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991.
E.G. Mishchenko M. Patra C.W.J. Beenakker 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,13(2):289-297
A theory is presented for the frequency dependence of the power spectrum of photon current fluctuations originating from a
disordered medium. Both the cases of an absorbing medium (“grey body”) and of an amplifying medium (“random laser”) are considered
in a waveguide geometry. The semiclassical approach (based on a Boltzmann-Langevin equation) is shown to be in complete agreement
with a fully quantum mechanical theory, provided that the effects of wave localization can be neglected. The width of the
peak in the power spectrum around zero frequency is much smaller than the inverse coherence time, characteristic for black-body
radiation. Simple expressions for the shape of this peak are obtained, in the absorbing case, for waveguide lengths large
compared to the absorption length, and, in the amplifying case, close to the laser threshold.
Received 8 August 2000 相似文献
992.
We derive a functional central limit theorem for quasi-Gaussian processes. In particular, we prove that the limit of the Mandelbrot–Weierstrass process is a complex fractional Brownian motion. 相似文献
993.
Harmonic maps between two Riemannian manifolds M and N are often constructed as energy minimizing maps. This construction is extended for the Dirichlet problem to the case where the Riemannian energy functional on M is replaced by a more general Dirichlet form. We obtain weakly harmonic maps and prove that these maps send the diffusion to N-valued martingales. The basic tools are the reflected Dirichlet space and the stochastic calculus for Dirichlet processes. 相似文献
994.
995.
J. Rosti L.I. Salminen E.T. Seppälä M.J. Alava K.J. Niskanen 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(2):259-263
We study the statistics of crack pinning in two dimensions by experiments and simulations of directed polymers in random media.
Mode I tensile tests on paper samples show a delocalization phenomenon as the notch length is varied if the fraction of cracks
pinned to the notch is monitored. This is compared with the behavior of directed polymers in the presence of both an energetically
favorable localized pinning center and bulk disorder. An analysis of the crack interface roughness indicates self-affine behavior
with a roughness exponent ζ in the proximity of the minimum energy surface value 2/3.
Received 4 April 2000 and Received in final form 10 October 2000 相似文献
996.
K. Saito 《The European Physical Journal A - Hadrons and Nuclei》2001,12(3):257-259
A novel nuclear effect on the flavour asymmetry of anti-quarks in the nucleon bound in a nucleus is discussed in terms of
the meson cloud model and the Pauli exclusion principle. It is expected that the flavour asymmetry is enhanced in a nucleus.
Received: 25 October 2001 / Accepted: 6 November 2001 相似文献
997.
M. Celasco R. Eggenhöffner 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(4):415-419
A dynamical percolative model explaining the universality of 1/
f
γ
noise is reported. Exponents γ ranging from 0 to 2 are obtained under the hypothesis that noise originates from random switching events between two ON-OFF
states in elemental parts (switchers) of a physical system. The usual noise behaviour with γ very close to 1 in an arbitrarily wide frequency range is obtained assuming a statistical distribution of switcher relaxation
time τ proportional to τ
-1
, as in McWhorter's model. The impact of these results with respect to recent self-organised criticality models is discussed.
Received 6 November 2000 and Received in final form 22 May 2001 相似文献
998.
This paper concerns nonstationary continuous-time Markov control processes on Polish spaces, with the infinite-horizon discounted cost criterion. Necessary and sufficient conditions are given for a control policy to be optimal and asymptotically optimal. In addition, under suitable hypotheses, it is shown that the successive approximation procedure converges in the sense that the sequence of finite-horizon optimal cost functions and the corresponding optimal control policies both converge. 相似文献
999.
1000.
ZHANG Jingbo LINYuan YIN Feng & XIAO Xurui 《中国科学B辑(英文版)》2000,43(4):443-449
Interfacial charge transfer kinetics of the nanocrystalline CdSe thin film electrodes have been studied in sodium polysulfide solutions by intensity modulated photocurrent spectroscopy (IMPS). The interfacial direct and indirect charge transfer and recombination processes were analyzed in terms of the parameters: normalized steady state photocurrents and surface state lifetimes obtained by measuring the IMPS responses under different applied potentials and different solution concentrations. IMPS responses of polycrystalline CdSe thin film electrodes were also presented for comparison. 相似文献