A streamlined simplex approach to the singly constrained transportation problem

A primal simplex procedure is developed to solve transportation problems with an arbitrary additional linear constraint. The approach is a specialization of the Double Reverse Method of Charnes and Cooper. Efficient procedures for pricing-out the basis, determining representations, and implementing the change of basis are presented. These procedures exploit the pure transportation substructure in such a manner that full advantage may be taken of the computational schemes and list structures used to store and update the basis in codifying the MODI method. Furthermore, the pricing-out and change-of-basis procedures are organized in a manner that permits the calculations for one to be utilized in the other. Computational results are presented which indicate that this method is at least 50 times faster than the state-of-the-art LP code, APEX-III. Methods for obtaining basic primal “feasible” starts and “good” feasible integer solutions are also presented.     

On single-machine sequencing with order constraints

A collection of jobs is to be processed by a single machine. Each job has a cost function associated with it which may be either linear or exponential, costs accruing when a job is completed. The machine may be allocated to the jobs according to a precedence relation. The problem is to find a strategy for allocating the machine which minimizes the total cost and which is consistent with the precedence relation. The paper extends and simplifies some previous work done by Sidney.     

A suboptimality bound for permutation policies in single machine stochastic scheduling

A general class of single machine stochastic scheduling problems incorporating precedence constraints is modelled as a family of competing Markov decision processes. A bound on the optimal return yields a suboptimality bound for permutation policies. This in turn leads to a generalised “used better than new” principle as a (highly intuitive) sufficient condition for the optimality of a permutation policy in the class of all (preemptive) policies. © 1995 John Wiley & Sons, Inc.     

机载合作辐射源空间定位误差分析及对策

在一些空地结合的双基地雷达系统中,机载辐射源的空间定位误差对目标定位有着重要影响.针对机载辐射源定位误差的重要来源GPS定位误差和空中气流扰动,研究了一种数据处理方案,通过建立GPS定位误差模型,并结合不同载体运动模型,对误差进行卡尔曼滤波处理.该方案有效减小了机载辐射源的定位误差,对双基地雷达研究具有重要意义.     

废旧轮胎压缩试验与数值模拟

为更好地将废旧轮胎应用于落石灾害防护领域,对不同型号的废旧轮胎进行了单向重复压缩试验,并对单个轮胎分别进行了2个相互垂直方向上的重复压缩试验,利用LS-DYNA软件模拟了废旧轮胎的压缩试验过程。结果表明:废旧轮胎具有明显的弹性特征和被重复利用的性质,能够重复承受较大变形且割线刚度降低较小;一个方向上被压缩过的废旧轮胎沿圆周方向旋转90°后再进行压缩,其割线刚度几乎能够恢复到初始状态;废旧轮胎的有限元简化模型较为合理,在落石灾害防护领域有着广阔的应用前景。     

Optimal patrol to uncover threats in time when detection is imperfect

Consider a patrol problem, where a patroller traverses a graph through edges to detect potential attacks at nodes. An attack takes a random amount of time to complete. The patroller takes one time unit to move to and inspect an adjacent node, and will detect an ongoing attack with some probability. If an attack completes before it is detected, a cost is incurred. The attack time distribution, the cost due to a successful attack, and the detection probability all depend on the attack node. The patroller seeks a patrol policy that minimizes the expected cost incurred when, and if, an attack eventually happens. We consider two cases. A random attacker chooses where to attack according to predetermined probabilities, while a strategic attacker chooses where to attack to incur the maximal expected cost. In each case, computing the optimal solution, although possible, quickly becomes intractable for problems of practical sizes. Our main contribution is to develop efficient index policies—based on Lagrangian relaxation methodology, and also on approximate dynamic programming—which typically achieve within 1% of optimality with computation time orders of magnitude less than what is required to compute the optimal policy for problems of practical sizes. © 2014 Wiley Periodicals, Inc. Naval Research Logistics, 61: 557–576, 2014     

Pakistan's Evolving Nuclear Weapon Posture

This essay provides an overview of the ongoing quantitative and qualitative changes in Pakistan's nuclear arsenal and their impact on deterrence stability vis-à-vis India. Prominent among these trends is a major expansion in fissile material production that enables the manufacture of lighter and more compact warheads optimized for battlefield missions; the development of cruise missiles and shorter-range ballistic missiles possessing dual-use capabilities; and a greater emphasis in doctrinal pronouncements on the need for strike options geared to all levels of conflict. Although these trends pose problematic ramifications for the risks of unauthorized and inadvertent escalation, deterrence stability in South Asia is not as precarious as many observers fear. The challenges of fashioning a robust nuclear peace between India and Pakistan cannot be lightly dismissed, however, and policy makers would do well to undertake some reinforcing measures.