Sojourn times in a processor sharing queue with service interruptions

We study the sojourn times of customers in an M/M/1 queue with the processor sharing service discipline and a server that is subject to breakdowns. The lengths of the breakdowns have a general distribution, whereas the on-periods are exponentially distributed. A branching process approach leads to a decomposition of the sojourn time, in which the components are independent of each other and can be investigated separately. We derive the Laplace–Stieltjes transform of the sojourn-time distribution in steady state, and show that the expected sojourn time is not proportional to the service requirement. In the heavy-traffic limit, the sojourn time conditioned on the service requirement and scaled by the traffic load is shown to be exponentially distributed. The results can be used for the performance analysis of elastic traffic in communication networks, in particular, the ABR service class in ATM networks, and best-effort services in IP networks.     

Applications of SMP Bounds to Multi-class Traffic in High-speed Networks

In this paper, we consider the stochastic fluid-flow model of a single node in a high-speed telecommunication network handling multi-class traffic. The node has multiple buffers, one for each class of traffic. The contents of these buffers are multiplexed onto a single output channel using one of the service scheduling policies: the Timed Round Robin Policy or the Static Priority Service Policy. The Quality of Service requirements for each class are based on cell loss probabilities. Using effective bandwidth methodologies and the recently developed bounds for semi-Markov modulated traffic, we solve call admission control problems for the two service scheduling policies at this node. We compare the performance of the effective bandwidth methodologies and the SMP bounds technique. We also numerically compare the performance of the two service scheduling policies.     

低噪声通过特性的测量仿真研究

本文研究运用组合传感器和声压、振速联合信息处理技术进行低品声通过特性的测量。通过特性的背景噪声出非相干的各向同性白噪声和相干的交通干扰组成,交通干扰又分为平稳与非平稳两种,用平均声强器来抗非相干干扰;用交通干扰能量流中心方位抑制技术来抗平稳的相干干扰;对于非平稳的相干干扰而能量流中心方位抑制技术。仿真试验表明效果良好。     

响应面方法计算HTR-10余热排出系统物理过程的失效概率

在核电站安全研究中，概率安全评价方法已经得到了广泛的应用.但是对于采用非能动设计的核电站系统，其可靠性分析的研究还处于初级阶段.非能动系统的失效不但要考虑常规可靠性分析中考虑的设备失效，还要考虑物理过程的失效.物理过程失效概率的计算方法和能动系统可靠性分析方法完全不同.本文给出物理过程失效的数学描述，介绍了一次二阶矩法、响应面方法，并且应用响应面方法计算了清华大学核能技术设计研究院10MW高温气冷实验堆(HTR-10)余热排出系统失效概率的近似值. 关键词： 概率安全评价 非能动系统 可靠性 响应面     

大气消光特性与机载激光雷达眼睛安全关系的研究

依据美国ANSI标准，定量分析了气溶胶、卷云和沙尘的垂直消光特性对机载激光雷达激光脉冲眼睛安全最大阈值能量的影响；以地基激光雷达探测得到的合肥上空沙尘暴为例，定量给出了大气中各成分消光特性对飞机眼睛安全最低高度的影响；模拟计算了各种大气成分的消光特性对激光脉冲眼睛安全系数的影响随高度的变化规律。计算结果表明：沙尘层对激光脉冲眼睛安全最大阈值能量的影响幅度可达几十毫焦。该结果为我国第一台机载大气探测激光雷达激光脉冲能量设置提供了基本依据。     

车辆的长度和速度对单车道混合交通流的影响

在NaSch交通流模型的基础上，建立了单车道上由两种长度不一样、可分别以不同最大速度行驶的车辆构成的混合交通流模型.在周期性边界条件下，通过计算机模拟研究了车辆的长度、最大速度和混合比例系数对混合交通流的影响. 关键词： 元胞自动机 混合交通流 计算机模拟     

A modified NaSch model with density-dependent randomization for traffic flow

Based on the Nagel-Schreckenberg (NaSch) model of traffic flow, a modified cellular automaton (CA) traffic model with the density-dependent randomization (abbreviated as the DDR model) is proposed to simulate traffic flow. The fundamental diagram obtained by simulation shows the ability of this modified NaSch model to capture the essential features of traffic flow, e.g., synchronized flow, metastable state, hysteresis and phase separation at higher densities. Comparisons are made between this DDR model and the NaSch model, also between this DDR model and the VDR model. And the underlying mechanism is analyzed. All these results indicate that the presented model is reasonable and more realistic.     

XPS investigations of ruthenium deposited onto representative inner surfaces of nuclear reactor containment buildings

In the case of a hypothetical severe accident in a nuclear power plant, interactions of gaseous RuO₄ with reactor containment building surfaces (stainless steel and epoxy paint) could possibly lead to a black Ru-containing deposit on these surfaces. Some scenarios include the possibility of formation of highly radiotoxic RuO₄(g) by the interactions of these deposits with the oxidizing medium induced by air radiolysis, in the reactor containment building, and consequently dispersion of this species. Therefore, the accurate determination of the chemical nature of ruthenium in the deposits is of the high importance for safety studies. An experiment was designed to model the interactions of RuO₄(g) with samples of stainless steel and of steel covered with epoxy paint. Then, these deposits have been carefully characterised by scanning electron microscopy (SEM/EDS), electron probe microanalysis (EPMA) and X-ray photoelectron spectroscopy (XPS). The analysis by XPS of Ru deposits formed by interaction of RuO₄(g), revealed that the ruthenium is likely to be in the IV oxidation state, as the shapes of the Ru 3d core levels are very similar with those observed on the RuO₂·xH₂O reference powder sample. The analysis of O 1s peaks indicates a large component attributed to the hydroxyl functional groups. From these results, it was concluded that Ru was present on the surface of the deposits as an oxyhydroxide of Ru(IV). It has also to be pointed out that the presence of “pure” RuO₂, or of a thin layer of RuO₃ or Ru₂O₅, coming from the decomposition of RuO₄ on the surface of samples of stainless steel and epoxy paint, could be ruled out. These findings will be used for further investigations of the possible revolatilisation phenomena induced by ozone.     

道路约束条件下的移动机器人跟踪

为提高移动机器人的位置估计精度和跟踪效果,提出一种基于道路约束条件下的移动机器人鲁棒约束H∞滤波(CHF)跟踪算法.首先,将机器人移动的道路网络作为跟踪的约束条件,并利用当前统计模型对机器人的运动进行建模.其次,将道路约束条件作为机器人跟踪的非线性状态约束,利用最小协方差估计推导了鲁棒CHF递推方程.通过拉格朗日乘子法对非线性约束优化估计问题进行求解,并利用约束信息对CHF算法的状态更新过程进行了改进.最后,通过对CHF算法和无约束的H∞滤波算法的跟踪性能进行了对比分析和验证.仿真结果表明,该算法可以实现机器人的跟踪,且跟踪精度优于HF算法.     

NONLOCAL CROWD DYNAMICS MODELS FOR SEVERAL POPULATIONS

This paper develops the basic analytical theory related to some recently introduced crowd dynamics models.Where well posedness was known only locally in time,it is here extended to all of R+.The result...