共查询到20条相似文献,搜索用时 93 毫秒
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ZHENGZhi-Gang LIXiao-Wen 《理论物理通讯》2001,36(2):151-156
Unidirectional transport of a particle in a spatially periodic and symmetric potential under a periodic force with broken temporal symmetry is studied.With a collaboration of the potential field and the asymmetric ac force,a dc current can be observed.Resonant current steps are found for a finite period of the ac force.A phase diagram of these resonant steps is given.Stochastic-resonance-like directional transport induced by thermal nonises is revealed. 相似文献
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用Robertson理论推导一个在纵磁场和横周期场作用下的自旋的运动方程。得到了阻尼和自旋稳定态对外场强度、频率及与热库的耦合系数的依赖关系。讨论了自旋稳定态的结构及其形成原因。
关键词: 相似文献
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基于并联耦合摆理论模型,利用数值方
法研究了在较大摆角情况下并联耦合摆的运动规律.
通过分析该系统在较大摆角时摆球的相轨迹图像和庞
加莱截面图像, 可发现并联耦合摆在较大摆角下的运
动是准周期运动, 该规律与摆球质量是否相同无关 相似文献
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对两种不同性质的有心力作用下的椭圆运动所遵循的规律从多方面进行论证、归纳和总结,对有关椭圆运动的两个物理问题进行巧妙解答. 相似文献
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研究了有界噪声与谐和激励作用下的Duffing-Rayleigh振子的动力学行为.首先运用随机Melnikov过程方法得到系统出现混沌的条件,结果表明随着非线性阻尼参数的增加系统会从混沌运动到周期运动,随着Wiener过程强度参数的增加,系统由混沌进入周期的临界幅值会先递增后不变.最后,用两类数值方法即最大Lyapunov指数与Poincare截面验证了上述结果.
关键词:
有界噪声
随机Melnikov过程
混沌运动
周期运动 相似文献
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Thomas F. Jordan 《Annals of Physics》2010,325(10):2075-2089
Two kinds of maps that describe evolution of states of a subsystem coming from dynamics described by a unitary operator for a larger system, maps defined for fixed mean values and maps defined for fixed correlations, are found to be quite different for the same unitary dynamics in the same situation in the larger system. An affine form is used for both kinds of maps to find necessary and sufficient conditions for inverse maps. All the different maps with the same homogeneous part in their affine forms have inverses if and only if the homogeneous part does. Some of these maps are completely positive; others are not, but the homogeneous part is always completely positive. The conditions for an inverse are the same for maps that are not completely positive as for maps that are. For maps defined for fixed mean values, the homogeneous part depends only on the unitary operator for the dynamics of the larger system, not on any state or mean values or correlations. Necessary and sufficient conditions for an inverse are stated several different ways: in terms of the maps of matrices, basis matrices, density matrices, or mean values. The inverse maps are generally not tied to the dynamics the way the maps forward are. A trace-preserving completely positive map that is unital cannot have an inverse that is obtained from any dynamics described by any unitary operator for any states of a larger system. 相似文献
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L. Blum 《Journal of statistical physics》1994,75(5-6):971-980
Contact theorems for rough surfaces are discussed. Simple relations for the average contact density are obtained for neutral and charged walls. When the walls are not planar there are new contributions proportional to the field gradients near the charged wall. 相似文献
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Cellular automaton fluids 1: Basic theory 总被引:7,自引:0,他引:7
Stephen Wolfram 《Journal of statistical physics》1986,45(3-4):471-526
Continuum equations are derived for the large-scale behavior of a class of cellular automaton models for fluids. The cellular automata are discrete analogues of molecular dynamics, in which particles with discrete velocities populate the links of a fixed array of sites. Kinetic equations for microscopic particle distributions are constructed. Hydrodynamic equations are then derived using the Chapman-Enskog expansion. Slightly modified Navier-Stokes equations are obtained in two and three dimensions with certain lattices. Viscosities and other transport coefficients are calculated using the Boltzmann transport equation approximation. Some corrections to the equations of motion for cellular automaton fluids beyond the Navier-Stokes order are given. 相似文献
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Bio-inspired optimization algorithms for optical parameter extraction of dielectric materials: A comparative study 下载免费PDF全文
Particle swarm optimization(PSO) and invasive weed optimization(IWO) algorithms are used for extracting the modeling parameters of materials useful for optics and photonics research community. These two bio-inspired algorithms are used here for the first time in this particular field to the best of our knowledge. The algorithms are used for modeling graphene oxide and the performances of the two are compared. Two objective functions are used for different boundary values. Root mean square(RMS) deviation is determined and compared. 相似文献
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Population-rate equations are analytically solved for constant pump rates. Conditions for population inversions are developed for this simplified case. Numbers appropriate for inner-shell photo-ionization of magnesium and neon are used. These allow back-of-the envelope calculations for predicting lasing duration. Pump-rate thresholds are also given which permit lasing for the duration of the pumping. Blackbody-source temperatures associated with such pump rates are calculated. A method of using the solution of the small-signal population-rate equations to determine the saturated intensity when the lower lasing level has a decay channel is given. This method is applied to the case of constant pump rates. An analytic expression for the saturated intensity is developed for this case. 相似文献
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Electronic stopping powers for 0. 05-10 MeV protons in a group of organic materials are systematically calculated. The calculations are based on Ashley's dielectric model, and an evaluation approach of optical energy loss function is incorporated into Ashley's model because no experimental optical data are available for most of the organic materials under consideration. The Barkas-effect correction and Bloch correction are included. The proton stopping powers for the considered organic materials except for mylar in the energy range from 0.05 to 10 MeV are presented for the first time. The results may be useful for studies of various radiation effects in these materials and for space research. 相似文献
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Ying-Tung Chen Kris Naessens Roel Baets Yunn-Shiuan Liao Ampere A. Tseng 《Optical Review》2005,12(6):427-441
For many years, the development of effective ablation or laser machining techniques for making micro-optical components has
been the key factor in the birth of new photonic devices and systems. In this article, the ablation characteristics of two
types of the most important transparent materials, transparent polymers and glasses, are studied. Simple shaped microcavities
are first machined for studying the fundamental ablation parameters, including threshold fluence, effective absorption coefficient,
and ablation rate. In studying polymer ablation, five standard grades and five proprietary polymeric compounds are selected.
Ablation techniques using these transparent polymers for making arrayed ferrules and curved microlenses are presented. Applications
of these ablated microstructures for optical fiber connectors, optical fiber coupling and alignment, and transparent chip
encapsulants, are introduced and demonstrated with emphasis on the quality of the ablated profiles and dimensions to satisfy
the required performance. In glass ablation, borosilicate glasses are considered and their associated ablation behaviors are
studied. The procedures to ablate glass-based arrayed microstructures with flat and curved surfaces are described. The utilizations
of these arrayed microstructures for optical waveguide, wave absorber, and beam guider, are specifically discussed. Finally,
concluding remakes for future trends are presented. 相似文献