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391.
Previous research on the scheduling of multimachine systems has generally focused on the optimization of individual performance measures. This article considers the sequencing of jobs through a multimachine flow shop, where the quality of the resulting schedule is evaluated according to the associated levels of two scheduling criteria, schedule makespan (Cmax) and maximum job tardiness (Tmax). We present constructive procedures that quantify the trade-off between Cmax and Tmax. The significance of this trade-off is that the optimal solution for any preference function involving only Cmax and Tmax must be contained among the set of efficient schedules that comprise the trade-off curve. For the special case of two-machine flow shops, we present an algorithm that identifies the exact set of efficient schedules. Heruistic procedures for approximating the efficient set are also provided for problems involving many jobs or larger flow shops. Computational results are reported for the procedures which indicate that both the number of efficient schedules and the error incurred by heuristically approximating the efficient set are quite small. 相似文献
392.
With repeated firing, fatigue cracks are produced in a gun barrel, and the barrel is no longer useful when a crack reaches a critical size. The initial crack size and the critical crack size, as well as the number of firings producing the critical crack size, may be considered as random variables. Assuming a proportional damage model for crack growth, a method for estimating the critical crack size distribution is presented. From these results, an estimate of the barrel life, or the residual barrel life once a crack of a given size is measured, can be obtained. 相似文献
393.
The standard problem in sampling inspection is to consider plans with and without curtailment. Curtailment causes difficulty and authors rarely give exact results (i.e., exact OC and ASN functions) for curtailed procedures. In this article we regard curtailment as an inverse sampling procedure and use Dirichlet integrals to obtain exact formulas for the OC, the ASN, and also the variance of the number of observations required under three types of plans: no curtailment, semicurtailment (for rejection only) and two-sided curtailment. Different sections of the article deal with the single sample, the two-stage, and the multiple-stage sampling problems. New tables for carrying out the single-sample procedure are included in the article. The authors feel that this article presents new directions and new ways of dealing with problems associated with quality control. 相似文献
394.
Alan J. Kaplan 《海军后勤学研究》1989,36(5):625-638
This article is concerned with evaluating the impact on weapon system availability of component and assembly redundancy. The evaluation must be efficient, and it must be possible to integrate the evaluation into multiechelon stockage models whose objective is to find the least cost mix of stockage consistent with the availability goals for weapon (or other type) systems. The mathematics to be discussed here provides a rigorous solution to the evaluation problem when there is only a single supply echelon; there can be upper-echelon repair, but not supply, unless the supply is from a “perfect” supplier, always in stock. For the more general multiechelon case, approximate approaches are presented. 相似文献
395.
This article extends the traditional median problem on a grid to include a diagonal line (e.g., a street). In contrast to the traditional median problem, this generalized problem is nonconvex and nonseparable, invalidating some of the properties on which well-known median-seeking algorithms are based. This work presents an algorithm for finding the median on this generalized grid and discusses the relationship between it and the traditional median. 相似文献
396.
Particulate composites are one of the widely used materials in producing numerous state-of-the-art components in biomedical, automobile, aerospace including defence technology. Variety of modelling techniques have been adopted in the past to model mechanical behaviour of particulate composites. Due to their favourable properties, particle-based methods provide a convenient platform to model failure or fracture of these composites. Smooth particle hydrodynamics (SPH) is one of such methods which demonstrate excellent potential for modelling failure or fracture of particulate composites in a Lagrangian setting. One of the major challenges in using SPH method for modelling composite materials depends on accurate and efficient way to treat interface and boundary conditions. In this paper, a master-slave method based multi-freedom constraints is proposed to impose essential boundary conditions and interfacial displacement constraints in modelling mechanical behaviour of composite materials using SPH method. The proposed methodology enforces the above constraints more accurately and requires only smaller condition number for system stiffness matrix than the procedures based on typical penalty function approach. A minimum cut-off value-based error criteria is employed to improve the compu-tational efficiency of the proposed methodology. In addition, the proposed method is further enhanced by adopting a modified numerical interpolation scheme along the boundary to increase the accuracy and computational efficiency. The numerical examples demonstrate that the proposed master-slave approach yields better accuracy in enforcing displacement constraints and requires approximately the same computational time as that of penalty method. 相似文献
397.
Matthew J. Webb 《Defense & Security Analysis》2015,31(1):22-34
A range of theories have sought to explain and predict secession with varying degrees of success. Arguing that a disproportionate focus upon the seceding group as the unit of analysis has frustrated the development of a comprehensive theoretical framework that is universally valid, this article highlights the role of predecessor institutions of governance and the failure of states to successfully incorporate these as an important, but neglected, causal factor in the study of secession. The inclusion of pre-state institutions of governance and processes of state formation not only results in a more complete, and therefore accurate, explanatory account of secession, but also explains why some regions have been more prone to secession than others. 相似文献
398.
Cyberspace has emerged as a potentially new (and unconventional) domain for warfare. Much debate has focused on understanding cyber conflict. The ability to critically analyse this phenomenon is important; however, the nascent nature of cyberwarfare and the complexity of the systems involved create challenges not met by conventional approaches. As a first step, this requires an analytical construct to frame discussions in a way that highlights distinct characteristics of the cyber domain. An approach proposed is one of the postulating conjectures for debate as a way to achieve this and to demonstrate its use, both at the strategic and operational levels. It is suggested that such an approach provides one component of a mature analytical framework for the analysis of cyber across a range of warfare domains. 相似文献
399.
Fodei J. Batty 《Civil Wars》2015,17(3):379-407
The utility of post-conflict elections in sub-Saharan Africa has been the subject of lively academic and policy debates. While some scholars associate several electoral outcomes with votes for peace, others argue that post-conflict elections exacerbate existing cleavages and could reproduce the conditions that led to civil war if the right electoral system is not employed. This paper examines these contesting claims using electoral data in a comparative study of the first truly post-conflict elections in Sierra Leone and Liberia. The analysis shows that political leaders in both countries received votes across numerous cleavage lines in contradiction with an ethnic census. 相似文献
400.
Thomas W. Lucas W. David Kelton Paul J. Sánchez Susan M. Sanchez Ben L. Anderson 《海军后勤学研究》2015,62(4):293-303
Decades ago, simulation was famously characterized as a “method of last resort,” to which analysts should turn only “when all else fails.” In those intervening decades, the technologies supporting simulation—computing hardware, simulation‐modeling paradigms, simulation software, design‐and‐analysis methods—have all advanced dramatically. We offer an updated view that simulation is now a very appealing option for modeling and analysis. When applied properly, simulation can provide fully as much insight, with as much precision as desired, as can exact analytical methods that are based on more restrictive assumptions. The fundamental advantage of simulation is that it can tolerate far less restrictive modeling assumptions, leading to an underlying model that is more reflective of reality and thus more valid, leading to better decisions. Published 2015 Wiley Periodicals, Inc. Naval Research Logistics 62: 293–303, 2015 相似文献