|
Selectivity (chromatography)
Selectivity may refer to: Psychology and behaviour * Choice, making a selection among options * Discrimination, the ability to recognize differences * Socioemotional selectivity theory, in social psychology Engineering * Selectivity (radio), a measure of the performance of a radio receiver to respond only to the radio signal it is tuned * Selectivity (circuit breakers), the coordination of overcurrent protection devices in an electrical installation Biology * Binding selectivity, in pharmacology * Functional selectivity, in pharmacology * Natural selection, in biology Chemistry * Reactivity–selectivity principle, in general chemistry * Chemoselectivity, a term used in organic chemistry to describe reactivity of one functional group in the presence of other groups * Stereoselectivity, a term used in organic chemistry to describe the distribution of isomers in reaction products * Regioselectivity, a term used in organic chemistry to describe reaction mechanisms and predict react ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Choice
A choice is the range of different things from which a being can choose. The arrival at a choice may incorporate motivators and models. For example, a traveler might choose a route for a journey based on the preference of arriving at a given destination at a specified time. The preferred (and therefore chosen) route can then account for information such as the length of each of the possible routes, the amount of fuel in the vehicle, traffic conditions, etc. Simple choices might include what to eat for dinner or what to wear on a Saturday morning – choices that have relatively low-impact on the chooser's life overall. More complex choices might involve (for example) what candidate to vote for in an election, what profession to pursue, a life partner, etc. – choices based on multiple influences and having larger ramifications. Freedom of choice is generally cherished, whereas a severely limited or artificially restricted choice can lead to discomfort with choosing, and p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Discrimination (information)
Discrimination in the original and broadest sense is the ability to distinguish one thing from another. Business and engineering * Discrimination testing is a technique employed in sensory analysis to determine whether there is a detectable difference among two or more products. * Markovian discrimination is a method used in spam filters to model the statistical behaviors of spam and nonspam. * Net bias (also called data discrimination) is the differentiation of price or quality of Internet data transmission. * Price discrimination, or price differentiation, is a pricing strategy where identical or similar goods or services are sold at different prices by the same provider to different customers. * Selectivity (circuit breakers) (also known as ''circuit breaker discrimination'') is the coordination of overcurrent protection devices so that a fault in the installation is cleared by the protection device located immediately upstream of the fault. * Term discrimination is a way to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Socioemotional Selectivity Theory
Socioemotional selectivity theory (SST; developed by Stanford psychologist Laura L. Carstensen) is a life-span theory of motivation. The theory maintains that as time horizons shrink, as they typically do with age, people become increasingly selective, investing greater resources in emotionally meaningful goals and activities. According to the theory, motivational shifts also influence cognitive processing. Aging is associated with a relative preference for positive over negative information in individuals who have had rewarding relationships.Santrock, J.W. (2008). ''A Topical Approach to Life-Span Development''. New York, NY: McGraw-Hill. This selective narrowing of social interaction maximizes positive emotional experiences and minimizes emotional risks as individuals become older. According to this theory, older adults systematically hone their social networks so that available social partners satisfy their emotional needs. The theory also focuses on the types of goals that indivi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Selectivity (radio)
Selectivity is a measure of the performance of a radio receiver to respond only to the radio signal it is tuned to (such as a radio station) and reject other signals nearby in frequency, such as another broadcast on an adjacent channel. Selectivity is usually measured as a ratio in decibels (dB), comparing the signal strength received against that of a similar signal on another frequency. If the signal is at the adjacent channel of the selected signal, this measurement is also known as adjacent-channel rejection ratio (ACRR). Selectivity also provides some immunity to blanketing interference. LC circuits are often used as filters; the Q ("Quality" factor) determines the bandwidth of each LC tuned circuit in the radio. The L/C ratio, in turn, determines their Q and so their selectivity, because the rest of the circuit - the aerial or amplifier feeding the tuned circuit for example - will contain present resistance. For a series resonant circuit, the higher the inductance and the l ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Selectivity (circuit Breakers)
Selectivity, also known as circuit breaker discrimination, is the coordination of overcurrent protection devices so that a fault in the installation is cleared by the protection device located immediately upstream of the fault. The purpose of selectivity is to minimize the impact of a failure on the network. Faults in an installation are, for example, overload and short circuit. There are four ways in which selectivity is achieved:{{cite web, url=https://eduscol.education.fr/sti/sites/eduscol.education.fr.sti/files/ressources/techniques/3363/3363-ect201.pdf, title=Discrimination with LV power circuit-breakers, author=Jean-Pierre Nereau, date=April 2001, publisher=Schneider Electric Schneider Electric SE is a French multinational company that specializes in digital automation and energy management. It addresses homes, buildings, data centers, infrastructure and industries, by combining energy technologies, real-time automatio ..., page=6, language=en, access-date=18 September 2021 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Binding Selectivity
Binding selectivity is defined with respect to the binding of ligands to a substrate forming a complex. Binding selectivity describes how a ligand may bind more preferentially to one receptor than another. A selectivity coefficient is the equilibrium constant for the reaction of displacement by one ligand of another ligand in a complex with the substrate. Binding selectivity is of major importance in biochemistry and in chemical separation processes. Selectivity coefficient The concept of selectivity is used to quantify the extent to which one chemical substance, A, binds each of two other chemical substances, B and C. The simplest case is where the complexes formed have 1:1 stoichiometry. Then, the two interactions may be characterized by equilibrium constants ''K''AB and ''K''AC.The constant used here are ''association'' constants. ''Dissociation'' constants are used in some contexts. A dissociation constant is the reciprocal of an association constant. : + B AB; \mathit K_ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Functional Selectivity
Functional selectivity (or “agonist trafficking”, “biased agonism”, “biased signaling”, "ligand bias" and “differential engagement”) is the ligand-dependent selectivity for certain signal transduction pathways relative to a reference ligand (often the endogenous hormone or peptide) at the same receptor. Functional selectivity can be present when a receptor has several possible signal transduction pathways. To which degree each pathway is activated thus depends on which ligand binds to the receptor. Functional selectivity, or biased signaling, is most extensively characterized at G protein coupled receptors (GPCRs). A number of biased agonists, such as those at muscarinic M2 receptors tested as analgesics or antiproliferative drugs, or those at opioid receptors that mediate pain, show potential at various receptor families to increase beneficial properties while reducing side effects. For example, pre-clinical studies with G protein biased agonists at the μ-opioid re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Natural Selection
Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Charles Darwin popularised the term "natural selection", contrasting it with selective breeding, artificial selection, which in his view is intentional, whereas natural selection is not. Genetic diversity, Variation exists within all populations of organisms. This occurs partly because random mutations arise in the genome of an individual organism, and their offspring can inherit such mutations. Throughout the lives of the individuals, their genomes interact with their environments to cause variations in traits. The environment of a genome includes the molecular biology in the Cell (biology), cell, other cells, other individuals, populations, species, as well as the abiotic environment. Because individuals with certain variants of the trait tend ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reactivity–selectivity Principle
In chemistry the reactivity–selectivity principle or RSP states that a more reactive chemical compound or reactive intermediate is less selective in chemical reactions. In this context selectivity represents the ratio of reaction rates. This principle was generally accepted until the 1970s when too many exceptions started to appear. The principle is now considered obsolete. A classic example of perceived RSP found in older organic chemistry textbooks concerns the free radical halogenation of simple alkanes. Whereas the relatively unreactive bromine reacts with 2-methylbutane predominantly to 2-bromo-2-methylbutane, the reaction with much more reactive chlorine results in a mixture of all four regioisomers. Another example of RSP can be found in the selectivity of the reaction of certain carbocations with azides and water. The very stable triphenylmethyl carbocation derived from solvolysis of the corresponding triphenylmethyl chloride reacts 100 times faster with the azide anion ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chemoselectivity
Chemoselectivity is the preferential outcome of a chemical reaction over a set of possible alternative reactions. In another definition, chemoselectivity refers to the selective reactivity of one functional group in the presence of others; often this process in convoluted and protecting groups are on the molecular connectivity alone. Such predictions based on connectivity are generally considered plausible, but the physical outcome of the actual reaction is ultimately dependent on a number of factors that are practically impossible to predict to any useful accuracy (solvent, atomic orbitals, etc.). Chemoselectivity can be difficult to predict, but observing selective outcomes in cases where many reactions are plausible, is common. Examples include the selective organic Redox, reduction of the greater relative chemoselectivity of sodium borohydride Redox, reduction versus lithium aluminium hydride Redox, reduction. In another example, the compound 4-methoxyacetophenone is oxidized ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stereoselectivity
In chemistry, stereoselectivity is the property of a chemical reaction in which a single reactant forms an unequal mixture of stereoisomers during a non- stereospecific creation of a new stereocenter or during a non-stereospecific transformation of a pre-existing one. The selectivity arises from differences in steric and electronic effects in the mechanistic pathways leading to the different products. Stereoselectivity can vary in degree but it can never be total since the activation energy difference between the two pathways is finite. Both products are at least possible and merely differ in amount. However, in favorable cases, the minor stereoisomer may not be detectable by the analytic methods used. An enantioselective reaction is one in which one enantiomer is formed in preference to the other, in a reaction that creates an optically active product from an achiral starting material, using either a chiral catalyst, an enzyme or a chiral reagent. The degree of selectivity is meas ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Regioselectivity
In chemistry, regioselectivity is the preference of chemical bonding or breaking in one direction over all other possible directions. It can often apply to which of many possible positions a reagent will affect, such as which proton a strong base will abstract from an organic molecule, or where on a substituted benzene ring a further substituent will be added. A specific example is a halohydrin formation reaction with 2-propenylbenzene: : Because of the preference for the formation of one product over another, the reaction is selective. This reaction is regioselective because it selectively generates one constitutional isomer rather than the other. Various examples of regioselectivity have been formulated as rules for certain classes of compounds under certain conditions, many of which are named. Among the first introduced to chemistry students are Markovnikov's rule for the addition of protic acids to alkenes, and the Fürst-Plattner rule for the addition of nucleophiles to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
