Estimation comparison on busy period for a controllable M/G/1 system with bicriterion policy

We propose an estimator for the expected busy period (denoted by β) of a controllable M/G/1 queueing system in which the server applies a bicriterion 〈p, N〉 policy during his idle period. Using this estimator, we construct new confidence intervals for β, which are based on five bootstrap methods; standard bootstrap (SB), percentile bootstrap (PB), bootstrap pivotal (BP), bias-corrected percentile bootstrap (BCPB), bias-corrected and accelerated bootstrap (BCa). A numerical simulation study is conducted in order to demonstrate performance of the proposed estimator $\hat{\beta }$ and bootstrap confidence intervals for β. From the simulation results, we show that $\hat{\beta }$ is a consistent estimator for β, which agrees with the theoretical results. In addition, we also investigate the accuracy of the five bootstrap confidence intervals by calculating the coverage percentage and the relative coverage (defined as the ratio of coverage percentage to average length of confidence interval). Detailed discussions of simulation results for three queueing models are presented.     

A simple approach for robust economic design of control charts

Robust economic control chart designs incorporating robustness with regard to the uncertainty in the cost and process parameters, reported in the literature, fall into two broad categories. One category of robust economic designs considers the uncertainty in the estimates of the cost and process parameters and makes the design suitable to operate well in any scenario arising out of the uncertainty. Other category of robust economic design considers different possible discrete scenarios for a single process and makes the control chart robust to all possible scenarios. The approach suggested for the robust designs for each category is different and somewhat complicated. The present paper proposes a design approach by introducing a simple statistic for the robust economic design problem of a ‘process with multiple scenarios’. SGA has been used in the optimization. The suggested statistic handles the information regarding the relative frequency of occurrence of each scenario of the process for the robust designs.     

How many servers are best in a dual-priority system?

We ask the question, “for minimizing mean response time (sojourn time), which is preferable: one fast server of speed 1, or k slow servers each of speed 1/k?” Our setting is the com/cache/MiamiImageURL/B6V13-4JHMHKK-1-3C/0?wchp=dGLbVzz-zSkWb" alt="View the MathML source" title="View the MathML source" align="absbottom" border="0" height=13 width="53"/> system with two priority classes of customers, high priority and low priority, where PH is a phase-type distribution. We find that multiple slow servers are often preferable, and we demonstrate exactly how many servers are preferable as a function of the load and service time distribution. In addition, we find that the optimal number of servers with respect to the high priority jobs may be very different from that preferred by low priority jobs, and we characterize these preferences. We also study the optimal number of servers with respect to overall mean response time, averaged over high and low priority jobs. Lastly, we ascertain the effect of the service demand variability of high priority jobs on low priority jobs.     

Multivariate time series modeling and classification via hierarchical VAR mixtures

A novel class of models for multivariate time series is presented. We consider hierarchical mixture-of-expert (HME) models in which the experts, or building blocks of the model, are vector autoregressions (VAR). It is assumed that the VAR-HME model partitions the covariate space, specifically including time as a covariate, into overlapping regions called overlays. In each overlay a given number of VAR experts compete with each other so that the most suitable one for the overlay is favored by a large weight. The weights have a particular parametric form that allows the modeler to include relevant covariates. Estimation of the model parameters is achieved via the EM (expectation-maximization) algorithm. A new algorithm to select the optimal number of overlays, the number of VAR models and the model orders of the VARs that define a particular VAR-HME model configuration, is also developed. The algorithm uses the Bayesian information criterion (BIC) as an optimality criterion. Issues of model checking and inference of latent structure in multiple time series are investigated. The new methodology is illustrated by analyzing a synthetic data set and a 7-channel electroencephalogram data set.     

Characterizations of context-sensitive languages and other language classes in terms of symport/antiport P systems

We give “syntactic’’ characterizations of context-sensitive languages (CSLs) in terms of some restricted models of symport/antiport P systems. These are the first such characterizations of CSLs in terms of P systems. In particular, we show the following for any language L over a binary alphabet:

(1)

Let m   be any integer ≥1$\ge 1$. Then L is a CSL if and only if it can be accepted by a restricted symport/antiport P system with m membranes and multiple number of symbols (objects). Moreover, holding the number of membranes at m, there is an infinite hierarchy in computational power (within the class of binary CSLs) with respect to the number of symbols.     

Computer-Mediated Word-of-Mouth Communication on RateMyProfessors.com: Expectancy Effects on Student Cognitive and Behavioral Learning

The purpose of this study was to experimentally test the influence of expectancies formed through computer-mediated word-of-mouth communication (WOM) on student learning. Increasingly, students rely on computer-mediated WOM through sites such as RateMyProfessors.com to aid in the process of information-gathering and course selection. It was hypothesized that students who received positive computer-mediated WOM about a course would demonstrate greater levels of cognitive and behavioral learning than would students who received no information or negative computer-mediated WOM. Results demonstrated the predicted effects for cognitive and behavioral learning. It was further hypothesized that observed expectancy effects would be mediated by affect toward learning. Results supported a partial mediational role for affect in the context of positive expectancies, but not negative expectancies. Results were discussed in terms of the role of computer-mediated WOM in generating expectations, the expectations-affect-behavior hypothesis, and the influence of student expectations on learning outcomes.     

DirectShow的原理及其应用

本文介绍了微软提供的多媒体开发工具DirectShow的工作原理,并给出了一个基于DirectShow的网络MPEG－1解码器的实例。     

电子商务应用中龙源网上中文书店的解决方案

文章在对目前开发电子商务应用系统可以选用的Ｗｅｂ数据库技术分析的基础上,介绍了电子商务应用系统龙源网上中文书店的解决方案。