Absence Of Shear Research Articles

Mesoscopic Simulation of Aggregate Characteristics of Asphaltene Molecules Under Shear Fields.

Behaviors of asphaltene molecules in toluene under a shear force field were investigated by dissipative particle dynamics (DPD). The results showed that asphaltene molecules aggregated into nanoaggregates (NAs) in three forms, mainly in the face-to-face type, which contained up to 7 asphaltene molecules. In the aggregates, the distance between aromatic sheets (ASes) of adjacent asphaltene molecules was about 6 Å, and the minimum was 5.49 Å. The composition of NAs changed dynamically. In the absence of shear, the aggregates lasted for more than 3000 ps and up to 8000 ps. The asphaltene molecules in an aggregate might reaggregate once dispersed. Both the number and size of the aggregates decreased under the shear force field, and the duration decreased to less than 1000 ps. The direction of the ASes was distributed randomly when the shear rate was zero. Once sheared, the angle between the ASes and the shear force field plane decreased while the range of it expanded. The ASes tended to be parallel to the shear field and the angle between the two concentrated below 40°. As the shear rate increased, the angle decreased and the distribution was more concentrated.

On the use of time-dependent fluids for delaying onset of transition to turbulence in the flat plate boundary-layer flow: A passive control of flow

Inelastic time-dependent fluids display continuous and reversible changes in viscosity when subjected to a constant shear-rate. These alterations arise from the gradual modification of the material’s microstructure due to shear-induced effects, known as shear rejuvenation. When this process generates smaller structural units, it is termed thixotropy; conversely, if it produces larger units, it is labeled anti-thixotropy. Aging is another characteristic of such fluids, denoting the capacity of the material to regain its original structure in the absence of shear, thus reversing the initial time-dependent change. This phenomenon often results from thermally activated Brownian motion prompting the reorganization of the material’s microconstituents. Consequently, attractive forces between these components can instigate the reconstruction of a network-like structure within the material. This study centers on investigating how variations in fluid microstructure impact the onset of transition to turbulence in a flat plate boundary-layer flow. Specifically, the focus is on cases where larger structural units emerge during the breakdown process (anti-thixotropy). To represent such fluids, the Quemada model, an inelastic structural-kinetic model, is employed. This model effectively captures thixotropy and anti-thixotropy by appropriately configuring model parameters. The analysis begins with obtaining a local similarity solution for the generalized Blasius equation, representing the base flow. Subsequently, the stability of this flow is assessed using linear temporal stability theory. This involves introducing infinitesimally-small normal-mode perturbations to the base flow, yielding the generalized Orr–Sommerfeld equation. Solving this equation using the spectral method provides insights into stability. Results from this study indicate that for low Deborah numbers, the shear-thickening behavior prevails, causing destabilization. In contrast, higher Deborah numbers lead to stability. This implies that anti-thixotropy effectively delays the onset of transition to turbulence and could hold practical applications for flow control.

The Anticoagulant Systems Cooperate Synergistically on Phospholipid Vesicle and Endothelial Cell Membranes, but Not on Platelets

Introduction: Thrombin, the enzyme which converts fibrinogen into a fibrin clot, is produced by the prothrombinase complex, composed of factor Xa (FXa) and factor Va (FVa). Down-regulation of this process is critical, as excess thrombin can lead to life threatening thrombotic events. FXa and FVa are inhibited by the anticoagulants tissue factor pathway inhibitor alpha (TFPIα) and activated protein C (APC), respectively, and their common cofactor protein S (PS). TFPIα, APC, and PS function synergistically on the surface of phospholipid vesicles (PLs). We have also recently reported a shear-dependent interaction between PS and von Willebrand factor (VWF), which partially blocks its anticoagulant function. Here, we investigated the function of the TFPIα/APC/PS anticoagulant system on physiologic membrane surfaces (platelets and endothelial cells, or ECs), and the effect of VWF on prothrombinase inhibition in these different membrane environments. Methods: Thrombin generation was measured in plasma and platelet-rich plasma (PRP) by calibrated automated thrombography, purified prothrombinase activity was assayed using a chromogenic substrate, and FVa cleavage was monitored by immunoblotting. Experiments were performed with synthetic PLs, washed platelets, or cultured EA.hy926 cells, an EC line. Experiments involving VWF were performed in the presence or absence of shear. Results: In plasma TG, as we have previously published, PS anticoagulant activity was greatly enhanced by addition of thrombomodulin (TM), to promote protein C (PC) activation. TM decreased thrombin generation in a PS-dependent manner. The effect of TM and PS was enhanced by the addition of TFPIα, particularly at low PS concentrations. Conversely, inhibitory antibodies against TFPI and PC had an additive effect on plasma TG which was mimicked by inhibiting PS alone. Similar results were obtained in plasma supplemented with ECs (which provide TM) or in PRP. However, in PRP, the antibodies reversed TG beyond what was seen with tissue factor-initiation alone. In purified protein systems, performed using either PLs or ECs, physiologic TFPIα concentrations had no detectable effect on thrombin activation by prothrombinase, unless APC was present in the system. The greatest inhibitory activity was observed when TFPIα, APC, and PS were all present, and was similar on ECs and PLs. Similarly, inhibition of FXa by TFPIα was found to render FVa susceptible to proteolysis by APC on either PLs or ECs. However, prothrombinase assembled on activated platelets was protected from inhibition, even in the presence of TFPIα, APC, and PS, as measured either by thrombin activation or FVa cleavage. Finally, we assessed the functional consequences of the PS/VWF interaction. In purified systems with PLs, sheared VWF dose-dependently reversed FXa inhibition by PS/TFPIα, measured using a chromogenic FXa substrate. Conversely, APC cofactor function, as measured by FVa cleavage, was unaffected on either PLs or activated platelets. Consistent with this, thrombin activation by prothrombinase was unaffected by sheared VWF on these surfaces. Interestingly, sheared VWF promoted prothrombinase function on ECs, increasing the rate of thrombin activation beyond that observed in the absence of the anticoagulants. Conclusions: We propose a model of prothrombinase inhibition through combined targeting of both FXa and FVa, and that this mechanism enables down-regulation of thrombin activation outside of a platelet clot. On PL or EC membranes in the plasma environment, APC, TFPIα, and PS cooperate synergistically to inhibit prothrombinase activity, preventing excessive clot propagation. Conversely, platelets protect prothrombinase from inhibition, supporting a procoagulant environment within the clot. The anticoagulant system appears to function similarly on PLs and on ECs, except that VWF has greater effect on ECs, suggesting that the protection mediated by platelets is due to a platelet component not present in ECs. We hypothesize that these regulatory mechanisms serve to localize procoagulant activity within the platelet plug and suppress it on ECs downstream of a clot.

Rate limiting step of the allosteric activation of the bacterial adhesin FimH investigated by molecular dynamics simulations.

The bacterial adhesin FimH is a model for the study of protein allostery because its structure has been resolved in multiple configurations, including the active and the inactive state. FimH consists of a pilin domain (PD) that anchors it to the rest of the fimbria and an allosterically regulated lectin domain (LD) that binds mannose on the surface of infected cells. Under normal conditions, the two domains are docked to each other and LD binds mannose weakly. However, in the presence of tensile force generated by shear the domains separate and conformational changes propagate across LD resulting in a stronger bond to mannose. Recently, the crystallographic structure of a variant of FimH has been resolved, called , where PD contains 10 mutations near the inter-domain interface. Although the X-ray structures of FimH and are almost identical, experimental evidence shows that is activated even in the absence of shear. Here, molecular dynamics simulations combined with the Jarzynski equality were used to investigate the discrepancy between the crystallographic structures and the functional assays. The results indicate that the free energy barrier of the unbinding process between LD and PD is drastically reduced in . Rupture of inter-domain hydrogen bonds involving R166 constitutes a rate limiting step of the domain separation process and occurs more readily in than FimH. In conclusion, the mutations in shift the equilibrium toward an equal occupancy of bound and unbound states for LD and PD by reducing a rate limiting step.

Sedimentation in particle-laden flows with and without velocity shear

The vertical transport of sediment from particle-laden flows in marine settings can be enhanced by a settling-driven convective instability. The presence of a horizontal velocity shear can further influence this vertical transport. We conduct numerical simulations to investigate the vertical sediment transport in the presence and absence of shear. We show how this transport is determined by a competition between the growth of the settling-driven convective instability (Rayleigh–Taylor) and the stratified shear instability (Kelvin–Helmholtz). In the absence of shear, the Rayleigh–Taylor instability drives enhanced vertical sediment transport; this effect increases with the Stokes settling velocity of the particles and decreases with the stratification strength. In the presence of shear, there are two regimes of effective settling. When the Kelvin–Helmholtz instability grows rapidly and suppresses the Rayleigh–Taylor instability, the effective settling velocity is significantly reduced. On the other hand, if the Rayleigh–Taylor instability dominates and completely inhibits the Kelvin–Helmholtz instability, the effective settling velocity is enhanced due to the additional energy input by shear. We explore the parameter space of these regimes and interpret their physics.

Microvoid Formation of Ferrite-martensite Dual-phase Steel via Tensile Deformation after Severe Plastic Shear-deformation

One of the objectives for the development of high-strength dual-phase (DP) steel is improving the stretch-flangeability. Large-strained sheared edges are deformed and frequently cracked during stretch-flange formation. Considering shearing as the first deformation, the stretch-flange deformation may be regarded as a secondary deformation. To improve the stretch-flangeability of the DP steels, many researchers have analyzed the microvoid formation. However, in these analyses, the shearing process was not considered. With this background, ex-situ mini-bending tests combined with scanning electron microscopy (SEM) monitoring of microvoid formation were conducted during the secondary deformation. Prior to the secondary deformation, several microvoids were observed on the sheared surface and fine subgrains formed in the ferrite. During secondary deformation, the preliminary microvoids present at the ferrite-martensite interface propagated into the ferrite phase. In contrast, this behavior was not observed for the reamed surface deformation, which was formed without preliminary deformation. Furthermore, microvoids were initiated on ferrite grains that were not present at the ferrite-martensite interface, and martensite islands were not cracked during secondary deformation. This result is noteworthy because martensite cracking was the main factor involved in microvoid initiation, in the absence of shearing. Electron backscattering diffraction analysis revealed that the work hardening of ferrite, prior to the secondary deformation, caused a deviation in the strain concentration sites from those found in the reamed surface deformation. Therefore, this study elucidated microvoid formation on preliminary deformed surfaces via shearing and provided insights for material development considering deformations on the sheared surfaces of materials.

Competition of shearing and cavitation effects on the deformation behavior of isotactic polypropylene during stretching

Owing to the unique cross-hatched structure of α crystal, the deformation behavior of isotactic polypropylene (iPP) differs considerably with the traditional polymers. The influence of crystalline structures on the cavitation and shearing effects of α-iPP under tensile loading is still not well established. In this work, various iPP samples were prepared via crystallizing from 0 °C to 130 °C, after which the crystalline structures were characterized via differential scanning calorimetry, polarized optical microscopy and scanning electron microscopy. The lamellar thickness and crystallinity of α-iPP precursor films change slightly, while the content of tangential lamellae in α-spherulite and the spherulite size increase significantly with the decreasing supercooling. On the other hand, the morphological evolution of α-iPP during stretching was tracked by in-situ two-dimensional small angle X-ray scattering. It is found that cavitation effect become dominant instead of shearing effect when the size of α-spherulite exceeds 25 μm. Furthermore, we disclose four typical deformation behaviors of α-iPP resulting from the competition between intra-spherulitic deformation and inter-spherulitic deformation, namely the shearing without cavitation, shearing then localized cavitation, homogeneous cavitation with concomitant shearing, and cavitation with absence of shearing. Accordingly, we construct a route for the structural evolution of α-iPP with different crystalline structures during stretching, which provides an effective guidance to produce diverse iPP films with desired structures and tunable functionalities.

Dynamic-bond-induced sticky friction tailors non-Newtonian rheology.

Frictional network formation has become a new paradigm for understanding the non-Newtonian shear-thickening behavior of dense suspensions. Recent studies have exclusively focused on interparticle friction that instantaneously vanishes when applied shear is ceased. Herein, we investigate a friction that emerges from dynamic chemical bridging of functionalized particle surfaces sheared into close proximity. This enables tailoring of both friction magnitude and the time release of the frictional coupling. The experiments use dense suspensions of thiol-functionalized particles suspended in ditopic polymers endcapped with benzalcyanoacetamide Michael-acceptors. The subsequent room temperature, catalyst-free dynamic thia-Michael reactions can form bridging interactions between the particles with dynamic covalent bonds that linger after formation and release in the absence of shear. This chemical friction mimics physical friction but is stickier, leading to tunable rheopexy. The effect of sticky friction on dense suspension rheology is explored by varying the electronic nature of the benzalcyanoacetamide moiety, the molecular weight of the ditopic polymers, the amount of a competitive bonding compound, and temperature. These results demonstrate how dynamic-bond-induced sticky friction can be used to systematically control the time dependence of the non-Newtonian suspension rheology.

РАСЧЕТ КОЭФФИЦИЕНТА СОПРОТИВЛЕНИЯ СВОБОДНОМУ КАЧЕНИЮ КОЛЕСА С ДЕФОРМИРУЕМЫМ ОБОДОМ

A new method for calculating rolling resistance is developed. This method includes a simplified structural model of a wheel in the form of a rigid cylinder with a thin viscoelastic rim. The wheel loading mode is considered in the absence of shearing (horizontal) force. In the entire contact area, it is assumed that the wheel is gripped with a non-deformable support surface. Deformation of the viscoelastic layer is analyzed on the basis of the Winkle model. In contrast to the previously known ones, the proposed method implies a description of the symmetry breaking in the distribution of contact pressure when a small torque is applied to the wheel, not exceeding the rolling resistance at rest. Contact pressure diagrams are obtained at different values of the torque applied to the wheel. It is shown that as the torque increases, the maximum value of the contact pressure increases, and the position of this maximum shifts in the direction of possible rolling. From the condition of violating the contact area dimensions at the beginning of rolling, an analytical expression is derived for the moment of rolling resistance at rest. The calculated dependence of this moment on the wheel draft is compared with known experimental data. When describing stationary free rolling, the asymmetry of the contact pressure corresponding to the beginning of rolling and the loss of energy during deformation of the viscoelastic material of the wheel rim are taken into account. The dependences of the coefficient of rolling resistance and wheel draft on the speed of the wheel center of mass at a fixed value of the vertical load are obtained. It is shown that taking into account the initial asymmetry of the contact pressure leads to a more intensive increase in the calculated estimates of the resistance coefficient and a less marked decrease in the wheel draft with an increase in rolling speed.

Hydrodynamic theory of p-atic liquid crystals.

We formulate a comprehensive hydrodynamic theory of two-dimensional liquid crystals with generic p-fold rotational symmetry, also known as p-atics, of which nematics (p=2) and hexatics (p=6) are the two best known examples. Previous hydrodynamic theories of p-atics are characterized by continuous O(2) rotational symmetry, which is higher than the discrete rotational symmetry of p-atic phases. By contrast, here we demonstrate that the discrete rotational symmetry allows the inclusion of additional terms in the hydrodynamic equations, which, in turn, lead to novel phenomena, such as the possibility of flow alignment at high shear rates, even for p>2. Furthermore, we show that any finite imposed shear will induce long-ranged orientational order in any p-atic liquid crystal, in contrast to the quasi-long-ranged order that occurs in the absence of shear. The induced order parameter scales like a nonuniversal power of the applied shear rate at small shear rates.

Roles of Focal Adhesion Kinase PTK2 and Integrin αIIbβ3 Signaling in Collagen- and GPVI-Dependent Thrombus Formation under Shear.

Glycoprotein (GP)VI and integrin αIIbβ3 are key signaling receptors in collagen-dependent platelet aggregation and in arterial thrombus formation under shear. The multiple downstream signaling pathways are still poorly understood. Here, we focused on disclosing the integrin-dependent roles of focal adhesion kinase (protein tyrosine kinase 2, PTK2), the shear-dependent collagen receptor GPR56 (ADGRG1 gene), and calcium and integrin-binding protein 1 (CIB1). We designed and synthetized peptides that interfered with integrin αIIb binding (pCIB and pCIBm) or mimicked the activation of GPR56 (pGRP). The results show that the combination of pGRP with PTK2 inhibition or of pGRP with pCIB > pCIBm in additive ways suppressed collagen- and GPVI-dependent platelet activation, thrombus buildup, and contraction. Microscopic thrombus formation was assessed by eight parameters (with script descriptions enclosed). The suppressive rather than activating effects of pGRP were confined to blood flow at a high shear rate. Blockage of PTK2 or interference of CIB1 no more than slightly affected thrombus formation at a low shear rate. Peptides did not influence GPVI-induced aggregation and Ca2+ signaling in the absence of shear. Together, these data reveal a shear-dependent signaling axis of PTK2, integrin αIIbβ3, and CIB1 in collagen- and GPVI-dependent thrombus formation, which is modulated by GPR56 and exclusively at high shear. This work thereby supports the role of PTK2 in integrin αIIbβ3 activation and signaling.

Recombinant FimH Adhesin Demonstrates How the Allosteric Catch Bond Mechanism Can Support Fast and Strong Bacterial Attachment in the Absence of Shear

The FimH protein of Escherichia coli is a model two-domain adhesin that is able to mediate an allosteric catch bond mechanism of bacterial cell attachment, where the mannose-binding lectin domain switches from an ‘inactive’ conformation with fast binding to mannose to an ‘active’ conformation with slow detachment from mannose. Because mechanical tensile force favors separation of the domains and, thus, FimH activation, it has been thought that the catch bonds can only be manifested in a fluidic shear-dependent mode of adhesion. Here, we used recombinant FimH variants with a weakened inter-domain interaction and show that a fast and sustained allosteric activation of FimH can also occur under static, non-shear conditions. Moreover, it appears that lectin domain conformational activation happens intrinsically at a constant rate, independently from its ability to interact with the pilin domain or mannose. However, the latter two factors control the rate of FimH deactivation. Thus, the allosteric catch bond mechanism can be a much broader phenomenon involved in both fast and strong cell-pathogen attachments under a broad range of hydrodynamic conditions. This concept that allostery can enable more effective receptor-ligand interactions is fundamentally different from the conventional wisdom that allostery provides a mechanism to turn binding off under specific conditions.

Dewetting of a thin polymer film under shear

The objective of this work is to give new insight into the stability of thin polymer films under shear, in order to pave the way to a better control of the nanolayer coextrusion process. To do so, a finite-difference numerical scheme for the resolution of the thin film equation was set up taking into account capillary and van der Waals (vdW) forces. This method was validated by comparing the dynamics obtained from an initial harmonic perturbation to established theoretical predictions. With the addition of shear, three regimes have then been evidenced as a function of the shear rate. In the case of low shear rates the rupture is delayed when compared to the no-shear problem, while at higher shear rates it is even suppressed: the perturbed interface goes back to its unperturbed state over time. In between these two limiting regimes, a transient one in which shear and vdW forces balance each other, leading to a non-monotonic temporal evolution of the perturbed interface, has been identified. While a linear analysis is sufficient to describe the rupture time in the absence of shear, the nonlinearities appear to be essential otherwise.

Effect of Shear Flow on Nanoparticles Migration near Liquid Interfaces.

The effect of shear flow on spherical nanoparticles (NPs) migration near a liquid–liquid interface is studied by numerical simulation. We have implemented a compact model through which we use the diffuse interface method for modeling the two fluids and the molecular dynamics method for the simulation of the motion of NPs. Two different cases regarding the state of the two fluids when introducing the NPs are investigated. First, we introduce the NPs randomly into the medium of the two immiscible liquids that are already separated, and the interface is formed between them. For this case, it is shown that before applying any shear flow, 30% of NPs are driven to the interface under the effect of the drag force resulting from the composition gradient between the two fluids at the interface. However, this percentage is increased to reach 66% under the effect of shear defined by a Péclet number Pe = 0.316. In this study, different shear rates are investigated in addition to different shearing times, and we show that both factors have a crucial effect regarding the migration of the NPs toward the interfacial region. In particular, a small shear rate applied for a long time will have approximately the same effect as a greater shear rate applied for a shorter time. In the second studied case, we introduce the NPs into the mixture of two fluids that are already mixed and before phase separation so that the NPs are introduced into the homogenous medium of the two fluids. For this case, we show that in the absence of shear, almost all NPs migrate to the interface during phase separation, whereas shearing has a negative result, mainly because it affects the phase separation.

Tempering of cocoa butter and chocolate using minor lipidic components

Chocolate manufacture includes a complex tempering procedure to direct the crystallization of cocoa butter towards the formation of fat crystal networks with specific polymorphism, nano- and microstructure, melting behavior, surface gloss and mechanical properties. Here we investigate the effects of adding various minor non-triglyceride lipidic components to refined cocoa butter and chocolate on their physical properties. We discover that addition of saturated phosphatidylcholine and phosphatidylethanolamine to neutralized and bleached cocoa butter or molten and recrystallized commercial chocolate at 0.1% (w/w) levels, followed by rapid cooling to 20 °C in the absence of shear, accelerates crystallization, stabilizes the desirable Form V polymorph and induces the formation of chocolate with an optimal microstructure, surface gloss and mechanical strength. Final chocolate structure and properties are comparable to those of a commercial tempered chocolate. Minor lipidic component addition represents an effective way to engineer chocolate material properties at different length scales, thus simplifying the entire tempering process.

Optimal perturbations in viscous channel flow with crossflow

This work is devoted to the studies of optimal perturbation and its transient growth characteristics in the Poiseuille flow with Reynolds number R = 1000 and with crossflow. The crossflow Reynolds number R v , based on the uniform velocity in the negative normal direction, is varied from 0 to 200. The numerical result shows that the crossflow enhances the transient growth for three-dimensional disturbance case when . Seen from the contours of optimal energy growth in the wave number plane, the optimal perturbation that corresponds to the peak value of optimal growth becomes oblique perturbation, when crossflow is introduced. The corresponding streamwise wave number α P increases continuously with increasing R v , while spanwise wave number β P drops firstly with increasing R v and later increases. The comparison of exponential growth and transient growth is performed. It is observed that exponential growth becomes profound and even predominant over transient growth after a short period when the crossflow is sufficiently strong. Moreover, the mechanism of transient growth is discussed and it is found that the uniform crossflow can not cause transient growth in the absence of shear in basic flow. With increasing R v , the Orr mechanism becomes more and more important relative to lift-up mechanism for the transient growth of optimal perturbation.

Eigenmode analysis of the sheared-flow Z-pinch

Experiments have demonstrated that a Z-pinch can persist for thousands of times longer than the growth time of global magnetohydrodynamic (MHD) instabilities such as the m=0 sausage and m=1 kink modes. These modes have growth times on the order of ta=a/vi, where vi is the ion thermal speed and a is the pinch radius. Axial flows with duz/dr ≲ vi/a have been measured during the stable period, and the commonly accepted theory is that this amount of shear is sufficient to stabilize these modes as predicted by numerical studies using the ideal MHD equations. However, these studies only consider specific equilibrium profiles that typically have a modest magnitude for the logarithmic pressure gradient, qP≡d ln P/d ln r, and may not represent experimental conditions. Linear stability of the sheared-flow Z-pinch is studied here via a direct eigen-decomposition of the matrix operator obtained from the linear ideal MHD equations. Several equilibrium profiles with a large variation of qP are examined. Considering a practical range of k, 1/3 ≲ ka ≲ 10, it is shown that the shear required to stabilize m=0 modes can be expressed as duz/dr≥Cγ0/(ka)α. Here, γ0=γ0(ka) is the profile-specific growth rate in the absence of shear, which scales approximately with |qP|. Both C and α are profile-specific constants, but C is order unity and α≈1. It is further demonstrated that even a large value of shear, duz/dr=3vi/a, is not sufficient to provide linear stabilization of the m=1 kink mode for all profiles considered. This result is in contrast to the currently accepted theory predicting stabilization at much lower shear, duz/dr=0.1vi/a, and suggests that the experimentally observed stability cannot be explained within the linear ideal-MHD model.

Aging in a mean field elastoplastic model of amorphous solids

We construct a mean-field elastoplastic description of the dynamics of amorphous solids under arbitrary time-dependent perturbations, building on the work of Lin and Wyart [Phys. Rev. X 6, 011005 (2016)] for steady shear. Local stresses are driven by power-law distributed mechanical noise from yield events throughout the material, in contrast to the well-studied Hébraud–Lequeux model where the noise is Gaussian. We first use a mapping to a mean first passage time problem to study the phase diagram in the absence of shear, which shows a transition between an arrested and a fluid state. We then introduce a boundary layer scaling technique for low yield rate regimes, which we first apply to study the scaling of the steady state yield rate on approaching the arrest transition. These scalings are further developed to study the aging behavior in the glassy regime for different values of the exponent μ characterizing the mechanical noise spectrum. We find that the yield rate decays as a power-law for 1 < μ < 2, a stretched exponential for μ = 1, and an exponential for μ < 1, reflecting the relative importance of far-field and near-field events as the range of the stress propagator is varied. A comparison of the mean-field predictions with aging simulations of a lattice elastoplastic model shows excellent quantitative agreement, up to a simple rescaling of time.

Targeting shear gradient activated von Willebrand factor by the novel single-chain antibody A1 reduces occlusive thrombus formation in vitro.

Intraluminal thrombus formation precipitates conditions such as acute myocardial infarction and disturbs local blood flow resulting in areas of rapidly changing blood flow velocities and steep gradients of blood shear rate. Shear rate gradients are known to be pro-thrombotic with an important role for the shear-sensitive plasma protein von Willebrand factor (VWF). Here, we developed a single-chain antibody (scFv) that targets a shear gradient specific conformation of VWF to specifically inhibit platelet adhesion at sites of shear rate gradients (SRG) but not in areas of constant shear. Microfluidic flow channels with stenotic segments were used to create SRG during blood perfusion. VWF-GPIbα interactions were increased at sites of SRG compared to constant shear rate of matched magnitude. The scFv-A1 specifically reduced VWF-GPIbα binding and thrombus formation at sites of SRG but did not block platelet deposition and aggregation under constant shear rate in upstream sections of the channels. Significantly, the scFv A1 attenuated platelet aggregation only in the later stages of thrombus formation. In the absence of shear, direct binding of scFv-A1 to VWF could not be detected and scFVA1 did not inhibit ristocetin induced platelet agglutination. We have exploited the pro-aggregatory effects of SRG on VWF dependent platelet aggregation and developed the shear gradient-sensitive scFv-A1 antibody that inhibits platelet aggregation exclusively at sites of SRG. The lack of VWF inhibition in non-stenosed vessel segments places scFV-A1 in an entirely new class of anti-platelet therapy for selective blockade of pathological thrombus formation while maintaining normal hemostasis.

An inverse technique for reconstructing ocean’s density stratification from surface data

In this article, we propose an inverse technique that accurately reconstructs the ocean’s density stratification profile simply from free surface elevation data. Satellite observations suggest that ocean surface contains the signature of internal tides, which are internal gravity waves generated by the barotropic tides. Since internal tides contain the information of ocean’s density stratification, the latter can in principle be reconstructed from the free surface signature. We consider a simple theoretical model that approximates a continuously stratified ocean as discrete layers of constant buoyancy frequency; this facilitates the derivation of a closed-form dispersion relation. First, we numerically simulate internal tide generation for toy ocean scenarios and subsequently perform Space–Time Fourier Transform (STFT) of the free surface, which yields internal tide spectra with wavenumbers corresponding to the tidal frequency. The density profile is reconstructed by substituting these wavenumbers into the dispersion relation. Finally, we consider a more realistic situation with rotation, bottom topography, shear and density profiles representative of the Strait of Gibraltar. Density reconstruction in the presence and absence of shear is respectively found to be 90.2% and 94.2% accurate. The proposed method can be used to reconstruct climatological mean ocean density field of uniform spatial resolution using only surface elevation data obtained via satellite altimetry.