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Effect of high shear stress on microbial viability

Effect of high shear stress on microbial viability

When S cerevisiae was submitted to 2770Pa shear stress, viability decreased rapidly as the duration of exposure to shear stress increased. Replicate experi- ments (duplicate), showed good reproducibility. There was clearly an intensity threshold above which the generated stress affected the viability of yeasts. The experiments described above indicate that the thresh- old should be set above 1292Pa and below 2770Pa but the experimental conditions did not allow the re®ning of its value.

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Wall shear stress and endothelial cells dysfunction in the context of abdominal aortic aneurysms

Wall shear stress and endothelial cells dysfunction in the context of abdominal aortic aneurysms

experiments, we used a parallel plate flow chamber, as described previously (Chotard-Ghodsnia et al., 2002). Constant shear stress applied on cells varies from 0.04 Pa to 3.7 Pa (0.4 to 37 dynes/cm 2 ), which corresponds to levels of WSS during enlargement of AAA (Salsac et al., 2004). Cell alignment and shape were investigated on digitized images, analyzed with MetaMorph software (n 500/per experiment). Cell orientation (alignment) was determined as an angle between the long axis of the cell and the chosen direction (0° indicated perfect alignment with respect to the flow direction while a value of 45° indicated no alignment). Elliptical form factor, the ratio of the cell's breadth to its length, determined the level of cells elongation (1 indicated circle i.e. no elongation). EC dysfunction was determined by immunocytochemistry, confocal fluorescence microscopy and flow cytometry. Data were analyzed using SigmaStat statistical software. One-way ANOVA followed by multiple comparisons with Holm-Sidak test was used. For direct comparisons, an unpaired Student’s t test was used. Values are presented as means±SE. Comparisons were judged to be significant at p < 0.05.
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Treated wastewater Reuse in micro-irrigation: effect of shear stress on biofilm development kinetics and chemical precipitation

Treated wastewater Reuse in micro-irrigation: effect of shear stress on biofilm development kinetics and chemical precipitation

To obtain the desired shear stress for biofilm development, angular velocity ( ) must be determined. The shear stress, which is mainly applied to the surface of the inner and outer cylinder, is connected to the tangential flow, itself linked to the rotation of the rotor. This shear stress is generated by the velocity gradient near the surface of the reactor. It is uniform over the internal and external cylinders. Different correlations have been established to estimate the shear stress on the inner cylinder surface. The equations used in the work of Rochex et al. (2008) (Equation 3 and Equation 4), based on the theoretical concept of Wendt (1933) were selected because, in their work, they used an annular reactor configuration with a radius ratio close to the present TCR ( = R 1 /R 2 = 0.808):
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Damage of woven composite under tensile and shear stress using infrared thermography and micrographic cuts

Damage of woven composite under tensile and shear stress using infrared thermography and micrographic cuts

Damage of woven composite under tensile and shear stress using infrared thermography and micrographic cuts T. Lisle 1 • C. Bouvet 1 • M. L. Pastor 1 • T. Rouault 2 • P. Marguere`s 1 Abstract Infrared thermography was used to study damage developing in woven fabrics. Two different experiments were performed, a ±45 tensile test and a rail shear test. These two different types of tests show different damage scenarios, even if the shear stress/strain curves are similar. The ±45 tension test shows matrix hardening and matrix cracking whereas the rail shear test shows only matrix hardening. The infrared thermography was used to perform an energy balance, which enabled the visualization of the portion of dissipated energy caused by matrix cracking. The results showed that when the resin is sub- jected to pure shear, a larger amount of energy is stored by the material, whereas when the resin is subjected to hydrostatic pressure, the main part of mechanical energy is dissipated as heat.
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Damage of woven composite under tensile and shear stress using infrared thermography and micrographic cuts

Damage of woven composite under tensile and shear stress using infrared thermography and micrographic cuts

Damage of woven composite under tensile and shear stress using infrared thermography and micrographic cuts T. Lisle 1 • C. Bouvet 1 • M. L. Pastor 1 • T. Rouault 2 • P. Marguere`s 1 Abstract Infrared thermography was used to study damage developing in woven fabrics. Two different experiments were performed, a ±45 tensile test and a rail shear test. These two different types of tests show different damage scenarios, even if the shear stress/strain curves are similar. The ±45 tension test shows matrix hardening and matrix cracking whereas the rail shear test shows only matrix hardening. The infrared thermography was used to perform an energy balance, which enabled the visualization of the portion of dissipated energy caused by matrix cracking. The results showed that when the resin is sub- jected to pure shear, a larger amount of energy is stored by the material, whereas when the resin is subjected to hydrostatic pressure, the main part of mechanical energy is dissipated as heat.
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Arterial Remodeling and Endothelial Shear Stress Exhibit Significant Longitudinal Heterogeneity Along the Length of Coronary Plaques

Arterial Remodeling and Endothelial Shear Stress Exhibit Significant Longitudinal Heterogeneity Along the Length of Coronary Plaques

Cambridge, MA, USA Atherosclerosis is determined by both systemic risk-factors and local vascular mechanisms. The arterial remodeling in response to plaque development plays a key role in atherosclerosis. Compensatory expansive remodeling is an adaptive mechanism which maintains lumen patency as a plaque develops. In contrast, excessive expansive remodeling, signifying an enlargement in vascular and lumen volume as a result of local plaque build-up, is a consistent attribute of high-risk plaques. Local hemodynamic factors, in particular low endothelial shear stress (ESS), is an intensely pro-inflammatory and pro-atherogenic stimulus and largely accounts for the spatially diverse distribution of atherosclerotic plaques. However, plaque, remodeling and ESS have hitherto been investigated only in the cross-
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Ependymal cilia beating induces an actin network to protect centrioles against shear stress

Ependymal cilia beating induces an actin network to protect centrioles against shear stress

Since no fragmented or whole centrioles were detected inside the cells when the apical actin network was impaired, we hypothesised that the centrioles might have been expelled from cells. To test this hypothesis, we collected the supernatant of mature ependymal cells in culture incubated with DMSO (controls) or cytochalasin-D, alone or in association with NiCl 2 . Centrioles with their associated cilia were frequently observed in the supernatants of cytochalasin-D-treated cells compared to the DMSO-treated controls or cells in which cilia motility was inhibited by NiCl 2 (Fig. 6 e, f). This suggests that when the actin network is destabilised, the forces generated by cilia beating cause the centrioles to detach from the apical membrane. To assess whether the flow induced by cilia beating is sufficient to expelled centriole/cilium from the ependymal cells, we applied an artificial external fluid flow 37 , comparable to physiological flow, on cells treated with cytochalasin-D and NiCl 2 . Since the number of centriole/cilium found in the supernatant was not significantly increased compared to controls, it is likely that the shear stress induced by the movement of the cilium itself promotes centriole destabilization in ependymal cells. Nevertheless, we cannot exclude a weak contribution of the collective flow on the expulsion.
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Maximal wall shear stress in arterial stenoses: application to the internal carotid arteries

Maximal wall shear stress in arterial stenoses: application to the internal carotid arteries

For example, Fig. 3 displays the results obtained in a 70 percent stenosis. Whatever the initial value of ⌬ 1 , Eq. 共11兲 holds and the curves of wall shear stress become superposed in the downstream part of the convergence, where the gradient parameter ⌳ 1 is greater than 0.6. Maximal difference from the mean for MWSS in all the cases studied is less than 0.25 percent. MWSS is therefore independent of inlet displacement thickness and thus, of the as- sumed entry velocity profile. This validates the use of the IBL theory.

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Fluid Shear Stress: a modulator of the vasculo-protective effects of polyphenols?

Fluid Shear Stress: a modulator of the vasculo-protective effects of polyphenols?

• The reduction of both adhesion and TEM by curcumin are enhanced under physiological shear stress. • In static conditions, curcumin modulates the TNF‐R pathway (NF‐B phosphorylation and its nuclear translocation), but does not affect the expression of adhesion molecules.

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Shear stress-responsive polymersome nanoreactors inspired by the marine bioluminescence of dinoflagellates

Shear stress-responsive polymersome nanoreactors inspired by the marine bioluminescence of dinoflagellates

The reaction of isoluminol with butanone peroxide in the presence of p-iodophenol did neither yield luminescence when a reaction mixture containing HRP-filled ADEN/THYM polymersomes was unperturbed, when it was sheared with a syringe nor when it was subjected to the high mechanical forces of an ultrasound bath (Supporting Information Fig. 15). In order to check that the reagents were intact, free HRP was added to the reaction mixture. Strong luminescence was observed. Thus, the reagents were intact, but isoluminol cannot cross the polymersome membrane. Moreover, the results confirm once more the integrity of the polymersome membrane during mechanical agitation, because ruptured polymersomes would release HRP and therefore trigger the chemoluminescent reaction. To observe the influence of peroxides on the luminescent reactions, 2-butanone peroxide was substituted by hydrogen peroxide. Initial permeation in the absence of shear stress stimulation was observed for long periods in reactions with ABEI (5 min) and luminol (2 h). In both cases, the formation of luminescence increased with the application of shear to the system. Reactions of isoluminol together with hydrogen peroxide were similar than those conducted with 2-butanone peroxide and isoluminol.
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Shear stress-responsive polymersome nanoreactors inspired by the marine bioluminescence of dinoflagellates

Shear stress-responsive polymersome nanoreactors inspired by the marine bioluminescence of dinoflagellates

The response to shear stress of these polymersomes was assessed by the release of sodium fluorescein from them. We loaded polymersomes containing 5 % of nucleobase residues (ADEN/THYM) in the hydrophobic leaflet with the dye at self-quenching concentration and introduced them into a microfluidic channel with varying widths (Figure 2 B and Supporting Information 5). An increase of fluorescence was observed as the polymersome dispersion was pushed through multiple constrictions where they were subjected to high shear stresses. This caused the release of the dye, indicating that the vesicle membrane became permeable for sodium fluorescein upon shearing. Polymersomes functionalised with inert hexylamine (HEX) did not yield an increase in fluorescence, indicating that the nucleobases in the hydro- phobic leaflet of the polymersome membrane are essential to render the vesicles shear force-responsive. Release of sodium fluorescein was also monitored using fluorescence spectros- copy (Figure 2 C and Supporting Information 6). In these experiments, polymersomes were continuously sheared by aspirating and ejecting the dispersions through a 0.65 mm diameter syringe needle at a flowrate of 70 mL min 1 . ADEN/ THYM polymersomes released 45 % of their contents within 21 min. The fluorescence did neither increase when ADEN/ THYM polymersomes were left unperturbed, nor when HEX polymersomes were sheared. These results support our hypothesis that in the absence of shear stress adenine and thymine form hydrophobic base pairs in the hydrophobic leaflet of the polymersome membrane. When shear is applied, the nucleobases unpair, exposing their polar motifs within the hydrophobic leaflet. This process reduces the hydrophobicity of the hydrophobic leaflet, thereby increasing its permeabil- ity.
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Distinct contributions of tensile and shear stress on E-cadherin levels during morphogenesis

Distinct contributions of tensile and shear stress on E-cadherin levels during morphogenesis

not essential for survival in Drosophila 58 , raising questions about the necessity of its function as a mechanotransducer. To reveal the mechanism by which actomyosin contractility regulates E- cadherin levels, it is essential to study the magnitude and orien- tation of contractile forces, the spatial distribution of mechanical coupling between the adhesion complexes and the actomyosin network, and the different modes of energy dissipation at adhe- sive complexes under mechanical forces. Given this distinction between tensile and shear stress in the regulation of E-cadherin at cell contacts, it will also be important to consider the dynamics of E-cadherin complexes at cell contacts as well as at vertices. Vinculin and E-cadherin are present at high levels at vertices. A recent study demonstrated that E-cadherin accumulation at ver- tices shows oscillatory patterns, which are coordinated with
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Effect of Inlet Type on Shear Stress and Mixing in an Annular Photobioreactor Involving a Swirling Decaying Flow

Effect of Inlet Type on Shear Stress and Mixing in an Annular Photobioreactor Involving a Swirling Decaying Flow

But biological applications imply particular constraints, particularly when stress-sensitive elements such as microalgae are involved. A disturbed flow leads to higher velocity gradient values, resulting in a greater shear stress-field. A compro- mise would be to ensure sufficient mixing while keeping the shear-stress forces within an acceptable range. However, little is known about the effects of hydrodynamic stress on microalgae, mainly because of the cell fragility of microalgae, which remains difficult to investigate (Chisti, 1999; Jaouen et al., 1999). The results depend on the species cultured, which exhibit quite different types of cell fragility and various physio- logical responses, from the decrease of the growth rate to the cell destruction. Thus, a hydrodynamic study cannot establish a definitive compromise solution for all microalgae, but can improve our understanding of the processing of microalgal cultures in photobioreactors. The characterization of a large set of operating conditions obtained with different inlets can elucidate the problems relating to microalgal cultures in a swirling decaying flow.
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Continuous shear stress alters metabolism, mass-transport, and growth in electroactive biofilms independent of surface substrate transport

Continuous shear stress alters metabolism, mass-transport, and growth in electroactive biofilms independent of surface substrate transport

than soluble respiring bacteria and might not be limited by respiration in high shear unlike aerobic biofilms 22 . Using the analytic equations for fluid flow and mass flux that exist for a rotating disk electrode, the absolute concentration of nutrients is reduced in a way that decouples the influence of mass flux and shear stress. We use a pure culture of a high-current producing bacteria to reduce the effect shear has on selection of species with high adhesion strength, exopolymeric substance production, or current production. However, there will still be phenotypic selection within the strain induced by time and possibly shear 23 . In doing so, we find high metabolic
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Influence of shear stress applied during flow stoppage and rest period on the mechanical properties of thixotropic suspensions

Influence of shear stress applied during flow stoppage and rest period on the mechanical properties of thixotropic suspensions

Laboratoire des Mat´eriaux et Structures du G´enie Civil (LCPC-ENPC-CNRS) 2, all´ee Kepler, 77420 Champs-sur-Marne, France Abstract We study the solid mechanical properties of several thixotropic suspensions as a function of the shear stress history applied during their flow stoppage and their aging in their solid state. We show that their elastic modulus and yield stress depend strongly on the shear stress applied during their solid-liquid transition (i.e. during flow stoppage) while applying the same stress only before or only after this transition may induce only second-order effects: there is negligible dependence of the mechanical properties on the preshear history and on the shear stress applied at rest. We also found that the suspensions age with a structuration rate that hardly depends on the stress history. We propose a physical sketch based on the freezing of a microstructure whose anisotropy depends on the stress applied during the liquid/solid transition to explain why the mechanical properties depend strongly on this stress. This sketch points out the role of the internal forces in the colloidal suspensions behavior. We finally discuss briefly the macroscopic consequences of this new phenomenon and show the importance of using a controlled-stress rheometer.
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Aeration mode, shear stress and sludge rheology in a submerged membrane bioreactor: some keys of energy saving

Aeration mode, shear stress and sludge rheology in a submerged membrane bioreactor: some keys of energy saving

Alternating stepped shear stress below and beyond the threshold (figure above) shows that the fluid can partly recover its structure. This explains why a continuous air injection leads to a more deflocculated sludge than an intermittent one. Moreover, this displays that pauses during the aeration process are of greatest interest and give keys to propose efficient aeration.

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Grain-size-sensitive flow and shear-stress enhancement at the brittle-ductile transition of the continental crust

Grain-size-sensitive flow and shear-stress enhancement at the brittle-ductile transition of the continental crust

FrØdØric Gueydan ´ Yves M. Leroy ´ Laurent Jolivet Grain-size-sensitive flow and shear-stress enhancement at the brittle±ductile transition of the continental crust Abstract Localized shear zones along low-angle nor- mal faults have been identified in regions of extension at the brittle±ductile transition of the continental crust.The possibility of the strain localizing at a depth of 10 km is interpreted here as a consequence of an increase in the equivalent shear stress applied to the flow of the lower crust.This enhancement of the flow stress is seen as a prerequisite for the triggering of brittle deformation mechanisms leading to strain local- ization.The lower crust rheology used to examine this stress increase is strain-rate, temperature and grain- size dependent, due to the coupling of dislocation and diffusion creep.The model structure proposed consists of a top layer, the upper crust, gliding rigidly above a bottom layer, the lower crust, which deforms in simple shear.During a short time interval (1400 years), the equivalent shear stress is found to increase by a factor of up to 3 (67 MPa for anorthite and 17 MPa for quartz).For anorthite, this stress could explain the activation of a Mohr-Coulomb failure with a friction coefficient of 0.2, which is reasonable at the depth of 10 km.Dislocation creep is activated during a rapid change in the prescribed velocity, whereas diffusion creep dominates if the velocity is held constant, high- lighting the importance of grain-size sensitivity for lower crustal rheology.
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Aeration mode, shear stress and sludge rheology in a submerged membrane bioreactor: some keys of energy saving

Aeration mode, shear stress and sludge rheology in a submerged membrane bioreactor: some keys of energy saving

Alternating stepped shear stress below and beyond the threshold (figure above) shows that the fluid can partly recover its structure. This explains why a continuous air injection leads to a more deflocculated sludge than an intermittent one. Moreover, this displays that pauses during the aeration process are of greatest interest and give keys to propose efficient aeration.

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Experimental SAC305 shear stress-strain hysteresis loop construction using Hall's one-dimensional model based on strain gages measurements

Experimental SAC305 shear stress-strain hysteresis loop construction using Hall's one-dimensional model based on strain gages measurements

5 Conclusions A specific test vehicle has been developed to measure the shear stress–strain hysteresis loop of SAC305 solder joints subjected to thermal cycling. According to Hall’s original work, four strain gages were accurately placed on top/bottom surfaces of the com- ponent and the PCB. This study allowed to improve the initial experimentation performed by Hall, which needed two test assem- blies to plot one hysteresis loop, whereas only one is required here. Using a specific assembly methodology, microstructure of as-reflowed solder joints was found representative of actual SAC305 interconnects, therefore ensuring a realistic thermome- chanical behavior under temperature cycles. Hall’s one- dimensional axisymmetric model was verified comparing the the- oretical assembly stiffness parameter with the value measured with the experimental SAC305 shear stress–strain hysteresis loop. The CTE differential between the component and the PCB obtained with the hysteresis loop was also found to be very close to the one optically measured on each part alone. Accelerated thermal cycling test was also conducted and the measured cyclic strain energy density dissipated in SAC305 solder joints was cor- related to the number of cycles to failure. Further work is needed to plot other hysteresis curves corresponding to different damage levels (i.e., different temperature cycle amplitudes and/or test assemblies with different constitutive materials that would hope- fully allow to cover several orders of magnitude in terms of fatigue criterion and number of cycles to failure) in order to obtain a complete experimental SAC305 fatigue model.
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Modeling shear stress distribution in a deformable airway tree

Modeling shear stress distribution in a deformable airway tree

The previous phenomena will also occur in the case of a constricted bronchus: at a given expiratory flow rate, pressure will increase upstream the bronchus, and upstream bronchi will be dilated. Maximal shear rate will then be located ex- actly at the constricted bronchus. If constriction is due to mucus accumulation, the high shear stress will help moving the extra mucus downstream. Consequently mucus motion in- duces a decrease of the airway tree’s hydrodynamic resistance. This behavior was previously observed in [11] using a more complex, but less tractable model of air-mucus interaction. An example of this previous model is shown on figure 5 where we mimicked the effect of chest physiotherapy on an airway tree with mucus excess. These results indicate that hydrodynamic resistance decrease is a direct consequence of the geometry and its influence on shear stress distribution; it might be a de facto effect of chest physiotherapy and should probably be a criterion for analysing chest physiotherapy efficiency.
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