新型膜-生物反应器中膜丝长度对临界通量的影响

为了优化膜-生物反应器中的膜组件长度,考察了4组不同长度膜组件(膜丝长度为0.2、0.4、0.6、0.7m)在不同曝气量下的临界通量区.试验结果发现,曝气强度相同时,膜丝长度为0.4m膜组件的临界通量区高于膜丝长度为0.2m、0.6m和0.7m的膜组件,说明膜丝长度存在最优值;膜组件中膜丝长度相同时,曝气强度越大临界通量区越高.膜丝(膜组件)长度对临界通量产生影响主要体现在2方面:一是膜丝长度的变化会改变膜丝上局部通量的非均匀分布状况;二是曝气气泡对不同长度膜丝的冲刷作用不同.应用局部通量分布方程模拟了清洁膜丝上局部通量的分布状况;结果表明,膜丝长度越长,沿膜丝长度方向的局部通量分布越不均匀,则膜组件的临界通量越小.从曝气气泡对膜丝的冲刷作用看,相同曝气量下膜组件(即膜丝)长度越长,形成的气泡越大,在大气泡的作用下膜丝更易于摇摆和震动以达到减轻膜表面污染物沉积的效果,即可能达到的临界通量越大.因此,对于减轻膜污染而言,即得到最高的临界通量区,膜丝(膜组件)长度存在最优值.     

链长和官能团对全氟有机酸降解路径的影响

考察了碳链长度和官能团对高强UV/SO₃^2-体系降解全氟有机酸的影响,选取典型全氟有机酸PFOA和PFOS,探明其降解机制.结果表明,高强UV/SO₃^2-体系可高效降解5种全氟有机酸.全氟有机酸的降解速率随着碳链长度的增加而增加.官能团对全氟有机酸的降解有重要影响,全氟羧酸在体系中的降解速率显著快于全氟磺酸.全氟羧酸是从与羧基相连的α碳上的氟原子开始,通过逐步脱CF₂单元的形式生成短链全氟羧酸进行降解.全氟磺酸主要有三条降解路径：脱磺酸基、α位脱氟以及中心C—C键断裂.     

倾斜工作面底板破坏深度计算方法研究

煤层倾角是影响底板破坏带深度的一个重要因素,为深入研究煤层倾角对底板破坏带深度的影响,采用断裂力学理论建立了煤层倾角对底板破坏带深度影响的计算模型,得出由于煤层倾角的存在,倾斜工作面上部破坏带深度小于下部破坏带深度。收集我国大量的突水案例与煤层倾角统计数据,以及破坏带深度与煤层倾角统计数据,从突水案例数据可以看出倾斜工作面下部由于底板破坏造成的突水次数明显多于上部,从破坏带深度与煤层倾角变化趋势可以看出随着倾角增大破坏带深度也在增大。统计得到数据的结论与应用断裂力学模型分析得到的结论一致。最后对建立的破坏带深度计算模型井下质量检验,检验结果显示该计算模型的精度较高,符合现场应用的要求。     

The Boundary-Quality Penalty: a Quantitative Method for Approximating Species Responses to Fragmentation in Reserve Selection

Abstract:  Aggregation of reserve networks is generally considered desirable for biological and economic reasons: aggregation reduces negative edge effects and facilitates metapopulation dynamics, which plausibly leads to improved persistence of species. Economically, aggregated networks are less expensive to manage than fragmented ones. Therefore, many reserve-design methods use qualitative heuristics, such as distance-based criteria or boundary-length penalties to induce reserve aggregation. We devised a quantitative method that introduces aggregation into reserve networks. We call the method the boundary-quality penalty (BQP) because the biological value of a land unit (grid cell) is penalized when the unit occurs close enough to the edge of a reserve such that a fragmentation or edge effect would reduce population densities in the reserved cell. The BQP can be estimated for any habitat model that includes neighborhood (connectivity) effects, and it can be introduced into reserve selection software in a standardized manner. We used the BQP in a reserve-design case study of the Hunter Valley of southeastern Australia. The BQP resulted in a more highly aggregated reserve network structure. The degree of aggregation required was specified by observed (albeit modeled) biological responses to fragmentation. Estimating the effects of fragmentation on individual species and incorporating estimated effects in the objective function of reserve-selection algorithms is a coherent and defensible way to select aggregated reserves. We implemented the BQP in the context of the Zonation method, but it could as well be implemented into any other spatially explicit reserve-planning framework .     

Determination of the critical length of the crack-like flaws and its effect on safety

Methodologies of API 579 have been widely accepted as the de-facto standard guideline for fitness for service assessment on crack-like flaws in pressure equipment. For different purposes and needs, the evaluation is divided into three levels, from critical length estimation in level 1, use of the failure analysis diagram (FAD) in level 2, to performing finite element stress analysis in level 3, that is from simplified to accurate. It is generally considered safe as long as the crack is smaller than the critical crack, but not all of them are actually the case. Therefore, it is very important to study the physical meaning behind the critical crack and understand the conservativeness of it.In this study, numerous examples of critical cracks determined according to API 579 Level 1 were put into Level 2 analysis for comparison. Each case is mapped onto the FAD of level 2 analysis to see its position and distance from the borderline between safe and danger zones. A huge amount of examples covering the majority of possible scenarios, including the geometry, thickness, inner diameter, pressure and half-length of the flaw, depth of the crack, crack tip and crack bottom, as a whole, there are 960 cases to be analyzed.Results show that cracks on the circumferential direction of the cylindrical and spherical vessels are distributed tightly in a small area far from the borderline on the FAD diagram. In these cases, the vessel is actually not as dangerous as the critical crack implies, since most of the points lie quite far from the danger zone. As for the longitudinal cracks of a cylindrical vessel, the results are scattered around, and three data points are located outside the allowable zone. The peculiar results are partly due to a discrepancy of interpolating procedure as the influence coefficient is being computed. Through this study, it is also found that the cumbersome process of estimating the critical crack length can be greatly simplified for longitudinal cracks in a cylindrical vessel.     

一种特殊电除尘器钢支架计算方法的讨论

以某工程为例,介绍了一种特殊电除尘器钢支架的结构形式,通过结构设计软件计算和有限元整体屈曲分析,证明采用传统的计算长度系数法进行立柱稳定计算,其结果偏不安全,建议采用整体屈曲分析计算.     

高炉喷吹用潞安贫瘦煤爆炸下限与返回火焰长度的试验研究

该试验通过测定爆炸下限与返回火焰长度这两个参数来确定4种煤粉的爆炸性。爆炸下限指能使喷入一定装置中的粉尘云点燃并维持火焰传播的最小粉尘浓度,是确定粉尘爆炸性重要参数,试验室通常使用20L的爆炸装置进行测定。喷吹现场广泛采用长管式煤粉爆炸性测试仪检测煤尘引燃后产生的返回火焰长度,该长度随煤粉爆炸性的强弱而显著变化:返回火焰长度大于600 mm可认定该煤粉具有强爆炸性;在400~600 mm之间则煤粉具有中强度爆炸性;小于400 mm则煤粉具有弱爆炸性。结果表明:20 L球测得4种煤粉的爆炸下限在60~85 g/m3之间;长管式煤粉爆炸性测定仪测得4种煤粉的返回火焰长度在20~50 mm之间。由测定的返回火焰长度可知,试验所用的4种煤样均属于弱爆炸性煤种。     

闽江干流下游河段纳污能力的研究

建立闽江干流下游河段二维非稳态水质水量模型,根据2004年实测资料对模型中的水质参数进行率定;对各排污口进行概化,应用模型模拟出闽江干流下游河段浓度场,并得出排污口混合带长度与排污量的响应关系;根据概化排污口在限定混合带长度下的平均纳污能力扩展到有效纳污能力计算长度后得到整个水体的纳污能力。经计算,闽江干流下游河段对COD的纳污能力为58195t/a。