Shear Index Research Articles

Exploring the Solar Wind-Planetary Interaction at Mars: Implication for Magnetic Reconnection.

The Martian crustal magnetic anomalies present a varied, asymmetric obstacle to the imposing draped interplanetary magnetic field (IMF) and solar wind plasma. Magnetic reconnection, a ubiquitous plasma phenomenon responsible for transferring energy and changing magnetic field topology, has been observed throughout the Martian magnetosphere. More specifically, reconnection can occur as a result of the interaction between crustal fields and the IMF, however, the global implications and changes to the overall magnetospheric structure of Mars have yet to be fully understood. Here, we present an analysis to determine these global implications by investigating external conditions that favor reconnection with the underlying crustal anomalies at Mars. To do so, we plot a map of the crustal anomalies' strength and orientation compiled from magnetic field data collected throughout the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. Then, we create "shear maps" which calculate and plot the angle of shear between the crustal fields and a chosen external field orientation. From there we define a "shear index" to quantify the susceptibility of a region to undergo reconnection based on a given overlaid, external field orientation and the resulting shear map for that region. We demonstrate that the shear analysis technique augments analysis of local reconnection events and suggests southward IMF conditions should favor dayside magnetic reconnection on a more global scale at Mars.

Experimental Investigation on the Shear Characteristics of Frozen Silty Clay and Grey Relational Analysis

In the spring thawing season, the decrease in the strength of frozen soil caused by temperature may lead to slope instability. Therefore, researchers have studied the relationship between the temperature and strength of the freeze-thaw zone. However, previous studies have considered the impact of thawing temperature on the strength, but less research on shaping temperature. Therefore, direct shear tests were performed on specimens with different thawing temperatures (i.e., −5, −2 and 1 °C) and different water contents (i.e., 9, 16, and 23%) at different shaping temperatures (i.e., −2, −7 and −12 °C). The results indicated that: the stress-strain curves under different test conditions exhibited strain softening characteristics; shear strength and shear index decreased with increasing shaping temperature; the effect of cohesion on strength was greater than that of internal friction angle; the mechanical mechanism in the freeze-thaw zone was related to the unfrozen water content of the specimen. In addition, the grey correlation analysis showed that the water content had the greatest effect on the shear index, while the shaping temperature had the least effect on the shear index. The grey relational grade of shaping temperature was greater than 0.5, indicating that the effect of shaping temperature on strength was not negligible.

Experimental study on shear characteristics of the silty clay soil-ice interface

During the spring thawing, the decrease of soil-ice interface strength by temperature may lead to slope instability. For this reason, some researchers have explored the relationship between temperature and soil-ice interface strength. However, previous studies have not systematically explored the change law of strength at the soil-ice interface from negative temperature to 0 °C. Therefore, direct shear tests were conducted at different shear temperatures and different moisture contents. The effects of temperature and moisture content on strength, cohesion, and internal friction angle are analyzed, while the shear failure mechanism of specimens at different temperatures is discussed according to the location of the shear failure surface. The results show that: Shear properties of soil ice specimens are related to the unfrozen moisture content. The strength of the sample decreases with increasing temperature, and the change in strength is most significant from − 2 to − 0 °C. The strength reduction in this range is from 21.8 to 74.8%, and the higher the moisture content the more obvious this phenomenon is. The shear index tends to decrease with the increase of unfrozen water content, and the greater the increase of unfrozen water, the faster the decrease of both, especially in stage 2. When the temperature is higher than − 5℃, the failure surface is located above the soil-ice interface, and the strength of the specimen is similar to that of the frozen soil. When the temperature is − 10℃, the shear damage surface appears at the soil-ice interface, and the strength of the specimen is determined by the strength of the soil-ice interface.

Carpal tunnel syndrome treatment and the subsequent alterations in tendon and connective tissue dynamics

BackgroundCarpal tunnel syndrome patients demonstrate diminished motion of the median nerve and fibrotic changes in the subsynovial connective tissue within the carpal tunnel. Currently, there are few prognostic factors to help predict the outcome of commonly performed treatments including surgical carpal tunnel release and corticosteroid injections. This study aimed to non-invasively assess the changes in the dynamic response of the subsynovial tissue relative to tendon motion after the intervention and to correlate this with disease severity. MethodsA total of 145 patients with carpal tunnel syndrome were recruited into this study. Clinical and demographic data, electrophysiological severity and dynamic ultrasound images were collected before and after treatment, either by injection or surgery. The relative motion of the subsynovial tissue with the underlying middle finger flexor digitorum superficialis tendon was measured using a speckle tracking algorithm and was expressed as a shear index (SI). Baseline and follow-up data, the association between change in SI and severity, and the role of treatment modality were analyzed and statistically compared. FindingsOverall, there was a significant increase (more relative motion) after treatment in the mean shear index from 79.9% (±15.4% SD) to 82.9% (±14.8% SD) (p = 0.03). Secondary analyses showed that this change was mostly present in those with mild disease severity undergoing surgery (p = 0.01). InterpretationThis study shows that the relative subsynovial tissue movement increases in patients after intervention. The present study lays a foundation for future studies to non-invasively assess the role of carpal tunnel dynamics in response to treatment.

Tensile strength of cohesive powders

Measurement and prediction of cohesive powder behaviour related to flowability, flooding or arching in silos is found to be very challenging. Previous round robin [52] attempts with ring shear testers did not furnish reliable data and have shown considerable degrees of scatter and uncertainty in key measurements. Thus studies to build a reliable experimental database using reference materials are needed in order to evaluate the repeatability and effectiveness of shear testers and the adopted procedures.In this paper, we study the effect of particle size on the yield locus for different grades of limestone (calcium carbonate). We use the nonlinear Warren Spring equation to obtain the values of cohesion C, tensile strength T, and the shear index n. We recover linear (n = 1) yield loci for d50>70 μm with respectively small C and T, with consistent, finite macroscopic friction C/T = 0.7. With particle size decreasing below 70 μm the response becomes more and more cohesive and non-linear (1<n<2).Then we compare the values of the parameters C,T and n obtained from two different shear testers (Schulze and Brookfield PFT). Both testers run at positive confining stresses (slightly different ranges) and give identical results for large fractions (weakly cohesive). For strongly cohesive samples, the PFT results are very similar to the ring shear tester, with slightly smaller values for T, C, and n. Further experiments with a variety of cohesive powders are needed to confirm or rebut this systematic difference the two testers display for cohesive powders.Finally, we compare the (extrapolated) values of T with a direct, transverse measurement running at negative stresses, using the Ajax tensile tester, and found a very good agreement, which validates the Warren Spring equation for negative stresses.

Age-Dependence of Flow Homeostasis in the Left Ventricle.

Background: Intracardiac flow homeostasis requires avoiding blood stasis and platelet activation during its transit through the cardiac chambers. However, the foundations of intraventricular blood washout and its exposure to shear stresses have been poorly addressed. We aimed to characterize and quantify these features in a wide population of healthy subjects and assess the relationships of these indices with age.Methods: We used color-Doppler echocardiography and custom post-processing methods to study 149 healthy volunteers from 26 days to 80 years old. From the intraventricular flow-velocity fields we obtained personalized maps of (1) the residence time of blood in the LV, and (2) the shear index, a metric accounting for the strongest occurrence of shear stresses inside the chamber. From these maps we derived quantitative indices of the overall intraventricular blood washout and shear exposure. We addressed the age-dependence of these indices and analyzed their relationship with age-related changes in filling-flow.Results: The entire intraventricular blood pool was replaced before 8 cycles. Average residence time of blood inside the LV was <3 cycles in all subjects and followed an inverse U-shape relationship with age, increasing from median (IQR) of 1.0 (0.7 to 1.2) cycles in the 1st year of life to 1.8 (1.4–2.2) cycles in young adults (17–30 years old), becoming shorter again thereafter. Shear index showed no relation with age and was bounded around 20 dyn·s/cm2. Regions with the longest residence time and highest shear index were identified near the apex. Differences in the degree of apical penetration of the filling waves and the duration of the late-filling phase explained the age-dependence of residence time ( = 0.48, p < 0.001).Conclusions: In average, blood spends 1 to 3 beats inside the LV with very low shear stress rates. The apical region is the most prone to blood stasis, particularly in mid-aged adults. The washout of blood in the normal LV is age-dependent due to physiological changes in the degree of apical penetration of the filling waves.

Test evaluation of rutting performance indicators of asphalt mixtures

Rutting indicators of asphalt mixtures were evaluated using wheel tracking testing results of AC-13 and AC-20 asphalt mixtures. A short term rutting period of 2520 cycles could be adequate for simulating heavy traffic and for prediction of long term rutting. Secondary rutting based indicators had higher rutting correlation coefficients than primary rutting based indicators (PRBI). The reliability of PRBI indicated that mixtures could be characterised based on primary rutting. The rutting at 2 cycles could be used for quick rutting prediction, but since the earliest recorded cycle was 2, it was hypothesised that even one cycle could as well be equally significant. A/C index, complex stability index and shear index were the most reliable indicators based on validating results of recycled hot mix asphalt mixtures. However, only A/C index could reliably screen mixtures with nearly the same secondary rutting rates. It was considered the best indicator, which could as well assess the performance of indirect rutting indicators. Its limiting mixture design values could be determined and validated.

Impact of satellite-retrieved atmospheric temperature profiles assimilation on Asian summer monsoon 2010 simulation

The impact of assimilation of satellite-retrieved atmospheric temperature profiles data in simulating mean monsoon circulation and rainfall of summer monsoon 2010 is examined in this study using the regional climate model, Weather Research and Forecasting model (WRF). Two experiments are performed; the first one is the control experiment (WRF-CTL) where no assimilation is carried out, and the second one is similar to the first one, but satellite-retrieved atmospheric temperature profiles are assimilated using a four-dimensional data assimilation method (WRF-AIRS). Mean monsoon features such as the low level jet, monsoon trough, tropical easterly jet, meridional pressure gradient and the spatial distribution of rainfall are better simulated in WRF-AIRS. Correlation coefficients between the observed and WRF-AIRS (WRF-CTL) daily zonal wind shear, meridional wind shear and rainfall indices over the Indian summer monsoon region are 0.98, 0.96 and 0.67 (0.32, 0.35 and 0.23), respectively. The zonal and meridional wind indices over the western Pacific and East Asia are 0.9 and 0.8 (0.6 and 0.5), respectively. Spatial distribution of rainfall displays double ITCZ like rainfall pattern over the tropical Indian Ocean in WRF-CTL, whereas WRF-AIRS display a single ITCZ pattern, which is similar to the observed one. The temporal evolution of the vertical structure of temperature (associated with rainfall activity over the monsoon core region) shows warming in the midtroposphere to upper troposphere (by 0.5 to 1.5 °C) and cooling in the midtroposphere to lower troposphere (by 0.5 to 1.0 °C). This atmospheric temperature distribution associated with rainfall is well simulated by WRF-AIRS. Under heavy rainfall conditions, WRF-AIRS produces strong vertical motion consistent with the observations but is absent (or weak) in WRF-CTL. This study deduces that the assimilation of temperature profiles in the regional climate model can significantly improve the dynamical and thermodynamical features of monsoon by representing the vertical distribution of temperature more realistically. Our analysis reiterates that the Asian summer monsoon circulation is mainly controlled by thermal forcing. Our study suggests that it is essential to improve the existing parameterization schemes for better simulation of summer monsoon.

Speckle-Tracking Sonographic Assessment of Longitudinal Motion of the Flexor Tendon and Subsynovial Tissue in Carpal Tunnel Syndrome

The aim of this study was to image both tendon and subsynovial connective tissue movement in patients with carpal tunnel syndrome and healthy control volunteers, using sonography with speckle tracking. To estimate accuracy of this tracking method, we used in vivo measurements during surgery to validate the motion estimated with sonography. We recruited 22 healthy volunteers and 18 patients with carpal tunnel syndrome. Longitudinal sonograms of the middle finger flexor digitorum superficialis tendon and subsynovial connective tissue were obtained during finger flexion and extension. The images were analyzed with a speckle-tracking algorithm. The ratio of the subsynovial connective tissue velocity to tendon velocity was calculated as the maximum velocity ratio, and the shear index, the ratio of tendon to subsynovial connective tissue motion, was calculated. For validation, we recorded flexor digitorum superficialis tendon motion during open carpal tunnel release. The shear index was higher in patients than controls (P < .05), whereas the maximum velocity ratio in extension was lower in patients than controls (P < .05). We found good intraclass correlation coefficients (>0.08) for shear index and maximum velocity ratio measurements between speckle-tracking and in vivo measurements. Bland-Altman analyses showed that all measurements remained within the limits of agreement. Speckle tracking is a potentially useful method to assess the biomechanics within the carpal tunnel and to distinguish between healthy individuals and patients with carpal tunnel syndrome. This method, however, needs to be further developed for clinical use, with the shear index and maximum velocity ratio as possible differentiating parameters between patients with carpal tunnel syndrome and healthy individuals.

Evaluation of performance of eccentric braced frame with friction damper

Nonlinear dynamic analysis and evaluation of eccentric braced steel frames (EBF) equipped with friction damper (FD) is studied in this research. Previous studies about assessment of seismic performance of steel braced frame with FD have been generally limited to installing this device in confluence of cross in concentrically braced frame such chevron and x-bracing. Investigation is carried out with three types of steel frames namely 5, 10 and 15 storeys, representing the short, medium and high structures respectively in series of nonlinear dynamic analysis and 10 slip force values subjected to three different earthquake records. The proper place of FD, rather than providing them at all level is also studied in 15 storey frame. Four dimensionless indices namely roof displacement, base shear, dissipated energy and relative performance index (RPI) are determined in about 100 nonlinear dynamic analyses. Then average values of maximum roof displacement, base shear, energy dissipated and storey drift under three records for both EBF and EBF equipped with friction damper are obtained. The result indicates that FD reduces the response compared to EBF and is more efficient than EBF for taller storey frames.

Site response studies in Agartala Urban agglomeration

A systematic investigation using digital microearthquake recorders with short period SS-1 seismometers, covering 76 sites in and around Agartala city, has been carried out for site response (SR) studies in the area. In the northern part of the area, SR varies from 1.15 to 1.85 corresponding to peak frequency 0.76 to 0.93 Hz where soil is mostly semi-consolidated and stiffer than recent Quaternary deposits (Haora River formation). In the southern part of the area, SR varies from 1.12 to 2.42 corresponding to peak frequency from 0.71 to 0.85 Hz within the Dupitila formation (early Quaternary). It is observed that estimated SR from H/V increases from edges to middle of the Haora River valley and impedance contrast fallows the similar trend. This reflects that site response by H/V is influenced by impedance contrast, whereas computed amplification from 1-D model shows opposite trend. The maximum amplification at fundamental frequency of resonance, 1.04 Hz estimated from H/V by near to BH-7, is 2.5 times greater than the impedance contrast/ratio derived from 1-D model for same location. Relationship between resonance frequency and depth was obtained by applying quarter wavelength and Bard (2000) methodologies, which shows linearity, whereas H/V shows its nonlinearity characteristic in soil across the valley part of Haora River. Shear wave velocities, and subsequently, SPT index and factor of safety (by cyclic stress approach) were estimated from geotechnical parameters. Vs30 and site response data were used in this study for getting a first hand information about soil stiffness condition in the area. The estimation of SPT index and factor of safety could be a useful tool for delineating liquefied and none liquefied zones at various depth levels, especially where water table exists at a very shallow level. The expected liquefiable zone was observed at depths varying from 6–25 m beneath the soil bearing zones where percentage of fines is estimated to be more than 35% for the area. This knowledge about subsurface soil characteristics will be useful for the civil engineers/city planners, which can be taken into account at the time of constructing earthquake-resistant structures in the area.

Shear Strain and Motion of the Subsynovial Connective Tissue and Median Nerve During Single-Digit Motion

The objective of this study was to measure the relative motion of the middle finger flexor digitorum superficialis (FDS) tendon, its adjacent subsynovial connective tissue (SSCT), and the median nerve during single-digit motion within the carpal tunnel in human cadaver specimens and to estimate the relative motions of these structures in different wrist positions. Using fluoroscopy during simulated single-digit flexion, we measured the relative motion of the middle finger FDS tendon, SSCT, and median nerve within the carpal tunnel in 12 human cadavers. Measurements were obtained for 3 wrist positions: neutral, 60 degrees flexion, and 60 degrees extension. After testing with an intact carpal tunnel was completed, the flexor retinaculum was cut with a scalpel, and the same testing procedure was repeated for each wrist position. The relative motions of the tendon, SSCT, and median nerve were compared using a shear index, defined as the ratio of the difference in motion along the direction of tendon excursion between 2 tissues divided by tendon excursion, expressed as a percentage. Both tendon-SSCT and tendon-nerve shear index were significantly higher in the 60 degrees of wrist flexion and extension positions than in the neutral position. After division of the flexor retinaculum, the shear index in the 60 degrees wrist extension position remained significantly different from that of the neutral position. We have found that the relative motion between a tendon and SSCT in the carpal tunnel is maximal at extremes of wrist motion. These positions may predispose the SSCT to shear injury.

Effects of carpal tunnel release on the relative motion of tendon, nerve, and subsynovial connective tissue in a human cadaver model

Background The purpose of this study was to evaluate the effect of flexor retinaculum division (simulated carpal tunnel release) on the relative motion of flexor tendon, subsynovial connective tissue, and median nerve in human cadaver specimens. Methods Using fluoroscopy, we measured the relative motion of middle finger flexor digitorum superficialis tendon, subsynovial connective tissue, and median nerve in twelve human cadavers with simulated fist motion. Measurements were obtained for three wrist positions: neutral; 60° flexion; and 60° extension. The shear index was defined as the difference in motion between two tissues (tendon, subsynovial connective tissue, or nerve) relative to tendon excursion, expressed as a percentage. After testing with an intact carpal tunnel, the flexor retinaculum was cut and the testing procedure was repeated. Findings With an intact flexor retinaculum, the wrist flexion position showed significantly less displacement for the subsynovial connective tissue and median nerve relative to tendon displacement, and thus the highest potential shear strain between subsynovial connective tissue–tendon, and tendon–nerve. The wrist extension position also had a significantly higher potential shear strain for tendon–nerve compared to the neutral position. After division of the flexor retinaculum, the differences in shear index among wrist positions were reduced. For the wrist flexion position, the subsynovial connective tissue and median nerve displacements significantly increased, indicating lower shear index values. Interpretation These findings suggest that division of flexor retinaculum reduces the potential shear strain and thus possibly the risk of shear injury to tissues with the carpal tunnel.

TEHD Behavior of Non-Newtonian Dynamically Loaded Journal Bearings in Mixed Lubrication for Direct Problem

A transient non-Newtonian TEHD analysis for dynamically loaded journal bearings in mixed lubrication is developed for direct problem. A mass conserving cavitation is included and viscoelasticity subsuming shear thinning is characterized by the upper converted Maxwell fluid and the power law fluid models. The Reynolds equation, the transient two-dimensional energy equation in the film, the quasi-steady-state two-dimensional heat conduction equation in the bushing and heat balance in the journal are solved using finite difference formulations. The thermal and elastic deformation equations are solved using the finite element method. The relation between the average contact pressure and the average gap is numerically determined in micro scale. Effects of roughness texture, degree of asperity contact, shear index, relaxation time, thermal and elastic deformations on bearing behavior are investigated.

Geotechnical Properties of Surface Sediments in the INDEX Area

As a part of the environmental impact assessment studies, geotechnical properties of sediments were determined in the Central Indian Basin. The undrained shear strength and index properties of the siliceous sediments were determined on 20 box cores of uniform dimension collected from various locations in five preselected sites. The maximum core length encountered was 41 cm and most of the sediments were siliceous oozes consisting of radiolarian or diatomaceous tests. The shear strength measurements revealed that surface sediments deposited in recent times (0–10 cm) have a shear strength of 0–1 kPa; this value increases with depth, reaching 10 kPa at 40 cm deep. Older sediments have greater strength because of compaction. Water content varies in the wide range of 312–577% and decreases with depth. The clay minerals such as smectite and illite are dominant and show some control over water content. Wet density, specific gravity, and porosity do not indicate any notable variation with depth, thereby indicating a uniform, slow rate of sedimentation. The average porosity of sediments is 90.2%, specific gravity 2.18, and wet bulk density 1.12 g/cm3. Sediments exhibit medium to high plasticity characteristics, with the average plasticity index varying between 105% and 136%. Preliminary studies on postdisturbance samples showed an increase in natural water content and a decrease in undrained shear strength of sediments in the top 10- to 15-cm layer.

Characteristics of laminar viscous shear-thinning fluid flows in eccentric annular channels

Laminar fully developed flows of time-independent viscous shear-thinning fluids in straight eccentric annuli are considered. The fluid rheology is modeled by the power-law constitutive equation, which is representative of many industrial process liquids. The annulus models flow channels in process heat exchangers, extruders, and drilling wells, among others. The flow cross-section geometry is mapped into a unit circle by means of a coordinate transformation, and the governing momentum equation is solved by finite-difference techniques using second-order accurate discretization. Numerical solutions for a wide variation of annuli radius ratio (0.2 ≤ r ∗ ≤ 0.8) , inner core eccentricity (0 ≤ ε ∗ ≤ 0.8) , and shear index (1 ≥n ≥ 0.2) , are presented. Both fluid rheology and annuli eccentricity are seen to have a strong influence on the flow behavior. The eccentricity causes the flow to stagnate in the narrow gap with higher peak velocities in wide gap, and large azimuthal variations in the velocity field. The fluid pseudoplasticity gives rise to even greater flow maldistribution around the annulus, with non-uniform velocity fields, wall shear-stress distribution, and friction factor characteristics.

On the relationship between shear lip, shear index and energy in dynamic tear specimens

In a previous paper [J. R. Matthews, On the relationship between shear index and energy in dynamic tear specimens. Engng Fracture Mech. 39, 131–140 (1991)], a relationship was shown to exist between the fracture energy and shear index in a series of dynamic tear (DT) test of quench and tempered carbon and low alloy steels, and their weldments over a wide range of temperatures, compositions and locations in the weldments. In this paper it will be shown that a relationship also exists between the shear lip size and the energy that fractured the specimen. More importantly the relationship between shear lip and energy is independent of specimen thickness as will be shown for a series of 16 and 25 mm specimens. Data used in this study have been acquired from samples of HY80, HY100 and HLES steels and gas metal arc welds of HY80 and HY100 steels.

The punch problem for shear-index granular materials

Experimental evidence indicates that a wide range of powders and granular materials have shear-index yield conditions of the form (τ/c) n = 1 - (σ/t), where τ and σ denote the shear and normal components of stress and c, t and n are experimentally-determined positive constants that are referred to as the cohesion, tensile strength and shear index respectively. This yield function is also known as the Warren Spring equation and experimentally-determined values of the shear index n indicate that n lies between the values 1 and 2. The value n = 1 corresponds to the well-known Coulomb-Mohr yield function and previous work shows that the special value n = 2 gives the simplest theory amongst those values of n which lie in the range of physical interest. We extend the known Coulomb-Mohr solution for the indentation of a granular material by a flat rigid punch to the case of shear-index materials and we determine an associated velocity field assuming a previously proposed dilatant double-shearing theory. The results obtained are illustrated numerically and it is shown how for general values of n in the range 1 < n < 2 the theories corresponding to n = and n = 2 bound the various quantities arising in the stress and velocity fields. The proposed solution is by no means unique and an alternative solution is noted in an Appendix which although a bonafide solution of the governing equations may not arise physically.

Evolutionary and flare-associated magnetic shear variations observed in a complex, flare-productive active region

Evolution of nonpotential structures in a complex, flare-productive active region NOAA AR 6555 has been studied during the period March 23–26, 1991, using a quantitative description of the degree of magnetic shear at both local and regional scales. Distinct shear evolution in four subareas of AR 6555 is inferred from daily variation of their shear indices. Subareas which showed significant evolution in their overall magnetic structure are found to be most active. Hα flare ribbons mostly formed bordering, andnot within, areas of large shear and expanded over areas of lower shear. Magnetic shear changes are also detected during several flares, including a major X4.7/4B flare. Out of the 14 events for which temporally contiguous magnetograms were available, a decrease, or dip, in area-averaged shear index around flare onset time followed by an increase was observed in eight cases. There were two events with increase, three events with continuous decrease, and one event with no change in the shear index during the flare.

On the relationship between shear index and energy in dynamic tear specimens

Comparison of fracture energy and shear index in a series of dynamic tear (DT) tests of quench and tempered carbon and low alloy steels and their weldments has shown that the shear index is related to the fracture energy of the specimens over a wide range of temperatures, compositions and weldment locations. Data have been acquired from samples of HY80, HY100 and QT28 steels, submerged arc welds of HY80 and HSLA80, gas metal arc welds of HY80 and shielded metal arc welds of HY100.