Biologie und Biochemie des Elements Selen

The importance of selenium as an essential trace element has progressively emerged during the last years due to the analysis of selenium deficiency diseases and to the identification and characterization of a number of selenoenzymes. Selenium is incorporated in the catalytic site of the enzymes as an integral selenocysteine residue. The pathway of selenocysteine biosynthesis and incorporation has been elucidated recently for Escherichia coli. This article presents an overview on these subjects and describes the mechanisms which confer selenocysteine specificity in the framework of protein biosynthesis. In addition, some considerations concerning the phylogeny of selenocysteine incorporation are presented and a model for the evolution of the selenocysteine pathway is proposed.     

A polyiodide with regular I 4 2− chains: Tl6PbI10

The Science of Nature -     

西部干旱半干旱地区水资源再生利用分析

结合西部干旱半干旱地区的地域特点、水文特征和水资源开发利用状况，分析论述了该地区水资源短缺与水污染加剧这一矛盾所决定的西部地区水资源开发利用的特点及其对地区经济发展的制约，认为水资源的再生利用是解决西部地区水资源危机的一条有效途径。以城市污水为再生水源，根据该区域特点，提出了西部干旱半干旱地区水资源再生利用的研究内容。     

Land use as a mitigation strategy for the water-quality impacts of global warming: a scenario analysis on two watersheds in the Ohio River Basin

This study uses an integrative approach to study the water-quality impacts of future global climate and land-use changes. In this study, changing land-use types was used as a mitigation strategy to reduce the adverse impacts of global climate change on water resources. The climate scenarios were based on projections made by the Intergovernmental Panel on Climate Change (IPCC) and the United Kingdom Hadley Centre's climate model (HadCM2). The Thornthwaite water-balance model was coupled with a land-use model (L-THIA) to investigate the hydrologic effects of future climate and land-use changes in the Ohio River Basin. The land-use model is based on the Soil Conservation Service's curve-number method. It uses the curve number, an index of land use and soil type, to calculate runoff volume and depth. The ArcView programming language, Avenue, was used to integrate the two models into a geographic information system (GIS). An output of the water-balance model, daily precipitation values adjusted for potential evapotranspiration, served as one of the inputs into the land-use model. Two watersheds were used in the present study: one containing the city of Cincinnati on the main stem of the Ohio River, and one containing the city of Columbus on a tributary of the Ohio River. These cities represent two major metropolitan areas in the Ohio River Basin with different land uses experiencing different rates of population growth. The projected hypothetical land-use changes were based on linear extrapolations of current population data. Results of the analyses indicate that conversion from agricultural land use to low-density residential land use may decrease the amount of surface runoff. The land-use practices which generate the least amount of runoff are forest, low-density residential, and agriculture; whereas high-density residential and commercial land-use types produce the highest runoff. The hydrologic soil type present was also an important factor in determining the amount of runoff and non-point-source pollution. A runoff-depth matrix and total nitrogen matrix were created for Cincinnati and Columbus to describe possible land-use mitigation measures in response to global climate change. The differences in Cincinnati and Columbus were due to differences in geographic location, air temperature, and total runoff. The results of this study may be useful to planners and policy makers for defining the possible impacts of future global climate and land-use changes on water resources.     

高校要加强大学生礼仪教育

本文列举了大学生在学校多种场合和情景中礼仪素养缺失的种种表现,并多方面分析问题产生的原因,最后简要提出了高校要加强大学生礼仪教育的对策。     

安太堡露天煤矿排土场刺槐生长状况研究

安太堡露天煤矿1993～1998年土地复垦试验结果表明,在排土场逆境条件下,刺槐可以正常生长.坡度、坡向、地表物质组成和植物配置模式是影响其生长的主要因子.在阳向坡、避风处生长良好.黄土母质有利于1年生刺槐的生长,岩土混排则更有利于2年生以上刺槐的生长.刺槐与草混交抑制刺槐生长.     

硫酸法钛白生产水洗工序清洁生产技术初探

通过开展水洗工段用水审计并试验了温度、偏钛酸ξ电位和漂白工艺对水洗的影响效果，从实践和理论上探讨了为其提高钛白质量改进水洗工艺的清洁生产方案的可行性和合理性。     

花键轴冷挤压成形工艺及模具设计

花键轴是机械中广泛使用的重要零件之一。制造工艺复杂,外观质量、尺寸精度、综合机械性能等要求高。采用冷挤压成形,可使成本降低、提高质量、使用可靠。此文对花键轴成形工艺,模具设计作了详细探讨。