排序方式: 共有19条查询结果,搜索用时 15 毫秒
1.
The gauge compensation fields induced by the differential operators of the Stueckelberg-Schrödinger equation are discussed, as well as the relation between these fields and the standard Maxwell fields; An action is constructed and the second quantization of the fields carried out using a constraint procedure. The properties of the second quantized matter fields are discussed. 相似文献
2.
The extinction of a single species due to demographic stochasticity is analyzed. The discrete nature of the individual agents
and the Poissonian noise related to the birth-death processes result in local extinction of a metastable population, as the
system hits the absorbing state. The Fokker-Planck formulation of that problem fails to capture the statistics of large deviations
from the metastable state, while approximations appropriate close to the absorbing state become, in general, invalid as the
population becomes large. To connect these two regimes, a real space WKB method based on the master equation is presented,
and is shown to yield an excellent approximation for the decay rate and the extreme events statistics all the way down to
the absorbing state. The details of the underlying microscopic process, smeared out in a mean field treatment, are shown to
be crucial for an exact determination of the extinction exponent. This general scheme is shown to reproduce the known results
in the field, to yield new corollaries and to fit quite precisely the numerical solutions. Moreover it allows for systematic
improvement via a series expansion where the small parameter is the inverse of the number of individuals in the metastable
state. 相似文献
3.
Yosef E. Maruvka Nadav M. Shnerb Sorin Solomon Gur Yaari David A. Kessler 《Journal of statistical physics》2011,142(6):1302-1316
The inference of past demographic parameters from current genetic polymorphism is a fundamental problem in population genetics.
The standard techniques utilize a reconstruction of the gene-genealogy, a cumbersome process that may be applied only to small
numbers of sequences. We present a method that compares the total number of haplotypes (distinct sequences) with the model
prediction. By chopping the DNA sequence into pieces we condense the immense information hidden in sequence space into a function
for the number of haplotypes versus subsequence size. The details of this curve are robust to statistical fluctuations and
are seen to reflect the process parameters. This procedure allows for a clear visualization of the quality of the fit and,
crucially, the numerical complexity grows only linearly with the number of sequences. Our procedure is tested against both
simulated data as well as empirical mtDNA data from China and provides excellent fits in both cases. 相似文献
4.
John W.Grove 《数学物理学报(B辑英文版)》2010,30(2):563-594
This article describes mathematical models for phase separated mixtures of materials that are in pressure and velocity equilibrium but not necessarily temperature equilibrium. General conditions for constitutive models for such mixtures that exhibit a single mixture sound speed are discussed and specific examples are described. 相似文献
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6.
A spin model that displays inverse melting and inverse glass transition is presented and analyzed. Strong degeneracy of the interacting states of an individual spin leads to entropic preference of the "ferromagnetic" phase, while lower energy associated with the noninteracting states yields a "paramagnetic" phase as temperature decreases. An infinite range model is solved analytically for constant paramagnetic exchange interaction, while for its random exchange analogous results based on the replica symmetric solution are presented. The qualitative features of this model are shown to resemble a large class of inverse melting phenomena. First and second order transition regimes are identified. 相似文献
7.
OG Khvostenko ZS Yarullina NM Shishlov VE Rusin 《Rapid communications in mass spectrometry : RCM》1999,13(12):1091-1097
A correlation between the energies of electronic singlet transitions in benzodiazepines and their biological activity, which was revealed earlier by means of negative ion mass spectrometry with resonance electron capture, has been verified with a UV absorption spectroscopy investigation. Also, it has been noted that the energies of electronic singlet transitions in benzodiazepines are close in value to the ionization energies of atoms Cs, Rb, K, Na, Li and Tl, the cations of which are known to play an important role in nerve cell excitation processes. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
8.
Y. Louzoun N. M. Shnerb S. Solomon 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,56(2):141-148
The survival of autocatalytic agents in hostile environments depends on their ability to adapt their spatial configuration
to local
fluctuations. A model of diffusive reactants that extract the
advantage of spatio-temporal fluctuations associated with the
stochastic wandering of diffusive catalysts is discussed. Two
arguments are presented for the basic processes behind this
extraordinary behavior. In the first, the local colonies that evolve
around any spatially advantageous region overlap in space-time and
an infinite directed percolation cluster emerges. The second
argument is based on the return probability of a diffusive agent
that is shown to yield finite density of active “oases" with an
exponentially large contribution to the reactant population. The
different range of applicability of these survival lower bounds to
small systems is discussed. 相似文献
9.
AM Cardoso SM Alexandre CM Barros AJ Correia NM Nibbering 《Rapid communications in mass spectrometry : RCM》1999,13(19):1885-1888
The collision-induced dissociation (CID) of deprotonated arylalkylamines of general formula R(1)C(6)H(4)CHR(2)CH(2)NR(3)(2) (where R(1) = H, OH, F or NO(2); R(2) = H or OH; R(3) = H or CH(3)) generated by negative chemical ionization with H(2)O and D(2)O as ionizing reagents, is discussed. The negative chemical ionization mass spectra show that, in the absence of a hydroxy group in the aromatic ring, deprotonation takes place at the benzylic position whereas the proton is lost from the OH group when present. The nitro compound forms only M(-.) ions. The CID spectra of the deprotonated molecules show that fragmentations are strongly dependent on the structural features of the molecules, namely the presence or absence of substituents in the aromatic ring or aliphatic chain. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
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