Inventory control with general demand and lead time distributions

This paper extends an earlier paper in this journal by Murphy (1975) by presenting practical approaches for determining the expected lost sales for a reorder level system of inventory control. First, a set of formulas are derived for computing the first four moments (f.f.m.) of the lead time demand, these formulas are applicable to any distribution forms of daily demand and lead time. By fitting the lead time demand's f.f.m. to either a beta or a Schmeiser-Deutsch distribution, this paper then demonstrates how the expected lost sales can be easily computed. The approaches presented provide accurate modelling for diversified situations and the computations can be easily performed manually.     

Transient current spectroscopy and frequency dispersion studies of low temperature GaAs and Al0.3Ga0.7As metal-insulator-semiconductor diodes

Low temperature (LT)-grown GaAs and Al_0.3Ga_0.7As metal-insulator-n⁺-GaAs (MIN) diodes have been fabricated and their electrical properties analyzed. Studies were carried out to evaluate the interfacial quality of the LT layer and the underlying n⁺-GaAs layer using transient current spectroscopy (TCS) and capacitance-frequency (C-f) characterization. TCS studies on LT-GaAs revealed a high concentration of a continuum of states anda dominant electron trap with an activation energy of 0.52eV. In LT-Al_0.3Ga_0.7As, a shallow trap at 0.36eV and two deep level traps at 0.85eV and 1.12eV were observed. Frequency dispersion was observed to be less for LT-GaAs samples with an AlAs barrier layer than without an AlAs barrier layer. However, LT-Al_0.3Ga_0.7As MIN diodes displayed a smaller frequency dispersion than LT-GaAs MIN diodes. Upon further investigation into MISFET devices, it was found that LT-Al_0.3Ga_0.7As MISFET devices had better transconductance frequency dispersion characteristics than LT-GaAs MISFET devices did.     

A low magnetic field gyrotron—gyro-magnetron

A gyrotron device operating at a substantially reduced magnetic field is proposed. The operating beam voltage is moderately low and the waveguide circuit resembles the anode block of a conventional magnetron. The dispersion relationship is given. A proof of principle experiment is suggested.     

一种基于电流阶梯波的相变存储器擦驱动电路

基于相变存储器的擦操作(SET)特性,设计了一种能够产生电流阶梯波的相变存储器擦驱动电路,采用130 nm标准CMOS工艺将其与128 kb的相变存储器实验芯片集成.相比传统的单一电流脉冲擦驱动电路,这种改进后的擦驱动电路能将相变存储单元的电阻均值从15 kΩ左右降至7 kΩ左右,并且存储阵列的阻值分布一致性也得到提升...     

卫星遥感气溶胶光学厚度在北京2008年地面空气质量监测上的应用

利用卫星遥感地面空气质量是近年来随着空间遥感手段的进步而发展起来的一项新技术,如何利用卫星遥感的大气气溶胶光学厚度产品来定量评估地面空气质量是个难题.利用高分辨率的大气气溶胶光学厚度产品,经过垂直分布的订正和湿度影响的订正,分别得到地面气溶胶消光系数和地面"干"气溶胶消光系数.通过与地面PM10质量浓度的相关分析表明,地面气溶胶消光系数具有比大气气溶胶光学厚度更高的相关系数,而经过湿度订正的"干"气溶胶消光系数具有比前两者更高的相关系数.利用华北地区"干"气溶胶消光系数的分布评估了2008年夏季气溶胶变化情况,与往年同期相比,地面气溶胶消光季节平均下降约17%～20%,而华北平原其他城市和地区则没有显著变化,说明北京地区气溶胶浓度的下降与局地减排有直接关系.     

建筑透视图以外的设计管理

境外建筑师事务所如何适应当前国内的建筑潮流并在其中有所作为？除了在方案竞赛中能展现具有“视觉震撼性”的透视效果图外,还要具备一套行之有效的设计管理系统。主要包括三方面内容：1.团队精神,2.各专业之间的协调,3.阶段性设计质量的保证。文章将就这三个内容展开讨论。     

The effects of skewness and kurtosis of processing times in unpaced lines

Numerous empirical studies have shown that, in unpaced lines, the stations' processing times have a variety of shapes (i.e., skewness and kurtosis))65. Thispaper investigates how the line's utilization factor is affected by these skewness and kurtosis measures. We found that positive skewness has a significant negative effect on utilization, and that the magnitude of this effect is greater if the line has more stations or less buffer capacity, or if the processing-times' cv is larger. Kurtosis also affects utilization significantly, but the effect may be negative or positive, depending upon the processing-times' skewness and the number of stations in the line. Our findings imply that when simulating long lines with small buffer capacities, it may be necessary to model more accurately the actual processing times. Also, the common practice of using normal distributions to approximate the typically positively-skewed processing times often leads to an overestimation of the actual utilization rate.     

甲氰菊酯的合成

:由异丙基氯通过格氏反应、硫酸催化脱水制备了四甲基丁烯 ,进而与二氯乙酰氯反应合成了氯代四甲基环丁酮 ;它可以水解生成四甲基环丙烷羧酸。由四甲基环丙烷羧酸或氯代四甲基环丁酮合成了甲氰菊酯。     

Spectrophotometric method for the determination of ethanol in beverages and beer samples using cerium (IV) as reagent

A simple and rapid (15min) spectrophotometric method for the determination of subpercentage ethanol in beverages is based on the colour reaction between ethanol and Ce(IV). Other alcohols and reducing substances interfere, but may be minimized by distilling the alkali and mercuric chloride treated sample. Calibration was linear up to 0.78% v/v, with r.s.d. of 5.0% at the ethanol level of 0.34% v/v. the ethanol contents of a number of non-alcoholic beverages and beer samples were determined and compared with results from AOAC and gas chromatographic methods.     

Solving non-linear equations by simulation

A method of finding an approximate solution to a system of non-linear equations by Monte Carlo simulation is described. The procedure is conceptually simple and easy for computer programming. The shortcomings of the method are discussed.