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In flowing water the incipient motion of sediment can be affected by the presence of microbial biofilm growth. This article documents a series of flume experiments using non‐uniform sediments, in which sediment entrainment was investigated for cases where the sediment was immersed in deionized water, so that no biofilm developed, and for cases where a bio‐sediment was cultivated by placing the sediment in a mixture of natural water and nutrient solution. Differences in entrainment and the velocity at incipient motion were measured over an eight week period, as biofilm grew. It was found that the incipient motion phenomena were quite distinct between the two kinds of sediment. Sediment with biofilm was more stable and, over time, incipient velocity increased to a threshold level, before declining. Biofilm development is clearly an important control on the stability of sediments, especially in eutrophic water bodies. Two incipient velocity formulas were derived for sliding and rolling conditions. Film water theory was utilized to describe the cohesive force between sediment particles and the adhesive force generated by biofilm was introduced into the formula derivation; the time variation characteristics of biofilm strength and the features of the substrate were also taken into consideration. Such analyses can help to predict sediment transport changes due to biofilm presence in nutrient‐rich water bodies.  相似文献   
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对固体火箭发动机粘接界面试验件进行了不同湿热条件下的加速老化试验,并测量了不同老化时间粘接界面的扯离强度,描述了湿热老化试验和性能测试中的试验现象,结合复合材料微粘接结构吸湿规律对试验现象和撤离强度随老化时间变化曲线进行了分析。研究结果表明:衬层-推进剂粘接界面是固体火箭发动机粘接结构中最薄弱环节,应予以重点考虑;湿热老化促进了环境水分从衬层–推进剂界面向推进剂内部的扩散和渗透,致使弱边界层向推进剂内部扩展,导致了衬层-推进剂界面粘接强度的降低。试验件平均扯离强度随老化时间呈下降趋势,中间有一个强度趋于稳定的平台期。   相似文献   
3.
To model the interaction between a buried pipeline and the surrounding soil either special interface elements or thin conventional elements may be used. In this study the CRISP90 interface element, the DRCRISP interface element and a conventional 8-noded quadrilateral element have been examined and their behaviour compared for a variety of loading conditions. Initial studies reveal that all these elements have limitations and are only suitable for monotonic loading and situations where tensile conditions do not occur across the interface. In the light of these findings the CRISP90 interface element has been modified by introducing a limiting adhesive strength in the normal direction; a flag system has also been introduced to track the various conditions of separation and closure for any gap that is formed. The results of single element and other benchmark tests show that the modified element can satisfactorily model the different modes of deformation relevant to soil–structure interface problems.  相似文献   
4.
一株自太湖微囊藻上分离到的细菌的生长及磷代谢   总被引:6,自引:2,他引:4  
磷是引起湖泊水华爆发的关键元素,微囊藻(Microcystis)是太湖水华的主要藻种,为了研究磷在湖泊水体低级食物链(细菌、浮游动植物等)中的代谢,以一株自太湖微囊藻上分离的假单胞菌(Pseudomonas sp.)X菌株为试验菌,研究了磷形态及生长因子对其生长的影响,结果表明无机磷浓度对X菌生长的影响不大,而ATP对X菌的生长有抑制作用;在含有无机磷和有机磷的培养基中,X菌优先利用无机磷盐,X菌  相似文献   
5.
对固体火箭发动机粘接界面试验件进行了不同湿热条件下的加速老化试验,并测量了不同老化时间粘接界面的扯离强度,描述了湿热老化试验和性能测试中的试验现象,结合复合材料微粘接结构吸湿规律对试验现象和撤离强度随老化时间变化曲线进行了分析。研究结果表明:衬层-推进剂粘接界面是固体火箭发动机粘接结构中最薄弱环节,应予以重点考虑;湿热老化促进了环境水分从衬层–推进剂界面向推进剂内部的扩散和渗透,致使弱边界层向推进剂内部扩展,导致了衬层-推进剂界面粘接强度的降低。试验件平均扯离强度随老化时间呈下降趋势,中间有一个强度趋于稳定的平台期。   相似文献   
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