In vivo label-free measurement of blood flow velocity symmetry based on dual line scanning third-harmonic generation microscopy excited at the 1700 nm window

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.

CFD numerical simulation of flow velocity characteristics of hydrocyclone

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.

Pore structure and liquid flow velocity distribution in water-saturated porous media probed by MRI

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.

EXPERIMENTAL INVESTIGATION ON INDUCED FLOW VELOCITY OF PLASMA AERODYNAMIC ACTUATION

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.

Effect of flow velocity on corrosion behavior of AZ91D magnesium alloy at elbow of loop system

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.

3D FEM simulation of flow velocity field for 5052 aluminum alloy multi-row sprocket in cold semi-precision forging process

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.

Model for seawater fouling and effects of temperature,flow velocity and surface free energy on seawater fouling

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.

Assessment of Coronary Flow Velocity Reserve by Noninvasive Transthoracic Doppler Echocardiography in Patients with Angiographically Normal Coronary Arteries

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.

Effective(kinetic freeze-out) temperature, transverse flow velocity, and kinetic freeze-out volume in high energy collisions

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.

Velocity distribution of the flow field in the cyclonic zone of cyclone-static micro-bubble flotation column

Laboratory experiments have been conducted to study the flow field in a cyclone static micro-bubble flotation column. The method of Particle Image Velocimetry (PIV) was used. The flow field velocity distribution in both cross section and longitudinal section within cyclonic zone was studied for different circulating volumes. The cross sectional vortex was also analyzed. The results show that in cross section as the circulating volume increases from 0.187 to 0.350 m 3 /h, the flow velocity ranges from 0 to 0.68 m/s. The flow field is mainly a non-vortex potential flow that forms a free vortex without outside energy input. In the cyclonic region the vortex deviates from the center of the flotation column because a single tangential opening introduces circulating fluid into the column. The tangential component of the velocity plays a defining role in the cross section. In the longitudinal section the velocity ranges from 0 to 0.08 m/s. The flow velocity increases as does the circulating volume. Advantageous mineral separation conditions arise from the combined effects of cyclonic flow in cross and longitudinal section.

Flow characteristics and regime transition of aqueous foams in porous media over a wide range of quality,velocity,and surfactant concentration

Aqueous foam is broadly applicable to enhanced oil recovery(EOR).The rheology of foam as a function of foam quality,gas and liquid velocities,and surfactant concentration constitute the foundation of its application.The great variations of the above factors can affect the effectiveness of N2 foam in EOR continuously in complex formations,which is rarely involved in previous relevant studies.This paper presents an experimental study of foam flow in porous media by injecting pre-generated N2 foam into a sand pack under the conditions of considering a wide range of gas and liquid velocities and surfactant concentrations.The results show that in a wide range of gas and liquid velocities,the pressure gradient contours are L-shaped near the coordinate axes,but V-shaped in other regions.And the surfactant concentration is a strong factor influencing the trend of pressure gradient contours.Foam flow resistance is very sensitive to the surfactant concentration in both the high-and low-foam quality regime,especially when the surfactant concentration is less than CMC.The foam quality is an important variable to the flow resistance obtained.There exists a transition point from low-to high-quality regime in a particular flow system,where has the maximum flow resistance,the corresponding foam quality is called transition foam quality,which increases as the surfactant concentration increases.The results can add to our knowledge base of foam rheology in porous media,and can provide a strong basis for the field application of foams.

Effects of flow velocity on electrochemical behavior of seachest 5083-H116 Al alloy for ship

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.

Rill flow velocity affected by the subsurface water flow depth of purple soil in Southwest China

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.

Theoretical analysis of stack gas emission velocity measurement by optical scintillation

Theoretical analysis for an online measurement of the stack gas flow velocity based on the optical scintillation method with a structure of two parallel optical paths is performed. The causes of optical scintillation in a stack are first introduced. Then, the principle of flow velocity measurement and its mathematical expression based on cross correlation of the optical scintillation are presented. The field test results show that the flow velocity measured by the proposed technique in this article is consistent with the value tested by the Pitot tube. It verifies the effectiveness of this method. Finally, by use of the structure function of logarithmic light intensity fluctuations, the theoretical explanation of optical scintillation spec- tral characteristic in low frequency is given. The analysis of the optical scintillation spectrum provides the basis for the measurement of the stack gas flow velocity and particle concentration simultaneously.

Modeling of the Changes in Flow Velocity on Seawalls under Different Conditions Using FLOW-3D Software

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°.

Design aspect of a novel L-shaped pulsed column for liquid–liquid extraction applications: Energy consumption and the characteristics velocity concept

This article deals with the evaluation of the consumption of energy for a steady state solvent extraction in a novel L-shaped pulsed sieve-plate column, which is highly required for design and optimization of the periodic flow processes for industrial applications. In this regard, a comprehensive evaluation on the energy consumption in case of a pulsed flow for three different chemical systems is conducted and besides the influence of pulsation intensity, the effect of geometrical parameters including the plate spacing and the plate free area is investigated as well. Moreover, the concept of characteristic velocity models at flooding points is evaluated with respect to the variation of pressure drop along the column at different operational conditions.

Multi-decadal variations in glacier flow velocity and the influencing factors of Urumqi Glacier No.1 in Tianshan Mountains, Northwest China

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.

Gas-kinetic numerical method for solving mesoscopic velocity distribution function equation

A gas-kinetic numerical method for directly solving the mesoscopic velocity distribution function equation is presented and applied to the study of three-dimensional complex flows and micro-channel flows covering various flow regimes. The unified velocity distribution function equation describing gas transport phenomena from rarefied transition to continuum flow regimes can be presented on the basis of the kinetic Boltzmann-Shakhov model equation. The gas-kinetic finite-difference schemes for the velocity distribution function are constructed by developing a discrete velocity ordinate method of gas kinetic theory and an unsteady time-splitting technique from computational fluid dynamics. Gas-kinetic boundary conditions and numerical modeling can be established by directly manipulating on the mesoscopic velocity distribution function. A new Gauss-type discrete velocity numerical integra- tion method can be developed and adopted to attack complex flows with different Mach numbers. HPF paral- lel strategy suitable for the gas-kinetic numerical method is investigated and adopted to solve three-dimensional complex problems. High Mach number flows around three-dimensional bodies are computed preliminarilywith massive scale parallel. It is noteworthy and of practical importance that the HPF parallel algorithm for solving three-dimensional complex problems can be effectively developed to cover various flow regimes. On the other hand, the gas-kinetic numerical method is extended and used to study micro-channel gas flows including the classical Couette flow, the Poiseuillechannel flow and pressure-driven gas flows in twodimensional short micro-channels. The numerical experience shows that the gas-kinetic algorithm may be a powerful tool in the numerical simulation of microscale gas flows occuring in the Micro-Electro-Mechanical System （MEMS）.

Detailed string stability analysis for bi-directional optimal velocity model

The class of bi-directional optimal velocity models can describe the bi-directional looking effect that usually exists in the reality and is even enhanced with the development of the connected vehicle technologies. Its combined string stability condition can be obtained through the method of the ring-road based string stability analysis. However, the partial string stability about traffic fluctuation propagated backward or forward was neglected, which will be analyzed in detail in this work by the method of transfer function and its H∞ norm from the viewpoint of control theory. Then, through comparing the conditions of combined and partial string stabilities, their relationships can make traffic flow be divided into three distinguishable regions, displaying various combined and partial string stability performance. Finally, the numerical experiments verify the theoretical results and find that the final displaying string stability or instability performance results from the accumulated and offset effects of traffic fluctuations propagated from different directions.

The Effects of Chinese Medicines on Micro-circulation of Nail Folds and Blood Flow Velocity of Limbs in the Patients with Arteriosclerotic Obliteration

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.