Ischemic stroke is the leading cause of death in the Chinese population.The incidence of cerebral infarction is higher in high-altitude regions,particularly those above 3,500 m,than in populations residing at lower al...Ischemic stroke is the leading cause of death in the Chinese population.The incidence of cerebral infarction is higher in high-altitude regions,particularly those above 3,500 m,than in populations residing at lower altitudes[1].There are various speculations regarding the mechanisms behind this phenomenon,one of which is that the low oxygen content and cold climate at high altitudes may increase the occurrence of vascular diseases[2].The multifactorial effect of high-altitude environments on residential populations makes it challenging for researchers to determine the specific pathways through which these diseases occur.展开更多
Visualizing blood flow velocity distribution is essential for comprehending the pathogenesis of various diseases and facilitating early diagnosis and treatment.Current hemodynamic studies utilizing optical coherence t...Visualizing blood flow velocity distribution is essential for comprehending the pathogenesis of various diseases and facilitating early diagnosis and treatment.Current hemodynamic studies utilizing optical coherence tomography(OCT)primarily rely on Doppler OCT(D-OCT)and OCT Angiography(OCTA),which measure axial blood vessel velocity or visualize the vascular architecture,respectively.However,these techniques have limitations in accurately quantifying the absolute velocity of red blood cells(RBCs).This study presents a novel method based on microsphere tracking,which enables precise quantification of absolute blood flow velocity along a blood vessel.In phantom experiments,freshly harvested blood mixed with microspheres was infused into a cellulose tube to simulate a single blood vessel.Experimental results,demon-strating an error margin of less than 10%,validated the effectiveness of this method.Blood flow velocities ranging from 0.472 mm/s to 18.9 mm/s were accurately measured.A preliminary in vivo examination of rabbit ear vessels was conducted,further validating the reliability of this method.This study presents a potential method for specific disease diagnosis by detecting tar-geted vessel flow velocity variations using swept-source optical coherence tomography(SS-OCT)combined with microsphere tracking.展开更多
A CFD based numerical simulation of flow velocity of hydrocyclone was conducted with different structural and operational parameters to investigate its distribution characteristics and influencing mechanism. The resul...A CFD based numerical simulation of flow velocity of hydrocyclone was conducted with different structural and operational parameters to investigate its distribution characteristics and influencing mechanism. The results show there exist several unsymmetrical envelopes of equal vertical velocities in both upward inner flows and downward outer flows in the hydrocyclone, and the cone angle and apex diameter have remarkable influence on the vertical location of the cone bottom of the envelope of zero vertical velocity. It is also found that the tangential velocity isolines exist in the horizontal planes located in the effective separation region of hydrocyclone. The increase of feed pressure has almost no effect on the distribution characteristics of both vertical velocity and tangential velocity in hydrocyclone, but the magnitude and gradient of tangential velocity are increased obviously to make the motion velocity of high density particles to the wall increased and to make the cyclonic separation effect improved.展开更多
Magnetic resonance imaging （MRI） was used to probe the structure and flow velocity within the interparticle space of a packed bed of agar beads under water-saturated condition. The images of the velocity field at th...Magnetic resonance imaging （MRI） was used to probe the structure and flow velocity within the interparticle space of a packed bed of agar beads under water-saturated condition. The images of the velocity field at three different flow rates were obtained. To determine the pore-parameter of the porous media, the internal structure of the bed was also obtained using image processing technique. The results show that the porosity of the sample is 31.28% and the fitting curve for the distribution of pore equivalent diameter follows Gaussian distribution. The velocity profiles do shift as the flow rate varies and the solution flow through the void space is not a homogeneous flow in any pores. The velocity distributions within the pore are roughly parabolic with the local maximum being near the center. About half of the velocity components are in the class of 0-1 cm/s. The frequency of lower velocity components is lower at higher flow rate, but to higher velocity components, it is just the opposite.展开更多
Plasma flow control is an active flow control technology that based on the plasma aerodynamic actuation. It can be used to enhance the aerodynamic characteristics of aircraft and propulsion systems. To study the pheno...Plasma flow control is an active flow control technology that based on the plasma aerodynamic actuation. It can be used to enhance the aerodynamic characteristics of aircraft and propulsion systems. To study the phenomena occurring in plasma aerodynamic actuation and the mechanism of plasma flow control, the induced flow velocity of the plasma aerodynamic actuator is experimentally investigated under a variety of parameter conditions. The results indicate that plasma aerodynamic actuation accelerates the near surface air at velocities of a few meters per second, and there is an angle about 5° between the mainstream and the actuator wall and a spiral vortex is formed when the induced flow is moving along the wall. Besides, with the fixed frequency, the induced flow velocity increases linearly with the applied voltage, but it is insensitive to the frequency when the applied voltage is fixed. And the configuration is an effective factor for the performance of the plasma aerodynamic actuator.展开更多
A loop system was used to investigate the effect of flow velocity on corrosion behavior of AZ91 D magnesium alloy at an elbow of loop system based on array electrode technology by polarization, computational fluid dyn...A loop system was used to investigate the effect of flow velocity on corrosion behavior of AZ91 D magnesium alloy at an elbow of loop system based on array electrode technology by polarization, computational fluid dynamics(CFD) simulation and surface analysis. The experimental results showed that the corrosion rate increased with increasing flow velocity, and a critical flow velocity could exist in the corrosion of AZ91 D magnesium alloy. When flow velocity exceeded the critical flow velocity, fluid hydrodynamics was dominant in the corrosion of AZ91 D magnesium alloy. On the contrary, the electrochemical factors were dominant.展开更多
Based on the design of the multi-row sprocket with a new tooth profile,a cold semi-precision forging process for manufacturing 5052 aluminum alloy multi-row sprocket was presented.Through simulating the forging proces...Based on the design of the multi-row sprocket with a new tooth profile,a cold semi-precision forging process for manufacturing 5052 aluminum alloy multi-row sprocket was presented.Through simulating the forging process of 5052 aluminum alloy sprocket billet with 3D rigid-viscoplastic FEM,both the distributions of flow velocity field in axial(U_Z),radial(U_R) and circumferential(U_θ) directions and the curves of velocity component in different deformation regions were respectively obtained.By comparison and analysis of the velocity varying curves,the velocity component relation conditions for filling the die cavity were clarified.It shows that when the die cavity is almost fully filled,the circumferential velocity U_θ increases sharply,implying that U_θplays a key role in fully filling the die cavity.展开更多
Objective Cerebral autoregulation(CA)is the mechanism by which constant cerebral blood flow is maintained despite changes in cerebral perfusion pressure.CA can be evaluated by dynamic monitoring of cerebral blood flow...Objective Cerebral autoregulation(CA)is the mechanism by which constant cerebral blood flow is maintained despite changes in cerebral perfusion pressure.CA can be evaluated by dynamic monitoring of cerebral blood flow velocity(CBFV)with transcranial Doppler sonography(TCD).The present study aimed to explore CA in chronic anxiety.Methods Subjects with Hamilton anxiety scale scores〉14 were enrolled and the dynamic changes of CBFV in response to an orthostatic challenge were investigated using TCD.Results In both the anxious and the healthy subjects,the mean CBFV was significantly lower in the upright position than when supine.However,the CBFV changes from supine to upright differed between the anxious and the healthy groups.Anxious subjects showed more pronounced decreases in CBFV with abrupt standing.Conclusion Our results indicate that cerebrovascular modulation is compromised in chronic anxiety;anxious subjects have some insufficiency in maintaining cerebral perfusion after postural change.Given the fact that anxiety and impaired CA are associated with cardiovascular disease,early ascertainment of compromised cerebrovascular modulation using TCD might suggest interventional therapies in the anxious population,and improve the primary prevention of cardiovascular disease.展开更多
Understanding the transport of humic acids（HAs） in porous media can provide important and practical evidence needed for accurate prediction of organic/inorganic contaminant transport in different environmental media...Understanding the transport of humic acids（HAs） in porous media can provide important and practical evidence needed for accurate prediction of organic/inorganic contaminant transport in different environmental media and interfaces. A series of column transport experiments was conducted to evaluate the transport of HA in different porous media at different flow velocities and influent HA concentrations. Low flow velocity and influent concentration were found to favor the adsorption and deposition of HA onto sand grains packed into columns and to give higher equilibrium distribution coefficients and deposition rate coefficients, which resulted in an increased fraction of HA being retained in columns.Consequently, retardation factors were increased and the transport of HA through the columns was delayed. These results suggest that the transport of HA in porous media is primarily controlled by the attachment of HA to the solid matrix. Accordingly, this attachment should be considered in studies of HA behavior in porous media.展开更多
A kinetic model was proposed to predict the seawater fouling process in the seawater heat exchangers.The new model adopted an expression combining depositional and removal behaviors for seawater fouling based on the K...A kinetic model was proposed to predict the seawater fouling process in the seawater heat exchangers.The new model adopted an expression combining depositional and removal behaviors for seawater fouling based on the Kern–Seaton model.The present model parameters include the integrated kinetic rate of deposition(k d)and the integrated kinetic rate of removal(k r),which have clear physical signi ficance.A seawater-fouling monitoring device was established to validate the model.The experimental data were well fitted to the model,and the parameters were obtained in different conditions.SEM and EDX analyses were performed after the experiments,and the results show that the main components of seawater fouling are magnesium hydroxide and aluminum hydroxide.The effects of surface temperature,flow velocity and surface free energy were assessed by the model and the experimental data.The results indicate that the seawater fouling becomes aggravated as the surface temperature increased in a certain range,and the seawater fouling resistance reduced as the flow velocity of seawater increased.Furthermore,the effect of the surface free energy of metals was analyzed,showing that the lower surface free energy mitigates the seawater fouling accumulation.展开更多
Summary： The measurement of coronary flow velocity reserve （CFVR） by transthoracic Doppler echocardiography （TTDE） with invasive intracoronary Doppler flow wire technique （ICD） was validated and the pathologica...Summary： The measurement of coronary flow velocity reserve （CFVR） by transthoracic Doppler echocardiography （TTDE） with invasive intracoronary Doppler flow wire technique （ICD） was validated and the pathological factors which influence CFVR in patients with angiographically normal coronary arteries were analyzed. CFVR was determined successfully in left anterior descending artery （LAD） in 37 of 40 patients with angiographically normal coronary arteries （men 22, women 15, age 20-75 years, mean age 54±12 years）. Coronary flow velocity was measured in the distal LAD by TTDE with contrast enhancement at baseline and during intravenous adenosine infusion of 110 μg/ kg per min within 48 h after ICD technique. Average peak velocity at baseline （APVb）, average peak velocity during hyperemia （APVh） and CFVR determined from TTDE were correlated closely with those from ICD measurements （APVb： y= 0. 64x＋ 5. 04, r=0. 86, P〈0. 001; APVh： y=0. 63x＋14. 36, r=0.82, P〈0.001; CFVR： y=0.65xq-0.92, r=0.88, P〈0.001）. For CFVR measurements, the mean differences between TTDE and ICD methods were 0. 12±0.39. CFVR in patients with history of hypertension was significantly lower than that in patients without history of hypertension （P〈0.05）. Intravascular ultrasound （IVUS） was performed in 34 patients. Plaque formation was found in LAD by IVUS in 17 （50%） patients. No significant difference in CFVR was found between the patients without plaque formation （3. 11±0. 49） and those with plaque formation （2. 76±0.53, P=0. 056）. It is suggested that TTDE with contrast enhancement provides reliable measurement of APV and CFVR in the distal I.AD. The early stage of atherosclerosis could be detected by IVUS, which may be normal in angiography. CFVR is impaired in patients with history of hypertension compared with that in patients without history of hypertension.展开更多
High-lift siphon drainage by 4-mm internal diameter siphon hoses is a real-time, free-power, and long-term approach for slope drainage. The conventional hydraulics formula for pressurized pipe flow is generally used t...High-lift siphon drainage by 4-mm internal diameter siphon hoses is a real-time, free-power, and long-term approach for slope drainage. The conventional hydraulics formula for pressurized pipe flow is generally used to calculate the single-phase velocity of siphon flow. However, an intensive cavitation phenomenon occurs in the high-lift siphon hose and then a two-phase flow is formed. Research on the velocity of high-lift siphon flow is a prerequisite for the application of siphon drainage with a 4-mm siphon hose. Few investigations of this subject have been carried out. Hence, experiments on the high-lift （8 m〈H0〈10.3 m） siphon drainage in a 4-mm siphon hose were performed. The characteristics of siphon flow under different conditions were ob- served and test data were obtained. Comparisons between test results and calculated results showed that significant errors were given by the hydraulics formula. It is demonstrated that the effect of gas in a siphon hose should be included in the calculation of flow velocity. The findings can be used to determine the number of siphon hoses and layout of siphon drainage holes, and provide valuable information for geotechnical companies.展开更多
The transverse momentum spectra of different types of particles produced in central and peripheral gold–gold(Au–Au)and inelastic proton–proton(pp)collisions at the Relativistic Heavy Ion Collider,as well as in cent...The transverse momentum spectra of different types of particles produced in central and peripheral gold–gold(Au–Au)and inelastic proton–proton(pp)collisions at the Relativistic Heavy Ion Collider,as well as in central and peripheral lead-lead(Pb–Pb)and pp collisions at the Large Hadron Collider,are analyzed by the multi-component standard(Boltzmann–Gibbs,Fermi–Dirac,and Bose–Einstein)distributions.The obtained results from the standard distribution give an approximate agreement with the measured experimental data by the STAR,PHENIX,and ALICE Collaborations.The behavior of the effective(kinetic freeze-out)temperature,transverse flow velocity,and kinetic freeze-out volume for particles with different masses is obtained,which observes the early kinetic freezeout of heavier particles as compared to the lighter particles.The parameters of emissions of different particles are observed to be different,which reveals a direct signature of the mass-dependent differential kinetic freeze-out.It is also observed that the peripheral nucleus–nucleus(AA)and pp collisions at the same center-of-mass energy per nucleon pair are in good agreement in terms of the extracted parameters.展开更多
Electrochemical behavior of 5083-H116 Al alloy with flow velocity of seachest material for Al ship was evaluated.To examine the electrochemical characteristics of flow velocity and its effects on the performance of th...Electrochemical behavior of 5083-H116 Al alloy with flow velocity of seachest material for Al ship was evaluated.To examine the electrochemical characteristics of flow velocity and its effects on the performance of the alloy,experiments were conducted at four flow velocity variables using static state with an agitator.An ultrasonic vibration generator using piezoelectric effect was used in cavitation test according to the requirements of in ASTM-G32.The results show that the corrosion current density and damage were increased by applying the flow velocity compared to static state.Therefore,it is determined that the case of applying flow velocity is weaker to the corrosion.展开更多
Subsurface water flow above the weakly permeable soil layer commonly occurs on purple soil slopes.However,it remains difficult to quantify the effect of subsurface water flow on the surface flow velocity.Laboratory ex...Subsurface water flow above the weakly permeable soil layer commonly occurs on purple soil slopes.However,it remains difficult to quantify the effect of subsurface water flow on the surface flow velocity.Laboratory experiments were performed to measure the rill flow velocity on purple soil slopes containing a subsurface water flow layer with the electrolyte tracer method considering 3 subsurface water flow depths(SWFDs:5,10,and 15 cm),3 flow rates(FRs:2,4,and 8 L min^(-1)),and 4 slope gradients(SGs:5°,10°,15°,and 20°).As a result,the pulse boundary model fit the electrolyte transport processes very well under the different SWFDs.The measured rill flow velocities were 0.202 to 0.610 m s^(-1) under the various SWFDs.Stepwise regression results indicated a positive dependence of the flow velocity on the FR and SG but a negative dependence on the SWFD.The SWFD had notable effects on the rill flow velocity.Decreasing the SWFD from 15 to 5 cm increased the flow velocity.Moreover,the flow velocities under the 10-and 15-cm SWFDs were 89%and 86%,respectively,of that under the 5-cm SWFD.The flow velocity under the 5-,10-and 15-cm SWFDs was decreased to 89%,80%,and 77%,respectively,of that on saturated soil slopes.The results will enhance the understanding of rill flow hydrological processes under SWFD impact.展开更多
Seawalls are among protective structures that are constructed for decreasing the level of wave force and/or protecting from other structures. In this regard, more accurate investigation of these structures takes great...Seawalls are among protective structures that are constructed for decreasing the level of wave force and/or protecting from other structures. In this regard, more accurate investigation of these structures takes great importance from different perspectives. This research investigates the change of the velocity on seawall crown by considering the obstacles in different layouts and slopes. FLOW-3D has been used in this research for modeling. The results of the modeling show that the existence of obstacles has a determinative role in decreasing flow rate in the crown of seawalls. Also, as it was expected, the slope factor on upstream seawalls is very determinative in decreasing this rate such that the lowest velocity on the wall occurs in D-state layout and the slope of 45°.展开更多
Measurement of bloodflow velocity is key to understanding physiology and pathology in vivo.While most measurements are performed at the middle of the blood vessel,little research has been done on characterizing the in...Measurement of bloodflow velocity is key to understanding physiology and pathology in vivo.While most measurements are performed at the middle of the blood vessel,little research has been done on characterizing the instantaneous bloodflow velocity distribution.This is mainly due to the lack of measurement technology with high spatial and temporal resolution.Here,we tackle this problem with our recently developed dual-wavelength line-scan third-harmonic generation(THG)imaging technology.Simultaneous acquisition of dual-wavelength THG line-scanning signals enables measurement of bloodflow velocities at two radially symmetric positions in both venules and arterioles in mouse brain in vivo.Our results clearly show that the instantaneous bloodflow velocity is not symmetric under general conditions.展开更多
Urumqi Glacier No. 1 is a representative glacier in the inland areas of Central Asia and is the only Chinese reference glacier in the World Glacier Monitoring Service. In this study, we explored multi-decadal variatio...Urumqi Glacier No. 1 is a representative glacier in the inland areas of Central Asia and is the only Chinese reference glacier in the World Glacier Monitoring Service. In this study, we explored multi-decadal variations in the flow velocity of the glacier and the influencing factors based on continuous field observations and path coefficient analysis. Results show that the glacier flow velocity decreased from 5.5 m/a in 1980/1981 to 3.3 m/a in 2010/2011. The annual variation in the direction of glacier flow velocity in the western branch and eastern branch was less than 1°–3°, and the change of glacier flow velocity in the western branch was more dramatic than that in the eastern branch. Glacier flow velocity was influenced by glacier morphology（including glacier area, glacier length, and ice thickness）, glacier mass balance and local climate conditions（air temperature and precipitation）, the glacier morphology being the leading factor. The long-term flow velocity data set of Urumqi Glacier No. 1 contributes to a better understanding of glacier dynamics within the context of climatic warming.展开更多
The effects of Chinese medicines on micro-circulation and blood flow velocity in arteries of the lower limbs were observed in 33 patients with arteriosclerotic obliteration(ASO).The results showed that the integral va...The effects of Chinese medicines on micro-circulation and blood flow velocity in arteries of the lower limbs were observed in 33 patients with arteriosclerotic obliteration(ASO).The results showed that the integral values of micro-circulation after treatment were obviously higher than those before treatment (P<0.05 or P<0.01).Blood flow velocity in arteries of the lower limbs determined with the color Doppler ultrasound detecting method after treatment were also obviously higher than those before treatment (P<0.05 or P<0.01).In tbis series of 33 ASO patients,the markedly effective rate was 36.36%,and the total effective rate was 63.64%.The observation indicates that the recipe prescribed according to the principle of supplementing qi and activating blood circulation can effectively improve micro-circulation in ASO patients,and accelerate blood flow in arteries of the lower limbs.展开更多
The rheological properties and limited flow velocities of solvent-free nanofluids are crucial for their technologically significant applications.In particular,the flow in a solvent-free nanofluid system is steady only...The rheological properties and limited flow velocities of solvent-free nanofluids are crucial for their technologically significant applications.In particular,the flow in a solvent-free nanofluid system is steady only when the flow velocity is lower than a critical value.In this paper,we establish a rigid-flexible dynamic model to investigate the existence of the upper bound on the steady flow velocities for three solvent-free nanofluid systems.Then,the effects of the structural parameters on the upper bound on the steady flow velocities are examined with the proposed structure-preserving method.It is found that each of these solvent-free nanofluid systems has an upper bound on the steady flow velocity,which exhibits distinct dependence on their structural parameters,such as the graft density of branch chains and the size of the cores.In addition,among the three types of solvent-free nanofluids,the magnetic solvent-free nanofluid poses the largest upper bound on the steady flow velocity,demonstrating that it is a better choice when a large flow velocity is required in real applications.展开更多
基金supported by the National Natural Science Foundation of Chongqing,China(CSTB2022NSCQ-MSX1100)National Natural Science Foundation of China(grant no.82101499).
文摘Ischemic stroke is the leading cause of death in the Chinese population.The incidence of cerebral infarction is higher in high-altitude regions,particularly those above 3,500 m,than in populations residing at lower altitudes[1].There are various speculations regarding the mechanisms behind this phenomenon,one of which is that the low oxygen content and cold climate at high altitudes may increase the occurrence of vascular diseases[2].The multifactorial effect of high-altitude environments on residential populations makes it challenging for researchers to determine the specific pathways through which these diseases occur.
基金supported by the National Natural Science Foundation of China(62175156,81827807)the Science and Technology Commission of Shanghai Municipality(22S31903000)+3 种基金the Collaborative Innovation Project of Shanghai Institute of Technology(XTCX2022-27)the Shenzhen Basic Research Key Project(JCYJ20220818103212026)the Shenzhen Key Technology Project(JSGGZD20220822095200002)the Shenzhen Outstanding Scientific and Technological Innovation Talents Distinguished Young Scientists(RCJC20210609104443085).
文摘Visualizing blood flow velocity distribution is essential for comprehending the pathogenesis of various diseases and facilitating early diagnosis and treatment.Current hemodynamic studies utilizing optical coherence tomography(OCT)primarily rely on Doppler OCT(D-OCT)and OCT Angiography(OCTA),which measure axial blood vessel velocity or visualize the vascular architecture,respectively.However,these techniques have limitations in accurately quantifying the absolute velocity of red blood cells(RBCs).This study presents a novel method based on microsphere tracking,which enables precise quantification of absolute blood flow velocity along a blood vessel.In phantom experiments,freshly harvested blood mixed with microspheres was infused into a cellulose tube to simulate a single blood vessel.Experimental results,demon-strating an error margin of less than 10%,validated the effectiveness of this method.Blood flow velocities ranging from 0.472 mm/s to 18.9 mm/s were accurately measured.A preliminary in vivo examination of rabbit ear vessels was conducted,further validating the reliability of this method.This study presents a potential method for specific disease diagnosis by detecting tar-geted vessel flow velocity variations using swept-source optical coherence tomography(SS-OCT)combined with microsphere tracking.
基金Project (50974033) supported by the National Natural Science Foundation of ChinaProject (N100301002) supported by the Fundamental Research Funds for the Universities, China
文摘A CFD based numerical simulation of flow velocity of hydrocyclone was conducted with different structural and operational parameters to investigate its distribution characteristics and influencing mechanism. The results show there exist several unsymmetrical envelopes of equal vertical velocities in both upward inner flows and downward outer flows in the hydrocyclone, and the cone angle and apex diameter have remarkable influence on the vertical location of the cone bottom of the envelope of zero vertical velocity. It is also found that the tangential velocity isolines exist in the horizontal planes located in the effective separation region of hydrocyclone. The increase of feed pressure has almost no effect on the distribution characteristics of both vertical velocity and tangential velocity in hydrocyclone, but the magnitude and gradient of tangential velocity are increased obviously to make the motion velocity of high density particles to the wall increased and to make the cyclonic separation effect improved.
基金Project(51374035)supported by the National Natural Science Foundation of ChinaProject(2012BAB08B02)supported by the National Science&Technology Pillar Program During the Twelfth Five-year Plan PeriodProject(NCET-13-0669)supported by the New Century Excellent Talents in University of Ministry of Education of China
文摘Magnetic resonance imaging （MRI） was used to probe the structure and flow velocity within the interparticle space of a packed bed of agar beads under water-saturated condition. The images of the velocity field at three different flow rates were obtained. To determine the pore-parameter of the porous media, the internal structure of the bed was also obtained using image processing technique. The results show that the porosity of the sample is 31.28% and the fitting curve for the distribution of pore equivalent diameter follows Gaussian distribution. The velocity profiles do shift as the flow rate varies and the solution flow through the void space is not a homogeneous flow in any pores. The velocity distributions within the pore are roughly parabolic with the local maximum being near the center. About half of the velocity components are in the class of 0-1 cm/s. The frequency of lower velocity components is lower at higher flow rate, but to higher velocity components, it is just the opposite.
基金Supported by the National High Technology Reserach and Development Program of China("863"program)(2005AA753031)the New Century Educational Talents Plan of Ministry of Education of China(NCET-05-0907)~~
文摘Plasma flow control is an active flow control technology that based on the plasma aerodynamic actuation. It can be used to enhance the aerodynamic characteristics of aircraft and propulsion systems. To study the phenomena occurring in plasma aerodynamic actuation and the mechanism of plasma flow control, the induced flow velocity of the plasma aerodynamic actuator is experimentally investigated under a variety of parameter conditions. The results indicate that plasma aerodynamic actuation accelerates the near surface air at velocities of a few meters per second, and there is an angle about 5° between the mainstream and the actuator wall and a spiral vortex is formed when the induced flow is moving along the wall. Besides, with the fixed frequency, the induced flow velocity increases linearly with the applied voltage, but it is insensitive to the frequency when the applied voltage is fixed. And the configuration is an effective factor for the performance of the plasma aerodynamic actuator.
基金Project(51401151)supported by the National Natural Science Foundation of ChinaProjects(2015T80792,2012M511207)supported by the Postdoctoral Science Foundation of China
文摘A loop system was used to investigate the effect of flow velocity on corrosion behavior of AZ91 D magnesium alloy at an elbow of loop system based on array electrode technology by polarization, computational fluid dynamics(CFD) simulation and surface analysis. The experimental results showed that the corrosion rate increased with increasing flow velocity, and a critical flow velocity could exist in the corrosion of AZ91 D magnesium alloy. When flow velocity exceeded the critical flow velocity, fluid hydrodynamics was dominant in the corrosion of AZ91 D magnesium alloy. On the contrary, the electrochemical factors were dominant.
基金Projects(51175363,51274149)supported by the National Natural Science Foundation of China
文摘Based on the design of the multi-row sprocket with a new tooth profile,a cold semi-precision forging process for manufacturing 5052 aluminum alloy multi-row sprocket was presented.Through simulating the forging process of 5052 aluminum alloy sprocket billet with 3D rigid-viscoplastic FEM,both the distributions of flow velocity field in axial(U_Z),radial(U_R) and circumferential(U_θ) directions and the curves of velocity component in different deformation regions were respectively obtained.By comparison and analysis of the velocity varying curves,the velocity component relation conditions for filling the die cavity were clarified.It shows that when the die cavity is almost fully filled,the circumferential velocity U_θ increases sharply,implying that U_θplays a key role in fully filling the die cavity.
基金supported by grants from China Scholarship Council
文摘Objective Cerebral autoregulation(CA)is the mechanism by which constant cerebral blood flow is maintained despite changes in cerebral perfusion pressure.CA can be evaluated by dynamic monitoring of cerebral blood flow velocity(CBFV)with transcranial Doppler sonography(TCD).The present study aimed to explore CA in chronic anxiety.Methods Subjects with Hamilton anxiety scale scores〉14 were enrolled and the dynamic changes of CBFV in response to an orthostatic challenge were investigated using TCD.Results In both the anxious and the healthy subjects,the mean CBFV was significantly lower in the upright position than when supine.However,the CBFV changes from supine to upright differed between the anxious and the healthy groups.Anxious subjects showed more pronounced decreases in CBFV with abrupt standing.Conclusion Our results indicate that cerebrovascular modulation is compromised in chronic anxiety;anxious subjects have some insufficiency in maintaining cerebral perfusion after postural change.Given the fact that anxiety and impaired CA are associated with cardiovascular disease,early ascertainment of compromised cerebrovascular modulation using TCD might suggest interventional therapies in the anxious population,and improve the primary prevention of cardiovascular disease.
基金supported by the Chinese Academy of Sciences(No.KZCX2-XB3-13-02)the National Natural Science Foundation of China(Nos.41271315,91025018)+1 种基金the Program for New Century Excellent Talents in University(No.NCET-13-0487)the Programs from the Northwest A&F University(No.2014YQ007)
文摘Understanding the transport of humic acids（HAs） in porous media can provide important and practical evidence needed for accurate prediction of organic/inorganic contaminant transport in different environmental media and interfaces. A series of column transport experiments was conducted to evaluate the transport of HA in different porous media at different flow velocities and influent HA concentrations. Low flow velocity and influent concentration were found to favor the adsorption and deposition of HA onto sand grains packed into columns and to give higher equilibrium distribution coefficients and deposition rate coefficients, which resulted in an increased fraction of HA being retained in columns.Consequently, retardation factors were increased and the transport of HA through the columns was delayed. These results suggest that the transport of HA in porous media is primarily controlled by the attachment of HA to the solid matrix. Accordingly, this attachment should be considered in studies of HA behavior in porous media.
基金Supported by the Leading Academic Discipline Project of Shanghai Municipal Education Commission(J50502)the Construction of Shanghai Science and Technology Commission(13DZ2260900)
文摘A kinetic model was proposed to predict the seawater fouling process in the seawater heat exchangers.The new model adopted an expression combining depositional and removal behaviors for seawater fouling based on the Kern–Seaton model.The present model parameters include the integrated kinetic rate of deposition(k d)and the integrated kinetic rate of removal(k r),which have clear physical signi ficance.A seawater-fouling monitoring device was established to validate the model.The experimental data were well fitted to the model,and the parameters were obtained in different conditions.SEM and EDX analyses were performed after the experiments,and the results show that the main components of seawater fouling are magnesium hydroxide and aluminum hydroxide.The effects of surface temperature,flow velocity and surface free energy were assessed by the model and the experimental data.The results indicate that the seawater fouling becomes aggravated as the surface temperature increased in a certain range,and the seawater fouling resistance reduced as the flow velocity of seawater increased.Furthermore,the effect of the surface free energy of metals was analyzed,showing that the lower surface free energy mitigates the seawater fouling accumulation.
文摘Summary： The measurement of coronary flow velocity reserve （CFVR） by transthoracic Doppler echocardiography （TTDE） with invasive intracoronary Doppler flow wire technique （ICD） was validated and the pathological factors which influence CFVR in patients with angiographically normal coronary arteries were analyzed. CFVR was determined successfully in left anterior descending artery （LAD） in 37 of 40 patients with angiographically normal coronary arteries （men 22, women 15, age 20-75 years, mean age 54±12 years）. Coronary flow velocity was measured in the distal LAD by TTDE with contrast enhancement at baseline and during intravenous adenosine infusion of 110 μg/ kg per min within 48 h after ICD technique. Average peak velocity at baseline （APVb）, average peak velocity during hyperemia （APVh） and CFVR determined from TTDE were correlated closely with those from ICD measurements （APVb： y= 0. 64x＋ 5. 04, r=0. 86, P〈0. 001; APVh： y=0. 63x＋14. 36, r=0.82, P〈0.001; CFVR： y=0.65xq-0.92, r=0.88, P〈0.001）. For CFVR measurements, the mean differences between TTDE and ICD methods were 0. 12±0.39. CFVR in patients with history of hypertension was significantly lower than that in patients without history of hypertension （P〈0.05）. Intravascular ultrasound （IVUS） was performed in 34 patients. Plaque formation was found in LAD by IVUS in 17 （50%） patients. No significant difference in CFVR was found between the patients without plaque formation （3. 11±0. 49） and those with plaque formation （2. 76±0.53, P=0. 056）. It is suggested that TTDE with contrast enhancement provides reliable measurement of APV and CFVR in the distal I.AD. The early stage of atherosclerosis could be detected by IVUS, which may be normal in angiography. CFVR is impaired in patients with history of hypertension compared with that in patients without history of hypertension.
基金Project supported by the National ＂Twelfth Five-Year＂ Plan for Science ＆ Technology Support Program of China （No. 2012BAK10B06） and the National Natural Science Foundation of China （No. 41272336）
文摘High-lift siphon drainage by 4-mm internal diameter siphon hoses is a real-time, free-power, and long-term approach for slope drainage. The conventional hydraulics formula for pressurized pipe flow is generally used to calculate the single-phase velocity of siphon flow. However, an intensive cavitation phenomenon occurs in the high-lift siphon hose and then a two-phase flow is formed. Research on the velocity of high-lift siphon flow is a prerequisite for the application of siphon drainage with a 4-mm siphon hose. Few investigations of this subject have been carried out. Hence, experiments on the high-lift （8 m〈H0〈10.3 m） siphon drainage in a 4-mm siphon hose were performed. The characteristics of siphon flow under different conditions were ob- served and test data were obtained. Comparisons between test results and calculated results showed that significant errors were given by the hydraulics formula. It is demonstrated that the effect of gas in a siphon hose should be included in the calculation of flow velocity. The findings can be used to determine the number of siphon hoses and layout of siphon drainage holes, and provide valuable information for geotechnical companies.
基金supported by the National Natural Science Foundation of China(Nos.11575103 and 11947418)the Chinese Government Scholarship(China Scholarship Council)+2 种基金the Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi(STIP)(No.201802017)the Shanxi Provincial Natural Science Foundation(No.201901D111043)the Fund for Shanxi‘‘1331 Project’’Key Subjects Construction。
文摘The transverse momentum spectra of different types of particles produced in central and peripheral gold–gold(Au–Au)and inelastic proton–proton(pp)collisions at the Relativistic Heavy Ion Collider,as well as in central and peripheral lead-lead(Pb–Pb)and pp collisions at the Large Hadron Collider,are analyzed by the multi-component standard(Boltzmann–Gibbs,Fermi–Dirac,and Bose–Einstein)distributions.The obtained results from the standard distribution give an approximate agreement with the measured experimental data by the STAR,PHENIX,and ALICE Collaborations.The behavior of the effective(kinetic freeze-out)temperature,transverse flow velocity,and kinetic freeze-out volume for particles with different masses is obtained,which observes the early kinetic freezeout of heavier particles as compared to the lighter particles.The parameters of emissions of different particles are observed to be different,which reveals a direct signature of the mass-dependent differential kinetic freeze-out.It is also observed that the peripheral nucleus–nucleus(AA)and pp collisions at the same center-of-mass energy per nucleon pair are in good agreement in terms of the extracted parameters.
基金Project supported by the Cooperative Promotion Center of Science & Technology of JEONNAM TECHNOPARK and Ministry of Education,Science and Technology (MEST) through the Research & Development support project of JEONNAM southwest science park,Korea
文摘Electrochemical behavior of 5083-H116 Al alloy with flow velocity of seachest material for Al ship was evaluated.To examine the electrochemical characteristics of flow velocity and its effects on the performance of the alloy,experiments were conducted at four flow velocity variables using static state with an agitator.An ultrasonic vibration generator using piezoelectric effect was used in cavitation test according to the requirements of in ASTM-G32.The results show that the corrosion current density and damage were increased by applying the flow velocity compared to static state.Therefore,it is determined that the case of applying flow velocity is weaker to the corrosion.
基金financially supported by the National Natural Science Foundation of China(Nos.41571265 and 42177314)the Key Research and Development Project of Social Livelihood in Chongqing(cstc2018jscx-mszd X0061)the Foundation of Graduate Research and Innovation in Chongqing(CYS21114)。
文摘Subsurface water flow above the weakly permeable soil layer commonly occurs on purple soil slopes.However,it remains difficult to quantify the effect of subsurface water flow on the surface flow velocity.Laboratory experiments were performed to measure the rill flow velocity on purple soil slopes containing a subsurface water flow layer with the electrolyte tracer method considering 3 subsurface water flow depths(SWFDs:5,10,and 15 cm),3 flow rates(FRs:2,4,and 8 L min^(-1)),and 4 slope gradients(SGs:5°,10°,15°,and 20°).As a result,the pulse boundary model fit the electrolyte transport processes very well under the different SWFDs.The measured rill flow velocities were 0.202 to 0.610 m s^(-1) under the various SWFDs.Stepwise regression results indicated a positive dependence of the flow velocity on the FR and SG but a negative dependence on the SWFD.The SWFD had notable effects on the rill flow velocity.Decreasing the SWFD from 15 to 5 cm increased the flow velocity.Moreover,the flow velocities under the 10-and 15-cm SWFDs were 89%and 86%,respectively,of that under the 5-cm SWFD.The flow velocity under the 5-,10-and 15-cm SWFDs was decreased to 89%,80%,and 77%,respectively,of that on saturated soil slopes.The results will enhance the understanding of rill flow hydrological processes under SWFD impact.
文摘Seawalls are among protective structures that are constructed for decreasing the level of wave force and/or protecting from other structures. In this regard, more accurate investigation of these structures takes great importance from different perspectives. This research investigates the change of the velocity on seawall crown by considering the obstacles in different layouts and slopes. FLOW-3D has been used in this research for modeling. The results of the modeling show that the existence of obstacles has a determinative role in decreasing flow rate in the crown of seawalls. Also, as it was expected, the slope factor on upstream seawalls is very determinative in decreasing this rate such that the lowest velocity on the wall occurs in D-state layout and the slope of 45°.
基金funded by the National Natural Science Foundation of China(Grant/Award Numbers 62075135 and 61975126)the Science and Technology Innovation Commission of Shenzhen(Grant/Award Numbers JCYJ20190808174819083 and JCYJ20190808175201640)Shenzhen Science and Technology Planning Project(ZDSYS 20210623092006020).
文摘Measurement of bloodflow velocity is key to understanding physiology and pathology in vivo.While most measurements are performed at the middle of the blood vessel,little research has been done on characterizing the instantaneous bloodflow velocity distribution.This is mainly due to the lack of measurement technology with high spatial and temporal resolution.Here,we tackle this problem with our recently developed dual-wavelength line-scan third-harmonic generation(THG)imaging technology.Simultaneous acquisition of dual-wavelength THG line-scanning signals enables measurement of bloodflow velocities at two radially symmetric positions in both venules and arterioles in mouse brain in vivo.Our results clearly show that the instantaneous bloodflow velocity is not symmetric under general conditions.
基金funded the National Natural Science Foundation of China (41501010, 41401611)the Funds for Creative Research Groups of China (41121001)the Youth Innovation Promotion Association of Chinese Academy of Sciences
文摘Urumqi Glacier No. 1 is a representative glacier in the inland areas of Central Asia and is the only Chinese reference glacier in the World Glacier Monitoring Service. In this study, we explored multi-decadal variations in the flow velocity of the glacier and the influencing factors based on continuous field observations and path coefficient analysis. Results show that the glacier flow velocity decreased from 5.5 m/a in 1980/1981 to 3.3 m/a in 2010/2011. The annual variation in the direction of glacier flow velocity in the western branch and eastern branch was less than 1°–3°, and the change of glacier flow velocity in the western branch was more dramatic than that in the eastern branch. Glacier flow velocity was influenced by glacier morphology（including glacier area, glacier length, and ice thickness）, glacier mass balance and local climate conditions（air temperature and precipitation）, the glacier morphology being the leading factor. The long-term flow velocity data set of Urumqi Glacier No. 1 contributes to a better understanding of glacier dynamics within the context of climatic warming.
文摘The effects of Chinese medicines on micro-circulation and blood flow velocity in arteries of the lower limbs were observed in 33 patients with arteriosclerotic obliteration(ASO).The results showed that the integral values of micro-circulation after treatment were obviously higher than those before treatment (P<0.05 or P<0.01).Blood flow velocity in arteries of the lower limbs determined with the color Doppler ultrasound detecting method after treatment were also obviously higher than those before treatment (P<0.05 or P<0.01).In tbis series of 33 ASO patients,the markedly effective rate was 36.36%,and the total effective rate was 63.64%.The observation indicates that the recipe prescribed according to the principle of supplementing qi and activating blood circulation can effectively improve micro-circulation in ASO patients,and accelerate blood flow in arteries of the lower limbs.
基金Project supported by the National Natural Science Foundation of China(No.12172281)the Fund of the Science and Technology Innovation Team of Shaanxi Province of China(No.2022TD-61)+2 种基金the Open Project of State Key Laboratory of Performance Monitoring and Protecting of Rail Transit InfrastructureEast China Jiaotong University(No.HJGZ2023102)the Shaanxi Province Key Research and Development Project(No.2024SFYBXM-531)。
文摘The rheological properties and limited flow velocities of solvent-free nanofluids are crucial for their technologically significant applications.In particular,the flow in a solvent-free nanofluid system is steady only when the flow velocity is lower than a critical value.In this paper,we establish a rigid-flexible dynamic model to investigate the existence of the upper bound on the steady flow velocities for three solvent-free nanofluid systems.Then,the effects of the structural parameters on the upper bound on the steady flow velocities are examined with the proposed structure-preserving method.It is found that each of these solvent-free nanofluid systems has an upper bound on the steady flow velocity,which exhibits distinct dependence on their structural parameters,such as the graft density of branch chains and the size of the cores.In addition,among the three types of solvent-free nanofluids,the magnetic solvent-free nanofluid poses the largest upper bound on the steady flow velocity,demonstrating that it is a better choice when a large flow velocity is required in real applications.
