ecotones such as savannas so often represent. == Savanna ecoregions == A savanna can simply be distinguished by the open savanna, where grass prevails and trees are rare; and the wooded savanna, where the trees are densest, bordering an open woodland or forest. Specific savanna ecoregions of several different types include: Tropical savannas are classified with tropical and subtropical grasslands and shrublands as the tropical and subtropical grasslands, savannas, and shrublands biome. The savannas of Africa, including the Serengeti, famous for its wildlife, are typical of this type. The Brazilian savanna (Cerrado) is also included in this category, known for its exotic and varied flora. Other examples include the Kimberley tropical savanna, Central Zambezian miombo woodlands, Guinean forest–savanna mosaic, Cape York Peninsula tropical savanna, Somali Acacia–Commiphora bushlands and thickets, Terai–Duar savanna and grasslands and the Victoria Basin forest–savanna mosaic. Subtropical and temperate savannas are mid-latitude savannas with wetter summers and drier winters. They are classified with temperate savannas and shrublands as the temperate grasslands, savannas, and shrublands biome, that for example cover much of the plains of southeastern Australia, northern India, Southern Africa, southeastern Argentina and Uruguay. Examples of subtropical and temperate savannas include the Southeast Australia temperate savanna, Argentine Espinal, Pampas, Cumberland Plain Woodland, Southern Cone Mesopotamian savanna, New England Peppermint Grassy Woodland and the Uruguayan savanna. Mediterranean savannas are mid-latitude savannas in Mediterranean climate regions, with mild, rainy winters and hot, dry summers, part of the Mediterranean forests, woodlands, and scrub biome. The oak tree savannas of California, part of
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{
"page_id": 198843,
"source": null,
"title": "Savanna"
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|
the California chaparral and woodlands ecoregion, fall into this category, including the Temperate Grassland of South Australia, which features eucalyptuses. Parts of the Middle East steppe and the Eastern Mediterranean conifer–sclerophyllous–broadleaf forests may also feature savanna-like landscapes. Flooded savannas are savannas that are flooded seasonally or year-round. They are classified with flooded savannas as the flooded grasslands and savannas biome, which occurs mostly in the tropics and subtropics. Examples include the Everglades, Mesopotamian Marshes, Pantanal, Nile Delta flooded savanna, Lake Chad flooded savanna, Zambezian flooded grasslands, and the Sudd. Montane savannas are mid- to high-altitude savannas, located in a few spots around the world's high mountain regions, part of the montane grasslands and shrublands biome. The Bogotá savanna, located at an average altitude of 2,550 metres (8,370 ft) on the Altiplano Cundiboyacense, Eastern Ranges of the Andes, is an example of a montane savanna. The savannas of the Angolan Scarp savanna and woodlands ecoregion are a lower altitude example, up to 1,000 metres (3,300 ft). Other examples include the Al Hajar montane woodlands and the southern part of the Eastern Anatolian montane steppe. == See also == Pampas Pasture Prairie Rangeland Steppe Veld == References == == External links == The Savanna at barrameda.com.ar (in Spanish and Brazilian Portuguese) "Savanna" . Encyclopædia Britannica (11th ed.). 1911. "Savannas" . New International Encyclopedia. 1905.
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"page_id": 198843,
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"title": "Savanna"
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Arachidonoyl serotonin (N-arachidonoyl-serotonin, AA-5-HT) is an endogenous lipid signaling molecule. It was first described in 1998 as being an inhibitor of fatty acid amide hydrolase (FAAH). In 2007, it was shown to have analgesic properties and to act as an antagonist of the TRPV1 receptor. In 2011, it was shown to be present in the ileum and jejunum of the gastrointestinal tract and modulate glucagon-like peptide-1 (GLP-1) secretion. In addition to this, in 2016, AA-5-HT was also found to affect the signaling mechanisms responsible for anxiety, by inhibiting dopamine release from the Basolateral amygdala following fear behavior. In 2017, AA-5-HT was tested in its effects on the sleep wake cycle, where it was found to affect the sleep homeostasis when used in conjunction with molecules and chemicals that affect wake-related neurotransmitters. == See also == Endocannabinoid system == References ==
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{
"page_id": 33818813,
"source": null,
"title": "Arachidonoyl serotonin"
}
|
In cell biology, there are a multitude of signalling pathways. Cell signalling is part of the molecular biology system that controls and coordinates the actions of cells. Akt/PKB signalling pathway AMPK signalling pathway cAMP-dependent pathway Eph/ephrin signalling pathway Hedgehog signalling pathway Hippo signalling pathway Insulin signal transduction pathway JAK-STAT signalling pathway MAPK/ERK signalling pathway mTOR signalling pathway Nodal signalling pathway Notch signalling pathway PI3K/AKT/mTOR signalling pathway TGF beta signalling pathway TLR signalling pathway VEGF signalling pathway Wnt signalling pathway == References ==
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{
"page_id": 52431039,
"source": null,
"title": "List of signalling pathways"
}
|
Filip Neriusz Walter or Philippe Walter (31 May 1810 – 9 April 1847) was a Polish chemist and pioneer of organic chemistry who worked in Paris. He extracted and characterized several compounds, including toluene and octene. == Life == At 15 years old, Walter was one of the youngest students of the Jagiellonian University in Kraków, where he studied history and chemistry in 1825–28. Subsequently, he studied at Berlin University, receiving a Ph.D. with his dissertation On Combination of Oxalic Acid and Alkali. Simultaneously he served as assistant to Professor Eilhard Mitscherlich. On the outbreak of the November 1830 Uprising, he went to Warsaw and joined the Polish Army. He served as adjutant to Colonel Samuel Różycki, commander of the 7th infantry regiment. In 1831, aged 21, he was named professor of chemistry at the Jagiellonian University, but he left to Paris where he worked with Jean-Baptiste Dumas at the École Centrale des Arts et Manufactures. Here Walter began to teach analytical chemistry. He examined plant extracts and along with Pierre Joseph Pelletier he extracted toluene by distillation of pine resin in 1838. In 1840 they extracted octene (C8H16) from naphtha. Walter was able to demonstrate the substitution of carbon by sulphur in camphor in 1842. His achievements won him recognition from the French Academy. In sum, he isolated and studied 24 new chemical compounds, including toluene, biphenyl, nitrotoluene, cedrene, potassium hydroxide dihydrate, chromyl chloride, cumene, benzyl chloride, benzyl bromide, and menthene. In 1847 he was decorated with the cross of the Legion of Honour. == See also == List of Poles == Notes == == Bibliography == "Walter, Filip Neriusz", in Stanley S. Sokol, The Polish Biographical Dictionary, Bolchazy-Carducci Publishers, 1992. Stefan Sękowski, Stefan Szostkiewicz, Serce i retorta (The Heart and the Retort), Warsaw, Wiedza Powszechna, 1957. Aleksander Jełowicki,
|
{
"page_id": 45615293,
"source": null,
"title": "Filip Neriusz Walter"
}
|
Wspomnienia (Memoirs), Paris, 1839. Stanisław Wodzicki, Wspomnienia z przeszłości (Memoirs of the Past). Kraków, 1873. Adolphe Wurz, Historia poglądów chemicznych (A History of Chemical Views), Warsaw, 1886.
|
{
"page_id": 45615293,
"source": null,
"title": "Filip Neriusz Walter"
}
|
In evolutionary biology, robustness of a biological system (also called biological or genetic robustness) is the persistence of a certain characteristic or trait in a system under perturbations or conditions of uncertainty. Robustness in development is known as canalization. According to the kind of perturbation involved, robustness can be classified as mutational, environmental, recombinational, or behavioral robustness etc. Robustness is achieved through the combination of many genetic and molecular mechanisms and can evolve by either direct or indirect selection. Several model systems have been developed to experimentally study robustness and its evolutionary consequences. == Classification == === Mutational robustness === Mutational robustness (also called mutation tolerance) describes the extent to which an organism's phenotype remains constant in spite of mutation. Robustness can be empirically measured for several genomes and individual genes by inducing mutations and measuring what proportion of mutants retain the same phenotype, function or fitness. More generally, robustness corresponds to the neutral band in the distribution of fitness effects of mutation (i.e. the frequencies of different fitnesses of mutants). Proteins so far investigated have shown a tolerance to mutations of roughly 66% (i.e. two thirds of mutations are neutral). Conversely, measured mutational robustnesses of organisms vary widely. For example, >95% of point mutations in C. elegans have no detectable effect and even 90% of single gene knockouts in E. coli are non-lethal. Viruses, however, only tolerate 20-40% of mutations and hence are much more sensitive to mutation. === Robustness to stochasticity === Biological processes at the molecular scale are inherently stochastic. They emerge from a combination of stochastic events that happen given the physico-chemical properties of molecules. For instance, gene expression is intrinsically noisy. This means that two cells in exactly identical regulatory states will exhibit different mRNA contents. The cell population level log-normal distribution of mRNA content
|
{
"page_id": 31066305,
"source": null,
"title": "Robustness (evolution)"
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|
follows directly from the application of the Central Limit Theorem to the multi-step nature of gene expression regulation. === Environmental robustness === In varying environments, perfect adaptation to one condition may come at the expense of adaptation to another. Consequently, the total selection pressure on an organism is the average selection across all environments weighted by the percentage time spent in that environment. Variable environment can therefore select for environmental robustness where organisms can function across a wide range of conditions with little change in phenotype or fitness (biology). Some organisms show adaptations to tolerate large changes in temperature, water availability, salinity or food availability. Plants, in particular, are unable to move when the environment changes and so show a range of mechanisms for achieving environmental robustness. Similarly, this can be seen in proteins as tolerance to a wide range of solvents, ion concentrations or temperatures. == Genetic, molecular and cellular causes == Genomes mutate by environmental damage and imperfect replication, yet they display remarkable tolerance. This comes from robustness both at many different levels. === Organism mutational robustness === There are many mechanisms that provide genome robustness. For example, genetic redundancy reduces the effect of mutations in any one copy of a multi-copy gene. Additionally the flux through a metabolic pathway is typically limited by only a few of the steps, meaning that changes in function of many of the enzymes have little effect on fitness. Similarly metabolic networks have multiple alternate pathways to produce many key metabolites. === Protein mutational robustness === Protein mutation tolerance is the product of two main features: the structure of the genetic code and protein structural robustness. Proteins are resistant to mutations because many sequences can fold into highly similar structural folds. A protein adopts a limited ensemble of native conformations because those
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{
"page_id": 31066305,
"source": null,
"title": "Robustness (evolution)"
}
|
conformers have lower energy than unfolded and mis-folded states (ΔΔG of folding). This is achieved by a distributed, internal network of cooperative interactions (hydrophobic, polar and covalent). Protein structural robustness results from few single mutations being sufficiently disruptive to compromise function. Proteins have also evolved to avoid aggregation as partially folded proteins can combine to form large, repeating, insoluble protein fibrils and masses. There is evidence that proteins show negative design features to reduce the exposure of aggregation-prone beta-sheet motifs in their structures. Additionally, there is some evidence that the genetic code itself may be optimised such that most point mutations lead to similar amino acids (conservative). Together these factors create a distribution of fitness effects of mutations that contains a high proportion of neutral and nearly-neutral mutations. === Gene expression robustness === During embryonic development, gene expression must be tightly controlled in time and space in order to give rise to fully functional organs. Developing organisms must therefore deal with the random perturbations resulting from gene expression stochasticity. In bilaterians, robustness of gene expression can be achieved via enhancer redundancy. This happens when the expression of a gene under the control of several enhancers encoding the same regulatory logic (ie. displaying binding sites for the same set of transcription factors). In Drosophila melanogaster such redundant enhancers are often called shadow enhancers. Furthermore, in developmental contexts were timing of gene expression in important for the phenotypic outcome, diverse mechanisms exist to ensure proper gene expression in a timely manner. Poised promoters are transcriptionally inactive promoters that display RNA polymerase II binding, ready for rapid induction. In addition, because not all transcription factors can bind their target site in compacted heterochromatin, pioneer transcription factors (such as Zld or FoxA) are required to open chromatin and allow the binding of other transcription
|
{
"page_id": 31066305,
"source": null,
"title": "Robustness (evolution)"
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factors that can rapidly induce gene expression. Open inactive enhancers are call poised enhancers. Cell competition is a phenomenon first described in Drosophila where mosaic Minute mutant cells (affecting ribosomal proteins) in a wild-type background would be eliminated. This phenomenon also happens in the early mouse embryo where cells expressing high levels of Myc actively kill their neighbors displaying low levels of Myc expression. This results in homogeneously high levels of Myc. === Developmental patterning robustness === Patterning mechanisms such as those described by the French flag model can be perturbed at many levels (production and stochasticity of the diffusion of the morphogen, production of the receptor, stochastic of the signaling cascade, etc). Patterning is therefore inherently noisy. Robustness against this noise and genetic perturbation is therefore necessary to ensure proper that cells measure accurately positional information. Studies of the zebrafish neural tube and antero-posterior patternings has shown that noisy signaling leads to imperfect cell differentiation that is later corrected by transdifferentiation, migration or cell death of the misplaced cells. Additionally, the structure (or topology) of signaling pathways has been demonstrated to play an important role in robustness to genetic perturbations. Self-enhanced degradation has long been an example of robustness in System biology. Similarly, robustness of dorsoventral patterning in many species emerges from the balanced shuttling-degradation mechanisms involved in BMP signaling. == Evolutionary consequences == Since organisms are constantly exposed to genetic and non-genetic perturbations, robustness is important to ensure the stability of phenotypes. Also, under mutation-selection balance, mutational robustness can allow cryptic genetic variation to accumulate in a population. While phenotypically neutral in a stable environment, these genetic differences can be revealed as trait differences in an environment-dependent manner (see evolutionary capacitance), thereby allowing for the expression of a greater number of heritable phenotypes in populations exposed to a
|
{
"page_id": 31066305,
"source": null,
"title": "Robustness (evolution)"
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|
variable environment. Being robust may even be a favoured at the expense of total fitness as an evolutionarily stable strategy (also called survival of the flattest). A high but narrow peak of a fitness landscape confers high fitness but low robustness as most mutations lead to massive loss of fitness. High mutation rates may favour population of lower, but broader fitness peaks. More critical biological systems may also have greater selection for robustness as reductions in function are more damaging to fitness. Mutational robustness is thought to be one driver for theoretical viral quasispecies formation. === Emergent mutational robustness === Natural selection can select directly or indirectly for robustness. When mutation rates are high and population sizes are large, populations are predicted to move to more densely connected regions of neutral network as less robust variants have fewer surviving mutant descendants. The conditions under which selection could act to directly increase mutational robustness in this way are restrictive, and therefore such selection is thought to be limited to only a few viruses and microbes having large population sizes and high mutation rates. Such emergent robustness has been observed in experimental evolution of cytochrome P450s and B-lactamase. Conversely, mutational robustness may evolve as a byproduct of natural selection for robustness to environmental perturbations. === Robustness and evolvability === Mutational robustness has been thought to have a negative impact on evolvability because it reduces the mutational accessibility of distinct heritable phenotypes for a single genotype and reduces selective differences within a genetically diverse population. Counter-intuitively however, it has been hypothesized that phenotypic robustness towards mutations may actually increase the pace of heritable phenotypic adaptation when viewed over longer periods of time. One hypothesis for how robustness promotes evolvability in asexual populations is that connected networks of fitness-neutral genotypes result in mutational robustness
|
{
"page_id": 31066305,
"source": null,
"title": "Robustness (evolution)"
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which, while reducing accessibility of new heritable phenotypes over short timescales, over longer time periods, neutral mutation and genetic drift cause the population to spread out over a larger neutral network in genotype space. This genetic diversity gives the population mutational access to a greater number of distinct heritable phenotypes that can be reached from different points of the neutral network. However, this mechanism may be limited to phenotypes dependent on a single genetic locus; for polygenic traits, genetic diversity in asexual populations does not significantly increase evolvability. In the case of proteins, robustness promotes evolvability in the form of an excess free energy of folding. Since most mutations reduce stability, an excess folding free energy allows toleration of mutations that are beneficial to activity but would otherwise destabilise the protein. In sexual populations, robustness leads to the accumulation of cryptic genetic variation with high evolutionary potential. Evolvability may be high when robustness is reversible, with evolutionary capacitance allowing a switch between high robustness in most circumstances and low robustness at times of stress. == Methods and model systems == There are many systems that have been used to study robustness. In silico models have been used to model promoters, RNA secondary structure, protein lattice models, or gene networks. Experimental systems for individual genes include enzyme activity of cytochrome P450, B-lactamase, RNA polymerase, and LacI have all been used. Whole organism robustness has been investigated in RNA virus fitness, bacterial chemotaxis, Drosophila fitness, segment polarity network, neurogenic network and bone morphogenetic protein gradient, C. elegans fitness and vulval development, and mammalian circadian clock. == See also == Distribution of fitness effects Evolvability Canalization Neutral network (evolution) Epistasis Evolutionary capacitance Fitness landscape Evolutionary developmental biology == References ==
|
{
"page_id": 31066305,
"source": null,
"title": "Robustness (evolution)"
}
|
The molecular formula C20H25N3O2 (molar mass: 339.43 g/mol, exact mass: 339.1947 u) may refer to: 12-Hydroxy-LSD Methylergometrine, or methylergonovine Propisergide WAY-317,538 (SEN-12333)
|
{
"page_id": 24053951,
"source": null,
"title": "C20H25N3O2"
}
|
Butterfly counts are often carried out in North America and Europe to estimate the populations of butterflies in a specific geographical area. The counts are conducted by interested, mostly non-professional, residents of the area who maintain an interest in determining the numbers and species of butterflies in their locale. A butterfly count usually occurs at a specific time during the year and is sometimes coordinated to occur with other counts which may include a park, county, entire state or country. The results of the counts are usually shared with other interested parties including professional lepidopterists and researchers. The data gathered during a count can indicate population changes and health within a species. == Sponsors == Professionals, universities, clubs, elementary and secondary schools, other educational providers, nature preserves, parks, and amateur organizations can organize a count. The participants often receive training to help them identify the butterfly species. The North American Butterfly Association organized over 400 counts in 2014. == Types of butterfly counts == There are several methods for counting butterflies currently in use, with the notable division being between restricted and open searches. Most counts are designed to count all butterflies observed in a locality. The purpose of a count is to estimate butterfly populations in a larger area from a smaller sample. Counts may be targeted at single species and, in some cases, butterflies are observed and counted as they move from one area to another. A heavily researched example of butterfly migration is the annual migration of monarch butterflies in North America. Some programs will tag butterflies to trace their migration routes, but these are migratory programs and not butterfly counts. Butterfly counts are sometimes done where there is a concentration (a roost) of a species of butterflies in an area. One example of this is the
|
{
"page_id": 43518148,
"source": null,
"title": "Butterfly count"
}
|
winter count of western monarch butterflies as they roost together at sites in California, northern Mexico and Arizona. === Restricted searches: transects === Frequently referred to as "Pollard Transects" or "Pollard Walks" in North America, a transect is a protocol designed to standardize the recording of butterfly observations, the initial format was outlined by Ernie Pollard in 1977. The transect protocol involves one observer walking a fixed path at a constant pace, multiple times in a season. Butterflies are counted when they are seen within a prescribed distance from the path, often 2.5 meters on either side of the path, and only when the butterflies are seen in front of, or above, the observer (i.e., no backtracking). A second person may work with the observer to identify and/or photograph insects spotted by the observer. Transects should not change from year to year and ideally should sample a variety of habitats. Examples of long-running restricted searches are Art Shapiro's Butterfly Project in the US (started in 1972), and the UK Butterfly Monitoring Scheme (started in 1976). === Open searches === Open searches, also sometimes referred to as "checklist searches", are intended to focus on the presence and abundance of butterflies in a given area. They can be single events such as the North American Butterfly Association's July 1 and July 4 counts in Canada and the U.S. respectively, or they can be regular or ad hoc counts conducted by individuals or groups. The lack of formal structure makes them suitable for many citizen science programs. In terms of the relative outcomes or the efficacy of open vs. restricted searches, studies have shown that open searches are more likely to find a greater number of species in a given area. Royer, et al. note that one reason for this is that during
|
{
"page_id": 43518148,
"source": null,
"title": "Butterfly count"
}
|
an open search, the "observer is free to search out places where butterflies typically would breed or congregate" rather than follow the fixed path of a transect. === Opportunistic sightings === Opportunistic or incidental sightings are butterfly sightings that are not part of a formal count. Observers may note signal butterflies or multiple species. An example of an opportunistic sighting is observing a butterfly in a garden and reporting it. === Atlas projects === Described as a "special type of open search", atlas projects are generally targeted at a specific geographical area such as a province or state. The goal is to assess the presence or absence of species, usually over a multi-year period. Each atlas program will design its own data requirements but as they are measuring abundance and presence, they tend to accept data from transects, counts, and opportunistic sightings to build a database. The longest-running atlas program in North America is the Ontario Butterfly Atlas Online, which is supported by the Toronto Entomologists' Association and began collecting data in 1969. === Bait stations === Transects and open searches are not as comprehensive in tropical locations due to issues such as the density of flora and the height of the forest canopy. A counting system using bait stations with fermenting fruit has been used to assess specific populations. == Quantifying observations == Participants are encouraged to employ a number of techniques to quantify large aggregations by making estimates of butterflies: concentrated along linear features concentrated in an area of uniform habitat concentrated on certain plants butterflies in flight The number of butterflies can be estimated by the area size they inhabit, for example, in the overwintering population present in Mexico the population expressed in hectares. Butterflies can be counted in their egg, larvae and instar number. Butterflies are
|
{
"page_id": 43518148,
"source": null,
"title": "Butterfly count"
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|
sometimes captured, tagged, and recovered. The number of tags recovered in a specific area is used to determine population size and direction of flight. == See also == Butterfly Conservation North American Butterfly Association Lepidoptera migration List of butterflies of Great Britain Monarch Butterfly Biosphere Reserve Animal Migration eButterfly == References == == External links == UK Big Butterfly Count eButterfly - North American butterfly reporting NABA Butterfly Counts Monarch Watch Ontario Butterfly Atlas - a dynamic map of 417,000 butterfly sightings in the province (as of June 2020) Butterfly Conservation Europe
|
{
"page_id": 43518148,
"source": null,
"title": "Butterfly count"
}
|
A backdraft (North American English), backdraught (British English) or smoke explosion is the abrupt burning of superheated gases in a fire caused when oxygen rapidly enters a hot, oxygen-depleted environment; for example, when a window or door to an enclosed space is opened or broken. Backdrafts are typically seen as a blast of smoke and/or flame out of an opening of a building. Backdrafts present a serious threat to firefighters. There is some debate concerning whether backdrafts should be considered a type of flashover. == Burning == When material is heated enough, it begins to break down into smaller compounds, including flammable or even explosive gas, typically hydrocarbons. This is called pyrolysis, and does not require oxygen. If oxygen is also provided, then the hydrocarbons can combust, starting a fire. If material undergoing pyrolysis is later given sufficient oxygen, the hydrocarbons will ignite, and therefore, combustion takes place. == Cause == A backdraft can occur when a compartment fire has little or no ventilation. Due to this, little or no oxygen can flow into the compartment. Then, because fires reduce oxygen, the oxygen concentration decreases. When the oxygen concentration becomes too low to support combustion, some or all of the combustion switches to pyrolysis. However, the hydrocarbons and smoke (primarily particulate matter) remain at a temperature hot enough to auto-ignite. If oxygen is then re-introduced to the compartment, e.g. by opening a door or window to a closed room, while the gasses are still hot enough to auto-ignite, combustion will restart, often abruptly or even explosively, as the gasses are heated by the combustion and expand rapidly because of the rapidly increasing temperature, combined with the energy released from combustion. The colour and movement of smoke is used by firefighters to infer fire conditions, including the risk of backdraft. Characteristic
|
{
"page_id": 460997,
"source": null,
"title": "Backdraft"
}
|
warning signs of a backdraft include yellow or brown smoke, smoke which exits small holes in puffs (a sort of breathing effect) and is often found around the edges of doors and windows, and windows which appear brown or black when viewed from the exterior due to soot from incomplete combustion. This is an indication that the room lacks enough oxygen to permit oxidation of the soot particles. Firefighters often look to see if there is soot on the inside of windows and in any cracks in the window (caused e.g. by the heat). The windows may also have a slight vibration due to varying pressure within the compartment due to intermittent combustion. If firefighters discover a room sucking air into itself, for example through a crack, they generally evacuate immediately, because this is a strong indication that a backdraft is imminent. Due to pressure differences, puffs of smoke are sometimes drawn back into the enclosed space from which they emanated, which is how the term backdraft originated. Backdrafts are very dangerous, often surprising even experienced firefighters. The most common tactic used by firefighters to defuse a potential backdraft is to ventilate a room from its highest point, allowing the heat and smoke to escape without igniting. Common signs of imminent backdraft include a sudden inrush of air upon creating an opening into a closed compartment, no visible signs of flame in a hot compartment (fire above its upper flammability limit), "pulsing" smoke plumes from openings, and auto-ignition of hot gases at openings as they mix with oxygen in the surrounding air. == Backdrafts and flashovers == ISO 13943 broadly defines flashover as a "transition to a state of total surface involvement in a fire of combustible materials within an enclosure." This definition embraces several different scenarios and includes backdrafts,
|
{
"page_id": 460997,
"source": null,
"title": "Backdraft"
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|
but there is considerable disagreement about categorizing backdrafts as flashovers. In common usage, the term flashover describes the near-simultaneous ignition of material caused by heat attaining the autoignition temperature of the combustible material and gases in an enclosure. Flashovers according to this narrower definition, i.e. those caused by rising temperatures, would not be considered backdrafts since backdrafts are caused by the introduction of oxygen into an enclosed space with conditions already suitable for ignition, and are thus caused by chemical change. == In popular culture == Backdrafts were publicized by the 1991 movie Backdraft, in which a serial arsonist in Chicago uses them as a means of assassinating conspirators in a scam. In the film adaptation of Stephen King's 1408, the protagonist Mike Enslin induces one as a last-ditch effort to kill the room. The term is also used and is the title of a scene in the 2012 video game Root Double: Before Crime * After Days. == References == == External links == A backdraft (still image and video) (in Swedish) Slow Motion Backdraft video White Smoke Warning Daniel's Block Fire-BACKDRAFT
|
{
"page_id": 460997,
"source": null,
"title": "Backdraft"
}
|
ASME BPE (American Society of Mechanical Engineers: Bioprocessing Equipment) is an international Standard developed as an aid for the design and construction of equipment intended for use in the manufacturing of biopharmaceuticals. The standard is approved as an American National Standard by the ASME Board of Pressure Technologies. The first edition of this Standard was approved as an American National Standard on May 20, 1997. The most recent edition was approved by ANSI on March 21, 2022. New editions of the standard are generally approved and published every two years. == Purpose and Scope == The ASME Bioprocessing Equipment (BPE) Standard was developed to aid in the design and construction of new fluid processing equipment used in the manufacture of biopharmaceuticals, where a defined level of purity and bioburden control is required. The Standard typically applies to (a) components that are in contact with the product, raw materials, or product intermediates during manufacturing, development, or scale-up (b) systems that are a critical part of product manufacture [e.g., water-for-injection (WFI), clean steam, filtration, and intermediate product storage]. Within scope also is the design and construction of piping systems for hygienic service. Multi-Use metallic, Multi-Use plastic and Single-Use materials of construction and design, are all covered in the scope of the 2022 edition. New editions of the ASME BPE Standard may be used beginning with the date of issuance and become effective 6 months after the date of issuance. The ASME BPE Standard provides requirements for systems and components that are subject to cleaning and sanitization and/or sterilization including systems that are cleaned in place (CIP’d) and/or steamed in place (SIP’d) and/or other suitable processes used in the manufacturing of biopharmaceuticals. It also provides requirements for single-use systems and components used in the above listed applications. This Standard may be used, in
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{
"page_id": 15599815,
"source": null,
"title": "ASME BPE"
}
|
whole or in part, for other applications where bioburden risk is a concern. This Standard applies to: (a) new system (and component) design and fabrication (b) definition of system boundaries (c) specific metallic, polymeric, and elastomeric (e.g., seals and gaskets) materials of construction (d) component dimensions and tolerances (e) surface finishes (f) materials joining (g) examinations, inspections, and testing (h) certification This Standard is intended to apply to new fabrication and construction. It may be used in other cases with consensus between the system owner/user, engineer, installation contractor, and inspection contractor. Please note: This paraphrased information comes from Part GR-1 and GR-2 of the ASME BPE Standard, 2022 edition, and was condensed for brevity to a broader audience. The intent of this article is general knowledge and general information for a wider audience outside of bioprocessing and engineering. Please purchase a copy of the most recent edition for complete understanding, reference, detail, context and content. == Structure == The ASME BPE is a voluntary consensus standard written by a team of over three hundred balanced subject matter experts. These individuals provide their knowledge and experience to drive technology and innovation forward safely and responsibly for the manufacturing of modern biopharmaceuticals. ASME controls the development and approval of all content by rigorous policies and procedures, ensuring that a thorough vetting process occurs and that the information published is reliable and trustworthy. The Standard (2022 Edition) is split into the following Chapters and Parts. The teams that develop each Part function as working teams, to develop, approve and refine content. == Chapter 1, Introduction, Scope, and General Requirements == Part GR, General Requirements == Chapter 2, Certification == Part CR, Certification Requirements == Chapter 3, Materials == Part MM, Metallic Materials Part PM, Polymeric and Other Nonmetallic Materials == Chapter 4, Design
|
{
"page_id": 15599815,
"source": null,
"title": "ASME BPE"
}
|
for Multiuse == Part SD, Systems Design for Multiuse == Chapter 5, Process Components for Multiuse == Part DT, Dimensions and Tolerances for Process Components Part PI, Process Instrumentation for Multiuse Part MC, Components for Multiuse == Chapter 6, Fabrication, Assembly, and Erection for Multiuse == Part MJ, Materials Joining for Multiuse Part SF, Process Contact Surface Finishes for Multiuse == Chapter 7, Design for Single-Use == Part SU, Systems Design for Single-Use == Chapter 8, Process Components for Single-Use == Part SC, Components for Single-Use == Chapter 9, Fabrication, Assembly, and Erection for Single-Use == Part SJ, Joining Methods for Single-Use == How to get involved == The ASME BPE meets three times a year in person, but offline meetings occur to develop and refine existing content. Unless otherwise stated, the sessions are free and open to all, and volunteers are welcome. ASME posts the details for all meetings on their website; the link is also below. == False claims of codification == At least as early as April 19, 2011, ASME published a web page which falsely indicated the ASME BPE standard had been adopted by the State of California. The statement was based upon California's codification of Section 443, Group L—known as the "L Occupancy"—within Part 1 of the California Building Code. The web page claimed that the "L Occupancy" referenced the ASME BPE standard, but no such reference appears as described. A codification of the ASME BPE standard via such a reference is generally precluded by the building code's own requirement that any content that is not a building standard as defined in California's Health and Safety Code Section 18909 shall not be construed as part of the provisions of the California Building Code (Part 1, Chapter 1, Section 1.1.6). The web page has been removed.
|
{
"page_id": 15599815,
"source": null,
"title": "ASME BPE"
}
|
== See also == ISO 2852 Single use systems == References == Huitt, Bill. (2016). Bioprocessing Piping and Equipment Design: A Companion Guide for the ASME BPE Standard (Wiley-ASME Press Series) 1st Edition. Wiley-ASME Press Series. https://www.amazon.com/Bioprocessing-Piping-Equipment-Design-Wiley-ASME/dp/1119284236 == External links == Bioprocessing Equipment Certification. ASME Certification Program application and details for stainless steel tubing and fittings ASME BPE, 2022 (Current) Edition. ASME BPE Codes & Standards, BPE-2022 ASME Calendar of Events. ASME Searchable Calendar of Events ASME Bioprocessing Equipment Standards Committee
|
{
"page_id": 15599815,
"source": null,
"title": "ASME BPE"
}
|
The molecular formula C21H27N3O2 (molar mass: 353.47 g/mol) may refer to: 1-Hydroxymethyl-LSD 12-Methoxy-LSD Methysergide
|
{
"page_id": 24053959,
"source": null,
"title": "C21H27N3O2"
}
|
Abiotic stress is the negative impact of non-living factors on the living organisms in a specific environment. The non-living variable must influence the environment beyond its normal range of variation to adversely affect the population performance or individual physiology of the organism in a significant way. Whereas a biotic stress would include living disturbances such as fungi or harmful insects, abiotic stress factors, or stressors, are naturally occurring, often intangible and inanimate factors such as intense sunlight, temperature or wind that may cause harm to the plants and animals in the area affected. Abiotic stress is essentially unavoidable. Abiotic stress affects animals, but plants are especially dependent, if not solely dependent, on environmental factors, so it is particularly constraining. Abiotic stress is the most harmful factor concerning the growth and productivity of crops worldwide. Research has also shown that abiotic stressors are at their most harmful when they occur together, in combinations of abiotic stress factors. == Examples == Abiotic stress comes in many forms. The most common of the stressors are the easiest for people to identify, but there are many other, less recognizable abiotic stress factors which affect environments constantly. The most basic stressors include: High winds Extreme temperatures Drought Flood Other natural disasters, such as tornadoes and wildfires. Cold Heat Nutrient deficiency Lesser-known stressors generally occur on a smaller scale. They include: poor edaphic conditions like rock content and pH levels, high radiation, compaction, contamination, and other, highly specific conditions like rapid rehydration during seed germination. == Effects == Abiotic stress, as a natural part of every ecosystem, will affect organisms in a variety of ways. Although these effects may be either beneficial or detrimental, the location of the area is crucial in determining the extent of the impact that abiotic stress will have. The higher the
|
{
"page_id": 2250,
"source": null,
"title": "Abiotic stress"
}
|
latitude of the area affected, the greater the impact of abiotic stress will be on that area. So, a taiga or boreal forest is at the mercy of whatever abiotic stress factors may come along, while tropical zones are much less susceptible to such stressors. === Benefits === While abiotic stress may have negative impacts on individual organisms, there are cases where abiotic stress plays an important role in maintaining a healthy ecosystem. Important ecosystem mechanisms and improved overall stress tolerance may rely on occasional low levels of abiotic stress. One example of a situation where abiotic stress plays a constructive role in an ecosystem is in natural wildfires. Smaller fires are useful in reducing the overall fuel load of an area of forest or prairie. By clearing out dead brush and other organic matter, the risk of catastrophic and widespread fire decreases, and the residual ash of smaller fires helps add nutrients back into the soil. The observed benefits of these smaller and more controlled fires on land usability and species populations have led to the use of prescribed burning by humans for centuries. Varying perspectives on the benefits and risks of fire to ecosystems have influenced official policy through history. The U.S. Forest Service, initially focused on fire control, changed its policy to one of fire management in 1974, recognizing these fires as a natural part of an ecosystem. There is also evidence that a diverse fire history between patches of land within an area has been shown to benefit transitional landscapes between savanna and forest. Even though it is healthy for an ecosystem, a wildfire can still be considered an abiotic stressor, because it puts stress on individual organisms within the area. On the larger scale, though, natural wildfires are positive manifestations of abiotic stress. What also
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{
"page_id": 2250,
"source": null,
"title": "Abiotic stress"
}
|
needs to be taken into account when looking for benefits of abiotic stress, is that one phenomenon may not affect an entire ecosystem in the same way. While a flood will kill most plants living low on the ground in a certain area, if there is rice there, it will thrive in the wet conditions. Another example of this is in phytoplankton and zooplankton. The same types of conditions are usually considered stressful for these two types of organisms. They act very similarly when exposed to ultraviolet light and most toxins, but at elevated temperatures the phytoplankton reacts negatively, while the thermophilic zooplankton reacts positively to the increase in temperature. The two may be living in the same environment, but an increase in temperature of the area would prove stressful only for one of the organisms. Lastly, abiotic stress has enabled species to grow, develop, and evolve, through the process of natural selection. Heritable traits that improve an organism's resiliency under stressed conditions increase the likelihood that the organism will survive and reproduce, enabling it to pass these traits to the next generation. Both plants and animals have evolved mechanisms allowing them to survive extremes. === Detriments === One of the detriments concerning abiotic stress involves farming. It has been claimed by one study that abiotic stress causes the most crop loss of any other factor and that most major crops are reduced in their yield by more than 50% from their potential yield. Because abiotic stress is widely considered a detrimental effect, the research on this branch of the issue is extensive. For more information on the harmful effects of abiotic stress, see the sections below on plants and animals. == In plants == A plant's first line of defense against abiotic stress is in its roots. If the
|
{
"page_id": 2250,
"source": null,
"title": "Abiotic stress"
}
|
soil holding the plant is healthy and biologically diverse, the plant will have a higher chance of surviving stressful conditions. The plant responses to stress are dependent on the tissue or organ affected by the stress. For example, transcriptional responses to stress are tissue or cell specific in roots and are quite different depending on the stress involved. One of the primary responses to abiotic stress such as high salinity is the disruption of the Na+/K+ ratio in the cytoplasm of the plant cell. High concentrations of Na+, for example, can decrease the capacity for the plant to take up water and also alter enzyme and transporter functions. Evolved adaptations to efficiently restore cellular ion homeostasis have led to a wide variety of stress tolerant plants. Facilitation, or the positive interactions between different species of plants, is an intricate web of association in a natural environment. It is how plants work together. In areas of high stress, the level of facilitation is especially high as well. This could possibly be because the plants need a stronger network to survive in a harsher environment, so their interactions between species, such as cross-pollination or mutualistic actions, become more common to cope with the severity of their habitat. Plants also adapt very differently from one another, even from a plant living in the same area. When a group of different plant species was prompted by a variety of different stress signals, such as drought or cold, each plant responded uniquely. Hardly any of the responses were similar, even though the plants had become accustomed to exactly the same home environment. Serpentine soils (media with low concentrations of nutrients and high concentrations of heavy metals) can be a source of abiotic stress. Initially, the absorption of toxic metal ions is limited by cell membrane
|
{
"page_id": 2250,
"source": null,
"title": "Abiotic stress"
}
|
exclusion. Ions that are absorbed into tissues are sequestered in cell vacuoles. This sequestration mechanism is facilitated by proteins on the vacuole membrane. An example of plants that adapt to serpentine soil are Metallophytes, or hyperaccumulators, as they are known for their ability to absorbed heavy metals using the root-to-shoot translocation (which it will absorb into shoots rather than the plant itself). They're also extinguished for their ability to absorb toxic substances from heavy metals. Chemical priming has been proposed to increase tolerance to abiotic stresses in crop plants. In this method, which is analogous to vaccination, stress-inducing chemical agents are introduced to the plant in brief doses so that the plant begins preparing defense mechanisms. Thus, when the abiotic stress occurs, the plant has already prepared defense mechanisms that can be activated faster and increase tolerance. Prior exposure to tolerable doses of biotic stresses such as phloem-feeding insect infestation have also been shown to increase tolerance to abiotic stresses in plant === Impact on food production === Abiotic stress mostly affects plants used in agriculture. Some examples of adverse conditions (which may be caused by climate change) are high or low temperatures, drought, salinity, and toxins. Rice (Oryza sativa) is a classic example. Rice is a staple food throughout the world, especially in China and India. Rice plants can undergo different types of abiotic stresses, like drought and high salinity. These stress conditions adversely affect rice production. Genetic diversity has been studied among several rice varieties with different genotypes, using molecular markers. Chickpea production is affected by drought. Chickpeas are one of the most important foods in the world. Wheat is another major crop that is affected by drought: lack of water affects the plant development, and can wither the leaves. Maize crops can be affected by high temperature
|
{
"page_id": 2250,
"source": null,
"title": "Abiotic stress"
}
|
and drought, leading to the loss of maize crops due to poor plant development. Soybean is a major source of protein, and its production is also affected by drought. === Salt stress in plants === Soil salinization, the accumulation of water-soluble salts to levels that negatively impact plant production, is a global phenomenon affecting approximately 831 million hectares of land. More specifically, the phenomenon threatens 19.5% of the world's irrigated agricultural land and 2.1% of the world's non-irrigated (dry-land) agricultural lands. High soil salinity content can be harmful to plants because water-soluble salts can alter osmotic potential gradients and consequently inhibit many cellular functions. For example, high soil salinity content can inhibit the process of photosynthesis by limiting a plant's water uptake; high levels of water-soluble salts in the soil can decrease the osmotic potential of the soil and consequently decrease the difference in water potential between the soil and the plant's roots, thereby limiting electron flow from H2O to P680 in Photosystem II's reaction center. Over generations, many plants have mutated and built different mechanisms to counter salinity effects. A good combatant of salinity in plants is the hormone ethylene. Ethylene is known for regulating plant growth and development and dealing with stress conditions. Many central membrane proteins in plants, such as ETO2, ERS1 and EIN2, are used for ethylene signaling in many plant growth processes. Mutations in these proteins can lead to heightened salt sensitivity and can limit plant growth. The effects of salinity has been studied on Arabidopsis plants that have mutated ERS1, ERS2, ETR1, ETR2 and EIN4 proteins. These proteins are used for ethylene signaling against certain stress conditions, such as salt and the ethylene precursor ACC is used to suppress any sensitivity to the salt stress. === Phosphate starvation in plants === Phosphorus (P) is
|
{
"page_id": 2250,
"source": null,
"title": "Abiotic stress"
}
|
an essential macronutrient required for plant growth and development, but it is present only in limited quantities in most of the world's soil. Plants use P mainly in the form of soluble inorganic phosphates (PO4−−−) but are subject to abiotic stress when there is not enough soluble PO4−−− in the soil. Phosphorus forms insoluble complexes with Ca and Mg in alkaline soils and with Al and Fe in acidic soils that make the phosphorus unavailable for plant roots. When there is limited bioavailable P in the soil, plants show extensive symptoms of abiotic stress, such as short primary roots and more lateral roots and root hairs to make more surface available for phosphate absorption, exudation of organic acids and phosphatase to release phosphates from complex P–containing molecules and make it available for growing plants' organs. It has been shown that PHR1, a MYB-related transcription factor, is a master regulator of P-starvation response in plants. PHR1 also has been shown to regulate extensive remodeling of lipids and metabolites during phosphorus limitation stress === Drought stress === Drought stress, defined as naturally occurring water deficit, is a main cause of crop losses in agriculture. This is because water is essential for many fundamental processes in plant growth. It has become especially important in recent years to find a way to combat drought stress. A decrease in precipitation and consequent increase in drought are extremely likely in the future due to an increase in global warming. Plants have come up with many mechanisms and adaptations to try and deal with drought stress. One of the leading ways that plants combat drought stress is by closing their stomata. A key hormone regulating stomatal opening and closing is abscisic acid (ABA). Synthesis of ABA causes the ABA to bind to receptors. This binding then affects
|
{
"page_id": 2250,
"source": null,
"title": "Abiotic stress"
}
|
the opening of ion channels, thereby decreasing turgor pressure in the stomata and causing them to close. Recent studies by Gonzalez-Villagra, et al., have shown how ABA levels increased in drought-stressed plants (2018). They showed that when plants were placed in a stressful situation, they produced more ABA to try to conserve any water they had in their leaves. Another extremely important factor in dealing with drought stress and regulating the uptake and export of water is aquaporins (AQPs). AQPs are integral membrane proteins that make up channels. These channels' main job is the transport of water and other essential solutes. AQPs are both transcriptionally and post-transcriptionally regulated by many different factors such as ABA, GA3, pH and Ca2+; and the specific levels of AQPs in certain parts of the plant, such as roots or leaves, helps to draw as much water into the plant as possible. By understanding the mechanisms of both AQPs and the hormone ABA, scientists will be better able to produce drought-resistant plants in the future. A study by Tombesi et al., found that plants which had previously been exposed to drought were able to minimize water loss and decrease water use. They found that plants which were exposed to drought conditions actually changed the way they regulated their stomata and what they called "hydraulic safety margin" so as to decrease the vulnerability of the plant. By changing the regulation of stomata and subsequently the transpiration, plants were able to function better when less water was available. == In animals == For animals, the most stressful of all the abiotic stressors is heat. This is because many species are unable to regulate their internal body temperature. Even in the species that are able to regulate their own temperature, it is not always a completely accurate system.
|
{
"page_id": 2250,
"source": null,
"title": "Abiotic stress"
}
|
Temperature determines metabolic rates, heart rates, and other very important factors within the bodies of animals, so an extreme temperature change can easily distress the animal's body. Animals can respond to extreme heat, for example, through natural heat acclimation or by burrowing into the ground to find a cooler space. It is also possible to see in animals that a high genetic diversity is beneficial in providing resiliency against harsh abiotic stressors. This acts as a sort of stock room when a species is plagued by the perils of natural selection. A variety of galling insects are among the most specialized and diverse herbivores on the planet, and their extensive protections against abiotic stress factors have helped the insect in gaining that position of honor. == In endangered species == Biodiversity is determined by many things, and one of them is abiotic stress. If an environment is highly stressful, biodiversity tends to be low. If abiotic stress does not have a strong presence in an area, the biodiversity will be much higher. This idea leads into the understanding of how abiotic stress and endangered species are related. It has been observed through a variety of environments that as the level of abiotic stress increases, the number of species decreases. This means that species are more likely to become population threatened, endangered, and even extinct, when and where abiotic stress is especially harsh. == Effects of anthropogenic climate change on abiotic stress == Data suggests that anthropogenic activity has increased the global temperature, and likely increased the odds of extreme climate events such as drought, fire conditions and flooding. Threats to organisms and ecosystem biodiversity due to increased abiotic stress are one major impact of this change. The effects of climate change on biomes vary due to the location, patterns of
|
{
"page_id": 2250,
"source": null,
"title": "Abiotic stress"
}
|
precipitation, and the organisms which inhabit them. On the species level, the increased abiotic stress due to climate change can lead to adaptations which increase a species' reproductive success under these conditions. However, such highly specialized adaptations may leave species vulnerable to other stresses. == See also == Ecophysiology == References ==
|
{
"page_id": 2250,
"source": null,
"title": "Abiotic stress"
}
|
Carbonic anhydrase-related protein is a protein that in humans is encoded by the CA8 gene. The CA8 protein lacks the catalytic activity of other carbonic anhydrase enzymes. A rare, autosomal recessive form of cerebellar ataxia known as "cerebellar ataxia, mental retardation, and dysequilibrium syndrome 3" (CAMRQ3) is caused by mutations in the CA8 gene. == Function == The protein encoded by this gene was initially named CA-related protein because of sequence similarity to other known carbonic anhydrase genes. However, the gene product lacks carbonic anhydrase activity (i.e., the reversible hydration of carbon dioxide). The gene product continues to carry a carbonic anhydrase designation based on clear sequence identity to other members of the carbonic anhydrase gene family. The absence of CA8 gene transcription in the cerebellum of the lurcher mutant in mice with a neurologic defect suggests an important role for this acatalytic form. == Interactions == CA8 has been shown to interact with ITPR1. == References == == Further reading == == External links == Human CA8 genome location and CA8 gene details page in the UCSC Genome Browser. PDBe-KB provides an overview of all the structure information available in the PDB for Human Carbonic anhydrase-related protein
|
{
"page_id": 15075531,
"source": null,
"title": "CA8"
}
|
Peter Michael Maitlis, FRS (15 January 1933 – 18 May 2022) was a British organometallic chemist. == Early life and education == Maitlis was born on 15 January 1933, and educated at Hendon School (then Hendon County School) in north London 1944–50. He was awarded a Bachelor's degree in Science from the University of Birmingham, and a PhD (1956, studying under Professor Michael J. S. Dewar, who helped to develop the Dewar–Chatt–Duncanson model for bonding in organometallic compounds) and a DSc (1970) from the University of London. == Career == After completing his doctorate, Maitlis worked as an Assistant Lecturer at the University of London. He undertook postdoctoral study at Cornell University as a Fulbright Fellow (1960–1961) and then as a research fellow at Harvard University (1961–1962) under F. G. A. Stone. While working and teaching at McMaster University in Hamilton, Ontario (1962–1972), he rose from Assistant Professor to a full Professorship. Returning to the United Kingdom in 1972, Maitlis was a professor of chemistry at the University of Sheffield for 30 years until his appointment as an emeritus professor in 2002. In 1971, he published two volumes on the organic chemistry of palladium which were "widely recognised as the most authoritative account of the organo-complexes of this metal". Maitlis was elected a Fellow of the Royal Society in 1984. The citation highlights his work on the platinum group metals palladium, rhodium and iridium. === Achievements in organometallic chemistry === The hexafluorophosphate ion is generally considered inert and hence a suitable counterion in organometallic synthesis. However, Maitlis' work has demonstrated a solvolysis reaction of the hexafluorophosphate ion. The tris(solvent) rhodium complex [(η5-C5Me5)Rh(Me2CO)3](PF6)2 undergoes solvolysis when heated in acetone, forming a difluorophosphate-bridged complex [(η5-C5Me5)Rh(μ-OPF2O)3Rh(η5-C5Me5)]PF6. Hexamethyl Dewar benzene (C6Me6) undergoes an unusual rearrangement reaction with hydrohalic acids to form a pentamethylcyclopentadiene derivative,
|
{
"page_id": 30738637,
"source": null,
"title": "Peter Maitlis"
}
|
and consequently can be used as a starting material for synthesising some pentamethylcyclopentadienyl organometallic compounds. Maitlis and colleagues demonstrated this synthesis and its applicability to the iridium analogue, [(η5-C5Me5)IrCl2]2. His group also demonstrated a more convenient synthesis for the bright orange, air-stable diamagnetic iridium reagent using pentamethylcyclopentadiene. Isocyanides can serve as ligands in co-ordination chemistry as a result of the lone electron pair on carbon, and are especially useful with metals in the 0, +1, and +2 oxidation states. In particular, Maitlis has demonstrated that tert-butyl isocyanide can stabilise metals in unusual oxidation states, such as palladium(I) in the complex [(t-BuNC)2Pd(μ-Cl)]2. === Metallomesogens === Metallomesogens are "metal complexes of organic ligands which exhibit liquid crystalline (mesomorphic) character [and thus they] combine the variety and range of metal-based coordination chemistry with the extraordinary physical properties exhibited by liquid crystals." They have been a research interest of Maitlis' group since the mid-1980s, and in fact Maitlis jointly directed the early investigations of these systems in the UK and actually coined the term metallomesogen. == Personal life == Maitlis was Jewish. He was the father of the journalist and newsreader Emily Maitlis, and the psychologist and academic Sally Maitlis. He died on 18 May 2022, at the age of 89. == Most cited publications == The following list shows the top 10 most cited journal articles by Maitlis according to Web of Science data. The number of citations indicated is current as at 27 May 2022: Kang, J. W.; Moseley, K.; Maitlis, P. M. (1969). "Pentamethylcyclopentadienylrhodium and -iridium Halides. I. Synthesis and Properties". J. Am. Chem. Soc. 91 (22): 5970–5977. Bibcode:1969JAChS..91.5970K. doi:10.1021/ja01050a008. --- 657 citations Giroud-Godquin, A.-M.; Maitlis, P. M. (1991). "Metallomesogens – Metal-Complexes in Organized Fluid Phases". Angew. Chem. Int. Ed. 30 (4): 375–402. doi:10.1002/anie.199103751. --- 570 citations Hudson, S. A.; Maitlis,
|
{
"page_id": 30738637,
"source": null,
"title": "Peter Maitlis"
}
|
P. M. (1993). "Calamitic Metallomesogens: Metal-Containing Liquid-Crystals with Rodlike Shapes". Chem. Rev. 93 (3): 861–885. doi:10.1021/cr00019a002. --- 482 citations Maitlis, P. M.; Haynes, A.; Sunley, G. J.; Howard, M. J. (1996). "Methanol Carbonylation Revisited: Thirty Years On". J. Chem.Soc., Dalton Trans. (11): 2187–2196. doi:10.1039/dt9960002187. --- 276 citations Maitlis, P. M. (1978). "(Pentamethylcyclopentadienyl)rhodium and -iridium Complexes – Approaches to New Types of Homogeneous Catalysts". Acc. Chem. Res. 11 (8): 301–307. doi:10.1021/ar50128a003. --- 265 citations White, C.; Thompson, S. J.; Maitlis, P. M. (1977). "Pentamethylcyclopentadienyl-Rhodium and -Iridium Complexes XII. Tris(solvent) Complexes and Complexes of η6-Benzene, -Naphthalene, -Phenanthrene, -Indene, -Indole, -Fluorene and η5-Indenyl and -Indolyl". J. Chem. Soc., Dalton Trans. (17): 1654–1661. doi:10.1039/DT9770001654. --- 247 citations Greaves, E. O.; Lock, C. J. L.; Maitlis, P. M. (1968). "Metal-Acetylene Complexes II. Acetylene Complexes of Nickel, Palladium and Platinum". Can. J. Chem. 46 (24): 3879–3891. doi:10.1139/v68-641. --- 240 citations Maitlis, P. M. (1976). "The Palladium(II)-Induced Oligomerization of Acetylenes: An Organometallic Detective Story". Acc. Chem. Res. 9 (3): 93–99. doi:10.1021/ar50099a003. --- 230 citations Maitlis, P. M. (1981). "Eta-5-Cyclopentadienyl and eta-6-Arene as Protecting Ligands Towards Platinum-Metal Complexes". Chem. Soc. Rev. 10 (1): 1–48. doi:10.1039/cs9811000001. --- 207 citations Haynes, A.; Maitlis, P. M.; Morris, G. E.; Sunley, G. J.; Adams, H.; Badger, P. W.; Bowers, C. M.; Cook, D. B.; Elliott, P. I. P.; Ghaffar, T.; Green, H.; Griffin, T. R.; Payne, M.; Pearson, J. M.; Taylor, M. J.; Vickers, P. W.; Watt, R. J. (2004). "Promotion of Iridium-Catalyzed Methanol Carbonylation: Mechanistic Studies of the Cativa Process". J. Am. Chem. Soc. 126 (9): 2847–2861. Bibcode:2004JAChS.126.2847H. doi:10.1021/ja039464y. PMID 14995202. --- 196 citations == References ==
|
{
"page_id": 30738637,
"source": null,
"title": "Peter Maitlis"
}
|
The Census of Coral Reefs (CReefs) is a field project of the Census of Marine Life that surveys the biodiversity of coral reef ecosystems internationally. The project works to study what species live in coral reef ecosystems, to develop standardized protocols for studying coral reef ecosystems, and to increase access to and exchange of information about coral reefs scattered throughout the globe. The CReefs project uses the implementation of autonomous reef-monitoring structures (ARMS) to study the species that inhabit coral reefs. These structures are placed on the sea floor in areas where coral reefs exist, where they are left for one year. At the end of the year, the ARMvS is pulled to the surface, along with the species which have inhabited it, for analysis. Coral reefs are thought to be the most organically different of all marine ecosystems. Major declines in key reef ecosystems suggest a decline in reef population throughout the world due to environmental stresses. The vulnerability of coral reef ecosystems is expected to increase significantly in response to climate change. The reefs are also being threatened by induced coral bleaching, ocean acidification, sea level rise, and changing storm tracks. Reef biodiversity could be in danger of being lost before it is even documented, and researchers will be left with a limited and poor understanding of these complex ecosystems. In an attempt to enhance global understanding of reef biodiversity, the goals of the CReefs Census of Coral Reef Ecosystems were to conduct a diverse global census of coral reef ecosystems. And increase access to and exchange of coral reef data throughout the world. Because coral reefs are the most diverse and among the most threatened of all marine ecosystems, there is great justification to learn more about them. == References == == External links == Official website
|
{
"page_id": 22022351,
"source": null,
"title": "Census of Coral Reefs"
}
|
PRNA may refer to: NoRC associated RNA, a non-coding RNA element which regulates ribosomal RNA transcription Tryptophan 7-halogenase, an enzyme
|
{
"page_id": 38406352,
"source": null,
"title": "PRNA"
}
|
The Institute of Theoretical Geophysics (ITG) is a research institute at the University of Cambridge, England. Most of the ITG's members are also members of DAMTP or the Department of Earth Sciences. Its research is chiefly on various aspects of geophysical fluid mechanics, as well as other aspects of geophysics such as vulcanology and tectonics. The ITG was founded in 1989. Its director is Herbert Huppert, and other senior members include Grae Worster and John Lister. == References == == External links == ITG website
|
{
"page_id": 46729423,
"source": null,
"title": "Institute of Theoretical Geophysics"
}
|
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