Pressure shift mediated anoikis of endothelial cells in the flow field in vitro

Dramatic changes of pressure in the local circulation flow field would lead to alterations in biorheological characteristics of Endothelial cells(ECs), and futher resulted in the apoptosis induced by loss of anchorage, a form of cell death known as anoikis. In this study, we set levels of pressure(negative and positive pressure) loaded ECs groups and non-activated cultured ECs ,single shear stress loaded ECs as control group to demonstrate the effects of pressure shift on cell morphogenesis and adhesion. Furthermore, we investigate the effects of pressure shift on ECs proli- feration and apoptosis to elucidate the influences of pressure shift on vitality of ECs. We present these data here to suggest that the negative pressure might be another important factor beyond velocity and shear stress in biomechanical impairment on ECs, then to trigger the apoptosis with the extracellular matrix (ECM) detachment (anoikis). As the negative pressure is thought to play a role in the anoikis process, these results have implications for both the path- ogenesis and therapeutics investigations of stenostic vessel diseases and the future vascular tissue engineering.

Local hydraulic jump effects on sediment deposition in open-channel flume experiments

When a river channel is narrow,bifurcated,or intersected,or when extreme weather or geological disasters cause shed rock masses to occupy a river flood channel,local hydraulic jumps may develop in the channel.Natural disasters such as landslides,floods,and debris flows occur upstream,will result in large transport rate of large-sized gravel particles.Those particles may be blocked in hydraulic jump areas,causing river channel water depth to rise.In this study,the effect of local hydraulic jumps on the sediment deposition rate was investigated in flume experiments.The ratio of upstream and downstream Froude numbers,particle size,Sediment supply intensity,and flow discharge all affected the sediment deposition rate.With increases in the ratio of upstream and downstream Froude numbers,particle size,and sediment supply intensity,the sediment deposition rate increased.The sediment deposition rate decreased with an increase in flow discharge.Approach hydraulic conditions and particle properties jointly determined the sediment deposition rate in a hydraulic jump section,and an empirical formula was developed using those parameters to calculate the sediment deposition rate.Thus,to identify risks and prevent disasters in mountain rivers,local changes in hydraulic conditions and particle properties need to be jointly evaluated.

Air bubble breakup in shear water flows generated by a plug conduit:An experimental investigation

In the context of a sudden contraction plug conduit,the near-wall area experiences a significant shearing effect of water flow,however,the extent to which this shearing effect occurs in bubble-water flow and the related variation mechanisms of air bubble size and number remain unclear.This study employs a model test method to investigate the diffusion process of bubble-water flow in a sudden contraction plug conduit.The size and number of bubbles,as well as their distribution along the shearing section under varying initial air volume conditions,are studied in detail using a high-speed image acquisition system.The experimental findings reveal a self-similar relationship between the number and size of bubbles and their cross-sectional distribution over time.The bubble number and size vary in three stages,i.e.,quasi-suspension,shearing,and shearing completion stages.The direction perpendicular to the conduit exhibits peak values in bubble number distribution over the three stages,with peak value location varying with the near-wall area.As time progresses,the peak value increases,and a larger initial air volume corresponds to a smaller distance of the peak value location from the wall.The size of air bubbles near the wall is consistent with the minimum diameter of air bubbles in shear flow and is hardly affected by the initial air volume.These results aid in comprehending the change law of two-phase water and air flow under a strong shearing effect in the plug conduit,and provide useful insights for hydraulic design in fluid engineering.

Experimental study of the flow field of a high head model pump turbine based on PIV technique

Pumped storage units are the main parts in China’s power construction,as a hot issue concerned by the industry.The pump turbine involves the two-way flows and a multiple condition operation,and its operation flow pattern is very complex.The particle image velocimetry(PIV)is a very effective test technique to determine the internal flow field of pump turbines.This paper discusses the key problems of the pump turbine,based on the PIV experiments under typical conditions of the pump turbine,especially for problems such as the S-shape problem,the hump problem,the pressure fluctuation problem and the cavitation problem.In the internal flow fields under typical conditions are determined.The vortices induced and their development are observed in the PTV test.The flow phenomenon is shown at each operating point.The typical problems of the pump turbine are closely related to the vortex distribution in the internal flow field.From the PIV test results under several working conditions and from the comparisons between the optimal condition and the part load condition,it is seen that the vortex distributions are very different.Vortices at the vane-less area between the guide vane and the runner are closely related to the strong pressure pulsation,the first hump and the S-shape curve.From the PIV results of the cavitation working points,it is seen that the flow angle is changed in the vane-less region and the runner leading edge because of the cavitation bubbles and that the flow angle deviates from the optimal setting angle.From the computational fluid dynamics(CFD)result of the second hump working points,it is concluded that the vortex shedding on the runner leading edge is the main cause of the second hump.

Collapse of cavitation bubbles near air bubbles

The cavitation erosion is one of the common damage modes in water engineering.The study of the interaction among cavitation bubbles,air bubbles and the wall is of great significance for understanding the mechanism of the air entrainment to alleviate the cavitation and to enhance the cavitation erosion mitigation effect of aeration.By using the high-speed camera,the regular patterns of the collapse of cavitation bubbles in the vicinity of the wall and the air bubbles are studied in this paper.It is shown that in the vicinity of air bubbles,the cavitation bubbles may only collapse towards or from air bubbles,while under the dual impacts of air bubbles and the wall,the direction of collapse of the cavitation bubbles depends on the combined vector of the impact forces of the air bubbles and the wall.When the air bubbles are very close to the cavitation bubbles,the air bubbles will be penetrated and stretched by the cavitation bubbles,when the distance between them is short enough,the cavitation bubbles and the air bubbles will connect to form gas-type cavitation bubbles,and the collapse strength will be significantly decreased,when there are two air bubbles near the cavitation bubbles,they may even be penetrated successively by the cavitation bubbles.Thus it can be concluded that during the air entrainment to alleviate the cavitation,the number of air bubbles is more important than the total air concentration.

Collapsing characteristics of gas-bearing cavitation bubble

The cavitation is directly related to the safety of many large water conservancy projects.There are two types of cavitation bubbles,one is generated by the gas nucleus,called the non gas-bearing cavitation bubble,and another is generated by the gas bubble,called the gas-bearing cavitation bubble.They have significantly different collapsing characteristics.This paper studies the cavitation bubbles,generated by a high voltage pulse bubble generation system,and discusses the gas-bearing cavitation bubble's characteristics a from the aspects of the collapse process,the cycle,the size and the collapse strength.It is shown that:(1) the collapse of the gas-bearing cavitation bubbles can be divided into two types:the centripetal collapse and the bisected collapse,(2) the cycle period and the size of the gas-bearing cavitation bubble increase significantly,and the increase norm has a certain relationship with the bubble diameter ratio,(3) the collapse strength of the gas-bearing cavitation bubble decreases significantly.The larger the bubble diameter ratio,the greater the effect will be.

Experimental study of air-water interface properties in self-aerated flows

The microscopic air-water structures and the interface area properties in the self-aerated flows are important research issues in the high-speed self-aerated flows.The present experimental study concerns the mean and medium air chord length distributions in the self-aerated chute flows for different flow Reynolds numbers and air concentration conditions.The relationship between the microscopic and the macroscopic aerated properties in the air-water mixture region is analyzed.The distribution of the microscopic specific air-water interface area with the macroscopic air concentration variation is self-similar in the self-aerated region.In view of the difference of the air-water structure in high and low aerated regions,a new relationship is proposed for predicting the distributions of a specific air-water interface area,and the agreement between the measured and predicted results is satisfactory.