Optimization of Simulated Inventory Systems: OptQuest and Alternatives

This article illustrates simulation optimization through an (s, S) inventory management system.In this system, the goal function to be minimized is the expected value of specific inventory costs.Moreover, specific constraints must be satisfied for some random simulation responses, namely the service or fill rate, and for some deterministic simulation inputs, namely the constraint sOptQuest software;Response Surface Methodology;Karesh-Kuhn-Tucker conditions;service constrained inventory system

Methodology for Determining the Acceptability of Given Designs in Uncertain Environments

Managers wish to verify that a particular engineering design meets their require- ments. This design's future environment will differ from the environment assumed during the design. Therefore it is crucial to determine which variations in the envi- ronment may make this design unacceptable. The proposed methodology estimates which uncertain environmental parameters are important (so managers can become pro-active) and which parameter combinations (scenarios) make the design unac- ceptable. The methodology combines simulation, bootstrapping, and metamodeling. The methodology is illustrated through a simulated manufacturing system, includ- ing fourteen uncertain parameters of the input distributions for the various arrival and service times. These parameters are investigated through sixteen scenarios, selected through a two-level fractional-factorial design. The resulting simulation In- put/Output (I/O) data are analyzed through a first-order polynomial metamodel and bootstrapping. A second experiment gives some outputs that are indeed un- acceptable. Polynomials fitted to the I/O data estimate the border line (frontier) between acceptable and unacceptable environments.Uncertainty modeling;Risk analysis;Robustness and sensitivity analysis;Simulation;Bootstrap

Sampling for quality inspection and correction: AOQL performance criteria

Probability

Techniques for sensitivity analysis of simulation models: A case study of the CO2 greenhouse effect

Environment;Simulation;environmental economics

The UK NHS Economic Evaluation Database : Economic issues in evaluations of health technology

Objective: The U.K. NHS Economic Evaluation Database (EED) project is commissioned to identify papers on economic evaluations of health technologies and to disseminate their findings to NHS decision makers by means of structured abstracts that are available through a public database and the Cochrane Library. This paper discusses current issues relating to the economic aspects of producing NHS EED abstracts. Methods: A review of NHS EED was undertaken between 1994 and 1999 to determine the methodologies adopted and issues that influence the usefulness of economic evaluations. Methods adopted to improve the quality of NHS EED abstracts are also reported. Results: Eighty-five percent of NHS EED abstracts are cost-effectiveness analyses (CEAs), 9.3% are cost-utility analyses (CUAs), and only 1.4% are cost-benefit analyses (CBAs). Of the total abstracts, 65.9% are based on single studies, 19.5% on reviews, 3.9% on estimates of effectiveness, and 10.7% on combinations of these sources. Models are utilized in 16.7% of CEAs, 60.2% of CUAs, and 20% of CBAs. Analyses of CBA studies reveal a degree of misuse of well-established definitions. NHS EED internal control mechanisms are reported that provide a means of ensuring that abstracts are based on sound academic principles. Conclusions: Most economic evaluations are conducted by means of CEA, followed by CUA, while CBA accounts for an extreme minority of cases. Single studies form the principal source of effectiveness data, although models are widely used, principally in CUA. The structure of NHS EED abstracts provides decision makers with the principal results and an interpretation of the relative strengths and weaknesses of economic evaluations

Pseudogaps in Underdoped Cuprates

It has become clear in the past several years that the cuprates show many unusual properties, both in the normal and superconducting states, especially in the underdoped region. In particular, gap-like behavior is observed in magnetic properties, c-axis conductivity and photoemission, whereas in-plane transport properties are only slightly affected by the pseudogap. I shall argue that these experimental evidences must be viewed in the context of the physics of a doped Mott insulator and that they support the notion of spin charge separation. I shall review recent theoretical developments, concentrating on studies based on the t-J model. I shall describe a model based on quasiparticle excitations, which predicts the doping dependence of T_c and anomalous energy-gap-to-T_c ratios. Finally, I shall outline how the model may be derived from a microscopic formulation of the t-J model. After a brief review of the U(1) formulation, I shall explain some of the difficulties encountered there, and how a new SU(2) formulation can resolve some of the difficulties.Comment: 9 pages, 4 figure

Sampling for quality inspection and correction: AOQL performance criteria (Version 3)

Sampling;mathematische statistiek

Optimization of Simulated Inventory Systems:OptQuest and Alternatives

This article illustrates simulation optimization through an (s, S) inventory management system.In this system, the goal function to be minimized is the expected value of specific inventory costs.Moreover, specific constraints must be satisfied for some random simulation responses, namely the service or fill rate, and for some deterministic simulation inputs, namely the constraint s < S. Results are reported for three optimization methods, including the popular OptQuest method.The optimality of the resulting solutions is tested through the so-called Karesh-Kuhn-Tucker (KKT) conditions.

Regression sampling in statistical auditing

Auditing;Regression Analysis;accountancy