Quantum diffusion in polaron model of poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers

We numerically investigate quantum diffusion of an electron in a model of poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers with fluctuation of the parameters due to the impact of colored noise. The randomness is introduced by fluctuations of distance between two consecutive bases along the stacked base pairs. We demonstrate that in the model the decay time of the correlation can control the spread of the electronic wavepacket. Furthermore it is shown that in a motional narrowing regime the averaging over fluctuation causes ballistic propagation of the wavepacket, and in the adiabatic regime the electronic states are affected by localization.     

The angle-of-arrival variance of optical waves propagating through turbulent atmosphere in the presence of random jitter

Dynamic wind loads, thermal expansion and other mechanical reasons cause optical platform mounts to sway. The sway distorts the alignment between transmitters and receivers, causing random pointing jitter, the outcome of which is the phase fluctuation of optical waves from the transmitter. Furthermore, atmospheric turbulence causes fluctuations in the phase of those optical waves. By using the extended Huygens-Fresnel principle, both phase fluctuations are considered and an analytic formulation for the angle-of-arrival variance of optical waves propagating through turbulent atmosphere in the presence of motion-induced pointing jitter is derived. The result shows that the angle-of-arrival variance of optical waves under the combined impact of motion-induced pointing jitter and atmospheric turbulence is the sum of the angle-of-arrival variances induced by them independently.     

蛋白质构型变化的二维广义郎之万方程描述

采用二维广义郎之万方程描述蛋白质构型的随机变化,并与电子输运过程的原子密度填充模型相协调. 假设通过键和通过空间的两类电子输运路径分别受到高斯分数噪声和高斯白噪声的影响. 推导了电子转移给体-受体距离涨落和荧光寿命涨落自相关函数的一般表达式. 采用数值拉普拉斯反变换计算了蛋白质构型涨落动力学,并详尽讨论了长时间和短时间行为的渐近解析. 最后,明确了基于二维广义郎之万方程的蛋白质构型描述与一维描述之间的关系.     

非线性激光场中量子噪声之间的耦合效应

用二维气体激光模型对量子噪声的实部和虚部存在耦合的激光场进行了理论分析，通过福克－普朗克方程导出了定态激光光场强度和位相的分布函数，算出了定态激光强度和位相的平均值，方差和偏斜度，与量子噪声的两个分量为独立随机变量的激光场相比，噪声间的耦合极大地改变了激光场强度和位相的涨落，并引起了激光场强度与位相之间的耦合。     

Prebifurcational noise rise in nonlinear systems

The phenomenon of prebifurcational noise increase in nonlinear systems in the process of period-doubling bifurcation is investigated. The study is conducted for a discrete system (quadratic mapping); how-ever, many of the laws discovered apply to more general systems. Estimates of the fluctuation variance are obtained both for the linear (away from the bifurcation threshold) and for the nonlinear mode (in the vicinity of the bifurcation threshold). It is shown that the variance of forced fluctuations in the strongly nonlinear mode is proportional to the root-mean-square of the noise intensity rather than to the variance. The possibility of measuring the noise in nonlinear systems on the basis of the prebifurcational noise amplification factor is demonstrated.     

超音速湍流脉动流场气动光学效应分析

对高超音速飞行器在大气中飞行时所产生的湍流脉动气动光学效应进行了理论分析与计算.根据CFD计算流场时所使用的湍流模型及其控制方程,推导出流场的折射率脉动方差控制方程.用统计方法,求出该脉动流场的系综平均光学传递函数及相位均方差,从不同角度描述了湍流脉动的气动光学效应.计算结果表明,气动光学传输函数的幅度响应函数具有低通特征,使所获得的图像发生像模糊,而相位响应函数则导致红外成像相位非线性偏移.此外,在相同飞行高度下,马赫数越高,图像模糊越严重.电弧风洞实验结果验证了本文理论分析的正确性.     

用一种分数阶算法研究非马尔可夫过程中阻尼与涨落的竞争机制

基于分数阶朗之万方程和随机行走理论, 建立了一种用于研究非马尔可夫系统中随机变量随时间演化的数值模拟算法, 称之为分数阶随机行走模拟法. 进一步运用此算法分别数值研究了无阻尼有涨落、 有阻尼无涨落和阻尼与涨落兼备三种情况下, 受欠扩散分数阶朗之万方程约束的随机变量随时间的演化行为. 结果显示阻尼和涨落存在竞争关系: 高斯型涨落的影响会随着时间的增长被"抹平", 从而凸显阻尼使系统趋于平衡的作用; 而长尾型涨落则由于包含"小概率大贡献"事件, 使得长时间演化之后系统变量仍以一定概率出现突然变化. 关键词： 非马尔可夫 欠扩散 阻尼与涨落 分数阶朗之万方程     

Large metric perturbations from rescattering

We study numerically evolution of metric perturbations during reheating in a model with two fields and a strong parametric resonance. Our calculation is fully nonlinear and includes gravity but is restricted to spherical symmetry. In this model, super-Hubble metric perturbations can grow during reheating only due to effects nonlinear in fluctuations of the fields. We find that they indeed grow and, soon after the growth begins, dominate variances of the metric functions. Thus, the metric functions become smooth but varying significantly over large scales. Their profiles at late times are interpreted as signaling a gravitational instability and formation of a black hole.     

Brownian motion under a time-dependent periodic potential proportional to the square of the position of a particle and classical fluctuation squeezing

A general stationary case of a Brownian particle with a time-dependent periodic potential proportional to the square of the position of the particle is treated. Even though the vigorous change of the time-dependent proportionality coefficient is applied, there are cases where the fluctuation of the particle decreases in contrary to our intuition, which is called classical fluctuation squeezing. We obtain time-average variances analytically for general cases of an arbitrary change in the coefficient and find conditions favorable for classical fluctuation squeezing. We introduce an asymmetric function behaves like trigonometric cosine one and consider its behavior explicitly.     

Genotype selection model with two time-correlated white noises

We study the steady state properties of a genotype selection model in the presence of two time correlated Gaussian white noises. Based on the corresponding Fokker-Planck equation the steady state solution of the probability distribution has been investigated. The fluctuation of both the mutation factor and the genetic factor can break the balance of the gene selection. The fluctuation of the genetic factor can facilitate the gene separation which allows us to select one gene-type haploid from a gene group while the fluctuation of the mutation factor impedes the gene separation. Remarkably, the correlation time between the two noises can induce the system to change from two states to one.     

On low frequency and 1/f noise from diffusion like processes

The noise spectrum resulting from diffusion like processes is calculated in two and three dimensions for two different forms of free energy fluctuation. For example it is shown that in a three dimensional system with ideal non-interacting particles the noise is almost white up to a certain frequency. In a two dimensional system where the free energy fluctuations are proportional to the gradient of a parameter modulating the electrical conductivity a 1/f noise power spectrum is expected in a certain frequency interval.     

The energy and dissipation of turbulent fluctuations of wind velocity and temperature in the boundary layer of the atmosphere

The relationships between the energy of small-scale turbulence and its dissipation rate are studied based on the data of long-term high-frequency measurements of temperature and wind velocity fluctuations in urban area. It is shown that the energy of wind velocity turbulent fluctuations is linearly related to the dissipation rate ɛ. The proportionality coefficient between turbulent kinetic energy (TKE) and ɛ is dimensional and does not depend on the stratification of the atmosphere, the Richardson number, or the Monin-Obukhov scale. Measurements in different seasons show that this coefficient can be related to the mean velocity of adiabatic motions (sound speed or air temperature), which enables one to select a more universal constant, γ. A linear relationship between the temperature fluctuations variance (the characteristic of the inner energy of turbulence) and their dissipation rate is also shown. The revealed proportionality is confirmed by measurements in urban and forest conditions, as well as in the surface layer over a flat desert terrain.     

Statistical fluctuations in a saturation laser model with correlated noises

We study the effects of correlations between quantum and pump noises on fluctuations of the laser intensity in a saturation laser model. An approximative Fokker--Planck equation and analytic expressions of the steady-state probability distribution function (SPD) of the laser system are derived. Based on the SPD, the normalized mean, the normalized variance, and the normalized skewness of the steady-state laser intensity are calculated numerically. The results indicate that (i) the correlation strength \lambda of correlated noises always enhances the fluctuation of laser intensity; (ii) the correlation time \tau of correlated noises strengthens the fluctuation of laser intensity for the below-threshold case but \tau weakens it for the above-threshold case.     

Additive noise-induced Turing transitions in spatial systems with application to neural fields and the Swift-Hohenberg equation

This work studies the spatio-temporal dynamics of a generic integral-differential equation subject to additive random fluctuations. It introduces a combination of the stochastic center manifold approach for stochastic differential equations and the adiabatic elimination for Fokker-Planck equations, and studies analytically the systems’ stability near Turing bifurcations. In addition two types of fluctuation are studied, namely fluctuations uncorrelated in space and time, and global fluctuations, which are constant in space but uncorrelated in time. We show that the global fluctuations shift the Turing bifurcation threshold. This shift is proportional to the fluctuation variance. Applications to a neural field equation and the Swift-Hohenberg equation reveal the shift of the bifurcation to larger control parameters, which represents a stabilization of the system. All analytical results are confirmed by numerical simulations of the occurring mode equations and the full stochastic integral-differential equation. To gain some insight into experimental manifestations, the sum of uncorrelated and global additive fluctuations is studied numerically and the analytical results on global fluctuations are confirmed qualitatively.     

Theory of fluctuations in quasiharmonic oscillators

An approach is developed for analyzing fluctuation effects in quasiharmonic oscillators formed by connecting a nonlinear inertialess element to a resonator. The effect of the nonlinear element on the resonator is treated as a pulsed process. It is assumed that the effect of noise on the system destroys the coherence and changes the response parameters of the resonator to pulse effects, this, ultimately, being responsible for the amplitude and frequency fluctuations. An equation is obtained that describes the fluctuations of the oscillation period. A detailed study is made of the fluctuations of the period in an electronic oscillator due to white noise.     

Exchange fluctuation theorems for a chain of interacting particles in presence of two heat baths

The exchange fluctuation theorem for heat exchanged between two systems at different temperatures, when kept in direct contact, has been investigated by Jarzynski and Wójcik [Phys. Rev. Lett. 92, 230602 (2004)]. We extend this result to the case where two Langevin reservoirs at different temperatures are connected via a conductor made of interacting particles, and are subjected to an external drive or work source. The Langevin reservoirs are characterized by Gaussian white noise fluctuations and concomitant friction coefficients. We first derive the Crooks theorem for the ratio between forward and reverse paths, and discuss the first law in this model. Then we derive the modified detailed fluctuation theorems (MDFT) for the heat exchanged at each end. These theorems differ from the usual form of the detailed fluctuation theorems (DFT) in literature, due the presence of an extra multiplicative factor. This factor quantifies the deviation of our MFDT from the DFT. Finally, we numerically study our model, with only two interacting particles for simplicity.     

基于辐照前1/f噪声的金属-氧化物-半导体场效应晶体管辐照退化模型

基于金属-氧化物-半导体场效应晶体管(MOSFET)噪声的载流子数涨落和迁移率涨落理论,建立了MOSFET辐照前1/f噪声参量与辐照后分别由氧化层陷阱和界面陷阱诱使阈值电压漂移之间的定量数学模型,并通过实验予以验证.研究结果表明,辐照诱生的氧化层陷阱通过俘获和发射过程与沟道交换载流子,在引起载流子数涨落的同时也通过库仑散射导致沟道迁移率的涨落,因此辐照前的1/f噪声幅值正比于辐照诱生的氧化层陷阱数.利用该模型对MOSFET辐照前1/f噪声与辐照退化的相关性从理论上 关键词： f噪声')" href="#">1/f噪声 辐照 金属-氧化物-半导体场效应晶体管 陷阱     

Probability characteristics of brownian motion in a stochastic potential profile of a specific type

Some probability characteristics of the Brownian motion in a symmetric potential profile with two equilibrium states subjected to a random force are obtained. Two types of potential fluctuations are considered: the delta-correlated Gaussian noise and the stochastic telegraph process with Poisson statistics of jumps. The stationary probability distributions of the particle coordinate are found, and the dependence on the properties of parametric and additive noise is studied. It is shown that nonzero equilibrium states approach each other and vanish as a result of strong potential fluctuations. Relaxation of intensity and variance of coordinate fluctuations are studied numerically for the case of delta-correlated random forces. The influence of the value of parametric and additive noise, system nonlinearity, and initial conditions on the relaxation process is determined. Architectural and Civil Engineering University, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 10, pp. 1290–1300, October 1998.