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51.
A laser-based light attenuation technique was successfully used to measure interfacial areas as high as 5832 m2/m3 and Sauter mean bubble diameter varying between 50 and 5600 μm. Good agreement between this approach and the photographic technique was obtained particularly at low gas holdups. 相似文献
52.
研究了直接纺丝制取芳纶短纤维的新方法。讨论了纤维长度、直径及力学性能与纺丝条件的关系。发现影响纤维长度的主要因素是空气层高度和喷丝速度,影响纤维直径的主要因素为喷口直径及喷丝速度。此外,还用PPTA短纤维制成了均匀的PPTA"浆粕"纤维。 相似文献
53.
针对大面积水域浓度场难以实现实时测量、测量精度不高等问题,采用了一种多通道荧光测试系统和方法。首先,基于单色光诱导荧光检测浓度(LIF)原理,使用探头获取离散点的浓度参数。然后,经总线或通信网络技术,将数百个测点连接起来。最后,通过数据总线或网络将采集的数据输送到中央测控计算机中,处理离散的数据后形成完整的浓度场。在恒定流浓度场中的试验结果表明,污染物测量相对误差均值不超过5%,单次测量相对误差最高值为8.33%,传感器线性度不超过5%,可检测的荧光素钠溶液浓度分辨率为0.001 ppm,系统测量稳定、精度较高。相较于其他浓度测量方法,该系统具有测量面积大、实时测量的优势,可为水污染防治等领域提供可靠的技术支撑。 相似文献
54.
Geomorphic diversity as a river management tool and its application to the Ganga River,India 总被引:1,自引:0,他引:1 下载免费PDF全文
Understanding of geomorphic processes and the determination of geomorphic diversity in catchments are prerequisites for the sustainable rehabilitation of river systems and for reach‐scale assessment of river health. The Ganga River system in India is a large, complex system consisting of several long tributaries, some >1,000 km, originating from 2 distinct hinterlands—the Himalaya to the north and the cratons to the south. Traversing through a diverse climatic regime across the Plain and through precipitation zones ranging from 600 mm/year near Delhi to 1,200 mm/year in the eastern plains, the Ganga River system has formed very diverse landform assemblages in 3 major geomorphic domains. We have recognized 10 different river classes for the trunk river from Gangotri (source) to Farakka (upstream of its confluence with the Brahmaputra) based on (a) landscape setting, (b) channel and active floodplain properties, and (c) channel planform parameters. The mountainous stretch is characterized by steep valleys and bedrock channels and is dominated by large‐scale sediment production and transport through hill slope processes. The alluvial part of the river is characterized by 8 different river classes of varying reach lengths (60–300 km) many of which show sharp transitions in landscape setting. We have highlighted the application of this approach for the assessment of habitat suitability, environmental flows, and flood risk all of which have been significantly modified during the last few decades due to large‐scale anthropogenic disturbances. We suggest that the diversity embedded in this geomorphic framework can be useful for developing a sustainable river management programme to “work with” the contemporary character and behaviour of rivers. 相似文献
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This paper addresses the problem of designing controllers that are robust to a great uncertainty in a time constant of the plant. Plants must be represented by minimum phase rational transfer functions of an arbitrary order. The design specifications are: (1) a phase margin for the nominal plant, (2) a gain crossover frequency for the nominal plant, (3) zero steady state error to step commands, and (4) a constant phase margin for all the possible values of the time constant (T): 0<T<∞. We propose a theorem that defines the structure of the set of controllers that fulfil these specifications and show that it is necessary for these robust controllers to include a fractional-order PI term. Examples are developed for both stable and unstable plants, and the results are compared with a standard PI controller and a robust controller designed using the QFT methodology. 相似文献
58.
Effect of Mode of Drying on Microstructure of Potato 总被引:2,自引:0,他引:2
Potato v. Irga was subjected to blanching, and thereafter was dried by convection, puff-drying, and freeze-drying. Microstructure of raw, blanched, and dried tissue was analyzed under the light microscope using computer image analysis. It was found that the tissue of the investigated variety is built up from cells much smaller than those described in literature for other cultivars. Blanching caused starch gelatinization and increase of cross-sectional area of cells. There was no evidence of broken cell walls. Convective drying resulted in cell shrinkage and some breaking of cell walls. It was estimated that some 12% of cells lost integrity during drying. Limited disintegration of the tissue caused by convective drying is attributed to small size of cells, large contact area, and high cohesive forces between cells. Puff-drying damaged the tissue much more than the convective drying. The most devastating to tissue microstructure was freeze-drying, probably freezing per se. 相似文献
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短纤维直径对橡胶复合材料性能的影响 总被引:5,自引:0,他引:5
制备了 3种具有不同直径、相同长径比及其分布的涤纶短纤维增强氯丁橡胶基复合材料。对屈服强度及伸长率、断裂强度及伸长率以及撕裂强度等力学性能的研究发现 :在相同长径比及其分布情况下 ,与传统混合法则不同的是屈服强度和伸长率不相等 ,也不是只取决于短纤维的直径 ,而是受直径和长度的共同作用 ;在相同的纤维体积分数时 ,复合材料的断裂强度基本相同 ,而断裂形变和撕裂强度随纤维直径的减小而增大 相似文献