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1
Du, Jun, Dong Li, Zhiming Xiong, Xinggang Shen, Chenchen Li e Weiwei Zhu. "Experimental Study on the Reciprocating Shear Characteristics and Strength Deterioration of Argillaceous Siltstone Rockfill Materials". Applied Sciences 13, n. 15 (2 agosto 2023): 8888. http://dx.doi.org/10.3390/app13158888.
Testo completoAbstract (sommario):
The reciprocating shear mechanical properties and strength deterioration mechanisms of rockfill materials are of great research significance for high-fill slope stability analysis. To study the shear strength characteristics of argillaceous siltstone rockfill materials with different fabric characteristics under reciprocating shear loading, we analyzed the shear strength, hysteresis loop area, damping ratio, shear strength parameter, and shear stiffness of coarse-grained soils with different coarse grain contents using a coarse-grained soil direct shear testing machine capable of reciprocating shear and revealed their strength deterioration mechanism. The test results show that the shear strength of argillaceous siltstone rockfill materials is significantly affected by the coarse grain content and the number of reciprocating shears. Specifically, the shear strength increases with the coarse grain content and decreases with the number of reciprocating shears. The hysteresis loop area is positively correlated with the coarse grain content and negatively correlated with the number of reciprocating shears. The damping ratio is not related to the coarse grain content but tends to decrease with the number of reciprocating shears. Soil cohesion and the internal friction angle increase with the coarse grain content and decrease with the number of reciprocating shears. The soil failure shear stiffness is linearly correlated with the coarse grain content, and the normalized shear stiffness is logarithmically related to the number of reciprocating shears. According to these relationships, an empirical formula for the shear stiffness of argillaceous siltstone rockfill materials under different coarse grain contents and different numbers of reciprocating shears can be established to provide a basis for analyzing rockfill stability.
2
Goel, Rakesh K. "Comparison of Base Shears Estimated from Floor Accelerations and Column Shears". Earthquake Spectra 27, n. 3 (agosto 2011): 939–46. http://dx.doi.org/10.1193/1.3610247.
Testo completoAbstract (sommario):
This paper compares base shears computed from floor accelerations (inertial base shear) and column shears (structural base shear) for two mid-rise, multistory buildings due to a suite of 30 earthquake ground motions. The presented results demonstrate that the inertial base shear exceeds the structural base shear in the median by 10% to 20% and may exceed the structural base shear by as much as 70% for individual ground motions. Therefore, it is concluded that the inertial base shear computed from strong motion records should be used with caution to estimate the structural base shear.
3
Ahn. "Shear Resistance of BESTOBEAM Shear Connector According to the Length". Journal of Korean Society of Steel Construction 27, n. 5 (2015): 483. http://dx.doi.org/10.7781/kjoss.2015.27.5.483.
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Jeong. "Shear Strain Big-Bang of RC Membrane Panel Subjected to Shear". Journal of the Korean Society of Civil Engineers 35, n. 1 (2015): 101. http://dx.doi.org/10.12652/ksce.2015.35.1.0101.
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McNeel, Joseph, e Frank Czerepinski. "Effect of Felling Head Design on Shear-Related Damage in Southern Yellow Pine". Southern Journal of Applied Forestry 11, n. 1 (1 febbraio 1987): 3–6. http://dx.doi.org/10.1093/sjaf/11.1.3.
Testo completoAbstract (sommario):
Abstract Use of feller-buncher and directional shears has increased the productivity and efficiency of many logging operations in the South. When felling sawlog and chip'n' saw-sized timber, hydraulic shears can damage the butt portion of the tree. Butt logs of trees felled with shears are subjectto damage in the form of ring-shake, stump-pull, shatter, and splitting (Porter et al. 1984). Logging equipment manufacturers have attempted to minimize shear-related damage through different felling head designs. Various designs have included ribbed blades, angled shear patterns, curved blades,modified blade angles, and modified shear speeds. Whereas a number of studies addressed the effect of a specific design on shear-related damage (Guimier 1981, Forrester 1980, Redman 1979, McLaucalan and Kusec 1974, Letkeman 1973, Johnson and St. Laurent 1970, McIntosh and Kerbes 1968), fewhave compared designs to determine the relative advantage of one over another in reducing shear-related damage. This paper presents the results of a recent study comparing six feller-buncher and directional shear head designs to determine their relative abilities in reducing shear-relateddamage. The study also details a quick and inexpensive method of quantifying shear-related damage in butt logs. South. J. Appl. For. 11(1):3-6.
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Davachi, M. M., B. J. Sinclair, H. H. Hartmaier, B. L. Baggott e J. E. Peters. "Determination of the Oldman River Dam foundation shear strength". Canadian Geotechnical Journal 28, n. 5 (1 ottobre 1991): 698–707. http://dx.doi.org/10.1139/t91-084.
Testo completoAbstract (sommario):
The paper describes the results of site investigation and laboratory testing and the analysis performed for the determination of foundation shear strength at the Oldman River Dam site in southwestern Alberta, Canada. Horizontally bedded claystones, siltstones, and sandstones at the site contain relatively weak bedding-plane shears that adversely affect foundation stability. Data on the bedding-plane shear characteristics were collected by mapping, borehole coring, shaft exploration, and large-diameter sampling. Shear planes of structure-wide continuity were identified. Numerous laboratory direct shear tests were done to measure in situ and residual shear strengths. The design angle of shearing resistance of selected continuous bedding-plane shears was evaluated by summing the representative residual angle of shearing resistance and components of the angle of shearing resistance due to in situ state, roughness, and thickness of the bedding-plane shears. Relatively flat dam slopes were found to be required for stability. The methods used at the Oldman River Dam should be applicable at other sites located in flat-lying mudrock sequences. Key words: Oldman River Dam, foundation shear strength, sedimentary rocks, bedding-plane shear, residual angle of shearing resistance, in situ state, roughness, thickness.
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Tsui, Po C., David M. Cruden e Stanley Thomson. "Mesofabric, microfabric, and submicrofabric of ice-thrust bedrock, Highvale mine, Wabamun Lake area, Alberta". Canadian Journal of Earth Sciences 25, n. 9 (1 settembre 1988): 1420–31. http://dx.doi.org/10.1139/e88-136.
Testo completoAbstract (sommario):
The fabric of the ice-thrust argillaceous bedrock from a shear zone was studied in hand specimens, under a polarizing microscope and a scanning electron microscope. The fabric included principal displacement shears, Riedel shears, conjugate sets of particle alignments, cutans, lithorelics, and aggregations which dense cores of randomly oriented groups of clay platelets wrapped by an external layer of oriented clay particles in a turbostatic arrangement. In addition, the bedrock has been disturbed by permafrost, cycles of loading and unloading, and weathering, causing the magnitude of deformation to vary within the ice-thrust shear zone.The fabric of the ice-thrust shear zone is similar to that of shear zones formed by tectonic activity and by laboratory shear tests, suggesting that all these shear zones were formed under conditions of similar kinematic restraint.
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Lui, Mathew, Elizabeth E. Gardiner, Jane F. Arthur, Isaac Pinar, Woei Ming Lee, Kris Ryan, Josie Carberry e Robert K. Andrews. "Novel Stenotic Microchannels to Study Thrombus Formation in Shear Gradients: Influence of Shear Forces and Human Platelet-Related Factors". International Journal of Molecular Sciences 20, n. 12 (18 giugno 2019): 2967. http://dx.doi.org/10.3390/ijms20122967.
Testo completoAbstract (sommario):
Thrombus formation in hemostasis or thrombotic disease is initiated by the rapid adhesion, activation, and aggregation of circulating platelets in flowing blood. At arterial or pathological shear rates, for example due to vascular stenosis or circulatory support devices, platelets may be exposed to highly pulsatile blood flow, while even under constant flow platelets are exposed to pulsation due to thrombus growth or changes in vessel geometry. The aim of this study is to investigate platelet thrombus formation dynamics within flow conditions consisting of either constant or variable shear. Human platelets in anticoagulated whole blood were exposed ex vivo to collagen type I-coated microchannels subjected to constant shear in straight channels or variable shear gradients using different stenosis geometries (50%, 70%, and 90% by area). Base wall shears between 1800 and 6600 s−1, and peak wall shears of 3700 to 29,000 s−1 within stenoses were investigated, representing arterial-pathological shear conditions. Computational flow-field simulations and stenosis platelet thrombi total volume, average volume, and surface coverage were analysed. Interestingly, shear gradients dramatically changed platelet thrombi formation compared to constant base shear alone. Such shear gradients extended the range of shear at which thrombi were formed, that is, platelets became hyperthrombotic within shear gradients. Furthermore, individual healthy donors displayed quantifiable differences in extent/formation of thrombi within shear gradients, with implications for future development and testing of antiplatelet agents. In conclusion, here, we demonstrate a specific contribution of blood flow shear gradients to thrombus formation, and provide a novel platform for platelet functional testing under shear conditions.
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Cruden, D. M., S. Thomson e P. C. Tsui. "The geotechnical characteristics of an ice-thrust mudstone, Wabamun Lake area, Alberta". Canadian Geotechnical Journal 26, n. 2 (1 maggio 1989): 227–34. http://dx.doi.org/10.1139/t89-032.
Testo completoAbstract (sommario):
This first detailed report of the geotechnical characteristics of ice-thrust soft rock examines Upper Cretaceous, once heavily overconsolidated mudstones in the Highvale coal mine, Alberta. The fissured and brecciated sample from an ice-thrust shear zone in the mine behaves as a lightly overconsolidated sediment in laboratory tests and shows a non-brittle mode of shear deformation with a maximum shear strength close to residual. This behaviour is due to weathering and glaciotectonic deformation, which have jointed, sheared, and remoulded the mudstone, thus eliminating the fabric formed by overconsolidation.In the ice-thrust mudstone, platy clay minerals dominate and have been grouped into aggregations or shear-remoulded matrices. The strength of the brecciated portion of the mudstone ranges from peak to residual. The strength along principal displacement shears is at or close to residual, as back analysis of a slope failure shows. Key words: ice-thrust shear zone, glaciotectonic deformation, consolidation, nonbrittle deformation, principal displacement shears, shear strength.
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Long, Chi, Tao Yu, Jian Zhang, Xiangxiang Yan, Na Yang, Jin Wang, Chunliang Xia, Yu Liang e Hailun Ye. "Sub-Hourly Variations of Wind Shear in the Mesosphere-Lower Thermosphere as Observed by the China Meteor Radar Chain". Remote Sensing 16, n. 7 (6 aprile 2024): 1291. http://dx.doi.org/10.3390/rs16071291.
Testo completoAbstract (sommario):
Wind shear has important implications for Kelvin–Helmholtz instability (KHI) and gravity waves (GWs) in the mesosphere–lower thermosphere (MLT) region where its momentum transport process is dominated by short-period (<1 h) GWs. However, the sub-hourly variation in wind shear is still not well quantified. This study aims to improve current understanding of vertical wind shear by analyzing multi-year meteor radar measurements at the Mohe (MH, 53.5°N, 122.3°E), Beijing (BJ, 40.3°N, 116.2°E), Wuhan (WH, 30.5°N, 114.6°E), and Fuke (FK, 19.5°N, 109.1°E) stations in China. The wind field is estimated by a new algorithm, e.g., the damped least squares fitting. Taking the wind shear estimated by normal products as a criterion, the shear produced by the new algorithm has more statistical convergence as compared to the traditional algorithm, e.g., the least squares fitting. Therefore, we argue that the 10 min DLSA wind probably produces a more reasonable vertical shear. Both intensive wind shears and GW kinetic energy can be simultaneously captured during the 0600–1600 UTs of May at MH and during the 1300–2400 UTs of March at FK, possibly implying that the up-propagation of GWs could contribute to the production of large wind shears. The sub-hourly variation in wind shears is potentially valuable for understanding the interrelationship between shear (or KHI) and GWs.
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Su, Guo Sheng, e Zhan Qiang Liu. "The Analysis of Saw-Tooth Chip Formation in High Speed Machining through Material Micro-Hardness Measurement". Advanced Materials Research 188 (marzo 2011): 9–14. http://dx.doi.org/10.4028/www.scientific.net/amr.188.9.
Testo completoAbstract (sommario):
The material micro-hardness is used to reflect the plastic deformation within the localized shear band and the segment of saw-tooth chip. A high strength alloy steel Aermet 100 is taken as the workpiece material. The saw-tooth chip roots are obtained by cutting operation. The material micro-harnesses along the shortly initiated localized shear band, across the shortly initiated localized shear band and fully developed localized shear band, and within the segment are examined and analyzed. The localized shear band initiation and propagation are revealed by a new proposed model. The results show the localized shear band initiates firstly at the tool tip end of the primary shear band, and consequently another localized shear nucleates at the free surface end of the primary shear band. These two localized shears propagate face to face until the whole localized shear band is formed.
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Lermontova, A. S. "STRESS FIELD IN A SHEAR ZONE, AND FORMATION OF THE MAIN FAULT". Geodynamics & Tectonophysics 12, n. 3 (17 settembre 2021): 499–507. http://dx.doi.org/10.5800/gt-2021-12-3-0536.
Testo completoAbstract (sommario):
Using the analytical approximation method, we calculated stress field parameters for cases with different relative positions of Riedel shears and loads required for shearing. Considering an internal friction angle of 30°, and the distance between adjacent shears exceeding 0.7 of the characteristic shear length, we estimated the Coulomb stress that can lead to fracturing. In the areas between the shears, it is below the shear strength value. This means that if an increase in the external load is lacking, there are no prerequisites for the formation of new fractures that may connect adjacent shears. If the shears are spaced closer to each other (i.e. at distances less than 0.7 of the shear length), the shear strength is exceeded in the areas between them, and new shears can occur there and connect the Riedel shears to each other. Therefore, in observations of a natural system of Riedel shears, it becomes possible to assess whether this system is sufficiently stable in its current status, or, in case of a critical increase in the Coulomb stress in the areas between adjacent shears, the equilibrium can be easily disturbed, and there is a possibility that the main fault forms in the strike-slip zone under study.
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Rosti, Marco E., e Shu Takagi. "Shear-thinning and shear-thickening emulsions in shear flows". Physics of Fluids 33, n. 8 (agosto 2021): 083319. http://dx.doi.org/10.1063/5.0063180.
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Muller, Caroline. "Impact of Convective Organization on the Response of Tropical Precipitation Extremes to Warming". Journal of Climate 26, n. 14 (12 luglio 2013): 5028–43. http://dx.doi.org/10.1175/jcli-d-12-00655.1.
Testo completoAbstract (sommario):
Abstract In this study the response of tropical precipitation extremes to warming in organized convection is examined using a cloud-resolving model. Vertical shear is imposed to organize the convection into squall lines. Earlier studies show that in disorganized convection, the fractional increase of precipitation extremes is similar to that of surface water vapor, which is substantially smaller than the increase in column water vapor. It has been suggested that organized convection could lead to stronger amplifications. Regardless of the strength of the shear, amplifications of precipitation extremes in the cloud-resolving simulations are comparable to those of surface water vapor and are substantially less than increases in column water vapor. The results without shear and with critical shear, for which the squall lines are perpendicular to the shear, are surprisingly similar with a fractional rate of increase of precipitation extremes slightly smaller than that of surface water vapor. Interestingly, the dependence on shear is nonmonotonic, and stronger supercritical shear yields larger rates, close to or slightly larger than surface humidity. A scaling is used to evaluate the thermodynamic and dynamic contributions to precipitation extreme changes. To first order, they are dominated by the thermodynamic component, which has the same magnitude for all shears, close to the change in surface water vapor. The dynamic contribution plays a secondary role and tends to weaken extremes without shear and with critical shear, while it strengthens extremes with supercritical shear. These different dynamic contributions for different shears are due to different responses of convective mass fluxes in individual updrafts to warming.
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Nhan, Tran Thanh, Hoang Thi Sinh Huong, Tran Ngoc Tin, Ho Trung Thanh e Le Thi Cat Tuong. "A LIQUEFACTION CRITERION FOR FINE-GRAINED SAND CONSTITUTING NAM O FORMATION SUBJECTED TO UNI-DIRECTIONAL AND MULTI-DIRECTIONAL CYCLIC SHEARS". Hue University Journal of Science: Natural Science 127, n. 1D (10 dicembre 2018): 37. http://dx.doi.org/10.26459/hueuni-jns.v127i1d.5071.
Testo completoAbstract (sommario):
In this paper, fine-grained samples at nominally 50% relative density of Nam O sand were tested by several series of uni-directional and multi-directional cyclic shears. The changes of cyclic shear-induced effective stress reduction were observed for a wide range of shear strain amplitudes and various cyclic shear directions and number of cycles. The effects of such cyclic shearing conditions on the liquefaction resistance of the soil were then clarified. It is indicated from experimental results that the effective stress in Nam O sand reduces quickly by the application of the cyclic shear and that the soil is liquefied even when the cyclic shear strain is at small amplitude (<em>g</em> = 0.1%). The effects of cyclic shear direction on the effective stress reduction and also on the liquefaction resistance of the soil are evident at small shear strain amplitude, these effects however decrease with <em>g</em> and become negligible when <em>g</em> ³ 1.0% at which the soil is liquefied after a very few number of cycles. The occurrence of liquefaction in Nam O sand can be observed precisely for various cyclic shear directions by using relations between the shear strain amplitude and the number of cycles. Liquefaction criterion of Nam O sand was finally obtained and discussed for both cases of uni-directional and multi-directional cyclic shears.
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SURESH, R. "On nowcasting wind shear induced turbulence over Chennai air field". MAUSAM 55, n. 1 (19 gennaio 2022): 103–18. http://dx.doi.org/10.54302/mausam.v55i1.933.
Testo completoAbstract (sommario):
With the newly installed Doppler Weather Radar at Cyclone Detection Radar station, Chennai during October 2001, it has been made possible to analyse the meteorological conditions conducive for the wind shear induced turbulence experienced by the pilots in the approach runway at the time of landing and take-off. The radar has been put into operation w.e.f. 21 February, 2002. Wind shears reported during February – October 2002, have been critically analysed in this study. The three dimensional shear (3DS), a combination of radial, azimuthal and elevation shears, gives a first hand information atleast half an hour before the occurrence of shear induced moderate turbulence when its value exceeds 16mps/km. The 3DS of more than 20mps/km is normally associated with turbulence experienced by the pilots. With the availability of sophisticated and vast computing power, it is now possible to delineate the layer at which the shear is active within 3-5 minutes from the receipt of the radar measured volume data by quickly computing elevation / vertical / radial / azimuthal shear etc. However, to arrive at a meaningful conclusion on the threshold values of shears that are conducive for wind shear induced turbulence and to make use of this information to alert the pilots, feed back from the pilots to build a detailed data base is absolutely inevitable. Monitoring of passage of sea breeze front may also be useful to issue wind shear warnings. The time tested Richardson number has also been verified for its ‘outlook predictability’ of the shear induced turbulence around the airport, though it can not pinpoint the exact location and the time at which turbulence is active. It is hoped that with precise, accurate and timely in-flight report about the wind shear experienced by the pilots and based on the experience gained in analyzing such information, it will be possible to issue probable ‘wind shear alert / warning’ in the near future.
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Boulanger, Ph, e M. Hayes. "Shear, shear stress and shearing". Journal of the Mechanics and Physics of Solids 40, n. 7 (ottobre 1992): 1449–57. http://dx.doi.org/10.1016/0022-5096(92)90028-z.
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Park, Wan Shin, Jeong Eun Kim, Sun Woong Kim, Song Hee Yun, Nam Young Eom e Hyun Do Yun. "Panel Shear Strength of Steel Coupling Beam-Pseudo Strain Hardening Cementitious Composite Wall Connection". Applied Mechanics and Materials 328 (giugno 2013): 965–69. http://dx.doi.org/10.4028/www.scientific.net/amm.328.965.
Testo completoAbstract (sommario):
Hybrid coupled wall systems, where steel coupling beams couple two or more pseudo strain hardening cementitious composite (PSH2C) shear wall can be used in medium and high-rise construction subjected to earthquake. This paper addresses the panel shear strength of steel coupling beams - PSH2C shear wall connection. Test variables included the connection detail in hybrid coupled shear wall system. The results show that Specimens PSH2C-PSFF and PSH2C-PSFFT exhibits greater panel shears strength than Specimen PSH2C-PSF.
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Bajad, Mohankumar, e Rakhi D. Patil. "SEISMIC ANALYSIS OF MULTISTORIED OPEN GROUND STORY BUILDING WITH DIAGONAL STRUT AND SHEAR WALLS". Journal of Engineering and Sustainable Development 28, n. 02 (1 marzo 2024): 160–77. http://dx.doi.org/10.31272/jeasd.28.2.2.
Testo completoAbstract (sommario):
The Open Ground Story (OGS) building is a functional need of all urban areas so cannot be eliminated. According to studies from previous earthquakes, when there is severe earthquake shaking, Reinforced Concrete (RC) frame buildings with open ground levels function badly. In this work, four models of G+14 RC frame buildings with and without a shear wall, coupled sheal wall, and diagonal strut were modeled and analyzed using ETABS-2018 software's static and dynamic response spectrum method. Model 1 open ground story RC building without strut and the shear wall was compared to the other three models that included a shear wall, coupled shear wall, and diagonal strut. As a result of the findings, it has been determined that shear wall, coupled shear wall, and diagonal strut not only increased the stiffness but also reduced displacement. A model with a combination of shear wall and coupled shear wall showed a minimum base shear and overturning moment than all other models.
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Li, Yu Gui, Quan Ye, Gao Ping Wang e Fei Fan. "The Analyze of Shear Force Calculation Model of Drum Type Linear Blade Flying Shear". Advanced Materials Research 503-504 (aprile 2012): 785–89. http://dx.doi.org/10.4028/www.scientific.net/amr.503-504.785.
Testo completoAbstract (sommario):
In this paper, the shear force in the shearing process of the drum type linear blade flying shear is done. Two different approaches were taken to establish the shear force formula, and then the finite element simulation. The comparison results of the calculated values and simulated values can be seen that as the thickness increases, the maximum shear force calculated by the pure shear force formula increases rapidly, the shear force calculated by the energy release rate formula is relatively small, and the finite element simulation values and calculated values close to each other when the plate thickness is small. The derived formula in this paper not only can be applied to complex engineering problems, but also has provided a theoretical basis for drum type linear blade flying shears on the shear force calculations and equipment design.
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Rehman, Zia ur, e Ga Zhang. "Shear coupling effect of monotonic and cyclic behavior of the interface between steel and gravel". Canadian Geotechnical Journal 56, n. 6 (giugno 2019): 876–84. http://dx.doi.org/10.1139/cgj-2018-0262.
Testo completoAbstract (sommario):
Three-dimensional behavior of the interface between a structure and gravelly soil is of great concern in the design and construction of large-scale projects. A series of three-dimensional tests were conducted to investigate the effect of shear coupling on the monotonic and cyclic behavior of such an interface. In these tests, monotonic shear was applied to the interface first and then the monotonic and cyclic shears were applied in the orthogonal direction while the original shear was maintained. Based on the test observations, the shear strength of the interface was found to be independent of the shear coupling and proportional to the normal stress. Significant tangential displacement is induced by the orthogonal shear application and the deflection direction of the tangential displacement is proportional to the square of the ratio between the orthogonal shear stress and shear strength. The interface exhibits significant dilatancy due to a three-dimensional shear application, which is divided into reversible and irreversible components. Shear coupling remarkably affects the magnitude and transition shear stress of the reversible dilatancy component. There persists a significant aeolotropy of the interface evenly under the shear coupling condition. Particle crushing near the structure was observed to be enhanced due to the shear coupling.
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VOLKOV, V. V., M. A. STRUNIN e A. M. STRUNIN. "DETERMINATION OF WIND SHEAR AND TURBULENCE INTENSITY ACCORDING TO YAK42-D “ROSHYDROMET” RESEARCH AIRCRAFT DATA". Meteorologiya i Gidrologiya, n. 9 (2021): 117–29. http://dx.doi.org/10.52002/0130-2906-2021-9-117-129.
Testo completoAbstract (sommario):
The results of the development and comparative analysis of methods for determining wind shear in the atmosphere (regression and difference ones) based on research aircraft data are presented. It is shown that shear calculation by the regression method gives the error of 0.002-0.006 (m/s)/km (depending on the length of the measurement sections) for horizontal shears and 0.04-0.12 (m/s)/100 m for vertical shears; the respective error of the difference method is 0.007 (m/s)/km and 0.07 (m/s)/100 m. Based on the Yak-42D “Roshydromet” research aircraft data, the values of shears of two horizontal components of wind speed in three directions (two horizontal and vertical) were calculated. According to the data of two research aircraft flights, the maximum values of the horizontal shear of wind speed components were reached above the boundary layer and were equal to 0.2 (m/s)/km, and the vertical shear was 1.2 (m/s)/100 m. The energy profiles of horizontal and vertical turbulent pulsations are constructed, it is shown that intense turbulence smooths wind shears in the convective atmospheric boundary layer.
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JOVANOVIĆ, D., F. PEGORARO e J. JUUL RASMUSSEN. "Tripolar shear-Alfvén vortex structures". Journal of Plasma Physics 60, n. 2 (settembre 1998): 383–91. http://dx.doi.org/10.1017/s0022377898006904.
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Henderson, J. R., e J. Broome. "Geometry and kinematics of Wager shear zone interpreted from structural fabrics and magnetic data". Canadian Journal of Earth Sciences 27, n. 4 (1 aprile 1990): 590–604. http://dx.doi.org/10.1139/e90-055.
Testo completoAbstract (sommario):
The Wager shear zone (WSZ) is characterized by progressive bending of northeast–southwest-trending aeromagnetic anomalies to the right as they merge with east–west-trending anomalies characterizing the shear zone. This feature indicates dextral net shear. Mapping of abundant and diverse asymmetrical structural fabric elements within the shear zone where it is well exposed along the south coast of Wager Bay, northwestern Hudson Bay, consistently confirmed dextral shear sense.Pervasive, dextral shear-zone mylonites were deformed by folds with hinges parallel to the shear direction (a folds), as well as by discrete, conjugate sinistral and dextral mylonitic shears. To form a folds in mylonites it is necessary for the mylonitic fabric to rotate out of a stable orientation in the plane of shear and flattening and also to rotate about an axis parallel to the shear direction, for which we have no general explanation.We conclude with the speculation that the WSZ is a strike-slip fault related to terminal collision of the Archean plate of Ungava with the Archean plate to the north marked by the 1.8 Ga Sugluk suture.
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MATSUDA, HIROSHI, TRAN THANH NHAN e RYOHEI ISHIKURA. "EXCESS PORE WATER PRESSURE ACCUMULATION AND RECOMPRESSION OF SATURATED SOFT CLAY SUBJECTED TO UNI-DIRECTIONAL AND MULTI-DIRECTIONAL CYCLIC SIMPLE SHEARS". Journal of Earthquake and Tsunami 07, n. 04 (novembre 2013): 1250027. http://dx.doi.org/10.1142/s1793431112500273.
Testo completoAbstract (sommario):
This paper is to investigate the effect of cyclic shear direction (or phase difference) on the accumulation of excess pore water pressure during cyclic shear and on the recompression after cyclic shear. Several series of uni-directional and multi-directional cyclic simple shear tests under undrained condition were carried out for normally consolidated Kaolin. From the test results it is shown that the accumulation of pore water pressure and the post-cyclic settlement increase with the shear strain amplitude and the phase difference. The values of the shear strain amplitude at which the effect of cyclic shear direction is most significant, decrease with the increase of the number of cycles. The change of the void ratio in the recompression stage increases approximately in proportion to the logarithm of the stress reduction ratio and is not affected by the shear strain amplitude. For multi-directional cyclic shear, this change of the void ratio depends on the phase difference and the number of cycles. The cyclic recompression indices in the recompression stage were obtained for uni-directional and multi-directional cyclic shears. The cyclic shear induced settlement can be calculated by using these indices.
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Xue, Xin, Hiroshi Seki e Yu Song. "Influence of Stirrup Corrosion on Shear Strength of RC Beams". Applied Mechanics and Materials 204-208 (ottobre 2012): 3287–93. http://dx.doi.org/10.4028/www.scientific.net/amm.204-208.3287.
Testo completoAbstract (sommario):
There have been few reports on shear behavior of reinforced concrete (RC) beams with corroded stirrups, and the influence of stirrup corrosion has yet to be identified. Given this background, experience was carried out to investigate the shear behavior of RC beams containing corroded stirrups. Investigation results indicate that if the percentage local maximum mass loss is below 35%, there is little influence on the load-carrying mechanism. The concrete shear resistance seems to change little and the shear capacity can be calculated by just taking into consideration the reduction in stirrup shear resistance. It is also found that the anchorage conditions of the stirrups have a predominant influence on the shears of RC beams.
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Helén, Andreas, Anders Eliasson e Sebastian K. T. S. Wärmländer. "Metallurgical Characterization of Two 11th–12th Century Single-Bow Shears from Sigtuna, Sweden". Acta Archaeologica 92, n. 2 (14 aprile 2023): 176–83. http://dx.doi.org/10.1163/16000390-20210032.
Testo completoAbstract (sommario):
Abstract Shears, being everyday objects, have received significantly less attention by archaeometallurgists than other edged tools or weapons. Yet, shear blades were forged with the same techniques as blades of, e.g. knives and swords. The most common shear type in ancient times was the bow shears, where the bow had to be flexible so it could be repeatedly bent without cracking or breaking. The shear-maker, therefore, faced the challenge of combining hard steel (the blades) with soft/flexible steel (the bow). In fact, bow shears are one of the first tools to be invented, where metal acts as a spring. Thus, ancient bow shears can be used for investigating the history and development of spring steel technology, which is currently unclear. Here, we present the metallurgical characterization of two 11th–12th c. single-bow shears from Sigtuna, Sweden. Both the blades and the bows of the two shears were found to be of decent quality and much better than in older shears from the Roman period. Although the steel qualities are not quite up to modern standards, this does not in itself prove that the Sigtuna blacksmiths lacked the technological knowledge to make ideal spring steel. Shears are relatively cheap everyday objects intended to be used until they break, at which point they are discarded. Therefore, it might not have been worth the Medieval blacksmiths’ time and effort to perfect the material properties of steel used in shears. The shears’ blades are on par with Medieval-period knife blades, and future studies on ancient shear-making should preferably involve comparisons of shears and knives from the same origins.
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Nightingale, James W., Amy Etherington e Richard Massey. "The “External” Shears In Strong Lens Models". Proceedings of the International Astronomical Union 18, S381 (dicembre 2022): 13–16. http://dx.doi.org/10.1017/s1743921323003691.
Testo completoAbstract (sommario):
AbstractThe distribution of mass in galaxy-scale strong gravitational lenses is often modelled as an elliptical power law plus ‘external shear’, which notionally accounts for line-of-sight galaxies and cosmic shear. We argue that it does not, using three lines of evidence from the analysis of 54 galaxy-scale strong lenses: (i) strong lensing external shears do not correlate with weak lensing; (ii) the measured shear magnitudes in strong lenses (which are field galaxies) are too large (exceeding 0.05) for their environment and; (iii) the external shear position angle preferentially aligns or anti-aligns with the mass model position angle, indicating an internal origin. We argue the measured strong lensing shears are therefore systematically accounting for missing complexity in the canonical elliptical power-law mass model. If we can introduce this complexity into our lens models, this will further lensing studies of galaxy formation, dark matter and Cosmology.
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Han, Ying, e Boualem Khouider. "Convectively Coupled Waves in a Sheared Environment". Journal of the Atmospheric Sciences 67, n. 9 (1 settembre 2010): 2913–42. http://dx.doi.org/10.1175/2010jas3335.1.
Testo completoAbstract (sommario):
Abstract A linear stability analysis, about a radiative–convective equilibrium in a sheared environment, on an equatorial beta plane, for a simple multicloud model for organized tropical convection is presented here. Both vertical/baroclinic and meridional/barotropic zonal wind shears are considered separately in a parameter regime for which the shear-free multicloud model exhibits synoptic-scale instability of Kelvin and n = 0 eastward inertio-gravity [eastward mixed Rossby–gravity (MRG)] waves only, with moderate growth rates. The maximum growth rates appear to increase significantly with the strength of the background wind shear, and new wave instabilities appear and/or disappear depending on the strength and type of the wind shear. It is found here that both high- and low-level vertical shears have a strong impact on the stability of convectively coupled waves (CCWs), consistent with the fact that the multicloud instability mechanism is controlled by both stratiform heating and low-level moisture and congestus heating. Typically, vertical shears with high-level easterly wind destabilize westward moving waves and stabilize eastward waves, whereas westerly winds aloft and on bottom tend to destabilize eastward moving and stabilize westward moving waves. In the mixed situation of high-level easterlies and low-level westerlies both eastward and westward waves are unstable, while in the case of high-level westerlies and low-level easterlies only eastward waves are unstable. In the presence of a barotropic/meridional shear, synoptic-scale convectively coupled westward MRG and Rossby waves emerge, when the shear strength is large enough, due essentially to pure shear instability of the dry dynamics. The meridional shear has also an important impact on the horizontal structure of the waves. Owing to the meridional shear, the Kelvin wave displays a nonzero meridional velocity that induces a significant contribution toward the horizontal convergence. The two-day waves adopt a crescentlike shape while the westward MRG, and somewhat the Rossby waves, become less trapped in the vicinity of the equator.
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Madougou, Saïdou, Frederique Saïd, Bernard Campistron e Fadel Kebe Cheikh. "Low Level Jet Wind Shear in the Sahel". International Journal of Engineering Research in Africa 11 (ottobre 2013): 1–10. http://dx.doi.org/10.4028/www.scientific.net/jera.11.1.
Testo completoAbstract (sommario):
In the Sahel, a vertical wind shear appears in the dry and in the wet seasons. In Niamey, Niger, during the dry season, the period of strong shears is clearly linked to the Nocturnal Low Level Jet (LLJ) since it occurs in a narrow time period around 06H00 UTC at 60% of the cases reach shears which require an alert to the pilots (higher than 4 ms-1 per 100 m). The majority of cases occur during the night with a wind shear direction between 90 and 150° per 100 m, which is shown that it is dangerous for aircraft. In Bamako, Mali, high wind shears represent (higher than 4 ms-1 per 100 m) only 16-22% of the cases and can occur at any time of the day. There are, however, 8% of the cases, the whole day long, when the wind shear can reach more than 6 ms-1 per 100 m. Most of the wind shear directions are also between 0 and 90° per 100 m during the night. This is why the Agency for the safety of aircraft navigation in Africa and Madagascar (ASECNA) has put in 2004 at Bamako airport an UHF wind profiler radar for monitoring nocturnal strong Low Level Jet wind shear which occur regularly in this airport.
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Kwan, A. K. H. "Shear Lag in Shear/Core Walls". Journal of Structural Engineering 122, n. 9 (settembre 1996): 1097–104. http://dx.doi.org/10.1061/(asce)0733-9445(1996)122:9(1097).
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Rao, Min, Tomy Varghese e Ernest L. Madsen. "Shear strain imaging using shear deformations". Medical Physics 35, n. 2 (9 gennaio 2008): 412–23. http://dx.doi.org/10.1118/1.2825621.
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Cárdenas-Montes, Miguel, Miguel A. Vega-Rodríguez, Christopher Bonnett, Ignacio Sevilla-Noarbe, Rafael Ponce, Eusebio Sánchez Alvaro e Juan José Rodríguez-Vázquez. "GPU-based shear–shear correlation calculation". Computer Physics Communications 185, n. 1 (gennaio 2014): 11–18. http://dx.doi.org/10.1016/j.cpc.2013.08.005.
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Kawashima, Masayuki. "Numerical Study of Horizontal Shear Instability Waves along Narrow Cold Frontal Rainbands". Journal of the Atmospheric Sciences 68, n. 4 (1 aprile 2011): 878–903. http://dx.doi.org/10.1175/2010jas3599.1.
Testo completoAbstract (sommario):
Abstract The effects of variations in low-level ambient vertical shear and horizontal shear on the alongfront variability of narrow cold frontal rainbands (NCFRs) that propagate into neutral and slightly unstable environments are investigated through a series of idealized cloud-resolving simulations. In cases initialized with slightly unstable sounding and weak ambient cross-frontal vertical shears, core-gap structures of precipitation along NCFRs occur that are associated with wavelike disturbances that derive their kinetic energy mainly from the mean local vertical shear and buoyancy. However, over a wide range of environmental conditions, core-gap structures of precipitation occur because of the development of a horizontal shear instability (HSI) wave along the NCFRs. The growth rate and amplitude of the HSI wave decrease significantly as the vertical shear of the ambient cross-front wind is reduced. These decreases are a consequence of the enhancement of the low-level local vertical shear immediately behind the leading edge. The strong local vertical shear acts to damp the vorticity edge wave on the cold air side of the shear zone, thereby suppressing the growth of the HSI wave through the interaction of the two vorticity edge waves. It is also noted that the initial wavelength of the HSI wave increases markedly with increasing horizontal shear. The local vertical shear around the leading edge is shown to damp long HSI waves more strongly than short waves, and the horizontal shear dependency of the wavelength is explained by the decrease in the magnitude of the vertical shear relative to that of the horizontal shear.
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Soljento, Juska E., Simon W. Good, Adnane Osmane e Emilia K. J. Kilpua. "Imbalanced Turbulence Modified by Large-scale Velocity Shears in the Solar Wind". Astrophysical Journal Letters 946, n. 1 (1 marzo 2023): L19. http://dx.doi.org/10.3847/2041-8213/acc071.
Testo completoAbstract (sommario):
Abstract We have investigated how the degree of imbalance in solar wind turbulence is modified by large-scale velocity shears in the solar wind plasma. The balance between counterpropagating Alfvénic fluctuations, which interact nonlinearly to generate the turbulence, has been quantified by the cross helicity and Elsasser ratio. Velocity shears at a 30 minute timescale were identified, with the shear amplitude defined in terms of the linear Kelvin–Helmholtz (KH) instability threshold. The shears were associated with 74 interplanetary coronal mass ejection (ICME) sheaths observed by the Wind spacecraft at 1 au between 1997 and 2018. Typically weaker shears upstream of the sheaths and downstream in the ICME ejecta were also analyzed. In shears below the KH threshold, imbalance was approximately invariant or weakly rising with shear amplitude. Above the KH threshold, fluctuations tended toward a balanced state with increasing shear amplitude. Magnetic compressibility was also found to increase above the KH threshold. These findings are consistent with velocity shears being local sources of sunward fluctuations that act to reduce net imbalances in the antisunward direction, and suggest that the KH instability plays a role in this process.
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Wolpert, Scott A. "Products of twists, geodesic lengths and Thurston shears". Compositio Mathematica 151, n. 2 (9 ottobre 2014): 313–50. http://dx.doi.org/10.1112/s0010437x1400757x.
Testo completoAbstract (sommario):
AbstractThurston introduced shear deformations (cataclysms) on geodesic laminations–deformations including left and right displacements along geodesics. For hyperbolic surfaces with cusps, we consider shear deformations on disjoint unions of ideal geodesics. The length of a balanced weighted sum of ideal geodesics is defined and the Weil–Petersson (WP) duality of shears and the defined length is established. The Poisson bracket of a pair of balanced weight systems on a set of disjoint ideal geodesics is given in terms of an elementary$2$-form. The symplectic geometry of balanced weight systems on ideal geodesics is developed. Equality of the Fock shear coordinate algebra and the WP Poisson algebra is established. The formula for the WP Riemannian pairing of shears is also presented.
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Strahilov, Dian, Plamen Doychev e Ivan Dimitrov. "Ore shoots formation in a sinistral strike-slip setting: an interpreted from the map of the Au-Ag Milin Kamak deposit in the Breznic area, Southwest Bulgaria". Review of the Bulgarian Geological Society 83, n. 3 (dicembre 2022): 131–34. http://dx.doi.org/10.52215/rev.bgs.2022.83.3.131.
Testo completoAbstract (sommario):
This work presents а structural interpretation of a well-known gold deposit from SW Bulgaria. The interpretation is based on the geological map and structural data, collected during the prospecting. The data indicates that а regional sinistral shearing was responsible for a low rank sinistral shear system, which created ore depositional space by the combined action of shear extension and compression. The two mechanisms opened tension gashes, dilated previously formed Riedel faults and buckled the veins and the faults. The buckling happened, when the structures were rotated anticlockwise in the compressional quadrant of the space between the regional shears thus creating buckling structures. Ore shoots have been formed in the extended domains of the main shear and along the dilated previously formed Riedel shears.
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Radko, Timour. "Instabilities of a Time-Dependent Shear Flow". Journal of Physical Oceanography 49, n. 9 (settembre 2019): 2377–92. http://dx.doi.org/10.1175/jpo-d-19-0067.1.
Testo completoAbstract (sommario):
AbstractThis study offers a systematic stability analysis of unsteady shear flows representing large-scale, low-frequency internal waves in the ocean. The analysis is based on the unbounded time-dependent Couette model. This setup makes it possible to isolate the instabilities caused by uniform shear from those that can be attributed to resonant triad interactions or to the presence of inflection points in vertical velocity profiles. Linear analysis suggests that time-dependent spatially uniform shears are unstable regardless of the Richardson number (Ri). However, the growth rate of instability monotonically decreases with increasing Ri and increases with increasing frequency of oscillations. Therefore, models assuming a steady basic state—which are commonly used to conceptualize shear-induced instability and mixing—can be viewed as singular limits of the corresponding time-dependent systems. The present investigation is focused on the supercritical range of Richardson numbers (Ri > 1/4) where steady parallel flows are stable. An explicit relation is proposed for the growth rate of shear instability as a function of background parameters. For moderately supercritical Richardson numbers (Ri ~ 1), we find that the growth rates obtained are less than, but comparable to, those expected for Kelvin–Helmholtz instabilities of steady shears at Ri < 1/4. Hence, we conclude that the instability of time-dependent flows could represent a viable mixing mechanism in the ocean, particular in regions characterized by relatively weak wave activity and predominantly supercritical large-scale shears.
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Schneibel, J. H., e L. Martínez. "Atomic force microscopy of slip lines in FeAl". Journal of Materials Research 10, n. 9 (settembre 1995): 2159–61. http://dx.doi.org/10.1557/jmr.1995.2159.
Testo completoAbstract (sommario):
Fe–40 at. % Al–0.1 at. % B specimens were polished flat, strained at room temperature, and examined in an atomic force microscope. The angles of height contours perpendicular to the slip lines were interpreted as shear strains and were statistically evaluated. The frequency distributions of these shear strains correlated well with the macroscopic strains. The maximum shear strains found were not much larger than the macroscopic strains. In particular, no steep slip steps corresponding to large local shears were found.
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Yin, Hang, Zhaoxin Meng, Yu Zhang e Bo Yu. "Based on MATLAB and Adams new pruning cutting edge shape and shear force simulation". MATEC Web of Conferences 175 (2018): 03065. http://dx.doi.org/10.1051/matecconf/201817503065.
Testo completoAbstract (sommario):
Pruning is an indispensable tool for gardening. The pruning mechanism of pruning scissors and the shape of the cutting edge directly affect the efficiency of shear. Therefore, it is of great significance to design a new type of pruning scissors to improve the efficiency of garden work. It accords with the concept of green manufacturing energy-saving and environmental protection. The blade shape directly affects the shear efficiency. Therefore, the blade of the best Angle can improve the shear efficiency and save energy. According to the motion track of the moving blade and the shear mode. Using MATLAB software to simulate the shape of the blade of the best Angle. This work is instructive to the design of the blade. The force of the blade in the working process of shear force reaction scissors. Using Adams software, the dynamic simulation of tree branch was carried out. It is helpful to verify the shear performance of new pruning shears.
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Sompie, Tampanatu P. F., e Syanne Pangemanan. "Shear Strength of Tack Coat on Flexible Pavement and Composite Pavement". Journal of the Civil Engineering Forum 4, n. 2 (13 maggio 2018): 121. http://dx.doi.org/10.22146/jcef.31945.
Testo completoAbstract (sommario):
Tack coat is a thin layer that spread on the surface of existing pavement or concrete pavement. The function of this layer is as an adhesive layer needed to give adhesive power between the existing pavement course and new pavement course or with the concrete pavement, therefore created one strong unity and would bond both, in order to withstand the sheer strength caused by the vehicle load on top of it. Strong adhesiveness of the tack coat course will add sheer strength between the interfaces of the pavement courses. Strong adhesiveness is gained from the asphalt mixed with solvent, therefore created the right viscosity level of the tack coat solution. This research was aimed to measure the sheer strength of tack coat by using modified direct shear asphalt samples. The research method used was by using gauge to measure the sheer strength of tack coat on asphalt sample which was the modified direct shear. While the samples were consisted of 2 types, the asphalt solvent sample as a model of flexible pavement course of AC-WC pavement type with optimum asphalt content of 6.1%, and concrete solvent sample as a model of rigid pavement. These samples were made in briquette form, made with Marshall Mould with 4 inches diameter. The tack coat solvent was made in three solvent variations, which was referring to the standard of the Directorate General of Highways. From this research, it could be concluded that the highest shear strength for flexible pavement was reached on the tack coal solvent mix composition of 30 pph and composite pavement of 15 pph. Tack coat spread rate of 0.25 l/m2 gave highest shear strength on flexible pavement and composition pavement of 0.35 l/m2. Balance was reached on flexible pavement on tack coat variation of 30 pph and 50 pph; while on composite pavement, balance was reached on tack coat solvent variation of 15 pph and 30 pph. This modified direct shear sample could be a method to measure shear strength of tack coat on flexible pavement and composite pavement.
42
Zhou, Guang Qiang, Qing Yang Liu e Xin Zhang. "Study on Shear-Shear Deformation Hysteresis Relationship of Reinforced Concrete Shear Walls". Applied Mechanics and Materials 638-640 (settembre 2014): 260–64. http://dx.doi.org/10.4028/www.scientific.net/amm.638-640.260.
Testo completoAbstract (sommario):
In order to study and improve shear-shear deformation hysteresis model of reinforced concrete shear walls, experiment of reinforced concrete shear walls was conducted. Based on experimental data, shear-shear deformation relationship is deduced and shear-shear deformation hysteresis curves are obtained. The existing shear-shear deformation hysteresis models of reinforced concrete walls are discussed and improved, and the calculated shear-shear deformation hysteresis curves with the modified model fit well with experimental results.
43
Suits, LD, TC Sheahan, T. Mirata e Y. Erzin. "Strength of Sands in Wedge Shear, Triaxial Shear, and Shear Box Tests". Geotechnical Testing Journal 30, n. 2 (2007): 100223. http://dx.doi.org/10.1520/gtj100223.
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Dutruge, Gérard, Jean-Pierri Burg, Johann Lapierre e Jean-Louis Vigneresse. "Shear strain analysis and periodicity within shear gradients of metagranite shear zones". Journal of Structural Geology 17, n. 6 (giugno 1995): 819–30. http://dx.doi.org/10.1016/0191-8141(94)00101-5.
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45
Cruden, D. M., e P. C. Tsui. "Some influences of ice thrusting in geotechnical engineering". Geological Society, London, Engineering Geology Special Publications 7, n. 1 (1991): 127–34. http://dx.doi.org/10.1144/gsl.eng.1991.007.01.09.
Testo completoAbstract (sommario):
AbstractIce-thrust features are widespread on the Interior Plains of Canada and cause geotechnical problems. Case histories here show that shear zones from ice-thrusting have strongly influenced design, construction and Instrumentation of coal mine slopes and earth and tailings dams.The identification of ice-thrust terrain requires aerial photograph analyses, geological field mapping and study of borehole logs and topographic maps. Three geomorphological settings which are susceptible to glaciotectonic deformation are described as escarpment, valley and plains settings. Ice-thrust features can be expected where local slopes are inclined toward the former glacier margin and where proglacial water bodies were impounded. These water bodies cause disintegration of proglacial permafrost hence decreasing the resistance of subglacial strata to ice thrusting.A fissured, brecciated Palaeocene mudstone, once heavily overconsolidated, from an ice-thrust shear zone, behaved as normally to lightly overconsolidated in laboratory tests. Shear deformation was non-brittle with a maximum strength close to residual. Fabric elements present included principal displacement shears, Reidel shears, conjugate sets of particle alignments, cutans, lithorelics and aggregations which had a dense core of randomly oriented clay platelets wrapped by an external layer of oriented clay particles. The fabric is similar to shear zones formed by tectonic activity and by laboratory shear tests, suggesting that all these shear zones were formed under similar kinematic restraints. This was confirmed by back analysis of movements of a mine highwall and two earth dams.
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Song, Jin Chun, Chang Zhou Wang e Dong Xu. "Dynamic Simulation and Control Strategy of Centrifugal Flying Shear". Applied Mechanics and Materials 16-19 (ottobre 2009): 278–82. http://dx.doi.org/10.4028/www.scientific.net/amm.16-19.278.
Testo completoAbstract (sommario):
Centrifugal Flying Shear is one of the most advanced equipments, which is widely used in tandem mill production lines because of its simple structure and high shearing precision. In this paper, the working principle of the centrifugal flying shear was introduced; the three-dimensional model of the centrifugal flying shear was established; the structural analysis and the dynamic simulation of the flying shear, with the movement rule and trajectory, were made based on MATLAB/SimMechanics and Solidworks/COSMOS Motion; and the control strategy of realizing scale shearing was proposed. The results obtained provide theoretical basis for design of the electronic control system, and facilitate further analysis of the shearing process and parameter optimization design of similar flying shears.
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Cowger, Nancy L., Edmund Benes, Patricia L. Allen e Timothy G. Hammond. "Expression of renal cell protein markers is dependent on initial mechanical culture conditions". Journal of Applied Physiology 92, n. 2 (1 febbraio 2002): 691–700. http://dx.doi.org/10.1152/jappl.2002.92.2.691.
Testo completoAbstract (sommario):
The rotating wall vessel is optimized for suspension culture, with laminar flow and adequate nutrient delivery, but minimal shear. However, higher shears may occur in vivo. During rotating wall vessel cultivation of human renal cells, size and density of glass-coated microcarrier beads were changed to modulate initial shear. Renal-specific proteins were assayed after 2 days. Flow cytometry antibody binding analysis of vitamin D receptor demonstrated peak expression at intermediate shears, with 30% reduction outside this range. Activity of cathepsin C showed the inverse pattern, lowest at midshear, with twofold increases at either extreme. Dipeptidyl-peptidase IV had no shear dependence, suggesting that the other results are specific, not universal, changes in membrane trafficking or protein synthesis. On addition of dextran, which changes medium density and viscosity but not shear, vitamin D receptor assay showed no differences from controls. Neither cell cycle, apoptosis/necrosis indexes, nor lactate dehydrogenase release varied between experiments, confirming that the changes are primary, not secondary to cell cycling or membrane damage. This study provides direct evidence that mechanical culture conditions modulate protein expression in suspension culture.
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Kuban, Barry D., e Morton H. Friedman. "The Effect of Pulsatile Frequency on Wall Shear in a Compliant Cast of a Human Aortic Bifurcation". Journal of Biomechanical Engineering 117, n. 2 (1 maggio 1995): 219–23. http://dx.doi.org/10.1115/1.2796004.
Testo completoAbstract (sommario):
A realistically compliant flow-through cast of a human aortic bifurcation was perfused with two almost identical physiological flow waves differing in pulsatile frequency. Near-wall fluid velocities were measured with a laser Doppler velocimeter at 14 sites along the flow divider and the lateral walls of the aorta and iliac arteries. The wall position at each site was tracked using a linescan camera. The temporal wall shear rate at each site was then calculated from the near-wall velocity profile and the instantaneous wall position. Increasing the frequency reduced the oscillatory component of shear rate at sites where it was greater than average, and increased it at sites where it was less, effectively reducing its site to site variability. Pulsatile frequency had no significant effect on mean shear rate at most sites. The phase shift between wall shear and radial strain was governed by the phase of the shear, and was linearly related to the extent of site dependent shear reversal The mean shear rate was inversely related to the extent of shear reversal. If atherosclerotic development depends chiefly on mean shear rate, heart rate would not be expected to affect susceptibility, however, if only the wall sites experiencing the lowest maximum shears are vulnerable, then the effect of increasing the heart rate would seem to be beneficial.
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Haney, Sean, Baylor Fox-Kemper, Keith Julien e Adrean Webb. "Symmetric and Geostrophic Instabilities in the Wave-Forced Ocean Mixed Layer". Journal of Physical Oceanography 45, n. 12 (dicembre 2015): 3033–56. http://dx.doi.org/10.1175/jpo-d-15-0044.1.
Testo completoAbstract (sommario):
AbstractHere, the effects of surface waves on submesoscale instabilities are studied through analytical and linear analyses as well as nonlinear large-eddy simulations of the wave-averaged Boussinesq equations. The wave averaging yields a surface-intensified current (Stokes drift) that advects momentum, adds to the total Coriolis force, and induces a Stokes shear force. The Stokes–Coriolis force alters the geostrophically balanced flow by reducing the burden on the Eulerian–Coriolis force to prop up the front, thereby potentially inciting an anti-Stokes Eulerian shear, while maintaining the Lagrangian (Eulerian plus Stokes) shear. Since the Lagrangian shear is maintained, the Charney–Stern–Pedlosky criteria for quasigeostrophic (QG) baroclinic instability are unchanged with the appropriate Lagrangian interpretation of the shear and QG potential vorticity. While the Stokes drift does not directly affect vorticity, the anti-Stokes Eulerian shear contributes to the Ertel potential vorticity (PV). When the Stokes shear and geostrophic shear are aligned (antialigned), the PV is more (less) cyclonic. If the Stokes-modified PV is anticyclonic, the flow is unstable to symmetric instabilities (SI). Stokes drift also weakly impacts SI through the Stokes shear force. When the Stokes and Eulerian shears are the same (opposite) sign, the Stokes shear force does positive (negative) work on the flow associated with SI. Stokes drift also allows SI to extract more potential energy from the front, providing an indirect mechanism for Stokes-induced restratification.
50
Horobin, Jarod T., Surendran Sabapathy, Lennart Kuck e Michael J. Simmonds. "Shear Stress and RBC-NOS Serine1177 Phosphorylation in Humans: A Dose Response". Life 11, n. 1 (8 gennaio 2021): 36. http://dx.doi.org/10.3390/life11010036.
Testo completoAbstract (sommario):
Red blood cells (RBC) express a nitric oxide synthase isoform (RBC-NOS) that appears dependent on shear stress for Serine1177 phosphorylation. Whether this protein is equally activated by varied shears in the physiological range is less described. Here, we explored RBC-NOS Serine1177 phosphorylation in response to shear stress levels reflective of in vivo conditions. Whole blood samples were exposed to specific magnitudes of shear stress (0.5, 1.5, 4.5, 13.5 Pa) for discrete exposure times (1, 10, 30 min). Thereafter, RBC-NOS Serine1177 phosphorylation was measured utilising immunofluorescence labelling. Shear stress exposure at 0.5, 1.5, and 13.5 Pa significantly increased RBC-NOS Serine1177 phosphorylation following 1 min (p < 0.0001); exposure to 4.5 Pa had no effect after 1 min. RBC-NOS Serine1177 phosphorylation was significantly increased following 10 min at each magnitude of shear stress (0.5, 1.5, 13.5 Pa, p < 0.0001; 4.5 Pa, p = 0.0042). Shear stress exposure for 30 min significantly increased RBC-NOS Serine1177 phosphorylation at 0.5 Pa and 13.5 Pa (p < 0.0001). We found that RBC-NOS phosphorylation via shear stress is non-linear and differs for a given magnitude and duration of exposure. This study provides a new understanding of the discrete relation between RBC-NOS and shear stress.