基于Pro/E的转换接头CAD/CAPP系统设计

钻柱转换接头是石油产品中的一类标准件,但在实际工作中,因需要不同而频繁变化且种类繁多。根据转换接头的特点,建立结构数据库,用VB语言编程,以Pro/E和AutoCAD为开发平台,完成了转换接头的CAD/CAPP集成系统软件设计。该软件利用Pro/PROGRAM实现转换接头的参数化设计,能自动生成转换接头的三维实体图、二维工程图、机械加工工艺过程卡和机械加工工序卡。     

“文献检索”课“5E”教学模式与大学生创新能力培养

在“文献检索”课中，通过引入建构主义环境下的教学新模式——“5E”教学模式，培养大学生的创新能力，可有效地提高大学生的信息素质，使他们成为适应信息化和学习型社会所需要的高素质人才。     

Risk and the Media: A Comparison of Print and Televised News Stories of a Canadian Drinking Water Risk Event

This article explores the utility of using media analyses as a method for risk researchers to gain an initial understanding of how the public may perceive a risk issue or event based on how it is presented and communicated in news media stories. In the area of risk research, newspapers consistently provide coverage of both acute and chronic risk events, whereas televised news broadcasts report primarily acute risk events. There is no consensus in the literature about which news format (print vs. televised) may be better to study public conceptualizations of risk, or if one format (e.g., print) may be used as a surrogate measure for another format (e.g., televised). This study compares Canadian national televised and newspaper coverage of the same risk event: the E. coli contamination of a public drinking water supply. Using a content analysis, this study empirically demonstrates the overall similarity in story content coverage in both televised and print coverage, noting that televised coverage promotes primarily emotional story themes while print coverage tends to also include coverage of analysis and process. On this basis, the research draws two conclusions: 1) given its more comprehensive coverage, newspaper broadsheets may provide a better measure of media coverage of a risk event than televised coverage (if only one format can be studied); and 2) when the risk area of interest is chronic, and/or if the scale of analysis is at a community/local level (i.e., when it is unlikely that archived televised coverage is available), then a researcher may find the print media to be a more useful format to study.     

An investigation on the effects of emerging 4G transmissions on 3G networks

Within the last 10 years, technological advances have allowed personal wireless communications to become part of our global, information-centric culture. Cellular telephones, personal digital assistants, and wireless computer networks allow for tetherless use anytime and almost anywhere. These wireless communication advances have quickly matured through three technological generations. Currently, wireless communications are considered to be in the third generation (3G) of deployment and are rapidly approaching the fourth (4G). As these wireless technologies advance to meet market demand, careful pre-market technical analysis of these new capabilities must be made to understand potential impact on existing communication systems. This paper provides a novel examination into the effects of 4G ultrawide band (UWB) signaling on a 3G wireless fidelity (WiFi) system. Through empirical and statistical analyses, we show that the throughput performance of the Wi-Fi system can be negatively impacted by up to 20%. We conclude that careful implementation of emerging 4G UWB systems must occur to mitigate the detriments to existing 3G communication systems.     

Star-shaped distributions and their generalizations

Elliptically contoured distributions can be considered to be the distributions for which the contours of the density functions are proportional ellipsoids. We generalize elliptically contoured densities to “star-shaped distributions” with concentric star-shaped contours and show that many results in the former case continue to hold in the more general case. We develop a general theory in the framework of abstract group invariance so that the results can be applied to other cases as well, especially those involving random matrices.     

职技高师农科专业“三三四”实践教学体系探索与实践

实践教学是职技高师院校教学的重要内容，是培养学生实践技能和创业、创新能力的重要途径，而为中高等职业教育输送具有“双师”素质师资是职技高师肩负的重要职能。论文以河北科技师范学院为例，对构建农科类专业“三三四”实践教学体系的的探索与实践进行了介绍。     

Statistical estimation errors of VaR under ARCH returns

In this paper we discuss some problems of existing methods for calculating the Value-at-Risk (VaR) in ARCH setting. It should be noted that the commonly used approaches often confuse the true innovations with the empirical residuals, i.e., estimation errors for unknown ARCH parameters are ignored. We adjust this by using the asymptotics of the residual empirical process, and propose a feasible VaR which, according to the spirit of VaR, keeps the assets away from a specified risk with high confidence level. Its meaningfulness in comparison with the usual VaR will be illustrated clearly by numerical studies.     

The Economic Efficiency of Sampling Size: The Case of Beef Trim Revisited

A recent paper by Ferrier and Buzby provides a framework for selecting the sample size when testing a lot of beef trim for Escherichia coli O157:H7 that equates the averted costs of recalls and health damages from contaminated meats sold to consumers with the increased costs of testing while allowing for uncertainty about the underlying prevalence of contamination. Ferrier and Buzby conclude that the optimal sample size is larger than the current sample size. However, Ferrier and Buzby's optimization model has a number of errors, and their simulations failed to consider available evidence about the likelihood of the scenarios explored under the model. After correctly modeling microbial prevalence as dependent on portion size and selecting model inputs based on available evidence, the model suggests that the optimal sample size is zero under most plausible scenarios. It does not follow, however, that sampling beef trim for E. coli O157:H7, or food safety sampling more generally, should be abandoned. Sampling is not generally cost effective as a direct consumer safety control measure due to the extremely large sample sizes required to provide a high degree of confidence of detecting very low acceptable defect levels. Food safety verification sampling creates economic incentives for food producing firms to develop, implement, and maintain effective control measures that limit the probability and degree of noncompliance with regulatory limits or private contract specifications.     

我国证券市场新股发行定价方法演变及评述

新股发行定价始终是我国证券市场引人关注的问题之一。本文以新股发行定价方法及发行定价方式为基础,回顾了我国新股发行定价的演进轨迹,并对各阶段定价方法进行了分析评述,得出应结合我国国情对证券市场新股发行定价进行市场化改革的结论。