An example of a phase transition in an open pseudobimolecular system

A phase transition at microscopic level is exhibited for an open bimolecular chemical system. We also give another interpretation of an apparent incompatibility between the microscopic and the macroscopic analysis shown by J. Keizer.     

Irreversible behavior of interacting systems. I. The approach to equilibrium

The Kac ring model is used to test the validity of some conjectures about irreversibility. If the whole system is regarded as the universe, then it is demonstrated that all clocks (subsystems) run in the same direction during those times when the universe is not in equilibrium. In addition, mathematical techniques are introduced by means of which the appropriate order parameter for large, finite Kac ring models can be evaluated asymptotically. It is shown that the relaxation of this order parameter to its equilibrium value of zero is not exponential.     

耗散系统不可逆过程中的可拓展广义相对论时空关系

在引入非保守非惯性系的基础上对不可逆过程建立非保守系等效性假设，在引入广域度规的基础上对具有复杂行为的时空建立非保守系协变性假设；利用密度分布的不均匀度h(ρ)和粗粒熵S（ρtε）及推导的多标度因数η*计算式，引入非保守惯性质量和非保守引力质量.分析表明，新结果使引力理论与非平衡态统计理论和非线性动力学达到应有的谐和，发展并修正广义相对论. 关键词： 时空关系 耗散系统 不可逆性 可拓展广义相对论 非保守引力质量     

Relation between the microscopic and macroscopic descriptions of the effect of a solid-substrate surface on a homeotropically aligned nematic liquid crystal

A simple microscopic mean-field model is proposed for a homeotropically aligned planar nematic liquid crystal (NLC) in contact with a solid-substrate surface. The intermolecular interaction in the NLC is simulated with the anisotropic McMillan potential, and the orienting effect of the substrate surface on the molecules in the NLC is described as that of an external field acting only on the first surface molecular layer of the sample. This model is used to describe the deformation of the director field of the sample caused by the external field and to determine the anchoring strength coefficient W, which is employed to macroscopically describe the orienting effect of the solid substrate on the NLC. The dependence of this coefficient on the strength of the short-range orienting field of the substrate surface used in the proposed microscopic model is found, and a unique correspondence between W and the profile of the orientational order parameter near the substrate surface is established. The temperature dependence of the anchoring strength coefficient is derived and found to agree well with experimental data for the MBBA NLC.     

人为扰动的模型势函数及其动力学特征

目前,结合高精度从头算方法和全维量子动力学计算,对四原子气相反应,理论计算可以获得与实验结果完全一致的结果。一般情况下,一个精确的量子动力学模拟需要一个精确的势能面,但是在实际的计算当中,势能面的拟合误差是不可避免的。在本文中,我们考察了在模型势能面外加各种扰动时的动力学反应行为,在2维的势能面上进行了量子动力学计算。反应速率常数对近反应能垒区域或最小能量反应路径上的干预是较为敏感的,但是在势能面上的其它地方加入的外加干扰对反应速率影响不大。本文给出一个比较重要的和比较简单的结论,在量子动力学模拟中,在精确的势能面上增加相关的扰动,会帮助我们更深入地理解给定类型的反应,对于一个特定体系,其精确势能面上可以作为一个模型体系研究。     

温度对有机物传热影响的分子动力学模拟及微观机理研究

热导率是表征物质导热性能的一个重要物性参数.通过分子模拟从微观角度揭示有机物分子液体导热机理并计算热导率具有重要的理论意义和应用价值.通过非平衡态分子动力学模拟方法,分别模拟了庚烷、己醛、2-己酮和己醇在263～363 K的热传导过程并得到了热导率.4种有机物在263～363 K下热导率的计算值与实验值的相对平均偏差分别小于5.40%,5.46%,4.29%和7.80%,表明模拟结果与实验结果基本一致.热流分解和原子热路径的结果表明,对总热流有显著贡献的库仑相互作用项、范德华相互作用项和扭转角项都随着温度的升高而减小,这使得4种有机物的热导率随着温度的升高而降低.同时研究表明温度的升高增大了分子的原子振动,加速了分子运动,降低了模拟体系的质量密度.本文为温度对液体热传导影响提供了微观解释和理论依据.     

Diffusion behavior of helium in titanium and the effect of grain boundaries revealed by molecular dynamics simulation

The microstructures of titanium(Ti), an attractive tritium(T) storage material, will affect the evolution process of the retained helium(He). Understanding the diffusion behavior of He at the atomic scale is crucial for the mechanism of material degradation. The novel diffusion behavior of He has been reported by molecular dynamics(MD) simulation for the bulk hcp-Ti system and the system with grain boundary(GB). It is observed that the diffusion of He in the bulk hcp-Ti is significantly anisotropic(the diffusion coefficient of the [0001] direction is higher than that of the basal plane),as represented by the different migration energies. Different from convention, the GB accelerates the diffusion of He in one direction but not in the other. It is observed that a twin boundary(TB) can serve as an effective trapped region for He.The TB accelerates diffusion of He in the direction perpendicular to the twinning direction(TD), while it decelerates the diffusion in the TD. This finding is attributable to the change of diffusion path caused by the distortion of the local favorable site for He and the change of its number in the TB region.     

An effect of particle size on the behavior of ferromagnetic materials

The dependence of magnetic behavior of media upon the particle/grain size is studied here. A model is presented to describe the behavior of nanomagnetic materials as a function of particle size. The model is applied to two types of experiments: (1) the decay rate of the magnetic aftereffect in nanomagnets and (2) the variation of spontaneous magnetization versus temperature. Both of these experiments show a deviation from the behavior of bulk media above a critical temperature.     

Temperature effect on the transport dynamics of a small molecule through a liposome bilayer

An ion having hydrophobic parts can directly transport through the liposome bilayer without an ion channel and its transport mechanism can be explained by the free-volume theory. This was confirmed by investigating the temperature effect on the transport dynamics of organic cations through anionic liposome bilayers made of unsaturated and saturated lipids by using optical second-harmonic generation (SHG) technique. This study provides useful information to design practical temperature-controlled drug delivery systems.     

Influences of decoherence on the generation of a macroscopic superposition state using weak cross-Kerr effect

Considering a system in which a single photon and a coherent field propagate through a Kerr medium, when the weak cross-Kerr interaction between the coherent state and the single photon under decoherence is involved, this paper derives analytically a macroscopic superposition state by the superoperator method and investigates the influences of decoherence on the coherence properties of the obtained state. It finds that the macroscopic superposition state will experience evolution from a pure superposition state to a mixed state in a dissipative environment and the Kerr effect makes the field display a periodic revival from decoherence for a short time.     

Influences of decoherence on the generation of a macroscopic superposition state using weak cross-Kerr effect

Considering a system in which a single photon and a coherent field propagate through a Kerr medium, when the weak cross-Kerr interaction between the coherent state and the single photon under decoherence is involved, this paper derives analytically a macroscopic superposition state by the superoperator method and investigates the influences of decoherence on the coherence properties of the obtained state. It finds that the macroscopic superposition state will experience evolution from a pure superposltion state to a mixed state in a dissipative environment and the Kerr effect makes the field display a periodic revival from decoherence for a short time.     

Change of the scaling behavior of the end-to-end square distance in a two-dimensional polydisperse system

The simulation of a two-dimensional, broadly polydisperse, living polymers system at high concentration reveals an unusual conformational behaviour for the longer chains. Unlike in three dimensions, the longer chains are not swollen but are squeezed by the smaller chains. This observation is discussed in terms of a two dimensional solvent- polymer mixture whose solvent particules are larger than the polymer monomers. Received: 13 December 1996 / Revised: 16 March 1998 / Accepted: 27 March 1998     

Effects of classical random external field on the dynamics of entanglement in a four-qubit system

We investigate the dynamics of entanglement through negativity and witness operators in a system of four non-interacting qubits driven by a classical phase noisy laser characterized by a classical random external field (CREF). The qubits are initially prepared in the GHZ-type and W-type states and interact with the CREF in two different qubit-field configurations, namely, common environment and independent environments in which the cases of equal and different field phase probabilities are distinguished. We find that entanglement exhibits different decaying behavior, depending on the input states of the qubits, the qubit-field coupling configuration, and field phase probabilities. On the one hand, we demonstrate that the coupling of the qubits in a common environment is an alternative and more efficient strategy to completely shield the system from the detrimental impacts of the decoherence process induced by a CREF, independent of the input state and the field phase probabilities considered. Also, we show that GHZ-type states have strong dynamics under CREF as compared to W-type states. On the other hand, we demonstrate that in the model investigated the system robustness's can be greatly improved by increasing the number of qubits constituting the system.     

The effect of cellular aging on the dynamics of spiral waves

Cellular aging can result in deterioration of electrical coupling, the extension of the action potential duration, and lower excitability of the cell. Those factors are introduced into the Greenberg–Hastings cellular automaton model and the effects of the cellular aging on the dynamics of spiral waves are studied. The numerical results show that a 50% reduction of the coupling strength of aging cells has a little influence on spiral waves. If the coupling strength of aging cells equals zero, the ability for the medium to maintain spiral waves will be reduced by approximately 50% when the aging cell ratio increases from 0 to 0.5, where the reduction of cell excitability plays a major role in inducing disappearance of spiral waves. When the relevant parameters are properly chosen, the cellular aging can lead to the meandering of spiral waves,the emergence of the binary spiral waves, and even the disappearance of spiral waves via the stopping rotation or shrinkage of wave. Physical mechanisms of the above phenomena are analyzed briefly.     

Modelling the effect of heterogeneous vaccination on metapopulation epidemic dynamics

Vaccination as an epidemic control strategy has a significant effect on epidemic spreading. In this paper, we propose a novel epidemic spreading model on metapopulation networks to study the impact of heterogeneous vaccination on epidemic dynamics, where nodes represent geographical areas and links connecting nodes correspond to human mobility between areas. Using a mean-field approach, we derive the theoretical spreading threshold revealing a non-trivial dependence on the heterogeneity of vaccination. Extensive Monte Carlo simulations validate the theoretical threshold and also show the complex temporal epidemic behaviours above the threshold.     

On the influence of a Rashba-type coupling induced by Lorentz-violating effects on a Landau system for a neutral particle

We study a possible scenario of the Lorentz symmetry violation background that allows us to build an analogue of the Landau system for a nonrelativistic Dirac neutral particle interacting with a field configuration of crossed electric and magnetic fields. We also discuss the arising of analogues of the Rashba coupling, the Zeeman term and the Darwin term from the Lorentz symmetry breaking effects, and the influence of these terms on the analogue of the Landau system confined to a two-dimensional quantum ring. Finally, we show that this analogy with the Landau system confined to a two-dimensional quantum ring allows us to establish an upper bound for the Lorentz symmetry breaking parameters.     

基于离焦的微操作机器人系统光轴方向深度测量

在分析显微物镜成像原理的基础上,提出并实现了一种微操作机器人系统光轴方向深度测量方法,该方法通过显微物镜离焦光学传递函数（optical transfer function, OTF）建立物方离焦程度与显微图像模糊程度的关系,由此实现深度测量.由于考虑了透镜参数与衍射效应的影响,方法具有较高的测量精度和较好的线性度,同时利用条状物体快速辨识算法,对原始方法进行了简化,使深度测量可在线完成.进一步,将上述方法应用于实际微操作机器人系统,通过离焦状态双针互插实验验证了方法的有效性,同时拓展了微操作机器人系统的有效操作空间. 关键词： 深度测量 微操作机器人 显微镜系统成像模型 光学传递函数     

The effect of the asymptotic response dynamics on the generalized synchronization

Generalized synchronization in a drive-response Chua circuits is investigated. A cascade of transitions to GS is observed with increasing the interaction strength. The mechanism on the transitions to GS is given based on the asymptotic behaviors of response dynamics.     

Hysteresis behavior of the random-field Ising model with 2-spin-flip dynamics: exact results on a Bethe lattice

We present an exact treatment of the hysteresis behavior of the zero-temperature random-field Ising model on a Bethe lattice when it is driven by an external field and evolved according to a 2-spin-flip dynamics. We focus on lattice connectivities z=2 (the one-dimensional chain) and z=3. For the latter case, we demonstrate the existence of an out-of-equilibrium phase transition, in contrast with the situation found with the standard 1-spin-flip dynamics. We discuss the influence of the degree of cooperativity of the (local) spin dynamics of the nonequilibrium response on the system.     

A new hierarchy system on the basis of a “Master” Boltzmann equation for microscopic density

It is shown that Boltzmann's equation written in terms of microscopic density (namely the unaveraged Boltzmann function) has a wider range of validity as well as finer resolvability for fluctuations than the conventional Boltzmann equation governing Boltzmann's function. In fact the new Boltzmann equation for ideal gases has implications as a microscopically exact continuity equation like Klimontovich's equation for plasmas, and can be derived without invoking any statistical concepts, e.g., distribution functions, or molecular chaos. The Boltzmann equation in the older formalism is obtained by averaging this equation only under a restricted condition of the molecular chaos. The new Boltzmann equation is seen to contain information comparable with Liouville's equation, and serves as a master kinetic equation. A new hierarchy system is formulated in a certain parallelism to the BBGKY hierarchy. They are shown to yield an identical one-particle equation. The difference between the two hierarchy systems first appears in the two-particle equation. The difference is twofold. First, the present formalism includes thermal fluctuations that are missing in the BBGKY formalism. Second, the former allows us to formulate multi-time correlations as well, whereas the latter is restricted to simultaneous correlation. These two features are favorably utilized in deriving the Landau-Lifshitz fluctuation law in a most straightforward manner. Also, equations describing the nonequilibrium interaction between thermal and fluid-dynamical fluctuations are derived.