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Definition: Chain reaction from Brewer's Dictionary of Modern Phrase and Fable

A series of events in which each event is caused by the previous one. The expression is of scientific origin, applied first in the 1920s to a chemical reaction in which the products themselves promote the reaction, which may in some cases accelerate dramatically, and second in the 1940s to a process of nuclear fission that occurs in nuclear reactors and bombs.


chain reaction

From The Columbia Encyclopedia
self-sustaining reaction that, once started, continues without further outside influence. Proper conditions for a chain reaction depend not only on various external factors, such as temperature, but also on the quantity and shape of the substance undergoing the reaction. A chain reaction can be of various types, but nuclear chain reactions are the best known. A line of dominoes falling after the first one has been pushed is an example of a mechanical chain reaction; a pile of wood burning after it has been kindled is an example of a chemical chain reaction. In the latter case each piece of wood, as it burns, must release enough heat to raise nearby pieces to the kindling point. The wood, therefore, must be piled close enough together so that not too much heat is lost to the surrounding air. The conditions for a nuclear chain reaction can be understood by analogy. In the case of the fission of a nucleus, the reaction is begun by the absorption of a slow neutron. Each fission produces…
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Full text Article chain reaction

From The Columbia Encyclopedia
self-sustaining reaction that, once started, continues without further outside influence. Proper conditions for a chain reaction depend not only on various external factors, such as temperature, but also on the quantity and shape of the substance undergoing the reaction. A chain reaction can be of…
| 385 words
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Full text Article chain reaction

From The Penguin Dictionary of Science
A reaction mechanism in which an overall process can be broken down into a series of steps, in which chain carriers are involved. A classic example is the radical chain reaction involved in the ➤ chlorination of methane. The three main stages are chain initiation , in which a chain carrier (here the…
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Full text Article polymerase chain reaction (PCR)

From Britannica Concise Encyclopedia
Laboratory technique used to make numerous copies of specific DNA segments quickly and accurately. These are needed for various experiments and procedures in molecular biology , forensic analysis ( DNA fingerprinting ), evolutionary biology (to amplify DNA fragments found in ancient specimens), and…
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Full text Article proton-proton chain reaction

From Collins Dictionary of Astronomy
Proton-proton chain reaction
A series of nuclear fusion reactions by which energy can be generated in the dense cores of stars. The overall effect of the chain reaction is the conversion of hydrogen nuclei to helium nuclei with the release of an immense amount of energy. The energy maintains the core temperature, some of it…
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Full text Article Polymerase Chain Reaction

From Brenner's Encyclopedia of Genetics
During a traditional PCR reaction, a...
Abstract The polymerase chain reaction (PCR) is a basic molecular technique used for amplifying target sequences from a DNA template in an exponential manner. This is accomplished by using thermal cycling, a process in which a solution that includes DNA is repeatedly heated and cooled in order to…
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Full text Article polymerase chain reaction (PCR)

From The Penguin Dictionary of Science
polymerase chain reaction The reaction starts...
A technique (see the diagram ) enabling multiple copies to be made of specific sections of ➤ DNA molecules. It allows isolation and amplification of such sections from large heterogeneous mixtures of DNA and has many diagnostic applications, for example in detecting genetic mutations and viral…
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Full text Article chain reaction

From Britannica Concise Encyclopedia
Process yielding products that initiate further processes of the same kind. Nuclear chain reactions are a series of nuclear fissions initiated by neutrons produced in a preceding fission. A critical mass , large enough to allow more than one fission-produced neutron to be captured, is necessary for…
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Full text Article chain reaction

From The Hutchinson Unabridged Encyclopedia with Atlas and Weather Guide
In chemistry, a succession of reactions, usually involving free radicals , where the products of one stage are the reactants of the next. A chain reaction is characterized by the continual generation of reactive substances. A chain reaction comprises three separate stages: initiation – the initial…
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Full text Article polymerase chain reaction (PCR)

From Penguin Dictionary of Biology
Very adaptable process for isolating and amplifying a specifically desired DNA sequence (see Fig. 136 ). Artificially mutated DNA can be amplified this way, as can samples of forensic interest and amber-trapped DNA (see FOSSIL ). Double-stranded DNA is first separated into its two complementary…
| 530 words
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Full text Article PCR (polymerase chain reaction)

From Dictionary of Microbiology & Molecular Biology
PCR (polymerase chain reaction): the basic method...
A method for copying (‘amplifying’) specific sequences of nucleotides (see AMPLICON senses 1 and 2) in DNA; a modified form of the process ( REVERSE TRANSCRIPTASE PCR ) is used for copying sequences in RNA. PCR depends on the ability of a (thermostable) DNA polymerase to extend a primer on a…
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