Inhibitory effect of Cr（Ⅵ） on activities of soil enzymes

To evaluate the influence of various Cr(VI) concentrations (0.05, 0.25, 0.50, 1.00 and 2.00 g/kg) on the activity of soil enzymes, the activities of catalase, polyphenol oxidase, dehydrogenase, alkaline phosphatase in soils were investigated in the incubation experiment with a period of 35 d. The results indicate that all the tested Cr(VI) concentrations significantly inhibit dehydrogenase activity by over 70% after 35 d. The activity of alkaline phosphatase is slightly inhibited during the whole experiment except for on the day 7. Cr(VI) has no obvious effect on the activity of catalase in soil. On the contrary, Cr(VI) stimulates the activity of polyphenol oxidase. The results suggest that dehydrogenase activity can be used as an indicator for assessing the severity of chromium pollution. Foundation item: Projects(2006AA06Z374, 2007AA021304) supported by the National High-Tech Research and Development Program of China; Project(2008SK2007) supported by the Key Program of Science and Technology of Hunan Province, China     

融合开放与传统实践教学管理模式的研究

当前,高校的实践教学管理普遍存在传统的相对集中和开放两种实践教学管理模式,它们各自存在优缺点,而且具有一定的互补性。提出探索建立一种全新的、相对独立的实验教学管理模式,以实现传统与开放二者间的优势互补,进而推动高校实践教学质量的进一步提高。     

关于工程公司走向国际市场的几点思考

介绍了国内工程公司向国际市场开拓过程中,应引起重视的一些问题及解决方法。     

Spatial distribution of chromium in soils contaminated by chromium-containing slag

To evaluate the metal chromium (Cr) contamination of soil at a chromium-containing slag site by ferrochromium production, the contaminated sites, under slag heap, in the vicinity of slag heap and arable soils near the outlet of sewer channel, and unpolluted site 5 km away from one ferroalloy plant in Hunan Province, China, were selected. The concentrations of total Cr and water soluble Cr in bulk soil samples and profile depth samples were determined. The results show that the soils in the vicinity of slag heap have the highest total Cr content followed by the soils under the slag heap and near the outlet of sewer channel of the factory. The mean concentrations of total Cr in the top soils at above three contaminated locations exceed the critical level of Secondary Environmental Quality Standard for Soil in China by 3.5, 5.4 and 1.8 times. In most Cr polluted soils, total Cr has a relative accumulation in soil depth of 40-60 cm, but this trend is not found in unpolluted soils. The average concentrations of water soluble Cr (Ⅵ) in top soils under slag heap and in the vicinity of slag heap are 176.9 times and 52.7 times higher than that in the uncontaminated soils, respectively. However, water soluble Cr (Ⅵ) contents in soils near sewer channel are all low and the values are close to that in the uncontaminated soils. Although water soluble Cr (Ⅵ) content in soil profiles decreases with soil depths, it in soils under slag heap maintains a high level even at a depth of 100-150 cm. The results imply that the transportation of Cr (Ⅵ) can result in a potential risk of groundwater system in this area.     

变压器屏蔽对开关电源电磁干扰(EMI)影响的分析

从变压器屏蔽对电源的EMI的作用入手，分析了屏蔽所影响的EMI的特性和传输路径，并通过仿真研究了屏蔽层对变压器损耗的影响。最后给出了一个改变屏蔽以简化变压器的制造的例子。     

遥控器漫谈

现今遥控器以各种形式或载体走进了千家万户,每个家庭都拥有若干类型的家电,相应遥控器就有一大堆,经常在使用中便会出现遥控故障。本刊2007年第一     

水库坝基帷幕灌浆施工技术及效果分析

帷幕灌浆作为地基处理方法之一,具有高效、低能、应用范围广等优点。文章就水库坝基帷幕灌浆施工技术及效果进行了分析,结合具体的工程实例,简述了帷幕灌浆的技术指标,详细阐述了帷幕灌浆的主要施工技术,并对灌浆的效果和质量作了系统的分析和评价,以期能为有关方面的需要提供参考借鉴。     

蒙乃尔合金的氩弧焊工艺研究

通过对蒙乃尔合金氩弧焊工艺的可行性研究结果表明：焊接规范必须控制在恰当的范围内，热输入太强则易产生热裂纹，太弱则易出现熔合不良和夹渣缺陷，增加操作难度。接头ＨＡＺ存在一低度，低塑性，低强度区，热裂纹及拉伸断裂多出现于该区。