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Logistics
Terms modified by Logistics Selected AbstractsOnline Testing for Logistics and Operations ManagementDECISION SCIENCES JOURNAL OF INNOVATIVE EDUCATION, Issue 2 2005Dag Naslund First page of article [source] Geography of Production Linkages in the Irish and Scottish Microcomputer Industry: The Role of LogisticsECONOMIC GEOGRAPHY, Issue 3 2005Chris van Egeraat Abstract: The economic crisis of the mid-1970s marked the transition from the traditional Fordist mode of industrial organization to one of time-based competition (TBC). It has been postulated that the rise of TBC will lead to an increase in local and regional production linkages. Part of the argument is that the associated search for logistical efficiency and the adoption of the just-in-time (JIT) principles will lead to closer buyer-supplier proximity. In this article, we test the relevance of this idea in a case study of the microcomputer hardware industry in Ireland and Scotland. Most of the data were collected during multiple interviews with subsidiaries of all global microcomputer assemblers with operations in one of the two countries. The study shows that rather than sourcing locally or regionally, the assemblers import the vast majority of their material inputs from regions outside Ireland and Britain, notably from the Far East, and that the inbound logistics pipelines of most components involve inventories, often hubbed in local warehouses. Such supply systems have been interpreted as pseudo-JIT, suboptimal inbound logistics systems that are organized on traditional Fordist principles. We argue that the logistics systems and the geography of the supply linkages should not be interpreted this way. Inbound inventories were tightly managed, leading to modest target buffer levels and high shipment frequencies. Even under JIT supply, the geographic configuration of production linkages and the details of logistics systems remain highly dependent on a range of contextual conditions and component characteristics. The findings of this study suggest that a strategy of building integrated vertical production clusters around subsidiaries of multinational enterprises is no longer suitable for Ireland and Scotland, at least not in the context of the microcomputer industry. [source] Special issue on the 7th International Conference on Industrial Logistics (ICIL 2005)INTERNATIONAL TRANSACTIONS IN OPERATIONAL RESEARCH, Issue 5 2006Héctor Cancela No abstract is available for this article. [source] Logistics and supply chain strategies in grain exportingAGRIBUSINESS : AN INTERNATIONAL JOURNAL, Issue 4 2004William W. Wilson The grain shipping industry is highly competitive and has become technically advanced during the past decade. These changes, along with the introduction of innovative shipping mechanisms, have made logistics management an important source of opportunity and risk for grain shippers. A stochastic simulation model was developed to evaluate tradeoffs and effects of key variables on logistical costs in the grain supply chain for an individual firm. Average demurrage for the supply chain was $2.14 million ($0.70/mt or 1.8 cent/bu) with the highest demurrage costs for vessels and lowest for railcars. Of the random variables modeled, unexpected changes in export demand had the greatest impact on costs. [EconLit citation: Q130.] © 2004 Wiley Periodicals, Inc. Agribusiness 20: 449,464, 2004. [source] Globalized Freight Transport: Intermodality, E-Commerce, Logistics and Sustainability, edited by Thomas R. Leinbach and Cristina CapineriJOURNAL OF REGIONAL SCIENCE, Issue 2 2009Peter F. Swan No abstract is available for this article. [source] Naval Logistics Conference 2000: "High Yield & Precision Logistics"NAVAL ENGINEERS JOURNAL, Issue 4 2000Article first published online: 18 MAR 200 No abstract is available for this article. [source] An extensible modeling framework for dynamic reassignment and rerouting in cooperative airborne operationsNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 7 2010Chase C. Murray Abstract Unmanned aerial vehicles (UAVs), increasingly vital to the success of military operations, operate in a complex and dynamic environment, sometimes in concert with manned aircraft. We present an extensible modeling framework for the solution to the dynamic resource management (DRM) problem, where airborne resources must be reassigned to time-sensitive tasks in response to changes in battlespace conditions. The DRM problem is characterized by diverse tasks with time windows, heterogeneous resources with fuel- and payload-capacity limitations, and multiple competing objectives. We propose an integer linear programing formulation for this problem, where mathematical feasibility is guaranteed. Although motivated by airborne military operations, the proposed general modeling framework is applicable to a wide array of settings, such as disaster relief operations. Additionally, land- or water-based operations may be modeled within this framework, as well as any combination of manned and unmanned vehicles. © 2010 Wiley Periodicals, Inc. Naval Research Logistics, 2010 [source] The one-warehouse multiretailer problem with an order-up-to level inventory policyNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 7 2010uz Solyal Abstract We consider a two-level system in which a warehouse manages the inventories of multiple retailers. Each retailer employs an order-up-to level inventory policy over T periods and faces an external demand which is dynamic and known. A retailer's inventory should be raised to its maximum limit when replenished. The problem is to jointly decide on replenishment times and quantities of warehouse and retailers so as to minimize the total costs in the system. Unlike the case in the single level lot-sizing problem, we cannot assume that the initial inventory will be zero without loss of generality. We propose a strong mixed integer program formulation for the problem with zero and nonzero initial inventories at the warehouse. The strong formulation for the zero initial inventory case has only T binary variables and represents the convex hull of the feasible region of the problem when there is only one retailer. Computational results with a state-of-the art solver reveal that our formulations are very effective in solving large-size instances to optimality. © 2010 Wiley Periodicals, Inc. Naval Research Logistics, 2010 [source] Analytic solution for the nucleolus of a three-player cooperative game,NAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 7 2010Mingming Leng Abstract The nucleolus solution for cooperative games in characteristic function form is usually computed numerically by solving a sequence of linear programing (LP) problems, or by solving a single, but very large-scale, LP problem. This article proposes an algebraic method to compute the nucleolus solution analytically (i.e., in closed-form) for a three-player cooperative game in characteristic function form. We first consider cooperative games with empty core and derive a formula to compute the nucleolus solution. Next, we examine cooperative games with nonempty core and calculate the nucleolus solution analytically for five possible cases arising from the relationship among the value functions of different coalitions. © 2010 Wiley Periodicals, Inc. Naval Research Logistics, 2010 [source] A nested benders decomposition approach for telecommunication network planningNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 6 2010Joe Naoum-Sawaya Abstract Despite its ability to result in more effective network plans, the telecommunication network planning problem with signal-to-interference ratio constraints gained less attention than the power-based one because of its complexity. In this article, we provide an exact solution method for this class of problems that combines combinatorial Benders decomposition, classical Benders decomposition, and valid cuts in a nested way. Combinatorial Benders decomposition is first applied, leading to a binary master problem and a mixed integer subproblem. The subproblem is then decomposed using classical Benders decomposition. The algorithm is enhanced using valid cuts that are generated at the classical Benders subproblem and are added to the combinatorial Benders master problem. The valid cuts proved efficient in reducing the number of times the combinatorial Benders master problem is solved and in reducing the overall computational time. More than 120 instances of the W-CDMA network planning problem ranging from 20 demand points and 10 base stations to 140 demand points and 30 base stations are solved to optimality. © 2010 Wiley Periodicals, Inc. Naval Research Logistics, 2010 [source] Inventory sharing under decentralized preventive transshipmentsNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 6 2010Ying Rong Abstract We consider preventive transshipments between two stores in a decentralized system with two demand subperiods. Replenishment orders are made before the first subperiod, and the stores may make transshipments to one another between the subperiods. We prove that the transshipment decision has a dominant strategy, called a control-band conserving transfer policy, under which each store chooses a quantity to transship in or out that will keep its second-subperiod starting inventory level within a range called a control band. We prove that the optimal replenishment policy is a threshold policy in which the threshold depends on the capacity level at the other store. Finally, we prove that there does not exist a transfer price that coordinates the decentralized supply chain. Our research also explains many of the differences between preventive and emergency transshipments, including differences in the optimal transfer policies and the existence or nonexistence of transfer prices that coordinate the system. © 2010 Wiley Periodicals, Inc. Naval Research Logistics, 2010 [source] Robustness of efficient server assignment policies to service time distributions in finite-buffered linesNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 6 2010Eser K, zlar Abstract We study the assignment of flexible servers to stations in tandem lines with service times that are not necessarily exponentially distributed. Our goal is to achieve optimal or near-optimal throughput. For systems with infinite buffers, it is already known that the effective assignment of flexible servers is robust to the service time distributions. We provide analytical results for small systems and numerical results for larger systems that support the same conclusion for tandem lines with finite buffers. In the process, we propose server assignment heuristics that perform well for systems with different service time distributions. Our research suggests that policies known to be optimal or near-optimal for Markovian systems are also likely to be effective when used to assign servers to tasks in non-Markovian systems. © 2010 Wiley Periodicals, Inc. Naval Research Logistics, 2010 [source] Path optimization for the resource-constrained searcher,NAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 5 2010Hiroyuki Sato Abstract We formulate and solve a discrete-time path-optimization problem where a single searcher, operating in a discretized three-dimensional airspace, looks for a moving target in a finite set of cells. The searcher is constrained by maximum limits on the consumption of one or more resources such as time, fuel, and risk along any path. We develop a specialized branch-and-bound algorithm for this problem that uses several network reduction procedures as well as a new bounding technique based on Lagrangian relaxation and network expansion. The resulting algorithm outperforms a state-of-the-art algorithm for solving time-constrained problems and also is the first algorithm to solve multi-constrained problems. © 2010 Wiley Periodicals, Inc. Naval Research Logistics, 2010 [source] Competing with channel partners: Supply chain conflict when retailers introduce store brandsNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 5 2010Hans Sebastian Heese Abstract Private-label products are of increasing importance in many retail categories. While national-brand products are designed by the manufacturer and sold by the retailer, the positioning of store-brand products is under the complete control of the retailer. We consider a scenario where products differ on a performance quality dimension and we analyze how retailer,manufacturer interactions in product positioning are affected by the introduction of a private-label product. Specifically, we consider a national-brand manufacturer who determines the quality of its product as well the product's wholesale price charged to the retailer. Given the national-brand quality and wholesale price, the retailer then decides the quality level of its store brand and sets the retail prices for both products. We find that a manufacturer can derive substantial benefits from considering a retailer's store-brand introduction when determining the national brand's quality and wholesale price. If the retailer has a significant cost disadvantage in producing high-quality products, the manufacturer does not need to adjust the quality of the national-brand product, but he should offer a wholesale price discount to ensure its distribution through the retailer. If the retailer is competitive in providing products of high-quality, the manufacturer should reduce this wholesale price discount and increase the national-brand quality to mitigate competition. Interestingly, we find the retailer has incentive to announce a store-brand introduction to induce the manufacturer's consideration of these plans in determining the national-brand product quality and wholesale price. © 2010 Wiley Periodicals, Inc. Naval Research Logistics, 2010 [source] The effects of model parameter deviations on the variance of a linearly filtered time seriesNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 5 2010Daniel W. Apley Abstract We consider a general linear filtering operation on an autoregressive moving average (ARMA) time series. The variance of the filter output, which is an important quantity in many applications, is not known with certainty because it depends on the true ARMA parameters. We derive an expression for the sensitivity (i.e., the partial derivative) of the output variance with respect to deviations in the model parameters. The results provide insight into the robustness of many common statistical methods that are based on linear filtering and also yield approximate confidence intervals for the output variance. We discuss applications to time series forecasting, statistical process control, and automatic feedback control of industrial processes. © 2010 Wiley Periodicals, Inc. Naval Research Logistics, 2010 [source] The transshipment fund mechanism: Coordinating the decentralized multilocation transshipment problemNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 4 2010Eran Hanany Abstract The multilocation replenishment and transshipment problem is concerned with several retailers facing random demand for the same item at distinct markets, that may use transshipments to eliminate excess inventory/shortages after demand realization. When the system is decentralized so that each retailer operates to maximize their own profit, there are incentive problems that prevent coordination. These problems arise even with two retailers who may pay each other for transshipped units. We propose a new mechanism based on a transshipment fund, which is the first to coordinate the system, in a fully noncooperative setting, for all instances of two retailers as well as all instances of any number of retailers. Moreover, our mechanism strongly coordinates the system, i.e., achieves coordination as the unique equilibrium. The computation and information requirements of this mechanism are realistic and relatively modest. We also present necessary and sufficient conditions for coordination and prove they are always satisfied with our mechanism. Numerical examples illustrate some of the properties underlying this mechanism for two retailers. © 2010 Wiley Periodicals, Inc. Naval Research Logistics, 2010 [source] Modeling and analysis of multiobjective lot splitting for N -product M -machine flowshop linesNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 4 2010Yossi Bukchin Abstract Lot splitting is a new approach for improving productivity by dividing production lots into sublots. This approach enables accelerating production flow, reducing lead-time and increasing the utilization of organization resources. Most of the lot splitting models in the literature have addressed a single objective problem, usually the makespan or flowtime objectives. Simultaneous minimization of these two objectives has rarely been addressed in the literature despite of its high relevancy to most industrial environments. This work aims at solving a multiobjective lot splitting problem for multiple products in a flowshop environment. Tight mixed-integer linear programming (MILP) formulations for minimizing the makespan and flowtime are presented. Then, the MinMax solution, which takes both objectives into consideration, is defined and suggested as an alternative objective. By solving the MILP model, it was found that minimizing one objective results in an average loss of about 15% in the other objective. The MinMax solution, on the other hand, results in an average loss of 4.6% from the furthest objective and 2.5% from the closest objective. © 2010 Wiley Periodicals, Inc. Naval Research Logistics, 2010 [source] Optimal job splitting on a multi-slot machine with applications in the printing industryNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 3 2010Ali Ekici Abstract In this article, we define a scheduling/packing problem called the Job Splitting Problem, motivated by the practices in the printing industry. There are n types of items to be produced on an m -slot machine. A particular assignment of the types to the slots is called a "run" configuration and requires a setup cost. Once a run begins, the production continues according to that configuration and the "length" of the run represents the quantity produced in each slot during that run. For each unit of production in excess of demand, there is a waste cost. Our goal is to construct a production plan, i.e., a set of runs, such that the total setup and waste cost is minimized. We show that the problem is strongly NP-hard and propose two integer programming formulations, several preprocessing steps, and two heuristics. We also provide a worst-case bound for one of the heuristics. Extensive tests on real-world and randomly generated instances show that the heuristics are both fast and effective, finding near-optimal solutions. © 2010 Wiley Periodicals, Inc. Naval Research Logistics, 2010 [source] Optimal control of a production-inventory system with both backorders and lost salesNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 3 2010Saif Benjaafar Abstract We consider the optimal control of a production inventory-system with a single product and two customer classes where items are produced one unit at a time. Upon arrival, customer orders can be fulfilled from existing inventory, if there is any, backordered, or rejected. The two classes are differentiated by their backorder and lost sales costs. At each decision epoch, we must determine whether or not to produce an item and if so, whether to use this item to increase inventory or to reduce backlog. At each decision epoch, we must also determine whether or not to satisfy demand from a particular class (should one arise), backorder it, or reject it. In doing so, we must balance inventory holding costs against the costs of backordering and lost sales. We formulate the problem as a Markov decision process and use it to characterize the structure of the optimal policy. We show that the optimal policy can be described by three state-dependent thresholds: a production base-stock level and two order-admission levels, one for each class. The production base-stock level determines when production takes place and how to allocate items that are produced. This base-stock level also determines when orders from the class with the lower shortage costs (Class 2) are backordered and not fulfilled from inventory. The order-admission levels determine when orders should be rejected. We show that the threshold levels are monotonic (either nonincreasing or nondecreasing) in the backorder level of Class 2. We also characterize analytically the sensitivity of these thresholds to the various cost parameters. Using numerical results, we compare the performance of the optimal policy against several heuristics and show that those that do not allow for the possibility of both backordering and rejecting orders can perform poorly.© 2010 Wiley Periodicals, Inc. Naval Research Logistics 2010 [source] Optimal operating policies in a commodity trading market with the manufacturer's presenceNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 2 2010Hui Zhao Abstract With the help of the Internet and express delivery at relatively low costs, trading markets have become increasingly popular as a venue to sell excess inventory and a source to obtain products at lower prices. In this article, we study the operational decisions in the presence of a trading market in a periodic-review, finite-horizon setting. Prices in the trading market change periodically and are determined endogenously by the demand and supply in the market. We characterize the retailers'optimal ordering and trading policies when the original manufacturer and the trading market co-exist and retailers face fees to participate in the trading market. Comparing with the case with no trading fees, we obtain insights into the impact of trading fees and the fee structure on the retailers and the manufacturer. Further, we find that by continually staying in the market, the manufacturer may use her pricing strategies to counter-balance the negative impact of the trading market on her profit. Finally, we extend the model to the case when retailers dynamically update their demand distribution based on demand observations in previous periods. A numerical study provides additional insights into the impact of demand updating in a trading market with the manufacturer's competition. © 2009 Wiley Periodicals, Inc. Naval Research Logistics, 2010 [source] A bivariate optimal replacement policy for a cold standby repairable system with repair priorityNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 2 2010Kit Nam Francis Leung Abstract In this article, an optimal replacement policy for a cold standby repairable system consisting of two dissimilar components with repair priority is studied. Assume that both Components 1 and 2, after repair, are not as good as new, and the main component (Component 1) has repair priority. Both the sequence of working times and that of the components'repair times are generated by geometric processes. We consider a bivariate replacement policy (T,N) in which the system is replaced when either cumulative working time of Component 1 reaches T, or the number of failures of Component 1 reaches N, whichever occurs first. The problem is to determine the optimal replacement policy (T,N)* such that the long run average loss per unit time (or simply the average loss rate) of the system is minimized. An explicit expression of this rate is derived, and then optimal policy (T,N)* can be numerically determined through a two-dimensional-search procedure. A numerical example is given to illustrate the model's applicability and procedure, and to illustrate some properties of the optimal solution. We also show that if replacements are made solely on the basis of the number of failures N, or solely on the basis of the cumulative working time T, the former class of policies performs better than the latter, albeit only under some mild conditions. © 2010 Wiley Periodicals, Inc. Naval Research Logistics, 2010 [source] Scheduling with variable time slot costsNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 2 2010Guohua Wan Abstract In this article, we study a class of new scheduling models where time slot costs have to be taken into consideration. In such models, processing a job will incur certain cost which is determined by the time slots occupied by the job in a schedule. The models apply when operational costs vary over time. The objective of the scheduling models is to minimize the total time slot costs plus a traditional scheduling performance measure. We consider the following performance measures: total completion time, maximum lateness/tardiness, total weighted number of tardy jobs, and total tardiness. We prove the intractability of the models under general parameters and provide polynomial-time algorithms for special cases with non-increasing time slot costs.© 2010 Wiley Periodicals, Inc. Naval Research Logistics, 2010 [source] Neighborhood search heuristics for selecting hierarchically well-formulated subsets in polynomial regressionNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 1 2010Michael J. Brusco Abstract The importance of subset selection in multiple regression has been recognized for more than 40 years and, not surprisingly, a variety of exact and heuristic procedures have been proposed for choosing subsets of variables. In the case of polynomial regression, the subset selection problem is complicated by two issues: (1) the substantial growth in the number of candidate predictors, and (2) the desire to obtain hierarchically well-formulated subsets that facilitate proper interpretation of the regression parameter estimates. The first of these issues creates the need for heuristic methods that can provide solutions in reasonable computation time; whereas the second requires innovative neighborhood search approaches that accommodate the hierarchical constraints. We developed tabu search and variable neighborhood search heuristics for subset selection in polynomial regression. These heuristics are applied to a classic data set from the literature and, subsequently, evaluated in a simulation study using synthetic data sets. © 2009 Wiley Periodicals, Inc. Naval Research Logistics, 2010 [source] A hybrid method for simulation factor screeningNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 1 2010Hua Shen Abstract Factor screening is performed to eliminate unimportant factors so that the remaining important factors can be more thoroughly studied in later experiments. Controlled sequential bifurcation (CSB) and controlled sequential factorial design (CSFD) are two new screening methods for discrete-event simulations. Both methods use hypothesis testing procedures to control the Type I Error and power of the screening results. The scenarios for which each method is most efficient are complementary. This study proposes a two-stage hybrid approach that combines CSFD and an improved CSB called CSB-X. In Phase 1, a prescreening procedure will estimate each effect and determine whether CSB-X or CSFD will be used for further screening. In Phase 2, CSB-X and CSFD are performed separately based on the assignment of Phase 1. The new method usually has the same error control as CSB-X and CSFD. The efficiency, on the other hand, is usually much better than either component method. © 2009 Wiley Periodicals, Inc. Naval Research Logistics, 2010 [source] New product introduction against a predator: A bilevel mixed-integer programming approachNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 8 2009J. Cole Smith Abstract We consider a scenario with two firms determining which products to develop and introduce to the market. In this problem, there exists a finite set of potential products and market segments. Each market segment has a preference list of products and will buy its most preferred product among those available. The firms play a Stackelberg game in which the leader firm first introduces a set of products, and the follower responds with its own set of products. The leader's goal is to maximize its profit subject to a product introduction budget, assuming that the follower will attempt to minimize the leader's profit using a budget of its own. We formulate this problem as a multistage integer program amenable to decomposition techniques. Using this formulation, we develop three variations of an exact mathematical programming method for solving the multistage problem, along with a family of heuristic procedures for estimating the follower solution. The efficacy of our approaches is demonstrated on randomly generated test instances. This article contributes to the operations research literature a multistage algorithm that directly addresses difficulties posed by degeneracy, and contributes to the product variety literature an exact optimization algorithm for a novel competitive product introduction problem. © 2009 Wiley Periodicals, Inc. Naval Research Logistics, 2009 [source] A two-echelon inventory-location problem with service considerationsNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 8 2009Ho-Yin Mak Abstract We study the problem of designing a two-echelon spare parts inventory system consisting of a central plant and a number of service centers each serving a set of customers with stochastic demand. Processing and storage capacities at both levels of facilities are limited. The manufacturing process is modeled as a queuing system at the plant. The goal is to optimize the base-stock levels at both echelons, the location of service centers, and the allocation of customers to centers simultaneously, subject to service constraints. A mixed integer nonlinear programming model (MINLP) is formulated to minimize the total expected cost of the system. The problem is NP-hard and a Lagrangian heuristic is proposed. We present computational results and discuss the trade-off between cost and service. © 2009 Wiley Periodicals, Inc. Naval Research Logistics 2009 [source] Free riding in a multi-channel supply chainNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 8 2009Fernando Bernstein Abstract Free riding in a multichannel supply chain occurs when one retail channel engages in the customer service activities necessary to sell a product, while another channel benefits from those activities by making the final sale. Although free riding is, in general, considered to have a negative impact on supply chain performance, certain recent industry practices suggest an opposite view: a manufacturer may purposely induce free riding by setting up a high-cost, customer service-oriented direct store to allow consumers to experience the product, anticipating their purchase at a retail store. This article examines how the free riding phenomenon affects a manufacturer's supply chain structure decision when there are fixed plus incremental variable costs for operating the direct store. We consider factors such as the effort required to find and buy the product at a retail store after visiting the direct store, the existence of competing products in the market, and the extent of consumer need to obtain direct-store service. © 2009 Wiley Periodicals, Inc. Naval Research Logistics, 2009 [source] Information security: Designing a stochastic-network for throughput and reliability,,NAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 7 2009Jeffrey Schavland Abstract Todas information and communication network requires a design that is secure to tampering. Traditional performance measures of reliability and throughput must be supplemented with measures of security. Recognition of an adversary who can inflict damage leads toward a game-theoretic model. Through such a formulation, guidelines for network designs and improvements are derived. We opt for a design that is most robust to withstand both natural degradation and adversarial attacks. Extensive computational experience with such a model suggests that a Nash-equilibrium design exists that can withstand the worst possible damage. Most important, the equilibrium is value-free in that it is stable irrespective of the unit costs associated with reliability vs. capacity improvement and how one wishes to trade between throughput and reliability. This finding helps to pinpoint the most critical components in network design. From a policy standpoint, the model also allows the monetary value of information-security to be imputed. © 2009 Wiley Periodicals, Inc. Naval Research Logistics, 2009 [source] Approximation algorithms for general one-warehouse multi-retailer systemsNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 7 2009Zuo-Jun Max Shen Abstract Logistical planning problems are complicated in practice because planners have to deal with the challenges of demand planning and supply replenishment, while taking into account the issues of (i) inventory perishability and storage charges, (ii) management of backlog and/or lost sales, and (iii) cost saving opportunities due to economies of scale in order replenishment and transportation. It is therefore not surprising that many logistical planning problems are computationally difficult, and finding a good solution to these problems necessitates the development of many ad hoc algorithmic procedures to address various features of the planning problems. In this article, we identify simple conditions and structural properties associated with these logistical planning problems in which the warehouse is managed as a cross-docking facility. Despite the nonlinear cost structures in the problems, we show that a solution that is within ,-optimality can be obtained by solving a related piece-wise linear concave cost multi-commodity network flow problem. An immediate consequence of this result is that certain classes of logistical planning problems can be approximated by a factor of (1 + ,) in polynomial time. This significantly improves upon the results found in literature for these classes of problems. We also show that the piece-wise linear concave cost network flow problem can be approximated to within a logarithmic factor via a large scale linear programming relaxation. We use polymatroidal constraints to capture the piece-wise concavity feature of the cost functions. This gives rise to a unified and generic LP-based approach for a large class of complicated logistical planning problems. © 2009 Wiley Periodicals, Inc. Naval Research Logistics, 2009 [source] On the exponentially weighted moving varianceNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 7 2009Longcheen Huwang Abstract MacGregor and Harris (J Quality Technol 25 (1993) 106,118) proposed the exponentially weighted mean squared deviation (EWMS) and the exponentially weighted moving variance (EWMV) charts as ways of monitoring process variability. These two charts are particularly useful for individual observations where no estimate of variability is available from replicates. However, the control charts derived by using the approximate distributions of the EWMS and EWMV statistics are difficult to interpret in terms of the average run length (ARL). Furthermore, both control charting schemes are biased procedures. In this article, we propose two new control charts by applying a normal approximation to the distributions of the logarithms of the weighted sum of chi squared random variables, which are respectively functions of the EWMS and EWMV statistics. These new control charts are easy to interpret in terms of the ARL. On the basis of the simulation studies, we demonstrate that the proposed charts are superior to the EWMS and EWMV charts and they both are nearly unbiased for the commonly used smoothing constants. We also compare the performance of the proposed charts with that of the change point (CP) CUSUM chart of Acosta-Mejia (1995). The design of the proposed control charts is discussed. An example is also given to illustrate the applicability of the proposed control charts. © 2009 Wiley Periodicals, Inc. Naval Research Logistics, 2009 [source] | |||||||||||||||||||