The effect of oxygen tension on colony formation and cell proliferation of amniotic fluid cellsin vitro

The effects of reduced oxygen concentrations in the gas phase over the culture medium on colony formation and cell proliferation were investigated in high and low cell density primary and secondary cultures of amniotic fluid cells. Using two standard culture methods (25 cm² plastic flasks and Leighton type tubes) a significantly reduced culture time was observed at high cell density for mass cultures by incubation within a low oxygen tension gas phase (2.5 per cent to 7.5 per cent O₂) instead of conventional air (18 per cent O₂). At low cell density colony formation was significantly enhanced in cultures grown at reduced oxygen tension. Using gas permeable membranes as support, lowering the oxygen tension from 7.5 per cent to 2.5 per cent yielded an increase in plating efficiency of cells from approximately 5 per cent to 25 per cent, whereas plating efficiency was less than 2 per cent for cells grown at ambient 18 per cent O₂. It is suggested that low oxygen tension in the gas phase is an effective means of enhancing clonal growth in amniotic fluid cell cultures, thereby reducing both culture time and risk of culture failure.     

思茅大气环境与气象条件的关系

对思茅地区大气环境监测数据进行统计、分析,与当地天气气候条件进行对比,探究思茅地区大气污染状况与气象条件之间的关系.     

秦皇岛市水环境现状与恢复

秦皇岛地区原始自然环境优越,多年来,不正当的人为活动、环境恶化趋势明显,也直接干扰与影响着水的良性循环。现状水环境:河流基流渐小,并季节性断流,坑塘减少,湿地萎缩水土流失,洪径增大。地下水位下降,水量减少,承压水无序开采,污净比失衡,河流承栽力降低。地下水垂直污染面扩大,点、面、垃圾污染源趋重。联通青一洋、石一起,实施水资源再分配。优化配置城乡用水。重视地下水源地建设,联合调度地表、地下水源。谨慎开发承压水。植树造林、涵养水分。注重防风林带建设,改善田间小气候。严控地下水采量,防止土壤旱化。搞好坑塘建设,解决乡镇污水出路与净化。保护湿地,促进水的良性循环。深度处理废污水.使之资源化。从源头抓好城市三大水源地污染源.察勘储备新地下水源地。改良恢复水环境,保障水资源循环利用。     

小径薄壁管射线透照布置方法

小径薄壁管广泛用于工艺管道中，在对其进行无损探伤时，一般采用双壁双影椭圆成像法和双壁重叠成像法，针对小径薄壁管对接焊缝透照成像的特殊要求，具体介绍双壁双影椭圆成像法的透照布置方法。     

顺德城市化进程的障碍、优势、目标与对策

文章对加快顺德市城市化进程的障碍因子和优势条件进行了分析，认为“滞后城市化”是经济增长和产业发展的主要瓶颈，并提出加快顺德城市化进程的优势条件已成熟，必须抓住机遇，确立发展目标，走可持续发展的城市化道路。     

Comparing Environmental Conditions Using Indicators of Pollution Hazard

/ Land use/land cover classifications for 1973 and 1991, derived from the interpretation of satellite imagery, are quantified on the basis of biophysical land units in a study area in southeastern Australia. Nutrient export potentials are estimated for each land unit based on their composition of land use/land cover classes. Spatial and temporal comparisons are made of the land units based on the calculated pollution hazard indicators to provide an insight into changes in the state of the environment and the regional significance of land use changes. For example, one ecosystem, unique to the study, showed a large increase in pollution hazard over the study period as a manifestation of an 11-fold rise in cleared area and an expansion of cropping activities. The benefits to environmental management in general are discussed.KEY WORDS: Land cover change; Nutrient export; Environmental condition; Pollution hazard; Agricultural pollution; Nonpoint source pollution; Diffuse pollution; Environmental degradation     

旱涝灾害的一些基本问题初探

首先就旱涝灾害对人类的作用进行了分析，认为它影响范围最大，危害程度最深．其次．对旱涝灾害的成因、确定旱涝灾害的定量指标以及评估旱涝灾害的指标体系进行分析探讨；最后对国内防御旱涝灾害的能力做了总体评价，并对其所采取的预防，救抗灾措施等进行分析．     

自然灾害不同灾情的比较方法探讨

用计算自然灾害不同灾情的灰色关联度的方法，来对不同灾情进行比较分析。该方法不仅能够比较同一灾级中不同的灾情，也能够对不同灾级的灾情差异程度作比较分析，因而它与现有的不同灾情的比较方法相比，更科学合理。     

特大型煤和瓦斯突出的地质条件及其成因

特大型煤和瓦斯突出危害极大，具有独特的发生条件，应专门研究。在全国９９ 次特大型煤和瓦斯突出详细研究的基础上，总结了特大型突出的一般特征及发生的地质和采矿条件，并给出了南桐矿区的几个临界值。对特大型突出地质条件的成因进行了较深入的探讨，提出了防止特大型突出的几点建议