Freezing the master production schedule in multilevel material requirements planning systems under deterministic demand

This paper extends the studies by Sridharan, Berry, and Udayabhanu from single-level MPS systems to multilevel material requirements planning (MRP) systems, and examines the impact of product structure, lot-sizing rules and cost parameters upon the selection of MPS freezing parameters under deterministic demand. A model is built to simulate the master production scheduling and material requirements planning operations in a make-to-order environment. The results show that all the MPS freezing parameters studied have a significant impact upon total inventory costs and schedule instability in multilevel MRP systems. First, the order-based freezing method is preferable to the period-based method. Secondly, the study finds that increasing the freezing proportion reduces both total inventory costs and schedule instability. This finding contradicts the finding by Sridharan et al. in single-level systems. Thirdly, the study finds that a higher replanning periodicity results in both lower total inventory cost and lower schedule instability. The study also indicates that the product structure and lot-sizing rules do not significantly influence the selection of MPS freezing parameters in a practical sense under most situations. However, the cost parameter seems to significantly influence the selection of replanning periodicity.     

21世纪中国当代文学研究在韩国--以相关期刊杂志为例

21世纪，韩国研究者对中国当代文学研究的视野逐渐开阔，所研究的课题也在与时俱进，从单一的研究模式扩大到“多元化”的角度发展，也突破了外国学者的局限。这些研究范围的扩展使“韩国的中国当代文学研究”更能实现“国际化”和“本土化”，同时也推进了中国当代文学在世界文化交流的发展。     

STATE MANAGEMENT OF CAREERS, WORKPLACE CONFLICT, AND REGIME LEGITIMACY IN SOCIALIST CHINA

Recent research indicates that career mobility under Chinese Communist rule has been shaped by state political screening and shifts in official ideology. Drawing on Weber's concept of modern bureaucracy and a study of schoolteachers in the Mao era (1949–1976), this article suggests that within the workplace official control of careers engendered an inferior and heterogeneous corps of management personnel, a deep schism between management and the staff, and a fractured division of labor. The antitheses of the rational features of modern bureaucracy, these arrangements fostered workplace friction and political resentment that precipitated post-Mao reforms. Primary evidence comes from recently declassified government documents and firsthand interviews with retired teachers.     

STRUCTURAL CHANGE, COMPETITIVE BALANCE, AND THE REST OF THE MAJOR LEAGUES

Analyzing North American major sports leagues other than baseball, we find no break points in competitive balance time series corresponding to rule changes, the draft, free agency, salary caps, or labor disputes except for the 1998 basketball lockout. Some expansion and team relocation correspond with break points. Mergers that do correspond with break points all enhance competitive balance. But not all expansions, moves, and mergers correspond with break points. Remaining explanatory challenges include a general negative trend in competitive balance in basketball and the occurrence of a break point in football, 1976–1977. ( JEL C32, L83)     

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.     

FINANCIAL RESTRAINTS AND PRIVATE INVESTMENT: EVIDENCE FROM A NONSTATIONARY PANEL

We employ recently developed panel data methods to estimate a model of private investment under financial restraints for 20 developing countries using annual data for 1972–2000. We show that the qualitative nature of the results varies depending on whether we take into account cross‐country effects. When we allow for cross‐sectional dependence, investment displays more sensitivity to world capital market conditions and exchange rate uncertainty. A perhaps even more surprising result is the finding that countries that managed to suppress domestic real interest rates without generating high inflation enjoyed higher levels of private investment than those that would have been obtained under liberalized conditions. (JEL O16, G18, G28)     

Optimizing lot size and setup time in a JIT environment: a multiple objective application

The just-in-time (JIT) system has been studied extensively and implemented by a number of US firms as an ell'ective production system. The core of JIT involves determination of lot size and setup time reduction so as to increase manufacturing flexibility while minimizing the inventory level. This decision problem usually involves multiple conflicting objectives and mixed-model production. In this paper, goal programming (GP) is applied to a real-world JIT problem involving fabrication of different automotive and industrial rubber composite belts. The model results provide new insights concerning the conflicting nature of several goals, especially between meeting demand and reducing setup or idle time. Also, the GP solution is superior to the current JIT practice of the company.     

ENDOGENOUS TIMING IN CONTESTS WITH DELEGATION

We study two‐player contests in which each player hires a delegate, and the delegates decide endogenously when to expend their effort. First, we look closely at the delegates' decisions on when to expend their effort, given contracts between the players and the delegates, and look at the players' decisions on their contracts. Then, we compare the outcomes of the endogenous‐timing framework with those of the simultaneous‐move framework. We show that the higher‐valuation player offers her delegate greater contingent compensation than her opponent, the delegate of the higher‐valuation player chooses his effort level after observing his counterpart's, the equilibrium expected payoff of the delegate of the higher‐valuation player is greater than that of his counterpart, and economic rent for each delegate exists. We show that, in the endogenous‐timing framework, each player offers her delegate better contingent compensation, each delegate's expected payoff is greater, and each player's expected payoff is smaller, as compared with the simultaneous‐move framework. (JEL D72)