Predictive buffer control in delivering remotely stored video using proxy servers

We study the problem of using proxy servers to stream video stored at a geographically separate location. The separation of the server and the storage introduces a non-negligible delay in retrieving video frames in real time. We assume an additive-increase/multiplicative-decrease transport protocol to support the streaming process and develop an effective scheme to achieve consistent, high streaming quality. The heart of the scheme is the control of buffer occupancy at the proxy server. We model the buffer as a bilinear dynamical system disturbed by a point process with stochastic state-dependent intensity. We first develop a buffer controller that does not exploit this model. Then, using the buffer model, we construct a second controller based on an optimal-control analysis for the case without retrieval delay. Extending these two controllers, we subsequently synthesize two controllers based on prediction of future system states using the model, taking into account both the delay and the state-dependent disturbance intensity. Our empirical study illustrates the effectiveness of the streaming scheme. We further find that the controllers exploiting the buffer model demonstrate performance significantly superior to that of the model-free controller in overcoming the adverse impact of the retrieval delay. We also conduct limited experiments to study the impact of variable retrieval delays.     

Approximate controllability of partial neutral functional differential systems of fractional order with state-dependent delay

We prove the approximate controllability of control systems governed by a class of partial neutral functional differential systems of fractional order with state-dependent delay in an abstract space. Sufficient conditions for approximate controllability of the control systems are established provided the approximate controllability of the corresponding linear control systems. The results are obtained by using the Krasnoselskii–Schaefer type fixed point theorem with the fractional power of operators. An example is provided to illustrate the main results.     

基于机电-刚柔混合的H型双驱进给系统状态相关动态特性分析

动态特性是影响H型双驱进给系统定位精度的关键因素。基于重心驱动原理的H型双驱进给系统在位置状态变化时无法保证双轴驱动力合力通过运动件重心造成系统产生动态误差,从而导致H型双驱进给系统的定位精度提升依然存在困难。从H型双驱进给系统的结构特性分析出发,考虑H型横梁和移动部件位置状态对系统动力学参数的影响,建立了H型双驱进给系统刚柔耦合动力学模型。结合伺服电机控制模型,采用状态空间方法得到H型双驱进给系统的机电-刚柔混合模型。利用模态实验验证所建立的动力学模型的正确性。通过数值仿真分析了系统对阶跃信号、S型信号和斜坡信号的响应特性,得到了H型横梁和移动部件位置状态、进给速度状态和同步控制策略对H型双驱进给系统的动态误差、跟踪误差和同步误差大小的影响规律。所建立的机电-刚柔混合模型能够有效地揭示H型双驱进给系统状态相关参数对系统定位精度的影响,可为H型双驱进给系统同步控制和误差补偿研究奠定理论基础。     

砂土的剪胀理论及其本构模型的发展

经典的应力剪胀理论被广泛应用于土体弹塑性本构模型的建立,较好地模拟了黏性土的变形特性。最新的研究表明:由于应力剪胀理论中忽略了土体内部状态参量对剪胀的影响,而使得该理论应用于砂土时发生了困难。近来一些学者纷纷将土的密度作为变量引入剪胀方程,提出了状态相关剪胀理论,成功地模拟了砂土的各种变形特性。本文就砂土的状态及其描述、剪胀理论的发展、砂土本构模拟等方面进行介绍。     

基于态关联性不完美的诱骗态量子密钥分配

 本文提出了态关联性不完美条件下诱骗态量子密钥分配(QKD)的安全性理论分析模型.借助于QKD的保密放大分析方法,采用实际QKD系统广泛使用的诱骗态编码方案,使相位误码的估计更加准确,进而给出了态关联性不完美条件下诱骗态QKD的最终安全密钥生成率的表达式,刻画了密钥生成率与态关联性不完美、探测器性能和密钥传输距离之间的关系.数值模拟表明,诱骗态QKD的最终安全密钥生成率对态关联性不完美的容忍程度,随着密钥传输距离的增大而逐渐减小,随着探测器探测性能的提升而逐渐增大,因而验证了所给表达式的正确性.     

Liquid–Liquid Phase Separation in the Presence of Macromolecular Crowding and State-dependent Kinetics

Biomolecular condensates formed via liquid–liquid phase separation (LLPS) are increasingly being shown to play major roles in cellular self-organization dynamics in health and disease. It is well established that macromolecular crowding has a profound impact on protein interactions, particularly those that lead to LLPS. Although synthetic crowding agents are used during in vitro LLPS experiments, they are considerably different from the highly crowded nucleo-/cytoplasm and the effects of in vivo crowding remain poorly understood. In this work, we applied computational modeling to investigate the effects of macromolecular crowding on LLPS. To include biologically relevant LLPS dynamics, we extended the conventional Cahn–Hilliard model for phase separation by coupling it to experimentally derived macromolecular crowding dynamics and state-dependent reaction kinetics. Through extensive field-theoretic computer simulations, we show that the inclusion of macromolecular crowding results in late-stage coarsening and the stabilization of relatively smaller condensates. At a high crowding concentration, there is an accelerated growth and late-stage arrest of droplet formation, effectively resulting in anomalous labyrinthine morphologies akin to protein gelation observed in experiments. These results not only elucidate the crowder effects observed in experiments, but also highlight the importance of including state-dependent kinetics in LLPS models, and may help in designing further experiments to probe the intricate roles played by LLPS in self-organization dynamics of cells.     

基于在线学习神经网络的状态依赖型故障预测

提出外部激励故障和内部激励故障的概念,研究非线性系统状态依赖型故障的预测问题.将非线性系统的故障模型描述成外部激励与内部激励相耦合的一般非线性函数形式,函数的结构未知.通过反向传播(BP)神经网络在线学习故障函数模型实时逼近故障模型,提出基于在线神经网络的状态依赖型故障的预测算法.该算法能够实时地检测故障,对系统状态和故障进行迭代估计和预测.利用系统状态的预测值实时预测了系统的失效时间.故障模型的一般化拓展充分体现了系统状态对故障的影响,增强了算法的实用性.仿真结果验证了该方法的有效性.     

Quadratic Stabilization of Switched Uncertain Linear Systems: A Convex Combination Approach

We consider quadratic stabilization for a class of switched systems which are composed of a finite set of continuoustime linear subsystems with norm bounded uncertainties. Under the assumption that there is no single quadratically stable subsystem, if a convex combination of subsystems is quadratically stable, then we propose a state-dependent switching law, based on the convex combination of subsystems, such that the entire switched linear system is quadratically stable. When the state information is not available, we extend the discussion to designing an output-dependent switching law by constructing a robust Luenberger observer for each subsystem.      

Exponentially incremental (Q,S, R)-dissipativity and incremental stability for switched time-varying nonlinear systems

Exponentially incremental (Q,S,R)-dissipativityand incremental stability for switched time-varying nonlinear systems are studied whose subsystems are not required to be exponentially incrementally (Q,S,R)-dissipative. The sufficient conditions for switched time-varying nonlinear systems to be exponentially incrementally (Q,S,R)-dissipative are presented by the design of state-dependent switching laws. Incremental stability for switched time-varying nonlinear systems are derived based on exponentially incremental (Q,S,R)-dissipativity. Exponentially incremental (Q,S,R)-dissipativity is shown to be preserved under feedback interconnection by the design of a composite state-dependent switching law. Two simulation examples are provided to show the effectiveness of the proposed approaches.     

Dynamic optimization of dual-mode hybrid systems with state-dependent switching conditions

This paper presents a computational approach for optimizing a class of hybrid systems in which the state dynamics switch between two distinct modes. The times at which the mode transitions occur cannot be specified directly, but are instead governed by a state-dependent switching condition. The control variables, which should be chosen optimally by the system designer, consist of a set of continuous-time input signals. By introducing an auxiliary binary-valued control function to represent the system's current mode, we show that any dual-mode hybrid system with state-dependent switching conditions can be transformed into a standard dynamic system subject to path constraints. We then develop a computational algorithm, based on control parameterization, the time-scaling transformation, and an exact penalty method, for determining the optimal piecewise constant input signals for the original hybrid system. A numerical example on cancer chemotherapy is included to demonstrate the effectiveness of the proposed algorithm.