Jeans criterion

For a cloud to collapse, the so called Jeans criterion has to be fulfilled Let us assume a cloud with mass M, radius R, total number of particles N, average particle mass m, and temperature T. The gravitational potential energy of this cloud is... 

Gravitational instability can occur in a cloud characterised by high density and low temperature (Jean s criterion). More precisely-, the mass of the cloud must be of the order of 20 M0 (where M0 is the solar mass) if the density (expressed as the number of dihydrogen molecules per cubic centimeter) is around 103 and the temperature around 10 K. Such a density is precisely what is observed in so-called dense clouds. These dense clouds are also regions of space where a lot of complex molecules are detected by spectroscopy, and where dust particles are observed. Readers interested in interstellar chemistry will find an excellent review of the subject in the recent book by Duley and Williams 13). 

Jeanes and associates23 used the ratio of the RF values of maltose and D-glucose as a criterion for choosing suitable solvent mixtures. The adaptability of ternary solvent mixtures was commended. After testing a number of mixtures made up of an alcohol (1-butanol, ethanol, or fusel oil), an acid or base, and water, as well as collidine-pyridine-water mixtures, they recommended basic mixtures, in particular, 1-butanol-pyridine-water. The composition of mixtures containing acid may change as a result of esterification. For example 1-butanol-acetic acid-water mixtures should be allowed to stand for some time before use.21 To obviate esterification of solvent, Hanes and Isherwood used ZerZ-pentyl alcohol in solvent mixtures containing acid.30... 

Rayleigh criterion See resolving power. Rayleigh-Jeans fonnula S Planck s... 

Under the ranking method devised by Jean Charles de Borda, (an eighteenth century French physicist) the DM is asked to rank the p criteria from the most important (ranked first) to the least important (ranked last). The criterion... 

Jean RH, Fan LS. Letter to the editor Bed contraction criterion for three phase fluidization. Can J Chem Eng 65 351-352, 1987. 

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