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191.
Using a birth‐and‐death process to estimate the steady‐state distribution of a periodic queue 下载免费PDF全文
If the number of customers in a queueing system as a function of time has a proper limiting steady‐state distribution, then that steady‐state distribution can be estimated from system data by fitting a general stationary birth‐and‐death (BD) process model to the data and solving for its steady‐state distribution using the familiar local‐balance steady‐state equation for BD processes, even if the actual process is not a BD process. We show that this indirect way to estimate the steady‐state distribution can be effective for periodic queues, because the fitted birth and death rates often have special structure allowing them to be estimated efficiently by fitting parametric functions with only a few parameters, for example, 2. We focus on the multiserver Mt/GI/s queue with a nonhomogeneous Poisson arrival process having a periodic time‐varying rate function. We establish properties of its steady‐state distribution and fitted BD rates. We also show that the fitted BD rates can be a useful diagnostic tool to see if an Mt/GI/s model is appropriate for a complex queueing system. © 2015 Wiley Periodicals, Inc. Naval Research Logistics 62: 664–685, 2015 相似文献
192.
Integrated scheduling of loading and transportation with tractors and semitrailers separated 下载免费PDF全文
Motivated by some practical applications, we study a new integrated loading and transportation scheduling problem. Given a set of jobs, a single crane is available to load jobs, one by one, onto semitrailers with a given capacity. Loaded semitrailers are assigned to tractors for transportation tasks. Subject to limited resources (crane, semitrailers, and tractors), the problem is to determine (1) an assignment of jobs to semitrailers for loading tasks, (2) a sequence for the crane to load jobs onto semitrailers, (3) an assignment of loaded semitrailers to tractors for transportation tasks, and (4) a transportation schedule of assigned tractors such that the completion time of the last transportation task is minimized. We first formulate the problem as a mixed integer linear programming model (MILPM) and prove that the problem is strongly NP‐hard. Then, optimality properties are provided which are useful in establishing an improved MILPM and designing solution algorithms. We develop a constructive heuristic, two LP‐based heuristics, and a recovering beam search heuristic to solve this problem. An improved procedure for solutions by heuristics is also presented. Furthermore, two branch‐and‐bound (B&B) algorithms with two different lower bounds are developed to solve the problem to optimality. Finally, computational experiments using both real data and randomly generated data demonstrate that our heuristics are highly efficient and effective. In terms of computational time and the number of instances solved to optimality in a time limit, the B&B algorithms are better than solving the MILPM. © 2015 Wiley Periodicals, Inc. Naval Research Logistics 62: 416–433, 2015 相似文献
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AbstractThe emergence of the Islamic sect, Boko Haram, and its transformation into a terrorist organisation has dominated recent discourse in the fields of political science and security studies, both within and without the socio-politico enclave known as Nigeria. Much of the discussion has centred on the extra-judicial execution of its founder, Mohammed Yusuf, which purportedly intensified the radicalisation of the group, and whether or not the sect receives operational and/or financial support from foreign terrorist associations. The interest of others has been to forecast the possibility of the internationalisation of the group's activities. This paper aligns with those whose interest is to identify and proffer ways of resolving factors that predisposed the Nigerian state to the levels of violence perpetrated by Boko Haram, with a view to averting much greater crises in the future. It adopts some historicism in demonstrating that the responsibility for the deepening insecurity in the country resides in the Nigerian state structure, which has often been seen as willing to sacrifice the well-being of the many for the benefit of a few. On the whole, the paper utilises state fragility as the framework of analysis by identifying the incapacity of the state in effective service delivery, which has as a result created a situation of mass unemployment and extreme poverty that has fanned the Boko Haram uprising. It concludes that a sustainable solution to the crisis lies in addressing the root causes of inequality, unemployment and poverty, with which most Nigerians, particularly in the north, subsist. 相似文献
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油罐是油品储运的重要设备,罐底最易出现穿孔渗漏油现象,致使罐基内部油气质量分数高于正常值。以油库中柴油覆土罐群为例,研究并试验了根据罐基油气质量分数识别罐底渗漏的方法:分析罐基探漏孔位置分布并钻孔;多次探测罐基油气质量分数,根据探测数据识别各罐有无底部渗漏;为了便于以后检测油库时识别各罐有无渗漏,为各罐建立状态监测表,并将无渗漏的罐基油气质量分数最高值暂定为该类罐的安全值,低于该安全值的油罐可直接判定为无渗漏。实践结果证明,这种不开罐检测罐底渗漏油的方法可及时发现故障并采取措施,对储油安全具有重要意义。 相似文献
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物业管理是城市社区管理中一个重要的基层管理体系,消防安全管理作为物业管理的一项重要工作,目前还存在着许多亟待解决的问题。从高层住宅物业消防管理的现状入手,分析其存在的问题及原因,探讨解决问题的措施,促进物业消防管理的发展完善。 相似文献
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为了保证视线角速率在弹目碰撞前收敛到零附近的较小邻域内从而达到准平行接近的状态,本文基于自抗扰控制的不确定性估计补偿思想,应用反演控制方法设计了一种考虑导弹自动驾驶仪二阶动态特性和目标机动的三维有限时间收敛导引律。根据有限时间收敛控制理论,严格证明了系统的有限时间收敛特性;为抑制量测噪声,将传统跟踪微分器进行改进并应用于扩张状态观测器与反演控制的设计中。仿真结果表明:在自动驾驶仪响应延迟情况下,所设计的导引律能够导引导弹在有限时间内精确地拦截高速机动目标;改进的跟踪微分器精度高、响应快;基于改进跟踪微分器的扩张观测器估计效果理想。 相似文献