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781.
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783.
Low pH markedly reduced heterotrophic microbial activity in sediment-lake water systems. A marked reduction in both the rate and the total amount of oxygen consumed occurred as pH decreased. In addition, low pH and also low temperature (0°C) resulted in longer turnover times (Tn) and also smaller Vmax values when the kinetics of 14C-glucose, 14C-glycine, and 14C-glutamic acid utilization were examined. When the response of the microorganisms to heavy metals was examined, mercury was generally more toxic than lead over the pH range of 4.5 to 7.5 but both metals were more toxic at pH 4.5 than at higher pH levels. Mercury also inhibited oxygen utilization and 14C-glucose mineralization more than lead at all pH levels. Bisulfite reduced microbial activity at all pH levels although it was always more toxic to the sediment microorganisms at pH values of 4 and 5 than at pH 7. 相似文献
784.
石化企业是噪声大户,由压缩机、鼓风机、机泵等声源设备及其它背景噪声构成了各种各样的噪声源,不但单源声级峰值高,而且面源辐射面积广,治理难度非常大,辽化公司采取自难而易的原则,对纤维生产中重点噪声源进行了治理,收到了明显的成效。 相似文献
785.
The effects of the herbicide (2,4-D) and six organophosphorus insecticides (Diazinon, Dimethoate, Fenitrothion, Malathion, Phenthoate and Quinalphos) on growth, photosynthesis and chlorophyll a synthesis of the fresh water green alga Chlamydomonas reinhardtii (mt +) were studied. At low concentrations (1 and 5 ppm), the herbicide and all six orgnophosphorus insecticides stimulated photosynthesis of the alga. The stimulating effects on algal growth and chlorophyll a synthesis were only observed in the presence of low concentration (1 ppm) of 2,4-D and Fenitrothion, Growth, photosynthesis and chlorophyll a synthesis of the alga were inhibited in the presence of high concentrations (10, 20 and 40 ppm) of the herbicide and all the six organophosphorus insecticides. Results also indicated that the toxicities of these organophosphorus insecticides on the tested alga were dependent on their chemical structures. 相似文献
786.
Recent reports of absent nasal bone in fetuses with Down syndrome have sparked much interest in the use of this finding for the screening of Down syndrome. We describe the histopathological findings of nasal bones of two fetuses with Down syndrome, one with absence and the other with normal ossification of the nasal bone. We propose that histopathological examination of the nasal bone could improve the accuracy of diagnosis of nasal hypoplasia among Down syndrome abortuses. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
787.
788.
Two different species of photosynthetic microalgae, Chlorella pyrenoidosa and Scenedesmus sp., were grown in settled and activated sewage filtrates at two different inoculum sizes, aimed to reduce nutrient load from wastewater. Higher growth rates were recorded in cultures with higher inoculum size, and algal cells usually grew better in settled sewage than in activated sewage. As algae started to grow and multiply, both nitrogen and phosphorus content in wastewater decreased significantly. The removal rate was rapid during the first week of growth and more than 2/3 of wastewater N and P was reduced. After the initial period, the removal rate slowed down. At the end of this study, more than 80% of total-P and inorganic N present in settled sewage were reduced but such removal efficiency was lower in activated sewage. In general, high inoculum size of algal cells provided more N and P removal than low inoculum, and Chlorella cells performed better than Scenedesmus. These results suggest that cultivation of Chlorella seems to be one of the feasible methods to reduce the amount of nitrogen and phosphorus entering the nearby coastal water, thus preventing the eutrophication problem. It is also clear that algal ponds with high inoculum size might be more suitable to be installed as a secondary rather than a tertiary treatment process. 相似文献
789.
790.
梅子坑钼矿位于九岭钨钼成矿带,为中型石英脉型钼矿床.矿区内地层和岩浆岩钼元素含量分别是克拉克值的43倍和21倍.矿体赋存于双桥山群修水组浅变质岩系中及北西向断裂控制的裂隙密集带中;矿石主要类型为石英脉型,矿石有益组分为辉钼矿,形成于石英-黄铁矿-辉钼矿-黄铜矿早期矿化阶段.矿床可能与隐伏的燕山期细粒花岗岩、花岗斑岩岩脉有成因关系,属与燕山期岩浆活动有关的中-高温热液矿床.北西向断裂密集带,硅化、云英岩化、黄铁矿化围岩蚀变,燕山期花岗岩类及双桥山群浅变质岩系,是其主要找矿标志. 相似文献