OSHA''s Permissible Exposure Limits: Regulatory Compliance Versus Health Risk

Workplace exposures to airborne chemicals are regulated in the U.S. by the Occupational Safety and Health Administration (OSHA) via the promulgation of permissible exposure limits (PELs). These limits, usually defined as eight-hour time-weighted average values, are enforced as concentrations never to be exceeded. In the case of chronic or delayed toxicants, the PEL is determined from epidemiological evidence and/or quantitative risk assessments based on long-term mean exposures or, equivalently, cumulative lifetime exposures. A statistical model was used to investigate the relation between the compliance strategy, the PEL as a limit never to be exceeded, and the health risk as measured by the probability that an individual's long-term mean exposure concentration is above the PEL. The model incorporates within-worker and between-worker variability in exposure, and assumes the relevant distributions to be log-normal. When data are inadequate to estimate the parameters of the full model, as it is in compliance inspections, it is argued that the probability of a random measurement being above the PEL must be regarded as a lower bound on the probability that a randomly selected worker's long-term mean exposure concentration will exceed the PEL. It is concluded that OSHA's compliance strategy is a reasonable, as well as a practical, means of limiting health risk for chronic or delayed toxicants.     

增加反应物量对化学平衡移动的讨论

本文提出了恒温恒压条件下，在多组分理想气体反应体系中，增加某一反应物的量，化学平衡有可能向反应物方向移动的实例，并引用化学反应进度的概念进行热力讨论．     

碱水驱组分输运过程有效性研究

建立了碱水驱组分孔隙输运数学模型,将模型中所需的物化参数描述为驱油剂浓度相关的函数,用“有效驱替带”量化和分析了吸附、驱油剂段塞尺寸、驱替速度、扩散弥散等因素对碱组分输运过程有效性的影响机理。在此基础上,进一步分析了大庆油田ASP复合驱用碱剂NaOH在孔隙输运过程中的有效性和持久性,并对模拟软件进行了实验验证,它们具有很好的一致性。经过实验验证的模拟软件,不仅可代替部分实验室流动实验和辅助机理分析,而且可以为碱水驱和ASP复合驱工程工艺方案设计和动态监测提供指导。     

重化工业园区构建循环经济动力机制研究

对重化工业园区开展循环经济的研究具有重大的现实意义和重要的理论价值.本文在研究重化工业园区循环经济动力机制的动力源和作用机理的基础上,分析了中国重化工业园区在构建循环经济动力机制方面的现状、特征和问题,提出了一系列的破解对策.     

Models for Dependent Extremes Using Stable Mixtures

Abstract.  This paper unifies and extends results on a class of multivariate extreme value (EV) models studied by Hougaard, Crowder and Tawn. In these models, both unconditional and conditional distributions are themselves EV distributions, and all lower-dimensional marginals and maxima belong to the class. One interpretation of the models is as size mixtures of EV distributions, where the mixing is by positive stable distributions. A second interpretation is as exponential-stable location mixtures (for Gumbel) or as power-stable scale mixtures (for non-Gumbel EV distributions). A third interpretation is through a peaks over thresholds model with a positive stable intensity. The mixing variables are used as a modelling tool and for better understanding and model checking. We study EV analogues of components of variance models, and new time series, spatial and continuous parameter models for extreme values. The results are applied to data from a pitting corrosion investigation.     

火电厂循环冷却水中铵态氮对铜设备的腐蚀研究

火电厂常通过提高循环冷却水的浓缩倍率达到节水的目的，一些机组凝汽器铜管因此产生了腐蚀问题。通过实验，分析了陕西某电厂循环冷却水中的铵态氮对凝汽器铜管的腐蚀影响。实验表明，为较好地控制腐蚀速率，应使铵态氮浓度控制在6mg／L以下。     

浅谈化学实验教学的改革与创新

化学课程相对于其他的课程而言,实验部分占据了重要的比例。而实验教学的灵活性,给化学课程的教学又提了新的要求。在化学实验中,针对目前存在的一些问题,应该采取相应的措施进行解决,才能真正实现实验教学的创新与改革发展,给化学实验的发展带去新的局面。     

关于我国化工企业实行绿色管理的思考

近年来 ,世界各国都十分注意经济发展与环境的关系问题。我国已在改革开放的过程中逐步确立了我国经济发展应以可持续发展为中心的战略。化工企业实行绿色管理是我国宏观经济可持续发展的客观要求 ,同时也是我国化工行业的生产和经营的特点所决定的。笔者从我国化工企业的角度出发论证了绿色管理对化工企业生存和发展的重要意义及化工企业实行绿色管理的关键因素 ,并针对我国化工企业的状况提出了可行性建议     

系统论在化学教学论教学中的应用

系统论在化学教学论教学中的应用的基本思想方法就是把所研究和处理的对象当作一个系统，分析系统的结构和功能。化学教学系统是由化学教师、学生和化学教学媒体等诸要素组成的一种复杂的组合体。这种组合体具有不同于其各个部分（要素）的新质的整体特性。研究化学教学系统的整体特性有助于从各要素的关系和相互作用中发现系统的规律性。     

陕北能源化工基地人才需求状况调查与思考

陕北地区是国家21世纪最重要的能源化工基地，但是由于自然条件相对艰苦以及吸引毕业生的政策等方面因素，使得人才问题一直成为制约陕北能源化工基地发展的瓶颈。在调研的基础上，针对陕北能源化工基地人才供需存在的主要矛盾和问题，提出了解决的思路。