Optimal lot sizing under continuous price decrease

An important characteristic of high-tech industries is decreasing component prices over time. In the personal computer industry, some component prices decline at a rate of 1% per week. This paper develops an inventory model for products experiencing continuous decrease in unit price. We develop an accurate closed-form approximate solution to the model. Our results indicate that declining prices lead to substantial decrease in the optimal cycle time and much frequent ordering. This explains the heavy emphasis on just-in-time inventory management practiced by successful companies in high-tech industries. While previous models attributed the success of just-in-time policies to reduced holding cost and improved quality, under declining prices a substantial source of savings becomes lower costs of raw materials which is significant part of cost in these industries. We illustrate the results of the model with a numerical example and perform sensitivity analysis.     

Revisiting retesting in the estimation of proportions by group testing

In the estimation of a proportion p by group testing (pooled testing), retesting of units within positive groups has received little attention due to the minimal gain in precision compared to testing additional units. If acquisition of additional units is impractical or too expensive, and testing is not destructive, we show that retesting can be a useful option. We propose the retesting of a random grouping of units from positive groups, and compare it with nested halving procedures suggested by others. We develop an estimator of p for our proposed method, and examine its variance properties. Using simulation we compare retesting methods across a range of group testing situations, and show that for most realistic scenarios, our method is more efficient.     

How much is too much: Does the size of income support transfers affect labor supply?

Cash transfer programs pursue mainly protective objectives, but can also impact rural livelihoods by inducing investments in productive activities and changing household labor allocation. We adopt a continuous treatment approach to quantify how households’ labor supply responds to transfer size. We find a shift from paid labor to own farm labor and find that the transfer size is well within a level that would have disincentive effects on time spent on own farm activities. The switch from paid to own farm labor occurs at lower levels of transfers for labor-constrained households, and at higher levels for non-labor constrained households.     

并行工程在管理中的应用

在 2 1世纪 ,企业绝不能象过去那样满足于某一方面的优势 ,而要尽可能全面发展。为此企业必须要寻找一种新的整体优化管理模式。针对产品的开发设计而言 ,则要摒弃原有的开发设计模式———串行方式 ,采用新的方式———并行工程。本文介绍了并行工程的基本概念和它作为一种新的管理思想的内涵 ,并重点阐述了这种管理思想在企业中的应用。     

气管切开术后持续气道湿化预防呼吸道阻塞与肺部感染

目的探讨气管切开术后如何进行气道湿化才能有效预防呼吸道阻塞与肺部感染的发生。方法2005年1月至2008年5月,将200例气管切开术后的患者随机分为实验组和对照组,实验组用输氧雾化面罩进行持续气道湿化,对照组用传统方式在气管切开处覆盖双层生理盐水湿纱布并辅以雾化吸入及气管滴药,比较两种方法的效果。结果实验组发生痰痂形成、气道粘膜出血、呛咳、肺部感染、窒息的比例远低于对照组。结论持续气道湿化更有利于患者痰液的排出,可有效地预防呼吸道阻塞及肺部感染的发生。     

抗战时期国共两党持久抗日战略方针之比较

抗日战争时期 ,共产党的抗日战略方针是“持久战” ,国民党的抗日战略方针并非通常所认为的“速胜论” ,而是“持久战” ,或叫“持久消耗”。两种抗日战略方针虽有某些相同相似之处 ,但也有许多不同。两者相比 ,国民党的抗日战略方针在许多方面都显得逊色 ,从而更显出毛泽东持久战理论的重大贡献     

Confidence Intervals for Gini's Diversity Measure and Shannon's Entropy Using Adjusted Proportions

Abstract

Asymptotic confidence intervals are given for two functions of multinomial outcome probabilities: Gini's diversity measure and Shannon's entropy. “Adjusted” proportions are used in all asymptotic mean and variance formulas, along with a possible logarithmic transformation. Exact confidence coefficients are computed in some cases. Monte Carlo simulation is used in other cases to compare actual coverages to nominal ones. Some recommendations are made.     

A note on new confidence intervals for the difference between two proportions based on an Edgeworth expansion

Zhou and Qin [2004. New intervals for the difference between two independent binomial proportions. J. Statist. Plann. Inference 123, 97–115; 2005. A new confidence interval for the difference between two binomial proportions of paired data. J. Statist. Plann. Inference 128, 527–542] “new confidence intervals” for the difference between two treatment proportions exhibit a severe lack of invariance property that is a compelling reason not to use them.     

Slack-variable models versus Scheffé's mixture models

Slack-variable models are compared against Scheffé's polynomial model for mixture experiments. The notion of model equivalence and the use of various diagnostic measures provide effective tools in making such comparisons, particularly when the experimental region is highly constrained. It is demonstrated that the choice of the best fitting model, through variable selection, depends on which mixture component is selected as a slack variable, and on the size of the fitted model. In addition, the equivalence of two well-known representations of a complete mixture model is shown to be valid. Two numerical examples are presented.