Demand shuffle—A method for multilevel proportional lot sizing and scheduling

This contribution acquaints the reader with a model for multilevel single-machine proportional lot sizing and scheduling problems (PLSPs) that appear in the scope of short-term production planning. It is one of the first articles that deals with dynamic capacitated multilevel lot sizing and scheduling, which is of great practical importance. The PLSP model refines well-known mixed-integer programming formulations for dynamic capacitated lot sizing and scheduling as, for instance, the DLSP or the CSLP. A special emphasis is given on a new method called demand shuffle to solve multilevel PLSP instances efficiently but suboptimally. Although the basic idea is very simple, it becomes clear that in the presence of precedence and capacity constraints many nontrivial details are to be concerned. Computational studies show that the presented approach decidedly improves recent results. © 1997 John Wiley & Sons, Inc. Naval Research Logistics 44: 319–340, 1997     

Leaderless Global Jihadism: The Paradox of Discriminate Violence

Jihadist violence is typically associated with being particularly indiscriminate. Often, as in variations of the ‘new terrorism’ thesis, this characteristic is proposed to correspond in some way to its other attributes such as its globalised, decentralised and ‘postmodern’ religious nature. Recent work appears to give more substance to such claims, by claiming to show a relationship between indiscriminate violence and decentralised group organisation. However, in this paper we show, based on an analysis of jihadist targeting in Western Europe and America from 2001 to 2013, that targeting choices by jihadists unconnected to organised militant groups have in fact been consistently more, rather than less discriminate in their targeting choices than their better-integrated peers. Drawing on this finding, as well as a broader reading of jihadist targeting discourses, we argue for a more complex understanding of the relationship between radicalisation, extremist ideology, decentralisation, and targeting choice.     

Inference for the maximum cell probability under multinomial sampling

This article investigates inference for p_max, the largest cell probability in multinomial trials for the case of a small to moderate number of trials. Emphasis focuses on point and interval estimation. Both frequentist and Bayesian approaches are developed. The results of extensive simulation investigation are included as well as the analysis of a set of crime data for the city of New Orleans taken from the National Crime Survey.     

A general model for accelerated life testing with time‐dependent covariates

This paper introduces a general or “distribution‐free” model to analyze the lifetime of components under accelerated life testing. Unlike the accelerated failure time (AFT) models, the proposed model shares the advantage of being “distribution‐free” with the proportional hazard (PH) model and overcomes the deficiency of the PH model not allowing survival curves corresponding to different values of a covariate to cross. In this research, we extend and modify the extended hazard regression (EHR) model using the partial likelihood function to analyze failure data with time‐dependent covariates. The new model can be easily adopted to create an accelerated life testing model with different types of stress loading. For example, stress loading in accelerated life testing can be a step function, cyclic, or linear function with time. These types of stress loadings reduce the testing time and increase the number of failures of components under test. The proposed EHR model with time‐dependent covariates which incorporates multiple stress loadings requires further verification. Therefore, we conduct an accelerated life test in the laboratory by subjecting components to time‐dependent stresses, and we compare the reliability estimation based on the developed model with that obtained from experimental results. The combination of the theoretical development of the accelerated life testing model verified by laboratory experiments offers a unique perspective to reliability model building and verification. © 1999 John Wiley & Sons, Inc. Naval Research Logistics 46: 303–321, 1999     

On testing for decreasing mean residual life ordering

We consider the problem of testing for the decreasing mean residual life ordering introduced in Kochar and Wiens [14]. We treat both the one-sample and two-sample problems. The limiting distributions of the proposed test statistics are derived. © 1993 John Wiley & Sons, Inc.     

Optimal stocking policies for low usage items in multi-echelon inventory systems

Multi-echelon logistic systems are essential parts of the service support function of high technology firms. The combination of technological developments and competitive pressures has led to the development of services systems with a unique set of characteristics. These characteristics include (1) low demand probabilities: (2) high cost items; (3) complex echelon structures; (4) existence of pooling mechanisms among stocking locations at the same echelon level; (5) high priority for service, which is often expressed in terms of response time service levels for product groups of items: (6) scrapping of failed parts; and (7) recycling of issued stock due to diagnostic use. This article develops a comprehensive model of a stochastic, multi-echelon inventory system that takes account of the above characteristics. Solutions to the constrained optimization problem are found using a branch and bound procedure. The results of applying this procedure to a spare parts inventory system for a computer manufacturer have led to a number of important policy conclusions.     

Test for the extreme value and weibull distributions based on normalized spacings

Discussed in this article are tests for the extreme-value distribution, or, equivalently, for the two-parameter Weibull distribution when parameters are unknown and the sample may be censored. The three tests investigated are based on the median, the mean, and the Anderson-Darling A² statistic calculated from a set zⁱ of values derived from the spacings of the sample. The median and the mean have previously been discussed by Mann, Scheuer, and Fertig [10] and by Tiku and Singh [14]. Asymptotic distributions and points are given for the test statistics, based on recently developed theory, and power studies are conducted to compare them with each other and with two other statistics suitable for the test. Of the normalized spacings tests, A² is recommended overall; the mean also gives good power in many situations, but can be nonconsistent.     

A branch and bound algorithm for solving a class of nonlinear integer programming problems

This article presents a branch and bound method for solving the problem of minimizing a separable concave function over a convex polyhedral set where the variables are restricted to be integer valued. Computational results are reported.