高剪切力下气泡聚并与破碎特性的数值研究

了解气泡在剪切力场中的聚并与破碎机理及生长与运动特性,对于气液搅拌槽中桨叶的优化设计具有重要意义。将欧拉-欧拉模型与群体平衡模型(population balance model,PBM)进行耦合,对不同剪切力下的气液两相流场进行求解,研究了剪切力、高剪切力下进气速度、气泡塔高度对气泡聚并与破碎的影响,并结合气泡的聚并与破碎模型对高剪切力下气泡的聚并与破碎机理进行了探究。研究表明,剪切力主要影响气泡的破碎,当剪切力较小时其对气泡破碎的影响较小,随着剪切力的增大其对气泡破碎的影响逐渐显著,使小气泡的含量大幅增多;高剪切力下进气速度、气泡塔高度对气泡的聚并与破碎的影响不明显。

高、低剪切力对内皮细胞紧密连接的影响

目的 :研究高、低剪切力对动脉内皮通透性和紧密连接的影响。方法 :饲以普通和高脂肪食的两组日本大耳白兔的腹主动脉狭窄至原横断面积的 6 0 7%± 7 0 % ,7d后处死。动脉用艾万斯蓝和苏丹Ⅳ染色。紧密连接用冷冻蚀刻法检测。结果 :未狭窄腹主动脉染色阴性 ,紧邻狭窄近、远侧 1mm有恒定环行阳性区和距狭窄 8mm远侧内有散在点、片状阳性区。冷冻蚀刻显示在通透性增高区 ,狭窄远侧小带状型紧密连接的百分率明显低于近侧(P <0 0 1) ,远侧小带状和斑状型紧密连接的条数明显低于近侧 (P <0 0 1)。结论 :高、低剪切力导致内皮通透性增高及紧密连接变化 。

高剪切力活化血小板钙离子反应的研究

目的 检测细胞外钙离子 (Ca2 + )浓度对高剪切力诱导血小板聚集的影响 ,并测定高剪切力活化血小板时血小板内Ca2 + 浓度的变化 ,探讨Ca2 + 在剪切力活化血小板中的作用。方法 用锥板黏度计施加高剪切力作用 ,以荧光抗体CD6 1PerCP标记血小板 ,流式细胞术 (FCM )测定血小板聚集率。以荧光染料Fluo 3AM标记血小板 ,FCM测定高剪切力作用后血小板内Ca2 + 浓度 ;并测定二磷酸腺苷 (ADP)对高剪切力作用下Ca2 + 反应的影响。结果 洗涤全血标本或加入钙离子螯合剂乙二醇四乙酸 (EGTA) ,造成细胞外低钙或无钙环境 ,高剪切力诱导的血小板聚集率由 5 9 6 %±5 1%下降到很低水平 ,而加入外源性Ca2 + 在一定程度上增强这种聚集。全血标本受到高剪切力作用 ,血小板内Ca2 + 浓度发生明显的升高 ;增加细胞外Ca2 + 浓度能增强这种反应 ,降低细胞外Ca2 + 浓度或阻断血小板膜糖蛋白GPⅠb/Ⅸ与血浆血管假性血友病因子 (vWF)之间的相互作用 ,使血小板Ca2 + 反应消失 ,而阻断GPⅡb/Ⅲa与血浆vWF之间的相互作用则无明显影响。低浓度的ADP与高剪切力对血小板钙离子反应有协同作用。结论 细胞外Ca2 + 是高剪切力诱导血小板聚集的必需条件 ,血小板内Ca2 + 反应可能是剪切力活化血小板时信息传递的重要物质基础。

老年大鼠后肢高血流剪切力诱导的侧支血管生长及其与血管生成素-1表达的关系

目的:检测老年大鼠后肢高血流剪切力诱导的侧支血管生长情况及其与血管生成素-1(Ang-1)表达的关系。方法:实验组取12只老年健康SD大鼠,左侧行股动静脉单纯分离,右侧行股动静脉吻合术,在1周与4周时间点分别处死6只大鼠,采用血管造影与共聚焦免疫荧光术分别观察侧支血管生长情况及Ang-1在血管处的表达情况,正常组3只大鼠用作正常对照组。结果:正常对照组的侧支血管生长与假手术侧无明显差异,但吻合侧的侧支血管生长明显增加,且4周组吻合侧的血管生长多于1周组。正常对照组的血管Ang-1表达与假手术组无明显差异,仅在血管外膜及部分中膜存在表达;1周组吻合侧的Ang-1不仅在原有表达区域明显表达增加,且在内皮细胞处也有所表达;4周组吻合侧Ang-1在血管各层均明显存在高表达。与假手术侧相比,吻合侧Ang-1表达增加,差异具有统计学意义;4周吻合侧的Ang-1荧光强度较1周吻合侧明显增加,其差异也具有统计学意义。结论:老年大鼠后肢高血流剪切力模型可以诱导侧支血管的生长,且与相应部位血管Ang-1表达的增长呈正相关。

剪切力和pH值的变化对SiC纳米粉体分散行为的影响

在采用超声波和分散剂的基础上,通过控制剪切力和pH值的分散方法,对SiC纳米粉体在水介质中的分散行为进行了研究。结果表明:经过处理后的SiC纳米粉体悬浮液的平均粒度可达51.7nm左右,稳定时间从几十分钟提高到一个月以上。

有机高分子絮凝剂动态絮凝的模拟研究

指出了在离心脱水过程中,需对污泥投加絮凝剂进行化学调理,保证脱水效果。通过对有机高分子絮凝剂静态与动态絮凝的模拟研究,考察了絮凝剂在高剪切力下的耐受程度,研究选择了适用于卧螺离心机的絮凝剂。

In-site core disking phenomenon and break mechanism of hard marble:Investigation in 2400 m deep-buried underground laboratory

The core-disk phenomenon has been observed generally in the drilling process under high-stress conditions.This paper presents the in-situ experimental study of the coring-disking failure mechanism of marble in an underground cavens with 2400 m depth.Based on the disk samples in several boreholes with different diameters,both macro-and micro-morphological characteristics of core-disks’break surface were analysis,using 3D optical scanning and electron microscope scanning.Moreover,the numerical back analysis was also used to simulate the drilling process for demonstrating the development of core disking.The in-situ experiment results showed that the failure types of core disking consisted of tensile break and shear break,i.e.,the shear break usually appears in the edge part of break surface,and tensile break appears in the central part.What’s more,the ration of core-disks thickness to borehole diameter is in a relatively stable range.Numerical back analysis indicated this micro asynchronous break of hard marble is induced by high geostress and unloading drill.

Wing crack propagation model under high hydraulic pressure in compressive-shear stress state

A new wing crack model subjected to hydraulic pressure and far-field stresses was proposed considering the effect of hydraulic pressure in wing crack and the connected part of the main crack on the stress intensity factor at the wing crack tip. With the equivalent crack length Ieq of the wing crack introduced, the stress intensity factor Kl at the wing crack tip was as- sumed to the sum of two terms： on one hand a component K1^（1） for a single isolated straight wing crack of length 21, and subjected to hydraulic pressure in the wing crack and far-field stresses; on the other hand a component K1（2） due to the effective shear stress induced by the presence of the equivalent main crack. The lateral tensile stress and hydraulic high pressure are the key factors that induce crack propagation unsteadily. The new wing crack theoretical model proposed can supply references for the study on hydraulic fracture in fractured masses, hydraulic fracturing in rock masses.

Characterization of shear stresses in nickel-based superalloy Mar-M247 when orthogonal machining with coated carbide tools

Mar-M247 is a nickel-based alloy which is well known as difficult-to-machine material due to its characteristics of high strength, poor thermal diffusion and work hardening. Calculation of shear stress by an analytical force model to indicate the effect of coating material, cutting speed, feed rate on tool life and surface roughness was conducted experimentally. Cutting tests were performed using round inserts, with cutting speeds ranging from 50 to 300 rn/min, and feed rates from 0.1 to 0.4 mm/tooth, without using cooling liquids. The behavior of the TiN and TiCN layers using various cutting conditions was analyzed with orthogonal machining force model. Cutting results indicate that different coated tools, together with cutting variables, play a significant role in determining the machinability when milling Mar-M247.

Physical and mechanical properties of sandstone containing a single fissure after exposure to high temperatures

In order to investigate the physical and mechanical properties of sandstone containing fissures after exposure to high temperatures,fissures with different angles α were prefabricated in the plate sandstone samples,and the processed samples were then heated at 5 different temperatures.Indoor uniaxial compression was conducted to analyze the change rules of physical properties of sandstone after exposure to high temperature,and the deformation,strength and failure characteristics of sandstone containing fissures.The results show that,with increasing temperature,the volume of sandstone increases gradually while the quality and density decrease gradually,and the color of sandstone remains basically unchanged while the brightness increases markedly when the temperature is higher than 585 ℃;the peak strength of sandstone containing fissures first decreases then increases when the temperature is between 25℃and 400℃.The peak strain of sandstone containing fissures increases gradually while the average modulus decreases gradually with increasing temperature,and the mechanical properties of sandstone show obvious deterioration after 400 ℃.The peak strain of sandstone containing fissures increases gradually while the average modulus decreases gradually with increasing temperature;with increasing angle αof the fissure,the evolution characteristics of the macro-mechanical parameters of sandstone are closely related to the their own mechanical properties.When the temperature is 800 ℃,the correlation between the peak strength and average modulus of sandstone and the angle α of the fissure is obviously weakened.The failure modes of sandstone containing fissures after high temperature exposure are of three different kinds including:tensile crack failure,tensile and shear cracks mixed failure,and shear crack failure.Tensile and shear crack mixed failure occur mainly at low temperatures and small angles;tensile crack failure occurs at high temperatures and large angles.

Nonlinear elastic-perfect plastic constitutive model of soil-structure interface under high stress

Briefly introduced the simple shear apparatus under high stress that was developed from RMT. A series simple shear tests under high stress show that the relationcurve between shear stress and tangential displacement under high normal stress is different from the hyperbolic curve in direct shear tests, and the complete deformation process of interface under high stress can be described as nonlinear elastic-perfect plastic(NEPP). According to some characteristics of the fitting curve, the deficiency of theNEPP was pointed out. The mathematic 'half value index' was used to illustrate thatWeibull distribution with three parameters (WNEPP) can overcome the mathematical deficiencies of the NEPP. The advantage of the WNEPP is that the fitting curve of WNEPPmore accurately coincided with the testing data was testified by further comparison.

血管性血友病因子与急性心肌梗死关系的研究进展

血管性血友病因子（von Willebrand factor,VWF）是一种主要由血管内皮细胞产生的多聚体糖蛋白,是评估出血和血栓状态的风险因子.在高剪切力环境下,VWF参与血小板的黏附和聚集,并引发血栓形成.急性心肌梗死（acutemyocardial infarction,AMI）是一种以动脉粥样硬化斑块破裂诱发血栓形成,进而使冠状动脉闭塞而发生心肌缺血为病理特征的血栓栓塞性疾病.2015年的统计显示,

Stress-dependent undrained shear behavior of remolded deep clay in East China

Consolidated-isotropically undrained triaxial compression （CIUC） tests were performed on the reconstituted deep clay from a mine in East China. It was consolidated to maximum stresses in the range of 0.3-2.6 MPa. The test results show that the stress-strain-strength properties of the clay during undrained shear are significantly stress-dependent. In particular, in the case of high consolidation pressure, the post-peak drop in strength on stress-strain curves and shear plane in soil specimens are more evident, the peak stress ratio and the axial strain at which this ratio was reached are smaller, and the relationship between pore pressure and axial strain is also significantly different from that for the case of low consolidation pressure. The environmental scanning electron microscope observations and micro analysis lead to an understanding of the physical mechanisms underlying the above stress-dependent mechanical behavior. In addition, the CIUC behaviors of the studied clay are discussed in the context of critical state soil mechanics.

Experimental study on transient flow patterns in simplified saccular intracranial aneurysm models using particle image velocimetry

The hemodynamics of intracranial aneurysm(IA)comprises complex transient flow patterns that affect its growth and rupture.Owing to the combined effects of geometrical factors and pulsatile flow conditions,the transient flow patterns in the IA are still unclear.The purpose of this work is to reveal the effect of the aspect ratio(AR,sac height/neck width)on the evolution of the internal flow patterns and the hemodynamics of the IA.We proposed an easy method to fabricate three simplified elastic IA models and measured the transient flow characteristics by using particle image velocimetry(PIV).Transient vortex structures in the IA modes during a cardiac cycle were systemically measured and many new flow phenomena were found,including the vortex morphology(size,structure,and core location),a high-speed jet,wall compliance effects,and three flow modes during retrograde flow phase.The results show that the AR of the IA affects the transient flow patterns as well as the wall shear stress(WSS)in complex ways.The results could deepen our understanding of the transient flow behaviors in IA and guide related clinical studies.