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Titolo: A diffusion equation for Brownian motion with arbitrary frictional coefficient: Application to the turnover problem
Autore: Battezzati, M;
 Indirizzi:
 CNR, Ist Cosmogeofis, I10133 Turin, Italy CNR Turin Italy I10133CNR, Ist Cosmogeofis, I10133 Turin, Italy
 Titolo Testata:
 JOURNAL OF CHEMICAL PHYSICS
fascicolo: 22,
volume: 111,
anno: 1999,
pagine: 9932  9943
 SICI:
 00219606(199912)111:22<9932:ADEFBM>2.0.ZU;2B
 Fonte:
 ISI
 Lingua:
 ENG
 Soggetto:
 CLASSICAL MECHANICAL SYSTEM; ACTIVATED RATEPROCESSES; BOUNDARYCONDITIONS; FORCE; FIELD;
 Tipo documento:
 Article
 Natura:
 Periodico
 Settore Disciplinare:
 Physical, Chemical & Earth Sciences
 Citazioni:
 22
 Recensione:
 Indirizzi per estratti:
 Indirizzo: Battezzati, M CNR, Ist Cosmogeofis, Corso Fiume 4, I10133 Turin, Italy CNR Corso Fiume 4 Turin Italy I10133 I10133 Turin, Italy



 Citazione:
 M. Battezzati, "A diffusion equation for Brownian motion with arbitrary frictional coefficient: Application to the turnover problem", J CHEM PHYS, 111(22), 1999, pp. 99329943
Abstract
After a brief reexposition of the procedure devised by the author in order to reobtain a diffusion equation from the equations of the motion of a mechanical system driven by a random force, this method is applied to derive a thirdorder diffusion equation for an anharmonic oscillator undergoing Brownian motion. This equation is exact to firstorder in the parameter of anharmonicity, and is valid for arbitrary values of the frictional coefficient. The confrontation of this equation with a similar equation obtained previously by asymptotic expansion in inverse powers of the frictional coefficient, shows that although the two equations are different, nevertheless theyreduce to the same equation (within the limits of validity of each approximation scheme) when they are both reduced to second order. An asymptotic formula for the mean firstpassage time (MFPT) for escaping over a barrier isthen proved in the lowtemperature limit, which is related to an eigenvalue of the diffusion operator, and to the solution of an integral equation with Smoluchowski boundary conditions. This equation yields the correct behavior of the eigenvalue in both limits of high and extremely low friction, with interpolation between the two limits, while in the oscillatory regime yields a complex eigenvalue, whose imaginary part can be interpreted as a stochastic resonance frequency between the anharmonic well and its mirror image beyond the barrier. It is shown how the Kramers' result for moderate or strong friction fits in with the present theory, and what is the origin of the discrepancies. (C) 1999 American Institute of Physics. [S00219606(99)001464].
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Documento generato il 25/10/20 alle ore 12:02:07