Heterogeneous dispatching rules in job and flow shops

This paper reports the results of a study of the use of heterogeneous dispatching rules for the scheduling of work in a job shop. The methodology employed included discrete event simulation, using rule combinations determined by prior genetic algorithm searches and generalization using neural networks. Eight dispatching rules were considered, including first in first out (FIFO), earliest due date ( EDD), shortest processing time (SPT), slack/ number of operations (SLK), critical ratio (CR), modified due date (MDD), modified operation due date (MOD), and apparent tardiness cost (ATC). A three-machine job shop was studied, in which three work organizations were employed, pure flow (fixed sequence), pure job shop ( random sequence), and a hybrid shop where flow is random but with unequal probabilities. Three levels of machine loading were used and average tardiness was used as the performance measure. In most cases, modified due date and apparent tardiness cost were the best rules. The application of the best rules effected the results primarily when applied to bottleneck machines or the first machine in a pure flow shop. Nearly any other rule was acceptable on non-botdeneck machines except FIFO and CR, which consistently perform poorly. No major advantage of mixing rules was found.     

Iterated Bootstrap-t Confidence Intervals for Density Functions

Abstract.  Conventional bootstrap- t intervals for density functions based on kernel density estimators exhibit poor coverages due to failure of the bootstrap to estimate the bias correctly. The problem can be resolved by either estimating the bias explicitly or undersmoothing the kernel density estimate to undermine its bias asymptotically. The resulting bias-corrected intervals have an optimal coverage error of order arbitrarily close to second order for a sufficiently smooth density function. We investigated the effects on coverage error of both bias-corrected intervals when the nominal coverage level is calibrated by the iterated bootstrap. In either case, an asymptotic reduction of coverage error is possible provided that the bias terms are handled using an extra round of smoothed bootstrapping. Under appropriate smoothness conditions, the optimal coverage error of the iterated bootstrap- t intervals has order arbitrarily close to third order. Examples of both simulated and real data are reported to illustrate the iterated bootstrap procedures.     

PRIVATE INTEREST SUPPORT FOR EFFICIENCY ENHANCING ANTITRUST POLICIES

Recent discussions of antitrust based on the private interest theory of government conclude that the real, as opposed to the stated, purpose of antitrust legislation is to protect politically influential industries against competition. Yet several prominent antitrust scholars who accept the private interest theory of government in general see antitrust legislation serving the public interest by increasing competition. We argue that the private interest theory of government is consistent with the view that antitrust legislation promotes competition. Indeed antitrust legislation may be supported by organized interest groups because such legislation increases the competition they face.     

Knowledge and Opinions About the Iranian Crisis: A Reconsideration of Three Models

This paper tests Gamson and Modigliani's enlightenment, mainstream,and cognitive consistency models of the linkage between knowledgeand foreign policy opinions. Data from a survey of Lexington,Kentucky residents shortly after the seizure of the Americanembassy in Teheran, Iran in late 1979 indicate that althoughthe mainstream model performs somewhat better than its two competitors,none of the Gamson-Modigliani models adequately explains publicopinion concerning American policy options. Concluding discussioncenters on the possible reasons for the weak showing of themodels.     

ESTIMATING COMMUNITY STANDARDS: THE USE OF SOCIAL SCIENCE EVIDENCE IN AN OBSCENITY PROSECUTION

Elements of the legal test for obscenity of sexually explicitmaterial indicted in a criminal case are examined. A cross-sectionof residents of Mecklenburg County (Charlotte, NC) were randomlyassigned to view either one of the sexually explicit films andthe sexually explicit magazine charged in the criminal case,or a control film. Before and after the viewing, residents judgedthe materials' appeal to a prurient interest (a shameful, morbid,unhealthy interest in sex) and patent offen siveness (communitytolerance for such material). The results indicated that therespondents felt that the films and magazine did not appealto a shameful, morbid, or unhealthy interest in sex, nor didthey perceive these materials as going beyond the level of toleranceregarding depictions of sexual conduct for the average adultin that community. A lower percentage of subjects thought thecommunity tolerated the materials they had just viewed thanwhen they were asked to report on what they personally tolerated.Fewer people felt the films appealed to a shameful, morbid,or unhealthy interest in sex after they had an opportunity tosee them than before viewing. The advantages of providing jurorsin obscenity cases with information about community standardsbased on summations of personal tolerance for materials actuallycharged in these cases, rather than hypothetical judgments aboutthe community and obscenity, is discussed.     

Independent Living Schemes: Organization, Resident Characteristics and Outcomes

Correspondence to David Phillips, Department of Sociological Studies, University of Sheffield, Sheffield S10 2TN. Summary This paper presents the findings of a major follow-up studyof independent living schemes (ILSs) for people with mentalhealth problems and people with learning difficulties. The surveywas undertaken in four local authority areas and covered 171schemes accommodating 481 residents. Information was gatheredon the characteristics of the schemes and their occupants, withparticular reference to the suitability of the ILSs in meetingresidents' needs. It was found that mixed-sex ILSs and ILSsrun by voluntary bodies in cooperation with statutory agencieshad higher than average success rates.