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Publishing type：Research paper (scientific journal)  

The continuous separation and filtration of particles immersed in fluid flows are important interests in various applications. Although the inertial focusing of particles suspended in a duct flow is promising in microfluidics, predicting the focusing positions depending on the parameters, such as the shape of the duct cross-section and the Reynolds number (Re) has not been achieved owing to the diversity of the inertial-focusing phenomena. In this study, we aimed to elucidate the variation of the inertial focusing depending on Re in rectangular duct flows. We performed a numerical simulation of the lift force exerted on a spherical particle flowing in a rectangular duct and determined the lift-force map within the duct cross-section over a wide range of Re. We estimated the particle trajectories based on the lift map and Stokes drag, and identified the particle-focusing points appeared in the cross-section. For an aspect ratio of the duct cross-section of 2, we found that the blockage ratio changes transition structure of particle focusing. For blockage ratios smaller than 0.3, particles focus near the centres of the long sides of the cross-section at low Re and near the centres of both the long and short sides at relatively higher Re. This transition is expressed as a subcritical pitchfork bifurcation. For blockage ratio larger than 0.3, another focusing pattern appears between these two focusing regimes, where particles are focused on the centres of the long sides and at intermediate positions near the corners. Thus, there are three regimes; the transition between adjacent regimes at lower Re is found to be expressed as a saddle-node bifurcation and the other transition as a supercritical pitchfork bifurcation.

DOI： 10.3390/mi12101242

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Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

Human red blood cells (RBCs) are subjected to high viscous shear stress, especially during microcirculation, resulting in stable deformed shapes such as parachute or slipper shape. Those unique deformed RBC shapes, accompanied with axial or nonaxial migration, cannot be fully described according to traditional knowledge about lateral movement of deformable spherical particles. Although several experimental and numerical studies have investigated RBC behavior in microchannels with similar diameters as RBCs, the detailed mechanical characteristics of RBC lateral movement—in particular, regarding the relationship between stable deformed shapes, equilibrium radial RBC position, and membrane load—has not yet been fully described. Thus, we numerically investigated the behavior of single RBCs with radii of 4 μm in a circular microchannel with diameters of 15 μm. Flow was assumed to be almost inertialess. The problem was characterized by the capillary number, which is the ratio between fluid viscous force and membrane elastic force. The power (or energy dissipation) associated with membrane deformations was introduced to quantify the state of membrane loads. Simulations were performed with different capillary numbers, viscosity ratios of the internal to external fluids of RBCs, and initial RBC centroid positions. Our numerical results demonstrated that axial or nonaxial migration of RBC depended on the stable deformed RBC shapes, and the equilibrium radial position of the RBC centroid correlated well with energy expenditure associated with membrane deformations.

DOI： 10.3390/mi12101162

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DOI： 10.1103/PhysRevFluids.6.L072301

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DOI： 10.3233/BIR-201010

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DOI： 10.1103/PhysRevFluids.4.124307

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer-Verlag Wien  

This paper numerically investigates the shear flow between double concentric spherical boundaries rotating differentially, the so-called spherical Couette flow, under unstable thermal stratification, focusing on the boundary of the axisymmetric/nonaxisymmetric transition in wide-gap cases where the inner radius is comparable to the clearance width. While the transition of SCF has been confirmed experimentally in cases without thermal factor, insufficient knowledge on SCF subject to thermal instability, related to geophysical problems especially in the wide-gap cases, has been accumulated mainly based on numerical analysis
our motivation is to bridge the knowledge gap by a parameter extension. We reconfirm that the transition under no thermal effect is initiated by a disturbance visualised as a spiral pattern with n arms extending from the equatorial zone to the pole in each hemisphere, at the critical Reynolds number, Recr, as previously reported. With increasing thermal factor, the buoyancy effect enables the system rotation to trigger a transition towards nonaxisymmetric states, resulting in a relative decrease in Recr. This is in contrast with the result that the system rotation apparently suppresses via Coriolis effect the transition to the thermally convective states at low Reynolds numbers. The present study elucidates that the existence of the axisymmetric state is restricted within a closed area in the extended parameter space, along the boundary of which the spiral patterns observed experimentally in SCF continuously connect to the classical spherical Bénard convective states.

DOI： 10.1007/s00707-019-02487-8

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DOI： 10.1017/jfm.2019.325

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Physics Publishing  

The osmotically driven flow across a semipermeable membrane under a constant static pressure difference is revisited with reference to previous reports on reverse osmosis. The osmosis due to the local solute concentration difference across the membrane induces solvent seeping flow, which advects solutes in a layer in contact with the membrane and reduces the osmosis itself as a result of nonlinear feedback. A few mathematical techniques for obtaining approximate solutions of the seeping flow and the layer thickness, such as that for inverse problems used in the field of heat transfer, are presented with an emphasis on nonlinear boundary conditions and the time-dependent solvent flow rate. We determined that the layer on the membrane forms rapidly and spontaneously through osmosis at a timescale of (formula presented) and that the layer thickness increases with no upper limit in an infinite time interval. Based on the obtained solution, we also discuss the thermodynamic output work in an irreversible process, which is extracted from the seeping flow as an osmotic engine.

DOI： 10.1088/2399-6528/aafc09

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.73.2.0_2297

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOS Press  

Background: In the microcirculation, red blood cells (RBCs) were observed to be confined to an axial stream surrounded by a marginal RBC depleted layer. This axial accumulation of RBCs is considered to arise from the RBC deformability. Objective: To quantitatively evaluate the effect of RBC deformability on their axial accumulation at a flow condition comparable to that in arterioles by developing a new observation system for accurate measurements of radial RBC positions in the cross section of capillary tubes. Methods: The cross-sectional distributions of normal and hardened RBCs as well as softened RBCs suspended in capillary tube flows were measured with high spatial resolution. A new observation system was developed in which enface views of the cross-section of the tube were obtained at small distances upstream of the outlet at various longitudinal positions in the tube. Results: The radial positions of individual RBCs were detected within 1 μm accuracy. It was found that normal and softened RBCs rapidly migrated away from the wall towards the tube axis, whereas glutaraldehyde-hardened RBCs were dispersed widely over the tube cross-section, depending on the concentration of glutaraldehyde solution. Conclusions: The newly devised observation system revealed quantitatively the essential role of RBC deformability in their axial accumulation.

DOI： 10.3233/BIR-18166

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

The inertial migration of neutrally buoyant spherical particles suspended in tube flows of square cross sections was investigated experimentally in the range of Reynolds numbers (Re) from 1 to 800 for particle-to-tube-size ratios from 0.075 to 0.175. Direct observations of the particle distribution in the cross section at various distances from the tube inlet revealed that at low Re, smaller than a certain critical value, particles were focused on four equilibrium positions, located at the center of channel faces, consistent with previous studies on microchannel flows, whereas at higher Re, larger than another critical value, four additional equilibrium positions were observed near the channel corners. At intermediate Re, between these two critical values, we observed new focusing positions of particles, located on a heteroclinic orbit joining the channel face and corner equilibrium positions. Comparing these results with corresponding numerical simulations, we examined the migration properties in detail and categorized their types. It was found that the critical Re values depended considerably on the particle-to-tube-size ratio.

DOI： 10.1103/PhysRevFluids.2.044201

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CAMBRIDGE UNIV PRESS  

An experimental study of the inertial migration of neutrally buoyant spherical particles suspended in the Poiseuille flow through circular tubes has been conducted at Reynolds numbers (Re) from 100 to 1100 for particle-to-tube diameter ratios of similar to 0.1. The distributions of particles in the tube cross-section were measured at various distances from the tube inlet and the radial probability function of particles was calculated. At relatively high Re, the radial probability function was found to have two peaks, corresponding to the so-called Segre Silberberg annulus and the inner annulus, the latter of which was first reported experimentally by Matas el al. (J. Fluid Mech. vol. 515, 2004, pp. 171-195) to represent accumulation of particles at smaller radial positions than the Segre Silberherg annulus. They assumed that the inner annulus would he an equilibrium position of particles, where the resultant lateral force on the particles disappears, similar to the Segre Silberberg annulus. The present experimental study showed that the fraction of particles observed on the Segre Silberberg annulus increased and the fraction on the inner annulus decreased further downstream, accompanying an outward shift of the inner annulus towards the Segre Silberherg annulus and a decrease in its width. These results suggested that if the tubes were long enough, the inner annulus would disappear such that all particles would be focused on the Segre Silberberg annulus for Re <1000. At the cross-section nearest to the tube inlet, particles were absent in the peripheral region close to the tube wall including the expected Segre Silberberg annulus position for Re > 700. In addition, the entry length after which radial migration has fully developed was found to increase with increasing Re, in contrast to the conventional estimate. These results may he related to the developing flow in the tube entrance region where the radial force profile would he different from that of the fully developed Poiseuille flow and there may not he an equilibrium position corresponding to the Segre Silberherg annulus.

DOI： 10.1017/jfm.2016.881

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The lateral migration of a neutrally buoyant rigid particle suspended in Poiseuille flow was studied using two-dimensional numerical simulations with Reynolds number (Re) ranging from 10 to 1000. A fractional step method and an immersed boundary method were used to analyze the motion of the particle and the lateral force exerted on it. Computation of the particle trajectories showed that suspended particles asymptotically approach a single equilibrium lateral position, the location of which depends on particle size and Re. As Re increases, the equilibrium position moves slightly towards the channel wall at first, then shifts towards the channel centerline. At low Re, the equilibrium positions are closer to the channel centerline for larger particles; at higher Re, equilibrium positions become almost insensitive to particle size.

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.71.1.0_3014

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.71.2.0_2689

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

We studied the single-arm spiral roll state in the system of Boussinesq fluid confined between nonrotating double concentric spherical boundaries with an opposing temperature gradient previously reported by Zhang et al. [Phys. Rev. E 66, 055203(R) (2002)]. It was found that the state exists even in a gap thicker than that used in this previous study, as an autonomously rotating wave solution with a finite constant angular velocity in a nonrotating geometry. We further confirmed that individual spiral roll states bifurcate directly from the static state at a number of intersections of the marginal stability curves. The double convective timescales peculiar to the state may involve global mixing through the entire domain albeit at the onset of convection, where a passive tracer geometrically explores through the entire spherical domain for sufficient time beyond a cell that would be formed by the other highly-symmetric steady states bifurcating at the onset.

DOI： 10.7566/JPSJ.84.103401

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Language：Japanese   Publisher：京都大学  

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Language：Japanese   Publisher：京都大学  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SOC RHEOLOGY, JAPAN  

In blood flow through microvessels, platelets are known to have enhanced concentrations near the vessel wall, which is the so-called "near-wall excess". In the present study, the spatial distribution of platelet-sized polystyrene particles in red cell suspension flowing through microchannels with a square cross-section of 50 pm width was measured by a confocal laser scanning microscope. The measurements were performed at the flow rate of 1.0 mu L/rain for various particle diameters (d = 1.0 - 4.8 mu m) and various volume fractions of red cells (hematocrit; Hct = 0 - 40 %). In the absence of red cells, the particles were uniformly distributed in the channel cross-section. For all cases studied, their distributions were also uniform at the inlet of the channel. At downstream cross-sections, high concentrations of particles near the channel wall were obtained in the presence of red cells. This tendency was enhanced for higher hematocrits and larger particles. The cross-sectional distribution of the particles revealed enhanced particle probability near the channel corners rather than near the center of the channel faces, suggesting that the particles are focused mainly close to the corners due to the square cross-section of the channel.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CAMBRIDGE UNIV PRESS  

The lateral migration properties of a rigid spherical particle suspended in a pressure-driven flow through channels with square cross-sections were investigated numerically, in the range of Reynolds numbers (Re) from 20 to 1000. 'The flow field around the particle was computed by the immersed boundary method to calculate the lateral forces exerted on the particle and its trajectories, starting from various initial positions. 'The numerical simulation showed that eight equilibrium positions of the particle are present at the centres of the channel faces and near the corners of the chatmel cross-section. 'Me equilibrium positions at the centres of the channel faces are always stable, whereas the equilibrium positions at the corners are unstable until Re exceeds a certain critical value, Re-e. At Re Re-e additional equilibrium positions appear on a heteroclinic orbit that joins the channel face and corner equilibrium positions, and the lateral forces along the heteroclinic orbit are very small. As Re increases, the channel face equilibrium positions are shifted towards the channel wall at first, and then shifted away from the channel wall. The channel corner equilibrium positions exhibit a monotonic shift towards the channel corner with increasing Re. Migration behaviours of the particle in the cross-section are also predicted for various Values of Re. rftlese numerical results account for the experimental observations of particle distributions in the cross-section of micro and millimetre scale channels, including the characteristic alignment and focusing of the particles, the absence of the corner equilibrium positions at low Re and the progressive shift of the equilibrium positions with Re.

DOI： 10.1017/jfm.2015.456

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.70.1.0_3143

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japanese Society of Biorheology  

The vascular endothelial surface glycocalyx layer consists of fibrous glycoproteins with a thickness of several hundred nanometers to a few microns. The present study focuses on the function of the glycocalyx layer as a modulator of permeability in water transport across the blood vessel wall. A particulate layer model is developed to analyze the fluid permeation through the glycocalyx layer, which has periodic fibrous structures and finite thickness. Theoretical and numerical computations of the permeation resistance across the layer are performed based on the Stokesian dynamics approach. The results show that the resistance near the ends of the layer is affected considerably by the anisotropy of adjacent particle configurations. We describe such an end effect on the permeability in relation to the layer thickness and particle spacing ratio. It is suggested that the variations in thickness or fiber spacing in the glycocalyx layer could significantly alter its fluid permeation properties.

DOI： 10.17106/jbr.29.11

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CAMBRIDGE UNIV PRESS  

The inertial migration of neutrally buoyant spherical particles in square channel flows was investigated experimentally in the range of Reynolds numbers (Re) from 100 to 1200. The observation of particle positions at several cross-sections downstream from the channel entrance revealed unique patterns of particle distribution which reflects the presence of eight equilibrium positions in the cross-section, located at the centres of the channel faces and at the corners, except for low Re. At Re smaller than approximately 250, equilibrium positions at the corners are absent. The corner equilibrium positions were found to arise initially in the band formed along the channel face, followed by a progressive shift almost parallel to the side wall up to the diagonal line with increasing Re. Further increase in Re moves the corner equilibrium positions slightly toward the channel corner, whereas the equilibrium positions at the channel face centres are shifted toward the channel centre. As the observation sites become downstream, the particles were found to be more focused near the equilibrium positions keeping their positions almost unchanged. These lateral migration behaviours and focusing properties of particles in square channels are different to that observed in microchannels at lower Re and to what would be expected from extrapolating from the results for circular pipes at comparable Re.

DOI： 10.1017/jfm.2014.232

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Science Council of Japan  

In order to investigate the segregation behavior induced by the size difference in suspended particles, we conduct a two-dimensional numerical simulation for suspensions of fluid droplets of two different sizes subjected to a Poiseuille flow between two parallel plates. The large and small droplets are assumed to have equal surface tensions and equal internal viscosities. From the temporal evolutions of the lateral positions of the large and small droplets, it is obtained that the small droplets are displaced closer to the channel walls with increasing fraction of the large droplets whereas the large droplets accumulate more preferentially near the channel centerline with increasing fraction of the small droplets. The probability distribution functions for the droplets indicate that a line of small droplets is formed next to the channel walls at high area fractions, which enhances the size segregation of the droplets.

DOI： 10.11345/nctam.62.69

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japanese Society of Biorheology  

Blood is composed of red blood cells, leukocytes and platelets, which are dispersed in plasma. These particulate components have different size and stiffness. In blood flow, red blood cells are found to flow in the center of vessels. On the other hand, leucocytes and platelets are observed in the vicinity of wall of vessels. This phenomenon is called ‘margination’. In this study, we simulate the behavior of binary droplet dispersion with size and surface tension differences under Couette flow, in order to investigate the mechanism of margination. We found that large floppy droplets migrate toward the center of channel, whereas small stiff droplets marginate near the wall of channel.

DOI： 10.17106/jbr.28.7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Forced retrograde perfusion through the venous system with arterial blood can provide adequate oxygen to peripheral tissues at rest through veno-capillary networks which is the basis for surgical restoration of blood flow by distal vein arterialization (DVA). To be successful such surgery requires disruption of valve leaflets in the veins, which can be accomplished easily in the larger vessels. However, the smallest veins (venules) of less than 100 mu m in diameter, also possess valves, are distributed widely throughout all tissues and are too fine for any effective surgical interference. Thus venular valves cannot be disrupted or dissected with presently available technology. Nevertheless, clinical observations suggest that retrograde peripheral blood flow is rapidly established after DVA surgery. There is as yet no rational explanation for this phenomenon. In the present study, using Laplace's law, we attempt to elucidate the mechanical properties of venules and their valves. We speculate that the remarkably thin venular walls (and especially those of the smaller vessels which have the thinnest walls), are capable of considerable, rapid distension when subjected to increased hemostatic pressure. The increase in diameter of venules in response to the increased blood pressure renders their valve leaflets incompetent, so that the valves themselves cannot close the vessel lumen. In addition, the thin bicuspid leaflets may also be forced open retrogradely by the increased blood pressure.

DOI： 10.1007/978-1-4939-0620-8_42

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

An outline of the state space of planar Couette flow at high Reynolds numbers (Re < 10(5)) is investigated via a variety of efficient numerical techniques. It is verified from nonlinear analysis that the lower branch of the hairpin vortex state (HVS) asymptotically approaches the primary (laminar) state with increasing Re. It is also predicted that the lower branch of the HVS at high Re belongs to the stability boundary that initiates a transition to turbulence, and that one of the unstable manifolds of the lower branch of HVS lies on the boundary. These facts suggest HVS may provide a criterion to estimate a minimum perturbation arising transition to turbulent states at the infinite Re limit.

DOI： 10.1103/PhysRevLett.111.184502

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Language：Japanese   Publishing type：Research paper (scientific journal)  

In order to improve the record of the javelic throw in the junior Olympic games, it is important to elucidate the flight characteristics of the "turbo-jav" used in this throwing event. Unlike the spear used in the javelin throw, the turbo-jav has four tail fins. Focusing on the effect of the fins, we investigate the flight characteristics of the turbo-jav, by means of wind tunnel tests, throwing experiments and numerical simulations. In the wind tunnel test, we measured the drag force, lift force and pitching moment acting on intact turbo-javs as well as turbo-javs with their fins cut, in a low speed wind tunnel at the flow speed up to 25 m/s. The experimental results showed that the drag and lift coefficients for the intact turbo-javs are larger than the corresponding values for the turbo-javs without fins. As the angle of attack increases from 0, the moment coefficients for the intact turbo-javs decrease from 0, whereas the moment coefficients for the turbo-javs without fins increase. In accord with this property for the pitching moment, the throwing experiments showed that intact turbo-javs fly stably with oscillating angle of attack around 0. The flying distance, the orbit and the variation of angle of attack for the intact turbo-javs launched by a launcher agree closely with the numerical simulation performed based on the wind tunnel test. A comparison of throwing experiments by an athlete and by the launcher suggested that the turbo-javs flying without rolling could reach farther than turbo-javs with rolling. © 2013 The Japan Society of Mechanical Engineers.

DOI： 10.1299/kikaib.79.1561

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOS PRESS  

In channel flow of multicomponent suspensions, segregation behavior of suspended components perpendicular to the flow direction is often observed, which is considered to be caused by the differential properties of the lateral migration depending on their shape, size, flexibility, and other characteristics. In the present study, we investigate the effect of size differences between suspended components on the segregation behavior, by a two-dimensional numerical simulation for binary dispersed suspensions of fluid droplets of two different sizes subjected to a plane Poiseuille channel flow. The small and large droplets are assumed to have equal surface tensions and equal viscosity ratios of internal to external fluids. The time evolutions of the lateral positions of large and small droplets relative to the channel centerline were computed by changing the area fraction of the small droplets in a mixture with a constant total area fraction. The large droplets are found to migrate closer to the channel centerline and the small droplets are found to migrate closer to the channel wall compared to the corresponding lateral positions in mono-dispersed suspensions at the same area fractions, although the mean lateral positions of the large and small droplets in mono-dispersed suspension are comparable. This segregation behavior as well as the margination of small droplets are enhanced when the size difference between large and small droplets is increased and the area fraction of large droplets is increased. These results may arise from higher tendencies for the large droplets to approach the channel centerline compared to the small droplets, which consequently expel small droplets from the central region toward the channel walls.

DOI： 10.3233/BIR-130638

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Language：English   Publishing type：Research paper (international conference proceedings)  

In order to investigate the effect of the size differences between suspended particles on the segregation behavior in channel flow of multicomponent suspensions, we conduct a two-dimensional numerical simulation for suspensions of fluid droplets of two different sizes subjected to a plane Poiseuille flow. The large and small droplets are assumed to have equal surface tensions and equal internal viscosities. The temporal evolutions of the lateral positions of the large and small droplets relative to the channel centerline are computed for various size ratios and area ratios of the large and small droplets. It is found that the small droplets tend to migrate toward the channel walls with increasing fraction of the large droplets and that the mean lateral positions of the large droplets are always closer to the channel centerline compared to the mean lateral positions of the small droplets, which represent the margination of the small droplets and the segregation of the droplets caused by the size difference. These trends are enhanced as the size ratio of large and small droplets is increased. Copyright © 2013 by ASME.

DOI： 10.1115/ICNMM2013-73126

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Language：English  

When two solutions differing in solute concentration are separated by a porous membrane, the osmotic pressure will generate a net volume flux of the suspending fluid across the membrane
this is termed osmotic flow. We consider the osmotic flow across a membrane with circular cylindrical pores when the solute and the pore walls are electrically charged, and the suspending fluid is an electrolytic solution containing small cations and anions. Under the condition in which the radius of the pores and that of the solute molecules greatly exceed those of the solvent as well as the ions, a fluid mechanical and electrostatic theory is introduced to describe the osmotic flow in the presence of electric charge. The interaction energy, including the electrostatic interaction between the solute and the pore wall, plays a key role in determining the osmotic flow. We examine the electrostatic effect on the osmotic flow and discuss the difference in the interaction energy determined from the nonlinear Poisson-Boltzmann equation and from its linearized equation (the Debye-Hückel equation). © 2012 Japanese Society of Biorheology.

DOI： 10.1007/s12573-012-0049-4

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOS PRESS  

A fluid mechanical and electrostatic model for the transport of solute molecules across the vascular endothelial surface glycocalyx layer (EGL) was developed to study the charge effect on the diffusive and convective transport of the solutes. The solute was assumed to be a spherical particle with a constant surface charge density, and the EGL was represented as an array of periodically arranged circular cylinders of like charge, with a constant surface charge density. By combining the fluid mechanical analyses for the flow around a solute suspended in an electrolyte solution and the electrostatic analyses for the free energy of the interaction between the solute and cylinders based on a mean field theory, we estimated the transport coefficients of the solute across the EGL. Both of diffusive and convective transports are reduced compared to those for an uncharged system, due to the stronger exclusion of the solute that results from the repulsive electrostatic interaction. The model prediction for the reflection coefficient for serum albumin agreed well with experimental observations if the charge density in the EGL is ranged from approximately -10 to -30 mEq/l.

DOI： 10.3233/BIR-120620

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The diffusion and convection of a solute suspended in a fluid across porous membranes are known to be reduced compared to those in a bulk solution, owing to the fluid mechanical interaction between the solute and the pore wall as well as steric restriction. If the solute and the pore wall are electrically charged, the electrostatic interaction between them could affect the hindrance to diffusion and convection. In this study, the transport of charged spherical solutes through charged circular cylindrical pores filled with an electrolyte solution containing small ions was studied numerically by using a fluid mechanical and electrostatic model. Based on a mean field theory, the electrostatic interaction energy between the solute and the pore wall was estimated from the Poisson-Boltzmann equation, and the charge effect on the solute transport was examined for the solute and pore wall of like charge. The results were compared with those obtained from the linearized form of the Poisson-Boltzmann equation, i.e. the Debye-Huckel equation.

DOI： 10.1088/0169-5983/44/6/065504

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The transport of a spherical solute through a long circular cylindrical pore filled with an electrolyte solution is studied numerically, in the presence of constant surface charge on the solute and the pore wall. Fluid dynamic analyses were carried out to calculate the flow field around the solute in the pore to evaluate the drag coefficients exerted on the solute. Electrical potentials around the solute in the electrolyte solution were computed based on a mean-field theory to provide the interaction energy between the charged solute and the pore wall. Combining the results of the fluid dynamic and electrostatic analyses, we estimated the rate of the diffusive and convective transport of the solute across the pore. Although the present estimates of the drag coefficients on the solute suggest more than 10% difference from existing studies, depending on the radius ratio of the solute relative to the pore and the radial position of the solute center in the pore, this difference leads to a minor effect on the hindrance factors. It was found that even at rather large ion concentrations, the repulsive electrostatic interaction between the charged solute and the pore wall of like charge could significantly reduce the transport rate of the solute.

DOI： 10.1088/0169-5983/43/6/065505

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CAMBRIDGE UNIV PRESS  

An electrostatic model is developed for osmotic flow across a layer consisting of identical circular cylinders with a fixed surface charge, aligned parallel to each other so as to form an ordered hexagonal arrangement. The expression of the osmotic reflection coefficient is derived for spherical solutes with a fixed surface charge suspended in an electrolyte, based on low-Reynolds-number hydrodynamics and a continuum, point-charge description of the electric double layers. The repulsive electrostatic interaction between the surface charges with the same sign on the solute and the cylinders is shown to increase the exclusion region of solute from the cylinder surface, which enhances the osmotic flow. Applying the present model to the study of osmotic flow across the endothelial surface glycocalyx of capillary walls has revealed that this electrostatic model could account well for the reflection coefficients measured for charged macromolecules, such as albumin, in the physiological range of charge density and ion concentration.

DOI： 10.1017/S0022112010003708

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Language：Japanese  

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Other Link： http://hdl.handle.net/10112/7869

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Publishing type：Research paper (scientific journal)  

The electrostatic model for osmotic flow across a porous membrane in our previous study (Akinaga et al. 2008)" was extended to include the streaming potential, for solutes and pores of like charge and fixed surface charge densities. The magnitude of the streaming potential was determined to satisfy zero current condition along the pore axis. It was found that the streaming potential affects the velocity profiles of the pressure driven flow as well as the osmotic flow through the pore, and decreases their flow rates, particularly in the case of large Debye length relative to the pore radius, whereas it has little effect on the reflection coefficients of spherical solutes through cylindrical pores.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：BEGELL HOUSE, INC  

This document describes briefly the homotopy route via which the Hairpin Vortex Solutions (HVS) were recently discovered. The bifurcation sequence starts from the geometrical configuration that is applicable to lateral heating in a vertical channel of infinite extent. Such a system has been studied before and in this note we expose its connection to the turbulent ubiquitous structure of the HVS.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

An electrostatic model for osmotic flow through circular cylindrical pores is developed to describe the reflection coefficient for the membrane transport in the presence of surface charges on the pore wall and the solute. For a spherical solute placed at an arbitrary radial position in the pore, the electrical potential was computed by a spectral element method applied to the Poisson-Boltzmann equation together with the condition of electrical neutrality. The interaction energy between the surface charges was used to estimate the osmotic reflection coefficient. The proposed model predicts that even for a small Debye length compared to the pore radius, the repulsive electrostatic interaction between the surface charges could significantly increase the osmotic flow through the pore.

DOI： 10.1143/JPSJ.77.053401

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

An ideal of osmotic equilibrium between an ideal solution and pure solvent separated by a semipermeable membrane is studied numerically using the method of molecular dynamics. The osmotic flow is observed as the inflow of the solvent across the membrane from the dilute to the concentrated side. The validity of van't Hoff's law for osmotic pressure is confirmed over a wide range of concentrations. It is found that the law is established by a balance between non-uniform partial pressures of solute and solvent. Furthermore, the present model permits an understanding of the mechanism of the osmotic flow in the relaxation process as the liquids evolve from the initial state to the equilibrium state. We focus in particular on the interaction between solute and solvent.

DOI： 10.1143/JPSJ.77.064605

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Science Council of Japan  

With the aid of molecular dynamics, osmotic equilibrium between ideal solution and pure solvent separated by semi-permeable membranes is investigated numeri- cally. The method using phantom molecules is developed to model the membranes reflecting solute molecules. The validity of van't Hoff law for the osmotic pressure is confirmed over a range of concentration up to 0.1 in mole fraction.

DOI： 10.11345/nctam.56.357

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Science Council of Japan  

An electrostatic model for osmotic flow through channels with surface charges is developed to understand the contribution of electrical charges to the transport of solution through narrow channels. The interaction energy between surface charges of the solute and the channel wall is used to express the osmotic reflection coefficient as a fi.mction of the surface charges, the ion concentration of the fluid, and the size ratio of the solute to the channel. Our model predicts that even for small Debye length compared to the channel size, the surface charges could significantly increase the osmotic flow, when the charges of the solute and the channel wall have the same sign.

DOI： 10.11345/nctam.56.365

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Science Council of Japan  

The luminal surface of capillmy walls is covered by a layer of macromolecules referred to as the glycocalyx. In order to examine the role of the glycocalyx in the microvessel permeability, we have estimated the transport property of the microvessel wall, by using a one-dimensional model for the solute exchange through a serial pathway of the glycocalyx and the interendothelial cleft. The model provided reasonable predictions for the diffusional permeability and the reflection coefficient for solutes up to the size of albt.nnin. The results suggest that the endothelial surface glycocalyx could form the primary molecular sieve in transcapillmy pathways.

DOI： 10.11345/nctam.56.373

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CAMBRIDGE UNIV PRESS  

A mathematical model is presented for steady fluid flow across microvessel walls through a serial pathway consisting of the endothelial surface glycocalyx and the intercellular cleft between adjacent endothelial cells, with junction strands and their discontinuous gaps. The three-dimensional flow through the pathway from the vessel lumen to the tissue space has been computed numerically based on a Brinkman equation with appropriate values of the Darcy permeability. The predicted values of the hydraulic conductivity LP, defined as the ratio of the flow rate per unit surface area of the vessel wall to the pressure drop across it, are close to experimental measurements for rat mesentery microvessels. If the values of the Darcy permeability for the surface glycocalyx are determined based on the regular arrangements of fibres with 6 nm radius and 8 nm spacing proposed recently from the detailed structural measurements, then the present study suggests that the surface glycocalyx could be much less resistant to flow compared to previous estimates by the one-dimensional flow analyses, and the intercellular cleft could be a major determinant of the hydraulic conductivity of the microvessel wall.

DOI： 10.1017/S0022112008000530

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Language：English   Publisher：IOS PRESS  

We review recent evidence which suggests that leukocytes in the circulation and in the tissue may readily respond to physiological levels of fluid shear stress in the range between about 1 and 10 dyn/cm(2), a range that is below the level to achieve a significant passive, viscoelastic response. The response of activated neutrophilic leukocytes to fluid shear consists of a rapid retraction of lamellipodia with membrane detachment from integrin binding sites. In contrast, a subgroup of non-activated neutrophils may project pseudopods after exposure to fluid shear stress. The evidence suggests that G-protein coupled receptor downregulation by fluid shear with concomitant downregulation of Rac-related small GTPases and depolymerization of F-actin serves to retract the lamellipodia in conjunction with proteolytic cleavage of beta(2) integrin to facilitate membrane detachment. Furthermore, there exists a mechanism to up- and down-regulate the fluid shear-response, which involves nitric oxide and the second messenger cyclic guanosine monophosphate (cGMP). Many physiological activities of circulating leukocytes are under the influence of fluid shear stress, including transendothelial migration of lymphocytes. We describe a disease model with chronic hypertension that suffers from an attenuated fluid shear-response with far reaching implications for microvascular blood flow.

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Language：English   Publisher：IOS PRESS  

We review recent evidence which suggests that leukocytes in the circulation and in the tissue may readily respond to physiological levels of fluid shear stress in the range between about 1 and 10 dyn/cm(2), a range that is below the level to achieve a significant passive, viscoelastic response. The response of activated neutrophilic leukocytes to fluid shear consists of a rapid retraction of lamellipodia with membrane detachment from integrin binding sites. In contrast, a subgroup of non-activated neutrophils may project pseudopods after exposure to fluid shear stress. The evidence suggests that G-protein coupled receptor downregulation by fluid shear with concomitant downregulation of Rac-related small GTPases and depolymerization of F-actin serves to retract the lamellipodia in conjunction with proteolytic cleavage of beta(2) integrin to facilitate membrane detachment. Furthermore, there exists a mechanism to up- and down-regulate the fluid shear-response, which involves nitric oxide and the second messenger cyclic guanosine monophosphate (cGMP). Many physiological activities of circulating leukocytes are under the influence of fluid shear stress, including transendothelial migration of lymphocytes. We describe a disease model with chronic hypertension that suffers from an attenuated fluid shear-response with far reaching implications for microvascular blood flow.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CAMBRIDGE UNIV PRESS  

The motion of a spherical particle suspended in an incompressible Newtonian fluid flowing longitudinally between hexagonally arranged Circular cylinders has been numerically analysed by a finite-element method in the Stokes flow regime. The results are applied to study the diffusive and convective transport of spherical solutes across the vascular endothelial Surface glycocalyx, based on the quasi-periodic ultrastructural model. The obtained values of diffusive permeability and reflection coefficient of the solutes show a reasonable agreement with experimental observations, and conform to the hypothesis that the endothelial surface glycocalyx forms the primary size selective structure to Solutes in microvascular permeability.

DOI： 10.1017/s022112005008359

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Language：English   Publisher：IOP PUBLISHING LTD  

The mechanics of blood flow in microvessels and microvessel permeability are reviewed. In the first part, characteristics of blood flow in vivo and in vitro are described from a fluid-mechanical point of view, and mathematical models for blood flow in microvessels are presented. Possible causes of the increased flow resistance obtained in vivo compared to in vitro are examined, including the effects of irregularities of vessel lumen, the presence of endothelial surface glycocalyx and white blood cells. In the second part, the ultrastructural pathways and mechanisms whereby endothelial cells and the clefts between the cells modulate microvessel permeability to water and solutes are introduced. Previous and current models for microvessel permeability to water and solutes are reviewed. These models examine the role of structural components of interendothelial cleft, such as junction strands and surface glycocalyx, in the determination of water and solute transport across the microvessel walls. Transport models in the tissue space surrounding the microvessel are also described. (C) 2005 Published by The Japan Society of Fluid Mechanics and Elsevier B.V. All rights reserved.

DOI： 10.1016/j.fluiddyn.2004.03.006

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

DOI： 10.1299/jsmebs.2004.17.0_233

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The motion of a spherical particle through a Brinkman medium in a circular cylindrical tube is numerically studied by a finite element method to examine the effect of the Brinkman medium on the free motion of a sphere in a tube, and the diffusive and convective transport of a spherical solute across a cylindrical pore. For this purpose, numerical results for the drag and torque exerted on a sphere, which is either translating, rotating, or embedded in a medium flow, are presented as functions of the radius ratio of the sphere to the tube, the radial position of the sphere, and the nondimensional parameter alpha(=R(p)rootK/mu), in which R(p) is the radius of the tube, mu is the viscosity and K is the hydraulic resistivity of the Brinkman medium. The present results confirm the validity of previous approximate estimates of the transport coefficients in a Newtonian fluid, and suggest a limitation of the continuum medium approach for evaluating the reflection coefficient of the solute transport through fibre matrix. (C) 2003 Published by The Japan Society of Fluid Mechanics and Elsevier B.V. All rights reserved.

DOI： 10.1016/j.fluiddyn.2003.08.007

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Recent evidence indicates that fluid shear stress on the membrane of leukocytes has a powerful control over several aspects of their cell function. The present study is aimed to examine numerically the magnitude and distribution of the fluid shear stress on the membrane of leukocytes in small postcapillary venules, where circulating leukocytes make their first contact with the endothelium. Using the Stokes equation for the motion of plasma, we computed the fluid shear stress on a leukocyte membrane in a microvessel for the cases when the leukocyte is freely suspended, as well as rolling along or attached to the vessel wall. The results indicate that the shear stress distribution on the leukocyte membrane is non-uniform with a sharp increase when the leukocyte makes membrane attachment to the vessel wall. In a microvessel of approximately 10mum diameter, the shear stress on the membrane of a freely suspended leukocyte is estimated to be several times larger than the wall shear stress exerted by the undisturbed Poiseuille flow, and increases on an adherent leukocyte up to ten times. High temporal stress gradients are present in freely suspended leukocytes and on the vascular endothelium.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOS PRESS  

The flow around adherent cells in a parallel-plate channel and that in a circular cylindrical tube are numerically analyzed, and their effects on the adherent cells are compared. The cells are modeled as rigid spherical particles and they are assumed to be attached to a wall of a 2D channel uniformly in a square array, or a wall of a circular tube regularly in a line along the tube axis. It is found that, when the size ratios of the particle-to-channel height and the particle-to-tube diameter are smaller than approximately 0.2, the distributions of the shear stress and the pressure exerted on the surface of an adherent particle as well as the drag force and torque acting on it compare favorably in the 2D channel Row and tube flow. As the size ratios increase from 0.2, the differences between the 2D channel and the tube increase drastically, especially when separation distances between neighboring particles are large.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC MECHANICAL ENGINEERS  

The flow past cells adherent to the bottom plate of a parallel plate channel is numerically analyzed in the zero-Reynolds-number limit, and the effect of the neigh. boring adherent cells on the drag force exerted on an adherent cell is examined. The cells are modeled as rigid spherical particles and they are assumed to be attached to the channel wall regularly in a square array. It is found that, when the size ratio of the cell-to-channel height is smaller than approximately 0.2, the drag force exerted oil an adherent cell is well approximated by a linear function of the size ratio, almost independently of the separation distances between neighboring cells except for the cases of very narrow spacing. For larger size ratios, the drag force oil all adherent cell in channel flow is generally smaller than the corresponding value in tube flow, but both values vary considerably, depending on the size ratios and the separation distances.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOS PRESS  

To evaluate the fluid forces acting on cells adhered to a microvessel wall, we numerically studied the flow field around adherent cells and the distribution of the stresses on their surfaces. For simplicity, the cells were modeled as rigid particles attached to a wall of a circular cylindrical tube regularly in the flow direction, in a row or two rows. It was found that not the detailed shape of the model cells but their height from the vessel wall is a key determinant of the fluid forces and torque acting on them. In both arrangements of one row and two rows, the axial spacing between neighboring adherent cells significantly affects the distributions of the stresses on them, which results in drastic variations of the fluid forces with the axial spacing and the relative positions with respect to their neighboring cells. The drag force acting on an adherent cell in the vessel was evaluated to be larger than the value in the 2D chamber flow at the same wall shear stress, mainly due to much larger variations of the pressure distribution on the cell surface in the vessel flow.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOS PRESS  

In spite of the relatively small number of leukocytes in the circulation, they have a significant influence on the perfusion of such organs as skeletal muscle or kidney. However, the underlying mechanisms are incompletely understood. In the current study a combined in vivo and computational approach is presented in which the interaction of individual freely flowing leukocytes with erythrocytes and its effect on apparent blood viscosity are explored. The skeletal muscle microcirculation was perfused with different cell suspensions with and without leukocytes or erythrocytes. We examined a three-dimensional numerical model of low Reynolds number flow in a capillary with a train of erythrocytes (small spheres) in off-axis positions and single larger leukocytes in axisymmetric positions. The results indicate that in order to match the slower axial velocity of leukocytes in capillaries, erythrocytes need to position themselves into an off-axis position in the capillary. In such off-axis positions at constant mean capillary velocity, erythrocyte axial velocity matches on average the axial velocity of the leukocytes, but the apparent viscosity is elevated, in agreement with the whole organ perfusion observations. Thus, leukocytes influence the whole organ resistance in skeletal muscle to a significant degree only in the presence of erythrocytes.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOS PRESS  

To evaluate the force and torque acting on leukocytes attached to the vessel wall, we numerically study the flow field around the leukocytes by using rigid spherical particles adhered to the wall of a circular cylindrical tube as a model of adherent leukocytes, The adherent particles are assumed to be placed regularly in the flow direction with equal spacings, in one row or two rows, The flow field of the suspending fluid is analyzed by a finite element method applied to the Stokes equations, and the drag force and torque acting on each particle, as well as the apparent viscosity, are evaluated as a function of the particle to tube diameter ratio and the particle arrangements, For two-row arrangements of adhered particles where neighboring particles are placed alternately on opposite sides of the vessel, the drag and the torque exerted on each particle are higher than those for single-row arrangements, for constant particle to tube diameter ratio and axial spacing between neighboring particles. This is enhanced for larger particles and smaller axial spacings, The apparent viscosity of the flow through vessels with adhered particles is found to be significantly higher than that without adhered particles or when the particles are freely floating through the vessels. (C) 1997 Elsevier Science Ltd.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

To study the rheological behavior of blood cells in various flow patterns through narrow vessels, we analyzed numerically the motion of blood cells arranged in one row or two rows in tube flow, at low Reynolds numbers, The particles are assumed to be identical rigid spheres placed periodically along the vessel axis at off-axis positions with equal spacings. The flow field of the suspending fluid in a circular cylindrical tube is analyzed by a finite element method applied to the Stokes equations, and the motion of each particle is simultaneously determined by a force-free and torque-free condition. In both cases of single-and two-file arrangements of the particles, their longitudinal and angular velocities are largely affected by the radial position and the axial spacing between neighboring particles, The apparent viscosity of the asymmetric flows is higher than that of the symmetric flow where particles are located on the tube centerline, and this is more pronounced when particles are placed farther from the tube centerline and when the axial distance between neighboring particles is reduced. (C) 1997 Elsevier Science Ltd.

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Language：Japanese   Publisher：関西大学工業技術研究所  

科研費基盤研究

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CAMBRIDGE UNIV PRESS  

The motion of a rigid ellipsoidal particle freely suspended in a Poiseuille how of an incompressible Newtonian fluid through a narrow tube is studied numerically in the zero-Reynolds-number limit. It is assumed that the effect of inertia forces on the motion of the particle and the fluid can be neglected and that no forces or torques act on the particle. The Stokes equation is solved by a finite element method for various positions and orientations of the particle to yield the instantaneous velocity of the particle as well as the how field around it, and the particle trajectories are determined for different initial configurations. A prolate spheroid is found to either tumble or oscillate in rotation, depending on the particle-tube size ratio, the axis ratio of the particle, and the initial conditions. A large oblate spheroid may approach asymptotically a steady, stable configuration, at which it is located close to the tube centreline, with its major axis slightly tilted from the undisturbed flow direction. The motion of non-axisymmetric ellipsoids is also illustrated and discussed with emphasis on the effect of the particle shape and size.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Irregularities of the vessel luminal geometry affect resistance to blood flow in microvessels. In the present study, the effect of the protrusion of endothelial cell nuclei into the vessel lumen on vascular resistance is numerically evaluated. It is assumed that nuclei of endothelial cells protrude regularly into the vessel lumen, which has an otherwise circular cross-section. The flow of an incompressible Newtonian fluid in these vessels is numerically analyzed by a finite element method applied to the Stokes equations, and the relationship of the flow rate and the pressure drop between upstream and downstream is used to calculate vascular resistance. It is found that the vascular resistance is constantly elevated compared to that for vessels without protrusions. The vascular resistance increases as the area of the vessel cross-section decreases, its shape is more distorted from the circular, or its variation along the vessel axis is more significant.

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Language：Japanese   Publisher：The Society of Rheology, Japan  

The motion of a rigid cylindrical particle freely suspended in a two-dimensional channel flow is studied numerically at low Reynolds numbers. The particle is assumed to be an elliptic cylinder or a doublet consisting of two equal-sized circular cylinders held in rigid contact. The Stokes equations for the suspending fluid are numerically solved with a finite element method for an estimate of the longitudinal, lateral and angular velocities of the particle at conditions of zero force and zero torque on the particle. Using the velocities obtained, the trajectories of the particle are determined for various initial configurations. The particle is found either to tumble or to oscillate cyclically, depending on the particle size / channel width ratio, particle shapes and initial conditions. In the former case, both of elliptic cylinders and doublets rotate continuously in one direction during one period, which is well approximated by so-called Jeffery's solutions for a spheroid in unbounded simple shear flow. In the latter case, the particle oscillates in rotation, accompanied by a periodic sidewise drift. The sidewise drift of doublets is about the centerplane of the channel, while the mean lateral position of elliptic cylinders is either on or of the centerplane.

DOI： 10.1678/rheology1973.22.1_27

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The motion of a doublet consisting of two rigidly connected circular cylinders freely suspended in an incompressible Newtonian fluid in a narrow channel bounded by two parallel planes is studied numerically at zero Reynolds number. The Stokes equations are solved by a finite element method for various positions and orientations of the particle, and the trajectories of the particle are determined for a number of initial configurations. A doublet of equal-sized cylinders is found either to tumble or oscillate in rotation, while a doublet of unequal-sized cylinders possesses a stable, steady equilibrium configuration, at which the particle is located close to the channel centerline with a constant angle of inclination. Thus, doublets of unequal diameters tumble, oscillate in rotation or approach the equilibrium configuration asymptotically, depending on the radius ratio of cylinders, particle size-channel width ratio and initial conditions.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CAMBRIDGE UNIV PRESS  

The motion of an elliptical cylindrical particle immersed in an incompressible Newtonian fluid in a narrow channel is examined numerically in the zero-Reynolds-number limit. It is assumed that no external forces or torques act on the elliptical cylinder, and the effects of inertia forces on the motion of the fluid and the particle are neglected. The Stokes equations are solved by a finite-element method for various positions and orientations of the cylinder, yielding the instantaneous velocities of the particle that satisfy the conditions of zero force and zero torque on the particle. Using the computed longitudinal, lateral, and angular velocities of the particle, the evolution of the particle's position and orientation is determined for various initial configurations. An elliptical cylinder is found to either tumble or oscillate in rotation, depending on the particle-channel size ratio, the axis ratio of the elliptical cylinder, and the initial conditions. In the first case, the particle rotates continuously in one direction that is well approximated by Jeffery's solution for an elliptical cylinder in unbounded shear flow with a so-called equivalent axis ratio; in the second case, the particle changes its direction of rotation during part of each period. In both cases, the particle translates with a periodically varying longitudinal velocity, accompanied by a considerable side drift due to the walls. The oscillatory motion is more likely to occur when the particle-channel size ratio or axis ratio is increased. The tumbling motion is inhibited for elliptic cylinders whose size ratios are larger than threshold values that depend on the axis ratio.

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Language：English   Publisher：ASME-AMER SOC MECHANICAL ENG  

The motion of two rigid circular cylinders in contact immersed in an incompressible Newtonian fluid in a channel is examined numerically in the zero Reynolds number limit, for various values of the cylinder radius/channel width ratio. Analyses of the time courses of the lateral position and the orientation of the doublet showed that, depending on the initial condition and the doublet/channel size ratio, the doublet exhibit one of the three types of motion: a continuous rotation in the same direction during a period, and a rotation changing its direction at every half period with a large or a small variation of the orientation.

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Language：Japanese   Publisher：JAPANESE SOCIETY OF BIORHEOLOGY  

A fiber-optic laser-Doppler anemometer microscope (FLDAM) was developed for the measurement of microvascular red cell velocity and its applicability was examined in <I>in vivo</I> experiments with emphasis on the temporal resolution of the system. Red cell velocity measured with the time resolution up to about 10 ms clearly showed pulsation synchronous with the systemic arterial pressure in mesenteric microvessels of spontaneously hypertensive rats (SHR) with diameters from 5.8 to 88.9 μm. The amplitude of pulsation decreased with decreasing arteriolar diameter, and the time lag of red cell velocity relative to the systemic arterial pressure monotonically increased from large arterioles through small arterioles, capillaries, small venules to large venules. The propagation velocity of the pulse wave was also obtained in arterioles. Thus, the FLDAM was proved to have the temporal resolution sufficient for the analysis of the pulse wave propagation in microvasculature of small animals with high heart rates.

DOI： 10.11262/jpnbr1987.5.2_20

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACADEMIC PRESS INC JNL-COMP SUBSCRIPTIONS  

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The effect of a tank-treading motion of the red cell membrane on a staggered "zipper"-type red cell flow in capillaries is examined, using a two-dimensional theoretical model. An approximately triangular cell with a thin flexible membrane enclosing a viscous fluid is adopted as a model of the red cell. The motion of model red cells arranged periodically along a two-dimensional channel in an idealized zipper-type arrangement is analyzed numerically by a finite element method applied to the Stokes equations for the flow both inside and outside the model cells. It is shown that, if the viscosity ratio of the internal fluid to the suspending fluid is lower than a critical value, there exists a stable zipper-type arrangement of cells. In that arrangement, the cells remain stationary relative to each other with the membrane tank-treading. In contrast, inhibiting tank-treading by increasing the viscosity ratio above the critical value induces a cyclic oscillatory motion of red cells. The critical viscosity ratio increases if the channel is narrowed or if the spacing between cells is reduced. The present results suggest that the membrane tank-treading tends to stabilize zipper-type arrangements of red cells in capillaries at high hematocrit. © 1990.

DOI： 10.1016/0026-2862(90)90034-O

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACADEMIC PRESS INC JNL-COMP SUBSCRIPTIONS  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACADEMIC PRESS INC JNL-COMP SUBSCRIPTIONS  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

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Language：English   Publisher：KARGER  

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Language：English   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ASME-AMER SOC MECHANICAL ENG  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ASME-AMER SOC MECHANICAL ENG  

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Language：English   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

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Language：English   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

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Language：English   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

An outline of the state space of planar Couette flow at high Reynolds numbers (Re < 10^4) is investigated via a variety of efficient numerical techniques. It is verified from nonlinear analysis that the lower branch of Hairpin Vortex State (HVS) asymptotically approaches the primary (laminar) state with increasing Re. It is also predicted that the lower branch of HVS at high Re belongs to the stability boundary that initiates transition to turbulence. These facts suggest HVS may provide a criterion to estimate a minimum perturbation arising transition to turbulent states at the infinite Re limit.

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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The shooting method is employed to outline a structural aspect of phase space of plane Couette flow, associated with laminar-Turbulent transition at moderate Reynolds numbers (Re ∼ 104). The basin boundary separating the laminar and the turbulent attractors in the phase space is emerged out of trajectories starting from initial conditions constituted by superposition of three distinct exact steady solutions of PCF, including the Hairpin Vortex Solution (Itano & Generalis (2009); Gibson et al. (2009)) and the so-called Nagata's solution (Nagata (1990)). The result implies that HVS is on the basin boundary even at moderate Reynolds numbers, and that one of the unstable manifolds of HVS heads towards the NBW, which lies on the basin boundary.

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Language：Japanese   Publisher：関西大学先端科学技術推進機構  

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Language：Japanese  

DOI： 10.11345/japannctam.61.0.86.0

J-GLOBAL

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Language：Japanese   Publisher：(NPO)日本バイオレオロジー学会  

J-GLOBAL

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Language：Japanese  

J-GLOBAL

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Language：Japanese   Publisher：(NPO)日本バイオレオロジー学会  

J-GLOBAL

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Books

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J-GLOBAL

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J-GLOBAL

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J-GLOBAL

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J-GLOBAL

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Language：Japanese   Publisher：日本流体力学会  

To estimate the magnitude of the shear stress acting on a leukocyte adhered to the microvessel wall, the flow field around a model leukocyte with a tear-drop shape is numerically analyzed by a finite element method. In the analysis, the blood is assumed to be an inhomogeneous Newtonian fluid and of the invariant viscosity along the streamlines.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

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Language：Japanese   Publisher：日本流体力学会  

The shear stress distribution on the surface of a leukocyte adhered to the microvessel wall was analyzed by a numerical simulation, taking the presence of a cell-free layer into account. The blood flow was modeled as a two-phase flow, consisting of a plasma flow in a cell-free layer adjacent to the vessel wall and the cell-rich flow in the central region of the vessel. It is assumed that the fluid in both regions is Newtonian with different viscosities and that the cell free layer covers the surface of the adherent leukocyte with a certain thickness. The flow field was calculated by a finite element method applied to the Stokes equation and the continuity equation. It was found that the profile of the shear stress distribution is not qualitatively affected by the presence of the cell-free layer but the maximum magnitude of the shear stress on a leukocyte may be reduced down to a low value that would not be realized in the absence of the plasma layer.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

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Language：Japanese   Publisher：Kansai University  

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

The flow field around a stationary sphere placed at an arbitrary radial position in a circular cylindrical tube was numerically analyzed by a finite element method applied to the Stokes equation and the continuity equation. The finite element mesh was progressively refined to obtain sufficient numerical accuracy. The results were used to evaluate the shear stress distributions on the surfaces of the sphere as well as the tube wall. It was found that the distribution of the shear stress and its magnitude drastically vary with the radial position of the sphere.

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Language：Japanese   Publisher：日本流体力学会  

To understand the flow field around a leukocyte adhered to a microvessel wall, we analyzed numerically the Stokes flow around a stationary sphere placed at an arbitrary radial position in a circular cylindrical tube using a finite element method. The finite element mesh was progressively refined to obtain sufficient numerical accuracy. The results were used to evaluate the shear stress distributions on the surfaces of the sphere as well as the tube wall. It was found that the distribution of the shear stress and its magnitude drastically vary with the radial position of the sphere.

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Language：Japanese  

The vascular endothelial cells are the principal barrier to, and regulator of, material exchange between circulating blood and body tissues. We consider the paracellular transport of fluid across the endothelial cells, and estimate the hydraulic conductivity to water, Lp, of the microvessel wall, by a fluid-mechanical analysis for a flow through serial pathways of the endothelial surface glycocalyx, the interendothelial cleft with junction strands and their discontinuous leakages, up to the interstitial space. The 3D structure of the pathway is found to affect largely the velocity profile of the fluid. The flow is concentrated near the streamlines going straight into the gap of the junction strand, so that the fluid stresses on the endothelial surface are locally increased in the region along these streamlines.

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Books

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Language：Japanese  

CiNii Books

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Language：Japanese   Publisher：関西大学  

CiNii Books

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Language：Japanese   Publisher：関西大学  

CiNii Books

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Language：English   Publishing type：Research paper, summary (international conference)   Publisher：IOS PRESS  

Web of Science

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Scopus

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Language：Japanese  

The governing equations for osmotic flow of solution through a simple membrane are derived as a model to the microvessel permeability in the microcirculation. The exact steady solution is obtained, and Kedem-Katchalsky relation for solvent and solute flux in the model is calculated in the equilibrium state. Solvent flux is a nonlinear function of differences of pressure and solute density, which describes an osmotic barrier effect of the microvessel.

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

The endothelial cells of microvessels form the critical barrier controlling the material exchange between the circulating blood and the body tissues. Recent experimental studies have shown that for similar size globular proteins, the microvessel permeability to positively charged proteins was much larger than that of negatively charged proteins. As a basis to investigate the mechanism of the charge effect on the microvessel permeability, we developed an electrostatic model of the transport of charged solutes through small cylindrical pores, and evaluated the permeability coefficient and the reflection coefficient, by taking into account the interaction between the surface charges of the solute and pore. It was found that even for small Debye length compared to the pore radius, the surface charge of the pore could significantly retard the transport of charged solutes with the same sign.

CiNii Books

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Language：Japanese  

The luminal surface of vascular endothelial cells is lined with the glycocalyx. In order to examine its effects on the microvascular permeability, we numerically evaluated the hydraulic conductivity, diffusive permeability and reflection coefficient, by using a simple model based on the glycocalyx detailed structure. The results suggest significant role of the glycocalyx as a molecular sieve.

CiNii Books

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

To evaluate the fluid force acting on leukocytes adhered to a venular wall and their effect on the flow resistance in the vessel, we numerically studied the blood flow around multiple adherent leukocytes. Each leukocyte was modeled as a rigid particle, and the model leukocytes were assumed to stick on the wall of a circular cylindrical tube regularly in the flow direction, in one row or two rows. The flow field around each adherent leukocyte was analyzed by a finite element method applied to the Stokes equations with periodic boundary conditions, and the distribution of the stresses on the leukocyte was calculated. It was found that not the detailed shape of the model leukocytes but their height from the vessel wall is a major determinant of the forces on them and the flow resistance in the vessel, although the stress distributions acting on the surfaces are significantly affected by their shape. In both arrangements of one row and two rows, the axial distance between neighboring leukocytes does not affect the maximum values of the tangential stresses on the leukocytes, but it considerably varies the distribution of the stresses on them, which results in drastic variations of the fluid forces on them with the number of adherent leukocytes.

CiNii Books

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Language：Japanese  

CiNii Books

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Language：Japanese  

CiNii Books

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Venue：京都大学  

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Venue：東海大学湘南キャンパス  

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Venue：福岡大学  

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Venue：関西大学  

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Venue：Seattle, USA  

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Venue：The Westin Hotel Awaji Island Resort & Conference Center  

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Venue：電通大  

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Venue：電通大  

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Venue：岐阜大学  

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Venue：九州大学  

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Venue：関西大学  

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Venue：Atlanta, USA  

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Venue：Atlanta, USA  

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Venue：Atlanta, USA  

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Venue：リファレンス駅東ビル(博多)  

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Venue：リファレンス駅東ビル(博多)  

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Venue：同志社大学  

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Venue：東北大学  

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Venue：Krakow (Porland)  

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Venue：名古屋大学  

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Venue：名古屋大学  

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Venue：東京理科大学  

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Venue：関西大学  

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Venue：京都大学  

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Venue：京都大学  

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Venue：SendaiInternational Center  

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Venue：Denver, USA  

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Venue：Denver, USA  

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Venue：大阪大学基礎工学部  

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Venue：東京理科大学  

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Venue：東京理科大学  

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Venue：電気通信大学  

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Venue：川﨑祐宣記念講堂(倉敷）  

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Venue：ウインクあいち(名古屋市)  

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Venue：ウインクあいち(名古屋市)  

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Venue：Portland, USA  

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Venue：Portland, USA  

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Venue：Portland, USA  

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Venue：山形テルサ(山形市)  

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Venue：大阪大学  

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Venue：名古屋工業大学  

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Venue：名古屋工業大学  

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Venue：金沢大学  

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Venue：金沢大学  

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Venue：京都テルサ  

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Venue：同志社大学  

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Venue：同志社大学  

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Venue：東海大学校友会館  

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Venue：東北学院大  

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Venue：東工大  

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Venue：Boston  

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Venue：Boston  

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Venue：Boston  

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Venue：仙台  

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Venue：東工大  

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Venue：関西大学  

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Venue：関西大学  

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Venue：電気通信大学  

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Venue：高知工科大学  

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Venue：高知工科大学  

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Venue：学術総合センター  

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Venue：学術総合センター  

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Venue：Seoul  

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Venue：Seoul  

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Venue：Seoul  

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Venue：Seoul  

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Venue：早稲田大学  

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Venue：関西大学  

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Venue：新潟  

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Venue：岡山大学  

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Venue：京都大学  

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Venue：San Francisco  

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Venue：San Francisco  

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Venue：San Francisco  

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Venue：San Francisco  

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Venue：San Francisco  

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Venue：San Francisco  

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Venue：San Francisco  

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Venue：San Francisco  

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Venue：福井市交流プラザ  

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Venue：福井市交流プラザ  

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Venue：福井市交流プラザ  

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Venue：東北大学  

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Venue：東北大学  

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Venue：東北大学  

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Venue：東北大学  

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Venue：東北大学  

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Venue：東北大学  

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Venue：東京電機大学  

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Venue：北海道大学  

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Venue：Barcelona  

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Venue：Barcelona  

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Venue：Barcelona  

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Venue：Barcelona  

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Venue：Barcelona  

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Venue：Barcelona  

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Venue：Barcelona  

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Venue：大宮ソニックシティー  

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Venue：東海大学（平塚）  

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Venue：関西大学  

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Venue：関西大学  

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Venue：九十九里（千葉）  

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Venue：九十九里（千葉）  

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Venue：工学院大学（東京）  

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Venue：山形大学（米沢）  

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Venue：東京農工大学  

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Venue：東京農工大学  

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Venue：東京農工大学  

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Venue：岡山大学  

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Venue：岡山大学  

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Venue：KIST(Seuol)  

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Venue：Hanover (USA)  

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Venue：Sapporo (Hokkaido University)  

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Venue：九州大学  

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Venue：九州大学  

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Venue：九州大学  

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Venue：広島大学  

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Venue：東京工業大学  

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Venue：関西大学  

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Venue：関西大学  

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Venue：関西大学  

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Venue：関西大学  

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Venue：名古屋大学  

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Venue：九州大学西新プラザ  

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Venue：高知  

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Venue：Istanbul  

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Venue：新潟  

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Venue：東京  

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Venue：Baltimore  

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Venue：桐生  

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Venue：東京  

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Venue：東京  

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Venue：関西大学  

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Venue：関西大学  

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Venue：関西大学  

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Venue：関西大学  

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Venue：京都  

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Venue：京都  

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Venue：東京  

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Venue：東京  

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Venue：仙台  

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Venue：札幌  

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Venue：札幌  

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Venue：名古屋  

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