Mitigation of the blast load effects on a building structure using newly composite structural configurations

In this study, a nonlinear three-dimensional hydrocode numerical simulation was carried out using AUTODYN-3D to investigate the effect of blasting of a high explosive material (TNT) against several configurations of the composite structure. Several numerical models were carried out to study the effect of varying the thickness of the walls and the effect of adding an air layer or aluminum foam layer inside two layers of concrete in mitigating the effect of blast waves on the structure walls. The results showed that increasing the thickness of walls has a good effect on mitigating the effect of blast waves. When a layer of air was added, the effect of blast waves was exaggerated, while when a layer of aluminum foam was added the blast wave effects were mitigated with a reasonable percentage.     

On‐line algorithms for minimizing makespan on batch processing machines

We consider problem of scheduling jobs on‐line on batch processing machines with dynamic job arrivals to minimize makespan. A batch machine can handle up to B jobs simultaneously. The jobs that are processed together from a batch, and all jobs in a batch start and complete at the same time. The processing time of a batch is given by the longest processing time of any job in the batch. Each job becomes available at its arrival time, which is unknown in advance, and its processing time becomes known upon its arrival. In the first part of this paper, we address the single batch processing machine scheduling problem. First we deal with two variants: the unbounded model where B is sufficiently large and the bounded model where jobs have two distinct arrival times. For both variants, we provide on‐line algorithms with worst‐case ratio (the inverse of the Golden ratio) and prove that these results are the best possible. Furthermore, we generalize our algorithms to the general case and show a worst‐case ratio of 2. We then consider the unbounded case for parallel batch processing machine scheduling. Lower bound are given, and two on‐line algorithms are presented. © 2001 John Wiley & Sons, Inc. Naval Research Logistics 48: 241–258, 2001     

Short-term retrenchment planning in hierarchical manpower systems

We address the issue of short-term retrenchment planning required of organizations that are phasing down their manpower levels at rates faster than are allowed by natural attrition. Specifically, the problem we study is as follows: given the initial and target grade populations in a hierarchical manpower system at the end of a finite time horizon and the per-period rate of natural attrition for each grade, find a stationary manpower policy that minimizes the maximum per-period rate of retrenchment across all the grades over all stationary policies that yield the target grade populations at the end of the horizon. Because the problem is a nonconvex, nonseparable, nonlinear program, we develop a heuristic in which the promotion proportions of all the grades are successively fixed, starting from the lowest grade. We prove optimality of the heuristic policy in three nontrivial situations. In a computational experiment, in 135 out of 150 randomly generated instances (i.e., in 90% of the cases), the heuristic yielded a solution that was as good or better than that yielded by a benchmark computer program that solves the present problem as a nonlinear program. Further, the average computational time under the heuristic was an order of magnitude less than that under the program. © 1995 John Wiley & Sons, Inc.     

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.     

The impact of exponential smoothing forecasts on the bullwhip effect

An important phenomenon often observed in supply chain management, known as the bullwhip effect, implies that demand variability increases as one moves up the supply chain, i.e., as one moves away from customer demand. In this paper we quantify this effect for simple, two‐stage, supply chains consisting of a single retailer and a single manufacturer. We demonstrate that the use of an exponential smoothing forecast by the retailer can cause the bullwhip effect and contrast these results with the increase in variability due to the use of a moving average forecast. We consider two types of demand processes, a correlated demand process and a demand process with a linear trend. We then discuss several important managerial insights that can be drawn from this research. © 2000 John Wiley & Sons, Inc. Naval Research Logistics 47: 269–286, 2000     

Interpreting the Ribchester Helmet

In 1796 a 13-year-old boy playing on wasteland behind his father’s house in Ribchester, Lancashire discovered an assemblage of over 30 Roman artefacts, including a decorated brass helmet. Although partially corroded the Ribchester helmet is a fine example of a first-century AD cavalry sports helmet. This article considers how the interpretation of the helmet has evolved since its discovery. The multi-faceted iconography of the helmet with its mural crown diadem is that of an elite soldier and is paralleled in other examples of cavalry sports helmets of the Ribchester type. The long-neglected imagery on the helmet bowl is reinterpreted and seen not as a haphazard collection of randomly placed combatants but as a highly structured, symmetrical composition specifically designed to be viewed from different directions.     

Explicit modeling of detection within a stochastic duel

Many mathematical models have been formulated to describe combat between two weapon systems. However, until recently duel models did not explicitly represent target detection within a duel, leading to the necessity for the development of new model for each tactical situation. An earlier article by two of the authors described a duel between weapons with constant firing times and explicit modeling of detection. This article enhances the study of this form of duel between weapons by introducing a variable parameter for firing times. This enhancement removes the discontinuities evident during parametric analysis of the earlier model and hence provides a more coherent model of this combat situation. © 1993 John Wiley & Sons, Inc.     

Timing replacement decisions under discontinuous technological change

We consider the problem of deciding whether to keep a piece of equipment or replace it with a more advanced technology in an environment of technological change. Our model assumes that the costs associated with the presently available technology and future technologies are known, but that the appearance times of future technologies are uncertain. We develop a procedure for computing the optimal keep-or-replace decision that iteratively incorporates a technological forecast. For a certain class of situations, we show that our approach requires the minimum possible amount of forecasted data.     

Integrating multiple criteria decision making models into the decision support system framework for marketing decisions

A large number of multiple criteria decision making (MCDM) models have evolved over the past decade. This field now seems to have reached a stage of maturity. However, the managerial community has not yet extensively adopted these models in solving practical decision problems. The present article focuses on integrating the MCDM models within the decision support system (DSS) framework to encourage greater use of these models. A DSS framework and the criteria used for the choice of a model is discussed. Based on these criteria MCDM models generally used in the marketing field are evaluated. The possibility of using a mixture of MCDM models within the DSS framework is also explored. Following this, the role of the MCDM models in DSS is delineated. It is argued that, within the problem-solving process, the confluence of MCDM models and DSS plays a vital role in developing high-quality solutions.     

Stochastic linear fractional programming with the ratio of independent Cauchy variates

In this article is studied a stochastic linear fractional programming problem, in which the parameters of both the numerator and the denominator are assumed to be mutually independent Cauchy variates. The deterministic equivalent of the problem is obtained and is shown to be a linear fractional program. A numerical example is also added for illustration.