层流剪应力对内皮细胞IL-8受体CXCR1表达的影响

为研究内皮细胞在不同时间、不同大小层流剪应力作用下IL-8受体CXCR 1的表达规律,通过体外培养人脐静脉内皮细胞株EA.Hy926细胞,分别施加5.56、10.02、15.27 dyn/cm2三种剪应力,选取剪切1、2、4和8 h等4个时间点进行观测,Western blot检测IL-8受体CXCR 1表达变化。结果表明,在5.56 dyn/cm2剪应力作用下,与静止组相比,CXCR 1表达随作用时间的增加而显著升高(P<0.01),至4h达到最大值,为对照组的2.2倍。在10.02dyn/cm2剪应力作用下,CXCR 1的表达随剪应力作用时间而相对缓慢增加,但仍高于对照组(P<0.05)。在15.27dyn/cm2剪应力作用下,其CXCR 1的表达随时间呈现较显著性降低(P<0.01),当持续作用8 h,其CXCR 1的表达为对照组62.59%。以上结果表明,不同强度、作用时间的层流剪应力参与调节IL-8受体CXCR 1的表达。

层流剪应力对内皮细胞IL-8受体CXCR2蛋白表达的影响

目的研究内皮细胞在不同时间、不同大小层流剪应力作用下IL-8受体CXCR2的表达规律。方法通过体外培养人脐静脉内皮细胞株EA.Hy926细胞,分别施加5.56、10.02、15.27dyn/cm23种剪应力,以静止组为对照,选取0、1、2、4和8h5个时间点进行采样,West blot检测IL-8受体CXCR2表达变化。结果在5.56dyn/cm2剪应力作用下,与静止组相比,CXCR2表达随作用时间的增加而显著升高(P<0.05),至4h达到最大值,为对照组的4.2倍。在10.02dyn/cm2剪应力作用下,CXCR2的表达随剪应力作用时间而相对缓慢增加,但仍高于对照组(P<0.05)。在15.27dyn/cm2剪应力作用下,其CXCR2的表达随时间呈现较显著性降低(P<0.05),当持续作用8h,其CXCR1的表达为对照组39.14%。结论不同强度、作用时间的层流剪应力参与调节IL-8受体CXCR2的表达。

层流剪应力抑制内皮细胞小管形成

目的流体剪切力是由于血液流动摩擦产生的,内皮细胞可以感应剪切力并根据力的不同调节自身形状和功能,以及病生理相关基因的表达。最近的研究显示,内皮细胞中至少有350种基因受剪切力调节,其中大部分与血管新生有关。血管新生是指在已有血管上形成新血管的过程,这一过程不仅在胚胎发育中起关键作用,在出生后的脏器生长中同样重要,不正常或不成熟的血管新生与多达70余种病变有关。许多证据表明血管新生与流体剪切力间可能存在密切联系,但剪切力的具体作用尚不明确。在过去,因其可以促进一氧化氮的生成,剪切力曾被认为是一种促进血管新生的因素。但近来的体外研究报道剪切力会抑制内皮细胞出芽和入侵三维胶原,这两项功能在血管生成中都具有重要作用。基于此,本文拟对模拟生理环境下,血管内皮细胞小管形成情况进行分析,以探究剪切力在血管新生中的具体作用。方法应用平行平板流动腔向接种于Matrigel胶原上的人脐静脉内皮细胞加载剪切力,并观察内皮细胞小管形成的过程。内皮细胞小管形成是研究血管新生的经典实验之一,主要用于研究血管新生中内皮细胞分化这一过程。整个过程根据基底膜成分的不同,一般持续4~24 h。小管形成实验常用四种变量评估,平均小管长度、小管数量、小管面积和分支点数量。本研究中,采用平均小管长度作为评估指标,因其最易准确测量。结果内皮细胞单层以15 dyn/cm2剪切4 h后,固定细胞并统计小管长度。结果发现层流组的平均小管长度小于静息对照组,表明层流剪切力抑制内皮细胞小管形成。结论应用自主设计的新型流动腔,可以直接对接种于Matrigel胶原上的内皮细胞加载剪切力,使其更接近体内生理环境。研究结果显示剪切环境下的平均小管长度低于静止环境下,说明生理环境下层流剪切力可能对血管新生起抑制作用。

Turbulent boundary layers and hydrodynamic flow analysis of nanofluids over a plate

A numerical analysis of the log-law behavior for the turbulent boundary layer of a wall-bounded flow is performed over a flat plate immersed in three nanofluids(Zn O-water,SiO_(2)-water,TiO_(2)-water).Numerical simulations using CFD code are employed to investigate the boundary layer and the hydrodynamic flow.To validate the current numerical model,measurement points from published works were used,and the compared results were in good compliance.Simulations were carried out for the velocity series of 0.04,0.4 and 4 m/s and nanoparticle concentrations0.1% and 5%.The influence of nanoparticles’ concentration on velocity,temperature profiles,wall shear stress,and turbulent intensity was investigated.The obtained results showed that the viscous sub-layer,the buffer layer,and the loglaw layer along the potential-flow layer could be analyzed based on their curving quality in the regions which have just a single wall distance.It was seen that the viscous sub-layer is the biggest area in comparison with other areas.Alternatively,the section where the temperature changes considerably correspond to the thermal boundary layer’s thickness goes a downward trend when the velocity decreases.The thermal boundary layer gets deep away from the leading edge.However,a rise in the volume fraction of nanoparticles indicated a minor impact on the shear stress developed in the wall.In all cases,the thickness of the boundary layer undergoes a downward trend as the velocity increases,whereas increasing the nanoparticle concentrations would enhance the thickness.More precisely,the log layer is closed with log law,and it is minimal between Y^(+)=50 and Y^(+)=95.The temperature for nanoparticle concentration φ=5%is higher than that for φ=0.1%,in boundary layers,for all studied nanofluids.However,it is established that the behavior is inverted from the value of Y^(+)=1 and the temperature for φ =0.1% is more important than the case of φ =5%.For turbulence intensity peak,this peak exists at Y^(+)=100 for v=4 m/s,Y^(+)=10 for v=0.4 m/s and Y^(+)=8 for v=0.04 m/s.

Interfacial Shear Stress of Stratified Flow in a Horizontal Pipe

Experimental data are presented for the void fraction and the shear stresses of stratified gas-liquid flow in a pipe. A new technique was used to measure the interface shear stress. The interfacial shear stress was determined by using two methods: a momentum balance of gas and an extrapolation of the Reynolds shear stress profile at the gas-liquid interface. A new formula , relating to the interfacial friction factor with the void fraction and superficial gas Reynold number, was developed to predict the interface shear stress . The predicted values are in good agreement with experimental data.

Experimental Investigation of Flow Instabilities in a Laminar Separation Bubble

The present paper reports the results of a detailed experimental study aimed at investigating the dynamics of a laminar separation bubble, from the origin of separation up to the breakdown to turbulence of the large scale co- herent structures generated as a consequence of the Kelvin-Helmholtz instability process. Measurements have been performed along a fiat plate installed within a double contoured test section, designed to produce an adverse pressure gradient typical of Ultra-High-Lift turbine blade profiles, which induces the formation of a laminar separation bubble at low Reynolds number condition. Measurements have been carried out by means of comple- mentary techniques： hot-wire （HW） anemometry, Laser Doppler Velocirnetry （LDV） and Particle Image Veloci- metry （PIV）. The high accuracy 2-dimensional LDV results allow investigating reverse flow magnitude and both Reynolds normal and shear stress distributions along the separated flow region, while the high frequency response of the HW anemometer allows analyzing the amplification process of flow oscillations induced by instability mechanisms. PIV results complement the flow field analysis providing information on the generation and evolu- tion of the large scale coherent structures shed as a consequence of the separated shear layer roll-up, through in- stantaneous velocity vector maps. The simultaneous analysis of the data obtained by means of the different meas- uring techniques allows an in depth view of the instability mechanisms involved in the transition/reattachrnent processes of the separated shear layer.

Experimental Investigation of Dimensionless Velocity and Shearing Stress in Boundary Layer Flow on Continuous Moving Surface in Power Law Fluids

An analysis is carried out to study the steady flow characteristics from a continuous flat surface moving in a parallel free stream of non-Newtonian power law fluid. The constitutive equations of the fluid are transformed into dimensionless ones. The velocity field is measured by Particle Image Velocimetry. Experimental results are obtained for the distribution of velocity. The influence of wall velocity ratio parameter on boundary layer flow field is observed in the experiment. Dimensionless velocity distribution and shearing stress distribution are obtained by post-processing experimental results. The effects of various physical parameters like velocity ratio parameter and similarity variable on various momentum transfer characteristics are discussed in detail and shown graphically. It is indicated that dimensionless velocity increases with velocity ratio parameter and similarity variable, and that dimensionless shearing stress decreases with velocity ratio parameter and similarity variable.