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Shear Flow (shear + flow)
Kinds of Shear Flow Selected AbstractsBlock Copolymers Under Shear FlowMACROMOLECULAR THEORY AND SIMULATIONS, Issue 4 2005Igor Rychkov Abstract Summary: Microphase separation transition in block copolymer melts and solutions in equilibrium and under shear flow is reviewed. The non-equilibrium molecular dynamics (NEMD) computer simulation methodology is presented in detail including the derivation of the SLLOD equations of motion, Gaussian thermostat, and operator-splitting symplectic integrators. Results of our recent NEMD computer simulation studies of diblock copolymers in a selective solvent under shear flow are presented. Shear-dependent structural, rheological, and microscopical properties are described. New phase transitions are discovered. The parallel-perpendicular orientational transition in a weak-strong flow is revealed. Theoretical approaches are reviewed including the Edwards Hamiltonian, Landau-Ginzburg model, self-consistent mean field theory, field-theoretic simulation, as well as the time-dependent Landau-Ginzburg framework and its application to the studies of complex fluids. [source] Chemokine Signaling to Lymphocyte Integrins Under Shear FlowMICROCIRCULATION, Issue 1 2009RONEN ALON ABSTRACT The arrest of lymphocytes at target vascular sites depends on the rapid activation of their integrins by specialized endothelial chemokines. For over a decade, the mechanisms by which these chemokines trigger initial integrin-mediated adhesiveness and subsequent adhesion strengthening and crawling over endothelial surfaces have been dissected in vitro using flow chamber setups. These studies revealed that lymph node chemokines and subsets of inflammatory chemokines, collectively termed "arrest chemokines," can trigger the fastest measurable inside-out integrin activation events. Recent studies indicate that shear forces applied on lymphocytes are instrumental in these rapid activation processes. Different GTPases have been implicated in these activation processes. As these enzymes contribute to successive integrin activation and redistribution processes in both early and prolonged contacts there is a growing need to dissect in vitro and validate in vivo specific signaling routes involved in early and late integrin activation events controlling lymphocyte arrest and their subsequent crawling to sites of diapedesis. In this article, we present an overview of both early and recent shear-flow studies of integrin activation in lymphocytes and discuss future perspectives of integrin activation research in vitro and in vivo. [source] Penetration of Shear Flow Into an Array of Rods Aligned With the FlowTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2004Anthony M. J. Davis Abstract Shear flow over a square array of widely-spaced rods aligned with the flow is investigated using singularity methods to solve Stokes equation. The flow field is determined for various arrays occupying a fraction of a Couette channel, for solid volume fractions from 0.001 to 0.1. Flow penetration into an array is quantified by the slip velocity at the array edge. This velocity is much greater than when the flow is across the array but still less than the value predicted by the use of Brinkman's equation. À l'aide de méthodes de singularité destinées à résoudre l'équation de Stokes, on a étudié l'écoulement de cisaillement sur un vaste arrangement carré de tiges largement espacées alignées à l'écoulement. Le champ d'écoulement est déterminé pour divers arrangements occupant partiellement un canal de Couette, pour des fractions volumiques de solides comprises entre 0,001 et 0,1. La pénétration de l'écoulement dans le dispositif est quantifiée par la « vitesse de glissement au bord du dispositif. Cette vitesse est beaucoup plus grande que dans le cas où l'écoulement est transversal par rapport au dispositif mais est encore inférieure à la valeur prédite au moyen de l'équation de Brinkman. [source] VOF-Simulation of the Lift Force for Single Bubbles in a Simple Shear FlowCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 9 2006D. Bothe Abstract Bubbles in shear flows experience a lift force, causing them to migrate sideways while they are rising. This lateral migration is investigated in numerical simulations, which are carried out with an extended version of the highly parallelized code FS3D, employing an advanced Volume-of-Fluid method. The movement of single bubbles in linear shear flows is simulated to obtain the magnitude of the lift force , expressed by the lift force coefficient CL , for various bubble diameters and material data. Simulation results are in good agreement with experiments for medium liquid phase viscosities. An investigation of the dynamic pressure on the bubble surface explains why large bubbles migrate in the opposite direction compared to small bubbles. [source] Electromagnetic Effects on Transport Barrier RelaxationsCONTRIBUTIONS TO PLASMA PHYSICS, Issue 1-3 2008G. Fuhr Abstract Results of transport barrier relaxations computed with a new 3D electromagnetic simulation code (EMEDGE3D) of resistive ballooning turbulence are presented. In these simulations, a barrier forms due to an imposed E × B shear flow. We report the first self-consistent electromagnetic simulations based on first principles which exhibit barrier relaxation cycles. This barrier relaxes intermittently on confinement time scales, even if fluctuations of the E × B flow are suppressed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Dual-asymmetry electrokinetic flow focusing for pre-concentration and analysis of catecholamines in CE electrochemical nanochannelsELECTROPHORESIS, Issue 14 2009Ren-Guei Wu Abstract In this research, a technique incorporating dual-asymmetry electrokinetic flow (DAEKF) was applied to a nanoCE electrochemical device for the pre-concentration and detection of catecholamines. The DAEKF was constructed by first generating a ,-potential difference between the top and bottom walls, which had been pre-treated with O2 and H2O surface plasma, respectively, yielding a 2-D gradient shear flow across the channel depth. The shear flow was then exposed to a varying ,-potential along the downstream direction by control of the field-effect in order to cause downward rotational flow in the channel. By this mechanism, almost all of the samples were effectively brought down to the electrode surface for analysis. Simulations were carried out to reveal the mechanism of concentration caused by the DAEKF, and the results reasonably describe our experiment findings. This DAEKF technique was applied to a glass/glass CE electrochemical nanochip for the analysis of catecholamines. The optimum detection limit was determined to be 1.25 and 3.3,nM of dopamine and catechol, respectively. A detection limit at the zeptomole level for dopamine can be obtained in this device, which is close to the level released by a single neuron cell in vitro. [source] Influence of shear flow on polymorphic behavior and microstructural development during palm oil crystallizationEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 3 2009Veerle De Graef Abstract The influence of shear on the crystallization of palm oil was studied at four different crystallization temperatures (18, 20, 22 and 25,°C). Time-resolved X-ray analyses were carried out to study the effect of continuous shear on the crystallization kinetics of the fat. Rheological measurements were used to assess the effect of a shear step on crystallization, and finally polarized light microscopy was used to follow changes in microstructure due to the applied initial shear step. It was shown that shear enhanced the primary crystallization, even when low shear rates were applied for a short period. Furthermore, a shear step prior to crystallization without shear has a marked influence on the microstructural development. [source] Seismic evidence for a mantle plume oceanwards of the Kamchatka,Aleutian trench junctionGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2001A. Gorbatov Summary A non-linear iterative P- wave traveltime tomography has revealed a mantle plume originating at a depth of nearly 1000 km, rising across the 600 km discontinuity, and deflecting subhorizontally in the uppermost mantle presumably by shear flow due to the overlying moving plate. Data from the Geophysical Survey of Russia (1955,1997) were inverted jointly with the catalogues of International Seismological Centre and USGS National Earthquake Information Centre (1964, 1998). The result shows a 300,500 km-wide cylindrical low-velocity anomaly (, , 2 per cent) that extends from a depth of greater than 900 km to shallower than 200 km. The anomaly is almost vertical at depths up to ,400 km and rises obliquely to the north up to ,200 km under the ocean floor near the northern end of Emperor seamounts. Above ,300 km depth a subsidiary anomaly extends subhorizontally to the NW in fair agreement with the direction of movement of the Pacific Plate. The overlying seafloor is characterized by anomalously high heat flow, which may be attributed to the thermal effect of the mantle plume. [source] Numerical simulation of drop deformation and breakup in shear flowHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 5 2007Lin Chang-Zhi Abstract Three-dimensional numerical simulation of the deformation and breakup of an isolated liquid drop suspended in immiscible viscous fluid under shear flow was performed with diffuse interface method. The governing equations of the model were described by Navier, Stokes, Cahn, Hilliard equations. The surface tension was treated as a modified stress. In this paper, a uniform staggered Cartesian grid was used. The transient Navier, Stokes equations were solved by an approximation projection method based on pressure increment formulation, while the Cahn, Hilliard equations were solved by a nonlinear full approximation multigrid method. The numerical results of the drop deformation and breakup were in good agreement with the experimental measurements. Therefore, the present model could be perfectly applied to study the mechanism of drop deformation and breakup. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(5): 286, 294, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20160 [source] Minimum shear wind strength required for dynamic soaring of albatrossesIBIS, Issue 1 2005GOTTFRIED SACHS The transfer of energy from the moving air in the shear wind above the sea surface to a bird is considered as an energy source for dynamic soaring, with the goal to determine the minimum shear wind strength required for the dynamic soaring of albatrosses. Focus is on energy-neutral trajectories, implying that the energy gain from the moving air is just sufficient to compensate for the energy loss due to drag for a dynamic soaring cycle. A mathematical optimization method is used for computing minimum shear wind energy-neutral trajectories, using a realistic flight mechanics model for the soaring of albatrosses. Thus, the minimum shear wind strength required for dynamic soaring is determined. The minimum shear wind strength is of a magnitude that often exists or is exceeded in areas in which albatrosses are found. This result holds for two control cases dealt with, one of which shows a freely selectable and the other a constant lift coefficient characteristic. The mechanism of energy transfer from the shear flow to the bird is considered, and it is shown that there is a significant energy gain in the upper curve and a loss in the lower curve. As a result, the upper curve can be qualified as the characteristic flight phase of dynamic soaring to achieve an energy gain. [source] Magnetic Hydrogel Particles: Microfluidic Assembly of Magnetic Hydrogel Particles with Uniformly Anisotropic Structure (Adv. Mater.ADVANCED MATERIALS, Issue 31 200931/2009) The inside cover shows magnetic hydrogel particles with uniform anisotropic features, synthesized using double emulsions as templates, as reported by Adam Abate and co-workers on p.3201. Microfluidic assembly using flow-focusing double emulsion drop makers provides excellent control over the size, morphology, and monodispersity of the products. The particles exhibit excellent rotational control under an external field, with a possibility of eccentric rotation inducing a significant localized shear flow, and have promise for a variety of biomedical applications. [source] An accurate integral-based scheme for advection,diffusion equationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 10 2001Tung-Lin Tsai Abstract This paper proposes an accurate integral-based scheme for solving the advection,diffusion equation. In the proposed scheme the advection,diffusion equation is integrated over a computational element using the quadratic polynomial interpolation function. Then elements are connected by the continuity of first derivative at boundary points of adjacent elements. The proposed scheme is unconditionally stable and results in a tridiagonal system of equations which can be solved efficiently by the Thomas algorithm. Using the method of fractional steps, the proposed scheme can be extended straightforwardly from one-dimensional to multi-dimensional problems without much difficulty and complication. To investigate the computational performances of the proposed scheme five numerical examples are considered: (i) dispersion of Gaussian concentration distribution in one-dimensional uniform flow; (ii) one-dimensional viscous Burgers equation; (iii) pure advection of Gaussian concentration distribution in two-dimensional uniform flow; (iv) pure advection of Gaussian concentration distribution in two-dimensional rigid-body rotating flow; and (v) three-dimensional diffusion in a shear flow. In comparison not only with the QUICKEST scheme, the fully time-centred implicit QUICK scheme and the fully time-centred implicit TCSD scheme for one-dimensional problem but also with the ADI-QUICK scheme, the ADI-TCSD scheme and the MOSQUITO scheme for two-dimensional problems, the proposed scheme shows convincing computational performances. Copyright © 2001 John Wiley & Sons, Ltd. [source] A two-grid fictitious domain method for direct simulation of flows involving non-interacting particles of a very small sizeINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2010A. Dechaume Abstract The full resolution of flows involving particles whose scale is hundreds or thousands of times smaller than the size of the flow domain is a challenging problem. A naive approach would require a tremendous number of degrees of freedom in order to bridge the gap between the two spatial scales involved. The approach used in the present study employs two grids whose grid size fits the two different scales involved, one of them (the micro-scale grid) being embedded into the other (the macro-scale grid). Then resolving first the larger scale on the macro-scale grid, we transfer the so obtained data to the boundary of the micro-scale grid and solve the smaller size problem. Since the particle is moving throughout the macro-scale domain, the micro-scale grid is fixed at the centroid of the moving particle and therefore moves with it. In this study we combine such an approach with a fictitious domain formulation of the problem resulting in a very efficient algorithm that is also easy to implement in an existing CFD code. We validate the method against existing experimental data for a sedimenting sphere, as well as analytical results for motion of an inertia-less ellipsoid in a shear flow. Finally, we apply the method to the flow of a high aspect ratio ellipsoid in a model of a human lung airway bifurcation. Copyright © 2009 John Wiley & Sons, Ltd. [source] Comparing vortex methods and finite difference methods in a homogeneous turbulent shear flowINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 7 2010R. Yokota Abstract The vortex method is applied to the calculation of a homogeneous shear turbulence, and compared with a finite difference code using identical calculation conditions. The core spreading method with spatial adaptation is selected as the viscous diffusion scheme of the vortex method. The shear rate is chosen so that it matches the maximum value observed in a fully developed channel flow. The isosurface, anisotropy tensors, and joint probability density functions reflect the ability of the present vortex method to quantitatively reproduce the anisotropic nature of strongly sheared turbulence, both instantaneously and statistically. Copyright © 2009 John Wiley & Sons, Ltd. [source] Numerical simulation of bubble and droplet deformation by a level set approach with surface tension in three dimensionsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 9 2010Roberto Croce Abstract In this paper we present a three-dimensional Navier,Stokes solver for incompressible two-phase flow problems with surface tension and apply the proposed scheme to the simulation of bubble and droplet deformation. One of the main concerns of this study is the impact of surface tension and its discretization on the overall convergence behavior and conservation properties. Our approach employs a standard finite difference/finite volume discretization on uniform Cartesian staggered grids and uses Chorin's projection approach. The free surface between the two fluid phases is tracked with a level set (LS) technique. Here, the interface conditions are implicitly incorporated into the momentum equations by the continuum surface force method. Surface tension is evaluated using a smoothed delta function and a third-order interpolation. The problem of mass conservation for the two phases is treated by a reinitialization of the LS function employing a regularized signum function and a global fixed point iteration. All convective terms are discretized by a WENO scheme of fifth order. Altogether, our approach exhibits a second-order convergence away from the free surface. The discretization of surface tension requires a smoothing scheme near the free surface, which leads to a first-order convergence in the smoothing region. We discuss the details of the proposed numerical scheme and present the results of several numerical experiments concerning mass conservation, convergence of curvature, and the application of our solver to the simulation of two rising bubble problems, one with small and one with large jumps in material parameters, and the simulation of a droplet deformation due to a shear flow in three space dimensions. Furthermore, we compare our three-dimensional results with those of quasi-two-dimensional and two-dimensional simulations. This comparison clearly shows the need for full three-dimensional simulations of droplet and bubble deformation to capture the correct physical behavior. Copyright © 2009 John Wiley & Sons, Ltd. [source] Turbulence in a three-dimensional wall-bounded shear flowINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 8 2010A. Holstad Abstract A new turbulent flow with distinct three-dimensional characteristics has been designed in order to study the impact of mean-flow skewing on the turbulent coherent vortices and Reynolds-averaged statistics. The skewing of a unidirectional plane Couette flow was achieved by means of a spanwise pressure gradient. Direct numerical simulations of the statistically steady Couette,Poiseuille flow enabled in-depth explorations of the turbulence field in the skewed flow. The imposition of a modest spanwise gradient turned the mean flow about 8° away from the original Couette flow direction and this turning angle remained nearly the same over the entire cross section. Nevertheless, a substantial non-alignment between the turbulent shear stress angle and the mean velocity gradient angle was observed. The structure parameter turned out to slightly exceed that in the pure Couette flow, contrary to the observations made in some other three-dimensional shear flows. Coherent flow structures, which are known to be associated with the Reynolds shear stress in near-wall regions, were identified by the ,2 -criterion. Instantaneous and ensemble-averaged vortices resembled those found in the unidirectional Couette flow. In the skewed flow, however, the vortex structures were turned to align with the local mean-flow direction. The conventional symmetry between Case 1 and Case 2 vortices was broken due to the mean-flow three-dimensionality. The turning of the coherent vortices and the accompanying symmetry-breaking gave rise to secondary and tertiary turbulent shear stress components. By averaging the already ensemble-averaged shear stresses associated with Case 1 and Case 2 vortices in the homogeneous directions, a direct link between the educed near-wall structures and the Reynolds-averaged turbulent stresses was established. These observations provide evidence in support of the hypothesis that the structural model proposed for two-dimensional turbulent boundary layers remains valid also in flows with moderate mean three-dimensionality. Copyright © 2009 John Wiley & Sons, Ltd. [source] A lattice Boltzmann method for solute transportINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 8 2009Jian Guo Zhou Abstract A lattice Boltzmann method is developed for solute transport. Proper expressions for the local equilibrium distribution functions enable the method to be formulated on rectangular lattice with the same simple procedure as that on a square lattice. This provides an additional advantage over a lattice Boltzmann method on a square lattice for problems characterized by dominant phenomenon in one direction and relatively weak in another such as solute transport in shear flow over a narrow channel, where the problems can efficiently be approached with fine and coarse meshes, respectively, resulting in more efficient algorithm. The stability conditions are also described. The proposed method on a square lattice is naturally recovered when a square lattice is used. It is verified by solving four tests and compared with the analytical/exact solutions. They are in good agreement, demonstrating that the method is simple, accurate and robust for solute transport. Copyright © 2008 John Wiley & Sons, Ltd. [source] Mobility of shear thinning viscous drops in a shear Newtonian carrying flow using DR-BEMINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2009M. Giraldo Abstract The study of drop behaviour has attracted great interest in the last years due to its importance in different industrial and biological systems. Most available works focus on Newtonian drops, excluding some very important applications such as polymer mixing. Simulations of non-Newtonian drops have had only limited study, mostly in time-dependent rheologies or simple flow cases. This work presents a boundary-only formulation based on the dual reciprocity method to model the motion and deformation of non-Newtonian shear thinning drops due to a shear Newtonian unbounded carrying flow. Pair-wise interactions at low Reynolds number between two viscous shear thinning non-Newtonian drops are numerically simulated in order to obtain mobility magnitudes under linear shear flow of different strengths. Separation of the drops in the direction perpendicular to the imposed flow field at high capillary number (small surface tension) and low viscosity ratio was favoured by shear thinning, increasing in magnitude as the capillary number increases and the viscous ratio decreases. Higher values of this separation occur at higher values of the viscosity ratio when compared with the case of Newtonian drops. In order to obtain a good physical description of the non-Newtonian drop behaviour, while maintaining good computational performance, the non-Newtonian viscosity is made to obey the truncated power law model. Copyright © 2008 John Wiley & Sons, Ltd. [source] A hybrid immersed boundary and material point method for simulating 3D fluid,structure interaction problemsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2008Anvar Gilmanov Abstract A numerical method is developed for solving the 3D, unsteady, incompressible Navier,Stokes equations in curvilinear coordinates containing immersed boundaries (IBs) of arbitrary geometrical complexity moving and deforming under forces acting on the body. Since simulations of flow in complex geometries with deformable surfaces require special treatment, the present approach combines a hybrid immersed boundary method (HIBM) for handling complex moving boundaries and a material point method (MPM) for resolving structural stresses and movement. This combined HIBM & MPM approach is presented as an effective approach for solving fluid,structure interaction (FSI) problems. In the HIBM, a curvilinear grid is defined and the variable values at grid points adjacent to a boundary are forced or interpolated to satisfy the boundary conditions. The MPM is used for solving the equations of solid structure and communicates with the fluid through appropriate interface-boundary conditions. The governing flow equations are discretized on a non-staggered grid layout using second-order accurate finite-difference formulas. The discrete equations are integrated in time via a second-order accurate dual time stepping, artificial compressibility scheme. Unstructured, triangular meshes are employed to discretize the complex surface of the IBs. The nodes of the surface mesh constitute a set of Lagrangian control points used for tracking the motion of the flexible body. The equations of the solid body are integrated in time via the MPM. At every instant in time, the influence of the body on the flow is accounted for by applying boundary conditions at stationary curvilinear grid nodes located in the exterior but in the immediate vicinity of the body by reconstructing the solution along the local normal to the body surface. The influence of the fluid on the body is defined through pressure and shear stresses acting on the surface of the body. The HIBM & MPM approach is validated for FSI problems by solving for a falling rigid and flexible sphere in a fluid-filled channel. The behavior of a capsule in a shear flow was also examined. Agreement with the published results is excellent. Copyright © 2007 John Wiley & Sons, Ltd. [source] A finite element strategy for the solution of interface tracking problemsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2005C. Devals Abstract A finite element-based numerical strategy for interface tracking is developed for the simulation of two-phase flows. The method is based on the solution of an advection equation for the so-called ,pseudo-concentration' of one of the phases. To obtain an accurate description of the interface, a streamline upwind Petrov,Galerkin (SUPG) scheme is combined with an automatic mesh refinement procedure and a filtering technique, making it possible to generate an oscillation-free pseudo-concentration field. The performance of the proposed approach is successfully tested on four classical two-dimensional benchmark problems: the advection skew to the mesh, the transport of a square shape in a constant velocity flow field, the transport of a cut-out cylinder in a rotating flow field and the transport of a disc in a shear flow. Copyright © 2005 John Wiley & Sons, Ltd. [source] Rheological behavior of polymer melts in monodimensional flow through low-angle convergence and spiralling diesADVANCES IN POLYMER TECHNOLOGY, Issue 2 2001L. Mascia An experimental study was carried out to examine the rheological behavior of polymer melts in laminar flows through channels with small-angle convergences (2,3°) and spiralling walls (6°/mm along the flow direction), using an extrusion grade of low-density polyethylene. The results show that convergence is the main factor responsible for the observed deviations from steady state laminar shear flow, particularly with respect to additional pressure requirements to maintain a constant mass output. The swell ratio, calculated from the dimensions of the channel at the exit, was found to be considerably higher for flow-through converging channels. Only a small increase in swell ratio could be attributed, on the other hand, to the rotational elements of the die configuration. It is inferred that even for small angles of convergence the increased level of swelling is associated with elongational stress components, which were grouped together and denoted as the "additional stress." This was obtained from the difference between the calculated average shear stress at the wall, using the recorded pressure at the die entry, and the value of the average shear stress at the wall calculated from the shear viscosity data for the melt. © 2001 John Wiley & Sons, Inc. Adv Polym Techn 20: 99,107, 2001 [source] Shear-induced migration of nanoclay during morphology evolution of PBT/PS blendJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008Joung Sook Hong Abstract In this study, we investigated clay migration and its localization in multiphase blend nanocomposite systems during the evolution of blend morphology to elucidate how a hydrodynamic stress and chemical affinity between the polymer and clay induce them. To observe the morphology evolution, a multilayered blend, alternatively superposed poly(butylenes terephthalate) (PBT) and polystyrene (PS)/clay films or PBT/clay and PS films, was subjected to homogeneous shear flow, 1 s,1. Furthermore, the morphology was observed at different shear rates 1 s,1. When the PBT/(PS/clay) multilayered blend is subjected to flow, the clay dispersed in the PS layer first migrates to the interface depending on the amount of applied strain. The clay at the interface causes the average drop size of blend morphology to become smaller and the blend morphology becomes more stable because of the coalescence suppression effect. As more shear is applied, the clay at the interface moves further into more compatible phase, PBT, although the viscosity of PBT is higher than PS. On the contrary, the clay in the PBT layer does not migrate to the PS phase at any shear rate, which means that its chemical affinity is strong enough to prevent shear-induced migration. The clay increases the viscosity of the PBT phase and results in a different morphology with a droplet, cocontinuous structure. As a result, when the clay is induced to migrate by hydrodynamic stress, it migrates into thermodynamically more stable positions at the interface or in the chemically more compatible phase, depending on the applied strain. Once it is located at a thermodynamically more stable position, it is difficult to push it out only by hydrodynamic stress. The location of clay is significantly affected by the morphology during evolution, which means that the blend morphology can control the droplet form and cocontinuous structure by control of the clay migration kinetics. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] THE ROLE OF CALCIUM IN FLOW-STIMULATED BIOLUMINESCENCE OF THE RED TIDE DINOFLAGELLATE LINGULODINIUM POLYEDRUMJOURNAL OF PHYCOLOGY, Issue 2000P. Von Dassow Many marine planktonic dinoflagellates emit flashes of light in response to either laminar or turbulent flows as well as direct mechanical stimulation. The production of a flash of light is known to be mediated by a proton-mediated action potential across the vacuolar membrane; the mechanotransduction process initiating this action potential is unknown. Here we report on an investigation into the role of Ca+2 in the mechanotransduction process regulating bioluminescence in the red tide dinoflagellate Lingulodinium polyedrum. Calcium ionophores and low concentrations of the membrane-disrupting agent digitonin stimulated bioluminescence only when calcium was present in the media or added with the agent, indicating that the flash-triggering vacuolar action potential is specifically stimulated by a calcium influx. A variety of known calcium channel blockers or antagonists inhibited mechanically stimulated bioluminescence but did not affect cellular bioluminescent capacity. In many cases the inhibitory affect occurred after only a brief exposure. In addition, gadolinium (Gd+3), a blocker of many stretch-activated ion channels, caused potent inhibition of mechanically stimulated bioluminescence. The order of potency of the transition metals tested was La+3 > Gd+3 > Co+2 > Mn+2 > Ni+2, similar to their potency as blockers of known calcium channels. Experiments with a quantified shear flow demonstrated that flow-stimulated bioluminescence depended on the level of extracellular calcium. Future work will elucidate the signaling pathway involving calcium-mediated flow-stimulated mechanotransduction. Our goal is to use bioluminescence as a proxy for the initial cellular mechanotransduction events triggered by fluid flow. [source] A Study on the Effect of Template Chain Length on the Synthesis of Mesoporous Silica in An Acidic ConditionJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2007Yang Yu-Xiang Hexagonal mesoporous silica materials were synthesized in an acidic medium using different chain length of the quaternary ammonium surfactants as a template. The effects of chain length on the physical property, morphology of mesoporous materials, and the temperature on synthesis of materials in CnTMBr,TEOS,HNO3,H2O (n=12,14,16,18) system were systematically studied. The synthesized products were characterized by X-ray diffraction patterns, scanning electron microscopy, transmission electron microscopy, and nitrogen sorption analysis. It was found that degree of ordering, the d spacing values, and pore size all increase with an increase in the chain length of the template. The optimum synthesis temperature for mesoporous silica using C18TMBr,TEOS,HNO3,H2O system is slightly higher than the Krafft point. The temperature and pH can all affect the expandability of micelles, and so an increase in temperature and decrease in pH all lead to an increase in the pore size. It is also found that the shear flow and chain length are two key factors inducing the formation of millimeter-scaled silica ropes and micrometer-scaled rope fibers. [source] Coarse-Grained Simulations of Elongational Viscosities, Superposition Rheology and Shear Banding in Model Core,Shell SystemsMACROMOLECULAR THEORY AND SIMULATIONS, Issue 8 2007A. van den Noort Abstract A recently developed coarse-grain model is used to investigate nonlinear rheological properties of model core,shell systems. The influence of several model parameters on the stresses and shear rates is investigated. Continuous planar elongational flow and superposition rheology are studied and compared to simple shear flow results. With particular values of the model parameters, an initially linear velocity profile splits into many bands with different shear rates and different densities, which finally merge into just two bands stacked along the gradient direction. With the box sizes used in our simulations, stick and Lees,Edwards boundary conditions lead to qualitatively similar results, with the stick boundary simulations showing better quantitative agreement with experiments. [source] Block Copolymers Under Shear FlowMACROMOLECULAR THEORY AND SIMULATIONS, Issue 4 2005Igor Rychkov Abstract Summary: Microphase separation transition in block copolymer melts and solutions in equilibrium and under shear flow is reviewed. The non-equilibrium molecular dynamics (NEMD) computer simulation methodology is presented in detail including the derivation of the SLLOD equations of motion, Gaussian thermostat, and operator-splitting symplectic integrators. Results of our recent NEMD computer simulation studies of diblock copolymers in a selective solvent under shear flow are presented. Shear-dependent structural, rheological, and microscopical properties are described. New phase transitions are discovered. The parallel-perpendicular orientational transition in a weak-strong flow is revealed. Theoretical approaches are reviewed including the Edwards Hamiltonian, Landau-Ginzburg model, self-consistent mean field theory, field-theoretic simulation, as well as the time-dependent Landau-Ginzburg framework and its application to the studies of complex fluids. [source] Role of ,4,1 Integrins in Chemokine-Induced Monocyte Arrest under Conditions of Shear StressMICROCIRCULATION, Issue 1 2009SHARON J. HYDUK ABSTRACT Monocyte recruitment or emigration to tissues is an essential component of host defense in both acute and chronic inflammatory responses. Sequential molecular interactions mediate a cascade of tethering, rolling, arrest, stable adhesion, and intravascular crawling that culminates in monocyte diapedesis across the vascular endothelium and migration through the basement membrane of postcapillary venules. Integrins are complex adhesion and signaling molecules. Dynamic alterations in their conformation and distribution on the monocyte cell surface are required for many steps of monocyte emigration. Intracellular signaling initiated by chemokine receptors induces conformational changes in integrins that upregulate their affinity for ligands, and this is essential for monocyte arrest. This review focuses on the activation of monocyte ,4,1 integrins by endothelial chemokines, which is required for the arrest of monocytes rolling on vascular cell adhesion molecule 1 under shear flow. Using soluble ligand-binding assays and adhesion assays in parallel-plate flow chambers, critical signaling mediators in chemokine-induced ,4,1 integrin affinity upregulation and monocyte arrest have been identified, including phospholipase C, calcium, and calmodulin. [source] Preparation and characterization of nylon 6/organoclay nanocomposite filament fibersPOLYMER COMPOSITES, Issue 3 2009Kap Jin Kim A series of nylon 6 (NY6)/organoclay nanocomposites were prepared via in situ polymerization of ,-caprolactam in the presence of 1,2-aminododecanoic acid-intercalated montmorillonite (ADA-MMT) organoclay (1,5 wt%) using 6-aminocaproic acid as polymerization catalyst. The extent of organoclay dispersion in NY6 matrix was analyzed using WAXD and SEM measurements. DSC studies revealed marginal shift in melting and melt-crystallization peaks toward lower temperature with increasing clay content. Melt viscosity studies for NY6/ADA-MMT exhibited higher shear-thinning behavior than neat NY6 probably due to the slip between NY6 matrix and exfoliated organoclay platelets during shear flow. The prepared nanocomposites were melt-spun and studied for their property improvements against varying clay content, draw ratios, and annealing conditions. Birefringence and sonic velocity values increased initially at lower draw ratios (,2.5) due to increased orientation of molecular chains along the drawing direction but saturated at higher draw ratio (3.0) for all the samples. At the same draw ratio; compared to neat NY6, NY6/organoclay fibers showed increased chain orientation along the drawing direction which can be attributed to the "tethering effect" of organoclay on NY6 matrix. The initial modulus and stress at break were sensitive to factors such as draw ratio, clay content, and annealing conditions. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers [source] Online light scattering measurements: A method to assess morphology development of polymer blends in a twin-screw extruderPOLYMER ENGINEERING & SCIENCE, Issue 10 2002G. Schlatter Light scattering has proved itself an efficient technique to determine particle diameters in heterogeneous dilute dispersions in the micrometer range. Extrusion of polymer blends is expected to give rise to very small particles, typically in the range from hundreds of nanometers to tens of micrometers. A light scattering device developed in our laboratory has been used to study the morphology of polymer blends obtained in a twin-screw extruder. The main advantage of this technique is the immediate response obtained without any surface or interface modification that can occur during the sample preparation by using more conventional techniques like electron microscopy. To show the possible applications of this light scattering device, preliminary tests have been carried out. First, we present a comparison between experimental measurements and theoretical results for dilute systems. Second, we have investigated the effect of shear flow on the droplet deformation. Finally, we have studied the variations of the light scattering pattern for a reactive blend. [source] Direct meso-scale simulations of fibres in turbulent liquid flowTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2010J. J. Derksen Abstract A procedure for direct, meso-scale simulations of flexible fibres immersed in liquid flow is introduced. The fibres are composed of chains of spherical particles connected through ball joints with the bending stiffness of the joints as a variable. The motion of the fibres and the liquid is two-way coupled with full resolution of the solid,liquid interface. First the simulation procedure is validated by means of an analytical solution for sphere doublets in zero-Reynolds simple shear flow. Subsequently we use the numerical method to study inertial flows with fibres, more specifically the interaction of a fibre with isotropic turbulence. Une procédure pour des simulations directes à la méso-échelle de fibres souples immergées dans la circulation de liquide est présentée. Les fibres sont composées de chaînes de particules sphériques reliées par des joints à rotule avec la rigidité à la flexion des joints comme variable. Le mouvement des fibres et du liquide est bidirectionnel avec une résolution intégrale de l'interface solide-liquide. D'abord, la procédure de simulation est validée au moyen d'une solution analytique pour les doublets de sphère dans un écoulement de cisaillement simple à nombre de Reynolds nul. Par la suite, nous utilisons la méthode numérique pour étudier les flux inertiels avec les fibres, plus précisément l'interaction d'une fibre avec la turbulence isotrope. [source] | ||||||||||||||||||||||||||||