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111.
Gerrit K. Janssens An Caris Katrien Ramaekers 《Expert systems with applications》2009,36(3):5987-5991
Congestion on roads leads to uncertainty in travel times, which is important in delivery of goods, especially in a business environment where high levels of customer service are expected. Delivery periods to customers might be constrained by time windows, which makes the scheduling and routing of vehicles from the supplier’s side more difficult. Operations Research methods turn into heuristics for this type of application. But when, on top, uncertainty on travel times are the case, any hope of a simple and well-performing heuristic is lost. This study applies a methodology in which a heuristic is used to find a solution for scheduling and routing under deterministic travel times and, by means of simulation, though the use of Time Petri nets evaluates the sensitivity of the solution to uncertainties in travel times from one customer to the next in a route. 相似文献
112.
TPS中调节控制点的综合应用 总被引:1,自引:1,他引:0
提出了在控制系统更新时,利用新系统的控制功能,实现对老系统中一些特殊控制回路的控制方法.详细介绍了利用Hon-eywell公司HPM中常规控制点的功能,对现场多变量参数求和运算以后进行大可调比参数的控制,以及这种控制回路的控制策略和组态方法.应用结果表明,该控制回路控制精度高、可靠性高.据此提出了充分利用系统软件提供的各种功能模块,解决生产实际问题的方法. 相似文献
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Identity based broadcast encryption allows a centralized transmitter to send encrypted messages to a set of identities S, so that only the users with identity in S can decrypt these ciphertexts using their respective private key. Recently [Information Processing Letters 109 (2009)], an identity-based broadcast encryption scheme was proposed (Ren and Gu, 2009) [1], and it was claimed to be fully chosen-ciphertext secure without random oracles. However, by giving a concrete attack, we indicate that this scheme is even not chosen-plaintext secure. 相似文献
116.
X.M. An L.X. Li G.W. Ma H.H. Zhang 《Computer Methods in Applied Mechanics and Engineering》2011,200(5-8):665-674
In the partition of unity (PU)-based methods, the global approximation is built by multiplying a partition of unity by local approximations. Within this framework, high-order approximations are achieved by directly adopting high-order polynomials as local approximations, and therefore nodes along sides or inside elements, which are usually adopted in the conventional finite element methods, are no more required. However, the PU-based approximation constructed in this way may suffer from rank deficiency due to the linear dependence of the global degrees of freedom. In this paper, the origin of the rank deficiency in the PU-based approximation space is first dissected at an element level, and then an approach to predict the rank deficiency for a mesh is proposed together with the principle of the increase of rank deficiency. Finally, examples are investigated to validate the present approach. The current work indicates such a fact that the rank deficiency is an unrelated issue to the nullity of the global matrix. It can be resolved in its own manner. 相似文献
117.
This paper considers an online hierarchical scheduling problem on parallel identical machines. We are given a set of m machines and a sequence of jobs. Each machine has a different hierarchy, and each job also has a hierarchy associated with it. A job can be assigned to a machine only if its hierarchy is no less than that of the machine. The objective is to minimize the makespan, i.e., the maximum load of all machines. Two models are studied in the paper. For the fractional model, we present an improved algorithm and lower bounds. Both the algorithm and the lower bound are based on solutions of mathematical programming. For any given m, our algorithm is optimal by numerical calculation. For the integral model, we present both a general algorithm for any m, and an improved algorithm with better competitive ratios of 2.333 and 2.610 for m=4 and 5, respectively. 相似文献
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为了准确检测轨道电路移频信号的参数,在分析国内外轨道电路移频信号频谱特点的基础上,提出了针对两种不同信号分别采用整周期和欠采样的采样方法,在以上采样的基础上,介绍了ZOOM-FFT算法的原理和实现步骤,并采用ZOOM-FFT对信号载频附近的频段进行频谱细化放大,提取实验数据。仿真结果表明上述方法是可行的,可以准确检测轨道电路移频信号的参数,有效提高了信号的频率分辨率,满足了技术指标的要求。 相似文献
120.