有无植物条件下明渠水流紊动特性对比

在可变坡水槽中，模拟了带枝杈植物对明渠水流的干扰作用，借助超声多普勒流速仪（ADV）测量了不同水深下垂线不同测点的瞬时流速，计算了各测点的三维时均流速、脉动强度及雷诺应力等紊动参数，通过与无植物干扰的明渠均匀流紊动特性进行对比，分析植物对水流紊动参数的影响规律。试验结果表明：在有植物明渠水流中，时均流速呈三区分布特征；脉动强度及雷诺应力均在植物顶部附近出现最大值；脉动强度明显增大，在3个方向上趋于接近；可以用植物顶部以上的雷诺应力分布推求摩阻流速。     

弯曲河流水流动力稳定性特征研究

弯曲型河流是自然界最为常见的河流形态,其水流特性以及河床泥沙的作用特性,对河流蠕动发展具有重要的影响,是河流动力学中研究的重要课题.弯曲河道中水流流态的转化涉及河床形态和河势单元的发展模式,包括：弯曲河道三维拟序涡与二次环流产生的条件;不同水流条件下拟序涡尺度分级情况;大尺度紊流结构与河湾自适应、互选择性,等等.本文以弯曲河流明渠为背景,首先对其层流转捩到紊流的特性进行研究,与顺直河道相比,其稳定中性曲线前移,失稳临界雷诺数降低,流动失稳过程中,对扰动波数的响应范围加大,层流更容易失稳.这些研究结果是传统流动稳定性理论中所没有的,本文的研究结果也弥补了这方面的不足和空白.     

基于磁力场与速度场协同的高效微通道磁泳分离

磁泳是实现生化分离的重要手段之一.根据微通道内磁珠运动基本方程导出了影响磁泳分离效率的新因素,即磁场力矢量与流体速度矢量的夹角,提出改善磁力场与流场的协同性是提高磁泳分离效率的重要途径之一,并基于此设计了T型结构微通道磁泳分离芯片.通过建立磁珠运动的二维动力学模型,并运用有限元和龙格库塔法,对微通道内的磁泳分离效率进行了数值模拟研究.结果发现：相同条件下T型微通道分离效率较普通平直微通道明显提高;在高流速下直通道对小粒径磁珠的磁泳分离失效时,T型微通道仍能实现高效分离.进一步分析表明,T型微通道内分离效率提高的本质在于磁力场与流场的协同作用使得磁珠产生更大的偏转速度,从而增加了分离效率.研究结果对磁泳芯片优化设计具有理论指导意义.     

冲泻区水动力特性的数值分析

基于三维非稳态的Navier．Stokes方程，采用有限体积法进行数值离散，在构造高分辨率STACS格式的VOF方法的基础上，建立基于气液两相流的三维自由面流动模型，并基于该模型对三维剪切流场和圆柱水体坍塌进行了三维模拟，检验其数值精度．应用该模型数值研究冲泻区内涌波（bore）在均匀斜坡上的动态传播过程．对上爬水流自由面水位高度与实验数值进行对比，结果显示数值解与实验解吻合较好，模型能很好描述水流的掺气运动．数值分析了涌波崩塌（BoreCollapse）、上冲流（Uprush）和回落流（Backwash）等过程中的自由水面、瞬时流速及床面最大剪切应力的时空分布．结果表明，冲泻区水动力结构时空变化非常复杂，模型能捕捉到高速薄层水流结构，优于前人的数值结果，研究有利于进一步了解冲泻区内的泥沙输运规律及岸滩演变机制．     

单一导电性能的单壁碳纳米管的分离

本文首先简单介绍了单壁碳纳米管的化学结构与导电性性能之间的关系，然后就单壁碳纳米管研究中的一个重要难题，即如何分离金属型和半导体型，概述了目前主要的分离方法和研究结果。     

水利水电工程施工水流控制过程的仿真与优化方法

针对水利水电工程施工水流控制过程中的工程技术问题及其仿真分析中存在的科学技术难题,通过分析施工导流系统动态、非线性的内外部结构,综合考虑主体建筑物、导流建筑物与水流控制三者间的复杂约束关系,建立复杂条件下施工导流系统的时空关系模型和施工导流过程的结构图仿真通用模型,提出了面向结构图的施工导流过程数值仿真方法和三维动态可视化仿真分析方法,并实现了集仿真建模、仿真计算和仿真可视化于一体的施工水流控制过程仿真与优化系统环境．工程实例应用表明,该方法建模过程便捷,仿真计算与数据可视化分析能有效地耦合,仿真与优化分析结果符合客观实际,为解决复杂条件下水利水电工程施工水流难以控制的问题提供了新的理论方法和技术手段．     

阶梯溢流坝水流数值模拟及特性分析

针对Mixture模型,考察了Realizable k-ε模型,SSTk-ω模型,v2-f模型,LES模型等4种湍流模型对阶梯溢流坝水流数值模拟的适用性.通过对非掺气区域坝面平均流速、旋度大小、边界层厚度的计算,并与实验结果进行分析比较,结果表明：Realizable k-ε模型考虑了流体微团的旋转效应,提高了对较大曲率流动、旋流流动和涡旋运动的计算精度,对阶梯溢流坝有很好的适用性.以Realizable k-ε模型计算结果为基础,进一步分析了边界层内的速度分布、阶梯面压力分布等坝面水流特性.     

黄土沟壑区产输沙特征的空间尺度效应研究

以黄土丘陵沟壑区的典型流域岔巴沟为例, 首先通过实测数据分析水沙过程的尺度现象和规律, 明确了流域产输沙的主要子过程及其影响因素和作用机理. 然后采用集成了坡面侵蚀、沟坡区重力侵蚀和沟道不平衡输沙3个子模型的黄河数字流域模型在较高分辨率的单元上模拟研究流域的暴雨—径流—产输沙响应, 结果重现了水沙过程的尺度现象. 在尺度现象是由不同产输沙子过程的空间尺度分布迭加引起的假定下, 对模拟结果进行分析, 发现重力侵蚀和高含沙水流特性是引起黄土沟壑区泥沙过程尺度现象的最主要因素.     

超音速分离管内多组分气体分离的相平衡计算

建立了超音速分离管内多组分气体分离的相平衡数学模型, 并给出了相应的计算方法. 用所提出的模型和求解方法对用于中试的天然气净化分离管内天然气的相平衡特性和分离效果进行了预测, 并与实测结果进行了比较. 结果表明, 预测结果与中试实验结果基本吻合, 证明所建立的数学模型和计算方法的可靠性, 能够较精确地预测气体超音速分离管分离得到的气液两相各组分含量等相平衡参数以及流量、密度等流动参数, 也为超音速分离管的结构优化提供了理论根据.     

液—液旋流分离管中强旋湍流的Reynold应力输运方程数值模拟

应用湍流Ｒｅｙｎｏｌｄ应力输运方程模型（ＤＳＭ）对液－液旋流分离管中的强旋湍流进行了数值模拟，并与ＬＤＶ测量结果进行了比较，结果表明：ＤＳＭ模型不仅较合理地预报出 切向速度的Ｒａｎｋｉｎｅ涡结构及其位置，而且提示了液－液旋流管中切向速度所特有的双峰分布现象；对轴向速度预报给出了近壁下行流，近轴上行流以及介于两者之间的零速区等；湍流动能在肇流管中的继上游近壁在、中部近轴大和下游近似均布，旋流管中的静     

人工蜂群优化算法在复数盲源分离中的应用

针对复值信号的源数估计和有序分离等关键技术,提出一种基于人工蜂群优化的源数未知的复值盲源分离方法,该方法首先利用交叉互验技术来估算复数源信号的个数,然后通过人工蜂群算法优化峰度的绝对值来获得最佳分离向量,并实现了逐次恢复源信号的目的.仿真实验结果表明,该方法不仅能依峰度绝对值的降序实现服从任何分布源信号的盲分离,同时比其他方法具有更优越的估计性能.另外,提出一种基于峰度的欠定复盲源分离算法,该算法根据信号的统计特性构造了用于欠定混合情况下盲抽取向量的代价函数,然后通过人工蜂群算法优化其函数来获得最佳分离向量,通过多次分离来实现欠定复盲源分离的目的.通过对混合分布类型的复值源信号欠定盲分离仿真实验验证了该算法的有效性.     

Tricellulin forms homomeric and heteromeric tight junctional complexes

Sealing of the paracellular cleft by tight junctions is of central importance for epithelia and endothelia to function as efficient barriers between the extracellular space and the inner milieu. Occludin and claudins represent the major tight junction components involved in establishing this barrier function. A special situation emerges at sites where three cells join together. Tricellulin, a recently identified tetraspan protein concentrated at tricellular contacts, was reported to organize tricellular as well as bicellular tight junctions. Here we show that in MDCK cells, the tricellulin C-terminus is important for the basolateral translocation of tricellulin, whereas the N-terminal domain appears to be involved in directing tricellulin to tricellular contacts. In this respect, identification of homomeric tricellulin-tricellulin and of heteromeric tricellulin-occludin complexes extends a previously published model and suggests that tricellulin and occludin are transported together to the edges of elongating bicellular junctions and get separated when tricellular contacts are formed.     

Ultrastructural investigation of fetal rat brain hemisphere tissue in nonadherent stationary organ culture

Summary Fetal rat brain fragments grown in nonadherent stationary organ culture for 50 days have been investigated ultrastructurally. Synaptogenesis and myelin formation occurred at the same time as the corresponding time-dependent events in the developing brain in vivo. Intermediate junctions were observed between cellular processes lining a central cavity in the fragments and later associated with astrocytes at the surface. Gap junctions and tight junctions were also present. In some fragments cilia were observed in the central cavity. Subependymal basement membrane labyrinths were observed in all fragments after 10 days in culture. The ultrastructural characteristics and the tissue-like structure in general were preserved for at least 50 days in this tissue culture system. The brain fragments may therefore be a valuable supplement to existing culture methods for nervous tissue.Research fellow from the Norwegian Research Council for Sciences and Humanities. This work was supported by the Norwegian Cancer Society.     

Intercellular junctions of hyperplastic retinal pigment epithelium

In rats with retinopathies induced by excess fluorescent light or injections of urethane, the retinal pigment epithelium (RPE) undergoes focal hyperplasia. Neither intravascularly injected horseradish peroxidase or lanthanum nitrate penetrated the sensory retina at these hyperplastic sites. Electron microscopy revealed that this was due to the persistence of intact tight junctions among a single layer of hyperplastic cells facing the sensory retina. These junctions prevented intraocularly injected microperoxidase from passing as well. Cells within the hyperplastic foci were connected only by adherent junctions that presented no permeability barrier.     

微纳流体样品片上分离技术

基于微流控技术的细胞或颗粒分离是样品前处理中的一个重要步骤,近些年在生物和化学分析中引起了极大关注,随着微纳米加工技术的发展,分离技术在片上实验室系统的微环境应用中得到快速发展.基于微流体细胞或颗粒的分选技术具有很多优点,包括减少了样品量、加速了样品处理速度、高灵敏度、高空间分辨率、成本低以及便携性等.本文介绍了当前最先进的基于连续微流体细胞或颗粒分选技术,从被动式与主动式分离两方面的典型实例详细阐述了各种分选原理及其在细胞或微颗粒分选中的应用,讨论了这些技术的主要指标,如分选标记、分辨率、效率以及处理量,同时讨论了各类在微流体下的微分离方法存在的缺点.微尺度下高效的微分离技术在实现片上实验室、现场微分析设备和家庭诊断中将会起着越来越重要的作用,引起了众多学者们的研究兴趣,能够促进微分离与检测和信号读取等集成于一体,形成一个便携式的诊疗设备.     

Ultrastructural investigation of fetal rat brain hemisphere tissue in nonadherent stationary organ culture

Fetal rat brain fragments grown in nonadherent stationary organ culture for 50 days have been investigated ultrastructurally. Synaptogenesis and myelin formation occurred at the same time as the corresponding time-dependent events in the developing brain in vivo. Intermediate junctions were observed between cellular processes lining a central cavity in the fragments and later associated with astrocytes at the surface. Gap junctions and tight junctions were also present. In some fragments cilia were observed in the central cavity. Subependymal basement membrane labyrinths were observed in all fragments after 10 days in culture. The ultrastructural characteristics and the tissue-like structure in general were preserved for at least 50 days in this tissue culture system. The brain fragments may therefore be a valuable supplement to existing culture methods for nervous tissue.     

Intercellular junctions of hyperplastic retinal pigment epithelium

Summary In rats with retinopathies induced by excess fluorescent light or injections of urethane, the retinal pigment epithelium (RPE) undergoes focal hyperplasia. Neither intravascularly injected horseradish peroxidase or lanthanum nitrate penetrated the sensory retina at these hyperplastic sites. Electron microscopy revealed that this was due to the persistence of intact, tight junctions among a single layer of hyperplastic cells facing the sensory retina. These junctions prevented intraocularly injected microperoxidase from passing as well. Cells within the hyperplastic foci were connected only by adherent junctions that presented no permeability barrier.Supported by a grant from the National Eye Institute to Dr R. Bellhorn, whose support is greatly appreciated, and an unrestricted grant and a Research Manpower Award from Research to Prevent Blindness, Inc.     

动物外周血单个核细胞分离方法探讨

目的 探索用人淋巴细胞分离液分离多种属动物外用血单个核细胞（PBMCs）的可行性及评价其分离效果,建立一种适于野外大规模多种属动物PBMCs的分离方法.方法 采用人淋巴细胞分离液分离来源于新疆的伊犁马、新疆驴、不同品种犬、新疆双峰驼、天山马鹿和来源于重庆的荣昌猪、中国荷斯坦奶牛、简阳大耳黑山羊外周血PBMCs.随机抽样检测分离的动物PBMCs细胞总数、细胞纯度和细胞活率.结果 用人淋巴细胞分离液成功分离上述8种动物PBMCs,每毫升动物外周血分离的PBMCs细胞总数为0.52×106～2.03×106个,纯度为67%～93%,细胞活率为92.5%-98.0%.结论 用人淋巴细胞分离液分离多种动物PB-MCs的方法宜在动物的病毒分子流行学调查中进一步推广.     

Experiential and cosmopolitan knowledge: The transcontinental field practices of the U.S. Bureau of Biological Survey

Before many of the global environmental knowledge producing networks and technologies emerged later in the twentieth century, another spatially extended form of field science was implemented at a continental scale by the U.S. Bureau of Biological Survey, revealing similar tensions and dynamics. Specimens and observations from across continental spaces were integrated through railroad-based transportation and communications networks in order to map distributions of birds and mammals and delineate “life zones” stretching across the continent. At the same time that field zoologists of the Biological Survey produced this cosmopolitan scientific knowledge, they also developed an intimate, experiential knowledge of many of the places where they traveled. By following the travels of Biological Survey field parties, especially the agency's long-time chief field naturalist Vernon Bailey, during the late nineteenth and early twentieth centuries when the railroad was dominant, this paper traces the interconnections between the two ways of knowing in the Biological Survey's practice. However, the integration of these different forms of knowledge was ultimately partial and incomplete, as seen through the Survey's daily practices such as food consumption, the seasonality of survey field practice, and limitations on what types of knowledge were incorporated from lay network collaborators and field assistants.     

基于恒模特性的单通道时频重叠信号盲分离算法

针对单通道同调制方式、同调制参数时频重叠信号的盲分离问题,基于MSK信号的恒模特性,及对MSK混合信号分量幅度的准确估计,构建了单通道信号盲分离欠定方程组.为解决该方程组的解模糊问题,根据MSK信号相位连续特性,提出了相位方差最小模糊解消除准则.但相位对噪声较为敏感,该准则可能会产生严重的误判现象,又提出了一种基于最小斜率的补充准则.基于以上两种模糊解消除准则,可对单通道信号盲分离欠定方程组的模糊解进行合理选择,有效地实现了MSK时频重叠信号的单通道盲分离.仿真结果表明:在信噪比大于5 dB的条件下,该算法对混合信号具有较好的分离效果.并且该算法具有复杂度低、计算量小的优点.