Transmission Of Shear Stress Research Articles

Modulation of endothelial glycocalyx structure under inflammatory conditions.

The glycocalyx of the endothelium is an intravascular compartment that creates a barrier between circulating blood and the vessel wall. The glycocalyx is suggested to play an important role in numerous physiological processes including the regulation of vascular permeability, the prevention of the margination of blood cells to the vessel wall, and the transmission of shear stress. Various theoretical models and experimental approaches provide data about changes to the structure and functions of the glycocalyx under various types of inflammatory conditions. These alterations are suggested to promote inflammatory processes in vessels and contribute to the pathogenesis of number of diseases. In this review we summarize current knowledge about the modulation of the glycocalyx under inflammatory conditions and the consequences for the course of inflammation in vessels. The structure and functions of endothelial glycocalyx are briefly discussed in the context of methodological approaches regarding the determination of endothelial glycocalyx and the uncertainty and challenges involved in glycocalyx structure determination. In addition, the modulation of glycocalyx structure under inflammatory conditions and the possible consequences for pathogenesis of selected diseases and medical conditions (in particular, diabetes, atherosclerosis, ischemia/reperfusion, and sepsis) are summarized. Finally, therapeutic strategies to ameliorate glycocalyx dysfunction suggested by various authors are discussed.

Numerical Simulation of Influence with Surface Contamination on Aerodynamic Performance of Dedicated Wind Turbine Airfoil

A Numerical simulation on the influence of airfoil surface contamination on the aerodynamic performance of wind turbines was performed. It chose the dedicated wind turbine airfoil as the research object. The k-ω Shear Stress Transmission (SST) turbulence model was selected for CFD calculation. The roughness height which arranged evenly on the airfoil was changed from 0.03mm to 2.0mm to obtain the sensitive roughness. The airfoil was divided into 18 sections for analyzing the effect on the lift & the drag coefficient, due to various locations of sensitive roughness. By comparing the result computed by XFOIL and CFD calculation, it can be known this airfoils sensitive locations in suction surface and pressure surface. The sensitive locations in suction surface were 53% and 92% from the chord line towards the leading edge, while 44% and 88% in pressure surface. The sensitive roughness in sensitive locations delayed the location of the transition point.

MRF in a plate-plate magnetorheometer: Numerical insight into the particle-wall interface

Particle-based simulations are a suitable tool to gain insight into the microstructural behavior of a magnetorheological fluid (MRF). For the application of MRF in clutches, the amount of torque transmission is a matter of particular interest. Concerning the contact between iron particles and clutch walls, several questions arise: Is a higher wall roughness beneficial for torque transmission? What is the influence of wall magnetism on torque transmission? What are the mechanisms on particle scale that lead to increased torque transmission? Inspired by a previous experimental study, we performed three-dimensional simulations based on the Discrete-Element-Method (DEM) with different wall roughnesses and different magnetic conditions to investigate the mechanisms of shear stress transmission at particle level. The simulations show that a higher wall roughness leads to higher torque transmission only in the case of non-magnetic walls. For ferromagnetic walls, no influence of wall roughness on torque transmission is observed. This is in qualitative agreement with the experimental results.

Distribution of Forces in Composite Concrete Slabs Between the Joint and the Reinforcement Anchored on the Support

In general composite concrete slabs consist of two concrete layers: a prefabricated reinforced floor plate and an additional layer of concrete cast in-situ. The interaction of the two layers is based on the transmission of shear stresses in the joint surface. Transmission is possible through the appropriate shaping of the joint surface and the use of vertical reinforcement in the form of truss.The results of tests for different composite concrete slabs presented here suggest that the interaction of the two concrete layers may depend on the suitable anchoring of the bottom reinforcement in a ring beam. The full anchoring of bottom reinforcement allowed to obtain the full load bearing capacity of the composite slab with no possibility of bond stress transmission in the joint surface. The distribution of forces between the joint surface and the bottom reinforcement anchored in the ring beam depends on the shape of the joint surface.

Proposed model for the flagellar rotary motor with shear stress transmission.

Most bacteria that swim are propelled by flagellar filaments, which are driven by a rotary motor powered by proton flux. The motor consists of the rotor and the stator. The stator consists of about 8 MotA-Mot B complex. There seems to be no definite information about the structure between the rotor and the stator, and it is examined whether the experimental data can be explained based upon the following assumptions. (a) There is viscoelastic medium between the rotor and the stator. (b) MotA-MotB complex has an electric dipole moment and produces shear stress in the electric field by a proton in the channel. Calculation results based upon these assumptions are in good agreement with the following experimental observations. (1) One revolution of the flagellar rotation consists of a constant number of steps. (2) The rotation velocity of the rotor is proportional to the trans-membrane potential difference. (3) When the rotational velocity of a flagellum is changed by adjusting the viscosity of the outer fluid, the torque for the cell to rotate a flagellum is practically constant but sharply decreases when the rotational velocity increases over a critical value. (4) The rotation direction remains the same when the sign of the electrochemical potential gradient is reversed. (5) The cell produces constant torque to rotate the flagellum even when the cell is rotated by externally applied torque. (6) A simple switch mechanism is proposed for chemotaxis.

Rotating Platform Revision Total Knee Arthroplasty

Although revision total knee arthroplasty (TKA) procedures are successful in relieving pain and restoring function in failed knees, long-term results are inferior to primary procedures. Mobile bearing (MB) revision knees can potentially improve functional performance. Clinical results of 44 MB rotating platform (RP) revision TKAs demonstrated mean knee injury and osteoarthritis outcome score (KOOS) activity of daily living score of 77 2 years postoperatively. Clinical results were put into context through wear testing which demonstrated improved wear performance compared with fixed bearing (FB) revision knees. The RP construct is a good choice for revision TKA because it permits the surgeon to align the tray for fixation, not compromise rotation of the tibial insert, and reduce transmission of shear stresses to the bone, cement and implant interface, which is a known cause of failure.

Shear Stress Transmission Model for the Flagellar Rotary Motor

Most bacteria that swim are propelled by flagellar filaments, which are driven by a rotary motor powered by proton flux. The mechanism of the flagellar motor is discussed by reforming the model proposed by the present authors in 2005. It is shown that the mean strength of Coulomb field produced by a proton passing the channel is very strong in the Mot assembly so that the Mot assembly can be a shear force generator and induce the flagellar rotation. The model gives clear calculation results in agreement with experimental observations, e g., for the charasteristic torque-velocity relationship of the flagellar rotation.

Turbulence manipulation in air–water flows on a stepped chute: An experimental study

In a stepped channel operating with large flow rates, the flow skims over the pseudo-bottom formed by the step edges as a coherent stream. Intense three-dimensional recirculation is maintained by shear stress transmission from the mainstream to the step cavities, while significant free-surface aeration takes place. The interactions between free-surface aeration and cavity recirculation are investigated herein with seven step cavity configurations. The experiments were conducted in a large stepped channel operating at large Reynolds numbers. For some experiments, triangular vanes, or longitudinal ribs, were placed across the step cavities to manipulate the flow turbulence to enhance the interactions between the mainstream flow and the cavity recirculation region. The results showed a strong influence of the vanes on the air–water flow properties in both free-stream and cavity flows. The findings demonstrate some passive turbulence manipulation in highly turbulent air–water flows.

Nanoscale High-Frequency Contact Mechanics Using an AFM Tip and a Quartz Crystal Resonator

The transmission of high-frequency shear stress through a microscopic contact between an AFM tip and an oscillating quartz plate was measured as a function of vertical pressure, amplitude, and surface properties by monitoring the MHz component of the tip's deflection. For dry surfaces, the transmission of shear stress is proportional to the vertical load across the contact. This provides a measure of the forces of adhesion between the substrate and the tip. When stretching soft polymeric fibers created by pulling on the surface of a pressure sensitive adhesive, the transmitted shear stress decreased linearly with extension over the entire range of pulling. This contrasts with the static adhesive force, which remained about constant until it discontinuously dropped at the point of rupture.

Experimental investigation of the time-dependent dry frictional behaviour of glass and aluminium

The bolted connection is probably the most common technique used for the assembling of glass beams or plates. In such connections, the transmission of shear stress is ensured by friction. The present experimental work aims at precisely characterizing the dry friction between a soft 1050 aluminium pad and a glass plate. A tribometer is specially designed and constructed to this end. The experimental results show that the glass–aluminium frictional behaviour is time-dependent. In particular, the friction coefficient turns out to increase with the duration of a constant normal pressure. This increase can reach 65% after 1 h. A state-dependent model involving one scalar internal variable is proposed to formulate the time dependence of the relevant friction coefficient.

２次元弾性解と個別要素解析によるトンネル支保特性曲線の考察

Active mobilization of bearing capacity of rock mass surrounding an underground opening characterizes the NATM (New Austrian Tunneling Method) concept of supporting. There have been many attempts to give quantitative expressions for this capacity but no one has ever completely solved the question. In the first part of this paper the theoretical relations between support pressure and tunnel wall displacements are briefly discussed. We derive a simplified solution of a circular lined-tunnel in an elastic ground under the plain strain for full-slip and no-slip conditions. These two conditions at the ground-lining interface make it possible to explain the effects of shear stress transmission and relative shear displacement. The lateral free-field ground stresses for this solution are restricted to a fixed value of the vertical stresses (σV*=-p, σH*=-kp). An actual tunnel opening is excavated and supported after the load corresponding to the free-field stresses. We introduce an assumption of the actual “excavation unloading” conditions that occur during tunneling. By advancing this derivation, the strict solution is utilized successfully to construct a theoretical characteristic curve of tunneling. The characteristic curve shows clearly the bearing capacities of a tunnel lining, the surrounding ground and the total by using an index, “relative-support-stiffness”.The elastic theory of the stress distribution around tunnels demonstrates that the deviatoric stresses are maximum at the periphery of the excavation. Therefore, the rock mass may yield in the overstressed zone surrounding the excavation. Discussion here should include the dependence of the characteristic curve on the zone of yielded ground and the discontinuity in the ground. We have carried out numerical simulations for a discontinuous ground with Distinct Element Modeling. The realistic ground reaction curves by the analyses are examined with the theoretical solution derived above. We will learn that while the ground may work, more or less, as a load bearing structural component to the load corresponding to the free-field stresses, overestimation must be avoided.

Mechanism for Water Film Generation and Lateral Flow in Liquefied Sand Layer

In view of the significant role of the water film effect in flow failure for a liquefied sandy deposit, the mechanism of water film generation is numerically studied based on a 1-dimensional model test. The process of water film growth and decay can be simulated to a certain extent by a simple consolidation analysis, which indicates that only a small difference in permeability in layered sand is enough for a water film to develop. A 1 G shaking table test for a two-dimensional slope model with an arc of silt within a saturated sand is then addressed to discuss the dilatancy effect exerted in sheared sand during flow failure. It is possible that, once the water film is formed, the transmission of shear stress through it is interrupted, leaving the sand below free from the dilatancy; this eventually allows the water film to stay without being absorbed during flow failure. The result of another shaking table test for a trapezoidal slope with horizontal silt seams indicate that water films beneath the seams enable the soil mass above them to laterally flow along water films very gently inclined even after shaking. If a silt seam breaks due to excessive pressure in the water film, it triggers re-liquefaction in the upper sand and leads to further instability.

Experiments on the relative mobility of muddy subaqueous and subaerial debris flows, and their capacity to remobilize antecedent deposits

Subaqueous debris flows share many similarities with their subaerial counterparts, but also differ in striking ways. The present treatment is devoted to an experimental comparison of paired subaqueous and subaerial debris flows. The debris slurry consisted of 39% water, 25% kaolin, 24% silt and 12% sand by weight. The debris flows ran down a rectangular channel with a length of 10 m and a width of 0.20 m. In some of the runs, the channel bottom was `hard' (i.e., a fixed, rough inerodible surface) and in others it was `soft' (i.e., an antecedent debris-flow deposit over which the debris flow was allowed to run). On the `hard' bottom, the subaqueous debris flows ran farther downslope than their subaerial counterparts with the same rheology. Their deposits also displayed extensional features not seen in the subaerial case, and were much thinner than that which would be expected based on yield strength. On the `soft' bottom, the subaerial debris flows extensively remobilized antecedent debris-flow deposits, whereas the corresponding subaqueous debris flows ran over antecedent debris-flow deposits with no detectable remobilization. The reason for these differences is hypothesized to be the incorporation of a thin layer of ambient water underneath a subaqueous debris flow as its head hydroplanes slightly above the bed. The lubricating layer appears to prevent the transmission of shear stress between the two layers.

Mechanisms of Shear Stress Transmission and Transduction in Endothelial Cells

Mechanisms of Shear Stress Transmission and Transduction in Endothelial Cells

FEM analysis of concrete structures subjected to mode-I and mixed-mode loading conditions

In this study, the finite element method (FEM) for a body containing displacement discontinuity is used for the investigation of tensile fracture behavior under mode-I and mixed-mode loading conditions in concrete structures. A mechanical model for the tensile fracture behavior is reduced to a mathematical problem, and the analysis method is proposed. With the aid of this method, several factors which govern tensile fracture are examined, such as the unloading path in the tension-softening behavior and the transmission of shear stresses across crack surfaces. A plain concrete beam without a notch is analyzed by first neglecting and then taking into account the unloading path in the tension-softening behavior to demonstrate the phenomenon of cracking localization in mode-I crack growth. Pullout test specimens of practical significance are analyzed in order to study the crack growth phenomenon under mixed-mode loading conditions. Cases with and without lateral confinement are considered and the results obtained from the present analysis are compared with those obtained from available experimental data. A simple model for shear transfer across crack surfaces is established. By incorporating this model in the program, a pullout test specimen with lateral confinement is analyzed to examine the influence of shear transfer across crack surfaces on cracking localization.

Acceleration from Field-Aligned Potential Drops

AbstractUnstable field-aligned currents are seen as the origin of field-aligned potential drops. They convert energy stored in magnetic shear stresses into kinetic energy. A good fraction of this energy is carried by runaway electrons and ions out of the acceleration region. The paper emphasizes the analogy with mechanical fractures. Simple expressions for the energy conversion rate and the parallel potential drop are derived, the two being linked by the critical current density needed for instability. The origin of the currents (generator) lies mostly in a region remote from that of energy conversion (fracture zone). The transmission of shear stresses and energy from the generator plasma, where the primary forces are applied to the fracture zone is also considered. A closed set of relations allows quantitative evaluation of the energetic particle production efficiency. The decoupling of the plasma on either side of the fracture zone which allows fast stress relief is described in detail, as well as a stationary model for the Alfvén wave interaction between fracture zone and generator plasma. A simple concept of the nature of the anomalous resistivity generated by the unstable current leads to an expression for the magnetic diffusivity inside the fracture zone and an estimate of the latter’s extent parallel to the magnetic field, whereas its width and length transverse to B follow from the macroscopic relations. Finally and as an example, the theory is applied to the problem of fast electron (and ion) acceleration well above 1 MeV seen to occur in many solar flares. It is obvious that this process belongs to the most powerful production processes of high-energy particles in stellar magnetic fields.Subject headings: acceleration of particles — MHD — plasmas

Unusual sea-floor fabric near the Bullard fracture zone imaged by GLORIA sidescan sonar

THE tectonic fabric of the sea floor created at spreading ridges generally curves in the direction of ridge offset near transform faults, owing to the influence of shearing stress on transform faults. Here we present new GLORIA sidescan sonar images from the South American–Antarctic Ridge, showing fabric to the north of the Bullard transform with a reversed sense of curvature. This curvature, and that observed in an area of older sea floor near the eastern ridge–transform intersection, appears to result from post-emplacement deformation, caused by the transmission of shear stresses across transforms. The deformation was probably related to a major Early Miocene change in spreading direction, which would have imposed a component of compression on the transforms. Such a sense of curvature has not, to our knowledge, been observed elsewhere on the deep ocean floor, although apparently similar patterns have been reported in ophiolites.

Evaluation of surface treatments for glass fibers in composite materials

AbstractThe thermomechanical stability of a number of organosilane surface treatments for glass fibers was evaluated for use in a fiber reinforced epoxy resin. All of the silane coatings were found to improve the tensile strength of E‐glass filaments, particularly at large gauge lengths. A phenylamino silane and an amino silane were particularly effective in this regard. The fiber/matrix interface was evaluated as a function of temperature and after exposure to boiling water using a single‐fiber composite test. All silane coatings transmitted a higher interfacial shear stress than obtained in composites with no coatings, and in all cases the shear stress transmission was considerably higher than would be expected from the yield properties of the resin. Measurements of the glass transition temperature of the epoxy resin, as well as Fourier‐Transform Infra‐Red analysis, indicated modification of resin properties in a zone around the glass fibers. Each of the silane coatings provided more stable thermomechanical properties than those obtained with uncoated glass, at least until the silanes were irreversibly degraded by boiling water. A phenylamino silane provided the most thermally stable properties. Finally, unidirectional E‐glass fiber reinforced laminae were fabricated and the measured values of longitudinal strength were compared favorably to theoretical predictions.

On the Mechanical Behavior of Entrained Materials in Concentrated Contacts

A quantitative discussion is presented that suggests the solid-like mechanical properties of liquids control the low sliding speed tractive behaviors of highly loaded elastohydrodynamic contacts. A new method to calculate transient density and viscosity response of a material is proposed. This response model is used in a simulation of isothermal-pure rolling line contacts with load, speed, and material parameters similar to those utilized by Trachman, et al. It is shown, using accepted linear viscoelastic arguments, that solid-like behavior is obtained except at low load and speed conditions. The tensile and shear mechanical properties of grossly deformed and compressed solids as a function of hydrostatic pressure and shear rate are reviewed: it is shown that at low sliding speed, shear modulus and yield stress mechanical properties of lubricants in highly loaded, high speed elastohydrodynamic contacts have the same functional dependencies. A viscoelastic model of the time dependent shear stress transmission capability of a liquid is proposed that predicts the inverse dependence of effective viscosity on rolling speed. Estimates of the shear stress transmitted under isothermal conditions are high and it is proposed that inclusion of irreversible compressional heating effects will improve the predictions but will allow retention of the solid-like character of the material.