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J. G. Lominadze - One of the best experts on this subject based on the ideXlab platform.
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On Hydrodynamic Shear turbulence in stratified Keplerian disks: Transient growth of small-scale 3D vortex mode perturbations
Astronomy & Astrophysics, 2003Co-Authors: Alexander G. Tevzadze, G. D. Chagelishvili, Jean-paul Zahn, R. G. Chanishvili, J. G. LominadzeAbstract:This is a sequel to Paper I (Chagelishvili et al. 2003), where we presented the so-called bypass concept for the onset of turbulence in Shearing flows. According to this concept, which was worked out during the last decade by the Hydrodynamic community for spectrally stable flows, vortical perturbations undergo transient growth by extracting energy from the Shear (a linear process), thereby reaching an amplitude which is sucient to allow for non-linear interactions which, by positive feedback, sustain turbulence. In Paper I we described this transient growth for 2D perturbations in a Keplerian disk; we showed that their kinematics was the same as in plane-parallel flow, and thus that they were not modified by the presence of the Coriolis force. In the present paper, we pursue our goal of applying the bypass scenario to astrophysical disks: we investigate the linear dynamics of 3D small-scale vortical perturbations for single spatial harmonics, in stably stratified, di erentially rotating disks, again in the framework of a nonmodal analysis. We find that these 3D perturbations also undergo substantial transient growth, and that they reach a peak amplitude that is comparable to that of 2D perturbations, as long as their vertical scale remains of the order of the azimuthal scale. When the vertical wave-number exceeds the azimuthal one, the amplification rate is reduced, but this may be more than compensated to by the huge Reynolds number and the high Shear rate characterizing astrophysical Keplerian disks. Whereas in 2D the Coriolis force had no impact on the transient growth, in 3D this force somewhat constricts the characteristics of the perturbation dynamics in disk flows, and the initial transient growth is followed by some reduction in amplitude. These dierences are quantitative, rather than of fundamental character. But the 3D case presents two interesting novelties. In plane parallel flow, the perturbations do not decay after their transient amplification, but their energy stays on a plateau before being dissipated through viscous friction. More importantly, especially for the astrophysicist, in disk flow the 3D vortex mode perturbations excite density-spiral waves, whose energy also settles on a plateau before viscous dissipation. These local vortex mode perturbations fit naturally into the bypass concept of Hydrodynamic Shear turbulence, which was first developed for plane-parallel flows. We submit that these perturbations will also play an important role in the onset and in the maintenance of turbulence in Keplerian disks.
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on Hydrodynamic Shear turbulence in keplerian disks via transient growth to bypass transition
Astronomy and Astrophysics, 2003Co-Authors: G. D. Chagelishvili, Jean-paul Zahn, Alexander G. Tevzadze, J. G. LominadzeAbstract:This paper deals with the problem of Hydrodynamic Shear turbulence in non-magnetized Keplerian disks. Several papers have appeared recently on the subject, on possible linear instabilities which may be due to the presence of a stable stratification, or caused by deviations from cylindrical rotation. Here we wish to draw attention to another route to Hydrodynamic turbulence, which seems to be little known by the astrophysical community, but which has been intensively discussed among fluid dynamicists during the past decade. In this so-called bypass concept for the onset of turbulence, perturbations undergo transient growth and if they have initially a finite amplitude they may reach an amplitude that is suciently large to allow positive feedback through nonlinear interactions. This transient growth is linear in nature, and thus it diers in principle from the well-known nonlinear instability. We describe the type of perturbations that according to this process are the most likely to lead to turbulence, namely non-axisymmetric vortex mode perturbations in the two dimensional limit. We show that the apparently inhibiting action of the Coriolis force on the dynamics of such vortical perturbations is substantially diminished due to the pressure perturbations, contrary to current opinion. We stress the similarity of the turbulent processes in Keplerian disks and in Cartesian flows and conclude that the prevalent skepticism of the astrophysical community about the occurrence of Hydrodynamic Shear turbulence in such disks is not founded.
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On Hydrodynamic Shear turbulence in Keplerian disks: via transient growth to bypass transition
Astronomy & Astrophysics, 2003Co-Authors: G. D. Chagelishvili, Jean-paul Zahn, Alexander G. Tevzadze, J. G. LominadzeAbstract:This paper deals with the problem of Hydrodynamic Shear turbulence in non-magnetized Keplerian disks. We wish to draw attention to a route to Hydrodynamic turbulence which seems to be little known by the astrophysical community, but which has been intensively discussed among fluid dynamicists during the past decade. In this so-called `bypass' concept for the onset of turbulence, perturbations undergo a transient growth, and they may reach an amplitude that is sufficiently large to allow positive feedback through nonlinear interactions. This transient growth is linear in nature, and thus it differs in principle from the well-known nonlinear instability. We describe the type of perturbations that according to this process are the most likely to lead to turbulence, namely non-axisymmetric vortex mode perturbations in the two dimensional limit. We show that the apparently inhibiting action of the Coriolis force on the dynamics of such vortical perturbations is substantially diminished due to the pressure perturbations, contrary to current opinion. We stress the similarity of the turbulent processes in Keplerian disks and in Cartesian flows and conclude that the prevalent skepticism of the astrophysical community on the occurrence of Hydrodynamic Shear turbulence in such disks is not founded.
G. D. Chagelishvili - One of the best experts on this subject based on the ideXlab platform.
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On Hydrodynamic Shear turbulence in stratified Keplerian disks: Transient growth of small-scale 3D vortex mode perturbations
Astronomy & Astrophysics, 2003Co-Authors: Alexander G. Tevzadze, G. D. Chagelishvili, Jean-paul Zahn, R. G. Chanishvili, J. G. LominadzeAbstract:This is a sequel to Paper I (Chagelishvili et al. 2003), where we presented the so-called bypass concept for the onset of turbulence in Shearing flows. According to this concept, which was worked out during the last decade by the Hydrodynamic community for spectrally stable flows, vortical perturbations undergo transient growth by extracting energy from the Shear (a linear process), thereby reaching an amplitude which is sucient to allow for non-linear interactions which, by positive feedback, sustain turbulence. In Paper I we described this transient growth for 2D perturbations in a Keplerian disk; we showed that their kinematics was the same as in plane-parallel flow, and thus that they were not modified by the presence of the Coriolis force. In the present paper, we pursue our goal of applying the bypass scenario to astrophysical disks: we investigate the linear dynamics of 3D small-scale vortical perturbations for single spatial harmonics, in stably stratified, di erentially rotating disks, again in the framework of a nonmodal analysis. We find that these 3D perturbations also undergo substantial transient growth, and that they reach a peak amplitude that is comparable to that of 2D perturbations, as long as their vertical scale remains of the order of the azimuthal scale. When the vertical wave-number exceeds the azimuthal one, the amplification rate is reduced, but this may be more than compensated to by the huge Reynolds number and the high Shear rate characterizing astrophysical Keplerian disks. Whereas in 2D the Coriolis force had no impact on the transient growth, in 3D this force somewhat constricts the characteristics of the perturbation dynamics in disk flows, and the initial transient growth is followed by some reduction in amplitude. These dierences are quantitative, rather than of fundamental character. But the 3D case presents two interesting novelties. In plane parallel flow, the perturbations do not decay after their transient amplification, but their energy stays on a plateau before being dissipated through viscous friction. More importantly, especially for the astrophysicist, in disk flow the 3D vortex mode perturbations excite density-spiral waves, whose energy also settles on a plateau before viscous dissipation. These local vortex mode perturbations fit naturally into the bypass concept of Hydrodynamic Shear turbulence, which was first developed for plane-parallel flows. We submit that these perturbations will also play an important role in the onset and in the maintenance of turbulence in Keplerian disks.
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on Hydrodynamic Shear turbulence in keplerian disks via transient growth to bypass transition
Astronomy and Astrophysics, 2003Co-Authors: G. D. Chagelishvili, Jean-paul Zahn, Alexander G. Tevzadze, J. G. LominadzeAbstract:This paper deals with the problem of Hydrodynamic Shear turbulence in non-magnetized Keplerian disks. Several papers have appeared recently on the subject, on possible linear instabilities which may be due to the presence of a stable stratification, or caused by deviations from cylindrical rotation. Here we wish to draw attention to another route to Hydrodynamic turbulence, which seems to be little known by the astrophysical community, but which has been intensively discussed among fluid dynamicists during the past decade. In this so-called bypass concept for the onset of turbulence, perturbations undergo transient growth and if they have initially a finite amplitude they may reach an amplitude that is suciently large to allow positive feedback through nonlinear interactions. This transient growth is linear in nature, and thus it diers in principle from the well-known nonlinear instability. We describe the type of perturbations that according to this process are the most likely to lead to turbulence, namely non-axisymmetric vortex mode perturbations in the two dimensional limit. We show that the apparently inhibiting action of the Coriolis force on the dynamics of such vortical perturbations is substantially diminished due to the pressure perturbations, contrary to current opinion. We stress the similarity of the turbulent processes in Keplerian disks and in Cartesian flows and conclude that the prevalent skepticism of the astrophysical community about the occurrence of Hydrodynamic Shear turbulence in such disks is not founded.
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On Hydrodynamic Shear turbulence in Keplerian disks: via transient growth to bypass transition
Astronomy & Astrophysics, 2003Co-Authors: G. D. Chagelishvili, Jean-paul Zahn, Alexander G. Tevzadze, J. G. LominadzeAbstract:This paper deals with the problem of Hydrodynamic Shear turbulence in non-magnetized Keplerian disks. We wish to draw attention to a route to Hydrodynamic turbulence which seems to be little known by the astrophysical community, but which has been intensively discussed among fluid dynamicists during the past decade. In this so-called `bypass' concept for the onset of turbulence, perturbations undergo a transient growth, and they may reach an amplitude that is sufficiently large to allow positive feedback through nonlinear interactions. This transient growth is linear in nature, and thus it differs in principle from the well-known nonlinear instability. We describe the type of perturbations that according to this process are the most likely to lead to turbulence, namely non-axisymmetric vortex mode perturbations in the two dimensional limit. We show that the apparently inhibiting action of the Coriolis force on the dynamics of such vortical perturbations is substantially diminished due to the pressure perturbations, contrary to current opinion. We stress the similarity of the turbulent processes in Keplerian disks and in Cartesian flows and conclude that the prevalent skepticism of the astrophysical community on the occurrence of Hydrodynamic Shear turbulence in such disks is not founded.
Alexander G. Tevzadze - One of the best experts on this subject based on the ideXlab platform.
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On Hydrodynamic Shear turbulence in stratified Keplerian disks: Transient growth of small-scale 3D vortex mode perturbations
Astronomy & Astrophysics, 2003Co-Authors: Alexander G. Tevzadze, G. D. Chagelishvili, Jean-paul Zahn, R. G. Chanishvili, J. G. LominadzeAbstract:This is a sequel to Paper I (Chagelishvili et al. 2003), where we presented the so-called bypass concept for the onset of turbulence in Shearing flows. According to this concept, which was worked out during the last decade by the Hydrodynamic community for spectrally stable flows, vortical perturbations undergo transient growth by extracting energy from the Shear (a linear process), thereby reaching an amplitude which is sucient to allow for non-linear interactions which, by positive feedback, sustain turbulence. In Paper I we described this transient growth for 2D perturbations in a Keplerian disk; we showed that their kinematics was the same as in plane-parallel flow, and thus that they were not modified by the presence of the Coriolis force. In the present paper, we pursue our goal of applying the bypass scenario to astrophysical disks: we investigate the linear dynamics of 3D small-scale vortical perturbations for single spatial harmonics, in stably stratified, di erentially rotating disks, again in the framework of a nonmodal analysis. We find that these 3D perturbations also undergo substantial transient growth, and that they reach a peak amplitude that is comparable to that of 2D perturbations, as long as their vertical scale remains of the order of the azimuthal scale. When the vertical wave-number exceeds the azimuthal one, the amplification rate is reduced, but this may be more than compensated to by the huge Reynolds number and the high Shear rate characterizing astrophysical Keplerian disks. Whereas in 2D the Coriolis force had no impact on the transient growth, in 3D this force somewhat constricts the characteristics of the perturbation dynamics in disk flows, and the initial transient growth is followed by some reduction in amplitude. These dierences are quantitative, rather than of fundamental character. But the 3D case presents two interesting novelties. In plane parallel flow, the perturbations do not decay after their transient amplification, but their energy stays on a plateau before being dissipated through viscous friction. More importantly, especially for the astrophysicist, in disk flow the 3D vortex mode perturbations excite density-spiral waves, whose energy also settles on a plateau before viscous dissipation. These local vortex mode perturbations fit naturally into the bypass concept of Hydrodynamic Shear turbulence, which was first developed for plane-parallel flows. We submit that these perturbations will also play an important role in the onset and in the maintenance of turbulence in Keplerian disks.
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on Hydrodynamic Shear turbulence in keplerian disks via transient growth to bypass transition
Astronomy and Astrophysics, 2003Co-Authors: G. D. Chagelishvili, Jean-paul Zahn, Alexander G. Tevzadze, J. G. LominadzeAbstract:This paper deals with the problem of Hydrodynamic Shear turbulence in non-magnetized Keplerian disks. Several papers have appeared recently on the subject, on possible linear instabilities which may be due to the presence of a stable stratification, or caused by deviations from cylindrical rotation. Here we wish to draw attention to another route to Hydrodynamic turbulence, which seems to be little known by the astrophysical community, but which has been intensively discussed among fluid dynamicists during the past decade. In this so-called bypass concept for the onset of turbulence, perturbations undergo transient growth and if they have initially a finite amplitude they may reach an amplitude that is suciently large to allow positive feedback through nonlinear interactions. This transient growth is linear in nature, and thus it diers in principle from the well-known nonlinear instability. We describe the type of perturbations that according to this process are the most likely to lead to turbulence, namely non-axisymmetric vortex mode perturbations in the two dimensional limit. We show that the apparently inhibiting action of the Coriolis force on the dynamics of such vortical perturbations is substantially diminished due to the pressure perturbations, contrary to current opinion. We stress the similarity of the turbulent processes in Keplerian disks and in Cartesian flows and conclude that the prevalent skepticism of the astrophysical community about the occurrence of Hydrodynamic Shear turbulence in such disks is not founded.
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On Hydrodynamic Shear turbulence in Keplerian disks: via transient growth to bypass transition
Astronomy & Astrophysics, 2003Co-Authors: G. D. Chagelishvili, Jean-paul Zahn, Alexander G. Tevzadze, J. G. LominadzeAbstract:This paper deals with the problem of Hydrodynamic Shear turbulence in non-magnetized Keplerian disks. We wish to draw attention to a route to Hydrodynamic turbulence which seems to be little known by the astrophysical community, but which has been intensively discussed among fluid dynamicists during the past decade. In this so-called `bypass' concept for the onset of turbulence, perturbations undergo a transient growth, and they may reach an amplitude that is sufficiently large to allow positive feedback through nonlinear interactions. This transient growth is linear in nature, and thus it differs in principle from the well-known nonlinear instability. We describe the type of perturbations that according to this process are the most likely to lead to turbulence, namely non-axisymmetric vortex mode perturbations in the two dimensional limit. We show that the apparently inhibiting action of the Coriolis force on the dynamics of such vortical perturbations is substantially diminished due to the pressure perturbations, contrary to current opinion. We stress the similarity of the turbulent processes in Keplerian disks and in Cartesian flows and conclude that the prevalent skepticism of the astrophysical community on the occurrence of Hydrodynamic Shear turbulence in such disks is not founded.
Jean-paul Zahn - One of the best experts on this subject based on the ideXlab platform.
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On Hydrodynamic Shear turbulence in stratified Keplerian disks: Transient growth of small-scale 3D vortex mode perturbations
Astronomy & Astrophysics, 2003Co-Authors: Alexander G. Tevzadze, G. D. Chagelishvili, Jean-paul Zahn, R. G. Chanishvili, J. G. LominadzeAbstract:This is a sequel to Paper I (Chagelishvili et al. 2003), where we presented the so-called bypass concept for the onset of turbulence in Shearing flows. According to this concept, which was worked out during the last decade by the Hydrodynamic community for spectrally stable flows, vortical perturbations undergo transient growth by extracting energy from the Shear (a linear process), thereby reaching an amplitude which is sucient to allow for non-linear interactions which, by positive feedback, sustain turbulence. In Paper I we described this transient growth for 2D perturbations in a Keplerian disk; we showed that their kinematics was the same as in plane-parallel flow, and thus that they were not modified by the presence of the Coriolis force. In the present paper, we pursue our goal of applying the bypass scenario to astrophysical disks: we investigate the linear dynamics of 3D small-scale vortical perturbations for single spatial harmonics, in stably stratified, di erentially rotating disks, again in the framework of a nonmodal analysis. We find that these 3D perturbations also undergo substantial transient growth, and that they reach a peak amplitude that is comparable to that of 2D perturbations, as long as their vertical scale remains of the order of the azimuthal scale. When the vertical wave-number exceeds the azimuthal one, the amplification rate is reduced, but this may be more than compensated to by the huge Reynolds number and the high Shear rate characterizing astrophysical Keplerian disks. Whereas in 2D the Coriolis force had no impact on the transient growth, in 3D this force somewhat constricts the characteristics of the perturbation dynamics in disk flows, and the initial transient growth is followed by some reduction in amplitude. These dierences are quantitative, rather than of fundamental character. But the 3D case presents two interesting novelties. In plane parallel flow, the perturbations do not decay after their transient amplification, but their energy stays on a plateau before being dissipated through viscous friction. More importantly, especially for the astrophysicist, in disk flow the 3D vortex mode perturbations excite density-spiral waves, whose energy also settles on a plateau before viscous dissipation. These local vortex mode perturbations fit naturally into the bypass concept of Hydrodynamic Shear turbulence, which was first developed for plane-parallel flows. We submit that these perturbations will also play an important role in the onset and in the maintenance of turbulence in Keplerian disks.
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on Hydrodynamic Shear turbulence in keplerian disks via transient growth to bypass transition
Astronomy and Astrophysics, 2003Co-Authors: G. D. Chagelishvili, Jean-paul Zahn, Alexander G. Tevzadze, J. G. LominadzeAbstract:This paper deals with the problem of Hydrodynamic Shear turbulence in non-magnetized Keplerian disks. Several papers have appeared recently on the subject, on possible linear instabilities which may be due to the presence of a stable stratification, or caused by deviations from cylindrical rotation. Here we wish to draw attention to another route to Hydrodynamic turbulence, which seems to be little known by the astrophysical community, but which has been intensively discussed among fluid dynamicists during the past decade. In this so-called bypass concept for the onset of turbulence, perturbations undergo transient growth and if they have initially a finite amplitude they may reach an amplitude that is suciently large to allow positive feedback through nonlinear interactions. This transient growth is linear in nature, and thus it diers in principle from the well-known nonlinear instability. We describe the type of perturbations that according to this process are the most likely to lead to turbulence, namely non-axisymmetric vortex mode perturbations in the two dimensional limit. We show that the apparently inhibiting action of the Coriolis force on the dynamics of such vortical perturbations is substantially diminished due to the pressure perturbations, contrary to current opinion. We stress the similarity of the turbulent processes in Keplerian disks and in Cartesian flows and conclude that the prevalent skepticism of the astrophysical community about the occurrence of Hydrodynamic Shear turbulence in such disks is not founded.
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On Hydrodynamic Shear turbulence in Keplerian disks: via transient growth to bypass transition
Astronomy & Astrophysics, 2003Co-Authors: G. D. Chagelishvili, Jean-paul Zahn, Alexander G. Tevzadze, J. G. LominadzeAbstract:This paper deals with the problem of Hydrodynamic Shear turbulence in non-magnetized Keplerian disks. We wish to draw attention to a route to Hydrodynamic turbulence which seems to be little known by the astrophysical community, but which has been intensively discussed among fluid dynamicists during the past decade. In this so-called `bypass' concept for the onset of turbulence, perturbations undergo a transient growth, and they may reach an amplitude that is sufficiently large to allow positive feedback through nonlinear interactions. This transient growth is linear in nature, and thus it differs in principle from the well-known nonlinear instability. We describe the type of perturbations that according to this process are the most likely to lead to turbulence, namely non-axisymmetric vortex mode perturbations in the two dimensional limit. We show that the apparently inhibiting action of the Coriolis force on the dynamics of such vortical perturbations is substantially diminished due to the pressure perturbations, contrary to current opinion. We stress the similarity of the turbulent processes in Keplerian disks and in Cartesian flows and conclude that the prevalent skepticism of the astrophysical community on the occurrence of Hydrodynamic Shear turbulence in such disks is not founded.
Sriram Neelamegham - One of the best experts on this subject based on the ideXlab platform.
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Von Willebrand Factor self-association on platelet GpIbα under Hydrodynamic Shear: effect on Shear-induced platelet activation
Blood, 2010Co-Authors: Kannayakanahalli M. Dayananda, Indrajeet Singh, Nandini Mondal, Sriram NeelameghamAbstract:The function of the mechanosensitive, multimeric blood protein von Willebrand factor (VWF) is dependent on its size. We tested the hypothesis that VWF may self-associate on the platelet glycoprotein Ibα (GpIbα) receptor under Hydrodynamic Shear. Consistent with this proposition, whereas Alexa-488–conjugated VWF (VWF-488) bound platelets at modest levels, addition of unlabeled VWF enhanced the extent of VWF-488 binding. Recombinant VWF lacking the A1-domain was conjugated with Alexa-488 to produce ΔA1-488. Although ΔA1-488 alone did not bind platelets under Shear, this protein bound GpIbα on addition of either purified plasma VWF or recombinant full-length VWF. The extent of self-association increased with applied Shear stress more than ∼ 60 to 70 dyne/cm2. ΔA1-488 bound platelets in the milieu of plasma. On application of fluid Shear to whole blood, half of the activated platelets had ΔA1-488 bound, suggesting that VWF self-association may be necessary for cell activation. Shearing platelets with 6-μm beads bearing either immobilized VWF or anti-GpIbα mAb resulted in cell activation at Shear stress down to 2 to 5 dyne/cm2. Taken together, the data suggest that fluid Shear in circulation can increase the effective size of VWF bound to platelet GpIbα via protein self-association. This can trigger mechanotransduction and cell activation by enhancing the drag force applied on the cell-surface receptor.
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Aspects of Hydrodynamic Shear regulating Shear-induced platelet activation and self-association of von Willebrand factor in suspension
Blood, 2002Co-Authors: Harish Shankaran, Paschalis Alexandridis, Sriram NeelameghamAbstract:The binding of plasma von Willebrand factor (VWF) to platelet receptor GpIb under high Hydrodynamic Shear leads to platelet activation and subsequent Shear-induced platelet aggregation (SIPA). We quantitatively examined the aspects of fluid flow that regulate platelet activation by subjecting human blood and isolated platelets to well-defined Shear conditions in a cone-plate viscometer. We made the following observations. First, Annexin V binding to phosphatidyl serine expressed on activated cells was detectable within 10 seconds of Shear application. Second, fluid Shear stress rather than Shear rate controls platelet activation, and a threshold Shear stress of approximately 80 dyn/cm2 is necessary to induce significant activation. Under these conditions, individual domains of soluble VWF and platelet GpIb are subjected to similar magnitudes of fluid forces on the order of 0.1 pN, whereas GpIb with bound VWF is subjected to 1 pN. Third, cell-cell collisions and time-varying stresses are not essential for platelet activation. Fourth, the mechanism of platelet activation can be resolved in 2 steps based on the contribution of VWF and fluid forces. Fluid Shear and VWF are required during the first step, when GpIb-VWF binding likely occurs. Subsequently, high Shear forces alone in the absence of VWF in suspension can induce platelet activation. In other experiments, purified VWF was subjected to Shear in the viscometer, and VWF morphology was assessed using light scattering. These studies demonstrate, for the first time, the ability of Hydrodynamic forces to induce VWF aggregation in suspension. This VWF self-association may be an additional feature involved in controlling cell adhesion rates in circulation.
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Modeling the reversible kinetics of neutrophil aggregation under Hydrodynamic Shear
Biophysical journal, 1997Co-Authors: Sriram Neelamegham, A.d. Taylor, J. D. Hellums, C. W. Smith, M. Dembo, Scott I. SimonAbstract:Neutrophil emigration into inflamed tissue is mediated by beta 2-integrin and L-selectin adhesion receptors. Homotypic neutrophil aggregation is also dependent on these molecules, and it provides a model system in which to study adhesion dynamics. In the current study we formulated a mathematical model for cellular aggregation in a linear Shear field based on Smoluchowski's two-body collision theory. Neutrophil suspensions activated with chemotactic stimulus and Sheared in a cone-plate viscometer rapidly aggregate. Over a range of Shear rates (400–800 s-1), approximately 90% of the single cells were recruited into aggregates ranging from doublets to groupings larger than sextuplets. The adhesion efficiency fit to these kinetics reached maximum levels of > 70%. Formed aggregates remained intact and resistant to Shear up to 120 s, at which time they spontaneously dissociated back to singlets. The rate of cell disaggregation was linearly proportional to the applied Shear rate, and it was approximately 60% lower for doublets as compared to larger aggregates. By accounting for the time-dependent changes in adhesion efficiency, disaggregation rate, and the effects of aggregate geometry, we succeeded in predicting the reversible kinetics of aggregation over a wide range of Shear rates and cell concentrations. The combination of viscometry with flow cytometry and mathematical analysis as presented here represents a novel approach to differentiating between the effects of Hydrodynamics and the intrinsic biological processes that control cell adhesion.
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Molecular dynamics of the transition from L-selectin- to beta 2-integrin-dependent neutrophil adhesion under defined Hydrodynamic Shear
Biophysical journal, 1996Co-Authors: A.d. Taylor, Sriram Neelamegham, J. D. Hellums, C. W. Smith, S.i. SimonAbstract:Homotypic adhesion o2 neutrophils stimulated with chemoattractant is analogous to capture on vascular endothelium in that both processes depend on L-selectin and beta 2-integrin adhesion receptors. Under Hydrodynamic Shear, cell adhesion requires that receptors bind sufficient ligand over the duration of intercellular contact to withstand Hydrodynamic stresses. Using cone-plate viscometry to apply a uniform linear Shear field to suspensions of neutrophils, we conducted a detailed examination of the effect of Shear rate and Shear stress on the kinetics of cell aggregation. A collisional analysis based on Smoluchowski's flocculation theory was employed to fit the kinetics of aggregation with an adhesion efficiency. Adhesion efficiency increased with Shear rate from approximately 20% at 100 s-1 to approximately 80% at 400 s-1. The increase in adhesion efficiency. Adhesion efficiency increased with Shear rate from approximately 20% at 100 s-1 to approximately 80% at 400 s-1. The increase in adhesion efficiency with Shear was dependent on L-selectin, and peak efficiency was maintained over a relatively narrow range of Shear rates (400–800 s-1) and Shear stresses (4–7 dyn/cm2). When L-selectin was blocked with antibody, beta 2-integrin (CD11a, b) supported adhesion at low Shear rates (
