A COMPARISON OF SEQUENCING RULES FOR A TWO-STATE HYBRID FLOW SHOP

A common manufacturing environment in many industries (such as the glass, steel, paper, costume jewelry, and textile industries) is a hybrid flow shop. This system has continuous-process machinery in the fist state of manufacturing and repetitive-batch equipment in the second. Little research has investigated this type system. Scheduling managers of hybrid flow shops tend either to use existing job-shop rules or to devise their own rules. These approaches often are less than adequate for efficient scheduling. In this paper we extend the rule presented by Narasimhan and Panwalker [4] to include a general class of hybrid flow shops. This extenstion, called the generalized cumulative minimum-deviation (GCMD) rule, is compared under various operation conditions to three other sequencing rules: shortest processing time, longest processing time, and minimum deviation. The operating conditions are determined by the number of machines at both stages. The results of 7200 simulation runs demonstrate that the GCMD rule is better than the other rules in minimizing each of five chosen criteria. Thus, the GCMD rule can help managers to schedule hybrid flow shops efficiently to achieve various corporate objectives.     

Tactical coordination in a multi-location and multi-stage operations structure: A model and a pharmaceutical company case

In this paper, we look at the internal supply chain of an internationally operating firm characterized by a multi-location and multi-stage operations structure. We address problems at three levels, namely the strategic, tactical, and operational levels. Our approach goes beyond the operational literature, and focuses primarily on the tactical level. We specify a model and a case that capture strategic and tactical issues and relate the tactical issues to organizational issues. We simulate coordination in different organizational forms pertaining to the ‘tactical control’ of the firm. Our analysis suggests that a functionally organized multi-location and multi-stage operations structure using traditional planning will not work. The choice is between a strongly IT-based, centralized organization or a more decentralized organization using transfer prices as the coordination device.     

Fractiles of an extended multiple outlier test

The widely-used Tietjen—Moore multiple outlier statistic has a defect as originally proposed in that it may test the wrong observations as outliers. The defect is corrected by redefinition and the statistic extended to make use of possible additional information on underlying variance. Results of simulation of the revised statistic are presented.     

On the accuracy and cost of numerical integration in several variables ∗

Identical numerical integration experiments are performed on a CYBER 205 and an IBM 3081 in order to gauge the relative performance of several methods of integration. The methods employed are the general methods of Gauss-Legendre, iterated Gauss-Legendre, Newton-Cotes, Romberg and Monte Carlo as well as three methods, due to Owen, Dutt, and Clark respectively, for integrating the normal density. The bi- and trivariate normal densities and four other functions are integrated; the latter four have integrals expressible in closed form and some of them can be parameterized to exhibit singularities or highly periodic behavior. The various Gauss-Legendre methods tend to be most accurate (when applied to the normal density they are even more accurate than the special purpose methods designed for the normal) and while they are not the fastest, they are at least competitive. In scalar mode the CYBER is about 2-6 times faster than the IBM 3081 and the speed advantage of vectorised to scalar mode ranges from 6 to 15. Large scale econometric problems of the probit type should now be routinely soluble.     

Comparison of permutation methods for the partial correlation and partial mantel tests

This study compares empirical type I error and power of different permutation techniques that can be used for partial correlation analysis involving three data vectors and for partial Mantel tests. The partial Mantel test is a form of first-order partial correlation analysis involving three distance matrices which is widely used in such fields as population genetics, ecology, anthropology, psychometry and sociology. The methods compared are the following: (1) permute the objects in one of the vectors (or matrices); (2) permute the residuals of a null model; (3) correlate residualized vector 1 (or matrix A) to residualized vector 2 (or matrix B); permute one of the residualized vectors (or matrices); (4) permute the residuals of a full model. In the partial correlation study, the results were compared to those of the parametric t-test which provides a reference under normality. Simulations were carried out to measure the type I error and power of these permutatio methods, using normal and non-normal data, without and with an outlier. There were 10 000 simulations for each situation (100 000 when n = 5); 999 permutations were produced per test where permutations were used. The recommended testing procedures are the following:(a) In partial correlation analysis, most methods can be used most of the time. The parametric t-test should not be used with highly skewed data. Permutation of the raw data should be avoided only when highly skewed data are combined with outliers in the covariable. Methods implying permutation of residuals, which are known to only have asymptotically exact significance levels, should not be used when highly skewed data are combined with small sample size. (b) In partial Mantel tests, method 2 can always be used, except when highly skewed data are combined with small sample size. (c) With small sample sizes, one should carefully examine the data before partial correlation or partial Mantel analysis. For highly skewed data, permutation of the raw data has correct type I error in the absence of outliers. When highly skewed data are combined with outliers in the covariable vector or matrix, it is still recommended to use the permutation of raw data. (d) Method 3 should never be used.     

Latin hypercube sampling with multidimensional uniformity

Complex models can only be realized a limited number of times due to large computational requirements. Methods exist for generating input parameters for model realizations including Monte Carlo simulation (MCS) and Latin hypercube sampling (LHS). Recent algorithms such as maximinLHS seek to maximize the minimum distance between model inputs in the multivariate space. A novel extension of Latin hypercube sampling (LHSMDU) for multivariate models is developed here that increases the multidimensional uniformity of the input parameters through sequential realization elimination. Correlations are considered in the LHSMDU sampling matrix using a Cholesky decomposition of the correlation matrix. Computer code implementing the proposed algorithm supplements this article. A simulation study comparing MCS, LHS, maximinLHS and LHSMDU demonstrates that increased multidimensional uniformity can significantly improve realization efficiency and that LHSMDU is effective for large multivariate problems.     

CFD技术在《液压与气压传动》课程教学中的应用

通过教学实例说明了CFD技术在《液压与气压传动》课程多媒体教学中的应用。利用CFD软件直观展现流场仿真的先进功能,可以直观地看到封闭流场的流动情况和相关参数,加深了学生对相应知识的理解,提高了学习效果。     

大型工程项目进度—费用联合风险分析

从工程项目风险管理的角度出发,阐述了大型工程项目的风险特征。基于Monte carlo仿真方法,建立了大型工程项目进度-费用联合风险估计仿真模型,并对仿真结果进行统计分析,获得了进度-费用联合风险曲面。由此得到各种进度费用组合下的风险概率分布。最后结合算例说明了进度-费用联合风险的定量估计方法。     

拟真时代:鲍德里亚媒介理论的后现代视角

作为后现代主义理论的中心人物之一,鲍德里亚以"拟像"、"拟真"和"超真实"等概念描述媒介与技术主导下的后现代社会形态。他将媒介阐释为主要的拟真机器,媒介的拟真不仅渗透到大众日常生活,同时也成为当代资本主义新的社会控制模型。在媒介与技术形成的超真实世界中,作为社会主体的大众被压制、消解而沦落为"沉默的大多数",最终导致了"社会的终结"。鲍德里亚的理论对理解后现代主义视野下的媒介批判理论、阐述媒介的意识形态功能提供了有益的启示。