侧向支承作用下简支钢梁整体稳定性研究

本文对简支工形钢梁受压翼缘有两道侧向支承时的整体稳定性能进行了系统研究。首先根据能量法原理,把中梁段单独取出来,推导了3种不同荷载类型作用下钢梁整体稳定临界弯矩;其次介绍了Nethercot和Trahair建议的考虑梁段相互约束效应的计算方法（简称“NT法”）。采用ANSYS有限元分析软件,对总跨度为15 m的简支钢梁,考虑其侧向支承条件、截面形式、荷载类型的变化,共计算了144根钢梁,对其进行了特征值屈曲分析。然后对3种方法计算的整体稳定临界荷载进行了对比分析,通过分析对比评价了两种理论方法的计算精度和实用性。最后根据有限元分析的结果,拟合了满跨均布荷载作用、跨中集中荷载作用、支承处集中荷载作用下钢梁等效弯矩系数的计算公式。     

不锈钢复合管缺陷概率的事故树分析

运用事故树分析研究不锈钢复合管的缺陷概率重要度和危险重要度。结果表明焊缝裂纹不但发生概率比较大,而且影响比较严重,因此降低复合管缺陷发生概率应优先考虑降低焊缝裂纹的产生。提出了影响质量的主要因素及改善质量的优先顺序,也为其他结构的机电产品提供了风险分析的途径。     

Quantile regression with sample selection: Estimating women's return to education in the U.S.

This study uses quantile regression techniques to analyze changes in the returns to education for women. The data used is the March Current Population Survey for the years 1968, 1973, 1979, 1986 and 1990. The first step in estimating the single (linear) index selection equation uses Ichimura's (1993) semiparametric procedure. To correct for an unknown form of a sample selection bias in the quantile regression, the second step incorporates a nonparametric method, using an idea similar to one developed by Heckman (1980) and Newey (1991) for mean regression, and Buchinsky (1998) for quantile regression.  The results show that: (a) the returns to education increased enormously for the younger cohorts, but very little for the older cohorts; (b) in general the returns are higher at the lower quantiles in the beginning of the sample period and higher at the higher quantiles by the end of the sample period; (c) there is a significant sample selection bias for all age groups at almost all quantiles; (d) toward the end of the sample period there is a significant convergence of the returns at the various quantiles, especially for the younger cohorts and age groups; and (e) the semiparametric estimates of the selection equation are considerably different from those obtained for a parametric probit model.     

基于决策树技术的信息化项目文化冲突研究

企业在信息化项目实施的各个环节中普遍存在各种各样的冲突．对冲突进行有效识别，依据冲突类型选择合适的对策．是降低项目风险、实现项目效益的关键。信息化项目的高复杂性、高风险性对项目的冲突管理提出了较高的要求．目前对信息化项目中的冲突管理研究较多集中于管理理念和理论分析层面。结合文化冲突特点的实证研究较少。决策树方法是数据挖掘及数据分析中广泛应用的技术。具有清晰直观、易于解释的优点。本文通过决策树C5．0算法，尝试运用数据挖掘技术进行文化冲突研究。通过对项目中6种冲突管理决策类型的分析，提供了依据冲突情景选择应对策略的分类决策方法。实验证明，该方法可行。本研究为我国企业在信息化项目中遇到的冲突问题。提供了应对方法，同时也扩展了数据挖掘决策树技术的应用领域。     

Tree farms: Driving forces and regional patterns in the global expansion of forest plantations

People have planted trees in rural places with increasing frequency during the past two decades, but the circumstances in which they plant and the social forces inducing them to plant remain unclear. While forests that produce wood for industrial uses comprise an increasing number of the plantations, most of the growth has occurred in Asia where plantations that produce wood for local consumption remain important. Explanations for these trends take economic, political, and human ecological forms. Growth in urban and global markets for forest products, coupled with rural to urban migration, may spur the conversion of fields into tree farms. Government programs also stimulate tree planting. These programs occur frequently in nations with high population densities. Quantitative, cross-national analyses suggest that these forces combine in regionally distinctive ways to promote the expansion of forest plantations. In Africa and Asia plantations have expanded most rapidly in nations with densely populated rural districts, rural to urban migration, and government policies that promote tree planting. In the Americas and Oceania plantations have expanded rapidly in countries with relatively stable rural populations, low densities, and extensive tracts of land in pasture. If, as anticipated, the growing concern with global warming spurs further expansion in forest plantations in an effort to sequester carbon, questions about their social and ecological effects should become more pressing.     

Socio-environmental drivers of forest change in rural Uganda

Tropical deforestation and forest degradation are among the top global threats to biodiversity, carbon storage and rural livelihoods, but the social processes underlying these changes remain difficult to observe across large spatial scales and in data-poor contexts such as tropical Africa. We link longitudinal survey data from agricultural households in rural Uganda to high-resolution satellite data on forest cover change, and use this linked dataset to investigate processes at two scales: tree planting and harvesting at the parcel scale, and deforestation and reforestation at the community scale. This multi-scale analysis reveals that tree planting is more common on parcels with secure tenure, by educated heads and in isolated communities. Deforestation is highest in land-rich, agrarian communities with low population density and high baseline forest cover. These results provide explicit evidence that the social drivers of forest change in Uganda vary across scales, indicating a need for additional multi-scale studies.     

Understanding Japanese tourists’ shopping preferences using the Decision Tree Analysis method

This study was designed to assess the factors affecting Japanese tourists’ shopping preference and intention to revisit Korea. The analytical method applied in this study was Decision Tree Analysis, which is under-utilized in tourism studies. A total of 300 questionnaires were collected on the basis of on-site survey method and used for data analysis. Among interesting findings, three groups including ‘respondents who were satisfied, accompanied, and spent US$50–300 on shopping’, ‘respondents who were satisfied, accompanied, and had a shopping expenditure of US$300–1000’ and ‘respondents who were satisfied, accompanied, and had a shopping expenditure of US$1000–5000,’ showed a high level of intention to return to Korea for the purpose of shopping. In addition, two groups ‘those who were interested in shopping in Korea, preferred a shopping mall as a shopping destination, and had an educational level of below high school’ and ‘those who were interested in shopping in Korea, preferred a shopping mall as a shopping destination, and had an educational level of a college graduate or above’ showed a higher level interest in merchandise than in shopping venue attractiveness.     

我国可转换债券价值影响因素的敏感度分析

本文采用修正的二叉树模型,对影响可转换债券价值的影响因素进行敏感度分析。分析结果表明,基础股价、股价波动率和公司债券利率是可转债价值最重要的影响因素。本文的分析和结论对于将来构建可转债多因素定价模型和从事可转债的套利分析具有较高的参考价值。     

基于多变量的中国货币需求函数实证分析

随着我国经济体制改革的深化,建立货币需求模型的变量因子也在发生变化。然后,根据我国近年来货币实际需求,选取变量因子建立货币需求模型,并进行了实证分析。在实证分析的基础上,提出了提高货币政策有效性的政策建议。     

山东上市公司财务危机预警研究

以1998年ST制度实施后山东省被ST的上市公司为研究对象,配以上市时间相同或相近的省内财务健康公司做控制样本,选取财务指标和非财务指标通过二元Logit回归建立了预测准确率高的模型,体现盈利能力的总资产收益率预测效果最显著。