Longitudinal assessment of blood flow velocity waveforms in the healthy human fetus

A longitudinal study was carried out on 30 healthy fetuses in order to assess the modifications of fetal blood flow throughout pregnancy. The pulsatility index was evaluated at two-week intervals by means of pulsed Doppler equipment. In the umbilical artery measurements were performed from 20 weeks onwards, whereas in the descending aorta and internal carotid artery analysis started from 26 weeks onwards. A decrease of the pulsatility index in umbilical artery and in the ratio between the pulsatility indexes in umbilical artery and internal carotid artery was found over the second half of pregnancy.     

Prenatal diagnosis of aortic atresia by colour doppler flow mapping

A case of aortic atresia with insufficiency of mitral valve diagnosed prenatally at 33 weeks of gestation is presented. An accurate diagnosis of this fetal cardiovascular malformation was possible by application of Doppler colour flow mapping, which demonstrated (a) the absence of forward flow in the hypoplastic ascending aorta, (b) reverse flow of blood from the ductus arteriosus into the severely hypoplastic ascending aorta in the late systole, (c) pansystolic mitral valve regurgitation, and (d) absent flow across the foramen ovale as a result of premature closure of the foramen ovale.     

横向极板电收尘器收尘极板的研究

系统地研究了不同形状、尺寸的收尘极板电流密度分布及背风面涡流结构,其结果表明:板型、板宽及回风沟槽高度对电流密度分布具有很大的影响;板宽对背风面涡流结构具有明显的影响;而板型及回风沟槽高度对背风面涡流几乎没有影响.通过比较分析,选出了一种比较理想的极板形状和尺寸.     

Rate constants for the reaction of hydroxyl radicals with HFC-134a

ＲａｔｅｃｏｎｓｔａｎｔｓｆｏｒｔｈｅｒｅａｃｔｉｏｎｏｆｈｙｄｒｏｘｙｌｒａｄｉｃａｌｓｗｉｔｈＨＦＣ－１３４ａＺｈａｎｇＤｅｑｉａｎｇ，ＺｈｏｎｇＪｉｎｘｉａｎＲｅｓｅａｒｃｈＣｅｎｔｅｒｆｏｒＥｃｏＥｎｖｉｒｏｎｍｅｎｔａｌＳｃｉｅｎｃ...     

竖直弯管中含固体颗粒分散泡状流冲蚀预测

目的研究竖直弯管在含固体颗粒分散泡状流下的冲蚀规律,探究管内气液分布、颗粒分布及三维冲蚀形貌之间的关系。方法提出基于VOF模型和DPM模型的瞬态冲蚀数值计算方法,利用Oka等人提出的冲蚀模型及Grant和Tabakoff提出的颗粒-壁面碰撞模型计算管壁冲蚀速率。结果基于VOF和DPM模型的CFD冲蚀计算结果与经验模型及简化CFD模型的计算结果相比,更接近实验值。分散泡状流中,固体颗粒大部分分散在液相中,管道不同截面处的含液率与颗粒粒含量相关性较大,下游直管段和弯头处固体颗粒的粒含量大于上游直管段。含固体颗粒弯管在分散泡状流作用下,冲蚀区域较大,冲蚀最严重位置出现在弯头出口处附近。结论含砂分散泡状流冲蚀条件下,竖直弯管冲蚀形貌与管内气液固分布直接相关,多相流冲蚀瞬态仿真方法可较准确计算气液固分布并预测管道冲蚀。     

环境样品中痕量铅的流动注射在线分离及分光光度检测

1　IntroductionLeadiswellknownasoneofthemosttoxicmetalsandnotedinthefieldofenvironmentalchemistry[1 ] .Theleadconcentrationinnaturalwaterisextremelylow (sub μg·l-1 level)sothatsomepreconcentrationstepmustbeincludedtoassurethesensitivityofaconventionalin…     

鄂中丘陵地区农户生态系统能流分析

本文分析了鄂中丘陵地区一个典型农户生态系统的能流途径,人工辅助能的输入结构,各亚系统的能量输入、输出组成和能量流动关系,以及能量转化效率。以70个农户的样本分析研究了投能结构对能效的影响规律。结果表明,当地农户生态系统仍是一种以有机能为主要人工辅助的封闭性较强的能量转化系统;增加人工辅助能,特别是无机能的投入可以增加能量产出。     

流式细胞计分析海洋微微型浮游生物:样品固定及贮存方法

以流式细胞计为海洋微微型浮游生物的分析工具,研究了醛类固定剂的固定、液氮贮存对于微微型浮游生物的细胞大小、密度、藻红素荧光值(FL2)和叶绿素荧光值(FL3)的影响.实验主要结论为1)液氮环境适于贮存固定的微微型浮游生物样品,而未固定样品在液氮中贮存后细胞密度有损失;2)醛类固定剂对微微型浮游生物样品的细胞密度基本没有影响;3)醛类固定剂可增强微微型浮游生物的荧光强度,其中戊二醛主要影响聚球藻的FL2强度,多聚甲醛主要影响FL3强度.认为多聚甲醛是适用于微微型浮游生物的固定剂,推荐使用浓度为0.8%~1.2%,此外戊二醛浓度为0.05%、多聚甲醛浓度为0.8%~1.2%的混合固定剂亦适用于固定微微型浮游生物.图4参15     

On the selection of primary variables in numerical formulation for modeling multiphase flow in porous media

Selecting the proper primary variables is a critical step in efficiently modeling the highly nonlinear problem of multiphase subsurface flow in a heterogeneous porous-fractured media. Current simulation and ground modeling techniques consist of (1) spatial discretization of mass and/or heat conservation equations using finite difference or finite element methods; (2) fully implicit time discretization; (3) solving the nonlinear, discrete algebraic equations using a Newton iterative scheme. Previous modeling efforts indicate that the choice of primary variables for a Newton iteration not only impacts computational performance of a numerical code, but may also determine the feasibility of a numerical modeling study in many field applications. This paper presents an analysis and general recommendations for selecting primary variables in simulating multiphase, subsurface flow for one-active phase (Richards' equation), two-phase (gas and liquid) and three-phase (gas, water and nonaqueous phase liquid or NAPL) conditions. In many cases, a dynamic variable switching or variable substitution scheme may have to be used in order to achieve optimal numerical performance and robustness. The selection of primary variables depends in general on the sensitivity of the system of equations to the variables selected at given phase and flow conditions. We will present a series of numerical tests and large-scale field simulation examples, including modeling one (active)-phase, two-phase and three-phase flow problems in multi-dimensional, porous-fractured subsurface systems.