Development of the vertebrate central nervous system: formation of the neural tube

The developmental process of neurulation involves a series of coordinated morphological events, which result in conversion of the flat neural plate into the neural tube, the primordium of the entire central nervous system (CNS). Failure of neurulation results in neural tube defects (NTDs), severe abnormalities of the CNS, which are among the commonest of congenital malformations in humans. In order to gain insight into the embryological basis of NTDs, such as spina bifida and anencephaly, it is necessary to understand the morphogenetic processes and molecular mechanisms underlying neural tube closure. The mouse is the most extensively studied mammalian experimental model for studies of neurulation, while considerable insight into underlying developmental mechanisms has also arisen from studies in other model systems, particularly birds and amphibians. We describe the process of neural tube formation, discuss the cellular mechanisms involved and highlight recent findings that provide links between molecular signaling pathways and morphogenetic tissue movements. Copyright © 2009 John Wiley & Sons, Ltd.     

A Stochastic Modeling Approach to Address Hydrogeologic Uncertainties in Modeling Wellhead Protection Boundaries in Karst Aquifers1

Abstract: Development of any numerical ground‐water model is dependent on hydrogeologic data describing the subsurface. These data are obtained from geologic core analyses, stratigraphic analyses, aquifer performance tests, and geophysical studies. But typically in remote areas, these types of data are very sparse and site‐specific in terms of the aerial extent of the resource to be modeled. Uncertainties exist as to how well the available data from a few locations defines a heterogeneous surficial aquifer such as the Biscayne Aquifer in Miami‐Dade County, Florida. This is particularly the case when an exceptionally conductive horizontal flow zone is detected at one site due to specialized testing that was not historically conducted at the other at sites that provided data for the model. Not adequately accounting for the potential effect of the high flow zone in the aquifer within a ground‐water numerical model, even though the zone may be of very limited thickness, might underpredict the well field protection capture boundaries. Applied Stochastic ground‐water modeling in determining well field protection zones is steadily becoming important in addressing the uncertainty of the hydrogeologic subsurface parameters, specifically in karstic heterogeneous aquifers. This is particularly important in addressing the uncertainty of a 60‐day travel time capture zone in the Northwest Well Field, Miami‐Dade County, where a predominantly high flow zone controls much of the flow in the production wells. A stochastic ground‐water modeling application along with combination of pilot points and regularization technique is presented to further consolidate the uncertainty of the subsurface.     

氨氮测定时应注意的几个问题

纳氏试剂比色法是测定水中氨氮的国家标准方法。标准方法对氨氮的介绍比较详细，测定步骤也较简单，但实际工作中，情况比较复杂，条件较苛刻，实验空白值难以达到要求（A≤0．030），很多具体的因素都干扰影响该方法的灵敏度，也直接影响分析结果的精密度和准确度。根据多年的实际工作经验，将氨氮测定过程中容易出现的问题及注意事项进行了总结。     

输变电环境影响评价及竣工环保验收相关要点分析

通过输变电环境影响评价及竣工环保验收工作的实践,从输变电环境影响评价及竣工环保验收的基本概念和相关法律、法规出发,分析了输变电环境影响评价及竣工环保验收工作的要点,包括敏感目标调查、生态环境影响评价与监测、声环境评价重点、公众参与等,在此基础上论述了两者之间的相互关系,最后针对输变电环境影响评价及竣工环保验收工作更加科学化提出了建议。     

医务人员职业健康危害及其关键控制环节

通过查阅、分析大量文献,结合实际工作经验,系统阐述了医务人员面临的主要职业危害因素,并针对我国医务人员职业危害现状和防治工作中存在的主要问题,提出防治关键环节和措施。分析表明:我国医务人员职业暴露危害严重;医务人员的生命质量和平均寿命低于普通人群;医院职业卫生立法和技术标准滞后;防治措施不力,医务人员职业健康权益得不到有效保护。同时指出对医务人员职业危害防治的关键措施:必须通过加强科学研究、制定法规标准、建设医院安全文化、加强宣传教育和培训、推广免疫接种和防护技术、科学设计工作流程、加强心理疏导等关键措施,有效防治医务人员职业健康危害。     

Safeguarding Crushing Points by Limitation of Forces

Limitation of forces can be a simple measure to safeguard crushing points at doors, machines, and vehicles. In this connection different standards define a threshold force value of 150 N. This widely accepted value refers to static forces only. The dynamic forces that arise from impact on a person are frequently ignored, although they are generally higher than the static forces.

The article describes an instrument for the measurement of static and dynamic crushing forces. This instrument has a stiffness that approximates the average stiffness of human fingers as one of the most at-risk parts of the human body with regard to crushing injuries. Sensory tests were carried out to define dynamic forces considered admissible at crushing points.     

电网规划环境影响评价应关注的几个要点

广州市城市高压电网规划环境影响评价是国家环境保护总局全国规划环境影响评价的试点项目，结合该专项规划环境影响评价在评价指标体系设计、评价标准、评价技术方法等方面的探索和研究成果，提出电网规划环境影响评价应关注的几个要点。     

基于改进贴近度法的水质监测点优化布设

贴近度法作为一种系统优化方法已被广泛应用于水质监测点优化中,然而此方法存在几方面的问题:一是仅考虑空间因素而未考虑时间因素对区域监测重要性的影响;二是用各指标监测数据平均值进行计算,从而导致聚类效果较差;三是未考虑指标权重对测点优化布设的影响。为此,将层次分析法与贴近度法相结合,提出了基于改进贴近度法的水质监测点优化布设方案。应用此方法对某引水明渠水质监测点进行优化布设,结果表明,改进方法有效提高了聚类效果,易于进行水质监测点的排序与分类。     

南渡江水质评价浅析

采用共源点灰色聚类法对南渡江海口水域 1 993年枯水期水质进行评价 ,结论为I类水质。与共斜率灰色聚类法进行比较 ,该法更简化 ,加权含义更确切。     

制苯装置职业病危害调查及关键控制点分析

通过识别和分析制苯生产装置的职业病危害因素,确定职业病危害的关键控制点,提出了防护措施对策,应重点加强作业人员接触有毒物质苯、硫化氢关键控制点的职业卫生管理。