Sample records for predicting shear type

  1. Predicting km-scale shear zone formation

    NASA Astrophysics Data System (ADS)

    Gerbi, Christopher; Culshaw, Nicholas; Shulman, Deborah; Foley, Maura; Marsh, Jeffrey

    2015-04-01

    gradients but are insufficient to maintain them because the stress perturbations will dissipate with deformation. Metamorphism can unquestionably cause sufficient rheological change, but only in certain rock types: for example, granitoids have much less capacity for metamorphically induced rheologic change than do mafic rocks. The magnitude of phase geometry variation observed in natural systems suggests that morphological change (e.g., interconnection of weak phases) likely has little direct affect on strength changes, although other textural factors related to diffusion paths and crystallographic orientation could play a significant role. Thermal perturbation, mainly in the form of shear heating, remains potentially powerful but inconclusive. Taken together, these observations indicate that a simple algorithm predicting shear zone formation will not succeed in many geologically relevant instances. One significant reason may be that the inherent lithologic variation at the km scale, such as observed in the Central Gneiss belt, prevents the development of self-organized strain patterns that would form in more rheologically uniform systems.

  2. Predicting Shear Transformation Events in Metallic Glasses

    NASA Astrophysics Data System (ADS)

    Xu, Bin; Falk, Michael L.; Li, J. F.; Kong, L. T.

    2018-03-01

    Shear transformation is the elementary process for plastic deformation of metallic glasses, the prediction of the occurrence of the shear transformation events is therefore of vital importance to understand the mechanical behavior of metallic glasses. In this Letter, from the view of the potential energy landscape, we find that the protocol-dependent behavior of shear transformation is governed by the stress gradient along its minimum energy path and we propose a framework as well as an atomistic approach to predict the triggering strains, locations, and structural transformations of the shear transformation events under different shear protocols in metallic glasses. Verification with a model Cu64 Zr36 metallic glass reveals that the prediction agrees well with athermal quasistatic shear simulations. The proposed framework is believed to provide an important tool for developing a quantitative understanding of the deformation processes that control mechanical behavior of metallic glasses.

  3. Predicting Shear Transformation Events in Metallic Glasses.

    PubMed

    Xu, Bin; Falk, Michael L; Li, J F; Kong, L T

    2018-03-23

    Shear transformation is the elementary process for plastic deformation of metallic glasses, the prediction of the occurrence of the shear transformation events is therefore of vital importance to understand the mechanical behavior of metallic glasses. In this Letter, from the view of the potential energy landscape, we find that the protocol-dependent behavior of shear transformation is governed by the stress gradient along its minimum energy path and we propose a framework as well as an atomistic approach to predict the triggering strains, locations, and structural transformations of the shear transformation events under different shear protocols in metallic glasses. Verification with a model Cu_{64}Zr_{36} metallic glass reveals that the prediction agrees well with athermal quasistatic shear simulations. The proposed framework is believed to provide an important tool for developing a quantitative understanding of the deformation processes that control mechanical behavior of metallic glasses.

  4. Analysis of the Shear Behavior of Stubby Y-Type Perfobond Rib Shear Connectors for a Composite Frame Structure.

    PubMed

    Kim, Sang-Hyo; Kim, Kun-Soo; Lee, Do-Hoon; Park, Jun-Seung; Han, Oneil

    2017-11-22

    Shear connectors are used in steel beam-concrete slabs of composite frame and bridge structures to transfer shear force according to design loads. The existing Y-type perfobond rib shear connectors are designed for girder slabs of composite bridges. Therefore, the rib and transverse rebars of the conventional Y-type perfobond rib shear connectors are extremely large for the composite frames of building structures. Thus, this paper proposes stubby Y-type perfobond rib shear connectors, redefining the existing connectors, for composite frames of building structures; these were used to perform push-out tests. These shear connectors have relatively small ribs compared to the conventional Y-type perfobond rib shear connectors. To confirm the shear resistance of these stubby shear connectors, we performed an experiment by using transverse rebars D13 and D16. The results indicate that these shear connectors have suitable shear strength and ductility for application in composite frame structures. The shear strengths obtained using D13 and D16 were not significantly different. However, the ductility of the shear connectors with D16 was 45.1% higher than that of the shear connectors with D13.

  5. Robust Kalman filter design for predictive wind shear detection

    NASA Technical Reports Server (NTRS)

    Stratton, Alexander D.; Stengel, Robert F.

    1991-01-01

    Severe, low-altitude wind shear is a threat to aviation safety. Airborne sensors under development measure the radial component of wind along a line directly in front of an aircraft. In this paper, optimal estimation theory is used to define a detection algorithm to warn of hazardous wind shear from these sensors. To achieve robustness, a wind shear detection algorithm must distinguish threatening wind shear from less hazardous gustiness, despite variations in wind shear structure. This paper presents statistical analysis methods to refine wind shear detection algorithm robustness. Computational methods predict the ability to warn of severe wind shear and avoid false warning. Comparative capability of the detection algorithm as a function of its design parameters is determined, identifying designs that provide robust detection of severe wind shear.

  6. Combined Resistivity and Shear Wave Velocity Soil-type Estimation Beneath a Coastal Protection Levee.

    NASA Astrophysics Data System (ADS)

    Lorenzo, J. M.; Goff, D.; Hayashi, K.

    2015-12-01

    Unconsolidated Holocene deltaic sediments comprise levee foundation soils in New Orleans, USA. Whereas geotechnical tests at point locations are indispensable for evaluating soil stability, the highly variable sedimentary facies of the Mississippi delta create difficulties to predict soil conditions between test locations. Combined electrical resistivity and seismic shear wave studies, calibrated to geotechnical data, may provide an efficient methodology to predict soil types between geotechnical sites at shallow depths (0- 10 m). The London Avenue Canal levee flank of New Orleans, which failed in the aftermath of Hurricane Katrina, 2005, presents a suitable site in which to pioneer these geophysical relationships. Preliminary cross-plots show electrically resistive, high-shear-wave velocity areas interpreted as low-permeability, resistive silt. In brackish coastal environments, low-resistivity and low-shear-wave-velocity areas may indicate both saturated, unconsolidated sands and low-rigidity clays. Via a polynomial approximation, soil sub-types of sand, silt and clay can be estimated by a cross-plot of S-wave velocity and resistivity. We confirm that existent boring log data fit reasonably well with the polynomial approximation where 2/3 of soil samples fall within their respective bounds—this approach represents a new classification system that could be used for other mid-latitude, fine-grained deltas.

  7. Prediction of turbulent shear layers in turbomachines

    NASA Technical Reports Server (NTRS)

    Bradshaw, P.

    1974-01-01

    The characteristics of turbulent shear layers in turbomachines are compared with the turbulent boundary layers on airfoils. Seven different aspects are examined. The limits of boundary layer theory are investigated. Boundary layer prediction methods are applied to analysis of the flow in turbomachines.

  8. Prediction of plantar shear stress distribution by artificial intelligence methods.

    PubMed

    Yavuz, Metin; Ocak, Hasan; Hetherington, Vincent J; Davis, Brian L

    2009-09-01

    Shear forces under the human foot are thought to be responsible for various foot pathologies such as diabetic plantar ulcers and athletic blisters. Frictional shear forces might also play a role in the metatarsalgia observed among hallux valgus (HaV) and rheumatoid arthritis (RA) patients. Due to the absence of commercial devices capable of measuring shear stress distribution, a number of linear models were developed. All of these have met with limited success. This study used nonlinear methods, specifically neural network and fuzzy logic schemes, to predict the distribution of plantar shear forces based on vertical loading parameters. In total, 73 subjects were recruited; 17 had diabetic neuropathy, 14 had HaV, 9 had RA, 11 had frequent foot blisters, and 22 were healthy. A feed-forward neural network (NN) and adaptive neurofuzzy inference system (NFIS) were built. These systems were then applied to a custom-built platform, which collected plantar pressure and shear stress data as subjects walked over the device. The inputs to both models were peak pressure, peak pressure-time integral, and time to peak pressure, and the output was peak resultant shear. Root-mean-square error (RMSE) values were calculated to test the models' accuracy. RMSE/actual shear ratio varied between 0.27 and 0.40 for NN predictions. Similarly, NFIS estimations resulted in a 0.28-0.37 ratio for local peak values in all subject groups. On the other hand, error percentages for global peak shear values were found to be in the range 11.4-44.1. These results indicate that there is no direct relationship between pressure and shear magnitudes. Future research should aim to decrease error levels by introducing shear stress dependent variables into the models.

  9. Prediction of residual shear strength of corroded reinforced concrete beams

    NASA Astrophysics Data System (ADS)

    Imam, Ashhad; Azad, Abul Kalam

    2016-09-01

    With the aim of providing experimental data on the shear capacity and behavior of corroded reinforced concrete beams that may help in the development of strength prediction models, the test results of 13 corroded and four un-corroded beams are presented. Corrosion damage was induced by accelerated corrosion induction through impressed current. Test results show that loss of shear strength of beams is mostly attributable to two important damage factors namely, the reduction in stirrups area due to corrosion and the corrosion-induced cracking of concrete cover to stirrups. Based on the test data, a method is proposed to predict the residual shear strength of corroded reinforced concrete beams in which residual shear strength is calculated first by using corrosion-reduced steel area alone, and then it is reduced by a proposed reduction factor, which collectively represents all other applicable corrosion damage factors. The method seems to yield results that are in reasonable agreement with the available test data.

  10. Ultrasonic Non-destructive Prediction of Spot Welding Shear Strength

    NASA Astrophysics Data System (ADS)

    Himawan, R.; Haryanto, M.; Subekti, R. M.; Sunaryo, G. R.

    2018-02-01

    To enhance a corrosion resistant of ferritic steel in reactor pressure vessel, stainless steel was used as a cladding. Bonding process between these two steels may result a inhomogenity either sub-clad crack or un-joined part. To ensure the integrity, effective inspection method is needed for this purpose. Therefore, in this study, an experiment of ultrasonic test for inspection of two bonding plate was performed. The objective of this study is to develop an effective method in predicting the shear fracture load of the join. For simplicity, these joined was modelled with two plate of stainless steel with spot welding. Ultrasonic tests were performed using contact method with 5 MHz in frequency and 10 mm in diameter of transducer. Amplitude of reflected wave from intermediate layer was used as a quantitative parameter. A set of experiment results show that shear fracture load has a linear correlation with amplitude of reflected wave. Besides, amplitude of reflected wave also has relation with nugget diameter. It could be concluded that ultrasonic contact method could be applied in predicting a shear fracture load.

  11. The Structure of Vertical Wind Shear in Tropical Cyclone Environments: Implications for Forecasting and Predictability

    NASA Astrophysics Data System (ADS)

    Finocchio, Peter M.

    The vertical wind shear measured between 200 and 850 hPa is commonly used to diagnose environmental interactions with a tropical cyclone (TC) and to forecast the storm's intensity and structural evolution. More often than not, stronger vertical shear within this deep layer prohibits the intensification of TCs and leads to predictable asymmetries in precipitation. But such bulk measures of vertical wind shear can occasionally mislead the forecaster. In the first part of this dissertation, we use a series of idealized numerical simulations to examine how a TC responds to changing the structure of unidirectional vertical wind shear while fixing the 200-850-hPa shear magnitude. These simulations demonstrate a significant intensity response, in which shear concentrated in shallow layers of the lower troposphere prevents vortex intensification. We attribute the arrested development of TCs in lower-level shear to the intrusion of mid-level environmental air over the surface vortex early in the simulations. Convection developing on the downshear side of the storm interacts with the intruding air so as to enhance the downward flux of low-entropy air into the boundary layer. We also construct a two-dimensional intensity response surface from a set of simulations that sparsely sample the joint shear height-depth parameter space. This surface reveals regions of the two-parameter space for which TC intensity is particularly sensitive. We interpret these parameter ranges as those which lead to reduced intensity predictability. Despite the robust response to changing the shape of a sheared wind profile in idealized simulations, we do not encounter such sensitivity within a large set of reanalyzed TCs in the Northern Hemisphere. Instead, there is remarkable consistency in the structure of reanalyzed wind profiles around TCs. This is evident in the distributions of two new parameters describing the height and depth of vertical wind shear, which highlight a clear preference for

  12. An experimental study on the shear strength of FRP perfobond shear connector

    NASA Astrophysics Data System (ADS)

    Gwon, S. C.; Kim, S. H.; Yoon, S. J.; Choi, C. W.

    2018-06-01

    In this study, push-out tests were conducted to investigate shear behaviour of FRP perfobond shear connector. The parameters influencing shear capacity of FRP perfobond shear connector are concrete dowel effect, shear resistance effect of the laterally reinforced FRP re- bar, and frictional effect between shear connector and concrete. The specimens were designed to consider these parameters. The specimens coated with sand to increase frictional resistance between the FRP re-bar and concrete. Based on the test results and the parameters, new equation was suggested to predict shear strength of FRP perfobond shear connectors. The predicted results and the experimental results were compared to check the feasibility of prediction.

  13. Prediction of shear critical behavior of high-strength reinforced concrete columns using finite element methods

    NASA Astrophysics Data System (ADS)

    Alrasyid, Harun; Safi, Fahrudin; Iranata, Data; Chen-Ou, Yu

    2017-11-01

    This research shows the prediction of shear behavior of High-Strength Reinforced Concrete Columns using Finite-Element Method. The experimental data of nine half scale high-strength reinforced concrete were selected. These columns using specified concrete compressive strength of 70 MPa, specified yield strength of longitudinal and transverse reinforcement of 685 and 785 MPa, respectively. The VecTor2 finite element software was used to simulate the shear critical behavior of these columns. The combination axial compression load and monotonic loading were applied at this prediction. It is demonstrated that VecTor2 finite element software provides accurate prediction of load-deflection up to peak at applied load, but provide similar behavior at post peak load. The shear strength prediction provide by VecTor 2 are slightly conservative compare to test result.

  14. Plasticity Tool for Predicting Shear Nonlinearity of Unidirectional Laminates Under Multiaxial Loading

    NASA Technical Reports Server (NTRS)

    Wang, John T.; Bomarito, Geoffrey F.

    2016-01-01

    This study implements a plasticity tool to predict the nonlinear shear behavior of unidirectional composite laminates under multiaxial loadings, with an intent to further develop the tool for use in composite progressive damage analysis. The steps for developing the plasticity tool include establishing a general quadratic yield function, deriving the incremental elasto-plastic stress-strain relations using the yield function with associated flow rule, and integrating the elasto-plastic stress-strain relations with a modified Euler method and a substepping scheme. Micromechanics analyses are performed to obtain normal and shear stress-strain curves that are used in determining the plasticity parameters of the yield function. By analyzing a micromechanics model, a virtual testing approach is used to replace costly experimental tests for obtaining stress-strain responses of composites under various loadings. The predicted elastic moduli and Poisson's ratios are in good agreement with experimental data. The substepping scheme for integrating the elasto-plastic stress-strain relations is suitable for working with displacement-based finite element codes. An illustration problem is solved to show that the plasticity tool can predict the nonlinear shear behavior for a unidirectional laminate subjected to multiaxial loadings.

  15. Effects of shear coupling on shear properties of wood

    Treesearch

    Jen Y. Liu

    2000-01-01

    Under pure shear loading, an off-axis element of orthotropic material such as pure wood undergoes both shear and normal deformations. The ratio of the shear strain to a normal strain is defined as the shear coupling coefficient associated with the direction of the normal strain. The effects of shear coupling on shear properties of wood as predicted by the orthotropic...

  16. Shear wave prediction using committee fuzzy model constrained by lithofacies, Zagros basin, SW Iran

    NASA Astrophysics Data System (ADS)

    Shiroodi, Sadjad Kazem; Ghafoori, Mohammad; Ansari, Hamid Reza; Lashkaripour, Golamreza; Ghanadian, Mostafa

    2017-02-01

    The main purpose of this study is to introduce the geological controlling factors in improving an intelligence-based model to estimate shear wave velocity from seismic attributes. The proposed method includes three main steps in the framework of geological events in a complex sedimentary succession located in the Persian Gulf. First, the best attributes were selected from extracted seismic data. Second, these attributes were transformed into shear wave velocity using fuzzy inference systems (FIS) such as Sugeno's fuzzy inference (SFIS), adaptive neuro-fuzzy inference (ANFIS) and optimized fuzzy inference (OFIS). Finally, a committee fuzzy machine (CFM) based on bat-inspired algorithm (BA) optimization was applied to combine previous predictions into an enhanced solution. In order to show the geological effect on improving the prediction, the main classes of predominate lithofacies in the reservoir of interest including shale, sand, and carbonate were selected and then the proposed algorithm was performed with and without lithofacies constraint. The results showed a good agreement between real and predicted shear wave velocity in the lithofacies-based model compared to the model without lithofacies especially in sand and carbonate.

  17. Real-time shear wave elastography may predict autoimmune thyroid disease.

    PubMed

    Vlad, Mihaela; Golu, Ioana; Bota, Simona; Vlad, Adrian; Timar, Bogdan; Timar, Romulus; Sporea, Ioan

    2015-05-01

    To evaluate and compare the values of the elasticity index as measured by shear wave elastography in healthy subjects and in patients with autoimmune thyroid disease, in order to establish if this investigation can predict the occurrence of autoimmune thyroid disease. A total of 104 cases were included in the study group: 91 women (87.5%), out of which 52 (50%) with autoimmune thyroid disease diagnosed by specific tests and 52 (50%) healthy volunteers, matched for age and gender. For all the subjects, three measurements were performed on each thyroid lobe and a mean value was calculated. The data were expressed in kPa. The investigation was performed with an Aixplorer system (SuperSonic Imagine, France), using a linear high-resolution 15-4 MHz transducer. The mean value for the elasticity index was similar in the right and the left thyroid lobes, both in normal subjects and in patients with autoimmune thyroid disease: 19.6 ± 6.6 vs. 19.5 ± 6.8 kPa, p = 0.92, and 26.6 ± 10.0 vs. 25.8 ± 11.7 kPa, p = 0.71, respectively. This parameter was significantly higher in patients with autoimmune thyroid disease than in controls (p < 0.001). For a cut-off value of 22.3 kPa, which resulted in the highest sum of sensitivity and specificity, the elasticity index assessed by shear wave elastography had a sensitivity of 59.6% and a specificity of 76.9% (AUROC = 0.71; p < 0.001) for predicting the presence of autoimmune thyroid disease. Quantitative elasticity index measured by shear wave elastography was significantly higher in autoimmune thyroid disease than in normal thyroid parenchyma and may predict the presence of autoimmune thyroid disease.

  18. Numerical Simulations of Flare-productive Active Regions: δ-sunspots, Sheared Polarity Inversion Lines, Energy Storage, and Predictions

    NASA Astrophysics Data System (ADS)

    Toriumi, Shin; Takasao, Shinsuke

    2017-11-01

    Solar active regions (ARs) that produce strong flares and coronal mass ejections (CMEs) are known to have a relatively high non-potentiality and are characterized by δ-sunspots and sheared magnetic structures. In this study, we conduct a series of flux emergence simulations from the convection zone to the corona and model four types of active regions that have been observationally suggested to cause strong flares, namely the spot-spot, spot-satellite, quadrupole, and inter-AR cases. As a result, we confirm that δ-spot formation is due to the complex geometry and interaction of emerging magnetic fields, and we find that the strong-field, high-gradient, highly sheared polarity inversion line (PIL) is created by the combined effect of the advection, stretching, and compression of magnetic fields. We show that free magnetic energy builds up in the form of a current sheet above the PIL. It is also revealed that photospheric magnetic parameters that predict flare eruptions reflect the stored free energy with high accuracy, while CME-predicting parameters indicate the magnetic relationship between flaring zones and entire ARs.

  19. A New Stochastic Approach to Predict Peak and Residual Shear Strength of Natural Rock Discontinuities

    NASA Astrophysics Data System (ADS)

    Casagrande, D.; Buzzi, O.; Giacomini, A.; Lambert, C.; Fenton, G.

    2018-01-01

    Natural discontinuities are known to play a key role in the stability of rock masses. However, it is a non-trivial task to estimate the shear strength of large discontinuities. Because of the inherent complexity to access to the full surface of the large in situ discontinuities, researchers or engineers tend to work on small-scale specimens. As a consequence, the results are often plagued by the well-known scale effect. A new approach is here proposed to predict shear strength of discontinuities. This approach has the potential to avoid the scale effect. The rationale of the approach is as follows: a major parameter that governs the shear strength of a discontinuity within a rock mass is roughness, which can be accounted for by surveying the discontinuity surface. However, this is typically not possible for discontinuities contained within the rock mass where only traces are visible. For natural surfaces, it can be assumed that traces are, to some extent, representative of the surface. It is here proposed to use the available 2D information (from a visible trace, referred to as a seed trace) and a random field model to create a large number of synthetic surfaces (3D data sets). The shear strength of each synthetic surface can then be estimated using a semi-analytical model. By using a large number of synthetic surfaces and a Monte Carlo strategy, a meaningful shear strength distribution can be obtained. This paper presents the validation of the semi-analytical mechanistic model required to support the new approach for prediction of discontinuity shear strength. The model can predict both peak and residual shear strength. The second part of the paper lays the foundation of a random field model to support the creation of synthetic surfaces having statistical properties in line with those of the data of the seed trace. The paper concludes that it is possible to obtain a reasonable estimate of peak and residual shear strength of the discontinuities tested from the

  20. Beam-column joint shear prediction using hybridized deep learning neural network with genetic algorithm

    NASA Astrophysics Data System (ADS)

    Mundher Yaseen, Zaher; Abdulmohsin Afan, Haitham; Tran, Minh-Tung

    2018-04-01

    Scientifically evidenced that beam-column joints are a critical point in the reinforced concrete (RC) structure under the fluctuation loads effects. In this novel hybrid data-intelligence model developed to predict the joint shear behavior of exterior beam-column structure frame. The hybrid data-intelligence model is called genetic algorithm integrated with deep learning neural network model (GA-DLNN). The genetic algorithm is used as prior modelling phase for the input approximation whereas the DLNN predictive model is used for the prediction phase. To demonstrate this structural problem, experimental data is collected from the literature that defined the dimensional and specimens’ properties. The attained findings evidenced the efficitveness of the hybrid GA-DLNN in modelling beam-column joint shear problem. In addition, the accurate prediction achived with less input variables owing to the feasibility of the evolutionary phase.

  1. Non-Darcian flow of shear-thinning fluids through packed beads: Experiments and predictions using Forchheimer's law and Ergun's equation

    NASA Astrophysics Data System (ADS)

    Rodríguez de Castro, Antonio; Radilla, Giovanni

    2017-02-01

    The flow of shear-thinning fluids through unconsolidated porous media is present in a number of important industrial applications such as soil depollution, Enhanced Oil Recovery or filtration of polymeric liquids. Therefore, predicting the pressure drop-flow rate relationship in model porous media has been the scope of major research efforts during the last decades. Although the flow of Newtonian fluids through packs of spherical particles is well understood in most cases, much less is known regarding the flow of shear-thinning fluids as high molecular weight polymer aqueous solutions. In particular, the experimental data for the non-Darcian flow of shear-thinning fluids are scarce and so are the current approaches for their prediction. Given the relevance of non-Darcian shear-thinning flow, the scope of this work is to perform an experimental study to systematically evaluate the effects of fluid shear rheology on the flow rate-pressure drop relationships for the non-Darcian flow through different packs of glass spheres. To do so, xanthan gum aqueous solutions with different polymer concentrations are injected through four packs of glass spheres with uniform size under Darcian and inertial flow regimes. A total of 1560 experimental data are then compared with predictions coming from different methods based on the extension of widely used Ergun's equation and Forchheimer's law to the case of shear thinning fluids, determining the accuracy of these predictions. The use of a proper definition for Reynolds number and a realistic model to represent the rheology of the injected fluids results in the porous media are shown to be key aspects to successfully predict pressure drop-flow rate relationships for the inertial shear-thinning flow in packed beads.

  2. Importance of Tensile Strength on the Shear Behavior of Discontinuities

    NASA Astrophysics Data System (ADS)

    Ghazvinian, A. H.; Azinfar, M. J.; Geranmayeh Vaneghi, R.

    2012-05-01

    In this study, the shear behavior of discontinuities possessing two different rock wall types with distinct separate compressive strengths was investigated. The designed profiles consisted of regular artificial joints molded by five types of plaster mortars, each representing a distinct uniaxial compressive strength. The compressive strengths of plaster specimens ranged from 5.9 to 19.5 MPa. These specimens were molded considering a regular triangular asperity profile and were designed so as to achieve joint walls with different strength material combinations. The results showed that the shear behavior of discontinuities possessing different joint wall compressive strengths (DDJCS) tested under constant normal load (CNL) conditions is the same as those possessing identical joint wall strengths, but the shear strength of DDJCS is governed by minor joint wall compressive strength. In addition, it was measured that the predicted values obtained by Barton's empirical criterion are greater than the experimental results. The finding indicates that there is a correlation between the joint roughness coefficient (JRC), normal stress, and mechanical strength. It was observed that the mode of failure of asperities is either pure tensile, pure shear, or a combination of both. Therefore, Barton's strength criterion, which considers the compressive strength of joint walls, was modified by substituting the compressive strength with the tensile strength. The validity of the modified criterion was examined by the comparison of the predicted shear values with the laboratory shear test results reported by Grasselli (Ph.D. thesis n.2404, Civil Engineering Department, EPFL, Lausanne, Switzerland, 2001). These comparisons infer that the modified criterion can predict the shear strength of joints more precisely.

  3. Predicting boundary shear stress and sediment transport over bed forms

    USGS Publications Warehouse

    McLean, S.R.; Wolfe, S.R.; Nelson, J.M.

    1999-01-01

    To estimate bed-load sediment transport rates in flows over bed forms such as ripples and dunes, spatially averaged velocity profiles are frequently used to predict mean boundary shear stress. However, such averaging obscures the complex, nonlinear interaction of wake decay, boundary-layer development, and topographically induced acceleration downstream of flow separation and often leads to inaccurate estimates of boundary stress, particularly skin friction, which is critically important in predicting bed-load transport rates. This paper presents an alternative methodology for predicting skin friction over 2D bed forms. The approach is based on combining the equations describing the mechanics of the internal boundary layer with semiempirical structure functions to predict the velocity at the crest of a bedform, where the flow is most similar to a uniform boundary layer. Significantly, the methodology is directed toward making specific predictions only at the bed-form crest, and as a result it avoids the difficulty and questionable validity of spatial averaging. The model provides an accurate estimate of the skin friction at the crest where transport rates are highest. Simple geometric constraints can be used to derive the mean transport rates as long as bed load is dominant.To estimate bed-load sediment transport rates in flows over bed forms such as ripples and dunes, spatially averaged velocity profiles are frequently used to predict mean boundary shear stress. However, such averaging obscures the complex, nonlinear interaction of wake decay, boundary-layer development, and topographically induced acceleration downstream of flow separation and often leads to inaccurate estimates of boundary stress, particularly skin friction, which is critically important in predicting bed-load transport rates. This paper presents an alternative methodology for predicting skin friction over 2D bed forms. The approach is based on combining the equations describing the mechanics of

  4. Predicting equilibrium states with Reynolds stress closures in channel flow and homogeneous shear flow

    NASA Technical Reports Server (NTRS)

    Abid, R.; Speziale, C. G.

    1993-01-01

    Turbulent channel flow and homogeneous shear flow have served as basic building block flows for the testing and calibration of Reynolds stress models. A direct theoretical connection is made between homogeneous shear flow in equilibrium and the log-layer of fully-developed turbulent channel flow. It is shown that if a second-order closure model is calibrated to yield good equilibrium values for homogeneous shear flow it will also yield good results for the log-layer of channel flow provided that the Rotta coefficient is not too far removed from one. Most of the commonly used second-order closure models introduce an ad hoc wall reflection term in order to mask deficient predictions for the log-layer of channel flow that arise either from an inaccurate calibration of homogeneous shear flow or from the use of a Rotta coefficient that is too large. Illustrative model calculations are presented to demonstrate this point which has important implications for turbulence modeling.

  5. Predicting equilibrium states with Reynolds stress closures in channel flow and homogeneous shear flow

    NASA Technical Reports Server (NTRS)

    Abid, R.; Speziale, C. G.

    1992-01-01

    Turbulent channel flow and homogeneous shear flow have served as basic building block flows for the testing and calibration of Reynolds stress models. A direct theoretical connection is made between homogeneous shear flow in equilibrium and the log-layer of fully-developed turbulent channel flow. It is shown that if a second-order closure model is calibrated to yield good equilibrium values for homogeneous shear flow it will also yield good results for the log-layer of channel flow provided that the Rotta coefficient is not too far removed from one. Most of the commonly used second-order closure models introduce an ad hoc wall reflection term in order to mask deficient predictions for the log-layer of channel flow that arise either from an inaccurate calibration of homogeneous shear flow or from the use of a Rotta coefficient that is too large. Illustrative model calculations are presented to demonstrate this point which has important implications for turbulence modeling.

  6. Interlayer shear behaviors of graphene-carbon nanotube network

    NASA Astrophysics Data System (ADS)

    Qin, Huasong; Liu, Yilun

    2017-09-01

    The interlayer shear resistance plays an important role in graphene related applications, and different mechanisms have been proposed to enhance its interlayer load capacity. In this work, we performed molecular dynamics (MD) simulations and theoretical analysis to study interlayer shear behaviors of three dimensional graphene-carbon (3D-GC) nanotube networks. The shear mechanical properties of carbon nanotubes (CNTs) crosslink with different diameters are obtained which is one order of magnitude larger than that of other types of crosslinks. Under shear loading, 3D-GC exhibits two failure modes, i.e., fracture of graphene sheet and failure of CNT crosslink, determined by the diameter of CNT crosslink, crosslink density, and length of 3D-GC. A modified tension-shear chain model is proposed to predict the shear mechanical properties and failure mode of 3D-GC, which agrees well with MD simulation results. The results presented in this work may provide useful insights for future development of high-performance 3D-GC materials.

  7. Strain accumulation in bituminous binders under repeated creep-recovery loading predicted from small-amplitude oscillatory shear (SAOS) experiments

    NASA Astrophysics Data System (ADS)

    Laukkanen, Olli-Ville; Winter, H. Henning

    2017-11-01

    The creep-recovery (CR) test starts out with a period of shearing at constant stress (creep) and is followed by a period of zero-shear stress where some of the accumulated shear strain gets reversed. Linear viscoelasticity (LVE) allows one to predict the strain response to repeated creep-recovery (RCR) loading from measured small-amplitude oscillatory shear (SAOS) data. Only the relaxation and retardation time spectra of a material need to be known and these can be determined from SAOS data. In an application of the Boltzmann superposition principle (BSP), the strain response to RCR loading can be obtained as a linear superposition of the strain response to many single creep-recovery tests. SAOS and RCR data were collected for several unmodified and modified bituminous binders, and the measured and predicted RCR responses were compared. Generally good agreement was found between the measured and predicted strain accumulation under RCR loading. However, in the case of modified binders, the strain accumulation was slightly overestimated (≤20% relative error) due to the insufficient SAOS information at long relaxation times. Our analysis also demonstrates that the evolution in the strain response under RCR loading, caused by incomplete recovery, can be reasonably well predicted by the presented methodology. It was also shown that the outlined modeling framework can be used, as a first approximation, to estimate the rutting resistance of bituminous binders by predicting the values of the Multiple Stress Creep Recovery (MSCR) test parameters.

  8. Flight in low-level wind shear

    NASA Technical Reports Server (NTRS)

    Frost, W.

    1983-01-01

    Results of studies of wind shear hazard to aircraft operation are summarized. Existing wind shear profiles currently used in computer and flight simulator studies are reviewed. The governing equations of motion for an aircraft are derived incorporating the variable wind effects. Quantitative discussions of the effects of wind shear on aircraft performance are presented. These are followed by a review of mathematical solutions to both the linear and nonlinear forms of the governing equations. Solutions with and without control laws are presented. The application of detailed analysis to develop warning and detection systems based on Doppler radar measuring wind speed along the flight path is given. A number of flight path deterioration parameters are defined and evaluated. Comparison of computer-predicted flight paths with those measured in a manned flight simulator is made. Some proposed airborne and ground-based wind shear hazard warning and detection systems are reviewed. The advantages and disadvantages of both types of systems are discussed.

  9. Computational modeling for prediction of the shear stress of three-dimensional isotropic and aligned fiber networks.

    PubMed

    Park, Seungman

    2017-09-01

    Interstitial flow (IF) is a creeping flow through the interstitial space of the extracellular matrix (ECM). IF plays a key role in diverse biological functions, such as tissue homeostasis, cell function and behavior. Currently, most studies that have characterized IF have focused on the permeability of ECM or shear stress distribution on the cells, but less is known about the prediction of shear stress on the individual fibers or fiber networks despite its significance in the alignment of matrix fibers and cells observed in fibrotic or wound tissues. In this study, I developed a computational model to predict shear stress for different structured fibrous networks. To generate isotropic models, a random growth algorithm and a second-order orientation tensor were employed. Then, a three-dimensional (3D) solid model was created using computer-aided design (CAD) software for the aligned models (i.e., parallel, perpendicular and cubic models). Subsequently, a tetrahedral unstructured mesh was generated and flow solutions were calculated by solving equations for mass and momentum conservation for all models. Through the flow solutions, I estimated permeability using Darcy's law. Average shear stress (ASS) on the fibers was calculated by averaging the wall shear stress of the fibers. By using nonlinear surface fitting of permeability, viscosity, velocity, porosity and ASS, I devised new computational models. Overall, the developed models showed that higher porosity induced higher permeability, as previous empirical and theoretical models have shown. For comparison of the permeability, the present computational models were matched well with previous models, which justify our computational approach. ASS tended to increase linearly with respect to inlet velocity and dynamic viscosity, whereas permeability was almost the same. Finally, the developed model nicely predicted the ASS values that had been directly estimated from computational fluid dynamics (CFD). The present

  10. Predicting bed shear stress and its role in sediment dynamics and restoration potential of the Everglades and other vegetated flow systems

    USGS Publications Warehouse

    Larsen, Laurel G.; Harvey, Judson; Crimaldi, John P.

    2009-01-01

    Entrainment of sediment by flowing water affects topography, habitat suitability, and nutrient cycling in vegetated floodplains and wetlands, impacting ecosystem evolution and the success of restoration projects. Nonetheless, restoration managers lack simple decision-support tools for predicting shear stresses and sediment redistribution potential in different vegetation communities. Using a field-validated numerical model, we developed state-space diagrams that provide these predictions over a range of water-surface slopes, depths, and associated velocities in Everglades ridge and slough vegetation communities. Diminished bed shear stresses and a consequent decrease in bed sediment redistribution are hypothesized causes of a recent reduction in the topographic and vegetation heterogeneity of this ecosystem. Results confirmed the inability of present-day flows to entrain bed sediment. Further, our diagrams showed bed shear stresses to be highly sensitive to emergent vegetation density and water-surface slope but less sensitive to water depth and periphyton or floating vegetation abundance. These findings suggested that instituting a pulsing flow regime could be the most effective means to restore sediment redistribution to the Everglades. However, pulsing flows will not be sufficient to erode sediment from sloughs with abundant spikerush, unless spikerush density first decreases by natural or managed processes. Our methods provide a novel tool for identifying restoration parameters and performance measures in many types of vegetated aquatic environments where sediment erosion and deposition are involved.

  11. Explicit use of the Biot coefficient in predicting shear-wave velocity of water-saturated sediments

    USGS Publications Warehouse

    Lee, M.W.

    2006-01-01

    Predicting the shear-wave (S-wave) velocity is important in seismic modelling, amplitude analysis with offset, and other exploration and engineering applications. Under the low-frequency approximation, the classical Biot-Gassmann theory relates the Biot coefficient to the bulk modulus of water-saturated sediments. If the Biot coefficient under in situ conditions can be estimated, the shear modulus or the S-wave velocity can be calculated. The Biot coefficient derived from the compressional-wave (P-wave) velocity of water-saturated sediments often differs from and is less than that estimated from the S-wave velocity, owing to the interactions between the pore fluid and the grain contacts. By correcting the Biot coefficients derived from P-wave velocities of water-saturated sediments measured at various differential pressures, an accurate method of predicting S-wave velocities is proposed. Numerical results indicate that the predicted S-wave velocities for consolidated and unconsolidated sediments agreewell with measured velocities. ?? 2006 European Association of Geoscientists & Engineers.

  12. Composite Behavior of a Novel Insulated Concrete Sandwich Wall Panel Reinforced with GFRP Shear Grids: Effects of Insulation Types.

    PubMed

    Kim, JunHee; You, Young-Chan

    2015-03-03

    A full-scale experimental program was used in this study to investigate the structural behavior of novel insulated concrete sandwich wall panels (SWPs) reinforced with grid-type glass-fiber-reinforced polymer (GFRP) shear connectors. Two kinds of insulation-expanded polystyrene (EPS) and extruded polystyrene (XPS) with 100 mm thickness were incased between the two concrete wythes to meet the increasing demand for the insulation performance of building envelope. One to four GFRP shear grids were used to examine the degree of composite action of the two concrete wythes. Ten specimens of SWPs were tested under displacement control subjected to four-point concentrated loads. The test results showed that the SWPs reinforced with GFRP grids as shear connectors developed a high degree of composite action resulting in high flexural strength. The specimens with EPS foam exhibited an enhanced load-displacement behavior compared with the specimens with XPS because of the relatively stronger bond between insulation and concrete. In addition, the ultimate strength of the test results was compared to the analytical prediction with the mechanical properties of only GRFP grids. The specimens with EPS insulation presented higher strength-based composite action than the ones with XPS insulation.

  13. Composite Behavior of a Novel Insulated Concrete Sandwich Wall Panel Reinforced with GFRP Shear Grids: Effects of Insulation Types

    PubMed Central

    Kim, JunHee; You, Young-Chan

    2015-01-01

    A full-scale experimental program was used in this study to investigate the structural behavior of novel insulated concrete sandwich wall panels (SWPs) reinforced with grid-type glass-fiber-reinforced polymer (GFRP) shear connectors. Two kinds of insulation-expanded polystyrene (EPS) and extruded polystyrene (XPS) with 100 mm thickness were incased between the two concrete wythes to meet the increasing demand for the insulation performance of building envelope. One to four GFRP shear grids were used to examine the degree of composite action of the two concrete wythes. Ten specimens of SWPs were tested under displacement control subjected to four-point concentrated loads. The test results showed that the SWPs reinforced with GFRP grids as shear connectors developed a high degree of composite action resulting in high flexural strength. The specimens with EPS foam exhibited an enhanced load-displacement behavior compared with the specimens with XPS because of the relatively stronger bond between insulation and concrete. In addition, the ultimate strength of the test results was compared to the analytical prediction with the mechanical properties of only GRFP grids. The specimens with EPS insulation presented higher strength-based composite action than the ones with XPS insulation. PMID:28787978

  14. a Predictive Model of Permeability for Fractal-Based Rough Rock Fractures during Shear

    NASA Astrophysics Data System (ADS)

    Huang, Na; Jiang, Yujing; Liu, Richeng; Li, Bo; Zhang, Zhenyu

    This study investigates the roles of fracture roughness, normal stress and shear displacement on the fluid flow characteristics through three-dimensional (3D) self-affine fractal rock fractures, whose surfaces are generated using the modified successive random additions (SRA) algorithm. A series of numerical shear-flow tests under different normal stresses were conducted on rough rock fractures to calculate the evolutions of fracture aperture and permeability. The results show that the rough surfaces of fractal-based fractures can be described using the scaling parameter Hurst exponent (H), in which H = 3 - Df, where Df is the fractal dimension of 3D single fractures. The joint roughness coefficient (JRC) distribution of fracture profiles follows a Gauss function with a negative linear relationship between H and average JRC. The frequency curves of aperture distributions change from sharp to flat with increasing shear displacement, indicating a more anisotropic and heterogeneous flow pattern. Both the mean aperture and permeability of fracture increase with the increment of surface roughness and decrement of normal stress. At the beginning of shear, the permeability increases remarkably and then gradually becomes steady. A predictive model of permeability using the mean mechanical aperture is proposed and the validity is verified by comparisons with the experimental results reported in literature. The proposed model provides a simple method to approximate permeability of fractal-based rough rock fractures during shear using fracture aperture distribution that can be easily obtained from digitized fracture surface information.

  15. Anisotropic shear stress patterns predict the orientation of convergent tissue movements in the embryonic heart

    PubMed Central

    2017-01-01

    Myocardial contractility and blood flow provide essential mechanical cues for the morphogenesis of the heart. In general, endothelial cells change their migratory behavior in response to shear stress patterns, according to flow directionality. Here, we assessed the impact of shear stress patterns and flow directionality on the behavior of endocardial cells, the specialized endothelial cells of the heart. At the early stages of zebrafish heart valve formation, we show that endocardial cells are converging to the valve-forming area and that this behavior depends upon mechanical forces. Quantitative live imaging and mathematical modeling allow us to correlate this tissue convergence with the underlying flow forces. We predict that tissue convergence is associated with the direction of the mean wall shear stress and of the gradient of harmonic phase-averaged shear stresses, which surprisingly do not match the overall direction of the flow. This contrasts with the usual role of flow directionality in vascular development and suggests that the full spatial and temporal complexity of the wall shear stress should be taken into account when studying endothelial cell responses to flow in vivo. PMID:29183943

  16. Determination of Shear Wave Velocity in Offshore Terengganu for Ground Response Analysis

    NASA Astrophysics Data System (ADS)

    Mazlina, M.; Liew, M. S.; Adnan, A.; Harahap, I. S. H.; Hamid, N. A.

    2018-04-01

    Amount of vibration received in any location can be analysed by conducting ground response analysis. Even though there are three different methods available in this analysis, One Dimensional ground response analysis method has been widely used. Shear wave velocity is one of the key parameters in this analysis. A lot of correlations have been formulated to determine shear wave velocity with cone penetration test. In this study, correlations developed for Quaternary geological age have been selected. Six equations have been adopted comprise of all soil and soil type dependent correlations. Two platforms sites consist of clay and combination of clay and sand have been analysed. Shear velocity to be used in ground response analysis has been obtained. Results have been illustrated in graphs where shear velocity for each case has been plotted. In avoiding under or over predicting of shear wave velocity, the average of all soil and soil type dependent results will be used as final Vs value.

  17. Clinical value of liver and spleen shear wave velocity in predicting the prognosis of patients with portal hypertension.

    PubMed

    Zhang, Yan; Mao, Da-Feng; Zhang, Mei-Wu; Fan, Xiao-Xiang

    2017-12-07

    To explore the relationship of liver and spleen shear wave velocity in patients with liver cirrhosis combined with portal hypertension, and assess the value of liver and spleen shear wave velocity in predicting the prognosis of patients with portal hypertension. All 67 patients with liver cirrhosis diagnosed as portal hypertension by hepatic venous pressure gradient in our hospital from June 2014 to December 2014 were enrolled into this study. The baseline information of these patients was recorded. Furthermore, 67 patients were followed-up at 20 mo after treatment, and liver and spleen shear wave velocity were measured by acoustic radiation force impulse at the 1 st week, 3 rd month and 9 th month after treatment. Patients with favorable prognosis were assigned into the favorable prognosis group, while patients with unfavorable prognosis were assigned into the unfavorable prognosis group. The variation and difference in liver and spleen shear wave velocity in these two groups were analyzed by repeated measurement analysis of variance. Meanwhile, in order to evaluate the effect of liver and spleen shear wave velocity on the prognosis of patients with portal hypertension, Cox's proportional hazard regression model analysis was applied. The ability of those factors in predicting the prognosis of patients with portal hypertension was calculated through receiver operating characteristic (ROC) curves. The liver and spleen shear wave velocity in the favorable prognosis group revealed a clear decline, while those in the unfavorable prognosis group revealed an increasing tendency at different time points. Furthermore, liver and spleen shear wave velocity was higher in the unfavorable prognosis group, compared with the favorable prognosis group; the differences were statistically significant ( P < 0.05). The prognosis of patients with portal hypertension was significantly affected by spleen hardness at the 3 rd month after treatment [relative risk (RR) = 3.481]. At the 9 th

  18. Shear buckling analysis of a hat-stiffened panel

    NASA Technical Reports Server (NTRS)

    Ko, William L.; Jackson, Raymond H.

    1994-01-01

    A buckling analysis was performed on a hat-stiffened panel subjected to shear loading. Both local buckling and global buckling were analyzed. The global shear buckling load was found to be several times higher than the local shear buckling load. The classical shear buckling theory for a flat plate was found to be useful in predicting the local shear buckling load of the hat-stiffened panel, and the predicted local shear buckling loads thus obtained compare favorably with the results of finite element analysis.

  19. Model predictions of deformation, embolization and permeability of partially obstructive blood clots under variable shear flow.

    PubMed

    Xu, Shixin; Xu, Zhiliang; Kim, Oleg V; Litvinov, Rustem I; Weisel, John W; Alber, Mark

    2017-11-01

    Thromboembolism, one of the leading causes of morbidity and mortality worldwide, is characterized by formation of obstructive intravascular clots (thrombi) and their mechanical breakage (embolization). A novel two-dimensional multi-phase computational model is introduced that describes active interactions between the main components of the clot, including platelets and fibrin, to study the impact of various physiologically relevant blood shear flow conditions on deformation and embolization of a partially obstructive clot with variable permeability. Simulations provide new insights into mechanisms underlying clot stability and embolization that cannot be studied experimentally at this time. In particular, model simulations, calibrated using experimental intravital imaging of an established arteriolar clot, show that flow-induced changes in size, shape and internal structure of the clot are largely determined by two shear-dependent mechanisms: reversible attachment of platelets to the exterior of the clot and removal of large clot pieces. Model simulations predict that blood clots with higher permeability are more prone to embolization with enhanced disintegration under increasing shear rate. In contrast, less permeable clots are more resistant to rupture due to shear rate-dependent clot stiffening originating from enhanced platelet adhesion and aggregation. These results can be used in future to predict risk of thromboembolism based on the data about composition, permeability and deformability of a clot under specific local haemodynamic conditions. © 2017 The Author(s).

  20. Shear Thinning in Xenon

    NASA Technical Reports Server (NTRS)

    Bergm Robert F.; Moldover, Michael R.; Yao, Minwu; Zimmerli, Gregory A.

    2009-01-01

    We measured shear thinning, a viscosity decrease ordinarily associated with complex liquids such as molten plastics or ketchup, near the critical point of xenon. The data span a wide range of dimensionless shear rate: the product of the shear rate and the relaxation time of critical fluctuations was greater than 0.001 and was less than 700. As predicted by theory, shear thinning occurred when this product was greater than 1. The measurements were conducted aboard the Space Shuttle Columbia to avoid the density stratification caused by Earth's gravity.

  1. Clinical value of liver and spleen shear wave velocity in predicting the prognosis of patients with portal hypertension

    PubMed Central

    Zhang, Yan; Mao, Da-Feng; Zhang, Mei-Wu; Fan, Xiao-Xiang

    2017-01-01

    AIM To explore the relationship of liver and spleen shear wave velocity in patients with liver cirrhosis combined with portal hypertension, and assess the value of liver and spleen shear wave velocity in predicting the prognosis of patients with portal hypertension. METHODS All 67 patients with liver cirrhosis diagnosed as portal hypertension by hepatic venous pressure gradient in our hospital from June 2014 to December 2014 were enrolled into this study. The baseline information of these patients was recorded. Furthermore, 67 patients were followed-up at 20 mo after treatment, and liver and spleen shear wave velocity were measured by acoustic radiation force impulse at the 1st week, 3rd month and 9th month after treatment. Patients with favorable prognosis were assigned into the favorable prognosis group, while patients with unfavorable prognosis were assigned into the unfavorable prognosis group. The variation and difference in liver and spleen shear wave velocity in these two groups were analyzed by repeated measurement analysis of variance. Meanwhile, in order to evaluate the effect of liver and spleen shear wave velocity on the prognosis of patients with portal hypertension, Cox’s proportional hazard regression model analysis was applied. The ability of those factors in predicting the prognosis of patients with portal hypertension was calculated through receiver operating characteristic (ROC) curves. RESULTS The liver and spleen shear wave velocity in the favorable prognosis group revealed a clear decline, while those in the unfavorable prognosis group revealed an increasing tendency at different time points. Furthermore, liver and spleen shear wave velocity was higher in the unfavorable prognosis group, compared with the favorable prognosis group; the differences were statistically significant (P < 0.05). The prognosis of patients with portal hypertension was significantly affected by spleen hardness at the 3rd month after treatment [relative risk (RR) = 3

  2. Charge-density-shear-moduli relationships in aluminum-lithium alloys.

    PubMed

    Eberhart, M

    2001-11-12

    Using the first principles full-potential linear-augmented-Slater-type orbital technique, the energies and charge densities of aluminum and aluminum-lithium supercells have been computed. The experimentally observed increase in aluminum's shear moduli upon alloying with lithium is argued to be the result of predictable changes to aluminum's total charge density, suggesting that simple rules may allow the alloy designer to predict the effects of dilute substitutional elements on alloy elastic response.

  3. Surface and downhole shear wave seismic methods for thick soil site investigations

    USGS Publications Warehouse

    Hunter, J.A.; Benjumea, B.; Harris, J.B.; Miller, R.D.; Pullan, S.E.; Burns, R.A.; Good, R.L.

    2002-01-01

    Shear wave velocity-depth information is required for predicting the ground motion response to earthquakes in areas where significant soil cover exists over firm bedrock. Rather than estimating this critical parameter, it can be reliably measured using a suite of surface (non-invasive) and downhole (invasive) seismic methods. Shear wave velocities from surface measurements can be obtained using SH refraction techniques. Array lengths as large as 1000 m and depth of penetration to 250 m have been achieved in some areas. High resolution shear wave reflection techniques utilizing the common midpoint method can delineate the overburden-bedrock surface as well as reflecting boundaries within the overburden. Reflection data can also be used to obtain direct estimates of fundamental site periods from shear wave reflections without the requirement of measuring average shear wave velocity and total thickness of unconsolidated overburden above the bedrock surface. Accurate measurements of vertical shear wave velocities can be obtained using a seismic cone penetrometer in soft sediments, or with a well-locked geophone array in a borehole. Examples from thick soil sites in Canada demonstrate the type of shear wave velocity information that can be obtained with these geophysical techniques, and show how these data can be used to provide a first look at predicted ground motion response for thick soil sites. ?? 2002 Published by Elsevier Science Ltd.

  4. Novel Composites for Wing and Fuselage Applications: Speedy Nonlinear Analysis of Postbuckled Panels in Shear (SNAPPS)

    NASA Technical Reports Server (NTRS)

    Sharp, Dave; Sobel, Larry

    1997-01-01

    A simple and rapid analysis method, consisting of a number of modular, 'strength-of-materials-type' models, is presented for predicting the nonlinear response and stiffener separation of postbuckled, flat, composite, shear panels. The analysis determines the maximum principal tensile stress in the skin surface layer under to toe. Failure is said to occur when this stress reaches the mean transverse tensile strength of the layer. The analysis methodology consists of a number of closed-form equations that can easily be used in a 'hand analysis. For expediency, they have been programmed into a preliminary design code called SNAPPS (Speedy Nonlinear Analysis of Postbuckled Panels in Shear), which rapidly predicts postbuckling response of the panel for each value of the applied shear load. SNAPPS response and failure predictions were found to agree well with test results for three panels with widely different geometries, laminates and stiffnesses. Design guidelines are given for increasing the load-carrying capacity of stiffened, composite shear panels.

  5. The Effect of Impeller Type on Floc Size and Structure during Shear-Induced Flocculation

    PubMed

    Spicer; Keller; Pratsinis

    1996-12-01

    The effect of impeller type and shear rate on the evolution of floc size and structure during shear-induced flocculation of polystyrene particles with aluminum sulfate is investigated by image analysis. One radial flow (six-blade Rushton turbine) and two axial flow (three-blade fluid foil, four-blade 45° pitch) impeller configurations are examined. The steady state average floc size is shown to depend on the frequency of recirculation to the impeller zone and its characteristic velocity gradient. The concepts of fractal geometry are used to characterize the floc structure. For all impellers, the two-dimensional floc fractal dimension, Dpf, increases during floc growth, indicating formation of more open structures. Later on, Dpf levels off at a steady state value as breakage becomes significant and the floc size distribution approaches steady state. The shear rate does not affect the steady state Dpf of the flocs within experimental uncertainty.

  6. Study on Shear Performance of Cold-formed Steel Composite Wall with New Type of stud

    NASA Astrophysics Data System (ADS)

    Wang, Chungang; Yue, Sizhe; Liu, Hong; Zhang, Zhuangnan

    2018-03-01

    The shear resistance of single oriented-strand board wall and single gypsum board wall can be improved in different degrees by increasing strength of steel. The experimental data of literatures were used, and the test specimens had been simulated and validated by ABAQUS finite element analysis. According to the research, it showed that the compressive bearing capacity of the new stud composite wall was much better than the common stud composite wall, so the establishment and research of all models had been based on the new section stud. The analysis results show that when using new type of stud the shear resistance of the single oriented-strand board wall can be improved efficiently by increasing strength of steel, but the shear resistance of the single gypsum wall can be increased little.

  7. Shear Capacity of C-Shaped and L-Shaped Angle Shear Connectors.

    PubMed

    Tahmasbi, Farzad; Maleki, Shervin; Shariati, Mahdi; Ramli Sulong, N H; Tahir, M M

    2016-01-01

    This paper investigates the behaviour of C-shaped and L-shaped angle shear connectors embedded in solid concrete slabs. An effective finite element model is proposed to simulate the push out tests of these shear connectors that encompass nonlinear material behaviour, large displacement and damage plasticity. The finite element models are validated against test results. Parametric studies using this nonlinear model are performed to investigate the variations in concrete strength and connector dimensions. The finite element analyses also confirm the test results that increasing the length of shear connector increases their shear strength proportionately. It is observed that the maximum stress in L-shaped angle connectors takes place in the weld attachment to the beam, whereas in the C-shaped angle connectors, it is in the attached leg. The location of maximum concrete compressive damage is rendered in each case. Finally, a new equation for prediction of the shear capacity of C-shaped angle connectors is proposed.

  8. Shear Capacity of C-Shaped and L-Shaped Angle Shear Connectors

    PubMed Central

    Tahmasbi, Farzad; Maleki, Shervin; Shariati, Mahdi; Ramli Sulong, N. H.; Tahir, M. M.

    2016-01-01

    This paper investigates the behaviour of C-shaped and L-shaped angle shear connectors embedded in solid concrete slabs. An effective finite element model is proposed to simulate the push out tests of these shear connectors that encompass nonlinear material behaviour, large displacement and damage plasticity. The finite element models are validated against test results. Parametric studies using this nonlinear model are performed to investigate the variations in concrete strength and connector dimensions. The finite element analyses also confirm the test results that increasing the length of shear connector increases their shear strength proportionately. It is observed that the maximum stress in L-shaped angle connectors takes place in the weld attachment to the beam, whereas in the C-shaped angle connectors, it is in the attached leg. The location of maximum concrete compressive damage is rendered in each case. Finally, a new equation for prediction of the shear capacity of C-shaped angle connectors is proposed. PMID:27478894

  9. Reliability of testicular stiffness quantification using shear wave elastography in predicting male fertility: a preliminary prospective study.

    PubMed

    Yavuz, Alpaslan; Yokus, Adem; Taken, Kerem; Batur, Abdussamet; Ozgokce, Mesut; Arslan, Harun

    2018-05-02

    To evaluate the reliability of testicular stiffness quantification using shear wave elastography in predicting the fertility potential of males and for the pre-diagnosis of disorders based upon sperm quantification. One hundred males between the ages of 19-49 years (mean age of 28.77±6.11), ninety of whom with complaints of infertility, were enrolled in this prospective study. Scrotal grey-scale, Doppler ultrasound (US), and mean testicular shear wave velocity quantifications (SWVQs) were performed. The volumes of testes, as well as the grade of varicocele if present, were recorded. The mean shear wave velocity values (SWVVs) of each testis and a mean testicular SWVV for each patient were calculated. The semen-analyses of patients were consecutively performed. There were significant negative correlations between the mean testicular SWVVs of patients and their sperm counts or the testis volumes (r=-0.399, r=-0.565; p<0.01, respectively). A positive correlation was found between testicular volumes and sperm counts (r=0.491, p<0.01). The cut-off values regarding mean testicular SWVV to distinguish normal sperm count from azoospermia and oligozoospermia were 1.465 m/s (75.0% sensitivity and 75.0% specificity) and 1.328 m/s (64.3% sensitivity and 68.2% specificity), respectively, and the value to distinguish oligozoospermia from azoospermia was 1.528 m/s (66.7% sensitivity, 60.7% specificity). The mean testicular SWVQ using the ARFI shear wave technique was a reliable, non-invasive and acceptably stable method for predicting male infertility, especially related to sperm count issues.

  10. Shear zone junctions: Of zippers and freeways

    NASA Astrophysics Data System (ADS)

    Passchier, Cees W.; Platt, John P.

    2017-02-01

    Ductile shear zones are commonly treated as straight high-strain domains with uniform shear sense and characteristic curved foliation trails, bounded by non-deforming wall rock. Many shear zones, however, are branched, and if movement on such branches is contemporaneous, the resulting shape can be complicated and lead to unusual shear sense arrangement and foliation geometries in the wall rock. For Y-shaped shear zone triple junctions with three joining branches and transport direction at a high angle to the branchline, only eight basic types of junction are thought to be stable and to produce significant displacement. The simplest type, called freeway junctions, have similar shear sense in all three branches. The other types show joining or separating behaviour of shear zone branches similar to the action of a zipper. Such junctions may have shear zone branches that join to form a single branch (closing zipper junction), or a single shear zone that splits to form two branches, (opening zipper junction). All categories of shear zone junctions show characteristic foliation patterns and deflection of markers in the wall rock. Closing zipper junctions are unusual, since they form a non-active zone with opposite deflection of foliations in the wall rock known as an extraction fault or wake. Shear zipper junctions can form domains of overprinting shear sense along their flanks. A small and large field example are given from NE Spain and Eastern Anatolia. The geometry of more complex, 3D shear zone junctions with slip parallel and oblique to the branchline is briefly discussed.

  11. Improved brachial artery shear patterns and increased flow-mediated dilation after low-volume high-intensity interval training in type 2 diabetes.

    PubMed

    Ghardashi Afousi, Alireza; Izadi, Mohammad Reza; Rakhshan, Kamran; Mafi, Farnoosh; Biglari, Soheil; Gandomkar Bagheri, Habibalah

    2018-06-22

    What is the central question of this study? Endothelial function is impaired because of increased oscillatory and retrograde shear in patients with type 2 diabetes. It is unclear whether low-volume high-intensity interval training and continuous moderate intensity exercise can modulate oscillatory and retrograde shear, blood flow and flow-mediated arterial dilation in these patients. What is the main finding and its importance? We found that low-volume high-intensity interval training, by increasing anterograde shear and decreasing retrograde shear and oscillatory index, can increase nitric oxide production and consequently result in increased flow-mediated dilation and outward arterial remodelling in patients with type 2 diabetes. Atherosclerosis in patients with type 2 diabetes is characterized by endothelial dysfunction associated with impaired flow-mediated dilation (FMD) and increases retrograde and oscillatory shear. The present study investigated endothelium-dependent vasodilation and shear rate in patients with type 2 diabetes at baseline and follow-up after 12 weeks of low-volume high-intensity interval training (LV-HIIT) or continuous moderate intensity training (CMIT). Seventy five sedentary patients with type 2 diabetes and untreated pre- or stage I hypertension were randomly divided into LV-HIIT, CMIT and control groups. The LV-HIIT group intervention was 12 intervals of 1.5 min at 85%-90% HR max and 2 min at 55%-60% HR max . The CMIT group intervention was 42 min of exercise at 70% HR max for 3 sessions per week during 12 weeks. High-resolution Doppler ultrasound was used to measure FMD, arterial diameter, anterograde and retrograde blood flow and shear rate patterns. Brachial artery FMD increased significantly in the LV-HIIT group (3.83 ± 1.13 baseline, 7.39 ± 3.6% follow-up), whereas there were no significant increase in the CMIT group (3.45 ± 0.97 baseline, 4.81 ± 2.36% follow-up) compared to the control group (3.16 ± 0

  12. Determination of the Shear Stress Distribution in a Laminate from the Applied Shear Resultant--A Simplified Shear Solution

    NASA Technical Reports Server (NTRS)

    Bednarcyk, Brett A.; Aboudi, Jacob; Yarrington, Phillip W.

    2007-01-01

    The simplified shear solution method is presented for approximating the through-thickness shear stress distribution within a composite laminate based on laminated beam theory. The method does not consider the solution of a particular boundary value problem, rather it requires only knowledge of the global shear loading, geometry, and material properties of the laminate or panel. It is thus analogous to lamination theory in that ply level stresses can be efficiently determined from global load resultants (as determined, for instance, by finite element analysis) at a given location in a structure and used to evaluate the margin of safety on a ply by ply basis. The simplified shear solution stress distribution is zero at free surfaces, continuous at ply boundaries, and integrates to the applied shear load. Comparisons to existing theories are made for a variety of laminates, and design examples are provided illustrating the use of the method for determining through-thickness shear stress margins in several types of composite panels and in the context of a finite element structural analysis.

  13. A modification of Murray's law for shear-thinning rheology.

    PubMed

    McGah, Patrick M; Capobianchi, Massimo

    2015-05-01

    This study reformulates Murray's well-known principle of minimum work as applied to the cardiovascular system to include the effects of the shear-thinning rheology of blood. The viscous behavior is described using the extended modified power law (EMPL), which is a time-independent, but shear-thinning rheological constitutive equation. The resulting minimization problem is solved numerically for typical parameter ranges. The non-Newtonian analysis still predicts the classical cubic diameter dependence of the volume flow rate and the cubic branching law. The current analysis also predicts a constant wall shear stress throughout the vascular tree, albeit with a numerical value about 15-25% higher than the Newtonian analysis. Thus, experimentally observed deviations from the cubic branching law or the predicted constant wall shear stress in the vasculature cannot likely be attributed to blood's shear-thinning behavior. Further differences between the predictions of the non-Newtonian and the Newtonian analyses are highlighted, and the limitations of the Newtonian analysis are discussed. Finally, the range and limits of applicability of the current results as applied to the human arterial tree are also discussed.

  14. Prediction Of Tensile And Shear Strength Of Friction Surfaced Tool Steel Deposit By Using Artificial Neural Networks

    NASA Astrophysics Data System (ADS)

    Manzoor Hussain, M.; Pitchi Raju, V.; Kandasamy, J.; Govardhan, D.

    2018-04-01

    Friction surface treatment is well-established solid technology and is used for deposition, abrasion and corrosion protection coatings on rigid materials. This novel process has wide range of industrial applications, particularly in the field of reclamation and repair of damaged and worn engineering components. In this paper, we present the prediction of tensile and shear strength of friction surface treated tool steel using ANN for simulated results of friction surface treatment. This experiment was carried out to obtain tool steel coatings of low carbon steel parts by changing contribution process parameters essentially friction pressure, rotational speed and welding speed. The simulation is performed by a 33-factor design that takes into account the maximum and least limits of the experimental work performed with the 23-factor design. Neural network structures, such as the Feed Forward Neural Network (FFNN), were used to predict tensile and shear strength of tool steel sediments caused by friction.

  15. Wind shear and wet and dry thermodynamic indices as predictors of thunderstorm motion and severity and application to the AVE 4 experimental data

    NASA Technical Reports Server (NTRS)

    Connell, J. R.; Ey, L.

    1977-01-01

    Two types of parameters are computed and mapped for use in assessing their individual merits as predictors of occurrence and severity of thunderstorms. The first group is comprised of equivalent potential temperature, potential temperature, water vapor mixing ratio, and wind speed. Equivalent potential temperature maxima and strong gradients of equivalent potential temperature at the surface correlate well with regions of thunderstorm activity. The second type, comprised of the energy index, shear index, and energy shear index, incorporates some model dynamics of thunderstorms, including nonthermodynamic forcing. The energy shear index is found to improve prediction of tornadic and high-wind situations slightly better than other indices. It is concluded that further development and refinement of nonthermodynamic aspects of predictive indices are definitely warranted.

  16. Evolution of Self-Organization in Adiabatic Shear Bands

    NASA Astrophysics Data System (ADS)

    Meyers, Marc A.; Xue, Qing; Nesterenko, Vitali F.

    2001-06-01

    The evolution of multiple adiabatic shear bands was investigated in stainless steel, an Fe-15%Cr-15% Ni alloy, titanium, and Ti-6%Al-4%V alloy through the radial collapse of a thick-walled cylinder under high-strain-rate deformation ( 10^4 s-1). The shear-band initiation, propagation, as well as spatial distribution were examined under different global strains(varied from 0 to 0.9). The shear-band spacing is compared with one-dimensional theoretical predictions based on perturbation (Ockendon- Wright and Molinari) and momentum diffusion (Grady-Kipp). The experimentally observed spacing reveals the two-dimensional character of self-organization. These aspects are incorporated into a novel analytical description, in which a distribution of embryos(potential initiation sites) is activated as a function of strain (greater than a threshold) accoding to a Weibull-type distribution. The model incorporates embryo disactivation by stress shielding as well as selective growth of shear bands. The imposed strain rate, embryo distribution, and rates of initiation and propagation determine the evolutionary shear band configurations. The microstructural parameter investigated for stainless steel was the grain size, that was varied from 30 and 500 um. The influence of grain size was found to be minor and through the flow stress. Titanium and Ti-6%Al-4%V displayed drastically different patterns of shear bands,which are explained in terms of the model proposed. Research Supported by US Army Research Office MURI Program (Contract DAAH 04-96-1-0376).

  17. Ericksen number and Deborah number cascade predictions of a model for liquid crystalline polymers for simple shear flow

    NASA Astrophysics Data System (ADS)

    Klein, D. Harley; Leal, L. Gary; García-Cervera, Carlos J.; Ceniceros, Hector D.

    2007-02-01

    We consider the behavior of the Doi-Marrucci-Greco (DMG) model for nematic liquid crystalline polymers in planar shear flow. We found the DMG model to exhibit dynamics in both qualitative and quantitative agreement with experimental observations reported by Larson and Mead [Liq. Cryst. 15, 151 (1993)] for the Ericksen number and Deborah number cascades. For increasing shear rates within the Ericksen number cascade, the DMG model displays three distinct regimes: stable simple shear, stable roll cells, and irregular structure accompanied by disclination formation. In accordance with experimental observations, the model predicts both ±1 and ±1/2 disclinations. Although ±1 defects form via the ridge-splitting mechanism first identified by Feng, Tao, and Leal [J. Fluid Mech. 449, 179 (2001)], a new mechanism is identified for the formation of ±1/2 defects. Within the Deborah number cascade, with increasing Deborah number, the DMG model exhibits a streamwise banded texture, in the absence of disclinations and roll cells, followed by a monodomain wherein the mean orientation lies within the shear plane throughout the domain.

  18. Prediction of shear wave velocity using empirical correlations and artificial intelligence methods

    NASA Astrophysics Data System (ADS)

    Maleki, Shahoo; Moradzadeh, Ali; Riabi, Reza Ghavami; Gholami, Raoof; Sadeghzadeh, Farhad

    2014-06-01

    Good understanding of mechanical properties of rock formations is essential during the development and production phases of a hydrocarbon reservoir. Conventionally, these properties are estimated from the petrophysical logs with compression and shear sonic data being the main input to the correlations. This is while in many cases the shear sonic data are not acquired during well logging, which may be for cost saving purposes. In this case, shear wave velocity is estimated using available empirical correlations or artificial intelligent methods proposed during the last few decades. In this paper, petrophysical logs corresponding to a well drilled in southern part of Iran were used to estimate the shear wave velocity using empirical correlations as well as two robust artificial intelligence methods knows as Support Vector Regression (SVR) and Back-Propagation Neural Network (BPNN). Although the results obtained by SVR seem to be reliable, the estimated values are not very precise and considering the importance of shear sonic data as the input into different models, this study suggests acquiring shear sonic data during well logging. It is important to note that the benefits of having reliable shear sonic data for estimation of rock formation mechanical properties will compensate the possible additional costs for acquiring a shear log.

  19. Qualitative cosmology - Diagrammatic solutions for Bianchi type IX universes with expansion, rotation, and shear. II.

    NASA Technical Reports Server (NTRS)

    Ryan, M. P., Jr.

    1971-01-01

    The investigation of expanding, rotating, shearing Bianchi type IX universes is extended to the most general case possible. Use is made of the techniques of Arnowitt et al. (1962). It is shown that the conclusion reached by Arnowitt et al. regarding the small effect of rotation on the singularity of type IX universes is true in general. The superspace approach to the motion of the universe is discussed in an appendix.

  20. Shear thickening regimes of dense non-Brownian suspensions.

    PubMed

    Ness, Christopher; Sun, Jin

    2016-01-21

    We propose a unifying rheological framework for dense suspensions of non-Brownian spheres, predicting the onsets of particle friction and particle inertia as distinct shear thickening mechanisms, while capturing quasistatic and soft particle rheology at high volume fractions and shear rates respectively. Discrete element method simulations that take suitable account of hydrodynamic and particle-contact interactions corroborate the model predictions, demonstrating both mechanisms of shear thickening, and showing that they can occur concurrently with carefully selected particle surface properties under certain flow conditions. Microstructural transitions associated with frictional shear thickening are presented. We find very distinctive divergences of both microstructural and dynamic variables with respect to volume fraction in the thickened and non-thickened states.

  1. Fast Shear Compounding Using Robust Two-dimensional Shear Wave Speed Calculation and Multi-directional Filtering

    PubMed Central

    Song, Pengfei; Manduca, Armando; Zhao, Heng; Urban, Matthew W.; Greenleaf, James F.; Chen, Shigao

    2014-01-01

    A fast shear compounding method was developed in this study using only one shear wave push-detect cycle, such that the shear wave imaging frame rate is preserved and motion artifacts are minimized. The proposed method is composed of the following steps: 1. applying a comb-push to produce multiple differently angled shear waves at different spatial locations simultaneously; 2. decomposing the complex shear wave field into individual shear wave fields with differently oriented shear waves using a multi-directional filter; 3. using a robust two-dimensional (2D) shear wave speed calculation to reconstruct 2D shear elasticity maps from each filter direction; 4. compounding these 2D maps from different directions into a final map. An inclusion phantom study showed that the fast shear compounding method could achieve comparable performance to conventional shear compounding without sacrificing the imaging frame rate. A multi-inclusion phantom experiment showed that the fast shear compounding method could provide a full field-of-view (FOV), 2D, and compounded shear elasticity map with three types of inclusions clearly resolved and stiffness measurements showing excellent agreement to the nominal values. PMID:24613636

  2. Shear layer excitation, experiment versus theory

    NASA Technical Reports Server (NTRS)

    Bechert, D. W.; Stahl, B.

    1984-01-01

    The acoustical excitation of shear layers is investigated. Acoustical excitation causes the so-called orderly structures in shear layers and jets. Also, the deviations in the spreading rate between different shear layer experiments are due to the same excitation mechanism. Measurements in the linear interaction region close to the edge from which the shear layer is shed are examined. Two sets of experiments (Houston 1981 and Berlin 1983/84) are discussed. The measurements were carried out with shear layers in air using hot wire anemometers and microphones. The agreement between these measurements and the theory is good. Even details of the fluctuating flow field correspond to theoretical predictions, such as the local occurrence of negative phase speeds.

  3. Wind shear predictive detector technology study status

    NASA Technical Reports Server (NTRS)

    Gandolfi, C.

    1990-01-01

    Among the different elements to be investigated when considering the Wind Shear hazard, the Aeronautical Navigation Technical Service (STNA/3E), whose task is to participate in the development of new technologies and equipments, focused its effort on airborne and ground sensors for the detection of low-level wind shear. The first task, initiated in 1986, consists in the evaluation of three candidate techniques for forward-looking sensors: lidar, sodar, and radar. No development is presently foreseen for an infrared based air turbulence advance warning system although some flight experiments took place in the 70's. A Thomson infrared radiometer was then installed on an Air France Boeing 707 to evaluate its capability of detecting clear air turbulence. The conclusion showed that this technique was apparently able to detect cloud layers but that additional experiments were needed; on the other hand, the rarity of the phenomenon and the difficulty in operating on a commercial aircraft were also mentioned.

  4. Modeling and measuring non-Newtonian shear flows of soft interfaces

    NASA Astrophysics Data System (ADS)

    Lopez, Juan; Raghunandan, Aditya; Underhill, Patrick; Hirsa, Amir

    2017-11-01

    Soft interfaces of polymers, particles, and proteins between fluid phases are ubiquitous in industrial and natural processes. The flow response of such systems to deformation is often not linear, as one would expect for Newtonian interfaces. The resistance to (pure shear) flow of interfaces is generally characterized by a single intrinsic material property, the surface shear viscosity. Predicted shear responses of Newtonian interfaces have achieved consensus across a wide range of flow conditions and measurement devices, when the nonlinear hydrodynamic coupling to the bulk phase is correctly accounted for. However, predicting the flows of sheared non-Newtonian interfaces remains a challenge. Here, we introduce a computational model that incorporates a non-Newtonian constitutive equation for the sheared interface and properly accounts for the coupled interfacial and bulk phase flows. We compare predictions to experiments performed with a model phospholipid system, DPPC - the main constituent of mammalian lung surfactant. Densely packed films of DPPC are directly sheared in a knife-edge surface viscometer. Yield-stress and shear thinning behaviors are shown to be accurately captured across hydrodynamic regimes straddling the Stokes flow limit to inertia dominated flows. Supported by NASA Grant NNX13AQ22G.

  5. Fast shear compounding using robust 2-D shear wave speed calculation and multi-directional filtering.

    PubMed

    Song, Pengfei; Manduca, Armando; Zhao, Heng; Urban, Matthew W; Greenleaf, James F; Chen, Shigao

    2014-06-01

    A fast shear compounding method was developed in this study using only one shear wave push-detect cycle, such that the shear wave imaging frame rate is preserved and motion artifacts are minimized. The proposed method is composed of the following steps: 1. Applying a comb-push to produce multiple differently angled shear waves at different spatial locations simultaneously; 2. Decomposing the complex shear wave field into individual shear wave fields with differently oriented shear waves using a multi-directional filter; 3. Using a robust 2-D shear wave speed calculation to reconstruct 2-D shear elasticity maps from each filter direction; and 4. Compounding these 2-D maps from different directions into a final map. An inclusion phantom study showed that the fast shear compounding method could achieve comparable performance to conventional shear compounding without sacrificing the imaging frame rate. A multi-inclusion phantom experiment showed that the fast shear compounding method could provide a full field-of-view, 2-D and compounded shear elasticity map with three types of inclusions clearly resolved and stiffness measurements showing excellent agreement to the nominal values. Copyright © 2014 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

  6. Nucleation of shear bands in amorphous alloys

    PubMed Central

    Perepezko, John H.; Imhoff, Seth D.; Chen, Ming-Wei; Wang, Jun-Qiang; Gonzalez, Sergio

    2014-01-01

    The initiation and propagation of shear bands is an important mode of localized inhomogeneous deformation that occurs in a wide range of materials. In metallic glasses, shear band development is considered to center on a structural heterogeneity, a shear transformation zone that evolves into a rapidly propagating shear band under a shear stress above a threshold. Deformation by shear bands is a nucleation-controlled process, but the initiation process is unclear. Here we use nanoindentation to probe shear band nucleation during loading by measuring the first pop-in event in the load–depth curve which is demonstrated to be associated with shear band formation. We analyze a large number of independent measurements on four different bulk metallic glasses (BMGs) alloys and reveal the operation of a bimodal distribution of the first pop-in loads that are associated with different shear band nucleation sites that operate at different stress levels below the glass transition temperature, Tg. The nucleation kinetics, the nucleation barriers, and the density for each site type have been determined. The discovery of multiple shear band nucleation sites challenges the current view of nucleation at a single type of site and offers opportunities for controlling the ductility of BMG alloys. PMID:24594599

  7. All you need is shape: Predicting shear banding in sand with LS-DEM

    NASA Astrophysics Data System (ADS)

    Kawamoto, Reid; Andò, Edward; Viggiani, Gioacchino; Andrade, José E.

    2018-02-01

    This paper presents discrete element method (DEM) simulations with experimental comparisons at multiple length scales-underscoring the crucial role of particle shape. The simulations build on technological advances in the DEM furnished by level sets (LS-DEM), which enable the mathematical representation of the surface of arbitrarily-shaped particles such as grains of sand. We show that this ability to model shape enables unprecedented capture of the mechanics of granular materials across scales ranging from macroscopic behavior to local behavior to particle behavior. Specifically, the model is able to predict the onset and evolution of shear banding in sands, replicating the most advanced high-fidelity experiments in triaxial compression equipped with sequential X-ray tomography imaging. We present comparisons of the model and experiment at an unprecedented level of quantitative agreement-building a one-to-one model where every particle in the more than 53,000-particle array has its own avatar or numerical twin. Furthermore, the boundary conditions of the experiment are faithfully captured by modeling the membrane effect as well as the platen displacement and tilting. The results show a computational tool that can give insight into the physics and mechanics of granular materials undergoing shear deformation and failure, with computational times comparable to those of the experiment. One quantitative measure that is extracted from the LS-DEM simulations that is currently not available experimentally is the evolution of three dimensional force chains inside and outside of the shear band. We show that the rotations on the force chains are correlated to the rotations in stress principal directions.

  8. Estimating boundary shear stress along vegetated streambanks with turbulent kinetic energy

    NASA Astrophysics Data System (ADS)

    Hopkinson, L. C.; Wynn, T.

    2010-12-01

    Boundary shear stress (BSS) is critical to correctly predict streambank erosion rates and stable channel design and has been estimated using turbulent kinetic energy (TKE). Typically TKE is used in ocean and fluvial environments to determine bed shear stress where the proportionality coefficient (C1) ranges from 0.19 to 0.21. TKE has only recently been used to estimate boundary shear stress along sloping streambanks. This study examined the relationship between boundary shear stress and turbulent kinetic energy along vegetated streambanks for three vegetation treatments: bare, tree, and shrub. A flume study was conducted, modeling a second order prototype stream (Tom’s Creek in Blacksburg, VA) with individual reaches dominated by two vegetation types (trees and shrubs). Boundary shear stress was measured using a flush-mount hot-film anemometer, and three-dimensional velocity was measured using an acoustic Doppler velocimeter 0.5 cm from the boundary. The relationship between TKE and BSS (BSS=C1TKE) was examined by calculating a no-intercept regression model. The calculated C1 ranged from 0.11 to 0.53 for all vegetation types (MRes=0.018-0.086). No-intercept regression models with TKE and the Reynolds stresses (τuv, τuw, and τvw) were also examined as Reynolds stresses have been used to calculate C1. There was better agreement with the reported C1 range for the TKE and Reynolds stress relationship (C1=0.17-0.21 and MRes<0.0072 for the τvw relationship) than with the measured values of shear stress, likely due to the dominance of turbulence generation. While these results are consistent with previously reported values, the relationship should be further explored with measured values of shear stress to determine the trends along hydraulically rough boundaries.

  9. The effects of transverse shearing and anisotropy on vibration frequencies of laminated cylinders

    NASA Technical Reports Server (NTRS)

    Jegley, D. C.

    1990-01-01

    The natural vibration frequencies of orthotropic and anisotropic, simply supported right circular cylinders are predicted using a theory which takes into account higher-order transverse shear deformation effects. A comparison between results based on first-order transverse shear deformation theory and the higher-order theory indicates that an additional allowance for transverse shear deformation has a negligible effect on the predicted natural vibration frequencies associated with long wavelengths, but significantly reduces the natural vibration frequencies associated with short wavelengths. Results of a parametric study of ply orientation for two classes of laminates indicates that while stacking sequence affects natural vibration frequencies, cylinder geometry and mode shape are more important in accurately predicting transverse shear deformation effects. Transverse shearing effects are less important in predicting natural vibration frequencies associated with long wavelength than in predicting axial compressive buckling loads.

  10. Instability analysis and free volume simulations of shear band directions and arrangements in notched metallic glasses

    DOE PAGES

    Li, Weidong; Gao, Yanfei; Bei, Hongbin

    2016-10-10

    As a commonly used method to enhance the ductility in bulk metallic glasses (BMGs), the introduction of geometric constraints blocks and confines the propagation of the shear bands, reduces the degree of plastic strain on each shear band so that the catastrophic failure is prevented or delayed, and promotes the formation of multiple shear bands. The clustering of multiple shear bands near notches is often interpreted as the reason for improved ductility. Experimental works on the shear band arrangements in notched metallic glasses have been extensively carried out, but a systematic theoretical study is lacking. Using instability theory that predictsmore » the onset of strain localization and the free-volume- based nite element simulations that predict the evolution of shear bands, this work reveals various categories of shear band arrangements in double edge notched BMGs with respect to the mode mixity of the applied stress fields. In conclusion, a mechanistic explanation is thus provided to a number of related experiments and especially the correlation between various types of shear bands and the stress state.« less

  11. Modeling of the reactant conversion rate in a turbulent shear flow

    NASA Technical Reports Server (NTRS)

    Frankel, S. H.; Madnia, C. K.; Givi, P.

    1992-01-01

    Results are presented of direct numerical simulations (DNS) of spatially developing shear flows under the influence of infinitely fast chemical reactions of the type A + B yields Products. The simulation results are used to construct the compositional structure of the scalar field in a statistical manner. The results of this statistical analysis indicate that the use of a Beta density for the probability density function (PDF) of an appropriate Shvab-Zeldovich mixture fraction provides a very good estimate of the limiting bounds of the reactant conversion rate within the shear layer. This provides a strong justification for the implementation of this density in practical modeling of non-homogeneous turbulent reacting flows. However, the validity of the model cannot be generalized for predictions of higher order statistical quantities. A closed form analytical expression is presented for predicting the maximum rate of reactant conversion in non-homogeneous reacting turbulence.

  12. Shear wave velocities of unconsolidated shallow sediments in the Gulf of Mexico

    USGS Publications Warehouse

    Lee, Myung W.

    2013-01-01

    Accurate shear-wave velocities for shallow sediments are important for a variety of seismic applications such as inver-sion and amplitude versus offset analysis. During the U.S. Department of Energy-sponsored Gas Hydrate Joint Industry Project Leg II, shear-wave velocities were measured at six wells in the Gulf of Mexico using the logging-while-drilling SonicScope acoustic tool. Because the tool measurement point was only 35 feet from the drill bit, the adverse effect of the borehole condition, which is severe for the shallow unconsolidated sediments in the Gulf of Mexico, was mini-mized and accurate shear-wave velocities of unconsolidated sediments were measured. Measured shear-wave velocities were compared with the shear-wave velocities predicted from the compressional-wave velocities using empirical formulas and the rock physics models based on the Biot-Gassmann theory, and the effectiveness of the two prediction methods was evaluated. Although the empirical equation derived from measured shear-wave data is accurate for predicting shear-wave velocities for depths greater than 500 feet in these wells, the three-phase Biot-Gassmann-theory -based theory appears to be optimum for predicting shear-wave velocities for shallow unconsolidated sediments in the Gulf of Mexico.

  13. Baseline predictability of daily east Asian summer monsoon circulation indices

    NASA Astrophysics Data System (ADS)

    Ai, Shucong; Chen, Quanliang; Li, Jianping; Ding, Ruiqiang; Zhong, Quanjia

    2017-05-01

    The nonlinear local Lyapunov exponent (NLLE) method is adopted to quantitatively determine the predictability limit of East Asian summer monsoon (EASM) intensity indices on a synoptic timescale. The predictability limit of EASM indices varies widely according to the definitions of indices. EASM indices defined by zonal shear have a limit of around 7 days, which is higher than the predictability limit of EASM indices defined by sea level pressure (SLP) difference and meridional wind shear (about 5 days). The initial error of EASM indices defined by SLP difference and meridional wind shear shows a faster growth than indices defined by zonal wind shear. Furthermore, the indices defined by zonal wind shear appear to fluctuate at lower frequencies, whereas the indices defined by SLP difference and meridional wind shear generally fluctuate at higher frequencies. This result may explain why the daily variability of the EASM indices defined by zonal wind shear tends be more predictable than those defined by SLP difference and meridional wind shear. Analysis of the temporal correlation coefficient (TCC) skill for EASM indices obtained from observations and from NCEP's Global Ensemble Forecasting System (GEFS) historical weather forecast dataset shows that GEFS has a higher forecast skill for the EASM indices defined by zonal wind shear than for indices defined by SLP difference and meridional wind shear. The predictability limit estimated by the NLLE method is shorter than that in GEFS. In addition, the June-September average TCC skill for different daily EASM indices shows significant interannual variations from 1985 to 2015 in GEFS. However, the TCC for different types of EASM indices does not show coherent interannual fluctuations.

  14. Tertiary creep test by ring shear apparatus in predicting initiation time of rainfall-induced-shallow landslide

    NASA Astrophysics Data System (ADS)

    Dok, A.; Fukuoka, H.

    2010-12-01

    Landslides are complex geo-disaters that frequently occur due to certain causes, but only one trigger such as earthquake or heavy rainfall or other related natural phenomenas. A slope failure seldom occurs without any creep deformation. Failure time of a slope as found by Fukuzono (1985) and Siato (1965) based on graphical analysis of extensometer monitoring data through large scale flume test for landslide studies, logarithm of acceleration is proportional to the logarithm of velocity of surface displacement immediately before the failure. It is expressed as d2x/dt2 = A(dx/dt)α, where x is surface displacement, t is time, and A and α are constant. And, Fukuzono (1985, 1989) proposed a simple method of predicting the time of falure by the inverse velocity (1/v) mean. The curve of inverse velocity is concave at 1< α<2, linear at α=2, and convex at α>2. Recently, Minamitani (2007) have researched on mechanism of Tertiary Creep deformation for landslide failure time prediction by increasing shear-stress development in order to understand the story behind the empirical relationship found by senior researcher Fukozono. He found a strong relationshp between constants A and α, expressed as α = 0.1781A+ 1.814. For deeper understanding, this study aims at learning in more detail on mechanism of landslides in tropical soils by ring shear apparatus (invented by DPRI, Disaster Prevention Research Institute) based on Tertiary Creep deformation theory in help issue warning on rainfall-induced landslides through back (pore-water) pressure control tests under combined conditions of particular normal stress and shear stress with pore-water pressure changes to simulate the potential sliding surface condition in the heavy rainfall, which no body experiences conducting such a test series, particularly by applying cyclic and actual groundwater change pattern to the soils. To reach the archivement, serie of back pressure control test were implemented by utilising stress

  15. Stable plume rise in a shear layer.

    PubMed

    Overcamp, Thomas J

    2007-03-01

    Solutions are given for plume rise assuming a power-law wind speed profile in a stably stratified layer for point and finite sources with initial vertical momentum and buoyancy. For a constant wind speed, these solutions simplify to the conventional plume rise equations in a stable atmosphere. In a shear layer, the point of maximum rise occurs further downwind and is slightly lower compared with the plume rise with a constant wind speed equal to the wind speed at the top of the stack. If the predictions with shear are compared with predictions for an equivalent average wind speed over the depth of the plume, the plume rise with shear is higher than plume rise with an equivalent average wind speed.

  16. Prediction of plastic instabilities under thermo-mechanical loadings in tension and simple shear

    NASA Astrophysics Data System (ADS)

    Manach, P. Y.; Mansouri, L. F.; Thuillier, S.

    2016-08-01

    Plastic instabilities like Portevin-Le Châtelier were quite thoroughly investigated experimentally in tension, under a large range of strain rates and temperatures. Such instabilities are characterized both by a jerky flow and a localization of the strain in bands. Similar phenomena were also recorded for example in simple shear [1]. Modelling of this phenomenon is mainly performed at room temperature, taking into account the strain rate sensitivity, though an extension of the classical Estrin-Kubin-McCormick was proposed in the literature, by making some of the material parameters dependent on temperature. A similar approach is considered in this study, furthermore extended for anisotropic plasticity with Hill's 1948 yield criterion. Material parameters are identified at 4 different temperatures, ranging from room temperature up to 250°C. The identification procedure is split in 3 steps, related to the elasticity, the average stress level and the magnitude of the stress drops. The anisotropy is considered constant in this temperature range, as evidenced by experimental results [2]. The model is then used to investigate the temperature dependence of the critical strain, as well as its capability to represent the propagation of the bands. Numerical predictions of the instabilities in tension and simple shear at room temperature and up to 250°C are compared with experimental results [3]. In the case of simple shear, a monotonic loading followed by unloading and reloading in the reverse direction (“Bauschinger-type” test) is also considered, showing that (i) kinematic hardening should be taken into account to fully describe the transition at re-yielding (ii) the modelling of the critical strain has to be improved.

  17. Compressional and shear-wave velocity versus depth relations for common rock types in northern California

    USGS Publications Warehouse

    Brocher, T.M.

    2008-01-01

    This article presents new empirical compressional and shear-wave velocity (Vp and Vs) versus depth relationships for the most common rock types in northern California. Vp versus depth relations were developed from borehole, laboratory, seismic refraction and tomography, and density measurements, and were converted to Vs versus depth relations using new empirical relations between Vp and Vs. The relations proposed here account for increasing overburden pressure but not for variations in other factors that can influence velocity over short distance scales, such as lithology, consolidation, induration, porosity, and stratigraphic age. Standard deviations of the misfits predicted by these relations thus provide a measure of the importance of the variability in Vp and Vs caused by these other factors. Because gabbros, greenstones, basalts, and other mafic rocks have a different Vp and Vs relationship than sedimentary and granitic rocks, the differences in Vs between these rock types at depths below 6 or 7 km are generally small. The new relations were used to derive the 2005 U.S. Geological Survey seismic velocity model for northern California employed in the broadband strong motion simulations of the 1989 Loma Prieta and 1906 San Francisco earthquakes; initial tests of the model indicate that the Vp model generally compares favorably to regional seismic tomography models but that the Vp and Vs values proposed for the Franciscan Complex may be about 5% too high.

  18. Timing of Multiple Stages of Granitic Magmatisms: Constraints on Shearing along the Ailao Shan-Red River Shear Zone

    NASA Astrophysics Data System (ADS)

    Chen, W.; Liu, J.; Fan, W.; Feng, J.; DAO, H.; Yan, J.

    2017-12-01

    The Ailao Shan-Red River (ASRR) shear zone is a large scale shear zone resulted from collision between India and Euro-Asia Plates in Cenozoic. Magmatisms related to the shear zone evolution took place before, during or after shearing process that contributes to pre-, syn- and post- granitic emplacement. Combined structure, fabric and geochronology analyses of granitic rocks within sheared Proterozoic country rocks along the ASRR shear zone offer important clues on timing of shearing activity and constraining on transformation of types of the shearing. Zircon U-Pb dating results indicate that the granitic intrusions within the ASRR shear zone are broadly grouped into two stages: Permo-Triassic (256.0±6.0 Ma, 244.0±7.6 Ma and 234.0±9.3 Ma) and Cenozoic (27.1±1.5 Ma, 26.34±0.62 Ma and 25.10±0.61 Ma). The Permo-Triassic intrusions show evidences for intensive mylonitization. The older Cenozoic granitic rocks were also strongly sheared, but the younger Cenozoic granites were weakly sheared and they cut across early intrusions (e.g. the Permo-Triassic and older Cenozoic intrusions). Petrographic microscope observations suggest that the Permo-Triassic granitic intrusions show prominent superimposition of high temperature mylonization by low temperature mylonization. Quartz c-axis fabrics of the granites demonstrate that there are multiple maxima due to the superimposition. The older Cenozoic granitic intrusion of 27.1±1.5 Ma shows weak mylonization and possess four symmetrical point maxima in their quartz c-axis fabrics. The EBSD data indicate that the intrusion experienced pure shearing. Intrusions of 26.34±0.62 Ma and 25.10±0.61 Ma show evidences for very weak mylonization. The quartz c-axis patterns of the rocks dominantly resulted from low temperature deformation by simple shearing. It is concluded, in summary, that: (1) Permo-Triassic granitic intrusions experienced superimposed shearing of high and low temperatures; (2) Evidences for both early pure

  19. On the asymmetric distribution of shear-relative typhoon rainfall

    NASA Astrophysics Data System (ADS)

    Gao, Si; Zhai, Shunan; Li, Tim; Chen, Zhifan

    2018-02-01

    The Tropical Rainfall Measuring Mission (TRMM) 3B42 precipitation, the National Centers for Environmental Prediction (NCEP) Final analysis and the Regional Specialized Meteorological Center (RSMC) Tokyo best-track data during 2000-2015 are used to compare spatial rainfall distribution associated with Northwest Pacific tropical cyclones (TCs) with different vertical wind shear directions and investigate possible mechanisms. Results show that the maximum TC rainfall are all located in the downshear left quadrant regardless of shear direction, and TCs with easterly shear have greater magnitudes of rainfall than those with westerly shear, consistent with previous studies. Rainfall amount of a TC is related to its relative position and proximity from the western Pacific subtropical high (WPSH) and the intensity of water vapor transport, and low-level jet is favorable for water vapor transport. The maximum of vertically integrated moisture flux convergence (MFC) are located on the downshear side regardless of shear direction, and the contribution of wind convergence to the total MFC is far larger than that of moisture advection. The cyclonic displacement of the maximum rainfall relative to the maximum MFC is possibly due to advection of hydrometeors by low- and middle-level cyclonic circulation of TCs. The relationship between TC rainfall and the WPSH through water vapor transport and vertical wind shear implies that TC rainfall may be highly predictable given the high predictability of the WPSH.

  20. A study of the second and third order closure models of turbulence for prediction of separated shear flows

    NASA Technical Reports Server (NTRS)

    Amano, R. S.

    1985-01-01

    The hybrid model of the Reynolds-stress turbulence closure is tested for the computation of the flows over a step and disk. Here it is attempted to improve the redistributive action of the turbulence energy among the Reynolds stresses. By evaluating the existing models for the pressure-strain correlation, better coefficients are obtained for the prediction of separating shear flows. Furthermore, the diffusion rate of the Reynolds stresses is reevaluated adopting several algebraic correlations for the triple-velocity products. The models of Cormack et al., Daly-Harlow, Hanjalic-Launder, and Shir were tested for the reattaching shear flows. It was generally observed that all these algebraic models give considerably low values of the triple-velocity products. This is attributed to the fact that none of the algebraic models can take the convective effect of the triple-velocity products into account in the separating shear flows, thus resulting in much lower diffusion rate than Reynolds stresses. In order to improve the evaluation of these quantities correction factors are introduced based on the comparison with some experimental data.

  1. Shear properties of pultruded fiber reinforced polymer composite materials

    NASA Astrophysics Data System (ADS)

    Seo, J. H.; Kim, S. H.; Ok, D. M.; An, D. J.; Yoon, S. J.

    2018-06-01

    This paper focuses on the mechanical properties of PFRP composite materials. Especially, relationship between shear property and the other mechanical properties of PFRP composite materials is investigated through comparison between experimental and theoretical results. The shear property of PFRP composite specimen is calculated from the theoretical equations which were suggested in previous studies. In addition, comparison between the shear property determined by the tensile test and the shear property calculated from theoretical equations is conducted and discussed. It was found that the theoretically predicted shear modulus of elasticity considering contiguity is close to the shear modulus of elasticity obtained by the 45° off-axis tensile test.

  2. Investigation of the shear response and geometrically necessary dislocation densities in shear localization in high-purity titanium

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zhu, Chaoyi; Livescu, Veronica; Harrington, Tyler

    The influence of microstructural anisotropy on shear response of high-purity titanium was studied using the compact forced-simple-shear specimen (CFSS) loaded under quasi-static loading conditions. Post-mortem characterization reveals significant difference in shear response of different directions in the same material due to material crystallographic texture anisotropy. Shear bands are narrower in specimens in which the shear zone is aligned along the direction with a strong {0001} basal texture. Twinning was identified as an active mechanism to accommodate strains in the shear region in both orientations. This paper confirms the applicability of the CFSS design for the investigation of differences in themore » shear response of materials as a function of process-induced crystallographic texture. A detailed, systematic approach to quantifying shear band evolution by evaluating geometrically necessary dislocations (GND) associated with crystallographic anisotropy is presented. Finally, the results show that: i) line average GND density profiles, for Ti samples that possess a uniform equiaxed-grain structure, but with strong crystallographic anisotropy, exhibit significant differences in GND density close to the shear band center; ii) GND profiles decrease steadily away from the shear band as the plastic strain diminishes, in agreement with Ashby's theory of work hardening, where the higher GND density in the through-thickness (TT) orientation is a result of restricted < a > type slip in the shear band compared with in-plane (IP) samples; iii) the anisotropy in deformation response is derived from initial crystallographic texture of the materials, where GND density of < a > GNDs are higher adjacent to the shear band in the through-thickness sample oriented away from easy slip, but the density of < c+a > type GNDs are very similar in these two samples; and iv) the increase in grain average GND density was determined to have strong correlation to an increase in the

  3. Investigation of the shear response and geometrically necessary dislocation densities in shear localization in high-purity titanium

    DOE PAGES

    Zhu, Chaoyi; Livescu, Veronica; Harrington, Tyler; ...

    2017-03-31

    The influence of microstructural anisotropy on shear response of high-purity titanium was studied using the compact forced-simple-shear specimen (CFSS) loaded under quasi-static loading conditions. Post-mortem characterization reveals significant difference in shear response of different directions in the same material due to material crystallographic texture anisotropy. Shear bands are narrower in specimens in which the shear zone is aligned along the direction with a strong {0001} basal texture. Twinning was identified as an active mechanism to accommodate strains in the shear region in both orientations. This paper confirms the applicability of the CFSS design for the investigation of differences in themore » shear response of materials as a function of process-induced crystallographic texture. A detailed, systematic approach to quantifying shear band evolution by evaluating geometrically necessary dislocations (GND) associated with crystallographic anisotropy is presented. Finally, the results show that: i) line average GND density profiles, for Ti samples that possess a uniform equiaxed-grain structure, but with strong crystallographic anisotropy, exhibit significant differences in GND density close to the shear band center; ii) GND profiles decrease steadily away from the shear band as the plastic strain diminishes, in agreement with Ashby's theory of work hardening, where the higher GND density in the through-thickness (TT) orientation is a result of restricted < a > type slip in the shear band compared with in-plane (IP) samples; iii) the anisotropy in deformation response is derived from initial crystallographic texture of the materials, where GND density of < a > GNDs are higher adjacent to the shear band in the through-thickness sample oriented away from easy slip, but the density of < c+a > type GNDs are very similar in these two samples; and iv) the increase in grain average GND density was determined to have strong correlation to an increase in the

  4. Acoustic wave propagation in a temporal evolving shear-layer for low-Mach number perturbations

    NASA Astrophysics Data System (ADS)

    Hau, Jan-Niklas; Müller, Björn

    2018-01-01

    We study wave packets with the small perturbation/gradient Mach number interacting with a smooth shear-layer in the linear regime of small amplitude perturbations. In particular, we investigate the temporal evolution of wave packets in shear-layers with locally curved regions of variable size using non-modal linear analysis and direct numerical simulations of the two-dimensional gas-dynamical equations. Depending on the wavenumber of the initially imposed wave packet, three different types of behavior are observed: (i) The wave packet passes through the shear-layer and constantly transfers energy back to the mean flow. (ii) It is turned around (or reflected) within the sheared region and extracts energy from the base flow. (iii) It is split into two oppositely propagating packages when reaching the upper boundary of the linearly sheared region. The conducted direct numerical simulations confirm that non-modal linear stability analysis is able to predict the wave packet dynamics, even in the presence of non-linearly sheared regions. In the light of existing studies in this area, we conclude that the sheared regions are responsible for the highly directed propagation of linearly generated acoustic waves when there is a dominating source, as it is the case for jet flows.

  5. Wave models for turbulent free shear flows

    NASA Technical Reports Server (NTRS)

    Liou, W. W.; Morris, P. J.

    1991-01-01

    New predictive closure models for turbulent free shear flows are presented. They are based on an instability wave description of the dominant large scale structures in these flows using a quasi-linear theory. Three model were developed to study the structural dynamics of turbulent motions of different scales in free shear flows. The local characteristics of the large scale motions are described using linear theory. Their amplitude is determined from an energy integral analysis. The models were applied to the study of an incompressible free mixing layer. In all cases, predictions are made for the development of the mean flow field. In the last model, predictions of the time dependent motion of the large scale structure of the mixing region are made. The predictions show good agreement with experimental observations.

  6. Critical shear stress for erosion of cohesive soils subjected to temperatures typical of wildfires

    USGS Publications Warehouse

    Moody, J.A.; Dungan, Smith J.; Ragan, B.W.

    2005-01-01

    [1] Increased erosion is a well-known response after wildfire. To predict and to model erosion on a landscape scale requires knowledge of the critical shear stress for the initiation of motion of soil particles. As this soil property is temperature-dependent, a quantitative relation between critical shear stress and the temperatures to which the soils have been subjected during a wildfire is required. In this study the critical shear stress was measured in a recirculating flume using samples of forest soil exposed to different temperatures (40??-550??C) for 1 hour. Results were obtained for four replicates of soils derived from three different types of parent material (granitic bedrock, sandstone, and volcanic tuffs). In general, the relation between critical shear stress and temperature can be separated into three different temperature ranges (275??C), which are similar to those for water repellency and temperature. The critical shear stress was most variable (1.0-2.0 N m-2) for temperatures 2.0 N m-2) between 175?? and 275??C, and was essentially constant (0.5-0.8 N m-2) for temperatures >275??C. The changes in critical shear stress with temperature were found to be essentially independent of soil type and suggest that erosion processes in burned watersheds can be modeled more simply than erosion processes in unburned watersheds. Wildfire reduces the spatial variability of soil erodibility associated with unburned watersheds by eliminating the complex effects of vegetation in protecting soils and by reducing the range of cohesion associated with different types of unburned soils. Our results indicate that modeling the erosional response after a wildfire depends primarily on determining the spatial distribution of the maximum soil temperatures that were reached during the wildfire. Copyright 2005 by the American Geophysical Union.

  7. Thrombus Formation at High Shear Rates.

    PubMed

    Casa, Lauren D C; Ku, David N

    2017-06-21

    The final common pathway in myocardial infarction and ischemic stroke is occlusion of blood flow from a thrombus forming under high shear rates in arteries. A high-shear thrombus forms rapidly and is distinct from the slow formation of coagulation that occurs in stagnant blood. Thrombosis at high shear rates depends primarily on the long protein von Willebrand factor (vWF) and platelets, with hemodynamics playing an important role in each stage of thrombus formation, including vWF binding, platelet adhesion, platelet activation, and rapid thrombus growth. The prediction of high-shear thrombosis is a major area of biofluid mechanics in which point-of-care testing and computational modeling are promising future directions for clinically relevant research. Further research in this area will enable identification of patients at high risk for arterial thrombosis, improve prevention and treatment based on shear-dependent biological mechanisms, and improve blood-contacting device design to reduce thrombosis risk.

  8. Simple shear of deformable square objects

    NASA Astrophysics Data System (ADS)

    Treagus, Susan H.; Lan, Labao

    2003-12-01

    Finite element models of square objects in a contrasting matrix in simple shear show that the objects deform to a variety of shapes. For a range of viscosity contrasts, we catalogue the changing shapes and orientations of objects in progressive simple shear. At moderate simple shear ( γ=1.5), the shapes are virtually indistinguishable from those in equivalent pure shear models with the same bulk strain ( RS=4), examined in a previous study. In theory, differences would be expected, especially for very stiff objects or at very large strain. In all our simple shear models, relatively competent square objects become asymmetric barrel shapes with concave shortened edges, similar to some types of boudin. Incompetent objects develop shapes surprisingly similar to mica fish described in mylonites.

  9. Turbulence Modeling Effects on the Prediction of Equilibrium States of Buoyant Shear Flows

    NASA Technical Reports Server (NTRS)

    Zhao, C. Y.; So, R. M. C.; Gatski, T. B.

    2001-01-01

    The effects of turbulence modeling on the prediction of equilibrium states of turbulent buoyant shear flows were investigated. The velocity field models used include a two-equation closure, a Reynolds-stress closure assuming two different pressure-strain models and three different dissipation rate tensor models. As for the thermal field closure models, two different pressure-scrambling models and nine different temperature variance dissipation rate, Epsilon(0) equations were considered. The emphasis of this paper is focused on the effects of the Epsilon(0)-equation, of the dissipation rate models, of the pressure-strain models and of the pressure-scrambling models on the prediction of the approach to equilibrium turbulence. Equilibrium turbulence is defined by the time rate (if change of the scaled Reynolds stress anisotropic tensor and heat flux vector becoming zero. These conditions lead to the equilibrium state parameters. Calculations show that the Epsilon(0)-equation has a significant effect on the prediction of the approach to equilibrium turbulence. For a particular Epsilon(0)-equation, all velocity closure models considered give an equilibrium state if anisotropic dissipation is accounted for in one form or another in the dissipation rate tensor or in the Epsilon(0)-equation. It is further found that the models considered for the pressure-strain tensor and the pressure-scrambling vector have little or no effect on the prediction of the approach to equilibrium turbulence.

  10. A viscoelastic model for the prediction of transcranial ultrasound propagation: application for the estimation of shear acoustic properties in the human skull

    NASA Astrophysics Data System (ADS)

    Pichardo, Samuel; Moreno-Hernández, Carlos; Drainville, Robert Andrew; Sin, Vivian; Curiel, Laura; Hynynen, Kullervo

    2017-09-01

    A better understanding of ultrasound transmission through the human skull is fundamental to develop optimal imaging and therapeutic applications. In this study, we present global attenuation values and functions that correlate apparent density calculated from computed tomography scans to shear speed of sound. For this purpose, we used a model for sound propagation based on the viscoelastic wave equation (VWE) assuming isotropic conditions. The model was validated using a series of measurements with plates of different plastic materials and angles of incidence of 0°, 15° and 50°. The optimal functions for transcranial ultrasound propagation were established using the VWE, scan measurements of transcranial propagation with an angle of incidence of 40° and a genetic optimization algorithm. Ten (10) locations over three (3) skulls were used for ultrasound frequencies of 270 kHz and 836 kHz. Results with plastic materials demonstrated that the viscoelastic modeling predicted both longitudinal and shear propagation with an average (±s.d.) error of 9(±7)% of the wavelength in the predicted delay and an error of 6.7(±5)% in the estimation of transmitted power. Using the new optimal functions of speed of sound and global attenuation for the human skull, the proposed model predicted the transcranial ultrasound transmission for a frequency of 270 kHz with an expected error in the predicted delay of 5(±2.7)% of the wavelength. The sound propagation model predicted accurately the sound propagation regardless of either shear or longitudinal sound transmission dominated. For 836 kHz, the model predicted accurately in average with an error in the predicted delay of 17(±16)% of the wavelength. Results indicated the importance of the specificity of the information at a voxel level to better understand ultrasound transmission through the skull. These results and new model will be very valuable tools for the future development of transcranial applications of

  11. Effective temperature dynamics of shear bands in metallic glasses

    NASA Astrophysics Data System (ADS)

    Daub, Eric G.; Klaumünzer, David; Löffler, Jörg F.

    2014-12-01

    We study the plastic deformation of bulk metallic glasses with shear transformation zone (STZ) theory, a physical model for plasticity in amorphous systems, and compare it with experimental data. In STZ theory, plastic deformation occurs when localized regions rearrange due to applied stress and the density of these regions is determined by a dynamically evolving effective disorder temperature. We compare the predictions of STZ theory to experiments that explore the low-temperature deformation of Zr-based bulk metallic glasses via shear bands at various thermal temperatures and strain rates. By following the evolution of effective temperature with time, strain rate, and temperature through a series of approximate and numerical solutions to the STZ equations, we successfully model a suite of experimentally observed phenomena, including shear-band aging as apparent from slide-hold-slide tests, a temperature-dependent steady-state flow stress, and a strain-rate- and temperature-dependent transition from stick-slip (serrated flow) to steady-sliding (nonserrated flow). We find that STZ theory quantitatively matches the observed experimental data and provides a framework for relating the experimentally measured energy scales to different types of atomic rearrangements.

  12. A model for predicting the shear bearing capacity of FRP-strengthened beams

    NASA Astrophysics Data System (ADS)

    Sas, G.; Carolin, A.; Täljsten, B.

    2008-05-01

    The shear failure of reinforced concrete beams needs more attention than the bending failure since no or only small warning precedes the failure. For this reason, it is of utmost importance to understand the shear bearing capacity and also to be able to undertake significant rehabilitation work if necessary. In this paper, a design model for the shear strengthening of concrete beams by using fiber-reinforced polymers (FRP) is presented, and the limitations of the truss model analogy are highlighted. The fracture mechanics approach is used in analyzing the bond behavior between the FRP composites and concrete. The fracture energy of concrete and the axial rigidity of the FRP are considered to be the most important parameters. The effective strain in the FRP when the debonding occurs is determined. The limitations of the anchorage length over the cross section are analyzed. A simple iterative design method for the shear debonding is finally proposed.

  13. An analytical study of the effects of transverse shear deformation and anisotropy on natural vibation frequencies of laminated cylinders

    NASA Technical Reports Server (NTRS)

    Jegley, Dawn C.

    1989-01-01

    Natural vibration frequencies of orthotropic and anisotropic simply supported right circular cylinders are predicted using a higher-order transverse-shear deformation theory. A comparison of natural vibration frequencies predicted by first-order transverse-shear deformation theory and the higher-order theory shows that an additional allowance for transverse shear deformation has a negligible effect on the lowest predicted natural vibration frequencies of laminated cylinders but significantly reduces the higher natural vibration frequencies. A parametric study of the effects of ply orientation on the natural vibration frequencies of laminated cylinders indicates that while stacking sequence affects natural vibration frequencies, cylinder geometry is more important in predicting transverse-shear deformation effects. Interaction curves for cylinders subjected to axial compressive loadings and low natural vibration frequencies indicate that transverse shearing effects are less important in predicting low natural vibration frequencies than in predicting axial compressive buckling loads. The effects of anisotropy are more important than the effects of transverse shear deformation for most strongly anisotropic laminated cylinders in predicting natural vibration frequencies. However, transverse-shear deformation effects are important in predicting high natural vibration frequencies of thick-walled laminated cylinders. Neglecting either anisotropic effects or transverse-shear deformation effects leads to non-conservative errors in predicted natural vibration frequencies.

  14. An analytical study of the effects of transverse shear deformation and anisotropy on natural vibration frequencies of laminated cylinders

    NASA Technical Reports Server (NTRS)

    Jegley, Dawn C.

    1988-01-01

    Natural vibration frequencies of orthotropic and anisotropic simply supported right circular cylinders are predicted using a higher-order transverse-shear deformation theory. A comparison of natural vibration frequencies predicted by first-order transverse-shear deformation theory and the higher-order theory shows that an additional allowance for transverse shear deformation has a negligible effect on the lowest predicted natural vibration frequencies of laminated cylinders but significantly reduces the higher natural vibration frequencies. A parametric study of the effects of ply orientation on the natural vibration frequencies of laminated cylinders indicates that while stacking sequence affects natural vibration frequencies, cylinder geometry is more important in predicting transverse-shear deformation effects. Interaction curves for cylinders subjected to axial compressive loadings and low natural vibration frequencies indicate that transverse shearing effects are less important in predicting low natural vibration frequencies than in predicting axial compressive buckling loads. The effects of anisotropy are more important than the effects of transverse shear deformation for most strongly anisotropic laminated cylinders in predicting natural vibration frequencies. However, transverse-shear deformation effects are important in predicting high natural vibration frequencies of thick-walled laminated cylinders. Neglecting either anisotropic effects or transverse-shear deformation effects leads to non-conservative errors in predicted natural vibration frequencies.

  15. Value of shear wave arrival time contour display in shear wave elastography for breast masses diagnosis.

    PubMed

    Zhou, Bang-Guo; Wang, Dan; Ren, Wei-Wei; Li, Xiao-Long; He, Ya-Ping; Liu, Bo-Ji; Wang, Qiao; Chen, Shi-Gao; Alizad, Azra; Xu, Hui-Xiong

    2017-08-01

    To evaluate the diagnostic performance of shear wave arrival time contour (SWATC) display for the diagnosis of breast lesions and to identify factors associated with the quality of shear wave propagation (QSWP) in breast lesions. This study included 277 pathologically confirmed breast lesions. Conventional B-mode ultrasound characteristics and shear wave elastography parameters were computed. Using the SWATC display, the QSWP of each lesion was assigned to a two-point scale: score 1 (low quality) and score 2 (high quality). Binary logistic regression analysis was performed to identify factors associated with QSWP. The area under the receiver operating characteristic curve (AUROC) for QSWP to differentiate benign from malignant lesions was 0.913, with a sensitivity of 91.9%, a specificity of 90.7%, a positive predictive value (PPV) of 74.0%, and a negative predictive value (NPV) of 97.5%. Compared with using the standard deviation of shear wave speed (SWS SD ) alone, SWS SD combined with QSWP increased the sensitivity from 75.8% to 93.5%, but decreased the specificity from 95.8% to 89.3% (P < 0.05). SWS SD was identified to be the strongest factor associated with the QSWP, followed by tumor malignancy and the depth of the lesion. In conclusion, SWATC display may be useful for characterization of breast lesions.

  16. Modeling transversely isotropic, viscoelastic, incompressible tissue-like materials with application in ultrasound shear wave elastography

    NASA Astrophysics Data System (ADS)

    Qiang, Bo; Brigham, John C.; Aristizabal, Sara; Greenleaf, James F.; Zhang, Xiaoming; Urban, Matthew W.

    2015-02-01

    In this paper, we propose a method to model the shear wave propagation in transversely isotropic, viscoelastic and incompressible media. The targeted application is ultrasound-based shear wave elastography for viscoelasticity measurements in anisotropic tissues such as the kidney and skeletal muscles. The proposed model predicts that if the viscoelastic parameters both across and along fiber directions can be characterized as a Voigt material, then the spatial phase velocity at any angle is also governed by a Voigt material model. Further, with the aid of Taylor expansions, it is shown that the spatial group velocity at any angle is close to a Voigt type for weakly attenuative materials within a certain bandwidth. The model is implemented in a finite element code by a time domain explicit integration scheme and shear wave simulations are conducted. The results of the simulations are analyzed to extract the shear wave elasticity and viscosity for both the spatial phase and group velocities. The estimated values match well with theoretical predictions. The proposed theory is further verified by an ex vivo tissue experiment measured in a porcine skeletal muscle by an ultrasound shear wave elastography method. The applicability of the Taylor expansion to analyze the spatial velocities is also discussed. We demonstrate that the approximations from the Taylor expansions are subject to errors when the viscosities across or along the fiber directions are large or the maximum frequency considered is beyond the bandwidth defined by radii of convergence of the Taylor expansions.

  17. Shear-lag analysis about an internally-dropped ply

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Vizzini, A.J.

    1995-12-31

    The region around a terminated ply is modeled as several elastic layers separated by shear regions. A shear-lag analysis is then performed allowing for the thickness of the elastic and shear layers to vary. Boundary conditions, away for the ply drop, are based on the deflections determined by a finite element model. The interlaminar stresses are compared against those generated by the finite element model for tapered laminates under pure extension, pure bending, and extension-bending coupling. The shear-lag analysis predicts the interlaminar shear at and near the ply drop for pure extension and in cases involving bending if the deflectionsmore » due to bending are removed. The interlaminar shear stress and force equilibrium are used to determine the interlaminar normal stress. The trends in the interlaminar normal stress shown by the finite element model are partially captured by the shear-lag analysis. This simple analysis indicates that the mechanism for load transfer about a ply drop is primarily due to shear transfer through the resin rich areas.« less

  18. Application of a soft computing technique in predicting the percentage of shear force carried by walls in a rectangular channel with non-homogeneous roughness.

    PubMed

    Khozani, Zohreh Sheikh; Bonakdari, Hossein; Zaji, Amir Hossein

    2016-01-01

    Two new soft computing models, namely genetic programming (GP) and genetic artificial algorithm (GAA) neural network (a combination of modified genetic algorithm and artificial neural network methods) were developed in order to predict the percentage of shear force in a rectangular channel with non-homogeneous roughness. The ability of these methods to estimate the percentage of shear force was investigated. Moreover, the independent parameters' effectiveness in predicting the percentage of shear force was determined using sensitivity analysis. According to the results, the GP model demonstrated superior performance to the GAA model. A comparison was also made between the GP program determined as the best model and five equations obtained in prior research. The GP model with the lowest error values (root mean square error ((RMSE) of 0.0515) had the best function compared with the other equations presented for rough and smooth channels as well as smooth ducts. The equation proposed for rectangular channels with rough boundaries (RMSE of 0.0642) outperformed the prior equations for smooth boundaries.

  19. An Experimental Investigation into Failure and Localization Phenomena in the Extension to Shear Fracture Transition in Rock

    NASA Astrophysics Data System (ADS)

    Choens, R. C., II; Chester, F. M.; Bauer, S. J.; Flint, G. M.

    2014-12-01

    Fluid-pressure assisted fracturing can produce mesh and other large, interconnected and complex networks consisting of both extension and shear fractures in various metamorphic, magmatic and tectonic systems. Presently, rock failure criteria for tensile and low-mean compressive stress conditions is poorly defined, although there is accumulating evidence that the transition from extension to shear fracture with increasing mean stress is continuous. We report on the results of experiments designed to document failure criteria, fracture mode, and localization phenomena for several rock types (sandstone, limestone, chalk and marble). Experiments were conducted in triaxial extension using a necked (dogbone) geometry to achieve mixed tension and compression stress states with local component-strain measurements in the failure region. The failure envelope for all rock types is similar, but are poorly described using Griffith or modified Griffith (Coulomb or other) failure criteria. Notably, the mode of fracture changes systematically from pure extension to shear with increase in compressive mean stress and display a continuous change in fracture orientation with respect to principal stress axes. Differential stress and inelastic strain show a systematic increase with increasing mean stress, whereas the axial stress decreases before increasing with increasing mean stress. The stress and strain data are used to analyze elastic and plastic strains leading to failure and compare the experimental results to predictions for localization using constitutive models incorporating on bifurcation theory. Although models are able to describe the stability behavior and onset of localization qualitatively, the models are unable to predict fracture type or orientation. Constitutive models using single or multiple yield surfaces are unable to predict the experimental results, reflecting the difficulty in capturing the changing micromechanisms from extension to shear failure. Sandia

  20. Behavior of Tilted Angle Shear Connectors.

    PubMed

    Khorramian, Koosha; Maleki, Shervin; Shariati, Mahdi; Ramli Sulong, N H

    2015-01-01

    According to recent researches, angle shear connectors are appropriate to transfer longitudinal shear forces across the steel-concrete interface. Angle steel profile has been used in different positions as L-shaped or C-shaped shear connectors. The application of angle shear connectors in tilted positions is of interest in this study. This study investigates the behaviour of tilted-shaped angle shear connectors under monotonic loading using experimental push out tests. Eight push-out specimens are tested to investigate the effects of different angle parameters on the ultimate load capacity of connectors. Two different tilted angles of 112.5 and 135 degrees between the angle leg and steel beam are considered. In addition, angle sizes and lengths are varied. Two different failure modes were observed consisting of concrete crushing-splitting and connector fracture. By increasing the size of connector, the maximum load increased for most cases. In general, the 135 degrees tilted angle shear connectors have a higher strength and stiffness than the 112.5 degrees type.

  1. Modeling Shear Induced Von Willebrand Factor Binding to Collagen

    NASA Astrophysics Data System (ADS)

    Dong, Chuqiao; Wei, Wei; Morabito, Michael; Webb, Edmund; Oztekin, Alparslan; Zhang, Xiaohui; Cheng, Xuanhong

    2017-11-01

    Von Willebrand factor (vWF) is a blood glycoprotein that binds with platelets and collagen on injured vessel surfaces to form clots. VWF bioactivity is shear flow induced: at low shear, binding between VWF and other biological entities is suppressed; for high shear rate conditions - as are found near arterial injury sites - VWF elongates, activating its binding with platelets and collagen. Based on parameters derived from single molecule force spectroscopy experiments, we developed a coarse-grain molecular model to simulate bond formation probability as a function of shear rate. By introducing a binding criterion that depends on the conformation of a sub-monomer molecular feature of our model, the model predicts shear-induced binding, even for conditions where binding is highly energetically favorable. We further investigate the influence of various model parameters on the ability to predict shear-induced binding (vWF length, collagen site density and distribution, binding energy landscape, and slip/catch bond length) and demonstrate parameter ranges where the model provides good agreement with existing experimental data. Our results may be important for understanding vWF activity and also for achieving targeted drug therapy via biomimetic synthetic molecules. National Science Foundation (NSF),Division of Mathematical Sciences (DMS).

  2. Shear-banding and superdiffusivity in entangled polymer solutions

    NASA Astrophysics Data System (ADS)

    Shin, Seunghwan; Dorfman, Kevin D.; Cheng, Xiang

    2017-12-01

    Using high-resolution confocal rheometry, we study the shear profiles of well-entangled DNA solutions under large-amplitude oscillatory shear in a rectilinear planar shear cell. With increasing Weissenberg number (Wi), we observe successive transitions from normal Newtonian linear shear profiles to wall-slip dominant shear profiles and, finally, to shear-banding profiles at high Wi. To investigate the microscopic origin of the observed shear banding, we study the dynamics of micron-sized tracers embedded in DNA solutions. Surprisingly, tracer particles in the shear frame exhibit transient superdiffusivity and strong dynamic heterogeneity. The probability distribution functions of particle displacements follow a power-law scaling at large displacements, indicating a Lévy-walk-type motion, reminiscent of tracer dynamics in entangled wormlike micelle solutions and sheared colloidal glasses. We further characterize the length and time scales associated with the abnormal dynamics of tracer particles. We hypothesize that the unusual particle dynamics arise from localized shear-induced chain disentanglement.

  3. Composite Interlaminar Shear Fracture Toughness, G(sub 2c): Shear Measurement of Sheer Myth?

    NASA Technical Reports Server (NTRS)

    OBrien, T. Kevin

    1997-01-01

    The concept of G2c as a measure of the interlaminar shear fracture toughness of a composite material is critically examined. In particular, it is argued that the apparent G2c as typically measured is inconsistent with the original definition of shear fracture. It is shown that interlaminar shear failure actually consists of tension failures in the resin rich layers between plies followed by the coalescence of ligaments created by these failures and not the sliding of two planes relative to one another that is assumed in fracture mechanics theory. Several strain energy release rate solutions are reviewed for delamination in composite laminates and structural components where failures have been experimentally documented. Failures typically occur at a location where the mode 1 component accounts for at least one half of the total G at failure. Hence, it is the mode I and mixed-mode interlaminar fracture toughness data that will be most useful in predicting delamination failure in composite components in service. Although apparent G2c measurements may prove useful for completeness of generating mixed-mode criteria, the accuracy of these measurements may have very little influence on the prediction of mixed-mode failures in most structural components.

  4. Highly elastic polymer solutions under shear: Polymer migration, viscoelastic instabilities, and anomalous rheology

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    MacDonald, M.J.; Muller, S.J.

    1996-12-31

    The use of highly elastic polymer solutions has been remarkably successful in elucidating the behavior of polymeric materials under flowing conditions. Here, we present the results of an extensive experimental study into the shear behavior of an athermal, dilute, binary polymer solution that is believed to be free of many of these effects. Under extended shearing, we observe the migration of polymer species: after shearing for several hundred hours, concentrations that are more than double the initial uniform value can be achieved. Although the solutions are well-described by dumbbell models in shear flows on short-time scales, theoretical predictions substantially underestimatemore » the rate of migration. Flow visualization and rheometric experiments suggest that the origin of this discrepancy could be the anomalous long-time rheology of these solutions. While these fluids display the well-known elastic instability in cone and plate flow above a critical Deborah number, extended shearing reveals that the toroidal secondary flow is eventually replaced by a purely azimuthal shearing flow. In addition, when sheared below the critical condition for the instability, the solutions exhibit a slow but reversible decay in normal stresses. The shear-induced migration of polymer species has been predicted by numerous theoretical studies. However, observations on the highly elastic polymer solutions that are most likely to show polymer migration, are complicated by a number of different physical processes that occur as a result of shearing. These phenomena, which include shear-induced phase separation, elastically-induced hydrodynamic instabilities, mixed solvent effects, shear-induced aggregation, and anomalous transient shear and normal stress behavior are often observed at times earlier than and at shear rates less than those where migration is predicted to occur; hence, the experimental detection of polymer migration has been thwarted by these other physical processes.« less

  5. Development of Wearable Sheet-Type Shear Force Sensor and Measurement System that is Insusceptible to Temperature and Pressure.

    PubMed

    Toyama, Shigeru; Tanaka, Yasuhiro; Shirogane, Satoshi; Nakamura, Takashi; Umino, Tokio; Uehara, Ryo; Okamoto, Takuma; Igarashi, Hiroshi

    2017-07-31

    A sheet-type shear force sensor and a measurement system for the sensor were developed. The sensor has an original structure where a liquid electrolyte is filled in a space composed of two electrode-patterned polymer films and an elastic rubber ring. When a shear force is applied on the surface of the sensor, the two electrode-patterned films mutually move so that the distance between the internal electrodes of the sensor changes, resulting in current increase or decrease between the electrodes. Therefore, the shear force can be calculated by monitoring the current between the electrodes. Moreover, it is possible to measure two-dimensional shear force given that the sensor has multiple electrodes. The diameter and thickness of the sensor head were 10 mm and 0.7 mm, respectively. Additionally, we also developed a measurement system that drives the sensor, corrects the baseline of the raw sensor output, displays data, and stores data as a computer file. Though the raw sensor output was considerably affected by the surrounding temperature, the influence of temperature was drastically decreased by introducing a simple arithmetical calculation. Moreover, the influence of pressure simultaneously decreased after the same calculation process. A demonstrative measurement using the sensor revealed the practical usefulness for on-site monitoring.

  6. A model for longitudinal and shear wave propagation in viscoelastic media

    PubMed

    Szabo; Wu

    2000-05-01

    Relaxation models fail to predict and explain loss characteristics of many viscoelastic materials which follow a frequency power law. A model based on a time-domain statement of causality is presented that describes observed power-law behavior of many viscoelastic materials. A Hooke's law is derived from power-law loss characteristics; it reduces to the Hooke's law for the Voigt model for the specific case of quadratic frequency loss. Broadband loss and velocity data for both longitudinal and shear elastic types of waves agree well with predictions. These acoustic loss models are compared to theories for loss mechanisms in dielectrics based on isolated polar molecules and cooperative interactions.

  7. Behaviour of steel-concrete composite beams using bolts as shear connectors

    NASA Astrophysics Data System (ADS)

    Tran, Minh-Tung; Nguyen Van Do, Vuong; Nguyen, Tuan-Anh

    2018-04-01

    The paper presents an experimental program on the application of bolts as shear connectors for steel-composite beams. Four steel- concrete composite beams and a reference steel beam were made and tested. The aim of the testing program is to examine which forms of the steel bolts can be used effectively for steel-composite beams. The four types of the bolts include: Type 1 the bolt with the nut at the end; Type 2 the bolt bending at 900 hook; Type 3 the bolt without the nut at the end and Type 4 the bolt with the nut at the end but connected with the steel beam by hand welding in other to be connected with the steel beam by bolt connection as in the first three types. The test results showed that beside the traditional shear connectors like shear studs, angle type, channel type, bolts can be used effectively as the shear connectors in steel-composite beams and the application of bolts in Types 1 and 2 in the composite beams gave the better performance for the tested beam.

  8. Periodic Viscous Shear Heating Instability in Fine-Grained Shear Zones: Mechanism for Intermediate Depth Earthquakes

    NASA Astrophysics Data System (ADS)

    Coon, E.; Kelemen, P.; Hirth, G.; Spiegelman, M.

    2005-12-01

    initial T of 600 to 850 C, this produced periodic viscous shear heating events with periods of 100's to 1000's of years. Strain rates during these events approach 1 per second as temperatures reach 1400. Cooling between events returns the shear zone almost to its initial temperature, though ultimately shear zone temperature between events exceeds 850 C resulting in stable viscous creep. Analysis shows that our system of equations jumps from one steady state to another, depending on a non-dimensional number relating the rate of shear heating to the rate of diffusive cooling. This year, Kelemen and Hirth show that the rate of stress drop during shear heating events is greater than the rate of elastic stress relaxation, so that shear heating events are a runaway instability. Rather than capping the temperature at 1400 C, we parameterize melt fraction as a function of T, and shear viscosity as a function of melt fraction. A problem with our 1D model is that predicted displacements are too large (1 to 20 m) during shear heating events, essentially because there is no resistance at shear zone ends. To address this, Coon and Spiegelman have embarked on a 3D model, incorporating a pre-existing fine-grained, tabular shear zone of finite extent, with a visco-elastic rheology for both shear zone and wall rocks. Preliminary 1D models using this approach show that the more complicated rheology yields the same result as the simpler model. We will present preliminary results, and determine the Maxwell time for this problem, since low strain rates could produce viscous relaxation in both shear zone and wall rocks with negligible shear heating.

  9. Parametric Study of Shear Strength of Concrete Beams Reinforced with FRP Bars

    NASA Astrophysics Data System (ADS)

    Thomas, Job; Ramadass, S.

    2016-09-01

    Fibre Reinforced Polymer (FRP) bars are being widely used as internal reinforcement in structural elements in the last decade. The corrosion resistance of FRP bars qualifies its use in severe and marine exposure conditions in structures. A total of eight concrete beams longitudinally reinforced with FRP bars were cast and tested over shear span to depth ratio of 0.5 and 1.75. The shear strength test data of 188 beams published in various literatures were also used. The model originally proposed by Indian Standard Code of practice for the prediction of shear strength of concrete beams reinforced with steel bars IS:456 (Plain and reinforced concrete, code of practice, fourth revision. Bureau of Indian Standards, New Delhi, 2000) is considered and a modification to account for the influence of the FRP bars is proposed based on regression analysis. Out of the 196 test data, 110 test data is used for the regression analysis and 86 test data is used for the validation of the model. In addition, the shear strength of 86 test data accounted for the validation is assessed using eleven models proposed by various researchers. The proposed model accounts for compressive strength of concrete ( f ck ), modulus of elasticity of FRP rebar ( E f ), longitudinal reinforcement ratio ( ρ f ), shear span to depth ratio ( a/ d) and size effect of beams. The predicted shear strength of beams using the proposed model and 11 models proposed by other researchers is compared with the corresponding experimental results. The mean of predicted shear strength to the experimental shear strength for the 86 beams accounted for the validation of the proposed model is found to be 0.93. The result of the statistical analysis indicates that the prediction based on the proposed model corroborates with the corresponding experimental data.

  10. Shear Model Development of Limestone Joints with Incorporating Variations of Basic Friction Coefficient and Roughness Components During Shearing

    NASA Astrophysics Data System (ADS)

    Mehrishal, Seyedahmad; Sharifzadeh, Mostafa; Shahriar, Korosh; Song, Jae-Jon

    2017-04-01

    In relation to the shearing of rock joints, the precise and continuous evaluation of asperity interlocking, dilation, and basic friction properties has been the most important task in the modeling of shear strength. In this paper, in order to investigate these controlling factors, two types of limestone joint samples were prepared and CNL direct shear tests were performed on these joints under various shear conditions. One set of samples were travertine and another were onyx marble with slickensided surfaces, surfaces ground to #80, and rough surfaces were tested. Direct shear experiments conducted on slickensided and ground surfaces of limestone indicated that by increasing the applied normal stress, under different shearing rates, the basic friction coefficient decreased. Moreover, in the shear tests under constant normal stress and shearing rate, the basic friction coefficient remained constant for the different contact sizes. The second series of direct shear experiments in this research was conducted on tension joint samples to evaluate the effect of surface roughness on the shear behavior of the rough joints. This paper deals with the dilation and roughness interlocking using a method that characterizes the surface roughness of the joint based on a fundamental combined surface roughness concept. The application of stress-dependent basic friction and quantitative roughness parameters in the continuous modeling of the shear behavior of rock joints is an important aspect of this research.

  11. Dynamics of Sheared Granular Materials

    NASA Technical Reports Server (NTRS)

    Kondic, Lou; Utter, Brian; Behringer, Robert P.

    2002-01-01

    characterize the transition region in an earth-bound experiment. In the DE modeling, we analyze dynamics of a sheared granular system in Couette geometry in two (2D) and three (3D) space dimensions. Here, the idea is to both better understand what we might encounter in a reduced-g environment, and at a deeper level to deduce the physics of sheared systems in a density regime that has not been addressed by past experiments or simulations. One aspect of the simulations addresses sheared 2D system in zero-g environment. For low volume fractions, the expected dynamics of this type of system is relatively well understood. However, as the volume fraction is increased, the system undergoes a phase transition, as explained above. The DES concentrate on the evolution of the system as the solid volume fraction is slowly increased, and in particular on the behavior of very dense systems. For these configurations, the simulations show that polydispersity of the sheared particles is a crucial factor that determines the system response. Figures 1 and 2 below, that present the total force on each grain, show that even relatively small (10 %) nonuniformity of the size of the grains (expected in typical experiments) may lead to significant modifications of the system properties, such as velocity profiles, temperature, force propagation, and formation shear bands. The simulations are extended in a few other directions, in order to provide additional insight to the experimental system analyzed above. In one direction, both gravity, and driving due to vibrations are included. These simulations allow for predictions on the driving regime that is required in the experiments in order to analyze the jamming transition. Furthermore, direct comparison of experiments and DES will allow for verification of the modeling assumptions. We have also extended our modeling efforts to 3D. The (preliminary) results of these simulations of an annular system in zero-g environment will conclude the presentation.

  12. Shear zones of the Verkhoyansk fold-and-thrust belt, Northeast Russia

    NASA Astrophysics Data System (ADS)

    Fridovsky, Valery; Polufuntikova, Lena

    2017-04-01

    The Verkhoyansk fold-and-thrust belt is situated on the submerged eastern margin of the North Asian craton, and is largely composed of the Ediacaran - Middle Paleozoic carbonate and the Upper Paleozoic-Mesozoic terrigenous rocks. The Upper Carboniferous - Jurassic sediments constitute the Verkhoyansk terrigenous complex containing economically viable orogenic gold deposits. The structure of the belt is mainly controlled by thrusts and associated diagonal strike slips. Linear concentric folds are common all over the area of the belt. Shear zones with associated similar folds are confined to long narrow areas. Shear zones were formed during the early stages of the Oxfordian-Kimmeridgian collisional and accretionary events prior to the emplacement of large orogenic granitoid plutons. The main ore-controlling structures are shear zones associated with slaty cleavage, shear folds, mullion- and boudinage-structures, and transposition features. The shear zones are listric-type, and represent branches of a detachment structure, which is assumed to be present at the base of the Verkhoyansk fold-and-thrust belt. A vertical zonation of shear zones is correlated with the distance to the detachment. Changes in the dip angle of the shear zones (as indicated mainly by cleavage), structural paragenesis, the degree of microdeformation of the host rocks, and the type of ore-controlling structures can be clearly observed in the direction away from the detachment. Structural zoning is evidenced, among other things, by changing morphologic types of microstructures and by strain-indicators of the degree of rock metamorphism. Four morphologic types of microstructures are identified. The first platy-shear type is characterized by aggregate cleavage and the coefficient of deformation (Cd) of single grains from 1.0 to 2.0. Irregular angular fragments of variously oriented grains can be observed in thin sections. The second shear-cataclastic morphologic type (Cd from 2.0 to 3.0) exhibits

  13. Surface temperatures and glassy state investigations in tribology, part 3. [limiting shear stress rheological model

    NASA Technical Reports Server (NTRS)

    Bair, S.; Winer, W. O.

    1980-01-01

    Research related to the development of the limiting shear stress rheological model is reported. Techniques were developed for subjecting lubricants to isothermal compression in order to obtain relevant determinations of the limiting shear stress and elastic shear modulus. The isothermal compression limiting shear stress was found to predict very well the maximum traction for a given lubricant. Small amounts of side slip and twist incorporated in the model were shown to have great influence on the rising portion of the traction curve at low slide-roll ratio. The shear rheological model was also applied to a Grubin-like elastohydrodynamic inlet analysis for predicting film thicknesses when employing the limiting shear stress model material behavior.

  14. Shear Elasticity and Shear Viscosity Imaging in Soft Tissue

    NASA Astrophysics Data System (ADS)

    Yang, Yiqun

    In this thesis, a new approach is introduced that provides estimates of shear elasticity and shear viscosity using time-domain measurements of shear waves in viscoelastic media. Simulations of shear wave particle displacements induced by an acoustic radiation force are accelerated significantly by a GPU. The acoustic radiation force is first calculated using the fast near field method (FNM) and the angular spectrum approach (ASA). The shear waves induced by the acoustic radiation force are then simulated in elastic and viscoelastic media using Green's functions. A parallel algorithm is developed to perform these calculations on a GPU, where the shear wave particle displacements at different observation points are calculated in parallel. The resulting speed increase enables rapid evaluation of shear waves at discrete points, in 2D planes, and for push beams with different spatial samplings and for different values of the f-number (f/#). The results of these simulations show that push beams with smaller f/# require a higher spatial sampling rate. The significant amount of acceleration achieved by this approach suggests that shear wave simulations with the Green's function approach are ideally suited for high-performance GPUs. Shear wave elasticity imaging determines the mechanical parameters of soft tissue by analyzing measured shear waves induced by an acoustic radiation force. To estimate the shear elasticity value, the widely used time-of-flight method calculates the correlation between shear wave particle velocities at adjacent lateral observation points. Although this method provides accurate estimates of the shear elasticity in purely elastic media, our experience suggests that the time-of-flight (TOF) method consistently overestimates the shear elasticity values in viscoelastic media because the combined effects of diffraction, attenuation, and dispersion are not considered. To address this problem, we have developed an approach that directly accounts for all

  15. Behavior of Tilted Angle Shear Connectors

    PubMed Central

    Khorramian, Koosha; Maleki, Shervin; Shariati, Mahdi; Ramli Sulong, N. H.

    2015-01-01

    According to recent researches, angle shear connectors are appropriate to transfer longitudinal shear forces across the steel-concrete interface. Angle steel profile has been used in different positions as L-shaped or C-shaped shear connectors. The application of angle shear connectors in tilted positions is of interest in this study. This study investigates the behaviour of tilted-shaped angle shear connectors under monotonic loading using experimental push out tests. Eight push-out specimens are tested to investigate the effects of different angle parameters on the ultimate load capacity of connectors. Two different tilted angles of 112.5 and 135 degrees between the angle leg and steel beam are considered. In addition, angle sizes and lengths are varied. Two different failure modes were observed consisting of concrete crushing-splitting and connector fracture. By increasing the size of connector, the maximum load increased for most cases. In general, the 135 degrees tilted angle shear connectors have a higher strength and stiffness than the 112.5 degrees type. PMID:26642193

  16. Application Of A New Semi-Empirical Model For Forming Limit Prediction Of Sheet Material Including Superposed Loads Of Bending And Shearing

    NASA Astrophysics Data System (ADS)

    Held, Christian; Liewald, Mathias; Schleich, Ralf; Sindel, Manfred

    2010-06-01

    The use of lightweight materials offers substantial strength and weight advantages in car body design. Unfortunately such kinds of sheet material are more susceptible to wrinkling, spring back and fracture during press shop operations. For characterization of capability of sheet material dedicated to deep drawing processes in the automotive industry, mainly Forming Limit Diagrams (FLD) are used. However, new investigations at the Institute for Metal Forming Technology have shown that High Strength Steel Sheet Material and Aluminum Alloys show increased formability in case of bending loads are superposed to stretching loads. Likewise, by superposing shearing on in plane uniaxial or biaxial tension formability changes because of materials crystallographic texture. Such mixed stress and strain conditions including bending and shearing effects can occur in deep-drawing processes of complex car body parts as well as subsequent forming operations like flanging. But changes in formability cannot be described by using the conventional FLC. Hence, for purpose of improvement of failure prediction in numerical simulation codes significant failure criteria for these strain conditions are missing. Considering such aspects in defining suitable failure criteria which is easy to implement into FEA a new semi-empirical model has been developed considering the effect of bending and shearing in sheet metals formability. This failure criterion consists of the combination of the so called cFLC (combined Forming Limit Curve), which considers superposed bending load conditions and the SFLC (Shear Forming Limit Curve), which again includes the effect of shearing on sheet metal's formability.

  17. Real time shear wave elastography in chronic liver diseases: Accuracy for predicting liver fibrosis, in comparison with serum markers

    PubMed Central

    Jeong, Jae Yoon; Kim, Tae Yeob; Sohn, Joo Hyun; Kim, Yongsoo; Jeong, Woo Kyoung; Oh, Young-Ha; Yoo, Kyo-Sang

    2014-01-01

    AIM: To evaluate the correlation between liver stiffness measurement (LSM) by real-time shear wave elastography (SWE) and liver fibrosis stage and the accuracy of LSM for predicting significant and advanced fibrosis, in comparison with serum markers. METHODS: We consecutively analyzed 70 patients with various chronic liver diseases. Liver fibrosis was staged from F0 to F4 according to the Batts and Ludwig scoring system. Significant and advanced fibrosis was defined as stage F ≥ 2 and F ≥ 3, respectively. The accuracy of prediction for fibrosis was analyzed using receiver operating characteristic curves. RESULTS: Seventy patients, 15 were belonged to F0-F1 stage, 20 F2, 13 F3 and 22 F4. LSM was increased with progression of fibrosis stage (F0-F1: 6.77 ± 1.72, F2: 9.98 ± 3.99, F3: 15.80 ± 7.73, and F4: 22.09 ± 10.09, P < 0.001). Diagnostic accuracies of LSM for prediction of F ≥ 2 and F ≥ 3 were 0.915 (95%CI: 0.824-0.968, P < 0.001) and 0.913 (95%CI: 0.821-0.967, P < 0.001), respectively. The cut-off values of LSM for prediction of F ≥ 2 and F ≥ 3 were 8.6 kPa with 78.2% sensitivity and 93.3% specificity and 10.46 kPa with 88.6% sensitivity and 80.0% specificity, respectively. However, there were no significant differences between LSM and serum hyaluronic acid and type IV collagen in diagnostic accuracy. CONCLUSION: SWE showed a significant correlation with the severity of liver fibrosis and was useful and accurate to predict significant and advanced fibrosis, comparable with serum markers. PMID:25320528

  18. Real time shear wave elastography in chronic liver diseases: accuracy for predicting liver fibrosis, in comparison with serum markers.

    PubMed

    Jeong, Jae Yoon; Kim, Tae Yeob; Sohn, Joo Hyun; Kim, Yongsoo; Jeong, Woo Kyoung; Oh, Young-Ha; Yoo, Kyo-Sang

    2014-10-14

    To evaluate the correlation between liver stiffness measurement (LSM) by real-time shear wave elastography (SWE) and liver fibrosis stage and the accuracy of LSM for predicting significant and advanced fibrosis, in comparison with serum markers. We consecutively analyzed 70 patients with various chronic liver diseases. Liver fibrosis was staged from F0 to F4 according to the Batts and Ludwig scoring system. Significant and advanced fibrosis was defined as stage F ≥ 2 and F ≥ 3, respectively. The accuracy of prediction for fibrosis was analyzed using receiver operating characteristic curves. Seventy patients, 15 were belonged to F0-F1 stage, 20 F2, 13 F3 and 22 F4. LSM was increased with progression of fibrosis stage (F0-F1: 6.77 ± 1.72, F2: 9.98 ± 3.99, F3: 15.80 ± 7.73, and F4: 22.09 ± 10.09, P < 0.001). Diagnostic accuracies of LSM for prediction of F ≥ 2 and F ≥ 3 were 0.915 (95%CI: 0.824-0.968, P < 0.001) and 0.913 (95%CI: 0.821-0.967, P < 0.001), respectively. The cut-off values of LSM for prediction of F ≥ 2 and F ≥ 3 were 8.6 kPa with 78.2% sensitivity and 93.3% specificity and 10.46 kPa with 88.6% sensitivity and 80.0% specificity, respectively. However, there were no significant differences between LSM and serum hyaluronic acid and type IV collagen in diagnostic accuracy. SWE showed a significant correlation with the severity of liver fibrosis and was useful and accurate to predict significant and advanced fibrosis, comparable with serum markers.

  19. Turbulent diffusion with memories and intrinsic shear

    NASA Technical Reports Server (NTRS)

    Tchen, C. M.

    1974-01-01

    The first part of the present theory is devoted to the derivation of a Fokker-Planck equation. The eddies smaller than the hydrodynamic scale of the diffusion cloud form a diffusivity, while the inhomogeneous, bigger eddies give rise to a nonuniform migratory drift. This introduces an eddy-induced shear which reflects on the large-scale diffusion. The eddy-induced shear does not require the presence of a permanent wind shear and is intrinsic to the diffusion. Secondly, a transport theory of diffusivity is developed by the method of repeated-cascade and is based upon a relaxation of a chain of memories with decreasing information. The full range of diffusion consists of inertia, composite, and shear subranges, for which variance and eddy diffusivities are predicted. The coefficients are evaluated. Comparison with experiments in the upper atmosphere and oceans is made.

  20. Comparative evaluation of compressive strength, diametral tensile strength and shear bond strength of GIC type IX, chlorhexidine-incorporated GIC and triclosan-incorporated GIC: An in vitro study.

    PubMed

    Jaidka, Shipra; Somani, Rani; Singh, Deepti J; Shafat, Shazia

    2016-04-01

    To comparatively evaluate the compressive strength, diametral tensile strength, and shear bond strength of glass ionomer cement type IX, chlorhexidine-incorporated glass ionomer cement, and triclosan-incorporated glass ionomer cement. In this study, glass ionomer cement type IX was used as a control. Chlorhexidine diacetate, and triclosan were added to glass ionomer cement type IX powder, respectively, in order to obtain 0.5, 1.25, and 2.5% concentrations of the respective experimental groups. Compressive strength, diametral tensile strength, and shear bond strength were evaluated after 24 h using Instron Universal Testing Machine. The results obtained were statistically analyzed using the independent t-test, Dunnett test, and Tukey test. There was no statistical difference in the compressive strength, diametral tensile strength, and shear bond strength of glass ionomer cement type IX (control), 0.5% triclosan-glass ionomer cement, and 0.5% chlorhexidine-glass ionomer cement. The present study suggests that the compressive strength, diametral tensile strength, and shear bond strength of 0.5% triclosan-glass ionomer cement and 0.5% chlorhexidine-glass ionomer cement were similar to those of the glass ionomer cement type IX, discernibly signifying that these can be considered as viable options for use in pediatric dentistry with the additional value of antimicrobial property along with physical properties within the higher acceptable range.

  1. Method for shearing spent nuclear fuel assemblies

    DOEpatents

    Weil, Bradley S.; Watson, Clyde D.

    1977-01-01

    A method is disclosed for shearing spent nuclear fuel assemblies of the type wherein a plurality of long metal tubes packed with ceramic fuel are supported in a spaced apart relationship within an outer metal shell or shroud which provides structural support to the assembly. Spent nuclear fuel assemblies are first compacted in a stepwise manner between specially designed gag-compactors and then sheared into short segments amenable to chemical processing by shear blades contoured to mate with the compacted surface of the fuel assembly.

  2. Free turbulent shear flows. Volume 2: Summary of data

    NASA Technical Reports Server (NTRS)

    Birch, S. F.

    1973-01-01

    The proceedings of a conference on free turbulent shear flows are presented. Objectives of the conference are as follows: (1) collect and process data for a variety of free mixing problems, (2) assess present theoretical capability for predicting mean velocity, concentration, and temperature distributions in free turbulent flows, (3) identify and recommend experimental studies to advance knowledge of free shear flows, and (4) increase understanding of basic turbulent mixing process for application to free shear flows. Examples of specific cases of jet flow are included.

  3. Nonlinear modeling of wave-topography interactions, shear instabilities and shear induced wave breaking using vortex method

    NASA Astrophysics Data System (ADS)

    Guha, Anirban

    2017-11-01

    Theoretical studies on linear shear instabilities as well as different kinds of wave interactions often use simple velocity and/or density profiles (e.g. constant, piecewise) for obtaining good qualitative and quantitative predictions of the initial disturbances. Moreover, such simple profiles provide a minimal model to obtain a mechanistic understanding of shear instabilities. Here we have extended this minimal paradigm into nonlinear domain using vortex method. Making use of unsteady Bernoulli's equation in presence of linear shear, and extending Birkhoff-Rott equation to multiple interfaces, we have numerically simulated the interaction between multiple fully nonlinear waves. This methodology is quite general, and has allowed us to simulate diverse problems that can be essentially reduced to the minimal system with interacting waves, e.g. spilling and plunging breakers, stratified shear instabilities (Holmboe, Taylor-Caulfield, stratified Rayleigh), jet flows, and even wave-topography interaction problem like Bragg resonance. We found that the minimal models capture key nonlinear features (e.g. wave breaking features like cusp formation and roll-ups) which are observed in experiments and/or extensive simulations with smooth, realistic profiles.

  4. Steel Shear Walls, Behavior, Modeling and Design

    NASA Astrophysics Data System (ADS)

    Astaneh-Asl, Abolhassan

    2008-07-01

    In recent years steel shear walls have become one of the more efficient lateral load resisting systems in tall buildings. The basic steel shear wall system consists of a steel plate welded to boundary steel columns and boundary steel beams. In some cases the boundary columns have been concrete-filled steel tubes. Seismic behavior of steel shear wall systems during actual earthquakes and based on laboratory cyclic tests indicates that the systems are quite ductile and can be designed in an economical way to have sufficient stiffness, strength, ductility and energy dissipation capacity to resist seismic effects of strong earthquakes. This paper, after summarizing the past research, presents the results of two tests of an innovative steel shear wall system where the boundary elements are concrete-filled tubes. Then, a review of currently available analytical models of steel shear walls is provided with a discussion of capabilities and limitations of each model. We have observed that the tension only "strip model", forming the basis of the current AISC seismic design provisions for steel shear walls, is not capable of predicting the behavior of steel shear walls with length-to-thickness ratio less than about 600 which is the range most common in buildings. The main reasons for such shortcomings of the AISC seismic design provisions for steel shear walls is that it ignores the compression field in the shear walls, which can be significant in typical shear walls. The AISC method also is not capable of incorporating stresses in the shear wall due to overturning moments. A more rational seismic design procedure for design of shear walls proposed in 2000 by the author is summarized in the paper. The design method, based on procedures used for design of steel plate girders, takes into account both tension and compression stress fields and is applicable to all values of length-to-thickness ratios of steel shear walls. The method is also capable of including the effect of

  5. Shear thinning of the Lennard-Jones fluid by molecular dynamics

    NASA Astrophysics Data System (ADS)

    Heyes, David M.

    1985-11-01

    Extensive Molecular Dynamics, MD, calculations of the Lennard-Jones, LJ, rheological equation of state have been made. Non-equilibrium MD permits evaluation of shear thinning of the dense LJ liquid which adheres in behaviour quite closely with that of more complex “real molecules”. However, quantitative correspondence with simple analytic formulae for non-Newtonian behaviour used in the treatment of experimental data is hindered by poor prediction of certain key parameters. For example, at low shear rates, the equilibrium Newtonian viscosity and, at high shear rates, a limiting shear stress are often required. Both are difficult to obtain by simulation in the portion of the LJ phase diagram which exhibits significant shear thinning and using present techniques. Suggestions for improving the Eyring model for shear thinning are made.

  6. Focusing of Shear Shock Waves

    NASA Astrophysics Data System (ADS)

    Giammarinaro, Bruno; Espíndola, David; Coulouvrat, François; Pinton, Gianmarco

    2018-01-01

    Focusing is a ubiquitous way to transform waves. Recently, a new type of shock wave has been observed experimentally with high-frame-rate ultrasound: shear shock waves in soft solids. These strongly nonlinear waves are characterized by a high Mach number, because the shear wave velocity is much slower, by 3 orders of magnitude, than the longitudinal wave velocity. Furthermore, these waves have a unique cubic nonlinearity which generates only odd harmonics. Unlike longitudinal waves for which only compressional shocks are possible, shear waves exhibit cubic nonlinearities which can generate positive and negative shocks. Here we present the experimental observation of shear shock wave focusing, generated by the vertical motion of a solid cylinder section embedded in a soft gelatin-graphite phantom to induce linearly vertically polarized motion. Raw ultrasound data from high-frame-rate (7692 images per second) acquisitions in combination with algorithms that are tuned to detect small displacements (approximately 1 μ m ) are used to generate quantitative movies of gel motion. The features of shear shock wave focusing are analyzed by comparing experimental observations with numerical simulations of a retarded-time elastodynamic equation with cubic nonlinearities and empirical attenuation laws for soft solids.

  7. Effects of Fluid Shear Stress on Cancer Stem Cell Viability

    NASA Astrophysics Data System (ADS)

    Sunday, Brittney; Triantafillu, Ursula; Domier, Ria; Kim, Yonghyun

    2014-11-01

    Cancer stem cells (CSCs), which are believed to be the source of tumor formation, are exposed to fluid shear stress as a result of blood flow within the blood vessels. It was theorized that CSCs would be less susceptible to cell death than non-CSCs after both types of cell were exposed to a fluid shear stress, and that higher levels of fluid shear stress would result in lower levels of cell viability for both cell types. To test this hypothesis, U87 glioblastoma cells were cultured adherently (containing smaller populations of CSCs) and spherically (containing larger populations of CSCs). They were exposed to fluid shear stress in a simulated blood flow through a 125-micrometer diameter polyetheretherketone (PEEK) tubing using a syringe pump. After exposure, cell viability data was collected using a BioRad TC20 Automated Cell Counter. Each cell type was tested at three physiological shear stress values: 5, 20, and 60 dynes per centimeter squared. In general, it was found that the CSC-enriched U87 sphere cells had higher cell viability than the CSC-depleted U87 adherent cancer cells. Interestingly, it was also observed that the cell viability was not negatively affected by the higher fluid shear stress values in the tested range. In future follow-up studies, higher shear stresses will be tested. Furthermore, CSCs from different tumor origins (e.g. breast tumor, prostate tumor) will be tested to determine cell-specific shear sensitivity. National Science Foundation Grant #1358991 supported the first author as an REU student.

  8. Rock physics model-based prediction of shear wave velocity in the Barnett Shale formation

    NASA Astrophysics Data System (ADS)

    Guo, Zhiqi; Li, Xiang-Yang

    2015-06-01

    Predicting S-wave velocity is important for reservoir characterization and fluid identification in unconventional resources. A rock physics model-based method is developed for estimating pore aspect ratio and predicting shear wave velocity Vs from the information of P-wave velocity, porosity and mineralogy in a borehole. Statistical distribution of pore geometry is considered in the rock physics models. In the application to the Barnett formation, we compare the high frequency self-consistent approximation (SCA) method that corresponds to isolated pore spaces, and the low frequency SCA-Gassmann method that describes well-connected pore spaces. Inversion results indicate that compared to the surroundings, the Barnett Shale shows less fluctuation in the pore aspect ratio in spite of complex constituents in the shale. The high frequency method provides a more robust and accurate prediction of Vs for all the three intervals in the Barnett formation, while the low frequency method collapses for the Barnett Shale interval. Possible causes for this discrepancy can be explained by the fact that poor in situ pore connectivity and low permeability make well-log sonic frequencies act as high frequencies and thus invalidate the low frequency assumption of the Gassmann theory. In comparison, for the overlying Marble Falls and underlying Ellenburger carbonates, both the high and low frequency methods predict Vs with reasonable accuracy, which may reveal that sonic frequencies are within the transition frequencies zone due to higher pore connectivity in the surroundings.

  9. Estimates of the low-level wind shear and turbulence in the vicinity of Kennedy International Airport on 24 June 1975

    NASA Technical Reports Server (NTRS)

    Lewellen, W. S.; Williamson, G. G.

    1976-01-01

    A study was conducted to estimate the type of wind and turbulence distributions which may have existed at the time of the crash of Eastern Airlines Flight 66 while attempting to land. A number of different wind and turbulence profiles are predicted for the site and date of the crash. The morning and mid-afternoon predictions are in reasonably good agreement with magnitude and direction as reported by the weather observer. Although precise predictions cannot be made during the passage of the thunderstorm which coincides with the time of the accident, a number of different profiles which might exist under or in the vicinity of a thunderstorm are presented. The profile that is most probable predicts the mean headwind shear over 100 m (300 feet) altitude change and the average fluctuations about the mean headwind distribution. This combination of means and fluctuations leads to a reasonable probability that the instantaneous headwind shear would equal the maximum value reported in the flight recorder data.

  10. Iosipescu shear properties of graphite fabric/epoxy composite laminates

    NASA Technical Reports Server (NTRS)

    Walrath, D. E.; Adams, D. F.

    1985-01-01

    The Iosipescu shear test method is used to measure the in-plane and interlaminar shear properties of four T300 graphite fabric/934 epoxy composite materials. Different weave geometries tested include an Oxford weave, a 5-harness satin weave, an 8-harness satin weave, and a plain weave with auxiliary warp yarns. Both orthogonal and quasi-isotropic layup laminates were tested. In-plane and interlaminar shear properties are obtained for laminates of all four fabric types. Overall, little difference in shear properties attributable to the fabric weave pattern is observed. The auxiliary warp material is significantly weaker and less stiff in interlaminar shear parallel to its fill direction. A conventional strain gage extensometer is modified to measure shear strains for use with the Iosipescu shear test. While preliminary results are encouraging, several design iterations failed to produce a reliable shear transducer prototype. Strain gages are still the most reliable shear strain transducers for use with this test method.

  11. Shear transfer capacity of reinforced concrete exposed to fire

    NASA Astrophysics Data System (ADS)

    Ahmad, Subhan; Bhargava, Pradeep; Chourasia, Ajay

    2018-04-01

    Shear transfer capacity of reinforced concrete elements is a function of concrete compressive strength and reinforcement yield strength. Exposure of concrete and steel to elevated temperature reduces their mechanical properties resulting in reduced shear transfer capacity of RC elements. The objective of present study is to find the effect of elevated temperature on shear transfer capacity of reinforced concrete. For this purpose pushoff specimens were casted using normal strength concrete. After curing, specimens were heated to 250°C and 500°C in an electric furnace. Cooled specimens were tested for shear transfer capacity in a universal testing machine. It was found that shear transfer capacity and stiffness (slope of load-slip curve) were reduced when the specimens were heated to 250°C and 500°C. Load level for the initiation of crack slip was found to be decreased as the temperature was increased. A simple analytical approach is also proposed to predict the shear transfer capacity of reinforced concrete after elevated temperature.

  12. Shear-enhanced compaction in viscoplastic rocks

    NASA Astrophysics Data System (ADS)

    Yarushina, V. M.; Podladchikov, Y. Y.

    2012-04-01

    The phenomenon of mutual influence of compaction and shear deformation was repeatedly reported in the literature over the past years. Dilatancy and shear-enhanced compaction of porous rocks were experimentally observed during both rate-independent and rate-dependent inelastic deformation. Plastic pore collapse was preceding the onset of dilatancy and shear-enhanced compaction. Effective bulk viscosity is commonly used to describe compaction driven fluid flow in porous rocks. Experimental data suggest that bulk viscosity of a fluid saturated rock might be a function of both the effective pressure and the shear stress. Dilatancy and shear-enhanced compaction can alter the transport properties of rocks through their influence on permeability and compaction length scale. Recent investigations show that shear stresses in deep mantle rocks can be responsible for spontaneous development of localized melt-rich bands and segregation of small amounts of melt from the solid rock matrix through shear channeling instability. Usually it is assumed that effective viscosity is a function of porosity only. Thus coupling between compaction and shear deformation is ignored. Spherical model which considers a hollow sphere subjected to homogeneous tractions on the outer boundary as a representative elementary volume succeeded in predicting the volumetric compaction behavior of porous rocks and metals to a hydrostatic pressure in a wide range of porosities. Following the success of this simple model we propose a cylindrical model of void compaction and decompaction due to the non-hydrostatic load. The infinite viscoplastic layer with a cylindrical hole is considered as a representative volume element. The remote boundary of the volume is subjected to a homogeneous non-hydrostatic load such that plane strain conditions are fulfilled through the volume. At some critical values of remote stresses plastic zone develops around the hole. The dependence of the effective bulk viscosity on the

  13. Weakly sheared active suspensions: hydrodynamics, stability, and rheology.

    PubMed

    Cui, Zhenlu

    2011-03-01

    We present a kinetic model for flowing active suspensions and analyze the behavior of a suspension subjected to a weak steady shear. Asymptotic solutions are sought in Deborah number expansions. At the leading order, we explore the steady states and perform their stability analysis. We predict the rheology of active systems including an activity thickening or thinning behavior of the apparent viscosity and a negative apparent viscosity depending on the particle type, flow alignment, and the anchoring conditions, which can be tested on bacterial suspensions. We find remarkable dualities that show that flow-aligning rodlike contractile (extensile) particles are dynamically and rheologically equivalent to flow-aligning discoid extensile (contractile) particles for both tangential and homeotropic anchoring conditions. Another key prediction of this work is the role of the concentration of active suspensions in controlling the rheological behavior: the apparent viscosity may decrease with the increase of the concentration.

  14. Methodology for calculating shear stress in a meandering channel

    Treesearch

    Kyung-Seop Sin

    2010-01-01

    Shear stress in meandering channels is the key parameter to predict bank erosion and bend migration. A representative study reach of the Rio Grande River in central New Mexico has been modeled in the Hydraulics Laboratory at CSU. To determine the shear stress distribution in a meandering channel, the large scale (1:12) physical modeling study was conducted in the...

  15. A comparison of simple shear characterization methods for composite laminates

    NASA Technical Reports Server (NTRS)

    Yeow, Y. T.; Brinson, H. F.

    1978-01-01

    Various methods for the shear stress/strain characterization of composite laminates are examined and their advantages and limitations are briefly discussed. Experimental results and the necessary accompanying analysis are then presented and compared for three simple shear characterization procedures. These are the off-axis tensile test method, the (+/- 45 deg)s tensile test method and the (0/90 deg)s symmetric rail shear test method. It is shown that the first technique indicates the shear properties of the graphite/epoxy laminates investigated are fundamentally brittle in nature while the latter two methods tend to indicate that these laminates are fundamentally ductile in nature. Finally, predictions of incrementally determined tensile stress/strain curves utilizing the various different shear behaviour methods as input information are presented and discussed.

  16. Temperature-dependent ideal strength and stacking fault energy of fcc Ni: a first-principles study of shear deformation.

    PubMed

    Shang, S L; Wang, W Y; Wang, Y; Du, Y; Zhang, J X; Patel, A D; Liu, Z K

    2012-04-18

    Variations of energy, stress, and magnetic moment of fcc Ni as a response to shear deformation and the associated ideal shear strength (τ(IS)), intrinsic (γ(SF)) and unstable (γ(US)) stacking fault energies have been studied in terms of first-principles calculations under both the alias and affine shear regimes within the {111} slip plane along the <112> and <110> directions. It is found that (i) the intrinsic stacking fault energy γ(SF) is nearly independent of the shear deformation regimes used, albeit a slightly smaller value is predicted by pure shear (with relaxation) compared to the one from simple shear (without relaxation); (ii) the minimum ideal shear strength τ(IS) is obtained by pure alias shear of {111}<112>; and (iii) the dissociation of the 1/2[110] dislocation into two partial Shockley dislocations (1/6[211] + 1/6[121]) is observed under pure alias shear of {111}<110>. Based on the quasiharmonic approach from first-principles phonon calculations, the predicted γ(SF) has been extended to finite temperatures. In particular, using a proposed quasistatic approach on the basis of the predicted volume versus temperature relation, the temperature dependence of τ(IS) is also obtained. Both the γ(SF) and the τ(IS) of fcc Ni decrease with increasing temperature. The computed ideal shear strengths as well as the intrinsic and unstable stacking fault energies are in favorable accord with experiments and other predictions in the literature.

  17. A test of the double-shearing model of flow for granular materials

    USGS Publications Warehouse

    Savage, J.C.; Lockner, D.A.

    1997-01-01

    The double-shearing model of flow attributes plastic deformation in granular materials to cooperative slip on conjugate Coulomb shears (surfaces upon which the Coulomb yield condition is satisfied). The strict formulation of the double-shearing model then requires that the slip lines in the material coincide with the Coulomb shears. Three different experiments that approximate simple shear deformation in granular media appear to be inconsistent with this strict formulation. For example, the orientation of the principal stress axes in a layer of sand driven in steady, simple shear was measured subject to the assumption that the Coulomb failure criterion was satisfied on some surfaces (orientation unspecified) within the sand layer. The orientation of the inferred principal compressive axis was then compared with the orientations predicted by the double-shearing model. The strict formulation of the model [Spencer, 1982] predicts that the principal stress axes should rotate in a sense opposite to that inferred from the experiments. A less restrictive formulation of the double-shearing model by de Josselin de Jong [1971] does not completely specify the solution but does prescribe limits on the possible orientations of the principal stress axes. The orientations of the principal compression axis inferred from the experiments are probably within those limits. An elastoplastic formulation of the double-shearing model [de Josselin de Jong, 1988] is reasonably consistent with the experiments, although quantitative agreement was not attained. Thus we conclude that the double-shearing model may be a viable law to describe deformation of granular materials, but the macroscopic slip surfaces will not in general coincide with the Coulomb shears.

  18. Energy consumption in terms of shear stress for two types of membrane bioreactors used for municipal wastewater treatment processes

    NASA Astrophysics Data System (ADS)

    Ratkovich, Nicolas; Bentzen, Thomas R.; Rasmussen, Michael R.

    2012-10-01

    Two types of submerged membrane bioreactors (MBR): hollow fiber (HF) and hollow sheet (HS), have been studied and compared in terms of energy consumption and average shear stress over the membrane wall. The analysis of energy consumption was made using the correlation to determine the blower power and the blower power demand per unit of permeate volume. Results showed that for the system geometries considered, in terms the of the blower power, the HF MBR requires less power compared to HS MBR. However, in terms of blower power per unit of permeate volume, the HS MBR requires less energy. The analysis of shear stress over the membrane surface was made using computational fluid dynamics (CFD) modelling. Experimental measurements for the HF MBR were compared with the CFD model and an error less that 8% was obtained. For the HS MBR, experimental measurements of velocity profiles were made and an error of 11% was found. This work uses an empirical relationship to determine the shear stress based on the ratio of aeration blower power to tank volume. This relationship is used in bubble column reactors and it is extrapolate to determine shear stress on MBR systems. This relationship proved to be overestimated by 28% compared to experimental measurements and CFD results. Therefore, a corrective factor is included in the relationship in order to account for the membrane placed inside the bioreactor.

  19. Quantifying Uncertainty in Inverse Models of Geologic Data from Shear Zones

    NASA Astrophysics Data System (ADS)

    Davis, J. R.; Titus, S.

    2016-12-01

    We use Bayesian Markov chain Monte Carlo simulation to quantify uncertainty in inverse models of geologic data. Although this approach can be applied to many tectonic settings, field areas, and mathematical models, we focus on transpressional shear zones. The underlying forward model, either kinematic or dynamic, produces a velocity field, which predicts the dikes, foliation-lineations, crystallographic preferred orientation (CPO), shape preferred orientation (SPO), and other geologic data that should arise in the shear zone. These predictions are compared to data using modern methods of geometric statistics, including the Watson (for lines such as dike poles), isotropic matrix Fisher (for orientations such as foliation-lineations and CPO), and multivariate normal (for log-ellipsoids such as SPO) distributions. The result of the comparison is a likelihood, which is a key ingredient in the Bayesian approach. The other key ingredient is a prior distribution, which reflects the geologist's knowledge of the parameters before seeing the data. For some parameters, such as shear zone strike and dip, we identify realistic informative priors. For other parameters, where the geologist has no prior knowledge, we identify useful uninformative priors.We investigate the performance of this approach through numerical experiments on synthetic data sets. A fundamental issue is that many models of deformation exhibit asymptotic behavior (e.g., flow apophyses, fabric attractors) or periodic behavior (e.g., SPO when the clasts are rigid), which causes the likelihood to be too uniform. Based on our experiments, we offer rules of thumb for how many data, of which types, are needed to constrain deformation.

  20. An equilibrium method for prediction of transverse shear stresses in a thick laminated plate

    NASA Technical Reports Server (NTRS)

    Chaudhuri, R. Z.

    1986-01-01

    First two equations of equilibrium are utilized to compute the transverse shear stress variation through thickness of a thick laminated plate after in-plane stresses have been computed using an assumed quadratic displacement triangular element based on transverse inextensibility and layerwise constant shear angle theory (LCST). Centroid of the triangle is the point of exceptional accuracy for transverse shear stresses. Numerical results indicate close agreement with elasticity theory. An interesting comparison between the present theory and that based on assumed stress hybrid finite element approach suggests that the latter does not satisfy the condition of free normal traction at the edge. Comparison with numerical results obtained by using constant shear angle theory suggests that LCST is close to the elasticity solution while the CST is closer to classical (CLT) solution. It is also demonstrated that the reduced integration gives faster convergence when the present theory is applied to a thin plate.

  1. Shear wave elastography of breast cancer: Sensitivity according to histological type in a large cohort.

    PubMed

    Evans, Andrew; Sim, Yee Ting; Thomson, Kim; Jordan, Lee; Purdie, Colin; Vinnicombe, Sarah J

    2016-04-01

    To define the shear wave elastography (SWE) characteristics of breast cancer histological types by size in a large cohort. Consecutive patients with US visible masses underwent SWE. All those with confirmed invasive breast cancer were included in the study. Histologic type was ascertained from core biopsy and surgical resection specimens. For each type, mean and median values for Emean and Emax were ascertained. Commoner tumour types were further analysed by invasive size. The significance of differences was established using the Chi-square test. 1137 tumours constituted the study group. The proportion of tumours with Emean below 50 kPa was higher in tubular cancers (23%) compared to ductal carcinomas of no specific type (DNST) (6%) (p < 0.001). Emax below 80 kPa was seen in 34% of tubular cancers compared to 16% of DNST (p < 0.002). Emean and Emax for lobular, mucinous, papillary and metaplastic cancers were not different from those of DNST. There were no significant differences in Emean or Emax between tumour types once broken down according to invasive size. Most breast cancer histological types have similar SWE characteristics. The exception is tubular cancer which has significantly lower stiffness than other histologic types, accounted for largely by their small size. Copyright © 2016 Elsevier Ltd. All rights reserved.

  2. Tuning Shear Jamming by Basal Assisted Couette Shear

    NASA Astrophysics Data System (ADS)

    Zhao, Yiqiu; Barés, Jonathan; Behringer, Robert

    Granular matter with packing fraction ϕS < ϕ <ϕJ can be jammed by applying shear strain. However, the stress-strain relation in shear jamming transition is not very well understood. Part of the difficulty is that the strain inside the granular system is very complicated and hard to control. In this work, by using a novel Couette shear apparatus capable of generating arbitrary shear profiles, we study the stress-strain relation during shear jamming transition for granular system under different kinds of controlled interior strain. The novel Couette shear apparatus consists of 21 independently movable rings and two circular boundaries. The apparatus can shear the granular sample not only from the boundaries but also from the bottom. The granular sample is made of about 2000 bi-disperse photo elastic disks, making it possible to extract force information. This work is supported by NSF-DMR1206351, DMS1248071, NASA NNX15AD38G.

  3. Raman spectroscopy compared against traditional predictors of shear force in lamb m. longissimus lumborum.

    PubMed

    Fowler, Stephanie M; Schmidt, Heinar; van de Ven, Remy; Wynn, Peter; Hopkins, David L

    2014-12-01

    A Raman spectroscopic hand held device was used to predict shear force (SF) of 80 fresh lamb m. longissimus lumborum (LL) at 1 and 5days post mortem (PM). Traditional predictors of SF including sarcomere length (SL), particle size (PS), cooking loss (CL), percentage myofibrillar breaks and pH were also measured. SF values were regressed against Raman spectra using partial least squares regression and against the traditional predictors using linear regression. The best prediction of shear force values used spectra at 1day PM to predict shear force at 1day which gave a root mean square error of prediction (RMSEP) of 13.6 (Null=14.0) and the R(2) between observed and cross validated predicted values was 0.06 (R(2)cv). Overall, for fresh LL, the predictability SF, by either the Raman hand held probe or traditional predictors was low. Copyright © 2014 Elsevier Ltd. All rights reserved.

  4. Viscoelastic shear lag model to predict the micromechanical behavior of tendon under dynamic tensile loading.

    PubMed

    Wu, Jiayu; Yuan, Hong; Li, Longyuan; Fan, Kunjie; Qian, Shanguang; Li, Bing

    2018-01-21

    Owing to its viscoelastic nature, tendon exhibits stress rate-dependent breaking and stiffness function. A Kelvin-Voigt viscoelastic shear lag model is proposed to illustrate the micromechanical behavior of the tendon under dynamic tensile conditions. Theoretical closed-form expressions are derived to predict the deformation and stress transfer between fibrils and interfibrillar matrix while tendon is dynamically stretched. The results from the analytical solutions demonstrate that how the fibril overlap length and fibril volume fraction affect the stress transfer and mechanical properties of tendon. We find that the viscoelastic property of interfibrillar matrix mainly results in collagen fibril failure under fast loading rate or creep rupture of tendon. However, discontinuous fibril model and hierarchical structure of tendon ensure relative sliding under slow loading rate, helping dissipate energy and protecting fibril from damage, which may be a key reason why regularly staggering alignment microstructure is widely selected in nature. According to the growth, injury, healing and healed process of tendon observed by many researchers, the conclusions presented in this paper agrees well with the experimental findings. Additionally, the emphasis of this paper is on micromechanical behavior of tendon, whereas this analytical viscoelastic shear lag model can be equally applicable to other soft or hard tissues, owning the similar microstructure. Copyright © 2017 Elsevier Ltd. All rights reserved.

  5. Shear Lag in Box Beams Methods of Analysis and Experimental Investigations

    NASA Technical Reports Server (NTRS)

    Kuhn, Paul; Chiarito, Patrick T

    1942-01-01

    The bending stresses in the covers of box beams or wide-flange beams differ appreciably from the stresses predicted by the ordinary bending theory on account of shear deformation of the flanges. The problem of predicting these differences has become known as the shear-lag problem. The first part of this paper deals with methods of shear-lag analysis suitable for practical use. The second part of the paper describes strain-gage tests made by the NACA to verify the theory. Three tests published by other investigators are also analyzed by the proposed method. The third part of the paper gives numerical examples illustrating the methods of analysis. An appendix gives comparisons with other methods, particularly with the method of Ebner and Koller.

  6. An improved shear beam method for the characterization of bonded composite joints

    NASA Technical Reports Server (NTRS)

    Hiel, Clem C.; Brinson, Hal F.

    1989-01-01

    Closed-form analytical solutions, which govern the displacements and stresses in an adhesive shear beam, are discussed. The remarkable precision with which the shear stresses in the adhesive can be predicted forms the basis of the proposed characterization procedure. The shear modulus of the adhesive is obtained by means of a parameter estimation procedure which requires a symbiosis of theoretical and experimental stress analysis.

  7. Prediction of Mechanical Properties of Polymers With Various Force Fields

    NASA Technical Reports Server (NTRS)

    Odegard, Gregory M.; Clancy, Thomas C.; Gates, Thomas S.

    2005-01-01

    The effect of force field type on the predicted elastic properties of a polyimide is examined using a multiscale modeling technique. Molecular Dynamics simulations are used to predict the atomic structure and elastic properties of the polymer by subjecting a representative volume element of the material to bulk and shear finite deformations. The elastic properties of the polyimide are determined using three force fields: AMBER, OPLS-AA, and MM3. The predicted values of Young s modulus and shear modulus of the polyimide are compared with experimental values. The results indicate that the mechanical properties of the polyimide predicted with the OPLS-AA force field most closely matched those from experiment. The results also indicate that while the complexity of the force field does not have a significant effect on the accuracy of predicted properties, small differences in the force constants and the functional form of individual terms in the force fields determine the accuracy of the force field in predicting the elastic properties of the polyimide.

  8. A comparison of simple shear characterization methods for composite laminates

    NASA Technical Reports Server (NTRS)

    Yeow, Y. T.; Brinson, H. F.

    1977-01-01

    Various methods for the shear stress-strain characterization of composite laminates are examined, and their advantages and limitations are briefly discussed. Experimental results and the necessary accompanying analysis are then presented and compared for three simple shear characterization procedures. These are the off-axis tensile test method, the + or - 45 degs tensile test method and the 0 deg/90 degs symmetric rail shear test method. It is shown that the first technique indicates that the shear properties of the G/E laminates investigated are fundamentally brittle in nature while the latter two methods tend to indicate that the G/E laminates are fundamentally ductile in nature. Finally, predictions of incrementally determined tensile stress-strain curves utilizing the various different shear behavior methods as input information are presented and discussed.

  9. Triplet correlation in sheared suspensions of Brownian particles

    NASA Astrophysics Data System (ADS)

    Yurkovetsky, Yevgeny; Morris, Jeffrey F.

    2006-05-01

    Triplet microstructure of sheared concentrated suspensions of Brownian monodisperse spherical particles is studied by sampling realizations of a three-dimensional unit cell subject to periodic boundary conditions obtained in accelerated Stokesian dynamics simulations. Triplets are regarded as a bridge between particle pairs and many-particle clusters thought responsible for shear thickening. Triplet-correlation data for weakly sheared near-equilibrium systems display an excluded volume effect of accumulated correlation for equilateral contacting triplets. As the Péclet number increases, there is a change in the preferred contacting isosceles triplet configuration, away from the "closed" triplet where the particles lie at the vertices of an equilateral triangle and toward the fully extended rod-like linear arrangement termed the "open" triplet. This transition is most pronounced for triplets lying in the plane of shear, where the open triplets' angular orientation with respect to the flow is very similar to that of a contacting pair. The correlation of suspension rheology to observed structure signals onset of larger clusters. An investigation of the predictive ability of Kirkwood's superposition approximation (KSA) provides valuable insights into the relationship between the pair and triplet probability distributions and helps achieve a better and more detailed understanding of the interplay of the pair and triplet dynamics. The KSA is seen more successfully to predict the shape of isosceles contacting triplet nonequilibrium distributions in the plane of shear than for similar configurations in equilibrium hard-sphere systems; in the sheared case, the discrepancies in magnitudes of distribution peaks are attributable to two interaction effects when pair average trajectories and locations of particles change in response to real, or "hard," and probabilistically favored ("soft") neighboring excluded volumes and, in the case of open triplets, due to changes in the

  10. Measurements of Shear Lift Force on a Bubble in Channel Flow in Microgravity

    NASA Technical Reports Server (NTRS)

    Nahra, Henry K.; Motil, Brian J.; Skor, Mark

    2003-01-01

    Under microgravity conditions, the shear lift force acting on bubbles, droplets or solid particles in multiphase flows becomes important because under normal gravity, this hydrodynamic force is masked by buoyancy. This force plays an important role in furnishing the detachment process of bubbles in a setting where a bubble suspension is needed in microgravity. In this work, measurements of the shear lift force acting on a bubble in channel flow are performed. The shear lift force is deduced from the bubble kinematics using scaling and then compared with predictions from models in literature that address different asymptotic and numerical solutions. Basic trajectory calculations are then performed and the results are compared with experimental data of position of the bubble in the channel. A direct comparison of the lateral velocity of the bubbles is also made with the lateral velocity prediction from investigators, whose work addressed the shear lift on a sphere in different two-dimensional shear flows including Poiseuille flow.

  11. An analysis of high-impact, low-predictive skill severe weather events in the northeast U.S

    NASA Astrophysics Data System (ADS)

    Vaughan, Matthew T.

    An objective evaluation of Storm Prediction Center slight risk convective outlooks, as well as a method to identify high-impact severe weather events with poor-predictive skill are presented in this study. The objectives are to assess severe weather forecast skill over the northeast U.S. relative to the continental U.S., build a climatology of high-impact, low-predictive skill events between 1980--2013, and investigate the dynamic and thermodynamic differences between severe weather events with low-predictive skill and high-predictive skill over the northeast U.S. Severe storm reports of hail, wind, and tornadoes are used to calculate skill scores including probability of detection (POD), false alarm ratio (FAR) and threat scores (TS) for each convective outlook. Low predictive skill events are binned into low POD (type 1) and high FAR (type 2) categories to assess temporal variability of low-predictive skill events. Type 1 events were found to occur in every year of the dataset with an average of 6 events per year. Type 2 events occur less frequently and are more common in the earlier half of the study period. An event-centered composite analysis is performed on the low-predictive skill database using the National Centers for Environmental Prediction Climate Forecast System Reanalysis 0.5° gridded dataset to analyze the dynamic and thermodynamic conditions prior to high-impact severe weather events with varying predictive skill. Deep-layer vertical shear between 1000--500 hPa is found to be a significant discriminator in slight risk forecast skill where high-impact events with less than 31-kt shear have lower threat scores than high-impact events with higher shear values. Case study analysis of type 1 events suggests the environment over which severe weather occurs is characterized by high downdraft convective available potential energy, steep low-level lapse rates, and high lifting condensation level heights that contribute to an elevated risk of severe wind.

  12. Novel transformation-based response prediction of shear building using interval neural network

    NASA Astrophysics Data System (ADS)

    Chakraverty, S.; Sahoo, Deepti Moyi

    2017-04-01

    Present paper uses powerful technique of interval neural network (INN) to simulate and estimate structural response of multi-storey shear buildings subject to earthquake motion. The INN is first trained for a real earthquake data, viz., the ground acceleration as input and the numerically generated responses of different floors of multi-storey buildings as output. Till date, no model exists to handle positive and negative data in the INN. As such here, the bipolar data in [ -1, 1] are converted first to unipolar form, i.e., to [0, 1] by means of a novel transformation for the first time to handle the above training patterns in normalized form. Once the training is done, again the unipolar data are converted back to its bipolar form by using the inverse transformation. The trained INN architecture is then used to simulate and test the structural response of different floors for various intensity earthquake data and it is found that the predicted responses given by INN model are good for practical purposes.

  13. Pure shear and simple shear calcite textures. Comparison of experimental, theoretical and natural data

    USGS Publications Warehouse

    Wenk, H.-R.; Takeshita, T.; Bechler, E.; Erskine, B.G.; Matthies, S.

    1987-01-01

    The pattern of lattice preferred orientation (texture) in deformed rocks is an expression of the strain path and the acting deformation mechanisms. A first indication about the strain path is given by the symmetry of pole figures: coaxial deformation produces orthorhombic pole figures, while non-coaxial deformation yields monoclinic or triclinic pole figures. More quantitative information about the strain history can be obtained by comparing natural textures with experimental ones and with theoretical models. For this comparison, a representation in the sensitive three-dimensional orientation distribution space is extremely important and efforts are made to explain this concept. We have been investigating differences between pure shear and simple shear deformation incarbonate rocks and have found considerable agreement between textures produced in plane strain experiments and predictions based on the Taylor model. We were able to simulate the observed changes with strain history (coaxial vs non-coaxial) and the profound texture transition which occurs with increasing temperature. Two natural calcite textures were then selected which we interpreted by comparing them with the experimental and theoretical results. A marble from the Santa Rosa mylonite zone in southern California displays orthorhombic pole figures with patterns consistent with low temperature deformation in pure shear. A limestone from the Tanque Verde detachment fault in Arizona has a monoclinic fabric from which we can interpret that 60% of the deformation occurred by simple shear. ?? 1987.

  14. Wind shear over the Nice Côte d'Azur airport: case studies

    NASA Astrophysics Data System (ADS)

    Boilley, A.; Mahfouf, J.-F.

    2013-09-01

    The Nice Côte d'Azur international airport is subject to horizontal low-level wind shears. Detecting and predicting these hazards is a major concern for aircraft security. A measurement campaign took place over the Nice airport in 2009 including 4 anemometers, 1 wind lidar and 1 wind profiler. Two wind shear events were observed during this measurement campaign. Numerical simulations were carried out with Meso-NH in a configuration compatible with near-real time applications to determine the ability of the numerical model to predict these events and to study the meteorological situations generating an horizontal wind shear. A comparison between numerical simulation and the observation dataset is conducted in this paper.

  15. Wind shear over the Nice Côte d'Azur airport: case studies

    NASA Astrophysics Data System (ADS)

    Boilley, A.; Mahfouf, J.-F.

    2013-04-01

    The Nice Côte d'Azur international airport is subject to horizontal low-level wind shears. Detecting and predicting these hazards is a major concern for aircraft security. A measurement campaign took place over the Nice airport in 2009 including 4 anemometers, 1 wind lidar and 1 wind profiler. Two wind shear events were observed during this measurement campaign. Numerical simulations were carried out with Meso-NH in a configuration compatible with near-real time applications to determine the ability of the numerical model to predict these events and to study the meteorological situations generating a horizontal wind shear. A comparison between numerical simulation and the observation dataset is conducted in this paper.

  16. Shear Resistance Variations in Experimentally Sheared Mudstone Granules: A Possible Shear-Thinning and Thixotropic Mechanism

    NASA Astrophysics Data System (ADS)

    Hu, Wei; Xu, Qiang; Wang, Gonghui; Scaringi, Gianvito; Mcsaveney, Mauri; Hicher, Pierre-Yves

    2017-11-01

    We present results of ring shear frictional resistance for mudstone granules of different size obtained from a landslide shear zone. Little rate dependency of shear resistance was observed in sand-sized granules in any wet or dry test, while saturated gravel-sized granules exhibited significant and abrupt reversible rate-weakening (from μ = 0.6 to 0.05) at about 2 mm/s. Repeating resistance variations occurred also under constant shear displacement rate. Mudstone granules generate mud as they are crushed and softened. Shear-thinning and thixotropic behavior of the mud can explain the observed behavior: with the viscosity decreasing, the mud can flow through the coarser soil pores and migrate out from the shear zone. This brings new granules into contact which produces new mud. Thus, the process can start over. Similarities between experimental shear zones and those of some landslides in mudstone suggest that the observed behavior may play a role in some landslide kinematics.

  17. Buckling of pressure-loaded, long, shear deformable, cylindrical laminated shells

    NASA Astrophysics Data System (ADS)

    Anastasiadis, John S.; Simitses, George J.

    A higher-order shell theory was developed (kinematic relations, constitutive relations, equilibrium equations and boundary conditions), which includes initial geometric imperfections and transverse shear effects for a laminated cylindrical shell under the action of pressure, axial compression and in-plane shear. Through the perturbation technique, buckling equations are derived for the corresponding 'perfect geometry' symmetric laminated configuration. Critical pressures are computed for very long cylinders for several stacking sequences, several radius-to-total-thickness ratios, three lamina materials (boron/epoxy, graphite/epoxy, and Kevlar/epoxy), and three shell theories: classical, first-order shear deformable and higher- (third-)order shear deformable. The results provide valuable information concerning the applicability (accurate prediction of buckling pressures) of the various shell theories.

  18. Effect of thermal noise on vesicles and capsules in shear flow.

    PubMed

    Abreu, David; Seifert, Udo

    2012-07-01

    We add thermal noise consistently to reduced models of undeformable vesicles and capsules in shear flow and derive analytically the corresponding stochastic equations of motion. We calculate the steady-state probability distribution function and construct the corresponding phase diagrams for the different dynamical regimes. For fluid vesicles, we predict that at small shear rates thermal fluctuations induce a tumbling motion for any viscosity contrast. For elastic capsules, due to thermal mixing, an intermittent regime appears in regions where deterministic models predict only pure tank treading or tumbling.

  19. The Need for a Shear Stress Calibration Standard

    NASA Technical Reports Server (NTRS)

    Scott, Michael A.

    2004-01-01

    By surveying current research of various micro-electro mechanical systems (MEMS) shear stress sensor development efforts we illustrate the wide variety of methods used to test and characterize these sensors. The different methods of testing these sensors make comparison of results difficult in some cases, and also this comparison is further complicated by the different formats used in reporting the results of these tests. The fact that making these comparisons can be so difficult at times clearly illustrates a need for standardized testing and reporting methodologies. This need indicates that the development of a national or international standard for the calibration of MEMS shear stress sensors should be undertaken. As a first step towards the development of this standard, two types of devices are compared and contrasted. The first type device is a laminar flow channel with two different versions considered: the first built with standard manufacturing techniques and the second with advanced precision manufacturing techniques. The second type of device is a new concept for creating a known shear stress consisting of a rotating wheel with the sensor mounted tangentially to the rim and positioned in close proximity to the rim. The shear stress generated by the flow at the sensor position is simply tau = (mu)r(omega)/h, where mu is the viscosity of the ambient gas, r the wheel radius, omega the angular velocity of the wheel, and h the width of the gap between the wheel rim and the sensor. Additionally, issues related to the development of a standard for shear stress calibration are identified and discussed.

  20. Effects of transverse shear deformation on buckling of laminated cylinders as a function of thickness and ply orientation

    NASA Technical Reports Server (NTRS)

    Jegley, Dawn C.

    1987-01-01

    Buckling loads of thick-walled, orthotropic, simply-supported right circular cylinders are predicted using a new higher-order transverse shear deformation theory. The higher-order theory shows that, by more accurately accounting for transverse shear deformation effects, the predicted buckling load may be reduced by as much as 80 percent compared to predictions based on conventional transverse shear deformation theory. A parametric study of the effect of ply orientation on the buckling load of axially compressed cylinders indicates that laminates containing 0 deg plies are the most sensitive to transverse shear deformation effects. Interaction curves for buckling of cylinders with axial compressive and external pressure loadings indicate that buckling loads due to external pressure loadings are much less sensitive to transverse shear deformation effects than those due to axial compressive loadings.

  1. Critical shear stress measurement of cohesive soils in streams: identifying device-dependent variability using an in-situ jet test device and conduit flume

    NASA Astrophysics Data System (ADS)

    Mahalder, B.; Schwartz, J. S.; Palomino, A.; Papanicolaou, T.

    2016-12-01

    Cohesive soil erodibility and threshold shear stress for stream bed and bank are dependent on both soil physical and geochemical properties in association with the channel vegetative conditions. These properties can be spatially variable therefore making critical shear stress measurement in cohesive soil challenging and leads to a need for a more comprehensive understanding of the erosional processes in streams. Several in-situ and flume-type test devices for estimating critical shear stress have been introduced by different researchers; however reported shear stress estimates per device vary widely in orders of magnitude. Advantages and disadvantages exist between these devices. Development of in-situ test devices leave the bed and/or bank material relatively undisturbed and can capture the variable nature of field soil conditions. However, laboratory flumes provide a means to control environmental conditions that can be quantify and tested. This study was conducted to observe differences in critical shear stress using jet tester and a well-controlled conduit flume. Soil samples were collected from the jet test locations and tested in a pressurized flume following standard operational procedure to calculate the critical shear stress. The results were compared using statistical data analysis (mean-separation ANOVA procedure) to identify possible differences. In addition to the device comparison, the mini jet device was used to measure critical shear stress across geologically diverse regions of Tennessee, USA. Statistical correlation between critical shear stress and the soil physical, and geochemical properties were completed identifying that geological origin plays a significant role in critical shear stress prediction for cohesive soils. Finally, the critical shear stress prediction equations using the jet test data were examined with possible suggestions to modify based on the flume test results.

  2. CDUCT-LaRC Status - Shear Layer Refraction and Noise Radiation

    NASA Technical Reports Server (NTRS)

    Nark, Douglas M.; Farassat, F.

    2006-01-01

    A proposed boundary condition accounting for shear layer effects within the Ffowcs Williams-Hawkings radiation module of the CDUCT-LaRC code is investigated. The development and numerical justification of the boundary condition formulation are reviewed. An initial assessment of the effectiveness of the shear layer correction is conducted through comparison with experimental data. Preliminary results indicate that the correction provides physically meaningful modifications of the baseline predicted directivity patterns. Trends of peak directivity steepening and shifting that appeared in predicted patterns were found to follow similar structures in measured data, particularly at higher radiation angles.

  3. Haptic Edge Detection Through Shear

    NASA Astrophysics Data System (ADS)

    Platkiewicz, Jonathan; Lipson, Hod; Hayward, Vincent

    2016-03-01

    Most tactile sensors are based on the assumption that touch depends on measuring pressure. However, the pressure distribution at the surface of a tactile sensor cannot be acquired directly and must be inferred from the deformation field induced by the touched object in the sensor medium. Currently, there is no consensus as to which components of strain are most informative for tactile sensing. Here, we propose that shape-related tactile information is more suitably recovered from shear strain than normal strain. Based on a contact mechanics analysis, we demonstrate that the elastic behavior of a haptic probe provides a robust edge detection mechanism when shear strain is sensed. We used a jamming-based robot gripper as a tactile sensor to empirically validate that shear strain processing gives accurate edge information that is invariant to changes in pressure, as predicted by the contact mechanics study. This result has implications for the design of effective tactile sensors as well as for the understanding of the early somatosensory processing in mammals.

  4. Haptic Edge Detection Through Shear

    PubMed Central

    Platkiewicz, Jonathan; Lipson, Hod; Hayward, Vincent

    2016-01-01

    Most tactile sensors are based on the assumption that touch depends on measuring pressure. However, the pressure distribution at the surface of a tactile sensor cannot be acquired directly and must be inferred from the deformation field induced by the touched object in the sensor medium. Currently, there is no consensus as to which components of strain are most informative for tactile sensing. Here, we propose that shape-related tactile information is more suitably recovered from shear strain than normal strain. Based on a contact mechanics analysis, we demonstrate that the elastic behavior of a haptic probe provides a robust edge detection mechanism when shear strain is sensed. We used a jamming-based robot gripper as a tactile sensor to empirically validate that shear strain processing gives accurate edge information that is invariant to changes in pressure, as predicted by the contact mechanics study. This result has implications for the design of effective tactile sensors as well as for the understanding of the early somatosensory processing in mammals. PMID:27009331

  5. Haptic Edge Detection Through Shear.

    PubMed

    Platkiewicz, Jonathan; Lipson, Hod; Hayward, Vincent

    2016-03-24

    Most tactile sensors are based on the assumption that touch depends on measuring pressure. However, the pressure distribution at the surface of a tactile sensor cannot be acquired directly and must be inferred from the deformation field induced by the touched object in the sensor medium. Currently, there is no consensus as to which components of strain are most informative for tactile sensing. Here, we propose that shape-related tactile information is more suitably recovered from shear strain than normal strain. Based on a contact mechanics analysis, we demonstrate that the elastic behavior of a haptic probe provides a robust edge detection mechanism when shear strain is sensed. We used a jamming-based robot gripper as a tactile sensor to empirically validate that shear strain processing gives accurate edge information that is invariant to changes in pressure, as predicted by the contact mechanics study. This result has implications for the design of effective tactile sensors as well as for the understanding of the early somatosensory processing in mammals.

  6. Influence of type-I fimbriae and fluid shear stress on bacterial behavior and multicellular architecture of early Escherichia coli biofilms at single-cell resolution.

    PubMed

    Wang, Liyun; Keatch, Robert; Zhao, Qi; Wright, John A; Bryant, Clare E; Redmann, Anna L; Terentjev, Eugene M

    2018-01-12

    Biofilm formation on abiotic surfaces in food and medical industry can cause severe contamination and infection, yet how biological and physical factors determine cellular architecture of early biofilms and bacterial behavior of the constituent cells remains largely unknown. In this study we examine the specific role of type-I fimbriae in nascent stages of biofilm formation and the response of micro-colonies to environmental flow shear at single-cell resolution. The results show that type-I fimbriae are not required for reversible adhesion from plankton, but critical for irreversible adhesion of Escherichia coli ( E.coli ) MG1655 forming biofilms on polyethylene terephthalate (PET) surfaces. Besides establishing a firm cell-surface contact, the irreversible adhesion seems necessary to initiate the proliferation of E.coli on the surface. After application of shear stress, bacterial retention is dominated by the 3D architecture of colonies independent of the population and the multi-layered structure could protect the embedded cells from being insulted by fluid shear, while cell membrane permeability mainly depends on the biofilm population and the duration time of the shear stress. Importance Bacterial biofilms could lead to severe contamination problems in medical devices and food processing equipment. However, biofilms are usually studied at a rough macroscopic level, thus little is known about how individual bacterial behavior within biofilms and multicellular architecture are influenced by bacterial appendages (e.g. pili/fimbriae) and environmental factors during early biofilm formation. We apply Confocal Laser Scanning Microscopy (CLSM) to visualize E.coli micro-colonies at single-cell resolution. Our findings suggest that type-I fimbriae are vital to the initiation of bacterial proliferation on surfaces and that the responses of biofilm architecture and cell membrane permeability of constituent bacteria to fluid shear stress are different, which are

  7. An Apparatus to Quantify Anteroposterior and Mediolateral Shear Reduction in Shoe Insoles

    PubMed Central

    Belmont, Barry; Wang, Yancheng; Ammanath, Peethambaran; Wrobel, James S.; Shih, Albert

    2013-01-01

    Background Many of the physiological changes that lead to diabetic foot ulceration, such as muscle atrophy and skin hardening, are manifested at the foot–ground interface via pressure and shear points. Novel shear-reducing insoles have been developed, but their magnitude of shear stiffness has not yet been compared with regular insoles. The aim of this study was to develop an apparatus that would apply shear force and displacement to an insole’s forefoot region, reliably measure deformation, and calculate insole shear stiffness. Methods An apparatus consisting of suspended weights was designed to test the forefoot region of insoles. Three separate regions representing the hallux; the first and second metatarsals; and the third, fourth, and fifth metatarsals were sheared at 20 mm/min for displacements from 0.1 to 1.0 mm in both the anteroposterior and mediolateral directions for two types of insoles (regular and shear reducing). Results Shear reduction was found to be significant for the intervention insoles under all testing conditions. The ratio of a regular insole’s effective stiffness and the experimental insole’s effective stiffness across forefoot position versus shear direction, gait instance versus shear direction, and forefoot position versus gait instance was 270% ± 79%, 270% ± 96%, and 270% ± 86%, respectively. The apparatus was reliable with an average measured coefficient of variation of 0.034 and 0.069 for the regular and shear-reducing insole, respectively. Conclusions An apparatus consisting of suspended weights resting atop three locations of interest sheared across an insole was demonstrated to be capable of measuring the insole shear stiffness accurately, thus quantifying shear-reducing effects of a new type of insole. PMID:23567000

  8. Particle sedimentation in a sheared viscoelastic fluid

    NASA Astrophysics Data System (ADS)

    Murch, William L.; Krishnan, Sreenath; Shaqfeh, Eric S. G.; Iaccarino, Gianluca

    2017-11-01

    Particle suspensions are ubiquitous in engineered processes, biological systems, and natural settings. For an engineering application - whether the intent is to suspend and transport particles (e.g., in hydraulic fracturing fluids) or allow particles to sediment (e.g., in industrial separations processes) - understanding and prediction of the particle mobility is critical. This task is often made challenging by the complex nature of the fluid phase, for example, due to fluid viscoelasticity. In this talk, we focus on a fully 3D flow problem in a viscoelastic fluid: a settling particle with a shear flow applied in the plane perpendicular to gravity (referred to as orthogonal shear). Previously, it has been shown that an orthogonal shear flow can reduce the settling rate of particles in viscoelastic fluids. Using experiments and numerical simulations across a wide range of sedimentation and shear Weissenberg number, this talk will address the underlying physical mechanism responsible for the additional drag experienced by a rigid sphere settling in a confined viscoelastic fluid with orthogonal shear. We will then explore multiple particle effects, and discuss the implications and extensions of this work for particle suspensions. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-114747 (WLM).

  9. Study on shear properties of coral sand under cyclic simple shear condition

    NASA Astrophysics Data System (ADS)

    Ji, Wendong; Zhang, Yuting; Jin, Yafei

    2018-05-01

    In recent years, the ocean development in our country urgently needs to be accelerated. The construction of artificial coral reefs has become an important development direction. In this paper, experimental studies of simple shear and cyclic simple shear of coral sand are carried out, and the shear properties and particle breakage of coral sand are analyzed. The results show that the coral sand samples show an overall shear failure in the simple shear test, which is more accurate and effective for studying the particle breakage. The shear displacement corresponding to the peak shear stress of the simple shear test is significantly larger than that corresponding to the peak shear stress of the direct shear test. The degree of particle breakage caused by the simple shear test is significantly related to the normal stress level. The particle breakage of coral sand after the cyclic simple shear test obviously increases compared with that of the simple shear test, and universal particle breakage occurs within the whole particle size range. The increasing of the cycle-index under cyclic simple shear test results in continuous compacting of the sample, so that the envelope curve of peak shearing force increases with the accumulated shear displacement.

  10. Crashworthiness Design of the Shear Bolts for Light Collision Safety Devices

    NASA Astrophysics Data System (ADS)

    Kim, Jin Sung; Huh, Hoon; Kwon, Tae Soo

    This paper introduces the jig set for the crash test and the crash test results of shear bolts which are designed to fail at train crash conditions. The tension and shear bolts are attached to Light Collision Safety Devices(LCSD) as a mechanical fuse when tension and shear bolts reach their failure load designed. The kinetic energy due to the crash is absorbed by the secondary energy absorbing device after LCSD are detached from the main body by the fracture of shear bolts. A single shear bolt was designed to fail at the load of 250 kN. The jig set designed to convert a compressive loading to a shear loading was installed to the high speed crash tester for dynamic shear tests. Two strain gauges were attached at the parallel section of the jig set to measure the load responses acting on the shear bolts. Crash tests were performed with a carrier whose mass was 250 kg and the initial speed of the carrier was 9 m/sec. From the quasi-static and dynamic experiments as well as the numerical analysis, the capacity of the shear bolts were accurately predicted for the crashworthiness design.

  11. Elevation in blood flow and shear rate prevents hyperglycemia-induced endothelial dysfunction in healthy subjects and those with type 2 diabetes.

    PubMed

    Greyling, Arno; Schreuder, Tim H A; Landman, Thijs; Draijer, Richard; Verheggen, Rebecca J H M; Hopman, Maria T E; Thijssen, Dick H J

    2015-03-01

    Hyperglycemia, commonly present after a meal, causes transient impairment in endothelial function. We examined whether increases in blood flow (BF) protect against the hyperglycemia-mediated decrease in endothelial function in healthy subjects and patients with type 2 diabetes mellitus (T2DM). Ten healthy subjects and 10 age- and sex-matched patients with T2DM underwent simultaneous bilateral assessment of brachial artery endothelial function by means of flow-mediated dilation (FMD) using high-resolution echo-Doppler. FMD was examined before and 60, 120, and 150 min after a 75-g oral glucose challenge. We unilaterally manipulated BF by heating one arm between minute 30 and minute 60. Oral glucose administration caused a statistically significant, transient increase in blood glucose in both groups (P < 0.001). Forearm skin temperature, brachial artery BF, and shear rate significantly increased in the heated arm (P < 0.001), and to a greater extent compared with the nonheated arm in both groups (interaction effect P < 0.001). The glucose load caused a transient decrease in FMD% (P < 0.05), whereas heating significantly prevented the decline (interaction effect P < 0.01). Also, when correcting for changes in diameter and shear rate, we found that the hyperglycemia-induced decrease in FMD can be prevented by local heating (P < 0.05). These effects on FMD were observed in both groups. Our data indicate that nonmetabolically driven elevation in BF and shear rate can similarly prevent the hyperglycemia-induced decline in conduit artery endothelial function in healthy volunteers and in patients with type 2 diabetes. Additional research is warranted to confirm that other interventions that increase BF and shear rate equally protect the endothelium when challenged by hyperglycemia. Copyright © 2015 the American Physiological Society.

  12. Quantification of shear stress in a meandering native topographic channel using a physical hydraulic model

    Treesearch

    Michael E. Ursic

    2011-01-01

    Current guidelines for predicting increases in shear stress in open-channel bends were developed from investigations that were primarily prismatic in cross section. This study provides possible increases in shear stress relative to approach flow conditions resulting from planimetric and topographic geometric features. Boundary shear stress estimates were determined by...

  13. Vibration Control by a Shear Type Semi-active Damper Using Magnetorheological Grease

    NASA Astrophysics Data System (ADS)

    Shiraishi, Toshihiko; Misaki, Hirotaka

    2016-09-01

    This paper describes semi-active vibration control by a controllable damper with high reliability and wide dynamic range using magnetorheological (MR) grease. Some types of cylindrical controllable dampers based on pressure difference between chambers in the dampers using “MR fluid”, whose rheological properties can be varied by applying a magnetic field, have been reported as a semi-active device. However, there are some challenging issues of them. One is to improve dispersion stability. The particles dispersed in MR fluid would make sedimentation after a period. Another is to expand dynamic range. Since cylindrical dampers require sealing elements because of pressure difference in the dampers, the dynamic range between the maximum and minimum damping force according to a magnetic field is reduced. In this study, a controllable damper using the MR effect was proposed and its performance was experimentally verified to improve the dispersion stability by using “MR grease”, which includes grease as the carrier of magnetic particles, and to expand the dynamic range by adopting a shear type structure not requiring sealing elements. Furthermore, semiactive vibration control experiments by the MR grease damper using a simple algorithm based on the skyhook damper scheme were conducted and its performance was investigated.

  14. Effects of planar shear on the three-dimensional instability in flow past a circular cylinder

    NASA Astrophysics Data System (ADS)

    Park, Doohyun; Yang, Kyung-Soo

    2018-03-01

    A Floquet stability analysis has been carried out in order to investigate how a planar shear in wake flow affects the three-dimensional (3D) instability in the near-wake region. We consider a circular cylinder immersed in a freestream with planar shear. The cylinder was implemented in a Cartesian grid system by means of an immersed boundary method. Planar shear tends to promote the primary instability, known as Hopf bifurcation where steady flow bifurcates into time-periodic flow, in the sense that its critical Reynolds number decreases with increasing planar shear. The effects of planar shear on the 3D instability are different depending on the type of 3D instability. The flow asymmetry caused by the planar shear suppresses a QP-type mode but generates a C-type mode. The conventional A and B modes are stabilized by the planar shear, whereas mode C is intensified with increasing shear. The criticality of each 3D mode is discussed, and the neutral stability curves for each 3D mode are presented. The current Floquet results have been validated by using direct numerical simulation for some selected cases of flow parameters.

  15. Cosmological constraints from the CFHTLenS shear measurements using a new, accurate, and flexible way of predicting non-linear mass clustering

    NASA Astrophysics Data System (ADS)

    Angulo, Raul E.; Hilbert, Stefan

    2015-03-01

    We explore the cosmological constraints from cosmic shear using a new way of modelling the non-linear matter correlation functions. The new formalism extends the method of Angulo & White, which manipulates outputs of N-body simulations to represent the 3D non-linear mass distribution in different cosmological scenarios. We show that predictions from our approach for shear two-point correlations at 1-300 arcmin separations are accurate at the ˜10 per cent level, even for extreme changes in cosmology. For moderate changes, with target cosmologies similar to that preferred by analyses of recent Planck data, the accuracy is close to ˜5 per cent. We combine this approach with a Monte Carlo Markov chain sampler to explore constraints on a Λ cold dark matter model from the shear correlation functions measured in the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS). We obtain constraints on the parameter combination σ8(Ωm/0.27)0.6 = 0.801 ± 0.028. Combined with results from cosmic microwave background data, we obtain marginalized constraints on σ8 = 0.81 ± 0.01 and Ωm = 0.29 ± 0.01. These results are statistically compatible with previous analyses, which supports the validity of our approach. We discuss the advantages of our method and the potential it offers, including a path to model in detail (i) the effects of baryons, (ii) high-order shear correlation functions, and (iii) galaxy-galaxy lensing, among others, in future high-precision cosmological analyses.

  16. Behavior of Rapidly Sheared Bubble Suspensions

    NASA Technical Reports Server (NTRS)

    Sangani, A. S.; Kushch, V. I.; Hoffmann, M.; Nahra, H.; Koch, D. L.; Tsang, Y.

    2002-01-01

    An experiment to be carried out aboard the International Space Station is described. A suspension consisting of millimeter-sized bubbles in water containing some dissolved salt, which prevents bubbles from coalescing, will be sheared in a Couette cylindrical cell. Rotation of the outer cylinder will produce centrifugal force which will tend to accumulate the bubbles near the inner wall. The shearing will enhance collisions among bubbles creating thereby bubble phase pressure that will resist the tendency of the bubbles to accumulate near the inner wall. The bubble volume fraction and velocity profiles will be measured and compared with the theoretical predictions. Ground-based research on measurement of bubble phase properties and flow in vertical channel are described.

  17. Turbulent shear layers in confining channels

    NASA Astrophysics Data System (ADS)

    Benham, Graham P.; Castrejon-Pita, Alfonso A.; Hewitt, Ian J.; Please, Colin P.; Style, Rob W.; Bird, Paul A. D.

    2018-06-01

    We present a simple model for the development of shear layers between parallel flows in confining channels. Such flows are important across a wide range of topics from diffusers, nozzles and ducts to urban air flow and geophysical fluid dynamics. The model approximates the flow in the shear layer as a linear profile separating uniform-velocity streams. Both the channel geometry and wall drag affect the development of the flow. The model shows good agreement with both particle image velocimetry experiments and computational turbulence modelling. The simplicity and low computational cost of the model allows it to be used for benchmark predictions and design purposes, which we demonstrate by investigating optimal pressure recovery in diffusers with non-uniform inflow.

  18. SHEAR ACCELERATION IN EXPANDING FLOWS

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Rieger, F. M.; Duffy, P., E-mail: frank.rieger@mpi-hd.mpg.de, E-mail: peter.duffy@ucd.ie

    Shear flows are naturally expected to occur in astrophysical environments and potential sites of continuous non-thermal Fermi-type particle acceleration. Here we investigate the efficiency of expanding relativistic outflows to facilitate the acceleration of energetic charged particles to higher energies. To this end, the gradual shear acceleration coefficient is derived based on an analytical treatment. The results are applied to the context of the relativistic jets from active galactic nuclei. The inferred acceleration timescale is investigated for a variety of conical flow profiles (i.e., power law, Gaussian, Fermi–Dirac) and compared to the relevant radiative and non-radiative loss timescales. The results exemplifymore » that relativistic shear flows are capable of boosting cosmic-rays to extreme energies. Efficient electron acceleration, on the other hand, requires weak magnetic fields and may thus be accompanied by a delayed onset of particle energization and affect the overall jet appearance (e.g., core, ridge line, and limb-brightening).« less

  19. An experimental investigation for external RC shear wall applications

    NASA Astrophysics Data System (ADS)

    Kaltakci, M. Y.; Ozturk, M.; Arslan, M. H.

    2010-09-01

    The strength and rigidity of most reinforced concrete (RC) buildings in Turkey, which are frequently hit by destructive earthquakes, is not at a sufficient level. Therefore, the result of earthquakes is a significant loss of life and property. The strengthening method most commonly preferred for these type of RC buildings is the application of RC infilled walls (shear walls) in the frame openings of the building. However, since the whole building has to be emptied and additional heavy costs arise during this type of strengthening, users prefer not to strengthen their buildings despite the heavy risk they are exposed to. Therefore, it is necessary to develop easier-to-apply and more effective methods for the rapid strengthening of housing and the heavily-used public buildings which cannot be emptied during the strengthening process (such as hospitals and schools). This study empirically analyses the different methods of a new system which can meet this need. In this new system, named "external shear wall application", RC shear walls are applied on the external surface of the building, along the frame plane rather than in the building. To this end, 7 test samples in 1/2 and 1/3 geometrical scale were designed to analyse the efficiency of the strengthening technique where the shear wall leans on the frame from outside of the building (external shear wall application) and of the strengthening technique where a specific space is left between the frame and the external shear wall by using a coupling beam to connect elements (application of external shear wall with coupling beam). Test results showed that the maximum lateral load capacity, initial rigidity and energy dissipation behaviours of the samples strengthened with external shear wall were much better than those of the bare frames.

  20. Designing shear-thinning

    NASA Astrophysics Data System (ADS)

    Nelson, Arif Z.; Ewoldt, Randy H.

    2017-11-01

    Design in fluid mechanics often focuses on optimizing geometry (airfoils, surface textures, microfluid channels), but here we focus on designing fluids themselves. The dramatically shear-thinning ``yield-stress fluid'' is currently the most utilized non-Newtonian fluid phenomenon. These rheologically complex materials, which undergo a reversible transition from solid-like to liquid-like fluid flow, are utilized in pedestrian products such as paint and toothpaste, but also in emerging applications like direct-write 3D printing. We present a paradigm for yield-stress fluid design that considers constitutive model representation, material property databases, available predictive scaling laws, and the many ways to achieve a yield stress fluid, flipping the typical structure-to-rheology analysis to become the inverse: rheology-to-structure with multiple possible materials as solutions. We describe case studies of 3D printing inks and other flow scenarios where designed shear-thinning enables performance remarkably beyond that of Newtonian fluids. This work was supported by Wm. Wrigley Jr. Company and the National Science Foundation under Grant No. CMMI-1463203.

  1. Monitoring of thermal therapy based on shear modulus changes: II. Shear wave imaging of thermal lesions.

    PubMed

    Arnal, Bastien; Pernot, Mathieu; Tanter, Mickael

    2011-08-01

    The clinical applicability of high-intensity focused ultrasound (HIFU) for noninvasive therapy is currently hampered by the lack of robust and real-time monitoring of tissue damage during treatment. The goal of this study is to show that the estimation of local tissue elasticity from shear wave imaging (SWI) can lead to a precise mapping of the lesion. HIFU treatment and monitoring were respectively performed using a confocal setup consisting of a 2.5-MHz single element transducer focused at 34 mm on ex vivo samples and an 8-MHz ultrasound diagnostic probe. Ultrasound-based strain imaging was combined with shear wave imaging on the same device. The SWI sequences consisted of 2 successive shear waves induced at different lateral positions. Each wave was created with pushing beams of 100 μs at 3 depths. The shear wave propagation was acquired at 17,000 frames/s, from which the elasticity map was recovered. HIFU sonications were interleaved with fast imaging acquisitions, allowing a duty cycle of more than 90%. Thus, elasticity and strain mapping was achieved every 3 s, leading to real-time monitoring of the treatment. When thermal damage occurs, tissue stiffness was found to increase up to 4-fold and strain imaging showed strong shrinkages that blur the temperature information. We show that strain imaging elastograms are not easy to interpret for accurate lesion characterization, but SWI provides a quantitative mapping of the thermal lesion. Moreover, the concept of shear wave thermometry (SWT) developed in the companion paper allows mapping temperature with the same method. Combined SWT and shear wave imaging can map the lesion stiffening and temperature outside the lesion, which could be used to predict the eventual lesion growth by thermal dose calculation. Finally, SWI is shown to be robust to motion and reliable in vivo on sheep muscle.

  2. Experimental Research on Boundary Shear Stress in Typical Meandering Channel

    NASA Astrophysics Data System (ADS)

    Chen, Kai-hua; Xia, Yun-feng; Zhang, Shi-zhao; Wen, Yun-cheng; Xu, Hua

    2018-06-01

    A novel instrument named Micro-Electro-Mechanical System (MEMS) flexible hot-film shear stress sensor was used to study the boundary shear stress distribution in the generalized natural meandering open channel, and the mean sidewall shear stress distribution along the meandering channel, and the lateral boundary shear stress distribution in the typical cross-section of the meandering channel was analysed. Based on the measurement of the boundary shear stress, a semi-empirical semi-theoretical computing approach of the boundary shear stress was derived including the effects of the secondary flow, sidewall roughness factor, eddy viscosity and the additional Reynolds stress, and more importantly, for the first time, it combined the effects of the cross-section central angle and the Reynolds number into the expressions. Afterwards, a comparison between the previous research and this study was developed. Following the result, we found that the semi-empirical semi-theoretical boundary shear stress distribution algorithm can predict the boundary shear stress distribution precisely. Finally, a single factor analysis was conducted on the relationship between the average sidewall shear stress on the convex and concave bank and the flow rate, water depth, slope ratio, or the cross-section central angle of the open channel bend. The functional relationship with each of the above factors was established, and then the distance from the location of the extreme sidewall shear stress to the bottom of the open channel was deduced based on the statistical theory.

  3. A rational approach to the use of Prandtl's mixing length model in free turbulent shear flow calculations

    NASA Technical Reports Server (NTRS)

    Rudy, D. H.; Bushnell, D. M.

    1973-01-01

    Prandtl's basic mixing length model was used to compute 22 test cases on free turbulent shear flows. The calculations employed appropriate algebraic length scale equations and single values of mixing length constant for planar and axisymmetric flows, respectively. Good agreement with data was obtained except for flows, such as supersonic free shear layers, where large sustained sensitivity changes occur. The inability to predict the more gradual mixing in these flows is tentatively ascribed to the presence of a significant turbulence-induced transverse static pressure gradient which is neglected in conventional solution procedures. Some type of an equation for length scale development was found to be necessary for successful computation of highly nonsimilar flow regions such as jet or wake development from thick wall flows.

  4. An analytical study of the effects of transverse shear deformation and anisotropy on buckling loads of laminated cylinders. M.S. Thesis - George Washington Univ.

    NASA Technical Reports Server (NTRS)

    Jegley, Dawn C.

    1987-01-01

    Buckling loads of thick-walled orthotropic and anisotropic simply supported circular cylinders are predicted using a higher-order transverse-shear deformation theory. A comparison of buckling loads predicted by the conventional first-order transverse-shear deformation theory and the higher-order theory show that the additional allowance for transverse shear deformation has a negligible effect on the predicted buckling loads of medium-thick metallic isotropic cylinders. However, the higher-order theory predicts buckling loads which are significantly lower than those predicted by the first-order transverse-shear deformation theory for certain short, thick-walled cylinders which have low through-the-thickness shear moduli. A parametric study of the effects of ply orientation on the buckling load of axially compressed cylinders indicates that laminates containing 45 degree plies are most sensitive to transverse-shear deformation effects. Interaction curves for buckling loads of cylinders subjected to axial compressive and external pressure loadings indicate that buckling loads due to external pressure loadings are as sensitive to transverse-shear deformation effects as buckling loads due to axial compressive loadings. The effects of anisotropy are important over a much wider range of cylinder geometries than the effects of transverse shear deformation.

  5. A master dynamic flow diagram for the shear thickening transition in micellar solutions.

    PubMed

    Bautista, F; Tepale, N; Fernández, V V A; Landázuri, G; Hernández, E; Macías, E R; Soltero, J F A; Escalante, J I; Manero, O; Puig, J E

    2016-01-07

    The shear thickening behavior of dilute micellar solutions of hexadecyltrimethylammonium-type surfactants with different counterions (tosylate, 3- and 4-fluorobenzoate, vinylbenzoate and salicylate) and of n-alkyltetradecylammonium bromide (CnTAB), with n = 14, 16 and 18, is examined here. These solutions undergo a shear thickening transition due to the formation of shear-induced structures (SISs) in the shear range studied. Here we report a relationship between the shear thickening intensity and the differences in the hydrophobicity of counterions according to the Hofmeister-like anion series, which leads to a master flow diagram. This master flow diagram is produced by plotting a normalized shear thickening intensity (Iη - 1)/(Imax - 1) versus CD/CD,max, where Iη is the shear-thickening intensity, defined as the largest viscosity obtained in the shear-thickening transition (STT) at a given surfactant concentration CD divided by the Newtonian viscosity η0, and Imax is the largest intensity value obtained in the STT at a surfactant concentration CD,max. The master flow diagram is built using several cetyltrimethylammonium-type surfactants with different counterions, according to a Hofmeister-like series, and by n-alkyltetradecylammonium bromide surfactants with different alkyl chain lengths.

  6. Large-Amplitude Long-Wave Instability of a Supersonic Shear Layer

    NASA Technical Reports Server (NTRS)

    Messiter, A. F.

    1995-01-01

    For sufficiently high Mach numbers, small disturbances on a supersonic vortex sheet are known to grow in amplitude because of slow nonlinear wave steepening. Under the same external conditions, linear theory predicts slow growth of long-wave disturbances to a thin supersonic shear layer. An asymptotic formulation is given here which adds nonzero shear-layer thickness to the weakly nonlinear formulation for a vortex sheet. Spatial evolution is considered, for a spatially periodic disturbance having amplitude of the same order, in Reynolds number, as the shear-layer thickness. A quasi-equilibrium inviscid nonlinear critical layer is found, with effects of diffusion and slow growth appearing through nonsecularity condition. Other limiting cases are also considered, in an attempt to determine a relationship between the vortex-sheet limit and the long-wave limit for a thin shear layer; there appear to be three special limits, corresponding to disturbances of different amplitudes at different locations along the shear layer.

  7. Parametric analysis of swept-wing geometry with sheared wing tips

    NASA Technical Reports Server (NTRS)

    Fremaux, C. M.; Vijgen, P. M. H. W.; Van Dam, C. P.

    1990-01-01

    A computational parameter study is presented of potential reductions in induced drag and increases in lateral-directional stability due to sheared wing tips attached to an untwisted wing of moderate sweep and aspect ratio. Sheared tips are swept and tapered wing-tip devices mounted in the plane of the wing. The induced-drag results are obtained using an inviscid, incompressible surface-panel method that models the nonlinear effects due to the deflected and rolled-up wake behind the lifting surface. The induced-drag results with planar sheared tips are compared to straight-tapered tip extensions and nonplanar winglet geometries. The lateral-directional static-stability characteristics of the wing with sheared tips are estimated using a quasi-vortex-lattice method. For certain combinations of sheared-tip sweep and taper, both the induced efficiency of the wing and the relevant static-stability derivatives are predicted to increase compared to the wing with a straight-tapered tip modification.

  8. Calculation and analysis of shear resistance of segment ring joint with shear pin

    NASA Astrophysics Data System (ADS)

    Wu, Shengzhi; Huang, Haibin; Wang, Mingnian; Xiao, Shihui; Liu, Dagang

    2018-03-01

    In order to get the effect of shear pins between segments on the shear resistance of segment girth joints. Take the Maliuzhou traffic tunnel project of Zhuhai which with super large diameter and Marine Composite strata as the research object, the longitudinal shear stiffness of tunnel shear considering the shear rigidity of shear pins was obtained through the finite element shear experiment of segment ring. By comparing the calculation results of shear pin and non shear pin between segment ring connections, the conclusion that shear pin setting can effectively decompose and transfer shear force and control the dislocation between segment ring blocks is obtained. The study can be used as reference for the design and construction of shield tunnel.

  9. Space-time correlations of fluctuating velocities in turbulent shear flows

    NASA Astrophysics Data System (ADS)

    Zhao, Xin; He, Guo-Wei

    2009-04-01

    Space-time correlations or Eulerian two-point two-time correlations of fluctuating velocities are analytically and numerically investigated in turbulent shear flows. An elliptic model for the space-time correlations in the inertial range is developed from the similarity assumptions on the isocorrelation contours: they share a uniform preference direction and a constant aspect ratio. The similarity assumptions are justified using the Kolmogorov similarity hypotheses and verified using the direct numerical simulation (DNS) of turbulent channel flows. The model relates the space-time correlations to the space correlations via the convection and sweeping characteristic velocities. The analytical expressions for the convection and sweeping velocities are derived from the Navier-Stokes equations for homogeneous turbulent shear flows, where the convection velocity is represented by the mean velocity and the sweeping velocity is the sum of the random sweeping velocity and the shear-induced velocity. This suggests that unlike Taylor’s model where the convection velocity is dominating and Kraichnan and Tennekes’ model where the random sweeping velocity is dominating, the decorrelation time scales of the space-time correlations in turbulent shear flows are determined by the convection velocity, the random sweeping velocity, and the shear-induced velocity. This model predicts a universal form of the space-time correlations with the two characteristic velocities. The DNS of turbulent channel flows supports the prediction: the correlation functions exhibit a fair good collapse, when plotted against the normalized space and time separations defined by the elliptic model.

  10. A candidate concept for display of forward-looking wind shear information

    NASA Technical Reports Server (NTRS)

    Hinton, David A.

    1989-01-01

    A concept is proposed which integrates forward-look wind shear information with airplane performance capabilities to predict future airplane energy state as a function of range. The information could be displayed to a crew either in terms of energy height or airspeed deviations. The anticipated benefits of the proposed display information concept are: (1) a wind shear hazard product that scales directly to the performance impact on the airplane and that has intuitive meaning to flight crews; (2) a reduction in flight crew workload by automatic processing of relevant hazard parameters; and (3) a continuous display of predicted airplane energy state if the approach is continued. Such a display may be used to improve pilot situational awareness or improve pilot confidence in wind shear alerts generated by other systems. The display is described and the algorithms necessary for implementation in a simulation system are provided.

  11. Colloidal Aggregate Structure under Shear by USANS

    NASA Astrophysics Data System (ADS)

    Chatterjee, Tirtha; van Dyk, Antony K.; Ginzburg, Valeriy V.; Nakatani, Alan I.

    2015-03-01

    Paints are complex formulations of polymeric binders, inorganic pigments, dispersants, surfactants, colorants, rheology modifiers, and other additives. A commercially successful paint exhibits a desired viscosity profile over a wide shear rate range from 10-5 s-1 for settling to >104 s-1 for rolling, and spray applications. Understanding paint formulation structure is critical as it governs the paint viscosity profile. However, probing paint formulation structure under shear is a challenging task due to the formulation complexity containing structures with different hierarchical length scales and their alterations under the influence of an external flow field. In this work mesoscale structures of paint formulations under shear are investigated using Ultra Small-Angle Neutron Scattering (rheo-USANS). Contrast match conditions were utilized to independently probe the structure of latex binder particle aggregates and the TiO2 pigment particle aggregates. Rheo-USANS data revealed that the aggregates are fractal in nature and their self-similarity dimensions and correlations lengths depend on the chemistry of the binder particles, the type of rheology modifier present and the shear stress imposed upon the formulation. These results can be explained in the framework of diffusion and reaction limited transient aggregates structure evolution under simple shear.

  12. Point-shear wave elastography predicts liver hypertrophy after portal vein embolization and postoperative liver failure.

    PubMed

    Hocquelet, A; Frulio, N; Gallo, G; Laurent, C; Papadopoulos, P; Salut, C; Denys, A; Trillaud, H

    2018-06-01

    To correlate point-shear wave elastography (SWE) with liver hypertrophy after right portal vein embolization (RPVE) and to determine its usefulness in predicting postoperative liver failure in patients undergoing partial liver resection. Point-SWE was performed the day before RPVE in 56 patients (41 men) with a median age of 66 years. The percentage (%) of future remnant liver (FRL) volume increase was defined as: %FRL post -%FRL pre %FRL pre ×100 and assessed on computed tomography performed 4 weeks after RPVE. Median (range) %FRL pre and %FRL post was respectively, 31.5% (12-48%) and 41% (23-61%) (P<0.001), with a median %FRL volume increase of 25.6% (-8; 123%). SWE correlated with %FRL volume increase (P=-0.510; P<0.001). SWV (P=0.003) and %FRL pre (P<0.001) were associated with %FRL volume increase at multivariate regression analysis. Forty-three patients (77%) were operated. Postoperative liver failure occurred in 14 patients (32.5%). Median SWE was different between the group with (1.68m/s) and without liver failure (1.07m/s) (P=0.018). The AUROC of SWE predicting liver failure was 0.724 with a best cut-off of 1.31m/s, corresponding to a sensitivity of 21%, specificity of 96%, positive predictive value 75% and negative predictive value of 72%. SWE was the single independent preoperative variable associated with liver failure. SWE assessed by point-SWE is a simple and useful tool to predict the FRL volume increase and postoperative liver failure in a population of patients with liver tumor. Copyright © 2018 Société française de radiologie. Published by Elsevier Masson SAS. All rights reserved.

  13. Predicting beta-turns and their types using predicted backbone dihedral angles and secondary structures.

    PubMed

    Kountouris, Petros; Hirst, Jonathan D

    2010-07-31

    Beta-turns are secondary structure elements usually classified as coil. Their prediction is important, because of their role in protein folding and their frequent occurrence in protein chains. We have developed a novel method that predicts beta-turns and their types using information from multiple sequence alignments, predicted secondary structures and, for the first time, predicted dihedral angles. Our method uses support vector machines, a supervised classification technique, and is trained and tested on three established datasets of 426, 547 and 823 protein chains. We achieve a Matthews correlation coefficient of up to 0.49, when predicting the location of beta-turns, the highest reported value to date. Moreover, the additional dihedral information improves the prediction of beta-turn types I, II, IV, VIII and "non-specific", achieving correlation coefficients up to 0.39, 0.33, 0.27, 0.14 and 0.38, respectively. Our results are more accurate than other methods. We have created an accurate predictor of beta-turns and their types. Our method, called DEBT, is available online at http://comp.chem.nottingham.ac.uk/debt/.

  14. Microscopic Characterization of Tensile and Shear Fracturing in Progressive Failure in Marble

    NASA Astrophysics Data System (ADS)

    Cheng, Yi; Wong, Louis Ngai Yuen

    2018-01-01

    Compression-induced tensile and shear fractures were reported to be the two fundamental fracture types in rock fracturing tests. This study investigates such tensile and shear fracturing process in marble specimens containing two different flaw configurations. Observations first reveal that the development of a tensile fracture is distinct from shear fracture with respect to their nucleation, propagation, and eventual formation in macroscale. Second, transgranular cracks and grain-scale spallings become increasingly abundant in shear fractures as loading increases, which is almost not observed in tensile fractures. Third, one or some dominant extensional microcracks are commonly observed in the center of tensile fractures, while such development of microcracks is almost absent in shear fractures. Microcracks are generally of a length comparable to grain size and distribute uniformly within the damage zone of the shear fracture. Fourth, the width of densely damaged zone in the shear fracture is nearly 10 times of that in the tensile fracture. Quantitative measurement on microcrack density suggests that (1) microcrack density in tensile and shear fractures display distinct characteristics with increasing loading, (2) transgranular crack density in the shear fracture decreases logarithmically with the distance away from the shear fracture center, and (3) whatever the fracture type, the anisotropy can only be observed for transgranular cracks with a large density, which partially explains why microcrack anisotropy usually tends to be unobvious until approaching peak stress in specimens undergoing brittle failure. Microcracking characteristics observed in this work likely shed light to some phenomena and conclusions generalized in seismological studies.

  15. Wind-invariant saltation heights imply linear scaling of aeolian saltation flux with shear stress.

    PubMed

    Martin, Raleigh L; Kok, Jasper F

    2017-06-01

    Wind-driven sand transport generates atmospheric dust, forms dunes, and sculpts landscapes. However, it remains unclear how the flux of particles in aeolian saltation-the wind-driven transport of sand in hopping trajectories-scales with wind speed, largely because models do not agree on how particle speeds and trajectories change with wind shear velocity. We present comprehensive measurements, from three new field sites and three published studies, showing that characteristic saltation layer heights remain approximately constant with shear velocity, in agreement with recent wind tunnel studies. These results support the assumption of constant particle speeds in recent models predicting linear scaling of saltation flux with shear stress. In contrast, our results refute widely used older models that assume that particle speed increases with shear velocity, thereby predicting nonlinear 3/2 stress-flux scaling. This conclusion is further supported by direct field measurements of saltation flux versus shear stress. Our results thus argue for adoption of linear saltation flux laws and constant saltation trajectories for modeling saltation-driven aeolian processes on Earth, Mars, and other planetary surfaces.

  16. Wind-invariant saltation heights imply linear scaling of aeolian saltation flux with shear stress

    PubMed Central

    Martin, Raleigh L.; Kok, Jasper F.

    2017-01-01

    Wind-driven sand transport generates atmospheric dust, forms dunes, and sculpts landscapes. However, it remains unclear how the flux of particles in aeolian saltation—the wind-driven transport of sand in hopping trajectories—scales with wind speed, largely because models do not agree on how particle speeds and trajectories change with wind shear velocity. We present comprehensive measurements, from three new field sites and three published studies, showing that characteristic saltation layer heights remain approximately constant with shear velocity, in agreement with recent wind tunnel studies. These results support the assumption of constant particle speeds in recent models predicting linear scaling of saltation flux with shear stress. In contrast, our results refute widely used older models that assume that particle speed increases with shear velocity, thereby predicting nonlinear 3/2 stress-flux scaling. This conclusion is further supported by direct field measurements of saltation flux versus shear stress. Our results thus argue for adoption of linear saltation flux laws and constant saltation trajectories for modeling saltation-driven aeolian processes on Earth, Mars, and other planetary surfaces. PMID:28630907

  17. Application of a Reynolds stress turbulence model to the compressible shear layer

    NASA Technical Reports Server (NTRS)

    Sarkar, S.; Balakrishnan, L.

    1990-01-01

    Theoretically based turbulence models have had success in predicting many features of incompressible, free shear layers. However, attempts to extend these models to the high-speed, compressible shear layer have been less effective. In the present work, the compressible shear layer was studied with a second-order turbulence closure, which initially used only variable density extensions of incompressible models for the Reynolds stress transport equation and the dissipation rate transport equation. The quasi-incompressible closure was unsuccessful; the predicted effect of the convective Mach number on the shear layer growth rate was significantly smaller than that observed in experiments. Having thus confirmed that compressibility effects have to be explicitly considered, a new model for the compressible dissipation was introduced into the closure. This model is based on a low Mach number, asymptotic analysis of the Navier-Stokes equations, and on direct numerical simulation of compressible, isotropic turbulence. The use of the new model for the compressible dissipation led to good agreement of the computed growth rates with the experimental data. Both the computations and the experiments indicate a dramatic reduction in the growth rate when the convective Mach number is increased. Experimental data on the normalized maximum turbulence intensities and shear stress also show a reduction with increasing Mach number.

  18. Compact forced simple-shear sample for studying shear localization in materials

    DOE PAGES

    Gray, George Thompson; Vecchio, K. S.; Livescu, Veronica

    2015-11-06

    In this paper, a new specimen geometry, the compact forced-simple-shear specimen (CFSS), has been developed as a means to achieve simple shear testing of materials over a range of temperatures and strain rates. The stress and strain state in the gage section is designed to produce essentially “pure” simple shear, mode II in-plane shear, in a compact-sample geometry. The 2-D plane of shear can be directly aligned along specified directional aspects of a material's microstructure of interest; i.e., systematic shear loading parallel, at 45°, and orthogonal to anisotropic microstructural features in a material such as the pancake-shaped grains typical inmore » many rolled structural metals, or to specified directions in fiber-reinforced composites. Finally, the shear-stress shear-strain response and the damage evolution parallel and orthogonal to the pancake grain morphology in 7039-Al are shown to vary significantly as a function of orientation to the microstructure.« less

  19. Wind shear and turbulence around airports

    NASA Technical Reports Server (NTRS)

    Lewellen, W. S.; Williamson, G. G.

    1976-01-01

    A two part study was conducted to determine the feasibility of predicting the conditions under which wind/turbulence environments hazardous to aviation operations exist. The computer model used to solve the velocity temperature, and turbulence distributions in the atmospheric boundary layer is described, and the results of a parameteric analysis to determine the expected range of wind shear and turbulence to be encountered in the vicinity of airports are given. The second part describes the delineation of an ensemble of aircraft accidents in which low level wind shear and/or turbulence appeared to be causative factors. This set of accidents, encompassing a wide range of meteorological conditions, should prove useful in developing techniques for reconstructing hazardous wind environments for aircraft safety investigation purposes.

  20. Swimming efficiency in a shear-thinning fluid

    NASA Astrophysics Data System (ADS)

    Nganguia, Herve; Pietrzyk, Kyle; Pak, On Shun

    2017-12-01

    Micro-organisms expend energy moving through complex media. While propulsion speed is an important property of locomotion, efficiency is another factor that may determine the swimming gait adopted by a micro-organism in order to locomote in an energetically favorable manner. The efficiency of swimming in a Newtonian fluid is well characterized for different biological and artificial swimmers. However, these swimmers often encounter biological fluids displaying shear-thinning viscosities. Little is known about how this nonlinear rheology influences the efficiency of locomotion. Does the shear-thinning rheology render swimming more efficient or less? How does the swimming efficiency depend on the propulsion mechanism of a swimmer and rheological properties of the surrounding shear-thinning fluid? In this work, we address these fundamental questions on the efficiency of locomotion in a shear-thinning fluid by considering the squirmer model as a general locomotion model to represent different types of swimmers. Our analysis reveals how the choice of surface velocity distribution on a squirmer may reduce or enhance the swimming efficiency. We determine optimal shear rates at which the swimming efficiency can be substantially enhanced compared with the Newtonian case. The nontrivial variations of swimming efficiency prompt questions on how micro-organisms may tune their swimming gaits to exploit the shear-thinning rheology. The findings also provide insights into how artificial swimmers should be designed to move through complex media efficiently.

  1. Formulating the shear stress distribution in circular open channels based on the Renyi entropy

    NASA Astrophysics Data System (ADS)

    Khozani, Zohreh Sheikh; Bonakdari, Hossein

    2018-01-01

    The principle of maximum entropy is employed to derive the shear stress distribution by maximizing the Renyi entropy subject to some constraints and by assuming that dimensionless shear stress is a random variable. A Renyi entropy-based equation can be used to model the shear stress distribution along the entire wetted perimeter of circular channels and circular channels with flat beds and deposited sediments. A wide range of experimental results for 12 hydraulic conditions with different Froude numbers (0.375 to 1.71) and flow depths (20.3 to 201.5 mm) were used to validate the derived shear stress distribution. For circular channels, model performance enhanced with increasing flow depth (mean relative error (RE) of 0.0414) and only deteriorated slightly at the greatest flow depth (RE of 0.0573). For circular channels with flat beds, the Renyi entropy model predicted the shear stress distribution well at lower sediment depth. The Renyi entropy model results were also compared with Shannon entropy model results. Both models performed well for circular channels, but for circular channels with flat beds the Renyi entropy model displayed superior performance in estimating the shear stress distribution. The Renyi entropy model was highly precise and predicted the shear stress distribution in a circular channel with RE of 0.0480 and in a circular channel with a flat bed with RE of 0.0488.

  2. Experimental study of shear rate dependence in perpetually sheared granular matter

    NASA Astrophysics Data System (ADS)

    Liu, Sophie Yang; Guillard, François; Marks, Benjy; Rognon, Pierre; Einav, Itai

    2017-06-01

    We study the shear behaviour of various granular materials by conducting novel perpetual simple shear experiments over four orders of magnitude of relatively low shear rates. The newly developed experimental apparatus employed is called "3D Stadium Shear Device" which is an extended version of the 2D Stadium Shear Device [1]. This device is able to provide a non-radial dependent perpetual shear flow and a nearly linear velocity profile between two oppositely moving shear walls. Using this device, we are able to test a large variety of granular materials. Here, we demonstrate the applicability of the device on glass beads (diameter 1 mm, 3 mm, and 14 mm) and rice. We particularly focus on studying these materials at very low inertial number I ranging from 10-6 to 10-2. We find that, within this range of I, the friction coefficient μ of glass beads has no shear rate dependence. A particularly appealing observation comes from testing rice, where the attainment of critical state develops under much longer duration than in other materials. Initially during shear we find a value of μ similar to that found for glass beads, but with time this value decreases gradually towards the asymptotic critical state value. The reason, we believe, lies in the fact that rice grains are strongly elongated; hence the time to achieve the stable μ is primarily controlled by the time for particles to align themselves with respect to the shear walls. Furthermore, the initial packing conditions of samples also plays a role in the evolution of μ when the shear strain is small, but that impact will eventually be erased after sufficient shear strain.

  3. Heating, weakening and shear localization in earthquake rupture

    NASA Astrophysics Data System (ADS)

    Rice, James R.

    2017-08-01

    Field and borehole observations of active earthquake fault zones show that shear is often localized to principal deforming zones of order 0.1-10 mm width. This paper addresses how frictional heating in rapid slip weakens faults dramatically, relative to their static frictional strength, and promotes such intense localization. Pronounced weakening occurs even on dry rock-on-rock surfaces, due to flash heating effects, at slip rates above approximately 0.1 m s-1 (earthquake slip rates are typically of the order of 1 m s-1). But weakening in rapid shear is also predicted theoretically in thick fault gouge in the presence of fluids (whether native ground fluids or volatiles such as H2O or CO2 released by thermal decomposition reactions), and the predicted localizations are compatible with such narrow shear zones as have been observed. The underlying concepts show how fault zone materials with high static friction coefficients, approximately 0.6-0.8, can undergo strongly localized shear at effective dynamic friction coefficients of the order of 0.1, thus fitting observational constraints, e.g. of earthquakes producing negligible surface heat outflow and, for shallow events, only rarely creating extensive melt. The results to be summarized include those of collaborative research published with Nicolas Brantut (University College London), Eric Dunham (Stanford University), Nadia Lapusta (Caltech), Hiroyuki Noda (JAMSTEC, Japan), John D. Platt (Carnegie Institution for Science, now at *gramLabs), Alan Rempel (Oregon State University) and John W. Rudnicki (Northwestern University). This article is part of the themed issue 'Faulting, friction and weakening: from slow to fast motion'.

  4. Development of a shear stress sensor to analyse the influence of polymers on the turbulent wall shear stress.

    PubMed

    Nottebrock, Bernardo; Grosse, Sebastian; Schröder, Wolfgang

    2011-05-11

    The drag reducing effect of polymers in a channel flow is well known and it is assumed that the polymer filaments interfere with the turbulent structures in the very near-wall flow. To analyse their precise effect, a micro-pillar shear stress sensor (MPS³) measurement system is developed which allows the detection of wall shear stress at high spatial and temporal resolutions. Different manufacturing techniques for the required micro-pillars are discussed and their influence on the flow is investigated evidencing the non-intrusive character of the pillars. Subsequently, a complete calibration is presented to relate the recorded deflection to wall shear stress values and to assure the correct detection over the whole expected frequency spectrum. A feasibility study about the ability to visualize the two-dimensional wall shear stress distribution completes the discussion about the validity of MPS³. In the last step, the drag reduction of a polymer filament grafted on a micro-pillar compared to a plain pillar and the application of MPS³ in an ocean-type polymer solution are investigated. The results confirm the expected behaviour found in the literature.

  5. The effect of shearing strain-rate on the ultimate shearing resistance of clay

    NASA Technical Reports Server (NTRS)

    Cheng, R. Y. K.

    1975-01-01

    An approach for investigating the shearing resistance of cohesive soils subjected to a high rate of shearing strain is described. A fast step-loading torque apparatus was used to induce a state of pure shear in a hollow cylindrical soil specimen. The relationship between shearing resistance and rate of shear deformation was established for various soil densities expressed in terms of initial void ratio or water content. For rate of shearing deformation studies, the shearing resistance increases initially with shearing velocity, but subsequently reaches a terminal value as the shearing velocity increases. The terminal shearing resistance is also found to increase as the density of the soil increases. The results of this investigation are useful in the rheological study of clay. It is particularly important for mobility problems of soil runways, since the soil resistance is found to be sensitive to the rate of shearing.

  6. Flagellated bacteria trace out a parabolic arc under low shear condition

    NASA Astrophysics Data System (ADS)

    Ahn, Yongtae; Hashmi, Sara; Walker, Sharon; Hill, Jane

    2010-03-01

    The measurement and prediction of bacterial transport of bacteria in aquatic systems is of fundamental importance to a variety of fields such as groundwater bioremediation ascending urinary tract infection. The motility of pathogenic bacteria is, however, often missing when considering pathogen translocation prediction. Previously, we reported that flagellated E. coli can translate upstream under low shear flow conditions (Hill et al., 2007). The upstream swimming of flagellated microorganisms depends on hydrodynamic interaction between cell body and surrounding fluid flow. In this study, we use a breathable microfluidic device to image swimming E. coli and P. aeruginosa at a glass surface under low shear flow condition. We find the dominant experimental variables that lead to upstream swimming are: fluid shear, bacterium velocity, and bacterium length. We will present data showing that the sum of forces and torques acting on a bacterium lead to them tracing out a parabolic arc as they turn into the flow to swim upstream.

  7. Shear modulus of porcine coronary artery in reference to a new strain measure.

    PubMed

    Zhang, Wei; Lu, Xiao; Kassab, Ghassan S

    2007-11-01

    To simplify the stress-strain relationship of blood vessels, we define a logarithmic-exponential (log-exp) strain measure to absorb the nonlinearity. As a result, the constitutive relation between the second Piola-Kirchhoff stress and the log-exp strain can be written as a generalized Hooke's law. In this work, the shear modulus of porcine coronary arteries is determined from the experimental data in inflation-stretch-torsion tests. It is found that the shear modulus with respect to the log-exp strain can be viewed as a material constant in the full range of elasticity, and the incremental shear modulus for Cauchy shear stress and small shear strain at various loading levels can be predicted by the proposed Hooke's law. This result further validates the linear constitutive relation for blood vessels when shear deformation is involved.

  8. Shear Wave Imaging of Breast Tissue by Color Doppler Shear Wave Elastography.

    PubMed

    Yamakoshi, Yoshiki; Nakajima, Takahito; Kasahara, Toshihiro; Yamazaki, Mayuko; Koda, Ren; Sunaguchi, Naoki

    2017-02-01

    Shear wave elastography is a distinctive method to access the viscoelastic characteristic of the soft tissue that is difficult to obtain by other imaging modalities. This paper proposes a novel shear wave elastography [color Doppler shear wave imaging (CD SWI)] for breast tissue. Continuous shear wave is produced by a small lightweight actuator, which is attached to the tissue surface. Shear wave wavefront that propagates in tissue is reconstructed as a binary pattern that consists of zero and the maximum flow velocities on color flow image (CFI). Neither any modifications of the ultrasound color flow imaging instrument nor a high frame rate ultrasound imaging instrument is required to obtain the shear wave wavefront map. However, two conditions of shear wave displacement amplitude and shear wave frequency are needed to obtain the map. However, these conditions are not severe restrictions in breast imaging. This is because the minimum displacement amplitude is [Formula: see text] for an ultrasonic wave frequency of 12 MHz and the shear wave frequency is available from several frequencies suited for breast imaging. Fourier analysis along time axis suppresses clutter noise in CFI. A directional filter extracts shear wave, which propagates in the forward direction. Several maps, such as shear wave phase, velocity, and propagation maps, are reconstructed by CD SWI. The accuracy of shear wave velocity measurement is evaluated for homogeneous agar gel phantom by comparing with the acoustic radiation force impulse method. The experimental results for breast tissue are shown for a shear wave frequency of 296.6 Hz.

  9. Structural predictor for nonlinear sheared dynamics in simple glass-forming liquids

    NASA Astrophysics Data System (ADS)

    Ingebrigtsen, Trond S.; Tanaka, Hajime

    2018-01-01

    Glass-forming liquids subjected to sufficiently strong shear universally exhibit striking nonlinear behavior; for example, a power-law decrease of the viscosity with increasing shear rate. This phenomenon has attracted considerable attention over the years from both fundamental and applicational viewpoints. However, the out-of-equilibrium and nonlinear nature of sheared fluids have made theoretical understanding of this phenomenon very challenging and thus slower to progress. We find here that the structural relaxation time as a function of the two-body excess entropy, calculated for the extensional axis of the shear flow, collapses onto the corresponding equilibrium curve for a wide range of pair potentials ranging from harsh repulsive to soft and finite. This two-body excess entropy collapse provides a powerful approach to predicting the dynamics of nonequilibrium liquids from their equilibrium counterparts. Furthermore, the two-body excess entropy scaling suggests that sheared dynamics is controlled purely by the liquid structure captured in the form of the two-body excess entropy along the extensional direction, shedding light on the perplexing mechanism behind shear thinning.

  10. Structural predictor for nonlinear sheared dynamics in simple glass-forming liquids.

    PubMed

    Ingebrigtsen, Trond S; Tanaka, Hajime

    2018-01-02

    Glass-forming liquids subjected to sufficiently strong shear universally exhibit striking nonlinear behavior; for example, a power-law decrease of the viscosity with increasing shear rate. This phenomenon has attracted considerable attention over the years from both fundamental and applicational viewpoints. However, the out-of-equilibrium and nonlinear nature of sheared fluids have made theoretical understanding of this phenomenon very challenging and thus slower to progress. We find here that the structural relaxation time as a function of the two-body excess entropy, calculated for the extensional axis of the shear flow, collapses onto the corresponding equilibrium curve for a wide range of pair potentials ranging from harsh repulsive to soft and finite. This two-body excess entropy collapse provides a powerful approach to predicting the dynamics of nonequilibrium liquids from their equilibrium counterparts. Furthermore, the two-body excess entropy scaling suggests that sheared dynamics is controlled purely by the liquid structure captured in the form of the two-body excess entropy along the extensional direction, shedding light on the perplexing mechanism behind shear thinning.

  11. Predicting β-turns and their types using predicted backbone dihedral angles and secondary structures

    PubMed Central

    2010-01-01

    Background β-turns are secondary structure elements usually classified as coil. Their prediction is important, because of their role in protein folding and their frequent occurrence in protein chains. Results We have developed a novel method that predicts β-turns and their types using information from multiple sequence alignments, predicted secondary structures and, for the first time, predicted dihedral angles. Our method uses support vector machines, a supervised classification technique, and is trained and tested on three established datasets of 426, 547 and 823 protein chains. We achieve a Matthews correlation coefficient of up to 0.49, when predicting the location of β-turns, the highest reported value to date. Moreover, the additional dihedral information improves the prediction of β-turn types I, II, IV, VIII and "non-specific", achieving correlation coefficients up to 0.39, 0.33, 0.27, 0.14 and 0.38, respectively. Our results are more accurate than other methods. Conclusions We have created an accurate predictor of β-turns and their types. Our method, called DEBT, is available online at http://comp.chem.nottingham.ac.uk/debt/. PMID:20673368

  12. The classification of wind shears from the point of view of aerodynamics and flight mechanics

    NASA Technical Reports Server (NTRS)

    Seidler, Fritz; Hensel, Gunter

    1987-01-01

    A study of international statistical data shows that in about three quarters of all serious accidents which occurred with jet propelled airliners wind shear was either one of the main causes of the accident or represented a major contributory cause. Wind shear related problems are examined. The necessity of a use of different concepts, definitions, and divisions is explained, and the concepts and definitions required for the division of wind and wind shear into different categories is discussed. A description of the context between meteorological and aerodynamics-flight mechanics concepts, definitions, and divisions is also provided. Attention is given to wind and wind components, general characteristics of wind shear and the meteorological terms, the basic types of wind shear for aerodynamics-flight mechanics investigations, special types of wind shear for aerodynamics-flight mechanics investigations, and possibilities regarding a change of the wind component.

  13. BOUNDARY SHEAR STRESS ALONG VEGETATED STREAMBANKS

    EPA Science Inventory

    This research is intended to improve our understanding of the role of riparian vegetation in stream morphology by evaluating the effects of vegetation on boundary shear stress, providing insight to the type and density of vegetation required for streambank stability. The resu...

  14. Shear-Flow Instability Saturation by Stable Modes: Hydrodynamics and Gyrokinetics

    NASA Astrophysics Data System (ADS)

    Fraser, Adrian; Pueschel, M. J.; Terry, P. W.; Zweibel, E. G.

    2017-10-01

    We present simulations of shear-driven instabilities, focusing on the impact of nonlinearly excited, large-scale, linearly stable modes on the nonlinear cascade, momentum transport, and secondary instabilities. Stable modes, which have previously been shown to significantly affect instability saturation [Fraser et al. PoP 2017], are investigated in a collisionless, gyrokinetic, periodic zonal flow using the type="smallcap">Gene code by projecting the results of nonlinear simulations onto a basis of linear eigenmodes that includes both stable and unstable modes. Benchmarking growth rates against previous gyrokinetic studies and an equivalent fluid system demonstrates comparable linear dynamics in the fluid and gyrokinetic systems. Cases of driven and decaying shear-flow turbulence are compared in type="smallcap">Gene by using a Krook operator as an effective forcing. For comparison with existing hydrodynamic and MHD shear-flow instability studies, we present results for the shear layer obtained by similar means with the code Dedalus. Supported by U.S. DOE Grant No. DE-FG02-89ER53291, the NSF, and UW-Madison.

  15. Meniscal shear stress for punching.

    PubMed

    Tuijthof, Gabrielle J M; Meulman, Hubert N; Herder, Just L; van Dijk, C Niek

    2009-01-01

    Experimental determination of the shear stress for punching meniscal tissue. Meniscectomy (surgical treatment of a lesion of one of the menisci) is the most frequently performed arthroscopic procedure. The performance of a meniscectomy is not optimal with the currently available instruments. To design new instruments, the punching force of meniscal tissue is an important parameter. Quantitative data are unavailable. The meniscal punching process was simulated by pushing a rod through meniscal tissue at constant speed. Three punching rods were tested: a solid rod of Oslash; 3.00 mm, and two hollow tubes (Oslash; 3.00-2.60 mm) with sharpened cutting edges of 0.15 mm and 0.125 mm thick, respectively. Nineteen menisci acquired from 10 human cadaveric knee joints were punched (30 tests). The force and displacement were recorded from which the maximum shear stress was determined (average added with three times the standard deviation). The maximum shear stress for the solid rod was determined at 10.2 N/mm2. This rod required a significantly lower punch force in comparison with the hollow tube having a 0.15 mm cutting edge (plt;0.01). The maximum shear stress for punching can be applied to design instruments, and virtual reality training environments. This type of experiment is suitable to form a database with material properties of human tissue similar to databases for the manufacturing industry.

  16. Shear failure of granular materials

    NASA Astrophysics Data System (ADS)

    Degiuli, Eric; Balmforth, Neil; McElwaine, Jim; Schoof, Christian; Hewitt, Ian

    2012-02-01

    Connecting the macroscopic behavior of granular materials with the microstructure remains a great challenge. Recent work connects these scales with a discrete calculus [1]. In this work we generalize this formalism from monodisperse packings of disks to 2D assemblies of arbitrarily shaped grains. In particular, we derive Airy's expression for a symmetric, divergence-free stress tensor. Using these tools, we derive, from first-principles and in a mean-field approximation, the entropy of frictional force configurations in the Force Network Ensemble. As a macroscopic consequence of the Coulomb friction condition at contacts, we predict shear failure at a critical shear stress, in accordance with the Mohr-Coulomb failure condition well known in engineering. Results are compared with numerical simulations, and the dependence on the microscopic geometric configuration is discussed. [4pt] [1] E. DeGiuli & J. McElwaine, PRE 2011. doi: 10.1103/PhysRevE.84.041310

  17. Vibration and damping of laminated, composite-material plates including thickness-shear effects

    NASA Technical Reports Server (NTRS)

    Bert, C. W.; Siu, C. C.

    1972-01-01

    An analytical investigation of sinusoidally forced vibration of laminated, anisotropic plates including bending-stretching coupling, thickness-shear flexibility, all three types of inertia effects, and material damping is presented. In the analysis the effects of thickness-shear deformation are considered by the use of a shear correction factor K, analogous to that used by Mindlin for homogeneous plates. Two entirely different approaches for calculating the thickness-shear factor for a laminate are presented. Numerical examples indicate that the value of K depends on the layer properties and the stacking sequence of the laminate.

  18. Shear thinning and shear thickening of a confined suspension of vesicles

    NASA Astrophysics Data System (ADS)

    Nait Ouhra, A.; Farutin, A.; Aouane, O.; Ez-Zahraouy, H.; Benyoussef, A.; Misbah, C.

    2018-01-01

    Widely regarded as an interesting model system for studying flow properties of blood, vesicles are closed membranes of phospholipids that mimic the cytoplasmic membranes of red blood cells. In this study we analyze the rheology of a suspension of vesicles in a confined geometry: the suspension, bound by two planar rigid walls on each side, is subject to a shear flow. Flow properties are then analyzed as a function of shear rate γ ˙, the concentration of the suspension ϕ , and the viscosity contrast λ =ηin/ηout , where ηin and ηout are the fluid viscosities of the inner and outer fluids, respectively. We find that the apparent (or effective viscosity) of the suspension exhibits both shear thinning (decreasing viscosity with shear rate) or shear thickening (increasing viscosity with shear rate) in the same concentration range. The shear thinning or thickening behaviors appear as subtle phenomena, dependant on viscosity contrast λ . We provide physical arguments on the origins of these behaviors.

  19. Viscoelastic shear zone model of a strike-slip earthquake cycle

    USGS Publications Warehouse

    Pollitz, F.F.

    2001-01-01

    I examine the behavior of a two-dimensional (2-D) strike-slip fault system embedded in a 1-D elastic layer (schizosphere) overlying a uniform viscoelastic half-space (plastosphere) and within the boundaries of a finite width shear zone. The viscoelastic coupling model of Savage and Prescott [1978] considers the viscoelastic response of this system, in the absence of the shear zone boundaries, to an earthquake occurring within the upper elastic layer, steady slip beneath a prescribed depth, and the superposition of the responses of multiple earthquakes with characteristic slip occurring at regular intervals. So formulated, the viscoelastic coupling model predicts that sufficiently long after initiation of the system, (1) average fault-parallel velocity at any point is the average slip rate of that side of the fault and (2) far-field velocities equal the same constant rate. Because of the sensitivity to the mechanical properties of the schizosphere-plastosphere system (i.e., elastic layer thickness, plastosphere viscosity), this model has been used to infer such properties from measurements of interseismic velocity. Such inferences exploit the predicted behavior at a known time within the earthquake cycle. By modifying the viscoelastic coupling model to satisfy the additional constraint that the absolute velocity at prescribed shear zone boundaries is constant, I find that even though the time-averaged behavior remains the same, the spatiotemporal pattern of surface deformation (particularly its temporal variation within an earthquake cycle) is markedly different from that predicted by the conventional viscoelastic coupling model. These differences are magnified as plastosphere viscosity is reduced or as the recurrence interval of periodic earthquakes is lengthened. Application to the interseismic velocity field along the Mojave section of the San Andreas fault suggests that the region behaves mechanically like a ???600-km-wide shear zone accommodating 50 mm/yr fault

  20. Predictions of the shear response of (Mg,Fe)SiO3 post-perovskite

    NASA Astrophysics Data System (ADS)

    Metsue, A.; Tsuchiya, T.

    2011-12-01

    Observation of seismic data put in forth evidence of a spatial anisotropy in the seismic wave velocities in the D'' layer, the lowermost part of the mantle. (Mg,Fe)SiO3 post-perovskite (PPv) is thought to be the most abundant phase in this part of the mantle, and this mineral exhibits a strong elastic anisotropy and may contribute significantly to the seismic anisotropy in the D'' layer. However, the seismic anisotropy cannot be expressed at the rock scale if the orientations of the grains are distributed randomly. Consequently, the formation of lattice preferred orientations with an anisotropic mechanism of plasticity, such as dislocation creep, can cause the seismic anisotropy in the D'' layer. Some experiments have been done on the plasticity of pure and Fe-bearing MgSiO3 post-perovskite and lead to textures of deformation dominated by the (100) and (110) slip planes (Merkel et al., 2007) and by the (001) slip plane (Miyagi et al., 2010). On the other hand, theoretical calculations on the dislocations mobility on pure MgSiO3 (Carrez et al., 2007; Metsue et al., 2009) suggested a texture dominated by the (010) slip plane. A first step to understanding the mechanisms of plasticity and, therefore, the shear wave splitting occurring in the deep Earth is to test the response of the PPv phase to a plastic shear in a geophysical relevant composition. In this study, we present new results from first-principles calculations on the shear response of pure and ferrous iron-bearing MgSiO3 PPv. The originality of this work is the use of internally consistent LSDA+U formalism to accurately describe the local interactions between the d-states of iron. About 8% of iron is incorporated in the high spin state as a Mg substitution defect, since several studies suggest that iron is in the high spin in the D'' layer pressure range (Stackhouse et al., 2006; Metsue and Tsuchiya, 2011). We also performed the calculations for incorporated iron in the low spin state if an eventual spin

  1. Shear load transfer in high and low stress tendons.

    PubMed

    Kondratko-Mittnacht, Jaclyn; Duenwald-Kuehl, Sarah; Lakes, Roderic; Vanderby, Ray

    2015-05-01

    Tendon is an integral part of joint movement and stability, as it functions to transmit load from muscle to bone. It has an anisotropic, fibrous hierarchical structure that is generally loaded in the direction of its fibers/fascicles. Internal load distributions are altered when joint motion rotates an insertion site or when local damage disrupts fibers/fascicles, potentially causing inter-fiber (or inter-fascicular) shear. Tendons with different microstructures (helical versus linear) may redistribute loads differently. This study explored how shear redistributes axial loads in rat tail tendon (low stress tendons with linear microstructure) and porcine flexor tendon (high stress with helical microstructure) by creating lacerations on opposite sides of the tendon, ranging from about 20% to 60% of the tendon width, to create various magnitudes of shear. Differences in fascicular orientation were quantified using polarized light microscopy. Unexpectedly, both tendon types maintained about 20% of pre-laceration stress values after overlapping cuts of 60% of tendon width (no intact fibers end to end) suggesting that shear stress transfer can contribute more to overall tendon strength and stiffness than previously reported. All structural parameters for both tendon types decreased linearly with increasing laceration depth. The tail tendon had a more rapid decline in post-laceration elastic stress and modulus parameters as well as a more linear and less tightly packed fascicular structure, suggesting that positional tendons may be less well suited to redistribute loads via a shear mechanism. Copyright © 2015 Elsevier Ltd. All rights reserved.

  2. Shear Load Transfer in High and Low Stress Tendons

    PubMed Central

    Kondratko-Mittnacht, Jaclyn; Duenwald-Kuehl, Sarah; Lakes, Roderic; Vanderby, Ray

    2016-01-01

    Background Tendon is an integral part of joint movement and stability, as it functions to transmit load from muscle to bone. It has an anisotropic, fibrous hierarchical structure that is generally loaded in the direction of its fibers/fascicles. Internal load distributions are altered when joint motion rotates an insertion site or when local damage disrupts fibers/fascicles, potentially causing inter-fiber (or inter-fascicular) shear. Tendons with different microstructure (helical versus linear) may redistribute loads differently. Method of Approach This study explored how shear redistributes axial loads in rat tail tendon (low stress tendons with linear microstructure) and porcine flexor tendon (high stress with helical microstructure) by creating lacerations on opposite sides of the tendon, ranging from about 20-60% of the tendon width, to create various magnitudes of shear. Differences in fascicular orientation were quantified using polarized light microscopy. Results and Conclusions Unexpectedly, both tendon types maintained about 20% of pre-laceration stress values after overlapping cuts of 60% of tendon width (no intact fibers end to end) suggesting that shear stress transfer can contribute more to overall tendon strength and stiffness than previously reported. All structural parameters for both tendon types decreased linearly with increasing laceration depth. The tail tendon had a more rapid decline in post-laceration elastic stress and modulus parameters as well as a more linear and less tightly packed fascicular structure, suggesting that positional tendons may be less well suited to redistribute loads via a shear mechanism. PMID:25700261

  3. Shear-band thickness and shear-band cavities in a Zr-based metallic glass

    DOE PAGES

    Liu, C.; Roddatis, V.; Kenesei, P.; ...

    2017-08-14

    Strain localization into shear bands in metallic glasses is typically described as a mechanism that occurs at the nano-scale, leaving behind a shear defect with a thickness of 10–20 nm. Here we sample the structure of a single system-spanning shear band that has carried all plastic flow with high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and high-energy x-ray tomography (XRT). It is found that the shear-band thickness and the density change relative to the matrix sensitively depend on position along the shear band. A wide distribution of shear-band thickness (10 nm–210 nm) and density change (–1% to –12%)more » is revealed. There is no obvious correlation between shear-band thickness and density change, but larger thicknesses correspond typically to higher density changes. More than 100 micron-size shear-band cavities were identified on the shear-band plane, and their three-dimensional arrangement suggests a strongly fluctuating local curvature of the shear plane. As a result, these findings urge for a more complex view of a shear band than a simple nano-scale planar defect.« less

  4. Shear-band thickness and shear-band cavities in a Zr-based metallic glass

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Liu, C.; Roddatis, V.; Kenesei, P.

    Strain localization into shear bands in metallic glasses is typically described as a mechanism that occurs at the nano-scale, leaving behind a shear defect with a thickness of 10–20 nm. Here we sample the structure of a single system-spanning shear band that has carried all plastic flow with high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and high-energy x-ray tomography (XRT). It is found that the shear-band thickness and the density change relative to the matrix sensitively depend on position along the shear band. A wide distribution of shear-band thickness (10 nm–210 nm) and density change (–1% to –12%)more » is revealed. There is no obvious correlation between shear-band thickness and density change, but larger thicknesses correspond typically to higher density changes. More than 100 micron-size shear-band cavities were identified on the shear-band plane, and their three-dimensional arrangement suggests a strongly fluctuating local curvature of the shear plane. As a result, these findings urge for a more complex view of a shear band than a simple nano-scale planar defect.« less

  5. The importance of flow history in mixed shear and extensional flows

    NASA Astrophysics Data System (ADS)

    Wagner, Caroline; McKinley, Gareth

    2015-11-01

    Many complex fluid flows of experimental and academic interest exhibit mixed kinematics with regions of shear and elongation. Examples include flows through planar hyperbolic contractions in microfluidic devices and through porous media or geometric arrays. Through the introduction of a ``flow-type parameter'' α which varies between 0 in pure shear and 1 in pure elongation, the local velocity fields of all such mixed flows can be concisely characterized. It is tempting to then consider the local stress field and interpret the local state of stress in a complex fluid in terms of shearing or extensional material functions. However, the material response of such fluids exhibit a fading memory of the entire deformation history. We consider a dilute solution of Hookean dumbbells and solve the Oldroyd-B model to obtain analytic expressions for the entire stress field in any arbitrary mixed flow of constant strain rate and flow-type parameter α. We then consider a more complex flow for which the shear rate is constant but the flow-type parameter α varies periodically in time (reminiscent of flow through a periodic array or through repeated contractions and expansions). We show that the flow history and kinematic sequencing (in terms of whether the flow was initialized as shearing or extensional) is extremely important in determining the ensuing stress field and rate of dissipated energy in the flow, and can only be ignored in the limit of infinitely slow flow variations.

  6. Comparisons of physical experiment and discrete element simulations of sheared granular materials in an annular shear cell

    USGS Publications Warehouse

    Ji, S.; Hanes, D.M.; Shen, H.H.

    2009-01-01

    In this study, we report a direct comparison between a physical test and a computer simulation of rapidly sheared granular materials. An annular shear cell experiment was conducted. All parameters were kept the same between the physical and the computational systems to the extent possible. Artificially softened particles were used in the simulation to reduce the computational time to a manageable level. Sensitivity study on the particle stiffness ensured such artificial modification was acceptable. In the experiment, a range of normal stress was applied to a given amount of particles sheared in an annular trough with a range of controlled shear speed. Two types of particles, glass and Delrin, were used in the experiment. Qualitatively, the required torque to shear the materials under different rotational speed compared well with those in the physical experiments for both the glass and the Delrin particles. However, the quantitative discrepancies between the measured and simulated shear stresses were nearly a factor of two. Boundary conditions, particle size distribution, particle damping and friction, including a sliding and rolling, contact force model, were examined to determine their effects on the computational results. It was found that of the above, the rolling friction between particles had the most significant effect on the macro stress level. This study shows that discrete element simulation is a viable method for engineering design for granular material systems. Particle level information is needed to properly conduct these simulations. However, not all particle level information is equally important in the study regime. Rolling friction, which is not commonly considered in many discrete element models, appears to play an important role. ?? 2009 Elsevier Ltd.

  7. The upper bounds of reduced axial and shear moduli in cross-ply laminates with matrix cracks

    NASA Technical Reports Server (NTRS)

    Lee, Jong-Won; Allen, D. H.; Harris, C. E.

    1991-01-01

    The present study proposes a mathematical model utilizing the internal state variable concept for predicting the upper bounds of the reduced axial and shear stiffnesses in cross-ply laminates with matrix cracks. The displacement components at the matrix crack surfaces are explicitly expressed in terms of the observable axial and shear strains and the undamaged material properties. The reduced axial and shear stiffnesses are predicted for glass/epoxy and graphite/epoxy laminates. Comparison of the model with other theoretical and experimental studies is also presented to confirm direct applicability of the model to angle-ply laminates with matrix cracks subjected to general in-plane loading.

  8. Shear in high strength concrete bridge girders : technical report.

    DOT National Transportation Integrated Search

    2013-04-01

    Prestressed Concrete (PC) I-girders are used extensively as the primary superstructure components in Texas highway bridges. : A simple semi-empirical equation was developed at the University of Houston (UH) to predict the shear strength of PC I-girde...

  9. Colorimetric qualification of shear sensitive liquid crystal coatings

    NASA Technical Reports Server (NTRS)

    Muratore, Joseph J., Jr.

    1993-01-01

    The work that has been done to date on the Shear Sensitive Liquid Crystal Project demonstrated that cholesteric liquid crystal coatings respond to both the direction and magnitude of a shearing force. The response of the coating is to selectively scatter incident white light into a spectrum of colors. Discernible color changes at a fixed angle of observation and illumination are the result of an applied shear stress. The intention was to be able to convert these observable color patterns from a flow visualization technique into a quantitative tool. One of the earlier intentions was to be able to use liquid crystals in dynamic flow fields. This was assumed possible because liquid crystals had made it possible to visualize transients in surface shear forces. Although the transients were visualized by color changes to an order one micro second, the time response of a coating to align to a shearing force is dependent on the magnitude of the change between its initial and final states. Unfortunately, the response is not instantaneous. It is for this reason any future attempt at quantifying the magnitude and directions of a shearing force are limited to surface shear stress vector fields in three dimensional steady state flows. This limitation does not significantly detract from the utility of liquid crystal coatings. The measurement of skin friction in the study of transition on wings, prediction of drag forces, performance assessment, and the investigation of boundary layer behavior is of great importance in aerodynamics. There exist numerous examples of techniques for the measurement of surface shear stress. Most techniques require arduous calibrations and necessitate extensive preparation of the receiving surfaces. However, the main draw back of instruments such as Preston tubes, hot films, buried wire gages, and floating element balances is that they only provide a point measurement. The advantages of capturing global shear data would be appreciable when compared

  10. Nonlinear Reynolds stress model for turbulent shear flows

    NASA Technical Reports Server (NTRS)

    Barton, J. Michael; Rubinstein, R.; Kirtley, K. R.

    1991-01-01

    A nonlinear algebraic Reynolds stress model, derived using the renormalization group, is applied to equilibrium homogeneous shear flow and fully developed flow in a square duct. The model, which is quadratically nonlinear in the velocity gradients, successfully captures the large-scale inhomogeneity and anisotropy of the flows studied. The ratios of normal stresses, as well as the actual magnitudes of the stresses are correctly predicted for equilibrium homogeneous shear flow. Reynolds normal stress anisotropy and attendant turbulence driven secondary flow are predicted for a square duct. Profiles of mean velocity and normal stresses are in good agreement with measurements. Very close to walls, agreement with measurements diminishes. The model has the benefit of containing no arbitrary constants; all values are determined directly from the theory. It seems that near wall behavior is influenced by more than the large scale anisotropy accommodated in the current model. More accurate near wall calculations may well require a model for anisotropic dissipation.

  11. Migration arising from gradients in shear stress: Particle distributions in Poiseuille flow

    NASA Technical Reports Server (NTRS)

    Leighton, D. T., Jr.

    1988-01-01

    Experimental evidence for the existence of shear induced migration processes is reviewed and the mechanism by Leighton and Acrivos (1987b) is described in detail. The proposed mechanism is shown to lead to the existence of an additional shear induced migration in the presence of gradients in shear stress such as would be found in Poiseuille flow, and which may be used to predict the amplitude of the observed short-term viscosity increase. The concentration and velocity profiles which result from such a migration are discussed in detail and are compared to the experimental observations of Karnis, Goldsmith and Mason (1966).

  12. Shear velocity criterion for incipient motion of sediment

    USGS Publications Warehouse

    Simoes, Francisco J.

    2014-01-01

    The prediction of incipient motion has had great importance to the theory of sediment transport. The most commonly used methods are based on the concept of critical shear stress and employ an approach similar, or identical, to the Shields diagram. An alternative method that uses the movability number, defined as the ratio of the shear velocity to the particle’s settling velocity, was employed in this study. A large amount of experimental data were used to develop an empirical incipient motion criterion based on the movability number. It is shown that this approach can provide a simple and accurate method of computing the threshold condition for sediment motion.

  13. Effects of shear flow on phase nucleation and crystallization.

    PubMed

    Mura, Federica; Zaccone, Alessio

    2016-04-01

    Classical nucleation theory offers a good framework for understanding the common features of new phase formation processes in metastable homogeneous media at rest. However, nucleation processes in liquids are ubiquitously affected by hydrodynamic flow, and there is no satisfactory understanding of whether shear promotes or slows down the nucleation process. We developed a classical nucleation theory for sheared systems starting from the molecular level of the Becker-Doering master kinetic equation and we analytically derived a closed-form expression for the nucleation rate. The theory accounts for the effect of flow-mediated transport of molecules to the nucleus of the new phase, as well as for the mechanical deformation imparted to the nucleus by the flow field. The competition between flow-induced molecular transport, which accelerates nucleation, and flow-induced nucleus straining, which lowers the nucleation rate by increasing the nucleation energy barrier, gives rise to a marked nonmonotonic dependence of the nucleation rate on the shear rate. The theory predicts an optimal shear rate at which the nucleation rate is one order of magnitude larger than in the absence of flow.

  14. A critical review of the experimental data for developed free turbulent shear layers

    NASA Technical Reports Server (NTRS)

    Birch, S. F.; Eggers, J. M.

    1973-01-01

    Experimental shear layer data are reviewed and the results are compared to numerical predictions for three test cases. It was concluded from the study that many, if not most, of the apparent inconsistencies which exist in the interpretation of the experimental data for free shear layers result from confusing data taken in developed turbulent flows with those taken in transitional or developing flows. Other conclusions drawn from the study include the following: (1) The effects of Mach number are more uncertain primarily because of limited data and the absence of any turbulence measurements for supersonic shear layers. (2) The data available for heterogeneous shear layers are not sufficient to clearly establish the effect of density ratio on mixing rate.

  15. Nonequilibrium thermodynamics in sheared hard-sphere materials.

    PubMed

    Lieou, Charles K C; Langer, J S

    2012-06-01

    We combine the shear-transformation-zone (STZ) theory of amorphous plasticity with Edwards' statistical theory of granular materials to describe shear flow in a disordered system of thermalized hard spheres. The equations of motion for this system are developed within a statistical thermodynamic framework analogous to that which has been used in the analysis of molecular glasses. For hard spheres, the system volume V replaces the internal energy U as a function of entropy S in conventional statistical mechanics. In place of the effective temperature, the compactivity X=∂V/∂S characterizes the internal state of disorder. We derive the STZ equations of motion for a granular material accordingly, and predict the strain rate as a function of the ratio of the shear stress to the pressure for different values of a dimensionless, temperature-like variable near a jamming transition. We use a simplified version of our theory to interpret numerical simulations by Haxton, Schmiedeberg, and Liu, and in this way are able to obtain useful insights about internal rate factors and relations between jamming and glass transitions.

  16. Shear localization in three-dimensional amorphous solids.

    PubMed

    Dasgupta, Ratul; Gendelman, Oleg; Mishra, Pankaj; Procaccia, Itamar; Shor, Carmel A B Z

    2013-09-01

    In this paper we extend the recent theory of shear localization in two-dimensional (2D) amorphous solids to three dimensions. In two dimensions the fundamental instability of shear localization is related to the appearance of a line of displacement quadrupoles that makes an angle of 45^{∘} with the principal stress axis. In three dimensions the fundamental plastic instability is also explained by the formation of a lattice of anisotropic elastic inclusions. In the case of pure external shear stress, we demonstrate that this is a 2D triangular lattice of similar elementary events. It is shown that this lattice is arranged on a plane that, similarly to the 2D case, makes an angle of 45^{∘} with the principal stress axis. This solution is energetically favorable only if the external strain exceeds a yield-strain value that is determined by the strain parameters of the elementary events and the Poisson ratio. The predictions of the theory are compared to numerical simulations and very good agreement is observed.

  17. Calculation Method of Lateral Strengths and Ductility Factors of Constructions with Shear Walls of Different Ductility

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Yamaguchi, Nobuyoshi; Nakao, Masato; Murakami, Masahide

    2008-07-08

    For seismic design, ductility-related force modification factors are named R factor in Uniform Building Code of U.S, q factor in Euro Code 8 and Ds (inverse of R) factor in Japanese Building Code. These ductility-related force modification factors for each type of shear elements are appeared in those codes. Some constructions use various types of shear walls that have different ductility, especially for their retrofit or re-strengthening. In these cases, engineers puzzle the decision of force modification factors of the constructions. Solving this problem, new method to calculate lateral strengths of stories for simple shear wall systems is proposed andmore » named 'Stiffness--Potential Energy Addition Method' in this paper. This method uses two design lateral strengths for each type of shear walls in damage limit state and safety limit state. Two lateral strengths of stories in both limit states are calculated from these two design lateral strengths for each type of shear walls in both limit states. Calculated strengths have the same quality as values obtained by strength addition method using many steps of load-deformation data of shear walls. The new method to calculate ductility factors is also proposed in this paper. This method is based on the new method to calculate lateral strengths of stories. This method can solve the problem to obtain ductility factors of stories with shear walls of different ductility.« less

  18. CLASH: Weak-lensing shear-and-magnification analysis of 20 galaxy clusters

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Umetsu, Keiichi; Czakon, Nicole; Medezinski, Elinor

    2014-11-10

    We present a joint shear-and-magnification weak-lensing analysis of a sample of 16 X-ray-regular and 4 high-magnification galaxy clusters at 0.19 ≲ z ≲ 0.69 selected from the Cluster Lensing And Supernova survey with Hubble (CLASH). Our analysis uses wide-field multi-color imaging, taken primarily with Suprime-Cam on the Subaru Telescope. From a stacked-shear-only analysis of the X-ray-selected subsample, we detect the ensemble-averaged lensing signal with a total signal-to-noise ratio of ≅ 25 in the radial range of 200-3500 kpc h {sup –1}, providing integrated constraints on the halo profile shape and concentration-mass relation. The stacked tangential-shear signal is well described bymore » a family of standard density profiles predicted for dark-matter-dominated halos in gravitational equilibrium, namely, the Navarro-Frenk-White (NFW), truncated variants of NFW, and Einasto models. For the NFW model, we measure a mean concentration of c{sub 200c}=4.01{sub −0.32}{sup +0.35} at an effective halo mass of M{sub 200c}=1.34{sub −0.09}{sup +0.10}×10{sup 15} M{sub ⊙}. We show that this is in excellent agreement with Λ cold dark matter (ΛCDM) predictions when the CLASH X-ray selection function and projection effects are taken into account. The best-fit Einasto shape parameter is α{sub E}=0.191{sub −0.068}{sup +0.071}, which is consistent with the NFW-equivalent Einasto parameter of ∼0.18. We reconstruct projected mass density profiles of all CLASH clusters from a joint likelihood analysis of shear-and-magnification data and measure cluster masses at several characteristic radii assuming an NFW density profile. We also derive an ensemble-averaged total projected mass profile of the X-ray-selected subsample by stacking their individual mass profiles. The stacked total mass profile, constrained by the shear+magnification data, is shown to be consistent with our shear-based halo-model predictions, including the effects of surrounding large

  19. Flaw Tolerance In Lap Shear Brazed Joints. Part 2

    NASA Technical Reports Server (NTRS)

    Wang, Len; Flom, Yury

    2003-01-01

    This paper presents results of the second part of an on-going effort to gain better understanding of defect tolerance in braze joints. In the first part of this three-part series, we mechanically tested and modeled the strength of the lap joints as a function of the overlap distance. A failure criterion was established based on the zone damage theory, which predicts the dependence of the lap joint shear strength on the overlap distance, based on the critical size of a finite damage zone or an overloaded region in the joint. In this second part of the study, we experimentally verified the applicability of the damage zone criterion on prediction of the shear strength of the lap joint and introduced controlled flaws into the lap joints. The purpose of the study was to evaluate the lap joint strength as a function of flaw size and its location through mechanical testing and nonlinear finite element analysis (FEA) employing damage zone criterion for definition of failure. The results obtained from the second part of the investigation confirmed that the failure of the ductile lap shear brazed joints occurs when the damage zone reaches approximately 10% of the overlap width. The same failure criterion was applicable to the lap joints containing flaws.

  20. Ultrasound shear wave imaging

    NASA Astrophysics Data System (ADS)

    Ye, Shigong; Wu, Junru

    2000-05-01

    Shear wave propagation properties including phase velocity and attenuation coefficient are indispensable information in materials characterization and nondestructive evaluation. A computer controlled scanning shear-wave ultrasonic imaging system has been developed. It consists of a pair of focusing broadband pvdf transducers of central frequency of 50 MHz immersed in distilled water. Shear waves in a solid specimen are generated by mode-conversion. When ultrasonic waves generated by one of the pvdf transducers impinge upon a solid specimen from water with angle of incidence of θ that is greater than θcr, the critical angle of the longitudinal wave in the solid, only shear waves can propagate in the solid and longitudinal waves become evanescent waves. The shear waves pass through the specimen and received by the other pvdf transducer. Meanwhile, the specimen was scanned by a stepped motor of a step of 10 μm. The system was used to generated shear waves amplitude and phase velocity images of bone specimen of 1280 μm and they are compared with their longitudinal wave counterparts. The results have shown shear wave images can provide additional shear modulus and shear viscous information that longitudinal waves can't provide. The lateral resolution of 60 μm was achieved using shear wave imaging technique applied in bone sample.

  1. Constitutive Behavior of Reinforced Concrete Membrane Elements under Tri-directional Shear

    NASA Astrophysics Data System (ADS)

    Labib, Moheb

    The two-dimensional behavior of typical reinforced concrete (RC) structures has been extensively studied in the past several decades by investigating the constitutive behavior of full-scale reinforced concrete elements subjected to a bi-axial state of stress. In order to understand the true behavior of many large complex structures, the goal of this investigation is to develop new constitutive relationships for RC elements subjected to tri-directional shear stresses. Recently, additional out-of-plane jacks were installed on the panel tester at University of Houston so that concrete elements could be subjected to tri-directional shear stresses. This upgrade makes the panel tester the only one of its kind in the US that is capable of applying such combinations of stresses on full-scale reinforced concrete elements. This dissertation presents the details of the mounting and installation of the additional hydraulic jacks on the universal panel tester. The experimental program includes a series of seven reinforced concrete elements subjected to different combinations of in-plane and out-of-plane shear stresses. Increasing the applied out-of-plane shear stresses reduced the membrane shear strength of the elements. The effect of applying out-of-plane shear stresses on the in-plane shear strength was represented by modifying the softening coefficient in the compression stress strain curve of concrete struts. The modified model was able to capture the behavior and the ultimate capacity of the tested elements. The effect of the in-plane shear reinforcement ratio on the interaction between in-plane and out-of-plane shear stresses was evaluated. The model was implemented in the Finite Element package FEAP and was used to predict the ultimate capacity of many structures subjected to a combination of in-plane and out-of-plane shear stresses. The results of the analytical model were used to develop simplified design equations for members subjected to bi-directional shear loads

  2. Experimental Validation of the Transverse Shear Behavior of a Nomex Core for Sandwich Panels

    NASA Astrophysics Data System (ADS)

    Farooqi, M. I.; Nasir, M. A.; Ali, H. M.; Ali, Y.

    2017-05-01

    This work deals with determination of the transverse shear moduli of a Nomex® honeycomb core of sandwich panels. Their out-of-plane shear characteristics depend on the transverse shear moduli of the honeycomb core. These moduli were determined experimentally, numerically, and analytically. Numerical simulations were performed by using a unit cell model and three analytical approaches. Analytical calculations showed that two of the approaches provided reasonable predictions for the transverse shear modulus as compared with experimental results. However, the approach based upon the classical lamination theory showed large deviations from experimental data. Numerical simulations also showed a trend similar to that resulting from the analytical models.

  3. The effect of prior sandblasting of the wire on the shear bond strength of two different types of lingual retainers.

    PubMed

    Kilinç, Delal Dara; Sayar, Gülşilay

    2018-04-07

    The aim of this study was to evaluate the effect of total surface sandblasting on the shear bond strength of two different retainer wires. The null hypothesis was that there is no difference in the bond strength of the two types of lingual retainer wires when they are sandblasted. One hundred and sixty human premolar teeth were equally divided into four groups (n=40). A pair of teeth was embedded in self-curing acrylic resin and polished. Retainer wires were applied on the etched and rinsed surfaces of the teeth. Four retainers were used: group 1: braided retainer (0.010×0.028″, Ortho Technology); group 2: sandblasted braided retainer (0.010×0.028″, Ortho Technology); group 3: coaxial retainer (0.0215″ Coaxial, 3M) and group 4: sandblasted coaxial retainer (0.0215″ Coaxial, 3M). The specimens were tested using a universal test machine in shear mode with a crosshead speed of one mm/min. One-way analysis of variance (Anova) was used to determine the significant differences among the groups. There was no significant difference (P=0.117) among the groups according to this test. The null hypothesis was accepted. There was no statistically significant difference among the shear bond strength values of the four groups. Copyright © 2018 CEO. Published by Elsevier Masson SAS. All rights reserved.

  4. Lightweight concrete modification factor for shear friction.

    DOT National Transportation Integrated Search

    2013-10-01

    This report describes the results of a study initiated to examine the influence of concrete unit weight on the direct shear transfer across an interface of concretes cast at different times. This type of interface is common with structural precast co...

  5. Automatic Earthquake Shear Stress Measurement Method Developed for Accurate Time- Prediction Analysis of Forthcoming Major Earthquakes Along Shallow Active Faults

    NASA Astrophysics Data System (ADS)

    Serata, S.

    2006-12-01

    The Serata Stressmeter has been developed to measure and monitor earthquake shear stress build-up along shallow active faults. The development work made in the past 25 years has established the Stressmeter as an automatic stress measurement system to study timing of forthcoming major earthquakes in support of the current earthquake prediction studies based on statistical analysis of seismological observations. In early 1982, a series of major Man-made earthquakes (magnitude 4.5-5.0) suddenly occurred in an area over deep underground potash mine in Saskatchewan, Canada. By measuring underground stress condition of the mine, the direct cause of the earthquake was disclosed. The cause was successfully eliminated by controlling the stress condition of the mine. The Japanese government was interested in this development and the Stressmeter was introduced to the Japanese government research program for earthquake stress studies. In Japan the Stressmeter was first utilized for direct measurement of the intrinsic lateral tectonic stress gradient G. The measurement, conducted at the Mt. Fuji Underground Research Center of the Japanese government, disclosed the constant natural gradients of maximum and minimum lateral stresses in an excellent agreement with the theoretical value, i.e., G = 0.25. All the conventional methods of overcoring, hydrofracturing and deformation, which were introduced to compete with the Serata method, failed demonstrating the fundamental difficulties of the conventional methods. The intrinsic lateral stress gradient determined by the Stressmeter for the Japanese government was found to be the same with all the other measurements made by the Stressmeter in Japan. The stress measurement results obtained by the major international stress measurement work in the Hot Dry Rock Projects conducted in USA, England and Germany are found to be in good agreement with the Stressmeter results obtained in Japan. Based on this broad agreement, a solid geomechanical

  6. Interaction of two cylinders in shear flow at low Wi

    NASA Astrophysics Data System (ADS)

    Brown, M. J.; Leal, L. G.

    2001-11-01

    Experiments [Lyon et al., 2001; Boussima et al., 1996; Michelle et al., 1977] have shown that non-Brownian, non-Colloidal, and charge-neutral particles, when suspended in viscoelastic media and subjected to shear, will aggregate and flow-align above a critical shear rate Wi O(10). Giesekus [1978] proposed a mechanism for aggregation based on the attractive hoop thrusts about two particles in viscoelastic flow. This pairwise mechanism of attraction is borne out in studies of sedimenting particles [Feng & Joseph, 1996; Joseph et al., 1994], and seems a valid explanation for the aggregation observed in sedimenting suspensions over all Wi > Re [Joseph et al., 1994; Phillips, 1996.] Consideration of the flow around two particles in shear would lead one to expect attraction by this hoop thrust mechanism as well. However, it remains unclear why shear-induced aggregation only occurs above a critical Wi. A first step in understanding this criticality is to establish the low Wi behavior of two particles in shear. In this talk, we report on the interaction of two freely-mobile cylinders as predicted by an n-th order fluid computation.

  7. Thermal effects on shearing resistance of fractures in Tak granite

    NASA Astrophysics Data System (ADS)

    Khamrat, S.; Thongprapha, T.; Fuenkajorn, K.

    2018-06-01

    Triaxial shear tests have been performed on tension-induced fractures and smooth saw-cut surfaces in Tak granite under temperatures up to 773 K. The objective is to gain an understanding of the movement of shallow faults that cause seismic activities in the Tak batholith in the north of Thailand. The results indicate that the peak and residual shear strengths and fracture dilations notably decrease as the temperatures increase. The thermal effect is enhanced under higher confining pressures. The areas of the sheared-off asperities increase with temperature and confining pressure. A power equation can describe the increase of shear strengths with normal stress where the normal stress exponent is a linear function of the temperature. The strain energy principle is applied to incorporate the principal stresses and strains into a strength criterion. A linear relation between the distortional strain energy (Wd) and the mean strain energy (Wm) of the fractures is obtained. The Wd-Wm slope depends on the fracture roughness and strength of the asperities, which can be defined as a function of shear and mean strains and dilation of the fractures. This may allow predicting the peak strength of the shallow faults in the Tak batholith.

  8. Dynamic motion of red blood cells in simple shear flow

    NASA Astrophysics Data System (ADS)

    Sui, Y.; Chew, Y. T.; Roy, P.; Cheng, Y. P.; Low, H. T.

    2008-11-01

    A three-dimensional numerical model is proposed to simulate the dynamic motion of red blood cells (RBCs) in simple shear flow. The RBCs are approximated by ghost cells consisting of Newtonian liquid drops enclosed by Skalak membranes which take into account the membrane shear elasticity and the membrane area incompressibility. The RBCs have an initially biconcave discoid resting shape, and the internal liquid is assumed to have the same physical properties as the matrix fluid. The simulation is based on a hybrid method, in which the immersed boundary concept is introduced into the framework of the lattice Boltzmann method, and a finite element model is incorporated to obtain the forces acting on the nodes of the cell membrane which is discretized into flat triangular elements. The dynamic motion of RBCs is investigated in simple shear flow under a broad range of shear rates. At large shear rates, the cells are found to carry out a swinging motion, in which periodic inclination oscillation and shape deformation superimpose on the membrane tank treading motion. With the shear rate decreasing, the swinging amplitude of the cell increases, and finally triggers a transition to tumbling motion. This is the first direct numerical simulation that predicts both the swinging motion of the RBCs and the shear rate induced transition, which have been observed in a recent experiment. It is also found that as the mode changes from swinging to tumbling, the apparent viscosity of the suspension increases monotonically.

  9. Hydrodynamics of CNT dispersion in high shear dispersion mixers

    NASA Astrophysics Data System (ADS)

    Park, Young Min; Lee, Dong Hyun; Hwang, Wook Ryol; Lee, Sang Bok; Jung, Seung-Il

    2014-11-01

    In this work, we investigate the carbon nanotube (CNT) fragmentation mechanism and dispersion in high shear homogenizers as a plausible dispersion technique, correlating with device geometries and processing conditions, for mass production of CNT-aluminum composites for automobile industries. A CNT dispersion model has been established in a turbulent flow regime and an experimental method in characterizing the critical yield stress of CNT flocs are presented. Considering CNT dispersion in ethanol as a model system, we tested two different geometries of high shear mixers — blade-stirrer type and rotor-stator type homogenizers — and reported the particle size distributions in time and the comparison has been made with the modeling approach and partly with the computational results.

  10. Assessment of the Effects of Entrainment and Wind Shear on Nuclear Cloud Rise Modeling

    NASA Astrophysics Data System (ADS)

    Zalewski, Daniel; Jodoin, Vincent

    2001-04-01

    Accurate modeling of nuclear cloud rise is critical in hazard prediction following a nuclear detonation. This thesis recommends improvements to the model currently used by DOD. It considers a single-term versus a three-term entrainment equation, the value of the entrainment and eddy viscous drag parameters, as well as the effect of wind shear in the cloud rise following a nuclear detonation. It examines departures from the 1979 version of the Department of Defense Land Fallout Interpretive Code (DELFIC) with the current code used in the Hazard Prediction and Assessment Capability (HPAC) code version 3.2. The recommendation for a single-term entrainment equation, with constant value parameters, without wind shear corrections, and without cloud oscillations is based on both a statistical analysis using 67 U.S. nuclear atmospheric test shots and the physical representation of the modeling. The statistical analysis optimized the parameter values of interest for four cases: the three-term entrainment equation with wind shear and without wind shear as well as the single-term entrainment equation with and without wind shear. The thesis then examines the effect of cloud oscillations as a significant departure in the code. Modifications to user input atmospheric tables are identified as a potential problem in the calculation of stabilized cloud dimensions in HPAC.

  11. Temperature lapse rate as an adjunct to wind shear detection

    NASA Technical Reports Server (NTRS)

    Zweifil, Terry

    1991-01-01

    Several meteorological parameters were examined to determine if measurable atmospheric conditions can improve windshear detection devices. Lapse rate, the temperature change with altitude, shows promise as being an important parameter in the prediction of severe wind shears. It is easily measured from existing aircraft instrumentation, and it can be important indicator of convective activity including thunderstorms and microbursts. The meteorological theory behind lapse rate measurement is briefly reviewed, and and FAA certified system is described that is currently implemented in the Honeywell Wind Shear Detection and Guidance System.

  12. Displacement-length scaling of brittle faults in ductile shear.

    PubMed

    Grasemann, Bernhard; Exner, Ulrike; Tschegg, Cornelius

    2011-11-01

    Within a low-grade ductile shear zone, we investigated exceptionally well exposed brittle faults, which accumulated antithetic slip and rotated into the shearing direction. The foliation planes of the mylonitic host rock intersect the faults approximately at their centre and exhibit ductile reverse drag. Three types of brittle faults can be distinguished: (i) Faults developing on pre-existing K-feldspar/mica veins that are oblique to the shear direction. These faults have triclinic flanking structures. (ii) Wing cracks opening as mode I fractures at the tips of the triclinic flanking structures, perpendicular to the shear direction. These cracks are reactivated as faults with antithetic shear, extend from the parent K-feldspar/mica veins and form a complex linked flanking structure system. (iii) Joints forming perpendicular to the shearing direction are deformed to form monoclinic flanking structures. Triclinic and monoclinic flanking structures record elliptical displacement-distance profiles with steep displacement gradients at the fault tips by ductile flow in the host rocks, resulting in reverse drag of the foliation planes. These structures record one of the greatest maximum displacement/length ratios reported from natural fault structures. These exceptionally high ratios can be explained by localized antithetic displacement along brittle slip surfaces, which did not propagate during their rotation during surrounding ductile flow.

  13. Displacement–length scaling of brittle faults in ductile shear

    PubMed Central

    Grasemann, Bernhard; Exner, Ulrike; Tschegg, Cornelius

    2011-01-01

    Within a low-grade ductile shear zone, we investigated exceptionally well exposed brittle faults, which accumulated antithetic slip and rotated into the shearing direction. The foliation planes of the mylonitic host rock intersect the faults approximately at their centre and exhibit ductile reverse drag. Three types of brittle faults can be distinguished: (i) Faults developing on pre-existing K-feldspar/mica veins that are oblique to the shear direction. These faults have triclinic flanking structures. (ii) Wing cracks opening as mode I fractures at the tips of the triclinic flanking structures, perpendicular to the shear direction. These cracks are reactivated as faults with antithetic shear, extend from the parent K-feldspar/mica veins and form a complex linked flanking structure system. (iii) Joints forming perpendicular to the shearing direction are deformed to form monoclinic flanking structures. Triclinic and monoclinic flanking structures record elliptical displacement–distance profiles with steep displacement gradients at the fault tips by ductile flow in the host rocks, resulting in reverse drag of the foliation planes. These structures record one of the greatest maximum displacement/length ratios reported from natural fault structures. These exceptionally high ratios can be explained by localized antithetic displacement along brittle slip surfaces, which did not propagate during their rotation during surrounding ductile flow. PMID:26806996

  14. The shear instability energy: a new parameter for materials design?

    NASA Astrophysics Data System (ADS)

    Kanani, M.; Hartmaier, A.; Janisch, R.

    2017-10-01

    Reliable and predictive relationships between fundamental microstructural material properties and observable macroscopic mechanical behaviour are needed for the successful design of new materials. In this study we establish a link between physical properties that are defined on the atomic level and the deformation mechanisms of slip planes and interfaces that govern the mechanical behaviour of a metallic material. To accomplish this, the shear instability energy Γ is introduced, which can be determined via quantum mechanical ab initio calculations or other atomistic methods. The concept is based on a multilayer generalised stacking fault energy calculation and can be applied to distinguish the different shear deformation mechanisms occurring at TiAl interfaces during finite-temperature molecular dynamics simulations. We use the new parameter Γ to construct a deformation mechanism map for different interfaces occurring in this intermetallic. Furthermore, Γ can be used to convert the results of ab initio density functional theory calculations into those obtained with an embedded atom method type potential for TiAl. We propose to include this new physical parameter into material databases to apply it for the design of materials and microstructures, which so far mainly relies on single-crystal values for the unstable and stable stacking fault energy.

  15. Prediction of clathrate structure type and guest position by molecular mechanics.

    PubMed

    Fleischer, Everly B; Janda, Kenneth C

    2013-05-16

    The clathrate hydrates occur in various types in which the number, size, and shape of the various cages differ. Usually the clathrate type of a specific guest is predicted by the size and shape of the molecular guest. We have developed a methodology to determine the clathrate type employing molecular mechanics with the MMFF force field employing a strategy to calculate the energy of formation of the clathrate from the sum of the guest/cage energies. The clathrate type with the most negative (most stable) energy of formation would be the type predicted (we mainly focused on type I, type II, or bromine type). This strategy allows for a calculation to predict the clathrate type for any cage guest in a few minutes on a laptop computer. It proved successful in predicting the clathrate structure for 46 out of 47 guest molecules. The molecular mechanics calculations also provide a prediction of the guest position within the cage and clathrate structure. These predictions are generally consistent with the X-ray and neutron diffraction studies. By supplementing the diffraction study with molecular mechanics, we gain a more detailed insight regarding the details of the structure. We have also compared MM calculations to studies of the multiple occupancy of the cages. Finally, we present a density functional calculation that demonstrates that the inside of the clathrates cages have a relatively uniform and low electrostatic potential in comparison with the outside oxygen and hydrogen atoms. This implies that van der Waals forces will usually be dominant in the guest-cage interactions.

  16. Prediction of soil stress-strain response incorporates mobilised shear strength envelope of granitic residual soil

    NASA Astrophysics Data System (ADS)

    Rahman, Abdul Samad Abdul; Noor, Mohd Jamaludin Md; Ahmad, Juhaizad Bin; Sidek, Norbaya

    2017-10-01

    The concept of effective stress has been the principal concept in characterizing soil volume change behavior in soil mechanics, the settlement models developed using this concept have been empirical in nature. However, there remain certain unexplained soil volume change behaviors that cannot be explained using the effective stress concept, one such behaviour is the inundation settlement. Studies have begun to indicate the inevitable role of shear strength as a critical element to be incorporated in models to unravel the unexplained soil behaviours. One soil volume change model that applies the concept of effective stress and the shear strength interaction is the Rotational Multiple Yield Surface Framework (RMYSF) model. This model has been developed from the soil-strain behavior under anisotropic stress condition. Hence, the RMYSF actually measure the soil actual elasto-plastic response to stress rather than assuming it to be fully elastic or plastic as normally perceived by the industry. The frameworks measures the increase in the mobilize shear strength when the soil undergo anisotropic settlement.

  17. Measurement of the Shear Lift Force on a Bubble in a Channel Flow

    NASA Technical Reports Server (NTRS)

    Nahra, Henry K.; Motil, Brian; Skor, Mark

    2005-01-01

    values for the shear lift are then compared with the theoretical predictions from various published works on shear lift in the open literature, which include asymptotic solutions at low bubble Reynolds number, potential flow predictions and numerical studies that deal with intermediate bubble Reynolds numbers.

  18. Kramers-Kronig based quality factor for shear wave propagation in soft tissue

    PubMed Central

    Urban, M W; Greenleaf, J F

    2009-01-01

    Shear wave propagation techniques have been introduced for measuring the viscoelastic material properties of tissue, but assessing the accuracy of these measurements is difficult for in vivo measurements in tissue. We propose using the Kramers-Kronig relationships to assess the consistency and quality of the measurements of shear wave attenuation and phase velocity. In ex vivo skeletal muscle we measured the wave attenuation at different frequencies, and then applied finite bandwidth Kramers-Kronig equations to predict the phase velocities. We compared these predictions with the measured phase velocities and assessed the mean square error (MSE) as a quality factor. An algorithm was derived for computing a quality factor using the Kramers-Kronig relationships. PMID:19759409

  19. Metaheuristic optimization approaches to predict shear-wave velocity from conventional well logs in sandstone and carbonate case studies

    NASA Astrophysics Data System (ADS)

    Emami Niri, Mohammad; Amiri Kolajoobi, Rasool; Khodaiy Arbat, Mohammad; Shahbazi Raz, Mahdi

    2018-06-01

    Seismic wave velocities, along with petrophysical data, provide valuable information during the exploration and development stages of oil and gas fields. The compressional-wave velocity (VP ) is acquired using conventional acoustic logging tools in many drilled wells. But the shear-wave velocity (VS ) is recorded using advanced logging tools only in a limited number of wells, mainly because of the high operational costs. In addition, laboratory measurements of seismic velocities on core samples are expensive and time consuming. So, alternative methods are often used to estimate VS . Heretofore, several empirical correlations that predict VS by using well logging measurements and petrophysical data such as VP , porosity and density are proposed. However, these empirical relations can only be used in limited cases. The use of intelligent systems and optimization algorithms are inexpensive, fast and efficient approaches for predicting VS. In this study, in addition to the widely used Greenberg–Castagna empirical method, we implement three relatively recently developed metaheuristic algorithms to construct linear and nonlinear models for predicting VS : teaching–learning based optimization, imperialist competitive and artificial bee colony algorithms. We demonstrate the applicability and performance of these algorithms to predict Vs using conventional well logs in two field data examples, a sandstone formation from an offshore oil field and a carbonate formation from an onshore oil field. We compared the estimated VS using each of the employed metaheuristic approaches with observed VS and also with those predicted by Greenberg–Castagna relations. The results indicate that, for both sandstone and carbonate case studies, all three implemented metaheuristic algorithms are more efficient and reliable than the empirical correlation to predict VS . The results also demonstrate that in both sandstone and carbonate case studies, the performance of an artificial bee

  20. Colloidal layers in magnetic fields and under shear flow

    NASA Astrophysics Data System (ADS)

    Löwen, H.; Messina, R.; Hoffmann, N.; Likos, C. N.; Eisenmann, C.; Keim, P.; Gasser, U.; Maret, G.; Goldberg, R.; Palberg, T.

    2005-11-01

    The behaviour of colloidal mono- and bilayers in external magnetic fields and under shear is discussed and recent progress is summarized. Superparamagnetic colloidal particles form monolayers when they are confined to a air-water interface in a hanging water droplet. An external magnetic field allows us to tune the strength of the mutual dipole-dipole interaction between the colloids and the anisotropy of the interaction can be controlled by the tilt angle of the magnetic field relative to the surface normal of the air-water interface. For sufficiently large magnetic field strength crystalline monolayers are found. The role of fluctuations in these two-dimensional crystals is discussed. Furthermore, clustering phenomena in binary mixtures of superparamagnetic particles forming fluid monolayers are predicted. Finally, we address sheared colloidal bilayers and find that the orientation of confined colloidal crystals can be tailored by a previously applied shear direction.

  1. Mean-field dynamo action in renovating shearing flows.

    PubMed

    Kolekar, Sanved; Subramanian, Kandaswamy; Sridhar, S

    2012-08-01

    We study mean-field dynamo action in renovating flows with finite and nonzero correlation time (τ) in the presence of shear. Previous results obtained when shear was absent are generalized to the case with shear. The question of whether the mean magnetic field can grow in the presence of shear and nonhelical turbulence, as seen in numerical simulations, is examined. We show in a general manner that, if the motions are strictly nonhelical, then such mean-field dynamo action is not possible. This result is not limited to low (fluid or magnetic) Reynolds numbers nor does it use any closure approximation; it only assumes that the flow renovates itself after each time interval τ. Specifying to a particular form of the renovating flow with helicity, we recover the standard dispersion relation of the α(2)Ω dynamo, in the small τ or large wavelength limit. Thus mean fields grow even in the presence of rapidly growing fluctuations, surprisingly, in a manner predicted by the standard quasilinear closure, even though such a closure is not strictly justified. Our work also suggests the possibility of obtaining mean-field dynamo growth in the presence of helicity fluctuations, although having a coherent helicity will be more efficient.

  2. Shear Adhesion of Tapered Nanopillar Arrays.

    PubMed

    Cho, Younghyun; Minsky, Helen K; Jiang, Yijie; Yin, Kaiyang; Turner, Kevin T; Yang, Shu

    2018-04-04

    Tapered nanopillars with various cross sections, including cone-shaped, stepwise, and pencil-like structures (300 nm in diameter at the base of the pillars and 1.1 μm in height), are prepared from epoxy resin templated by nanoporous anodic aluminum oxide (AAO) membranes. The effect of pillar geometry on the shear adhesion behavior of these nanopillar arrays is investigated via sliding experiments in a nanoindentation system. In a previous study of arrays with the same geometry, it was shown that cone-shaped nanopillars exhibit the highest adhesion under normal loading while stepwise and pencil-like nanopillars exhibit lower normal adhesion strength due to significant deformation of the pillars that occurs with increasing indentation depth. Contrary to the previous studies, here, we show that pencil-like nanopillars exhibit the highest shear adhesion strength at all indentation depths among three types of nanopillar arrays and that the shear adhesion increases with greater indentation depth due to the higher bending stiffness and closer packing of the pencil-like nanopillar array. Finite element simulations are used to elucidate the deformation of the pillars during the sliding experiments and agree with the nanoindentation-based sliding measurements. The experiments and finite element simulations together demonstrate that the shape of the nanopillars plays a key role in shear adhesion and that the mechanism is quite different from that of adhesion under normal loading.

  3. Approximate Dispersion Relations for Waves on Arbitrary Shear Flows

    NASA Astrophysics Data System (ADS)

    Ellingsen, S. À.; Li, Y.

    2017-12-01

    An approximate dispersion relation is derived and presented for linear surface waves atop a shear current whose magnitude and direction can vary arbitrarily with depth. The approximation, derived to first order of deviation from potential flow, is shown to produce good approximations at all wavelengths for a wide range of naturally occuring shear flows as well as widely used model flows. The relation reduces in many cases to a 3-D generalization of the much used approximation by Skop (1987), developed further by Kirby and Chen (1989), but is shown to be more robust, succeeding in situations where the Kirby and Chen model fails. The two approximations incur the same numerical cost and difficulty. While the Kirby and Chen approximation is excellent for a wide range of currents, the exact criteria for its applicability have not been known. We explain the apparently serendipitous success of the latter and derive proper conditions of applicability for both approximate dispersion relations. Our new model has a greater range of applicability. A second order approximation is also derived. It greatly improves accuracy, which is shown to be important in difficult cases. It has an advantage over the corresponding second-order expression proposed by Kirby and Chen that its criterion of accuracy is explicitly known, which is not currently the case for the latter to our knowledge. Our second-order term is also arguably significantly simpler to implement, and more physically transparent, than its sibling due to Kirby and Chen.type="synopsis">type</span>="main">Plain Language SummaryIn order to answer key questions such as how the ocean surface affects the climate, erodes the coastline and transports nutrients, we must understand how waves move. This is not so easy when depth varying currents are present, as they often are in coastal waters. We have developed a modeling tool for accurately <span class="hlt">predicting</span> wave properties in such situations, ready for use, for example, in the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.usgs.gov/of/1983/0491/report.pdf','USGSPUBS'); return false;" href="https://pubs.usgs.gov/of/1983/0491/report.pdf"><span>A microcomputer-based data acquisition and control system for the direct <span class="hlt">shear</span>, ring <span class="hlt">shear</span>, triaxial <span class="hlt">shear</span>, and consolidation tests</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Powers, Philip S.</p> <p>1983-01-01</p> <p>This report is intended to provide internal documentation for the U.S. Geological Survey laboratory's automatic data acquisition system. The operating procedures for each <span class="hlt">type</span> of test are designed to independently lead a first-time user through the various stages of using the computer to control the test. Continuing advances in computer technology and the availability of desktop microcomputers with a wide variety of peripheral equipment at a reasonable cost can create an efficient automated geotechnical testing environment. A geotechnical testing environment is shown in figure 1. Using an automatic data acquisition system, laboratory test data from a variety of sensors can be collected, and manually or automatically recorded on a magnetic device at the same apparent time. The responses of a test can be displayed graphically on a CRT in a matter of seconds, giving the investigator an opportunity to evaluate the test data, and to make timely, informed decisions on such matters as whether to continue testing, abandon a test, or modify procedures. Data can be retrieved and results reported in tabular form, or graphic plots, suitable for publication. Thermistors, thermocouples, load cells, pressure transducers, and linear variable differential transformers are typical sensors which are incorporated in automated systems. The geotechnical tests which are most practical to automate are the long-term tests which often require readings to be recorded outside normal work hours and on weekends. Automation applications include incremental load consolidation tests, constant-rate-of-strain consolidation tests, direct <span class="hlt">shear</span> tests, ring <span class="hlt">shear</span> tests, and triaxial <span class="hlt">shear</span> tests.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/pages/biblio/1430903-experimental-development-low-frequency-shear-modulus-attenuation-measurements-mated-rock-fractures-shear-mechanics-due-asperity-contact-area-changes-normal-stress','SCIGOV-DOEP'); return false;" href="https://www.osti.gov/pages/biblio/1430903-experimental-development-low-frequency-shear-modulus-attenuation-measurements-mated-rock-fractures-shear-mechanics-due-asperity-contact-area-changes-normal-stress"><span>Experimental development of low-frequency <span class="hlt">shear</span> modulus and attenuation measurements in mated rock fractures: <span class="hlt">Shear</span> mechanics due to asperity contact area changes with normal stress</span></a></p> <p><a target="_blank" href="http://www.osti.gov/pages">DOE PAGES</a></p> <p>Saltiel, Seth; Selvadurai, Paul A.; Bonner, Brian P.; ...</p> <p>2017-02-16</p> <p>Reservoir core measurements can help guide seismic monitoring of fluid-induced pressure variations in tight fractured reservoirs including those targeted for supercritical CO 2 injection. We present the first seismic-frequency ‘room-dry’ measurements of fracture specific <span class="hlt">shear</span> stiffness, using artificially fractured standard granite samples with different degrees of mating, a well-mated tensile fracture from a dolomite reservoir core, as well as simple roughened polymethyl methacrylate (PMMA) surfaces. We have adapted a low-frequency (0.01 to 100 Hz) <span class="hlt">shear</span> modulus and attenuation apparatus to explore the seismic signature of fractures and understand the mechanics of asperity contacts under a range of normal stress conditions.more » Our instrument is unique in its ability to measure at low normal stresses (0.5 – 20 MPa), simulating 'open' fractures in shallow or high fluid pressure reservoirs. The accuracy of our instrument is demonstrated by calibration and comparison to ultrasonic measurements and low-frequency direct <span class="hlt">shear</span> measurements of intact samples from the literature. Pressure sensitive film was used to measure real contact area of the fracture surfaces. The fractured <span class="hlt">shear</span> modulus for the majority of the samples shows an exponential dependence on real contact area. A simple numerical model, with one bonded circular asperity, <span class="hlt">predicts</span> this behavior and matches the data for the simple PMMA surfaces. The rock surfaces reach their intact moduli at lower contact area than the model <span class="hlt">predicts</span>, likely due to more complex geometry. Lastly, we apply our results to a Linear-Slip Interface Model to estimate reflection coefficients and calculate <span class="hlt">shear</span> wave time delays due to the lower wave velocities through the fractured zone. We find that cross-well surveys could detect even well-mated hard rock fractures assuming the availability of high repeatability acquisition systems.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/servlets/purl/1430903','SCIGOV-STC'); return false;" href="https://www.osti.gov/servlets/purl/1430903"><span>Experimental development of low-frequency <span class="hlt">shear</span> modulus and attenuation measurements in mated rock fractures: <span class="hlt">Shear</span> mechanics due to asperity contact area changes with normal stress</span></a></p> <p><a target="_blank" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Saltiel, Seth; Selvadurai, Paul A.; Bonner, Brian P.</p> <p></p> <p>Reservoir core measurements can help guide seismic monitoring of fluid-induced pressure variations in tight fractured reservoirs including those targeted for supercritical CO 2 injection. We present the first seismic-frequency ‘room-dry’ measurements of fracture specific <span class="hlt">shear</span> stiffness, using artificially fractured standard granite samples with different degrees of mating, a well-mated tensile fracture from a dolomite reservoir core, as well as simple roughened polymethyl methacrylate (PMMA) surfaces. We have adapted a low-frequency (0.01 to 100 Hz) <span class="hlt">shear</span> modulus and attenuation apparatus to explore the seismic signature of fractures and understand the mechanics of asperity contacts under a range of normal stress conditions.more » Our instrument is unique in its ability to measure at low normal stresses (0.5 – 20 MPa), simulating 'open' fractures in shallow or high fluid pressure reservoirs. The accuracy of our instrument is demonstrated by calibration and comparison to ultrasonic measurements and low-frequency direct <span class="hlt">shear</span> measurements of intact samples from the literature. Pressure sensitive film was used to measure real contact area of the fracture surfaces. The fractured <span class="hlt">shear</span> modulus for the majority of the samples shows an exponential dependence on real contact area. A simple numerical model, with one bonded circular asperity, <span class="hlt">predicts</span> this behavior and matches the data for the simple PMMA surfaces. The rock surfaces reach their intact moduli at lower contact area than the model <span class="hlt">predicts</span>, likely due to more complex geometry. Lastly, we apply our results to a Linear-Slip Interface Model to estimate reflection coefficients and calculate <span class="hlt">shear</span> wave time delays due to the lower wave velocities through the fractured zone. We find that cross-well surveys could detect even well-mated hard rock fractures assuming the availability of high repeatability acquisition systems.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20070031587&hterms=stress+relationship&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dstress%2Brelationship','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20070031587&hterms=stress+relationship&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dstress%2Brelationship"><span><span class="hlt">Shear</span> Stress Partitioning in Large Patches of Roughness in the Atmospheric Inertial Sublayer</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Gillies, John A.; Nickling, William G.; King, James</p> <p>2007-01-01</p> <p>Drag partition measurements were made in the atmospheric inertial sublayer for six roughness configurations made up of solid elements in staggered arrays of different roughness densities. The roughness was in the form of a patch within a large open area and in the shape of an equilateral triangle with 60 m long sides. Measurements were obtained of the total <span class="hlt">shear</span> stress (tau) acting on the surfaces, the surface <span class="hlt">shear</span> stress on the ground between the elements (tau(sub S)) and the drag force on the elements for each roughness array. The measurements indicated that tau(sub S) quickly reduced near the leading edge of the roughness compared with tau, and a tau(sub S) minimum occurs at a normalized distance (x/h, where h is element height) of approx. -42 (downwind of the roughness leading edge is negative), then recovers to a relatively stable value. The location of the minimum appears to scale with element height and not roughness density. The force on the elements decreases exponentially with normalized downwind distance and this rate of change scales with the roughness density, with the rate of change increasing as roughness density increases. Average tau(sub S): tau values for the six roughness surfaces scale <span class="hlt">predictably</span> as a function of roughness density and in accordance with a <span class="hlt">shear</span> stress partitioning model. The <span class="hlt">shear</span> stress partitioning model performed very well in <span class="hlt">predicting</span> the amount of surface <span class="hlt">shear</span> stress, given knowledge of the stated input parameters for these patches of roughness. As the <span class="hlt">shear</span> stress partitioning relationship within the roughness appears to come into equilibrium faster for smaller roughness element sizes it would also appear the <span class="hlt">shear</span> stress partitioning model can be applied with confidence for smaller patches of smaller roughness elements than those used in this experiment.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014RPPh...77d6602B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014RPPh...77d6602B"><span><span class="hlt">Shear</span> thickening in concentrated suspensions: phenomenology, mechanisms and relations to jamming</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Brown, Eric; Jaeger, Heinrich M.</p> <p>2014-04-01</p> <p><span class="hlt">Shear</span> thickening is a <span class="hlt">type</span> of non-Newtonian behavior in which the stress required to <span class="hlt">shear</span> a fluid increases faster than linearly with <span class="hlt">shear</span> rate. Many concentrated suspensions of particles exhibit an especially dramatic version, known as Discontinuous <span class="hlt">Shear</span> Thickening (DST), in which the stress suddenly jumps with increasing <span class="hlt">shear</span> rate and produces solid-like behavior. The best known example of such counter-intuitive response to applied stresses occurs in mixtures of cornstarch in water. Over the last several years, this <span class="hlt">shear</span>-induced solid-like behavior together with a variety of other unusual fluid phenomena has generated considerable interest in the physics of densely packed suspensions. In this review, we discuss the common physical properties of systems exhibiting <span class="hlt">shear</span> thickening, and different mechanisms and models proposed to describe it. We then suggest how these mechanisms may be related and generalized, and propose a general phase diagram for <span class="hlt">shear</span> thickening systems. We also discuss how recent work has related the physics of <span class="hlt">shear</span> thickening to that of granular materials and jammed systems. Since DST is described by models that require only simple generic interactions between particles, we outline the broader context of other concentrated many-particle systems such as foams and emulsions, and explain why DST is restricted to the parameter regime of hard-particle suspensions. Finally, we discuss some of the outstanding problems and emerging opportunities.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24838372','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24838372"><span><span class="hlt">Type</span> I and II β-turns <span class="hlt">prediction</span> using NMR chemical shifts.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wang, Ching-Cheng; Lai, Wen-Chung; Chuang, Woei-Jer</p> <p>2014-07-01</p> <p>A method for <span class="hlt">predicting</span> <span class="hlt">type</span> I and II β-turns using nuclear magnetic resonance (NMR) chemical shifts is proposed. Isolated β-turn chemical-shift data were collected from 1,798 protein chains. One-dimensional statistical analyses on chemical-shift data of three classes β-turn (<span class="hlt">type</span> I, II, and VIII) showed different distributions at four positions, (i) to (i + 3). Considering the central two residues of <span class="hlt">type</span> I β-turns, the mean values of Cο, Cα, H(N), and N(H) chemical shifts were generally (i + 1) > (i + 2). The mean values of Cβ and Hα chemical shifts were (i + 1) < (i + 2). The distributions of the central two residues in <span class="hlt">type</span> II and VIII β-turns were also distinguishable by trends of chemical shift values. Two-dimensional cluster analyses on chemical-shift data show positional distributions more clearly. Based on these propensities of chemical shift classified as a function of position, rules were derived using scoring matrices for four consecutive residues to <span class="hlt">predict</span> <span class="hlt">type</span> I and II β-turns. The proposed method achieves an overall <span class="hlt">prediction</span> accuracy of 83.2 and 84.2% with the Matthews correlation coefficient values of 0.317 and 0.632 for <span class="hlt">type</span> I and II β-turns, indicating that its higher accuracy for <span class="hlt">type</span> II turn <span class="hlt">prediction</span>. The results show that it is feasible to use NMR chemical shifts to <span class="hlt">predict</span> the β-turn <span class="hlt">types</span> in proteins. The proposed method can be incorporated into other chemical-shift based protein secondary structure <span class="hlt">prediction</span> methods.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018RMRE...51.1885W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018RMRE...51.1885W"><span><span class="hlt">Shear</span> Behaviour and Acoustic Emission Characteristics of Bolted Rock Joints with Different Roughnesses</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Gang; Zhang, Yongzheng; Jiang, Yujing; Liu, Peixun; Guo, Yanshuang; Liu, Jiankang; Ma, Ming; Wang, Ke; Wang, Shugang</p> <p>2018-06-01</p> <p>To study <span class="hlt">shear</span> failure, acoustic emission counts and characteristics of bolted jointed rock-like specimens are evaluated under compressive <span class="hlt">shear</span> loading. Model joint surfaces with different roughnesses are made of rock-like material (i.e. cement). The jointed rock masses are anchored with bolts with different elongation rates. The characteristics of the <span class="hlt">shear</span> mechanical properties, the failure mechanism, and the acoustic emission parameters of the anchored joints are studied under different surface roughnesses and anchorage conditions. The <span class="hlt">shear</span> strength and residual strength increase with the roughness of the anchored joint surface. With an increase in bolt elongation, the <span class="hlt">shear</span> strength of the anchored joint surface gradually decreases. When the anchored structural plane is <span class="hlt">sheared</span>, the ideal cumulative impact curve can be divided into four stages: initial emission, critical instability, cumulative energy, and failure. With an increase in the roughness of the anchored joint surface, the peak energy rate and the cumulative number of events will also increase during macro-scale <span class="hlt">shear</span> failure. With an increase in the bolt elongation, the energy rate and the event number increase during the <span class="hlt">shearing</span> process. Furthermore, the peak energy rate, peak number of events and cumulative energy will all increase with the bolt elongation. The results of this study can provide guidance for the use of the acoustic emission technique in monitoring and <span class="hlt">predicting</span> the static <span class="hlt">shear</span> failure of anchored rock masses.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017PhRvF...2l3301M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017PhRvF...2l3301M"><span>Giant deviation of a relaxation time from generalized Newtonian theory in discontinuous <span class="hlt">shear</span> thickening suspensions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Maharjan, Rijan; Brown, Eric</p> <p>2017-12-01</p> <p>We investigated the transient relaxation of a discontinuous <span class="hlt">shear</span> thickening (DST) suspension of cornstarch in water. We performed two <span class="hlt">types</span> of relaxation experiments starting from a steady <span class="hlt">shear</span> in a parallel-plate rheometer, followed either by stopping the top plate rotation and measuring the transient torque relaxation or by removing the torque on the plate and measuring the transient rotation of the tool. We found that at low effective weight fraction ϕeff<58.8 ±0.4 % , the suspensions exhibited a relaxation behavior consistent with a generalized Newtonian fluid in which the relaxation is determined by the steady-state relationship between <span class="hlt">shear</span> stress and <span class="hlt">shear</span> rate. However, for larger weight fraction 58.8 %<ϕeff<61.0 % , near the liquid-solid transition ϕc=61.0 ±0.7 % , we found relaxation behaviors qualitatively and quantitatively different from the generalized Newtonian model. The regime where the relaxation was inconsistent with the generalized Newtonian model was the same where we found positive normal stress during relaxation, and in some cases we found an oscillatory response, suggestive of a solidlike structure consisting of a system-spanning contact network of particles. This regime also corresponds to the same packing fraction range where we consistently found discontinuous <span class="hlt">shear</span> thickening in rate-controlled, steady-state measurements. The relaxation time in this range scales with the inverse of the critical <span class="hlt">shear</span> rate at the onset of <span class="hlt">shear</span> thickening, which may correspond to a contact relaxation time for nearby particles in the structure to flow away from each other. In this range, the relaxation time was the same in both stress- and rate-controlled relaxation experiments, indicating the relaxation time is more intrinsic than an effective viscosity in this range and is needed in addition to the steady-state viscosity function to describe transient flows. The discrepancy between the measured relaxation times and the generalized Newtonian</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018ApJ...853...25W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018ApJ...853...25W"><span>Full-sky Ray-tracing Simulation of Weak Lensing Using ELUCID Simulations: Exploring Galaxy Intrinsic Alignment and Cosmic <span class="hlt">Shear</span> Correlations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wei, Chengliang; Li, Guoliang; Kang, Xi; Luo, Yu; Xia, Qianli; Wang, Peng; Yang, Xiaohu; Wang, Huiyuan; Jing, Yipeng; Mo, Houjun; Lin, Weipeng; Wang, Yang; Li, Shijie; Lu, Yi; Zhang, Youcai; Lim, S. H.; Tweed, Dylan; Cui, Weiguang</p> <p>2018-01-01</p> <p>The intrinsic alignment of galaxies is an important systematic effect in weak-lensing surveys, which can affect the derived cosmological parameters. One direct way to distinguish different alignment models and quantify their effects on the measurement is to produce mock weak-lensing surveys. In this work, we use the full-sky ray-tracing technique to produce mock images of galaxies from the ELUCID N-body simulation run with WMAP9 cosmology. In our model, we assume that the shape of the central elliptical galaxy follows that of the dark matter halo, and that of the spiral galaxy follows the halo spin. Using the mock galaxy images, a combination of galaxy intrinsic shape and the gravitational <span class="hlt">shear</span>, we compare the <span class="hlt">predicted</span> tomographic <span class="hlt">shear</span> correlations to the results of the Kilo-Degree Survey (KiDS) and Deep Lens Survey (DLS). We find that our <span class="hlt">predictions</span> stay between the KiDS and DLS results. We rule out a model in which the satellite galaxies are radially aligned with the center galaxy; otherwise, the <span class="hlt">shear</span> correlations on small scales are too high. Most importantly, we find that although the intrinsic alignment of spiral galaxies is very weak, they induce a positive correlation between the gravitational <span class="hlt">shear</span> signal and the intrinsic galaxy orientation (GI). This is because the spiral galaxy is tangentially aligned with the nearby large-scale overdensity, contrary to the radial alignment of the elliptical galaxy. Our results explain the origin of the detected positive GI term in the weak-lensing surveys. We conclude that in future analyses, the GI model must include the dependence on galaxy <span class="hlt">types</span> in more detail.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..1613703B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..1613703B"><span>The brittle-viscous-plastic evolution of <span class="hlt">shear</span> bands in the South Armorican <span class="hlt">Shear</span> Zone</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bukovská, Zita; Jeřábek, Petr; Morales, Luiz F. G.; Lexa, Ondrej; Milke, Ralf</p> <p>2014-05-01</p> <p><span class="hlt">Shear</span> bands are microscale <span class="hlt">shear</span> zones that obliquely crosscut an existing anisotropy such as a foliation. The resulting S-C fabrics are characterized by angles lower than 45° and the C plane parallel to <span class="hlt">shear</span> zone boundaries. The S-C fabrics typically occur in granitoids deformed at greenschist facies conditions in the vicinity of major <span class="hlt">shear</span> zones. Despite their long recognition, mechanical reasons for localization of deformation into <span class="hlt">shear</span> bands and their evolution is still poorly understood. In this work we focus on microscale characterization of the <span class="hlt">shear</span> bands in the South Armorican <span class="hlt">Shear</span> Zone, where the S-C fabrics were first recognized by Berthé et al. (1979). The initiation of <span class="hlt">shear</span> bands in the right-lateral South Armorican <span class="hlt">Shear</span> Zone is associated with the occurrence of microcracks crosscutting the recrystallized quartz aggregates that define the S fabric. In more advanced stages of <span class="hlt">shear</span> band evolution, newly formed dominant K-feldspar, together with plagioclase, muscovite and chlorite occur in the microcracks, and the <span class="hlt">shear</span> bands start to widen. K-feldspar replaces quartz by progressively bulging into the grain boundaries of recrystallized quartz grains, leading to disintegration of quartz aggregates and formation of fine-grained multiphase matrix mixture. The late stages of <span class="hlt">shear</span> band development are marked by interconnection of fine-grained white mica into a band that crosscuts the original <span class="hlt">shear</span> band matrix. In its extremity, the <span class="hlt">shear</span> band widening may lead to the formation of ultramylonites. With the increasing proportion of <span class="hlt">shear</span> band matrix from ~1% to ~12%, the angular relationship between S and C fabrics increases from ~30° to ~40°. The matrix phases within <span class="hlt">shear</span> bands show differences in chemical composition related to distinct evolutionary stages of <span class="hlt">shear</span> band formation. The chemical evolution is well documented in K-feldspar, where the albite component is highest in porphyroclasts within S fabric, lower in the newly formed grains within</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017MS%26E..245c2044R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017MS%26E..245c2044R"><span>Experimental Verification of Same Simple Equilibrium Models of Masonry <span class="hlt">Shear</span> Walls</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Radosław, Jasiński</p> <p>2017-10-01</p> <p>This paper contains theoretical fundamentals of strut and tie models, used in unreinforced horizontal <span class="hlt">shear</span> walls. Depending on support conditions and wall loading, we can distinguish models with discrete bars when point load is applied to the wall (<span class="hlt">type</span> I model) or with continuous bars (<span class="hlt">type</span> II model) when load is uniformly distributed at the wall boundary. The main part of this paper compares calculated results with the own tests on horizontal <span class="hlt">shear</span> walls made of solid brick, silicate elements and autoclaved aerated concrete. The tests were performed in Poland. The model required some modifications due to specific load and static diagram.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21386428','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21386428"><span>The continuum theory of <span class="hlt">shear</span> localization in two-dimensional foam.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Weaire, Denis; Barry, Joseph D; Hutzler, Stefan</p> <p>2010-05-19</p> <p>We review some recent advances in the rheology of two-dimensional liquid foams, which should have implications for three-dimensional foams, as well as other mechanical systems that have a yield stress. We focus primarily on <span class="hlt">shear</span> localization under steady <span class="hlt">shear</span>, an effect first highlighted in an experiment by Debrégeas et al. A continuum theory which incorporates wall drag has reproduced the effect. Its further refinements are successful in matching results of more extensive observations and making interesting <span class="hlt">predictions</span> regarding experiments for low strain rates and non-steady <span class="hlt">shear</span>. Despite these successes, puzzles remain, particularly in relation to quasistatic simulations. The continuum model is semi-empirical: the meaning of its parameters may be sought in comparison with more detailed simulations and other experiments. The question of the origin of the Herschel-Bulkley relation is particularly interesting.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3858002','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3858002"><span>Cylinders vs. Spheres: Biofluid <span class="hlt">Shear</span> Thinning in Driven Nanoparticle Transport</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Cribb, Jeremy A.; Meehan, Timothy D.; Shah, Sheel M.; Skinner, Kwan; Superfine, Richard</p> <p>2011-01-01</p> <p>Increasingly, the research community applies magnetophoresis to micro and nanoscale particles for drug delivery applications and the nanoscale rheological characterization of complex biological materials. Of particular interest is the design and transport of these magnetic particles through entangled polymeric fluids commonly found in biological systems. We report the magnetophoretic transport of spherical and rod-shaped particles through viscoelastic, entangled solutions using lambda-phage DNA (λ-DNA) as a model system. In order to understand and <span class="hlt">predict</span> the observed phenomena, we fully characterize three fundamental components: the magnetic field and field gradient, the shape and magnetic properties of the probe particles, and the macroscopic rheology of the solution. Particle velocities obtained in Newtonian solutions correspond to macroscale rheology, with forces calculated via Stokes Law. In λ-DNA solutions, nanorod velocities are 100 times larger than <span class="hlt">predicted</span> by measured zero-<span class="hlt">shear</span> viscosity. These results are consistent with particles experiencing transport through a <span class="hlt">shear</span> thinning fluid, indicating magnetically driven transport in <span class="hlt">shear</span> thinning may be especially effective and favor narrow diameter, high aspect ratio particles. A complete framework for designing single-particle magnetic-based delivery systems results when we combine a quantified magnetic system with qualified particles embedded in a characterized viscoelastic medium. PMID:20571853</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1992JSMET..58..436K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1992JSMET..58..436K"><span>Analysis of <span class="hlt">shear</span> buckling of cylindrical shells. II - Effects of combined loadings</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kokubo, Kunio; Nagashima, Hideaki; Takayanagi, Masaaki; Madokoro, Manabu; Mochizuki, Akira; Ikeuchi, Hisaaki</p> <p>1992-03-01</p> <p>Cylindrical shells subjected to lateral loads buckle in <span class="hlt">shear</span> or bending buckling modes. The effects of combined loadings are investigated by developing a special-purpose FEM program using the 8-node isoparametric shell element. Three <span class="hlt">types</span> of loading, lateral and axial loads, and pure bending moments are considered. For short cylindrical shells, <span class="hlt">shear</span> buckling modes are dominant, but elephant-foot bulges take place with an increase in bending moments. Effects of axial loads on <span class="hlt">shear</span> buckling and the elephant-foot bulge are investigated. In the case of <span class="hlt">shear</span> buckling the axial load affects the buckling mode as well as the buckling load. For bending bucklings, the axial loads have a great effect on the buckling load.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ars.usda.gov/research/publications/publication/?seqNo115=281296','TEKTRAN'); return false;" href="http://www.ars.usda.gov/research/publications/publication/?seqNo115=281296"><span>A fluidized bed technique for estimating soil critical <span class="hlt">shear</span> stress</span></a></p> <p><a target="_blank" href="https://www.ars.usda.gov/research/publications/find-a-publication/">USDA-ARS?s Scientific Manuscript database</a></p> <p></p> <p></p> <p>Soil erosion models, depending on how they are formulated, always have erodibilitiy parameters in the erosion equations. For a process-based model like the Water Erosion <span class="hlt">Prediction</span> Project (WEPP) model, the erodibility parameters include rill and interrill erodibility and critical <span class="hlt">shear</span> stress. Thes...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012APS..DFDD26005H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012APS..DFDD26005H"><span>LES-ODT Simulations of Turbulent Reacting <span class="hlt">Shear</span> Layers</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hoffie, Andreas; Echekki, Tarek</p> <p>2012-11-01</p> <p>Large-eddy simulations (LES) combined with the one-dimensional turbulence (ODT) simulations of a spatially developing turbulent reacting <span class="hlt">shear</span> layer with heat release and high Reynolds numbers were conducted and compared to results from direct numerical simulations (DNS) of the same configuration. The LES-ODT approach is based on LES solutions for momentum on a coarse grid and solutions for momentum and reactive scalars on a fine ODT grid, which is embedded in the LES computational domain. The <span class="hlt">shear</span> layer is simulated with a single-step, second-order reaction with an Arrhenius reaction rate. The transport equations are solved using a low Mach number approximation. The LES-ODT simulations yield reasonably accurate <span class="hlt">predictions</span> of turbulence and passive/reactive scalars' statistics compared to DNS results.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1184349','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1184349"><span>Modeling the reversible kinetics of neutrophil aggregation under hydrodynamic <span class="hlt">shear</span>.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Neelamegham, S; Taylor, A D; Hellums, J D; Dembo, M; Smith, C W; Simon, S I</p> <p>1997-01-01</p> <p>Neutrophil emigration into inflamed tissue is mediated by beta 2-integrin and L-selectin adhesion receptors. Homotypic neutrophil aggregation is also dependent on these molecules, and it provides a model system in which to study adhesion dynamics. In the current study we formulated a mathematical model for cellular aggregation in a linear <span class="hlt">shear</span> field based on Smoluchowski's two-body collision theory. Neutrophil suspensions activated with chemotactic stimulus and <span class="hlt">sheared</span> in a cone-plate viscometer rapidly aggregate. Over a range of <span class="hlt">shear</span> rates (400-800 s-1), approximately 90% of the single cells were recruited into aggregates ranging from doublets to groupings larger than sextuplets. The adhesion efficiency fit to these kinetics reached maximum levels of > 70%. Formed aggregates remained intact and resistant to <span class="hlt">shear</span> up to 120 s, at which time they spontaneously dissociated back to singlets. The rate of cell disaggregation was linearly proportional to the applied <span class="hlt">shear</span> rate, and it was approximately 60% lower for doublets as compared to larger aggregates. By accounting for the time-dependent changes in adhesion efficiency, disaggregation rate, and the effects of aggregate geometry, we succeeded in <span class="hlt">predicting</span> the reversible kinetics of aggregation over a wide range of <span class="hlt">shear</span> rates and cell concentrations. The combination of viscometry with flow cytometry and mathematical analysis as presented here represents a novel approach to differentiating between the effects of hydrodynamics and the intrinsic biological processes that control cell adhesion. Images FIGURE 3 FIGURE 5 PMID:9083659</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li class="active"><span>14</span></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_14 --> <div id="page_15" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li class="active"><span>15</span></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="281"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018PhFl...30c2108A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018PhFl...30c2108A"><span>Orbitally shaken shallow fluid layers. II. An improved wall <span class="hlt">shear</span> stress model</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Alpresa, Paola; Sherwin, Spencer; Weinberg, Peter; van Reeuwijk, Maarten</p> <p>2018-03-01</p> <p>A new model for the analytical <span class="hlt">prediction</span> of wall <span class="hlt">shear</span> stress distributions at the base of orbitally shaken shallow fluid layers is developed. This model is a generalisation of the classical extended Stokes solution and will be referred to as the potential theory-Stokes model. The model is validated using a large set of numerical simulations covering a wide range of flow regimes representative of those used in laboratory experiments. It is demonstrated that the model is in much better agreement with the simulation data than the classical Stokes solution, improving the <span class="hlt">prediction</span> in 63% of the studied cases. The central assumption of the model—which is to link the wall <span class="hlt">shear</span> stress with the surface velocity—is shown to hold remarkably well over all regimes covered.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016PhDT.......169L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016PhDT.......169L"><span>A Multi-Scale Simulation Approach to Deformation Mechanism <span class="hlt">Prediction</span> in Superalloys</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lv, Duchao</p> <p></p> <p>High-temperature alloys in general and superalloys in particular are crucial for manufacturing gas turbines for aircraft and power generators. Among the superalloy family, the Ni-based superalloys are the most frequently used due to their excellent strength-to-weight ratio. Their strength results from their ordered intermetallic phases (precipitates), which are relatively stable at elevated temperatures. The major deformation processes of Ni-based and Co-based superalloys are precipitate <span class="hlt">shearing</span> and Orowan looping. The key to developing physics-based models of creep and yield strength of aircraft engine components is to understand the two deformation mechanisms mentioned above. Recent discoveries of novel dislocation structures and stacking-fault configurations in deformed superalloys implied that the traditional anti-phase boundary (APB)-<span class="hlt">type</span>, yield-strength model is unable to explain the <span class="hlt">shearing</span> mechanisms of the gamma" phase in 718-<span class="hlt">type</span> (Ni-based) superalloys. While the onset of plastic deformation is still related to the formation of highly-energetic stacking faults, the physics-based yield strength <span class="hlt">prediction</span> requires that the novel dislocation structure and the correct intermediate stacking-fault be considered in the mathematical expressions. In order to obtain the dependence of deformation mechanisms on a materials chemical composition, the relationship between the generalized-stacking-fault (GSF) surface and its chemical composition must be understood. For some deformation scenarios in which one precipitate phase and one mechanism are dominant (e.g., Orowan looping), their use in industry requires a fast-acting model that can capture the features of the deformation (e.g., the volume fraction of the <span class="hlt">sheared</span> matrix) and reduces lost time by not repeating fine-scale simulations. The objective of this thesis was to develop a multi-scale, physics-based simulation approach that can be used to optimize existing superalloys and to accelerate the design of new</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19840063207&hterms=order+mixed&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dorder%2Bmixed','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19840063207&hterms=order+mixed&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dorder%2Bmixed"><span>A mixed <span class="hlt">shear</span> flexible finite element for the analysis of laminated plates</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Putcha, N. S.; Reddy, J. N.</p> <p>1984-01-01</p> <p>A mixed <span class="hlt">shear</span> flexible finite element based on the Hencky-Mindlin <span class="hlt">type</span> <span class="hlt">shear</span> deformation theory of laminated plates is presented and their behavior in bending is investigated. The element consists of three displacements, two rotations, and three moments as the generalized degrees of freedom per node. The numerical convergence and accuracy characteristics of the element are investigated by comparing the finite element solutions with the exact solutions. The present study shows that reduced-order integration of the stiffness coefficients due to <span class="hlt">shear</span> is necessary to obtain accurate results for thin plates.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26763173','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26763173"><span>Experimental verification of nanofluid <span class="hlt">shear</span>-wave reconversion in ultrasonic fields.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Forrester, Derek Michael; Huang, Jinrui; Pinfield, Valerie J; Luppé, Francine</p> <p>2016-03-14</p> <p>Here we present the verification of <span class="hlt">shear</span>-mediated contributions to multiple scattering of ultrasound in suspensions. Acoustic spectroscopy was carried out with suspensions of silica of differing particle sizes and concentrations in water to find the attenuation at a broad range of frequencies. As the particle sizes approach the nanoscale, commonly used multiple scattering models fail to match experimental results. We develop a new model, taking into account <span class="hlt">shear</span> mediated contributions, and find excellent agreement with the attenuation spectra obtained using two <span class="hlt">types</span> of spectrometer. The results determine that <span class="hlt">shear</span>-wave phenomena must be considered in ultrasound characterisation of nanofluids at even relatively low concentrations of scatterers that are smaller than one micrometre in diameter.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2000PhRvB..62.2271Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2000PhRvB..62.2271Z"><span>Evidence for a <span class="hlt">shear</span> horizontal resonance in supported thin films</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhang, X.; Manghnani, M. H.; Every, A. G.</p> <p>2000-07-01</p> <p>We report evidence for a different <span class="hlt">type</span> of acoustic film excitation, identified as a <span class="hlt">shear</span> horizontal resonance, in amorphous silicon oxynitride films on GaAs substrate. Observation of this excitation has been carried out using surface Brillouin scattering of light. A Green's function formalism is used for analyzing the experimental spectra, and successfully simulates the spectral features associated with this mode. The attributes of this mode are described; these include its phase velocity which is nearly equal to that of a bulk <span class="hlt">shear</span> wave propagating parallel to the surface and is almost independent of film thickness and scattering angle, its localization mainly in the film, and its polarization in the <span class="hlt">shear</span> horizontal direction.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018JEMat.tmp.2629R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018JEMat.tmp.2629R"><span><span class="hlt">Shear</span> Strength of Square Graphene Nanoribbons beyond Wrinkling</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ragab, Tarek; Basaran, Cemal</p> <p>2018-04-01</p> <p>Atomistic modeling of armchair and zigzag graphene nanoribbons (GNRs) has been performed to investigate the post-wrinkling behavior under in-plane (x-y) <span class="hlt">shear</span> deformation. Simulations were performed at 300 K for square GNRs with size ranging from 2.5 nm to 20 nm. <span class="hlt">Shear</span> stresses led only to diagonal tension, and wrinkling was not accompanied by any diagonal compressive force. Once the diagonal tension reached its ultimate elastic level, three major stress-relaxing phenomena were observed. The <span class="hlt">type</span> of stress-relaxing phenomenon involved greatly affected the mechanical behavior in terms of the slope of the stress-strain diagram beyond the elastic range. The results showed that the average slope of the stress-strain relation beyond the ultimate elastic stress decreased with the increase of the GNR size. Moreover, the slope of the <span class="hlt">shear</span> stress-strain curve beyond the ultimate elastic stress was always greater for armchair than for zigzag GNRs. GNRs can sustain very high plastic <span class="hlt">shear</span> strains beyond 100% before failure. The ultimate elastic stress can range from 20 GPa to 50 GPa, occurring at <span class="hlt">shear</span> strain ranging from 52% to 19%. The ultimate elastic stress and strain were inversely proportional to the size of the GNR with a power factor ranging from 0.261 for armchair GNRs to 0.354 for zigzag GNRs due to the decrease in the effective width for diagonal tension.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018JEMat..47.3891R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018JEMat..47.3891R"><span><span class="hlt">Shear</span> Strength of Square Graphene Nanoribbons beyond Wrinkling</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ragab, Tarek; Basaran, Cemal</p> <p>2018-07-01</p> <p>Atomistic modeling of armchair and zigzag graphene nanoribbons (GNRs) has been performed to investigate the post-wrinkling behavior under in-plane ( x- y) <span class="hlt">shear</span> deformation. Simulations were performed at 300 K for square GNRs with size ranging from 2.5 nm to 20 nm. <span class="hlt">Shear</span> stresses led only to diagonal tension, and wrinkling was not accompanied by any diagonal compressive force. Once the diagonal tension reached its ultimate elastic level, three major stress-relaxing phenomena were observed. The <span class="hlt">type</span> of stress-relaxing phenomenon involved greatly affected the mechanical behavior in terms of the slope of the stress-strain diagram beyond the elastic range. The results showed that the average slope of the stress-strain relation beyond the ultimate elastic stress decreased with the increase of the GNR size. Moreover, the slope of the <span class="hlt">shear</span> stress-strain curve beyond the ultimate elastic stress was always greater for armchair than for zigzag GNRs. GNRs can sustain very high plastic <span class="hlt">shear</span> strains beyond 100% before failure. The ultimate elastic stress can range from 20 GPa to 50 GPa, occurring at <span class="hlt">shear</span> strain ranging from 52% to 19%. The ultimate elastic stress and strain were inversely proportional to the size of the GNR with a power factor ranging from 0.261 for armchair GNRs to 0.354 for zigzag GNRs due to the decrease in the effective width for diagonal tension.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018CQGra..35i5011T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018CQGra..35i5011T"><span>Balancing anisotropic curvature with gauge fields in a class of <span class="hlt">shear</span>-free cosmological models</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Thorsrud, Mikjel</p> <p>2018-05-01</p> <p>We present a complete list of general relativistic <span class="hlt">shear</span>-free solutions in a class of anisotropic, spatially homogeneous and orthogonal cosmological models containing a collection of n independent p-form gauge fields, where p\\in\\{0, 1, 2, 3\\} , in addition to standard ΛCDM matter fields modelled as perfect fluids. Here a (collection of) gauge field(s) balances anisotropic spatial curvature on the right-hand side of the <span class="hlt">shear</span> propagation equation. The result is a class of solutions dynamically equivalent to standard FLRW cosmologies, with an effective curvature constant Keff that depends both on spatial curvature and the energy density of the gauge field(s). In the case of a single gauge field (n  =  1) we show that the only spacetimes that admit such solutions are the LRS Bianchi <span class="hlt">type</span> III, Bianchi <span class="hlt">type</span> VI0 and Kantowski–Sachs metric, which are dynamically equivalent to open (Keff<0 ), flat (Keff=0 ) and closed (Keff>0 ) FLRW models, respectively. With a collection of gauge fields (n  >  1) also Bianchi <span class="hlt">type</span> II admits a <span class="hlt">shear</span>-free solution (Keff>0 ). We identify the LRS Bianchi <span class="hlt">type</span> III solution to be the unique <span class="hlt">shear</span>-free solution with a gauge field Hamiltonian bounded from below in the entire class of models.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014PhDT.......132K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014PhDT.......132K"><span><span class="hlt">Shear</span>-induced aggregation dynamics in a polymer microrod suspension</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kumar, Pramukta S.</p> <p></p> <p>A non-Brownian suspension of micron scale rods is found to exhibit reversible <span class="hlt">shear</span>-driven formation of disordered aggregates resulting in dramatic viscosity enhancement at low <span class="hlt">shear</span> rates. Aggregate formation is imaged at low magnification using a combined rheometer and fluorescence microscope system. The size and structure of these aggregates are found to depend on <span class="hlt">shear</span> rate and concentration, with larger aggregates present at lower <span class="hlt">shear</span> rates and higher concentrations. Quantitative measurements of the early-stage aggregation process are modeled by a collision driven growth of porous structures which show that the aggregate density increases with a <span class="hlt">shear</span> rate. A Krieger-Dougherty <span class="hlt">type</span> constitutive relation and steady-state viscosity measurements are used to estimate the intrinsic viscosity of complex structures developed under <span class="hlt">shear</span>. Higher magnification images are collected and used to validate the aggregate size versus density relationship, as well as to obtain particle flow fields via PIV. The flow fields provide a tantalizing view of fluctuations involved in the aggregation process. Interaction strength is estimated via contact force measurements and JKR theory and found to be extremely strong in comparison to <span class="hlt">shear</span> forces present in the system, estimated using hydrodynamic arguments. All of the results are then combined to produce a consistent conceptual model of aggregation in the system that features testable consequences. These results represent a direct, quantitative, experimental study of aggregation and viscosity enhancement in rod suspension, and demonstrate a strategy for inferring inaccessible microscopic geometric properties of a dynamic system through the combination of quantitative imaging and rheology.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26113291','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26113291"><span>Factors that influence muscle <span class="hlt">shear</span> modulus during passive stretch.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Koo, Terry K; Hug, François</p> <p>2015-09-18</p> <p>Although elastography has been increasingly used for evaluating muscle <span class="hlt">shear</span> modulus associated with age, sex, musculoskeletal, and neurological conditions, its physiological meaning is largely unknown. This knowledge gap may hinder data interpretation, limiting the potential of using elastography to gain insights into muscle biomechanics in health and disease. We derived a mathematical model from a widely-accepted Hill-<span class="hlt">type</span> passive force-length relationship to gain insight about the physiological meaning of resting <span class="hlt">shear</span> modulus of skeletal muscles under passive stretching, and validated the model by comparing against the ex-vivo animal data reported in our recent work (Koo et al. 2013). The model suggested that resting <span class="hlt">shear</span> modulus of a slack muscle is a function of specific tension and parameters that govern the normalized passive muscle force-length relationship as well as the degree of muscle anisotropy. The model also suggested that although the slope of the linear <span class="hlt">shear</span> modulus-passive force relationship is primarily related to muscle anatomical cross-sectional area (i.e. the smaller the muscle cross-sectional area, the more the increase in <span class="hlt">shear</span> modulus to result in the same passive muscle force), it is also governed by the normalized passive muscle force-length relationship and the degree of muscle anisotropy. Taken together, although muscle <span class="hlt">shear</span> modulus under passive stretching has a strong linear relationship with passive muscle force, its actual value appears to be affected by muscle's mechanical, material, and architectural properties. This should be taken into consideration when interpreting the muscle <span class="hlt">shear</span> modulus values. Copyright © 2015 Elsevier Ltd. All rights reserved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1814109Q','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1814109Q"><span>Explicit wave action conservation for water waves on vertically <span class="hlt">sheared</span> flows</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Quinn, Brenda; Toledo, Yaron; Shrira, Victor</p> <p>2016-04-01</p> <p>Water waves almost always propagate on currents with a vertical structure such as currents directed towards the beach accompanied by an under-current directed back toward the deep sea or wind-induced currents which change magnitude with depth due to viscosity effects. On larger scales they also change their direction due to the Coriolis force as described by the Ekman spiral. This implies that the existing wave models, which assume vertically-averaged currents, is an approximation which is far from realistic. In recent years, ocean circulation models have significantly improved with the capability to model vertically-<span class="hlt">sheared</span> current profiles in contrast with the earlier vertically-averaged current profiles. Further advancements have coupled wave action models to circulation models to relate the mutual effects between the two <span class="hlt">types</span> of motion. Restricting wave models to vertically-averaged non-turbulent current profiles is obviously problematic in these cases and the primary goal of this work is to derive and examine a general wave action equation which accounts for these shortcoming. The formulation of the wave action conservation equation is made explicit by following the work of Voronovich (1976) and using known asymptotic solutions of the boundary value problem which exploit the smallness of the current magnitude compared to the wave phase velocity and/or its vertical <span class="hlt">shear</span> and curvature. The adopted approximations are shown to be sufficient for most of the conceivable applications. This provides correction terms to the group velocity and wave action definition accounting for the <span class="hlt">shear</span> effects, which are fitting for application to operational wave models. In the limit of vanishing current <span class="hlt">shear</span>, the new formulation reduces to the commonly used Bretherton & Garrett (1968) no-<span class="hlt">shear</span> wave action equation where the invariant is calculated with the current magnitude taken at the free surface. It is shown that in realistic oceanic conditions, the neglect of the vertical</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29477745','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29477745"><span><span class="hlt">Shear</span> Wave Speed Estimation Using Reverberant <span class="hlt">Shear</span> Wave Fields: Implementation and Feasibility Studies.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ormachea, Juvenal; Castaneda, Benjamin; Parker, Kevin J</p> <p>2018-05-01</p> <p>Elastography is a modality that estimates tissue stiffness and, thus, provides useful information for clinical diagnosis. Attention has focused on the measurement of <span class="hlt">shear</span> wave propagation; however, many methods assume <span class="hlt">shear</span> wave propagation is unidirectional and aligned with the lateral imaging direction. Any deviations from the assumed propagation result in biased estimates of <span class="hlt">shear</span> wave speed. To address these challenges, directional filters have been applied to isolate <span class="hlt">shear</span> waves with different propagation directions. Recently, a new method was proposed for tissue stiffness estimation involving creation of a reverberant <span class="hlt">shear</span> wave field propagating in all directions within the medium. These reverberant conditions lead to simple solutions, facile implementation and rapid viscoelasticity estimation of local tissue. In this work, this new approach based on reverberant <span class="hlt">shear</span> waves was evaluated and compared with another well-known elastography technique using two calibrated elastic and viscoelastic phantoms. Additionally, the clinical feasibility of this technique was analyzed by assessing <span class="hlt">shear</span> wave speed in human liver and breast tissues, in vivo. The results indicate that it is possible to estimate the viscoelastic properties in each scanned medium. Moreover, a better approach to estimation of <span class="hlt">shear</span> wave speed was obtained when only the phase information was taken from the reverberant waves, which is equivalent to setting all magnitudes within the bandpass equal to unity: an idealization of a perfectly isotropic reverberant <span class="hlt">shear</span> wave field. Copyright © 2018 World Federation for Ultrasound in Medicine and Biology. Published by Elsevier Inc. All rights reserved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19880005588','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19880005588"><span>Wind <span class="hlt">shear</span> detection. Forward-looking sensor technology</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bracalente, E. M. (Compiler); Delnore, V. E. (Compiler)</p> <p>1987-01-01</p> <p>A meeting took place at NASA Langley Research Center in February 1987 to discuss the development and eventual use of forward-looking remote sensors for the detection and avoidance of wind <span class="hlt">shear</span> by aircraft. The participants represented industry, academia, and government. The meeting was structured to provide first a review of the current FAA and NASA wind <span class="hlt">shear</span> programs, then to define what really happens to the airplane, and finally to give technology updates on the various <span class="hlt">types</span> of forward-looking sensors. This document is intended to informally record the essence of the technology updates (represented here through unedited duplication of the vugraphs used), and the floor discussion following each presentation. Also given are key issues remaining unresolved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/pages/biblio/1227899-modifying-mixing-instability-growth-through-adjustment-initial-conditions-high-energy-density-counter-propagating-shear-experiment-omega','SCIGOV-DOEP'); return false;" href="https://www.osti.gov/pages/biblio/1227899-modifying-mixing-instability-growth-through-adjustment-initial-conditions-high-energy-density-counter-propagating-shear-experiment-omega"><span>Modifying mixing and instability growth through the adjustment of initial conditions in a high-energy-density counter-propagating <span class="hlt">shear</span> experiment on OMEGA</span></a></p> <p><a target="_blank" href="http://www.osti.gov/pages">DOE PAGES</a></p> <p>Merritt, E. C.; Doss, F. W.; Loomis, E. N.; ...</p> <p>2015-06-24</p> <p>Counter-propagating <span class="hlt">shear</span> experiments conducted at the OMEGA Laser Facility have been evaluating the effect of target initial conditions, specifically the characteristics of a tracer foil located at the <span class="hlt">shear</span> boundary, on Kelvin-Helmholtz instability evolution and experiment transition toward nonlinearity and turbulence in the high-energy-density (HED) regime. Experiments are focused on both identifying and uncoupling the dependence of the model initial turbulent length scale in variable-density turbulence models of k-ϵ <span class="hlt">type</span> on competing physical instability seed lengths as well as developing a path toward fully developed turbulent HED experiments. We present results from a series of experiments controllably and independently varyingmore » two initial <span class="hlt">types</span> of scale lengths in the experiment: the thickness and surface roughness (surface perturbation scale spectrum) of a tracer layer at the <span class="hlt">shear</span> interface. We show that decreasing the layer thickness and increasing the surface roughness both have the ability to increase the relative mixing in the system, and thus theoretically decrease the time required to begin transitioning to turbulence in the system. In addition, we also show that we can connect a change in observed mix width growth due to increased foil surface roughness to an analytically <span class="hlt">predicted</span> change in model initial turbulent scale lengths.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007PhDT........30Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007PhDT........30Z"><span><span class="hlt">Shear</span> band evolution in zirconium/hafnium-based bulk metallic glasses under static and dynamic indentations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhang, Hongwen</p> <p></p> <p>In this thesis, a detailed investigation of thermal stability and mechanical deformation behavior of Zr/Hf-based Bulk Metallic Glasses is conducted. First, systematic studies had been implemented to understand the influence of relative compositions of Zr and Hf on thermal stability and mechanical property evolution. Second, <span class="hlt">shear</span> band evolution under indentations were investigated experimentally and theoretically. It was found in the present work that gradually replacing Zr by Hf remarkably increases the density and improves the mechanical properties. However, a slight decrease in glass forming ability with increasing Hf content has also been identified through thermodynamic analysis although all the materials in the current study were still found to be amorphous. Many indentation studies have revealed only a few <span class="hlt">shear</span> bands surrounding the indent on the top surface of the specimen. This small number of <span class="hlt">shear</span> bands cannot account for the large plastic deformation beneath the indentations. Therefore, a bonded interface technique has been used to observe the slip-steps due to <span class="hlt">shear</span> band evolution. Vickers indentations were performed along the interface of the bonded split specimen at increasing loads. At small indentation loads, the plastic deformation was primarily accommodated by semi-circular primary <span class="hlt">shear</span> bands surrounding the indentation. At higher loads, secondary and tertiary <span class="hlt">shear</span> bands were formed inside this plastic zone. A modified expanding cavity model was then used to <span class="hlt">predict</span> the plastic zone size characterized by the <span class="hlt">shear</span> bands and to identify the stress components responsible for the evolution of the various <span class="hlt">types</span> of <span class="hlt">shear</span> bands. The applicability of various hardness - yield-strength (H-sigma y) relationships currently available in the literature for bulk metallic glasses (BMGs) is also investigated. Experimental data generated on ZrHf-based BMGs in the current study and those available elsewhere on other BMG compositions were used to validate the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.T13D0552F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.T13D0552F"><span>On the competing affects of <span class="hlt">shear</span> heating and grainsize reduction in lithospheric <span class="hlt">shear</span> zone formation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Foley, B. J.</p> <p>2017-12-01</p> <p>Grain-size reduction is thought to play an important role in <span class="hlt">shear</span> localization within the lithosphere, as mylonites are commonly seen in regions that have undergone intense deformation. However, flow in lithospheric <span class="hlt">shear</span> zones can also cause heating due to the energy dissipated by deformation. As grain growth is strongly enhanced by warmer temperatures, <span class="hlt">shear</span> heating may impede grainsize reduction and the formation of mylonite zones. I use models of simple <span class="hlt">shear</span>, with length-scales representative of lithospheric <span class="hlt">shear</span> zones and plate boundaries, including <span class="hlt">shear</span> heating and grainsize evolution. Grain-damage theory is used to represent the evolution of grainsize. The models are used to determine conditions where grainsize reduction dominates versus those where <span class="hlt">shear</span> heating dominates; if grainsize reduction dominates, then heating is held in check by the drop in viscosity brought about by small grains. On the other hand, if heating dominates then grain-reduction is prevented by fast grain-growth rates. From the numerical models, simple scaling laws are developed that give the stready-state grainsize and temperature rise as a function of strain-rate, background temperature, and parameters for grain-growth and grain-reduction. I find that for parameter ranges constrained by field observations of <span class="hlt">shear</span> zones and rock deformation experiments, grainsize reduction dominated over <span class="hlt">shear</span> heating. Very high strain-rates or driving stresses, above what is typically expected in natural <span class="hlt">shear</span> zones, are needed for <span class="hlt">shear</span> heating to dominate over grainsize reduction. Also explored is the timescale to reach steady-state grainsize and temperature conditions in a <span class="hlt">shear</span> zone. For realistic driving stress or strain-rate, timescales to reach steady-state are often very long, on the order of hundreds of millions of years or longer. This might indicate that natural <span class="hlt">shear</span> zones do not reach steady-state, or that additional processes are important in initiating lithospheric <span class="hlt">shear</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29336568','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29336568"><span>Strain Distribution Across an Individual <span class="hlt">Shear</span> Band in Real and Simulated Metallic Glasses.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Scudino, Sergio; Şopu, Daniel</p> <p>2018-02-14</p> <p>Because of the fast dynamics of <span class="hlt">shear</span> band formation and propagation along with the small size and transient character of the <span class="hlt">shear</span> transformation zones (STZs), the elementary units of plasticity in metallic glasses, the description of the nanoscale mechanism of <span class="hlt">shear</span> banding often relies on molecular dynamics (MD) simulations. However, the unrealistic parameters used in the simulations related to time constraints may raise questions about whether quantitative comparison between results from experimental and computational analyses is possible. Here, we have experimentally analyzed the strain field arising across an individual <span class="hlt">shear</span> band by nanobeam X-ray diffraction and compared the results with the strain characterizing a <span class="hlt">shear</span> band generated by MD simulations. Despite their largely different spatiotemporal scales, the characteristic features of real and simulated <span class="hlt">shear</span> bands are strikingly similar: the magnitude of the strain across the <span class="hlt">shear</span> band is discontinuous in both cases and the direction of the principal strain axes exhibits the same antisymmetric profile. This behavior can be explained by considering the mechanism of STZ activation and percolation at the nanoscale, indicating that the nanoscale effects of <span class="hlt">shear</span> banding are not limited to the area within the band but they extend well into the surrounding elastic matrix. These findings not only demonstrate the reliability of MD simulations for explaining (also quantitatively) experimental observations of <span class="hlt">shear</span> banding but also suggest that designed experiments can be used the other way around to verify numerical <span class="hlt">predictions</span> of the atomic rearrangements occurring within a band.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018JSV...419..140B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018JSV...419..140B"><span>An improved wavelet-Galerkin method for dynamic response reconstruction and parameter identification of <span class="hlt">shear-type</span> frames</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bu, Haifeng; Wang, Dansheng; Zhou, Pin; Zhu, Hongping</p> <p>2018-04-01</p> <p>An improved wavelet-Galerkin (IWG) method based on the Daubechies wavelet is proposed for reconstructing the dynamic responses of <span class="hlt">shear</span> structures. The proposed method flexibly manages wavelet resolution level according to excitation, thereby avoiding the weakness of the wavelet-Galerkin multiresolution analysis (WGMA) method in terms of resolution and the requirement of external excitation. IWG is implemented by this work in certain case studies, involving single- and n-degree-of-freedom frame structures subjected to a determined discrete excitation. Results demonstrate that IWG performs better than WGMA in terms of accuracy and computation efficiency. Furthermore, a new method for parameter identification based on IWG and an optimization algorithm are also developed for <span class="hlt">shear</span> frame structures, and a simultaneous identification of structural parameters and excitation is implemented. Numerical results demonstrate that the proposed identification method is effective for <span class="hlt">shear</span> frame structures.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19950016046','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19950016046"><span>A method for obtaining a statistically stationary turbulent free <span class="hlt">shear</span> flow</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Timson, Stephen F.; Lele, S. K.; Moser, R. D.</p> <p>1994-01-01</p> <p>The long-term goal of the current research is the study of Large-Eddy Simulation (LES) as a tool for aeroacoustics. New algorithms and developments in computer hardware are making possible a new generation of tools for aeroacoustic <span class="hlt">predictions</span>, which rely on the physics of the flow rather than empirical knowledge. LES, in conjunction with an acoustic analogy, holds the promise of <span class="hlt">predicting</span> the statistics of noise radiated to the far-field of a turbulent flow. LES's <span class="hlt">predictive</span> ability will be tested through extensive comparison of acoustic <span class="hlt">predictions</span> based on a Direct Numerical Simulation (DNS) and LES of the same flow, as well as a priori testing of DNS results. The method presented here is aimed at allowing simulation of a turbulent flow field that is both simple and amenable to acoustic <span class="hlt">predictions</span>. A free <span class="hlt">shear</span> flow is homogeneous in both the streamwise and spanwise directions and which is statistically stationary will be simulated using equations based on the Navier-Stokes equations with a small number of added terms. Studying a free <span class="hlt">shear</span> flow eliminates the need to consider flow-surface interactions as an acoustic source. The homogeneous directions and the flow's statistically stationary nature greatly simplify the application of an acoustic analogy.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28706344','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28706344"><span>A new model of cavern diameter based on a validated CFD study on stirring of a highly <span class="hlt">shear</span>-thinning fluid.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Story, Anna; Jaworski, Zdzisław</p> <p>2017-01-01</p> <p>Results of numerical simulations of momentum transfer for a highly <span class="hlt">shear</span>-thinning fluid (0.2% Carbopol) in a stirred tank equipped with a Prochem Maxflo T <span class="hlt">type</span> impeller are presented. The simulation results were validated using LDA data and both tangential and axial force measurements in the laminar and early transitional flow range. A good agreement between the <span class="hlt">predicted</span> and experimental results of the local fluid velocity components was found. From the <span class="hlt">predicted</span> and experimental values of both tangential and axial forces, the power number, Po , and thrust number, Th , were also calculated. Values of the absolute relative deviations were below 4.0 and 10.5%, respectively, for Po and Th , which confirms a satisfactory agreement with experiments. An intensive mixing zone, known as cavern, was observed near the impeller. In this zone, the local values of fluid velocity, strain rate, Metzner-Otto coefficient, <span class="hlt">shear</span> stress and intensity of energy dissipation were all characterized by strong variability. Based on the results of experimental study a new model using non-dimensional impeller force number was proposed to <span class="hlt">predict</span> the cavern diameter. Comparative numerical simulations were also carried out for a Newtonian fluid (water) and their results were similarly well verified using LDA measurements, as well as experimental power number values.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li class="active"><span>15</span></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_15 --> <div id="page_16" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="301"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018AIPC.1960i0013U','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018AIPC.1960i0013U"><span>Improved failure <span class="hlt">prediction</span> in forming simulations through pre-strain mapping</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Upadhya, Siddharth; Staupendahl, Daniel; Heuse, Martin; Tekkaya, A. Erman</p> <p>2018-05-01</p> <p>The sensitivity of <span class="hlt">sheared</span> edges of advanced high strength steel (AHSS) sheets to cracking during subsequent forming operations and the difficulty to <span class="hlt">predict</span> this failure with any degree of accuracy using conventionally used FLC based failure criteria is a major problem plaguing the manufacturing industry. A possible method that allows for an accurate <span class="hlt">prediction</span> of edge cracks is the simulation of the <span class="hlt">shearing</span> operation and carryover of this model into a subsequent forming simulation. But even with an efficient combination of a solid element <span class="hlt">shearing</span> operation and a shell element forming simulation, the need for a fine mesh, and the resulting high computation time makes this approach not viable from an industry point of view. The crack sensitivity of <span class="hlt">sheared</span> edges is due to work hardening in the <span class="hlt">shear</span>-affected zone (SAZ). A method to <span class="hlt">predict</span> plastic strains induced by the <span class="hlt">shearing</span> process is to measure the hardness after <span class="hlt">shearing</span> and calculate the ultimate tensile strength as well as the flow stress. In combination with the flow curve, the relevant strain data can be obtained. To eliminate the time-intensive <span class="hlt">shearing</span> simulation necessary to obtain the strain data in the SAZ, a new pre-strain mapping approach is proposed. The pre-strains to be mapped are, hereby, determined from hardness values obtained in the proximity of the <span class="hlt">sheared</span> edge. To investigate the performance of this approach the ISO/TS 16630 hole expansion test was simulated with shell elements for different materials, whereby the pre-strains were mapped onto the edge of the hole. The hole expansion ratios obtained from such pre-strain mapped simulations are in close agreement with the experimental results. Furthermore, the simulations can be carried out with no increase in computation time, making this an interesting and viable solution for <span class="hlt">predicting</span> edge failure due to <span class="hlt">shearing</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA087765','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA087765"><span><span class="hlt">Shear</span> Strains, Strain Rates and Temperature Changes in Adiabatic <span class="hlt">Shear</span> Bands</span></a></p> <p><a target="_blank" href="http://www.dtic.mil/">DTIC Science & Technology</a></p> <p></p> <p>1980-05-01</p> <p>X14A. It has been found that when bainitic and martensitic steels are <span class="hlt">sheared</span> adiabatically, a layer of material within ths <span class="hlt">shear</span> zone is altezed and...Sooiety for Metals, Metals Park, Ohio, 1978, pp. 148-0. 21 TABLE II SOLID-STATE TRANSFORMATIONS IN BAINITIC STEEL TRANSFORMATION TRANSFORMATION...<span class="hlt">shear</span>, thermoplastic, plasticity, plastic deformation, armor, steel IL AnSRACT ( -=nba asoa.tm a naeoesM iN faity by bleak n bet/2972 Experiments</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017A%26A...599A..73H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017A%26A...599A..73H"><span><span class="hlt">Shear</span> nulling after PSF Gaussianisation: Moment-based weak lensing measurements with subpercent noise bias</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Herbonnet, Ricardo; Buddendiek, Axel; Kuijken, Konrad</p> <p>2017-03-01</p> <p>Context. Current optical imaging surveys for cosmology cover large areas of sky. Exploiting the statistical power of these surveys for weak lensing measurements requires shape measurement methods with subpercent systematic errors. Aims: We introduce a new weak lensing <span class="hlt">shear</span> measurement algorithm, <span class="hlt">shear</span> nulling after PSF Gaussianisation (SNAPG), designed to avoid the noise biases that affect most other methods. Methods: SNAPG operates on images that have been convolved with a kernel that renders the point spread function (PSF) a circular Gaussian, and uses weighted second moments of the sources. The response of such second moments to a <span class="hlt">shear</span> of the pre-seeing galaxy image can be <span class="hlt">predicted</span> analytically, allowing us to construct a <span class="hlt">shear</span> nulling scheme that finds the <span class="hlt">shear</span> parameters for which the observed galaxies are consistent with an unsheared, isotropically oriented population of sources. The inverse of this nulling <span class="hlt">shear</span> is then an estimate of the gravitational lensing <span class="hlt">shear</span>. Results: We identify the uncertainty of the estimated centre of each galaxy as the source of noise bias, and incorporate an approximate estimate of the centroid covariance into the scheme. We test the method on extensive suites of simulated galaxies of increasing complexity, and find that it is capable of <span class="hlt">shear</span> measurements with multiplicative bias below 0.5 percent.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19730019438','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19730019438"><span>An integral turbulent kinetic energy analysis of free <span class="hlt">shear</span> flows</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Peters, C. E.; Phares, W. J.</p> <p>1973-01-01</p> <p>Mixing of coaxial streams is analyzed by application of integral techniques. An integrated turbulent kinetic energy (TKE) equation is solved simultaneously with the integral equations for the mean flow. Normalized TKE profile shapes are obtained from incompressible jet and <span class="hlt">shear</span> layer experiments and are assumed to be applicable to all free turbulent flows. The <span class="hlt">shear</span> stress at the midpoint of the mixing zone is assumed to be directly proportional to the local TKE, and dissipation is treated with a generalization of the model developed for isotropic turbulence. Although the analysis was developed for ducted flows, constant-pressure flows were approximated with the duct much larger than the jet. The axisymmetric flows under consideration were <span class="hlt">predicted</span> with reasonable accuracy. Fairly good results were also obtained for the fully developed two-dimensional <span class="hlt">shear</span> layers, which were computed as thin layers at the boundary of a large circular jet.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26764819','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26764819"><span>Numerical analysis of the angular motion of a neutrally buoyant spheroid in <span class="hlt">shear</span> flow at small Reynolds numbers.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Rosén, T; Einarsson, J; Nordmark, A; Aidun, C K; Lundell, F; Mehlig, B</p> <p>2015-12-01</p> <p>We numerically analyze the rotation of a neutrally buoyant spheroid in a <span class="hlt">shear</span> flow at small <span class="hlt">shear</span> Reynolds number. Using direct numerical stability analysis of the coupled nonlinear particle-flow problem, we compute the linear stability of the log-rolling orbit at small <span class="hlt">shear</span> Reynolds number Re(a). As Re(a)→0 and as the box size of the system tends to infinity, we find good agreement between the numerical results and earlier analytical <span class="hlt">predictions</span> valid to linear order in Re(a) for the case of an unbounded <span class="hlt">shear</span>. The numerical stability analysis indicates that there are substantial finite-size corrections to the analytical results obtained for the unbounded system. We also compare the analytical results to results of lattice Boltzmann simulations to analyze the stability of the tumbling orbit at <span class="hlt">shear</span> Reynolds numbers of order unity. Theory for an unbounded system at infinitesimal <span class="hlt">shear</span> Reynolds number <span class="hlt">predicts</span> a bifurcation of the tumbling orbit at aspect ratio λ(c)≈0.137 below which tumbling is stable (as well as log rolling). The simulation results show a bifurcation line in the λ-Re(a) plane that reaches λ≈0.1275 at the smallest <span class="hlt">shear</span> Reynolds number (Re(a)=1) at which we could simulate with the lattice Boltzmann code, in qualitative agreement with the analytical results.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007IJNAM..31...23T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007IJNAM..31...23T"><span>On double <span class="hlt">shearing</span> in frictional materials</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Teunissen, J. A. M.</p> <p>2007-01-01</p> <p>This paper evaluates the mechanical behaviour of yielding frictional geomaterials. The general Double <span class="hlt">Shearing</span> model describes this behaviour. Non-coaxiality of stress and plastic strain increments for plane strain conditions forms an important part of this model. The model is based on a micro-mechanical and macro-mechanical formulation. The stress-dilatancy theory in the model combines the mechanical behaviour on both scales.It is shown that the general Double <span class="hlt">Shearing</span> formulation comprises other Double <span class="hlt">Shearing</span> models. These models differ in the relation between the mobilized friction and dilatancy and in non-coaxiality. In order to describe reversible and irreversible deformations the general Double <span class="hlt">Shearing</span> model is extended with elasticity.The failure of soil masses is controlled by <span class="hlt">shear</span> mechanisms. These <span class="hlt">shear</span> mechanisms are determined by the conditions along the <span class="hlt">shear</span> band. The <span class="hlt">shear</span> stress ratio of a <span class="hlt">shear</span> band depends on the orientation of the stress in the <span class="hlt">shear</span> band. There is a difference between the peak strength and the residual strength in the <span class="hlt">shear</span> band. While peak stress depends on strength properties only, the residual strength depends upon the yield conditions and the plastic deformation mechanisms and is generally considerably lower than the maximum strength. It is shown that non-coaxial models give non-unique solutions for the <span class="hlt">shear</span> stress ratio on the <span class="hlt">shear</span> band. The Double <span class="hlt">Shearing</span> model is applied to various failure problems of soils such as the direct simple <span class="hlt">shear</span> test, the biaxial test, infinite slopes, interfaces and for the calculation of the undrained <span class="hlt">shear</span> strength. Copyright</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25853777','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25853777"><span>Validity of measurement of <span class="hlt">shear</span> modulus by ultrasound <span class="hlt">shear</span> wave elastography in human pennate muscle.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Miyamoto, Naokazu; Hirata, Kosuke; Kanehisa, Hiroaki; Yoshitake, Yasuhide</p> <p>2015-01-01</p> <p>Ultrasound <span class="hlt">shear</span> wave elastography is becoming a valuable tool for measuring mechanical properties of individual muscles. Since ultrasound <span class="hlt">shear</span> wave elastography measures <span class="hlt">shear</span> modulus along the principal axis of the probe (i.e., along the transverse axis of the imaging plane), the measured <span class="hlt">shear</span> modulus most accurately represents the mechanical property of the muscle along the fascicle direction when the probe's principal axis is parallel to the fascicle direction in the plane of the ultrasound image. However, it is unclear how the measured <span class="hlt">shear</span> modulus is affected by the probe angle relative to the fascicle direction in the same plane. The purpose of the present study was therefore to examine whether the angle between the principal axis of the probe and the fascicle direction in the same plane affects the measured <span class="hlt">shear</span> modulus. <span class="hlt">Shear</span> modulus in seven specially-designed tissue-mimicking phantoms, and in eleven human in-vivo biceps brachii and medial gastrocnemius were determined by using ultrasound <span class="hlt">shear</span> wave elastography. The probe was positioned parallel or 20° obliquely to the fascicle across the B-mode images. The reproducibility of <span class="hlt">shear</span> modulus measurements was high for both parallel and oblique conditions. Although there was a significant effect of the probe angle relative to the fascicle on the <span class="hlt">shear</span> modulus in human experiment, the magnitude was negligibly small. These findings indicate that the ultrasound <span class="hlt">shear</span> wave elastography is a valid tool for evaluating the mechanical property of pennate muscles along the fascicle direction.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.fs.usda.gov/treesearch/pubs/10626','TREESEARCH'); return false;" href="https://www.fs.usda.gov/treesearch/pubs/10626"><span>Design of thin <span class="hlt">shear</span> blades for crosscut <span class="hlt">shearing</span> of wood.</span></a></p> <p><a target="_blank" href="http://www.fs.usda.gov/treesearch/">Treesearch</a></p> <p>Rodger A. Arola; Thomas R. Grimm</p> <p>1974-01-01</p> <p>Discusses principles and presents formulations for evaluating the elastic stability of thin plates subjected to edge loadings. Three different prestress methods to increase late stability are presented. A procedure is given to evaluate the elastic stability of thin <span class="hlt">shear</span> blades under expected <span class="hlt">shearing</span> loads.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.fs.usda.gov/treesearch/pubs/27344','TREESEARCH'); return false;" href="https://www.fs.usda.gov/treesearch/pubs/27344"><span>Study on <span class="hlt">shearing</span> force and impact force of a volcanic mud flow on Mt. Sakurajima</span></a></p> <p><a target="_blank" href="http://www.fs.usda.gov/treesearch/">Treesearch</a></p> <p>Yoshinobu Taniguchi</p> <p>1991-01-01</p> <p>Two kinds of <span class="hlt">shearing</span> stress meters (<span class="hlt">type</span> A and <span class="hlt">type</span> B) were set on the channel bottom in the Arimura River and the Mochiki River on Mt. Sakurajima. Volcanic mud flows take place there about 100 times a year. The results of the surveys demonstrated that the actual <span class="hlt">shearing</span> force of a volcanic mud flow on Mt. Sakurajima was from 0.46 to 2.50 kgf/cm2...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/biblio/250825-inverse-design-centrifugal-compressor-vaned-diffusers-inlet-shear-flows','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/250825-inverse-design-centrifugal-compressor-vaned-diffusers-inlet-shear-flows"><span>Inverse design of centrifugal compressor vaned diffusers in inlet <span class="hlt">shear</span> flows</span></a></p> <p><a target="_blank" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Zangeneh, M.</p> <p>1996-04-01</p> <p>A three-dimensional inverse design method in which the blade (or vane) geometry is designed for specified distributions of circulation and blade thickness is applied to the design of centrifugal compressor vaned diffusers. Two generic diffusers are designed, one with uniform inlet flow (equivalent to a conventional design) and the other with a <span class="hlt">sheared</span> inlet flow. The inlet <span class="hlt">shear</span> flow effects are modeled in the design method by using the so-called ``Secondary Flow Approximation`` in which the Bernoulli surfaces are convected by the tangentially mean inviscid flow field. The difference between the vane geometry of the uniform inlet flow and nonuniformmore » inlet flow diffusers is found to be most significant from 50 percent chord to the trailing edge region. The flows through both diffusers are computed by using Denton`s three-dimensional inviscid Euler solver and Dawes` three-dimensional Navier-Stokes solver under <span class="hlt">sheared</span> in-flow conditions. The <span class="hlt">predictions</span> indicate improved pressure recovery and internal flow field for the diffuser designed for <span class="hlt">shear</span> inlet flow conditions.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009PPCF...51g5009P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009PPCF...51g5009P"><span>Scaling results for the magnetic field line trajectories in the stochastic layer near the separatrix in divertor tokamaks with high magnetic <span class="hlt">shear</span> using the higher <span class="hlt">shear</span> map</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Punjabi, Alkesh; Ali, Halima; Farhat, Hamidullah</p> <p>2009-07-01</p> <p>Extra terms are added to the generating function of the simple map (Punjabi et al 1992 Phys. Rev. Lett. 69 3322) to adjust <span class="hlt">shear</span> of magnetic field lines in divertor tokamaks. From this new generating function, a higher <span class="hlt">shear</span> map is derived from a canonical transformation. A continuous analog of the higher <span class="hlt">shear</span> map is also derived. The method of maps (Punjabi et al 1994 J. Plasma Phys. 52 91) is used to calculate the average <span class="hlt">shear</span>, stochastic broadening of the ideal separatrix near the X-point in the principal plane of the tokamak, loss of poloidal magnetic flux from inside the ideal separatrix, magnetic footprint on the collector plate, and its area, and the radial diffusion coefficient of magnetic field lines near the X-point. It is found that the width of the stochastic layer near the X-point and the loss of poloidal flux from inside the ideal separatrix scale linearly with average <span class="hlt">shear</span>. The area of magnetic footprints scales roughly linearly with average <span class="hlt">shear</span>. Linear scaling of the area is quite good when the average <span class="hlt">shear</span> is greater than or equal to 1.25. When the average <span class="hlt">shear</span> is in the range 1.1-1.25, the area of the footprint fluctuates (as a function of average <span class="hlt">shear</span>) and scales faster than linear scaling. Radial diffusion of field lines near the X-point increases very rapidly by about four orders of magnitude as average <span class="hlt">shear</span> increases from about 1.15 to 1.5. For higher values of average <span class="hlt">shear</span>, diffusion increases linearly, and comparatively very slowly. The very slow scaling of the radial diffusion of the field can flatten the plasma pressure gradient near the separatrix, and lead to the elimination of <span class="hlt">type</span>-I edge localized modes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19830055988&hterms=disorder+stress&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Ddisorder%2Bstress','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19830055988&hterms=disorder+stress&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Ddisorder%2Bstress"><span>Unsteady behavior of a reattaching <span class="hlt">shear</span> layer</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Driver, D. M.; Seegmiller, H. L.; Marvin, J.</p> <p>1983-01-01</p> <p>A detailed investigation of the unsteadiness in a reattaching, turbulent <span class="hlt">shear</span> layer is reported. Laser-Doppler velocimeter measurements were conditionally sampled on the basis of instantaneous flow direction near reattachment. Conditions of abnormally short reattachment and abnormally long reattachment were considered. Ensemble-averaging of measurements made during these conditions was used to obtain mean velocities and Rreynolds stresses. In the mean flow, conditional streamlines show a global change in flow pattern which correlates with wall-flow direction. This motion can loosely be described as a 'flapping' of the <span class="hlt">shear</span> layer. Tuft probes show that the flow direction reversals occur quite randomly and are shortlived. Streses shown also vary with the change in flow pattern. Yet, the global'flapping' motion does not appear to contribute significantly to the stress in the flow. A second <span class="hlt">type</span> of unsteady motion was identified. Spectral analysis of both wall static pressure and streamwise velocity shows that most of the energy in the flow resides in frequencies that are significantly lower than that of the turbulence. The dominant frequency is at a Strouhal number equal to 0.2, which is the characteristic frequency of roll-up and pairing of vortical structure seen in free <span class="hlt">shear</span> layers. It is conjectured that the 'flapping' is a disorder of the roll-up and pairing process occurring in the <span class="hlt">shear</span> layer.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JSG....66..188C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JSG....66..188C"><span>Potential of pressure solution for strain localization in the Baccu Locci <span class="hlt">Shear</span> Zone (Sardinia, Italy)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Casini, Leonardo; Funedda, Antonio</p> <p>2014-09-01</p> <p>The mylonites of the Baccu Locci <span class="hlt">Shear</span> Zone (BLSZ), Sardinia (Italy), were deformed during thrusting along a bottom-to-top strain gradient in lower greenschist facies. The microstructure of metavolcanic protoliths shows evidence for composite deformation accommodated by dislocation creep within strong quartz porphyroclasts, and pressure solution in the finer grained matrix. The evolution of mylonite is simulated in two sets of numerical experiments, assuming either a constant width of the deforming zone (model 1) or a narrowing <span class="hlt">shear</span> zone (model 2). A 2-5 mm y-1 constant-external-velocity boundary condition is applied on the basis of geologic constraints. Inputs to the models are provided by inverting paleostress values obtained from quartz recrystallized grain-size paleopiezometry. Both models <span class="hlt">predict</span> a significant stress drop across the <span class="hlt">shear</span> zone. However, model 1 involves a dramatic decrease in strain rate towards the zone of apparent strain localization. In contrast, model 2 <span class="hlt">predicts</span> an increase in strain rate with time (from 10-14 to 10-12 s-1), which is consistent with stabilization of the <span class="hlt">shear</span> zone profile and localization of deformation near the hanging wall. Extrapolating these results to the general context of crust strength suggests that pressure-solution creep may be a critical process for strain softening and for the stabilization of deformation within <span class="hlt">shear</span> zones.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70024460','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70024460"><span>A pitfall in shallow <span class="hlt">shear</span>-wave refraction surveying</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Xia, J.; Miller, R.D.; Park, C.B.; Wightman, E.; Nigbor, R.</p> <p>2002-01-01</p> <p>The shallow <span class="hlt">shear</span>-wave refraction method works successfully in an area with a series of horizontal layers. However, complex near-surface geology may not fit into the assumption of a series of horizontal layers. That a plane SH-wave undergoes wave-<span class="hlt">type</span> conversion along an interface in an area of nonhorizontal layers is theoretically inevitable. One real example shows that the shallow <span class="hlt">shear</span>-wave refraction method provides velocities of a converted wave rather than an SH- wave. Moreover, it is impossible to identify the converted wave by refraction data itself. As most geophysical engineering firms have limited resources, an additional P-wave refraction survey is necessary to verify if velocities calculated from a <span class="hlt">shear</span>-wave refraction survey are velocities of converted waves. The alternative at this time may be the surface wave method, which can provide reliable S-wave velocities, even in an area of velocity inversion (a higher velocity layer underlain by a lower velocity layer). ?? 2002 Elsevier Science B.V. All rights reserved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018RMRE...51.1521D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018RMRE...51.1521D"><span>Discrete Analysis of Damage and <span class="hlt">Shear</span> Banding in Argillaceous Rocks</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dinç, Özge; Scholtès, Luc</p> <p>2018-05-01</p> <p>A discrete approach is proposed to study damage and failure processes taking place in argillaceous rocks which present a transversely isotropic behavior. More precisely, a dedicated discrete element method is utilized to provide a micromechanical description of the mechanisms involved. The purpose of the study is twofold: (1) presenting a three-dimensional discrete element model able to simulate the anisotropic macro-mechanical behavior of the Callovo-Oxfordian claystone as a particular case of argillaceous rocks; (2) studying how progressive failure develops in such material. Material anisotropy is explicitly taken into account in the numerical model through the introduction of weakness planes distributed at the interparticle scale following predefined orientation and intensity. Simulations of compression tests under plane-strain and triaxial conditions are performed to clarify the development of damage and the appearance of <span class="hlt">shear</span> bands through micromechanical analyses. The overall mechanical behavior and <span class="hlt">shear</span> banding patterns <span class="hlt">predicted</span> by the numerical model are in good agreement with respect to experimental observations. Both tensile and <span class="hlt">shear</span> microcracks emerging from the modeling also present characteristics compatible with microstructural observations. The numerical results confirm that the global failure of argillaceous rocks is well correlated with the mechanisms taking place at the local scale. Specifically, strain localization is shown to directly result from <span class="hlt">shear</span> microcracking developing with a preferential orientation distribution related to the orientation of the <span class="hlt">shear</span> band. In addition, localization events presenting characteristics similar to <span class="hlt">shear</span> bands are observed from the early stages of the loading and might thus be considered as precursors of strain localization.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19910014828','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19910014828"><span>CLASS: Coherent Lidar Airborne <span class="hlt">Shear</span> Sensor. Windshear avoidance</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Targ, Russell</p> <p>1991-01-01</p> <p>The coherent lidar airborne <span class="hlt">shear</span> sensor (CLASS) is an airborne CO2 lidar system being designed and developed by Lockheed Missiles and Space Company, Inc. (LMSC) under contract to NASA Langley Research Center. The goal of this program is to develop a system with a 2- to 4-kilometer range that will provide a warning time of 20 to 40 seconds, so that the pilot can avoid the hazards of low-altitude wind <span class="hlt">shear</span> under all weather conditions. It is a <span class="hlt">predictive</span> system which will warn the pilot about a hazard that the aircraft will experience at some later time. The ability of the system to provide <span class="hlt">predictive</span> warnings of clear air turbulence will also be evaluated. A one-year flight evaluation program will measure the line-of-sight wind velocity from a wide variety of wind fields obtained by an airborne radar, an accelerometer-based reactive wind-sensing system, and a ground-based Doppler radar. The success of the airborne lidar system will be determined by its correlation with the windfield as indicated by the onboard reactive system, which indicates the winds actually experienced by the NASA Boeing 737 aircraft.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3974553','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3974553"><span>Effects of dentin surface treatments on <span class="hlt">shear</span> bond strength of glass-ionomer cements</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Poggio, Claudio; Beltrami, Riccardo; Scribante, Andrea; Colombo, Marco; Lombardini, Marco</p> <p>2014-01-01</p> <p>Summary Aim The aim of this in vitro study was to evaluate the effect of different surface treatments on <span class="hlt">shear</span> bond strength of a conventional glass-ionomer cement (GIC) and a resin-modified glass-ionomer cement (RMGIC) to dentin. Materials and methods 80 bovine permanent incisors were used. 40 cylindrical specimens of a GIC (Fuji IX GP Extra) and 40 cylindrical specimens of a RMGIC (Fuji II LC) were attached to the dentin. The teeth were then randomly assigned to 8 groups of equal size (n=10), 4 for every <span class="hlt">type</span> of glass-ionomer cement, corresponding to <span class="hlt">type</span> of dentin surface treatments. Group 1: GC Cavity Conditioner; Group 2: 37% phosphoric acid gel; Group 3: Clearfil SE Bond; Group 4: no dentin conditioning (control). The specimens were placed in a universal testing machine (Model 3343, Instron Corp., Canton, Mass., USA) and subsequently tested for <span class="hlt">shear</span> bond strength (MPa). Results ANOVA showed the presence of significant differences among the various groups. Post hoc Tukey test showed different values of <span class="hlt">shear</span> bond strength for Fuji IX GP Extra and for Fuji II LC. The different conditioners variably influence the adhesion of the glass-ionomer cements tested. Conclusions. RMGIC <span class="hlt">shear</span> bond to dentin was higher than GIC. The use of a Self-etch adhesive system improved the <span class="hlt">shear</span> bond strength values of RMGIC and lowered the <span class="hlt">shear</span> bond strength values of GIC significantly. PMID:24753797</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017PhRvE..95e2903V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017PhRvE..95e2903V"><span><span class="hlt">Shear</span> banding, discontinuous <span class="hlt">shear</span> thickening, and rheological phase transitions in athermally <span class="hlt">sheared</span> frictionless disks</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vâgberg, Daniel; Olsson, Peter; Teitel, S.</p> <p>2017-05-01</p> <p>We report on numerical simulations of simple models of athermal, bidisperse, soft-core, massive disks in two dimensions, as a function of packing fraction ϕ , inelasticity of collisions as measured by a parameter Q , and applied uniform <span class="hlt">shear</span> strain rate γ ˙. Our particles have contact interactions consisting of normally directed elastic repulsion and viscous dissipation, as well as tangentially directed viscous dissipation, but no interparticle Coulombic friction. Mapping the phase diagram in the (ϕ ,Q ) plane for small γ ˙, we find a sharp first-order rheological phase transition from a region with Bagnoldian rheology to a region with Newtonian rheology, and show that the system is always Newtonian at jamming. We consider the rotational motion of particles and demonstrate the crucial importance that the coupling between rotational and translational degrees of freedom has on the phase structure at small Q (strongly inelastic collisions). At small Q , we show that, upon increasing γ ˙, the sharp Bagnoldian-to-Newtonian transition becomes a coexistence region of finite width in the (ϕ ,γ ˙) plane, with coexisting Bagnoldian and Newtonian <span class="hlt">shear</span> bands. Crossing this coexistence region by increasing γ ˙ at fixed ϕ , we find that discontinuous <span class="hlt">shear</span> thickening can result if γ ˙ is varied too rapidly for the system to relax to the <span class="hlt">shear</span>-banded steady state corresponding to the instantaneous value of γ ˙.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29018925','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29018925"><span>The diagnostic performance of <span class="hlt">shear</span>-wave elastography for liver fibrosis in children and adolescents: A systematic review and diagnostic meta-analysis.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kim, Jeong Rye; Suh, Chong Hyun; Yoon, Hee Mang; Lee, Jin Seong; Cho, Young Ah; Jung, Ah Young</p> <p>2018-03-01</p> <p>To assess the diagnostic performance of <span class="hlt">shear</span>-wave elastography for determining the severity of liver fibrosis in children and adolescents. An electronic literature search of PubMed and EMBASE was conducted. Bivariate modelling and hierarchical summary receiver-operating-characteristic modelling were performed to evaluate the diagnostic performance of <span class="hlt">shear</span>-wave elastography. Meta-regression and subgroup analyses according to the modality of <span class="hlt">shear</span>-wave imaging and the degree of liver fibrosis were also performed. Twelve eligible studies with 550 patients were included. <span class="hlt">Shear</span>-wave elastography showed a summary sensitivity of 81 % (95 % CI: 71-88) and a specificity of 91 % (95 % CI: 83-96) for the <span class="hlt">prediction</span> of significant liver fibrosis. The number of measurements of <span class="hlt">shear</span>-wave elastography performed was a significant factor influencing study heterogeneity. Subgroup analysis revealed <span class="hlt">shear</span>-wave elastography to have an excellent diagnostic performance according to each degree of liver fibrosis. Supersonic <span class="hlt">shear</span> imaging (SSI) had a higher sensitivity (p<.01) and specificity (p<.01) than acoustic radiation force impulse imaging (ARFI). <span class="hlt">Shear</span>-wave elastography is an excellent modality for the evaluation of the severity of liver fibrosis in children and adolescents. Compared with ARFI, SSI showed better diagnostic performance for <span class="hlt">prediction</span> of significant liver fibrosis. • <span class="hlt">Shear</span>-wave elastography is beneficial for determining liver fibrosis severity in children. • <span class="hlt">Shear</span>-wave elastography showed summary sensitivity of 81 %, specificity of 91 %. • SSI showed better diagnostic performance than ARFI for significant liver fibrosis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018PhRvE..97e2601A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018PhRvE..97e2601A"><span>Transient <span class="hlt">shear</span> banding in the nematic dumbbell model of liquid crystalline polymers</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Adams, J. M.; Corbett, D.</p> <p>2018-05-01</p> <p>In the <span class="hlt">shear</span> flow of liquid crystalline polymers (LCPs) the nematic director orientation can align with the flow direction for some materials but continuously tumble in others. The nematic dumbbell (ND) model was originally developed to describe the rheology of flow-aligning semiflexible LCPs, and flow-aligning LCPs are the focus in this paper. In the <span class="hlt">shear</span> flow of monodomain LCPs, it is usually assumed that the spatial distribution of the velocity is uniform. This is in contrast to polymer solutions, where highly nonuniform spatial velocity profiles have been observed in experiments. We analyze the ND model, with an additional gradient term in the constitutive model, using a linear stability analysis. We investigate the separate cases of constant applied <span class="hlt">shear</span> stress and constant applied <span class="hlt">shear</span> rate. We find that the ND model has a transient flow instability to the formation of a spatially inhomogeneous flow velocity for certain starting orientations of the director. We calculate the spatially resolved flow profile in both constant applied stress and constant applied <span class="hlt">shear</span> rate in start up from rest, using a model with one spatial dimension to illustrate the flow behavior of the fluid. For low <span class="hlt">shear</span> rates flow reversal can be seen as the director realigns with the flow direction, whereas for high <span class="hlt">shear</span> rates the director reorientation occurs simultaneously across the gap. Experimentally, this inhomogeneous flow is <span class="hlt">predicted</span> to be observed in flow reversal experiments in LCPs.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_16 --> <div id="page_17" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="321"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/servlets/purl/1012608','DOE-PATENT-XML'); return false;" href="https://www.osti.gov/servlets/purl/1012608"><span>Angular <span class="hlt">shear</span> plate</span></a></p> <p><a target="_blank" href="http://www.osti.gov/doepatents">DOEpatents</a></p> <p>Ruda, Mitchell C [Tucson, AZ; Greynolds, Alan W [Tucson, AZ; Stuhlinger, Tilman W [Tucson, AZ</p> <p>2009-07-14</p> <p>One or more disc-shaped angular <span class="hlt">shear</span> plates each include a region thereon having a thickness that varies with a nonlinear function. For the case of two such <span class="hlt">shear</span> plates, they are positioned in a facing relationship and rotated relative to each other. Light passing through the variable thickness regions in the angular plates is refracted. By properly timing the relative rotation of the plates and by the use of an appropriate polynomial function for the thickness of the <span class="hlt">shear</span> plate, light passing therethrough can be focused at variable positions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AIPC.1794b0038C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AIPC.1794b0038C"><span>Research on wall <span class="hlt">shear</span> stress considering wall roughness when <span class="hlt">shear</span> swirling flow vibration cementing</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cui, Zhihua; Ai, Chi; Feng, Fuping</p> <p>2017-01-01</p> <p>When <span class="hlt">shear</span> swirling flow vibration cementing, the casing is revolving periodically and eccentrically, which leads to the annulus fluid in turbulent swirling flow state. The wall <span class="hlt">shear</span> stress is more than that in laminar flow field when conventional cementing. The paper mainly studied the wall <span class="hlt">shear</span> stress distribution on the borehole wall when <span class="hlt">shear</span> swirling flow vibration cementing based on the finite volume method. At the same time, the wall roughness affected and changed the turbulent flow near the borehole wall and the wall <span class="hlt">shear</span> stress. Based on the wall function method, the paper established boundary conditions considering the wall roughness and derived the formula of the wall <span class="hlt">shear</span> stress. The results showed that the wall roughness significantly increases the wall <span class="hlt">shear</span> stress. However, the larger the wall roughness, the greater the thickness of mud cake, which weakening the cementing strength. Considering the effects in a comprehensive way, it is discovered that the particle size of solid phase in drilling fluid is about 0.1 mm to get better cementing quality.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/biblio/22360145-origin-shear-thickening-semidilute-wormlike-micellar-solutions-evidence-elastic-turbulence','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/22360145-origin-shear-thickening-semidilute-wormlike-micellar-solutions-evidence-elastic-turbulence"><span>Origin of <span class="hlt">shear</span> thickening in semidilute wormlike micellar solutions and evidence of elastic turbulence</span></a></p> <p><a target="_blank" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Marín-Santibáñez, Benjamín M.; Pérez-González, José, E-mail: jpg@esfm.ipn.mx; Rodríguez-González, Francisco</p> <p>2014-11-01</p> <p>The origin of <span class="hlt">shear</span> thickening in an equimolar semidilute wormlike micellar solution of cetylpyridinium chloride and sodium salicylate was investigated in this work by using Couette rheometry, flow visualization, and capillary Rheo-particle image velocimetry. The use of the combined methods allowed the discovery of gradient <span class="hlt">shear</span> banding flow occurring from a critical <span class="hlt">shear</span> stress and consisting of two main bands, one isotropic (transparent) of high viscosity and one structured (turbid) of low viscosity. Mechanical rheometry indicated macroscopic <span class="hlt">shear</span> thinning behavior in the <span class="hlt">shear</span> banding regime. However, local velocimetry showed that the turbid band increased its viscosity along with the shearmore » stress, even though barely reached the value of the viscosity of the isotropic phase. This <span class="hlt">shear</span> band is the precursor of <span class="hlt">shear</span> induced structures that subsequently give rise to the average increase in viscosity or apparent <span class="hlt">shear</span> thickening of the solution. Further increase in the <span class="hlt">shear</span> stress promoted the growing of the turbid band across the flow region and led to destabilization of the <span class="hlt">shear</span> banding flow independently of the <span class="hlt">type</span> of rheometer used, as well as to vorticity banding in Couette flow. At last, vorticity banding disappeared and the flow developed elastic turbulence with chaotic dynamics.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26745014','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26745014"><span>Interfacial <span class="hlt">Shear</span> Strength of Multilayer Graphene Oxide Films.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Daly, Matthew; Cao, Changhong; Sun, Hao; Sun, Yu; Filleter, Tobin; Singh, Chandra Veer</p> <p>2016-02-23</p> <p>Graphene oxide (GO) is considered as one of the most promising layered materials with tunable physical properties and applicability in many important engineering applications. In this work, the interfacial behavior of multilayer GO films was directly investigated via GO-to-GO friction force microscopy, and the interfacial <span class="hlt">shear</span> strength (ISS) was measured to be 5.3 ± 3.2 MPa. Based on high resolution atomic force microscopy images and the available chemical data, targeted molecular dynamics simulations were performed to evaluate the influence of functional structure, topological defects, and interlayer registry on the <span class="hlt">shear</span> response of the GO films. Theoretical values for <span class="hlt">shear</span> strength ranging from 17 to 132 MPa were <span class="hlt">predicted</span> for the different structures studied, providing upper bounds for the ISS. Computational results also revealed the atomic origins of the stochastic nature of friction measurements. Specifically, the wide scatter in experimental measurements was attributed to variations in functional structure and topological defects within the sliding volume. The findings of this study provide important insight for understanding the significant differences in strength between monolayer and bulk graphene oxide materials and can be useful for engineering topological structures with tunable mechanical properties.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28882058','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28882058"><span>Role of acoustic radiation force impulse and <span class="hlt">shear</span> wave velocity in <span class="hlt">prediction</span> of preterm birth: a prospective study.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Agarwal, Arjit; Agarwal, Shubhra; Chandak, Shruti</p> <p>2018-06-01</p> <p>Background Preterm birth is one of the important causes of neonatal morbidity where we rely on subjective criteria such as modified Bishop's scoring and contemporary sonographic measurement of cervical length. Acoustic radiation force impulse (ARFI) is a technological advancement in elastography that can be employed in <span class="hlt">prediction</span> of cervical softening and preterm labor. Purpose To evaluate the role of ARFI technique and <span class="hlt">shear</span> wave velocity (SWV) estimates as a predictor of preterm birth and its comparison with other clinical and sono-elastographic measures. Material and Methods Thirty-four pregnant women (gestation age = 28-37 weeks age) showing features suggestive of preterm labor were included and evaluated with modified Bishop's score, cervical length by ultrasound (US), ARFI to derive Elastography index (EI), and SWV of the cervix. The patients were later divided into two groups, using the clinical outcome of preterm or term delivery. Results Twenty patients delivered at term (gestational age > 37 weeks) and 14 were preterm. Receiver operating characteristics (ROC) curves showed SWV with highest sensitivity and specificity (93% and 90%, respectively) for the <span class="hlt">prediction</span> of preterm birth at a cutoff value of 2.83 m/s. EI and modified Bishop's score were comparable to each other, but were less sensitive techniques. Conclusion Elastographic assessment of antenatal cervix is a novel technique of virtual palpation of internal os and can be utilized as an objective criterion for preterm birth <span class="hlt">prediction</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018AdWR..113..141E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018AdWR..113..141E"><span><span class="hlt">Shear</span> and shearless Lagrangian structures in compound channels</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Enrile, F.; Besio, G.; Stocchino, A.</p> <p>2018-03-01</p> <p>Transport processes in a physical model of a natural stream with a composite cross-section (compound channel) are investigated by means of a Lagrangian analysis based on nonlinear dynamical system theory. Two-dimensional free surface Eulerian experimental velocity fields of a uniform flow in a compound channel form the basis for the identification of the so-called Lagrangian Coherent Structures. Lagrangian structures are recognized as the key features that govern particle trajectories. We seek for two particular class of Lagrangian structures: <span class="hlt">Shear</span> and shearless structures. The former are generated whenever the <span class="hlt">shear</span> dominates the flow whereas the latter behave as jet-cores. These two <span class="hlt">type</span> of structures are detected as ridges and trenches of the Finite-Time Lyapunov Exponents fields, respectively. Besides, shearlines computed applying the geodesic theory of transport barriers mark <span class="hlt">Shear</span> Lagrangian Coherent Structures. So far, the detection of these structures in real experimental flows has not been deeply investigated. Indeed, the present results obtained in a wide range of the controlling parameters clearly show a different behaviour depending on the shallowness of the flow. <span class="hlt">Shear</span> and Shearless Lagrangian Structures detected from laboratory experiments clearly appear as the flow develops in shallow conditions. The presence of these Lagrangian Structures tends to fade in deep flow conditions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19930010405','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19930010405"><span>Air/ground wind <span class="hlt">shear</span> information integration: Flight test results</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hinton, David A.</p> <p>1992-01-01</p> <p>An element of the NASA/FAA wind <span class="hlt">shear</span> program is the integration of ground-based microburst information on the flight deck, to support airborne wind <span class="hlt">shear</span> alerting and microburst avoidance. NASA conducted a wind <span class="hlt">shear</span> flight test program in the summer of 1991 during which airborne processing of Terminal Doppler Weather Radar (TDWR) data was used to derive microburst alerts. High level microburst products were extracted from TDWR, transmitted to a NASA Boeing 737 in flight via data link, and processed to estimate the wind <span class="hlt">shear</span> hazard level (F-factor) that would be experienced by the aircraft in the core of each microburst. The microburst location and F-factor were used to derive a situation display and alerts. The situation display was successfully used to maneuver the aircraft for microburst penetrations, during which in situ 'truth' measurements were made. A total of 19 penetrations were made of TDWR-reported microburst locations, resulting in 18 airborne microburst alerts from the TDWR data and two microburst alerts from the airborne in situ measurements. The primary factors affecting alerting performance were spatial offset of the flight path from the region of strongest <span class="hlt">shear</span>, differences in TDWR measurement altitude and airplane penetration altitude, and variations in microburst outflow profiles. <span class="hlt">Predicted</span> and measured F-factors agreed well in penetrations near microburst cores. Although improvements in airborne and ground processing of the TDWR measurement would be required to support an airborne executive-level alerting protocol, the feasibility of airborne utilization of TDWR data link data has been demonstrated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012EGUGA..14.3597R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012EGUGA..14.3597R"><span>Microstructures and kinematic vorticity analysis from the mylonites along the Karakoram <span class="hlt">Shear</span> Zone, Pangong Mountains, Karakoram</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Roy, P.</p> <p>2012-04-01</p> <p>The Karakoram <span class="hlt">Shear</span> Zone is a northwest-southeast trending dextral ductile <span class="hlt">shear</span> zone, which has affected the granitic and granodioritic bodies of the southern Asian Plate margin in three distinct episodes. The ductile <span class="hlt">shearing</span> of the granitic bodies at Tangste and Darbuk has resulted in the development of mylonites with mylonitic foliation and stretching lineation. More intense deformation is noted in the Tangste granite grading upto orthomylonite, as compared to the Darbuk granite. Kinematic indicators include S-C foliation, synthetic C' and C" antithetic <span class="hlt">shear</span> bands, <span class="hlt">Type</span> A σ-mantled porphyroclasts, oblique quartz foliation, micro-<span class="hlt">shears</span> with bookshelf gliding, mineral fishes including Group 2 mica fishes, and <span class="hlt">Type</span> 1 and 2a pull-apart microstructures, and exhibit strong dextral sense of ductile <span class="hlt">shearing</span> towards southeast. The textural features of the minerals especially that of quartz and feldspar, indicate temperature of mylonitisation ranging between 300° C and 500° C in the upper greenschist facies. The mylonitic rocks of the KSZ provide an opportunity for the possible utilization of the deformational structures namely that of quartz and feldspar porphyroclast as well as, well developed <span class="hlt">shear</span> bands for kinematic vorticity studies. Well developed quartz and feldspar porphyroclasts and synthetic and antithetic <span class="hlt">shear</span> bands from six different mylonitic samples of the mylonitic Tangste granite has been used to estimate the bulk kinematic vorticity (Wk) involved in the overall deformation of the KSZ using the Porphyroclast Hyperbolic Distribution (PHD) method and <span class="hlt">Shear</span> band (SB) analysis. The PHD method yields Wk values that range from Wk = 0.29 to Wk =0.43, where as the <span class="hlt">Shear</span> bands yields values ranging from Wk = 0.45 to Wk =0.93, thus indicating distinct pure and simple <span class="hlt">shear</span> regimes at different stages of the evolution of the KSZ.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018PhRvL.120n8004B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018PhRvL.120n8004B"><span>Normal Stresses, Contraction, and Stiffening in <span class="hlt">Sheared</span> Elastic Networks</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Baumgarten, Karsten; Tighe, Brian P.</p> <p>2018-04-01</p> <p>When elastic solids are <span class="hlt">sheared</span>, a nonlinear effect named after Poynting gives rise to normal stresses or changes in volume. We provide a novel relation between the Poynting effect and the microscopic Grüneisen parameter, which quantifies how stretching shifts vibrational modes. By applying this relation to random spring networks, a minimal model for, e.g., biopolymer gels and solid foams, we find that networks contract or develop tension because they vibrate faster when stretched. The amplitude of the Poynting effect is sensitive to the network's linear elastic moduli, which can be tuned via its preparation protocol and connectivity. Finally, we show that the Poynting effect can be used to <span class="hlt">predict</span> the finite strain scale where the material stiffens under <span class="hlt">shear</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3012006','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3012006"><span>Impact of <span class="hlt">shear</span> rate modulation on vascular function in humans</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Tinken, Toni M.; Thijssen, Dick H.J.; Hopkins, Nicola; Black, Mark A.; Dawson, Ellen A.; Minson, Christopher T.; Newcomer, Sean C.; Laughlin, M. Harold; Cable, N. Timothy; Green, Daniel J.</p> <p>2010-01-01</p> <p><span class="hlt">Shear</span> stress is an important stimulus to arterial adaptation in response to exercise and training in humans. We recently observed significant reverse arterial flow and <span class="hlt">shear</span> during exercise and different antegrade/retrograde patterns of <span class="hlt">shear</span> and flow in response to different <span class="hlt">types</span> of exercise. The purpose of this study was to simultaneously examine flow mediated dilation (FMD), a largely nitric oxide mediated vasodilator response, in both brachial arteries of healthy young men before and after 30-minute interventions consisting of bilateral forearm heating, recumbent leg cycling and bilateral handgrip exercise. During each intervention, a cuff inflated to 60mmHg was placed on one arm to unilaterally manipulate the <span class="hlt">shear</span> rate stimulus. In the non-cuffed arm, antegrade flow and <span class="hlt">shear</span> increased similarly in response to each intervention (ANOVA; P<0.001, no interaction between interventions; P=0.71). Baseline FMD (4.6, 6.9 and 6.7%) increased similarly in response to heating, handgrip and cycling (8.1, 10.4 and 8.9%, ANOVA; P<0.001, no interaction; 0.89). In contrast, cuffed arm antegrade <span class="hlt">shear</span> rate was lower than in the non-cuffed arm for all conditions (P<0.05) and the increase in FMD was abolished in this arm (4.7, 6.7 and 6.1%) (2-way ANOVA: all conditions interacted P<0.05). These results suggest that differences in the magnitude of antegrade <span class="hlt">shear</span> rate transduce differences in endothelial vasodilator function in humans, a finding which may have relevance for the impact of different exercise interventions on vascular adaptation in humans. PMID:19546374</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018PhBio..15d6006M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018PhBio..15d6006M"><span>Modeling cell-substrate de-adhesion dynamics under fluid <span class="hlt">shear</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Maan, Renu; Rani, Garima; Menon, Gautam I.; Pullarkat, Pramod A.</p> <p>2018-07-01</p> <p>Changes in cell-substrate adhesion are believed to signal the onset of cancer metastasis, but such changes must be quantified against background levels of intrinsic heterogeneity between cells. Variations in cell-substrate adhesion strengths can be probed through biophysical measurements of cell detachment from substrates upon the application of an external force. Here, we investigate, theoretically and experimentally, the detachment of cells adhered to substrates when these cells are subjected to fluid <span class="hlt">shear</span>. We present a theoretical framework within which we calculate the fraction of detached cells as a function of <span class="hlt">shear</span> stress for fast ramps as well as the decay in this fraction at fixed <span class="hlt">shear</span> stress as a function of time. Using HEK and 3T3 fibroblast cells as experimental model systems, we extract characteristic force scales for cell adhesion as well as characteristic detachment times. We estimate force-scales of  ∼500 pN associated to a single focal contact, and characteristic time-scales of s representing cell-spread-area dependent mean first passage times to the detached state at intermediate values of the <span class="hlt">shear</span> stress. Variations in adhesion across cell <span class="hlt">types</span> are especially prominent when cell detachment is probed by applying a time-varying <span class="hlt">shear</span> stress. These methods can be applied to characterizing changes in cell adhesion in a variety of contexts, including metastasis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5125588','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5125588"><span>Pulsatility Index as a Diagnostic Parameter of Reciprocating Wall <span class="hlt">Shear</span> Stress Parameters in Physiological Pulsating Waveforms</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Avrahami, Idit; Kersh, Dikla</p> <p>2016-01-01</p> <p>Arterial wall <span class="hlt">shear</span> stress (WSS) parameters are widely used for <span class="hlt">prediction</span> of the initiation and development of atherosclerosis and arterial pathologies. Traditional clinical evaluation of arterial condition relies on correlations of WSS parameters with average flow rate (Q) and heart rate (HR) measurements. We show that for pulsating flow waveforms in a straight tube with flow reversals that lead to significant reciprocating WSS, the measurements of HR and Q are not sufficient for <span class="hlt">prediction</span> of WSS parameters. Therefore, we suggest adding a third quantity—known as the pulsatility index (PI)—which is defined as the peak-to-peak flow rate amplitude normalized by Q. We examine several pulsating flow waveforms with and without flow reversals using a simulation of a Womersley model in a straight rigid tube and validate the simulations through experimental study using particle image velocimetry (PIV). The results indicate that clinically relevant WSS parameters such as the percentage of negative WSS (P[%]), oscillating <span class="hlt">shear</span> index (OSI) and the ratio of minimum to maximum <span class="hlt">shear</span> stress rates (min/max), are better <span class="hlt">predicted</span> when the PI is used in conjunction with HR and Q. Therefore, we propose to use PI as an additional and essential diagnostic quantity for improved <span class="hlt">predictability</span> of the reciprocating WSS. PMID:27893801</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17124126','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17124126"><span>Nucleation of protein crystals under the influence of solution <span class="hlt">shear</span> flow.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Penkova, Anita; Pan, Weichun; Hodjaoglu, Feyzim; Vekilov, Peter G</p> <p>2006-09-01</p> <p>Several recent theories and simulations have <span class="hlt">predicted</span> that <span class="hlt">shear</span> flow could enhance, or, conversely, suppress the nucleation of crystals from solution. Such modulations would offer a pathway for nucleation control and provide a novel explanation for numerous mysteries in nucleation research. For experimental tests of the effects of <span class="hlt">shear</span> flow on protein crystal nucleation, we found that if a protein solution droplet of approximately 5 microL (2-3 mm diameter at base) is held on a hydrophobic substrate in an enclosed environment and in a quasi-uniform constant electric field of 2 to 6 kV cm(-1), a rotational flow with a maximum rate at the droplet top of approximately 10 microm s(-1) is induced. The <span class="hlt">shear</span> rate varies from 10(-3) to 10(-1) s(-1). The likely mechanism of the rotational flow involves adsorption of the protein and amphiphylic buffer molecules on the air-water interface and their redistribution in the electric field, leading to nonuniform surface tension of the droplet and surface tension-driven flow. Observations of the number of nucleated crystals in 24- and 72-h experiments with the proteins ferritin, apoferritin, and lysozyme revealed that the crystals are typically nucleated at a certain radius of the droplet, that is, at a preferred <span class="hlt">shear</span> rate. Variations of the rotational flow velocity resulted in suppression or enhancement of the total number of nucleated crystals of ferritin and apoferritin, while all solution flow rates were found to enhance lysozyme crystal nucleation. These observations show that <span class="hlt">shear</span> flow may strongly affect nucleation, and that for some systems, an optimal flow velocity, leading to fastest nucleation, exists. Comparison with the <span class="hlt">predictions</span> of theories and simulations suggest that the formation of ordered nuclei in a "normal" protein solution cannot be affected by such low <span class="hlt">shear</span> rates. We conclude that the flow acts by helping or suppressing the formation of ordered nuclei within mesoscopic metastable dense liquid</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016MAP...128..565G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016MAP...128..565G"><span>Organization of vertical <span class="hlt">shear</span> of wind and daily variability of monsoon rainfall</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gouda, K. C.; Goswami, P.</p> <p>2016-10-01</p> <p>Very little is known about the mechanisms that govern the day to day variability of the Indian summer monsoon (ISM) rainfall; in the current dominant view, the daily rainfall is essentially a result of chaotic dynamics. Most studies in the past have thus considered monsoon in terms of its seasonal (June-September) or monthly rainfall. We show here that the daily rainfall in June is associated with vertical <span class="hlt">shear</span> of horizontal winds at specific scales. While vertical <span class="hlt">shear</span> had been used in the past to investigate interannual variability of seasonal rainfall, rarely any effort has been made to examine daily rainfall. Our work shows that, at least during June, the daily rainfall variability of ISM rainfall is associated with a large scale dynamical coherence in the sense that the vertical <span class="hlt">shear</span> averaged over large spatial extents are significantly correlated with area-averaged daily rainfall. An important finding from our work is the existence of a clearly delineated monsoon <span class="hlt">shear</span> domain (MSD) with strong coherence between area-averaged <span class="hlt">shear</span> and area-averaged daily rainfall in June; this association of daily rainfall is not significant with <span class="hlt">shear</span> over only MSD. Another important feature is that the association between daily rainfall and vertical <span class="hlt">shear</span> is present only during the month of June. Thus while ISM (June-September) is a single seasonal system, it is important to consider the dynamics and variation of June independently of the seasonal ISM rainfall. The association between large-scale organization of circulation and daily rainfall is suggested as a basis for attempting <span class="hlt">prediction</span> of daily rainfall by ensuring accurate simulation of wind <span class="hlt">shear</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JaJAP..54gHC16Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JaJAP..54gHC16Y"><span><span class="hlt">Shear</span> wave mapping of skeletal muscle using <span class="hlt">shear</span> wave wavefront reconstruction based on ultrasound color flow imaging</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yamakoshi, Yoshiki; Yamamoto, Atsushi; Kasahara, Toshihiro; Iijima, Tomohiro; Yuminaka, Yasushi</p> <p>2015-07-01</p> <p>We have proposed a quantitative <span class="hlt">shear</span> wave imaging technique for continuous <span class="hlt">shear</span> wave excitation. <span class="hlt">Shear</span> wave wavefront is observed directly by color flow imaging using a general-purpose ultrasonic imaging system. In this study, the proposed method is applied to experiments in vivo, and <span class="hlt">shear</span> wave maps, namely, the <span class="hlt">shear</span> wave phase map, which shows the <span class="hlt">shear</span> wave propagation inside the medium, and the <span class="hlt">shear</span> wave velocity map, are observed for the skeletal muscle in the shoulder. To excite the <span class="hlt">shear</span> wave inside the skeletal muscle of the shoulder, a hybrid ultrasonic wave transducer, which combines a small vibrator with an ultrasonic wave probe, is adopted. The <span class="hlt">shear</span> wave velocity of supraspinatus muscle, which is measured by the proposed method, is 4.11 ± 0.06 m/s (N = 4). This value is consistent with those obtained by the acoustic radiation force impulse method.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19770021194','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19770021194"><span>A theoretical analysis of airplane longitudinal stability and control as affected by wind <span class="hlt">shear</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sherman, W. L.</p> <p>1977-01-01</p> <p>The longitudinal equations of motion with wind <span class="hlt">shear</span> terms were used to analyze the stability and motions of a jet transport. A positive wind <span class="hlt">shear</span> gives a decreasing head wind or changes a head wind into a tail wind. A negative wind <span class="hlt">shear</span> gives a decreasing tail wind or changes a tail wind into a head wind. It was found that wind <span class="hlt">shear</span> had very little effect on the short period mode and that negative wind <span class="hlt">shear</span>, although it affected the phugoid, did not cause stability problems. On the other hand, it was found that positive wind <span class="hlt">shear</span> can cause the phugoid to become aperiodic and unstable. In this case, a stability boundary for the phugoid was found that is valid for most aircraft at all flight speeds. Calculations of aircraft motions confirmed the results of the stability analysis. It was found that a flight path control automatic pilot and an airspeed control system provide good control in all <span class="hlt">types</span> of wind <span class="hlt">shear</span>. Appendixes give equations of motion that include the effects of downdrafts and updrafts and extend the longitudinal equations of motion for <span class="hlt">shear</span> to six degrees of freedom.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28415257','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28415257"><span>Effect of single-particle magnetostriction on the <span class="hlt">shear</span> modulus of compliant magnetoactive elastomers.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kalita, Viktor M; Snarskii, Andrei A; Shamonin, Mikhail; Zorinets, Denis</p> <p>2017-03-01</p> <p>The influence of an external magnetic field on the static <span class="hlt">shear</span> strain and the effective <span class="hlt">shear</span> modulus of a magnetoactive elastomer (MAE) is studied theoretically in the framework of a recently introduced approach to the single-particle magnetostriction mechanism [V. M. Kalita et al., Phys. Rev. E 93, 062503 (2016)10.1103/PhysRevE.93.062503]. The planar problem of magnetostriction in an MAE with magnetically soft inclusions in the form of a thin disk (platelet) having the magnetic anisotropy in the plane of this disk is solved analytically. An external magnetic field acts with torques on magnetic filler particles, creates mechanical stresses in the vicinity of inclusions, induces <span class="hlt">shear</span> strain, and increases the effective <span class="hlt">shear</span> modulus of these composite materials. It is shown that the largest effect of the magnetic field on the effective <span class="hlt">shear</span> modulus should be expected in MAEs with soft elastomer matrices, where the <span class="hlt">shear</span> modulus of the matrix is less than the magnetic anisotropy constant of inclusions. It is derived that the effective <span class="hlt">shear</span> modulus is nonlinearly dependent on the external magnetic field and approaches the saturation value in magnetic fields exceeding the field of particle anisotropy. It is shown that model calculations of the effective <span class="hlt">shear</span> modulus correspond to a phenomenological definition of effective elastic moduli and magnetoelastic coupling constants. The obtained theoretical results compare well with known experimental data. Determination of effective elastic coefficients in MAEs and their dependence on magnetic field is discussed. The concentration dependence of the effective <span class="hlt">shear</span> modulus at higher filler concentrations has been estimated using the method of Padé approximants, which <span class="hlt">predicts</span> that both the absolute and relative changes of the magnetic-field-dependent effective <span class="hlt">shear</span> modulus will significantly increase with the growing concentration of filler particles.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017PhRvE..95c2503K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017PhRvE..95c2503K"><span>Effect of single-particle magnetostriction on the <span class="hlt">shear</span> modulus of compliant magnetoactive elastomers</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kalita, Viktor M.; Snarskii, Andrei A.; Shamonin, Mikhail; Zorinets, Denis</p> <p>2017-03-01</p> <p>The influence of an external magnetic field on the static <span class="hlt">shear</span> strain and the effective <span class="hlt">shear</span> modulus of a magnetoactive elastomer (MAE) is studied theoretically in the framework of a recently introduced approach to the single-particle magnetostriction mechanism [V. M. Kalita et al., Phys. Rev. E 93, 062503 (2016), 10.1103/PhysRevE.93.062503]. The planar problem of magnetostriction in an MAE with magnetically soft inclusions in the form of a thin disk (platelet) having the magnetic anisotropy in the plane of this disk is solved analytically. An external magnetic field acts with torques on magnetic filler particles, creates mechanical stresses in the vicinity of inclusions, induces <span class="hlt">shear</span> strain, and increases the effective <span class="hlt">shear</span> modulus of these composite materials. It is shown that the largest effect of the magnetic field on the effective <span class="hlt">shear</span> modulus should be expected in MAEs with soft elastomer matrices, where the <span class="hlt">shear</span> modulus of the matrix is less than the magnetic anisotropy constant of inclusions. It is derived that the effective <span class="hlt">shear</span> modulus is nonlinearly dependent on the external magnetic field and approaches the saturation value in magnetic fields exceeding the field of particle anisotropy. It is shown that model calculations of the effective <span class="hlt">shear</span> modulus correspond to a phenomenological definition of effective elastic moduli and magnetoelastic coupling constants. The obtained theoretical results compare well with known experimental data. Determination of effective elastic coefficients in MAEs and their dependence on magnetic field is discussed. The concentration dependence of the effective <span class="hlt">shear</span> modulus at higher filler concentrations has been estimated using the method of Padé approximants, which <span class="hlt">predicts</span> that both the absolute and relative changes of the magnetic-field-dependent effective <span class="hlt">shear</span> modulus will significantly increase with the growing concentration of filler particles.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005PhDT........27B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005PhDT........27B"><span>Aeroacoustic <span class="hlt">prediction</span> of turbulent free <span class="hlt">shear</span> flows</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bodony, Daniel Joseph</p> <p>2005-12-01</p> <p>For many people living in the immediate vicinity of an active airport the noise of jet aircraft flying overhead can be a nuisance, if not worse. Airports, which are held accountable for the noise they produce, and upcoming international noise limits are pressuring the major airframe and jet engine manufacturers to bring quieter aircraft into service. However, component designers need a <span class="hlt">predictive</span> tool that can estimate the sound generated by a new configuration. Current noise <span class="hlt">prediction</span> techniques are almost entirely based on previously collected experimental data and are applicable only to evolutionary, not revolutionary, changes in the basic design. Physical models of final candidate designs must still be built and tested before a single design is selected. By focusing on the noise produced in the jet engine exhaust at take-off conditions, the <span class="hlt">prediction</span> of sound generated by turbulent flows is addressed. The technique of large-eddy simulation is used to calculate directly the radiated sound produced by jets at different operating conditions. <span class="hlt">Predicted</span> noise spectra agree with measurements for frequencies up to, and slightly beyond, the peak frequency. Higher frequencies are missed, however, due to the limited resolution of the simulations. Two methods of estimating the 'missing' noise are discussed. In the first a subgrid scale noise model, analogous to a subgrid scale closure model, is proposed. In the second method the governing equations are expressed in a wavelet basis from which simplified time-dependent equations for the subgrid scale fluctuations can be derived. These equations are inexpensively integrated to yield estimates of the subgrid scale fluctuations with proper space-time dynamics.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013APS..MARW28011T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013APS..MARW28011T"><span>Soft-Matter Resistive Sensor for Measuring <span class="hlt">Shear</span> and Pressure Stresses</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tepayotl-Ramirez, Daniel; Roberts, Peter; Majidi, Carmel</p> <p>2013-03-01</p> <p>Building on emerging paradigms in soft-matter electronics, we introduce liquid-phase electronic sensors that simultaneously measures elastic pressure and <span class="hlt">shear</span> deformation. The sensors are com- posed of a sheet of elastomer that is embedded with fluidic channels containing eutectic Gallium- Indium (EGaIn), a metal alloy that is liquid at room temperature. Applying pressure or <span class="hlt">shear</span> traction to the surface of the surrounding elastomer causes the elastomer to elastically deform and changes the geometry and electrical properties of the embedded liquid-phase circuit elements. We introduce analytic models that <span class="hlt">predict</span> the electrical response of the sensor to prescribed surface tractions. These models are validated with both Finite Element Analysis (FEA) and experimental measurements.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_17 --> <div id="page_18" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="341"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011CRMec.339...27K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011CRMec.339...27K"><span>A priori evaluation of the Pantano and Sarkar model in compressible homogeneous <span class="hlt">shear</span> flows</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Khlifi, Hechmi; Abdallah, J.; Aïcha, H.; Taïeb, L.</p> <p>2011-01-01</p> <p>In this study, a Reynolds stress closure, including the Pantano and Sarkar model of the mean part of the pressure-strain correlation is used for the computation of compressible homogeneous at high-speed <span class="hlt">shear</span> flow. Several studies concerning the compressible homogeneous <span class="hlt">shear</span> flow show that the changes of the turbulence structures are principally due to the structural compressibility effects which significantly affect the pressure field and then the pressure-strain correlation. Eventually, this term appears as the main term responsible for the changes in the magnitude of the Reynolds stress anisotropies. The structure of the gradient Mach number is similar to that of turbulence, therefore this parameter may be appropriate to study the changes in turbulence structures that arise from structural compressibility effects. Thus, the incompressible model of the pressure strain correlation and its corrected form by using the turbulent Mach turbulent only, fail to correctly evaluate the compressibility effects at high <span class="hlt">shear</span> flow. An extension of the widely used incompressible Launder, Reece and Rodi model on compressible homogeneous <span class="hlt">shear</span> flow is the major aim of the present work. From this extension, the standard coefficients C become a function of the extra compressibility parameters (the turbulent Mach number M and the gradient Mach number M) through the Pantano and Sarkar model. Application of the model on compressible homogeneous <span class="hlt">shear</span> flow by considering various initial conditions shows reasonable agreement with the DNS results of Simone et al. and Sarkar. The observed trend of the dramatic increase in the normal Reynolds stress anisotropies, the significant decrease in the Reynolds <span class="hlt">shear</span> stress anisotropy and the increase of the turbulent kinetic energy amplification rate with increasing the gradient Mach number are well <span class="hlt">predicted</span> by the model. The ability of the model to <span class="hlt">predict</span> the equilibrium states for the flow in cases A to A from DNS results of Sarkar is</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19830012947','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19830012947"><span>Excited waves in <span class="hlt">shear</span> layers</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bechert, D. W.</p> <p>1982-01-01</p> <p>The generation of instability waves in free <span class="hlt">shear</span> layers is investigated. The model assumes an infinitesimally thin <span class="hlt">shear</span> layer shed from a semi-infinite plate which is exposed to sound excitation. The acoustical <span class="hlt">shear</span> layer excitation by a source further away from the plate edge in the downstream direction is very weak while upstream from the plate edge the excitation is relatively efficient. A special solution is given for the source at the plate edge. The theory is then extended to two streams on both sides of the <span class="hlt">shear</span> layer having different velocities and densities. Furthermore, the excitation of a <span class="hlt">shear</span> layer in a channel is calculated. A reference quantity is found for the magnitude of the excited instability waves. For a comparison with measurements, numerical computations of the velocity field outside the <span class="hlt">shear</span> layer were carried out.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20040088014&hterms=physiology+stress&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Dphysiology%2Bstress','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20040088014&hterms=physiology+stress&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Dphysiology%2Bstress"><span>Low-<span class="hlt">Shear</span> modeled microgravity alters the Salmonella enterica serovar typhimurium stress response in an RpoS-independent manner</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Wilson, James W.; Ott, C. Mark; Ramamurthy, Rajee; Porwollik, Steffen; McClelland, Michael; Pierson, Duane L.; Nickerson, Cheryl A.</p> <p>2002-01-01</p> <p>We have previously demonstrated that low-<span class="hlt">shear</span> modeled microgravity (low-<span class="hlt">shear</span> MMG) serves to enhance the virulence of a bacterial pathogen, Salmonella enterica serovar Typhimurium. The Salmonella response to low-<span class="hlt">shear</span> MMG involves a signaling pathway that we have termed the low-<span class="hlt">shear</span> MMG stimulon, though the identities of the low-<span class="hlt">shear</span> MMG stimulon genes and regulatory factors are not known. RpoS is the primary sigma factor required for the expression of genes that are induced upon exposure to different environmental-stress signals and is essential for virulence in mice. Since low-<span class="hlt">shear</span> MMG induces a Salmonella acid stress response and enhances Salmonella virulence, we reasoned that RpoS would be a likely regulator of the Salmonella low-<span class="hlt">shear</span> MMG response. Our results demonstrate that low-<span class="hlt">shear</span> MMG provides cross-resistance to several environmental stresses in both wild-<span class="hlt">type</span> and isogenic rpoS mutant strains. Growth under low-<span class="hlt">shear</span> MMG decreased the generation time of both strains in minimal medium and increased the ability of both strains to survive in J774 macrophages. Using DNA microarray analysis, we found no evidence of induction of the RpoS regulon by low-<span class="hlt">shear</span> MMG but did find that other genes were altered in expression under these conditions in both the wild-<span class="hlt">type</span> and rpoS mutant strains. Our results indicate that, under the conditions of these studies, RpoS is not required for transmission of the signal that induces the low-<span class="hlt">shear</span> MMG stimulon. Moreover, our studies also indicate that low-<span class="hlt">shear</span> MMG can be added to a short list of growth conditions that can serve to preadapt an rpoS mutant for resistance to multiple environmental stresses.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27692789','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27692789"><span>Constant load and constant volume response of municipal solid waste in simple <span class="hlt">shear</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Zekkos, Dimitrios; Fei, Xunchang</p> <p>2017-05-01</p> <p>Constant load and constant volume simple <span class="hlt">shear</span> testing was conducted on relatively fresh municipal solid waste (MSW) from two landfills in the United States, one in Michigan and a second in Texas, at respective natural moisture content below field capacity. The results were assessed in terms of two failure strain criteria, at 10% and 30% <span class="hlt">shear</span> strain, and two interpretations of effective friction angle. Overall, friction angle obtained assuming that the failure plane is horizontal and at 10% <span class="hlt">shear</span> strain resulted in a conservative estimation of <span class="hlt">shear</span> strength of MSW. Comparisons between constant volume and constant load simple <span class="hlt">shear</span> testing results indicated significant differences in the <span class="hlt">shear</span> response of MSW with the <span class="hlt">shear</span> resistance in constant volume being lower than the <span class="hlt">shear</span> resistance in constant load. The majority of specimens were nearly uncompacted during specimen preparation to reproduce the state of MSW in bioreactor landfills or in uncontrolled waste dumps. The specimens had identical percentage of <20mm material but the <span class="hlt">type</span> of <20mm material was different. The <20mm fraction from Texas was finer and of high plasticity. MSW from Texas was overall weaker in both constant load and constant volume conditions compared to Michigan waste. The results of these tests suggest the possibility of significantly lower <span class="hlt">shear</span> strength of MSW in bioreactor landfills where waste is placed with low compaction effort and constant volume, i.e., "undrained", conditions may occur. Compacted MSW specimens resulted in <span class="hlt">shear</span> strength parameters that are higher than uncompacted specimens and closer to values reported in the literature. However, the normalized undrained <span class="hlt">shear</span> strength in simple <span class="hlt">shear</span> for uncompacted and compacted MSW was still higher than the normalized undrained <span class="hlt">shear</span> strength reported in the literature for clayey and silty soils. Copyright © 2016 Elsevier Ltd. All rights reserved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19910057967&hterms=comparative+study&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Dcomparative%2Bstudy','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19910057967&hterms=comparative+study&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Dcomparative%2Bstudy"><span>A comparative study of several compressibility corrections to turbulence models applied to high-speed <span class="hlt">shear</span> layers</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Viegas, John R.; Rubesin, Morris W.</p> <p>1991-01-01</p> <p>Several recently published compressibility corrections to the standard k-epsilon turbulence model are used with the Navier-Stokes equations to compute the mixing region of a large variety of high speed flows. These corrections, specifically developed to address the weakness of higher order turbulence models to accurately <span class="hlt">predict</span> the spread rate of compressible free <span class="hlt">shear</span> flows, are applied to two stream flows of the same gas mixing under a large variety of free stream conditions. Results are presented for two <span class="hlt">types</span> of flows: unconfined streams with either (1) matched total temperatures and static pressures, or (2) matched static temperatures and pressures, and a confined stream.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018AIPA....8c5104W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018AIPA....8c5104W"><span>Numerical simulation of the multiple core localized low <span class="hlt">shear</span> toroidal Alfvenic eigenmodes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Wenjia; Zhou, Deng; Hu, Youjun; Ming, Yue</p> <p>2018-03-01</p> <p>In modern tokamak experiments, scenarios with weak central magnetic <span class="hlt">shear</span> has been proposed. It is necessary to study the Alfvenic mode activities in such scenarios. Theoretical researches have <span class="hlt">predicted</span> the multiplicity of core-localized toroidally induced Alfvenic eigenmodes for ɛ/s > 1, where ɛ is the inverse aspect ratio and s is magnetic <span class="hlt">shear</span>. We numerically investigate the existence of multiplicity of core-localized TAEs and mode characteristics using NOVA code in the present work. We firstly verify the existence of the multiplicity for zero beta plasma and the even mode at the forbidden zone. For finite beta plasma, the mode parities become more distinguishable, and the frequencies of odd modes are close to the upper tip of the continuum, while the frequencies of even modes are close to the lower tip of the continuum. Their frequencies are well separated by the forbidden zone. With the increasing value of ɛ/s, more modes with multiple radial nodes will appear, which is in agreement with theoretical <span class="hlt">prediction</span>. The discrepancy between theoretical <span class="hlt">prediction</span> and our numerical simulation is also discussed in the main text.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EEEV...15..197L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EEEV...15..197L"><span>Seismic behavior of outrigger truss-wall <span class="hlt">shear</span> connections using multiple steel angles</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Li, Xian; Wang, Wei; Lü, Henglin; Zhang, Guangchang</p> <p>2016-06-01</p> <p>An experimental investigation on the seismic behavior of a <span class="hlt">type</span> of outrigger truss-reinforced concrete wall <span class="hlt">shear</span> connection using multiple steel angles is presented. Six large-scale <span class="hlt">shear</span> connection models, which involved a portion of reinforced concrete wall and a <span class="hlt">shear</span> tab welded onto a steel endplate with three steel angles, were constructed and tested under combined actions of cyclic axial load and eccentric <span class="hlt">shear</span>. The effects of embedment lengths of steel angles, wall boundary elements, <span class="hlt">types</span> of anchor plates, and thicknesses of endplates were investigated. The test results indicate that properly detailed connections exhibit desirable seismic behavior and fail due to the ductile fracture of steel angles. Wall boundary elements provide beneficial confinement to the concrete surrounding steel angles and thus increase the strength and stiffness of connections. Connections using whole anchor plates are prone to suffer concrete pry-out failure while connections with thin endplates have a relatively low strength and fail due to large inelastic deformations of the endplates. The current design equations proposed by Chinese Standard 04G362 and Code GB50011 significantly underestimate the capacities of the connection models. A revised design method to account for the influence of previously mentioned test parameters was developed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015KARJ...27..297L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015KARJ...27..297L"><span>Time-dependent rheological behavior of natural polysaccharide xanthan gum solutions in interrupted <span class="hlt">shear</span> and step-incremental/reductional <span class="hlt">shear</span> flow fields</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lee, Ji-Seok; Song, Ki-Won</p> <p>2015-11-01</p> <p>The objective of the present study is to systematically elucidate the time-dependent rheological behavior of concentrated xanthan gum systems in complicated step-<span class="hlt">shear</span> flow fields. Using a strain-controlled rheometer (ARES), step-<span class="hlt">shear</span> flow behaviors of a concentrated xanthan gum model solution have been experimentally investigated in interrupted <span class="hlt">shear</span> flow fields with a various combination of different <span class="hlt">shear</span> rates, <span class="hlt">shearing</span> times and rest times, and step-incremental and step-reductional <span class="hlt">shear</span> flow fields with various <span class="hlt">shearing</span> times. The main findings obtained from this study are summarized as follows. (i) In interrupted <span class="hlt">shear</span> flow fields, the <span class="hlt">shear</span> stress is sharply increased until reaching the maximum stress at an initial stage of <span class="hlt">shearing</span> times, and then a stress decay towards a steady state is observed as the <span class="hlt">shearing</span> time is increased in both start-up <span class="hlt">shear</span> flow fields. The <span class="hlt">shear</span> stress is suddenly decreased immediately after the imposed <span class="hlt">shear</span> rate is stopped, and then slowly decayed during the period of a rest time. (ii) As an increase in rest time, the difference in the maximum stress values between the two start-up <span class="hlt">shear</span> flow fields is decreased whereas the <span class="hlt">shearing</span> time exerts a slight influence on this behavior. (iii) In step-incremental <span class="hlt">shear</span> flow fields, after passing through the maximum stress, structural destruction causes a stress decay behavior towards a steady state as an increase in <span class="hlt">shearing</span> time in each step <span class="hlt">shear</span> flow region. The time needed to reach the maximum stress value is shortened as an increase in step-increased <span class="hlt">shear</span> rate. (iv) In step-reductional <span class="hlt">shear</span> flow fields, after passing through the minimum stress, structural recovery induces a stress growth behavior towards an equilibrium state as an increase in <span class="hlt">shearing</span> time in each step <span class="hlt">shear</span> flow region. The time needed to reach the minimum stress value is lengthened as a decrease in step-decreased <span class="hlt">shear</span> rate.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018AIPC.1963b0061I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018AIPC.1963b0061I"><span><span class="hlt">Shear</span> modulus and damping ratio of natural rubber containing carbon nanotubes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ismail, R.; Ibrahim, A.; Rusop, M.; Adnan, A.</p> <p>2018-05-01</p> <p>This paper presents the results of an investigation into the potential application of Natural rubber (NR) containing Carbon Nanotubes (CNTs) by measuring its <span class="hlt">shear</span> modulus and damping ratio. Four different <span class="hlt">types</span> of rubber specimens which fabricated with different MWCNT loadings: 0 wt% (pure natural rubber), 1 wt%, 3 wt%, and 5 wt%. It is observed that the <span class="hlt">shear</span> modulus and damping ratio of CNTs filled rubber composites are remarkably higher than that of raw rubber indicating the inherent reinforcing potential of CNTs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29608886','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29608886"><span>Using Computational Fluid Dynamics to Compare <span class="hlt">Shear</span> Rate and Turbulence in the TIM-Automated Gastric Compartment With USP Apparatus II.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Hopgood, Matthew; Reynolds, Gavin; Barker, Richard</p> <p>2018-03-30</p> <p>We use computational fluid dynamics to compare the <span class="hlt">shear</span> rate and turbulence in an advanced in vitro gastric model (TIMagc) during its simulation of fasted state Migrating Motor Complex phases I and II, with the United States Pharmacopeia paddle dissolution apparatus II (USPII). A specific focus is placed on how <span class="hlt">shear</span> rate in these apparatus affects erosion-based solid oral dosage forms. The study finds that tablet surface <span class="hlt">shear</span> rates in TIMagc are strongly time dependant and fluctuate between 0.001 and 360 s -1 . In USPII, tablet surface <span class="hlt">shear</span> rates are approximately constant for a given paddle speed and increase linearly from 9 s -1 to 36 s -1 as the paddle speed is increased from 25 to 100 rpm. A strong linear relationship is observed between tablet surface <span class="hlt">shear</span> rate and tablet erosion rate in USPII, whereas TIMagc shows highly variable behavior. The flow regimes present in each apparatus are compared to in vivo <span class="hlt">predictions</span> using Reynolds number analysis. Reynolds numbers for flow in TIMagc lie predominantly within the <span class="hlt">predicted</span> in vivo bounds (0.01-30), whereas Reynolds numbers for flow in USPII lie above the <span class="hlt">predicted</span> upper bound when operating with paddle speeds as low as 25 rpm (33). Copyright © 2018 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015NatSR...515611A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015NatSR...515611A"><span>Suppression of <span class="hlt">Shear</span> Banding and Transition to Necking and Homogeneous Flow in Nanoglass Nanopillars</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Adibi, Sara; Branicio, Paulo S.; Joshi, Shailendra P.</p> <p>2015-10-01</p> <p>In order to improve the properties of metallic glasses (MG) a new <span class="hlt">type</span> of MG structure, composed of nanoscale grains, referred to as nanoglass (NG), has been recently proposed. Here, we use large-scale molecular dynamics (MD) simulations of tensile loading to investigate the deformation and failure mechanisms of Cu64Zr36 NG nanopillars with large, experimentally accessible, 50 nm diameter. Our results reveal NG ductility and failure by necking below the average glassy grain size of 20 nm, in contrast to brittle failure by <span class="hlt">shear</span> band propagation in MG nanopillars. Moreover, the results <span class="hlt">predict</span> substantially larger ductility in NG nanopillars compared with previous <span class="hlt">predictions</span> of MD simulations of bulk NG models with columnar grains. The results, in excellent agreement with experimental data, highlight the substantial enhancement of plasticity induced in experimentally relevant MG samples by the use of nanoglass architectures and point out to exciting novel applications of these materials.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23781409','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23781409"><span><span class="hlt">Prediction</span> of morbidity and mortality in patients with <span class="hlt">type</span> 2 diabetes.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wells, Brian J; Roth, Rachel; Nowacki, Amy S; Arrigain, Susana; Yu, Changhong; Rosenkrans, Wayne A; Kattan, Michael W</p> <p>2013-01-01</p> <p>Introduction. The objective of this study was to create a tool that accurately <span class="hlt">predicts</span> the risk of morbidity and mortality in patients with <span class="hlt">type</span> 2 diabetes according to an oral hypoglycemic agent. Materials and Methods. The model was based on a cohort of 33,067 patients with <span class="hlt">type</span> 2 diabetes who were prescribed a single oral hypoglycemic agent at the Cleveland Clinic between 1998 and 2006. Competing risk regression models were created for coronary heart disease (CHD), heart failure, and stroke, while a Cox regression model was created for mortality. Propensity scores were used to account for possible treatment bias. A <span class="hlt">prediction</span> tool was created and internally validated using tenfold cross-validation. The results were compared to a Framingham model and a model based on the United Kingdom Prospective Diabetes Study (UKPDS) for CHD and stroke, respectively. Results and Discussion. Median follow-up for the mortality outcome was 769 days. The numbers of patients experiencing events were as follows: CHD (3062), heart failure (1408), stroke (1451), and mortality (3661). The <span class="hlt">prediction</span> tools demonstrated the following concordance indices (c-statistics) for the specific outcomes: CHD (0.730), heart failure (0.753), stroke (0.688), and mortality (0.719). The <span class="hlt">prediction</span> tool was superior to the Framingham model at <span class="hlt">predicting</span> CHD and was at least as accurate as the UKPDS model at <span class="hlt">predicting</span> stroke. Conclusions. We created an accurate tool for <span class="hlt">predicting</span> the risk of stroke, coronary heart disease, heart failure, and death in patients with <span class="hlt">type</span> 2 diabetes. The calculator is available online at http://rcalc.ccf.org under the heading "<span class="hlt">Type</span> 2 Diabetes" and entitled, "<span class="hlt">Predicting</span> 5-Year Morbidity and Mortality." This may be a valuable tool to aid the clinician's choice of an oral hypoglycemic, to better inform patients, and to motivate dialogue between physician and patient.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19890005991','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19890005991"><span>Structure of wind-<span class="hlt">shear</span> turbulence</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Trevino, G.; Laituri, T. R.</p> <p>1989-01-01</p> <p>The statistical characteristics of wind <span class="hlt">shear</span> turbulence are modelled. Isotropic turbulence serves as the basis of comparison for the anisotropic turbulence which exists in wind <span class="hlt">shear</span>. The question of turbulence scales in wind <span class="hlt">shear</span> is addressed from the perspective of power spectral density.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013ApPhL.102y1902I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013ApPhL.102y1902I"><span>Nonlinear damping for vibration isolation of microsystems using <span class="hlt">shear</span> thickening fluid</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Iyer, S. S.; Vedad-Ghavami, R.; Lee, H.; Liger, M.; Kavehpour, H. P.; Candler, R. N.</p> <p>2013-06-01</p> <p>This work reports the measurement and analysis of nonlinear damping of micro-scale actuators immersed in <span class="hlt">shear</span> thickening fluids (STFs). A power-law damping term is added to the linear second-order model to account for the <span class="hlt">shear</span>-dependent viscosity of the fluid. This nonlinear model is substantiated by measurements of oscillatory motion of a torsional microactuator. At high actuation forces, the vibration velocity amplitude saturates. The model accurately <span class="hlt">predicts</span> the nonlinear damping characteristics of the STF using a power-law index extracted from independent rheology experiments. This result reveals the potential to use STFs as adaptive, passive dampers for vibration isolation of microelectromechanical systems.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017APS..DPPU11048L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017APS..DPPU11048L"><span>The temporal evolution of the resistive pressure-gradient-driven turbulence and anomalous transport in <span class="hlt">shear</span> flow across the magnetic field</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lee, Hae June; Mikhailenko, Vladmir; Mikhailenko, Vladimir</p> <p>2017-10-01</p> <p>The temporal evolution of the resistive pressure-gradient-driven mode in the <span class="hlt">sheared</span> flow is investigated by employing the <span class="hlt">shearing</span> modes approach. It reveals an essential difference in the processes, which occur in the case of the flows with velocity <span class="hlt">shearing</span> rate less than the growth rate of the instability in the steady plasmas, and in the case of the flows with velocity <span class="hlt">shear</span> larger than the instability growth rate in steady plasmas. It displays the physical content of the empirical ``quench rule'' which <span class="hlt">predicts</span> the suppression of the turbulence in the <span class="hlt">sheared</span> flows when the velocity <span class="hlt">shearing</span> rate becomes larger than the maximum growth rate of the possible instability. We found that the distortion of the perturbations by the <span class="hlt">sheared</span> flow with such velocity <span class="hlt">shear</span> introduces the time dependencies into the governing equations, which prohibits the application of the eigenmodes formalism and requires the solution of the initial value problem.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20160001622','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20160001622"><span>Flexible Micropost Arrays for <span class="hlt">Shear</span> Stress Measurement</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Wohl, Christopher J.; Palmieri, Frank L.; Hopkins, John W.; Jackson, Allen M.; Connell, John W.; Lin, Yi; Cisotto, Alexxandra A.</p> <p>2015-01-01</p> <p>Increased fuel costs, heightened environmental protection requirements, and noise abatement continue to place drag reduction at the forefront of aerospace research priorities. Unfortunately, shortfalls still exist in the fundamental understanding of boundary-layer airflow over aerodynamic surfaces, especially regarding drag arising from skin friction. For example, there is insufficient availability of instrumentation to adequately characterize complex flows with strong pressure gradients, heat transfer, wall mass flux, three-dimensionality, separation, shock waves, and transient phenomena. One example is the acoustic liner efficacy on aircraft engine nacelle walls. Active measurement of <span class="hlt">shear</span> stress in boundary layer airflow would enable a better understanding of how aircraft structure and flight dynamics affect skin friction. Current <span class="hlt">shear</span> stress measurement techniques suffer from reliability, complexity, and airflow disruption, thereby compromising resultant <span class="hlt">shear</span> stress data. The state-of-the-art for <span class="hlt">shear</span> stress sensing uses indirect or direct measurement techniques. Indirect measurements (e.g., hot-wire, heat flux gages, oil interferometry, laser Doppler anemometry, small scale pressure drag surfaces, i.e., fences) require intricate knowledge of the studied flow, restrictive instrument arrangements, large surface areas, flow disruption, or seeding material; with smaller, higher bandwidth probes under development. Direct measurements involve strain displacement of a sensor element and require no prior knowledge of the flow. Unfortunately, conventional "floating" recessed components for direct measurements are mm to cm in size. Whispering gallery mode devices and Fiber Bragg Gratings are examples of recent additions to this <span class="hlt">type</span> of sensor with much smaller (?m) sensor components. Direct detection techniques are often single point measurements and difficult to calibrate and implement in wind tunnel experiments. In addition, the wiring, packaging, and installation</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JAP...122v4304T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JAP...122v4304T"><span><span class="hlt">Shear</span>-induced aggregation or disaggregation in edible oils: Models, computer simulation, and USAXS measurements</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Townsend, B.; Peyronel, F.; Callaghan-Patrachar, N.; Quinn, B.; Marangoni, A. G.; Pink, D. A.</p> <p>2017-12-01</p> <p>The effects of <span class="hlt">shear</span> upon the aggregation of solid objects formed from solid triacylglycerols (TAGs) immersed in liquid TAG oils were modeled using Dissipative Particle Dynamics (DPD) and the <span class="hlt">predictions</span> compared to experimental data using Ultra-Small Angle X-ray Scattering (USAXS). The solid components were represented by spheres interacting via attractive van der Waals forces and short range repulsive forces. A velocity was applied to the liquid particles nearest to the boundary, and Lees-Edwards boundary conditions were used to transmit this motion to non-boundary layers via dissipative interactions. The <span class="hlt">shear</span> was created through the dissipative forces acting between liquid particles. Translational diffusion was simulated, and the Stokes-Einstein equation was used to relate DPD length and time scales to SI units for comparison with USAXS results. The SI values depended on how large the spherical particles were (250 nm vs. 25 nm). Aggregation was studied by (a) computing the Structure Function and (b) quantifying the number of pairs of solid spheres formed. Solid aggregation was found to be enhanced by low <span class="hlt">shear</span> rates. As the <span class="hlt">shear</span> rate was increased, a transition <span class="hlt">shear</span> region was manifested in which aggregation was inhibited and <span class="hlt">shear</span> banding was observed. Aggregation was inhibited, and eventually eliminated, by further increases in the <span class="hlt">shear</span> rate. The magnitude of the transition region <span class="hlt">shear</span>, γ˙ t, depended on the size of the solid particles, which was confirmed experimentally.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018PhRvB..97i4102L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018PhRvB..97i4102L"><span>Tensile and <span class="hlt">shear</span> loading of four fcc high-entropy alloys: A first-principles study</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Li, Xiaoqing; Schönecker, Stephan; Li, Wei; Varga, Lajos K.; Irving, Douglas L.; Vitos, Levente</p> <p>2018-03-01</p> <p>Ab initio density-functional calculations are used to investigate the response of four face-centered-cubic (fcc) high-entropy alloys (HEAs) to tensile and <span class="hlt">shear</span> loading. The ideal tensile and <span class="hlt">shear</span> strengths (ITS and ISS) of the HEAs are studied by employing first-principles alloy theory formulated within the exact muffin-tin orbital method in combination with the coherent-potential approximation. We benchmark the computational accuracy against literature data by studying the ITS under uniaxial [110] tensile loading and the ISS for the [11 2 ¯] (111 ) <span class="hlt">shear</span> deformation of pure fcc Ni and Al. For the HEAs, we uncover the alloying effect on the ITS and ISS. Under <span class="hlt">shear</span> loading, relaxation reduces the ISS by ˜50 % for all considered HEAs. We demonstrate that the dimensionless tensile and <span class="hlt">shear</span> strengths are significantly overestimated by adopting two widely used empirical models in comparison with our ab initio calculations. In addition, our <span class="hlt">predicted</span> relationship between the dimensionless <span class="hlt">shear</span> strength and <span class="hlt">shear</span> instability are in line with the modified Frenkel model. Using the computed ISS, we derive the half-width of the dislocation core for the present HEAs. Employing the ratio of ITS to ISS, we discuss the intrinsic ductility of HEAs and compare it with a common empirical criterion. We observe a strong linear correlation between the <span class="hlt">shear</span> instability and the ratio of ITS to ISS, whereas a weak positive correlation is found in the case of the empirical criterion.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.fs.usda.gov/treesearch/pubs/27670','TREESEARCH'); return false;" href="https://www.fs.usda.gov/treesearch/pubs/27670"><span>Effects of various fire-retardants on plate <span class="hlt">shear</span> and five-point flexural <span class="hlt">shear</span> properties of plywood</span></a></p> <p><a target="_blank" href="http://www.fs.usda.gov/treesearch/">Treesearch</a></p> <p>Nadir Ayrilmis; Jerrold E. Winandy</p> <p>2007-01-01</p> <p>The influence of four fire-retardant systems on the planar (rolling) <span class="hlt">shear</span> properties of structural hardwood plywood is evaluated using two possible ASTM D2718 test methodologies: the plate-<span class="hlt">shear</span> method and the five-point flexural <span class="hlt">shear</span> method. Knowing the planar <span class="hlt">shear</span> properties and the potential of the various fire-retardant systems to affect properties is critical...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014MMI....20..585S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014MMI....20..585S"><span>Evaluation of <span class="hlt">shear</span>-compressive strength properties for laminated GFRP composites in electromagnet system</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Song, Jun Hee; Kim, Hak Kun; Kim, Sam Yeon</p> <p>2014-07-01</p> <p>Laminated fiber-reinforced composites can be applied to an insulating structure of a nuclear fusion device. It is necessary to investigate the interlaminar fracture characteristics of the laminated composites for the assurance of design and structural integrity. The three methods used to prepare the glass fiber reinforced plastic composites tested in this study were vacuum pressure impregnation, high pressure laminate (HPL), and prepreg laminate. We discuss the design criteria for safe application of composites and the <span class="hlt">shear</span>-compressive test methods for evaluating mechanical properties of the material. <span class="hlt">Shear</span>-compressive tests could be performed successfully using series-<span class="hlt">type</span> test jigs that were inclined 0°, 30°, 45°, 60°, and 75° to the normal axis. <span class="hlt">Shear</span> strength depends strongly on the applied compressive stress. The design range of allowable <span class="hlt">shear</span> stress was extended by use of the appropriate composite fabrication method. HPL had the largest design range, and the allowable interlaminar <span class="hlt">shear</span> stress was 0.254 times the compressive stress.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_18 --> <div id="page_19" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="361"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19890001988','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19890001988"><span>Structure of wind-<span class="hlt">shear</span> turbulence</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Trevino, G.; Laituri, T. R.</p> <p>1988-01-01</p> <p>The statistical characteristics of wind-<span class="hlt">shear</span> turbulence are modelled. Isotropic turbulence serves as the basis of comparison for the anisotropic turbulence which exists in wind <span class="hlt">shear</span>. The question of how turbulence scales in a wind <span class="hlt">shear</span> is addressed from the perspective of power spectral density.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19940012654','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19940012654"><span>Investigation of high-speed free <span class="hlt">shear</span> flows using improved pressure-strain correlated Reynolds stress turbulence model</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Tiwari, S. N.; Lakshmanan, B.</p> <p>1993-01-01</p> <p>A high-speed <span class="hlt">shear</span> layer is studied using compressibility corrected Reynolds stress turbulence model which employs newly developed model for pressure-strain correlation. MacCormack explicit <span class="hlt">prediction</span>-corrector method is used for solving the governing equations and the turbulence transport equations. The stiffness arising due to source terms in the turbulence equations is handled by a semi-implicit numerical technique. Results obtained using the new model show a sharper reduction in growth rate with increasing convective Mach number. Some improvements were also noted in the <span class="hlt">prediction</span> of the normalized streamwise stress and Reynolds <span class="hlt">shear</span> stress. The computed results are in good agreement with the experimental data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3677718','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3677718"><span><span class="hlt">Shear</span> wave propagation in anisotropic soft tissues and gels</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Namani, Ravi; Bayly, Philip V.</p> <p>2013-01-01</p> <p>The propagation of <span class="hlt">shear</span> waves in soft tissue can be visualized by magnetic resonance elastography (MRE) [1] to characterize tissue mechanical properties. Dynamic deformation of brain tissue arising from <span class="hlt">shear</span> wave propagation may underlie the pathology of blast-induced traumatic brain injury. White matter in the brain, like other biological materials, exhibits a transversely isotropic structure, due to the arrangement of parallel fibers. Appropriate mathematical models and well-characterized experimental systems are needed to understand wave propagation in these structures. In this paper we review the theory behind waves in anisotropic, soft materials, including small-amplitude waves superimposed on finite deformation of a nonlinear hyperelastic material. Some <span class="hlt">predictions</span> of this theory are confirmed in experimental studies of a soft material with controlled anisotropy: magnetically-aligned fibrin gel. PMID:19963987</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20060008919','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20060008919"><span>Life Limiting Behavior in Interlaminar <span class="hlt">Shear</span> of Continuous Fiber-Reinforced Ceramic Matrix Composites at Elevated Temperatures</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Choi, Sung R.; Calomino, Anthony M.; Bansal, Narottam P.; Verrilli, Michael J.</p> <p>2006-01-01</p> <p>Interlaminar <span class="hlt">shear</span> strength of four different fiber-reinforced ceramic matrix composites was determined with doublenotch <span class="hlt">shear</span> test specimens as a function of test rate at elevated temperatures ranging from 1100 to 1316 C in air. Life limiting behavior, represented as interlaminar <span class="hlt">shear</span> strength degradation with decreasing test rate, was significant for 2-D crossplied SiC/MAS-5 and 2-D plain-woven C/SiC composites, but insignificant for 2-D plain-woven SiC/SiC and 2-D woven Sylramic (Dow Corning, Midland, Michigan) SiC/SiC composites. A phenomenological, power-law delayed failure model was proposed to account for and to quantify the rate dependency of interlaminar <span class="hlt">shear</span> strength of the composites. Additional stress rupture testing in interlaminar <span class="hlt">shear</span> was conducted at elevated temperatures to validate the proposed model. The model was in good agreement with SiC/MAS-5 and C/SiC composites, but in poor to reasonable agreement with Sylramic SiC/SiC. Constant <span class="hlt">shear</span> stress-rate testing was proposed as a possible means of life <span class="hlt">prediction</span> testing methodology for ceramic matrix composites subjected to interlaminar <span class="hlt">shear</span> at elevated temperatures when short lifetimes are expected.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010cosp...38.3519P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010cosp...38.3519P"><span>Dynamics of model blood cells in <span class="hlt">shear</span> flow</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Podgorski, Thomas; Callens, Natacha; Minetti, Christophe; Coupier, Gwennou; Dubois, Frank; Misbah, Chaouqi</p> <p></p> <p>The dynamics of a vesicle suspension in <span class="hlt">shear</span> flow was investigated by digital holographic microscopy [1] in parabolic flights and in the MASER 11 sounding rocket. Vesicles are lipid membranes which mimic the mechanical behaviour of cells, such as red blood cells in flow. In a simple <span class="hlt">shear</span> flow between parallel walls, a lift force of purely viscous origin pushes vesicles away from walls. Our parabolic flight experiments [2] reveal that the lift velocity in a dilute suspen-sion is well described by theoretical <span class="hlt">predictions</span> by Olla. As vesicles gather near the center of the flow chamber due to lift forces from both walls, one expects hydrodynamic interactions of pairs of vesicles to result in <span class="hlt">shear</span> induced diffusion in the suspension. The BIOMICS experi-ment in the MASER 11 sounding rocket revealed a complex spatial structure of a polydisperse vesicle suspension due to the interplay between lift forces from the walls and hydrodynamic interactions. These phenomena have a strong impact on the structure and rheology of blood in small vessels, and a precise knowledge of the dynamics of migration and diffusion of soft particles in flow can lead to alternative ways to separate and sort blood cells. 1. Dubois, F., Schockaert, C., Callens, N., Yourrassowsky, C., "Focus plane detection criteria in digital holography microscopy by amplitude analysis", Opt. Express, Vol. 14, pp 5895-5908, 2006 2. Callens, N., Minetti, C., Coupier, G., Mader, M.-A., Dubois, F., Misbah, C., Podgorski, T., "Hydrodynamics lift of vesicles under <span class="hlt">shear</span> flow in microgravity", Europhys. Lett., Vol. 83, p. 24002, 2008</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JChPh.147q4903S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JChPh.147q4903S"><span>Non-constant link tension coefficient in the tumbling-snake model subjected to simple <span class="hlt">shear</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stephanou, Pavlos S.; Kröger, Martin</p> <p>2017-11-01</p> <p>The authors of the present study have recently presented evidence that the tumbling-snake model for polymeric systems has the necessary capacity to <span class="hlt">predict</span> the appearance of pronounced undershoots in the time-dependent <span class="hlt">shear</span> viscosity as well as an absence of equally pronounced undershoots in the transient two normal stress coefficients. The undershoots were found to appear due to the tumbling behavior of the director u when a rotational Brownian diffusion term is considered within the equation of motion of polymer segments, and a theoretical basis concerning the use of a link tension coefficient given through the nematic order parameter had been provided. The current work elaborates on the quantitative <span class="hlt">predictions</span> of the tumbling-snake model to demonstrate its capacity to <span class="hlt">predict</span> undershoots in the time-dependent <span class="hlt">shear</span> viscosity. These <span class="hlt">predictions</span> are shown to compare favorably with experimental rheological data for both polymer melts and solutions, help us to clarify the microscopic origin of the observed phenomena, and demonstrate in detail why a constant link tension coefficient has to be abandoned.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017PhyS...92l4002M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017PhyS...92l4002M"><span>Scaling of turbulence spectra measured in strong <span class="hlt">shear</span> flow near the Earth’s surface</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mikkelsen, T.; Larsen, S. E.; Jørgensen, H. E.; Astrup, P.; Larsén, X. G.</p> <p>2017-12-01</p> <p>Within the lowest kilometer of the Earth’s atmosphere, in the so-called atmospheric boundary layer, winds are often gusty and turbulent. Nearest to the ground, the turbulence is predominately generated by mechanical wall-bounded wind <span class="hlt">shear</span>, whereas at higher altitudes turbulent mixing of heat and moisture also play a role. The variance (square of the standard deviation) of the fluctuation around the mean wind speed is a measure of the kinetic energy content of the turbulence. This kinetic energy can be resolved into the spectral distributions, or spectra, as functions of eddy size, wavenumber, or frequency. Spectra are derived from Fourier transforms of wind records as functions of space or time corresponding to wavenumber and frequency spectra, respectively. Atmospheric spectra often exhibit different subranges that can be distinguished and scaled by the physical parameters responsible for: (1) their generation; (2) the cascade of energy across the spectrum from large- to small-scale; and (3) the eventual decay of turbulence into heat owing to viscosity effects on the Kolmogorov microscale, in which the eddy size is only a fraction of a millimeter. This paper addresses atmospheric turbulence spectra in the lowest part of the atmospheric boundary layer—the so-called surface layer—where the wind <span class="hlt">shear</span> is strong owing to the nonslip condition at the ground. Theoretical results dating back to Tchen’s early work in 1953 ‘on the spectrum of energy in turbulent <span class="hlt">shear</span> flow’ led Tchen to <span class="hlt">predict</span> a <span class="hlt">shear</span> production subrange with a distinct inverse-linear power law for turbulence in a strongly <span class="hlt">sheared</span> high-Reynolds number wall-bounded flow, as is encountered in the lowest <span class="hlt">sheared</span> part of the atmospheric boundary layer, also known as the eddy surface layer. This paper presents observations of spectra measured in a meteorological mast at Høvsøre, Denmark, that support Tchen’s <span class="hlt">prediction</span> of a <span class="hlt">shear</span> production subrange following a distinct power law of degree -1</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70022226','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70022226"><span>Clast-fabric development in a <span class="hlt">shearing</span> granular material: Implications for subglacial till and fault gouge</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Hooyer, T.S.; Iverson, N.R.</p> <p>2000-01-01</p> <p>Elongate clasts in subglacial till and in fault gouge align during <span class="hlt">shearing</span>, but the relation between clast-fabric strength and cumulative <span class="hlt">shear</span> strain for such materials is effectively unknown. This relation was explored in experiments with a large ring-<span class="hlt">shear</span> device in which a till and a viscous putty that contained isolated clasts were <span class="hlt">sheared</span> to high strains. As expected, rotation of clasts in the putty is closely approximated by the theory of G.B. Jeffrey, who derived the orbits of rigid ellipsoids in a slowly <span class="hlt">shearing</span> fluid. Clast rotation in the till, however, is strikingly different. Rather than orbiting through the <span class="hlt">shear</span> plane as <span class="hlt">predicted</span> by Jeffery, most clasts rotate into the <span class="hlt">shear</span> plane and remain there, resulting in strong fabrics regardless of the aspect ratios and initial orientations of clasts. This divergent behavior is likely due to slip of the till matrix along the surfaces of clasts, which is a natural expectation in a granular material but violates the no-slip condition of Jeffery's model. These results do not support the widespread belief that subglacial till deformation results in weak clast fabrics. Thus, many tills with weak fabrics thought to have been <span class="hlt">sheared</span> subglacially to high strains, like many basal tills of the Laurentide Ice Sheet, may have been <span class="hlt">sheared</span> only slightly with little effect on either ice-sheet dynamics or sediment transport. In addition, these results indicate that in simple <span class="hlt">shear</span> the rotation of clasts in till and in fault gouge is best analyzed with the model of A. March, who treated inclusions as passive markers.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AIPC.1875c0010J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AIPC.1875c0010J"><span>To determine the slow <span class="hlt">shearing</span> rate for consolidation drained <span class="hlt">shear</span> box tests</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jamalludin, Damanhuri; Ahmad, Azura; Nordin, Mohd Mustaqim Mohd; Hashim, Mohamad Zain; Ibrahim, Anas; Ahmad, Fauziah</p> <p>2017-08-01</p> <p>Slope failures always occur in Malaysia especially during the rainy seasons. They cause damage to properties and fatalities. In this study, a total of 24 one dimensional consolidation tests were carried out on soil samples taken from 16 slope failures in Penang Island and in Baling, Kedah. The slope failures in Penang Island are within the granitic residual soil while in Baling, Kedah they are situated within the sedimentary residual soil. Most of the disturbed soil samples were taken at 100mm depth from the existing soil surface while some soil samples were also taken at 400, 700 and 1000mm depths from the existing soil surface. They were immediately placed in 2 layers of plastic bag to prevent moisture loss. Field bulk density tests were also carried out at all the locations where soil samples were taken. The field bulk density results were later used to re-compact the soil samples for the consolidation tests. The objective of the research is to determine the slow <span class="hlt">shearing</span> rate to be used in consolidated drained <span class="hlt">shear</span> box for residual soils taken from slope failures so that the effective <span class="hlt">shear</span> strength parameters can be determined. One dimensional consolidation tests were used to determine the slow <span class="hlt">shearing</span> rate. The slow <span class="hlt">shearing</span> rate found in this study to be used in the consolidated drained <span class="hlt">shear</span> box tests especially for Northern Malaysian residual soils was 0.286mm/minute.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20090008373&hterms=xenon&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dxenon','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20090008373&hterms=xenon&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dxenon"><span><span class="hlt">Shear</span> Thinning Near the Critical Point of Xenon</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Zimmerli, Gregory A.; Berg, Robert F.; Moldover, Michael R.; Yao, Minwu</p> <p>2008-01-01</p> <p>We measured <span class="hlt">shear</span> thinning, a viscosity decrease ordinarily associated with complex liquids, near the critical point of xenon. The data span a wide range of reduced <span class="hlt">shear</span> rate: 10(exp -3) < gamma-dot tau < 700, where gamma-dot tau is the <span class="hlt">shear</span> rate scaled by the relaxation time tau of critical fluctuations. The measurements had a temperature resolution of 0.01 mK and were conducted in microgravity aboard the Space Shuttle Columbia to avoid the density stratification caused by Earth's gravity. The viscometer measured the drag on a delicate nickel screen as it oscillated in the xenon at amplitudes 3 mu,m < chi (sub 0) >430 mu, and frequencies 1 Hz < omega/2 pi < 5 Hz. To separate <span class="hlt">shear</span> thinning from other nonlinearities, we computed the ratio of the viscous force on the screen at gamma-dot tau to the force at gamma-dot tau approximates 0: C(sub gamma) is identical with F(chi(sub 0), omega tau, gamma-dot tau )/F)(chi(sub 0, omega tau, 0). At low frequencies, (omega tau)(exp 2) < gamma-dot tau, C(sub gamma) depends only on gamma-dot tau, as <span class="hlt">predicted</span> by dynamic critical scaling. At high frequencies, (omega tau)(exp 2) > gamma-dot tau, C(sub gamma) depends also on both x(sub 0) and omega. The data were compared with numerical calculations based on the Carreau-Yasuda relation for complex fluids: eta(gamma-dot)/eta(0)=[1+A(sub gamma)|gamma-dot tau|](exp - chi(sub eta)/3+chi(sub eta)), where chi(sub eta) =0.069 is the critical exponent for viscosity and mode-coupling theory <span class="hlt">predicts</span> A(sub gamma) =0.121. For xenon we find A(sub gamma) =0.137 +/- 0.029, in agreement with the mode coupling value. Remarkably, the xenon data close to the critical temperature T(sub c) were independent of the cooling rate (both above and below T(sub c) and these data were symmetric about T(sub c) to within a temperature scale factor. The scale factors for the magnitude of the oscillator s response differed from those for the oscillator's phase; this suggests that the surface tension of the two</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010CQGra..27k4104C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010CQGra..27k4104C"><span>On the <span class="hlt">shear</span> instability in relativistic neutron stars</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Corvino, Giovanni; Rezzolla, Luciano; Bernuzzi, Sebastiano; De Pietri, Roberto; Giacomazzo, Bruno</p> <p>2010-06-01</p> <p>We present new results on instabilities in rapidly and differentially rotating neutron stars. We model the stars in full general relativity and describe the stellar matter adopting a cold realistic equation of state based on the unified SLy prescription (Douchin and Haensel 2001 Astron. Astrophys. 380 151-67). We provide evidence that rapidly and differentially rotating stars that are below the expected threshold for the dynamical bar-mode instability, βc ≡ T/|W| ~= 0.25, do nevertheless develop a <span class="hlt">shear</span> instability on a dynamical timescale and for a wide range of values of β. This class of instability, which has so far been found only for small values of β and with very small growth rates, is therefore more generic than previously found and potentially more effective in producing strong sources of gravitational waves. Overall, our findings support the phenomenological <span class="hlt">predictions</span> made by Watts et al (2005 Astrophys. J. 618 L37) on the nature of the low-T/|W| instability as the manifestation of a <span class="hlt">shear</span> instability in a region where the latter is possible only for small values of β. Furthermore, our results provide additional insight on <span class="hlt">shear</span> instabilities and on the necessary conditions for their development.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/pages/biblio/1412883-simulating-stick-slip-failure-sheared-granular-layer-using-physics-based-constitutive-model','SCIGOV-DOEP'); return false;" href="https://www.osti.gov/pages/biblio/1412883-simulating-stick-slip-failure-sheared-granular-layer-using-physics-based-constitutive-model"><span>Simulating stick-slip failure in a <span class="hlt">sheared</span> granular layer using a physics-based constitutive model</span></a></p> <p><a target="_blank" href="http://www.osti.gov/pages">DOE PAGES</a></p> <p>Lieou, Charles K. C.; Daub, Eric G.; Guyer, Robert A.; ...</p> <p>2017-01-14</p> <p>In this paper, we model laboratory earthquakes in a biaxial <span class="hlt">shear</span> apparatus using the <span class="hlt">Shear</span>-Transformation-Zone (STZ) theory of dense granular flow. The theory is based on the observation that slip events in a granular layer are attributed to grain rearrangement at soft spots called STZs, which can be characterized according to principles of statistical physics. We model lab data on granular <span class="hlt">shear</span> using STZ theory and document direct connections between the STZ approach and rate-and-state friction. We discuss the stability transition from stable <span class="hlt">shear</span> to stick-slip failure and show that stick slip is <span class="hlt">predicted</span> by STZ when the applied shearmore » load exceeds a threshold value that is modulated by elastic stiffness and frictional rheology. Finally, we also show that STZ theory mimics fault zone dilation during the stick phase, consistent with lab observations.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009ExFl...47.1033E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009ExFl...47.1033E"><span>Degradation of homogeneous polymer solutions in high <span class="hlt">shear</span> turbulent pipe flow</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Elbing, B. R.; Winkel, E. S.; Solomon, M. J.; Ceccio, S. L.</p> <p>2009-12-01</p> <p>This study quantifies degradation of polyethylene oxide (PEO) and polyacrylamide (PAM) polymer solutions in large diameter (2.72 cm) turbulent pipe flow at Reynolds numbers to 3 × 105 and <span class="hlt">shear</span> rates greater than 105 1/s. The present results support a universal scaling law for polymer chain scission reported by Vanapalli et al. (2006) that <span class="hlt">predicts</span> the maximum chain drag force to be proportional to Re 3/2, validating this scaling law at higher Reynolds numbers than prior studies. Use of this scaling gives estimated backbone bond strengths from PEO and PAM of 3.2 and 3.8 nN, respectively. Additionally, with the use of synthetic seawater as a solvent the onset of drag reduction occurred at higher <span class="hlt">shear</span> rates relative to the pure water solvent solutions, but had little influence on the extent of degradation at higher <span class="hlt">shear</span> rates. These results are significant for large diameter pipe flow applications that use polymers to reduce drag.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011APS..DPPJP9038W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011APS..DPPJP9038W"><span>Simulation of <span class="hlt">Shear</span> Alfvén Waves in LAPD using the BOUT++ code</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wei, Di; Friedman, B.; Carter, T. A.; Umansky, M. V.</p> <p>2011-10-01</p> <p>The linear and nonlinear physics of <span class="hlt">shear</span> Alfvén waves is investigated using the 3D Braginskii fluid code BOUT++. The code has been verified against analytical calculations for the dispersion of kinetic and inertial Alfvén waves. Various mechanisms for forcing Alfvén waves in the code are explored, including introducing localized current sources similar to physical antennas used in experiments. Using this foundation, the code is used to model nonlinear interactions among <span class="hlt">shear</span> Alfvén waves in a cylindrical magnetized plasma, such as that found in the Large Plasma Device (LAPD) at UCLA. In the future this investigation will allow for examination of the nonlinear interactions between <span class="hlt">shear</span> Alfvén waves in both laboratory and space plasmas in order to compare to <span class="hlt">predictions</span> of MHD turbulence.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21230671','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21230671"><span>Nonlinear response of dense colloidal suspensions under oscillatory <span class="hlt">shear</span>: mode-coupling theory and Fourier transform rheology experiments.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Brader, J M; Siebenbürger, M; Ballauff, M; Reinheimer, K; Wilhelm, M; Frey, S J; Weysser, F; Fuchs, M</p> <p>2010-12-01</p> <p>Using a combination of theory, experiment, and simulation we investigate the nonlinear response of dense colloidal suspensions to large amplitude oscillatory <span class="hlt">shear</span> flow. The time-dependent stress response is calculated using a recently developed schematic mode-coupling-<span class="hlt">type</span> theory describing colloidal suspensions under externally applied flow. For finite strain amplitudes the theory generates a nonlinear response, characterized by significant higher harmonic contributions. An important feature of the theory is the <span class="hlt">prediction</span> of an ideal glass transition at sufficiently strong coupling, which is accompanied by the discontinuous appearance of a dynamic yield stress. For the oscillatory <span class="hlt">shear</span> flow under consideration we find that the yield stress plays an important role in determining the nonlinearity of the time-dependent stress response. Our theoretical findings are strongly supported by both large amplitude oscillatory experiments (with Fourier transform rheology analysis) on suspensions of thermosensitive core-shell particles dispersed in water and Brownian dynamics simulations performed on a two-dimensional binary hard-disk mixture. In particular, theory <span class="hlt">predicts</span> nontrivial values of the exponents governing the final decay of the storage and loss moduli as a function of strain amplitude which are in good agreement with both simulation and experiment. A consistent set of parameters in the presented schematic model achieves to jointly describe linear moduli, nonlinear flow curves, and large amplitude oscillatory spectroscopy.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011MNRAS.416...22B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011MNRAS.416...22B"><span><span class="hlt">Shear</span> modulus of neutron star crust</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Baiko, D. A.</p> <p>2011-09-01</p> <p>The <span class="hlt">shear</span> modulus of solid neutron star crust is calculated by the thermodynamic perturbation theory, taking into account ion motion. At a given density, the crust is modelled as a body-centred cubic Coulomb crystal of fully ionized atomic nuclei of one <span class="hlt">type</span> with a uniform charge-compensating electron background. Classic and quantum regimes of ion motion are considered. The calculations in the classic temperature range agree well with previous Monte Carlo simulations. At these temperatures, the <span class="hlt">shear</span> modulus is given by the sum of a positive contribution due to the static lattice and a negative ∝ T contribution due to the ion motion. The quantum calculations are performed for the first time. The main result is that at low temperatures the contribution to the <span class="hlt">shear</span> modulus due to the ion motion saturates at a constant value, associated with zero-point ion vibrations. Such behaviour is qualitatively similar to the zero-point ion motion contribution to the crystal energy. The quantum effects may be important for lighter elements at higher densities, where the ion plasma temperature is not entirely negligible compared to the typical Coulomb ion interaction energy. The results of numerical calculations are approximated by convenient fitting formulae. They should be used for precise neutron star oscillation modelling, a rapidly developing branch of stellar seismology.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/20485990','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/20485990"><span>[Comparative study of 4 <span class="hlt">types</span> of luting cements on <span class="hlt">shear</span> bond strength of Zirconia ceramics to dentin].</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Yin, Bao-di; Zhang, Xian-fang; Zheng, Hu; Han, Dong-wei</p> <p>2010-04-01</p> <p>To investigate the adequate luting cements for zirconia ceramics to dentin. Blocks of sintered zirconia ceramics were randomly divided into 4 groups with 8 slices in each. After saliva immersion,airborne-particle abraded ceramic specimens were cleaned with phosphoric acid gel(containing 35% phosphoric acid) and then bonded to dentin with these four kinds of luting cements. After preserved in 37 degrees centigrade distilled water for 24 hours, the <span class="hlt">shear</span> bonding strength of these specimens was tested and the data was analyzed with SPSS12.0 software package. The Multilink Automix could attain the highest <span class="hlt">shear</span> bonding strength and the 3M RelyXTM Unicem AplicapTM could attain higher <span class="hlt">shear</span> bonding strength, which were both significantly higher than in the Tokuso Ionomer and Shofu Polycarboxylate Cement groups(P<0.05). Total etching resin luting cement is an ideal option to the bonding of zirconia ceramics and can provide a strong bonding.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..1919424G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..1919424G"><span>Fifty years of <span class="hlt">shear</span> zones</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Graham, Rodney</p> <p>2017-04-01</p> <p>We are here, of course, because 1967 saw the publication of John Ramsay's famous book. Two years later a memorable field trip from Imperial College to the Outer Hebrides saw John on a bleak headland on the coast of North Uist where a relatively undeformed metadolerite within Lewisian (Precambrian) gneisses contained ductile <span class="hlt">shear</span> zones with metamorphic fabrics in amphibolite facies. One particular outcrop was very special - a <span class="hlt">shear</span> zone cutting otherwise completely isotropic, undeformed metadolerite, with an incremental foliation starting to develop at 45° to the deformation zone, and increasing in intensity as it approached the <span class="hlt">shear</span> direction. Here was proof of the process of simple <span class="hlt">shear</span> under ductile metamorphic conditions - the principles of simple <span class="hlt">shear</span> outlined in John Ramsay's 1967 book clearly visible in nature, and verified by Ramsay's mathematical proofs in the eventual paper (Ramsay and Graham, 1970). Later work on the Lewisian on the mainland of Scotland, in South Harris, in Africa, and elsewhere applied Ramsay's simple <span class="hlt">shear</span> principles more liberally, more imprecisely and on larger scale than at Caisteal Odair, but in retrospect it documented what seems now to be the generality of mid and lower crustal deformation. Deep seismic reflection data show us that on passive margins hyper-stretched continental crust (whether or not cloaked by Seaward Dipping Reflectors) seems to have collapsed onto the mantle. Crustal faults mostly sole out at or above the mantle - so the Moho is a detachment- an 'outer marginal detachment', if you like, and, of course, it must be a ductile <span class="hlt">shear</span>. On non-volcanic margins this <span class="hlt">shear</span> zone forms the first formed ocean floor before true sea floor spreading gets going to create real oceanic crust. Gianreto Manatschal, Marcel Lemoine and others realised that the serpentinites described in parts of the Alps are exposed remnants of this ductile <span class="hlt">shear</span> zone. Associated ophicalcite breccias tell of sea floor exposure, while high</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20130011519','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20130011519"><span>Recalibration of the <span class="hlt">Shear</span> Stress Transport Model to Improve Calculation of Shock Separated Flows</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Georgiadis, Nicholas J.; Yoder, Dennis A.</p> <p>2013-01-01</p> <p>The Menter <span class="hlt">Shear</span> Stress Transport (SST) k . turbulence model is one of the most widely used two-equation Reynolds-averaged Navier-Stokes turbulence models for aerodynamic analyses. The model extends Menter s baseline (BSL) model to include a limiter that prevents the calculated turbulent <span class="hlt">shear</span> stress from exceeding a prescribed fraction of the turbulent kinetic energy via a proportionality constant, a1, set to 0.31. Compared to other turbulence models, the SST model yields superior <span class="hlt">predictions</span> of mild adverse pressure gradient flows including those with small separations. In shock - boundary layer interaction regions, the SST model produces separations that are too large while the BSL model is on the other extreme, <span class="hlt">predicting</span> separations that are too small. In this paper, changing a1 to a value near 0.355 is shown to significantly improve <span class="hlt">predictions</span> of shock separated flows. Several cases are examined computationally and experimental data is also considered to justify raising the value of a1 used for shock separated flows.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20010061424&hterms=acoustic+waves&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dacoustic%2Bwaves','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20010061424&hterms=acoustic+waves&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dacoustic%2Bwaves"><span>Comparison with Analytical Solution: Generation and Radiation of Acoustic Waves from a 2-D <span class="hlt">Shear</span> Layer</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Dahl, Milo D.</p> <p>2000-01-01</p> <p>An acoustic source inside of a 2-D jet excites an instability wave in the <span class="hlt">shear</span> layer resulting in sound radiating away from the <span class="hlt">shear</span> layer. Solve the linearized Euler equations to <span class="hlt">predict</span> the sound radiation outside of the jet. The jet static pressure is assumed to be constant. The jet flow is parallel and symmetric about the x-axis. Use a symmetry boundary condition along the x-axis.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_19 --> <div id="page_20" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="381"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014PhDT.......105B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014PhDT.......105B"><span>High strength semi-active energy absorbers using <span class="hlt">shear</span>- and mixedmode operation at high <span class="hlt">shear</span> rates</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Becnel, Andrew C.</p> <p></p> <p>This body of research expands the design space of semi-active energy absorbers for shock isolation and crash safety by investigating and characterizing magnetorheological fluids (MRFs) at high <span class="hlt">shear</span> rates ( > 25,000 1/s) under <span class="hlt">shear</span> and mixed-mode operation. Magnetorheological energy absorbers (MREAs) work well as adaptive isolators due to their ability to quickly and controllably adjust to changes in system mass or impact speed while providing fail-safe operation. However, typical linear stroking MREAs using pressure-driven flows have been shown to exhibit reduced controllability as impact speed (<span class="hlt">shear</span> rate) increases. The objective of this work is to develop MREAs that improve controllability at high <span class="hlt">shear</span> rates by using pure <span class="hlt">shear</span> and mixed <span class="hlt">shear</span>-squeeze modes of operation, and to present the fundamental theory and models of MR fluids under these conditions. A proof of concept instrument verified that the MR effect persists in <span class="hlt">shear</span> mode devices at <span class="hlt">shear</span> rates corresponding to low speed impacts. This instrument, a concentric cylinder Searle cell magnetorheometer, was then used to characterize three commercially available MRFs across a wide range of <span class="hlt">shear</span> rates, applied magnetic fields, and temperatures. Characterization results are presented both as flow curves according to established practice, and as an alternate nondimensionalized analysis based on Mason number. The Mason number plots show that, with appropriate correction coefficients for operating temperature, the varied flow curve data can be collapsed to a single master curve. This work represents the first <span class="hlt">shear</span> mode characterization of MRFs at <span class="hlt">shear</span> rates over 10 times greater than available with commercial rheometers, as well as the first validation of Mason number analysis to high <span class="hlt">shear</span> rate flows in MRFs. Using the results from the magnetorheometer, a full scale rotary vane MREA was developed as part of the Lightweight Magnetorheological Energy Absorber System (LMEAS) for an SH-60 Seahawk helicopter</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012RMRE...45...45A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012RMRE...45...45A"><span><span class="hlt">Prediction</span> of Compressional, <span class="hlt">Shear</span>, and Stoneley Wave Velocities from Conventional Well Log Data Using a Committee Machine with Intelligent Systems</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Asoodeh, Mojtaba; Bagheripour, Parisa</p> <p>2012-01-01</p> <p>Measurement of compressional, <span class="hlt">shear</span>, and Stoneley wave velocities, carried out by dipole sonic imager (DSI) logs, provides invaluable data in geophysical interpretation, geomechanical studies and hydrocarbon reservoir characterization. The presented study proposes an improved methodology for making a quantitative formulation between conventional well logs and sonic wave velocities. First, sonic wave velocities were <span class="hlt">predicted</span> from conventional well logs using artificial neural network, fuzzy logic, and neuro-fuzzy algorithms. Subsequently, a committee machine with intelligent systems was constructed by virtue of hybrid genetic algorithm-pattern search technique while outputs of artificial neural network, fuzzy logic and neuro-fuzzy models were used as inputs of the committee machine. It is capable of improving the accuracy of final <span class="hlt">prediction</span> through integrating the outputs of aforementioned intelligent systems. The hybrid genetic algorithm-pattern search tool, embodied in the structure of committee machine, assigns a weight factor to each individual intelligent system, indicating its involvement in overall <span class="hlt">prediction</span> of DSI parameters. This methodology was implemented in Asmari formation, which is the major carbonate reservoir rock of Iranian oil field. A group of 1,640 data points was used to construct the intelligent model, and a group of 800 data points was employed to assess the reliability of the proposed model. The results showed that the committee machine with intelligent systems performed more effectively compared with individual intelligent systems performing alone.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3916349','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3916349"><span>Rac1 mediates laminar <span class="hlt">shear</span> stress-induced vascular endothelial cell migration</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Huang, Xianliang; Shen, Yang; Zhang, Yi; Wei, Lin; Lai, Yi; Wu, Jiang; Liu, Xiaojing; Liu, Xiaoheng</p> <p>2013-01-01</p> <p>The migration of endothelial cells (ECs) plays an important role in vascular remodeling and regeneration. ECs are constantly subjected to <span class="hlt">shear</span> stress resulting from blood flow and are able to convert mechanical stimuli into intracellular signals that affect cellular behaviors and functions. The aim of this study is to elucidate the effects of Rac1, which is the member of small G protein family, on EC migration under different laminar <span class="hlt">shear</span> stress (5.56, 10.02, and 15.27 dyn/cm2). The cell migration distance under laminar <span class="hlt">shear</span> stress increased significantly than that under the static culture condition. Especially, under relative high <span class="hlt">shear</span> stress (15.27 dyn/cm2) there was a higher difference at 8 h (P < 0.01) and 2 h (P < 0.05) compared with static controls. RT-PCR results further showed increasing mRNA expression of Rac1 in ECs exposed to laminar <span class="hlt">shear</span> stress than that exposed to static culture. Using plasmids encoding the wild-<span class="hlt">type</span> (WT), an activated mutant (Q61L), and a dominant-negative mutant (T17N), plasmids encoding Rac1 were transfected into EA.hy 926 cells. The average net migration distance of Rac1Q61L group increased significantly, while Rac1T17N group decreased significantly in comparison with the static controls. These results indicated that Rac1 mediated <span class="hlt">shear</span> stress-induced EC migration. Our findings conduce to elucidate the molecular mechanisms of EC migration induced by <span class="hlt">shear</span> stress, which is expected to understand the pathophysiological basis of wound healing in health and diseases. PMID:24430179</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19840012629','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19840012629"><span><span class="hlt">Shearing</span> stability of lubricants</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Shiba, Y.; Gijyutsu, G.</p> <p>1984-01-01</p> <p><span class="hlt">Shearing</span> stabilities of lubricating oils containing a high mol. wt. polymer as a viscosity index improver were studied by use of ultrasound. The oils were degraded by cavitation and the degradation generally followed first order kinetics with the rate of degradation increasing with the intensity of the ultrasonic irradiation and the cumulative energy applied. The <span class="hlt">shear</span> stability was mainly affected by the mol. wt. of the polymer additive and could be determined in a short time by mechanical <span class="hlt">shearing</span> with ultrasound.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFM.T33E..05H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFM.T33E..05H"><span>Viscous <span class="hlt">shear</span> heating instabilities in a 1-D viscoelastic <span class="hlt">shear</span> zone</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Homburg, J. M.; Coon, E. T.; Spiegelman, M.; Kelemen, P. B.; Hirth, G.</p> <p>2010-12-01</p> <p>Viscous <span class="hlt">shear</span> instabilities may provide a possible mechanism for some intermediate depth earthquakes where high confining pressure makes it difficult to achieve frictional failure. While many studies have explored the feedback between temperature-dependent strain rate and strain-rate dependent <span class="hlt">shear</span> heating (e.g. Braeck and Podladchikov, 2007), most have used thermal anomalies to initiate a <span class="hlt">shear</span> instability or have imposed a low viscosity region in their model domain (John et al., 2009). By contrast, Kelemen and Hirth (2007) relied on an initial grain size contrast between a predetermined fine-grained <span class="hlt">shear</span> zone and coarse grained host rock to initiate an instability. This choice is supported by observations of numerous fine grained ductile <span class="hlt">shear</span> zones in shallow mantle massifs as well as the possibility that annealed fine grained fault gouge, formed at oceanic transforms, subduction related thrusts and ‘outer rise’ faults, could be carried below the brittle/ductile transition by subduction. Improving upon the work of Kelemen and Hirth (2007), we have developed a 1-D numerical model that describes the behavior of a Maxwell viscoelastic body with the rheology of dry olivine being driven at a constant velocity at its boundary. We include diffusion and dislocation creep, dislocation accommodated grain boundary sliding, and low-temperature plasticity (Peierls mechanism). Initial results suggest that including low-temperature plasticity inhibits the ability of the system to undergo an instability, similar to the results of Kameyama et al. (1999). This is due to increased deformation in the background allowing more <span class="hlt">shear</span> heating to take place, and thus softening the system prior to reaching the peak stress. However if the applied strain rate is high enough (e.g. greater than 0.5 x 10-11 s-1 for a domain size of 2 km, an 8 m wide <span class="hlt">shear</span> zone, a background grain size of 1 mm, a <span class="hlt">shear</span> zone grain size of 150 μm, and an initial temperature of 650°C) dramatic</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27176525','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27176525"><span>Vortex Dynamics and <span class="hlt">Shear</span>-Layer Instability in High-Intensity Cyclotrons.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Cerfon, Antoine J</p> <p>2016-04-29</p> <p>We show that the space-charge dynamics of high-intensity beams in the plane perpendicular to the magnetic field in cyclotrons is described by the two-dimensional Euler equations for an incompressible fluid. This analogy with fluid dynamics gives a unified and intuitive framework to explain the beam spiraling and beam breakup behavior observed in experiments and in simulations. Specifically, we demonstrate that beam breakup is the result of a classical instability occurring in fluids subject to a <span class="hlt">sheared</span> flow. We give scaling laws for the instability and <span class="hlt">predict</span> the nonlinear evolution of beams subject to it. Our work suggests that cyclotrons may be uniquely suited for the experimental study of <span class="hlt">shear</span> layers and vortex distributions that are not achievable in Penning-Malmberg traps.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19810008332','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19810008332"><span>Refraction and scattering of sound by a <span class="hlt">shear</span> layer</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Schlinker, R. H.; Amiet, R. K.</p> <p>1980-01-01</p> <p>The angle and amplitude changes for acoustic waves refracted by a circular open jet <span class="hlt">shear</span> layer were determined. The generalized refraction theory was assessed experimentally for on axis and off axis acoustic source locations as source frequency varied from 1 kHz to 10 kHz and free stream Mach number varied from 0.1 to 0.4. Angle and amplitude changes across the <span class="hlt">shear</span> layer show good agreement with theory. Experiments confirm that the refraction theory is independent of <span class="hlt">shear</span> layer thickness, acoustic source frequency, and source <span class="hlt">type</span>. A generalized theory is, thus, available for correcting far field noise data acquired in open jet test facilities. The effect of discrete tone scattering by the open jet turbulent <span class="hlt">shear</span> layer was also studied. Scattering effects were investigated over the same Mach number range as frequency varied from 5 kHz to 15 kHz. Attenuation of discrete tone amplitude and tone broadening were measured as a function of acoustic source position and radiation angle. Scattering was found to be stronger at angles close to the open jet axis than at 90 deg, and becomes stronger as the acoustic source position shifts downstream. A scattering analysis provided an estimate of the onset of discrete tone scattering.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20170007245','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20170007245"><span>Influence of <span class="hlt">Shear</span> Stiffness Degradation on Crack Paths in Uni-Directional Composite Laminates</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Satyanarayana, Arunkumar; Bogert, Phil B.</p> <p>2017-01-01</p> <p>Influence of <span class="hlt">shear</span> stiffness degradation in an element, due to damage, on crack paths in uni-directional laminates has been demonstrated. A new <span class="hlt">shear</span> stiffness degradation approach to improve crack path <span class="hlt">prediction</span> has been developed and implemented in an ABAQUS/Explicit frame work using VUMAT. Three progressive failure analysis models, built-in ABAQUS (TradeMark), original COmplete STress Reduction (COSTR) and the modified COSTR damage models have been utilized in this study to simulate crack paths in five unidirectional notched laminates, 15deg, 30deg, 45deg, 60deg and 75deg under uniaxial tension load. Results such as crack paths and load vs. edge displacement curves are documented in this report. Modified COSTR damage model shows better accuracy in <span class="hlt">predicting</span> crack paths in all the uni-directional laminates compared to the ABAQUS (TradeMark) and the original COSTR damage models.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2863059','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2863059"><span>SeqRate: sequence-based protein folding <span class="hlt">type</span> classification and rates <span class="hlt">prediction</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p></p> <p>2010-01-01</p> <p>Background Protein folding rate is an important property of a protein. <span class="hlt">Predicting</span> protein folding rate is useful for understanding protein folding process and guiding protein design. Most previous methods of <span class="hlt">predicting</span> protein folding rate require the tertiary structure of a protein as an input. And most methods do not distinguish the different kinetic nature (two-state folding or multi-state folding) of the proteins. Here we developed a method, SeqRate, to <span class="hlt">predict</span> both protein folding kinetic <span class="hlt">type</span> (two-state versus multi-state) and real-value folding rate using sequence length, amino acid composition, contact order, contact number, and secondary structure information <span class="hlt">predicted</span> from only protein sequence with support vector machines. Results We systematically studied the contributions of individual features to folding rate <span class="hlt">prediction</span>. On a standard benchmark dataset, the accuracy of folding kinetic <span class="hlt">type</span> classification is 80%. The Pearson correlation coefficient and the mean absolute difference between <span class="hlt">predicted</span> and experimental folding rates (sec-1) in the base-10 logarithmic scale are 0.81 and 0.79 for two-state protein folders, and 0.80 and 0.68 for three-state protein folders. SeqRate is the first sequence-based method for protein folding <span class="hlt">type</span> classification and its accuracy of fold rate <span class="hlt">prediction</span> is improved over previous sequence-based methods. Its performance can be further enhanced with additional information, such as structure-based geometric contacts, as inputs. Conclusions Both the web server and software of <span class="hlt">predicting</span> folding rate are publicly available at http://casp.rnet.missouri.edu/fold_rate/index.html. PMID:20438647</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19780008823','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19780008823"><span>Propagation of sound waves through a linear <span class="hlt">shear</span> layer: A closed form solution</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Scott, J. N.</p> <p>1978-01-01</p> <p>Closed form solutions are presented for sound propagation from a line source in or near a <span class="hlt">shear</span> layer. The analysis was exact for all frequencies and was developed assuming a linear velocity profile in the <span class="hlt">shear</span> layer. This assumption allowed the solution to be expressed in terms of parabolic cyclinder functions. The solution is presented for a line monopole source first embedded in the uniform flow and then in the <span class="hlt">shear</span> layer. Solutions are also discussed for certain <span class="hlt">types</span> of dipole and quadrupole sources. Asymptotic expansions of the exact solutions for small and large values of Strouhal number gave expressions which correspond to solutions previously obtained for these limiting cases.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24305976','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24305976"><span>Does <span class="hlt">shear</span> wave ultrasound independently <span class="hlt">predict</span> axillary lymph node metastasis in women with invasive breast cancer?</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Evans, Andrew; Rauchhaus, Petra; Whelehan, Patsy; Thomson, Kim; Purdie, Colin A; Jordan, Lee B; Michie, Caroline O; Thompson, Alastair; Vinnicombe, Sarah</p> <p>2014-01-01</p> <p><span class="hlt">Shear</span> wave elastography (SWE) shows promise as an adjunct to greyscale ultrasound examination in assessing breast masses. In breast cancer, higher lesion stiffness on SWE has been shown to be associated with features of poor prognosis. The purpose of this study was to assess whether lesion stiffness at SWE is an independent predictor of lymph node involvement. Patients with invasive breast cancer treated by primary surgery, who had undergone SWE examination were eligible. Data were retrospectively analysed from 396 consecutive patients. The mean stiffness values were obtained using the Aixplorer® ultrasound machine from SuperSonic Imagine Ltd. Measurements were taken from a region of interest positioned over the stiffest part of the abnormality. The average of the mean stiffness value obtained from each of two orthogonal image planes was used for analysis. Associations between lymph node involvement and mean lesion stiffness, invasive cancer size, histologic grade, tumour <span class="hlt">type</span>, ER expression, HER-2 status and vascular invasion were assessed using univariate and multivariate logistic regression. At univariate analysis, invasive size, histologic grade, HER-2 status, vascular invasion, tumour <span class="hlt">type</span> and mean stiffness were significantly associated with nodal involvement. Nodal involvement rates ranged from 7 % for tumours with mean stiffness <50 kPa to 41 % for tumours with a mean stiffness of >150 kPa. At multivariate analysis, invasive size, tumour <span class="hlt">type</span>, vascular invasion, and mean stiffness maintained independent significance. Mean stiffness at SWE is an independent predictor of lymph node metastasis and thus can confer prognostic information additional to that provided by conventional preoperative tumour assessment and staging.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFMSM13E4206D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMSM13E4206D"><span>Asymmetric Reconnection With A <span class="hlt">Shear</span> Flow and Applications to X-line Motion at the Polar Cusps</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Doss, C.; Komar, C. M.; Beidler, M.; Cassak, P.; Wilder, F. D.; Eriksson, S.</p> <p>2014-12-01</p> <p>Magnetic reconnection at the polar cusps of the magnetosphere is marked by strong asymmetries in plasma density and magnetic field strength in addition to a potentially strong bulk flow <span class="hlt">shear</span> parallel to the reconnecting magnetic field caused by the solar wind. Much has been learned about the effect of either asymmetries or <span class="hlt">shear</span> flow on reconnection, but only a handful of studies have addressed systems with both. We perform a careful theoretical, numerical, and observational study of such systems. It is known that an asymmetry in magnetic field offsets the X-line from the center of the diffusion region in the inflow direction toward the weaker magnetic field. A key finding is that this alters the flow profile seen at the X-line relative to expectations from symmetric reconnection results. This causes the X-line to drift in the outflow direction due to the <span class="hlt">shear</span> flow. We calculate a <span class="hlt">prediction</span> for the X-line drift speed for arbitrary asymmetric magnetic field strengths and show the result is consistent with two-fluid numerical simulations. These <span class="hlt">predictions</span> are also shown to be consistent with recent observations of a tailward moving X-line in Cluster observations of reconnection at the polar cusp. The reconnection rate with a <span class="hlt">shear</span> flow is observed to drop as in symmetric reconnection, and the behavior of the reconnection qualitatively changes when the <span class="hlt">shear</span> flow speed exceeds the hybrid Alfven speed of the outflow known from asymmetric reconnection theory.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3221959','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3221959"><span>Fiber Angle and Aspect Ratio Influence the <span class="hlt">Shear</span> Mechanics of Oriented Electrospun Nanofibrous Scaffolds</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Driscoll, Tristan P.; Nerurkar, Nandan L.; Jacobs, Nathan T.; Elliott, Dawn M.; Mauck, Robert L.</p> <p>2011-01-01</p> <p>Fibrocartilages, including the knee meniscus and the annulus fibrosus (AF) of the intervertebral disc, play critical mechanical roles in load transmission across joints and their function is dependent upon well-defined structural hierarchies, organization, and composition. All, however, are compromised in the pathologic transformations associated with tissue degeneration. Tissue engineering strategies that address these key features, for example, aligned nanofibrous scaffolds seeded with mesenchymal stem cells (MSCs), represent a promising approach for the regeneration of these fibrous structures. While such engineered constructs can replicate native tissue structure and uniaxial tensile properties, the multidirectional loading encountered by these tissues in vivo necessitates that they function adequately in other loading modalities as well, including <span class="hlt">shear</span>. As previous findings have shown that native tissue tensile and <span class="hlt">shear</span> properties are dependent on fiber angle and sample aspect ratio, respectively, the objective of the present study was to evaluate the effects of a changing fiber angle and sample aspect ratio on the <span class="hlt">shear</span> properties of aligned electrospun poly(ε-caprolactone) (PCL) scaffolds, and to determine how extracellular matrix deposition by resident MSCs modulates the measured <span class="hlt">shear</span> response. Results show that fiber orientation and sample aspect ratio significantly influence the response of scaffolds in <span class="hlt">shear</span>, and that measured <span class="hlt">shear</span> strains can be <span class="hlt">predicted</span> by finite element models. Furthermore, acellular PCL scaffolds possessed a relatively high <span class="hlt">shear</span> modulus, 2–4 fold greater than native tissue, independent of fiber angle and aspect ratio. It was further noted that under testing conditions that engendered significant fiber stretch, the aggregate resistance to <span class="hlt">shear</span> was higher, indicating a role for fiber stretch in the overall <span class="hlt">shear</span> response. Finally, with time in culture, the <span class="hlt">shear</span> modulus of MSC laden constructs increased, suggesting that</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28864311','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28864311"><span>Factors affecting the <span class="hlt">shear</span> strength behavior of municipal solid wastes.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Pulat, Hasan Firat; Yukselen-Aksoy, Yeliz</p> <p>2017-11-01</p> <p>In this study, the <span class="hlt">shear</span> strength behavior of European (E-1), Turkey (T-1), and United States of America (U-1) average synthetic municipal solid waste (MSW) compositions were investigated. The large-scale direct <span class="hlt">shear</span> tests were conducted using fresh and aged MSW samples collected from the Manisa Landfill. The natural samples' test results were compared with synthetic samples. The affecting factors such as ageing, waste composition, and waste <span class="hlt">type</span> (synthetic and natural) on the <span class="hlt">shear</span> strength of MSWs were investigated. The effect of composition was evaluated using three main and six modified synthetic MSW compositions. In addition to the synthetic fresh MSW samples, synthetic aged samples were also used. Angle of <span class="hlt">shearing</span> resistance decreased with increasing organic content whereas cohesion intercept increased with increasing organic content. The fresh and aged wastes with higher coarse fraction lead to a higher angle of <span class="hlt">shearing</span> resistance. The synthetic aged samples had higher internal friction angles but lower cohesion values than the synthetic fresh samples. Waste with average European composition had the highest internal friction angle as it has the highest fibrous content. On the other hand, the highest cohesion belonged to the Turkey composition, which had the highest organic matter ratio. The main differences between E-1, T-1 and U-1 samples in terms of compositions were observed. The results of this study indicated that <span class="hlt">shear</span> strength of waste significantly depends on composition and hence a site specific evaluation is recommended. Copyright © 2017 Elsevier Ltd. All rights reserved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20160007836','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20160007836"><span>A Piezoelectric <span class="hlt">Shear</span> Stress Sensor</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Kim, Taeyang; Saini, Aditya; Kim, Jinwook; Gopalarathnam, Ashok; Zhu, Yong; Palmieri, Frank L.; Wohl, Christopher J.; Jiang, Xiaoning</p> <p>2016-01-01</p> <p>In this paper, a piezoelectric sensor with a floating element was developed for <span class="hlt">shear</span> stress measurement. The piezoelectric sensor was designed to detect the pure <span class="hlt">shear</span> stress suppressing effects of normal stress generated from the vortex lift-up by applying opposite poling vectors to the: piezoelectric elements. The sensor was first calibrated in the lab by applying <span class="hlt">shear</span> forces and it showed high sensitivity to <span class="hlt">shear</span> stress (=91.3 +/- 2.1 pC/Pa) due to the high piezoelectric coefficients of PMN-33%PT (d31=-1330 pC/N). The sensor also showed almost no sensitivity to normal stress (less than 1.2 pC/Pa) because of the electromechanical symmetry of the device. The usable frequency range of the sensor is 0-800 Hz. Keywords: Piezoelectric sensor, <span class="hlt">shear</span> stress, floating element, electromechanical symmetry</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018JMPSo.112..472G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018JMPSo.112..472G"><span>The dynamics of a <span class="hlt">shear</span> band</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Giarola, Diana; Capuani, Domenico; Bigoni, Davide</p> <p>2018-03-01</p> <p>A <span class="hlt">shear</span> band of finite length, formed inside a ductile material at a certain stage of a continued homogeneous strain, provides a dynamic perturbation to an incident wave field, which strongly influences the dynamics of the material and affects its path to failure. The investigation of this perturbation is presented for a ductile metal, with reference to the incremental mechanics of a material obeying the J2-deformation theory of plasticity (a special form of prestressed, elastic, anisotropic, and incompressible solid). The treatment originates from the derivation of integral representations relating the incremental mechanical fields at every point of the medium to the incremental displacement jump across the <span class="hlt">shear</span> band faces, generated by an impinging wave. The boundary integral equations (under the plane strain assumption) are numerically approached through a collocation technique, which keeps into account the singularity at the <span class="hlt">shear</span> band tips and permits the analysis of an incident wave impinging a <span class="hlt">shear</span> band. It is shown that the presence of the <span class="hlt">shear</span> band induces a resonance, visible in the incremental displacement field and in the stress intensity factor at the <span class="hlt">shear</span> band tips, which promotes <span class="hlt">shear</span> band growth. Moreover, the waves scattered by the <span class="hlt">shear</span> band are shown to generate a fine texture of vibrations, parallel to the <span class="hlt">shear</span> band line and propagating at a long distance from it, but leaving a sort of conical shadow zone, which emanates from the tips of the <span class="hlt">shear</span> band.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015E%26PSL.430..356S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015E%26PSL.430..356S"><span>Modeling the effect of subgrain rotation recrystallization on the evolution of olivine crystal preferred orientations in simple <span class="hlt">shear</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Signorelli, Javier; Tommasi, Andréa</p> <p>2015-11-01</p> <p>Homogenization models are widely used to <span class="hlt">predict</span> the evolution of texture (crystal preferred orientations) and resulting anisotropy of physical properties in metals, rocks, and ice. They fail, however, in <span class="hlt">predicting</span> two main features of texture evolution in simple <span class="hlt">shear</span> (the dominant deformation regime on Earth) for highly anisotropic crystals, like olivine: (1) the fast rotation of the CPO towards a stable position characterized by parallelism of the dominant slip system and the macroscopic <span class="hlt">shear</span> and (2) the asymptotical evolution towards a constant intensity. To better <span class="hlt">predict</span> CPO-induced anisotropy in the mantle, but limiting computational costs and use of poorly-constrained physical parameters, we modified a viscoplastic self-consistent code to simulate the effects of subgrain rotation recrystallization. To each crystal is associated a finite number of fragments (possible subgrains). Formation of a subgrain corresponds to introduction of a disorientation (relative to the parent) and resetting of the fragment strain and internal energy. The probability of formation of a subgrain is controlled by comparison between the local internal energy and the average value in the polycrystal. A two-level mechanical interaction scheme is applied for simulating the intracrystalline strain heterogeneity allowed by the formation of low-angle grain boundaries. Within a crystal, interactions between subgrains follow a constant stress scheme. The interactions between grains are simulated by a tangent viscoplastic self-consistent approach. This two-level approach better reproduces the evolution of olivine CPO in simple <span class="hlt">shear</span> in experiments and nature. It also <span class="hlt">predicts</span> a marked weakening at low <span class="hlt">shear</span> strains, consistently with experimental data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19880060335&hterms=WITHOUT+ENGINE+OIL&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3DWITHOUT%2BENGINE%2BOIL','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19880060335&hterms=WITHOUT+ENGINE+OIL&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3DWITHOUT%2BENGINE%2BOIL"><span><span class="hlt">Shear</span> rheological characterization of motor oils</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bair, Scott; Winer, Ward O.</p> <p>1988-01-01</p> <p>Measurements of high pressure viscosity, traction coefficient, and EHD film thickness were performed on twelve commercial automotive engine oils, a reference oil, two unformulated base oils and two unformated base oil and polymer blends. An effective high <span class="hlt">shear</span> rate inlet viscosity was calculated from film thickness and pressure viscosity coefficient. The difference between measured and effective viscosity is a function of the polymer <span class="hlt">type</span> and concentration. Traction measurements did not discriminate mileage formulated oils from those not so designated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5372360','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5372360"><span>Differentiation of Pancreatic Cyst <span class="hlt">Types</span> by Analysis of Rheological Behavior of Pancreatic Cyst Fluid</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Khamaysi, Iyad; Abu Ammar, Aiman; Vasilyev, Gleb; Arinstein, Arkadii; Chowers, Yehuda; Zussman, Eyal</p> <p>2017-01-01</p> <p>Differentiation between mucinous and non-mucinous pancreatic cysts is exceedingly important and challenging, particularly as the former bears malignant transformation potential. Pancreatic cyst fluid (PCF)-based diagnostics, including analyses of biochemical markers, as well as cytology, has shown inadequate accuracy. Herein, a preliminary single-center study of 22 PCF samples, collected by endoscopic ultrasound-guided fine needle aspiration (EUS-FNA), assessed the rheological behavior of PCF and its correlation with lesion <span class="hlt">type</span>. The dependence of PCF <span class="hlt">shear</span> viscosity on <span class="hlt">shear</span> rate was found to follow a power law and could be fitted using Ostwald–de Waele model. Three <span class="hlt">types</span> of flow curves were identified, where two <span class="hlt">types</span> correlated with non-mucinous cysts, differing by their power law exponent, and the third <span class="hlt">type</span> corresponding to mucinous cysts. Viscosity measured at a high <span class="hlt">shear</span> rate was shown to serve as an accurate and independent marker distinguishing between mucinous and non-mucinous cysts, with an optimal cutoff value of ηc = 1.3 cP The accuracy of this novel technique proved superior to string-sign, cytology, carcinoembryonic antigen, and amylase assessments. Moreover, the combined <span class="hlt">predictive</span> value of ηc and patient age provided for sensitivity and specificity of 100% and 95.5%, respectively. This simple and rapid diagnostic tool can be immediately implemented after EUS-FNA sampling. PMID:28358122</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012VSD....50.1761G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012VSD....50.1761G"><span><span class="hlt">Shear</span> forces in the contact patch of a braked-racing tyre</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gruber, Patrick; Sharp, Robin S.</p> <p>2012-12-01</p> <p>This article identifies tyre modelling features that are fundamental to the accurate simulation of the <span class="hlt">shear</span> forces in the contact patch of a steady-rolling, slipping and cambered racing tyre. The features investigated include contact patch shape, contact pressure distribution, carcass flexibility, rolling radius (RR) variations and friction coefficient. Using a previously described physical tyre model of modular nature, validated for static conditions, the influence of each feature on the <span class="hlt">shear</span> forces generated is examined under different running conditions, including normal loads of 1500, 3000 and 4500 N, camber angles of 0° and-3°, and longitudinal slip ratios from 0 to-20%. Special attention is paid to heavy braking, in which context the aligning moment is of great interest in terms of its connection with the limit-handling feel. The results of the simulations reveal that true representations of the contact patch shape, carcass flexibility and lateral RR variation are essential for an accurate <span class="hlt">prediction</span> of the distribution and the magnitude of the <span class="hlt">shear</span> forces generated at the tread-road interface of the cambered tyre. Independent of the camber angle, the contact pressure distribution primarily influences the <span class="hlt">shear</span> force distribution and the slip characteristics around the peak longitudinal force. At low brake-slip ratios, the friction coefficient affects the <span class="hlt">shear</span> forces in terms of their distribution, while, at medium to high-slip ratios, the force magnitude is significantly affected. On the one hand, these findings help in the creation of efficient yet accurate tyre models. On the other hand, the research results allow improved understanding of how individual tyre components affect the generation of <span class="hlt">shear</span> forces in the contact patch of a rolling and slipping tyre.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_20 --> <div id="page_21" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="401"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19780016810','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19780016810"><span>CAT LIDAR wind <span class="hlt">shear</span> studies</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Goff, R. W.</p> <p>1978-01-01</p> <p>The studies considered the major meteorological factors producing wind <span class="hlt">shear</span>, methods to define and classify wind <span class="hlt">shear</span> in terms significant from an aircraft perturbation standpoint, the significance of sensor location and scan geometry on the detection and measurement of wind <span class="hlt">shear</span>, and the tradeoffs involved in sensor performance such as range/velocity resolution, update frequency and data averaging interval.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012APS..DFDG10006G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012APS..DFDG10006G"><span>Evolution of inviscid Kelvin-Helmholtz instability from a piecewise linear <span class="hlt">shear</span> layer</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Guha, Anirban; Rahmani, Mona; Lawrence, Gregory</p> <p>2012-11-01</p> <p>Here we study the evolution of 2D, inviscid Kelvin-Helmholtz instability (KH) ensuing from a piecewise linear <span class="hlt">shear</span> layer. Although KH pertaining to smooth <span class="hlt">shear</span> layers (eg. Hyperbolic tangent profile) has been thorough investigated in the past, very little is known about KH resulting from sharp <span class="hlt">shear</span> layers. Pozrikidis and Higdon (1985) have shown that piecewise <span class="hlt">shear</span> layer evolves into elliptical vortex patches. This non-linear state is dramatically different from the well known spiral-billow structure of KH. In fact, there is a little acknowledgement that elliptical vortex patches can represent non-linear KH. In this work, we show how such patches evolve through the interaction of vorticity waves. Our work is based on two <span class="hlt">types</span> of computational methods (i) Contour Dynamics: a boundary-element method which tracks the evolution of the contour of a vortex patch using Lagrangian marker points, and (ii) Direct Numerical Simulation (DNS): an Eulerian pseudo-spectral method heavily used in studying hydrodynamic instability and turbulence.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26439616','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26439616"><span>Generation of remote adaptive torsional <span class="hlt">shear</span> waves with an octagonal phased array to enhance displacements and reduce variability of <span class="hlt">shear</span> wave speeds: comparison with quasi-plane <span class="hlt">shear</span> wavefronts.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ouared, Abderrahmane; Montagnon, Emmanuel; Cloutier, Guy</p> <p>2015-10-21</p> <p>A method based on adaptive torsional <span class="hlt">shear</span> waves (ATSW) is proposed to overcome the strong attenuation of <span class="hlt">shear</span> waves generated by a radiation force in dynamic elastography. During the inward propagation of ATSW, the magnitude of displacements is enhanced due to the convergence of <span class="hlt">shear</span> waves and constructive interferences. The proposed method consists in generating ATSW fields from the combination of quasi-plane <span class="hlt">shear</span> wavefronts by considering a linear superposition of displacement maps. Adaptive torsional <span class="hlt">shear</span> waves were experimentally generated in homogeneous and heterogeneous tissue mimicking phantoms, and compared to quasi-plane <span class="hlt">shear</span> wave propagations. Results demonstrated that displacement magnitudes by ATSW could be up to 3 times higher than those obtained with quasi-plane <span class="hlt">shear</span> waves, that the variability of <span class="hlt">shear</span> wave speeds was reduced, and that the signal-to-noise ratio of displacements was improved. It was also observed that ATSW could cause mechanical inclusions to resonate in heterogeneous phantoms, which further increased the displacement contrast between the inclusion and the surrounding medium. This method opens a way for the development of new noninvasive tissue characterization strategies based on ATSW in the framework of our previously reported <span class="hlt">shear</span> wave induced resonance elastography (SWIRE) method proposed for breast cancer diagnosis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014IJEaS.103..953C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014IJEaS.103..953C"><span>Structure of pseudotachylyte vein systems as a key to co-seismic rupture dynamics: the case of Gavilgarh-Tan <span class="hlt">Shear</span> Zone, central India</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chattopadhyay, A.; Bhattacharjee, D.; Mukherjee, S.</p> <p>2014-04-01</p> <p>The secondary fractures associated with a major pseudotachylyte-bearing fault vein in the <span class="hlt">sheared</span> aplitic granitoid of the Proterozoic Gavilgarh-Tan <span class="hlt">Shear</span> Zone in central India are mapped at the outcrop scale. The fracture maps help to identify at least three different <span class="hlt">types</span> of co-seismic ruptures, e.g., X-X', T1 and T2, which characterize sinistral-sense <span class="hlt">shearing</span> of rocks, confined between two sinistral strike-slip faults slipping at seismic rate. From the asymmetric distribution of tensile fractures around the sinistral-sense fault vein, the direction of seismic rupture propagation is <span class="hlt">predicted</span> to have occurred from west-southwest to east-northeast, during an ancient (Ordovician?) earthquake. Calculations of approximate co-seismic displacement on the faults and seismic moment ( M 0) of the earthquake are attempted, following the methods proposed by earlier workers. These estimates broadly agree to the findings from other studied fault zones (e.g., Gole Larghe Fault zone, Italian Alps). This study supports the proposition by some researchers that important seismological information can be extracted from tectonic pseudotachylytes of all ages, provided they are not reworked by subsequent tectonic activity.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28843154','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28843154"><span>Numerical analysis of wall <span class="hlt">shear</span> stress in ascending aorta before tearing in <span class="hlt">type</span> A aortic dissection.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Chi, Qingzhuo; He, Ying; Luan, Yong; Qin, Kairong; Mu, Lizhong</p> <p>2017-10-01</p> <p>Although the incidence of many cardiovascular diseases has declined as medical treatments have improved, the prevalence of aortic dissection (AD) has increased. Compared to <span class="hlt">type</span> B dissections, <span class="hlt">type</span> A dissections are more severe, and most patients with <span class="hlt">type</span> A dissections require surgical treatment. The objective of this study was to investigate the relationships between the wall <span class="hlt">shear</span> stress (WSS) on the aortic endothelium and the frequent tearing positions using computational fluid dynamics. Five <span class="hlt">type</span> A dissection cases and two normal aortas were included in the study. First, the structures of the aortas before the <span class="hlt">type</span> A dissection were reconstructed on the basis of the original imaging data. Analyses of flow in the reconstructed premorbid structures reveals that the rupture positions in three of the five cases corresponded to the area of maximum elevated WSS. Moreover, the WSS at the junction of the aortic arch and descending aorta was found to be elevated, which is considered to be related to the locally disturbed helical flow. Meanwhile, the highest WSS in the patients with premorbid AD was found to be almost double that of the control group. Due to the noticeable morphological differences between the AD cases and the control group, the WSSs in the premorbid structures without vasodilation in the ascending part were estimated. The computational results revealed that the WSS was lower in the aorta without vasodilation, but the pressure drop in this situation was higher than that with vasodilation in the ascending aorta. Significant differences were seen between the AD cases and the control group in the angles of the side branches of the aortic arch and its bending degree. Dilation of the ascending aorta and alterations in the branching angles may be the key determinants of a high WSS that leads to <span class="hlt">type</span> A dissection. Greater tortuosity of the aortic arch leads to stronger helical flow through the distal aortic arch, which may be related to tears in this region</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/biblio/22261666-plane-strain-shear-fracture-advanced-high-strength-steels','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/22261666-plane-strain-shear-fracture-advanced-high-strength-steels"><span>The plane strain <span class="hlt">shear</span> fracture of the advanced high strength steels</span></a></p> <p><a target="_blank" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Sun, Li, E-mail: li.sun@gm.com</p> <p>2013-12-16</p> <p>The “<span class="hlt">shear</span> fracture” which occurs at the high-curvature die radii in the sheet metal forming has been reported to remarkably limit the application of the advanced high strength steels (AHSS) in the automobile industry. However, this unusual fracture behavior generally cannot be <span class="hlt">predicted</span> by the traditional forming limit diagram (FLD). In this research, a new experimental system was developed in order to simulate the <span class="hlt">shear</span> fracture, especially at the plane strain state which is the most common state in the auto-industry and difficult to achieve in the lab due to sample size. Furthermore, the system has the capability to operatemore » in a strain rate range from quasi-static state to the industrial forming state. One kinds of AHSS, Quenching-Partitioning (QP) steels have been performed in this test and the results show that the limiting fracture strain is related to the bending ratio and strain rate. The experimental data support that deformation-induced heating is an important cause of “<span class="hlt">shear</span> fracture” phenomena for AHSS: a deformation-induced quasi-heating caused by smaller bending ratio and high strain rate produce a smaller limiting plane strain and lead a “<span class="hlt">shear</span> fracture” in the component.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AIPC.1770c0098S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AIPC.1770c0098S"><span>Diagnostics of boundary layer transition by <span class="hlt">shear</span> stress sensitive liquid crystals</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shapoval, E. S.</p> <p>2016-10-01</p> <p>Previous research indicates that the problem of boundary layer transition visualization on metal models in wind tunnels (WT) which is a fundamental question in experimental aerodynamics is not solved yet. In TsAGI together with Khristianovich Institute of Theoretical and Applied Mechanics (ITAM) a method of <span class="hlt">shear</span> stress sensitive liquid crystals (LC) which allows flow visualization was proposed. This method allows testing several flow conditions in one wind tunnel run and does not need covering the investigated model with any special heat-insulating coating which spoils the model geometry. This coating is easily applied on the model surface by spray or even by brush. Its' thickness is about 40 micrometers and it does not spoil the surface quality. At first the coating obtains some definite color. Under <span class="hlt">shear</span> stress the LC coating changes color and this change is proportional to <span class="hlt">shear</span> stress. The whole process can be visually observed and during the tests it is recorded by camera. The findings of the research showed that it is possible to visualize boundary layer transition, flow separation, shock waves and the flow image on the whole. It is possible to <span class="hlt">predict</span> that the proposed method of <span class="hlt">shear</span> stress sensitive liquid crystals is a promise for future research.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014APS..MARY17008W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014APS..MARY17008W"><span>Effect of friction on <span class="hlt">shear</span> jamming</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Dong; Ren, Jie; Dijksman, Joshua; Behringer, Robert</p> <p>2014-03-01</p> <p><span class="hlt">Shear</span> Jamming of granular materials was first found for systems of frictional disks, with a static friction coefficients μs ~= 0 . 6 . Jamming by <span class="hlt">shear</span> is obtained by starting from a zero-stress state with a packing fraction ϕS <= ϕ <=ϕJ between ϕJ (isotropic jamming) and a lowest ϕS for <span class="hlt">shear</span> jamming. This phenomenon is associated with strong anisotropy in stress and the contact network in the form of ``force chains,'' which are stabilized and/or enhanced by the presence of friction. We address experimentally how reducing friction affects <span class="hlt">shear</span> jamming by using either teflon disks of teflon wrapped photoelastic particles. The teflon disks were placed in a wall driven 2D <span class="hlt">shear</span> apparatus, in which we can probe <span class="hlt">shear</span> stresses mechanically. Teflon-wrapped disks were placed in a bottom driven 2D <span class="hlt">shear</span> apparatus (Ren et al., PRL 2013). Both apparatuses provide uniform simple <span class="hlt">shear</span>. In all low- μ experiments, the <span class="hlt">shear</span> jamming occurred, as observed through stress increases on the packing. However, the low- μ differences observed for ϕJ -ϕS were smaller than for higher friction particles. Ongoing work is studying systems using hydrogel disks, which have a lower friction coefficient than teflon. We acknowledge support from NSF Grant No. DMR12-06351, ARO Grant No. W911NF-1-11-0110, and NASA Grant No. NNX10AU01G.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29117043','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29117043"><span>Quantitative Characterization of <span class="hlt">Shear</span>-Induced Platelet Receptor Shedding: Glycoprotein Ibα, Glycoprotein VI, and Glycoprotein IIb/IIIa.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Chen, Zengsheng; Koenig, Steven C; Slaughter, Mark S; Griffith, Bartley P; Wu, Zhongjun J</p> <p>2017-11-07</p> <p>The structural integrity of platelet receptors is essential for platelets to play the normal hemostatic function. The high non-physiologic <span class="hlt">shear</span> stress (NPSS) commonly exists in blood-contacting medical devices and has been shown to cause platelet receptor shedding. The loss of platelet receptors may impair the normal hemostatic function of platelets. The aim of this study was to quantify NPSS-induced shedding of three key receptors on the platelet surface. Human blood was subjected to the matrix of well-defined <span class="hlt">shear</span> stresses and exposure times, generated by using a custom-designed blood-<span class="hlt">shearing</span> device. The expression of three key platelet receptors, glycoprotein (GP) Ibα, GPVI, and GPIIb/IIIa, in <span class="hlt">sheared</span> blood was quantified using flow cytometry. The quantitative relationship between the loss of each of the three receptors on the platelet surface and <span class="hlt">shear</span> condition (<span class="hlt">shear</span> stress level and exposure time) was explored. It was found that these relationships followed well the power law functional form. The coefficients of the power law models for the <span class="hlt">shear</span>-induced shedding of these platelet receptors were derived with coefficients of determination (R) of 0.77, 0.73, and 0.78, respectively. The power law models with these coefficients may be potentially used to <span class="hlt">predict</span> the <span class="hlt">shear</span>-induced platelet receptor shedding of human blood.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/biblio/1328542-dem-study-fabric-features-governing-undrained-post-liquefaction-shear-deformation-sand','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/1328542-dem-study-fabric-features-governing-undrained-post-liquefaction-shear-deformation-sand"><span>DEM study of fabric features governing undrained post-liquefaction <span class="hlt">shear</span> deformation of sand</span></a></p> <p><a target="_blank" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Wang, Rui; Fu, Pengcheng; Zhang, Jian-Min</p> <p></p> <p>In an effort to study undrained post-liquefaction <span class="hlt">shear</span> deformation of sand, the discrete element method (DEM) is adopted to conduct undrained cyclic biaxial compression simulations on granular assemblies consisting of 2D circular particles. The simulations are able to successfully reproduce the generation and eventual saturation of <span class="hlt">shear</span> strain through the series of liquefaction states that the material experiences during cyclic loading after the initial liquefaction. Also, DEM simulations with different deviatoric stress amplitudes and initial mean effective stresses on samples with different void ratios and loading histories are carried out to investigate the relationship between various mechanics- or fabric-related variablesmore » and post-liquefaction <span class="hlt">shear</span> strain development. It is found that well-known metrics such as deviatoric stress amplitude, initial mean effective stress, void ratio, contact normal fabric anisotropy intensity, and coordination number, are not adequately correlated to the observed <span class="hlt">shear</span> strain development and, therefore, could not possibly be used for its <span class="hlt">prediction</span>. A new fabric entity, namely the Mean Neighboring Particle Distance (MNPD), is introduced to reflect the space arrangement of particles. It is found that the MNPD has an extremely strong and definitive relationship with the post-liquefaction <span class="hlt">shear</span> strain development, showing MNPD’s potential role as a parameter governing post-liquefaction behavior of sand.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/pages/biblio/1328542-dem-study-fabric-features-governing-undrained-post-liquefaction-shear-deformation-sand','SCIGOV-DOEP'); return false;" href="https://www.osti.gov/pages/biblio/1328542-dem-study-fabric-features-governing-undrained-post-liquefaction-shear-deformation-sand"><span>DEM study of fabric features governing undrained post-liquefaction <span class="hlt">shear</span> deformation of sand</span></a></p> <p><a target="_blank" href="http://www.osti.gov/pages">DOE PAGES</a></p> <p>Wang, Rui; Fu, Pengcheng; Zhang, Jian-Min; ...</p> <p>2016-10-05</p> <p>In an effort to study undrained post-liquefaction <span class="hlt">shear</span> deformation of sand, the discrete element method (DEM) is adopted to conduct undrained cyclic biaxial compression simulations on granular assemblies consisting of 2D circular particles. The simulations are able to successfully reproduce the generation and eventual saturation of <span class="hlt">shear</span> strain through the series of liquefaction states that the material experiences during cyclic loading after the initial liquefaction. Also, DEM simulations with different deviatoric stress amplitudes and initial mean effective stresses on samples with different void ratios and loading histories are carried out to investigate the relationship between various mechanics- or fabric-related variablesmore » and post-liquefaction <span class="hlt">shear</span> strain development. It is found that well-known metrics such as deviatoric stress amplitude, initial mean effective stress, void ratio, contact normal fabric anisotropy intensity, and coordination number, are not adequately correlated to the observed <span class="hlt">shear</span> strain development and, therefore, could not possibly be used for its <span class="hlt">prediction</span>. A new fabric entity, namely the Mean Neighboring Particle Distance (MNPD), is introduced to reflect the space arrangement of particles. It is found that the MNPD has an extremely strong and definitive relationship with the post-liquefaction <span class="hlt">shear</span> strain development, showing MNPD’s potential role as a parameter governing post-liquefaction behavior of sand.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018JNR....20...53S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018JNR....20...53S"><span>Dynamic <span class="hlt">shear</span> rheology of colloidal suspensions of surface-modified silica nanoparticles in PEG</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Swarna; Pattanayek, Sudip Kumar; Ghosh, Anup Kumar</p> <p>2018-03-01</p> <p>The present work illustrates the effect of surface modification of silica nanoparticles (500 nm) with 3-(glycidoxypropyl)trimethoxy silane which was carried out at different reaction times. The suspensions prepared from modified and unmodified silica nanoparticles were evaluated for their <span class="hlt">shear</span> rate-dependent viscosity and strain-frequency-dependent modulus. The linear viscoelastic moduli, viz., storage modulus and loss modulus, were compared with those of nonlinear moduli. The <span class="hlt">shear</span>-thickened suspensions displayed strain thinning at low-frequency smaller strains and a strong strain overshoot at higher strains, characteristics of a continuous <span class="hlt">shear</span> thickening fluids. The <span class="hlt">shear</span>-thinned suspension, conversely, exhibited a strong elastic dominance at smaller strains, but at higher strains, its strain softened observed in the steady <span class="hlt">shear</span> viscosity plot indicating characteristics of yielding material. Considering higher order harmonic components, the decomposed elastic and viscous stress revealed a pronounced elastic response up to 10% strain and a high viscous damping at larger strains. The current work is one of a kind in demonstrating the effect of silica surface functionalization on the linear and nonlinear viscoelasticity of suspensions showing a unique rheological fingerprint. The suspensions can thus be <span class="hlt">predicted</span> through rheological studies for their applicability in energy absorbing and damping materials with respect to their mechanical properties.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013PhFl...25g3104C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013PhFl...25g3104C"><span><span class="hlt">Shear</span> thinning effects on blood flow in straight and curved tubes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cherry, Erica M.; Eaton, John K.</p> <p>2013-07-01</p> <p>Simulations were performed to determine the magnitude and <span class="hlt">types</span> of errors one can expect when approximating blood in large arteries as a Newtonian fluid, particularly in the presence of secondary flows. This was accomplished by running steady simulations of blood flow in straight and curved tubes using both Newtonian and <span class="hlt">shear</span>-thinning viscosity models. In the <span class="hlt">shear</span>-thinning simulations, the viscosity was modeled as a <span class="hlt">shear</span> rate-dependent function fit to experimental data. Simulations in straight tubes were modeled after physiologically relevant arterial flows, and flow parameters for the curved tube simulations were chosen to examine a variety of secondary flow strengths. The diameters ranged from 1 mm to 10 mm and the Reynolds numbers from 24 to 1500. Pressure and velocity data are reported for all simulations. In the straight tube simulations, the <span class="hlt">shear</span>-thinning flows had flattened velocity profiles and higher pressure gradients compared to the Newtonian simulations. In the curved tube flows, the <span class="hlt">shear</span>-thinning simulations tended to have blunted axial velocity profiles, decreased secondary flow strengths, and decreased axial vorticity compared to the Newtonian simulations. The cross-sectionally averaged pressure drops in the curved tubes were higher in the <span class="hlt">shear</span>-thinning flows at low Reynolds number but lower at high Reynolds number. The maximum deviation in secondary flow magnitude averaged over the cross sectional area was 19% of the maximum secondary flow and the maximum deviation in axial vorticity was 25% of the maximum vorticity.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018RMRE...51..101S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018RMRE...51..101S"><span>Physical Modeling of <span class="hlt">Shear</span> Behavior of Infilled Rock Joints Under CNL and CNS Boundary Conditions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shrivastava, Amit Kumar; Rao, K. Seshagiri</p> <p>2018-01-01</p> <p>Despite their frequent natural occurrence, filled discontinuities under constant normal stiffness (CNS) boundary conditions have been studied much less systematically, perhaps because of the difficulties arising from the increased number of variable parameters. Because of the lack of reliable and realistic theoretical or empirical relations and the difficulties in obtaining and testing representative samples, engineers rely on judgment and often consider the <span class="hlt">shear</span> strength of the infilled material itself as <span class="hlt">shear</span> strength of rock joints. This assumption leads to uneconomical and also sometimes the unsafe design of underground structures, slopes, rock-socketed piles and foundations. To study the effect of infill on the <span class="hlt">shear</span> behavior of rock joints, tests were performed on the modeled infilled rock joint having different joint roughness under constant normal load (CNL) and CNS boundary conditions at various initial normal stress and varying thickness of the infilled material. The test results indicate that <span class="hlt">shear</span> strength decreases with an increase in t/ a ratio for both CNL and CNS conditions, but the reduction in <span class="hlt">shear</span> strength is more for CNL than for CNS condition for a given initial normal stress. The detailed account of the effect of thickness of infilled material on <span class="hlt">shear</span> and deformation behavior of infilled rock joint is discussed in this paper, and a model is proposed to <span class="hlt">predict</span> <span class="hlt">shear</span> strength of infilled rock joint.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017KARJ...29..281S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017KARJ...29..281S"><span>A comparative study of the effects of cone-plate and parallel-plate geometries on rheological properties under oscillatory <span class="hlt">shear</span> flow</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Song, Hyeong Yong; Salehiyan, Reza; Li, Xiaolei; Lee, Seung Hak; Hyun, Kyu</p> <p>2017-11-01</p> <p>In this study, the effects of cone-plate (C/P) and parallel-plate (P/P) geometries were investigated on the rheological properties of various complex fluids, e.g. single-phase (polymer melts and solutions) and multiphase systems (polymer blend and nanocomposite, and suspension). Small amplitude oscillatory <span class="hlt">shear</span> (SAOS) tests were carried out to compare linear rheological responses while nonlinear responses were compared using large amplitude oscillatory <span class="hlt">shear</span> (LAOS) tests at different frequencies. Moreover, Fourier-transform (FT)-rheology method was used to analyze the nonlinear responses under LAOS flow. Experimental results were compared with <span class="hlt">predictions</span> obtained by single-point correction and <span class="hlt">shear</span> rate correction. For all systems, SAOS data measured by C/P and P/P coincide with each other, but results showed discordance between C/P and P/P measurements in the nonlinear regime. For all systems except xanthan gum solutions, first-harmonic moduli were corrected using a single horizontal shift factor, whereas FT rheology-based nonlinear parameters ( I 3/1, I 5/1, Q 3, and Q 5) were corrected using vertical shift factors that are well <span class="hlt">predicted</span> by single-point correction. Xanthan gum solutions exhibited anomalous corrections. Their first-harmonic Fourier moduli were superposed using a horizontal shift factor <span class="hlt">predicted</span> by <span class="hlt">shear</span> rate correction applicable to highly <span class="hlt">shear</span> thinning fluids. The distinguished corrections were observed for FT rheology-based nonlinear parameters. I 3/1 and I 5/1 were superposed by horizontal shifts, while the other systems displayed vertical shifts of I 3/1 and I 5/1. Q 3 and Q 5 of xanthan gum solutions were corrected using both horizontal and vertical shift factors. In particular, the obtained vertical shift factors for Q 3 and Q 5 were twice as large as <span class="hlt">predictions</span> made by single-point correction. Such larger values are rationalized by the definitions of Q 3 and Q 5. These results highlight the significance of horizontal shift</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23240445','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23240445"><span>[Research on lateral <span class="hlt">shearing</span> interferometer for field monitoring of natural gas pipeline leak].</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Zhang, Xue-Feng; Gao, Yu-Bin</p> <p>2012-09-01</p> <p>Aimed at the mechanical scanning spectroscopy equipment with poor anti-interference and anti-jamming ability, which affects the accuracy of its natural gas pipeline leak detection in the wild, a new <span class="hlt">type</span> of lateral <span class="hlt">shearing</span> interferometer system was designed. The system uses a beam splitter to get optical path difference by a mechanical scanning part, and it cancel the introduction of external vibration interference through the linkage between the two beam splitterw. The interference intensity of interference fringes produced was calculated, and analysis of a rotating beam splitter corresponds to the angle of the optical path difference function, solving for the maximum angle of the forward rotation and reverse rotation, which is the maximum optical path range. Experiments using the gas tank deflated simulated natural gas pipeline leak process, in the interference conditions, and the test data of the <span class="hlt">type</span> WQF530 spectrometer and the new <span class="hlt">type</span> of lateral <span class="hlt">shearing</span> interferometer system were comparedt. The experimental results show that the relative error of both systems is about 1% in indoor conditions without interference. However, in interference environment, the error of WQF530 <span class="hlt">type</span> spectrometer becomes larger, more than 10%, but the error of the new <span class="hlt">type</span> of lateral <span class="hlt">shearing</span> interferometer system is still below 5%. The detection accuracy of the <span class="hlt">type</span> WQF530 spectrometer decreased significantly due to the environment. Therefore, the seismic design of the system can effectively offset power deviation and half-width increases of center wavelength caused by external interference, and compared to conventional mechanical scanning interferometer devices the new system is more suitable for field detection.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018PhRvF...3c3301K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018PhRvF...3c3301K"><span>Structural state diagram of concentrated suspensions of jammed soft particles in oscillatory <span class="hlt">shear</span> flow</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Khabaz, Fardin; Cloitre, Michel; Bonnecaze, Roger T.</p> <p>2018-03-01</p> <p>In a recent study [Khabaz et al., Phys. Rev. Fluids 2, 093301 (2017), 10.1103/PhysRevFluids.2.093301], we showed that jammed soft particle glasses (SPGs) crystallize and order in steady <span class="hlt">shear</span> flow. Here we investigate the rheology and microstructures of these suspensions in oscillatory <span class="hlt">shear</span> flow using particle-dynamics simulations. The microstructures in both <span class="hlt">types</span> of flows are similar, but their evolutions are very different. In both cases the monodisperse and polydisperse suspensions form crystalline and layered structures, respectively, at high <span class="hlt">shear</span> rates. The crystals obtained in the oscillatory <span class="hlt">shear</span> flow show fewer defects compared to those in the steady <span class="hlt">shear</span>. SPGs remain glassy for maximum oscillatory strains less than about the yield strain of the material. For maximum strains greater than the yield strain, microstructural and rheological transitions occur for SPGs. Polydisperse SPGs rearrange into a layered structure parallel to the flow-vorticity plane for sufficiently high maximum <span class="hlt">shear</span> rates and maximum strains about 10 times greater than the yield strain. Monodisperse suspensions form a face-centered cubic (FCC) structure when the maximum <span class="hlt">shear</span> rate is low and hexagonal close-packed (HCP) structure when the maximum <span class="hlt">shear</span> rate is high. In steady <span class="hlt">shear</span>, the transition from a glassy state to a layered one for polydisperse suspensions included a significant induction strain before the transformation. In oscillatory <span class="hlt">shear</span>, the transformation begins to occur immediately and with different microstructural changes. A state diagram for suspensions in large amplitude oscillatory <span class="hlt">shear</span> flow is found to be in close but not exact agreement with the state diagram for steady <span class="hlt">shear</span> flow. For more modest amplitudes of around one to five times the yield strain, there is a transition from a glassy structure to FCC and HCP crystals, at low and high frequencies, respectively, for monodisperse suspensions. At moderate frequencies, the transition is from glassy to HCP via</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22044232','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22044232"><span>Collective school-<span class="hlt">type</span> identity: <span class="hlt">predicting</span> students' motivation beyond academic self-concept.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Knigge, Michel; Hannover, Bettina</p> <p>2011-06-01</p> <p>In Germany, according to their prior achievement students are tracked into different <span class="hlt">types</span> of secondary school that provide profoundly different options for their future educational careers. In this paper we suggest that as a result, school tracks clearly differ in their social status or reputation. This should translate into different collective school-<span class="hlt">type</span> identities for their students, irrespective of the students' personal academic self-concepts. We examine the extent to which collective school-<span class="hlt">type</span> identity systematically varies as a function of the school track students are enrolled in, and the extent to which students' collective school-<span class="hlt">type</span> identity makes a unique contribution beyond academic self-concept and school track in <span class="hlt">predicting</span> scholastic motivation. In two cross-sectional studies a measure of collective school-<span class="hlt">type</span> identity is established and applied to explain motivational differences between two school tracks in Berlin. In Study 1 (N = 39 students) the content of the collective school-<span class="hlt">type</span> identity is explored by means of an open format questionnaire. Based on these findings a structured instrument (semantic differential) to measure collective school-<span class="hlt">type</span> identity is developed. In Study 2 (N = 1278 students) the assumed structure with four subscales (Stereotype Achievement, Stereotype Motivation, Stereotype Social, and Compensation) is proved with confirmatory factor analysis. This measure is used to compare the collective school-<span class="hlt">type</span> identity across school tracks and <span class="hlt">predict</span> motivational outcomes. Results show large differences in collective school-<span class="hlt">type</span> identity between students of different school tracks. Furthermore, these differences can explain motivational differences between school tracks. Collective school-<span class="hlt">type</span> identity has incremental <span class="hlt">predictive</span> power for scholastic motivation, over and above the effects of academic self-concept and school track.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140006399','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140006399"><span>CFD Analysis of Flexible Thermal Protection System <span class="hlt">Shear</span> Configuration Testing in the LCAT Facility</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Ferlemann, Paul G.</p> <p>2014-01-01</p> <p>This paper documents results of computational analysis performed after flexible thermal protection system <span class="hlt">shear</span> configuration testing in the LCAT facility. The primary objectives were to <span class="hlt">predict</span> the <span class="hlt">shear</span> force on the sample and the sensitivity of all surface properties to the shape of the sample. Bumps of 0.05, 0.10,and 0.15 inches were created to approximate the shape of some fabric samples during testing. A large amount of information was extracted from the CFD solutions for comparison between runs and also current or future flight simulations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27076352','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27076352"><span>Probe Oscillation <span class="hlt">Shear</span> Elastography (PROSE): A High Frame-Rate Method for Two-Dimensional Ultrasound <span class="hlt">Shear</span> Wave Elastography.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Mellema, Daniel C; Song, Pengfei; Kinnick, Randall R; Urban, Matthew W; Greenleaf, James F; Manduca, Armando; Chen, Shigao</p> <p>2016-09-01</p> <p>Ultrasound <span class="hlt">shear</span> wave elastography (SWE) utilizes the propagation of induced <span class="hlt">shear</span> waves to characterize the <span class="hlt">shear</span> modulus of soft tissue. Many methods rely on an acoustic radiation force (ARF) "push beam" to generate <span class="hlt">shear</span> waves. However, specialized hardware is required to generate the push beams, and the thermal stress that is placed upon the ultrasound system, transducer, and tissue by the push beams currently limits the frame-rate to about 1 Hz. These constraints have limited the implementation of ARF to high-end clinical systems. This paper presents Probe Oscillation <span class="hlt">Shear</span> Elastography (PROSE) as an alternative method to measure tissue elasticity. PROSE generates <span class="hlt">shear</span> waves using a harmonic mechanical vibration of an ultrasound transducer, while simultaneously detecting motion with the same transducer under pulse-echo mode. Motion of the transducer during detection produces a "strain-like" compression artifact that is coupled with the observed <span class="hlt">shear</span> waves. A novel symmetric sampling scheme is proposed such that pulse-echo detection events are acquired when the ultrasound transducer returns to the same physical position, allowing the <span class="hlt">shear</span> waves to be decoupled from the compression artifact. Full field-of-view (FOV) two-dimensional (2D) <span class="hlt">shear</span> wave speed images were obtained by applying a local frequency estimation (LFE) technique, capable of generating a 2D map from a single frame of <span class="hlt">shear</span> wave motion. The <span class="hlt">shear</span> wave imaging frame rate of PROSE is comparable to the vibration frequency, which can be an order of magnitude higher than ARF based techniques. PROSE was able to produce smooth and accurate <span class="hlt">shear</span> wave images from three homogeneous phantoms with different moduli, with an effective frame rate of 300 Hz. An inclusion phantom study showed that increased vibration frequencies improved the accuracy of inclusion imaging, and allowed targets as small as 6.5 mm to be resolved with good contrast (contrast-to-noise ratio ≥ 19 dB) between the target and</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_21 --> <div id="page_22" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="421"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5495143','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5495143"><span>Probe Oscillation <span class="hlt">Shear</span> Elastography (PROSE): A High Frame-Rate Method for Two-Dimensional Ultrasound <span class="hlt">Shear</span> Wave Elastography</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Mellema, Daniel C.; Song, Pengfei; Kinnick, Randall R.; Urban, Matthew W.; Greenleaf, James F.; Manduca, Armando; Chen, Shigao</p> <p>2017-01-01</p> <p>Ultrasound <span class="hlt">shear</span> wave elastography (SWE) utilizes the propagation of induced <span class="hlt">shear</span> waves to characterize the <span class="hlt">shear</span> modulus of soft tissue. Many methods rely on an acoustic radiation force (ARF) “push beam” to generate <span class="hlt">shear</span> waves. However, specialized hardware is required to generate the push beams, and the thermal stress that is placed upon the ultrasound system, transducer, and tissue by the push beams currently limits the frame-rate to about 1 Hz. These constraints have limited the implementation of ARF to high-end clinical systems. This paper presents Probe Oscillation <span class="hlt">Shear</span> Elastography (PROSE) as an alternative method to measure tissue elasticity. PROSE generates <span class="hlt">shear</span> waves using a harmonic mechanical vibration of an ultrasound transducer, while simultaneously detecting motion with the same transducer under pulse-echo mode. Motion of the transducer during detection produces a “strain-like” compression artifact that is coupled with the observed <span class="hlt">shear</span> waves. A novel symmetric sampling scheme is proposed such that pulse-echo detection events are acquired when the ultrasound transducer returns to the same physical position, allowing the <span class="hlt">shear</span> waves to be decoupled from the compression artifact. Full field-of-view (FOV) two-dimensional (2D) <span class="hlt">shear</span> wave speed images were obtained by applying a local frequency estimation (LFE) technique, capable of generating a 2D map from a single frame of <span class="hlt">shear</span> wave motion. The <span class="hlt">shear</span> wave imaging frame rate of PROSE is comparable to the vibration frequency, which can be an order of magnitude higher than ARF based techniques. PROSE was able to produce smooth and accurate <span class="hlt">shear</span> wave images from three homogeneous phantoms with different moduli, with an effective frame rate of 300Hz. An inclusion phantom study showed that increased vibration frequencies improved the accuracy of inclusion imaging, and allowed targets as small as 6.5 mm to be resolved with good contrast (contrast-to-noise ratio ≥19 dB) between the target and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70033017','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70033017"><span>Spatial correlation of <span class="hlt">shear</span>-wave velocity in the San Francisco Bay Area sediments</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Thompson, E.M.; Baise, L.G.; Kayen, R.E.</p> <p>2007-01-01</p> <p>Ground motions recorded within sedimentary basins are variable over short distances. One important cause of the variability is that local soil properties are variable at all scales. Regional hazard maps developed for <span class="hlt">predicting</span> site effects are generally derived from maps of surficial geology; however, recent studies have shown that mapped geologic units do not correlate well with the average <span class="hlt">shear</span>-wave velocity of the upper 30 m, Vs(30). We model the horizontal variability of near-surface soil <span class="hlt">shear</span>-wave velocity in the San Francisco Bay Area to estimate values in unsampled locations in order to account for site effects in a continuous manner. Previous geostatistical studies of soil properties have shown horizontal correlations at the scale of meters to tens of meters while the vertical correlations are on the order of centimeters. In this paper we analyze <span class="hlt">shear</span>-wave velocity data over regional distances and find that surface <span class="hlt">shear</span>-wave velocity is correlated at horizontal distances up to 4 km based on data from seismic cone penetration tests and the spectral analysis of surface waves. We propose a method to map site effects by using geostatistical methods based on the <span class="hlt">shear</span>-wave velocity correlation structure within a sedimentary basin. If used in conjunction with densely spaced <span class="hlt">shear</span>-wave velocity profiles in regions of high seismic risk, geostatistical methods can produce reliable continuous maps of site effects. ?? 2006 Elsevier Ltd. All rights reserved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/servlets/purl/674974','SCIGOV-STC'); return false;" href="https://www.osti.gov/servlets/purl/674974"><span>Characteristics of <span class="hlt">shear</span> damage for 60Sn-40Pb solder material</span></a></p> <p><a target="_blank" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Fang, H.E.; Chow, C.L.; Wei, Y.</p> <p></p> <p>This paper presents an investigation of the development of a continuum damage model capable of accurately analyzing <span class="hlt">shear</span> damage in 60Sn-40Pb solder material. Based on the theory of damage mechanics, an internal state variable known as the damage variable is introduced to characterize material degradation caused by the change of material microstructures under load. A damage surface in stress space is proposed to quantify damage initiation and its successive expanding surfaces to represent damage hardening. With the aid of irreversible thermodynamics, the damage-coupled constitutive equations and the damage evolution equations are established. A failure criterion is proposed based on themore » accumulation of overall damage in the material. The damage model is implemented in a general purpose finite element program ABAQUS through its user-defined material subroutine UMAT. The program is applied to <span class="hlt">predict</span> <span class="hlt">shear</span> deformation in a notched specimen. The <span class="hlt">predicted</span> failure mode and maximum load agree well with those measured experimentally. The effect of finite element meshing on the numerical results is also examined and discussed.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JPhCS.896a2098Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JPhCS.896a2098Y"><span>Blanking Method with Aid of Scrap to Reduce Tensile Residual Stress on <span class="hlt">Sheared</span> Edge</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yasutomi, T.; Yonemura, S.; Yoshida, T.; Mizumura, M.; Hiwatashi, S.</p> <p>2017-09-01</p> <p>A simple <span class="hlt">shearing</span> method to reduce tensile residual stress on a <span class="hlt">sheared</span> edge is highly desired in the automotive industry because this <span class="hlt">type</span> of stress deteriorates the fatigue property of automotive parts. In this study, the effect of a coining method with a <span class="hlt">shearing</span> scrap material on a <span class="hlt">sheared</span> edge was investigated. The scrap part of a <span class="hlt">sheared</span> plate has a fracture surface shape similar to that of the product part since these parts are generated by separation of a single plate with crack propagation. Therefore, it is possible to impose plastic strain over the entire fracture surface by using the scrap part as a coining tool. Effectiveness of this method was investigated for high-tensile-strength steel. Using this method, the tensile residual stress on the <span class="hlt">sheared</span> surface was significantly reduced and work hardening was slightly increased. The effects of <span class="hlt">shearing</span> clearance and coining stroke were also investigated. Tensile residual stress decreased as the coining stroke increased; however, it saturated at a certain stroke. The stroke at which tensile residual stress saturated was relatively small at a large clearance. In particular, the amount of plastic deformation on fracture surface increased when coining stroke became large. These tendencies could be explained by the conditions of contact, which were investigated using finite element analysis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20100033581','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20100033581"><span>True <span class="hlt">Shear</span> Parallel Plate Viscometer</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Ethridge, Edwin; Kaukler, William</p> <p>2010-01-01</p> <p>This viscometer (which can also be used as a rheometer) is designed for use with liquids over a large temperature range. The device consists of horizontally disposed, similarly sized, parallel plates with a precisely known gap. The lower plate is driven laterally with a motor to apply <span class="hlt">shear</span> to the liquid in the gap. The upper plate is freely suspended from a double-arm pendulum with a sufficiently long radius to reduce height variations during the swing to negligible levels. A sensitive load cell measures the <span class="hlt">shear</span> force applied by the liquid to the upper plate. Viscosity is measured by taking the ratio of <span class="hlt">shear</span> stress to <span class="hlt">shear</span> rate.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013APS..DFDR26004M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013APS..DFDR26004M"><span><span class="hlt">Shear</span> alters motility of Escherichia coli</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Molaei, Mehdi; Jalali, Maryam; Sheng, Jian</p> <p>2013-11-01</p> <p>Understanding of locomotion of microorganisms in <span class="hlt">shear</span> flows drew a wide range of interests in microbial related topics such as biological process including pathogenic infection and biophysical interactions like biofilm formation on engineering surfaces. We employed microfluidics and digital holography microscopy to study motility of E. coli in <span class="hlt">shear</span> flows. We controlled the <span class="hlt">shear</span> flow in three different <span class="hlt">shear</span> rates: 0.28 s-1, 2.8 s-1, and 28 s-1 in a straight channel with the depth of 200 μm. Magnified holograms, recorded at 15 fps with a CCD camera over more than 20 minutes, are analyzed to obtain 3D swimming trajectories and subsequently used to extract <span class="hlt">shear</span> responses of E.coli. Thousands of 3-D bacterial trajectories are tracked. The change of bacteria swimming characteristics including swimming velocity, reorientation, and dispersion coefficient are computed directly for individual trajectory and ensemble averaged over thousands of realizations. The results show that <span class="hlt">shear</span> suppresses the bacterial dispersions in bulk but promote dispersions near the surface contrary to those in quiescent flow condition. Ongoing analyses are focusing to quantify effect of <span class="hlt">shear</span> rates on tumbling frequency and reorientation of cell body, and its implication in locating the hydrodynamic mechanisms for <span class="hlt">shear</span> enhanced angular scattering. NIH, NSF, GoMRI.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23825112','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23825112"><span><span class="hlt">Prediction</span> of fracture healing under axial loading, <span class="hlt">shear</span> loading and bending is possible using distortional and dilatational strains as determining mechanical stimuli.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Steiner, Malte; Claes, Lutz; Ignatius, Anita; Niemeyer, Frank; Simon, Ulrich; Wehner, Tim</p> <p>2013-09-06</p> <p>Numerical models of secondary fracture healing are based on mechanoregulatory algorithms that use distortional strain alone or in combination with either dilatational strain or fluid velocity as determining stimuli for tissue differentiation and development. Comparison of these algorithms has previously suggested that healing processes under torsional rotational loading can only be properly simulated by considering fluid velocity and deviatoric strain as the regulatory stimuli. We hypothesize that sufficient calibration on uncertain input parameters will enhance our existing model, which uses distortional and dilatational strains as determining stimuli, to properly simulate fracture healing under various loading conditions including also torsional rotation. Therefore, we minimized the difference between numerically simulated and experimentally measured courses of interfragmentary movements of two axial compressive cases and two <span class="hlt">shear</span> load cases (torsional and translational) by varying several input parameter values within their predefined bounds. The calibrated model was then qualitatively evaluated on the ability to <span class="hlt">predict</span> physiological changes of spatial and temporal tissue distributions, based on respective in vivo data. Finally, we corroborated the model on five additional axial compressive and one asymmetrical bending load case. We conclude that our model, using distortional and dilatational strains as determining stimuli, is able to simulate fracture-healing processes not only under axial compression and torsional rotation but also under translational <span class="hlt">shear</span> and asymmetrical bending loading conditions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/biblio/22391682-study-shear-strengthening-rc-continuous-beams-using-different-layers-cfrp-strips','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/22391682-study-shear-strengthening-rc-continuous-beams-using-different-layers-cfrp-strips"><span>Study on <span class="hlt">shear</span> strengthening of RC continuous T-beams using different layers of CFRP strips</span></a></p> <p><a target="_blank" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Alferjani, M. B. S.; Samad, A. A. Abdul; Mohamad, Noridah</p> <p>2015-05-15</p> <p>Carbon fiber reinforced polymer (CFRP) laminates are externally bonded to reinforced concrete (RC) members to provide additional strength such as flexural, <span class="hlt">shear</span>, etc. However, this paper presents the results of an experimental investigation for enhancing the <span class="hlt">shear</span> capacity of reinforced concrete (RC) continuous T- beams using different layers of CFRP wrapping schemes. A total of three concrete beams were tested and various sheet configurations and layouts were studied to determine their effects on ultimate <span class="hlt">shear</span> strength and <span class="hlt">shear</span> capacity of the beams. One beam was kept as control beams, while other beams were strengthened with externally bonded CFRP strips withmore » three side bonding and one or two layers of CFRP strips. From the test results, it was found that all schemes were found to be effective in enhancing the <span class="hlt">shear</span> strength of RC beams. It was observed that the strength increases with the number of sheet layers provided the most effective strengthening for RC continuous T- beam. Beam strengthened using this scheme showed 23.21% increase in <span class="hlt">shear</span> capacity as compared to the control beam. Two <span class="hlt">prediction</span> models available in literature were used for computing the contribution of CFRP strips and compared with the experimental results.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19910043323&hterms=group+theory&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dgroup%2Btheory','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19910043323&hterms=group+theory&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dgroup%2Btheory"><span>Renormalization group analysis of anisotropic diffusion in turbulent <span class="hlt">shear</span> flows</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Rubinstein, Robert; Barton, J. Michael</p> <p>1991-01-01</p> <p>The renormalization group is applied to compute anisotropic corrections to the scalar eddy diffusivity representation of turbulent diffusion of a passive scalar. The corrections are linear in the mean velocity gradients. All model constants are computed theoretically. A form of the theory valid at arbitrary Reynolds number is derived. The theory applies only when convection of the velocity-scalar correlation can be neglected. A ratio of diffusivity components, found experimentally to have a nearly constant value in a variety of <span class="hlt">shear</span> flows, is computed theoretically for flows in a certain state of equilibrium. The theoretical value is well within the fairly narrow range of experimentally observed values. Theoretical <span class="hlt">predictions</span> of this diffusivity ratio are also compared with data from experiments and direct numerical simulations of homogeneous <span class="hlt">shear</span> flows with constant velocity and scalar gradients.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/12563690','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/12563690"><span>Intermittent hydrostatic pressure inhibits <span class="hlt">shear</span> stress-induced nitric oxide release in human osteoarthritic chondrocytes in vitro.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Lee, Mel S; Trindade, Michael C D; Ikenoue, Takashi; Schurman, David J; Goodman, Stuart B; Smith, R Lane</p> <p>2003-02-01</p> <p>To test the effects of intermittent hydrostatic pressure (IHP) on nitric oxide (NO) release induced by <span class="hlt">shear</span> stress and matrix macromolecule gene expression in human osteoarthritic chondrocytes in vitro. Chondrocytes isolated from cartilage samples from 9 patients with osteoarthritis were cultured and exposed to either <span class="hlt">shear</span> stress or an NO donor. Nitrite concentration was measured using the Griess reaction. Matrix macromolecule mRNA signal levels were determined using reverse-transcriptase polymerase chain reaction and quantified by imaging analysis software. Exposure to <span class="hlt">shear</span> stress upregulated NO release in a dose and time-dependent manner. Application of IHP inhibited <span class="hlt">shear</span> stress induced NO release but did not alter NO release from chondrocytes not exposed to <span class="hlt">shear</span> stress. <span class="hlt">Shear</span> stress induced NO or addition of an NO donor (sodium nitroprusside) was associated with decreased mRNA signal levels for the cartilage matrix proteins, aggrecan, and <span class="hlt">type</span> II collagen. Intermittent hydrostatic pressure blocked the inhibitory effects of sodium nitroprusside but did not alter the inhibitory effects of <span class="hlt">shear</span> stress on cartilage macromolecule gene expression. Our data show that <span class="hlt">shear</span> stress and IHP differentially alter chondrocyte metabolism and suggest that a balance of effects between different loading forces preserve cartilage extracellular matrix in vivo.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3046449','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3046449"><span>Quantitative <span class="hlt">shear</span> wave ultrasound elastography: initial experience in solid breast masses</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p></p> <p>2010-01-01</p> <p> wave elastography versus greyscale BI-RADS performance figures were sensitivity: 97% vs 87%, specificity: 83% vs 78%, positive <span class="hlt">predictive</span> value (PPV): 88% vs 84%, negative <span class="hlt">predictive</span> value (NPV): 95% vs 82% and accuracy: 91% vs 83% respectively. These differences were not statistically significant. Conclusions <span class="hlt">Shear</span> wave elastography gives quantitative and reproducible information on solid breast lesions with diagnostic accuracy at least as good as greyscale ultrasound with BI-RADS classification. PMID:21122101</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21122101','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21122101"><span>Quantitative <span class="hlt">shear</span> wave ultrasound elastography: initial experience in solid breast masses.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Evans, Andrew; Whelehan, Patsy; Thomson, Kim; McLean, Denis; Brauer, Katrin; Purdie, Colin; Jordan, Lee; Baker, Lee; Thompson, Alastair</p> <p>2010-01-01</p> <p> greyscale BI-RADS performance figures were sensitivity: 97% vs 87%, specificity: 83% vs 78%, positive <span class="hlt">predictive</span> value (PPV): 88% vs 84%, negative <span class="hlt">predictive</span> value (NPV): 95% vs 82% and accuracy: 91% vs 83% respectively. These differences were not statistically significant. <span class="hlt">Shear</span> wave elastography gives quantitative and reproducible information on solid breast lesions with diagnostic accuracy at least as good as greyscale ultrasound with BI-RADS classification.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23004740','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23004740"><span>Nanoscale simple-fluid behavior under steady <span class="hlt">shear</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Yong, Xin; Zhang, Lucy T</p> <p>2012-05-01</p> <p>In this study, we use two nonequilibrium molecular dynamics algorithms, boundary-driven <span class="hlt">shear</span> and homogeneous <span class="hlt">shear</span>, to explore the rheology and flow properties of a simple fluid undergoing steady simple <span class="hlt">shear</span>. The two distinct algorithms are designed to elucidate the influences of nanoscale confinement. The results of rheological material functions, i.e., viscosity and normal pressure differences, show consistent Newtonian behaviors at low <span class="hlt">shear</span> rates from both systems. The comparison validates that confinements of the order of 10 nm are not strong enough to deviate the simple fluid behaviors from the continuum hydrodynamics. The non-Newtonian phenomena of the simple fluid are further investigated by the homogeneous <span class="hlt">shear</span> simulations with much higher <span class="hlt">shear</span> rates. We observe the "string phase" at high <span class="hlt">shear</span> rates by applying both profile-biased and profile-unbiased thermostats. Contrary to other findings where the string phase is found to be an artifact of the thermostats, we perform a thorough analysis of the fluid microstructures formed due to <span class="hlt">shear</span>, which shows that it is possible to have a string phase and second <span class="hlt">shear</span> thinning for dense simple fluids.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3475422','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3475422"><span>Comb-push Ultrasound <span class="hlt">Shear</span> Elastography (CUSE): A Novel Method for Two-dimensional <span class="hlt">Shear</span> Elasticity Imaging of Soft Tissues</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Song, Pengfei; Zhao, Heng; Manduca, Armando; Urban, Matthew W.; Greenleaf, James F.; Chen, Shigao</p> <p>2012-01-01</p> <p>Fast and accurate tissue elasticity imaging is essential in studying dynamic tissue mechanical properties. Various ultrasound <span class="hlt">shear</span> elasticity imaging techniques have been developed in the last two decades. However, to reconstruct a full field-of-view 2D <span class="hlt">shear</span> elasticity map, multiple data acquisitions are typically required. In this paper, a novel <span class="hlt">shear</span> elasticity imaging technique, comb-push ultrasound <span class="hlt">shear</span> elastography (CUSE), is introduced in which only one rapid data acquisition (less than 35 ms) is needed to reconstruct a full field-of-view 2D <span class="hlt">shear</span> wave speed map (40 mm × 38 mm). Multiple unfocused ultrasound beams arranged in a comb pattern (comb-push) are used to generate <span class="hlt">shear</span> waves. A directional filter is then applied upon the <span class="hlt">shear</span> wave field to extract the left-to-right (LR) and right-to-left (RL) propagating <span class="hlt">shear</span> waves. Local <span class="hlt">shear</span> wave speed is recovered using a time-of-flight method based on both LR and RL waves. Finally a 2D <span class="hlt">shear</span> wave speed map is reconstructed by combining the LR and RL speed maps. Smooth and accurate <span class="hlt">shear</span> wave speed maps are reconstructed using the proposed CUSE method in two calibrated homogeneous phantoms with different moduli. Inclusion phantom experiments demonstrate that CUSE is capable of providing good contrast (contrast-to-noise-ratio ≥ 25 dB) between the inclusion and background without artifacts and is insensitive to inclusion positions. Safety measurements demonstrate that all regulated parameters of the ultrasound output level used in CUSE sequence are well below the FDA limits for diagnostic ultrasound. PMID:22736690</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018RScI...89d5107M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018RScI...89d5107M"><span>Design and implementation of a <span class="hlt">shearing</span> apparatus for the experimental study of <span class="hlt">shear</span> displacement in rocks</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Moore, Johnathan; Crandall, Dustin; Gill, Magdalena; Brown, Sarah; Tennant, Bryan</p> <p>2018-04-01</p> <p>Fluid flow in the subsurface is not well understood in the context of "impermeable" geologic media. This is especially true of formations that have undergone significant stress fluctuations due to injection or withdrawal of fluids that alters the localized pressure regime. When the pressure regime is altered, these formations, which are often already fractured, move via <span class="hlt">shear</span> to reduce the imbalance in the stress state. While this process is known to happen, the evolution of these fractures and their effects on fluid transport are still relatively unknown. Numerous simulation and several experimental studies have been performed that characterize the relationship between <span class="hlt">shearing</span> and permeability in fractures; while many of these studies utilize measurements of fluid flow or the starting and ending geometries of the fracture to characterize <span class="hlt">shear</span>, they do not characterize the intermediate stages during <span class="hlt">shear</span>. We present an experimental apparatus based on slight modifications to a commonly available Hassler core holder that allows for <span class="hlt">shearing</span> of rocks, while measuring the hydraulic and mechanical changes to geomaterials during intermediate steps. The core holder modification employs the use of semi-circular end caps and structural supports for the confining membrane that allow for free movement of the <span class="hlt">sheared</span> material while preventing membrane collapse. By integrating this modified core holder with a computed tomography scanner, we show a new methodology for understanding the interdependent behavior between fracture structure and flow properties during intermediate steps in <span class="hlt">shearing</span>. We include a case study of this device function which is shown here through <span class="hlt">shearing</span> of a fractured shale core and simultaneous observation of the mechanical changes and evolution of the hydraulic properties during <span class="hlt">shearing</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29716362','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29716362"><span>Design and implementation of a <span class="hlt">shearing</span> apparatus for the experimental study of <span class="hlt">shear</span> displacement in rocks.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Moore, Johnathan; Crandall, Dustin; Gill, Magdalena; Brown, Sarah; Tennant, Bryan</p> <p>2018-04-01</p> <p>Fluid flow in the subsurface is not well understood in the context of "impermeable" geologic media. This is especially true of formations that have undergone significant stress fluctuations due to injection or withdrawal of fluids that alters the localized pressure regime. When the pressure regime is altered, these formations, which are often already fractured, move via <span class="hlt">shear</span> to reduce the imbalance in the stress state. While this process is known to happen, the evolution of these fractures and their effects on fluid transport are still relatively unknown. Numerous simulation and several experimental studies have been performed that characterize the relationship between <span class="hlt">shearing</span> and permeability in fractures; while many of these studies utilize measurements of fluid flow or the starting and ending geometries of the fracture to characterize <span class="hlt">shear</span>, they do not characterize the intermediate stages during <span class="hlt">shear</span>. We present an experimental apparatus based on slight modifications to a commonly available Hassler core holder that allows for <span class="hlt">shearing</span> of rocks, while measuring the hydraulic and mechanical changes to geomaterials during intermediate steps. The core holder modification employs the use of semi-circular end caps and structural supports for the confining membrane that allow for free movement of the <span class="hlt">sheared</span> material while preventing membrane collapse. By integrating this modified core holder with a computed tomography scanner, we show a new methodology for understanding the interdependent behavior between fracture structure and flow properties during intermediate steps in <span class="hlt">shearing</span>. We include a case study of this device function which is shown here through <span class="hlt">shearing</span> of a fractured shale core and simultaneous observation of the mechanical changes and evolution of the hydraulic properties during <span class="hlt">shearing</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22948939','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22948939"><span>The role of mentor <span class="hlt">type</span> and timing in <span class="hlt">predicting</span> educational attainment.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Fruiht, Veronica M; Wray-Lake, Laura</p> <p>2013-09-01</p> <p>Having an adult mentor during adolescence has been found to <span class="hlt">predict</span> academic success. Building on previous work, the present study examined interactions between the <span class="hlt">type</span> of mentor (i.e., kin, teacher, friend, or community), the time that mentor became important (i.e., before, during, or after high school), and the ethnicity of the protégé in <span class="hlt">predicting</span> educational attainment in young adulthood. Analyses used Waves III and IV of the National Longitudinal Study of Adolescent Health (N = 2,409). Participants' ages ranged from 18 to 27 (M = 21.75, SD = 1.79). The sample was 56.7 % female and nationally representative of ethnic diversity. Analyses showed that having a teacher-mentor was more <span class="hlt">predictive</span> of educational attainment than having other <span class="hlt">types</span> of mentors and that overall, having a mentor after high school <span class="hlt">predicts</span> the most educational attainment. Kin- and community-mentors appeared to be more important to educational attainment during and before high school, respectively. Findings were consistent across ethnic groups. Overall, results highlight the value of teacher-mentors throughout childhood, adolescence, and early adulthood and our study further suggests that different <span class="hlt">types</span> of mentors may be particularly useful at specific points in development.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/16906816','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/16906816"><span><span class="hlt">Shear</span>-induced crystallization of a dense rapid granular flow: hydrodynamics beyond the melting point.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Khain, Evgeniy; Meerson, Baruch</p> <p>2006-06-01</p> <p>We investigate <span class="hlt">shear</span>-induced crystallization in a very dense flow of monodisperse inelastic hard spheres. We consider a steady plane Couette flow under constant pressure and neglect gravity. We assume that the granular density is greater than the melting point of the equilibrium phase diagram of elastic hard spheres. We employ a Navier-Stokes hydrodynamics with constitutive relations all of which (except the <span class="hlt">shear</span> viscosity) diverge at the crystal-packing density, while the <span class="hlt">shear</span> viscosity diverges at a smaller density. The phase diagram of the steady flow is described by three parameters: an effective Mach number, a scaled energy loss parameter, and an integer number m: the number of half-oscillations in a mechanical analogy that appears in this problem. In a steady <span class="hlt">shear</span> flow the viscous heating is balanced by energy dissipation via inelastic collisions. This balance can have different forms, producing either a uniform <span class="hlt">shear</span> flow or a variety of more complicated, nonlinear density, velocity, and temperature profiles. In particular, the model <span class="hlt">predicts</span> a variety of multilayer two-phase steady <span class="hlt">shear</span> flows with sharp interphase boundaries. Such a flow may include a few zero-<span class="hlt">shear</span> (solidlike) layers, each of which moving as a whole, separated by fluidlike regions. As we are dealing with a hard sphere model, the granulate is fluidized within the "solid" layers: the granular temperature is nonzero there, and there is energy flow through the boundaries of the solid layers. A linear stability analysis of the uniform steady <span class="hlt">shear</span> flow is performed, and a plausible bifurcation diagram of the system, for a fixed m, is suggested. The problem of selection of m remains open.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29485877','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29485877"><span>Gas Hydrate Formation Probability Distributions: The Effect of <span class="hlt">Shear</span> and Comparisons with Nucleation Theory.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>May, Eric F; Lim, Vincent W; Metaxas, Peter J; Du, Jianwei; Stanwix, Paul L; Rowland, Darren; Johns, Michael L; Haandrikman, Gert; Crosby, Daniel; Aman, Zachary M</p> <p>2018-03-13</p> <p>Gas hydrate formation is a stochastic phenomenon of considerable significance for any risk-based approach to flow assurance in the oil and gas industry. In principle, well-established results from nucleation theory offer the prospect of <span class="hlt">predictive</span> models for hydrate formation probability in industrial production systems. In practice, however, heuristics are relied on when estimating formation risk for a given flowline subcooling or when quantifying kinetic hydrate inhibitor (KHI) performance. Here, we present statistically significant measurements of formation probability distributions for natural gas hydrate systems under <span class="hlt">shear</span>, which are quantitatively compared with theoretical <span class="hlt">predictions</span>. Distributions with over 100 points were generated using low-mass, Peltier-cooled pressure cells, cycled in temperature between 40 and -5 °C at up to 2 K·min -1 and analyzed with robust algorithms that automatically identify hydrate formation and initial growth rates from dynamic pressure data. The application of <span class="hlt">shear</span> had a significant influence on the measured distributions: at 700 rpm mass-transfer limitations were minimal, as demonstrated by the kinetic growth rates observed. The formation probability distributions measured at this <span class="hlt">shear</span> rate had mean subcoolings consistent with theoretical <span class="hlt">predictions</span> and steel-hydrate-water contact angles of 14-26°. However, the experimental distributions were substantially wider than <span class="hlt">predicted</span>, suggesting that phenomena acting on macroscopic length scales are responsible for much of the observed stochastic formation. Performance tests of a KHI provided new insights into how such chemicals can reduce the risk of hydrate blockage in flowlines. Our data demonstrate that the KHI not only reduces the probability of formation (by both shifting and sharpening the distribution) but also reduces hydrate growth rates by a factor of 2.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3685199','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3685199"><span>Cross-<span class="hlt">Shear</span> in Metal-on-Polyethylene Articulation of Orthopaedic Implants and its Relationship to Wear</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Schwenke, T.; Wimmer, M. A.</p> <p>2013-01-01</p> <p>Wear of polyethylene (UHMWPE) is dependent on cross-<span class="hlt">shear</span>. The aim of the present study was: 1) to develop a theoretical description of cross-<span class="hlt">shear</span>, 2) to experimentally determine the relationship between cross-<span class="hlt">shear</span> motion and UHMWPE wear using a wheel-on-flat apparatus, and 3) to calculate the work it takes to remove a unit volume of wear for the use in advanced computational models of wear. The theoretical description of cross-<span class="hlt">shear</span> has been based on the previously reported finding that cross-<span class="hlt">shear</span> is maximal when movement occurs perpendicular to fibril orientation. Here, cross-<span class="hlt">shear</span> is described with a double-sinusoidal function that uses the angle between fibril orientation and velocity vector as input, and maximum cross-<span class="hlt">shear</span> occurs at 90° and 270°. In the experimental part of the study, friction and wear of polyethylene were plotted against increasing sliding velocity vector angles, i.e. increasing cross-<span class="hlt">shear</span>. It was found that wear intensified with increasing cross-<span class="hlt">shear</span>, and wear depth could be <span class="hlt">predicted</span> well using the double-sinusoidal function for cross-<span class="hlt">shear</span> (r2=0.983). The friction data were then used to calculate the work to remove a unit particle by integrating the frictional force over the directional sliding distance. Using the wear volumes, determined for both longitudinal and perpendicular motion directions, the work to remove a unit volume of material was qy= 8.473 × 108 J/mm3 and qx= 1.321 × 108 J/mm3, respectively. Hence, 6.4 times more work was necessary to remove a unit wear volume in the direction of principal motion (i.e. along the molecular fibril orientation) than 90° perpendicular to it. In the future, these findings will be implemented in computational models to assess wear. PMID:23794761</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_22 --> <div id="page_23" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="441"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018CMT....30..291A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018CMT....30..291A"><span>General stability of memory-<span class="hlt">type</span> thermoelastic Timoshenko beam acting on <span class="hlt">shear</span> force</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Apalara, Tijani A.</p> <p>2018-03-01</p> <p>In this paper, we consider a linear thermoelastic Timoshenko system with memory effects where the thermoelastic coupling is acting on <span class="hlt">shear</span> force under Neumann-Dirichlet-Dirichlet boundary conditions. The same system with fully Dirichlet boundary conditions was considered by Messaoudi and Fareh (Nonlinear Anal TMA 74(18):6895-6906, 2011, Acta Math Sci 33(1):23-40, 2013), but they obtained a general stability result which depends on the speeds of wave propagation. In our case, we obtained a general stability result irrespective of the wave speeds of the system.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22417431','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22417431"><span>Online <span class="hlt">shear</span> viscosity measurement of starchy melts enriched in wheat bran.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Robin, Frédéric; Bovet, Nicolas; Pineau, Nicolas; Schuchmann, Heike P; Palzer, Stefan</p> <p>2011-01-01</p> <p>Addition of wheat bran to flours modifies their expansion properties after cooking extrusion. This can be attributed to changes in the melt <span class="hlt">shear</span> viscosity at the die. The effect of wheat bran concentration added to achieve 2 levels of dietary fibers of 12. 6% and 24.4%, and process conditions on the <span class="hlt">shear</span> viscosity of wheat flour was therefore assessed using an online twin-slit rheometer. The <span class="hlt">shear</span> viscosity measured at 30 s⁻¹ ranged from 9.5 × 10³ to 53.4 × 10³ Pa s. Regardless of the process conditions and bran concentration, the extruded melts showed a pseudoplastic behavior with a power law index n ranging from 0.05 to 0.27. Increasing the barrel temperature of the extruder from 120 to 180 °C, the water content from 18% to 22% or the screw speed from 400 to 800 rpm significantly decreased the melt <span class="hlt">shear</span> viscosity at the extruder exit. The addition of bran significantly increased the melt <span class="hlt">shear</span> viscosity only at the highest bran concentration. The effect was process condition dependant. Mathematical interpretations, based upon observations, of the experimental data were carried out. They can be used to <span class="hlt">predict</span> the effect of the process conditions on the melt <span class="hlt">shear</span> viscosity at the die of extruded wheat flour with increasing bran concentration. The viscosity data will be applied in future works to study the expansion properties of extruded wheat flour supplemented with bran. Incorporation of wheat bran, a readily available and low cost by-product, in extruded puffed foods is constrained due to its negative effect on the product texture. Understanding the effect of wheat bran on rheological properties of extruded melts, driving the final product properties, is essential to provide solutions to the food industry and enhance its use. © 2011 Institute of Food Technologists®</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016APS..DPPCI3003S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016APS..DPPCI3003S"><span>Increasing Plasma Parameters using <span class="hlt">Sheared</span> Flow Stabilization of a Z-Pinch</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shumlak, Uri</p> <p>2016-10-01</p> <p>Recent experiments on the ZaP Flow Z-Pinch at the University of Washington have been successful in compressing the plasma column to smaller radii, producing the <span class="hlt">predicted</span> increases in plasma density (1018 cm-3), temperature (200 eV), and magnetic fields (4 T), while maintaining plasma stability for many Alfven times (over 40 μs) using <span class="hlt">sheared</span> plasma flows. These results indicate the suitability of the device as a discovery science platform for astrophysical and high energy density plasma research, and keeps open a possible path to achieving burning plasma conditions in a compact fusion device. Long-lived Z-pinch plasmas have been produced with dimensions of 1 cm radius and 100 cm long that are stabilized by <span class="hlt">sheared</span> axial flows for over 1000 Alfven radial transit times. The observed plasma stability is coincident with the presence of a <span class="hlt">sheared</span> flow as measured by time-resolved multi-chord ion Doppler spectroscopy applied to impurity ion radiation. These measurements yield insights into the evolution of the velocity profile and show that the stabilizing behavior of flow <span class="hlt">shear</span> agrees with theoretical calculations and 2-D MHD computational simulations. The flow <span class="hlt">shear</span> value, extent, and duration are shown to be consistent with theoretical models of the plasma viscosity, which places a design constraint on the maximum axial length of a <span class="hlt">sheared</span> flow stabilized Z-pinch. Measurements of the magnetic field topology indicate simultaneous azimuthal symmetry and axial uniformity along the entire 100 cm length of the Z-pinch plasma. Separate control of plasma acceleration and compression have increased the accessible plasma parameters and have generated stable plasmas with radii below 0.5 cm, as measured with a high resolution digital holographic interferometer. This work was supported by Grants from U.S. DOE, NNSA, and ARPA-E.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28788495','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28788495"><span>Effects of Particle Size on the <span class="hlt">Shear</span> Behavior of Coarse Grained Soils Reinforced with Geogrid.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kim, Daehyeon; Ha, Sungwoo</p> <p>2014-02-07</p> <p>In order to design civil structures that are supported by soils, the <span class="hlt">shear</span> strength parameters of soils are required. Due to the large particle size of coarse-grained soils, large direct <span class="hlt">shear</span> tests should be performed. In this study, large direct <span class="hlt">shear</span> tests on three <span class="hlt">types</span> of coarse grained soils (4.5 mm, 7.9 mm, and 15.9 mm) were performed to evaluate the effects of particle size on the <span class="hlt">shear</span> behavior of coarse grained soils with/without geogrid reinforcements. Based on the direct <span class="hlt">shear</span> test results, it was found that, in the case of no-reinforcement, the larger the maximum particle size became, the larger the friction angle was. Compared with the no-reinforcement case, the cases reinforced with either soft geogrid or stiff geogrid have smaller friction angles. The cohesion of the soil reinforced with stiff geogrid was larger than that of the soil reinforced with soft geogrid. The difference in the <span class="hlt">shear</span> strength occurs because the case with a stiff geogrid has more soil to geogrid contact area, leading to the reduction in interlocking between soil particles.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24827245','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24827245"><span>Microstructural evolution of a model, <span class="hlt">shear</span>-banding micellar solution during <span class="hlt">shear</span> startup and cessation.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>López-Barrón, Carlos R; Gurnon, A Kate; Eberle, Aaron P R; Porcar, Lionel; Wagner, Norman J</p> <p>2014-04-01</p> <p>We present direct measurements of the evolution of the segmental-level microstructure of a stable <span class="hlt">shear</span>-banding polymerlike micelle solution during flow startup and cessation in the plane of flow. These measurements provide a definitive, quantitative microstructural understanding of the stages observed during flow startup: an initial elastic response with limited alignment that yields with a large stress overshoot to a homogeneous flow with associated micellar alignment that persists for approximately three relaxation times. This transient is followed by a <span class="hlt">shear</span> (kink) band formation with a flow-aligned low-viscosity band that exhibits <span class="hlt">shear</span>-induced concentration fluctuations and coexists with a nearly isotropic band of homogenous, highly viscoelastic micellar solution. Stable, steady banding flow is achieved only after approximately two reptation times. Flow cessation from this <span class="hlt">shear</span>-banded state is also found to be nontrivial, exhibiting an initial fast relaxation with only minor structural relaxation, followed by a slower relaxation of the aligned micellar fluid with the equilibrium fluid's characteristic relaxation time. These measurements resolve a controversy in the literature surrounding the mechanism of <span class="hlt">shear</span> banding in entangled wormlike micelles and, by means of comparison to existing literature, provide further insights into the mechanisms driving <span class="hlt">shear</span>-banding instabilities in related systems. The methods and instrumentation described should find broad use in exploring complex fluid rheology and testing microstructure-based constitutive equations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004JTurb...5...33B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004JTurb...5...33B"><span>A second-order modelling of a stably stratified <span class="hlt">sheared</span> turbulence submitted to a non-vertical <span class="hlt">shear</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bouzaiane, Mounir; Ben Abdallah, Hichem; Lili, Taieb</p> <p>2004-09-01</p> <p>In this work, the evolution of homogeneous stably stratified turbulence submitted to a non-vertical <span class="hlt">shear</span> is studied using second-order closure models. Two cases of turbulent flows are considered. Firstly, the case of a purely horizontal <span class="hlt">shear</span> is considered. In this case, the evolution of the turbulence is studied according to the Richardson number Ri which is varied from 0.2 to 2.0 when other parameters are kept constant. In the second case, two components of <span class="hlt">shear</span> are present. The turbulence is submitted to a vertical component Sv = partU1/partx3 = S cos(thgr) and a horizontal component Sh = partU1/partx2 = S sin(thgr). In this case, we study the influence of <span class="hlt">shear</span> inclination angle thgr on the evolution of turbulence. In both cases, we are referred respectively to the recent direct numerical simulations of Jacobitz (2002 J. Turbulence 3 055) and Jacobitz and Sarkar (1998 Phys. Fluids 10 1158-68) which are, to our knowledge, the most recent results of the above-mentioned flows. Transport equations of second-order moments \\overline{u_{i} u_{j}} , \\overline{u_{i} \\rho } , \\overline{\\rho^{2}} are derived. The Shih-Lumley (SL) (Shih T H 1996 Turbulence Transition and Modeling ed H D S Henningson, A V Johansson and P H Alfredsson (Dordrecht: Kluwer); Shih and Lumley J L 1989 27th Aerospace Meeting 9-12 January, Center of Turbulent Research, Nevada) and the Craft-Launder (CL) (Craft T J and Launder B E 1989 Turbulent <span class="hlt">Shear</span> Flow Stanford University, USA, pp 12-1-12-6 Launder B E 1996 Turbulence Transition and Modeling ed H D S Henningson, A V Johansson and P H Alfredsson (Dordrecht: Kluwer)) second-order models are retained for the pressure-strain correlation phgrij and the pressure-scalar gradient correlation phgrirgr. The corresponding models are also retained for the dissipation egr of the turbulent kinetic energy and an algebraic model is retained for the dissipation egrrgrrgr of the variance of the scalar. A fourth-order Runge-Kutta method is used for the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/servlets/purl/1247999','SCIGOV-STC'); return false;" href="https://www.osti.gov/servlets/purl/1247999"><span>Inductive <span class="hlt">shearing</span> of drilling pipe</span></a></p> <p><a target="_blank" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Ludtka, Gerard M.; Wilgen, John; Kisner, Roger</p> <p></p> <p>Induction <span class="hlt">shearing</span> may be used to cut a drillpipe at an undersea well. Electromagnetic rings may be built into a blow-out preventer (BOP) at the seafloor. The electromagnetic rings create a magnetic field through the drillpipe and may transfer sufficient energy to change the state of the metal drillpipe to <span class="hlt">shear</span> the drillpipe. After <span class="hlt">shearing</span> the drillpipe, the drillpipe may be sealed to prevent further leakage of well contents.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014APS..DFDA23003K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014APS..DFDA23003K"><span>Turbulence and mixing from optimal perturbations to a stratified <span class="hlt">shear</span> layer</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kaminski, Alexis; Caulfield, C. P.; Taylor, John</p> <p>2014-11-01</p> <p>The stability and mixing of stratified <span class="hlt">shear</span> layers is a canonical problem in fluid dynamics with relevance to flows in the ocean and atmosphere. The Miles-Howard theorem states that a necessary condition for normal-mode instability in parallel, inviscid, steady stratified <span class="hlt">shear</span> flows is that the gradient Richardson number, Rig is less than 1/4 somewhere in the flow. However, substantial transient growth of non-normal modes may be possible at finite times even when Rig > 1 / 4 everywhere in the flow. We have calculated the ``optimal perturbations'' associated with maximum perturbation energy gain for a stably-stratified <span class="hlt">shear</span> layer. These optimal perturbations are then used to initialize direct numerical simulations. For small but finite perturbation amplitudes, the optimal perturbations grow at the <span class="hlt">predicted</span> linear rate initially, but then experience sufficient transient growth to become nonlinear and susceptible to secondary instabilities, which then break down into turbulence. Remarkably, this occurs even in flows for which Rig > 1 / 4 everywhere. We will describe the nonlinear evolution of the optimal perturbations and characterize the resulting turbulence and mixing.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19850021120','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19850021120"><span>Contributions on the Subject of Longitudinal Movements of Aircraft in Wind <span class="hlt">Shears</span>. Ph.D. Thesis - Technischen Univ., 1983</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Krauspe, P.</p> <p>1985-01-01</p> <p>The effect of downburst-<span class="hlt">type</span> wind <span class="hlt">shears</span> on the longitudinal dynamic behavior of an unguided aircraft is simulated numerically on the basis of published meteorological data and the flight characteristics of an A300-B passenger jet. The nonlinear differential equations of the aircraft motion are linearized by conventional methods, and the wind effects are introduced via the linear derivatives of the wind components referred to the wind gradients to obtain simplified technical models of the longitudinal response to all possible <span class="hlt">types</span> of constant-gradient wind <span class="hlt">shears</span> during the first 20-60 sec. Graphs, maps, and diagrams are provided, and a number of accidents presumed to have involved wind <span class="hlt">shears</span> are analyzed in detail.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1984PhRvA..30.1465D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1984PhRvA..30.1465D"><span>Diffusion in <span class="hlt">shear</span> flow</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dufty, J. W.</p> <p>1984-09-01</p> <p>Diffusion of a tagged particle in a fluid with uniform <span class="hlt">shear</span> flow is described. The continuity equation for the probability density describing the position of the tagged particle is considered. The diffusion tensor is identified by expanding the irreversible part of the probability current to first order in the gradient of the probability density, but with no restriction on the <span class="hlt">shear</span> rate. The tensor is expressed as the time integral of a nonequilibrium autocorrelation function for the velocity of the tagged particle in its local fluid rest frame, generalizing the Green-Kubo expression to the nonequilibrium state. The tensor is evaluated from results obtained previously for the velocity autocorrelation function that are exact for Maxwell molecules in the Boltzmann limit. The effects of viscous heating are included and the dependence on frequency and <span class="hlt">shear</span> rate is displayed explicitly. The mode-coupling contributions to the frequency and <span class="hlt">shear</span>-rate dependent diffusion tensor are calculated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008APS..DFD.GS003B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008APS..DFD.GS003B"><span>A dynamic jamming point for <span class="hlt">shear</span> thickening suspensions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Brown, Eric; Jaeger, Heinrich</p> <p>2008-11-01</p> <p>Densely packed suspensions can <span class="hlt">shear</span> thicken, in which the viscosity increases with <span class="hlt">shear</span> rate. We performed rheometry measurements on two model systems: corn starch in water and glass spheres in oils. In both systems we observed <span class="hlt">shear</span> thickening up to a critical packing fraction φc (=0.55 for spherical grains) above which the flow abruptly transitions to <span class="hlt">shear</span> thinning. The viscosity and yield stress diverge as power laws at φc. Extrapolating the dynamic ranges of <span class="hlt">shear</span> rate and stress in the <span class="hlt">shear</span> thickening regime up to φc suggests a finite change in <span class="hlt">shear</span> stress with zero change in <span class="hlt">shear</span> rate. This is a dynamic analog to the jamming point with a yield stress at zero <span class="hlt">shear</span> rate.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/11783566','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/11783566"><span><span class="hlt">Prediction</span> of three social cognitive-motivational structure <span class="hlt">types</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Malerstein, A J; Ahern, M M; Pulos, S</p> <p>2001-10-01</p> <p>Previously, using interviews from Baumrind's longitudinal study, three cognitive-motivational structures (CMSs) were <span class="hlt">predicted</span> in 68 adolescents from caregiving settings and from the CMS <span class="hlt">types</span> of their mothers, based on the mothers' interviews elicited six years earlier. CMS theory proposes that during Piaget's Concrete Operational Period care-receiving influences the child's adoption of a social cognitive style, which corresponds to one of Piaget's stages of cognitive development. One who is classified as an Operational experiences the caregiving setting as tuned to the child's long-term interests, becomes focused on function and control of function and grasps the distinctions between and gradations of social attributes. One classified as future Intuitive experiences the caregiving as insufficient or unreliable and becomes focused on getting and having, and assesses social situations based on current striking dimensions. A person classified as being future Symbolic experiences the caregiving as out of tune with the self or the world, becomes focused on identity and emotional closeness, and may define self or object by a single attribute. This previous study did not distinguish between the influence of caregiving (including mothers' CMS) on the formation of adolescent CMS <span class="hlt">type</span> and the possible constancy of CMS <span class="hlt">type</span> from ages 9 to 15 years. The current study was designed to distinguish between these two possibilities, using data from 67 of the same mothers. Mothers' interviews were purged of descriptions of her child's behavior. Another interview was composed of the purged descriptions of child behavior. This was also done for interviews held when the child was 4 and 15 as well as at 9. From interviews with descriptions of child behavior purged, mother's CMS <span class="hlt">type</span> at the child's age of 4 and 9 yr. agreed with her adolescent's previously assigned CMS <span class="hlt">type</span> (p<.05), and caregiving setting at 9 years <span class="hlt">predicted</span> the adolescent's CMS <span class="hlt">type</span> (p<.05). From interviews composed</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/20542586','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/20542586"><span>Urinary <span class="hlt">type</span> IV collagen excretion <span class="hlt">predicts</span> subsequent declining renal function in <span class="hlt">type</span> 2 diabetic patients with proteinuria.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Katavetin, Pisut; Katavetin, Paravee; Susantitaphong, Paweena; Townamchai, Natavudh; Tiranathanagul, Khajohn; Tungsanga, Kriang; Eiam-Ong, Somchai</p> <p>2010-08-01</p> <p>Baseline urinary <span class="hlt">type</span> IV collagen excretion was negatively correlated with the subsequent GFR change (r(s)=-0.39, p=0.04) in our cohort of 30 <span class="hlt">type</span> 2 diabetic patients with proteinuria. Therefore, it could be used to <span class="hlt">predict</span> subsequent declining renal function in <span class="hlt">type</span> 2 diabetic patients with proteinuria. Copyright 2010 Elsevier Ireland Ltd. All rights reserved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/20370003','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/20370003"><span><span class="hlt">Shear</span> horizontal guided wave modes to infer the <span class="hlt">shear</span> stiffness of adhesive bond layers.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Le Crom, Bénédicte; Castaings, Michel</p> <p>2010-04-01</p> <p>This paper presents a non-destructive, ultrasonic technique to evaluate the quality of bonds between substrates. <span class="hlt">Shear</span>-horizontally polarized (SH) wave modes are investigated to infer the <span class="hlt">shear</span> stiffness of bonds, which is necessarily linked to the <span class="hlt">shear</span> resistance that is a critical parameter for bonded structures. Numerical simulations are run for selecting the most appropriate SH wave modes, i.e., with higher sensitivity to the bond than to other components, and experiments are made for generating-detecting pre-selected SH wave modes and for measuring their phase velocities. An inverse problem is finally solved, consisting of the evaluation of the <span class="hlt">shear</span> stiffness modulus of a bond layer at different curing times between a metallic plate and a composite patch, such assembly being investigated in the context of repair of aeronautical structures.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015APS..MARW44008W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015APS..MARW44008W"><span>Effect of Friction on <span class="hlt">Shear</span> Jamming</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Dong; Ren, Jie; Dijksman, Joshua; Bares, Jonathan; Behringer, Robert</p> <p>2015-03-01</p> <p><span class="hlt">Shear</span> jamming of granular materials was first found for systems of frictional disks, with a static friction coefficient μ ~ 0 . 6 (Bi et al. Nature (2011)). Jamming by <span class="hlt">shear</span> is obtained by starting from a zero-stress state with a packing fraction ϕ between ϕJ (isotropic jamming) and a lowest ϕS for <span class="hlt">shear</span> jamming. This phenomenon is associated with strong anisotropy in stress and the contact network in the form of force chains, which are stabilized and/or enhanced by the presence of friction. Whether <span class="hlt">shear</span> jamming occurs for frictionless particles is under debate. The issue we address experimentally is how reducing friction affects <span class="hlt">shear</span> jamming. We put the Teflon-wrapped photoelastic disks, lowering the friction substantially from previous experiments, in a well-studied 2D <span class="hlt">shear</span> apparatus (Ren et al. PRL (2013)), which provides a uniform simple <span class="hlt">shear</span>. <span class="hlt">Shear</span> jamming is still observed; however, the difference ϕJ -ϕS is smaller with lower friction. We also observe larger anisotropies in fragile states compared to experiments with higher friction particles at the same density. In ongoing work we are studying systems using photoelastic disks with fine gears on the edge to generate very large effective friction. We acknowledge support from NSF Grant DMR1206351, NSF Grant DMS-1248071, NASA Grant NNX10AU01G and William M. Keck Foundation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014APS..DFDR24004W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014APS..DFDR24004W"><span>Effect of friction on <span class="hlt">shear</span> jamming</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Dong; Ren, Jie; Dijksman, Joshua; Behringer, Robert</p> <p>2014-11-01</p> <p><span class="hlt">Shear</span> Jamming of granular materials was first found for systems of frictional disks, with a static friction coefficients μs ~= 0 . 6 . Jamming by <span class="hlt">shear</span> is obtained by starting from a zero-stress state with a packing fraction ϕS <= ϕ <=ϕJ between ϕJ (isotropic jamming) and a lowest ϕS for <span class="hlt">shear</span> jamming. This phenomenon is associated with strong anisotropy in stress and the contact network in the form of ``force chains,'' which are stabilized and/or enhanced by the presence of friction. The issue that we address experimentally is how reducing friction affects <span class="hlt">shear</span> jamming. We use photoelastic disks that have been wrapped with Teflon, lowering the friction coefficient substantially from previous experiments. The Teflon-wrapped disks were placed in a well-studied 2D <span class="hlt">shear</span> apparatus (Ren et al., PRL, 110, 018302 (2013)), which provides uniform simple <span class="hlt">shear</span> without generating <span class="hlt">shear</span> bands. <span class="hlt">Shear</span> jamming is still observed, but the difference ϕJ -ϕS is smaller than for higher friction particles. With Teflon-wrapped disks, we observe larger anisotropies compared to the previous experiment with higher friction particles at the same packing fraction, which indicates force chains tending to be straight in the low friction system. We acknowledge support from NSF Grant No. DMR12-06351, ARO Grant No. W911NF-1-11-0110, and NASA Grant No. NNX10AU01G.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016APS..MARS35004S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016APS..MARS35004S"><span>Non-homogeneous flow profiles in <span class="hlt">sheared</span> bacterial suspensions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Samanta, Devranjan; Cheng, Xiang</p> <p></p> <p>Bacterial suspensions under <span class="hlt">shear</span> exhibit interesting rheological behaviors including the remarkable ``superfluidic'' state with vanishing viscosity at low <span class="hlt">shear</span> rates. Theoretical studies have shown that such ``superfluidic'' state is linked with non-homogeneous <span class="hlt">shear</span> flows, which are induced by coupling between nematic order of active fluids and hydrodynamics of <span class="hlt">shear</span> flows. However, although bulk rheology of bacterial suspensions has been experimentally studied, <span class="hlt">shear</span> profiles within bacterial suspensions have not been explored so far. Here, we experimentally investigate the flow behaviors of E. coli suspensions under planar oscillatory <span class="hlt">shear</span>. Using confocal microscopy and PIV, we measure velocity profiles across gap between two <span class="hlt">shear</span> plates. We find that with increasing <span class="hlt">shear</span> rates, high-concentration bacterial suspensions exhibit an array of non-homogeneous flow behaviors like yield-stress flows and <span class="hlt">shear</span> banding. We show that these non-homogeneous flows are due to collective motion of bacterial suspensions. The phase diagram of <span class="hlt">sheared</span> bacterial suspensions is systematically mapped as functions of <span class="hlt">shear</span> rates an bacterial concentrations. Our experiments provide new insights into rheology of bacterial suspensions and shed light on <span class="hlt">shear</span> induced dynamics of active fluids. Chemical Engineering and Material Science department.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..1713949J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..1713949J"><span>Rheology linked with phase changes as recorded by development of <span class="hlt">shear</span> bands in the South Armorican <span class="hlt">Shear</span> Zone</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jeřábek, Petr; Bukovská, Zita</p> <p>2015-04-01</p> <p>The South Armorican <span class="hlt">Shear</span> Zone in France represents a major right-lateral strike slip <span class="hlt">shear</span> zone formed in the late stages of Variscan orogeny. The active deformation in this <span class="hlt">shear</span> zone is associated with the development of S-C fabrics in granitoids where thin <span class="hlt">shear</span> bands (C) overprint an earlier higher grade metamorphic foliation (S). In the studied samples covering low to high intensity of <span class="hlt">shear</span> band overprint, we identified three stages of <span class="hlt">shear</span> band evolution associated with distinct microstructures and deformation mechanisms. The initiation of <span class="hlt">shear</span> bands stage I is associated with the formation of microcracks crosscutting the S fabric and detected namely in the recrystallized quartz aggregates. The microcracks of suitable orientation are filled by microcline, albite, muscovite and chlorite which is a typical assemblage also for the well developed <span class="hlt">shear</span> bands. Phase equilibrium modeling in PERPLEX indicates that this assemblage formed at pressure-temperature range of 0.1-0.4 GPa and 300-340 °C. Stage II of <span class="hlt">shear</span> band evolution is characterized by dynamic recrystallization and grain size reduction of quartz aggregates along the microcracks and replacement of quartz by microcline along grain boundaries. This process leads to disintegration of quartz aggregate fabric and phase mixing in the <span class="hlt">shear</span> bands. The inferred deformation mechanism for this stage is solution-precipitation creep although recrystallization of quartz is still active at the contact between quartz aggregates and <span class="hlt">shear</span> bands. The coarse grained microstructure of quartz aggregates with ca ~250 microns average grain size reduces to ~10 microns grain size when recrystallized along extremely thin <span class="hlt">shear</span> bands/microcracks and to ~20 microns grain size when recrystallized along the thicker <span class="hlt">shear</span> bands. By using the flow law of Patterson and Luan (1990) for dislocation creep in quartz and the quartz piezometer of Stipp and Tullis (2003) corrected after Holyoke and Kronenberg (2010), the quartz</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26725654','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26725654"><span>Micro-mechanics of electrostatically stabilized suspensions of cellulose nanofibrils under steady state <span class="hlt">shear</span> flow.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Martoïa, F; Dumont, P J J; Orgéas, L; Belgacem, M N; Putaux, J-L</p> <p>2016-02-14</p> <p>In this study, we characterized and modeled the rheology of TEMPO-oxidized cellulose nanofibril (NFC) aqueous suspensions with electrostatically stabilized and unflocculated nanofibrous structures. These colloidal suspensions of slender and wavy nanofibers exhibited a yield stress and a <span class="hlt">shear</span> thinning behavior at low and high <span class="hlt">shear</span> rates, respectively. Both the <span class="hlt">shear</span> yield stress and the consistency of these suspensions were power-law functions of the NFC volume fraction. We developed an original multiscale model for the <span class="hlt">prediction</span> of the rheology of these suspensions. At the nanoscale, the suspensions were described as concentrated systems where NFCs interacted with the Newtonian suspending fluid through Brownian motion and long range fluid-NFC hydrodynamic interactions, as well as with each other through short range hydrodynamic and repulsive colloidal interaction forces. These forces were estimated using both the experimental results and 3D networks of NFCs that were numerically generated to mimic the nanostructures of NFC suspensions under <span class="hlt">shear</span> flow. They were in good agreement with theoretical and measured forces for model colloidal systems. The model showed the primary role played by short range hydrodynamic and colloidal interactions on the rheology of NFC suspensions. At low <span class="hlt">shear</span> rates, the origin of the yield stress of NFC suspensions was attributed to the combined contribution of repulsive colloidal interactions and the topology of the entangled NFC networks in the suspensions. At high <span class="hlt">shear</span> rates, both concurrent colloidal and short (in some cases long) range hydrodynamic interactions could be at the origin of the <span class="hlt">shear</span> thinning behavior of NFC suspensions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19960020383&hterms=stress+relationship&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dstress%2Brelationship','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19960020383&hterms=stress+relationship&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dstress%2Brelationship"><span>Wall <span class="hlt">Shear</span> Stress, Wall Pressure and Near Wall Velocity Field Relationships in a Whirling Annular Seal</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Morrison, Gerald L.; Winslow, Robert B.; Thames, H. Davis, III</p> <p>1996-01-01</p> <p>The mean and phase averaged pressure and wall <span class="hlt">shear</span> stress distributions were measured on the stator wall of a 50% eccentric annular seal which was whirling in a circular orbit at the same speed as the shaft rotation. The <span class="hlt">shear</span> stresses were measured using flush mounted hot-film probes. Four different operating conditions were considered consisting of Reynolds numbers of 12,000 and 24,000 and Taylor numbers of 3,300 and 6,600. At each of the operating conditions the axial distribution (from Z/L = -0.2 to 1.2) of the mean pressure, <span class="hlt">shear</span> stress magnitude, and <span class="hlt">shear</span> stress direction on the stator wall were measured. Also measured were the phase averaged pressure and <span class="hlt">shear</span> stress. These data were combined to calculate the force distributions along the seal length. Integration of the force distributions result in the net forces and moments generated by the pressure and <span class="hlt">shear</span> stresses. The flow field inside the seal operating at a Reynolds number of 24,000 and a Taylor number of 6,600 has been measured using a 3-D laser Doppler anemometer system. Phase averaged wall pressure and wall <span class="hlt">shear</span> stress are presented along with phase averaged mean velocity and turbulence kinetic energy distributions located 0.16c from the stator wall where c is the seal clearance. The relationships between the velocity, turbulence, wall pressure and wall <span class="hlt">shear</span> stress are very complex and do not follow simple bulk flow <span class="hlt">predictions</span>.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_23 --> <div id="page_24" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li class="active"><span>24</span></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="461"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22525766','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22525766"><span>Artificial neural networks to <span class="hlt">predict</span> activity <span class="hlt">type</span> and energy expenditure in youth.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Trost, Stewart G; Wong, Weng-Keen; Pfeiffer, Karen A; Zheng, Yonglei</p> <p>2012-09-01</p> <p>Previous studies have demonstrated that pattern recognition approaches to accelerometer data reduction are feasible and moderately accurate in classifying activity <span class="hlt">type</span> in children. Whether pattern recognition techniques can be used to provide valid estimates of physical activity (PA) energy expenditure in youth remains unexplored in the research literature. The objective of this study is to develop and test artificial neural networks (ANNs) to <span class="hlt">predict</span> PA <span class="hlt">type</span> and energy expenditure (PAEE) from processed accelerometer data collected in children and adolescents. One hundred participants between the ages of 5 and 15 yr completed 12 activity trials that were categorized into five PA <span class="hlt">types</span>: sedentary, walking, running, light-intensity household activities or games, and moderate-to-vigorous-intensity games or sports. During each trial, participants wore an ActiGraph GT1M on the right hip, and VO2 was measured using the Oxycon Mobile (Viasys Healthcare, Yorba Linda, CA) portable metabolic system. ANNs to <span class="hlt">predict</span> PA <span class="hlt">type</span> and PAEE (METs) were developed using the following features: 10th, 25th, 50th, 75th, and 90th percentiles and the lag one autocorrelation. To determine the highest time resolution achievable, we extracted features from 10-, 15-, 20-, 30-, and 60-s windows. Accuracy was assessed by calculating the percentage of windows correctly classified and root mean square error (RMSE). As window size increased from 10 to 60 s, accuracy for the PA-<span class="hlt">type</span> ANN increased from 81.3% to 88.4%. RMSE for the MET <span class="hlt">prediction</span> ANN decreased from 1.1 METs to 0.9 METs. At any given window size, RMSE values for the MET <span class="hlt">prediction</span> ANN were 30-40% lower than the conventional regression-based approaches. ANNs can be used to <span class="hlt">predict</span> both PA <span class="hlt">type</span> and PAEE in children and adolescents using count data from a single waist mounted accelerometer.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3956153','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3956153"><span>Surface <span class="hlt">shear</span> inviscidity of soluble surfactants</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Zell, Zachary A.; Nowbahar, Arash; Mansard, Vincent; Leal, L. Gary; Deshmukh, Suraj S.; Mecca, Jodi M.; Tucker, Christopher J.; Squires, Todd M.</p> <p>2014-01-01</p> <p>Foam and emulsion stability has long been believed to correlate with the surface <span class="hlt">shear</span> viscosity of the surfactant used to stabilize them. Many subtleties arise in interpreting surface <span class="hlt">shear</span> viscosity measurements, however, and correlations do not necessarily indicate causation. Using a sensitive technique designed to excite purely surface <span class="hlt">shear</span> deformations, we make the most sensitive and precise measurements to date of the surface <span class="hlt">shear</span> viscosity of a variety of soluble surfactants, focusing on SDS in particular. Our measurements reveal the surface <span class="hlt">shear</span> viscosity of SDS to be below the sensitivity limit of our technique, giving an upper bound of order 0.01 μN·s/m. This conflicts directly with almost all previous studies, which reported values up to 103–104 times higher. Multiple control and complementary measurements confirm this result, including direct visualization of monolayer deformation, for SDS and a wide variety of soluble polymeric, ionic, and nonionic surfactants of high- and low-foaming character. No soluble, small-molecule surfactant was found to have a measurable surface <span class="hlt">shear</span> viscosity, which seriously undermines most support for any correlation between foam stability and surface <span class="hlt">shear</span> rheology of soluble surfactants. PMID:24563383</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2148129','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2148129"><span>An Automatic Braking System That Stabilizes Leukocyte Rolling by an Increase in Selectin Bond Number with <span class="hlt">Shear</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Chen, Shuqi; Springer, Timothy A.</p> <p>1999-01-01</p> <p>Wall <span class="hlt">shear</span> stress in postcapillary venules varies widely within and between tissues and in response to inflammation and exercise. However, the speed at which leukocytes roll in vivo has been shown to be almost constant within a wide range of wall <span class="hlt">shear</span> stress, i.e., force on the cell. Similarly, rolling velocities on purified selectins and their ligands in vitro tend to plateau. This may be important to enable rolling leukocytes to be exposed uniformly to activating stimuli on endothelium, independent of local hemodynamic conditions. Wall <span class="hlt">shear</span> stress increases the rate of dissociation of individual selectin–ligand tether bonds exponentially (1, 4) thereby destabilizing rolling. We find that this is compensated by a <span class="hlt">shear</span>-dependent increase in the number of bonds per rolling step. We also find an increase in the number of microvillous tethers to the substrate. This explains (a) the lack of firm adhesion through selectins at low <span class="hlt">shear</span> stress or high ligand density, and (b) the stability of rolling on selectins to wide variation in wall <span class="hlt">shear</span> stress and ligand density, in contrast to rolling on antibodies (14). Furthermore, our data successfully <span class="hlt">predict</span> the threshold wall <span class="hlt">shear</span> stress below which rolling does not occur. This is a special case of the more general regulation by <span class="hlt">shear</span> of the number of bonds, in which the number of bonds falls below one. PMID:9885254</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/9885254','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/9885254"><span>An automatic braking system that stabilizes leukocyte rolling by an increase in selectin bond number with <span class="hlt">shear</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Chen, S; Springer, T A</p> <p>1999-01-11</p> <p>Wall <span class="hlt">shear</span> stress in postcapillary venules varies widely within and between tissues and in response to inflammation and exercise. However, the speed at which leukocytes roll in vivo has been shown to be almost constant within a wide range of wall <span class="hlt">shear</span> stress, i.e., force on the cell. Similarly, rolling velocities on purified selectins and their ligands in vitro tend to plateau. This may be important to enable rolling leukocytes to be exposed uniformly to activating stimuli on endothelium, independent of local hemodynamic conditions. Wall <span class="hlt">shear</span> stress increases the rate of dissociation of individual selectin-ligand tether bonds exponentially (, ) thereby destabilizing rolling. We find that this is compensated by a <span class="hlt">shear</span>-dependent increase in the number of bonds per rolling step. We also find an increase in the number of microvillous tethers to the substrate. This explains (a) the lack of firm adhesion through selectins at low <span class="hlt">shear</span> stress or high ligand density, and (b) the stability of rolling on selectins to wide variation in wall <span class="hlt">shear</span> stress and ligand density, in contrast to rolling on antibodies (). Furthermore, our data successfully <span class="hlt">predict</span> the threshold wall <span class="hlt">shear</span> stress below which rolling does not occur. This is a special case of the more general regulation by <span class="hlt">shear</span> of the number of bonds, in which the number of bonds falls below one.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/pages/biblio/1249129-direct-numerical-simulation-shear-localization-decomposition-reactions-shock-loaded-hmx-crystal','SCIGOV-DOEP'); return false;" href="https://www.osti.gov/pages/biblio/1249129-direct-numerical-simulation-shear-localization-decomposition-reactions-shock-loaded-hmx-crystal"><span>Direct numerical simulation of <span class="hlt">shear</span> localization and decomposition reactions in shock-loaded HMX crystal</span></a></p> <p><a target="_blank" href="http://www.osti.gov/pages">DOE PAGES</a></p> <p>Austin, Ryan A.; Barton, Nathan R.; Reaugh, John E.; ...</p> <p>2015-05-14</p> <p>A numerical model is developed to study the shock wave ignition of HMX crystal. The model accounts for the coupling between crystal thermal/mechanical responses and chemical reactions that are driven by the temperature field. This allows for the direct numerical simulation of decomposition reactions in the hot spots formed by shock/impact loading. The model is used to simulate intragranular pore collapse under shock wave loading. In a reference case: (i) <span class="hlt">shear</span>-enabled micro-jetting is responsible for a modest extent of reaction in the pore collapse region, and (ii) <span class="hlt">shear</span> banding is found to be an important mode of localization. The shearmore » bands, which are filled with molten HMX, grow out of the pore collapse region and serve as potential ignition sites. The model <span class="hlt">predictions</span> of <span class="hlt">shear</span> banding and reactivity are found to be quite sensitive to the respective flow strengths of the solid and liquid phases. In this regard, it is shown that reasonable assumptions of liquid-HMX viscosity can lead to chemical reactions within the <span class="hlt">shear</span> bands on a nanosecond time scale.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017MS%26E..245c2064M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017MS%26E..245c2064M"><span>Review of Punching <span class="hlt">Shear</span> Behaviour of Flat Slabs Reinforced with FRP Bars</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mohamed, Osama A.; Khattab, Rania</p> <p>2017-10-01</p> <p>Using Fibre Reinforced Polymer (FRP) bars to reinforce two-way concrete slabs can extend the service life, reduce maintenance cost and improve-life cycle cost efficiency. FRP reinforcing bars are more environmentally friendly alternatives to traditional reinforcing steel. <span class="hlt">Shear</span> behaviour of reinforced concrete structural members is a complex phenomenon that relies on the development of internal load-carrying mechanisms, the magnitude and combination of which is still a subject of research. Many building codes and design standards provide design formulas for estimation of punching <span class="hlt">shear</span> capacity of FRP reinforced flat slabs. Building code formulas take into account the effects of the axial stiffness of main reinforcement bars, the ratio of the perimeter of the critical section to the slab effective depth, and the slab thickness on the punching <span class="hlt">shear</span> capacity of two-way slabs reinforced with FRP bars or grids. The goal of this paper is to compare experimental data published in the literature to the equations offered by building codes for the estimation of punching <span class="hlt">shear</span> capacity of concrete flat slabs reinforced with FRP bars. Emphasis in this paper is on two North American codes, namely, ACI 440.1R-15 and CSA S806-12. The experimental data covered in this paper include flat slabs reinforced with GFRP, BFRP, and CFRP bars. Both ACI 440.1R-15 and CSA S806-12 are shown to be in good agreement with test results in terms of <span class="hlt">predicting</span> the punching <span class="hlt">shear</span> capacity.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17979430','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17979430"><span>A new parallel plate <span class="hlt">shear</span> cell for in situ real-space measurements of complex fluids under <span class="hlt">shear</span> flow.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wu, Yu Ling; Brand, Joost H J; van Gemert, Josephus L A; Verkerk, Jaap; Wisman, Hans; van Blaaderen, Alfons; Imhof, Arnout</p> <p>2007-10-01</p> <p>We developed and tested a parallel plate <span class="hlt">shear</span> cell that can be mounted on top of an inverted microscope to perform confocal real-space measurements on complex fluids under <span class="hlt">shear</span>. To follow structural changes in time, a plane of zero velocity is created by letting the plates move in opposite directions. The location of this plane is varied by changing the relative velocities of the plates. The gap width is variable between 20 and 200 microm with parallelism better than 1 microm. Such a small gap width enables us to examine the total sample thickness using high numerical aperture objective lenses. The achieved <span class="hlt">shear</span> rates cover the range of 0.02-10(3) s(-1). This <span class="hlt">shear</span> cell can apply an oscillatory <span class="hlt">shear</span> with adjustable amplitude and frequency. The maximum travel of each plate equals 1 cm, so that strains up to 500 can be applied. For most complex fluids, an oscillatory <span class="hlt">shear</span> with such a large amplitude can be regarded as a continuous <span class="hlt">shear</span>. We measured the flow profile of a suspension of silica colloids in this <span class="hlt">shear</span> cell. It was linear except for a small deviation caused by sedimentation. To demonstrate the excellent performance and capabilities of this new setup we examined <span class="hlt">shear</span> induced crystallization and melting of concentrated suspensions of 1 microm diameter silica colloids.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5107252','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5107252"><span>The Impact of Variable Wind <span class="hlt">Shear</span> Coefficients on Risk Reduction of Wind Energy Projects</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Thomson, Allan; Yoonesi, Behrang; McNutt, Josiah</p> <p>2016-01-01</p> <p>Estimation of wind speed at proposed hub heights is typically achieved using a wind <span class="hlt">shear</span> exponent or wind <span class="hlt">shear</span> coefficient (WSC), variation in wind speed as a function of height. The WSC is subject to temporal variation at low and high frequencies, ranging from diurnal and seasonal variations to disturbance caused by weather patterns; however, in many cases, it is assumed that the WSC remains constant. This assumption creates significant error in resource assessment, increasing uncertainty in projects and potentially significantly impacting the ability to control gird connected wind generators. This paper contributes to the body of knowledge relating to the evaluation and assessment of wind speed, with particular emphasis on the development of techniques to improve the accuracy of estimated wind speed above measurement height. It presents an evaluation of the use of a variable wind <span class="hlt">shear</span> coefficient methodology based on a distribution of wind <span class="hlt">shear</span> coefficients which have been implemented in real time. The results indicate that a VWSC provides a more accurate estimate of wind at hub height, ranging from 41% to 4% reduction in root mean squared error (RMSE) between <span class="hlt">predicted</span> and actual wind speeds when using a variable wind <span class="hlt">shear</span> coefficient at heights ranging from 33% to 100% above the highest actual wind measurement. PMID:27872898</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://earthquake.usgs.gov/research/rockphysics/papers/Hayward_MS_Moore.pdf','USGSPUBS'); return false;" href="http://earthquake.usgs.gov/research/rockphysics/papers/Hayward_MS_Moore.pdf"><span>Anomalously low strength of serpentinite <span class="hlt">sheared</span> against granite and implications for creep on the Hayward and Calaveras Faults</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Moore, Diane E.; Lockner, David A.; Ponce, David A.</p> <p>2010-01-01</p> <p>Serpentinized ophiolitic rocks are juxtaposed against quartzofeldspathic rocks at depth across considerable portions of the Hayward and Calaveras Faults. The marked compositional contrast between these rock <span class="hlt">types</span> may contribute to fault creep that has been observed along these faults. To investigate this possibility, we are conducting hydrothermal <span class="hlt">shearing</span> experiments to look for changes in frictional properties resulting from the <span class="hlt">shear</span> of ultramafic rock juxtaposed against quartzose rock units. In this paper we report the first results in this effort: <span class="hlt">shear</span> of bare-rock surfaces of serpentinite and granite, and <span class="hlt">shear</span> of antigorite-serpentinite gouge between forcing blocks of granitic rock. All experiments were conducted at 250°C. Serpentinite <span class="hlt">sheared</span> against granite at 50 MPa pore-fluid pressure is weaker than either rock <span class="hlt">type</span> separately, and the weakening is significantly more pronounced at lower <span class="hlt">shearing</span> rates. In contrast, serpentinite gouge <span class="hlt">sheared</span> dry between granite blocks is as strong as the bare granite surface. We propose that the weakening is the result of a solution-transfer process involving the dissolution of serpentine minerals at grain-to-grain contacts. Dissolution of serpentine is enhanced by modifications to pore-fluid chemistry caused by interaction of the fluid with the quartz-bearing rocks. The compositional differences between serpentinized ultramafic rocks of the Coast Range Ophiolite and quartzofeldspathic rock units such as those of the Franciscan Complex may provide the mechanism for aseismic slip (creep) in the shallow crust along the Hayward, Calaveras, and other creeping faults in central and northern California.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25927794','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25927794"><span>Imaging and characterizing <span class="hlt">shear</span> wave and <span class="hlt">shear</span> modulus under orthogonal acoustic radiation force excitation using OCT Doppler variance method.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Zhu, Jiang; Qu, Yueqiao; Ma, Teng; Li, Rui; Du, Yongzhao; Huang, Shenghai; Shung, K Kirk; Zhou, Qifa; Chen, Zhongping</p> <p>2015-05-01</p> <p>We report on a novel acoustic radiation force orthogonal excitation optical coherence elastography (ARFOE-OCE) technique for imaging <span class="hlt">shear</span> wave and quantifying <span class="hlt">shear</span> modulus under orthogonal acoustic radiation force (ARF) excitation using the optical coherence tomography (OCT) Doppler variance method. The ARF perpendicular to the OCT beam is produced by a remote ultrasonic transducer. A <span class="hlt">shear</span> wave induced by ARF excitation propagates parallel to the OCT beam. The OCT Doppler variance method, which is sensitive to the transverse vibration, is used to measure the ARF-induced vibration. For analysis of the <span class="hlt">shear</span> modulus, the Doppler variance method is utilized to visualize <span class="hlt">shear</span> wave propagation instead of Doppler OCT method, and the propagation velocity of the <span class="hlt">shear</span> wave is measured at different depths of one location with the M scan. In order to quantify <span class="hlt">shear</span> modulus beyond the OCT imaging depth, we move ARF to a deeper layer at a known step and measure the time delay of the <span class="hlt">shear</span> wave propagating to the same OCT imaging depth. We also quantitatively map the <span class="hlt">shear</span> modulus of a cross-section in a tissue-equivalent phantom after employing the B scan.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/biblio/22486497-periodically-sheared-yukawa-systems','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/22486497-periodically-sheared-yukawa-systems"><span>Periodically <span class="hlt">sheared</span> 2D Yukawa systems</span></a></p> <p><a target="_blank" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Kovács, Anikó Zsuzsa; Hartmann, Peter; Center for Astrophysics, Space Physics and Engineering Research</p> <p>2015-10-15</p> <p>We present non-equilibrium molecular dynamics simulation studies on the dynamic (complex) <span class="hlt">shear</span> viscosity of a 2D Yukawa system. We have identified a non-monotonic frequency dependence of the viscosity at high frequencies and <span class="hlt">shear</span> rates, an energy absorption maximum (local resonance) at the Einstein frequency of the system at medium <span class="hlt">shear</span> rates, an enhanced collective wave activity, when the excitation is near the plateau frequency of the longitudinal wave dispersion, and the emergence of significant configurational anisotropy at small frequencies and high <span class="hlt">shear</span> rates.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29772822','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29772822"><span>Measurement of Wall <span class="hlt">Shear</span> Stress in High Speed Air Flow Using <span class="hlt">Shear</span>-Sensitive Liquid Crystal Coating.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Zhao, Jisong</p> <p>2018-05-17</p> <p>Wall <span class="hlt">shear</span> stress is an important quantity in fluid mechanics, but its measurement is a challenging task. An approach to measure wall <span class="hlt">shear</span> stress vector distribution using <span class="hlt">shear</span>-sensitive liquid crystal coating (SSLCC) is described. The wall <span class="hlt">shear</span> stress distribution on the test surface beneath high speed jet flow is measured while using the proposed technique. The flow structures inside the jet flow are captured and the results agree well with the streakline pattern that was visualized using the oil-flow technique. In addition, the shock diamonds inside the supersonic jet flow are visualized clearly using SSLCC and the results are compared with the velocity contour that was measured using the particle image velocimetry (PIV) technique. The work of this paper demonstrates the application of SSLCC in the measurement/visualization of wall <span class="hlt">shear</span> stress in high speed flow.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5981805','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5981805"><span>Measurement of Wall <span class="hlt">Shear</span> Stress in High Speed Air Flow Using <span class="hlt">Shear</span>-Sensitive Liquid Crystal Coating</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Zhao, Jisong</p> <p>2018-01-01</p> <p>Wall <span class="hlt">shear</span> stress is an important quantity in fluid mechanics, but its measurement is a challenging task. An approach to measure wall <span class="hlt">shear</span> stress vector distribution using <span class="hlt">shear</span>-sensitive liquid crystal coating (SSLCC) is described. The wall <span class="hlt">shear</span> stress distribution on the test surface beneath high speed jet flow is measured while using the proposed technique. The flow structures inside the jet flow are captured and the results agree well with the streakline pattern that was visualized using the oil-flow technique. In addition, the shock diamonds inside the supersonic jet flow are visualized clearly using SSLCC and the results are compared with the velocity contour that was measured using the particle image velocimetry (PIV) technique. The work of this paper demonstrates the application of SSLCC in the measurement/visualization of wall <span class="hlt">shear</span> stress in high speed flow. PMID:29772822</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.2446T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.2446T"><span>Fan-structure waves in <span class="hlt">shear</span> ruptures</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tarasov, Boris</p> <p>2016-04-01</p> <p>This presentation introduces a recently identified <span class="hlt">shear</span> rupture mechanism providing a paradoxical feature of hard rocks - the possibility of <span class="hlt">shear</span> rupture propagation through the highly confined intact rock mass at <span class="hlt">shear</span> stress levels significantly less than frictional strength. According to the fan-mechanism the <span class="hlt">shear</span> rupture propagation is associated with consecutive creation of small slabs in the fracture tip which, due to rotation caused by <span class="hlt">shear</span> displacement of the fracture interfaces, form a fan-structure representing the fracture head. The fan-head combines such unique features as: extremely low <span class="hlt">shear</span> resistance (below the frictional strength), self-sustaining stress intensification in the rupture tip (providing easy formation of new slabs), and self-unbalancing conditions in the fan-head (making the failure process inevitably spontaneous and violent). An important feature of the fan-mechanism is the fact that for the initial formation of the fan-structure an enhanced local <span class="hlt">shear</span> stress is required, however, after completion of the fan-structure it can propagate as a dynamic wave through intact rock mass at <span class="hlt">shear</span> stresses below the frictional strength. Paradoxically low <span class="hlt">shear</span> strength of pristine rocks provided by the fan-mechanism determines the correspondingly low transient strength of the lithosphere, which favours generation of new earthquake faults in the intact rock mass adjoining pre-existing faults in preference to frictional stick-slip instability along these faults. The new approach reveals an alternative role of pre-existing faults in earthquake activity: they represent local stress concentrates in pristine rock adjoining the fault where special conditions for the fan-mechanism nucleation are created, while further dynamic propagation of the new fault (earthquake) occurs at low field stresses even below the frictional strength.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.fs.usda.gov/treesearch/pubs/7677','TREESEARCH'); return false;" href="https://www.fs.usda.gov/treesearch/pubs/7677"><span>Effect of tree roots on a <span class="hlt">shear</span> zone: modeling reinforced <span class="hlt">shear</span> stress.</span></a></p> <p><a target="_blank" href="http://www.fs.usda.gov/treesearch/">Treesearch</a></p> <p>Kazutoki Abe; Robert R. Ziemer</p> <p>1991-01-01</p> <p>Tree roots provide important soil reinforcement that impoves the stability of hillslopes. After trees are cut and roots begin to decay, the frequency of slope failures can increase. To more fully understand the mechanics of how tree roots reinforce soil, fine sandy soil containing pine roots was placed in a large <span class="hlt">shear</span> box in horizontal layers and <span class="hlt">sheared</span> across a...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017PhRvF...2l3602C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017PhRvF...2l3602C"><span>Droplet breakup driven by <span class="hlt">shear</span> thinning solutions in a microfluidic T-junction</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chiarello, Enrico; Gupta, Anupam; Mistura, Giampaolo; Sbragaglia, Mauro; Pierno, Matteo</p> <p>2017-12-01</p> <p>Droplet-based microfluidics turned out to be an efficient and adjustable platform for digital analysis, encapsulation of cells, drug formulation, and polymerase chain reaction. Typically, for most biomedical applications, the handling of complex, non-Newtonian fluids is involved, e.g., synovial and salivary fluids, collagen, and gel scaffolds. In this study, we investigate the problem of droplet formation occurring in a microfluidic T-shaped junction, when the continuous phase is made of <span class="hlt">shear</span> thinning liquids. At first, we review in detail the breakup process, providing extensive, side-by-side comparisons between Newtonian and non-Newtonian liquids over unexplored ranges of flow conditions and viscous responses. The non-Newtonian liquid carrying the droplets is made of Xanthan solutions, a stiff, rodlike polysaccharide displaying a marked <span class="hlt">shear</span> thinning rheology. By defining an effective Capillary number, a simple yet effective methodology is used to account for the <span class="hlt">shear</span>-dependent viscous response occurring at the breakup. The droplet size can be <span class="hlt">predicted</span> over a wide range of flow conditions simply by knowing the rheology of the bulk continuous phase. Experimental results are complemented with numerical simulations of purely <span class="hlt">shear</span> thinning fluids using lattice Boltzmann models. The good agreement between the experimental and numerical data confirm the validity of the proposed rescaling with the effective Capillary number.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017APS..DFDG29004O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017APS..DFDG29004O"><span>Effects of the <span class="hlt">shear</span> layer growth rate on the supersonic jet noise</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ozawa, Yuta; Nonomura, Taku; Oyama, Akira; Mamori, Hiroya; Fukushima, Naoya; Yamamoto, Makoto</p> <p>2017-11-01</p> <p>Strong acoustic waves emitted from rocket plume might damage to rocket payloads because their payloads consist of fragile structure. Therefore, understanding and <span class="hlt">prediction</span> of acoustic wave generation are of importance not only in science, but also in engineering. The present study makes experiments of a supersonic jet flow at the Mach number of 2.0 and investigates a relationship between growth rate of a <span class="hlt">shear</span> layer and noise generation of the supersonic jet. We conducted particle image velocimetry (PIV) and acoustic measurements for three different shaped nozzles. These nozzles were employed to control the condition of a <span class="hlt">shear</span> layer of the supersonic jet flow. We applied single-pixel ensemble correlation method (Westerweel et al., 2004) for the PIV images to obtain high-resolution averaged velocity profiles. This correlation method enabled us to obtain detailed data of the <span class="hlt">shear</span> layer. For all cases, acoustic measurements clearly shows the noise source position at the end of a potential core of the jet. In the case where laminar to turbulent transition occurred in the <span class="hlt">shear</span> layer, the sound pressure level increased by 4 dB at the maximum. This research is partially supported by Presto, JST (JPMJPR1678) and KAKENHI (25709009 and 17H03473).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017PhRvL.119c6101W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017PhRvL.119c6101W"><span>Measuring Interlayer <span class="hlt">Shear</span> Stress in Bilayer Graphene</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Guorui; Dai, Zhaohe; Wang, Yanlei; Tan, PingHeng; Liu, Luqi; Xu, Zhiping; Wei, Yueguang; Huang, Rui; Zhang, Zhong</p> <p>2017-07-01</p> <p>Monolayer two-dimensional (2D) crystals exhibit a host of intriguing properties, but the most exciting applications may come from stacking them into multilayer structures. Interlayer and interfacial <span class="hlt">shear</span> interactions could play a crucial role in the performance and reliability of these applications, but little is known about the key parameters controlling <span class="hlt">shear</span> deformation across the layers and interfaces between 2D materials. Herein, we report the first measurement of the interlayer <span class="hlt">shear</span> stress of bilayer graphene based on pressurized microscale bubble loading devices. We demonstrate continuous growth of an interlayer <span class="hlt">shear</span> zone outside the bubble edge and extract an interlayer <span class="hlt">shear</span> stress of 40 kPa based on a membrane analysis for bilayer graphene bubbles. Meanwhile, a much higher interfacial <span class="hlt">shear</span> stress of 1.64 MPa was determined for monolayer graphene on a silicon oxide substrate. Our results not only provide insights into the interfacial <span class="hlt">shear</span> responses of the thinnest structures possible, but also establish an experimental method for characterizing the fundamental interlayer <span class="hlt">shear</span> properties of the emerging 2D materials for potential applications in multilayer systems.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29587472','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29587472"><span>2D Analytical Model for the Directivity <span class="hlt">Prediction</span> of Ultrasonic Contact <span class="hlt">Type</span> Transducers in the Generation of Guided Waves.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Tiwari, Kumar Anubhav; Raisutis, Renaldas; Mazeika, Liudas; Samaitis, Vykintas</p> <p>2018-03-26</p> <p>In this paper, a novel 2D analytical model based on the Huygens's principle of wave propagation is proposed in order to <span class="hlt">predict</span> the directivity patterns of contact <span class="hlt">type</span> ultrasonic transducers in the generation of guided waves (GWs). The developed model is able to estimate the directivity patterns at any distance, at any excitation frequency and for any configuration and shape of the transducers with prior information of phase dispersive characteristics of the guided wave modes and the behavior of transducer. This, in turn, facilitates to choose the appropriate transducer or arrays of transducers, suitable guided wave modes and excitation frequency for the nondestructive testing (NDT) and structural health monitoring (SHM) applications. The model is demonstrated for P1-<span class="hlt">type</span> macro-fiber composite (MFC) transducer glued on a 2 mm thick aluminum (Al) alloy plate. The directivity patterns of MFC transducer in the generation of fundamental guided Lamb modes (the S0 and A0) and <span class="hlt">shear</span> horizontal mode (the SH0) are successfully obtained at 80 kHz, 5-period excitation signal. The results are verified using 3D finite element (FE) modelling and experimental investigation. The results obtained using the proposed model shows the good agreement with those obtained using numerical simulations and experimental analysis. The calculation time using the analytical model was significantly shorter as compared to the time spent in experimental analysis and FE numerical modelling.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017RMRE...50.1141B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017RMRE...50.1141B"><span>Effect of Boundary Condition on the <span class="hlt">Shear</span> Behaviour of Rock Joints in the Direct <span class="hlt">Shear</span> Test</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bahaaddini, M.</p> <p>2017-05-01</p> <p>The common method for determination of the mechanical properties of the rock joints is the direct <span class="hlt">shear</span> test. This paper aims to study the effect of boundary condition on the results of direct <span class="hlt">shear</span> tests. Experimental studies undertaken in this research showed that the peak <span class="hlt">shear</span> strength is mostly overestimated. This problem is more pronounced for steep asperities and under high normal stresses. Investigation of the failure mode of these samples showed that tensile cracks are generated at the boundary of sample close to the specimen holders and propagated inside the intact materials. In order to discover the reason of observed failure mechanism in experiments, the direct <span class="hlt">shear</span> test was simulated using PFC2D. Results of numerical models showed that the gap zone size between the upper and lower specimen holders has a significant effect on the <span class="hlt">shear</span> mechanism. For the high gap size, stresses concentrate at the vicinity of the tips of specimen holders and result in generation and propagation of tensile cracks inside the intact material. However, by reducing the gap size, stresses are concentrated on asperities, and damage of specimen at its boundary is not observed. Results of this paper show that understanding the <span class="hlt">shear</span> mechanism of rock joints is an essential step prior to interpreting the results of direct <span class="hlt">shear</span> tests.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li class="active"><span>24</span></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_24 --> <div id="page_25" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li class="active"><span>25</span></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="481"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015SPIE.9327E..0YS','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015SPIE.9327E..0YS"><span>Mapping tissue <span class="hlt">shear</span> modulus on Thiel soft-embalmed mouse skin with <span class="hlt">shear</span> wave optical coherence elastography</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Song, Shaozhen; Joy, Joyce; Wang, Ruikang K.; Huang, Zhihong</p> <p>2015-03-01</p> <p>A quantitative measurement of the mechanical properties of biological tissue is a useful assessment of its physiologic conditions, which may aid medical diagnosis and treatment of, e.g., scleroderma and skin cancer. Traditional elastography techniques such as magnetic resonance elastography and ultrasound elastography have limited scope of application on skin due to insufficient spatial resolution. Recently, dynamic / transient elastography are attracting more applications with the advantage of non-destructive measurements, and revealing the absolute moduli values of tissue mechanical properties. <span class="hlt">Shear</span> wave optical coherence elastography (SW-OCE) is a novel transient elastography method, which lays emphasis on the propagation of dynamic mechanical waves. In this study, high speed <span class="hlt">shear</span> wave imaging technique was applied to a range of soft-embalmed mouse skin, where 3 kHz <span class="hlt">shear</span> waves were launched with a piezoelectric actuator as an external excitation. The <span class="hlt">shear</span> wave velocity was estimated from the <span class="hlt">shear</span> wave images, and used to recover a <span class="hlt">shear</span> modulus map in the same OCT imaging range. Results revealed significant difference in <span class="hlt">shear</span> modulus and structure in compliance with gender, and images on fresh mouse skin are also compared. Thiel embalming technique is also proven to present the ability to furthest preserve the mechanical property of biological tissue. The experiment results suggest that SW-OCE is an effective technique for quantitative estimation of skin tissue biomechanical status.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20040088158&hterms=wheat&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dwheat','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20040088158&hterms=wheat&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dwheat"><span>Comparison of observed rheological properties of hard wheat flour dough with <span class="hlt">predictions</span> of the Giesekus-Leonov, White-Metzner and Phan-Thien Tanner models</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Dhanasekharan, M.; Huang, H.; Kokini, J. L.; Janes, H. W. (Principal Investigator)</p> <p>1999-01-01</p> <p>The measured rheological behavior of hard wheat flour dough was <span class="hlt">predicted</span> using three nonlinear differential viscoelastic models. The Phan-Thien Tanner model gave good zero <span class="hlt">shear</span> viscosity <span class="hlt">prediction</span>, but overpredicted the <span class="hlt">shear</span> viscosity at higher <span class="hlt">shear</span> rates and the transient and extensional properties. The Giesekus-Leonov model gave similar <span class="hlt">predictions</span> to the Phan-Thien Tanner model, but the extensional viscosity <span class="hlt">prediction</span> showed extension thickening. Using high values of the mobility factor, extension thinning behavior was observed but the <span class="hlt">predictions</span> were not satisfactory. The White-Metzner model gave good <span class="hlt">predictions</span> of the steady <span class="hlt">shear</span> viscosity and the first normal stress coefficient but it was unable to <span class="hlt">predict</span> the uniaxial extensional viscosity as it exhibited asymptotic behavior in the tested extensional rates. It also <span class="hlt">predicted</span> the transient <span class="hlt">shear</span> properties with moderate accuracy in the transient phase, but very well at higher times, compared to the Phan-Thien Tanner model and the Giesekus-Leonov model. None of the models <span class="hlt">predicted</span> all observed data consistently well. Overall the White-Metzner model appeared to make the best <span class="hlt">predictions</span> of all the observed data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018PhRvP...9a4023L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018PhRvP...9a4023L"><span>Dilatancy of <span class="hlt">Shear</span> Transformations in a Colloidal Glass</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lu, Y. Z.; Jiang, M. Q.; Lu, X.; Qin, Z. X.; Huang, Y. J.; Shen, J.</p> <p>2018-01-01</p> <p><span class="hlt">Shear</span> transformations, as fundamental rearrangement events operating in local regions, hold the key of plastic flow of amorphous solids. Despite their importance, the dynamic features of <span class="hlt">shear</span> transformations are far from clear, which is the focus of the present study. Here, we use a colloidal glass under <span class="hlt">shear</span> as the prototype to directly observe the <span class="hlt">shear</span>-transformation events in real space. By tracing the colloidal-particle rearrangements, we quantitatively determine two basic properties of <span class="hlt">shear</span> transformations: local <span class="hlt">shear</span> strain and dilatation (or free volume). It is revealed that the local free volume undergoes a significantly temporary increase prior to <span class="hlt">shear</span> transformations, eventually leading to a jump of local <span class="hlt">shear</span> strain. We clearly demonstrate that <span class="hlt">shear</span> transformations have no memory of the initial free volume of local regions. Instead, their emergence strongly depends on the dilatancy ability of these local regions, i.e., the dynamic creation of free volume. More specifically, the particles processing the high dilatancy ability directly participate in subsequent <span class="hlt">shear</span> transformations. These results experimentally enrich Argon's statement about the dilatancy nature of <span class="hlt">shear</span> transformations and also shed insight into the structural origin of amorphous plasticity.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1990MolPh..71..123B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1990MolPh..71..123B"><span><span class="hlt">Shear</span> viscosity in monatomic liquids: a simple mode-coupling approach</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Balucani, Umberto</p> <p></p> <p>The value of the <span class="hlt">shear</span>-viscosity coefficient in fluids is controlled by the dynamical processes affecting the time decay of the associated Green-Kubo integrand, the stress autocorrelation function (SACF). These processes are investigated in monatomic liquids by means of a microscopic approach with a minimum use of phenomenological assumptions. In particular, mode-coupling effects (responsible for the presence in the SACF of a long-lasting 'tail') are accounted for by a simplified approach where the only requirement is knowledge of the structural properties. The theory readily yields quantitative <span class="hlt">predictions</span> in its domain of validity, which comprises ordinary and moderately supercooled 'simple' liquids. The framework is applied to liquid Ar and Rb near their melting points, and quite satisfactory agreement with the simulation data is found for both the details of the SACF and the value of the <span class="hlt">shear</span>-viscosity coefficient.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://eric.ed.gov/?q=type+AND+hand+AND+writing&pg=6&id=EJ729603','ERIC'); return false;" href="https://eric.ed.gov/?q=type+AND+hand+AND+writing&pg=6&id=EJ729603"><span>Using Word <span class="hlt">Prediction</span> Software to Increase <span class="hlt">Typing</span> Fluency with Students with Physical Disabilities</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Tumlin, Jennifer; Heller, Kathryn Wolff</p> <p>2004-01-01</p> <p>The purpose of this study was to examine the use of word <span class="hlt">prediction</span> software to increase <span class="hlt">typing</span> speed and decrease spelling errors for students who have physical disabilities that affect hand use. Student perceptions regarding the effectiveness of word <span class="hlt">prediction</span> was examined as well as their <span class="hlt">typing</span> rates and spelling accuracy. Four students with…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5095657','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5095657"><span>Large enhancement of superconducting transition temperature in single-element superconducting rhenium by <span class="hlt">shear</span> strain</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Mito, Masaki; Matsui, Hideaki; Tsuruta, Kazuki; Yamaguchi, Tomiko; Nakamura, Kazuma; Deguchi, Hiroyuki; Shirakawa, Naoki; Adachi, Hiroki; Yamasaki, Tohru; Iwaoka, Hideaki; Ikoma, Yoshifumi; Horita, Zenji</p> <p>2016-01-01</p> <p>Finding a physical approach for increasing the superconducting transition temperature (Tc) is a challenge in the field of material science. <span class="hlt">Shear</span> strain effects on the superconductivity of rhenium were investigated using magnetic measurements, X-ray diffraction, transmission electron microscopy, and first-principles calculations. A large <span class="hlt">shear</span> strain reduces the grain size and simultaneously expands the unit cells, resulting in an increase in Tc. Here we show that this <span class="hlt">shear</span> strain approach is a new method for enhancing Tc and differs from that using hydrostatic strain. The enhancement of Tc is explained by an increase in net electron–electron coupling rather than a change in the density of states near the Fermi level. The <span class="hlt">shear</span> strain effect in rhenium could be a successful example of manipulating Bardeen–Cooper–Schrieffer-<span class="hlt">type</span> Cooper pairing, in which the unit cell volumes are indeed a key parameter. PMID:27811983</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015SPIE.9597E..09Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015SPIE.9597E..09Z"><span>Smooth affine <span class="hlt">shear</span> tight frames: digitization and applications</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhuang, Xiaosheng</p> <p>2015-08-01</p> <p>In this paper, we mainly discuss one of the recent developed directional multiscale representation systems: smooth affine <span class="hlt">shear</span> tight frames. A directional wavelet tight frame is generated by isotropic dilations and translations of directional wavelet generators, while an affine <span class="hlt">shear</span> tight frame is generated by anisotropic dilations, <span class="hlt">shears</span>, and translations of shearlet generators. These two tight frames are actually connected in the sense that the affine <span class="hlt">shear</span> tight frame can be obtained from a directional wavelet tight frame through subsampling. Consequently, an affine <span class="hlt">shear</span> tight frame indeed has an underlying filter bank from the MRA structure of its associated directional wavelet tight frame. We call such filter banks affine <span class="hlt">shear</span> filter banks, which can be designed completely in the frequency domain. We discuss the digitization of affine <span class="hlt">shear</span> filter banks and their implementations: the forward and backward digital affine <span class="hlt">shear</span> transforms. Redundancy rate and computational complexity of digital affine <span class="hlt">shear</span> transforms are also investigated in this paper. Numerical experiments and comparisons in image/video processing show the advantages of digital affine <span class="hlt">shear</span> transforms over many other state-of-art directional multiscale representation systems.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014PhRvL.113f8301P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014PhRvL.113f8301P"><span>Multiple Transient Memories in Experiments on <span class="hlt">Sheared</span> Non-Brownian Suspensions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Paulsen, Joseph D.; Keim, Nathan C.; Nagel, Sidney R.</p> <p>2014-08-01</p> <p>A system with multiple transient memories can remember a set of inputs but subsequently forgets almost all of them, even as they are continually applied. If noise is added, the system can store all memories indefinitely. The phenomenon has recently been <span class="hlt">predicted</span> for cyclically <span class="hlt">sheared</span> non-Brownian suspensions. Here we present experiments on such suspensions, finding behavior consistent with multiple transient memories and showing how memories can be stabilized by noise.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.T21A2543Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.T21A2543Y"><span>Hydrothermal quartz formation during fluctuations of brittle <span class="hlt">shear</span>-zone activity and fluid flow: grain growth and deformation structures of the Pfahl <span class="hlt">shear</span> zone (Germany)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yilmaz, T.; Prosser, G.; Liotta, D.; Kruhl, J. H.</p> <p>2012-12-01</p> <p>The Bavarian Pfahl <span class="hlt">shear</span> zone is a WNW-ESE trending dextral strike-slip <span class="hlt">shear</span> zone at the SW margin of the Bohemian Massif (Central Europe). It was discontinuously active during decreasing PT-conditions, i.e. from ductile to brittle, from the late-Carboniferous to the late-Cretaceous - Paleocene times. Triassic hydrothermal activity produced a 150 km long and 30-100 m wide quartz dyke along the main fault, surrounded by <span class="hlt">sheared</span> basement rocks. Within a zone of >10 m metasomatism transformed the wall rocks to mostly kaolinite, chlorite and phyllosilicates. The quartz dyke exhibits a layered to lenticular and partly symmetric structure with different <span class="hlt">types</span> of quartz masses, transected by a complex quartz vein network. This already indicates pulses of fluid flux and fragmentation during the lifetime of the <span class="hlt">shear</span> zone. Analyses by optical microscopy, cathodoluminescence (CL) and SEM-EDX reveal at least four subsequent stages of quartz crystallization and fragmentation. (i) The oldest generation of quartz is represented by a homogeneous dark grey to reddish quartz mass made up by ~10-20 μm-sized crystals. It contains mm- to cm-sized angular wall-rock fragments, completely altered to kaolinite, indicating intense wall-rock alteration prior to the earliest event of silica precipitation. This rules out the possibility that the quartz mass developed from silicification of the wall rocks. This first <span class="hlt">type</span> of quartz occurs as cm- to dm-large angular fragments in (ii) a light grey to pink quartz mass formed by ~10-50 μm-sized crystals. The different colours result from variable <span class="hlt">types</span> and amounts of inclusions. Quartz of both generations shows random crystallographic orientations and complex inclusion structures. It probably developed during two fragmentation events and possibly from a silica gel precursor that crystallized after precipitation. (iii) The third quartz generation formed as a set of mm- to dm-wide veins roughly parallel to the trend of the Pfahl zone</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017Metro..54..821D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017Metro..54..821D"><span><span class="hlt">Predictable</span> quantum efficient detector based on n-<span class="hlt">type</span> silicon photodiodes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dönsberg, Timo; Manoocheri, Farshid; Sildoja, Meelis; Juntunen, Mikko; Savin, Hele; Tuovinen, Esa; Ronkainen, Hannu; Prunnila, Mika; Merimaa, Mikko; Tang, Chi Kwong; Gran, Jarle; Müller, Ingmar; Werner, Lutz; Rougié, Bernard; Pons, Alicia; Smîd, Marek; Gál, Péter; Lolli, Lapo; Brida, Giorgio; Rastello, Maria Luisa; Ikonen, Erkki</p> <p>2017-12-01</p> <p>The <span class="hlt">predictable</span> quantum efficient detector (PQED) consists of two custom-made induced junction photodiodes that are mounted in a wedged trap configuration for the reduction of reflectance losses. Until now, all manufactured PQED photodiodes have been based on a structure where a SiO2 layer is thermally grown on top of p-<span class="hlt">type</span> silicon substrate. In this paper, we present the design, manufacturing, modelling and characterization of a new <span class="hlt">type</span> of PQED, where the photodiodes have an Al2O3 layer on top of n-<span class="hlt">type</span> silicon substrate. Atomic layer deposition is used to deposit the layer to the desired thickness. Two sets of photodiodes with varying oxide thicknesses and substrate doping concentrations were fabricated. In order to <span class="hlt">predict</span> recombination losses of charge carriers, a 3D model of the photodiode was built into Cogenda Genius semiconductor simulation software. It is important to note that a novel experimental method was developed to obtain values for the 3D model parameters. This makes the <span class="hlt">prediction</span> of the PQED responsivity a completely autonomous process. Detectors were characterized for temperature dependence of dark current, spatial uniformity of responsivity, reflectance, linearity and absolute responsivity at the wavelengths of 488 nm and 532 nm. For both sets of photodiodes, the modelled and measured responsivities were generally in agreement within the measurement and modelling uncertainties of around 100 parts per million (ppm). There is, however, an indication that the modelled internal quantum deficiency may be underestimated by a similar amount. Moreover, the responsivities of the detectors were spatially uniform within 30 ppm peak-to-peak variation. The results obtained in this research indicate that the n-<span class="hlt">type</span> induced junction photodiode is a very promising alternative to the existing p-<span class="hlt">type</span> detectors, and thus give additional credibility to the concept of modelled quantum detector serving as a primary standard. Furthermore, the manufacturing of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/19657444','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/19657444"><span><span class="hlt">Type</span> 1 diabetes: New horizons in <span class="hlt">prediction</span> and prevention.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Razack, Natasha N; Wherrett, Diane K</p> <p>2005-01-01</p> <p>Significant advances have been made in our understanding of the pathogenesis of <span class="hlt">type</span> 1 diabetes and our ability to <span class="hlt">predict</span> risk for the condition. This knowledge is being used to develop new and innovative strategies to prevent <span class="hlt">type</span> 1 diabetes or to prevent further destruction of beta cells in those who are newly diagnosed. Several multicentre studies are underway investigating the natural history of the disease, the genetics behind the disease and ways to stop the autoimmune reaction against beta cells (<span class="hlt">Type</span> 1 Diabetes TrialNet, <span class="hlt">Type</span> 1 Diabetes Genetics Consortium and the Trial to Reduce Diabetes in the Genetically at Risk [TRIGR] Study Group). The stage is set to find an agent or strategy to prevent <span class="hlt">type</span> 1 diabetes or to preserve the residual beta cell mass in new-onset patients.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29215124','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29215124"><span><span class="hlt">Shear</span> thinning in non-Brownian suspensions.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Chatté, Guillaume; Comtet, Jean; Niguès, Antoine; Bocquet, Lydéric; Siria, Alessandro; Ducouret, Guylaine; Lequeux, François; Lenoir, Nicolas; Ovarlez, Guillaume; Colin, Annie</p> <p>2018-02-14</p> <p>We study the flow of suspensions of non-Brownian particles dispersed into a Newtonian solvent. Combining capillary rheometry and conventional rheometry, we evidence a succession of two <span class="hlt">shear</span> thinning regimes separated by a <span class="hlt">shear</span> thickening one. Through X-ray radiography measurements, we show that during each of those regimes, the flow remains homogeneous and does not involve particle migration. Using a quartz-tuning fork based atomic force microscope, we measure the repulsive force profile and the microscopic friction coefficient μ between two particles immersed into the solvent, as a function of normal load. Coupling measurements from those three techniques, we propose that (1) the first <span class="hlt">shear</span>-thinning regime at low <span class="hlt">shear</span> rates occurs for a lubricated rheology and can be interpreted as a decrease of the effective volume fraction under increasing particle pressures, due to short-ranged repulsive forces and (2) the second <span class="hlt">shear</span> thinning regime after the <span class="hlt">shear</span>-thickening transition occurs for a frictional rheology and can be interpreted as stemming from a decrease of the microscopic friction coefficient at large normal load.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/16912395','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/16912395"><span>The effect of hydrodynamic <span class="hlt">shear</span> on 3D engineered chondrocyte systems subject to direct perfusion.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Raimondi, Manuela T; Moretti, Matteo; Cioffi, Margherita; Giordano, Carmen; Boschetti, Federica; Laganà, Katia; Pietrabissa, Riccardo</p> <p></p> <p>Bioreactors allowing direct-perfusion of culture medium through tissue-engineered constructs may overcome diffusion limitations associated with static culturing, and may provide flow-mediated mechanical stimuli. The hydrodynamic stress imposed on cells within scaffolds is directly dependent on scaffold microstructure and on bioreactor configuration. Aim of this study is to investigate optimal <span class="hlt">shear</span> stress ranges and to quantitatively <span class="hlt">predict</span> the levels of hydrodynamic <span class="hlt">shear</span> imposed to cells during the experiments. Bovine articular chondrocytes were seeded on polyestherurethane foams and cultured for 2 weeks in a direct perfusion bioreactor designed to impose 4 different values of <span class="hlt">shear</span> level at a single flow rate (0.5 ml/min). Computational fluid dynamics (CFD) simulations were carried out on reconstructions of the scaffold obtained from micro-computed tomography images. Biochemistry analyses for DNA and sGAG were performed, along with electron microscopy. The hydrodynamic <span class="hlt">shear</span> induced on cells within constructs, as estimated by CFD simulations, ranged from 4.6 to 56 mPa. This 12-fold increase in the level of applied <span class="hlt">shear</span> stress determined a 1.7-fold increase in the mean content in DNA and a 2.9-fold increase in the mean content in sGAG. In contrast, the mean sGAG/DNA ratio showed a tendency to decrease for increasing <span class="hlt">shear</span> levels. Our results suggest that the optimal condition to favour sGAG synthesis in engineered constructs, at least at the beginning of culture, is direct perfusion at the lowest level of hydrodynamic <span class="hlt">shear</span>. In conclusion, the presented results represent a first attempt to quantitatively correlate the imposed hydrodynamic <span class="hlt">shear</span> level and the invoked biosynthetic response in 3D engineered chondrocyte systems.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/pages/biblio/1360803-cosmic-shear-probe-galaxy-formation-physics','SCIGOV-DOEP'); return false;" href="https://www.osti.gov/pages/biblio/1360803-cosmic-shear-probe-galaxy-formation-physics"><span>Cosmic <span class="hlt">shear</span> as a probe of galaxy formation physics</span></a></p> <p><a target="_blank" href="http://www.osti.gov/pages">DOE PAGES</a></p> <p>Foreman, Simon; Becker, Matthew R.; Wechsler, Risa H.</p> <p>2016-09-01</p> <p>Here, we evaluate the potential for current and future cosmic <span class="hlt">shear</span> measurements from large galaxy surveys to constrain the impact of baryonic physics on the matter power spectrum. We do so using a model-independent parametrization that describes deviations of the matter power spectrum from the dark-matter-only case as a set of principal components that are localized in wavenumber and redshift. We perform forecasts for a variety of current and future data sets, and find that at least ~90 per cent of the constraining power of these data sets is contained in no more than nine principal components. The constraining powermore » of different surveys can be quantified using a figure of merit defined relative to currently available surveys. With this metric, we find that the final Dark Energy Survey data set (DES Y5) and the Hyper Suprime-Cam Survey will be roughly an order of magnitude more powerful than existing data in constraining baryonic effects. Upcoming Stage IV surveys (Large Synoptic Survey Telescope, Euclid, and Wide Field Infrared Survey Telescope) will improve upon this by a further factor of a few. We show that this conclusion is robust to marginalization over several key systematics. The ultimate power of cosmic <span class="hlt">shear</span> to constrain galaxy formation is dependent on understanding systematics in the <span class="hlt">shear</span> measurements at small (sub-arcminute) scales. Lastly, if these systematics can be sufficiently controlled, cosmic <span class="hlt">shear</span> measurements from DES Y5 and other future surveys have the potential to provide a very clean probe of galaxy formation and to strongly constrain a wide range of <span class="hlt">predictions</span> from modern hydrodynamical simulations.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/biblio/343677-adaptive-mesh-refinement-front-tracking-shear-bands-antiplane-shear-model','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/343677-adaptive-mesh-refinement-front-tracking-shear-bands-antiplane-shear-model"><span>Adaptive mesh refinement and front-tracking for <span class="hlt">shear</span> bands in an antiplane <span class="hlt">shear</span> model</span></a></p> <p><a target="_blank" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Garaizar, F.X.; Trangenstein, J.</p> <p>1998-09-01</p> <p>In this paper the authors describe a numerical algorithm for the study of hear-band formation and growth in a two-dimensional antiplane <span class="hlt">shear</span> of granular materials. The algorithm combines front-tracking techniques and adaptive mesh refinement. Tracking provides a more careful evolution of the band when coupled with special techniques to advance the ends of the <span class="hlt">shear</span> band in the presence of a loss of hyperbolicity. The adaptive mesh refinement allows the computational effort to be concentrated in important areas of the deformation, such as the <span class="hlt">shear</span> band and the elastic relief wave. The main challenges are the problems related to shearmore » bands that extend across several grid patches and the effects that a nonhyperbolic growth rate of the <span class="hlt">shear</span> bands has in the refinement process. They give examples of the success of the algorithm for various levels of refinement.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3933478','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3933478"><span><span class="hlt">Predicting</span> the Occurrence of Oxygenation Impairment in Patients with <span class="hlt">Type</span>-B Acute Aortic Dissection</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Tomita, Kazunori; Hata, Noritake; Kobayashi, Nobuaki; Shinada, Takuro; Shirakabe, Akihiro</p> <p>2014-01-01</p> <p>Complicated respiratory failure requiring mechanical ventilation in patients with <span class="hlt">type</span>-B acute aortic dissection (AAD) has been previously reported, and inflammatory reactions have been found to be associated with the occurrence of oxygenation impairment (OI). However, the possibility of <span class="hlt">predicting</span> the occurrence of OI in patients with <span class="hlt">type</span>-B AAD has not yet been evaluated. This study was performed to investigate the possibility of <span class="hlt">predicting</span> the occurrence of OI in <span class="hlt">type</span>-B AAD. In this study, 79 <span class="hlt">type</span>-B AAD patients were enrolled to investigate the possibility of <span class="hlt">predicting</span> the occurrence of OI. OI was defined as Po 2/Fio 2 ≤ 200. Patient characteristics, <span class="hlt">type</span> of AAD, vital signs on admission, and the presence of inflammatory reactions obtained on admission day were evaluated. OI occurred in 39 patients (49%) on hospital day 2.5 ± 1.4 on average. Younger age, male gender, nonslender frame (body mass index ≥ 22 kg/m2), a relatively high maximum body temperature on the admission day (≥ 36.5°C), DeBakey IIIb <span class="hlt">type</span>, patent false lumen, and lower Po 2/Fio 2 on admission were found to be associated with the occurrence of OI. Multivariate analysis revealed that nonslender frame, relatively high body temperature on the admission day, and lower Po 2/Fio 2 on admission were reliable for <span class="hlt">predicting</span> the occurrence of oxygen impairment. The occurrence of OI in <span class="hlt">type</span>-B AAD can be <span class="hlt">predicted</span> in the clinical setting. PMID:24627618</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003GeoJI.155..221C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003GeoJI.155..221C"><span>A review of <span class="hlt">shear</span> wave splitting in the crack-critical crust</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Crampin, Stuart; Chastin, Sebastien</p> <p>2003-10-01</p> <p>Over the last 15 years, it has become established that crack-induced stress-aligned <span class="hlt">shear</span> wave splitting, with azimuthal anisotropy, is an inherent characteristic of almost all rocks in the crust. This means that most in situ rocks are pervaded by fluid-saturated microcracks and consequently are highly compliant. The evolution of such stress-aligned fluid-saturated grain-boundary cracks and pore throats in response to changing conditions can be calculated, in some cases with great accuracy, using anisotropic poro-elasticity (APE). APE is tightly constrained with no free parameters, yet dynamic modelling with APE currently matches a wide range of phenomena concerning anisotropy, stress, <span class="hlt">shear</span> waves and cracks. In particular, APE has allowed the anisotropic response of a reservoir to injection to be calculated (<span class="hlt">predicted</span> with hindsight), and the time and magnitude of an earthquake to be correctly stress-forecast. The reason for this calculability and <span class="hlt">predictability</span> is that the microcracks in the crust are so closely spaced that they form critical systems. This crack-critical crust leads to a new style of geophysics that has profound implications for almost all aspects of pre-fracturing deformation of the crust and for solid-earth geophysics and geology. We review past, present and speculate about the future of <span class="hlt">shear</span> wave splitting in the crack-critical crust. <span class="hlt">Shear</span> wave splitting is seen to be a dynamic measure of the deformation of the rock mass. There is some good news and some bad news for conventional geophysics. Many accepted phenomena are no longer valid at high spatial and temporal resolution. A major effect is that the detailed crack geometry changes with time and varies from place to place in response to very small previously negligible changes. However, at least in some circumstances, the behaviour of the rock in the highly complex inhomogeneous Earth may be calculated and the response <span class="hlt">predicted</span>, opening the way to possible control by feedback. The need is</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21342822','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21342822"><span>Monitoring of thermal therapy based on <span class="hlt">shear</span> modulus changes: I. <span class="hlt">shear</span> wave thermometry.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Arnal, Bastien; Pernot, Mathieu; Tanter, Mickael</p> <p>2011-02-01</p> <p>The clinical applicability of high-intensity focused ultrasound (HIFU) for noninvasive therapy is today hampered by the lack of robust and real-time monitoring of tissue damage during treatment. The goal of this study is to show that the estimation of local tissue elasticity from <span class="hlt">shear</span> wave imaging (SWI) can lead to the 2-D mapping of temperature changes during HIFU treatments. This new concept of <span class="hlt">shear</span> wave thermometry is experimentally implemented here using conventional ultrasonic imaging probes. HIFU treatment and monitoring were, respectively, performed using a confocal setup consisting of a 2.5-MHz single-element transducer focused at 30 mm on ex vivo samples and an 8-MHz ultrasound diagnostic probe. Thermocouple measurements and ultrasound-based thermometry were used as a gold standard technique and were combined with SWI on the same device. The SWI sequences consisted of 2 successive <span class="hlt">shear</span> waves induced at different lateral positions. Each wave was created using 100-μs pushing beams at 3 depths. The <span class="hlt">shear</span> wave propagation was acquired at 17,000 frames/s, from which the elasticity map was recovered. HIFU sonications were interleaved with fast imaging acquisitions, allowing a duty cycle of more than 90%. Elasticity and temperature mapping was achieved every 3 s, leading to realtime monitoring of the treatment. Tissue stiffness was found to decrease in the focal zone for temperatures up to 43°C. Ultrasound-based temperature estimation was highly correlated to stiffness variation maps (r² = 0.91 to 0.97). A reversible calibration phase of the changes of elasticity with temperature can be made locally using sighting shots. This calibration process allows for the derivation of temperature maps from <span class="hlt">shear</span> wave imaging. Compared with conventional ultrasound-based approaches, <span class="hlt">shear</span> wave thermometry is found to be much more robust to motion artifacts.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4884854','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4884854"><span>Ultrasound <span class="hlt">Shear</span> Wave Simulation of Breast Tumor Using Nonlinear Tissue Elasticity</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Park, Dae Woo</p> <p>2016-01-01</p> <p><span class="hlt">Shear</span> wave elasticity imaging (SWEI) can assess the elasticity of tissues, but the <span class="hlt">shear</span> modulus estimated in SWEI is often less sensitive to a subtle change of the stiffness that produces only small mechanical contrast to the background tissues. Because most soft tissues exhibit mechanical nonlinearity that differs in tissue <span class="hlt">types</span>, mechanical contrast can be enhanced if the tissues are compressed. In this study, a finite element- (FE-) based simulation was performed for a breast tissue model, which consists of a circular (D: 10 mm, hard) tumor and surrounding tissue (soft). The SWEI was performed with 0% to 30% compression of the breast tissue model. The <span class="hlt">shear</span> modulus of the tumor exhibited noticeably high nonlinearity compared to soft background tissue above 10% overall applied compression. As a result, the elastic modulus contrast of the tumor to the surrounding tissue was increased from 0.46 at 0% compression to 1.45 at 30% compression. PMID:27293476</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004AGUFM.T23A0563K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004AGUFM.T23A0563K"><span>Periodic Viscous <span class="hlt">Shear</span> Heating Instability in Fine-Grained <span class="hlt">Shear</span> Zones: Possible Mechanism for Intermediate Depth Earthquakes and Slow Earthquakes?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kelemen, P. B.; Hirth, G.</p> <p>2004-12-01</p> <p>Localized ductile <span class="hlt">shear</span> zones with widths of cm to m are observed in exposures of Earth's shallow mantle (e.g., Kelemen & Dick JGR 95; Vissers et al. Tectonophys 95) and dredged from oceanic fracture zones (e.g., Jaroslow et al. Tectonophys 96). These are mylonitic (grain size 10 to 100 microns) and record mineral cooling temperatures from 1100 to 600 C. Pseudotachylites in a mantle <span class="hlt">shear</span> zone show that <span class="hlt">shear</span> heating temperatures can exceed the mantle solidus (e.g., Obata & Karato Tectonophys 95). Simple <span class="hlt">shear</span>, recrystallization, and grain boundary sliding all decrease the spacing between pyroxenes, so olivine grain growth at lower stress is inhibited; thus, once formed, these <span class="hlt">shear</span> zones do not "heal" on geological time scales. Reasoning that grain-size sensitive creep will be localized within these <span class="hlt">shear</span> zones, rather than host rocks (grain size 1 to 10 mm), and inspired by the work of Whitehead & Gans (GJRAS 74), we thought these might undergo repeated <span class="hlt">shear</span> heating instabilities. In this view, as elastic stress increases, the <span class="hlt">shear</span> zone weakens via <span class="hlt">shear</span> heating; rapid deformation of the weak <span class="hlt">shear</span> zone releases most stored elastic stress; lower stress and strain rate coupled with diffusion of heat into host rocks leads to cooling and strengthening, after which the cycle repeats. We constructed a simple numerical model incorporating olivine flow laws for dislocation creep, diffusion creep, grain boundary sliding, and low T plasticity. We assumed that viscous deformation remains localized in <span class="hlt">shear</span> zones, surrounded by host rocks undergoing elastic deformation. We fixed the velocity along one side of an elastic half space, and calculated stress due to elastic strain. This stress drives viscous deformation in a <span class="hlt">shear</span> zone of specified width. <span class="hlt">Shear</span> heating and thermal diffusion control temperature evolution in the <span class="hlt">shear</span> zone and host rocks. A maximum of 1400 C (where substantial melting of peridotite would occur) is imposed. 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