一种改进型体液表观粘度函数测量仪

本文介绍一种性能较好的体液表观粘度函数快测系统,它是在较严密的流变学理论基础上通过较精细的硬、软件设计而研究成功的.其前身为L-1型粘度计,但作了重要改进.它的最大特点是能在一次测量过程完后得到不同切变率下的表观粘度;同时能在通常认为困难却十分重要的“低剪切”段令人满意地工作.     

血液的触变性和粘弹性研究及其临床意义

血液流变性研究,到目前为止,多集中于稳定流动条件下血液的表观粘度及其影响因素。由于血液已达到流变学平衡,用稳态处理方法及表观粘度无法得知和反映决定血液流变性特点的血液内部结构成份是否随时间而变化的情况。实际上,人体血液流动是由心脏搏出的脉动流。血液在这种非平衡条件下的瞬时流动和周期流动中具有许多重要性质。近年来引起人们注意并研究得最多的是血液的触变性(thixotropy)和粘弹性。从单纯的流变学观     

纳米通道技术及应用

纳米通道技术是近年来发展的一种直接解读核酸分子编码信息的新方法,它通过将单链核酸上的核苷酸序列直接转化为电信号,能以每秒超过1 000个碱基的速度对其进行超快速序列分析,较现有测序方法更简便快速和省钱.该技术除可用于核酸超快速外,还在病原体基因诊断、单核苷酸多态性和样品多成分的快速检测等多个领域有重要用途.     

蛇口壳属一中国新记录种

Ophiostoma Syd.& P.Syd.(蛇口壳属)建于1919年(见Kirk et al.2001),该属真菌是经济上重要的病原真菌.它的许多种都能引起木材变色,如O.piliferum(Fr)Syd.& P. Syd.和O.ips(Rumbold)Nannf.是较普遍的木材变色真菌(Verral 1939).     

蛇口壳属一中国新纪录种

<正>Ophiostoma Syd.&P.Syd.(蛇口壳属)建于1919年(见Kirk et al.2001),该属真菌是经济上重要的病原真菌。它的许多种都能引起木材变色,如O.piliferum(Fr.)Syd.&P.Syd.和O.ips(Rumbold)Nannf.是较普遍的木材变色真菌(Verral 1939)。另外,O.ulmi(Buisman)Nannf.是荷兰榆树病的病原菌,致病性     

EN-2:脊椎动物中一种多功能转录因子

EN-2(Engrailed-2)蛋白是同源盒蛋白转录因子EN(Engrailed)在脊椎动物中的一个亚型,它能被细胞分泌和内摄,并调节转录和翻译.EN-2蛋白在脊椎动物的胚胎发育过程中具有重要作用,是神经系统喙尾(A-P)轴分化的重要决定因子,并控制着中脑多巴胺能神经元的发育和存活.新近研究发现,EN-2蛋白还具有更多的功能,包括轴突导向等;并且与一些疾病相关,如帕金森病;它还被认为是自闭症一类疾病和乳腺癌的候选基因.本文就EN-2蛋白的结构、分布、功能及其与疾病的关系作一综述.     

生物课教改要为当地农村经济发展服务

在长期的生物教学实践中,我深刻地体会到,生物科学在农村具有广阔的应用前景,它不但是一门自然科学的必修课,更重要的是能为农村经济的自我发展,与当地农村的脱贫致富直接相联系.     

取整对Logistic种群模型动态的影响

不考虑环境嗓音,Logistic取整模型的种群动态是非混沌的,只会出现稳态和周期;在1＜r＜3和0＜r＜1区间,取整模型较原始模型能较快收敛到定态或者灭绝;增大K不能消除取整效应;取整模型周期长度受初值、K值和r值的影响;取整是混沌控制的一条新途径,它可能是自然种群中很少能检测到混沌的重要原因之一．     

血浆浓度对人全血粘弹特性的影响

改变人血的血浆浓度,观察人血粘弹性和不同剪切率下表观粘度的变化,目的是了解血浆浓度与血液粘弹性以及不同剪切率下表观粘度之间的关系。为临床上采取血浆除去法(Plasmapheresis)提供理论基础。 11袋新鲜人血由中心血站供给,血液是从健康输血员肘前静脉抽取,用枸橼酸钠粉剂抗凝。先将血液分装在10个试管内,离心10分钟,转速2500rpm。将血浆和血细胞分开。取     

B淋巴细胞刺激因子（BLyS）研究进展

B淋巴细胞刺激因子（BLyS）是1999年新发现的一种重要的细胞因子,属于肿瘤坏死因子(TNF)超家族成员.在体液免疫调控中起重要作用.它能强烈地刺激B淋巴细胞的增殖和分化并分泌大量免疫球蛋白(主要为IgM);在体外其过量表达能促进多种B系肿瘤细胞的生长.BLyS转基因小鼠出现严重的红斑狼疮样症状.对BLyS的基因和蛋白质结构、免疫调控功能、受体和信号通路及其在自身免疫性疾病和恶性肿瘤中的作用进行了综述.     

Some perspectives on the viscosity of actin filaments

Measurements of the dynamic viscosity of various actin filament preparations under conditions of low and controlled shear: (a) confirm the shear rate dependence of F-actin viscosities and show that this dependence obeys the power law relationship observed for entangled synthetic polymers; (b) permit estimation of the extent to which shear artifact amplifies changes in the apparent viscosity of F-actin measured in a falling ball viscometer; (c) show that gel-filtration chromatography of actin and the addition of cytochalasin B to F-actin bring about small (20-40%) changes in the viscosity of the F-actin solutions. These variations are consistent with alterations in the actin-binding protein concentrations required for incipient gelation, a parameter inversely related to average filament length. Therefore: (a) changes in the viscosity of F-actin can be magnified by use of the falling ball viscometer, and may exaggerate their biological importance; (b) chromatography of actin may not be required to obtain meaningful information about the rheology of actin filaments; (c) changes in actin filament length can satisfactorily explain alterations in F-actin viscosity exerted by cytochalasin B and by chromatography, obviating the need to postulate specific interfilament interactions.     

A programmable, computer-controlled cone-plate viscometer for the application of pulsatile shear stress to platelet suspensions

Described is a special purpose cone-plate viscometer that is capable of acceleration or deceleration through a step change in speed in less than 0.7s. The speed of the rotating cone is controlled by a microcomputer which can be programmed to generate speed vs time ramp functions of variable slope. Prior calibration of motor power required to shear Newtonian fluids of known viscosity at various speeds provides the basis for determination of apparent suspension viscosity and enables the viscometer automatically to compensate for changing sample viscosity during shear. The viscometer was used to carry out a series of preliminary studies in which platelet-rich plasma (PRP) was subjected to continuous and pulsatile shear stress at 37 degrees C. Shear-induced platelet aggregation (SIPAG) was significantly greater in response to pulsatile versus continuous shearing except at the lowest applied stress (10 dyn/cm2). Increases ranged from about 40 percent at a stress amplitude of 25 dyn/cm2 to nearly 55 percent at dyn/cm2. This increasing trend with stress amplitude might be interpreted as a positive correlation between SIPAG and the loading rate. Dense granule release, as indicated by serotonin release, was dependent on both stress amplitude and number of pulses even at the higher stress where SIPAG was independent of pulse number.     

Measurement of blood viscosity using mass-detecting sensor

A newly designed mass-detecting capillary viscometer is extended to measure the viscosity of whole blood over a range of shear rates without the use of anticoagulants in a clinical setting. In the present study as proof of principle, a single measurement of liquid-mass variation with time replaces the flow rate and pressure drop measurements that are usually required for the operation of a capillary tube viscometer. Using a load cell and capillary, we measured the change of mass flowing through capillary tube with respect to the time, m(t), from which viscosity and shear rate were mathematically calculated. For water and adulterated bloods, excellent agreement was found between the results from the mass-detecting capillary viscometer and those from a commercially available rotating viscometer. Also, the mass-detecting capillary viscometer measured the viscosity of unadulterated whole blood without heparin or EDTA. This new method overcomes the drawbacks of conventional viscometers in the measurement of the whole blood viscosity. First, the mass-detecting capillary viscometer can accurately and consistently measure the unadulterated blood viscosity over a range of shear rates in less than 2 min without any anticoagulants. Second, this design provides simplicity (i.e. ease of operation, no moving parts, and disposable) and low cost.     

Quantitative characterization of blood rheological behavior in transient flow with a model including a structure parameter

Transient rheological behavior of blood which involves non newtonian viscosity, elasticity and thixotropy can be modelized with a Maxwell rheological state equation which depends on a structure parameter having dimension of a shear rate. Identification of the model parameters leads to use an exponential apparent shear rate step and to use recursive filters for taking into account the impulse response of the viscometer servo-control device. Typical results for a normal blood sample are given.     

Blood's critical Taylor number and its flow behavior at supercritical Taylor numbers

When the inner cylinder of a fluid-filled Couette viscometer is rotated rapidly, a vortical flow pattern develops when a dimensionless value referred to as the critical Taylor number (Tc) is reached. We have determined its magnitude in our viscometer for three Newtonian fluids and for blood at 37 degrees C, using the inflection point of torque/RPM vs. RPM (sudden rise in apparent viscosity). Its position was identified by least squares line fitting. Because blood was studied, the viscosity used in Tc calculation was the apparent bob shear stress/shear rate ratio at the inflection marking vortical flow onset. For glycerol-water mixtures Tc was 41.8 +/- 0.3 (N = 11), for propylene glycol 42.0 +/- 0.2 (N = 14), for silicone oil 41.8 +/- 0.2 (N = 11). For healthy blood Tc was 40.7 +/- 0.9 (N = 140). This evidence against blood's increased resistance to flow instability was accompanied by a slower rate of rise in torque both above and below Tc compared to the three Newtonian fluids. Newtonian fluids and blood both developed wavy vortical flow at a rotation rate moderately higher than Tc. Blood resisted this unstable flow behavior more than the Newtonian fluids but it also experienced a slower rate of rise in torque with increasing rotation rate above the critical Taylor number. Shear-thinning is the simplest explanation for blood's mildly altered Taylor vortex behavior; blood's resistance to flow instability is otherwise not found to be sufficient to affect its flow stability in man.     

Cell concentration control by viscosity

The apparent viscosity of baker's yeast suspensions was employed to control the cell concentration of the mixing of baker's yeast and distilled water. The apparent viscosity of baker's yeast was found to be a function of cell concentration and independent of the flow rate through the rotational viscometer. The viscometer and mixing unit were found to have first order dynamics. The open loop dynamics of the control system were nonlinear but could be linearized for small perturbations. The control system was employed to successfully control the cell concentration but exhibited nonlinear behavior.     

A new capillary viscometer for whole blood viscosimetry

A new capillary system was developed, incorporating infrared sensors, which allowed the determination of whole blood viscosity over a wide range of shear stresses. Flow conditions were defined by the geometry of the capillary and the sample pressure head. Whole blood was considered to be a power law fluid and a modified Mooney's formula was used for the calculation of the related invariants. The new viscometer proved to be very simple in use, requiring one run, had a short measuring time and utilised a small test sample volume. However it can be used for whole blood viscosity measurements only at medium and high shear stresses.     

Theoretical and experimental analysis of the sedimentation kinetics of concentrated red cell suspensions in a centrifugal field: determination of the aggregation and deformation of RBC by flux density and viscosity functions

The flow properties of blood are mostly determined using various viscometric approaches, and described in terms of a shear rate or shear stress dependent apparent viscosity. The interpretation of results are rather difficult, especially at low shear rates when particle sedimentation and migration within the viscometer gap are significant. By contrast, analysing the separation process in concentrated RBC suspensions in a centrifugal field also yields information about the viscosity function, including particle-particle interaction and deformation parameters. In this paper, the sedimentation process is approached by means of the theory of kinematic waves and theoretically described by solving the corresponding one-dimensional quasi-linear partial differential equation based on viscosity/flow function as a function of volume concentration. The sedimentation kinetics of rigid spherical RBC suspended in saline and normal RBC suspended in Dx-saline solutions were investigated by means of a separation analyser (LUMiFuge 114). The instrument detects the light transmission over the total length of the cell containing the suspension. During centrifugation the analyser automatically determines the position of the particle free fluid/suspension interface or the sediment by means of a special algorithm. The data obtained with sedimentation of rigid spherical RBC at different volume concentrations demonstrate that, in the case of suspensions rotated in containers of constant cross section, there is good agreement between the theory of kinematic waves developed by Anestis and Schneider (1983) and the results of the experiments. Such good agreement was obtained even though a restrictive one-dimensional model was used to obtain the theoretically derived sedimentation time course. In addition, we describe an algorithm enabling the experimental determination of the viscosity and related flux density function to be made for any suspension. Through this approach, we investigated in detail the rheological behavior of suspended rigid spheres at low Reynolds numbers ranging from 10(-6) to 10(-3). The method here introduced also enabled us to investigate RBC suspensions with respect to the deformability and interactions of the cells by means of the separation analysis. Normal, rigid as well as aggregating RBC exhibited marked differences in the sedimentation kinetics, which were quantified by means of the flux and viscosity functions based on the theory of kinematic waves.     

Model-independent relationships between hematocrit,blood viscosity,and yield stress derived from Couette viscometry data

This paper describes a procedure, based on Tikhonov regularization, for obtaining the shear rate function or equivalently the viscosity function of blood from Couette viscometry data. For data sets that include points where the sample in the annulus is partially sheared the yield stress of blood will also be obtained. For data sets that do not contain partially sheared points, provided the shear stress is sufficiently low, a different method of estimating the yield stress is proposed. Both the shear rate function and yield stress obtained in this investigation are independent of any rheological model of blood. This procedure is applied to a large set of Couette viscometer data taken from the literature. Results in the form of shear rate and viscosity functions and yield stress are presented for a wide range of hematocrits and are compared against those reported by the originators of the data and against independently measured shear properties of blood.     

Rheology of embryonic avian blood

Shear stress, a mechanical force created by blood flow, is known to affect the developing cardiovascular system. Shear stress is a function of both shear rate and viscosity. While established techniques for measuring shear rate in embryos have been developed, the viscosity of embryonic blood has never been known but always assumed to be like adult blood. Blood is a non-Newtonian fluid, where the relationship between shear rate and shear stress is nonlinear. In this work, we analyzed the non-Newtonian behavior of embryonic chicken blood using a microviscometer and present the apparent viscosity at different hematocrits, different shear rates, and at different stages during development from 4 days (Hamburger-Hamilton stage 22) to 8 days (about Hamburger-Hamilton stage 34) of incubation. We chose the chicken embryo since it has become a common animal model for studying hemodynamics in the developing cardiovascular system. We found that the hematocrit increases with the stage of development. The viscosity of embryonic avian blood in all developmental stages studied was shear rate dependent and behaved in a non-Newtonian manner similar to that of adult blood. The range of shear rates and hematocrits at which non-Newtonian behavior was observed is, however, outside the physiological range for the larger vessels of the embryo. Under low shear stress conditions, the spherical nucleated blood cells that make up embryonic blood formed into small aggregates of cells. We found that the apparent blood viscosity decreases at a given hematocrit during embryonic development, not due to changes in protein composition of the plasma but possibly due to the changes in cellular composition of embryonic blood. This decrease in apparent viscosity was only visible at high hematocrit. At physiological values of hematocrit, embryonic blood viscosity did not change significantly with the stage of development.