共查询到20条相似文献,搜索用时 187 毫秒
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为互联网中的流量控制协议构建恰当模型,从而阐明具体协议算法与网络宏观性能间的关系,一直是互联网研究者面临的重大挑战.本文通过逻辑演绎,建立了互联网传输控制协议下流量的朗之万方程.在此基础上,细致分析了主动队列管理算法的有效性,在理论上证明了此类算法存在从畅通态到拥塞态到瘫痪态的相变过程,并给出了相变临界点与系统参数的显式关系.本建模与分析方法虽以具体的主动队列管理算法为例,但其方法可以应用于一般的网络流量控制问题.
关键词:
互联网
流量控制
朗之万方程
相变 相似文献
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阐述了一个产生从红噪声到绿噪声的多色噪声源的途径,给出了这种噪声的关联函数和谱密度。提出用积分闭合方法模拟多色噪声,用龙格-库塔方法求解朗之万方程的整体。研究了在锯齿型周期势场中运动的布朗粒子的平均输运行为。结果表明:绿噪声所趋动的粒子的稳定速流与通常的红噪声的结果相反,存在一个使粒子运动方向反转的某种颜色噪声。 相似文献
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机械振子的基态冷却是腔量子光力学中的基本问题之一.所谓的基态冷却就是让机械振子的稳态声子数小于1.本文通过光压涨落谱和稳态声子数研究双光腔光力系统(标准单光腔光力系统中引入第二个光腔,并与第一个光腔直接耦合)的基态冷却.首先得到系统的有效哈密顿量,然后给出朗之万方程和速率方程,最后分别给出空腔和原子腔的光压涨落谱、冷却率和稳态声子数.通过光压涨落谱、冷却率和稳态声子数表达式,重点讨论空腔时机械振子的基态冷却,发现当满足最佳参数条件(机械振子的冷却跃迁速率对应光压涨落谱的最大值,而加热跃迁速率对应光压涨落谱的最小值)时,机械振子可以被冷却到稳态声子数足够少.此外分析:当辅助腔内注入原子系综时,若参数选择恰当可能更利于基态冷却. 相似文献
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C.H. Eab 《Physica A》2010,389(13):2510-3636
Fractional generalized Langevin equation with external force is used to model single-file diffusion. It is found that for external force that varies with power law the solution for such a fractional Langevin equation gives the correct short and long time behavior for the mean square displacement of single-file diffusion when appropriate choice of parameters associated with fractional generalized Langevin equation are used. By considering some special cases of the fractional generalized Langevin equation, a new class of closed analytic expressions for the mean square displacement of single-file diffusion can be obtained. The effective Fokker-Planck equation associated with single-file diffusion is briefly considered. 相似文献
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研究了在内噪声、外噪声(固有频率涨落噪声)及周期激励信号共同作用下具有指数型记忆阻尼的广义Langevin方程的共振行为.首先将其转化为等价的三维马尔可夫线性系统,再利用Shapiro-Loginov公式和Laplace变换导出系统响应一阶矩和稳态响应振幅的解析表达式.研究发现,当系统参数满足Routh-Hurwitz稳定条件时,稳态响应振幅随周期激励信号频率、记忆阻尼及外噪声参数的变化存在"真正"随机共振、传统随机共振和广义随机共振,且随机共振随着系统记忆时间的增加而减弱.数值模拟计算结果表明系统响应功率谱与理论结果相符. 相似文献
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本文从分数阶谱形式的气固耦合模型出发, 理论推导出具有幂律记忆核的广义朗之万方程. 研究气体分子在自由场和简谐势场中的动力学演化和长时渐进行为, 着重分析三种各态历经判据: Khinchin判据、Lee判据以及内在判据和外在表现的适用性. 研究结果表明: Khinchin判据适用于广义朗之万方程描述的所有扩散和输运过程; Lee判据并不适用于布朗运动, 只能用来区分不同类型的扩散过程; 而内在判据和外在表现不仅能够把非各态历经分为两类, 同时可以揭示非各态历经的物理内在根源. 相似文献
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Starting from classical Hamiltonian mechanics, we derive for the dynamics of gross variables in nonequilibrium systems exact nonlinear generalized Fokker-Planck and Langevin equations in which the effect of the initial preparation is taken into account explicitly. This latter concept allows for the construction of a uniquely determined projection operator. The memory functions occurring in the Langevin equations are related to the random forces by a fluctuation-dissipation theorem of the second kind. We discuss the connection with the generalized Fokker-Planck equation. The known results for equilibrium fluctuations are recovered as a special case.Supported in part by the National Science Foundation, Grant CHE78-21460. 相似文献
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N. G. van Kampen 《Journal of statistical physics》1981,25(3):431-442
In the presence of internal noise the variables describing a system are intrinsically stochastic. If they constitute a Markov process the expansion enables one to extract a deterministic macroscopic equation and to compute the fluctuations in successive approximations. In the lowest or linear noise approximation the fluctuations can be represented by a Langevin equation, provided it is handled appropriately. Higher orders cannot be described by any white noise Langevin equation. The question whether the equation has to be interpreted according to Itô or Stratonovich concerns these higher orders, for which the equation is not valid anyway. 相似文献
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Hiroshi Ueyama 《Journal of statistical physics》1980,23(4):463-482
The method of the nonlinear Langevin equation is generalized to ordinary mixed and to chemically reacting gases. The stochastic Boltzmann equations of these gases, the fluctuating hydrodynamic equations of mixed gases, and the Langevin equations for the number density of each component of a reaction-diffusion system are obtained.This work was supported financially by the Alexander von Humboldt Foundation. The main part of the paper was written during the author's stay at the Max-Planck Institut für Festkörperforschung (Stuttgart) as a Humboldt fellow. 相似文献
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In this paper, the generalized Langevin equation introduced by Kubo and Mori is formulated as a random integral equation. We consider (1) the existence and uniqueness of the solution, (2) moments of the solution process, (3) a comparison theorem for solution processes, and (4) the Cauchy polygonal approximation to the solution. 相似文献
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Stochastic differential equations, especially the one called Langevin equation, play an important role in many fields of modern science. In this paper, we use the bicolour rooted tree method, which is based on the stochastic Taylor expansion, to get the systematic pattern of the high order algorithm for Langevin equation. We propose a popular test problem, which is related to the energy relaxation in the double well, to test the validity of our algorithm and compare our algorithm with other usually used algorithms in simulations. And we also consider the time-dependent Langevin equation with the Ornstein-Uhlenbeck noise as our second example to demonstrate the versatility of our method. 相似文献