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Using an exact expression for the average velocity of inertialess motion of pulsating ratchets, a simple proof is given for the recently discovered hidden space-time symmetry of Cubero–Renzoni (D. Cubero, F. Renzoni, 2016). The conditions are revealed for the absence of the ratchet effect in systems with potential energies described by products of periodic functions of coordinate and time possessing the symmetry of the main types. In particular, it is shown that the ratchet effect is absent for the time dependence of the universal symmetry type (which combines three standard symmetries), and this restriction is removed when inertia is taken into account, unless the coordinate dependence of the potential energy is related to symmetric or antisymmetric functions. 相似文献
3.
V. M. Rozenbaum M. L. Dekhtyar’ L. I. Trakhtenberg 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2017,91(10):1951-1956
An expression for the average velocity of a semiconductor photomotor has been obtained. A threelevel model of the electron subsystem of a photomotor with arbitrary transition rate constants was considered, and the time dependences of the occupation of its electronic levels were calculated. Variation of the occupation of the levels with time determines the time dependence of the potential energy and the average velocity of the photomotor motion along the polar substrate. The optimum conditions of laser photoexcitation and the kinetic characteristics of electron transitions in the photomotor that provide the maximum velocity of its directional motion were determined. 相似文献
4.
We use tools of the equilibrium statistical mechanics of disordered systems to study analytically the statistical properties of an ecosystem composed of N species interacting via random mutual interactions, as well as via deterministic self-interactions of order p>/=2. We show that the main effect of increasing the order of the interactions among the species is to make the system less competitive, in the sense that the fraction of extinct species is greatly reduced. In addition, we find that for p>2 there is a threshold value which gives a lower bound to the concentration of the surviving species, preventing then the existence of rare species and, consequently, increasing the robustness of the ecosystem to external perturbations. 相似文献
5.
Exact and approximate compact analytical expressions have been obtained for thermally stimulated polarization and depolarization
currents of polar inclusions embedded in a solid-state matrix. By using the derived expressions, mixed processes, including
the polarization preparation of samples during their cooling and the action of an external polarizing electric field during
their heating at a constant rate, can be described within a unified context. The results are specifically applied to a system
of reorienting polar molecules adsorbed by finely dispersed powders. 相似文献
6.
The mechanism of directed substrate-parallel motion of molecules caused by photoinduced potential energy fluctuations is investigated. Unlike simplistic models (e.g., an on-off ratchet), the approach suggested implies that the necessary asymmetry of the potential energy can arise not only from the asymmetry of the substrate potential but also from an asymmetric distribution of the fluctuating charge density in the molecule. The thus induced asymmetry of the potential energy governs the direction motion and enables, under certain conditions, its reversal at some frequencies of resonant laser pulses or temperature. These inferences are exemplified by the model charge distributions in the molecule and substrate, and the charge density fluctuations which are obtained by quantum chemical calculations for the realistic molecule of a substituted phenylpyrene compound on a model substrate. 相似文献
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8.
Makhnovskii YA Rozenbaum VM Yang DY Lin SH 《The journal of physical chemistry. A》2007,111(38):9486-9493
This paper analyzes the confined motion of a Brownian particle fluctuating between two conformational states with different potential profiles and different position-dependent rate constants of the transitions, the fluctuations arising from both thermal (equilibrium) and external (nonequilibrium) noise. The model illustrates a mechanism to transduce, on the nanoscale, the energy of nonequilibrium fluctuations into mechanical energy of reciprocating motion. Expressions for the reciprocating velocity and the efficiency of energy conversion are derived. These expressions are treated in more detail in the slow-fluctuation (quasi-equilibrium) regime, by simple perturbation theory arguments, and in the fast fluctuation limit, in terms of the potential of mean force. A notable observation is that the generalized driving force of the reciprocating motion is caused by two sources: the energy contribution due to the difference between the potential profiles of the states and the entropic contribution due to the difference between the position-dependent rate constants. Two illustrative examples are presented, where one of the two sources can be ignored and an exact solution is allowed. Among other aspects, we also discuss the ways to construct a molecular motor based on the reciprocating engine. 相似文献
9.
Applicability of the Rayleigh-Gans-Debye (RGD) approximation for describing light scattering by nanoparticles with large dielectric losses (such as carbon nanotubes) is analyzed. By a comparison of the approximate results with exact ones, it is shown that the presence of dielectric losses expands the range of applicability of the RGD approximation. This conclusion is illustrated by a differential cross-section diagram of scattering by a multiwall carbon nanotube. 相似文献
10.