scholarly journals Hydrous oceanic crust hosts megathrust creep at low shear stresses

2020 ◽  
Vol 6 (22) ◽  
pp. eaba1529
Author(s):  
Christopher J. Tulley ◽  
Åke Fagereng ◽  
Kohtaro Ujiie
Keyword(s):  
Oceanic Crust ◽  
Shear Zones ◽  
Interface Strength ◽  
Shear Stresses ◽  
Plate Interface ◽  
Strength And Deformation ◽  
Transition Field ◽  
Flow Laws ◽  
Sw Japan ◽  
Low Shear

The rheology of the metamorphosed oceanic crust may be a critical control on megathrust strength and deformation style. However, little is known about the strength and deformation style of metamorphosed basalt. Exhumed megathrust shear zones exposed on Kyushu, SW Japan, contain hydrous metabasalts deformed at temperatures between ~300° and ~500°C, spanning the inferred temperature-controlled seismic-aseismic transition. Field and microstructural observations of these shear zones, combined with quartz grain-size piezometry, indicate that metabasalts creep at shear stresses <100 MPa at ~370°C and at shear stresses <30 MPa at ~500°C. These values are much lower than those suggested by viscous flow laws for basalt. The implication is that relatively weak, hydrous, metamorphosed oceanic crust can creep at low viscosities over a wide shear zone and have a critical influence on plate interface strength and deformation style around the seismic-aseismic transition.

Susceptibility of density-fractionated erythrocytes to subhaemolytic mechanical shear stress

2018 ◽  
Vol 42 (3) ◽  
pp. 151-157 ◽  
Author(s):  
Antony P McNamee ◽  
Kieran Richardson ◽  
Jarod Horobin ◽  
Lennart Kuck ◽  
Michael J Simmonds
Keyword(s):  
Blood Cell ◽  
Red Blood Cells ◽  
Red Blood Cell ◽  
Blood Cells ◽  
Shear Stresses ◽  
Mechanical Stimuli ◽  
Cell Deformability ◽  
Red Blood Cell Deformability ◽  
Cell Age ◽  
Low Shear

Introduction: Accumulating evidence demonstrates that subhaemolytic mechanical stresses, typical of circulatory support, induce physical and biochemical changes to red blood cells. It remains unclear, however, whether cell age affects susceptibility to these mechanical forces. This study thus examined the sensitivity of density-fractionated red blood cells to sublethal mechanical stresses. Methods: Red blood cells were isolated and washed twice, with the least and most dense fractions being obtained following centrifugation (1500 g × 5 min). Red blood cell deformability was determined across an osmotic gradient and a range of shear stresses (0.3–50 Pa). Cell deformability was also quantified before and after 300 s exposure to shear stresses known to decrease (64 Pa) or increase (10 Pa) red blood cell deformability. The time course of accumulated sublethal damage that occurred during exposure to 64 Pa was also examined. Results: Dense red blood cells exhibited decreased capacity to deform when compared with less dense cells. Cellular response to mechanical stimuli was similar in trend for all red blood cells, independent of density; however, the magnitude of impairment in cell deformability was exacerbated in dense cells. Moreover, the rate of impairment in cellular deformability, induced by 64 Pa, was more rapid for dense cells. Relative improvement in red blood cell deformability, due to low-shear conditioning (10 Pa), was consistent for both cell populations. Conclusion: Red blood cell populations respond differently to mechanical stimuli: older (more dense) cells are highly susceptible to sublethal mechanical trauma, while cell age (density) does not appear to alter the magnitude of improved cell deformability following low-shear conditioning.

scholarly journals Velocity and density characteristics of subducted oceanic crust and the origin of lower-mantle heterogeneities

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Wenzhong Wang ◽  
Yinhan Xu ◽  
Daoyuan Sun ◽  
Sidao Ni ◽  
Renata Wentzcovitch ◽  
...  
Keyword(s):  
Phase Transition ◽  
Oceanic Crust ◽  
Seismic Tomography ◽  
Lower Mantle ◽  
Shear Velocity ◽  
Calcium Ferrite ◽  
Velocity Anomaly ◽  
Mantle Heterogeneities ◽  
Subducted Oceanic Crust ◽  
Low Shear

AbstractSeismic heterogeneities detected in the lower mantle were proposed to be related to subducted oceanic crust. However, the velocity and density of subducted oceanic crust at lower-mantle conditions remain unknown. Here, we report ab initio results for the elastic properties of calcium ferrite‐type phases and determine the velocities and density of oceanic crust along different mantle geotherms. We find that the subducted oceanic crust shows a large negative shear velocity anomaly at the phase boundary between stishovite and CaCl2-type silica, which is highly consistent with the feature of mid-mantle scatterers. After this phase transition in silica, subducted oceanic crust will be visible as high-velocity heterogeneities as imaged by seismic tomography. This study suggests that the presence of subducted oceanic crust could provide good explanations for some lower-mantle seismic heterogeneities with different length scales except large low shear velocity provinces (LLSVPs).

Rheology of Fluoride Gels

1976 ◽  
Vol 55 (3) ◽  
pp. 353-356 ◽  
Author(s):  
M. Braden ◽  
Ratna Perera
Keyword(s):  
Infrared Spectroscopy ◽  
Shear Rate ◽  
Elastic Behavior ◽  
Shear Stresses ◽  
High Shear ◽  
Shear Rates ◽  
Extreme Stress ◽  
Thickening Agents ◽  
Shear Rate Dependence ◽  
Low Shear

Six commercial fluoride gels have been studied, using a cone and plate viscometer. Also, the thickening agents have been analyzed using infrared spectroscopy. All gels showed stress thinning, which is the decrease of viscosity with shear rate. Such shear rate dependence is clinically convenient in that the gel will flow readily at the high shear stresses present when the gel is applied but will not flow readily under its own weight when on the tooth. Five materials containing hydroxyalkyl celluloses showed similar degrees of shear thinning. One material with a non-cellulosic thickener showed much more extreme stress thinning together with elastic behavior at low shear rates; such behavior may be clinically advantageous. All of the gels showed only slight temperature dependence of rheological properties.

Eosinophil Tethering to Interleukin-4–Activated Endothelial Cells Requires Both P-Selectin and Vascular Cell Adhesion Molecule-1

Blood ◽  
1998 ◽  
Vol 92 (10) ◽  
pp. 3904-3911 ◽  
Author(s):  
Kamala D. Patel
Keyword(s):  
Endothelial Cells ◽  
Cell Adhesion ◽  
Adhesion Molecule ◽  
Cell Adhesion Molecule ◽  
Interleukin 4 ◽  
Shear Stresses ◽  
Vascular Cell Adhesion ◽  
Vascular Cell ◽  
Cell Adhesion Molecule 1 ◽  
Low Shear

We examined the mechanisms used by eosinophils to tether and accumulate on interleukin-4 (IL-4)–stimulated human umbilical vein endothelial cells (HUVECs) under flow conditions. As previously reported, HUVECs treated for 24 hours with 20 ng/mL IL-4 had increased expression of P-selectin and vascular cell adhesion molecule-1 (VCAM-1) but not E-selectin. We found that eosinophils tethered and rolled on IL-4–stimulated HUVECs at physiologic shear stresses. Eosinophil rolling was quickly followed by firm adhesion. Treatment with either an anti–P-selectin monoclonal antibody (MoAb) or an anti–VCAM-1 MoAb decreased both eosinophil tethering and accumulation at 2 dyn/cm2. VCAM-1 interacts with 4-integrins expressed on eosinophils. We found that an anti–4-integrin MoAb also blocked eosinophil tethering and accumulation at 2 dyn/cm2. None of these MoAbs alone had an impact on eosinophil accumulation at lower shear stresses, but when either an anti–VCAM-1 or an anti–4-integrin MoAb was used in combination with an anti–P-selectin MoAb, all eosinophil tethering and accumulation on IL-4–stimulated HUVECs were blocked. This was true at both high and low shear stresses. These data show that both P-selectin and VCAM-1 are required to tether eosinophils at high shear stresses, but at low shear stresses these adhesion proteins can act independently to recruit eosinophils to IL-4–stimulated HUVECs.

The shear strength of soils containing undulating shear zones—a numerical study

1988 ◽  
Vol 25 (3) ◽  
pp. 550-558 ◽  
Author(s):  
George T. Dounias ◽  
David M. Potts ◽  
Peter R. Vaughan
Keyword(s):  
Strain Softening ◽  
Numerical Study ◽  
Finite Thickness ◽  
Shear Zones ◽  
Shear Surface ◽  
Weak Zone ◽  
Surface Finite Elements ◽  
Soil Block ◽  
Strength And Deformation ◽  
Intact Soil

This paper investigates the behaviour of a clay layer containing an undulating shear surface, when sheared across the undulations. A relatively long soil block containing an undulating weak zone of finite thickness is assumed. A finite element study is undertaken, examining the effect of the thickness and the amplitude of the weak zone on the overall strength and deformation of the block. Also examined is the behaviour of the block when either only the weak zone or both the weak zone and the intact soil are strain softening. Key words: undulating shear surface, finite elements, strain softening.

Method of Obtaining Viscosity Curves with Mooney Rheometer

1979 ◽  
Vol 52 (1) ◽  
pp. 9-19 ◽  
Author(s):  
N. Nakajima ◽  
E. R. Harrell
Keyword(s):  
Conversion Factor ◽  
Mathematical Expression ◽  
Shear Stresses ◽  
Rotor Design ◽  
Torque Values ◽  
Low Shear

Abstract A mathematical expression is derived for calculating shear stresses from torque values observed with the Mooney rheometer. Examination of this expression indicates that some improvement is possible in the rotor design. The numerical values of the conversion factor are given for both small and large rotors. The application of these factors to the observed data give viscosities in agreement with those obtained with other instruments. Low shear viscosities down to 10−3 and in some cases 10−4s−1 are obtained with the Mooney rheometer operated at 0.05 rpm for several minutes.

Cohesion and detachment in biofilm systems for different electron acceptor and donors

2007 ◽  
Vol 55 (8-9) ◽  
pp. 421-428 ◽  
Author(s):  
C. Coufort ◽  
N. Derlon ◽  
J. Ochoa-Chaves ◽  
A. Liné ◽  
E. Paul
Keyword(s):  
Basal Layer ◽  
Middle Layer ◽  
Electron Donors ◽  
Shear Stresses ◽  
Average Thickness ◽  
Low Shear Stress ◽  
Erosion Test ◽  
Biofilm Structure ◽  
Initial Biofilm ◽  
Low Shear

This work deals with the cohesion and detachment in biofilm systems for two electron acceptors and for two electron donors. Biofilms were developed on plates, under very low shear stress for one month and then subjected to an erosion test for two hours in a Couette-Taylor reactor. Biofilm was characterised in terms of average thickness and residual TOC mass. It was found that the biofilm structure is very heterogeneous and stratified. The top layer, which represents 60% of the biofilm mass, is very fragile and can be easily detached; the basal layer, which represents 20% of the biofilm mass, is very cohesive and can resist shear stresses up to 13 Pa. Between these two layers, a middle layer of intermediary cohesion represents 20% of the initial biofilm mass.

scholarly journals Lagrangian modeling of bedload movement via the impulse entrainment method

2018 ◽  
Vol 40 ◽  
pp. 05041
Author(s):  
Micah A. Wyssmann ◽  
A.N. (Thanos) Papanicolaou
Keyword(s):  
Momentum Transfer ◽  
Sharp Decrease ◽  
Streamwise Velocity ◽  
Shear Stresses ◽  
Velocity Spectrum ◽  
Travel Patterns ◽  
Lagrangian Modeling ◽  
Model Predictions ◽  
Spectrum Model ◽  
Low Shear

At low shear stresses merely above incipient conditions, the characteristic travel patterns of bedload particles remain difficult to predict due to intermittent movement. At these conditions, particles rest, are entrained into the flow when sufficient momentum transfer from near-bed turbulence occurs, and then come to rest again. The overarching goal of this research is to close the critical gaps related to intermittent movement in order to allow for Lagrangian modeling of bedload at near incipient conditions. Thereby, the specific objectives of the present work are to predict the statistics of (1) the particle resting time, tR, and (2) the magnitude of hydrodynamic momentum transfer (or impulse) during entrainment, Ient. To predict these statistics, we employed the conceptual framework of the impulse entrainment method and predicted impulse statistics by simulating turbulent time series realizations with a generic, regime-based streamwise velocity spectrum. Model validation was carried out by directly comparing simulation results with published experimental impulse and particle entrainment statistics. Model predictions showed that an increase in stress was correlated with a sharp decrease in the average tR and an increase in Ient.

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