A preemptive discrete-time priority buffer system with partial buffer sharing

This paper considers a Geo/Geo/1 discrete-time queue with preemptive priority. Both the arrival and service processes are Bernoulli processes. There are two kinds of customers: low-priority and high-priority customers. The high-priority customers have a preemptive priority over low-priority customers. If the total number of customers is equal or more than the threshold (k), the arrival of low-priority customers will be ignored. Hence the system buffer size is finite only for the low-priority customers. A recursive numerical procedure is developed to find the steady-state probabilities. With the aid of recursive equations, we transform the infinite steady-state departure-epoch equations set to a set of (k + 1) × (k + 2)/2 linear equations set based on the embedded Markov Chain technique. Then, this reduced linear equations set is used to compute the steady-state departure-epoch probabilities. The important performance measures of the system are calculated. Finally, the applicability of the solution procedure is shown by a numerical example and the sensitivity of the performance measures to the changes in system parameters is analyzed.     

基于优先级的进离港航班排序优化问题研究

研究机场终端区进离港航班排序优化问题,对于提高跑道利用率以及降低航班延误损失具有重要意义。本文首先考虑航班运行方式(降落和起飞)、飞机类型以及航班的重要程度(航程是否连续)的不同所造成延误损失的不同,设计三维优先级表反映调度优先等级,并将其转化为延误成本系数。其次,为实现调度的公平性和减轻管制人员的工作负荷,设置允许延误的航班架次约束、邻边约束以及最大限制位置约束。再次,以最小化航班总延误成本为目标建立模型,提出相应的改进蚁群算法(GJAC)进行求解。最后通过数值实验验证所提算法在考虑调度优先等级及上述约束条件的同时能有效减少进离港航班队列的总延误成本。     

考虑可信度和优先级的对偶犹豫模糊多属性决策在绿色审计中的应用研究

针对目前专家和属性对于方案比选的重要性致使企业迫切需要将其定量化分析的问题,以及企业环境行为中公司需要承担环保责任,在绿色采购方面要将环境属性引入供应商比选标准的问题,本文提出了考虑专家可信度和属性优先级的对偶犹豫模糊多属性决策方法,将专家对于该领域的熟悉程度及所选属性的重要程度融入到供应商的绿色评估指标定量化分析与评选中。结合对偶犹豫模糊集的隶属度与非隶属度,给出了对偶犹豫模糊熵值、混合平均算子和混合几何算子的计算模型与该方法模型的具体步骤,通过对某企业绿色审计在内的四种属性进行评估来选择最佳供应商的实例,验证了此模型的可行性和有效性。     

多属性决策中的目标规划

针对只有部分权重信息的对方案有偏好的多属性决策问题,本文给出了一种简单的目标规划模型,通过对该模型的求解却可得到决策方案的排序。最后给出了一个算例。     

Book review of advances in gabor analysis,applied and numerical harmonic analysis,Hans G. Feichtinger and Thomas Strohmer (Eds.), Birkhäuser,Boston-Basel-Berlin, 2002, 356 pages. ISBN 0-8176-4239-0

In some recent publications it was shown that certain stationary stochastic dynamic programming problems with general state and action spaces can be solved by generalized linear programming. It Is the main aim of the present paper to demonstrate that a similar linear programming approach is feasible even in the non-stationary case. For this end, we formulate a programming problem (D^?) and show that (D^?) is equivalent to the problem of finding a p=optimal policy for the stochastic dynamic program, whereas a modification of (D^?) turns out to be the dual program of a pair of general linear programs.     

8-3线优先编码器74LS148的级联分析及研究

74LS148是一种带扩展功能的8-3线优先编码器,将多片74LS148集成8-3线优先编码器级联构成不同的编码器,能够灵活、有效地扩大编码器的使用范围。不同的74LS148进行级联时,任何时候只对其中优先级别最高的输入信号进行编码,编码器的工作状态由使能输入端决定。     

Analytical Standards and Methods for the Determination of Polynuclear Aromatic Hydrocarbons in Environmental Samplest

Abstract

Standard reference materials (SRM's) have been produced, certified, and issued by the United States National Bureau of Standards (NBS) since 1905. NBS currently issues more than 1000 SRM's of various types, including nuclear materials, rubber, clinical and environmental trace metal standards. The most recent addition to this group is a series of environmental trace organic materials with certified concentrations of selected polynuclear aromatic hydrocarbons (PAH), phenols, and N-heterocyclic compounds. Until recently, trace organic SRM's were non-existent due to the lack of analytical methodology necessary for certification. Details concerning the analytical methods developed and used for certification of the concentrations of several PAH in SRM's 1580 (Organics in Shale Oil), 1644 (Generator Columns for PAH in water), 1647 (PAH in Acetonitrile), and 1649 (Urban Particulate Matter) are given along with some suggested uses for these SRM's.     

Hybrid buffering architecture for packet contention resolution of an optical packet switch

Packet contention is a major issue in optical packet switching network and it is not a trivial task to resolve due to lack of optical RAM technology. In order to resolve contention optical buffering approach is used using fiber delay lines (FDLs). Yet there is a heavy packet loss rate due to unavailability of output port and free FDLs. This paper proposes a hybrid buffering architecture using feed-forward and feedback shared FLDs to resolve packet contention resolution of an optical packet switch. Feed-forward FDLs are used as primary buffer and feedback FDLs are implemented as supplementary buffer. Simulation result shows that proposed hybrid buffering switch achieves packet loss rate between 10⁻¹ and 10⁻² at heavy traffic load (ρ = 0.9) for a 32 × 32 switch using different FDL length.     

Fair and efficient student placement with couples

We study situations of allocating positions to students based on priorities. An example is the assignment of medical students to hospital residencies on the basis of entrance exams. For markets without couples, e.g., for undergraduate student placement, acyclicity is a necessary and sufficient condition for the existence of a fair and efficient placement mechanism (Ergin in Econometrica 70:2489–2497, 2002). We show that in the presence of couples acyclicity is still necessary, but not sufficient. A second necessary condition is priority-togetherness of couples. A priority structure that satisfies both necessary conditions is called pt-acyclic. For student placement problems where all quotas are equal to one we characterize pt-acyclicity and show that it is a sufficient condition for the existence of a fair and efficient placement mechanism. If in addition to pt-acyclicity we require reallocation- and vacancy-fairness for couples, the so-called dictator- bidictator placement mechanism is the unique fair and efficient placement mechanism. Finally, for general student placement problems, we show that pt-acyclicity may not be sufficient for the existence of a fair and efficient placement mechanism. We identify a sufficient condition such that the so-called sequential placement mechanism produces a fair and efficient allocation.      

The throughput performance of a prioritized LIFO service discipline

The LIFO service discipline maximizes throughput for certain queuing systems with delay-dependent customer behavior. To study the effects of priorities in such a system, we obtain delay distributions for each customer class of a K-class, single server system with nonpreemptive priorities and LIFO within each queue.